Large Deformation Diffeomorphic Metric Curve Mapping
Glaunès, Joan; Miller, Michael I.; Younes, Laurent
2010-01-01
We present a matching criterion for curves and integrate it into the large deformation diffeomorphic metric mapping (LDDMM) scheme for computing an optimal transformation between two curves embedded in Euclidean space ℝd. Curves are first represented as vector-valued measures, which incorporate both location and the first order geometric structure of the curves. Then, a Hilbert space structure is imposed on the measures to build the norm for quantifying the closeness between two curves. We describe a discretized version of this, in which discrete sequences of points along the curve are represented by vector-valued functionals. This gives a convenient and practical way to define a matching functional for curves. We derive and implement the curve matching in the large deformation framework and demonstrate mapping results of curves in ℝ2 and ℝ3. Behaviors of the curve mapping are discussed using 2D curves. The applications to shape classification is shown and experiments with 3D curves extracted from brain cortical surfaces are presented. PMID:20419045
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
Large deformation diffeomorphic metric mapping of orientation distribution functions.
Du, Jia; Goh, Alvina; Qiu, Anqi
2011-01-01
We propose a novel large deformation diffeomorphic registration algorithm to align high angular resolution diffusion images (HARDI) characterized by Orientation Distribution Functions (ODF). Our proposed algorithm seeks an optimal diffeomorphism of large deformation between two ODF fields in a spatial volume domain and at the same time, locally reorients an ODF in a manner such that it remains consistent with the surrounding anatomical structure. We first extend ODFs traditionally defined in a unit sphere to a generalized ODF defined in R3. This makes it easy for an affine transformation as well as a diffeomorphic group action to be applied on the ODF. We then construct a Riemannian space of the generalized ODFs and incorporate its Riemannian metric for the similarity of ODFs into a variational problem defined under the large deformation diffeomorphic metric mapping (LDDMM) framework. We finally derive the gradient of the cost function in both Riemannian spaces of diffeomorphisms and the generalized ODFs, and present its numerical implementation. Both synthetic and real brain HARDI data are used to illustrate the performance of our registration algorithm.
Multistructure large deformation diffeomorphic brain registration.
Khan, Ali R; Wang, Lei; Beg, Mirza Faisal
2013-02-01
Whole brain MRI registration has many useful applications in group analysis and morphometry, yet accurate registration across different neuropathological groups remains challenging. Structure-specific information, or anatomical guidance, can be used to initialize and constrain registration to improve accuracy and robustness. We describe here a multistructure diffeomorphic registration approach that uses concurrent subcortical and cortical shape matching to guide the overall registration. Validation experiments carried out on openly available datasets demonstrate comparable or improved alignment of subcortical and cortical brain structures over leading brain registration algorithms. We also demonstrate that a group-wise average atlas built with multistructure registration accounts for greater intersubject variability and provides more sensitive tensor-based morphometry measurements.
Large deformation diffeomorphic registration of diffusion-weighted images.
Zhang, Pei; Niethammer, Marc; Shen, Dinggang; Yap, Pew-Thian
2012-01-01
Registration of Diffusion-weighted imaging (DWI) data emerges as an important topic in magnetic resonance (MR) image analysis. As existing methods are often designed for specific diffusion models, it is difficult to fit to the registered data different models other than the one used for registration. In this paper we describe a diffeomorphic registration algorithm for DWI data in a large deformation setting. Our method generates spatially normalized DWI data and it is thus possible to fit various diffusion models after registration for comparison purposes. Our algorithm includes (1) a reorientation component, where each diffusion profile (DWI signal as a function on a unit sphere) is decomposed, reoriented and recomposed to form the orientation-corrected DWI profile, and (2) a large deformation diffeomorphic registration component to ensure one-to-one mapping in a large-structural-variation scenario. In addition our algorithm uses a geodesic shooting mechanism to avoid the huge computational resources that are needed to register high-dimensional vector-valued data. We also incorporate into our algorithm a multi-kernel strategy where anatomical structures at different scales are considered simultaneously during registration. We demonstrate the efficacy of our method using in vivo data.
Large deformation diffeomorphic registration of diffusion-weighted imaging data.
Zhang, Pei; Niethammer, Marc; Shen, Dinggang; Yap, Pew-Thian
2014-12-01
Registration plays an important role in group analysis of diffusion-weighted imaging (DWI) data. It can be used to build a reference anatomy for investigating structural variation or tracking changes in white matter. Unlike traditional scalar image registration where spatial alignment is the only focus, registration of DWI data requires both spatial alignment of structures and reorientation of local signal profiles. As such, DWI registration is much more complex and challenging than scalar image registration. Although a variety of algorithms has been proposed to tackle the problem, most of them are restricted by the diffusion model used for registration, making it difficult to fit to the registered data a different model. In this paper we describe a method that allows any diffusion model to be fitted after registration for subsequent multifaceted analysis. This is achieved by directly aligning DWI data using a large deformation diffeomorphic registration framework. Our algorithm seeks the optimal coordinate mapping by simultaneously considering structural alignment, local signal profile reorientation, and deformation regularization. Our algorithm also incorporates a multi-kernel strategy to concurrently register anatomical structures at different scales. We demonstrate the efficacy of our approach using in vivo data and report detailed qualitative and quantitative results in comparison with several different registration strategies. Copyright © 2014 Elsevier B.V. All rights reserved.
Large deformation diffeomorphic registration of diffusion-weighted imaging data
Zhang, Pei; Niethammer, Marc; Shen, Dinggang; Yap, Pew-Thian
2014-01-01
Registration plays an important role in group analysis of diffusion-weighted imaging (DWI) data. It can be used to build a reference anatomy for investigating structural variation or tracking changes in white matter. Unlike traditional scalar image registration where spatial alignment is the only focus, registration of DWI data requires both spatial alignment of structures and reorientation of local signal profiles. As such, DWI registration is much more complex and challenging than scalar image registration. Although a variety of algorithms has been proposed to tackle the problem, most of them are restricted by the zdiffusion model used for registration, making it difficult to fit to the registered data a different model. In this paper we describe a method that allows any diffusion model to be fitted after registration for subsequent multifaceted analysis. This is achieved by directly aligning DWI data using a large deformation diffeomorphic registration framework. Our algorithm seeks the optimal coordinate mapping by simultaneously considering structural alignment, local signal profile reorientation, and deformation regularization. Our algorithm also incorporates a multi-kernel strategy to concurrently register anatomical structures at different scales. We demonstrate the efficacy of our approach using in vivo data and report detailed qualitative and quantitative results in comparison with several different registration strategies. PMID:25106710
Zhang, Pei; Niethammer, Marc; Shen, Dinggang; Yap, Pew-Thian
2014-01-01
We seek to compute a diffeomorphic map between a pair of diffusion-weighted images under large deformation. Unlike existing techniques, our method allows any diffusion model to be fitted after registration for subsequent multifaceted analysis. This is achieved by directly aligning the diffusion-weighted images using a large deformation diffeomorphic registration framework formulated from an optimal control perspective. Our algorithm seeks the optimal coordinate mapping by simultaneously considering structural alignment, local fiber reorientation, and deformation regularization. Our algorithm also incorporates a multi-kernel strategy to concurrently register anatomical structures of different scales. We demonstrate the efficacy of our approach using in vivo data and report on detailed qualitative and quantitative results in comparison with several different registration strategies. PMID:24579120
Zhang, Pei; Niethammer, Marc; Shen, Dinggang; Yap, Pew-Thian
2013-01-01
We seek to compute a diffeomorphic map between a pair of diffusion-weighted images under large deformation. Unlike existing techniques, our method allows any diffusion model to be fitted after registration for subsequent multifaceted analysis. This is achieved by directly aligning the diffusion-weighted images using a large deformation diffeomorphic registration framework formulated from an optimal control perspective. Our algorithm seeks the optimal coordinate mapping by simultaneously considering structural alignment, local fiber reorientation, and deformation regularization. Our algorithm also incorporates a multi-kernel strategy to concurrently register anatomical structures of different scales. We demonstrate the efficacy of our approach using in vivo data and report on detailed qualitative and quantitative results in comparison with several different registration strategies.
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.
A large deformation diffeomorphic metric mapping solution for diffusion spectrum imaging datasets.
Hsu, Yung-Chin; Hsu, Ching-Han; Tseng, Wen-Yih Isaac
2012-11-01
Spatial transformation for diffusion spectrum imaging (DSI) is an important step for group analyses of DSI datasets. In this study, we developed a transformation method for DSI datasets under the framework of large deformation diffeomorphic metric mapping (LDDMM), which is termed LDDMM-DSI. The proposed method made use of the fact that a DSI dataset is 6D, and generalized the original 2D/3D LDDMM algorithm to the 6D case with some modifications made for the DSI datasets. In this manner, the conventional reorientation problem that arises from transforming diffusion-weighted datasets was avoided by making the DSI datasets capable of being freely deformed in the q-space. The algorithm treated the data-matching task as a variational problem under the LDDMM framework and sought optimal velocity fields from which the generated transformations were diffeomorphic and the transformation curve was a geodesic. The mathematical materials and numerical implementation are detailed in the paper, and experiments were performed to analyze the proposed method on real brain DSI datasets. The results showed that the method was capable of registering different DSI datasets in both global structural shapes and local diffusion profiles. In conclusion, the proposed method can facilitate group analyses of DSI datasets and the generation of a DSI template. Copyright © 2012 Elsevier Inc. All rights reserved.
Gauss-Newton inspired preconditioned optimization in large deformation diffeomorphic metric mapping.
Hernandez, Monica
2014-10-21
In this work, we propose a novel preconditioned optimization method in the paradigm of Large Deformation Diffeomorphic Metric Mapping (LDDMM). The preconditioned update scheme is formulated for the non-stationary and the stationary parameterizations of diffeomorphisms, yielding three different LDDMM methods. The preconditioning matrices are inspired in the Hessian approximation used in Gauss-Newton method. The derivatives are computed using Frechet differentials. Thus, optimization is performed in a Sobolev space, in contrast to optimization in L(2) commonly used in non-rigid registration literature. The proposed LDDMM methods have been evaluated and compared with their respective implementations of gradient descent optimization. Evaluation has been performed using real and simulated images from the Non-rigid Image Registration Evaluation Project (NIREP). The experiments conducted in this work reported that our preconditioned LDDMM methods achieved a performance similar or superior to well-established-in-literature gradient descent non-stationary LDDMM in the great majority of cases. Moreover, preconditioned optimization showed a substantial reduction in the execution time with an affordable increase of the memory usage per iteration. Additional experiments reported that optimization using Frechet differentials should be preferable to optimization using L(2) differentials.
Gauss-Newton inspired preconditioned optimization in large deformation diffeomorphic metric mapping
NASA Astrophysics Data System (ADS)
Hernandez, Monica
2014-10-01
In this work, we propose a novel preconditioned optimization method in the paradigm of Large Deformation Diffeomorphic Metric Mapping (LDDMM). The preconditioned update scheme is formulated for the non-stationary and the stationary parameterizations of diffeomorphisms, yielding three different LDDMM methods. The preconditioning matrices are inspired in the Hessian approximation used in Gauss-Newton method. The derivatives are computed using Frechet differentials. Thus, optimization is performed in a Sobolev space, in contrast to optimization in L2 commonly used in non-rigid registration literature. The proposed LDDMM methods have been evaluated and compared with their respective implementations of gradient descent optimization. Evaluation has been performed using real and simulated images from the Non-rigid Image Registration Evaluation Project (NIREP). The experiments conducted in this work reported that our preconditioned LDDMM methods achieved a performance similar or superior to well-established-in-literature gradient descent non-stationary LDDMM in the great majority of cases. Moreover, preconditioned optimization showed a substantial reduction in the execution time with an affordable increase of the memory usage per iteration. Additional experiments reported that optimization using Frechet differentials should be preferable to optimization using L2 differentials.
Simultaneous multi-scale registration using large deformation diffeomorphic metric mapping.
Risser, Laurent; Vialard, François-Xavier; Wolz, Robin; Murgasova, Maria; Holm, Darryl D; Rueckert, Daniel
2011-10-01
In the framework of large deformation diffeomorphic metric mapping (LDDMM), we present a practical methodology to integrate prior knowledge about the registered shapes in the regularizing metric. Our goal is to perform rich anatomical shape comparisons from volumetric images with the mathematical properties offered by the LDDMM framework. We first present the notion of characteristic scale at which image features are deformed. We then propose a methodology to compare anatomical shape variations in a multi-scale fashion, i.e., at several characteristic scales simultaneously. In this context, we propose a strategy to quantitatively measure the feature differences observed at each characteristic scale separately. After describing our methodology, we illustrate the performance of the method on phantom data. We then compare the ability of our method to segregate a group of subjects having Alzheimer's disease and a group of controls with a classical coarse to fine approach, on standard 3D MR longitudinal brain images. We finally apply the approach to quantify the anatomical development of the human brain from 3D MR longitudinal images of pre-term babies. Results show that our method registers accurately volumetric images containing feature differences at several scales simultaneously with smooth deformations. © 2011 British Crown Copyright
Computing Diffeomorphic Paths for Large Motion Interpolation*
Seo, Dohyung; Jeffrey, Ho; Vemuri, Baba C.
2013-01-01
In this paper, we introduce a novel framework for computing a path of diffeomorphisms between a pair of input diffeomorphisms. Direct computation of a geodesic path on the space of diffeomorphisms Diff(Ω) is difficult, and it can be attributed mainly to the infinite dimensionality of Diff(Ω). Our proposed framework, to some degree, bypasses this difficulty using the quotient map of Diff(Ω) to the quotient space Diff(M)/Diff(M)μ obtained by quotienting out the subgroup of volume-preserving diffeomorphisms Diff(M)μ. This quotient space was recently identified as the unit sphere in a Hilbert space in mathematics literature, a space with well-known geometric properties. Our framework leverages this recent result by computing the diffeomorphic path in two stages. First, we project the given diffeomorphism pair onto this sphere and then compute the geodesic path between these projected points. Second, we lift the geodesic on the sphere back to the space of diffeomerphisms, by solving a quadratic programming problem with bilinear constraints using the augmented Lagrangian technique with penalty terms. In this way, we can estimate the path of diffeomorphisms, first, staying in the space of diffeomorphisms, and second, preserving shapes/volumes in the deformed images along the path as much as possible. We have applied our framework to interpolate intermediate frames of frame-sub-sampled video sequences. In the reported experiments, our approach compares favorably with the popular Large Deformation Diffeomorphic Metric Mapping framework (LDDMM). PMID:25364222
Computing Diffeomorphic Paths for Large Motion Interpolation.
Seo, Dohyung; Jeffrey, Ho; Vemuri, Baba C
2013-06-01
In this paper, we introduce a novel framework for computing a path of diffeomorphisms between a pair of input diffeomorphisms. Direct computation of a geodesic path on the space of diffeomorphisms Diff(Ω) is difficult, and it can be attributed mainly to the infinite dimensionality of Diff(Ω). Our proposed framework, to some degree, bypasses this difficulty using the quotient map of Diff(Ω) to the quotient space Diff(M)/Diff(M) μ obtained by quotienting out the subgroup of volume-preserving diffeomorphisms Diff(M) μ . This quotient space was recently identified as the unit sphere in a Hilbert space in mathematics literature, a space with well-known geometric properties. Our framework leverages this recent result by computing the diffeomorphic path in two stages. First, we project the given diffeomorphism pair onto this sphere and then compute the geodesic path between these projected points. Second, we lift the geodesic on the sphere back to the space of diffeomerphisms, by solving a quadratic programming problem with bilinear constraints using the augmented Lagrangian technique with penalty terms. In this way, we can estimate the path of diffeomorphisms, first, staying in the space of diffeomorphisms, and second, preserving shapes/volumes in the deformed images along the path as much as possible. We have applied our framework to interpolate intermediate frames of frame-sub-sampled video sequences. In the reported experiments, our approach compares favorably with the popular Large Deformation Diffeomorphic Metric Mapping framework (LDDMM).
Miller, Michael I; Beg, M Faisal; Ceritoglu, Can; Stark, Craig
2005-07-05
The functional magnetic resonance imagery responses of declarative memory tasks in the medial temporal lobe (MTL) are examined by using large deformation diffeomorphic metric mapping (LDDMM) to remove anatomical variations across subjects. LDDMM is used to map the structures of the MTL in multiple subjects into extrinsic atlas coordinates; these same diffeomorphic mappings are used to transfer the corresponding functional data activation to the same extrinsic coordinates. The statistical power in the averaged LDDMM mapped signals is significantly increased over conventional Talairach-Tournoux averaging. Activation patterns are highly localized within the MTL. Whereas the present demonstration has been aimed at enhancing alignment within the MTL, this technique is general and can be applied throughout the brain.
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.
Deep Adaptive Log-Demons: Diffeomorphic Image Registration with Very Large Deformations
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
Khan, Ali R.; Wang, Lei
2010-01-01
Fully-automated brain segmentation methods have not been widely adopted for clinical use because of issues related to reliability, accuracy, and limitations of delineation protocol. By combining the probabilistic-based FreeSurfer (FS) method with the Large Deformation Diffeomorphic Metric Mapping (LDDMM) based label propagation method, we are able to increase reliability and accuracy, and allow for flexibility in template choice. Our method uses the automated FreeSurfer subcortical labeling to provide a coarse to fine introduction of information in the LDDMM template-based segmentation resulting in a fully-automated subcortical brain segmentation method (FS+LDDMM). One major advantage of the FS+LDDMM-based approach is that the automatically generated segmentations generated are inherently smooth, thus subsequent steps in shape analysis can directly follow without manual post-processing or loss of detail. We have evaluated our new FS+LDDMM method on several databases containing a total of 50 subjects with different pathologies, scan sequences and manual delineation protocols for labeling the basal ganglia, thalamus, and hippocampus. In healthy controls we report Dice overlap measures of 0.81, 0.83, 0.74, 0.86 and 0.75 for the right caudate nucleus, putamen, pallidum, thalamus and hippocampus respectively. We also find statistically significant improvement of accuracy in FS+LDDMM over FreeSurfer for the caudate nucleus and putamen of Huntington’s disease and Tourette’s syndrome subjects, and the right hippocampus of Schizophrenia subjects. PMID:18455931
Huang, Hao; Ceritoglu, Can; Li, Xin; Qiu, Anqi; Miller, Michael I.; van Zijl, Peter C.M.; Mori, Susumu
2008-01-01
Geometric distortion caused by B0-inhomogeneity is one of the most important problems for diffusion weighted images (DWI) using single shot, echo planar imaging (SS-EPI). In this study, large-Deformation, Diffeomorphic Metric Mapping (LDDMM) algorithm has been tested for the correction of geometric distortion in diffusion tensor images (DTI). Based on data from nine normal subjects, the amount of distortion caused by B0-susceptibility in the 3T magnet was characterized. The distortion quality was validated by manually placing landmarks in the target and DTI images before and after distortion correction. The distortion was found to be up to 15 millimeters in the population-averaged map and could be more than 20 millimeters in individual images. Both qualitative demonstration and quantitative statistical results suggest that the highly elastic geometric distortion caused by spatial inhomogeneity of the B0 field in DTI using SS-EPI can be effectively corrected by LDDMM. This postprocessing method is especially useful for correcting existent DTI data without phase maps. PMID:18499384
Ceritoglu, Can; Wang, Lei; Selemon, Lynn D.; Csernansky, John G.; Miller, Michael I.; Ratnanather, J. Tilak
2009-01-01
Our current understanding of neuroanatomical abnormalities in neuropsychiatric diseases is based largely on magnetic resonance imaging (MRI) and post mortem histological analyses of the brain. Further advances in elucidating altered brain structure in these human conditions might emerge from combining MRI and histological methods. We propose a multistage method for registering 3D volumes reconstructed from histological sections to corresponding in vivo MRI volumes from the same subjects: (1) manual segmentation of white matter (WM), gray matter (GM) and cerebrospinal fluid (CSF) compartments in histological sections, (2) alignment of consecutive histological sections using 2D rigid transformation to construct a 3D histological image volume from the aligned sections, (3) registration of reconstructed 3D histological volumes to the corresponding 3D MRI volumes using 3D affine transformation, (4) intensity normalization of images via histogram matching, and (5) registration of the volumes via intensity based large deformation diffeomorphic metric (LDDMM) image matching algorithm. Here we demonstrate the utility of our method in the transfer of cytoarchitectonic information from histological sections to identify regions of interest in MRI scans of nine adult macaque brains for morphometric analyses. LDDMM improved the accuracy of the registration via decreased distances between GM/CSF surfaces after LDDMM (0.39 ± 0.13 mm) compared to distances after affine registration (0.76 ± 0.41 mm). Similarly, WM/GM distances decreased to 0.28 ± 0.16 mm after LDDMM compared to 0.54 ± 0.39 mm after affine registration. The multistage registration method may find broad application for mapping histologically based information, for example, receptor distributions, gene expression, onto MRI volumes. PMID:20577633
Collocation for Diffeomorphic Deformations in Medical Image Registration.
Darkner, Sune; Pai, Akshay; G Liptrot, Matthew; Sporring, Jon
2017-07-21
Diffeomorphic deformation is a popular choice in medical image registration. A fundamental property of diffeomorphisms is in vertibility, implying that once the relation between two points A to B is found, then the relation B to A is given per definition. Consistency is a measure of a numerical algorithm's ability to mimic this invertibility, and achieving consistency has proven to be a challenge for many state-of-the-art algorithms.
Oishi, Kenichi; Faria, Andreia; Jiang, Hangyi; Li, Xin; Akhter, Kazi; Zhang, Jiangyang; Hsu, John T.; Miller, Michael I.; van Zijl, Peter C.M.; Albert, Marilyn; Lyketsos, Constantine G.; Woods, Roger; Toga, Arthur W.; Pike, G. Bruce; Rosa-Neto, Pedro; Evans, Alan; Mazziotta, John; Mori, Susumu
2010-01-01
The purpose of this paper is to establish single-participant white matter atlases based on diffusion tensor imaging. As one of the applications of the atlas, automated brain segmentation was performed and the accuracy was measured using Large Deformation Diffeomorphic Metric Mapping (LDDMM). High-quality diffusion tensor imaging (DTI) data from a single-participant were B0-distortion-corrected and transformed to the ICBM-152 atlas or to Talairach coordinates. The deep white matter structures, which have been previously well documented and clearly identified by DTI, were manually segmented. The superficial white matter areas beneath the cortex were defined, based on a population-averaged white matter probability map. The white matter was parcellated into 176 regions based on the anatomical labeling in the ICBM-DTI-81 atlas. The automated parcellation was achieved by warping this parcellation map to normal controls and to Alzheimer’s disease patients with severe anatomical atrophy. The parcellation accuracy was measured by a kappa analysis between the automated and manual parcellation at 11 anatomical regions. The kappa values were 0.70 for both normal controls and patients while the inter-rater reproducibility was 0.81 (controls) and 0.82 (patients), suggesting “almost perfect” agreement. A power analysis suggested that the proposed method is suitable for detecting FA and size abnormalities of the white matter in clinical studies. PMID:19385016
Ceyhan, Elvan; Beg, M. Faisal; Ceritog̃lu, Can; Wang, Lei; Morris, John C.; Csernansky, John G.; Miller, Michael I.; Ratnanather, J. Tilak
2011-01-01
The metric distance obtained from the Large Deformation Diffeomorphic Metric Mapping (LDDMM) algorithm is used to quantize changes in morphometry of brain structures due to neuropsychiatric diseases. For illustrative purposes we consider changes in hippocampal morphometry (shape and size) due to very mild dementia of the Alzheimer type (DAT). LDDMM, which was previously used to calculate dense one-to-one correspondence vector fields between hippocampal shapes, measures the morphometric differences with respect to a template hippocampus by assigning metric distances on the space of anatomical images thereby allowing for direct comparison of morphometric differences. We characterize what information the metric distances provide in terms of size and shape given the hippocampal, brain and intracranial volumes. We demonstrate that metric distance is a measure of morphometry (i.e., shape and size) but mostly a measure of shape, while volume is mostly a measure of size. Moreover, we show how metric distances can be used in cross-sectional, longitudinal analysis, as well as left-right asymmetry comparisons, and provide how the metric distances can serve as a discriminative tool using logistic regression. Thus, we show that metric distances with respect to a template computed via LDDMM can be a powerful tool in detecting differences in shape. PMID:21345652
Sakamoto, Ryo; Mori, Susumu; Miller, Michael I; Okada, Tomohisa; Togashi, Kaori
2014-01-01
To evaluate the accuracy of advanced non-linear registration of serial lung Computed Tomography (CT) images using Large Deformation Diffeomorphic Metric Mapping (LDDMM). FIFTEEN CASES OF LUNG CANCER WITH SERIAL LUNG CT IMAGES (INTERVAL: 62.2±26.9 days) were used. After affine transformation, three dimensional, non-linear volume registration was conducted using LDDMM with or without cascading elasticity control. Registration accuracy was evaluated by measuring the displacement of landmarks placed on vessel bifurcations for each lung segment. Subtraction images and Jacobian color maps, calculated from the transformation matrix derived from image warping, were generated, which were used to evaluate time-course changes of the tumors. The average displacement of landmarks was 0.02±0.16 mm and 0.12±0.60 mm for proximal and distal landmarks after LDDMM transformation with cascading elasticity control, which was significantly smaller than 3.11±2.47 mm and 3.99±3.05 mm, respectively, after affine transformation. Emerged or vanished nodules were visualized on subtraction images, and enlarging or shrinking nodules were displayed on Jacobian maps enabled by highly accurate registration of the nodules using LDDMM. However, some residual misalignments were observed, even with non-linear transformation when substantial changes existed between the image pairs. LDDMM provides accurate registration of serial lung CT images, and temporal subtraction images with Jacobian maps help radiologists to find changes in pulmonary nodules.
Individualized diffeomorphic mapping of brains with large cortical infarcts.
Soon, Hock Wei; Qiu, Anqi
2015-01-01
Whole brain mapping of stroke patients with large cortical infarcts is not trivial due to the complexity of infarcts' anatomical location and appearance in magnetic resonance image. In this study, we proposed an individualized diffeomorphic mapping framework for solving this problem. This framework is based on our recent work of large deformation diffeomorphic metric mapping (LDDMM) in Du et al. (2011) and incorporates anatomical features, such as sulcal/gyral curves, cortical surfaces, brain intensity image, and masks of infarcted regions, in order to align a normal brain to the brain of stroke patients. We applied this framework to synthetic data and data of stroke patients and validated the mapping accuracy in terms of the alignment of gyral/sulcal curves, sulcal regions, and brain segmentation. Our results revealed that this framework provided comparable mapping results for stroke patients and healthy controls, suggesting the importance of incorporating individualized anatomical features in whole brain mapping of brains with large cortical infarcts.
Homogeneous Yang–Baxter deformations as generalized diffeomorphisms
NASA Astrophysics Data System (ADS)
Sakamoto, Jun-ichi; Sakatani, Yuho; Yoshida, Kentaroh
2017-10-01
Yang–Baxter (YB) deformations of string sigma model provide deformed target spaces. We propose that homogeneous YB deformations always lead to a certain class of β-twisted backgrounds and represent the bosonic part of the supergravity fields in terms of the classical r-matrix associated with the YB deformation. We then show that various β-twisted backgrounds can be realized by considering generalized diffeomorphisms in the undeformed background. Our result extends the notable relation between the YB deformations and (non-commuting) TsT transformations. We also discuss more general deformations beyond the YB deformations.
Large gravitons and near-horizon diffeomorphisms
NASA Astrophysics Data System (ADS)
Carneiro da Cunha, Bruno; Rudrigues, Filipe
2017-04-01
Usual gauge fixing procedures in classical general relativity rely on the existence of solutions of a second order wave equation. We propose to use these equations to relate asymptotic symmetries at infinity to asymptotic symmetries of a black hole horizon, in tune with recent proposals. We illustrate the construction for the Bañados-Teitelboim-Zanelli (BTZ) and four-dimensional Kerr black holes. We find in both cases a realization of the group of diffeomorphisms of the real line.
Inferring brain variability from diffeomorphic deformations of currents: an integrative approach
Durrleman, Stanley; Pennec, Xavier; Trouvé, Alain; Thompson, Paul; Ayache, Nicholas
2008-01-01
In the context of computational anatomy, one aims at understanding and modelling the anatomy of the brain and its variations across a population. This geometrical variability is often measured from precisely defined anatomical landmarks such as sulcal lines or meshes of brain structures. This requires (1) to compare geometrical objects without introducing too many non realistic priors and (2) to retrieve the variability of the whole brain from the variability of the landmarks. We propose, in this paper, to infer a statistical brain model from the consistent integration of variability of sulcal lines. The similarity between two sets of lines is measured by a distance on currents that does not assume any type of point correspondences and it is not sensitive to the sampling of lines. This shape similarity measure is used in a diffeomorphic registrations which retrieves a single deformation of the whole 3D space. This diffeomorphism integrates the variability of all lines in a as spatially consistent manner as possible. Based on repeated pairwise registrations on a large database, we learn how the mean anatomy varies in a population by computing statistics on diffeomorphisms. Whereas usual methods lead to descriptive measures of variability, such as variability maps or statistical tests, our model is generative: we can simulate new observations according to the learned probability law on deformations. In practice, this variability captured by the model is synthesized in the principal modes of deformations. As a deformation is dense, we can also apply it to other anatomical structures defined in the template space. This is illustrated the action of the principal modes of deformations to a mean cortical surface. Eventually, our current-based diffeomorphic registration (CDR) approach is carefully compared to a pointwise line correspondences (PLC) method. Variability measures are computed with both methods on the same dataset of sulcal lines. The results suggest that we
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.
Reaungamornrat, Sureerat; De Silva, Tharindu; Uneri, Ali; Vogt, Sebastian; Kleinszig, Gerhard; Khanna, Akhil J; Wolinsky, Jean-Paul; Prince, Jerry L.
2016-01-01
Intraoperative localization of target anatomy and critical structures defined in preoperative MR/CT images can be achieved through the use of multimodality deformable registration. 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. The method, called MIND Demons, finds a deformation field between two images by optimizing an energy functional that incorporates both the forward and inverse deformations, smoothness on the integrated velocity fields, a modality-insensitive similarity function suitable to multimodality images, and smoothness on the diffeomorphisms themselves. Direct optimization without relying on the exponential map and stationary velocity field approximation 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, phantom experiments, and clinical studies emulating application in image-guided spine surgery, and results were compared to mutual information (MI) free-form deformation (FFD), local MI (LMI) FFD, normalized MI (NMI) Demons, and MIND with a diffusion-based registration method (MIND-elastic). The method yielded sub-voxel invertibility (0.008 mm) and nonzero-positive Jacobian determinants. It also showed improved registration accuracy in comparison to the reference methods, with mean target registration error (TRE) of 1.7 mm compared to 11.3, 3.1, 5.6, and 2.4 mm for MI FFD, LMI FFD, NMI Demons, and MIND-elastic methods, respectively. Validation in clinical studies demonstrated realistic deformations with sub-voxel TRE in cases of cervical, thoracic, and lumbar spine. PMID:27295656
Reaungamornrat, Sureerat; De Silva, Tharindu; Uneri, Ali; Vogt, Sebastian; Kleinszig, Gerhard; Khanna, Akhil J; Wolinsky, Jean-Paul; Prince, Jerry L; Siewerdsen, Jeffrey H
2016-11-01
Intraoperative localization of target anatomy and critical structures defined in preoperative MR/CT images can be achieved through the use of multimodality deformable registration. 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. The method, called MIND Demons, finds a deformation field between two images by optimizing an energy functional that incorporates both the forward and inverse deformations, smoothness on the integrated velocity fields, a modality-insensitive similarity function suitable to multimodality images, and smoothness on the diffeomorphisms themselves. Direct optimization without relying on the exponential map and stationary velocity field approximation 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, phantom experiments, and clinical studies emulating application in image-guided spine surgery, and results were compared to mutual information (MI) free-form deformation (FFD), local MI (LMI) FFD, normalized MI (NMI) Demons, and MIND with a diffusion-based registration method (MIND-elastic). The method yielded sub-voxel invertibility (0.008 mm) and nonzero-positive Jacobian determinants. It also showed improved registration accuracy in comparison to the reference methods, with mean target registration error (TRE) of 1.7 mm compared to 11.3, 3.1, 5.6, and 2.4 mm for MI FFD, LMI FFD, NMI Demons, and MIND-elastic methods, respectively. Validation in clinical studies demonstrated realistic deformations with sub-voxel TRE in cases of cervical, thoracic, and lumbar spine.
Observer’s observables. Residual diffeomorphisms
NASA Astrophysics Data System (ADS)
Duch, P.; Lewandowski, J.; Świeżewski, J.
2017-06-01
We investigate the fate of diffeomorphisms when the radial gauge is imposed in canonical general relativity. As shown elsewhere, the radial gauge is closely related to the observer’s observables. These observables are invariant under a large subgroup of diffeomorphisms which results in their usefulness for canonical general relativity. There are, however, some diffeomorphisms, called residual diffeomorphisms, which might be ‘observed’ by the observer as they do not preserve her observables. The present paper is devoted to the analysis of these diffeomorphisms in the case of the spatial and spacetime radial gauges. Although the residual diffeomorphisms do not form a subgroup of all diffeomorphisms, we show that their induced action in the phase space does form a group. We find the generators of the induced transformations and compute the structure functions of the algebras they form. The obtained algebras are deformations of the algebra of the Euclidean group and the algebra of the Poincaré group in the spatial and spacetime case, respectively. In both cases the deformation depends only on the Riemann curvature tensor and in particular vanishes when the space or spacetime is flat.
Multiresolution Diffeomorphic Mapping for Cortical Surfaces.
Tan, Mingzhen; Qiu, Anqi
2015-01-01
Due to the convoluted folding pattern of the cerebral cortex, accurate alignment of cortical surfaces remains challenging. In this paper, we present a multiresolution diffeomorphic surface mapping algorithm under the framework of large deformation diffeomorphic metric mapping (LDDMM). Our algorithm takes advantage of multiresolution analysis (MRA) for surfaces and constructs cortical surfaces at multiresolution. This family of multiresolution surfaces are used as natural sparse priors of the cortical anatomy and provide the anchor points where the parametrization of deformation vector fields is supported. This naturally constructs tangent bundles of diffeomorphisms at different resolution levels and hence generates multiresolution diffeomorphic transformation. We show that our construction of multiresolution LDDMM surface mapping can potentially reduce computational cost and improves the mapping accuracy of cortical surfaces.
De Craene, Mathieu; Piella, Gemma; Camara, Oscar; Duchateau, Nicolas; Silva, Etelvino; Doltra, Adelina; D'hooge, Jan; Brugada, Josep; Sitges, Marta; Frangi, Alejandro F
2012-02-01
This paper presents a new registration algorithm, called Temporal Diffeomorphic Free Form Deformation (TDFFD), and its application to motion and strain quantification from a sequence of 3D ultrasound (US) images. The originality of our approach resides in enforcing time consistency by representing the 4D velocity field as the sum of continuous spatiotemporal B-Spline kernels. The spatiotemporal displacement field is then recovered through forward Eulerian integration of the non-stationary velocity field. The strain tensor is computed locally using the spatial derivatives of the reconstructed displacement field. The energy functional considered in this paper weighs two terms: the image similarity and a regularization term. The image similarity metric is the sum of squared differences between the intensities of each frame and a reference one. Any frame in the sequence can be chosen as reference. The regularization term is based on the incompressibility of myocardial tissue. TDFFD was compared to pairwise 3D FFD and 3D+t FFD, both on displacement and velocity fields, on a set of synthetic 3D US images with different noise levels. TDFFD showed increased robustness to noise compared to these two state-of-the-art algorithms. TDFFD also proved to be more resistant to a reduced temporal resolution when decimating this synthetic sequence. Finally, this synthetic dataset was used to determine optimal settings of the TDFFD algorithm. Subsequently, TDFFD was applied to a database of cardiac 3D US images of the left ventricle acquired from 9 healthy volunteers and 13 patients treated by Cardiac Resynchronization Therapy (CRT). On healthy cases, uniform strain patterns were observed over all myocardial segments, as physiologically expected. On all CRT patients, the improvement in synchrony of regional longitudinal strain correlated with CRT clinical outcome as quantified by the reduction of end-systolic left ventricular volume at follow-up (6 and 12months), showing the potential
Principal Component Based Diffeomorphic Surface Mapping
Younes, Laurent; Miller, Michael I.
2013-01-01
We present a new diffeomorphic surface mapping algorithm under the framework of large deformation diffeomorphic metric mapping (LDDMM). Unlike existing LDDMM approaches, this new algorithm reduces the complexity of the estimation of diffeomorphic transformations by incorporating a shape prior in which a nonlinear diffeomorphic shape space is represented by a linear space of initial momenta of diffeomorphic geodesic flows from a fixed template. In addition, for the first time, the diffeomorphic mapping is formulated within a decision-theoretic scheme based on Bayesian modeling in which an empirical shape prior is characterized by a low dimensional Gaussian distribution on initial momentum. This is achieved using principal component analysis (PCA) to construct the eigenspace of the initial momentum. A likelihood function is formulated as the conditional probability of observing surfaces given any particular value of the initial momentum, which is modeled as a random field of vector-valued measures characterizing the geometry of surfaces. We define the diffeomorphic mapping as a problem that maximizes a posterior distribution of the initial momentum given observable surfaces over the eigenspace of the initial momentum. We demonstrate the stability of the initial momentum eigenspace when altering training samples using a bootstrapping method. We then validate the mapping accuracy and show robustness to outliers whose shape variation is not incorporated into the shape prior. PMID:21937344
Principal component based diffeomorphic surface mapping.
Qiu, Anqi; Younes, Laurent; Miller, Michael I
2012-02-01
We present a new diffeomorphic surface mapping algorithm under the framework of large deformation diffeomorphic metric mapping (LDDMM). Unlike existing LDDMM approaches, this new algorithm reduces the complexity of the estimation of diffeomorphic transformations by incorporating a shape prior in which a nonlinear diffeomorphic shape space is represented by a linear space of initial momenta of diffeomorphic geodesic flows from a fixed template. In addition, for the first time, the diffeomorphic mapping is formulated within a decision-theoretic scheme based on Bayesian modeling in which an empirical shape prior is characterized by a low dimensional Gaussian distribution on initial momentum. This is achieved using principal component analysis (PCA) to construct the eigenspace of the initial momentum. A likelihood function is formulated as the conditional probability of observing surfaces given any particular value of the initial momentum, which is modeled as a random field of vector-valued measures characterizing the geometry of surfaces. We define the diffeomorphic mapping as a problem that maximizes a posterior distribution of the initial momentum given observable surfaces over the eigenspace of the initial momentum. We demonstrate the stability of the initial momentum eigenspace when altering training samples using a bootstrapping method. We then validate the mapping accuracy and show robustness to outliers whose shape variation is not incorporated into the shape prior.
Zhou, Lu; Zhou, Linghong; Zhang, Shuxu; Zhen, Xin; Yu, Hui; Zhang, Guoqian; Wang, Ruihao
2014-01-01
Deformable image registration (DIR) was widely used in radiation therapy, such as in automatic contour generation, dose accumulation, tumor growth or regression analysis. To achieve higher registration accuracy and faster convergence, an improved 'diffeomorphic demons' registration algorithm was proposed and validated. Based on Brox et al.'s gradient constancy assumption and Malis's efficient second-order minimization (ESM) algorithm, a grey value gradient similarity term and a transformation error term were added into the demons energy function, and a formula was derived to calculate the update of transformation field. The limited Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm was used to optimize the energy function so that the iteration number could be determined automatically. The proposed algorithm was validated using mathematically deformed images and physically deformed phantom images. Compared with the original 'diffeomorphic demons' algorithm, the registration method proposed achieve a higher precision and a faster convergence speed. Due to the influence of different scanning conditions in fractionated radiation, the density range of the treatment image and the planning image may be different. In such a case, the improved demons algorithm can achieve faster and more accurate radiotherapy.
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.
Temporal diffeomorphic free-form deformation for strain quantification in 3D-US images.
De Craene, Mathieu; Piella, Gemma; Duchateau, Nicolas; Silva, Etel; Doltra, Adelina; Gao, Hang; D'hooge, Jan; Camara, Oscar; Brugada, Josep; Sitges, Marta; Frangi, Alejandro F
2010-01-01
This paper presents a new diffeomorphic temporal registration algorithm and its application to motion and strain quantification from a temporal sequence of 3D images. The displacement field is computed by forward eulerian integration of a non-stationary velocity field. The originality of our approach resides in enforcing time consistency by representing the velocity field as a sum of continuous spatiotemporal B-Spline kernels. The accuracy of the developed diffeomorphic technique was first compared to a simple pairwise strategy on synthetic US images with known ground truth motion and with several noise levels, being the proposed algorithm more robust to noise than the pairwise case. Our algorithm was then applied to a database of cardiac 3D+t Ultrasound (US) images of the left ventricle acquired from eight healthy volunteers and three Cardiac Resynchronization Therapy (CRT) patients. On healthy cases, the measured regional strain curves provided uniform strain patterns over all myocardial segments in accordance with clinical literature. On CRT patients, the obtained normalization of the strain pattern after CRT agreed with clinical outcome for the three cases.
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
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.
Left-invariant metrics for diffeomorphic image registration with spatially-varying regularisation.
Schmah, Tanya; Risser, Laurent; Vialard, François-Xavier
2013-01-01
We present a new framework for diffeomorphic image registration which supports natural interpretations of spatially-varying metrics. This framework is based on left-invariant diffeomorphic metrics (LIDM) and is closely related to the now standard large deformation diffeomorphic metric mapping (LDDMM). We discuss the relationship between LIDM and LDDMM and introduce a computationally convenient class of spatially-varying metrics appropriate for both frameworks. Finally, we demonstrate the effectiveness of our method on a 2D toy example and on the 40 3D brain images of the LPBA40 dataset.
Unbiased atlas formation via large deformations metric mapping.
Lorenzen, Peter; Davis, Brad; Joshi, Sarang
2005-01-01
The construction of population atlases is a key issue in medical image analysis, and particularly in brain mapping. Large sets of images are mapped into a common coordinate system to study intra-population variability and inter-population differences, to provide voxel-wise mapping of functional sites, and to facilitate tissue and object segmentation via registration of anatomical labels. We formulate the unbiased atlas construction problem as a Fréchet mean estimation in the space of diffeomorphisms via large deformations metric mapping. A novel method for computing constant speed velocity fields and an analysis of atlas stability and robustness using entropy are presented. We address the question: how many images are required to build a stable brain atlas?
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.
Mang, A; Toma, A; Schuetz, T A; Becker, S; Buzug, T M
2012-01-01
In the present paper a novel computational framework for modeling tumor induced brain deformation as a biophysical prior for non-rigid image registration is described. More precisely, we aim at providing a generic building block for non-rigid image registration that can be used to resolve inherent irregularities in non-diffeomorphic registration problems that naturally arise in serial and cross-population brain tumor imaging studies due to the presence (or progression) of pathology. The model for the description of brain cancer dynamics on a tissue level is based on an initial boundary value problem (IBVP). The IBVP follows the accepted assumption that the progression of primary brain tumors on a tissue level is governed by proliferation and migration of cancerous cells into surrounding healthy tissue. The model of tumor induced brain deformation is phrased as a parametric, constrained optimization problem. As a basis of comparison and to demonstrate generalizability additional soft constraints (penalties) are considered. A back-tracking line search is implemented in conjunction with a limited memory Broyden-Fletcher-Goldfarb-Shanno (LBFGS) method in order to handle the numerically delicate log-barrier strategy for confining volume change. Numerical experiments are performed to test the flexible control of the computed deformation patterns in terms of varying model parameters. The results are qualitatively and quantitatively related to patterns in patient individual magnetic resonance imaging data. Numerical experiments demonstrate the flexible control of the computed deformation patterns. This in turn strongly suggests that the model can be adapted to patient individual imaging patterns of brain tumors. Qualitative and quantitative comparison of the computed cancer profiles to patterns in medical imaging data of an exemplary patient demonstrates plausibility. The designed optimization problem is based on computational tools widely used in non-rigid image
Du, Jia; Goh, Alvina; Qiu, Anqi
2012-05-01
In this paper, we propose a novel large deformation diffeomorphic registration algorithm to align high angular resolution diffusion images (HARDI) characterized by orientation distribution functions (ODFs). Our proposed algorithm seeks an optimal diffeomorphism of large deformation between two ODF fields in a spatial volume domain and at the same time, locally reorients an ODF in a manner such that it remains consistent with the surrounding anatomical structure. To this end, we first review the Riemannian manifold of ODFs. We then define the reorientation of an ODF when an affine transformation is applied and subsequently, define the diffeomorphic group action to be applied on the ODF based on this reorientation. We incorporate the Riemannian metric of ODFs for quantifying the similarity of two HARDI images into a variational problem defined under the large deformation diffeomorphic metric mapping framework. We finally derive the gradient of the cost function in both Riemannian spaces of diffeomorphisms and the ODFs, and present its numerical implementation. Both synthetic and real brain HARDI data are used to illustrate the performance of our registration algorithm.
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.
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
Diffeomorphic registration using B-splines.
Rueckert, Daniel; Aljabar, Paul; Heckemann, Rolf A; Hajnal, Joseph V; Hammers, Alexander
2006-01-01
In this paper we propose a diffeomorphic non-rigid registration algorithm based on free-form deformations (FFDs) which are modelled by B-splines. In contrast to existing non-rigid registration methods based on FFDs the proposed diffeomorphic non-rigid registration algorithm based on free-form deformations (FFDs) which are modelled by B-splines. To construct a diffeomorphic transformation we compose a sequence of free-form deformations while ensuring that individual FFDs are one-to-one transformations. We have evaluated the algorithm on 20 normal brain MR images which have been manually segmented into 67 anatomical structures. Using the agreement between manual segmentation and segmentation propagation as a measure of registration quality we have compared the algorithm to an existing FFD registration algorithm and a modified FFD registration algorithm which penalises non-diffeomorphic transformations. The results show that the proposed algorithm generates diffeomorphic transformations while providing similar levels of performance as the existing FFD registration algorithm in terms of registration accuracy.
Diffeomorphisms of Quantum Fields
NASA Astrophysics Data System (ADS)
Kreimer, Dirk; Yeats, Karen
2017-06-01
We study field diffeomorphisms φ (x)\\to F(φ (x))=a0φ (x)+a1φ 2(x)+\\ldots ={\\sum }_{j+0}^{\\infty } aj φ ^{j+1}, for free and interacting quantum fields Φ. We find that the theory is invariant under such diffeomorphisms if and only if kinematic renormalization schemes are used.
Bayesian estimation of regularization and atlas building in diffeomorphic image registration.
Zhang, Miaomiao; Singh, Nikhil; Fletcher, P Thomas
2013-01-01
This paper presents a generative Bayesian model for diffeomorphic image registration and atlas building. We develop an atlas estimation procedure that simultaneously estimates the parameters controlling the smoothness of the diffeomorphic transformations. To achieve this, we introduce a Monte Carlo Expectation Maximization algorithm, where the expectation step is approximated via Hamiltonian Monte Carlo sampling on the manifold of diffeomorphisms. An added benefit of this stochastic approach is that it can successfully solve difficult registration problems involving large deformations, where direct geodesic optimization fails. Using synthetic data generated from the forward model with known parameters, we demonstrate the ability of our model to successfully recover the atlas and regularization parameters. We also demonstrate the effectiveness of the proposed method in the atlas estimation problem for 3D brain images.
Splines for diffeomorphic image regression.
Singh, Nikhil; Niethammer, Marc
2014-01-01
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.
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
Finite-Dimensional Lie Algebras for Fast Diffeomorphic Image Registration.
Zhang, Miaomiao; Fletcher, P Thomas
2015-01-01
This paper presents a fast geodesic shooting algorithm for diffeomorphic image registration. We first introduce a novel finite-dimensional Lie algebra structure on the space of bandlimited velocity fields. We then show that this space can effectively represent initial velocities for diffeomorphic image registration at much lower dimensions than typically used, with little to no loss in registration accuracy. We then leverage the fact that the geodesic evolution equations, as well as the adjoint Jacobi field equations needed for gradient descent methods, can be computed entirely in this finite-dimensional Lie algebra. The result is a geodesic shooting method for large deformation metric mapping (LDDMM) that is dramatically faster and less memory intensive than state-of-the-art methods. We demonstrate the effectiveness of our model to register 3D brain images and compare its registration accuracy, run-time, and memory consumption with leading LDDMM methods. We also show how our algorithm breaks through the prohibitive time and memory requirements of diffeomorphic atlas building.
Diffeomorphic registration using geodesic shooting and Gauss–Newton optimisation
Ashburner, John; Friston, Karl J.
2011-01-01
This paper presents a nonlinear image registration algorithm based on the setting of Large Deformation Diffeomorphic Metric Mapping (LDDMM), but with a more efficient optimisation scheme — both in terms of memory required and the number of iterations required to reach convergence. Rather than perform a variational optimisation on a series of velocity fields, the algorithm is formulated to use a geodesic shooting procedure, so that only an initial velocity is estimated. A Gauss–Newton optimisation strategy is used to achieve faster convergence. The algorithm was evaluated using freely available manually labelled datasets, and found to compare favourably with other inter-subject registration algorithms evaluated using the same data. PMID:21216294
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. Copyright © 2011 Elsevier Inc. All rights reserved.
Du, Jia; Younes, Laurent; Qiu, Anqi
2011-01-01
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 Actuator Count MEMS Deformable Mirror Development
2010-06-07
Large-actuator-count deformable mirrors (DM) are essential for high-contrast imaging systems NASA is developing for exoplanet detection. These same...applications: Nulling coronagraphs for exoplanet imaging, Atmospheric turbulence compensation for free-space laser communication, laser guide star
Embedding smooth diffeomorphisms in flows
NASA Astrophysics Data System (ADS)
Zhang, Xiang
In this paper we study the problem on embedding germs of smooth diffeomorphisms in flows in higher dimensional spaces. First we prove the existence of embedding vector fields for a local diffeomorphism with its nonlinear term a resonant polynomial. Then using this result and the normal form theory, we obtain a class of local C diffeomorphisms for k∈N∪{∞,ω} which admit embedding vector fields with some smoothness. Finally we prove that for any k∈N∪{∞} under the coefficient topology the subset of local C diffeomorphisms having an embedding vector field with some smoothness is dense in the set of all local C diffeomorphisms.
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
Diffeomorphic metric surface mapping in subregion of the superior temporal gyrus.
Vaillant, Marc; Qiu, Anqi; Glaunès, Joan; Miller, Michael I
2007-02-01
This paper describes the application of large deformation diffeomorphic metric mapping to cortical surfaces based on the shape and geometric properties of subregions of the superior temporal gyrus in the human brain. The anatomical surfaces of the cortex are represented as triangulated meshes. The diffeomorphic matching algorithm is implemented by defining a norm between the triangulated meshes, based on the algorithms of Vaillant and Glaunès. The diffeomorphic correspondence is defined as a flow of the extrinsic three dimensional coordinates containing the cortical surface that registers the initial and target geometry by minimizing the norm. The methods are demonstrated in 40 high-resolution MRI cortical surfaces of planum temporale (PT) constructed from subsets of the superior temporal gyrus (STG). The effectiveness of the algorithm is demonstrated via the Euclidean positional distance, distance of normal vectors, and curvature before and after the surface matching as well as the comparison with a landmark matching algorithm. The results demonstrate that both the positional and shape variability of the anatomical configurations are being represented by the diffeomorphic maps.
Diffeomorphism invariance and black hole entropy
NASA Astrophysics Data System (ADS)
Huang, Chao-Guang; Guo, Han-Ying; Wu, Xiaoning
2003-11-01
The Noether-charge and the Hamiltonian realizations for the diff(M) algebra in diffeomorphism-invariant gravitational theories without a cosmological constant in any dimension are studied in a covariant formalism. We analyze how the Hamiltonian functionals form the diff(M) algebra under the Poisson brackets and show how the Noether charges with respect to the diffeomorphism generated by the vector fields and their variations in n-dimensional general relativity form this algebra. The asymptotic behaviors of vector fields generating diffeomorphism of the manifold with boundaries are discussed. It is shown that the “central extension” for a large class of vector fields is always zero on the Killing horizon. We also check whether choosing the vector fields near the horizon may pick up the Virasoro algebra. The conclusion is unfortunately negative in any dimension.
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.
Non-parametric diffeomorphic image registration with the demons algorithm.
Vercauteren, Tom; Pennec, Xavier; Perchant, Aymeric; Ayache, Nicholas
2007-01-01
We propose a non-parametric diffeomorphic image registration algorithm based on Thirion's demons algorithm. The demons algorithm can be seen as an optimization procedure on the entire space of displacement fields. The main idea of our algorithm is to adapt this procedure 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 free form deformations 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 true ones in terms of Jacobians.
Diffeomorphic brain registration under exhaustive sulcal constraints.
Auzias, Guillaume; Colliot, Olivier; Glaunès, Joan Alexis; Perrot, Matthieu; Mangin, Jean-François; Trouvé, Alain; Baillet, Sylvain
2011-06-01
The alignment and normalization of individual brain structures is a prerequisite for group-level analyses of structural and functional neuroimaging data. The techniques currently available are either based on volume and/or surface attributes, with limited insight regarding the consistent alignment of anatomical landmarks across individuals. This article details a global, geometric approach that performs the alignment of the exhaustive sulcal imprints (cortical folding patterns) across individuals. This DIffeomorphic Sulcal-based COrtical (DISCO) technique proceeds to the automatic extraction, identification and simplification of sulcal features from T1-weighted Magnetic Resonance Image (MRI) series. These features are then used as control measures for fully-3-D diffeomorphic deformations. Quantitative and qualitative evaluations show that DISCO correctly aligns the sulcal folds and gray and white matter volumes across individuals. The comparison with a recent, iconic diffeomorphic approach (DARTEL) highlights how the absence of explicit cortical landmarks may lead to the misalignment of cortical sulci. We also feature DISCO in the automatic design of an empirical sulcal template from group data. We also demonstrate how DISCO can efficiently be combined with an image-based deformation (DARTEL) to further improve the consistency and accuracy of alignment performances. Finally, we illustrate how the optimized alignment of cortical folds across subjects improves sensitivity in the detection of functional activations in a group-level analysis of neuroimaging data.
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.
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 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 30 deg or 15 deg off-axis plies occured in several events. All laminates exhibited bimodular elastic properties. Using empirically determined flexural properties, a finite element analysis was reasonably accurate in predicting the static and dynamic deformation response.
Large deformation mechanics of the enucleated eyeball.
Taber, L A
1984-08-01
Large deformation of enucleated pig eyeballs under rigid cylindrical indenters was studied analytically and experimentally. The analytic model for the eyeball consists of a fluid-filled spherical membrane composed of an incompressible, elastic material with an exponential strain energy function. The Rayleigh-Ritz technique provided an approximate solution via a potential energy formulation. Comparison with results from tests on eyeballs and a water-filled rubber (Mooney-Rivlin) shell shows good agreement at large deflection, where membrane action dominates. Due to the highly nonlinear stress-strain relations for the sclera, the load remains relatively small until the indenter displacement approaches 40-60 percent of the eyeball radius, and then the load increases rapidly. Depending on the indenter size, either a perforation or a rupture type of failure occurs.
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
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.
Large primary leiomyoma causing progressive cervical deformity
Al-Habib, Amro; Elgamal, Essam A.; Aldhahri, Saleh; Alokaili, Riyadh; AlShamrani, Rami; Abobotain, Abdulaziz; AlRaddadi, Khulood; Alkhalidi, Hisham
2016-01-01
Leiomyomas are benign smooth tumors that rarely affect the neck area. Complete surgical resection is the treatment of choice. Here, we describe a 13-year-old girl with a large leiomyoma of the neck, which increased in size after incomplete resection. The tumor caused progressive cervical kyphotic deformity, difficulty breathing and severe malnourishment. The tumor was resected successfully in a second surgery, and the patient is stable after 3 years of follow-up. Histopathologically, the tumor was consistent with leiomyoma and showed strong reactivity to specific smooth muscle markers, such as desmin and caldesmon. This is the second reported case demonstrating massive growth of a leiomyoma, with emphasis on complete resection from the beginning. PMID:27887011
A contact layer element for large deformations
NASA Astrophysics Data System (ADS)
Weißenfels, C.; Wriggers, P.
2015-05-01
In many contact situations the material behavior of one contact member strongly influences the force acting between the two bodies. Unfortunately standard friction models cannot reproduce all of these material effects at the contact layer and often continuum interface elements are used instead. These elements are intrinsically tied to the fixed grid and hence cannot be used in large sliding simulations. Due to the shortcomings of the standard contact formulations and of the interface elements a new type of a contact layer element is developed in this work. The advantages of this element are the direct implementation of continuum models into the contact formulation and the application to arbitrary large deformations. Showing a relation between continuum and contact kinematics based on the solid-shell concept the new contact element is at the end a natural extension of the standard contact formulations into 3D. Two examples show that the continuum behavior can be exactly reproduced at the contact surface even in large sliding situations using this contact layer element. For the discretization of the new contact element the Mortar method is chosen exemplary, but it can be combined with all kinds of contact formulations.
Risser, Laurent; Vialard, François-Xavier; Baluwala, Habib Y; Schnabel, Julia A
2013-02-01
In this paper, we propose a new strategy for modelling sliding conditions when registering 3D images in a piecewise-diffeomorphic framework. More specifically, our main contribution is the development of a mathematical formalism to perform Large Deformation Diffeomorphic Metric Mapping registration with sliding conditions. We also show how to adapt this formalism to the LogDemons diffeomorphic registration framework. We finally show how to apply this strategy to estimate the respiratory motion between 3D CT pulmonary images. Quantitative tests are performed on 2D and 3D synthetic images, as well as on real 3D lung images from the MICCAI EMPIRE10 challenge. Results show that our strategy estimates accurate mappings of entire 3D thoracic image volumes that exhibit a sliding motion, as opposed to conventional registration methods which are not capable of capturing discontinuous deformations at the thoracic cage boundary. They also show that although the deformations are not smooth across the location of sliding conditions, they are almost always invertible in the whole image domain. This would be helpful for radiotherapy planning and delivery. Crown Copyright © 2012. Published by Elsevier B.V. All rights reserved.
DR-BUDDI: diffeomorphic registration for blip up-down diffusion imaging.
Irfanoglu, M Okan; Modi, Pooja; Nayak, Amritha; Knutsen, Andrew; Sarlls, Joelle; Pierpaoli, Carlo
2014-01-01
In this work we propose a novel method to correct echo planar imaging (EPI) distortions in diffusion MRI data acquired with reversed phase encoding directions ("blip-up blip-down" acquisitions). The transformation model is symmetric, diffeomorphic and capable of capturing large deformations. It can take advantage of a structural MRI target and include the contribution of diffusion weighted images, in addition to EPI images acquired without diffusion sensitization. The proposed correction significantly outperform existing strategies, assuring anatomically accurate characterization of the orientation, mean diffusivity, and anisotropy of white matter structures in the human brain.
Spatially-varying metric learning for diffeomorphic image registration: a variational framework.
Vialard, François-Xavier; Risser, Laurent
2014-01-01
This paper introduces a variational strategy to learn spatially-varying metrics on large groups of images, in the Large Deformation Diffeomorphic Metric Mapping (LDDMM) framework. Spatially-varying metrics we learn not only favor local deformations but also correlated deformations in different image regions and in different directions. In addition, metric parameters can be efficiently estimated using a gradient descent method. We first describe the general strategy and then show how to use it on 3D medical images with reasonable computational ressources. Our method is assessed on the 3D brain images of the LPBA40 dataset. Results are compared with ANTS-SyN and LDDMM with spatially-homogeneous metrics.
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}.
Sakamoto, Ryo; Yakami, Masahiro; Fujimoto, Koji; Nakagomi, Keita; Kubo, Takeshi; Emoto, Yutaka; Akasaka, Thai; Aoyama, Gakuto; Yamamoto, Hiroyuki; Miller, Michael I; Mori, Susumu; Togashi, Kaori
2017-07-03
Purpose To determine the improvement of radiologist efficiency and performance in the detection of bone metastases at serial follow-up computed tomography (CT) by using a temporal subtraction (TS) technique based on an advanced nonrigid image registration algorithm. Materials and Methods This retrospective study was approved by the institutional review board, and informed consent was waived. CT image pairs (previous and current scans of the torso) in 60 patients with cancer (primary lesion location: prostate, n = 14; breast, n = 16; lung, n = 20; liver, n = 10) were included. These consisted of 30 positive cases with a total of 65 bone metastases depicted only on current images and confirmed by two radiologists who had access to additional imaging examinations and clinical courses and 30 matched negative control cases (no bone metastases). Previous CT images were semiautomatically registered to current CT images by the algorithm, and TS images were created. Seven radiologists independently interpreted CT image pairs to identify newly developed bone metastases without and with TS images with an interval of at least 30 days. Jackknife free-response receiver operating characteristics (JAFROC) analysis was conducted to assess observer performance. Reading time was recorded, and usefulness was evaluated with subjective scores of 1-5, with 5 being extremely useful and 1 being useless. Significance of these values was tested with the Wilcoxon signed-rank test. Results The subtraction images depicted various types of bone metastases (osteolytic, n = 28; osteoblastic, n = 26; mixed osteolytic and blastic, n = 11) as temporal changes. The average reading time was significantly reduced (384.3 vs 286.8 seconds; Wilcoxon signed rank test, P = .028). The average figure-of-merit value increased from 0.758 to 0.835; however, this difference was not significant (JAFROC analysis, P = .092). The subjective usefulness survey response showed a median score of 5 for use of the technique (range, 3-5). Conclusion TS images obtained from serial CT scans using nonrigid registration successfully depicted newly developed bone metastases and showed promise for their efficient detection. (©) RSNA, 2017 Online supplemental material is available for this article.
Large Deformation Analysis of Hyperelastic Materials Using SPH Method
NASA Astrophysics Data System (ADS)
Kawashima, Yoichi; Sakai, Yuzuru
The importance of large deformation problems in the manufacture of rubber products is increasing. Thus far, these deformations can be analyzed by FEM. However, large deformation cause severe mesh distortions in elements near the boundary, thereby reducing the stable time increment while obtaining the solution. On the other hand, particle methods are meshless techniques that no longer use connectivity data. Therefore, users do not encounter such problems.
Deformation behaviour of a large underground cavern
NASA Astrophysics Data System (ADS)
Mizukoshi, Tatsuo; Mimaki, Youichi
1985-10-01
The Imaichi underground power station, with a cross sectional area of 1420 m2, which is now under construction by Tokyo Electric Power Co., Inc., is one of the largest underground caverns in the world. Due to the considerable depth of the over-burden of 400 m, the horseshoe-shaped section was adopted for the first time in Japan to minimize excesive stress concentration on the surrounding bedrock and keep loosened zones to a minimum. The bedrock consists of sandstone, slate, siliceous sandstone and breccia. The rock is generally hard and compact, with few fractured zones which may have an adverse influence on the excavation of the cavern. The supporting system of the cavern consists of prestressed rock anchors, rock bolts and shotcrete. Approximately 800 instruments, mainly multiple stage extensometers, were used to monitor behaviour of the surrounding rock during excavation of the cavern. With the exception of some cracks which occurred in a portion of the shotcrete when about half the height of the cavern had been excavated, excavation work was completed without any major trouble. In spite of the symmetrical shape of the cavern, the deformation behaviour of the surrounding rock during excavation was remarkedly asymmetric. The reason for this was concluded to be the peculiar deformation behaviour exhibited by Breccia during stress relief, as shown by in-situ rock tests, etc., and analysis of deformation data after completion of the excavation work.
S-HAMMER: hierarchical attribute-guided, symmetric diffeomorphic registration for MR brain images.
Wu, Guorong; Kim, Minjeong; Wang, Qian; Shen, Dinggang
2014-03-01
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. Copyright © 2013 Wiley Periodicals, Inc.
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
Multi-manifold diffeomorphic metric mapping for aligning cortical hemispheric surfaces.
Zhong, Jidan; Qiu, Anqi
2010-01-01
Cortical surface-based analysis has been widely used in anatomical and functional studies because it is geometrically appropriate for the cortex. One of the main challenges in the cortical surface-based analysis is to optimize the alignment of the cortical hemispheric surfaces across individuals. In this paper, we introduce a multi-manifold large deformation diffeomorphic metric mapping (MM-LDDMM) algorithm that allows simultaneously carrying the cortical hemispheric surface and its sulcal curves from one to the other through a flow of diffeomorphisms. We present an algorithm based on recent derivation of a law of momentum conservation for the geodesics of diffeomorphic flow. Once a template is fixed, the space of initial momentum becomes an appropriate space for studying shape via geodesic flow since the flow at any point on curves and surfaces along the geodesic is completely determined by the momentum at the origin. We solve for trajectories (geodesics) of the kinetic energy by computing its variation with respect to the initial momentum and by applying a gradient descent scheme. The MM-LDDMM algorithm optimizes the initial momenta encoding the anatomical variation of each individual relative to a common coordinate system in a linear space, which provides a natural scheme for shape deformation average and template (or atlas) generation. We applied the MM-LDDMM algorithm for constructing the templates for the cortical surface and 14 sulcal curves of each hemisphere using a group of 40 subjects. The estimated template shape reflects regions which are highly variable across these subjects. Compared with existing single-manifold LDDMM algorithms, such as the LDDMM-curve mapping and the LDDMM-surface mapping, the MM-LDDMM mapping provides better results in terms of surface to surface distances in five predefined regions.
Large deformation analysis of gellan gels
NASA Astrophysics Data System (ADS)
Kawai, Shinnosuke; Nitta, Yoko; Nishinari, Katsuyoshi
2007-08-01
Gellan gel, a typical polysaccharide gel, is ruptured with different deformation behaviors from gelatin gel or rubber. It exhibits both strain hardening and softening; hardening is observed for moderate strain and softening occurs for larger strain. From the analyses of stress-strain curves of gellan gels, we propose forms of strain energy function. The fit with the proposed equation was excellent, while the existing models fail because they consider only one of hardening or softening effect. Furthermore, these equations are shown to be capable of extracting the hardening and softening effects separately from the observed stress-strain curves. By using these fitting equations, the concentration dependences of hardening and softening are investigated. It is shown that the degrees of hardening and softening both increase with increasing gellan concentration.
Deformable image registration for tissues with large displacements.
Huang, Xishi; Ren, Jing; Abdalbari, Anwar; Green, Mark
2017-01-01
Image registration for internal organs and soft tissues is considered extremely challenging due to organ shifts and tissue deformation caused by patients' movements such as respiration and repositioning. In our previous work, we proposed a fast registration method for deformable tissues with small rotations. We extend our method to deformable registration of soft tissues with large displacements. We analyzed the deformation field of the liver by decomposing the deformation into shift, rotation, and pure deformation components and concluded that in many clinical cases, the liver deformation contains large rotations and small deformations. This analysis justified the use of linear elastic theory in our image registration method. We also proposed a region-based neuro-fuzzy transformation model to seamlessly stitch together local affine and local rigid models in different regions. We have performed the experiments on a liver MRI image set and showed the effectiveness of the proposed registration method. We have also compared the performance of the proposed method with the previous method on tissues with large rotations and showed that the proposed method outperformed the previous method when dealing with the combination of pure deformation and large rotations. Validation results show that we can achieve a target registration error of [Formula: see text] and an average centerline distance error of [Formula: see text]. The proposed technique has the potential to significantly improve registration capabilities and the quality of intraoperative image guidance. To the best of our knowledge, this is the first time that the complex displacement of the liver is explicitly separated into local pure deformation and rigid motion.
Time Sequence Diffeomorphic Metric Mapping and Parallel Transport Track Time-Dependent Shape Changes
Qiu, Anqi; Albert, Marilyn; Younes, Laurent; Miller, Michael I.
2009-01-01
Serial MRI human brain scans have facilitated the detection of brain development and of the earliest signs of neuropsychiatric and neurodegenerative diseases, monitoring disease progression, and resolving drug effects in clinical trials for preventing or slowing the rate of brain degeneration. To track anatomical shape changes in serial images, we introduce new point-based time sequence large deformation diffeomorphic metric mapping (TS-LDDMM) to infer the time flow of within-subject geometric shape changes that carry known observations through a period. Its Euler-Lagrange equation is generalized for anatomies whose shapes are characterized by point sets, such as landmarks, curves, and surfaces. The time-dependent momentum obtained from the TS-LDDMM encodes within-subject shape changes. For the purpose of across-subject shape comparison, we then propose a diffeomorphic analysis framework to translate within-subject deformation in a global template without incorporating across-subject anatomical variations via parallel transport technique. The analysis involves the retraction of the within-subject timedependent momentum along the TS-LDDMM trajectory from each time to the baseline, the translation of the momentum in a global template, and the reconstruction of the TS-LDDMM trajectory starting from the global template. PMID:19041947
Bayesian principal geodesic analysis in diffeomorphic image registration.
Zhang, Miaomiao; Fletcher, P Thomas
2014-01-01
Computing a concise representation of the anatomical variability found in large sets of images is an important first step in many statistical shape analyses. In this paper, we present a generative Bayesian approach for automatic dimensionality reduction of shape variability represented through diffeomorphic mappings. To achieve this, we develop a latent variable model for principal geodesic analysis (PGA) that provides a probabilistic framework for factor analysis on diffeomorphisms. Our key contribution is a Bayesian inference procedure for model parameter estimation and simultaneous detection of the effective dimensionality of the latent space. We evaluate our proposed model for atlas and principal geodesic estimation on the OASIS brain database of magnetic resonance images. We show that the automatically selected latent dimensions from our model are able to reconstruct unseen brain images with lower error than equivalent linear principal components analysis (LPCA) models in the image space, and it also outperforms tangent space PCA (TPCA) models in the diffeomorphism setting.
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.
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
High resolution, large deformation 3D traction force microscopy.
Toyjanova, Jennet; Bar-Kochba, Eyal; 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.
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.
Global feedforward and glocal feedback control of large deformable mirrors
NASA Astrophysics Data System (ADS)
Ruppel, Thomas; Sawodny, Oliver
2011-09-01
With an increasing demand for high spatial resolution and fast temporal response of AO components for ELTs, the need for actively controlled, electronically damped deformable mirrors is evident. With typically more than 1000 actuators and collocated sensors, the evolving multi-input multi-output control task for shaping the deformable mirror requires sophisticated control concepts. Although global position control of the mirror would be the most promising solution, the computational complexity for high order spatial control of the deformable element typically exceeds available computing power. Due to this reason, existing deformable membrane mirrors for large telescopes incorporate local feedback instead of global feedback control and neglect some of the global dynamics of the deformable mirror. As a side effect, coupling of the separately controlled actuators through the deformable membrane can lead to instability of the individually stable loops and draws the need for carefully designing the control parameters of the local feedback loops. In this presentation, the computational demands for global position control of deformable mirrors are revisited and a less demanding model-based modal control concept for large deformable membrane mirrors with distributed force actuators and collocated position sensors is presented. Both global feedforward and glocal feedback control is employed in a two-degree-of-freedom control structure allowing for separately designing tracking performance and disturbance rejection. In order to implement state feedback control, non-measureable state information is reconstructed by using model-based distributed state observers. By taking into account the circular symmetry of the deformable mirror geometry, the computational complexity of the algorithms is discussed and model reduction techniques with quasi-static state approximation are presented. As an example, the geometric layout of required sensor / actuator wiring and computational
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.
Diffeomorphisms in group field theories
Baratin, Aristide; Girelli, Florian; Oriti, Daniele
2011-05-15
We study the issue of diffeomorphism symmetry in group field theories (GFT), using the noncommutative metric representation introduced by A. Baratin and D. Oriti [Phys. Rev. Lett. 105, 221302 (2010).]. In the colored Boulatov model for 3d gravity, we identify a field (quantum) symmetry which ties together the vertex translation invariance of discrete gravity, the flatness constraint of canonical quantum gravity, and the topological (coarse-graining) identities for the 6j symbols. We also show how, for the GFT graphs dual to manifolds, the invariance of the Feynman amplitudes encodes the discrete residual action of diffeomorphisms in simplicial gravity path integrals. We extend the results to GFT models for higher-dimensional BF theories and discuss various insights that they provide on the GFT formalism itself.
Material and Geometric Analysis of Structures Subjected to Large Deformation
NASA Astrophysics Data System (ADS)
Ferranto, Justin
The two major focuses of this dissertation are: (1) Studying the structural behaviors of hyper-elastic membranes subjected to extremely large deformation. These membranes are used in a reconfigurable tooling system (RTS) which was under development during the course of this study. (2) Establishing a continuum constitutive model for fabric materials under in-plane large deformation through theoretical and numerical analyses. This model may also be applied to study a class of materials which involve significant internal structure reconfiguration during deformation. The RTS allows quick onsite fabrication of high temperature composite parts. RTS applications include rapid onsite repair of aircraft components. The RTS uses a hyperelastic membrane as an interface between the state-change material and model. This membrane may be subjected to 800% engineering strain during operation. In this part of the study, material properties of the membranes have been characterized through three tests: simple tension, equal biaxial tension and planar tension. Nine-term Money-Rivlin constants are obtained through data regression. Finite element simulations have been conducted to simulate the deformed shapes of a membrane around several representative geometries under various vacuum pressure and constraint conditions. Experimental results have been compared with predictions from finite element simulations. This study contributes to understanding the behavior of membrane structures under large deformations in general; the results are used to generate design guidelines for RTS applicability. Fabric materials are widely used in industry for numerous applications. They exhibit a meso-scale complexity and involve significant internal structure reconfiguration during large deformation, which prohibits the direct application of the theory of continuum mechanics when studying these materials. In the second part of this work, a unique meso-scale FEA model, utilizing new modeling techniques and
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').
Diffeomorphic Image Registration of Diffusion MRI Using Spherical Harmonics
Geng, Xiujuan; Ross, Thomas J.; Gu, Hong; Shin, Wanyong; Zhan, Wang; Chao, Yi-Ping; Lin, Ching-Po; Schuff, Norbert; Yang, Yihong
2013-01-01
Non-rigid registration of diffusion MRI is crucial for group analyses and building white matter and fiber tract atlases. Most current diffusion MRI registration techniques are limited to the alignment of diffusion tensor imaging (DTI) data. We propose a novel diffeomorphic registration method for high angular resolution diffusion images by mapping their orientation distribution functions (ODFs). ODFs can be reconstructed using q-ball imaging (QBI) techniques and represented by spherical harmonics (SHs) to resolve intra-voxel fiber crossings. The registration is based on optimizing a diffeomorphic demons cost function. Unlike scalar images, deforming ODF maps requires ODF reorientation to maintain its consistency with the local fiber orientations. Our method simultaneously reorients the ODFs by computing a Wigner rotation matrix at each voxel, and applies it to the SH coefficients during registration. Rotation of the coefficients avoids the estimation of principal directions, which has no analytical solution and is time consuming. The proposed method was validated on both simulated and real data sets with various metrics, which include the distance between the estimated and simulated transformation fields, the standard deviation of the general fractional anisotropy and the directional consistency of the deformed and reference images. The registration performance using SHs with different maximum orders were compared using these metrics. Results show that the diffeomorphic registration improved the affine alignment, and registration using SHs with higher order SHs further improved the registration accuracy by reducing the shape difference and improving the directional consistency of the registered and reference ODF maps. PMID:21134814
Diffeomorphic image registration of diffusion MRI using spherical harmonics.
Geng, Xiujuan; Ross, Thomas J; Gu, Hong; Shin, Wanyong; Zhan, Wang; Chao, Yi-Ping; Lin, Ching-Po; Schuff, Norbert; Yang, Yihong
2011-03-01
Nonrigid registration of diffusion magnetic resonance imaging (MRI) is crucial for group analyses and building white matter and fiber tract atlases. Most current diffusion MRI registration techniques are limited to the alignment of diffusion tensor imaging (DTI) data. We propose a novel diffeomorphic registration method for high angular resolution diffusion images by mapping their orientation distribution functions (ODFs). ODFs can be reconstructed using q-ball imaging (QBI) techniques and represented by spherical harmonics (SHs) to resolve intra-voxel fiber crossings. The registration is based on optimizing a diffeomorphic demons cost function. Unlike scalar images, deforming ODF maps requires ODF reorientation to maintain its consistency with the local fiber orientations. Our method simultaneously reorients the ODFs by computing a Wigner rotation matrix at each voxel, and applies it to the SH coefficients during registration. Rotation of the coefficients avoids the estimation of principal directions, which has no analytical solution and is time consuming. The proposed method was validated on both simulated and real data sets with various metrics, which include the distance between the estimated and simulated transformation fields, the standard deviation of the general fractional anisotropy and the directional consistency of the deformed and reference images. The registration performance using SHs with different maximum orders were compared using these metrics. Results show that the diffeomorphic registration improved the affine alignment, and registration using SHs with higher order SHs further improved the registration accuracy by reducing the shape difference and improving the directional consistency of the registered and reference ODF maps.
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.
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.
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.
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.
Space-Time Diffeomorphisms in Noncommutative Gauge Theories
NASA Astrophysics Data System (ADS)
Rosenbaum, Marcos; Vergara, J. David; Juarez, L. Román
2008-07-01
In previous work [Rosenbaum M. et al., J. Phys. A: Math. Theor. 40 (2007), 10367-10382] we have shown how for canonical parametrized field theories, where space-time is placed on the same footing as the other fields in the theory, the representation of space-time diffeomorphisms provides a very convenient scheme for analyzing the induced twisted deformation of these diffeomorphisms, as a result of the space-time noncommutativity. However, for gauge field theories (and of course also for canonical geometrodynamics) where the Poisson brackets of the constraints explicitely depend on the embedding variables, this Poisson algebra cannot be connected directly with a representation of the complete Lie algebra of space-time diffeomorphisms, because not all the field variables turn out to have a dynamical character [Isham C.J., Kuchar K.V., Ann. Physics 164 (1985), 288-315, 316-333]. Nonetheless, such an homomorphic mapping can be rec! uperated by first modifying the original action and then adding additional constraints in the formalism in order to retrieve the original theory, as shown by Kuchar and Stone for the case of the parametrized Maxwell field in [Kuchar K.V., Stone S.L., Classical Quantum Gravity 4 (1987), 319-328]. Making use of a combination of all of these ideas, we are therefore able to apply our canonical reparametrization approach in order to derive the deformed Lie algebra of the noncommutative space-time diffeomorphisms as well as to consider how gauge transformations act on the twisted algebras of gauge and particle fields. Thus, hopefully, adding clarification on some outstanding issues in the literature concerning the symmetries for gauge theories in noncommutative space-times.
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.
On the Uniqueness of Diffeomorphism Symmetry in Conformal Field Theory
NASA Astrophysics Data System (ADS)
Carpi, Sebastiano; Weiner, Mihály
2005-08-01
A Möbius covariant net of von Neumann algebras on S1 is diffeomorphism covariant if its Möbius symmetry extends to diffeomorphism symmetry. We prove that in case the net is either a Virasoro net or any at least 4-regular net such an extension is unique: the local algebras together with the Möbius symmetry (equivalently: the local algebras together with the vacuum vector) completely determine it. We draw the two following conclusions for such theories. (1) The value of the central charge c is an invariant and hence the Virasoro nets for different values of c are not isomorphic as Möbius covariant nets. (2) A vacuum preserving internal symmetry always commutes with the diffeomorphism symmetries. We further use our result to give a large class of new examples of nets (even strongly additive ones), which are not diffeomorphism covariant; i.e. which do not admit an extension of the symmetry to Diff+(S1).
Diffeomorphic metric mapping of hybrid diffusion imaging based on BFOR signal basis.
Du, Jia; Hosseinbor, A Pasha; Chung, Moo K; Bendlin, Barbara B; Suryawanshi, Gaurav; Suryawanshi, Gaurav; Qiu, Anqi
2013-01-01
In this paper, we 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), denoted as LDDMM-HYDI. 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 thus reduces memory requirement. In addition, since the BFOR signal basis is orthonormal, the L2 norm that quantifies the differences in 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. Using real HYDI datasets, 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.
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.
A large deformation poroplasticity theory for microporous polymeric materials
NASA Astrophysics Data System (ADS)
Anand, Lallit
2017-01-01
A coupled theory accounting for fluid diffusion and large deformations of elastic-viscoplastic microporous polymeric materials is presented. The theory is intended to represent the coupled deformation-diffusion response of a material which at a microscopic scale consists of a porous polymeric skeleton and a freely moving fluid in a fully connected pore space. Potential applications of the theory include modeling the response of polymer microfiltration membranes, as well as modeling the response of several hydrated biological tissues which are microporous polymeric materials containing a high concentration of liquids.
Large elastic deformation of nonlinear axisymmetric membranes: a variational approach
Nielan, P.E.
1982-10-01
Variational equations for determining the deformed configuration of a pressurized axisymmetric membrane undergoing constant acceleration are derived. The general formulation is similar to that of Tielking and Feng. A Mooney-Rivlin material model is used for the membrane and large deformations and strains are accounted for. A Ritz procedure reduces the governing equations to a nonlinear algebraic form. Tensile instabilities are discussed in the context of the analytical solution available for a sphere. In a forthcoming report a computer program written to solve these equations will be described. The analysis and software will be verified by comparison with existing finite elasticity solutions. Solutions to new problems will be given. Ongoing work considering the coupling between structural deformation and the thermodynamics of inflation will be described and the effects of the acceleration on the pressure loads due to the gas will be discussed.
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
Bayesian principal geodesic analysis for estimating intrinsic diffeomorphic image variability.
Zhang, Miaomiao; Fletcher, P Thomas
2015-10-01
In this paper, we present a generative Bayesian approach for estimating the low-dimensional latent space of diffeomorphic shape variability in a population of images. We develop a latent variable model for principal geodesic analysis (PGA) that provides a probabilistic framework for factor analysis in the space of diffeomorphisms. A sparsity prior in the model results in automatic selection of the number of relevant dimensions by driving unnecessary principal geodesics to zero. To infer model parameters, including the image atlas, principal geodesic deformations, and the effective dimensionality, we introduce an expectation maximization (EM) algorithm. We evaluate our proposed model on 2D synthetic data and the 3D OASIS brain database of magnetic resonance images, and show that the automatically selected latent dimensions from our model are able to reconstruct unobserved testing images with lower error than both linear principal component analysis (LPCA) in the image space and tangent space principal component analysis (TPCA) in the diffeomorphism space. Copyright © 2015 Elsevier B.V. All rights reserved.
Ahn, Bummo; Kim, Jung
2010-04-01
Soft tissue characterization with the inverse finite element method (FEM) optimization algorithm plays an important role in developing a physical model for medical simulations. However, tissue characterization that takes into account comprehensive boundary conditions for large deformations remains a challenge due to computational complexities and a lack of experimental data. In this study, soft tissue experiments on porcine livers were performed to measure the surface deformation and force response of soft tissues resulting from indentation loading depending on various indentation depths and two different tip shapes. Measurements were carried out with a three-dimensional (3D) optical system and a force transducer. Using the surface deformation and force response results, we estimated the maximum radius of influence, which can be utilized to determine the minimal required soft tissue model size for the FEM simulation. Considering the influence of the boundary conditions, the model was designed and integrated into an inverse FEM optimization algorithm to estimate the model parameters. The mechanical behavior of large deformations was characterized with FE modeling via hyperelastic and linear viscoelastic models. Copyright 2009 Elsevier B.V. All rights reserved.
Large Scale Deformation Monitoring and Atmospheric Removal in Mexico City
NASA Astrophysics Data System (ADS)
McCardle, Adrian; McCardel, Jim; Ramos, Fernanda Ledo G.
2010-03-01
Large scale, accurate measurement of non-linear ground movement is required for monitoring applications pertaining to groundwater extraction, oil and gas production, and carbon capture and storage. Mexico City experiences severe subsidence as high as 35 centimeters per year due to continued exploitation of groundwater. Such extreme ground deformation has caused damage to infrastructure and many areas of the city are now subjected to periodic flooding. Furthermore, subsidence rates change seasonally creating a non-linear deformation signature manifesting over an area larger than 30 x 30 kilometers. The geographical location and climate of Mexico City, coupled with aforementioned subsidence characteristics create unique challenges for repeat-pass InSAR processing: Firstly, Mexico City is a tropical highland and experiences an oceanic climate that leads to significant temporal de-correlation. Secondly, the large magnitude subsidence leads to phase aliasing over coherent targets, particularly for interferograms with large temporal separation. Lastly, the expansive deformation is spatially correlated on scales similar to the long-range atmosphere, complicating the separation of the two signals. This paper discusses the results from the application of traditional DInSAR techniques combined with Multi-temporal InSAR Network Analysis processing algorithms to accurately identify and measure displacement, specifically in light of the challenges peculiar to Mexico City. Multi-temporal InSAR Network Analysis techniques are used to identify non-linear displacement and remove atmospheric noise from 38 ENVISAT images that were acquired over Mexico City from 2002 to 2007.
A large deformation viscoelastic model for double-network hydrogels
NASA Astrophysics Data System (ADS)
Mao, Yunwei; Lin, Shaoting; Zhao, Xuanhe; Anand, Lallit
2017-03-01
We present a large deformation viscoelasticity model for recently synthesized double network hydrogels which consist of a covalently-crosslinked polyacrylamide network with long chains, and an ionically-crosslinked alginate network with short chains. Such double-network gels are highly stretchable and at the same time tough, because when stretched the crosslinks in the ionically-crosslinked alginate network rupture which results in distributed internal microdamage which dissipates a substantial amount of energy, while the configurational entropy of the covalently-crosslinked polyacrylamide network allows the gel to return to its original configuration after deformation. In addition to the large hysteresis during loading and unloading, these double network hydrogels also exhibit a substantial rate-sensitive response during loading, but exhibit almost no rate-sensitivity during unloading. These features of large hysteresis and asymmetric rate-sensitivity are quite different from the response of conventional hydrogels. We limit our attention to modeling the complex viscoelastic response of such hydrogels under isothermal conditions. Our model is restricted in the sense that we have limited our attention to conditions under which one might neglect any diffusion of the water in the hydrogel - as might occur when the gel has a uniform initial value of the concentration of water, and the mobility of the water molecules in the gel is low relative to the time scale of the mechanical deformation. We also do not attempt to model the final fracture of such double-network hydrogels.
Djamanakova, Aigerim; Faria, Andreia V; Hsu, John; Ceritoglu, Can; Oishi, Kenichi; Miller, Michael I; Hillis, Argye E; Mori, Susumu
2013-01-01
To improve image registration accuracy in neurodegenerative populations. This study used primary progressive aphasia, aged control, and young control T1-weighted images. Mapping to a template image was performed using single-channel Large Deformation Diffeomorphic Metric Mapping (LDDMM), a dual-channel method with ventricular anatomy in the second channel, and a dual-channel with appendage method, which utilized a priori knowledge of template ventricular anatomy in the deformable atlas. Our results indicated substantial improvement in the registration accuracy over single-contrast-based brain mapping, mainly in the lateral ventricles and regions surrounding them. Dual-channel mapping significantly (P < 0.001) reduced the number of misclassified lateral ventricle voxels (based on a manually defined reference) over single-channel mapping. The dual-channel (w/appendage) method further reduced (P < 0.001) misclassification over the dual-channel method, indicating that the appendage provides more accurate anatomical correspondence for deformation. Brain anatomical mapping by shape normalization is widely used for quantitative anatomical analysis. However, in many geriatric and neurodegenerative disorders, severe tissue atrophy poses a unique challenge for accurate mapping of voxels, especially around the lateral ventricles. In this study we demonstrate our ability to improve mapping accuracy by incorporating ventricular anatomy in LDDMM and by utilizing a priori knowledge of ventricular anatomy in the deformable atlas. Copyright © 2012 Wiley Periodicals, Inc.
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.
Large deformations of reconfigurable active membranes: a finite element model
NASA Astrophysics Data System (ADS)
Son, Seyul; Goulbourne, N. C.
2010-04-01
In this paper, a finite element model is used to describe the inhomogeneous deformations of dielectric elastomers (DE). In our previous work, inhomogeneous deformations of the DE with simple boundary conditions represented by a system of highly nonlinear coupled differential equations (ordinary and partial) were solved using numerical approaches [1-3]. To solve for the electromechanical response for complex shapes (asymmetric), nonuniform loading, and complex boundary conditions a finite element scheme is required. This paper describes a finite element implementation of the DE material model proposed in our previous work in a commercial FE code (ABAQUS 6.8-1, PAWTUCKET, R.I, USA). The total stress is postulated as the summation of the elastic stress tensor and the Maxwell stress tensor, or more generally the electrostatic stress tensor. The finite element model is verified by analytical solutions and experimental results for planar membrane extensions subject to mechanical loads and an electric field: (i) equibiaxial extension and (ii) generalized biaxial extension. Specifically, the analytical solutions for equibiaxial extension of the DE is obtained by combining a modified large deformation membrane theory that accounts for the electromechanical coupling effect in actuation commonly referred to as the Maxwell stress [4]. A Mooney-Rivlin strain energy function is employed to describe the constitutive stress strain behavior of the DE. For the finite element implementation, the constitutive relationships from our previously proposed mathematical model [4] are implemented into the finite element code. Experimentally, a 250% equibiaxially prestretched DE sample is attached to a rigid joint frame and inhomogeneous deformations of the reconfigurable DE are observed with respect to mechanical loads and an applied electric field. The computational result for the reconfigurable DE is compared with the test result to validate the accuracy and robustness of the finite
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.
Modeling the behaviour of shape memory materials under large deformations
NASA Astrophysics Data System (ADS)
Rogovoy, A. A.; Stolbova, O. S.
2017-06-01
In this study, the models describing the behavior of shape memory alloys, ferromagnetic materials and polymers have been constructed, using a formalized approach to develop the constitutive equations for complex media under large deformations. The kinematic and constitutive equations, satisfying the principles of thermodynamics and objectivity, have been derived. The application of the Galerkin procedure to the systems of equations of solid mechanics allowed us to obtain the Lagrange variational equation and variational formulation of the magnetostatics problems. These relations have been tested in the context of the problems of finite deformation in shape memory alloys and ferromagnetic materials during forward and reverse martensitic transformations and in shape memory polymers during forward and reverse relaxation transitions from a highly elastic to a glassy state.
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.
Risser, Laurent; Vialard, François-Xavier; Wolz, Robin; Holm, Darryl D; Rueckert, Daniel
2010-01-01
In this paper, we present a fine and coarse approach for the multiscale registration of 3D medical images using Large Deformation Diffeomorphic Metric Mapping (LDDMM). This approach has particularly interesting properties since it estimates large, smooth and invertible optimal deformations having a rich descriptive power for the quantification of temporal changes in the images. First, we show the importance of the smoothing kernel and its influence on the final solution. We then propose a new strategy for the spatial regularization of the deformations, which uses simultaneously fine and coarse smoothing kernels. We have evaluated the approach on both 2D synthetic images as well as on 3D MR longitudinal images out of the Alzheimer's Disease Neuroimaging Initiative (ADNI) study. Results highlight the regularizing properties of our approach for the registration of complex shapes. More importantly, the results also demonstrate its ability to measure shape variations at several scales simultaneously while keeping the desirable properties of LDDMM. This opens new perspectives for clinical applications.
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.
Hybrid stress finite elements for large deformations of inelastic solids
NASA Technical Reports Server (NTRS)
Reed, K. W.; Atluri, S. N.
1984-01-01
A new hybrid stress finite element algorithm, based on a generalization of Fraeijs de Veubeke's complementary energy principle is presented. Analyses of large quasistatic deformation of inelastic solids (hypoelastic, plastic, viscoplastic) are within its capability. Principle variables in the formulation are the nominal stress rate and spin. A brief account is given of the boundary value problem in these variables, and the 'equivalent' variational principle. The finite element equation, along with initial positions and stresses, comprise an initial value problem. Factors affecting the choice of time integration schemes are discussed. Results found by application of the new algorithm are compared to those obtained by a velocity based finite element algorithm.
Miller, Michael I; Younes, Laurent; Ratnanather, J Tilak; Brown, Timothy; Reigel, Tommy; Trinh, Huong; Tang, Xiaoying; Barker, Peter; Mori, Susumu; Albert, Marilyn
2012-10-01
Surface-based deformation markers obtained from diffeomorphic mapping of the amygdala are used to study specific atrophy patterns in a combined mild cognitively impaired and demented cohort compared with cognitively normal aging subjects. Statistical analysis demonstrates with high significance in a small sample of legacy data that deformation-based morphometry provides sensitive markers for locating atrophy in the amygdala. With respect to a high-field amygdala atlas, significant atrophy was found in the basomedial and lateral nucleus subregions.
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
An Inexact Newton-Krylov Algorithm for Constrained Diffeomorphic Image Registration.
Mang, Andreas; Biros, George
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 H(1)- or H(2)-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
Planar radial weakly dissipative diffeomorphisms.
Simó, C; Vieiro, A
2010-12-01
We study the effect of a small dissipative radial perturbation acting on a one parameter family of area preserving diffeomorphisms. This is a specific type of dissipative perturbation. The interest is on the global effect of the dissipation on a fixed domain around an elliptic fixed/periodic point of the family, rather than on the effects around a single resonance. We describe the local/global bifurcations observed in the transition from the conservative to a weakly dissipative case: the location of the resonant islands, the changes in the domains of attraction of the foci inside these islands, how the resonances disappear, etc. The possible ω-limits are determined in each case. This topological description gives rise to three different dynamical regimes according to the size of dissipative perturbation. Moreover, we determine the conservative limit of the probability of capture in a generic resonance from the interpolating flow approximation, hence assuming no homoclinics in the resonance. As a paradigm of weakly dissipative radial maps, we use a dissipative version of the Hénon map. © 2010 American Institute of Physics.
Nonlinear elastic effects on permanent deformation due to large earthquakes
NASA Astrophysics Data System (ADS)
Bataille, Klaus; Contreras, Marcelo
2009-06-01
Large earthquakes generate significant deformations near fault zones, and it is known that under such conditions rocks do not behave linearly. This nonlinearity is generally assumed to be due to ductile processes, however, some nonlinear elastic behavior is possible as well, and this should have an effect on the ground deformation near fault zones which might be observable seismically or geodetically. We calculate the difference of the permanent displacement field, due to an earthquake, when we consider Hooke's law and a general nonlinear law. Under the simplified assumption that the nonlinear part of the constitutive law has a small effect, we use a perturbation approach and keep only the first term. This first term depends on Mo/r3, implying that for large Moments ( Mo) and small distances ( r), the seismic Moment (as obtained far away from the source and within the linear regime) will always be greater than the geodetic Moment (obtained within the nonlinear regime). This result is in principle against our intuition since seismic Moments relate to the rupture process of the main event, which normally takes place during minutes, while geodetic Moments relate to the rupture process of the main event plus foreshocks (if any), aftershocks and other slow afterslip processes, which normally occur during hours and days. Aftershocks normally share the same mechanism as the main event, increasing thus the total Moment of the sequence, therefore, geodetic Moment should intuitively be greater than the seismic Moment. Interestingly, this reasoning yields the opposite effect than what is observed for large earthquakes as the cases of the Chile 1960 ( Mw=9.5), Alaska 1964 ( Mw=9.2) and some evidence for the Sumatra 2005 ( Mw=9.3) as well as other smaller earthquakes. If the difference of geodetic and seismic Moments is a real phenomenon, it could be due to several factors. We suggest here that one of these factors, could be due to a nonlinear elastic effect.
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
Elastic deformations disrupt structural superlubricity in large contacts
NASA Astrophysics Data System (ADS)
Sharp, Tristan A.; Pastewka, Lars; Robbins, Mark O.
Force microscopy experiments observe ultra-low friction between solids with incommensurate lattice structures. This phenomenon is referred to as superlubricity and is due to a cancellation of lateral forces because surfaces sample all relative local configurations with equal probability. We use simulations to show that elasticity disrupts superlubricity in sufficiently large circular contacts. The simulations include atomic-scale geometry and reach micron-scales. For rigid solids, cancellation is complete except at the contact boundary. The static friction force per contact area, τ, falls as a power of contact radius, τ ~a - 3 / 2 . Elastic deformations limit this cancellation when the contact radius a is larger than a characteristic length scale set by the core width of interfacial dislocations, bcore. For a >bcore sliding of moderately incommensurate contacts is dominated by dislocation motion and, at large a, τ approaches a constant value near the Peierls stress needed to move edge dislocations. Surprisingly, the stress in commensurate contacts drops to nearly the same value at large a. We conclude that true structural lubricity does not occur in large contacts, although the constant shear stress drops rapidly with bcore. NSF IGERT, DAAD.
Large Deviations for Stochastic Flows of Diffeomorphisms
2007-01-01
be the unique solution of the ordinary differential equation ∂ηs,t(x) ∂t .= b ( ηs,t(x), t ) , ηs,s(x) = x, 0 ≤ s ≤ t ≤ 1. (5.2) Then it follows that...solving finite dimensional Itô stochastic differential equations . More precisely, suppose b, fi, i = 1, . . . ,m are functions from Rd × [0, T ] to Rd...s, T ]. This stochastic process is called the solution of Itô’s stochastic differential equation based on the Brownian motion F . From [15, Theorem
Large-strain deformation and fracture of tough hydrogels
NASA Astrophysics Data System (ADS)
Webber, Rebecca; Miquelard, Guillaume; Creton, Costantino; Gong, Jian Ping
2006-03-01
Highly-swollen, chemically-crosslinked hydrogels generally behave in a very brittle manner, fracturing suddenly after a small amount of reversible deformation. Because of their importance as biomaterials, it is useful to control and augment the resistance to fracture of these materials. Tougher, stronger hydrogels are emerging, and it is important to understand the structural origins of strength in these relatively robust, highly-swollen, polymer systems. We have investigated the rheological, mechanical and fracture properties of tough hydrogels, using novel testing techniques and focusing on the high-strain compression and tension behavior. Results from large-strain and fracture experiments were correlated to the chemical structure of the hydrogels. Because we believe that the mechanical properties of these tough hydrogels are due to the presence of dissipative mechanisms at the molecular level, we have explored several methods of synthesis to create these materials.
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.
Large Deformation Change in Iridium Isotopes from Laser Spectroscopy
D. Verney; L. Cabaret; J. Crawford; H.T. Duong; J. Genevey; G. Hubert; F. Ibrahim; M. Krieg; F. Le Blanc; J.K.P. Lee; G. Le Scornet; D. Lunney; J. Obert; J. Oms; J. Pinard; J.C. Putaux; B. Roussiere; J. Sauvage; V. Sebastian
1999-12-31
Laser spectroscopy measurements have been performed on neutron-deficient iridium isotopes. The hyperfine structure and isotope shift of the optical Ir I transition 5d{sup 7}6s{sup 2} {sup 4}F{sub 9/2} {yields}5d{sup 7}6s6p {sup 6}F{sub 11/2} have been studied for the {sup 182-189}Ir, {sup 186}Ir{sup m} and {sup 191,193}Ir isotopes. The nuclear magnetic and quadrupole moments were obtained from the hyperfine splitting measurements and the changes of the mean square charge radii from the isotope shift measurements. A large deformation change between {sup 187}Ir and {sup 186}Ir and between {sup 186}Ir{sup m} and {sup 186}Ir{sup g} has been observed.
Hierarchical attribute-guided symmetric diffeomorphic registration for MR brain images.
Wu, Guorong; Kim, Minjeong; Wang, Qian; Shen, Dinggang
2012-01-01
Deformable registration has been widely used in neuroscience studies for spatial normalization of brain images onto a standard space. Due to high anatomical variances across individual brains, registration performance could be limited when trying to estimate entire deformation pathway either from template to subject or subject to template. Symmetric image registration offers an effective way to simultaneously deform template and subject images towards each other until they meet at the middle point. Although some intensity-based registration algorithms have nicely incorporated this concept of symmetric deformation, the intensity matching between two images may not necessarily imply the correct matching of anatomical correspondences. In this paper, we integrate both strategies of hierarchical attribute matching and symmetric diffeomorphic deformation for building a new symmetric-diffeomorphic registration algorithm for MR brain images. The performance of our proposed method has been extensively evaluated and further compared with top-ranked image registration methods (SyN and diffeomorphic Demons) on brain MR images. In all experiments, our registration method achieves the best registration performance, compared to all other state-of-the-art registration methods.
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 a standard space. Due to high anatomical variances across individual brains, registration performance could be limited when trying to estimate entire deformation pathway either from template to subject or subject to template. Symmetric image registration offers an effective way to simultaneously deform template and subject images towards each other until they meet at the middle point. Although some intensity-based registration algorithms have nicely incorporated this concept of symmetric deformation, the intensity matching between two images may not necessarily imply the correct matching of anatomical correspondences. In this paper, we integrate both strategies of hierarchical attribute matching and symmetric diffeomorphic deformation for building a new symmetric-diffeomorphic registration algorithm for MR brain images. The performance of our proposed method has been extensively evaluated and further compared with top-ranked image registration methods (SyN and diffeomorphic Demons) on brain MR images. In all experiments, our registration method achieves the best registration performance, compared to all other state-of-the-art registration methods. PMID:23286036
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
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.
Effective field theory of broken spatial diffeomorphisms
Lin, Chunshan; Labun, Lance Z.
2016-03-17
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. In conclusion, we discuss several examples relevant to theories of massive gravity.
Effective field theory of broken spatial diffeomorphisms
Lin, Chunshan; Labun, Lance Z.
2016-03-17
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 constantmore » 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. In conclusion, we discuss several examples relevant to theories of massive gravity.« less
New diffeomorphism invariant states on a holonomy-flux algebra
NASA Astrophysics Data System (ADS)
Dziendzikowski, Michał; Okołów, Andrzej
2010-11-01
The theorem by Lewandowski et al stating uniqueness of a diffeomorphism invariant state on an algebra of quantum observables for background-independent theories of connections is based on some technical assumptions imposed on the algebra and the diffeomorphisms. In this paper we present a class of diffeomorphism invariant states on an algebra of this sort, which exist when the algebra and the diffeomorphisms satisfy alternative assumptions.
Shape-Dependent Global Deformation Modes of Large Protein Structures
Miloshevsky, Gennady V.; Hassanein, Ahmed; Jordan, Peter C.
2010-01-01
Conformational changes are central to the functioning of pore-forming proteins that open and close their molecular gates in response to external stimuli such as pH, ionic strength, membrane voltage or ligand binding. Normal mode analysis (NMA) is used to identify and characterize the slowest motions in the gA, KcsA, ClC-ec1, LacY and LeuTAa proteins at the onset of gating. Global deformation modes of the essentially cylindrical gA, KcsA, LacY and LeuTAa biomolecules are reminiscent of global twisting, transverse and longitudinal motions in a homogeneous elastic rod. The ClC-ec1 protein executes a splaying motion in the plane perpendicular to the lipid bilayer. These global collective deformations are determined by protein shape. New methods, all-atom Monte Carlo Normal Mode Following and its simplification using a rotation-translation of protein blocks (RTB), are described and applied to gain insight into the nature of gating transitions in gA and KcsA. These studies demonstrate the severe limitations of standard NMA in characterizing the structural rearrangements associated with gating transitions. Comparison of all-atom and RTB transition pathways in gA clearly illustrates the impact of the rigid protein block approximation and the need to include all degrees of freedom and their relaxation in computational studies of protein gating. The effects of atomic level structure, pH, hydrogen bonding and charged residues on the large scale conformational changes associated with gating transitions are discussed. PMID:20526444
A large adaptive deformable membrane mirror with highactuator density
NASA Astrophysics Data System (ADS)
Hamelinck, Roger; Rosielle, Nick; Kappelhof, Pieter; Snijders, Bart; Steinbuch, Maarten
2004-10-01
With the future growing size of telescopes, new, high-resolution, affordable wavefront corrector technology with low power dissipation is needed. A new adaptive deformable mirror concept is presented, to meet such requirements. The adaptive mirror consists of a thin (30-50 μm), highly reflective, deformable membrane. An actuator grid with thousands of actuators is designed which push and pull at the membrane"s surface, free from pinning and piston effects. The membrane and the actuator grid are supported by an optimized light and stiff honeycomb sandwich structure. This mechanically stable and thermally insensitive support structure provides a stiff reference plane for the actuators. The design is extendable up to several hundreds of mm's. Low-voltage electro-magnetic actuators have been designed. These highly linear actuators can provide a stroke of 15 micrometers. The design allows for a stroke difference between adjacent actuators larger than 1 micron. The actuator grid has a layer-based design; these layers extend over a large numbers of actuators. The current actuator design allows for actuator pitches of 3 mm or more. Actuation is free from play, friction and mechanical hysteresis and therefore has a high positioning resolution and is highly repeatable. The lowest mechanical resonance frequency is in the range of kHz so a high control bandwidth can be achieved. The power dissipation in the actuator grid is in the order of milliwatts per actuator. Because of this low power dissipation active cooling is not required. A first prototype is currently being developed. Prototypes will be developed with increasing number of actuators.
Shape-dependent global deformation modes of large protein structures
NASA Astrophysics Data System (ADS)
Miloshevsky, Gennady V.; Hassanein, Ahmed; Jordan, Peter C.
2010-05-01
Conformational changes are central to the functioning of pore-forming proteins that open and close their molecular gates in response to external stimuli such as pH, ionic strength, membrane voltage or ligand binding. Normal mode analysis (NMA) is used to identify and characterize the slowest motions in the gA, KcsA, ClC-ec1, LacY and LeuT Aa proteins at the onset of gating. Global deformation modes of the essentially cylindrical gA, KcsA, LacY and LeuT Aa biomolecules are reminiscent of global twisting, transverse and longitudinal motions in a homogeneous elastic rod. The ClC-ec1 protein executes a splaying motion in the plane perpendicular to the lipid bilayer. These global collective deformations are determined by protein shape. New methods, all-atom Monte Carlo Normal Mode Following and its simplification using a rotation-translation of protein blocks (RTB), are described and applied to gain insight into the nature of gating transitions in gA and KcsA. These studies demonstrate the severe limitations of standard NMA in characterizing the structural rearrangements associated with gating transitions. Comparison of all-atom and RTB transition pathways in gA clearly illustrates the impact of the rigid protein block approximation and the need to include all degrees of freedom and their relaxation in computational studies of protein gating. The effects of atomic level structure, pH, hydrogen bonding and charged residues on the large-scale conformational changes associated with gating transitions are discussed.
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.
Optimal Data-Driven Sparse Parameterization of Diffeomorphisms for Population Analysis
Durrleman, Stanley; Prastawa, Marcel; Gerig, Guido; Joshi, Sarang
2013-01-01
In this paper, we propose a novel approach for intensity based atlas construction from a population of anatomical images, that estimates not only a template representative image but also a common optimal parameterization of the anatomical variations evident in the population. First, we introduce a discrete parameterization of large diffeomorphic deformations based on a finite set of control points, so that deformations are characterized by a low dimensional geometric descriptor. Second, we optimally estimate the position of the control points in the template image domain. As a consequence, control points move to where they are needed most to capture the geometric variability evident in the population. Third, the optimal number of control points is estimated by using a log −L1 sparsity penalty. The estimation of the template image, the template-to-subject mappings and their optimal parameterization is done via a single gradient descent optimization, and at the same computational cost as independent template-to-subject registrations. We present results that show that the anatomical variability of the population can be encoded efficiently with these compact and adapted geometric descriptors. PMID:21761651
Diffeomorphic spectral matching of cortical surfaces.
Lombaert, Herve; Sporring, Jon; Siddiqi, Kaleem
2013-01-01
Accurate matching of cortical surfaces is necessary in many neuroscience applications. In this context diffeomorphisms are often sought, because they facilitate further statistical analysis and atlas building. Present methods for computing diffeomorphisms are based on optimizing flows or on inflating surfaces to a common template, but they are often computationally expensive. It typically takes several hours on a conventional desktop computer to match a single pair of cortical surfaces having a few hundred thousand vertices. We propose a very fast alternative based on an application of spectral graph theory on a novel association graph. Our symmetric approach can generate a diffeomorphic correspondence map within a few minutes on high-resolution meshes while avoiding the sign and multiplicity ambiguities of conventional spectral matching methods. The eigenfunctions are shared between surfaces and provide a smooth parameterization of surfaces. These properties are exploited to compute differentials on highly folded cortical surfaces. Diffeomorphisms can thus be verified and invalid surface folding detected. Our method is demonstrated to attain a vertex accuracy that is at least as good as that of FreeSurfer and Spherical Demons but in only a fraction of their processing time. As a practical experiment, we construct an unbiased atlas of cortical surfaces with a speed several orders of magnitude faster than current methods.
NASA Astrophysics Data System (ADS)
Ramanujan, S.; Pozrikidis, C.
1998-04-01
The deformation of a liquid capsule enclosed by an elastic membrane in an infinite simple shear flow is studied numerically at vanishing Reynolds numbers using a boundary-element method. The surface of the capsule is discretized into quadratic triangular elements that form an evolving unstructured grid. The elastic membrane tensions are expressed in terms of the surface deformation gradient, which is evaluated from the position of the grid points. Compared to an earlier formulation that uses global curvilinear coordinates, the triangular-element formulation suppresses numerical instabilities due to uneven discretization and thus enables the study of large deformations and the investigation of the effect of fluid viscosities. Computations are performed for capsules with spherical, spheroidal, and discoidal unstressed shapes over an extended range of the dimensionless shear rate and for a broad range of the ratio of the internal to surrounding fluid viscosities. Results for small deformations of spherical capsules are in quantitative agreement with the predictions of perturbation theories. Results for large deformations of spherical capsules and deformations of non-spherical capsules are in qualitative agreement with experimental observations of synthetic capsules and red blood cells. We find that initially spherical capsules deform into steady elongated shapes whose aspect ratios increase with the magnitude of the shear rate. A critical shear rate above which capsules exhibit continuous elongation is not observed for any value of the viscosity ratio. This behaviour contrasts with that of liquid drops with uniform surface tension and with that of axisymmetric capsules subject to a stagnation-point flow. When the shear rate is sufficiently high and the viscosity ratio is sufficiently low, liquid drops exhibit continuous elongation leading to breakup. Axisymmetric capsules deform into thinning needles at sufficiently high rates of elongation, independent of the fluid
Incremental analysis of large elastic deformation of a rotating cylinder
NASA Technical Reports Server (NTRS)
Buchanan, G. R.
1976-01-01
The effect of finite deformation upon a rotating, orthotropic cylinder was investigated using a general incremental theory. The incremental equations of motion are developed using the variational principle. The governing equations are derived using the principle of virtual work for a body with initial stress. The governing equations are reduced to those for the title problem and a numerical solution is obtained using finite difference approximations. Since the problem is defined in terms of one independent space coordinate, the finite difference grid can be modified as the incremental deformation occurs without serious numerical difficulties. The nonlinear problem is solved incrementally by totaling a series of linear solutions.
Zhang, Zhijun; Ashraf, Muhammad; Sahn, David J; Song, Xubo
2014-05-01
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. 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. Experiments with simulated datasets, images of anex 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. 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.
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
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
STRESS CONCENTRATION IN AN ELASTOMERIC SHEET SUBJECT TO LARGE DEFORMATIONS
results were obtained for a sheet with a rigid circular inclusion. It is shown that the stress concentration factor for a Rivlin - Mooney material... Rivlin - Mooney material, however, leads to a decrease in stress concentration with increasing deformations....Biaxial and uniaxial experiments have been conducted on a thin sheet of natural rubber , which can be assumed to be incompressible, isotropic, and
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
Dirac operator on spinors and diffeomorphisms
NASA Astrophysics Data System (ADS)
Dąbrowski, Ludwik; Dossena, Giacomo
2013-01-01
The issue of general covariance of spinors and related objects is reconsidered. Given an oriented manifold M, to each spin structure σ and Riemannian metric g there is associated a space Sσ, g of spinor fields on M and a Hilbert space {H}_{σ, g}= L^2(S_{σ, g}, vol_{g}(M)) of L2-spinors of Sσ, g. The group Diff+(M) of orientation-preserving diffeomorphisms of M acts both on g (by pullback) and on [σ] (by a suitably defined pullback f*σ). Any f ∈ Diff+(M) lifts in exactly two ways to a unitary operator U from {H}_{σ, g} to {H}_{f^*σ ,f^*g}. The canonically defined Dirac operator is shown to be equivariant with respect to the action of U, so in particular its spectrum is invariant under the diffeomorphisms.
Local perturbations of conservative C 1 diffeomorphisms
NASA Astrophysics Data System (ADS)
Buzzi, Jérôme; Crovisier, Sylvain; Fisher, Todd
2017-09-01
A number of techniques have been developed to perturb the dynamics of C 1-diffeomorphisms and to modify the properties of their periodic orbits. For instance, one can locally linearize the dynamics, change the tangent dynamics, or create local homoclinic orbits. These techniques have been crucial for the understanding of C 1 dynamics, but their most precise forms have mostly been shown in the dissipative setting. This work extends these results to volume-preserving and especially symplectic systems. These tools underlie our study of the entropy of C 1-diffeomorphisms in Buzzi et al (2016 (arXiv:1606.01765)). We also give an application to the approximation of transitive invariant sets without genericity assumptions.
Spherical demons: fast diffeomorphic landmark-free surface registration.
Yeo, B T Thomas; Sabuncu, Mert R; Vercauteren, Tom; Ayache, Nicholas; Fischl, Bruce; Golland, Polina
2010-03-01
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 160 k nodes requires less than 5 min when warping the atlas and less than 3 min when warping the subject on a Xeon 3.2 GHz single processor machine. This is comparable to the fastest nondiffeomorphic 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.
Large deformation micromechanics of particle filled acrylics at elevated temperatures
NASA Astrophysics Data System (ADS)
Gunel, Eray Mustafa
The main aim of this study is to investigate stress whitening and associated micro-deformation mechanism in thermoformed particle filled acrylic sheets. For stress whitening quantification, a new index was developed based on image histograms in logarithmic scale of gray level. Stress whitening levels in thermoformed acrylic composites was observed to increase with increasing deformation limit, decreasing forming rate and increasing forming temperatures below glass transition. Decrease in stress whitening levels above glass transition with increasing forming temperature was attributed to change in micro-deformation behavior. Surface deformation feature investigated with scanning electron microscopy showed that source of stress whitening in thermoformed samples was a combination of particle failure and particle disintegration depending on forming rate and temperature. Stress whitening level was strongly correlated to intensity of micro-deformation features. On the other hand, thermoformed neat acrylics displayed no surface discoloration which was attributed to absence of micro-void formation on the surface of neat acrylics. Experimental damage measures (degradation in initial, secant, unloading modulus and strain energy density) have been inadequate in describing damage evolution in successive thermoforming applications on the same sample at different levels of deformation. An improved version of dual-mechanism viscoplastic material model was proposed to predict thermomechanical behavior of neat acrylics under non-isothermal conditions. Simulation results and experimental results were in good agreement and failure of neat acrylics under non-isothermal conditions ar low forming temperatures were succesfully predicted based on entropic damage model. Particle and interphase failure observed in acrylic composites was studied in a multi-particle unit cell model with different volume fractions. Damage evolution due to particle failure and interphase failure was simulated
NASA Astrophysics Data System (ADS)
Brock, Kristy K.; Ménard, Cynthia; Hensel, Jennifer; Jaffray, David A.
2006-03-01
Magnetic resonance imaging (MRI) with an endorectal receiver coil (ERC) provides superior visualization of the prostate gland and its surrounding anatomy at the expense of large anatomical deformation. The ability to correct for this deformation is critical to integrate the MR images into the CT-based treatment planning for radiotherapy. The ability to quantify and understand the physiological motion due to large changes in rectal filling can also improve the precision of image-guided procedures. The purpose of this study was to understand the biomechanical relationship between the prostate, rectum, and bladder using a finite element-based multi-organ deformable image registration method, 'Morfeus' developed at our institution. Patients diagnosed with prostate cancer were enrolled in the study. Gold seed markers were implanted in the prostate and MR scans performed with the ERC in place and its surrounding balloon inflated to varying volumes (0-100cc). The prostate, bladder, and rectum were then delineated, converted into finite element models, and assigned appropriate material properties. Morfeus was used to assign surface interfaces between the adjacent organs and deform the bladder and rectum from one position to another, obtaining the position of the prostate through finite element analysis. This approach achieves sub-voxel accuracy of image co-registration in the context of a large ERC deformation, while providing a biomechanical understanding of the multi-organ physiological relationship between the prostate, bladder, and rectum. The development of a deformable registration strategy is essential to integrate the superior information offered in MR images into the treatment planning process.
Numerical modeling of a large deformation thermoforming process
Schrank, M.G.
1988-04-01
A numerical solution, using finite element methods, is presented for the simulation of a blow-molding process used to form a thermoplastic polymer (polyethylene terephthalate). The constitutive relationship employed in the analysis is a modification of the creep power law, allowing both strain hardening and strain rate hardening of the material. Analytical results compare well with experimental data for both rate of deformation during the forming process and strain distribution in the final formed configuration. 15 figs.
Rate type method for large deformation problems of nonlinear elasticity
NASA Astrophysics Data System (ADS)
Liang, Fei; Zhang, Shanyuan
1994-02-01
Firstly, the rate type constitutive expressions of the nonlinear isotropic elasticity by using the Jaumann, Truesdell, and Green-Naghdi stress rate are obtained respectively. Then, through analyzing the simple shear deformation for Mooney-Rivlin material, three kinds of rate type constitutive equations are verified to be equivalent to the original equation. Finally, the rate type variational principles are also presented and the Ritz method is used to obtain the numerical solution of a rectangular rubber membrane under uniaxial stretch.
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
Large stable deformation of dielectric elastomers driven on mode of steady electric field
NASA Astrophysics Data System (ADS)
Zhang, Junshi; Zhao, Jianwen; Wang, Shu; Chen, Hualing; Li, Dichen
2017-05-01
Dielectric elastomers (DEs) are capable of large deformation under the actuation of applied voltage and sprayed charge. Actuation of DE under voltage control is prone to electromechanical instabilities, while the DE under charge control always survives from instabilities with sacrificing a large deformation. In this article, a novel actuation mode of steady electric field is proposed. By tuning applied voltage and sprayed charge during viscoelastic creep, an invariable electric field is generated. Such an actuation method can both avoid the occurrence of electromechanical instabilities and guarantee a large deformation in DE actuation.
Role of Higher-Order Elastic Moduli in Large Elastic Finite Deformation
NASA Astrophysics Data System (ADS)
Suzuki, Tetsuro; Osuka, Ken'ichi
1993-05-01
It is proposed here that the change in free energy of crystals associated with large elastic finite deformation can be estimated using higher-order elastic moduli up to a limited order. Numerical estimation of the change in free energy is performed for two examples of finite elastic deformation, with use of the data for higher-order elastic moduli of β-brass obtained by Swartz. One example is Bain deformation, which converts a bcc lattice into an fcc lattice or vice versa. The other is shear deformation along the (100) atomic plane.
Tunability of soft phononic crystals through large deformation (Conference Presentation)
NASA Astrophysics Data System (ADS)
Bao, Ronghao; Chen, Weiqiu
2017-04-01
Phononic crystals (PCs) have attracted plenty of attention during the past two decades, and a lot of work has been devoted to the numerical, theoretical and experimental analysis of the band gaps of the PCs with 1D, 2D and 3D structures, respectively. The band gaps have been found to be related to the topology of the unit cell, filling ratio, contrast of the material properties between matrix and inclusion, and so on. However, they are fixed when the fabrication of corresponding devices is finished in most cases. Usually, biasing fields (e.g. initial stress, initial deformation, pre-existing electric field, external electric field and magnetic field, etc.) can be utilized to tailor the band gaps in flexible and reconfigurable ways. Recently, the instability-induced deformations triggered by external mechanical loadings have been found to be an effective and reversible way to tune the band gaps and the directionality of PCs made from soft materials, such as silicon and rubber. In this project, a novel design of PCs will be proposed, which consists of perforated plate with some individual beams fixed on the boundary of internal holes. When the external mechanical loading applied on the PCs reaches a threshold value, instability-induced buckling will be triggered and the internal beams might be in contact with each other, which will significantly alter the topology of PCs, and therefore effectively tune the band gaps of PCs. A systematical analysis will be carried out to study the influences on the tunability of PCs with different designs through finite element methods (FEM).
Large Elasto-Plastic Deformations in Bi-Material Components by Coupled FE-EFGM
NASA Astrophysics Data System (ADS)
Harmain, G. A.; Jameel, Azher; Najar, Farooq A.; Masoodi, Junaid H.
2017-08-01
In the recent years, the coupled finite element-element free Galerkin method (coupled FE-EFGM) has found wide application in modeling large elasto-plastic deformations in bi-material components. The coupled FE-EFGM applies EFGM in the portion of the domain where large deformations are expected to occur, whereas the rest of the domain is discretized into conventional finite elements. The large deformation occurring in the domain has been modeled by using the total Lagrangian approach. The non-linear elasto-plastic behavior of the material has been represented by the Ramberg-Osgood model. Finally, two numerical problems are solved by the coupled FE-EFGM to illustrate its applicability, efficiency and accuracy in modeling large elasto-plastic deformations in bi-material samples.
Du, Jia; Hosseinbor, A Pasha; Chung, Moo K; Bendlin, Barbara B; Suryawanshi, Gaurav; Alexander, Andrew L; Qiu, Anqi
2014-10-01
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. (2013) 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) reconstruction, as well as reduces memory requirement. In addition, since the BFOR signal basis is orthonormal, the L(2) 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 that 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. Copyright © 2014 The Authors. Published by Elsevier B.V. All rights
Doh, I; Lee, W C; Cho, Y-H; Pisano, A P; Kuypers, F A
2012-04-23
We analyze the deformability of individual red blood cells (RBCs) using SiCMA technology. Our approach is adequate to quickly measure large numbers of individual cells in heterogeneous populations. Individual cells are trapped in a large-scale array of micro-wells, and dielectrophoretic (DEP) force is applied to deform the cells. The simple structures of micro-wells and DEP electrodes facilitate the analysis of thousands of RBCs in parallel. This unique method allows the correlation of red cell deformation with cell surface and cytosolic characteristics to define the distribution of individual cellular characteristics in heterogeneous populations.
Symmetric diffeomorphic modeling of longitudinal structural MRI.
Ashburner, John; Ridgway, Gerard R
2012-01-01
This technology report describes the longitudinal registration approach that we intend to incorporate into SPM12. It essentially describes a group-wise intra-subject modeling framework, which combines diffeomorphic and rigid-body registration, incorporating a correction for the intensity inhomogeneity artifact usually seen in MRI data. Emphasis is placed on achieving internal consistency and accounting for many of the mathematical subtleties that most implementations overlook. The implementation was evaluated using examples from the OASIS Longitudinal MRI Data in Non-demented and Demented Older Adults.
Symmetric Diffeomorphic Modeling of Longitudinal Structural MRI
Ashburner, John; Ridgway, Gerard R.
2013-01-01
This technology report describes the longitudinal registration approach that we intend to incorporate into SPM12. It essentially describes a group-wise intra-subject modeling framework, which combines diffeomorphic and rigid-body registration, incorporating a correction for the intensity inhomogeneity artifact usually seen in MRI data. Emphasis is placed on achieving internal consistency and accounting for many of the mathematical subtleties that most implementations overlook. The implementation was evaluated using examples from the OASIS Longitudinal MRI Data in Non-demented and Demented Older Adults. PMID:23386806
Hemi-wedge osteotomy in the management of large angular deformities around the knee joint.
El-Alfy, Barakat Sayed
2016-08-01
Angular deformity around the knee joint is a common orthopedic problem. Many options are available for the management of such problem with varying degrees of success and failure. The aim of the present study was to assess the results of hemi-wedge osteotomy in the management of big angular deformities about the knee joint. Twenty-eight limbs in 21 patients with large angular deformities around the knee joint were treated by the hemi-wedge osteotomy technique. The ages ranged from 12 to 43 years with an average of 19.8 years. The deformity ranged from 20° to 40° with a mean of 30.39° ± 5.99°. The deformities were genu varum in 12 cases and genu valgum in 9 cases. Seven cases had bilateral deformities. Small wedge was removed from the convex side of the bone and put in the gap created in the other side after correction of the deformity. At the final follow-up, the deformity was corrected in all cases except two. Full range of knee movement was regained in all cases. The complications included superficial wound infection in two cases, overcorrection in one case, pain along the lateral aspect of the knee in one case and recurrence of the deformity in one case. No cases were complicated by nerve injury or vascular injury. Hemi-wedge osteotomy is a good method for treatment of deformities around the knee joint. It can correct large angular deformities without major complications.
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.
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.
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
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.
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.
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.
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.
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.
Filtering in the Diffeomorphism Group and the Registration of Point Sets
Gao, Yi; Rathi, Yogesh; Bouix, Sylvain; Tannenbaum, Allen
2013-01-01
The registration of a pair of point sets as well as the estimation of their pointwise correspondences is a challenging and important task in computer vision. In this paper, we present a method to estimate the diffeomorphic deformation, together with the pointwise correspondences, between a pair of point sets. Many of the registration problems are iteratively solved by estimating the correspondence, locally optimizing certain cost functionals over the rigid or similarity or affine transformation group, then estimating the correspondence again, and so on. This type of approach, however, is well-known to be susceptible to suboptimal local solutions. In this paper, we first adopt the perspective of treating the registration as a posterior estimation optimization problem and solve it accordingly via a particle-filtering framework. Second, within such a framework, the diffeomorphic registration is performed to correct the nonlinear deformation of the points. In doing so, we provide a solution less susceptible to local minima. We provide the experimental results, which include challenging medical data sets where the two point sets differ by 180° rotation as well as local deformations, to highlight the algorithm’s capability of robustly finding the more globally optimal solution for the registration task. PMID:22752129
Progressive failure of large deformation composites under dynamic tensile loading
NASA Astrophysics Data System (ADS)
Xing, Liqun
The applications of polymer based composite materials in structural components under dynamic loading have increased dramatically. The accurate understanding and modeling of the material mechanical behavior is the basis for the composite structure design and analysis. This research was designed to investigate the progressive failure nature of woven polymer-based composites under dynamic tensile loading conditions. A plain-woven E-glass/vinyl ester composite was selected and a generalized anisotropic material characterization procedure was developed. Off-axial tensile dynamic loading experiments with different strain rates and temperature was conducted. A nonlinear and rate dependent constitutive model used for the polymer-based composites under tensile dynamic tensile loading was constructed. The comparison shows a good match with testing data and a good prediction of stress to failure values. A hybrid method that combined the classical laminate theory with material microstructure analysis was presented to model the large strain to failure phenomenon. A single material parameter failure criteria based on Monkman-Grant concept was built to represent the materials anisotropic and rate dependency natural for tensile loading. And the strength concept based on the material constitution relationship and failure criteria was established to for structure analyses.
Diffeomorphic sulcal shape analysis on the cortex.
Joshi, Shantanu H; Cabeen, Ryan P; Joshi, Anand A; Sun, Bo; Dinov, Ivo; Narr, Katherine L; Toga, Arthur W; Woods, Roger P
2012-06-01
We present a diffeomorphic approach for constructing intrinsic shape atlases of sulci on the human cortex. Sulci are represented as square-root velocity functions of continuous open curves in R³, and their shapes are studied as functional representations of an infinite-dimensional sphere. This spherical manifold has some advantageous properties--it is equipped with a Riemannian L² metric on the tangent space and facilitates computational analyses and correspondences between sulcal shapes. Sulcal shape mapping is achieved by computing geodesics in the quotient space of shapes modulo scales, translations, rigid rotations, and reparameterizations. The resulting sulcal shape atlas preserves important local geometry inherently present in the sample population. The sulcal shape atlas is integrated in a cortical registration framework and exhibits better geometric matching compared to the conventional euclidean method. We demonstrate experimental results for sulcal shape mapping, cortical surface registration, and sulcal classification for two different surface extraction protocols for separate subject populations.
Diffeomorphic Sulcal Shape Analysis on the Cortex
Joshi, Shantanu H.; Cabeen, Ryan P.; Joshi, Anand A.; Sun, Bo; Dinov, Ivo; Narr, Katherine L.; Toga, Arthur W.; Woods, Roger P.
2014-01-01
We present a diffeomorphic approach for constructing intrinsic shape atlases of sulci on the human cortex. Sulci are represented as square-root velocity functions of continuous open curves in ℝ3, and their shapes are studied as functional representations of an infinite-dimensional sphere. This spherical manifold has some advantageous properties – it is equipped with a Riemannian metric on the tangent space and facilitates computational analyses and correspondences between sulcal shapes. Sulcal shape mapping is achieved by computing geodesics in the quotient space of shapes modulo scales, translations, rigid rotations and reparameterizations. The resulting sulcal shape atlas preserves important local geometry inherently present in the sample population. The sulcal shape atlas is integrated in a cortical registration framework and exhibits better geometric matching compared to the conventional euclidean method. We demonstrate experimental results for sulcal shape mapping, cortical surface registration, and sulcal classification for two different surface extraction protocols for separate subject populations. PMID:22328177
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.
Effect of membrane constitutive equation on the recovery of capsules from large deformations
NASA Astrophysics Data System (ADS)
Gonzalez-Mancera, Andres
2005-11-01
The recovery of capsules after large deformations can be used to calculate its material properties. We focus our attention on the influence of varying the membrane constitutive model and the initial geometry of the capsule on the recovery process. An axisymmetric computational model based on the boundary element method (BEM) is used to simulate the recovery of capsules from small and large deformations. Comparison is made between capsules having: (1) constant cortical (surface) tension [CCT], (2) two-dimensional Hooke's law [H], (3) Mooney-Rivlin law [MR] and (4) Evans and Skalak [ES] membrane models. At small initial deformations similar behavior is observed for all models and appears independent of initial geometry. The recovery process is more sensitive to initial conditions for large deformations due to the non-linear behavior of the elastic membranes. The difference in the local strain distribution caused by variations in the initial geometry significantly affects the membrane stress field at large deformations, and thus the recovery process.
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.
Incremental Carcass Theory of Polycrystalline Media at Large Elastic and Plastic Deformations
NASA Astrophysics Data System (ADS)
Akhundov, V. M.
2016-11-01
A two-level carcass theory as applied to media with a polycrystalline structure at large elastic and plastic deformation of crystals (crystal grains) is presented. The theory is incremental, in accordance with the incremental nature of governing equations of a crystal, which take into account the prehistory of its deformation in the medium. The theory is based on the field of carcass (macroscopic) displacements, which determines the material displacements of carcass points and carcass (macroscopic) deformations of the medium. At the macromechanical level, the equations of macroscopic deformation and motion are given in an incremental form. At the micromechanical (locally structural) level, incremental microboundary-value problems for nodal presentation blocks of the polycrystalline material are solved on the basis of carcass displacements and their increments. From the internal fields of nodal blocks and their increments found, the incremental macroscopic stresses are determined, which allow one to close the system of equations of the macromechanical level of analysis.
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.
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.
Distinctive signatures of space-time diffeomorphism breaking in EFT of inflation
Bartolo, Nicola; Cannone, Dario; Ricciardone, Angelo; Tasinato, Gianmassimo E-mail: dario.cannone@pd.infn.it E-mail: g.tasinato@swansea.ac.uk
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.
Effect of GFRP spacer on local deformation of large superconductor in coil pack
Nishimura, Arata; Tamura, Hitoshi; Mito, Toshiyuki; Yamamoto, Junya
1994-07-01
Design and construction of the Large Helical Device (LHD) are in progress at the National Institute for Fusion Science (NIFS) in Japan. The LHD has superconducting poloidal and helical coils, and many efforts have been undertaken to develop these large superconductors. When designing a large superconducting magnet, the mechanical behavior of the wound structure becomes a very important factor since the apparent rigidity affects the design of a coil support structure and the superconducting coil needs to endure the large electro-magnetic force it creates. Also, non-linear mechanical behavior should yield the instability of the magnet. In this paper, local deformation in a large conductor caused by GFRP 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 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.
Horseshoe and entropy for C1 surface diffeomorphisms
NASA Astrophysics Data System (ADS)
Gan, Shaobo
2002-05-01
Let M be a two-dimensional closed Riemannian manifold and denote by Diff1(M) the set of C1 diffeomorphisms on M. Then, the C1 interior of {f in Diff1(M):h(f) = 0} is equal to the C1 interior of the closure of the Morse-Smale systems and equal to the C1 interior of the set of diffeomorphisms having no horseshoe.
Gravity and thermal deformation of large primary mirror in space telescope
NASA Astrophysics Data System (ADS)
Wang, Xin; Jiang, Shouwang; Wan, Jinlong; Shu, Rong
2016-10-01
The technology of integrating mechanical FEA analysis with optical estimation is essential to simulate the gravity deformation of large main mirror and the thermal deformation such as static or temperature gradient of optical structure. We present the simulation results of FEA analysis, data processing, and image performance. Three kinds of support structure for large primary mirror which have the center holding structure, the edge glue fixation and back support, are designed and compared to get the optimal gravity deformation. Variable mirror materials Zerodur/SiC are chosen and analyzed to obtain the small thermal gradient distortion. The simulation accuracy is dependent on FEA mesh quality, the load definition of structure, the fitting error from discrete data to smooth surface. A main mirror with 1m diameter is designed as an example. The appropriate structure material to match mirror, the central supporting structure, and the key aspects of FEA simulation are optimized for space application.
DIFFEOMORPHIC SURFACE FLOWS: A NOVEL METHOD OF SURFACE EVOLUTION.
Zhang, Sirong; Younes, Laurent; Zweck, John; Ratnanather, J Tilak
2008-01-01
We describe a new class of surface flows, diffeomorphic surface flows, induced by restricting diffeomorphic flows of the ambient Euclidean space to a surface. Different from classical surface PDE flows such as mean curvature flow, diffeomorphic surface flows are solutions of integro-differential equations in a group of diffeomorphisms. They have the potential advantage of being both topology-invariant and singularity free, which can be useful in computational anatomy and computer graphics. We first derive the Euler-Lagrange equation of the elastic energy for general diffeomorphic surface flows, which can be regarded as a smoothed version of the corresponding classical surface flows. Then we focus on diffeomorphic mean curvature flow. We prove the short-time existence and uniqueness of the flow, and study the long-time existence of the flow for surfaces of revolution. We present numerical experiments on synthetic and cortical surfaces from neuroimaging studies in schizophrenia and auditory disorders. Finally we discuss unresolved issues and potential applications.
DIFFEOMORPHIC SURFACE FLOWS: A NOVEL METHOD OF SURFACE EVOLUTION*
Zhang, Sirong; Younes, Laurent; Zweck, John; Ratnanather, J. Tilak
2009-01-01
We describe a new class of surface flows, diffeomorphic surface flows, induced by restricting diffeomorphic flows of the ambient Euclidean space to a surface. Different from classical surface PDE flows such as mean curvature flow, diffeomorphic surface flows are solutions of integro-differential equations in a group of diffeomorphisms. They have the potential advantage of being both topology-invariant and singularity free, which can be useful in computational anatomy and computer graphics. We first derive the Euler–Lagrange equation of the elastic energy for general diffeomorphic surface flows, which can be regarded as a smoothed version of the corresponding classical surface flows. Then we focus on diffeomorphic mean curvature flow. We prove the short-time existence and uniqueness of the flow, and study the long-time existence of the flow for surfaces of revolution. We present numerical experiments on synthetic and cortical surfaces from neuroimaging studies in schizophrenia and auditory disorders. Finally we discuss unresolved issues and potential applications. PMID:20016768
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
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.
Why is the tube model inapplicable for entangled polymer dynamics at large deformation
NASA Astrophysics Data System (ADS)
Wang, Shi-Qing; Wang, Yangyang
2011-03-01
Accumulating experimental revelation of the phenomenology governing dynamics of entangled linear polymers at large deformations has caused us to question the legitimacy of the tube model as an acceptable theoretical description of nonlinear polymer rheology. Upon an explicit investigation of its premise, we have come to realize that the tube model did not overcome the difficulty confronted by other theories and did not contain the basic physics required to explain why and how the entanglement network must break down during large deformations. It considered an unrealistic situation where a load-bearing chain relaxed fast in an affinely deformed tube so that only the chain segment orientation produced the shear stress for applied rates lower than the Rouse rate. A non-monotonic relation between the resulting shear stress and imposed strain for startup shear and step deformations arose from excessive chain orientation not collapse of the entanglement network. In the tube model, the nature of the overshoot is not yielding (transition from elastic deformation to flow), but an elastic instability. Accumulating experimental observations contradict this picture. This presentation will elucidate how the emerging physical picture differs from that of the unrealistic tube model.
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.
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 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%.
Hybrid feature-based diffeomorphic registration for tumor tracking in 2-D liver ultrasound images.
Cifor, Amalia; Risser, Laurent; Chung, Daniel; Anderson, Ewan M; Schnabel, Julia A
2013-09-01
Real-time ultrasound image acquisition is a pivotal resource in the medical community, in spite of its limited image quality. This poses challenges to image registration methods, particularly to those driven by intensity values. We address these difficulties in a novel diffeomorphic registration technique for tumor tracking in series of 2-D liver ultrasound. Our method has two main characteristics: 1) each voxel is described by three image features: intensity, local phase, and phase congruency; 2) we compute a set of forces from either local information (Demons-type of forces), or spatial correspondences supplied by a block-matching scheme, from each image feature. A family of update deformation fields which are defined by these forces, and inform upon the local or regional contribution of each image feature are then composed to form the final transformation. The method is diffeomorphic, which ensures the invertibility of deformations. The qualitative and quantitative results yielded by both synthetic and real clinical data show the suitability of our method for the application at hand.
Liu, Xiaozheng; Yuan, Zhenming; Zhu, Junming; Xu, Dongrong
2013-12-07
The demons algorithm is a popular algorithm for non-rigid image registration because of its computational efficiency and simple implementation. The deformation forces of the classic demons algorithm were derived from image gradients by considering the deformation to decrease the intensity dissimilarity between images. However, the methods using the difference of image intensity for medical image registration are easily affected by image artifacts, such as image noise, non-uniform imaging and partial volume effects. The gradient magnitude image is constructed from the local information of an image, so the difference in a gradient magnitude image can be regarded as more reliable and robust for these artifacts. Then, registering medical images by considering the differences in both image intensity and gradient magnitude is a straightforward selection. In this paper, based on a diffeomorphic demons algorithm, we propose a chain-type diffeomorphic demons algorithm by combining the differences in both image intensity and gradient magnitude for medical image registration. Previous work had shown that the classic demons algorithm can be considered as an approximation of a second order gradient descent on the sum of the squared intensity differences. By optimizing the new dissimilarity criteria, we also present a set of new demons forces which were derived from the gradients of the image and gradient magnitude image. We show that, in controlled experiments, this advantage is confirmed, and yields a fast convergence.
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.
Shao, Yongliang; Zhang, Lei; Hao, Xiaopeng; Wu, Yongzhong; Dai, Yuanbin; Tian, Yuan; Huo, Qin
2014-08-05
We report a method to obtain the stress of crystalline materials directly from lattice deformation by Hooke's law. The lattice deformation was calculated using the crystallographic orientations obtained from electron backscatter diffraction (EBSD) technology. The stress distribution over a large area was obtained efficiently and accurately using this method. Wurtzite structure gallium nitride (GaN) crystal was used as the example of a hexagonal crystal system. With this method, the stress distribution of a GaN crystal was obtained. Raman spectroscopy was used to verify the stress distribution. The cause of the stress distribution found in the GaN crystal was discussed from theoretical analysis and EBSD data. Other properties related to lattice deformation, such as piezoelectricity, can also be analyzed by this novel approach based on EBSD data.
NASA Astrophysics Data System (ADS)
Shao, Yongliang; Zhang, Lei; Hao, Xiaopeng; Wu, Yongzhong; Dai, Yuanbin; Tian, Yuan; Huo, Qin
2014-08-01
We report a method to obtain the stress of crystalline materials directly from lattice deformation by Hooke's law. The lattice deformation was calculated using the crystallographic orientations obtained from electron backscatter diffraction (EBSD) technology. The stress distribution over a large area was obtained efficiently and accurately using this method. Wurtzite structure gallium nitride (GaN) crystal was used as the example of a hexagonal crystal system. With this method, the stress distribution of a GaN crystal was obtained. Raman spectroscopy was used to verify the stress distribution. The cause of the stress distribution found in the GaN crystal was discussed from theoretical analysis and EBSD data. Other properties related to lattice deformation, such as piezoelectricity, can also be analyzed by this novel approach based on EBSD data.
Shao, Yongliang; Zhang, Lei; Hao, Xiaopeng; Wu, Yongzhong; Dai, Yuanbin; Tian, Yuan; Huo, Qin
2014-01-01
We report a method to obtain the stress of crystalline materials directly from lattice deformation by Hooke's law. The lattice deformation was calculated using the crystallographic orientations obtained from electron backscatter diffraction (EBSD) technology. The stress distribution over a large area was obtained efficiently and accurately using this method. Wurtzite structure gallium nitride (GaN) crystal was used as the example of a hexagonal crystal system. With this method, the stress distribution of a GaN crystal was obtained. Raman spectroscopy was used to verify the stress distribution. The cause of the stress distribution found in the GaN crystal was discussed from theoretical analysis and EBSD data. Other properties related to lattice deformation, such as piezoelectricity, can also be analyzed by this novel approach based on EBSD data. PMID:25091314
Lefever, Joel A; Jaime García, José; Smith, Joshua H
2013-05-31
A biphasic model for noncommunicating hydrocephalus in patient-specific geometry is proposed. The model can take into account the nonlinear behavior of brain tissue under large deformation, the nonlinear variation of hydraulic conductivity with deformation, and contact with a rigid, impermeable skull using a recently developed algorithm. The model was capable of achieving over a 700 percent ventricular enlargement, which is much greater than in previous studies, primarily due to the use of an anatomically realistic skull recreated from magnetic resonance imaging rather than an artificial skull created by offsetting the outer surface of the cerebrum. The choice of softening or stiffening behavior of brain tissue, both having been demonstrated in previous experimental studies, was found to have a significant effect on the volume and shape of the deformed ventricle, and the consideration of the variation of the hydraulic conductivity with deformation had a modest effect on the deformed ventricle. The model predicts that noncommunicating hydrocephalus occurs for ventricular fluid pressure on the order of 1300 Pa.
Qiu, Anqi; Younes, Laurent; Wang, Lei; Ratnanather, J. Tilak; Gillepsie, Sarah K.; Kaplan, Gillian; Csernansky, John; Miller, Michael I.
2015-01-01
Spatial normalization is a crucial step in assessing patterns of neuroanatomical structure and function associated with health and disease. Errors that occur during spatial normalization can influence hypothesis testing due to the dimensionalities of mapping algorithms and anatomical manifolds (landmarks, curves, surfaces, volumes) used to drive the mapping algorithms. The primary aim of this paper is to improve statistical inference using multiple anatomical manifolds and Large Deformation Diffeomorphic Metric Mapping (LDDMM) algorithms. We propose that combining information generated by the various manifolds and algorithms improves the reliability of hypothesis testing. We used this unified approach to assess variation in the thickness of the cingulate gyrus in subjects with schizophrenia and healthy comparison subjects. Three different LDDMM algorithms for mapping landmarks, curves and triangulated meshes were used to transform thickness maps of the cingulate surfaces into an atlas coordinate system. We then tested for group differences by combining the information from the three types of anatomical manifolds and LDDMM mapping algorithms. The unified approach provided reliable statistical results and eliminated ambiguous results due to surface mismatches. Subjects with schizophrenia had non-uniform cortical thinning over the left and right cingulate gyri, especially in the anterior portion, as compared to healthy comparison subjects. PMID:17613251
A closed form large deformation solution of plate bending with surface effects.
Liu, Tianshu; Jagota, Anand; Hui, Chung-Yuen
2017-01-04
We study the effect of surface stress on the pure bending of a finite thickness plate under large deformation. The surface is assumed to be isotropic and its stress consists of a part that can be interpreted as a residual stress and a part that stiffens as the surface increases its area. Our results show that residual surface stress and surface stiffness can both increase the overall bending stiffness but through different mechanisms. For sufficiently large residual surface tension, we discover a new type of instability - the bending moment reaches a maximum at a critical curvature. Effects of surface stress on different stress components in the bulk of the plate are discussed and the possibility of self-bending due to asymmetry of the surface properties is also explored. The results of our calculations provide insights into surface stress effects in the large deformation regime and can be used as a test for implementation of finite element methods for surface elasticity.
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
Microstructure and micro-texture evolution during large strain deformation of Inconel alloy IN718
Nayan, Niraj; Gurao, N.P.; Narayana Murty, S.V.S.; Jha, Abhay K.; Pant, Bhanu; George, Koshy M.
2015-12-15
The hot deformation behaviour of Inconel alloy IN718 was studied in the temperature range of 950–1100 °C and at strain rates of 0.01 and 1 s{sup −1} with a view to understand the microstructural evolution as a function of strain rate and temperature. For this purpose, a single hit, hot isothermal plane strain compression (PSC) technique was used. The flow curves obtained during PSC exhibited weak flow softening at higher temperatures. Electron backscattered diffraction analysis (EBSD) of the PSC tested samples at the location of maximum strain revealed dynamic recrystallisation occurring at higher temperatures. Based on detailed microstructure and microtexture analyses, it was concluded that single step, large strain deformation has a distinct advantage in the thermo-mechanical processing of Inconel alloy IN718. - Highlights: • Plane strain compression (PSC) on IN718 was conducted. • Evolution of microstructure during large strain deformation was studied. • Flow curves exhibited weak softening at higher temperatures and dipping of the flow curve at a strain rate of 1 s{sup −1}. • Optimization of microstructure and process parameter for hot rolling possible by plane strain compression testing • Dynamic recrystallisation occurs in specimens deformed at higher temperatures and lower strain rates.
NASA Astrophysics Data System (ADS)
Wang, Bing; Wang, Zhengang; He, Tianhu
2016-12-01
To explore the time-dependent dissipative behaviors of a circular dielectric elastomer membrane subject to force and voltage, a viscoelastic model is formulated based on the nonlinear theory for dissipative dielectrics. The circular membrane is attached centrally to a light rigid disk and then connected to a fixed rigid ring. When subject to force and voltage, the membrane deforms into an out-of plane shape, undergoing large deformation. The governing equations to describe the large deformation are derived by using energy variational principle while the viscoelasticity of the membrane is describe by a two-unit spring-dashpot model. The evolutions of the considered variables and the deformed shape are illustrated graphically. In calculation, the effects of the voltage and the pre-stretch on the electromechanical behaviors of the membrane are examined and the results show that they significantly influence the electromechanical behaviors of the membrane. It is expected that the present model may provide some guidelines in the design and application of such dielectric elastomer transducers.
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.
NASA Technical Reports Server (NTRS)
Ko, William L.; Fleischer, Van Tran; Lung, Shun-Fat
2017-01-01
For shape predictions of structures under large geometrically nonlinear deformations, Curved Displacement Transfer Functions were formulated based on a curved displacement, traced by a material point from the undeformed position to deformed position. The embedded beam (depth-wise cross section of a structure along a surface strain-sensing line) was discretized into multiple small domains, with domain junctures matching the strain-sensing stations. Thus, the surface strain distribution could be described with a piecewise linear or a piecewise nonlinear function. The discretization approach enabled piecewise integrations of the embedded-beam curvature equations to yield the Curved Displacement Transfer Functions, expressed in terms of embedded beam geometrical parameters and surface strains. By entering the surface strain data into the Displacement Transfer Functions, deflections along each embedded beam can be calculated at multiple points for mapping the overall structural deformed shapes. Finite-element linear and nonlinear analyses of a tapered cantilever tubular beam were performed to generate linear and nonlinear surface strains and the associated deflections to be used for validation. The shape prediction accuracies were then determined by comparing the theoretical deflections with the finiteelement- generated deflections. The results show that the newly developed Curved Displacement Transfer Functions are very accurate for shape predictions of structures under large geometrically nonlinear deformations.
NASA Astrophysics Data System (ADS)
Shao, Xinxing; Dai, Xiangjun; Chen, Zhenning; Dai, Yuntong; Dong, Shuai; He, Xiaoyuan
2016-12-01
The development of stereo-digital image correlation (stereo-DIC) enables the application of vision-based technique that uses digital cameras to the deformation measurement of materials and structures. Compared with traditional contact measurements, the stereo-DIC technique allows for non-contact measurement, has a non-intrusive characteristic, and can obtain full-field deformation information. In this paper, a speckle-based calibration method is developed to calibrate the stereo-DIC system when the system is applied for deformation measurement of large engineering components. By combining speckle analysis with the classical relative orientation algorithm, relative rotation and translation between cameras can be calibrated based on analysis of experimental speckle images. For validation, the strain fields of a four-point bending beam and an axially loaded concrete column were determined by the proposed calibration method and stereovision measurement. As a practical application, the proposed calibration method was applied for strain measurement of a ductile iron cylindrical vessel in the drop test. The measured results verify that the proposed calibration method is effective for deformation measurement of large engineering components.
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
2016-04-13
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.
Symmetry reduction for quantized diffeomorphism-invariant theories of connections
NASA Astrophysics Data System (ADS)
Bojowald, M.; Kastrup, H. A.
2000-08-01
Given a symmetry group acting on a principal fibre bundle, symmetric states of the quantum theory of a diffeomorphism-invariant theory of connections on this fibre bundle are defined. These symmetric states, equipped with a scalar product derived from the Ashtekar-Lewandowski measure for loop quantum gravity, form a Hilbert space of their own. Restriction to this Hilbert space yields a quantum symmetry reduction procedure within the framework of spin-network states, the structure of which is analysed in detail. Three illustrating examples are discussed: reduction of (3+1)- to (2+1)-dimensional quantum gravity, spherically symmetric quantum electromagnetism and spherically symmetric quantum gravity. In the latter system the eigenvalues of the area operator applied to the spherically symmetric spin-network states have the form An∝(n(n + 2))1/2, n = 0,1,2,..., giving An∝n for large n. This result clarifies (and reconciles) the relationship between the more complicated spectrum of the general (non-symmetric) area operator in loop quantum gravity and the old Bekenstein proposal that An∝n.
NASA Astrophysics Data System (ADS)
Tao, Xiaoming
2008-11-01
This paper presents a systematic study of various fibrous structures that exhibit excellent strain/force sensing properties for repeated large deformation (up to 50% or more). The multiple-scaled investigation has been conducted with fibers, yarns and fabrics made from intrinsic electrically conductive materials or coated with conductive polymers or composites. The structures and electrical conductivity of these fibrous assemblies during large deformation have been characterized by various experimental techniques. Several challenges of using textiles as strain sensors and solutions to various problems are discussed. A theoretical analysis of knitted fabric strain sensors is presented to link the fiber properties and fabric structure with the electrical conductivity of the sensors as a function of strain/force.
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.
Study of superplastic deformation in an FeAl based alloy with large grains
Li, D.; Shan, A.; Liu, Y.; Lin, D.
1995-08-15
In this paper some results of studies on a superplastically deformed FeAl based alloy are reported. The tensile behavior of the FeAl based alloy Fe-36.5Al-2Ti (in atomic percent) under different strain rates at high temperatures was examined by optical microscopy. The results revealed that the FeAl based alloy with the grain size of 350 {micro}m exhibited a large elongation of more than 140% at 900 C and 1,000 C under a strain rate range of 1.39{times}10{sup {minus}4}/s{approximately}2.78{times}10{sup {minus}2}/s. The maximum elongation is 208% at 1,000 C under a strain rate of 1.39{times}10{sup {minus}2}/s. The reason for the large elongation is ascribed to the dynamic recovery and recrystallization in this alloy during deformation at high temperatures.
Computational Modeling for Fluid-Porous Structure Interaction with Large Structural Deformation
NASA Astrophysics Data System (ADS)
Zakerzadeh, Rana; Zunino, Paolo
2016-11-01
In this work, we utilize numerical models to investigate the importance of poroelasticity in the interaction of blood flow with a porohyperelastic vessel wall, and to establish a connection between the apparent viscoelastic behavior of the structure part and the intramural filtration flow. The main novelty is in the design of a Nitsche's splitting strategy, which separates the fluid from the structure sub-problems for the Fluid-Porous Structure Interaction system undergoing large deformations. The general idea is to use this model to study the influence of different parameters on energy dissipation in a poroelastic medium. We also study a new benchmark test specifically designed to investigate the effect of poroelasticity on large deformations.
Diffeomorphic functional brain surface alignment: Functional demons.
Nenning, Karl-Heinz; Liu, Hesheng; Ghosh, Satrajit S; Sabuncu, Mert R; Schwartz, Ernst; Langs, Georg
2017-08-01
Aligning brain structures across individuals is a central prerequisite for comparative neuroimaging studies. Typically, registration approaches assume a strong association between the features used for alignment, such as macro-anatomy, and the variable observed, such as functional activation or connectivity. Here, we propose to use the structure of intrinsic resting state fMRI signal correlation patterns as a basis for alignment of the cortex in functional studies. Rather than assuming the spatial correspondence of functional structures between subjects, we have identified locations with similar connectivity profiles across subjects. We mapped functional connectivity relationships within the brain into an embedding space, and aligned the resulting maps of multiple subjects. We then performed a diffeomorphic alignment of the cortical surfaces, driven by the corresponding features in the joint embedding space. Results show that functional alignment based on resting state fMRI identifies functionally homologous regions across individuals with higher accuracy than alignment based on the spatial correspondence of anatomy. Further, functional alignment enables measurement of the strength of the anatomo-functional link across the cortex, and reveals the uneven distribution of this link. Stronger anatomo-functional dissociation was found in higher association areas compared to primary sensory- and motor areas. Functional alignment based on resting state features improves group analysis of task based functional MRI data, increasing statistical power and improving the delineation of task-specific core regions. Finally, a comparison of the anatomo-functional dissociation between cohorts is demonstrated with a group of left and right handed subjects. Copyright © 2017 Elsevier Inc. All rights reserved.
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
NASA Astrophysics Data System (ADS)
Reed, Kenneth W.
1992-09-01
A new hybrid stress finite element algorithm suitable for analyses of large quasistatic deformation of inelastic solids is presented. Principal variables in the formulation are the nominal stress rate and spin. The finite element equations which result are discrete versions of the equations of compatibility and angular momentum balance. Consistent reformulation of the constitutive equation and accurate and stable time integration of the stress are discussed at length. Examples which bring out the feasibility and performance of the algorithm conclude the work.
Integration of Large Deformation Finite Element Formulations in Flexible Multibody System Algorithms
2010-07-01
important ANCF feature was demonstrated by using the general large deformation Neo-Hookean and Mooney - Rivlin constitutive models [5]. The results...applications will include belt drives and rubber chain tracked vehicles. In the applications considered in this research project, the important features of...nonlinear dynamic rubber chains and belt drives models are developed using ANCF finite elements that allow for a straight forward implementation of
NASA Technical Reports Server (NTRS)
Neiswander, R. S.
1978-01-01
A technology base was developed for a wide variety of applications oriented sensors to meet requirements for the fabrication, assembly, test, surface figure monitoring, and ultimately surface figure active control of large space antennas. An optical sensor technique is described which establishes an ideal centerline at each beam during fabrication or later during assembly. Deviations from the centerline, either in lateral deformation or in twist, are measured to produce limit warnings or to evoke active control at the building machine.
NASA Technical Reports Server (NTRS)
Neiswander, R. S.
1978-01-01
A technology base was developed for a wide variety of applications oriented sensors to meet requirements for the fabrication, assembly, test, surface figure monitoring, and ultimately surface figure active control of large space antennas. An optical sensor technique is described which establishes an ideal centerline at each beam during fabrication or later during assembly. Deviations from the centerline, either in lateral deformation or in twist, are measured to produce limit warnings or to evoke active control at the building machine.
Non Linear Effects of Applied Loads and Large Deformations on Aircraft Normal Modes
2000-05-01
the sBams secteo lia base for the solution of many structural dynamics and static dermations. aeroelastic problems (flutter, response to gust and 0...manufacturing and certification of the Horizontal Tailplanes (HTP). In the case of a megaliner, the Figure 1. Beam with static axial load and dynamic...method. The effect of in-plane loading is considered large static deformations. in two parts. First, effects of direct in-plane loading only Most of the
Deformation of large micro-electromechanical systems (MEMS) due to thermal and intrinsic stresses
NASA Astrophysics Data System (ADS)
Saif, Mohammed T.; MacDonald, Noel C.
1995-05-01
We present a theoretical and experimental study of large micro mechanical cantilever beams fabricated by the SCREAM (single crystal reactive ion etching and metallization) process. SCREAM beams consist of an SCS core coated by films of SiO2 or nitride and metal. Thermal and intrinsic stresses develop in the beams due to the films and tend to deform them. Such deformations result in non-planar structures. For small micro mechanical systems, the non-planarity is negligible. When the structures' size is of the order of few millimeters, the non-planarity may limit the performance of the device. Here, we first treat the thermal and intrinsic strains of the films as material properties and measure them experimentally for PECVD SiO2. We then develop a simple model to predict the deformation of cantilever beams due to the thermal and intrinsic strains of SiO2 or nitride film. The model predicts that the non-planarity of the beam can be controlled by properly choosing the cross sectional dimension of the beam. We validate the theoretical prediction by fabricating cantilever beams which deform with negative, positive, and almost zero curvature.
A study of the proximal wedge shelf osteotomy for correction of large IM angle HAV deformity.
Fabrikant, Jerry M; Colarco, Justin
2012-02-01
Many procedures have been identified to correct hallux abducto valgus deformity of the foot. Due to surgical skill level, complexity, and risk of complications, more procedures have been defined for distal than proximal correction. The senior author has used an alternative proximal procedure to correct larger hallux abducto valgus deformities, which may prove to be as effective as traditional procedures. The purpose of this study was to examine the short-term clinical and radiographic results of the proximal wedge shelf osteotomy and evaluate its potential as a satisfactory option for correction of larger bunion deformities. The study revealed many positive outcomes as measured radiographically in preoperative and postoperative hallux abductus, intermetatarsal and metatarsal elevation/declination angles, and clinically by first metatarsophalangeal joint scores and patients' subjective postoperative responses. From a review of the literature and results of the study, the authors conclude that the wedge shelf osteotomy can be used as an effective alternative for correcting larger bunion deformities with an intermetatarsal angle as large as 20° and a hallux valgus angle up to 38°. The advantages of this procedure include ability to correct in more than one plane, good bone-to-bone contact, and ease of fixation with 2 screws in an easily visible dorsal-to-plantar area. Disadvantages include the technical challenge of the procedure and its learning curve and some shortening of the first metatarsal. Levels of Evidence : Therapeutic Level IV.
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 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
General framework for dynamic large deformation contact problems based on phantom-node X-FEM
NASA Astrophysics Data System (ADS)
Broumand, P.; Khoei, A. R.
2017-08-01
This paper presents a general framework for modeling dynamic large deformation contact-impact problems based on the phantom-node extended finite element method. The large sliding penalty contact formulation is presented based on a master-slave approach which is implemented within the phantom-node X-FEM and an explicit central difference scheme is used to model the inertial effects. The method is compared with conventional contact X-FEM; advantages, limitations and implementational aspects are also addressed. Several numerical examples are presented to show the robustness and accuracy of the proposed method.
Dynamics of diffeomorphism degrees of freedom at a horizon
Chung, Hyeyoun
2011-04-15
We define a set of boundary conditions that ensure the presence of a null hypersurface with the essential characteristics of a horizon, using the formalism of weakly isolated horizons as a guide. We then determine the diffeomorphisms that preserve these boundary conditions, and derive a dynamical action for these diffeomorphisms in a neighborhood of the horizon. The action is similar to that of the Liouville theory, and the equation of motion of the gravitational degrees of freedom approaches that of a free two-dimensional conformal field in the near-horizon region.
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.
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.
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.
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.
Modelling the large strain solid phase deformation behaviour of polymer nanoclay composites
NASA Astrophysics Data System (ADS)
Spencer, P. E.; Spares, R.; Sweeney, J.; Coates, P. D.
2008-12-01
This work concerns the solid phase deformation processing of polypropylene/nanoclay composites, for which the materials are stretched to large tensile deformations at elevated temperatures. Under these conditions the polymer matrix is nonlinearly dependent on time and strain rate. A constitutive model that is a combination of an Eyring process and physically-based molecular chain models has been shown to give a good representation of the polymer behavior, which includes strain-rate dependent yielding and stress relaxation. In order to model the nanocomposite, platelike regions that are relatively stiff are introduced into a continuum of model polymer material. This is done using a Monte Carlo approach that sequentially places non-overlapping platelets in the matrix. The process for introducing the platelets has the potential to produce platelet orientation distributions that conform with prescribed statistics, such as may be deduced from observations on real nanocomposite.
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.
Extensional Elastica in large deformation as $Gamma $ Γ -limit of a discrete 1D mechanical system
NASA Astrophysics Data System (ADS)
Alibert, Jean-Jacques; Della Corte, Alessandro; Giorgio, Ivan; Battista, Antonio
2017-04-01
The present paper deals with the rigorous homogenization of a discrete system consisting of extensible rods linked by rotational springs. Specifically, a Γ -convergence result is proven for a sequence of discrete measure functionals En, describing the energy of the discrete system, toward the continuous energy functional for the extensible Euler beam model ( Elastica) in large deformation regime. A relative compactness result for the sequence En is also proven. Moreover, numerical results are shown on the deformed shape and on the total energy of the system when the number of elements of the discrete system increases. The numerical convergence of the energy to a definite value is shown in two cases. The results provide rigorous justification of a very commonly used algorithm for the discretization of the extensible Euler beam, namely Hencky-type beam model.
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.
NASA Astrophysics Data System (ADS)
Akhundov, V. M.
2010-12-01
On the basis of a mathematical model of large deformations of homogeneous and fiber-reinforced bodies of revolution, the deformation of all-rubber and rubber-cord clutches made by using the tire technology is investigated. The results of a theoretical and numerical analysis of torsion of the clutches are compared with experimental data.
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.
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
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.
Zhang, Jie; Sheng, Lei; Liu, Jing
2014-11-19
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.
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.
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.
Friction and scale-dependent deformation processes of large experimental carbonate faults
NASA Astrophysics Data System (ADS)
Tesei, Telemaco; Carpenter, Brett M.; Giorgetti, Carolina; Scuderi, Marco M.; Sagy, Amir; Scarlato, Piergiorgio; Collettini, Cristiano
2017-07-01
We studied the frictional behaviour and deformation products of large (20 cm × 20 cm bare surfaces) experimental limestone faults. We sheared samples in a direct shear configuration, with an imposed normal force of 40-200 kN and shear velocity of 10 μm/s. The steady-state shearing of these surfaces yielded a coefficient of friction 0.7<μ<1 (average μ∼0.9), significantly higher than gouge friction of the same material, μ∼0.6. Frictional healing, studied via slide-hold-slide tests, is null (Δμ≤0 upon re-shear). Moreover, sliding of these surfaces is accompanied by dilatation and production of grooves, gouge striations and fault mirrors. These products are entirely analogous to slip surface phenomena found on natural limestone-bearing faults at both the macroscale and at the microscale. We infer that high friction, accompanied by dilatant deformation, and null frictional healing are the macroscopic effect of brittle damage on the sliding surface, constrained by the strength of the rock and by fast healing processes in the gouge. Simultaneously to brittle failure, plastic deformation occurs on the sliding surface and inside the intact rock via nanoparticle formation (mirrors) and twinning at the micron scale. Because of the similarity between experimental and natural structures, we suggest that sliding of carbonate-bearing faults in the uppermost crust could be characterized by high friction, fast healing and strongly dilatant deformation, which would help to explain shallow seismicity frequently documented in carbonatic terrains such as the Northern Apennines of Italy.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Liu, Liwu; Sun, Shouhua; Yu, Kai; Zhang, Zhen; Liu, Yanju; Leng, Jinsong
2009-07-01
Dielectric elastomers (DE) are one of the important electroactive polymers used as actuators in adaptive structures due to their outstanding abilities to generate very large deformations while subjected to an external electric filed. In this paper, Mooney-Rivlin elastic strain energy function with two material constants is applied to analyze the electromechanical stability performance of DE. This elastic strain energy couplied with the electric energy incorporating linear permittivity is the main item to construct the free energy of the system. Particular numerical results are also processing for further understanding of DE's typical stability performance. The proposed model offers great help in guiding the design and fabrication of actuators featuring DE.
Accounting for Large Amplitude Protein Deformation during in Silico Macromolecular Docking
Bastard, Karine; Saladin, Adrien; Prévost, Chantal
2011-01-01
Rapid progress of theoretical methods and computer calculation resources has turned in silico methods into a conceivable tool to predict the 3D structure of macromolecular assemblages, starting from the structure of their separate elements. Still, some classes of complexes represent a real challenge for macromolecular docking methods. In these complexes, protein parts like loops or domains undergo large amplitude deformations upon association, thus remodeling the surface accessible to the partner protein or DNA. We discuss the problems linked with managing such rearrangements in docking methods and we review strategies that are presently being explored, as well as their limitations and success. PMID:21541061
NASA Astrophysics Data System (ADS)
Kadashevich, Yu. I.; Pomytkin, S. P.
2010-12-01
The history of origination and development of the endochronic approach is briefly described. The Novozhilov-Kadashevich version of the flow theory is used to write the constitutive relations of endochronic type and to present a method for their generalization to the domain of large deformations and rotations. Several examples of qualitative description of inelastic second-order effects are demonstrated. It is also noted that, within the framework of geometrically linear theories of phenomenological-type inelasticity, such effects cannot be explained theoretically from unified positions.
Accounting for large amplitude protein deformation during in silico macromolecular docking.
Bastard, Karine; Saladin, Adrien; Prévost, Chantal
2011-02-22
Rapid progress of theoretical methods and computer calculation resources has turned in silico methods into a conceivable tool to predict the 3D structure of macromolecular assemblages, starting from the structure of their separate elements. Still, some classes of complexes represent a real challenge for macromolecular docking methods. In these complexes, protein parts like loops or domains undergo large amplitude deformations upon association, thus remodeling the surface accessible to the partner protein or DNA. We discuss the problems linked with managing such rearrangements in docking methods and we review strategies that are presently being explored, as well as their limitations and success.
A framework for deformable image registration validation in radiotherapy clinical applications
Varadhan, Raj; Karangelis, Grigorios; Krishnan, Karthik; Hui, Susanta
2013-01-01
Quantitative validation of deformable image registration (DIR) algorithms is extremely difficult because of the complexity involved in constructing a deformable phantom that can duplicate various clinical scenarios. The purpose of this study is to describe a framework to test the accuracy of DIR based on computational modeling and evaluating using inverse consistency and other methods. Three clinically relevant organ deformations were created in prostate (distended rectum and rectal gas), head and neck (large neck flexion), and lung (inhale and exhale lung volumes with variable contrast enhancement) study sets. DIR was performed using both B-spline and diffeomorphic demons algorithms in the forward and inverse direction. A compositive accumulation of forward and inverse deformation vector fields was done to quantify the inverse consistency error (ICE). The anatomical correspondence of tumor and organs at risk was quantified by comparing the original RT structures with those obtained after DIR. Further, the physical characteristics of the deformation field, namely the Jacobian and harmonic energy, were computed to quantify the preservation of image topology and regularity of spatial transformation obtained in DIR. The ICE was comparable in prostate case but the B-spline algorithm had significantly better anatomical correspondence for rectum and prostate than diffeomorphic demons algorithm. The ICE was 6.5 mm for demons algorithm for head and neck case when compared to 0.7 mm for B-spline. Since the induced neck flexion was large, the average Dice similarity coefficient between both algorithms was only 0.87, 0.52, 0.81, and 0.67 for tumor, cord, parotids, and mandible, respectively. The B-spline algorithm accurately estimated deformations between images with variable contrast in our lung study, while diffeomorphic demons algorithm led to gross errors on structures affected by contrast variation. The proposed framework offers the application of known deformations on
Samdani, Amer F; Hwang, Steven W; Singla, Anuj; Bennett, James T; Ames, Robert J; Kimball, Jeff S
2017-10-01
A paucity of data exists studying outcomes of patients with syringomyelia undergoing spinal deformity correction. The literature does not stratify patients by syrinx size, which is likely a major contributor to outcomes. The study aimed to compare differences in outcomes between patients with large (≥4 mm) and small syrinxes (<4 mm) undergoing spinal deformity correction. This is a retrospective review. The sample included 28 patients (11 with large syrinx [LS, >4 mm] and 17 with small syrinx [SS, <4 mm]). The outcome measures were radiographic, operative, and neurophysiological measures. We retrospectively reviewed 28 patients with syringomyelia who underwent spine deformity surgery with 2-year follow-up. Demographic, surgical, and radiographic data were collected and compared preoperatively and at 2 years. The LS group (11 patients) trended toward more left-sided thoracic curves (36% vs. 18%, p=.38) and was more likely to have had a Chiari decompression (45% vs. 12%, p=.08). The LS patients had larger preoperative major curves (LS=66° vs. SS=57°, p=.05), more thoracic kyphosis (LS=42°, SS=24°, p<.01), and greater rib prominences (LS=16°, SS=13°, p=.04). The LS patients had more levels fused (LS=12.2, SS=11.2, p=.05), higher estimated blood loss (EBL) (LS=1068 cc, SS=832 cc, p=.04), and a trend toward less percent correction of the major curve (LS=57%, SS=65%, p=.18). Four of 11 LS patients (36%) did not have somatosensory evoked potentials, and one of these also did not have motor evoked potentials. Neuromonitoring changes occurred in 3 of 11 (27%) LS patients and in none of the SS patients, with no postoperative deficits. Outcomes of patients with syringomyelia undergoing spine deformity surgery are dependent on the size of the syrinx. Those with large syringomyelia are fused longer with more EBL and less correction. Spine surgeons should be aware that these patients are more likely to have less reliable neuromonitoring, with a higher chance
Roeder, Blayne A; Kokini, Klod; Robinson, J Paul; Voytik-Harbin, Sherry L
2004-12-01
The ability to create extracellular matrix (ECM) constructs that are mechanically and biochemically similar to those found in vivo and to understand how their properties affect cellular responses will drive the next generation of tissue engineering strategies. To date, many mechanisms by which cells biochemically communicate with the ECM are known. However the mechanisms by which mechanical information is transmitted between cells and their ECM remain to be elucidated. "Self-assembled" collagen matrices provide an in vitro-model system to study the mechanical behavior of ECM. To begin to understand how the ECM and the cells interact mechanically, the three-dimensional (3D) mechanical properties of the ECM must be quantified at the micro-(local) level in addition to information measured at the macro-(global) level. Here we describe an incremental digital volume correlation (IDVC) algorithm to quantify large (>0.05) 3D mechanical strains in the microstructure of 3D collagen matrices in response to applied mechanical loads. Strain measurements from the IDVC algorithm rely on 3D confocal images acquired from collagen matrices under applied mechanical loads. The accuracy and the precision of the IDVC algorithm was verified by comparing both image volumes collected in succession when no deformation was applied to the ECM (zero strain) and image volumes to which simulated deformations were applied in both ID and 3D (simulated strains). Results indicate that the IDVC algorithm can accurately and precisely determine the 3D strain state inside largely deformed collagen ECMs. Finally, the usefulness of the algorithm was demonstrated by measuring the microlevel 3D strain response of a collagen ECM loaded in tension.
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.
NASA Astrophysics Data System (ADS)
Guallini, Luca; Brozzetti, Francesco; Marinangeli, Lucia
2012-08-01
The present study is the first attempt at a detailed structural and kinematic analysis of large-scale deformational systems observed in the South Polar Layered Deposits (SPLDs) in the Promethei Lingula (PL) margins (Mars). By systematically collecting attitude data referable to previously unknown deformational structures and defining the cross-cut relationships of the structures, we reconstructed a deformational history consisting of two superimposed, well-defined stages. The first stage is dominated by large-scale strike-slip and transtensional faults arranged into conjugate systems and delimiting shear zones that show a wide range of subsidiary structures, including normal and reverse faults, drag folds, boudins, S-C tectonites and sub-horizontal interstratal shear planes marked by sygmoidal boudins. Other typical structures referable to this event are ductile folds (locally true convolute folds) and lobes (ball-and-pillow structures) affecting certain marker beds of the succession. We suggest that the structural assemblage might be the expression of a shallow soft-sediment tectonics that possibly occurred during warm periods of the South Pole climate. The second stage seems to affect the weaker and in certain cases pre-deformed stratigraphic levels of the SPLD succession. This stage is mainly characterized by extensional deformations caused by gravity. The consequence of the deformations is the nucleation of Deep-Seated Gravitational Slope Deformations (DSGSDs) marked by typical morphostructures, such as scarps, trenches and bulging basal contractant zones. These phenomena were never observed within an ice cap. According to terrestrial modeling, these slow collapses were caused by (1) the presence of detachment levels (i.e., subhorizontal bedding planes) along which the ice-sheet margins can slide and (2) the development of listric faults within the glacial mass, which merge with sub-horizontal shear planes in the subsurface. The presence of complex
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.
Bevill, Grant; Eswaran, Senthil K; Gupta, Atul; Papadopoulos, Panayiotis; Keaveny, Tony M
2006-12-01
Large-deformation bending and buckling have long been proposed as failure mechanisms by which the strength of trabecular bone can be affected disproportionately to changes in bone density, and thus may represent an important aspect of bone quality. We sought here to quantify the contribution of large-deformation failure mechanisms on strength, to determine the dependence of these effects on bone volume fraction and architecture, and to confirm that the inclusion of large-deformation effects in high-resolution finite element models improves predictions of strength versus experiment. Micro-CT-based finite element models having uniform hard tissue material properties were created from 54 cores of human trabecular bone taken from four anatomic sites (age = 70+/-11; 24 male, 27 female donors), which were subsequently biomechanically tested to failure. Strength predictions were made from the models first including, then excluding, large-deformation failure mechanisms, both for compressive and tensile load cases. As expected, strength predictions versus experimental data for the large-deformation finite element models were significantly improved (p < 0.001) relative to the small deformation models in both tension and compression. Below a volume fraction of about 0.20, large-deformation failure mechanisms decreased trabecular strength from 5-80% for compressive loading, while effects were negligible above this volume fraction. Step-wise nonlinear multiple regression revealed that structure model index (SMI) and volume fraction (BV/TV) were significant predictors of these reductions in strength (R2 = 0.83, p < 0.03). Even so, some low-density specimens having nearly identical volume fraction and SMI exhibited up to fivefold differences in strength reduction. We conclude that within very low-density bone, the potentially important biomechanical effect of large-deformation failure mechanisms on trabecular bone strength is highly heterogeneous and is not well explained by
Sub-subleading soft gravitons and large diffeomorphisms
NASA Astrophysics Data System (ADS)
Campiglia, Miguel; Laddha, Alok
2017-01-01
We present strong evidence that the sub-subleading soft theorem in semiclassical (tree level) gravity discovered by Cachazo and Strominger is equivalent to the conservation of asymptotic charges associated to a new class of vector fields not contained within the previous extensions of BMS algebra. Our analysis crucially relies on analyzing the hitherto established equivalences between soft theorems and Ward identities from a new perspective. In this process we naturally (re)discover a class of `magnetic' charges at null infinity that are associated to the dual of the Weyl tensor.
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
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
Seismic and gravity anomaly evidence of large-scale compressional deformation off SW Portugal
NASA Astrophysics Data System (ADS)
Cunha, T. A.; Watts, A. B.; Pinheiro, L. M.; Myklebust, R.
2010-04-01
Multi-channel seismic and gravity anomaly data have been used to determine the extent of compressional deformation along the SW Portugal rifted continental margin and place constraints on the long-term (> 1 M.a.) strength of the lithosphere. The seismic sections suggest that the region of compressional deformation is broad (˜ 100 km) and has been active since the Miocene. Integration with recently compiled high-resolution bathymetric data shows that the main thrust front is located along the base of the continental slope, between north of the Gorringe Bank and the Setúbal Canyon. Gravity data show that the thrust front is associated with a narrow isostatic anomaly 'high' of up to 70 mGal that is flanked on its NW edge by a broad 'low' of up to 20 mGal. This high-low 'couple' can be explained by compressional loading of extended continental lithosphere that increased its flexural strength (or equivalent elastic thickness, Te) since rifting. Based on combined 2-D backstripping and gravity modelling techniques we estimate a Te of ˜ 10 km during the main stretching episode, in the Late Jurassic (maybe earliest Cretaceous?), and of 35-50 km during the Miocene to Recent compression. The existence of a broad region of deformation off SW Portugal together with a strong lithosphere have implications for the rupture models of large earthquakes in the region, such as the 1755 Great Lisbon earthquake, particularly when accounting for a complex, multiple rupture in faults which cut through lithosphere of distinct nature and origin, as appears to be required by modellers to explain the historical observational data.
NASA Astrophysics Data System (ADS)
Guyard, H.; Le Friant, A.; Brunet, M.; Boudon, G.; Emmanuel, L.; Caron, B.; Villemant, B.; Feuillet, N.
2015-12-01
Flank-instabilities constitute a recurrent process in the long-term evolution of many volcanoes. A very large submarine landslide deposit (~2100 km2, ~300 km3) drilled southwest Martinique island during the IODP Exp. 340 in 2012 is likely associated with one (or more) major volcanic flank collapse of Mount Pelée during the Late Pleistocene. A recent study revealed that this D1/D2 deposit is emergent in its central part, frontally confined, and mainly comprises remobilized seafloor sediments rather than debris avalanche material from the volcanic edifice (Brunet et al., subm). Here, we investigate the sedimentary microstructures and timing of deformation from the central (Hole 1400B, ~37 km from the coastline) and distal (Hole 1399A, ~70 km from the coastline) units of the D1/D2 deposit, in order to better understand the emplacement dynamics of such potentially tsunamigenic submarine landslides. High resolution CT-Scan analyses were continuously performed on more than 300 m of sediment cores, in order to characterize and distinguish the internal architecture and the complex deformation features of the sediments at each drilling site. The establishment of the stratigraphy, based on δ18O measurements and AMS 14C dating, is still in progress and may confirm the possible link between the submarine landslide deposits and the flank collapse scars observed on the subaerial part of Martinique. These new insights into the timing and emplacement processes of this large submarine landslide will have important implications for tsunami hazards. ReferenceBrunet, M., Le Friant, A., Boudon, G., Lafuerza, S., Talling, P., Hornbach, M., Lebas, E., Guyard, H., and IODP Expedition 340 science party, submitted. Composition, geometry and emplacement dynamics of a large volcanic island landslide offshore Martinique: from volcano flank-collapse to seafloor sediment failure? Geochemistry, Geophysics, Geosystems.
An improved approach to estimate large-gradient deformation using high resolution TerraSAR-X data
NASA Astrophysics Data System (ADS)
Liu, D.; Chen, R.; Riedel, B.; Niemeier, W.
2014-09-01
Interferometric Synthetic Aperture Radar (InSAR) has shown unique capabilities in numerous applications for deformation monitoring. However, InSAR will lose effectiveness with large-gradient deformation due to the limitation of maximum detectable phase gradient and the phase unwrapping step of InSAR. Coalfield is the exact object providing such challenges for InSAR technique. Strong mining activities often induces large scale non-linear deformation with large gradient. This paper integrates offset tracking technique based on Corner Reflector (CR) and InSAR to overcome relevant problems. By applying offset tracking to high resolution TerraSAR-X intensity images, the coarse estimation of large deformation was obtained and extracted, allowing the following InSAR processing to carry out phase unwrapping correctly. Finally, the fine estimation of deformation was done by the Persistent Scatterer InSAR (PSI) technique. The detected deformation time series indicated good root-mean-square errors (RMSE), validated by GPS in situ investigation. All InSAR data were processed in the open source software StaMPS and one in-house InSAR package.
Steps Towards Understanding Large-scale Deformation of Gas Hydrate-bearing Sediments
NASA Astrophysics Data System (ADS)
Gupta, S.; Deusner, C.; Haeckel, M.; Kossel, E.
2016-12-01
Marine sediments bearing gas hydrates are typically characterized by heterogeneity in the gas hydrate distribution and anisotropy in the sediment-gas hydrate fabric properties. Gas hydrates also contribute to the strength and stiffness of the marine sediment, and any disturbance in the thermodynamic stability of the gas hydrates is likely to affect the geomechanical stability of the sediment. Understanding mechanisms and triggers of large-strain deformation and failure of marine gas hydrate-bearing sediments is an area of extensive research, particularly in the context of marine slope-stability and industrial gas production. The ultimate objective is to predict severe deformation events such as regional-scale slope failure or excessive sand production by using numerical simulation tools. The development of such tools essentially requires a careful analysis of thermo-hydro-chemo-mechanical behavior of gas hydrate-bearing sediments at lab-scale, and its stepwise integration into reservoir-scale simulators through definition of effective variables, use of suitable constitutive relations, and application of scaling laws. One of the focus areas of our research is to understand the bulk coupled behavior of marine gas hydrate systems with contributions from micro-scale characteristics, transport-reaction dynamics, and structural heterogeneity through experimental flow-through studies using high-pressure triaxial test systems and advanced tomographical tools (CT, ERT, MRI). We combine these studies to develop mathematical model and numerical simulation tools which could be used to predict the coupled hydro-geomechanical behavior of marine gas hydrate reservoirs in a large-strain framework. Here we will present some of our recent results from closely co-ordinated experimental and numerical simulation studies with an objective to capture the large-deformation behavior relevant to different gas production scenarios. We will also report on a variety of mechanically relevant
NASA Astrophysics Data System (ADS)
Goh, C. P.; Ismail, H.; Yen, K. S.; Ratnam, M. M.
2017-01-01
The incremental digital image correlation (DIC) method has been applied in the past to determine strain in large deformation materials like rubber. This method is, however, prone to cumulative errors since the total displacement is determined by combining the displacements in numerous stages of the deformation. In this work, a method of mapping large strains in rubber using DIC in a single-step without the need for a series of deformation images is proposed. The reference subsets were deformed using deformation factors obtained from the fitted mean stress-axial stretch ratio curve obtained experimentally and the theoretical Poisson function. The deformed reference subsets were then correlated with the deformed image after loading. The recently developed scanner-based digital image correlation (SB-DIC) method was applied on dumbbell rubber specimens to obtain the in-plane displacement fields up to 350% axial strain. Comparison of the mean axial strains determined from the single-step SB-DIC method with those from the incremental SB-DIC method showed an average difference of 4.7%. Two rectangular rubber specimens containing circular and square holes were deformed and analysed using the proposed method. The resultant strain maps from the single-step SB-DIC method were compared with the results of finite element modeling (FEM). The comparison shows that the proposed single-step SB-DIC method can be used to map the strain distribution accurately in large deformation materials like rubber at much shorter time compared to the incremental DIC method.
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
NASA Astrophysics Data System (ADS)
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.
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.
Group-wise diffeomorphic diffusion tensor image registration.
Geng, Xiujuan; Gu, Hong; Shin, Wanyong; Ross, Thomas J; Yang, Yihong
2010-01-01
We propose an unbiased group-wise diffeomorphic registration technique to normalize a group of diffusion tensor (DT) images. Our method uses an implicit reference group-wise registration framework to avoid bias caused by reference selection. Log-Euclidean metrics on diffusion tensors are used for the tensor interpolation and computation of the similarity cost functions. The overall energy function is constructed by a diffeomorphic demons approach. The tensor reorientation is performed and implicitly optimized during the registration procedure. The performance of the proposed method is compared with reference-based diffusion tensor imaging (DTI) registration methods. The registered DTI images have smaller shape differences in terms of reduced variance of the fractional anisotropy maps and more consistent tensor orientations. We demonstrate that fiber tract atlas construction can benefit from the group-wise registration by producing fiber bundles with higher overlaps.
Representations of spacetime diffeomorphisms. I. Canonical parametrized field theories
Isham, C.J.; Kuchar, K.V.
1985-10-15
The super-Hamiltonian and supermomentum in canonical geometrodynamics or in a parametried field theory on a given Riemannian background have Poisson brackets which obey the Dirac relations. By smearing the supermomentum with vector fields VepsilonL Diff..sigma.. on the space manifold ..sigma.., the Lie algebra L Diff ..sigma.. of the spatial diffeomorphism group Diff ..sigma.. can be mapped antihomomorphically into the Poisson bracket algebra on the phase space of the system. The explicit dependence of the Poisson brackets between two super-Hamiltonians on canonical coordinates (spatial metrics in geometrodynamics and embedding variables in parametrized theories) is usually regarded as an indication that the Dirac relations cannot be connected with a representation of the complete Lie algebra L Diff M of spacetime diffeomorphisms.
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.
Large N limit of β-ensembles and deformed Seiberg-Witten relations
NASA Astrophysics Data System (ADS)
Bourgine, Jean-Emile
2012-08-01
We study the β-ensemble that represents conformal blocks of Liouville theory on the sphere. This quantity is related through AGT conjecture to the Nekrasov instanton partition function of 4d {N} = 2 SU (2) gauge theory with four flavors. We focus on the large N limit, equivalent to the Nekrasov-Shatashvili limit where one of the Ω-background deformation parameters is vanishing. A quantized Seiberg-Witten differential form is defined perturbatively in ℏ as the singular part of the β-ensemble resolvent. Using the Dyson collective field action, we show that the free energy obeys the Seiberg-Witten relations. As suggested by Mironov and Morozov, the quantized differential form can be obtained from the classical one by the action of a differential operator in the hypermultiplet masses and the Coulomb branch modulus.
NASA Astrophysics Data System (ADS)
Liu, Yanju; Liu, Liwu; Yu, Kai; Sun, Shouhua; Leng, Jinsong
2009-09-01
Dielectric elastomers are one of the important electroactive polymers used as actuators in adaptive structures due to their outstanding ability to generate very large deformations when subjected to an external electric field. In this paper, the Mooney-Rivlin elastic strain energy function with two material constants is used to analyze the electromechanical stability performance of a dielectric elastomer. This elastic strain energy together with the electric energy incorporating linear permittivity are the main items to construct the free energy of the system. Particular numerical results are also calculated for a further understanding of the dielectric elastomer's typical stability performance. The proposed model offers great help in guiding the design and fabrication of actuators featuring dielectric elastomers.
NASA Astrophysics Data System (ADS)
Zhao, Jian-Fu; Li, Zhen-Dong; Li, Hui-Xiong; Li, Jing
2010-09-01
Using the level-set method and the continuum interface model, the axisymmetric thermocapillary migration of gas bubbles in an immiscible bulk liquid with a temperature gradient at moderate to large Marangoni number is simulated numerically. Constant material properties of the two phases are assumed. Steady state of the motion can always be reached. The terminal migration velocity decreases monotonously with the increase of the Marangoni number due to the wrapping of isotherms around the front surface of the bubble. Good agreements with space experimental data and previous theoretical and numerical studies in the literature are evident. Slight deformation of bubble is observed, but no distinct influence on the motion occurs. It is also found that the influence of the convective transport of heat inside bubbles cannot be neglected at finite Marangoni number, while the influence of the convective transport of momentum inside bubbles may be actually negligible.
Large-deformation and long-time behavior of entangled melts in complex geometries
NASA Astrophysics Data System (ADS)
Zhu, Xiangyang; Wang, Shi-Qing
2012-02-01
Recent particle-tracking velocimetric (PTV) observations have revealed strain localization either during startup shear beyond the stress overshoot or after a large step shear of entangled polymers [e.g., Macromolecules, 42, 6261 (2009)]. The physical pictures leading to these decohesion events have been put forward [J. Chem. Phys. 127, 064903(2007); J. Rheol. 53, 1389 (2009)]. In this presentation we apply the particle-tracking velocimetric method [Macromol. Mater. Engr. 292, 15 (2007)] to study similar strain localization phenomena originating from yielding of the entanglement network in other forms of deformation including uniaxial extension, ``squeeze flow'' and extrusion of polymers from a wide open space into a narrow opening. The striking discontinuities in the velocity profile can all be understood in terms of a shear yielding criterion. The research is funded, in part, by a grant from the National Science Foundation (CMMI-0926522)
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.
Implications of diffeomorphism invariance for observables in gravity
NASA Astrophysics Data System (ADS)
Donnelly, William
2017-01-01
Physical observables in quantum gravity must be diffeomorphism-invariant. Such observables are nonlocal and hence do not obey the standard field-theoretic formulation of microcausality. I will show how to construct such 'gravitationally dressed' observables in perturbative gravity that become local in the weak gravity limit, and characterize gravitational corrections to microcausality. I will also derive bounds on how localized an operator's gravitational dressing can be. Based on with Steve Giddings, and with Don Marolf and Eric Mintun.
Diffeomorphic Multi-Frame Non-Rigid Registration of Cell Nuclei in 2D and 3D Live Cell Images.
Tektonidis, Marco; Rohr, Karl
2017-03-01
To gain a better understanding of cellular and molecular processes, it is important to quantitatively analyze the motion of subcellular particles in live cell microscopy image sequences. Since, generally, the subcellular particles move and cell nuclei move as well as deform, it is important to decouple the movement of particles from that of the cell nuclei using non-rigid registration methods. We have developed a diffeomorphic multi-frame approach for non-rigid registration of cell nuclei in 2D and 3D live cell fluorescence microscopy images. Our non-rigid registration approach is based on local optic flow estimation, exploits information from multiple consecutive image frames, and determines diffeomorphic transformations in the log-domain, which allows efficient computation of the inverse transformations. To register single images of an image sequence to a reference image, we use a temporally weighted mean image, which is constructed based on inverse transformations and multiple consecutive frames. Using multiple consecutive frames improves the registration accuracy compared to pairwise registration, and using a temporally weighted mean image significantly reduces the computation time compared with previous work. In addition, we use a flow boundary preserving method for regularization of computed deformation vector fields, which prevents from over-smoothing compared to standard Gaussian filtering. Our approach has been successfully applied to 2D and 3D synthetic as well as real live cell microscopy image sequences, and an experimental comparison with non-rigid pairwise, multi-frame, and temporal groupwise registration has been carried out.
Renormalization of circle diffeomorphisms with a break-type singularity
NASA Astrophysics Data System (ADS)
Akhadkulov, Habibulla; Noorani, Mohd Salmi Md; Akhatkulov, Sokhobiddin
2017-07-01
Let f be an orientation-preserving circle diffeomorphism with an irrational rotation number and with a break point ξ0, that is, its derivative f\\prime has a jump discontinuity at this point. Suppose that f\\prime satisfies a certain Zygmund condition dependent on a parameter γ>0. We prove that the renormalizations of f are approximated by Möbius transformations in C 1-topology if γ\\in (0, 1] and in C 2-topology if γ\\in (1, +∞). Moreover, it is shown that, in case of γ\\in (1, +∞) the coefficients of Möbius transformations get asymptotically linearly dependent. Further, consider two circle diffeomorphisms with a break point, with the same size of the break and satisfying Zygmund condition with γ\\in (1, +∞). We prove that, under a certain technical condition on rotation numbers, the renormalizations of these diffeomorphisms approach each other in C 2-topology. This paper is dedicated to Professors Akhtam Abdurakhmanovich Dzhalilov and Konstantin Mikhailovich Khanin on the occasion of their 60th birthdays.
Diffeomorphisms as symplectomorphisms in history phase space: Bosonic string model
NASA Astrophysics Data System (ADS)
Kouletsis, I.; Kuchař, K. V.
2002-06-01
The structure of the history phase space G of a covariant field system and its history group (in the sense of Isham and Linden) is analyzed on an example of a bosonic string. The history space G includes the time map
Gravitational and electroweak unification by replacing diffeomorphisms with larger group
NASA Astrophysics Data System (ADS)
Pandres, Dave
2009-11-01
The covariance group for general relativity, the diffeomorphisms, is replaced by a group of coordinate transformations which contains the diffeomorphisms as a proper subgroup. The larger group is defined by the assumption that all observers will agree whether any given quantity is conserved. Alternatively, and equivalently, it is defined by the assumption that all observers will agree that the general relativistic wave equation describes the propagation of light. Thus, the group replacement is analogous to the replacement of the Lorentz group by the diffeomorphisms that led Einstein from special relativity to general relativity, and is also consistent with the assumption of constant light velocity that led him to special relativity. The enlarged covariance group leads to a non-commutative geometry based not on a manifold, but on a nonlocal space in which paths, rather than points, are the most primitive invariant entities. This yields a theory which unifies the gravitational and electroweak interactions. The theory contains no adjustable parameters, such as those that are chosen arbitrarily in the standard model.
NASA Astrophysics Data System (ADS)
Fleitout, L.; Trubienko, O.; Garaud, J.; Vigny, C.; Cailletaud, G.; Simons, W. J.; Satirapod, C.; Shestakov, N.
2012-12-01
A 3D finite element code (Zebulon-Zset) is used to model deformations through the seismic cycle in the areas surrounding the last three large subduction earthquakes: Sumatra, Japan and Chile. The mesh featuring a broad spherical shell portion with a viscoelastic asthenosphere is refined close to the subduction zones. The model is constrained by 6 years of postseismic data in Sumatra area and over a year of data for Japan and Chile plus preseismic data in the three areas. The coseismic displacements on the subduction plane are inverted from the coseismic displacements using the finite element program and provide the initial stresses. The predicted horizontal postseismic displacements depend upon the thicknesses of the elastic plate and of the low viscosity asthenosphere. Non-dimensionalized by the coseismic displacements, they present an almost uniform value between 500km and 1500km from the trench for elastic plates 80km thick. The time evolution of the velocities is function of the creep law (Maxwell, Burger or power-law creep). Moreover, the forward models predict a sizable far-field subsidence, also with a spatial distribution which varies with the geometry of the asthenosphere and lithosphere. Slip on the subduction interface does not induce such a subsidence. The observed horizontal velocities, divided by the coseismic displacement, present a similar pattern as function of time and distance from trench for the three areas, indicative of similar lithospheric and asthenospheric thicknesses and asthenospheric viscosity. This pattern cannot be fitted with power-law creep in the asthenosphere but indicates a lithosphere 60 to 90km thick and an asthenosphere of thickness of the order of 100km with a burger rheology represented by a Kelvin-Voigt element with a viscosity of 3.1018Pas and μKelvin=μelastic/3. A second Kelvin-Voigt element with very limited amplitude may explain some characteristics of the short time-scale signal. The postseismic subsidence is
Numerical simulation of sloshing with large deforming free surface by MPS-LES method
NASA Astrophysics Data System (ADS)
Pan, Xu-jie; Zhang, Huai-xin; Sun, Xue-yao
2012-12-01
Moving particle semi-implicit (MPS) method is a fully Lagrangian particle method which can easily solve problems with violent free surface. Although it has demonstrated its advantage in ocean engineering applications, it still has some defects to be improved. In this paper, MPS method is extended to the large eddy simulation (LES) by coupling with a sub-particle-scale (SPS) turbulence model. The SPS turbulence model turns into the Reynolds stress terms in the filtered momentum equation, and the Smagorinsky model is introduced to describe the Reynolds stress terms. Although MPS method has the advantage in the simulation of the free surface flow, a lot of non-free surface particles are treated as free surface particles in the original MPS model. In this paper, we use a new free surface tracing method and the key point is "neighbor particle". In this new method, the zone around each particle is divided into eight parts, and the particle will be treated as a free surface particle as long as there are no "neighbor particles" in any two parts of the zone. As the number density parameter judging method has a high efficiency for the free surface particles tracing, we combine it with the neighbor detected method. First, we select out the particles which may be mistreated with high probabilities by using the number density parameter judging method. And then we deal with these particles with the neighbor detected method. By doing this, the new mixed free surface tracing method can reduce the mistreatment problem efficiently. The serious pressure fluctuation is an obvious defect in MPS method, and therefore an area-time average technique is used in this paper to remove the pressure fluctuation with a quite good result. With these improvements, the modified MPS-LES method is applied to simulate liquid sloshing problems with large deforming free surface. Results show that the modified MPS-LES method can simulate the large deforming free surface easily. It can not only capture
Large Inelastic Strain Deformation and Fracture of Hexagonal Close Packed Crystalline Alloys
NASA Astrophysics Data System (ADS)
Ziaei, Shoayb
A dislocation-density based multiple slip crystalline plasticity formulation, a nonlinear finite-element approach, and a microstructurally-based fracture methodology were developed and used to investigate behavior in hexagonal close packed (h.c.p.) with a focus on zircaloy-2 polycrystalline aggregates. The validated predictive framework can account for the interrelated effects of dislocation-density interactions, generation, and recovery. An energy criterion was formulated and used to identify 63 unique slip system interactions that can result in either junction formation or slip-system annihilation. These dislocation-density interactions, with the interrelated mechanisms due to recovery and generation, were then used to understand and predict why basal planes are strengthening planes and prismatic planes are the dominant toughening planes. Coherent interfaces, between face-centered cubic (f.c.c.) and h.c.p. crystalline systems, and semi-coherent interfaces, between body-centered cubic (b.c.c.) and h.c.p. systems, were developed to understand how large strain deformation and fracture modes in h.c.p. zircaloy aggregates with f.c.c. and b.c.c. hydrides evolve at different scales. Thirty-six unique transformations were derived for both coherent interfaces between f.c.c. and h.c.p. systems, and semi-coherent interfaces between b.c.c. and h.c.p. systems. For the semicoherent interfaces, misfit strains were determined at the interfaces in terms of the deformation-rate tensor, then used these ORs and initial misfit strains with the dislocation-density crystalline plasticity formulation, the non-linear finite-element and the fracture approach to account for crack nucleation and propagation, and how inelastic slip evolution, stress accumulation, lattice rotation, and adiabatic heating affected nucleation and crack path orientations. The predictions indicate that the physical representation of ORs affect local deformation and fracture behavior due to the interfacial
On Combinatorial Analogs of the Group of Diffeomorphisms of the Circle
NASA Astrophysics Data System (ADS)
Neretin, Yu A.
1993-04-01
The goal of this article is to construct and study groups which, from the point of view of the theory of representations, should resemble the group of diffeomorphisms of the circle. The first type of such groups are the diffeomorphism groups of p-adic projective lines. The second type are groups consisting of diffeomorphisms (satisfying certain conditions) of the absolutes of Bruhat-Tits trees; they can be regarded as precisely the diffeomorphism groups of Cantor perfect sets. Several series of unitary representations of these groups are constructed, including the analogs of highest-weight representations.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Noble, Todd E.; Dixon, John M.
2011-02-01
We investigate the structural evolution of fault-propagation folds and fold-thrust systems with scaled analog modeling carried out using the 5.5 m radius geotechnical centrifuge at C-CORE, St. John's NL. The experiments presented here are the first of their kind, scaled ten times larger than predecessors and deformed using a custom rig with load monitoring and displacement control. Plane-layered models approximately 1 m long and representing 50 km sections are shortened horizontally under an enhanced gravity field of 160 g. The large model scale allows for a proportionally large number of bedding laminations that act as strain markers. This allows detailed analysis of strain partitioning and interplay, both at the scale of a fold-thrust system and the individual fold-thrust structure. Layer-parallel shortening ("LPS") and rotation of fault-bounded blocks are revealed by mapping contraction fault populations and bedding-contraction fault intersection angles. Low-angle contraction faulting and LPS are found to be dominant at early stages of development and rotation of fault-bounded blocks occurs during progressive folding of the hanging-wall panel during fault-propagation folding. Displacement-distance data obtained from major thrusts in the model show relative stretch values, and consequently fault slip/propagation ratios, that are similar to natural structures.
NASA Astrophysics Data System (ADS)
Bouter, Anton; Alderliesten, Tanja; Bosman, Peter A. N.
2017-02-01
Taking a multi-objective optimization approach to deformable image registration has recently gained attention, because such an approach removes the requirement of manually tuning the weights of all the involved objectives. Especially for problems that require large complex deformations, this is a non-trivial task. From the resulting Pareto set of solutions one can then much more insightfully select a registration outcome that is most suitable for the problem at hand. To serve as an internal optimization engine, currently used multi-objective algorithms are competent, but rather inefficient. In this paper we largely improve upon this by introducing a multi-objective real-valued adaptation of the recently introduced Gene-pool Optimal Mixing Evolutionary Algorithm (GOMEA) for discrete optimization. In this work, GOMEA is tailored specifically to the problem of deformable image registration to obtain substantially improved efficiency. This improvement is achieved by exploiting a key strength of GOMEA: iteratively improving small parts of solutions, allowing to faster exploit the impact of such updates on the objectives at hand through partial evaluations. We performed experiments on three registration problems. In particular, an artificial problem containing a disappearing structure, a pair of pre- and post-operative breast CT scans, and a pair of breast MRI scans acquired in prone and supine position were considered. Results show that compared to the previously used evolutionary algorithm, GOMEA obtains a speed-up of up to a factor of 1600 on the tested registration problems while achieving registration outcomes of similar quality.
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
2009-01-01
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.
Pai, Akshay; Sommer, Stefan; Sorensen, Lauge; Darkner, Sune; Sporring, Jon; Nielsen, Mads
2015-12-23
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.
A coupled theory of fluid permeation and large deformations for elastomeric materials
NASA Astrophysics Data System (ADS)
Chester, Shawn A.; Anand, Lallit
2010-11-01
An elastomeric gel is a cross-linked polymer network swollen with a solvent (fluid). A continuum-mechanical theory to describe the various coupled aspects of fluid permeation and large deformations (e.g., swelling and squeezing) of elastomeric gels is formulated. The basic mechanical force balance laws and the balance law for the fluid content are reviewed, and the constitutive theory that we develop is consistent with modern treatments of continuum thermodynamics, and material frame-indifference. In discussing special constitutive equations we limit our attention to isotropic materials, and consider a model for the free energy based on a Flory-Huggins model for the free energy change due to mixing of the fluid with the polymer network, coupled with a non-Gaussian statistical-mechanical model for the change in configurational entropy—a model which accounts for the limited extensibility of polymer chains. As representative examples of application of the theory, we study (a) three-dimensional swelling-equilibrium of an elastomeric gel in an unconstrained, stress-free state; and (b) the following one-dimensional transient problems: (i) free-swelling of a gel; (ii) consolidation of an already swollen gel; and (iii) pressure-difference-driven diffusion of organic solvents across elastomeric membranes.
Large adaptive deformable membrane mirror with high actuator density: design and first prototypes
NASA Astrophysics Data System (ADS)
Hamelinck, Roger; Rosielle, Nick; Steinbuch, Maarten; Doelman, Niek
2005-12-01
A large adaptive deformable mirror with high actuator density is presented. The DM consists of a thin continuous membrane which acts as the correcting element. A grid of low voltage electro-magnetical push-pull actuators, - located in an actuator plate -, impose out-of-plane displacements in the mirror's membrane. To provide a stable and stiff reference plane for the actuators, a mechanically stable and thermally decoupled honeycomb support structure is added. The design is suited for mirrors up to several hundred mm with an actuator pitch of a few mm. One of the key elements in the design is the actuator grid. Each actuator consists of a closed magnetic circuit in which a strong permanent magnet (PM) attracts a ferromagnetic core. Movement of this core is provided by a low stiffness elastic guiding. A coil surrounds the PM. Both the coil and the PM are connected to the fixed world. By applying a current through the coil, the magnetic force acting on the core can be influenced. This force variation will lead to translation of the ferromagnetic core. This movement is transferred to the reflective mirror surface in a piston-free manner. The design allows for a long total stroke and a large inter actuator stroke. The actuators are produced in arrays which make the design modular and easily extendable. The first actuators and an actuator grid are produced and tested in a dedicated test set-up. This paper describes how relevant actuator properties, such as stiffness and efficiency, can be influenced by the design. The power dissipation in the actuator grid is optimized to a few milliwatts per actuator, thereby avoiding active cooling.
Slomka, Noa; Gefen, Amit
2010-06-18
This study introduces a new confocal microscopy-based three-dimensional cell-specific finite element (FE) modeling methodology for simulating cellular mechanics experiments involving large cell deformations. Three-dimensional FE models of undifferentiated skeletal muscle cells were developed by scanning C2C12 myoblasts using a confocal microscope, and then building FE model geometries from the z-stack images. Strain magnitudes and distributions in two cells were studied when the cells were subjected to compression and stretching, which are used in pressure ulcer and deep tissue injury research to induce large cell deformations. Localized plasma membrane and nuclear surface area (NSA) stretches were observed for both the cell compression and stretching simulation configurations. It was found that in order to induce large tensile strains (>5%) in the plasma membrane and NSA, one needs to apply more than approximately 15% of global cell deformation in cell compression tests, or more than approximately 3% of tensile strains in the elastic plate substrate in cell stretching experiments. Utilization of our modeling can substantially enrich experimental cellular mechanics studies in classic cell loading designs that typically involve large cell deformations, such as static and cyclic stretching, cell compression, micropipette aspiration, shear flow and hydrostatic pressure, by providing magnitudes and distributions of the localized cellular strains specific to each setup and cell type, which could then be associated with the applied stimuli.
Extraordinary properties of functional integrals and groups of diffeomorphisms
NASA Astrophysics Data System (ADS)
Belokurov, V. V.; Shavgulidze, E. T.
2017-03-01
A review of the work of the authors is presented, in which corollaries of the quasi-invariance of functional integrals on the Wiener measure with respect to the action of a group of diffeomorphisms are studied, and the behavior of functional integrals with nonlinear nonlocal change of variables of integration is investigated as well. Using these substitutions, the functional integrals over discontinuous paths can be determined. The simplest models of the (Euclidean) quantum field theory are offered, in which the presence of hidden internal symmetries or the allowance for discontinuous paths in functional integrals leads to a number of paradoxical properties contradicting the conventional view.
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.
A Livšic type theorem for germs of analytic diffeomorphisms
NASA Astrophysics Data System (ADS)
Navas, Andrés; Ponce, Mario
2013-01-01
We deal with the problem of the validity of the Livšic theorem for cocycles of diffeomorphisms over a hyperbolic dynamics that satisfy the periodic orbit condition. We give a result in the positive direction for cocycles of germs of analytic diffeomorphisms at the origin.
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.
Wang, X Y; Wang, J B; Qiu, B B; Hu, L F
2015-12-01
Based on the proposed higher order gradient quasi-continuum model, the numerical investigations of the basic mechanical properties and deformation behaviors of human red blood cell (RBC) membrane under large deformation at room temperature (i.e., 300 K) are carried out in the present paper. The results show that RBC membrane is a nonlinear hyperelastic material. The mechanical properties of RBC membrane is dominated by isotropic nature at the stage of initial deformation, however, its anisotropic material properties emerge clearly with the loading increasing. The out-of-plane wrinkling of RBC membrane upon shear loading can be reproduced numerically. With the use of the so-called higher order Cauchy-Born rule as the kinematic description, the bending stiffness of RBC membrane can be considered conveniently.
NASA Technical Reports Server (NTRS)
Reed, K. W.; Atluri, S. N.
1983-01-01
A new hybrid-stress finite element algorithm suitable for analyzing large quasistatic deformations of inelastic solids is presented and its feasibility and performance are demonstrated with examples. The algorithm provides extremely accurate bifurcation analysis which is stable with respect to variation in the finite element mesh, so long as the same type of element is used in every mesh. When the mesh element is varied, the result changes in a predictable manner. The method does not necessarily lead to an upper or lower bound for the critical load. An explicit forward gradient scheme is used to improve stability and is shown to be useful also for elongation-dominated deformations. The application of the method to the onset of necking in plane extension and to deformation and stress in plane extension of an elasticoviscous fluid with an array of cylindrical voids is given in detail.
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.
NASA Astrophysics Data System (ADS)
Makarov, Plotnikov, V. A.; Lysikov, M. V.
2017-07-01
The following study investigates the large-deformation plasticity behavior and acoustic emission in Al-Mg alloy (1560) under high-temperature loading. The accumulation of deformation in the alloy, in conditions of change from room temperature to 500°C, occurs in two temperature intervals (I, II), characterized by different rates of deformation. The rate of deformation accumulation is correlated with acoustic emission. With load increasing in cycles from 40 to 200 MPa, the value of the boundary temperature (Tb) between intervals I and II changes non-monotonically. In cycles with load up to 90 MPa, the Tb value increases, while an increase up to 200 MPa makes Tb shift toward lower temperatures. This suggests that the shift of boundaries in the region of low temperatures and the appearance of high-amplitude pulses of acoustic emission characterize the decrease of the magnitude of thermal fluctuations with increasing mechanical load, leading to the rupture of interatomic bonds in an elementary deformation event.
The diffeomorphism constraint operator in loop quantum gravity
NASA Astrophysics Data System (ADS)
Laddha, Alok; Varadarajan, Madhavan
2011-10-01
We construct the smeared diffeomorphism constraint operator at finite triangulation from the basic holonomy-flux operators of loop quantum gravity (LQG), evaluate its continuum limit on the Lewandowski-Marolf habitat and show that the action of the continuum operator provides an anomaly-free representation of the Lie algebra of diffeomorphisms of the 3-manifold. Key features of our analysis include (i) finite triangulation approximants to the curvature, Fiab, of the Ashtekar-Barbero connection which involve not only small loop holonomies but also small surface fluxes as well as an explicit dependence on the edge labels of the spin network being acted on (ii) the dependence of the small loop underlying the holonomy on both the direction and magnitude of the shift vector field, (iii) continuum constraint operators which do not have finite action on the kinematic Hilbert space, thus implementing a key lesson from recent studies of parameterized field theory by the authors. Features (i) and (ii) provide the first hints in LQG of a conceptual similarity with the so-called mu-bar scheme of loop quantum cosmology. We expect our work to be of use in the construction of an anomaly-free quantum dynamics for LQG.
Quantization of diffeomorphism-invariant theories with fermions
NASA Astrophysics Data System (ADS)
Baez, John C.; Krasnov, Kirill V.
1998-03-01
We extend ideas developed for the loop representation of quantum gravity to diffeomorphism-invariant gauge theories coupled to fermions. Let P→Σ be a principal G-bundle over space and let F be a vector bundle associated to P whose fiber is a sum of continuous unitary irreducible representations of the compact connected gauge group G, each representation appearing together with its dual. We consider theories whose classical configuration space is A×F, where A is the space of connections on P and F is the space of sections of F, regarded as a collection of Grassmann-valued fermionic fields. We construct the "quantum configuration space" Ā×F¯ as a completion of A×F. Using this, we construct a Hilbert space L2(Ā×F¯) for the quantum theory on which all automorphisms of P act as unitary operators, and determine an explicit "spin network basis" of the subspace L2((Ā×F¯)/Ḡ) consisting of gauge-invariant states. We represent observables constructed from holonomies of the connection along paths together with fermionic fields and their conjugate momenta as operators on L2((Ā×F¯)/Ḡ). We also construct a Hilbert space Hdiff of diffeomorphism-invariant states using the group averaging procedure of Ashtekar, Lewandowski, Marolf, Mourão and Thiemann.
Constraining the break of spatial diffeomorphism invariance with Planck data
NASA Astrophysics Data System (ADS)
Graef, L. L.; Benetti, M.; Alcaniz, J. S.
2017-07-01
The current most accepted paradigm for the early universe cosmology, the inflationary scenario, shows a good agreement with the recent Cosmic Microwave Background (CMB) and polarization data. However, when the inflation consistency relation is relaxed, these observational data exclude a larger range of red tensor tilt values, prevailing the blue ones which are not predicted by the minimal inflationary models. Recently, it has been shown that the assumption of spatial diffeomorphism invariance breaking (SDB) in the context of an effective field theory of inflation leads to interesting observational consequences. Among them, the possibility of generating a blue tensor spectrum, which can recover the specific consistency relation of the String Gas Cosmology, for a certain choice of parameters. We use the most recent CMB data to constrain the SDB model and test its observational viability through a Bayesian analysis assuming as reference an extended ΛCDM+tensor perturbation model, which considers a power-law tensor spectrum parametrized in terms of the tensor-to-scalar ratio, r, and the tensor spectral index, nt. If the inflation consistency relation is imposed, r=-8 nt, we obtain a strong evidence in favor of the reference model whereas if such relation is relaxed, a weak evidence in favor of the model with diffeomorphism breaking is found. We also use the same CMB data set to make an observational comparison between the SDB model, standard inflation and String Gas Cosmology.
NASA Astrophysics Data System (ADS)
Yasuda, K.; Tadokoro, K.; Matsuhiro, K.
2015-12-01
We monitor seafloor crustal deformation at two observation points (south and north of Nankai Trough (TOA and TCA)) across the Nankai Trough, Japan, from 2013 to 2015. A ocean current flows frequently above our points called the Kuroshio current that has temperature difference perpendicular to the flow axis down to 1000 m in depths. Sound speed in the water depends on temperature (Del Grosso, 1974). Determination of seafloor benchmark position (SBP) has a bias when the sound speed structure includes a horizontal inhomogeneity (HI) in large-scale ocean current area. This bias is caused by trade-off between estimated spatial-temporal variation of sound speed structure and SBP. In this study, we propose a new observation system and analytical method, which directly observe the HI of sound speed derived from Underway CTD (UCTD) measurement and we introduce the HI to analytical method. We performed the observation in May 2015. We measured acoustic ranging during marine navigation on a circle with radius of 2 miles. At the same time, we observed six UCTD measurements down to 700 m in depths at both points. We use analytical method of Ikuta et al. (2008) for determination of SBP and adopt estimated HI of sound speed structure from UCTD measurements. We use the following equation to adopt the HI model: S(t,x,X)=S(t)+∆S(R(X)+ar(x,X)), where S(t,x,X) is the spatial-temporal variation of slowness but spatial variation is the uniform during the observation period, S(t) is the estimated temporal variation of sound speed structure following Ikuta et al. (2008), ∆S is the horizontal gradient of slowness estimated from UCTD measurement, R(x) is the distance of a ship from center of three SBPs, r(x,X) is the distance between ship position and benchmark position, a is the ratio of layer of HI for the whole depth, x is the ship position, and X is the benchmark position. SBP adopted the HI model is determined 74.9 cm toward N17.4˚E at TCA and 90.0 cm toward N7.8˚E at TOA. The
NASA Astrophysics Data System (ADS)
Negahdar, Mohammadreza; Zacarias, Albert; Milam, Rebecca A.; Dunlap, Neal; Woo, Shiao Y.; Amini, Amir A.
2012-03-01
The treatment plan evaluation for lung cancer patients involves pre-treatment and post-treatment volume CT imaging of the lung. However, treatment of the tumor volume lung results in structural changes to the lung during the course of treatment. In order to register the pre-treatment volume to post-treatment volume, there is a need to find robust and homologous features which are not affected by the radiation treatment along with a smooth deformation field. Since airways are well-distributed in the entire lung, in this paper, we propose use of airway tree bifurcations for registration of the pre-treatment volume to the post-treatment volume. A dedicated and automated algorithm has been developed that finds corresponding airway bifurcations in both images. To derive the 3-D deformation field, a B-spline transformation model guided by mutual information similarity metric was used to guarantee the smoothness of the transformation while combining global information from bifurcation points. Therefore, the approach combines both global statistical intensity information with local image feature information. Since during normal breathing, the lung undergoes large nonlinear deformations, it is expected that the proposed method would also be applicable to large deformation registration between maximum inhale and maximum exhale images in the same subject. The method has been evaluated by registering 3-D CT volumes at maximum exhale data to all the other temporal volumes in the POPI-model data.
NASA Astrophysics Data System (ADS)
van Dam, R. L.
2010-12-01
An outcrop at the western edge of a large NW-SE trending ridge along the eastern shore of Lake Michigan south of Ludington contains Late Wisconsin deformation structures. Differential loading associated with a glacial re-advance caused glaciolacustrine loamy material to deform into several narrow anticlinal structures that rise from below beach level to near the top of the ~50 m high cliff. The anticlines separate ~100 m broad synclines that control local ground water flow and impact cliff stability. The objective of this study was to characterize the orientation and lateral extent of the structures below the ridge using different galvanic electrical resistivity methods. These methods exploit the large electrical contrast between the glaciolacustrine loams and overlying sandy outwash material. Electrical resistivity methods have long been part of the geophysical tool set. Recent advances, including the availability of multi-electrode systems and advanced data processing software, have made electrical resistivity tomography (ERT) a popular tool to obtain 2D models of subsurface resistivity. In this study, vertical electrical soundings (VES) were combined with borehole logs and lab-derived petrophysical relationships to characterize the site stratigraphy. Constant-spread traverses (CST) and ERT data were used to map the spatial extent of deformation structures. Field, lab, and modeling results presented in this work identify various strengths and limitations of electrical resistivity methods for the characterization of deformation structures in general and glaciotectonic structures in particular.
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
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. Copyright © 2016 Elsevier Inc. All rights reserved.
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
2016-01-01
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
Large deformation image classification using generalized locality-constrained linear coding.
Zhang, Pei; Wee, Chong-Yaw; Niethammer, Marc; Shen, Dinggang; Yap, Pew-Thian
2013-01-01
Magnetic resonance (MR) imaging has been demonstrated to be very useful for clinical diagnosis of Alzheimer's disease (AD). A common approach to using MR images for AD detection is to spatially normalize the images by non-rigid image registration, and then perform statistical analysis on the resulting deformation fields. Due to the high nonlinearity of the deformation field, recent studies suggest to use initial momentum instead as it lies in a linear space and fully encodes the deformation field. In this paper we explore the use of initial momentum for image classification by focusing on the problem of AD detection. Experiments on the public ADNI dataset show that the initial momentum, together with a simple sparse coding technique-locality-constrained linear coding (LLC)--can achieve a classification accuracy that is comparable to or even better than the state of the art. We also show that the performance of LLC can be greatly improved by introducing proper weights to the codebook.
Bossa, Matias; Zacur, Ernesto; Olmos, Salvador
2010-01-01
Tensor-based morphometry (TBM) is an analysis technique where anatomical information is characterized by means of the spatial transformations mapping a customized template with the observed images. Therefore, accurate inter-subject non-rigid registration is an essential prerequisite for both template estimation and image warping. Subsequent statistical analysis on the spatial transformations is performed to highlight voxel-wise differences. Most of previous TBM studies did not explore the influence of the registration parameters, such as the parameters defining the deformation and the regularization models. In this work performance evaluation of TBM using stationary velocity field (SVF) diffeomorphic registration was performed in a subset of subjects from Alzheimer’s Disease Neuroimaging Initiative (ADNI) study. A wide range of values of the registration parameters that define the transformation smoothness and the balance between image matching and regularization were explored in the evaluation. The proposed methodology provided brain atrophy maps with very detailed anatomical resolution and with a high significance level compared with results recently published on the same data set using a non-linear elastic registration method. PMID:20211269
LCC-Demons: a robust and accurate symmetric diffeomorphic registration algorithm.
Lorenzi, M; Ayache, N; Frisoni, G B; Pennec, X
2013-11-01
Non-linear registration is a key instrument for computational anatomy to study the morphology of organs and tissues. However, in order to be an effective instrument for the clinical practice, registration algorithms must be computationally efficient, accurate and most importantly robust to the multiple biases affecting medical images. In this work we propose a fast and robust registration framework based on the log-Demons diffeomorphic registration algorithm. The transformation is parameterized by stationary velocity fields (SVFs), and the similarity metric implements a symmetric local correlation coefficient (LCC). Moreover, we show how the SVF setting provides a stable and consistent numerical scheme for the computation of the Jacobian determinant and the flux of the deformation across the boundaries of a given region. Thus, it provides a robust evaluation of spatial changes. We tested the LCC-Demons in the inter-subject registration setting, by comparing with state-of-the-art registration algorithms on public available datasets, and in the intra-subject longitudinal registration problem, for the statistically powered measurements of the longitudinal atrophy in Alzheimer's disease. Experimental results show that LCC-Demons is a generic, flexible, efficient and robust algorithm for the accurate non-linear registration of images, which can find several applications in the field of medical imaging. Without any additional optimization, it solves equally well intra & inter-subject registration problems, and compares favorably to state-of-the-art methods. Copyright © 2013 Elsevier Inc. All rights reserved.
On the importance of nonlinearity of brain tissue under large deformations.
Takhounts, Erik G; Crandall, Jeff R; Darvish, Kurosh
2003-10-01
Linear shear properties of human and bovine brain tissue were determined from transient stress-relaxation experiments and their material functions were compared. Quasi-linear viscoelastic theory was then utilized to determine material constants for bovine brain tissue subjected to large deformations. The range of applicability for linear and quasi-linear constitutive models of brain tissue was determined. A nonlinear Green-Rivlin constitutive model was subsequently applied to characterize temporal nonlinearity of bovine brain tissue in shear. Overall, 10 brain specimens from 5 fresh human cadavers and 156 brain specimens from 26 fresh bovine cadaver brains were used to quantify and compare shear brain responses under various loading conditions. The assumptions of homogeneity, isotropy, and incompressibility of brain material were made in order to reduce the required number of experiments. A series of single-, two-, and three-step strain inputs was applied to one end of a cylindrical brain specimen and the stress-time histories were measured at the other end. The time delays between the applied strain step inputs were altered in order to determine the temporal nonlinearity of brain tissue. The study resulted in linear constitutive models for human and bovine brain tissue, and quasi-linear and nonlinear constitutive equations for bovine brain tissue in shear. It was found that human brain is somewhat stiffer than bovine brain; the difference, however, was not statistically significant and bovine brain may be a good substitute in studying nonlinear human brain response. A linear constitutive model was found to be sufficient to characterize brain tissue response when Lagrangian shear strains do not exceed 0.2 (advised to limit the range to the shear strain of 0.175), a quasi-linear constitutive model can then be used for loading conditions of up to 0.5 of Lagrangian shear strains (advised to limit the range to the shear strain of 0.325). For any shear strain magnitudes
Risser, Laurent; Dolius, Lionel; Fonta, Caroline; Mescam, Muriel
2014-01-01
Cerebral aging has been linked to structural and functional changes in the brain throughout life. Here, we study the marmoset, a small non-human primate, in order to get insights into the mechanisms of brain aging in normal and pathological conditions. Imaging the brain of small animals with techniques such as MRI, quickly becomes a challenging task when compared with human brain imaging. Very often, a simple pre-processing step such as brain extraction cannot be achieved with classical tools. In this paper, we propose a diffeomorphic registration algorithm, which makes use of learned constraints to propagate the manual segmentation of a marmoset brain template to other MR images of marmoset brains. The main methological contribution of our paper is to explore a new strategy to automatically tune the spatial regularization of the deformations. Results show that we obtain a robust segmentation of the brain, even for images with a low contrast.
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.
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.
Deformations Associated With Large Interplate Earthquakes Along the Sumatra-Andaman Subduction Zone
NASA Astrophysics Data System (ADS)
Hashimoto, M.; Fukushima, Y.; Katagi, T.; Hashizume, M.; Satomura, M.; Wu, P.; Kato, T.
2008-12-01
Since the occurrence of the 2004 Sumatra-Andaman earthquake (Mw9.2), the Sumatra-Andaman Subduction zone has attracted geophysicists' attention. We have been carrying on CGPS observation in Thailand and Myanmar to detect postseismic deformation following this gigantic event. Since CGPS on land is not enough to clarify the detailed image of postseismic deformation, we also make InSAR analyses in Andaman and Phuket Islands. On September 12, 2007, another Mw8.4 event occurred SW off Sumatra. We report deformations observed with GPS and SAR including co- and postseismic deformation following this event. We have analyzed CGPS data up to the end of 2007 and detected postseismic displacements all over the Indochina peninsula. Phuket, which suffered from about 26cm coseismic displacement, has shifted by 26cm southwestward till July, 2007. Postseismic transient is clearly recognized and already exceeds coseismic movements at remote sites such as Bangkok and Chiang Mai in Thailand. We processed ALOS/PALSAR data in Andaman and Phuket islands. No remarkable deformation is found in Andaman and Phuket Islands, since the operation period of ALOS/PALSAR is not long enough and the wavelength of postseismic deformation may be much longer than the swath. We try to synthesize the postseismic displacement using a 3-D viscoelastic FEM model. Its results imply that viscoelastic relaxation in mantle with a typical mantle viscosity may play an important role for the observed postseismic transients except during the first six month. An extremely low viscosity is not required beneath the Andaman Sea, though this back arc is now actively opening. Coseismic motion following the 2007 Sumatra event is detected north of Benkgulu on the coast of southern Sumatra with InSAR. The largest LOS displacement of about 35cm is observed 100km NW of Bengkulu. Coseismic westward displacements of 3.5cm from the 2007 Sumatra event are also observed at Singapore, whose epicentral distance is about 700km, with
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.
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
Hot Deformation Mechanisms of an As-Extruded TiAl Alloy with Large Amount of Remnant Lamellae
NASA Astrophysics Data System (ADS)
Liu, Hongwu; Rong, Rong; Gao, Fan; Liu, Yanguo; Li, Zhenxi; Wang, Qingfeng
2017-07-01
The hot deformation mechanisms of an as-extruded Ti-44Al-5V-1Cr alloy with a large amount of remnant lamellae were investigated by hot compression tests at temperatures of 900-1250 °C and strain rates of 0.001-1 s-1. The hot processing map of the as-extruded Ti-44Al-5V-1Cr alloy was developed on the basis of dynamic materials modeling and the Prasad criteria. There were four different domains in the hot processing map, according to the efficiency of power dissipation, η. The flow soft and hot deformation mechanisms for different domains were illustrated in the context of microstructural evolution during the process of deformation. As a result, the dynamic recrystallization and superplastic deformation occurred at 1125-1150 °C near 0.001 s-1, and this region is suitable for superplastic forming. The α phase dynamic recrystallization and dynamic recovery occurred at 1250 °C and 0.1 s-1. The existence of small amount of the γ and β phases effectively inhibited the growth of α grains.
Gao, Lei; Yang, Kai; Chen, Xiaorui; Yu, Xiangjuan
2017-01-01
Compared with conventional piles such as the circle pile, the cast-in-place large-diameter pile (PCC pile) has many advantages: the lateral area of PCC pile is larger and the bearing capacity of PCC pile is higher. It is more cost-effective than other piles such as square pile under the same condition. The deformation of the PCC pile is very important for its application. In order to obtain the deformation of the PCC pile, a new type of quasi-distributed optical fiber sensing technology named a fiber Bragg grating (FBG) is used to monitor the deformation of the PCC pile. The PCC model pile is made, the packaging process of the PCC model pile and the layout of fiber sensors are designed, and the strains of the PCC model pile based on FBG sensors are monitored. The strain of the PCC pile is analyzed by the static load test. The results show that FBG technology is successfully applied for monitoring the deformation of the PCC pile, the monitoring data is more useful for the PCC pile. It will provide a reference for the engineering applications. PMID:28273817
Gao, Lei; Yang, Kai; Chen, Xiaorui; Yu, Xiangjuan
2017-03-03
Compared with conventional piles such as the circle pile, the cast-in-place large-diameter pile (PCC pile) has many advantages: the lateral area of PCC pile is larger and the bearing capacity of PCC pile is higher. It is more cost-effective than other piles such as square pile under the same condition. The deformation of the PCC pile is very important for its application. In order to obtain the deformation of the PCC pile, a new type of quasi-distributed optical fiber sensing technology named a fiber Bragg grating (FBG) is used to monitor the deformation of the PCC pile. The PCC model pile is made, the packaging process of the PCC model pile and the layout of fiber sensors are designed, and the strains of the PCC model pile based on FBG sensors are monitored. The strain of the PCC pile is analyzed by the static load test. The results show that FBG technology is successfully applied for monitoring the deformation of the PCC pile, the monitoring data is more useful for the PCC pile. It will provide a reference for the engineering applications.
NASA Astrophysics Data System (ADS)
Bull, J. M.; Geersen, J.; McNeill, L. C.; Henstock, T.; Gaedicke, C.; Chamot-Rooke, N. R. A.; Delescluse, M.
2015-12-01
Large-magnitude intraplate earthquakes within the ocean basins are not well understood. The Mw 8.6 and Mw 8.2 strike-slip intraplate earthquakes on 11 April 2012, while clearly occurring in the equatorial Indian Ocean diffuse plate boundary zone, are a case in point, with disagreement on the nature of the focal mechanisms and the faults that ruptured. We use bathymetric and seismic reflection data from the rupture area of the earthquakes in the northern Wharton Basin to demonstrate pervasive brittle deformation between the Ninetyeast Ridge and the Sunda subduction zone. In addition to evidence of recent strike-slip deformation along approximately north-south-trending fossil fracture zones, we identify a new type of deformation structure in the Indian Ocean: conjugate Riedel shears limited to the sediment section and oriented oblique to the north-south fracture zones. The Riedel shears developed in the Miocene, at a similar time to the onset of diffuse deformation in the central Indian Ocean. However, left-lateral strike-slip reactivation of existing fracture zones started earlier, in the Paleocene to early Eocene, and compartmentalizes the Wharton Basin. Modeled rupture during the 11 April 2012 intraplate earthquakes is consistent with the location of two reactivated, closely spaced, approximately north-south-trending fracture zones. However, we find no evidence for WNW-ESE-trending faults in the shallow crust, which is at variance with most of the earthquake fault models.
A Generalization of Denjoy’s Theorem on Diffeomorphisms of the Circle.
1983-05-01
generalize Denjoy’s theorem on circle maps to maps of two-dimensional manifolds. In particular, we prove that if a C 3 diffeomorphism of a compact two...are sufficiently smooth diffeomorphism of the circle, these are the only examples of stable orbits, i.e. any stable orbit must be asymptotic to a...such that there exists V2 > 0 with h2 2 (B) C B. continuing in this manner we can create a seauence of C diffeomorphisms into A converging to the
Sharpness for C1 linearization of planar hyperbolic diffeomorphisms
NASA Astrophysics Data System (ADS)
Zhang, Wenmeng; Zhang, Weinian
2014-12-01
C1 linearization preserves smooth dynamical behaviors and distinguishes qualitative properties in characteristic directions. Planar hyperbolic diffeomorphisms are the most elementary ones of representatively technical difficulties in the study of C1 linearization. In the Poincaré domain (both eigenvalues inside the unit circle S1) a lower bound α0 was given such that C smoothness with α0<α≤1 admits C1 linearization. Our first purpose of this paper is to prove the sharpness of α0 and give a weaker linearization for α≤α0. In the Siegel domain (one eigenvalue inside S1 but the other outside S1) it is known that C smoothness admits C1 linearization for all α∈(0,1]. The second purpose is to prove that the C1 linearization is actually a C linearization and give sharp estimates for β.
Large deformation solid-fluid interaction via a level set approach.
Schunk, Peter Randall; Noble, David R.; Baer, Thomas A.; Rao, Rekha Ranjana; Notz, Patrick K.; Wilkes, Edward Dean
2003-12-01
Solidification and blood flow seemingly have little in common, but each involves a fluid in contact with a deformable solid. In these systems, the solid-fluid interface moves as the solid advects and deforms, often traversing the entire domain of interest. Currently, these problems cannot be simulated without innumerable expensive remeshing steps, mesh manipulations or decoupling the solid and fluid motion. Despite the wealth of progress recently made in mechanics modeling, this glaring inadequacy persists. We propose a new technique that tracks the interface implicitly and circumvents the need for remeshing and remapping the solution onto the new mesh. The solid-fluid boundary is tracked with a level set algorithm that changes the equation type dynamically depending on the phases present. This novel approach to coupled mechanics problems promises to give accurate stresses, displacements and velocities in both phases, simultaneously.
Large-scale rheomorphic shear deformation in Miocene peralkaline ignimbrite E, Gran Canaria
NASA Astrophysics Data System (ADS)
Leat, Philip T.; Schmincke, Hans-Ulrich
1993-02-01
the single ignimbrite cooling unit E (average thickness, 28 m; volume, ca. 30 km3) forms the uppermost member of the Miocene Upper Mogán Formation on Gran Canaria. It is strongly chemically zoned from basal, first-erupted comendite (peralkaline rhyolite) to late-erupted trachyte, and, apart from an upper trachytic zone, it is densely welded. E was emplaced onto a surface inclined ca. 2 5° from the source caldera. Detailed mapping of key sections, up to 300 m long, exposed in barranco walls, ca. 10 km from the caldera margin, reveals structures that are interpreted to have been produced by rheomorphic deformation of the ignimbrite along shear zones. The shear zones formed within the lower-viscosity comenditic tuff. Extensional structures include mega-boudinage and ‘decapitated sequences’ and compression resulted in sequence repitition by overthrusting. Mechanisms traditionally thought to be important during rheomorphic deformation of welded tuffs (compaction, lateral creep, folding, vertical density-driven diapirism) cannot account for these features, which reflect lateral (post-compactional) rheomorphic movement locally in excess of 800 m. We suggest the following sequence of events: emplacement of the several flow units; compaction, with little lateral movement; rheomorphic deformation. During and after compaction, layers of secondary porosity developed within the comenditic tuff, possibly where upward escape of gas was prevented by overlying, relatively impermeable layers of densely compacted ignimbrite. These structurally weak layers of high porosity subsequently acted as shear zones.
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
1998-01-01
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
Nonlinear plate equation analysis for the design of large stroke deformable mirror
NASA Astrophysics Data System (ADS)
Azucena, Oscar A.; Fernandez, Bautista; Kubby, Joel A.
2008-02-01
Adaptive Optics (AO) improves the quality of astronomical imaging systems by using real time measurement of the turbulent medium in the optical path. The measurements are then taken and applied to a deformable mirror (DM) that is in the conjugate position of the aberrations in the optical path. The quality of the reconstructed wavefront directly affects the images obtained. One of the limiting factors in current DM technology is the amount of stroke available to correct the wavefront distortions which can be as high as 20 microns of optical path difference. We have developed a simulation analysis using Galerkin's method to solve the nonlinear plate equation. The analysis uses a set of orthogonal equations that satisfied the boundary condition to solve for the linear deformation on the mirror surface. This deformation is used to iteratively converge to the final solution by applying the nonlinear plate equation and the nonlinear actuator forces. This simulation was used to design a microelectromechanical DM with 10 μm of stroke.
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.
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.
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.
Rizvi, Mohd Suhail; Pal, Anupam
2014-09-01
The fibrous matrices are widely used as scaffolds for the regeneration of load-bearing tissues due to their structural and mechanical similarities with the fibrous components of the extracellular matrix. These scaffolds not only provide the appropriate microenvironment for the residing cells but also act as medium for the transmission of the mechanical stimuli, essential for the tissue regeneration, from macroscopic scale of the scaffolds to the microscopic scale of cells. The requirement of the mechanical loading for the tissue regeneration requires the fibrous scaffolds to be able to sustain the complex three-dimensional mechanical loading conditions. In order to gain insight into the mechanical behavior of the fibrous matrices under large amount of elongation as well as shear, a statistical model has been formulated to study the macroscopic mechanical behavior of the electrospun fibrous matrix and the transmission of the mechanical stimuli from scaffolds to the cells via the constituting fibers. The study establishes the load-deformation relationships for the fibrous matrices for different structural parameters. It also quantifies the changes in the fiber arrangement and tension generated in the fibers with the deformation of the matrix. The model reveals that the tension generated in the fibers on matrix deformation is not homogeneous and hence the cells located in different regions of the fibrous scaffold might experience different mechanical stimuli. The mechanical response of fibrous matrices was also found to be dependent on the aspect ratio of the matrix. Therefore, the model establishes a structure-mechanics interdependence of the fibrous matrices under large deformation, which can be utilized in identifying the appropriate structure and external mechanical loading conditions for the regeneration of load-bearing tissues. Copyright © 2014 Elsevier Ltd. All rights reserved.
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.
Wu, Tim; Hung, Alice P-L; Hunter, Peter; Mithraratne, Kumar
2015-01-01
This study addresses the issue of modelling material heterogeneity of incompressible bodies. It is seen that when using a mixed (displacement-pressure) finite element formulation, the basis functions used for pressure field may not be able to capture the nonlinearity of material parameters, resulting in pseudo-residual stresses. This problem can be resolved by modifying the constitutive relation using Flory's decomposition of the deformation gradient. A two-parameter Mooney-Rivlin constitutive relation is used to demonstrate the methodology. It is shown that for incompressible materials, the modification does not alter the mechanical behaviour described by the original constitutive model. In fact, the modified constitutive equation shows a better predictability when compared against analytical solutions. Two strategies of describing the material variation (i.e. linear and step change) are explained, and their solutions are evaluated for an ideal two-material interfacing problem. When compared with the standard tied coupling approach, the step change method exhibited a much better agreement because of its ability to capture abrupt changes of the material properties. The modified equation in conjunction with integration point-based material heterogeneity is then used to simulate the deformations of heterogeneous biological structures to illustrate its applications.
NASA Astrophysics Data System (ADS)
Branício, Paulo S.; Rino, José-Pedro
2000-12-01
Molecular-dynamics simulations were employed to study deformations on nickel nanowires subjected to uniaxial strain at 300 K using a recently reported embedded-atom (many body) model potential. This embedded-atom model can reproduce exactly the experimental second-order and third-order elastic moduli as well as the phase stability, equation of state and phonon frequency spectra are also in good agreement with experiments. Strong influence was observed in the Young modulus and force constant due to surface effects when considering nanowires with different cross sections. Applying strain rates, from 0.05 to 15% ps-1, we found elastic behavior up to 11.5% strain with corresponding stress of 9.4 GPa. At low strain rates (<0.05% ps-1) the system passes through plastic deformations although keeping the crystalline structure. This ductile process is showed by several snapshots. At this low strain rate regime we observed that the nanowires shows superplasticity. For high strain rates (>=7% ps-1) the system changes continuously from crystalline to amorphous phase. Although this amorphization occurs with no use of liquid quenching or introduction of chemical or physical disorder, so being a different and interesting process, the amorphous resulted is unstable. We studied this instability monitoring the recrystallization process.
Ion-assisted coating for large-scale Bimorph deformable mirror
NASA Astrophysics Data System (ADS)
Mikami, Takuya; Okamoto, Takayuki; Yoshida, Kunio; Jitsuno, Takahisa; Motokoshi, Shinji; Samarkin, Vadim V.; Kudryashov, Alexis V.; Kawanaka, Junji; Miyanaga, Noriaki
2016-07-01
We have fabricated a 410 x 468 mm size deformable mirror with 100 Bimorph piezoceramic actuators for the LFEX laser system at Osaka University. In the case of Bimorph-type deformable mirrors, the mirror surface had to be polished and coated after bonding the piezoceramic actuators to the rear side of the thin mirror substrate. This provides a good surface figure, but the coating temperature for the high-reflection mirror was strictly limited because of the thermal fragility of piezoceramic actuators. The mirror substrate with the actuators was polished, and an ion-assisted multilayer dielectric coating was produced at 60 degrees Celsius with our 80-inch coating chamber. The flatness of the mirror just after coating was 7 μm, and reduced by aging to 3.2 μm when the mirror was assembled. The surface figure of the assembled mirror with 20 piezostack bonded actuators is demonstrated and a laser-induced damage threshold tested with a witness sample is also reported.
Large deformation ionic polymer-metal composites actuators based on porous Nafion membranes
NASA Astrophysics Data System (ADS)
Zhao, Dongxu; Li, Dichen; Wang, Yanjie; Luo, Meng; Chen, Hualing
2016-04-01
With advantages of low driving voltage, good flexibility and high electromechanical efficiency, ionic polymer-metal composites (IPMCs), which are one of the most attractive smart materials, have been research hotspot in actuators, sensors and artificial muscles. However, a serious drawback of little deformation of thick IPMC actuator limits its application. In this paper, we fabricated thick porous Nafion membranes by freeze-drying process. A series of Thermogravimetric analyses (TGA), Field emission scanning electron microscopy (FE-SEM) and Water uptake (WUP) tests were performed to examine the validity of the freeze-drying process and the pore size and the porosity. Then, the porous IPMCs were fabricated with the freeze-drying processed Nafion membranes by the solution casting and reducing plating. Finally, the IPMC actuators with the dimensions of 25× 5× 1 in millimeters were achieved and tested. The terminal deformation of the porous IPMC actuator increased by 739.7%, compared with the ordinary IPMC actuator with the same dimensions under the driving voltage of 2VDC.
Thin zoom camera module by large-stroke micromachined deformable mirrors
NASA Astrophysics Data System (ADS)
Huang, Yu-Hung; Lin, Yu-Hung; Su, Guo-Dong J.
2012-10-01
Miniaturization is the key point to design image system for portable devices. Motor-driven lens technique is the traditional way to achieve auto-focus and zoom functions, this method usually requires a larger space and causes greater power consumption. Reflective optics is a technology not only can make the space application become more efficient and flexible, but also has the advantage that it induces low chromatic aberrations. In this paper, we use organic deformable mirror (DM) as reflective element of the system. PDMS used as an actuated membrane of DM has lower young's modulus and residual stress. The maximum stoke is 90 um and corresponding diopter is 39.964m(-1) . The system we designed with MEMS deformable mirror is a 5M pixel zoom image system which is only 10mm in thickness before packaging and 16mm in thickness after packaging. The smallest EFL (effective focal length) is 4.7 mm at full field angle of 52° and the f/# is 4.4. The longest EFL of the module is 9.4 mm and the f/# is 6.4.
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.
Henshall, G.A. ); Kassner, M.E. . Dept. of Mechanical Engineering); McQueen, H.J. . Dept. of Mechanical Engineering)
1991-12-01
An Al-5.8 at. % Mg (5.2 wt. % Mg) alloy was deformed in torsion within the solute drag regime to various strains, up to the failure strain of 10.8. Optical and transmission electron microscopy were used to analyze the evolution of the microstructure and to determine the dynamic restoration mechanism. TEM revealed that subgrain is sluggish but that subgrains eventually ({bar {var epsilon}} {approx} 1) fill the grains. The steady-state subgrain size ({lambda} {approx} 6 {mu}m) and misorientation angle ({Theta} {approx} 1.6{degrees}) are reached by {bar {var epsilon}} {approx} 2. These observations confirm that subgrains eventually form during deformation in the solute drag regime, though they do not appear to significantly influence the strength. At low strains, nearly all of the boundaries form by dislocation reaction and are low angle ({Theta} < 10{degrees}). At a strain of 10.8, however, the boundary misorientation histogram is bimodal, with nearly 25% of the boundaries having high angles due to their ancestry in the original grain boundaries. This is consistent with optical microscopy observations of the elongation and thinning of the original grains as they spiral around the torsion axis. No evidence was found for discontinuous dynamic recrystallization, a repeating process in which strain-free nucleate, grow, deform and give rise to new nuclei. It is concluded that dynamic recovery in the solute drag regime gives rise to geometric dynamic recrystallization in a manner very similar to that already established for pure aluminum, suggesting that geometric dynamic recrystallization may occur generally in materials with a high stacking-fault energy deformed to large strains.
Henshall, G.A.; Kassner, M.E.; McQueen, H.J.
1991-12-01
An Al-5.8 at. % Mg (5.2 wt. % Mg) alloy was deformed in torsion within the solute drag regime to various strains, up to the failure strain of 10.8. Optical and transmission electron microscopy were used to analyze the evolution of the microstructure and to determine the dynamic restoration mechanism. TEM revealed that subgrain is sluggish but that subgrains eventually ({bar {var_epsilon}} {approx} 1) fill the grains. The steady-state subgrain size ({lambda} {approx} 6 {mu}m) and misorientation angle ({Theta} {approx} 1.6{degrees}) are reached by {bar {var_epsilon}} {approx} 2. These observations confirm that subgrains eventually form during deformation in the solute drag regime, though they do not appear to significantly influence the strength. At low strains, nearly all of the boundaries form by dislocation reaction and are low angle ({Theta} < 10{degrees}). At a strain of 10.8, however, the boundary misorientation histogram is bimodal, with nearly 25% of the boundaries having high angles due to their ancestry in the original grain boundaries. This is consistent with optical microscopy observations of the elongation and thinning of the original grains as they spiral around the torsion axis. No evidence was found for discontinuous dynamic recrystallization, a repeating process in which strain-free nucleate, grow, deform and give rise to new nuclei. It is concluded that dynamic recovery in the solute drag regime gives rise to geometric dynamic recrystallization in a manner very similar to that already established for pure aluminum, suggesting that geometric dynamic recrystallization may occur generally in materials with a high stacking-fault energy deformed to large strains.
Quinn, David J; Pivkin, Igor; Wong, Sophie Y; Chiam, Keng-Hwee; Dao, Ming; Karniadakis, George Em; Suresh, Subra
2011-03-01
We investigate the biophysical characteristics of healthy human red blood cells (RBCs) traversing microfluidic channels with cross-sectional areas as small as 2.7 × 3 μm. We combine single RBC optical tweezers and flow experiments with corresponding simulations based on dissipative particle dynamics (DPD), and upon validation of the DPD model, predictive simulations and companion experiments are performed in order to quantify cell deformation and pressure-velocity relationships for different channel sizes and physiologically relevant temperatures. We discuss conditions associated with the shape transitions of RBCs along with the relative effects of membrane and cytosol viscosity, plasma environments, and geometry on flow through microfluidic systems at physiological temperatures. In particular, we identify a cross-sectional area threshold below which the RBC membrane properties begin to dominate its flow behavior at room temperature; at physiological temperatures this effect is less profound.
Quinn, David J.; Pivkin, Igor; Wong, Sophie Y.; Chiam, Keng-Hwee; Dao, Ming; Karniadakis, George Em; Suresh, Subra
2011-01-01
We investigate the biophysical characteristics of healthy human red blood cells (RBCs) traversing microfluidic channels with cross-sectional areas as small as 2.7 × 3 μm. We combine single RBC optical tweezers and flow experiments with corresponding simulations based on dissipative particle dynamics (DPD), and upon validation of the DPD model, predictive simulations and companion experiments are performed in order to quantify cell deformation and pressure–velocity relationships for different channel sizes and physiologically relevant temperatures. We discuss conditions associated with the shape transitions of RBCs along with the relative effects of membrane and cytosol viscosity, plasma environments, and geometry on flow through microfluidic systems at physiological temperatures. In particular, we identify a cross-sectional area threshold below which the RBC membrane properties begin to dominate its flow behavior at room temperature; at physiological temperatures this effect is less profound. PMID:21240637
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
Large-Aperture Deformable Mirror Correction of Tiled-Grating Wavefront Error
Kruschwitz, B.E.; Jungquist, R.; Qiao, J.; Abbey, S.; Dean, S.E.; Maywar, D.N.; Moore, M.D.; Waxer, L.J.; Wilson, M. E.
2006-07-13
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.
Atlas construction for dynamic (4D) PET using diffeomorphic transformations.
Bieth, Marie; Lombaert, Hervé; Reader, Andrew J; Siddiqi, Kaleem
2013-01-01
A novel dynamic (4D) PET to PET image registration procedure is proposed and applied to multiple PET scans acquired with the high resolution research tomograph (HRRT), the highest resolution human brain PET scanner available in the world. By extending the recent diffeomorphic log-demons (DLD) method and applying it to multiple dynamic [11C]raclopride scans from the HRRT, an important step towards construction of a PET atlas of unprecedented quality for [11C]raclopride imaging of the human brain has been achieved. Accounting for the temporal dimension in PET data improves registration accuracy when compared to registration of 3D to 3D time-averaged PET images. The DLD approach was chosen for its ease in providing both an intensity and shape template, through iterative sequential pair-wise registrations with fast convergence. The proposed method is applicable to any PET radiotracer, providing 4D atlases with useful applications in high accuracy PET data simulations and automated PET image analysis.
Diffeomorphic Shape Trajectories for Improved Longitudinal Segmentation and Statistics
Muralidharan, Prasanna; Fishbaugh, James; Johnson, Hans J; Durrleman, Stanley; Paulsen, Jane S; Gerig, Guido; Fletcher, P. Thomas
2015-01-01
Longitudinal imaging studies involve tracking changes in individuals by repeated image acquisition over time. The goal of these studies is to quantify biological shape variability within and across individuals, and also to distinguish between normal and disease populations. However, data variability is influenced by outside sources such as image acquisition, image calibration, human expert judgment, and limited robustness of segmentation and registration algorithms. In this paper, we propose a two-stage method for the statistical analysis of longitudinal shape. In the first stage, we estimate diffeomorphic shape trajectories for each individual that minimize inconsistencies in segmented shapes across time. This is followed by a longitudinal mixed-effects statistical model in the second stage for testing differences in shape trajectories between groups. We apply our method to a longitudinal database from PREDICT-HD and demonstrate our approach reduces unwanted variability for both shape and derived measures, such as volume. This leads to greater statistical power to distinguish differences in shape trajectory between healthy subjects and subjects with a genetic biomarker for Huntington’s disease (HD). PMID:25320781
Diffeomorphic shape trajectories for improved longitudinal segmentation and statistics.
Muralidharan, Prasanna; Fishbaugh, James; Johnson, Hans J; Durrleman, Stanley; Paulsen, Jane S; Gerig, Guido; Fletcher, P Thomas
2014-01-01
Longitudinal imaging studies involve tracking changes in individuals by repeated image acquisition over time. The goal of these studies is to quantify biological shape variability within and across individuals, and also to distinguish between normal and disease populations. However, data variability is influenced by outside sources such as image acquisition, image calibration, human expert judgment, and limited robustness of segmentation and registration algorithms. In this paper, we propose a two-stage method for the statistical analysis of longitudinal shape. In the first stage, we estimate diffeomorphic shape trajectories for each individual that minimize inconsistencies in segmented shapes across time. This is followed by a longitudinal mixed-effects statistical model in the second stage for testing differences in shape trajectories between groups. We apply our method to a longitudinal database from PREDICT-HD and demonstrate our approach reduces unwanted variability for both shape and derived measures, such as volume. This leads to greater statistical power to distinguish differences in shape trajectory between healthy subjects and subjects with a genetic biomarker for Huntington's disease (HD).
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)
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.
Patil, Sampat Dumbre; Patil, Vaishali Dumbre; Khan, Ashraf; Khanore, Charudatta
2016-01-01
Solitary osteochondroma is the most common bone tumor, accounting for 20% to 50% of all benign bony tumors. Osteochondromas are usually found on the metaphysis of the long bones near the physis; the bones of the foot are less commonly involved. We describe a 13-year-old female with a large osteochondroma arising from the fourth metatarsal. Pressure from the tumor on the adjacent metatarsals had deformed her forefoot, creating cosmetic and functional problems. The second and third toes were deviated laterally at the metatarsophalangeal joint, and the fourth and fifth toes were deviated medially. In addition, the fourth and fifth toes were flexed at the proximal interphalangeal joint. We excised the osteochondroma and stabilized the metatarsophalangeal joints. After 3 years, the cosmetic and functional results were satisfactory. The subluxation at the metatarsophalangeal joints had resolved without treatment. Her Revised Foot Function Index score had improved from 141 preoperatively to 95 postoperatively, and her Manchester-Oxford Foot Questionnaire score had improved from 25 to 0. This case is a rare example of a large metatarsal osteochondroma in a growing child in which pressure from the tumor caused secondary forefoot deformities. The management of this case also shows the potential for the forefoot to remodel itself during adolescence, after the tumor has been resected and the joints stabilized.
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)
Bai, Ruixiang; Jiang, Hao; Lei, Zhenkun; Li, Weikang
2017-03-01
Compared with the traditional forward compositional matching strategy, the inverse compositional matching strategy has almost the same accuracy, but has an obviously higher efficiency than the former in digital image correlation (DIC) algorithms. Based on the inverse compositional matching strategy and the auxiliary displacement functions, a more accurate inverse compositional Gauss-Newton (IC-GN2) algorithm with a new second-order shape operator is proposed for nonuniform and large deformation measurements. A theoretical deduction showed that the new proposed second-order shape operator is invertible and can steadily attain second-order precision. The result of the numerical simulation showed that the matching accuracy of the new IC-GN2 algorithm is the same as that of the forward compositional Gauss-Newton (FC-GN2) algorithm and is relatively better than in IC-GN2 algorithm. Finally, a rubber tension experiment with a large deformation of 27% was performed to validate the feasibility of the proposed algorithm.
Large-scale deformation related to the collision of the Aleutian Arc with Kamchatka
Gesit, Eric L.; Scholl, David W.
1994-01-01
The far western Aleutian Island Arc is actively colliding with Kamchatka. Westward motion of the Aleutian Arc is brought about by the tangential relative motion of the Pacific plate transferred to major, right-lateral shear zones north and south of the arc. Early geologic mapping of Cape Kamchatka (a promontory of Kamchatka along strike with the Aleutian Arc) revealed many similarities to the geology of the Aleutian Islands. Later studies support the notion that Cape Kamchatka is the farthest west Aleutian “island” and that it has been accreted to Kamchatka by the process of arc-continent collision. Deformation associated with the collision onshore Kamchatka includes gravimetrically determined crustal thickening and formation of a narrow thrust belt of intensely deformed rocks directly west of Cape Kamchatka. The trend of the thrust faults is concave toward the collision zone, indicating a radial distribution of maximum horizontal compressive stress. Offshore, major crustal faults trend either oblique to the Kamchatka margin or parallel to major Aleutian shear zones. These offshore faults are complex, accommodating both strike-slip and thrust displacements as documented by focal mechanisms and seismic reflection data. Earthquake activity is much higher in the offshore region within a zone bounded to the north by the northernmost Aleutian shear zone and to the west by an apparent aseismic front. Analysis of focal mechanisms in the region indicate that the present-day arc-continent “contact zone” is located directly east of Cape Kamchatka. In modeling the dynamics of the collision zone using thin viscous sheet theory, the rheological parameters are only partially constrained to values of n (the effective power law exponent) ≥ 3 and Ar(the Argand number) ≤ 30. These values are consistent with a forearc thermal profile of Kamchatka, previously determined from heat flow modeling. The thin viscous sheet modeling also indicates that onshore thrust faulting
NASA Astrophysics Data System (ADS)
Wang, Jian; Ye, Zheng-Ren; He, Jian-Kun
2008-01-01
We present a quantitative model for the crustal movement in China with respect to the Eurasia plate by using the three-dimensional finite element code ADELI. The model consists of an elastoplastic upper lithosphere and a viscoelastic lower lithosphere. The lithosphere is supported by the hydrostatic pressure at its base. The India-Eurasia collision is modeled as a velocity boundary condition. Ten large-scale faults are introduced as Coulomb-type frictional zones in the modeling. The values for the root mean square (RMS) of the east and north velocity components differences (RMS(Ue) and RMS(Un)), which are between the observation and the prediction, are regarded as the measurements to evaluate our simulations. We model the long-term crustal deformation in China by adjusting the faults frictions ranged from 0.01 to 0.5 and considering the effects resulted from lithospheric viscosity variation and topographic loading. Our results suggest most of the large-scale faults frictions are not larger than 0.1, which is consistent with other large-scale faults such as the North Anatolian fault (Provost, A.S., Chery, J., Hassani, R., 2003. Three-dimensional mechanical modeling of the GPS velocity field along the North Anatolian fault. Earth Planet. Sci. Lett. 209, 361-377) and the San Andreas fault (Mount, V.S., Suppe, J., 1987. State of stress near the San Andreas fault: implications for wrench tectonics. Geology, 15, 1143-1146). Further, we examine the effects on the long-term crustal deformation in China of three causes: the large-scale faults, lithospheric viscosity structure and topographic loading. Results indicate that the lithospheric viscosity structure and the topographic loading have important influences on the crustal deformation in China, while the influences caused by the large-scale faults are small. Although our simulations satisfactorily reproduce the general picture of crustal movement in China, there is a poor agreement between the model and the observed GPS
Statistical modeling of 4D respiratory lung motion using diffeomorphic image registration.
Ehrhardt, Jan; Werner, René; Schmidt-Richberg, Alexander; Handels, Heinz
2011-02-01
Modeling of respiratory motion has become increasingly important in various applications of medical imaging (e.g., radiation therapy of lung cancer). Current modeling approaches are usually confined to intra-patient registration of 3D image data representing the individual patient's anatomy at different breathing phases. We propose an approach to generate a mean motion model of the lung based on thoracic 4D computed tomography (CT) data of different patients to extend the motion modeling capabilities. Our modeling process consists of three steps: an intra-subject registration to generate subject-specific motion models, the generation of an average shape and intensity atlas of the lung as anatomical reference frame, and the registration of the subject-specific motion models to the atlas in order to build a statistical 4D mean motion model (4D-MMM). Furthermore, we present methods to adapt the 4D mean motion model to a patient-specific lung geometry. In all steps, a symmetric diffeomorphic nonlinear intensity-based registration method was employed. The Log-Euclidean framework was used to compute statistics on the diffeomorphic transformations. The presented methods are then used to build a mean motion model of respiratory lung motion using thoracic 4D CT data sets of 17 patients. We evaluate the model by applying it for estimating respiratory motion of ten lung cancer patients. The prediction is evaluated with respect to landmark and tumor motion, and the quantitative analysis results in a mean target registration error (TRE) of 3.3 ±1.6 mm if lung dynamics are not impaired by large lung tumors or other lung disorders (e.g., emphysema). With regard to lung tumor motion, we show that prediction accuracy is independent of tumor size and tumor motion amplitude in the considered data set. However, tumors adhering to non-lung structures degrade local lung dynamics significantly and the model-based prediction accuracy is lower in these cases. The statistical respiratory
NASA Astrophysics Data System (ADS)
Konyakhin, Igor; Hoang, Van Phong; Artemenko, Yury; Li, Renpu; Smekhov, Andrey
2015-05-01
The improved autocollimation system for measuring three-dimension angular deformations of pipe sections at large constructions as support tube of radio telescope mirror is analyzed. New type of the reflector for autocollimators is researched. The reflector is the trihedral mirror composition of three reflecting sides. It advantage is the measurement pitch, yaw and torsion as three angular rotation of controlled object. The second advantage of reflector is the measurements on the large work distances. Causes are the small value of the conversion coefficient and two orthogonal reference axes of trihedral reflector. The technical characteristics of the experimental setups of new reflector are presented. The features of trihedral reflector as the reflectors for optic-electronic autocollimators are discussed.
Leow, Alex D; Yanovsky, Igor; Chiang, Ming-Chang; Lee, Agatha D; Klunder, Andrea D; Lu, Allen; Becker, James T; Davis, Simon W; Toga, Arthur W; Thompson, Paul M
2007-06-01
Maps of local tissue compression or expansion are often computed by comparing magnetic resonance imaging (MRI) scans using nonlinear image registration. The resulting changes are commonly analyzed using tensor-based morphometry to make inferences about anatomical differences, often based on the Jacobian map, which estimates local tissue gain or loss. Here, we provide rigorous mathematical analyses of the Jacobian maps, and use themto motivate a new numerical method to construct unbiased nonlinear image registration. First, we argue that logarithmic transformation is crucial for analyzing Jacobian values representing morphometric differences. We then examine the statistical distributions of log-Jacobian maps by defining the Kullback-Leibler (KL) distance on material density functions arising in continuum-mechanical models. With this framework, unbiased image registration can be constructed by quantifying the symmetric KL-distance between the identity map and the resulting deformation. Implementation details, addressing the proposed unbiased registration as well as the minimization of symmetric image matching functionals, are then discussed and shown to be applicable to other registration methods, such as inverse consistent registration. In the results section, we test the proposed framework, as well as present an illustrative application mapping detailed 3-D brain changes in sequential magnetic resonance imaging scans of a patient diagnosed with semantic dementia. Using permutation tests, we show that the symmetrization of image registration statistically reduces skewness in the log-Jacobian map.
Homogenized modeling methodology for 18650 lithium-ion battery module under large deformation.
Tang, Liang; Zhang, Jinjie; Cheng, Pengle
2017-01-01
Effective lithium-ion battery module modeling has become a bottleneck for full-size electric vehicle crash safety numerical simulation. Modeling every single cell in detail would be costly. However, computational accuracy could be lost if the module is modeled by using a simple bulk material or rigid body. To solve this critical engineering problem, a general method to establish a computational homogenized model for the cylindrical battery module is proposed. A single battery cell model is developed and validated through radial compression and bending experiments. To analyze the homogenized mechanical properties of the module, a representative unit cell (RUC) is extracted with the periodic boundary condition applied on it. An elastic-plastic constitutive model is established to describe the computational homogenized model for the module. Two typical packing modes, i.e., cubic dense packing and hexagonal packing for the homogenized equivalent battery module (EBM) model, are targeted for validation compression tests, as well as the models with detailed single cell description. Further, the homogenized EBM model is confirmed to agree reasonably well with the detailed battery module (DBM) model for different packing modes with a length scale of up to 15 × 15 cells and 12% deformation where the short circuit takes place. The suggested homogenized model for battery module makes way for battery module and pack safety evaluation for full-size electric vehicle crashworthiness analysis.
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
Homogenized modeling methodology for 18650 lithium-ion battery module under large deformation
Tang, Liang; Cheng, Pengle
2017-01-01
Effective lithium-ion battery module modeling has become a bottleneck for full-size electric vehicle crash safety numerical simulation. Modeling every single cell in detail would be costly. However, computational accuracy could be lost if the module is modeled by using a simple bulk material or rigid body. To solve this critical engineering problem, a general method to establish a computational homogenized model for the cylindrical battery module is proposed. A single battery cell model is developed and validated through radial compression and bending experiments. To analyze the homogenized mechanical properties of the module, a representative unit cell (RUC) is extracted with the periodic boundary condition applied on it. An elastic–plastic constitutive model is established to describe the computational homogenized model for the module. Two typical packing modes, i.e., cubic dense packing and hexagonal packing for the homogenized equivalent battery module (EBM) model, are targeted for validation compression tests, as well as the models with detailed single cell description. Further, the homogenized EBM model is confirmed to agree reasonably well with the detailed battery module (DBM) model for different packing modes with a length scale of up to 15 × 15 cells and 12% deformation where the short circuit takes place. The suggested homogenized model for battery module makes way for battery module and pack safety evaluation for full-size electric vehicle crashworthiness analysis. PMID:28746390
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.
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.
NASA Astrophysics Data System (ADS)
Sawazaki, K.
2016-12-01
It is well known that seismic velocity of the subsurface medium changes after a large earthquake. The cause of the velocity change is roughly attributed to strong ground motion (dynamic strain change), crustal deformation (static strain change), and fracturing around the fault zone. Several studies have revealed that the velocity reduction down to several percent concentrates at the depths shallower than several hundred meters. The amount of velocity reduction correlates well with the intensity of strong ground motion, which indicates that the strong motion is the primary cause of the velocity reduction. Although some studies have proposed contributions of coseismic static strain change and fracturing around fault zone to the velocity change, separation of their contributions from the site-related velocity change is usually difficult. Velocity recovery after a large earthquake is also widely observed. The recovery process is generally proportional to logarithm of the lapse time, which is similar to the behavior of "slow dynamics" recognized in laboratory experiments. The time scale of the recovery is usually months to years in field observations, while it is several hours in laboratory experiments. Although the factor that controls the recovery speed is not well understood, cumulative strain change due to post-seismic deformation, migration of underground water, mechanical and chemical reactions on the crack surface could be the candidate. In this study, I summarize several observations that revealed spatiotemporal distribution of seismic velocity change due to large earthquakes; especially I focus on the case of the M9.0 2011 Tohoku earthquake. Combining seismograms of Hi-net (high-sensitivity) and KiK-net (strong motion), geodetic records of GEONET and the seafloor GPS/Acoustic ranging, I investigate contribution of the strong ground motion and crustal deformation to the velocity change associated with the Tohoku earthquake, and propose a gross view of
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 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; ...
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
2014-10-24
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.
NASA Astrophysics Data System (ADS)
Subramanian, A.; Krol, A.; Poddar, A. H.; Price, R. L.; Swarnkar, R.; Feiglin, D. H.
2007-03-01
In biomedical research, there is an increased need for reconstruction of large soft tissue volumes (e.g. whole organs) at the microscopic scale from images obtained using laser scanning microscopy (LSM) with fluorescent dyes targeting selected cellular features. However, LSM allows reconstruction of volumes not exceeding a few hundred ım in size and most LSM procedures require physical sectioning of soft tissue resulting in tissue deformation. Micro-CT (μCT) can provide deformation free tomographic image of the whole tissue volume before sectioning. Even though, the spatial resolution of μCT is around 5 μm and its contrast resolution is poor, it could provide information on external and internal interfaces of the investigated volume and therefore could be used as a template in the volume reconstruction from a very large number of LSM images. Here we present a method for accurate 3D reconstruction of the murine heart from large number of images obtained using confocal LSM. The volume is reconstructed in the following steps: (i) Montage synthesis of individual LSM images to form a set of aligned optical planes within given physical section; (ii) Image enhancement and segmentation to correct for non-uniform illumination and noise; (iii) Volume matching of a synthesized physical section to a corresponding sub-volume of μCT (iv) Affine registration of the physical section to the selected μCT sub-volume. We observe correct gross alignment of the physical sections. However, many sections still exhibit local misalignment that could be only corrected via local nonrigid registration to μCT template and we plan to do it in the future.
NASA Astrophysics Data System (ADS)
Zaitsev, Vladimir Y.; Matveyev, Alexander L.; Matveev, Lev A.; Gelikonov, Grigory V.; Omelchenko, Alexander I.; Shabanov, Dmitry V.; Baum, Olga I.; Svistushkin, Valery M.; Sobol, Emil N.
2016-11-01
In the context of the development of emerging laser-assisted thermo-mechanical technologies for non-destructive reshaping of avascular collagenous tissues (cartilages and cornea), we report the first application of phase-sensitive optical coherence tomography (OCT) for visualizing transient strains involving supra-wavelength inter-frame displacements of scatterers. Usually phase-sensitive OCT assumes the visualization of sub-pixel and even sub-wavelength displacements of scatterers and fairly small strains (say, <10-3), which conventionally implies the necessity of averaging for enhancing the effective signal-to-noise ratio and, correspondingly, the application of small-amplitude actuators producing periodic deformations. The original approach used here allows for direct estimation of elevated strains ~10-2 (close to onset of intense speckle blinking) obviating the necessity of averaging and phase unwrapping for supra-wavelength inter-frame displacements. We demonstrate the possibility of mapping aperiodic thermally-induced transient strains with resultant large deformations on order of tens per cent. Such strains are typical in laser tissue reshaping, but are far beyond the range of conventionally discussed OCT-based strain mapping.
NASA Astrophysics Data System (ADS)
Elkhodary, K. I.; Zikry, M. A.
2012-11-01
The major objective of this work was to model within a continuum framework the dynamic nucleation and evolution of failure surfaces in aluminum alloys with complex microstructures, using a recently developed compatibility-based fracture criterion for large deformations. Computational analyses were conducted to understand how Mn-bearing dispersoids, Ω and θ‧ precipitates affect dynamic fracture processes in an Al-Cu-Mg-Ag alloys (2139-Al). High strain-rate simulations were based on a rate-dependent dislocation-density-based crystalline plasticity formulation and a nonlinear explicit dynamic finite-element approach. Results indicate that the fracture criterion elucidated how dispersoids and precipitates have a dominant role in dynamic crack blunting,branching and arrest. Rationally orientated precipitates result in overall dynamic microstructural strengthening and enhanced uniformity of deformation. These precipitates, however, accelerated unstable crack propagation, and this is amplified in the presence of a pre-crack. In contrast, dispersoids decreased microstructural toughness and ductility, but greatly improved dynamic damage tolerance, especially in the presence of a pre-crack. It can also be predicted that low angle boundaries can change the propagation direction of ductile cracks, and contribute to damage tolerance without crack initiation. Collectively, rationally oriented precipitates and dispersoids can significantly improve the combined dynamic strength, toughness and damage tolerance of crystalline aluminum alloys.
Liu, Tianshu; Long, Rong; Hui, Chung-Yuen
2014-10-21
In this paper we present a theoretical study on how surface tension affects fracture of soft solids. In classical fracture theory, the resistance to fracture is partly attributed to the energy required to create new surfaces. Thus, the energy released to the crack tip must overcome the surface energy in order to propagate a crack. In soft materials, however, surface tension can cause significant deformation and can reduce the energy release rate for crack propagation by resisting the stretch of crack surfaces. We quantify this effect by studying the inflation of a penny-shaped crack in an infinite elastic body with applied pressure. To avoid numerical difficulty caused by singular fields near the crack tip, we derived an expression for the energy release rate which depends on the applied pressure, the surface tension, the inflated crack volume and the deformed crack area. This expression is evaluated using a newly developed finite element method with surface tension elements. Our calculation shows that, when the elasto-capillary number ω ≡ σ/Ea is sufficiently large, where σ is the isotropic surface tension, E is the small strain Young's modulus and a is the initial crack radius, both the energy release rate and the crack opening displacement of an incompressible neo-Hookean solid are significantly reduced by surface tension. For a sufficiently high elasto-capillary number, the energy release rate can be negative for applied pressure less than a critical amount, suggesting that surface tension can cause crack healing in soft elastic materials.
Analysis of large, non-isothermal elastic-visco-plastic deformations
NASA Technical Reports Server (NTRS)
Riff, R.; Carlson, R. L.; Simitses, G. J.
1984-01-01
The development of a general mathematical model and solutions of test problems to analyze large nonisothermal elasto-visco-plastic deformatisms of structures is discussed. Geometric and material type nonlinearities of higher order are present in the development of the mathematical model and in the developed solution methodology.
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
NASA Astrophysics Data System (ADS)
Agata, R.; Ichimura, T.; Hori, T.; Hirahara, K.; Hashimoto, C.; Hori, M.
2015-12-01
Inverse analysis of the coseismic/postseismic slip using postseismic deformation observation data is an important topic in geodetic inversion. Inverse analysis method may be improved by using numerical simulation (e.g. finite element (FE) method) of viscoelastic deformation, the model of which is of high-fidelity to the available high-resolution crustal data. The authors had been developing a large-scale simulation method using such FE high-fidelity models (HFM), assuming use of K computer, the current fastest supercomputer in Japan. In this study, we developed an inverse analysis method incorporating HFM, in which the asthenosphere viscosity and fault slip are estimated simultaneously, since the value of viscosity in the simulation is not trivial. We carried out numerical experiments using synthetic crustal deformation data. Based on Ichimura et al. (2013), we constructed an HFM in the domain of 2048x1536x850 km, which includes the Tohoku region in northeast Japan. We used the data set of JTOPO30 (2003), Koketsu et al. (2008) and CAMP standard model (Hashimoto et al. 2004) for the model geometry. The HFM is currently in 2km resolution, resulting in 0.5 billion degrees-of-freedom. The figure shows the overview of HFM. Synthetic crustal deformation data of three years after an earthquake in the location of GEONET, GPS/A observation points, and S-net were used. Inverse analysis was formulated as minimization of L2 norm of the difference between the FE simulation results and the observation data with respect to viscosity and fault slip, combining quasi-Newton algorithm with adjoint method. Coseismic slip was expressed by superposition of 53 subfaults, with four viscoelastic layers. We carried out 90 forward simulations, and the 57 parameters converged to the true values. Due to the fast computation method, it took only five hours using 2048 nodes (1/40 of entire resource) of K computer. In the future, we would like to also consider estimation of after slip and apply
NASA Astrophysics Data System (ADS)
Fuchs, L.; Schmeling, H.
2013-08-01
A key to understand many geodynamic processes is studying the associated large deformation fields. Finite deformation can be measured in the field by using geological strain markers giving the logarithmic strain f = log 10(R), where R is the ellipticity of the strain ellipse. It has been challenging to accurately quantify finite deformation of geodynamic models for inhomogeneous and time-dependent large deformation cases. We present a new formulation invoking a 2-D marker-in-cell approach. Mathematically, one can describe finite deformation by a coordinate transformation to a Lagrangian reference frame. For a known velocity field the deformation gradient tensor, F, can be calculated by integrating the differential equation DtFij = LikFkj, where L is the velocity gradient tensor and Dt the Lagrangian derivative. The tensor F contains all information about the minor and major semi-half axes and orientation of the strain ellipse and the rotation. To integrate the equation centrally in time and space along a particle's path, we use the numerical 2-D finite difference code FDCON in combination with a marker-in-cell approach. For a sufficiently high marker density we can accurately calculate F for any 2-D inhomogeneous and time-dependent creeping flow at any point for a deformation f up to 4. Comparison between the analytical and numerical solution for the finite deformation within a Poiseuille-Couette flow shows an error of less than 2 per cent for a deformation up to f = 1.7. Moreover, we determine the finite deformation and strain partitioning within Rayleigh-Taylor instabilities (RTIs) of different viscosity and layer thickness ratios. These models provide a finite strain complement to the RTI benchmark of van Keken et al. Large finite deformation of up to f = 4 accumulates in RTIs within the stem and near the compositional boundaries. Distinction between different stages of diapirism shows a strong correlation between a maximum occurring deformation of f = 1, 3 and
A constitutive theory for shape memory polymers: coupling of small and large deformation
NASA Astrophysics Data System (ADS)
Tan, Qiao; Liu, Liwu; Liu, Yanju; Leng, Jinsong; Yan, Xiangqiao; Wang, Haifang
2013-04-01
At high temperatures, SMPs share attributes like rubber and exhibit long-range reversibility. In contrast, at low temperatures they become very rigid and are susceptible to plastic, only small strains are allowable. But there relatively little literature has considered the unique small stain (rubber phase) and large stain (glass phase) coupling in SMPs when developing the constitutive modeling. In this work, we present a 3D constitutive model for shape memory polymers in both low temperature small strain regime and high temperature large strain regime. The theory is based on the work of Liu et al. [15]. Four steps of SMP's thermomechanical loadings cycle are considered in the constitutive model completely. The linear elastic and hyperelastic effects of SMP in different temperatures are also fully accounted for in the proposed model by adopt the neo-Hookean model and the Generalized Hooke's laws.
Gray, G.T. III; Bingert, S.R.; Chen, S.R.; Bingert, J.F.; Wright, S.I.
1996-03-01
Numerous studies have established the influence of impurities, crystallographic texture, temperature, and strain rate separately or collectively on the constitutive response of annealed tantalum, in particular plate Ta-stock. However, fewer detailed studies have examined the evolution of crystallographic texture and the mechanical response of tantalum bar or rod material following prestraining to large strains {epsilon} > I. In this paper the influence of large plastic prestraining on the microstructure evolution, texture evolution, and mechanical response of high-purity tantalum bar material is presented. Tantalum cylinders annealed at 1200 {degrees}C were quasi-statically upset forged, with intermediate lubrication, to true strains of 0.4, 0.95, and 1.85. Microstructural and textural banding within the starting Ta-bar was characterized in detail. It was found that different oriented bands evolved differently during large-strain forging leading to significant scatter in the mechanical response. Aspects of defect storage, work-hardening response, and texture evolution in Ta-bar as a function of forging strain are discussed.
Deformation of the turbulent/non-turbulent interface by large-scale motions in boundary layers
NASA Astrophysics Data System (ADS)
Lee, Jin; Sung, Hyung Jin; Zaki, Tamer A.
2014-11-01
The relationship between large-scale motions (LSMs) and the shape of the turbulent/non-turbulent interface (TNTI) is examined using data from direct numerical simulation (DNS) of turbulent boundary layer (TBL) flow. The Reynolds number based on the momentum thickness and the free-stream velocity ranges from 1180 to 3500. Feature extraction techniques are used to identify cores of the large-scale motions in the perturbation fields. Since turbulence kinetic energy and enstrophy are different inside low- and high-speed LSMs, the wall-normal elevation of TNTI is correlated with the streamwise momentum of these structures. The large-scale crests and troughs of TNTI are matched to the locations of the wall-detached LSMs of low- and high-speed streaks, respectively. In addition, abrupt changes in turbulence statistics across the TNTI reported in previous studies are associated with population trends of the wall-detached LSMs near the TNTI. This work was supported by the Creative Research Initiatives (No. 2014-001493) program of the National Research Foundation of Korea (MSIP).
NASA Astrophysics Data System (ADS)
Chen, L. Y.; Ge, Q.; Qu, S.; Jiang, Q. K.; Nie, X. P.; Jiang, J. Z.
2008-05-01
The limited plastic deformation and lack of work hardening seriously restrict the applications of bulk metallic glasses (BMGs). Here, large macroscopic compressive plastic deformation (over 15%) and work-hardening-like behavior were achieved in a monolithic BMG through tailoring loading stress distribution experimentally. Numerical analysis was also carried out to investigate the stress distribution under the same mechanical condition. It is shown that loading induced stress gradient is responsible for the achievement mentioned above.
ɛ-neighbourhoods of orbits of parabolic diffeomorphisms and cohomological equations
NASA Astrophysics Data System (ADS)
Resman, Maja
2014-12-01
In this article, we study the analyticity of (directed) areas of ɛ-neighbourhoods of orbits of parabolic germs. The article is motivated by the question of analytic classification using ɛ-neighbourhoods of orbits in the simplest formal class. We show that the coefficient in front of the ɛ2 term in the asymptotic expansion in ɛ, which we call the principal part of the area, is a sectorially analytic function in the initial point of the orbit. It satisfies a cohomological equation similar to the standard trivialization equation for parabolic diffeomorphisms. We give necessary and sufficient conditions on a diffeomorphism f for the existence of a globally analytic solution of this equation. Furthermore, we introduce a new classification type for diffeomorphisms implied by this new equation and investigate the relative position of its classes with respect to the analytic classes.
Commowick, Olivier; Wiest-Daesslé, Nicolas; Prima, Sylvain
2012-01-01
We propose an iterative two-step method to compute a diffeomorphic non-rigid transformation between images of anatomical structures with rigid parts, without any user intervention or prior knowledge on the image intensities. First we compute spatially sparse, locally optimal rigid transformations between the two images using a new block matching strategy and an efficient numerical optimiser (BOBYQA). Then we derive a dense, regularised velocity field based on these local transformations using matrix logarithms and M-smoothing. These two steps are iterated until convergence and the final diffeomorphic transformation is defined as the exponential of the accumulated velocity field. We show our algorithm to outperform the state-of-the-art log-domain diffeomorphic demons method on dynamic cervical MRI data.
Auzias, Guillaume; Glaunès, Joan; Colliot, Olivier; Perrot, Matthieu; Mangin, Jean-François; Trouvé, Alain; Baillet, Sylvain
2009-01-01
Neuroimaging at the group level requires spatial normalization of individual structural data. We propose a geometric approach that consists in matching a series of cortical surfaces through diffeomorphic registration of their sulcal imprints. The resulting 3D transforms naturally extends to the entire MRI volumes. The Diffeomorphic Sulcal-based COrtical (DISCO) registration integrates two recent technical outcomes: 1) the automatic extraction, identification and simplification of numerous sulci from T1-weighted MRI data series hereby revealing the sulcal imprint and 2) the measure-based diffeomorphic registration of those crucial anatomical landmarks. We show how the DISCO registration may be used to elaborate a sulcal template which optimizes the distribution of constraints over the entire cortical ribbon. DISCO was evaluated through a group of 20 individual brains. Quantitative and qualitative indices attest how this approach may improve both alignment of sulcal folds and overlay of gray and white matter volumes at the group level.
A hybrid multimodal non-rigid registration of MR images based on diffeomorphic demons.
Lu, Huanxiang; Cattin, Philippe C; Reyes, Mauricio
2010-01-01
In this paper we present a novel hybrid approach for multimodal medical image registration based on diffeomorphic demons. Diffeomorphic demons have proven to be a robust and efficient way for intensity-based image registration. A very recent extension even allows to use mutual information (MI) as a similarity measure to registration multimodal images. However, due to the intensity correspondence uncertainty existing in some anatomical parts, it is difficult for a purely intensity-based algorithm to solve the registration problem. Therefore, we propose to combine the resulting transformations from both intensity-based and landmark-based methods for multimodal non-rigid registration based on diffeomorphic demons. Several experiments on different types of MR images were conducted, for which we show that a better anatomical correspondence between the images can be obtained using the hybrid approach than using either intensity information or landmarks alone.
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.
Internal strain, deformation, and failure of large scale pullout tests in concrete
NASA Astrophysics Data System (ADS)
Stone, W. C.
1982-05-01
Detailed experimental data on crack propagation and internal strain distribution for the pullout test is presented. A 12:1 scaled-up pullout test was designed, using a commercial pullout insert for the prototype dimensions, and was instrumented with small waterproof embedment strain gages so as to obtain internal strain profiles at critical locations. Two large scale specimens were tested with apex angles falling at the upper and lower bounds currently recommended in ASTM C-900. Two dimensional axisymmetric finite element analyses were performed for the two experimental specimens and the results were compared with measured strains for load stages below the onset of internal cracking.
Alsinnawi, M; Torreggiani, W C; Flynn, R; McDermott, T E D; Grainger, R; Thornhill, J A
2013-09-01
To present our experience in patients with spina bifida with severe spinal abnormality undergoing percutaneous nephrolithotomy (PCNL) for large stone burden. A retrospective review identified five spina bifida patients with abnormal spinal curvature who had a PCNL for large kidney stones. The mean age was 28 years. In two patients, stones were on the concave side of the scoliotic spine further limiting percutaneous access. Mean stone burden was 940 mm2. All patients were paraplegic, three patients had symptomatic stone disease. We performed initial percutaneous renal access in radiology department and staged nephrolithotomy in operating room. Tract dilatation was accomplished using Amplatz dilators and a 24 Ch or 26 Ch nephroscope was used. Fragmentation and stone removal were accomplished in all patients using pneumatic and or ultrasound lithotripter and a retrieval grasper. No anaesthetic complications were recorded. One patient required multiple percutaneous tracts, four had single tract to access stones. Three patients were stone free after PCNL. One required second PCNL through the same tract and another patient had multiple adjunctive ESWL. All five patients were stone clear after the final procedure. Two patients required blood transfusion. No patient had major complication or admission to intensive care unit. Percutaneous nephrolithotomy in patients with spina bifida is challenging but safe. Detailed pre-operative anaesthetic assessment and precise uroradiological evaluation of renal anatomy is essential. Second-look PCNL and additional ESWL/URS treatment may be required to completely clear stones.
Large deformation contact mechanics of a pressurized long rectangular membrane. II. Adhesive contact
Srivastava, Abhishek; Hui, Chung-Yuen
2013-01-01
In part I of this work, we presented a theory for adhesionless contact of a pressurized neo-Hookean plane-strain membrane to a rigid substrate. Here, we extend our theory to include adhesion using a fracture mechanics approach. This theory is used to study contact hysteresis commonly observed in experiments. Detailed analysis is carried out to highlight the differences between frictionless and no-slip contact. Membrane detachment is found to be strongly dependent on adhesion: for low adhesion, the membrane ‘pinches-off’, whereas for large adhesions, it detaches unstably at finite contact (‘pull-off’). Expressions are derived for the critical adhesion needed for pinch-off to pull-off transition. Above a threshold adhesion, the membrane exhibits bistability, two stable states at zero applied pressure. The condition for bistability for both frictionless and no-slip boundary conditions is obtained explicitly. PMID:24353472
Multiscale Characterization of bcc Crystals Deformed to Large Extents of Strain
Florando, J; LeBlanc, M; Lassila, D; Bulatov, V; Rhee, M; Arsenlis, A; Becker, R; Jr., J M; Magid, K
2007-02-20
In an effort to help advance the predictive capability of LLNL's multiscale modeling program a new experimental technique has been developed to provide high fidelity data on metallic single crystals out to relatively large extents of strain. The technique uses a '6 Degrees of Freedom' testing apparatus in conjunction with a 3-D image correlation system. Utilizing this technique, a series of experiments have been performed that reveal unexpected behavior which cannot be explained using traditional crystal plasticity theory. In addition, analysis and characterization techniques have also been developed to help quantify the unexpected behavior. Interactions with multiscale modelers include the development of a possible mechanism that might explain the anomalous behavior, as well as the discovery of a new 4-node dislocation junction.
Variationally consistent coupling of non-matching discretizations for large deformation problems
NASA Astrophysics Data System (ADS)
Wang, Xiaowo; Prakash, Arun; Chen, Jiun-Shyan; Taciroglu, Ertugrul
2017-05-01
Non-matching interfaces occur in large computational models of complicated structures when different discretizations are used in different regions of the problem domain. Presence of non-matching interfaces, for instance, between two or more finite element meshes of different refinement, or between a meshfree region and a finite element region, can lead to erroneous results. In this work, a variationally consistent coupling method is developed to ensure that such patch tests are passed for any choice of numerical integration over the interface. This is achieved by constructing an integration constraint over the non-matching interface and by modifying the approximation basis functions for the adjacent discretizations in a way that guarantees passing the patch test. Numerical examples are presented to verify the formulation and study the performance of the proposed method.
NASA Astrophysics Data System (ADS)
Setare, M. R.; Adami, H.
2016-01-01
In the first order formalism of gravity theories, there are some theories which are not Lorentz-diffeomorphism covariant. In the framework of such theories we cannot apply the method of conserved charge calculation used in Lorentz-diffeomorphism covariant theories. In this paper we firstly introduce the total variation of a quantity due to an infinitesimal Lorentz-diffeomorphism transformation. Secondly, in order to obtain the conserved charges of Lorentz-diffeomorphism non-covariant theories, we extend the Tachikawa method [1]. This extension includes not only Lorentz gauge transformation but also the diffeomorphism. We apply this method to the Chern-Simons-like theories of gravity (CSLTG) and obtain a general formula for the entropy of black holes in those theories. Finally, some examples on CSLTG are provided and the entropy of the BTZ black hole is calculated in the context of the examples.
On the number of heteroclinic curves of diffeomorphisms with surface dynamics
NASA Astrophysics Data System (ADS)
Grines, Vyacheslav Z.; Gurevich, Elena Ya.; Pochinka, Olga V.
2017-03-01
Separators are fundamental plasma physics objects that play an important role in many astrophysical phenomena. Looking for separators and their number is one of the first steps in studying the topology of the magnetic field in the solar corona. In the language of dynamical systems, separators are noncompact heteroclinic curves. In this paper we give an exact lower estimation of the number of noncompact heteroclinic curves for a 3-diffeomorphism with the so-called "surface dynamics". Also, we prove that ambient manifolds for such diffeomorphisms are mapping tori.
Groups of line and circle diffeomorphisms. Criteria for almost nilpotency and structure theorems
NASA Astrophysics Data System (ADS)
Beklaryan, L. A.
2016-08-01
Almost nilpotency criteria and structure theorems are presented for the class of finitely generated groups of line and circle diffeomorphisms with mutually transversal elements. Key ingredients in the proof of the structure theorems are the existence/absence of an invariant measure, the (previously established) criterion for the existence of an invariant measure and restatements of this criterion in terms of various (topological, algebraic, combinatorial) characteristics of the group. The question of whether certain features of these characteristics or the existence of an invariant measure are typical for groups of line and circle diffeomorphisms is discussed. Bibliography: 34 titles.
Scheer, Justin K; Tang, Jessica A; Smith, Justin S; Klineberg, Eric; Hart, Robert A; Mundis, Gregory M; Burton, Douglas C; Hostin, Richard; O'Brien, Michael F; Bess, Shay; Kebaish, Khaled M; Deviren, Vedat; Lafage, Virginie; Schwab, Frank; Shaffrey, Christopher I; Ames, Christopher P
2013-10-01
within 1 year after the initial surgery, including 17 reoperations (5%) within 30 days. Two hundred sixty-eight patients had a minimum of 1 year of follow-up. Fifty-three (20%) of these patients had a 3-column osteotomy, and 10 (19%) of these 53 required reoperation within 1 year of the initial procedure. However, 3-column osteotomy was not predictive of reoperation within 1 year, p = 0.5476). There were no significant differences between groups with regard to the distribution of UIV, and UIV did not have a significant effect on reoperation rates. Patients needing reoperation within 1 year had worse ODI and SRS-22 scores measured at 1-year follow-up than patients not requiring operation. Analysis of data from a large multicenter adult spinal deformity database shows an overall 17% reoperation rate, with a 19% reoperation rate for patients treated with 3-column osteotomy and a 16% reoperation rate for patients not treated with 3-column osteotomy. The most common indications for reoperation included instrumentation complications and radiographic failure. Reoperation significantly affected HRQOL outcomes at 1-year follow-up. The need for reoperation may be minimized by carefully considering spinal alignment, termination of fixation, and type of surgical procedure (presence of osteotomy). Precautions should be taken to avoid malposition or instrumentation (rod) failure.
Fiot, Jean-Baptiste; Raguet, Hugo; Risser, Laurent; Cohen, Laurent D; Fripp, Jurgen; Vialard, François-Xavier
2014-01-01
In the context of Alzheimer's disease, two challenging issues are (1) the characterization of local hippocampal shape changes specific to disease progression and (2) the identification of mild-cognitive impairment patients likely to convert. In the literature, (1) is usually solved first to detect areas potentially related to the disease. These areas are then considered as an input to solve (2). As an alternative to this sequential strategy, we investigate the use of a classification model using logistic regression to address both issues (1) and (2) simultaneously. The classification of the patients therefore does not require any a priori definition of the most representative hippocampal areas potentially related to the disease, as they are automatically detected. We first quantify deformations of patients' hippocampi between two time points using the large deformations by diffeomorphisms framework and transport these deformations to a common template. Since the deformations are expected to be spatially structured, we perform classification combining logistic loss and spatial regularization techniques, which have not been explored so far in this context, as far as we know. The main contribution of this paper is the comparison of regularization techniques enforcing the coefficient maps to be spatially smooth (Sobolev), piecewise constant (total variation) or sparse (fused LASSO) with standard regularization techniques which do not take into account the spatial structure (LASSO, ridge and ElasticNet). On a dataset of 103 patients out of ADNI, the techniques using spatial regularizations lead to the best classification rates. They also find coherent areas related to the disease progression.
Shear deformation plate continua of large double-layered space structures
NASA Technical Reports Server (NTRS)
Hefzy, M. S.; Nayfeh, A. H.
1984-01-01
The energy equivalence to construct equivalent continua for the actual lattice structure is described. An energy equivalent continuum is defined as that which has the same amount of strain and kinetic energies stored in it as the original lattice structure when both are subjected to the same loading conditions. The equivalent continuum is characterized by its strain and kinetic energies from which the constitutive relations and the equations of motion can be derived. A simple method to model large rigid jointed lattices as continuous media with couple stresses is presented. The transition from the discrete system to the continuous medium is achieved by expanding the displacements and the rotations of the nodal points in a Taylor series about a suitable chosen origin. Basic kinematic assumptions are introduced to insure that the assumptions used in deriving the governing equations of the modeled continuum are satisfied. The number of terms retained in the Taylor series expansion will depend upon the properties to be evaluated. This implies that the kind of continuum needed to model from the discrete lattice, before the actual properties are derived was to predetermined.
Del Frari, Barbara; Schoeller, Thomas; Wechselberger, Gottfried
2010-01-01
Microvascular free flaps continue to revolutionize coverage options in head and neck reconstruction. The authors describe their experience with the gracilis free flap and the myocutaneous gracilis free flap with reconstruction of head and neck defects. Eleven patients underwent 12 free tissue transfer to the head and neck region. The reconstruction was performed with the transverse myocutaneous gracilis (TMG) flap (n = 7) and the gracilis muscle flap with skin graft (n = 5). The average patient age was 63.4 years (range, 17-82 years). The indications for this procedure were tumor and haemangioma resections. The average patient follow-up was 20.7 months (range, 1 month-5.7 years). Total flap survival was 100%. There were no partial flap losses. Primary wound healing occurred in all cases. Recipient site morbidities included one hematoma. In our experience for reconstruction of moderate volume and surface area defects, muscle flaps with skin graft provide a better color match and skin texture relative to myocutaneous or fasciocutaneous flaps. The gracilis muscle free flap is not widely used for head and neck reconstruction but has the potential to give good results. As a filling substance for large cavities, the transverse myocutaneus gracilis flap has many advantages including reliable vascular anatomy, relatively great plasticity and a concealed donor area.
Brannon, R.M.
1996-12-31
A mathematical framework is developed for the study of materials containing axisymmetric inclusions or flaws such as ellipsoidal voids, penny-shaped cracks, or fibers of circular cross-section. The general case of nonuniform statistical distributions of such heterogeneities is attacked by first considering a spatially uniform distribution of flaws that are all oriented in the same direction. Assuming an isotropic substrate, the macroscopic material properties of this simpler microstructure naturally should be transversely isotropic. An orthogonal basis for the linear subspace consisting of all double-symmetric transversely-isotropic fourth-order tensors associated with a given material vector is applied to deduce the explicit functional dependence of the material properties of these aligned materials on the shared symmetry axis. The aligned and uniform microstructure seems geometrically simple enough that the macroscopic transversely isotropic properties could be derived in closed form. Since the resulting properties are transversely isotropic, the analyst must therefore be able to identify the appropriate coefficients of the transverse basis. Once these functions are identified, a principle of superposition of strain rates ay be applied to define an expectation integral for the composite properties of a material containing arbitrary anisotropic distributions of axisymmetric inhomogeneities. A proposal for coupling plastic anisotropy to the elastic anisotropy is presented in which the composite yield surface is interpreted as a distortion of the isotropic substrate yield surface; the distortion directions are coupled to the elastic anisotropy directions. Finally, some commonly assumed properties (such as major symmetry) of the Cauchy tangent stiffness tensor are shown to be inappropriate for large distortions of anisotropic materials.
NASA Astrophysics Data System (ADS)
Zhang, Qingchao; Li, Rui; Gu, Xue; Qin, Jieming; Jia, Xiaopeng; Ma, Hongan
2015-06-01
The temperature-field in diamond synthesis cell was simulated by a finite element method. A three-dimensional model of the China-type cubic press with large deformation of the synthesis cell was established successfully, which has been verified by situ measurements of synthesis cell. In addition, the distributions of temperature and its gradient in the synthesis sample were described. We found there is a large temperature drop in the synthesis sample, which brings some uncertainties in a synthesis process, such as the phenomenon of "wasteland, on which there is no nucleation and growth of diamond". Furthermore, the formation mechanism of wasteland was studied in detail. It indicates that the wasteland is inevitably exists in the synthesis sample, the distribution of growth region of the diamond with hex-octahedral is move to the center of the synthesis sample from near the heater as the power increasing, and the growth conditions of high quality diamond is locate at the center of the synthesis sample. This work can offer suggestion and advice to the development and optimization of a diamond production process.
A viscoelastic analysis of the P56 mouse brain under large-deformation dynamic indentation.
MacManus, David B; Pierrat, Baptiste; Murphy, Jeremiah G; Gilchrist, Michael D
2017-01-15
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 within individual brain regions. The regional viscoelastic properties of P56 mouse brain tissue, up to 70μm displacement, are presented and discussed in the context of traumatic brain injury, particularly how the different regions of the brain respond to mechanical loads. Force-relaxation data obtained from micro-indentation measurements were fit to both linear and quasi-linear viscoelastic models to determine the time and frequency domain viscoelastic response of the pons, cortex, medulla oblongata, cerebellum, and thalamus. The damping ratio of each region was also determined. Each region was found to have a unique mechanical response to the applied displacement, with the pons and thalamus exhibiting the largest and smallest force-response, respectively. All brain regions appear to have an optimal frequency for the dissipation of energies which lies between 1 and 10Hz. We present the first mechanical characterization of the viscoelastic response for different regions of mouse brain. Force-relaxation tests are performed under large strain dynamic micro-indentation, and viscoelastic models are used subsequently, providing time-dependent mechanical properties of brain tissue under loading conditions comparable to what is experienced in TBI. The unique mechanical properties of different brain regions are highlighted, with substantial variations in the viscoelastic properties and damping ratio of each region. Cortex and pons were the stiffest regions, while the thalamus and medulla were most compliant. The cerebellum and thalamus had highest damping ratio values and those of the medulla were lowest. The reported
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
NASA Astrophysics Data System (ADS)
Chadha, K.; Shahriari, D.; Tremblay, R.; Bhattacharjee, P. P.; Jahazi, M.
2017-07-01
Constitutive modeling of the ingot breakdown process of large size ingots of high strength steel was carried out through comprehensive thermomechanical processing using Gleeble 3800® thermomechanical simulator, finite element modeling (FEM), optical and electron back scatter diffraction (EBSD). For this purpose, hot compression tests in the range of 1473 K to 1323 K (1200 °C to 1050 °C) and strain rates of 0.25 to 2 s-1 were carried out. The stress-strain curves describing the deformation behavior of the dendritic microstructure of the cast ingot were analyzed in terms of the Arrhenius and Hansel-Spittel models which were implemented in Forge NxT 1.0® FEM software. The results indicated that the Arrhenius model was more reliable in predicting microstructure evolution of the as-cast structure during ingot breakdown, particularly the occurrence of dynamic recrystallization (DRX) process which was a vital parameter in estimating the optimum loads for forming of large size components. The accuracy and reliability of both models were compared in terms of correlation coefficient (R) and the average absolute relative error (ARRE).
NASA Astrophysics Data System (ADS)
Chadha, K.; Shahriari, D.; Tremblay, R.; Bhattacharjee, P. P.; Jahazi, M.
2017-09-01
Constitutive modeling of the ingot breakdown process of large size ingots of high strength steel was carried out through comprehensive thermomechanical processing using Gleeble 3800® thermomechanical simulator, finite element modeling (FEM), optical and electron back scatter diffraction (EBSD). For this purpose, hot compression tests in the range of 1473 K to 1323 K (1200 °C to 1050 °C) and strain rates of 0.25 to 2 s-1 were carried out. The stress-strain curves describing the deformation behavior of the dendritic microstructure of the cast ingot were analyzed in terms of the Arrhenius and Hansel-Spittel models which were implemented in Forge NxT 1.0® FEM software. The results indicated that the Arrhenius model was more reliable in predicting microstructure evolution of the as-cast structure during ingot breakdown, particularly the occurrence of dynamic recrystallization (DRX) process which was a vital parameter in estimating the optimum loads for forming of large size components. The accuracy and reliability of both models were compared in terms of correlation coefficient (R) and the average absolute relative error (ARRE).
Stojanoski, Bobby; Cusack, Rhodri
2014-10-09
To isolate the neural mechanisms associated with recognizing objects from those processing basic visual properties, control stimuli are required that contain the same perceptual properties as the objects but are unrecognizable. We demonstrate that conventional methods for generating control stimuli (phase scrambling, box scrambling, texture scrambling) yield poor controls because they dramatically distort the basic visual properties (e.g., spatial frequency, perceptual organization) to which even the earliest stages of visual processing are sensitive. We developed a new scrambling method, using a diffeomorphic transformation that preserves the basic perceptual properties of the image while removing meaning. We acquired perceptual ratings to determine the least amount of scrambling necessary to remove recognition. We hypothesized that our "diffeomorphic" images would produce neural activity at the earliest stages of the visual system that more closely matched activity in response to intact images relative to the other scrambling methods. To test this hypothesis, we used the HMAX computational model of object recognition and compared the simulated neural activity at the earliest stages of the visual system (layers S1, C1, and S2) between a set of 149 images scrambled using each distortion method to their intact version. We found that scrambled "diffeomorphed" images were indistinguishable to intact images in each layer of the model, but all of the other distortion methods yielded quite different patterns. Our results indicate that "diffeomorphed" images serve as more appropriate control stimuli in neuroimaging studies that aim to disentangle the representations of perceptual and semantic object properties. © 2014 ARVO.
Polynomial Normal Forms for Some Germs of Nonstrongly 1-Resonant Diffeomorphisms
NASA Astrophysics Data System (ADS)
Guo, Lingling; Ren, Zhihua
2015-12-01
We study in this paper a class of smoothly finite determined germs of diffeomorphisms which have infinitely many resonant relations near a nonstrongly 1-resonant fixed point on ℝ3 and derive the simplest normal forms of such germs with nondegenerated nonlinear parts.
NASA Astrophysics Data System (ADS)
Vandenrijt, Jean-François; Thizy, Cédric; Martin, Laurent; Beaumont, Florent; Garcia, José; Fabron, Christophe; Prieto, Éric; Maciaszek, Thierry; Georges, Marc P.
2016-12-01
We present digital holographic interferometry (DHI) in the long-wave infrared for monitoring the deformation under cryogenic conditions of a segmented focal plane array to be used in a space mission. The long wavelength was chosen for its ability to allow measurement of displacements 20 times larger than DHI in the visible, which were foreseen with the test object under large temperature variations. The latter is a mosaic of 4×4 detectors assembled on a frame. DHI was required to assess the global deformation of the assembly, the deformation of each detector, and out-of-plane movements of each of them with respect to their neighbors. For that reason, we incorporated the temporal phase unwrapping by capturing a sufficiently high number of holograms between which the phase does not undergo large variations. At last, since the specimen exhibits specular reflectivity at that wavelength, it is illuminated by means of a reflective diffuser.
Approximations of the diffeomorphic metric and their applications in shape learning.
Yang, Xianfeng; Goh, Alvina; Qiu, Anqi
2011-01-01
In neuroimaging studies based on anatomical shapes, it is well-known that the dimensionality of the shape information is much higher than the number of subjects available. A major challenge in shape analysis is to develop a dimensionality reduction approach that is able to efficiently characterize anatomical variations in a low-dimensional space. For this, there is a need to characterize shape variations among individuals for N given subjects. Therefore, one would need to calculate (2(N)) mappings between any two shapes and obtain their distance matrix. In this paper, we propose a method that reduces the computational burden to N mappings. This is made possible by making use of the first- and second-order approximations of the metric distance between two brain structural shapes in a diffeomorphic metric space. We directly derive these approximations based on the so-called conservation law of momentum, i.e., the diffeomorphic transformation acting on anatomical shapes along the geodesic is completely determined by its velocity at the origin of a fixed template. This allows for estimating morphological variation of two shapes through the first- and second-order approximations of the initial velocity in the tangent space of the diffeomorphisms at the template. We also introduce an alternative representation of these approximations through the initial momentum, i.e., a linear transformation of the initial velocity, and provide a simple computational algorithm for the matrix of the diffeomorphic metric. We employ this algorithm to compute the distance matrix of hippocampal shapes among an aging population used in a dimensionality reduction analysis, namely, ISOMAP. Our results demonstrate that the first- and second-order approximations are sufficient to characterize shape variations when compared to the diffeomorphic metric constructed through (2(N)) mappings in ISOMAP analysis.
NASA Astrophysics Data System (ADS)
Reinoso, J.; Paggi, M.; Linder, C.
2017-02-01
Fracture of technological thin-walled components can notably limit the performance of their corresponding engineering systems. With the aim of achieving reliable fracture predictions of thin structures, this work presents a new phase field model of brittle fracture for large deformation analysis of shells relying on a mixed enhanced assumed strain (EAS) formulation. The kinematic description of the shell body is constructed according to the solid shell concept. This enables the use of fully three-dimensional constitutive models for the material. The proposed phase field formulation integrates the use of the (EAS) method to alleviate locking pathologies, especially Poisson thickness and volumetric locking. This technique is further combined with the assumed natural strain method to efficiently derive a locking-free solid shell element. On the computational side, a fully coupled monolithic framework is consistently formulated. Specific details regarding the corresponding finite element formulation and the main aspects associated with its implementation in the general purpose packages FEAP and ABAQUS are addressed. Finally, the applicability of the current strategy is demonstrated through several numerical examples involving different loading conditions, and including linear and nonlinear hyperelastic constitutive models.
Jiang, Chen; Liu, Gui-Rong; Han, Xu; Zhang, Zhi-Qian; Zeng, Wei
2015-01-01
The smoothed FEM (S-FEM) is firstly extended to explore the behavior of 3D anisotropic large deformation of rabbit ventricles during the passive filling process in diastole. Because of the incompressibility of myocardium, a special method called selective face-based/node-based S-FEM using four-node tetrahedral elements (FS/NS-FEM-TET4) is adopted in order to avoid volumetric locking. To validate the proposed algorithms of FS/NS-FEM-TET4, the 3D Lame problem is implemented. The performance contest results show that our FS/NS-FEM-TET4 is accurate, volumetric locking-free and insensitive to mesh distortion than standard linear FEM because of absence of isoparametric mapping. Actually, the efficiency of FS/NS-FEM-TET4 is comparable with higher-order FEM, such as 10-node tetrahedral elements. The proposed method for Holzapfel myocardium hyperelastic strain energy is also validated by simple shear tests through the comparison outcomes reported in available references. Finally, the FS/NS-FEM-TET4 is applied in the example of the passive filling of MRI-based rabbit ventricles with fiber architecture derived from rule-based algorithm to demonstrate its efficiency. Hence, we conclude that FS/NS-FEM-TET4 is a promising alternative other than FEM in passive cardiac mechanics.
NASA Astrophysics Data System (ADS)
Reinoso, J.; Paggi, M.; Linder, C.
2017-06-01
Fracture of technological thin-walled components can notably limit the performance of their corresponding engineering systems. With the aim of achieving reliable fracture predictions of thin structures, this work presents a new phase field model of brittle fracture for large deformation analysis of shells relying on a mixed enhanced assumed strain (EAS) formulation. The kinematic description of the shell body is constructed according to the solid shell concept. This enables the use of fully three-dimensional constitutive models for the material. The proposed phase field formulation integrates the use of the (EAS) method to alleviate locking pathologies, especially Poisson thickness and volumetric locking. This technique is further combined with the assumed natural strain method to efficiently derive a locking-free solid shell element. On the computational side, a fully coupled monolithic framework is consistently formulated. Specific details regarding the corresponding finite element formulation and the main aspects associated with its implementation in the general purpose packages FEAP and ABAQUS are addressed. Finally, the applicability of the current strategy is demonstrated through several numerical examples involving different loading conditions, and including linear and nonlinear hyperelastic constitutive models.
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.
Zuniga, Aimée; Michos, Odyssé; Spitz, François; Haramis, Anna-Pavlina G; Panman, Lia; Galli, Antonella; Vintersten, Kristina; Klasen, Christian; Mansfield, William; Kuc, Sylwia; Duboule, Denis; Dono, Rosanna; Zeller, Rolf
2004-07-01
The mouse limb deformity (ld) mutations cause limb malformations by disrupting epithelial-mesenchymal signaling between the polarizing region and the apical ectodermal ridge. Formin was proposed as the relevant gene because three of the five ld alleles disrupt its C-terminal domain. In contrast, our studies establish that the two other ld alleles directly disrupt the neighboring Gremlin gene, corroborating the requirement of this BMP antagonist for limb morphogenesis. Further doubts concerning an involvement of Formin in the ld limb phenotype are cast, as a targeted mutation removing the C-terminal Formin domain by frame shift does not affect embryogenesis. In contrast, the deletion of the corresponding genomic region reproduces the ld limb phenotype and is allelic to mutations in Gremlin. We resolve these conflicting results by identifying a cis-regulatory region within the deletion that is required for Gremlin activation in the limb bud mesenchyme. This distant cis-regulatory region within Formin is also altered by three of the ld mutations. Therefore, the ld limb bud patterning defects are not caused by disruption of Formin, but by alteration of a global control region (GCR) required for Gremlin transcription. Our studies reveal the large genomic landscape harboring this GCR, which is required for tissue-specific coexpression of two structurally and functionally unrelated genes.
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.
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
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
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.
Reaungamornrat, S; De Silva, T; Uneri, A; Wolinsky, J-P; Khanna, A J; Kleinszig, G; Vogt, S; Prince, J L; Siewerdsen, J H
2016-02-27
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. 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. 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. A modality-independent deformable registration method has been developed to estimate a viscoelastic diffeomorphic map between preoperative MR and intraoperative CT. The method yields registration
NASA Astrophysics Data System (ADS)
Kondoh, K.; Atluri, S. N.
1987-03-01
Simple and economical procedures for large-deformation elasto-plastic analysis of frames, whose members can be characterized as beams, are presented. An assumed stress approach is employed to derive the tangent stiffness of the beam, subjected in general to non-conservative type distributed loading. The beam is assumed to undergo arbitrarily large rigid rotations but small axial stretch and relative (non-rigid) point-wise rotations. It is shown that if a plastic-hinge method (with allowance being made for the formation of the hinge at an arbitrary location or locations along the beam) is employed, the tangent stiffness matrix may be derived in an explicit fashion, without numerical integration. Several examples are given to illustrate the relative economy and efficiency of the method in solving large-deformation elasto-plastic problems. The method is of considerable utility in analysing off-shore structures and large structures that are likely to be deployed in outerspace.
Valdivia, G G; Fassier, F; Hamdy, R C
1998-01-01
Distraction through the physis (chondrodiatasis) is a controversial technique with unpredictable results. However, it has been used in the past for the lengthening and correction of angular deformities of long bones. We report the case of an 11-year-old patient with spondyloepimetaphyseal dysplasia (SEMD) who presented with a severe recurvatum deformity of the left proximal tibia secondary to collapse of the tibial plateau into a large metaphyseal cystic lesion. Using the chondrodiatasis technique with a percutaneously applied Ilizarov circular frame, we were able to correct this deformity. Surprisingly, healing and ossification of the metaphyseal lesion was simultaneously observed at the end of the treatment, a finding which, to the best of our knowledge, has not been previously reported.
NASA Astrophysics Data System (ADS)
Martini, M.; Péru, S.; Hilaire, S.; Goriely, S.; Lechaftois, F.
2016-07-01
Valuable theoretical predictions of nuclear dipole excitations in the whole chart are of great interest for different nuclear applications, including in particular nuclear astrophysics. Here we present large-scale calculations of the E 1 γ -ray strength function obtained in the framework of the axially symmetric deformed quasiparticle random-phase approximation based on the finite-range Gogny force. This approach is applied to even-even nuclei, the strength function for odd nuclei being derived by interpolation. The convergence with respect to the adopted number of harmonic oscillator shells and the cutoff energy introduced in the 2-quasiparticle (2 -q p ) excitation space is analyzed. The calculations performed with two different Gogny interactions, namely D1S and D1M, are compared. A systematic energy shift of the E 1 strength is found for D1M relative to D1S, leading to a lower energy centroid and a smaller energy-weighted sum rule for D1M. When comparing with experimental photoabsorption data, the Gogny-QRPA predictions are found to overestimate the giant dipole energy by typically ˜2 MeV. Despite the microscopic nature of our self-consistent Hartree-Fock-Bogoliubov plus QRPA calculation, some phenomenological corrections need to be included to take into account the effects beyond the standard 2 -q p QRPA excitations and the coupling between the single-particle and low-lying collective phonon degrees of freedom. For this purpose, three prescriptions of folding procedure are considered and adjusted to reproduce experimental photoabsorption data at best. All of them are shown to lead to somewhat similar predictions of the E 1 strength, both at low energies and for exotic neutron-rich nuclei. Predictions of γ -ray strength functions and Maxwellian-averaged neutron capture rates for the whole Sn isotopic chain are also discussed and compared with previous theoretical calculations.
NASA Astrophysics Data System (ADS)
Tegner, C.; Storey, M.; Holm, P. M.; Thorarinsson, S. B.; Zhao, X.; Tappe, S.; Heaman, L.; Knudsen, M. F.
2013-12-01
Age, compositional and geological data show the High Arctic Large Igneous Province is unusual on two counts: first, magmatism was prolonged and include an initial tholeiitic phase (130-80 Ma) and a second alkaline phase (85-60 Ma); second, it was subsequently deformed during the Eurekan orogeny. New 40Ar-39Ar and U-Pb dating provides emplacement ages of 71-68 Ma for most of the Kap Washington alkaline volcanics of North Greenland, but with activity continuing down to 61 Ma. A thermal resetting age of 49-47 Ma is also identified in 40Ar-39Ar whole-rock data for trachyte flows. Patch perthite feldspars and coeval resetting of Rb-Sr isotopes by hydrothermal fluids provide further support for thermal overprinting, interpreted as a result of Eurekan compressional tectonism. The formation of the tholeiitic suite (130-80 Ma) appears to be associated with the opening of the Canada Basin and may have involved mantle plume action. Formation of the alkaline suite (85-60 Ma) is attributed to continental rifting in the Lincoln Sea area linked to seafloor spreading in the Labrador Sea and the Baffin Bay. The alkaline and tholeiitic suites of the High Arctic may therefore be unrelated. It is striking that High Arctic volcanism terminates at about the same time (c. 60 Ma) as magmatism in the North Atlantic Large Igneous Province begins. We suggest this is a corollary of a change from extensional to compressional tectonism in the High Arctic. In the period when Greenland moved together with Eurasia (>60 Ma), the separation from North America resulted in rift-related alkaline magmatism in the High Arctic. When Greenland subsequently moved as a separate plate (60-35 Ma), overlapping spreading on both sides pushed it northwards and volcanism in the High Arctic stopped due to compression. Evaluation of plate kinematic models shows that the relative northwards movement of Greenland culminated in the Eocene, coinciding with thermal resetting. We conclude that compression in North
Omori, T; Ishikawa, T; Barthès-Biesel, D; Salsac, A-V; Walter, J; Imai, Y; Yamaguchi, T
2011-04-01
A capsule is a liquid drop enclosed by a solid, deformable membrane. To analyze the deformation of a capsule accurately, both the fluid mechanics of the internal and external fluids and the solid mechanics of the membrane must be solved precisely. Recently, many researchers have used discrete spring network models to express the membrane mechanics of capsules and biological cells. However, it is unclear whether such modeling is sufficiently accurate to solve for capsule deformation. This study examines the correlations between the mechanical properties of the discrete spring network model and continuum constitutive laws. We first compare uniaxial and isotropic deformations of a two-dimensional (2D) sheet, both analytically and numerically. The 2D sheet is discretized with four kinds of mesh to analyze the effect of the spring network configuration. We derive the relationships between the spring constant and continuum properties, such as the Young modulus, Poisson ratio, area dilation modulus, and shear modulus. It is found that the mechanical properties of spring networks are strongly dependent on the mesh configuration. We then calculate the deformation of a capsule under inflation and in a simple shear flow in the Stokes flow regime, using various membrane models. To achieve high accuracy in the flow calculation, a boundary-element method is used. Comparing the results between the different membrane models, we find that it is hard to express the area incompressibility observed in biological membranes using a simple spring network model.
Kupka–Smale diffeomorphisms at the boundary of uniform hyperbolicity: a model
NASA Astrophysics Data System (ADS)
Leplaideur, Renaud; Lugão Rios, Isabel
2017-10-01
We construct an explicit example of a family of non-uniformly hyperbolic diffeomorphisms, at the boundary of a set of uniformly hyperbolic systems, with one orbit of cubic heteroclinic tangency. One of the leaves involved in this heteroclinic tangency is periodic, and there is a Cantor set of choices of the second one. For a non-countable subset of these choices, the second leaf is not periodic and the diffeomorphism is Kupka–Smale: every periodic point is hyperbolic and the intersections of stable and unstable leaves of periodic points are transverse. The bifurcating system is Hölder-conjugated to a subshift of finite type; thus every Hölder potential admits a unique equilibrium state associated with it.
Singh, Nikhil; Hinkle, Jacob; Joshi, Sarang; Fletcher, P Thomas
2013-04-01
This paper presents a novel approach for diffeomorphic image regression and atlas estimation that results in improved convergence and numerical stability. We use a vector momenta representation of a diffeomorphism's initial conditions instead of the standard scalar momentum that is typically used. The corresponding variational problem results in a closed-form update for template estimation in both the geodesic regression and atlas estimation problems. While we show that the theoretical optimal solution is equivalent to the scalar momenta case, the simplification of the optimization problem leads to more stable and efficient estimation in practice. We demonstrate the effectiveness of our method for atlas estimation and geodesic regression using synthetically generated shapes and 3D MRI brain scans.
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.
Registration of 4D time-series of cardiac images with multichannel Diffeomorphic Demons.
Peyrat, Jean-Marc; Delingette, Hervé; Sermesant, Maxime; Pennec, Xavier; Xu, Chenyang; Ayache, Nicholas
2008-01-01
In this paper, we propose a generic framework for intersubject non-linear registration of 4D time-series images. In this framework, spatio-temporal registration is defined by mapping trajectories of physical points as opposed to spatial registration that solely aims at mapping homologous points. First, we determine the trajectories we want to register in each sequence using a motion tracking algorithm based on the Diffeomorphic Demons algorithm. Then, we perform simultaneously pairwise registrations of corresponding time-points with the constraint to map the same physical points over time. We show this trajectory registration can be formulated as a multichannel registration of 3D images. We solve it using the Diffeomorphic Demons algorithm extended to vector-valued 3D images. This framework is applied to the inter-subject non-linear registration of 4D cardiac CT sequences.
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.
NASA Astrophysics Data System (ADS)
Chen, Di; Kamlah, Marc
2015-11-01
Digital image correlation, a noncontact and nondestructive method, was employed to monitor the deformation of lead zirconate titanate piezoelectric ceramics. This method is based on imaging a speckle pattern on the specimen surface during the test and subsequently correlating each image of the deformed pattern to that in the reference state. In our work, both longitudinal and transverse strains were calculated from imaging a bulk sample under a ±2 kV/mm electric field. Compared with linear variable displacement transducer data, the results from this correlation method were validated. At the same time, based on this optical technique, different strain-electric field butterfly loops can be drawn from correspondingly selected regions of interest. Combined with contour plots of strain on the surface of the sample, the deformation of bulk ceramic sample under uniaxial electric field loading without any mechanical constraints is proven to be highly homogenous under macro-observing scale.
Chen, Di; Kamlah, Marc
2015-11-01
Digital image correlation, a noncontact and nondestructive method, was employed to monitor the deformation of lead zirconate titanate piezoelectric ceramics. This method is based on imaging a speckle pattern on the specimen surface during the test and subsequently correlating each image of the deformed pattern to that in the reference state. In our work, both longitudinal and transverse strains were calculated from imaging a bulk sample under a ±2 kV/mm electric field. Compared with linear variable displacement transducer data, the results from this correlation method were validated. At the same time, based on this optical technique, different strain-electric field butterfly loops can be drawn from correspondingly selected regions of interest. Combined with contour plots of strain on the surface of the sample, the deformation of bulk ceramic sample under uniaxial electric field loading without any mechanical constraints is proven to be highly homogenous under macro-observing scale.
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.
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)
Scott, T.; Kohlstedt, D. L.
2003-12-01
To date, laboratory studies of partially molten mantle rocks have reached melt fractions φ ˜ 0.15, a value much smaller than thought to be appropriate for the asthenosphere of Io where the degree of partial melting may be 40% or higher. Therefore, we have performed a series of high temperature, triaxial compressive creep experiments on dry synthetic peridotites in a gas medium apparatus at a confining pressure of 300 MPa and temperatures from 1450 to 1523 K in order to understand the influence of large amounts of melt (0.15 < φ < 0.40) on the rheological behavior of partially molten rocks. Mechanical mixtures of crushed and dried San Carlos olivine (1-10 μ m) plus MORB ( ˜8 μ m) were isostatically hot pressed at 1450 K and 300 MPa for 4 h. Microstructural analysis indicates that after hot pressing the melt is homogeneously distributed between grain-size melt pockets at triple junctions and smaller pockets at two, three and four grain junctions. Analysis of stress vs. strain rate data from a sample containing φ = 0.23 +/- 0.04 MORB with a grain size {d} = 9.3 +/- 2.3 μ m deformed at 1450 K and differential stresses of 10 to 75 MPa in the diffusional creep regime (stress exponent {n} = 1) demonstrates that the viscosity may be as much as three orders of magnitude higher than that predicted by a flow law reported for peridotites, where viscosity η ~ exp(-25 φ ). For example, diffusional creep data from the sample with φ = 0.23 scaled to a grain size of 1 mm and extrapolated to a temperature of 1900 K (a possible value in Io's interior) yields a viscosity of 3x1018 Pa s, compared to a viscosity of 2x1015 Pa s calculated from the flow law and published results from numerical models with viscosity values of 1017 Pa s for a homogeneous convecting mantle and 108 to 1012 Pa s for a thin convecting asthenosphere. Therefore, additional experiments on partially molten mantle rocks with relatively high φ are required to constrain the dynamic properties of Io
NASA Astrophysics Data System (ADS)
Klein, E.; Fleitout, L.; Vigny, C.; Garaud, J. D.
2016-06-01
Megathrust earthquakes of magnitude close to 9 are followed by large-scale (thousands of km) and long-lasting (decades), significant crustal and mantle deformation. This deformation can be observed at the surface and quantified with GPS measurements. Here we report on deformation observed during the 5 yr time span after the 2010 Mw 8.8 Maule Megathrust Earthquake (2010 February 27) over the whole South American continent. With the first 2 yr of those data, we use finite element modelling (FEM) to relate this deformation to slip on the plate interface and relaxation in the mantle, using a realistic layered Earth model and Burgers rheologies. Slip alone on the interface, even up to large depths, is unable to provide a satisfactory fit simultaneously to horizontal and vertical displacements. The horizontal deformation pattern requires relaxation both in the asthenosphere and in a low-viscosity channel along the deepest part of the plate interface and no additional low-viscosity wedge is required by the data. The vertical velocity pattern (intense and quick uplift over the Cordillera) is well fitted only when the channel extends deeper than 100 km. Additionally, viscoelastic relaxation alone cannot explain the characteristics and amplitude of displacements over the first 200 km from the trench and aseismic slip on the fault plane is needed. This aseismic slip on the interface generates stresses, which induce additional relaxation in the mantle. In the final model, all three components (relaxation due to the coseismic slip, aseismic slip on the fault plane and relaxation due to aseismic slip) are taken into account. Our best-fit model uses slip at shallow depths on the subduction interface decreasing as function of time and includes (i) an asthenosphere extending down to 200 km, with a steady-state Maxwell viscosity of 4.75 × 1018 Pa s; and (ii) a low-viscosity channel along the plate interface extending from depths of 55-135 km with viscosities below 1018 Pa s.
NASA Technical Reports Server (NTRS)
Reed, Kenneth W.
1992-01-01
A new hybrid stress finite element algorithm suitable for analyses of large quasistatic deformation of inelastic solids is presented. Principal variables in the formulation are the nominal stress rate and spin. The finite element equations which result are discrete versions of the equations of compatibility and angular momentum balance. Consistent reformulation of the constitutive equation and accurate and stable time integration of the stress are discussed at length. Examples which bring out the feasibility and performance of the algorithm conclude the work.
NASA Astrophysics Data System (ADS)
Brendan, Simon; François, Guillocheau; Cécile, Robin; Jean, Braun; Olivier, Dauteuil; Massimo, Dall'Asta
2016-04-01
African relief is characterized by planation surfaces, some of them of continental scale. These surfaces are slightly deformed according to different wavelengths (x10 km; x100 km, x1000 km) which record both mantle dynamics (very long wavelength, x 1000 km) and lithosphere deformation (long wavelength deformation, x 100 km). Different types of these planation surfaces are recognized: - Etchplains capped by iron-duricrust which correspond to erosional nearly flat weathered surfaces resulting from the growth of laterites under warm and humid conditions. - Pediments which define mechanical erosional surfaces with concave or rectilinear profiles delimited by upslope scarps connected upstream with the upper landforms. We here focused on the Lake Albert Rift at the northern termination of the western branch of the East African Rift System of which the two branches are surimposed on the East-African Dome. Different wavelengths of deformation were characterized based on the 3D mapping of stepped planation surfaces: (1) very long wavelength deformations resulting from the uplift of the East African Dome; (2) long wavelength deformations resulting from the opening of the eastern branch and (3) medium wavelength deformations represented by the uplift of rift shoulders like the Rwenzori Mountains. The paleo-landscape reconstruction of Uganda shows the existence of four generations of landforms dated according to their geometrical relationships with volcanic rocks. A four stepped evolution of the Ugandan landforms is proposed: • 70 - 22 Ma: generation of two weathered planation surfaces (etchplain Uw and Iw). The upper one (Uw) records a very humid period culminating at time of the Early Eocene Climatic Optimum (70-45 Ma). It corresponds to the African Surface. A first uplift of the East African Dome generates a second lower planation surface (Iw) connected to the Atlantic Ocean base level; • 17-2.7 Ma: planation of large pediplains connected to the local base level induced
NASA Technical Reports Server (NTRS)
Ambur, Damodar R.; Starnes, James H., Jr.; Prasad, Chunchu B.
1993-01-01
An analytical procedure is presented for determining the transient response of simply supported, rectangular laminated composite plates subjected to impact loads from airgun-propelled or dropped-weight impactors. A first-order shear-deformation theory is included in the analysis to represent properly any local short-wave-length transient bending response. The impact force is modeled as a locally distributed load with a cosine-cosine distribution. A double Fourier series expansion and the Timoshenko small-increment method are used to determine the contact force, out-of-plane deflections, and in-plane strains and stresses at any plate location due to an impact force at any plate location. The results of experimental and analytical studies are compared for quasi-isotropic laminates. The results indicate that using the appropriate local force distribution for the locally loaded area and including transverse-shear-deformation effects in the laminated plate response analysis are important. The applicability of the present analytical procedure based on small deformation theory is investigated by comparing analytical and experimental results for combinations of quasi-isotropic laminate thicknesses and impact energy levels. The results of this study indicate that large-deformation effects influence the response of both 24- and 32-ply laminated plates, and that a geometrically nonlinear analysis is required for predicting the response accurately.
2014-11-01
Stabilized Finite Element Implementation The nonlinear finite element formulation and implementation (Newton-Raphson nonlinear solution, Newmark time...media at finite strain. Comp. Meth. App. Mech. Engr., vol. 193, no. 36-38, pp. 3837 – 70. Ogden, R. W. (1984): Nonlinear Elastic Deformations. Chicheste...theories. Handbuch der Physik, Springer, Berlin. Truty, A.; Zimmermann, T. (2006): Stabilized mixed finite element formulations for materially nonlinear
Exactly marginal deformations from exceptional generalised geometry
NASA Astrophysics Data System (ADS)
Ashmore, Anthony; Gabella, Maxime; Graña, Mariana; Petrini, Michela; Waldram, Daniel
2017-01-01
We apply exceptional generalised geometry to the study of exactly marginal deformations of N = 1 SCFTs that are dual to generic AdS5 flux backgrounds in type IIB or eleven-dimensional supergravity. In the gauge theory, marginal deformations are parametrised by the space of chiral primary operators of conformal dimension three, while exactly marginal deformations correspond to quotienting this space by the complexified global symmetry group. We show how the supergravity analysis gives a geometric interpretation of the gauge theory results. The marginal deformations arise from deformations of generalised structures that solve moment maps for the generalised diffeomorphism group and have the correct charge under the generalised Reeb vector, generating the R-symmetry. If this is the only symmetry of the background, all marginal deformations are exactly marginal. If the background possesses extra isometries, there are obstructions that come from fixed points of the moment maps. The exactly marginal deformations are then given by a further quotient by these extra isometries.
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)
Bekaert, D. P.; Hooper, A. J.; Wright, T. J.; Walters, R. J.
2013-12-01
For Interferometric Synthetic Aperture Radar (InSAR) the atmosphere forms one of the biggest challenges when it comes to the extraction of small-magnitude long-wavelength tectonics signals. Spatio-temporal variation of water vapour, pressure and temperature in the lower 15 km of the troposphere is the main cause of these signals, introducing apparent differential path delays in interferograms of up to 15 cm. Several correction techniques have been applied in the past that rely on external data from weather models, GPS or spectrometer data, but these are typically limited by the lower spatial resolution of the auxiliary data. Alternatively, time-series InSAR techniques and filtering of the interferometric phase in space and time can be applied, but separating atmospheric delays from non-linear deformation is challenging. Another method, which can be applied to individual interferograms, is to estimate the correlation between interferometric phase and topography, either in a non-deforming area or using a frequency band insensitive to deformation. While this method can be successful for small areas, it does not account for spatial variation of atmospheric properties, which can be significant across regions larger than 100 km. While the slope relating phase and topography can be reliably estimated for subregions, the intercept cannot, as it is biased by the presence of unrelated signals. The intercept cannot however be neglected, as the mean height of each subregion typically varies, leading to a different intercept for each window. Here we present a new power law representation of the topographically-correlated phase delay that can be applied locally and which is able to account for these spatial variations in atmospheric properties. We estimate the power law from sounding data to fit altitudes of up to 4 km, as this includes most of the topography range in our/most regions of interest. We also constrain the power law by specifying the height above which the relative
NASA Astrophysics Data System (ADS)
Bekaert, David; Walters, Richard; Hooper, Andrew; Wright, Tim; Parker, Doug
2014-05-01
For Interferometric Synthetic Aperture Radar (InSAR) the atmosphere forms one of the biggest challenges when it comes to the extraction of small-magnitude long-wavelength tectonic signals. Spatio-temporal variation of water vapour, pressure and temperature in the troposphere is the main cause of these signals, introducing apparent differential path delays in interferograms of up to 15 cm. Several correction techniques have been applied in the past that rely on external data from weather models, GPS or spectrometer data, but these are typically limited by the lower spatial resolution of the auxiliary data. Alternatively, time-series InSAR techniques and filtering of the interferometric phase in space and time can be applied, but separating atmospheric delays from non-linear deformation is challenging. Another method, which can be applied to individual interferograms, is to estimate the correlation between interferometric phase and topography, either in a non-deforming area or using a frequency band insensitive to deformation. While this method can be successful for small areas, it does not account for spatial variation of atmospheric properties, which can be significant across regions larger than 100 km. While the slope relating phase and topography can be reliably estimated for subregions, the intercept cannot, as it is biased by the presence of unrelated signals. The intercept cannot however be neglected, as the mean height of each subregion typically varies, leading to a different intercept for each window. Here we present a new power-law representation of the topographically-correlated phase delay that can be applied locally and which is able to account for these spatial variations in atmospheric properties. We estimate the power-law from sounding data to fit altitudes of up to 4 km, as this includes the topography range in most regions of interest. We also constrain the power-law by specifying the height above which the relative tropospheric delays are
Xiong, Ding-Bang; Cao, Mu; Guo, Qiang; Tan, Zhanqiu; Fan, Genlian; Li, Zhiqiang; Zhang, Di
2016-01-01
By using CuO/graphene-oxide/CuO sandwich-like nanosheets as the building blocks, bulk nacre-inspired copper matrix nano-laminated composite reinforced by molecular-level dispersed and ordered reduced graphene oxide (rGO) with content as high as ∼45 vol% was fabricated via a combined process of assembly, reduction and consolidation. Thanks to nanoconfinement effect, reinforcing effect, as well as architecture effect, the nanocomposite shows increased specific strength and at least one order of magnitude greater recoverable deformation ability as compared with monolithic Cu matrix. PMID:27647264
NASA Astrophysics Data System (ADS)
Xiong, Ding-Bang; Cao, Mu; Guo, Qiang; Tan, Zhanqiu; Fan, Genlian; Li, Zhiqiang; Zhang, Di
2016-09-01
By using CuO/graphene-oxide/CuO sandwich-like nanosheets as the building blocks, bulk nacre-inspired copper matrix nano-laminated composite reinforced by molecular-level dispersed and ordered reduced graphene oxide (rGO) with content as high as ∼45 vol% was fabricated via a combined process of assembly, reduction and consolidation. Thanks to nanoconfinement effect, reinforcing effect, as well as architecture effect, the nanocomposite shows increased specific strength and at least one order of magnitude greater recoverable deformation ability as compared with monolithic Cu matrix.
NASA Astrophysics Data System (ADS)
Agosta, Fabrizio
2006-04-01
A challenging theme of research in structural geology is the process of faulting in carbonate rocks: how do the resulting internal architecture and petrophysical properties of faults affect subsurface fluid flow. A better understanding of this process is important to evaluate the potential oil and gas recovery from carbonate reservoirs, and to plan CO 2 containment in the depleted reservoirs. Carbonate rocks may deform with different mechanisms depending primarily on their original sedimentary fabric, diagenetic history, fluid content, and tectonic environment. In this dissertation I investigate the deformation mechanisms, petrophysics, and internal fluid composition of large, seismic, basin-bounding normal faults in low porosity platform carbonates. Based on the nature, orientation, and abutting relationships of the structural elements preserved within the faults and in the surrounding carbonate host rocks, I was able to characterize the mechanisms of fault growth and the fault architecture. Incipient faulting occurred at shallow depths by sequential formation and shearing of pressure solution seams and joints/veins; with ongoing deformation and exhumation, the joint-based mechanism became predominant. The end result is a mature normal fault that juxtaposes basin sedimentary rocks of the hanging wall against deformed carbonates of the footwall. The deformed carbonates of the fault footwalls are composed of rocks with low porosity and permeability and major slip surfaces in the fault core, and fragmented carbonate matrices with high porosity and permeability, and small faults in the damage zone. The degree of fragmentation in the damage zone generally increases towards the fault hanging wall, forming structural domains characterized by different deformation intensity. The rocks of the fault core have sub-spherical pores, those of the damage zone have elongated, crack-like, pores. The permeability structure of the normal fault zones is therefore made up of a fault
NASA Astrophysics Data System (ADS)
Akilan, A.; Abdul Azeez, K. K.; Schuh, H.; Yuvraaj, N.
2015-10-01
The dynamics of the planet Earth are manifestations of diverse plate tectonic processes which have been occurring since the Archean period of the Earth's evolution and continue to deform the plate boundaries. Very long baseline interferometry (VLBI) is an efficient space geodetic method that enables precise measurement of plate motion and associated deformations. We analyze here VLBI measurements made during a period of approximately three decades at five locations on the Eastern hemisphere of the globe, which are geographically distributed over five continents (plates) around the Indian Ocean. Computed rate of change of baseline length show the deformation pattern and its rate at the boundaries between the major tectonic plates constituting the Eastern hemisphere of the Earth. The African (Nubian) and Antarctic plates are moving apart at 13.5 mm/year, which is mostly attributed to spreading of the South West Indian Ridge. Similarly, spreading of 59.0 mm/year is observed for the South East Indian Ridge that separates the Antarctic and Australian plates. Shortening at the rate of 3.9 mm/year is estimated across the subduction boundary between Africa (Nubia) and Eurasia. Similar convergence is evident between the Australian and Sunda blocks (of the Eurasian plate). The associated deformation of -54.8 mm/year seems to be chiefly accommodated along the Banda arc system, where the Australian plate is subducting under the Sunda block. VLBI sites within the Eurasian plate, Wettzell in Germany, and Seshan on the South China block, are moving apart at 3.6 mm/year. This relative motion between locations on the same plate is interpreted as a result of the deformation process along a large strike-slip fault, which is identified as the Western boundary of the South China block. Expansion of the Indian Ocean, at +91.5 m2/year, is also estimated from the rate of deformation estimated within the five baselines studied here. From the Hurst exponent values, which are indicators of
NASA Astrophysics Data System (ADS)
Kiani, Keivan
2017-09-01
Large deformation regime of micro-scale slender beam-like structures subjected to axially pointed loads is of high interest to nanotechnologists and applied mechanics community. Herein, size-dependent nonlinear governing equations are derived by employing modified couple stress theory. Under various boundary conditions, analytical relations between axially applied loads and deformations are presented. Additionally, a novel Galerkin-based assumed mode method (AMM) is established to solve the highly nonlinear equations. In some particular cases, the predicted results by the analytical approach are also checked with those of AMM and a reasonably good agreement is reported. Subsequently, the key role of the material length scale on the load-deformation of microbeams is discussed and the deficiencies of the classical elasticity theory in predicting such a crucial mechanical behavior are explained in some detail. The influences of slenderness ratio and thickness of the microbeam on the obtained results are also examined. The present work could be considered as a pivotal step in better realizing the postbuckling behavior of nano-/micro- electro-mechanical systems consist of microbeams.
On the question of symmetries in nonrelativistic diffeomorphism-invariant theories
NASA Astrophysics Data System (ADS)
Banerjee, Rabin; Gangopadhyay, Sunandan; Mukherjee, Pradip
2017-07-01
A novel algorithm is provided to couple a Galilean-invariant model with curved spatial background by taking nonrelativistic limit of a unique minimally coupled relativistic theory, which ensures Galilean symmetry in the flat limit and canonical transformation of the original fields. That the twin requirements are fulfilled is ensured by a new field, the existence of which was demonstrated recently from Galilean gauge theory. The ambiguities and anomalies concerning the recovery of Galilean symmetry in the flat limit of spatial nonrelativistic diffeomorphic theories, reported in the literature, are focused and resolved from a new angle.
NASA Astrophysics Data System (ADS)
Schmidt-Richberg, Alexander; Ehrhardt, Jan; Werner, René; Handels, Heinz
Verfahren zur integrierten Segmentierung und Registrierung von 4D-Bilddaten ermöglichen die Berücksichtigung der gegenseitigen Abhängigkeiten beider Komponenten. Bestehende Ansätze konzentrieren sich dabei meist auf die Betrachtung zweier 3D-Bilder und lassen sich nicht direkt auf vollständige Bildfolgen übertragen. In dieser Arbeit wird ein Verfahren vorgestellt, in dem ein diffeomorpher Registrierungsansatz verwendet wird, um eine integrierte Berechnung von Segmentierungen und 3D-Voxeltrajektorien in 4D-Daten zu ermöglichen.
Graef, L.L.; Brandenberger, R. E-mail: rhb@physics.mcgill.ca
2015-10-01
Standard inflationary models yield a characteristic signature of a primordial power spectrum with a red tensor and scalar tilt. Nevertheless, Cannone et al. [1] recently suggested that, by breaking the assumption of spatial diffeomorphism invariance in the context of the effective field theory of inflation, a blue tensor spectrum can be achieved without violating the Null Energy Condition. In this context, we explore in which cases the inflationary model of [2] can yield a blue tilt of the tensor modes along with a red tilt in the scalar spectrum. Ultimately, we analyze under which conditions the model of [3] can reproduce the specific consistency relation of String Gas Cosmology.
Evaluation of GMI and PMI diffeomorphic-based demons algorithms for aligning PET and CT Images.
Yang, Juan; Wang, Hongjun; Zhang, You; Yin, Yong
2015-07-08
Fusion of anatomic information in computed tomography (CT) and functional information in 18F-FDG positron emission tomography (PET) is crucial for accurate differentiation of tumor from benign masses, designing radiotherapy treatment plan and staging of cancer. Although current PET and CT images can be acquired from combined 18F-FDG PET/CT scanner, the two acquisitions are scanned separately and take a long time, which may induce potential positional errors in global and local caused by respiratory motion or organ peristalsis. So registration (alignment) of whole-body PET and CT images is a prerequisite for their meaningful fusion. The purpose of this study was to assess the performance of two multimodal registration algorithms for aligning PET and CT images. The proposed gradient of mutual information (GMI)-based demons algorithm, which incorporated the GMI between two images as an external force to facilitate the alignment, was compared with the point-wise mutual information (PMI) diffeomorphic-based demons algorithm whose external force was modified by replacing the image intensity difference in diffeomorphic demons algorithm with the PMI to make it appropriate for multimodal image registration. Eight patients with esophageal cancer(s) were enrolled in this IRB-approved study. Whole-body PET and CT images were acquired from a combined 18F-FDG PET/CT scanner for each patient. The modified Hausdorff distance (d(MH)) was used to evaluate the registration accuracy of the two algorithms. Of all patients, the mean values and standard deviations (SDs) of d(MH) were 6.65 (± 1.90) voxels and 6.01 (± 1.90) after the GMI-based demons and the PMI diffeomorphic-based demons registration algorithms respectively. Preliminary results on oncological patients showed that the respiratory motion and organ peristalsis in PET/CT esophageal images could not be neglected, although a combined 18F-FDG PET/CT scanner was used for image acquisition. The PMI diffeomorphic-based demons
NASA Astrophysics Data System (ADS)
Vigny, C.; Klein, E.; Fleitout, L.; Garaud, J. D.
2015-12-01
Postseismic deformation following the large subduction earthquake of Maule (Chile, Mw8.8, February 27th 2010) have been closely monitored with GPS from 70 km up to 2000 km away from the trench. They exhibit a behavior generally similar to that already observed after the Aceh and Tohoku-Oki earthquakes. Vertical uplift is observed on the volcanic arc and a moderate large scale subsidence is associated with sizeable horizontal deformation in the far-field (500-2000km from the trench). In addition, near-field data (70-200km from the trench) feature a rather complex deformation pattern. A 3D FE code (Zebulon Zset) is used to relate these deformation to slip on the plate interface and relaxation in the mantle. The mesh features a spherical shell-portion from the core-mantle boundary to the Earth's surface, extending over more than 60 degrees in latitude and longitude. The overridding and subducting plates are elastic, and the asthenosphere is viscoelastic. A viscoelastic Low Viscosity Channel (LVC) is also introduced along the plate interface. Both the asthenosphere and the channel feature Burger's rheologies and we invert for their mechanical properties and geometrical characteristics simultaneously with the afterslip distribution. The horizontal deformation pattern requires relaxation both in i) the asthenosphere extending down to 270km, with a 'long-term' viscosity of the order of 4.8.1018 Pa.s and ii) in the channel, that has to extend from depth of 50 to 150 km with viscosities slightly below 1018 Pa.s, to fit well the vertical velocity pattern (intense and quick uplift over the Cordillera). Aseismic slip on the plate interface, at shallow depth, is necessary to explain all the characteristics of the near-field displacements. We then detect two main patches of high slip, one updip of the coseismic slip distribution in the northernmost part of the rupture zone, and the other one downdip, at the latitude of Constitucion (35°S). We finally study the temporel
NASA Astrophysics Data System (ADS)
Yin, Youbing; Hoffman, Eric A.; Ding, Kai; Reinhardt, Joseph M.; Lin, Ching-Long
2011-01-01
The goal of this study is to develop a matching algorithm that can handle large geometric changes in x-ray computed tomography (CT)-derived lung geometry occurring during deep breath maneuvers. These geometric relationships are further utilized to build a dynamic lung airway model for computational fluid dynamics (CFD) studies of pulmonary air flow. The proposed algorithm is based on a cubic B-spline-based hybrid registration framework that incorporates anatomic landmark information with intensity patterns. A sequence of invertible B-splines is composed in a multiresolution framework to ensure local invertibility of the large deformation transformation and a physiologically meaningful similarity measure is adopted to compensate for changes in voxel intensity due to inflation. Registrations are performed using the proposed approach to match six pairs of 3D CT human lung datasets. Results show that the proposed approach has the ability to match the intensity pattern and the anatomical landmarks, and ensure local invertibility for large deformation transformations. Statistical results also show that the proposed hybrid approach yields significantly improved results as compared with approaches using either landmarks or intensity alone.
Yin, Youbing; Hoffman, Eric A; Ding, Kai; Reinhardt, Joseph M; Lin, Ching-Long
2011-01-01
The goal of this study is to develop a matching algorithm that can handle large geometric changes in x-ray computed tomography (CT)-derived lung geometry occurring during deep breath maneuvers. These geometric relationships are further utilized to build a dynamic lung airway model for computational fluid dynamics (CFD) studies of pulmonary air flow. The proposed algorithm is based on a cubic B-spline-based hybrid registration framework that incorporates anatomic landmark information with intensity patterns. A sequence of invertible B-splines is composed in a multiresolution framework to ensure local invertibility of the large deformation transformation and a physiologically meaningful similarity measure is adopted to compensate for changes in voxel intensity due to inflation. Registrations are performed using the proposed approach to match six pairs of 3D CT human lung datasets. Results show that the proposed approach has the ability to match the intensity pattern and the anatomical landmarks, and ensure local invertibility for large deformation transformations. Statistical results also show that the proposed hybrid approach yields significantly improved results as compared with approaches using either landmarks or intensity alone. PMID:21149947
Yin, Youbing; Hoffman, Eric A; Ding, Kai; Reinhardt, Joseph M; Lin, Ching-Long
2011-01-07
The goal of this study is to develop a matching algorithm that can handle large geometric changes in x-ray computed tomography (CT)-derived lung geometry occurring during deep breath maneuvers. These geometric relationships are further utilized to build a dynamic lung airway model for computational fluid dynamics (CFD) studies of pulmonary air flow. The proposed algorithm is based on a cubic B-spline-based hybrid registration framework that incorporates anatomic landmark information with intensity patterns. A sequence of invertible B-splines is composed in a multiresolution framework to ensure local invertibility of the large deformation transformation and a physiologically meaningful similarity measure is adopted to compensate for changes in voxel intensity due to inflation. Registrations are performed using the proposed approach to match six pairs of 3D CT human lung datasets. Results show that the proposed approach has the ability to match the intensity pattern and the anatomical landmarks, and ensure local invertibility for large deformation transformations. Statistical results also show that the proposed hybrid approach yields significantly improved results as compared with approaches using either landmarks or intensity alone.
Hutula, D.N.; Wiancko, B.E.
1980-03-01
ACCEPT is a three-dimensional finite element computer program for analysis of large-deformation elastic-plastic-creep response of Zircaloy tubes subjected to temperature, surface pressures, and axial force. A twenty-mode, tri-quadratic, isoparametric element is used along with a Zircaloy materials model. A linear time-incremental procedure with residual force correction is used to solve for the time-dependent response. The program features an algorithm which automatically chooses the time step sizes to control the accuracy and numerical stability of the solution. A contact-separation capability allows modeling of interaction of reactor fuel rod cladding with fuel pellets or external supports.
1992-03-01
From Eigenvalue Testing B. L. Croft rNp) TTISjCA, A c sio nl F orc DTiC TA3 [ By..... Dist NAVAL COMMAND, CONTROL AND OCEAN SURVEILLANCE CENTERRDT& E ...angle 3 for a plane stress element ... ........... .113 4.31 Derivative of strain energy density ratio with e respect to skew angle versus skew angle for...element solutions which utilize Lagrangian meshes for large 12 I deformation problems, the solution process tends to loose accuracy as the e ±ements become
Yang, J
2008-05-01
A set of nonlinear two-dimensional equations for thin electroelastic shells in vibrations with moderately large shear deformation in the tangent plane are obtained from the three-dimensional equations of nonlinear electroelasticity. As an example for application, the equations are used to study nonlinear torsional vibration of a circular cylindrical piezoelectric shell. It is shown that torsion is nonlinearly coupled to axial extension and circumferential extension. The results of this paper emphasize the need for further study of mode coupling induced by nonlinearity.
NASA Technical Reports Server (NTRS)
Wu, R. W.; Witmer, E. A.
1972-01-01
A user-oriented FORTRAN 4 computer program, called JET 3, is presented. The JET 3 program, which employs the spatial finite-element and timewise finite-difference method, can be used to predict the large two-dimensional elastic-plastic transient Kirchhoff-type deformations of a complete or partial structural ring, with various support conditions and restraints, subjected to a variety of initial velocity distributions and externally-applied transient forcing functions. The geometric shapes of the structural ring can be circular or arbitrarily curved and with variable thickness. Strain-hardening and strain-rate effects of the material are taken into account.
Sedaghatizadeh, N; Atefi, G; Fardad, A A; Barari, A; Soleimani, Soheil; Khani, S
2011-10-01
In this investigation, semiempirical and numerical studies of blood flow in a viscoelastic artery were performed using the Cosserat continuum model. The large-amplitude oscillatory shear deformation model was used to quantify the nonlinear viscoelastic response of blood flow. The finite difference method was used to solve the governing equations, and the particle swarm optimization algorithm was utilized to identify the non-Newtonian coefficients (k(υ) and γ(υ)). The numerical results agreed well with previous experimental results. Copyright © 2011 Elsevier Ltd. All rights reserved.
A new cohomological formula for helicity in R2 reveals the effect of a diffeomorphism on helicity
NASA Astrophysics Data System (ADS)
Cantarella, Jason; Parsley, Jason
2010-09-01
The helicity of a vector field is a measure of the average linking of pairs of integral curves of the field. Computed by a six-dimensional integral, it is widely useful in the physics of fluids. For a divergence-free field tangent to the boundary of a domain in 3-space, helicity is known to be invariant under volume-preserving diffeomorphisms of the domain that are homotopic to the identity. We give a new construction of helicity for closed (k+1)-forms on a domain in (2k+1)-space that vanish when pulled back to the boundary of the domain. Our construction expresses helicity in terms of a cohomology class represented by the form when pulled back to the compactified configuration space of pairs of points in the domain. We show that our definition is equivalent to the standard one. We use our construction to give a new formula for computing helicity by a four-dimensional integral. We provide a Biot-Savart operator that computes a primitive for such forms; utilizing it, we obtain another formula for helicity. As a main result, we find a general formula for how much the value of helicity changes when the form is pushed forward by a diffeomorphism of the domain; it relies upon understanding the effect of the diffeomorphism on the homology of the domain and the de Rham cohomology class represented by the form. Our formula allows us to classify the helicity-preserving diffeomorphisms on a given domain, finding new helicity-preserving diffeomorphisms on the two-holed solid torus and proving that there are no new helicity-preserving diffeomorphisms on the standard solid torus. We conclude by defining helicities for forms on submanifolds of Euclidean space. In addition, we provide a detailed exposition of some standard 'folk' theorems about the cohomology of the boundary of domains in R.
Robust Automated Amygdala Segmentation via Multi-Atlas Diffeomorphic Registration
Hanson, Jamie L.; Suh, Jung W.; Nacewicz, Brendon M.; Sutterer, Matthew J.; Cayo, Amelia A.; Stodola, Diane E.; Burghy, Cory A.; Wang, Hongzhi; Avants, Brian B.; Yushkevich, Paul A.; Essex, Marilyn J.; Pollak, Seth D.; Davidson, Richard J.
2012-01-01
Here, we describe a novel method for volumetric segmentation of the amygdala from MRI images collected from 35 human subjects. This approach is adapted from open-source techniques employed previously with the hippocampus (Suh et al., 2011; Wang et al., 2011a,b). Using multi-atlas segmentation and machine learning-based correction, we were able to produce automated amygdala segments with high Dice (Mean = 0.918 for the left amygdala; 0.916 for the right amygdala) and Jaccard coefficients (Mean = 0.850 for the left; 0.846 for the right) compared to rigorously hand-traced volumes. This automated routine also produced amygdala segments with high intra-class correlations (consistency = 0.830, absolute agreement = 0.819 for the left; consistency = 0.786, absolute agreement = 0.783 for the right) and bivariate (r = 0.831 for the left; r = 0.797 for the right) compared to hand-drawn amygdala. Our results are discussed in relation to other cutting-edge segmentation techniques, as well as commonly available approaches to amygdala segmentation (e.g., Freesurfer). We believe this new technique has broad application to research with large sample sizes for which amygdala quantification might be needed. PMID:23226114
Robust Automated Amygdala Segmentation via Multi-Atlas Diffeomorphic Registration.
Hanson, Jamie L; Suh, Jung W; Nacewicz, Brendon M; Sutterer, Matthew J; Cayo, Amelia A; Stodola, Diane E; Burghy, Cory A; Wang, Hongzhi; Avants, Brian B; Yushkevich, Paul A; Essex, Marilyn J; Pollak, Seth D; Davidson, Richard J
2012-01-01
Here, we describe a novel method for volumetric segmentation of the amygdala from MRI images collected from 35 human subjects. This approach is adapted from open-source techniques employed previously with the hippocampus (Suh et al., 2011; Wang et al., 2011a,b). Using multi-atlas segmentation and machine learning-based correction, we were able to produce automated amygdala segments with high Dice (Mean = 0.918 for the left amygdala; 0.916 for the right amygdala) and Jaccard coefficients (Mean = 0.850 for the left; 0.846 for the right) compared to rigorously hand-traced volumes. This automated routine also produced amygdala segments with high intra-class correlations (consistency = 0.830, absolute agreement = 0.819 for the left; consistency = 0.786, absolute agreement = 0.783 for the right) and bivariate (r = 0.831 for the left; r = 0.797 for the right) compared to hand-drawn amygdala. Our results are discussed in relation to other cutting-edge segmentation techniques, as well as commonly available approaches to amygdala segmentation (e.g., Freesurfer). We believe this new technique has broad application to research with large sample sizes for which amygdala quantification might be needed.
NASA Astrophysics Data System (ADS)
Cheng, Sheng-Lin; Tsai, Tsung-Heng; Lee, Carina Jean-Tien; Hsu, Yu-Hsiang; Lee, Chih-Kung
2016-03-01
A pressure ulcer is one of the most important concerns for wheelchair bound patients with spinal cord injuries. A pressure ulcer is a localized injury near the buttocks that bear ischial tuberosity oppression over a long period of time. Due to elevated compression to blood vessels, the surrounding tissues suffer from a lack of oxygen and nutrition. The ulcers eventually lead to skin damage followed by tissue necrosis. The current medical strategy is to minimize the occurrence of pressure ulcers by regularly helping patients change their posture. However, these methods do not always work effectively or well. As a solution to fundamentally prevent pressure ulcers, a smart air cushion system was developed to detect and control pressure actively. The air cushion works by automatically adjusting a patient's sitting posture to effectively relieve the buttock pressure. To analyze the correlation between the dynamic pressure profiles of an air cell with a patient's weight, a projection Moiré system was adopted to measure the deformation of an air cell and its associated stress distribution. Combining a full-field deformation imaging with air pressure measured within an air cell, the patient's weight and the stress distribution can be simultaneously obtained. By integrating a full-field optical metrology with a time varying pressure sensor output coupled with different active air control algorithms for various designs, we can tailor the ratio of the air cells. Our preliminary data suggests that this newly developed smart air cushion has the potential to selectively reduce localized compression on the tissues at the buttocks. Furthermore, it can take a patient's weight which is an additional benefit so that medical personnel can reference it to prescribe the correct drug dosages.
NASA Astrophysics Data System (ADS)
Katagi, Takeshi; Yoshioka, Shoichi; Hashimoto, Manabu
2008-06-01
over Shikoku. The postseismic horizontal principal strain field for MODEL P2 is characterized by contractions in the N-S to NW-SE directions at amounts smaller than those for MODELs L1 and P1. Postseismic surface deformations for MODEL P3 are almost the same as those for MODEL P2. The observed postseismic vertical displacement and horizontal principal strain fields could not be explained by the viscoelastic response for the realistic viscoelastic structure models P2 and P3. This indicates that the effects of elastic and viscoelastic responses due to interplate coupling on the plate interface, after-slip at the extension of the coseismic slipped region, and poroelasticity should be taken into account to precisely estimate postseismic surface deformation. This also suggests that, in order to evaluate postseismic crustal deformations derived from a large interplate subduction zone earthquake, it is essential to use realistic temperature- and depth-dependent viscoelastic structure models.
Fu, Zhenrong; Lin, Lan; Tian, Miao; Wang, Jingxuan; Zhang, Baiwen; Chu, Pingping; Li, Shaowu; Pathan, Muhammad Mohsin; Deng, Yulin; Wu, Shuicai
2017-06-14
The development of genetically engineered mouse models for neuronal diseases and behavioural disorders have generated a growing need for small animal imaging. High-resolution magnetic resonance microscopy (MRM) provides powerful capabilities for noninvasive studies of mouse brains, while avoiding some limits associated with the histological procedures. Quantitative comparison of structural images is a critical step in brain imaging analysis, which highly relies on the performance of image registration techniques. Nowadays, there is a mushrooming growth of human brain registration algorithms, while fine-tuning of those algorithms for mouse brain MRMs is rarely addressed. Because of their topology preservation property and outstanding performance in human studies, diffeomorphic transformations have become popular in computational anatomy. In this study, we specially tuned five diffeomorphic image registration algorithms [DARTEL, geodesic shooting, diffeo-demons, SyN (Greedy-SyN and geodesic-SyN)] for mouse brain MRMs and evaluated their performance using three measures [volume overlap percentage (VOP), residual intensity error (RIE) and surface concordance ratio (SCR)]. Geodesic-SyN performed significantly better than the other methods according to all three different measures. These findings are important for the studies on structural brain changes that may occur in wild-type and transgenic mouse brains. © 2017 The Authors Journal of Microscopy © 2017 Royal Microscopical Society.
Video texture synthesis with multi-frame LBP-TOP and diffeomorphic growth model.
Guo, Yimo; Zhao, Guoying; Zhou, Ziheng; Pietikainen, Matti
2013-10-01
Video texture synthesis is the process of providing a continuous and infinitely varying stream of frames, which plays an important role in computer vision and graphics. However, it still remains a challenging problem to generate high-quality synthesis results. Considering the two key factors that affect the synthesis performance, frame representation and blending artifacts, we improve the synthesis performance from two aspects: 1) Effective frame representation is designed to capture both the image appearance information in spatial domain and the longitudinal information in temporal domain. 2) Artifacts that degrade the synthesis quality are significantly suppressed on the basis of a diffeomorphic growth model. The proposed video texture synthesis approach has two major stages: video stitching stage and transition smoothing stage. In the first stage, a video texture synthesis model is proposed to generate an infinite video flow. To find similar frames for stitching video clips, we present a new spatial-temporal descriptor to provide an effective representation for different types of dynamic textures. In the second stage, a smoothing method is proposed to improve synthesis quality, especially in the aspect of temporal continuity. It aims to establish a diffeomorphic growth model to emulate local dynamics around stitched frames. The proposed approach is thoroughly tested on public databases and videos from the Internet, and is evaluated in both qualitative and quantitative ways.
NASA Astrophysics Data System (ADS)
Précigout, J.; Hirth, G.
2011-12-01
peridotites were deformed at pressures lower than 2 GPa at sub-solidus conditions (Garrido et al., 2011), and 3) the A-type/B-type transition correlates with a decrease of temperature, grain size and fabric strength (Jindex) towards the inner shear zone. Our results moreover indicate that B-type fabric is somehow related to large-scale mantle shear zones, and hence it could characterize a signature of lithosphere-scale mantle strain localization.
SU-F-BRF-03: Quality Assurance of Deformable Image Registration in Radiotherapy
Watkins, W.T.; Siebers, J.V.; Bzdusek, K.
2014-06-15
Purpose: To introduce methods to analyze Deformable Image Registration (DIR) and identify regions of potential DIR errors. Methods: DIR Deformable Vector Fields (DVFs) quantifying patient anatomic changes were evaluated using the Jacobian determinant and the magnitude of DVF curl as functions of tissue density and tissue type. These quantities represent local relative deformation and rotation, respectively. Large values in dense tissues can potentially identify non-physical DVF errors. For multiple DVFs per patient, histograms and visualization of DVF differences were also considered. To demonstrate the capabilities of methods, we computed multiple DVFs for each of five Head and Neck (H'N) patients (P1–P5) via a Fast-symmetric Demons (FSD) algorithm and via a Diffeomorphic Demons (DFD) algorithm, and show the potential to identify DVF errors. Results: Quantitative comparisons of the FSD and DFD registrations revealed <0.3 cm DVF differences in >99% of all voxels for P1, >96% for P2, and >90% of voxels for P3. While the FSD and DFD registrations were very similar for these patients, the Jacobian determinant was >50% in 9–15% of soft tissue and in 3–17% of bony tissue in each of these cases. The volumes of large soft tissue deformation were consistent for all five patients using the FSD algorithm (mean 15%±4% volume), whereas DFD reduced regions of large deformation by 10% volume (785 cm{sup 3}) for P4 and by 14% volume (1775 cm{sup 3}) for P5. The DFD registrations resulted in fewer regions of large DVF-curl; 50% rotations in FSD registrations averaged 209±136 cm{sup 3} in soft tissue and 10±11 cm{sup 3} in bony tissue, but using DFD these values were reduced to 42±53 cm{sup 3} and 1.1±1.5 cm{sup 3}, respectively. Conclusion: Analysis of Jacobian determinant and curl as functions of tissue density can identify regions of potential DVF errors by identifying non-physical deformations and rotations. Collaboration with Phillips Healthcare, as indicated in
NASA Astrophysics Data System (ADS)
Hu, Hai-xiang; Qi, Erhui; Cole, Glen; Hu, Hai-fei; Luo, Xiao; Zhang, Xue-jun
2016-10-01
Large flat mirrors play important roles in large aperture telescopes. However, they also introduce unpredictable problems. The surface errors created during manufacturing, testing, and supporting are all combined during measurement, thus making understanding difficult for diagnosis and treatment. Examining a high diameter-to-thickness ratio flat mirror, TMT M3MP, and its unexpected deformation during processing, we proposed a strain model of subsurface damage to explain the observed phenomenon. We designed a set of experiment, and checked the validity of our diagnosis. On that basis, we theoretical predicted the trend of this strain and its scale effect on Zerodur®, and checked the validity on another piece experimentally. This work guided the grinding-polishing process of M3MP, and will be used as reference for M3M processing as well.