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.
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.
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.
Deep Adaptive Log-Demons: Diffeomorphic Image Registration with Very Large Deformations
Zhao, Liya; Jia, Kebin
2015-01-01
This paper proposes a new framework for capturing large and complex deformation in image registration. Traditionally, this challenging problem relies firstly on a preregistration, usually an affine matrix containing rotation, scale, and translation and afterwards on a nonrigid transformation. According to preregistration, the directly calculated affine matrix, which is obtained by limited pixel information, may misregistrate when large biases exist, thus misleading following registration subversively. To address this problem, for two-dimensional (2D) images, the two-layer deep adaptive registration framework proposed in this paper firstly accurately classifies the rotation parameter through multilayer convolutional neural networks (CNNs) and then identifies scale and translation parameters separately. For three-dimensional (3D) images, affine matrix is located through feature correspondences by a triplanar 2D CNNs. Then deformation removal is done iteratively through preregistration and demons registration. By comparison with the state-of-the-art registration framework, our method gains more accurate registration results on both synthetic and real datasets. Besides, principal component analysis (PCA) is combined with correlation like Pearson and Spearman to form new similarity standards in 2D and 3D registration. Experiment results also show faster convergence speed. PMID:26120356
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
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
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.
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.
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
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
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?
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
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.
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.
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
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.
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
Leukocyte deformability: finite element modeling of large viscoelastic deformation.
Dong, C; Skalak, R
1992-09-21
An axisymmetric deformation of a viscoelastic sphere bounded by a prestressed elastic thin shell in response to external pressure is studied by a finite element method. The research is motivated by the need for understanding the passive behavior of human leukocytes (white blood cells) and interpreting extensive experimental data in terms of the mechanical properties. The cell at rest is modeled as a sphere consisting of a cortical prestressed shell with incompressible Maxwell fluid interior. A large-strain deformation theory is developed based on the proposed model. General non-linear, large strain constitutive relations for the cortical shell are derived by neglecting the bending stiffness. A representation of the constitutive equations in the form of an integral of strain history for the incompressible Maxwell interior is used in the formulation of numerical scheme. A finite element program is developed, in which a sliding boundary condition is imposed on all contact surfaces. The mathematical model developed is applied to evaluate experimental data of pipette tests and observations of blood flow.
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
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.
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.
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.
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.
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
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.
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
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.
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.
Large Scale Deformation of the Western US Cordillera
NASA Technical Reports Server (NTRS)
Bennett, Richard A.
2001-01-01
Destructive earthquakes occur throughout the western US Cordillera (WUSC), not just within the San Andreas fault zone. But because we do not understand the present-day large-scale deformations of the crust throughout the WUSC, our ability to assess the potential for seismic hazards in this region remains severely limited. To address this problem, we are using a large collection of Global Positioning System (GPS) networks which spans the WUSC to precisely quantify present-day large-scale crustal deformations in a single uniform reference frame. Our work can roughly be divided into an analysis of the GPS observations to infer the deformation field across and within the entire plate boundary zone and an investigation of the implications of this deformation field regarding plate boundary dynamics.
Symmetric log-domain diffeomorphic Registration: a demons-based approach.
Vercauteren, Tom; Pennec, Xavier; Perchant, Aymeric; Ayache, Nicholas
2008-01-01
Modern morphometric studies use non-linear image registration to compare anatomies and perform group analysis. Recently, log-Euclidean approaches have contributed to promote the use of such computational anatomy tools by permitting simple computations of statistics on a rather large class of invertible spatial transformations. In this work, we propose a non-linear registration algorithm perfectly fit for log-Euclidean statistics on diffeomorphisms. Our algorithm works completely in the log-domain, i.e. it uses a stationary velocity field. This implies that we guarantee the invertibility of the deformation and have access to the true inverse transformation. This also means that our output can be directly used for log-Euclidean statistics without relying on the heavy computation of the log of the spatial transformation. As it is often desirable, our algorithm is symmetric with respect to the order of the input images. Furthermore, we use an alternate optimization approach related to Thirion's demons algorithm to provide a fast non-linear registration algorithm. First results show that our algorithm outperforms both the demons algorithm and the recently proposed diffeomorphic demons algorithm in terms of accuracy of the transformation while remaining computationally efficient.
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.
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').
NASA Astrophysics Data System (ADS)
Kustas, A. B.; Sagapuram, D.; Chandrasekar, S.; Trumble, K. P.
2015-04-01
Machining is used as a deformation technique to impose large shear strains (γ ˜ 2) in a commercial Fe-4%Si alloy. The partial <111> and {110} - fiber texture components are generated throughout the as-deformed microstructure, which is expected of BCC metals deformed in simple shear. Using an annealing schedule similar to that in the commercial rolling process, samples retain the deformation texture, consistent with a continuous-type recrystallization mechanism. Fine-grained annealed samples reveal two different partial fiber orientations, one of which becomes the dominate texture, following the high-temperature growth treatment. The mechanisms of texture evolution and implications for texture control in the machining-based process are discussed.
Large Scale Deformation of the Western U.S. Cordillera
NASA Technical Reports Server (NTRS)
Bennett, Richard A.
2002-01-01
Over the past couple of years, with support from NASA, we used a large collection of data from GPS, VLBI, SLR, and DORIS networks which span the 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.
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.
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.
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.
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
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
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
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.
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.
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
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.
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.
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.
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.
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.
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.
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
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-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 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.
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.
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.
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
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.
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
Explicit versus spontaneous diffeomorphism breaking in gravity
NASA Astrophysics Data System (ADS)
Bluhm, Robert
2015-03-01
Gravitational theories with fixed background fields break local Lorentz and diffeomorphism invariance either explicitly or spontaneously. In the case of explicit breaking it is known that conflicts can arise between the dynamics and geometrical constraints, while spontaneous breaking evades this problem. It is for this reason that in the gravity sector of the Standard-Model extension (SME) it is assumed that the background fields (SME coefficients) originate from spontaneous symmetry breaking. However, in other examples, such as Chern-Simons gravity and massive gravity, diffeomorphism invariance is explicitly broken by the background fields, and the potential conflicts between the dynamics and geometry can be avoided in most cases. An analysis of how this occurs is given, and the conditions that are placed on the metric tensor and gravitational structure as a result of the presence of an explicit-breaking background are described. The gravity sector of the SME is then considered for the case of explicit breaking. However, it is found that a useful post-Newtonian limit is only obtained when the symmetry breaking is spontaneous.
Fabric strain sensor integrated with CNPECs for repeated large deformation
NASA Astrophysics Data System (ADS)
Yi, Weijing
Flexible and soft strain sensors that can be used in smart textiles for wearable applications are much desired. They should meet the requirements of low modulus, large working range and good fatigue resistance as well as good sensing performances. However, there were no commercial products available and the objective of the thesis is to investigate fabric strain sensors based on carbon nanoparticle (CNP) filled elastomer composites (CNPECs) for potential wearing applications. Conductive CNPECs were fabricated and investigated. The introduction of silicone oil (SO) significantly decreased modulus of the composites to less than 1 MPa without affecting their deformability and they showed good stability after heat treatment. With increase of CNP concentration, a percolation appeared in electrical resistivity and the composites can be divided into three ranges. I-V curves and impedance spectra together with electro-mechanical studies demonstrated a balance between sensitivity and working range for the composites with CNP concentrations in post percolation range, and were preferred for sensing applications only if the fatigue life was improved. Due to the good elasticity and failure resist property of knitted fabric under repeated extension, it was adopted as substrate to increase the fatigue life of the conductive composites. After optimization of processing parameters, the conductive fabric with CNP concentration of 9.0CNP showed linear I-V curves when voltage is in the range of -1 V/mm and 1 V/mm and negligible capacitive behavior when frequency below 103 Hz even with strain of 60%. It showed higher sensitivity due to the combination of nonlinear resistance-strain behavior of the CNPECs and non-even strain distribution of knitted fabric under extension. The fatigue life of the conductive fabric was greatly improved. Extended on the studies of CNPECs and the coated conductive fabrics, a fabric strain sensor was designed, fabricated and packaged. The Young's modulus of
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
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
Procedures for experimental measurement and theoretical analysis of large plastic deformations
NASA Technical Reports Server (NTRS)
Morris, R. E.
1974-01-01
Theoretical equations are derived and analytical procedures are presented for the interpretation of experimental measurements of large plastic strains in the surface of a plate. Orthogonal gage lengths established on the metal surface are measured before and after deformation. The change in orthogonality after deformation is also measured. Equations yield the principal strains, deviatoric stresses in the absence of surface friction forces, true stresses if the stress normal to the surface is known, and the orientation angle between the deformed gage line and the principal stress-strain axes. Errors in the measurement of nominal strains greater than 3 percent are within engineering accuracy. Applications suggested for this strain measurement system include the large-strain-stress analysis of impact test models, burst tests of spherical or cylindrical pressure vessels, and to augment small-strain instrumentation tests where large strains are anticipated.
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.
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.
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.
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
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.
Large Deformation of an Elastic Rod with Structural Anisotropy Subjected to Fluid Flow
NASA Astrophysics Data System (ADS)
Hassani, Masoud; Mureithi, Njuki; Gosselin, Frederick
2015-11-01
In the present work, we seek to understand the fundamental mechanisms of three-dimensional reconfiguration of plants by studying the large deformation of a flexible rod in fluid flow. Flexible rods made of Polyurethane foam and reinforced with Nylon fibers are tested in a wind tunnel. The rods have bending-torsion coupling which induces a torsional deformation during asymmetric bending. A mathematical model is also developed by coupling the Kirchhoff rod theory with a semi-empirical drag formulation. Different alignments of the material frame with respect to the flow direction and a range of structural properties are considered to study their effect on the deformation of the flexible rod and its drag scaling. Results show that twisting causes the flexible rods to reorient and bend with the minimum bending rigidity. It is also found that the drag scaling of the rod in the large deformation regime is not affected by torsion. Finally, using a proper set of dimensionless numbers, the state of a bending and twisting rod is characterized as a beam undergoing a pure bending deformation.
Depalle, Baptiste; Qin, Zhao; Shefelbine, Sandra J; Buehler, Markus J
2016-02-01
Mineralized collagen fibrils are composed of tropocollagen molecules and mineral crystals derived from hydroxyapatite to form a composite material that combines optimal properties of both constituents and exhibits incredible strength and toughness. Their complex hierarchical structure allows collagen fibrils to sustain large deformation without breaking. In this study, we report a mesoscale model of a single mineralized collagen fibril using a bottom-up approach. By conserving the three-dimensional structure and the entanglement of the molecules, we were able to construct finite-size fibril models that allowed us to explore the deformation mechanisms which govern their mechanical behavior under large deformation. We investigated the tensile behavior of a single collagen fibril with various intrafibrillar mineral content and found that a mineralized collagen fibril can present up to five different deformation mechanisms to dissipate energy. These mechanisms include molecular uncoiling, molecular stretching, mineral/collagen sliding, molecular slippage, and crystal dissociation. By multiplying its sources of energy dissipation and deformation mechanisms, a collagen fibril can reach impressive strength and toughness. Adding mineral into the collagen fibril can increase its strength up to 10 times and its toughness up to 35 times. Combining crosslinks with mineral makes the fibril stiffer but more brittle. We also found that a mineralized fibril reaches its maximum toughness to density and strength to density ratios for a mineral density of around 30%. This result, in good agreement with experimental observations, attests that bone tissue is optimized mechanically to remain lightweight but maintain strength and toughness.
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%.
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 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.
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.
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.
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.
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 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
2016-01-01
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
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.
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.
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.
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.
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
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
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.
Euclidean space-time diffeomorphisms and their Fueter subgroups
Guersey, F.; Jiang, W. )
1992-02-01
Holomorphic Fueter functions of the position quaternion form a subgroup of Euclidean space-time diffeomorphisms. An {ital O}(4) covariant treatment of such mappings is presented with the quaternionic argument {ital x} being replaced by either {ital {bar p}x} or {ital x{bar p}} involving self-dual and anti-self-dual structures and {ital p} denoting an arbitrary Euclidean time direction. An infinite group (the quasiconformal group) is exhibited that admits the conformal group SO(5,1) as a subgroup, in analogy to the two-dimensional case in which the Moebius group SO(3,1) is a subgroup of the infinite Virasoro group. The ensuing (3+1) covariant decomposition of diffeomorphisms suggests covariant gauges that throw the metric and the stress tensors in standard forms suitable for canonical quantization, leading to improved'' energy-momentum tensors. Other possible applications to current algebra and gravity will be mentioned.
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.
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.
Large Deformation Analysis of a High Steep Slope Relating to the Laxiwa Reservoir, China
NASA Astrophysics Data System (ADS)
Lin, Peng; Liu, Xiaoli; Hu, Senying; Li, Pujian
2016-06-01
The unstable rock slope in the Laxiwa reservoir area of the Yellow River upstream, China, shows the signs of gravitational and water-impounding induced large deformations over an area of 1.15 × 105 m2. Slope movements have been measured daily at more than 560 observation points since 2009, when the reservoir was first impounded. At two of these points, an average daily movement of around 60-80 mm has ever been observed since the beginning of the impounding. Based on the observed deformations and the geology of the site, a fluid-solid coupling model was then adopted to investigate the existing rockslide activity to better understand the mechanism underlying the large deformations. The results from the field observation, kinematic analysis and numerical modeling indicate that the slope instability is dominated by the strong structurally controlled unstable rock mass. Based on an integrated overview of these analyses, a new toppling mode, i.e. the so-called `conjugate block' mode, is proposed to explain the large deformation mechanism of the slope. The conjugate block is formed by a `dumping block' and toppling blocks. The large deformation of the slope is dominated by (1) a toppling component and (2) a subsiding bilinear wedge induced by planar sliding along the deep-seated faults. Following a thorough numerical analysis, it is concluded that small collapses of rock blocks along the slope will be more frequent with the impounding process continuing and the water level fluctuating during the subsequent operation period. Based on a shear strength reduction method and field monitoring, four controlling faults are identified and the instability of the loose structure in the surface layer is analyzed and discussed. The factor of safety against the sliding failure along the deep seated fractures in the slope is 1.72, which reveals that (1) the collapse of the free-standing fractured blocks cannot be ruled out and the volume of the unstable blocks may be greater than 100
Deformation regime and long-term precursors to eruption at large calderas: Rabaul, Papua New Guinea
NASA Astrophysics Data System (ADS)
Robertson, Robert M.; Kilburn, Christopher R. J.
2016-03-01
Eruptions at large calderas are normally preceded by variable rates of unrest that continue for decades or more. A classic example is the 1994 eruption of Rabaul caldera, in Papua New Guinea, which began after 23 years of surface uplift and volcano-tectonic (VT) seismicity at rates that changed unevenly with time by an order of magnitude. Although the VT event rate and uplift rate peaked in 1983-1985, eruptions only began a decade later and followed just 27 hours of anomalous changes in precursory signal. Here we argue that the entire 23 years of unrest belongs to a single sequence of damage accumulation in the crust and that, in 1991-1992, the crust's response to applied stress changed from quasi-elastic (elastic deformation with minor fault movement) to inelastic (deformation predominantly by fault movement alone). The change in behaviour yields limiting trends in the variation of VT event rate with deformation and can be quantified with a mean-field model for an elastic crust that contains a dispersed population of small faults. The results show that identifying the deformation regime for elastic-brittle crust provides new criteria for using precursory time series to evaluate the potential for eruption. They suggest that, in the quasi-elastic regime, short-term increases in rates of deformation and VT events are unreliable indicators of an imminent eruption, but that, in the inelastic regime, the precursory rates may follow hyperbolic increases with time and offer the promise of developing forecasts of eruption as much as months beforehand.
Surface deformations as indicators of deep ebullition fluxes in a large northern peatland
Glaser, P.H.; Chanton, J.P.; Morin, P.; Rosenberry, D.O.; Siegel, D.I.; Ruud, O.; Chasar, L.I.; Reeve, A.S.
2004-01-01
Peatlands deform elastically during precipitation cycles by small (??3 cm) oscillations in surface elevation. In contrast, we used a Global Positioning System network to measure larger oscillations that exceeded 20 cm over periods of 4-12 hours during two seasonal droughts at a bog and fen site in northern Minnesota. The second summer drought also triggered 19 depressuring cycles in an overpressured stratum under the bog site. The synchronicity between the largest surface deformations and the depressuring cycles indicates that both phenomena are produced by the episodic release of large volumes of gas from deep semi-elastic compartments confined by dense wood layers. We calculate that the three largest surface deformations were associated with the release of 136 g CH4 m-2, which exceeds by an order of magnitude the annual average chamber fluxes measured at this site. Ebullition of gas from the deep peat may therefore be a large and previously unrecognized source of radiocarbon depleted methane emissions from northern peatlands. Copyright 2004 by the American Geophysical Union.
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.
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.
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.
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.
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)
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
2014-11-19
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.
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
2014-01-01
Reversible deformation of a machine holds enormous promise across many scientific areas ranging from mechanical engineering to applied physics. So far, such capabilities are still hard to achieve through conventional rigid materials or depending mainly on elastomeric materials, which however own rather limited performances and require complicated manipulations. Here, we show a basic strategy which is fundamentally different from the existing ones to realize large scale reversible deformation through controlling the working materials via the synthetically chemical-electrical mechanism (SCHEME). Such activity incorporates an object of liquid metal gallium whose surface area could spread up to five times of its original size and vice versa under low energy consumption. Particularly, the alterable surface tension based on combination of chemical dissolution and electrochemical oxidation is ascribed to the reversible shape transformation, which works much more flexible than many former deformation principles through converting electrical energy into mechanical movement. A series of very unusual phenomena regarding the reversible configurational shifts are disclosed with dominant factors clarified. This study opens a generalized way to combine the liquid metal serving as shape-variable element with the SCHEME to compose functional soft machines, which implies huge potential for developing future smart robots to fulfill various complicated tasks. PMID:25408295
A large-deformation thin plate theory with application to one-atom-thick layers
NASA Astrophysics Data System (ADS)
Delfani, M. R.; Shodja, H. M.
2016-02-01
Nowadays, two-dimensional materials due to their vast engineering and biomedical applications have been the focus of many researches. The present paper proposes a large-deformation theory for thin plates with application to one-atom-thick layers (OATLs). The deformation is formulated exactly in the mathematical framework of Lagrangian description. In particular, an exact finite strain analysis is given - in addition to the usual strain tensor associated to the middle surface, the second and third fundamental forms of the middle surface of the deformed thin plate are also maintained in the analysis. Exact closed-form solutions for a uniaxially curved thin plate due to pure bending in one case and due to a combination of vertical and horizontal loading in another are obtained. As a special case of the latter problem, the exact solution for the plane-strain bulge test of thin plates is derived. Subsequently, the approximation of Vlassak and Nix [Vlassak, J.J., Nix, W.D., 1992. J. Mater. Res., 7(12), 3242-3249] for the load-deflection equation is recovered. The given numerical results are devoted to graphene as the most well-known OATL.
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.
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.
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.
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
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.
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.
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.
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
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.
NASA Astrophysics Data System (ADS)
Salvetti, M.; Duchenne, S.; Parks, D. M.; Marzari, N.
2010-03-01
Within a continuum approach, the prediction of the mechanical response of single crystals at large elastic deformations relies on the accurate description of the strain energy density function ψ. The coupling of hydrostatic and deviatoric terms at high compressions is of particular interest for applications, and the effect is generally not taken into account by current models available in the literature [1,2]. We present a general approach that leads to the construction of strain energy density functions of cubic single crystals based on data obtained from density functional theory (DFT) calculations. We connect the deformation-induced energy changes and Cauchy stress calculated from DFT calculations to the Lagrangian description frequently adopted within the continuum theory of hyperelasticity [3]. In particular, we adopt a coordinate--free invariant formulation [4] that intrinsically preserves the properties of the cubic symmetry group. We present results on diamond and silicon single crystals, and highlight both similarities and striking differences. [1] R.G.Veprek et. al, Mater. Sci. Eng. A 4248, 366-378 (2007) [2] B.P Gearing, L. Anand, Int. J. Solids Struct. 41, 827-845 (2004) [3] A.N. Norris, J. Mech. Mater. Struct. 3, No.2, 243-260 (2008) [4] J.P. Boehler, Z. Angew. Math. Mech. 59, 157-167 (1979)
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.
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.
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
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.
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.
Charette, P G; Hunter, I W; Hunter, P J
1997-04-01
This paper describes an apparatus designed to study large mechanical deformations in biological membranes. The task of mechanically characterizing biological membranes is challenging because of the anisotropic and nonlinear nature of their material properties. The apparatus described here is well suited to the task because it uses speckle interferometry to measure in-plane displacements in a distributed fashion and has multiple degrees of freedom in the applied stress mechanism. In this way few a priori assumptions or restrictions are imposed on the applied stress and strain fields. The interferometer operates in transmission mode to increase the light efficiency of the system since the sample biological membranes are translucent and reflect little light. The experimental results confirm that the strain fields in the biological membranes that are generated in the experiments are highly nonuniform and cannot be properly estimated from a small number of point measurements.
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
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.
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
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.
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.
Charette, P G; Hunter, P J; Hunter, I W
1997-04-01
In holography and speckle interferometry the measurement range is generally limited by the greatest number of fringes that can be resolved in a single image. As a result these techniques have been generally confined to small displacement measurement applications. In the case of out-of-plane measurements one can overcome this limitation by simply adding incremental measurements at individual detector pixels. In the case of in-plane measurements, however, summing incremental measurements is not a straightforward procedure since the interference pattern moves laterally across the detector as the material deforms. We describe a modeling technique based on finite elements which solves this problem. In combination with a full field method such as holography or speckle interferometry, it provides a very sensitive measurement technique with dense spatial sampling and large dynamic range. Experimental results of speckle interferometry operating in transmission to measure in-plane displacements of biological membranes are presented, where total material displacements are of the order of millimeters. The results also demonstrate how the finite strain tensor is calculated analytically from the data at any point on the material.
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.
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.
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.
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.
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
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
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.
2014-11-01
1–39. 14. ABSTRACT The report presents three-dimensional, large deformation, coupled finite element analysis ( FEA ) of dynamic loading on soft...including inertia terms. The solid skeleton is modeled as an isotropic, compressible, hyperelastic material. FEA simulations include: (1...displacement nodes, and “P” the number of pore fluid pressure nodes). The FEA results demonstrate the interplay of dynamics (wave propagation through solid
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
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.
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.
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
NASA Astrophysics Data System (ADS)
Molnar, P. H.
2010-12-01
Tibetan Plateau illustrates this failing of plate tectonics (or crustal blocks) especially well. In particular, because of the large lateral variations in gravitational potential energy, it offers the best region in which to study dynamics of continental deformation.
Stone, C.M.
1997-07-01
SANTOS is a finite element program designed to compute the quasistatic, large deformation, inelastic response of two-dimensional planar or axisymmetric solids. The code is derived from the transient dynamic code PRONTO 2D. The solution strategy used to compute the equilibrium states is based on a self-adaptive dynamic relaxation solution scheme, which is based on explicit central difference pseudo-time integration and artificial mass proportional damping. The element used in SANTOS is a uniform strain 4-node quadrilateral element with an hourglass control scheme to control the spurious deformation modes. Finite strain constitutive models for many common engineering materials are included. A robust master-slave contact algorithm for modeling sliding contact is implemented. An interface for coupling to an external code is also provided. 43 refs., 22 figs.
NASA Astrophysics Data System (ADS)
Tao, Wei; Jiang, Kai; Zhao, Hui
2015-02-01
Large frames made of compound material are widely used in many areas such as industry and aerospace. To ensure the frames working properly, monitor of its deformation after expansion is of great importance. A real time measurement system based on retro-reflective technique and vision method is proposed. Several round retro-reflective marks are placed on some defined positions of the frame as mark points which can precisely describe the shape of the frame. The marks are illuminated by laser beams and the image of the marks is captured by a camera. The positions of the marks on the camera are determined by designed image process program. Experimental results show that the whole process can be finished within 0.1 second. The designed system can measure the deformation of up to 50mm and the accuracy of the measurement is better than 0.02 mm.
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.
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.
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 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.
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.
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.
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
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.
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.
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
Mechanical characterization of the P56 mouse brain under large-deformation dynamic indentation
MacManus, David B.; Pierrat, Baptiste; Murphy, Jeremiah G.; Gilchrist, Michael D.
2016-01-01
The brain is a complex organ made up of many different functional and structural regions consisting of different types of cells such as neurons and glia, as well as complex anatomical geometries. It is hypothesized that the different regions of the brain exhibit significantly different mechanical properties, which may be attributed to the diversity of cells and anisotropy of neuronal fibers within individual brain regions. The regional dynamic mechanical properties of P56 mouse brain tissue in vitro and in situ at velocities of 0.71–4.28 mm/s, up to a deformation of 70 μm are presented and discussed in the context of traumatic brain injury. The experimental data obtained from micro-indentation measurements were fit to three hyperelastic material models using the inverse Finite Element method. The cerebral cortex elicited a stiffer response than the cerebellum, thalamus, and medulla oblongata regions for all velocities. The thalamus was found to be the least sensitive to changes in velocity, and the medulla oblongata was most compliant. The results show that different regions of the mouse brain possess significantly different mechanical properties, and a significant difference also exists between the in vitro and in situ brain. PMID:26898475
Mechanical characterization of the P56 mouse brain under large-deformation dynamic indentation
NASA Astrophysics Data System (ADS)
MacManus, David B.; Pierrat, Baptiste; Murphy, Jeremiah G.; Gilchrist, Michael D.
2016-02-01
The brain is a complex organ made up of many different functional and structural regions consisting of different types of cells such as neurons and glia, as well as complex anatomical geometries. It is hypothesized that the different regions of the brain exhibit significantly different mechanical properties, which may be attributed to the diversity of cells and anisotropy of neuronal fibers within individual brain regions. The regional dynamic mechanical properties of P56 mouse brain tissue in vitro and in situ at velocities of 0.71–4.28 mm/s, up to a deformation of 70 μm are presented and discussed in the context of traumatic brain injury. The experimental data obtained from micro-indentation measurements were fit to three hyperelastic material models using the inverse Finite Element method. The cerebral cortex elicited a stiffer response than the cerebellum, thalamus, and medulla oblongata regions for all velocities. The thalamus was found to be the least sensitive to changes in velocity, and the medulla oblongata was most compliant. The results show that different regions of the mouse brain possess significantly different mechanical properties, and a significant difference also exists between the in vitro and in situ brain.
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.
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.
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.
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.
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.
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.
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
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).
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.
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.
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.
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.
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)
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.
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.
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.
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.
2017-02-01
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.
MIND Demons for MR-to-CT Deformable Image Registration In Image-Guided Spine Surgery
Reaungamornrat, S.; De Silva, T.; Uneri, A.; Wolinsky, J.-P.; Khanna, A. J.; Kleinszig, G.; Vogt, S.; Prince, J. L.; Siewerdsen, J. H.
2016-01-01
Purpose Localization of target anatomy and critical structures defined in preoperative MR images can be achieved by means of multi-modality deformable registration to intraoperative CT. We propose a symmetric diffeomorphic deformable registration algorithm incorporating a modality independent neighborhood descriptor (MIND) and a robust Huber metric for MR-to-CT registration. Method The method, called MIND Demons, solves for the deformation field between two images by optimizing an energy functional that incorporates both the forward and inverse deformations, smoothness on the velocity fields and the diffeomorphisms, a modality-insensitive similarity function suitable to multi-modality images, and constraints on geodesics in Lagrangian coordinates. Direct optimization (without relying on an exponential map of stationary velocity fields used in conventional diffeomorphic Demons) is carried out using a Gauss-Newton method for fast convergence. Registration performance and sensitivity to registration parameters were analyzed in simulation, in phantom experiments, and clinical studies emulating application in image-guided spine surgery, and results were compared to conventional mutual information (MI) free-form deformation (FFD), local MI (LMI) FFD, and normalized MI (NMI) Demons. Result The method yielded sub-voxel invertibility (0.006 mm) and nonsingular spatial Jacobians with capability to preserve local orientation and topology. It demonstrated improved registration accuracy in comparison to the reference methods, with mean target registration error (TRE) of 1.5 mm compared to 10.9, 2.3, and 4.6 mm for MI FFD, LMI FFD, and NMI Demons methods, respectively. Validation in clinical studies demonstrated realistic deformation with sub-voxel TRE in cases of cervical, thoracic, and lumbar spine. Conclusions A modality-independent deformable registration method has been developed to estimate a viscoelastic diffeomorphic map between preoperative MR and intraoperative CT. The
MIND Demons for MR-to-CT deformable image registration in image-guided spine surgery
NASA Astrophysics Data System (ADS)
Reaungamornrat, S.; De Silva, T.; Uneri, A.; Wolinsky, J.-P.; Khanna, A. J.; Kleinszig, G.; Vogt, S.; Prince, J. L.; Siewerdsen, J. H.
2016-03-01
Purpose: Localization of target anatomy and critical structures defined in preoperative MR images can be achieved by means of multi-modality deformable registration to intraoperative CT. We propose a symmetric diffeomorphic deformable registration algorithm incorporating a modality independent neighborhood descriptor (MIND) and a robust Huber metric for MR-to-CT registration. Method: The method, called MIND Demons, solves for the deformation field between two images by optimizing an energy functional that incorporates both the forward and inverse deformations, smoothness on the velocity fields and the diffeomorphisms, a modality-insensitive similarity function suitable to multi-modality images, and constraints on geodesics in Lagrangian coordinates. Direct optimization (without relying on an exponential map of stationary velocity fields used in conventional diffeomorphic Demons) is carried out using a Gauss-Newton method for fast convergence. Registration performance and sensitivity to registration parameters were analyzed in simulation, in phantom experiments, and clinical studies emulating application in image-guided spine surgery, and results were compared to conventional mutual information (MI) free-form deformation (FFD), local MI (LMI) FFD, and normalized MI (NMI) Demons. Result: The method yielded sub-voxel invertibility (0.006 mm) and nonsingular spatial Jacobians with capability to preserve local orientation and topology. It demonstrated improved registration accuracy in comparison to the reference methods, with mean target registration error (TRE) of 1.5 mm compared to 10.9, 2.3, and 4.6 mm for MI FFD, LMI FFD, and NMI Demons methods, respectively. Validation in clinical studies demonstrated realistic deformation with sub-voxel TRE in cases of cervical, thoracic, and lumbar spine. Conclusions: A modality-independent deformable registration method has been developed to estimate a
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Salisbury, Donald; Renn, Jürgen; Sundermeyer, Kurt
2016-02-01
Classical background independence is reflected in Lagrangian general relativity through covariance under the full diffeomorphism group. We show how this independence can be maintained in a Hamilton-Jacobi approach that does not accord special privilege to any geometric structure. Intrinsic space-time curvature-based coordinates grant equal status to all geometric backgrounds. They play an essential role as a starting point for inequivalent semiclassical quantizations. The scheme calls into question Wheeler’s geometrodynamical approach and the associated Wheeler-DeWitt equation in which 3-metrics are featured geometrical objects. The formalism deals with variables that are manifestly invariant under the full diffeomorphism group. Yet, perhaps paradoxically, the liberty in selecting intrinsic coordinates is precisely as broad as is the original diffeomorphism freedom. We show how various ideas from the past five decades concerning the true degrees of freedom of general relativity can be interpreted in light of this new constrained Hamiltonian description. In particular, we show how the Kuchař multi-fingered time approach can be understood as a means of introducing full four-dimensional diffeomorphism invariants. Every choice of new phase space variables yields new Einstein-Hamilton-Jacobi constraining relations, and corresponding intrinsic Schrödinger equations. We show how to implement this freedom by canonical transformation of the intrinsic Hamiltonian. We also reinterpret and rectify significant work by Dittrich on the construction of “Dirac observables.”
Diffeomorphic susceptibility artifact correction of diffusion-weighted magnetic resonance images
NASA Astrophysics Data System (ADS)
Ruthotto, L.; Kugel, H.; Olesch, J.; Fischer, B.; Modersitzki, J.; Burger, M.; Wolters, C. H.
2012-09-01
Diffusion-weighted magnetic resonance imaging is a key investigation technique in modern neuroscience. In clinical settings, diffusion-weighted imaging and its extension to diffusion tensor imaging (DTI) are usually performed applying the technique of echo-planar imaging (EPI). EPI is the commonly available ultrafast acquisition technique for single-shot acquisition with spatial encoding in a Cartesian system. A drawback of these sequences is their high sensitivity against small perturbations of the magnetic field, caused, e.g., by differences in magnetic susceptibility of soft tissue, bone and air. The resulting magnetic field inhomogeneities thus cause geometrical distortions and intensity modulations in diffusion-weighted images. This complicates the fusion with anatomical T1- or T2-weighted MR images obtained with conventional spin- or gradient-echo images and negligible distortion. In order to limit the degradation of diffusion-weighted MR data, we present here a variational approach based on a reference scan pair with reversed polarity of the phase- and frequency-encoding gradients and hence reversed distortion. The key novelty is a tailored nonlinear regularization functional to obtain smooth and diffeomorphic transformations. We incorporate the physical distortion model into a variational image registration framework and derive an accurate and fast correction algorithm. We evaluate the applicability of our approach to distorted DTI brain scans of six healthy volunteers. For all datasets, the automatic correction algorithm considerably reduced the image degradation. We show that, after correction, fusion with T1- or T2-weighted images can be obtained by a simple rigid registration. Furthermore, we demonstrate the improvement due to the novel regularization scheme. Most importantly, we show that it provides meaningful, i.e. diffeomorphic, geometric transformations, independent of the actual choice of the regularization parameters.
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)
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 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.
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.
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.
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)
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.
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.
Curiale, Ariel H; Vegas-Sánchez-Ferrero, Gonzalo; Bosch, Johan G; Aja-Fernández, Santiago
2015-08-01
The strain and strain-rate measures are commonly used for the analysis and assessment of regional myocardial function. In echocardiography (EC), the strain analysis became possible using Tissue Doppler Imaging (TDI). Unfortunately, this modality shows an important limitation: the angle between the myocardial movement and the ultrasound beam should be small to provide reliable measures. This constraint makes it difficult to provide strain measures of the entire myocardium. Alternative non-Doppler techniques such as Speckle Tracking (ST) can provide strain measures without angle constraints. However, the spatial resolution and the noisy appearance of speckle still make the strain estimation a challenging task in EC. Several maximum likelihood approaches have been proposed to statistically characterize the behavior of speckle, which results in a better performance of speckle tracking. However, those models do not consider common transformations to achieve the final B-mode image (e.g. interpolation). This paper proposes a new maximum likelihood approach for speckle tracking which effectively characterizes speckle of the final B-mode image. Its formulation provides a diffeomorphic scheme than can be efficiently optimized with a second-order method. The novelty of the method is threefold: First, the statistical characterization of speckle generalizes conventional speckle models (Rayleigh, Nakagami and Gamma) to a more versatile model for real data. Second, the formulation includes local correlation to increase the efficiency of frame-to-frame speckle tracking. Third, a probabilistic myocardial tissue characterization is used to automatically identify more reliable myocardial motions. The accuracy and agreement assessment was evaluated on a set of 16 synthetic image sequences for three different scenarios: normal, acute ischemia and acute dyssynchrony. The proposed method was compared to six speckle tracking methods. Results revealed that the proposed method is the most
Shi, X; Lin, J; Diwanji, T; Mooney, K; D'Souza, W; Mistry, N
2014-06-01
Purpose: Recently, template matching has been shown to be able to track tumor motion on cine-MRI images. However, artifacts such as deformation, rotation, and/or out-of-plane movement could seriously degrade the performance of this technique. In this work, we demonstrate the utility of multiple templates derived from different phases of tumor motion in reducing the negative effects of artifacts and improving the accuracy of template matching methods. Methods: Data from 2 patients with large tumors and significant tumor deformation were analyzed from a group of 12 patients from an earlier study. Cine-MRI (200 frames) imaging was performed while the patients were instructed to breathe normally. Ground truth tumor position was established on each frame manually by a radiation oncologist. Tumor positions were also automatically determined using template matching with either single or multiple (5) templates. The tracking errors, defined as the absolute differences in tumor positions determined by the manual and automated methods, when using either single or multiple templates were compared in both the AP and SI directions, respectively. Results: Using multiple templates reduced the tracking error of template matching. In the SI direction where the tumor movement and deformation were significant, the mean tracking error decreased from 1.94 mm to 0.91 mm (Patient 1) and from 6.61 mm to 2.06 mm (Patient 2). In the AP direction where the tumor movement was small, the reduction of the mean tracking error was significant in Patient 1 (from 3.36 mm to 1.04 mm), but not in Patient 2 ( from 3.86 mm to 3.80 mm). Conclusion: This study shows the effectiveness of using multiple templates in improving the performance of template matching when artifacts like large tumor deformation or out-of-plane motion exists. Accurate tumor tracking capabilities can be integrated with MRI guided radiation therapy systems. This work was supported in part by grants from NIH/NCI CA 124766 and Varian
Wu Shaofeng; Ge Xianhui; Yang Guohong; Wang Bin
2010-02-15
Motivated by the analogy between the spacetime and the solid with inhomogeneous elasticity modulus, we present an alternative method to obtain the field equation of any diffeomorphism-invariant gravity, by extremizing the constructed entropy function of the displacement vector field of spacetime solid. In general stationary spacetimes, we show that the Wald entropy of horizon arises from the on-shell entropy function of spacetime solid.
New phases of D greater than or equal to 2 current and diffeomorphism algebras in particle physics
NASA Astrophysics Data System (ADS)
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 greater than or equal to 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.
NASA Astrophysics Data System (ADS)
van der Hilst, R. D.; Huang, H.; Yao, H.
2010-12-01
delineate the 3-D anisotropic structure of the crust and lithospheric mantle at length scales as small as 100 km beneath SE Asia. These inversions revealed (i) the presence of intra-crustal low velocity zones (perhaps bounded by major faults), (ii) a strong correlation between these low velocity zones and radial anisotropy (Vsh faster than Vsv), and (iii) that the pattern of crustal (azimuthal) anisotropy is quite different from that in the deep crust and mantle lithosphere. Furthermore, the spatial relationship with high heat flow, high (electrical) conductivity, and high Poisson’s ratio’s suggests that the crustal zones of low shear velocity are mechanically weak. Collectively, these inferences suggest that deformation is generally not vertically coherent and that (horizontal) ductile flow occurs (at least locally) in the deep crust of SE Tibet. Deformation of the lithosphere in SE Tibet may thus occur through interaction of geological units with and without crustal flow that are separated by major faults.
Appearance and incomplete label matching for diffeomorphic template based hippocampus segmentation.
Pluta, John; Avants, Brian B; Glynn, Simon; Awate, Suyash; Gee, James C; Detre, John A
2009-06-01
We present a robust, high-throughput, semiautomated template-based protocol for segmenting the hippocampus in temporal lobe epilepsy. The semiautomated component of this approach, which minimizes user effort while maximizing the benefit of human input to the algorithm, relies on "incomplete labeling." Incomplete labeling requires the user to quickly and approximately segment a few key regions of the hippocampus through a user-interface. Subsequently, this partial labeling of the hippocampus is combined with image similarity terms to guide volumetric diffeomorphic normalization between an individual brain and an unbiased disease-specific template, with fully labeled hippocampi. We solve this many-to-few and few-to-many matching problem, and gain robustness to inter and intrarater variability and small errors in user labeling, by embedding the template-based normalization within a probabilistic framework that examines both label geometry and appearance data at each label. We evaluate the reliability of this framework with respect to manual labeling and show that it increases minimum performance levels relative to fully automated approaches and provides high inter-rater reliability. Thus, this approach does not require expert neuroanatomical training and is viable for high-throughput studies of both the normal and the highly atrophic hippocampus.
Clouthier, Allison L; Hosseini, Hadi S; Maquer, Ghislain; Zysset, Philippe K
2015-06-01
Vertebral compression fractures are becoming increasingly common. Patient-specific nonlinear finite element (FE) models have shown promise in predicting yield strength and damage pattern but have not been experimentally validated for clinically relevant vertebral fractures, which involve loading through intervertebral discs with varying degrees of degeneration up to large compressive strains. Therefore, stepwise axial compression was applied in vitro on segments and performed in silico on their FE equivalents using a nonlocal damage-plastic model including densification at large compression for bone and a time-independent hyperelastic model for the disc. The ability of the nonlinear FE models to predict the failure pattern in large compression was evaluated for three boundary conditions: healthy and degenerated intervertebral discs and embedded endplates. Bone compaction and fracture patterns were predicted using the local volume change as an indicator and the best correspondence was obtained for the healthy intervertebral discs. These preliminary results show that nonlinear finite element models enable prediction of bone localisation and compaction. To the best of our knowledge, this is the first study to predict the collapse of osteoporotic vertebral bodies up to large compression using realistic loading via the intervertebral discs.
Li, Yan; Zeng, Changchun
2016-04-13
A novel compressed carbon dioxide assisted fabrication method is demonstrated to produce auxetic PU foam. Auxetic PU foams can be fabricated at room temperature (25°C) in several seconds with compressed CO2. This technology overcomes some key challenging issues in the large-scale production of auxetic PU foams.
NASA Astrophysics Data System (ADS)
Karimi, Saman; Dombard, Andrew J.
2016-09-01
The asteroid Vesta, located within the inner asteroid belt, is a differentiated body with a prominent rotational bulge. NASA's Dawn mission revealed the presence of two large, relatively shallow impact craters in the south polar region, one with a high-standing central peak. The shallowness and prominent central peak are reminiscent of large craters on some icy satellites that may have experienced strong topographic relaxation. The location of these basins near the south pole is also unusual and suggests true polar wander, which requires relaxation of the rotational bulge. Thus, we use the finite element method and a viscoelastic rheology to examine the feasibility of relaxation processes operating on Vesta. Given the plausible thermal state of Vesta by the decay of long-lived radioactive elements, we find that the lithosphere is not compliant enough to allow strong relaxation of the large south polar craters, and thus the peculiar morphology is possibly a product of the formation of these large basins at a planetary scale. Additionally, the asteroid has not been warm enough to permit the relaxation of the rotational bulge. Consequently, these craters both happened to form near the south pole, as unlikely as that is.
Mourad, Hashem Mourad; Bronkhorst, Curt Allan; Livescu, Veronica; Plohr, JeeYeon Nam; Cerreta, Ellen Kathleen
2016-09-23
This study describes a theoretical and computational framework for the treatment of adiabatic shear band formation in rate-sensitive polycrystalline metallic materials. From a computational perspective, accurate representation of strain localization behavior has been a long-standing challenge. In addition, the underlying physical mechanisms leading to the localization of plastic deformation are still not fully understood. The proposed framework is built around an enhanced-strain finite element formulation, designed to alleviate numerical pathologies known to arise in localization problems, by allowing a localization band of given finite width (weak discontinuity) to be embedded within individual elements. The mechanical threshold strength (MTS) model is used to represent the temperature and strain rate-dependent viscoplastic response of the material. This classical flow stress model employs an internal state variable to quantify the effect of dislocation structure evolution (work hardening and recovery). In light of growing evidence suggesting that the softening effect of dynamic recrystallization may play a significant role, alongside thermal softening, in the process of shear band formation and growth, a simple dynamic recrystallization model is proposed and cast within the context of the MTS model with the aid of the aforementioned internal state variable. An initiation criterion for shear localization in rate and temperature-sensitive materials is introduced and used in the present context of high-rate loading, where material rate-dependence is pronounced and substantial temperature increases are achieved due to the dissipative nature of viscoplastic processes. In addition, explicit time integration is adopted to facilitate treatment of the dynamic problems under consideration, where strain rates in excess of 10^{4} s^{–1} are typically attained. Two series of experiments are conducted on AISI 316L stainless steel, employing the commonly used
Mourad, Hashem Mourad; Bronkhorst, Curt Allan; Livescu, Veronica; ...
2016-09-23
This study describes a theoretical and computational framework for the treatment of adiabatic shear band formation in rate-sensitive polycrystalline metallic materials. From a computational perspective, accurate representation of strain localization behavior has been a long-standing challenge. In addition, the underlying physical mechanisms leading to the localization of plastic deformation are still not fully understood. The proposed framework is built around an enhanced-strain finite element formulation, designed to alleviate numerical pathologies known to arise in localization problems, by allowing a localization band of given finite width (weak discontinuity) to be embedded within individual elements. The mechanical threshold strength (MTS) model ismore » used to represent the temperature and strain rate-dependent viscoplastic response of the material. This classical flow stress model employs an internal state variable to quantify the effect of dislocation structure evolution (work hardening and recovery). In light of growing evidence suggesting that the softening effect of dynamic recrystallization may play a significant role, alongside thermal softening, in the process of shear band formation and growth, a simple dynamic recrystallization model is proposed and cast within the context of the MTS model with the aid of the aforementioned internal state variable. An initiation criterion for shear localization in rate and temperature-sensitive materials is introduced and used in the present context of high-rate loading, where material rate-dependence is pronounced and substantial temperature increases are achieved due to the dissipative nature of viscoplastic processes. In addition, explicit time integration is adopted to facilitate treatment of the dynamic problems under consideration, where strain rates in excess of 104 s–1 are typically attained. Two series of experiments are conducted on AISI 316L stainless steel, employing the commonly used top-hat sample
Double metric, generalized metric, and α' -deformed double field theory
NASA Astrophysics Data System (ADS)
Hohm, Olaf; Zwiebach, Barton
2016-03-01
We relate the unconstrained "double metric" of the "α' -geometry" formulation of double field theory to the constrained generalized metric encoding the spacetime metric and b -field. This is achieved by integrating out auxiliary field components of the double metric in an iterative procedure that induces an infinite number of higher-derivative corrections. As an application, we prove that, to first order in α' and to all orders in fields, the deformed gauge transformations are Green-Schwarz-deformed diffeomorphisms. We also prove that to first order in α' the spacetime action encodes precisely the Green-Schwarz deformation with Chern-Simons forms based on the torsionless gravitational connection. This seems to be in tension with suggestions in the literature that T-duality requires a torsionful connection, but we explain that these assertions are ambiguous since actions that use different connections are related by field redefinitions.
NASA Astrophysics Data System (ADS)
Sargeant, B.; Robson, S.; Szigeti, E.; Richardson, P.; El-Nounu, A.; Rafla, M.
2016-06-01
When using any optical measurement system one important factor to consider is the placement of the sensors in relation to the workpiece being measured. When making decisions on sensor placement compromises are necessary in selecting the best placement based on the shape and size of the object of interest and the desired resolution and accuracy. One such compromise is in the distance the sensors are placed from the measurement surface, where a smaller distance gives a higher spatial resolution and local accuracy and a greater distance reduces the number of measurements necessary to cover a large area reducing the build-up of errors between measurements and increasing global accuracy. This paper proposes a photogrammetric approach whereby a number of sensors on a continuously flexible mobile platform are used to obtain local measurements while the position of the sensors is determined by a 6DoF tracking solution and the results combined to give a single set of measurement data within a continuous global coordinate system. The ability of this approach to achieve both high accuracy measurement and give results over a large volume is then tested and areas of weakness to be improved upon are identified.
NASA Technical Reports Server (NTRS)
Scott, T.; Kohlstedt, D. L.
2004-01-01
One key constraint needed for refinement of the interior geochemical and geodynamic models of Io is the viscosity of the convecting partially- molten silicate mantle. To date, laboratory studies of partially molten mantle rocks have reached melt fractions up to approx.0.12, a value much smaller than thought to be appropriate for the asthenosphere of Io where the degree of partial melting may be 0.15 0.40 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 1473 to 1573 K in order to understand the influence of large amounts of melt (0.15 < phi < 0.40) on the rheological behavior of partially molten rocks.
NASA Astrophysics Data System (ADS)
Van Mieghem, Bart; Ivens, Jan; Van Bael, Albert
2017-04-01
A problem that arises when performing stereo digital image correlation in applications with large out-of-plane displacements is that the images may become unfocused. This unfocusing could result in correlation instabilities or inaccuracies. When performing DIC measurements and expecting large out-of-plane displacements researchers either trust on their experience or use the equations from photography to estimate the parameters affecting the depth of field (DOF) of the camera. A limitation of the latter approach is that the definition of sharpness is a human defined parameter and that it does not reflect the performance of the digital image correlation system. To get a more representative DOF value for DIC applications, a standardised testing method is presented here, making use of real camera and lens combinations as well as actual image correlation results. The method is based on experimental single camera DIC measurements of a backwards moving target. Correlation results from focused and unfocused images are compared and a threshold value defines whether or not the correlation results are acceptable even if the images are (slightly) unfocused. By following the proposed approach, the complete DOF of a specific camera/lens combination as function of the aperture setting and distance from the camera to the target can be defined. The comparison between the theoretical and the experimental DOF results shows that the achievable DOF for DIC applications is larger than what theoretical calculations predict. Practically this means that the cameras can be positioned closer to the target than what is expected from the theoretical approach. This leads to a gain in resolution and measurement accuracy.
NASA Astrophysics Data System (ADS)
Wilms, M.; Werner, R.; Ehrhardt, J.; Schmidt-Richberg, A.; Schlemmer, H.-P.; Handels, H.
2014-03-01
Breathing-induced location uncertainties of internal structures are still a relevant issue in the radiation therapy of thoracic and abdominal tumours. Motion compensation approaches like gating or tumour tracking are usually driven by low-dimensional breathing signals, which are acquired in real-time during the treatment. These signals are only surrogates of the internal motion of target structures and organs at risk, and, consequently, appropriate models are needed to establish correspondence between the acquired signals and the sought internal motion patterns. In this work, we present a diffeomorphic framework for correspondence modelling based on the Log-Euclidean framework and multivariate regression. Within the framework, we systematically compare standard and subspace regression approaches (principal component regression, partial least squares, canonical correlation analysis) for different types of common breathing signals (1D: spirometry, abdominal belt, diaphragm tracking; multi-dimensional: skin surface tracking). Experiments are based on 4D CT and 4D MRI data sets and cover intra- and inter-cycle as well as intra- and inter-session motion variations. Only small differences in internal motion estimation accuracy are observed between the 1D surrogates. Increasing the surrogate dimensionality, however, improved the accuracy significantly; this is shown for both 2D signals, which consist of a common 1D signal and its time derivative, and high-dimensional signals containing the motion of many skin surface points. Eventually, comparing the standard and subspace regression variants when applied to the high-dimensional breathing signals, only small differences in terms of motion estimation accuracy are found.
NASA Astrophysics Data System (ADS)
Svartsjaern, M.; Saiang, D.; Nordlund, E.; Eitzenberger, A.
2016-03-01
Over the last 30 years, the Kiirunavaara mine has experienced a slow but progressive fracturing and movement in the footwall rock mass, which is directly related to the sublevel caving (SLC) method utilized by Luossavaara-Kiirunavaara Aktiebolag (LKAB). As part of an ongoing work, this paper focuses on describing and explaining a likely evolution path of large-scale fracturing in the Kiirunavaara footwall. The trace of this fracturing was based on a series of damage mapping campaigns carried out over the last 2 years, accompanied by numerical modeling. Data collected from the damage mapping between mine levels 320 and 907 m was used to create a 3D surface representing a conceptual boundary for the extent of the damaged volume. The extent boundary surface was used as the basis for calibrating conceptual numerical models created in UDEC. The mapping data, in combination with the numerical models, indicated a plausible evolution path of the footwall fracturing that was subsequently described. Between levels 320 and 740 m, the extent of fracturing into the footwall appears to be controlled by natural pre-existing discontinuities, while below 740 m, there are indications of a curved shear or step-path failure. The step-path is hypothesized to be activated by rock mass heave into the SLC zone above the current extraction level. Above the 320 m level, the fracturing seems to intersect a subvertical structure that daylights in the old open pit slope. Identification of these probable damage mechanisms was an important step in order to determine the requirements for a monitoring system for tracking footwall damage. This paper describes the background work for the design of the system currently being installed.
NASA Astrophysics Data System (ADS)
Aldaya, V.; Navarro-Salas, J.
1991-04-01
We introduce a highest weight type representation of the Rovelli-Smolin algebra of loop observables for quantum gravity. In terms of this representation, new solutions of the hamiltonian and diffeomorphism constraints are given. Assuming the locality of the quantum hamiltonian constraint we show that any functional depending on the generalized link class of the disjoint union of arbitrary simple loops is a solution. Finally we argue that this is the general solution in the irreducible representation space. On leave of absence from the Departamento de Fisica Teorica, Universidad de Valencia, and IFIC, Centro Mixto Universidad de Valencia - CSIC, Burjassot, Spain.
Piella, Gemma; De Craene, Mathieu; Butakoff, Constantine; Grau, Vicente; Yao, Cheng; Nedjati-Gilani, Shahrum; Penney, Graeme P; Frangi, Alejandro F
2013-04-01
This paper presents a new registration framework for quantifying myocardial motion and strain from the combination of multiple 3D ultrasound (US) sequences. The originality of our approach lies in the estimation of the transformation directly from the input multiple views rather than from a single view or a reconstructed compounded sequence. This allows us to exploit all spatiotemporal information available in the input views avoiding occlusions and image fusion errors that could lead to some inconsistencies in the motion quantification result. We propose a multiview diffeomorphic registration strategy that enforces smoothness and consistency in the spatiotemporal domain by modeling the 4D velocity field continuously in space and time. This 4D continuous representation considers 3D US sequences as a whole, therefore allowing to robustly cope with variations in heart rate resulting in different number of images acquired per cardiac cycle for different views. This contributes to the robustness gained by solving for a single transformation from all input sequences. The similarity metric takes into account the physics of US images and uses a weighting scheme to balance the contribution of the different views. It includes a comparison both between consecutive images and between a reference and each of the following images. The strain tensor is computed locally using the spatial derivatives of the reconstructed displacement fields. Registration and strain accuracy were evaluated on synthetic 3D US sequences with known ground truth. Experiments were also conducted on multiview 3D datasets of 8 volunteers and 1 patient treated by cardiac resynchronization therapy. Strain curves obtained from our multiview approach were compared to the single-view case, as well as with other multiview approaches. For healthy cases, the inclusion of several views improved the consistency of the strain curves and reduced the number of segments where a non-physiological strain pattern was
Zhang, Zhiqun; Kong, Zhuqing; Zhu, Miao; Lu, Wenxiang; Ni, Lei; Bai, Yunfei; Lou, Yue
2016-10-01
The aim of this study was to characterize a previously uncharacterized genetic disorder associated with equinus deformity in a large Chinese family at the genetic level. Blood samples were obtained and whole genome sequencing was performed. Differential gene variants were identified and potential impacts on protein structure were predicted. Based on the control sample, several diseases associated variants were identified and selected for further validation. One of the potential variants identified was a ANXA3 gene [chr4, c.C820T(p.R274*)] variant. Further bioinformatic analysis showed that the observed mutation could lead to a three-dimensional conformational change. Moreover, a MTHFR variant that is different from variants associated with clubfoot was also identified. Bioinformatic analysis showed that this mutation could alter the protein binding region. These findings imply that this uncharacterized genetic disorder is not clubfoot, despite sharing some similar symptoms. Furthermore, specific CNV profiles were identified in association with the diseased samples, thus further speaking to the complexity of this multigenerational disorder. This study examined a previously uncharacterized genetic disorder appearing similar to clubfoot and yet having distinct features. Following whole genome sequencing and comparative analysis, several differential gene variants were identified to enable a further distinction from clubfoot. It is hoped that these findings will provide further insight into this disorder and other similar disorders.
Mid-space-independent deformable image registration.
Aganj, Iman; Iglesias, Juan Eugenio; Reuter, Martin; Sabuncu, Mert Rory; Fischl, Bruce
2017-02-24
Aligning images in a mid-space is a common approach to ensuring that deformable image registration is symmetric - that it does not depend on the arbitrary ordering of the input images. The results are, however, generally dependent on the mathematical definition of the mid-space. In particular, the set of possible solutions is typically restricted by the constraints that are enforced on the transformations to prevent the mid-space from drifting too far from the native image spaces. The use of an implicit atlas has been proposed as an approach to mid-space image registration. In this work, we show that when the atlas is aligned to each image in the native image space, the data term of implicit-atlas-based deformable registration is inherently independent of the mid-space. In addition, we show that the regularization term can be reformulated independently of the mid-space as well. We derive a new symmetric cost function that only depends on the transformation morphing the images to each other, rather than to the atlas. This eliminates the need for anti-drift constraints, thereby expanding the space of allowable deformations. We provide an implementation scheme for the proposed framework, and validate it through diffeomorphic registration experiments on brain magnetic resonance images.
Commutative deformations of general relativity: nonlocality, causality, and dark matter
NASA Astrophysics Data System (ADS)
de Vegvar, P. G. N.
2017-01-01
Hopf algebra methods are applied to study Drinfeld twists of (3+1)-diffeomorphisms and deformed general relativity on commutative manifolds. A classical nonlocality length scale is produced above which microcausality emerges. Matter fields are utilized to generate self-consistent Abelian Drinfeld twists in a background independent manner and their continuous and discrete symmetries are examined. There is negligible experimental effect on the standard model of particles. While baryonic twist producing matter would begin to behave acausally for rest masses above {˜ }1-10 TeV, other possibilities are viable dark matter candidates or a right-handed neutrino. First order deformed Maxwell equations are derived and yield immeasurably small cosmological dispersion and produce a propagation horizon only for photons at or above Planck energies. This model incorporates dark matter without any appeal to extra dimensions, supersymmetry, strings, grand unified theories, mirror worlds, or modifications of Newtonian dynamics.
NASA Astrophysics Data System (ADS)
Han, Yuefeng; Weinbaum, Sheldon; Spaan, Jos A. E.; Vink, Hans
2006-05-01
There is wide interest in the role of the endothelial surface layer (ESL) in transmitting blood shear stress to the intracellular cytoskeleton of the endothelial cell. However, very little is known about the mechanical properties of the glycocalyx or the flexural rigidity of the core proteins that comprise it. Vink, Duling & Spaan (FASEB J., vol. 13, 1999, p. A 11) measured the time-dependent restoration of the ESL after it had been nearly completely compressed by the passage of a white blood cell (WBC) in a tightly fitting capillary. Using this initial experiment, Weinbaum et al. (Proc. Natl. Acad. Sci. USA, vol. 100, 2003, p. 7988) predicted that the core proteins have a flexural rigidity EI of 700 pN nm(2) , which is ˜1/20 the measured value for an actin filament. However, their analysis assumes small deflections and only the fibre motion is considered. In the present paper we report additional experiments and apply large-deformation theory for ‘elastica’ to describe the restoration of the fibres in a Brinkman medium which absorbs fluid as the ESL expands. We find that there are two phases in the fibre recoil: an initial phase for large compressions where the ESL thickness is <0.36 its undisturbed thickness, and the ends of the fibres overlap and are parallel to the capillary wall; and a second phase where the fibres assume a shape that is close to the solutions for an elastic bar with linearly distributed vertical loading. The predicted time-dependent change in thickness of the ESL provides remarkably good agreement with experiment and yields an estimate of 490 pN nm(2) for the flexural rigidity EI of the core protein fibres, which is unexpectedly close to that predicted by the linear theory in Weinbaum et al. (2003).
NASA Astrophysics Data System (ADS)
Guerricchio, A.; Simeone, V.
2012-04-01
Deep seated gravitational slope deformations (DSGSD) characterize the north west and south side of Mount Poro headland, mid Calabria, south Italy, as reported by Guerrichio (2000). This work investigates the DSGSD of Mount Poro headland, in particular the gravitational collapses, occurring between the coast and the western flank of the headland up to an elevation of about 500-600 m AMSL. These collapses seem to be inconsistent with the local lithotypes, made by the substratum of granitic complex of Polia-Copanello. In particular, Ietto and Calcaterra (1988) identified DSGSDs in the area of Zaccanopoli. They assumed these phenomena on the edge between post-uplift gravitative tectonics and deep seated gravitational deformations that were referred to morphologies sub-parallel to the banks of two important local rivers. The local geology comprises severely fractured and sometimes cataclastic granitic rocks. These show deep sub-vertical fracture, bow-shaped and oriented along the direction NNE-SSW in the upstream areas, at an elevation between 500 and 600 m AMSL. For those areas on the right side of the headland, fractures are oriented along NE-SW, N-S and NW-SE, while on the left side of the headland fractures are oriented W-E and NW-SE. In the upstream areas, there are frequent depressed and stretched stripes of land, which are crossed by fractures, which affect granitic masses for a difference of elevation ranging between few tens of meters and one hundred meters. Similar differences of elevation can also be observed either inside the DSGSDs, and the large landslides, like that located immediately upstream Dropia town, where for instance a one hundred meters concave scarp shows. Inside the DSGSDs and inside the topping Pleistocenic deposits, there are frequent twofold terraces, which can be hardly dated. In fact, no fossils are present, and then it is possible to assume their age just on a geomorphologic base. The entire area involved by the DSGSD is few tens of
A Stochastic Approach to Diffeomorphic Point Set Registration With Landmark Constraints
Kolesov, Ivan; Lee, Jehoon; Sharp, Gregory; Vela, Patricio; Tannenbaum, Allen
2016-01-01
This work presents a deformable point set registration algorithm that seeks an optimal set of radial basis functions to describe the registration. A novel, global optimization approach is introduced composed of simulated annealing with a particle filter based generator function to perform the registration. It is shown how constraints can be incorporated into this framework. A constraint on the deformation is enforced whose role is to ensure physically meaningful fields (i.e., invertible). Further, examples in which landmark constraints serve to guide the registration are shown. Results on 2D and 3D data demonstrate the algorithm’s robustness to noise and missing information. PMID:26761731
NASA Astrophysics Data System (ADS)
Baumberger, R.; Wehrens, Ph.; Herwegh, M.
2012-04-01
Allowing deep insight into the formation history of a rock complex, shear zones, faults and joint systems represent important sources of geological information. The granitic rocks of the Haslital valley (Switzerland) show very good outcrop conditions to study these mechanical anisotropies. Furthermore, they permit a quantitative characterisation of the above-mentioned deformation structures on the large-scale, in terms of their 3D orientation, 3D spatial distribution, kinematics and evolution in 3D. A key problem while developing valid geological 3D models is the three-dimensional spatial distribution of geological structures, particularly with increasing distance from the surface. That is especially true in regions, where only little or even no "hard" underground data (e.g. bore holes, tunnel mappings and seismics) is available. In the study area, many subsurface data are available (e.g. cross sections, tunnel and pipeline mappings, bore holes etc.). Therefore, two methods dealing with the problems mentioned are developed: (1) A data acquisition, processing and visualisation method, (2) A methodology to improve the reliability of 3D models regarding the spatial trend of geological structures with increasing depth: 1) Using aerial photographs and a high-resolution digital elevation model, a GIS-based remote-sensing structural map of large-scale structural elements (shear zones, faults) of the study area was elaborated. Based on that lineament map, (i) a shear zone map was derived and (ii) a geostatistical analysis was applied to identify sub regions applicable for serving as field areas to test the methodology presented above. During fieldwork, the shear zone map was evaluated by verifying the occurrence and spatial distribution of the structures designated by remote sensing. Additionally, the geometry of the structures (e.g. 3D orientation, width, kinematics) was characterised and parameterised accordingly. These tasks were partially done using a GPS based Slate
Principles of rock deformation
Nicolas, A.
1987-01-01
This text focuses on the recent achievements in the analysis of rock deformation. It gives an analytical presentation of the essential structures in terms of kinetic and dynamic interpretation. The physical properties underlying the interpretation of rock structures are exposed in simple terms. Emphasized in the book are: the role of fluids in rock fracturing; the kinematic analysis of magnetic flow structures; the application of crystalline plasticity to the kinematic and dynamic analysis of the large deformation imprinted in many metamorphic rocks.
Stoica, Mihai Scudino, Sergio; Bednarčik, Jozef; Kaban, Ivan; Eckert, Jürgen
2014-02-07
By adding 0.5 at. % Cu to the strong but brittle [(Fe{sub 0.5}Co{sub 0.5}){sub 0.75}Si{sub 0.05}B{sub 0.20}]{sub 96}Nb{sub 4} bulk metallic glass, fully amorphous rods with diameters up to 2 mm were obtained. The monolithic samples with 1 mm diameter revealed a fracture strain of 3.80% and a maximum stress of 4143 MPa upon compression, together with a slight work-hardening behavior. SEM micrographs of fractured samples did neither reveal any shear bands on the lateral surface nor the typical vein patterns which characterize ductile fracture. However, some layers appear to have flowed and this phenomenon took place before the brittle final fracture. An estimate of the temperature rise ΔT in the shear plane gives 1039 K, which is large enough to melt a layer of 120 nm. The overall performance and the macroscopic plastic strain depend on the interaction between cleavage-like and viscous flow-like features. Mechanical tests performed in-situ under synchrotron radiation allowed the calculation of the strain tensor components, using the reciprocal-space data and analyzing the shift of the first (the main) and the second broad peak positions in the X-ray diffraction patterns. The results revealed that each atomic shell may have a different stiffness, which may explain the macroscopic compressive plastic deformation. Also, there were no signs of (nano) crystallization induced by the applied stress, but the samples preserve a monolithic amorphous structure until catastrophic failure occurs.
NASA Astrophysics Data System (ADS)
Milliner, C. W. D.; Dolan, J. F.; Hollingsworth, J.; Leprince, S.; Ayoub, F.
2014-12-01
Coseismic surface deformation is typically measured in the field by geologists and with a range of geophysical methods such as InSAR, LiDAR and GPS. Current methods, however, either fail to capture the near-field coseismic surface deformation pattern where vital information is needed, or lack pre-event data. We develop a standardized and reproducible methodology to fully constrain the surface, near-field, coseismic deformation pattern in high resolution using aerial photography. We apply our methodology using the program COSI-corr to successfully cross-correlate pairs of aerial, optical imagery before and after the 1992, Mw 7.3 Landers and 1999, Mw 7.1 Hector Mine earthquakes. This technique allows measurement of the coseismic slip distribution and magnitude and width of off-fault deformation with sub-pixel precision. This technique can be applied in a cost effective manner for recent and historic earthquakes using archive aerial imagery. We also use synthetic tests to constrain and correct for the bias imposed on the result due to use of a sliding window during correlation. Correcting for artificial smearing of the tectonic signal allows us to robustly measure the fault zone width along a surface rupture. Furthermore, the synthetic tests have constrained for the first time the measurement precision and accuracy of estimated fault displacements and fault-zone width. Our methodology provides the unique ability to robustly understand the kinematics of surface faulting while at the same time accounting for both off-fault deformation and measurement biases that typically complicates such data. For both earthquakes we find that our displacement measurements derived from cross-correlation are systematically larger than the field displacement measurements, indicating the presence of off-fault deformation. We show that the Landers and Hector Mine earthquake accommodated 46% and 38% of displacement away from the main primary rupture as off-fault deformation, over a mean
NASA Astrophysics Data System (ADS)
Setare, M. R.; Adami, H.
2016-08-01
The Chern-Simons-like theories of gravity (CSLTG) are formulated at first order formalism. In this formalism, the derivation of the entropy of a black hole on bifurcation surface, as a quasi-local conserved charge is problematic. In this paper we overcome these problems by considering the concept of total variation and the Lorentz-Lie derivative. We firstly find an expression for the ADT conserved current in the context of the CSLTG which is based on the concept of the Killing vector fields. Then, we generalize it to be conserved for all diffeomorphism generators. Thus, we can extract an off-shell conserved charge for any vector field which generates a diffeomorphism. The formalism presented here is based on the concept of quasi-local conserved charges which are off-shell. The charges can be calculated on any codimension two space-like surface surrounding a black hole and the results are independent of the chosen surface. By using the off-shell quasi-local conserved charge, we investigate the Virasoro algebra and find a formula to calculate the central extension term. We apply the formalism to the BTZ black hole solution in the context of the Einstein gravity and the Generalized massive gravity, then we find the eigenvalues of their Virasoro generators as well as the corresponding central charges. Eventually, we calculate the entropy of the BTZ black hole by the Cardy formula and we show that the result exactly matches the one obtained by the concept of the off-shell conserved charges.
Bunnell, W P
1986-12-01
Spinal deformity is a relatively common disorder, particularly in teenage girls. Early detection is possible by a simple, quick visual inspection that should be a standard part of the routine examination of all preteen and teenage patients. Follow-up observation will reveal those curvatures that are progressive and permit orthotic treatment to prevent further increase in the deformity. Spinal fusion offers correction and stabilization of more severe degrees of scoliosis.
NASA Astrophysics Data System (ADS)
Guerrero, Jesús; Gutiérrez, Francisco; Galve, Jorge P.
2013-08-01
excavations excavated in the bottom of some depressions and the correlation between the altitudinal distribution of these basins and that of the glauberite-rich unit reveal that subsidence related to interstratal glauberite karstification is the main process involved in their genesis. This research ascribes for the first time the thickenings and deformation of specific terrace levels and pediment levels and the development of large karstic depressions to interstratal karstification of exceptionally thick glauberite units.
Peroni, M; Golland, P; Sharp, G C; Baroni, G
2016-02-01
A crucial issue in deformable image registration is achieving a robust registration algorithm at a reasonable computational cost. Given the iterative nature of the optimization procedure an algorithm must automatically detect convergence, and stop the iterative process when most appropriate. This paper ranks the performances of three stopping criteria and six stopping value computation strategies for a Log-Domain Demons Deformable registration method simulating both a coarse and a fine registration. The analyzed stopping criteria are: (a) velocity field update magnitude, (b) mean squared error, and (c) harmonic energy. Each stoping condition is formulated so that the user defines a threshold ∊, which quantifies the residual error that is acceptable for the particular problem and calculation strategy. In this work, we did not aim at assigning a value to e, but to give insights in how to evaluate and to set the threshold on a given exit strategy in a very popular registration scheme. Experiments on phantom and patient data demonstrate that comparing the optimization metric minimum over the most recent three iterations with the minimum over the fourth to sixth most recent iterations can be an appropriate algorithm stopping strategy. The harmonic energy was found to provide best trade-off between robustness and speed of convergence for the analyzed registration method at coarse registration, but was outperformed by mean squared error when all the original pixel information is used. This suggests the need of developing mathematically sound new convergence criteria in which both image and vector field information could be used to detect the actual convergence, which could be especially useful when considering multi-resolution registrations. Further work should be also dedicated to study same strategies performances in other deformable registration methods and body districts.
Micromachined, Electrostatically Deformable Reflectors
NASA Technical Reports Server (NTRS)
Bartman, Randall K.; Wang, Paul K. C.; Miller, Linda M.; Kenny, Thomas W.; Kaiser, William J.; Hadaegh, Fred Y.; Agronin, Michael L.
1995-01-01
Micromachined, closed-loop, electrostatically actuated reflectors (microCLEARs) provide relatively simple and inexpensive alternatives to large, complex, expensive adaptive optics used to control wavefronts of beams of light in astronomy and in experimental laser weapons. Micromachining used to make deformable mirror, supporting structure, and actuation circuitry. Development of microCLEARs may not only overcome some of disadvantages and limitations of older adaptive optics but may also satisfy demands of potential market for small, inexpensive deformable mirrors in electronically controlled film cameras, video cameras, and other commercial optoelectronic instruments.
NASA Astrophysics Data System (ADS)
Márton, Emö; Tokarski, Antek K.
2016-04-01
The paleomagnetic and magnetic anisotropy results interpreted in this presentation in terms of tectonics were obtained on the fine grained members, mostly mudstones/claystones, of the flysch from the Magura, the Silesian and the Dukla rootless nappes. The results are the best from the Upper Oligocene Krosno beds, which were affected by compression soon after deposition. These beds were available for sampling in the Silesian and Dukla nappes, but absent in the Magura nappe. Thus, in the latter older Paleogene strata were tested. A common feature of all sampled sediments is the low susceptibility (in the range of 10-4 SI or lower), weak remanence and the presence of pyrite. AMS measurements point to quite strong and probably repeated deformation in the Magura nappe, and the remanence is of-post-folding age. The AMS of the Silesian and Dukla nappes indicate weaker deformation, the orientations of the AMS lineations reflect compression. The remanence is of pre-folding age in the western and central segments of the Silesian nappe and is a mixture of pre and post-folding magnetization in the eastern segment. All the so far mentioned areas must have been affected by about 60° CCW rotation which followed the internal deformation. The Dukla nappe also rotated in the CCW sense, but the angle is far from well-defined. This can be attributed to the complicated internal structure of the nappe (e.g. presence of olistoliths) and non-removable overprint magnetizations. The relationship between local tectonic strikes and AMS lineations seems to imply that the ductile deformation responsible for the AMS lineations were acquired first, and the map-scale structures came into being during the CCW rotation of the studied segment of the nappe. AARM measurements documented that the fabrics of the ferrimagnetic minerals are often different from the orientation of the AMS fabrics. In such cases, they either fail to define an ellipsoid or the general orientations of the maxima are different
Deformation mechanisms in experimentally deformed Boom Clay
NASA Astrophysics Data System (ADS)
Desbois, Guillaume; Schuck, Bernhard; Urai, Janos
2016-04-01
Bulk mechanical and transport properties of reference claystones for deep disposal of radioactive waste have been investigated since many years but little is known about microscale deformation mechanisms because accessing the relevant microstructure in these soft, very fine-grained, low permeable and low porous materials remains difficult. Recent development of ion beam polishing methods to prepare high quality damage free surfaces for scanning electron microscope (SEM) is opening new fields of microstructural investigation in claystones towards a better understanding of the deformation behavior transitional between rocks and soils. We present results of Boom Clay deformed in a triaxial cell in a consolidated - undrained test at a confining pressure of 0.375 MPa (i.e. close to natural value), with σ1 perpendicular to the bedding. Experiments stopped at 20 % strain. As a first approximation, the plasticity of the sample can be described by a Mohr-Coulomb type failure envelope with a coefficient of cohesion C = 0.117 MPa and an internal friction angle ϕ = 18.7°. After deformation test, the bulk sample shows a shear zone at an angle of about 35° from the vertical with an offset of about 5 mm. We used the "Lamipeel" method that allows producing a permanent absolutely plane and large size etched micro relief-replica in order to localize and to document the shear zone at the scale of the deformed core. High-resolution imaging of microstructures was mostly done by using the BIB-SEM method on key-regions identified after the "Lamipeel" method. Detailed BIB-SEM investigations of shear zones show the following: the boundaries between the shear zone and the host rock are sharp, clay aggregates and clastic grains are strongly reoriented parallel to the shear direction, and the porosity is significantly reduced in the shear zone and the grain size is smaller in the shear zone than in the host rock but there is no evidence for broken grains. Comparison of microstructures
Singh, S; Modi, S; Bagga, D; Kaur, P; Shankar, L R; Khushu, S
2013-03-01
The present study aimed to investigate whether brain morphological differences exist between adult hypothyroid subjects and age-matched controls using voxel-based morphometry (VBM) with diffeomorphic anatomic registration via an exponentiated lie algebra algorithm (DARTEL) approach. High-resolution structural magnetic resonance images were taken in ten healthy controls and ten hypothyroid subjects. The analysis was conducted using statistical parametric mapping. The VBM study revealed a reduction in grey matter volume in the left postcentral gyrus and cerebellum of hypothyroid subjects compared to controls. A significant reduction in white matter volume was also found in the cerebellum, right inferior and middle frontal gyrus, right precentral gyrus, right inferior occipital gyrus and right temporal gyrus of hypothyroid patients compared to healthy controls. Moreover, no meaningful cluster for greater grey or white matter volume was obtained in hypothyroid subjects compared to controls. Our study is the first VBM study of hypothyroidism in an adult population and suggests that, compared to controls, this disorder is associated with differences in brain morphology in areas corresponding to known functional deficits in attention, language, motor speed, visuospatial processing and memory in hypothyroidism.
NASA Astrophysics Data System (ADS)
Cottle, John M.; Larson, Kyle P.; Kellett, Dawn A.
2015-09-01
The presence of hot, weak crust is a central component of recent hypotheses that seek to explain the evolution of continent-continent collisions, and in particular may play an important role in accommodating the >3000 km of convergence within the Himalaya-Tibetan collision over the last ∼55 Myr. Models that implicate flow of semi-viscous midcrustal rocks south toward the front of the Himalayan orogen, 'channel flow', are able to account for many geologic observations in the Himalaya, while alternative models of collision, particularly 'thrust-wedge taper', demonstrate that much of the observed geology could have formed in the absence of a low-viscosity mid-crustal layer. Several recent studies, synthesized here, have prompted a shift from initial assumptions that channel flow and thrust-wedge taper processes are by definition mutually exclusive. These new studies reveal the presence of several tectonometamorphic discontinuities in the midcrust that appear to reflect a continuum of deformation in which both channel- and wedge-type processes operate in spatially and temporally distinct domains within the orogen, and further, that the system may migrate back and forth between these types of behavior. This continuum of deformation styles within the collisional system is of crucial importance for explaining the evolution of the Himalayan orogen and, hence, for understanding the evolution of Earth's many continent-continent collision zones.
Advanced Curvature Deformable Mirrors
2010-09-01
designs using just a glass wafer and a wafer of Carbon Fiber Reinforced Polymer ( CFRP ). In both cases minimum bend radius decreases and the resonant... matrix is consequently nearly diagonal. The long actuators at the outer edge of the deformable mirror are largely outside the working pupil so their...formal reconstruction of the wave front either explicitly or implicitly in the control matrix . The WFS-DM combination is acting like an analog computer
Subleading soft photons and large gauge transformations
NASA Astrophysics Data System (ADS)
Campiglia, Miguel; Laddha, Alok
2016-11-01
Lysov, Pasterski and Strominger have shown how Low's subleading soft photon theorem can be understood as Ward identities of new symmetries of massless QED. In this paper we offer a different perspective and show that there exists a class of large U(1) gauge transformations such that (i) the associated (electric and magnetic) charges can be computed from first principles, (ii) their Ward identities are equivalent to Low's theorem. Our framework paves the way to analyze the sub-subleading theorem in gravity in terms of Ward identities associated to large diffeomorphisms.
NASA Astrophysics Data System (ADS)
Kim, Sang-Youn; Yeo, Myoung; Shin, Eun-Jae; Park, Won-Hyeong; Jang, Jong-Seok; Nam, Byeong-Uk; Bae, Jin Woo
2015-11-01
In this paper, we propose a variable focus microlens module based on a transparent, electroactive, and non-ionic PVC/DBA gel. A non-ionic PVC/DBA (nPVC) gel on an ITO glass was confined beneath a rigid annular electrode, and applied pressure squeezed a bulge of the nPVC gel into the annular electrode, resulting in a hemispherical plano-convex nPVC gel microlens. The proposed nPVC gel microlens was analyzed and optimized. When voltage is applied to the circular perimeter (the annular electrode) of this fabricated microlens, electrically induced creep deformation of the nPVC gel occurs, changing its optical focal length. The focal length remarkably increases from 3.8 mm up to 14.3 mm with increasing applied voltages from 300 V to 800 V. Due to its compact, transparent, and electroactive characteristics, the proposed nPVC gel microlens can be easily inserted into small consumer electronic devices, such as digital cameras, camcorders, cell phones, and other portable optical devices.
Videogrammetric Model Deformation Measurement Technique
NASA Technical Reports Server (NTRS)
Burner, A. W.; Liu, Tian-Shu
2001-01-01
The theory, methods, and applications of the videogrammetric model deformation (VMD) measurement technique used at NASA for wind tunnel testing are presented. The VMD technique, based on non-topographic photogrammetry, can determine static and dynamic aeroelastic deformation and attitude of a wind-tunnel model. Hardware of the system includes a video-rate CCD camera, a computer with an image acquisition frame grabber board, illumination lights, and retroreflective or painted targets on a wind tunnel model. Custom software includes routines for image acquisition, target-tracking/identification, target centroid calculation, camera calibration, and deformation calculations. Applications of the VMD technique at five large NASA wind tunnels are discussed.
Gholipour, Ali; Limperopoulos, Catherine; Clancy, Sean; Clouchoux, Cedric; Akhondi-Asl, Alireza; Estroff, Judy A; Warfield, Simon K
2014-01-01
The development and identification of best methods in fetal brain MRI analysis is crucial as we expect an outburst of studies on groupwise and longitudinal analysis of early brain development in the upcoming years. To address this critical need, in this paper, we have developed a mathematical framework for the construction of an unbiased deformable spatiotemporal atlas of the fetal brain MRI and compared it to alternative configurations in terms of similarity metrics and deformation models. Our contributions are twofold: first we suggest a novel approach to fetal brain spatiotemporal atlas construction that shows high capability in capturing anatomic variation between subjects; and second, within our atlas construction framework we evaluate and compare a set of plausible configurations for inter-subject fetal brain MRI registration and identify the most accurate approach that can potentially lead to most accurate results in population atlas construction, atlas-based segmentation, and group analysis. Our evaluation results indicate that symmetric diffeomorphic deformable registration with cross correlation similarity metric outperforms other configurations in this application and results in sharp unbiased atlases that can be used in fetal brain MRI analysis.
Cohen, Bruce E; Nicholson, Christopher W
2007-05-01
The bunionette, or tailor's bunion, is a lateral prominence of the fifth metatarsal head. Most commonly, bunionettes are the result of a widened 4-5 intermetatarsal angle with associated varus of the metatarsophalangeal joint. When symptomatic, these deformities often respond to nonsurgical treatment methods, such as wider shoes and padding techniques. When these methods are unsuccessful, surgical treatment is based on preoperative radiographs and associated lesions, such as hyperkeratoses. In rare situations, a simple lateral eminence resection is appropriate; however, the risk of recurrence or overresection is high with this technique. Patients with a lateral bow to the fifth metatarsal are treated with a distal chevron-type osteotomy. A widened 4-5 intermetatarsal angle often requires a diaphyseal osteotomy for correction.
Finite deformation analysis of geomaterials
NASA Astrophysics Data System (ADS)
Jeremi, Boris; Runesson, Kenneth; Sture, Stein
2001-07-01
The mathematical structure and numerical analysis of classical small deformation elasto-plasticity is generally well established. However, development of large deformation elastic-plastic numerical formulation for dilatant, pressure sensitive material models is still a research area.In this paper we present development of the finite element formulation and implementation for large deformation, elastic-plastic analysis of geomaterials. Our developments are based on the multiplicative decomposition of the deformation gradient into elastic and plastic parts. A consistent linearization of the right deformation tensor together with the Newton method at the constitutive and global levels leads toward an efficient and robust numerical algorithm. The presented numerical formulation is capable of accurately modelling dilatant, pressure sensitive isotropic and anisotropic geomaterials subjected to large deformations. In particular, the formulation is capable of simulating the behaviour of geomaterials in which eigentriads of stress and strain do not coincide during the loading process.The algorithm is tested in conjunction with the novel hyperelasto-plastic model termed the B material model, which is a single surface (single yield surface, affine single ultimate surface and affine single potential surface) model for dilatant, pressure sensitive, hardening and softening geomaterials. It is specifically developed to model large deformation hyperelasto-plastic problems in geomechanics.We present an application of this formulation to numerical analysis of low confinement tests on cohesionless granular soil specimens recently performed in a SPACEHAB module aboard the Space Shuttle during the STS-89 mission. We compare numerical modelling with test results and show the significance of added confinement by the thin hyperelastic latex membrane undergoing large stretching.
NASA Astrophysics Data System (ADS)
Kim, Jung Min; Gurnon, A. Kate; Wagner, Norman; Eberle, Aaron
2013-03-01
Large amplitude oscillatory shear (LAOS) rheology is an effective way of studying the nonlinear dynamics of complex fluids. Here, we present a new method for a direct, quantitative study of the microstructure under LAOS deformation in the framework of the alignment factor, Af. We use a model thermoreversible adhesive hard-sphere system composed of octadecyl-coated silica particles suspended in n-tetradecane. With temperature the particle potential is controlled and the system is shifted from behaving as a near hard-sphere to an adhesive hard-sphere system leading to aggregation and ultimately a dynamical arrest transition to macroscopic gelation. Time-resolved oscillatory rheo-small-angle neutron scattering (tOr-SANS) measurements in the 1-3 plane are performed by stroboscopically probing the structural evolution as a function of time during LAOS. Under strong shear, the 2D scattering pattern of the system in the gelled state exhibits a strong anisotropy commonly known as a ``butterfly'' pattern, which corresponds to the stretching of the microstructure along the flow direction. The first structure-Lissajous plots of this model system are presented in terms of an order parameter and Af as a function of instantaneous strain and strain rate. This new analysis demonstrates a novel method for simultaneously measuring the rheology and microstructure during a time-dependent deformation (LAOS).
Osteotomies for bunionette deformity.
Weil, Lowell; Weil, Lowell Scott
2011-12-01
A variety of surgical osteotomy procedures have been described for the bunionette deformity.Metatarsal osteotomies narrow the forefoot, maintain the length of the metatarsal, and preserve function of the metatarsophalangeal joint. Distal metatarsal osteotomies produce less correction and reduce postoperative disability; however, they pose a risk of inadequate correction because of the small width of the fifth metatarsal head and transfer lesions if shortened or dorsiflexed excessively. The sliding oblique metaphyseal osteotomy described by Smith and Weil (without fixation) and later by Steinke (with fixation) is easy to perform and provides good cancellous bone contact. Fixation is sometimes difficult and bone healing can take a few months owing to the unstable construct of this osteotomy. Kitaoka described a distal chevron osteotomy, which provides lateral pressure relief and reduced plantar pressure. This osteotomy is currently the most common procedure used; however, it may prove difficult to perform if the deformity is large and the bone is narrow. Diaphyseal osteotomies are indicated when greater correction is needed; however, they require more dissection and there is greater postoperative convalescence with non–weight bearing for several weeks. Proximal base osteotomies may be used to address significantly increased 4–5 IMAs or when a large degree of sagittal plane correction is required. Approaches that have been described include opening and closing base wedges and basal chevrons. Advantages to this approach are the ability to avoid epiphyseal plates in pediatric patients and maintain function of the MTPJ, while disadvantages include inherent instability of the location of the osteotomy, embarrassment of intraosseous and extraosseus blood supply of the metatarsal, and technical demand. Non–weight bearing is essential for several weeks. The Scarfette procedure is a combination head–shaft procedure, which is indicated to treat mild to moderate
NASA Astrophysics Data System (ADS)
Gatti, Vijay; Hill, Jason; Mitra, Sunanda; Nutter, Brian
2014-03-01
Despite the current availability in resource-rich regions of advanced technologies in scanning and 3-D imaging in current ophthalmology practice, world-wide screening tests for early detection and progression of glaucoma still consist of a variety of simple tools, including fundus image-based parameters such as CDR (cup to disc diameter ratio) and CAR (cup to disc area ratio), especially in resource -poor regions. Reliable automated computation of the relevant parameters from fundus image sequences requires robust non-rigid registration and segmentation techniques. Recent research work demonstrated that proper non-rigid registration of multi-view monocular fundus image sequences could result in acceptable segmentation of cup boundaries for automated computation of CAR and CDR. This research work introduces a composite diffeomorphic demons registration algorithm for segmentation of cup boundaries from a sequence of monocular images and compares the resulting CAR and CDR values with those computed manually by experts and from 3-D visualization of stereo pairs. Our preliminary results show that the automated computation of CDR and CAR from composite diffeomorphic segmentation of monocular image sequences yield values comparable with those from the other two techniques and thus may provide global healthcare with a cost-effective yet accurate tool for management of glaucoma in its early stage.
Keefer, David K.; Harp, Edwin L.; Griggs, Gary B.; Evans, Stephen G.; DeGraff, Jerome V.
2002-01-01
The Villa Del Monte landslide was one of 20 large and complex landslides triggered by the 1989 LomaPrieta, California, earthquake in a zone of pervasive coseismicground cracking near the fault rupture. The landslide was approximately 980 m long, 870 m wide, and encompassed an area of approximately 68 ha. Drilling data suggested that movement may have extended to depths as great as 85 m below the ground surface. Even though the landslide moved <1 m, it caused substantial damage to numerous dwellings and other structures, primarily as a result of differential displacements and internal Assuring. Surface cracks, scarps, and compression features delineating the Villa Del Monte landslide were discontinuous, probably because coseismic displacements were small; such discontinuous features were also characteristic of the other large, coseismic landslides in the area, which also moved only short distances during the earthquake. Because features marking landslide boundaries were discontinuous and because other types of coseismic ground cracks were widespread in the area, identification of the landslides required detailed mapping and analysis. Recognition that landslides such as that at Villa Del Monte may occur near earthquake-generating fault ruptures should aid in future hazard evaluations of areas along active faults.
Deformable micro torque swimmer
NASA Astrophysics Data System (ADS)
Ishikawa, Takuji; Tanaka, Tomoyuki; Omori, Toshihiro; Imai, Yohsuke
2015-11-01
We investigated the deformation of a ciliate swimming freely in a fluid otherwise at rest. The cell body was modeled as a capsule with a hyper elastic membrane enclosing Newtonian fluid. Thrust forces due to the ciliary beat were modeled as torques distributed above the cell body. Effects of the membrane elasticity, the aspect ratio of cell's reference shape and the density difference between the cell and the surrounding fluid were investigated. The results showed that the cell deformed like heart shape when Capillary number (Ca) was sufficiently large, and the swimming velocity decreased as Ca was increased. The gravity effect on the membrane tension suggested that the upwards and downwards swimming velocities of Paramecium might be reglated by the calcium ion channels distributed locally around the anterior end. Moreover, the gravity induced deformation made a cell directed vertically downwards, which resulted in a positive geotaxis like behavior with physical origin. These results are important to understand physiology of ciliate's biological responses to mechanical stimuli.
NASA Astrophysics Data System (ADS)
Mohammed-Azizi, B.; Medjadi, D. E.
2014-11-01
, WINDOWS 7, LINUX. RAM: 256 Mb (depending on nmax). Swap file: 4Gb (depending on nmax) Classification: 17.7. Does the new version supersede the previous version?: Yes Catalogue identifier of previous version: ADSK_v2_0 Journal reference of previous version: Comput. Phys. Comm. 176 (2007) 634 Nature of problem: The Single particle energies and the single particle wave functions are calculated from one-body Hamiltonian including a central field of Woods-Saxon type, a spin-orbit interaction, and the Coulomb potential for the protons. We consider only ellipsoidal (triaxial) shapes. The deformation of the nuclear shape is fixed by the usual Bohr parameters (β,γ). Solution method: The representative matrix of the Hamiltonian is built by means of the Cartesian basis of the anisotropic harmonic oscillator, and then diagonalized by a set of subroutines of the EISPACK library. Two quadrature methods of Gauss are employed to calculate respectively the integrals of the matrix elements of the Hamiltonian, and the integral defining the Coulomb potential. Two quantum numbers are conserved: the parity and the signature. Due to the Kramers degeneracy, only positive signature is considered. Therefore, calculations are made for positive and negative parity separately (with positive signature only). Reasons for new version: Now, there are several ways to obtain the eigenvalues and the eigenfunctions. The eigenvalues can be obtained from the subroutine ‘eigvals’ or from the array ‘energies’ or also from the formatted files ‘valuu.dat’, ‘eigenvalo.dat’, ‘eigenva.dat’ or better from the unformatted file ‘eigenvaunf.dat’. The eigenfunctions can be obtained straightforwardly in configuration space from the subroutine ‘eigfunc’ or by their components on the oscillator basis from the subroutine ‘compnts’. The latter are also recorded on a formatted file ‘componento.dat’ or on an unformatted file ‘componentounf.dat’. Summary of revisions: This version is
NASA Technical Reports Server (NTRS)
Strauss, Karl F.; Sheldon, Douglas J.
2011-01-01
Several missions and instruments in the conceptual design phase rely on the technique of interferometry to create detectable fringe patterns. The intimate emplacement of reflective material upon electron device cells based upon chalcogenide material technology permits high-speed, predictable deformation of the reflective surface to a subnanometer or finer resolution with a very high degree of accuracy. In this innovation, a layer of reflective material is deposited upon a wafer containing (perhaps in the millions) chalcogenic memory cells with the reflective material becoming the front surface of a mirror and the chalcogenic material becoming a means of selectively deforming the mirror by the application of heat to the chalcogenic material. By doing so, the mirror surface can deform anywhere from nil to nanometers in spots the size of a modern day memory cell, thereby permitting realtime tuning of mirror focus and reflectivity to mitigate aberrations caused elsewhere in the optical system. Modern foundry methods permit the design and manufacture of individual memory cells having an area of or equal to the Feature (F) size of the design (assume 65 nm). Fabrication rules and restraints generally require the instantiation of one memory cell to another no closer than 1.5 F, or, for this innovation, 90 nm from its neighbor in any direction. Chalcogenide is a semiconducting glass compound consisting of a combination of chalcogen ions, the ratios of which vary according to properties desired. It has been shown that the application of heat to cells of chalcogenic material cause a large alteration in resistance to the range of 4 orders of magnitude. It is this effect upon which chalcogenidebased commercial memories rely. Upon removal of the heat source, the chalcogenide rapidly cools and remains frozen in the excited state. It has also been shown that the chalcogenide expands in volume because of the applied heat, meaning that the coefficient of expansion of chalcogenic
Solute transport through a deforming porous medium
NASA Astrophysics Data System (ADS)
Peters, Glen P.; Smith, David W.
2002-06-01
Solute transport through a porous medium is typically modelled assuming the porous medium is rigid. However, many applications exist where the porous medium is deforming, including, municipal landfill liners, mine tailings dams, and land subsidence. In this paper, mass balance laws are used to derive the flow and transport equations for a deforming porous medium. The equations are derived in both spatial and material co-ordinate systems. Solute transport through an engineered landfill liner is used as an illustrative example to show the differences between the theory for a rigid porous medium, and small and large deformation analysis of a deforming porous medium. It is found that the large deformation model produces shorter solute breakthrough times, followed by the small deformation model, and then the rigid porous medium model. It is also found that it is important to include spatial and temporal void ratio variations in the large deformation analysis. It is shown that a non-linear large deformation model may greatly reduce the solute breakthrough time, compared to a standard transport analysis typically employed by environmental engineers.
Exploiting Adaptive Optics with Deformable Secondary Mirrors
2007-03-08
progress in tomographic wavefront sensing and altitude conjugated adaptive correction, and is a critical step forward for adaptive optics for future large...geostationary satellites, captured at the 6.5 m MMT telescope, using the deformable secondary adaptive optics system....new technology to the unique development of deformable secondary mirrors pioneered at the University of Arizona’s Center for Astronomical Adaptive
Deform PF-MT: Particle Filter With Mode Tracker for Tracking Nonaffine Contour Deformations
Vaswani, Namrata; Rathi, Yogesh; Yezzi, Anthony; Tannenbaum, Allen
2013-01-01
We propose algorithms for tracking the boundary contour of a deforming object from an image sequence, when the nonaffine (local) deformation over consecutive frames is large and there is overlapping clutter, occlusions, low contrast, or outlier imagery. When the object is arbitrarily deforming, each, or at least most, contour points can move independently. Contour deformation then forms an infinite (in practice, very large), dimensional space. Direct application of particle filters (PF) for large dimensional problems is impractically expensive. However, in most real problems, at any given time, most of the contour deformation occurs in a small number of dimensions (“effective basis space”) while the residual deformation in the rest of the state space (“residual space”) is small. This property enables us to apply the particle filtering with mode tracking (PF-MT) idea that was proposed for such large dimensional problems in recent work. Since most contour deformation is low spatial frequency, we propose to use the space of deformation at a subsampled set of locations as the effective basis space. The resulting algorithm is called deform PF-MT. It requires significant modifications compared to the original PF-MT because the space of contours is a non-Euclidean infinite dimensional space. PMID:19933014
Finite Deformation of Magnetoelastic Film
Barham, Matthew Ian
2011-05-31
A nonlinear two-dimensional theory is developed for thin magnetoelastic lms capable of large deformations. This is derived directly from three-dimensional theory. Signi cant simpli cations emerge in the descent from three dimensions to two, permitting the self eld generated by the body to be computed a posteriori. The model is specialized to isotropic elastomers with two material models. First weak magnetization is investigated leading to a free energy where magnetization and deformation are un-coupled. The second closely couples the magnetization and deformation. Numerical solutions are obtained to equilibrium boundary-value problems in which the membrane is subjected to lateral pressure and an applied magnetic eld. An instability is inferred and investigated for the weak magnetization material model.
The role of regularization in deformable image registration for head and neck adaptive radiotherapy.
Ciardo, D; Peroni, M; Riboldi, M; Alterio, D; Baroni, G; Orecchia, R
2013-08-01
Deformable image registration provides a robust mathematical framework to quantify morphological changes that occur along the course of external beam radiotherapy treatments. As clinical reliability of deformable image registration is not always guaranteed, algorithm regularization is commonly introduced to prevent sharp discontinuities in the quantified deformation and achieve anatomically consistent results. In this work we analyzed the influence of regularization on two different registration methods, i.e. B-Splines and Log Domain Diffeomorphic Demons, implemented in an open-source platform. We retrospectively analyzed the simulation computed tomography (CTsim) and the corresponding re-planning computed tomography (CTrepl) scans in 30 head and neck cancer patients. First, we investigated the influence of regularization levels on hounsfield units (HU) information in 10 test patients for each considered method. Then, we compared the registration results of the open-source implementation at selected best performing regularization levels with a clinical commercial software on the remaining 20 patients in terms of mean volume overlap, surface and center of mass distances between manual outlines and propagated structures. The regularized B-Splines method was not statistically different from the commercial software. The tuning of the regularization parameters allowed open-source algorithms to achieve better results in deformable image registration for head and neck patients, with the additional benefit of a framework where regularization can be tuned on a patient specific basis.
Active Beam Shaping System and Method Using Sequential Deformable Mirrors
NASA Technical Reports Server (NTRS)
Norman, Colin A. (Inventor); Pueyo, Laurent A. (Inventor)
2015-01-01
An active optical beam shaping system includes a first deformable mirror arranged to at least partially intercept an entrance beam of light and to provide a first reflected beam of light, a second deformable mirror arranged to at least partially intercept the first reflected beam of light from the first deformable mirror and to provide a second reflected beam of light, and a signal processing and control system configured to communicate with the first and second deformable mirrors. The first deformable mirror, the second deformable mirror and the signal processing and control system together provide a large amplitude light modulation range to provide an actively shaped optical beam.
NASA Technical Reports Server (NTRS)
Clark, T. A.; Thomsen, P.
1988-01-01
A study is presented of deformations in antennas with the emphasis on their influence on VLBI measurements. The GIFTS structural analysis program has been used to model the VLBI antenna in Fairbanks (Alaska). The report identifies key deformations and studies the effect of gravity, wind, and temperature. Estimates of expected deformations are given.
NASA Astrophysics Data System (ADS)
Price, C. E.; Shepard, J. R.
1991-04-01
We compute properties of the nucleon in a hybrid chiral model based on the linear σ-model with quark degrees of freedom treated explicity. In contrast to previous calculations, we do not use the hedgehog ansatz. Instead we solve self-consistently for a state with well defined spin and isospin projections. We allow this state to be deformed and find that, although d- and g-state admixtures in the predominantly s-state single quark wave functions are not large, they have profound effects on many nucleon properties including magnetic moments and gA. Our best fit parameters provide excellent agreement with experiment but are much different from those determined in hedgehog calculations.
Deformations of superconformal theories
NASA Astrophysics Data System (ADS)
Córdova, Clay; Dumitrescu, Thomas T.; Intriligator, Kenneth
2016-11-01
We classify possible supersymmetry-preserving relevant, marginal, and irrelevant deformations of unitary superconformal theories in d ≥ 3 dimensions. Our method only relies on symmetries and unitarity. Hence, the results are model independent and do not require a Lagrangian description. Two unifying themes emerge: first, many theories admit deformations that reside in multiplets together with conserved currents. Such deformations can lead to modifications of the supersymmetry algebra by central and non-central charges. Second, many theories with a sufficient amount of supersymmetry do not admit relevant or marginal deformations, and some admit neither. The classification is complicated by the fact that short superconformal multiplets display a rich variety of sporadic phenomena, including supersymmetric deformations that reside in the middle of a multiplet. We illustrate our results with examples in diverse dimensions. In particular, we explain how the classification of irrelevant supersymmetric deformations can be used to derive known and new constraints on moduli-space effective actions.
Mounting with compliant cylinders for deformable mirrors.
Reinlein, Claudia; Goy, Matthias; Lange, Nicolas; Appelfelder, Michael
2015-04-01
A method is presented to mount large aperture unimorph deformable mirrors by compliant cylinders (CC). The CCs are manufactured from a soft silicone, and shear testing is performed in order to evaluate the Young's modulus. A scale mirror model is assembled to evaluate mount-induced change of piezoelectric deformation, and its applicability for tightly focusing mirrors. Experiments do not show any decrease of piezoelectric stroke. Further it is shown that the changes of surface fidelity by the attachment of the deformable mirror to its mount are neglectable.
Duchateau, Nicolas; Giraldeau, Geneviève; Gabrielli, Luigi; Fernández-Armenta, Juan; Penela, Diego; Evertz, Reinder; Mont, Lluis; Brugada, Josep; Berruezo, Antonio; Sitges, Marta; Bijnens, Bart H
2015-01-01
Time-to-peak measurements and single-parameter observations are cumbersome and often confusing for quantifying local changes in myocardial function. Recent spatiotemporal normalization techniques can provide a global picture of myocardial motion and strain patterns and overcome some of these limitations. Despite these advances, the quantification of pattern changes remains descriptive, which limits their relevance for longitudinal studies. Our paper provides a new perspective to the longitudinal analysis of myocardial motion. Non-rigid registration (diffeomorphic registration via currents) is used to match pairs of patterns, and pattern changes are inferred from the registration output. Scalability is added to the different components of the input patterns in order to tune up the contributions of the spatial, temporal and magnitude dimensions to data changes, which are of interest for our application. The technique is illustrated on 2D echocardiographic sequences from 15 patients with hypertrophic obstructive cardiomyopathy. These patients underwent biventricular pacing, which aims at provoking mechanical dyssynchrony to reduce left ventricular outflow tract (LVOT) obstruction. We demonstrate that our method can automatically quantify timing and magnitude changes in myocardial motion between baseline (non-paced) and 1 year follow-up (pacing on), resulting in a more robust analysis of complex patterns and subtle changes. Our method helps confirming that the reduction of LVOT pressure gradient actually comes from the induction of the type of dyssynchrony that was expected.
GPS constraints on the kinematics of continental deformation
Thatcher, W.
2003-01-01
Recent GPS observations from the western United States, New Zealand, central Greece, and Japan indicate that present-day continental deformation is typically focused in narrow deforming zones whose extent is much smaller than the intervening largely inactive regions. However, these narrow zones are heterogeneously distributed, reflecting the inherent heterogeneity of continental lithospheric strength and internal buoyancy. Plate driving and resisting forces stress plate boundary zones and plate interiors and drive deformation. These forces change continuously and discontinuously, leading to continental deformation that typically evolves and migrates with time. Magmatic and tectonic processes alter lithospheric rheology and internal buoyancy and also contribute to the time-varying character of continental deformation.
Motion of deformable ring made of IPMC
NASA Astrophysics Data System (ADS)
Firouzeh, Amir; Alasty, Aria; Ozmaeian, Masoumeh
2012-04-01
In this paper application of Ionic Polymer Metal Composite (IPMC) as actuator in a deformable ring capable of locomotion is studied. Such a deformable ring moves as a result of gravitational force acting on its body when its shape changes. It can be used in exploration, search and rescue missions in future, where using conventional robots with rigid bodies and actuators is impossible. Large deformation induced by small stimulating voltage, low stiffness the sensing characteristics that in future work can be used in feedback control make IPMC a good choice for such an application. In this work first a model for IPMC is introduce that can be used in simulating deformation of IPMC in different arrangements of actuators. Since in this research we used our own fabricated IPMC, next we present characterization tests and identification results for model's parameters. Then using this model in simulation possibility of generating locomotion using body deformation in a ring made of IPMC is confirmed. Finally result of experiment on deformable ring is presented and possibility of implementation of the proposed design is confirmed. Based on this work, more accurate models can be developed to get better compatibility between experiment and simulation results. Also by modifying fabrication techniques, a deformable ring with faster and steadier movement can be made in future.
Motion of deformable ring made of IPMC
NASA Astrophysics Data System (ADS)
Firouzeh, Amir; Alasty, Aria; Ozmaeian, Masoumeh
2011-11-01
In this paper application of Ionic Polymer Metal Composite (IPMC) as actuator in a deformable ring capable of locomotion is studied. Such a deformable ring moves as a result of gravitational force acting on its body when its shape changes. It can be used in exploration, search and rescue missions in future, where using conventional robots with rigid bodies and actuators is impossible. Large deformation induced by small stimulating voltage, low stiffness the sensing characteristics that in future work can be used in feedback control make IPMC a good choice for such an application. In this work first a model for IPMC is introduce that can be used in simulating deformation of IPMC in different arrangements of actuators. Since in this research we used our own fabricated IPMC, next we present characterization tests and identification results for model's parameters. Then using this model in simulation possibility of generating locomotion using body deformation in a ring made of IPMC is confirmed. Finally result of experiment on deformable ring is presented and possibility of implementation of the proposed design is confirmed. Based on this work, more accurate models can be developed to get better compatibility between experiment and simulation results. Also by modifying fabrication techniques, a deformable ring with faster and steadier movement can be made in future.
Simple shear deformation of partially molten aplite
NASA Astrophysics Data System (ADS)
Stipp, Michael; Tullis, Jan; Berger, Alfons
2013-04-01
The tectonic processes which are important for melt distribution and transport in the intermediate and lower crust and which can result in crustal weakening are not yet well understood. Natural migmatites are usually overprinted by annealing and retrogression during uplift and exhumation, largely obliterating the deformation structures and microstructures of their partially molten history. Deformation experiments on partially molten crustal rocks have so far been conducted in pure shear geometry and mostly under low confining pressures in the brittle deformation field, both of which are not representative of nature. We carried out deformation experiments in simple shear that predominates in the crust and especially crustal shear zones. Undrained experiments were carried out on Enfield aplite at ~1.5 GPa, 900° -1000° C, and ˜ 5*10-6 s-1, conditions which favor crystal plastic deformation of quartz and feldspar (Dell'Angelo and Tullis, 1988). Sample slices 1.0-1.5 mm thick were placed between the shear pistons with the shear plane at a 45° -angle to the compression direction. Maximum shear strain in the experiments is ? ?2.8. Despite difficulties in controlling the melt content by varying the amount of added water, we were able to achieve the full range of brittle to crystal plastic deformation mechanisms. With decreasing melt content Enfield aplite displays a transition from discrete fracturing at a high angle (~70-90° ) to the shear plane (>20 vol.% melt), to cataclastic shearing (10-20 vol.% melt) and to crystal plastic deformation (
Nuclear Deformation Effects in the Cluster Radioactivity
NASA Astrophysics Data System (ADS)
Misicu, Serban; Protopopescu, Dan
1999-01-01
We investigate the influence of the nuclear deformation on the decay rates of some cluster emission processes. The interaction between the daughter and the cluster is given by a double folding potential including quadrupole and hexadecupole deformed densities of both fragments. The nuclear part of the nucleus--nucleus interaction is density dependent and at small distances a repulsive core in the potential will occur. In the frame of the WKB-approximation the assault frequency of the cluster will depend on the geometric properties of the potential pocket whereas the penetrability will be sensitive to changes in the barrier location. The results obtained in this paper point out that various combinations of cluster and daughter deformations may account for the measured values of the decay rate. The decay rates are however more sensitive to the changes in the daughter deformation due to the large mass asymmetry of the process.
Evans, D
1975-08-01
A discussion of the essential deformity in calcaneo-valgus feet develops a theme originally put forward in 1961 on the relapsed club foot (Evans 1961). Whereas in the normal foot the medial and lateral columns are about equal in length, in talipes equino-varus the lateral column is longer and in calcaneo-valgus shorter than the medial column. The suggestion is that in the treatment of both deformities the length of the columns be made equal. A method is described of treating calcaneo-valgus deformity by inserting cortical bone grafts taken from the tibia to elongate the anterior end of the calcaneus.
NASA Astrophysics Data System (ADS)
Green, Harry
The Third Rock Deformation Colloquium was held December 4, 1989, at the AGU Fall Meeting in San Francisco. Steve Kirby of the U.S. Geological Survey, Menlo Park, Calif., reported on actions taken by the rock deformation steering committee. Brian Wernicke of Harvard University, Cambridge, Mass., talked on the structural geology of the Great Basin.The steering committee voted for “Committee on Deformation of Earth Materials” as the name for the AGU technical committee on rock deformation, Kirby said. Considerable discussion has occurred in the steering committee over our relationship to the AGU Mineral Physics Committee. Indeed, Kirby will become chairman of that committee in 1990, underlining the overlap of the two groups. It was agreed that we will pursue closer association with Mineral Physics.
Wrist deformities after fracture.
Vanheest, Ann
2006-02-01
Wrist deformities can occur after fracture because of malunion of the fracture or injury to the growth plate leading to imbalance of growth. Prevention of malunion is paramount by early recognition with proper reduction and casting or fixation with casting. If a mal-union occurs, an osteotomy may be necessary if anticipated growth will not correct the deformity. Injury of the growth plate may lead to wrist deformity in two ways: angular growth or growth arrest. Angular growth deformities are corrected most commonly by osteotomy. Growth arrest of the radius or the ulna leads to an ulnar-positive or an ulnar-negative variance at the wrist. If the ulnar variance is symptomatic, treatment is centered on achieving a level joint. Options for joint leveling procedures include epiphysiodesis or physeal stapling of the longer bone, lengthening osteotomy of the shorter bone, or shortening osteotomy of the longer bone.
NASA Astrophysics Data System (ADS)
Antonellini, Marco; Mollema, Pauline Nella
2015-12-01
We report for the first time the occurrence of polygonal faults in sandstone, which is compelling given that layer-bound polygonal fault systems have been observed so far only in fine-grained sediments such as clay and chalk. The polygonal faults are shear deformation bands that developed under shallow burial conditions via strain hardening in dm-wide zones. The edges of the polygons are 1-5 m long. The shear deformation bands are organized as conjugate faults along each edge of the polygon and form characteristic horst-like structures. The individual deformation bands have slip magnitudes ranging from a few mm to 1.5 cm; the cumulative average slip magnitude in a zone is up to 10 cm. The deformation bands heaves, in aggregate form, accommodate a small isotropic horizontal extension (strain <0.005). The individual shear deformation bands show abutting T-junctions, veering, curving, and merging where they mechanically interact. Crosscutting relationships are rare. The interactions of the deformation bands are similar to those of mode I opening fractures. The documented fault networks have important implications for evaluating the geometry of km-scale polygonal fault systems in the subsurface, top seal integrity, as well as constraining paleo-tectonic stress regimes.
Passive deformation analysis of human leukocytes.
Dong, C; Skalak, R; Sung, K L; Schmid-Schönbein, G W; Chien, S
1988-02-01
The following analysis presents an experimental and theoretical study of the passive viscoelastic behavior of human leukocytes. Individual neutrophils in EDTA were observed both during their partial aspiration into a small micropipette and after expulsion from a large micropipette where the cell had been totally aspirated and deformed into a sausage shape. To analyze the data, a passive model of leukocyte rheology has been developed consisting of a cortical shell containing a Maxwell fluid which describes the average properties of the cell cytoplasm. The cortical shell represents a crosslinked actin layer near the surface of the cell and is assumed to be under pre-stressed tension. This model can reproduce the results of experiments using micropipette for both short-time small deformation and slow recovery data after large deformation. In addition, a finite element scheme has been established for the same model which shows close agreement with the analytical solution.
Exactly isochoric deformations of soft solids
NASA Astrophysics Data System (ADS)
Biggins, John S.; Wei, Z.; Mahadevan, L.
2014-12-01
Many materials of contemporary interest, such as gels, biological tissues and elastomers, are easily deformed but essentially incompressible. Traditional linear theory of elasticity implements incompressibility only to first order and thus permits some volume changes, which become problematically large even at very small strains. Using a mixed coordinate transformation originally due to Gauss, we enforce the constraint of isochoric deformations exactly to develop a linear theory with perfect volume conservation that remains valid until strains become geometrically large. We demonstrate the utility of this approach by calculating the response of an infinite soft isochoric solid to a point force that leads to a nonlinear generalization of the Kelvin solution. Our approach naturally generalizes to a range of problems involving deformations of soft solids and interfaces in two-dimensional and axisymmetric geometries, which we exemplify by determining the solution to a distributed load that mimics muscular contraction within the bulk of a soft solid.
Experimental Deformation of Magnetite
NASA Astrophysics Data System (ADS)
Till, J. L.; Rybacki, E.; Morales, L. F. G.
2015-12-01
Magnetite is an important iron ore mineral and the most prominent Fe-oxide phase in the Earth's crust. The systematic occurrence of magnetite in zones of intense deformation in oceanic core complexes suggests that it may play a role in strain localization in some silicate rocks. We performed a series of high-temperature deformation experiments on synthetic magnetite aggregates and natural single crystals to characterize the rheological behavior of magnetite. As starting material, we used fine-grained magnetite powder that was hot isostatically pressed at 1100°C for several hours, resulting in polycrystalline material with a mean grain size of around 40 μm and containing 3-5% porosity. Samples were deformed to 15-20% axial strain under constant load (approximating constant stress) conditions in a Paterson-type gas apparatus for triaxial deformation at temperatures between 900 and 1100°C and 300 MPa confining pressure. The aggregates exhibit typical power-law creep behavior. At high stresses, samples deformed by dislocation creep exhibit stress exponents close to 3, revealing a transition to near-Newtonian creep with stress exponents around 1.3 at lower stresses. Natural magnetite single crystals deformed at 1 atm pressure and temperatures between 950°C and 1150 °C also exhibit stress exponents close to 3, but with lower flow stresses and a lower apparent activation energy than the aggregates. Such behavior may result from the different oxygen fugacity buffers used. Crystallographic-preferred orientations in all polycrystalline samples are very weak and corroborate numerical models of CPO development, suggesting that texture development in magnetite may be inherently slow compared with lower symmetry phases. Comparison of our results with experimental deformation data for various silicate minerals suggests that magnetite should be weaker than most silicates during ductile creep in dry igneous rocks.
Crustal deformation and earthquakes
NASA Technical Reports Server (NTRS)
Cohen, S. C.
1984-01-01
The manner in which the Earth's surface deforms during the cycle of stress accumulation and release along major faults is investigated. In an investigation of the crustal deformation associated with a thin channel asthenosphere displacements are reduced from those computed for a half space asthenosphere. A previous finding by other workers that displacements are enhanced when flow is confined to a thin channel is based on several invalid approximations. The major predictions of the finite element model are that the near field postseismic displacements and strain rates are less than those for a half space asthenosphere and that the postseismic strain rates at intermediate distances are greater (in magnitude). The finite width of the asthenosphere ceases to have a significant impact on the crustal deformation pattern when its magnitude exceeds about three lithosphere thicknesses.
Interfacial Bubble Deformations
NASA Astrophysics Data System (ADS)
Seymour, Brian; Shabane, Parvis; Cypull, Olivia; Cheng, Shengfeng; Feitosa, Klebert
Soap bubbles floating at an air-water experience deformations as a result of surface tension and hydrostatic forces. In this experiment, we investigate the nature of such deformations by taking cross-sectional images of bubbles of different volumes. The results show that as their volume increases, bubbles transition from spherical to hemispherical shape. The deformation of the interface also changes with bubble volume with the capillary rise converging to the capillary length as volume increases. The profile of the top and bottom of the bubble and the capillary rise are completely determined by the volume and pressure differences. James Madison University Department of Physics and Astronomy, 4VA Consortium, Research Corporation for Advancement of Science.
Minster, B.; Prescott, W.; Royden, L.
1991-02-01
Our goal is to understand the motions of the plates, the deformation along their boundaries and within their interiors, and the processes that control these tectonic phenomena. In the broadest terms, we must strive to understand the relationships of regional and local deformation to flow in the upper mantle and the rheological, thermal and density structure of the lithosphere. The essential data sets which we require to reach our goal consist of maps of current strain rates at the earth's surface and the distribution of integrated deformation through time as recorded in the geologic record. Our success will depend on the effective synthesis of crustal kinematics with a variety of other geological and geophysical data, within a quantitative theoretical framework describing processes in the earth's interior. Only in this way can we relate the snapshot of current motions and earth structure provided by geodetic and geophysical data with long-term processes operating on the time scales relevant to most geological processes. The wide-spread use of space-based techniques, coupled with traditional geological and geophysical data, promises a revolution in our understanding of the kinematics and dynamics of plate motions over a broad range of spatial and temporal scales and in a variety of geologic settings. The space-based techniques that best address problems in plate motion and deformation are precise space-geodetic positioning -- on land and on the seafloor -- and satellite acquisition of detailed altimetric and remote sensing data in oceanic and continental areas. The overall science objectives for the NASA Solid Earth Science plan for the 1990's, are to Understand the motion and deformation of the lithosphere within and across plate boundaries'', and to understand the dynamics of the mantle, the structure and evolution of the lithosphere, and the landforms that result from local and regional deformation. 57 refs., 7 figs., 2 tabs.
Diffusion in κ-deformed space and spectral dimension
NASA Astrophysics Data System (ADS)
Anjana, V.
2016-03-01
In this paper, we derive the expression for spectral dimension using a modified diffusion equation in the κ-deformed spacetime. We start with the Beltrami-Laplace operator in the κ-Minkowski spacetime and obtain the deformed diffusion equation. From the solution of this deformed diffusion equation, we calculate the spectral dimension which depends on the deformation parameter “a = 1 κ” and also on an integer “l”, apart from the topological dimension. Using this, we show that, for large diffusion times the spectral dimension approaches the usual topological dimension whereas spectral dimension diverges to + ∞ for l ≥ 0 and -∞ for l < 0 at high energies.
f-Deformed Boson Algebra Related to Gentile Statistics
NASA Astrophysics Data System (ADS)
Chung, Won Sang; Hassanabadi, Hassan
2017-02-01
In this paper the deformed boson algebra giving the Gentile distribution function is constructed by using the model of ideal gas of deformed bosons and some properties of a root of unity. As an example we discuss the quantum optical problem related to the Gentile (or f-deformed) boson algebra with large but finite M. For this algebra we construct the Gentile (or f-deformed) coherent state and discuss its nonclassical properties such as sub-Poissonian statistics and anti-bunching effect.
Nanolaminate deformable mirrors
Papavasiliou, Alexandros P.; Olivier, Scot S.
2009-04-14
A deformable mirror formed out of two layers of a nanolaminate foil attached to a stiff substrate is introduced. Deformation is provided by an electrostatic force between two of the layers. The internal stiffness of the structure allows for high-spatial-frequency shapes. The nanolaminate foil of the present invention allows for a high-quality mirror surface. The device achieves high precision in the vertical direction by using foils with accurately controlled thicknesses, but does not require high precision in the lateral dimensions, allowing such mirrors to be fabricated using crude lithography techniques. Such techniques allow structures up to about the meter scale to be fabricated.
Nanolaminate deformable mirrors
Papavasiliou, Alexandros P.; Olivier, Scot S.
2010-04-06
A deformable mirror formed out of two layers of a nanolaminate foil attached to a stiff substrate is introduced. Deformation is provided by an electrostatic force between two of the layers. The internal stiffness of the structure allows for high-spatial-frequency shapes. The nanolaminate foil of the present invention allows for a high-quality mirror surface. The device achieves high precision in the vertical direction by using foils with accurately controlled thicknesses, but does not require high precision in the lateral dimensions, allowing such mirrors to be fabricated using crude lithography techniques. Such techniques allow structures up to about the meter scale to be fabricated.
An autoregulatory enhancer element of the Drosophila homeotic gene Deformed.
Bergson, C; McGinnis, W
1990-12-01
The stable determination of different anterior-posterior regions of the Drosophila embryo is controlled by the persistent expression of homeotic selector genes. One mechanism that has been proposed to explain the persistent expression of the homeotic gene Deformed is an autoactivation circuit that would be used once Deformed expression had been established by earlier acting patterning genes. Here we show that a large cis-regulatory element mapping approximately 5 kb upstream of the Deformed transcription start has the properties predicted for a Deformed autoregulatory enhancer. This element provides late, spatially localized expression in the epidermal cells of the maxillary and mandibular segments which is wholly dependent upon endogenous Deformed function. In addition, the autoregulatory enhancer can be activated ectopically in embryos and in imaginal disc cells by ectopic expression of Deformed protein. Deletion analysis of the autoregulatory element indicates that it contains compartment specific sub-elements similar to those of other homeotic loci.
Scarfette osteotomy for surgical treatment of bunionette deformity.
Glover, Jason P; Weil, Lowell; Weil, Lowell S
2009-04-01
Numerous procedures have been described for a bunionette deformity. Choosing a specific osteotomy depends largely on the degree of the deformity and surgeon preference. The Scarfette osteotomy is a versatile procedure that addresses specific etiologic factors associated with bunionette deformities. The primary aim of this study is to show the versatility of the Scarfette osteotomy in varying degrees of bunionette deformities. A retrospective review of 50 cases was performed with a follow-up of 12 months. Objective information was obtained by measuring specific radiographic variables on preoperative and postoperative weight-bearing radiographs. Mean radiographic results are presented for the intermetatarsal 4-5 angle, lateral deviation angle, and fifth metatarsophalangeal angles postoperatively. The authors report short-term results of the Scarfette osteotomy in the correction of bunionette deformities. The Scarfette is a predictable and versatile osteotomy to correct varying degrees of bunionette deformities. The Scarfette is not technically demanding and allows early postoperative ambulation.
Bulk metallic glasses deform via slip avalanches.
Antonaglia, James; Wright, Wendelin J; Gu, Xiaojun; Byer, Rachel R; Hufnagel, Todd C; LeBlanc, Michael; Uhl, Jonathan T; Dahmen, Karin A
2014-04-18
For the first time in metallic glasses, we extract both the exponents and scaling functions that describe the nature, statistics, and dynamics of slip events during slow deformation, according to a simple mean field model. We model the slips as avalanches of rearrangements of atoms in coupled shear transformation zones (STZs). Using high temporal resolution measurements, we find the predicted, different statistics and dynamics for small and large slips thereby excluding self-organized criticality. The agreement between model and data across numerous independent measures provides evidence for slip avalanches of STZs as the elementary mechanism of inhomogeneous deformation in metallic glasses.
Bulk Metallic Glasses Deform via Slip Avalanches
NASA Astrophysics Data System (ADS)
Antonaglia, James; Wright, Wendelin J.; Gu, Xiaojun; Byer, Rachel R.; Hufnagel, Todd C.; LeBlanc, Michael; Uhl, Jonathan T.; Dahmen, Karin A.
2014-04-01
For the first time in metallic glasses, we extract both the exponents and scaling functions that describe the nature, statistics, and dynamics of slip events during slow deformation, according to a simple mean field model. We model the slips as avalanches of rearrangements of atoms in coupled shear transformation zones (STZs). Using high temporal resolution measurements, we find the predicted, different statistics and dynamics for small and large slips thereby excluding self-organized criticality. The agreement between model and data across numerous independent measures provides evidence for slip avalanches of STZs as the elementary mechanism of inhomogeneous deformation in metallic glasses.
Postural deformities in congenital nephrotic syndrome.
Morgan, G; Postlethwaite, R J; Lendon, M; Houston, I B; Savage, J M
1981-01-01
Six successive cases of congenital nephrotic syndrome are described. Each one showed flexion deformities of the knees and hips, widely open anterior and posterior fontanelles, and wide separation of the skull sutures. These abnormalities were present not only in cases in which the renal histology was of the microcystic Finnish type of congenital nephrotic syndrome, but also in those in which the histological picture was one of the variants associated with congenital nephrotic syndrome. It is suggested that such abnormalities are postural deformities, possibly produced by the large placenta. Images Fig. 1 Fig. 2 PMID:7332344
Correction and adjusting for the deformation on solar sail
NASA Astrophysics Data System (ADS)
Shen, Fan; Rong, Siyuan; Zhang, Hualan; Peng, Fujun; Cui, Naigang
2016-12-01
A research on structural deformation of solar sail was presented. Nonlinear deformation of the sail was discussed, which will cause an additional devastating torque because of the shifting of the center of mass (CM). Finite-element analysis (FEA) method was carried out. In the computation, a correction was brought in, and a gradually increasing load method was presented. A more accurate membrane deformation result was obtained, and the photons pressure on the membrane was corrected. In purpose to guarantee the control ability in the long mission, a lifting mechanism is developed to adjust the large deformation. The lifting motion and result are verified by Abaqus. The research can be used in the solar sail controlling, where a large deformation may occur and an additional torque will disturb the controlling.
Clinical Implications of Nasal Septal Deformities
Mladina, Ranko; Skitarelić, Neven; Poje, Gorazd; Šubarić, Marin
2015-01-01
The first attempts to systematize septal distortions have been given by Cottle who defined four groups of septal deformities: subluxation, large spurs, caudal deflection and tension septum. Fortunately, the variations of the septal deformities show a certain order, thus enabling more precise classification. Mladina was the first to make user-friendly classification of septal deformities in six basic types. He also described the seventh type, named “Passali deformity”, which presents individually, but is always a well-defined combination between some of the previous six types. Mladina types of septal deformities (SD) are divided in two main groups: so called “vertical” deformities (types 1, 2, 3 and 4), and “horizontal” ones (types 5 and 6). This classification was immediately well accepted by rhinologists worldwide and started to be cited from the very beginning. Since then it has been continuously cited increasingly more often, thus making Mladina classification a gold standard whenever clinical researches on nasal septum are concerned. More than forty clinical studies based on this classification have been performed to date. It is extremely important to make a strict distinction between the types of SD since all of them play some specific role in the nasal and general physiology in man. PMID:26167337
Deformation Mechanisms during Hot Working of Titanium
NASA Astrophysics Data System (ADS)
Semiatin, S. L.; Bieler, T. R.; Miller, J. D.; Glavicic, M. G.
2004-06-01
Computer models of metal flow and texture evolution during hot working require accurate descriptions of deformation mechanisms and constitutive behavior. Such descriptions for titanium alloys can be very complex because of the variety of slip systems in the hexagonal (alpha) phase, let alone the complications associated with the deformation of two-phase (alpha/beta) microstructures in commercial alloys. Methods to elucidate the deformation behavior of unalloyed alpha titanium and two-phase Ti-6Al-4V will be described. First, the analysis of the hot deformation of heavily textured bar and plate materials will be described. In these instances, the anisotropy in flow stress and in sample deformation pattern have been used in conjunction with a crystal plasticity code to deduce the relative values of the critical resolved shear stresses for basal , prism , and pyramidal
Nanoscale buckling deformation in layered copolymer materials
Makke, Ali; Perez, Michel; Lame, Olivier; Barrat, Jean-Louis
2012-01-01
In layered materials, a common mode of deformation involves buckling of the layers under tensile deformation in the direction perpendicular to the layers. The instability mechanism, which operates in elastic materials from geological to nanometer scales, involves the elastic contrast between different layers. In a regular stacking of “hard” and “soft” layers, the tensile stress is first accommodated by a large deformation of the soft layers. The inhibited Poisson contraction results in a compressive stress in the direction transverse to the tensile deformation axis. The hard layers sustain this transverse compression until buckling takes place and results in an undulated structure. Using molecular simulations, we demonstrate this scenario for a material made of triblock copolymers. The buckling deformation is observed to take place at the nanoscale, at a wavelength that depends on strain rate. In contrast to what is commonly assumed, the wavelength of the undulation is not determined by defects in the microstructure. Rather, it results from kinetic effects, with a competition between the rate of strain and the growth rate of the instability. PMID:22203970
Nanoscale deformation mechanisms in bone.
Gupta, Himadri S; Wagermaier, Wolfgang; Zickler, Gerald A; Raz-Ben Aroush, D; Funari, Sérgio S; Roschger, Paul; Wagner, H Daniel; Fratzl, Peter
2005-10-01
Deformation mechanisms in bone matrix at the nanoscale control its exceptional mechanical properties, but the detailed nature of these processes is as yet unknown. In situ tensile testing with synchrotron X-ray scattering allowed us to study directly and quantitatively the deformation mechanisms at the nanometer level. We find that bone deformation is not homogeneous but distributed between a tensile deformation of the fibrils and a shearing in the interfibrillar matrix between them.
Deformation in the continental lithosphere
NASA Astrophysics Data System (ADS)
The Physical Properties of Earth Materials Committee, a technical committee of AGU's Tectonophysics Section, is organizing a dinner/colloquium as part of the Fall Meeting in San Francisco, Calif. This event will be held Monday, December 3rd, in the Gold Rush Room of the Holiday Inn Golden Gateway Hotel at 1500 Van Ness St. There will be a no-host bar from 6:30 to 7:30 P.M., followed by dinner from 7:30 to 8:30 P.M. Paul Tapponnier will deliver the after-dinner talk, “Large-Scale Deformation Mechanisms in the Continental Lithosphere: Where Do We Stand?” It will start at 8:30 P.M. and a business meeting will follow at 9:30 P.M.
Wang, Bo; Xiao, Xuan; Xia, Yuanqing; Fu, Mengyin
2013-11-15
Shipboard is not an absolute rigid body. Many factors could cause deformations which lead to large errors of mounted devices, especially for the navigation systems. Such errors should be estimated and compensated effectively, or they will severely reduce the navigation accuracy of the ship. In order to estimate the deformation, an unscented particle filter method for estimation of shipboard deformation based on an inertial measurement unit is presented. In this method, a nonlinear shipboard deformation model is built. Simulations demonstrated the accuracy reduction due to deformation. Then an attitude plus angular rate match mode is proposed as a frame to estimate the shipboard deformation using inertial measurement units. In this frame, for the nonlinearity of the system model, an unscented particle filter method is proposed to estimate and compensate the deformation angles. Simulations show that the proposed method gives accurate and rapid deformation estimations, which can increase navigation accuracy after compensation of deformation.
Wang, Bo; Xiao, Xuan; Xia, Yuanqing; Fu, Mengyin
2013-01-01
Shipboard is not an absolute rigid body. Many factors could cause deformations which lead to large errors of mounted devices, especially for the navigation systems. Such errors should be estimated and compensated effectively, or they will severely reduce the navigation accuracy of the ship. In order to estimate the deformation, an unscented particle filter method for estimation of shipboard deformation based on an inertial measurement unit is presented. In this method, a nonlinear shipboard deformation model is built. Simulations demonstrated the accuracy reduction due to deformation. Then an attitude plus angular rate match mode is proposed as a frame to estimate the shipboard deformation using inertial measurement units. In this frame, for the nonlinearity of the system model, an unscented particle filter method is proposed to estimate and compensate the deformation angles. Simulations show that the proposed method gives accurate and rapid deformation estimations, which can increase navigation accuracy after compensation of deformation. PMID:24248280
Probing deformed quantum commutators
NASA Astrophysics Data System (ADS)
Rossi, Matteo A. C.; Giani, Tommaso; Paris, Matteo G. A.
2016-07-01
Several quantum gravity theories predict a minimal length at the order of magnitude of the Planck length, under which the concepts of space and time lose their physical meaning. In quantum mechanics, the insurgence of such a minimal length can be described by introducing a modified position-momentum commutator, which in turn yields a generalized uncertainty principle, where the uncertainty on position measurements has a lower bound. The value of the minimal length is not predicted by theories and must be estimated experimentally. In this paper, we address the quantum bound to the estimability of the minimal uncertainty length by performing measurements on a harmonic oscillator, which is analytically solvable in the deformed algebra induced by the deformed commutation relations.
[Babies with cranial deformity].
Feijen, Michelle M W; Claessens, Edith A W M Habets; Dovens, Anke J Leenders; Vles, Johannes S; van der Hulst, Rene R W J
2009-01-01
Plagiocephaly was diagnosed in a baby aged 4 months and brachycephaly in a baby aged 5 months. Positional or deformational plagio- or brachycephaly is characterized by changes in shape and symmetry of the cranial vault. Treatment options are conservative and may include physiotherapy and helmet therapy. During the last two decades the incidence of positional plagiocephaly has increased in the Netherlands. This increase is due to the recommendation that babies be laid on their backs in order to reduce the risk of sudden infant death syndrome. We suggest the following: in cases of positional preference of the infant, referral to a physiotherapist is indicated. In cases of unacceptable deformity of the cranium at the age 5 months, moulding helmet therapy is a possible treatment option.
Partially segmented deformable mirror
Bliss, Erlan S.; Smith, James R.; Salmon, J. Thaddeus; Monjes, Julio A.
1991-01-01
A partially segmented deformable mirror is formed with a mirror plate having a smooth and continuous front surface and a plurality of actuators to its back surface. The back surface is divided into triangular areas which are mutually separated by grooves. The grooves are deep enough to make the plate deformable and the actuators for displacing the mirror plate in the direction normal to its surface are inserted in the grooves at the vertices of the triangular areas. Each actuator includes a transducer supported by a receptacle with outer shells having outer surfaces. The vertices have inner walls which are approximately perpendicular to the mirror surface and make planar contacts with the outer surfaces of the outer shells. The adhesive which is used on these contact surfaces tends to contract when it dries but the outer shells can bend and serve to minimize the tendency of the mirror to warp.
Partially segmented deformable mirror
Bliss, E.S.; Smith, J.R.; Salmon, J.T.; Monjes, J.A.
1991-05-21
A partially segmented deformable mirror is formed with a mirror plate having a smooth and continuous front surface and a plurality of actuators to its back surface. The back surface is divided into triangular areas which are mutually separated by grooves. The grooves are deep enough to make the plate deformable and the actuators for displacing the mirror plate in the direction normal to its surface are inserted in the grooves at the vertices of the triangular areas. Each actuator includes a transducer supported by a receptacle with outer shells having outer surfaces. The vertices have inner walls which are approximately perpendicular to the mirror surface and make planar contacts with the outer surfaces of the outer shells. The adhesive which is used on these contact surfaces tends to contract when it dries but the outer shells can bend and serve to minimize the tendency of the mirror to warp. 5 figures.
Covariant deformed oscillator algebras
NASA Technical Reports Server (NTRS)
Quesne, Christiane
1995-01-01
The general form and associativity conditions of deformed oscillator algebras are reviewed. It is shown how the latter can be fulfilled in terms of a solution of the Yang-Baxter equation when this solution has three distinct eigenvalues and satisfies a Birman-Wenzl-Murakami condition. As an example, an SU(sub q)(n) x SU(sub q)(m)-covariant q-bosonic algebra is discussed in some detail.
Surface Deformation in Imperial Valley, Southern California
NASA Astrophysics Data System (ADS)
Eneva, M.; Adams, D.; Falorni, G.; Morgan, J.
2013-12-01
The Imperial Valley in southern California is subjected to significant tectonic deformation resulting from the relative movement of the North American and Pacific plates. It is characterized by large earthquakes, frequent swarm activity, and aseismic events. High heat flow makes possible the operation of geothermal fields, some of which cause man-made surface displacements superimposed on the tectonic deformation. We apply radar interferometry (InSAR) to analyze Envisat ASAR data for the period 2003-2010. The SqueeSAR technique is used to obtain deformation time series and annual rates at numerous locations of permanent and distributed scatterers (PS and DS). SqueeSAR works very well in agricultural areas, where conventional differential InSAR (DinSAR) fails. We observe differential movements marking the Superstition Hills, San Andreas, and Imperial faults. The Imperial fault traverses agricultural fields, where DInSAR does not work and thus our SqueeSAR observations are the first for this fault (Fig. 1). We also observe steps in the deformation time series around the Superstition Hills fault from an October 2006 aseismic event and the April 2010 M7.2 earthquake south of the U.S.-Mexico border. Significant annual deformation rates are detected in the current geothermal fields. For example, subsidence of up to -50 mm/year is seen at the Salton Sea field (Fig. 2), and both subsidence and uplift are seen at Heber. We also determine the deformation baseline at prospective geothermal fields, thus making it possible in the future to distinguish between man-made and tectonic causes of surface deformation. Fig. 1. Line-of-sight (LOS) deformation indicates differential displacement on both sides of Imperial Fault. Movements away from the satellite are shown in yellow to red, and towards the satellite in blue. Larger deformation is associated with two geothermal fields, Heber (to the south-west) and East Mesa (to the east). Fig. 2. Subsidence in the Salton Sea geothermal
Deformation of Wrinkled Graphene
2015-01-01
The deformation of monolayer graphene, produced by chemical vapor deposition (CVD), on a polyester film substrate has been investigated through the use of Raman spectroscopy. It has been found that the microstructure of the CVD graphene consists of a hexagonal array of islands of flat monolayer graphene separated by wrinkled material. During deformation, it was found that the rate of shift of the Raman 2D band wavenumber per unit strain was less than 25% of that of flat flakes of mechanically exfoliated graphene, whereas the rate of band broadening per unit strain was about 75% of that of the exfoliated material. This unusual deformation behavior has been modeled in terms of mechanically isolated graphene islands separated by the graphene wrinkles, with the strain distribution in each graphene island determined using shear lag analysis. The effect of the size and position of the Raman laser beam spot has also been incorporated in the model. The predictions fit well with the behavior observed experimentally for the Raman band shifts and broadening of the wrinkled CVD graphene. The effect of wrinkles upon the efficiency of graphene to reinforce nanocomposites is also discussed. PMID:25765609
[Neurogenic foot deformities].
Senst, S
2010-01-01
There is a multitude of neurological diseases which may lead to neuro-orthopaedic problems and subsequently to neurogenic foot deformities. For this reason the diagnostician will be consistently surprised that there is a great multitude of different foot abnormalities and that not only the typical spastic talipes equines dominates. Of particular significance here is that these deformities almost always develop progressively, whereas most diseases persist per se, cerebral palsy being a typical case in point. However, in MMC (myelomeningocele) patients, there is also the danger of a worsening of the basic problem in the case of tethered cord syndrome. Unlike congenital talipes equinovarus, neuro-orthopaedic talipes equinovarus often shows over- or undercorrection postoperatively due to a shift in muscle imbalance. It is important, therefore, that the basis of conservative therapy include regular physiotherapy and orthoses during the day and, if necessary, at night. Botulinum toxin has been established as an additional measure for spasticity; however, this cannot always prevent surgical intervention, but is able to delay this to a better point in the development of the child/patient. The present article describes the diversity of neurological deformities and presents conservative as well as surgical therapeutic approaches.
Triangles bridge the scales: Quantifying cellular contributions to tissue deformation
NASA Astrophysics Data System (ADS)
Merkel, Matthias; Etournay, Raphaël; Popović, Marko; Salbreux, Guillaume; Eaton, Suzanne; Jülicher, Frank
2017-03-01
In this article, we propose a general framework to study the dynamics and topology of cellular networks that capture the geometry of cell packings in two-dimensional tissues. Such epithelia undergo large-scale deformation during morphogenesis of a multicellular organism. Large-scale deformations emerge from many individual cellular events such as cell shape changes, cell rearrangements, cell divisions, and cell extrusions. Using a triangle-based representation of cellular network geometry, we obtain an exact decomposition of large-scale material deformation. Interestingly, our approach reveals contributions of correlations between cellular rotations and elongation as well as cellular growth and elongation to tissue deformation. Using this triangle method, we discuss tissue remodeling in the developing pupal wing of the fly Drosophila melanogaster.
Prediction and classification of Alzheimer disease based on quantification of MRI deformation
Jiang, Chunxiang; Zhang, Lijuan
2017-01-01
Detecting early morphological changes in the brain and making early diagnosis are important for Alzheimer’s disease (AD). High resolution magnetic resonance imaging can be used to help diagnosis and prediction of the disease. In this paper, we proposed a machine learning method to discriminate patients with AD or mild cognitive impairment (MCI) from healthy elderly and to predict the AD conversion in MCI patients by computing and analyzing the regional morphological differences of brain between groups. Distance between each pair of subjects was quantified from a symmetric diffeomorphic registration, followed by an embedding algorithm and a learning approach for classification. The proposed method obtained accuracy of 96.5% in differentiating mild AD from healthy elderly with the whole-brain gray matter or temporal lobe as region of interest (ROI), 91.74% in differentiating progressive MCI from healthy elderly and 88.99% in classifying progressive MCI versus stable MCI with amygdala or hippocampus as ROI. This deformation-based method has made full use of the pair-wise macroscopic shape difference between groups and consequently increased the power for discrimination. PMID:28264071
Detail-preserving controllable deformation from sparse examples.
Huang, Haoda; Yin, KangKang; Zhao, Ling; Qi, Yue; Yu, Yizhou; Tong, Xin
2012-08-01
Recent advances in laser scanning technology have made it possible to faithfully scan a real object with tiny geometric details, such as pores and wrinkles. However, a faithful digital model should not only capture static details of the real counterpart but also be able to reproduce the deformed versions of such details. In this paper, we develop a data-driven model that has two components; the first accommodates smooth large-scale deformations and the second captures high-resolution details. Large-scale deformations are based on a nonlinear mapping between sparse control points and bone transformations. A global mapping, however, would fail to synthesize realistic geometries from sparse examples, for highly deformable models with a large range of motion. The key is to train a collection of mappings defined over regions locally in both the geometry and the pose space. Deformable fine-scale details are generated from a second nonlinear mapping between the control points and per-vertex displacements. We apply our modeling scheme to scanned human hand models, scanned face models, face models reconstructed from multiview video sequences, and manually constructed dinosaur models. Experiments show that our deformation models, learned from extremely sparse training data, are effective and robust in synthesizing highly deformable models with rich fine features, for keyframe animation as well as performance-driven animation. We also compare our results with those obtained by alternative techniques.
Learning a hierarchical deformable template for rapid deformable object parsing.
Zhu, Long Leo; Chen, Yuanhao; Yuille, Alan
2010-06-01
In this paper, we address the tasks of detecting, segmenting, parsing, and matching deformable objects. We use a novel probabilistic object model that we call a hierarchical deformable template (HDT). The HDT represents the object by state variables defined over a hierarchy (with typically five levels). The hierarchy is built recursively by composing elementary structures to form more complex structures. A probability distribution--a parameterized exponential model--is defined over the hierarchy to quantify the variability in shape and appearance of the object at multiple scales. To perform inference--to estimate the most probable states of the hierarchy for an input image--we use a bottom-up algorithm called compositional inference. This algorithm is an approximate version of dynamic programming where approximations are made (e.g., pruning) to ensure that the algorithm is fast while maintaining high performance. We adapt the structure-perceptron algorithm to estimate the parameters of the HDT in a discriminative manner (simultaneously estimating the appearance and shape parameters). More precisely, we specify an exponential distribution for the HDT using a dictionary of potentials, which capture the appearance and shape cues. This dictionary can be large and so does not require handcrafting the potentials. Instead, structure-perceptron assigns weights to the potentials so that less important potentials receive small weights (this is like a "soft" form of feature selection). Finally, we provide experimental evaluation of HDTs on different visual tasks, including detection, segmentation, matching (alignment), and parsing. We show that HDTs achieve state-of-the-art performance for these different tasks when evaluated on data sets with groundtruth (and when compared to alternative algorithms, which are typically specialized to each task).
Dynamic Recrystallization: The Dynamic Deformation Regime
NASA Astrophysics Data System (ADS)
Murr, L. E.; Pizaña, C.
2007-11-01
Severe plastic deformation (PD), especially involving high strain rates (>103 s 1), occurs through solid-state flow, which is accommodated by dynamic recrystallization (DRX), either in a continuous or discontinuous mode. This flow can be localized in shear instability zones (or adiabatic shear bands (ASBs)) with dimensions smaller than 5 μ, or can include large volumes with flow zone dimensions exceeding centimeters. This article illustrates these microstructural features using optical and electron metallography to examine a host of dynamic deformation examples: shaped charge jet formation, high-velocity and hypervelocity impact crater formation, rod penetration into thick targets (which includes rod and target DRX flow and mixing), large projectile-induced target plug formation and failure, explosive welding, and friction-stir welding and processing. The DRX is shown to be a universal mechanism that accommodates solid-state flow in extreme (or severe) PD regimes.
NASA Technical Reports Server (NTRS)
Stenholm, Stig
1993-01-01
A single mode cavity is deformed smoothly to change its electromagnetic eigenfrequency. The system is modeled as a simple harmonic oscillator with a varying period. The Wigner function of the problem is obtained exactly by starting with a squeezed initial state. The result is evaluated for a linear change of the cavity length. The approach to the adiabatic limit is investigated. The maximum squeezing is found to occur for smooth change lasting only a fraction of the oscillational period. However, only a factor of two improvement over the adiabatic result proves to be possible. The sudden limit cannot be investigated meaningfully within the model.
A microfluidic technique to probe cell deformability.
Hoelzle, David J; Varghese, Bino A; Chan, Clara K; Rowat, Amy C
2014-09-03
Here we detail the design, fabrication, and use of a microfluidic device to evaluate the deformability of a large number of individual cells in an efficient manner. Typically, data for ~10(2) cells can be acquired within a 1 hr experiment. An automated image analysis program enables efficient post-experiment analysis of image data, enabling processing to be complete within a few hours. Our device geometry is unique in that cells must deform through a series of micron-scale constrictions, thereby enabling the initial deformation and time-dependent relaxation of individual cells to be assayed. The applicability of this method to human promyelocytic leukemia (HL-60) cells is demonstrated. Driving cells to deform through micron-scale constrictions using pressure-driven flow, we observe that human promyelocytic (HL-60) cells momentarily occlude the first constriction for a median time of 9.3 msec before passaging more quickly through the subsequent constrictions with a median transit time of 4.0 msec per constriction. By contrast, all-trans retinoic acid-treated (neutrophil-type) HL-60 cells occlude the first constriction for only 4.3 msec before passaging through the subsequent constrictions with a median transit time of 3.3 msec. This method can provide insight into the viscoelastic nature of cells, and ultimately reveal the molecular origins of this behavior.
Deformation of a micro-torque swimmer
Ishikawa, Takuji; Tanaka, Tomoyuki; Imai, Yohsuke; Omori, Toshihiro; Matsunaga, Daiki
2016-01-01
The membrane tension of some kinds of ciliates has been suggested to regulate upward and downward swimming velocities under gravity. Despite its biological importance, deformation and membrane tension of a ciliate have not been clarified fully. In this study, we numerically investigated the deformation of a ciliate swimming freely in a fluid otherwise at rest. The cell body was modelled as a capsule with a hyperelastic membrane enclosing a Newtonian fluid. Thrust forces due to the ciliary beat were modelled as torques distributed above the cell body. The effects of membrane elasticity, the aspect ratio of the cell's reference shape, and the density difference between the cell and the surrounding fluid were investigated. The results showed that the cell deformed like a heart shape, when the capillary number was sufficiently large. Under the influence of gravity, the membrane tension at the anterior end decreased in the upward swimming while it increased in the downward swimming. Moreover, gravity-induced deformation caused the cells to move gravitationally downwards or upwards, which resulted in a positive or negative geotaxis-like behaviour with a physical origin. These results are important in understanding the physiology of a ciliate's biological responses to mechanical stimuli. PMID:26997893
Elastic wave propagation in finitely deformed layered materials
NASA Astrophysics Data System (ADS)
Galich, Pavel I.; Fang, Nicholas X.; Boyce, Mary C.; Rudykh, Stephan
2017-01-01
We analyze elastic wave propagation in highly deformable layered media with isotropic hyperelastic phases. Band gap structures are calculated for the periodic laminates undergoing large deformations. Compact explicit expressions for the phase and group velocities are derived for the long waves propagating in the finitely deformed composites. Elastic wave characteristics and band gaps are shown to be highly tunable by deformation. The influence of deformation on shear and pressure wave band gaps for materials with various composition and constituent properties are studied, finding advantageous compositions for producing highly tunable complete band gaps in low-frequency ranges. The shear wave band gaps are influenced through the deformation induced changes in effective material properties, whereas pressure wave band gaps are mostly influenced by deformation induced geometry changes. The wide shear wave band gaps are found in the laminates with small volume fractions of a soft phase embedded in a stiffer material; pressure wave band gaps of the low-frequency range appear in the laminates with thin highly compressible layers embedded in a nearly incompressible phase. Thus, by constructing composites with a small amount of a highly compressible phase, wide complete band gaps at the low-frequency range can be achieved; furthermore, these band gaps are shown to be highly tunable by deformation.
Overview of deformable mirror technologies for adaptive optics and astronomy
NASA Astrophysics Data System (ADS)
Madec, P.-Y.
2012-07-01
From the ardent bucklers used during the Syracuse battle to set fire to Romans’ ships to more contemporary piezoelectric deformable mirrors widely used in astronomy, from very large voice coil deformable mirrors considered in future Extremely Large Telescopes to very small and compact ones embedded in Multi Object Adaptive Optics systems, this paper aims at giving an overview of Deformable Mirror technology for Adaptive Optics and Astronomy. First the main drivers for the design of Deformable Mirrors are recalled, not only related to atmospheric aberration compensation but also to environmental conditions or mechanical constraints. Then the different technologies available today for the manufacturing of Deformable Mirrors will be described, pros and cons analyzed. A review of the Companies and Institutes with capabilities in delivering Deformable Mirrors to astronomers will be presented, as well as lessons learned from the past 25 years of technological development and operation on sky. In conclusion, perspective will be tentatively drawn for what regards the future of Deformable Mirror technology for Astronomy.
Algorithmic deformation of matrix factorisations
NASA Astrophysics Data System (ADS)
Carqueville, Nils; Dowdy, Laura; Recknagel, Andreas
2012-04-01
Branes and defects in topological Landau-Ginzburg models are described by matrix factorisations. We revisit the problem of deforming them and discuss various deformation methods as well as their relations. We have implemented these algorithms and apply them to several examples. Apart from explicit results in concrete cases, this leads to a novel way to generate new matrix factorisations via nilpotent substitutions, and to criteria whether boundary obstructions can be lifted by bulk deformations.
Modelling highly deformable metal extrusion using SPH
NASA Astrophysics Data System (ADS)
Prakash, Mahesh; Cleary, Paul W.
2015-05-01
Computational modelling is often used to reduce trial extrusions through accurate defect prediction. Traditionally, metal extrusion is modelled using mesh based finite element methods. However, large plastic deformations can lead to heavy re-meshing and numerical diffusion. Here we use the mesh-less smoothed particle hydrodynamics method since it allows simulation of large deformations without re-meshing and the tracking of history dependent properties such as plastic strain making it suitable for defect prediction. The variation in plastic strain and deformation for aluminium alloy in a cylindrical 3D geometry with extrusion ratio and die angle is evaluated. The extrusion process is found to have three distinct phases consisting of an initial sharp rise in extrusion force, a steady phase requiring constant force and terminating in a sharp decline in force as metal is completely extruded. Deformation and plastic strain increased significantly with extrusion ratio but only moderately with die angle. Extrusion force increased by 150 % as the extrusion ratio increased from 2:1 to 4:1 but had only a marginal change with die angle. A low strain zone in the centre of the extruded product was found to be a function of extrusion ratio but was persistent and did not vary with die angle. Simulation of a complex 3D building industry component showed large variations in plastic strain along the length of the product at two scales. These were due to change in metal behaviour as extrusion progressed from phase 1 to phase 2. A stagnation zone at the back of the die was predicted that could lead to the "funnel" or "pipe" defect.
Global organization of tectonic deformation on Venus
NASA Technical Reports Server (NTRS)
Bilotti, Frank; Connors, Chris; Suppe, John
1993-01-01
The geographic organization of surface deformation on Venus as on Earth is a key to understanding the global tectonic system. To date we have mapped the distribution of three unambiguous tectonic land forms on Venus: (1) linear foldbelts analogous to those at plate margins of the Earth; (2) linear rift zones, analogous to continental rifts on the Earth; and (3) distributed plains deformation in the form of wrinkle ridges and extensional faults and fractures. The linear foldbelts are the dominant structural style in the Northern Hemisphere; ninety percent of the planet's foldbelts lie above the equator. In contrast, compressive deformation in the Southern Hemisphere is dominated by two large, sweeping patterns of wrinkle ridges. The two hemispheres are divided by an equatorial region that is largely covered by rift zones and several large tessera blocks. A tectonic model of generally poleward convergence of the Northern Hemisphere explains the distribution of foldbelts and rift zones. In our model, a northern hemispherical plate (or system of plates) moves poleward and deforms along discrete, predominately longitudinal bands. We recognize four types of foldbelts based on their relationships to other large-scale tectonic features on Venus. There are foldbelts that lie within the low plains, foldbelts associated with coronae, novae and chasmata, foldbelts that lie at the margins of poly-deformed tessera plateaus, and the folded mountain belts around Lakshmi Planum. We see a geometric increase in the area of fold belts when normalized to percent area at a given latitude. This increase is consistent with our model of poleward convergence. Also, the orientations of most foldbelts are either approximately north-south or parallel to lines of latitude in the northern hemisphere. This observation is also consistent with the model in that the longitudinal bands are the result of the decreasing area of the sphere as the plate moves poleward and the latitudinal belts are the
NASA Astrophysics Data System (ADS)
Milton, Graeme Walter
2013-07-01
A complete characterization is given of the possible macroscopic deformations of periodic non-linear affine unimode metamaterials constructed from rigid bars and pivots. The materials are affine in the sense that their macroscopic deformations can only be affine deformations: on a local level the deformation may vary from cell to cell. Unimode means that macroscopically the material can only deform along a one dimensional trajectory in the six dimensional space of invariants describing the deformation (excluding translations and rotations). We show by explicit construction that any continuous trajectory is realizable to an arbitrarily high degree of approximation provided at all points along the trajectory the geometry does not collapse to a lower dimensional one. In particular, we present two and three dimensional dilational materials having an arbitrarily large flexibility window. These are perfect auxetic materials for which a dilation is the only easy mode of deformation. They are free to dilate to arbitrarily large strain with zero bulk modulus.
[Rheumatic forefoot deformities].
Fuhrmann, R
2014-11-01
The frequency and extent of rheumatic forefoot deformities have been greatly reduced since the introduction of disease-modifying antirheumatic drugs (DMARD). The accompanying reduction in arthritic destruction of joints opens up new treatment options whereby priority is given to joint preservation. This is true for the first middle foot ray as well as for the small toe rays. Whereas resection arthroplasty of the metatarsophalangeal joints II-V was previously considered the gold standard treatment, joint-preserving operative procedures (e.g. metatarsal osteotomy and periarticular soft tissue interventions) are now being increasingly more propagated. Resection arthroplasty of the first midfoot ray has major biomechanical disadvantages so that it is not surprising that reconstructive procedures are given priority. In patients with severe arthritic destruction of the first metatarsophalangeal joint, arthrodesis has substantial biomechanical advantages compared to resection arthroplasty. Nevertheless, it has not yet been confirmed that fusion leads to superior clinical results.
NASA Technical Reports Server (NTRS)
Wu, R. W. H.; Stagliano, T. R.; Witmer, E. A.; Spilker, R. L.
1978-01-01
These structural ring deflections lie essentially in one plane and, hence, are called two-dimensional (2-d). The structural rings may be complete or partial; the former may be regarded as representing a fragment containment ring while the latter may be viewed as a 2-d fragment-deflector structure. These two types of rings may be either free or supported in various ways (pinned-fixed, locally clamped, elastic-foundation supported, mounting-bracket supported, etc.). The initial geometry of each ring may be circular or arbitrarily curved; uniform-thickness or variable-thickness rings may be analyzed. Strain-hardening and strain-rate effects of initially-isotropic material are taken into account. An approximate analysis utilizing kinetic energy and momentum conservation relations is used to predict the after-impact velocities of each fragment and of the impact-affected region of the ring; this procedure is termed the collision-imparted velocity method (CIVM) and is used in the CIVM-JET 5 B program. This imparted-velocity information is used in conjunction with a finite-element structural response computation code to predict the transient, large-deflection, elastic-plastic responses of the ring. Similarly, the equations of motion of each fragment are solved in small steps in time. Provisions are made in the CIVM-JET 5B code to analyze structural ring response to impact attack by from 1 to 3 fragments, each with its own size, mass, translational velocity components, and rotational velocity. The effects of friction between each fragment and the impacted ring are included.
Grain boundary engineering of highly deformable ceramics
Mecartney, M.L.
2000-07-01
Highly deformable ceramics can be created with the addition of intergranular silicate phases. These amorphous intergranular phases can assist in superplastic deformation by relieving stress concentrations and minimizing grain growth if the appropriate intergranular compositions are selected. Examples from 3Y-TZP and 8Y-CSZ ceramics are discussed. The grain boundary chemistry is analyzed by high resolution analytical TEM is found to have a strong influence on the cohesion of the grains both at high temperature and at room temperature. Intergranular phases with a high ionic character and containing large ions with a relatively weak bond strength appear to cause premature failure. In contrast, intergranular phases with a high degree of covalent character and similar or smaller ions than the ceramic and a high ionic bond strength are the best for grain boundary adhesion and prevention of both cavitation at high temperatures and intergranular fracture at room temperature.
High strain rate deformation of layered nanocomposites.
Lee, Jae-Hwang; Veysset, David; Singer, Jonathan P; Retsch, Markus; Saini, Gagan; Pezeril, Thomas; Nelson, Keith A; Thomas, Edwin L
2012-01-01
Insight into the mechanical behaviour of nanomaterials under the extreme condition of very high deformation rates and to very large strains is needed to provide improved understanding for the development of new protective materials. Applications include protection against bullets for body armour, micrometeorites for satellites, and high-speed particle impact for jet engine turbine blades. Here we use a microscopic ballistic test to report the responses of periodic glassy-rubbery layered block-copolymer nanostructures to impact from hypervelocity micron-sized silica spheres. Entire deformation fields are experimentally visualized at an exceptionally high resolution (below 10 nm) and we discover how the microstructure dissipates the impact energy via layer kinking, layer compression, extreme chain conformational flattening, domain fragmentation and segmental mixing to form a liquid phase. Orientation-dependent experiments show that the dissipation can be enhanced by 30% by proper orientation of the layers.
Regional Deformation Studies with GRACE and GPS
NASA Technical Reports Server (NTRS)
Davis, J. L.; Elosequi, P.; Tamisiea, M.; Mitrovica, J. X.
2005-01-01
GRACE data indicate large seasonal variations in gravity that have been shown to be to be related to climate-driven fluxes of surface water. Seasonal redistribution of surface mass deforms the Earth, and our previous study using GRACE data demonstrate that annual radial deformations of +/-13 mm in the region of Amazon River Basin were observed by both GRACE and ten GPS sites in the region. For the GRACE determinations, we estimate in a least-squares solution for each Stokes coefficient parameters that represent the amplitudes of the annual variation. We then filter these parameters based on a statistical test that uses the scatter of the postfit residuals. We demonstrate by comparison to the GPS amplitudes that this method is more accurate, for this region, than Gaussian smoothing. Our model for the temporal behavior of the gravity coefficients includes a rate term, and although the time series are noisy, the glacial isostatic adjustment signal over Hudson s Bay can be observed. .
Explicit Seesaw Model and Deformed Fermion Universality
NASA Astrophysics Data System (ADS)
Krolikowski, Wojciech
2003-01-01
In the simple model of neutrino texture presented in this paper, the Majorana lefthanded mass matrix is zero, the Majorana righthanded mass matrix --- diagonal and degenerate, and the Dirac mass matrix has a hierarchical structure, deformed unitarily by nearly bimaximal mixing. In the case, when the Majorana righthanded term dominates over the Dirac term, the familiar seesaw mechanism leads effectively to the nearly bimaximal oscillations of active neutrinos, consistent with solar and atmospheric neutrino experiments. If the Dirac term, before its unitary deformation, is similar in shape to the known charged-lepton mass matrix, then parameters for solar ν e's and atmospheric ν μ 's become related to each other, predicting from the SuperKamiokande value of Δ m322 a tiny Δ m212 typical for MSW LOW solar solution rather than for MSW Large Mixing Angle solution. The predicted mass spectrum is then hierarchical. In Appendix a suggestive form of nearly bimaximal effective mass matrix is derived.
Sensitivity errors in interferometric deformation metrology.
Farrant, David I; Petzing, Jon N
2003-10-01
Interferometric measurement techniques such as holographic interferometry and electronic speckle-pattern interferometry are valuable for measuring the deformation of objects. Conventional theoretical models of deformation measurement assume collimated illumination and telecentric imaging, which are usually only practical for small objects. Large objects often require divergent illumination, for which the models are valid only when the object is planar, and then only in the paraxial region. We present an analysis and discussion of the three-dimensional systematic sensitivity errors for both in-plane and out-of-plane interferometer configurations, where it is shown that the errors can be significant. A dimensionless approach is adopted to make the analysis generic and hence scalable to a system of any size.
Viscoelastic deformation near active plate boundaries
NASA Technical Reports Server (NTRS)
Ward, S. N.
1986-01-01
Model deformations near the active plate boundaries of Western North America using space-based geodetic measurements as constraints are discussed. The first six months of this project were spent gaining familarity with space-based measurements, accessing the Crustal Dynamics Data Information Computer, and building time independent deformation models. The initial goal was to see how well the simplest elastic models can reproduce very long base interferometry (VLBI) baseline data. From the Crustal Dynamics Data Information Service, a total of 18 VLBI baselines are available which have been surveyed on four or more occasions. These data were fed into weighted and unweighted inversions to obtain baseline closure rates. Four of the better quality lines are illustrated. The deformation model assumes that the observed baseline rates result from a combination of rigid plate tectonic motions plus a component resulting from elastic strain build up due to a failure of the plate boundary to slip at the full plate tectonic rate. The elastic deformation resulting from the locked plate boundary is meant to portray interseismic strain accumulation. During and shortly after a large interplate earthquake, these strains are largely released, and points near the fault which were previously retarded suddenly catch up to the positions predicted by rigid plate models. Researchers judge the quality of fit by the sum squares of weighted residuals, termed total variance. The observed baseline closures have a total variance of 99 (cm/y)squared. When the RM2 velocities are assumed to model the data, the total variance increases to 154 (cm/y)squared.
[Spectrum research on metamorphic and deformation of tectonically deformed coals].
Li, Xiao-Shi; Ju, Yi-Wen; Hou, Quan-Lin; Lin, Hong
2011-08-01
The structural and compositive evolution of tectonically deformed coals (TDCs) and their influencing factors were investigated and analyzed in detail through Fourier transform infrared spectroscopy (FTIR) and laser Raman spectra analysis. The TDC samples (0.7% < Ro,max <3.1%) were collected from Huaibei coalfield with different deformation mechanisms and intensity. The FTIR of TDCs shows that the metamorphism and the deformation affect the degradation and polycondensation process of macromolecular structure to different degree. The Raman spectra analysis indicates that secondary structure defects can be produced mainly by structural deformation, also the metamorphism influences the secondary structure defects and aromatic structure. Through comprehensive analysis, it was discussed that the ductile deformation could change to strain energy through the increase and accumulation of dislocation in molecular structure units of TDC, and it could make an obvious influence on degradation and polycondensation. While the brittle deformation could change to frictional heat energy and promote the metamorphism and degradation of TDC structure, but has less effect on polycondensation. Furthermore, degradation is the main reason for affecting the structural evolution of coal in lower metamorphic stage, and polycondensation is the most important controlling factor in higher metamorphic stage. Under metamorphism and deformation, the small molecules which break and fall off from the macromolecular tructure of TDC are preferentially replenished and embedded into the secondary structure defects or the residual aromatic rings were formed into aromatic structure by polycondensation. This process improved the stability of coal structure. It is easier for ductile deformation of coal to induce the secondary structure defects than brittle deformation.
NASA Astrophysics Data System (ADS)
Reaungamornrat, S.; De Silva, T.; Uneri, A.; Goerres, J.; Jacobson, M.; Ketcha, M.; Vogt, S.; Kleinszig, G.; Khanna, A. J.; Wolinsky, J.-P.; Prince, J. L.; Siewerdsen, J. H.
2016-12-01
Accurate intraoperative localization of target anatomy and adjacent nervous and vascular tissue is essential to safe, effective surgery, and multimodality deformable registration can be used to identify such anatomy by fusing preoperative CT or MR images with intraoperative images. A deformable image registration method has been developed to estimate viscoelastic diffeomorphisms between preoperative MR and intraoperative CT using modality-independent neighborhood descriptors (MIND) and a Huber metric for robust registration. The method, called MIND Demons, optimizes a constrained symmetric energy functional incorporating priors on smoothness, geodesics, and invertibility by alternating between Gauss-Newton optimization and Tikhonov regularization in a multiresolution scheme. Registration performance was evaluated for the MIND Demons method with a symmetric energy formulation in comparison to an asymmetric form, and sensitivity to anisotropic MR voxel-size was analyzed in phantom experiments emulating image-guided spine-surgery in comparison to a free-form deformation (FFD) method using local mutual information (LMI). Performance was validated in a clinical study involving 15 patients undergoing intervention of the cervical, thoracic, and lumbar spine. The target registration error (TRE) for the symmetric MIND Demons formulation (1.3 ± 0.8 mm (median ± interquartile)) outperformed the asymmetric form (3.6 ± 4.4 mm). The method demonstrated fairly minor sensitivity to anisotropic MR voxel size, with median TRE ranging 1.3-2.9 mm for MR slice thickness ranging 0.9-9.9 mm, compared to TRE = 3.2-4.1 mm for LMI FFD over the same range. Evaluation in clinical data demonstrated sub-voxel TRE (<2 mm) in all fifteen cases with realistic deformations that preserved topology with sub-voxel invertibility (0.001 mm) and positive-determinant spatial Jacobians. The approach therefore appears robust against realistic
NASA Astrophysics Data System (ADS)
Liu, Yuan; D'Haese, Pierre-Francois; Dawant, Benoit M.
2014-03-01
Deep brain stimulation, which is used to treat various neurological disorders, involves implanting a permanent electrode into precise targets deep in the brain. Accurate pre-operative localization of the targets on pre-operative MRI sequence is challenging as these are typically located in homogenous regions with poor contrast. Population-based statistical atlases can assist with this process. Such atlases are created by acquiring the location of efficacious regions from numerous subjects and projecting them onto a common reference image volume using some normalization method. In previous work, we presented results concluding that non-rigid registration provided the best result for such normalization. However, this process could be biased by the choice of the reference image and/or registration approach. In this paper, we have qualitatively and quantitatively compared the performance of six recognized deformable registration methods at normalizing such data in poor contrasted regions onto three different reference volumes using a unique set of data from 100 patients. We study various metrics designed to measure the centroid, spread, and shape of the normalized data. This study leads to a total of 1800 deformable registrations and results show that statistical atlases constructed using different deformable registration methods share comparable centroids and spreads with marginal differences in their shape. Among the six methods being studied, Diffeomorphic Demons produces the largest spreads and centroids that are the furthest apart from the others in general. Among the three atlases, one atlas consistently outperforms the other two with smaller spreads for each algorithm. However, none of the differences in the spreads were found to be statistically significant, across different algorithms or across different atlases.
Problems of nonlinear deformation
NASA Astrophysics Data System (ADS)
Grigoliuk, E. I.; Shalashilin, V. I.
A method of continuing the solution is discussed with respect to a parameter for a certain class of nonlinear problems in solid mechanics. Modifications of the method are developed in order to implement a unified continuation process at regular and limit points in the set of solutions, with extensions to nonlinear boundary value problems. Algorithms are developed for solving large deflection problems of elastic arches and large axisymmetric deflection problems for shells of revolution. In particular, the algorithms are used for the analysis of large deflections of circular arches and toroidal shells. Examples of natural vibration and stability problems for parallelograms and trapezoidal membranes and panels are given.
Perceptual transparency from image deformation
Kawabe, Takahiro; Maruya, Kazushi; Nishida, Shin’ya
2015-01-01
Human vision has a remarkable ability to perceive two layers at the same retinal locations, a transparent layer in front of a background surface. Critical image cues to perceptual transparency, studied extensively in the past, are changes in luminance or color that could be caused by light absorptions and reflections by the front layer, but such image changes may not be clearly visible when the front layer consists of a pure transparent material such as water. Our daily experiences with transparent materials of this kind suggest that an alternative potential cue of visual transparency is image deformations of a background pattern caused by light refraction. Although previous studies have indicated that these image deformations, at least static ones, play little role in perceptual transparency, here we show that dynamic image deformations of the background pattern, which could be produced by light refraction on a moving liquid’s surface, can produce a vivid impression of a transparent liquid layer without the aid of any other visual cues as to the presence of a transparent layer. Furthermore, a transparent liquid layer perceptually emerges even from a randomly generated dynamic image deformation as long as it is similar to real liquid deformations in its spatiotemporal frequency profile. Our findings indicate that the brain can perceptually infer the presence of “invisible” transparent liquids by analyzing the spatiotemporal structure of dynamic image deformation, for which it uses a relatively simple computation that does not require high-level knowledge about the detailed physics of liquid deformation. PMID:26240313
Derivation of deformation characteristics in fast-moving glaciers
NASA Astrophysics Data System (ADS)
Herzfeld, Ute C.; Clarke, Garry K. C.; Mayer, Helmut; Greve, Ralf
2004-04-01
Crevasse patterns are the writings in a glacier's history book—the movement, strain and deformation frozen in ice. Therefore by analysis of crevasse patterns we can learn about the ice-dynamic processes which the glacier has experienced. Direct measurement of ice movement and deformation is time-consuming and costly, in particular for large glaciers; typically, observations are lacking when sudden changes occur. Analysis of crevasse patterns provides a means to reconstruct past and ongoing deformation processes mathematically. This is especially important for fast-moving ice. Ice movement and deformation are commonly described and analyzed using continuum mechanics and measurements of ice velocities or strain rates. Here, we present a different approach to the study of ice deformation based on principles of structural geology. Fast ice movement manifests itself in the occurrence of crevasses. Because crevasses remain after the deformation event and may be transported, overprinted or closed, their analysis based on aerial videography and photography or satellite data gives information on past deformation events and resulting strain states. In our treatment, we distinguish (A) continuously fast-moving glaciers and ice streams, and (B) surge-type glaciers, based on observations of two prototypes, Jakobshavns Isbræ, Greenland, for (A), and Bering Glacier, Alaska, during the 1993-1995 surge, for (B). Classes of ice-deformation types are derived from aerial images of ice surfaces using structural geology, i.e. structural glaciology. For each type, the deformation gradient matrix is formed. Relationships between invariants used in structural geology and continuum mechanics and the singular value decomposition are established and applied to ice-surface classification. Deformation during a surge is mostly one of the extensional deformation types. Continuously, or infinitesimally repeated, deformation acting in continuously fast-moving ice causes different typical
Scaling properties of sea ice deformation from buoy dispersion analysis
NASA Astrophysics Data System (ADS)
Rampal, P.; Weiss, J.; Marsan, D.; Lindsay, R.; Stern, H.
2008-03-01
A temporal and spatial scaling analysis of Arctic sea ice deformation is performed over timescales from 3 h to 3 months and over spatial scales from 300 m to 300 km. The deformation is derived from the dispersion of pairs of drifting buoys, using the IABP (International Arctic Buoy Program) buoy data sets. This study characterizes the deformation of a very large solid plate (the Arctic sea ice cover) stressed by heterogeneous forcing terms like winds and ocean currents. It shows that the sea ice deformation rate depends on the scales of observation following specific space and time scaling laws. These scaling properties share similarities with those observed for turbulent fluids, especially for the ocean and the atmosphere. However, in our case, the time scaling exponent depends on the spatial scale, and the spatial exponent on the temporal scale, which implies a time/space coupling. An analysis of the exponent values shows that Arctic sea ice deformation is very heterogeneous and intermittent whatever the scales, i.e., it cannot be considered as viscous-like, even at very large time and/or spatial scales. Instead, it suggests a deformation accommodated by a multiscale fracturing/faulting processes.
A simulation study of planar swaging deformation
NASA Astrophysics Data System (ADS)
Zhang, Cheng-Gen; Jen, Gwang-Shen; Su, Gwang-Huei
1992-08-01
Planar swaging deformation was studied with a photoplastic method. The domestic polycarbonate was used as a simulation material. The full-field strain distribution for planar swaging deformation was obtained. The average error of the calculated strain was less than 7 percent. The deformation area and the effect of friction on deformation area were studied with the characteristics of photoplasticity. This paper points out the special features of planar swaging deformation and the effect of lubrication on deformation flow.
Femoral deformity planning: intentional placement of the apex of deformity.
Fabricant, Peter D; Camara, James M; Rozbruch, S Robert
2013-05-01
Traditionally, correction of femoral deformity has been performed with osteotomies through the center of rotation of angulation (CORA), but the CORA location is not always practical. If the osteotomy is created at a site adjacent to the CORA, an additional translation must be performed to accurately correct the deformity. However, at times, the ideal osteotomy site may require an unfeasible amount of translation. Multiple osteotomies may also be problematic, and when overcorrection of the mechanical axis is planned, the CORA method is not practical.This article describes a novel method by which the surgeon may choose the location of the osteotomy regardless of the location of the CORA and may consolidate a multiapical deformity into a single corrective osteotomy. Furthermore, intentional mechanical axis overcorrection may be performed to unload knee joint arthritis. Simple, complex, and multiapical deformities may now be corrected via a single familiar surgical procedure, such as a distal femoral osteotomy, and the need for translation is eliminated.
3D deformation field throughout the interior of materials.
Jin, Huiqing; Lu, Wei-Yang
2013-09-01
This report contains the one-year feasibility study for our three-year LDRD proposal that is aimed to develop an experimental technique to measure the 3D deformation fields inside a material body. In this feasibility study, we first apply Digital Volume Correlation (DVC) algorithm to pre-existing in-situ Xray Computed Tomography (XCT) image sets with pure rigid body translation. The calculated displacement field has very large random errors and low precision that are unacceptable. Then we enhance these tomography images by setting threshold of the intensity of each slice. DVC algorithm is able to obtain accurate deformation fields from these enhanced image sets and the deformation fields are consistent with the global mechanical loading that is applied to the specimen. Through this study, we prove that the internal markers inside the pre-existing tomography images of aluminum alloy can be enhanced and are suitable for DVC to calculate the deformation field throughout the material body.
Friction and deformation behavior of single-crystal silicon carbide
NASA Technical Reports Server (NTRS)
Miyoshi, K.; Buckley, D. H.
1977-01-01
Friction and deformation studies were conducted with single-crystal silicon carbide in sliding contact with diamond. When the radius of curvature of the spherical diamond rider was large (0.3), deformation of silicon carbide was primarily elastic. Under these conditions the friction coefficient was low and did not show a dependence on the silicon carbide orientation. Further, there was no detectable cracking of the silicon carbide surfaces. When smaller radii of curvature of the spherical diamond riders (0.15 and 0.02 mm) or a conical diamond rider was used, plastic grooving occured and the silicon carbide exhibited anisotropic friction and deformation behavior. Under these conditions the friction coefficient depended on load. Anisotropic friction and deformation of the basal plane of silicon carbide was controlled by the slip system. 10101120and cleavage of1010.
Control of micromachined deformable mirrors
NASA Technical Reports Server (NTRS)
Agronin, M. L.; Bartman, R.; Hadaegh, F. Y.; Kaiser, W.; Wang, P. K. C.
1993-01-01
A micromachined deformable mirror with pixelated electrostatic actuators is proposed. The paper begins with a physical description of the proposed mirror. Then a mathematical model in the form of a nonlinear partial differential equation describing the mirror surface deformations is derived. This model is used to derive the required voltages for the actuators to achieve a specified static deformation of the mirror surface. This is followed by the derivation of a static nonlinear feedback controller for achieving noninteracting actuation. Then the structure for a complete control system for wavefront correction is proposed. The paper concludes with a discussion of the physical implementation of the proposed control system.
NASA Technical Reports Server (NTRS)
Imbriale, W. A.; Moore, M.; Rochblatt, D. J.; Veruttipong, W.
1995-01-01
At the NASA Deep Space Network (DSN) Goldstone Complex, a 34-meter- diameter beam-waveguide antenna, DSS-13, was constructed in 1988-1990 and has become an integral part of an advanced systems program and a test bed for technologies being developed to introduce Ka-band (32 GHz) frequencies into the DSN. A method for compensating the gravity- induced structural deformations in this large antenna is presented.
Deformation behavior of aluminum alloy 6111-T4
NASA Astrophysics Data System (ADS)
Tseng, Carol
2000-10-01
Although aluminum alloys have found increasing usage in the automotive industry, their lower tensile elongations as compared with the low carbon steels they replace has raised concern about their lower formability. Lower formability imposes design and economic constraints on the automakers. The cause behind this lower elongation is the primary focus of this research. The specific alloy studied is 6111-T4 (Al-0.76Si-0.61Mg-0.82Cu in w/o), which is used in automobile outer body panels. In order to determine the factors that are limiting the elongation, it is critical to understand the deformation behavior of this alloy. To investigate the deformation behavior of this alloy, uniaxial tensile tests were performed at various temperatures (300K, 77K and 4.2K), strain rates (10-4, 5 x 10-4 , 10-3, 10-2, 10 -1/s) and specimen geometries. The work hardening and deformation behavior were examined both qualitatively and quantitatively. Ex-situ and in-situ observations were made on the tensile samples by using videography and optical microscopy. Several important findings resulted from this study. First, oscillations in the work hardening are due to the formation and propagation of deformation islands and deformation bands. Deformation islands are areas of localized deformation that occur in a cluster of grains. Second, the microstructural feature dominating the formation and propagation of the islands are the clustering of similarly oriented grains and the clustering of large sized grains. Third, the sharp drop in work hardening near the diffuse necking criterion for the 300K, 10-4 is test samples is due to the inhomogeneous deformation arising from these clusters. Finally, diffuse and local necks form before the theoretical predictions. The inhomogeneous microstructures causing the deformation islands and bands to form and propagate, thus leading to strain localization and eventual premature failure.
Sensing surface mechanical deformation using active probes driven by motor proteins
Inoue, Daisuke; Nitta, Takahiro; Kabir, Arif Md. Rashedul; Sada, Kazuki; Gong, Jian Ping; Konagaya, Akihiko; Kakugo, Akira
2016-01-01
Studying mechanical deformation at the surface of soft materials has been challenging due to the difficulty in separating surface deformation from the bulk elasticity of the materials. Here, we introduce a new approach for studying the surface mechanical deformation of a soft material by utilizing a large number of self-propelled microprobes driven by motor proteins on the surface of the material. Information about the surface mechanical deformation of the soft material is obtained through changes in mobility of the microprobes wandering across the surface of the soft material. The active microprobes respond to mechanical deformation of the surface and readily change their velocity and direction depending on the extent and mode of surface deformation. This highly parallel and reliable method of sensing mechanical deformation at the surface of soft materials is expected to find applications that explore surface mechanics of soft materials and consequently would greatly benefit the surface science. PMID:27694937
NMR study on mechanisms of ionic polymer-metal composites deformation with water content
NASA Astrophysics Data System (ADS)
Zhu, Zicai; Chen, Hualing; Wang, Yongquan; Luo, Bin; Chang, Longfei; Li, Bo; Chen, Luping
2011-10-01
Ionic polymer-metal composites (IPMCs) exhibit a large dynamic bending deformation under exterior electric field. The states and proportions of water within the IPMCs have great effect on the IPMCs deformation properties. This letter investigates the influence of the proportion changes of different types of water on the deformation, which may disclose the working mechanisms of the IPMCs. We give a deformation trend of IPMCs with the reduction of water content firstly. Then by the method of nuclear magnetic resonance, various water types (water bonded to sulfonates, loosely bound water and free water) of IPMCs and their proportions are investigated in the drying process which corresponds to their different deformation states. It is obtained that the deformation properties of IPMCs depend strongly on their water content and the excess free water is responsible for the relaxation deformation.
Stability in holographic theories with irrelevant deformations
NASA Astrophysics Data System (ADS)
Amsel, Aaron J.; Roberts, Matthew M.
2013-04-01
We investigate the nonperturbative stability of asymptotically anti-de Sitter gravity coupled to tachyonic scalar fields with mass near the Breitenlohner-Freedman bound. Such scalars are characterized by power-law radial decay near the anti-de Sitter boundary, and typical boundary conditions are “Dirichlet” (which fix the slower falloff mode) or “Neumann” (which fix the faster falloff mode) type. More generally though, these “designer gravity” theories admit a large class of boundary conditions defined by a functional relation between the two modes. While previous stability proofs have considered boundary conditions that are deformations of the Neumann theory, the goal of this paper is to analyze stability in designer gravity with boundary conditions that are irrelevant deformations of the Dirichlet theory. We obtain a lower bound on the energy using spinor charge methods and show that, for the most interesting class of such boundary conditions, the theory is always stable. We argue that the deformed theory flows to a new fixed point in the ultraviolet, which is just the Neumann theory. We also derive a corresponding “effective potential” that implies stability if it has a global minimum.
Actuators of 3-element unimorph deformable mirror
NASA Astrophysics Data System (ADS)
Fu, Tianyang; Ning, Yu; Du, Shaojun
2016-10-01
Kinds of wavefront aberrations exist among optical systems because of atmosphere disturbance, device displacement and a variety of thermal effects, which disturb the information of transmitting beam and restrain its energy. Deformable mirror(DM) is designed to adjust these wavefront aberrations. Bimorph DM becomes more popular and more applicable among adaptive optical(AO) systems with advantages in simple structure, low cost and flexible design compared to traditional discrete driving DM. The defocus aberration accounted for a large proportion of all wavefront aberrations, with a simpler surface and larger amplitude than others, so it is very useful to correct the defocus aberration effectively for beam controlling and aberration adjusting of AO system. In this study, we desired on correcting the 3rd and 10th Zernike modes, analyze the characteristic of the 3rd and 10th defocus aberration surface distribution, design 3-element actuators unimorph DM model study on its structure and deformation principle theoretically, design finite element models of different electrode configuration with different ring diameters, analyze and compare effects of different electrode configuration and different fixing mode to DM deformation capacity through COMSOL finite element software, compare fitting efficiency of DM models to the 3rd and 10th Zernike modes. We choose the inhomogeneous electrode distribution model with better result, get the influence function of every electrode and the voltage-PV relationship of the model. This unimorph DM is suitable for the AO system with a mainly defocus aberration.
The role of crustal quartz in controlling Cordilleran deformation.
Lowry, Anthony R; Pérez-Gussinyé, Marta
2011-03-17
Large-scale deformation of continents remains poorly understood more than 40 years after the plate tectonic revolution. Rock flow strength and mass density variations both contribute to stress, so both are certain to be important, but these depend (somewhat nebulously) on rock type, temperature and whether or not unbound water is present. Hence, it is unclear precisely how Earth material properties translate to continental deformation zones ranging from tens to thousands of kilometres in width, why deforming zones are sometimes interspersed with non-deforming blocks and why large earthquakes occasionally rupture in otherwise stable continental interiors. An important clue comes from observations that mountain belts and rift zones cyclically form at the same locations despite separation across vast gulfs of time (dubbed the Wilson tectonic cycle), accompanied by inversion of extensional basins and reactivation of faults and other structures formed in previous deformation events. Here we show that the abundance of crustal quartz, the weakest mineral in continental rocks, may strongly condition continental temperature and deformation. We use EarthScope seismic receiver functions, gravity and surface heat flow measurements to estimate thickness and seismic velocity ratio, v(P)/v(S), of continental crust in the western United States. The ratio v(P)/v(S) is relatively insensitive to temperature but very sensitive to quartz abundance. Our results demonstrate a surprising correlation of low crustal v(P)/v(S) with both higher lithospheric temperature and deformation of the Cordillera, the mountainous region of the western United States. The most plausible explanation for the relationship to temperature is a robust dynamical feedback, in which ductile strain first localizes in relatively weak, quartz-rich crust, and then initiates processes that promote advective warming, hydration and further weakening. The feedback mechanism proposed here would not only explain
A Solution Method for Large Deformation Contact Problems.
1984-10-01
number) Contact Problem Algorithm Implicit Solution Technique 20. ANSTNACT’ (rntftae r eves aIi N yaeemy mrd identify by block numnber) P. solution...WITHOUT oL0 H! 0-CONTACT ALGORITHM Z w 00 0 ev 0.8- w kL 0.0 0 U< O0.26 U)_ * z Z OBTINE 0H53 56 59 ANGE,4 Ficure~~~~~ ~*A G RI H 17 Peitdtatoso iesi itrae...41, Division of Applied Sciences, Harvard Univ., March 1983. [20] Rabinowicz , E., Friction and Wear of Materials, J. Wiley and Sons, 1965. [21
Microstructure evolution of compressible granular systems under large deformations
NASA Astrophysics Data System (ADS)
Gonzalez, Marcial; Cuitiño, Alberto M.
2016-08-01
We report three-dimensional particle mechanics static calculations that predict the microstructure evolution during die-compaction of elastic spherical particles up to relative densities close to one. We employ a nonlocal contact formulation that remains predictive at high levels of confinement by removing the classical assumption that contacts between particles are formulated locally as independent pair-interactions. The approach demonstrates that the coordination number depends on the level of compressibility, i.e., on Poisson's ratio, of the particles. Results also reveal that distributions of contact forces between particles and between particles and walls, although similar at jamming onset, are very different at full compaction. Particle-wall forces are in remarkable agreement with experimental measurements reported in the literature, providing a unifying framework for bridging experimental boundary observations with bulk behavior.
The Overall Response of Composite Materials Undergoing Large Elastic Deformations
1990-06-13
linear case, it has been shown (MILTON, 1985; AVELLANEDA , 1987) that the DSC estimates can be attained by particular microstructures. Then, we could...with the support of the Air Force Office of Scientific Research under Grant No. 89-0288. 26 P. CASTA.EDA REFERENCES AVELLANEDA . N. 1987 Commun. Pure appl
The Overall Response of Composite Materials Undergoing Large Elastic Deformations
1990-10-30
procedure in general to es.et the energy of the composite W (i). For the linear case, it has been shown (MILTON, 1985; AVELLANEDA , 1987) that the DSC...No. 89-0288. 26 P. . CASTAFEDA REFRENcEs AVELLANEDA . M. 1987 Commun. Pure appi. Math. 40, 527. BOUCHER. S. 1974 J. Compos. Mater. 8, 82. BUDIANSKY, B
The Overall Response of Composite Materials Undergoing Large Deformations
1991-11-15
anisotropic composites with prescribed volume fractions, the Voigt/Reuss bounds on the effective energy function U are known to be non-optimal. AVELLANEDA ...discussions. References M. AVELLANEDA (1987) SIAM J. appl. Math. 47, 1216. M. BERAN AND J. MOLYNEUX (1984) Q. appl. Math. 24, 107. G. DE BOTTON and P
The Overall Response of Composite Materials Undergoing Large Deformations
1992-10-15
University, December 11, 1991. "Propiedades effectivas de materiales compuestos." & "Propiedades effectivas de materiales compuestos no- lineales ...unlike the corresponding problem for a general composite. simplifies to an algebraic one. Although. in principle. the resulting problem can always...take the form of complicated sets of nonlinear algebraic equations. However, if the composite is made up of linear phases (with quadratic energy
Large deformations of a new class of incompressible elastic bodies
NASA Astrophysics Data System (ADS)
Bustamante, R.; Orellana, O.; Meneses, R.; Rajagopal, K. R.
2016-06-01
The consequences of the constraint of incompressibility is studied for a new class of constitutive relation for elastic bodies, for which the left Cauchy-Green tensor is a function of the Cauchy stress tensor. The requirement of incompressibility is imposed directly in the constitutive relation, and it is not necessary to assume a priori that the stress tensor should be divided into two parts, a constraint stress and a constitutively specified part, as in the classical theory of nonlinear elasticity.
Large deformation of self-oscillating polymer gel
NASA Astrophysics Data System (ADS)
Maeda, Shingo; Kato, Terukazu; Otsuka, Yuji; Hosoya, Naoki; Cianchetti, Matteo; Laschi, Cecilia
2016-01-01
A self-oscillating gel is a system that generates an autonomous volume oscillation. This oscillation is powered by the chemical energy of the Belousov-Zhabotinsky (BZ) reaction, which demonstrates metal ion redox oscillation. A self-oscillating gel is composed of Poly-N -isopropylacrylamide (PNIPAAm) with a metal ion. In this study, we found that the displacement of the volume oscillation in a self-oscillating gel could be controlled by its being subjected to a prestraining process. We also revealed the driving mechanism of the self-oscillating gel from the point of view of thermodynamics. We observed that the polymer-solvent interaction parameter χ is altered by the redox changes to the metal ion incorporated in the self-oscillating gel. The prestraining process leads to changes in χ and changes in enthalpy and entropy when the self-oscillating gel is in a reduced and oxidized state. We found that nonprestrained gel samples oscillate in a poor solution (χ >0.5 ) and prestrained gel samples oscillate in a good solution (χ <0.5 ).
Anisotropic viscoelastic models in large deformation for architectured membranes
NASA Astrophysics Data System (ADS)
Rebouah, Marie; Chagnon, Gregory; Heuillet, Patrick
2016-08-01
Due to the industrial elaboration process, membranes can have an in-plane anisotropic mechanical behaviour. In this paper, anisotropic membranes elaborated with two different materials were developed either by calendering or by inducing a force in one direction during the process. Experimental tests are developed to measure the differences of mechanical behaviour for both materials in different in-plane properties: stiffness, viscoelasticity and stress-softening. A uniaxial formulation is developed, and a homogenisation by means of a sphere unit approach is used to propose a three-dimensional formulation to represent the materials behaviour. An evolution of the mechanical parameters, depending on the direction, is imposed to reproduce the anisotropic behaviour of the materials. Comparison with experimental data highlights very promising results.
Variable focal length deformable mirror
Headley, Daniel; Ramsey, Marc; Schwarz, Jens
2007-06-12
A variable focal length deformable mirror has an inner ring and an outer ring that simply support and push axially on opposite sides of a mirror plate. The resulting variable clamping force deforms the mirror plate to provide a parabolic mirror shape. The rings are parallel planar sections of a single paraboloid and can provide an on-axis focus, if the rings are circular, or an off-axis focus, if the rings are elliptical. The focal length of the deformable mirror can be varied by changing the variable clamping force. The deformable mirror can generally be used in any application requiring the focusing or defocusing of light, including with both coherent and incoherent light sources.
ROCK DEFORMATION. Final Progress Report
2002-05-24
The Gordon Research Conference (GRC) on ROCK DEFORMATION was held at II Ciocco from 5/19/02 thru 5/24/02. Emphasis was placed on current unpublished research and discussion of the future target areas in this field.
Taylor, W. C.
1965-01-01
Ten children with gross deformity of the external ear were observed. In six the facial bones were underdeveloped on the same side as the deformed ear. In all six there was a congenital abnormality of the kidney or upper urinary tract, usually on the same side as the deformed ear. In addition there were usually other associated congenital defects in each case. In the remaining four children the facial bones appeared normal, and pyelography showed no abnormality of the urinary tract. In these four children there were no other associated defects. These observations emphasize the importance of investigating the urinary tract in children with gross deformity of the external ear, especially where there is an associated underdevelopment of the facial bones. PMID:14317453
Anisotropic ripple deformation in phosphorene
Kou, Liangzhi; Ma, Yandong; Smith, Sean C.; ...
2015-04-07
Here, two-dimensional materials tend to become crumpled according to the Mermin-Wagner theorem, and the resulting ripple deformation may significantly influence electronic properties as observed in graphene and MoS2. Here, we unveil by first-principles calculations a new, highly anisotropic ripple pattern in phosphorene, a monolayer black phosphorus, where compression-induced ripple deformation occurs only along the zigzag direction in the strain range up to 10%, but not the armchair direction. This direction-selective ripple deformation mode in phosphorene stems from its puckered structure with coupled hinge-like bonding configurations and the resulting anisotropic Poisson ratio. We also construct an analytical model using classical elasticitymore » theory for ripple deformation in phosphorene under arbitrary strain. The present results offer new insights into the mechanisms governing the structural and electronic properties of phosphorene crucial to its device applications.« less
Anisotropic ripple deformation in phosphorene
Kou, Liangzhi; Ma, Yandong; Smith, Sean C.; Chen, Changfeng
2015-04-07
Here, two-dimensional materials tend to become crumpled according to the Mermin-Wagner theorem, and the resulting ripple deformation may significantly influence electronic properties as observed in graphene and MoS_{2}. Here, we unveil by first-principles calculations a new, highly anisotropic ripple pattern in phosphorene, a monolayer black phosphorus, where compression-induced ripple deformation occurs only along the zigzag direction in the strain range up to 10%, but not the armchair direction. This direction-selective ripple deformation mode in phosphorene stems from its puckered structure with coupled hinge-like bonding configurations and the resulting anisotropic Poisson ratio. We also construct an analytical model using classical elasticity theory for ripple deformation in phosphorene under arbitrary strain. The present results offer new insights into the mechanisms governing the structural and electronic properties of phosphorene crucial to its device applications.
Anisotropic Ripple Deformation in Phosphorene.
Kou, Liangzhi; Ma, Yandong; Smith, Sean C; Chen, Changfeng
2015-05-07
Two-dimensional materials tend to become crumpled according to the Mermin-Wagner theorem, and the resulting ripple deformation may significantly influence electronic properties as observed in graphene and MoS2. Here, we unveil by first-principles calculations a new, highly anisotropic ripple pattern in phosphorene, a monolayer black phosphorus, where compression-induced ripple deformation occurs only along the zigzag direction in the strain range up to 10%, but not the armchair direction. This direction-selective ripple deformation mode in phosphorene stems from its puckered structure with coupled hinge-like bonding configurations and the resulting anisotropic Poisson ratio. We also construct an analytical model using classical elasticity theory for ripple deformation in phosphorene under arbitrary strain. The present results offer new insights into the mechanisms governing the structural and electronic properties of phosphorene crucial to its device applications.
Unified Model Deformation and Flow Transition Measurements
NASA Technical Reports Server (NTRS)
Burner, Alpheus W.; Liu, Tianshu; Garg, Sanjay; Bell, James H.; Morgan, Daniel G.
1999-01-01
The number of optical techniques that may potentially be used during a given wind tunnel test is continually growing. These include parameter sensitive paints that are sensitive to temperature or pressure, several different types of off-body and on-body flow visualization techniques, optical angle-of-attack (AoA), optical measurement of model deformation, optical techniques for determining density or velocity, and spectroscopic techniques for determining various flow field parameters. Often in the past the various optical techniques were developed independently of each other, with little or no consideration for other techniques that might also be used during a given test. Recently two optical techniques have been increasingly requested for production measurements in NASA wind tunnels. These are the video photogrammetric (or videogrammetric) technique for measuring model deformation known as the video model deformation (VMD) technique, and the parameter sensitive paints for making global pressure and temperature measurements. Considerations for, and initial attempts at, simultaneous measurements with the pressure sensitive paint (PSP) and the videogrammetric techniques have been implemented. Temperature sensitive paint (TSP) has been found to be useful for boundary-layer transition detection since turbulent boundary layers convect heat at higher rates than laminar boundary layers of comparable thickness. Transition is marked by a characteristic surface temperature change wherever there is a difference between model and flow temperatures. Recently, additional capabilities have been implemented in the target-tracking videogrammetric measurement system. These capabilities have permitted practical simultaneous measurements using parameter sensitive paint and video model deformation measurements that led to the first successful unified test with TSP for transition detection in a large production wind tunnel.
Plastic Deformation of Granular Materials
1993-01-25
discontinuities. These result will be important in our granular flow work, when considering viscoplastic constitutive relations (i.e. relaxation systems...5 CUNDN( NUMRES Plastic Deformation of Granular Materials (U) 61102F 6. AUTHOR(S) 2304/A4 Dr. E. Bruce Pitman 7 PERFORMING ORGANIZATION NA .h • 8...lose hyperbolicity. 98 3 81 061! SUBJECT TERMS 15. NUMBER OF PAGES granular material ; plastic deformation; hyperbolic 12 equations 16. PRICE CODE 17
Cleft Nasal Deformity and Rhinoplasty
Kaufman, Yoav; Buchanan, Edward P.; Wolfswinkel, Erik M.; Weathers, William M.; Stal, Samuel
2012-01-01
The cleft nasal deformity is a complex challenge in plastic surgery involving the skin, cartilage, mucosa, and skeletal platform. Ever since Blair and Brown first described the intricacies of the cleft pathology in 1931, the appropriate approach has been extensively debated in the literature with respect to timing, technique, and extent of surgical intervention. In this article, the authors review the literature and summarize the various modalities for achieving a successful rhinoplasty in the patient with a cleft nasal deformity. PMID:24179452
A novel three-dimensional mesh deformation method based on sphere relaxation
Zhou, Xuan; Li, Shuixiang
2015-10-01
In our previous work (2013) [19], we developed a disk relaxation based mesh deformation method for two-dimensional mesh deformation. In this paper, the idea of the disk relaxation is extended to the sphere relaxation for three-dimensional meshes with large deformations. We develop a node based pre-displacement procedure to apply initial movements on nodes according to their layer indices. Afterwards, the nodes are moved locally by the improved sphere relaxation algorithm to transfer boundary deformations and increase the mesh quality. A three-dimensional mesh smoothing method is also adopted to prevent the occurrence of the negative volume of elements, and further improve the mesh quality. Numerical applications in three-dimension including the wing rotation, bending beam and morphing aircraft are carried out. The results demonstrate that the sphere relaxation based approach generates the deformed mesh with high quality, especially regarding complex boundaries and large deformations.
Balancing induced seismicity and permeability creation through aseismic deformation
NASA Astrophysics Data System (ADS)
Schoenball, M.; Kohl, T.
2014-12-01
The mitigation of induced seismicity is a challenge for a sustained production of unconventional hydrocarbons involving waste water disposal and of geothermal power production where large volumes of fluid are circulated in the subsurface. Large pore pressure perturbations localize where fluid flow is limited by the pre-existing joint set. It drives deformation that - if it occurs in brittle mode - manifests as seismicity leading to dilation of the reactivated fracture network. Therefore, induced seismicity is a process which is accompanied by permeability creation. In many geothermal systems, seismicity is deliberately induced to enhance the reservoir. Experience collected at the EGS at Soultz-sous-Forêts, France has revealed evidence for a large proportion of the induced deformation to be aseismic. Indicators are temporally resolved velocity changes, changes of the stress tensor resolved from inversion of focal mechanisms and direct observation of large slip at wellbores. Furthermore, seismic multiplets, i.e. repeated slippage of asperities with considerable slip accumulation, have been observed not only in Soultz-sous-Forêts but also at other similar systems like in Basel, Switzerland and Landau, Germany. Displacement in the order of up to 0.1 m has been inferred from these observations, which is about one order of magnitude larger than what was observed seismically. To explain this discrepancy we propose a conceptual model of creep-dominated aseismic deformation that is promoted through elevated pore pressures. While few asperities of the pre-existing fracture network experience repeated brittle deformation evidenced as multiple seismic events, the majority of the fault surface is in a subcritical creeping stage. Elevated pore pressure brings them closer to the failure criterion which can enhance the ductile deformation by several orders of magnitude. Relaxation leads to large-scale deformation accompanied by a strong reduction of differential stresses.
Deformable Mirror Materials Issue Assessment
Rudd, R E
2008-05-27
It was a pleasure to speak with you and Dr. Olivier Guyon about your project to develop a coronagraph and in particular about materials science considerations in the development of the deformable mirror (DM) for the coronagraph. The coronagraph application will demand more of a DM than previous applications with regard to precision, and since the characterization and modeling tools are currently under development, you asked me to comment on materials issues that might impact the DM design and testing. I have not conducted research on this question, and my own research on modeling MEMS has not included DM systems. I am only in a position to discuss some general considerations that may help in developing a research plan for the DM system. As I understand it, the relevant points about the DM system are as follows. The DM surface needs to be positioned to less than 1 {angstrom} RMS of the desired shape, and be stable to 0.3 {angstrom} RMS for an hour. In the ultimate application in space the stability requirements may be greater. For example, the DM shape can be set using a bright star and then allow the coronagraph to be turned to a dim star to collect data for several hours, counting on the mirror shape to be stable. The DM is made of a polysilicon membrane coated with one or more metal layers for the reflective surface and actuated by 32x32 or 64x64 electrostatic actuators on the back side. The uncertainty in the position of any one actuator should be at the few-picometer level or less averaged over the 300-{micro}m region of the actuator. Currently, experiments are conducted that can characterize the surface shape to the 1 nm level, and it is anticipated that the experiments will be able to characterize the shape at the sub-Angstrom level but not in the immediate future. Regarding stability, under relatively large deformations (10's of nm), the DM mirror surface shows no hysteresis at the measurable nm level. Let me begin by saying that I am not aware of any
Analysis of Mining Terrain Deformation Characteristics with Deformation Information System
NASA Astrophysics Data System (ADS)
Blachowski, Jan; Milczarek, Wojciech; Grzempowski, Piotr
2014-05-01
Mapping and prediction of mining related deformations of the earth surface is an important measure for minimising threat to surface infrastructure, human population, the environment and safety of the mining operation itself arising from underground extraction of useful minerals. The number of methods and techniques used for monitoring and analysis of mining terrain deformations is wide and increasing with the development of geographical information technologies. These include for example: terrestrial geodetic measurements, global positioning systems, remote sensing, spatial interpolation, finite element method modelling, GIS based modelling, geological modelling, empirical modelling using the Knothe theory, artificial neural networks, fuzzy logic calculations and other. The aim of this paper is to introduce the concept of an integrated Deformation Information System (DIS) developed in geographic information systems environment for analysis and modelling of various spatial data related to mining activity and demonstrate its applications for mapping and visualising, as well as identifying possible mining terrain deformation areas with various spatial modelling methods. The DIS concept is based on connected modules that include: the spatial database - the core of the system, the spatial data collection module formed by: terrestrial, satellite and remote sensing measurements of the ground changes, the spatial data mining module for data discovery and extraction, the geological modelling module, the spatial data modeling module with data processing algorithms for spatio-temporal analysis and mapping of mining deformations and their characteristics (e.g. deformation parameters: tilt, curvature and horizontal strain), the multivariate spatial data classification module and the visualization module allowing two-dimensional interactive and static mapping and three-dimensional visualizations of mining ground characteristics. The Systems's functionality has been presented on
Preferred orientation in experimentally deformed stishovite: implications for deformation mechanisms
NASA Astrophysics Data System (ADS)
Kaercher, P. M.; Zepeda-Alarcon, E.; Prakapenka, V.; Kanitpanyacharoen, W.; Smith, J.; Sinogeikin, S. V.; Wenk, H. R.
2014-12-01
The crystal structure of the high pressure SiO2 polymorph stishovite has been studied in detail, yet little is known about its deformation mechanisms. Information about how stishovite deforms under stress is important for understanding subduction of quartz-bearing crustal rocks into the mantle. Particularly, stishovite is elastically anisotropic and thus development of crystallographic preferred orientation (CPO) during deformation may contribute to seismic anomalies in the mantle. We converted a natural sample of flint to stishovite in a laser heated diamond anvil cell and compressed the stishovite aggregate up to 38 GPa. Diffraction patterns were collected in situ in radial geometry at the Advanced Light Source (ALS) and the Advanced Photon Source (APS) to examine development of CPO during deformation. We find that (001) poles preferentially align with the compression direction and infer deformation mechanisms leading to the observed CPO with visco-plastic self consistent (VPSC) polycrystal plasticity models. Our results show pyramidal and basal slip are most likely active at high pressure and ambient temperature, in agreement with transmission electron microscopy (TEM) studies of rutile (TiO2) and paratellurite (TeO2), which are isostructural to stishovite. Conversely other TEM studies of stishovite done at higher temperature suggest dominant prismatic slip. This indicates that a variety of slip systems may be active in stishovite, depending on conditions. As a result, stishovite's contribution to the seismic signature in the mantle may vary as a function of pressure and temperature and thus depth.
Development of large aperture composite adaptive optics
NASA Astrophysics Data System (ADS)
Kmetik, Viliam; Vitovec, Bohumil; Jiran, Lukas; Nemcova, Sarka; Zicha, Josef; Inneman, Adolf; Mikulickova, Lenka; Pavlica, Richard
2015-01-01
Large aperture composite adaptive optics for laser applications is investigated in cooperation of Institute of Plasma Physic, Department of Instrumentation and Control Engineering FME CTU and 5M Ltd. We are exploring opportunity of a large-size high-power-laser deformable-mirror production using a lightweight bimorph actuated structure with a composite core. In order to produce a sufficiently large operational free aperture we are developing new technologies for production of flexible core, bimorph actuator and deformable mirror reflector. Full simulation of a deformable-mirrors structure was prepared and validated by complex testing. A deformable mirror actuation and a response of a complicated structure are investigated for an accurate control of the adaptive optics. An original adaptive optics control system and a bimorph deformable mirror driver were developed. Tests of material samples, components and sub-assemblies were completed. A subscale 120 mm bimorph deformable mirror prototype was designed, fabricated and thoroughly tested. A large-size 300 mm composite-core bimorph deformable mirror was simulated and optimized, fabrication of a prototype is carried on. A measurement and testing facility is modified to accommodate large sizes optics.
Unimorph deformable mirror for space telescopes: design and manufacturing.
Rausch, Peter; Verpoort, Sven; Wittrock, Ulrich
2015-07-27
Large space telescopes made of deployable and lightweight structures suffer from aberrations caused by thermal deformations, gravitational release, and alignment errors which occur during the deployment procedure. An active optics system would allow on-site correction of wave-front errors, and ease the requirements on thermal and mechanical stability of the optical train. In the course of a project funded by the European Space Agency we have developed and manufactured a unimorph deformable mirror based on piezoelectric actuation. The mirror is able to work in space environment and is designed to correct for large aberrations of low order with high surface fidelity. This paper discusses design, manufacturing and performance results of the deformable mirror.
Structure modulated electrostatic deformable mirror for focus and geometry control.
Nam, Saekwang; Park, Suntak; Yun, Sungryul; Park, Bongje; Park, Seung Koo; Kyung, Ki-Uk
2016-01-11
We suggest a way to electrostatically control deformed geometry of an electrostatic deformable mirror (EDM) based on geometric modulation of a basement. The EDM is composed of a metal coated elastomeric membrane (active mirror) and a polymeric basement with electrode (ground). When an electrical voltage is applied across the components, the active mirror deforms toward the stationary basement responding to electrostatic attraction force in an air gap. Since the differentiated gap distance can induce change in electrostatic force distribution between the active mirror and the basement, the EDMs are capable of controlling deformed geometry of the active mirror with different basement structures (concave, flat, and protrusive). The modulation of the deformed geometry leads to significant change in the range of the focal length of the EDMs. Even under dynamic operations, the EDM shows fairly consistent and large deformation enough to change focal length in a wide frequency range (1~175 Hz). The geometric modulation of the active mirror with dynamic focus tunability can allow the EDM to be an active mirror lens for optical zoom devices as well as an optical component controlling field of view.
Biaxial deformation of collagen and elastin fibers in coronary adventitia
Chen, Huan; Slipchenko, Mikhail N.; Liu, Yi; Zhao, Xuefeng; Cheng, Ji-Xin; Lanir, Yoram
2013-01-01
The microstructural deformation-mechanical loading relation of the blood vessel wall is essential for understanding the overall mechanical behavior of vascular tissue in health and disease. We employed simultaneous mechanical loading-imaging to quantify in situ deformation of individual collagen and elastin fibers on unstained fresh porcine coronary adventitia under a combination of vessel inflation and axial extension loading. Specifically, the specimens were imaged under biaxial loads to study microscopic deformation-loading behavior of fibers in conjunction with morphometric measurements at the zero-stress state. Collagen fibers largely orientate in the longitudinal direction, while elastin fibers have major orientation parallel to collagen, but with additional orientation angles in each sublayer of the adventitia. With an increase of biaxial load, collagen fibers were uniformly stretched to the loading direction, while elastin fibers gradually formed a network in sublayers, which strongly depended on the initial arrangement. The waviness of collagen decreased more rapidly at a circumferential stretch ratio of λθ = 1.0 than at λθ = 1.5, while most collagen became straightened at λθ = 1.8. These microscopic deformations imply that the longitudinally stiffer adventitia is a direct result of initial fiber alignment, and the overall mechanical behavior of the tissue is highly dependent on the corresponding microscopic deformation of fibers. The microstructural deformation-loading relation will serve as a foundation for micromechanical models of the vessel wall. PMID:24092692
Controlled deformation of vesicles by flexible structured media
Zhang, Rui; Zhou, Ye; Martínez-González, José A.; Hernández-Ortiz, Juan P.; Abbott, Nicholas L.; de Pablo, Juan J.
2016-01-01
Liquid crystalline (LC) materials, such as actin or tubulin networks, are known to be capable of deforming the shape of cells. Here, elements of that behavior are reproduced in a synthetic system, namely, a giant vesicle suspended in a LC, which we view as a first step toward the preparation of active, anisotropic hybrid systems that mimic some of the functionality encountered in biological systems. To that end, we rely on a coupled particle-continuum representation of deformable networks in a nematic LC represented at the level of a Landau–de Gennes free energy functional. Our results indicate that, depending on its elastic properties, the LC is indeed able to deform the vesicle until it reaches an equilibrium, anisotropic shape. The magnitude of the deformation is determined by a balance of elastic and surface forces. For perpendicular anchoring at the vesicle, a Saturn ring defect forms along the equatorial plane, and the vesicle adopts a pancake-like, oblate shape. For degenerate planar anchoring at the vesicle, two boojum defects are formed at the poles of the vesicle, which adopts an elongated, spheroidal shape. During the deformation, the volume of the topological defects in the LC shrinks considerably as the curvature of the vesicle increases. These predictions are confirmed by our experimental observations of spindle-like shapes in experiments with giant unilamellar vesicles with planar anchoring. We find that the tension of the vesicle suppresses vesicle deformation, whereas anchoring strength and large elastic constants promote shape anisotropy. PMID:27532056
Fast free-form deformable registration via calculus of variations.
Lu, Weiguo; Chen, Ming-Li; Olivera, Gustavo H; Ruchala, Kenneth J; Mackie, Thomas R
2004-07-21
In this paper, we present a fully automatic, fast and accurate deformable registration technique. This technique deals with free-form deformation. It minimizes an energy functional that combines both similarity and smoothness measures. By using calculus of variations, the minimization problem was represented as a set of nonlinear elliptic partial differential equations (PDEs). A Gauss-Seidel finite difference scheme is used to iteratively solve the PDE. The registration is refined by a multi-resolution approach. The whole process is fully automatic. It takes less than 3 min to register two three-dimensional (3D) image sets of size 256 x 256 x 61 using a single 933 MHz personal computer. Extensive experiments are presented. These experiments include simulations, phantom studies and clinical image studies. Experimental results show that our model and algorithm are suited for registration of temporal images of a deformable body. The registration of inspiration and expiration phases of the lung images shows that the method is able to deal with large deformations. When applied to the daily CT images of a prostate patient, the results show that registration based on iterative refinement of displacement field is appropriate to describe the local deformations in the prostate and the rectum. Similarity measures improved significantly after the registration. The target application of this paper is for radiotherapy treatment planning and evaluation that incorporates internal organ deformation throughout the course of radiation therapy. The registration method could also be equally applied in diagnostic radiology.
Bilateral cleft lip nasal deformity
Singh, Arun Kumar; Nandini, R.
2009-01-01
Bilateral cleft lip nose deformity is a multi-factorial and complex deformity which tends to aggravate with growth of the child, if not attended surgically. The goals of primary bilateral cleft lip nose surgery are, closure of the nasal floor and sill, lengthening of the columella, repositioning of the alar base, achieving nasal tip projection, repositioning of the lower lateral cartilages, and reorienting the nares from horizontal to oblique position. The multiplicity of procedures in the literature for correction of this deformity alludes to the fact that no single procedure is entirely effective. The timing for surgical intervention and its extent varies considerably. Early surgery on cartilage may adversely affect growth and development; at the same time, allowing the cartilage to grow in an abnormal position and contributing to aggravation of deformity. Some surgeons advocate correction of deformity at an early age. However, others like the cartilages to grow and mature before going in for surgery. With peer pressure also becoming an important consideration during the teens, the current trend is towards early intervention. There is no unanimity in the extent of nasal dissection to be done at the time of primary lip repair. While many perform limited nasal dissection for the fear of growth retardation, others opt for full cartilage correction at the time of primary surgery itself. The value of naso-alveolar moulding (NAM) too is not universally accepted and has now more opponents than proponents. Also most centres in the developing world have neither the personnel nor the facilities for the same. The secondary cleft nasal deformity is variable and is affected by the extent of the original abnormality, any prior surgeries performed and alteration due to nasal growth. This article reviews the currently popular methods for correction of nasal deformity associated with bilateral cleft lip, it's management both at the time of cleft lip repair and also secondarily
Deformation of second and third quantization
NASA Astrophysics Data System (ADS)
Faizal, Mir
2015-03-01
In this paper, we will deform the second and third quantized theories by deforming the canonical commutation relations in such a way that they become consistent with the generalized uncertainty principle. Thus, we will first deform the second quantized commutator and obtain a deformed version of the Wheeler-DeWitt equation. Then we will further deform the third quantized theory by deforming the third quantized canonical commutation relation. This way we will obtain a deformed version of the third quantized theory for the multiverse.
Instabilities in shear and simple shear deformations of gold crystals
NASA Astrophysics Data System (ADS)
Pacheco, A. A.; Batra, R. C.
We use the tight-binding potential and molecular mechanics simulations to study local and global instabilities in shear and simple shear deformations of three initially defect-free finite cubes of gold single crystal containing 3480, 7813, and 58,825 atoms. Displacements on all bounding surfaces are prescribed while studying simple shear deformations, but displacements on only two opposite surfaces are assigned during simulations of shear deformations with the remaining four surfaces kept free of external forces. The criteria used to delineate local instabilities in the system include the following: (i) a component of the second-order spatial gradients of the displacement field having large values relative to its average value in the body, (ii) the minimum eigenvalue of the Hessian of the energy of an atom becoming non-positive, and (iii) structural changes represented by a high value of the common neighborhood parameter. It is found that these criteria are met essentially simultaneously at the same atomic position. Effects of free surfaces are evidenced by different deformation patterns for the same specimen deformed in shear and simple shear. The shear strength of a specimen deformed in simple shear is more than three times that of the same specimen deformed in shear. It is found that for each cubic specimen deformed in simple shear the evolution with the shear strain of the average shear stress, prior to the onset of instabilities, is almost identical to that in an equivalent hyperelastic material with strain energy density derived from the tight-binding potential and the assumption that it obeys the Cauchy-Born rule. Even though the material response of the hyperelastic body predicted from the strain energy density is stable over the range of the shear strain simulated in this work, the molecular mechanics simulations predict local and global instabilities in the three specimens.
DAM Safety and Deformation Monitoring in Dams
NASA Astrophysics Data System (ADS)
Kalkan, Y.; Bilgi, S.; Potts, L.; Miiama, J.; Mahgoub, M.; Rahman, S.
2013-12-01
Water is the life and necessity to water is increasing day by day with respect to the World population, rising of living standards and destruction of nature. Thus, the importance of water and water structures have been increasing gradually. Dams are among the most important engineering structures used for water supplies, flood controls, agricultural purposes as well as drinking and hydroelectric power. There are about 150.000 large size dams in the World. Especially after the Second World War, higher and larger capacity dams have been constructed. Dams create certain risks like the other manmade structures. No one knows precisely how many dam failures have occurred in the World, whereas hundreds of dam failures have occurred throughout the U.S. history. Some basic physical data are very important for assessing the safety and performance of dams. These are movement, water pressure, seepage, reservoir and tail-water elevations, local seismic activities, total pressure, stress and strain, internal concrete temperature, ambient temperature and precipitation. These physical data are measured and monitored by the instruments and equipment. Dams and their surroundings have to be monitored by using essential methods at periodic time intervals in order to determine the possible changes that may occur over the time. Monitoring programs typically consist of; surveillance or visual observation. These programs on dams provide information for evaluating the dam's performance related to the design intent and expected changes that could affect the safety performance of the dam. Additionally, these programs are used for investigating and evaluating the abnormal or degrading performance where any remedial action is necessary. Geodetic and non-geodetic methods are used for monitoring. Monitoring the performance of the dams is critical for producing and maintaining the safe dams. This study provides some information, safety and the techniques about the deformation monitoring of the
Evaluation of 14 nonlinear deformation algorithms applied to human brain MRI registration
Klein, Arno; Andersson, Jesper; Ardekani, Babak A.; Ashburner, John; Avants, Brian; Chiang, Ming-Chang; Christensen, Gary E.; Collins, D. Louis; Gee, James; Hellier, Pierre; Song, Joo Hyun; Jenkinson, Mark; Lepage, Claude; Rueckert, Daniel; Thompson, Paul; Vercauteren, Tom; Woods, Roger P.; Mann, J. John; Parsey, Ramin V.
2009-01-01
All fields of neuroscience that employ brain imaging need to communicate their results with reference to anatomical regions. In particular, comparative morphometry and group analysis of functional and physiological data require coregistration of brains to establish correspondences across brain structures. It is well established that linear registration of one brain to another is inadequate for aligning brain structures, so numerous algorithms have emerged to nonlinearly register brains to one another. This study is the largest evaluation of nonlinear deformation algorithms applied to brain image registration ever conducted. Fourteen algorithms from laboratories around the world are evaluated using 8 different error measures. More than 45,000 registrations between 80 manually labeled brains were performed by algorithms including: AIR, ANIMAL, ART, Diffeomorphic Demons, FNIRT, IRTK, JRD-fluid, ROMEO, SICLE, SyN, and four different SPM5 algorithms (“SPM2-type” and regular Normalization, Unified Segmentation, and the DARTEL Toolbox). All of these registrations were preceded by linear registration between the same image pairs using FLIRT. One of the most significant findings of this study is that the relative performances of the registration methods under comparison appear to be little affected by the choice of subject population, labeling protocol, and type of overlap measure. This is important because it suggests that the findings are generalizable to new subject populations that are labeled or evaluated using different labeling protocols. Furthermore, we ranked the 14 methods according to three completely independent analyses (permutation tests, one-way ANOVA tests, and indifference-zone ranking) and derived three almost identical top rankings of the methods. ART, SyN, IRTK, and SPM's DARTEL Toolbox gave the best results according to overlap and distance measures, with ART and SyN delivering the most consistently high accuracy across subjects and label sets
Deformation Behavior of Nanoporous Metals
Biener, J; Hodge, A M; Hamza, A V
2007-11-28
Nanoporous open-cell foams are a rapidly growing class of high-porosity materials (porosity {ge} 70%). The research in this field is driven by the desire to create functional materials with unique physical, chemical and mechanical properties where the material properties emerge from both morphology and the material itself. An example is the development of nanoporous metallic materials for photonic and plasmonic applications which has recently attracted much interest. The general strategy is to take advantage of various size effects to introduce novel properties. These size effects arise from confinement of the material by pores and ligaments, and can range from electromagnetic resonances to length scale effects in plasticity. In this chapter we will focus on the mechanical properties of low density nanoporous metals and how these properties are affected by length scale effects and bonding characteristics. A thorough understanding of the mechanical behavior will open the door to further improve and fine-tune the mechanical properties of these sometimes very delicate materials, and thus will be crucial for integrating nanoporous metals into products. Cellular solids with pore sizes above 1 micron have been the subject of intense research for many years, and various scaling relations describing the mechanical properties have been developed.[4] In general, it has been found that the most important parameter in controlling their mechanical properties is the relative density, that is, the density of the foam divided by that of solid from which the foam is made. Other factors include the mechanical properties of the solid material and the foam morphology such as ligament shape and connectivity. The characteristic internal length scale of the structure as determined by pores and ligaments, on the other hand, usually has only little effect on the mechanical properties. This changes at the submicron length scale where the surface-to-volume ratio becomes large and the effect
Near real-time skin deformation mapping
NASA Astrophysics Data System (ADS)
Kacenjar, Steve; Chen, Suzie; Jafri, Madiha; Wall, Brian; Pedersen, Richard; Bezozo, Richard
2013-02-01
A novel in vivo approach is described that provides large area mapping of the mechanical properties of the skin in human patients. Such information is important in the understanding of skin health, cosmetic surgery[1], aging, and impacts of sun exposure. Currently, several methods have been developed to estimate the local biomechanical properties of the skin, including the use of a physical biopsy of local areas of the skin (in vitro methods) [2, 3, and 4], and also the use of non-invasive methods (in vivo) [5, 6, and 7]. All such methods examine localized areas of the skin. Our approach examines the local elastic properties via the generation of field displacement maps of the skin created using time-sequence imaging [9] with 2D digital imaging correlation (DIC) [10]. In this approach, large areas of the skin are reviewed rapidly, and skin displacement maps are generated showing the contour maps of skin deformation. These maps are then used to precisely register skin images for purposes of diagnostic comparison. This paper reports on our mapping and registration approach, and demonstrates its ability to accurately measure the skin deformation through a described nulling interpolation process. The result of local translational DIC alignment is compared using this interpolation process. The effectiveness of the approach is reported in terms of residual RMS, image entropy measures, and differential segmented regional errors.
Transverse deformations of extreme horizons
NASA Astrophysics Data System (ADS)
Li, Carmen; Lucietti, James
2016-04-01
We consider the inverse problem of determining all extreme black hole solutions to the Einstein equations with a prescribed near-horizon geometry. We investigate this problem by considering infinitesimal deformations of the near-horizon geometry along transverse null geodesics. We show that, up to a gauge transformation, the linearised Einstein equations reduce to an elliptic PDE for the extrinsic curvature of a cross-section of the horizon. We deduce that for a given near-horizon geometry there exists a finite dimensional moduli space of infinitesimal transverse deformations. We then establish a uniqueness theorem for transverse deformations of the extreme Kerr horizon. In particular, we prove that the only smooth axisymmetric transverse deformation of the near-horizon geometry of extreme Kerr, such that cross-sections of the horizon are marginally trapped surfaces, corresponds to that of the extreme Kerr black hole. Furthermore, we determine all smooth and biaxisymmetric transverse deformations of the near-horizon geometry of the five-dimensional extreme Myers-Perry black hole with equal angular momenta. We find a three parameter family of solutions such that cross-sections of the horizon are marginally trapped, which is more general than the known black hole solutions. We discuss the possibility that they correspond to new five-dimensional vacuum black holes.
Deformation and annealing response of TD-nickel chromium sheet
NASA Technical Reports Server (NTRS)
Kane, R. D.; Ebert, L. J.
1973-01-01
The deformation and annealing response of TD-nickel chromium (TD-NiCr) 0.1 inch thick sheet was examined using various cold-rolling and annealing treatments. Upon annealing (above 816 C (1500 F), the as-received material was converted from an initially ultra-fine grain size (average grain dimension 0.51 micron) to a large grain structure. Increases in grain size by a factor of 100 to 200 were observed for this transformation. However, in those material states where the large grain transformation was absent, a fine grain recrystallized structure formed upon annealing (above 732 C (1350 F)). The deformation and annealing response of TD-NiCr sheet was evaluated with respect to the processing related variables as mode and severity of deformation and annealing temperature. Results indicate that the large grain transformation, classical primary recrystallization occurs. Using selected materials produced during the deformation and annealing study, the elevated temperature tensile properties of TD-NiCr sheet were examined in the temperature range 593 C (1100 F) to 1093 C (2000 F). It was observed that the elevated temperature tensile properties of TD-NiCr sheet could be optimized by the stabilization of a large grain size in this material using the cold working and/or annealing treatments developed during the present investigation.
Testing device subjects elastic materials to biaxial deformations
NASA Technical Reports Server (NTRS)
Becker, G. W.
1965-01-01
Testing device stretches elastic materials biaxially over large deformation ranges and varies strain ratios in two perpendicular directions. The device is used in conjunction with a tensile testing machine, which holds the specimen and permits control over the direction and magnitude of the stresses applied.
An unusual exostosis presenting as a bunion deformity.
Beskin, J L
2001-07-01
A large exostosis was the source of a bunion deformity in a 60-year-old woman. Its unusual clinical and radiographic features were suggestive of a bizarre parosteal osteochondromatous proliferation. However, histologic features were most consistent with a benign osteocartilaginous exostosis.
Time-variable deformation in the New Madrid seismic zone.
Calais, Eric; Stein, Seth
2009-03-13
New geodetic measurements show that the New Madrid is currently deforming too slowly, if at all, to account for large earthquakes in the region over the past 5000 years. This result, together with increasing evidence for temporal clustering and spatial migration of earthquake sequences in continental interiors, indicates that either tectonic loading rates or fault properties vary over a few thousand years.
Characteristics of aluminum alloy microplastic deformation in different structural states
Seregin, G.V.; Efimenko, L.L.; Leonov, M.V.
1995-07-01
The solution to the problem of improving the mechanical properties (including cyclic strength) of structural materials is largely dependent on our knowledge of the laws governing the development of microplastic deformations in them. The effect of heat and mechanical treatment on the elastoplastic properties and fatigue resistance of the commercial aluminum alloys AK4-1 and D16 is analyzed.
Redistribution of Core-forming Melt During Shear Deformation of Partially Molten Peridotite
NASA Technical Reports Server (NTRS)
Hustoft, J. W.; Kohlstedt, D. L.
2002-01-01
To investigate the role of deformation on the distribution of core-forming melt in a partially molten peridotite, samples of olivine-basalt-iron sulfide were sheared to large strains. Dramatic redistribution of sulfide and silicate melts occur during deformation. Additional information is contained in the original extended abstract.
Internal friction peaks observed in explosively deformed polycrystalline Mo, Nb, and Cu
NASA Technical Reports Server (NTRS)
Rieu, G. E.; Grimes, H. H.; Romain, J. P.; Defouquet, J.
1974-01-01
Explosive deformation (50 kbar range) induced, in Cu, Mo and Nb, internal friction peaks identical to those observed after large normal deformation. The variation of the peaks with pressure for Mo and Nb lead to an explanation of these processes in terms of double kink generation in screw and edge dislocations.
Chaetal deformities in aquatic oligochaeta
Brinkhurst, R.O.; Wetzel, M.J.
1994-12-31
Gross deformities in the chaetae of specimens of the tubificid Potamothrix hammoniensis were described by Milbrink from Lake Vaenern, Sweden. This lake is one of the most mercury-polluted major lakes of the world. Statistical tests showed a highly significant correlation between the incidence of deformities and the mercury concentration in the sediments. Changes in the pulp and paper mill process led to marked reduction in specimens with deformities. Similarly modified specimens of various species have been observed at a number of sites contaminated with heavy metals or oil residues in North America. Experimental work on chaetal form has demonstrated changes due to conductivity which have also been observed in saline inland waters. These experiments suggest that chaetae may be shed and replaced by worms every few days. EDX observation of chaetae indicated that metals may accumulate in them, and so provide a potential depuration mechanism. Independent physiological studies suggest that worms may be capable of regulating their metal levels.
Deformed Richardson-Gaudin model
NASA Astrophysics Data System (ADS)
Kulish, P.; Stolin, A.; Johannesson, L. H.
2014-09-01
The Richardson-Gaudin model describes strong pairing correlations of fermions confined to a finite chain. The integrability of the Hamiltonian allows the algebraic construction of its eigenstates. In this work we show that the quantum group theory provides a possibility to deform the Hamiltonian preserving integrability. More precisely, we use the so-called Jordanian r-matrix to deform the Hamiltonian of the Richardson-Gaudin model. In order to preserve its integrability, we need to insert a special nilpotent term into the auxiliary L-operator which generates integrals of motion of the system. Moreover, the quantum inverse scattering method enables us to construct the exact eigenstates of the deformed Hamiltonian. These states have a highly complex entanglement structure which require further investigation.
Deformation of Unentangled Swollen Gels
NASA Astrophysics Data System (ADS)
Sariyer, Ozan; Panyukov, Sergey; Rubinstein, Michael
2014-03-01
We study the deformation characteristics (Poisson's ratios and stress-strain relations) of unentangled gels swollen and uniaxially or biaxially deformed in excess solvent by considering the balance of osmotic pressure and elastic stress in unconstrained dimensions. Our scaling theory predicts a crossover from theta solvent behavior to marginal solvent behavior upon stretching gels that are in concentrated regime at swelling equilibrium - a phenomenon that was experimentally observed long ago, but not understood theoretically. For gels that are in the semidilute good solvent regime at swelling equilibrium, we predict a crossover to theta solvent behavior upon compression and a crossover to marginal solvent behavior upon stretching. Our theory reproduces the previously known results for equilibrium swelling degree as well as known deformation characteristics in theta and athermal solvents.
Shock metamorphism of deformed quartz
NASA Technical Reports Server (NTRS)
Gratz, Andrew J.; Christie, John; Tyburczy, James; Ahrens, Thomas; Pongratz, Peter
1988-01-01
The effect produced by shock loading (to peak pressures of 12 and 24) on deformed synthetic quartz containing a dislocation and abundant bubbles and small inclusions was investigated, and the relationships between preexisting dislocation density shock lamellae in the target material were examined. The resultant material was found to be inhomogeneously deformed and extremely fractured. Results of TEM examinations indicate that no change in dislocation density was caused by shock loading except in regions containing shock lamellae, where the dislocation density was lowered. The shock-induced defects tend to nucleate on and be controlled by preexisting stress concentrators; shock lamellae, glassy veins, and most curviplanar defects form in tension, presumably during release. An extremely mobile silica fluid is formed and injected into fractures during release, which forcibly removes crystalline fragments from vein walls. It is concluded that shock deformation in quartz is dominated by fracture and melting.
Deformation processes in forging ceramics
NASA Technical Reports Server (NTRS)
Cannon, R. M.; Rhodes, W. H.
1973-01-01
The deformation processes involved in the forging of refractory ceramic oxides were investigated. A combination of mechanical testing and forging was utilized to investigate both the flow and fracture processes involved. Deformation studies of very fine grain Al203 revealed an apparent transition in behavior, characterized by a shift in the strain rate sensitivity from 0.5 at low stresses to near unity at higher stresses. The behavior is indicative of a shift in control between two dependent mechanisms, one of which is indicated to be cation limited diffusional creep with significant boundary enhancement. The possible contributions of slip, indicated by crystallographic texture, interface control of the diffusional creep and inhomogeneous boundary sliding are also discussed. Additional experiments indicated an independence of deformation behavior on MgO doping and retained hot pressing impurities, at least for ultrafine grained material, and also an independence of test atmosphere.
Microstructure of deformed graywacke sandstones
Dengler, L.A.
1980-03-05
Microsctures in low-permeability graywacke sandstones were studied by optical and scanning electron microscopy (SEM). SEM specimens were prepared by ion-bombardment of thick polished samples. The undeformed rock contains grains in a matrix composed primarily of authigenic chlorite and kaolinite. Chlorite platelets are randomly arranged in face-to-edge relation to one another. Kaolinite occurs as pseudohexagonal crystals stacked face-to-face in pore filling books. Uniaxial-stress experiments covered a range of confining pressures from .1 to 600 MPa. Below 50 MPa confining pressure, intergranular fracturing occurs within the fault zone and near the sample's cylindrical surface. Between 100 and 300 MPa confining pressure, fault zones contain highly fractured grains, gauge and slickensides on grain surfaces. At 600 MPa, the sample contains a diffuse shear zone of highly fractured grains and no well-defined fault. In all samples, the distribution of microcracks is heterogeneous. Different clay minerals exhibit different modes of deformation. Chlorite structure responds to applied stress by compaction, reducing both pore size and volume. Chlorite platelets are plastically deformed in even the least strained samples. Kaolinite does not deform plastically in any of the samples examined. Deformation of kaolinite is restricted to toppling of the book structure. Dilatant crack growth was studied in two samples unloaded prior to failure. Uniaxially-strained samples deform primarily along grain boundaries, producing intergranular cracks and realignment of chlorite platelets. Intragranular crack density is linearly related to axial-strain, although grains are less fractured than in uniaxially-stressed samples tested at equivalent mean pressures. Cracks are rarely longer than a grain diameter. Nuclear-explosively deformed samples were recovered after the Rio Blanco gas stimulation experiment. (JGB)
Effects of Structural Deformation and Tube Chirality on Electronic Conductance of Carbon Nanotubes
NASA Technical Reports Server (NTRS)
Svizhenko, Alexei; Maiti, Amitesh; Anantram, M. P.; Biegel, Bryan A. (Technical Monitor)
2002-01-01
A combination of large scale classical force-field (UFF), density functional theory (DFT), and tight-binding Green's function transport calculations is used to study the electronic properties of carbon nanotubes under the twist, bending, and atomic force microscope (AFM)-tip deformation. We found that in agreement with experiment a significant change in electronic conductance can be induced by AFM-tip deformation of metallic zigzag tubes and by twist deformation of armchair tubes. The effect is explained in terms of bandstructure change under deformation.
NASA Astrophysics Data System (ADS)
Maeder, X.; Trullenque, G.; Drury, M. R.; de Bresser, J.
2007-12-01
Understanding of texture development and its relation to grain size sensitive (GSS) deformation mechanism is of great importance since the rheological behavior of rocks varies substantially depending on which deformation mechanisms are controlling. Recent studies on naturally and experimentally deformed calcite and olivine aggregates have demonstrated that even fine grained materials that are expected to deform by grain size sensitive (GSS) mechanisms, develop a weak but distinct LPO (texture) at high strain. To investigate this behavior we conducted new deformation experiments on Solnhofen limestone in direct shear. This study is part of a wider investigation on large strain deformation in different deformation modes from G. Trullenque, in collaboration with D.L. Kohlstedt (Minneapolis, USA), R. Heilbronner and H. Stuenitz (Basel, Switzerland) and the Utrecht group. The samples have been deformed to high strain both in the conditions of the transition between the GSS and GSI creep regime and in the GSS creep regime. We used Electron Backscatter Diffraction (EBSD) to determine the texture strength of the samples, the distribution of misorientation axes and the grain size distributions. The results show an oblique shape preferred orientation at 35° to 40° to the shear plane and a moderate LPO. The c-axis preferred orientation shows a girdle with one main maximum at a high angle to the shear plane, displaced towards the shortening direction of the imposed shear. The a-axes present a weak girdle perpendicular to the c-axis. Grain growth occurred during high deformation. The misorientation angle distribution has a main peak at low angle. This is due to the progressive subgrain formation and rotation which occurred mainly in the larger grains. Subgrain rotation with misorientations up to 10° occured but most boundaries are low angle (< 5°). This shows the formation of new high angle boundaries and grain size reduction. The formation of subgrains and subgrain
Controllable objective with deformable mirrors
Agafonov, V V; Safronov, A G
2004-03-31
A new optical device - an objective with deformable mirrors and parameters controlled in the dynamic regime is proposed. The computer simulation of the objective is performed. The dependences of some parameters of the objective on the control voltage are determined. The simulation showed that the ranges of control of the rear focal segment and the focal distance for the objective with the focal distance 602 mm were 1057 and 340 mm, respectively, which is substantially greater than in the control of an equivalent deformable mirror. (laser applications and other topics in quantum electronics)
Analytical volcano deformation source models
Lisowski, Michael; Dzurisin, Daniel
2007-01-01
Primary volcanic landforms are created by the ascent and eruption of magma. The ascending magma displaces and interacts with surrounding rock and fluids as it creates new pathways, flows through cracks or conduits, vesiculates, and accumulates in underground reservoirs. The formation of new pathways and pressure changes within existing conduits and reservoirs stress and deform the surrounding rock. Eruption products load the crust. The pattern and rate of surface deformation around volcanoes reflect the tectonic and volcanic processes transmitted to the surface through the mechanical properties of the crust.
Ilizarov principles of deformity correction.
Spiegelberg, B; Parratt, T; Dheerendra, S K; Khan, W S; Jennings, R; Marsh, D R
2010-03-01
Ilizarov frames provide a versatile fixation system for the management of bony deformities, fractures and their complications. The frames give stability, soft tissue preservation, adjustability and functionality allowing bone to realise its full osteogenic potential. It is important that we have a clear and concise understanding of the Ilizarov principles of deformity correction to best make use of this fixation system. In this review article, the history of Ilizarov frame, the basic sciences behind it, the mechanical principles governing its use and the clinical use of the fixation system are discussed.
Ilizarov principles of deformity correction
Spiegelberg, B; Parratt, T; Dheerendra, SK; Khan, WS; Jennings, R; Marsh, DR
2010-01-01
Ilizarov frames provide a versatile fixation system for the management of bony deformities, fractures and their complications. The frames give stability, soft tissue preservation, adjustability and functionality allowing bone to realise its full osteogenic potential. It is important that we have a clear and concise understanding of the Ilizarov principles of deformity correction to best make use of this fixation system. In this review article, the history of Ilizarov frame, the basic sciences behind it, the mechanical principles governing its use and the clinical use of the fixation system are discussed. PMID:20353638
Cavity coalescence in superplastic deformation
Stowell, M.J.; Livesey, D.W.; Ridley, N.
1984-01-01
An analysis of the probability distribution function of particles randomly dispersed in a solid has been applied to cavitation during superplastic deformation and a method of predicting cavity coalescence developed. Cavity size distribution data were obtained from two microduplex nickel-silver alloys deformed superplastically to various extents at elevated temperature, and compared to theoretical predictions. Excellent agreement occurred for small void sizes but the model underestimated the number of voids in the largest size groups. It is argued that the discrepancy results from a combination of effects due to non-random cavity distributions and to enhanced growth rates and incomplete spheroidization of the largest cavities.
Uncovering deformation processes from surface displacements
NASA Astrophysics Data System (ADS)
Stramondo, Salvatore
2013-04-01
The aim of this talk is to provide an overview about the most recent outcomes in Earth Sciences, describe the role of satellite remote sensing, together with GPS, ground measurement and further data, for geophysical parameter retrieval in well known case studies where the combined approach dealing with the use of two or more techniques/datasets have demonstrated their effectiveness. The Earth Sciences have today a wide availability of instruments and sensors able to provide scientists with an unprecedented capability to study the physical processes driving earthquakes, volcanic eruptions, landslides, and other dynamic Earth systems. Indeed measurements from satellites allow systematic observation of the Earth surface covering large areas, over a long time period and characterized by growing sample intervals. Interferometric Synthetic Aperture Radar (InSAR) technique has demonstrated its effectiveness to investigate processes responsible for crustal faulting stemming from the detection of surface deformation patterns. Indeed using satellite data along ascending and descending orbits, as well as different incident angles, it is possible in principle to retrieve the full 3D character of the ground motion. To such aim the use of GPS stations providing 3D displacement components is a reliable complementary instrument. Finally, offset tracking techniques and Multiple Aperture Interferometry (MAI) may provide a contribution to the analysis of horizontal and NS deformation vectors. The estimation of geophysical parameters using InSAR has been widely discussed in seismology and volcanology, and also applied to deformation associated with groundwater and other subsurface fluids. These applications often involve the solution of an inverse problem, which means the retrieval of optimal source parameters at depth for volcanoes and earthquakes, from the knowledge of surface deformation from InSAR. In recent years, InSAR measurements combined with traditional seismological and
A modified digital phase-shift moiré technique for impact deformation measurements
NASA Astrophysics Data System (ADS)
Verleysen, Patricia; Degrieck, Joris
2004-12-01
Due to the short loading times and high deformation rates inherent to impact experiments, measurement of the occurring deformations is not straightforward. Presented in this paper is a technique to obtain the displacements and deformations of a specimen subjected to a uni-axial impact load. During the experiment the deformation of a line grating attached to the specimen is captured using a streak camera. From the recorded deforming grating the specimen displacements are automatically derived using an advanced numerical algorithm, based on the interference between the specimen grating and a virtual reference grating. Numerical interference is considered because it allows that the pitch of the reference grating is adapted to the changing amplitude of the deformation. Indeed, at each moment of the deformation process the pitch of the reference grating is chosen such that the highest possible accuracy and sensitivity is guaranteed. Because of this, large changes in deformation amplitude are allowed, and the technique is applicable to a wide range of materials. Eventual imperfections of the specimen grating and temperature effects are taken into account. Specimen displacements are extracted automatically by means of a phase-shifting technique. The non-contact measurement technique yields high resolution, quantitative information on the specimen deformation, along the entire length of the specimen and during the full duration of the experiment. Interaction by the operator is excluded. Results are presented of a high strain rate tensile test on a steel sheet specimen showing local deformations up to about 170%.
Extracting Cell Stiffness from Real-Time Deformability Cytometry: Theory and Experiment.
Mietke, Alexander; Otto, Oliver; Girardo, Salvatore; Rosendahl, Philipp; Taubenberger, Anna; Golfier, Stefan; Ulbricht, Elke; Aland, Sebastian; Guck, Jochen; Fischer-Friedrich, Elisabeth
2015-11-17
Cell stiffness is a sensitive indicator of physiological and pathological changes in cells, with many potential applications in biology and medicine. A new method, real-time deformability cytometry, probes cell stiffness at high throughput by exposing cells to a shear flow in a microfluidic channel, allowing for mechanical phenotyping based on single-cell deformability. However, observed deformations of cells in the channel not only are determined by cell stiffness, but also depend on cell size relative to channel size. Here, we disentangle mutual contributions of cell size and cell stiffness to cell deformation by a theoretical analysis in terms of hydrodynamics and linear elasticity theory. Performing real-time deformability cytometry experiments on both model spheres of known elasticity and biological cells, we demonstrate that our analytical model not only predicts deformed shapes inside the channel but also allows for quantification of cell mechanical parameters. Thereby, fast and quantitative mechanical sampling of large cell populations becomes feasible.
Extracting Cell Stiffness from Real-Time Deformability Cytometry: Theory and Experiment
Mietke, Alexander; Otto, Oliver; Girardo, Salvatore; Rosendahl, Philipp; Taubenberger, Anna; Golfier, Stefan; Ulbricht, Elke; Aland, Sebastian; Guck, Jochen; Fischer-Friedrich, Elisabeth
2015-01-01
Cell stiffness is a sensitive indicator of physiological and pathological changes in cells, with many potential applications in biology and medicine. A new method, real-time deformability cytometry, probes cell stiffness at high throughput by exposing cells to a shear flow in a microfluidic channel, allowing for mechanical phenotyping based on single-cell deformability. However, observed deformations of cells in the channel not only are determined by cell stiffness, but also depend on cell size relative to channel size. Here, we disentangle mutual contributions of cell size and cell stiffness to cell deformation by a theoretical analysis in terms of hydrodynamics and linear elasticity theory. Performing real-time deformability cytometry experiments on both model spheres of known elasticity and biological cells, we demonstrate that our analytical model not only predicts deformed shapes inside the channel but also allows for quantification of cell mechanical parameters. Thereby, fast and quantitative mechanical sampling of large cell populations becomes feasible. PMID:26588562
Deformation Mechanisms of Gum Metals Under Nanoindentation
NASA Astrophysics Data System (ADS)
Sankaran, Rohini Priya
defect structures to applied loading, we perform ex-situ nanoindentation. Nanoindentation is a convenient method as the plastic deformation is localized and probes a nominally defect free volume of the material. We subsequently characterize the defect structures in these alloys with both conventional TEM and advanced techniques such as HAADF HRSTEM and nanoprobe diffraction. These advanced techniques allow for a more thorough understanding of the observed deformation features. The main findings from this investigation are as follows. As expected we observe that a non-equilibrium phase, o, is present in the leaner beta-stabilized alloy, ST Ref-1. We do not find any direct evidence of secondary phases in STGM, and we find the beta phase in CWGM, along with lath microstructure with subgrain structure consisting of dislocation cell networks. Upon nanoindentation, we find twinning accompanied by beta nucleation on the twin boundary in ST Ref-1 samples. This result is consistent with previous findings and is reasonable considering the alloy is unstable with respect to beta transformation. We find deformation nanotwinning in cold worked gum metals under nanoindentation, which is initially surprising. We argue that when viewed as a nanocrystalline material, such a deformation mechanism is consistent with previous work, and furthermore, a deformation nanotwinned structure does not preclude an ideal shear mechanism from operating in the alloy. Lastly, we observe continuous lattice rotations in STGM under nanoindentation via nanoprobe diffraction. With this technique, for the first time we can demonstrate that the lattice rotations are truly continuous at the nanoscale. We can quantify this lattice rotation, and find that even though the rotation is large, it may be mediated by a reasonable geometrically necessary dislocation density, and note that similar rotations are typically observed in other materials under nanoindentation. HRSTEM and conventional TEM data confirm the
A tumor growth model with deformable ECM.
Sciumè, G; Santagiuliana, R; Ferrari, M; Decuzzi, P; Schrefler, B A
2014-11-26
Existing tumor growth models based on fluid analogy for the cells do not generally include the extracellular matrix (ECM), or if present, take it as rigid. The three-fluid model originally proposed by the authors and comprising tumor cells (TC), host cells (HC), interstitial fluid (IF) and an ECM, considered up to now only a rigid ECM in the applications. This limitation is here relaxed and the deformability of the ECM is investigated in detail. The ECM is modeled as a porous solid matrix with Green-elastic and elasto-visco-plastic material behavior within a large strain approach. Jauman and Truesdell objective stress measures are adopted together with the deformation rate tensor. Numerical results are first compared with those of a reference experiment of a multicellular tumor spheroid (MTS) growing in vitro, then three different tumor cases are studied: growth of an MTS in a decellularized ECM, growth of a spheroid in the presence of host cells and growth of a melanoma. The influence of the stiffness of the ECM is evidenced and comparison with the case of a rigid ECM is made. The processes in a deformable ECM are more rapid than in a rigid ECM and the obtained growth pattern differs. The reasons for this are due to the changes in porosity induced by the tumor growth. These changes are inhibited in a rigid ECM. This enhanced computational model emphasizes the importance of properly characterizing the biomechanical behavior of the malignant mass in all its components to correctly predict its temporal and spatial pattern evolution.
Polyphase deformation in Marathon basin, west Texas
Sims, D.; Morris, A.
1989-03-01
Marathon basin, Texas, is the westernmost window into the Ouachita orogene. Interpreted as a result of northwest-southeast compression, intermittent orogenic pulses began in the Mississippian and continued into the Early Permian (Wolfcampian). However, the northeastern portion of the basin contains structures that could not have resulted from a single compression orientation and indicate that deformation continued to affect Wolfcampian and Leonardian rocks. Their work confirms the protracted nature of upper Paleozoic deformation and indicates that late- and postorogenic events were not related to the northwest-southeast compression manifest throughout the Marathon basin. The northeastern part of the basin exposes Morrowan( )-Desmoinesian rocks. The authors recognize a duplex thrust system, traceable for 10 km, rooted in the uppermost Morrowan( ) Tesnus Formation and creating a double thickness of (Morrowan-Atokan) Dimple Limestone. The duplex is folded by 50 to 2000-m half-wavelength northwestverging folds which plunge gently southwestward. Dimple thickness is further increased by a large number of contraction faults, each with up to 2 m of stratigraphic throw. Superimposed upon these structures are southeast-plunging, 10-20-m half-wavelength open kinks with vergence sympathetic with the regional trend variation apparent in this part of the basin. The superimposed structures are the result of a northeast-southwest compressive event. North of the Ouachita exposure, rocks containing lower Leonardian fusulinids are deformed into gentle east-west-trending 500-m half-wavelength folds which are likely the result of another distinct compression orientation trending north-south. Pervasive east-west extension in all Pennsylvania-age rocks is indicated by subvertical, calcite-filled veins.
A tumor growth model with deformable ECM
Sciumè, G; Santagiuliana, R; Ferrari, M; Decuzzi, P; Schrefler, B A
2015-01-01
Existing tumor growth models based on fluid analogy for the cells do not generally include the extracellular matrix (ECM), or if present, take it as rigid. The three-fluid model originally proposed by the authors and comprising tumor cells (TC), host cells (HC), interstitial fluid (IF) and an ECM, considered up to now only a rigid ECM in the applications. This limitation is here relaxed and the deformability of the ECM is investigated in detail. The ECM is modeled as a porous solid matrix with Green-elastic and elasto-visco-plastic material behavior within a large strain approach. Jauman and Truesdell objective stress measures are adopted together with the deformation rate tensor. Numerical results are first compared with those of a reference experiment of a multicellular tumor spheroid (MTS) growing in vitro, then three different tumor cases are studied: growth of an MTS in a decellularized ECM, growth of a spheroid in the presence of host cells and growth of a melanoma. The influence of the stiffness of the ECM is evidenced and comparison with the case of a rigid ECM is made. The processes in a deformable ECM are more rapid than in a rigid ECM and the obtained growth pattern differs. The reasons for this are due to the changes in porosity induced by the tumor growth. These changes are inhibited in a rigid ECM. This enhanced computational model emphasizes the importance of properly characterizing the biomechanical behavior of the malignant mass in all its components to correctly predict its temporal and spatial pattern evolution. PMID:25427284
Highly deformable nanofilaments in flow
NASA Astrophysics Data System (ADS)
Pawłowska, S.
2016-10-01
Experimental analysis of hydrogel nanofilaments conveyed by flow is conducted to help in understanding physical phenomena responsible for transport properties and shape deformations of long bio-objects, like DNA or proteins. Investigated hydrogel nanofilaments exhibit typical macromolecules-like behavior, as spontaneous conformational changes and cross-flow migration. Results of the experiments indicate critical role of thermal fluctuations behavior of single filaments.
Ground Deformation Extraction Using Visible Images and LIDAR Data in Mining Area
NASA Astrophysics Data System (ADS)
Hu, Wenmin; Wu, Lixin
2016-06-01
Recognition and extraction of mining ground deformation can help us understand the deformation process and space distribution, and estimate the deformation laws and trends. This study focuses on the application of ground deformation detection and extraction combining with high resolution visible stereo imagery, LiDAR observation point cloud data and historical data. The DEM in large mining area is generated using high-resolution satellite stereo images, and ground deformation is obtained through time series analysis combined with historical DEM data. Ground deformation caused by mining activities are detected and analyzed to explain the link between the regional ground deformation and local deformation. A district of covering 200 km2 around the West Open Pit Mine in Fushun of Liaoning province, a city located in the Northeast China is chosen as the test area for example. Regional and local ground deformation from 2010 to 2015 time series are detected and extracted with DEMs derived from ZY-3 images and LiDAR point DEMs in the case study. Results show that the mean regional deformation is 7.1 m of rising elevation with RMS 9.6 m. Deformation of rising elevation and deformation of declining elevation couple together in local area. The area of higher elevation variation is 16.3 km2 and the mean rising value is 35.8 m with RMS 15.7 m, while the deformation area of lower elevation variation is 6.8 km2 and the mean declining value is 17.6 m with RMS 9.3 m. Moreover, local large deformation and regional slow deformation couple together, the deformation in local mining activities has expanded to the surrounding area, a large ground fracture with declining elevation has been detected and extracted in the south of West Open Pit Mine, the mean declining elevation of which is 23.1 m and covering about 2.3 km2 till 2015. The results in this paper are preliminary currently; we are making efforts to improve more precision results with invariant ground control data for validation.
A satellite geodetic survey of spatiotemporal deformation of Iranian volcanos
NASA Astrophysics Data System (ADS)
Shirzaei, M.
2012-04-01
Surface deformation in volcanic areas is usually due to movement of magma, hydrothermal activity at depth, weight of volcano, landside, etc. Iran, located at the convergence of the Eurasian and Arabian tectonic plates, is the host of five apparently inactive volcanoes, named 'Damavand', 'Taftan', 'Bazman', 'Sabalan' and 'Sahand'. Through investigation of the long term surface deformation rate at Damavand volcano, the highest point in the middle east, Shirzaei et al. (2011) demonstrated that a slow gravity-driven deformation in the form of spreading is going on at this volcano. Extending the earlier work, in this study, I explore large sets of SAR data obtained by Envisat radar satellite from 2003 through 2010 at all Iranian volcanoes. Multitemporal interferometric analysis of the SAR data sets allows retrieving sub-millimeter surface deformation at these volcanic systems. As a result, I detect a transient flank failure in the form of landslide at Damavand that is followed by elevated fumarolic activity. This suggests that landslide might have triggered volcanic unrest. Moreover, I measure significant surface deformation at Taftan and Bazman volcanos associated with different episodes of uplift and subsidence. The inverse model simulations suggest that the time-dependent inflations and deflations of extended and spherical pressurized magma chambers are responsible for the surface displacements at these volcanoes. I also detect time-dependent surface displacements at Sabalan and Sahand volcanoes, where the investigation of the type and the sources of the observed deformation is subject of ongoing research. This study is a best example that shows the absent of recent eruption can not be used as a reliable factor in volcanic hazard assessment and a continuous monitoring system is of vital importance. Reference Shirzaei, M., Walter, T.R., Nankali, H.R. and Holohan, E.P., 2011. Gravity-driven deformation of Damavand volcano, Iran, detected through InSAR time series
Local gate effect of mechanically deformed crossed carbon nanotube junction.
Qing, Quan; Nezich, Daniel A; Kong, Jing; Wu, Zhongyun; Liu, Zhongfan
2010-11-10
In this work, we have demonstrated that the local deformation at the crossed carbon nanotube (CNT) junctions can introduce significant tunable local gate effect under ambient environment. Atomic force microscope (AFM) manipulation of the local deformation yielded a variation in transconductance that was retained after removing the AFM tip. Application of a large source-drain voltage and pressing the CNT junction above a threshold pressure can respectively erase and recover the transconductance modulation reversibly. The local gate effect is found to be independent of the length of the crossed CNT and attributed to the charges residing at the deformed junctions due to formation of localized states. The number of localized charges is estimated to be in the range of 10(2) to 10(3). These results may find potential applications in electromechanical sensors and could have important implications for designing nonvolatile devices based on crossed CNT junctions.
Deformations of Flat Unsymmetric Laminates Subjected to Inplane Loads
NASA Technical Reports Server (NTRS)
Hyer, Michael W.; Ochinero, Tomoya T.; Majeed, Majed
2004-01-01
The geometrically nonlinear deformation response of initially flat unsymmetric cross-ply laminates subjected to an inplane compressive load and two sets of boundary conditions is studied. Stability of the deformations is considered. At issue is whether or not the plate remains flat with increased compressive loading, and whether it buckles. A semi-infinite unsymmetric cross-ply laminate is used to show the combined effects of geometric nonlinearities and bending-stretch coupling. Finite element results for finite laminates are then presented, and it is shown that to a large degree the boundary conditions control the character of the deformation response. It appears that clamped boundary conditions support buckling behavior, in the classic sense of bifurcation, whereas simply-supported conditions do not.
On the deformation of gas bubbles in liquids
NASA Astrophysics Data System (ADS)
Legendre, Dominique; Zenit, Roberto; Velez-Cordero, J. Rodrigo
2012-04-01
We consider the deformation of gas bubbles rising in different liquids over a wide range of Morton numbers, from O(10-11) to O(1), and bubble diameters. We have collected data from the literature and performed new experiments for relatively large Morton numbers. A simple expression is proposed to describe the evolution of the bubble deformation, which is consistent with the analytical solution of Moore ["The rise of a gas bubble in a viscous liquid," J. Fluid Mech. 6, 113 (1959)]. It appears that deformation can be predicted correctly by considering the Morton and Weber numbers. The variation of the bubble interfacial area is also analyzed; this quantity is very important for the case of bubbly flow modeling but has not been measured directly to date.
Videogrammetric Model Deformation Measurement Technique for Wind Tunnel Applications
NASA Technical Reports Server (NTRS)
Barrows, Danny A.
2006-01-01
Videogrammetric measurement technique developments at NASA Langley were driven largely by the need to quantify model deformation at the National Transonic Facility (NTF). This paper summarizes recent wind tunnel applications and issues at the NTF and other NASA Langley facilities including the Transonic Dynamics Tunnel, 31-Inch Mach 10 Tunnel, 8-Ft high Temperature Tunnel, and the 20-Ft Vertical Spin Tunnel. In addition, several adaptations of wind tunnel techniques to non-wind tunnel applications are summarized. These applications include wing deformation measurements on vehicles in flight, determining aerodynamic loads based on optical elastic deformation measurements, measurements on ultra-lightweight and inflatable space structures, and the use of an object-to-image plane scaling technique to support NASA s Space Exploration program.
Symmetry Based No Core Shell Model in a Deformed Basis
NASA Astrophysics Data System (ADS)
Kekejian, David; Draayer, Jerry; Launey, Kristina
2017-01-01
To address current limitations of shell-model descriptions of large spatial deformation and cluster structures, we adopt a no-core shell model with a deformed harmonic oscillator basis and implement an angular momentum projection in a symmetry-adapted scheme. This approach allows us to reach larger model spaces as a result of computational memory savings for calculations of highly deformed states, such as the Hoyle state in C-12. The method is first tested with schematic interactions, but the ultimate goal is to carry forward calculations with realistic nucleon-nucleon interactions in future work. Supported by the U.S. NSF (OCI-0904874, ACI-1516338) and the U.S. DOE (DE-SC0005248), and benefitted from computing resources provided by Blue Waters and LSU's Center for Computation & Technology.
Ruthenium Aluminides: Deformation Mechanisms and Substructure Development
Tresa M. Pollock
2005-05-11
Structural and functional materials that can operate in severe, high temperature environments are key to the operation of a wide range of energy generation systems. Because continued improvements in the energy efficiency of these systems is critical, the need for new materials with higher temperature capabilities is inevitable. Intermetallic compounds, with strong bonding and generally high melting points offer this possibility for a broad array of components such as coatings, electrode materials, actuators and/or structural elements. RuAl is a very unusual intermetallic compound among the large number of B2compounds that have been identified and investigated to date. This material has a very high melting temperature of 2050?C, low thermal expansion, high thermal conductivity and good corrosion resistance. Unlike most other high temperature B2 intermetallics, RuAl possesses good intrinsic deformability at low temperatures. In this program fundamental aspects of low and high temperature mechanical properties and deformation mechanisms in binary and higher order RuAl-based systems have been investigated. Alloying additions of interest included platinum, boron and niobium. Additionally, preliminary studies on high temperature oxidation behavior of these materials have been conducted.
Scale properties of sea ice deformation and fracturing
NASA Astrophysics Data System (ADS)
Weiss, Jérôme; Marsan, David
2004-09-01
The sea ice cover, which insulates the ocean from the atmosphere, plays a fundamental role in the Earth's climate system. This cover deforms and fractures under the action of winds, ocean currents and thermal stresses. Along with thermodynamics, this deformation and fracturing largely controls the amount of open water within the ice cover and the distribution of ice thickness, two parameters of high climatic importance, especially during fall and winter (no melting). Here we present a scaling analysis of sea ice deformation and fracturing that allows us to characterize the heterogeneity of fracture patterns and of deformation fields, as well as the intermittency of stress records. We discuss the consequences of these scaling properties, particularly for sea ice modelling in global climate models. We show how multifractal scaling laws can be extrapolated to small scales to learn about the nature of the mechanisms that accommodate the deformation. We stress that these scaling properties preclude the use of homogenisation techniques (i.e. the use of mean values) to link different scales, and we discuss how these detailed observations should be used to constrain sea ice dynamics modelling. To cite this article: J. Weiss, D. Marsan, C. R. Physique 5 (2004).
Hydrodynamic resistance and mobility of deformable objects in microfluidic channels
Sajeesh, P.; Doble, M.; Sen, A. K.
2014-01-01
This work reports experimental and theoretical studies of hydrodynamic behaviour of deformable objects such as droplets and cells in a microchannel. Effects of mechanical properties including size and viscosity of these objects on their deformability, mobility, and induced hydrodynamic resistance are investigated. The experimental results revealed that the deformability of droplets, which is quantified in terms of deformability index (D.I.), depends on the droplet-to-channel size ratio ρ and droplet-to-medium viscosity ratio λ. Using a large set of experimental data, for the first time, we provide a mathematical formula that correlates induced hydrodynamic resistance of a single droplet ΔRd with the droplet size ρ and viscosity λ. A simple theoretical model is developed to obtain closed form expressions for droplet mobility ϕ and ΔRd. The predictions of the theoretical model successfully confront the experimental results in terms of the droplet mobility ϕ and induced hydrodynamic resistance ΔRd. Numerical simulations are carried out using volume-of-fluid model to predict droplet generation and deformation of droplets of different size ratio ρ and viscosity ratio λ, which compare well with that obtained from the experiments. In a novel effort, we performed experiments to measure the bulk induced hydrodynamic resistance ΔR of different biological cells (yeast, L6, and HEK 293). The results reveal that the bulk induced hydrodynamic resistance ΔR is related to the cell concentration and apparent viscosity of the cells. PMID:25538806
Fluid-Driven Deformation of a Soft Granular Material
NASA Astrophysics Data System (ADS)
MacMinn, Christopher W.; Dufresne, Eric R.; Wettlaufer, John S.
2015-01-01
Compressing a porous, fluid-filled material drives the interstitial fluid out of the pore space, as when squeezing water out of a kitchen sponge. Inversely, injecting fluid into a porous material can deform the solid structure, as when fracturing a shale for natural gas recovery. These poromechanical interactions play an important role in geological and biological systems across a wide range of scales, from the propagation of magma through Earth's mantle to the transport of fluid through living cells and tissues. The theory of poroelasticity has been largely successful in modeling poromechanical behavior in relatively simple systems, but this continuum theory is fundamentally limited by our understanding of the pore-scale interactions between the fluid and the solid, and these problems are notoriously difficult to study in a laboratory setting. Here, we present a high-resolution measurement of injection-driven poromechanical deformation in a system with granular microsctructure: We inject fluid into a dense, confined monolayer of soft particles and use particle tracking to reveal the dynamics of the multiscale deformation field. We find that a continuum model based on poroelasticity theory captures certain macroscopic features of the deformation, but the particle-scale deformation field exhibits dramatic departures from smooth, continuum behavior. We observe particle-scale rearrangement and hysteresis, as well as petal-like mesoscale structures that are connected to material failure through spiral shear banding.
Preferred orientation in experimentally deformed stishovite: implications for deformation mechanisms
Kaercher, Pamela M.; Zepeda-Alarcon, Eloisa; Prakapenka, Vitali B.; ...
2014-11-07
Although the crystal structure of the high pressure SiO2 polymorph stishovite has been studied in detail, little is known about the development of crystallographic preferred orientation (CPO) during deformation in stishovite. Insight into CPO and associated deformation mechanics of stishovite would provide important information for understanding subduction of quartz-bearing crustal rocks into the mantle. To study CPO development, we converted a natural sample of flint to stishovite in a laser heated diamond anvil cell and compressed the stishovite aggregate up to 38 GPa. We collected diffraction patterns in radial geometry to examine in situ development of crystallographic preferred orientation andmore » find that (001) poles preferentially align with the compression direction. Viscoplastic self-consistent modeling suggests the most likely slip systems at high pressure and ambient temperature are pyramidal and basal slip.« less
Preferred orientation in experimentally deformed stishovite: implications for deformation mechanisms
NASA Astrophysics Data System (ADS)
Kaercher, Pamela M.; Zepeda-Alarcon, Eloisa; Prakapenka, Vitali B.; Kanitpanyacharoen, Waruntorn; Smith, Jesse S.; Sinogeikin, Stanislav; Wenk, Hans-Rudolf
2015-04-01
Although the crystal structure of the high-pressure SiO2 polymorph stishovite has been studied in detail, little is known about the development of crystallographic preferred orientation (CPO) during deformation in stishovite. Insight into CPO and associated deformation mechanics of stishovite would provide important information for understanding subduction of quartz-bearing crustal rocks into the mantle. To study CPO development, we converted a natural sample of flint to stishovite in a laser-heated diamond anvil cell and compressed the stishovite aggregate up to 38 GPa. We collected diffraction patterns in radial geometry to examine in situ development of crystallographic preferred orientation and find that (001) poles preferentially align with the compression direction. Viscoplastic self-consistent modeling suggests the most likely slip systems at high pressure and ambient temperature are pyramidal and basal slip.
Highly deformable bones: unusual deformation mechanisms of seahorse armor.
Porter, Michael M; Novitskaya, Ekaterina; Castro-Ceseña, Ana Bertha; Meyers, Marc A; McKittrick, Joanna
2013-06-01
Multifunctional materials and devices found in nature serve as inspiration for advanced synthetic materials, structures and robotics. Here, we elucidate the architecture and unusual deformation mechanisms of seahorse tails that provide prehension as well as protection against predators. The seahorse tail is composed of subdermal bony plates arranged in articulating ring-like segments that overlap for controlled ventral bending and twisting. The bony plates are highly deformable materials designed to slide past one another and buckle when compressed. This complex plate and segment motion, along with the unique hardness distribution and structural hierarchy of each plate, provide seahorses with joint flexibility while shielding them against impact and crushing. Mimicking seahorse armor may lead to novel bio-inspired technologies, such as flexible armor, fracture-resistant structures or prehensile robotics.
Preferred orientation in experimentally deformed stishovite: implications for deformation mechanisms
Kaercher, Pamela M.; Zepeda-Alarcon, Eloisa; Prakapenka, Vitali B.; Kanitpanyacharoen, Waruntorn; Smith, Jesse S.; Sinogeikin, Stanislav; Wenk, Hans-Rudolf
2014-11-07
Although the crystal structure of the high pressure SiO_{2} polymorph stishovite has been studied in detail, little is known about the development of crystallographic preferred orientation (CPO) during deformation in stishovite. Insight into CPO and associated deformation mechanics of stishovite would provide important information for understanding subduction of quartz-bearing crustal rocks into the mantle. To study CPO development, we converted a natural sample of flint to stishovite in a laser heated diamond anvil cell and compressed the stishovite aggregate up to 38 GPa. We collected diffraction patterns in radial geometry to examine in situ development of crystallographic preferred orientation and find that (001) poles preferentially align with the compression direction. Viscoplastic self-consistent modeling suggests the most likely slip systems at high pressure and ambient temperature are pyramidal and basal slip.
Clusterization and quadrupole deformation in nuclei
Cseh, J.; Algora, A.; Antonenko, N. V.; Jolos, R. V.; Scheid, W.; Darai, J.; Hess, P. O.
2006-04-26
We study the interrelation of the clusterization and quadrupole deformation of atomic nuclei, by applying cluster models. Both the energetic stability and the exclusion principle is investigated. Special attention is paid to the relative orientations of deformed clusters.
Flextensional Single Crystal Piezoelectric Actuators for Membrane Deformable Mirrors
NASA Technical Reports Server (NTRS)
Jiang, Xiaoning; Sahul, Raffi; Hackenberger, Wesley S.
2006-01-01
Large aperture and light weight space telescopes requires adaptive optics with deformable mirrors capable of large amplitude aberration corrections at a broad temperature range for space applications including NASA missions such as SAFIR, TPF, Con-X, etc. The single crystal piezoelectric actuators produced at TRS offer large stroke, low hysteresis, and an excellent cryogenic strain response. Specifically, the recently developed low profile, low voltage flextensional single crystal piezoelectric actuators with dimensions of 18 x 5 x 1 mm showed stroke larger than 95 microns under 300 V. Furthermore, flextensional actuator retained approx. 40-50% of its room temperature strain at liquid Nitrogen environment. In this paper, ATILA FEM design of flextensional actuators, actuator fabrication, and characterization results will be presented for the future work on membrane deformable mirror.
Deformed special relativity and deformed symmetries in a canonical framework
Ghosh, Subir; Pal, Probir
2007-05-15
In this paper we have studied the nature of kinematical and dynamical laws in {kappa}-Minkowski spacetime from a new perspective: the canonical phase space approach. We discuss a particular form of {kappa}-Minkowski phase space algebra that yields the {kappa}-extended finite Lorentz transformations derived in [D. Kimberly, J. Magueijo, and J. Medeiros, Phys. Rev. D 70, 084007 (2004).]. This is a particular form of a deformed special relativity model that admits a modified energy-momentum dispersion law as well as noncommutative {kappa}-Minkowski phase space. We show that this system can be completely mapped to a set of phase space variables that obey canonical (and not {kappa}-Minkowski) phase space algebra and special relativity Lorentz transformation (and not {kappa}-extended Lorentz transformation). The complete set of deformed symmetry generators are constructed that obeys an unmodified closed algebra but induce deformations in the symmetry transformations of the physical {kappa}-Minkowski phase space variables. Furthermore, we demonstrate the usefulness and simplicity of this approach through a number of phenomenological applications both in classical and quantum mechanics. We also construct a Lagrangian for the {kappa}-particle.
NASA Astrophysics Data System (ADS)
Dudarev, E. F.; Pochivalova, G. P.; Kolobov, Yu. R.; Bakach, G. P.; Skosyrskii, A. B.; Zhorovkov, M. F.; Goraynov, А. А.
2013-10-01
The results of an experimental investigation of the effect of mechanical-thermal treatment of submicrocrystalline and coarse-grained titanium on the deformation behavior in the stage of microplastic deformation at room and elevated temperatures are reported. The structural factors giving rise to the flowstress changes in the stage of microplastic deformation as a result of mechanical-thermal treatment are discussed. The general tendencies and special features of the effect of annealing and testing temperatures on the deformation behavior and flow stress in the first and second stages of microplastic deformation of submicrocrystalline and coarse-grained titanium subjected to large plastic deformation at 295 K are clarified.
Latifi, Kujtim; Forster, Kenneth M; Hoffe, Sarah E; Dilling, Thomas J; van Elmpt, Wouter; Dekker, Andre; Zhang, Geoffrey G
2013-07-08
Ventilation imaging using 4D CT is a convenient and low-cost functional imaging methodology which might be of value in radiotherapy treatment planning to spare functional lung volumes. Deformable image registration (DIR) is needed to calculate ventilation imaging from 4D CT. This study investigates the dependence of calculated ventilation on DIR methods and ventilation algorithms. DIR of the normal end expiration and normal end inspiration phases of the 4D CT images was used to correlate the voxels between the two respiratory phases. Three different DIR algorithms, optical flow (OF), diffeomorphic demons (DD), and diffeomorphic morphons (DM) were retrospectively applied to ten esophagus and ten lung cancer cases with 4D CT image sets that encompassed the entire lung volume. The three ventilation extraction methods were used based on either the Jacobian, the change in volume of the voxel, or directly calculated from Hounsfield units. The ventilation calculation algorithms used are the Jacobian, ΔV, and HU method. They were compared using the Dice similarity coefficient (DSC) index and Bland-Altman plots. Dependence of ventilation images on the DIR was greater for the ΔV and the Jacobian methods than for the HU method. The DSC index for 20% of low-ventilation volume for ΔV was 0.33 ± 0.03 (1 SD) between OF and DM, 0.44 ± 0.05 between OF and DD, and 0.51 ± 0.04 between DM and DD. The similarity comparisons for Jacobian were 0.32 ± 0.03, 0.44 ± 0.05, and 0.51 ± 0.04, respectively, and for HU they were 0.53 ± 0.03, 0.56 ± 0.03, and 0.76 ± 0.04, respectively. Dependence of extracted ventilation on the ventilation algorithm used showed good agreement between the ΔV and Jacobian methods, but differed significantly for the HU method. DSC index for using OF as DIR was 0.86 ± 0.01 between ΔV and Jacobian, 0.28 ± 0.04 between ΔV and HU, and 0.28 ± 0.04 between Jacobian and HU, respectively. When using DM or DD as DIR, similar values were obtained when
High stroke pixel for a deformable mirror
Miles, Robin R.; Papavasiliou, Alexandros P.
2005-09-20
A mirror pixel that can be fabricated using standard MEMS methods for a deformable mirror. The pixel is electrostatically actuated and is capable of the high deflections needed for spaced-based mirror applications. In one embodiment, the mirror comprises three layers, a top or mirror layer, a middle layer which consists of flexures, and a comb drive layer, with the flexures of the middle layer attached to the mirror layer and to the comb drive layer. The comb drives are attached to a frame via spring flexures. A number of these mirror pixels can be used to construct a large mirror assembly. The actuator for the mirror pixel may be configured as a crenellated beam with one end fixedly secured, or configured as a scissor jack. The mirror pixels may be used in various applications requiring high stroke adaptive optics.
Small-scale auroral Arc deformations
NASA Astrophysics Data System (ADS)
Wagner, J. S.; Sydora, R. D.; Tajima, T.; Hallinan, T.; Lee, L. C.; Akasofu, S.-I.
1983-10-01
An auroral arc undergoes various types of deformations, such as curls, folds and spirals. In this paper the formation mechanism of folds is examined by a plasma simulation method. It is suggested that folds, as well as curls, can arise from electrostatic shear-induced instabilities. The differences between the two forms are controlled by the presence of ambient ions that must be present to shield the electric field of the precipitating electron charge sheet. It is shown that curls form when the ion sheath thickness is large in comparison with the electron sheet. Folds form when the ion sheath is thin and lags slightly behind the electron guiding centers, setting up an additional electric field that controls the late stages of instability growth.
Deformation of noncommutative quantum mechanics
NASA Astrophysics Data System (ADS)
Jiang, Jian-Jian; Chowdhury, S. Hasibul Hassan
2016-09-01
In this paper, the Lie group GNC α , β , γ , of which the kinematical symmetry group GNC of noncommutative quantum mechanics (NCQM) is a special case due to fixed nonzero α, β, and γ, is three-parameter deformation quantized using the method suggested by Ballesteros and Musso [J. Phys. A: Math. Theor. 46, 195203 (2013)]. A certain family of QUE algebras, corresponding to GNC α , β , γ with two of the deformation parameters approaching zero, is found to be in agreement with the existing results of the literature on quantum Heisenberg group. Finally, we dualize the underlying QUE algebra to obtain an expression for the underlying star-product between smooth functions on GNC α , β , γ .
Variational approach and deformed derivatives
NASA Astrophysics Data System (ADS)
Weberszpil, J.; Helayël-Neto, J. A.
2016-05-01
Recently, we have demonstrated that there exists a possible relationship between q-deformed algebras in two different contexts of Statistical Mechanics, namely, the Tsallis' framework and the Kaniadakis' scenario, with a local form of fractional-derivative operators for fractal media, the so-called Hausdorff derivatives, mapped into a continuous medium with a fractal measure. Here, in this paper, we present an extension of the traditional calculus of variations for systems containing deformed-derivatives embedded into the Lagrangian and the Lagrangian densities for classical and field systems. The results extend the classical Euler-Lagrange equations and the Hamiltonian formalism. The resulting dynamical equations seem to be compatible with those found in the literature, specially with mass-dependent and with nonlinear equations for systems in classical and quantum mechanics. Examples are presented to illustrate applications of the formulation. Also, the conserved Noether current is worked out.
Deformation processes in forging ceramics
NASA Technical Reports Server (NTRS)
Cannon, R. M.; Rhodes, W. H.
1972-01-01
The deformation processes involved in the forging of refractory ceramic oxides were investigated. A combination of mechanical testing and forging are utilized to investigate both the flow and fracture processes involved. An additional hemisphere forging was done which failed prematurely. Analysis and comparison with available fracture data for AL2O3 indicated possible causes of the failure. Examination of previous forgings indicated an increase in grain boundary cavitation with increasing strain.
Static deformation of space elevator tether due to climber
NASA Astrophysics Data System (ADS)
Cohen, Stephen; Misra, Arun K.
2015-06-01
As higher strength to density ratio materials become available, the construction of a space elevator on Earth becomes more plausible. Though many fundamental aspects of the mechanical behaviour of a space elevator have been previously analysed, several details have not been rigorously explored. This paper examines the deformation of the tether from its nominal state when it is loaded with a climber at any altitude. Using an assumed modes numerical approach, the equilibrium conditions governing the static deformation of the elevator tether are derived, taking into account the presence of a climber. These discretised equations are solved numerically to determine the static deformation of the tether. A spectrum of statically deformed tether profiles is presented. Strain, stress and tension profiles are also computed and discussed. In general, when a climber is present below GEO, the extension (and stress) of the portion of tether below it is reduced and that above it is largely unaffected. When a climber is present above GEO, the extension (and stress) of the portion of tether below it is increased (that above it remains largely unaffected). Finally, the absolute displacement of the apex anchor (counterweight) is plotted against climber locations.
Nonlinear, finite deformation, finite element analysis
NASA Astrophysics Data System (ADS)
Nguyen, Nhung; Waas, Anthony M.
2016-06-01
The roles of the consistent Jacobian matrix and the material tangent moduli, which are used in nonlinear incremental finite deformation mechanics problems solved using the finite element method, are emphasized in this paper, and demonstrated using the commercial software ABAQUS standard. In doing so, the necessity for correctly employing user material subroutines to solve nonlinear problems involving large deformation and/or large rotation is clarified. Starting with the rate form of the principle of virtual work, the derivations of the material tangent moduli, the consistent Jacobian matrix, the stress/strain measures, and the objective stress rates are discussed and clarified. The difference between the consistent Jacobian matrix (which, in the ABAQUS UMAT user material subroutine is referred to as DDSDDE) and the material tangent moduli ( C e ) needed for the stress update is pointed out and emphasized in this paper. While the former is derived based on the Jaumann rate of the Kirchhoff stress, the latter is derived using the Jaumann rate of the Cauchy stress. Understanding the difference between these two objective stress rates is crucial for correctly implementing a constitutive model, especially a rate form constitutive relation, and for ensuring fast convergence. Specifically, the implementation requires the stresses to be updated correctly. For this, the strains must be computed directly from the deformation gradient and corresponding strain measure (for a total form model). Alternatively, the material tangent moduli derived from the corresponding Jaumann rate of the Cauchy stress of the constitutive relation (for a rate form model) should be used. Given that this requirement is satisfied, the consistent Jacobian matrix only influences the rate of convergence. Its derivation should be based on the Jaumann rate of the Kirchhoff stress to ensure fast convergence; however, the use of a different objective stress rate may also be possible. The error associated
Intrafraction Variability and Deformation Quantification in the Breast
Glide-Hurst, Carri K.; Shah, Mira M.; Price, Ryan G.; Liu, Chang; Kim, Jinkoo; Mahan, Meredith; Fraser, Correen; Chetty, Indrin J.; Aref, Ibrahim; Movsas, Benjamin; Walker, Eleanor M.
2015-03-01
deformation and proximity to chest wall or breast surface. Conclusions: Lumpectomy cavity and breast deformation and motion demonstrated large variability. A PTV{sub 4DCT} approach showed value in patient-specific margins, particularly if robust interfraction setup analysis can be performed.
Graviton resonances on deformed branes
NASA Astrophysics Data System (ADS)
Cruz, W. T.; Gomes, A. R.; Almeida, C. A. S.
2011-11-01
Plane-wave solutions of Schrödinger-like equations obtained from the metric perturbations in 5D braneworld scenarios can present resonant modes. The search for those structures is important because they can provide us with massive modes with not suppressed couplings with the membrane. We propose in this paper the study of graviton Kaluza-Klein spectrum in a special kind of membrane that possesses internal structure. The interest in the study of these deformed defects is due to the fact that they have a richer internal structure that has implications in the matter energy density along the extra dimensions and this produces a space-time background whose curvature has a splitting, if compared to the usual kink-like models. Such models arise from (4, 1)-branes constructed with one scalar field coupled with gravity where we find two-kink solutions from deformations of a phi4 potential. The main objective of this work is to observe the effects of deformation process in the resonant modes as well as in the coupling between the graviton massive modes and the brane.
NASA Technical Reports Server (NTRS)
Leone, Frank A., Jr.
2015-01-01
A method is presented to represent the large-deformation kinematics of intraply matrix cracks and delaminations in continuum damage mechanics (CDM) constitutive material models. The method involves the additive decomposition of the deformation gradient tensor into 'crack' and 'bulk material' components. The response of the intact bulk material is represented by a reduced deformation gradient tensor, and the opening of an embedded cohesive interface is represented by a normalized cohesive displacement-jump vector. The rotation of the embedded interface is tracked as the material deforms and as the crack opens. The distribution of the total local deformation between the bulk material and the cohesive interface components is determined by minimizing the difference between the cohesive stress and the bulk material stress projected onto the cohesive interface. The improvements to the accuracy of CDM models that incorporate the presented method over existing approaches are demonstrated for a single element subjected to simple shear deformation and for a finite element model of a unidirectional open-hole tension specimen. The material model is implemented as a VUMAT user subroutine for the Abaqus/Explicit finite element software. The presented deformation gradient decomposition method reduces the artificial load transfer across matrix cracks subjected to large shearing deformations, and avoids the spurious secondary failure modes that often occur in analyses based on conventional progressive damage models.
Integrable Deformations of T -Dual σ Models
NASA Astrophysics Data System (ADS)
Borsato, Riccardo; Wulff, Linus
2016-12-01
We present a method to deform (generically non-Abelian) T duals of two-dimensional σ models, which preserves classical integrability. The deformed models are identified by a linear operator ω on the dualized subalgebra, which satisfies the 2-cocycle condition. We prove that the so-called homogeneous Yang-Baxter deformations are equivalent, via a field redefinition, to our deformed models when ω is invertible. We explain the details for deformations of T duals of principal chiral models, and present the corresponding generalization to the case of supercoset models.
Accidental degeneracies in nonlinear quantum deformed systems
NASA Astrophysics Data System (ADS)
Aleixo, A. N. F.; Balantekin, A. B.
2011-09-01
We construct a multi-parameter nonlinear deformed algebra for quantum confined systems that includes many other deformed models as particular cases. We demonstrate that such systems exhibit the property of accidental pairwise energy level degeneracies. We also study, as a special case of our multi-parameter deformation formalism, the extension of the Tamm-Dancoff cutoff deformed oscillator and the occurrence of accidental pairwise degeneracy in the energy levels of the deformed system. As an application, we discuss the case of a trigonometric Rosen-Morse potential, which is successfully used in models for quantum confined systems, ranging from electrons in quantum dots to quarks in hadrons.