Peng, Juan; Zu, Lily; Fang, Weihai; Huang, Lingyun; Wang, Yaru; He, Dacheng
2010-06-01
An understanding of the dissociation of penetratin is important for improving its metabolic stability and cargo-delivery efficiency. In this study, we describe the selective cleavage of the K15-K16 amide bond of penetratin under the low-energy collision-induced dissociation condition in mass spectrometry. A variety of penetratin substitutes have been studied in which key basic amino acids have been substituted within the sequence. The calculated structure indicates that an alpha-helix structure prevents the fragmentation of the central peptide domain and the side chain of lysine is involved in the proton translocation process.
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. Copyright © 2012 Elsevier B.V. All rights reserved.
A Critical Reassessment of Penetratin Translocation Across Lipid Membranes
Bárány-Wallje, Elsa; Keller, Sandro; Serowy, Steffen; Geibel, Sebastian; Pohl, Peter; Bienert, Michael; Dathe, Margitta
2005-01-01
Penetratin is a short, basic cell-penetrating peptide able to induce cellular uptake of a vast variety of large, hydrophilic cargos. We have reassessed the highly controversial issue of direct permeation of the strongly cationic peptide across negatively charged lipid membranes. Confocal laser scanning microscopy on rhodamine-labeled giant vesicles incubated with carboxyfluorescein-labeled penetratin yielded no evidence of transbilayer movement, in contradiction to previously reported results. Confocal fluorescence spectroscopy on black lipid membranes confirmed this finding, which was also not affected by application of a transmembrane electric potential difference. A novel dialysis assay based on tryptophan absorbance and fluorescence spectroscopy demonstrated that the permeability of small and large unilamellar vesicles to penetratin is <10−13 m/s. Taken together, the results show that penetratin is not capable of overcoming model membrane systems irrespective of the bilayer curvature or the presence of a transmembrane voltage. Thus, direct translocation across the hydrophobic core of the plasma membrane cannot account for the efficient uptake of penetratin into live cells, which is in accord with recent in vitro studies underlining the importance of endocytosis in the internalization process of cationic cell-penetrating peptides. PMID:16040762
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).
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.
Maniti, Ofelia; Blanchard, Elise; Trugnan, Germain; Lamazière, Antonin; Ayala-Sanmartin, Jesus
2012-06-01
Cellular uptake of vector peptides used for internalization of hydrophilic molecules into cells is known to follow two different pathways: direct translocation of the plasma membrane and internalization by endocytosis followed by release into the cytosol. These pathways differ in their energy dependence. The first does not need metabolic energy while the second requires metabolic energy. Herein we used erythrocytes and plasma membrane vesicles to study membrane perturbations induced by the cell penetrating peptide penetratin. The results show that cell penetrating peptides are able to be internalized by two metabolic energy-independent pathways: direct crossing of the plasma membrane and endocytosis-like mechanisms. The last mechanism involves the induction of membrane negative curvature resulting in invaginations that mimic the endosomal uptake in the absence of ATP. This new mechanism called "physical endocytosis" or "self-induced endocytosis" might explain different data concerning the independence or dependence on metabolic energy during cellular uptake and reveals the autonomous capacity of peptides to induce their internalization. Copyright © 2012 Elsevier Ltd. All rights reserved.
Fringes of equal tangential inclination by curvature-induced birefringence
NASA Astrophysics Data System (ADS)
Medhat, M.; Hendawy, N. I.; Zaki, A. A.
2003-02-01
A new kind of interference fringes, fringes of equal tangential inclination by curvature-induced birefringence, is presented. These are two-beam interference fringes produced by bending a thin sheet of birefringent material into a part of an exact cylinder such that the curvature is constant. Due to this curvature there is a uniform birefringence being induced. The change in birefringence induced by applying different radii of curvatures to a Fortepan sheet is measured. The stored (fixed) or natural birefringence of this sheet is deduced.
NASA Astrophysics Data System (ADS)
Liu, Jin; Tourdot, Richard; Ramanan, Vyas; Agrawal, Neeraj J.; Radhakrishanan, Ravi
2012-06-01
The membrane-surface migration of curvature-inducing proteins in response to membrane curvature gradients has been investigated using Monte Carlo simulations of a curvilinear membrane model based on the Helfrich Hamiltonian. Consistent with theoretical and experimental data, we find the proteins that generate curvature can also sense the background membrane curvature, wherein they preferentially partition to the high curvature regions. The partitioning strength depends linearly on local membrane curvature and the slope (or the coupling constant) of the partitioning probability versus mean curvature depends on the membrane bending rigidity and instantaneous curvature field caused by different proteins. Our simulation study allows us to quantitatively characterize and identify the important factors affecting the coupling constant (slope), which may be difficult to determine in experiments. Furthermore, the membrane model is used to study budding of vesicles where it is found that in order to stabilize a mature vesicle with a stable 'neck-region' (or stable membrane overhangs), the area (extent) of the intrinsic curvature region needs to exceed a threshold-critical value. The migration and partitioning of curvature-inducing proteins in a budding vesicle with a stable neck (with a characteristic negative value of the Gaussian curvature) is investigated.
Liu, Jin; Tourdot, Richard; Ramanan, Vyas; Agrawal, Neeraj J.; Radhakrishanan, Ravi
2015-01-01
The membrane-surface migration of curvature-inducing proteins in response to membrane curvature gradients has been investigated using Monte Carlo simulations of a curvilinear membrane model based on the Helfrich Hamiltonian. Consistent with theoretical and experimental data, we find the proteins that generate curvature can also sense the background membrane curvature, wherein they preferentially partition to the high curvature regions. The partitioning strength depends linearly on local membrane curvature and the slope (or the coupling constant) of the partitioning probability versus mean curvature depends on the membrane bending rigidity and instantaneous curvature field caused by different proteins. Our simulation study allows us to quantitatively characterize and identify the important factors affecting the coupling constant (slope), which may be difficult to determine in experiments. Furthermore, the membrane model is used to study budding of vesicles where it is found that in order to stabilize a mature vesicle with a stable ‘neck-region’ (or stable membrane overhangs), the area (extent) of the intrinsic curvature region needs to exceed a threshold-critical value. The migration and partitioning of curvature-inducing proteins in a budding vesicle with a stable neck (with a characteristic negative value of the Gaussian curvature) is investigated. PMID:26500377
Liu, Jin; Tourdot, Richard; Ramanan, Vyas; Agrawal, Neeraj J; Radhakrishanan, Ravi
2012-06-01
The membrane-surface migration of curvature-inducing proteins in response to membrane curvature gradients has been investigated using Monte Carlo simulations of a curvilinear membrane model based on the Helfrich Hamiltonian. Consistent with theoretical and experimental data, we find the proteins that generate curvature can also sense the background membrane curvature, wherein they preferentially partition to the high curvature regions. The partitioning strength depends linearly on local membrane curvature and the slope (or the coupling constant) of the partitioning probability versus mean curvature depends on the membrane bending rigidity and instantaneous curvature field caused by different proteins. Our simulation study allows us to quantitatively characterize and identify the important factors affecting the coupling constant (slope), which may be difficult to determine in experiments. Furthermore, the membrane model is used to study budding of vesicles where it is found that in order to stabilize a mature vesicle with a stable 'neck-region' (or stable membrane overhangs), the area (extent) of the intrinsic curvature region needs to exceed a threshold-critical value. The migration and partitioning of curvature-inducing proteins in a budding vesicle with a stable neck (with a characteristic negative value of the Gaussian curvature) is investigated.
Zhang, Zhongwei; Chen, Jie; Li, Baowen
2017-09-28
From the mathematic category of surface Gaussian curvature, carbon allotropes can be classified into three types: zero curvature, positive curvature, and negative curvature. By performing Green-Kubo equilibrium molecular dynamics simulations, we found that surface curvature has a significant impact on the phonon vibration and thermal conductivity (κ) of carbon crystals. When curving from zero curvature to negative or positive curvature structures, κ is reduced by several orders of magnitude. Interestingly, we found that κ of negatively curved carbon crystals exhibits a monotonic dependence on curvature. Through phonon mode analysis, we show that curvature induces remarkable phonon softening in phonon dispersion, which results in the reduction of phonon group velocity and flattening of phonon band structure. Furthermore, the curvature was found to induce phonon mode hybridization, leading to the suppression of phonon relaxation time. Our study provides physical insight into thermal transport in curvature materials, and will be valuable in the modulation of phonon activity through surface curvature.
Curvature-induced geometrical frustration in magnetic systems
Saxena, A.; Dandoloff, R.
1997-05-01
We study classical Heisenberg spins in the continuum limit (i.e., the nonlinear {sigma} model) on an elastic two-dimensional manifold with at least one nonconstant principal curvature. If the corresponding Euler-Lagrange equations support a soliton solution, the nonconstant curvature of the geometry induces geometrical frustration in the region of the soliton which is relieved by a deformation of the manifold in the region of the soliton. We illustrate these results on an elliptic cylinder where we find an elastic soliton in terms of the variable ellipticity along the axis of the cylinder. {copyright} {ital 1997} {ital The American Physical Society}
Changes in lipid density induce membrane curvature.
de Jesus, Armando J; Kastelowitz, Noah; Yin, Hang
2013-09-07
Highly curved bilayer lipid membranes make up the shell of many intra- and extracellular compartments, including organelles and vesicles. Using all-atom molecular dynamics simulations, we show that increasing the density of lipids in the bilayer membrane can induce the membrane to form a curved shape.
Curvature-Induced Asymmetric Spin-Wave Dispersion
NASA Astrophysics Data System (ADS)
Otálora, Jorge A.; Yan, Ming; Schultheiss, Helmut; Hertel, Riccardo; Kákay, Attila
2016-11-01
In magnonics, spin waves are conceived of as electron-charge-free information carriers. Their wave behavior has established them as the key elements to achieve low power consumption, fast operative rates, and good packaging in magnon-based computational technologies. Hence, knowing alternative ways that reveal certain properties of their undulatory motion is an important task. Here, we show using micromagnetic simulations and analytical calculations that spin-wave propagation in ferromagnetic nanotubes is fundamentally different than in thin films. The dispersion relation is asymmetric regarding the sign of the wave vector. It is a purely curvature-induced effect and its fundamental origin is identified to be the classical dipole-dipole interaction. The analytical expression of the dispersion relation has the same mathematical form as in thin films with the Dzyalonshiinsky-Moriya interaction. Therefore, this curvature-induced effect can be seen as a "dipole-induced Dzyalonshiinsky-Moriya-like" effect.
Relaxation and curvature-induced molecular flows within multicomponent membranes
NASA Astrophysics Data System (ADS)
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.
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.
Bera, Swapna; Kar, Rajiv K; Mondal, Susanta; Pahan, Kalipada; Bhunia, Anirban
2016-09-06
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.
Defining the free-energy landscape of curvature-inducing proteins on membrane bilayers
Tourdot, Richard W.; Ramakrishnan, N.; Radhakrishnan, Ravi
2015-01-01
Curvature-sensing and curvature-remodeling proteins, such as Amphiphysin, Epsin, and Exo70, are known to reshape cell membranes, and this remodeling event is essential for key biophysical processes such as tubulation, exocytosis, and endocytosis. Curvature-inducing proteins can act as curvature sensors; they aggregate to membrane regions matching their intrinsic curvature; as well as induce curvature in cell membranes to stabilize emergent high curvature, nonspherical, structures such as tubules, discs, and caveolae. A definitive understanding of the interplay between protein recruitment and migration, the evolution of membrane curvature, and membrane morphological transitions is emerging but remains incomplete. Here, within a continuum framework and using the machinery of Monte Carlo simulations, we introduce and compare three free-energy methods to delineate the free-energy landscape of curvature-inducing proteins on bilayer membranes. We demonstrate the utility of the Widom test particle (or field) insertion methodology in computing the excess chemical potentials associated with curvature-inducing proteins on the membrane—in particular, we use this method to track the onset of morphological transitions in the membrane at elevated protein densities. We validate this approach by comparing the results from the Widom method with those of thermodynamic integration and Bennett acceptance ratio methods. Furthermore, the predictions from the Widom method have been tested against analytical calculations of the excess chemical potential at infinite dilution. Our results are useful in precisely quantifying the free-energy landscape, and also in determining the phase boundaries associated with curvature-induction, curvature-sensing, and morphological transitions. This approach can be extended to studies exploring the role of thermal fluctuations and other external (control) variables, such as membrane excess area, in shaping curvature-mediated interactions on bilayer
Defining the free-energy landscape of curvature-inducing proteins on membrane bilayers
NASA Astrophysics Data System (ADS)
Tourdot, Richard W.; Ramakrishnan, N.; Radhakrishnan, Ravi
2014-08-01
Curvature-sensing and curvature-remodeling proteins, such as Amphiphysin, Epsin, and Exo70, are known to reshape cell membranes, and this remodeling event is essential for key biophysical processes such as tubulation, exocytosis, and endocytosis. Curvature-inducing proteins can act as curvature sensors; they aggregate to membrane regions matching their intrinsic curvature; as well as induce curvature in cell membranes to stabilize emergent high curvature, nonspherical, structures such as tubules, discs, and caveolae. A definitive understanding of the interplay between protein recruitment and migration, the evolution of membrane curvature, and membrane morphological transitions is emerging but remains incomplete. Here, within a continuum framework and using the machinery of Monte Carlo simulations, we introduce and compare three free-energy methods to delineate the free-energy landscape of curvature-inducing proteins on bilayer membranes. We demonstrate the utility of the Widom test particle (or field) insertion methodology in computing the excess chemical potentials associated with curvature-inducing proteins on the membrane—in particular, we use this method to track the onset of morphological transitions in the membrane at elevated protein densities. We validate this approach by comparing the results from the Widom method with those of thermodynamic integration and Bennett acceptance ratio methods. Furthermore, the predictions from the Widom method have been tested against analytical calculations of the excess chemical potential at infinite dilution. Our results are useful in precisely quantifying the free-energy landscape, and also in determining the phase boundaries associated with curvature-induction, curvature-sensing, and morphological transitions. This approach can be extended to studies exploring the role of thermal fluctuations and other external (control) variables, such as membrane excess area, in shaping curvature-mediated interactions on bilayer
Curvature-induced radiation of surface plasmon polaritons propagating around bends
Hasegawa, Keisuke; Noeckel, Jens U.; Deutsch, Miriam
2007-06-15
We present a theoretical study of the curvature-induced radiation of surface plasmon polaritons propagating around bends at metal-dielectric interfaces. We explain qualitatively how the curvature leads to distortion of the phase front, causing the fields to radiate energy away from the metal-dielectric interface. We then quantify, both analytically and numerically, radiation losses and energy transmission efficiencies of surface plasmon polaritons propagating around bends with varying radii as well as sign of curvature.
Engineering Curvature-Induced Anisotropy in Thin Ferromagnetic Films
NASA Astrophysics Data System (ADS)
Tretiakov, Oleg A.; Morini, Massimiliano; Vasylkevych, Sergiy; Slastikov, Valeriy
2017-08-01
We investigate the effect of large curvature and dipolar energy in thin ferromagnetic films with periodically modulated top and bottom surfaces on magnetization behavior. We predict that the dipolar interaction and surface curvature can produce perpendicular anisotropy which can be controlled by engineering special types of periodic surface structures. Similar effects can be achieved by a significant surface roughness in the film. We demonstrate that, in general, the anisotropy can point in an arbitrary direction depending on the surface curvature. Furthermore, we provide simple examples of these periodic surface structures to show how to engineer particular anisotropies in thin films.
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.
Maniti, Ofelia; Alves, Isabel; Trugnan, Germain; Ayala-Sanmartin, Jesus
2010-01-01
Background Penetratin is a protein transduction domain derived from the homeoprotein Antennapedia. Thereby it is currently used as a cell penetrating peptide to introduce diverse molecules into eukaryotic cells, and it could also be involved in the cellular export of transcription factors. Moreover, it has been shown that it is able to act as an antimicrobial agent. The mechanisms involved in all these processes are quite controversial. Methodology/Principal Findings In this article, we report spectroscopic, calorimetric and biochemical data on the penetratin interaction with three different phospholipids: phosphatidylcholine (PC) and phosphatidylethanolamine (PE) to mimic respectively the outer and the inner leaflets of the eukaryotic plasma membrane and phosphatidylglycerol (PG) to mimic the bacterial membrane. We demonstrate that with PC, penetratin is able to form vesicle aggregates with no major change in membrane fluidity and presents no well defined secondary structure organization. With PE, penetratin aggregates vesicles, increases membrane rigidity and acquires an α-helical structure. With PG membranes, penetratin does not aggregate vesicles but decreases membrane fluidity and acquires a structure with both α-helical and β–sheet contributions. Conclusions/Significance These data from membrane models suggest that the different penetratin actions in eukaryotic cells (membrane translocation during export and import) and on prokaryotes may result from different peptide and lipid structural arrangements. The data suggest that, for eukaryotic cell penetration, penetratin does not acquire classical secondary structure but requires a different conformation compared to that in solution. PMID:21209890
Curvature-induced stiffening of a fish fin.
Nguyen, Khoi; Yu, Ning; Bandi, Mahesh M; Venkadesan, Madhusudhan; Mandre, Shreyas
2017-05-01
How fish modulate their fin stiffness during locomotive manoeuvres remains unknown. We show that changing the fin's curvature modulates its stiffness. Modelling the fin as bendable bony rays held together by a membrane, we deduce that fin curvature is manifested as a misalignment of the principal bending axes between neighbouring rays. An external force causes neighbouring rays to bend and splay apart, and thus stretches the membrane. This coupling between bending the rays and stretching the membrane underlies the increase in stiffness. Using three-dimensional reconstruction of a mackerel (Scomber japonicus) pectoral fin for illustration, we calculate the range of stiffnesses this fin is expected to span by changing curvature. The three-dimensional reconstruction shows that, even in its geometrically flat state, a functional curvature is embedded within the fin microstructure owing to the morphology of individual rays. As the ability of a propulsive surface to transmit force to the surrounding fluid is limited by its stiffness, the fin curvature controls the coupling between the fish and its surrounding fluid. Thereby, our results provide mechanical underpinnings and morphological predictions for the hypothesis that the spanned range of fin stiffnesses correlates with the behaviour and the ecological niche of the fish. © 2017 The Author(s).
Curvature-induced stiffening of a fish fin
2017-01-01
How fish modulate their fin stiffness during locomotive manoeuvres remains unknown. We show that changing the fin's curvature modulates its stiffness. Modelling the fin as bendable bony rays held together by a membrane, we deduce that fin curvature is manifested as a misalignment of the principal bending axes between neighbouring rays. An external force causes neighbouring rays to bend and splay apart, and thus stretches the membrane. This coupling between bending the rays and stretching the membrane underlies the increase in stiffness. Using three-dimensional reconstruction of a mackerel (Scomber japonicus) pectoral fin for illustration, we calculate the range of stiffnesses this fin is expected to span by changing curvature. The three-dimensional reconstruction shows that, even in its geometrically flat state, a functional curvature is embedded within the fin microstructure owing to the morphology of individual rays. As the ability of a propulsive surface to transmit force to the surrounding fluid is limited by its stiffness, the fin curvature controls the coupling between the fish and its surrounding fluid. Thereby, our results provide mechanical underpinnings and morphological predictions for the hypothesis that the spanned range of fin stiffnesses correlates with the behaviour and the ecological niche of the fish. PMID:28566508
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
Schmidt, Nathan W.; Wong, Gerard C. L.
2013-01-01
Short cationic, amphipathic antimicrobial peptides are multi-functional molecules that have roles in host defense as direct microbicides and modulators of the immune response. While a general mechanism of microbicidal activity involves the selective disruption and permeabilization of cell membranes, the relationships between peptide sequence and membrane activity are still under investigation. Here, we review the diverse functions that AMPs collectively have in host defense, and show that these functions can be multiplexed with a membrane mechanism of activity derived from the generation of negative Gaussian membrane curvature. As AMPs preferentially generate this curvature in model bacterial cell membranes, the selective generation of negative Gaussian curvature provides AMPs with a broad mechanism to target microbial membranes. The amino acid constraints placed on AMPs by the geometric requirement to induce negative Gaussian curvature are consistent with known AMP sequences. This ‘saddle-splay curvature selection rule’ is not strongly restrictive so AMPs have significant compositional freedom to multiplex membrane activity with other useful functions. The observation that certain proteins involved in cellular processes which require negative Gaussian curvature contain domains with similar motifs as AMPs, suggests this rule may be applicable to other curvature-generating proteins. Since our saddle-splay curvature design rule is based upon both a mechanism of activity and the existing motifs of natural AMPs, we believe it will assist the development of synthetic antimicrobials. PMID:24778573
Curvature-Induced Spatial Ordering of Composition in Lipid Membranes
Katz, Shimrit
2017-01-01
Phase segregation of membranal components, such as proteins, lipids, and cholesterols, leads to the formation of aggregates or domains that are rich in specific constituents. This process is important in the interaction of the cell with its surroundings and in determining the cell's behavior and fate. Motivated by published experiments on curvature-modulated phase separation in lipid membranes, we formulate a mathematical model aiming at studying the spatial ordering of composition in a two-component biomembrane that is subjected to a prescribed (imposed) geometry. Based on this model, we identified key nondimensional quantities that govern the biomembrane response and performed numerical simulations to quantitatively explore their influence. We reproduce published experimental observations and extend them to surfaces with geometric features (imposed geometry) and lipid phases beyond those used in the experiments. In addition, we demonstrate the possibility for curvature-modulated phase separation above the critical temperature and propose a systematic procedure to determine which mechanism, the difference in bending stiffness or difference in spontaneous curvatures of the two phases, dominates the coupling between shape and composition. PMID:28473867
Stress-induced curvature engineering in surface-micromachined devices
NASA Astrophysics Data System (ADS)
Aksyuk, Vladimir A.; Pardo, Flavio; Bishop, David J.
1999-03-01
Residual stress and stress gradients play an important role in determining equilibrium shape and behavior of various Si surface-micromachined devices under applied loads. This is particularly true for system having large-area plates and long beams where curvature resulting from stress can lead to significant deviations from stress-free shape. To gain better understanding of these properties, we have measured the equilibrium shapes of various structures built on the MCNC MUMPs using an interferometric profiler. The structures were square plates and long beams composed of various combinations of polysilicon an oxide layers. Some of the structures had additional MUMPs metal layer on top, while on others in-house chromium-gold stacks of varying thickness have been deposited. Temperature dependence of the curvature was measured for some plates. We have used these data in conjunction with simple models to significantly improve the performance of our micromachined devices. While for some structures such as large area reflectors the curvature had to be minimized, it could be advantageously exploited by others, for example vertical actuators for self-assembly.
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.
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
NASA Astrophysics Data System (ADS)
van der Wel, Casper; Vahid, Afshin; Šarić, Anđela; Idema, Timon; Heinrich, Doris; Kraft, Daniela J.
2016-09-01
The interplay of membrane proteins is vital for many biological processes, such as cellular transport, cell division, and signal transduction between nerve cells. Theoretical considerations have led to the idea that the membrane itself mediates protein self-organization in these processes through minimization of membrane curvature energy. Here, we present a combined experimental and numerical study in which we quantify these interactions directly for the first time. In our experimental model system we control the deformation of a lipid membrane by adhering colloidal particles. Using confocal microscopy, we establish that these membrane deformations cause an attractive interaction force leading to reversible binding. The attraction extends over 2.5 times the particle diameter and has a strength of three times the thermal energy (-3.3 kBT). Coarse-grained Monte-Carlo simulations of the system are in excellent agreement with the experimental results and prove that the measured interaction is independent of length scale. Our combined experimental and numerical results reveal membrane curvature as a common physical origin for interactions between any membrane-deforming objects, from nanometre-sized proteins to micrometre-sized particles.
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
Curvature induced phase stability of an intensely heated liquid
NASA Astrophysics Data System (ADS)
Sasikumar, Kiran; Liang, Zhi; Cahill, David G.; Keblinski, Pawel
2014-06-01
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.
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.
Flow-induced buckling of flexible shells with non-zero Gaussian curvatures and thin spots.
Chang, Gary Han; Modarres-Sadeghi, Yahya
2017-03-29
We study the influence of one or multiple thin spots on the flow-induced instabilities of flexible shells of revolution with non-zero Gaussian curvatures. The shell's equation of motion is described by a thin doubly-curved shell theory and is coupled with perturbed flow pressure, calculated based on an inviscid flow model. We show that for shells with positive Gaussian curvatures conveying fluid, the existence of a thin spot results in a localized flow-induced buckling response of the shell in the neighborhood of the thin spot, and significantly reduces the critical flow velocity for buckling instability. For shells with negative Gaussian curvatures, the buckling response is extended along the shell's characteristic lines and the critical flow velocity is only slightly reduced. We also show that the length scale of the localized deformation generated by a thin spot is proportional to the shell's global thickness when the stiffness of the thin spot is negligible compared with the stiffness of the rest of the shell. When two thin spots exist at a distance, their influences are independent from each other for shells with positive Gaussian curvatures, but large-scale deformations can be created due to multiple thin spots on shells with negative curvatures, depending on the thin spots' relative position.
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.
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
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
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
Maier, Oana; Galan, Debra L.; Wodrich, Harald; Wiethoff, Christopher M.
2010-01-01
Adenovirus (Ad) membrane penetration during cell entry is poorly understood. Here we show that antibodies which neutralize the membrane lytic activity of the Ad capsid protein VI interfere with Ad endosomal membrane penetration. In vitro studies using a peptide corresponding to an N-terminal amphipathic α-helix of protein VI (VI-Φ), as well as other truncated forms of protein VI suggest that VI-Φ is largely responsible for protein VI binding to and lysing of membranes. Additional studies suggest that VI-Φ lies nearly parallel to the membrane surface. Protein VI fragments membranes and induces highly curved structures. Further studies suggest that Protein VI induces positive membrane curvature. These data support a model in which protein VI binds membranes, inducing positive curvature strain which ultimately leads to membrane fragmentation. These results agree with previous observations of Ad membrane permeabilization during cell entry and provide an initial mechanistic description of a nonenveloped virus membrane lytic protein. PMID:20409568
Membrane-Mediated Aggregation of Curvature-Inducing Nematogens and Membrane Tubulation
Ramakrishnan, N.; Sunil Kumar, P.B.; Ipsen, John H.
2013-01-01
The shapes of cell membranes are largely regulated by membrane-associated, curvature-active proteins. Herein, we use a numerical model of the membrane, recently developed by us, with elongated membrane inclusions possessing spontaneous directional curvatures that could be different along, and perpendicular to, the membrane’s long axis. We show that, due to membrane-mediated interactions, these curvature-inducing membrane-nematogens can aggregate spontaneously, even at low concentrations, and change the local shape of the membrane. We demonstrate that for a large group of such inclusions, where the two spontaneous curvatures have equal sign, the tubular conformation and sometimes the sheet conformation of the membrane are the common equilibrium shapes. We elucidate the factors necessary for the formation of these protein lattices. Furthermore, the elastic properties of the tubes, such as their compressional stiffness and persistence length, are calculated. Finally, we discuss the possible role of nematic disclination in capping and branching of the tubular membranes. PMID:23473484
Membrane-mediated aggregation of curvature-inducing nematogens and membrane tubulation.
Ramakrishnan, N; Sunil Kumar, P B; Ipsen, John H
2013-03-05
The shapes of cell membranes are largely regulated by membrane-associated, curvature-active proteins. Herein, we use a numerical model of the membrane, recently developed by us, with elongated membrane inclusions possessing spontaneous directional curvatures that could be different along, and perpendicular to, the membrane's long axis. We show that, due to membrane-mediated interactions, these curvature-inducing membrane-nematogens can aggregate spontaneously, even at low concentrations, and change the local shape of the membrane. We demonstrate that for a large group of such inclusions, where the two spontaneous curvatures have equal sign, the tubular conformation and sometimes the sheet conformation of the membrane are the common equilibrium shapes. We elucidate the factors necessary for the formation of these protein lattices. Furthermore, the elastic properties of the tubes, such as their compressional stiffness and persistence length, are calculated. Finally, we discuss the possible role of nematic disclination in capping and branching of the tubular membranes. Copyright © 2013 Biophysical Society. Published by Elsevier Inc. All rights reserved.
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.
Curvature Induced by Amyloplast Magnetophoresis in Protonemata of the Moss Ceratodon purpureus1
Kuznetsov, Oleg A.; Schwuchow, Jochen; Sack, Fred D.; Hasenstein, Karl 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. PMID:9952461
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.
Kegulian, Natalie C.; Sankhagowit, Shalene; Apostolidou, Melania; Jayasinghe, Sajith A.; Malmstadt, Noah; Butler, Peter C.; Langen, Ralf
2015-01-01
Islet amyloid polypeptide (IAPP) is a 37-amino acid amyloid protein intimately associated with pancreatic islet β-cell dysfunction and death in type II diabetes. In this study, we combine spectroscopic methods and microscopy to investigate α-helical IAPP-membrane interactions. Using light scattering and fluorescence microscopy, we observe that larger vesicles become smaller upon treatment with human or rat IAPP. Electron microscopy shows the formation of various highly curved structures such as tubules or smaller vesicles in a membrane-remodeling process, and spectrofluorometric detection of vesicle leakage shows disruption of membrane integrity. This effect is stronger for human IAPP than for the less toxic rat IAPP. From CD spectra in the presence of different-sized vesicles, we also uncover the membrane curvature-sensing ability of IAPP and find that it transitions from inducing to sensing membrane curvature when lipid negative charge is decreased. Our in vivo EM images of immunogold-labeled rat IAPP and human IAPP show both forms to localize to mitochondrial cristae, which contain not only locally curved membranes but also phosphatidylethanolamine and cardiolipin, lipids with high spontaneous negative curvature. Disruption of membrane integrity by induction of membrane curvature could apply more broadly to other amyloid proteins and be responsible for membrane damage observed in other amyloid diseases as well. PMID:26283787
Ramírez-Garza, O A; Méndez-Alcaraz, J M; González-Mozuelos, P
2017-05-21
Paramagnetic colloidal particles distributed along an ellipse are used as a model system to study the effects of curvature gradients on the structure and dynamics of colloids in curved manifolds. Unlike what happens for circular and spherical systems, in the present case, the equilibrium one-particle distribution function displays inhomogeneities due to the changing curvature along the ellipse. The ensuing effects on the two-body correlations are also analyzed, leading to the observation of anisotropic and long-ranged effects. Another noticeable consequence is the slowing down of the self-diffusion of these particles, which for large eccentricities may induce metastable states; this is evaluated by means of the time-dependent self-distribution.
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.
Agudo-Canalejo, Jaime; Lipowsky, Reinhard
2017-03-15
Biological membranes and lipid vesicles often display complex shapes with non-uniform membrane curvature. When adhesive nanoparticles with chemically uniform surfaces come into contact with such membranes, they exhibit four different engulfment regimes as recently shown by a systematic stability analysis. Depending on the local curvature of the membrane, the particles either remain free, become partially or completely engulfed by the membrane, or display bistability between free and completely engulfed states. Here, we go beyond stability analysis and develop an analytical theory to leading order in the ratio of particle-to-vesicle size. This theory allows us to determine the local and global energy landscapes of uniform nanoparticles that are attracted towards membranes and vesicles. While the local energy landscape depends only on the local curvature of the vesicle membrane and not on the overall membrane shape, the global energy landscape describes the variation of the equilibrium state of the particle as it probes different points along the membrane surface. In particular, we find that the binding energy of a partially engulfed particle depends on the 'unperturbed' local curvature of the membrane in the absence of the particle. This curvature dependence leads to local forces that pull the partially engulfed particles towards membrane segments with lower and higher mean curvature if the particles originate from the exterior and interior solution, respectively, corresponding to endo- and exocytosis. Thus, for partial engulfment, endocytic particles undergo biased diffusion towards the membrane segments with the lowest membrane curvature, whereas exocytic particles move towards segments with the highest curvature. The curvature-induced forces are also effective for Janus particles with one adhesive and one non-adhesive surface domain. In fact, Janus particles with a strongly adhesive surface domain are always partially engulfed which implies that they provide
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
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
2013-06-04
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.
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.
Modeling of stress-induced curvature in surface-micromachined devices
NASA Astrophysics Data System (ADS)
Cowan, William D.; Bright, Victor M.; Elvin, Alex A.; Koester, David A.
1997-09-01
This paper compares measured to modeled stress-induced curvature of simple piston micromirrors. Two similar flexure-beam micromirror designs were fabricate using the 11th DARPA-supported multi-user MEMS processes (MUMPs) run. The test devices vary only in the MUMPs layers used for fabrication. In one case the mirror plate is the 1.5 micrometers thick Poly2 layer. The other mirror design employs stacked Poly1 and Poly2 layers for a total thickness of 3.5 micrometers . Both mirror structures are covered with the standard MUMPs metallization of approximately 200 angstrom of chromium and 0.5 micrometers of gold. Curvature of these devices was measured to within +/- 5 nm with a computer controlled microscope laser interferometer system. As intended, the increased thickness of the stacked polysilicon layers reduces the mirror curvature by a factor of 4. The two micromirror designs were modeled using IntelliCAD, a commercial CAD system for MEMS. The basis of analysis was the finite element method. Simulated results using MUMPs 11 film parameters showed qualitative agreement with measured data, but obvious quantitative differences. Subsequent remeasurement of the metal stress and use of the new value significantly improved model agreement with the measured data. The paper explores the effect of several film parameters on the modeled structures. Implications for MEMS film metrology, and test structures are considered.
Mesoscale computational studies of membrane bilayer remodeling by curvature-inducing proteins
NASA Astrophysics Data System (ADS)
Ramakrishnan, N.; Sunil Kumar, P. B.; Radhakrishnan, Ravi
2014-10-01
Biological membranes constitute boundaries of cells and cell organelles. These membranes are soft fluid interfaces whose thermodynamic states are dictated by bending moduli, induced curvature fields, and thermal fluctuations. Recently, there has been a flood of experimental evidence highlighting active roles for these structures in many cellular processes ranging from trafficking of cargo to cell motility. It is believed that the local membrane curvature, which is continuously altered due to its interactions with myriad proteins and other macromolecules attached to its surface, holds the key to the emergent functionality in these cellular processes. Mechanisms at the atomic scale are dictated by protein-lipid interaction strength, lipid composition, lipid distribution in the vicinity of the protein, shape and amino acid composition of the protein, and its amino acid contents. The specificity of molecular interactions together with the cooperativity of multiple proteins induce and stabilize complex membrane shapes at the mesoscale. These shapes span a wide spectrum ranging from the spherical plasma membrane to the complex cisternae of the Golgi apparatus. Mapping the relation between the protein-induced deformations at the molecular scale and the resulting mesoscale morphologies is key to bridging cellular experiments across various length scales. In this review, we focus on the theoretical and computational methods used to understand the phenomenology underlying protein-driven membrane remodeling. Interactions at the molecular scale can be computationally probed by all atom and coarse grained molecular dynamics (MD, CGMD), as well as dissipative particle dynamics (DPD) simulations, which we only describe in passing. We choose to focus on several continuum approaches extending the Canham-Helfrich elastic energy model for membranes to include the effect of curvature-inducing proteins and explore the conformational phase space of such systems. In this description, the
Mesoscale computational studies of membrane bilayer remodeling by curvature-inducing proteins
Ramakrishnan, N.; Sunil Kumar, P. B.; Radhakrishnan, Ravi
2014-01-01
Biological membranes constitute boundaries of cells and cell organelles. These membranes are soft fluid interfaces whose thermodynamic states are dictated by bending moduli, induced curvature fields, and thermal fluctuations. Recently, there has been a flood of experimental evidence highlighting active roles for these structures in many cellular processes ranging from trafficking of cargo to cell motility. It is believed that the local membrane curvature, which is continuously altered due to its interactions with myriad proteins and other macromolecules attached to its surface, holds the key to the emergent functionality in these cellular processes. Mechanisms at the atomic scale are dictated by protein-lipid interaction strength, lipid composition, lipid distribution in the vicinity of the protein, shape and amino acid composition of the protein, and its amino acid contents. The specificity of molecular interactions together with the cooperativity of multiple proteins induce and stabilize complex membrane shapes at the mesoscale. These shapes span a wide spectrum ranging from the spherical plasma membrane to the complex cisternae of the Golgi apparatus. Mapping the relation between the protein-induced deformations at the molecular scale and the resulting mesoscale morphologies is key to bridging cellular experiments across the various length scales. In this review, we focus on the theoretical and computational methods used to understand the phenomenology underlying protein-driven membrane remodeling. Interactions at the molecular scale can be computationally probed by all atom and coarse grained molecular dynamics (MD, CGMD), as well as dissipative particle dynamics (DPD) simulations, which we only describe in passing. We choose to focus on several continuum approaches extending the Canham - Helfrich elastic energy model for membranes to include the effect of curvature-inducing proteins and explore the conformational phase space of such systems. In this
Mesoscale computational studies of membrane bilayer remodeling by curvature-inducing proteins.
Ramakrishnan, N; Sunil Kumar, P B; Radhakrishnan, Ravi
2014-10-01
Biological membranes constitute boundaries of cells and cell organelles. These membranes are soft fluid interfaces whose thermodynamic states are dictated by bending moduli, induced curvature fields, and thermal fluctuations. Recently, there has been a flood of experimental evidence highlighting active roles for these structures in many cellular processes ranging from trafficking of cargo to cell motility. It is believed that the local membrane curvature, which is continuously altered due to its interactions with myriad proteins and other macromolecules attached to its surface, holds the key to the emergent functionality in these cellular processes. Mechanisms at the atomic scale are dictated by protein-lipid interaction strength, lipid composition, lipid distribution in the vicinity of the protein, shape and amino acid composition of the protein, and its amino acid contents. The specificity of molecular interactions together with the cooperativity of multiple proteins induce and stabilize complex membrane shapes at the mesoscale. These shapes span a wide spectrum ranging from the spherical plasma membrane to the complex cisternae of the Golgi apparatus. Mapping the relation between the protein-induced deformations at the molecular scale and the resulting mesoscale morphologies is key to bridging cellular experiments across the various length scales. In this review, we focus on the theoretical and computational methods used to understand the phenomenology underlying protein-driven membrane remodeling. Interactions at the molecular scale can be computationally probed by all atom and coarse grained molecular dynamics (MD, CGMD), as well as dissipative particle dynamics (DPD) simulations, which we only describe in passing. We choose to focus on several continuum approaches extending the Canham - Helfrich elastic energy model for membranes to include the effect of curvature-inducing proteins and explore the conformational phase space of such systems. In this
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.
NASA Astrophysics Data System (ADS)
Lee, Michelle; Hwee Lai, Ghee; Schmidt, Nathan; Xian, Wujing; Wong, Gerard C. L.
2013-03-01
Mitochondria form a dynamic and interconnected network, which disintegrates during apoptosis to generate numerous smaller mitochondrial fragments. This process is at present not well understood. Yeast mitochondrial fission machinery proteins, Dnm1 and Fis1, are believed to regulate programmed cell death in yeast. Yeast Dnm1 has been previously shown to promote mitochondrial fragmentation and degradation characteristic of apoptotic cells, while yeast Fis1 inhibits cell death by limiting the mitochondrial fission induced by Dnm1 [Fannjiang et al, Genes & Dev. 2004. 18: 2785-2797]. To better understand the mechanisms of these antagonistic fission proteins, we use synchrotron small angle x-ray scattering (SAXS) to investigate their interaction with model cell membranes. The relationship between each protein, Dnm1 and Fis1, and protein-induced changes in membrane curvature and topology is examined. Through the comparison of the membrane rearrangement and phase behavior induced by each protein, we will discuss their respective roles in the regulation of mitochondrial fission.
Curvature induced quasi-melting from rough surfaces in nematic liquid crystals
NASA Astrophysics Data System (ADS)
Barbero, G.; Durand, G.
1991-06-01
The Berreman-de Gennes model, describing the azimutal anchoring energy of a nematic material oriented by a grooved surface, is revisited. When the groove wave-length is shorter than the nematic-isotropic coherence lenght, the nematic should decrease locally its order parameter to decrease the too large curvature energy induced by the boundaries. This curvature induced surface quasi-melting could explain recent observations on the order parameter decrease close to oblique SiO evaporated rough surfaces. Le modèle de Berreman-de Gennes, qui décrit l'ancrage azimuthal d'un nématique orienté par une surface ondulée est rediscuté. Quand la période des ondulations est plus courte que la longueur de cohérence nématique-isotrope, le nématique préfère fondre que se courber. Ce mécanisme explique la décroissance du paramètre d'ordre observée sur des surfaces rugueuses obtenues par évaporation oblique de SiO.
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.
Curvature-Induced Bunch Self-Interaction for an Energy-Chirped Bunch in Magnetic Bends
Rui Li
2006-01-04
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. In this paper, for an electron distribution moving ultrarelativistically in a bending system, the dynamics of a particle in the electron distribution is derived from the Hamiltonian of the particle 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.
Membrane nanotubes induced by aqueous phase separation and stabilized by spontaneous curvature
Li, Yanhong; Lipowsky, Reinhard; Dimova, Rumiana
2011-01-01
Tubular membrane structures are widespread in eukaryotic cells, but the mechanisms underlying their formation and stability are not well understood. Previous work has focused on tube extrusion from cells and model membranes under the application of external forces. Here, we present novel membrane/polymer systems, where stable tubes form in the absence of externally applied forces. Solutions of two water-soluble polymers, polyethylene glycol and dextran, were encapsulated in giant lipid vesicles, cell-size model systems. Hypertonic deflation induced phase separation of the enclosed solution. The excess membrane area created during the deflation process was stored in a large number of membrane nanotubes inside the vesicle. The tubes had a diameter below optical resolution and became visible only when fluorescently labeled. The tubes were rather stable: In the absence of external forces, they existed for several days. A theoretical analysis of the shapes of the deflated vesicles reveals that these shapes would be unstable if the membranes had no spontaneous curvature. Using the large separation of length scales between the tube diameter and the overall size of the vesicles, the spontaneous curvature can be calculated and is found to be about -1/(240 nm) for a certain range of polymer concentrations. The nanotubes could also be retracted back into the mother vesicle by increasing the membrane tension via micropipette aspiration of the vesicle. Membrane tubes, which can form and be retracted easily, should be relevant for lipid storage in cells. PMID:21383120
NASA Astrophysics Data System (ADS)
Lim, Jin-Myoung; Chun, Myung-Suk
2011-10-01
In order to exactly understand the curvature-induced secondary flow motion, the steady electro-osmotic flow (EOF) is investigated by applying the full Poisson-Boltzmann/Navier-Stokes equations in a whole domain of the rectangular microchannel. The momentum equation is solved with the continuity equation as the pressure-velocity coupling achieves convergence by employing the advanced algorithm, and generalized Navier's slip boundary conditions are applied at the hydrophobic curved surface. Two kinds of channels widely used for lab-on-chips are explored with the glass channel and the heterogeneous channel consisting of glass and hydrophobic polydimethylsiloxane, spanning thin to thick electric double layer (EDL) problem. According to a sufficiently low Dean number, an inward skewness in the streamwise velocity profile is observed at the turn. With increasing EDL thickness, the electrokinetic effect gets higher contribution in the velocity profile. Simulation results regarding the variations of streamwise velocity depending on the electrokinetic parameters and hydrodynamic fluid slippage are qualitatively consistent with the predictions documented in the literature. Secondary flows arise due to a mismatch of streamline velocity between fluid in the channel center and near-wall regions. Strengthened secondary flow results from increasing the EDL thickness and the contribution of fluid inertia (i.e., electric field and channel curvature), providing a scaling relation with the same slope. Comparing with and between the cases enables us to identify the optimum selection in applications of curved channel for enhanced EOF and stronger secondary motion relevant to the mixing effect.
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.
Structure and dynamics of Penetratin's association and translocation to a lipid bilayer
NASA Astrophysics Data System (ADS)
Ignacio J., General; Asciutto, Eliana K.
2017-03-01
Penetratin belongs to the important class of small and positively charged peptides, capable of entering cells. The determination of the optimal peptidic structure for translocation is challenging; results obtained so far are varied and dependent on several factors. In this work, we review the dynamics of association of Penetratin with a modeled dioleoyl-phosphatidylcholine (DOPC) lipid membrane using molecular dynamics simulations with last generation force fields. Penetratin's structural preferences are determined using a Markov state model. It is observed that the peptide retains a helical form in the membrane associated state, just as in water, with the exception of both termini which lose helicity, facilitating the interaction of terminal residues with the phosphate groups on the membrane's outer layer. The optimal orientation for insertion is found to be with the peptide's axis forming a small angle with the interface, and with R1 stretching toward the bilayer. The interaction between arginine side-chains and phosphate groups is found to be greater than the corresponding to lysine, mainly due to a higher number of hydrogen bonds between them. The free energy profile of translocation is qualitatively studied using Umbrella Sampling. It is found that there are different paths of penetration, that greatly differ in size of free energy barrier. The lowest path is compatible with residues R10 to K13 leading the way through the membrane and pulling the rest of the peptide. When the other side is reached, the C-terminus overtakes those residues, and finally breaks out of the membrane. The peptide's secondary structure during this traversal suffers some changes with respect to the association structure but, overall, conserves its helicity, with both termini in a more disordered state.
Curvature induced L-defects in water conduction in carbon nanotubes.
Zimmerli, Urs; Gonnet, Pedro G; Walther, Jens H; Koumoutsakos, Petros
2005-06-01
We conduct molecular dynamics simulations to study the effect of the curvature induced static dipole moment of small open-ended single-walled carbon nanotubes (CNTs) immersed in water. This dipole moment generates a nonuniform electric field, changing the energy landscape in the CNT and altering the water conduction process. The CNT remains practically filled with water at all times, whereas intermittent filling is observed when the dipole term is not included. In addition, the dipole moment induces a preferential orientation of the water molecules near the end regions of the nanotube, which in turn causes a reorientation of the water chain in the middle of the nanotube. The most prominent feature of this reorientation is an L-defect in the chain of water molecules inside the CNT. The analysis of the water energetics and structural characteristics inside and in the vicinity of the CNT helps to identify the role of the dipole moment and to suggest possible mechanisms for controlled water and proton transport at the nanoscale.
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
Tai, Lingyu; Liu, Chang; Jiang, Kuan; Chen, Xishan; Feng, Linglin; Pan, Weisan; Wei, Gang; Lu, Weiyue
2017-08-30
Inhibition of gene expression by nucleic acids is a promising strategy in the treatment of ocular diseases. However, intraocular delivery of nucleic acids to the posterior ocular tissues remains a great challenge due to the presence of various biological barriers. To circumvent this problem, we established a novel penetratin (P) modified poly(amidoamine) dendrimer (D)/hyaluronic acid (H) complex to deliver antisense oligonucleotides (ASOs, O). Complexes (D/O, HD/O and PHD/O) were easily prepared and modification layers (hyaluronic acid and penetratin) were respectively absorbed on the surface via electrostatic interaction. Complexes with different outer layers were characterized as spherical particles with reversed charges. In vitro cellular uptake of ASOs in PHD/O complex was significantly increased than those in other formulations. In vivo studies were carried out after topical instillation of the complexes in the conjunctival sac of mice. Compared with D/O and HD/O, PHD/O exhibited much more distribution in the posterior segment of the eyes and prolonged retention time of ASOs in retina for more than 8h. Taken together, these results indicated that PHD/O complex possessed substantially improved ocular permeability and distribution in the posterior ocular tissues. This work provided a promising noninvasive intraocular delivery strategy for nucleic acids via topical administration. Copyright © 2017 Elsevier B.V. All rights reserved.
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.
NASA Astrophysics Data System (ADS)
Cotte, Eric P.; Engelstad, Roxann L.; Lovell, Edward G.; Tanzil, Daniel; Eschbach, Florence O.; Korobko, Yulia O.; Fujita, Minoru; Nakagawa, Hiroaki
2003-06-01
Lithography registration errors induced by the attachment of soft pellicles on reticles can significantly affect wafer overlay performance for sub-90 nm lithography chip manufacturing. Intel Corporation, Mitsui Chemicals, and the University of Wisconsin Computational Mechanics Center (UW-CMC) have conducted an extensive experimental study to quantify and minimize the pellicle-induced distortions in order to meet advanced mask manufacturing requirements. A comprehensive design of experiment was elaborated to evaluate the effects of frame curvature, adhesive gasket compliance, and mounting load on pellicle-induced distortions for soft pellicle systems. A frame curvature measurement tool was custom-made at the UW-CMC, employing an MTI Instruments capacitive sensor. A TA Instruments dynamic mechanical analyzer was used to determine the elastic modulus of the adhesive gasket materials. Registration measurements were conducted by Intel on test reticles on a 21 × 21 array of grid points, before and after pellicle attachment, to obtain pellicle-induced distortion results. Results characterize the influence of attachment process, type of adhesive gasket, frame curvature, reticle guiding plate configuration, and attachment load on pellicle-induced distortions.
Pannuzzo, Martina; Raudino, Antonio; Böckmann, Rainer A
2014-07-14
Peptide- or protein-induced curvatures of lipid membranes may be studied in molecular dynamics (MD) simulations. In these, membranes are usually modeled as infinitely extended bilayers by using periodic boundary conditions. However, the enforced periodicity results in an underestimation of the bending power of peptides, unless the patch size is much larger than the induced curvature radii. In this letter, we propose a novel approach to evaluate the bending power of a given distribution and/or density of peptides based on the use of flat open-edged lipid patches. To ensure long-lived metastable structures, the patch rim is stabilized in MD simulations by a local enrichment with short-chain lipids. By combining the theory of continuum elastic media with MD simulations, we prove that open-edged patches evolve from a planar state to a closed vesicle, with a transition rate that strongly depends on the concentration of lipid soluble peptides. For close-to-critical values for the patch size and edge energy, the response to even small changes in peptide concentration adopts a transition-like behavior (buckling instability). The usage of open-edged membrane patches amplifies the bending power of peptides, thereby enabling the analysis of the structural properties of membrane-peptide systems. We applied the presented method to investigate the curvature induced by aggregating β -amyloid peptides, unraveling a strong sensitivity of membrane deformation to the peptide concentration.
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.
Asymmetric spin-wave dispersion in ferromagnetic nanotubes induced by surface curvature
NASA Astrophysics Data System (ADS)
Otálora, Jorge A.; Yan, Ming; Schultheiss, Helmut; Hertel, Riccardo; Kákay, Attila
2017-05-01
We present a detailed analytical derivation of the spin wave (SW) dispersion relation in magnetic nanotubes with magnetization along the azimuthal direction. The obtained formula can be used to calculate the dispersion relation for any longitudinal and azimuthal mode. The obtained dispersion is asymmetric for all azimuthal modes traveling along the axial direction. As reported in our recent publication [Phys. Rev. Lett. 117, 227203 (2016), 10.1103/PhysRevLett.117.227203], the asymmetry is a curvature-induced effect originating from the dipole-dipole interaction. Here, we discuss the asymmetry of the dispersion for azimuthal modes by analyzing the SW asymmetry Δ f (kz) =fn(kz) -fn(-kz) , where fn(kz) is the eigenfrequency of a magnon with a longitudinal and azimuthal wave vectors, kz and n , respectively; and the dependence of the maximum asymmetry with the nanotube radius R . The analytical results are in perfect agreement with micromagnetic simulations. Furthermore, we show that the dispersion relation simplifies to the thin-film dispersion relation with in-plane magnetization when analyzing the three limiting cases: (i) kz=0 , (ii) kz≫1 /R , and (iii) kz≪1 /R . In the first case, for the zeroth-order modes the thin-film Kittel formula is obtained. For modes with higher order the dispersion relation for the Backward-Volume geometry is recovered. In the second case, for the zeroth-order mode the exchange dominated dispersion relation for SW in Damon-Esbach configuration is obtained. For the case kz≪1 /R , we find that the dispersion relation can be reduced to a formula similar to the Kalinikos-Slavin [J. Phys. C: Sol. State Phys. 19, 7013 (1986), 10.1088/0022-3719/19/35/014] type.
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
2015-08-06
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.
Self-assembly of a filament by curvature-inducing proteins
NASA Astrophysics Data System (ADS)
Kwiecinski, James; Chapman, S. Jonathan; Goriely, Alain
2017-04-01
We explore a simplified macroscopic model of membrane shaping by means of curvature-sensing BAR proteins. Equations describing the interplay between the shape of a freely floating filament in a fluid and the adhesion kinetics of proteins are derived from mechanical principles. The constant curvature solutions that arise from this system are studied using weakly nonlinear analysis. We show that the stability of the filament's shape is completely characterized by the parameters associated with protein recruitment and establish that in the bistable regime, proteins aggregate on the filament forming regions of high and low curvatures. This pattern formation is then followed by phase-coarsening that resolves on a time-scale dependent on protein diffusion and drift across the filament, which contend to smooth and maintain the pattern respectively. The model is generalized for multiple species of BAR proteins and we show that the stability of the assembled shape is determined by a competition between proteins attaching on opposing sides.
Spatial Control of Epsin-induced Clathrin Assembly by Membrane Curvature*♦
Holkar, Sachin S.; Kamerkar, Sukrut C.; Pucadyil, Thomas J.
2015-01-01
Epsins belong to the family of highly conserved clathrin-associated sorting proteins that are indispensable for clathrin-mediated endocytosis, but their precise functions remain unclear. We have developed an assay system of budded supported membrane tubes displaying planar and highly curved membrane surfaces to analyze intrinsic membrane curvature preference shown by clathrin-associated sorting proteins. Using real-time fluorescence microscopy, we find that epsin preferentially partitions to and assembles clathrin on highly curved membrane surfaces. Sorting of epsin to regions of high curvature strictly depends on binding to phosphatidylinositol 4,5-bisphosphate. Fluorescently labeled clathrins rapidly assemble as foci, which in turn cluster epsin, while maintaining tube integrity. Clathrin foci grow in intensity with a typical time constant of ∼75 s, similar to the time scales for coated pit formation seen in cells. Epsin therefore effectively senses membrane curvature to spatially control clathrin assembly. Our results highlight the potential role of membrane curvature in orchestrating the myriad molecular interactions necessary for the success of clathrin-mediated membrane budding. PMID:25837255
Spatial Control of Epsin-induced Clathrin Assembly by Membrane Curvature.
Holkar, Sachin S; Kamerkar, Sukrut C; Pucadyil, Thomas J
2015-06-05
Epsins belong to the family of highly conserved clathrin-associated sorting proteins that are indispensable for clathrin-mediated endocytosis, but their precise functions remain unclear. We have developed an assay system of budded supported membrane tubes displaying planar and highly curved membrane surfaces to analyze intrinsic membrane curvature preference shown by clathrin-associated sorting proteins. Using real-time fluorescence microscopy, we find that epsin preferentially partitions to and assembles clathrin on highly curved membrane surfaces. Sorting of epsin to regions of high curvature strictly depends on binding to phosphatidylinositol 4,5-bisphosphate. Fluorescently labeled clathrins rapidly assemble as foci, which in turn cluster epsin, while maintaining tube integrity. Clathrin foci grow in intensity with a typical time constant of ∼75 s, similar to the time scales for coated pit formation seen in cells. Epsin therefore effectively senses membrane curvature to spatially control clathrin assembly. Our results highlight the potential role of membrane curvature in orchestrating the myriad molecular interactions necessary for the success of clathrin-mediated membrane budding. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.
Toroidal curvature induced screening of external fields by a resistive plasma response
Liu Yueqiang; Connor, J. W.; Cowley, S. C.; Ham, C. J.; Hastie, R. J.; Hender, T. C.
2012-07-15
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 {approx}10{sup -5}{omega}{sub A}, with {omega}{sub A} being the Alfven 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.
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.
Mechanisms of protein transduction domains: HIV TAT and ANTP penetratin as prototypical cases
NASA Astrophysics Data System (ADS)
Mishra, Abhijit; Schmidt, Nathan; Gordon, Vernita; Wong, Gerard
2007-03-01
Biologically active molecules such as proteins and oligonucleotides can be transduced across cell membranes with high efficiency when covalently linked to a Protein Transduction Domain (PTD), such as the TAT domain in the HIV virus and ANTP from the fruitfly. All PTDs have a high content of basic amino acids resulting in a net positive charge. Electrostatic interactions between cationic PTDs and the negatively charged phospholipids that constitute the plasma membrane are likely to be responsible for peptide uptake, but no detailed structural studies exist. We examined membrane structures induced by the cationic TAT domain and those induced by other cationic polypeptides as a function of membrane composition using synchrotron x-ray scattering. We find that both the TAT PTD and ANTP generate negative Gaussian curvature, which is necessary for pore formation, and produce a bicontinuous Pn3m double diamond cubic phase. A general mechanism is proposed.
Doppler indices in the umbilical arteries: influence of vessel curvature induced by bladder filling.
Balbis, Sonia; Gaglioti, Pietro; Todros, Tullia; Guiot, Caterina
2007-12-01
Doppler indices are widely used to assess normal versus pathologic haemodynamics. In obstetrics, the assessment of abnormal values in some critical compartments, such as the umbilical arteries (UA), may be crucial in the clinical management of growth-restricted foetuses. It was recently proposed that the UA should be sampled in their perivesical portion (PVC), i.e., where they surround the foetal urinary bladder. However, measurements at this site could be biased by the degree of curvature of the vessel due to bladder filling. We investigated this possibility in vivo and in vitro, i.e., measurements on rubber tubes at different radii of curvature R(c). There was significant dependence of the Doppler indices A/B and PI on the vessel curvature and insonation angle; in fact, we recorded errors of about 25% when R(c) was 10 times larger than the radius of the vessel and about 100% when R(c) was five times larger than the radius of the vessel. Therefore, measurements of the UA at the PVC site should only be performed when the foetal bladder is empty.
SARS-CoV fusion peptides induce membrane surface ordering and curvature
Basso, Luis G. M.; Vicente, Eduardo F.; Crusca Jr., Edson; Cilli, Eduardo M.; Costa-Filho, Antonio J.
2016-01-01
Viral membrane fusion is an orchestrated process triggered by membrane-anchored viral fusion glycoproteins. The S2 subunit of the spike glycoprotein from severe acute respiratory syndrome (SARS) coronavirus (CoV) contains internal domains called fusion peptides (FP) that play essential roles in virus entry. Although membrane fusion has been broadly studied, there are still major gaps in the molecular details of lipid rearrangements in the bilayer during fusion peptide-membrane interactions. Here we employed differential scanning calorimetry (DSC) and electron spin resonance (ESR) to gather information on the membrane fusion mechanism promoted by two putative SARS FPs. DSC data showed the peptides strongly perturb the structural integrity of anionic vesicles and support the hypothesis that the peptides generate opposing curvature stresses on phosphatidylethanolamine membranes. ESR showed that both FPs increase lipid packing and head group ordering as well as reduce the intramembrane water content for anionic membranes. Therefore, bending moment in the bilayer could be generated, promoting negative curvature. The significance of the ordering effect, membrane dehydration, changes in the curvature properties and the possible role of negatively charged phospholipids in helping to overcome the high kinetic barrier involved in the different stages of the SARS-CoV-mediated membrane fusion are discussed. PMID:27892522
SARS-CoV fusion peptides induce membrane surface ordering and curvature.
Basso, Luis G M; Vicente, Eduardo F; Crusca, Edson; Cilli, Eduardo M; Costa-Filho, Antonio J
2016-11-28
Viral membrane fusion is an orchestrated process triggered by membrane-anchored viral fusion glycoproteins. The S2 subunit of the spike glycoprotein from severe acute respiratory syndrome (SARS) coronavirus (CoV) contains internal domains called fusion peptides (FP) that play essential roles in virus entry. Although membrane fusion has been broadly studied, there are still major gaps in the molecular details of lipid rearrangements in the bilayer during fusion peptide-membrane interactions. Here we employed differential scanning calorimetry (DSC) and electron spin resonance (ESR) to gather information on the membrane fusion mechanism promoted by two putative SARS FPs. DSC data showed the peptides strongly perturb the structural integrity of anionic vesicles and support the hypothesis that the peptides generate opposing curvature stresses on phosphatidylethanolamine membranes. ESR showed that both FPs increase lipid packing and head group ordering as well as reduce the intramembrane water content for anionic membranes. Therefore, bending moment in the bilayer could be generated, promoting negative curvature. The significance of the ordering effect, membrane dehydration, changes in the curvature properties and the possible role of negatively charged phospholipids in helping to overcome the high kinetic barrier involved in the different stages of the SARS-CoV-mediated membrane fusion are discussed.
Lowengrub, John; Allard, Jun; Aland, Sebastian
2016-03-15
The formation of membrane vesicles from a larger membrane that occurs during endocytosis and other cell processes are 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.
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.
Sodemann, Inti; Fu, Liang
2015-11-20
It is well known that a nonvanishing Hall conductivity requires broken time-reversal symmetry. However, in this work, we demonstrate that Hall-like currents can occur in second-order response to external electric fields in a wide class of time-reversal invariant and inversion breaking materials, at both zero and twice the driving frequency. This nonlinear Hall effect has a quantum origin arising from the dipole moment of the Berry curvature in momentum space, which generates a net anomalous velocity when the system is in a current-carrying state. The nonlinear Hall coefficient is a rank-two pseudotensor, whose form is determined by point group symmetry. We discus optimal conditions to observe this effect and propose candidate two- and three-dimensional materials, including topological crystalline insulators, transition metal dichalcogenides, and Weyl semimetals.
Berry curvature induced nonlinear Hall effect in time-reversal invariant materials
NASA Astrophysics Data System (ADS)
Sodemann, Inti; Fu, Liang
2015-03-01
It is well-known that a non-vanishing Hall conductivity requires time-reversal symmetry breaking. However, in this work, we demonstrate that a Hall-like transverse current can occur in second-order response to an external electric field in a wide class of time-reversal invariant and inversion breaking materials. This nonlinear Hall effect arises from the dipole moment of the Berry curvature in momentum space, which generates a net anomalous velocity when the system is in a current-carrying state. We show that the nonlinear Hall coefficient is a rank-two pseudo-tensor, whose form is determined by point group symmetry. We will describe the optimal conditions and candidate materials to observe this effect. IS is supported by the Pappalardo Fellowship in Physics. LF is supported by DOE Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-SC0010526.
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.
Kazama, Itsuro; Maruyama, Yoshio; Baba, Asuka
2014-02-01
Microparticles produced from the membrane surface of adipocytes promote lipid biosynthesis and angiogenesis in adipose tissues. Thus, they are deeply associated with the onset of metabolic disorders. Despite our understanding of their roles in physiological or pathological responses, we know little about the mechanism by which microparticles are produced from adipocytes. Based on our previous studies using rat megakaryocytes or mast cells during exocytosis, we proposed that membrane curvature induced by amphiphilic reagents, such as chlorpromazine or salicylate, facilitate or inhibit the formation of microparticles. Since the plasma membranes in adipocytes share many common biophysiological features with those in megakaryocytes or mast cells during exocytosis, the same stimulatory or inhibitory mechanism of microparticle formation would exist in adipocytes. Therefore, we hypothesize here that amphiphilic reagents would also change the membrane curvature in adipocytes, and that such changes would facilitate or inhibit the microparticle formation from adipocytes. Our hypothesis is unique because it sheds light for the first time on the physiological mechanism by which microparticles are produced in adipocytes. It is also important because the idea could have novel therapeutic implications for metabolic disorders that are triggered by increases in the microparticle formation. Copyright © 2013 Elsevier Ltd. All rights reserved.
NASA Astrophysics Data System (ADS)
Crawford, David F.
Curvature Cosmology proposes a new cosmological model very different from, and more elegant than, the Big-Bang Theory. Curvature Cosmology is based on two major hypotheses that Hubble redshift is due to an interaction of photons with curved spacetime and that there is a pressure that acts to stabilise expansion and provides a static, stable universe. The main focus of this book is to describe these two hypotheses in detail and to examine all relevant cosmological data in the context of this new model of the universe. This model proposes that, though evolution of stars and galaxies is evident, the statistical properties of the universe are the same at all places and at all times. In short, the universe is ageless, has no defined beginning (unlike the Big-Bang model), and carries no evidence of expansion, despite the changeability of its components. Curvature Cosmology calls for a paradigm shift in current cosmology and requires at least basic (if not more complex) knowledge of past and current cosmological models and equations.
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.
Hasenstein, K H; Kuznetsov, O A
1999-03-01
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 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 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.
Ward, Katherine E.; Ropa, James P.; Adu-Gyamfi, Emmanuel; Stahelin, Robert V.
2012-01-01
Group IVA cytosolic phospholipase A2 (cPLA2α) is an 85 kDa enzyme that regulates the release of arachidonic acid (AA) from the sn-2 position of membrane phospholipids. It is well established that cPLA2α binds zwitterionic lipids such as phosphatidylcholine in a Ca2+-dependent manner through its N-terminal C2 domain, which regulates its translocation to cellular membranes. In addition to its role in AA synthesis, it has been shown that cPLA2α promotes tubulation and vesiculation of the Golgi and regulates trafficking of endosomes. Additionally, the isolated C2 domain of cPLA2α is able to reconstitute Fc receptor-mediated phagocytosis, suggesting that C2 domain membrane binding is sufficient for phagosome formation. These reported activities of cPLA2α and its C2 domain require changes in membrane structure, but the ability of the C2 domain to promote changes in membrane shape has not been reported. Here we demonstrate that the C2 domain of cPLA2α is able to induce membrane curvature changes to lipid vesicles, giant unilamellar vesicles, and membrane sheets. Biophysical assays combined with mutagenesis of C2 domain residues involved in membrane penetration demonstrate that membrane insertion by the C2 domain is required for membrane deformation, suggesting that C2 domain-induced membrane structural changes may be an important step in signaling pathways mediated by cPLA2α. PMID:22991194
Hansen, Anne; Schäfer, Ingo; Knappe, Daniel; Seibel, Peter
2012-01-01
The health threat caused by multiresistant bacteria has continuously increased and recently peaked with pathogens resistant to all current drugs. This has triggered intense research efforts to develop novel compounds to overcome the resistance mechanisms. Thus, antimicrobial peptides (AMPs) have been intensively studied, especially the family of proline-rich AMPs (PrAMPs) that was successfully tested very recently in murine infection models. PrAMPs enter bacteria and inhibit chaperone DnaK. Here, we studied the toxicity of intracellular PrAMPs in HeLa and SH-SY5Y cells. As PrAMPs cannot enter most mammalian cells, we coupled the PrAMPs with penetratin (residues 43 to 58 in the antennapedia homeodomain) via a C-terminally added cysteine utilizing a thioether bridge. The resulting construct could transport the covalently linked PrAMP into mammalian cells. Penetratin ligation reduced the MIC for Gram-negative Escherichia coli only slightly (1 to 8 μmol/liter) but increased the activity against the Gram-positive Micrococcus luteus up to 32-fold (MIC ≈ 1 μmol/liter), most likely due to more effective penetration through the bacterial membrane. In contrast to native PrAMPs, the penetratin-PrAMP constructs entered the mammalian cells, aligned around the nucleus, and associated with the Golgi apparatus. At higher concentrations, the constructs reduced the cell viability (50% inhibitory concentration [IC50] ≈ 40 μmol/liter) and changed the morphology of the cells. No toxic effects or morphological changes were observed at concentrations of 10 μmol/liter or below. Thus, the IC50 values were around 5 to 40 times higher than the MIC values. In conclusion, PrAMPs are in general not toxic to mammalian cells, as they do not pass through the membrane. When shuttled into mammalian cells, however, PrAMPs are only slightly cross-reactive to mammalian chaperones or other intracellular mammalian proteins, providing a second layer of safety for in vivo applications, even if they
Hansen, Anne; Schäfer, Ingo; Knappe, Daniel; Seibel, Peter; Hoffmann, Ralf
2012-10-01
The health threat caused by multiresistant bacteria has continuously increased and recently peaked with pathogens resistant to all current drugs. This has triggered intense research efforts to develop novel compounds to overcome the resistance mechanisms. Thus, antimicrobial peptides (AMPs) have been intensively studied, especially the family of proline-rich AMPs (PrAMPs) that was successfully tested very recently in murine infection models. PrAMPs enter bacteria and inhibit chaperone DnaK. Here, we studied the toxicity of intracellular PrAMPs in HeLa and SH-SY5Y cells. As PrAMPs cannot enter most mammalian cells, we coupled the PrAMPs with penetratin (residues 43 to 58 in the antennapedia homeodomain) via a C-terminally added cysteine utilizing a thioether bridge. The resulting construct could transport the covalently linked PrAMP into mammalian cells. Penetratin ligation reduced the MIC for Gram-negative Escherichia coli only slightly (1 to 8 μmol/liter) but increased the activity against the Gram-positive Micrococcus luteus up to 32-fold (MIC ≈ 1 μmol/liter), most likely due to more effective penetration through the bacterial membrane. In contrast to native PrAMPs, the penetratin-PrAMP constructs entered the mammalian cells, aligned around the nucleus, and associated with the Golgi apparatus. At higher concentrations, the constructs reduced the cell viability (50% inhibitory concentration [IC(50)] ≈ 40 μmol/liter) and changed the morphology of the cells. No toxic effects or morphological changes were observed at concentrations of 10 μmol/liter or below. Thus, the IC(50) values were around 5 to 40 times higher than the MIC values. In conclusion, PrAMPs are in general not toxic to mammalian cells, as they do not pass through the membrane. When shuttled into mammalian cells, however, PrAMPs are only slightly cross-reactive to mammalian chaperones or other intracellular mammalian proteins, providing a second layer of safety for in vivo applications, even if
Agrawal, Neeraj J.; Weinstein, Joshua; Radhakrishnan, Ravi
2011-01-01
Using a recently developed multiscale simulation methodology, we describe the equilibrium behaviour of bilayer membranes under the influence of curvature-inducing proteins using a linearized elastic free energy model. In particular, we describe how the cooperativity associated with a multitude of protein–membrane interactions and protein diffusion on a membrane-mediated energy landscape elicits emergent behaviour in the membrane phase. Based on our model simulations, we predict that, depending on the density of membrane-bound proteins and the degree to which a single protein molecule can induce intrinsic mean curvature in the membrane, a range of membrane phase behaviour can be observed including two different modes of vesicle-bud nucleation and repressed membrane undulations. A state diagram as a function of experimentally tunable parameters to classify the underlying states is proposed. PMID:21243078
EAU guidelines on penile curvature.
Hatzimouratidis, Konstantinos; Eardley, Ian; Giuliano, François; Hatzichristou, Dimitrios; Moncada, Ignacio; Salonia, Andrea; Vardi, Yoram; Wespes, Eric
2012-09-01
Penile curvature can be congenital or acquired. Acquired curvature is secondary due to La Peyronie (Peyronie's) disease. To provide clinical guidelines on the diagnosis and treatment of penile curvature. A systematic literature search on the epidemiology, diagnosis, and treatment of penile curvature was performed. Articles with the highest evidence available were selected and formed the basis for assigning levels of evidence and grades of recommendations. The pathogenesis of congenital penile curvature is unknown. Peyronie's disease is a poorly understood connective tissue disorder most commonly attributed to repetitive microvascular injury or trauma during intercourse. Diagnosis is based on medical and sexual histories, which are sufficient to establish the diagnosis. Physical examination includes assessment of palpable nodules and penile length. Curvature is best documented by a self-photograph or pharmacologically induced erection. The only treatment option for congenital penile curvature is surgery based on plication techniques. Conservative treatment for Peyronie's disease is associated with poor outcomes. Pharmacotherapy includes oral potassium para-aminobenzoate, intralesional treatment with verapamil, clostridial collagenase or interferon, topical verapamil gel, and iontophoresis with verapamil and dexamethasone. They can be efficacious in some patients, but none of these options carry a grade A recommendation. Steroids, vitamin E, and tamoxifen cannot be recommended. Extracorporeal shock wave treatment and penile traction devices may only be used to treat penile pain and reduce penile deformity, respectively. Surgery is indicated when Peyronie's disease is stable for at least 3 mo. Tunical shortening procedures, especially plication techniques, are the first treatment options. Tunical lengthening procedures are preferred in more severe curvatures or in complex deformities. Penile prosthesis implantation is recommended in patients with erectile dysfunction
Tourdot, Richard W.; Ramakrishnan, N.; Baumgart, Tobias; Radhakrishnan, Ravi
2016-01-01
We investigate the phenomenon of protein-induced tubulation of lipid bilayer membranes within a continuum framework using Monte Carlo simulations coupled with the Widom insertion technique to compute excess chemical potentials. Tubular morphologies are spontaneously formed when the density and the curvature-field strength of the membrane-bound proteins exceed their respective thresholds and this transition is marked by a sharp drop in the excess chemical potential. We find that the planar to tubular transition can be described by a micellar model and that the corresponding free-energy barrier increases with an increase in the curvature-field strength (i.e., of protein-membrane interactions) and also with an increase in membrane tension. PMID:26565280
NASA Astrophysics Data System (ADS)
Tourdot, Richard W.; Ramakrishnan, N.; Baumgart, Tobias; Radhakrishnan, Ravi
2015-10-01
We investigate the phenomenon of protein-induced tubulation of lipid bilayer membranes within a continuum framework using Monte Carlo simulations coupled with the Widom insertion technique to compute excess chemical potentials. Tubular morphologies are spontaneously formed when the density and the curvature-field strength of the membrane-bound proteins exceed their respective thresholds and this transition is marked by a sharp drop in the excess chemical potential. We find that the planar to tubular transition can be described by a micellar model and that the corresponding free-energy barrier increases with an increase in the curvature-field strength (i.e., of protein-membrane interactions) and also with an increase in membrane tension.
Prosseda, Gianni; Mazzola, Alessia; Di Martino, Maria Letizia; Tielker, Denis; Micheli, Gioacchino; Colonna, Bianca
2010-04-06
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)
Bykov, A. D.; Lavrent'eva, N. N.; Sinitsa, L. N.
1992-09-01
The paper is concerned with the effect of trajectory curvature in calculations of the vibrational-rotational lines of molecules. The first-order term of the interruption function is calculated using exact solutions of classical dynamic equations. A universal function for two reduced arguments is obtained which is independent of the potential parameter and initial collision conditions; the function is capable of accounting for actual trajectories. Errors resulting from the use of a linear trajectory model are estimated for water vapor and methane expanded by various gases.
Urade, Vikrant N; Bollmann, Luis; Kowalski, Jonathan D; Tate, Michael P; Hillhouse, Hugh W
2007-04-10
The double-gyroid phase of nanoporous silica films has been shown to possess facile mass-transport properties and may be used as a mold to fabricate a variety of highly ordered inverse double-gyroid metal and semiconductor films. This phase exists only over a very small region of the binary phase diagram for most surfactants, and it has been very difficult to synthesize metal oxide films with this structure by evaporation-induced self-assembly (EISA). Here, we show the interplay of the key parameters needed to synthesize these structures reproducibly and show that the interfacial curvature may be systematically controlled. Grazing angle of incidence small-angle X-ray scattering (GISAXS) is used to determine the structure and orientation of nanostructured silica films formed by EISA from dilute silica/(poly(ethylene oxide)-b-poly(propylene oxide)-b-alkyl) surfactant solutions. Four different highly ordered film structures are observed by changing only the concentration of the surfactant, the relative humidity during dip-coating, and the aging time of the solution prior to coating. The highly ordered films progress from rhombohedral (Rm) to 2D rectangular (c2m) to double-gyroid (distorted Iad) to lamellar systematically as interfacial curvature decreases. Under all experimental conditions investigated, increasing the aging time of the coating solution was found to decrease the interfacial curvature. In particular, this parameter was critical to being able to synthesize highly ordered, pure-phase double-gyroid films. The key role of the aging time is shown via processing diagrams that map out the interplay between the aging time, composition, and relative humidity. 29Si nuclear magnetic resonance (NMR) spectroscopy and solution-phase small-angle X-ray scattering (SAXS) of the aged coating solutions presented in part I of this series are then used to interpret the effects of aging prior to dip-coating. Specifically, it was found that a predictive model based on volume
Stowe-Evans, Emily L.; Luesse, Darron R.; Liscum, Emmanuel
2001-01-01
The induction of phototropism in etiolated (dark-grown) seedlings exposed to an unidirectional pulse or extended irradiation with low fluence rate blue light (BL) requires the action of the phototropin (nph1) BL receptor. Although cryptochromes and phytochromes are not required for phototropic induction, these photoreceptors do modulate the magnitude of curvature resulting from phototropin activation. Modulatory increases in the magnitude of phototropic curvature have been termed “enhancement.” Here, we show that phototropic enhancement is primarily a phytochrome A (phyA)-dependent red/far-red-reversible low fluence response. This phyA-dependent response is genetically separable from the basal phototropin-dependent response, as demonstrated by its retention under extended irradiation conditions in the nph4 mutant background, which normally lacks the basal BL-induced response. It is interesting that the nph4 mutants fail to exhibit the basal phototropin-dependent and phyA-dependent enhancement responses under limiting light conditions. Given that NPH4 encodes a transcriptional activator, auxin response factor 7 (ARF7), we hypothesize that the ultimate target(s) of phyA action during the phototropic enhancement response is a rate-limiting ARF-containing transcriptional complex in which the constituent ARFs can vary in identity or activity depending upon the irradiation condition. PMID:11402210
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.
da Hora, G C A; Archilha, N L; Lopes, J L S; Müller, D M; Coutinho, K; Itri, R; Soares, T A
2016-11-04
Antimicrobial peptides (AMPs) are cationic peptides that kill bacteria with a broad spectrum of action, low toxicity to mammalian cells and exceptionally low rates of bacterial resistance. These features have led to considerable efforts in developing AMPs as an alternative antibacterial therapy. In vitro studies have shown that AMPs interfere with membrane bilayer integrity via several possible mechanisms, which are not entirely understood. We have performed the synthesis, membrane lysis measurements, and biophysical characterization of a novel hybrid peptide. These measurements show that PA-Pln149 does not form nanopores, but instead promotes membrane rupture. It causes fast rupture of the bacterial model membrane (POPG-rich) at concentrations 100-fold lower than that required for the disruption of mammalian model membranes (POPC-rich). Atomistic molecular dynamics (MD) simulations were performed for single and multiple copies of PA-Pln149 in the presence of mixed and pure POPC/POPG bilayers to investigate the concentration-dependent membrane disruption by the hybrid peptide. These simulations reproduced the experimental trend and provided a potential mechanism of action for PA-Pln149. It shows that the PA-Pln149 does not form nanopores, but instead promotes membrane destabilization through peptide aggregation and induction of membrane negative curvature with the collapse of the lamellar arrangement. The sequence of events depicted for PA-Pln149 may offer insights into the mechanism of action of AMPs previously shown to induce negative deformation of membrane curvature and often associated with peptide translocation via non-bilayer intermediate structures.
Lin, Sheng-Fong; Lin, Gong-Ru
2014-09-08
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.
Instant curvature measurement for microcantilever sensors
Jeon, Sangmin; Thundat, Thomas
2004-08-09
A multiple-point deflection technique has been developed for the instant measurement of microcantilever curvature. Eight light-emitting diodes are focused on various positions of a gold-coated silicon cantilever through optical fibers, and temperature change or chemical adsorption induces cantilever bending. The deflection at each point on the cantilever is measured with subnanometer precision by a position-sensitive detector, and thus the curvature of the cantilever is obtained.
Anisotropic Membrane Curvature Sensing by Amphipathic Peptides
Gómez-Llobregat, Jordi; Elías-Wolff, Federico; Lindén, Martin
2016-01-01
Many proteins and peptides have an intrinsic capacity to sense and induce membrane curvature, and play crucial roles for organizing and remodeling cell membranes. However, the molecular driving forces behind these processes are not well understood. Here, we describe an approach to study curvature sensing by simulating the interactions of single molecules with a buckled lipid bilayer. We analyze three amphipathic antimicrobial peptides, a class of membrane-associated molecules that specifically target and destabilize bacterial membranes, and find qualitatively different sensing characteristics that would be difficult to resolve with other methods. Our findings provide evidence for direction-dependent curvature sensing mechanisms in amphipathic peptides and challenge existing theories of hydrophobic insertion. The buckling approach is generally applicable to a wide range of curvature-sensing molecules, and our results provide strong motivation to develop new experimental methods to track position and orientation of membrane proteins. PMID:26745422
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.
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.
NASA Astrophysics Data System (ADS)
Monga, Olivier; Ayache, Nicholas; Sander, Peter T.
1991-09-01
Modern medical image techniques, such as magnetic resonance image (MRI) or x-ray computed tomography provide three dimensional images of internal structures of the body, usually by means of a stack of tomographic images. The first stage in the automatic analysis of such data is 3-D edge detection1,2 which provides points corresponding to the boundaries of the surfaces forming the 3-D structure. The next stage is to characterize the local geometry of these surfaces in order to extract points or lines on which registration and/or tracking procedures can rely.3,4,5,6 This paper presents a pipeline of processes which define a hierarchical description of the second order differential characteristics of the surfaces. The focus is on the theoretical coherence of these levels of representation. Using uncertainty, a link is established between the edge detection and the local surface approximation by addressing the uncertainties inherent to edge detection in 2-D or 3-D images; and how to incorporate these uncertainties into the computation of local geometric models. In particular, calculate the uncertainty of edge location, direction, and magnitude for the 3-D Deriche operator is calculated.1,2 Statistical results are then used as a solid theoretical foundation on which to base subsequent computations, such as the determination of local surface curvature using local geometric models for surface segmentation. From the local fitting, for each edge point the mean and Gaussian curvature, principal curvatures and directions, curvature singularities, lines of curvature singularities, and covariance matrices defining the uncertainties are calculated. Experimental results for real data using two 3-D scanner images of the same organ taken at different positions demonstrate the stability of the mean and Gaussian curvatures. Experimental results for real data showing the determination of local curvature extremes of surfaces extracted from MR images are presented.
Optimal Spatial Scale for Curvature Calculations in Multiphase Flows
NASA Astrophysics Data System (ADS)
Senecal, Jacob; Owkes, Mark
2016-11-01
In gas-liquid flows, the surface tension force often controls the dynamics of the flow and an accurate calculation of this force is necessary for predictive simulations. The surface tension force is directly proportional to the curvature of the gas-liquid interface, making accurate curvature calculations an essential consideration. Multiple methods have been developed to calculate the curvature of volume of fluid (VoF) interface capturing schemes, such as the height function method. These methods have been extensively tested. However, the impact of the scale or size of computational stencil on which the curvature is computed, has not been correlated with the rate at which interface perturbations relax under the surface tension force. In this work, the effect of varying the scale on which the curvature is computed has been tested and quantified. An optimal curvature scale is identified that leads to accurate and converging curvatures, and accurate timescales for surface tension induced, interface dynamics.
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
Engineering curvature in graphene ribbons using ultrathin polymer films.
Li, Chunyu; Koslowski, Marisol; Strachan, Alejandro
2014-12-10
We propose a method to induce curvature in graphene nanoribbons in a controlled manner using an ultrathin thermoset polymer in a bimaterial strip setup and test it via molecular dynamics (MD) simulations. Continuum mechanics shows that curvature develops to release the residual stress caused by the chemical and thermal shrinkage of the polymer during processing and that this curvature increases with decreasing film thickness; however, significant deformation is only achieved for ultrathin polymer films. Quite surprisingly, explicit MD simulations of the curing and annealing processes show that the predicted trend not just continues down to film thicknesses of 1-2 nm but that the curvature development is enhanced significantly in such ultrathin films due to surface tension effects. This combination of effects leads to very large curvatures of over 0.14 nm(-1) that can be tuned via film thickness. This provides a new avenue to engineer curvature and, thus, electromagnetic properties of graphene.
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.
NASA Astrophysics Data System (ADS)
Chambolle, Antonin; Morini, Massimiliano; Ponsiglione, Marcello
2015-12-01
This paper aims at building a unified framework to deal with a wide class of local and nonlocal translation-invariant geometric flows. We introduce a class of nonlocal generalized mean curvatures and prove the existence and uniqueness for the level set formulation of the corresponding geometric flows. We then introduce a class of generalized perimeters, whose first variation is an admissible generalized curvature. Within this class, we implement a minimizing movements scheme and we prove that it approximates the viscosity solution of the corresponding level set PDE. We also describe several examples and applications. Besides recovering and presenting in a unified way existence, uniqueness, and approximation results for several geometric motions already studied and scattered in the literature, the theory developed in this paper also allows us to establish new results.
Forman curvature for complex networks
NASA Astrophysics Data System (ADS)
Sreejith, R. P.; Mohanraj, Karthikeyan; Jost, Jürgen; Saucan, Emil; Samal, Areejit
2016-06-01
We adapt Forman’s discretization of Ricci curvature to the case of undirected networks, both weighted and unweighted, and investigate the measure in a variety of model and real-world networks. We find that most nodes and edges in model and real networks have a negative curvature. Furthermore, the distribution of Forman curvature of nodes and edges is narrow in random and small-world networks, while the distribution is broad in scale-free and real-world networks. In most networks, Forman curvature is found to display significant negative correlation with degree and centrality measures. However, Forman curvature is uncorrelated with clustering coefficient in most networks. Importantly, we find that both model and real networks are vulnerable to targeted deletion of nodes with highly negative Forman curvature. Our results suggest that Forman curvature can be employed to gain novel insights on the organization of complex networks.
Curvature modulates the self-assembly of amphiphilic molecules.
Tian, Falin; Luo, Yu; Zhang, Xianren
2010-10-14
In this work, we used lattice Monte Carlo simulations and theoretical model calculations to show how the self-assembly of adsorbed amphiphilic molecules is affected by the local curvature of solid surfaces. It is found that, beyond a critical curvature value, solid surface geometry governs the spatial ordering of aggregates and may induce the morphological transitions. The simulation results show how the curvature of solid surfaces modulates the distribution of aggregates: the anisotropy in local curvature along and perpendicular to the cylindrical surfaces tends to generate orientationally ordered cylindrical micelles. To account for the morphological transitions induced by the local curvature of solid surfaces, we constructed a theoretical model which includes the Helfrich bending energy, the deformation energy of aggregates induced by solid surfaces, and the adsorption energy. The model calculations indicate that on highly curved solid surfaces the bending energy for bilayer structure sharply increases with surface curvature, which in turn induces the morphological transition from bilayer to cylindrical structure. Our results suggest that the local curvature provides a means of controlling the spatial organization of amphiphilic molecules.
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.
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.
NASA Astrophysics Data System (ADS)
Berry, M. V.
2013-10-01
Wave streamlines are integral curves of the local wavevector (phase gradient). An exact formula is derived, giving the curvature of streamlines as the component transverse to the local wavevector of the gradient of the logarithm of the local wavenumber. The formula is applied to quantum particles moving in a potential and classical light in the presence of a refractive-index gradient. Three limiting regimes are encompassed. The first is geometrical, in which the bending of streamlines arises solely from the classical force or optical index gradient. The second and third limits concern singularities in the pattern of wave streamlines, of two types: optical vortices, near which the streamlines are asymptotically circular, and phase saddles, near which the streamlines are asymptotically hyperbolic.
On nonlinear higher spin curvature
NASA Astrophysics Data System (ADS)
Manvelyan, Ruben; Mkrtchyan, Karapet; Rühl, Werner; Tovmasyan, Murad
2011-05-01
We present the first nonlinear term of the higher spin curvature which is covariant with respect to deformed gauge transformations that are linear in the field. We consider the case of spin 3 after presenting spin 2 as an example, and then construct the general spin s quadratic term of the de Wit-Freedman curvature.
Controllable curvature from planar polymer sheets in response to light.
Hubbard, Amber M; Mailen, Russell W; Zikry, Mohammed A; Dickey, Michael D; Genzer, Jan
2017-02-24
The ability to change shape and control curvature in 3D structures starting from planar sheets can aid in assembly and add functionality to an object. Herein, we convert planar sheets of shape memory polymers (SMPs) into 3D objects with controllable curvature by dictating where the sheets shrink. Ink patterned on the surface of the sheet absorbs infrared (IR) light, resulting in localized heating, and the material shrinks locally wherever the temperature exceeds the activation temperature, Ta. We introduce two different mechanisms for controlling curvature within SMP sheets. The 'direct' mechanism uses localized shrinkage to induce curvature only in regions patterned with ink. The 'indirect' mechanism uses localized shrinkage in regions patterned with ink to induce curvature in neighboring regions without ink through a balance of internal stresses. Finite element analysis predicts the final shape of the polymer sheets with excellent qualitative agreement with experimental studies. Results from this study show that curvature can be controlled by the distribution and darkness of the ink pattern on the polymer sheet. Additionally, we utilize the direct and indirect curvature mechanisms to demonstrate the formation and actuation of gripper devices, which represent the potential utility of this approach.
Geometrical interpretation and curvature distribution in nanocarbons
NASA Astrophysics Data System (ADS)
Gupta, Sanju; Saxena, Avadh
2011-04-01
Despite extensive research on microscopic structure and physical property characterization of advanced nanocarbon systems, they have not been viewed as topologically distinct nanoscale materials with various geometries (curvature). This work is motivated by our recent work [S. Gupta and A. Saxena, J. Raman Spectrosc. 40, 1127 (2009)] where we introduced the notion of "global" topology for novel nanocarbons and provided systematic trends by monitoring the phonon spectra via resonance Raman spectroscopy, which led to the paradigm of curvature/topology → property → functionality relationship in these materials. Here we determined the distribution of the mean (H) and Gaussian (K) curvatures as pertinent observables for geometric characterization taking into account the observed geometrical parameters, that is, radius, polar, azimuthal, or conical angle associated with tubular (single, double-, and multi-walled nanotubes; K = 0), spherical (hypo- and hyperfullerenes; K > 0) and complex (helical nanoribbons and nanotori/nanorings; K < 0) nanocarbon geometries to quantify the interplay of intrinsic surface curvature and topology, wherein global topology of the overall sp2-bonded carbon (sp2C) constrains local topology of the constituent carbon rings. We also studied various other structures such as catenoid and saddle-shaped surfaces as interesting nanocarbons. We compared these results with highly oriented pyrolytic graphite and monolayer graphene as layered and planar systems, respectively. Moreover, nanocarbons discussed herein are their derivatives. Curvature leads to nonlinearity that manifests itself in some form of symmetry breaking which can be extrapolated to topological variation due to nanoscale defects. Thus it may either close/open the bandgap leading to the introduction of new Raman spectroscopy signatures and optical absorption peaks, changes in mechanical properties, electrical behavior, and electronic density of states and possibly inducing magnetism
Wallace, John Paul; Myneni, Ganapati Rao; Pike, Robert
2011-03-31
The manufacturing of niobium SRF accelerator cavities is plagued by a mobile point defect, hydrogen. For efficient accelerator operation, niobium must function at both high electric and magnetic fields, and is compromised if magnetic impurities are located in the surface regions of the material. The finding that trace hydrogen in niobium can produce structures with magnetic properties is a feature that is not acceptable for a high performance cavity. X-ray diffraction has proved to be the key tool in assessing irreversible process damage to the niobium substrate. In future generations of accelerators, niobium will actually be merely the substrate for more effective superconductors that will allow for more efficient operation. The substrate analogy to the silicon wafer industry is useful since for niobium it may be possible to avoid some of the mistakes made in silicon technology. Because hydrogen attacks niobium on a number of different size scales, there is an inherent complexity in the trouble sources. There are also features in cavity design that are benign, such as local curvature considerations, requiring a fully non symmetric analysis of current flow to be appreciated.
Cosmic curvature and condensation
NASA Technical Reports Server (NTRS)
Harwit, Martin
1992-01-01
It is shown that the universe may consist of a patchwork of domains with different Riemann curvature constants k = 0, +/-1. Features of a phase transition in which flat space breaks up in a transition 2k0 - k(-) + k(+) with initial scale factors R(-) = R(+) are postulated and explored. It is shown that such a transition is energetically permitted, has the equivalent of a Curie temperature, and can lead in a natural way to the formation of voids and galaxies. It is predicted that, if the ambient universe on average is well fitted by a purely k(-) space, with only occasional domains of k(+) containing galaxies, a density parameter of (A(z sub c + 1)) super -1 should be expected, where z sub c represents the redshift of the earliest objects to have condensed, and A takes on values ranging from about 5 to 3. Present observations of quasars would suggest a density of about 0.03 or 0.05, respectively, but it could be lower if earlier condensation took place.
John Paul Wallace, Ganapati Rao Myneni, and Robert Pike
2011-03-01
The manufacturing of niobium SRF accelerator cavities is plagued by a mobile point defect, hydrogen. For efficient accelerator operation, niobium must function at both high electric and magnetic fields, and is compromised if magnetic impurities are located in the surface regions of the material. The finding that trace hydrogen in niobium can produce structures with magnetic properties is a feature that is not acceptable for a high performance cavity. X-ray diffraction has proved to be the key tool in assessing irreversible process damage to the niobium substrate. In future generations of accelerators, niobium will actually be merely the substrate for more effective superconductors that will allow for more efficient operation. The substrate analogy to the silicon wafer industry is useful since for niobium it may be possible to avoid some of the mistakes made in silicon technology. Because hydrogen attacks niobium on a number of different size scales, there is an inherent complexity in the trouble sources. There are also features in cavity design that are benign, such as local curvature considerations, requiring a fully non symmetric analysis of current flow to be appreciated.
Chou, James J; Kaufman, Joshua D; Stahl, Stephen J; Wingfield, Paul T; Bax, Ad
2002-03-20
The structure of a water-insoluble fragment encompassing residues 282-304 of the HIV envelope protein gp41 is studied when solubilized by dihexanoyl phosphatidylcholine (DHPC) and by small bicelles, consisting of a 4:1 molar ratio of DHPC and dimyristoyl phosphatidylcholine (DMPC). Weak alignment with the magnetic field was accomplished in a stretched polyacrylamide gel, permitting measurement of one-bond (1)H-(15)N, (13)Ca-(13)C', and (13)C'-(15)N dipolar couplings, which formed the basis for determining the peptide structure. In both detergent systems, the peptide adopts an alpha-helical conformation from residue 4 through 18. In the presence of the DHPC micelles the helix is strongly curved towards the hydrophobic surface, whereas in the presence of bicelles a much weaker curvature in the opposite direction is observed.
Stiffness Modulation of Rayed Fins by Curvature
NASA Astrophysics Data System (ADS)
Nguyen, Khoi; Yu, Ning; Venkadesan, Madhusudhan; Bandi, Mahesh; Mandre, Shreyas
2016-11-01
Fishes with rayed fins comprise over 99% of all extant fish species. Multifunctional use of fins, from propulsion to station holding, requires substantial modulation of stiffness. We propose that fishes stiffen the fin by curving it transverse to its length. This effect is similar to stiffening a dollar bill by curling it because of curvature-induced coupling of out-of-plane bending with in-plane stretching. Unlike a piece of paper, rayed fins are a composite of rays and membranes. We model this as parallel elastic beams (rays) with springy interconnections (membranes). Our analysis shows that the key parameters stiffening the fin are the ray anisotropy to bending, the misalignment of principal bending directions of adjacent rays, and the membrane elasticity. The composite fin stiffens when the principal bending directions of adjacent rays are misaligned due to fin curvature, which necessarily causes the membrane to stretch. Unlike a homogenous thin sheet, composite rayed structures are able to mimic curvature-induced stiffening by using misaligned rays even if the fin appears geometrically flat. Preliminary radiographic evidence from the rays of fish fins supports such a mechanism. Funding by Human Frontier Science Program.
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.
Sigma models with negative curvature
Alonso, Rodrigo; Jenkins, Elizabeth E.; Manohar, Aneesh V.
2016-03-16
Here, 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.
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.
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.
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.
Curvature of the localized surface plasmon resonance peak.
Chen, Peng; Liedberg, Bo
2014-08-05
Localized surface plasmon resonance (LSPR) occurring in noble metal nanoparticles (e.g., Au) is a widely used phenomenon to report molecular interactions. Traditional LSPR sensors typically monitor shifts in the peak position or extinction in response to local refractive index changes in the close vicinity of the nanoparticle surface. The ability to resolve minute shifts/extinction changes is to a large extent limited by instrumental noise. A new strategy to evaluate LSPR responses utilizing changes in the shape of the extinction spectrum (the curvature) is proposed. The response of curvature to refractive index changes is investigated theoretically using Mie theory and an analytical expression relating the curvature to the refractive index is presented. The experimentally derived curvatures for 13 nm spherical gold nanoparticles (AuNPs) exposed to solvents with different bulk refractive indices confirm the theoretical predictions. Moreover, both the calculated and experimental findings suggest that the curvature is approximately a linear function of refractive index in regimes relevant to bio and chemical sensing. We demonstrate that curvature is superior over peak shift and extinction both in terms of signal-to-noise (S/N) ratio and reliability of LSPR sensors. With a curvature, one could readily monitor submonolayer adsorption of a low molecular weight thiol molecule (M(w) = 458.6) onto 13 nm AuNPs. It is also worthwhile mentioning that curvature is virtually insensitive to instrumental instabilities and artifacts occurring during measurement. Instabilities such as baseline tilt and shift, shift in peak position as well as sharp spikes/steps in the extinction spectra do not induce artifacts in the sensorgrams of curvature.
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
Spacetime curvature and the Higgs stability during inflation.
Herranen, M; Markkanen, T; Nurmi, S; Rajantie, A
2014-11-21
It has been claimed that the electroweak vacuum may be unstable during inflation due to large fluctuations of the order H in the case of a high inflationary scale as suggested by BICEP2. We compute the standard model Higgs effective potential including UV-induced curvature corrections at one-loop level. We find that for a high inflationary scale a large curvature mass is generated due to renormalization group running of nonminimal coupling ξ, which either stabilizes the potential against fluctuations for ξEW≳6×10(-2), or destabilizes it for ξEW≲2×10(-2) when the generated curvature mass is negative. Only in the narrow intermediate region may the effect of the curvature mass be significantly smaller.
Curvature reduces bending strains in the quokka femur
McCabe, Kyle; Henderson, Keith; Pantinople, Jess; Milne, Nick
2017-01-01
This study explores how curvature in the quokka femur may help to reduce bending strain during locomotion. The quokka is a small wallaby, but the curvature of the femur and the muscles active during stance phase are similar to most quadrupedal mammals. Our hypothesis is that the action of hip extensor and ankle plantarflexor muscles during stance phase place cranial bending strains that act to reduce the caudal curvature of the femur. Knee extensors and biarticular muscles that span the femur longitudinally create caudal bending strains in the caudally curved (concave caudal side) bone. These opposing strains can balance each other and result in less strain on the bone. We test this idea by comparing the performance of a normally curved finite element model of the quokka femur to a digitally straightened version of the same bone. The normally curved model is indeed less strained than the straightened version. To further examine the relationship between curvature and the strains in the femoral models, we also tested an extra-curved and a reverse-curved version with the same loads. There appears to be a linear relationship between the curvature and the strains experienced by the models. These results demonstrate that longitudinal curvature in bones may be a manipulable mechanism whereby bone can induce a strain gradient to oppose strains induced by habitual loading. PMID:28348929
Nanoscale Membrane Curvature detected by Polarized Localization Microscopy
NASA Astrophysics Data System (ADS)
Kelly, Christopher; Maarouf, Abir; Woodward, Xinxin
Nanoscale membrane curvature is a necessary component of countless cellular processes. Here we present Polarized Localization Microscopy (PLM), a super-resolution optical imaging technique that enables the detection of nanoscale membrane curvature with order-of-magnitude improvements over comparable optical techniques. PLM combines the advantages of polarized total internal reflection fluorescence microscopy and fluorescence localization microscopy to reveal single-fluorophore locations and orientations without reducing localization precision by point spread function manipulation. PLM resolved nanoscale membrane curvature of a supported lipid bilayer draped over polystyrene nanoparticles on a glass coverslip, thus creating a model membrane with coexisting flat and curved regions and membrane radii of curvature as small as 20 nm. Further, PLM provides single-molecule trajectories and the aggregation of curvature-inducing proteins with super-resolution to reveal the correlated effects of membrane curvature, dynamics, and molecular sorting. For example, cholera toxin subunit B has been observed to induce nanoscale membrane budding and concentrate at the bud neck. PLM reveals a previously hidden and critical information of membrane topology.
Curvature reduces bending strains in the quokka femur.
McCabe, Kyle; Henderson, Keith; Pantinople, Jess; Richards, Hazel L; Milne, Nick
2017-01-01
This study explores how curvature in the quokka femur may help to reduce bending strain during locomotion. The quokka is a small wallaby, but the curvature of the femur and the muscles active during stance phase are similar to most quadrupedal mammals. Our hypothesis is that the action of hip extensor and ankle plantarflexor muscles during stance phase place cranial bending strains that act to reduce the caudal curvature of the femur. Knee extensors and biarticular muscles that span the femur longitudinally create caudal bending strains in the caudally curved (concave caudal side) bone. These opposing strains can balance each other and result in less strain on the bone. We test this idea by comparing the performance of a normally curved finite element model of the quokka femur to a digitally straightened version of the same bone. The normally curved model is indeed less strained than the straightened version. To further examine the relationship between curvature and the strains in the femoral models, we also tested an extra-curved and a reverse-curved version with the same loads. There appears to be a linear relationship between the curvature and the strains experienced by the models. These results demonstrate that longitudinal curvature in bones may be a manipulable mechanism whereby bone can induce a strain gradient to oppose strains induced by habitual loading.
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.
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
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.
Membrane curvature at a glance
McMahon, Harvey T.; Boucrot, Emmanuel
2015-01-01
ABSTRACT Membrane curvature is an important parameter in defining the morphology of cells, organelles and local membrane subdomains. Transport intermediates have simpler shapes, being either spheres or tubules. The generation and maintenance of curvature is of central importance for maintaining trafficking and cellular functions. It is possible that local shapes in complex membranes could help to define local subregions. In this Cell Science at a Glance article and accompanying poster, we summarize how generating, sensing and maintaining high local membrane curvature is an active process that is mediated and controlled by specialized proteins using general mechanisms: (i) changes in lipid composition and asymmetry, (ii) partitioning of shaped transmembrane domains of integral membrane proteins or protein or domain crowding, (iii) reversible insertion of hydrophobic protein motifs, (iv) nanoscopic scaffolding by oligomerized hydrophilic protein domains and, finally, (v) macroscopic scaffolding by the cytoskeleton with forces generated by polymerization and by molecular motors. We also summarize some of the discoveries about the functions of membrane curvature, where in addition to providing cell or organelle shape, local curvature can affect processes like membrane scission and fusion as well as protein concentration and enzyme activation on membranes. PMID:25774051
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.
NASA Astrophysics Data System (ADS)
Dempsey, D.; Suckale, J.; Huang, Y.
2015-12-01
In 2010-11, a sequence of earthquakes occurred on an unmapped basement fault near Guy, Arkansas. The events are likely to have been triggered by a nine month period of wastewater disposal during which 4.5x105 m2 of water was injected at two nearby wells. Magnitude-frequency distributions (MFD) for the induced sequence show two interesting properties: (i) a low Gutenberg-Richter (GR) b-value of ~0.8 during injection, increasing to 1.0 post-injection (ii) and downward curvature of the MFD at the upper magnitude limit. We use a coupled model of injection-triggering and earthquake rupture to show how the evolving MFD can be understood in terms of an effective stress increase on the fault, which arises from overpressuring and strength reduction. Reservoir simulation is used to model injection into a horizontally extensive aquifer that overlies an impermeable basement containing a single permeable fault. Earthquake triggering occurs when the static strength, reduced by the modeled pressure increase, satisfies a Mohr-Coulomb criterion. Pressure evolution is also incorporated in a model of fault rupture, which is based on an expanding bilateral crack approximation to quasidynamic rupture propagation and static/dynamic friction evolution. An earthquake sequence is constructed as an ensemble of triggered ruptures for many realizations of a heterogeneous fractal stress distribution. During injection, there is a steady rise in fluid pressure on the fault. In addition to its role in triggering earthquakes, rising pressure affects the rupture process by reducing the dynamic strength relative to fault shear stress; this is equivalent to tectonic stress increase in natural seismicity. As mean stress increases, larger events are more frequent and this is reflected in a lower b-value. The largest events, however, occur late in the loading cycle at very high stress; their absence in the early stages of injection manifests as downward curvature in the MFD at large magnitudes.
Curvature generation in nematic surfaces
NASA Astrophysics Data System (ADS)
Mostajeran, Cyrus
2015-06-01
In recent years there has been a growing interest in the study of shape formation using modern responsive materials that can be preprogrammed to undergo spatially inhomogeneous local deformations. In particular, nematic liquid crystalline solids offer exciting possibilities in this context. Considerable recent progress has been made in achieving a variety of shape transitions in thin sheets of nematic solids by engineering isolated points of concentrated Gaussian curvature using topological defects in the nematic director field across textured surfaces. In this paper, we consider ways of achieving shape transitions in thin sheets of nematic glass by generation of nonlocalized Gaussian curvature in the absence of topological defects in the director field. We show how one can blueprint any desired Gaussian curvature in a thin nematic sheet by controlling the nematic alignment angle across the surface and highlight specific patterns which present feasible initial targets for experimental verification of the theory.
Nonlinear Sorting, Curvature Generation, and Crowding of Endophilin N-BAR on Tubular Membranes
Zhu, Chen; Das, Sovan L.; Baumgart, Tobias
2012-01-01
The curvature of biological membranes is controlled by membrane-bound proteins. For example, during endocytosis, the sorting of membrane components, vesicle budding, and fission from the plasma membrane are mediated by adaptor and accessory proteins. Endophilin is a peripherally binding membrane protein that functions as an endocytic accessory protein. Endophilin's membrane tubulation capacity is well known. However, to understand the thermodynamic and mechanical aspects of endophilin function, experimental measurements need to be compared to quantitative theoretical models. We present measurements of curvature sorting and curvature generation of the endophilin A1 N-BAR domain on tubular membranes pulled from giant unilamellar vesicles. At low concentration, endophilin functions primarily as a membrane curvature sensor; at high concentrations, it also generates curvature. We determine the spontaneous curvature induced by endophilin and observe sigmoidal curvature/composition coupling isotherms that saturate at high membrane tensions and protein solution concentrations. The observation of saturation is supported by a strong dependence of lateral diffusion coefficients on protein density on the tether membrane. We develop a nonlinear curvature/composition coupling model that captures our experimental observations. Our model predicts a curvature-induced phase transition among two states with varying protein density and membrane curvature. This transition could act as a switch during endocytosis. PMID:22768939
Geometric curvature and phase of the Rabi model
Mao, Lijun; Huai, Sainan; Guo, Liping; Zhang, Yunbo
2015-11-15
We study the geometric curvature and phase of the Rabi model. Under the rotating-wave approximation (RWA), we apply the gauge independent Berry curvature over a surface integral to calculate the Berry phase of the eigenstates for both single and two-qubit systems, which is found to be identical with the system of spin-1/2 particle in a magnetic field. We extend the idea to define a vacuum-induced geometric curvature when the system starts from an initial state with pure vacuum bosonic field. The induced geometric phase is related to the average photon number in a period which is possible to measure in the qubit–cavity system. We also calculate the geometric phase beyond the RWA and find an anomalous sudden change, which implies the breakdown of the adiabatic theorem and the Berry phases in an adiabatic cyclic evolution are ill-defined near the anti-crossing point in the spectrum.
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)
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)
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.
Katayama, Sayaka; Nakase, Ikuhiko; Yano, Yoshiaki; Murayama, Tomo; Nakata, Yasushi; Matsuzaki, Katsumi; Futaki, Shiroh
2013-09-01
Arginine-rich cell-penetrating peptides, including octaarginine (R8) and HIV-1 TAT peptides, have the ability to translocate through cell membranes and transport exogenous bioactive molecules into cells. Hydrophobic counteranions such as pyrenebutyrate (PyB) have been reported to markedly promote the membrane translocation of these peptides. In this study, using model membranes having liquid-ordered (Lo) and liquid-disordered (Ld) phases, we explored the effects of PyB on the promotion of R8 translocation. Confocal microscopic observations of giant unilamellar vesicles (GUVs) showed that PyB significantly accelerated the accumulation of R8 on membranes containing negatively charged lipids, leading to the internalization of R8 without collapse of the GUV structures. PyB displayed an alternative activity, increasing the fluidity of the negatively charged membranes, which diminished the distinct Lo/Ld phase separation on GUVs. This was supported by the decrease in fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH). Additionally, PyB induced membrane curvature, which has been suggested as a possible mechanism of membrane translocation for R8. Taken together, our results indicate that PyB may have multiple effects that promote R8 translocation through cell membranes. Copyright © 2013 Elsevier B.V. All rights reserved.
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
Classification and quantification of leaf curvature.
Liu, Zhongyuan; Jia, Liguo; Mao, Yanfei; He, Yuke
2010-06-01
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.
Novel tilt-curvature coupling in lipid membranes
NASA Astrophysics Data System (ADS)
Terzi, M. Mert; Deserno, Markus
2017-08-01
On mesoscopic scales, lipid membranes are well described by continuum theories whose main ingredients are the curvature of a membrane's reference surface and the tilt of its lipid constituents. In particular, Hamm and Kozlov [Eur. Phys. J. E 3, 323 (2000)] have shown how to systematically derive such a tilt-curvature Hamiltonian based on the elementary assumption of a thin fluid elastic sheet experiencing internal lateral pre-stress. Performing a dimensional reduction, they not only derive the basic form of the effective surface Hamiltonian but also express its emergent elastic couplings as trans-membrane moments of lower-level material parameters. In the present paper, we argue, though, that their derivation unfortunately missed a coupling term between curvature and tilt. This term arises because, as one moves along the membrane, the curvature-induced change of transverse distances contributes to the area strain—an effect that was believed to be small but nevertheless ends up contributing at the same (quadratic) order as all other terms in their Hamiltonian. We illustrate the consequences of this amendment by deriving the monolayer and bilayer Euler-Lagrange equations for the tilt, as well as the power spectra of shape, tilt, and director fluctuations. A particularly curious aspect of our new term is that its associated coupling constant is the second moment of the lipid monolayer's lateral stress profile—which within this framework is equal to the monolayer Gaussian curvature modulus, κ¯ m. On the one hand, this implies that many theoretical predictions now contain a parameter that is poorly known (because the Gauss-Bonnet theorem limits access to the integrated Gaussian curvature); on the other hand, the appearance of κ¯ m outside of its Gaussian curvature provenance opens opportunities for measuring it by more conventional means, for instance by monitoring a membrane's undulation spectrum at short scales.
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.
Quantum complexity and negative curvature
NASA Astrophysics Data System (ADS)
Brown, Adam R.; Susskind, Leonard; Zhao, Ying
2017-02-01
As time passes, once simple quantum states tend to become more complex. For strongly coupled k -local Hamiltonians, this growth of computational complexity has been conjectured to follow a distinctive and universal pattern. In this paper we show that the same pattern is exhibited by a much simpler system—classical geodesics on a compact two-dimensional geometry of uniform negative curvature. This striking parallel persists whether the system is allowed to evolve naturally or is perturbed from the outside.
Curvatures Estimation in Orientation Selection
1991-01-31
than is-obtained in length-tuning measurements . Hence, over a limited range, increasing the size or gain of the small RF has a similar effect . The...the remaining larger, lower curvature units to represent the curve. An indirect test involves measuring the time for the effect to set in, with and...31Jan 91 By, Steen .Zcke * ax . Cnadr tDistribution/ Steen .Zcke *MaxS. ynaer ~ Availability Codes Dist Special Computer Vision and Robotics Laboratory
Disformal invariance of curvature perturbation
Motohashi, Hayato; White, Jonathan E-mail: jwhite@post.kek.jp
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.
Substrate curvature regulates cell migration
NASA Astrophysics Data System (ADS)
He, Xiuxiu; Jiang, Yi
2017-06-01
Cell migration is essential in many aspects of biology. Many basic migration processes, including adhesion, membrane protrusion and tension, cytoskeletal polymerization, and contraction, have to act in concert to regulate cell migration. At the same time, substrate topography modulates these processes. In this work, we study how substrate curvature at micrometer scale regulates cell motility. We have developed a 3D mechanical model of single cell migration and simulated migration on curved substrates with different curvatures. The simulation results show that cell migration is more persistent on concave surfaces than on convex surfaces. We have further calculated analytically the cell shape and protrusion force for cells on curved substrates. We have shown that while cells spread out more on convex surfaces than on concave ones, the protrusion force magnitude in the direction of migration is larger on concave surfaces than on convex ones. These results offer a novel biomechanical explanation to substrate curvature regulation of cell migration: geometric constrains bias the direction of the protrusion force and facilitates persistent migration on concave surfaces.
Substrate curvature regulates cell migration.
He, Xiuxiu; Jiang, Yi
2017-05-23
Cell migration is essential in many aspects of biology. Many basic migration processes, including adhesion, membrane protrusion and tension, cytoskeletal polymerization, and contraction, have to act in concert to regulate cell migration. At the same time, substrate topography modulates these processes. In this work, we study how substrate curvature at micrometer scale regulates cell motility. We have developed a 3D mechanical model of single cell migration and simulated migration on curved substrates with different curvatures. The simulation results show that cell migration is more persistent on concave surfaces than on convex surfaces. We have further calculated analytically the cell shape and protrusion force for cells on curved substrates. We have shown that while cells spread out more on convex surfaces than on concave ones, the protrusion force magnitude in the direction of migration is larger on concave surfaces than on convex ones. These results offer a novel biomechanical explanation to substrate curvature regulation of cell migration: geometric constrains bias the direction of the protrusion force and facilitates persistent migration on concave surfaces.
Brane Localized Curvature for Warped Gravitons
Rizzo, Thomas G.
2003-06-26
We study the effects of including brane localized curvature terms in the Randall-Sundrum (RS) model of the hierarchy. This leads to the existence of brane localized kinetic terms for the graviton. Such terms can be induced by brane and bulk quantum effects as well as Higgs-curvature mixing on the brane. We derive the modified spectrum of Kaluza-Klein (KK) gravitons and their couplings to 4-dimensional fields in the presence of these terms. We find that the masses and couplings of the KK gravitons have considerable dependence on the size of the brane localized terms; the weak-scale phenomenology of the model is consequently modified . In particular, the weak-scale spin-2 graviton resonances which generically appear in the RS model may be significantly lighter than previously assumed. However, they may avoid detection as their widths may be too narrow to be observable at colliders. In the contact interaction limit, for a certain range of parameters, the experimental reach for the scale of the theory is independent of the size of the boundary terms.
Actin filament curvature biases branching direction
Risca, Viviana I.; Wang, Evan B.; Chaudhuri, Ovijit; Chia, Jia Jun; Geissler, Phillip L.; Fletcher, Daniel A.
2012-01-01
Mechanical cues affect many important biological processes in metazoan cells, such as migration, proliferation, and differentiation. Such cues are thought to be detected by specialized mechanosensing molecules linked to the cytoskeleton, an intracellular network of protein filaments that provide mechanical rigidity to the cell and drive cellular shape change. The most abundant such filament, actin, forms branched networks nucleated by the actin-related protein (Arp) 2/3 complex that support or induce membrane protrusions and display adaptive behavior in response to compressive forces. Here we show that filamentous actin serves in a mechanosensitive capacity itself, by biasing the location of actin branch nucleation in response to filament bending. Using an in vitro assay to measure branching from curved sections of immobilized actin filaments, we observed preferential branch formation by the Arp2/3 complex on the convex face of the curved filament. To explain this behavior, we propose a fluctuation gating model in which filament binding or branch nucleation by Arp2/3 occur only when a sufficiently large, transient, local curvature fluctuation causes a favorable conformational change in the filament, and we show with Monte Carlo simulations that this model can quantitatively account for our experimental data. We also show how the branching bias can reinforce actin networks in response to compressive forces. These results demonstrate how filament curvature can alter the interaction of cytoskeletal filaments with regulatory proteins, suggesting that direct mechanotransduction by actin may serve as a general mechanism for organizing the cytoskeleton in response to force. PMID:22308368
Relationship between peptide membrane curvature generation and bactericidal activities
NASA Astrophysics Data System (ADS)
Schmidt, Nathan; Lee, Michelle; Kuo, David; Ouellette, Andre; Wong, Gerard
2013-03-01
Many amphipathic peptides and amphipathic domains in proteins can restructure biological membranes. Two examples are host defense antimicrobial peptides (AMPs) which disrupt and destabilize the cell membranes of microbes, and apolipoproteins which help stabilize nanoscale lipid aggregates. We use complementary x-ray and bacterial cell assays to elucidate the molecular length scale membrane deformations generated by amphipathic peptides with different structural motifs and relate these deformations to their activities on bacteria. Small angle x-ray scattering is used to study the interactions of model membranes with prototypical AMPs and consensus peptides from the amphipathic domains in apolipoproteins. By characterizing the nanoscale curvature deformations induced by these two distinct classes of membrane restructuring peptides we will discuss the role of amino acid composition on curvature generation. Bactericidal assays are used to access the in vivo activities of different amphipathic peptide motifs in order to understand the relationships between cell viability and membrane curvature generation.
Curvature-Controlled Defect Localization in Elastic Surface Crystals.
Jiménez, Francisco López; Stoop, Norbert; Lagrange, Romain; Dunkel, Jörn; Reis, Pedro M
2016-03-11
We investigate the influence of curvature and topology on crystalline dimpled patterns on the surface of generic elastic bilayers. Our numerical analysis predicts that the total number of defects created by adiabatic compression exhibits universal quadratic scaling for spherical, ellipsoidal, and toroidal surfaces over a wide range of system sizes. However, both the localization of individual defects and the orientation of defect chains depend strongly on the local Gaussian curvature and its gradients across a surface. Our results imply that curvature and topology can be utilized to pattern defects in elastic materials, thus promising improved control over hierarchical bending, buckling, or folding processes. Generally, this study suggests that bilayer systems provide an inexpensive yet valuable experimental test bed for exploring the effects of geometrically induced forces on assemblies of topological charges.
Sculpting membranes: a mechanism of curvature generation by proteins
NASA Astrophysics Data System (ADS)
Campelo, Felix
2010-03-01
A wide spectrum of intracellular processes is dependent on the ability of cells to dynamically regulate membrane shape. Membrane bending by proteins is necessary for the generation of intracellular transport carriers and for the maintenance of otherwise intrinsically unstable regions of high membrane curvature in cell organelles. Understanding the mechanisms by which proteins curve membranes is therefore of primary importance. Crescent shaped N-BAR domains containing amphipathic helices can induce membrane curvature by two mechanisms: the scaffolding mechanism due to the very shape of the BAR dimer, and the hydrophobic insertion mechanism by which small shallow inclusions penetrate the membrane matrix and act as a wedge changing the local membrane curvature. We will focus on this latter mechanism, and study it from a quantitative point of view. We use an elastic model of the lipid bilayer, taking into account the internal strains and stresses generated by the presence of an inclusion. We show that large membrane curvatures found in in vitro experiments can be ascribed to this mechanism, and that shallow insertions are more powerful curvature generators than lipids.
Sorting of Lipids and Proteins in Membrane Curvature Gradients
Tian, A.; Baumgart, T.
2009-01-01
The sorting of lipids and proteins in cellular trafficking pathways is a process of central importance in maintaining compartmentalization in eukaryotic cells. However, the mechanisms behind these sorting phenomena are currently far from being understood. Among several mechanistic suggestions, membrane curvature has been invoked as a means to segregate lipids and proteins in cellular sorting centers. To assess this hypothesis, we investigate the sorting of lipid analog dye trace components between highly curved tubular membranes and essentially flat membranes of giant unilamellar vesicles. Our experimental findings indicate that intracellular lipid sorting, contrary to frequent assumptions, is unlikely to occur by lipids fitting into membrane regions of appropriate curvature. This observation is explained in the framework of statistical mechanical lattice models that show that entropy, rather than curvature energy, dominates lipid distribution in the absence of strongly preferential lateral intermolecular interactions. Combined with previous findings of curvature induced phase segregation, we conclude that lipid cooperativity is required to enable efficient sorting. In contrast to lipid analog dyes, the peripheral membrane binding protein Cholera toxin subunit B is effectively curvature-sorted. The sorting of Cholera toxin subunit B is rationalized by statistical models. We discuss the implications of our findings for intracellular sorting mechanisms. PMID:19348750
Nonminimal coupling of perfect fluids to curvature
Bertolami, Orfeu; Lobo, Francisco S. N.; Paramos, Jorge
2008-09-15
In this work, we consider different forms of relativistic perfect fluid Lagrangian densities that yield the same gravitational field equations in general relativity (GR). A particularly intriguing example is the case with couplings of the form [1+f{sub 2}(R)]L{sub m}, where R is the scalar curvature, which induces an extra force that depends on the form of the Lagrangian density. It has been found that, considering the Lagrangian density L{sub m}=p, where p is the pressure, the extra-force vanishes. We argue that this is not the unique choice for the matter Lagrangian density, and that more natural forms for L{sub m} do not imply the vanishing of the extra force. Particular attention is paid to the impact on the classical equivalence between different Lagrangian descriptions of a perfect fluid.
Hair curvature: a natural dialectic and review.
Nissimov, Joseph N; Das Chaudhuri, Asit Baran
2014-08-01
Although hair forms (straight, curly, wavy, etc.) are present in apparently infinite variations, each fibre can be reduced to a finite sequence of tandem segments of just three types: straight, bent/curly, or twisted. Hair forms can thus be regarded as resulting from genetic pathways that induce, reverse or modulate these basic curvature modes. However, physical interconversions between twists and curls demonstrate that strict one-to-one correspondences between them and their genetic causes do not exist. Current hair-curvature theories do not distinguish between bending and twisting mechanisms. We here introduce a multiple papillary centres (MPC) model which is particularly suitable to explain twisting. The model combines previously known features of hair cross-sectional morphology with partially/completely separated dermal papillae within single follicles, and requires such papillae to induce differential growth rates of hair cortical material in their immediate neighbourhoods. The MPC model can further help to explain other, poorly understood, aspects of hair growth and morphology. Separate bending and twisting mechanisms would be preferentially affected at the major or minor ellipsoidal sides of fibres, respectively, and together they exhaust the possibilities for influencing hair-form phenotypes. As such they suggest dialectic for hair-curvature development. We define a natural-dialectic (ND) which could take advantage of speculative aspects of dialectic, but would verify its input data and results by experimental methods. We use this as a top-down approach to first define routes by which hair bending or twisting may be brought about and then review evidence in support of such routes. In particular we consider the wingless (Wnt) and mammalian target of rapamycin (mTOR) pathways as paradigm pathways for molecular hair bending and twisting mechanisms, respectively. In addition to the Wnt canonical pathway, the Wnt/Ca(2+) and planar cell polarity (PCP) pathways
Salvage penile curvature correction surgery.
Hsieh, Cheng-Hsing; Chen, Heng-Shuen; Lee, Wen-Yuan; Chen, Kuo-Liang; Chang, Chao-Hsiang; Hsu, Geng-Long
2010-01-01
It is commonly believed that coarser suture materials should be used to provide sufficient tenacity in surgery for penile curvature correction. We report our 15-year experience of fine sutures in a second operation in 31 patients who underwent prior curvature correction elsewhere with coarser sutures, resulting in recurrent penile curvature. Suture materials used in prior surgeries in these patients were either 2-0 or 3-0 nylon sutures. In this series, all 31 patients underwent a modified Nesbit procedure at the level of the collagen bundles using finer sutures. Prior to July 1998, 10 men underwent salvage surgery using 4-0 polyglactin sutures. Thereafter, we adapted 6-0 nylon sutures for another 21 patients. We categorized the patients into the polyglactin (n = 10) and nylon (n = 21) groups respectively. Overall, 29 patients were available for follow-up while using the abridged 5-item version of the International Index of Erectile Function (IIEF-5) scoring system, with 21 patients in the nylon group. We have found cavernosography a practical and reliable method to objectively assess penile morphology in these patients. The penile morphology both subjectively and objectively was excellent in all patients, except for 1 in each group. Erectile function restoration showed a trend of satisfaction in the polyglactin group and based on IIEF-5 was significantly improved in the nylon group (14.2 ± 3.6 vs 21.9 ± 2.1, n = 20, P < .001). These results suggest that in penile tunical surgery, fine sutures such as 6-0 nylon may result in better penile morphology and functional outcomes.
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.
Intracellular magnetophoresis of amyloplasts and induction of root curvature.
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.
Effect of topological defects and curvature on anisotropic crystal growth
NASA Astrophysics Data System (ADS)
Azadi, Amir; Grason, Gregory M.
2015-03-01
The equilibrium shapes and symmetries of crystals are vestiges of the physical principles underlying their formation. We perform particle-based simulations guided by analytical analysis to investigate the structure of crystalline domains on curved substrates, a focus on the impact of topological defects on domain morphology. We find at low area fraction, as has been argued previously, that isotropic crystal growth with relatively compact domains generates large curvature-induced strains accommodated by relative ductile interactions, while the formation of anisotropic ribbon-like structures with lower-curvature induced stresses, introduces a larger line tension cost, and is thus favored for brittle crystals. Our results show that for ductile crystals with large surface coverage, appearance of stable topological defects precludes the formation of anisotropic, ribbon domains. However branch-like structures with large interfacial area are stable for certain values of intermediate curvature and crystalline ductility. These processes are guided by the interplay between elastic shape instability, defects, and curvature, where pattern formations are not related to kinetic instabilities.
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.
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.
Quantifying the Relationship between Curvature and Electric Potential in Lipid Bilayers.
Bruhn, Dennis S; Lomholt, Michael A; Khandelia, Himanshu
2016-06-02
Cellular membranes mediate vital cellular processes by being subject to curvature and transmembrane electrical potentials. Here we build upon the existing theory for flexoelectricity in liquid crystals to quantify the coupling between lipid bilayer curvature and membrane potentials. Using molecular dynamics simulations, we show that headgroup dipole moments, the lateral pressure profile across the bilayer, and spontaneous curvature all systematically change with increasing membrane potentials. In particular, there is a linear dependence between the bending moment (the product of bending rigidity and spontaneous curvature) and the applied membrane potentials. We show that biologically relevant membrane potentials can induce biologically relevant curvatures corresponding to radii of around 500 nm. The implications of flexoelectricity in lipid bilayers are thus likely to be of considerable consequence both in biology and in model lipid bilayer systems.
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.
Forelimb bone curvature in terrestrial and arboreal mammals
Henderson, Keith; Pantinople, Jess; McCabe, Kyle; Milne, Nick
2017-01-01
It has recently been proposed that the caudal curvature (concave caudal side) observed in the radioulna of terrestrial quadrupeds is an adaptation to the habitual action of the triceps muscle which causes cranial bending strains (compression on cranial side). The caudal curvature is proposed to be adaptive because longitudinal loading induces caudal bending strains (increased compression on the caudal side), and these opposing bending strains counteract each other leaving the radioulna less strained. If this is true for terrestrial quadrupeds, where triceps is required for habitual elbow extension, then we might expect that in arboreal species, where brachialis is habitually required to maintain elbow flexion, the radioulna should instead be cranially curved. This study measures sagittal curvature of the ulna in a range of terrestrial and arboreal primates and marsupials, and finds that their ulnae are curved in opposite directions in these two locomotor categories. This study also examines sagittal curvature in the humerus in the same species, and finds differences that can be attributed to similar adaptations: the bone is curved to counter the habitual muscle action required by the animal’s lifestyle, the difference being mainly in the distal part of the humerus, where arboreal animals tend have a cranial concavity, thought to be in response the carpal and digital muscles that pull cranially on the distal humerus. PMID:28462036
Forelimb bone curvature in terrestrial and arboreal mammals.
Henderson, Keith; Pantinople, Jess; McCabe, Kyle; Richards, Hazel L; Milne, Nick
2017-01-01
It has recently been proposed that the caudal curvature (concave caudal side) observed in the radioulna of terrestrial quadrupeds is an adaptation to the habitual action of the triceps muscle which causes cranial bending strains (compression on cranial side). The caudal curvature is proposed to be adaptive because longitudinal loading induces caudal bending strains (increased compression on the caudal side), and these opposing bending strains counteract each other leaving the radioulna less strained. If this is true for terrestrial quadrupeds, where triceps is required for habitual elbow extension, then we might expect that in arboreal species, where brachialis is habitually required to maintain elbow flexion, the radioulna should instead be cranially curved. This study measures sagittal curvature of the ulna in a range of terrestrial and arboreal primates and marsupials, and finds that their ulnae are curved in opposite directions in these two locomotor categories. This study also examines sagittal curvature in the humerus in the same species, and finds differences that can be attributed to similar adaptations: the bone is curved to counter the habitual muscle action required by the animal's lifestyle, the difference being mainly in the distal part of the humerus, where arboreal animals tend have a cranial concavity, thought to be in response the carpal and digital muscles that pull cranially on the distal humerus.
Dehydrating agents sharply reduce curvature in DNAs containing A tracts.
Sprous, D; Zacharias, W; Wood, Z A; Harvey, S C
1995-05-25
The structural basis of DNA curvature remains elusive, because models for curvature based on crystallographic structures of molecules containing A tracts do not agree with any of the models for sequence-directed curvature based on solution studies. Here we demonstrate that the difference is probably due to MPD (2-methyl-2,4-pentanediol), the dehydrating agent commonly used in crystallography. One characteristic signature of curved DNA molecules is that they run anomalously slowly on polyacrylamide gels, appearing to be larger than they actually are. The gel anomalies of three curved DNAs from trypanosome kinetoplast minicircles drop monotonically with increasing MPD concentration, indicating that MPD straightens molecules that are curved in aqueous solution. This is not due to some non-specific effect of MPD on poly(dA) or polypurine tracts, because control molecules containing dA70 and dG43 run normally over the full range of MPD concentrations. Circular dichroism spectra are not affected by MPD, ruling out a conformational change to a structure outside the B-DNA family. The effect is not due to MPD-induced changes in phasing of the curved sequences, because MPD has virtually no effect on the linking numbers of relaxed plasmids containing either curved sequences or dA70. At the concentrations of MPD used in X-ray crystallography, the curvature of DNAs containing A tracts is substantially lower than in solution, which probably explains the ongoing discrepancies between the crystallographic results and models based on solution studies.
Wiet, S P; Vonesh, M J; Waligora, M J; Kane, B J; McPherson, D D
1996-01-01
To characterize the effect of vessel curvature on the geometric accuracy of conventional three-dimensional reconstruction (3DR) algorithms for intravascular ultrasound image data. A common method of 3DR for intravascular ultrasound image data involves geometric reassembly and volumetric interpolation of a spatially related sequence of tomographic cross sections generated by an ultrasound catheter withdrawn at a constant rate through a vascular segment of interest. The resulting 3DR is displayed as a straight segment, with inherent vascular curvature neglected. Most vascular structures, however, are not straight but curved to some degree. For this reason, vascular curvature may influence the accuracy of computer-generated 3DR. We collected image data using three different intravascular ultrasound catheters (2.9 Fr, 4.3 Fr, 8.0 Fr) during a constant-rate pullback of 1 mm/sec through tubing of known diameter with imposed radii of curvature ranging from 2 to 10 cm. Image data were also collected from straight tubing. Image data were digitized at 1.0-mm intervals through a length of 25 mm. Two passes through each radius of curvature were performed with each intravascular ultrasound catheter. 3DR lumen volume for each radius of curvature was compared to that theoretically expected from a straight cylindrical segment. Differences between 3DR lumen volume of theoretical versus curved (actual) tubes were quantified as absolute percentage error and categorized as a function of curvature. Tubing deformation error was quantified by quantitative coronary angiography (QCA). Volumetric errors ranged from 1% to 35%, with an inverse relationship demonstrated between 3DR lumen volume and segmental radius of curvature. Higher curvatures (r < 6.0 cm) induced greater lumen volume error when compared to lower curvatures (r > 6.0 cm). This trend was exhibited for all three catheters and was shown to be independent of tubing deformation artifacts. QCA-determined percentage diameter
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.
Relationship between peptide amino acid sequence and membrane curvature generation
NASA Astrophysics Data System (ADS)
Schmidt, Nathan; Kuo, David; Hwee Lai, Ghee; Mishra, Abhijit; Wong, Gerard
2012-02-01
Amphipathic peptides and amphipathic domains in proteins can perturb and restructure biological membranes. For example, it is believed that the cationic, amphipathic motif found in membrane active antimicrobial peptides (AMPs) is responsible for their membrane disruption mechanisms of action. And ApoA-I, the main apolipoprotein in high density lipoprotein contains a series of amphipathic α-helical repeats which are responsible for its lipid associating properties. We use small angle x-ray scattering (SAXS) to investigate the interaction of model cell membranes with prototypical AMPs and consensus peptides derived from the helical structural motif of ApoA-I. The relationship between peptide sequence and the peptide-induced changes in membrane curvature and topology is examined. By comparing the membrane rearrangement and corresponding phase behavior induced by these two distinct classes of membrane restructuring peptides we will discuss the role of amino acid sequence on membrane curvature generation.
[The relationship between upper airway curvature and obstructive sleep apnea and hypopnea syndrome].
Zhu, Min; Lu, Xiao-feng; Shi, Hui-min
2007-08-01
The fluid flow through curved tubes has characteristics that an increase in the curvature induces pressure losses as well as higher resistance in the same region. The purpose of this study is to analyze the relationship between upper airway curvature and obstructive sleep apnea and hypopnea syndrome(OSAHS). 18 male OSAHS patients were paired by age with 18 males with no snoring. The mean AHI was 58.8. The supine lateral cephalometric films were obtained from CT and analysed using curvature software. Data were presented as mean and paired t test was conducted using SPSS10.0 software package. Correlative analysis was performed to indicate the relationship between BMI and AHI, curvature and BMI, respectively. The airway curvature was significantly different between the two groups(P<0.01). The curvature radius was significantly correlative with BMI (P<0.01), but not with AHI(P>0.05). Upper airway curvature was related significantly to the pathogenesis of OSAHS. An increase of curvature on anterior wall of velopharynx in OSAHS patients can change the pressure and resistance distribution in upper airway.
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.
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.
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.
Streamline curvature effects on turbulent boundary layers
NASA Technical Reports Server (NTRS)
Wilcox, D. C.; Chambers, T. L.
1976-01-01
A theoretical tool has been developed for predicting, in a nonempirical manner, effects of streamline curvature and coordinate-system rotation on turbulent boundary layers. The second-order closure scheme developed by Wilcox and Traci has been generalized for curved streamline flow and for flow in a rotating coordinate system. A physically based straightforward argument shows that curvature/rotation primarily affects the turbulent mixing energy; the argument yields suitable curvature/rotation terms which are added to the mixing-energy equation. Singular-perturbation solutions valid in the wall layer of a curved-wall boundary layer and a fully developed rotating channel flow demonstrate that, with the curvature/rotation terms, the model predicts the curved-wall and the rotating coordinate system laws of the wall. Results of numerical computations of curved-wall boundary layers and of rotating channel flow show that curvature/rotation effects can be computed accurately with second-order closure.
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.
Importance of plan curvature in watershed modeling
NASA Astrophysics Data System (ADS)
Boll, J.; Ribail, J.; Zhao, M.
2016-12-01
A hillslope's hydrologic response to precipitation events is largely controlled by the topographic features of a given hillslope, specifically the profile and plan curvature. Many models simplify hillslope topography and ignore the curvature properties, and some use alternate measures such as a topographic index or the hillslope width function. Models that ignore curvature properties may be calibrated to produce the statistically acceptable integrated response of runoff at a watershed outlet, but incorporating these properties is necessary to model accurately hydrologic processes such as surface flow, erosion, subsurface lateral flow, location of runoff generation and drainage response. In this study, we evaluated the sensitivity of rainfall-runoff modelling to profile and plan curvature in two models. In the first model, the Water Erosion Prediction Project (WEPP) model, hillslope uses a representative width to the hillslope by dividing the drainage area by the average surface channel length. Profile curvature is preserved with a limited spatial resolution due to the number of overland flow elements. In the second model, the distributed Soil Moisture Routing (SMR) model, the geographic information system uses the D8 algorithm to capture profile and plan curvature. Sensitivity to topographic features was tested for three profile curvatures (convex, concave, straight) combined with three plan curvatures (diverging, converging, uniform) resulting in a total of nine hillslopes. Each hillslope was subjected to different rainfall events to detect threshold behavior for when topographic features cannot be ignored. Our findings indicate that concave and convex plan curvature need to be included when subsurface flow processes are the dominant flow process for surface flow runoff generation. We present thresholds for acceptable cases when profile and plan curvature can be simplified in larger spatial hydrologic units.
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.
Programming curvature using origami tessellations
NASA Astrophysics Data System (ADS)
Dudte, Levi H.; Vouga, Etienne; Tachi, Tomohiro; Mahadevan, L.
2016-05-01
Origami describes rules for creating folded structures from patterns on a flat sheet, but does not prescribe how patterns can be designed to fit target shapes. Here, starting from the simplest periodic origami pattern that yields one-degree-of-freedom collapsible structures--we show that scale-independent elementary geometric constructions and constrained optimization algorithms can be used to determine spatially modulated patterns that yield approximations to given surfaces of constant or varying curvature. Paper models confirm the feasibility of our calculations. We also assess the difficulty of realizing these geometric structures by quantifying the energetic barrier that separates the metastable flat and folded states. Moreover, we characterize the trade-off between the accuracy to which the pattern conforms to the target surface, and the effort associated with creating finer folds. Our approach enables the tailoring of origami patterns to drape complex surfaces independent of absolute scale, as well as the quantification of the energetic and material cost of doing so.
Curvature function and coarse graining
NASA Astrophysics Data System (ADS)
Díaz-Marín, Homero; Zapata, José A.
2010-12-01
A classic theorem in the theory of connections on principal fiber bundles states that the evaluation of all holonomy functions gives enough information to characterize the bundle structure (among those sharing the same structure group and base manifold) and the connection up to a bundle equivalence map. This result and other important properties of holonomy functions have encouraged their use as the primary ingredient for the construction of families of quantum gauge theories. However, in these applications often the set of holonomy functions used is a discrete proper subset of the set of holonomy functions needed for the characterization theorem to hold. We show that the evaluation of a discrete set of holonomy functions does not characterize the bundle and does not constrain the connection modulo gauge appropriately. We exhibit a discrete set of functions of the connection and prove that in the abelian case their evaluation characterizes the bundle structure (up to equivalence), and constrains the connection modulo gauge up to "local details" ignored when working at a given scale. The main ingredient is the Lie algebra valued curvature function F_S (A) defined below. It covers the holonomy function in the sense that exp {F_S (A)} = Hol(l= partial S, A).
Curvature function and coarse graining
Diaz-Marin, Homero; Zapata, Jose A.
2010-12-15
A classic theorem in the theory of connections on principal fiber bundles states that the evaluation of all holonomy functions gives enough information to characterize the bundle structure (among those sharing the same structure group and base manifold) and the connection up to a bundle equivalence map. This result and other important properties of holonomy functions have encouraged their use as the primary ingredient for the construction of families of quantum gauge theories. However, in these applications often the set of holonomy functions used is a discrete proper subset of the set of holonomy functions needed for the characterization theorem to hold. We show that the evaluation of a discrete set of holonomy functions does not characterize the bundle and does not constrain the connection modulo gauge appropriately. We exhibit a discrete set of functions of the connection and prove that in the abelian case their evaluation characterizes the bundle structure (up to equivalence), and constrains the connection modulo gauge up to ''local details'' ignored when working at a given scale. The main ingredient is the Lie algebra valued curvature function F{sub S}(A) defined below. It covers the holonomy function in the sense that expF{sub S}(A)=Hol(l={partial_derivative}S,A).
Soliton curvatures of surfaces and spaces
Konopelchenko, B.G.
1997-01-01
An intrinsic geometry of surfaces and three-dimensional Riemann spaces is discussed. In the geodesic coordinates the Gauss equation for two-dimensional Riemann spaces (surfaces) is reduced to the one-dimensional Schr{umlt o}dinger equation, where the Gaussian curvature plays a role of potential. The use of this fact provides an infinite set of explicit expressions for curvature and metric of surface. A special case is governed by the KdV equation for the Gaussian curvature. Integrable dynamics of curvature via the KdV equation, higher KdV equations, and 2+1-dimensional integrable equations with breaking solitons is considered. For a special class of three-dimensional Riemann spaces the relation between metric and scalar curvature is given by the two-dimensional stationary Schr{umlt o}dinger or perturbed string equations. This provides us an infinite family of Riemann spaces with explicit scalar curvature and metric. Particular class of spaces and their integrable evolutions are described by the Nizhnik{endash}Veselov{endash}Novikov equation and its higher analogs. Surfaces and three-dimensional Riemann spaces with large curvature and slow dependence on the variable are considered. They are associated with the Burgers and Kadomtsev{endash}Petviashvili equations, respectively. {copyright} {ital 1997 American Institute of Physics.}
Curvature and torsion in growing actin networks
NASA Astrophysics Data System (ADS)
Shaevitz, Joshua W.; Fletcher, Daniel A.
2008-06-01
Intracellular pathogens such as Listeria monocytogenes and Rickettsia rickettsii move within a host cell by polymerizing a comet-tail of actin fibers that ultimately pushes the cell forward. This dense network of cross-linked actin polymers typically exhibits a striking curvature that causes bacteria to move in gently looping paths. Theoretically, tail curvature has been linked to details of motility by considering force and torque balances from a finite number of polymerizing filaments. Here we track beads coated with a prokaryotic activator of actin polymerization in three dimensions to directly quantify the curvature and torsion of bead motility paths. We find that bead paths are more likely to have low rather than high curvature at any given time. Furthermore, path curvature changes very slowly in time, with an autocorrelation decay time of 200 s. Paths with a small radius of curvature, therefore, remain so for an extended period resulting in loops when confined to two dimensions. When allowed to explore a three-dimensional (3D) space, path loops are less evident. Finally, we quantify the torsion in the bead paths and show that beads do not exhibit a significant left- or right-handed bias to their motion in 3D. These results suggest that paths of actin-propelled objects may be attributed to slow changes in curvature, possibly associated with filament debranching, rather than a fixed torque.
Curvature and torsion in growing actin networks
Shaevitz, Joshua W; Fletcher, Daniel A
2011-01-01
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. PMID:18560043
Curvature in solid oxide fuel cells
NASA Astrophysics Data System (ADS)
Li, Wenxia; Hasinska, Kathy; Seabaugh, Matt; Swartz, Scott; Lannutti, John
At this point in history, curvature is inherent to the laminated components that comprise solid oxide fuel cells (SOFCs). Surprisingly, however, this fact has never been previously quantified in the literature. In addition, potential curvature changes associated with NiO reduction and re-oxidation during operation have not been investigated. In this report, an optical profilometer was employed to non-destructively quantify the surface curvature or cracking behavior observed on a large scale in industrially manufactured cells. This provides insights into the challenges that the component materials face as well as additional appreciation for why, in spite of a concerted effort to commercialize SOFC power generation, all currently manufactured SOFC stacks fail. Our results demonstrate that cracked electrolyte areas (caused by differential sintering) are flatter than uncracked regions. The height of the electrolyte surface ranged from 86 to 289 μm above the baseline following sintering. Reduction typically results in increases in curvature of up to 214 μm. Initial crack density appears to affect curvature evolution during reduction; the higher the crack density, the smaller the curvature increase following reduction at 600 °C. In general, however, we observed that the electrolyte layer is remarkably resistant to further cracking during these typographic changes. Following oxidation at 750 °C, large changes in curvature (up to 280 μm) are noted that appear to be related to the strength of the bond between the electrolyte and the underlying anode.
Influence of firing time and framework thickness on veneered Y-TZP discs curvature.
Jakubowicz-Kohen, Boris D; Sadoun, Michaël J; Douillard, Thierry; Mainjot, Amélie K
2014-02-01
The objective of the present work was to study the curvature of very thinly, veneered Y-TZP discs of different framework thicknesses submitted to different firing times. Fifteen 20-mm-wide Y-TZP discs were produced in three different thicknesses: 0.75, 1, 1.5mm. One disc from each group was left unveneered while the others were layered with a 0.1mm veneering ceramic layer. All discs underwent five firing cycles for a total cumulative firing time of 30 min, 1, 2, 5 and 10h at 900°C. The curvature profile was measured using a profilometer after the veneering process and after each firing cycle respectively. A fitted curve was then used to estimate the, curvature radius. The coefficient of thermal expansion (CTE) measurements were taken on veneering, ceramic and Y-TZP beam samples that underwent the same firing schedule. Those data were used to calculate the curvature generated by CTE variations over firing time. All bilayered samples exhibited a curvature that increased over firing time inversely to framework thickness. However non-veneered samples did not exhibit any curvature modification. The results of the present study reveal that even a very thin veneer layer (0.1mm) can induce a significant curvature of Y-TZP discs. The dilatometric results showed that Tg and CTE, variations are not sufficient to explain this curvature. A chemical-induced zirconia volume, augmentation located at the framework sub-surface near the interface could explain the sample, curvature and its increase with firing time. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
Magnetic curvature effects on plasma interchange turbulence
Li, B. Liao, X.; Sun, C. K.; Ou, W.; Liu, D.; Gui, G.; Wang, X. G.
2016-06-15
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.
Impact of curvature on topological defects
NASA Astrophysics Data System (ADS)
Mesarec, L.; Góźdź, W.; Iglič, A.; Kralj, S.
2017-01-01
We analyze the impact of extrinsic and intrinsic curvature on positions of topological defects (TDs) in two-dimensional (2D) nematic films. We demonstrate that both these curvature contributions are commonly present and are expected to be weighted by comparable elastic constants. A simple Landau-de Gennes approach in terms of tensor nematic order parameter is used to numerically demonstrate impact of the curvatures on position of TDs on 2D ellipsoidal nematic shells. In particular, in oblate ellipsoids the extrinsic and intrinsic elastic terms enforce conflicting tendencies to positions of TDs.
Aggregation and vesiculation of membrane proteins by curvature-mediated interactions
NASA Astrophysics Data System (ADS)
Reynwar, Benedict J.; Illya, Gregoria; Harmandaris, Vagelis A.; Müller, Martin M.; Kremer, Kurt; Deserno, Markus
2007-05-01
Membrane remodelling plays an important role in cellular tasks such as endocytosis, vesiculation and protein sorting, and in the biogenesis of organelles such as the endoplasmic reticulum or the Golgi apparatus. It is well established that the remodelling process is aided by specialized proteins that can sense as well as create membrane curvature, and trigger tubulation when added to synthetic liposomes. Because the energy needed for such large-scale changes in membrane geometry significantly exceeds the binding energy between individual proteins and between protein and membrane, cooperative action is essential. It has recently been suggested that curvature-mediated attractive interactions could aid cooperation and complement the effects of specific binding events on membrane remodelling. But it is difficult to experimentally isolate curvature-mediated interactions from direct attractions between proteins. Moreover, approximate theories predict repulsion between isotropically curving proteins. Here we use coarse-grained membrane simulations to show that curvature-inducing model proteins adsorbed on lipid bilayer membranes can experience attractive interactions that arise purely as a result of membrane curvature. We find that once a minimal local bending is realized, the effect robustly drives protein cluster formation and subsequent transformation into vesicles with radii that correlate with the local curvature imprint. Owing to its universal nature, curvature-mediated attraction can operate even between proteins lacking any specific interactions, such as newly synthesized and still immature membrane proteins in the endoplasmic reticulum.
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.
Detonation front curvatures and detonation rates
NASA Astrophysics Data System (ADS)
Lauderbach, Lisa M.; Lorenz, K. Thomas; Lee, Edward L.; Souers, P. Clark
2017-01-01
Many detonation front curvatures are reviewed. Most are of the Shock Dynamics type, which are described as a combination of quadratic and 8th power-of-the-radius curves. The integrated fraction of the 8th power curve is taken as a measure of curvature, which we are able to relate to the logarithm of the detonation rate. This provides a means of estimating the rates of some unknown explosives from the curvature. Using the edge lag divided by the radius is an even better way. A second group of curvatures are almost or purely quadratic. This is probably not associated with density gradients but may be caused by low sound speeds. A final group of "sombreros" show curvy fronts for ideal explosives, which appear to be caused by density gradients.
Helical Microfilaments with Alternating Imprinted Intrinsic Curvatures.
Silva, Pedro Emanuel Santos; Godinho, Maria Helena
2017-03-01
There has been an intense research for developing techniques that can produce filaments with helical shapes, given the widespread of potential applications. In this work, how helices with different curvatures can be precisely imprinted in microfilaments is shown. It is also shown that using this technique, it is possible to produce, in a single fiber, helices with different curvatures. This striking and innovative behavior is observed when one side of the stretched filaments is irradiated with UV light, modifying the mechanical properties at surface. Upon release, the regions with higher curvature start to curl first, while regions with lower intrinsic curvature remain stretched until start to curl later. The results presented here can be important to understand why structures adopt a helical shape in general, which can be of interest in nanotechnology, biomolecular science, or even to understand why plant filaments curl. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Role of feature curvature in contact guidance
Mathur, Anurag; Moore, Simon W.; Sheetz, Michael P.; Hone, James
2012-01-01
This study examines the role of feature curvature in cellular topography sensing. To separate the effects of feature size and curvature, we have developed a method to fabricate grooved substrates whose radius of curvature (r) is varied from under 10 nm to 400 nm, while all other dimensions are kept constant. With increasing r up to 200 nm, mouse embryonic fibroblasts increased their spread area, but reduced their polarization (aspect ratio). Interestingly, on features with an r of 200 and 400 nm - where there was very little effect on spreading area and polarization - we find that internal structures such as stress fibers are nevertheless still strongly aligned to the topography. These findings are of importance to studies of both tissue engineering and curvature sensing proteins. PMID:22426288
Gravitational energy in quadratic-curvature gravities.
Deser, S; Tekin, Bayram
2002-09-02
We define energy (E) and compute its values for gravitational systems involving terms quadratic in curvature. There are significant differences, both conceptually and concretely, from Einstein theory. For D=4, all purely quadratic models admit constant curvature vacua with arbitrary Lambda, and E is the "cosmological" Abbott-Deser (AD) expression; instead, E always vanishes in flat, Lambda=0, background. For combined Einstein-quadratic curvature systems without explicit Lambda-term vacuum must be flat space, and E has the usual Arnowitt-Deser-Misner form. A Lambda-term forces unique de Sitter vacuum, with E the sum of contributions from Einstein and quadratic parts to the AD form. We also discuss the effects on energy definition of higher curvature terms and of higher dimension.
Spline-Based Smoothing of Airfoil Curvatures
NASA Technical Reports Server (NTRS)
Li, W.; Krist, S.
2008-01-01
Constrained fitting for airfoil curvature smoothing (CFACS) is a splinebased method of interpolating airfoil surface coordinates (and, concomitantly, airfoil thicknesses) between specified discrete design points so as to obtain smoothing of surface-curvature profiles in addition to basic smoothing of surfaces. CFACS was developed in recognition of the fact that the performance of a transonic airfoil is directly related to both the curvature profile and the smoothness of the airfoil surface. Older methods of interpolation of airfoil surfaces involve various compromises between smoothing of surfaces and exact fitting of surfaces to specified discrete design points. While some of the older methods take curvature profiles into account, they nevertheless sometimes yield unfavorable results, including curvature oscillations near end points and substantial deviations from desired leading-edge shapes. In CFACS as in most of the older methods, one seeks a compromise between smoothing and exact fitting. Unlike in the older methods, the airfoil surface is modified as little as possible from its original specified form and, instead, is smoothed in such a way that the curvature profile becomes a smooth fit of the curvature profile of the original airfoil specification. CFACS involves a combination of rigorous mathematical modeling and knowledge-based heuristics. Rigorous mathematical formulation provides assurance of removal of undesirable curvature oscillations with minimum modification of the airfoil geometry. Knowledge-based heuristics bridge the gap between theory and designers best practices. In CFACS, one of the measures of the deviation of an airfoil surface from smoothness is the sum of squares of the jumps in the third derivatives of a cubicspline interpolation of the airfoil data. This measure is incorporated into a formulation for minimizing an overall deviation- from-smoothness measure of the airfoil data within a specified fitting error tolerance. CFACS has been
Curvature Analysis of Cardiac Excitation Wavefronts
2013-04-01
computational cardiac-cell network accurately reproduces a particular kind of cardiac arrhythmia , such as ventricular fibrillation. Curvature Analysis of Cardiac...network accurately reproduces a particular kind of cardiac arrhythmia , such as ventricular fibrillation. Index Terms Cardiac excitation waves...isopotentials, Bézier curves, curvature, cardiac arrhythmia and fibrillation Ç 1 INTRODUCTION AN estimated 81,000,000 American adults, more than onein three
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.
Curvature adaptive optics and low light imaging
NASA Astrophysics Data System (ADS)
Ftaclas, C.; Chun, M.; Kuhn, J.; Ritter, J.
We review the basic approach of curvature adaptive optics (AO) and show how its many advantages arise. A curvature wave front sensor (WFS) measures exactly what a curvature deformable mirror (DM) generates. This leads to the computational and operational simplicity of a nearly diagonal control matrix. The DM automatically reconstructs the wave front based on WFS curvature measurements. Thus, there is no formal wave front reconstruction. This poses an interesting challenge to post-processing of AO images. Physical continuity of the DM and the reconstruction of phase from wave front curvature data assure that each actuated region of the DM corrects local phase, tip-tilt and focus. This gain in per-channel correction efficiency, combined with the need for only one pixel per channel detector reads in the WFS allows the use of photon counting detectors for wave front sensing. We note that the use of photon counting detectors implies penalty-free combination of correction channels either in the WFS or on the DM. This effectively decouples bright and faint source performance in that one no longer predicts the other. The application of curvature AO to the low light moving target detection problem, and explore the resulting challenges to components and control systems. Rapidly moving targets impose high-speed operation posing new requirements unique to curvature components. On the plus side, curvature wave front sensors, unlike their Shack-Hartmann counterparts, are tunable for optimum sensitivity to seeing and we are examining autonomous optimization of the WFS to respond to rapid changes in seeing.
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.
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.
Nonadditive Compositional Curvature Energetics of Lipid Bilayers.
Sodt, A J; Venable, R M; Lyman, E; Pastor, R W
2016-09-23
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.
Anisotropic Cosmology and Curvature Invariants.
NASA Astrophysics Data System (ADS)
Skea, James E. F.
greater when non-axisymmetric cosmologies are considered. In the limit where the particle production is switched on at the Planck time (t _{rm Pl}), isotropisation is found to occur at _{Omega } 10^5 t_ {rm Pl}, compatible with restrictions on anistropy at that time. Particle production is not found to isotropise Bianchi VIII and IX cosmologies. In Part 3, we study the structure of various curvature invariants and, following a suggestion by Karlhede, we investigate their relationship to horizons in particular space-times. (Abstract shortened by UMI.).
Falk, Kerstin; Sedlmeier, Felix; Joly, Laurent; Netz, Roland R; Bocquet, Lydéric
2010-10-13
In this paper, we study the interfacial friction of water at graphitic interfaces with various topologies, water between planar graphene sheets, inside and outside carbon nanotubes, with the goal to disentangle confinement and curvature effects on friction. We show that the friction coefficient exhibits a strong curvature dependence; while friction is independent of confinement for the graphene slab, it decreases with carbon nanotube radius for water inside, but increases for water outside. As a paradigm the friction coefficient is found to vanish below a threshold diameter for armchair nanotubes. Using a statistical description of the interfacial friction, we highlight here a structural origin of this curvature dependence, mainly associated with a curvature-induced incommensurability between the water and carbon structures. These results support the recent experiments reporting fast transport of water in nanometric carbon nanotube membranes.
Dehydrating agents sharply reduce curvature in DNAs containing A tracts.
Sprous, D; Zacharias, W; Wood, Z A; Harvey, S C
1995-01-01
The structural basis of DNA curvature remains elusive, because models for curvature based on crystallographic structures of molecules containing A tracts do not agree with any of the models for sequence-directed curvature based on solution studies. Here we demonstrate that the difference is probably due to MPD (2-methyl-2,4-pentanediol), the dehydrating agent commonly used in crystallography. One characteristic signature of curved DNA molecules is that they run anomalously slowly on polyacrylamide gels, appearing to be larger than they actually are. The gel anomalies of three curved DNAs from trypanosome kinetoplast minicircles drop monotonically with increasing MPD concentration, indicating that MPD straightens molecules that are curved in aqueous solution. This is not due to some non-specific effect of MPD on poly(dA) or polypurine tracts, because control molecules containing dA70 and dG43 run normally over the full range of MPD concentrations. Circular dichroism spectra are not affected by MPD, ruling out a conformational change to a structure outside the B-DNA family. The effect is not due to MPD-induced changes in phasing of the curved sequences, because MPD has virtually no effect on the linking numbers of relaxed plasmids containing either curved sequences or dA70. At the concentrations of MPD used in X-ray crystallography, the curvature of DNAs containing A tracts is substantially lower than in solution, which probably explains the ongoing discrepancies between the crystallographic results and models based on solution studies. Images PMID:7784188
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.
Strong curvature effects in Neumann wave problems
NASA Astrophysics Data System (ADS)
Willatzen, M.; Pors, A.; Gravesen, J.
2012-08-01
Waveguide phenomena play a major role in basic sciences and engineering. The Helmholtz equation is the governing equation for the electric field in electromagnetic wave propagation and the acoustic pressure in the study of pressure dynamics. The Schrödinger equation simplifies to the Helmholtz equation for a quantum-mechanical particle confined by infinite barriers relevant in semiconductor physics. With this in mind and the interest to tailor waveguides towards a desired spectrum and modal pattern structure in classical structures and nanostructures, it becomes increasingly important to understand the influence of curvature effects in waveguides. In this work, we demonstrate analytically strong curvature effects for the eigenvalue spectrum of the Helmholtz equation with Neumann boundary conditions in cases where the waveguide cross section is a circular sector. It is found that the linear-in-curvature contribution originates from parity symmetry breaking of eigenstates in circular-sector tori and hence vanishes in a torus with a complete circular cross section. The same strong curvature effect is not present in waveguides subject to Dirichlet boundary conditions where curvature contributions contribute to second-order in the curvature only. We demonstrate this finding by considering wave propagation in a circular-sector torus corresponding to Neumann and Dirichlet boundary conditions, respectively. Results for relative eigenfrequency shifts and modes are determined and compared with three-dimensional finite element method results. Good agreement is found between the present analytical method using a combination of differential geometry with perturbation theory and finite element results for a large range of curvature ratios.
Schmidt, Nathan W.; Lis, Michael; Zhao, Kun; Lai, Ghee Hwee; Alexandrova, Anastassia; Tew, Gregory N.; Wong, Gerard C. L.
2013-01-01
We investigate the physical origin of peptide-induced membrane curvature by contrasting differences between H-bonding interactions of prototypical cationic amino acids, arginine (Arg) and lysine (Lys), with phosphate groups of phospholipid heads using quantum mechanical (QM) calculations of a minimum model, and test the results via synthetic oxaorbornene-based transporter sequences without the geometric constraints of polypeptide backbones. QM calculations suggest that although individual Lys can in principle coordinate two phosphates, they are not able to do so at small inter-Lys distances without drastic energetic penalties. In contrast, Arg can coordinate two phosphates down to less than 5 Å, where guanidinium groups can stack ‘face to face’. In agreement with these observations, poly-Lys cannot generate the nanoscale positive curvature necessary for inducing negative Gaussian membrane curvature, in contrast to poly-Arg. Also consistent with QM calculations, polyguanidine-oxanorbornene homopolymers (PGONs) showed that curvature generation is exquisitely sensitive to the guanidinium group spacing when the phosphate groups are near close packing. Addition of phenyl or butyl hydrophobic groups into guanidine-oxanorbornene polymers increased the amount of induced saddle-splay membrane curvature, and broadened the range of lipid compositions where saddle-splay curvature was induced. The enhancement of saddle-splay curvature generation and relaxation of lipid composition requirements via addition of hydrophobicity is consistent with activity profiles. While PGON polymers displayed selective antimicrobial activity against prototypical (Gram positive and negative) bacteria, polymers with phenyl and butyl groups were also active against red blood cells. Our results suggest that it is possible to achieve deterministic molecular design of pore forming peptides. PMID:23061419
Magnetization in narrow ribbons: curvature effects
NASA Astrophysics Data System (ADS)
Gaididei, Yuri; Goussev, Arseni; Kravchuk, Volodymyr P.; Pylypovskyi, Oleksandr V.; Robbins, J. M.; Sheka, Denis D.; Slastikov, Valeriy; Vasylkevych, Sergiy
2017-09-01
A ribbon is a surface swept out by a line segment turning as it moves along a central curve. For narrow magnetic ribbons, for which the length of the line segment is much less than the length of the curve, the anisotropy induced by the magnetostatic interaction is biaxial, with a hard axis normal to the ribbon and an easy axis along the central curve. The micromagnetic energy of a narrow ribbon reduces to that of a one-dimensional ferromagnetic wire, but with curvature, torsion and local anisotropy modified by the rate of turning. These general results are applied to two examples, namely a helicoid ribbon, for which the central curve is a straight line, and a Möbius ribbon, for which the central curve is a circle about which the line segment executes a {{180}\\circ} twist. In both examples, for large positive tangential anisotropy, the ground state magnetization lies tangent to the central curve. As the tangential anisotropy is decreased, the ground state magnetization undergoes a transition, acquiring an in-surface component perpendicular to the central curve. For the helicoid ribbon, the transition occurs at vanishing anisotropy, below which the ground state is uniformly perpendicular to the central curve. The transition for the Möbius ribbon is more subtle; it occurs at a positive critical value of the anisotropy, below which the ground state is nonuniform. For the helicoid ribbon, the dispersion law for spin wave excitations about the tangential state is found to exhibit an asymmetry determined by the geometric and magnetic chiralities.
Lipids, curvature, and nano-medicine*
Mouritsen, Ole G
2011-01-01
The physical properties of the lamellar lipid-bilayer component of biological membranes are controlled by a host of thermodynamic forces leading to overall tensionless bilayers with a conspicuous lateral pressure profile and build-in curvature-stress instabilities that may be released locally or globally in terms of morphological changes. In particular, the average molecular shape and the propensity of the different lipid and protein species for forming non-lamellar and curved structures are a source of structural transitions and control of biological function. The effects of different lipids, sterols, and proteins on membrane structure are discussed and it is shown how one can take advantage of the curvature-stress modulations brought about by specific molecular agents, such as fatty acids, lysolipids, and other amphiphilic solutes, to construct intelligent drug-delivery systems that function by enzymatic triggering via curvature. Practical applications: The simple concept of lipid molecular shape and how it impacts on the structure of lipid aggregates, in particular the curvature and curvature stress in lipid bilayers and liposomes, can be exploited to construct liposome-based drug-delivery systems, e.g., for use as nano-medicine in cancer therapy. Non-lamellar-forming lysolipids and fatty acids, some of which may be designed to be prodrugs, can be created by phospholipase action in diseased tissues thereby providing for targeted drug release and proliferation of molecular entities with conical shape that break down the permeability barrier of the target cells and may hence enhance efficacy. PMID:22164124
Curvature 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 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.
On the curvature effect of thin membranes
NASA Astrophysics Data System (ADS)
Wang, Duo; Jiao, Xiangmin; Conley, Rebecca; Glimm, James
2013-01-01
We investigate the curvature effect of a thin, curved elastic interface that separates two subdomains and exerts a pressure due to a curvature effect. This pressure, which we refer to as interface pressure, is similar to the surface tension in fluid mechanics. It is important in some applications, such as the canopy of parachutes, biological membranes of cells, balloons, airbags, etc., as it partially balances a pressure jump between the two sides of an interface. In this paper, we show that the interface pressure is equal to the trace of the matrix product of the curvature tensor and the Cauchy stress tensor in the tangent plane. We derive the theory for interfaces in both 2-D and 3-D, and present numerical discretizations for computing the quality over triangulated surfaces.
Cosmic curvature from de Sitter equilibrium cosmology.
Albrecht, Andreas
2011-10-07
I show that the de Sitter equilibrium cosmology generically predicts observable levels of curvature in the Universe today. The predicted value of the curvature, Ω(k), depends only on the ratio of the density of nonrelativistic matter to cosmological constant density ρ(m)(0)/ρ(Λ) and the value of the curvature from the initial bubble that starts the inflation, Ω(k)(B). The result is independent of the scale of inflation, the shape of the potential during inflation, and many other details of the cosmology. Future cosmological measurements of ρ(m)(0)/ρ(Λ) and Ω(k) will open up a window on the very beginning of our Universe and offer an opportunity to support or falsify the de Sitter equilibrium cosmology.
HEREDITARY DISTAL FORELEG CURVATURE IN THE RABBIT
Pearce, Louise
1960-01-01
An inwardly directed curvature of the distal segment of both forelegs of the rabbit has been described. The condition was detected at 2 to 3 weeks of age, developed rapidly, and reached its final and permanent stage at 2 to 3 months of age. Only the distal epiphysis of the ulna was primarily affected and this in the form of a massive chondrodystrophic lesion accompanied by a progressive curvature of the shaft. The curvature of the growing radius was a secondary effect due to the firm, immovable, anatomical connection of the ulna and radius. The positional changes of the wrist and paw were likewise effects secondary to the changed form of the ulna and radius. The bowing abnormality occurred only in certain families of pure bred Beveren, Belgian, French Silver, and Dutch rabbits and was found to be inherited. The mode of inheritance was on the basis of a single recessive unit factor (5). PMID:13733755
Principal curvature for infrared small target detection
NASA Astrophysics Data System (ADS)
Zhao, Yao; Pan, Haibin; Du, Changping; Zheng, Yao
2015-03-01
Small target detection in infrared image with complex background and low signal-noise ratio is an important and difficult task in the infrared target tracking system. In this paper, a principal curvature-based method is proposed. The principal curvatures of target pixels are negative and their absolute values are larger than that of background pixels and noise pixels in a Gaussian-blurred infrared image. The proposed filter takes a composite function of the curvatures for detection. An approximate model is also built for optimizing the parameters. Experimental results show that the proposed algorithm is effective and adaptable for infrared small target detection in complex background. Compared with several popular methods, the proposed algorithm demonstrates significant improvement on detection performance in terms of the parameters of signal clutter ratio gain, background suppression factor and ROC.
Ray Curvature and Refraction of Wave Packets.
1978-09-01
1!~~~~~ _ ‘ AD AOM 302 FLORIDA STATE UNIV TALLAHASSEE DEPT OF OCEANOGRAPHY FIG B/3 RAY CURVATURE AND REFRACTION OF WAVE PACKETS. (U) SEP 78 .J E...BREEDING N00014—77—C—0329 UNCLASSIFIED TR JE6 3 NL _ _ _ rwii__ _ ~iU ir!I I -~~ RAYOJR\\1L~[UREAND REFRACI ION OF WAVE F1~\\CKET~S ~y J. Ernest Breeding...01 29 014 -~ Technical Report No. JEB-3 Department of Oceanography • Florida State University RAY CURVATURE AND REFRACTION OF WAVE PACKETS b O G • J
NASTRAN modifications for recovering strains and curvatures
NASA Technical Reports Server (NTRS)
Hennrich, C. W.
1975-01-01
Modifications to the NASTRAN structural analysis computer program are described. The modifications allow the recovery of strain and curvature data for the general two-dimensional elements, in addition to the usual stress data. Option features allow the transformation of the strain/curvature (or stress) data to a common coordinate system and representation at the grid points of the structural model rather than at the conventional element center locations. Usage information is provided which will allow present users of NASTRAN to easily utilize the new capability.
Cholesterol Mediates Membrane Curvature during Fusion Events
NASA Astrophysics Data System (ADS)
Ivankin, Andrey; Kuzmenko, Ivan; Gidalevitz, David
2012-06-01
Biomembranes undergo extensive shape changes as they perform vital cellular functions. The mechanisms by which lipids and proteins control membrane curvature remain unclear. We use x-ray reflectivity, grazing incidence x-ray diffraction, and epifluorescence microscopy to study binding of HIV-1 glycoprotein gp41’s membrane-bending domain to DPPC/cholesterol monolayers of various compositions at the air-liquid interface. The results offer a new insight into how membrane curvature could be regulated by cholesterol during fusion of the viral lipid envelope and the host cell membranes.
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.
Hysteresis compensation technique for POF curvature sensors
NASA Astrophysics Data System (ADS)
Leal, Arnaldo G.; Frizera, Anselmo; Pontes, Maria José
2017-04-01
Polymer optical fibers (POF) have higher strain limits, fracture toughness and flexibility in bend if compared to glass optical fibers. These characteristics enable the application of POFs as curvature sensors. However, the polymer is a viscoelastic material, which does not have a constant response with stress or strain. For this reason, a curvature sensor based on POF may present high hysteresis. This paper proposes a dynamic compensation technique based on the angular velocity of the sensor. Results show a hysteresis up to 10 times lower. Furthermore, it results on a simple calibration equation, which can be applied in real-time measurements.
Curvature suppresses the Rayleigh-Taylor instability
Trinh, Philippe H.; Kim, Hyoungsoo; Hammoud, Naima; Howell, Peter D.; Chapman, S. Jonathan; Stone, Howard A.
2014-05-01
The dynamics of a thin liquid #12;lm on the underside of a curved cylindrical substrate is studied. The evolution of the liquid layer is investigated as the #12;lm thickness and the radius of curvature of the substrate are varied. A dimensionless parameter (a modi#12;ed Bond number) that incorporates both geometric parameters, gravity, and surface tension is identified, and allows the observations to be classified according to three different flow regimes: stable films, films with transient growth of perturbations followed by decay, and unstable films. Experiments and theory confirm that, below a critical value of the Bond number, curvature of the substrate suppresses the Rayleigh-Taylor instability.
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.
Curvature-driven capillary migration and assembly of rod-like particles
Cavallaro, Marcello; Botto, Lorenzo; Lewandowski, Eric P.; Wang, Marisa; Stebe, Kathleen J.
2011-01-01
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. PMID:22184218
Bending stiffness depends on curvature of ternary lipid mixture tubular membranes.
Tian, Aiwei; Capraro, Benjamin R; Esposito, Cinzia; Baumgart, Tobias
2009-09-16
Lipid and protein sorting and trafficking in intracellular pathways maintain cellular function and contribute to organelle homeostasis. Biophysical aspects of membrane shape coupled to sorting have recently received increasing attention. Here we determine membrane tube bending stiffness through measurements of tube radii, and demonstrate that the stiffness of ternary lipid mixtures depends on membrane curvature for a large range of lipid compositions. This observation indicates amplification by curvature of cooperative lipid demixing. We show that curvature-induced demixing increases upon approaching the critical region of a ternary lipid mixture, with qualitative differences along two roughly orthogonal compositional trajectories. Adapting a thermodynamic theory earlier developed by M. Kozlov, we derive an expression that shows the renormalized bending stiffness of an amphiphile mixture membrane tube in contact with a flat reservoir to be a quadratic function of curvature. In this analytical model, the degree of sorting is determined by the ratio of two thermodynamic derivatives. These derivatives are individually interpreted as a driving force and a resistance to curvature sorting. We experimentally show this ratio to vary with composition, and compare the model to sorting by spontaneous curvature. Our results are likely to be relevant to the molecular sorting of membrane components in vivo.
Fengjie, Xi; Zongfu, Jiang; Xiaojun, Xu; Jing, Hou; Zejin, Liu
2009-03-02
In this paper we determine the optimum propagation distance between measurement planes and the plane of the lens in a wavefront curvature sensor with the diffraction optics approach. From the diffraction viewpoint, the measured wavefront aberration can be decomposed into Fourier harmonics at various frequencies. The curvature signal produced by a single harmonic is analyzed with the wave propagation transfer function approach, which is the frequency analysis of wavefront curvature sensing. The intensity of the curvature signal is a sine function of the product of the propagation distance and the squared frequency. To maximize the curvature signal, the optimum propagation distance is proposed as one quarter of the Talbot length at the critical frequency (average power point at which the power spectrum density is the average power spectrum density). Following the determination of the propagation distance, the intensity of the curvature signal varies sinusoidally with the squared frequencies, vanishing at some higher frequency bands just like a comb filter. To cover these insensitive bands, wavefront curvature sensing with dual propagation distances or with multi-propagation distances is proposed.
Mixed lipid bilayers with locally varying spontaneous curvature and bending.
Gueguen, Guillaume; Destainville, Nicolas; Manghi, Manoel
2014-08-01
A model of lipid bilayers made of a mixture of two lipids with different average compositions on both leaflets, is developed. A Landau Hamiltonian describing the lipid-lipid interactions on each leaflet, with two lipidic fields ψ 1 and ψ 2, is coupled to a Helfrich one, accounting for the membrane elasticity, via both a local spontaneous curvature, which varies as C 0 + C 1(ψ 1 - ψ 2/2), and a bending modulus equal to κ 0 + κ 1(ψ 1 + ψ 2)/2. This model allows us to define curved patches as membrane domains where the asymmetry in composition, ψ 1 - ψ 2, is large, and thick and stiff patches where ψ 1 + ψ 2 is large. These thick patches are good candidates for being lipidic rafts, as observed in cell membranes, which are composed primarily of saturated lipids forming a liquid-ordered domain and are known to be thick and flat nano-domains. The lipid-lipid structure factors and correlation functions are computed for globally spherical membranes and planar ones and for a whole set of parameters including the surface tension and the coupling in the two leaflet compositions. Phase diagrams are established, within a Gaussian approximation, showing the occurrence of two types of Structure Disordered phases, with correlations between either curved or thick patches, and an Ordered phase, corresponding to the divergence of the structure factor at a finite wave vector. The varying bending modulus plays a central role for curved membranes, where the driving force κ 1 C 0 (2) is balanced by the line tension, to form raft domains of size ranging from 10 to 100 nm. For planar membranes, raft domains emerge via the cross-correlation with curved domains. A global picture emerges from curvature-induced mechanisms, described in the literature for planar membranes, to coupled curvature- and bending-induced mechanisms in curved membranes forming a closed vesicle.
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.
Membrane Curvature Sensing by Amphipathic Helices
Jensen, Martin Borch; Bhatia, Vikram Kjøller; Jao, Christine C.; Rasmussen, Jakob Ewald; Pedersen, Søren L.; Jensen, Knud J.; Langen, Ralf; Stamou, Dimitrios
2011-01-01
Preferential binding of proteins on curved membranes (membrane curvature sensing) is increasingly emerging as a general mechanism whereby cells may effect protein localization and trafficking. Here we use a novel single liposome fluorescence microscopy assay to examine a common sensing motif, the amphipathic helix (AH), and provide quantitative measures describing and distinguishing membrane binding and sensing behavior. By studying two AH-containing proteins, α-synuclein and annexin B12, as well as a range of AH peptide mutants, we reveal that both the hydrophobic and hydrophilic faces of the helix greatly influence binding and sensing. Although increased hydrophobic and electrostatic interactions with the membrane both lead to greater densities of bound protein, the former yields membrane curvature-sensitive binding, whereas the latter is not curvature-dependent. However, the relative contributions of both components determine the sensing of AHs. In contrast, charge density in the lipid membrane seems important primarily in attracting AHs to the membrane but does not significantly influence sensing. These observations were made possible by the ability of our assay to distinguish within our samples liposomes with and without bound protein as well as the density of bound protein. Our findings suggest that the description of membrane curvature-sensing requires consideration of several factors such as short and long range electrostatic interactions, hydrogen bonding, and the volume and structure of inserted hydrophobic residues. PMID:21953452
Geodesic curvature driven surface microdomain formation.
Adkins, Melissa R; Zhou, Y C
2017-09-15
Lipid bilayer membranes are not uniform and clusters of lipids in a more ordered state exist within the generally disorder lipid milieu of the membrane. These clusters of ordered lipids microdomains are now referred to as lipid rafts. Recent reports attribute the formation of these microdomains to the geometrical and molecular mechanical mismatch of lipids of different species on the boundary. Here we introduce the geodesic curvature to characterize the geometry of the domain boundary, and develop a geodesic curvature energy model to describe the formation of these microdomains as a result of energy minimization. Our model accepts the intrinsic geodesic curvature of any binary lipid mixture as an input, and will produce microdomains of the given geodesic curvature as demonstrated by three sets of numerical simulations. Our results are in contrast to the surface phase separation predicted by the classical surface Cahn-Hilliard equation, which tends to generate large domains as a result of the minimizing line tension. Our model provides a direct and quantified description of the structure inhomogeneity of lipid bilayer membrane, and can be coupled to the investigations of biological processes on membranes for which such inhomogeneity plays essential roles.
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
Geodesic curvature driven surface microdomain formation
NASA Astrophysics Data System (ADS)
Adkins, Melissa R.; Zhou, Y. C.
2017-09-01
Lipid bilayer membranes are not uniform and clusters of lipids in a more ordered state exist within the generally disorder lipid milieu of the membrane. These clusters of ordered lipids microdomains are now referred to as lipid rafts. Recent reports attribute the formation of these microdomains to the geometrical and molecular mechanical mismatch of lipids of different species on the boundary. Here we introduce the geodesic curvature to characterize the geometry of the domain boundary, and develop a geodesic curvature energy model to describe the formation of these microdomains as a result of energy minimization. Our model accepts the intrinsic geodesic curvature of any binary lipid mixture as an input, and will produce microdomains of the given geodesic curvature as demonstrated by three sets of numerical simulations. Our results are in contrast to the surface phase separation predicted by the classical surface Cahn-Hilliard equation, which tends to generate large domains as a result of the minimizing line tension. Our model provides a direct and quantified description of the structure inhomogeneity of lipid bilayer membrane, and can be coupled to the investigations of biological processes on membranes for which such inhomogeneity plays essential roles.
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.
Stability and control of compressible flows over a surface with concave-conves curvature
NASA Technical Reports Server (NTRS)
Maestrello, L.; Bayliss, A.; Parikh, P.; Turkel, E.
1986-01-01
The active control of spatially unstable disturbances in a laminar, two-dimensional, compressible boundary layer over a curved surface is numerically simulated. The control is effected by localized time-periodic surface heating. We consider two similar surfaces of different heights with concave-convex curvature. In one, the height is sufficiently large so that the favorable pressure gradient is sufficient to stabilize a particular disturbance. In the other case the pressure gradient induced by the curvature is destabilizing. It is shown that by using active control that the disturbance can be stabilized. The results demonstrate that the curvature induced mean pressure gradient significantly enhances the receptivity of the flow localized time-periodic surface heating and that this is a potentially viable mechanism in air.
Seismological Constraints on Fault Plane Curvature
NASA Astrophysics Data System (ADS)
Reynolds, K.
2015-12-01
The down-dip geometry of seismically active normal faults is not well known. Many examples of normal faults with down-dip curvature exist, such as listric faults revealed in cross-section or in seismic reflection data, or the exposed domes of core complexes. However, it is not understood: (1) whether curved faults fail in earthquakes, and (2) if those faults have generated earthquakes, is the curvature a primary feature of the rupture or due to later modification of the plane? Even if an event is surface-rupturing, because of the limited depth-extent over which observations can be made, it is difficult to reliably constrain the change in dip with depth (if any) and therefore the fault curvature. Despite the uncertainty in seismogenic normal fault geometries, published slip inversions most commonly use planar fault models. We investigate the seismological constraints on normal fault geometry using a forward-modelling approach and present a seismological technique for determining down-dip geometry. We demonstrate that complexity in the shape of teleseismic body waveforms may be used to investigate the presence of down-dip fault plane curvature. We have applied this method to a catalogue of continental and oceanic normal faulting events. Synthetic models demonstrate that the shapes of SH waveforms at along-strike stations are particularly sensitive to fault plane geometry. It is therefore important to consider the azimuthal station coverage before modelling an event. We find that none of the data require significant down-dip curvature, although the modelling results for some events remain ambiguous. In some cases we can constrain that the down-dip fault geometry is within 20° of planar.
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.
Improving the Sensitivity of Astronomical Curvature Wavefront Sensor Using Dual-Stroke Curvature
NASA Astrophysics Data System (ADS)
Guyon, Olivier; Blain, Celia; Takami, Hideki; Hayano, Yutaka; Hattori, Masayuki; Watanabe, Makoto
2008-06-01
Curvature wavefront sensors measure wavefront phase aberration by acquiring two intensity images on either side of the pupil plane. Low-order adaptive optics (AO) systems using curvature wavefront sensing (CWFS) have proved to be highly efficient for astronomical applications: they are more sensitive, use fewer detector elements, and achieve, for the same number of actuators, higher Strehl ratios than AO systems using more traditional Shack-Hartmann wavefront sensors. In higher-order systems, however, curvature wavefront sensors lose sensitivity to low spatial frequencies wavefront aberrations. This effect, often described as “noise propagation,” limits the usefulness of curvature wavefront sensing for high-order AO systems and/or large telescopes. In this paper, we first explain how this noise propagation effect occurs and then show that this limitation can be overcome by acquiring four defocused images of the pupil instead of two. This solution can be implemented without significant technology development and can run with a simple linear wavefront reconstruction algorithm at >kHz speed. We have successfully demonstrated in the laboratory that the four conjugation planes can be sequentially obtained at >kHz speed using a speaker-vibrating membrane assembly commonly used in current curvature AO systems. Closed loop simulations show that implementing this scheme is equivalent to making the guide star 1 to 1.5 magnitude brighter for the configuration tested (188 actuator elements on 8-m telescope). Higher sensitivity gains are expected on curvature systems with higher number of actuators.
Inequalities for scalar curvature of pseudo-Riemannian submanifolds
NASA Astrophysics Data System (ADS)
Tripathi, Mukut Mani; Gülbahar, Mehmet; Kılıç, Erol; Keleş, Sadık
2017-02-01
Some basic inequalities, involving the scalar curvature and the mean curvature, for a pseudo-Riemannian submanifold of a pseudo-Riemannian manifold are obtained. We also find inequalities for spacelike submanifolds. Equality cases are also discussed.
Seo, Shogo; Ochi, Takanori; Yazaki, Yuta; Murakami, Hiroshi; Okawada, Manabu; Doi, Takashi; Miyano, Go; Koga, Hiroyuki; Lane, Geoffrey J; Yamataka, Atsuyuki
2016-10-01
To report our experience of correcting penile ventral curvature associated with minor or no hypospadias. We reviewed 43 penile ventral curvature patients treated by a single surgeon from 1997 to 2015. Of these, 23 had minor hypospadias. Curvature was corrected using degloving, chordectomy, dorsal plication (DP), tunica albuginea incision (TAI), or a combination of these. Outcome was confirmed by induced artificial erection and post-operative appearance. Mean age at curvature correction was 3.2 ± 2.6 years. 17/43 had degloving and chordectomy (DC), 16/43 had DP after DC, and 10/43 had TAI after DC, because of ventral shortening and severe curvature caused by a short hypoplastic urethra. Other procedures required were primary meatoplasty (n = 4) and urethroplasty (UP; n = 1) at the time of curvature correction, and UP after correction of curvature (n = 11). Complications included recurrence of curvature after DP (n = 3/16; 18.8 %) and urethral stenosis after UP with tubed peritoneum (n = 1/10; 10 %). There were no recurrences of curvature in TAI cases. Parents reported penile cosmesis as good (n = 38; 88.4 %), acceptable (n = 4; 9.3 %), or poor (n = 1; 2.3 %). We recommend TAI followed by UP for correcting penile ventral curvature with short hypoplastic urethra. Tubed peritoneum is not recommended for UP.
Laser triangulation measurements of scoliotic spine curvatures.
Čelan, Dušan; Jesenšek Papež, Breda; Poredoš, Primož; Možina, Janez
2015-01-01
The main purpose of this research was to develop a new method for differentiating between scoliotic and healthy subjects by analysing the curvatures of their spines in the cranio-caudal view. The study included 247 subjects with physiological curvatures of the spine and 28 subjects with clinically confirmed scoliosis. The curvature of the spine was determined by a computer analysis of the surface of the back, measured with a non-invasive, 3D, laser-triangulation system. The determined spinal curve was represented in the transversal plane, which is perpendicular to the line segment that was defined by the initial point and the end point of the spinal curve. This was achieved using a rotation matrix. The distances between the extreme points in the antero-posterior (AP) and left-right (LR) views were calculated in relation to the length of the spine as well as the quotient of these two values LR/AP. All the measured parameters were compared between the scoliotic and control groups using the Student's t-Test in case of normal data and Kruskal-Wallis test in case of non-normal data. Besides, a comprehensive diagram representing the distances between the extreme points in the AP and LR views was introduced, which clearly demonstrated the direction and the size of the thoracic and lumbar spinal curvatures for each individual subject. While the distances between the extreme points of the spine in the AP view were found to differ only slightly between the groups (p = 0.1), the distances between the LR extreme points were found to be significantly greater in the scoliosis group, compared to the control group (p < 0.001). The quotient LR/AP was statistically significantly different in both groups (p < 0.001). The main innovation of the presented method is the ability to differentiate a scoliotic subject from a healthy subject by assessing the curvature of the spine in the cranio-caudal view. Therefore, the proposed method could be useful for human posture
Zemel, Assaf; Ben-Shaul, Avinoam; May, Sylvio
2008-06-12
Amphipathic alpha-helical peptides are often ascribed an ability to induce curvature stress in lipid membranes. This may lead directly to a bending deformation of the host membrane, or it may promote the formation of defects that involve highly curved lipid layers present in membrane pores, fusion intermediates, and solubilized peptide-micelle complexes. The driving force is the same in all cases: peptides induce a spontaneous curvature in the host lipid layer, the sign of which depends sensitively on the peptide's structural properties. We provide a quantitative account for this observation on the basis of a molecular-level method. To this end, we consider a lipid membrane with peptides interfacially adsorbed onto one leaflet at high peptide-to-lipid ratio. The peptides are modeled generically as rigid cylinders that interact with the host membrane through a perturbation of the conformational properties of the lipid chains. Through the use of a molecular-level chain packing theory, we calculate the elastic properties, that is, the spontaneous curvature and bending stiffness, of the peptide-decorated lipid membrane as a function of the peptide's insertion depth. We find a positive spontaneous curvature (preferred bending of the membrane away from the peptide) for small penetration depths of the peptide. At a penetration depth roughly equal to half-insertion into the hydrocarbon core, the spontaneous curvature changes sign, implying negative spontaneous curvature (preferred bending of the membrane toward the peptide) for large penetration depths. Despite thinning of the membrane upon peptide insertion, we find an increase in the bending stiffness. We discuss these findings in terms of how the peptide induces elastic stress.
Nontopological Saddle-Splay and Curvature Instabilities from Anisotropic Membrane Inclusions
NASA Astrophysics Data System (ADS)
Fournier, J. B.
1996-06-01
Anisotropic inclusions are shown to induce spontaneous deviatoric bendings in lipidic membranes, by orienting at right angles across the bilayer. In the limit of strong membrane curvatures, a nonanalytical bending energy term is generated that favors saddlelike and cylindrical shapes, without penalizing spherical ones. An ``egg-carton'' instability results in flat membranes as well as a wormlike shape instability for vesicles.
Constraining inverse-curvature gravity with supernovae.
Mena, Olga; Santiago, José; Weller, Jochen
2006-02-03
We show that models of generalized modified gravity, with inverse powers of the curvature, can explain the current accelerated expansion of the Universe without resorting to dark energy and without conflicting with solar system experiments. We have solved the Friedmann equations for the full dynamical range of the evolution of the Universe and performed a detailed analysis of supernovae data in the context of such models that results in an excellent fit. If we further include constraints on the current expansion of the Universe and on its age, we obtain that the matter content of the Universe is 0.07
Static optical designs for Wavefront Curvature Sensing
NASA Astrophysics Data System (ADS)
Bharmal, Nazim A.
2006-06-01
A bulk optic is presented, the Parallel Output Beamsplitter, which allows simultaneous imaging of two planes either side of the focus using static imaging optics. The POB is used to create novel optical configurations for Wavefront Curvature Sensing and two designs are presented. The first is suited to small-amplitude aberration measurements in situations where compactness, a large field of view, and high optical throughput are desirable. A laboratory experiment using a POB to make such a wavefront sensor was undertaken, and results are presented. The second design is a conceptual idea which offers image-scale invariant imaging of two planes whose conjugation satisfies the requirements of a conventional Wavefront Curvature Sensor concept.
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.
Effect of intrinsic curvature on semiflexible polymers
NASA Astrophysics Data System (ADS)
Ghosh, Surya K.; Singh, Kulveer; Sain, Anirban
2009-11-01
Recently many important biopolymers have been found to possess intrinsic curvature. Tubulin protofilaments in animal cells, FtsZ filaments in bacteria and double stranded DNA are examples. We examine how intrinsic curvature influences the conformational statistics of such polymers. We give exact results for the tangent-tangent spatial correlation function C(r)=⟨t̂(s).t̂(s+r)⟩ , both in two and three dimensions. Contrary to expectation, C(r) does not show any oscillatory behavior, rather decays exponentially and the effective persistence length has strong length dependence for short polymers. We also compute the distribution function P(R) of the end to end distance R and show how curved chains can be distinguished from wormlike chains using loop formation probability.
Curvature suppresses the Rayleigh-Taylor instability
Trinh, Philippe H.; Kim, Hyoungsoo; Hammoud, Naima; ...
2014-05-20
We studied the dynamics of a thin liquid film on the underside of a curved cylindrical substrate. The evolution of the liquid layer is investigated as the film thickness and the radius of curvature of the substrate are varied. A dimensionless parameter (a modified Bond number) that incorporates both geometric parameters, gravity, and surface tension is identified, and allows the observations to be classified according to three different flow regimes: stable films, films with transient growth of perturbations followed by decay, and unstable films. We found that the experiments and theory confirm that, below a critical value of the Bondmore » number, curvature of the substrate suppresses the Rayleigh-Taylor instability.« less
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.
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.
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
Pereira, Thiago S.; Marugán, Guillermo A. Mena; Carneiro, Saulo E-mail: mena@iem.cfmac.csic.es
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.
2012-09-01
comparisons. The importance of not suffering from flow induced side forces and yawing moments is critical since the UCAV 1303 is a tailless aircraft and...A MANEUVERING UCAV 1303 AIRCRAFT MODEL AND ITS CONTROL THROUGH LEADING EDGE CURVATURE CHANGE by Christopher M. Medford September 2012...COVERED Master’s Thesis 4. TITLE AND SUBTITLE The Aerodynamics of a Maneuvering UCAV 1303 Aircraft Model and its Control through Leading Edge Curvature
CURVATURE EFFECT QUANTIFICATION FOR IN-VIVO IR THERMOGRAPHY
Cheng, Tze-Yuan; Deng, Daxiang; Herman, Cila
2013-01-01
Medical Infrared (IR) Imaging has become an important diagnostic tool over recent years. However, one underlying problem in medical diagnostics is associated with accurate quantification of body surface temperatures. This problem is caused by the artifacts induced by the curvature of objects, which leads to inaccurate temperature mapping and biased diagnostic results. Therefore, in our study, an experiment-based analysis is conducted to address the curvature effects toward the 3D temperature reconstruction of the IR thermography image. For quantification purposes, an isothermal copper plate with flat surface, and a cylindrical metal container filled with water are imaged. For the flat surface, the tilting angle measured from camera axis was varied incrementally from 0° to 60 °, such that the effects of surface viewing angle and travel distance on the measured temperature can be explored. On the cylindrical curved surface, the points viewed from 0° to 90° with respect to the camera axis are simultaneously imaged at different temperature levels. The experimental data obtained for the flat surface indicate that both viewing angle and distance effects become noticeable for angles over 40 °. The travel distance contributes a minor change when compared with viewing angle. The experimental results from the curved surface indicate that the curvature effect becomes pronounced when the viewing angle is larger than 60 °. The measurement error on the curved surface is compared with the simulation using the non-dielectric model, and the normalized temperature difference relative to 0° viewing angle was analyzed at six temperature levels. These results indicate that the linear formula associated with directional emissivity is a reasonable approximation for the measurement error, and the normalized error curves change consistently with viewing angle at various temperatures. Therefore, the analysis in this study implies that the directional emissivity based on the non
Controlling Hamiltonian chaos via Gaussian curvature.
Oloumi, A; Teychenné, D
1999-12-01
We present a method allowing one to partly stabilize some chaotic Hamiltonians which have two degrees of freedom. The purpose of the method is to avoid the regions of V(q(1),q(2)) where its Gaussian curvature becomes negative. We show the stabilization of the Hénon-Heiles system, over a wide area, for the critical energy E=1/6. Total energy of the system varies only by a few percent.
Generalization of Seidel astigmatism and Petzval curvature.
Gaj, M
1966-06-01
In a paper probably to be published in Optika i Spektroskopiya the wave aberration for sagittal focus for the arbitrary surface of rotational symmetry has been carried out on the base of the astigmatic beam invariant D(s) = nu(s)d(s). The resulting expression for the wave aberration has been reformulated into three terms which, in the Seidel region, go over into astigmatism (the first) and into the Petzval curvature (the second) while the third disappears.
Breeding curvature from extended gauge covariance
NASA Astrophysics Data System (ADS)
Aldrovandi, R.
1991-05-01
Independence between spacetime and “internal” space in gauge theories is related to the adjoint-covariant behaviour of the gauge potential. The usual gauge scheme is modified to allow a coupling between both spaces. Gauging spacetime translations produce field equations similar to Einstein equations. A curvature-like quantity of mixed differential-algebraic character emerges. Enlarged conservation laws are present, pointing to the presence of an covariance.
Curvature of spacetime: A simple student activity
NASA Astrophysics Data System (ADS)
Wood, Monika; Smith, Warren; Jackson, Matthew
2016-12-01
The following is a description of an inexpensive and simple student experiment for measuring the differences between the three types of spacetime topology—Euclidean (flat), Riemann (spherical), and Lobachevskian (saddle) curvatures. It makes use of commonly available tools and materials, and requires only a small amount of construction. The experiment applies to astronomical topics such as gravity, spacetime, general relativity, as well as geometry and mathematics.
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.
Holonomy Attractor Connecting Spaces of Different Curvature Responsible for ``Anomalies''
NASA Astrophysics Data System (ADS)
Binder, Bernd
2009-03-01
In this lecture paper we derive Magic Angle Precession (MAP) from first geometric principles. MAP can arise in situations, where precession is multiply related to spin, linearly by time or distance (dynamic phase, rolling, Gauss law) and transcendentally by the holonomy loop path (geometric phase). With linear spin-precession coupling, gyroscopes can be spun up and down to very high frequencies via low frequency holonomy control induced by external accelerations, which provides for extreme coupling strengths or "anomalies" that can be tested by the powerball or gyrotwister device. Geometrically, a gyroscopic manifold with spherical metric is tangentially aligned to a precession wave channel with conic or hyperbolic metric (like the relativistic Thomas precession). Transporting triangular spin/precession vector relations across the tangential boundary of contact with SO(3) Lorentz symmetry, we get extreme vector currents near the attractor fixed points in precession phase space, where spin currents remain intact while crossing the contact boundaries between regions of different curvature signature (-1, 0, +1). The problem can be geometrically solved by considering a curvature invariant triangular condition, which holds on surfaces with different curvature that are in contact and locally parallel. In this case two out of three angles are identical, whereas the third angle is different due to holonomy. If we require that the side length ratio corresponding to these angles are invariant we get a geodesic chaotic attractor, which is a cosine map cos(x)˜Mx in parameter space providing for fixed points, limit cycle bifurcations, and singularities. The situation could be quite natural and common in the context of vector currents in curved spacetime and gauge theories. MAP could even be part of the electromagnetic interaction, where the electric charge is the geometric U(1) precession spin current and gauge potential with magnetic effects given by extra rotations under the
Intrinsically disordered proteins drive membrane curvature
Busch, David J.; Houser, Justin R.; Hayden, Carl C.; Sherman, Michael B.; Lafer, Eileen M.; Stachowiak, Jeanne C.
2015-01-01
Assembly of highly curved membrane structures is essential to cellular physiology. The prevailing view has been that proteins with curvature-promoting structural motifs, such as wedge-like amphipathic helices and crescent-shaped BAR domains, are required for bending membranes. Here we report that intrinsically disordered domains of the endocytic adaptor proteins, Epsin1 and AP180 are highly potent drivers of membrane curvature. This result is unexpected since intrinsically disordered domains lack a well-defined three-dimensional structure. However, in vitro measurements of membrane curvature and protein diffusivity demonstrate that the large hydrodynamic radii of these domains generate steric pressure that drives membrane bending. When disordered adaptor domains are expressed as transmembrane cargo in mammalian cells, they are excluded from clathrin-coated pits. We propose that a balance of steric pressure on the two surfaces of the membrane drives this exclusion. These results provide quantitative evidence for the influence of steric pressure on the content and assembly of curved cellular membrane structures. PMID:26204806
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
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.
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.
Effects of wall curvature on turbulence statistics
NASA Technical Reports Server (NTRS)
Moser, R. D.; Moin, P.
1985-01-01
A three-dimensional, time-dependent, direct numerical simulation of low-Reynolds number turbulent flow in a mildly curved channel was performed, and the results examined to determine the mechanism by which curvature affects wall-bounded turbulent shear flows. A spectral numerical method with about one-million modes was employed, and no explicit subgrid scale model was used. The effects of curvature on this flow were determined by comparing the concave and convex sides of the channel. The observed effects are consistent with experimental observations for mild curvature. The most significant difference in the turbulence statistics between the concave and convex sides is in the Reynolds shear stress. This is accompanied by significant differences in the terms of the Reynolds shear stress balance equations. In addition, it was found that stationary Taylor-Goertler vortices were present and that they had a significant effect on the flow by contributing to the mean Reynolds shear stress, and by enhancing the difference between the wall shear stresses.
Intrinsically disordered proteins drive membrane curvature.
Busch, David J; Houser, Justin R; Hayden, Carl C; Sherman, Michael B; Lafer, Eileen M; Stachowiak, Jeanne C
2015-07-24
Assembly of highly curved membrane structures is essential to cellular physiology. The prevailing view has been that proteins with curvature-promoting structural motifs, such as wedge-like amphipathic helices and crescent-shaped BAR domains, are required for bending membranes. Here we report that intrinsically disordered domains of the endocytic adaptor proteins, Epsin1 and AP180 are highly potent drivers of membrane curvature. This result is unexpected since intrinsically disordered domains lack a well-defined three-dimensional structure. However, in vitro measurements of membrane curvature and protein diffusivity demonstrate that the large hydrodynamic radii of these domains generate steric pressure that drives membrane bending. When disordered adaptor domains are expressed as transmembrane cargo in mammalian cells, they are excluded from clathrin-coated pits. We propose that a balance of steric pressure on the two surfaces of the membrane drives this exclusion. These results provide quantitative evidence for the influence of steric pressure on the content and assembly of curved cellular membrane structures.
Biophysical and genetic aspects of light-potentiated gravitropic curvature in the maize primary root
Fantin, D.M.
1991-04-01
This thesis explores issues related to light-induced gravitotropic curvature in maize primary roots, such as the root cap as the potential photosensor, entrainment by light of curvature in the gravistimulated root, and the possibility of genetic control of bending response variation. Central to this thesis is a mathematical model, emphasizing physical forces and molecular flows, linking the stages of light-stimulated gravitropic curvature. The model assumes a growth inhibitor is produced in the root cap, transported by diffusion to the extension zone, transported by convection around the extension zone where it retards growth at a rate proportional to its concentration. Model predictions were compared to experimental data to evaluate these assumptions. The root cap is shown to be the photosensor, and genetic crosses show that more than two genes must control the bending response. 140 refs., 31 figs., 11 tabs.
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.
Anomalous Nernst and Righi-Leduc Effects in Mn3Sn : Berry Curvature and Entropy Flow
NASA Astrophysics Data System (ADS)
Li, Xiaokang; Xu, Liangcai; Ding, Linchao; Wang, Jinhua; Shen, Mingsong; Lu, Xiufang; Zhu, Zengwei; Behnia, Kamran
2017-08-01
We present a study of electric, thermal and thermoelectric response in noncollinear antiferromagnet Mn3Sn , which hosts a large anomalous Hall effect (AHE). Berry curvature generates off-diagonal thermal (Righi-Leduc) and thermoelectric (Nernst) signals, which are detectable at room temperature and invertible with a small magnetic field. The thermal and electrical Hall conductivities respect the Wiedemann-Franz law, implying that the transverse currents induced by the Berry curvature are carried by Fermi surface quasiparticles. In contrast to conventional ferromagnets, the anomalous Lorenz number remains close to the Sommerfeld number over the whole temperature range of study, excluding any contribution by inelastic scattering and pointing to the Berry curvature as the unique source of AHE. The anomalous off-diagonal thermo-electric and Hall conductivities are strongly temperature dependent and their ratio is close to kB/e .
NASA Astrophysics Data System (ADS)
Enea Romano, Antonio; Sanes Negrete, Sergio; Sasaki, Misao; Starobinsky, Alexei A.
2014-06-01
We study effects on the luminosity distance of a local inhomogeneity seeded by primordial curvature perturbations of the type predicted by the inflationary scenario and constrained by the cosmic microwave background radiation. We find that a local underdensity originated from a one, two or three standard deviations peaks of the primordial curvature perturbations field can induce corrections to the value of a cosmological constant of the order of 0.6{%},1{%},1.5{%} , respectively. These effects cannot be neglected in the precision cosmology era in which we are entering. Our results can be considered an upper bound for the effect of the monopole component of the local non-linear structure which can arise from primordial curvature perturbations and requires a fully non-perturbative relativistic treatment.
Curvature-driven lateral segregation of membrane constituents in Golgi cisternae
NASA Astrophysics Data System (ADS)
Derganc, Jure
2007-12-01
Lateral segregation of mobile membrane constituents (e.g. lipids, proteins or membrane domains) into the regions of their preferred curvature relaxes stresses in the membrane. The equilibrium distribution of the constituents in the membrane is thus a balance between the gains in the membrane elastic energy and the segregation-induced loss of entropy. The membrane in the Golgi cisternae is particularly susceptible to the curvature-driven segregation because it possesses two very different curvatures—the highly curved membrane in the cisternal rims and the flat membrane in the cisternal sides. In this work, we calculate the extent of lateral segregation in the Golgi cisternae in the case where the segregation is driven by the Helfrich bending energy. It is assumed that the membrane bending constant and spontaneous curvature depend on the local membrane composition. A simple analytical expression for the extent of the lateral segregation is derived. The results show that the segregation depends on the ratio between the bending constant and the thermal energy, the difference of the preferred curvatures of the constituents and the sizes of the constituents. Applying the model to a typical Golgi cisterna, it was found that entropy can effectively limit the extent of the curvature-driven lateral segregation.
Congenital penile curvature: long-term results of operative treatment using the plication procedure.
Lee, S-S; Meng, E; Chuang, F-P; Yen, C-Y; Chang, S-Y; Yu, D-S; Sun, G-H
2004-09-01
To determine the long-term outcome, effectiveness and patient satisfaction of congenital penile curvature correction by plication of tunica albuginea. From January 1992 to January 2002, 106 young patients underwent surgical correction of congenital penile curvature by corporeal plication. Indications for operation were difficult or impossible vaginal penetration and cosmetic problems. The technique of corporeal plication consists of placing longitudinal plication sutures of 2-zero braided polyester on the convex side of the curvature until the curvature is corrected when erection is artificially induced. Results of this procedure were obtained by retrospective chart reviews and questionnaires via mail. Long-term follow-up ranged from 11 to 132 (mean 69.3) months and data were available for 68 patients. Penile straightening was excellent in 62 patients (91 %) and good with less than 15 degree of residual curvature in 6 patients (9 %). Sixty-seven patients reported no change in erectile rigidity or maintenance postoperatively, while 1 described early detumescence. Shortening of the penis without functional problems was noted by 26 patients (38 %). Thirty-Five patients (51 %) reported feeling palpable indurations (suture knots) on the penis. Temporary numbness of glans penis was described in 3 patients. Overall, 60 patients were very satisfied, 6 satisfied, 2 unsatisfied. Corporeal plication is an effective and durable procedure with a high rate of patient satisfaction.
Free-streaming radiation in cosmological models with spatial curvature
NASA Technical Reports Server (NTRS)
Wilson, M. L.
1982-01-01
The effects of spatial curvature on radiation anisotropy are examined for the standard Friedmann-Robertson-Walker model universes. The effect of curvature is found to be very important when considering fluctuations with wavelengths comparable to the horizon. It is concluded that the behavior of radiation fluctuations in models with spatial curvature is quite different from that in spatially flat models, and that models with negative curvature are most strikingly different. It is therefore necessary to take the curvature into account in careful studies of the anisotropy of the microwave background.
Schmidt, Nathan W.; Mishra, Abhijit; Wang, Jun; DeGrado, William F.; Wong, Gerard C. L.
2013-01-01
The M2 protein is a multi-functional protein, which plays several roles in the replication cycle of the influenza A virus. Here we focus on its ability to promote budding of the mature virus from the cell surface. Using high resolution small angle X-ray scattering we show that M2 can restructure lipid membranes into bicontinuous cubic phases which are rich in negative Gaussian curvature (NGC). The active generation of negative Gaussian membrane curvature by M2 is essential to influenza virus budding. M2 has been observed to colocalize with the region of high NGC at the neck of a bud. The structural requirements for scission are even more stringent than those for budding, as the neck must be considerably smaller than the virus during ‘pinch off’. Consistent with this, the amount of NGC in the induced cubic phases suggests that M2 proteins can generate high curvatures comparable to those on a neck with size 10x smaller than a spherical influenza virus. Similar experiments on variant proteins containing different M2 domains show that the cytoplasmic amphipathic helix is necessary and sufficient for NGC generation. Mutations to the helix which reduce its amphiphilicity and are known to diminish budding attenuated NGC generation. An M2 construct comprising the membrane interactive domains, the transmembrane helix and the cytoplasmic helix, displayed enhanced ability to generate NGC, suggesting that other domains cooperatively promote membrane curvature. These studies establish the importance of M2-induced negative Gaussian curvature during budding and suggest that antagonizing this curvature is a viable anti-influenza strategy. PMID:23962302
On the Riemann Curvature Operators in Randers Spaces
NASA Astrophysics Data System (ADS)
Rafie-Rad, M.
2013-05-01
The Riemann curvature in Riemann-Finsler geometry can be regarded as a collection of linear operators on the tangent spaces. The algebraic properties of these operators may be linked to the geometry and the topology of the underlying space. The principal curvatures of a Finsler space (M, F) at a point x are the eigenvalues of the Riemann curvature operator at x. They are real functions κ on the slit tangent manifold TM0. A principal curvature κ(x, y) is said to be isotropic (respectively, quadratic) if κ(x, y)/F(x, y) is a function of x only (respectively, κ(x, y) is quadratic with respect to y). On the other hand, the Randers metrics are the most popular and prominent metrics in pure and applied disciplines. Here, it is proved that if a Randers metric admits an isotropic principal curvature, then F is of isotropic S-curvature. The same result is also established for F to admit a quadratic principal curvature. These results extend Shen's verbal results about Randers metrics of scalar flag curvature K = K(x) as well as those Randers metrics with quadratic Riemann curvature operator. The Riemann curvature Rik may be broken into two operators Rik and Jik. The isotropic and quadratic principal curvature are characterized in terms of the eigenvalues of R and J.
A Novel Quantitative Measure of Breast Curvature Based on Catenary
Lee, Juhun; Chen, Si; Reece, Gregory P.; Crosby, Melissa A.; Beahm, Elisabeth K.
2012-01-01
Quantitative, objective measurements of breast curvature computed from clinical photographs could be used to investigate factors that impact reconstruction and facilitate surgical planning. This paper introduces a novel quantitative measure of breast curvature based on catenary. A catenary curve is used to approximate the overall curvature of the breast contour, and the curvature measure is extracted from the catenary curve. The catenary curve was verified by comparing its length, the area enclosed by the curve, and the curvature measure from the catenary curve to those from manual tracings of the breast contour. The evaluation of the proposed analysis employed untreated and postoperative clinical photographs of women who were undergoing tissue expander/implant (TE/Implant) reconstruction. Logistic regression models were developed to distinguish between the curvature of breasts undergoing TE/Implant reconstruction and that of untreated breasts based on the curvature measure and patient variables (age and body mass index). The relationships between the curvature measures of untreated breasts and patient variables were also investigated. The catenary curve approximates breast curvature reliably. The curvature measure contains useful information for quantifying the curvature differences between breasts undergoing TE/Implant reconstruction and untreated breasts, and identifying the effect of patient variables on the breast shape. PMID:22271826
A novel quantitative measure of breast curvature based on catenary.
Lee, Juhun; Chen, Si; Reece, Gregory P; Crosby, Melissa A; Beahm, Elisabeth K; Markey, Mia K
2012-04-01
Quantitative, objective measurements of breast curvature computed from clinical photographs could be used to investigate factors that impact reconstruction and facilitate surgical planning. This paper introduces a novel quantitative measure of breast curvature based on catenary. A catenary curve is used to approximate the overall curvature of the breast contour, and the curvature measure is extracted from the catenary curve. The catenary curve was verified by comparing its length, the area enclosed by the curve, and the curvature measure from the catenary curve to those from manual tracings of the breast contour. The evaluation of the proposed analysis employed untreated and postoperative clinical photographs of women who were undergoing tissue expander/implant (TE/Implant) reconstruction. Logistic regression models were developed to distinguish between the curvature of breasts undergoing TE/Implant reconstruction and that of untreated breasts based on the curvature measure and patient variables (age and body mass index). The relationships between the curvature measures of untreated breasts and patient variables were also investigated. The catenary curve approximates breast curvature reliably. The curvature measure contains useful information for quantifying the curvature differences between breasts undergoing TE/Implant reconstruction and untreated breasts, and identifying the effect of patient variables on the breast shape.
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
2016-12-01
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.
Higher Curvature Gravity in TeV-Scale Extra Dimensions
Rizzo, Thomas G.
2006-03-31
We begin a general exploration of the phenomenology of TeV-scale extra-dimensional models with gravitational actions that contain higher curvature terms. In particular, we examine how the classic collider signatures of the models of Arkani-Hamed, Dimopoulos and Dvali (missing energy and new dimension-8 contact interactions) and of Randall and Sundrum (TeV-scale graviton Kaluza-Klein resonances) are altered by these modifications to the usual Einstein-Hilbert action. We find that not only are the detailed signatures for these gravitationally induced processes altered but new contributions are found to arise due to the existence of additional scalar Kaluza-Klein states in the spectrum.
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
2014-01-01
SUMMARY 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
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. Copyright © 2014 Elsevier Inc. All rights reserved.
Amplification of curvature perturbations in cyclic cosmology
NASA Astrophysics Data System (ADS)
Zhang, Jun; Liu, Zhi-Guo; Piao, Yun-Song
2010-12-01
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.
Solitons in curved space of constant curvature
Batz, Sascha; Peschel, Ulf
2010-05-15
We consider spatial solitons as, for example, self-confined optical beams in spaces of constant curvature, which are a natural generalization of flat space. Due to the symmetries of these spaces we are able to define respective dynamical parameters, for example, velocity and position. For positively curved space we find stable multiple-hump solitons as a continuation from the linear modes. In the case of negatively curved space we show that no localized solution exists and a bright soliton will always decay through a nonlinear tunneling process.
Zero curvature-surface driven small objects
NASA Astrophysics Data System (ADS)
Dou, Xiaoxiao; Li, Shanpeng; Liu, Jianlin
2017-08-01
In this study, we investigate the spontaneous migration of small objects driven by surface tension on a catenoid, formed by a layer of soap constrained by two rings. Although the average curvature of the catenoid is zero at each point, the small objects always migrate to the position near the ring. The force and energy analyses have been performed to uncover the mechanism, and it is found that the small objects distort the local shape of the liquid film, thus making the whole system energetically favorable. These findings provide some inspiration to design microfluidics, aquatic robotics, and miniature boats.
Double curvature mirrors for linear concentrators
NASA Astrophysics Data System (ADS)
Lance, Tamir; Ackler, Harold; Finot, Marc
2012-10-01
Skyline Solar's medium concentration photovoltaic system uses quasi-parabolic mirrors and one axis tracking. Improvements in levelized cost of energy can be achieved by effective management of non-uniformity of the flux line on the panels. To reduce non uniformity of the flux line due to mirror to mirror gaps, Skyline developed a dual curvature mirror that stretches the flux line along the panel. Extensive modeling and experiments have been conducted to analyze the impact of this new design and to optimize the design.
Steering electromagnetic beams with conical curvature singularities.
Zhang, Yong-Liang; Dong, Xian-Zi; Zheng, Mei-Ling; Zhao, Zhen-Sheng; Duan, Xuan-Ming
2015-10-15
We describe how the transformation-optics technique can be used to design an effective medium mimicking the conical curvature singularity. Anholonomic coordinate transformation gives rise to linear topological defects that break the rotational symmetry. The bending and splitting of the optical beams are found analytically and numerically, depending on the incident direction and the topological charge. Beyond their practical applications to omnidirectional beam steering for photonics, our findings set forth an attractive realm to simulate the relevant physical phenomena in the optical laboratory.
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.
Curvature-Driven Lipid Sorting in Biomembranes
Callan-Jones, Andrew; Sorre, Benoit; Bassereau, Patricia
2011-01-01
It has often been suggested that the high curvature of transport intermediates in cells may be a sufficient means to segregate different lipid populations based on the relative energy costs of forming bent membranes. In this review, we present in vitro experiments that highlight the essential physics of lipid sorting at thermal equilibrium: It is driven by a trade-off between bending energy, mixing entropy, and interactions between species. We collect evidence that lipid sorting depends strongly on lipid–lipid and protein–lipid interactions, and hence on the underlying composition of the membrane and on the presence of bound proteins. PMID:21421916
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.
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.
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
Lauric, Alexandra; Hippelheuser, James; Safain, Mina G.; Malek, Adel M.
2014-01-01
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 3 mm 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. PMID:25062932
Xu, Jinyu; Wu, Zhichen; Yu, Ying; Lv, Nan; Wang, Shengzhang; Karmonik, Christof; Liu, Jian-Min; Huang, Qinghai
2015-01-01
Flow diverters (FD) are increasingly being considered for treating large or giant wide-neck aneurysms. Clinical outcome is highly variable and depends on the type of aneurysm, the flow diverting device and treatment strategies. The objective of this study was to analyze the effect of different flow diverting strategies together with parent artery curvature variations on altering intra-aneurysmal hemodynamics. Four ideal intracranial aneurysm models with different parent artery curvature were constructed. Computational fluid dynamics (CFD) simulations of the hemodynamics before and after applying five types of flow diverting strategies (single FD, single FD with 5% and 10% packing density of coils, two FDs with 25% and 50% overlapping rate) were performed. Changes in pressure, wall shear stress (WSS), relative residence time (RRT), inflow velocity and inflow volume rate were calculated and compared. Each flow diverting strategy resulted in enhancement of RRT and reduction of normalized mean WSS, inflow volume rate and inflow velocity in various levels. Among them, 50% overlapped FD induced most effective hemodynamic changes in RRT and inflow volume rate. The mean pressure only slightly decreased after treatment. Regardless of the kind of implantation of FD, the mean pressure, inflow volume rate and inflow velocity increased and the RRT decreased as the curvature of the parent artery increased. Of all flow diverting strategies, overlapping FDs induced most favorable hemodynamic changes. Hemodynamics alterations post treatment were substantially influenced by parent artery curvature. Our results indicate the need of an individualized flow diverting strategy that is tailored for a specific aneurysm.
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.
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.
Kinetic information from detonation front curvature
Souers, P. C., LLNL
1998-06-15
The time constants for time-dependent modeling may be estimated from reaction zone lengths, which are obtained from two sources One is detonation front curvature, where the edge lag is close to being a direct measure The other is the Size Effect, where the detonation velocity decreases with decreasing radius as energy is lost to the cylinder edge A simple theory that interlocks the two effects is given A differential equation for energy flow in the front is used, the front is described by quadratic and sixth-power radius terms The quadratic curvature comes from a constant power source of energy moving sideways to the walls Near the walls, the this energy rises to the total energy of detonation and produces the sixth-power term The presence of defects acting on a short reaction zone can eliminate the quadratic part while leaving the wall portion of the cuvature A collection of TNT data shows that the reaction zone increases with both the radius and the void fraction
Effects of streamline curvature on separation prediction
NASA Astrophysics Data System (ADS)
Arolla, Sunil K.; Durbin, Paul A.
2009-11-01
In this study, the effects of streamline curvature on prediction of flow separation are investigated. The geometry is a circulation control airfoil, a high-lift configuration that has been under extensive research for more than two decades. A tangential jet is blown over a thick, rounded trailing edge, using the Coanda effect to delay separation. An attempt is made to understand, through numerical simulations, the dynamics of turbulent separation and reattachment on the Coanda surface. Highly curved, attached recirculation regions are seen to form. A physics based curvature correction proposed by Pettersson-Reif et al. (1999) is used in conjunction with ζ-f turbulence model. The chord-based Reynolds number is Re = 10^6. Two jet momentum coefficients of Cμ=0.03 and 0.1 are computed. In this paper, comparisons between the computed and experimental pressure distributions, velocity profiles and the position of flow detachment are presented. Comparisons with other closures such as Menter's SST model are also discussed.
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.
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.
Emergent gravity in spaces of constant curvature
NASA Astrophysics Data System (ADS)
Alvarez, Orlando; Haddad, Matthew
2017-03-01
In physical theories where the energy (action) is localized near a submanifold of a constant curvature space, there is a universal expression for the energy (or the action). We derive a multipole expansion for the energy that has a finite number of terms, and depends on intrinsic geometric invariants of the submanifold and extrinsic invariants of the embedding of the submanifold. This is the second of a pair of articles in which we try to develop a theory of emergent gravity arising from the embedding of a submanifold into an ambient space equipped with a quantum field theory. Our theoretical method requires a generalization of a formula due to by Hermann Weyl. While the first paper discussed the framework in Euclidean (Minkowski) space, here we discuss how this framework generalizes to spaces of constant sectional curvature. We focus primarily on anti de Sitter space. We then discuss how such a theory can give rise to a cosmological constant and Planck mass that are within reasonable bounds of the experimental values.
Curvature Filters Efficiently Reduce Certain Variational Energies.
Gong, Yuanhao; Sbalzarini, Ivo F
2017-04-01
In image processing, the rapid approximate solution of variational problems involving generic data-fitting terms is often of practical relevance, for example in real-time applications. Variational solvers based on diffusion schemes or the Euler-Lagrange equations are too slow and restricted in the types of data-fitting terms. Here, we present a filter-based approach to reduce variational energies that contain generic data-fitting terms, but are restricted to specific regularizations. Our approach is based on reducing the regularization part of the variational energy, while guaranteeing non-increasing total energy. This is applicable to regularization-dominated models, where the data-fitting energy initially increases, while the regularization energy initially decreases. We present fast discrete filters for regularizers based on Gaussian curvature, mean curvature, and total variation. These pixel-local filters can be used to rapidly reduce the energy of the full model. We prove the convergence of the resulting iterative scheme in a greedy sense, and we show several experiments to demonstrate applications in image-processing problems involving regularization-dominated variational models.
Asymptotic behavior of curvature of surface elements in isotropic turbulence
NASA Technical Reports Server (NTRS)
Girimaji, S. S.
1991-01-01
The asymptotic behavior of the curvature of material elements in turbulence is investigated using Lagrangian velocity-gradient time series obtained from direct numerical simulations of isotropic turbulence. Several material-element ensembles of different initial curvatures and shapes are studied. It is found that, at long times, the (first five) moments of the logarithm of characteristic curvature and shape factor asymptote to values that are independent of the initial curvature or shape. This evidence strongly suggests that the asymptotic pdf's of the curvature and shape of material elements are stationary and independent of initial conditions. Irrespective of initial curvature or shape, the asymptotic shape of a material surface is cylindrical with a high probability.
Curvature and Tangency Handles for Control of Convex Cubic Shapes
2000-01-01
looked at A-splines constructed with segments of singular al- gebraic cubics, which are just rational cubics, with new, geometrically more meaningful...contact interpolation , and curvatures at three prescribed points, see Figures 1-4. Curve and Surface Design: Saint-Malo 1999 91 Pierre-Jean Laurent...curvature at one contact point. §2. Barycentric Coordinates and Curvature at the Endpoints The general algebraic cubic in cartesian coordinates x, y is
The curvature measurement of Sagnac loop based on PMF
NASA Astrophysics Data System (ADS)
Zhao, Yu; Jin, Yongxing; Gong, Huaping; Wang, Jianfeng
2010-12-01
An optical fiber curvature sensor is fabricated by using a short section of polarization maintaining fiber (PMF) as the sensing component spliced in an optical fiber Sagnac loop. The length of the sensing element for the curvature sensing is about 142 mm. The sensitivity of the curvature measurement of 0.0344 m-1/pm is achieved experimentally. The propose sensor is more convenient and simply than that of photonic crystal fiber (PCF).
Radius of Curvature of Off-Axis Paraboloids
NASA Technical Reports Server (NTRS)
Robinson, Brian; Reardon, Patrick; Hadaway, James; Geary, Joseph; Russell, Kevin (Technical Monitor)
2002-01-01
We present several methods for measuring the vertex radius of curvature of off-axis paraboloidal mirrors. One is based on least-squares fitting of interferometer output, one on comparison of sagittal and tangential radii of curvature, and another on measurement of displacement of the nulled test article from the ideal reference wave. Each method defines radius of curvature differently and, as a consequence, produces its own sort of errors.
A Direct Estimate of the Spatial Curvature of the Universe
NASA Astrophysics Data System (ADS)
Rosquist, Kjell; Samuelsson, Lars
The main idea of this contribution is to calculate the average spatial curvature directly from the observed mass distribution of the universe. In short, our philosophy is that the curvature of the universe is generated solely by the matter it contains. Although this may seem as self-evident in the context of general relativity, the usual practice in cosmology is rather to use a top-down approach in which the curvature is calculated indirectly using a prescribed matter distribution as a source of the Einstein equations. By contrast, our approach may be seen as part of a bottom-up approach. In practical terms, we first calculate the far field spatial curvature generated by an isolated matter distribution which is in arbitrary motion. At this stage we obtain the result that the sign of the spatial curvature is necessarily positive. For the spatial curvature generated by multiple sources we show that it is sufficient to use linearized theory to compute the leading contributions. In the matter dominated era the spatial curvature is then seen to be generated by local sources at small redshifts. This fact makes it possible to calculate the total spatial curvature just by summing up the contributions from the observed discrete mass distribution. A crude estimate gives a very small value for the curvature.
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.
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.
Evolution of the curvature perturbations during warm inflation
NASA Astrophysics Data System (ADS)
Matsuda, Tomohiro
2009-06-01
This paper considers warm inflation as an interesting application of multi-field inflation. Delta-N formalism is used for the calculation of the evolution of the curvature perturbations during warm inflation. Although the perturbations considered in this paper are decaying after the horizon exit, the corrections to the curvature perturbations sourced by these perturbations can remain and dominate the curvature perturbations at large scales. In addition to the typical evolution of the curvature perturbations, inhomogeneous diffusion rate is considered for warm inflation, which may lead to significant non-Gaussianity of the spectrum.
Inconsistency of scale invariant curvature coupled to gravity
Zoller, D.
1990-01-01
We show that the scale invariant curvature action for paths, the point particle version of Polyakov's extrinsic curvature action for surfaces, does not couple consistently to gravity. Although the curvature action for paths yields a massless representation of the Poincare group with fixed helicity and so potentially provides a description of single photons and gravitons, the inconsistent coupling to gravity apparently suggests such a description is not viable. We present a physical interpretation of the inconsistency in terms of the non-localizability of the photon and point out a conceptual kinship between the local symmetry of the curvature theory and the local supersymmetry of a spinning particle or spinning string. 11 refs.
The curvature index and synchronization of dynamical systems.
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.
Multi-scale curvature tensor analysis of machined surfaces
NASA Astrophysics Data System (ADS)
Bartkowiak, Tomasz; Brown, Christopher
2016-12-01
This paper demonstrates the use of multi-scale curvature analysis, an areal new surface characterization technique for better understanding topographies, for analyzing surfaces created by conventional machining and grinding. Curvature, like slope and area, changes with scale of observation, or calculation, on irregular surfaces, therefore it can be used for multi-scale geometric analysis. Curvatures on a surface should be indicative of topographically dependent behavior of a surface and curvatures are, in turn, influenced by the processing and use of the surface. Curvatures have not been well characterized previously. Curvature has been used for calculations in contact mechanics and for the evaluation of cutting edges. In the current work two parts were machined and then one of them was ground. The surface topographies were measured with a scanning laser confocal microscope. Plots of curvatures as a function of position and scale are presented, and the means and standard deviations of principal curvatures are plotted as a function of scale. Statistical analyses show the relations between curvature and these two manufacturing processes at multiple scales.
Anoxia promotes gravitropic curvature in rice pulvini but inhibits it in wheat and oat pulvini.
Azuma, Tetsushi; Inoue, Yoshitaka; Hamada, Yuma; Okishio, Takuma; Sasayama, Daisuke; Itoh, Kazuyuki
2013-09-01
Gravitropic curvature of pulvini of wheat and oat stem segments gradually declined with decreasing atmospheric O₂ concentration and was almost completely blocked under anoxia, whereas that of rice stem segments was enhanced under hypoxia and anoxia. Anoxia substantially increased the ethanol content in pulvini of gravistimulated stem segments in rice, wheat and oat, but the ethanol content showed no marked difference between rice pulvini and wheat and oat pulvini. The concentrations of exogenous ethanol and acetaldehyde required to inhibit the gravitropic curvature of pulvini were significantly higher in rice segments than in wheat and oat segments. However, in all three species, the concentrations of ethanol and acetaldehyde required to completely inhibit curvature were several-fold higher than the endogenous levels that accumulated in pulvini gravistimulated in N₂. The pulvini of rice segments gravistimulated in N₂ did not contain much more ATP than those of wheat or oat segments gravistimulated in N₂. When applied unilaterally to the pulvini of vertically oriented stem segments incubated in N₂, indole-3-acetic acid induced bending in rice stem segments but not in wheat and oat stem segments. Transference of graviresponsive pulvini of rice, as well as those of wheat and oat, from aerobic conditions to anaerobic conditions led to cessation of gravitropic curvature within several minutes, but subsequently only gravitropic curvature of anoxic rice pulvini was completely recovered within 2 h. A large portion of this recovery was blocked by cordycepin, a transcription inhibitor. These results suggested that anoxia-induced expression of any gene or genes enables rice pulvini to respond to gravistimulation under anaerobic conditions, and that such a gene or genes might be unrelated to ethanol fermentation and ATP production in anaerobic conditions. Copyright © 2013 Elsevier GmbH. All rights reserved.
Wang,W.; Yang, L.; Huang, H.
2007-01-01
Recent experiments suggested that cholesterol and other lipid components of high negative spontaneous curvature facilitate membrane fusion. This is taken as evidence supporting the stalk-pore model of membrane fusion in which the lipid bilayers go through intermediate structures of high curvature. How do the high-curvature lipid components lower the free energy of the curved structure? Do the high-curvature lipid components modify the average spontaneous curvature of the relevant monolayer, thereby facilitate its bending, or do the lipid components redistribute in the curved structure so as to lower the free energy? This question is fundamental to the curvature elastic energy for lipid mixtures. Here we investigate the lipid distribution in a monolayer of a binary lipid mixture before and after bending, or more precisely in the lamellar, hexagonal, and distorted hexagonal phases. The lipid mixture is composed of 2:1 ratio of brominated di18:0PC and cholesterol. Using a newly developed procedure for the multiwavelength anomalous diffraction method, we are able to isolate the bromine distribution and reconstruct the electron density distribution of the lipid mixture in the three phases. We found that the lipid distribution is homogenous and uniform in the lamellar and hexagonal phases. But in the distorted hexagonal phase, the lipid monolayer has nonuniform curvature, and cholesterol almost entirely concentrates in the high curvature region. This finding demonstrates that the association energies between lipid molecules vary with the curvature of membrane. Thus, lipid components in a mixture may redistribute under conditions of nonuniform curvature, such as in the stalk structure. In such cases, the spontaneous curvature depends on the local lipid composition and the free energy minimum is determined by lipid distribution as well as curvature.
Influences of aortic motion and curvature on vessel expansion in murine experimental aneurysms
Goergen, Craig J.; Azuma, Junya; Barr, Kyla N.; Magdefessel, Lars; Kallop, Dara Y.; Gogineni, Alvin; Grewall, Amarjeet; Weimer, Robby M.; Connolly, Andrew J.; Dalman, Ronald L.; Taylor, Charles A.; Tsao, Philip S.; Greve, Joan M.
2010-01-01
Objective The purpose of this study was to quantitatively compare aortic curvature and motion to resulting aneurysm location, direction of expansion, and pathophysiology in experimental abdominal aortic aneurysms (AAAs). Methods and Results Magnetic resonance imaging was performed at 4.7T with: 1) a 3D acquisition for vessel geometry and 2) a 2D cardiac-gated acquisition to quantify luminal motion. Male 24-week-old mice were imaged before and after AAA formation induced by angiotensin II (AngII)-filled osmotic pump implantation or infusion of elastase. AngII-induced AAAs formed near the location of maximum abdominal aortic curvature, and the leftward direction of expansion was correlated with the direction of suprarenal aortic motion. Elastase-induced AAAs formed in a region of low vessel curvature and had no repeatable direction of expansion. AngII significantly increased mean blood pressure (22.7mmHg; p<0.05), while both models showed a significant two-fold decrease in aortic cyclic strain (p<0.05). Differences in patterns of elastin degradation and localization of fluorescent signal from protease-activated probes were also observed. Conclusions The direction of AngII aneurysm expansion correlated with the direction of motion, medial elastin dissection, and adventitial remodeling. Anterior infrarenal aortic motion correlated with medial elastin degradation in elastase-induced aneurysms. Results from both models suggest a relationship between aneurysm pathology and aortic geometry and motion. PMID:21071686
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.
Band geometry, Berry curvature, and superfluid weight
NASA Astrophysics Data System (ADS)
Liang, Long; Vanhala, Tuomas I.; Peotta, Sebastiano; Siro, Topi; Harju, Ari; Törmä, Päivi
2017-01-01
We present a theory of the superfluid weight in multiband attractive Hubbard models within the Bardeen-Cooper-Schrieffer (BCS) mean-field framework. We show how to separate the geometric contribution to the superfluid weight from the conventional one, and that the geometric contribution is associated with the interband matrix elements of the current operator. Our theory can be applied to systems with or without time-reversal symmetry. In both cases the geometric superfluid weight can be related to the quantum metric of the corresponding noninteracting systems. This leads to a lower bound on the superfluid weight given by the absolute value of the Berry curvature. We apply our theory to the attractive Kane-Mele-Hubbard and Haldane-Hubbard models, which can be realized in ultracold atom gases. Quantitative comparisons are made to state of the art dynamical mean-field theory and exact diagonalization results.
Curvature-tuned electronic properties of bilayer graphene in an effective four-dimensional spacetime
NASA Astrophysics Data System (ADS)
Cariglia, Marco; Giambò, Roberto; Perali, Andrea
2017-06-01
We show that in A B stacked bilayer graphene low-energy excitations around the semimetallic points are described by massless, four-dimensional Dirac fermions. There is an effective reconstruction of the four-dimensional spacetime, including in particular the dimension perpendicular to the sheet, that arises dynamically from the physical graphene sheet and the interactions experienced by the carriers. The effective spacetime is the Eisenhart-Duval lift of the dynamics experienced by Galilei invariant Lévy-Leblond spin-1/2 particles near the Dirac points. We find that changing the intrinsic curvature of the bilayer sheet induces a change in the energy level of the electronic bands, switching from a conducting regime for negative curvature to an insulating one when curvature is positive. In particular, curving graphene bilayers allow opening or closing the energy gap between conduction and valence bands, a key effect for electronic devices. Thus, using curvature as a tunable parameter opens the way for the beginning of curvatronics in bilayer graphene.
Holographic curvature perturbations in a cosmology with a space-like singularity
Ferreira, Elisa G.M.; Brandenberger, Robert
2016-07-19
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.
Soil Moisture, Coastline Curvature, and Sea Breeze Initiated Precipitation Over Florida
NASA Technical Reports Server (NTRS)
Baker, R. David; Lynn, Barry H.; Boone, Aaron; Tao, Wei-Kuo
1999-01-01
Land surface-atmosphere interaction plays a key role in the development of summertime convection and precipitation over the Florida peninsula. Land-ocean temperature contrasts induce sea-breeze circulations along both coasts. Clouds develop along sea-breeze fronts, and significant precipitation can occur during the summer months. However, other factors such as soil moisture distribution and coastline curvature may modulate the timing, location, and intensity of sea breeze initiated precipitation. Here, we investigate the role of soil moisture and coastline curvature on Florida precipitation using the 3-D Goddard Cumulus Ensemble (GCE) cloud model coupled with the Parameterization for Land-Atmosphere-Cloud Exchange (PLACE) land surface model. This study utilizes data from the Convection and Precipitation Electrification Experiment (CaPE) collected on 27 July 1991. Our numerical simulations suggest that a realistic distribution of soil moisture influences the location and intensity of precipitation but not the timing of precipitation. In contrast, coastline curvature affects the timing and location of precipitation but has little influence on peak rainfall rates. However, both factors (soil moisture and coastline curvature) are required to fully account for observed rainfall amounts.
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.
Comprehensive Use of Curvature For Robust And Accurate Online Surface Reconstruction.
Lefloch, Damien; Kluge, Markus; Sarbolandi, Hamed; Weyrich, Tim; Kolb, Andreas
2017-01-05
Interactive real-time scene acquisition from hand-held depth cameras has recently developed much momentum, enabling applications in ad-hoc object acquisition, augmented reality and other fields. A key challenge to online reconstruction remains error accumulation in the reconstructed camera trajectory, due to drift-inducing instabilities in the range scan alignments of the underlying iterative-closest-point (ICP) algorithm. Various strategies have been proposed to mitigate that drift, including SIFT-based pre-alignment, color-based weighting of ICP pairs, stronger weighting of edge features, and so on. In our work, we focus on surface curvature as a feature that is detectable on range scans alone and hence does not depend on accurate multi-sensor alignment. In contrast to previous work that took curvature into consideration, however, we treat curvature as an independent quantity that we consistently incorporate into every stage of the real-time reconstruction pipeline, including densely curvature-weighted ICP, range image fusion, local surface reconstruction, and rendering. Using multiple benchmark sequences, and in direct comparison to other state-of-the-art online acquisition systems, we show that our approach significantly reduces drift, both when analyzing individual pipeline stages in isolation, as well as seen across the online reconstruction pipeline as a whole.
Few-mode optical fiber based simultaneously distributed curvature and temperature sensing.
Wu, Hao; Tang, Ming; Wang, Meng; Zhao, Can; Zhao, Zhiyong; Wang, Ruoxu; Liao, Ruolin; Fu, Songnian; Yang, Chen; Tong, Weijun; Shum, Perry Ping; Liu, Deming
2017-05-29
The few-mode fiber (FMF) based Brillouin sensing operated in quasi-single mode (QSM) has been reported to achieve the distributed curvature measurement by monitoring the bend-induced strain variation. However, its practicality is limited by the inherent temperature-strain cross-sensitivity of Brillouin sensors. Here we proposed and experimentally demonstrated an approach for simultaneously distributed curvature and temperature sensing, which exploits a hybrid QSM operated Raman-Brillouin system in FMFs. Thanks to the larger spot size of the fundamental mode in the FMF, the Brillouin frequency shift change of the FMF is used for curvature estimation while the temperature variation is alleviated through Raman signals with the enhanced signal-to-noise ratio (SNR). Within 2 minutes measuring time, a 1.5 m spatial resolution is achieved along a 2 km FMF. The worst resolution of the square of fiber curvature is 0.333 cm(-2) while the temperature resolution is 1.301 °C at the end of fiber.
Molecular Modeling of Lipid Membrane Curvature Induction by a Peptide: More than Simply Shape
Sodt, Alexander J.; Pastor, Richard W.
2014-01-01
Molecular dynamics simulations of an amphipathic helix embedded in a lipid bilayer indicate that it will induce substantial positive curvature (e.g., a tube of diameter 20 nm at 16% surface coverage). The induction is twice that of a continuum model prediction that only considers the shape of the inclusion. The discrepancy is explained in terms of the additional presence of specific interactions described only by the molecular model. The conclusion that molecular shape alone is insufficient to quantitatively model curvature is supported by contrasting molecular and continuum models of lipids with large and small headgroups (choline and ethanolamine, respectively), and of the removal of a lipid tail (modeling a lyso-lipid). For the molecular model, curvature propensity is analyzed by computing the derivative of the free energy with respect to bending. The continuum model predicts that the inclusion will soften the bilayer near the headgroup region, an effect that may weaken curvature induction. The all-atom predictions are consistent with experimental observations of the degree of tubulation by amphipathic helices and variation of the free energy of binding to liposomes. PMID:24806928
Molecular modeling of lipid membrane curvature induction by a peptide: more than simply shape.
Sodt, Alexander J; Pastor, Richard W
2014-05-06
Molecular dynamics simulations of an amphipathic helix embedded in a lipid bilayer indicate that it will induce substantial positive curvature (e.g., a tube of diameter 20 nm at 16% surface coverage). The induction is twice that of a continuum model prediction that only considers the shape of the inclusion. The discrepancy is explained in terms of the additional presence of specific interactions described only by the molecular model. The conclusion that molecular shape alone is insufficient to quantitatively model curvature is supported by contrasting molecular and continuum models of lipids with large and small headgroups (choline and ethanolamine, respectively), and of the removal of a lipid tail (modeling a lyso-lipid). For the molecular model, curvature propensity is analyzed by computing the derivative of the free energy with respect to bending. The continuum model predicts that the inclusion will soften the bilayer near the headgroup region, an effect that may weaken curvature induction. The all-atom predictions are consistent with experimental observations of the degree of tubulation by amphipathic helices and variation of the free energy of binding to liposomes. Copyright © 2014 Biophysical Society. Published by Elsevier Inc. All rights reserved.
Application of the normalized curvature ratio to an in-service structure
NASA Astrophysics Data System (ADS)
Kliewer, Kaitlyn; Glisic, Branko
2017-04-01
Fiber optic sensors (FOS) offer numerous advantages for structural health monitoring. In addition to being durable, lightweight, and capable of multiplexing, they offer the ability to simultaneously monitor both static and dynamic strain. FOS also allow for the instrumentation of large areas of a structure with long-gages sensors which helps enable global monitoring of the structure. Drawing upon these benefits, the Normalized Curvature Ratio (NCR), a curvature based damage detection method, has been developed. This method utilizes a series of long-gage fiber Bragg grating (FBG) strain sensors for damage detection of a structure through dynamic strain measurements and curvature analysis. While dynamic SHM methods typically rely up frequency and acceleration based analysis, it has been found that strain and curvature based analysis may be a more reliable means for structural monitoring. Previous research was performed through small scale experimental testing and analytical models were developed and provided promising results for the NCR as a potential damage sensitive feature. Based on this success, this research focuses on the application of the NCR to an existing in-service structure, the US202/NJ23 highway overpass located in Wayne, NJ. The overpass is currently instrumented with a series of long-gage FBG strains sensors and periodic strain measurements for dynamic events induced by heavy weight vehicles have been recorded for more than 5 years. This research shows encouraging results and the potential for the NCR to be used as a simplistic metric for damage detection using FBG strain sensors.
Phase Shift in an Atom Interferometer due to Spacetime Curvature across its Wave Function.
Asenbaum, Peter; Overstreet, Chris; Kovachy, Tim; Brown, Daniel D; Hogan, Jason M; Kasevich, Mark A
2017-05-05
Spacetime curvature induces tidal forces on the wave function of a single quantum system. Using a dual light-pulse atom interferometer, we measure a phase shift associated with such tidal forces. The macroscopic spatial superposition state in each interferometer (extending over 16 cm) acts as a nonlocal probe of the spacetime manifold. Additionally, we utilize the dual atom interferometer as a gradiometer for precise gravitational measurements.
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.
Gaussian and mean curvatures for discrete asymptotic nets
NASA Astrophysics Data System (ADS)
Schief, W. K.
2017-04-01
We propose discretisations of Gaussian and mean curvatures of surfaces parametrised in terms of asymptotic coordinates and examine their relevance in the context of integrable discretisations of classical classes of surfaces and their underlying integrable systems. We also record discrete analogues of the classical relation between the Gaussian curvature of hyperbolic surfaces and the torsion of their asymptotic lines.
Effects of curvature on asymmetric steady states in catalyst particles
Lucier, B J
1981-02-01
The effects of curvature on steady states of chemical catalytic reactions are investigated by studying the cases of the catalytic particle being a spherical or cylindrical shell. Existence and stability of solutions are studied. It is shown that the solutions converge to the solutions for the catalytic slab when the curvature goes to 0 in each case.
An analytical approach to estimate curvature effect of coseismic deformations
NASA Astrophysics Data System (ADS)
Dong, Jie; Sun, Wenke; Zhou, Xin; Wang, Rongjiang
2016-08-01
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.
The development of curvature in the porcine radioulna.
Pantinople, Jess; McCabe, Kyle; Henderson, Keith; Richards, Hazel L; Milne, Nick
2017-01-01
Long bone curvature in animal limbs has long been a subject of interest and much work has explored why long bones should be curved. However, the 'when' and 'how' of curvature development is poorly understood. It has been shown that the rat tibia fails to attain its normal curvature if the action of muscles is removed early in life, but it is not clear if this is because the curvature fails to develop or if the bone becomes straighter without the action of muscles. No studies have examined the development of bone curvature in a normally developing quadruped, so this study tracks the course of curvature formation in the radioulna in a series of growing pigs. We also histologically examined the epiphyseal growth plates of these bones to determine if they contribute to the formation of curvature. In all three epiphyseal plates examined, the proliferative zone is thicker and more densely populated with chondrocytes on the cranial (convex) side than the caudal (concave) side. Frost's chondral modelling theory would suggest that the cranial side of the bone is under more compression than the caudal side, and we conclude that this is due to the action of triceps extending the elbow by pulling on the olecranon process. These results support the idea that bone curvature is an adaptation to habitual loading, where longitudinal loads acting on the curved bone cause bending strains that counter the bending resulting from the habitual muscle action.
Curvature-processing network in macaque visual cortex.
Yue, Xiaomin; Pourladian, Irene S; Tootell, Roger B H; Ungerleider, Leslie G
2014-08-19
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.
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.
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
Nastic curvatures of wheat coleoptiles that develop in true microgravity.
Heathcote, D G; Chapman, D K; Brown, A H
1995-07-01
Dark-grown wheat coleoptiles developed strong curvatures within 5 h of being transferred in orbit from a 1 g centrifuge to microgravity during an experiment flown on the IML-1 shuttle mission. The curving tendency was strongest in seedlings that were immature, with coleoptiles shorter than 10 mm at the time of transfer. The curvature direction was non-random, and directed away from the caryopsis (the coleptile face adjacent to the caryopsis becoming convex). The curvatures were most marked in the basal third of the coleoptiles, contrasting with phototropic responses, which occur in the apical third. We interpret these curvatures as being nastic, and related to the curvatures commonly reported to occur during clinostat rotation treatments.
Curvature dependence of the interfacial heat and mass transfer coefficients
NASA Astrophysics Data System (ADS)
Glavatskiy, K. S.; Bedeaux, D.
2014-03-01
Nucleation is often accompanied by heat transfer between the surroundings and a nucleus of a new phase. The interface between two phases gives an additional resistance to this transfer. For small nuclei the interfacial curvature is high, which affects not only equilibrium quantities such as surface tension, but also the transport properties. In particular, high curvature affects the interfacial resistance to heat and mass transfer. We develop a framework for determining the curvature dependence of the interfacial heat and mass transfer resistances. We determine the interfacial resistances as a function of a curvature. The analysis is performed for a bubble of a one-component fluid and may be extended to various nuclei of multicomponent systems. The curvature dependence of the interfacial resistances is important in modeling transport processes in multiphase systems.
Effects of Iris Surface Curvature on Iris Recognition
Thompson, Joseph T; Flynn, Patrick J; Bowyer, Kevin W; Santos-Villalobos, Hector J
2013-01-01
To focus on objects at various distances, the lens of the eye must change shape to adjust its refractive power. This change in lens shape causes a change in the shape of the iris surface which can be measured by examining the curvature of the iris. This work isolates the variable of iris curvature in the recognition process and shows that differences in iris curvature degrade matching ability. To our knowledge, no other work has examined the effects of varying iris curvature on matching ability. To examine this degradation, we conduct a matching experiment across pairs of images with varying degrees of iris curvature differences. The results show a statistically signi cant degradation in matching ability. Finally, the real world impact of these ndings is discussed
Nastic curvatures of wheat coleoptiles that develop in true microgravity
NASA Technical Reports Server (NTRS)
Heathcote, D. G.; Chapman, D. K.; Brown, A. H.
1995-01-01
Dark-grown wheat coleoptiles developed strong curvatures within 5 h of being transferred in orbit from a 1 g centrifuge to microgravity during an experiment flown on the IML-1 shuttle mission. The curving tendency was strongest in seedlings that were immature, with coleoptiles shorter than 10 mm at the time of transfer. The curvature direction was non-random, and directed away from the caryopsis (the coleptile face adjacent to the caryopsis becoming convex). The curvatures were most marked in the basal third of the coleoptiles, contrasting with phototropic responses, which occur in the apical third. We interpret these curvatures as being nastic, and related to the curvatures commonly reported to occur during clinostat rotation treatments.
Effect of curvature on cholesteric liquid crystals in toroidal geometries
NASA Astrophysics Data System (ADS)
Fialho, Ana R.; Bernardino, Nelson R.; Silvestre, Nuno M.; Telo da Gama, Margarida M.
2017-01-01
The confinement of liquid crystals inside curved geometries leads to exotic structures, with applications ranging from biosensors to optical switches and privacy windows. Here we study how curvature affects the alignment of a cholesteric liquid crystal. We model the system on the mesoscale using the Landau-de Gennes model. Our study was performed in three stages, analyzing different curved geometries from cylindrical walls and pores, to toroidal domains, in order to isolate the curvature effects. Our results show that the stresses introduced by the curvature influence the orientation of the liquid crystal molecules, and cause distortions in the natural periodicity of the cholesteric that depend on the radius of curvature, on the pitch, and on the dimensions of the system. In particular, the cholesteric layers of toroidal droplets exhibit a symmetry breaking not seen in cylindrical pores and that is driven by the additional curvature.
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.
Nagi, Sana Ehsen; Khan, Farhan Raza
2017-01-01
With root canal treatment, the organic debris and micro-organisms from pulp space is removed and an ideal canal preparation is achieved that is conducive of hermetic obturation. The purpose of this study was to correlate the pre-operative canal curvature with the postoperative curvature in human extracted teeth prepared with K-3 rotary systems. The root canal preparation was carried out on extracted human molars and premolars using K-3 endodontic rotary files. A pre and post-operative image of the teeth using digital radiograph were taken in order to compare pre and post-operative canal curvature. The images were saved in an images retrieval system (Gendex software, USA). Change in the canal curvature was measured using the software measuring tool (Vixwin software, USA). Student paired t-test and Pearson correlation test was applied at 0.05 level of significance. There is a statistically significant difference between pre-operative and post-operative canal curvature (p-value <0.001) and a strong positive correlation (91% correlation) between pre-operative and post-operative canal curvature in teeth prepared with the K-3 rotary files. A significant difference between pre and post instrumentation curvature was found. Degree of canal curvature was not correlated with time taken for canal preparation.
The apoptotic protein tBid promotes leakage by altering membrane curvature.
Epand, Raquel F; Martinou, Jean-Claude; Fornallaz-Mulhauser, Monique; Hughes, Donald W; Epand, Richard M
2002-09-06
The apoptotic protein tBid is effective in promoting both leakage and lipid mixing in liposomes composed of cardiolipin and phosphatidylcholine at a molar ratio of 1:2 in the presence of calcium. When half of the phosphatidylcholine component of these liposomes is replaced with phosphatidylethanolamine, a lipid that promotes negative membrane curvature, the rates of both leakage and lipid mixing caused by tBid are substantially increased. Replacement of cardiolipin with phosphatidylglycerol, a lipid that is structurally similar to cardiolipin but does not promote negative membrane curvature in the presence of calcium, prevents the tBid from promoting leakage. The promotion of leakage by tBid is also inhibited by several substances that promote positive membrane curvature, including lysophosphatidylcholine, tritrpticin, a potent antimicrobial peptide, and cyclosporin A, a known inhibitor of cytochrome c release from mitochondria. We directly measured the effect of tBid on membrane curvature by (31)P NMR. We found that tBid promotes the formation of highly curved non-lamellar phases. All of these data are consistent with the hypothesis that tBid promotes negative curvature, and as a result it destabilizes bilayer membranes. Bcl-X(L) inhibits leakage and lipid mixing induced by tBid. Bcl-X(L) is anti-apoptotic. It reduces the promotion of non-bilayer phases by tBid, although by itself Bcl-X(L) is capable of promoting their formation. Bcl-X(L) has little effect on liposomal integrity. Our results suggest that the anti-apoptotic activity of Bcl-X(L) is not a consequence of its interaction with membranes, but rather with other proteins, such as tBid.
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.
Dynamical and statistical effects of the intrinsic curvature of internal space of molecules
NASA Astrophysics Data System (ADS)
Teramoto, Hiroshi; Takatsuka, Kazuo
2005-02-01
The Hamilton dynamics of a molecule in a translationally and/or rotationally symmetric field is kept rigorously constrained in its phase space. The relevant dynamical laws should therefore be extracted from these constrained motions. An internal space that is induced by a projection of such a limited phase space onto configuration space is an intrinsically curved space even for a system of zero total angular momentum. In this paper we discuss the general effects of this curvedness on dynamics and structures of molecules in such a manner that is invariant with respect to the selection of coordinates. It is shown that the regular coordinate originally defined by Riemann is particularly useful to expose the curvature correction to the dynamics and statisitcal properties of molecules. These effects are significant both qualitatively and quantitatively and are studied in two aspects. One is the direct effect on dynamics: A trajectory receives a Lorentz-like force from the curved space as though it was placed in a magnetic field. The well-known problem of the trapping phenomenon at the transition state is analyzed from this point of view. By showing that the trapping force is explicitly described in terms of the curvature of the internal space, we clarify that the physical origin of the trapped motion is indeed originated from the curvature of the internal space and hence is not dependent of the selection of coordinate system. The other aspect is the effect of phase space volume arising from the curvedness: We formulate a general expression of the curvature correction of the classical density of states and extract its physical significance in the molecular geometry along with reaction rate in terms of the scalar curvature and volume loss (gain) due to the curvature. The transition state theory is reformulated from this point of view and it is applied to the structural transition of linear chain molecules in the so-called dihedral angle model. It is shown that the
Hawes, Martha C; O'Brien, Joseph P
2006-01-01
Background This review summarizes what is known about the pathological processes (e.g. structural and functional changes), by which spinal curvatures develop and evolve into spinal deformities. Methods Comprehensive review of articles (English language only) published on 'scoliosis,' whose content yielded data on the pathological changes associated with spinal curvatures. Medline, Science Citation Index and other searches yielded > 10,000 titles each of which was surveyed for content related to 'pathology' and related terms such as 'etiology,' 'inheritance,' 'pathomechanism,' 'signs and symptoms.' Additional resources included all books published on 'scoliosis' and available through the Arizona Health Sciences Library, Interlibrary Loan, or through direct contact with the authors or publishers. Results A lateral curvature of the spine–'scoliosis'–can develop in association with postural imbalance due to genetic defects and injury as well as pain and scarring from trauma or surgery. Irrespective of the factor that triggers its appearance, a sustained postural imbalance can result, over time, in establishment of a state of continuous asymmetric loading relative to the spinal axis. Recent studies support the longstanding hypothesis that spinal deformity results directly from such postural imbalance, irrespective of the primary trigger, because the dynamics of growth within vertebrae are altered by continuous asymmetric mechanical loading. These data suggest that, as long as growth potential remains, evolution of a spinal curvature into a spinal deformity can be prevented by reversing the state of continuous asymmetric loading. Conclusion Spinal curvatures can routinely be diagnosed in early stages, before pathological deformity of the vertebral elements is induced in response to asymmetric loading. Current clinical approaches involve 'watching and waiting' while mild reversible spinal curvatures develop into spinal deformities with potential to cause symptoms
Dynamical and statistical effects of the intrinsic curvature of internal space of molecules.
Teramoto, Hiroshi; Takatsuka, Kazuo
2005-02-15
The Hamilton dynamics of a molecule in a translationally and/or rotationally symmetric field is kept rigorously constrained in its phase space. The relevant dynamical laws should therefore be extracted from these constrained motions. An internal space that is induced by a projection of such a limited phase space onto configuration space is an intrinsically curved space even for a system of zero total angular momentum. In this paper we discuss the general effects of this curvedness on dynamics and structures of molecules in such a manner that is invariant with respect to the selection of coordinates. It is shown that the regular coordinate originally defined by Riemann is particularly useful to expose the curvature correction to the dynamics and statistical properties of molecules. These effects are significant both qualitatively and quantitatively and are studied in two aspects. One is the direct effect on dynamics: A trajectory receives a Lorentz-like force from the curved space as though it was placed in a magnetic field. The well-known problem of the trapping phenomenon at the transition state is analyzed from this point of view. By showing that the trapping force is explicitly described in terms of the curvature of the internal space, we clarify that the physical origin of the trapped motion is indeed originated from the curvature of the internal space and hence is not dependent of the selection of coordinate system. The other aspect is the effect of phase space volume arising from the curvedness: We formulate a general expression of the curvature correction of the classical density of states and extract its physical significance in the molecular geometry along with reaction rate in terms of the scalar curvature and volume loss (gain) due to the curvature. The transition state theory is reformulated from this point of view and it is applied to the structural transition of linear chain molecules in the so-called dihedral angle model. It is shown that the
Programming curvature using origami tessellations.
Dudte, Levi H; Vouga, Etienne; Tachi, Tomohiro; Mahadevan, L
2016-05-01
Origami describes rules for creating folded structures from patterns on a flat sheet, but does not prescribe how patterns can be designed to fit target shapes. Here, starting from the simplest periodic origami pattern that yields one-degree-of-freedom collapsible structures-we show that scale-independent elementary geometric constructions and constrained optimization algorithms can be used to determine spatially modulated patterns that yield approximations to given surfaces of constant or varying curvature. Paper models confirm the feasibility of our calculations. We also assess the difficulty of realizing these geometric structures by quantifying the energetic barrier that separates the metastable flat and folded states. Moreover, we characterize the trade-off between the accuracy to which the pattern conforms to the target surface, and the effort associated with creating finer folds. Our approach enables the tailoring of origami patterns to drape complex surfaces independent of absolute scale, as well as the quantification of the energetic and material cost of doing so.
Characterizing repulsive gravity with curvature eigenvalues
NASA Astrophysics Data System (ADS)
Luongo, Orlando; Quevedo, Hernando
2014-10-01
Repulsive gravity has been investigated in several scenarios near compact objects by using different intuitive approaches. Here, we propose an invariant method to characterize regions of repulsive gravity, associated to black holes and naked singularities. Our method is based upon the behavior of the curvature tensor eigenvalues, and leads to an invariant definition of a repulsion radius. The repulsion radius determines a physical region, which can be interpreted as a repulsion sphere, where the effects due to repulsive gravity naturally arise. Further, we show that the use of effective masses to characterize repulsion regions can lead to coordinate-dependent results whereas, in our approach, repulsion emerges as a consequence of the spacetime geometry in a completely invariant way. Our definition is tested in the spacetime of an electrically charged Kerr naked singularity and in all its limiting cases. We show that a positive mass can generate repulsive gravity if it is equipped with an electric charge or an angular momentum. We obtain reasonable results for the spacetime regions contained inside the repulsion sphere whose size and shape depend on the value of the mass, charge and angular momentum. Consequently, we define repulsive gravity as a classical relativistic effect by using the geometry of spacetime only.
Cosmological spatial curvature probed by microwave polarization
Matzner, R.A.; Tolman, B.W.
1982-11-15
If there is a large-scale anisotropy in the expansion of the universe, the microwave background radiation is expected to be linearly polarized. This communication shows that spatial curvature is capable of rotating the polarization of the microwaves relative to its direction at last scattering, which is directly correlated with the expansion anisotropy (and so also the observed intensity anisotropy). In Friedmann-Robertson-Walker models of the universe with additional small expansion anisotropy, the observed rotation relative to the intensity anisotropy would be appreciable and constant over the celestial sphere in the closed (type IX) model, but in the flat and open models, it must either vanish (types I and V) or vary ina complicated way over the celestial sphere (type VII/sub h/). These facts suggest a clear observational test of the closure of the universe. Also, an ambiguity inherent in the homogeneity of the universe does not allow prediction of the direction of rotation; thus homogeneous universes possess a property which might be called ''handedness.''
Actin filament curvature biases branching direction
NASA Astrophysics Data System (ADS)
Wang, Evan; Risca, Viviana; Chaudhuri, Ovijit; Chia, Jia-Jun; Geissler, Phillip; Fletcher, Daniel
2012-02-01
Actin filaments are key components of the cellular machinery, vital for a wide range of processes ranging from cell motility to endocytosis. Actin filaments can branch, and essential in this process is a protein complex known as the Arp2/3 complex, which nucleate new ``daughter'' filaments from pre-existing ``mother'' filaments by attaching itself to the mother filament. Though much progress has been made in understanding the Arp2/3-actin junction, some very interesting questions remain. In particular, F-actin is a dynamic polymer that undergoes a wide range of fluctuations. Prior studies of the Arp2/3-actin junction provides a very static notion of Arp2/3 binding. The question we ask is how differently does the Arp2/3 complex interact with a straight filament compared to a bent filament? In this study, we used Monte Carlo simulations of a surface-tethered worm-like chain to explore possible mechanisms underlying the experimental observation that there exists preferential branch formation by the Arp2/3 complex on the convex face of a curved filament. We show that a fluctuation gating model in which Arp2/3 binding to the actin filament is dependent upon a rare high-local-curvature shape fluctuation of the filament is consistent with the experimental data.
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.
BICEP2, the curvature perturbation and supersymmetry
Lyth, David H.
2014-11-01
The tensor fraction r ≅ 0.16 found by BICEP2 corresponds to a Hubble parameter H ≅ 1.0 × 10{sup 14} GeV during inflation. This has two implications for the (single-field) slow-roll inflation hypothesis. First, the inflaton perturbation must account for much more than 10% of the curvature perturbation ζ, which barring fine-tuning means that it accounts for practically all of it. It follows that a curvaton-like mechanism for generating ζ requires an alternative to slow roll such as k-inflation. Second, accepting slow-roll inflation, the excursion of the inflaton field is at least of order Planck scale. As a result, the flatness of the inflaton presumably requires a shift symmetry. I point out that if such is the case, the resulting potential is likely to have at least approximately the quadratic form suggested in 1983 by Linde, which is known to be compatible with the observed r as well as the observed spectral index n{sub s}. The shift symmetry does not require supersymmetry. Also, the big H may rule out a GUT by restoring the symmetry and producing fatal cosmic strings. The absence of a GUT would correspond to the absence of superpartners for the Standard Model particles, which indeed have yet to be found at the LHC.
Nonlinear diffusion filtering influenced by mean curvature
NASA Astrophysics Data System (ADS)
Kollár, Michal; Mikula, Karol; Čunderlík, Róbert
2016-04-01
The presentation introduces a new nonlinear diffusion filtering method on closed surfaces such as a sphere, ellipsoid or the Earth's surface. Our new model extends the regularized surface Perona-Malik model by including a local extrema detector based on a mean curvature of processed data. The model is thus represented by a nonlinear diffusion equation which filters noise while preserves main edges, local extrema and details important for a correct interpretation of data. We define a surface finite-volume method to approximate numerically the nonlinear parabolic partial differential equation on a closed surface. The closed surface is approximated by a polyhedral surface created by planar triangles representing subdivision of an initial icosahedron grid and we use a piece-wise linear approximation of a solution in space and the backward Euler time discretization. Numerical experiments present nonlinear diffusion filtering of artificial data and real measurements, namely the GOCE satellite observations. They aim to point out a main advantage of the new nonlinear model which, on the contrary of Perona-Malik model, preserves local extremal values of filtered data.
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.
Gradient expansion, curvature perturbations, and magnetized plasmas
Giovannini, Massimo; Rezaei, Zahra
2011-04-15
The properties of magnetized plasmas are always investigated under the hypothesis that the relativistic inhomogeneities stemming from the fluid sources and from the geometry itself are sufficiently small to allow for a perturbative description prior to photon decoupling. The latter assumption is hereby relaxed and predecoupling plasmas are described within a suitable expansion where the inhomogeneities are treated to a given order in the spatial gradients. It is argued that the (general relativistic) gradient expansion shares the same features of the drift approximation, customarily employed in the description of cold plasmas, so that the two schemes are physically complementary in the large-scale limit and for the low-frequency branch of the spectrum of plasma modes. The two-fluid description, as well as the magnetohydrodynamical reduction, is derived and studied in the presence of the spatial gradients of the geometry. Various solutions of the coupled system of evolution equations in the anti-Newtonian regime and in the quasi-isotropic approximation are presented. The relation of this analysis to the so-called separate universe paradigm is outlined. The evolution of the magnetized curvature perturbations in the nonlinear regime is addressed for the magnetized adiabatic mode in the plasma frame.
2010-01-01
Background The curveback lineage of guppy is characterized by heritable idiopathic-type spinal curvature that develops during growth. Prior work has revealed several important developmental similarities to the human idiopathic scoliosis (IS) syndrome. In this study we investigate structural and histological aspects of the vertebrae that are associated with spinal curvature in the curveback guppy and test for sexual dimorphism that might explain a female bias for severe curve magnitudes in the population. Methods Vertebrae were studied from whole-mount skeletal specimens of curved and non-curved adult males and females. A series of ratios were used to characterize structural aspects of each vertebra. A three-way analysis of variance tested for effects of sex, curvature, vertebral position along the spine, and all 2-way interactions (i.e., sex and curvature, sex and vertebra position, and vertebra position and curvature). Histological analyses were used to characterize micro-architectural changes in affected vertebrae and the intervertebral region. Results In curveback, vertebrae that are associated with curvature demonstrate asymmetric shape distortion, migration of the intervertebral ligament, and vertebral thickening on the concave side of curvature. There is sexual dimorphism among curved individuals such that for several vertebrae, females have more slender vertebrae than do males. Also, in the region of the spine where lordosis typically occurs, curved and non-curved females have a reduced width at the middle of their vertebrae, relative to males. Conclusions Based on similarities to human spinal curvatures and to animals with induced curves, the concave-convex biases described in the guppy suggest that there is a mechanical component to curve pathogenesis in curveback. Because idiopathic-type curvature in curveback is primarily a sagittal deformity, it is structurally more similar to Scheuermann kyphosis than IS. Anatomical differences between teleosts and
Effect of curvature on domain wall motion in elliptical nanorings
NASA Astrophysics Data System (ADS)
Kaya, Fikriye Idil; Bickel, Jessica; Aidala, Katherine
2014-03-01
Understanding domain wall (DW) motion in ferromagnetic nanostructures is important to realize proposed magnetic data storage and logic devices. We investigate the effect of curvature on DW pinning and motion by studying elliptical rings using micromagnetic simulations. Elliptical rings with constant width have varying curvature, with the lowest curvature at the minor axis, and the greatest curvature at the major axis. DWs can be created at any angular position within the ellipse by the application of an appropriate uniform magnetic field. However, only some of these positions are stable when the field is removed. We study the stability and depinning of the DWs by applying a slowly increasing elliptical magnetic field to determine the magnitude of the field at which the DWs begin to move. By varying the major to minor axis ratio, we examine the effect of curvature on DW pinning. A larger field is required to move DWs in regions of higher curvature (near the major axis) than lower curvature (near the minor axis). Overall, we see that increasing the major to minor axis ratio of elliptical nanorings requires increasing field strength to depin the DWs along the major axis. Work supported in part by NSF DMR-1207924 and NSF CMMI-1025020. Simulations performed at the CNS computational facilities at Harvard University, a member of the NNIN supported by NSF Award No. ECS-0335765.
On 3-gauge transformations, 3-curvatures, and Gray-categories
Wang, Wei
2014-04-15
In the 3-gauge theory, a 3-connection is given by a 1-form A valued in the Lie algebra g, a 2-form B valued in the Lie algebra h, and a 3-form C valued in the Lie algebra l, where (g,h,l) constitutes a differential 2-crossed module. We give the 3-gauge transformations from one 3-connection to another, and show the transformation formulae of the 1-curvature 2-form, the 2-curvature 3-form, and the 3-curvature 4-form. The gauge configurations can be interpreted as smooth Gray-functors between two Gray 3-groupoids: the path 3-groupoid P{sub 3}(X) and the 3-gauge group G{sup L} associated to the 2-crossed module L, whose differential is (g,h,l). The derivatives of Gray-functors are 3-connections, and the derivatives of lax-natural transformations between two such Gray-functors are 3-gauge transformations. We give the 3-dimensional holonomy, the lattice version of the 3-curvature, whose derivative gives the 3-curvature 4-form. The covariance of 3-curvatures easily follows from this construction. This Gray-categorical construction explains why 3-gauge transformations and 3-curvatures have the given forms. The interchanging 3-arrows are responsible for the appearance of terms with the Peiffer commutator (, )
3D curvature of muscle fascicles in triceps surae.
Rana, Manku; Hamarneh, Ghassan; Wakeling, James M
2014-12-01
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.
Gao, Yuan; Cheung, Gary S P; Shen, Ya; Zhou, Xuedong
2011-10-01
The purpose of this study was to visualize the stresses and strain distribution patterns in ProTaper Universal F2 files (Dentsply Maillefer, Ballaigues, Switzerland) and to establish the stress- and strain-curvature relationship for this instrument under various conditions by using a dynamic, three-dimensional finite-element model. An accurate geometric model of a ProTaper Universal F2 instrument was created. Two short, straight tubes were also modeled to represent the parts of root canal apical and coronal to the curvature. Then, the file was constrained to a curve of varying degree, curve length, and position. The maximum von Mises stress and strain on the tension side of the instrument was measured at 5-degree intervals in a numerical simulation package (LS-DYNA; Livermore Software Technology, Livermore, CA). The mechanical performance of the ProTaper F2 file under various conditions was simulated. A long curvature length produced lower values of stress and strain under the same angle of curvature. An increase in the curvature angle generally induces higher stress and strain. For the same degree and curve length, the stress and strain increased if the curved portion was situated further up the shaft of the instrument (ie, with a larger diameter). The dynamic, numerical model may be used to evaluate and compare the effect of various root canal curvatures on the behavior of different designs of root canal instrument. The magnitude of stress and strain imposed on the instrument is influenced by the abruptness and degree of curvature as well as the location of the curved portion. Crown Copyright © 2011. Published by Elsevier Inc. All rights reserved.
The influence of soft contact lens wear and two weeks cessation of lens wear on corneal curvature.
Lloyd McKernan, Aoife; O'Dwyer, Veronica; Simo Mannion, Luisa
2014-02-01
Accurate corneal measurements are crucial in corneal refractive surgery (CRS) to ensure successful outcomes. Soft contact lens (SCL) wear may result in changes to corneal curvature and structure. United States Food and Drug Administration (FDA) pre-operative guidelines recommend that prior to CRS, SCL wearers cease SCL wear for "at least two weeks before examination and treatment" [1]. Corneal curvature changes induced by SCL wear may take longer than two weeks to resolve. To examine the effect of SCL wear on corneal curvature before and following two weeks SCL wear cessation. To explore the possible impact of different SCL materials and years of SCL wear. Retrospective data analysis, between a group of SCL wearers (SCL: n=45); and a non-contact lens control group (NCL: n=45). Corneal curvature parameters were measured using the Pentacam (Oculus, Germany), before and following two weeks cessation of SCL wear. No significant differences in keratometry or Sagittal radius of curvature between SCL and NCL groups prior to or following SCL cessation. Tangential radius of curvature showed significant inferior steepening for the SCL group prior to SCL cessation (SCL vs. NCL; 7.77±0.30mm vs. 7.90±0.30mm; p=0.04). Following two weeks cessation of SCL wear this appeared to have resolved. Two weeks cessation of SCL wear appears sufficient for resolution of corneal curvature changes with modern SCL materials and years of SCL wear. However, further studies with longer lens deprivation periods are required to ensure stability for all SCL wearing patients. Copyright © 2013 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.
Holomorphic bisectional curvatures, supersymmetry breaking, and Affleck-Dine baryogenesis
NASA Astrophysics Data System (ADS)
Dutta, Bhaskar; Sinha, Kuver
2012-11-01
Working in D=4, N=1 supergravity, we utilize relations between holomorphic sectional and bisectional curvatures of Kahler manifolds to constrain Affleck-Dine baryogenesis. We show the following no-go result: Affleck-Dine baryogenesis cannot be performed if the holomorphic sectional curvature at the origin is isotropic in tangent space; as a special case, this rules out spaces of constant holomorphic sectional curvature (defined in the above sense) and in particular maximally symmetric coset spaces. We also investigate scenarios where inflationary supersymmetry breaking is identified with the supersymmetry breaking responsible for mass splitting in the visible sector, using conditions of sequestering to constrain manifolds where inflation can be performed.
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.
LPG-based sensor for curvature and vibration
NASA Astrophysics Data System (ADS)
Nascimento, I. M.; Chesini, G.; Baptista, J. M.; Cordeiro, Cristiano M. B.; Jorge, P. A. S.
2016-05-01
A long-period grating (LPG) written on a standard single mode fiber is investigated as a curvature and vibration sensor. It is demonstrated a high sensitivity to applied curvature and the possibility to monitor vibration in a wide range of frequencies from 30 Hz to 2000 Hz. The system was tested using an intensity based interrogation scheme with the LPG sensor operating in the curvature regime. Results have shown a reproducible frequency discrimination in the 30 Hz to 2000 Hz, with resolutions between 11 mHz and 913 mHz. Frequency retrieval could be performed independent of temperature up to 86 °C.
Measurement of the gravity-field curvature by atom interferometry.
Rosi, G; Cacciapuoti, L; Sorrentino, F; Menchetti, M; Prevedelli, M; Tino, G M
2015-01-09
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.
Inconsistency of scale-invariant curvature coupled to gravity
Zoller, D. )
1990-10-29
We show that the scale-invariant curvature action for paths, the point-particle version of Polyakov's extrinsic-curvature action for surfaces, does not couple consistently to gravity. The curvature action for paths yields a massless representation of the Poincare group with fixed helicity and so potentially provides a description of single photons and gravitons. We present a physical interpretation of the inconsistency in terms of the nonlocalizability of the photon and point out a conceptual kinship with the local supersymmetry of a spinning particle.
Inconsistency of scale-invariant curvature coupled to gravity
NASA Astrophysics Data System (ADS)
Zoller, D.
1990-10-01
We show that the scale-invariant curvature action for paths, the point-particle version of Polyakov's extrinsic-curvature action for surfaces, does not couple consistently to gravity. The curvature action for paths yields a massless representation of the Poincaré group with fixed helicity and so potentially provides a description of single photons and gravitons. We present a physical interpretation of the inconsistency in terms of the nonlocalizability of the photon and point out a conceptual kinship with the local supersymmetry of a spinning particle.
Motion on constant curvature spaces and quantization using Noether symmetries.
Bracken, Paul
2014-12-01
A general approach is presented for quantizing a metric nonlinear system on a manifold of constant curvature. It makes use of a curvature dependent procedure which relies on determining Noether symmetries from the metric. The curvature of the space functions as a constant parameter. For a specific metric which defines the manifold, Lie differentiation of the metric gives these symmetries. A metric is used such that the resulting Schrödinger equation can be solved in terms of hypergeometric functions. This permits the investigation of both the energy spectrum and wave functions exactly for this system.
Enhancing magnetoelectric effect via the curvature of composite cylinder
NASA Astrophysics Data System (ADS)
Wang, H. M.; Pan, E.; Chen, W. Q.
2010-05-01
We solved analytically the magnetoelectric (ME) effect in a bilayered piezoelectric/piezomagnetic cylinder under harmonic excitation. We revealed that at a fixed thickness ratio of the layers, the static or low-frequency ME effect can be substantially enhanced by increasing the curvature of the cylinder. In the megahertz frequency domain, on the other hand, we observed that the peak ME effect can be considerably increased by decreasing the curvature. We further showed that at a fixed curvature, the ME effect can be tuned to be around the resonant frequency for giant output by varying the boundary condition and thickness ratio.
Characterizing the curvature and its first derivative for imperfect fluids
NASA Astrophysics Data System (ADS)
Machado Ramos, Maria da Piedade
2017-04-01
The curvature tensor and its derivatives up to any order can be covariantly characterized by a minimal set of spinor quantities. On the other hand it might be useful, particularly in cosmology, to describe the geometry of a spacetime in a (1+3) formalism, based on an invariantly defined fluid velocity. In this work, we consider an imperfect fluid possessing both isotropic and anisotropic pressure. For these fluids, we determine the (1+3) matter terms of the curvature as well as the parts of the first order covariant derivative of the curvature (\
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
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.
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.
NASA Astrophysics Data System (ADS)
Angel, J. Roger P.; Burge, James H.; Hege, E. Keith; Kenworthy, Matthew A.; Woolf, Neville J.
2000-07-01
Very large space telescopes with primary mirrors made of flat segments have been recently proposed. The segments would be extremely lightweight, made like pellicles from stretched, reflective membranes. Here we consider the use of such membrane primary mirrors in which slight concave curvature is induced by electrostatic force, by application of a potential difference between the membrane and a control electrode behind. In this way segmented spherical or paraboloidal primaries of long focal length can be made directly, eliminating the correction optics needed when flat segments are used. The electric potential would be spatially and temporally controlled to obtain uniform curvature despite non-uniformity in membrane tension, to create slight asphericity if needed and to provide active damping of vibrations. We report the operation of a small prototype telescope with a SEMC primary.
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.
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-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'. © 2016 The Author(s).
Yu, Ying; Lv, Nan; Wang, Shengzhang; Karmonik, Christof; Liu, Jian-Min; Huang, Qinghai
2015-01-01
Purpose Flow diverters (FD) are increasingly being considered for treating large or giant wide-neck aneurysms. Clinical outcome is highly variable and depends on the type of aneurysm, the flow diverting device and treatment strategies. The objective of this study was to analyze the effect of different flow diverting strategies together with parent artery curvature variations on altering intra-aneurysmal hemodynamics. Methods Four ideal intracranial aneurysm models with different parent artery curvature were constructed. Computational fluid dynamics (CFD) simulations of the hemodynamics before and after applying five types of flow diverting strategies (single FD, single FD with 5% and 10% packing density of coils, two FDs with 25% and 50% overlapping rate) were performed. Changes in pressure, wall shear stress (WSS), relative residence time (RRT), inflow velocity and inflow volume rate were calculated and compared. Results Each flow diverting strategy resulted in enhancement of RRT and reduction of normalized mean WSS, inflow volume rate and inflow velocity in various levels. Among them, 50% overlapped FD induced most effective hemodynamic changes in RRT and inflow volume rate. The mean pressure only slightly decreased after treatment. Regardless of the kind of implantation of FD, the mean pressure, inflow volume rate and inflow velocity increased and the RRT decreased as the curvature of the parent artery increased. Conclusions Of all flow diverting strategies, overlapping FDs induced most favorable hemodynamic changes. Hemodynamics alterations post treatment were substantially influenced by parent artery curvature. Our results indicate the need of an individualized flow diverting strategy that is tailored for a specific aneurysm. PMID:26398847
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.
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.
Saiki, Mizue; Fujita, Hiroshi; Soga, Kouichi; Wakabayashi, Kazuyuki; Kamisaka, Seiichiro; Yamashita, Masamichi; Hoson, Takayuki
2005-06-01
Coleoptiles of rice (Oryza sativa L.) show a spontaneous (automorphic) curvature toward the caryopsis under microgravity conditions. The possible involvement of the reorientation of cortical microtubules in automorphic curvature was studied in rice coleoptiles grown on a three-dimensional clinostat. When rice seedlings that had been grown in the normal gravitational field were transferred to the clinostat in the dark, cortical microtubules of epidermal cells in the dorsal side of the coleoptiles oriented more transversely than the ventral side within 0.5 h. The rotation on the clinostat also increased the cell wall extensibility in the dorsal side and decreased the extensibility in the ventral side, and induced automorphic curvature. The reorientation of cortical microtubules preceded the changes in the cell wall extensibility and the curvature. The irradiation of rice seedlings with white light from above inhibited microtubule reorientation and changes in the cell wall extensibility, as well as curvature of coleoptiles. Also, colchicine, applied to the bending region of coleoptiles, partially inhibited the automorphic curvature. These results suggest that reorientation of cortical microtubules is involved in causing automorphic curvature in rice coleoptiles on the clinostat.
On semidiscrete constant mean curvature surfaces and their associated families.
Carl, Wolfgang
2017-01-01
The present paper studies semidiscrete surfaces in three-dimensional Euclidean space within the framework of integrable systems. In particular, we investigate semidiscrete surfaces with constant mean curvature along with their associated families. The notion of mean curvature introduced in this paper is motivated by a recently developed curvature theory for quadrilateral meshes equipped with unit normal vectors at the vertices, and extends previous work on semidiscrete surfaces. In the situation of vanishing mean curvature, the associated families are defined via a Weierstrass representation. For the general cmc case, we introduce a Lax pair representation that directly defines associated families of cmc surfaces, and is connected to a semidiscrete [Formula: see text]-Gordon equation. Utilizing this theory we investigate semidiscrete Delaunay surfaces and their connection to elliptic billiards.
Bacterial cell curvature through mechanical control of cell growth
Cabeen, Matthew T; Charbon, Godefroid; Vollmer, Waldemar; Born, Petra; Ausmees, Nora; Weibel, Douglas B; Jacobs-Wagner, Christine
2009-01-01
The cytoskeleton is a key regulator of cell morphogenesis. Crescentin, a bacterial intermediate filament-like protein, is required for the curved shape of Caulobacter crescentus and localizes to the inner cell curvature. Here, we show that crescentin forms a single filamentous structure that collapses into a helix when detached from the cell membrane, suggesting that it is normally maintained in a stretched configuration. Crescentin causes an elongation rate gradient around the circumference of the sidewall, creating a longitudinal cell length differential and hence curvature. Such curvature can be produced by physical force alone when cells are grown in circular microchambers. Production of crescentin in Escherichia coli is sufficient to generate cell curvature. Our data argue for a model in which physical strain borne by the crescentin structure anisotropically alters the kinetics of cell wall insertion to produce curved growth. Our study suggests that bacteria may use the cytoskeleton for mechanical control of growth to alter morphology. PMID:19279668
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).
Uniform background curvature: Foam families and frustrated discs
NASA Astrophysics Data System (ADS)
Modes, Carl Douglas
The introduction of background curvature to systems in soft condensed matter, and across all of physics, has a long standing history of success. Particularly in cases where the role of curvature is a surprise, a great deal of new insight may be derived from this technique. This thesis carries on in that tradition, applying uniform background curvature to study varied systems. The glass transition of amorphous materials, and the hard sphere interactions that underlie it, is modeled with hard discs in a space of constant negative curvature. We examine random packing on negatively curved, triply periodic surfaces. Continuous families of Plateau's Laws-commensurate foam bubbles are generated by conformal projection of regular foams in positively-curved space.
Dimensional curvature identities on pseudo-Riemannian geometry
NASA Astrophysics Data System (ADS)
Navarro, Alberto; Navarro, José
2014-12-01
For a fixed n ∈ N, the curvature tensor of a pseudo-Riemannian metric, as well as its covariant derivatives, satisfies certain identities that hold on any manifold of dimension less than or equal to n. In this paper, we re-elaborate recent results by Gilkey-Park-Sekigawa regarding these p-covariant curvature identities, for p = 0 , 2. To this end, we use the classical theory of natural operations that allows us to simplify some arguments and to generalize the description of Gilkey-Park-Sekigawa, both by dropping a symmetry hypothesis and by including p-covariant curvature identities, for any even p. Thus, for any dimension n, our main result describes the first space (i.e., that of highest weight) of p-covariant dimensional curvature identities, for any even p.
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.
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
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.
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.
Stability of the cylindrical shell of variable curvature
NASA Technical Reports Server (NTRS)
Marguerre, Karl
1951-01-01
This report is a first attempt to devise a calculation method for representing the buckling behavior of cylindrical shells of variable curvature. The problem occurs, for instance, in dimensioning wing noses, the stability of which is decisively influenced by the variability of curvature. The calculation is made possible by simplifying the stability equations (permissible for the shell of small curvature) and by assuming that the curvature 1/R as a function of the arc lengths can be represented by a very few Fourier terms. The formulas for the special case of an ellipse-like half oval with an axis ratio 1/3 ?= e ?= 1 under compression in longitudinal direction,shear, and a combination of shear and compression were evaluated. However, the results can also be applied approximately to an unsymmetrical oval-shell segment under compression, shear, and bending so that the numerical values contained in the diagrams 10 to 12 represent directly dimensioning data for the wing nose.
Three dimensional computer vision: Potential applications with curvature tracking
Sanford, Adam
1996-05-01
The purpose of this project is to develop a method of tracking data points for computer vision systems using curvature analysis. This is of particular importance to fellow researchers at the Lab, who have developed a markerless video computer vision system and are in need of such a method to track data points. A three dimensional viewing program was created to analyze the geometry of surface patches. Virtual surfaces were plotted and processed by the program to determine the Mean and Gaussian Curvature parameters for each point on the surface, thus defining each point`s surface geometry type. The same computer processes are then applied to each frame of data acquired by the computer vision system to find surface {open_quotes}landmarks{close_quotes} that hold constant curvature during motion. Preliminary results indicate that curvature analysis shows great promise and could solve the tracking dilemma faced by those in the field of markerless imaging systems.
Correlation between thoracolumbar curvatures and respiratory function in older adults
Rahman, Nor Najwatul Akmal Ab; Singh, Devinder Kaur Ajit; Lee, Raymond
2017-01-01
Aging is associated with alterations in thoracolumbar curvatures and respiratory function. Research information regarding the correlation between thoracolumbar curvatures and a comprehensive examination of respiratory function parameters in older adults is limited. The aim of the present study was to examine the correlation between thoracolumbar curvatures and respiratory function in community-dwelling older adults. Thoracolumbar curvatures (thoracic and lumbar) were measured using a motion tracker. Respiratory function parameters such as lung function, respiratory rate, respiratory muscle strength and respiratory muscle thickness (diaphragm and intercostal) were measured using a spirometer, triaxial accelerometer, respiratory pressure meter and ultrasound imaging, respectively. Sixty-eight community-dwelling older males and females from Kuala Lumpur, Malaysia, with mean (standard deviation) age of 66.63 (5.16) years participated in this cross-sectional study. The results showed that mean (standard deviation) thoracic curvature angle and lumbar curvature angles were −46.30° (14.66°) and 14.10° (10.58°), respectively. There was a significant negative correlation between thoracic curvature angle and lung function (forced expiratory volume in 1 second: r=−0.23, P<0.05; forced vital capacity: r=−0.32, P<0.05), quiet expiration intercostal thickness (r=−0.22, P<0.05) and deep expiration diaphragm muscle thickness (r=−0.21, P<0.05). The lumbar curvature angle had a significant negative correlation with respiratory muscle strength (r=−0.29, P<0.05) and diaphragm muscle thickness at deep inspiration (r=−0.22, P<0.05). However, respiratory rate was correlated neither with thoracic nor with lumbar curvatures. The findings of this study suggest that increase in both thoracic and lumbar curvatures is correlated with decrease in respiratory muscle strength, respiratory muscle thickness and some parameters of lung function. Clinically, both thoracic and lumbar
Correlation between thoracolumbar curvatures and respiratory function in older adults.
Rahman, Nor Najwatul Akmal Ab; Singh, Devinder Kaur Ajit; Lee, Raymond
2017-01-01
Aging is associated with alterations in thoracolumbar curvatures and respiratory function. Research information regarding the correlation between thoracolumbar curvatures and a comprehensive examination of respiratory function parameters in older adults is limited. The aim of the present study was to examine the correlation between thoracolumbar curvatures and respiratory function in community-dwelling older adults. Thoracolumbar curvatures (thoracic and lumbar) were measured using a motion tracker. Respiratory function parameters such as lung function, respiratory rate, respiratory muscle strength and respiratory muscle thickness (diaphragm and intercostal) were measured using a spirometer, triaxial accelerometer, respiratory pressure meter and ultrasound imaging, respectively. Sixty-eight community-dwelling older males and females from Kuala Lumpur, Malaysia, with mean (standard deviation) age of 66.63 (5.16) years participated in this cross-sectional study. The results showed that mean (standard deviation) thoracic curvature angle and lumbar curvature angles were -46.30° (14.66°) and 14.10° (10.58°), respectively. There was a significant negative correlation between thoracic curvature angle and lung function (forced expiratory volume in 1 second: r=-0.23, P<0.05; forced vital capacity: r=-0.32, P<0.05), quiet expiration intercostal thickness (r=-0.22, P<0.05) and deep expiration diaphragm muscle thickness (r=-0.21, P<0.05). The lumbar curvature angle had a significant negative correlation with respiratory muscle strength (r=-0.29, P<0.05) and diaphragm muscle thickness at deep inspiration (r=-0.22, P<0.05). However, respiratory rate was correlated neither with thoracic nor with lumbar curvatures. The findings of this study suggest that increase in both thoracic and lumbar curvatures is correlated with decrease in respiratory muscle strength, respiratory muscle thickness and some parameters of lung function. Clinically, both thoracic and lumbar curvatures
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.
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.
Hedgehogs in higher dimensional gravity with curvature self-interactions
NASA Astrophysics Data System (ADS)
Giovannini, Massimo
2001-04-01
Static solutions of the higher dimensional Einstein-Hilbert gravity supplemented by quadratic curvature self-interactions are discussed in the presence of hedgehog configurations along the transverse dimensions. The quadratic part of the action is parametrized in terms of the (ghost-free) Euler-Gauss-Bonnet curvature invariant. Spherically symmetric profiles of the transverse metric admit exponentially decaying warp factors both for positive and negative bulk cosmological constants.
Curvature-driven acceleration: a utopia or a reality?
NASA Astrophysics Data System (ADS)
Das, Sudipta; Banerjee, Narayan; Dadhich, Naresh
2006-06-01
The present work shows that a combination of nonlinear contributions from the Ricci curvature in Einstein field equations can drive a late time acceleration of expansion of the universe. The transit from the decelerated to the accelerated phase of expansion takes place smoothly without having to resort to a study of asymptotic behaviour. This result emphasizes the need for thorough and critical examination of models with nonlinear contribution from the curvature.
Fresnel diffractive imaging: Experimental study of coherence and curvature
Whitehead, L. W.; Williams, G. J.; Quiney, H. M.; Nugent, K. A.; Peele, A. G.; Paterson, D.; Jonge, M. D. de; 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.
A novel curvature-controllable steerable needle for percutaneous intervention.
Bui, Van Khuyen; Park, Sukho; Park, Jong-Oh; Ko, Seong Young
2016-08-01
Over the last few decades, flexible steerable robotic needles for percutaneous intervention have been the subject of significant interest. However, there still remain issues related to (a) steering the needle's direction with less damage to surrounding tissues and (b) increasing the needle's maximum curvature for better controllability. One widely used approach is to control the fixed-angled bevel-tip needle using a "duty-cycle" algorithm. While this algorithm has shown its applicability, it can potentially damage surrounding tissue, which has prevented the widespread adoption of this technology. This situation has motivated the development of a new steerable flexible needle that can change its curvature without axial rotation, while at the same time producing a larger curvature. In this article, we propose a novel curvature-controllable steerable needle. The proposed robotic needle consists of two parts: a cannula and a stylet with a bevel-tip. The curvature of the needle's path is controlled by a control offset, defined by the offset between the bevel-tip and the cannula. As a result, the necessity of rotating the whole needle's body is decreased. The duty-cycle algorithm is utilized to a limited degree to obtain a larger radius of curvature, which is similar to a straight path. The first prototype of 0.46 mm (outer diameter) was fabricated and tested with both in vitro gelatin phantom and ex vivo cow liver tissue. The maximum curvatures measured 0.008 mm(-1) in 6 wt% gelatin phantom, 0.0139 mm(-1) in 10 wt% gelatin phantom, and 0.0038 mm(-1) in cow liver. The experimental results show a linear relationship between the curvature and the control offset, which can be utilized for future implementation of this control algorithm.
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.
Analysis of curvature effects on plasmon biosensing of molecular interactions
NASA Astrophysics Data System (ADS)
Lee, Hyunwoong; Kim, Donghyun
2017-02-01
Surface plasmon represents oscillations of electrons at the interface between metal and dielectric layers. Surface plasmon resonance (SPR) is influenced by the environment near the surface, which has been the basis for label-free biosensor structure for various applications of molecular detection. An important aspect of SPR biosensing is that its characteristics are affected by the geometrical structure. Yet most research has focused largely on a structure using flat surface. Although flat structure is suitable for typical sensor applications, it may not be appropriate for wearable or in vivo applications. In this study, we analyzed the effects of surface curvature on flexible SPR biosensors. Curved surface was approximated using a segmented model in which each segment is treated as a flat surface with a different incident angle and then optical characteristics of the overall model were calculated by rigorous coupled wave analysis in two different configurations of light incidence. We calculated curvature effects on SPR with curvature radius larger than 255 μm. It was found that regardless of the incident configurations, resonance curves tend to broaden with increased curvature due to larger momentum dispersion. Resonance shifts as a result of DNA immobilization and hybridization decrease with curvature. The analysis was extended to multi-curvature structure and finds significant fluctuation of resonance shift for parallel light incidence. The study can be of profound importance for plasmonic devices using flexible substrates.
Non-additive compositional curvature energetics of lipid bilayers
Sodt, A.J.; Venable, R.M.; Lyman, E.; Pastor, R.W.
2016-01-01
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 will thus 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. The letter describes observations from simulations of unexpected non-additive 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. PMID:27715135
The effect of illuminant position on perceived curvature.
Curran, W; Johnston, A
1996-05-01
In shaded scenes surface features can appear either concave or convex, depending upon the viewer's judgement about the direction of the prevailing illumination. If other curvature cues are added to the image this ambiguity can be removed. However, it is not clear to what extent, if any, illuminant position exerts an influence on the perceived magnitude of surface curvature. Subjects were presented with pairs of spherical surface patches in a curvature matching task. The patches were defined by shading and texture cues. The perceived curvature of a standard patch was measured as a function of light source position. We found a clear effect of light source position on apparent curvature. Perceived curvature decreased as light source tilt increased and as light source slant decreased. We also found that the strength of this effect is determined partly by a surface's reflectance function and partly by the relative weight of the texture cue. When a specular component was added to the stimuli, the effect of light source orientation was weakened. The weight of the texture cue was manipulated by disrupting the regular distribution of texture elements. We found an inverse relationship between the strength of the effect and the weight of the texture cue: lowering the texture cue weight resulted in an enhancement of the illuminant position effect.
A multiscale approach to curvature modulated sorting in biological membranes.
Mercker, M; Ptashnyk, M; Kühnle, J; Hartmann, D; Weiss, M; Jäger, W
2012-05-21
Combining different theoretical approaches, curvature modulated sorting in lipid bilayers fixed on non-planar surfaces is investigated. First, we present a continuous model of lateral membrane dynamics, described by a nonlinear PDE of fourth order. We then prove the existence and uniqueness of solutions of the presented model and simulate membrane dynamics using a finite element approach. Adopting a truly multiscale approach, we use dissipative particle dynamics (DPD) to parameterize the continuous model, i.e. to derive a corresponding macroscopic model. Our model predicts that curvature modulated sorting can occur if lipids or proteins differ in at least one of their macroscopic elastic moduli. Gradients in the spontaneous curvature, the bending rigidity or the Gaussian rigidity create characteristic (metastable) curvature dependent patterns. The structure and dynamics of these membrane patterns are investigated qualitatively and quantitatively using simulations. These show that the decomposition time decreases and the stability of patterns increases with enlarging moduli differences or curvature gradients. Presented phase diagrams allow to estimate if and how stable curvature modulated sorting will occur for a given geometry and set of elastic parameters. In addition, we find that the use of upscaled models is imperative studying membrane dynamics. Compared with common linear approximations the system can evolve to different (meta)stable patterns. This emphasizes the importance of parameters and realistic dynamics in mathematical modeling of biological membranes. Copyright © 2012 Elsevier Ltd. All rights reserved.
The Induction of Negative Curvature as a Mechanism of Cell Toxicity by Amyloidogenic Peptides
Smith, Pieter E. S.; Brender, Jeffrey R.; Ramamoorthy, Ayyalusamy
2009-01-01
The death of insulin-producing β-cells is a key step in the pathogenesis of type 2 diabetes. The amyloidogenic peptide Islet Amyloid Polypeptide (IAPP, also known as amylin) has been shown to disrupt β-cell membranes leading to β-cell death. Despite the strong evidence linking IAPP to the destruction of β-cell membrane integrity and cell death, the mechanism of IAPP toxicity is poorly understood. In particular, the effect of IAPP on the bilayer structure has largely been uncharacterized. In this study, we have determined the effect of the amyloidogenic and toxic hIAPP1-37 peptide and the non-toxic and non-amyloidogenic rIAPP1-37 peptide on membranes by a combination of DSC and solid-state NMR spectroscopy. We also characterized the toxic but largely non-amyloidogenic rIAPP1-19 and hIAPP1-19 fragments. DSC shows that both amyloidogenic (hIAPP1-37) and largely non-amyloidogenic (hIAPP1-19 and rIAPP1-19) toxic versions of the peptide strongly favor the formation of negative curvature in lipid bilayers, while the non-toxic full-length rat IAPP1-37 peptide does not. This result was confirmed by solid-state NMR spectroscopy which shows that in bicelles composed of regions of high curvature and low curvature, non-toxic rIAPP1-37 binds to the regions of low curvature while toxic rIAPP1-19 binds to regions of high curvature. Similarly, solid-state NMR spectroscopy shows that the toxic rIAPP1-19 peptide significantly disrupts the lipid bilayer structure, whereas the non-toxic rIAPP1-37 does not have a significant effect. These results indicate IAPP may induce the formation of pores by the induction of excess membrane curvature and can be used to guide the design of compounds that can prevent the cell-toxicity of IAPP. This mechanism may be important to understand the toxicity of other amyloidogenic proteins. Our solid-state NMR results also demonstrate the possibility of using bicelles to measure the affinity of biomolecules for negatively or positively curved regions of
Calculation of Scale-Dependent Curvatures of Geological Surfaces
NASA Astrophysics Data System (ADS)
Bergbauer, S.; Mukerji, T.; Pollard, D. D.; Hennings, P. H.
2001-12-01
A comparison between a spectral and a factorial kriging analysis is presented for the calculation of scale -dependent normal surface curvatures. Knowledge of scale -dependent curvatures of geological surfaces plays an important role in quantitative structural geology. Often, curvature analyses of geological surfaces, such as horizon tops, are performed to estimate the strain resulting from deformation. The final shape of the horizon, however, is a superposition of natural structures of different sizes ranging from the grain scale to the basin scale. Performing a curvature analysis on the raw data often leads to patchy, un-interpretable surface curvatures. Separating the surface curvature of the overall structure from the curvature of minor surface undulations can therefore be crucial in any quantitative structural analysis that uses the absolute value of surface curvature. The two methods are applied to a seismically mapped and depth-converted horizon of domal structures from the North Sea to investigate their applicability in a sub-surface context. For the spectral analysis the surface is transformed into a discrete frequency spectrum. When the overall curvature of the horizon is of interest, only the low-frequency components of the spectrum are used for the curvature analysis. The frequency bin width is determined such that only those frequencies that make up the overall surface structure are used, and that aliasing is minimized. The remaining high-frequency spectrum can be added back to address quantitatively the alias introduced by this filtering. In geostatistical factorial kriging analyses, the spatial covariance (variogram) is estimated from the data, and modeled as a sum of independent factors with different ranges. Short range variogram factors correspond to high frequency spectral components of the surface while long range factors contribute low frequency components. Using the modeled variogram, factorial kriging filters out the desired long range
Xue, Yao-Hong; Zhu, You-Liang; Quan, Wei; Qu, Fu-Heng; Han, Cheng; Fan, Jing-Tao; Liu, Hong
2013-10-07
The polymer-grafted nanoparticles prepared by the surface-initiated polymerization induced from the spherical surface is studied by coarse-grained molecular dynamics simulations combined with the stochastic reaction model. The coupling effect of the initiator density and the grafting surface curvature is mainly investigated. The confinement degree greatly changes with the grafting surface curvature, thus the initiation efficiency, the grafted chain polydispersity, as well as the chain mass distribution show great dependence on the surface curvature. The results reveal that preparing the nanoparticle with desired size (i.e., grafting surface curvature) is crucial for control of the grafted chain polydispersity and even its dispersion in the polymer matrix. Our studies shed light on better design of grafted nanoparticles and better control of dispersion in polymer matrices for improving the performance of polymer nanocomposite materials.
Spin-curvature interaction from curved Dirac equation: Application to single-wall carbon nanotubes
NASA Astrophysics Data System (ADS)
Zhang, Kai; Zhang, Erhu; Chen, Huawei; Zhang, Shengli
2017-06-01
The spin-curvature interaction (SCI) and its effects are investigated based on curved Dirac equation. Through the low-energy approximation of curved Dirac equation, the Hamiltonian of SCI is obtained and depends on the geometry and spinor structure of manifold. We find that the curvature can be considered as field strength and couples with spin through Zeeman-like term. Then, we use dimension reduction to derive the local Hamiltonian of SCI for cylinder surface, which implies that the effective Hamiltonian of single-wall carbon nanotubes results from the geometry and spinor structure of lattice and includes two types of interactions: one does not break any symmetries of the lattice and only shifts the Dirac points for all nanotubes, while the other one does and opens the gaps except for armchair nanotubes. At last, analytical expressions of the band gaps and the shifts of their positions induced by curvature are given for metallic nanotubes. These results agree well with experiments and can be verified experimentally.
Kapnisis, Konstantinos K; Halwani, Dina O; Brott, Brigitta C; Anderson, Peter G; Lemons, Jack E; Anayiotos, Andreas S
2013-04-01
Preliminary studies have revealed that some stents undergo corrosion and fatigue-induced fracture in vivo, with significant release of metallic ions into surrounding tissues. A direct link between corrosion and in-stent restenosis has not been clearly established; nonetheless in vitro studies have shown that relatively high concentrations of heavy metal ions can stimulate both inflammatory and fibrotic reactions, which are the main steps in the process of restenosis. To isolate the mechanical effects from the local biochemical effects, accelerated biomechanical testing was performed on single and overlapping Nickel-Titanium (NiTi) stents subjected to various degrees of curvature. Post testing, stents were evaluated using Scanning Electron Microscopy (SEM) to identify the type of surface alterations. Fretting wear was observed in overlapping cases, in both straight and curved configurations. Stent strut fractures occurred in the presence of geometric curvature. Fretting wear and fatigue fractures observed on stents following mechanical simulation were similar to those from previously reported human stent explants. It has been shown that biomechanical factors such as arterial curvature combined with stent overlapping enhance the incidence and degree of wear and fatigue fracture when compared to single stents in a straight tube configuration.
Heuvingh, Julien; Bonneau, Stéphanie
2009-01-01
Abstract Oxidation of unsaturated lipids is a fundamental process involved in cell bioenergetics as well as in cell death. Using giant unilamellar vesicles and a chlorin photosensitizer, we asymmetrically oxidized the outer or inner monolayers of lipid membranes. We observed different shape transitions such as oblate to prolate and budding, which are typical of membrane curvature modifications. The asymmetry of the shape transitions is in accordance with a lowered effective spontaneous curvature of the leaflet being targeted. We interpret this effect as a decrease in the preferred area of the targeted leaflet compared to the other, due to the secondary products of oxidation (cleaved-lipids). Permeabilization of giant vesicles by light-induced oxidation is observed after a lag and is characterized in relation with the photosensitizer concentration. We interpret permeabilization as the opening of a pore above a critical membrane tension, resulting from the budding of vesicles. The evolution of photosensitized giant vesicle lysis tension was measured and yields an estimation of the effective spontaneous curvature at lysis. Additionally photo-oxidation was shown to be fusogenic. PMID:19948119
Cheng, Han-Wen; Yan, Shan; Han, Li; Chen, Yong; Kang, Ning; Skeete, Zakiya; Luo, Jin; Zhong, Chuan-Jian
2017-03-17
Interparticle spatial properties influence the electrical and functional properties of nanoparticle-structured assemblies. This report describes the nanoscale curvature-induced change in chemiresistive properties of molecularly-linked assemblies of gold nanoparticles on multiwalled carbon nanotubes, which are exploited for sensitive detection of volatile organic compounds. In addition to using linking/capping molecules to define interparticle spatial distances, the nanoscale curvature radius of the carbon nanotubes provides intriguing tunability of the interparticle spatial properties to influence electrical properties, which contrast with those observed for nanoparticle thin films assembled directly on chemiresistor devices. The electrical characteristics of the nanoparticle-nanotube composite give positive response profiles for the vapor molecules that are distinctively different to those observed for conventional nanoparticle thin-film assemblies. The dominant effect of electron coupling on overall chemiresistive properties is shown in relation to that of nanoscale curvature radius on the nanoparticle thin-film sensing properties. Sensing data are also further assessed in correlation with the solubility parameters of the vapor molecule. These findings have significant implications for the design of sensitive interfaces with nanocomposite-structured sensing materials and microfabricated chemiresistor devices.
Arenavirus budding resulting from viral-protein-associated cell membrane curvature.
Schley, David; Whittaker, Robert J; Neuman, Benjamin W
2013-09-06
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.
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.
Curvature of Double-Membrane Organelles Generated by Changes in Membrane Size and Composition
Knorr, Roland L.; Dimova, Rumiana; Lipowsky, Reinhard
2012-01-01
Transient double-membrane organelles are key players in cellular processes such as autophagy, reproduction, and viral infection. These organelles are formed by the bending and closure of flat, double-membrane sheets. Proteins are believed to be important in these morphological transitions but the underlying mechanism of curvature generation is poorly understood. Here, we describe a novel mechanism for this curvature generation which depends primarily on three membrane properties: the lateral size of the double-membrane sheets, the molecular composition of their highly curved rims, and a possible asymmetry between the two flat faces of the sheets. This mechanism is evolutionary advantageous since it does not require active processes and is readily available even when resources within the cell are restricted as during starvation, which can induce autophagy and sporulation. We identify pathways for protein-assisted regulation of curvature generation, organelle size, direction of bending, and morphology. Our theory also provides a mechanism for the stabilization of large double-membrane sheet-like structures found in the endoplasmic reticulum and in the Golgi cisternae. PMID:22427874
NASA Astrophysics Data System (ADS)
Guan, Ben; Zhai, Zhigang; Si, Ting; Lu, Xiyun; Luo, Xisheng
2017-03-01
The characteristics of three-dimensional (3D) Richtmyer-Meshkov instability (RMI) in the early stages are studied numerically. By designing 3D interfaces that initially possess various identical and opposite principal curvature combinations, the growth rate of perturbations can be effectively manipulated. The weighted essentially nonoscillatory scheme and the level set method combined with the real ghost fluid method are used to simulate the flow. The results indicate that the interface development and the shock propagation in 3D cases are much more complicated than those in 2D case, and the evolution of 3D interfaces is heavily dependent on the initial interfacial principal curvatures. The 3D structure of wave patterns induces high pressure zones in the flow field, and the pressure oscillations change the local instabilities of interfaces. In the linear stages, the perturbation growth rate follows regularity as the interfacial principal curvatures vary, which is further predicted by the stability theory of 2D and 3D interfaces. It is also found that hysteresis effects exist at the onset of the linear stages in the 3D case for the same initial perturbations as the 2D case, resulting in different evolutions of 3D RMI in the nonlinear stages.
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
The curvature of material surfaces in isotropic turbulence
NASA Astrophysics Data System (ADS)
Pope, S. B.; Yeung, P. K.; Girimaji, S. S.
1989-12-01
Direct numerical simulation is used to study the curvature of material surfaces in isotropic turbulence. The Navier-Stokes equation is solved by a 643 pseudospectral code for constant-density homogeneous isotropic turbulence, which is made statistically stationary by low-wavenumber forcing. The Taylor-scale Reynolds number is 39. An ensemble of 8192 infinitesimal material surface elements is tracked through the turbulence. For each element, a set of exact ordinary differential equations is integrated in time to determine, primarily, the two principal curvatures k1 and k2. Statistics are then deduced of the mean-square curvature M= (1)/(2) (k21+k22), and of the mean radius of curvature R=(k21+k22)-1/2. Curvature statistics attain an essentially stationary state after about 15 Kolmogorov time scales. Then the area-weighted expectation of R is found to be 12η, where η is the Kolmogorov length scale. For moderate and small radii (less than 10η) the probability density function (pdf) of R is approximately uniform, there being about 5% probability of R being less than η. The uniformity of the pdf of R, for small R, implies that the expectation of M is infinite. It is found that the surface elements with large curvatures are nearly cylindrical in shape (i.e., ‖k1‖≫‖k2‖ or ‖k2‖≫‖k1‖), consistent with the folding of the surface along nearly straight lines. Nevertheless the variance of the Gauss curvature K=k1k2 is infinite.
A novel approach in assessment of root canal curvature
Sadeghi, Shiva; Poryousef, Vahideh
2009-01-01
Introduction: The purpose of this in vitro study was to introduce a new method to describe root canal curvatures and to assess the degree of curvature of human permanent mandibular teeth with curved root canals. Materials and Methods: One hundred and thirty five mesial root canals of mandibular first and second molar teeth were selected. Access cavities were prepared. After inserting a K-file size #10 into each canal, radiographs were taken. Canal curvature was determined by measuring the Schneider angle, canal access angle, as well as the canal radius, length, height and curvature starting distance on scanned radiographs using a computerized image processing system. Data was evaluated statistically using Pearson correlation. Results: The mean canal access angle (CAA) and Schneider angle (S) were 8.04◦ (3.46) and 19◦ (6.99), respectively. The Pearson correlation analysis found significant positive correlation between S and CAA (r=0.826, P<0.0001). Negative correlations were found between radius and length (r= –0.4, P<0.0001), radius and Schneider angle (r= –0.4, P<0.0001), radius and CAA (r= –0.24, P=0.004) and CAA and curvature starting distance (r= 0.4, P<0.0001). There was no correlation between height and distance (r=0.013, P=0.789), as well as CAA and height (r=0.654, P=0.001). Conclusion: Under the limitations of this study, the results indicated that the shape of root canal curvature can be more accurately described using two angles, Schneider in combination with Canal access angle. The related parameters included radius, length, distance and height of curvature. [Iranian Endodontic Journal 2009;4(4):131-4] PMID:24019833
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.
Turning maneuvers in sharks: Predicting body curvature from axial morphology.
Porter, Marianne E; Roque, Cassandra M; Long, John H
2009-08-01
Given the diversity of vertebral morphologies among fishes, it is tempting to propose causal links between axial morphology and body curvature. We propose that shape and size of the vertebrae, intervertebral joints, and the body will more accurately predict differences in body curvature during swimming rather than a single meristic such as total vertebral number alone. We examined the correlation between morphological features and maximum body curvature seen during routine turns in five species of shark: Triakis semifasciata, Heterodontus francisci, Chiloscyllium plagiosum, Chiloscyllium punctatum, and Hemiscyllium ocellatum. We quantified overall body curvature using three different metrics. From a separate group of size-matched individuals, we measured 16 morphological features from precaudal vertebrae and the body. As predicted, a larger pool of morphological features yielded a more robust prediction of maximal body curvature than vertebral number alone. Stepwise linear regression showed that up to 11 features were significant predictors of the three measures of body curvature, yielding highly significant multiple regressions with r(2) values of 0.523, 0.537, and 0.584. The second moment of area of the centrum was always the best predictor, followed by either centrum length or transverse height. Ranking as the fifth most important variable in three different models, the body's total length, fineness ratio, and width were the most important non-vertebral morphologies. Without considering the effects of muscle activity, these correlations suggest a dominant role for the vertebral column in providing the passive mechanical properties of the body that control, in part, body curvature during swimming. (c) 2009 Wiley-Liss, Inc.
Spinal curvature and characteristics of postural change in pregnant women.
Okanishi, Natsuko; Kito, Nobuhiro; Akiyama, Mitoshi; Yamamoto, Masako
2012-07-01
Pregnant women often report complaints due to physiological and postural changes. Postural changes during pregnancy may cause low back pain and pelvic girdle pain. This study aimed to compare the characteristics of postural changes in pregnant compared with non-pregnant women. Prospective case-control study. Pregnancy care center. Fifteen women at 17-34 weeks pregnancy comprised the study group, while 10 non-pregnant female volunteers comprised the control group. Standing posture was evaluated in the sagittal plane with static digital pictures. Two angles were measured by image analysis software: (1) between the trunk and pelvis; and (2) between the trunk and lower extremity. Spinal curvature was measured with Spinal Mouse® to calculate the means of sacral inclination, thoracic and lumbar curvature and inclination. The principal components were calculated until eigenvalues surpassed 1. Three distinct factors with eigenvalues of 1.00-2.49 were identified, consistent with lumbosacral spinal curvature and inclination, thoracic spine curvature, and inclination of the body. These factors accounted for 77.2% of the total variance in posture variables. Eleven pregnant women showed postural characteristics of lumbar kyphosis and sacral posterior inclination. Body inclination showed a variety of patterns compared with those in healthy women. Spinal curvature demonstrated a tendency for lumbar kyphosis in pregnant women. Pregnancy may cause changes in spinal curvature and posture, which may in turn lead to relevant symptoms. Our data provide a basis for investigating the effects of spinal curvature and postural changes on symptoms during pregnancy. © 2012 The Authors Acta Obstetricia et Gynecologica Scandinavica© 2012 Nordic Federation of Societies of Obstetrics and Gynecology.
On the determination of curvature and dynamical dark energy
Virey, J-M; Taxil, P; Talon-Esmieu, D; Ealet, A; Tilquin, A E-mail: talon@cppm.in2p3.fr E-mail: taxil@cpt.univ-mrs.fr
2008-12-15
Constraining simultaneously the dark energy (DE) equation of state and the curvature of the universe is difficult due to strong degeneracies. To circumvent this problem when analyzing data it is usual to assume flatness to constrain the DE or, conversely, to assume that the DE is a cosmological constant to constrain the curvature. In this paper, we quantify the impact of such assumptions with an eye to future large surveys. We simulate future data for type Ia supernovae, the cosmic microwave background and baryon acoustic oscillations for a large range of fiducial cosmologies allowing a small spatial curvature. We take into account a possible time evolution of DE through a parameterized equation of state: w(a) = w{sub 0}+(1-a)w{sub a}. We then fit the simulated data with a wrong assumption on the curvature or on the DE parameters. For a fiducial {Lambda}CDM cosmology, if flatness is incorrectly assumed in the fit and if the true curvature is within the ranges 0.01<{Omega}{sub k}<0.03 and -0.07<{Omega}{sub k}<-0.01, one will be led to conclude erroneously that an evolving DE is present, even with high statistics. On the other hand, models with curvature and dynamical DE can be confused with a flat {Lambda}CDM model when the fit ignores a possible DE evolution. We find that, in the future, with high statistics, such risks of confusion should be limited, but they are still possible, and biases in the cosmological parameters might be important. We conclude by recalling that, in the future, it will be mandatory to perform some complete multi-probe analyses, leaving the DE parameters as well as the curvature as free parameters.
Curvature Sorting of Peripheral Proteins on Solid-Supported Wavy Membranes
Hsieh, Wan-Ting; Hsu, Chih-Jung; Capraro, Benjamin R.; Wu, Tingting; Chen, Chi-Mon; Yang, Shu; Baumgart, Tobias
2013-01-01
Cellular membrane deformation and the associated redistribution of membrane-bound proteins are important aspects of membrane function. Current model membrane approaches for studying curvature sensing are limited to positive curvatures, and often require complex and delicate experimental setups. To overcome these challenges, we fabricated a wavy substrate imposing a range of curvatures onto an adhering lipid bilayer membrane. We examined the curvature sorting of several peripheral proteins binding to the wavy membrane and observed them to partition into distinct regions of curvature. Furthermore, single molecule imaging experiments suggested that curvature sensing of proteins on low-curvature substrates requires cooperative interactions. PMID:22881196
Electron microscopy mapping of pBR322 DNA curvature. Comparison with theoretical models.
Muzard, G; Théveny, B; Révet, B
1990-01-01
A map of local curvature of the pBR322 DNA has been established by electron microscopy analysis of linearized plasmid molecules. To determine their polarity these molecules are one end labelled with an avidin-ferritin-biotin complex and the images are digitized. Local curvature is calculated from two mathematical treatments of the DNA trajectory and expressed in term of a mean dinucleotide wedge angle. Eight regions of curvature are distinguished. The four main regions of curvature have a high content of phased AA runs. The experimental curvature map is compared to theoretical maps of curvature obtained from four available models for DNA curvature. Images Fig. 2. PMID:2323339
Displacement Forces in Stent Grafts: Influence of Diameter Variation and Curvature Asymmetry.
Roos, H; Tokarev, M; Chernoray, V; Ghaffari, M; Falkenberg, M; Jeppsson, A; Nilsson, H
2016-08-01
Long-term durability after endovascular aortic repair is influenced by stent graft migration causing types I and III endoleaks. Flow induced displacement forces have been shown to have the potential to cause migration. In this study, the influence of the distal diameter of iliac limb stent grafts and the shape of graft curvature on flow induced displacement forces, were investigated. In an experimental pulsatile flow model mimicking aortic conditions in vivo, flow induced displacement forces at the proximal and distal ends of iliac limb stent grafts were studied at different angles (0-90°) and perfusion pressures (145/80, 170/90, 195/100 mmHg). Bell-bottomed, tapered, and non-tapered stent grafts and also asymmetric stent graft curvatures at 90° bend were studied. Measurements of graft movement were performed at all studied angulations and graft shapes. For all stent graft diameters, flow induced displacement forces increased with higher pressure and increased stent graft angulation. Forces in the bell-bottom graft were considerably higher than in tapered and non-tapered grafts, with a markedly elevated peak force at the distal end (proximal end, 2.3 ± 0.06 N and distal end, 6.9 ± 0.05 N compared with 1.7 ± 0.08 N and 1.6 ± 0.08 N in non-tapered grafts; p < .001 both). Peak forces in tapered and non-tapered grafts were not significantly different between the proximal and distal end. In asymmetric stent graft curvatures, a significant increase in displacement forces was observed in the attachment zone that was closest to the stent graft bend. Graft movement increased with greater displacement forces. Flow induced displacement forces in iliac limb stent grafts are significant and are influenced by distal stent graft diameter and the shape of the graft curvature. The displacement forces are particularly high at the large distal end of bell-bottom grafts. Wide iliac arteries treated with bell-bottom stent grafts may require more vigilant
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.
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.
Studying Biomolecule Localization by Engineering Bacterial Cell Wall Curvature
Renner, Lars D.; Eswaramoorthy, Prahathees; Ramamurthi, Kumaran S.; Weibel, Douglas B.
2013-01-01
In this article we describe two techniques for exploring the relationship between bacterial cell shape and the intracellular organization of proteins. First, we created microchannels in a layer of agarose to reshape live bacterial cells and predictably control their mean cell wall curvature, and quantified the influence of curvature on the localization and distribution of proteins in vivo. Second, we used agarose microchambers to reshape bacteria whose cell wall had been chemically and enzymatically removed. By combining microstructures with different geometries and fluorescence microscopy, we determined the relationship between bacterial shape and the localization for two different membrane-associated proteins: i) the cell-shape related protein MreB of Escherichia coli, which is positioned along the long axis of the rod-shaped cell; and ii) the negative curvature-sensing cell division protein DivIVA of Bacillus subtilis, which is positioned primarily at cell division sites. Our studies of intracellular organization in live cells of E. coli and B. subtilis demonstrate that MreB is largely excluded from areas of high negative curvature, whereas DivIVA localizes preferentially to regions of high negative curvature. These studies highlight a unique approach for studying the relationship between cell shape and intracellular organization in intact, live bacteria. PMID:24391905
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
The role of curvature in silica mesoporous crystals
Miyasaka, Keiichi; Garcia Bennett, Alfonso; Han, Lu; Han, Yu; Xiao, Changhong; Fujita, Nobuhisa; Castle, Toen; Sakamoto, Yasuhiro; Che, Shunai; Terasaki, Osamu
2012-01-01
Silica mesoporous crystals (SMCs) offer a unique opportunity to study micellar mesophases. Replication of non-equilibrium mesophases into porous silica structures allows the characterization of surfactant phases under a variety of chemical and physical perturbations, through methods not typically accessible to liquid crystal chemists. A poignant example is the use of electron microscopy and crystallography, as discussed herein, for the purpose of determining the fundamental role of amphiphile curvature, namely mean curvature and Gaussian curvature, which have been extensively studied in various fields such as polymer, liquid crystal, biological membrane, etc. The present work aims to highlight some current studies devoted to the interface curvature on SMCs, in which electron microscopy and electron crystallography (EC) are used to understand the geometry of silica wall surface in bicontinuous and cage-type mesostructures through the investigation of electrostatic potential maps. Additionally, we show that by altering the synthesis conditions during the preparation of SMCs, it is possible to isolate particles during micellar mesophase transformations in the cubic bicontinuous system, allowing us to view and study epitaxial relations under the specific synthesis conditions. By studying the relationship between mesoporous structure, interface curvature and micellar mesophases using electron microscopy and EC, we hope to bring new insights into the formation mechanism of these unique materials but also contribute a new way of understanding periodic liquid crystal systems. PMID:24098848
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.
Emergent Gauge Fields from Curvature in Single Layers of Transition-Metal Dichalcogenides
NASA Astrophysics Data System (ADS)
Ochoa, Héctor; Zarzuela, Ricardo; Tserkovnyak, Yaroslav
2017-01-01
We analyze the electron dynamics in corrugated layers of transition-metal dichalcogenides. Due to the strong spin-orbit coupling, the intrinsic (Gaussian) curvature leads to an emergent gauge field associated with the Berry connection of the spinor wave function. We discuss the gauge field created by topological defects of the lattice, namely, tetragonal and octogonal disclinations and edge dislocations. Ripples and topological disorder induce the same dephasing effects as a random magnetic field, suppressing the weak localization effects. This geometric magnetic field can be detected in an Aharonov-Bohm interferometry experiment by measuring the local density of states in the vicinity of corrugations.
Particle acceleration and curvature TeV emission by rotating, supermassive black holes
Levinson
2000-07-31
It is shown that particles accelerating near the event horizon of a spinning supermassive black hole that is threaded by externally supported magnetic field lines suffer severe curvature losses that limit the maximum energy they can attain to values well below that imposed by the maximum voltage drop induced by the black hole dynamo. It is further shown that the dominant fraction of the rotational energy extracted from the black hole is radiated in the TeV band. The implications for vacuum breakdown and the observational consequences are discussed.
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.
Kinetics for phototropic curvature by etiolated seedlings of Arabidopsis thaliana
NASA Technical Reports Server (NTRS)
Orbovic, V.; Poff, K. L.
1991-01-01
An infrared-imaging system has been used to study the influence of gravity on the kinetics of first positive phototropism. The development of phototropic curvature of etiolated seedlings of Arabidopsis thaliana was measured in the absence of visible radiation. Following a pulse of blue light, stationary seedlings curved to a maximum of approximately 16 degrees about 80 minutes after stimulation. The seedlings then curved upward again or straightened by about 6 degrees during the subsequent 100 minutes. Seedlings rotated on a clinostat reached a similar maximum curvature following photostimulation. These seedlings maintained that curvature for 30 to 40 minutes before subsequently straightening to the same extent as the stationary seedlings. It is concluded that straightening is not a consequence of gravitropism, although gravity has some effect on the phototropism kinetics.
Curvature-dependent surface energy and implications for nanostructures
NASA Astrophysics Data System (ADS)
Chhapadia, P.; Mohammadi, P.; Sharma, P.
2011-10-01
At small length scales, several size-effects in both physical phenomena and properties can be rationalized by invoking the concept of surface energy. Conventional theoretical frameworks of surface energy, in both the mechanics and physics communities, assume curvature independence. In this work we adopt a simplified and linearized version of a theory proposed by Steigmann-Ogden to capture curvature-dependence of surface energy. Connecting the theory to atomistic calculations and the solution to an illustrative paradigmatical problem of a bent cantilever beam, we catalog the influence of curvature-dependence of surface energy on the effective elastic modulus of nanostructures. The observation in atomistic calculations that the elastic modulus of bent nanostructures is dramatically different than under tension - sometimes softer, sometimes stiffer - has been a source of puzzlement to the scientific community. We show that the corrected surface mechanics framework provides a resolution to this issue. Finally, we propose an unambiguous definition of the thickness of a crystalline surface.
Spinor description of the curvatures of D = 5 gauge fields
NASA Astrophysics Data System (ADS)
Uvarov, D. V.
2017-03-01
Spinor description of the curvatures of D = 5 Yang-Mills, Rarita-Schwinger and gravitational fields is considered. Restrictions imposed on the curvature spinors by the dynamical equations and Bianchi identities are studied. In the absence of sources symmetric curvature spinors with 2 s indices obey first-order equations that in the linearized limit reduce to Dirac-type equations for massless free fields. These equations allow for a higher-spin generalization similarly to 4 d case. Their solution in the form of the integral over Lorentz-harmonic variables parametrizing coset manifold SO(1, 4)/( SO(1,1) × ISO(3)) isomorphic to the three-sphere is considered.
a Curvature Based Adaptive Neighborhood for Individual Point Cloud Classification
NASA Astrophysics Data System (ADS)
He, E.; Chen, Q.; Wang, H.; Liu, X.
2017-09-01
As a key step in 3D scene analysis, point cloud classification has gained a great deal of concerns in the past few years. Due to the uneven density, noise and data missing in point cloud, how to automatically classify the point cloud with a high precision is a very challenging task. The point cloud classification process typically includes the extraction of neighborhood based statistical information and machine learning algorithms. However, the robustness of neighborhood is limited to the density and curvature of the point cloud which lead to a label noise behavior in classification results. In this paper, we proposed a curvature based adaptive neighborhood for individual point cloud classification. Our main improvement is the curvature based adaptive neighborhood method, which could derive ideal 3D point local neighborhood and enhance the separability of features. The experiment result on Oakland benchmark dataset shows that the proposed method can effectively improve the classification accuracy of point cloud.
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.
Curvature affects Doppler investigation of vessels: implications for clinical practice.
Balbis, S; Roatta, S; Guiot, C
2005-01-01
In clinical practice, blood velocity estimations from Doppler examination of curved vascular segments are normally different from those of nearby straight segments. The observed "accelerations," sometimes considered as a sort of stochastic disturbances, can actually be related to very specific physical effects due to vessel curvature (i.e., the development of nonaxial velocity [NAV] components) and the spreading of the axial velocity direction in the Doppler sample volume with respect to the insonation axis. The relevant phenomena and their dependence on the radius of curvature of the vessels and on the insonation angle are investigated with a beam-vessel geometry as close as possible to clinical setting, with the simplifying assumptions of steady flow, mild vessel curvature, uniform ultrasonic beam and complete vessel insonation. The insonation angles that minimize the errors are provided on the basis of the study results.
Path planning using FMM with direction and curvature constrained
NASA Astrophysics Data System (ADS)
Li, Shidong; Ding, Mingyue; Cai, Chao
2009-10-01
It is difficult to meet both direction and curvature constraints for traditional Fast Marching (FM) method in path planning. Based on adjusting the cost function in Eiknoal equation-the control equation for FM, a new model for computing the integrated cost function was presented in this paper. A relationship formula about curvature radius was obtained and three kinds of adjusting strategies were given; two of them were used to modify the route to meet with the requires of turning constraint in this paper. Experiments showed that the improved model can be used to plan the path with FMM for agent such as unmanned aerial vehicle (UAV) or robot, which is limited to pass through the scene matching areas. And our preliminary experiments demonstrated that the strategies are feasible and efficient to obtain path with certain curvature radius. The model can also be used to represent the problem such as an aircraft flying in a flow field.
Stretching weakly bending filaments with spontaneous curvature in two dimensions.
Benetatos, Panayotis; Terentjev, Eugene M
2010-03-01
Some important biomolecules (for instance, bacterial FtsZ and eukaryotic DNA) are known to posses spontaneous (intrinsic) curvature. Using a simple extension of the wormlike chain model, we study the response of a weakly bending filament in two dimensions to a pulling force applied at its ends (a configuration common in classical in-vitro experiments and relevant to several in-vivo cell cases). The spontaneous curvature of such a chain or filament can in general be arc-length dependent and we study a case of sinusoidal variation, from which an arbitrary case can be reconstructed via Fourier transformation. We obtain analytic results for the force-extension relationship and the width of transverse fluctuations. We show that spontaneous-curvature undulations can affect the force-extension behavior even in relatively flexible filaments with a persistence length smaller than the contour length.
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.
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.
Model-independent Constraints on Cosmic Curvature and Opacity
NASA Astrophysics Data System (ADS)
Wang, Guo-Jian; Wei, Jun-Jie; Li, Zheng-Xiang; Xia, Jun-Qing; Zhu, Zong-Hong
2017-09-01
In this paper, we propose to estimate the spatial curvature of the universe and the cosmic opacity in a model-independent way with expansion rate measurements, H(z), and type Ia supernova (SNe Ia). On the one hand, using a nonparametric smoothing method Gaussian process, we reconstruct a function H(z) from opacity-free expansion rate measurements. Then, we integrate the H(z) to obtain distance modulus μ H, which is dependent on the cosmic curvature. On the other hand, distances of SNe Ia can be determined by their photometric observations and thus are opacity-dependent. In our analysis, by confronting distance moduli μ H with those obtained from SNe Ia, we achieve estimations for both the spatial curvature and the cosmic opacity without any assumptions for the cosmological model. Here, it should be noted that light curve fitting parameters, accounting for the distance estimation of SNe Ia, are determined in a global fit together with the cosmic opacity and spatial curvature to get rid of the dependence of these parameters on cosmology. In addition, we also investigate whether the inclusion of different priors for the present expansion rate (H 0: global estimation, 67.74 ± 0.46 km s‑1 Mpc‑1, and local measurement, 73.24 ± 1.74 km s‑1 Mpc‑1) exert influence on the reconstructed H(z) and the following estimations of the spatial curvature and cosmic opacity. Results show that, in general, a spatially flat and transparent universe is preferred by the observations. Moreover, it is suggested that priors for H 0 matter a lot. Finally, we find that there is a strong degeneracy between the curvature and the opacity.
Torsion and curvature of FtsZ filaments.
González de Prado Salas, Pablo; Hörger, Ines; Martín-García, Fernando; Mendieta, Jesús; Alonso, Álvaro; Encinar, Mario; Gómez-Puertas, Paulino; Vélez, Marisela; Tarazona, Pedro
2014-03-28
FtsZ filaments participate in bacterial cell division, but it is still not clear how their dynamic polymerization and shape exert force on the underlying membrane. We present a theoretical description of individual filaments that incorporates information from molecular dynamic simulations. The structure of the crystallized Methanococcus jannaschii FtsZ dimer was used to model a FtsZ pentamer that showed a curvature and a twist. The estimated bending and torsion angles between monomers and their fluctuations were included in the theoretical description. The MD data also permitted positioning the curvature with respect to the protein coordinates and allowed us to explore the effect of the relative orientation of the preferred curvature with respect to the surface plane. We find that maximum tension is attained when filaments are firmly attached and oriented with their curvature perpendicular to the surface and that the twist serves as a valve to release or to tighten the tension exerted by the curved filaments on the membrane. The theoretical model also shows that the presence of torsion can explain the shape distribution of short filaments observed by Atomic Force Microscopy in previously published experiments. New experiments with FtsZ covalently attached to lipid membranes show that the filament on-plane curvature depends on lipid head charge, confirming the predicted monomer orientation effects. This new model underlines the fact that the combination of the three elements, filament curvature, twist and the strength and orientation of its surface attachment, can modulate the force exerted on the membrane during cell division.
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.
Adiabatic approximation via hodograph translation and zero-curvature equations
NASA Astrophysics Data System (ADS)
Karasev, M. V.
2014-04-01
For quantum as well classical slow-fast systems, we develop a general method which allows one to compute the adiabatic invariant (approximate integral of motion), its symmetries, the adiabatic guiding center coordinates and the effective scalar Hamiltonian in all orders of a small parameter. The scheme does not exploit eigenvectors or diagonalization, but is based on the ideas of isospectral deformation and zero-curvature equations, where the role of "time" is played by the adiabatic (quantization) parameter. The algorithm includes the construction of the zero-curvature adiabatic connection and its splitting generated by averaging up to an arbitrary order in the small parameter.
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.
Equal-curvature grazing-incidence x-ray telescopes.
Saha, Timo T; Zhang, William
2003-08-01
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 such that the on-axis image spot at the focal plane is minimized. The on-axis rms spot diameter of two telescopes that we studied is less than 0.2 arc sec. The off-axis performance is comparable with that of equivalent Wolter type 1 telescopes.
Curvature and gravity actions for matrix models
NASA Astrophysics Data System (ADS)
Blaschke, Daniel N.; Steinacker, Harold
2010-08-01
We show how gravitational actions, in particular the Einstein-Hilbert action, can be obtained from additional terms in Yang-Mills matrix models. This is consistent with recent results on induced gravitational actions in these matrix models, realizing spacetime as four-dimensional brane solutions. It opens up the possibility for a controlled non-perturbative description of gravity through simple matrix models, with interesting perspectives for the problem of vacuum energy. The relation with UV/IR mixing and non-commutative gauge theory is discussed.
Influence of trunk muscle co-contraction on spinal curvature during sitting cross-legged.
Watanabe, S; Kobara, K; Ishida, H; Eguchi, A
2010-01-01
In Asia, many activities of daily living (ADL) are performed while sitting cross-legged on the floor. This sitting posture rotates the pelvis in a more dorsal direction and lumbar lordosis is more flattened than while sitting on a chair. Sitting cross-legged induces a greater load on the intervertebral discs and spine, especially when in a slumped position that is known to increase disc pressure even more and to aggravate chronic low back pain (CLBP). Therefore, it is very important to instruct Asian people about the correct sitting posture. In addition, it is known that co-contraction of the deep spine-stabilizing muscles enhances lumbar segmental stability and the sacroiliac joint. However, little is known about the influence of co-contraction of the trunk deep muscles on spinal curvature while sitting cross-legged on the floor. The purpose of this study was to compare EMG (electromyographic) activity of the trunk muscles while slump cross-legged sitting with that during co-contraction of the trunk muscles and to investigate how this co-contraction influences spinal curvature. Ten healthy male volunteers (21.7 +/- 2.5 years old) without CLBP participated in the study. Bipolar surface electrodes were attached to the rectus abdominis, the obliquus externus abdominis, the obliquus internus abdominis, the lower back extensor muscles (L3) and the multifidus on the right side. EMG signals were continuously recorded while slump sitting cross-legged and during co-contraction of the trunk muscles. They were amplified, band-pass filtered, digitized and stored by a data acquisition system. The average muscle activity values over the five-second sample for each sitting posture were normalized to maximal voluntary contractions (%MVC). While the subjects performed both sitting postures, the curvature of the spine was measured using a skin-surface and hand-held device, the "Spinal Mouse". More significant activities of the trunk muscles, with the exception of the rectus
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.
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.
Hosseinzadeh Nik, Tahereh; Janbaz Aciyabar, Pejman
2011-11-01
For determining the cervical column curvature, the curve fitting method is the most precise method, but using this method in clinic seems to be difficult if not possible. In this study, we used a modification of cervical column inclination angle that has been already mentioned The aim of this study was to evaluate the posture and curvature of the cervical column introducing a modified constructed angle in order to evaluate the cervical column curvature in a relax position in relation to the jaws sagittal position. The lateral cephalometries of patients with no anomaly were taken in the natural head position. The mean age of the patients was 13.49 years including 56 female and 44 male. Steiner and Wits analysis was used to evaluate the sagittal position of the jaws. Modified constructed CVT/HOR and OPT/HOR angles were used to evaluate the cervical column posture and curvature. Patients were classified into three groups according to the angle's classification. The results showed a significant positive correlation between modified constructed angles and sagittal jaw relationships (P < 0.05). Besides, in class II patients, there was a significant correlation between OPT/HOR and parameters ANB and Wits (P < 0.05 and P < 0.01, respectively). Age could not affect the curvature and posture of the cervical column. According to the result of this study using modified constructed angles may be a simple method for evaluation of the relation between cervical column curvature and sagittal position of the jaws. There is significant correlation between cervical column posture angles and parameters ANB and Wits in Cl. II patients.
Romero, R; Frazão, O; Pereira, D A; Salgado, H M; Araújo, F M; Ferreira, L A
2005-06-20
An intensity-referenced temperature-independent curvature-measurement technique that uses a smart composite that comprises two chirped fiber Bragg gratings is demonstrated. The two gratings are embedded on opposite sides of the composite laminate and act simultaneously as curvature sensors and as wavelength discriminators, enabling a temperature-independent intensity-based scheme to measure radius of curvature. Also, the system's performance is independent of arbitrary power losses that are induced in the lead fibers to the sensing head. It is demonstrated that the measurement range depends on the relative positions of the chirped fiber Bragg gratings and on their spectral bandwidths. By using two chirped fiber Bragg gratings with bandwidths W1 = 2.8 nm and W2 = 3.7 nm and with central wavelengths at lambda 01 = 1560.3 nm and lambda 02 = 1563.7 nm, we obtained a resolution of 1.6 mm/square root of Hz for the measurement of the radius of curvature (approximately R = 350 mm) over the measurement range 190 mm < R < infinity.
Park, Sungryul; Choi, Donghee; Yi, Jihhyeon; Lee, Songil; Lee, Ja Eun; Choi, Byeonghwa; Lee, Seungbae; Kyung, Gyouhyung
2017-04-01
This study examined the effects of display curvature (400, 600, 1200 mm, and flat), display zone (5 zones), and task duration (15 and 30 min) on legibility and visual fatigue. Each participant completed two 15-min visual search task sets at each curvature setting. The 600-mm and 1200-mm settings yielded better results than the flat setting in terms of legibility and perceived visual fatigue. Relative to the corresponding centre zone, the outermost zones of the 1200-mm and flat settings showed a decrease of 8%-37% in legibility, whereas those of the flat setting showed an increase of 26%-45% in perceived visual fatigue. Across curvatures, legibility decreased by 2%-8%, whereas perceived visual fatigue increased by 22% during the second task set. The two task sets induced an increase of 102% in the eye complaint score and a decrease of 0.3 Hz in the critical fusion frequency, both of which indicated an increase in visual fatigue. In summary, a curvature of around 600 mm, central display zones, and frequent breaks are recommended to improve legibility and reduce visual fatigue. Copyright © 2016 Elsevier Ltd. All rights reserved.
Rodríguez-García, R; Arriaga, L R; Mell, M; Moleiro, L H; López-Montero, I; Monroy, F
2009-03-27
We study thermal undulations of giant bilayer vesicles by flickering spectroscopy. The experimental fluctuation spectra are scrutinized in view of the classical Helfrich theory. Pure bending modes are revealed to be unable to predict the large fluctuations systematically found at a high wave vector. Hybrid curvature-dilational modes are then invoked as a more efficient mode of motion in producing high curvatures. A bimodal spectrum of the thermal undulations has been theoretically developed for the shell-like topology. Reconciliation between experiments and theory is achieved when this bimodal spectrum is considered.
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.
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).
Cosmological models with positive scalar spatial curvature and Λ>0
NASA Astrophysics Data System (ADS)
Ponce de Leon, J.
1987-12-01
Some exact spherically symmetric solutions of the Einstein field equations with Λ>0 and positive three-curvature are given. They have reasonable physical properties and represent universes which do not undergo inflation but have a non-de Sitter behaviour for large times. This paper extends some previous results in the literature. Permanent address: Apartado 2816, Caracas 1010-A, Venezuela.
Supported lipid bilayers with controlled curvature via colloidal lithography.
Sundh, Maria; Manandhar, Michal; Svedhem, Sofia; Sutherland, Duncan S
2011-09-01
Supported lipid bilayers (SLBs) at surfaces provide a route to quantitatively study molecular interactions with and at lipid membranes via different surface-based analytical techniques. Here, a method to fabricate SLBs with controlled curvatures, in the nanometer regime over large areas, is presented, utilizing lipid vesicle rupture onto nanostructured sensor substrates. Heat treated colloidal particle masks were used as templates to produce silicon dioxide films with systematically varied radius of curvature (ROC, 70 to 170 nm are demonstrated) and quartz crystal microbalance with dissipation monitoring (QCM-D) was used to confirm vesicle rupture onto such structured surfaces. Fluorescence microscopy was used to show fluidity of the supported membranes. The formation of confluent SLBs is demonstrated at the nanostructured surfaces from vesicles composed of POPC lipids. However, at surfaces with decreasing ROCs, vesicle rupture was hindered but with an increasing fraction of the positively charged lipid POEPC in the vesicles, it was possible to form good quality supported bilayers on all curvatures studied. Curved SLBs open up the possibility to systematically study the influence of curvature on molecular interactions at lipid membranes. © 2011 IEEE
Three-dimensional ultrasound palmprint recognition using curvature methods
NASA Astrophysics Data System (ADS)
Iula, Antonio; Nardiello, Donatella
2016-05-01
Palmprint recognition systems that use three-dimensional (3-D) information of the palm surface are the most recently explored techniques to overcome some two-dimensional palmprint difficulties. These techniques are based on light structural imaging. In this work, a 3-D ultrasound palmprint recognition system is proposed and evaluated. Volumetric images of a region of the human hand are obtained by moving an ultrasound linear array along its elevation direction and one by one acquiring a number of B-mode images, which are then grouped in a 3-D matrix. The acquisition time was contained in about 5 s. Much information that can be exploited for 3-D palmprint recognition is extracted from the ultrasound volumetric images, including palm curvature and other under-skin information as the depth of the various traits. The recognition procedure developed in this work is based on the analysis of the principal curvatures of palm surface, i.e., mean curvature image, Gaussian curvature image, and surface type. The proposed method is evaluated by performing verification and identification experiments. Preliminary results have shown that the proposed system exhibits an acceptable recognition rate. Further possible improvements of the proposed technique are finally highlighted and discussed.
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.
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.
Biostereometric Analysis Of Spine Curvatures On Living Human Body
NASA Astrophysics Data System (ADS)
Pineau, J.-C.; Ignazi, G.; Prudent, J.
1986-07-01
An analysis of the external and internal curvatures of spine was carried out on a sample of nine males from biostereometric measurements for different imposed postures. The results concerning the modifications of the external shape of the curves are used for the 3-D human body modeling in C.A.D. applications.
Special-holonomy manifolds and quartic-curvature string corrections
NASA Astrophysics Data System (ADS)
Stelle, K. S.
2004-06-01
The quartic-curvature corrections derived from string theory have a very specific impact on the geometry of target-space manifolds of special holonomy. In the cases of Calabi-Yau manifolds and D = 7 manifolds of G2 holonomy, we show how the corrections conspire to preserve the unbroken supersymmetry of these backgrounds.
Symmetric curvature descriptors for label-free analysis of DNA
Buzio, Renato; Repetto, Luca; Giacopelli, Francesca; Ravazzolo, Roberto; Valbusa, Ugo
2014-01-01
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. PMID:25248631