Cortical Hemisphere Registration Via Large Deformation Diffeomorphic Metric Curve Mapping
Qiu, Anqi; Miller, Michael I.
2010-01-01
We present large deformation diffeomorphic metric curve mapping (LDDMM-Curve) for registering cortical hemispheres. We showed global cortical hemisphere matching and evaluated the mapping accuracy in five subregions of the cortex in fourteen MRI scans. PMID:18051058
Tan, Mingzhen; Qiu, Anqi
2016-09-01
Brain surface registration is an important tool for characterizing cortical anatomical variations and understanding their roles in normal cortical development and psychiatric diseases. However, surface registration remains challenging due to complicated cortical anatomy and its large differences across individuals. In this paper, we propose a fast coarse-to-fine algorithm for surface registration by adapting the large diffeomorphic deformation metric mapping (LDDMM) framework for surface mapping and show improvements in speed and accuracy via a multiresolution analysis of surface meshes and the construction of multiresolution diffeomorphic transformations. The proposed method constructs a family of multiresolution meshes that are used as natural sparse priors of the cortical morphology. At varying resolutions, these meshes act as anchor points where the parameterization of multiresolution deformation vector fields can be supported, allowing the construction of a bundle of multiresolution deformation fields, each originating from a different resolution. Using a coarse-to-fine approach, we show a potential reduction in computation cost along with improvements in sulcal alignment when compared with LDDMM surface mapping. PMID:27254865
Multi-contrast large deformation diffeomorphic metric mapping for diffusion tensor imaging
Ceritoglu, Can; Oishi, Kenichi; Li, Xin; Chou, Ming-Chung; Younes, Laurent; Albert, Marilyn; Lyketsos, Constantine; van Zijl, Peter C.M.; Miller, Michael I.; Mori, Susumu
2010-01-01
Diffusion tensor imaging (DTI) can reveal detailed white matter anatomy and has the potential to detect abnormalities in specific white matter structures. Such detection and quantification are, however, not straightforward. The voxel-based analysis after image normalization is one of the most widely used methods for quantitative image analyses. To apply this approach to DTI, it is important to examine if structures in the white matter are well registered among subjects, which would be highly dependent on employed algorithms for normalization. In this paper, we evaluate the accuracy of normalization of DTI data using a highly elastic transformation algorithm, called large deformation diffeomorphic metric mapping. After simulation-based validation of the algorithm, DTI data from normal subjects were used to measure the registration accuracy. To examine the impact of morphological abnormalities on the accuracy, the algorithm was also tested using data from Alzheimer’s disease (AD) patients with severe brain atrophy. The accuracy level was measured by using manual landmark-based white matter matching and surface-based brain and ventricle matching as gold standard. To improve the accuracy level, cascading and multi-contrast approaches were developed. The accuracy level for the white matter was 1.88 ± 0.55 and 2.19 ± 0.84 mm for the measured locations in the controls and patients, respectively. PMID:19398016
Deep Adaptive Log-Demons: Diffeomorphic Image Registration with Very Large Deformations
Zhao, Liya; Jia, Kebin
2015-01-01
This paper proposes a new framework for capturing large and complex deformation in image registration. Traditionally, this challenging problem relies firstly on a preregistration, usually an affine matrix containing rotation, scale, and translation and afterwards on a nonrigid transformation. According to preregistration, the directly calculated affine matrix, which is obtained by limited pixel information, may misregistrate when large biases exist, thus misleading following registration subversively. To address this problem, for two-dimensional (2D) images, the two-layer deep adaptive registration framework proposed in this paper firstly accurately classifies the rotation parameter through multilayer convolutional neural networks (CNNs) and then identifies scale and translation parameters separately. For three-dimensional (3D) images, affine matrix is located through feature correspondences by a triplanar 2D CNNs. Then deformation removal is done iteratively through preregistration and demons registration. By comparison with the state-of-the-art registration framework, our method gains more accurate registration results on both synthetic and real datasets. Besides, principal component analysis (PCA) is combined with correlation like Pearson and Spearman to form new similarity standards in 2D and 3D registration. Experiment results also show faster convergence speed. PMID:26120356
Deep Adaptive Log-Demons: Diffeomorphic Image Registration with Very Large Deformations.
Zhao, Liya; Jia, Kebin
2015-01-01
This paper proposes a new framework for capturing large and complex deformation in image registration. Traditionally, this challenging problem relies firstly on a preregistration, usually an affine matrix containing rotation, scale, and translation and afterwards on a nonrigid transformation. According to preregistration, the directly calculated affine matrix, which is obtained by limited pixel information, may misregistrate when large biases exist, thus misleading following registration subversively. To address this problem, for two-dimensional (2D) images, the two-layer deep adaptive registration framework proposed in this paper firstly accurately classifies the rotation parameter through multilayer convolutional neural networks (CNNs) and then identifies scale and translation parameters separately. For three-dimensional (3D) images, affine matrix is located through feature correspondences by a triplanar 2D CNNs. Then deformation removal is done iteratively through preregistration and demons registration. By comparison with the state-of-the-art registration framework, our method gains more accurate registration results on both synthetic and real datasets. Besides, principal component analysis (PCA) is combined with correlation like Pearson and Spearman to form new similarity standards in 2D and 3D registration. Experiment results also show faster convergence speed. PMID:26120356
Large chiral diffeomorphisms on Riemann surfaces and W-algebras
Bandelloni, G.; Lazzarini, S.
2006-10-15
The diffeomorphism action lifted on truncated (chiral) Taylor expansion of a complex scalar field over a Riemann surface is presented in the paper under the name of large diffeomorphisms. After an heuristic approach, we show how a linear truncation in the Taylor expansion can generate an algebra of symmetry characterized by some structure functions. Such a linear truncation is explicitly realized by introducing the notion of Forsyth frame over the Riemann surface with the help of a conformally covariant algebraic differential equation. The large chiral diffeomorphism action is then implemented through a Becchi-Rouet-Stora (BRS) formulation (for a given order of truncation) leading to a more algebraic setup. In this context the ghost fields behave as holomorphically covariant jets. Subsequently, the link with the so-called W-algebras is made explicit once the ghost parameters are turned from jets into tensorial ghost ones. We give a general solution with the help of the structure functions pertaining to all the possible truncations lower or equal to the given order. This provides another contribution to the relationship between Korteweg-de Vries (KdV) flows and W-diffeomorphims.
Fermions, q-deformed diffeomorphism and the evolution of spin networks
NASA Astrophysics Data System (ADS)
Mullick, L.; Bandyopadhyay, P.
2015-06-01
We have considered here the emergence of diffeomorphism symmetry in quantum gravity in the framework of the quantization of a fermion. It is pointed out that a closed loop having the holonomy associated with the SU(2) gauge group is realized from the rotation of the direction vector associated with the quantization of a fermion depicting spin degrees of freedom which appear as SU(2) gauge bundle. During the formation of a loop, a noncyclic path with open ends can be mapped onto a closed loop when the holonomy involves q-deformed gauge group SUq(2). This gives rise to q-deformed diffeomorphism and helps to realize diffeomorphism invariance in quantum gravity through a sequence of q-deformed diffeomorphism in the limit q = 1. We can consider adiabatic iteration such that the quasispin associated with the quantum group SUq(2) gradually evolves as the time dependent deformation parameter q changes and in the limit q = 1, we achieve the standard spin. This essentially depicts the evolution of spin network as the loop is being formed and links fermionic degrees of freedom with loop quantum gravity.
Volume-preserving diffeomorphisms in integrable deformations of self-dual gravity
NASA Astrophysics Data System (ADS)
Takasaki, Kanehisa
1992-07-01
A group of volume-preserving diffeomorphisms in 3D turns out to play a key role in an Einstein-Maxwell theory whose Weyl tensor is self-dual and whose Maxwell tensor has an algebraically general anti-self-dual part. This model was first introduced by Flaherty and recently studied by Park as an integrable deformation of self-dual gravity. A twisted volume form on the corresponding twistor space is shown to be the origin of volume-preserving diffeomorphisms. An immediate consequence is the existence of an infinite number of symmetries as a generalization of w 1 + ∞ symmetries in self-dual gravity. A possible relation to Witten's 2D string theory is pointed out.
Hadj-Hamou, Mehdi; Lorenzi, Marco; Ayache, Nicholas; Pennec, Xavier
2016-01-01
We propose and detail a deformation-based morphometry computational framework, called Longitudinal Log-Demons Framework (LLDF), to estimate the longitudinal brain deformations from image data series, transport them in a common space and perform statistical group-wise analyses. It is based on freely available software and tools, and consists of three main steps: (i) Pre-processing, (ii) Position correction, and (iii) Non-linear deformation analysis. It is based on the LCC log-Demons non-linear symmetric diffeomorphic registration algorithm with an additional modulation of the similarity term using a confidence mask to increase the robustness with respect to brain boundary intensity artifacts. The pipeline is exemplified on the longitudinal Open Access Series of Imaging Studies (OASIS) database and all the parameters values are given so that the study can be reproduced. We investigate the group-wise differences between the patients with Alzheimer's disease and the healthy control group, and show that the proposed pipeline increases the sensitivity with no decrease in the specificity of the statistical study done on the longitudinal deformations. PMID:27375408
Hadj-Hamou, Mehdi; Lorenzi, Marco; Ayache, Nicholas; Pennec, Xavier
2016-01-01
We propose and detail a deformation-based morphometry computational framework, called Longitudinal Log-Demons Framework (LLDF), to estimate the longitudinal brain deformations from image data series, transport them in a common space and perform statistical group-wise analyses. It is based on freely available software and tools, and consists of three main steps: (i) Pre-processing, (ii) Position correction, and (iii) Non-linear deformation analysis. It is based on the LCC log-Demons non-linear symmetric diffeomorphic registration algorithm with an additional modulation of the similarity term using a confidence mask to increase the robustness with respect to brain boundary intensity artifacts. The pipeline is exemplified on the longitudinal Open Access Series of Imaging Studies (OASIS) database and all the parameters values are given so that the study can be reproduced. We investigate the group-wise differences between the patients with Alzheimer's disease and the healthy control group, and show that the proposed pipeline increases the sensitivity with no decrease in the specificity of the statistical study done on the longitudinal deformations. PMID:27375408
Robust Diffeomorphic Mapping via Geodesically Controlled Active Shapes
Tward, Daniel J.; Ma, Jun; Miller, Michael I.; Younes, Laurent
2013-01-01
This paper presents recent advances in the use of diffeomorphic active shapes which incorporate the conservation laws of large deformation diffeomorphic metric mapping. The equations of evolution satisfying the conservation law are geodesics under the diffeomorphism metric and therefore termed geodesically controlled diffeomorphic active shapes (GDAS). Our principal application in this paper is on robust diffeomorphic mapping methods based on parameterized surface representations of subcortical template structures. Our parametrization of the GDAS evolution is via the initial momentum representation in the tangent space of the template surface. The dimension of this representation is constrained using principal component analysis generated from training samples. In this work, we seek to use template surfaces to generate segmentations of the hippocampus with three data attachment terms: surface matching, landmark matching, and inside-outside modeling from grayscale T1 MR imaging data. This is formulated as an energy minimization problem, where energy describes shape variability and data attachment accuracy, and we derive a variational solution. A gradient descent strategy is employed in the numerical optimization. For the landmark matching case, we demonstrate the robustness of this algorithm as applied to the workflow of a large neuroanatomical study by comparing to an existing diffeomorphic landmark matching algorithm. PMID:23690757
Large Scale Nanolaminate Deformable Mirror
Papavasiliou, A; Olivier, S; Barbee, T; Miles, R; Chang, K
2005-11-30
This work concerns the development of a technology that uses Nanolaminate foils to form light-weight, deformable mirrors that are scalable over a wide range of mirror sizes. While MEMS-based deformable mirrors and spatial light modulators have considerably reduced the cost and increased the capabilities of adaptive optic systems, there has not been a way to utilize the advantages of lithography and batch-fabrication to produce large-scale deformable mirrors. This technology is made scalable by using fabrication techniques and lithography that are not limited to the sizes of conventional MEMS devices. Like many MEMS devices, these mirrors use parallel plate electrostatic actuators. This technology replicates that functionality by suspending a horizontal piece of nanolaminate foil over an electrode by electroplated nickel posts. This actuator is attached, with another post, to another nanolaminate foil that acts as the mirror surface. Most MEMS devices are produced with integrated circuit lithography techniques that are capable of very small line widths, but are not scalable to large sizes. This technology is very tolerant of lithography errors and can use coarser, printed circuit board lithography techniques that can be scaled to very large sizes. These mirrors use small, lithographically defined actuators and thin nanolaminate foils allowing them to produce deformations over a large area while minimizing weight. This paper will describe a staged program to develop this technology. First-principles models were developed to determine design parameters. Three stages of fabrication will be described starting with a 3 x 3 device using conventional metal foils and epoxy to a 10-across all-metal device with nanolaminate mirror surfaces.
Locally Linear Diffeomorphic Metric Embedding (LLDME) for surface-based anatomical shape modeling.
Yang, Xianfeng; Goh, Alvina; Qiu, Anqi
2011-05-01
This paper presents the algorithm, Locally Linear Diffeomorphic Metric Embedding (LLDME), for constructing efficient and compact representations of surface-based brain shapes whose variations are characterized using Large Deformation Diffeomorphic Metric Mapping (LDDMM). Our hypothesis is that the shape variations in the infinite-dimensional diffeomorphic metric space can be captured by a low-dimensional space. To do so, traditional Locally Linear Embedding (LLE) that reconstructs a data point from its neighbors in Euclidean space is extended to LLDME that requires interpolating a shape from its neighbors in the infinite-dimensional diffeomorphic metric space. This is made possible through the conservation law of momentum derived from LDDMM. It indicates that initial momentum, a linear transformation of the initial velocity of diffeomorphic flows, at a fixed template shape determines the geodesic connecting the template to a subject's shape in the diffeomorphic metric space and becomes the shape signature of an individual subject. This leads to the compact linear representation of the nonlinear diffeomorphisms in terms of the initial momentum. Since the initial momentum is in a linear space, a shape can be approximated by a linear combination of its neighbors in the diffeomorphic metric space. In addition, we provide efficient computations for the metric distance between two shapes through the first order approximation of the geodesic using the initial momentum as well as for the reconstruction of a shape given its low-dimensional Euclidean coordinates using the geodesic shooting with the initial momentum as the initial condition. Experiments are performed on the hippocampal shapes of 302 normal subjects across the whole life span (18-94years). Compared with Principal Component Analysis and ISOMAP, LLDME provides the most compact and efficient representation of the age-related hippocampal shapes. Even though the hippocampal volumes among young adults are as
Explicit B-spline regularization in diffeomorphic image registration
Tustison, Nicholas J.; Avants, Brian B.
2013-01-01
Diffeomorphic mappings are central to image registration due largely to their topological properties and success in providing biologically plausible solutions to deformation and morphological estimation problems. Popular diffeomorphic image registration algorithms include those characterized by time-varying and constant velocity fields, and symmetrical considerations. Prior information in the form of regularization is used to enforce transform plausibility taking the form of physics-based constraints or through some approximation thereof, e.g., Gaussian smoothing of the vector fields [a la Thirion's Demons (Thirion, 1998)]. In the context of the original Demons' framework, the so-called directly manipulated free-form deformation (DMFFD) (Tustison et al., 2009) can be viewed as a smoothing alternative in which explicit regularization is achieved through fast B-spline approximation. This characterization can be used to provide B-spline “flavored” diffeomorphic image registration solutions with several advantages. Implementation is open source and available through the Insight Toolkit and our Advanced Normalization Tools (ANTs) repository. A thorough comparative evaluation with the well-known SyN algorithm (Avants et al., 2008), implemented within the same framework, and its B-spline analog is performed using open labeled brain data and open source evaluation tools. PMID:24409140
NASA Astrophysics Data System (ADS)
Chen, Jingyun; Palmer, Samantha J.; Khan, Ali R.; Mckeown, Martin J.; Beg, Mirza Faial
2009-02-01
We apply a recently developed automated brain segmentation method, FS+LDDMM, to brain MRI scans from Parkinson's Disease (PD) subjects, and normal age-matched controls and compare the results to manual segmentation done by trained neuroscientists. The data set consisted of 14 PD subjects and 12 age-matched control subjects without neurologic disease and comparison was done on six subcortical brain structures (left and right caudate, putamen and thalamus). Comparison between automatic and manual segmentation was based on Dice Similarity Coefficient (Overlap Percentage), L1 Error, Symmetrized Hausdorff Distance and Symmetrized Mean Surface Distance. Results suggest that FS+LDDMM is well-suited for subcortical structure segmentation and further shape analysis in Parkinson's Disease. The asymmetry of the Dice Similarity Coefficient over shape change is also discussed based on the observation and measurement of FS+LDDMM segmentation results.
Splines for Diffeomorphic Image Regression
Singh, Nikhil; Niethammer, Marc
2016-01-01
This paper develops a method for splines on diffeomorphisms for image regression. In contrast to previously proposed methods to capture image changes over time, such as geodesic regression, the method can capture more complex spatio-temporal deformations. In particular, it is a first step towards capturing periodic motions for example of the heart or the lung. Starting from a variational formulation of splines the proposed approach allows for the use of temporal control points to control spline behavior. This necessitates the development of a shooting formulation for splines. Experimental results are shown for synthetic and real data. The performance of the method is compared to geodesic regression. PMID:25485370
Large Deformations of a Soft Porous Material
NASA Astrophysics Data System (ADS)
MacMinn, Christopher W.; Dufresne, Eric R.; Wettlaufer, John S.
2016-04-01
Compressing a porous material will decrease the volume of the pore space, driving fluid out. Similarly, injecting fluid into a porous material can expand the pore space, distorting the solid skeleton. This poromechanical coupling has applications ranging from cell and tissue mechanics to geomechanics and hydrogeology. The classical theory of linear poroelasticity captures this coupling by combining Darcy's law with Terzaghi's effective stress and linear elasticity in a linearized kinematic framework. Linear poroelasticity is a good model for very small deformations, but it becomes increasingly inappropriate for moderate to large deformations, which are common in the context of phenomena such as swelling and damage, and for soft materials such as gels and tissues. The well-known theory of large-deformation poroelasticity combines Darcy's law with Terzaghi's effective stress and nonlinear elasticity in a rigorous kinematic framework. This theory has been used extensively in biomechanics to model large elastic deformations in soft tissues and in geomechanics to model large elastoplastic deformations in soils. Here, we first provide an overview and discussion of this theory with an emphasis on the physics of poromechanical coupling. We present the large-deformation theory in an Eulerian framework to minimize the mathematical complexity, and we show how this nonlinear theory simplifies to linear poroelasticity under the assumption of small strain. We then compare the predictions of linear poroelasticity with those of large-deformation poroelasticity in the context of two uniaxial model problems: fluid outflow driven by an applied mechanical load (the consolidation problem) and compression driven by a steady fluid throughflow. We explore the steady and dynamical errors associated with the linear model in both situations, as well as the impact of introducing a deformation-dependent permeability. We show that the error in linear poroelasticity is due primarily to kinematic
Du, Jia; Younes, Laurent; Qiu, Anqi
2011-05-01
This paper introduces a novel large deformation diffeomorphic metric mapping algorithm for whole brain registration where sulcal and gyral curves, cortical surfaces, and intensity images are simultaneously carried from one subject to another through a flow of diffeomorphisms. To the best of our knowledge, this is the first time that the diffeomorphic metric from one brain to another is derived in a shape space of intensity images and point sets (such as curves and surfaces) in a unified manner. We describe the Euler-Lagrange equation associated with this algorithm with respect to momentum, a linear transformation of the velocity vector field of the diffeomorphic flow. The numerical implementation for solving this variational problem, which involves large-scale kernel convolution in an irregular grid, is made feasible by introducing a class of computationally friendly kernels. We apply this algorithm to align magnetic resonance brain data. Our whole brain mapping results show that our algorithm outperforms the image-based LDDMM algorithm in terms of the mapping accuracy of gyral/sulcal curves, sulcal regions, and cortical and subcortical segmentation. Moreover, our algorithm provides better whole brain alignment than combined volumetric and surface registration (Postelnicu et al., 2009) and hierarchical attribute matching mechanism for elastic registration (HAMMER) (Shen and Davatzikos, 2002) in terms of cortical and subcortical volume segmentation. PMID:21281722
Large poroelastic deformation of a soft material
NASA Astrophysics Data System (ADS)
MacMinn, Christopher W.; Dufresne, Eric R.; Wettlaufer, John S.
2014-11-01
Flow through a porous material will drive mechanical deformation when the fluid pressure becomes comparable to the stiffness of the solid skeleton. This has applications ranging from hydraulic fracture for recovery of shale gas, where fluid is injected at high pressure, to the mechanics of biological cells and tissues, where the solid skeleton is very soft. The traditional linear theory of poroelasticity captures this fluid-solid coupling by combining Darcy's law with linear elasticity. However, linear elasticity is only volume-conservative to first order in the strain, which can become problematic when damage, plasticity, or extreme softness lead to large deformations. Here, we compare the predictions of linear poroelasticity with those of a large-deformation framework in the context of two model problems. We show that errors in volume conservation are compounded and amplified by coupling with the fluid flow, and can become important even when the deformation is small. We also illustrate these results with a laboratory experiment.
The algebra of diffeomorphisms from the world sheet
NASA Astrophysics Data System (ADS)
Schulgin, Waldemar; Troost, Jan
2014-09-01
The quantum theory of a massless spin two particle is strongly constrained by diffeomorphism invariance, which is in turn implied by unitarity. We explicitly exhibit the space-time diffeomorphism algebra of string theory, realizing it in terms of world sheet vertex operators. Viewing diffeomorphisms as field redefinitions in the two-dimensional conformal field theory renders the calculation of their algebra straightforward. Next, we generalize the analysis to combinations of space-time anti-symmetric tensor gauge transformations and diffeomorphisms. We also point out a left-right split of the algebra combined with a twist that reproduces the C-bracket of double field theory. We further compare our derivation to an analysis in terms of marginal deformations as well as vertex operator algebras.
Diffeomorphic Registration of Images with Variable Contrast Enhancement
Janssens, Guillaume; Jacques, Laurent; Orban de Xivry, Jonathan; Geets, Xavier; Macq, Benoit
2011-01-01
Nonrigid image registration is widely used to estimate tissue deformations in highly deformable anatomies. Among the existing methods, nonparametric registration algorithms such as optical flow, or Demons, usually have the advantage of being fast and easy to use. Recently, a diffeomorphic version of the Demons algorithm was proposed. This provides the advantage of producing invertible displacement fields, which is a necessary condition for these to be physical. However, such methods are based on the matching of intensities and are not suitable for registering images with different contrast enhancement. In such cases, a registration method based on the local phase like the Morphons has to be used. In this paper, a diffeomorphic version of the Morphons registration method is proposed and compared to conventional Morphons, Demons, and diffeomorphic Demons. The method is validated in the context of radiotherapy for lung cancer patients on several 4D respiratory-correlated CT scans of the thorax with and without variable contrast enhancement. PMID:21197460
Diffeomorphism groups and anyon fields
Goldin, G.A.; Sharp, D.H.
1995-09-01
We make use of unitary representations of the group of diffeomorphisms of the plane to construct an explicit field theory of anyons. The resulting anyon fields satisfy q-commutators, where q is the well-known phase shift associated with a single counterclockwise exchange of a pair of anyons. Our method uses a realization of the braid group by means of paths in the plane, that transform naturally under diffeomorphisms of R{sup 2}.
Large Deformation Dynamic Bending of Composite Beams
NASA Technical Reports Server (NTRS)
Derian, E. J.; Hyer, M. W.
1986-01-01
Studies were conducted on the large deformation response of composite beams subjected to a dynamic axial load. The beams were loaded with a moderate eccentricity to promote bending. The study was primarily experimental but some finite element results were obtained. Both the deformation and the failure of the beams were of interest. The static response of the beams was also studied to determine potential differences between the static and dynamic failure. Twelve different laminate types were tested. The beams tested were 23 in. by 2 in. and generally 30 plies thick. The beams were loaded dynamically with a gravity-driven impactor traveling at 19.6 ft/sec and quasi-static tests were conducted on identical beams in a displacement controlled manner. For laminates of practical interest, the failure modes under static and dynamic loadings were identical. Failure in most of the laminate types occurred in a single event involving 40% to 50% of the plies. However, failure in laminates with 300 or 150 off-axis plies occurred in several events. All laminates exhibited bimodular elastic properties. The compressive flexural moduli in some laminates was measured to be 1/2 the tensile flexural modulus. No simple relationship could be found among the measured ultimate failure strains of the different laminate types. Using empirically determined flexural properties, a finite element analysis was reasonably accurate in predicting the static and dynamic deformation response.
Analysis of deformations of large earth dams
NASA Astrophysics Data System (ADS)
Szostak-Chrzanowski, Anna; Massiéra, Michel; Chrzanowski, Adam
2007-09-01
Safety of earth dams depends on the proper design, construction, and monitoring of actual behaviour during the construction and during the operation of the structure. The most critical factor in the assessment of the safety threshold value of any structure is the acceleration of its deformation. Therefore, the designed accuracy of monitoring surveys must fulfill requirements of detecting accelerations at critical locations of the investigated object. As an example, time dependant behavior of a large embankment dam during filling up the reservoir has been analyzed and verified by comparing monitoring results with the deterministic (prediction) model of the deformation. The geotechnical and geodetic monitoring besides providing a warning system in case of an abnormal behaviour of the dam, may be used as a tool for a verification of design parameters where geotechnical parameters are of the highest importance. Modeling of deformation of earth dams is a complex process in which one should consider the nonlinear behaviour of the construction material, interaction between the structure and the underlying foundation strata, influence of water load on the structure and on the foundation bedrock, and the effects of water saturation. Due to the uncertainty of the model parameters, careful monitoring of the dam and its surroundings are required in order to verify and enhance the model. In addition, with properly designed monitoring surveys, one may also determine the actual deformation mechanism. The finite element method may be useful tool in the proper design of the monitoring scheme by providing information on the locations and magnitude of the expected maximum displacements and velocites of movements. The discussed problems are illustrated by three types of earth dams located in California, U.S.A. and in Quebec, Canada.
Local remeshing for large amplitude grid deformations
NASA Astrophysics Data System (ADS)
Moyle, Keri R.; Ventikos, Yiannis
2008-02-01
Fluid-structure interaction (FSI) modelling can involve large deformations in the fluid domain, which could lead to degenerating mesh quality and numerical inaccuracies or instabilities, if allowed to amplify unchecked. Complete remeshing of the entire domain during the solution process is computationally expensive, and can require interpolation of solution variables between meshes. As an alternative, we investigate a local remeshing algorithm, with two emphases: (a) the identification and remedy of flat, degenerate tetrahedra, and (b) the avoidance of node motion, and hence associated interpolation errors. Initially, possible topological changes are examined using a dynamic programming algorithm to maximise the minimum local element quality through edge reconnection. In the 3D situation it was found that reconnection improvements tend to be limited to long edges, and those with few (three or four) element neighbours. The remaining degenerate elements are classified into one of four types using three proposed metrics - the minimum edge-to-edge distance (EE), the minimum node-to-edge distance (NE), and the shortest edge length (SE) - and removed according to the best manner for their type. Optimised thresholds for identifying and classifying elements for removal were found to be EE < 0.18, NE < 0.21, SE < 0.2.
S-HAMMER: Hierarchical Attribute-Guided, Symmetric Diffeomorphic Registration for MR Brain Images
Wu, Guorong; Kim, Minjeong; Wang, Qian; Shen, Dinggang
2013-01-01
Deformable registration has been widely used in neuroscience studies for spatial normalization of brain images onto the standard space. Because of possible large anatomical differences across different individual brains, registration performance could be limited when trying to estimate a single directed deformation pathway, i.e., either from template to subject or from subject to template. Symmetric image registration, however, offers an effective way to simultaneously deform template and subject images toward each other until they meet at the middle point. Although some intensity-based registration algorithms have nicely incorporated this concept of symmetric deformation, the pointwise intensity matching between two images may not necessarily imply the matching of correct anatomical correspondences. Based on HAMMER registration algorithm (Shen and Davatzikos, [2002]: IEEE Trans Med Imaging 21:1421–1439), we integrate the strategies of hierarchical attribute matching and symmetric diffeomorphic deformation to build a new symmetric-diffeomorphic HAMMER registration algorithm, called as S-HAMMER. The performance of S-HAMMER has been extensively compared with 14 state-of-the-art nonrigid registration algorithms evaluated in (Klein et al., [2009]: NeuroImage 46:786–802) by using real brain images in LPBA40, IBSR18, CUMC12, and MGH10 datasets. In addition, the registration performance of S-HAMMER, by comparison with other methods, is also demonstrated on both elderly MR brain images (>70 years old) and the simulated brain images with ground-truth deformation fields. In all experiments, our proposed method achieves the best registration performance over all other registration methods, indicating the high applicability of our method in future neuroscience and clinical applications. PMID:23283836
On the distinction between large deformation and large distortion for anisotropic materials
BRANNON,REBECCA M.
2000-02-24
A motion involves large distortion if the ratios of principal stretches differ significantly from unity. A motion involves large deformation if the deformation gradient tensor is significantly different from the identity. Unfortunately, rigid rotation fits the definition of large deformation, and models that claim to be valid for large deformation are often inadequate for large distortion. An exact solution for the stress in an idealized fiber-reinforced composite is used to show that conventional large deformation representations for transverse isotropy give errant results. Possible alternative approaches are discussed.
Induced gravity from curvature density preserving diffeomorphisms
NASA Astrophysics Data System (ADS)
Oda, Ichiro
2016-08-01
We construct not only an induced gravity model with restricted diffeomorphisms, that is, transverse diffeomorphisms that preserve the curvature density, but also with full diffeomorphisms. By solving the equations of motion, it turns out that these models produce Einstein's equations with a certain Newton constant in addition to the constraint for the curvature density. In the limit of the infinite Newton constant, the models give rise to induced gravity. Moreover, we discuss cosmological solutions on the basis of the gravitational models at hand.
DIFFEOMORPHIC POINT SET REGISTRATION USING NON-STATIONARY MIXTURE MODELS
Wassermann, D.; Ross, J.; Washko, G.; Westin, C-F; Estépar, R. San José
2013-01-01
This paper investigates a diffeomorphic point-set registration based on non-stationary mixture models. The goal is to improve the non-linear registration of anatomical structures by representing each point as a general non-stationary kernel that provides information about the shape of that point. Our framework generalizes work done by others that use stationary models. We achieve this by integrating the shape at each point when calculating the point-set similarity and transforming it according to the calculated deformation. We also restrict the non-rigid transform to the space of symmetric diffeomorphisms. Our algorithm is validated in synthetic and human datasets in two different applications: fiber bundle and lung airways registration. Our results shows that non-stationary mixture models are superior to Gaussian mixture models and methods that do not take into account the shape of each point. PMID:24419463
The 2D large deformation analysis using Daubechies wavelet
NASA Astrophysics Data System (ADS)
Liu, Yanan; Qin, Fei; Liu, Yinghua; Cen, Zhangzhi
2010-01-01
In this paper, Daubechies (DB) wavelet is used for solution of 2D large deformation problems. Because the DB wavelet scaling functions are directly used as basis function, no meshes are needed in function approximation. Using the DB wavelet, the solution formulations based on total Lagrangian approach for two-dimensional large deformation problems are established. Due to the lack of Kroneker delta properties in wavelet scaling functions, Lagrange multipliers are used for imposition of boundary condition. Numerical examples of 2D large deformation problems illustrate that this method is effective and stable.
Displacement and deformation measurement for large structures by camera network
NASA Astrophysics Data System (ADS)
Shang, Yang; Yu, Qifeng; Yang, Zhen; Xu, Zhiqiang; Zhang, Xiaohu
2014-03-01
A displacement and deformation measurement method for large structures by a series-parallel connection camera network is presented. By taking the dynamic monitoring of a large-scale crane in lifting operation as an example, a series-parallel connection camera network is designed, and the displacement and deformation measurement method by using this series-parallel connection camera network is studied. The movement range of the crane body is small, and that of the crane arm is large. The displacement of the crane body, the displacement of the crane arm relative to the body and the deformation of the arm are measured. Compared with a pure series or parallel connection camera network, the designed series-parallel connection camera network can be used to measure not only the movement and displacement of a large structure but also the relative movement and deformation of some interesting parts of the large structure by a relatively simple optical measurement system.
Hybrid natural element method for large deformation elastoplasticity problems
NASA Astrophysics Data System (ADS)
Ma, Yong-Qi; Zhou, Yan-Kai
2015-03-01
We present the hybrid natural element method (HNEM) for two-dimensional elastoplastic large deformation problems. Sibson interpolation is adopted to construct the shape functions of nodal incremental displacements and incremental stresses. The incremental form of Hellinger-Reissner variational principle for elastoplastic large deformation problems is deduced to obtain the equation system. The total Lagrangian formulation is used to describe the discrete equation system. Compared with the natural element method (NEM), the HNEM has higher computational precision and efficiency in solving elastoplastic large deformation problems. Some numerical examples are selected to demonstrate the advantage of the HNEM for large deformation elastoplasticity problems. Project supported by the Natural Science Foundation of Shanghai, China (Grant No. 13ZR1415900).
Large Scale Deformation of the Western US Cordillera
NASA Technical Reports Server (NTRS)
Bennett, Richard A.
2001-01-01
Destructive earthquakes occur throughout the western US Cordillera (WUSC), not just within the San Andreas fault zone. But because we do not understand the present-day large-scale deformations of the crust throughout the WUSC, our ability to assess the potential for seismic hazards in this region remains severely limited. To address this problem, we are using a large collection of Global Positioning System (GPS) networks which spans the WUSC to precisely quantify present-day large-scale crustal deformations in a single uniform reference frame. Our work can roughly be divided into an analysis of the GPS observations to infer the deformation field across and within the entire plate boundary zone and an investigation of the implications of this deformation field regarding plate boundary dynamics.
Symmetric log-domain diffeomorphic Registration: a demons-based approach.
Vercauteren, Tom; Pennec, Xavier; Perchant, Aymeric; Ayache, Nicholas
2008-01-01
Modern morphometric studies use non-linear image registration to compare anatomies and perform group analysis. Recently, log-Euclidean approaches have contributed to promote the use of such computational anatomy tools by permitting simple computations of statistics on a rather large class of invertible spatial transformations. In this work, we propose a non-linear registration algorithm perfectly fit for log-Euclidean statistics on diffeomorphisms. Our algorithm works completely in the log-domain, i.e. it uses a stationary velocity field. This implies that we guarantee the invertibility of the deformation and have access to the true inverse transformation. This also means that our output can be directly used for log-Euclidean statistics without relying on the heavy computation of the log of the spatial transformation. As it is often desirable, our algorithm is symmetric with respect to the order of the input images. Furthermore, we use an alternate optimization approach related to Thirion's demons algorithm to provide a fast non-linear registration algorithm. First results show that our algorithm outperforms both the demons algorithm and the recently proposed diffeomorphic demons algorithm in terms of accuracy of the transformation while remaining computationally efficient. PMID:18979814
High Resolution, Large Deformation 3D Traction Force Microscopy
López-Fagundo, Cristina; Reichner, Jonathan; Hoffman-Kim, Diane; Franck, Christian
2014-01-01
Traction Force Microscopy (TFM) is a powerful approach for quantifying cell-material interactions that over the last two decades has contributed significantly to our understanding of cellular mechanosensing and mechanotransduction. In addition, recent advances in three-dimensional (3D) imaging and traction force analysis (3D TFM) have highlighted the significance of the third dimension in influencing various cellular processes. Yet irrespective of dimensionality, almost all TFM approaches have relied on a linear elastic theory framework to calculate cell surface tractions. Here we present a new high resolution 3D TFM algorithm which utilizes a large deformation formulation to quantify cellular displacement fields with unprecedented resolution. The results feature some of the first experimental evidence that cells are indeed capable of exerting large material deformations, which require the formulation of a new theoretical TFM framework to accurately calculate the traction forces. Based on our previous 3D TFM technique, we reformulate our approach to accurately account for large material deformation and quantitatively contrast and compare both linear and large deformation frameworks as a function of the applied cell deformation. Particular attention is paid in estimating the accuracy penalty associated with utilizing a traditional linear elastic approach in the presence of large deformation gradients. PMID:24740435
A large stroke magnetic fluid deformable mirror for focus control
NASA Astrophysics Data System (ADS)
Min, Ling-kun; Wu, Zhi-zheng; Huang, Ming-shuang; Kong, Xiang-hui
2016-03-01
A liquid deformable mirror, which can provide a large stroke deflection more than 100 μm, is proposed for focus control. The deformable mirror utilizes the concept of magnetic fluid deformation shaped with electromagnetic fields to achieve concave or convex surface and to change the optical focus depth of the mirrors. The free surface of the magnetic fluid is coated with a thin layer of metal-liquid-like film (MELLF) prepared from densely packed silver nanoparticles to enhance the reflectance of the deformable mirror. The experimental results on the fabricated prototype magnetic fluid deformable mirror (MFDM) show that the desired concave/convex surface shape can be controlled precisely with a closed-loop adaptive optical system.
Large-deformation modal coordinates for nonrigid vehicle dynamics
NASA Technical Reports Server (NTRS)
Likins, P. W.; Fleischer, G. E.
1972-01-01
The derivation of minimum-dimension sets of discrete-coordinate and hybrid-coordinate equations of motion of a system consisting of an arbitrary number of hinge-connected rigid bodies assembled in tree topology is presented. These equations are useful for the simulation of dynamical systems that can be idealized as tree-like arrangements of substructures, with each substructure consisting of either a rigid body or a collection of elastically interconnected rigid bodies restricted to small relative rotations at each connection. Thus, some of the substructures represent elastic bodies subjected to small strains or local deformations, but possibly large gross deformations, in the hybrid formulation, distributed coordinates referred to herein as large-deformation modal coordinates, are used for the deformations of these substructures. The equations are in a form suitable for incorporation into one or more computer programs to be used as multipurpose tools in the simulation of spacecraft and other complex electromechanical systems.
Fracture Deformation Measurements in the Large Block Test
Carlson, S R; Blair, S C; Wagoner, J L
2002-03-08
Fracture deformations were measured in a 3m x 3m x 4.5m block of Topopah Spring tuff as part of a larger effort to characterize coupled thermal-hydrologic-mechanical-chemical processes in an isolated rock mass subjected to a one-dimensional thermal gradient. The fracture deformations were measured in three orthogonal directions at 17 points on the vertical faces of the block over a time span of 19 months. Eight fractures, including a major sub-horizontal fracture near the top of the block and five large, sub-vertical fractures, were selected for study. The data provide point measurements of apparent aperture change and slip motions parallel and perpendicular to the block faces. The fracture aperture and slip motions, though only a few tenths of a millimeter, form a significant portion of the total block deformation. The data reveal some fairly complex behaviors, such as nonuniform slip motions along individual fractures and sub-vertical fractures that sometimes open and close simultaneously at different elevations. Slip motions along sub-vertical fractures near the heater plane were relatively large and well correlated with temperature. The heating phase deformations were only partially recovered during cool-down. The fracture deformation data show that fractures deformed in conjunction with water movements and associated temperature fluctuations during the test. Simultaneous slip and aperture data also provide estimates of fracture dilation angle.
Control and large deformations of marginal disordered structures
NASA Astrophysics Data System (ADS)
Murugan, Arvind; Pinson, Matthew; Chen, Elizabeth
Designed deformations, such as origami patterns, provide a way to make easily controlled mechanical metamaterials with tailored responses to external forces. We focus on an often overlooked regime of origami - non-linear deformations of large disordered origami patterns with no symmetries. We find that practical questions of control in origami have counterintuitive answers, because of intimate connections to spin glasses and neural networks. For example, 1 degree of freedom origami structures are actually difficult to control about the flat state with a single actuator; the actuator is thrown off by an exponential number of `red herring' zero modes for small deformations, all but one of which disappear at larger deformations. Conversely, structures with multiple programmed motions are much easier to control than expected - in fact, they are as easy to control as a dedicated single-motion structure if the number of programmed motions is below a threshold (`memory capacity').
NASA Astrophysics Data System (ADS)
Kustas, A. B.; Sagapuram, D.; Chandrasekar, S.; Trumble, K. P.
2015-04-01
Machining is used as a deformation technique to impose large shear strains (γ ˜ 2) in a commercial Fe-4%Si alloy. The partial <111> and {110} - fiber texture components are generated throughout the as-deformed microstructure, which is expected of BCC metals deformed in simple shear. Using an annealing schedule similar to that in the commercial rolling process, samples retain the deformation texture, consistent with a continuous-type recrystallization mechanism. Fine-grained annealed samples reveal two different partial fiber orientations, one of which becomes the dominate texture, following the high-temperature growth treatment. The mechanisms of texture evolution and implications for texture control in the machining-based process are discussed.
Large Scale Deformation of the Western U.S. Cordillera
NASA Technical Reports Server (NTRS)
Bennett, Richard A.
2002-01-01
Over the past couple of years, with support from NASA, we used a large collection of data from GPS, VLBI, SLR, and DORIS networks which span the Westem U.S. Cordillera (WUSC) to precisely quantify present-day large-scale crustal deformations in a single uniform reference frame. Our work was roughly divided into an analysis of these space geodetic observations to infer the deformation field across and within the entire plate boundary zone, and an investigation of the implications of this deformation field regarding plate boundary dynamics. Following the determination of the first generation WUSC velocity solution, we placed high priority on the dissemination of the velocity estimates. With in-kind support from the Smithsonian Astrophysical Observatory, we constructed a web-site which allows anyone to access the data, and to determine their own velocity reference frame.
Large Scale Deformation of the Western U.S. Cordillera
NASA Technical Reports Server (NTRS)
Bennett, Richard A.
2002-01-01
Over the past couple of years, with support from NASA, we used a large collection of data from GPS, VLBI, SLR, and DORIS networks which span the Western U.S. Cordillera (WUSC) to precisely quantify present-day large-scale crustal deformations in a single uniform reference frame. Our work was roughly divided into an analysis of these space geodetic observations to infer the deformation field across and within the entire plate boundary zone, and an investigation of the implications of this deformation field regarding plate boundary dynamics. Following the determination of the first generation WUSC velocity solution, we placed high priority on the dissemination of the velocity estimates. With in-kind support from the Smithsonian Astrophysical Observatory, we constructed a web-site which allows anyone to access the data, and to determine their own velocity reference frame.
Electrohydrodynamic deformation of drops and bubbles at large Reynolds numbers
NASA Astrophysics Data System (ADS)
Schnitzer, Ory
2015-11-01
In Taylor's theory of electrohydrodynamic drop deformation by a uniform electric field, inertia is neglected at the outset, resulting in fluid velocities that scale with E2, E being the applied-field magnitude. When considering strong fields and low viscosity fluids, the Reynolds number predicted by this scaling may actually become large, suggesting the need for a complementary large-Reynolds-number analysis. Balancing viscous and electrical stresses reveals that the velocity scales with E 4 / 3. Considering a gas bubble, the external flow is essentially confined to two boundary layers propagating from the poles to the equator, where they collide to form a radial jet. Remarkably, at leading order in the Capillary number the unique scaling allows through application of integral mass and momentum balances to obtain a closed-form expression for the O (E2) bubble deformation. Owing to a concentrated pressure load at the vicinity of the collision region, the deformed profile features an equatorial dimple which is non-smooth on the bubble scale. The dynamical importance of internal circulation in the case of a liquid drop leads to an essentially different deformation mechanism. This is because the external boundary layer velocity attenuates at a short distance from the interface, while the internal boundary-layer matches with a Prandtl-Batchelor (PB) rotational core. The dynamic pressure associated with the internal circulation dominates the interfacial stress profile, leading to an O (E 8 / 3) deformation. The leading-order deformation can be readily determined, up to the PB constant, without solving the circulating boundary-layer problem. To encourage attempts to verify this new scaling, we shall suggest a favourable experimental setup in which inertia is dominant, while finite-deformation, surface-charge advection, and gravity effects are negligible.
NASA Astrophysics Data System (ADS)
Barnhoorn, A.
2012-04-01
Ductile deformation in the Earth's crust and mantle is often concentrated in narrow shear zones. These shear zones play a fundamental role in the deformation dynamics of the earth's lithosphere during mountain building, subduction and continental break-up. Shear zones exhibit large amounts of strain with an increase in strain from the edge to the center of the shear zone. Those large strains are often accompanied with large changes in microstructure due to processes such as dynamic recrystallization, grain size refinement, development of strong foliations, development of crystallographic preferred orientations, weakening of the rock as well as progressive localisation of the deformation into more and more concentrated zones. The interplay between all those different processes produce the various microstructures that are often studied in natural shear zones to assess the deformation conditions and history of plate tectonic processes. Experimental deformation studies under controlled conditions are used to produce relationships between the different processes active in shear zones (rheology, microstructural changes, and CPO development) in order to make those quantitative inferences on natural shear zones, Here I will present the outcomes from large strain torsion experiments at elevated temperatures and pressures on monophase calcitic rocks showing that very large strains are needed before true steady-state conditions in rocks are attained. Continuous changes in crystallographic preferred orientations and continuous dynamic recrystallization by grain boundary migration and subgrain rotation recrystallization occur up to the largest shear strains achieved in the study (shear strain of 50). Dynamic recrystallization from an undeformed coarse-grained calcite rock types towards a fine-grained ultramylonite is accompanied by a modest (~20%) weakening of the rock. However, this modest weakening never caused strain localisation in the samples. In contrast to the
Geodesic estimation for large deformation anatomical shape averaging and interpolation.
Avants, Brian; Gee, James C
2004-01-01
The goal of this research is to promote variational methods for anatomical averaging that operate within the space of the underlying image registration problem. This approach is effective when using the large deformation viscous framework, where linear averaging is not valid, or in the elastic case. The theory behind this novel atlas building algorithm is similar to the traditional pairwise registration problem, but with single image forces replaced by average forces. These group forces drive an average transport ordinary differential equation allowing one to estimate the geodesic that moves an image toward the mean shape configuration. This model gives large deformation atlases that are optimal with respect to the shape manifold as defined by the data and the image registration assumptions. We use the techniques in the large deformation context here, but they also pertain to small deformation atlas construction. Furthermore, a natural, inherently inverse consistent image registration is gained for free, as is a tool for constant arc length geodesic shape interpolation. The geodesic atlas creation algorithm is quantitatively compared to the Euclidean anatomical average to elucidate the need for optimized atlases. The procedures generate improved average representations of highly variable anatomy from distinct populations. PMID:15501083
Spherical Demons: Fast Diffeomorphic Landmark-Free Surface Registration
Yeo, B.T. Thomas; Sabuncu, Mert R.; Vercauteren, Tom; Ayache, Nicholas; Fischl, Bruce; Golland, Polina
2010-01-01
We present the Spherical Demons algorithm for registering two spherical images. By exploiting spherical vector spline interpolation theory, we show that a large class of regularizors for the modified Demons objective function can be efficiently approximated on the sphere using iterative smoothing. Based on one parameter subgroups of diffeomorphisms, the resulting registration is diffeomorphic and fast. The Spherical Demons algorithm can also be modified to register a given spherical image to a probabilistic atlas. We demonstrate two variants of the algorithm corresponding to warping the atlas or warping the subject. Registration of a cortical surface mesh to an atlas mesh, both with more than 160k nodes requires less than 5 minutes when warping the atlas and less than 3 minutes when warping the subject on a Xeon 3.2GHz single processor machine. This is comparable to the fastest non-diffeomorphic landmark-free surface registration algorithms. Furthermore, the accuracy of our method compares favorably to the popular FreeSurfer registration algorithm. We validate the technique in two different applications that use registration to transfer segmentation labels onto a new image: (1) parcellation of in-vivo cortical surfaces and (2) Brodmann area localization in ex-vivo cortical surfaces. PMID:19709963
Large Deformation Constitutive Laws for Isotropic Thermoelastic Materials
Plohr, Bradley J.; Plohr, Jeeyeon N.
2012-07-25
We examine the approximations made in using Hooke's law as a constitutive relation for an isotropic thermoelastic material subjected to large deformation by calculating the stress evolution equation from the free energy. For a general thermoelastic material, we employ the volume-preserving part of the deformation gradient to facilitate volumetric/shear strain decompositions of the free energy, its first derivatives (the Cauchy stress and entropy), and its second derivatives (the specific heat, Grueneisen tensor, and elasticity tensor). Specializing to isotropic materials, we calculate these constitutive quantities more explicitly. For deformations with limited shear strain, but possibly large changes in volume, we show that the differential equations for the stress components involve new terms in addition to the traditional Hooke's law terms. These new terms are of the same order in the shear strain as the objective derivative terms needed for frame indifference; unless the latter terms are negligible, the former cannot be neglected. We also demonstrate that accounting for the new terms requires that the deformation gradient be included as a field variable
An Inexact Newton–Krylov Algorithm for Constrained Diffeomorphic Image Registration*
Mang, Andreas; Biros, George
2016-01-01
We propose numerical algorithms for solving large deformation diffeomorphic image registration problems. We formulate the nonrigid image registration problem as a problem of optimal control. This leads to an infinite-dimensional partial differential equation (PDE) constrained optimization problem. The PDE constraint consists, in its simplest form, of a hyperbolic transport equation for the evolution of the image intensity. The control variable is the velocity field. Tikhonov regularization on the control ensures well-posedness. We consider standard smoothness regularization based on H1- or H2-seminorms. We augment this regularization scheme with a constraint on the divergence of the velocity field (control variable) rendering the deformation incompressible (Stokes regularization scheme) and thus ensuring that the determinant of the deformation gradient is equal to one, up to the numerical error. We use a Fourier pseudospectral discretization in space and a Chebyshev pseudospectral discretization in time. The latter allows us to reduce the number of unknowns and enables the time-adaptive inversion for nonstationary velocity fields. We use a preconditioned, globalized, matrix-free, inexact Newton–Krylov method for numerical optimization. A parameter continuation is designed to estimate an optimal regularization parameter. Regularity is ensured by controlling the geometric properties of the deformation field. Overall, we arrive at a black-box solver that exploits computational tools that are precisely tailored for solving the optimality system. We study spectral properties of the Hessian, grid convergence, numerical accuracy, computational efficiency, and deformation regularity of our scheme. We compare the designed Newton–Krylov methods with a globalized Picard method (preconditioned gradient descent). We study the influence of a varying number of unknowns in time. The reported results demonstrate excellent numerical accuracy, guaranteed local deformation
Generic Rigidity for Circle Diffeomorphisms with Breaks
NASA Astrophysics Data System (ADS)
Kocić, Saša
2016-05-01
We prove that C^r -smooth (r > 2 ) circle diffeomorphisms with a break, i.e., circle diffeomorphisms with a single singular point where the derivative has a jump discontinuity, are generically, i.e., for almost all irrational rotation numbers, not C^1+ɛ -rigid, for any ɛ > 0 . This result complements our recent proof, joint with Khanin (Geom Funct Anal 24:2002-2028, 2014), that such maps are generically C^1 -rigid. It stands in remarkable contrast to the result of Yoccoz (Ann Sci Ec Norm Sup 17:333-361, 1984) that C^r -smooth circle diffeomorphisms are generically C^r-1-κ -rigid, for any κ > 0.
Generic Rigidity for Circle Diffeomorphisms with Breaks
NASA Astrophysics Data System (ADS)
Kocić, Saša
2016-06-01
We prove that {C^r}-smooth ({r > 2}) circle diffeomorphisms with a break, i.e., circle diffeomorphisms with a single singular point where the derivative has a jump discontinuity, are generically, i.e., for almost all irrational rotation numbers, not {C^{1+\\varepsilon}}-rigid, for any {\\varepsilon > 0}. This result complements our recent proof, joint with Khanin (Geom Funct Anal 24:2002-2028, 2014), that such maps are generically {C^1}-rigid. It stands in remarkable contrast to the result of Yoccoz (Ann Sci Ec Norm Sup 17:333-361, 1984) that {C^r}-smooth circle diffeomorphisms are generically {C^{r-1-κ}}-rigid, for any {κ > 0}.
Effective field theory of broken spatial diffeomorphisms
NASA Astrophysics Data System (ADS)
Lin, Chunshan; Labun, Lance Z.
2016-03-01
We study the low energy effective theory describing gravity with broken spatial diffeomorphism invariance. In the unitary gauge, the Goldstone bosons associated with broken diffeomorphisms are eaten and the graviton becomes a massive spin-2 particle with 5 well-behaved degrees of freedom. In this gauge, the most general theory is built with the lowest dimension operators invariant under only temporal diffeomorphisms. Imposing the additional shift and SO(3) internal symmetries, we analyze the perturbations on a FRW background. At linear perturbation level, the observables of this theory are characterized by five parameters, including the usual cosmological parameters and one additional coupling constant for the symmetry-breaking scalars. In the de Sitter and Minkowski limit, the three Goldstone bosons are supermassive and can be integrated out, leaving two massive tensor modes as the only propagating degrees of freedom. We discuss several examples relevant to theories of massive gravity.
Generic area-preserving reversible diffeomorphisms
NASA Astrophysics Data System (ADS)
Bessa, Mário; Carvalho, Maria; Rodrigues, Alexandre
2015-06-01
Let M be a surface and R : M → M an area-preserving C∞ diffeomorphism which is an involution and whose set of fixed points is a submanifold with dimension one. We will prove that C1 - generically either an area-preserving R-reversible diffeomorphism, is Anosov, or, for μ-almost every x ∈ M, the Lyapunov exponents at x vanish or else the orbit of x belongs to a compact hyperbolic set with an empty interior. We will also describe a nonempty C1-open subset of area-preserving R-reversible diffeomorphisms where for C1 - generically each map is either Anosov or its Lyapunov exponents vanish from almost everywhere.
Large N behavior of mass deformed ABJM theory
NASA Astrophysics Data System (ADS)
Nosaka, Tomoki; Shimizu, Kazuma; Terashima, Seiji
2016-03-01
In this paper, using the localization technique we analyze the large N limit of the mass deformed Aharony-Bergman-Jafferis-Maldacena (ABJM) theory on the three sphere with a finite mass parameter and finite Chern-Simons levels. We find two different solutions of the saddle point equations in the large N limit. With these solutions we compute the free energy limit and find that there is a first order phase transition. Our results may predict a phase transition in the dual gravity theory.
Development of thermoplastic composite tubes for large deformation
NASA Astrophysics Data System (ADS)
Derisi, Bijan
Composites have proved their great potentials for many aerospace applications, where the high performance can justify the high cost. However, the brittleness of the composites has been a main drawback for many applications that require large deformation, high failure strain and extensive energy absorption before final fracture. The objective of this research is to present a solution to the brittleness of the composites in tubular form and to introduce a composite tube that shows the same strength, stiffness and failure strain as its high grade Aluminum 7075-T6 counterpart tube. One application of this research can be in the development of composite landing gear for helicopters. Up to date, almost all helicopter landing gears are made of high strength aluminum, and despite their major issues in maintenance and fabrication, aluminum landing gears have remained the only choice for the helicopter manufacturing industry. Substitution of aluminum landing gear for helicopters with a thermoplastic composite landing gear is really a challenge, but if this can be done, it would be for the first time in the world! Through this research, the mechanical behavior of flat plate Carbon AS4/PEKK is characterized, and the potential mechanisms for large deformation of composite laminates are sought. The outcomes are used to design a composite tube that shows the same strength, stiffness and deformability as its high grade aluminum counterpart. The accuracy of the design is verified through progressive failure by ANSYS analysis and experimental work. Strain Controlled Design is introduced as a new design technique to substitute for the traditional stiffness-controlled techniques whenever large deformation from composite laminates is expected. The analytical techniques for stress analysis of composite tubes are reviewed, and the cumbersomeness of the method is highlighted. Finally, a simplified technique is presented to analyze composite tubes as a sandwich panel model. The results of
Large Deformation Behavior of Long Shallow Cylindrical Composite Panels
NASA Technical Reports Server (NTRS)
Carper, Douglas M.; Hyer, Michael W.; Johnson, Eric R.
1991-01-01
An exact solution is presented for the large deformation response of a simply supported orthotropic cylindrical panel subjected to a uniform line load along a cylinder generator. The cross section of the cylinder is circular and deformations up to the fully snapped through position are investigated. The orthotropic axes are parallel to the generator and circumferential directions. The governing equations are derived using laminated plate theory, nonlinear strain-displacement relations, and applying variational principles. The response is investigated for the case of a panel loaded exactly at midspan and for a panel with the load offset from midspan. The mathematical formulation is one dimensional in the circumferential coordinate. Solutions are obtained in closed-form. An experimental apparatus was designed to load the panels. Experimental results of displacement controlled tests performed on graphite-epoxy curved panels are compared with analytical predictions.
Modeling Large-Strain, High-Rate Deformation in Metals
Lesuer, D R; Kay, G J; LeBlanc, M M
2001-07-20
The large strain deformation response of 6061-T6 and Ti-6Al-4V has been evaluated over a range in strain rates from 10{sup -4} s{sup -1} to over 10{sup 4} s{sup -1}. The results have been used to critically evaluate the strength and damage components of the Johnson-Cook (JC) material model. A new model that addresses the shortcomings of the JC model was then developed and evaluated. The model is derived from the rate equations that represent deformation mechanisms active during moderate and high rate loading. Another model that accounts for the influence of void formation on yield and flow behavior of a ductile metal (the Gurson model) was also evaluated. The characteristics and predictive capabilities of these models are reviewed.
Du, Jia; Hosseinbor, A. Pasha; Chung, Moo K.; Bendlin, Barbara B.; Suryawanshi, Gaurav; Alexander, Andrew L.; Qiu, Anqi
2015-01-01
We first propose a large deformation diffeomorphic metric mapping algorithm to align multiple b-value diffusion weighted imaging (mDWI) data, specifically acquired via hybrid diffusion imaging (HYDI).We denote this algorithm as LDDMM-HYDI. We then propose a Bayesian probabilistic model for estimating the white matter atlas from HYDIs. We adopt the work given in Hosseinbor et al. (2012) and represent the q-space diffusion signal with the Bessel Fourier orientation reconstruction (BFOR) signal basis. The BFOR framework provides the representation of mDWI in the q-space and the analytic form of the emsemble average propagator (EAP) reconstructure, as well as reduces memory requirement. In addition, since the BFOR signal basis is orthonormal, the L2 norm that quantifies the differences in the q-space signals of any two mDWI datasets can be easily computed as the sum of the squared differences in the BFOR expansion coefficients. In this work, we show that the reorientation of the q-space signal due to spatial transformation can be easily defined on the BFOR signal basis. We incorporate the BFOR signal basis into the LDDMM framework and derive the gradient descent algorithm for LDDMM-HYDI with explicit orientation optimization. Additionally, we extend the previous Bayesian atlas estimation framework for scalar-valued images to HYDIs and derive the expectation-maximization algorithm for solving the HYDI atlas estimation problem. Using real HYDI datasets, we show the Bayesian model generates the white matter atlas with anatomical details. Moreover, we show that it is important to consider the variation of mDWI reorientation due to a small change in diffeomorphic transformation in the LDDMM-HYDI optimization and to incorporate the full information of HYDI for aligning mDWI. Finally, we show that the LDDMM-HYDI outperforms the LDDMM algorithm with diffusion tensors generated from each shell of HYDI. PMID:24972378
The large deformation elastic response of woven Kevlar fabric
Warren, W.E.
1991-01-01
The large deformation elastic response of a plane woven Kevlar fabric is investigated analytically and experimentally. The analysis assumes the undeformed geometry to be a sequence of interlaced arcs of circles which reverse at each yarn midpoint, ad each yarn is modeled as an extensible elastical subject to certain compatibility conditions. Deflection-force relations for the fabric are determined in terms of the initial weave geometry and the elastic properties of the individual yarns. The theoretical results agree well with the results of experiments performed on a fabric woven from 400 denier Kevlar yarns under conditions of uniaxial loading in both warp and fill directions. 13 refs., 4 figs.
Contactless Large Deformable Mirrors: ELT AO corrector technology available now
NASA Astrophysics Data System (ADS)
Biasi, Roberto; Gallieni, Daniele
2011-09-01
We present our design of ESO E-ELT M4 deformable mirror and GMT Adaptive Secondary Mirrors unit. Both systems are based on our consolidated design of large deformable mirrors for 8-m class telescopes, successfully implemented on MMT and LBT and currently in advanced construction and testing phase for VLT and Magellan telescopes respectively. We describe the main features of the technology adopted: thin Zerodur mirror shell with contactless voice coil motors, co-located capacitive sensors to close a local position loop at each actuator, centralized control by force feedforward, embedded real time control and communication electronics. We then highlight how the same concept has been scaled up on the E-ELT M4AU and the GMT-ASM cases, adapting the technology to deal with thousands of actuators, while maintaining its intrinsic advantages: tolerance to actuators' failures, mechanical de-coupling and relaxed tolerances between correcting mirror and reference structure, large stroke, hysteresis-free behavior. For the next generation systems, we report the predicted performances based on the actual results attained on our 1-m class DMs currently in use: the LBT adaptive secondary for the GMT-ASM and the 330 actuators Demonstration Prototype for the E-ELT M4AU.
Large anisotropic deformation of skyrmions in strained crystal.
Shibata, K; Iwasaki, J; Kanazawa, N; Aizawa, S; Tanigaki, T; Shirai, M; Nakajima, T; Kubota, M; Kawasaki, M; Park, H S; Shindo, D; Nagaosa, N; Tokura, Y
2015-07-01
Mechanical control of magnetism is an important and promising approach in spintronics. To date, strain control has mostly been demonstrated in ferromagnetic structures by exploiting a change in magnetocrystalline anisotropy. It would be desirable to achieve large strain effects on magnetic nanostructures. Here, using in situ Lorentz transmission electron microscopy, we demonstrate that anisotropic strain as small as 0.3% in a chiral magnet of FeGe induces very large deformations in magnetic skyrmions, as well as distortions of the skyrmion crystal lattice on the order of 20%. Skyrmions are stabilized by the Dzyaloshinskii-Moriya interaction, originating from a chiral crystal structure. Our results show that the change in the modulation of the strength of this interaction is amplified by two orders of magnitude with respect to changes in the crystal lattice due to an applied strain. Our findings may provide a mechanism to achieve strain control of topological magnetic structures based on the Dzyaloshinskii-Moriya interaction. PMID:26030654
Manifestly diffeomorphism invariant classical Exact Renormalization Group
NASA Astrophysics Data System (ADS)
Morris, Tim R.; Preston, Anthony W. H.
2016-06-01
We construct a manifestly diffeomorphism invariant Wilsonian (Exact) Renor-malization Group for classical gravity, and begin the construction for quantum gravity. We demonstrate that the effective action can be computed without gauge fixing the diffeo-morphism invariance, and also without introducing a background space-time. We compute classical contributions both within a background-independent framework and by perturbing around a fixed background, and verify that the results are equivalent. We derive the exact Ward identities for actions and kernels and verify consistency. We formulate two forms of the flow equation corresponding to the two choices of classical fixed-point: the Gaussian fixed point, and the scale invariant interacting fixed point using curvature-squared terms. We suggest how this programme may completed to a fully quantum construction.
Large Deformation and Adhesive Contact Studies of Axisymmetric Membranes
Laprade, Evan J.; Long, Rong; Pham, Jonathan; Lawrence, Jimmy; Emrick, Todd; Crosby, Alfred; Hui, Chung-Yuen; Shull, Kenneth R.
2013-01-01
A model membrane contact system consisting of an acrylic copolymer membrane and polydimethyl-siloxane substrate was utilized to evaluate a recently developed nonlinear large-deformation adhesive contact analysis. Direct measurements of the local membrane apex strain during non-contact inflation indicated that the neo-Hookean model provides an accurate measure of membrane strain and supports its use as the strain energy function for the analysis. A time dependent modulus emerges from the analysis, with principal tensions obtained from a comparison of predicted and experimental membrane profiles. A displacement controlled geometry was more easily modeled than the pressure controlled geometry, the applicability of the analysis was limited by wrinkling instabilities. The substantial viscoelastic behavior of these membranes made it difficult to describe the entire membrane with a single modulus, given the nonuniform deformation history of the membranes. Given the difficulty in determining membrane tension from the measured pressure and profile fits using the model, the peel energy was used as a simpler measure of adhesion. Using an analytical balance in the displacement controlled geometry, the membrane tension at the contact line was directly measured. Coupled with contact angle imaging, the peel energy was determined. For the model membranes studied, this peel energy described the membrane/substrate adhesive interactions quite well, giving well-defined peel energies that were independent of the detailed strain state of the membrane. PMID:23289644
Large deformation finite element analysis of undrained pile installation
NASA Astrophysics Data System (ADS)
Konkol, Jakub; Bałachowski, Lech
2016-03-01
In this paper, a numerical undrained analysis of pile jacking into the subsoil using Abaqus software suit has been presented. Two different approaches, including traditional Finite Element Method (FEM) and Arbitrary Lagrangian-Eulerian (ALE) formulation, were tested. In the first method, the soil was modelled as a two-phase medium and effective stress analysis was performed. In the second one (ALE), a single-phase medium was assumed and total stress analysis was carried out. The fitting between effective stress parameters and total stress parameters has been presented and both solutions have been compared. The results, discussion and verification of numerical analyzes have been introduced. Possible applications and limitations of large deformation modelling techniques have been explained.
Zhang, Zhijun; Ashraf, Muhammad; Sahn, David J.; Song, Xubo
2014-01-01
Purpose: Quantitative analysis of cardiac motion is important for evaluation of heart function. Three dimensional (3D) echocardiography is among the most frequently used imaging modalities for motion estimation because it is convenient, real-time, low-cost, and nonionizing. However, motion estimation from 3D echocardiographic sequences is still a challenging problem due to low image quality and image corruption by noise and artifacts. Methods: The authors have developed a temporally diffeomorphic motion estimation approach in which the velocity field instead of the displacement field was optimized. The optimal velocity field optimizes a novel similarity function, which we call the intensity consistency error, defined as multiple consecutive frames evolving to each time point. The optimization problem is solved by using the steepest descent method. Results: Experiments with simulated datasets, images of an ex vivo rabbit phantom, images of in vivo open-chest pig hearts, and healthy human images were used to validate the authors’ method. Simulated and real cardiac sequences tests showed that results in the authors’ method are more accurate than other competing temporal diffeomorphic methods. Tests with sonomicrometry showed that the tracked crystal positions have good agreement with ground truth and the authors’ method has higher accuracy than the temporal diffeomorphic free-form deformation (TDFFD) method. Validation with an open-access human cardiac dataset showed that the authors’ method has smaller feature tracking errors than both TDFFD and frame-to-frame methods. Conclusions: The authors proposed a diffeomorphic motion estimation method with temporal smoothness by constraining the velocity field to have maximum local intensity consistency within multiple consecutive frames. The estimated motion using the authors’ method has good temporal consistency and is more accurate than other temporally diffeomorphic motion estimation methods. PMID:24784402
Interferogram formation in the presence of complex and large deformation
Yun, S.-H.; Zebker, H.; Segall, P.; Hooper, A.; Poland, M.
2007-01-01
Sierra Negra volcano in Isabela island, Gala??pagos, erupted from October 22 to October 30 in 2005. During the 8 days of eruption, the center of Sierra Negra's caldera subsided about 5.4 meters. Three hours prior to the onset of the eruption, an earthquake (Mw 5.4) occurred, near the caldera. Because of the large and complex phase gradient due to the huge subsidence and the earthquake, it is difficult to form an interferogram inside the caldera that spans the eruption. The deformation is so large and spatially variable that the approximations used in existing InSAR software (ROI, ROI_PAC, DORIS, GAMMA) cannot properly coregister SAR image pairs spanning the eruption. We have developed here a two-step algorithm that can form intra-caldera interferograms from these data. The first step involves a "rubber-sheeting" SAR image coregistration. In the second step we use range offset estimates to mitigate the steep phase gradient. Using this new algorithm, we retrieve an interferogram with the best coverage to date inside the caldera of Sierra Negra. Copyright 2007 by the American Geophysical Union.
Interferogram formation in the presence of complex and large deformation
NASA Astrophysics Data System (ADS)
Yun, Sang-Ho; Zebker, Howard; Segall, Paul; Hooper, Andrew; Poland, Michael
2007-06-01
Sierra Negra volcano in Isabela island, Galápagos, erupted from October 22 to October 30 in 2005. During the 8 days of eruption, the center of Sierra Negra's caldera subsided about 5.4 meters. Three hours prior to the onset of the eruption, an earthquake (Mw 5.4) occurred, near the caldera. Because of the large and complex phase gradient due to the huge subsidence and the earthquake, it is difficult to form an interferogram inside the caldera that spans the eruption. The deformation is so large and spatially variable that the approximations used in existing InSAR software (ROI, ROI_PAC, DORIS, GAMMA) cannot properly coregister SAR image pairs spanning the eruption. We have developed here a two-step algorithm that can form intra-caldera interferograms from these data. The first step involves a ``rubber-sheeting'' SAR image coregistration. In the second step we use range offset estimates to mitigate the steep phase gradient. Using this new algorithm, we retrieve an interferogram with the best coverage to date inside the caldera of Sierra Negra.
Speckle photography applied to measure deformations of very large structures
NASA Astrophysics Data System (ADS)
Conley, Edgar; Morgan, Chris K.
1995-04-01
Fundamental principles of mechanics have recently been brought to bear on problems concerning very large structures. Fields of study include tectonic plate motion, nuclear waste repository vault closure mechanisms, the flow of glacier and sea ice, and highway bridge damage assessment and residual life prediction. Quantitative observations, appropriate for formulating and verifying models, are still scarce however, so the need to adapt new methods of experimental mechanics is clear. Large dynamic systems often exist in environments subject to rapid change. Therefore, a simple field technique that incorporates short time scales and short gage lengths is required. Further, the measuring methods must yield displacements reliably, and under oft-times adverse field conditions. Fortunately, the advantages conferred by an experimental mechanics technique known as speckle photography nicely fulfill this rather stringent set of performance requirements. Speckle seemed to lend itself nicely to the application since it is robust and relatively inexpensive. Experiment requirements are minimal -- a camera, high resolution film, illumination, and an optically rough surface. Perhaps most important is speckle's distinct advantage over point-by-point methods: It maps the two dimensional displacement vectors of the whole field of interest. And finally, given the method's high spatial resolution, relatively short observation times are necessary. In this paper we discuss speckle, two variations of which were used to gage the deformation of a reinforced concrete bridge structure subjected to bending loads. The measurement technique proved to be easily applied, and yielded the location of the neutral axis self consistently. The research demonstrates the feasibility of using whole field techniques to detect and quantify surface strains of large structures under load.
Large deformation measurement scheme for 3D digital image correlation method
NASA Astrophysics Data System (ADS)
Tang, Zhengzong; Liang, Jin; Xiao, Zhenzhong; Guo, Cheng
2012-02-01
Difficulties often arise for digital image correlation (DIC) technique when serious de-correlation occurs between the reference image and the deformed image due to large deformation. An updating reference image scheme could be employed to deal with large deformation situation, however that will introduce accumulated errors. A large deformation measurement scheme, combining improved coarse search method and updating reference image scheme, is proposed in this paper. For a series of deformation images, the correlation calculation begins with a seed point and spreads out. An improved coarse search method is developed to calculate the initial correlation parameters for the seed point, which guarantees that the correlation calculation can be carried out successfully even in large deformation situation. Only for extremely large deformation, the reference image is updated. Using this method, not only extremely large deformation can be measured successfully but also the accumulated error could be controlled. A polymer material tensile test and a foam compression test are used to verify the proposed scheme. Experimental results show that up to 450% tensile deformation and 83% compression deformation can be measured successfully.
Breaking and Restoring of Diffeomorphism Symmetry in Discrete Gravity
Bahr, B.; Dittrich, B.
2009-12-15
We discuss the fate of diffeomorphism symmetry in discrete gravity. Diffeomorphism symmetry is typically broken by the discretization. This has repercussions for the observable content and the canonical formulation of the theory. It might however be possible to construct discrete actions, so-called perfect actions, with exact symmetries and we will review first steps towards this end.
Explicit versus spontaneous diffeomorphism breaking in gravity
NASA Astrophysics Data System (ADS)
Bluhm, Robert
2015-03-01
Gravitational theories with fixed background fields break local Lorentz and diffeomorphism invariance either explicitly or spontaneously. In the case of explicit breaking it is known that conflicts can arise between the dynamics and geometrical constraints, while spontaneous breaking evades this problem. It is for this reason that in the gravity sector of the Standard-Model extension (SME) it is assumed that the background fields (SME coefficients) originate from spontaneous symmetry breaking. However, in other examples, such as Chern-Simons gravity and massive gravity, diffeomorphism invariance is explicitly broken by the background fields, and the potential conflicts between the dynamics and geometry can be avoided in most cases. An analysis of how this occurs is given, and the conditions that are placed on the metric tensor and gravitational structure as a result of the presence of an explicit-breaking background are described. The gravity sector of the SME is then considered for the case of explicit breaking. However, it is found that a useful post-Newtonian limit is only obtained when the symmetry breaking is spontaneous.
Fabric strain sensor integrated with CNPECs for repeated large deformation
NASA Astrophysics Data System (ADS)
Yi, Weijing
Flexible and soft strain sensors that can be used in smart textiles for wearable applications are much desired. They should meet the requirements of low modulus, large working range and good fatigue resistance as well as good sensing performances. However, there were no commercial products available and the objective of the thesis is to investigate fabric strain sensors based on carbon nanoparticle (CNP) filled elastomer composites (CNPECs) for potential wearing applications. Conductive CNPECs were fabricated and investigated. The introduction of silicone oil (SO) significantly decreased modulus of the composites to less than 1 MPa without affecting their deformability and they showed good stability after heat treatment. With increase of CNP concentration, a percolation appeared in electrical resistivity and the composites can be divided into three ranges. I-V curves and impedance spectra together with electro-mechanical studies demonstrated a balance between sensitivity and working range for the composites with CNP concentrations in post percolation range, and were preferred for sensing applications only if the fatigue life was improved. Due to the good elasticity and failure resist property of knitted fabric under repeated extension, it was adopted as substrate to increase the fatigue life of the conductive composites. After optimization of processing parameters, the conductive fabric with CNP concentration of 9.0CNP showed linear I-V curves when voltage is in the range of -1 V/mm and 1 V/mm and negligible capacitive behavior when frequency below 103 Hz even with strain of 60%. It showed higher sensitivity due to the combination of nonlinear resistance-strain behavior of the CNPECs and non-even strain distribution of knitted fabric under extension. The fatigue life of the conductive fabric was greatly improved. Extended on the studies of CNPECs and the coated conductive fabrics, a fabric strain sensor was designed, fabricated and packaged. The Young's modulus of
Anosov Diffeomorphisms and {γ}-Tilings
NASA Astrophysics Data System (ADS)
Almeida, João P.; Pinto, Alberto A.
2016-07-01
We consider a toral Anosov automorphism {G_γ:{mathbb{T}}_γto{mathbb{T}}_γ} given by {G_γ(x,y)=(ax+y,x)} in the { < v,w > } base, where {ainmathbb{N} backslash\\{1\\}}, {γ=1/(a+1/(a+1/ldots))}, {v=(γ,1)} and {w=(-1,γ)} in the canonical base of {{mathbb{R}}^2} and {{mathbb{T}}_γ={mathbb{R}}^2/(v{mathbb{Z}} × w{mathbb{Z}})}. We introduce the notion of {γ}-tilings to prove the existence of a one-to-one correspondence between (i) marked smooth conjugacy classes of Anosov diffeomorphisms, with invariant measures absolutely continuous with respect to the Lebesgue measure, that are in the isotopy class of {G_γ}; (ii) affine classes of {γ}-tilings; and (iii) {γ}-solenoid functions. Solenoid functions provide a parametrization of the infinite dimensional space of the mathematical objects described in these equivalences.
Strain localization in usnaturated soils with large deformation
NASA Astrophysics Data System (ADS)
Song, X.; Borja, R. I.
2014-12-01
Strain localization is a ubiquitous feature of granular materials undergoing nonhomogeneous deformation. In unsaturated porous media, how the localized deformation band is formed depends crucially on the degree of saturation, since fluid in the pores of a solid imposes a volume constraint on the deformation of the solid. When fluid flow is involved, the inception of the localized deformation band also depends on the heterogeneity of a material, which is quantified in terms of the spatial variation of density, the degree of saturation, and matric suction. We present a mathematical framework for coupled solid-deformation/fluid-diffusion in unsaturated porous media that takes into account material and geometric nonlinearities [1, 2]. The framework relies on the continuum principle of thermodynamics to identify an effective, or constitutive, stress for the solid matrix, and a water retention law that highlights the interdependence of degree of saturation, suction, and porosity of the material. We discuss the role of heterogeneity, quantified either deterministically or stochastically, on the development of a persistent shear band. We derive bifurcation conditions [3] governing the initiation of such a shear band. This research is inspired by current testing techniques that allow nondestructive and non-invasive measurement of density and the degree of saturation through high-resolution imaging [4]. The numerical simulations under plane strain condition demonstrate that the bifurcation not only manifests itself on the loading response curve and but also in the space of the degree of saturation, specific volume and suction stress. References[1] Song X, Borja RI, Mathematical framework for unsaturated flow in the finite deformation range. Int. J. Numer. Meth. Engng 2014; 97: 658-686. [2] Song X, Borja RI, Finite deformation and fluid flow in unsaturated soils with random heterogeneity. Vadose Zone Journal 2014; doi:10.2136/vzj2013.07.0131. [3] Song X, Borja RI, Instability
New approach to nonrelativistic diffeomorphism invariance and its applications
NASA Astrophysics Data System (ADS)
Banerjee, Rabin; Mukherjee, Pradip
2016-04-01
A comprehensive account of a new structured algorithm for obtaining nonrelativistic diffeomorphism invariances in both space and spacetime by gauging the Galilean symmetry in a generic nonrelativistic field theoretical model is provided. Various applications like the obtention of nonrelativistic diffeomorphism invariance, the introduction of the Chern-Simons term and its role in fractional quantum Hall effect, the induction of diffeomorphism in the irrotational fluid model, the abstraction of Newton-Cartan geometry, and the emergence of Horava-Lifshitz gravity are discussed in details.
Distinctive signatures of space-time diffeomorphism breaking in EFT of inflation
NASA Astrophysics Data System (ADS)
Bartolo, Nicola; Cannone, Dario; Ricciardone, Angelo; Tasinato, Gianmassimo
2016-03-01
The effective field theory of inflation is a powerful tool for obtaining model independent predictions common to large classes of inflationary models. It requires only information about the symmetries broken during the inflationary era, and on the number and nature of fields that drive inflation. In this paper, we consider the case for scenarios that simultaneously break time reparameterization and spatial diffeomorphisms during inflation. We examine how to analyse such systems using an effective field theory approach, and we discuss several observational consequences for the statistics of scalar and tensor modes. For example, examining the three point functions, we show that this symmetry breaking pattern can lead to an enhanced amplitude for the squeezed bispectra, and to a distinctive angular dependence between their three wavevectors. We also discuss how our results indicate prospects for constraining the level of spatial diffeomorphism breaking during inflation.
Grid-based matching for full-field large-area deformation measurement
NASA Astrophysics Data System (ADS)
Du, Xian; Anthony, Brian W.; C. Kojimoto, Nigel
2015-03-01
Grid-based measurement can facilitate metrology and inspection of flexible electronics manufacturing. Multiple fundamental difficulties, however, arise in the large-area and full-field deformation measurement of deformable grid patterns including noise, occlusions, and artifacts. This paper addresses one of the key issues in deformation measurement: the registration and matching of deformed grid patterns. The emphasis is on accurate and robust periodicity tracing registration and constellation matching algorithms for grid pattern fidelity. The registration algorithm uses deviation metrics in deformed grids to estimate global translation, rotation and scaling; the matching algorithm uses the constellation reference grid to mine buried deformed point patterns. Using synthetic data, the validity of the registration algorithm is proved by registering noisy deformed grid patterns with various distortion scales and transformations; the validity of the matching algorithm is proved by matching deformed grid point patterns with various distortion scales, extra point rates and missing point rates. Compared to established non-rigid registration and point pattern matching algorithms, our algorithms demonstrate higher speed, sub-pixel accuracy and robustness in the matching of highly-deformed and noisy grids.
Time-dependent recovery of passive neutrophils after large deformation.
Tran-Son-Tay, R; Needham, D; Yeung, A; Hochmuth, R M
1991-01-01
Experiments are performed in which a passive human neutrophil is deformed into an elongated "sausage" shape by aspirating it into a small glass pipette. When expelled from the pipette the neutrophil recovers its natural spherical shape in approximately 1 minute. This recovery process is analyzed according to a Newtonian, liquid-drop model in which a variational method is used to simultaneously solve the hydrodynamic equations for low Reynolds-number flow and the equations for membrane equilibrium with a constant membrane tension. The theoretical model gives a good fit to the experimental data for a ratio of membrane cortical tension to cytoplasmic viscosity of approximately 1.7 x 10(-5) cm/s (0.17 micron/s). However, when the cell is held in the pipette for only a short time period of 5 s or less, and then expelled, the cell undergoes an initial, rapid elastic rebound suggesting that the cell behaves in this instance as a Maxwell viscoelastic liquid rather than a Newtonian liquid with constant cortical tension. PMID:1742456
Finite-element formulations for problems of large elastic-plastic deformation
NASA Technical Reports Server (NTRS)
Mcmeeking, R. M.; Rice, J. R.
1975-01-01
An Eulerian finite element formulation is presented for problems of large elastic-plastic flow. The method is based on Hill's variational principle for incremental deformations, and is ideally suited to isotropically hardening Prandtl-Reuss materials. Further, the formulation is given in a manner which allows any conventional finite element program, for 'small strain' elastic-plastic analysis, to be simply and rigorously adapted to problems involving arbitrary amounts of deformation and arbitrary levels of stress in comparison to plastic deformation moduli. The method is applied to a necking bifurcation analysis of a bar in plane-strain tension. The paper closes with a unified general formulation of finite element equations, both Lagrangian and Eulerian, for large deformations, with arbitrary choice of the conjugate stress and strain measures. Further, a discussion is given of other proposed formulations for elastic-plastic finite element analysis at large strain, and the inadequacies of some of these are commented upon.
Finite element formulations for problems of large elastic-plastic deformation
NASA Technical Reports Server (NTRS)
Mcmeeking, R. M.; Rice, J. R.
1974-01-01
An Eulerian finite element formulation is presented for problems of large elastic-plastic flow. The method is based on Hill's variational principle for incremental deformations, and is suited to isotropically hardening Prandtl-Reuss materials. The formulation is given in a manner which allows any conventional finite element program, for "small strain" elasticplastic analysis, to be simply and rigorously adapted to problems involving arbitrary amounts of deformation and arbitrary levels of stress in comparison to plastic deformation moduli. The method is applied to a necking bifurcation analysis of a bar in plane-strain tension. A unified general formulation of finite element equations, both Lagrangian and Eulerian, for large deformations, with arbitrary choice of the conjugate stress and strain measures, and a discussion is given of other proposed formulations for elastic-plastic finite element analysis at large strain.
Large-Scale Deformation and Uplift Associated with Serpentinization
NASA Astrophysics Data System (ADS)
Germanovich, L. N.; Lowell, R. P.; Smith, J. E.
2014-12-01
Geologic and geophysical data suggest that partially serpentinized peridotites and serpentinites are a significant part of the oceanic lithosphere. All serpentinization reactions are exothermic and result in volume expansion as high as 40%. Volume expansion beneath the seafloor will lead to surface uplift and elevated stresses in the neighborhood of the region undergoing serpentinization. The serpentinization-induced stresses are likely to result in faulting or tensile fracturing that promote the serpentinization process by creating new permeability and allowing fluid access to fresh peridotite. To explore these issues, we developed a first-order model of crustal deformation by considering an inclusion undergoing transformation strain in an elastic half-space. Using solutions for inclusions of different shapes, orientations, and depths, we calculate the surface uplift and mechanical stresses generated by the serpentinization processes. We discuss the topographic features at the TAG hydrothermal field (Mid-Atlantic Ridge, 26°N), uplift of the Miyazaki Plain (Southwestern Japan), and tectonic history of the Atlantic Massif (inside corner high of the Mid-Atlantic Ridge, 30°N, and the Atlantis Transform Fault). Our analysis suggests that an anomalous salient of 3 km in diameter and 100 m high at TAG may have resulted from approximately 20% transformational strain in a region beneath the footwall of the TAG detachment fault. This serpentinization process tends to promote slip along some overlying normal faults, which may then enhance fluid pathways to the deeper crust to continue the serpentinization process. The serpentinization also favors slip and seismicity along the antithetic faults identified below the TAG detachment fault. Our solution for the Miyazaki Plain above the Kyushu-Palau subduction zone explains the observed uplift of 120 m, but the transformational strain needs only be 3%. Transformational strains associated with serpentinization in this region may
Automated registration of large deformations for adaptive radiation therapy of prostate cancer
Godley, Andrew; Ahunbay, Ergun; Peng Cheng; Li, X. Allen
2009-04-15
Available deformable registration methods are often inaccurate over large organ variation encountered, for example, in the rectum and bladder. The authors developed a novel approach to accurately and effectively register large deformations in the prostate region for adaptive radiation therapy. A software tool combining a fast symmetric demons algorithm and the use of masks was developed in C++ based on ITK libraries to register CT images acquired at planning and before treatment fractions. The deformation field determined was subsequently used to deform the delivered dose to match the anatomy of the planning CT. The large deformations involved required that the bladder and rectum volume be masked with uniform intensities of -1000 and 1000 HU, respectively, in both the planning and treatment CTs. The tool was tested for five prostate IGRT patients. The average rectum planning to treatment contour overlap improved from 67% to 93%, the lowest initial overlap is 43%. The average bladder overlap improved from 83% to 98%, with a lowest initial overlap of 60%. Registration regions were set to include a volume receiving 4% of the maximum dose. The average region was 320x210x63, taking approximately 9 min to register on a dual 2.8 GHz Linux system. The prostate and seminal vesicles were correctly placed even though they are not masked. The accumulated doses for multiple fractions with large deformation were computed and verified. The tool developed can effectively supply the previously delivered dose for adaptive planning to correct for interfractional changes.
Large-Amplitude Deformation and Bond Breakage in Shock-Induced Reactions of Explosive Molecules
NASA Astrophysics Data System (ADS)
Kay, Jeffrey
The response of explosive molecules to large-amplitude mechanical deformation plays an important role in shock-induced reactions and the initiation of detonation in explosive materials. In this presentation, the response of a series of explosive molecules (nitromethane, 2,4,6-trinitrotoluene [TNT], and 2,4,6-triamino-1,3,5-trinitrobenzene [TATB]) to a variety of large-amplitude deformations are examined using ab initio quantum chemical calculations. Large-amplitude motions that result in bond breakage are described, and the insights these results provide into both previous experimental observations and previous theoretical predictions of shock-induced reactions are discussed.
Development of patient-specific biomechanical models for predicting large breast deformation
NASA Astrophysics Data System (ADS)
Han, Lianghao; Hipwell, John H.; Tanner, Christine; Taylor, Zeike; Mertzanidou, Thomy; Cardoso, Jorge; Ourselin, Sebastien; Hawkes, David J.
2012-01-01
Physically realistic simulations for large breast deformation are of great interest for many medical applications such as cancer diagnosis, image registration, surgical planning and image-guided surgery. To support fast, large deformation simulations of breasts in clinical settings, we proposed a patient-specific biomechanical modelling framework for breasts, based on an open-source graphics processing unit-based, explicit, dynamic, nonlinear finite element (FE) solver. A semi-automatic segmentation method for tissue classification, integrated with a fully automated FE mesh generation approach, was implemented for quick patient-specific FE model generation. To solve the difficulty in determining material parameters of soft tissues in vivo for FE simulations, a novel method for breast modelling, with a simultaneous material model parameter optimization for soft tissues in vivo, was also proposed. The optimized deformation prediction was obtained through iteratively updating material model parameters to maximize the image similarity between the FE-predicted MR image and the experimentally acquired MR image of a breast. The proposed method was validated and tested by simulating and analysing breast deformation experiments under plate compression. Its prediction accuracy was evaluated by calculating landmark displacement errors. The results showed that both the heterogeneity and the anisotropy of soft tissues were essential in predicting large breast deformations under plate compression. As a generalized method, the proposed process can be used for fast deformation analyses of soft tissues in medical image analyses and surgical simulations.
Development of patient-specific biomechanical models for predicting large breast deformation.
Han, Lianghao; Hipwell, John H; Tanner, Christine; Taylor, Zeike; Mertzanidou, Thomy; Cardoso, Jorge; Ourselin, Sebastien; Hawkes, David J
2012-01-21
Physically realistic simulations for large breast deformation are of great interest for many medical applications such as cancer diagnosis, image registration, surgical planning and image-guided surgery. To support fast, large deformation simulations of breasts in clinical settings, we proposed a patient-specific biomechanical modelling framework for breasts, based on an open-source graphics processing unit-based, explicit, dynamic, nonlinear finite element (FE) solver. A semi-automatic segmentation method for tissue classification, integrated with a fully automated FE mesh generation approach, was implemented for quick patient-specific FE model generation. To solve the difficulty in determining material parameters of soft tissues in vivo for FE simulations, a novel method for breast modelling, with a simultaneous material model parameter optimization for soft tissues in vivo, was also proposed. The optimized deformation prediction was obtained through iteratively updating material model parameters to maximize the image similarity between the FE-predicted MR image and the experimentally acquired MR image of a breast. The proposed method was validated and tested by simulating and analysing breast deformation experiments under plate compression. Its prediction accuracy was evaluated by calculating landmark displacement errors. The results showed that both the heterogeneity and the anisotropy of soft tissues were essential in predicting large breast deformations under plate compression. As a generalized method, the proposed process can be used for fast deformation analyses of soft tissues in medical image analyses and surgical simulations. PMID:22173131
The influence of large deformations on mechanical properties of sinusoidal ligament structures
NASA Astrophysics Data System (ADS)
Strek, Tomasz; Jopek, Hubert; Wojciechowski, Krzysztof W.
2016-05-01
Studies of mechanical properties of materials, both theoretical and experimental, usually deal with linear characteristics assuming a small range of deformations. In particular, not much research has been published devoted to large deformations of auxetic structures – i.e. structures exhibiting negative Poisson’s ratio. This paper is focused on mechanical properties of selected structures that are subject to large deformations. Four examples of structure built of sinusoidal ligaments are studied and for each geometry the impact of deformation size and geometrical parameters on the effective mechanical properties of these structures are investigated. It is shown that some of them are auxetic when compressed and non-auxetic when stretched. Geometrical parameters describing sinusoidal shape of ligaments strongly affect effective mechanical properties of the structure. In some cases of deformation, the increase of the value of amplitude of the sinusoidal shape decreases the effective Poisson’s ratio by 0.7. Therefore the influence of geometry, as well as the arrangement of ligaments allows for smart control of mechanical properties of the sinusoidal ligament structure being considered. Given the large deformation of the structure, both a linear elastic material model, and a hyperelastic Neo-Hookean material model are used.
Thermophoretically induced large-scale deformations around microscopic heat centers
NASA Astrophysics Data System (ADS)
Puljiz, Mate; Orlishausen, Michael; Köhler, Werner; Menzel, Andreas M.
2016-05-01
Selectively heating a microscopic colloidal particle embedded in a soft elastic matrix is a situation of high practical relevance. For instance, during hyperthermic cancer treatment, cell tissue surrounding heated magnetic colloidal particles is destroyed. Experiments on soft elastic polymeric matrices suggest a very long-ranged, non-decaying radial component of the thermophoretically induced displacement fields around the microscopic heat centers. We theoretically confirm this conjecture using a macroscopic hydrodynamic two-fluid description. Both thermophoretic and elastic effects are included in this theory. Indeed, we find that the elasticity of the environment can cause the experimentally observed large-scale radial displacements in the embedding matrix. Additional experiments confirm the central role of elasticity. Finally, a linearly decaying radial component of the displacement field in the experiments is attributed to the finite size of the experimental sample. Similar results are obtained from our theoretical analysis under modified boundary conditions.
The quantum holonomy-diffeomorphism algebra and quantum gravity
NASA Astrophysics Data System (ADS)
Aastrup, Johannes; Grimstrup, Jesper Møller
2016-03-01
We introduce the quantum holonomy-diffeomorphism ∗-algebra, which is generated by holonomy-diffeomorphisms on a three-dimensional manifold and translations on a space of SU(2)-connections. We show that this algebra encodes the canonical commutation relations of canonical quantum gravity formulated in terms of Ashtekar variables. Furthermore, we show that semiclassical states exist on the holonomy-diffeomorphism part of the algebra but that these states cannot be extended to the full algebra. Via a Dirac-type operator we derive a certain class of unbounded operators that act in the GNS construction of the semiclassical states. These unbounded operators are the type of operators, which we have previously shown to entail the spatial three-dimensional Dirac operator and Dirac-Hamiltonian in a semiclassical limit. Finally, we show that the structure of the Hamilton constraint emerges from a Yang-Mills-type operator over the space of SU(2)-connections.
Large deformation polymer optical fiber sensors for civil infrastructure systems
NASA Astrophysics Data System (ADS)
Abdi, Omid; Kowalsky, Mervyn; Hassan, Tasnim; Kiesel, Sharon; Peters, Kara
2008-03-01
This paper presents intrinsic polymer fiber (POF) sensors for high-strain applications such as the performance-based assessment and health monitoring of civil infrastructure systems subjected to earthquake loading or morphing aircraft. POFs provide a potential maximum strain range of 6-12%, are more flexible that silica optical fibers, and are more durable in harsh chemical or environmental conditions. Recent advances in the fabrication of single mode POFs have made it possible to extend POFs to interferometric sensor capabilities. Furthermore, the interferometric nature of intrinsic sensors permits high accuracy for such measurements. Measurements of the mechanical response of the sensor at various strain rates are presented. Several cleaving methods were also tested in order to appropriately cleave POFs for coupling purposes. In addition, the design of a time-of-flight interferometer for phase measurements over the large strain range required is discussed. Finally the bond strength between the embedded POF and various structural materials is investigated and a methodology demonstrated for embedment of the sensors into a reinforced concrete structural component.
Chen, D; Jones, S M; Silva, D A; Olivier, S S
2007-01-25
Scanning laser ophthalmoscopes with adaptive optics (AOSLO) have been shown previously to provide a noninvasive, cellular-scale view of the living human retina. However, the clinical utility of these systems has been limited by the available deformable mirror technology. In this paper, we demonstrate that the use of dual deformable mirrors can effectively compensate large aberrations in the human retina, making the AOSLO system a viable, non-invasive, high-resolution imaging tool for clinical diagnostics. We used a bimorph deformable mirror to correct low-order aberrations with relatively large amplitudes. The bimorph mirror is manufactured by Aoptix, Inc. with 37 elements and 18 {micro}m stroke in a 10 mm aperture. We used a MEMS deformable mirror to correct high-order aberrations with lower amplitudes. The MEMS mirror is manufactured by Boston Micromachine, Inc with 144 elements and 1.5 {micro}m stroke in a 3 mm aperture. We have achieved near diffraction-limited retina images using the dual deformable mirrors to correct large aberrations up to {+-} 3D of defocus and {+-} 3D of cylindrical aberrations with test subjects. This increases the range of spectacle corrections by the AO systems by a factor of 10, which is crucial for use in the clinical environment. This ability for large phase compensation can eliminate accurate refractive error fitting for the patients, which greatly improves the system ease of use and efficiency in the clinical environment.
NASA Astrophysics Data System (ADS)
Li, D. M.; Liew, K. M.; Cheng, Y. M.
2014-06-01
Using the complex variable moving least-squares (CVMLS) approximation, a complex variable element-free Galerkin (CVEFG) method for two-dimensional elastoplastic large deformation problems is presented. This meshless method has higher computational precision and efficiency because in the CVMLS approximation, the trial function of a two-dimensional problem is formed with a one-dimensional basis function. For two-dimensional elastoplastic large deformation problems, the Galerkin weak form is employed to obtain its equation system. The penalty method is used to impose essential boundary conditions. Then the corresponding formulae of the CVEFG method for two-dimensional elastoplastic large deformation problems are derived. In comparison with the conventional EFG method, our study shows that the CVEFG method has higher precision and efficiency. For illustration purpose, a few selected numerical examples are presented to demonstrate the advantages of the CVEFG method.
NASA Astrophysics Data System (ADS)
Zhang, Jiaping; Zhao, Xuanhe; Suo, Zhigang; Jiang, Hanqing
2009-05-01
A gel is an aggregate of polymers and solvent molecules. The polymers crosslink into a three-dimensional network by strong chemical bonds and enable the gel to retain its shape after a large deformation. The solvent molecules, however, interact among themselves and with the network by weak physical bonds and enable the gel to be a conduit of mass transport. The time-dependent concurrent process of large deformation and mass transport is studied by developing a finite element method. We combine the kinematics of large deformation, the conservation of the solvent molecules, the conditions of local equilibrium, and the kinetics of migration to evolve simultaneously two fields: the displacement of the network and the chemical potential of the solvent. The finite element method is demonstrated by analyzing several phenomena, such as swelling, draining and buckling. This work builds a platform to study diverse phenomena in gels with spatial and temporal complexity.
Black hole entropy and Lorentz-diffeomorphism Noether charge
NASA Astrophysics Data System (ADS)
Jacobson, Ted; Mohd, Arif
2015-12-01
We show that, in the first or second order orthonormal frame formalism, black hole entropy is the horizon Noether charge for a combination of diffeomorphism and local Lorentz symmetry involving the Lie derivative of the frame. The Noether charge for diffeomorphisms alone is unsuitable, since a regular frame cannot be invariant under the flow of the Killing field at the bifurcation surface. We apply this formalism to Lagrangians polynomial in wedge products of the frame field 1-form and curvature 2-form, including general relativity, Lovelock gravity, and "topological" terms in four dimensions.
Experimental analysis of crack tip fields in rubber materials under large deformation
NASA Astrophysics Data System (ADS)
Xiao, Xia; Song, Hai-Peng; Kang, Yi-Lan; Li, Xiao-Lei; Tan, Xiao-Hua; Tan, Hao-Yun
2012-04-01
A three-nested-deformation model is proposed to describe crack-tip fields in rubber-like materials with large deformation. The model is inspired by the distribution of the measured in-plane and out-of-plane deformation. The inplane displacement of crack-tip fields under both Mode I and mixed-mode (Mode I-II) fracture conditions is measured by using the digital Moiré method. The deformation characteristics and experimental sector division mode are investigated by comparing the measured displacement fields under different fracture modes. The out-of-plane displacement field near the crack tip is measured using the three-dimensional digital speckle correlation method.
Effect of GFRP spacer on local deformation of large superconductor in coil pack
NASA Astrophysics Data System (ADS)
Nishimura, Arata; Tamura, Hitoshi; Mito, Toshiyuki; Yamamoto, Junya
1994-07-01
Local deformation in a large superconductor caused by GFRP (glass fiber reinforced plastic) spacers and epoxy adhesives was investigated after compressive rigidity testing. The epoxy adhesive used for attaching the GFRP spacers to the superconductor changed shape from an almost square sheet into a lens-like sheet during deformation, and a dent appeared on the surface of the superconductor. Three-dimensional FEM (finite element method) analysis showed that a compressive stress in the vertical direction of the loading axis existed in the adhesive plane. This stress component makes the adhesive lens-like and it results in the dent created during the compressive testing. This local deformation should yield a part of the permanent deformation observed after the compressive load cycle at 4.2 K.
Large deformation analysis of Euler-Bernoulli beamshell under own weight based on HAM
NASA Astrophysics Data System (ADS)
Sohouli, Abdol; Kimiaeifar, Amin; Mohsenzadeh, Afshin; Mohebpour, Saeed
2012-03-01
Large deformation of a horizontally uniform cantilevered Euler-Bernoulli beamshell subjected to its own weight is studied. The governing equation for the first time is analytically solved using the analytical technique for nonlinear problems Homotopy Analysis Method (HAM). A series solution is presented that can be used for the analysis of beamshells undergoing large deformations with wide range of weight, material/cross section properties and lengths. The results obtained by HAM are compared with the results reported in the previous works, and good agreement is found. Finally, the load-displacement characteristics of a uniform cantilever beamshell under different load conditions, dimensionless weight parameter are presented.
Zinc selenide-based large aperture photo-controlled deformable mirror.
Quintavalla, Martino; Bonora, Stefano; Natali, Dario; Bianco, Andrea
2016-06-01
Realization of large aperture deformable mirrors with a large density of actuators is important in many applications, and photo-controlled deformable mirrors (PCDMs) represent an innovation. Herein we show that PCDMs are scalable realizing a 2-inch aperture device based on a polycrystalline zinc selenide (ZnSe) as the photoconductive substrate and a thin polymeric reflective membrane. ZnSe is electrically characterized and analyzed through a model that we previously introduced. The PCDM is then optically tested, demonstrating its capabilities in adaptive optics. PMID:27244417
A satellite geodetic survey of large-scale deformation of volcanic centres in the central Andes
NASA Astrophysics Data System (ADS)
Pritchard, Matthew E.; Simons, Mark
2002-07-01
Surface deformation in volcanic areas usually indicates movement of magma or hydrothermal fluids at depth. Stratovolcanoes tend to exhibit a complex relationship between deformation and eruptive behaviour. The characteristically long time spans between such eruptions requires a long time series of observations to determine whether deformation without an eruption is common at a given edifice. Such studies, however, are logistically difficult to carry out in most volcanic arcs, as these tend to be remote regions with large numbers of volcanoes (hundreds to even thousands). Here we present a satellite-based interferometric synthetic aperture radar (InSAR) survey of the remote central Andes volcanic arc, a region formed by subduction of the Nazca oceanic plate beneath continental South America. Spanning the years 1992 to 2000, our survey reveals the background level of activity of about 900 volcanoes, 50 of which have been classified as potentially active. We find four centres of broad (tens of kilometres wide), roughly axisymmetric surface deformation. None of these centres are at volcanoes currently classified as potentially active, although two lie within about 10km of volcanoes with known activity. Source depths inferred from the patterns of deformation lie between 5 and 17km. In contrast to the four new sources found, we do not observe any deformation associated with recent eruptions of Lascar, Chile.
A satellite geodetic survey of large-scale deformation of volcanic centres in the central Andes.
Pritchard, Matthew E; Simons, Mark
2002-07-11
Surface deformation in volcanic areas usually indicates movement of magma or hydrothermal fluids at depth. Stratovolcanoes tend to exhibit a complex relationship between deformation and eruptive behaviour. The characteristically long time spans between such eruptions requires a long time series of observations to determine whether deformation without an eruption is common at a given edifice. Such studies, however, are logistically difficult to carry out in most volcanic arcs, as these tend to be remote regions with large numbers of volcanoes (hundreds to even thousands). Here we present a satellite-based interferometric synthetic aperture radar (InSAR) survey of the remote central Andes volcanic arc, a region formed by subduction of the Nazca oceanic plate beneath continental South America. Spanning the years 1992 to 2000, our survey reveals the background level of activity of about 900 volcanoes, 50 of which have been classified as potentially active. We find four centres of broad (tens of kilometres wide), roughly axisymmetric surface deformation. None of these centres are at volcanoes currently classified as potentially active, although two lie within about 10 km of volcanoes with known activity. Source depths inferred from the patterns of deformation lie between 5 and 17 km. In contrast to the four new sources found, we do not observe any deformation associated with recent eruptions of Lascar, Chile. PMID:12110886
Diffeomorphic demons: efficient non-parametric image registration.
Vercauteren, Tom; Pennec, Xavier; Perchant, Aymeric; Ayache, Nicholas
2009-03-01
We propose an efficient non-parametric diffeomorphic image registration algorithm based on Thirion's demons algorithm. In the first part of this paper, we show that Thirion's demons algorithm can be seen as an optimization procedure on the entire space of displacement fields. We provide strong theoretical roots to the different variants of Thirion's demons algorithm. This analysis predicts a theoretical advantage for the symmetric forces variant of the demons algorithm. We show on controlled experiments that this advantage is confirmed in practice and yields a faster convergence. In the second part of this paper, we adapt the optimization procedure underlying the demons algorithm to a space of diffeomorphic transformations. In contrast to many diffeomorphic registration algorithms, our solution is computationally efficient since in practice it only replaces an addition of displacement fields by a few compositions. Our experiments show that in addition to being diffeomorphic, our algorithm provides results that are similar to the ones from the demons algorithm but with transformations that are much smoother and closer to the gold standard, available in controlled experiments, in terms of Jacobians. PMID:19041946
NASA Astrophysics Data System (ADS)
McKnight, G. P.; Henry, C. P.
2008-03-01
Morphing or reconfigurable structures potentially allow for previously unattainable vehicle performance by permitting several optimized structures to be achieved using a single platform. The key to enabling this technology in applications such as aircraft wings, nozzles, and control surfaces, are new engineered materials which can achieve the necessary deformations but limit losses in parasitic actuation mass and structural efficiency (stiffness/weight). These materials should exhibit precise control of deformation properties and provide high stiffness when exercised through large deformations. In this work, we build upon previous efforts in segmented reinforcement variable stiffness composites employing shape memory polymers to create prototype hybrid composite materials that combine the benefits of cellular materials with those of discontinuous reinforcement composites. These composites help overcome two key challenges for shearing wing skins: the resistance to out of plane buckling from actuation induced shear deformation, and resistance to membrane deflections resulting from distributed aerodynamic pressure loading. We designed, fabricated, and tested composite materials intended for shear deformation and address out of plane deflections in variable area wing skins. Our designs are based on the kinematic engineering of reinforcement platelets such that desired microstructural kinematics is achieved through prescribed boundary conditions. We achieve this kinematic control by etching sheets of metallic reinforcement into regular patterns of platelets and connecting ligaments. This kinematic engineering allows optimization of materials properties for a known deformation pathway. We use mechanical analysis and full field photogrammetry to relate local scale kinematics and strains to global deformations for both axial tension loading and shear loading with a pinned-diamond type fixture. The Poisson ratio of the kinematically engineered composite is ~3x higher than
Fast deformable registration for soft organs with large motion in HIFU treatment
NASA Astrophysics Data System (ADS)
Huang, Xishi; Abdalbari, Anwar; Zaheer, Sameer; Looi, Thomas; Ren, Jing; Drake, James
2013-03-01
In noninvasive high intensity focused ultrasound (HIFU) treatment, we often need to register MR images acquired with different patient positioning or at different respiratory instances. In these scenarios, the abdominal organs such as the liver exhibit a large motion in different images. In our previous work, we proposed a fast neuro-fuzzy technique for deformable registration with small motion. In this study, based on elastic solid mechanics, we extend our previous results to deformation with large motion which is often the case for soft tissues in HIFU treatment. The proposed method involves minimizing strain energy of soft tissues which is constrained by 3D curves of blood vessels and point marks. It provides fast and robust deformable match for internal structures such as blood vessels, and eliminates local minima. Furthermore, the strain energy constraint provides good generalization properties, prevents the issue of overfitting, and leads to physically consistent deformable registration results. We have demonstrated the effectiveness of our deformable technique in registering MR liver images. Validation shows a target registration error of 2.31 mm and an average centerline distance error of 2.30 mm. This technique has the potential to significantly improve the registration capability and the quality of intra-operative image guidance in HIFU procedures.
Large Deformation of an Elastic Rod with Structural Anisotropy Subjected to Fluid Flow
NASA Astrophysics Data System (ADS)
Hassani, Masoud; Mureithi, Njuki; Gosselin, Frederick
2015-11-01
In the present work, we seek to understand the fundamental mechanisms of three-dimensional reconfiguration of plants by studying the large deformation of a flexible rod in fluid flow. Flexible rods made of Polyurethane foam and reinforced with Nylon fibers are tested in a wind tunnel. The rods have bending-torsion coupling which induces a torsional deformation during asymmetric bending. A mathematical model is also developed by coupling the Kirchhoff rod theory with a semi-empirical drag formulation. Different alignments of the material frame with respect to the flow direction and a range of structural properties are considered to study their effect on the deformation of the flexible rod and its drag scaling. Results show that twisting causes the flexible rods to reorient and bend with the minimum bending rigidity. It is also found that the drag scaling of the rod in the large deformation regime is not affected by torsion. Finally, using a proper set of dimensionless numbers, the state of a bending and twisting rod is characterized as a beam undergoing a pure bending deformation.
Depalle, Baptiste; Qin, Zhao; Shefelbine, Sandra J; Buehler, Markus J
2016-02-01
Mineralized collagen fibrils are composed of tropocollagen molecules and mineral crystals derived from hydroxyapatite to form a composite material that combines optimal properties of both constituents and exhibits incredible strength and toughness. Their complex hierarchical structure allows collagen fibrils to sustain large deformation without breaking. In this study, we report a mesoscale model of a single mineralized collagen fibril using a bottom-up approach. By conserving the three-dimensional structure and the entanglement of the molecules, we were able to construct finite-size fibril models that allowed us to explore the deformation mechanisms which govern their mechanical behavior under large deformation. We investigated the tensile behavior of a single collagen fibril with various intrafibrillar mineral content and found that a mineralized collagen fibril can present up to five different deformation mechanisms to dissipate energy. These mechanisms include molecular uncoiling, molecular stretching, mineral/collagen sliding, molecular slippage, and crystal dissociation. By multiplying its sources of energy dissipation and deformation mechanisms, a collagen fibril can reach impressive strength and toughness. Adding mineral into the collagen fibril can increase its strength up to 10 times and its toughness up to 35 times. Combining crosslinks with mineral makes the fibril stiffer but more brittle. We also found that a mineralized fibril reaches its maximum toughness to density and strength to density ratios for a mineral density of around 30%. This result, in good agreement with experimental observations, attests that bone tissue is optimized mechanically to remain lightweight but maintain strength and toughness. PMID:26866939
NASA Technical Reports Server (NTRS)
Hishinumat, Yoshikazu; Yang, Eui - Hyeok (EH)
2005-01-01
We have demonstrated a large aperture (50 mm x 50 mm) continuous membrane deformable mirror (DM) with a large-stroke piezoelectric unimorph actuator array. The DM consists of a continuous, large aperture, silicon membrane 'transferred' in its entirety onto a 20 x 20 piezoelectric unimorph actuator array. A PZT unimorph actuator, 2.5 mm in diameter with optimized PZT/Si thickness and design showed a deflection of 5.7 [m at 20V. An assembled DM showed an operating frequency bandwidth of 30 kHz and influence function of approximately 30%.
NASA Astrophysics Data System (ADS)
Hansbo, Peter; Larson, Mats G.; Larsson, Fredrik
2015-07-01
We develop a finite element method for a large deformation membrane elasticity problem on meshed curved surfaces using a tangential differential calculus approach that avoids the use of classical differential geometric methods. The method is also applied to form finding problems.
NASA Technical Reports Server (NTRS)
Ko, William L.; Fleischer, Van Tran
2013-01-01
Large deformation displacement transfer functions were formulated for deformed shape predictions of highly flexible slender structures like aircraft wings. In the formulation, the embedded beam (depth wise cross section of structure along the surface strain sensing line) was first evenly discretized into multiple small domains, with surface strain sensing stations located at the domain junctures. Thus, the surface strain (bending strains) variation within each domain could be expressed with linear of nonlinear function. Such piecewise approach enabled piecewise integrations of the embedded beam curvature equations [classical (Eulerian), physical (Lagrangian), and shifted curvature equations] to yield closed form slope and deflection equations in recursive forms.
X-ray microbeam quantification of grain subdivision accompanying large deformations of copper
Butler, G.C.; Guvenilir, A.; McDowell, D.L.; Stock, S.R.
1998-12-31
Polychromatic synchrotron x-ray microbeams offer a very efficient alternative to electron beam methods for quantifying the amount and character of grain subdivision accompanying large deformations. With a 0.01 mm diameter collimator, bending magnet radiation from a 3.0 GeV source and image storage plates, samples of copper with thicknesses greater than 0.1 mm have been studied. Results from an as-received sample and a sample deformed to 100% torsion are compared and illustrate how efficiently grain subdivision can be quantified with polychromatic microbeam diffraction.
Solitons in a baby-Skyrme model with invariance under area-preserving diffeomorphisms
NASA Astrophysics Data System (ADS)
Gisiger, T.; Paranjape, M. B.
1997-06-01
We study the properties of soliton solutions in an analogue of the Skyrme model in 2+1 dimensions whose Lagrangian contains the Skyrme term and the mass term, but no usual kinetic term. The model admits a symmetry under area-preserving diffeomorphisms. We solve the dynamical equations of motion analytically for the case of spinning isolated baryon-type solitons. We take fully into account the induced deformation of the spinning Skyrmions and the consequent modification of its moment of inertia to give an analytical example of related numerical behavior found by Piette, Schroers, and Zakrzewski. We solve the equations of motion also for the case of an infinite, open string, and a closed annular string. In each case, the solitons are of finite extent, so called ``compactons,'' being exactly the vacuum outside a compact region. We end with indications on the scattering of baby Skyrmions, as well as some considerations as the properties of solitons on a curved space.
NASA Astrophysics Data System (ADS)
Zhao, Xuanhe; Wang, Qiming
2014-06-01
Widely used as insulators, capacitors, and transducers in daily life, soft dielectrics based on polymers and polymeric gels play important roles in modern electrified society. Owning to their mechanical compliance, soft dielectrics subject to voltages frequently undergo large deformation and mechanical instabilities. The deformation and instabilities can lead to detrimental failures in some applications of soft dielectrics such as polymer capacitors and insulating gels but can also be rationally harnessed to enable novel functions such as artificial muscle, dynamic surface patterning, and energy harvesting. According to mechanical constraints on soft dielectrics, we classify their deformation and instabilities into three generic modes: (i) thinning and pull-in, (ii) electro-creasing to cratering, and (iii) electro-cavitation. We then provide a systematic understanding of different modes of deformation and instabilities of soft dielectrics by integrating state-of-the-art experimental methods and observations, theoretical models, and applications. Based on the understanding, a systematic set of strategies to prevent or harness the deformation and instabilities of soft dielectrics for diverse applications are discussed. The review is concluded with perspectives on future directions of research in this rapidly evolving field.
A dynamic tree-based registration could handle possible large deformations among MR brain images.
Zhang, Pei; Wu, Guorong; Gao, Yaozong; Yap, Pew-Thian; Shen, Dinggang
2016-09-01
Multi-atlas segmentation is a powerful approach to automated anatomy delineation via fusing label information from a set of spatially normalized atlases. For simplicity, many existing methods perform pairwise image registration, leading to inaccurate segmentation especially when shape variation is large. In this paper, we propose a dynamic tree-based strategy for effective large-deformation registration and multi-atlas segmentation. To deal with local minima caused by large shape variation, coarse estimates of deformations are first obtained via alignment of automatically localized landmark points. The dynamic tree capturing the structural relationships between images is then employed to further reduce misalignment errors. Evaluation based on two real human brain datasets, ADNI and LPBA40, shows that our method significantly improves registration and segmentation accuracy. PMID:27235894
NASA Technical Reports Server (NTRS)
Yang, Eui-Hyeok; Shcheglov, Kirill
2002-01-01
Future concepts of ultra large space telescopes include segmented silicon mirrors and inflatable polymer mirrors. Primary mirrors for these systems cannot meet optical surface figure requirements and are likely to generate over several microns of wavefront errors. In order to correct for these large wavefront errors, high stroke optical quality deformable mirrors are required. JPL has recently developed a new technology for transferring an entire wafer-level mirror membrane from one substrate to another. A thin membrane, 100 mm in diameter, has been successfully transferred without using adhesives or polymers. The measured peak-to-valley surface error of a transferred and patterned membrane (1 mm x 1 mm x 0.016 mm) is only 9 nm. The mirror element actuation principle is based on a piezoelectric unimorph. A voltage applied to the piezoelectric layer induces stress in the longitudinal direction causing the film to deform and pull on the mirror connected to it. The advantage of this approach is that the small longitudinal strains obtainable from a piezoelectric material at modest voltages are thus translated into large vertical displacements. Modeling is performed for a unimorph membrane consisting of clamped rectangular membrane with a PZT layer with variable dimensions. The membrane transfer technology is combined with the piezoelectric bimorph actuator concept to constitute a compact deformable mirror device with a large stroke actuation of a continuous mirror membrane, resulting in a compact A0 systems for use in ultra large space telescopes.
Large-deformation and high-strength amorphous porous carbon nanospheres
NASA Astrophysics Data System (ADS)
Yang, Weizhu; Mao, Shimin; Yang, Jia; Shang, Tao; Song, Hongguang; Mabon, James; Swiech, Wacek; Vance, John R.; Yue, Zhufeng; Dillon, Shen J.; Xu, Hangxun; Xu, Baoxing
2016-04-01
Carbon is one of the most important materials extensively used in industry and our daily life. Crystalline carbon materials such as carbon nanotubes and graphene possess ultrahigh strength and toughness. In contrast, amorphous carbon is known to be very brittle and can sustain little compressive deformation. Inspired by biological shells and honeycomb-like cellular structures in nature, we introduce a class of hybrid structural designs and demonstrate that amorphous porous carbon nanospheres with a thin outer shell can simultaneously achieve high strength and sustain large deformation. The amorphous carbon nanospheres were synthesized via a low-cost, scalable and structure-controllable ultrasonic spray pyrolysis approach using energetic carbon precursors. In situ compression experiments on individual nanospheres show that the amorphous carbon nanospheres with an optimized structure can sustain beyond 50% compressive strain. Both experiments and finite element analyses reveal that the buckling deformation of the outer spherical shell dominates the improvement of strength while the collapse of inner nanoscale pores driven by twisting, rotation, buckling and bending of pore walls contributes to the large deformation.
Large-deformation and high-strength amorphous porous carbon nanospheres
Yang, Weizhu; Mao, Shimin; Yang, Jia; Shang, Tao; Song, Hongguang; Mabon, James; Swiech, Wacek; Vance, John R.; Yue, Zhufeng; Dillon, Shen J.; Xu, Hangxun; Xu, Baoxing
2016-01-01
Carbon is one of the most important materials extensively used in industry and our daily life. Crystalline carbon materials such as carbon nanotubes and graphene possess ultrahigh strength and toughness. In contrast, amorphous carbon is known to be very brittle and can sustain little compressive deformation. Inspired by biological shells and honeycomb-like cellular structures in nature, we introduce a class of hybrid structural designs and demonstrate that amorphous porous carbon nanospheres with a thin outer shell can simultaneously achieve high strength and sustain large deformation. The amorphous carbon nanospheres were synthesized via a low-cost, scalable and structure-controllable ultrasonic spray pyrolysis approach using energetic carbon precursors. In situ compression experiments on individual nanospheres show that the amorphous carbon nanospheres with an optimized structure can sustain beyond 50% compressive strain. Both experiments and finite element analyses reveal that the buckling deformation of the outer spherical shell dominates the improvement of strength while the collapse of inner nanoscale pores driven by twisting, rotation, buckling and bending of pore walls contributes to the large deformation. PMID:27072412
Large-deformation and high-strength amorphous porous carbon nanospheres.
Yang, Weizhu; Mao, Shimin; Yang, Jia; Shang, Tao; Song, Hongguang; Mabon, James; Swiech, Wacek; Vance, John R; Yue, Zhufeng; Dillon, Shen J; Xu, Hangxun; Xu, Baoxing
2016-01-01
Carbon is one of the most important materials extensively used in industry and our daily life. Crystalline carbon materials such as carbon nanotubes and graphene possess ultrahigh strength and toughness. In contrast, amorphous carbon is known to be very brittle and can sustain little compressive deformation. Inspired by biological shells and honeycomb-like cellular structures in nature, we introduce a class of hybrid structural designs and demonstrate that amorphous porous carbon nanospheres with a thin outer shell can simultaneously achieve high strength and sustain large deformation. The amorphous carbon nanospheres were synthesized via a low-cost, scalable and structure-controllable ultrasonic spray pyrolysis approach using energetic carbon precursors. In situ compression experiments on individual nanospheres show that the amorphous carbon nanospheres with an optimized structure can sustain beyond 50% compressive strain. Both experiments and finite element analyses reveal that the buckling deformation of the outer spherical shell dominates the improvement of strength while the collapse of inner nanoscale pores driven by twisting, rotation, buckling and bending of pore walls contributes to the large deformation. PMID:27072412
A mesh density study for application to large deformation rolling process evaluations
Martin, J.A.
1997-12-01
When addressing large deformation through an elastic-plastic analysis the mesh density is paramount in determining the accuracy of the solution. However, given the nonlinear nature of the problem, a highly-refined mesh will generally require a prohibitive amount of computer resources. This paper addresses finite element mesh optimization studies considering accuracy of results and computer resource needs as applied to large deformation rolling processes. In particular, the simulation of the thread rolling manufacturing process is considered using the MARC software package and a Cray C90 supercomputer. Both mesh density and adaptive meshing on final results for both indentation of a rigid body to a specified depth and contact rolling along a predetermined length are evaluated.
Diffeomorphism invariant cosmological symmetry in full quantum gravity
NASA Astrophysics Data System (ADS)
Beetle, Christopher; Engle, Jonathan S.; Hogan, Matthew E.; Mendonça, Phillip
2016-06-01
This paper summarizes a new proposal to define rigorously a sector of loop quantum gravity at the diffeomorphism invariant level corresponding to homogeneous and isotropic cosmologies, thereby enabling a detailed comparison of results in loop quantum gravity and loop quantum cosmology. The key technical steps we have completed are (a) to formulate conditions for homogeneity and isotropy in a diffeomorphism covariant way on the classical phase-space of general relativity, and (b) to translate these conditions consistently using well-understood techniques to loop quantum gravity. Some additional steps, such as constructing a specific embedding of the Hilbert space of loop quantum cosmology into a space of (distributional) states in the full theory, remain incomplete. However, we also describe, as a proof of concept, a complete analysis of an analogous embedding of homogeneous and isotropic loop quantum cosmology into the quantum Bianchi I model of Ashtekar and Wilson-Ewing. Details will appear in a pair of forthcoming papers.
Euclidean space-time diffeomorphisms and their Fueter subgroups
Guersey, F.; Jiang, W. )
1992-02-01
Holomorphic Fueter functions of the position quaternion form a subgroup of Euclidean space-time diffeomorphisms. An {ital O}(4) covariant treatment of such mappings is presented with the quaternionic argument {ital x} being replaced by either {ital {bar p}x} or {ital x{bar p}} involving self-dual and anti-self-dual structures and {ital p} denoting an arbitrary Euclidean time direction. An infinite group (the quasiconformal group) is exhibited that admits the conformal group SO(5,1) as a subgroup, in analogy to the two-dimensional case in which the Moebius group SO(3,1) is a subgroup of the infinite Virasoro group. The ensuing (3+1) covariant decomposition of diffeomorphisms suggests covariant gauges that throw the metric and the stress tensors in standard forms suitable for canonical quantization, leading to improved'' energy-momentum tensors. Other possible applications to current algebra and gravity will be mentioned.
Depalle, Baptiste; Qin, Zhao; Shefelbine, Sandra J
2016-01-01
ABSTRACT Mineralized collagen fibrils are composed of tropocollagen molecules and mineral crystals derived from hydroxyapatite to form a composite material that combines optimal properties of both constituents and exhibits incredible strength and toughness. Their complex hierarchical structure allows collagen fibrils to sustain large deformation without breaking. In this study, we report a mesoscale model of a single mineralized collagen fibril using a bottom‐up approach. By conserving the three‐dimensional structure and the entanglement of the molecules, we were able to construct finite‐size fibril models that allowed us to explore the deformation mechanisms which govern their mechanical behavior under large deformation. We investigated the tensile behavior of a single collagen fibril with various intrafibrillar mineral content and found that a mineralized collagen fibril can present up to five different deformation mechanisms to dissipate energy. These mechanisms include molecular uncoiling, molecular stretching, mineral/collagen sliding, molecular slippage, and crystal dissociation. By multiplying its sources of energy dissipation and deformation mechanisms, a collagen fibril can reach impressive strength and toughness. Adding mineral into the collagen fibril can increase its strength up to 10 times and its toughness up to 35 times. Combining crosslinks with mineral makes the fibril stiffer but more brittle. We also found that a mineralized fibril reaches its maximum toughness to density and strength to density ratios for a mineral density of around 30%. This result, in good agreement with experimental observations, attests that bone tissue is optimized mechanically to remain lightweight but maintain strength and toughness. © 2015 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research (ASBMR). PMID:26866939
Breaking diffeomorphism invariance and tests for the emergence of gravity
Anber, Mohamed M.; Aydemir, Ufuk; Donoghue, John F.
2010-04-15
If general relativity is an emergent phenomenon, there may be small violations of diffeomorphism invariance. We propose a phenomenology of perturbatively small violations of general relativity by the inclusion of terms which break general covariance. These can be tested by matching to the parameterized post-Newtonian formalism. The most sensitive tests involve pulsar timing and provide an extremely strong bound, with a dimensionless constraint of order 10{sup -20} relative to gravitational strength.
Kurtz, S M; Rimnac, C M; Pruitt, L; Jewett, C W; Goldberg, V; Edidin, A A
2000-02-01
Many aspects of the proposed relationship between material properties and clinical performance of UHMWPE components remain unclear. In this study, we explored the hypothesis that the clinical performance of tibial inserts is directly related to its large-deformation mechanical behavior measured near the articulating surface. Retrieval analysis was performed on three conventional UHMWPE and three Hylamer-M tibial components of the same design and manufacturer. Samples of material were then obtained from the worn regions of each implant and subjected to mechanical characterization using the small punch test. Statistically significant relationships were observed between the metrics of the small punch test and the total damage score and the burnishing damage score of the implants. We also examined the near-surface morphology of the retrievals using transmission electron microscopy. TEM analysis revealed lamellar alignment at and below the wear surfaces of the conventional UHMWPE retrievals up to a maximum depth of approximately 8 microm, consistent with large-deformation crystalline plasticity. The depth of the plasticity-induced damage layer varied not only between the retrievals, but also between the conventional UHMWPE and Hylamer-M components. Thus, the results of this study support the hypothesis that the clinical performance of UHMWPE tibial inserts is related to the large-deformation mechanical behavior measured near the articulating surface. PMID:10646945
Transient elasticity and the rheology of polymeric fluids with large amplitude deformations.
Müller, Oliver; Liu, Mario; Pleiner, Harald; Brand, Helmut R
2016-02-01
Transient elasticity is a systematic generalization of viscoelasticity. Its purpose is to give a coherent description of non-Newtonian effects displayed by soft-matter systems, especially polymer melts and solutions. Using the concept of transient elasticity we describe here a hydrodynamic model for polymeric fluids, which is applicable for large amplitude deformations. We present an energy density with only two independent parameters, which is compatible with all thermodynamic requirements and which reduces for small deformations to models studied previously. The expression discussed is simple enough to allow full analytic treatment and shows semiquantitative agreement with experimental data. This model is used to capture many of the interesting effects thought to be characteristic of polymer rheology for large deformations including viscosity overshoot near the onset of shear flow, the onset of elongational flows in situations for which there is no stationary solution as well as shear thinning and normal stress differences for a large range of shear rates. In addition, we analyze how well our model accounts for empirical relations including the Cox-Merz rule, the Yamamoto relation, and Gleißle's mirror relations. PMID:26986420
Transient elasticity and the rheology of polymeric fluids with large amplitude deformations
NASA Astrophysics Data System (ADS)
Müller, Oliver; Liu, Mario; Pleiner, Harald; Brand, Helmut R.
2016-02-01
Transient elasticity is a systematic generalization of viscoelasticity. Its purpose is to give a coherent description of non-Newtonian effects displayed by soft-matter systems, especially polymer melts and solutions. Using the concept of transient elasticity we describe here a hydrodynamic model for polymeric fluids, which is applicable for large amplitude deformations. We present an energy density with only two independent parameters, which is compatible with all thermodynamic requirements and which reduces for small deformations to models studied previously. The expression discussed is simple enough to allow full analytic treatment and shows semiquantitative agreement with experimental data. This model is used to capture many of the interesting effects thought to be characteristic of polymer rheology for large deformations including viscosity overshoot near the onset of shear flow, the onset of elongational flows in situations for which there is no stationary solution as well as shear thinning and normal stress differences for a large range of shear rates. In addition, we analyze how well our model accounts for empirical relations including the Cox-Merz rule, the Yamamoto relation, and Gleißle's mirror relations.
Large deformation analysis of a dielectric elastomer membrane-spring system
NASA Astrophysics Data System (ADS)
He, Tianhu; Cui, Leilei; Chen, Cheng
2009-07-01
Due to the capability of large strain, dielectric elastomers are promising for applications as transducers in cameras, robots, valves, pumps, energy harvesters and so on. The dielectric elastomer transducers are based on the deformation of a soft polymer membrane contracting in thickness and expanding in area, which is induced by the application of a voltage across the two compliant electrodes coated on both sides of the membrane. This paper focuses on the large deformation analysis of a dielectric elastomer membrane-spring system. The system is constructed from attaching a disk in the middle of a circular dielectric membrane and then connecting the disk with a spring. This configuration can be potentially used as a key part in valves. The basic governing equations describing the large out-of-plane deformations are formulated, and the obtained equations are solved numerically. The relations related to the displacement of the disk, the spring force, the applied voltage, and the parameters of spring including stiffness and initial length are illustrated. The results show the anticipated displacement of the disk can be controlled by adjusting the parameters of spring and the applied voltage individually or simultaneously, and the parameters of the spring, that is, stiffness and initial length, play an important role in the performance of the membrane-spring system.
On the large Ω-deformations in the Nekrasov-Shatashvili limit of N={2}^{*} SYM
NASA Astrophysics Data System (ADS)
Beccaria, Matteo
2016-07-01
We study the multi-instanton partition functions of the Ω-deformed N={2}^{*} SU(2) gauge theory in the Nekrasov-Shatashvili (NS) limit. They depend on the deformation parameters ɛ1, the scalar field expectation value a, and the hypermultiplet mass m. At fixed instanton number k, they are rational functions of ɛ1 , a, m and we look for possible regularities that admit a parametrical description in the number of instantons. In each instanton sector, the contribution to the deformed Nekrasov prepotential has poles for large deformation parameters. To clarify the properties of these singularities we exploit Bethe/gauge correspondence and examine the special ratios m/ɛ1 at which the associated spectral problem is n-gap. At these special points we illustrate several structural simpli-fications occurring in the partition functions. After discussing various tools to compute the prepotential, we analyze the non-perturbative corrections up to k = 24 instantons and present various closed expressions for the coefficients of the singular terms. Both the regular and singular parts of the prepotential are resummed over all instantons and compared successfully with the exact prediction from the spectral theory of the Lamé equation, showing that the pole singularities are an artifact of the instanton expansion. The analysis is fully worked out in the 1-gap case, but the final pole cancellation is proved for a generic ratio m/ɛ1 relating it to the gap width of the Lamé equation.
Large Deformation Analysis of a High Steep Slope Relating to the Laxiwa Reservoir, China
NASA Astrophysics Data System (ADS)
Lin, Peng; Liu, Xiaoli; Hu, Senying; Li, Pujian
2016-06-01
The unstable rock slope in the Laxiwa reservoir area of the Yellow River upstream, China, shows the signs of gravitational and water-impounding induced large deformations over an area of 1.15 × 105 m2. Slope movements have been measured daily at more than 560 observation points since 2009, when the reservoir was first impounded. At two of these points, an average daily movement of around 60-80 mm has ever been observed since the beginning of the impounding. Based on the observed deformations and the geology of the site, a fluid-solid coupling model was then adopted to investigate the existing rockslide activity to better understand the mechanism underlying the large deformations. The results from the field observation, kinematic analysis and numerical modeling indicate that the slope instability is dominated by the strong structurally controlled unstable rock mass. Based on an integrated overview of these analyses, a new toppling mode, i.e. the so-called `conjugate block' mode, is proposed to explain the large deformation mechanism of the slope. The conjugate block is formed by a `dumping block' and toppling blocks. The large deformation of the slope is dominated by (1) a toppling component and (2) a subsiding bilinear wedge induced by planar sliding along the deep-seated faults. Following a thorough numerical analysis, it is concluded that small collapses of rock blocks along the slope will be more frequent with the impounding process continuing and the water level fluctuating during the subsequent operation period. Based on a shear strength reduction method and field monitoring, four controlling faults are identified and the instability of the loose structure in the surface layer is analyzed and discussed. The factor of safety against the sliding failure along the deep seated fractures in the slope is 1.72, which reveals that (1) the collapse of the free-standing fractured blocks cannot be ruled out and the volume of the unstable blocks may be greater than 100
Deformation regime and long-term precursors to eruption at large calderas: Rabaul, Papua New Guinea
NASA Astrophysics Data System (ADS)
Robertson, Robert M.; Kilburn, Christopher R. J.
2016-03-01
Eruptions at large calderas are normally preceded by variable rates of unrest that continue for decades or more. A classic example is the 1994 eruption of Rabaul caldera, in Papua New Guinea, which began after 23 years of surface uplift and volcano-tectonic (VT) seismicity at rates that changed unevenly with time by an order of magnitude. Although the VT event rate and uplift rate peaked in 1983-1985, eruptions only began a decade later and followed just 27 hours of anomalous changes in precursory signal. Here we argue that the entire 23 years of unrest belongs to a single sequence of damage accumulation in the crust and that, in 1991-1992, the crust's response to applied stress changed from quasi-elastic (elastic deformation with minor fault movement) to inelastic (deformation predominantly by fault movement alone). The change in behaviour yields limiting trends in the variation of VT event rate with deformation and can be quantified with a mean-field model for an elastic crust that contains a dispersed population of small faults. The results show that identifying the deformation regime for elastic-brittle crust provides new criteria for using precursory time series to evaluate the potential for eruption. They suggest that, in the quasi-elastic regime, short-term increases in rates of deformation and VT events are unreliable indicators of an imminent eruption, but that, in the inelastic regime, the precursory rates may follow hyperbolic increases with time and offer the promise of developing forecasts of eruption as much as months beforehand.
Surface deformations as indicators of deep ebullition fluxes in a large northern peatland
Glaser, P.H.; Chanton, J.P.; Morin, P.; Rosenberry, D.O.; Siegel, D.I.; Ruud, O.; Chasar, L.I.; Reeve, A.S.
2004-01-01
Peatlands deform elastically during precipitation cycles by small (??3 cm) oscillations in surface elevation. In contrast, we used a Global Positioning System network to measure larger oscillations that exceeded 20 cm over periods of 4-12 hours during two seasonal droughts at a bog and fen site in northern Minnesota. The second summer drought also triggered 19 depressuring cycles in an overpressured stratum under the bog site. The synchronicity between the largest surface deformations and the depressuring cycles indicates that both phenomena are produced by the episodic release of large volumes of gas from deep semi-elastic compartments confined by dense wood layers. We calculate that the three largest surface deformations were associated with the release of 136 g CH4 m-2, which exceeds by an order of magnitude the annual average chamber fluxes measured at this site. Ebullition of gas from the deep peat may therefore be a large and previously unrecognized source of radiocarbon depleted methane emissions from northern peatlands. Copyright 2004 by the American Geophysical Union.
Characterizing large-scale glaciotectonic sediment deformation using electrical resistivity methods
NASA Astrophysics Data System (ADS)
Aylsworth, R. L., Jr.; Van Dam, R. L.; Larson, G. J.; Jessee, M. A.
2016-04-01
Large-scale sediment deformation structures formed by glaciotectonic processes have been identified south of Ludington, USA. Here, several apparent clay diapirs rise from below beach level to near the top of an approximately 60 m high bluff along the eastern shore of Lake Michigan. Throughout the area, the surface topography and locations of springs indicate a complicated subsurface structure and a preferred pattern of groundwater drainage. Since public borehole information is sparse, it is not known whether the structures exposed in the bluff are true diapirs or ridges, and if the latter, what is their orientation. In this paper we present the results of field, laboratory, and modeling studies to characterize the inland extent and orientation of these deformation structures using galvanic-source electrical geophysical methods. We exploit the large electrical contrast between a sandy sedimentary layer and an underlying clayey silt sedimentary layer in which the deformation occurred. Constant-spread traverses and multi-electrode tomographic data demonstrate that at least one of the narrow structures extends a significant distance inland.
Hydrothermal fluid flow and deformation in large calderas: Inferences from numerical simulations
Hurwitz, S.; Christiansen, L.B.; Hsieh, P.A.
2007-01-01
Inflation and deflation of large calderas is traditionally interpreted as being induced by volume change of a discrete source embedded in an elastic or viscoelastic half-space, though it has also been suggested that hydrothermal fluids may play a role. To test the latter hypothesis, we carry out numerical simulations of hydrothermal fluid flow and poroelastic deformation in calderas by coupling two numerical codes: (1) TOUGH2 [Pruess et al., 1999], which simulates flow in porous or fractured media, and (2) BIOT2 [Hsieh, 1996], which simulates fluid flow and deformation in a linearly elastic porous medium. In the simulations, high-temperature water (350??C) is injected at variable rates into a cylinder (radius 50 km, height 3-5 km). A sensitivity analysis indicates that small differences in the values of permeability and its anisotropy, the depth and rate of hydrothermal injection, and the values of the shear modulus may lead to significant variations in the magnitude, rate, and geometry of ground surface displacement, or uplift. Some of the simulated uplift rates are similar to observed uplift rates in large calderas, suggesting that the injection of aqueous fluids into the shallow crust may explain some of the deformation observed in calderas.
Effect of large deformation pre-loads on the wave properties of hexagonal lattices
NASA Astrophysics Data System (ADS)
Pal, Raj Kumar; Rimoli, Julian; Ruzzene, Massimo
2016-05-01
We study linear wave propagation in nonlinear hexagonal lattices capable of undergoing large deformations, under different levels of pre-load. The lattices are composed of a set of masses connected by linear axial and angular springs, with the nonlinearity arising solely from geometric effects. By applying different levels of pre-load, the small amplitude linear wave propagation response can be varied from isotropic to highly directional. Analytical expressions for the stiffness of a unit cell in the deformed configuration are derived and they are used to analyze the dispersion surfaces and group velocity variation with pre-load. Numerical simulations on finite lattices demonstrate the validity of our unit cell predictions and illustrate the wave steering potential of our lattice.
Thermal Deformation and RF Performance Analyses for the SWOT Large Deployable Ka-Band Reflectarray
NASA Technical Reports Server (NTRS)
Fang, H.; Sunada, E.; Chaubell, J.; Esteban-Fernandez, D.; Thomson, M.; Nicaise, F.
2010-01-01
A large deployable antenna technology for the NASA Surface Water and Ocean Topography (SWOT) Mission is currently being developed by JPL in response to NRC Earth Science Tier 2 Decadal Survey recommendations. This technology is required to enable the SWOT mission due to the fact that no currently available antenna is capable of meeting SWOT's demanding Ka-Band remote sensing requirements. One of the key aspects of this antenna development is to minimize the effect of the on-orbit thermal distortion to the antenna RF performance. An analysis process which includes: 1) the on-orbit thermal analysis to obtain the temperature distribution; 2) structural deformation analysis to get the geometry of the antenna surface; and 3) the RF performance with the given deformed antenna surface has been developed to accommodate the development of this antenna technology. The detailed analysis process and some analysis results will be presented and discussed by this paper.
Rudd, R E
2009-02-05
Recent advances in the ability to generate extremes of pressure and temperature in dynamic experiments and to probe the response of materials has motivated the need for special materials optimized for those conditions as well as a need for a much deeper understanding of the behavior of materials subjected to high pressure and/or temperature. Of particular importance is the understanding of rate effects at the extremely high rates encountered in those experiments, especially with the next generation of laser drives such as at the National Ignition Facility. Here we use large-scale molecular dynamics (MD) simulations of the high-rate deformation of nanocrystalline tantalum to investigate the processes associated with plastic deformation for strains up to 100%. We use initial atomic configurations that were produced through simulations of solidification in the work of Streitz et al [Phys. Rev. Lett. 96, (2006) 225701]. These 3D polycrystalline systems have typical grain sizes of 10-20 nm. We also study a rapidly quenched liquid (amorphous solid) tantalum. We apply a constant volume (isochoric), constant temperature (isothermal) shear deformation over a range of strain rates, and compute the resulting stress-strain curves to large strains for both uniaxial and biaxial compression. We study the rate dependence and identify plastic deformation mechanisms. The identification of the mechanisms is facilitated through a novel technique that computes the local grain orientation, returning it as a quaternion for each atom. This analysis technique is robust and fast, and has been used to compute the orientations on the fly during our parallel MD simulations on supercomputers. We find both dislocation and twinning processes are important, and they interact in the weak strain hardening in these extremely fine-grained microstructures.
Statistical shape analysis: From landmarks to diffeomorphisms.
Zhang, Miaomiao; Golland, Polina
2016-10-01
We offer a blazingly brief review of evolution of shape analysis methods in medical imaging. As the representations and the statistical models grew more sophisticated, the problem of shape analysis has been gradually redefined to accept images rather than binary segmentations as a starting point. This transformation enabled shape analysis to take its rightful place in the arsenal of tools for extracting and understanding patterns in large clinical image sets. We speculate on the future developments in shape analysis and potential applications that would bring this mathematically rich area to bear on clinical practice. PMID:27377332
Low-Dimensional Generalized Coordinate Models of Large-Deformation Elastic Joints
NASA Astrophysics Data System (ADS)
Odhner, Lael; Dollar, Aaron
2012-02-01
In the field of robotics, it is increasingly common to use elastic elements such as rods, beams or sheets to allow motion between the rigid links of a robot, rather than conventional sliding mechanisms such as pin joints. Although these elastic joints are simpler to manufacture, especially at meso- and micro-scales, representational simplicity is sacrificed. It is far easier to compute the Lagrangian of a robot using joint angles as generalized coordinates, rather than by considering the large-deformation continuum behavior of elastic joints. In this talk, we will discuss our work toward finding accurate, low-dimensional discretizations of elastic joint mechanics, suitable for use in generalized coordinate models of robot kinematics and dynamics. We use modally parameterized backbone curves to describe the kinematic configuration of the elastic joints, and compute the energy associated with deformation using rod and shell theory. In the plane, only three smooth deformation modes are sufficient to describe Euler-Bernoulli bending of 90 degrees to within 1 percent. Parametric models for the three-dimensional motion of sheet hinges are more complex, but can be simplified significantly using boundary conditions and constraints imposed by ruled surface assumptions.
NASA Astrophysics Data System (ADS)
Zhang, Jie; Sheng, Lei; Liu, Jing
2014-11-01
Reversible deformation of a machine holds enormous promise across many scientific areas ranging from mechanical engineering to applied physics. So far, such capabilities are still hard to achieve through conventional rigid materials or depending mainly on elastomeric materials, which however own rather limited performances and require complicated manipulations. Here, we show a basic strategy which is fundamentally different from the existing ones to realize large scale reversible deformation through controlling the working materials via the synthetically chemical-electrical mechanism (SCHEME). Such activity incorporates an object of liquid metal gallium whose surface area could spread up to five times of its original size and vice versa under low energy consumption. Particularly, the alterable surface tension based on combination of chemical dissolution and electrochemical oxidation is ascribed to the reversible shape transformation, which works much more flexible than many former deformation principles through converting electrical energy into mechanical movement. A series of very unusual phenomena regarding the reversible configurational shifts are disclosed with dominant factors clarified. This study opens a generalized way to combine the liquid metal serving as shape-variable element with the SCHEME to compose functional soft machines, which implies huge potential for developing future smart robots to fulfill various complicated tasks.
Zhang, Jie; Sheng, Lei; Liu, Jing
2014-01-01
Reversible deformation of a machine holds enormous promise across many scientific areas ranging from mechanical engineering to applied physics. So far, such capabilities are still hard to achieve through conventional rigid materials or depending mainly on elastomeric materials, which however own rather limited performances and require complicated manipulations. Here, we show a basic strategy which is fundamentally different from the existing ones to realize large scale reversible deformation through controlling the working materials via the synthetically chemical-electrical mechanism (SCHEME). Such activity incorporates an object of liquid metal gallium whose surface area could spread up to five times of its original size and vice versa under low energy consumption. Particularly, the alterable surface tension based on combination of chemical dissolution and electrochemical oxidation is ascribed to the reversible shape transformation, which works much more flexible than many former deformation principles through converting electrical energy into mechanical movement. A series of very unusual phenomena regarding the reversible configurational shifts are disclosed with dominant factors clarified. This study opens a generalized way to combine the liquid metal serving as shape-variable element with the SCHEME to compose functional soft machines, which implies huge potential for developing future smart robots to fulfill various complicated tasks. PMID:25408295
A large-deformation thin plate theory with application to one-atom-thick layers
NASA Astrophysics Data System (ADS)
Delfani, M. R.; Shodja, H. M.
2016-02-01
Nowadays, two-dimensional materials due to their vast engineering and biomedical applications have been the focus of many researches. The present paper proposes a large-deformation theory for thin plates with application to one-atom-thick layers (OATLs). The deformation is formulated exactly in the mathematical framework of Lagrangian description. In particular, an exact finite strain analysis is given - in addition to the usual strain tensor associated to the middle surface, the second and third fundamental forms of the middle surface of the deformed thin plate are also maintained in the analysis. Exact closed-form solutions for a uniaxially curved thin plate due to pure bending in one case and due to a combination of vertical and horizontal loading in another are obtained. As a special case of the latter problem, the exact solution for the plane-strain bulge test of thin plates is derived. Subsequently, the approximation of Vlassak and Nix [Vlassak, J.J., Nix, W.D., 1992. J. Mater. Res., 7(12), 3242-3249] for the load-deflection equation is recovered. The given numerical results are devoted to graphene as the most well-known OATL.
Zhang, Jie; Sheng, Lei; Liu, Jing
2014-01-01
Reversible deformation of a machine holds enormous promise across many scientific areas ranging from mechanical engineering to applied physics. So far, such capabilities are still hard to achieve through conventional rigid materials or depending mainly on elastomeric materials, which however own rather limited performances and require complicated manipulations. Here, we show a basic strategy which is fundamentally different from the existing ones to realize large scale reversible deformation through controlling the working materials via the synthetically chemical-electrical mechanism (SCHEME). Such activity incorporates an object of liquid metal gallium whose surface area could spread up to five times of its original size and vice versa under low energy consumption. Particularly, the alterable surface tension based on combination of chemical dissolution and electrochemical oxidation is ascribed to the reversible shape transformation, which works much more flexible than many former deformation principles through converting electrical energy into mechanical movement. A series of very unusual phenomena regarding the reversible configurational shifts are disclosed with dominant factors clarified. This study opens a generalized way to combine the liquid metal serving as shape-variable element with the SCHEME to compose functional soft machines, which implies huge potential for developing future smart robots to fulfill various complicated tasks. PMID:25408295
NASA Astrophysics Data System (ADS)
Figiel, Łukasz; Dunne, Fionn P. E.; Buckley, C. Paul
2010-01-01
Layered-silicate nanoparticles offer a cost-effective reinforcement for thermoplastics. Computational modelling has been employed to study large deformations in layered-silicate/poly(ethylene terephthalate) (PET) nanocomposites near the glass transition, as would be experienced during industrial forming processes such as thermoforming or injection stretch blow moulding. Non-linear numerical modelling was applied, to predict the macroscopic large deformation behaviour, with morphology evolution and deformation occurring at the microscopic level, using the representative volume element (RVE) approach. A physically based elasto-viscoplastic constitutive model, describing the behaviour of the PET matrix within the RVE, was numerically implemented into a finite element solver (ABAQUS) using an UMAT subroutine. The implementation was designed to be robust, for accommodating large rotations and stretches of the matrix local to, and between, the nanoparticles. The nanocomposite morphology was reconstructed at the RVE level using a Monte-Carlo-based algorithm that placed straight, high-aspect ratio particles according to the specified orientation and volume fraction, with the assumption of periodicity. Computational experiments using this methodology enabled prediction of the strain-stiffening behaviour of the nanocomposite, observed experimentally, as functions of strain, strain rate, temperature and particle volume fraction. These results revealed the probable origins of the enhanced strain stiffening observed: (a) evolution of the morphology (through particle re-orientation) and (b) early onset of stress-induced pre-crystallization (and hence lock-up of viscous flow), triggered by the presence of particles. The computational model enabled prediction of the effects of process parameters (strain rate, temperature) on evolution of the morphology, and hence on the end-use properties.
NASA Astrophysics Data System (ADS)
Flesch, L. M.; Holt, W. E.; Haines, A. J.
2003-04-01
The deformation of continental lithosphere is controlled by a variety of factors, including (1) body forces, (2) basal tractions, (3) boundary forces, and (4) rheology. Obtaining unique solutions that describe the dynamics of continental lithosphere is extremely challenging. Limitations are associated with inadequate observations that can uniquely constrain the dynamics as well as inadequate numerical methods. However, the compilation of space geodetic, seismic, and geologic data over the past 10-15 years have made it possible to make significant strides toward understanding the dynamics of large-scale continental deformation. The first step in making inferences about continental dynamics involves a quantification of the kinematics of active deformation (measurement of the velocity gradient tensor field). We interpolate both GPS velocity vectors and Quaternary strain rates with continuous spline functions (bi-cubic Bessel interpolation) to define a model velocity gradient tensor field solution (strain rates, rotation rates, and relative motions). In our methodology grid areas can be defined to be small enough such that fault zones are narrow and regions between faults (crustal blocks) possess rigid behavior. Our dynamic models are solutions to equations for a thin sheet, accounting for body forces associated with horizontal density variations and edge forces associated with accommodation of relative plate motion. The formalism can also include basal tractions associated with coupling between lithosphere and deeper mantle circulation. These dynamic models allow for lateral variations of viscosity and they allow for different power-law rheologies with power law exponents ranging from n = 1-9. Thus our dynamic models account for possible block-like behavior (high effective viscosity) as well as concentrated strain within shear zones. Kinematic results to date for central Asia show block-like behavior for large regions such as South China, Tarim Basin, Amurian block
Deformation mechanisms, defects, heat treatment, and thermal conductivity in large grain niobium
NASA Astrophysics Data System (ADS)
Bieler, Thomas R.; Kang, Di; Baars, Derek C.; Chandrasekaran, Saravan; Mapar, Aboozar; Ciovati, Gianluigi; Wright, Neil T.; Pourboghrat, Farhang; Murphy, James E.; Compton, Chris C.; Myneni, Ganapati Rao
2015-12-01
The physical and mechanical metallurgy underlying fabrication of large grain cavities for superconducting radio frequency accelerators is summarized, based on research of 1) grain orientations in ingots, 2) a metallurgical assessment of processing a large grain single cell cavity and a tube, 3) assessment of slip behavior of single crystal tensile samples extracted from a high purity ingot slice before and after annealing at 800 °C / 2 h, 4) development of crystal plasticity models based upon the single crystal experiments, and 5) assessment of how thermal conductivity is affected by strain, heat treatment, and exposure to hydrogen. Because of the large grains, the plastic anisotropy of deformation is exaggerated, and heterogeneous strains and localized defects are present to a much greater degree than expected in polycrystalline material, making it highly desirable to computationally anticipate potential forming problems before manufacturing cavities.
A 3D Frictional Segment-to-Segment Contact Method for Large Deformations and Quadratic Elements
Puso, M; Laursen, T; Solberg, J
2004-04-01
Node-on-segment contact is the most common form of contact used today but has many deficiencies ranging from potential locking to non-smooth behavior with large sliding. Furthermore, node-on-segment approaches are not at all applicable to higher order discretizations (e.g. quadratic elements). In a previous work, [3, 4] we developed a segment-to-segment contact approach for eight node hexahedral elements based on the mortar method that was applicable to large deformation mechanics. The approach proved extremely robust since it eliminated the over-constraint that caused 'locking' and provided smooth force variations in large sliding. Here, we extend this previous approach to treat frictional contact problems. In addition, the method is extended to 3D quadratic tetrahedrals and hexahedrals. The proposed approach is then applied to several challenging frictional contact problems that demonstrate its effectiveness.
Deformation mechanisms, defects, heat treatment, and thermal conductivity in large grain niobium
Bieler, Thomas R. Kang, Di Baars, Derek C.; Chandrasekaran, Saravan; Mapar, Aboozar Wright, Neil T.; Ciovati, Gianluigi Myneni, Ganapati Rao; Pourboghrat, Farhang; Murphy, James E.; Compton, Chris C.
2015-12-04
The physical and mechanical metallurgy underlying fabrication of large grain cavities for superconducting radio frequency accelerators is summarized, based on research of 1) grain orientations in ingots, 2) a metallurgical assessment of processing a large grain single cell cavity and a tube, 3) assessment of slip behavior of single crystal tensile samples extracted from a high purity ingot slice before and after annealing at 800 °C / 2 h, 4) development of crystal plasticity models based upon the single crystal experiments, and 5) assessment of how thermal conductivity is affected by strain, heat treatment, and exposure to hydrogen. Because of the large grains, the plastic anisotropy of deformation is exaggerated, and heterogeneous strains and localized defects are present to a much greater degree than expected in polycrystalline material, making it highly desirable to computationally anticipate potential forming problems before manufacturing cavities.
Shear bands in a bulk metallic glass after large plastic deformation
Qu, D.D.; Wang, Y.B.; Liao, X.Z.; Shen, J.
2012-10-23
A transmission electron microscopy investigation is conducted to trace shear bands in a Zr{sub 53}Cu{sub 18.7}Ni{sub 12}Al{sub 16.3} bulk metallic glass after experiencing 4% plastic deformation. Shear band initiation, secondary shear band interactions, mature shear band broadening and the interactions of shear bands with shear-induced nanocrystals are captured. Results suggest that the plasticity of the bulk metallic glass is enhanced by complex shear bands and their interactions which accommodate large plastic strain and prevent catastrophic shear band propagation.
X-ray microbeam quantification of grain subdivision accompanying large deformations of copper
Guvenilir, A.; Butler, G.C.; Haase, J.D.; McDowell, D.L.; Stock, S.R.
1998-11-20
This work reports the application of X-ray microbeam diffraction to quantifying grain subdivision processes in copper. Polychromatic synchrotron X-radiation was used to study samples in the as-received (low deformation) and 100% torsion strained material. The large range of domain disorientations (within individual grains) observed in the highly strained material agrees with results on other f.c.c. materials obtained by electron beam methods; it is not surprising, therefore, that models of texture development which do not include this effect predict too rapid sharpening of preferred orientation compared to experimental pole figures.
Martin, S.E.; Newman, J.B.
1980-11-01
A thermomechanical theory of large deformation elastic-inelastic material behavior is developed which is based on a multiplicative decomposition of the strain. Very general assumptions are made for the elastic and inelastic constitutive relations and effects such as thermally-activated creep, fast-neutron-flux-induced creep and growth, annealing, and strain recovery are compatible with the theory. Reduced forms of the constitutive equations are derived by use of the second law of thermodynamics in the form of the Clausius-Duhem inequality. Observer invariant equations are derived by use of an invariance principle which is a generalization of the principle of material frame indifference.
Comparison of spacetime defects which are homeomorphic but not diffeomorphic
Klinkhamer, F. R. Sorba, F.
2014-11-15
Certain remnants of a quantum spacetime foam can be modeled by a distribution of defects embedded in a flat classical spacetime. The presence of such spacetime defects affects the propagation of elementary particles. In this article, we show explicitly that both topology and differential structure of the defects are important for the particle motion. Specifically, we consider three types of spacetime defects which are described by the same topological manifold R×(RP{sup 3}−(point)) but which are not diffeomorphic to each other. We investigate the propagation of a massless scalar field over the three different manifolds and find different solutions of the Klein–Gordon equation.
Non-diffeomorphic registration of brain tumor images by simulating tissue loss and tumor growth.
Zacharaki, Evangelia I; Hogea, Cosmina S; Shen, Dinggang; Biros, George; Davatzikos, Christos
2009-07-01
Although a variety of diffeomorphic deformable registration methods exist in the literature, application of these methods in the presence of space-occupying lesions is not straightforward. The motivation of this work is spatial normalization of MR images from patients with brain tumors in a common stereotaxic space, aiming to pool data from different patients into a common space in order to perform group analyses. Additionally, transfer of structural and functional information from neuroanatomical brain atlases into the individual patient's space can be achieved via the inverse mapping, for the purpose of segmenting brains and facilitating surgical or radiotherapy treatment planning. A method that estimates the brain tissue loss and replacement by tumor is applied for achieving equivalent image content between an atlas and a patient's scan, based on a biomechanical model of tumor growth. Automated estimation of the parameters modeling brain tissue loss and displacement is performed via optimization of an objective function reflecting feature-based similarity and elastic stretching energy, which is optimized in parallel via APPSPACK (Asynchronous Parallel Pattern Search). The results of the method, applied to 21 brain tumor patients, indicate that the registration accuracy is relatively high in areas around the tumor, as well as in the healthy portion of the brain. Also, the calculated deformation in the vicinity of the tumor is shown to correlate highly with expert-defined visual scores indicating the tumor mass effect, thereby potentially leading to an objective approach to quantification of mass effect, which is commonly used in diagnosis. PMID:19408350
Pai, Akshay; Sommer, Stefan; Sorensen, Lauge; Darkner, Sune; Sporring, Jon; Nielsen, Mads
2016-06-01
In this paper, we propose a multi-scale, multi-kernel shape, compactly supported kernel bundle framework for stationary velocity field-based image registration (Wendland kernel bundle stationary velocity field, wKB-SVF). We exploit the possibility of directly choosing kernels to construct a reproducing kernel Hilbert space (RKHS) instead of imposing it from a differential operator. The proposed framework allows us to minimize computational cost without sacrificing the theoretical foundations of SVF-based diffeomorphic registration. In order to recover deformations occurring at different scales, we use compactly supported Wendland kernels at multiple scales and orders to parameterize the velocity fields, and the framework allows simultaneous optimization over all scales. The performance of wKB-SVF is extensively compared to the 14 non-rigid registration algorithms presented in a recent comparison paper. On both MGH10 and CUMC12 datasets, the accuracy of wKB-SVF is improved when compared to other registration algorithms. In a disease-specific application for intra-subject registration, atrophy scores estimated using the proposed registration scheme separates the diagnostic groups of Alzheimer's and normal controls better than the state-of-the-art segmentation technique. Experimental results show that wKB-SVF is a robust, flexible registration framework that allows theoretically well-founded and computationally efficient multi-scale representation of deformations and is equally well-suited for both inter- and intra-subject image registration. PMID:26841388
NASA Astrophysics Data System (ADS)
Voyiadjis, George Z.; Samadi-Dooki, Aref
2016-06-01
Due to the lack of the long-range order in their molecular structure, amorphous polymers possess a considerable free volume content in their inter-molecular space. During finite deformation, these free volume holes serve as the potential sites for localized permanent plastic deformation inclusions which are called shear transformation zones (STZs). While the free volume content has been experimentally shown to increase during the course of plastic straining in glassy polymers, thermal analysis of stored energy due to the deformation shows that the STZ nucleation energy decreases at large plastic strains. The evolution of the free volume, and the STZs number density and nucleation energy during the finite straining are formulated in this paper in order to investigate the uniaxial post-yield softening-hardening behavior of the glassy polymers. This study shows that the reduction of the STZ nucleation energy, which is correlated with the free volume increase, brings about the post-yield primary softening of the amorphous polymers up to the steady-state strain value; and the secondary hardening is a result of the increased number density of the STZs, which is required for large plastic strains, while their nucleation energy is stabilized beyond the steady-state strain. The evolutions of the free volume content and STZ nucleation energy are also used to demonstrate the effect of the strain rate, temperature, and thermal history of the sample on its post-yield behavior. The obtained results from the model are compared with the experimental observations on poly(methyl methacrylate) which show a satisfactory consonance.
Large-scale deformation of Tibet measured with Envisat ScanSAR interferometry
NASA Astrophysics Data System (ADS)
Fielding, E. J.; Rosen, P. A.; Burgmann, R.
2007-12-01
Scanning synthetic aperture radar (ScanSAR) interferometry has the potential to map deformation over large areas. The large actively deforming area and arid climate of Tibet make it an excellent test area for the ScanSAR interferometry technique, which has been proposed as a possible SAR operation mode for the DESDynI mission recommended by the Decadal Survey. The Envisat C-band (5.6 cm wavelength) ScanSAR is called Wide Swath (WS) mode and images a track that is over 400 km wide, with five subswaths. Envisat WS was not originally designed for interferometry, but about one in five pairs have the required burst synchronization. Since January 2007, the European Space Agency have been attempting to greatly improve the burst synchronization and reduce the variation in baselines. Unfortunately, some of the WS data over Tibet has been acquired in HH polarization and some in VV polarization, causing an additional limitation on usable interferometric pairs. Several Envisat tracks across Tibet have appropriate WS acquisitions to form interferometric pairs. Initial results show a reduction of coherence in eastern Tibet where the plateau climate is wetter and allows more vegetation cover. Processing long strips (>1000 km) with the full WS width gives strong constraints on the baseline between the two orbits of image-pair acquisitions and enables better separation of atmospheric effects and orbit errors from moderate- wavelength (~ 100 km) deformation signals. Long-wavelength control from GPS or other ground-based data is still required for the longest wavelengths (>300 km).
Magneto-induced large deformation and high-damping performance of a magnetorheological plastomer
NASA Astrophysics Data System (ADS)
Liu, Taixiang; Gong, Xinglong; Xu, Yangguang; Pang, Haoming; Xuan, Shouhu
2014-10-01
A magnetorheological plastomer (MRP) is a new kind of soft magneto-sensitive polymeric composite. This work reports on the large magneto-deforming effect and high magneto-damping performance of MRPs under a quasi-statical shearing condition. We demonstrate that an MRP possesses a magnetically sensitive malleability, and its magneto-mechanical behavior can be analytically described by the magneto-enhanced Bingham fluid-like model. The magneto-induced axial stress, which drives the deformation of the MRP with 70 wt % carbonyl iron powder, can be tuned in a large range from nearly 0.0 kPa to 55.4 kPa by an external 662.6 kA m-1 magnetic field. The damping performance of an MRP has a significant correlation with the magnetic strength, shear rate, carbonyl iron content and shear strain amplitude. For an MRP with 60 wt % carbonyl iron powder, the relative magneto-enhanced damping effect can reach as high as 716.2% under a quasi-statically shearing condition. Furthermore, the related physical mechanism is proposed, and we reveal that the magneto-induced, particle-assembled microstructure directs the magneto-mechanical behavior of the MRP.
A Novel Concept for a Deformable Membrane Mirror for Correction of Large Amplitude Aberrations
NASA Technical Reports Server (NTRS)
Moore, Jim; Patrick, Brian
2006-01-01
Very large, light weight mirrors are being developed for applications in space. Due to launch mass and volume restrictions these mirrors will need to be much more flexible than traditional optics. The use of primary mirrors with these characteristics will lead to requirements for adaptive optics capable of correcting wave front errors with large amplitude relatively low spatial frequency aberrations. The use of low modulus membrane mirrors actuated with electrostatic attraction forces is a potential solution for this application. Several different electrostatic membrane mirrors are now available commercially. However, as the dynamic range requirement of the adaptive mirror is increased the separation distance between the membrane and the electrodes must increase to accommodate the required face sheet deformations. The actuation force applied to the mirror decreases inversely proportional to the square of the separation distance; thus for large dynamic ranges the voltage requirement can rapidly increase into the high voltage regime. Experimentation with mirrors operating in the KV range has shown that at the higher voltages a serious problem with electrostatic field cross coupling between actuators can occur. Voltage changes on individual actuators affect the voltage of other actuators making the system very difficult to control. A novel solution has been proposed that combines high voltage electrodes with mechanical actuation to overcome this problem. In this design an array of electrodes are mounted to a backing structure via light weight large dynamic range flextensional actuators. With this design the control input becomes the separation distance between the electrode and the mirror. The voltage on each of the actuators is set to a uniform relatively high voltage, thus the problem of cross talk between actuators is avoided and the favorable distributed load characteristic of electrostatic actuation is retained. Initial testing and modeling of this concept
Longitudinal diffeomorphisms obstruct the protection of vacuum energy
NASA Astrophysics Data System (ADS)
Carballo-Rubio, Raúl
2015-06-01
To guarantee the stability of the cosmological constant sector against radiative corrections coming from quantum matter fields, one of the most natural ingredients to invoke is the symmetry under scale transformations of the gravitational field. Previous attempts to follow this path have nevertheless failed in providing a consistent picture. Here, we point out that this failure is intimately tied up to an assumption that is typically embedded in modern studies of the gravitational interaction: invariance under the full group of diffeomorphisms. We base the discussion on the gravitational theory known as Weyl transverse gravity. While leading to the same classical solutions as general relativity, and so to the same classical phenomenology, we show that in the presence of quantum matter (i) the degeneracy between these theories is broken (general relativity exhibits the well-known cosmological constant problem, while in Weyl transverse gravity, the cosmological constant sector is protected due to gravitational scale invariance), and (ii) this is possible as the result of abandoning the assumption of full diffeomorphism invariance, which permits circumventing classic results on scale-invariance anomalies and guarantees that gravitational scale invariance survives quantum corrections. Both results signal new directions in the quest of finding an ultraviolet completion of gravity.
A combinatorial approach to diffeomorphism invariant quantum gauge theories
Zapata, J.A.
1997-11-01
Quantum gauge theory in the connection representation uses functions of holonomies as configuration observables. Physical observables (gauge and diffeomorphism invariant) are represented in the Hilbert space of physical states; physical states are gauge and diffeomorphism invariant distributions on the space of functions of the holonomies of the edges of a certain family of graphs. Then a family of graphs embedded in the space manifold (satisfying certain properties) induces a representation of the algebra of physical observables. We construct a quantum model from the set of piecewise linear graphs on a piecewise linear manifold, and another manifestly combinatorial model from graphs defined on a sequence of increasingly refined simplicial complexes. Even though the two models are different at the kinematical level, they provide unitarily equivalent representations of the algebra of physical observables in {ital separable} Hilbert spaces of physical states (their s-knot basis is countable). Hence, the combinatorial framework is compatible with the usual interpretation of quantum field theory. {copyright} {ital 1997 American Institute of Physics.}
NASA Astrophysics Data System (ADS)
Bouklas, Nikolaos; Landis, Chad M.; Huang, Rui
2015-06-01
Hydrogels are capable of coupled mass transport and large deformation in response to external stimuli. In this paper, a nonlinear, transient finite element formulation is presented for initial boundary value problems associated with swelling and deformation of hydrogels, based on a nonlinear continuum theory that is consistent with classical theory of linear poroelasticity. A mixed finite element method is implemented with implicit time integration. The incompressible or nearly incompressible behavior at the initial stage imposes a constraint to the finite element discretization in order to satisfy the Ladyzhenskaya-Babuska-Brezzi (LBB) condition for stability of the mixed method, similar to linear poroelasticity as well as incompressible elasticity and Stokes flow; failure to choose an appropriate discretization would result in locking and numerical oscillations in transient analysis. To demonstrate the numerical method, two problems of practical interests are considered: constrained swelling and flat-punch indentation of hydrogel layers. Constrained swelling may lead to instantaneous surface instability for a soft hydrogel in a good solvent, which can be regulated by assuming a stiff surface layer. Indentation relaxation of hydrogels is simulated beyond the linear regime under plane strain conditions, in comparison with two elastic limits for the instantaneous and equilibrium states. The effects of Poisson's ratio and loading rate are discussed. It is concluded that the present finite element method is robust and can be extended to study other transient phenomena in hydrogels.
Investigating viscoelastic postseismic deformation due to large earthquakes in East Anatolia, Turkey
NASA Astrophysics Data System (ADS)
Sunbul, Fatih; Nalbant, Suleyman S.; Simão, Nuno M.; Steacy, Sandy
2016-03-01
We investigate the postseismic viscoelastic flow in the lower crust and upper mantle due to the 19th and 20th century large earthquakes in eastern Turkey. Three possible rheological models are used in the viscoelastic postseismic deformation analysis to assess the extent to which these events influence the velocity fields at GPS sites in the region. Our models show that the postseismic signal currently contributes to the observed deformation in the eastern part of the North Anatolian fault and northern and middle parts of the East Anatolian Fault Zone, primarily due to the long-lasting effect of the Ms 7.9 1939 earthquake. None of the postseismic displacement generated by the Ms 7.5 1822 earthquake, which is the earliest and the second largest event in the calculations, exceeds observed error range at the GPS stations. Our results demonstrate that a postseismic signal can be identified in the region and could contribute up to 3-25% of the observed GPS measurements.
A three-dimensional FE analysis of large deformations for impact loadings using tetrahedral elements
NASA Astrophysics Data System (ADS)
Yoo, Y. H.; Lee, M.
A three-dimensional dynamic program for the anaysis of large deformations in contact-penetration problems is developed using the finite element Lagrangian method with explicit time integration. By incorporating a tetrahedral element, which allows a single-point integration without a special hourglass control scheme, this program can be more effective to the present problem. The position code algorithm is used to search contact surface. Eroding surfaces are also considered. The defense node algorithm was slightly modified for the calculation of contact forces. A study of obliquity effects on metallic plate perforation and ricochet processes in thin plates impacted by a sphere was conducted. It is well simulated that on separation of two parts of the sphere, the portion still within the crater tends to perforate, while the portion in contact with the plate surface ricochets. This deformation pattern is observed in experiments, especially at high obliquities. A long rod that impacts an oblique steel plate at high impact velocity was also simulated in order to study the dynamics of the rod caused by the three dimensional asymmetric contact. The agreement between simulated and experimental results is quite good. Fracture phenomena occuring at high obliquity deserves further investigations.
NASA Astrophysics Data System (ADS)
Xia, Zhiyong; Sue, Hung-Jue
2001-03-01
In this study, the morphological evolution of semi-crystalline poly(ethylene terephthalate) (PET) under large scale simple shear is investigated. The equal channel angular extrusion (ECAE) process is used to induce the simple shear deformation. The deformation of semi-crystalline PET at different length scales is studied. At the spherulite scale, optical microscopy (OM) and scanning electron microscopy (SEM) are used. Lamellar scale information is obtained by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Molecular chains in the crystalline lamellae are obtained by wide-angle X-ray scattering (WAXS), and the molecular chains in the amorphous phase are studied by annealing the sample at temperatures above glass transition but below melting point. Structural characterization shows that PET spherulites are highly elongated into macrofibrils after ECAE. Within the macrofibrils, a "V-type" of crystalline lamellar orientation is induced. Molecular chains in the crystalline lamellae are tilted to the lamellar surface, whereas the molecular chains in the amorphous phase are highly stretched.
Tian, Fang-Bao; Dai, Hu; Luo, Haoxiang; Doyle, James F.; Rousseau, Bernard
2013-01-01
Three-dimensional fluid–structure interaction (FSI) involving large deformations of flexible bodies is common in biological systems, but accurate and efficient numerical approaches for modeling such systems are still scarce. In this work, we report a successful case of combining an existing immersed-boundary flow solver with a nonlinear finite-element solid-mechanics solver specifically for three-dimensional FSI simulations. This method represents a significant enhancement from the similar methods that are previously available. Based on the Cartesian grid, the viscous incompressible flow solver can handle boundaries of large displacements with simple mesh generation. The solid-mechanics solver has separate subroutines for analyzing general three-dimensional bodies and thin-walled structures composed of frames, membranes, and plates. Both geometric nonlinearity associated with large displacements and material nonlinearity associated with large strains are incorporated in the solver. The FSI is achieved through a strong coupling and partitioned approach. We perform several validation cases, and the results may be used to expand the currently limited database of FSI benchmark study. Finally, we demonstrate the versatility of the present method by applying it to the aerodynamics of elastic wings of insects and the flow-induced vocal fold vibration. PMID:24415796
Tian, Fang-Bao; Dai, Hu; Luo, Haoxiang; Doyle, James F; Rousseau, Bernard
2014-02-01
Three-dimensional fluid-structure interaction (FSI) involving large deformations of flexible bodies is common in biological systems, but accurate and efficient numerical approaches for modeling such systems are still scarce. In this work, we report a successful case of combining an existing immersed-boundary flow solver with a nonlinear finite-element solid-mechanics solver specifically for three-dimensional FSI simulations. This method represents a significant enhancement from the similar methods that are previously available. Based on the Cartesian grid, the viscous incompressible flow solver can handle boundaries of large displacements with simple mesh generation. The solid-mechanics solver has separate subroutines for analyzing general three-dimensional bodies and thin-walled structures composed of frames, membranes, and plates. Both geometric nonlinearity associated with large displacements and material nonlinearity associated with large strains are incorporated in the solver. The FSI is achieved through a strong coupling and partitioned approach. We perform several validation cases, and the results may be used to expand the currently limited database of FSI benchmark study. Finally, we demonstrate the versatility of the present method by applying it to the aerodynamics of elastic wings of insects and the flow-induced vocal fold vibration. PMID:24415796
An internal variable constitutive model for the large deformation of metals at high temperatures
NASA Technical Reports Server (NTRS)
Brown, Stuart; Anand, Lallit
1988-01-01
The advent of large deformation finite element methodologies is beginning to permit the numerical simulation of hot working processes whose design until recently has been based on prior industrial experience. Proper application of such finite element techniques requires realistic constitutive equations which more accurately model material behavior during hot working. A simple constitutive model for hot working is the single scalar internal variable model for isotropic thermal elastoplasticity proposed by Anand. The model is recalled and the specific scalar functions, for the equivalent plastic strain rate and the evolution equation for the internal variable, presented are slight modifications of those proposed by Anand. The modified functions are better able to represent high temperature material behavior. The monotonic constant true strain rate and strain rate jump compression experiments on a 2 percent silicon iron is briefly described. The model is implemented in the general purpose finite element program ABAQUS.
Verification and large deformation analysis using the reproducing kernel particle method
Beckwith, Frank
2015-09-01
The reproducing kernel particle method (RKPM) is a meshless method used to solve general boundary value problems using the principle of virtual work. RKPM corrects the kernel approximation by introducing reproducing conditions which force the method to be complete to arbritrary order polynomials selected by the user. Effort in recent years has led to the implementation of RKPM within the Sierra/SM physics software framework. The purpose of this report is to investigate convergence of RKPM for verification and validation purposes as well as to demonstrate the large deformation capability of RKPM in problems where the finite element method is known to experience difficulty. Results from analyses using RKPM are compared against finite element analysis. A host of issues associated with RKPM are identified and a number of potential improvements are discussed for future work.
Efficient Meshfree Large Deformation Simulation of Rainfall Induced Soil Slope Failure
NASA Astrophysics Data System (ADS)
Wang, Dongdong; Li, Ling
2010-05-01
An efficient Lagrangian Galerkin meshfree framework is presented for large deformation simulation of rainfall-induced soil slope failure. Detailed coupled soil-rainfall seepage equations are given for the proposed formulation. This nonlinear meshfree formulation is featured by the Lagrangian stabilized conforming nodal integration method where the low cost nature of nodal integration approach is kept and at the same time the numerical stability is maintained. The initiation and evolution of progressive failure in the soil slope is modeled by the coupled constitutive equations of isotropic damage and Drucker-Prager pressure-dependent plasticity. The gradient smoothing in the stabilized conforming integration also serves as a non-local regularization of material instability and consequently the present method is capable of effectively capture the shear band failure. The efficacy of the present method is demonstrated by simulating the rainfall-induced failure of two typical soil slopes.
Hermann, Max; Schunke, Anja C; Schultz, Thomas; Klein, Reinhard
2016-01-01
Large image deformations pose a challenging problem for the visualization and statistical analysis of 3D image ensembles which have a multitude of applications in biology and medicine. Simple linear interpolation in the tangent space of the ensemble introduces artifactual anatomical structures that hamper the application of targeted visual shape analysis techniques. In this work we make use of the theory of stationary velocity fields to facilitate interactive non-linear image interpolation and plausible extrapolation for high quality rendering of large deformations and devise an efficient image warping method on the GPU. This does not only improve quality of existing visualization techniques, but opens up a field of novel interactive methods for shape ensemble analysis. Taking advantage of the efficient non-linear 3D image warping, we showcase four visualizations: 1) browsing on-the-fly computed group mean shapes to learn about shape differences between specific classes, 2) interactive reformation to investigate complex morphologies in a single view, 3) likelihood volumes to gain a concise overview of variability and 4) streamline visualization to show variation in detail, specifically uncovering its component tangential to a reference surface. Evaluation on a real world dataset shows that the presented method outperforms the state-of-the-art in terms of visual quality while retaining interactive frame rates. A case study with a domain expert was performed in which the novel analysis and visualization methods are applied on standard model structures, namely skull and mandible of different rodents, to investigate and compare influence of phylogeny, diet and geography on shape. The visualizations enable for instance to distinguish (population-)normal and pathological morphology, assist in uncovering correlation to extrinsic factors and potentially support assessment of model quality. PMID:26390470
DR-TAMAS: Diffeomorphic Registration for Tensor Accurate Alignment of Anatomical Structures.
Irfanoglu, M Okan; Nayak, Amritha; Jenkins, Jeffrey; Hutchinson, Elizabeth B; Sadeghi, Neda; Thomas, Cibu P; Pierpaoli, Carlo
2016-05-15
In this work, we propose DR-TAMAS (Diffeomorphic Registration for Tensor Accurate alignMent of Anatomical Structures), a novel framework for intersubject registration of Diffusion Tensor Imaging (DTI) data sets. This framework is optimized for brain data and its main goal is to achieve an accurate alignment of all brain structures, including white matter (WM), gray matter (GM), and spaces containing cerebrospinal fluid (CSF). Currently most DTI-based spatial normalization algorithms emphasize alignment of anisotropic structures. While some diffusion-derived metrics, such as diffusion anisotropy and tensor eigenvector orientation, are highly informative for proper alignment of WM, other tensor metrics such as the trace or mean diffusivity (MD) are fundamental for a proper alignment of GM and CSF boundaries. Moreover, it is desirable to include information from structural MRI data, e.g., T1-weighted or T2-weighted images, which are usually available together with the diffusion data. The fundamental property of DR-TAMAS is to achieve global anatomical accuracy by incorporating in its cost function the most informative metrics locally. Another important feature of DR-TAMAS is a symmetric time-varying velocity-based transformation model, which enables it to account for potentially large anatomical variability in healthy subjects and patients. The performance of DR-TAMAS is evaluated with several data sets and compared with other widely-used diffeomorphic image registration techniques employing both full tensor information and/or DTI-derived scalar maps. Our results show that the proposed method has excellent overall performance in the entire brain, while being equivalent to the best existing methods in WM. PMID:26931817
A 1-metre Ni coated CFRP demonstrator for large deformable mirrors
NASA Astrophysics Data System (ADS)
Thompson, Samantha J.; Doel, Peter; Brooks, David; Strangwood, Martin
We present results from our current project to develop an alternative substrate for large deformable mirrors, particularly with the European Extremely Large Telescope (E-ELT) in mind. Our mirror substrate consists of a carbon-fibre reinforced polymer (CFRP) core encapsulated in a thick (50µm) coating of nickel; the coating entirely covers the CFRP front, back and edges. The benefits of CFRP are: that it has high tensile strength, making it exceptionally resistant to breakage and able to withstand high inter-actuator forces; that it can be fabricated in large sections, allowing the production of a 2.6 m monolithic mirror, simplifying system control and eliminating additional diffraction/scattering introduced by segmented mirror systems; its low density (< 1800 kgm-3 for a Ni coated substrate). By the end of summer this year (2009) we aim to have constructed a 19 cm diameter fully actuated (37 piezo-stack actuators on a 29 mm triangular grid) prototype and a 1.0 m diameter substrate mounted on a static set of points to demonstrate the scalability of the technology. We discuss the processes involved in forming a Ni-CFRP mirror, the results obtained so far and a current status update.
Concept, modeling, and performance prediction of a low-cost, large deformable mirror.
Heimsten, Rikard; MacMynowski, Douglas G; Andersen, Torben; Owner-Petersen, Mette
2012-02-10
While it is attractive to integrate a deformable mirror (DM) for adaptive optics (AO) into the telescope itself rather than using relay optics within an instrument, the resulting large DM can be expensive, particularly for extremely large telescopes. A low-cost approach for building a large DM is to use voice-coil actuators connected to the back of the DM through suction cups. Use of such inexpensive voice-coil actuators leads to a poorly damped system with many structural modes within the desired bandwidth. Control of the mirror dynamics using electro-mechanical sensors is thus required for integration within an AO system. We introduce a distributed control approach, and we show that the "inner" back sensor control loop does not need to function at low frequencies, leading to significant cost reduction for the sensors. Incorporating realistic models of low-cost actuators and sensors together with an atmospheric seeing model, we demonstrate that the low-cost mirror strategy is feasible within a closed-loop AO system. PMID:22330282
Coupling Dynamical Quantum Diffeomorphisms to Matter Degrees of Freedom
NASA Astrophysics Data System (ADS)
Aldaya, V.; Jaramillo, J. L.
2002-12-01
We introduce matter degrees of freedom into a recently proposed 2D quantum gravity model based on the Virasoro group. Quantum diffeomorphisms have dynamical content in this model, thus spoiling their classical gauge nature. The algebra of observables is enlarged now with the inclusion of an ensemble of new operators closing the affine Kac-Moody algebra of the (non-compact) semi-simple group SL(2, R), and constituting the modes of a set of scalar fields. The gravity effect on those new fields is accomplished by the natural semi-direct action of the Virasoro group on the new subalgebra. While the model is rather entangled at the severe quantum regime, at the semi-classical level we recover the action of the scalar fields modified with an added gravitational interaction term...
Solitons in a baby-Skyrme model with invariance under area-preserving diffeomorphisms
Gisiger, T.; Paranjape, M.B.
1997-06-01
We study the properties of soliton solutions in an analogue of the Skyrme model in 2+1 dimensions whose Lagrangian contains the Skyrme term and the mass term, but no usual kinetic term. The model admits a symmetry under area-preserving diffeomorphisms. We solve the dynamical equations of motion analytically for the case of spinning isolated baryon-type solitons. We take fully into account the induced deformation of the spinning Skyrmions and the consequent modification of its moment of inertia to give an analytical example of related numerical behavior found by Piette, Schroers, and Zakrzewski. We solve the equations of motion also for the case of an infinite, open string, and a closed annular string. In each case, the solitons are of finite extent, so called {open_quotes}compactons,{close_quotes} being exactly the vacuum outside a compact region. We end with indications on the scattering of baby Skyrmions, as well as some considerations as the properties of solitons on a curved space. {copyright} {ital 1997} {ital The American Physical Society}
NASA Astrophysics Data System (ADS)
Zhao, Jia-qing; Zeng, Pan; Lei, Li-ping; Ma, Yuan
2012-03-01
Digital image correlation (DIC) has received a widespread research and application in experimental mechanics. In DIC, the performance of subpixel registration algorithm (e.g., Newton-Raphson method, quasi-Newton method) relies heavily on the initial guess of deformation. In the case of small inter-frame deformation, the initial guess could be found by simple search scheme, the coarse-fine search for instance. While for large inter-frame deformation, it is difficult for simple search scheme to robustly estimate displacement parameters and deformation parameters simultaneously with low computational cost. In this paper, we proposed three improving strategies, i.e. Q-stage evolutionary strategy (T), parameter control strategy (C) and space expanding strategy (E), and then combined them into three population-based intelligent algorithms (PIAs), i.e. genetic algorithm (GA), differential evolution (DE) and particle swarm optimization (PSO), and finally derived eighteen different algorithms to calculate the initial guess for qN. The eighteen algorithms were compared in three sets of experiments including large rigid body translation, finite uniaxial strain and large rigid body rotation, and the results showed the effectiveness of proposed improving strategies. Among all compared algorithms, DE-TCE is the best which is robust, convenient and efficient for large inter-frame deformation measurement.
NASA Astrophysics Data System (ADS)
Mellbin, Y.; Hallberg, H.; Ristinmaa, M.
2015-06-01
A mesoscale model of microstructure evolution is formulated in the present work by combining a crystal plasticity model with a graph-based vertex algorithm. This provides a versatile formulation capable of capturing finite-strain deformations, development of texture and microstructure evolution through recrystallization. The crystal plasticity model is employed in a finite element setting and allows tracing of stored energy build-up in the polycrystal microstructure and concurrent reorientation of the crystal lattices in the grains. This influences the progression of recrystallization as nucleation occurs at sites with sufficient stored energy and since the grain boundary mobility and energy is allowed to vary with crystallographic misorientation across the boundaries. The proposed graph-based vertex model describes the topological changes to the grain microstructure and keeps track of the grain inter-connectivity. Through homogenization, the macroscopic material response is also obtained. By the proposed modeling approach, grain structure evolution at large deformations as well as texture development are captured. This is in contrast to most other models of recrystallization which are usually limited by assumptions of one or the other of these factors. In simulation examples, the model is in the present study shown to capture the salient features of dynamic recrystallization, including the effects of varying initial grain size and strain rate on the transitions between single-peak and multiple-peak oscillating flow stress behavior. Also the development of recrystallization texture and the influence of different assumptions on orientation of recrystallization nuclei are investigated. Further, recrystallization kinetics are discussed and compared to classical JMAK theory. To promote computational efficiency, the polycrystal plasticity algorithm is parallelized through a GPU implementation that was recently proposed by the authors.
NASA Astrophysics Data System (ADS)
Miller, Victoria M.; Johnson, Anthony E.; Torbet, Chris J.; Pollock, Tresa M.
2016-04-01
The formation of abnormally large grains has been investigated in the polycrystalline nickel-based superalloy René 88DT. Cylindrical specimens with a 15 μm grain size were compressed to plastic strains up to 11.0 pct and subsequently rapidly heated to above the γ' solvus at 1423 K (1150° C) and held for 60 seconds. All deformed samples partially recrystallized during the heat treatment, with the recrystallized grain size varying with the degree of deformation. The largest final grain size occurred in samples deformed to approximately 2 pct strain, with isolated grains as large as 700 μm in diameter observed. It is proposed that abnormally large grains appear due to nucleation-limited recrystallization, not abnormal grain growth, based on the high boundary velocities measured and the observed reduction in grain orientation spread.
Small and large deformation analysis with the p- and B-spline versions of the Finite Cell Method
NASA Astrophysics Data System (ADS)
Schillinger, Dominik; Ruess, Martin; Zander, Nils; Bazilevs, Yuri; Düster, Alexander; Rank, Ernst
2012-10-01
The Finite Cell Method (FCM) is an embedded domain method, which combines the fictitious domain approach with high-order finite elements, adaptive integration, and weak imposition of unfitted Dirichlet boundary conditions. For smooth problems, FCM has been shown to achieve exponential rates of convergence in energy norm, while its structured cell grid guarantees simple mesh generation irrespective of the geometric complexity involved. The present contribution first unhinges the FCM concept from a special high-order basis. Several benchmarks of linear elasticity and a complex proximal femur bone with inhomogeneous material demonstrate that for small deformation analysis, FCM works equally well with basis functions of the p-version of the finite element method or high-order B-splines. Turning to large deformation analysis, it is then illustrated that a straightforward geometrically nonlinear FCM formulation leads to the loss of uniqueness of the deformation map in the fictitious domain. Therefore, a modified FCM formulation is introduced, based on repeated deformation resetting, which assumes for the fictitious domain the deformation-free reference configuration after each Newton iteration. Numerical experiments show that this intervention allows for stable nonlinear FCM analysis, preserving the full range of advantages of linear elastic FCM, in particular exponential rates of convergence. Finally, the weak imposition of unfitted Dirichlet boundary conditions via the penalty method, the robustness of FCM under severe mesh distortion, and the large deformation analysis of a complex voxel-based metal foam are addressed.
Features of the low-temperature creep of a Nb-Ti alloy after large plastic deformations at 77 K
NASA Astrophysics Data System (ADS)
Aksenov, V. K.; Volchok, O. I.; Karaseva, E. V.; Starodubov, Ya. D.
2004-04-01
The low-temperature (77 K) creep and the corresponding changes in the resistivity of a niobium-titanium alloy subjected to plastic deformation by drawing at 77 K are investigated. It is shown that after large plastic deformations (ɛ>99%) one observes anomalies of the low-temperature creep which do not appear in tests of samples subjected to low and medium deformations. The creep rate in the transient stage is significantly higher than would follow from the classical ideas about the mechanisms of low-temperature creep (logarithmic law), and the time dependence of the creep deformations is described by a power law, which corresponds to recovery creep. In the creep process oscillations appear on the resistivity curves; these are especially pronounced after drawing in liquid nitrogen. Possible causes of the observed effects are discussed.
A Mortar Segment-to-Segment Frictional Contact Method for Large Deformations
Puso, M; Laursen, T
2003-10-29
Contact modeling is still one of the most difficult aspects of nonlinear implicit structural analysis. Most 3D contact algorithms employed today use node-on-segment approaches for contacting dissimilar meshes. Two pass node-on-segment contact approaches have the well known deficiency of locking due to over constraint. Furthermore, node-on-segment approaches suffer when individual nodes slide out of contact at contact surface boundaries or when contacting nodes slide from facet to facet. This causes jumps in the contact forces due to the discrete nature of the constraint enforcement and difficulties in convergence for implicit solution techniques. In a previous work, we developed a segment-to-segment contact approach based on the mortar method that was applicable to large deformation mechanics. The approach proved extremely robust since it eliminated the overconstraint which caused ''locking'' and provided smooth force variations in large sliding. Here, we extend this previous approach in to treat frictional contact problems. The proposed approach is then applied to several challenging frictional contact problems which demonstrate its effectiveness.
Study on internal flow and surface deformation of large droplet levitated by ultrasonic wave.
Abe, Yutaka; Hyuga, Daisuke; Yamada, Shogo; Aoki, Kazuyoshi
2006-09-01
It is expected that new materials will be manufactured with containerless processing under the microgravity environment in space. Under the microgravity environment, handling technology of molten metal is important for such processes. There are a lot of previous studies about droplet levitation technologies, including the use of acoustic waves, as the holding technology. However, experimental and analytical information about the relationship between surface deformation and internal flow of a large levitated droplet is still unknown. The purpose of this study is to experimentally investigate the large droplet behavior levitated by the acoustic wave field and its internal flow. To achieve this, first, numerical simulation is conducted to clarify the characteristics of acoustic wave field. Second, the levitation characteristic and the internal flow of the levitated droplet are investigated by the ultrasonic standing wave under normal gravity environment. Finally, the levitation characteristic and internal flow of levitated droplet are observed under microgravity in an aircraft to compare results with the experiment performed under the normal gravity environment. PMID:17124114
Lyapunov Exponents of Minimizing Measures for Globally Positive Diffeomorphisms in All Dimensions
NASA Astrophysics Data System (ADS)
Arnaud, M.-C.
2016-05-01
The globally positive diffeomorphisms of the 2 n-dimensional annulus are important because they represent what happens close to a completely elliptic periodic point of a symplectic diffeomorphism where the torsion is positive definite. For these globally positive diffeomorphisms, an Aubry-Mather theory was developed by Garibaldi and Thieullen that provides the existence of some minimizing measures. Using the two Green bundles {G_-} and {G_+} that can be defined along the support of these minimizing measures, we will prove that there is a deep link between: the angle between {G_-} and {G_+} along the support of the considered measure {μ};
Distributed deformation measurement of large space deployable mechanism based on FBG sensors
NASA Astrophysics Data System (ADS)
Dong, Yanfang; Zhou, Zude; Liu, Yi; Liu, Mingyao; Li, Ruiya; Li, Tianliang
2015-10-01
Space deployable mechanisms are widely used, important and multi-purpose components in aerospace fields. In order to ensure the mechanism in normal situation after unfolded, detecting the deformation caused by huge temperature difference in real-time is necessary. This paper designed a deployable mechanism setup, completed its distributed deformation measurement by means of fiber Bragg grating (FBG) sensors and BP neural network, proved the mechanism distributed strain takes place sequence and FBG sensor is capable for space deployable mechanisms deformation measuring.
An explicit solution of the large deformation of a cantilever beam under point load at the free tip
NASA Astrophysics Data System (ADS)
Wang, Ji; Chen, Jian-Kang; Liao, Shijun
2008-03-01
The large deformation of a cantilever beam under point load at the free tip is investigated by an analytic method, namely the homotopy analysis method (HAM). The explicit analytic formulas for the rotation angle at the free tip are given, which provide a convenient and straightforward approach to calculate the vertical and horizontal displacements of a cantilever beam with large deformation. These explicit formulas are valid for most practical problems, thus providing a useful reference for engineering applications. The corresponding Mathematica code is given in the Appendix.
Fluid-like flows in large-strain deformation of metals
NASA Astrophysics Data System (ADS)
Yeung, Ho; Sagapuram, Dinakar; Viswanathan, Koushik; Sundaram, Narayan; Mahato, Anirban; Trumble, Kevin; Chandrasekar, Srinivasan
Laminar or smooth plastic flow, commonly observed in large deformation of metals, becomes unstable under certain conditions, resulting in inhomogeneous plastic flow. Using in situ imaging, we demonstrate the unique features of two inhomogeneous flow modes in metal plasticity -- the well-known shear band flow and the recently discovered sinuous flow -- and methods for suppressing them. Both modes occur via a two stage process -- nucleation and flow development. The nucleation stage results in a weak material zone and the development stage involves imposition of significant strains. In the case of shear bands, using additional micro-marker techniques, we show that the second stage is well described by a viscous slider model. As a result, controlling the second stage causes band formation to cease. We demonstrate the use of this method -- Passive Geometric Flow control -- to form long strips from metallic alloys that are difficult to form conventionally. For sinuous flow, nucleation and flow formation kinematics show remarkable resemblance with flows in complex fluids. The nucleation stage can be altered using suitable ink coatings on the free surface or by surface pre-straining, and we use this idea to demonstrate complete sinuous flow suppression. Membership pending.
NASA Astrophysics Data System (ADS)
Huang, Run; Su, Peng; Horne, Todd; Brusa Zappellini, Guido; Burge, Jim H.
2013-09-01
The software configurable optical test system (SCOTS) is an efficient metrology technology based on reflection deflectometry that uses only an LCD screen and a camera to measure surface slope. The surface slope is determined by triangulations using the coordinates of the display screen, camera and test mirror. We present our recent SCOTS test results concentrated on high dynamic range measurements of low order aberrations. The varying astigmatism in the 91 cm diameter aspheric deformable secondary mirror for the Large Binocular Telescope (LBT) was measured with SCOTS, requiring no null corrector. The SCOTS system was designed on axis with camera and screen aligned on the optical axis of the test mirror with the help of a 6 inch pellicle beam splitter. The on-axis design gives better control of the astigmatism in the test. The high dynamic range of slope provided a measurement of astigmatism with 0.2 μm rms accuracy in the presence of 231 μm peak-to-valley (PV) aspheric departure. The simplicity of the test allowed the measurements to be performed at multiple elevation angles.
NASA Astrophysics Data System (ADS)
Bassetto, Antonio; DePol, Giancarlo; Torrielli, Alessandro; Vian, Federica
2005-05-01
We present an investigation on the invariance properties of noncommutative Yang-Mills theory in two dimensions under area preserving diffeomorphisms. Stimulated by recent remarks by Ambjorn, Dubin and Makeenko who found a breaking of such an invariance, we confirm both on a fairly general ground and by means of perturbative analytical and numerical calculations that indeed invariance under area preserving diffeomorphisms is lost. However a remnant survives, namely invariance under linear unimodular tranformations.
Large-scale deformed QRPA calculations of the gamma-ray strength function based on a Gogny force
NASA Astrophysics Data System (ADS)
Martini, M.; Goriely, S.; Hilaire, S.; Péru, S.; Minato, F.
2016-01-01
The dipole excitations of nuclei play an important role in nuclear astrophysics processes in connection with the photoabsorption and the radiative neutron capture that take place in stellar environment. We present here the results of a large-scale axially-symmetric deformed QRPA calculation of the γ-ray strength function based on the finite-range Gogny force. The newly determined γ-ray strength is compared with experimental photoabsorption data for spherical as well as deformed nuclei. Predictions of γ-ray strength functions and Maxwellian-averaged neutron capture rates for Sn isotopes are also discussed.
Modelling Deformation and Texture Evolution in OFHC Copper at Large Strain and High Strain Rate
NASA Astrophysics Data System (ADS)
Bonora, Nicola; Testa, Gabriel; Ruggiero, Andrew; Iannitti, Gianluca; Hörnqvist, Magnus; Mortazavi, Nooshin
2015-06-01
In this work, a two-scale approach to simulate high rate deformation and texture evolution in OFHC copper is presented. The modified Rusinek-Klepaczko material model was used to simulate the response of the material at continuum scale accounting for different deformation mechanisms occurring over an extensive range of strain rate and temperature. Material model parameters were determined from characterization test (mainly uniaxial tests) results. Successively, the model was validated simulating material deformation in Taylor anvil impact, symmetric Taylor impact (rod-on-rod) and dynamic tensile extrusion (DTE) tests. Texture evolution, under different deformation paths was simulated using the crystal plasticity package CPFEM and results were compared with those obtained by EBSD analysis. The possibility to incorporate the effect of grain size evolution and fragmentation at continuum scale is discussed.
Active control of a large deformable mirror for future E-ELT
NASA Astrophysics Data System (ADS)
Gasmi, R.; Le Bihan, D.; Dournaux, J. L.; Sinquin, J. C.; Jagourel, P.
2010-07-01
Increasing dimensions of ground based telescopes and adaptive optics needs for these instruments require wide deformable mirrors with a high number of actuators to compensate the effects of the atmospheric turbulence on the wave fronts. The new dimensions and characteristics of these deformable mirrors lead to the apparition of structural vibrations, which may reduce the rejection band width of the adaptive optics control loop. The aim of this paper is the study of the dynamic behavior of a 1-meter prototype of E-ELT's deformable mirror in order to identify its eigenmodes and to propose some ways to control its vibrations. We first present the first eigenmodes of the structure determined by both finite element analysis and experimental modal analysis. Then we present the frequency response of the prototype to a tilt excitation to estimate the effects of its vibrations on the adaptive optics loop. Finally we suggest a method to control the dynamics of the deformable mirror.
A first analysis regarding matter-dynamical diffeomorphism coupling
NASA Astrophysics Data System (ADS)
Aldaya, V.; Jaramillo, J. L.
2000-12-01
A first attempt at adding matter degrees of freedom to the two-dimensional `vacuum' gravity model presented in Aldaya and Jaramillo (2000 Class. Quantum Grav. 17 1649) is analysed in this paper. Just as in the previous pure gravity case, quantum diffeomorphism operators (constructed from a Virasoro algebra) possess a dynamical content; their gauge nature is recovered only after the classical limit. Emphasis is placed on the new physical modes modelled on an SU(1,1)-Kac-Moody algebra. The non-trivial coupling to `gravity' is a consequence of the natural semi-direct structure of the entire extended algebra. A representation associated with the discrete series of the rigid SU(1,1) algebra is revisited in the light of previously neglected crucial global features which imply the appearance of an SU(1,1)-Kac-Moody fusion rule, determining the rather entangled quantum structure of the physical system. In the classical limit, an action which explicitly couples gravity and matter modes governs the dynamics.
NASA Astrophysics Data System (ADS)
Gahalaut, V. K.; Catherine, J. K.; Jade, Sridevi; Gireesh, R.; Gupta, D. C.; Narsaiah, M.; Ambikapathy, A.; Bansal, A.; Chadha, R. K.
2008-05-01
Static offsets due to the 26 December 2004 Sumatra-Andaman earthquake have been reported from the campaign mode GPS measurements in the Andaman-Nicobar region. However, these measurements contain contributions from postseismic deformation that must have occurred in the 16-25 days period between the earthquake and the measurements. We analyse these and tide gauge measurements of coseismic deformation, a longer time series of postseismic deformation from GPS measurements at Port Blair in the South Andaman and aftershocks, to suggest that postseismic displacement not larger than 7 cm occurred in the 16-25 days following the earthquake in the South Andaman and probably elsewhere in the Andaman Nicobar region. Earlier, this contribution was estimated to be as large as 1 m in the Andaman region, which implied that the magnitude of the earthquake based on these campaign mode measurements should be decreased. We suggest an Mw for this earthquake as 9.23.
NASA Astrophysics Data System (ADS)
Abe, R.; Hamada, K.; Hirata, N.; Tamura, R.; Nishi, N.
2015-05-01
As well as the BIM of quality management in the construction industry, demand for quality management of the manufacturing process of the member is higher in shipbuilding field. The time series of three-dimensional deformation of the each process, and are accurately be grasped strongly demanded. In this study, we focused on the shipbuilding field, will be examined three-dimensional measurement method. The shipyard, since a large equipment and components are intricately arranged in a limited space, the installation of the measuring equipment and the target is limited. There is also the element to be measured is moved in each process, the establishment of the reference point for time series comparison is necessary to devise. In this paper will be discussed method for measuring the welding deformation in time series by using a total station. In particular, by using a plurality of measurement data obtained from this approach and evaluated the amount of deformation of each process.
Bergström, J S; Kurtz, S M; Rimnac, C M; Edidin, A A
2002-06-01
When subjected to a monotonically increasing deformation state, the mechanical behavior of UHMWPE is characterized by a linear elastic response followed by distributed yielding and strain hardening at large deformations. During the unloading phases of an applied cyclic deformation process, the response is characterized by nonlinear recovery driven by the release of stored internal energy. A number of different constitutive theories can be used to model these experimentally observed events. We compare the ability of the J2-plasticity theory, the "Arruda-Boyce" model, the "Hasan-Boyce" model, and the "Bergström-Boyce" model to reproduce the observed mechanical behavior of ultra-high molecular weight polyethylene (UHMWPE). In addition a new hybrid model is proposed, which incorporates many features of the previous theories. This hybrid model is shown to most effectively predict the experimentally observed mechanical behavior of UHMWPE. PMID:12013180
NASA Astrophysics Data System (ADS)
Calahorrano Betancourt, A.; Ranero, C. R.; Barckhausen, U.; Reichert, C. J.; Grevemeyer, I.
2009-12-01
We present three multichannel seismic (MCS) lines, collected during the CINCA ‘95 experiment with German research vessel Sonne by the BGR. The data image the subduction zone of the North Chile, with 3 lines that extend 400-500 hundred km into the incoming plate. We focus on the deformation of the incoming 50 Myr old oceanic Nazca plate converging nearly orthogonally (N83 S) with the South American Plate at ~60-65 mm/yr. The 3 seismic profiles provide a detailed image of the crustal and uppermost mantle deformation structure across the underformed segment of plate, the entire outer rise, and extreme deformation at the trench slope just before underthusting. A compilation of multibeam bathymetry in the area, although not providing full seafloor coverage, shows the lateral extension of the deformation fabrics. Seawards from the trench slope, the seafloor morphology shows mainly the spreading ridge fabric with a NW lineation. At the trench slope, the spreading fabric is superimposed by a new fabric, oriented parallel to the trench axis, corresponding to the horst and graben pattern related to bending deformation of the incoming plate. Seismic cross sections image the incoming plate with a strong, continuous and irregular reflection characterizing the top of the oceanic crust. This roughness is related, locally to volcanic activity (p.e. Iquique Ridge), and to the spreading fabric and the horst-and-graben pattern observed in bathymetry. Sedimentary pelagic coverage is only about 100 m thick and only locally small turbidite accumulations are observed in grabens. The Moho reflection is fairly continuous typically at 2 seconds two way time (stwt) below the seafloor, but can be about 3 stwt locally indicating crustal thickening related to volcanism. Looking at its whole extent, these images illustrate the flexure of the downgoing plate as it reaches the subduction zone. This bending, characterizing the outer rise, is observed along 250 km seaward from the trench axis, and
Long-lived large-scale ground deformation caused by a buoyantly rising magma resevoir
NASA Astrophysics Data System (ADS)
Del Potro, R.; Diez, M.; Muller, C.; Perkins, J. P.; Finnegan, N. J.; Gottsmann, J.
2013-12-01
Recent InSAR studies have identified a constant, long-wavelength ground deformation pattern, comprising a central uplift and peripheral subsidence, centred on Uturuncu volcano in the Altiplano Puna Volcanic Complex of the Central Andes. This so-called 'sombrero uplift' has been consistent over the time scales of InSAR observations (1992-2010); however, it is unclear how long this deformation has persisted over the history of Uturuncu. Here we constrain the duration and causes of the ground deformation through a combination of available geodetic data, geomorphological studies and numerical modelling. GPS data from re-occupation of a nearby levelling line show that the observed ground deformation from 1965 to 2012 is compatible with the extent and the rate observed with InSAR, and thus suggests that the 'sombrero uplift' may have been constant for at least 50 years. In addition, from geomorphological measurements using shorelines from nearby lakes as inclinometers, we conclude that the total uplift of Uturuncu has not been more than 30 m, or that the constant ongoing uplift cannot have been active for more than 3000 years. Following our recent geophysical studies in the area, we explore the possibility that the observed ground deformation is caused by a rising felsic diapir and test this hypothesis numerically to show that the process is viable under these specific conditions, and accounts for the observed uplift rate. Our findings have significant implications for volcanologists inferring the characteristics of magma reservoirs from ground deformation data as it offers an alternative explanation of the causes driving ground deformation, and the growth and failure of magma reservoirs in a hot multiphase viscous crust.
NASA Astrophysics Data System (ADS)
Izadbakhsh, Adel; Inal, Kaan; Mishra, Raja K.
2012-04-01
In this paper, the finite strain plastic deformation of AM30 magnesium alloy has been simulated using the crystal plasticity finite element method. The simulations have been carried out using a rate-dependent elastic-viscoplastic crystal plasticity constitutive model implemented in a user defined material subroutine (UMAT) in the commercial software LS-DYNA. The plastic deformation mechanisms accounted for in the model are the slip systems in the matrix (parent grain), extension twinning systems and the slip systems inside the extension twinned regions. The parameters of the constitutive model have been calibrated using the experimental data. The calibrated model has then been used to predict the deformation of AM30 magnesium alloy in bending and simple shear. For the bending strain path, the effects of texture on the strain accommodated by the deformation mechanisms and bending moment have been investigated. For simple shear, the effects of texture on the relative activity of deformation mechanisms, shear stress and texture evolution have been investigated. Also, the effect of twinning on shear stress and texture evolution has been studied. The numerical analyses predicted a more uniform strain distribution during bending and simple shear for rolled texture compared with extruded texture.
NASA Astrophysics Data System (ADS)
Lanari, Riccardo
2010-05-01
Satellite time series have already provided key measurements to retrieve information on the dynamic nature of Earth surface processes. We exploit in this work the availability of the large archives of spaceborne Synthetic Aperture Radar (SAR) data acquired by the ERS-1/2 and ENVISAT sensors of the European Space Agency (ESA) during the 1992-2009 time period, in order to investigate long term surface deformation of large areas. To achieve this result we take advantage of the Differential SAR Interferometry (InSAR) algorithm referred to as Small BAseline Subset (SBAS) technique (Berardino et al., 2002), which allows us to generate mean deformation velocity maps and corresponding time-series by exploiting temporally overlapping SAR dataset collected by the ERS and ENVISAT sensors (Pepe et al., 2005). In particular, we focus on the results obtained by retrieving ERS-ENVISAT deformation time-series from 1992 till today in selected case studies relevant to different scenarios. We start from the analysis of the Mt. Etna volcano (Italy) and the Napoli Bay area (Italy), the latter including three volcanic systems (the Campi Flegrei caldera, the Somma-Vesuvio volcanic complex and the Ischia island) and the city of Napoli. In addition, we present the results relevant to the cities of Istanbul (Turkey) and Roma (Italy). The overall analyses are carried out by using averaged (multilook) InSAR interferograms with a spatial resolution of about 100 x 100 m. Moreover, in selected zones we further investigate localized phenomena by zooming in the areas of interest and carrying out a InSAR analysis at full spatial resolution scale (Lanari et al., 2004). In these cases we also exploit the doppler centroid variations of the post-2000 acquisitions of the ERS-2 sensor and the carrier frequency difference between the ERS-1/2 and the ENVISAT systems in order to maximize the number of investigated SAR pixels and to improve their geocoding. The presented results demonstrate the unique
Path-dependent J-integral evaluations around an elliptical hole for large deformation theory
NASA Astrophysics Data System (ADS)
Unger, David J.
2016-08-01
An exact expression is obtained for a path-dependent J-integral for finite strains of an elliptical hole subject to remote tensile tractions under the Tresca deformation theory for a thin plate composed of non-work hardening material. Possible applications include an analytical resistance curve for the initial stage of crack propagation due to crack tip blunting.
Sattler, A.R.; Christensen, C.L.
1980-01-01
Room and pillar deformation were measured in conjunction with a relatively new type of mining operation in a southeastern New Mexico potash mine. The extraction ration was approximately 90 percent in a first mining operation. Due to severe deformations encountered, instrumentation had to be developed/modified for these measurements. This paper concentrates on experiment design, design of special instrumentation, field installation of equipment, and presentation of the data. Measurements made include extensometers in the pillar, in the floor and ceiling in the room between pillars, absolute level measurements, floor ceiling closure, and stress (strain) measurements. Associated laboratory rock mechanics measurements of samples from the mine are being done separately. Two separate room pillar complexes were instrumented. In the first complex, floor-ceiling deformations of approximately 1 inch/day and pillar deformations around 1/2 inch/day were measured. In the second complex, instrumentation was installed while the pillar was a part of a long wall and the subsequent sequential mining (long wall-pillar with only one adjoining room on one side - pillar in the middle of room pillar complex) was observed. Data return from this operation was good.
Avants, B B; Epstein, C L; Grossman, M; Gee, J C
2008-02-01
One of the most challenging problems in modern neuroimaging is detailed characterization of neurodegeneration. Quantifying spatial and longitudinal atrophy patterns is an important component of this process. These spatiotemporal signals will aid in discriminating between related diseases, such as frontotemporal dementia (FTD) and Alzheimer's disease (AD), which manifest themselves in the same at-risk population. Here, we develop a novel symmetric image normalization method (SyN) for maximizing the cross-correlation within the space of diffeomorphic maps and provide the Euler-Lagrange equations necessary for this optimization. We then turn to a careful evaluation of our method. Our evaluation uses gold standard, human cortical segmentation to contrast SyN's performance with a related elastic method and with the standard ITK implementation of Thirion's Demons algorithm. The new method compares favorably with both approaches, in particular when the distance between the template brain and the target brain is large. We then report the correlation of volumes gained by algorithmic cortical labelings of FTD and control subjects with those gained by the manual rater. This comparison shows that, of the three methods tested, SyN's volume measurements are the most strongly correlated with volume measurements gained by expert labeling. This study indicates that SyN, with cross-correlation, is a reliable method for normalizing and making anatomical measurements in volumetric MRI of patients and at-risk elderly individuals. PMID:17659998
Pianigiani, Silvia; Ruggiero, Leonardo; Innocenti, Bernardo
2015-01-01
The large deformation of the human breast threatens proper nodules tracking when the subject mammograms are used as pre-planning data for biopsy. However, techniques capable of accurately supporting the surgeons during biopsy are missing. Finite element (FE) models are at the basis of currently investigated methodologies to track nodules displacement. Nonetheless, the impact of breast material modeling on the mechanical response of its tissues (e.g., tumors) is not clear. This study proposes a subject-specific FE model of the breast, obtained by anthropometric measurements, to predict breast large deformation. A healthy breast subject-specific FE parametric model was developed and validated by Cranio-caudal (CC) and Medio-Lateral Oblique (MLO) mammograms. The model was successively modified, including nodules, and utilized to investigate the effect of nodules size, typology, and material modeling on nodules shift under the effect of CC, MLO, and gravity loads. Results show that a Mooney-Rivlin material model can estimate healthy breast large deformation. For a pathological breast, under CC compression, the nodules displacement is very close to zero when a linear elastic material model is used. Finally, when nodules are modeled, including tumor material properties, under CC, or MLO or gravity loads, nodules shift shows ~15% average relative difference. PMID:26734604
Pianigiani, Silvia; Ruggiero, Leonardo; Innocenti, Bernardo
2015-01-01
The large deformation of the human breast threatens proper nodules tracking when the subject mammograms are used as pre-planning data for biopsy. However, techniques capable of accurately supporting the surgeons during biopsy are missing. Finite element (FE) models are at the basis of currently investigated methodologies to track nodules displacement. Nonetheless, the impact of breast material modeling on the mechanical response of its tissues (e.g., tumors) is not clear. This study proposes a subject-specific FE model of the breast, obtained by anthropometric measurements, to predict breast large deformation. A healthy breast subject-specific FE parametric model was developed and validated by Cranio-caudal (CC) and Medio-Lateral Oblique (MLO) mammograms. The model was successively modified, including nodules, and utilized to investigate the effect of nodules size, typology, and material modeling on nodules shift under the effect of CC, MLO, and gravity loads. Results show that a Mooney–Rivlin material model can estimate healthy breast large deformation. For a pathological breast, under CC compression, the nodules displacement is very close to zero when a linear elastic material model is used. Finally, when nodules are modeled, including tumor material properties, under CC, or MLO or gravity loads, nodules shift shows ~15% average relative difference. PMID:26734604
NASA Astrophysics Data System (ADS)
Schnitzer, Ory; Frankel, Itzchak; Yariv, Ehud
2013-11-01
In Taylor's theory of electrohydrodynamic drop deformation (Proc. R. Soc. Lond. A, vol. 291, 1966, pp. 159-166), inertia is neglected at the outset, resulting in fluid velocity that scales as the square of the applied-field magnitude. For large drops, with increasing field strength the Reynolds number predicted by this scaling may actually become large, suggesting the need for a complementary large-Reynolds-number investigation. Balancing viscous stresses and electrical shear forces in this limit reveals a different velocity scaling, with the 4/3-power of the applied-field magnitude. We focus here on the flow over a gas bubble. It is essentially confined to two boundary layers propagating from the poles to the equator, where they collide to form a radial jet. At leading order in the Capillary number, the bubble deforms due to (i) Maxwell stresses; (ii) the hydrodynamic boundary-layer pressure associated with centripetal acceleration; and (iii) the intense pressure distribution acting over the narrow equatorial deflection zone, appearing as a concentrated load. Remarkably, the unique flow topology and associated scalings allow to obtain a closed-form expression for this deformation through application of integral mass and momentum balances. On the bubble scale, the concentrated pressure load is manifested in the appearance of a non-smooth equatorial dimple.
NASA Astrophysics Data System (ADS)
Rogovoi, A. A.
2015-09-01
The dependence of a scalar measure of the structural changes occurring in a material under plastic deformation on a plastic strain measure and the dependence of a free energy measure on a structural change measure are constructed using experimental data that allow the expended plastic work to be divided into a latent part and a thermal part. The obtained dependences, kinematic relations, a constitutive equation, and a heat-conduction equation that satisfy the principles of thermodynamics and objectivity are used to construct a model of thermo-elastic-inelastic processes in the presence of finite deformations and structural changes in the material. The model is tested on the problem of temperature changes in the process of adiabatic elastic-plastic compression, which has experimental support.
In Situ Neutron Diffraction Studies of Large Monotonic Deformations of Superelastic Nitinol
NASA Astrophysics Data System (ADS)
Stebner, Aaron P.; Paranjape, Harshad M.; Clausen, Bjørn; Brinson, L. Catherine; Pelton, Alan R.
2015-06-01
Superelastic Nitinol micromechanics are studied well into plastic deformation regimes using neutron diffraction. Insights are made into the nature of initial transformation, bulk transformation, plastic deformation, and unloading. Schmid factor predictions based on habit plane variants are found to best describe the very first grains that transform, prior to the transformation plateaus. However, the bulk transformation behavior that gives rise to transformation plateaus violates single crystal Schmid factor analyses, indicating that in bulk polycrystals, it is the effect of grain neighborhoods, not the orientations of individual grains, that drives transformation behaviors. Beyond the plateaus, a sudden shift in micromechanical deformation mechanisms is observed at ~8.50 %/4.75 % tension/compression engineering strain. This mechanism results in reverse-phase transformation in both cases, indicating a strong relaxation in internal stresses of the samples. It is inferred that this mechanism is most likely initial bulk plastic flow, and postulated that it is the reason for a transition from fatigue life enhancement to detriment when pre-straining superelastic Nitinol. The data presented in this work provide critical datasets for development and verification of both phenomenological internal variable-driven and micromechanical theories of transformation-plasticity coupling in shape memory alloys.
Simulations of the erythrocyte cytoskeleton at large deformation. II. Micropipette aspiration.
Discher, D E; Boal, D H; Boey, S K
1998-09-01
Coarse-grained molecular models of the erythrocyte membrane's spectrin cytoskeleton are presented in Monte Carlo simulations of whole cells in micropipette aspiration. The nonlinear chain elasticity and sterics revealed in more microscopic cytoskeleton models (developed in a companion paper; Boey et al., 1998. Biophys. J. 75:1573-1583) are faithfully represented here by two- and three-body effective potentials. The number of degrees of freedom of the system are thereby reduced to a range that is computationally tractable. Three effective models for the triangulated cytoskeleton are developed: two models in which the cytoskeleton is stress-free and does or does not have internal attractive interactions, and a third model in which the cytoskeleton is prestressed in situ. These are employed in direct, finite-temperature simulations of erythrocyte deformation in a micropipette. All three models show reasonable agreement with aspiration measurements made on flaccid human erythrocytes, but the prestressed model alone yields optimal agreement with fluorescence imaging experiments. Ensemble-averaging of nonaxisymmetrical, deformed structures exhibiting anisotropic strain are thus shown to provide an answer to the basic question of how a triangulated mesh such as that of the red cell cytoskeleton deforms in experiment. PMID:9726959
Simulations of the erythrocyte cytoskeleton at large deformation. II. Micropipette aspiration.
Discher, D E; Boal, D H; Boey, S K
1998-01-01
Coarse-grained molecular models of the erythrocyte membrane's spectrin cytoskeleton are presented in Monte Carlo simulations of whole cells in micropipette aspiration. The nonlinear chain elasticity and sterics revealed in more microscopic cytoskeleton models (developed in a companion paper; Boey et al., 1998. Biophys. J. 75:1573-1583) are faithfully represented here by two- and three-body effective potentials. The number of degrees of freedom of the system are thereby reduced to a range that is computationally tractable. Three effective models for the triangulated cytoskeleton are developed: two models in which the cytoskeleton is stress-free and does or does not have internal attractive interactions, and a third model in which the cytoskeleton is prestressed in situ. These are employed in direct, finite-temperature simulations of erythrocyte deformation in a micropipette. All three models show reasonable agreement with aspiration measurements made on flaccid human erythrocytes, but the prestressed model alone yields optimal agreement with fluorescence imaging experiments. Ensemble-averaging of nonaxisymmetrical, deformed structures exhibiting anisotropic strain are thus shown to provide an answer to the basic question of how a triangulated mesh such as that of the red cell cytoskeleton deforms in experiment. PMID:9726959
NASA Astrophysics Data System (ADS)
Molnar, P. H.
2010-12-01
Tibetan Plateau illustrates this failing of plate tectonics (or crustal blocks) especially well. In particular, because of the large lateral variations in gravitational potential energy, it offers the best region in which to study dynamics of continental deformation.
Stone, C.M.
1997-07-01
SANTOS is a finite element program designed to compute the quasistatic, large deformation, inelastic response of two-dimensional planar or axisymmetric solids. The code is derived from the transient dynamic code PRONTO 2D. The solution strategy used to compute the equilibrium states is based on a self-adaptive dynamic relaxation solution scheme, which is based on explicit central difference pseudo-time integration and artificial mass proportional damping. The element used in SANTOS is a uniform strain 4-node quadrilateral element with an hourglass control scheme to control the spurious deformation modes. Finite strain constitutive models for many common engineering materials are included. A robust master-slave contact algorithm for modeling sliding contact is implemented. An interface for coupling to an external code is also provided. 43 refs., 22 figs.
NASA Astrophysics Data System (ADS)
Qu, T.; Lu, P.; Liu, C.; Wan, H.
2016-06-01
Western China is very susceptible to landslide hazards. As a result, landslide detection and early warning are of great importance. This work employs the SBAS (Small Baseline Subset) InSAR Technique for detection and monitoring of large-scale landslides that occurred in Li County, Sichuan Province, Western China. The time series INSAR is performed using descending scenes acquired from TerraSAR-X StripMap mode since 2014 to get the spatial distribution of surface displacements of this giant landslide. The time series results identify the distinct deformation zone on the landslide body with a rate of up to 150mm/yr. The deformation acquired by SBAS technique is validated by inclinometers from diverse boreholes of in-situ monitoring. The integration of InSAR time series displacements and ground-based monitoring data helps to provide reliable data support for the forecasting and monitoring of largescale landslide.
NASA Astrophysics Data System (ADS)
Bell, T. H.; Sanislav, I. V.
2011-07-01
Regional distributions of axial plane trends retain information on the orientation in which successive generations formed because multi-scale partitioning results in most orogenic belts preserving subsequently undeformed portions of all large-scale folds. At depths greater than ˜10 km within orogens, successions of regional folds are accompanied by the sequential development of crenulation hinges in pelites, which are commonly overgrown early during their development by successive generations of porphyroblasts. Consequently, the original trends of the axial planes of these folds are preserved within the distribution of foliation inflection/intersection axes within porphyroblasts (FIAs). Peaks in the distribution of FIA trends in western Maine predominantly coincide with peaks in the distribution of trends of the axial planes of macroscopic and regional folds. The WNW-ESE (˜420 Ma), N-S (408 ± 10 Ma), W-E (388 ± 9 Ma), WSW-ENE (372 ± 5 Ma), SW-NE (353 ± 4 Ma) succession of FIA peaks defines the sequence of folds and accords with map scale overprinting relationships. This quantitative approach to interpreting fold successions in multiply deformed terrains resolves timing where overprinting criteria are rare, uncertain or obliterated by younger events in portions of the orogen. Significantly, lengthy detailed histories of structural development can be extracted from a small area containing porphyroblastic rocks and applied to very large-scale regions.
Miller, M.P.; McDowell, D.L.
1996-01-01
In metals, large strain inelastic deformation processes such as the formation of a preferred crystallographic orientation (crystallographic texture) and strain hardening processes such as the formation and evolution of dislocation substructures depend on stress-state. Much of the current large strain research has focused on texture. Crystallographic texture development and strain-hardening processes each contribute to the overall material behavior, and a complete description of large strain inelastic material response should reflect both. An investigation of the large strain behavior of 304L stainless steel (SS 304L) subjected to compression, torsion, and sequences of compression followed by torsion and torsion followed by tension is reported. This paper focuses on the stress-state dependence of strain-hardening processes as well as the relative effect such processes have on the overall material behavior. To characterize these processes, transmission electron microscopy (TEM) as well as magnetization investigations were conducted at different strain levels and under different deformation modes. The {gamma} {yields} {alpha}{prime} martensitic transformation which occurs in this material was found to be related to both the strain level and stress state. Dislocation substructures in the form of Taylor lattices, dense dislocation walls, and microbands were also present. The ramifications of using a thin-walled tubular torsion specimen were also explored.
NASA Technical Reports Server (NTRS)
Imbriale, W.; Rengarajan, S.; Cramer, P., Jr.
1998-01-01
This paper presents a novel design of a deformed flat plate, wherein known amounts of distortion are introduced in a compensating flat plate, to recover the gain-loss due to the gravity-induced surface deformations of a large reflector antenna.
NASA Astrophysics Data System (ADS)
Rooms, F.; Camet, S.; Curis, J. F.
2010-02-01
A new technology of deformable mirror will be presented. Based on magnetic actuators, these deformable mirrors feature record strokes (more than +/- 45μm of astigmatism and focus correction) with an optimized temporal behavior. Furthermore, the development has been made in order to have a large density of actuators within a small clear aperture (typically 52 actuators within a diameter of 9.0mm). We will present the key benefits of this technology for vision science: simultaneous correction of low and high order aberrations, AO-SLO image without artifacts due to the membrane vibration, optimized control, etc. Using recent papers published by Doble, Thibos and Miller, we show the performances that can be achieved by various configurations using statistical approach. The typical distribution of wavefront aberrations (both the low order aberration (LOA) and high order aberration (HOA)) have been computed and the correction applied by the mirror. We compare two configurations of deformable mirrors (52 and 97 actuators) and highlight the influence of the number of actuators on the fitting error, the photon noise error and the effective bandwidth of correction.
NASA Technical Reports Server (NTRS)
Reed, K. W.; Atluri, S. N.
1983-01-01
A new hybrid-stress finite element algorithm, suitable for analyses of large, quasistatic, inelastic deformations, is presented. The algorithm is base upon a generalization of de Veubeke's complementary energy principle. The principal variables in the formulation are the nominal stress rate and spin, and thg resulting finite element equations are discrete versions of the equations of compatibility and angular momentum balance. The algorithm produces true rates, time derivatives, as opposed to 'increments'. There results a complete separation of the boundary value problem (for stress rate and velocity) and the initial value problem (for total stress and deformation); hence, their numerical treatments are essentially independent. After a fairly comprehensive discussion of the numerical treatment of the boundary value problem, we launch into a detailed examination of the numerical treatment of the initial value problem, covering the topics of efficiency, stability and objectivity. The paper is closed with a set of examples, finite homogeneous deformation problems, which serve to bring out important aspects of the algorithm.
On the large deformation behaviour of reinforced rubber at different temperatures
NASA Astrophysics Data System (ADS)
Lion, Alexander
1997-11-01
This essay investigates the temperature dependence of the mechanical properties of a filler-loaded tread compound experimentally and proposes a physically based method to represent this behaviour in the framework of non-linear continuum thermomechanics. To this end, we realise a series of monotonic and cyclic strain controlled tests on cylindrical specimens in tension at different temperature levels. The experimental data show the isothermal mechanical behaviour to be mainly influenced by non-linear elasticity in combination with non-linear rate dependence and weak equilibrium hysteresis. We observe that the rate sensitivity of the material depends strongly on the temperature : at low temperature levels, the rate sensitivity is essentially higher than at high temperatures. The elastic properties of the material depend comparatively less on the temperature. Nevertheless, higher temperature levels lead to higher equilibrium stresses. In order to represent the material behaviour, we start with a multiplicative split of the deformation gradient into a mechanical and a thermal part as proposed by Lu and Pister (1975). Physically, this idea corresponds to a stress-free thermal expansion followed by an isothermal stress-producing deformation. We suppose the thermal part of the deformation gradient to be isotropic. As a consequence of this, the velocity gradient decomposes additively into a pure thermal and a pure mechanical part. By using these elements, we exploit the Clausius Duhem inequality and assume the so-called 'mechanical second Piola Kirchhoff stress tensor' to be a functional of the 'mechanical Green's strain tensor'. In a further step, we define this functional by a system of constitutive equations which are based on a rheological model. The evolution equations for the internal variables are formulated by using the concept of dual variables proposed by Haupt and Tsakmakis (1989, 1996). The rate sensitivity is modelled by a stress and temperature dependent
Large-aperture deformable mirror correction of tiled-grating wavefront error
NASA Astrophysics Data System (ADS)
Kruschwitz, B. E.; Jungquist, R.; Qiao, J.; Abbey, S.; Dean, S. E.; Maywar, D. N.; Moore, M. D.; Waxer, L. J.; Wilson, M. E.
2006-06-01
When tiling three gratings, with each individually exhibiting astigmatism and power due to holographic errors and coating stress, the resulting wavefront aberrations contain high-frequency components as well as the fundamental frequency, which is nearly three cycles across the aperture in the tiling direction. A deformable mirror (DM) that was designed to compensate for much slower errors (e.g., those arising from distortion in amplifier disks) is being used to compensate for this tiling-induced error. This investigation studies the effectiveness of compensating only the fundamental frequency of the tiled aberration, and shows that this provides a significant improvement that is adequate for a range of expected aberrations. Limitations of the DM correction technique are also studied.
Long-term geodetic measurements of large scale deformation at Iwo-jima caldera, Japan
NASA Astrophysics Data System (ADS)
Ukawa, M.; Fujita, E.; Ueda, H.; Kumagai, T.; Nakajima, H.; Morita, H.
2006-02-01
Iwo-jima is a volcanic caldera located 1250 km south of Tokyo, and is part of the Izu-Ogasawara arc. An extremely high uplift rate (averaging 0.25 m/a over several hundred years) characterizes the volcanic activity of Iwo-jima. This deformation is believed to be due to post caldera uplift. To investigate the mechanisms contributing to the high uplift rate, we have repeatedly conducted leveling and trilateration surveys from 1976 to 1995, and GPS surveys from 1996 to 2002. These observations have detected two patterns of continuous crustal deformation: concentric subsidence around Motoyama at the center of the Iwo-jima caldera and uplift surrounding the subsiding area. During the period from 1977 to 1995, subsidence at Motoyama reached 0.54 m and uplift in the southwestern part of the island exceeded 3 m. In addition, the island has experienced broad, episodic uplift, which amounted to more than 1 m during volcanic unrest both in 1982 and 2001. Horizontal displacements around Motoyama exhibit contraction due to the concentric subsidence, indicating the presence of a deflating source at depth. Vertical deformation dominates the displacement field during periods of broad episodic uplift, suggesting a deeper and/or more extensive source. Focusing the Motoyama area, we modeled the subsidence source simultaneously with the broad episodic uplift, which is approximated by deformation with a planar gradient, for 14 times between 1976 and 2002, using a grid search combined with a least-squares method. By assuming the subsidence source could be located at any grid point, we applied the least-squares method to calculate the intensity of subsidence source and the parameters for the uplift with a planar gradient and then selected the best-fitting source location. The best-fitting subsidence source geometries for 1998-2000 and 2000-2002 (the two time periods with GPS results) are horizontal, squared-shaped sills with side lengths of 4 and 5 km, respectively. Adopting the
Learning layer-specific edges for segmenting retinal layers with large deformations
Karri, S. P. K.; Chakraborthi, Debjani; Chatterjee, Jyotirmoy
2016-01-01
We present an algorithm for layer-specific edge detection in retinal optical coherence tomography images through a structured learning algorithm to reinforce traditional graph-based retinal layer segmentation. The proposed algorithm simultaneously identifies individual layers and their corresponding edges, resulting in the computation of layer-specific edges in 1 second. These edges augment classical dynamic programming based segmentation under layer deformation, shadow artifacts noise, and without heuristics or prior knowledge. We considered Duke’s online data set containing 110 B-scans of 10 diabetic macular edema subjects with 8 retinal layers annotated by two experts for experimentation, and achieved a mean distance error of 1.38 pixels whereas that of the state-of-the-art was 1.68 pixels. PMID:27446714
Learning layer-specific edges for segmenting retinal layers with large deformations.
Karri, S P K; Chakraborthi, Debjani; Chatterjee, Jyotirmoy
2016-07-01
We present an algorithm for layer-specific edge detection in retinal optical coherence tomography images through a structured learning algorithm to reinforce traditional graph-based retinal layer segmentation. The proposed algorithm simultaneously identifies individual layers and their corresponding edges, resulting in the computation of layer-specific edges in 1 second. These edges augment classical dynamic programming based segmentation under layer deformation, shadow artifacts noise, and without heuristics or prior knowledge. We considered Duke's online data set containing 110 B-scans of 10 diabetic macular edema subjects with 8 retinal layers annotated by two experts for experimentation, and achieved a mean distance error of 1.38 pixels whereas that of the state-of-the-art was 1.68 pixels. PMID:27446714
C*-algebras of holonomy-diffeomorphisms and quantum gravity: I
NASA Astrophysics Data System (ADS)
Aastrup, Johannes; Møller Grimstrup, Jesper
2013-04-01
A new approach to a unified theory of quantum gravity based on noncommutative geometry and canonical quantum gravity is presented. The approach is built around a *-algebra generated by local holonomy-diffeomorphisms on a 3-manifold and a quantized Dirac-type operator, the two capturing the kinematics of quantum gravity formulated in terms of Ashtekar variables. We prove that the separable part of the spectrum of the algebra is contained in the space of measurable connections modulo gauge transformations and we give limitations to the non-separable part. The construction of the Dirac-type operator—and thus the application of noncommutative geometry—is motivated by the requirement of diffeomorphism invariance. We conjecture that a semi-finite spectral triple, which is invariant under volume-preserving diffeomorphisms, arises from a GNS construction of a semi-classical state. Key elements of quantum field theory emerge from the construction in a semi-classical limit, as does an almost commutative algebra. Finally, we note that the spectrum of loop quantum gravity emerges from a discretization of our construction. Certain convergence issues are left unresolved. This paper is the first of two where the second paper [1] is concerned with mathematical details and proofs concerning the spectrum of the holonomy-diffeomorphism algebra.
Gauge theory of a group of diffeomorphisms. II. The conformal and de Sitter groups
NASA Astrophysics Data System (ADS)
Lord, Eric A.
1986-12-01
The extension of Hehl's Poincaré gauge theory to more general groups that include space-time diffeomorphisms is worked out for two particular examples, one corresponding to the action of the conformal group on Minkowski space, and the other to the action of the de Sitter group on de Sitter space, and the effect of these groups on physical fields.
NASA Astrophysics Data System (ADS)
An, Yonghao; Jiang, Hanqing
2013-10-01
Lithium-ion batteries have attracted great deal of attention recently. Silicon is one of the most promising anode materials for high-performance lithium-ion batteries, due to its highest theoretical specific capacity. However, the short lifetime confined by mechanical failure in the silicon anode is now considered to be the biggest challenge in desired applications. High stress induced by the huge volume change due to lithium insertion/extraction is the main reason underlying this problem. Some theoretical models have been developed to address this issue. In order to properly implement these models, we develop a finite element based numerical method using a commercial software package, ABAQUS, as a platform at the continuum level to study fully coupled large deformation and mass diffusion problem. Using this method, large deformation, elasticity-plasticity of the electrodes, various spatial and temporal conditions, arbitrary geometry and dimension could be fulfilled. The interaction between anode and other components of the lithium ion batteries can also be studied as an integrated system. Several specific examples are presented to demonstrate the capability of this numerical platform.
NASA Astrophysics Data System (ADS)
Frei, S.; Richter, T.; Wick, T.
2016-09-01
In this work, we develop numerical schemes for mechano-chemical fluid-structure interactions with long-term effects. We investigate a model of a growing solid interacting with an incompressible fluid. A typical example for such a situation is the formation and growth of plaque in blood vessels. This application includes two particular difficulties: First, growth may lead to very large deformations, up to full clogging of the fluid domain. We derive a simplified set of equations including a fluid-structure interaction system coupled to an ODE model for plaque growth in Arbitrary Lagrangian Eulerian (ALE) coordinates and in Eulerian coordinates. The latter novel technique is capable of handling very large deformations up to contact. The second difficulty stems from the different time scales: while the dynamics of the fluid demand to resolve a scale of seconds, growth typically takes place in a range of months. We propose a temporal two-scale approach using local small-scale problems to compute an effective wall stress that will enter a long-scale problem. Our proposed techniques are substantiated with several numerical tests that include comparisons of the Eulerian and ALE approaches as well as convergence studies.
NASA Astrophysics Data System (ADS)
de Vicente, G.; Vegas, R.
2009-09-01
In the interior of the Iberian Peninsula, the main geomorphic features, mountain ranges and basins, seems to be arranged in several directions whose origin can be related to the N-S plate convergence which occurred along the Cantabro-Pyrenean border during the Eocene-Lower Miocene time span. The Iberian Variscan basement accommodated part of this plate convergence in three E-W trending crustal folds as well as in the reactivation of two left-lateral NNE-SSW strike-slip belts. The rest of the convergence was assumed through the inversion of the Iberian Mesozoic Rift to form the Iberian Chain. This inversion gave rise to a process of oblique crustal shortening involving the development of two right lateral NW-SE shear zones. Crustal folds, strike-slip corridors and one inverted rift compose a tectonic mechanism of pure shear in which the shortening is solved vertically by the development of mountain ranges and related sedimentary basins. This model can be expanded to NW Africa, up to the Atlasic System, where N-S plate convergence seems also to be accommodated in several basement uplifts, Anti-Atlas and Meseta, and through the inversion of two Mesozoic rifts, High and Middle Atlas. In this tectonic situation, the microcontinent Iberia used to be firmly attached to Africa during most part of the Tertiary, in such a way that N-S compressive stresses could be transmitted from the collision of the Pyrenean boundary. This tectonic scenario implies that most part of the Tertiary Eurasia-Africa convergence was not accommodated along the Iberia-Africa interface, but in the Pyrenean plateboundary. A broad zone of distributed deformation resulted from the transmission of compressive stresses from the collision at the Pyrenean border. This distributed, intraplate deformation, can be easily related to the topographic pattern of the Africa-Eurasia interface at the longitude of the Iberian Peninsula. Shortening in the Rif-Betics external zones - and their related topographic
Mechanical characterization of the P56 mouse brain under large-deformation dynamic indentation
MacManus, David B.; Pierrat, Baptiste; Murphy, Jeremiah G.; Gilchrist, Michael D.
2016-01-01
The brain is a complex organ made up of many different functional and structural regions consisting of different types of cells such as neurons and glia, as well as complex anatomical geometries. It is hypothesized that the different regions of the brain exhibit significantly different mechanical properties, which may be attributed to the diversity of cells and anisotropy of neuronal fibers within individual brain regions. The regional dynamic mechanical properties of P56 mouse brain tissue in vitro and in situ at velocities of 0.71–4.28 mm/s, up to a deformation of 70 μm are presented and discussed in the context of traumatic brain injury. The experimental data obtained from micro-indentation measurements were fit to three hyperelastic material models using the inverse Finite Element method. The cerebral cortex elicited a stiffer response than the cerebellum, thalamus, and medulla oblongata regions for all velocities. The thalamus was found to be the least sensitive to changes in velocity, and the medulla oblongata was most compliant. The results show that different regions of the mouse brain possess significantly different mechanical properties, and a significant difference also exists between the in vitro and in situ brain. PMID:26898475
Mechanical characterization of the P56 mouse brain under large-deformation dynamic indentation
NASA Astrophysics Data System (ADS)
MacManus, David B.; Pierrat, Baptiste; Murphy, Jeremiah G.; Gilchrist, Michael D.
2016-02-01
The brain is a complex organ made up of many different functional and structural regions consisting of different types of cells such as neurons and glia, as well as complex anatomical geometries. It is hypothesized that the different regions of the brain exhibit significantly different mechanical properties, which may be attributed to the diversity of cells and anisotropy of neuronal fibers within individual brain regions. The regional dynamic mechanical properties of P56 mouse brain tissue in vitro and in situ at velocities of 0.71-4.28 mm/s, up to a deformation of 70 μm are presented and discussed in the context of traumatic brain injury. The experimental data obtained from micro-indentation measurements were fit to three hyperelastic material models using the inverse Finite Element method. The cerebral cortex elicited a stiffer response than the cerebellum, thalamus, and medulla oblongata regions for all velocities. The thalamus was found to be the least sensitive to changes in velocity, and the medulla oblongata was most compliant. The results show that different regions of the mouse brain possess significantly different mechanical properties, and a significant difference also exists between the in vitro and in situ brain.
Effects of dehydration on the viscoelastic properties of vocal folds in large deformations.
Miri, Amir K; Barthelat, François; Mongeau, Luc
2012-11-01
Dehydration may alter vocal fold viscoelastic properties, thereby hampering phonation. The effects of water loss induced by an osmotic pressure potential on vocal fold tissue viscoelastic properties were investigated. Porcine vocal folds were dehydrated by immersion in a hypertonic solution, and quasi-static and low-frequency dynamic traction tests were performed for elongations of up to 50%. Digital image correlation was used to determine local strains from surface deformations. The elastic modulus and the loss factor were then determined for normal and dehydrated tissues. An eight-chain hyperelastic model was used to describe the observed nonlinear stress-stretch behavior. Contrary to the expectations, the mass history indicated that the tissue absorbed water during cyclic extension when submerged in a hypertonic solution. During loading history, the elastic modulus was increased for dehydrated tissues as a function of strain. The response of dehydrated tissues was much less affected when the load was released. This observation suggests that hydration should be considered in micromechanical models of the vocal folds. The internal hysteresis, which is often linked to phonation effort, increased significantly with water loss. The effects of dehydration on the viscoelastic properties of vocal fold tissue were quantified in a systematic way. A better understanding of the role of hydration on the mechanical properties of vocal fold tissue may help to establish objective dehydration and phonotrauma criteria. PMID:22483778
Effects of Dehydration on the Viscoelastic Properties of Vocal Folds in Large Deformations
Miri, Amir K.; Barthelat, François; Mongeau, Luc
2012-01-01
Summary Dehydration may alter vocal fold viscoelastic properties, which may hamper phonation. The effects of water loss induced by an osmotic-pressure potential on vocal fold tissue viscoelastic properties were investigated. Porcine vocal folds were dehydrated by immersion in a hypertonic solution, and quasi-static and low-frequency dynamic traction tests were performed for elongations of up to 50%. Digital image correlation was used to determine local strains from surface deformations. The elastic modulus and the loss factor were then determined for normal and dehydrated tissues. An eight-chain hyperelastic model was used to describe the observed nonlinear stress-stretch behavior. Contrary to expectations, the mass history indicated that the tissue absorbed water during cyclic extension when submerged in a hypertonic solution. During loading history, the elastic modulus was increased for dehydrated tissues as a function of strain. The response of dehydrated tissues was much less affected when the load was releasing. This calls more attention to the modeling of vocal folds in micromechanics modeling. The internal hysteresis, which is often linked to phonation effort, increased significantly with water loss. The effects of dehydration on the viscoelastic properties of vocal fold tissue were quantified in a systematic way. The results will contribute to a better understanding of the basic biomechanics of voice production and ultimately will help establish objective dehydration and phonotrauma criteria. PMID:22483778
NASA Technical Reports Server (NTRS)
Wu, R. W.; Witmer, E. A.
1972-01-01
Assumed-displacement versions of the finite-element method are developed to predict large-deformation elastic-plastic transient deformations of structures. Both the conventional and a new improved finite-element variational formulation are derived. These formulations are then developed in detail for straight-beam and curved-beam elements undergoing (1) Bernoulli-Euler-Kirchhoff or (2) Timoshenko deformation behavior, in one plane. For each of these categories, several types of assumed-displacement finite elements are developed, and transient response predictions are compared with available exact solutions for small-deflection, linear-elastic transient responses. The present finite-element predictions for large-deflection elastic-plastic transient responses are evaluated via several beam and ring examples for which experimental measurements of transient strains and large transient deformations and independent finite-difference predictions are available.
Seismic observations of large-scale deformation at the bottom of fast-moving plates
NASA Astrophysics Data System (ADS)
Debayle, E.; Ricard, Y. R.
2012-12-01
We investigate the global SV-wave azimuthal anisotropy from a new dataset of around 375 000 fundamental and higher mode Rayleigh waveforms. Our azimuthal anisotropy model improves upon DKP2005 seismic model (Debayle et al., Nature 2005) through a larger dataset (expanded by a factor 3.8) and a new approach which allows us to better extract fundamental and higher mode information. Our results confirm that in average, azimuthal anisotropy is significant only in the uppermost 200-250 km of the upper mantle and weak below. A clear root square of age dependence of anisotropy is observed beneath oceanic plates. The anisotropy projected in the direction of plate motion is more or less proportional to the plate velocity. Plate-scale present-day deformation is remarkably well recorded beneath the fastest moving plates (Indo-Australian, Coco, Nazca, Philippine Sea and Pacific plates). Under these plates, the amplitude of anisotropy does not change much with the distance to the ridge, indicating that the lattice preferred orientation rotates and saturates quickly. Beneath slower plates, plate-motion parallel anisotropy is observed only locally, which suggests, not surprisingly that the convection flow is only partly controlled by the surface motion. Within the lithosphere itself, the anisotropy is weak and likely frozen in; rather aligned with the plate velocity at its age of formation which is recorded by the local age gradient, than with the present-day motion. Although for young ages, the difference between the velocity recorded by the isochrons and the present-day velocity is small, for ages larger than 80 ~myrs the anisotropy rotates with depth from the fossil direction in the lithosphere to the present-day direction in the asthenosphere. Under fast continents (mostly Australia and India), the present day velocity orients the anisotropy around 150-200 km depth.
Wang, Shan; Cui, Lishan; Hao, Shijie; Jiang, Daqiang; Liu, Yinong; Liu, Zhenyang; Mao, Shengcheng; Han, Xiaodong; Ren, Yang
2014-10-24
This study investigated the elastic deformation behaviour of Nb nanowires embedded in a NiTi matrix. The Nb nanowires exhibited an ultra-large elastic deformation, which is found to be dictated by the martensitic transformation of the NiTi matrix, thus exhibiting unique characteristics of locality and rapidity. These are in clear contrast to our conventional observation of elastic deformations of crystalline solids, which is a homogeneous lattice distortion with a strain rate controlled by the applied strain. The Nb nanowires are also found to exhibit elastic-plastic deformation accompanying the martensitic transformation of the NiTi matrix in the case when the transformation strain of the matrix over-matches the elastic strain limit of the nanowires, or exhibit only elastic deformation in the case of under-matching. Such insight provides an important opportunity for elastic strain engineering and composite design.
Wang, Shan; Cui, Lishan; Hao, Shijie; Jiang, Daqiang; Liu, Yinong; Liu, Zhenyang; Mao, Shengcheng; Han, Xiaodong; Ren, Yang
2014-10-24
This study investigated the elastic deformation behaviour of Nb nanowires embedded in a NiTi matrix. The Nb nanowires exhibited an ultra-large elastic deformation, which is found to be dictated by the martensitic transformation of the NiTi matrix, thus exhibiting unique characteristics of locality and rapidity. These are in clear contrast to our conventional observation of elastic deformations of crystalline solids, which is a homogeneous lattice distortion with a strain rate controlled by the applied strain. The Nb nanowires are also found to exhibit elastic-plastic deformation accompanying the martensitic transformation of the NiTi matrix in the case when the transformation strainmore » of the matrix over-matches the elastic strain limit of the nanowires, or exhibit only elastic deformation in the case of under-matching. Such insight provides an important opportunity for elastic strain engineering and composite design.« less
Wang, Shan; Cui, Lishan; Hao, Shijie; Jiang, Daqiang; Liu, Yinong; Liu, Zhenyang; Mao, Shengcheng; Han, Xiaodong; Ren, Yang
2014-01-01
This study investigated the elastic deformation behaviour of Nb nanowires embedded in a NiTi matrix. The Nb nanowires exhibited an ultra-large elastic deformation, which is found to be dictated by the martensitic transformation of the NiTi matrix, thus exhibiting unique characteristics of locality and rapidity. These are in clear contrast to our conventional observation of elastic deformations of crystalline solids, which is a homogeneous lattice distortion with a strain rate controlled by the applied strain. The Nb nanowires are also found to exhibit elastic-plastic deformation accompanying the martensitic transformation of the NiTi matrix in the case when the transformation strain of the matrix over-matches the elastic strain limit of the nanowires, or exhibit only elastic deformation in the case of under-matching. Such insight provides an important opportunity for elastic strain engineering and composite design. PMID:25341619
NASA Astrophysics Data System (ADS)
Sheridan, Robert; Roche, Juan; Lofland, Samuel E.; vonLockette, Paris R.
2014-09-01
This work seeks to provide a framework for the numerical simulation of magneto-active elastomer (MAE) composite structures for use in origami engineering applications. The emerging field of origami engineering employs folding techniques, an array of crease patterns traditionally on a single flat sheet of paper, to produce structures and devices that perform useful engineering operations. Effective means of numerical simulation offer an efficient way to optimize the crease patterns while coupling to the performance and behavior of the active material. The MAE materials used herein are comprised of nominally 30% v/v, 325 mesh barium hexafarrite particles embedded in Dow HS II silicone elastomer compound. These particulate composites are cured in a magnetic field to produce magneto-elastic solids with anisotropic magnetization, e.g. they have a preferred magnetic axis parallel to the curing axis. The deformed shape and/or blocked force characteristics of these MAEs are examined in three geometries: a monolithic cantilever as well as two- and four-segment composite accordion structures. In the accordion structures, patches of MAE material are bonded to a Gelest OE41 unfilled silicone elastomer substrate. Two methods of simulation, one using the Maxwell stress tensor applied as a traction boundary condition and another employing a minimum energy kinematic (MEK) model, are investigated. Both methods capture actuation due to magnetic torque mechanisms that dominate MAE behavior. Comparison with experimental data show good agreement with only a single adjustable parameter, either an effective constant magnetization of the MAE material in the finite element models (at small and moderate deformations) or an effective modulus in the minimum energy model. The four-segment finite element model was prone to numerical locking at large deformation. The effective magnetization and modulus values required are a fraction of the actual experimentally measured values which suggests a
Seismic observations of large-scale deformation at the bottom of fast-moving plates
NASA Astrophysics Data System (ADS)
Debayle, Eric; Ricard, Yanick
2014-05-01
We present a new tomographic model of azimuthal anisotropy in the upper mantle and discuss in details the geodynamical causes of this anisotropy. Our model improves upon DKP2005 seismic model (Debayle et al., 2005) through a larger dataset (expanded by a factor ~ 4) and a new approach which allows us to better extract fundamental and higher mode information. Our results confirm that on average, azimuthal anisotropy is only significant in the uppermost 200-250 km of the upper mantle where it decreases regularly with depth. We do not see a significant difference in the amplitude of anisotropy beneath fast oceanic plates, slow oceanic plates or continents. The anisotropy projected onto the direction of present plate motion shows a very specific relation with the plate velocity; it peaks in the asthenosphere around 150 km depth, it is very weak for plate velocities smaller than 3 cm yr-1, increases significantly between 3 and 5 cm yr-1, and saturates for plate velocities larger than 5 cm yr-1. Plate-scale present-day deformation is remarkably well and uniformly recorded beneath the fastest moving plates (India, Coco, Nazca, Australia, Philippine Sea and Pacific plates). Beneath slower plates, plate-motion parallel anisotropy is only observed locally, which suggests that the mantle flow below these plates is not controlled by the lithospheric motion (a minimum plate velocity of around 4 cm yr-1 is necessary for a plate to organize the flow in its underlying asthenosphere). The correlation of oceanic anisotropy with the actual plate motion in the shallow lithosphere is very weak. A better correlation is obtained with the fossil accretion velocity recorded by the gradient of local seafloor age. The transition between frozen-in and active anisotropy occurs across the typical age- isotherm that defines the bottom of the thermal lithosphere around 1100 °C. Under fast continents (mostly under Australia and India), the present day velocity orients also the anisotropy in a
Seismic observations of large-scale deformation at the bottom of fast-moving plates
NASA Astrophysics Data System (ADS)
Debayle, Eric; Ricard, Yanick
2013-08-01
We present a new tomographic model of azimuthal anisotropy in the upper mantle, DR2012, and discuss in details the geodynamical causes of this anisotropy. Our model improves upon DKP2005 seismic model (Debayle et al., 2005) through a larger dataset (expanded by a factor ˜3.7) and a new approach which allows us to better extract fundamental and higher-mode information. Our results confirm that on average, azimuthal anisotropy is only significant in the uppermost 200-250 km of the upper mantle where it decreases regularly with depth. We do not see a significant difference in the amplitude of anisotropy beneath fast oceanic plates, slow oceanic plates or continents. The anisotropy projected onto the direction of present plate motion shows a very specific relation with the plate velocity; it peaks in the asthenosphere around 150 km depth, it is very weak for plate velocities smaller than 3 cm yr, increases significantly between 3 and 5 cm yr, and saturates for plate velocities larger than 5 cm yr. Plate-scale present-day deformation is remarkably well and uniformly recorded beneath the fastest-moving plates (India, Coco, Nazca, Australia, Philippine Sea and Pacific plates). Beneath slower plates, plate-motion parallel anisotropy is only observed locally, which suggests that the mantle flow below these plates is not controlled by the lithospheric motion (a minimum plate velocity of around 4 cm yr is necessary for a plate to organize the flow in its underlying asthenosphere). The correlation of oceanic anisotropy with the actual plate motion in the shallow lithosphere is very weak. A better correlation is obtained with the fossil accretion velocity recorded by the gradient of local seafloor age. The transition between frozen-in and active anisotropy occurs across the typical √{age} isotherm that defines the bottom of the thermal lithosphere around 1100 °C. Under fast continents (mostly under Australia and India), the present-day velocity orients also the anisotropy
Rare, large earthquakes at the laramide deformation front - Colorado (1882) and Wyoming (1984)
Spence, W.; Langer, C.J.; Choy, G.L.
1996-01-01
The largest historical earthquake known in Colorado occurred on 7 November 1882. Knowledge of its size, location, and specific tectonic environment is important for the design of critical structures in the rapidly growing region of the Southern Rocky Mountains. More than one century later, on 18 October 1984, an mb 5.3 earthquake occurred in the Laramie Mountains, Wyoming. By studying the 1984 earthquake, we are able to provide constraints on the location and size of the 1882 earthquake. Analysis of broadband seismic data shows the 1984 mainshock to have nucleated at a depth of 27.5 ?? 1.0 km and to have ruptured ???2.7 km updip, with a corresponding average displacement of about 48 cm and average stress drop of about 180 bars. This high stress drop may explain why the earthquake was felt over an area about 3.5 times that expected for a shallow earthquake of the same magnitude in this region. A microearthquake survey shows aftershocks to be just above the mainshock's rupture, mostly in a volume measuring 3 to 4 km across. Focal mechanisms for the mainshock and aftershocks have NE-SW-trending T axes, a feature shared by most earthquakes in western Colorado and by the induced Denver earthquakes of 1967. The only data for the 1882 earthquake were intensity reports from a heterogeneously distributed population. Interpretation of these reports also might be affected by ground-motion amplification from fluvial deposits and possible significant focal depth for the mainshock. The primary aftershock of the 1882 earthquake was felt most strongly in the northern Front Range, leading Kirkham and Rogers (1985) to locate the epicenters of the aftershock and mainshock there. The Front Range is a geomorphic extension of the Laramie Mountains. Both features are part of the eastern deformation front of the Laramide orogeny. Based on knowledge of regional tectonics and using intensity maps for the 1984 and the 1967 Denver earthquakes, we reinterpret prior intensity maps for the 1882
Large-strain, rigid-to-rigid deformation of bistable electroactive polymers
NASA Astrophysics Data System (ADS)
Yu, Zhibin; Yuan, Wei; Brochu, Paul; Chen, Bin; Liu, Zhitian; Pei, Qibing
2009-11-01
Thermoplastic poly(tert-butyl acrylate) (PTBA) is reported as an electroactive polymer that is rigid at ambient conditions and turns into a dielectric elastomer above a transition temperature. In the rubbery state, a PTBA thin film can be electrically actuated to strains up to 335% in area expansion. The calculated actuation pressure is 3.2 MPa. The actuation is made bistable by cooling to below glass transition temperature. The PTBA represents the bistable electroactive polymer (BSEP) that can be actuated to various largely strained, rigid shapes. The application of the BSEP for refreshable Braille display, an active tactile display, is also demonstrated.
Size effect of large deformable nanopillar by focused-ion-beam chemical vapor deposition
NASA Astrophysics Data System (ADS)
Tanaka, H.; Shinkai, M.; Shibutani, Y.; Kogo, Y.
2009-11-01
Nanoscopic fabrication technique has been achieved by the direct deposition methods using focused-ion-beam chemical vapor deposition (FIB-CVD). The nanopillar fabricated by FIB-CVD consists of an outer amorphous carbon ring and a inner gallium core. We developed the original double-cantilever (DC) bending test using two pillars rigidly connected by the exposure of a focused electron beam in a scanning electron microscope. The obtained deflection curves suggest that nanopillars have the size dependence to the mechanical response. The pillar with the diameter over 180 nm exhibits a wide region of stiffness weakening after linear response and then becomes extremely hardened at a large deflection. Thus, the pillar intrinsically possesses much more flexibility for bending without any fracturing. The accuracy of a DC testing is also discussed by estimating the bending rigidities of nanopillars, comparing to those obtained by resonance frequency tests.
NASA Astrophysics Data System (ADS)
Jouili, Khalil; Benhadj Braiek, Naceur
2015-06-01
In this paper we propose a control approach for the stabilization of a class of switched nonlinear systems where each mode may be non-minimum phase. The proposed approach is based on the exact input-output linearization and the Lyapunov stability theory. The main contribution in this work is to elaborate a strategy of switching that recourse to the concept of multi-diffeomorphism makes it possible to guarantee an improvement of the transient state compared to a feedback linearization based on one diffeomorphism. Specifically, we show the sufficient condition for the exponential stability and the exponential upper bound of the trajectory of the switched system. The theoretical results are applied to a non-minimum phase inverted cart-pendulum in order to illustrate the effectiveness of the proposed approach.
Becchi-Rouet-Stora-Tyutin structure for the mixed Weyl-diffeomorphism residual symmetry
NASA Astrophysics Data System (ADS)
François, J.; Lazzarini, S.; Masson, T.
2016-03-01
In this paper, we show the compatibility of the so-called "dressing field method," which allows a systematic reduction of gauge symmetries, with the inclusion of diffeomorphisms in the Becchi-Rouet-Stora-Tyutin (BRST) algebra of a gauge theory. The robustness of the scheme is illustrated on two examples where Cartan connections play a significant role. The former is General Relativity, while the latter concerns the second-order conformal structure where one ends up with a BRST algebra handling both the Weyl residual symmetry and diffeomorphisms of spacetime. We thereby provide a geometric counterpart to the BRST cohomological treatment used in Boulanger [J. Math. Phys. 46, 053508 (2005)] in the construction of a Weyl covariant tensor calculus.
New phases of D ge 2 current and diffeomorphism algebras in particle physics
Tze, Chia-Hsiung.
1990-09-01
We survey some global results and open issues of current algebras and their canonical field theoretical realization in D {ge} 2 dimensional spacetime. We assess the status of the representation theory of their generalized Kac-Moody and diffeomorphism algebras. Particular emphasis is put on higher dimensional analogs of fermi-bose correspondence, complex analyticity and the phase entanglements of anyonic solitons with exotic spin and statistics. 101 refs.
Notes on diffeomorphisms symmetry of f(R) gravity in the cosmological context
NASA Astrophysics Data System (ADS)
Ghalee, Amir
2016-03-01
We study the metric perturbations in the context of restricted f(R) gravity, in which a parameter for deviation from the full diffeomorphisms of space-time is introduced. We demonstrate that one can choose the parameter to remove the induced anisotropic stress, which is present in the usual f(R) gravity. Moreover, to prevent instability for the vector and tensor metric perturbations, some constraints on the restricted f(R) gravity are obtained.
Quasi-local conserved charges in Lorenz-diffeomorphism covariant theory of gravity
NASA Astrophysics Data System (ADS)
Adami, H.; Setare, M. R.
2016-04-01
In this paper, using the combined Lorenz-diffeomorphism symmetry, we find a general formula for the quasi-local conserved charge of the covariant gravity theories in a first order formalism of gravity. We simplify the general formula for the Lovelock theory of gravity. Afterwards, we apply the obtained formula on BHT gravity to obtain the energy and angular momentum of the rotating OTT black hole solution in the context of this theory.
NASA Astrophysics Data System (ADS)
Hugot, E.; Ferrari, M.; Riccardi, A.; Xompero, M.; Lemaître, G. R.; Arsenault, R.; Hubin, N.
2011-03-01
Context. Adaptive secondary mirrors (ASM) are, or will be, key components on all modern telescopes, providing improved seeing conditions or diffraction limited images, thanks to the high-order atmospheric turbulence correction obtained by controlling the shape of a thin mirror. Their development is a key milestone towards future extremely large telescopes (ELT) where this technology is mandatory for successful observations. Aims: The key point of actual adaptive secondaries technology is the thin glass mirror that acts as a deformable membrane, often aspheric. On 6 m - 8 m class telescopes, these are typically 1 m-class with a 2 mm thickness. The optical quality of this shell must be sufficiently good not to degrade the correction, meaning that high spatial frequency errors must be avoided. The innovative method presented here aims at generating aspherical shapes by elastic bending to reach high optical qualities. Methods: This method is called stress polishing and allows generating aspherical optics of a large amplitude with a simple spherical polishing with a full sized lap applied on a warped blank. The main advantage of this technique is the smooth optical quality obtained, free of high spatial frequency ripples as they are classically caused by subaperture toolmarks. After describing the manufacturing process we developed, our analytical calculations lead to a preliminary definition of the geometry of the blank, which allows a precise bending of the substrate. The finite element analysis (FEA) can be performed to refine this geometry by using an iterative method with a criterion based on the power spectral density of the displacement map of the optical surface. Results: Considering the specific case of the Very Large Telescope (VLT) deformable secondary mirror (DSM), extensive FEA were performed for the optimisation of the geometry. Results are showing that the warping will not introduce surface errors higher than 0.3 nm rms on the minimal spatial scale
Large Deformation Dynamic Response
Energy Science and Technology Software Center (ESTSC)
1993-08-23
HONDO2-SLA is used to compute the time-dependent displacements, velocities, accelerations, and stresses within elastic or inelastic, two-dimensional or axisymmetric or planar bodies of arbitrary shape and materials.
Chen, Luzhuo; Weng, Mingcen; Zhou, Zhiwei; Zhou, Yi; Zhang, Lingling; Li, Jiaxin; Huang, Zhigao; Zhang, Wei; Liu, Changhong; Fan, Shoushan
2015-12-22
In recent years, electroactive polymers have been developed as actuator materials. As an important branch of electroactive polymers, electrothermal actuators (ETAs) demonstrate potential applications in the fields of artificial muscles, biomimetic devices, robotics, and so on. Large-shape deformation, low-voltage-driven actuation, and ultrafast fabrication are critical to the development of ETA. However, a simultaneous optimization of all of these advantages has not been realized yet. Practical biomimetic applications are also rare. In this work, we introduce an ultrafast approach to fabricate a curling actuator based on a newly designed carbon nanotube and polymer composite, which completely realizes all of the above required advantages. The actuator shows an ultralarge curling actuation with a curvature greater than 1.0 cm(-1) and bending angle larger than 360°, even curling into a tubular structure. The driving voltage is down to a low voltage of 5 V. The remarkable actuation is attributed not only to the mismatch in the coefficients of thermal expansion but also to the mechanical property changes of materials during temperature change. We also construct an S-shape actuator to show the possibility of building advanced-structure actuators. A weightlifting walking robot is further designed that exhibits a fast-moving motion while lifting a sample heavier than itself, demonstrating promising biomimetic applications. PMID:26512734
NASA Astrophysics Data System (ADS)
Rousseau, Christiane
In this paper we describe the moduli space of germs of generic analytic families of complex 1-dimensional resonant analytic diffeomorphisms of codimension 1. In Rousseau and Christopher (2007) [11], it was shown that the Ecalle modulus can be unfolded to give a complete modulus for such germs. As function of the canonical parameter, the modulus is defined on two sectors giving a covering of a neighborhood of the origin in the parameter space. As in the case of the Ecalle modulus, the modulus is defined up to a linear scaling depending only on the parameter. The compatibility condition is obtained by considering the region of intersection of the two sectors in parameter space, which we call the Glutsyuk sectors. There, both the fixed point and the periodic orbit are hyperbolic and they are connected by the orbits of the diffeomorphism. This yields an alternate description of the equivalence class by the Glutsyuk modulus: near each of the fixed point and of the periodic orbit we construct a change of coordinate to the normal form. The Glutsyuk modulus measures the obstruction of having one being the analytic extension of the other. In the intersection of the two sectors, we have two representatives of the modulus which describe the same dynamics. A necessary compatibility condition is that they have the same Glutsyuk modulus. This necessary condition becomes sufficient for realizability. The compatibility condition implies the existence of a linear scaling for which the modulus is 1-summable in ɛ, whose directions of non-summability coincide with the direction of real multipliers at the fixed point and periodic orbit. Conversely, we show that the compatibility condition (which implies the summability property) is sufficient to realize the modulus as coming from an analytic unfolding, thus giving a complete description of the space of moduli.
NASA Astrophysics Data System (ADS)
Liang, Cunren; Zeng, Qiming; Jia, Jianying; Jiao, Jian; Cui, Xi'ai
2013-02-01
Scanning synthetic aperture radar (ScanSAR) mode is an efficient way to map large scale geophysical phenomena at low cost. The work presented in this paper is dedicated to ScanSAR interferometric processing and its implementation by making full use of existing standard interferometric synthetic aperture radar (InSAR) software. We first discuss the properties of the ScanSAR signal and its phase-preserved focusing using the full aperture algorithm in terms of interferometry. Then a complete interferometric processing flow is proposed. The standard ScanSAR product is decoded subswath by subswath with burst gaps padded with zero-pulses, followed by a Doppler centroid frequency estimation for each subswath and a polynomial fit of all of the subswaths for the whole scene. The burst synchronization of the interferometric pair is then calculated, and only the synchronized pulses are kept for further interferometric processing. After the complex conjugate multiplication of the interferometric pair, the residual non-integer pulse repetition interval (PRI) part between adjacent bursts caused by zero padding is compensated by resampling using a sinc kernel. The subswath interferograms are then mosaicked, in which a method is proposed to remove the subswath discontinuities in the overlap area. Then the following interferometric processing goes back to the traditional stripmap processing flow. A processor written with C and Fortran languages and controlled by Perl scripts is developed to implement these algorithms and processing flow based on the JPL/Caltech Repeat Orbit Interferometry PACkage (ROI_PAC). Finally, we use the processor to process ScanSAR data from the Envisat and ALOS satellites and obtain large scale deformation maps in the radar line-of-sight (LOS) direction.
NASA Astrophysics Data System (ADS)
Gilmanov, Anvar; Le, Trung Bao; Sotiropoulos, Fotis
2015-11-01
We present a new numerical methodology for simulating fluid-structure interaction (FSI) problems involving thin flexible bodies in an incompressible fluid. The FSI algorithm uses the Dirichlet-Neumann partitioning technique. The curvilinear immersed boundary method (CURVIB) is coupled with a rotation-free finite element (FE) model for thin shells enabling the efficient simulation of FSI problems with arbitrarily large deformation. Turbulent flow problems are handled using large-eddy simulation with the dynamic Smagorinsky model in conjunction with a wall model to reconstruct boundary conditions near immersed boundaries. The CURVIB and FE solvers are coupled together on the flexible solid-fluid interfaces where the structural nodal positions, displacements, velocities and loads are calculated and exchanged between the two solvers. Loose and strong coupling FSI schemes are employed enhanced by the Aitken acceleration technique to ensure robust coupling and fast convergence especially for low mass ratio problems. The coupled CURVIB-FE-FSI method is validated by applying it to simulate two FSI problems involving thin flexible structures: 1) vortex-induced vibrations of a cantilever mounted in the wake of a square cylinder at different mass ratios and at low Reynolds number; and 2) the more challenging high Reynolds number problem involving the oscillation of an inverted elastic flag. For both cases the computed results are in excellent agreement with previous numerical simulations and/or experiential measurements. Grid convergence tests/studies are carried out for both the cantilever and inverted flag problems, which show that the CURVIB-FE-FSI method provides their convergence. Finally, the capability of the new methodology in simulations of complex cardiovascular flows is demonstrated by applying it to simulate the FSI of a tri-leaflet, prosthetic heart valve in an anatomic aorta and under physiologic pulsatile conditions.
MIND Demons for MR-to-CT Deformable Image Registration In Image-Guided Spine Surgery
Reaungamornrat, S.; De Silva, T.; Uneri, A.; Wolinsky, J.-P.; Khanna, A. J.; Kleinszig, G.; Vogt, S.; Prince, J. L.; Siewerdsen, J. H.
2016-01-01
Purpose Localization of target anatomy and critical structures defined in preoperative MR images can be achieved by means of multi-modality deformable registration to intraoperative CT. We propose a symmetric diffeomorphic deformable registration algorithm incorporating a modality independent neighborhood descriptor (MIND) and a robust Huber metric for MR-to-CT registration. Method The method, called MIND Demons, solves for the deformation field between two images by optimizing an energy functional that incorporates both the forward and inverse deformations, smoothness on the velocity fields and the diffeomorphisms, a modality-insensitive similarity function suitable to multi-modality images, and constraints on geodesics in Lagrangian coordinates. Direct optimization (without relying on an exponential map of stationary velocity fields used in conventional diffeomorphic Demons) is carried out using a Gauss-Newton method for fast convergence. Registration performance and sensitivity to registration parameters were analyzed in simulation, in phantom experiments, and clinical studies emulating application in image-guided spine surgery, and results were compared to conventional mutual information (MI) free-form deformation (FFD), local MI (LMI) FFD, and normalized MI (NMI) Demons. Result The method yielded sub-voxel invertibility (0.006 mm) and nonsingular spatial Jacobians with capability to preserve local orientation and topology. It demonstrated improved registration accuracy in comparison to the reference methods, with mean target registration error (TRE) of 1.5 mm compared to 10.9, 2.3, and 4.6 mm for MI FFD, LMI FFD, and NMI Demons methods, respectively. Validation in clinical studies demonstrated realistic deformation with sub-voxel TRE in cases of cervical, thoracic, and lumbar spine. Conclusions A modality-independent deformable registration method has been developed to estimate a viscoelastic diffeomorphic map between preoperative MR and intraoperative CT. The
MIND Demons for MR-to-CT deformable image registration in image-guided spine surgery
NASA Astrophysics Data System (ADS)
Reaungamornrat, S.; De Silva, T.; Uneri, A.; Wolinsky, J.-P.; Khanna, A. J.; Kleinszig, G.; Vogt, S.; Prince, J. L.; Siewerdsen, J. H.
2016-03-01
Purpose: Localization of target anatomy and critical structures defined in preoperative MR images can be achieved by means of multi-modality deformable registration to intraoperative CT. We propose a symmetric diffeomorphic deformable registration algorithm incorporating a modality independent neighborhood descriptor (MIND) and a robust Huber metric for MR-to-CT registration. Method: The method, called MIND Demons, solves for the deformation field between two images by optimizing an energy functional that incorporates both the forward and inverse deformations, smoothness on the velocity fields and the diffeomorphisms, a modality-insensitive similarity function suitable to multi-modality images, and constraints on geodesics in Lagrangian coordinates. Direct optimization (without relying on an exponential map of stationary velocity fields used in conventional diffeomorphic Demons) is carried out using a Gauss-Newton method for fast convergence. Registration performance and sensitivity to registration parameters were analyzed in simulation, in phantom experiments, and clinical studies emulating application in image-guided spine surgery, and results were compared to conventional mutual information (MI) free-form deformation (FFD), local MI (LMI) FFD, and normalized MI (NMI) Demons. Result: The method yielded sub-voxel invertibility (0.006 mm) and nonsingular spatial Jacobians with capability to preserve local orientation and topology. It demonstrated improved registration accuracy in comparison to the reference methods, with mean target registration error (TRE) of 1.5 mm compared to 10.9, 2.3, and 4.6 mm for MI FFD, LMI FFD, and NMI Demons methods, respectively. Validation in clinical studies demonstrated realistic deformation with sub-voxel TRE in cases of cervical, thoracic, and lumbar spine. Conclusions: A modality-independent deformable registration method has been developed to estimate a