Shape Analysis Of Curves Research Articles

Charge balance and photon collection in polymer based ternary bulk heterojunction photovoltaic devices containing cadmium selenide nanoparticles

Solar cells employing a ternary bulk heterojunction active layer comprised of poly(3-hexylthiophene) (P3HT), 6,6-phenyl C61-butyric acid methyl ester (PCBM) doped with composites constructed from a combination of 2.5 nm CdSe nanoparticles (NP), and methyl viologen (MV) have been examined. It was found that the devices containing the CdSe NP/MV composite exhibit significantly more photocurrent in a region surrounding the absorption peak of the particles (560-660 nm) when compared to pristine P3HT:PCBM devices. For a low ratio of CdSe to PCBM, the photocurrent collection was accompanied by space charge build up that limited the performance of the devices. When the ratio of CdSe to PCBM was raised, the space charge dissipated and performance recovered. JV curve shape analysis suggests that charge balance was achieved; however, electrode selectivity was reduced.

A New 3D-Matching Method of Nonrigid and Partially Similar Models Using Curve Analysis

The 3D-shape matching problem plays a crucial role in many applications, such as indexing or modeling, by example. Here, we present a novel approach to matching 3D objects in the presence of nonrigid transformation and partially similar models. In this paper, we use the representation of surfaces by 3D curves extracted around feature points. Indeed, surfaces are represented with a collection of closed curves, and tools from shape analysis of curves are applied to analyze and to compare curves. The belief functions are used to define a global distance between 3D objects. The experimental results obtained on the TOSCA and the SHREC07 data sets show that the system performs efficiently in retrieving similar 3D models.

Constant rate thermal analysis for thermal stability studies of polymers

This paper explores the relationship between the shapes of temperature–time curves obtained from experimental data recorded by means of constant rate thermal analysis (CRTA) and the kinetic model followed by the thermal degradation reaction. A detailed shape analysis of CRTA curves has been performed as a function of the most common kinetic models. The analysis has been validated with simulated data, and with experimental data recorded from the thermal degradation of polytetrafluoroethylene (PTFE), poly(1,4-butylene terephthalate) (PBT), polyethylene (PE) and poly(vinyl chloride) (PVC). The resulting temperature–time profiles indicate that the studied polymers decompose through phase boundary, random scission, diffusion and nucleation mechanisms respectively. The results here presented demonstrate that the strong dependence of the temperature–time profile on the reaction mechanism would allow the real kinetic model obeyed by a reaction to be discerned from a single CRTA curve.

A Mathematical Framework for Protein Structure Comparison

Comparison of protein structures is important for revealing the evolutionary relationship among proteins, predicting protein functions and predicting protein structures. Many methods have been developed in the past to align two or multiple protein structures. Despite the importance of this problem, rigorous mathematical or statistical frameworks have seldom been pursued for general protein structure comparison. One notable issue in this field is that with many different distances used to measure the similarity between protein structures, none of them are proper distances when protein structures of different sequences are compared. Statistical approaches based on those non-proper distances or similarity scores as random variables are thus not mathematically rigorous. In this work, we develop a mathematical framework for protein structure comparison by treating protein structures as three-dimensional curves. Using an elastic Riemannian metric on spaces of curves, geodesic distance, a proper distance on spaces of curves, can be computed for any two protein structures. In this framework, protein structures can be treated as random variables on the shape manifold, and means and covariance can be computed for populations of protein structures. Furthermore, these moments can be used to build Gaussian-type probability distributions of protein structures for use in hypothesis testing. The covariance of a population of protein structures can reveal the population-specific variations and be helpful in improving structure classification. With curves representing protein structures, the matching is performed using elastic shape analysis of curves, which can effectively model conformational changes and insertions/deletions. We show that our method performs comparably with commonly used methods in protein structure classification on a large manually annotated data set.

Shape Analysis of Elastic Curves in Euclidean Spaces

This paper introduces a square-root velocity (SRV) representation for analyzing shapes of curves in euclidean spaces under an elastic metric. In this SRV representation, the elastic metric simplifies to the IL(2) metric, the reparameterization group acts by isometries, and the space of unit length curves becomes the unit sphere. The shape space of closed curves is the quotient space of (a submanifold of) the unit sphere, modulo rotation, and reparameterization groups, and we find geodesics in that space using a path straightening approach. These geodesics and geodesic distances provide a framework for optimally matching, deforming, and comparing shapes. These ideas are demonstrated using: 1) shape analysis of cylindrical helices for studying protein structure, 2) shape analysis of facial curves for recognizing faces, 3) a wrapped probability distribution for capturing shapes of planar closed curves, and 4) parallel transport of deformations for predicting shapes from novel poses.

Probing In Vitro Interactions between Lactococcus lactis and Mucins Using AFM

This work was devoted to the first AFM investigation of the adhesion force to pig gastric mucin (PGM) using Lactococcus lactis as the model for lactic acid bacteria. The PGM coating on polystyrene was characterized using a complementary set of multiscale analytical methods, including AFM (HarmoniX mode), XPS, and the sessile drop method. The PGM layer, which was mainly composed of C-O, C-N, COOH, CONH, and sulfur-related species (protein core and oligosaccharide side chains), was quite homogeneous and hydrophilic, with an estimated thickness of 3.4 nm. L. lactis cells were immobilized on the AFM tip (lacto probe) and used as a force probe to measure the interaction forces between bacteria and PGM-coated polystyrene on the nanoscale. After mucin adsorption, adhesion force levels were lower because of the interplay of electrostatic, hydrophilic, and steric repulsions. For example, the adhesion forces of the lacto probe to bare and PGM-coated polymer were 0.74 +/- 0.10 and 0.12 +/- 0.06 nN, respectively. The shape analysis of retraction force-distance curves highlighted the contribution of both nonspecific and specific forces (ligand/receptor bonding). The lacto probe concept and the associated AFM measurements may now provide a powerful framework for understanding interaction mechanisms between mucins and lactic acid bacteria.

Elastic Shape Models for Face Analysis Using Curvilinear Coordinates

This paper studies the problem of analyzing variability in shapes of facial surfaces using a Riemannian framework, a fundamental approach that allows for joint matchings, comparisons, and deformations of faces under a chosen metric. The starting point is to impose a curvilinear coordinate system, named the Darcyan coordinate system, on facial surfaces; it is based on the level curves of the surface distance function measured from the tip of the nose. Each facial surface is now represented as an indexed collection of these level curves. The task of finding optimal deformations, or geodesic paths, between facial surfaces reduces to that of finding geodesics between level curves, which is accomplished using the theory of elastic shape analysis of 3D curves. The elastic framework allows for nonlinear matching between curves and between points across curves. The resulting geodesics between facial surfaces provide optimal elastic deformations between faces and an elastic metric for comparing facial shapes. We demonstrate this idea using examples from FSU face database.

Removing Shape-Preserving Transformations in Square-Root Elastic (SRE) Framework for Shape Analysis of Curves.

This paper illustrates and extends an efficient framework, called the square-root-elastic (SRE) framework, for studying shapes of closed curves, that was first introduced in [2]. This framework combines the strengths of two important ideas - elastic shape metric and path-straightening methods - for finding geodesics in shape spaces of curves. The elastic metric allows for optimal matching of features between curves while path-straightening ensures that the algorithm results in geodesic paths. This paper extends this framework by removing two important shape preserving transformations: rotations and re-parameterizations, by forming quotient spaces and constructing geodesics on these quotient spaces. These ideas are demonstrated using experiments involving 2D and 3D curves.

Theoretical and practical implications of creep curve shape analyses for 7010 and 7075

Over tensile stress ranges giving creep lives up to 2000 hours at 373 to 463 K, the creep and creep fracture properties of 7010 are compared with results recorded for 7075 and other precipitation-hardened aluminum alloys. Using the ϑ methodology to quantify the systematic variations in creep curve shape with changing test conditions, the behavior patterns displayed by the different alloys are shown to depend on the extent to which precipitate coarsening causes a progressive loss of creep strength with increasing test duration and temperature. The ϑ relationships also introduce new approaches for rationalization and interpretation of creep data sets, based on the activation energy for lattice diffusion in the alloy matrices and the yield stress or UTS at the creep temperatures.

Theoretical and practical implications of creep curve shape analyses for 7010 and 7075

Theoretical and practical implications of creep curve shape analyses for 7010 and 7075

Theoretical and practical implications of creep curve shape analyses for 7010 and 7075

Theoretical and practical implications of creep curve shape analyses for 7010 and 7075

Contrast‐enhanced MRI of ductal carcinoma in situ: Characteristics of a new intensity‐modulated parametric mapping technique correlated with histopathologic findings

To identify morphologic and dynamic enhancement magnetic resonance imaging (MRI) features of pure ductal carcinoma in situ (DCIS) by using a new intensity-modulated parametric mapping technique, and to correlate the MRI features with histopathologic findings. Fourteen patients with pure DCIS on pathology underwent conventional mammography and contrast-enhanced (CE) MRI using the intensity-modulated parametric mapping technique. The MR images were reviewed and the lesions were categorized according to morphologic and kinetic criteria from the ACR BI-RADS-MRI Lexicon, with BI-RADS 4 and 5 lesions classified as suspicious. With the use of a kinetic curve shape analysis, MRI classified seven of 14 lesions (50%) as suspicious, including four with initial-rapid/late-washout and three with initial-rapid/late-plateau. Using morphologic criteria, MRI classified 10/14 (71%) as suspicious, with the most prominent morphologic feature being a regional enhancement pattern. Using the intensity modulated parametric mapping technique, MRI classified 12/14 cases (86%) as suspicious. Parametric mapping identified all intermediate- and high-grade DCIS lesions. The intensity-modulated parametric mapping technique for breast MRI resulted in the highest detection rate for the DCIS cases. Furthermore, the parametric mapping technique identified all intermediate- and high-grade DCIS lesions, suggesting that a negative MRI using the parametric mapping technique may exclude intermediate- and high-grade DCIS. This finding has potential clinical implications.

Tertiary creep of metals and alloys

Abstract The variations in strain rate with increasing strain are documented for tensile creep curves obtained under constant-stress test conditions for a range of pure metals and commercial creep-resistant alloys. These curve shape analyses are discussed in relation to information derived from microstructural studies and determinations of creep damage tolerance values, allowing identification of the damage processes governing tertiary creep and fracture.

Theoretical and practical implications of creep curve shape analyses for 8090

For tensile stresses applied parallel to the elongated grain structure of the aluminum alloy, 8090, the creep and creep fracture properties are discussed in relation to the changes in precipitate dispersion and transgranular failure mode observed over stress ranges giving creep lives up to 6000 hours at 373 to 463 K. Specifically, a transition from growth of cracks nucleating on the short transverse boundaries to neck formation occurs when the deformation resistance is reduced progressively by precipitate coarsening as the test duration increases at 427 K and above. All features of the recorded behavior patterns are then explained in terms of the processes governing strain accumulation and damage development by using the ϑ methodology to quantify the systematic variations in creep curve shape with changing stress and temperature.

Deformation and damage processes during creep of Incoloy MA957

Tensile creep and creep facture properties at 873–973 K are reported for the oxide-dispersion-strengthened (ODS) ferritic steel, Incoloy MA957. The results are interpreted on the basis of information derived from microstructural studies, yield stress data, creep curve shape analyses and comparisons of tensile and compressive creep characteristics. Using this combination of approaches, the observed behaviour patterns can be rationalized in a manner consistent with the processes shown to govern strain accumulation and damage development during creep of ODS alloys produced with high grain aspect ratios.

Deformation and damage processes during creep of Incoloy MA957

Abstract Tensile creep and creep facture properties at 873–973 K are reported for the oxide-dispersion-strengthened (ODS) ferritic steel, Incoloy MA957. The results are interpreted on the basis of information derived from microstructural studies, yield stress data, creep curve shape analyses and comparisons of tensile and compressive creep characteristics. Using this combination of approaches, the observed behaviour patterns can be rationalized in a manner consistent with the processes shown to govern strain accumulation and damage development during creep of ODS alloys produced with high grain aspect ratios.

Theoretical and practical implications of creep curve shape analyses for 2124 and 2419

Creep and creep fracture properties are presented for two commercial aluminum alloys, 2124 and 2419, tested at stresses giving creep lives up to about 1000 hours at 373 to 463 K. The results are analyzed using the ϑ methodology, which quantifies the shape of individual creep curves and the variations in curve shape with changing stress and temperature. The ϑ relationships are shown to allow reasonable prediction of 100,000-hour stress rupture values, while also explaining the complex creep behavior patterns widely observed with precipitation-hardened alloys.

Evolution of electrical properties of some conductive polymer composite textiles with organic solvent vapours diffusion

The sensitivity of several conductive polymer composites (CPC) to solvent vapours has been studied. Electrical properties of three CPC poly(amide12-b-tetramethylene oxide)-carbon black (PEBAX-CB), poly(propylene)-carbon black (PP-CB) and poly(ethylene-co-ethyl acrylate)-carbon black (EEA-CB) were investigated in the presence of four organic solvent vapours, chloroform, toluene, methanol and ethanol. The experiments show that it is possible to use extruded CPC textiles to combine acceptable conductivity for heating and satisfying response for vapour detection. Moreover, the investigation of the mechanisms involved during the solvent vapours diffusion into the CPC, shows that not only the response of the systems Δ R/ R 0 can be used for vapour detection but also the shape of the curves, i.e., the diffusion mode characterised by Δ R/ R max versus t curves slope and onset. The diffusion curve shape analysis together with the use of CPC of different chemical nature and structure (comonomer content and crystallinity) is expected to decrease the number of CPC necessary for vapour detection.

Observations, theories, and predictions of high-temperature creep behavior

The key observations that have underpinned traditional power-law approaches to creep mechanism identification have been re-evaluated, using information obtained for aluminum, copper, and 0.5Cr0.5Mo0.25V steel. In particular, stress/creep rate plots produced over extended stress ranges for all three materials are shown to be well represented by continuous curves, contradicting the common assumption that different creep mechanisms are dominant over different stress/temperature regimes. Evidence is also introduced to demonstrate that the theoretical and practical limitations of power-law descriptions of steady-state creep rates can be overcome by quantifying the shapes of normal creep curves and the variations in curve shape with changing test conditions. In this way, the behavior patterns displayed by pure metals and particle-hardened alloys can be interpreted in terms of the deformation processes controlling creep-strain accumulation and the damage/degradation processes causing the creep rate to accelerate into the tertiary stages that usually precede fracture. Moreover, the superior predictive capabilities of curve shape analysis are then illustrated by results showing that short-term property values can be extrapolated to provide accurate long-term engineering design data.

Assigning Possible Ion Exchange Sites in Cerium(IV) Antimonates

Empirical formulae, based upon thermo-analytical investigations, have been assigned for different cerium(IV) antimonate samples prepared under varying conditions of precipitation. Equilibria and apparent Na+-capacity measurements at different pH values were carried out to throw more light on their sorption behavior. From the general curve shape analysis of the capacity-pH curves, the possible ion exchange site acidity and site group concentration were characterized. The samples showed almost bifunctional cation exchange behavior. The results obtained are discussed in detail referring to some conclusions.