Curvature Domain Research Articles

Direct Numerical Simulation of Involute Channel Turbulence

Abstract A direct numerical simulation (DNS) study was performed on turbulent flow in the high flux isotope reactor involute channel geometry to develop a numerical database and determine the differences compared with a flat parallel channel. The varying channel curvature along the walls was studied for differences in mean profiles. Parameters of interest include streamwise velocity, turbulent kinetic energy (TKE), and turbulence dissipation rate, as well as Reynolds stresses and turbulence transport terms. Profile sampling was carried out at 10 locations along the span of the involute. Additional DNS studies were performed on smaller domains of comparable curvature to the involute domain: a high curvature channel (high circular), a low curvature channel (low circular), and a flat channel (flat). Each of these four cases was compared against each other and to other DNS studies performed on parallel flows. The results indicate that the bulk involute channel flow does not differ significantly from a flat parallel channel flow and that the curvature of the walls does not significantly alter the mean flow parameters. However, the regions of the involute channel near the side walls exhibit relatively low magnitude twin recirculation structures driven toward the side walls from the centerline of the channel, which warrants further study.

Impact of generic complexity factor on gravitationally decoupled solutions

In this work, we address the analysis of gravitationally decoupled sources within the context of f(R) gravity. By doing so, complete geometric deformation (CGD) strategy is deployed which makes it easier to comfortably identify the exact solutions of anisotropic spherical complex system by executing the Kuchowicz-ansatz for the metric potential of the seed (parent) solution. The generalized notion of complexity is then applied to Class-one spacetime for bounded spheres at large curvature domains. This CGD strategy, along with the extent to which null effective anisotropy and null complexity result in an isotropic structure, is then used to deduce the deformed functions. To understand the full gravitational features of non-dynamic compact spheres and the implications of the f(R) matter profile, the Karmarkar constraint is followed. Two distinct aspects of the related relativistic consequences are thus provided, and their physical credibility is subsequently discussed. Additionally, role of the decoupling parameter in governing the energy transition across the usual and effective matter profile is exhibited. We also indicate how the presence of R+βR2 modifications in pressure anisotropy and density inhomogeneity within the enclosed spheres have a profound impact on determining its stability.

A curvature-driven cloud removal method for remote sensing images

ABSTRACT Cloud coverage has become a significant factor affecting the availability of remote-sensing images in many applications. To mitigate the adverse impact of cloud coverage and recover ground information obscured by clouds, this paper presents a curvature-driven cloud removal method. Considering that each image can be regarded as a curved surface and the curvature can reflect the texture information well due to its dependence on the surface’s undulation degree, the presented method transforms image from natural domain to curvature domain for information reconstruction to maintain details of reference image. In order to improve the overall consistency and continuity of cloud removal results, the optimal boundary for cloud coverage area replacement is determined first to make the boundary pass through pixels with minimum curvature difference. Then, the curvature of missing area is reconstructed based on the curvature of reference image, and the reconstructed curvature is inversely transformed to natural domain to obtain a cloud-free image. In addition, considering the possible significant radiometric differences between different images, the initial cloud-free result will be further refined based on specific checkpoints to improve the local accuracy. To evaluate the performance of the proposed method, both simulated experiments and real data experiments are carried out. Experimental results show that the proposed method can achieve satisfactory results in terms of radiometric accuracy and consistency.

Vps501, a novel vacuolar SNX-BAR protein cooperates with the SEA complex to regulate TORC1 signaling.

The sorting nexins (SNXs), constitute a diverse family of molecules that play varied roles in membrane trafficking, cell signaling, membrane remodeling, organelle motility and autophagy. In particular, the SNX‐Bin‐Amphiphysin‐Rvs (BAR) proteins, a SNX subfamily characterized by a C‐terminal dimeric BAR lipid curvature domain and a conserved Phox‐homology domain, are of great interest. In budding yeast, many SNX‐BAR proteins have well‐characterized endo‐vacuolar trafficking roles. Phylogenetic analyses allowed us to identify an additional SNX‐BAR protein, Vps501, with a novel endo‐vacuolar role. We report that Vps501 uniquely localizes to the vacuolar membrane and has physical and genetic interactions with the SEA complex to regulate TORC1 inactivation. We found cells displayed a severe deficiency in starvation‐induced/nonselective autophagy only when SEA complex subunits are ablated in combination with Vps501, indicating a cooperative role with the SEA complex during TORC1 signaling during autophagy induction. Additionally, we found the SEACIT complex becomes destabilized in vps501Δsea1Δ cells, which resulted in aberrant endosomal TORC1 activity and subsequent Atg13 hyperphosphorylation. We have also discovered that the vacuolar localization of Vps501 is dependent upon a direct interaction with Sea1 and a unique lipid binding specificity that is also required for its function.

Signatures of Einstein-Maxwell dilaton-axion gravity from the observed jet power and the radiative efficiency

The Einstein-Maxwell dilaton-axion (EMDA) gravity arises in the low energy effective action of the heterotic string theory and provides a simple framework to explore the signatures of the same. The dilaton and the axion fields inherited in the action from string compactifications have interesting consequences in inflationary cosmology and in explaining the present accelerated expansion of the universe. It is therefore worthwhile to search for the footprints of these fields in the available astrophysical observations. Since Einstein gravity is expected to receive quantum corrections in the high curvature domain, the near horizon regime of black holes seems to be the ideal astrophysical laboratory to test these deviations from general relativity. Exact, stationary and axisymmetric black hole solution in EMDA gravity corresponds to the Kerr-Sen spacetime which carries dilaton charge, while the angular momentum is sourced by the axion field. The ballistic jets and the peak emission of the continuum spectrum from the accretion disk are believed to be launched very close to the event horizon and hence should bear the imprints of the background spacetime. We compute the jet power and the radiative efficiency derived from the continuum spectrum in the Kerr-Sen background and compare them with the corresponding observations of microquasars. Our analysis reveals that Kerr black holes are more favored compared to Kerr-Sen black holes with dilaton charges.

Curvature-processing domains in primate V4.

Neurons in primate V4 exhibit various types of selectivity for contour shapes, including curves, angles, and simple shapes. How are these neurons organized in V4 remains unclear. Using intrinsic signal optical imaging and two-photon calcium imaging, we observed submillimeter functional domains in V4 that contained neurons preferring curved contours over rectilinear ones. These curvature domains had similar sizes and response amplitudes as orientation domains but tended to separate from these regions. Within the curvature domains, neurons that preferred circles or curve orientations clustered further into finer scale subdomains. Nevertheless, individual neurons also had a wide range of contour selectivity, and neighboring neurons exhibited a substantial diversity in shape tuning besides their common shape preferences. In strong contrast to V4, V1 and V2 did not have such contour-shape-related domains. These findings highlight the importance and complexity of curvature processing in visual object recognition and the key functional role of V4 in this process.

Complementary Fluorescence Emission and Second Harmonic Spectra Improve Bilayer Characterization.

Complementary investigation of Laurdan fluorescence emission and second harmonic (SH) spectra in nonpolar, protic and aprotic polar solvents and phospholipid bilayers was carried out. SH of spectra computed using methods familiar in electro spin resonance spectroscopy yielded better resolution. Spectra were fit to log-normal distributions. SH spectra showed presence of two emissions in protic polar and nonpolar solvents and in both bilayer gel and liquid phases and a single line in aprotic polar solvents. Each of the half maximal positions of each line in both homogenous solvents and bilayers, expresses similar linearity with peak position. This shared feature suggests planar and nonplanar Laurdan conformation respectively in the longer (red) and shorter (blue) wavelength emitting states. The weaker 432nm blue line, not detected before in the gel phase, is distinguishable in the SH. Temperature trajectories of areas and peak positions of the individual lines bring new insight into the nature of lipid packing and evolution of domains, indicating inhomogeneous lipid packing even in the gel phase. The blue line identifies as emission from Laurdan in tighter packed regions and the dominant 445-448nm red line in the gel phase shifting to 484nm in the liquid phase as emission from Laurdan-water coupled states that are in varying stages of relaxation according to temperature and phase. Unexpected increase in the area of the blue line with temperature through the gel-liquid transition is consistent with coexisting low and high curvature domains and Laurdan's preference for less polar low curvature domains.

The Role of Phosphorylation Dynamics of CURVATURE THYLAKOID 1B in Plant Thylakoid Membranes.

Thylakoid membranes in land plant chloroplasts are organized into appressed and nonappressed membranes, which contribute to the control of energy distribution between the two photosystems (PSI and PSII) from the associated light-harvesting complexes (LHCs). Under fluctuating light conditions, fast reversible phosphorylation of the N-terminal thylakoid protein domains and changes in electrostatic forces induce modifications in thylakoid organization. To gain insight into the role and dynamics of thylakoid protein phosphorylation, we used targeted proteomics to quantify amounts of the structural proteins CURVATURE THYLAKOID1 (CURT1), including the levels of CURT1B N terminus phosphorylation and acetylation, after short-term fluctuating light treatments of Arabidopsis (Arabidopsis thaliana). The CURT1B protein was localized to a specific curvature domain separated from the margin domain, and specifically depleted of chlorophyll-binding protein complexes. The acetylation and phosphorylation of the CURT1B N terminus were mutually exclusive. The level of CURT1B phosphorylation, but not of acetylation, increased upon light shifts that also led to an increase in PSII core protein phosphorylation. These dynamics were largely absent in the knockout mutant of PSII core protein kinase SER/THR PROTEIN KINASE8 (STN8). Moreover, in mutants impaired in interaction between phosphorylated LHCII and PSI, the phosphorylation dynamics of CURT1B and the amount of the other CURT1 proteins were misregulated, indicating a functional interaction between CURT1B and PSI-LHCII complexes in grana margins. The complex relationships between phosphorylation of PSII, LHCII, and CURT1B support the dynamics of thylakoid protein complexes that are crucial in the optimization of photosynthesis under fluctuating light intensities.

Cell-free formation and interactome analysis of caveolae.

Caveolae have been linked to the regulation of signaling pathways in eukaryotic cells through direct interactions with caveolins. Here, we describe a cell-free system based on Leishmania tarentolae (Lt) extracts for the biogenesis of caveolae and show its use for single-molecule interaction studies. Insertion of expressed caveolin-1 (CAV1) into Lt membranes was analogous to that of caveolin in native membranes. Electron tomography showed that caveolins generate domains of precise size and curvature. Cell-free caveolae were used in quantitative assays to test the interaction of membrane-inserted caveolin with signaling proteins and to determine the stoichiometry of interactions. Binding of membrane-inserted CAV1 to several proposed binding partners, including endothelial nitric-oxide synthase, was negligible, but a small number of proteins, including TRAF2, interacted with CAV1 in a phosphorylation-(CAV1Y14)-stimulated manner. In cells subjected to oxidative stress, phosphorylated CAV1 recruited TRAF2 to the early endosome forming a novel signaling platform. These findings lead to a novel model for cellular stress signaling by CAV1.

Large curvature and background scale independence in single-metric approximations to asymptotic safety

In single-metric approximations to the exact renormalization group (RG) for quantum gravity, it has been not been clear how to treat the large curvature domain beyond the point where the effective cutoff scale $k$ is less than the lowest eigenvalue of the appropriate modified Laplacian. We explain why this puzzle arises from background dependence, resulting in Wilsonian RG concepts being inapplicable. We show that when properly formulated over an ensemble of backgrounds, the Wilsonian RG can be restored. This in turn implies that solutions should be smooth and well defined no matter how large the curvature is taken. Even for the standard single-metric type approximation schemes, this construction can be rigorously derived by imposing a modified Ward identity (mWI) corresponding to rescaling the background metric by a constant factor. However compatibility in this approximation requires the space-time dimension to be six. Solving the mWI and flow equation simultaneously, new variables are then derived that are independent of overall background scale.

Redefining caveolae as signalling platforms: specificity of interactions on endocytic caveolae in response to stress

Caveolae are small invaginations of the plasma membrane, which can expand upon stimulation and be internalized as endocytic vesicles. In addition to their role in clathrin‐independent endocytosis, caveolae play a role in many different signalling pathways.The major caveolar membrane protein, caveolin‐1 (CAV1) forms a dense coat of approx. 150 monomers assembled at the surface of the caveolae. CAV1 is believed to possess a “scaffolding domain” capable of interacting directly with numerous signalling proteins; its high oligomeric state amplifies its potency as a signalling platform.Here we have conducted a comprehensive in vitro screen of potential interacting partners to verify this “caveolin signalling” hypothesis. We have developped a binding assay using co‐expression of interactors and CAV1 in a cell‐free system which mimics the folding and insertion of caveolin in native membranes. Electron tomography shows that CAV1 generates membrane domains of uniform size and curvature and that we can re‐create small decorated vesicles that closely resemble endocytic caveolae.We measured binding of 40 potential interactors on these “reconstituted” caveolae using single‐molecule fluorescence and screened for interaction at the monomer level (non‐inserted CAV1) using a binding assay (AlphaScreen). We reveal exquisite selectivity of the assembled caveolae compared to monomeric CAV1. CAV1 phosphorylation, as found in cellular stress, showed amplification of binding to a subset of interactors. We further characterized binding sites by testing different mutations and truncations that alter the structure and oligomerisation state of CAV1. The results were confirmed in cells by proximity ligation assay, validating protein‐protein interactions and the effect of protein posttranslational modifications.Taken together, our findings create a novel picture of the role of caveolae in cell signalling and stress‐response.

Biaxial deformation and ductility domains for engineered rectangular RC cross-sections: A parametric study highlighting the positive roles of axial load, geometry and materials

Axial load and biaxial bending strongly influence the deformation capacity of column cross-sections, in most cases causing a non-negligible loss of curvature and ductility with respect to the case of pure bending along principal axes, commonly assumed as the basic condition to assess the inelastic capacity. In consideration of this the paper investigates the biaxial deformation performance of RC rectangular cross-sections belonging to one-dimensional elements, focusing on the influence of some parameters as the cross-section aspect ratio and the distribution of the rebars, as well as the mechanical characteristics of concrete and steel and the impact of biaxial/axial stresses.In the paper ultimate curvature domains, yielding curvature domains and ductility domains as novel assessment tools are provided. The deformation performance of the cross-sections, represented by the above domains, is discussed through a parametric study on the sensitivity of the domain shape to the major governing geometrical and mechanical factors. Further the role of axial load in terms of capability to level out the deformation capacity associated to different planes of bending is highlighted. Finally, a definition of specific biaxial ductility indicators is provided. The latter are proposed as measures to classify the biaxial deformation capacity associated with rectangular RC cross-sections for an engineered design.

곡판 가공방법 적용을 위한 곡률면적 분석

The ship hull is accomplished by assembling various curved surfaces. There are numerous existing methods for ship hull processing, which need certain appropriate processing methods to enable it to be more efficient. The curved hull plates can be divided into convex region and saddle region. It is common to use line heating method to form a saddle region, when it comes to a convex region, it will be triangle heating method to be utilized. A precise analysis for curvature domain is required for the application of proper processing method. There exist various problems on existing calculation methods of curvature domain. Therefore, a more powerful method is demanded to it more accurately. In this study, a method called Dual Contouring is applied to extract curved surfaces, which is able to improve accuracy of extracted area. Based on all above, a best-suited heat processing method should be selected.

An Analytical Step-by-Step Procedure to Derive the Flexural Response of RC Sections in Compression

This paper proposes an analysis procedure able to determine the flexural response of rectangular symmetrically reinforced concrete sections subjected to axial load and uniaxial bending. With respect to the usual numerical approaches, based on the fibre decomposition method, this procedure is based on the use of analytical expressions of the contributions to the equilibrium given by the longitudinal reinforcement and the concrete region in compression, which depend on the neutral axis depth and the curvature at each analysis step. The formulation is developed in dimensionless terms, after a preliminary definition of the geometrical and mechanical parameters involved, so that the results are valid for classes of RC sections. The constitutive laws of the materials include confinement effect on the concrete and postyielding behaviour of the steel reinforcement, which can be assumed to be softening behaviour for buckled reinforcing bars. The strength and curvature domains at the first yielding of the reinforcement in tension and at the ultimate state are derived in the form of analytical curves depending on the compression level; therefore, the role of a single parameter on the shape of these curves can easily be deduced. The procedure is validated by comparing some results with those numerically obtained by other authors.

Total curvature and simple pursuit on domains of curvature bounded above

We show how circumradius and asymptotic behavior of curves in cat(0) and cat(K) spaces (K > 0) are controlled by growth rates of total curvature. We apply our results to pursuit and evasion games of capture type with simple pursuit motion, generalizing results that are known for convex Euclidean domains, and obtaining results that are new for convex Euclidean domains and hold on playing fields vastly more general than these.

Shape deformation and fission route of the lipid domain in a multicomponent vesicle

In this paper, the curvature changes and fission routes of the lipid domains in a multicomponent vesicle are studied by dissipative particle dynamics. Under different conditions of asymmetric distribution of lipids in two leaflets of lipid bilayer and area-to-volume ratio of the vesicle, we obtained different configurations of the domain in the vesicle: three typical curvature characters of the lipid domain, namely, positive, negative, and invariable curvatures compared to the vesicle are observed. Furthermore, some other morphologies of the domain and two vesicle fission routes (i.e., exocytic and endocytic fissions) are also obtained in our simulations. Particular emphasis is put on the formation of the negative curvature domain and on the behavior of endocytic fission. Based on our simulations, it is indicated that water plays an important role in the invagination and endocytic fission processes of the domain in a vesicle. For endocytic fission, domains of different sizes are evolved according to different routes under the effect of the water. Additionally, we find that both the spontaneous curvature of lipid molecules and area-to-volume ratio can promote or restrain the shape deformation of the lipid domain. Under the competition of these two factors, another possible route of endocytic fission is observed in our simulations, in that only a part of the lipid domain invaginates into the interior of the vesicle to complete the endocytic fission. Our study is helpful for understanding the possible mechanism of the shape transformation of the cellular membrane and the difference of several kinds of routes of vesicle fission.

Curvature‐Domain Shape Processing

AbstractWe propose a framework for 3D geometry processing that provides direct access to surface curvature to facilitate advanced shape editing, filtering, and synthesis algorithms. The central idea is to map a given surface to the curvature domain by evaluating its principle curvatures, apply filtering and editing operations to the curvature distribution, and reconstruct the resulting surface using an optimization approach. Our system allows the user to prescribe arbitrary principle curvature values anywhere on the surface. The optimization solves a nonlinear least‐squares problem to find the surface that best matches the desired target curvatures while preserving important properties of the original shape. We demonstrate the effectiveness of this processing metaphor with several applications, including anisotropic smoothing, feature enhancement, and multi‐scale curvature editing.

Coexistence of Spheres and Rods in Micellar Solution of Dodecyldimethylamine Oxide

Micelles of dimethyldodecylamine oxide (DMDAO) are known to exhibit sphere-to-rod transitions as a function of pH and ionic strength. Long micelles are stabilized at pH corresponding to half-protonation, because hydrogen bonding between nonionic and protonated monomers yields an effectively double-tailed monomer whose geometry favors cylindrical growth. Dynamic light scattering (DLS) was used to follow particle size distribution as a function of pH, ionic strength (I), and surfactant concentration. The key finding was the coexistence of spherical micelles with rodlike ones at 4 < pH < 6 and I > 0.2 M. These observations have been verified by varying the algorithm used for the Laplace transformation of the autocorrelation function and also with different DLS systems. The effect of surfactant concentration was used to confirm the absence of any influence of micelle−micelle interaction on the dynamics of diffusion. A molecular level self-consistent field analysis of finite size rodlike micelles confirms the idea that the endcaps are swollen with respect to the cylindrical part. The theoretical results support the coexistence of rods and spherical micelles, i.e., the existence of gaps in the size distribution of wormlike micelles. The cause of coexistence has been explained in terms of the instability of dumbbell-like micelles with domains of negative curvature (neck). The endcap energy is shown to be given (in first order) by the grand potential of spherical micelles that coexist with the wormlike micelles.

It's Crowded Inside

The lipid bilayer structure of biological membranes is well defined conceptually—hydrophilic and charged head groups on the outside and nonpolar hydrocarbon tails on the inside—but not as well described at the atomic scale. Marrink and Mark have carried out computer simulations of vesicle formation and vesicle fusion in a system holding about a thousand dipalmitoyl phosphatidylcholine (DPPC) molecules and hundreds of thousands of water molecules. In general terms, the lipids behave pretty much as expected, coalescing first into micelles and then aggregating into a vesicle, with a higher initial lipid concentration yielding two micelles and a hemifused vesicle. Replacing a quarter of the DPPC with dipalmitoyl phosphatidylethanolamine produced vesicles with an excess of the smaller ethanolamine head group in the inner monolayer, consistent with its known preference for negative curvature domains. Close examination of the nonpolar core revealed that some of the hydrocarbon tails of the outer lipids extended across the midway point, whereas others folded back on themselves and occupied the extra space available in the head group region of the outer layer. Although these vesicles are small and thus more curved than most cellular membranes, these packing modes may nevertheless be relevant to the lipid gymnastics during membrane fusion. — GJC

Activity of phosphatidylinositol transfer protein is sensitive to ethanol and membrane curvature

Phosphatidylinositol transfer protein (PITP) is critical for many cellular signalling and trafficking events that are influenced by ethanol. The influence of ethanol and membrane curvature on the activity of recombinant mouse PITP-α in vitro is evaluated by monitoring the transfer of phosphatidylinositol (PtdIns) from rat hepatic microsomes to unilamellar vesicles. Acute exposure to pharmacological levels of ethanol enhanced the function of PITP. Chloroform shared a similar ability to enhance function when both drug concentrations were normalized to their respective octanol/water partition coefficients, indicating that the effect is not unique to ethanol and might be common to hydrophobic solutes. Neither the PITP activity nor its ethanol enhancement was altered by using thermally pretreated (denatured) or protease-treated microsomes, indicating that the native microsomal protein structure was unlikely to be a determinant of transfer. Kinetic analyses indicated that ethanol acted by increasing the PITP-mediated flux of PtdIns from both microsomal and liposomal surfaces. The activity of PITP was strongly dependent on the lipid structure, with a steep dependence on the expressed curvature of the membrane. Activity was greatest for small, highly curved sonicated vesicles and decreased markedly for large, locally planar unilamellar vesicles. Ethanol enhanced PITP-mediated PtdIns transfer to all vesicles, but its effect was much smaller than the enhancement due to curvature, which is consistent with ethanol's comparatively modest ability to perturb membrane lipids. The ethanol efficacy observed is as pronounced as any previously described lipid-mediated ethanol action. In addition, these observations raise the possibility that PITP specifically delivers PtdIns to metabolically active membrane domains of convex curvature and/or low surface densities of lipid.