A geometric deformable model for echocardiographic image segmentation
NASA Technical Reports Server (NTRS)
Hang, X.; Greenberg, N. L.; Thomas, J. D.
2002-01-01
Gradient vector flow (GVF), an elegant external force for parametric deformable models, can capture object boundaries from both sides. A new geometric deformable model is proposed that combines GVF and the geodesic active contour model. The level set method is used as the numerical method of this model. The model is applied for echocardiographic image segmentation.
Water flow based geometric active deformable model for road network
NASA Astrophysics Data System (ADS)
Leninisha, Shanmugam; Vani, Kaliaperumal
2015-04-01
A width and color based geometric active deformable model is proposed for road network extraction from remote sensing images with minimal human interception. Orientation and width of road are computed from a single manual seed point, from which the propagation starts both right and left hand directions of the starting point, which extracts the interconnected road network from the aerial or high spatial resolution satellite image automatically. Here the propagation (like water flow in canal with defined boundary) is restricted with color and width of the road. Road extraction is done for linear, curvilinear (U shape and S shape) roads first, irrespective of width and color. Then, this algorithm is improved to extract road with junctions in a shape of L, T and X along with center line. Roads with small break or disconnected roads are also extracts by a modified version of this same algorithm. This methodology is tested and evaluated with various remote sensing images. The experimental results show that the proposed method is efficient and extracting roads accurately with less computation time. However, in complex urban areas, the identification accuracy declines due to the various sizes of obstacles, over bridges, multilane etc.
Deformations of Geometric Structures in Topological Sigma Models
Bytsenko, A. A.
2010-11-25
We study a Lie algebra of formal vector fields W{sub n} with it application to the perturbative deformed holomorphic symplectic structure in the A-model, and a Calabi-Yau manifold with boundaries in the B-model. We show that equivalent classes of deformations are described by a Hochschild cohomology of the DG-algebra A = (A,Q), Q = {partial_derivative}-bar+{partial_derivative}{sub deform,} which is defined to be the cohomology of (-1){sup n}Q+d{sub Hoch}. Here {partial_derivative}-bar is the initial non-deformed BRST operator while {partial_derivative}{sub deform} is the deformed part whose algebra is a Lie algebra of linear vector fields gl{sub n}.
Research on geometrical model and mechanism for metal deformation based on plastic flow
NASA Astrophysics Data System (ADS)
An, H. P.; Rui, Z. Y.; Li, X.
2015-12-01
Starting with general conditions of metal plastic deformation, it analyses the relation between the percentage spread and geometric parameters of a forming body with typical machining process are studied. A geometrical model of deforming metal is set up according to the characteristic of a flowing metal particle. Starting from experimental results, the effect of technological parameters and friction between workpiece and dies on plastic deformation of a material were studied and a slippage deformation model of mass points within the material was proposed. Finally, the computing methods for strain and deformation energy and temperature rise are derived from homogeneous deformation. The results can be used to select technical parameters and compute physical quantities such as strain, deformation energy, and temperature rise.
NASA Astrophysics Data System (ADS)
Philippon, Mélody; Le Carlier de Veslud, Christian; Gueydan, Frédéric; Brun, Jean-Pierre; Caumon, Guillaume
2015-09-01
Superposed to ductile syn-metamorphic deformations, post-foliation deformations affect metamorphic units during their exhumation. Understanding the role of such deformations in the structuration of metamorphic units is key for understanding the tectonic evolution of convergence zones. We characterize post-foliations deformations using 3D modelling which is a first-order tool to describe complex geological structures, but a challenging task where based only on surface data. We propose a modelling procedure that combines fast draft models (interpolation of orientation data), with more complex ones where the structural context is better understood (implicit modelling), allowing us to build a 3D geometrical model of Syros Island blueschists (Cyclades), based on field data. With our approach, the 3D model is able to capture the complex present-day geometry of the island, mainly controlled by the superposition of three types of post-metamorphic deformations affecting the original metamorphic pile: i) a top-to-South ramp-flat extensional system that dominates the overall island structure, ii) large-scale folding of the metamorphic units associated with ramp-flat extensional system, and iii) steeply-dipping normal faults trending dominantly NNW-SSE and EW. The 3D surfaces produced by this method match outcrop data, are geologically consistent, and provide reasonable estimates of geological structures in poorly constrained areas.
NASA Astrophysics Data System (ADS)
Azimi, Maryam
Radiation therapy has been used in the treatment of cancer tumors for several years and many cancer patients receive radiotherapy. It may be used as primary therapy or with a combination of surgery or other kinds of therapy such as chemotherapy, hormone therapy or some mixture of the three. The treatment objective is to destroy cancer cells or shrink the tumor by planning an adequate radiation dose to the desired target without damaging the normal tissues. By using the pre-treatment Computer Tomography (CT) images, most of the radiotherapy planning systems design the target and assume that the size of the tumor will not change throughout the treatment course, which takes 5 to 7 weeks. Based on this assumption, the total amount of radiation is planned and fractionated for the daily dose required to be delivered to the patient's body. However, this assumption is flawed because the patients receiving radiotherapy have marked changes in tumor geometry during the treatment period. Therefore, there is a critical need to understand the changes of the tumor shape and size over time during the course of radiotherapy in order to prevent significant effects of inaccuracy in the planning. In this research, a methodology is proposed in order to monitor and predict daily (fraction day) tumor volume and surface changes of head and neck cancer tumors during the entire treatment period. In the proposed method, geometrical modeling and data mining techniques will be used rather than repetitive CT scans data to predict the tumor deformation for radiation planning. Clinical patient data were obtained from the University of Texas-MD Anderson Cancer Center (MDACC). In the first step, by using CT scan data, the tumor's progressive geometric changes during the treatment period are quantified. The next step relates to using regression analysis in order to develop predictive models for tumor geometry based on the geometric analysis results and the patients' selected attributes (age, weight
Multiple-object geometric deformable model for segmentation of macular OCT
Carass, Aaron; Lang, Andrew; Hauser, Matthew; Calabresi, Peter A.; Ying, Howard S.; Prince, Jerry L.
2014-01-01
Optical coherence tomography (OCT) is the de facto standard imaging modality for ophthalmological assessment of retinal eye disease, and is of increasing importance in the study of neurological disorders. Quantification of the thicknesses of various retinal layers within the macular cube provides unique diagnostic insights for many diseases, but the capability for automatic segmentation and quantification remains quite limited. While manual segmentation has been used for many scientific studies, it is extremely time consuming and is subject to intra- and inter-rater variation. This paper presents a new computational domain, referred to as flat space, and a segmentation method for specific retinal layers in the macular cube using a recently developed deformable model approach for multiple objects. The framework maintains object relationships and topology while preventing overlaps and gaps. The algorithm segments eight retinal layers over the whole macular cube, where each boundary is defined with subvoxel precision. Evaluation of the method on single-eye OCT scans from 37 subjects, each with manual ground truth, shows improvement over a state-of-the-art method. PMID:24761289
The minimal geometric deformation approach extended
NASA Astrophysics Data System (ADS)
Casadio, R.; Ovalle, J.; da Rocha, Roldão
2015-11-01
The minimal geometric deformation approach was introduced in order to study the exterior spacetime around spherically symmetric self-gravitating systems, such as stars or similar astrophysical objects, in the Randall-Sundrum brane-world framework. A consistent extension of this approach is developed here, which contains modifications of both the time component and the radial component of a spherically symmetric metric. A modified Schwarzschild geometry is obtained as an example of its simplest application, and a new solution that is potentially useful to describe stars in the brane-world is also presented.
NASA Astrophysics Data System (ADS)
Derez, T.; Pennock, G.; Drury, M. R.; Sintubin, M.
2013-12-01
Although quartz is one of the most studied minerals in the Earth's crust when it comes to its rheology, the interpretation of intracrystalline deformation microstructures with respect to deformation conditions and mechanisms, remains highly contentious. Moreover, inconsistent use of terminology for both deformation microstructures and mechanisms makes a correct assessment of observations and interpretations in published material very difficult. With respect to low-temperature intracrystalline deformation microstructures in quartz, different conflicting genetic models have been proposed. Most probably, the lack of consensus means that there is no unique interpretation for these microstructures, primarily because their initiation and development depend on many ambient conditions. We extensively studied these intracrystalline deformation microstructures by means of optical microscopy, Hot-Cathodoluminescence, SEM-Cathodoluminescence and Electron Backscatter Diffraction Orientation Imaging, in vein quartz of the High-Ardenne slate belt (Belgium, France, Luxemburg, Germany), (de)formed in a low-temperature regime. Firstly, we propose a new, purely descriptive terminology for the low-temperature intracrystalline deformation microstructures in naturally deformed quartz: fine extinction bands (FEB), wide extinction bands (WEB) and strings. The strings can be further subdivided into blocky (BS), straight (SS) and recrystallised (RS) morphological types. FEBs have consistently been called deformation lamellae in quartz and planar slip bands in metals. WEBs have been called deformation bands, prismatic kink bands or type II kink bands. Strings have formerly been called shear bands, deformation bands or type I kink bands. No distinction between blocky and straight morphological string types had ever been made. Secondly, a survey of the pre-recrystallisation stages in the history of the intracrystalline deformation microstructures reveals that the different types of low
Descriptive Geometry and Geometric Modeling.
ERIC Educational Resources Information Center
Adams, J. Alan
1988-01-01
Describes experiences for engineering students to develop spatial awareness and reasoning capability. Describes geometric modeling, basic geometric concepts, operations, surface modeling, and conclusions. (YP)
The effect of electron beam geometric deformation errors on the small-signal characteristic of ECRM
NASA Astrophysics Data System (ADS)
Yongjian, Yu
1993-08-01
In this paper is studied the effect of electron beam geometric deformation errors on the small — signal characteristics of the TE{mn/o} mode Electron Cyclotron Resonance Maser (ECRM), based on the elliptically cross—sectional e—beam deformation model. As an example, the effect of small geometric deformation errors on the TE{01/o} mode fundamental ECRM coupling coefficient is quantitatively shown.
Pragmatic geometric model evaluation
NASA Astrophysics Data System (ADS)
Pamer, Robert
2015-04-01
Quantification of subsurface model reliability is mathematically and technically demanding as there are many different sources of uncertainty and some of the factors can be assessed merely in a subjective way. For many practical applications in industry or risk assessment (e. g. geothermal drilling) a quantitative estimation of possible geometric variations in depth unit is preferred over relative numbers because of cost calculations for different scenarios. The talk gives an overview of several factors that affect the geometry of structural subsurface models that are based upon typical geological survey organization (GSO) data like geological maps, borehole data and conceptually driven construction of subsurface elements (e. g. fault network). Within the context of the trans-European project "GeoMol" uncertainty analysis has to be very pragmatic also because of different data rights, data policies and modelling software between the project partners. In a case study a two-step evaluation methodology for geometric subsurface model uncertainty is being developed. In a first step several models of the same volume of interest have been calculated by omitting successively more and more input data types (seismic constraints, fault network, outcrop data). The positions of the various horizon surfaces are then compared. The procedure is equivalent to comparing data of various levels of detail and therefore structural complexity. This gives a measure of the structural significance of each data set in space and as a consequence areas of geometric complexity are identified. These areas are usually very data sensitive hence geometric variability in between individual data points in these areas is higher than in areas of low structural complexity. Instead of calculating a multitude of different models by varying some input data or parameters as it is done by Monte-Carlo-simulations, the aim of the second step of the evaluation procedure (which is part of the ongoing work) is to
Iris-based medical analysis by geometric deformation features.
Ma, Lin; Zhang, D; Li, Naimin; Cai, Yan; Zuo, Wangmeng; Wang, Kuanguan
2013-01-01
Iris analysis studies the relationship between human health and changes in the anatomy of the iris. Apart from the fact that iris recognition focuses on modeling the overall structure of the iris, iris diagnosis emphasizes the detecting and analyzing of local variations in the characteristics of irises. This paper focuses on studying the geometrical structure changes in irises that are caused by gastrointestinal diseases, and on measuring the observable deformations in the geometrical structures of irises that are related to roundness, diameter and other geometric forms of the pupil and the collarette. Pupil and collarette based features are defined and extracted. A series of experiments are implemented on our experimental pathological iris database, including manual clustering of both normal and pathological iris images, manual classification by non-specialists, manual classification by individuals with a medical background, classification ability verification for the proposed features, and disease recognition by applying the proposed features. The results prove the effectiveness and clinical diagnostic significance of the proposed features and a reliable recognition performance for automatic disease diagnosis. Our research results offer a novel systematic perspective for iridology studies and promote the progress of both theoretical and practical work in iris diagnosis. PMID:23144041
Ye, Chuyang; Yang, Zhen; Ying, Sarah H.; Prince, Jerry L.
2016-01-01
The cerebellar peduncles, comprising the superior cerebellar peduncles (SCPs), the middle cerebellar peduncle (MCP), and the inferior cerebellar peduncles (ICPs), are white matter tracts that connect the cerebellum to other parts of the central nervous system. Methods for automatic segmentation and quantification of the cerebellar peduncles are needed for objectively and efficiently studying their structure and function. Diffusion tensor imaging (DTI) provides key information to support this goal, but it remains challenging because the tensors change dramatically in the decussation of the SCPs (dSCP), the region where the SCPs cross. This paper presents an automatic method for segmenting the cerebellar peduncles, including the dSCP. The method uses volumetric segmentation concepts based on extracted DTI features. The dSCP and noncrossing portions of the peduncles are modeled as separate objects, and are initially classified using a random forest classifier together with the DTI features. To obtain geometrically correct results, a multi-object geometric deformable model is used to refine the random forest classification. The method was evaluated using a leave-one-out cross-validation on five control subjects and four patients with spinocerebellar ataxia type 6 (SCA6). It was then used to evaluate group differences in the peduncles in a population of 32 controls and 11 SCA6 patients. In the SCA6 group, we have observed significant decreases in the volumes of the dSCP and the ICPs and significant increases in the mean diffusivity in the noncrossing SCPs, the MCP, and the ICPs. These results are consistent with a degeneration of the cerebellar peduncles in SCA6 patients. PMID:25749985
Extending the geometric deformation: New black hole solutions
NASA Astrophysics Data System (ADS)
Ovalle, Jorge
2016-03-01
By using the extension of the Minimal Geometric Deformation approach, recently developed to investigate the exterior spacetime of a self-gravitating system in the Braneworld, we identified a master solution for the deformation undergone by the radial metric component when time deformations are produced by bulk gravitons. A specific form for the temporal deformation is used to generate a new exterior solution with a tidal charge Q. The main feature of this solution is the presence of higher-order terms in the tidal charge, thus generalizing the well known tidally charged solution. The horizon of the black hole lies inside the Schwarzschild radius, h < rs = 2ℳ, indicating that extra-dimensional effects weaken the gravitational field.
Geometrical modelling of textile reinforcements
NASA Technical Reports Server (NTRS)
Pastore, Christopher M.; Birger, Alexander B.; Clyburn, Eugene
1995-01-01
The mechanical properties of textile composites are dictated by the arrangement of yarns contained with the material. Thus to develop a comprehensive understanding of the performance of these materials, it is necessary to develop a geometrical model of the fabric structure. This task is quite complex, as the fabric is made form highly flexible yarn systems which experience a certain degree of compressability. Furthermore there are tremendous forces acting on the fabric during densification typically resulting in yarn displacement and misorientation. The objective of this work is to develop a methodology for characterizing the geometry of yarns within a fabric structure including experimental techniques for evaluating these models. Furthermore, some applications of these geometric results to mechanical prediction models are demonstrated. Although more costly than its predecessors, the present analysis is based on the detailed architecture developed by one of the authors and his colleagues and accounts for many of the geometric complexities that other analyses ignore.
ERIC Educational Resources Information Center
Nika, G. Gerald; Parameswaran, R.
1997-01-01
Describes a visual approach for explaining the filling of electrons in the shells, subshells, and orbitals of the chemical elements. Enables students to apply the principles of atomic electron configuration while using manipulatives to model the building up of electron configurations as the atomic numbers of elements increase on the periodic…
Geometrical modelling of textile reinforcements
NASA Technical Reports Server (NTRS)
Pastore, Christopher M.; Birger, Alexander B.; Clyburn, Eugene
1995-01-01
The mechanical properties of textile composites are dictated by the arrangement of yarns contained within the material. Thus, to develop a comprehensive understanding of the performance of these materials, it is necessary to develop a geometrical model of the fabric structure. This task is quite complex, as the fabric is made from highly flexible yarn systems which experience a certain degree of compressibility. Furthermore there are tremendous forces acting on the fabric during densification typically resulting in yarn displacement and misorientation. The objective of this work is to develop a methodology for characterizing the geometry of yarns within a fabric structure including experimental techniques for evaluating these models. Furthermore, some applications of these geometric results to mechanical property predictions models are demonstrated.
Geometric Modelling of Octagonal Lamp Poles
NASA Astrophysics Data System (ADS)
Chan, T. O.; Lichti, D. D.
2014-06-01
Lamp poles are one of the most abundant highway and community components in modern cities. Their supporting parts are primarily tapered octagonal cones specifically designed for wind resistance. The geometry and the positions of the lamp poles are important information for various applications. For example, they are important to monitoring deformation of aged lamp poles, maintaining an efficient highway GIS system, and also facilitating possible feature-based calibration of mobile LiDAR systems. In this paper, we present a novel geometric model for octagonal lamp poles. The model consists of seven parameters in which a rotation about the z-axis is included, and points are constrained by the trigonometric property of 2D octagons after applying the rotations. For the geometric fitting of the lamp pole point cloud captured by a terrestrial LiDAR, accurate initial parameter values are essential. They can be estimated by first fitting the points to a circular cone model and this is followed by some basic point cloud processing techniques. The model was verified by fitting both simulated and real data. The real data includes several lamp pole point clouds captured by: (1) Faro Focus 3D and (2) Velodyne HDL-32E. The fitting results using the proposed model are promising, and up to 2.9 mm improvement in fitting accuracy was realized for the real lamp pole point clouds compared to using the conventional circular cone model. The overall result suggests that the proposed model is appropriate and rigorous.
NASA Technical Reports Server (NTRS)
Librescu, L.; Stein, M.
1990-01-01
The effects of initial geometrical imperfections on the postbuckling response of flat laminated composite panels to uniaxial and biaxial compressive loading are investigated analytically. The derivation of the mathematical model on the basis of first-order transverse shear deformation theory is outlined, and numerical results for perfect and imperfect, single-layer and three-layer square plates with free-free, clamped-clamped, or free-clamped edges are presented in graphs and briefly characterized. The present approach is shown to be more accurate than analyses based on the classical Kirchhoff plate model.
NASA Astrophysics Data System (ADS)
Pallozzi Lavorante, Luca; Dirk Ebert, Hans
2008-07-01
Tensor3D is a geometric modeling program with the capacity to simulate and visualize in real-time the deformation, specified through a tensor matrix and applied to triangulated models representing geological bodies. 3D visualization allows the study of deformational processes that are traditionally conducted in 2D, such as simple and pure shears. Besides geometric objects that are immediately available in the program window, the program can read other models from disk, thus being able to import objects created with different open-source or proprietary programs. A strain ellipsoid and a bounding box are simultaneously shown and instantly deformed with the main object. The principal axes of strain are visualized as well to provide graphical information about the orientation of the tensor's normal components. The deformed models can also be saved, retrieved later and deformed again, in order to study different steps of progressive strain, or to make this data available to other programs. The shape of stress ellipsoids and the corresponding Mohr circles defined by any stress tensor can also be represented. The application was written using the Visualization ToolKit, a powerful scientific visualization library in the public domain. This development choice, allied to the use of the Tcl/Tk programming language, which is independent on the host computational platform, makes the program a useful tool for the study of geometric deformations directly in three dimensions in teaching as well as research activities.
Compensation of geometrical deformations for watermark extraction in digital cinema application
NASA Astrophysics Data System (ADS)
Delannay, Damien; Delaigle, Jean-Francois; Macq, Benoit M. M.; Barlaud, Michel
2001-08-01
In this paper, we investigate the restoration of geometrically altered digital images with the aim of recovering an embedded watermark information. More precisely, we focus on the distorsion taking place by the camera acquisition of an image. Indeed, in the cinema industry, a large part of early movie piracy comes from copies made in the theater itself with a camera. The evolution towards digital cinema broadcast enables watermark based fingerprinting protection systems. The first step for fingerprint extraction of a counterfeit material is the compensation of the geometrical deformation inherent to the acquisition process. In order to compensate the deformations, we use a modified 12-parameters bilinear transformation model which closely matches the deformations taking place by an analog acquisition process. The estimation of the parameters can either be global, either vary across regions within the image. Our approach consist in the estimation of the displacement of a number of of pixels via a modified block-matching technique followed by a minimum mean square error optimization of the parameters on basis of those estimated displacement-vectors. The estimated transformation is applied to the candidate image to get a reconstruction as close as possible to the original image. Classical watermark extraction procedure can follow.
Phenomenological modeling of geometric metasurfaces.
Ye, Weimin; Guo, Qinghua; Xiang, Yuanjiang; Fan, Dianyuan; Zhang, Shuang
2016-04-01
Metasurfaces, with their superior capability in manipulating the optical wavefront at the subwavelength scale and low manufacturing complexity, have shown great potential for planar photonics and novel optical devices. However, vector field simulation of metasurfaces is so far limited to periodic-structured metasurfaces containing a small number of meta-atoms in the unit cell by using full-wave numerical methods. Here, focusing on achiral meta-atoms only with electric polarizability and thickness far less than the wavelength of light, and ignoring the coupling between meta-atoms, we propose a general phenomenological method to analytically model the metasurfaces based on the assumption that the meta-atoms possess localized resonances with Lorentz-Drude forms, whose exact form can be retrieved from the full wave simulation of a single element. Applied to phase modulated geometric metasurfaces constituted by identical meta-atoms with different orientations, our analytical results show good agreement with full-wave numerical simulations. The proposed theory provides an efficient method to model and design optical devices based on metasurfaces. PMID:27137005
Black strings from minimal geometric deformation in a variable tension brane-world
NASA Astrophysics Data System (ADS)
Casadio, R.; Ovalle, J.; da Rocha, Roldão
2014-02-01
We study brane-world models with variable brane tension and compute corrections to the horizon of a black string along the extra dimension. The four-dimensional geometry of the black string on the brane is obtained by means of the minimal geometric deformation approach, and the bulk corrections are then encoded in additional terms involving the covariant derivatives of the variable brane tension. Our investigation shows that the variable brane tension strongly affects the shape and evolution of the black string horizon along the extra dimension, at least in a near-brane expansion. In particular, we apply our general analysis to a model motivated by the Eötvös branes, where the variable brane tension is related to the Friedmann-Robertson-Walker brane-world cosmology. We show that for some stages in the evolution of the universe, the black string warped horizon collapses to a point and the black string has correspondingly finite extent along the extra dimension. Furthermore, we show that in the minimal geometric deformation of a black hole on the variable tension brane, the black string has a throat along the extra dimension, whose area tends to zero as time goes to infinity.
Kuprat, A.; George, D.
1998-12-01
When modeling deformation of geometrically complex regions, unstructured tetrahedral meshes provide the flexibility necessary to track interfaces as they change geometrically and topologically. In the class of time-dependent simulations considered in this paper, multimaterial interfaces are represented by sets of triangular facets, and motion of the interfaces is controlled by physical considerations. The motion of interior points in the conforming tetrahedral mesh (i.e., points not on interfaces) is arbitrary and may be chosen to produce good element shapes. In the context of specified boundary motion driven by physical considerations, they have found that a rather large glossary of mesh changes is required to allow the simulation to survive all the transitions of interface geometry and topology that occur during time evolution. This paper will describe mesh changes required to maintain good element quality as the geometry evolves, as well as mesh changes required to capture changes i n topology that occur when material regions collapse or pinch off. This paper will present a detailed description of mesh changes necessary for capturing the aforementioned geometrical and topological changes, as implemented in the code GRAIN3D, and will provide examples from a metallic grain growth simulation in which the normal velocity of the grain boundary is proportional to mean curvature.
Geometric effects in the electronic transport of deformed nanotubes
NASA Astrophysics Data System (ADS)
Santos, Fernando; Fumeron, Sébastien; Berche, Bertrand; Moraes, Fernando
2016-04-01
Quasi-two-dimensional systems may exibit curvature, which adds three-dimensional influence to their internal properties. As shown by da Costa (1981 Phys. Rev. A 23 1982-7), charged particles moving on a curved surface experience a curvature-dependent potential which greatly influence their dynamics. In this paper, we study the electronic ballistic transport in deformed nanotubes. The one-electron Schrödinger equation with open boundary conditions is solved numerically with a flexible MAPLE code made available as supplementary data. We find that the curvature of the deformations indeed has strong effects on the electron dynamics, suggesting its use in the design of nanotube-based electronic devices.
Geometric effects in the electronic transport of deformed nanotubes.
Santos, Fernando; Fumeron, Sébastien; Berche, Bertrand; Moraes, Fernando
2016-04-01
Quasi-two-dimensional systems may exibit curvature, which adds three-dimensional influence to their internal properties. As shown by da Costa (1981 Phys. Rev. A 23 1982-7), charged particles moving on a curved surface experience a curvature-dependent potential which greatly influence their dynamics. In this paper, we study the electronic ballistic transport in deformed nanotubes. The one-electron Schrödinger equation with open boundary conditions is solved numerically with a flexible MAPLE code made available as supplementary data. We find that the curvature of the deformations indeed has strong effects on the electron dynamics, suggesting its use in the design of nanotube-based electronic devices. PMID:26900666
Geometrical analysis of deformation band lozenges and their scaling relationships to fault lenses
NASA Astrophysics Data System (ADS)
Awdal, Abdullah; Healy, David; Alsop, G. Ian
2014-09-01
Deformation bands can influence fluid flow in sandstone hydrocarbon reservoirs and therefore, understanding the geometrical attributes of individual bands and their patterns is a critical step in quantifying their connectivity. We present a geometrical study of deformation band lozenges, which are rock volumes contained between deformation bands, and fault lenses, which are rock volumes bounded by slip surfaces in fault cores. We investigate the statistical trends among data sets for deformation band lozenges and fault lenses in sandstones from the Moray Firth (Scotland) and southeastern Utah (USA), and explore their potential correlation to other attributes of the fracture pattern and petrophysical properties. The aspect ratio of lozenges, that represents the ratio of length or height to the maximum thickness of a lozenge, displays an oblate-shaped geometry in relation to fault-zone orientation. The length-thickness scaling relationships of lozenges are statistically similar to lenses. The scaling relationships show a slope break between lozenges bounded by deformation bands and lenses bounded by slip surfaces in the fault core. This break is inferred to mark the boundary between the lozenge domain and lens domain, and is likely due to a deformation transition from distributed strain for deformation bands to localised strain for slip surfaces. Furthermore, the integration of geometrical analysis with an understanding of scaling properties can help to make better predictions of fractures and fault properties in subsurface reservoirs.
NASA Astrophysics Data System (ADS)
Deng, Zhipeng; Lei, Lin; Zhou, Shilin
2015-10-01
Automatic image registration is a vital yet challenging task, particularly for non-rigid deformation images which are more complicated and common in remote sensing images, such as distorted UAV (unmanned aerial vehicle) images or scanning imaging images caused by flutter. Traditional non-rigid image registration methods are based on the correctly matched corresponding landmarks, which usually needs artificial markers. It is a rather challenging task to locate the accurate position of the points and get accurate homonymy point sets. In this paper, we proposed an automatic non-rigid image registration algorithm which mainly consists of three steps: To begin with, we introduce an automatic feature point extraction method based on non-linear scale space and uniform distribution strategy to extract the points which are uniform distributed along the edge of the image. Next, we propose a hybrid point matching algorithm using DaLI (Deformation and Light Invariant) descriptor and local affine invariant geometric constraint based on triangulation which is constructed by K-nearest neighbor algorithm. Based on the accurate homonymy point sets, the two images are registrated by the model of TPS (Thin Plate Spline). Our method is demonstrated by three deliberately designed experiments. The first two experiments are designed to evaluate the distribution of point set and the correctly matching rate on synthetic data and real data respectively. The last experiment is designed on the non-rigid deformation remote sensing images and the three experimental results demonstrate the accuracy, robustness, and efficiency of the proposed algorithm compared with other traditional methods.
Geometric interpretation of Planck-scale-deformed co-products
NASA Astrophysics Data System (ADS)
Lobo, Iarley P.; Palmisano, Giovanni
2016-03-01
For theories formulated with a maximally symmetric momentum space we propose a general characterization for the description of interactions in terms of the isometry group of the momentum space. The well known cases of κ-Poincaré-inspired and (2+1)-dimensional gravity-inspired composition laws both satisfy our condition. Future applications might include the proposal of a class of models based on momenta spaces with anti-de Sitter geometry.
Uncertainty estimation in reconstructed deformable models
Hanson, K.M.; Cunningham, G.S.; McKee, R.
1996-12-31
One of the hallmarks of the Bayesian approach to modeling is the posterior probability, which summarizes all uncertainties regarding the analysis. Using a Markov Chain Monte Carlo (MCMC) technique, it is possible to generate a sequence of objects that represent random samples drawn from the posterior distribution. We demonstrate this technique for reconstructions of two-dimensional objects from noisy projections taken from two directions. The reconstructed object is modeled in terms of a deformable geometrically-defined boundary with a constant interior density yielding a nonlinear reconstruction problem. We show how an MCMC sequence can be used to estimate uncertainties in the location of the edge of the reconstructed object.
Geometric Models for Collaborative Search and Filtering
ERIC Educational Resources Information Center
Bitton, Ephrat
2011-01-01
This dissertation explores the use of geometric and graphical models for a variety of information search and filtering applications. These models serve to provide an intuitive understanding of the problem domains and as well as computational efficiencies to our solution approaches. We begin by considering a search and rescue scenario where both…
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.
Geometric simplification of analysis models
Watterberg, P.A.
1999-12-01
Analysis programs have been having to deal with more and more complex objects as the capability to model fine detail increases. This can make them unacceptably slow. This project attempts to find heuristics for removing features from models in an automatic fashion in order to reduce polygon count. The approach is not one of theoretical completeness but rather one of trying to achieve useful results with scattered practical ideas. By removing a few simple things such as screw holes, slots, chambers, and fillets, large gains can be realized. Results varied but a reduction in the number of polygons by a factor of 10 is not unusual.
NASA Astrophysics Data System (ADS)
Dai, Xianglu; Xie, Huimin; Wang, Qinghua
2014-06-01
The geometric phase analysis (GPA), an important image-based deformation measurement method, has been used at both micro- and nano-scale. However, when a deformed image has apparent distortion, non-ignorable error in the obtained deformation field could occur by using this method. In this paper, the geometric phase analysis based on the windowed Fourier transform (WFT) is proposed to solve the above-mentioned issue, defined as the WFT-GPA method. In WFT-GPA, instead of the Fourier transform (FT), the WFT is utilized to extract the phase field block by block, and therefore more accurate local phase information can be acquired. The simulation tests, which include detailed discussion of influence factors for measurement accuracy such as window size and image noise, are conducted with digital deformed grids. The results verify that the WFT-GPA method not only keeps all advantages of traditional GPA method, but also owns a better accuracy for deformation measurement. Finally, the WFT-GPA method is applied to measure the machining distortion incurred in soft ultraviolet nanoimprint lithography (UV-NIL) process. The successful measurement shows the feasibility of this method and offers a full-field way for characterizing the replication quality of UV-NIL process.
Yang-Mills generalization of the geometrical collective model
NASA Astrophysics Data System (ADS)
Rosensteel, George; Sparks, Nick
2015-04-01
The geometrical or Bohr-Mottelson model is generalized and recast as a Yang-Mills theory. The gauge symmetry determines conservation of Kelvin circulation. The circulation commutes with the Hamiltonian when it is the sum of the kinetic energy and a potential that depends only on deformation. The conventional Bohr-Mottelson model is the special case of circulation zero, and wave functions are complex-valued. In the generalization, any quantized value of the circulation is allowed, and the wave functions are vector-valued. The Yang-Mills formulation introduces a new coupling between the geometrical and intrinsic degrees of freedom. The coupling appears in the covariant derivative term of the collective kinetic energy. This kind of coupling is sometimes called ``magnetic'' because of the analogy with electrodynamics.
Symmetries and deformations in the spherical shell model
NASA Astrophysics Data System (ADS)
Van Isacker, P.; Pittel, S.
2016-02-01
We discuss symmetries of the spherical shell model that make contact with the geometric collective model of Bohr and Mottelson. The most celebrated symmetry of this kind is SU(3), which is the basis of Elliott’s model of rotation. It corresponds to a deformed mean field induced by a quadrupole interaction in a single major oscillator shell N and can be generalized to include several major shells. As such, Elliott’s SU(3) model establishes the link between the spherical shell model and the (quadrupole component of the) geometric collective model. We introduce the analogue symmetry induced by an octupole interaction in two major oscillator shells N-1 and N, leading to an octupole-deformed solution of the spherical shell model. We show that in the limit of large oscillator shells, N\\to ∞ , the algebraic octupole interaction tends to that of the geometric collective model.
Brane-world stars from minimal geometric deformation, and black holes
NASA Astrophysics Data System (ADS)
Casadio, Roberto; Ovalle, Jorge
2014-02-01
Using the effective four-dimensional Einstein field equations, we build analytical models of spherically symmetric stars in the brane-world, in which the external space-time contains both an ADM mass and a tidal charge. In order to determine the interior geometry, we apply the principle of minimal geometric deformation, which allows one to map general relativistic solutions to solutions of the effective four-dimensional brane-world equations. We further restrict our analysis to stars with a radius linearly related to the total general relativistic mass, and obtain a general relation between the latter, the brane-world ADM mass and the tidal charge. In these models, the value of the star's radius can then be taken to zero smoothly, thus obtaining brane-world black hole metrics with a tidal charge solely determined by the mass of the source and the brane tension. We find configurations which entail a partial screening of the gravitational mass, and general conclusions regarding the minimum mass for semiclassical black holes are also drawn.
Classical tests of general relativity: Brane-world Sun from minimal geometric deformation
NASA Astrophysics Data System (ADS)
Casadio, R.; Ovalle, J.; da Rocha, Roldão
2015-05-01
We consider a solution of the effective four-dimensional brane-world equations, obtained from the general relativistic Schwarzschild metric via the principle of minimal geometric deformation, and investigate the corresponding signatures stemming from the possible existence of a warped extra-dimension. In particular, we derive bounds on an extra-dimensional parameter, closely related with the fundamental gravitational length, from the experimental results of the classical tests of general relativity in the Solar system.
Model-based vision using geometric hashing
NASA Astrophysics Data System (ADS)
Akerman, Alexander, III; Patton, Ronald
1991-04-01
The Geometric Hashing technique developed by the NYU Courant Institute has been applied to various automatic target recognition applications. In particular, I-MATH has extended the hashing algorithm to perform automatic target recognition ofsynthetic aperture radar (SAR) imagery. For this application, the hashing is performed upon the geometric locations of dominant scatterers. In addition to being a robust model-based matching algorithm -- invariant under translation, scale, and 3D rotations of the target -- hashing is of particular utility because it can still perform effective matching when the target is partially obscured. Moreover, hashing is very amenable to a SIMD parallel processing architecture, and thus potentially realtime implementable.
Modelling magnetically deformed neutron stars
NASA Astrophysics Data System (ADS)
Haskell, B.; Samuelsson, L.; Glampedakis, K.; Andersson, N.
2008-03-01
Rotating deformed neutron stars are important potential sources for ground-based gravitational wave interferometers such as LIGO, GEO600 and VIRGO. One mechanism that may lead to significant non-asymmetries is the internal magnetic field. It is well known that a magnetic star will not be spherical and, if the magnetic axis is not aligned with the spin axis, the deformation will lead to the emission of gravitational waves. The aim of this paper is to develop a formalism that would allow us to model magnetically deformed stars, using both realistic equations of state and field configurations. As a first step, we consider a set of simplified model problems. Focusing on dipolar fields, we determine the internal magnetic field which is consistent with a given neutron star model and calculate the associated deformation. We discuss the relevance of our results for current gravitational wave detectors and future prospects.
Geometric modeling for computer aided design
NASA Technical Reports Server (NTRS)
Schwing, James L.
1993-01-01
Over the past several years, it has been the primary goal of this grant to design and implement software to be used in the conceptual design of aerospace vehicles. The work carried out under this grant was performed jointly with members of the Vehicle Analysis Branch (VAB) of NASA LaRC, Computer Sciences Corp., and Vigyan Corp. This has resulted in the development of several packages and design studies. Primary among these are the interactive geometric modeling tool, the Solid Modeling Aerospace Research Tool (smart), and the integration and execution tools provided by the Environment for Application Software Integration and Execution (EASIE). In addition, it is the purpose of the personnel of this grant to provide consultation in the areas of structural design, algorithm development, and software development and implementation, particularly in the areas of computer aided design, geometric surface representation, and parallel algorithms.
Geometrical geodesy techniques in Goddard earth models
NASA Technical Reports Server (NTRS)
Lerch, F. J.
1974-01-01
The method for combining geometrical data with satellite dynamical and gravimetry data for the solution of geopotential and station location parameters is discussed. Geometrical tracking data (simultaneous events) from the global network of BC-4 stations are currently being processed in a solution that will greatly enhance of geodetic world system of stations. Previously the stations in Goddard earth models have been derived only from dynamical tracking data. A linear regression model is formulated from combining the data, based upon the statistical technique of weighted least squares. Reduced normal equations, independent of satellite and instrumental parameters, are derived for the solution of the geodetic parameters. Exterior standards for the evaluation of the solution and for the scale of the earth's figure are discussed.
Ground and Structure Deformation 3d Modelling with a Tin Based Property Model
NASA Astrophysics Data System (ADS)
TIAN, T.; Zhang, J.; Jiang, W.
2013-12-01
With the development of 3D( three-dimensional) modeling and visualization, more and more 3D tectonics are used to assist the daily work in Engineering Survey, in which the prediction of deformation field in strata and structure induced by underground construction is an essential part. In this research we developed a TIN (Triangulated Irregular Network) based property model for the 3D (three dimensional) visualization of ground deformation filed. By record deformation vector for each nodes, the new model can express the deformation with geometric-deformation-style by drawing each node in its new position and deformation-attribute-distribution-style by drawing each node in the color correspond with its deformation attribute at the same time. Comparing with the volume model based property model, this new property model can provide a more precise geometrical shape for structure objects. Furthermore, by recording only the deformation data of the user-interested 3d surface- such as the ground surface or the underground digging surface, the new property model can save a lot of space, which makes it possible to build the deformation filed model of a much more large scale. To construct the models of deformation filed based on TIN model, the refinement of the network is needed to increase the nodes number, which is necessary to express the deformation filed with a certain resolution. The TIN model refinement is a process of sampling the 3D deformation field values on points on the TIN surface, for which we developed a self-adapting TIN refinement method. By set the parameter of the attribute resolution, this self-adapting method refines the input geometric-expressing TIN model by adding more vertexes and triangles where the 3D deformation filed changing faster. Comparing with the even refinement method, the self-adapting method can generate a refined TIN model with nodes counted less by two thirds. Efficiency Comparison between Self-adapting Refinement Method and Even
Non-geometric fluxes, quasi-Hopf twist deformations, and nonassociative quantum mechanics
Mylonas, Dionysios Szabo, Richard J.; Schupp, Peter
2014-12-15
We analyse the symmetries underlying nonassociative deformations of geometry in non-geometric R-flux compactifications which arise via T-duality from closed strings with constant geometric fluxes. Starting from the non-abelian Lie algebra of translations and Bopp shifts in phase space, together with a suitable cochain twist, we construct the quasi-Hopf algebra of symmetries that deforms the algebra of functions and the exterior differential calculus in the phase space description of nonassociative R-space. In this setting, nonassociativity is characterised by the associator 3-cocycle which controls non-coassociativity of the quasi-Hopf algebra. We use abelian 2-cocycle twists to construct maps between the dynamical nonassociative star product and a family of associative star products parametrized by constant momentum surfaces in phase space. We define a suitable integration on these nonassociative spaces and find that the usual cyclicity of associative noncommutative deformations is replaced by weaker notions of 2-cyclicity and 3-cyclicity. Using this star product quantization on phase space together with 3-cyclicity, we formulate a consistent version of nonassociative quantum mechanics, in which we calculate the expectation values of area and volume operators, and find coarse-graining of the string background due to the R-flux.
Overview of geometrical room acoustic modeling techniques.
Savioja, Lauri; Svensson, U Peter
2015-08-01
Computerized room acoustics modeling has been practiced for almost 50 years up to date. These modeling techniques play an important role in room acoustic design nowadays, often including auralization, but can also help in the construction of virtual environments for such applications as computer games, cognitive research, and training. This overview describes the main principles, landmarks in the development, and state-of-the-art for techniques that are based on geometrical acoustics principles. A focus is given to their capabilities to model the different aspects of sound propagation: specular vs diffuse reflections, and diffraction. PMID:26328688
Validation of geometric models for fisheye lenses
NASA Astrophysics Data System (ADS)
Schneider, D.; Schwalbe, E.; Maas, H.-G.
The paper focuses on the photogrammetric investigation of geometric models for different types of optical fisheye constructions (equidistant, equisolid-angle, sterographic and orthographic projection). These models were implemented and thoroughly tested in a spatial resection and a self-calibrating bundle adjustment. For this purpose, fisheye images were taken with a Nikkor 8 mm fisheye lens on a Kodak DSC 14n Pro digital camera in a hemispherical calibration room. Both, the spatial resection and the bundle adjustment resulted in a standard deviation of unit weight of 1/10 pixel with a suitable set of simultaneous calibration parameters introduced into the camera model. The camera-lens combination was treated with all of the four basic models mentioned above. Using the same set of additional lens distortion parameters, the differences between the models can largely be compensated, delivering almost the same precision parameters. The relative object space precision obtained from the bundle adjustment was ca. 1:10 000 of the object dimensions. This value can be considered as a very satisfying result, as fisheye images generally have a lower geometric resolution as a consequence of their large field of view and also have a inferior imaging quality in comparison to most central perspective lenses.
NASA Astrophysics Data System (ADS)
Liao, Fei; Ye, Zhengyin
2015-12-01
Despite significant progress in recent computational techniques, the accurate numerical simulations, such as direct-numerical simulation and large-eddy simulation, are still challenging. For accurate calculations, the high-order finite difference method (FDM) is usually adopted with coordinate transformation from body-fitted grid to Cartesian grid. But this transformation might lead to failure in freestream preservation with the geometric conservation law (GCL) violated, particularly in high-order computations. GCL identities, including surface conservation law (SCL) and volume conservation law (VCL), are very important in discretization of high-order FDM. To satisfy GCL, various efforts have been made. An early and successful approach was developed by Thomas and Lombard [6] who used the conservative form of metrics to cancel out metric terms to further satisfy SCL. Visbal and Gaitonde [7] adopted this conservative form of metrics for SCL identities and satisfied VCL identity through invoking VCL equation to acquire the derivative of Jacobian in computation on moving and deforming grids with central compact schemes derived by Lele [5]. Later, using the metric technique from Visbal and Gaitonde [7], Nonomura et al. [8] investigated the freestream and vortex preservation properties of high-order WENO and WCNS on stationary curvilinear grids. A conservative metric method (CMM) was further developed by Deng et al. [9] with stationary grids, and detailed discussion about the innermost difference operator of CMM was shown with proof and corresponding numerical test cases. Noticing that metrics of CMM is asymmetrical without coordinate-invariant property, Deng et al. proposed a symmetrical CMM (SCMM) [12] by using the symmetric forms of metrics derived by Vinokur and Yee [10] to further eliminate asymmetric metric errors with stationary grids considered only. The research from Abe et al. [11] presented new asymmetric and symmetric conservative forms of time metrics and
Improved geometrical model of fringe projection profilometry.
Huang, Zhengrong; Xi, Jiangtao; Yu, Yanguang; Guo, Qinghua; Song, Limei
2014-12-29
The accuracy performance of fringe projection profilometry (FPP) depends on accurate phase-to-height (PTH) mapping and system calibration. The existing PTH mapping is derived based on the condition that the plane formed by axes of camera and projector is perpendicular to the reference plane, and measurement error occurs when the condition is not met. In this paper, a new geometric model for FPP is presented to lift the condition, resulting in a new PTH mapping relationship. The new model involves seven parameters, and a new system calibration method is proposed to determine their values. Experiments are conducted to verify the performance of the proposed technique, showing a noticeable improvement in the accuracy of 3D shape measurement. PMID:25607188
Geometric Model of a Coronal Cavity
NASA Technical Reports Server (NTRS)
Kucera, Therese A.; Gibson, S. E.; Ratawicki, D.; Dove, J.; deToma, G.; Hao, J.; Hudson, H. S.; Marque, C.; McIntosh, P. S.; Reeves, K. K.; Schmidt, D. J.; Sterling, A. C.; Tripathi, D. K.; Williams, D. R.; Zhang, M.
2010-01-01
We observed a coronal cavity from August 8-18 2007 during a multi-instrument observing campaign organized under the auspices of the International Heliophysical Year (IHY). Here we present initial efforts to model the cavity with a geometrical streamer-cavity model. The model is based the white-light streamer mode] of Gibson et a]. (2003 ), which has been enhanced by the addition of a cavity and the capability to model EUV and X-ray emission. The cavity is modeled with an elliptical cross-section and Gaussian fall-off in length and width inside the streamer. Density and temperature can be varied in the streamer and cavity and constrained via comparison with data. Although this model is purely morphological, it allows for three-dimensional, multi-temperature analysis and characterization of the data, which can then provide constraints for future physical modeling. Initial comparisons to STEREO/EUVI images of the cavity and streamer show that the model can provide a good fit to the data. This work is part of the effort of the International Space Science Institute International Team on Prominence Cavities
Deformation quantization of cosmological models
NASA Astrophysics Data System (ADS)
Cordero, Rubén; García-Compeán, Hugo; Turrubiates, Francisco J.
2011-06-01
The Weyl-Wigner-Groenewold-Moyal formalism of deformation quantization is applied to cosmological models in the minisuperspace. The quantization procedure is performed explicitly for quantum cosmology in a flat minisuperspace. The de Sitter cosmological model is worked out in detail and the computation of the Wigner functions for the Hartle-Hawking, Vilenkin and Linde wave functions are done numerically. The Wigner function is analytically calculated for the Kantowski-Sachs model in (non)commutative quantum cosmology and for string cosmology with dilaton exponential potential. Finally, baby universes solutions are described in this context and the Wigner function is obtained.
Geometrical basis for the Standard Model
Potter, F. )
1994-02-01
The robust character of the Standard Model is confirmed. Examination of its geometrical basis in three equivalent internal symmetry spaces - the unitary plane C[sup 2], the quaternion space Q, and the real space R[sup 4] - as well as the real space R[sup 3] uncovers mathematical properties that predict the physical properties of leptons and quarks. The finite rotational subgroups of the gauge group SU(2)[sub L] [times] U(1)[sub Y] generate exactly three lepton families and four quark families and reveal how quarks and leptons are related. Among the physical properties explained are the mass ratios of the six leptons and eight quarks, the origin of the left-handed preference by the weak interaction, the geometrical source of color symmetry, and the zero neutrino masses. The (u,d) and (c,s) quark families team together to satisfy the triangle anomaly cancellation with the electron family, while the other families pair one-to-one for cancellation. The spontaneously broken symmetry is discrete and needs no Higgs mechanism. Predictions include all massless neutrinos, the top quark at 160 GeV/c[sup 2], the b[prime] quark at 80 GeV/c[sup 2], and the t[prime] quark at 2600 GeV/c[sup 2].
Geometrical model of the Baltic artesian basin
NASA Astrophysics Data System (ADS)
Sennikovs, J.; Virbulis, J.; Bethers, U.
2012-04-01
Baltic artesian basin (BAB) is a multi-layer sedimentary basin spanning around 480'000 km2. BAB is located in the territory of Latvia, Lithuania and Estonia, parts of Poland, Russia, Belarus and large area of the Baltic Sea, including island of Gotland. The thickness of sedimentary cover is about 5000 m in the south-western part. Crystalline bedding reaches the surface in the northern and north-western parts. The aim of the present work is development of the model of geometric structure and three dimensional finite element mesh for the hydrogeological model of the whole BAB. The information that is used to build the geometrical structure includes: (1) Stratigraphic information from boreholes in Latvia and Estonia (2) Maps of height isolines of geological layers for Latvia and Lithuania (3) Maps of sub-quaternary deposits in Latvia and Lithuania (4) Maps of fault lines on the crystalline basement surface in Latvia, Lithuania and Estonia (5) Buried valley data from Latvia and Estonia (6) Earth topography data (7) Baltic sea depth data (8) Data from published geological cross-sections, information from books and other sources. Unification of the heterogeneous information from different sources, which are employed for building of the geometrical structure of the model are performed. Special algorithms are developed for this purpose considering the priority, importance and plausibility of each of the data sources. Pre-processing of the borehole information to screen out the outlying borehole data has been performed. Model of geological structure contains 42 layers. It includes aquifers and aquitards from Cambrian up to the Quaternary deposits. Fault displacements are incorporated into the model taking into account data from the published structural maps. Four reconstructed regional erosion surfaces (upper Ordovician, Devonian, Permian and Quaternary) are included into the model Three dimensional mesh of the geological structure is constructed layer-wise. The triangular
Nuclear deformability and telomere dynamics are regulated by cell geometric constraints
Makhija, Ekta; Jokhun, D. S.; Shivashankar, G. V.
2016-01-01
Forces generated by the cytoskeleton can be transmitted to the nucleus and chromatin via physical links on the nuclear envelope and the lamin meshwork. Although the role of these active forces in modulating prestressed nuclear morphology has been well studied, the effect on nuclear and chromatin dynamics remains to be explored. To understand the regulation of nuclear deformability by these active forces, we created different cytoskeletal states in mouse fibroblasts using micropatterned substrates. We observed that constrained and isotropic cells, which lack long actin stress fibers, have more deformable nuclei than elongated and polarized cells. This nuclear deformability altered in response to actin, myosin, formin perturbations, or a transcriptional down-regulation of lamin A/C levels in the constrained and isotropic geometry. Furthermore, to probe the effect of active cytoskeletal forces on chromatin dynamics, we tracked the spatiotemporal dynamics of heterochromatin foci and telomeres. We observed increased dynamics and decreased correlation of the heterochromatin foci and telomere trajectories in constrained and isotropic cell geometry. The observed enhanced dynamics upon treatment with actin depolymerizing reagents in elongated and polarized geometry were regained once the reagent was washed off, suggesting an inherent structural memory in chromatin organization. We conclude that active forces from the cytoskeleton and rigidity from lamin A/C nucleoskeleton can together regulate nuclear and chromatin dynamics. Because chromatin remodeling is a necessary step in transcription control and its memory, genome integrity, and cellular deformability during migration, our results highlight the importance of cell geometric constraints as critical regulators in cell behavior. PMID:26699462
NASA Astrophysics Data System (ADS)
Zhevlakov, A. P.; Zatsepina, M. E.; Kirillovskii, V. K.
2014-06-01
The principles of transformation of a Foucault shadowgram into a quantitative map of wave-front deformation based on creation of a system of isophotes are unveiled. The presented studies and their results prove that there is a high degree of correspondence between a Foucault shadowgram and the geometrical model of a shear interferogram with respect to displaying wave-front deformations.
Geometrically engineering the standard model: Locally unfolding three families out of E{sub 8}
Bourjaily, Jacob L.
2007-08-15
This paper extends and builds upon the results of [J. L. Bourjaily, arXiv:0704.0444.], in which we described how to use the tools of geometrical engineering to deform geometrically engineered grand unified models into ones with lower symmetry. This top-down unfolding has the advantage that the relative positions of singularities giving rise to the many 'low-energy' matter fields are related by only a few parameters which deform the geometry of the unified model. And because the relative positions of singularities are necessary to compute the superpotential, for example, this is a framework in which the arbitrariness of geometrically engineered models can be greatly reduced. In [J. L. Bourjaily, arXiv:0704.0444.], this picture was made concrete for the case of deforming the representations of an SU{sub 5} model into their standard model content. In this paper we continue that discussion to show how a geometrically engineered 16 of SO{sub 10} can be unfolded into the standard model, and how the three families of the standard model uniquely emerge from the unfolding of a single, isolated E{sub 8} singularity.
Geometric Modeling of Inclusions as Ellipsoids
NASA Technical Reports Server (NTRS)
Bonacuse, Peter J.
2008-01-01
Nonmetallic inclusions in gas turbine disk alloys can have a significant detrimental impact on fatigue life. Because large inclusions that lead to anomalously low lives occur infrequently, probabilistic approaches can be utilized to avoid the excessively conservative assumption of lifing to a large inclusion in a high stress location. A prerequisite to modeling the impact of inclusions on the fatigue life distribution is a characterization of the inclusion occurrence rate and size distribution. To help facilitate this process, a geometric simulation of the inclusions was devised. To make the simulation problem tractable, the irregularly sized and shaped inclusions were modeled as arbitrarily oriented, three independent dimensioned, ellipsoids. Random orientation of the ellipsoid is accomplished through a series of three orthogonal rotations of axes. In this report, a set of mathematical models for the following parameters are described: the intercepted area of a randomly sectioned ellipsoid, the dimensions and orientation of the intercepted ellipse, the area of a randomly oriented sectioned ellipse, the depth and width of a randomly oriented sectioned ellipse, and the projected area of a randomly oriented ellipsoid. These parameters are necessary to determine an inclusion s potential to develop a propagating fatigue crack. Without these mathematical models, computationally expensive search algorithms would be required to compute these parameters.
Deformable human body model development
Wray, W.O.; Aida, T.
1998-11-01
This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). A Deformable Human Body Model (DHBM) capable of simulating a wide variety of deformation interactions between man and his environment has been developed. The model was intended to have applications in automobile safety analysis, soldier survivability studies and assistive technology development for the disabled. To date, we have demonstrated the utility of the DHBM in automobile safety analysis and are currently engaged in discussions with the U.S. military involving two additional applications. More specifically, the DHBM has been incorporated into a Virtual Safety Lab (VSL) for automobile design under contract to General Motors Corporation. Furthermore, we have won $1.8M in funding from the U.S. Army Medical Research and Material Command for development of a noninvasive intracranial pressure measurement system. The proposed research makes use of the detailed head model that is a component of the DHBM; the project duration is three years. In addition, we have been contacted by the Air Force Armstrong Aerospace Medical Research Laboratory concerning possible use of the DHBM in analyzing the loads and injury potential to pilots upon ejection from military aircraft. Current discussions with Armstrong involve possible LANL participation in a comparison between DHBM and the Air Force Articulated Total Body (ATB) model that is the current military standard.
A non-geometrically similar model for predicting the wake field of full-scale ships
NASA Astrophysics Data System (ADS)
Guo, Chunyu; Zhang, Qi; Shen, Yu
2015-07-01
The scale effect leads to large discrepancies between the wake fields of model-scale and actual ships, and causes differences in cavitation performance and exciting forces tests in predicting the performance of actual ships. Therefore, when test data from ship models are directly applied to predict the performance of actual ships, test results must be subjected to empirical corrections. This study proposes a method for the reverse design of the hull model. Compared to a geometrically similar hull model, the wake field generated by the modified model is closer to that of an actual ship. A non- geometrically similar model of a Korean Research Institute of Ship and Ocean Engineering (KRISO)'s container ship (KCS) was designed. Numerical simulations were performed using this model, and its results were compared with full-scale calculation results. The deformation method of getting the wake field of full-scale ships by the non-geometrically similar model is applied to the KCS successfully.
A geometric model of defensive peripersonal space
Bufacchi, R. J.; Liang, M.; Griffin, L. D.
2015-01-01
Potentially harmful stimuli occurring within the defensive peripersonal space (DPPS), a protective area surrounding the body, elicit stronger defensive reactions. The spatial features of the DPPS are poorly defined and limited to descriptive estimates of its extent along a single dimension. Here we postulated a family of geometric models of the DPPS, to address two important questions with respect to its spatial features: What is its fine-grained topography? How does the nervous system represent the body area to be defended? As a measure of the DPPS, we used the strength of the defensive blink reflex elicited by electrical stimulation of the hand (hand-blink reflex, HBR), which is reliably modulated by the position of the stimulated hand in egocentric coordinates. We tested the goodness of fit of the postulated models to HBR data from six experiments in which we systematically explored the HBR modulation by hand position in both head-centered and body-centered coordinates. The best-fitting model indicated that 1) the nervous system's representation of the body area defended by the HBR can be approximated by a half-ellipsoid centered on the face and 2) the DPPS extending from this area has the shape of a bubble elongated along the vertical axis. Finally, the empirical observation that the HBR is modulated by hand position in head-centered coordinates indicates that the DPPS is anchored to the face. The modeling approach described in this article can be generalized to describe the spatial modulation of any defensive response. PMID:26510762
A geometric model of defensive peripersonal space.
Bufacchi, R J; Liang, M; Griffin, L D; Iannetti, G D
2016-01-01
Potentially harmful stimuli occurring within the defensive peripersonal space (DPPS), a protective area surrounding the body, elicit stronger defensive reactions. The spatial features of the DPPS are poorly defined and limited to descriptive estimates of its extent along a single dimension. Here we postulated a family of geometric models of the DPPS, to address two important questions with respect to its spatial features: What is its fine-grained topography? How does the nervous system represent the body area to be defended? As a measure of the DPPS, we used the strength of the defensive blink reflex elicited by electrical stimulation of the hand (hand-blink reflex, HBR), which is reliably modulated by the position of the stimulated hand in egocentric coordinates. We tested the goodness of fit of the postulated models to HBR data from six experiments in which we systematically explored the HBR modulation by hand position in both head-centered and body-centered coordinates. The best-fitting model indicated that 1) the nervous system's representation of the body area defended by the HBR can be approximated by a half-ellipsoid centered on the face and 2) the DPPS extending from this area has the shape of a bubble elongated along the vertical axis. Finally, the empirical observation that the HBR is modulated by hand position in head-centered coordinates indicates that the DPPS is anchored to the face. The modeling approach described in this article can be generalized to describe the spatial modulation of any defensive response. PMID:26510762
Geometric modeling for computer aided design
NASA Technical Reports Server (NTRS)
Schwing, James L.; Olariu, Stephen
1995-01-01
The primary goal of this grant has been the design and implementation of software to be used in the conceptual design of aerospace vehicles particularly focused on the elements of geometric design, graphical user interfaces, and the interaction of the multitude of software typically used in this engineering environment. This has resulted in the development of several analysis packages and design studies. These include two major software systems currently used in the conceptual level design of aerospace vehicles. These tools are SMART, the Solid Modeling Aerospace Research Tool, and EASIE, the Environment for Software Integration and Execution. Additional software tools were designed and implemented to address the needs of the engineer working in the conceptual design environment. SMART provides conceptual designers with a rapid prototyping capability and several engineering analysis capabilities. In addition, SMART has a carefully engineered user interface that makes it easy to learn and use. Finally, a number of specialty characteristics have been built into SMART which allow it to be used efficiently as a front end geometry processor for other analysis packages. EASIE provides a set of interactive utilities that simplify the task of building and executing computer aided design systems consisting of diverse, stand-alone, analysis codes. Resulting in a streamlining of the exchange of data between programs reducing errors and improving the efficiency. EASIE provides both a methodology and a collection of software tools to ease the task of coordinating engineering design and analysis codes.
NASA Astrophysics Data System (ADS)
Ottosson, W.; Lykkegaard Andersen, J. A.; Borrisova, S.; Mellemgaard, A.; Behrens, C. F.
2014-03-01
Respiration and anatomical variation during radiotherapy (RT) of lung cancer yield dosimetric uncertainties of the delivered dose, possibly affecting the clinical outcome if not corrected for. Adaptive radiotherapy (ART), based on deformable image registration (DIR) and Deep-Inspiration-Breath-Hold (DIBH) gating can potentially improve the accuracy of RT. Purpose: The objective was to investigate the performance of contour propagation on repeated CT and Cone Beam CT (CBCT) images in DIBH compared to images acquired in free breathing (FB), using a recently released DIR software. Method: Three locally advanced non-small cell lung cancer patients were included, each with a planning-, midterm- and final CT (pCT, mCT, fCT) and 7 CBCTs acquired weekly and on the same day as the mCT and fCT. All imaging were performed in both FB and DIBH, using Varian RPM system for respiratory tracking. Delineations of anatomical structures were performed on each image set. The CT images were retrospective rigidly and deformable registered to all obtained images using the Varian Smart Adapt v. 11.0. The registered images were analysed for volume change and Dice Similarity Coefficient (DSC). Result: Geometrical similarities were found between propagated and manually delineated structures, with a slightly favour of FB imaging. Special notice should be taken to registrations where image artefacts or low tissue contrast are present. Conclusion: This study does not support the hypothesis that DIBH images perform better image registration than FB images. However DIR is a feasible tool for ART of lung cancer.
Geometric deviation modeling by kinematic matrix based on Lagrangian coordinate
NASA Astrophysics Data System (ADS)
Liu, Weidong; Hu, Yueming; Liu, Yu; Dai, Wanyi
2015-09-01
Typical representation of dimension and geometric accuracy is limited to the self-representation of dimension and geometric deviation based on geometry variation thinking, yet the interactivity affection of geometric variation and gesture variation of multi-rigid body is not included. In this paper, a kinematic matrix model based on Lagrangian coordinate is introduced, with the purpose of unified model for geometric variation and gesture variation and their interactive and integrated analysis. Kinematic model with joint, local base and movable base is built. The ideal feature of functional geometry is treated as the base body; the fitting feature of functional geometry is treated as the adjacent movable body; the local base of the kinematic model is fixed onto the ideal geometry, and the movable base of the kinematic model is fixed onto the fitting geometry. Furthermore, the geometric deviation is treated as relative location or rotation variation between the movable base and the local base, and it's expressed by the Lagrangian coordinate. Moreover, kinematic matrix based on Lagrangian coordinate for different types of geometry tolerance zones is constructed, and total freedom for each kinematic model is discussed. Finally, the Lagrangian coordinate library, kinematic matrix library for geometric deviation modeling is illustrated, and an example of block and piston fits is introduced. Dimension and geometric tolerances of the shaft and hole fitting feature are constructed by kinematic matrix and Lagrangian coordinate, and the results indicate that the proposed kinematic matrix is capable and robust in dimension and geometric tolerances modeling.
Uncertainties in tomographic reconstructions based on deformable models
NASA Astrophysics Data System (ADS)
Hanson, Kenneth M.; Cunningham, Gregory S.; McKee, Robert J.
1997-04-01
Deformable geometric models fit very naturally into the context of Bayesian analysis. The prior probability of boundary shapes is taken to proportional to the negative exponential of the deformation energy used to control the boundary. This probabilistic interpretation is demonstrated using a Markov-Chain Monte-Carlo (MCMC) technique, which permits one to generate configurations that populate the prior. One of may uses for deformable models is to solve ill-posed tomographic reconstruction problems, which we demonstrate by reconstructing a two-dimensional object from two orthogonal noisy projections. We show how MCMC samples drawn from the posterior can be used to estimate uncertainties in the location of the edge of the reconstructed object.
Modal Substructuring of Geometrically Nonlinear Finite-Element Models
Kuether, Robert J.; Allen, Matthew S.; Hollkamp, Joseph J.
2016-02-01
The efficiency of a modal substructuring method depends on the component modes used to reduce each subcomponent model. Methods such as Craig–Bampton have been used extensively to reduce linear finite-element models with thousands or even millions of degrees of freedom down orders of magnitude while maintaining acceptable accuracy. A novel reduction method is proposed here for geometrically nonlinear finite-element models using the fixed-interface and constraint modes of the linearized system to reduce each subcomponent model. The geometric nonlinearity requires an additional cubic and quadratic polynomial function in the modal equations, and the nonlinear stiffness coefficients are determined by applying amore » series of static loads and using the finite-element code to compute the response. The geometrically nonlinear, reduced modal equations for each subcomponent are then coupled by satisfying compatibility and force equilibrium. This modal substructuring approach is an extension of the Craig–Bampton method and is readily applied to geometrically nonlinear models built directly within commercial finite-element packages. The efficiency of this new approach is demonstrated on two example problems: one that couples two geometrically nonlinear beams at a shared rotational degree of freedom, and another that couples an axial spring element to the axial degree of freedom of a geometrically nonlinear beam. The nonlinear normal modes of the assembled models are compared with those of a truth model to assess the accuracy of the novel modal substructuring approach.« less
Integration of geometric modeling and advanced finite element preprocessing
NASA Technical Reports Server (NTRS)
Shephard, Mark S.; Finnigan, Peter M.
1987-01-01
The structure to a geometry based finite element preprocessing system is presented. The key features of the system are the use of geometric operators to support all geometric calculations required for analysis model generation, and the use of a hierarchic boundary based data structure for the major data sets within the system. The approach presented can support the finite element modeling procedures used today as well as the fully automated procedures under development.
Analytical volcano deformation source models
Lisowski, Michael
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.
Sigma models for genuinely non-geometric backgrounds
NASA Astrophysics Data System (ADS)
Chatzistavrakidis, Athanasios; Jonke, Larisa; Lechtenfeld, Olaf
2015-11-01
The existence of genuinely non-geometric backgrounds, i.e. ones without geometric dual, is an important question in string theory. In this paper we examine this question from a sigma model perspective. First we construct a particular class of Courant algebroids as protobialgebroids with all types of geometric and non-geometric fluxes. For such structures we apply the mathematical result that any Courant algebroid gives rise to a 3D topological sigma model of the AKSZ type and we discuss the corresponding 2D field theories. It is found that these models are always geometric, even when both 2-form and 2-vector fields are neither vanishing nor inverse of one another. Taking a further step, we suggest an extended class of 3D sigma models, whose world volume is embedded in phase space, which allow for genuinely non-geometric backgrounds. Adopting the doubled formalism such models can be related to double field theory, albeit from a world sheet perspective.
3D geometric modelling of hand-woven textile
NASA Astrophysics Data System (ADS)
Shidanshidi, H.; Naghdy, F.; Naghdy, G.; Conroy, D. Wood
2008-02-01
Geometric modeling and haptic rendering of textile has attracted significant interest over the last decade. A haptic representation is created by adding the physical properties of an object to its geometric configuration. While research has been conducted into geometric modeling of fabric, current systems require time-consuming manual recognition of textile specifications and data entry. The development of a generic approach for construction of the 3D geometric model of a woven textile is pursued in this work. The geometric model would be superimposed by a haptic model in the future work. The focus at this stage is on hand-woven textile artifacts for display in museums. A fuzzy rule based algorithm is applied to the still images of the artifacts to generate the 3D model. The derived model is exported as a 3D VRML model of the textile for visual representation and haptic rendering. An overview of the approach is provided and the developed algorithm is described. The approach is validated by applying the algorithm to different textile samples and comparing the produced models with the actual structure and pattern of the samples.
Models of the Dynamic Deformations of Polymers
NASA Astrophysics Data System (ADS)
Merzhievsky, Lev; Voronin, Mihail; Korchagina, Anna
2013-06-01
In the process of deformation under the influence of external loading polymeric mediums show the complicated behavior connected with features of their structure. For amorphous polymers distinguish three physical conditions - glasslike, highlyelastic and viscoplastic. To each of the listed conditions there corresponds to mikro - meso- and macrostructural mechanisms of irreversible deformation. In the report the review of results of construction of models for the description of dynamic and shock-wave deformation of the polymers which are based on developed authors representations about mechanisms of irreversible deformation is made. Models include the formulation of the equations of conservation laws, considering effect of a relaxation of shear stresses in the process of deformation. For closing of models the equations of states with nonspherical tensor of deformations and relation for time of a relaxation of shear stresses are constructed. With using of the formulated models a number of problems of dynamic and shock wave deformations has been solved. The results are compared with corresponding experimental date. Development of the used approach are in summary discussed. To taking into account memory and fractal properties of real polymers is supposed of derivatives and integrals of a fractional order to use. Examples of constitutive equations with derivatives of a fractional order are presented. This work is supported by the Integration project of the Siberian Branch of the Russian Academy of Science 64 and grant RFBR 12-01-00726.
Multiscale geometric modeling of macromolecules II: Lagrangian representation
Feng, Xin; Xia, Kelin; Chen, Zhan; Tong, Yiying; Wei, Guo-Wei
2013-01-01
Geometric modeling of biomolecules plays an essential role in the conceptualization of biolmolecular structure, function, dynamics and transport. Qualitatively, geometric modeling offers a basis for molecular visualization, which is crucial for the understanding of molecular structure and interactions. Quantitatively, geometric modeling bridges the gap between molecular information, such as that from X-ray, NMR and cryo-EM, and theoretical/mathematical models, such as molecular dynamics, the Poisson-Boltzmann equation and the Nernst-Planck equation. In this work, we present a family of variational multiscale geometric models for macromolecular systems. Our models are able to combine multiresolution geometric modeling with multiscale electrostatic modeling in a unified variational framework. We discuss a suite of techniques for molecular surface generation, molecular surface meshing, molecular volumetric meshing, and the estimation of Hadwiger’s functionals. Emphasis is given to the multiresolution representations of biomolecules and the associated multiscale electrostatic analyses as well as multiresolution curvature characterizations. The resulting fine resolution representations of a biomolecular system enable the detailed analysis of solvent-solute interaction, and ion channel dynamics, while our coarse resolution representations highlight the compatibility of protein-ligand bindings and possibility of protein-protein interactions. PMID:23813599
Multiscale geometric modeling of macromolecules II: Lagrangian representation.
Feng, Xin; Xia, Kelin; Chen, Zhan; Tong, Yiying; Wei, Guo-Wei
2013-09-15
Geometric modeling of biomolecules plays an essential role in the conceptualization of biolmolecular structure, function, dynamics, and transport. Qualitatively, geometric modeling offers a basis for molecular visualization, which is crucial for the understanding of molecular structure and interactions. Quantitatively, geometric modeling bridges the gap between molecular information, such as that from X-ray, NMR, and cryo-electron microscopy, and theoretical/mathematical models, such as molecular dynamics, the Poisson-Boltzmann equation, and the Nernst-Planck equation. In this work, we present a family of variational multiscale geometric models for macromolecular systems. Our models are able to combine multiresolution geometric modeling with multiscale electrostatic modeling in a unified variational framework. We discuss a suite of techniques for molecular surface generation, molecular surface meshing, molecular volumetric meshing, and the estimation of Hadwiger's functionals. Emphasis is given to the multiresolution representations of biomolecules and the associated multiscale electrostatic analyses as well as multiresolution curvature characterizations. The resulting fine resolution representations of a biomolecular system enable the detailed analysis of solvent-solute interaction, and ion channel dynamics, whereas our coarse resolution representations highlight the compatibility of protein-ligand bindings and possibility of protein-protein interactions. PMID:23813599
Geometrical model for non-zero θ13
NASA Astrophysics Data System (ADS)
Chen, Jun-Mou; Wang, Bin; Li, Xue-Qian
2011-10-01
Based on Friedberg and Lee’s geometric picture by which the tribimaximal Pontecorvo-Maki-Nakawaga-Sakata leptonic mixing matrix is constructed, namely, corresponding mixing angles correspond to the geometric angles among the sides of a cube. We suggest that the three realistic mixing angles, which slightly deviate from the values determined for the cube, are due to a viable deformation from the perfectly cubic shape. Taking the best-fitted results of θ12 and θ23 as inputs, we determine the central value of sin22θ13 should be 0.0238, with a relatively large error tolerance; this value lies in the range of measurement precision of the Daya Bay experiment and is consistent with recent results from the T2K Collaboration.
Geometrical model for non-zero {theta}{sub 13}
Chen Junmou; Wang Bin; Li Xueqian
2011-10-01
Based on Friedberg and Lee's geometric picture by which the tribimaximal Pontecorvo-Maki-Nakawaga-Sakata leptonic mixing matrix is constructed, namely, corresponding mixing angles correspond to the geometric angles among the sides of a cube. We suggest that the three realistic mixing angles, which slightly deviate from the values determined for the cube, are due to a viable deformation from the perfectly cubic shape. Taking the best-fitted results of {theta}{sub 12} and {theta}{sub 23} as inputs, we determine the central value of sin{sup 2}2{theta}{sub 13} should be 0.0238, with a relatively large error tolerance; this value lies in the range of measurement precision of the Daya Bay experiment and is consistent with recent results from the T2K Collaboration.
MOEMS Modeling Using the Geometrical Matrix Toolbox
NASA Technical Reports Server (NTRS)
Wilson, William C.; Atkinson, Gary M.
2005-01-01
New technologies such as MicroOptoElectro-Mechanical Systems (MOEMS) require new modeling tools. These tools must simultaneously model the optical, electrical, and mechanical domains and the interactions between these domains. To facilitate rapid prototyping of these new technologies an optical toolbox has been developed for modeling MOEMS devices. The toolbox models are constructed using MATLAB's dynamical simulator, Simulink. Modeling toolboxes will allow users to focus their efforts on system design and analysis as opposed to developing component models. This toolbox was developed to facilitate rapid modeling and design of a MOEMS based laser ultrasonic receiver system.
Geometric modeling of subcellular structures, organelles, and multiprotein complexes
Feng, Xin; Xia, Kelin; Tong, Yiying; Wei, Guo-Wei
2013-01-01
SUMMARY Recently, the structure, function, stability, and dynamics of subcellular structures, organelles, and multi-protein complexes have emerged as a leading interest in structural biology. Geometric modeling not only provides visualizations of shapes for large biomolecular complexes but also fills the gap between structural information and theoretical modeling, and enables the understanding of function, stability, and dynamics. This paper introduces a suite of computational tools for volumetric data processing, information extraction, surface mesh rendering, geometric measurement, and curvature estimation of biomolecular complexes. Particular emphasis is given to the modeling of cryo-electron microscopy data. Lagrangian-triangle meshes are employed for the surface presentation. On the basis of this representation, algorithms are developed for surface area and surface-enclosed volume calculation, and curvature estimation. Methods for volumetric meshing have also been presented. Because the technological development in computer science and mathematics has led to multiple choices at each stage of the geometric modeling, we discuss the rationales in the design and selection of various algorithms. Analytical models are designed to test the computational accuracy and convergence of proposed algorithms. Finally, we select a set of six cryo-electron microscopy data representing typical subcellular complexes to demonstrate the efficacy of the proposed algorithms in handling biomolecular surfaces and explore their capability of geometric characterization of binding targets. This paper offers a comprehensive protocol for the geometric modeling of subcellular structures, organelles, and multiprotein complexes. PMID:23212797
NASA Technical Reports Server (NTRS)
Librescu, L.; Souza, M. A.
1993-01-01
The static post-buckling of simply-supported flat panels exposed to a stationary nonuniform temperature field and subjected to a system of subcritical in-plane compressive edge loads is investigated. The study is performed within a refined theory of composite laminated plates incorporating the effect of transverse shear and the geometric nonlinearities. The influence played by a number of effects, among them transverse shear deformation, initial geometric imperfections, the character of the in-plane boundary conditions and thickness ratio are studied and a series of conclusions are outlined. The influence played by the complete temperature field (i.e., the uniform through thickness and thickness-wise gradient) as compared to the one induced by only the uniform one, is discussed and the peculiarities of the resulting post-buckling behaviors are enlightened.
Decoherence of spin-deformed bosonic model
Dehdashti, Sh.; Mahdifar, A.; Bagheri Harouni, M.; Roknizadeh, R.
2013-07-15
The decoherence rate and some parameters affecting it are investigated for the generalized spin-boson model. We consider the spin-bosonic model when the bosonic environment is modeled by the deformed harmonic oscillators. We show that the state of the environment approaches a non-linear coherent state. Then, we obtain the decoherence rate of a two-level system which is in contact with a deformed bosonic environment which is either in thermal equilibrium or in the ground state. By using some recent realization of f-deformed oscillators, we show that some physical parameters strongly affect the decoherence rate of a two-level system. -- Highlights: •Decoherence of the generalized spin-boson model is considered. •In this model the environment consists of f-oscillators. •Via the interaction, the state of the environment approaches non-linear coherent states. •Effective parameters on decoherence are considered.
3-D Geometric Modeling for the 21st Century.
ERIC Educational Resources Information Center
Ault, Holly K.
1999-01-01
Describes new geometric computer models used in contemporary computer-aided design (CAD) software including wire frame, surface, solid, and parametric models. Reviews their use in engineering design and discusses the impact of these new technologies on the engineering design graphics curriculum. (Author/CCM)
Digital deformation model for fisheye image rectification.
Hou, Wenguang; Ding, Mingyue; Qin, Nannan; Lai, Xudong
2012-09-24
Fisheye lens can provide a wide view over 180°. It then has prominence advantages in three dimensional reconstruction and machine vision applications. However, the serious deformation in the image limits fisheye lens's usage. To overcome this obstacle, a new rectification method named DDM (Digital Deformation Model) is developed based on two dimensional perspective transformation. DDM is a type of digital grid representation of the deformation of each pixel on CCD chip which is built by interpolating the difference between the actual image coordinate and pseudo-ideal coordinate of each mark on a control panel. This method obtains the pseudo-ideal coordinate according to two dimensional perspective transformation by setting four mark's deformations on image. The main advantages are that this method does not rely on the optical principle of fisheye lens and has relatively less computation. In applications, equivalent pinhole images can be obtained after correcting fisheye lens images using DDM. PMID:23037373
Geometrical Scaling of Hall Thruster Particle Model
Taccogna, Francesco; Longo, Savino; Capitelli, Mario; Schneider, Ralf
2005-05-16
Non-Maxwellian behaviour and plasma-wall interaction are key processes in the physics of Hall thrusters. For this purpose, a 2D{l_brace}r,z{r_brace}-3V axisymmetric fully kinetic Particle-in-Cell/Monte Carlo Collision (PIC-MCC) model of the acceleration channel including the process of secondary electron emission (SEE) from the dielectric walls has been developed. In order to make the simulation possible with regard to the computational time, a reduction of the thruster dimension was done. This was derived from a new physics-based scaling law. This model has demonstrated its outstanding capability in improving the physics insight into the processes in Stationary Plasma Thruster (SPT) and in reproducing accurately well experimental data.
Model the Deformation and Failure of Solids
2001-10-19
EMU models the deformation and failure of solids based on a reformulated theory of continuum mechanics known as the Peridynamic model. This approach allows dynamic fracture and other failure mechanisms to be simulated with a minimum of mesh effeces and without a need for supplementary kinetic relations for crack growth. Penetration by a rigid projectile is also included in the code.
Modelling deformation and fracture in confectionery wafers
Mohammed, Idris K.; Charalambides, Maria N.; Williams, J. Gordon; Rasburn, John
2015-01-22
The aim of this research is to model the deformation and fracture behaviour of brittle wafers often used in chocolate confectionary products. Three point bending and compression experiments were performed on beam and circular disc samples respectively to determine the 'apparent' stress-strain curves in bending and compression. The deformation of the wafer for both these testing types was observed in-situ within an SEM. The wafer is modeled analytically and numerically as a composite material with a core which is more porous than the skins. X-ray tomography was used to generate a three dimensional volume of the wafer microstructure which was then meshed and used for quantitative analysis. A linear elastic material model, with a damage function and element deletion, was used and the XMT generated architecture was loaded in compression. The output from the FE simulations correlates closely to the load-deflection deformation observed experimentally.
Modelling deformation and fracture in confectionery wafers
NASA Astrophysics Data System (ADS)
Mohammed, Idris K.; Charalambides, Maria N.; Williams, J. Gordon; Rasburn, John
2015-01-01
The aim of this research is to model the deformation and fracture behaviour of brittle wafers often used in chocolate confectionary products. Three point bending and compression experiments were performed on beam and circular disc samples respectively to determine the 'apparent' stress-strain curves in bending and compression. The deformation of the wafer for both these testing types was observed in-situ within an SEM. The wafer is modeled analytically and numerically as a composite material with a core which is more porous than the skins. X-ray tomography was used to generate a three dimensional volume of the wafer microstructure which was then meshed and used for quantitative analysis. A linear elastic material model, with a damage function and element deletion, was used and the XMT generated architecture was loaded in compression. The output from the FE simulations correlates closely to the load-deflection deformation observed experimentally.
Geometric Modeling, Radiation Simulation, Rendering, Analysis Package
1995-01-17
RADIANCE is intended to aid lighting designers and architects by predicting the light levels and appearance of a space prior to construction. The package includes programs for modeling and translating scene geometry, luminaire data and material properties, all of which are needed as input to the simulation. The lighting simulation itself uses ray tracing techniques to compute radiance values (ie. the quantity of light passing through a specific point in a specific direction), which aremore » typically arranged to form a photographic quality image. The resulting image may be analyzed, displayed and manipulated within the package, and converted to other popular image file formats for export to other packages, facilitating the production of hard copy output.« less
Geometric modeling for computer aided design
NASA Technical Reports Server (NTRS)
Schwing, James L.
1992-01-01
The goal was the design and implementation of software to be used in the conceptual design of aerospace vehicles. Several packages and design studies were completed, including two software tools currently used in the conceptual level design of aerospace vehicles. These tools are the Solid Modeling Aerospace Research Tool (SMART) and the Environment for Software Integration and Execution (EASIE). SMART provides conceptual designers with a rapid prototyping capability and additionally provides initial mass property analysis. EASIE provides a set of interactive utilities that simplify the task of building and executing computer aided design systems consisting of diverse, stand alone analysis codes that result in the streamlining of the exchange of data between programs, reducing errors and improving efficiency.
Multiscale geometric modeling of macromolecules I: Cartesian representation
NASA Astrophysics Data System (ADS)
Xia, Kelin; Feng, Xin; Chen, Zhan; Tong, Yiying; Wei, Guo-Wei
2014-01-01
This paper focuses on the geometric modeling and computational algorithm development of biomolecular structures from two data sources: Protein Data Bank (PDB) and Electron Microscopy Data Bank (EMDB) in the Eulerian (or Cartesian) representation. Molecular surface (MS) contains non-smooth geometric singularities, such as cusps, tips and self-intersecting facets, which often lead to computational instabilities in molecular simulations, and violate the physical principle of surface free energy minimization. Variational multiscale surface definitions are proposed based on geometric flows and solvation analysis of biomolecular systems. Our approach leads to geometric and potential driven Laplace-Beltrami flows for biomolecular surface evolution and formation. The resulting surfaces are free of geometric singularities and minimize the total free energy of the biomolecular system. High order partial differential equation (PDE)-based nonlinear filters are employed for EMDB data processing. We show the efficacy of this approach in feature-preserving noise reduction. After the construction of protein multiresolution surfaces, we explore the analysis and characterization of surface morphology by using a variety of curvature definitions. Apart from the classical Gaussian curvature and mean curvature, maximum curvature, minimum curvature, shape index, and curvedness are also applied to macromolecular surface analysis for the first time. Our curvature analysis is uniquely coupled to the analysis of electrostatic surface potential, which is a by-product of our variational multiscale solvation models. As an expository investigation, we particularly emphasize the numerical algorithms and computational protocols for practical applications of the above multiscale geometric models. Such information may otherwise be scattered over the vast literature on this topic. Based on the curvature and electrostatic analysis from our multiresolution surfaces, we introduce a new concept, the
Multiscale geometric modeling of macromolecules I: Cartesian representation
Xia, Kelin; Feng, Xin; Chen, Zhan; Tong, Yiying; Wei, Guo-Wei
2014-01-15
This paper focuses on the geometric modeling and computational algorithm development of biomolecular structures from two data sources: Protein Data Bank (PDB) and Electron Microscopy Data Bank (EMDB) in the Eulerian (or Cartesian) representation. Molecular surface (MS) contains non-smooth geometric singularities, such as cusps, tips and self-intersecting facets, which often lead to computational instabilities in molecular simulations, and violate the physical principle of surface free energy minimization. Variational multiscale surface definitions are proposed based on geometric flows and solvation analysis of biomolecular systems. Our approach leads to geometric and potential driven Laplace–Beltrami flows for biomolecular surface evolution and formation. The resulting surfaces are free of geometric singularities and minimize the total free energy of the biomolecular system. High order partial differential equation (PDE)-based nonlinear filters are employed for EMDB data processing. We show the efficacy of this approach in feature-preserving noise reduction. After the construction of protein multiresolution surfaces, we explore the analysis and characterization of surface morphology by using a variety of curvature definitions. Apart from the classical Gaussian curvature and mean curvature, maximum curvature, minimum curvature, shape index, and curvedness are also applied to macromolecular surface analysis for the first time. Our curvature analysis is uniquely coupled to the analysis of electrostatic surface potential, which is a by-product of our variational multiscale solvation models. As an expository investigation, we particularly emphasize the numerical algorithms and computational protocols for practical applications of the above multiscale geometric models. Such information may otherwise be scattered over the vast literature on this topic. Based on the curvature and electrostatic analysis from our multiresolution surfaces, we introduce a new concept, the
Multiscale geometric modeling of macromolecules I: Cartesian representation
Xia, Kelin; Feng, Xin; Chen, Zhan; Tong, Yiying; Wei, Guo Wei
2013-01-01
This paper focuses on the geometric modeling and computational algorithm development of biomolecular structures from two data sources: Protein Data Bank (PDB) and Electron Microscopy Data Bank (EMDB) in the Eulerian (or Cartesian) representation. Molecular surface (MS) contains non-smooth geometric singularities, such as cusps, tips and self-intersecting facets, which often lead to computational instabilities in molecular simulations, and violate the physical principle of surface free energy minimization. Variational multiscale surface definitions are proposed based on geometric flows and solvation analysis of biomolecular systems. Our approach leads to geometric and potential driven Laplace-Beltrami flows for biomolecular surface evolution and formation. The resulting surfaces are free of geometric singularities and minimize the total free energy of the biomolecular system. High order partial differential equation (PDE)-based nonlinear filters are employed for EMDB data processing. We show the efficacy of this approach in feature-preserving noise reduction. After the construction of protein multiresolution surfaces, we explore the analysis and characterization of surface morphology by using a variety of curvature definitions. Apart from the classical Gaussian curvature and mean curvature, maximum curvature, minimum curvature, shape index, and curvedness are also applied to macromolecular surface analysis for the first time. Our curvature analysis is uniquely coupled to the analysis of electrostatic surface potential, which is a by-product of our variational multiscale solvation models. As an expository investigation, we particularly emphasize the numerical algorithms and computational protocols for practical applications of the above multiscale geometric models. Such information may otherwise be scattered over the vast literature on this topic. Based on the curvature and electrostatic analysis from our multiresolution surfaces, we introduce a new concept, the
Multiscale geometric modeling of macromolecules I: Cartesian representation.
Xia, Kelin; Feng, Xin; Chen, Zhan; Tong, Yiying; Wei, Guo Wei
2014-01-01
This paper focuses on the geometric modeling and computational algorithm development of biomolecular structures from two data sources: Protein Data Bank (PDB) and Electron Microscopy Data Bank (EMDB) in the Eulerian (or Cartesian) representation. Molecular surface (MS) contains non-smooth geometric singularities, such as cusps, tips and self-intersecting facets, which often lead to computational instabilities in molecular simulations, and violate the physical principle of surface free energy minimization. Variational multiscale surface definitions are proposed based on geometric flows and solvation analysis of biomolecular systems. Our approach leads to geometric and potential driven Laplace-Beltrami flows for biomolecular surface evolution and formation. The resulting surfaces are free of geometric singularities and minimize the total free energy of the biomolecular system. High order partial differential equation (PDE)-based nonlinear filters are employed for EMDB data processing. We show the efficacy of this approach in feature-preserving noise reduction. After the construction of protein multiresolution surfaces, we explore the analysis and characterization of surface morphology by using a variety of curvature definitions. Apart from the classical Gaussian curvature and mean curvature, maximum curvature, minimum curvature, shape index, and curvedness are also applied to macromolecular surface analysis for the first time. Our curvature analysis is uniquely coupled to the analysis of electrostatic surface potential, which is a by-product of our variational multiscale solvation models. As an expository investigation, we particularly emphasize the numerical algorithms and computational protocols for practical applications of the above multiscale geometric models. Such information may otherwise be scattered over the vast literature on this topic. Based on the curvature and electrostatic analysis from our multiresolution surfaces, we introduce a new concept, the
Geometric Aspects of Force Controllability for a Swimming Model
Khapalov, A. Y.
2008-02-15
We study controllability properties (swimming capabilities) of a mathematical model of an abstract object which 'swims' in the 2-D Stokes fluid. Our goal is to investigate how the geometric shape of this object affects the forces acting upon it. Such problems are of interest in biology and engineering applications dealing with propulsion systems in fluids.
Three dimensional geometric modeling of processing-tomatoes
Technology Transfer Automated Retrieval System (TEKTRAN)
Characterizing tomato geometries with different shapes and sizes would facilitate the design of tomato processing equipments and promote computer-based engineering simulations. This research sought to develop a three-dimensional geometric model that can describe the morphological attributes of proce...
From Prototypes to Caricatures: Geometrical Models for Concept Typicality
ERIC Educational Resources Information Center
Ameel, Eef; Storms, Gert
2006-01-01
In three studies, we investigated to what extent a geometrical representation in a psychological space succeeds in predicting typicality in animal, natural food and artifact concepts and whether contrast categories contribute to the prediction. In Study 1, we compared the predictive value of a family resemblance-based prototype model with a…
Geometric model from microscopic theory for nuclear absorption
NASA Technical Reports Server (NTRS)
John, Sarah; Townsend, Lawrence W.; Wilson, John W.; Tripathi, Ram K.
1993-01-01
A parameter-free geometric model for nuclear absorption is derived herein from microscopic theory. The expression for the absorption cross section in the eikonal approximation, taken in integral form, is separated into a geometric contribution that is described by an energy-dependent effective radius and two surface terms that cancel in an asymptotic series expansion. For collisions of light nuclei, an expression for the effective radius is derived from harmonic oscillator nuclear density functions. A direct extension to heavy nuclei with Woods-Saxon densities is made by identifying the equivalent half-density radius for the harmonic oscillator functions. Coulomb corrections are incorporated, and a simplified geometric form of the Bradt-Peters type is obtained. Results spanning the energy range from 1 MeV/nucleon to 1 GeV/nucleon are presented. Good agreement with experimental results is obtained.
Comparison and Analysis of Geometric Correction Models of Spaceborne SAR
Jiang, Weihao; Yu, Anxi; Dong, Zhen; Wang, Qingsong
2016-01-01
Following the development of synthetic aperture radar (SAR), SAR images have become increasingly common. Many researchers have conducted large studies on geolocation models, but little work has been conducted on the available models for the geometric correction of SAR images of different terrain. To address the terrain issue, four different models were compared and are described in this paper: a rigorous range-doppler (RD) model, a rational polynomial coefficients (RPC) model, a revised polynomial (PM) model and an elevation derivation (EDM) model. The results of comparisons of the geolocation capabilities of the models show that a proper model for a SAR image of a specific terrain can be determined. A solution table was obtained to recommend a suitable model for users. Three TerraSAR-X images, two ALOS-PALSAR images and one Envisat-ASAR image were used for the experiment, including flat terrain and mountain terrain SAR images as well as two large area images. Geolocation accuracies of the models for different terrain SAR images were computed and analyzed. The comparisons of the models show that the RD model was accurate but was the least efficient; therefore, it is not the ideal model for real-time implementations. The RPC model is sufficiently accurate and efficient for the geometric correction of SAR images of flat terrain, whose precision is below 0.001 pixels. The EDM model is suitable for the geolocation of SAR images of mountainous terrain, and its precision can reach 0.007 pixels. Although the PM model does not produce results as precise as the other models, its efficiency is excellent and its potential should not be underestimated. With respect to the geometric correction of SAR images over large areas, the EDM model has higher accuracy under one pixel, whereas the RPC model consumes one third of the time of the EDM model. PMID:27347973
Comparison and Analysis of Geometric Correction Models of Spaceborne SAR.
Jiang, Weihao; Yu, Anxi; Dong, Zhen; Wang, Qingsong
2016-01-01
Following the development of synthetic aperture radar (SAR), SAR images have become increasingly common. Many researchers have conducted large studies on geolocation models, but little work has been conducted on the available models for the geometric correction of SAR images of different terrain. To address the terrain issue, four different models were compared and are described in this paper: a rigorous range-doppler (RD) model, a rational polynomial coefficients (RPC) model, a revised polynomial (PM) model and an elevation derivation (EDM) model. The results of comparisons of the geolocation capabilities of the models show that a proper model for a SAR image of a specific terrain can be determined. A solution table was obtained to recommend a suitable model for users. Three TerraSAR-X images, two ALOS-PALSAR images and one Envisat-ASAR image were used for the experiment, including flat terrain and mountain terrain SAR images as well as two large area images. Geolocation accuracies of the models for different terrain SAR images were computed and analyzed. The comparisons of the models show that the RD model was accurate but was the least efficient; therefore, it is not the ideal model for real-time implementations. The RPC model is sufficiently accurate and efficient for the geometric correction of SAR images of flat terrain, whose precision is below 0.001 pixels. The EDM model is suitable for the geolocation of SAR images of mountainous terrain, and its precision can reach 0.007 pixels. Although the PM model does not produce results as precise as the other models, its efficiency is excellent and its potential should not be underestimated. With respect to the geometric correction of SAR images over large areas, the EDM model has higher accuracy under one pixel, whereas the RPC model consumes one third of the time of the EDM model. PMID:27347973
Mathematical modeling of deformation during hot rolling
Jin, D.; Stachowiak, R.G.; Samarasekera, I.V.; Brimacombe, J.K.
1994-12-31
The deformation that occurs in the roll bite during the hot rolling of steel, particularly the strain-rate and strain distribution, has been mathematically modeled using finite-element analysis. In this paper three different finite-element models are compared with one another and with industrial measurements. The first model is an Eulerian analysis based on the flow formulation method, while the second utilizes an Updated Lagrangian approach. The third model is based on a commercially available program DEFORM which also utilizes a Lagrangian reference frame. Model predictions of strain and strain-rate distribution, particularly near the surface of the slab, are strongly influenced by the treatment of friction at the boundary and the magnitude of the friction coefficient or shear factor. Roll forces predicted by the model have been compared with industrial rolling loads from a seven-stand hot-strip mill.
A Geometric Crescent Model for Black Hole Images
NASA Astrophysics Data System (ADS)
Kamruddin, Ayman Bin; Dexter, J.
2013-01-01
The Event Horizon Telescope (EHT), a global very long baseline interferometry array operating at millimeter wavelengths, is spatially resolving the immediate environment of black holes for the first time. The current observations of the Galactic center black hole, Sagittarius A* (Sgr A*), have been interpreted in terms of unmotivated geometric models (e.g., a symmetric Gaussian) or detailed calculations involving accretion onto a black hole. The latter are subject to large systematic uncertainties. Motivated by relativistic effects around black holes, we propose a geometric crescent model for black hole images. We show that this simple model provides an excellent statistical description of the existing EHT data of Sgr A*, superior to the Gaussian. It also closely matches physically predicted models, bridging accretion theory and observation. Based on our results, we make predictions for future observations for the accessibility of the black hole shadow, direct evidence for a black hole event horizon.
Geometric-optical Modeling of a Conifer Forest Canopy
NASA Technical Reports Server (NTRS)
Strahler, A. H. (Principal Investigator)
1985-01-01
The objective of this research is to explore how the geometry of trees in forest stands influences the reflectance of the forest as imaged from space. Most plant canopy modeling has viewed the canopy as an assemblage of plane-parallel layers on top of a soil surface. For these models, leaf angle distribution, leaf area index, and the angular transmittance and reflectance of leaves are the primary optical and geometric parameters. Such models are now sufficiently well developed to explain most of the variance in angular reflectance measurements observed from homogeneous plant canopies. However, forest canopies as imaged by airborne and spaceborne scanners exhibit considerable variance at quite a different scale. Brightness values vary strongly from one pixel to the next primarily as a function of the number of trees they contain. At this scale, the forest canopy is nonuniform and discontinuous. This research focuses on a discrete-element, geometric-optical view of the forest canopy.
Geometric and kinematic modelling of a human costal slice.
Minotti, P; Lexcellent, C
1991-01-01
More and more powerful calculation methods are being used in the modelization of the human thorax, and considering the progress made in the domain of numerical analysis, this modelization is naturally being oriented toward the utilization of finite element methods. However, thoracic models are usually based on extremely simple geometric hypotheses, due mostly to the lack of dependable experimental data. Hence, the exploitation of sophisticated software is far from optimal. This study is based on experimental observations which allow the capabilities of the current means of calculation to be exploited to a maximum. The objectives of the study are the geometric and kinematic representations of a typical costal slice. A precise topographical measurement, performed by a robot, allows description of the costal geometry. The exploitation of these measurements then allows the identification of the costo-vertebral articulation. PMID:2055910
Characterization and modeling of heterogeneous deformation in commercial purity titanium
Yang, Y; Wang, Leyun; Zambaldi, Dr C; Eisenlohr, P; Barabash, Rozaliya; Liu, W.; Stoudt, Dr M R; Crimp, Prof M A; Bieler, Prof T R
2011-01-01
Heterogeneous deformation, including local dislocation shear activity and lattice rotation, was analyzed in microstructure patches of polycrystalline commercial purity titanium specimens using three different experimental methods. The measurements were compared with crystal plasticity finite element (CPFE) simulations for the same region that incorporate a local phenomenological hardening constitutive model. The dislocation activity was measured using techniques associated with atomic force microscopy (AFM), confocal microscopy, three-dimensional-X-ray diffraction (3D-XRD), and nano-indentation. These measurements allow assessment and guidance for strategic improvement of the accuracy of CPFE model development. The CPFE model successfully predicted most types of active dislocation systems within grains at the correct magnitudes, but the simulation of spatial distribution of strain was not always similar to experimental observations. To obtain an accurate CPFE model, the critical resolved shear stresses for major deformation systems in -titanium were assessed using an optimization strategy with CPFE predictions of the measured pile-up topography surrounding axisymmetric nano-indentation. Only modest improvements were noted over the simulations done without such optimized parameters. This indicates that a major challenge for model development is to effectively predict conditions where slip transfer occurs, and where geometrically necessary dislocations (GND) accumulate.
Shekhar, Raj; Lei, Peng; Castro-Pareja, Carlos R.; Plishker, William L.; D'Souza, Warren D.
2007-07-15
Conventional radiotherapy is planned using free-breathing computed tomography (CT), ignoring the motion and deformation of the anatomy from respiration. New breath-hold-synchronized, gated, and four-dimensional (4D) CT acquisition strategies are enabling radiotherapy planning utilizing a set of CT scans belonging to different phases of the breathing cycle. Such 4D treatment planning relies on the availability of tumor and organ contours in all phases. The current practice of manual segmentation is impractical for 4D CT, because it is time consuming and tedious. A viable solution is registration-based segmentation, through which contours provided by an expert for a particular phase are propagated to all other phases while accounting for phase-to-phase motion and anatomical deformation. Deformable image registration is central to this task, and a free-form deformation-based nonrigid image registration algorithm will be presented. Compared with the original algorithm, this version uses novel, computationally simpler geometric constraints to preserve the topology of the dense control-point grid used to represent free-form deformation and prevent tissue fold-over. Using mean squared difference as an image similarity criterion, the inhale phase is registered to the exhale phase of lung CT scans of five patients and of characteristically low-contrast abdominal CT scans of four patients. In addition, using expert contours for the inhale phase, the corresponding contours were automatically generated for the exhale phase. The accuracy of the segmentation (and hence deformable image registration) was judged by comparing automatically segmented contours with expert contours traced directly in the exhale phase scan using three metrics: volume overlap index, root mean square distance, and Hausdorff distance. The accuracy of the segmentation (in terms of radial distance mismatch) was approximately 2 mm in the thorax and 3 mm in the abdomen, which compares favorably to the
A geometric crescent model for black hole images
NASA Astrophysics Data System (ADS)
Kamruddin, Ayman Bin; Dexter, Jason
2013-09-01
The Event Horizon Telescope (EHT), a global very long baseline interferometry array operating at millimetre wavelengths, is spatially resolving the immediate environments of black holes for the first time. The current observations of the Galactic centre black hole, Sagittarius A* (Sgr A*), and M87 have been interpreted in terms of either geometric models (e.g. a symmetric Gaussian) or detailed calculations of the appearance of black hole accretion flows. The former are not physically motivated, while the latter are subject to large systematic uncertainties. Motivated by the dominant relativistic effects of Doppler beaming and gravitational lensing in many calculations, we propose a geometric crescent model for black hole images. We show that this simple model provides an excellent statistical description of the existing EHT data of Sgr A* and M87, superior to other geometric models for Sgr A*. It also qualitatively matches physically predicted models, bridging accretion theory and observation. Based on our results, we make predictions for the detectability of the black hole shadow, a signature of strong gravity, in future observations.
Measurement of ship deformation based on ARX model
NASA Astrophysics Data System (ADS)
Ma, Xianglu; Qin, Shiqiao; Wang, Xingshu; Hu, Feng; Wu, Wei; Zheng, JiaXing
2016-01-01
Ship deformation is the main error source of partial reference. Such deformation can be estimated by laser gyro units and Kalman filter technology. For Kalman filter, deformation was divide into two parts, dynamic deformation, and static deformation. Traditionally, dynamic deformation is treated as AR2 model .In this paper, dynamic deformation is taken as a kind of ARX model. Based on actual data measured by Yuanwang-3 Space Survey Ship, simulation experiments are studied. Results show that the novel model can improve the measurement precision.
Workshop on the Integration of Finite Element Modeling with Geometric Modeling
NASA Technical Reports Server (NTRS)
Wozny, Michael J.
1987-01-01
The workshop on the Integration of Finite Element Modeling with Geometric Modeling was held on 12 May 1987. It was held to discuss the geometric modeling requirements of the finite element modeling process and to better understand the technical aspects of the integration of these two areas. The 11 papers are presented except for one for which only the abstract is given.
Liquid ropes: a geometrical model for thin viscous jet instabilities.
Brun, P-T; Audoly, Basile; Ribe, Neil M; Eaves, T S; Lister, John R
2015-05-01
Thin, viscous fluid threads falling onto a moving belt behave in a way reminiscent of a sewing machine, generating a rich variety of periodic stitchlike patterns including meanders, W patterns, alternating loops, and translated coiling. These patterns form to accommodate the difference between the belt speed and the terminal velocity at which the falling thread strikes the belt. Using direct numerical simulations, we show that inertia is not required to produce the aforementioned patterns. We introduce a quasistatic geometrical model which captures the patterns, consisting of three coupled ordinary differential equations for the radial deflection, the orientation, and the curvature of the path of the thread's contact point with the belt. The geometrical model reproduces well the observed patterns and the order in which they appear as a function of the belt speed. PMID:25978238
Liquid Ropes: A Geometrical Model for Thin Viscous Jet Instabilities
NASA Astrophysics Data System (ADS)
Brun, P.-T.; Audoly, Basile; Ribe, Neil M.; Eaves, T. S.; Lister, John R.
2015-05-01
Thin, viscous fluid threads falling onto a moving belt behave in a way reminiscent of a sewing machine, generating a rich variety of periodic stitchlike patterns including meanders, W patterns, alternating loops, and translated coiling. These patterns form to accommodate the difference between the belt speed and the terminal velocity at which the falling thread strikes the belt. Using direct numerical simulations, we show that inertia is not required to produce the aforementioned patterns. We introduce a quasistatic geometrical model which captures the patterns, consisting of three coupled ordinary differential equations for the radial deflection, the orientation, and the curvature of the path of the thread's contact point with the belt. The geometrical model reproduces well the observed patterns and the order in which they appear as a function of the belt speed.
A simulation model for analysing brain structure deformations
NASA Astrophysics Data System (ADS)
Di Bona, Sergio; Lutzemberger, Ludovico; Salvetti, Ovidio
2003-12-01
Recent developments of medical software applications—from the simulation to the planning of surgical operations—have revealed the need for modelling human tissues and organs, not only from a geometric point of view but also from a physical one, i.e. soft tissues, rigid body, viscoelasticity, etc. This has given rise to the term 'deformable objects', which refers to objects with a morphology, a physical and a mechanical behaviour of their own and that reflects their natural properties. In this paper, we propose a model, based upon physical laws, suitable for the realistic manipulation of geometric reconstructions of volumetric data taken from MR and CT scans. In particular, a physically based model of the brain is presented that is able to simulate the evolution of different nature pathological intra-cranial phenomena such as haemorrhages, neoplasm, haematoma, etc and to describe the consequences that are caused by their volume expansions and the influences they have on the anatomical and neuro-functional structures of the brain.
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.
Geometric assortative growth model for small-world networks.
Shang, Yilun
2014-01-01
It has been shown that both humanly constructed and natural networks are often characterized by small-world phenomenon and assortative mixing. In this paper, we propose a geometrically growing model for small-world networks. The model displays both tunable small-world phenomenon and tunable assortativity. We obtain analytical solutions of relevant topological properties such as order, size, degree distribution, degree correlation, clustering, transitivity, and diameter. It is also worth noting that the model can be viewed as a generalization for an iterative construction of Farey graphs. PMID:24578661
Assessment of a Model-Based Deformable Image Registration Approach for Radiation Therapy Planning
Kaus, Michael R. . E-mail: Michael.kaus@philips.com; Brock, Kristy K.; Pekar, Vladimir; Dawson, Laura A.; Nichol, Alan M.; Jaffray, David A.
2007-06-01
Purpose: The aim of this study is to develop a surface-based deformable image registration strategy and to assess the accuracy of the system for the integration of multimodality imaging, image-guided radiation therapy, and assessment of geometrical change during and after therapy. Methods and Materials: A surface-model-based deformable image registration system has been developed that enables quantitative description of geometrical change in multimodal images with high computational efficiency. Based on the deformation of organ surfaces, a volumetric deformation field is derived using different volumetric elasticity models as alternatives to finite-element modeling. Results: The accuracy of the system was assessed both visually and quantitatively by tracking naturally occurring landmarks (bronchial bifurcations in the lung, vessel bifurcations in the liver, implanted gold markers in the prostate). The maximum displacements for lung, liver and prostate were 5.3 cm, 3.2 cm, and 0.6 cm respectively. The largest registration error (direction, mean {+-} SD) for lung, liver and prostate were (inferior-superior, -0.21 {+-} 0.38 cm) (anterior-posterior, -0.09 {+-} 0.34 cm), and (left-right, 0.04 {+-} 0.38 cm) respectively, which was within the image resolution regardless of the deformation model. The computation time (2.7 GHz Intel Xeon) was on the order of seconds (e.g., 10 s for 2 prostate datasets), and deformed axial images could be viewed at interactive speed (less than 1 s for 512 x 512 voxels). Conclusions: Surface-based deformable image registration enables the quantification of geometrical change in normal tissue and tumor with acceptable accuracy and speed.
Geometrical measurement of cardiac wavelength in reaction-diffusion models
NASA Astrophysics Data System (ADS)
Dupraz, Marie; Jacquemet, Vincent
2014-09-01
The dynamics of reentrant arrhythmias often consists in multiple wavelets propagating throughout an excitable medium. An arrhythmia can be sustained only if these reentrant waves have a sufficiently short wavelength defined as the distance traveled by the excitation wave during its refractory period. In a uniform medium, wavelength may be estimated as the product of propagation velocity and refractory period (electrophysiological wavelength). In order to accurately measure wavelength in more general substrates relevant to atrial arrhythmias (heterogeneous and anisotropic), we developed a mathematical framework to define geometrical wavelength at each time instant based on the length of streamlines following the propagation velocity field within refractory regions. Two computational methods were implemented: a Lagrangian approach in which a set of streamlines were integrated, and an Eulerian approach in which wavelength was the solution of a partial differential equation. These methods were compared in 1D/2D tissues and in a model of the left atrium. An advantage of geometrical definition of wavelength is that the wavelength of a wavelet can be tracked over time with high temporal resolution and smaller temporal variability in an anisotropic and heterogeneous medium. The results showed that the average electrophysiological wavelength was consistent with geometrical measurements of wavelength. Wavelets were however often shorter than the electrophysiological wavelength due to interactions with boundaries and other wavelets. These tools may help to assess more accurately the relation between substrate properties and wavelet dynamics in computer models.
Geometrical measurement of cardiac wavelength in reaction-diffusion models.
Dupraz, Marie; Jacquemet, Vincent
2014-09-01
The dynamics of reentrant arrhythmias often consists in multiple wavelets propagating throughout an excitable medium. An arrhythmia can be sustained only if these reentrant waves have a sufficiently short wavelength defined as the distance traveled by the excitation wave during its refractory period. In a uniform medium, wavelength may be estimated as the product of propagation velocity and refractory period (electrophysiological wavelength). In order to accurately measure wavelength in more general substrates relevant to atrial arrhythmias (heterogeneous and anisotropic), we developed a mathematical framework to define geometrical wavelength at each time instant based on the length of streamlines following the propagation velocity field within refractory regions. Two computational methods were implemented: a Lagrangian approach in which a set of streamlines were integrated, and an Eulerian approach in which wavelength was the solution of a partial differential equation. These methods were compared in 1D/2D tissues and in a model of the left atrium. An advantage of geometrical definition of wavelength is that the wavelength of a wavelet can be tracked over time with high temporal resolution and smaller temporal variability in an anisotropic and heterogeneous medium. The results showed that the average electrophysiological wavelength was consistent with geometrical measurements of wavelength. Wavelets were however often shorter than the electrophysiological wavelength due to interactions with boundaries and other wavelets. These tools may help to assess more accurately the relation between substrate properties and wavelet dynamics in computer models. PMID:25273213
Multiple representation approach to geometric model construction from range data
NASA Astrophysics Data System (ADS)
Koivunen, Visa; Vezien, Jean-Marc; Bajcsy, Ruzena
1995-04-01
A method is presented for constructing geometric design data from noisy 3-D sensor measurements of physical parts. In early processing phase, RLTS regression filters stemming from robust estimation theory are used for separating the desired part of the signal in contaminated sensor data from undesired part. Strategies for producing a complete 3-D data set from partial views are studied. Surface triangulation, NURBS, and superellipsoids are employed in model construction to be able to represent efficiently polygonal shapes, free form surfaces and standard primitive solids. Multiple representations are used because there is no single representation that would be most appropriate in all situations. The size of the required control point mesh for spline description is estimated using a surface characterization process. Surfaces of arbitrary topology are modeled using triangulation and trimmed NURBS. A user given tolerance value is driving refinement of the obtained surface model. The resulting model description is a procedural CAD model which can convey structural information in addition to low level geometric primitives. The model is translated to IGES standard product data exchange format to enable data sharing with other processes in concurrent engineering environment. Preliminary results on view registration and integration using simulated data are shown. Examples of model construction using both real and simulated data are also given.
Adaptive deformable model for mouth boundary detection
NASA Astrophysics Data System (ADS)
Mirhosseini, Ali R.; Yan, Hong; Lam, Kin-Man
1998-03-01
A new generalized algorithm is proposed to automatically extract a mouth boundary model form human face images. Such an algorithm can contribute to human face recognition and lip-reading-assisted speech recognition systems, in particular, and multimodal human computer interaction system, in general. The new model is an iterative algorithm based on a hierarchical model adaptation scheme using deformable templates, as a generalization of some of the previous works. The role of prior knowledge is essential for perceptual organization in the algorithm. The prior knowledge about the mouth shape is used to define and initialize a primary deformable mode. Each primary boundary curve of a mouth is formed on three control points, including two mouth corners, whose locations are optimized using a primary energy functional. This energy functional essentially captures the knowledge of the mouth shape to perceptually organize image information. The primary model is finely tuned in the second stage of optimization algorithm using a generalized secondary energy functional. Basically each boundary curve is finely tuned using more control points. The primary model is replaced by an adapted model if there is an increase in the secondary energy functional. The results indicate that the new model adaptation technique satisfactorily generalizes the mouth boundary model extraction in an automated fashion.
NASA Astrophysics Data System (ADS)
Badami, Devavrat V.; Jahed, Zeinab; Seo, Brandon B.; Burek, Michael J.; Tsui, Ting Y.
2016-03-01
The effects of microstructure, sample dimensions, and cross-sectional geometry on the deformation characteristics of electroplated nanocrystalline copper sub-micron pillars are investigated. Nanocrystalline copper pillars were produced with four types of geometry—solid core, hollow, c-shaped, and x-shaped—with outer diameters of ~1000 or 220 nm and three different average grain sizes (between 5.1 and 49.3 nm). Flow stress results from uniaxial compression tests of 1000- and 220-nm-outer-diameter pillars, with average grain sizes in the range between ~32 and 50 nm, revealed there are no observable strength dependences with the pillar cross-sectional geometries. This suggests that they behave with bulk-like character: mechanical properties independent of size and sample geometry. All of the pillar specimens examined exhibit an increase in mechanical strength with reduction of grain sizes, but soften as the crystalline dimensions are smaller than 10 to 20 nm threshold limits. Interestingly, pillars with outer diameters of 220 nm are distinctively softer than the 1000-nm-diameter samples when their grain size is at and below this threshold limit. These results indicate a strength specimen size effect exists for such fine grain copper pillars.
NASA Astrophysics Data System (ADS)
Protaziuk, Elżbieta
2016-06-01
Satellite measurements become competitive in many tasks of engineering surveys, however, in many requiring applications possibilities to apply such solutions are still limited. The possibility to widely apply satellite technologies for displacements measurements is related with new challenges; the most important of them relate to increasing requirements concerning the accuracy, reliability and continuity of results of position determination. One of the solutions is a ground augmentation of satellite network, which intention is to improve precision of positioning, ensure comparable accuracy of coordinates and reduce precision fluctuations over time. The need for augmentation of GNSS is particularly significant in situations: where the visibility of satellites is poor because of terrain obstacles, when the determined position is not precise enough or a satellites constellation does not allow for reliable positioning. Ground based source/sources of satellite signal placed at a ground, called pseudosatellites, or pseudolites were intensively investigated during the last two decades and finally were developed into groundbased, time-synchronized transceivers, that can transmit and receive a proprietary positioning signal. The paper presents geometric aspects of the ground based augmentation of the satellite networks using various quality measures of positioning geometry, which depends on access to the constellation of satellites and the conditions of the observation environment. The issue of minimizing these measures is the key problem that allows to obtain the position with high accuracy. For this purpose, the use of an error ellipsoid is proposed and compared with an error ellipse. The paper also describes the results of preliminary accuracy analysis obtained at test area and a comparison of various measures of the quality of positioning geometry.
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.
Subjective surfaces: a geometric model for boundary completion
Sarti, Alessandro; Malladi, Ravi; Sethian, J.A.
2000-06-01
We present a geometric model and a computational method for segmentation of images with missing boundaries. In many situations, the human visual system fills in missing gaps in edges and boundaries, building and completing information that is not present. Boundary completion presents a considerable challenge in computer vision, since most algorithms attempt to exploit existing data. A large body of work concerns completion models, which postulate how to construct missing data; these models are often trained and specific to particular images. In this paper, we take the following, alternative perspective: we consider a reference point within an image as given, and then develop an algorithm which tries to build missing information on the basis of the given point of view and the available information as boundary data to the algorithm. Starting from this point of view, a surface is constructed. It is then evolved with the mean curvature flow in the metric induced by the image until a piecewise constant solution is reached. We test the computational model on modal completion, amodal completion, texture, photo and medical images. We extend the geometric model and the algorithm to 3D in order to extract shapes from low signal/noise ratio medical volumes. Results in 3D echocardiography and 3D fetal echography are presented.
Tracking of object deformations in color and depth video: deformation models and applications
NASA Astrophysics Data System (ADS)
Jordt, Andreas; Reinhold, Stefan; Koch, Reinhard
2015-05-01
The research on deformation tracking based on color image data has continuously gained a wide interest in the last 15 years. In addition, using depth sensors such as the Microsoft Kinect, allows to mitigate the ambiguity problems that arise when trying to solve the deformation tracking tasks on color images only, by adding depth information. However, the fusion of color and depth data is not straight forward, and the deformation tracking task is still ill-posed due to the lack of a general deformation model. The problem is usually circumvented by providing special deformation functions for the task at hand, e.g., skeleton-based for reconstructing people or triangle-based for tracking planar surfaces. In this article we summarize the Analysis by Synthesis (AbS) approach for deformation tracking in depth and color video and show some successful applications of specialized deformation functions. To overcome the issues with NURBS based deformation tracking we propose a new geodesic RBF-based deformation model, which can adapt to any surface topology and shape, while keeping the number of deformation parameters low. Example deformations for objects of different topologies are given, showing the versatility and efficiency of the proposed model.
Numerical treatment of a geometrically nonlinear planar Cosserat shell model
NASA Astrophysics Data System (ADS)
Sander, Oliver; Neff, Patrizio; Bîrsan, Mircea
2016-05-01
We present a new way to discretize a geometrically nonlinear elastic planar Cosserat shell. The kinematical model is similar to the general six-parameter resultant shell model with drilling rotations. The discretization uses geodesic finite elements (GFEs), which leads to an objective discrete model which naturally allows arbitrarily large rotations. GFEs of any approximation order can be constructed. The resulting algebraic problem is a minimization problem posed on a nonlinear finite-dimensional Riemannian manifold. We solve this problem using a Riemannian trust-region method, which is a generalization of Newton's method that converges globally without intermediate loading steps. We present the continuous model and the discretization, discuss the properties of the discrete model, and show several numerical examples, including wrinkling of thin elastic sheets in shear.
The geometrical optics approach to atmospheric propagation models
NASA Astrophysics Data System (ADS)
Doss-Hammel, Stephen M.
2003-04-01
An accurate model for the propagation of infrared and optical frequencies through the atmosphere is a requirement for a number of important communications and surveillance systems. These systems operate over long nearly-horizontal paths that are close to the land or sea surface. There can be strong heat and mass flux gradients near the surface which make accurate transmission predictions difficult. The development and utility of geometrical optics, or ray-trace, methods for the EOSTAR and IRWarp models will be addressed. Both models are driven by bulk meteorological models to provide the environmental fields that can subsequently be used to define the refractivity field. The ray-trace algorithm uses the refractivity field to generate a transfer map. The transfer map provides precise information concerning the number, location, and orientation of the images of a source point. One application of this information is the geometric gain, or the refractive propagation factor, which is an output consisting of a vertical signal intensity profile at a given range. A second application is a passive ranging capability for sub-refractive conditions. The ranging calculation uses the existence of an inferior mirage image to deduce the target range and height.
High-fidelity geometric modeling for biomedical applications
Yu, Zeyun; Holst, Michael J.; Andrew McCammon, J.
2008-07-01
We describe a combination of algorithms for high fidelity geometric modeling and mesh generation. Although our methods and implementations are application-neutral, our primary target application is multiscale biomedical models that range in scales across the molecular, cellular, and organ levels. Our software toolchain implementing these algorithms is general in the sense that it can take as input a molecule in PDB/PQR forms, a 3D scalar volume, or a user-defined triangular surface mesh that may have very low quality. The main goal of our work presented is to generate high quality and smooth surface triangulations from the aforementioned inputs, and to reduce the mesh sizes by mesh coarsening. Tetrahedral meshes are also generated for finite element analysis in biomedical applications. Experiments on a number of bio-structures are demonstrated, showing that our approach possesses several desirable properties: feature-preservation, local adaptivity, high quality, and smoothness (for surface meshes). The availability of this software toolchain will give researchers in computational biomedicine and other modeling areas access to higher-fidelity geometric models.
Geometric modeling of the temporal bone for cochlea implant simulation
NASA Astrophysics Data System (ADS)
Todd, Catherine A.; Naghdy, Fazel; O'Leary, Stephen
2004-05-01
The first stage in the development of a clinically valid surgical simulator for training otologic surgeons in performing cochlea implantation is presented. For this purpose, a geometric model of the temporal bone has been derived from a cadaver specimen using the biomedical image processing software package Analyze (AnalyzeDirect, Inc) and its three-dimensional reconstruction is examined. Simulator construction begins with registration and processing of a Computer Tomography (CT) medical image sequence. Important anatomical structures of the middle and inner ear are identified and segmented from each scan in a semi-automated threshold-based approach. Linear interpolation between image slices produces a three-dimensional volume dataset: the geometrical model. Artefacts are effectively eliminated using a semi-automatic seeded region-growing algorithm and unnecessary bony structures are removed. Once validated by an Ear, Nose and Throat (ENT) specialist, the model may be imported into the Reachin Application Programming Interface (API) (Reachin Technologies AB) for visual and haptic rendering associated with a virtual mastoidectomy. Interaction with the model is realized with haptics interfacing, providing the user with accurate torque and force feedback. Electrode array insertion into the cochlea will be introduced in the final stage of design.
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
A tumor growth model with deformable ECM
NASA Astrophysics Data System (ADS)
Sciumè, G.; Santagiuliana, R.; Ferrari, M.; Decuzzi, P.; Schrefler, B. A.
2014-12-01
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.
A geometric snake model for segmentation of medical imagery.
Yezzi, A; Kichenassamy, S; Kumar, A; Olver, P; Tannenbaum, A
1997-04-01
In this note, we employ the new geometric active contour models formulated in [25] and [26] for edge detection and segmentation of magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound medical imagery. Our method is based on defining feature-based metrics on a given image which in turn leads to a novel snake paradigm in which the feature of interest may be considered to lie at the bottom of a potential well. Thus, the snake is attracted very quickly and efficiently to the desired feature. PMID:9101329
Geometric modeling of inflatable structures for lunar base.
Nowak, P S; Sadeh, W Z; Morroni, L A
1992-07-01
A modular inflatable structure consisting of thin, composite membranes is presented for use in a lunar base. Results from a linear elastic analysis of the structure indicate that it is feasible in the lunar environment. Further analysis requires solving nonlinear equations and accurately specifying the geometries of the structural members. A computerized geometric modeling technique, using bicubic Bezier surfaces to generate the geometries of the inflatable structure, was conducted. Simulated results are used to create three-dimensional wire frames and solid renderings of the individual components of the inflatable structure. The component geometries are connected into modules, which are then assembled based upon the desired architecture of the structure. PMID:11537646
Mask roughness induced LER: geometric model at long correlation lengths
McClinton, Brittany M.; Naulleau, Patrick P.
2011-02-11
Collective understanding of how both the resist and line-edge roughness (LER) on the mask affect the final printed LER has made significant advances. What is poorly understood, however, is the extent to which mask surface roughness couples to image plane LER as a function of illumination conditions, NA, and defocus. Recently, progress has been made in formulating a simplified solution for mask roughness induced LER. Here, we investigate the LER behavior at long correlation lengths of surface roughness on the mask. We find that for correlation lengths greater than 3/NA in wafer dimensions and CDs greater than approximately 0.75/NA, the previously described simplified model, which remains based on physical optics, converges to a 'geometric regime' which is based on ray optics and is independent of partial coherence. In this 'geometric regime', the LER is proportional to the mask slope error as it propagates through focus, and provides a faster alternative to calculating LER in contrast to either full 2D aerial image simulation modeling or the newly proposed physical optics model. Data is presented for both an NA = 0.32 and an NA = 0.5 imaging system for CDs of 22-nm and 50-nm horizontal-line-dense structures.
Solar UV geometric conversion factors: horizontal plane to cylinder model.
Pope, Stanley J; Godar, Dianne E
2010-01-01
Most solar UV measurements are relative to the horizontal plane. However, problems arise when one uses those UV measurements to perform risk or benefit assessments because they do not yield the actual doses people get while they are outdoors. To better estimate the UV doses people actually get while outdoors, scientists need geometric conversion factors (GCF) that change horizontal plane irradiances to average irradiances on the human body. Here we describe a simple geometric method that changes unweighted, erythemally weighted and previtamin D(3)-weighted UV irradiances on the horizontal plane to full cylinder and semicylinder irradiances. Scientists can use the full cylinder model to represent the complete human body, while they can use the semicylinder model to represent the face, shoulders, tops of hands and feet. We present daily, monthly and seasonally calculated averages of the GCF for these cylinder models every 5 degrees from 20 to 70 degrees N so that scientists can now get realistic UV doses for people who are outdoors doing a variety of different activities. The GCF show that people actually get less than half their annual erythemally weighted, and consequently half their previtamin D(3)-weighted, UV doses relative to the horizontal plane. Thus, scientists can now perform realistic UV risk and benefit assessments. PMID:20059727
Recent progress in modelling 3D lithospheric deformation
NASA Astrophysics Data System (ADS)
Kaus, B. J. P.; Popov, A.; May, D. A.
2012-04-01
Modelling 3D lithospheric deformation remains a challenging task, predominantly because the variations in rock types, as well as nonlinearities due to for example plastic deformation result in sharp and very large jumps in effective viscosity contrast. As a result, there are only a limited number of 3D codes available, most of which are using direct solvers which are computationally and memory-wise very demanding. As a result, the resolutions for typical model runs are quite modest, despite the use of hundreds of processors (and using much larger computers is unlikely to bring much improvement in this situation). For this reason we recently developed a new 3D deformation code,called LaMEM: Lithosphere and Mantle Evolution Model. LaMEM is written on top of PETSc, and as a result it runs on massive parallel machines and we have a large number of iterative solvers available (including geometric and algebraic multigrid methods). As it remains unclear which solver combinations work best under which conditions, we have implemented most currently suggested methods (such as schur complement reduction or Fully coupled iterations). In addition, we can use either a finite element discretization (with Q1P0, stabilized Q1Q1 or Q2P-1 elements) or a staggered finite difference discretization for the same input geometry, which is based on a marker and cell technique). This gives us he flexibility to test various solver methodologies on the same model setup, in terms of accuracy, speed, memory usage etc. Here, we will report on some features of LaMEM, on recent code additions, as well as on some lessons we learned which are important for modelling 3D lithospheric deformation. Specifically we will discuss: 1) How we combine a particle-and-cell method to make it work with both a finite difference and a (lagrangian, eulerian or ALE) finite element formulation, with only minor code modifications code 2) How finite difference and finite element discretizations compare in terms of
Discrete element modelling of subglacial sediment deformation
NASA Astrophysics Data System (ADS)
Christensen, A. D.; Egholm, D. L.; Piotrowski, J. A.; Tulaczyk, S.
2012-04-01
Soft, deformable sediments are often present under glaciers. Subglacial sediments deform under the differential load of the ice, and this causes the overlying glacier to accelerate its motion. Understanding the rheology of subglacial sediment is therefore important for models of glacial dynamics. Previous studies of the mechanical behaviour of subglacial sediments have primarily relied on analytical considerations and laboratory shearing experiments. As a novel approach, the Discrete Element Method (DEM) is used to explore the highly nonlinear dynamics of a granular bed that is exposed to stress conditions comparable to subglacial environments. The numerical approach allows close monitoring of the mechanical and rheological behaviour under a range of conditions. Of special interest is bed shear strength, strain distribution and -localization, mode of deformation, and role of effective normal pressure during shearing. As a calibration benchmark, results from laboratory ring-shear experiments on granular material are compared to similar numerical experiments. The continuously recorded stress dynamics in the laboratory shear experiments are compared to DEM experiments, and the micro-mechanical parameters in the contact model of the DEM code are calibrated to match the macroscopic Mohr-Coulomb failure criteria parameters, constrained from successive laboratory shear tests under a range of normal pressures. The data-parallel nature of the basic DEM formulation makes the problem ideal for utilizing the high arithmetic potential of modern general-purpose GPUs. Using the Nvidia Cuda C toolkit, the algorithm is formulated for spherical particles in three dimensions with a soft-body contact model. Scene rendering is performed using a custom Cuda ray-tracing algorithm. Efforts on optimization of the particle algorithm are discussed, and future plans of expansion are presented.
A Geometrically Exact Model for Externally Loaded Concentric-Tube Continuum Robots.
Rucker, D Caleb; Jones, Bryan A; Webster, Robert J
2010-01-01
Continuum robots, which are composed of multiple concentric, precurved elastic tubes, can provide dexterity at diameters equivalent to standard surgical needles. Recent mechanics-based models of these "active cannulas" are able to accurately describe the curve of the robot in free space, given the preformed tube curves and the linear and angular positions of the tube bases. However, in practical applications, where the active cannula must interact with its environment or apply controlled forces, a model that accounts for deformation under external loading is required. In this paper, we apply geometrically exact rod theory to produce a forward kinematic model that accurately describes large deflections due to a general collection of externally applied point and/or distributed wrench loads. This model accommodates arbitrarily many tubes, with each having a general preshaped curve. It also describes the independent torsional deformation of the individual tubes. Experimental results are provided for both point and distributed loads. Average tip error under load was 2.91 mm (1.5%-3% of total robot length), which is similar to the accuracy of existing free-space models. PMID:21566688
Shen, Z; Greskovich, J; Xia, P; Bzdusek, K
2015-06-15
Purpose: To generate virtual phantoms with clinically relevant deformation and use them to objectively evaluate geometric and dosimetric uncertainties of deformable image registration (DIR) algorithms. Methods: Ten lung cancer patients undergoing adaptive 3DCRT planning were selected. For each patient, a pair of planning CT (pCT) and replanning CT (rCT) were used as the basis for virtual phantom generation. Manually adjusted meshes were created for selected ROIs (e.g. PTV, lungs, spinal cord, esophagus, and heart) on pCT and rCT. The mesh vertices were input into a thin-plate spline algorithm to generate a reference displacement vector field (DVF). The reference DVF was used to deform pCT to generate a simulated replanning CT (srCT) that was closely matched to rCT. Three DIR algorithms (Demons, B-Spline, and intensity-based) were applied to these ten virtual phantoms. The images, ROIs, and doses were mapped from pCT to srCT using the DVFs computed by these three DIRs and compared to those mapped using the reference DVF. Results: The average Dice coefficients for selected ROIs were from 0.85 to 0.96 for Demons, from 0.86 to 0.97 for intensity-based, and from 0.76 to 0.95 for B-Spline. The average Hausdorff distances for selected ROIs were from 2.2 to 5.4 mm for Demons, from 2.3 to 6.8 mm for intensity-based, and from 2.4 to 11.4 mm for B-Spline. The average absolute dose errors for selected ROIs were from 0.2 to 0.6 Gy for Demons, from 0.1 to 0.5 Gy for intensity-based, and from 0.5 to 1.5 Gy for B-Spline. Conclusion: Virtual phantoms were modeled after patients with lung cancer and were clinically relevant for adaptive radiotherapy treatment replanning. Virtual phantoms with known DVFs serve as references and can provide a fair comparison when evaluating different DIRs. Demons and intensity-based DIRs were shown to have smaller geometric and dosimetric uncertainties than B-Spline. Z Shen: None; K Bzdusek: an employee of Philips Healthcare; J Greskovich: None; P Xia
NASA Astrophysics Data System (ADS)
Dai, Xianglu; Xie, Huimin; Wang, Huaixi; Li, Chuanwei; Liu, Zhanwei; Wu, Lifu
2014-02-01
The geometric phase analysis (GPA) method based on the local high resolution discrete Fourier transform (LHR-DFT) for deformation measurement, defined as LHR-DFT GPA, is proposed to improve the measurement accuracy. In the general GPA method, the fundamental frequency of the image plays a crucial role. However, the fast Fourier transform, which is generally employed in the general GPA method, could make it difficult to locate the fundamental frequency accurately when the fundamental frequency is not located at an integer pixel position in the Fourier spectrum. This study focuses on this issue and presents a LHR-DFT algorithm that can locate the fundamental frequency with sub-pixel precision in a specific frequency region for the GPA method. An error analysis is offered and simulation is conducted to verify the effectiveness of the proposed method; both results show that the LHR-DFT algorithm can accurately locate the fundamental frequency and improve the measurement accuracy of the GPA method. Furthermore, typical tensile and bending tests are carried out and the experimental results verify the effectiveness of the proposed method.
NASA Astrophysics Data System (ADS)
Rafiee, M.; Liu, X. F.; He, X. Q.; Kitipornchai, S.
2014-07-01
The nonlinear free vibration of carbon nanotubes/fiber/polymer composite (CNTFPC) multi-scale plates with surface-bonded piezoelectric actuators is studied in this paper. The governing equations of the piezoelectric nanotubes/fiber/polymer multiscale laminated composite plates are derived based on first-order shear deformation plate theory (FSDT) and von Kármán geometrical nonlinearity. Halpin-Tsai equations and fiber micromechanics are used in hierarchy to predict the bulk material properties of the multiscale composite. The carbon nanotubes are assumed to be uniformly distributed and randomly oriented through the epoxy resin matrix. A perturbation scheme of multiple time scales is employed to determine the nonlinear vibration response and the nonlinear natural frequencies of the plates with immovable simply supported boundary conditions. The effects of the applied constant voltage, plate geometry, volume fraction of fibers and weight percentage of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) on the linear and nonlinear natural frequencies of the piezoelectric nanotubes/fiber/polymer multiscale composite plate are investigated through a detailed parametric study.
Modeling Connectionist Networks: Categorical, Geometric Aspects (Towards ``Homomorphic Learning'')
NASA Astrophysics Data System (ADS)
Pfalzgraf, Jochen
2004-08-01
Work in interdisciplinary fields is very interesting and always a great challenge. We present work on applications of mathematical methods to modeling problems arising in the area of artificial neural networks (ANN). We concentrate on modeling network structures that are motivated and based on knowledge about net structures coming from neurophysiology. In past years such insights have been exploited already in computer based ANN-simulations which are well suited for industrial applications. In the analysis of network structures, considering assemblies of cells (neurons) in biological nets, from a geometric point of view one can indentify and interpret, locally, what is called a geometric configuration. Following notions from algebraic topology, we are speaking about simplicial configurations (e.g. triangular, tetrahedral configurations, etc.). It turns out that category theory, geometry, algebra (group theory), graph theory (more general, net theory) come together, in a natural interdisciplinary way. Simplices are of basic importance.The interpretation of a learning step as a morphism in categorical terms suggests the opening of a systematic theory of learning (we call it "Homomorphic Learning").
Modelling Polymer Deformation during 3D Printing
NASA Astrophysics Data System (ADS)
McIlroy, Claire; Olmsted, Peter
Three-dimensional printing has the potential to transform manufacturing processes, yet improving the strength of printed parts, to equal that of traditionally-manufactured parts, remains an underlying issue. The fused deposition modelling technique involves melting a thermoplastic, followed by layer-by-layer extrusion to fabricate an object. The key to ensuring strength at the weld between layers is successful inter-diffusion. However, prior to welding, both the extrusion process and the cooling temperature profile can significantly deform the polymer micro-structure and, consequently, how well the polymers are able to ``re-entangle'' across the weld. In particular, polymer alignment in the flow can cause de-bonding of the layers and create defects. We have developed a simple model of the non-isothermal extrusion process to explore the effects that typical printing conditions and material rheology have on the conformation of a polymer melt. In particular, we incorporate both stretch and orientation using the Rolie-Poly constitutive equation to examine the melt structure as it flows through the nozzle, the subsequent alignment with the build plate and the resulting deformation due to the fixed nozzle height, which is typically less than the nozzle radius.
Estimation of radiative heat transfer using a geometric human model.
Kakuta, N; Yokoyama, S; Nakamura, M; Mabuchi, K
2001-03-01
In order to provide a detailed estimate of radiative heat transfer between a human body and its surrounding environment, we have developed a geometric model of a human form and an algorithm. The model closely resembles the actual shape of a human body and is composed of small quadrilateral surfaces. Dealing with an object or a space with an arbitrary shape, the developed algorithm can judge efficiently whether there is an obstruction between a pair of surfaces. As a result, the angle factors between a pair of surfaces that only occur during radiative heat transfer can be defined. The distribution of the radiative heat transfer rates shows the characteristics of body shape and variations in posture. PMID:11327500
Rule-based spatial modeling with diffusing, geometrically constrained molecules
2010-01-01
Background We suggest a new type of modeling approach for the coarse grained, particle-based spatial simulation of combinatorially complex chemical reaction systems. In our approach molecules possess a location in the reactor as well as an orientation and geometry, while the reactions are carried out according to a list of implicitly specified reaction rules. Because the reaction rules can contain patterns for molecules, a combinatorially complex or even infinitely sized reaction network can be defined. For our implementation (based on LAMMPS), we have chosen an already existing formalism (BioNetGen) for the implicit specification of the reaction network. This compatibility allows to import existing models easily, i.e., only additional geometry data files have to be provided. Results Our simulations show that the obtained dynamics can be fundamentally different from those simulations that use classical reaction-diffusion approaches like Partial Differential Equations or Gillespie-type spatial stochastic simulation. We show, for example, that the combination of combinatorial complexity and geometric effects leads to the emergence of complex self-assemblies and transportation phenomena happening faster than diffusion (using a model of molecular walkers on microtubules). When the mentioned classical simulation approaches are applied, these aspects of modeled systems cannot be observed without very special treatment. Further more, we show that the geometric information can even change the organizational structure of the reaction system. That is, a set of chemical species that can in principle form a stationary state in a Differential Equation formalism, is potentially unstable when geometry is considered, and vice versa. Conclusions We conclude that our approach provides a new general framework filling a gap in between approaches with no or rigid spatial representation like Partial Differential Equations and specialized coarse-grained spatial simulation systems like
Cox, P G; Fagan, M J; Rayfield, E J; Jeffery, N
2011-01-01
Rodents are defined by a uniquely specialized dentition and a highly complex arrangement of jaw-closing muscles. Finite element analysis (FEA) is an ideal technique to investigate the biomechanical implications of these specializations, but it is essential to understand fully the degree of influence of the different input parameters of the FE model to have confidence in the model's predictions. This study evaluates the sensitivity of FE models of rodent crania to elastic properties of the materials, loading direction, and the location and orientation of the models’ constraints. Three FE models were constructed of squirrel, guinea pig and rat skulls. Each was loaded to simulate biting on the incisors, and the first and the third molars, with the angle of the incisal bite varied over a range of 45°. The Young's moduli of the bone and teeth components were varied between limits defined by findings from our own and previously published tests of material properties. Geometric morphometrics (GMM) was used to analyse the resulting skull deformations. Bone stiffness was found to have the strongest influence on the results in all three rodents, followed by bite position, and then bite angle and muscle orientation. Tooth material properties were shown to have little effect on the deformation of the skull. The effect of bite position varied between species, with the mesiodistal position of the biting tooth being most important in squirrels and guinea pigs, whereas bilateral vs. unilateral biting had the greatest influence in rats. A GMM analysis of isolated incisor deformations showed that, for all rodents, bite angle is the most important parameter, followed by elastic properties of the tooth. The results here elucidate which input parameters are most important when defining the FE models, but also provide interesting glimpses of the biomechanical differences between the three skulls, which will be fully explored in future publications. PMID:21974720
Geometrical model for DBMS: an experimental DBMS using IBM solid modeling
Ali, D.E.D.L.
1985-01-01
This research presents a new model for data base management systems (DBMS). The new model, Geometrical DBMS, is based on using solid modelling technology in designing and implementing DBMS. The Geometrical DBMS is implemented using the IBM solid modelling Geometric Design Processor (GDP). Built basically on computer-graphics concepts, Geometrical DBMS is indeed a unique model. Traditionally, researchers start with one of the existent DBMS models and then put a graphical front end on it. In Geometrical DBMS, the graphical aspect of the model is not an alien concept tailored to the model but is, as a matter of fact, the atom around which the model is designed. The main idea in Geometrical DBMS is to allow the user and the system to refer to and manipulate data items as a solid object in 3D space, and representing a record as a group of logically related solid objects. In Geometical DBMS, hierarchical structure is used to present the data relations and the user sees the data as a group of arrays; yet, for the user and the system together, the data structure is a multidimensional tree.
Geometric algorithms for electromagnetic modeling of large scale structures
NASA Astrophysics Data System (ADS)
Pingenot, James
With the rapid increase in the speed and complexity of integrated circuit designs, 3D full wave and time domain simulation of chip, package, and board systems becomes more and more important for the engineering of modern designs. Much effort has been applied to the problem of electromagnetic (EM) simulation of such systems in recent years. Major advances in boundary element EM simulations have led to O(n log n) simulations using iterative methods and advanced Fast. Fourier Transform (FFT), Multi-Level Fast Multi-pole Methods (MLFMM), and low-rank matrix compression techniques. These advances have been augmented with an explosion of multi-core and distributed computing technologies, however, realization of the full scale of these capabilities has been hindered by cumbersome and inefficient geometric processing. Anecdotal evidence from industry suggests that users may spend around 80% of turn-around time manipulating the geometric model and mesh. This dissertation addresses this problem by developing fast and efficient data structures and algorithms for 3D modeling of chips, packages, and boards. The methods proposed here harness the regular, layered 2D nature of the models (often referred to as "2.5D") to optimize these systems for large geometries. First, an architecture is developed for efficient storage and manipulation of 2.5D models. The architecture gives special attention to native representation of structures across various input models and special issues particular to 3D modeling. The 2.5D structure is then used to optimize the mesh systems First, circuit/EM co-simulation techniques are extended to provide electrical connectivity between objects. This concept is used to connect independently meshed layers, allowing simple and efficient 2D mesh algorithms to be used in creating a 3D mesh. Here, adaptive meshing is used to ensure that the mesh accurately models the physical unknowns (current and charge). Utilizing the regularized nature of 2.5D objects and
Methods for Geometric Data Validation of 3d City Models
NASA Astrophysics Data System (ADS)
Wagner, D.; Alam, N.; Wewetzer, M.; Pries, M.; Coors, V.
2015-12-01
Geometric quality of 3D city models is crucial for data analysis and simulation tasks, which are part of modern applications of the data (e.g. potential heating energy consumption of city quarters, solar potential, etc.). Geometric quality in these contexts is however a different concept as it is for 2D maps. In the latter case, aspects such as positional or temporal accuracy and correctness represent typical quality metrics of the data. They are defined in ISO 19157 and should be mentioned as part of the metadata. 3D data has a far wider range of aspects which influence their quality, plus the idea of quality itself is application dependent. Thus, concepts for definition of quality are needed, including methods to validate these definitions. Quality on this sense means internal validation and detection of inconsistent or wrong geometry according to a predefined set of rules. A useful starting point would be to have correct geometry in accordance with ISO 19107. A valid solid should consist of planar faces which touch their neighbours exclusively in defined corner points and edges. No gaps between them are allowed, and the whole feature must be 2-manifold. In this paper, we present methods to validate common geometric requirements for building geometry. Different checks based on several algorithms have been implemented to validate a set of rules derived from the solid definition mentioned above (e.g. water tightness of the solid or planarity of its polygons), as they were developed for the software tool CityDoctor. The method of each check is specified, with a special focus on the discussion of tolerance values where they are necessary. The checks include polygon level checks to validate the correctness of each polygon, i.e. closeness of the bounding linear ring and planarity. On the solid level, which is only validated if the polygons have passed validation, correct polygon orientation is checked, after self-intersections outside of defined corner points and edges
Discrete element modeling of subglacial sediment deformation
NASA Astrophysics Data System (ADS)
Damsgaard, Anders; Egholm, David L.; Piotrowski, Jan A.; Tulaczyk, Slawek; Larsen, Nicolaj K.; Tylmann, Karol
2013-12-01
The Discrete Element Method (DEM) is used in this study to explore the highly nonlinear dynamics of a granular bed when exposed to stress conditions comparable to those at the bed of warm-based glaciers. Complementary to analog experiments, the numerical approach allows a detailed analysis of the material dynamics and the shear zone development during progressive shear strain. The geometry of the heterogeneous stress network is visible in the form of force-carrying grain bridges and adjacent, volumetrically dominant, inactive zones. We demonstrate how the shear zone thickness and dilation depend on the level of normal (overburden) stress, and we show how high normal stress can mobilize material to great depths. The particle rotational axes tend to align with progressive shear strain, with rotations both along and reverse to the shear direction. The results from successive laboratory ring-shear experiments on simple granular materials are compared to results from similar numerical experiments. The simulated DEM material and all tested laboratory materials deform by an elastoplastic rheology under the applied effective normal stress. These results demonstrate that the DEM is a viable alternative to continuum models for small-scale analysis of sediment deformation. It can be used to simulate the macromechanical behavior of simple granular sediments, and it provides an opportunity to study how microstructures in subglacial sediments are formed during progressive shear strain.
A geometric model of anorexia and its treatment.
Callahan, J
1982-04-01
Anorexia is a severe psychological disorder in which a person's dieting turns into compulsive fasting. Some victims develop, after a time, a bulimic phase; their fasting is interrupted at intervals by bouts of indiscriminate gorging. One successful treatment makes use of a naturally occurring trance state, in which the anorexic's obsession with food recedes temporarily, to offer reassurance and rebuild a personality free of the obsession. The proposed model is catastrophe-theoretic. It assumes (a) that the bifurcation of eating attitudes typical of anorexia can be modeled by a cusp whose controls are hunger and eating regimen; and (b) that the normal cycle of falling asleep and waking up can be modeled by a hysteresis loop controlled by alertness. Catastrophe theory predicts two additional controls, and a larger model organized by the E6 singularity. The new controls are identified with loss of self-control and insecurity, and anorexia is correlated with high insecurity. The model makes the following predictions. First, under moderate levels of self-control and eating regimen, an anorexic has access to balanced, nonobsessive attitudes toward food at a reduced level of wakefulness. This is the trance state. Second, a healthy individual has two distinct sleep modes, dominated by cerebral and somatic elements, respectively. Third, with increasing insecurity the distinct modes fuse together, so that an anorexic's sleep patterns are abnormal. The model is geometric because the connection between behavior and controlling factors is made by graphs of certain standard form. PMID:7092772
The genetics of speciation: Insights from Fisher's geometric model.
Fraïsse, Christelle; Gunnarsson, P Alexander; Roze, Denis; Bierne, Nicolas; Welch, John J
2016-07-01
Research in speciation genetics has uncovered many robust patterns in intrinsic reproductive isolation, and fitness landscape models have been useful in interpreting these patterns. Here, we examine fitness landscapes based on Fisher's geometric model. Such landscapes are analogous to models of optimizing selection acting on quantitative traits, and have been widely used to study adaptation and the distribution of mutational effects. We show that, with a few modifications, Fisher's model can generate all of the major findings of introgression studies (including "speciation genes" with strong deleterious effects, complex epistasis and asymmetry), and the major patterns in overall hybrid fitnesses (including Haldane's Rule, the speciation clock, heterosis, hybrid breakdown, and male-female asymmetry in the F1). We compare our approach to alternative modeling frameworks that assign fitnesses to genotypes by identifying combinations of incompatible alleles. In some cases, the predictions are importantly different. For example, Fisher's model can explain conflicting empirical results about the rate at which incompatibilities accumulate with genetic divergence. In other cases, the predictions are identical. For example, the quality of reproductive isolation is little affected by the manner in which populations diverge. PMID:27252049
Geometric and colour data fusion for outdoor 3D models.
Merchán, Pilar; Adán, Antonio; Salamanca, Santiago; Domínguez, Vicente; Chacón, Ricardo
2012-01-01
This paper deals with the generation of accurate, dense and coloured 3D models of outdoor scenarios from scanners. This is a challenging research field in which several problems still remain unsolved. In particular, the process of 3D model creation in outdoor scenes may be inefficient if the scene is digitalized under unsuitable technical (specific scanner on-board camera) and environmental (rain, dampness, changing illumination) conditions. We address our research towards the integration of images and range data to produce photorealistic models. Our proposal is based on decoupling the colour integration and geometry reconstruction stages, making them independent and controlled processes. This issue is approached from two different viewpoints. On the one hand, given a complete model (geometry plus texture), we propose a method to modify the original texture provided by the scanner on-board camera with the colour information extracted from external images taken at given moments and under specific environmental conditions. On the other hand, we propose an algorithm to directly assign external images onto the complete geometric model, thus avoiding tedious on-line calibration processes. We present the work conducted on two large Roman archaeological sites dating from the first century A.D., namely, the Theatre of Segobriga and the Fori Porticus of Emerita Augusta, both in Spain. The results obtained demonstrate that our approach could be useful in the digitalization and 3D modelling fields. PMID:22969327
Modeling Secular Deformation of Kilauea Volcano, Hawaii
NASA Astrophysics Data System (ADS)
Sinnett, D. K.; Montgomery-Brown, E. D.; Casu, F.; Segall, P.; Fukushima, Y.; Miklius, A.; Poland, M. P.
2010-12-01
Kilauea volcano, Hawaii, is a dynamic volcanic and tectonic system that hosts rift intrusions and eruptions, summit inflation/deflation and eruptions, flank earthquakes and slow slip events, as well as quasi-steady flank motion. We seek to identify and characterize the actively deforming structures on Kilauea and study their interactions using a combination of GPS, InSAR, and seismic data. In addition we examine whether the change from summit subsidence to inflation in 2003, led to changes elsewhere in the volcano. We begin by modeling velocities of 16 continuous GPS and 28 campaign GPS sites and mean velocities from three ENVISAT tracks (T93 ascending: 10 acquisitions from 20030120 to 20041115; T200 descending: 13 acquisitions from 20030127 to 20041122, T429 descending: 10 acquisitions from 20030212 to 20041103) between 2003 and 2004, a period lacking major episodic events. We use triangular dislocations to mesh the curving rift zones and décollement. The southwest and east rift zones are continuous through the summit caldera area, where we also include a point center of dilatation beneath the southwest caldera. A décollement beginning about 12 km offshore at seven km depth dips approximately eight degrees northwest to achieving a depth of nine kilometers beneath the summit/rift zone. The décollement mesh continues at a shallower dip beneath the north flank of Kilauea reaching a final depth of 9.5 km beneath the north flank of Kilauea/south flank of Mauna Loa. Kinematic constraints enforce that opening at the base of the rift equal the differential décollement slip across the rift. Future modeling will include tests of Koae and Hilina fault geometries as well as time-dependent modeling of the deformation field.
Fast Geometric Consensus Approach for Protein Model Quality Assessment
Adamczak, Rafal; Pillardy, Jaroslaw; Vallat, Brinda K.
2011-01-01
Abstract Model quality assessment (MQA) is an integral part of protein structure prediction methods that typically generate multiple candidate models. The challenge lies in ranking and selecting the best models using a variety of physical, knowledge-based, and geometric consensus (GC)-based scoring functions. In particular, 3D-Jury and related GC methods assume that well-predicted (sub-)structures are more likely to occur frequently in a population of candidate models, compared to incorrectly folded fragments. While this approach is very successful in the context of diversified sets of models, identifying similar substructures is computationally expensive since all pairs of models need to be superimposed using MaxSub or related heuristics for structure-to-structure alignment. Here, we consider a fast alternative, in which structural similarity is assessed using 1D profiles, e.g., consisting of relative solvent accessibilities and secondary structures of equivalent amino acid residues in the respective models. We show that the new approach, dubbed 1D-Jury, allows to implicitly compare and rank N models in O(N) time, as opposed to quadratic complexity of 3D-Jury and related clustering-based methods. In addition, 1D-Jury avoids computationally expensive 3D superposition of pairs of models. At the same time, structural similarity scores based on 1D profiles are shown to correlate strongly with those obtained using MaxSub. In terms of the ability to select the best models as top candidates 1D-Jury performs on par with other GC methods. Other potential applications of the new approach, including fast clustering of large numbers of intermediate structures generated by folding simulations, are discussed as well. PMID:21244273
NASA Astrophysics Data System (ADS)
Shibkov, A. A.; Zolotov, A. E.; Zheltov, M. A.; Denisov, A. A.; Gasanov, M. F.; Kochegarov, S. S.
2016-05-01
The effect of holes on the band formation and the serrated deformation in planar specimens of aluminum-magnesium alloys AlMg5 and AlMg6 is studied by high-speed video filming of moving deformation bands. It is found that the concentration of an elastic field near a hole causes early nucleation of macrolocalized deformation bands and decreases the critical deformation of the first stress drop. Differences between the spatial-temporal patterns of deformation bands near holes under various deformation conditions are revealed.
Geometrical Custom Modeling of Human Cornea In Vivo and Its Use for the Diagnosis of Corneal Ectasia
Cavas-Martínez, Francisco; Fernández-Pacheco, Daniel G.; De la Cruz-Sánchez, Ernesto; Nieto Martínez, José; Fernández Cañavate, Francisco J.; Vega-Estrada, Alfredo; Plaza-Puche, Ana B.; Alió, Jorge L.
2014-01-01
Aim To establish a new procedure for 3D geometric reconstruction of the human cornea to obtain a solid model that represents a personalized and in vivo morphology of both the anterior and posterior corneal surfaces. This model is later analyzed to obtain geometric variables enabling the characterization of the corneal geometry and establishing a new clinical diagnostic criterion in order to distinguish between healthy corneas and corneas with keratoconus. Method The method for the geometric reconstruction of the cornea consists of the following steps: capture and preprocessing of the spatial point clouds provided by the Sirius topographer that represent both anterior and posterior corneal surfaces, reconstruction of the corneal geometric surfaces and generation of the solid model. Later, geometric variables are extracted from the model obtained and statistically analyzed to detect deformations of the cornea. Results The variables that achieved the best results in the diagnosis of keratoconus were anterior corneal surface area (ROC area: 0.847, p<0.000, std. error: 0.038, 95% CI: 0.777 to 0.925), posterior corneal surface area (ROC area: 0.807, p<0.000, std. error: 0.042, 95% CI: 0,726 to 0,889), anterior apex deviation (ROC area: 0.735, p<0.000, std. error: 0.053, 95% CI: 0.630 to 0.840) and posterior apex deviation (ROC area: 0.891, p<0.000, std. error: 0.039, 95% CI: 0.8146 to 0.9672). Conclusion Geometric modeling enables accurate characterization of the human cornea. Also, from a clinical point of view, the procedure described has established a new approach for the study of eye-related diseases. PMID:25329896
Videogrammetric Model Deformation Measurement System User's Manual
NASA Technical Reports Server (NTRS)
Dismond, Harriett R.
2002-01-01
The purpose of this manual is to provide the user of the NASA VMD system, running the MDef software, Version 1.10, all information required to operate the system. The NASA Videogrammetric Model Deformation system consists of an automated videogrammetric technique used to measure the change in wing twist and bending under aerodynamic load in a wind tunnel. The basic instrumentation consists of a single CCD video camera and a frame grabber interfaced to a computer. The technique is based upon a single view photogrammetric determination of two-dimensional coordinates of wing targets with fixed (and known) third dimensional coordinate, namely the span-wise location. The major consideration in the development of the measurement system was that productivity must not be appreciably reduced.
Rapid world modeling: Fitting range data to geometric primitives
Feddema, J.; Little, C.
1996-12-31
For the past seven years, Sandia National Laboratories has been active in the development of robotic systems to help remediate DOE`s waste sites and decommissioned facilities. Some of these facilities have high levels of radioactivity which prevent manual clean-up. Tele-operated and autonomous robotic systems have been envisioned as the only suitable means of removing the radioactive elements. World modeling is defined as the process of creating a numerical geometric model of a real world environment or workspace. This model is often used in robotics to plan robot motions which perform a task while avoiding obstacles. In many applications where the world model does not exist ahead of time, structured lighting, laser range finders, and even acoustical sensors have been used to create three dimensional maps of the environment. These maps consist of thousands of range points which are difficult to handle and interpret. This paper presents a least squares technique for fitting range data to planar and quadric surfaces, including cylinders and ellipsoids. Once fit to these primitive surfaces, the amount of data associated with a surface is greatly reduced up to three orders of magnitude, thus allowing for more rapid handling and analysis of world data.
Generalised geometrical CP violation in a T ' lepton flavour model
NASA Astrophysics Data System (ADS)
Girardi, Ivan; Meroni, Aurora; Petcov, S. T.; Spinrath, Martin
2014-02-01
We analyse the interplay of generalised CP transformations and the non-Abelian discrete group T ' and use the semi-direct product G f = T ' ⋊ H CP, as family symmetry acting in the lepton sector. The family symmetry is shown to be spontaneously broken in a geometrical manner. In the resulting flavour model, naturally small Majorana neutrino masses for the light active neutrinos are obtained through the type I see-saw mechanism. The known masses of the charged leptons, lepton mixing angles and the two neutrino mass squared differences are reproduced by the model with a good accuracy. The model allows for two neutrino mass spectra with normal ordering (NO) and one with inverted ordering (IO). For each of the three spectra the absolute scale of neutrino masses is predicted with relatively small uncertainty. The value of the Dirac CP violation (CPV) phase δ in the lepton mixing matrix is predicted to be δ = π/2 or 3 π/2. Thus, the CP violating effects in neutrino oscillations are predicted to be maximal (given the values of the neutrino mixing angles) and experimentally observable. We present also predictions for the sum of the neutrino masses, for the Majorana CPV phases and for the effective Majorana mass in neutrinoless double beta decay. The predictions of the model can be tested in a variety of ongoing and future planned neutrino experiments.
Nonlinear modeling and estimation of slew induced structural deformations
NASA Technical Reports Server (NTRS)
Dwyer, T. A. W., III; Karray, F.
1988-01-01
A model of the nonlinear dynamics of a deformable maneuvering multibody system is described, whereby elastic deformation are modeled by restoring forces and dissipative forces at point mass appendages. This model is brought into bilinear form. Estimation of deformations occasioned by rapid slewing maneuvers is carried out by a filter based on a globally equivalent linear model of the bilinear dynamics, and is shown to be an improvement over the extended Kalman filter. To further alleviate the computational burden, the estimated deformation state is propagated between observations by a low dimensional operator spline interpolator of bilinear system Volterra series, which is easily implemented.
Geometrical model for malaria parasite migration in structured environments
NASA Astrophysics Data System (ADS)
Battista, Anna; Frischknecht, Friedrich; Schwarz, Ulrich S.
2014-10-01
Malaria is transmitted to vertebrates via a mosquito bite, during which rodlike and crescent-shaped parasites, called sporozoites, are injected into the skin of the host. Searching for a blood capillary to penetrate, sporozoites move quickly in locally helical trajectories, that are frequently perturbed by interactions with the extracellular environment. Here we present a theoretical analysis of the active motility of sporozoites in a structured environment. The sporozoite is modelled as a self-propelled rod with spontaneous curvature and bending rigidity. It interacts with hard obstacles through collision rules inferred from experimental observation of two-dimensional sporozoite movement in pillar arrays. Our model shows that complex motion patterns arise from the geometrical shape of the parasite and that its mechanical flexibility is crucial for stable migration patterns. Extending the model to three dimensions reveals that a bent and twisted rod can associate to cylindrical obstacles in a manner reminiscent of the association of sporozoites to blood capillaries, supporting the notion of a prominent role of cell shape during malaria transmission.
NASA Astrophysics Data System (ADS)
Kashani, Rojano
External beam radiation therapy is an effective method for treating cancer in many body sites. Highly conformal plans can be created to provide good target coverage while sparing the surrounding normal tissue. A fundamental problem in delivering these conformal plans is the inter- and intra-fractional variations in patient geometry, which result in deviation of the delivered dose from the planned dose, thus reducing the probability of tumor control or increasing the risk of normal tissue toxicity. To address this problem, various motion management strategies have been implemented in the clinic, and several others are under investigation. While the technique employed for management of geometric variation can change depending on the type and source of the variation (set up error, respiratory-induced motion and deformation, or tumor shrinkage or tissue loss in response to treatment) as well as other clinical factors, all these techniques have one thing in common and that is the fact that they are not perfect. This work investigates the uncertainties associated with the measurement and management of motion and deformation, and evaluates the impact of these uncertainties on the accuracy of geometry and dose tracking for treatment adaptation. This research quantified the magnitude and distribution of error in deformable image registration for aligning image volumes acquired at different breathing states. It further explored the potential of reducing the registration error in deforming lung geometry, by applying a method from multivariate statistics (principal component analysis) to identify the significant modes of variation in this geometry. It also demonstrated the potential for tracking respiratory induced deformation in various regions in the lung, using a few surrogates such as implanted markers. In addition to the evaluation of registration error for thoracic geometry affected by respiratory motion, this work also investigates the accuracy of deformable image
NASA Astrophysics Data System (ADS)
Kaden, R.; Kolbe, T. H.
2012-07-01
Virtual 3D city models are integrated complex compositions of spatial data of different themes, origin, quality, scale, and dimensions. Within this paper, we address the problem of spatial compatibility of geodata aiming to provide support for ad-hoc integration of virtual 3D city models including geodata of different sources and themes like buildings, terrain, and city furniture. In contrast to related work which is dealing with the integration of redundant geodata structured according to different data models and ontologies, we focus on the integration of complex 3D models of the same representation (here: CityGML) but regarding to the geometric-topological consistent matching of non-homologous objects, e.g. a building is connected to a road, and their geometric homogenisation. Therefore, we present an approach including a data model for a Geodata Join and the general concept of an integration procedure using the join information. The Geodata Join aims to bridge the lack of information between fragmented geodata by describing the relationship between adjacent objects from different datasets. The join information includes the geometrical representation of those parts of an object, which have a specific/known topological or geometrical relationship to another object. This part is referred to as a Connector and is either described by points, lines, or surfaces of the existing object geometry or by additional join geometry. In addition, the join information includes the specification of the connected object in the other dataset and the description of the topological and geometrical relationship between both objects, which is used to aid the matching process. Furthermore, the Geodata Join contains object-related information like accuracy values and restrictions of movement and deformation which are used to optimize the integration process. Based on these parameters, a functional model including a matching algorithm, transformation methods, and conditioned adjustment
dMODELS: A software package for modeling volcanic deformation
NASA Astrophysics Data System (ADS)
Battaglia, M.
2013-12-01
dMODELS is software package including the most common source models used to interpret deformation measurements near active volcanic centers. The emphasis is on estimating the parameters of analytical models of deformation by inverting data from the Global Positioning System (GPS), InSAR, tiltmeters and strainmeters. Source models include: (a) pressurized spherical, ellipsoidal and sill-like magma chambers in an elastic, homogeneous, flat half-space; and (b) pressurized spherical magma chamber with correction for the effect of topography (i.e., Williams and Wadge, 1998). All the expressions have been extended to include deformation and strain within the Earth's crust (as opposed to only the Earth's surface) and verified against finite element models. The software has been developed using Matlab but compiled versions that can be run using the free Matlab Compiler Runtime (MCR) are available for Linux, and Windows 7 (32bit and 64bit). The MATLAB scripts and compiled files are open source and intended for teaching and research. The software can be downloaded from the USGS web site pubs.usgs.gov/tm/13/b1/. Please e-mail the author at mbattaglia@usgs.gov if you would like to be included in the dMODELS mail list to get information about the release of software updates.
NASA Astrophysics Data System (ADS)
Song, Pengchao
Recent studies of the occurrence of post-flutter limit cycle oscillations (LCO) of the F-16 have provided good support to the long-standing hypothesis that this phenomenon involves a nonlinear structural damping. A potential mechanism for the appearance of nonlinearity in the damping are the nonlinear geometric effects that arise when the deformations become large enough to exceed the linear regime. In this light, the focus of this investigation is first on extending nonlinear reduced order modeling (ROM) methods to include viscoelasticity which is introduced here through a linear Kelvin-Voigt model in the undeformed configuration. Proceeding with a Galerkin approach, the ROM governing equations of motion are obtained and are found to be of a generalized van der Pol-Duffing form with parameters depending on the structure and the chosen basis functions. An identification approach of the nonlinear damping parameters is next proposed which is applicable to structures modeled within commercial finite element software. The effects of this nonlinear damping mechanism on the post-flutter response is next analyzed on the Goland wing through time-marching of the aeroelastic equations comprising a rational fraction approximation of the linear aerodynamic forces. It is indeed found that the nonlinearity in the damping can stabilize the unstable aerodynamics and lead to finite amplitude limit cycle oscillations even when the stiffness related nonlinear geometric effects are neglected. The incorporation of these latter effects in the model is found to further decrease the amplitude of LCO even though the dominant bending motions do not seem to stiffen as the level of displacements is increased in static analyses.
Content-Based Search on a Database of Geometric Models: Identifying Objects of Similar Shape
XAVIER, PATRICK G.; HENRY, TYSON R.; LAFARGE, ROBERT A.; MEIRANS, LILITA; RAY, LAWRENCE P.
2001-11-01
The Geometric Search Engine is a software system for storing and searching a database of geometric models. The database maybe searched for modeled objects similar in shape to a target model supplied by the user. The database models are generally from CAD models while the target model may be either a CAD model or a model generated from range data collected from a physical object. This document describes key generation, database layout, and search of the database.
Blanc-Benon, Philippe; Lipkens, Bart; Dallois, Laurent; Hamilton, Mark F; Blackstock, David T
2002-01-01
Sonic boom propagation can be affected by atmospheric turbulence. It has been shown that turbulence affects the perceived loudness of sonic booms, mainly by changing its peak pressure and rise time. The models reported here describe the nonlinear propagation of sound through turbulence. Turbulence is modeled as a set of individual realizations of a random temperature or velocity field. In the first model, linear geometrical acoustics is used to trace rays through each realization of the turbulent field. A nonlinear transport equation is then derived along each eigenray connecting the source and receiver. The transport equation is solved by a Pestorius algorithm. In the second model, the KZK equation is modified to account for the effect of a random temperature field and it is then solved numerically. Results from numerical experiments that simulate the propagation of spark-produced N waves through turbulence are presented. It is observed that turbulence decreases, on average, the peak pressure of the N waves and increases the rise time. Nonlinear distortion is less when turbulence is present than without it. The effects of random vector fields are stronger than those of random temperature fields. The location of the caustics and the deformation of the wave front are also presented. These observations confirm the results from the model experiment in which spark-produced N waves are used to simulate sonic boom propagation through a turbulent atmosphere. PMID:11837954
Meshless Modeling of Deformable Shapes and their Motion
Adams, Bart; Ovsjanikov, Maks; Wand, Michael; Seidel, Hans-Peter; Guibas, Leonidas J.
2010-01-01
We present a new framework for interactive shape deformation modeling and key frame interpolation based on a meshless finite element formulation. Starting from a coarse nodal sampling of an object’s volume, we formulate rigidity and volume preservation constraints that are enforced to yield realistic shape deformations at interactive frame rates. Additionally, by specifying key frame poses of the deforming shape and optimizing the nodal displacements while targeting smooth interpolated motion, our algorithm extends to a motion planning framework for deformable objects. This allows reconstructing smooth and plausible deformable shape trajectories in the presence of possibly moving obstacles. The presented results illustrate that our framework can handle complex shapes at interactive rates and hence is a valuable tool for animators to realistically and efficiently model and interpolate deforming 3D shapes. PMID:24839614
Geometrical MTF computation method based on the irradiance model
NASA Astrophysics Data System (ADS)
Lin, P.-D.; Liu, C.-S.
2011-01-01
The Modulation Transfer Function (MTF) is a measure of an optical system's ability to transfer contrast from the specimen to the image plane at a specific resolution. It can be computed either numerically by geometrical optics or measured experimentally by imaging a knife edge or a bar-target pattern of varying spatial frequency. Previously, MTF accuracy was generally affected by the size of the mesh on the image plane. This paper presents a new MTF computation method based on the irradiance model, without counting the number of rays hitting each grid. To verify the method, the MTF in the sagittal and meridional directions of an axis-symmetrical optical system is computed by both the ray-counting and the proposed methods. It is found that the grid size meshed on the image plane significantly affects the MTF of the ray-counting method, sometimes with significantly negative results. The proposed irradiance method is immune to issues of grid size. The CPU computation time for the two methods is approximately the same.
A deformable model for hippocampus segmentation: Improvements and extension to 3D
Ghanei, A.; Soltanian-Zadeh, H. |; Windham, J.P.
1996-12-31
In this work, the application of a deformable model to the segmentation of hippocampus in brain MRI has been investigated. Common problems of the model in this case and similar cases have been discussed and solved. A new method for extracting discontinuous boundaries of an object with multiple unwanted edges has been developed. This method is based on detecting and following the edge by external forces. For improving the contour stability, its movement has been limited. Also, adaptive values for internal force weights have been used. In the next step, the model has been extended to 3D which is a Deformable Surface Model. A geometric structure used for this purpose. This helps in definition of normal vectors and internal forces. Finally, a method for generating the initial volume from individual initial polygons has been developed.
Deformation modeling and constitutive modeling for anisotropic superalloys
NASA Technical Reports Server (NTRS)
Milligan, Walter W.; Antolovich, Stephen D.
1989-01-01
A study of deformation mechanisms in the single crystal superalloy PWA 1480 was conducted. Monotonic and cyclic tests were conducted from 20 to 1093 C. Both (001) and near-(123) crystals were tested, at strain rates of 0.5 and 50 percent/minute. The deformation behavior could be grouped into two temperature regimes: low temperatures, below 760 C; and high temperatures, above 820 to 950 C depending on the strain rate. At low temperatures, the mechanical behavior was very anisotropic. An orientation dependent CRSS, a tension-compression asymmetry, and anisotropic strain hardening were all observed. The material was deformed by planar octahedral slip. The anisotropic properties were correlated with the ease of cube cross-slip, as well as the number of active slip systems. At high temperatures, the material was isotropic, and deformed by homogeneous gamma by-pass. It was found that the temperature dependence of the formation of superlattice-intrinsic stacking faults was responsible for the local minimum in the CRSS of this alloy at 400 C. It was proposed that the cube cross-slip process must be reversible. This was used to explain the reversible tension-compression asymmetry, and was used to study models of cross-slip. As a result, the cross-slip model proposed by Paidar, Pope and Vitek was found to be consistent with the proposed slip reversibility. The results were related to anisotropic viscoplastic constitutive models. The model proposed by Walter and Jordan was found to be capable of modeling all aspects of the material anisotropy. Temperature and strain rate boundaries for the model were proposed, and guidelines for numerical experiments were proposed.
Jordanian deformation of the open sℓ(2) Gaudin model
NASA Astrophysics Data System (ADS)
António, N. Cirilo; Manojlović, N.; Nagy, Z.
2014-04-01
We derive a deformed sℓ( 2) Gaudin model with integrable boundaries. Starting from the Jordanian deformation of the SL( 2)-invariant Yang R-matrix and generic solutions of the associated reflection equation and the dual reflection equation, we obtain the corresponding inhomogeneous spin- 1/2 XXX chain. The semiclassical expansion of the transfer matrix yields the deformed sℓ( 2) Gaudin Hamiltonians with boundary terms.
NASA Technical Reports Server (NTRS)
Strahler, Alan H.; Jupp, David L. B.
1990-01-01
Geometric-optical discrete-element mathematical models for forest canopies have been developed using the Boolean logic and models of Serra. The geometric-optical approach is considered to be particularly well suited to describing the bidirectional reflectance of forest woodland canopies, where the concentration of leaf material within crowns and the resulting between-tree gaps make plane-parallel, radiative-transfer models inappropriate. The approach leads to invertible formulations, in which the spatial and directional variance provides the means for remote estimation of tree crown size, shape, and total cover from remotedly sensed imagery.
HSR Model Deformation Measurements from Subsonic to Supersonic Speeds
NASA Technical Reports Server (NTRS)
Burner, A. W.; Erickson, G. E.; Goodman, W. L.; Fleming, G. A.
1999-01-01
This paper describes the video model deformation technique (VMD) used at five NASA facilities and the projection moire interferometry (PMI) technique used at two NASA facilities. Comparisons between the two techniques for model deformation measurements are provided. Facilities at NASA-Ames and NASA-Langley where deformation measurements have been made are presented. Examples of HSR model deformation measurements from the Langley Unitary Wind Tunnel, Langley 16-foot Transonic Wind Tunnel, and the Ames 12-foot Pressure Tunnel are presented. A study to improve and develop new targeting schemes at the National Transonic Facility is also described. The consideration of milled targets for future HSR models is recommended when deformation measurements are expected to be required. Finally, future development work for VMD and PMI is addressed.
Discrete element modeling of subglacial sediment deformation
NASA Astrophysics Data System (ADS)
Damsgaard, A.; Egholm, D. L.; Piotrowski, J. A.; Tulaczyk, S. M.; Larsen, N. K.
2013-12-01
The Discrete Element Method (DEM) is used to explore the highly nonlinear dynamics of a granular bed when exposed to stress conditions comparable to those at the bed of warm-based glaciers. In the DEM, the material is simulated on a grain-by-grain basis, and defining the micromechanical properties of the inter-particle contacts parameterizes the model. For validating the numerical approach, the macromechanical behavior of the numerical material is compared to the results from successive laboratory ring-shear experiments. Overall, there is a good agreement between the geotechnical behavior of the real granular materials and the numerical results. The materials deform by an elasto-plastic rheology under the applied effective normal stress and horizontal shearing. The peak and ultimate shear strengths depend linearly on the magnitude of the normal stress by the Mohr-Coulomb constitutive relationship. The numerical approach allows for a detailed analysis of the material dynamics and shear zone development during progressive shear strain. We demonstrate how the shear zone thickness and dilation increase with the magnitude of the normal stress. The stresses are distributed heterogeneously through the granular material along stress-carrying force chains. Between the force chains are the volumetrically dominant inactive zones. Overall, the force chain orientation is parallel to the maximum compressive stress. The data-parallel nature of the basic DEM formulation makes the problem ideal for utilizing the high arithmetic potential of modern general-purpose GPUs. Using the Nvidia CUDA C toolkit, the algorithm is formulated for spherical particles in three dimensions with a linear-elastic soft-body contact model. We have coupled the DEM model to a model for porewater flow, and we present early results of particle-porewater interactions. The two-way mechanical coupling is used to investigate pore-pressure feedbacks, which may be very important for the dynamics of soft
Dahmen, Karin A.; Ben-Zion, Yehuda; Uhl, Jonathan T.
2009-05-01
A basic micromechanical model for deformation of solids with only one tuning parameter (weakening {epsilon}) is introduced. The model can reproduce observed stress-strain curves, acoustic emissions and related power spectra, event statistics, and geometrical properties of slip, with a continuous phase transition from brittle to ductile behavior. Exact universal predictions are extracted using mean field theory and renormalization group tools. The results agree with recent experimental observations and simulations of related models for dislocation dynamics, material damage, and earthquake statistics.
Preliminary deformation model for National Seismic Hazard map of Indonesia
Meilano, Irwan; Gunawan, Endra; Sarsito, Dina; Prijatna, Kosasih; Abidin, Hasanuddin Z.; Susilo,; Efendi, Joni
2015-04-24
Preliminary deformation model for the Indonesia’s National Seismic Hazard (NSH) map is constructed as the block rotation and strain accumulation function at the elastic half-space. Deformation due to rigid body motion is estimated by rotating six tectonic blocks in Indonesia. The interseismic deformation due to subduction is estimated by assuming coupling on subduction interface while deformation at active fault is calculated by assuming each of the fault‘s segment slips beneath a locking depth or in combination with creeping in a shallower part. This research shows that rigid body motion dominates the deformation pattern with magnitude more than 15 mm/year, except in the narrow area near subduction zones and active faults where significant deformation reach to 25 mm/year.
Modeling thermomechanical processes in shape memory polymers under finite deformations
NASA Astrophysics Data System (ADS)
Rogovoi, A. A.; Stolbova, O. S.
2015-11-01
A model taking into account finite deformations is constructed for the behavior of a shape memory polymer which undergoes a transition from the highly elastic to the vitreous state and back during deformation and temperature change. The obtained relations are tested on problems which have experimental support.
A quantitative evaluation of models for Aegean crustal deformation
NASA Astrophysics Data System (ADS)
Nyst, M.; Thatcher, W.
2003-04-01
Modeling studies of eastern Mediterranean tectonics show that Aegean deformation is mainly determined by WSW directed expulsion of Anatolia and SW directed extension due to roll-back of African lithosphere along the Hellenic trench. How motion is transferred across the Aegean remains a subject of debate. The two most widely used hypotheses for Aegean tectonics assert fundamentally different mechanisms. The first model describes deformation as a result of opposing rotations of two rigid microplates separated by a zone of extension. In the second model most motion is accommodated by shear on a series of dextral faults and extension on graben systems. These models make different quantitative predictions for the crustal deformation field that can be tested by a new, spatially dense GPS velocity data set. To convert the GPS data into crustal deformation parameters we use different methods to model complementary aspects of crustal deformation. We parameterize the main fault and plate boundary structures of both models and produce representations for the crustal deformation field that range from purely rigid rotations of microplates, via interacting, elastically deforming blocks separated by crustal faults to a continuous velocity gradient field. Critical evaluation of these models indicates strengths and limitations of each and suggests new measurements for further refining understanding of present-day Aegean tectonics.
Geometric modeling and analysis of large latticed surfaces
NASA Technical Reports Server (NTRS)
Nayfeh, A. H.; Hefzy, M. S.
1980-01-01
The application of geometrical schemes, similar to geodesic domes, to large spherical antenna reflectors was investigated. The shape and size of flat segmented latticed surfaces which approximate general shells of revolution, and in particular spherical and paraboloidal reflective surfaces, were determined. The extensive mathematical and computational geometric analyses of the reflector resulted in the development of a general purpose computer program capable of generating the complete design parameters of the dish. The program also includes a graphical self contained subroutine for graphic display of the required design.
Deformable template models for emission tomography
Amit, Y. . Dept. of Statistics); Manbeck, K.M. . Div. of Applied Mathematics)
1993-06-01
The reconstruction of emission tomography data is an ill-posed inverse problem and, as such, requires some form of regularization. Previous efforts to regularize the restoration process have incorporated rather general assumptions about the isotope distribution within a patient's body. Here, the authors present a theoretical and algorithmic framework in which the notion of a deformable template can be used to identify and quantify brain tumors in pediatric patients. Patient data and computer simulation experiments are presented which illustrate the performance of the deformable template approach to single photon emission computed tomography (SPECT).
NASA Astrophysics Data System (ADS)
Kobayashi, S.; Hosaka, S.; Tamatsukuri, H.; Nakajima, T.; Mitsuda, S.; Prokeš, K.; Kiefer, K.
2014-08-01
We report neutron diffraction measurement results for an Ising antiferromagnet CoNb2O6 under uniaxial pressure along the geometrically frustrated isosceles-triangular-lattice direction. We find that an onset incommensurate wave number at the Néel temperature increases with pressure from 0.378 to 0.411 at 400 MPa. The observations suggest that the anisotropic deformation of the lattice by the uniaxial pressure significantly modifies the spin frustration, leading to an increase in the nearest-neighbor to next-nearest-neighbor interaction ratio from 1.33 to 1.81.
Pickup, Brian A; Thomson, Scott L
2011-04-01
Simplified models have been used to simulate and study the flow-induced vibrations of the human vocal folds. While it is clear that the models' responses are sensitive to geometry, it is not clear how and to what extent specific geometric features influence model motion. In this study geometric features that played significant roles in governing the motion of a two-layer (body-cover), two-dimensional, finite element vocal fold model were identified. The model was defined using a flow solver based on the viscous, unsteady, Navier-Stokes equations and a solid solver that allowed for large strain and deformation. A screening-type design-of-experiments approach was used to identify the relative importance of 13 geometric parameters. Five output measures were analyzed to assess the magnitude of each geometric parameter's effect on the model's motion. The measures related to frequency, glottal width, flow rate, intraglottal angle, and intraglottal phase delay. The most significant geometric parameters were those associated with the cover--primarily the pre-phonatory intraglottal angle--as well as the body inferior angle. Some models exhibited evidence of improved model motion, including mucosal wave-like motion and alternating convergent-divergent glottal profiles, although further improvements are still needed to more closely mimic human vocal fold motion. PMID:21476668
Modeling of regional earthquakes, aseismic deformation and fault patterns
NASA Astrophysics Data System (ADS)
Lyakhovsky, V.; Ben-Zion, Y.
2005-12-01
We study the coupled evolution of earthquakes and faults in a 3-D lithospheric model consisting of a weak sedimentary layer over a crystalline crust and upper mantle. The total strain tensor in each layer is the sum of (1) elastic strain, (2) damage-related inelastic strain, and (3) ductile strain. We use a visco-elastic damage rheology model (Lyakhovsky et al., 1997; Hamiel et al., 2004) to calculate elastic strain coupled with evolving material damage and damage-related inelastic strain accumulation. A thermodynamically based equation for damage evolution accounts for degradation and healing as a function of the elastic strain tensor and material properties (rate coefficients and ratio of strain invariants separating states of degradation and healing). Analyses of stress-strain, acoustic emission and frictional data provide constraints on the damage model parameters. The ductile strain in the sedimentary layer is governed by Newtonian viscosity, while power-law rheology is used for the ductile strain in the lower crust and upper mantle. Each mechanism of strain and damage evolution is associated with its own timescale. In our previous study of earthquakes and faults in a 2-D model with averaged stress distribution over the seismogenic zone (thin sheet approximation) we demonstrated effects associated with the ratio between time scales for damage healing and for tectonic loading. The results indicated that low ratio leads to the development of geometrically regular fault systems and the characteristic frequency-size earthquake statistics, while high ratio leads to the development of a network of disordered fault systems and the Gutenberg-Richter statistics. Stress relaxation through ductile creep and damage-related strain mechanisms is associated with two additional time scales. In contrast to the previous 2-D model, the thickness of the seismogenic zone is not prescribed by the model set-up, but is a function of the ratio between timescale of damage accumulation
NASA Astrophysics Data System (ADS)
Goren, L.; Castelltort, S.; Klinger, Y.
2014-12-01
The Dead Sea Fault System changes its orientation across Lebanon and forms a restraining bend. The oblique deformation along the Lebanese restraining bend is characterized by a complex suite of tectonic structures, among which, the Yammouneh Fault (YF), is believed to be the main strand that relays deformation from the southern section to the northern section of the Dead Sea Fault System. However, uncertainties regarding slip rates and strain partitioning in Lebanon still prevail. Here, we use morphometric analysis together with analytical and numerical models to constrain rates and modes of distributed and localized deformation along the Lebanese restraining bend.The rivers that drain the western flank of Mount Lebanon show a consistent counterclockwise rotation with respect to an expected orogen perpendicular orientation. Moreover, a pattern of divide disequilibrium in between these rivers emerges from an application of the χ mapping technique, which aims at estimating the degree of geometrical and topological disequilibrium in river networks. These geometrical patterns are compatible with simulation results using a landscape evolution model, which imposes a distributed velocity field along a domain that represents the western flank of Mount Lebanon. We further develop an analytical model that relates the river orientation to a set of kinematic parameters that represents a combined pure and simple shear strain field, and we find the parameters that best explain the present orientation of the western Lebanon rivers. Our results indicate that distributed deformation to the west of the YF takes as much as 30% of the relative Arabia-Sinai plate velocity since the late Miocene, and that the average slip rate along the YF during the same time interval has been 3.8-4.4 mm/yr. The theoretical model can further explain the inferred rotation from Paleomagnetic measurements.
Geometric models of folding at Loch Monar, Scotland, using computer simulation
NASA Astrophysics Data System (ADS)
Watkinson, A. J.; Thiessen, R. L.
1988-06-01
Small-scale hand specimens were collected at Loch Monar, Scotland, one of the classic areas of fold interference patterns. From the analysis of these, the geometries of the F 1 and F 2 folds were derived. By computer simulation, the complex three-dimensional form of the fold interference shapes can then be reproduced very closely. F 2 fold shapes and motion directions derived from the small-scale structures, along with those derived from field observations of F 1 lineations deformed about F 2 folds, were then applied to an extrapolated pre-F 2 shape of the Loch Monar synform. This generated a map pattern strikingly similar to that mapped by Ramsay (1958). The geometric models provide useful information for mechanical hypotheses of the folding observed at Loch Monar. The simulation reveals an interesting problem that whereas many small-scale interference patterns reflect the map pattern of the major structure, there are exposures of interference patterns that do not. These are dome and basin (type 1) patterns found in an area where a major F 2 fold hinge crosses an F 1 fold hinge zone. By examining the deformed L 1 lineation patterns found in this area, along with the computed D 2 strain orientations and the field observations of F 2 fold geometries, we suggest that those patterns formed due to local variations in the displacement directions during the F 2 folding, perhaps due to the mechanical influence of relatively competent pegmatite veins on the small-scale F 2 folds. The very high D 2 strain has then amplified the dome and basin elements to very elongate cone and cylinder forms. This creates local type 1 patterns within a regional type 2 interference pattern structure.
Modeling concepts for communication of geometric shape data
NASA Technical Reports Server (NTRS)
Collins, M. F.; Emnett, R. F.; Magedson, R. L.; Shu, H. H.
1984-01-01
ANSI5, an abbreviation for Section 5 of the American National Standard under Engineering Drawing and Related Documentation Practices (Committee Y14) on Digital Representation for Communication of Product Definition Data (ANSI Y14.26M-1981), allows encoding of a broad range of geometric shapes to be communicated through digital channels. A brief review of its underlying concepts is presented. The intent of ANSI5 is to devise a unified set of concise language formats for transmission of data pertaining to five types of geometric entities in Euclidean 3 space (E(3)). These are regarded as point like, curve like, surface like, solid like, and a combination of these types. For the first four types, ANSI5 makes a distinction between the geometry and topology. Geometry is a description of the spatial occupancy of the entity, and topology discusses the interconnectedness of the entity's boundary components.
Deformation texture development in a model composite system
Poole, W.J.; MacEwen, S.; Kocks, U.F.; Embury, J.D.
1995-05-01
Model composites fabricated with a polycrystalline copper matrix and continuous tungsten fibres were deformed in plane strain compression with the fibres perpendicular to the loading axis and parallel to the direction of zero strain. The development of texture in the matrix due to deformation was measured using x-ray diffraction. It was observed that the macroscopic texture development in the composite was weaker than for unreinforced copper. The pattern of deformation in the matrix was quantified using experimental measurements and finite element method calculations. By carefully sectioning the composite after deformation, texture measurements were conducted for regions which exhibited characteristic types of deformation. These measurements showed that there is a variety of local textures (some weaker, some stronger than the texture in the unreinforced matrix) which when summed give the result of a weak global texture. This result is in agreement with the predictions from the computer simulations of Bolmaro et al.
Modeling and inversion of volcanic surface deformation based on Mogi model and McTigue model
NASA Astrophysics Data System (ADS)
Srigutomo, Wahyu; Trimadona, Martakusumah, Rocky; Anwar, Hairil
2015-04-01
Surface deformation occurred in a volcano is related strongly to the magmatic deformation beneath it. In this work we calculate the surface vertical and horizontal displacements due to hydrostatic pressure change of magma cavity based on point pressure source (Mogi) model and finite spherical source (McTigue) model. We apply the Levenberg-Marquardt inversion scheme to estimate the physical parameters contributing to the deformation.
Droplet Deformation Prediction With the Droplet Deformation and Breakup Model (DDB)
NASA Technical Reports Server (NTRS)
Vargas, Mario
2012-01-01
The Droplet Deformation and Breakup Model was used to predict deformation of droplets approaching the leading edge stagnation line of an airfoil. The quasi-steady model was solved for each position along the droplet path. A program was developed to solve the non-linear, second order, ordinary differential equation that governs the model. A fourth order Runge-Kutta method was used to solve the equation. Experimental slip velocities from droplet breakup studies were used as input to the model which required slip velocity along the particle path. The center of mass displacement predictions were compared to the experimental measurements from the droplet breakup studies for droplets with radii in the range of 200 to 700 mm approaching the airfoil at 50 and 90 m/sec. The model predictions were good for the displacement of the center of mass for small and medium sized droplets. For larger droplets the model predictions did not agree with the experimental results.
NASA Astrophysics Data System (ADS)
Rincon, Marta; Marquez, Alvaro; van Wyk de Vries, Benjamin; Herrera, Raquel; Granja Bruña, Jose Luis; Llanes, Pilar
2014-05-01
The morphology of volcanoes provides important information about edifice evolution. Volcanoes can deform by gravitational instability and intrusions. This deformation can compromise volcano structural stability, promoting flank collapse even at dormant edifices. Identification of past/active deformation processes is therefore important not only for the understanding of volcano evolution but also for volcanic hazards. Both deformation due to the flank spreading of a volcano over its weak core and due to the intrusion of a cryptodome in the volcano edifice can produce faulting and changes in the morphology of volcano flanks. These morpho-structural changes in the volcano open the possibility to identify potential deformed and unstable volcanoes using remote sensing techniques and DEMs. We have used analogue models of flank spreading and intrusion processes to make progress in the morpho-structural identification of deformation features which can provide criteria for distinguishing processes. We have geometrically and mechanically scaled two different sets of experiments using a sand-plaster mixture for volcano materials, silicone putty for weak core rocks and Golden Syrup for magma intrusions. For monitoring changes in the volcano morphology we have used a Kinect sensor (Microsoft), which provides us vertical displacements of volcano flanks several times per second with a 1 mm precision. We have synchronized the Kinect sensor with a digital camera for monitoring the spatio-temporal evolution of tectonic structures together with morphology. All experiments produce asymmetrical changes in volcano morphology, developing convex-concave geometries in the deformed flank. However, the spatial relationships of structures with changes in volcano flank curvature are different for the two processes, as noted by previous authors. The morphometric tools developed for analyzing volcano topography allow us to identify intrusion processes due to volcano volume increase. We have
On the impact of reducing global geophysical fluid model deformations in SLR data processing
NASA Astrophysics Data System (ADS)
Weigelt, Matthias; Thaller, Daniela
2016-04-01
Mass redistributions in the atmosphere, oceans and the continental hydrology cause elastic loading deformations of the Earth's crust and thus systematically influence Earth-bound observation systems such as VLBI, GNSS or SLR. Causing non-linear station variations, these loading deformations have a direct impact on the estimated station coordinates and an indirect impact on other parameters of global space-geodetic solutions, e.g. Earth orientation parameters, geocenter coordinates, satellite orbits or troposphere parameters. Generally, the impact can be mitigated by co-parameterisation or by reducing deformations derived from global geophysical fluid models. Here, we focus on the latter approach. A number of data sets modelling the (non-tidal) loading deformations are generated by various groups. They show regionally and locally significant differences and consequently the impact on the space-geodetic solutions heavily depends on the available network geometry. We present and discuss the differences between these models and choose SLR as the speace-geodetic technique of interest in order to discuss the impact of atmospheric, oceanic and hydrological loading on the parameters of space-geodetic solutions when correcting for the global geophysical fluid models at the observation level. Special emphasis is given to a consistent usage of models for geometric and gravimetric corrections during the data processing. We quantify the impact of the different deformation models on the station coordinates and discuss the improvement in the Earth orientation parameters and the geocenter motion. We also show that a significant reduction in the RMS of the station coordinates can be achieved depending on the model of choice.
Modelling continental deformation within global plate tectonic reconstructions
NASA Astrophysics Data System (ADS)
Williams, S.; Whittaker, J.; Heine, C.; Müller, P.
2010-12-01
A limitation of regional and global plate tectonic models is the way continental deformation is represented. Continental blocks are typically represented as rigid polygons - overlaps or gaps between adjacent continental blocks represent extension or compression respectively. Full-fit reconstructions of major ocean basins result in large overlaps between the conjugate continental plates, on the basis that the continental margins are highly extended compared to their pre-rift state. A fundamental challenge in generating more robust global-scale plate reconstructions is the incorporation of a more quantitative description of the kinematics within extended passive margins, based on observations. We have used the conjugate Southern Australia and Wilkes Land, Antarctica margins as a case study, and as part of this work have generated revised sediment thickness maps for these margins. These datasets are used to test different approaches for generating full-fit reconstructions in order to create a framework of methodologies that is globally applicable. One approach is to restore two conjugate continent-ocean boundaries (COBs) to their pre-rift configuration and then use the geometric fitting method of Hellinger (1981) and Royer and Chang (1991), used to generate fits of seafloor isochrons, to generate a “full-fit” Euler pole. To quantitatively restore the COBs to their palinspastic pre-rift configuration we integrate estimates of crustal thickness along small circle paths, defined by an initial estimate of the Euler stage pole describing plate motions during continental rifting. We then use the conjugate sets of restored COB’s as inputs to the geometric fitting method, treating them as isochrons, and so generate poles of rotation for the plate configuration prior to rifting. Two potential shortcomings of this methodology are that (1) the conjugate margins are treated independently, whereas in reality they were actually one continuous continental basin during rifting
Deformable models with sparsity constraints for cardiac motion analysis.
Yu, Yang; Zhang, Shaoting; Li, Kang; Metaxas, Dimitris; Axel, Leon
2014-08-01
Deformable models integrate bottom-up information derived from image appearance cues and top-down priori knowledge of the shape. They have been widely used with success in medical image analysis. One limitation of traditional deformable models is that the information extracted from the image data may contain gross errors, which adversely affect the deformation accuracy. To alleviate this issue, we introduce a new family of deformable models that are inspired from the compressed sensing, a technique for accurate signal reconstruction by harnessing some sparseness priors. In this paper, we employ sparsity constraints to handle the outliers or gross errors, and integrate them seamlessly with deformable models. The proposed new formulation is applied to the analysis of cardiac motion using tagged magnetic resonance imaging (tMRI), where the automated tagging line tracking results are very noisy due to the poor image quality. Our new deformable models track the heart motion robustly, and the resulting strains are consistent with those calculated from manual labels. PMID:24721617
Battaglia, Maurizio; Cervelli; Peter, F.; Murray, Jessica R.
2013-01-01
This manual provides the physical and mathematical concepts for selected models used to interpret deformation measurements near active faults and volcanic centers. The emphasis is on analytical models of deformation that can be compared with data from the Global Positioning System (GPS) receivers, Interferometric synthetic aperture radar (InSAR), leveling surveys, tiltmeters and strainmeters. Source models include pressurized spherical, ellipsoidal, and horizontal penny-shaped geometries in an elastic, homogeneous, flat half-space. Vertical dikes and faults are described following the mathematical notation for rectangular dislocations in an elastic, homogeneous, flat half-space. All the analytical expressions were verified against numerical models developed by use of COMSOL Multyphics, a Finite Element Analysis software (http://www.comsol.com). In this way, typographical errors present were identified and corrected. Matlab scripts are also provided to facilitate the application of these models.
A geometric level set model for ultrasounds analysis
Sarti, A.; Malladi, R.
1999-10-01
We propose a partial differential equation (PDE) for filtering and segmentation of echocardiographic images based on a geometric-driven scheme. The method allows edge-preserving image smoothing and a semi-automatic segmentation of the heart chambers, that regularizes the shapes and improves edge fidelity especially in presence of distinct gaps in the edge map as is common in ultrasound imagery. A numerical scheme for solving the proposed PDE is borrowed from level set methods. Results on human in vivo acquired 2D, 2D+time,3D, 3D+time echocardiographic images are shown.
A fractal model for crustal deformation
NASA Technical Reports Server (NTRS)
Turcotte, D. L.
1986-01-01
It is hypothesized that crustal deformation occurs on a scale-invariant matrix of faults. For simplicity, a two-dimensional pattern of hexagons on which strike-slip faulting occurs is considered. The behavior of the system is controlled by a single parameter, the fractal dimension. Deformation occurs on all scales of faults. The fractal dimension determines the fraction of the total displacement that occurs on the first-order or primary faults. The value of the fractal dimension can be obtained from the frequency-magnitude relation for earthquakes. The results are applied to the San Andreas fault system in central California. Earthquake studies give D = 1.90. The main strand of the San Andreas fault is associated with the primary faults of the fractal system. It is predicted that the relative velocity across the main strand is 2.93 cm/yr. The remainder of the relative velocity of 5.5 cm/yr between the Pacific and North American plates occurs on higher-order faults. The predicted value is in reasonably good agreement with the value 3.39 + or - 0.29 cm/yr obtained from geological studies.
Fluctuating Nonlinear Spring Model of Mechanical Deformation of Biological Particles.
Kononova, Olga; Snijder, Joost; Kholodov, Yaroslav; Marx, Kenneth A; Wuite, Gijs J L; Roos, Wouter H; Barsegov, Valeri
2016-01-01
The mechanical properties of virus capsids correlate with local conformational dynamics in the capsid structure. They also reflect the required stability needed to withstand high internal pressures generated upon genome loading and contribute to the success of important events in viral infectivity, such as capsid maturation, genome uncoating and receptor binding. The mechanical properties of biological nanoparticles are often determined from monitoring their dynamic deformations in Atomic Force Microscopy nanoindentation experiments; but a comprehensive theory describing the full range of observed deformation behaviors has not previously been described. We present a new theory for modeling dynamic deformations of biological nanoparticles, which considers the non-linear Hertzian deformation, resulting from an indenter-particle physical contact, and the bending of curved elements (beams) modeling the particle structure. The beams' deformation beyond the critical point triggers a dynamic transition of the particle to the collapsed state. This extreme event is accompanied by a catastrophic force drop as observed in the experimental or simulated force (F)-deformation (X) spectra. The theory interprets fine features of the spectra, including the nonlinear components of the FX-curves, in terms of the Young's moduli for Hertzian and bending deformations, and the structural damage dependent beams' survival probability, in terms of the maximum strength and the cooperativity parameter. The theory is exemplified by successfully describing the deformation dynamics of natural nanoparticles through comparing theoretical curves with experimental force-deformation spectra for several virus particles. This approach provides a comprehensive description of the dynamic structural transitions in biological and artificial nanoparticles, which is essential for their optimal use in nanotechnology and nanomedicine applications. PMID:26821264
Fluctuating Nonlinear Spring Model of Mechanical Deformation of Biological Particles
Kononova, Olga; Snijder, Joost; Kholodov, Yaroslav; Marx, Kenneth A.; Wuite, Gijs J. L.; Roos, Wouter H.; Barsegov, Valeri
2016-01-01
The mechanical properties of virus capsids correlate with local conformational dynamics in the capsid structure. They also reflect the required stability needed to withstand high internal pressures generated upon genome loading and contribute to the success of important events in viral infectivity, such as capsid maturation, genome uncoating and receptor binding. The mechanical properties of biological nanoparticles are often determined from monitoring their dynamic deformations in Atomic Force Microscopy nanoindentation experiments; but a comprehensive theory describing the full range of observed deformation behaviors has not previously been described. We present a new theory for modeling dynamic deformations of biological nanoparticles, which considers the non-linear Hertzian deformation, resulting from an indenter-particle physical contact, and the bending of curved elements (beams) modeling the particle structure. The beams’ deformation beyond the critical point triggers a dynamic transition of the particle to the collapsed state. This extreme event is accompanied by a catastrophic force drop as observed in the experimental or simulated force (F)-deformation (X) spectra. The theory interprets fine features of the spectra, including the nonlinear components of the FX-curves, in terms of the Young’s moduli for Hertzian and bending deformations, and the structural damage dependent beams’ survival probability, in terms of the maximum strength and the cooperativity parameter. The theory is exemplified by successfully describing the deformation dynamics of natural nanoparticles through comparing theoretical curves with experimental force-deformation spectra for several virus particles. This approach provides a comprehensive description of the dynamic structural transitions in biological and artificial nanoparticles, which is essential for their optimal use in nanotechnology and nanomedicine applications. PMID:26821264
Effect of Shear Deformation and Continuity on Delamination Modelling with Plate Elements
NASA Technical Reports Server (NTRS)
Glaessgen, E. H.; Riddell, W. T.; Raju, I. S.
1998-01-01
The effects of several critical assumptions and parameters on the computation of strain energy release rates for delamination and debond configurations modeled with plate elements have been quantified. The method of calculation is based on the virtual crack closure technique (VCCT), and models that model the upper and lower surface of the delamination or debond with two-dimensional (2D) plate elements rather than three-dimensional (3D) solid elements. The major advantages of the plate element modeling technique are a smaller model size and simpler geometric modeling. Specific issues that are discussed include: constraint of translational degrees of freedom, rotational degrees of freedom or both in the neighborhood of the crack tip; element order and assumed shear deformation; and continuity of material properties and section stiffness in the vicinity of the debond front, Where appropriate, the plate element analyses are compared with corresponding two-dimensional plane strain analyses.
Patient-specific liver deformation modeling for tumor tracking
NASA Astrophysics Data System (ADS)
Oh, Young-Taek; Hwang, Youngkyoo; Kim, Jung-Bae; Bang, Won-Chul; Kim, James D. K.; Kim, Chang Yeong
2013-03-01
We present a new method for patient-specific liver deformation modeling for tumor tracking. Our method focuses on deforming two main blood vessels of the liver - hepatic and portal vein - to utilize them as features. A novel centerline editing algorithm based on ellipse fitting is introduced for vessel deformation. Centerline-based blood vessel model and various interpolation methods are often used for generating a deformed model at the specific time t. However, it may introduce artifacts when models used in interpolation are not consistent. One of main reason of this inconsistency is the location of bifurcation points differs from each image. To solve this problem, our method generates a base model from one of patient's CT images. Next, we apply a rigid iterative closest point (ICP) method to the base model with centerlines of other images. Because the transformation is rigid, the length of each vessel's centerline is preserved while some part of the centerline is slightly deviated from centerlines of other images. We resolve this mismatch using our centerline editing algorithm. Finally, we interpolate three deformed models of liver, blood vessels, tumor using quadratic Bézier curves. We demonstrate the effectiveness of the proposed approach with the real patient data.
Performance Analysis of Tandem-L Mission for Modeling Volcanic and Seismic Deformation Sources
NASA Astrophysics Data System (ADS)
Ansari, Homa; Goel, Kanika; Parizzi, Alessandro; Sudhaus, Henriette; Adam, Nico; Eineder, Michael
2015-04-01
Although a great number of publications have focused on the application of InSAR in deformation source modeling as well as the development of different algorithms in this regard, little investigation has been dedicated to the sensitivity analysis of the InSAR in deformation source modeling. Our purpose is to address this issue by analyzing the reliability of InSAR in modeling the deformation sources due to landslides, seismic and volcanic activities, with special focus on the L band SAR measurements. The sensitivity analysis is considered for three commonly used geophysical models in case of subsidence, seismic and volcanic activities; namely, the Gaussian subsidence bowl, Okada and Mogi point source, respectively. In each of the cases, the InSAR sensitivity is analytically formulated and its performance is investigated using simulated SAR data. The investigations are carried out using stochastic error propagation approaches to infer the precision of the models' parameters as well as their mutual covariance. The limiting factors in SAR interferometry are categorized in two groups and investigated separately in sensitivity analysis; with the first dealing with the geometrical limits imposed by the side looking geometry of the SAR measurements and the second focusing on the InSAR stochastic characteristics in the L band.
Collaborative multi organ segmentation by integrating deformable and graphical models.
Uzunbaş, Mustafa Gökhan; Chen, Chao; Zhang, Shaoting; Poh, Kilian M; Li, Kang; Metaxas, Dimitris
2013-01-01
Organ segmentation is a challenging problem on which significant progress has been made. Deformable models (DM) and graphical models (GM) are two important categories of optimization based image segmentation methods. Efforts have been made on integrating two types of models into one framework. However, previous methods are not designed for segmenting multiple organs simultaneously and accurately. In this paper, we propose a hybrid multi organ segmentation approach by integrating DM and GM in a coupled optimization framework. Specifically, we show that region-based deformable models can be integrated with Markov Random Fields (MRF), such that multiple models' evolutions are driven by a maximum a posteriori (MAP) inference. It brings global and local deformation constraints into a unified framework for simultaneous segmentation of multiple objects in an image. We validate this proposed method on two challenging problems of multi organ segmentation, and the results are promising. PMID:24579136
Cheung, Y; Sawant, A
2014-06-15
Purpose: Most clinically-deployed strategies for respiratory motion management in lung radiotherapy (e.g., gating, tracking) use external markers that serve as surrogates for tumor motion. However, typical lung phantoms used to validate these strategies are rigid-exterior+rigid-interior or rigid-exterior+deformable-interior. Neither class adequately represents the human anatomy, which is deformable internally as well as externally. We describe the construction and experimental validation of a more realistic, externally- and internally-deformable, programmable lung phantom. Methods: The outer shell of a commercially-available lung phantom (RS- 1500, RSD Inc.) was used. The shell consists of a chest cavity with a flexible anterior surface, and embedded vertebrae, rib-cage and sternum. A 3-axis platform was programmed with sinusoidal and six patient-recorded lung tumor trajectories. The platform was used to drive a rigid foam ‘diaphragm’ that compressed/decompressed the phantom interior. Experimental characterization comprised of mapping the superior-inferior (SI) and anterior-posterior (AP) trajectories of external and internal radioopaque markers with kV x-ray fluoroscopy and correlating these with optical surface monitoring using the in-room VisionRT system. Results: The phantom correctly reproduced the programmed motion as well as realistic effects such as hysteresis. The reproducibility of marker trajectories over multiple runs for sinusoidal as well as patient traces, as characterized by fluoroscopy, was within 0.4 mm RMS error for internal as well as external markers. The motion trajectories of internal and external markers as measured by fluoroscopy were found to be highly correlated (R=0.97). Furthermore, motion trajectories of arbitrary points on the deforming phantom surface, as recorded by the VisionRT system also showed a high correlation with respect to the fluoroscopically-measured trajectories of internal markers (R=0.92). Conclusion: We have
Hippocampal Shape Modeling Based on a Progressive Template Surface Deformation and its Verification.
Kim, Jaeil; Valdes-Hernandez, Maria Del C; Royle, Natalie A; Park, Jinah
2015-06-01
Accurately recovering the hippocampal shapes against rough and noisy segmentations is as challenging as achieving good anatomical correspondence between the individual shapes. To address these issues, we propose a mesh-to-volume registration approach, characterized by a progressive model deformation. Our model implements flexible weighting scheme for model rigidity under a multi-level neighborhood for vertex connectivity. This method induces a large-to-small scale deformation of a template surface to build the pairwise correspondence by minimizing geometric distortion while robustly restoring the individuals' shape characteristics. We evaluated the proposed method's (1) accuracy and robustness in smooth surface reconstruction, (2) sensitivity in detecting significant shape differences between healthy control and disease groups (mild cognitive impairment and Alzheimer's disease), (3) robustness in constructing the anatomical correspondence between individual shape models, and (4) applicability in identifying subtle shape changes in relation to cognitive abilities in a healthy population. We compared the performance of the proposed method with other well-known methods--SPHARM-PDM, ShapeWorks and LDDMM volume registration with template injection--using various metrics of shape similarity, surface roughness, volume, and shape deformity. The experimental results showed that the proposed method generated smooth surfaces with less volume differences and better shape similarity to input volumes than others. The statistical analyses with clinical variables also showed that it was sensitive in detecting subtle shape changes of hippocampus. PMID:25532173
NASA Astrophysics Data System (ADS)
Burkett, Michael; Clancy, Sean; Maudlin, Paul; Holian, Kathleen
2001-06-01
: Previously developed constitutive models and solution algorithms for anisotropic elastoplastic material strength has been implemented in the three-dimensional CONEJO hydrodynamics code. CONEJO is an explicit, Eulerian continuum mechanics code that is utilized to predict formation processes associated with material deformation at elevated strain-rates and is a code development project under the Accelerated Strategic Computing Initiative (ASCI) program. Some special features of CONEJO include a high-order advection algorithm, a material interface tracking scheme, and van Leer monotonic advection-limiting. The anisotropic constitutive modeling is posed in an unrotated material frame using the theorem of polar decomposition to describe rigid body rotation. An Euler-Rodrigues description is used to quantify the rigid body rotations. Continuous quadratic yield functions fitted from polycrystal simulations for a metallic hexagonal-close-packed structure were utilized. Associative flow formulations incorporating these yield functions were solved using a geometric normal return method. Simple rectangular shear problems, "R-value" problems, and Taylor cylinder impact test data were utilized to verify and validate the implementation of the anisotropic model. A "stretching rod" problem (involving large strain and strain-rate deformation) was selected to investigate the effects of material anisotropy for this deformation process. The rod necking rate and topology was compared for CONEJO simulations using several isotropic and anisotropic descriptions that utilized the Mechanical Threshold Stress (MTS) model.
NASA Astrophysics Data System (ADS)
Svehla, Drazen; Rothacher, Markus; Hugentobler, Urs; Steigenberger, Peter; Ziebart, Marek
2014-05-01
Solar radiation pressure is the main source of errors in the precise orbit determination of GNSS satellites. All deficiencies in the modeling of Solar radiation pressure map into estimated terrestrial reference frame parameters as well as into derived gravity field coefficients and altimetry results when LEO orbits are determined using GPS. Here we introduce a new approach to geometrically map radial orbit perturbations of GNSS satellites using highly-performing clocks on board the first Galileo satellites. Only a linear model (time bias and time drift) needs to be removed from the estimated clock parameters and the remaining clock residuals map all radial orbit perturbations along the orbit. With the independent SLR measurements, we show that a Galileo clock is stable enough to map radial orbit perturbations continuously along the orbit with a negative sign in comparison to SLR residuals. Agreement between the SLR residuals and the clock residuals is at the 1 cm RMS for an orbit arc of 24 h. Looking at the clock parameters determined along one orbit revolution over a period of one year, we show that the so-called SLR bias in Galileo and GPS orbits can be explained by the translation of the determined orbit in the orbital plane towards the Sun. This orbit translation is due to thermal re-radiation and not accounting for the Sun elevation in the parameterization of the estimated Solar radiation pressure parameters. SLR ranging to GNSS satellites takes place typically at night, e.g. between 6 pm and 6 am local time when the Sun is in opposition to the satellite. Therefore, SLR observes only one part of the GNSS orbit with a negative radial orbit error that is mapped as an artificial bias in SLR observables. The Galileo clocks clearly show orbit translation for all Sun elevations: the radial orbit error is positive when the Sun is in conjuction (orbit noon) and negative when the Sun is in opposition (orbit midnight). The magnitude of this artificial negative SLR bias
Sparse deformable models with application to cardiac motion analysis.
Yu, Yang; Zhang, Shaoting; Huang, Junzhou; Metaxas, Dimitris; Axel, Leon
2013-01-01
Deformable models have been widely used with success in medical image analysis. They combine bottom-up information derived from image appearance cues, with top-down shape-based constraints within a physics-based formulation. However, in many real world problems the observations extracted from the image data often contain gross errors, which adversely affect the deformation accuracy. To alleviate this issue, we introduce a new family of deformable models that are inspired from compressed sensing, a technique for efficiently reconstructing a signal based on its sparseness in some domain. In this problem, we employ sparsity to represent the outliers or gross errors, and combine it seamlessly with deformable models. The proposed new formulation is applied to the analysis of cardiac motion, using tagged magnetic resonance imaging (tMRI), where the automated tagging line tracking results are very noisy due to the poor image quality. Our new deformable models track the heart motion robustly, and the resulting strains are consistent with those calculated from manual labels. PMID:24683970
Computational model of deformable lenses actuated by dielectric elastomers
NASA Astrophysics Data System (ADS)
Lu, Tongqing; Cai, Shengqiang; Wang, Huiming; Suo, Zhigang
2013-09-01
A recent design of deformable lens mimics the human eye, adjusting its focal length in response to muscle-like actuation. The artificial muscle is a membrane of a dielectric elastomer subject to a voltage. Here, we calculate the coupled and inhomogeneous deformation of the lens and the dielectric elastomer actuator by formulating a nonlinear boundary-value problem. We characterize the strain-stiffening elastomer with the Gent model and describe the voltage-induced deformation using the model of ideal dielectric elastomer. The computational predictions agree well with experimental data. We use the model to explore the space of parameters, including the prestretch of the membrane, the volume of the liquid in the lens, and the size of the dielectric elastomer actuator relative to the lens. We examine how various modes of failure limit the minimum radius of curvature.
Interpretation of postseismic deformation with a viscoelastic relaxation model
NASA Technical Reports Server (NTRS)
Wahr, J.; Wyss, M.
1980-01-01
A viscoelastic relaxation model is used to interpret postseismic surface deformation for the large-magnitude Aleutian earthquakes of 1957 and 1965. The lithosphere and asthenosphere are modeled as elastic solids with an anomalous viscoelastic inclusion below the island arc volcanoes. It is found that the observed postseismic surface deformation is a corollary of the known island arc structure. A satisfactory fit to the uplift following the 1957 earthquake is found for a viscoelastic volume with 80-km width extending from a depth of 50 to 200 km.
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.
NASA Astrophysics Data System (ADS)
Yan, Dongmei; Wang, Fenfei; Kou, Tianyou; Chen, Shirong
2010-11-01
With the start tracker and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), SPOT5 satellite point positioning error is lower than 50m. In this paper, two terrains, mountainous areas and plain areas, are defined by terrain gradient. The ground check points are chosen on these terrains with the geometric error and the elevation error both lower than 1m. The coordinate in UTM of each point is calculated both in the Rigorous Sensor Model and the Simple Polynomial Direct Location Model, and the differences between the computed coordinates and the surveyed coordinates are discussed. According to the experiment results, the two models have their own advantage in different circumstances. In mountainous areas, the Rigorous Sensor Model can get higher location accuracy. In plain areas, the two models can locate with same accuracy, but the Simple Polynomial Direct Location Model performs better in the aspect of speed and the simplicity.
Matrix model description of baryonic deformations
Bena, Iosif; Murayama, Hitoshi; Roiban, Radu; Tatar, Radu
2003-03-13
We investigate supersymmetric QCD with N{sub c} + 1 flavors using an extension of the recently proposed relation between gauge theories and matrix models.The impressive agreement between the two sides provides a beautiful confirmation of the extension of the gauge theory-matrix model relation to this case.
Wang, L.; Barabash, R. I.; Yang, Y.; Bieler, T. R.; Crimp, M. A.; Eisenlohr, P.; Liu, W.; Ice, G. E.
2011-03-01
Grain-level heterogeneous deformation was studied in a polycrystalline {alpha}-Ti specimen deformed by four-point bending. Dislocation slip activity in the microstructure was investigated by surface slip trace analysis. Three-dimensional-X-ray diffraction (3D-XRD) was used to investigate subsurface lattice rotations and to identify geometrically necessary dislocations (GNDs). The slip systems of local GNDs were analyzed by studying the streaking directions of reflections in corresponding Laue patterns. The analysis performed in one grain indicated that the subsurface GNDs were from the same slip system identified using slip trace analysis in backscattered electron images. A crystal plasticity finite element (CPFE) model was used to simulate deformation of the same microstructural region. The predictions of dislocation slip activity match the general aspects of the experimental observations, including the ability to simulate the activation of different slip systems in grains where multiple slip systems were activated. Prediction of local crystal rotations, however, was the least accurate aspect of the CPFE model.
Wang, Leyun; Barabash, Rozaliya; Yang, Y; Bieler, Prof T R; Crimp, Prof M A; Eisenlohr, P; Liu, W.; Ice, Gene E
2011-01-01
Grain-level heterogeneous deformation was studied in a polycrystalline {alpha}-Ti specimen deformed by four-point bending. Dislocation slip activity in the microstructure was investigated by surface slip trace analysis. Three-dimensional-X-ray diffraction (3D-XRD) was used to investigate subsurface lattice rotations and to identify geometrically necessary dislocations (GNDs). The slip systems of local GNDs were analyzed by studying the streaking directions of reflections in corresponding Laue patterns. The analysis performed in one grain indicated that the subsurface GNDs were from the same slip system identified using slip trace analysis in backscattered electron images. A crystal plasticity finite element (CPFE) model was used to simulate deformation of the same microstructural region. The predictions of dislocation slip activity match the general aspects of the experimental observations, including the ability to simulate the activation of different slip systems in grains where multiple slip systems were activated. Prediction of local crystal rotations, however, was the least accurate aspect of the CPFE model.
Modeling deformation behavior of the baseball.
Nicholls, Rochelle Llewelyn; Miller, Karol; Elliott, Bruce C
2005-02-01
Regulating ball response to impact is one way to control ball exit velocity in baseball. This is necessary to reduce injuries to defensive players and maintain the balance between offense and defense in the game. This paper presents a model for baseball velocity-dependent behavior. Force-displacement data were obtained using quasi-static compression tests to 50% of ball diameter (n = 70 baseballs). The force-displacement curves for a very stiff baseball (Model B) and a softer type (Model C) were characterized by a Mooney-Rivlin model using implicit finite element analysis (ANSYS software, version 6.1). Agreement between experimental and numerical results was excellent for both Model B (C(10) = 0, C(01) = 3.7e(6) Pa) and Model C (C(10) = 0, C(01) = 2.6e(6) Pa). However, this material model was not available in the ANSYS/LSDYNA explicit dynamic software (version 6.1) used to quantify the transient behavior of the ball. Therefore the modeling process was begun again using a linear viscoelastic material. G(infinity), the long-term shear modulus of the material, was determined by the same implicit FEA procedure. Explicit FEA was used to quantify the time-dependent response of each ball in terms of instantaneous shear modulus (G0) and a decay term (beta). The results were evaluated with respect to published experimental data for the ball coefficient of restitution at five velocities (13.4-40.2 ms(-1)) and were in agreement with the experimental values. The model forms the basis for future research on baseball response to impact with the bat. PMID:16131702
NASA Astrophysics Data System (ADS)
Bartlewska-Urban, Monika; Zombroń, Marek; Strzelecki, Tomasz
2016-03-01
The following study presents numerical calculations for establishing the impact of temperature changes on the process of distortion of bi-phase medium represented using Biot consolidation equations with Kelvin-Voigt rheological skeleton presented, on the example of thermo-consolidation of a pavement of expressway S17. We analyzed the behavior of the expressway under the action of its own weight, dynamic load caused by traffic and temperature gradient. This paper presents the application of the Biot consolidation model with the Kelvin-Voigt skeleton rheological characteristics and the influence of temperature on the deformation process is taken into account. A three-dimensional model of the medium was created describing the thermal consolidation of a porous medium. The 3D geometrical model of the area under investigation was based on data obtained from the land surveying and soil investigation of a 200 m long section of the expressway and its shoulders.
Target Recognition Using Neural Networks for Model Deformation Measurements
NASA Technical Reports Server (NTRS)
Ross, Richard W.; Hibler, David L.
1999-01-01
Optical measurements provide a non-invasive method for measuring deformation of wind tunnel models. Model deformation systems use targets mounted or painted on the surface of the model to identify known positions, and photogrammetric methods are used to calculate 3-D positions of the targets on the model from digital 2-D images. Under ideal conditions, the reflective targets are placed against a dark background and provide high-contrast images, aiding in target recognition. However, glints of light reflecting from the model surface, or reduced contrast caused by light source or model smoothness constraints, can compromise accurate target determination using current algorithmic methods. This paper describes a technique using a neural network and image processing technologies which increases the reliability of target recognition systems. Unlike algorithmic methods, the neural network can be trained to identify the characteristic patterns that distinguish targets from other objects of similar size and appearance and can adapt to changes in lighting and environmental conditions.
NASA Astrophysics Data System (ADS)
Takizawa, Kenji; Tezduyar, Tayfun E.; Boben, Joseph; Kostov, Nikolay; Boswell, Cody; Buscher, Austin
2013-12-01
To increase aerodynamic performance, the geometric porosity of a ringsail spacecraft parachute canopy is sometimes increased, beyond the "rings" and "sails" with hundreds of "ring gaps" and "sail slits." This creates extra computational challenges for fluid-structure interaction (FSI) modeling of clusters of such parachutes, beyond those created by the lightness of the canopy structure, geometric complexities of hundreds of gaps and slits, and the contact between the parachutes of the cluster. In FSI computation of parachutes with such "modified geometric porosity," the flow through the "windows" created by the removal of the panels and the wider gaps created by the removal of the sails cannot be accurately modeled with the Homogenized Modeling of Geometric Porosity (HMGP), which was introduced to deal with the hundreds of gaps and slits. The flow needs to be actually resolved. All these computational challenges need to be addressed simultaneously in FSI modeling of clusters of spacecraft parachutes with modified geometric porosity. The core numerical technology is the Stabilized Space-Time FSI (SSTFSI) technique, and the contact between the parachutes is handled with the Surface-Edge-Node Contact Tracking (SENCT) technique. In the computations reported here, in addition to the SSTFSI and SENCT techniques and HMGP, we use the special techniques we have developed for removing the numerical spinning component of the parachute motion and for restoring the mesh integrity without a remesh. We present results for 2- and 3-parachute clusters with two different payload models.
Geometrical Standard Model Enhancements to the Standard Model of Particle Physics
NASA Astrophysics Data System (ADS)
Strickland, Ken; Duvernois, Michael
2011-10-01
The Standard Model (SM) is the triumph of our age. As experimentation at the LHC tracks particles for the Higgs phenomena, theoreticians and experimentalist struggle to close in on a cohesive theory. Both suffer greatly as expectation waivers those who seek to move beyond the SM and those who cannot do without. When it seems like there are no more good ideas enter Rate Change Graph Technology (RCGT). From the science of the rate change graph, a Geometrical Standard Model (GSM) is available for comprehensive modeling, giving rich new sources of data and pathways to those ultimate answers we punish ourselves to achieve. As a new addition to science, GSM is a tool that provides a structured discovery and analysis environment. By eliminating value and size, RCGT operates with the rules of RCGT mechanics creating solutions derived from geometry. The GSM rate change graph could be the ultimate validation of the Standard Model yet. In its own right, GSM is created from geometrical intersections and comes with RCGT mechanics, yet parallels the SM to offer critical enhancements. The Higgs Objects along with a host of new objects are introduced to the SM and their positions revealed in this proposed modification to the SM.
Human supervisory approach to modeling industrial scenes using geometric primitives
Luck, J.P.; Little, C.Q.; Roberts, R.S.
1997-11-19
A three-dimensional world model is crucial for many robotic tasks. Modeling techniques tend to be either fully manual or autonomous. Manual methods are extremely time consuming but also highly accurate and flexible. Autonomous techniques are fast but inflexible and, with real-world data, often inaccurate. The method presented in this paper combines the two, yielding a highly efficient, flexible, and accurate mapping tool. The segmentation and modeling algorithms that compose the method are specifically designed for industrial environments, and are described in detail. A mapping system based on these algorithms has been designed. It enables a human supervisor to quickly construct a fully defined world model from unfiltered and unsegmented real-world range imagery. Examples of how industrial scenes are modeled with the mapping system are provided.
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.
Deformable part models for object detection in medical images
2014-01-01
Background Object detection in 3-D medical images is often necessary for constraining a segmentation or registration task. It may be a task in its own right as well, when instances of a structure, e.g. the lymph nodes, are searched. Problems from occlusion, illumination and projection do not arise, making the problem simpler than object detection in photographies. However, objects of interest are often not well contrasted against the background. Influence from noise and other artifacts is much stronger and shape and appearance may vary substantially within a class. Methods Deformable models capture the characteristic shape of an anatomic object and use constrained deformation for hypothesing object boundaries in image regions of low or non-existing contrast. Learning these constraints requires a large sample data base. We show that training may be replaced by readily available user knowledge defining a prototypical deformable part model. If structures have a strong part-relationship, or if they may be found based on spatially related guiding structures, or if the deformation is rather restricted, the supporting data information suffices for solving the detection task. We use a finite element model to represent anatomic variation by elastic deformation. Complex shape variation may be represented by a hierarchical model with simpler part variation. The hierarchy may be represented explicitly as a hierarchy of sub-shapes, or implicitly by a single integrated model. Data support and model deformation of the complete model can be represented by an energy term, serving as quality-of-fit function for object detection. Results The model was applied to detection and segmentation tasks in various medical applications in 2- and 3-D scenes. It has been shown that model fitting and object detection can be carried out efficiently by a combination of a local and global search strategy using models that are parameterized for the different tasks. Conclusions A part-based elastic
A New Model for Episodic Caldera Deformation at Yellowstone
NASA Astrophysics Data System (ADS)
Cervelli, P. F.; Gervais, S. M.; Lowenstern, J. B.; Wicks, C. W.
2012-12-01
For nearly 90 years, geodetic measurements at Yellowstone have shown recurring episodes of uplift and subsidence confined mostly to the caldera but also extending into the Norris Geyser Basin. The most recent such episode began in late 2004 with the onset of caldera-wide uplift that continued for about 5 years before switching to subsidence in late 2009. The physical mechanism driving the deformation is unknown, though several researchers have proposed kinematic models that can reproduce the observed data. The "Lake" earthquake swarm, which occurred in the northern part of Yellowstone Lake from December 2008 through January 2009, provides a new constraint on caldera deformation models. The timing of the swarm correlates with an abrupt change in local deformation, which preceded the gradual transition from uplift to subsidence in late 2009. Thus, caldera deformation, at least in the vicinity of Yellowstone Lake, consists of two (or more) distinct parts, implying the existence of two (or more) distinct deformation sources. This fresh information leads us to propose a new kinematic model for deformation at Yellowstone, which we develop from the last 15 years of continuous GPS and InSAR data. Our new model consists of three deformation sources: (1) a cauldron block source that is subject to a constant displacement at its base while its surrounding ring fault remains locked; (2) a pressurizing (or depressurizing) spherical cavity near the Norris Geyser Basin, which is known to deform separately from the caldera; and (3) a pressurizing (or depressurizing) spherical cavity at the Sour Creek Dome, which we infer from the abrupt change in deformation rate after the Lake Swarm. We use the GPS and InSAR data from the period of strongest signal, summer 2005 through summer 2007, to optimize the geometry of the three sources: the locations and depths of the spherical cavity, and the perimeter of the cauldron block. We then, while holding their geometry fixed, estimate the
NASA Astrophysics Data System (ADS)
Raziperchikolaee, S.; Alvarado, V.; Yin, S.
2014-09-01
Studying rock joint deformation including both slippage and opening mechanisms provides an opportunity to investigate the connection between the permeability and seismic source mechanisms. A microscale fluid flow-geomechanics-seismicity model was built to evaluate the transport response and failure mechanism of microcracks developed along a joint in Berea sandstone samples during deformation. The modeling method considers comprehensive grain-cement interactions. Fluid flow behavior is obtained through a realistic network model of the pore space in the compacted assembly. The geometric description of the complex pore structure is characterized to predict permeability of the rock sample as a function of rock deformation by using a dynamic pore network model. As a result of microcracks development, forces and displacements in grains involved in bond breakage are measured to determine seismic moment tensor. Shear and nonshear displacements are applied to the joint samples to investigate their effects on permeability evolution and failure mechanism of microcracks during joint deformation. In addition, the effect of joint roughness is analyzed by performing numerical compression tests. We also investigate how confining pressure affects volumetric deformation leading to opening or closure of developed microcracks and permeability changes of samples with joints.
Finite element modelling of frictional instability between deformable rocks
NASA Astrophysics Data System (ADS)
Xing, H. L.; Makinouchi, A.
2003-10-01
Earthquakes are recognized as resulting from a stick-slip frictional instability along faults. Based on the node-to-point contact element strategy (an arbitrarily shaped contact element strategy applied with the static-explicit algorithm for modelling non-linear frictional contact problems proposed by authors), a finite element code for modelling the 3-D non-linear friction contact between deformable bodies has been developed and extended here to analyse the non-linear stick-slip frictional instability between deformable rocks with a rate- and state-dependent friction law. A typical fault bend model is taken as an application example to be analysed here. The variations of the normal contact force, the frictional force, the transition of stick-slip instable state and the related relative slip velocity along the fault between the deformable rocks and the stress evolution in the total bodies during the different stages are investigated, respectively. The calculated results demonstrate the usefulness of this code for simulating the non-linear frictional instability between deformable rocks. Copyright
Analysis on sheet cyclic plastic deformation using mixed hardening model
NASA Astrophysics Data System (ADS)
Li, Qun; Jin, Miao; Yuxin, Zhu
2013-05-01
Treating the cyclic deformation problem of sheet flowing through drawbead as the object of the research, using HILL anisotropy yield criterion and mixed hardening model, the cyclic plastic deformation mechanism of sheet was studied, the deformation characteristics of sheet subjected to cyclic loads were revealed, and the influence of Bauschinger effect on stress-strain circulating relationship and the influence of bending neutral layer migration on the stress of sheet's intermediate integral point were analyzed as well. The effectiveness of the model was verified by experiments. The results of analysis were showed that the stress values influenced by Bauschinger effect were different at the yield point of reverse loading and the point of unloading during the cyclic deformation. The stress rate at the yield point of reverse loading and the point of unloading in different loading branches was also different. The stress-strain circulating relationship in different loading branches can be approximately treated as bilinear. The tangent modulus of each loading branch showed a significant downward trend as the times of the reverse loading increased. The tangent modulus calculated by the mixed hardening model after the second loading branch reduced to less than 21% of the first loading tangent modulus. Effected by the neutral layer migration, the stress-strain curve of integral point of sheet's intermediate layer showed alternating transition phenomenon of the tensile stress and compressive stress.
Models for determining the geometrical properties of halo coronal mass ejections
NASA Astrophysics Data System (ADS)
Zhao, X.; Liu, Y.
2005-12-01
To this day, the prediction of space weather effects near the Earth suffer from a fundamental problem: the necessary condition for determining whether or not and when a part of the huge interplanetary counterpart (ICME) of frontside halo coronal mass ejections (CMEs) is able to hit the Earth and generate goemagnetic storms, i.e., the real angular width, the propagation direction and speed of the CMEs, cannot be measured directly because of the unfavorable geometry. To inverse these geometrical and kinematical properties we have recently developed a few geometrical models, such as the cone model, the ice cream cone model, and the spherical cone model. The inversing solution of the cone model for the 12 may 1997 halo CME has been used as an input to the ENLIL model (a 3D MHD solar wind code) and successfully predicted the ICME near the Earth (Zhao, Plukett & Liu, 2002; Odstrcil, Riley & Zhao, 2004). After briefly describing the geometrical models this presentation will discuss: 1. What kind of halo CMEs can be inversed? 2. How to select the geometrical models given a specific halo CME? 3. Whether or not the inversing solution is unique?
In-room breathing motion estimation from limited projection views using a sliding deformation model
NASA Astrophysics Data System (ADS)
Delmon, V.; Vandemeulebroucke, J.; Pinho, R.; Vila Oliva, M.; Sarrut, D.; Rit, S.
2014-03-01
Purpose: To estimate in-room breathing motion from a limited number of 2D cone-beam (CB) projection images by registering them to a phase of the 4D planning CT. Methods: Breathing motion was modelled using a piecewise continuous B-spline representation [1], allowing to preserve the sliding along the thoracic wall while limiting the degrees of freedom. The deformed target 3D image was subsequently used to generate Digitally Reconstructed Radiographs (DRR). The Normalized Correlation Coefficient (NCC) between the measured projection images and the DRR was computed in the 2D projection space. However, the partial derivatives of the NCC relative to the transform parameters were backprojected into the 3D space, avoiding the projection of the transform Jacobian matrix which is computationally intractable [2]. Results: The method was quantitatively evaluated on 16 lung cancer patients. 40 CB projection images were simulated using the end-exhale phase of the 4D planning CT and the geometric parameters of a clinical CB protocol. The end-inhale phase was deformed to match these simulated projections. The Target Registration Error (TRE) decreased from 8.8 mm to 2.0 mm while the TRE obtained from the 3D/3D registration of the reconstructed CBCT was significantly worse (2.6 mm), due to view aliasing artefacts. We also provide the motion compensated image reconstructed from a real CB acquisition showing the quality improvement brought by the in-room deformation model compared to the planning motion model. Conclusions: We have developed a 2D/3D deformable registration algorithm that enables in-room breathing motion estimation from cone-beam projection images.
Sensitivity analysis of geometric errors in additive manufacturing medical models.
Pinto, Jose Miguel; Arrieta, Cristobal; Andia, Marcelo E; Uribe, Sergio; Ramos-Grez, Jorge; Vargas, Alex; Irarrazaval, Pablo; Tejos, Cristian
2015-03-01
Additive manufacturing (AM) models are used in medical applications for surgical planning, prosthesis design and teaching. For these applications, the accuracy of the AM models is essential. Unfortunately, this accuracy is compromised due to errors introduced by each of the building steps: image acquisition, segmentation, triangulation, printing and infiltration. However, the contribution of each step to the final error remains unclear. We performed a sensitivity analysis comparing errors obtained from a reference with those obtained modifying parameters of each building step. Our analysis considered global indexes to evaluate the overall error, and local indexes to show how this error is distributed along the surface of the AM models. Our results show that the standard building process tends to overestimate the AM models, i.e. models are larger than the original structures. They also show that the triangulation resolution and the segmentation threshold are critical factors, and that the errors are concentrated at regions with high curvatures. Errors could be reduced choosing better triangulation and printing resolutions, but there is an important need for modifying some of the standard building processes, particularly the segmentation algorithms. PMID:25649961
Reappraisal of a model for deformed special relativity
NASA Astrophysics Data System (ADS)
Gubitosi, Giulia; Magueijo, João
2016-06-01
We revisit one of the earliest proposals for deformed dispersion relations in the light of recent results on dynamical dimensional reduction and production of cosmological fluctuations. Depending on the specification of the measure of integration and the addition rule in momentum space the model may be completed so as to merely deform Lorentz invariance, or so as to introduce a preferred frame. Models which violate Lorentz invariance have a negative UV asymptotic dimension and a very red spectrum of quantum vacuum fluctuations. Instead, models which preserve frame independence can exhibit running to a UV dimension of two, and a scale-invariant spectrum of fluctuations. The bispectrum of the fluctuations is another point of divergence between the two casings proposed here for the original model.
Evolution of Geometric Sensitivity Derivatives from Computer Aided Design Models
NASA Technical Reports Server (NTRS)
Jones, William T.; Lazzara, David; Haimes, Robert
2010-01-01
The generation of design parameter sensitivity derivatives is required for gradient-based optimization. Such sensitivity derivatives are elusive at best when working with geometry defined within the solid modeling context of Computer-Aided Design (CAD) systems. Solid modeling CAD systems are often proprietary and always complex, thereby necessitating ad hoc procedures to infer parameter sensitivity. A new perspective is presented that makes direct use of the hierarchical associativity of CAD features to trace their evolution and thereby track design parameter sensitivity. In contrast to ad hoc methods, this method provides a more concise procedure following the model design intent and determining the sensitivity of CAD geometry directly to its respective defining parameters.
Probabilistic Cross-matching of Radio Catalogs with Geometric Models
NASA Astrophysics Data System (ADS)
Fan, D.; Budavári, T.
2014-05-01
Cross-matching radio is different from that in the optical. Radio sources can have multiple corresponding detections, the core and its lobes, which makes identification and cross-identification to other catalogs much more difficult. Traditionally, these cases have been handled manually, with researchers looking at the possible candidates; this will not be possible for the upcoming radio ultimately leading to the Square Kilometer Array. We present a probabilistic method that can automatically associate radio sources by explicitly modeling their morphology. Our preliminary results based on a simple straight-line model seem to be on par with the manual associations.
Fairing geometric modeling based on 4-point interpolatory subdivision scheme
NASA Astrophysics Data System (ADS)
Luo, Xiaonan; Liu, Ning; Gao, Chengying
2004-02-01
A 4-point interpolatory subdivision scheme with a tension parameter is analyzed, and the local property of 4-point interpolatory subdivision scheme and a kind of G1-continuity sufficient condition between surfaces as well as between curves are discussed. An efficient method of generating natural boundary points of 4-point interpolatory curve is presented, as well as a surface modeling method with the entire fairing property by combining energy optimization with subdivision scheme. The method has been applied in modeling 3D virtual garment surface.
Anatomically Based Geometric Modelling Using Medical Image Data: Methods and Programs
Wang, Monan; Sun, Lei; Liu, Yuming
2015-01-01
The human organs geometric modeling software which can achieve two-dimensional medical image browsing, pretreatment and three dimensional (3D) reconstruction in this paper is designed. This software implements medical image segmentation using the method combining the region growing and the interactive segmentation. Also, the MC surface reconstruction algorithm is utilized to achieve the three-dimensional reconstruction. Furthermore, the software is projected by Visual C++. And then, to legitimately express the structural information of skeleton and muscle, the software is employed to obtain the geometric model using the segmentation and three-dimensional reconstruction for data of skeleton and muscle medical images of the object of study. PMID:26089991
Geometric phases and quantum correlations dynamics in spin-boson model
Wu, Wei; Xu, Jing-Bo
2014-01-28
We explore the dynamics of spin-boson model for the Ohmic bath by employing the master equation approach and obtain an explicit expression of reduced density matrix. We also calculate the geometric phases of the spin-boson model by making use of the analytical results and discuss how the dissipative bosonic environment affects geometric phases. Furthermore, we investigate the dynamics of quantum discord and entanglement of two qubits each locally interacting with its own independent bosonic environments. It is found that the decay properties of quantum discord and entanglement are sensitive to the choice of initial state's parameter and coupling strength between system and bath.
Quantitative comparisons of numerical models of brittle deformation
NASA Astrophysics Data System (ADS)
Buiter, S.
2009-04-01
Numerical modelling of brittle deformation in the uppermost crust can be challenging owing to the requirement of an accurate pressure calculation, the ability to achieve post-yield deformation and localisation, and the choice of rheology (plasticity law). One way to approach these issues is to conduct model comparisons that can evaluate the effects of different implementations of brittle behaviour in crustal deformation models. We present a comparison of three brittle shortening experiments for fourteen different numerical codes, which use finite element, finite difference, boundary element and distinct element techniques. Our aim is to constrain and quantify the variability among models in order to improve our understanding of causes leading to differences between model results. Our first experiment of translation of a stable sand-like wedge serves as a reference that allows for testing against analytical solutions (e.g., taper angle, root-mean-square velocity and gravitational rate of work). The next two experiments investigate an unstable wedge in a sandbox-like setup which deforms by inward translation of a mobile wall. All models accommodate shortening by in-sequence formation of forward shear zones. We analyse the location, dip angle and spacing of thrusts in detail as previous comparisons have shown that these can be highly variable in numerical and analogue models of crustal shortening and extension. We find that an accurate implementation of boundary friction is important for our models. Our results are encouraging in the overall agreement in their dynamic evolution, but show at the same time the effort that is needed to understand shear zone evolution. GeoMod2008 Team: Markus Albertz, Michele Cooke, Susan Ellis, Taras Gerya, Luke Hodkinson, Kristin Hughes, Katrin Huhn, Boris Kaus, Walter Landry, Bertrand Maillot, Christophe Pascal, Anton Popov, Guido Schreurs, Christopher Beaumont, Tony Crook, Mario Del Castello and Yves Leroy
A geometric modeler based on a dual-geometry representation polyhedra and rational b-splines
NASA Technical Reports Server (NTRS)
Klosterman, A. L.
1984-01-01
For speed and data base reasons, solid geometric modeling of large complex practical systems is usually approximated by a polyhedra representation. Precise parametric surface and implicit algebraic modelers are available but it is not yet practical to model the same level of system complexity with these precise modelers. In response to this contrast the GEOMOD geometric modeling system was built so that a polyhedra abstraction of the geometry would be available for interactive modeling without losing the precise definition of the geometry. Part of the reason that polyhedra modelers are effective is that all bounded surfaces can be represented in a single canonical format (i.e., sets of planar polygons). This permits a very simple and compact data structure. Nonuniform rational B-splines are currently the best representation to describe a very large class of geometry precisely with one canonical format. The specific capabilities of the modeler are described.
NASA Astrophysics Data System (ADS)
Ukass, J.; Saks, T.; Popovs, K.
2012-04-01
In present study we attempt to verify the 3D geological model, which has been built on a variety of heterogeneous data sources for the Baltic Basin (BB). Data describing the displacement along the faults and associated thickness changes of the syntectonic strata is sparse and reflects only regional relevance (Brangulis & Konsins 2002). Borehole logs provide most reliable and comprehensive data source for reconstructing the structural geology of the Latvia sedimentary cover as sufficient quality seismic data is available only for the local scale structures. Based on the thickness analysis of the boreholes rough resolution 3D geological tectonic block model was developed to deconstruct the geological structure of the Latvia Caledonian sedimentary sequence. MOSYS modeling system was used for the geological structure modeling, developed within the PUMA project (Sennikovs et al, 2011). Algorithmic genetic approach was applied to interpolate data of well logs as strata volume and sequentially to reconstruct the post-deformation situation. This approach allows modifying model construction in any step and all processes are fully documented and are repeatable. Geometrical model consists of 33 tectonic blocks bordered by the faults which were distributed by interpreting displacement amount of the blocks along the faults providing an opportunity to characterize common tectonic evolution. The study results indicate insignificant thickness change of the Ordovician and Silurian strata along the faults suggesting that major slip event along the faults occurred during the late Silurian and early Devonian, and some secondary fault reactivation during the middle Devonian Narva time. Uplift of the territory during this time is confirmed by the presence of the regional unconformity. Constructed rough resolution 3D geometrical model suggests shortening along the horizontal axis approximately 10 - 20% but most of the shortening has occurred in the central-west part of Latvia where it
A deformable model for tracking tumors across consecutive imaging studies
Nosher, John L.; Schneider, M. D. Benjamin; Foran, David J.
2009-01-01
Objective A deformable registration technique was developed and evaluated to track and quantify tumor response to radiofrequency ablation for patients with liver malignancies. Materials and methods The method uses the combined power of global and local alignment of pre- and post-treatment computed tomography image data sets. The strategy of the algorithm is to infer volumetric deformation based upon surface displacements using a linearly elastic finite element model (FEM). Using this framework, the major challenge for tracking tumor location is not the tissue mechanical properties for FEM modeling but rather the evaluation of boundary conditions. Three different methods were systematically investigated to automatically determine the boundary conditions defined by the correspondences on liver surfaces. Results Using both 2D synthetic phantoms and imaged 3D beef liver data we performed gold standard registration while measuring the accuracy of non-rigid deformation. The fact that the algorithms could support mean displacement error of tumor deformation up to 2 mm indicates that this technique may serve as a useful tool for surgical interventions. The method was further demonstrated and evaluated using consecutive imaging studies for three liver cancer patients. Conclusion The FEM-based surface registration technique provides accurate tracking and monitoring of tumor and surrounding tissue during the course of treatment and follow-up. PMID:19774096
Three-Dimensional Geometric Modeling for Anatomical Structures
Shani, Uri
1981-01-01
Computer analysis of images of anatomical structures can benefit from the use of a priori knowledge about the inspected domain. Even though the anatomy structure of humans is variable, it is far more organized than other domains which are commonly used for image understanding (e.g., outdoor scenes or even images of a boxes-and-cylinders world). This paper discusses an organization scheme for modeling the 3-D structure of the abdominal anatomy and its use for analyzing 3-D CAT (Computed Axial Tomography) scans of the abdomen. The discussion is divided into two major portions of the knowledge organization: a relational database for gross anatomy and a 3-D shape model for individual organs using generalized cylinders. The paper also includes an example of 3-D image analysis for the detection of the kidneys' 3-D shape from abdominal CAT scans.
Country neighborhood network on territory and its geometrical model
NASA Astrophysics Data System (ADS)
Xuan, Qi; Wu, Tie-Jun
2009-04-01
The country neighborhood network, where nodes represent countries and two nodes are considered linked if the corresponding countries are neighbors on territory, is created and its giant component, the Asia, Europe, and Africa (AEA) cluster, is carefully studied in this paper. It is found that, as common, the degree distribution and the clustering function of the AEA cluster are both compatible with scale-free property, besides, the AEA cluster presents a little disassortativity, and its near power-law country area-degree relationship with the exponent close to 1.7 may imply a fractal dimension close to 1.2 of country borderlines in the AEA continent. It is also revealed that the average difference of population density between two countries obeys an approximately increasing function of the shortest path length between them, which may suggest a gradual consensus of population density in the AEA cluster. A simple unity rule is then adopted to model the AEA cluster and such model explains the AEA cluster very well in most aspects, e.g., power-law domain area distribution and fractal domain borderlines, etc., except that the network derived by the model has stronger disassortativity, which may be explained by the fact that, in the evolution history of countries, unbalanced neighbors are more likely to be united as one than balanced neighbors. Additionally, the network evolving process can be divided into three periods, defined as formation period, growth period, and combination period, and there are indications that the AEA cluster is in its third period.
Dynamic deformable models for 3D MRI heart segmentation
NASA Astrophysics Data System (ADS)
Zhukov, Leonid; Bao, Zhaosheng; Gusikov, Igor; Wood, John; Breen, David E.
2002-05-01
Automated or semiautomated segmentation of medical images decreases interstudy variation, observer bias, and postprocessing time as well as providing clincally-relevant quantitative data. In this paper we present a new dynamic deformable modeling approach to 3D segmentation. It utilizes recently developed dynamic remeshing techniques and curvature estimation methods to produce high-quality meshes. The approach has been implemented in an interactive environment that allows a user to specify an initial model and identify key features in the data. These features act as hard constraints that the model must not pass through as it deforms. We have employed the method to perform semi-automatic segmentation of heart structures from cine MRI data.
Phenomenological model for transient deformation based on state variables
Jackson, M S; Cho, C W; Alexopoulos, P; Mughrabi, H; Li, C Y
1980-01-01
The state variable theory of Hart, while providing a unified description of plasticity-dominated deformation, exhibits deficiencies when it is applied to transient deformation phenomena at stresses below yield. It appears that the description of stored anelastic strain is oversimplified. Consideration of a simple physical picture based on continuum dislocation pileups suggests that the neglect of weak barriers to dislocation motion is the source of these inadequacies. An appropriately modified description incorporating such barriers then allows the construction of a macroscopic model including transient effects. Although the flow relations for the microplastic element required in the new theory are not known, tentative assignments may be made for such functions. The model then exhibits qualitatively correct behavior when tensile, loading-unloading, reverse loading, and load relaxation tests are simulated. Experimental procedures are described for determining the unknown parameters and functions in the new model.
NASA Astrophysics Data System (ADS)
Martínez, Fabio; Romero, Eduardo; Dréan, Gaël; Simon, Antoine; Haigron, Pascal; de Crevoisier, Renaud; Acosta, Oscar
2014-03-01
Accurate segmentation of the prostate and organs at risk in computed tomography (CT) images is a crucial step for radiotherapy planning. Manual segmentation, as performed nowadays, is a time consuming process and prone to errors due to the a high intra- and inter-expert variability. This paper introduces a new automatic method for prostate, rectum and bladder segmentation in planning CT using a geometrical shape model under a Bayesian framework. A set of prior organ shapes are first built by applying principal component analysis to a population of manually delineated CT images. Then, for a given individual, the most similar shape is obtained by mapping a set of multi-scale edge observations to the space of organs with a customized likelihood function. Finally, the selected shape is locally deformed to adjust the edges of each organ. Experiments were performed with real data from a population of 116 patients treated for prostate cancer. The data set was split in training and test groups, with 30 and 86 patients, respectively. Results show that the method produces competitive segmentations w.r.t standard methods (averaged dice = 0.91 for prostate, 0.94 for bladder, 0.89 for rectum) and outperforms the majority-vote multi-atlas approaches (using rigid registration, free-form deformation and the demons algorithm).
Modeling of friction-induced deformation and microstructures.
Michael, Joseph Richard; Prasad, Somuri V.; Jungk, John Michael; Cordill, Megan J.; Bammann, Douglas J.; Battaile, Corbett Chandler; Moody, Neville Reid; Majumdar, Bhaskar Sinha (New Mexico Institure of Mining and Technology)
2006-12-01
Frictional contact results in surface and subsurface damage that could influence the performance, aging, and reliability of moving mechanical assemblies. Changes in surface roughness, hardness, grain size and texture often occur during the initial run-in period, resulting in the evolution of subsurface layers with characteristic microstructural features that are different from those of the bulk. The objective of this LDRD funded research was to model friction-induced microstructures. In order to accomplish this objective, novel experimental techniques were developed to make friction measurements on single crystal surfaces along specific crystallographic surfaces. Focused ion beam techniques were used to prepare cross-sections of wear scars, and electron backscattered diffraction (EBSD) and TEM to understand the deformation, orientation changes, and recrystallization that are associated with sliding wear. The extent of subsurface deformation and the coefficient of friction were strongly dependent on the crystal orientation. These experimental observations and insights were used to develop and validate phenomenological models. A phenomenological model was developed to elucidate the relationships between deformation, microstructure formation, and friction during wear. The contact mechanics problem was described by well-known mathematical solutions for the stresses during sliding friction. Crystal plasticity theory was used to describe the evolution of dislocation content in the worn material, which in turn provided an estimate of the characteristic microstructural feature size as a function of the imposed strain. An analysis of grain boundary sliding in ultra-fine-grained material provided a mechanism for lubrication, and model predictions of the contribution of grain boundary sliding (relative to plastic deformation) to lubrication were in good qualitative agreement with experimental evidence. A nanomechanics-based approach has been developed for characterizing the
A complete VLBI delay model for deforming radio telescopes: the Effelsberg case
NASA Astrophysics Data System (ADS)
Artz, T.; Springer, A.; Nothnagel, A.
2014-12-01
Deformations of radio telescopes used in geodetic and astrometric very long baseline interferometry (VLBI) observations belong to the class of systematic error sources which require correction in data analysis. In this paper we present a model for all path length variations in the geometrical optics of radio telescopes which are due to gravitational deformation. The Effelsberg 100 m radio telescope of the Max Planck Institute for Radio Astronomy, Bonn, Germany, has been surveyed by various terrestrial methods. Thus, all necessary information that is needed to model the path length variations is available. Additionally, a ray tracing program has been developed which uses as input the parameters of the measured deformations to produce an independent check of the theoretical model. In this program as well as in the theoretical model, the illumination function plays an important role because it serves as the weighting function for the individual path lengths depending on the distance from the optical axis. For the Effelsberg telescope, the biggest contribution to the total path length variations is the bending of the main beam located along the elevation axis which partly carries the weight of the paraboloid at its vertex. The difference in total path length is almost 100 mm when comparing observations at 90 and at 0 elevation angle. The impact of the path length corrections is validated in a global VLBI analysis. The application of the correction model leads to a change in the vertical position of mm. This is more than the maximum path length, but the effect can be explained by the shape of the correction function.
Resurgence in η-deformed Principal Chiral Models
NASA Astrophysics Data System (ADS)
Demulder, Saskia; Dorigoni, Daniele; Thompson, Daniel C.
2016-07-01
We study the SU(2) Principal Chiral Model (PCM) in the presence of an integrable η-deformation. We put the theory on {R}× {S}^1 with twisted boundary conditions and then reduce the circle to obtain an effective quantum mechanics associated with the Whittaker-Hill equation. Using resurgent analysis we study the large order behaviour of perturbation theory and recover the fracton events responsible for IR renormalons. The fractons are modified from the standard PCM due to the presence of this η-deformation but they are still the constituents of uniton-like solutions in the deformed quantum field theory. We also find novel SL(2,{C}) saddles, thus strengthening the conjecture that the semi-classical expansion of the path integral gives rise to a resurgent transseries once written as a sum over Lefschetz thimbles living in a complexification of the field space. We conclude by connecting our quantum mechanics to a massive deformation of the {N} = 2 4-d gauge theory with gauge group SU(2) and N f = 2.
Experimental modelling of ground deformation associated with shallow magma intrusions
NASA Astrophysics Data System (ADS)
Galland, Olivier
2012-02-01
Active volcanoes experience ground deformation as a response to the dynamics of underground magmatic systems. The analysis of ground deformation patterns may provide important constraints on the dynamics and shape of the underlying volcanic plumbing systems. Nevertheless, these analyses usually take into account simplistic shapes (sphere, dykes, sills) and the results cannot be verified as the modelled systems are buried. In this paper, I present new results from experimental models of magma intrusion, in which both the evolution of ground deformation during intrusion and the shape of the underlying intrusion are monitored. The models consisted of a molten vegetable oil, simulating low viscosity magma, injected into cohesive fine-grained silica flour, simulating the brittle upper crust; oil injection resulted is sheet intrusions (dykes, sills and cone sheets). The initial topography in the models was flat. While the oil was intruding, the surface of the models slightly lifted up to form a smooth relief, which was mapped through time. After an initial symmetrical development, the uplifted area developed asymmetrically; at the end of the experiments, the oil always erupted at the steepest edge of the uplifted area. After the experiment, the oil solidified, the intrusion was excavated and the shape of its top surface mapped. The comparison between the uplifted zone and the underlying intrusions showed that (1) the complex shapes of the uplifted areas reflected the complex shapes of the underlying intrusions, (2) the time evolution of the uplifted zone was correlated with the evolution of the underlying intrusion, and (3) the early asymmetrical evolution of the uplifted areas can be used to predict the location of the eruption of the oil. The experimental results also suggest that complex intrusion shapes (inclined sheet, cone sheet, complex sill) may have to be considered more systematically in the analyses of ground deformation patterns on volcanoes.
Experimental modelling of ground deformation associated with shallow magma intrusions
NASA Astrophysics Data System (ADS)
Galland, O.
2012-04-01
Active volcanoes experience ground deformation as a response to the dynamics of underground magmatic systems. The analysis of ground deformation patterns may provide important constraints on the dynamics and shape of the underlying volcanic plumbing systems. Nevertheless, these analyses usually take into account simplistic shapes (sphere, dykes, sills) and the results cannot be verified as the modelled systems are buried. In this contribution, I will present new results from experimental models of magma intrusion, in which both the evolution of ground deformation during intrusion and the shape of the underlying intrusion are monitored in 3D. The models consisted of a molten vegetable oil, simulating low viscosity magma, injected into cohesive fine-grained silica flour, simulating the brittle upper crust; oil injection resulted is sheet intrusions (dykes, sills and cone sheets). The initial topography in the models was flat. While the oil was intruding, the surface of the models slightly lifted up to form a smooth relief, which was mapped through time. After an initial symmetrical development, the uplifted area developed asymmetrically; at the end of the experiments, the oil always erupted at the steepest edge of the uplifted area. After the experiment, the oil solidified, the intrusion was excavated and the shape of its top surface mapped. The comparison between the uplifted zone and the underlying intrusions showed that (1) the complex shapes of the uplifted areas reflected the complex shapes of the underlying intrusions, (2) the time evolution of the uplifted zone was correlated with the evolution of the underlying intrusion, and (3) the early asymmetrical evolution of the uplifted areas can be used to predict the location of the eruption of the oil. The experimental results also suggest that complex intrusion shapes (inclined sheet, cone sheet, complex sill) may have to be considered more systematically in analyses of ground deformation patterns on volcanoes.
NASA Astrophysics Data System (ADS)
Ishimoto, Yukitaka; Morishita, Yoshihiro
2014-11-01
In order to describe two-dimensionally packed cells in epithelial tissues both mathematically and physically, there have been developed several sorts of geometrical models, such as the vertex model, the finite element model, the cell-centered model, and the cellular Potts model. So far, in any case, pressures have not neatly been dealt with and the curvatures of the cell boundaries have been even omitted through their approximations. We focus on these quantities and formulate them in the vertex model. Thus, a model with the curvatures is constructed, and its algorithm for simulation is provided. The possible extensions and applications of this model are also discussed.
NASA Astrophysics Data System (ADS)
Vile, Douglas J.
In radiation therapy, interfraction organ motion introduces a level of geometric uncertainty into the planning process. Plans, which are typically based upon a single instance of anatomy, must be robust against daily anatomical variations. For this problem, a model of the magnitude, direction, and likelihood of deformation is useful. In this thesis, principal component analysis (PCA) is used to statistically model the 3D organ motion for 19 prostate cancer patients, each with 8-13 fractional computed tomography (CT) images. Deformable image registration and the resultant displacement vector fields (DVFs) are used to quantify the interfraction systematic and random motion. By applying the PCA technique to the random DVFs, principal modes of random tissue deformation were determined for each patient, and a method for sampling synthetic random DVFs was developed. The PCA model was then extended to describe the principal modes of systematic and random organ motion for the population of patients. A leave-one-out study tested both the systematic and random motion model's ability to represent PCA training set DVFs. The random and systematic DVF PCA models allowed the reconstruction of these data with absolute mean errors between 0.5-0.9 mm and 1-2 mm, respectively. To the best of the author's knowledge, this study is the first successful effort to build a fully 3D statistical PCA model of systematic tissue deformation in a population of patients. By sampling synthetic systematic and random errors, organ occupancy maps were created for bony and prostate-centroid patient setup processes. By thresholding these maps, PCA-based planning target volume (PTV) was created and tested against conventional margin recipes (van Herk for bony alignment and 5 mm fixed [3 mm posterior] margin for centroid alignment) in a virtual clinical trial for low-risk prostate cancer. Deformably accumulated delivered dose served as a surrogate for clinical outcome. For the bony landmark setup
Dislocation models of interseismic deformation in the western United States
Pollitz, F.F.; McCrory, P.; Svarc, J.; Murray, J.
2008-01-01
The GPS-derived crustal velocity field of the western United States is used to construct dislocation models in a viscoelastic medium of interseismic crustal deformation. The interseismic velocity field is constrained by 1052 GPS velocity vectors spanning the ???2500-km-long plate boundary zone adjacent to the San Andreas fault and Cascadia subduction zone and extending ???1000 km into the plate interior. The GPS data set is compiled from U.S. Geological Survey campaign data, Plate Boundary Observatory data, and the Western U.S. Cordillera velocity field of Bennett et al. (1999). In the context of viscoelastic cycle models of postearthquake deformation, the interseismic velocity field is modeled with a combination of earthquake sources on ???100 known faults plus broadly distributed sources. Models that best explain the observed interseismic velocity field include the contributions of viscoelastic relaxation from faulting near the major plate margins, viscoelastic relaxation from distributed faulting in the plate interior, as well as lateral variations in depth-averaged rigidity in the elastic lithosphere. Resulting rigidity variations are consistent with reduced effective elastic plate thickness in a zone a few tens of kilometers wide surrounding the San Andreas fault (SAF) system. Primary deformation characteristics are captured along the entire SAF system, Eastern California Shear Zone, Walker Lane, the Mendocino triple junction, the Cascadia margin, and the plate interior up to ???1000 km from the major plate boundaries.
Dislocation models of interseismic deformation in the western United States
NASA Astrophysics Data System (ADS)
Pollitz, Fred F.; McCrory, Patricia; Svarc, Jerry; Murray, Jessica
2008-04-01
The GPS-derived crustal velocity field of the western United States is used to construct dislocation models in a viscoelastic medium of interseismic crustal deformation. The interseismic velocity field is constrained by 1052 GPS velocity vectors spanning the ˜2500-km-long plate boundary zone adjacent to the San Andreas fault and Cascadia subduction zone and extending ˜1000 km into the plate interior. The GPS data set is compiled from U.S. Geological Survey campaign data, Plate Boundary Observatory data, and the Western U.S. Cordillera velocity field of Bennett et al. (1999). In the context of viscoelastic cycle models of postearthquake deformation, the interseismic velocity field is modeled with a combination of earthquake sources on ˜100 known faults plus broadly distributed sources. Models that best explain the observed interseismic velocity field include the contributions of viscoelastic relaxation from faulting near the major plate margins, viscoelastic relaxation from distributed faulting in the plate interior, as well as lateral variations in depth-averaged rigidity in the elastic lithosphere. Resulting rigidity variations are consistent with reduced effective elastic plate thickness in a zone a few tens of kilometers wide surrounding the San Andreas fault (SAF) system. Primary deformation characteristics are captured along the entire SAF system, Eastern California Shear Zone, Walker Lane, the Mendocino triple junction, the Cascadia margin, and the plate interior up to ˜1000 km from the major plate boundaries.
NASA Astrophysics Data System (ADS)
Boyer, Frederic; Porez, Mathieu; Renda, Federico
This talk presents recent geometric tools developed to model the locomotion dynamics of bio-inspired robots. Starting from the model of discrete rigid multibody systems we will rapidly shift to the case of continuous systems inspired from snakes and fish. To that end, we will build on the model of Cosserat media. This extended picture of geometric locomotion dynamics (inspired from fields' theory) will allow us to introduce models of swimming recently used in biorobotics. We will show how modeling a fish as a one-dimensional Cosserat medium allows to recover and extend the Large Amplitude Elongated Body theory of J. Lighthill and to apply it to an eel-like robot. In the same vein, modeling the mantle of cephalopods as a two dimensional Cosserat medium will build a basis for studying the jet propelling of a soft octopus like robot.
Odenthal, Tim; Smeets, Bart; Van Liedekerke, Paul; Tijskens, Engelbert; Van Oosterwyck, Hans; Ramon, Herman
2013-01-01
Adhesion governs to a large extent the mechanical interaction between a cell and its microenvironment. As initial cell spreading is purely adhesion driven, understanding this phenomenon leads to profound insight in both cell adhesion and cell-substrate interaction. It has been found that across a wide variety of cell types, initial spreading behavior universally follows the same power laws. The simplest cell type providing this scaling of the radius of the spreading area with time are modified red blood cells (RBCs), whose elastic responses are well characterized. Using a mechanistic description of the contact interaction between a cell and its substrate in combination with a deformable RBC model, we are now able to investigate in detail the mechanisms behind this universal power law. The presented model suggests that the initial slope of the spreading curve with time results from a purely geometrical effect facilitated mainly by dissipation upon contact. Later on, the spreading rate decreases due to increasing tension and dissipation in the cell's cortex as the cell spreads more and more. To reproduce this observed initial spreading, no irreversible deformations are required. Since the model created in this effort is extensible to more complex cell types and can cope with arbitrarily shaped, smooth mechanical microenvironments of the cells, it can be useful for a wide range of investigations where forces at the cell boundary play a decisive role. PMID:24146605
Parametric shape representation by a deformable NURBS model for cardiac functional measurements.
Chen, Sheng Yong; Guan, Qiu
2011-03-01
This paper proposes a method of parametric representation and functional measurement of 3-D cardiac shapes in a deformable nonuniform rational B-splines (NURBS) model. This representation makes it very easy to automatically evaluate the functional parameters and myocardial kinetics of the heart, since quantitative analysis can be followed in a simple way. In the model, local deformation and motion on the cardiac shape are expressed in adjustable parameters. Especially, an effective integral algorithm is used for volumetric measurement of a NURBS shape since the volume is the most basic parameter in cardiac functional analysis. This method promises the numerical computation to be very convenient, efficient, and accurate, in comparison with traditional methods. Practical experiments are carried out, and results show that the algorithm can get satisfactory measurement accuracy and efficiency. The parametric NURBS model in cylindrical coordinates is not only very suitable to fit the anatomical surfaces of a cardiac shape, but also easy for geometric transformation and nonrigid registration, and able to represent local dynamics and kinetics, and thus, can easily be applied for quantitative and functional analysis of the heart. PMID:20952325
Modeling cotton (Gossypium spp) leaves and canopy using computer aided geometric design (CAGD)
Technology Transfer Automated Retrieval System (TEKTRAN)
The goal of this research is to develop a geometrically accurate model of cotton crop canopies for exploring changes in canopy microenvironment and physiological function with leaf structure. We develop an accurate representation of the leaves, including changes in three-dimensional folding and orie...
Extension of non-linear beam models with deformable cross sections
NASA Astrophysics Data System (ADS)
Sokolov, I.; Krylov, S.; Harari, I.
2015-12-01
Geometrically exact beam theory is extended to allow distortion of the cross section. We present an appropriate set of cross-section basis functions and provide physical insight to the cross-sectional distortion from linear elastostatics. The beam formulation in terms of material (back-rotated) beam internal force resultants and work-conjugate kinematic quantities emerges naturally from the material description of virtual work of constrained finite elasticity. The inclusion of cross-sectional deformation allows straightforward application of three-dimensional constitutive laws in the beam formulation. Beam counterparts of applied loads are expressed in terms of the original three-dimensional data. Special attention is paid to the treatment of the applied stress, keeping in mind applications such as hydrogel actuators under environmental stimuli or devices made of electroactive polymers. Numerical comparisons show the ability of the beam model to reproduce finite elasticity results with good efficiency.
Active deformation in Western Turkey: new GPS observations and models
NASA Astrophysics Data System (ADS)
Nocquet, J.; Aktug, B.; Parsons, B.; Cingoz, A.; England, P.; Erkan, Y.; Soyer, N.; Akdeniz, H.; Kilicoglu, A.
2007-12-01
How the continents deform remains a matter of debate. One view postulates that continental deforming zones are comprised of a limited numbers of rigid (elastic) microplates. If true, the surface motion can then be described by the relative rotation of blocks, and strain should be localized along the major faults separating the blocks. An alternative view is that the deformation at depth is distributed over wide areas, can be modelled by a viscous flow responding to boundary conditions applied on it and gravitational potential energy gradients related to variations in topography, and the surface strain simply reflects this deformation. Western Turkey is a region of crustal extension, part of the Nubia/Eurasia plate boundary. Its kinematics is often modelled by the relative motion of a small number of rigid blocks (Nyst & Thatcher, 2005, Reilinger et al., 2006). However, until now, the limited number of GPS velocity vectors available has prevented a detailed examination of which is the more appropriate description. We present a new geodetic velocity field including ~100 sites from the longitude the Central Anatolian plateau to the Aegean coast, derived from a combination of campaigns carried out between 1997 and 2006, and continuous GPS operating since 2003, which we use to test the different models. While the kinematics of the area can be correctly modelled by a block model, a good fit to the velocity field requires blocks with sizes smaller than 100 km and still fails to adequately predict the strain rate observed within blocks . Alternatively, we test an approach where the lithosphere is modelled as a thin viscous sheet, responding to the gravitational potentiel energy contrast between the high plateau of eastern Turkey to the east and the subduction along the Hellenic trench in the southwest. The simplistic model has only one free parameter (the force applied by the subducting oceanic lithosphere on the Aegean ), but provides a good agreement with the observed
Modeling and analysis methodology for aeroelastically tailored chordwise deformable wings
NASA Technical Reports Server (NTRS)
Rehfield, Lawrence W.; Chang, Stephen; Zischka, Peter J.
1992-01-01
Structural concepts have been created which produce chordwise camber deformation that results in enhanced lift. A wing box can be tailored to utilize each of these with composites. In attempting to optimize the aerodynamic benefits, we have found there are two optimal designs that are of interest. There is a weight optimum which corresponds to the maximum lift per unit structural weight. There is also a lift optimum that corresponds to maximum absolute lift. New structural models, the basic deformation mechanisms that are utilized and typical analytical results are presented. It appears that lift enhancements of sufficient magnitude can be produced to render this type of wing tailoring of practical interest. Experiments and finite element correlations are performed which confirm the validity of the theoretical models utilized.
[A proposal for a geometrical delimitation model for ventro-gluteal injection].
de Meneses, Abel Silva; Marques, Isaac Rosa
2007-01-01
This study aimed at presenting and comparing geometrical and traditional technique for intramuscular injection in the ventrogluteal area. This is a quasi-experimental study of non-equivalent control group type, carried out with anatomical parts of corpses to verify the precision of function between traditional delimitation using hand as reference and the geometrical model which was constituted by tracing imaginary lines across bone structures of the hip, making a configuration of a triangle whose barycenter points the punction site. The study demonstrated that the punction site delimited by the geometrical technique keeped proportion of the envolved structures, and matched with the muscular womb of the ventrogluteal area in 100% of punctions. In another hand, in the traditional technique the punction site varied in 39.9% of punctions. PMID:18041556
NASA Astrophysics Data System (ADS)
Xin, Q.; Gong, P.; Li, W.
2015-02-01
Modeling vegetation photosynthesis is essential for understanding carbon exchanges between terrestrial ecosystems and the atmosphere. The radiative transfer process within plant canopies is one of the key drivers that regulate canopy photosynthesis. Most vegetation cover consists of discrete plant crowns, of which the physical observation departs from the underlying assumption of a homogenous and uniform medium in classic radiative transfer theory. Here we advance the Geometric Optical Radiative Transfer (GORT) model to simulate photosynthesis activities for discontinuous plant canopies. We separate radiation absorption into two components that are absorbed by sunlit and shaded leaves, and derive analytical solutions by integrating over the canopy layer. To model leaf-level and canopy-level photosynthesis, leaf light absorption is then linked to the biochemical process of gas diffusion through leaf stomata. The canopy gap probability derived from GORT differs from classic radiative transfer theory, especially when the leaf area index is high, due to leaf clumping effects. Tree characteristics such as tree density, crown shape, and canopy length affect leaf clumping and regulate radiation interception. Modeled gross primary production (GPP) for two deciduous forest stands could explain more than 80% of the variance of flux tower measurements at both near hourly and daily time scales. We also demonstrate that the ambient CO2 concentration influences daytime vegetation photosynthesis, which needs to be considered in state-of-the-art biogeochemical models. The proposed model is complementary to classic radiative transfer theory and shows promise in modeling the radiative transfer process and photosynthetic activities over discontinuous forest canopies.
Geometric Mixing, Peristalsis, and the Geometric Phase of the Stomach
Arrieta, Jorge; Cartwright, Julyan H. E.; Gouillart, Emmanuelle; Piro, Nicolas; Piro, Oreste; Tuval, Idan
2015-01-01
Mixing fluid in a container at low Reynolds number— in an inertialess environment—is not a trivial task. Reciprocating motions merely lead to cycles of mixing and unmixing, so continuous rotation, as used in many technological applications, would appear to be necessary. However, there is another solution: movement of the walls in a cyclical fashion to introduce a geometric phase. We show using journal-bearing flow as a model that such geometric mixing is a general tool for using deformable boundaries that return to the same position to mix fluid at low Reynolds number. We then simulate a biological example: we show that mixing in the stomach functions because of the “belly phase,” peristaltic movement of the walls in a cyclical fashion introduces a geometric phase that avoids unmixing. PMID:26154384
Geometric Mixing, Peristalsis, and the Geometric Phase of the Stomach.
Arrieta, Jorge; Cartwright, Julyan H E; Gouillart, Emmanuelle; Piro, Nicolas; Piro, Oreste; Tuval, Idan
2015-01-01
Mixing fluid in a container at low Reynolds number--in an inertialess environment--is not a trivial task. Reciprocating motions merely lead to cycles of mixing and unmixing, so continuous rotation, as used in many technological applications, would appear to be necessary. However, there is another solution: movement of the walls in a cyclical fashion to introduce a geometric phase. We show using journal-bearing flow as a model that such geometric mixing is a general tool for using deformable boundaries that return to the same position to mix fluid at low Reynolds number. We then simulate a biological example: we show that mixing in the stomach functions because of the "belly phase," peristaltic movement of the walls in a cyclical fashion introduces a geometric phase that avoids unmixing. PMID:26154384
Virasoro irregular conformal block and beta deformed random matrix model
NASA Astrophysics Data System (ADS)
Choi, Sang Kwan; Rim, Chaiho; Zhang, Hong
2015-03-01
Virasoro irregular conformal block is presented as the expectation value of Jack-polynomials of the beta-deformed Penner-type matrix model and is compared with the inner product of Gaiotto states with arbitrary rank. It is confirmed that there are non-trivial modifications of the Gaiotto states due to the normalization of the states. The relation between the two is explicitly checked for rank 2 irregular conformal block.
Model Deformation Measurements at a Cryogenic Wind Tunnel Using Photogrammetry
NASA Technical Reports Server (NTRS)
Burner, A. W.; Snow, W. L.; Goad, W. K.
1982-01-01
A photogrammetric closed circuit television system to measure model deformation at the National Transonic Facility (NTF) is described. The photogrammetric approach was chosen because of its inherent rapid data recording of the entire object field. Video cameras are used to acquire data instead of film cameras due to the inaccessibility of cameras which must be housed within the cryogenic, high pressure plenum of this facility. Data reduction procedures and the results of tunnel tests at the NTF are presented.
Model deformation measurements at a cryogenic wind tunnel using photogrammetry
NASA Technical Reports Server (NTRS)
Burner, A. W.; Snow, W. L.; Goad, W. K.
1985-01-01
A photogrammetric closed circuit television system to measure model deformation at the National Transonic Facility (NTF) is described. The photogrammetric approach was chosen because of its inherent rapid data recording of the entire object field. Video cameras are used to acquire data instead of film cameras due to the inaccessibility of cameras which must be housed within the cryogenic, high pressure plenum of this facility. Data reduction procedures and the results of tunnel tests at the NTF are presented.
Heterogeneous Deformable Modeling of Bio-Tissues and Haptic Force Rendering for Bio-Object Modeling
NASA Astrophysics Data System (ADS)
Lin, Shiyong; Lee, Yuan-Shin; Narayan, Roger J.
This paper presents a novel technique for modeling soft biological tissues as well as the development of an innovative interface for bio-manufacturing and medical applications. Heterogeneous deformable models may be used to represent the actual internal structures of deformable biological objects, which possess multiple components and nonuniform material properties. Both heterogeneous deformable object modeling and accurate haptic rendering can greatly enhance the realism and fidelity of virtual reality environments. In this paper, a tri-ray node snapping algorithm is proposed to generate a volumetric heterogeneous deformable model from a set of object interface surfaces between different materials. A constrained local static integration method is presented for simulating deformation and accurate force feedback based on the material properties of a heterogeneous structure. Biological soft tissue modeling is used as an example to demonstrate the proposed techniques. By integrating the heterogeneous deformable model into a virtual environment, users can both observe different materials inside a deformable object as well as interact with it by touching the deformable object using a haptic device. The presented techniques can be used for surgical simulation, bio-product design, bio-manufacturing, and medical applications.
A geometric graph model for citation networks of exponentially growing scientific papers
NASA Astrophysics Data System (ADS)
Xie, Zheng; Ouyang, Zhenzheng; Liu, Qi; Li, Jianping
2016-08-01
In citation networks, the content relativity of papers is a precondition of engendering citations, which is hard to model by a topological graph. A geometric graph is proposed to predict some features of the citation networks with exponentially growing papers, which addresses the precondition by using coordinates of nodes to model the research contents of papers, and geometric distances between nodes to diversities of research contents between papers. Citations between modeled papers are drawn according to a geometric rule, which addresses the precondition as well as some other factors engendering citations, namely academic influences of papers, aging of those influences, and incomplete copying of references. Instead of cumulative advantage of degree, the model illustrates that the scale-free property of modeled networks arises from the inhomogeneous academic influences of modeled papers. The model can also reproduce some other statistical features of citation networks, e.g. in- and out-assortativities, which show the model provides a suitable tool to understand some aspects of citation networks by geometry.
Surrogate modeling of deformable joint contact using artificial neural networks.
Eskinazi, Ilan; Fregly, Benjamin J
2015-09-01
Deformable joint contact models can be used to estimate loading conditions for cartilage-cartilage, implant-implant, human-orthotic, and foot-ground interactions. However, contact evaluations are often so expensive computationally that they can be prohibitive for simulations or optimizations requiring thousands or even millions of contact evaluations. To overcome this limitation, we developed a novel surrogate contact modeling method based on artificial neural networks (ANNs). The method uses special sampling techniques to gather input-output data points from an original (slow) contact model in multiple domains of input space, where each domain represents a different physical situation likely to be encountered. For each contact force and torque output by the original contact model, a multi-layer feed-forward ANN is defined, trained, and incorporated into a surrogate contact model. As an evaluation problem, we created an ANN-based surrogate contact model of an artificial tibiofemoral joint using over 75,000 evaluations of a fine-grid elastic foundation (EF) contact model. The surrogate contact model computed contact forces and torques about 1000 times faster than a less accurate coarse grid EF contact model. Furthermore, the surrogate contact model was seven times more accurate than the coarse grid EF contact model within the input domain of a walking motion. For larger input domains, the surrogate contact model showed the expected trend of increasing error with increasing domain size. In addition, the surrogate contact model was able to identify out-of-contact situations with high accuracy. Computational contact models created using our proposed ANN approach may remove an important computational bottleneck from musculoskeletal simulations or optimizations incorporating deformable joint contact models. PMID:26220591
Multi-scale simulation of plant tissue deformation using a model for individual cell mechanics.
Ghysels, P; Samaey, G; Tijskens, B; Van Liedekerke, P; Ramon, H; Roose, D
2009-01-01
We present a micro-macro method for the simulation of large elastic deformations of plant tissue. At the microscopic level, we use a mass-spring model to describe the geometrical structure and basic properties of individual plant cells. The macroscopic domain is discretized using standard finite elements, in which the macroscopic material properties (the stress-strain relation) are not given in analytical form, but are computed using the microscopic model in small subdomains, called representative volume elements (RVEs), centered around the macroscopic quadrature points. The boundary conditions for these RVEs are derived from the macroscopic deformation gradient. The computation of the macroscopic stress tensor is based on the definition of virial stress, as defined in molecular dynamics. The anisotropic Eulerian elasticity tensor is estimated using a forward finite difference approximation for the Truesdell rate of the Cauchy stress tensor. We investigate the influence of the size of the RVE and the boundary conditions. This multi-scale method converges to the solution of the full microscopic simulation, for both globally and adaptively refined finite element meshes, and achieves a significant speedup compared to the full microscopic simulation. PMID:19321921
Accurate, efficient, and (iso)geometrically flexible collocation methods for phase-field models
NASA Astrophysics Data System (ADS)
Gomez, Hector; Reali, Alessandro; Sangalli, Giancarlo
2014-04-01
We propose new collocation methods for phase-field models. Our algorithms are based on isogeometric analysis, a new technology that makes use of functions from computational geometry, such as, for example, Non-Uniform Rational B-Splines (NURBS). NURBS exhibit excellent approximability and controllable global smoothness, and can represent exactly most geometries encapsulated in Computer Aided Design (CAD) models. These attributes permitted us to derive accurate, efficient, and geometrically flexible collocation methods for phase-field models. The performance of our method is demonstrated by several numerical examples of phase separation modeled by the Cahn-Hilliard equation. We feel that our method successfully combines the geometrical flexibility of finite elements with the accuracy and simplicity of pseudo-spectral collocation methods, and is a viable alternative to classical collocation methods.
Electrohydrodynamic Model of Vesicle Deformation in Alternating Electric Fields
Vlahovska, Petia M.; Gracià, Rubèn Serral; Aranda-Espinoza, Said; Dimova, Rumiana
2009-01-01
Abstract We develop an analytical theory to explain the experimentally observed morphological transitions of quasispherical giant vesicles induced by alternating electric fields. The model treats the inner and suspending media as lossy dielectrics, and the membrane as an impermeable flexible incompressible–fluid sheet. The vesicle shape is obtained by balancing electric, hydrodynamic, bending, and tension stresses exerted on the membrane. Our approach, which is based on force balance, also allows us to describe the time evolution of the vesicle deformation, in contrast to earlier works based on energy minimization, which are able to predict only stationary shapes. Our theoretical predictions for vesicle deformation are consistent with experiment. If the inner fluid is more conducting than the suspending medium, the vesicle always adopts a prolate shape. In the opposite case, the vesicle undergoes a transition from a prolate to oblate ellipsoid at a critical frequency, which the theory identifies with the inverse membrane charging time. At frequencies higher than the inverse Maxwell-Wagner polarization time, the electrohydrodynamic stresses become too small to alter the vesicle's quasispherical rest shape. The model can be used to rationalize the transient and steady deformation of biological cells in electric fields. PMID:19527639
Linking plate reconstructions with deforming lithosphere to geodynamic models
NASA Astrophysics Data System (ADS)
Müller, R. D.; Gurnis, M.; Flament, N.; Seton, M.; Spasojevic, S.; Williams, S.; Zahirovic, S.
2011-12-01
While global computational models are rapidly advancing in terms of their capabilities, there is an increasing need for assimilating observations into these models and/or ground-truthing model outputs. The open-source and platform independent GPlates software fills this gap. It was originally conceived as a tool to interactively visualize and manipulate classical rigid plate reconstructions and represent them as time-dependent topological networks of editable plate boundaries. The user can export time-dependent plate velocity meshes that can be used either to define initial surface boundary conditions for geodynamic models or alternatively impose plate motions throughout a geodynamic model run. However, tectonic plates are not rigid, and neglecting plate deformation, especially that of the edges of overriding plates, can result in significant misplacing of plate boundaries through time. A new, substantially re-engineered version of GPlates is now being developed that allows an embedding of deforming plates into topological plate boundary networks. We use geophysical and geological data to define the limit between rigid and deforming areas, and the deformation history of non-rigid blocks. The velocity field predicted by these reconstructions can then be used as a time-dependent surface boundary condition in regional or global 3-D geodynamic models, or alternatively as an initial boundary condition for a particular plate configuration at a given time. For time-dependent models with imposed plate motions (e.g. using CitcomS) we incorporate the continental lithosphere by embedding compositionally distinct crust and continental lithosphere within the thermal lithosphere. We define three isostatic columns of different thickness and buoyancy based on the tectonothermal age of the continents: Archean, Proterozoic and Phanerozoic. In the fourth isostatic column, the oceans, the thickness of the thermal lithosphere is assimilated using a half-space cooling model. We also
A nonaffine network model for elastomers undergoing finite deformations
NASA Astrophysics Data System (ADS)
Davidson, Jacob D.; Goulbourne, N. C.
2013-08-01
In this work, we construct a new physics-based model of rubber elasticity to capture the strain softening, strain hardening, and deformation-state dependent response of rubber materials undergoing finite deformations. This model is unique in its ability to capture large-stretch mechanical behavior with parameters that are connected to the polymer chemistry and can also be easily identified with the important characteristics of the macroscopic stress-stretch response. The microscopic picture consists of two components: a crosslinked network of Langevin chains and an entangled network with chains confined to a nonaffine tube. These represent, respectively, changes in entropy due to thermally averaged chain conformations and changes in entropy due to the magnitude of these conformational fluctuations. A simple analytical form for the strain energy density is obtained using Rubinstein and Panyukov's single-chain description of network behavior. The model only depends on three parameters that together define the initial modulus, extent of strain softening, and the onset of strain hardening. Fits to large stretch data for natural rubber, silicone rubber, VHB 4905 (polyacrylate rubber), and b186 rubber (a carbon black-filled rubber) are presented, and a comparison is made with other similar constitutive models of large-stretch rubber elasticity. We demonstrate that the proposed model provides a complete description of elastomers undergoing large deformations for different applied loading configurations. Moreover, since the strain energy is obtained using a clear set of physical assumptions, this model may be tested and used to interpret the results of computer simulation and experiments on polymers of known microscopic structure.
Quasiequilibrium models for triaxially deformed rotating compact stars
NASA Astrophysics Data System (ADS)
Huang, Xing; Markakis, Charalampos; Sugiyama, Noriyuki; Uryū, Kōji
2008-12-01
Quasiequilibrium models of rapidly rotating triaxially deformed stars are computed in general relativistic gravity, assuming a conformally flat spatial geometry (Isenberg-Wilson-Mathews formulation) and a polytropic equation of state. Highly deformed solutions are calculated on the initial slice covered by spherical coordinate grids, centered at the source, in all angular directions up to a large truncation radius. Constant rest mass sequences are calculated from nearly axisymmetric to maximally deformed triaxial configurations. Selected parameters are to model (proto-) neutron stars; the compactness is M/R=0.001, 0.1, 0.14, and 0.2 for polytropic index n=0.3 and M/R=0.001, 0.1, 0.12, and 0.14 for n=0.5, where M/R refers to that of a nonrotating spherical star having the same rest mass. We confirmed that the triaxial solutions exist for these parameters as in the case of Newtonian polytropes. However, it is also found that the triaxial sequences become shorter for higher compactness, and those disappear at a certain large compactness for the n=0.5 case. In the scenario of the contraction of proto-neutron stars being subject to strong viscosity and rapid cooling, it is plausible that, once the viscosity driven secular instability sets in during the contraction, the proto-neutron stars are always maximally deformed triaxial configurations, as long as the compactness and the equation of state parameters allow such triaxial sequences. Detection of gravitational waves from such sources may be used as another probe for the nuclear equation of state.
Shen, Z; Koyfman, S; Xia, P; Bzdusek, K
2015-06-15
Purpose: To evaluate geometric and dosimetric uncertainties of CT-CBCT deformable image registration (DIR) algorithms using digital phantoms generated from real patients. Methods: We selected ten H&N cancer patients with adaptive IMRT. For each patient, a planning CT (CT1), a replanning CT (CT2), and a pretreatment CBCT (CBCT1) were used as the basis for digital phantom creation. Manually adjusted meshes were created for selected ROIs (e.g. PTVs, brainstem, spinal cord, mandible, and parotids) on CT1 and CT2. The mesh vertices were input into a thin-plate spline algorithm to generate a reference displacement vector field (DVF). The reference DVF was applied to CBCT1 to create a simulated mid-treatment CBCT (CBCT2). The CT-CBCT digital phantom consisted of CT1 and CBCT2, which were linked by the reference DVF. Three DIR algorithms (Demons, B-Spline, and intensity-based) were applied to these ten digital phantoms. The images, ROIs, and volumetric doses were mapped from CT1 to CBCT2 using the DVFs computed by these three DIRs and compared to those mapped using the reference DVF. Results: The average Dice coefficients for selected ROIs were from 0.83 to 0.94 for Demons, from 0.82 to 0.95 for B-Spline, and from 0.67 to 0.89 for intensity-based DIR. The average Hausdorff distances for selected ROIs were from 2.4 to 6.2 mm for Demons, from 1.8 to 5.9 mm for B-Spline, and from 2.8 to 11.2 mm for intensity-based DIR. The average absolute dose errors for selected ROIs were from 0.7 to 2.1 Gy for Demons, from 0.7 to 2.9 Gy for B- Spline, and from 1.3 to 4.5 Gy for intensity-based DIR. Conclusion: Using clinically realistic CT-CBCT digital phantoms, Demons and B-Spline were shown to have similar geometric and dosimetric uncertainties while intensity-based DIR had the worst uncertainties. CT-CBCT DIR has the potential to provide accurate CBCT-based dose verification for H&N adaptive radiotherapy. Z Shen: None; K Bzdusek: an employee of Philips Healthcare; S Koyfman: None; P Xia
Geant4.10 simulation of geometric model for metaphase chromosome
NASA Astrophysics Data System (ADS)
Rafat-Motavalli, L.; Miri-Hakimabad, H.; Bakhtiyari, E.
2016-04-01
In this paper, a geometric model of metaphase chromosome is explained. The model is constructed according to the packing ratio and dimension of the structure from nucleosome up to chromosome. A B-DNA base pair is used to construct 200 base pairs of nucleosomes. Each chromatin fiber loop, which is the unit of repeat, has 49,200 bp. This geometry is entered in Geant4.10 Monte Carlo simulation toolkit and can be extended to the whole metaphase chromosomes and any application in which a DNA geometrical model is needed. The chromosome base pairs, chromosome length, and relative length of chromosomes are calculated. The calculated relative length is compared to the relative length of human chromosomes.
NASA Astrophysics Data System (ADS)
Lüdde, Hans Jürgen; Achenbach, Alexander; Kalkbrenner, Thilo; Jankowiak, Hans-Christian; Kirchner, Tom
2016-04-01
A new model to account for geometric screening corrections in an independent-atom-model description of ion-molecule collisions is introduced. The ion-molecule cross sections for net capture and net ionization are represented as weighted sums of atomic cross sections with weight factors that are determined from a geometric model of overlapping cross section areas. Results are presented for proton collisions with targets ranging from diatomic to complex polyatomic molecules. Significant improvement compared to simple additivity rule results and in general good agreement with experimental data are found. The flexibility of the approach opens up the possibility to study more detailed observables such as orientation-dependent and charge-state-correlated cross sections for a large class of complex targets ranging from biomolecules to atomic clusters.
NASA Astrophysics Data System (ADS)
Hansbo, Peter; Larson, Mats G.; Larsson, Fredrik
2015-07-01
We develop a finite element method for a large deformation membrane elasticity problem on meshed curved surfaces using a tangential differential calculus approach that avoids the use of classical differential geometric methods. The method is also applied to form finding problems.
Facial Performance Transfer via Deformable Models and Parametric Correspondence.
Asthana, Akshay; de la Hunty, Miles; Dhall, Abhinav; Goecke, Roland
2012-09-01
The issue of transferring facial performance from one person's face to another's has been an area of interest for the movie industry and the computer graphics community for quite some time. In recent years, deformable face models, such as the Active Appearance Model (AAM), have made it possible to track and synthesize faces in real time. Not surprisingly, deformable face model-based approaches for facial performance transfer have gained tremendous interest in the computer vision and graphics community. In this paper, we focus on the problem of real-time facial performance transfer using the AAM framework. We propose a novel approach of learning the mapping between the parameters of two completely independent AAMs, using them to facilitate the facial performance transfer in a more realistic manner than previous approaches. The main advantage of modeling this parametric correspondence is that it allows a "meaningful" transfer of both the nonrigid shape and texture across faces irrespective of the speakers' gender, shape, and size of the faces, and illumination conditions. We explore linear and nonlinear methods for modeling the parametric correspondence between the AAMs and show that the sparse linear regression method performs the best. Moreover, we show the utility of the proposed framework for a cross-language facial performance transfer that is an area of interest for the movie dubbing industry. PMID:21931176
Evaluation of Geometrically Nonlinear Reduced Order Models with Nonlinear Normal Modes
Kuether, Robert J.; Deaner, Brandon J.; Hollkamp, Joseph J.; Allen, Matthew S.
2015-09-15
Several reduced-order modeling strategies have been developed to create low-order models of geometrically nonlinear structures from detailed finite element models, allowing one to compute the dynamic response of the structure at a dramatically reduced cost. But, the parameters of these reduced-order models are estimated by applying a series of static loads to the finite element model, and the quality of the reduced-order model can be highly sensitive to the amplitudes of the static load cases used and to the type/number of modes used in the basis. Our paper proposes to combine reduced-order modeling and numerical continuation to estimate the nonlinearmore » normal modes of geometrically nonlinear finite element models. Not only does this make it possible to compute the nonlinear normal modes far more quickly than existing approaches, but the nonlinear normal modes are also shown to be an excellent metric by which the quality of the reduced-order model can be assessed. Hence, the second contribution of this work is to demonstrate how nonlinear normal modes can be used as a metric by which nonlinear reduced-order models can be compared. Moreover, various reduced-order models with hardening nonlinearities are compared for two different structures to demonstrate these concepts: a clamped–clamped beam model, and a more complicated finite element model of an exhaust panel cover.« less
Evaluation of Geometrically Nonlinear Reduced Order Models with Nonlinear Normal Modes
Kuether, Robert J.; Deaner, Brandon J.; Hollkamp, Joseph J.; Allen, Matthew S.
2015-09-15
Several reduced-order modeling strategies have been developed to create low-order models of geometrically nonlinear structures from detailed finite element models, allowing one to compute the dynamic response of the structure at a dramatically reduced cost. But, the parameters of these reduced-order models are estimated by applying a series of static loads to the finite element model, and the quality of the reduced-order model can be highly sensitive to the amplitudes of the static load cases used and to the type/number of modes used in the basis. Our paper proposes to combine reduced-order modeling and numerical continuation to estimate the nonlinear normal modes of geometrically nonlinear finite element models. Not only does this make it possible to compute the nonlinear normal modes far more quickly than existing approaches, but the nonlinear normal modes are also shown to be an excellent metric by which the quality of the reduced-order model can be assessed. Hence, the second contribution of this work is to demonstrate how nonlinear normal modes can be used as a metric by which nonlinear reduced-order models can be compared. Moreover, various reduced-order models with hardening nonlinearities are compared for two different structures to demonstrate these concepts: a clamped–clamped beam model, and a more complicated finite element model of an exhaust panel cover.
NASA Astrophysics Data System (ADS)
Gance, Julien; Bernardie, Séverine; Grandjean, Gilles; Malet, Jean-Philippe
2014-05-01
Landslide hazard can be assessed through numerical hydro-mechanical models. These methods require different input data such as a geometric model, rheological constitutive laws and associated hydro-mechanical parameters, and boundary conditions. The objective of this study is to fill the gap existing between geophysical and engineering communities. This gap prevents the engineering community to use the full information available in geophysical imagery. A landslide geometrical model contains information on the geometry and extent of the different geotechnical units of the landslide, and describes the layering and the discontinuities. It is generally drawn from punctual geotechnical tests, using interpolation, or better, from the combined use of a geotechnical test and the iso-value of geophysical tomographies. In this context, we propose to use a multi-source geophysical data fusion strategy as an aid for the construction of landslide geometric models. Based on a fuzzy logic data fusion method, we propose to use different geophysical tomographies and their associated uncertainty and sensitivity tomograms to design a "probable" geometric model. This strategy is tested on a profile of the Super-Sauze landslide using P-wave velocity, P-wave attenuation and electrical resistivity tomography. We construct a probable model and a true model for numerical modeling. Using basic elastic constitutive laws, we show that the model geometry is sufficiently detailed to simulate the complex surface displacements pattern.
A comparison of descriptive models of a single spike train by information-geometric measure.
Nakahara, Hiroyuki; Amari, Shun-ichi; Richmond, Barry J
2006-03-01
In examining spike trains, different models are used to describe their structure. The different models often seem quite similar, but because they are cast in different formalisms, it is often difficult to compare their predictions. Here we use the information-geometric measure, an orthogonal coordinate representation of point processes, to express different models of stochastic point processes in a common coordinate system. Within such a framework, it becomes straightforward to visualize higher-order correlations of different models and thereby assess the differences between models. We apply the information-geometric measure to compare two similar but not identical models of neuronal spike trains: the inhomogeneous Markov and the mixture of Poisson models. It is shown that they differ in the second- and higher-order interaction terms. In the mixture of Poisson model, the second- and higher-order interactions are of comparable magnitude within each order, whereas in the inhomogeneous Markov model, they have alternating signs over different orders. This provides guidance about what measurements would effectively separate the two models. As newer models are proposed, they also can be compared to these models using information geometry. PMID:16483407
Predicting tumor location by modeling the deformation of the breast.
Pathmanathan, Pras; Gavaghan, David J; Whiteley, Jonathan P; Chapman, S Jonathan; Brady, J Michael
2008-10-01
Breast cancer is one of the biggest killers in the western world, and early diagnosis is essential for improved prognosis. The shape of the breast varies hugely between the scenarios of magnetic resonance (MR) imaging (patient lies prone, breast hanging down under gravity), X-ray mammography (breast strongly compressed) and ultrasound or biopsy/surgery (patient lies supine), rendering image fusion an extremely difficult task. This paper is concerned with the use of the finite-element method and nonlinear elasticity to build a 3-D, patient-specific, anatomically accurate model of the breast. The model is constructed from MR images and can be deformed to simulate breast shape and predict tumor location during mammography or biopsy/surgery. Two extensions of the standard elasticity problem need to be solved: an inverse elasticity problem (arising from the fact that only a deformed, stressed, state is known initially), and the contact problem of modeling compression. The model is used for craniocaudal mediolateral oblique mammographic image matching, and a number of numerical experiments are performed. PMID:18838373
NASA Astrophysics Data System (ADS)
Kwon, H.
2011-12-01
The impact of climate variation on monsoon seasonal rainfall has been generally well documented in the climate literature. However, rather limited efforts have been done to understand moisture transport and their impact on extreme rainfall in the hydrology field. This study developed a new model for extracting moisture tracks associated with extreme events as a way to characterize large scale climate system. Main interests are to derive location, size and direction of the rainfall field and this study developed an algorithm to extract the above characteristics from global climate data set. In order to facilitate characterization of synoptic patterns, geometric moment based ellipsoid models are introduced. Local weather station data in Korea and NCEP reanalysis data are mainly utilized to identify synoptic patterns. The proposed geometric moments based ellipsoid model works equally well with regularly and irregularly distributed synthetic grid data. Finally, the proposed model was applied to space-time real moisture transport. We extracted daily wind patterns and specific humidity on top 20 extreme rainfall events and apply a 90% threshold to isolate high magnitude of moisture transport associated with extreme rainfall in South Korea. It was found that location, size and direction of the rainfall field was successfully extracted. Our analyses of daily synoptic moisture transport patterns defined by geometric moments suggest can be possibly clustered given their intensity, direction and position properties. Acknowledgement : This work was supported by National Research Foundation of Korea Grant funded by the Korean Government (NRF-2010-220-D00083)
A human supervisory approach to rapid world modeling through the use of geometric primitives
Luck, J.; Roberts, R.
1997-08-11
A three-dimensional world model is crucial for many robot-oriented tasks. The most efficient mapping configuration use geometric primitives to model environments, and are easy to store and process. In the past, modeling techniques have been either fully manual or autonomous. Manual methods are extremely time consuming but also highly accurate and flexible. On the other hand autonomous techniques are fast but inflexible and often inaccurate. The method presented in this paper combines the two thereby yielding a highly efficient, flexible, and accurate tool. Our methods enable a human supervisor to quickly construct a fully defined world model from unfiltered and unsegmented real-world range data.
Hubble space telescope observations and geometric models of compact multipolar planetary nebulae
Hsia, Chih-Hao; Chau, Wayne; Zhang, Yong; Kwok, Sun E-mail: wwlljj1314@gmail.com E-mail: sunkwok@hku.hk
2014-05-20
We report high angular resolution Hubble Space Telescope observations of 10 compact planetary nebulae (PNs). Many interesting internal structures, including multipolar lobes, arcs, two-dimensional rings, tori, and halos, are revealed for the first time. These results suggest that multipolar structures are common among PNs, and these structures develop early in their evolution. From three-dimensional geometric models, we have determined the intrinsic dimensions of the lobes. Assuming the lobes are the result of interactions between later-developed fast winds and previously ejected asymptotic giant branch winds, the geometric structures of these PNs suggest that there are multiple phases of fast winds separated by temporal variations and/or directional changes. A scenario of evolution from lobe-dominated to cavity-dominated stages is presented. The results reported here will provide serious constraints on any dynamical models of PNs.
Dislocation model for aseismic crustal deformation at Hollister, California
NASA Technical Reports Server (NTRS)
Matsuura, Mitsuhiro; Jackson, David D.; Cheng, Abe
1986-01-01
A model of crustal deformation during the interseismic phase is developed and applied (using the improved Bayesian inversion algorithm described by Jackson and Matsu'ura, 1985) to trilateration data for the USGS Hollister (CA) network. In the model, rigid blocks in motion relative to each other experience friction only in a brittle upper zone, while their ductile lower zones slide freely; the Hollister model comprises five blocks and nine rectangular fault patches. The data and results are presented in tables, graphs, and maps and characterized in detail. The model predicts steady block motion on time scales between 10 yr and 1 Myr, with net motion across the San Andreas/Calaveras fault system 38 + or - 3 mm/yr and brittle/ductile transition depths ranging from 0.4 to 11 km. Two San Andreas segments with higher probabilities of moderate-to-large earthquakes are identified.
Comparison of Three Optical Methods for Measuring Model Deformation
NASA Technical Reports Server (NTRS)
Burner, A. W.; Fleming, G. A.; Hoppe, J. C.
2000-01-01
The objective of this paper is to compare the current state-of-the-art of the following three optical techniques under study by NASA for measuring model deformation in wind tunnels: (1) video photogrammetry, (2) projection moire interferometry, and (3) the commercially available Optotrak system. An objective comparison of these three techniques should enable the selection of the best technique for a particular test undertaken at various NASA facilities. As might be expected, no one technique is best for all applications. The techniques are also not necessarily mutually exclusive and in some cases can be complementary to one another.
Algebraic approach to the projected deformed oscillator model
NASA Astrophysics Data System (ADS)
Asherova, R. M.; Smirnov, Yu. F.; Tolstoy, V. N.; Shustov, A. P.
1981-03-01
A new method of calculation in terms of the projected deformed oscillator model is proposed. The method involves expansion of its wave functions in terms of the wave functions of an isotropic oscillator potential. Only overlap integrals between projected wave functions and reduced probabilities B(E2) of E2 transitions are examined. B(E2) values are expressed as a series containing the corresponding values of the Elliott SU(3) scheme. The convergence of these expansions is shown to be fairly good. The expectation values of operators ( QQ) and ( QQQ), which characterize the effective internal non-sphericity and non-axiality of the nucleus, are also calculated and discussed.
NASA Astrophysics Data System (ADS)
Wu, Chensheng; Nelson, William; Davis, Christopher C.
2014-10-01
Plenoptic functions are functions that preserve all the necessary light field information of optical events. Theoretical work has demonstrated that geometric based plenoptic functions can serve equally well in the traditional wave propagation equation known as the "scalar stochastic Helmholtz equation". However, in addressing problems of 3D turbulence simulation, the dominant methods using phase screen models have limitations both in explaining the choice of parameters (on the transverse plane) in real-world measurements, and finding proper correlations between neighboring phase screens (the Markov assumption breaks down). Though possible corrections to phase screen models are still promising, the equivalent geometric approach based on plenoptic functions begins to show some advantages. In fact, in these geometric approaches, a continuous wave problem is reduced to discrete trajectories of rays. This allows for convenience in parallel computing and guarantees conservation of energy. Besides the pairwise independence of simulated rays, the assigned refractive index grids can be directly tested by temperature measurements with tiny thermoprobes combined with other parameters such as humidity level and wind speed. Furthermore, without loss of generality one can break the causal chain in phase screen models by defining regional refractive centers to allow rays that are less affected to propagate through directly. As a result, our work shows that the 3D geometric approach serves as an efficient and accurate method in assessing relevant turbulence problems with inputs of several environmental measurements and reasonable guesses (such as Cn 2 levels). This approach will facilitate analysis and possible corrections in lateral wave propagation problems, such as image de-blurring, prediction of laser propagation over long ranges, and improvement of free space optic communication systems. In this paper, the plenoptic function model and relevant parallel algorithm computing
NASA Astrophysics Data System (ADS)
Changyong, Dou; Huadong, Guo; Chunming, Han; yuquan, Liu; Xijuan, Yue; Yinghui, Zhao
2014-03-01
Raw signal simulation is a useful tool for the system design, mission planning, processing algorithm testing, and inversion algorithm design of Synthetic Aperture Radar (SAR). Due to the wide and high frequent variation of aircraft's trajectory and attitude, and the low accuracy of the Position and Orientation System (POS)'s recording data, it's difficult to quantitatively study the sensitivity of the key parameters, i.e., the baseline length and inclination, absolute phase and the orientation of the antennas etc., of the airborne Interferometric SAR (InSAR) system, resulting in challenges for its applications. Furthermore, the imprecise estimation of the installation offset between the Global Positioning System (GPS), Inertial Measurement Unit (IMU) and the InSAR antennas compounds the issue. An airborne interferometric SAR (InSAR) simulation based on the rigorous geometric model and real navigation data is proposed in this paper, providing a way for quantitatively studying the key parameters and for evaluating the effect from the parameters on the applications of airborne InSAR, as photogrammetric mapping, high-resolution Digital Elevation Model (DEM) generation, and surface deformation by Differential InSAR technology, etc. The simulation can also provide reference for the optimal design of the InSAR system and the improvement of InSAR data processing technologies such as motion compensation, imaging, image co-registration, and application parameter retrieval, etc.
Modeling and Prediction of Hot Deformation Flow Curves
NASA Astrophysics Data System (ADS)
Mirzadeh, Hamed; Cabrera, Jose Maria; Najafizadeh, Abbas
2012-01-01
The modeling of hot flow stress and prediction of flow curves for unseen deformation conditions are important in metal-forming processes because any feasible mathematical simulation needs accurate flow description. In the current work, in an attempt to summarize, generalize, and introduce efficient methods, the dynamic recrystallization (DRX) flow curves of a 17-4 PH martensitic precipitation hardening stainless steel, a medium carbon microalloyed steel, and a 304 H austenitic stainless steel were modeled and predicted using (1) a hyperbolic sine equation with strain dependent constants, (2) a developed constitutive equation in a simple normalized stress-normalized strain form and its modified version, and (3) a feed-forward artificial neural network (ANN). These methods were critically discussed, and the ANN technique was found to be the best for the modeling available flow curves; however, the developed constitutive equation showed slightly better performance than that of ANN and significantly better predicted values than those of the hyperbolic sine equation in prediction of flow curves for unseen deformation conditions.
Hirzel, Alexandre H; Arlettaz, Raphaël
2003-11-01
This paper presents a new habitat suitability modeling method whose main properties are as follows: (1) It is based on the density of observation points in the environmental space, which enables it to fit complex distributions (e.g. nongaussian, bimodal, asymmetrical, etc.). (2) This density is modeled by computing the geometric mean to all observation points, which we show to be a good trade-off between goodness of fit and prediction power. (3) It does not need any absence information, which is generally difficult to collect and of dubious reliability. (4) The environmental space is represented either by an expert-selection of standardized variables or the axes of a factor analysis [in this paper we used the Ecological Niche Factor Analysis (ENFA)]. We first explain the details of the geometric mean algorithm and then we apply it to the bearded vulture (Gypaetus barbatus) habitat in the Swiss Alps. The results are compared to those obtained by the "median algorithm" and tested by jack-knife cross-validation. We also discuss other related algorithms (BIOCLIM, HABITAT, and DOMAIN). All these analyses were implemented into and performed with the ecology-oriented GIS software BIOMAPPER 2.0.The results show the geometric mean to perform better than the median algorithm, as it produces a tighter fit to the bimodal distribution of the bearded vulture in the environmental space. However, the "median algorithm" being quicker, it could be preferred when modeling more usual distribution. PMID:15015699
Telfer, Scott; Erdemir, Ahmet; Woodburn, James; Cavanagh, Peter R
2016-01-25
Integration of patient-specific biomechanical measurements into the design of therapeutic footwear has been shown to improve clinical outcomes in patients with diabetic foot disease. The addition of numerical simulations intended to optimise intervention design may help to build on these advances, however at present the time and labour required to generate and run personalised models of foot anatomy restrict their routine clinical utility. In this study we developed second-generation personalised simple finite element (FE) models of the forefoot with varying geometric fidelities. Plantar pressure predictions from barefoot, shod, and shod with insole simulations using simplified models were compared to those obtained from CT-based FE models incorporating more detailed representations of bone and tissue geometry. A simplified model including representations of metatarsals based on simple geometric shapes, embedded within a contoured soft tissue block with outer geometry acquired from a 3D surface scan was found to provide pressure predictions closest to the more complex model, with mean differences of 13.3kPa (SD 13.4), 12.52kPa (SD 11.9) and 9.6kPa (SD 9.3) for barefoot, shod, and insole conditions respectively. The simplified model design could be produced in <1h compared to >3h in the case of the more detailed model, and solved on average 24% faster. FE models of the forefoot based on simplified geometric representations of the metatarsal bones and soft tissue surface geometry from 3D surface scans may potentially provide a simulation approach with improved clinical utility, however further validity testing around a range of therapeutic footwear types is required. PMID:26708965
Technology Transfer Automated Retrieval System (TEKTRAN)
Fractal and prefractal geometric models have substantial potential of contributing to the analysis of flow and transport in porous media such as soils and reservoir rocks. In this study, geometric and hydrodynamic parameters of saturated 3D mass and pore-solid prefractal porous media were characteri...
Multi-view and 3D deformable part models.
Pepik, Bojan; Stark, Michael; Gehler, Peter; Schiele, Bernt
2015-11-01
As objects are inherently 3D, they have been modeled in 3D in the early days of computer vision. Due to the ambiguities arising from mapping 2D features to 3D models, 3D object representations have been neglected and 2D feature-based models are the predominant paradigm in object detection nowadays. While such models have achieved outstanding bounding box detection performance, they come with limited expressiveness, as they are clearly limited in their capability of reasoning about 3D shape or viewpoints. In this work, we bring the worlds of 3D and 2D object representations closer, by building an object detector which leverages the expressive power of 3D object representations while at the same time can be robustly matched to image evidence. To that end, we gradually extend the successful deformable part model [1] to include viewpoint information and part-level 3D geometry information, resulting in several different models with different level of expressiveness. We end up with a 3D object model, consisting of multiple object parts represented in 3D and a continuous appearance model. We experimentally verify that our models, while providing richer object hypotheses than the 2D object models, provide consistently better joint object localization and viewpoint estimation than the state-of-the-art multi-view and 3D object detectors on various benchmarks (KITTI [2] , 3D object classes [3] , Pascal3D+ [4] , Pascal VOC 2007 [5] , EPFL multi-view cars[6] ). PMID:26440264
Modeling Permanent Deformations of Superelastic and Shape Memory Materials
Urbano, Marco Fabrizio; Auricchio, Ferdinando
2015-01-01
In this paper we propose a modification of the polycrystalline shape memory alloy constitutive model originally proposed by Souza. By introducing a transformation strain energy with two different hardening coefficients, we are able to take into account the effect of the martensitic transformation of unfavorably oriented grains occurring after the main plateau. By choosing a proper second hardening coefficient, it is possible to reproduce the correct stress strain behavior of the material after the plateau without the need of introducing a much smaller Young modulus for martensite. The proposed modification is introduced in the model comprising permanent deformation effects. Model results for uniaxial stress tests are compared to experimental results showing good agreement. PMID:26110494
Statistical Modeling of CTV Motion and Deformation for IMRT of Early-Stage Rectal Cancer
Bondar, Luiza; Intven, Martijn; Burbach, J.P. Maarten; Budiarto, Eka; Kleijnen, Jean-Paul; Philippens, Marielle; Asselen, Bram van; Seravalli, Enrica; Reerink, Onne; Raaymakers, Bas
2014-11-01
Purpose: To derive and validate a statistical model of motion and deformation for the clinical target volume (CTV) of early-stage rectal cancer patients. Methods and Materials: For 16 patients, 4 to 5 magnetic resonance images (MRI) were acquired before each fraction was administered. The CTV was delineated on each MRI. Using a leave-one-out methodology, we constructed a population-based principal component analysis (PCA) model of the CTV motion and deformation of 15 patients, and we tested the model on the left-out patient. The modeling error was calculated as the amount of the CTV motion-deformation of the left-out-patient that could not be explained by the PCA model. Next, the PCA model was used to construct a PCA target volume (PCA-TV) by accumulating motion-deformations simulated by the model. A PCA planning target volume (PTV) was generated by expanding the PCA-TV by uniform margins. The PCA-PTV was compared with uniform and nonuniform CTV-to-PTV margins. To allow comparison, geometric margins were determined to ensure adequate coverage, and the volume difference between the PTV and the daily CTV (CTV-to-PTV volume) was calculated. Results: The modeling error ranged from 0.9 ± 0.5 to 2.9 ± 2.1 mm, corresponding to a reduction of the CTV motion-deformation between 6% and 60% (average, 23% ± 11%). The reduction correlated with the magnitude of the CTV motion-deformation (P<.001, R=0.66). The PCA-TV and the CTV required 2-mm and 7-mm uniform margins, respectively. The nonuniform CTV-to-PTV margins were 4 mm in the left, right, inferior, superior, and posterior directions and 8 mm in the anterior direction. Compared to uniform and nonuniform CTV-to-PTV margins, the PCA-based PTV significantly decreased (P<.001) the average CTV-to-PTV volume by 128 ± 20 mL (49% ± 4%) and by 35 ± 6 mL (20% ± 3.5%), respectively. Conclusions: The CTV motion-deformation of a new patient can be explained by a population-based PCA model. A PCA model
Phase field modeling of partially saturated deformable porous media
NASA Astrophysics Data System (ADS)
Sciarra, Giulio
2016-09-01
A poromechanical model of partially saturated deformable porous media is proposed based on a phase field approach at modeling the behavior of the mixture of liquid water and wet air, which saturates the pore space, the phase field being the saturation (ratio). While the standard retention curve is expected still^ to provide the intrinsic retention properties of the porous skeleton, depending on the porous texture, an enhanced description of surface tension between the wetting (liquid water) and the non-wetting (wet air) fluid, occupying the pore space, is stated considering a regularization of the phase field model based on an additional contribution to the overall free energy depending on the saturation gradient. The aim is to provide a more refined description of surface tension interactions. An enhanced constitutive relation for the capillary pressure is established together with a suitable generalization of Darcy's law, in which the gradient of the capillary pressure is replaced by the gradient of the so-called generalized chemical potential, which also accounts for the "force", associated to the local free energy of the phase field model. A micro-scale heuristic interpretation of the novel constitutive law of capillary pressure is proposed, in order to compare the envisaged model with that one endowed with the concept of average interfacial area. The considered poromechanical model is formulated within the framework of strain gradient theory in order to account for possible effects, at laboratory scale, of the micro-scale hydro-mechanical couplings between highly localized flows (fingering) and localized deformations of the skeleton (fracturing).
Tian, Liang; Russell, Alan; Anderson, Iver
2014-01-03
Deformation processed metal–metal composites (DMMCs) are high-strength, high-electrical conductivity composites developed by severe plastic deformation of two ductile metal phases. The extraordinarily high strength of DMMCs is underestimated using the rule of mixture (or volumetric weighted average) of conventionally work-hardened metals. A dislocation-density-based, strain–gradient–plasticity model is proposed to relate the strain-gradient effect with the geometrically necessary dislocations emanating from the interface to better predict the strength of DMMCs. The model prediction was compared with our experimental findings of Cu–Nb, Cu–Ta, and Al–Ti DMMC systems to verify the applicability of the new model. The results show that this model predicts the strength of DMMCs better than the rule-of-mixture model. The strain-gradient effect, responsible for the exceptionally high strength of heavily cold worked DMMCs, is dominant at large deformation strain since its characteristic microstructure length is comparable with the intrinsic material length.
Tian, Liang; Russell, Alan; Anderson, Iver
2014-01-03
Deformation processed metal–metal composites (DMMCs) are high-strength, high-electrical conductivity composites developed by severe plastic deformation of two ductile metal phases. The extraordinarily high strength of DMMCs is underestimated using the rule of mixture (or volumetric weighted average) of conventionally work-hardened metals. In this article, a dislocation-density-based, strain–gradient–plasticity model is proposed to relate the strain-gradient effect with the geometrically necessary dislocations emanating from the interface to better predict the strength of DMMCs. The model prediction was compared with the experimental findings of Cu–Nb, Cu–Ta, and Al–Ti DMMC systems to verify the applicability of the new model. The results show that this model predicts the strength of DMMCs better than the rule-of-mixture model. The strain-gradient effect, responsible for the exceptionally high strength of heavily cold worked DMMCs, is dominant at large deformation strain since its characteristic microstructure length is comparable with the intrinsic material length.
Tian, Liang; Russell, Alan; Anderson, Iver
2014-01-03
Deformation processed metal–metal composites (DMMCs) are high-strength, high-electrical conductivity composites developed by severe plastic deformation of two ductile metal phases. The extraordinarily high strength of DMMCs is underestimated using the rule of mixture (or volumetric weighted average) of conventionally work-hardened metals. A dislocation-density-based, strain–gradient–plasticity model is proposed to relate the strain-gradient effect with the geometrically necessary dislocations emanating from the interface to better predict the strength of DMMCs. The model prediction was compared with our experimental findings of Cu–Nb, Cu–Ta, and Al–Ti DMMC systems to verify the applicability of the new model. The results show that this model predicts themore » strength of DMMCs better than the rule-of-mixture model. The strain-gradient effect, responsible for the exceptionally high strength of heavily cold worked DMMCs, is dominant at large deformation strain since its characteristic microstructure length is comparable with the intrinsic material length.« less
Tracheal stent prediction using statistical deformable models of tubular shapes
NASA Astrophysics Data System (ADS)
Pinho, R.; Huysmans, T.; Vos, W.; Sijbers, J.
2008-03-01
Tracheal stenosis is a narrowing of the trachea that impedes normal breathing. Tracheotomy is one solution, but subjects patients to intubation. An alternative technique employs tracheal stents, which are tubular structures that push the walls of the stenotic areas to their original location. They are implanted with endoscopes, therefore reducing the surgical risk to the patient. Stents can also be used in tracheal reconstruction to aid the recovery of reconstructed areas. Correct preoperative stent length and diameter specification is crucial to successful treatment, otherwise stents might not cover the stenotic area nor push the walls as required. The level of stenosis is usually measured from inside the trachea, either with endoscopes or with image processing techniques that, eg compute the distance from the centre line to the walls of the trachea. These methods are not suited for the prediction of stent sizes because they can not trivially estimate the healthy calibre of the trachea at the stenotic region. We propose an automatic method that enables the estimation of stent dimensions with statistical shape models of the trachea. An average trachea obtained from a training set of CT scans of healthy tracheas is placed in a CT image of a diseased person. The shape deforms according to the statistical model to match the walls of the trachea, except at stenotic areas. Since the deformed shape gives an estimation of the healthy trachea, it is possible to predict the size and diameter of the stent to be implanted in that specific subject.
Continuum modeling of deformation and aggregation of red blood cells.
Yoon, Daegeun; You, Donghyun
2016-07-26
In order to gain better understanding for rheology of an isolated red blood cell (RBC) and a group of multiple RBCs, new continuum models for describing mechanical properties of cellular structures of an RBC and inter-cellular interactions among multiple RBCs are developed. The viscous property of an RBC membrane, which characterizes dynamic behaviors of an RBC under stress loading and unloading processes, is determined using a generalized Maxwell model. The present model is capable of predicting stress relaxation and stress-strain hysteresis, of which prediction is not possible using the commonly used Kelvin-Voigt model. Nonlinear elasticity of an RBC is determined using the Yeoh hyperelastic material model in a framework of continuum mechanics using finite-element approximation. A novel method to model inter-cellular interactions among multiple adjacent RBCs is also developed. Unlike the previous modeling approaches for aggregation of RBCs, where interaction energy for aggregation is curve-fitted using a Morse-type potential function, the interaction energy is analytically determined. The present aggregation model, therefore, allows us to predict various effects of physical parameters such as the osmotic pressure, the thickness of a glycocalyx layer, the penetration depth, and the permittivity, on the depletion and electrostatic energy among RBCs. Simulations for elongation and recovery deformation of an RBC and for aggregation of multiple RBCs are conducted to evaluate the efficacy of the present continuum modeling methods. PMID:26706720
Automated 3D Motion Tracking using Gabor Filter Bank, Robust Point Matching, and Deformable Models
Wang, Xiaoxu; Chung, Sohae; Metaxas, Dimitris; Axel, Leon
2013-01-01
Tagged Magnetic Resonance Imaging (tagged MRI or tMRI) provides a means of directly and noninvasively displaying the internal motion of the myocardium. Reconstruction of the motion field is needed to quantify important clinical information, e.g., the myocardial strain, and detect regional heart functional loss. In this paper, we present a three-step method for this task. First, we use a Gabor filter bank to detect and locate tag intersections in the image frames, based on local phase analysis. Next, we use an improved version of the Robust Point Matching (RPM) method to sparsely track the motion of the myocardium, by establishing a transformation function and a one-to-one correspondence between grid tag intersections in different image frames. In particular, the RPM helps to minimize the impact on the motion tracking result of: 1) through-plane motion, and 2) relatively large deformation and/or relatively small tag spacing. In the final step, a meshless deformable model is initialized using the transformation function computed by RPM. The model refines the motion tracking and generates a dense displacement map, by deforming under the influence of image information, and is constrained by the displacement magnitude to retain its geometric structure. The 2D displacement maps in short and long axis image planes can be combined to drive a 3D deformable model, using the Moving Least Square method, constrained by the minimization of the residual error at tag intersections. The method has been tested on a numerical phantom, as well as on in vivo heart data from normal volunteers and heart disease patients. The experimental results show that the new method has a good performance on both synthetic and real data. Furthermore, the method has been used in an initial clinical study to assess the differences in myocardial strain distributions between heart disease (left ventricular hypertrophy) patients and the normal control group. The final results show that the proposed method
Analysis of deformable image registration accuracy using computational modeling.
Zhong, Hualiang; Kim, Jinkoo; Chetty, Indrin J
2010-03-01
Computer aided modeling of anatomic deformation, allowing various techniques and protocols in radiation therapy to be systematically verified and studied, has become increasingly attractive. In this study the potential issues in deformable image registration (DIR) were analyzed based on two numerical phantoms: One, a synthesized, low intensity gradient prostate image, and the other a lung patient's CT image data set. Each phantom was modeled with region-specific material parameters with its deformation solved using a finite element method. The resultant displacements were used to construct a benchmark to quantify the displacement errors of the Demons and B-Spline-based registrations. The results show that the accuracy of these registration algorithms depends on the chosen parameters, the selection of which is closely associated with the intensity gradients of the underlying images. For the Demons algorithm, both single resolution (SR) and multiresolution (MR) registrations required approximately 300 iterations to reach an accuracy of 1.4 mm mean error in the lung patient's CT image (and 0.7 mm mean error averaged in the lung only). For the low gradient prostate phantom, these algorithms (both SR and MR) required at least 1600 iterations to reduce their mean errors to 2 mm. For the B-Spline algorithms, best performance (mean errors of 1.9 mm for SR and 1.6 mm for MR, respectively) on the low gradient prostate was achieved using five grid nodes in each direction. Adding more grid nodes resulted in larger errors. For the lung patient's CT data set, the B-Spline registrations required ten grid nodes in each direction for highest accuracy (1.4 mm for SR and 1.5 mm for MR). The numbers of iterations or grid nodes required for optimal registrations depended on the intensity gradients of the underlying images. In summary, the performance of the Demons and B-Spline registrations have been quantitatively evaluated using numerical phantoms. The results show that parameter
Analysis of deformable image registration accuracy using computational modeling
Zhong Hualiang; Kim, Jinkoo; Chetty, Indrin J.
2010-03-15
Computer aided modeling of anatomic deformation, allowing various techniques and protocols in radiation therapy to be systematically verified and studied, has become increasingly attractive. In this study the potential issues in deformable image registration (DIR) were analyzed based on two numerical phantoms: One, a synthesized, low intensity gradient prostate image, and the other a lung patient's CT image data set. Each phantom was modeled with region-specific material parameters with its deformation solved using a finite element method. The resultant displacements were used to construct a benchmark to quantify the displacement errors of the Demons and B-Spline-based registrations. The results show that the accuracy of these registration algorithms depends on the chosen parameters, the selection of which is closely associated with the intensity gradients of the underlying images. For the Demons algorithm, both single resolution (SR) and multiresolution (MR) registrations required approximately 300 iterations to reach an accuracy of 1.4 mm mean error in the lung patient's CT image (and 0.7 mm mean error averaged in the lung only). For the low gradient prostate phantom, these algorithms (both SR and MR) required at least 1600 iterations to reduce their mean errors to 2 mm. For the B-Spline algorithms, best performance (mean errors of 1.9 mm for SR and 1.6 mm for MR, respectively) on the low gradient prostate was achieved using five grid nodes in each direction. Adding more grid nodes resulted in larger errors. For the lung patient's CT data set, the B-Spline registrations required ten grid nodes in each direction for highest accuracy (1.4 mm for SR and 1.5 mm for MR). The numbers of iterations or grid nodes required for optimal registrations depended on the intensity gradients of the underlying images. In summary, the performance of the Demons and B-Spline registrations have been quantitatively evaluated using numerical phantoms. The results show that parameter
Modelling couplings between reaction, fluid flow and deformation: Kinetics
NASA Astrophysics Data System (ADS)
Malvoisin, Benjamin; Podladchikov, Yury Y.; Connolly, James A. D.
2016-04-01
Mineral assemblages out of equilibrium are commonly found in metamorphic rocks testifying of the critical role of kinetics for metamorphic reactions. As experimentally determined reaction rates in fluid-saturated systems generally indicate complete reaction in less than several years, i.e. several orders of magnitude faster than field-based estimates, metamorphic reaction kinetics are generally thought to be controlled by transport rather than by processes at the mineral surface. However, some geological processes like earthquakes or slow-slip events have shorter characteristic timescales, and transport processes can be intimately related to mineral surface processes. Therefore, it is important to take into account the kinetics of mineral surface processes for modelling fluid/rock interactions. Here, a model coupling reaction, fluid flow and deformation was improved by introducing a delay in the achievement of equilibrium. The classical formalism for dissolution/precipitation reactions was used to consider the influence of the distance from equilibrium and of temperature on the reaction rate, and a dependence on porosity was introduced to model evolution of reacting surface area during reaction. The fitting of experimental data for three reactions typically occurring in metamorphic systems (serpentine dehydration, muscovite dehydration and calcite decarbonation) indicates a systematic faster kinetics close from equilibrium on the dehydration side than on the hydration side. This effect is amplified through the porosity term in the reaction rate since porosity is formed during dehydration. Numerical modelling indicates that this difference in reaction rate close from equilibrium plays a key role in microtextures formation. The developed model can be used in a wide variety of geological systems where couplings between reaction, deformation and fluid flow have to be considered.
Multiple unfoldings of orbifold singularities: Engineering geometric analogies to unification
Bourjaily, Jacob L.
2009-02-15
Katz and Vafa [Nucl. Phys. B497, 146 (1997)] showed how charged matter can arise geometrically by the deformation of ADE-type orbifold singularities in type IIa, M-theory, and F-theory compactifications. In this paper we use those same basic ingredients, used there to geometrically engineer specific matter representations, here to deform the compactification manifold itself in a way which naturally compliments many features of unified model building. We realize this idea explicitly by deforming a manifold engineered to give rise to an SU{sub 5} grand unified model into a one giving rise to the standard model. In this framework, the relative local positions of the singularities giving rise to standard model fields are specified in terms of the values of a small number of complex structure moduli which deform the original manifold, greatly reducing the arbitrariness of their relative positions.
On the Modeling of Plastic Deformation of Magnesium Alloys
Ertuerk, S.; Steglich, D.; Bohlen, J.; Letzig, D.; Brocks, W.
2007-05-17
Magnesium alloys are promising materials due to their low density and therefore high specific strength. However, the industrial application is not well established so far, especially for wrought products such as sheets or profiles. Due to its hexagonal crystallographic structure, deformation mechanisms observed in magnesium alloys are rather different from those in face centered cubic metals such as aluminum alloys. This leads not only to a mechanical anisotropy, but also to a tension-compression asymmetry, i.e. unequal compressive and tensile yield strength. The resulting complexity in the yielding behavior of such materials cannot be captured by conventional models of J2 plasticity. Cazacu and Barlat, therefore, proposed a phenomenological yield potential which accounts for the respective phenomena by introducing the third invariant of the stress tensor. Simulations based on this model are performed with ABAQUS/Explicit and a user defined routine VUMAT for validating the respective implementation. The application aims at simulating the extrusion process of magnesium alloys.
Meshless analysis of shear deformable shells: the linear model
NASA Astrophysics Data System (ADS)
Costa, Jorge C.; Tiago, Carlos M.; Pimenta, Paulo M.
2013-10-01
This work develops a kinematically linear shell model departing from a consistent nonlinear theory. The initial geometry is mapped from a flat reference configuration by a stress-free finite deformation, after which, the actual shell motion takes place. The model maintains the features of a complete stress-resultant theory with Reissner-Mindlin kinematics based on an inextensible director. A hybrid displacement variational formulation is presented, where the domain displacements and kinematic boundary reactions are independently approximated. The resort to a flat reference configuration allows the discretization using 2-D Multiple Fixed Least-Squares (MFLS) on the domain. The consistent definition of stress resultants and consequent plane stress assumption led to a neat formulation for the analysis of shells. The consistent linear approximation, combined with MFLS, made possible efficient computations with a desired continuity degree, leading to smooth results for the displacement, strain and stress fields, as shown by several numerical examples.
Modeling level structures of odd-odd deformed nuclei
Hoff, R.W.; Kern, J.; Piepenbring, R.; Boisson, J.P.
1985-01-15
A technique for modeling quasiparticle excitation energies and rotational parameters in odd-odd deformed nuclei has been applied to actinide species where new experimental data have been obtained by use of neutron-capture gamma-ray spectroscopy. The input parameters required for the calculation were derived from empirical data on single-particle excitations in neighboring odd-mass nuclei. Calculated configuration-specific values for the Gallagher-Moszkowski splittings were used. Calculated and experimental level structures for /sup 238/Np, /sup 244/Am, and /sup 250/Bk are compared, as well as those for several nuclei in the rare-earch region. The agreement for the actinide species is excellent, with bandhead energies deviating 22 keV and rotational parameters 5%, on the average. Corresponding average deviations for five rare-earth nuclei are 47 keV and 7%. Several applications of this modeling technique are discussed.
Modeling level structures of odd-odd deformed nuclei
Hoff, R.W.; Kern, J.; Piepenbring, R.; Boisson, J.P.
1984-09-07
A technique for modeling quasiparticle excitation energies and rotational parameters in odd-odd deformed nuclei has been applied to actinide species where new experimental data have been obtained by use of neutron-capture gamma-ray spectroscopy. The input parameters required for the calculation were derived from empirical data on single-particle excitations in neighboring odd-mass nuclei. Calculated configuration-specific values for the Gallagher-Moszkowski splittings were used. Calculated and experimental level structures for /sup 238/Np, /sup 244/Am, and /sup 250/Bk are compared, as well as those for several nuclei in the rare-earth region. The agreement for the actinide species is excellent, with bandhead energies deviating 22 keV and rotational parameters 5%, on the average. Corresponding average deviations for five rare-earth nuclei are 47 keV and 7%. Several applications of this modeling technique are discussed. 18 refs., 5 figs., 4 tabs.
A micromechanical model for the deformation behavior of titanium polycrystals
NASA Astrophysics Data System (ADS)
Romanova, V.; Balokhonov, R.; Shakhidjanov, V.; Zinovieva, O.
2015-10-01
A microstructure-based constitutive model for a polycrystalline titanium alloy is constructed on the basis of anisotropic elasticity and crystal plasticity theory, with allowance made for the prismatic and basal slip systems. A three-dimensional polycrystalline structure consisting of 1600 grains is designed by a step-by-step packing method and introduced explicitly into finite-element calculations. Numerical modeling of uniaxial tension is performed using Abaqus/Explicit. Grains unfavorably oriented to the loading axis are shown to remain elastic, while slip occurs in the neighboring grains. As this takes place, rotational modes of deformation are activated in addition to shear strain (translational) modes, and surface grains with a low ability to yield demonstrate a tendency towards extrusion.
Variable-intercept panel model for deformation zoning of a super-high arch dam.
Shi, Zhongwen; Gu, Chongshi; Qin, Dong
2016-01-01
This study determines dam deformation similarity indexes based on an analysis of deformation zoning features and panel data clustering theory, with comprehensive consideration to the actual deformation law of super-high arch dams and the spatial-temporal features of dam deformation. Measurement methods of these indexes are studied. Based on the established deformation similarity criteria, the principle used to determine the number of dam deformation zones is constructed through entropy weight method. This study proposes the deformation zoning method for super-high arch dams and the implementation steps, analyzes the effect of special influencing factors of different dam zones on the deformation, introduces dummy variables that represent the special effect of dam deformation, and establishes a variable-intercept panel model for deformation zoning of super-high arch dams. Based on different patterns of the special effect in the variable-intercept panel model, two panel analysis models were established to monitor fixed and random effects of dam deformation. Hausman test method of model selection and model effectiveness assessment method are discussed. Finally, the effectiveness of established models is verified through a case study. PMID:27386345
NASA Astrophysics Data System (ADS)
Invernizzi, Davide; Dozio, Lorenzo
2016-05-01
The equations of motions governing the free vibrations of prismatic slender beams rotating in a plane at constant angular velocity are derived according to a geometrically exact approach. Compared to other modeling methods, additional stiffening terms induced by pre-stress are found in the dynamic equations after fully consistent linearization about the deformed equilibrium configuration. These terms include axial, bending and torsional stiffening effects which arise when second-order generalized strains are retained. It is shown that their contribution becomes relevant at moderate to high angular speeds, where high means that the equilibrium state is subject to strains close to the limit where a physically linear constitutive law still applies. In particular, the importance of the axial stiffening is specifically investigated. The natural frequencies as a function of the angular velocity and other system parameters are computed and compared with benchmark cases available in the literature. Finally, the error on the modal characteristics of the rotating beam is evaluated when the linearization is carried out about the undeformed configuration.
Neotectonic deformation model of the Northern Algeria from Paleomagnetic data
NASA Astrophysics Data System (ADS)
Derder, M. E. M.; Henry, B.; Maouche, S.; Amenna, M.; Bayou, B.; Djellit, H.; Ymel, H.; Gharbi, S.; Abtout, A.; Ayache, M.
2012-04-01
The seismic activity of the Western Mediterranean area is partly concentrated in northern Africa, particularly in northern Algeria, as it is shown by the strongest recent earthquakes of "Zemmouri" 21 May 2003 Mw=6.9 and the "El Asnam" 10 October 1980 Ms= 7.3. This seismicity is due to the tectonic activity related to the convergence between Africa and Eurasia plates since at least the Oligocene. The deformation is mostly compressional with associated folds, strike-slip faults and thrusts, and a direction of shortening between N-S and NNW-SSE. This convergence involves a tectonic transpression which is expressed by active deformation along the plate boundary. In northern Algeria, the seismicity is concentrated in a coastal E-W thin band zone (the Tell Atlas). Active structures define there NE-SW trending folds and NE-SW sinistral transpressive faults, which affect the intermountain and coastal Neogene to Quaternary sedimentary basins (e.g. " Cheliff "basin, " Mitidja "basin, …). These reverse faults are associated with NW-SE to E-W strike-slips deep faults. The active tectonics could be explained by a simple blocks rotation kinematics model. In order to test the validity of this kinematic model, three different paleomagnetic studies have been conducted. The first one concerned the "Cheliff" basin where sedimentary Neogene formations were extensively sampled (66 sites). The second study was carried out on Miocene andesite and dacite rocks cropping out along the northern coastal zone of the "Cheliff" basin ("Beni Haoua" area, 19 sites). The third study has been carried out on the Miocene magmatic rocks (rhyolites and basalts) cropping out north-eastern part of the "Mitidja" basin ("Cap Djinet" - "Boumerdes" area, 23 sites). The obtained results show existence of paleomagnetic clockwise rotations in all the studied areas and then validates the kinematics block rotation model. Accordingly, the deformation related to the convergence between the Africa and Eurasia
A Computational Model of Deformable Cell Rolling in Shear Flow
NASA Astrophysics Data System (ADS)
Eggleton, Charles; Jadhav, Sameer
2005-03-01
Selectin-mediated rolling of polymorphonuclear leukocytes (PMNs) on activated endothelium is critical to their recruitment to sites of inflammation. The cell rolling velocity is influenced by bond interactions on the molecular scale that oppose hydrodynamic forces at the mesoscale. Recent studies have shown that PMN rolling velocity on selectin-coated surfaces in shear flow is significantly slower compared to that of microspheres bearing a similar density of selectin ligands. To investigate whether cell deformability is responsible for these differences, we developed a 3-D computational model which simulates rolling of a deformable cell on a selectin-coated surface under shear flow with a stochastic description of receptor-ligand bond interaction. We observed that rolling velocity increases with increasing membrane stiffness and this effect is larger at high shear rates. The average bond lifetime, number of receptor-ligand bonds and the cell-substrate contact area decreased with increasing membrane stiffness. This study shows that cellular properties along with the kinetics of selectin-ligand interactions affect leukocyte rolling on selectin-coated surfaces.
Modeling Cyclic Deformation of HSLA Steels Using Crystal Plasticity
NASA Astrophysics Data System (ADS)
Ghosh, Somnath; Xie, Chunlei
2004-06-01
In this paper, we propose a multi-time scale modeling technique for analyzing cyclic plastic deformation in crystalline solids subject to periodic loading. An asymptotic expansion of the variables in the time domain, together with homogenization forms the basis of multi-time scaling. In the macroscopic scale analysis, the oscillatory behavior of the load is averaged out and neglected, and the rate of averaged material behavior is quite slow in cyclic deformation. Implicitly, this means that the periodicity of some variables may be assumed for the oscillatory potion of the material behavior may be approximated. In this formulation, the governing equations are divided into two initial-boundary value problems with two different time scale: one is long time scale problem for describing the smooth averaged solution (global problem) and the other is for the remaining oscillatory potion (local problem). For the global problem, long time increments, which are longer than one cycle period, can be used and this multi-time scaling becomes an effective integrator.
Development of a 10-year-old full body geometric dataset for computational modeling.
Mao, Haojie; Holcombe, Sven; Shen, Ming; Jin, Xin; Wagner, Christina D; Wang, Stewart C; Yang, King H; King, Albert I
2014-10-01
The objective of this study was to create a computer-aided design (CAD) geometric dataset of a 10-year-old (10 YO) child. The study includes two phases of efforts. At Phase One, the 10 YO whole body CAD was developed from component computed tomography and magnetic resonance imaging scans of 12 pediatric subjects. Geometrical scaling methods were used to convert all component parts to the average size for a 10 YO child, based on available anthropometric data. Then the component surfaces were compiled and integrated into a complete body. The bony structures and flesh were adjusted as symmetrical to minimize the bias from a single subject while maintaining anthropometrical measurements. Internal organs including the liver, spleen, and kidney were further verified by literature data. At Phase Two, internal characteristics for the cervical spine disc, wrist, hand, pelvis, femur, and tibia were verified with data measured from additional 94 10 YO children. The CAD dataset developed through these processes was mostly within the corridor of one standard deviation (SD) of the mean. In conclusion, a geometric dataset for an average size 10 YO child was created. The dataset serves as a foundation to develop computational 10 YO whole body models for enhanced pediatric injury prevention. PMID:25118667
A unified asperity-deformation model for cracked rocks
NASA Astrophysics Data System (ADS)
Gao, K.; Gibson, R. L.; Ge, J.
2010-12-01
Seismic velocities in rocks increase with pressure, a pattern often explained by changes in cracks within the rock volume. Specifically, the width of microcracks will decrease, increasing the contact area of crack surfaces, which in turn leads to increased stiffness of the crack. This causes P- and S-wave velocities to increase, and having accurate models of this behavior is important in many applications where it is important to related stress changes and observed seismic velocities, such as investigations of both fault zones and changing conditions in geothermal fields or hydrocarbon reservoirs. Several different models have been proposed to explain and quantify the relationship between confining pressure and the physical properties of cracked rocks, including a number of solutions describing cracks as ellipsoidal voids (penny-shaped cracks) of with varying aspect ratios that close at different pressures. Differential effective medium theories based on this model will typically use a fairly large number of parameters to fit measured data. An alternative approach describes cracks or fractures as rough surfaces that do not fully close with increasing pressure, and estimates the increase in contact area as asperities come into contact. An asperity-deformation model of this type was developed by, e.g., Gangi and Carlson (1985), and it parameterizes asperities on crack surfaces in terms of a set of cylindrical rods with heights following power-law distribution. The model results in a simple expression for the increase in velocity caused by increased number of asperities (rods) in contact with increasing pressure, an expression that accurately models increases in velocity using only three parameters. However, the model was formulated only for normal modulus of the cracks, the modulus relevant for P-wave propagation across the crack. Since S-waves are controlled by the tangential or shear modulus of the crack, this model cannot be used to jointly invert both P- and S
The geometric signature: Quantifying landslide-terrain types from digital elevation models
Pike, R.J.
1988-01-01
Topography of various types and scales can be fingerprinted by computer analysis of altitude matrices (digital elevation models, or DEMs). The critical analytic tool is the geometric signature, a set of measures that describes topographic form well enough to distinguish among geomorphically disparate landscapes. Different surficial processes create topography with diagnostic forms that are recognizable in the field. The geometric signature abstracts those forms from contour maps or their DEMs and expresses them numerically. This multivariate characterization enables once-in-tractable problems to be addressed. The measures that constitute a geometric signature express different but complementary attributes of topographic form. Most parameters used here are statistical estimates of central tendency and dispersion for five major categories of terrain geometry; altitude, altitude variance spectrum, slope between slope reversals, and slope and its curvature at fixed slope lengths. As an experimental application of geometric signatures, two mapped terrain types associated with different processes of shallow landsliding in Marin County, California, were distinguished consistently by a 17-variable description of topography from 21??21 DEMs (30-m grid spacing). The small matrix is a statistical window that can be used to scan large DEMs by computer, thus potentially automating the mapping of contrasting terrain types. The two types in Marin County host either (1) slow slides: earth flows and slump-earth flows, or (2) rapid flows: debris avalanches and debris flows. The signature approach should adapt to terrain taxonomy and mapping in other areas, where conditions differ from those in Central California. ?? 1988 International Association for Mathematical Geology.
Texture informed crystal plasticity finite element modeling of polycrystalline material deformation
NASA Astrophysics Data System (ADS)
Leng, Zhe
Metallic materials, such as aluminum, ferrite, magnesium, are used in a wide variety of applications such as structure components of automobiles and plane industry, due to its high strength and low density. It is of great importance to understand the mechanical behavior of these structure metals, such as the relationship between the microstructure and the local deformation and stress state. In this study, a dislocation density based crystal plasticity finite element model has been developed and applied to aluminum and ferrite, respectively. The dislocation is represented as a square loop and its density and other related quantities is tracked explicitly as state variables, based on the crystal kinematics and dislocation related mechanisms. The dislocation generation and annihilation is modeled, in addition, the dislocation flux which is caused by the density gradient is also included in the model. The simulation is then conducted on both single and polycrystalline metallic materials using the initial measured sample texture. Both the experiment and the simulation results indicated localized plastic strain and dislocation patterning, which were controlled by the individual crystallite orientations and the grain boundary effects. The results also revealed that the level of concentrated stress at the grain boundaries depends on misorientation of the interface, besides, grain boundaries and triple junctions had higher hardening effects than the grain interiors. The interaction between the dislocation and the grain boundaries is also incorporated in the model. For the near grain boundary regions, particular consideration and finite element formula is applied to account for the additional activation energy term as well as the geometric compatibility of the grain boundary during dislocation penetration events, both of the energy term and the geometric barrier depend on the grain boundary character. The formulations applied here provide a reasonable methodology to
Wang, Yi; Ni, Dong; Qin, Jing; Xu, Ming; Xie, Xiaoyan; Heng, Pheng-Ann
2016-01-01
Image-guided prostate interventions often require the registration of preoperative magnetic resonance (MR) images to real-time transrectal ultrasound (TRUS) images to provide high-quality guidance. One of the main challenges for registering MR images to TRUS images is how to estimate the TRUS-probe-induced prostate deformation that occurs during TRUS imaging. The combined statistical and biomechanical modeling approach shows promise for the adequate estimation of prostate deformation. However, the right setting of the biomechanical parameters is very crucial for realistic deformation modeling. We propose a patient-specific deformation model equipped with personalized biomechanical parameters obtained from shear wave elastography to reliably predict the prostate deformation during image-guided interventions. Using data acquired from a prostate phantom and twelve patients with suspected prostate cancer, we compared the prostate deformation model with and without patient-specific biomechanical parameters in terms of deformation estimation accuracy. The results show that the patient-specific deformation model possesses favorable model ability, and outperforms the model without patient-specific biomechanical parameters. The employment of the patient-specific biomechanical parameters obtained from elastography for deformation modeling shows promise for providing more precise deformation estimation in applications that use computer-assisted image-guided intervention systems. PMID:27272239
Wang, Yi; Ni, Dong; Qin, Jing; Xu, Ming; Xie, Xiaoyan; Heng, Pheng-Ann
2016-01-01
Image-guided prostate interventions often require the registration of preoperative magnetic resonance (MR) images to real-time transrectal ultrasound (TRUS) images to provide high-quality guidance. One of the main challenges for registering MR images to TRUS images is how to estimate the TRUS-probe-induced prostate deformation that occurs during TRUS imaging. The combined statistical and biomechanical modeling approach shows promise for the adequate estimation of prostate deformation. However, the right setting of the biomechanical parameters is very crucial for realistic deformation modeling. We propose a patient-specific deformation model equipped with personalized biomechanical parameters obtained from shear wave elastography to reliably predict the prostate deformation during image-guided interventions. Using data acquired from a prostate phantom and twelve patients with suspected prostate cancer, we compared the prostate deformation model with and without patient-specific biomechanical parameters in terms of deformation estimation accuracy. The results show that the patient-specific deformation model possesses favorable model ability, and outperforms the model without patient-specific biomechanical parameters. The employment of the patient-specific biomechanical parameters obtained from elastography for deformation modeling shows promise for providing more precise deformation estimation in applications that use computer-assisted image-guided intervention systems. PMID:27272239
NASA Astrophysics Data System (ADS)
Mercier, Patrick H. J.
Seventy-five synthetic powder trioctahedral mica samples (between Mg, Co, Ni, and Fe end members, with different degrees of oxidation, vacancy and Al/Si contents, and including an OH/F substitution series) were studied by room-temperature powder X-ray diffraction. The iron-bearing samples were studied by 57Fe Mossbauer spectroscopy. Subsets of the samples were also characterized by scanning electron microscopy combined with energy dispersive spectroscopy, optical microscopy, X-ray fluorescence spectroscopy, and gas chromatography. Lattice parameters (refined under the 1M stacking polytype, space group C2/m) were determined for all powder samples and iron site populations ([4]Fe 3+, [6]Fe2+, and [6]Fe 2+) were obtained from Mossbauer spectroscopy. The relation (c/a)cosbeta* = 113 was found to hold exactly (within experimental error) for all synthetic powders whereas it does not hold in general for synthetic and natural 1M single-crystals. The above relation is predicted to hold for geometric home-octahedral sheets (having equal M1 and M2 site bond lengths) and not to hold for geometric meso-octahedral sheets (having unequal M1 and M2 site bond lengths). The counter-rotation of the M2 site of 1M single-crystals exactly (within experimental error) follows the geometric meso-octahedral sheet model, which, assuming a uniform octahedral sheet height and site-specific M1 and M2 bond lengths, predicts site-specific flattening angles and a counter-rotation angle for the M2 site which is uniquely determined by the bond length difference between the M1 and M2 sites. A geometric meso-octahedral 2:1 layer silicate was shown to require corrugated tetrahedral sheets composed of bond-distorted tetrahedra. Key geometric meso-octahedral distortions in 1M single-crystals were identified and elucidated: (i) intra-layer top-bottom displacements within a TOT layer; and (ii) a tetrahedral bending angle between the apical bond and the pyramidal base formed by the three basal bonds. Plots
NASA Technical Reports Server (NTRS)
Schairer, Edward T.; Kushner, Laura K.; Garbeff, Theodore J.; Heineck, James T.
2015-01-01
The deformations of two sonic-boom models were measured by stereo photogrammetry during tests in the 9- by 7-Ft Supersonic Wind Tunnel at NASA Ames Research Center. The models were geometrically similar but one was 2.75 times as large as the other. Deformation measurements were made by simultaneously imaging the upper surfaces of the models from two directions by calibrated cameras that were mounted behind windows of the test section. Bending and twist were measured at discrete points using conventional circular targets that had been marked along the leading and trailing edges of the wings and tails. In addition, continuous distributions of bending and twist were measured from ink speckles that had been applied to the upper surfaces of the model. Measurements were made at wind-on (M = 1.6) and wind-off conditions over a range of angles of attack between 2.5 deg. and 5.0 deg. At each condition, model deformation was determined by comparing the wind-off and wind-on coordinates of each measurement point after transforming the coordinates to reference coordinates tied to the model. The necessary transformations were determined by measuring the positions of a set of targets on the rigid center-body of the models whose model-axes coordinates were known. Smoothly varying bending and twist measurements were obtained at all conditions. Bending displacements increased in proportion to the square of the distance to the centerline. Maximum deflection of the wingtip of the larger model was about 5 mm (2% of the semispan) and that of the smaller model was 0.9 mm (1% of the semispan). The change in wing twist due to bending increased in direct proportion to distance from the centerline and reached a (absolute) maximum of about -1? at the highest angle of attack for both models. The measurements easily resolved bending displacements as small as 0.05 mm and bending-induced changes in twist as small as 0.05 deg.
An elastoviscoplastic finite element model of lithospheric deformation
NASA Astrophysics Data System (ADS)
Albert, Richard Alan
1998-12-01
Via the finite element method, the stress state and deformation of the lithosphere were investigated with topographic loading. An elastoviscoplastic (EVP) rheology governed the mechanical response in a 40 km thick lithospheric plate of wet olivine. The viscous aspect of the rheology utilized a steady-state dislocation creep constitutive relation. The plastic part of the rheology treated frictional slip on faults within pervasively fractured rock via Byerlee's rule. The first studies use a time-invariant, steady-state conduction temperature distribution in the plate. These studies involved topographic loading with different maximum loads and different load growth rates. The EVP results were compared to elastic perfectly-plastic (EPP) solutions for plate bending as constrained by the Yield Strength Envelope (YSE) formulation for lithospheric mechanics. The EVP results included the often-overlooked effect that the load has on strengthening underlying rock against brittle deformation. The creep strain rate in the EVP models varied with time, depth, and lateral location, unlike the EPP/YSE models that constrain all creep to a single a priori creep strain rate. At the transition from frictional slip to creep, the EVP models showed a three km zone with contributions from both mechanisms, relative to the EPP/YSE's artificially sharp and immediate transition. The last study incorporated two variations on the temperature distribution in the EVP lithosphere. The "whole-lithosphere cooling model" cooled the plate during and after the load growth period, following the half-space cooling model for oceanic lithosphere. Unlike its non-cooling counterpart, the whole-lithosphere cooling model showed no further frictional slip after the load growth period. The "magma conduit model" used an initial temperature distribution that had a high temperature along a vertical symmetry axis during loading to approximate temperature effects from a magma conduit. After loading, its temperature
Colwell, Robert K; Gotelli, Nicholas J; Ashton, Louise A; Beck, Jan; Brehm, Gunnar; Fayle, Tom M; Fiedler, Konrad; Forister, Matthew L; Kessler, Michael; Kitching, Roger L; Klimes, Petr; Kluge, Jürgen; Longino, John T; Maunsell, Sarah C; McCain, Christy M; Moses, Jimmy; Noben, Sarah; Sam, Katerina; Sam, Legi; Shapiro, Arthur M; Wang, Xiangping; Novotny, Vojtech
2016-09-01
We introduce a novel framework for conceptualising, quantifying and unifying discordant patterns of species richness along geographical gradients. While not itself explicitly mechanistic, this approach offers a path towards understanding mechanisms. In this study, we focused on the diverse patterns of species richness on mountainsides. We conjectured that elevational range midpoints of species may be drawn towards a single midpoint attractor - a unimodal gradient of environmental favourability. The midpoint attractor interacts with geometric constraints imposed by sea level and the mountaintop to produce taxon-specific patterns of species richness. We developed a Bayesian simulation model to estimate the location and strength of the midpoint attractor from species occurrence data sampled along mountainsides. We also constructed midpoint predictor models to test whether environmental variables could directly account for the observed patterns of species range midpoints. We challenged these models with 16 elevational data sets, comprising 4500 species of insects, vertebrates and plants. The midpoint predictor models generally failed to predict the pattern of species midpoints. In contrast, the midpoint attractor model closely reproduced empirical spatial patterns of species richness and range midpoints. Gradients of environmental favourability, subject to geometric constraints, may parsimoniously account for elevational and other patterns of species richness. PMID:27358193
NASA Astrophysics Data System (ADS)
Li, Xiaowen; Strahler, Alan H.; Woodcock, Curtis E.
1995-01-01
A new model for the bidirectional reflectance of a vegetation cover combines principles of geometric optics and radiative transfer. It relies on gap probabilities and path length distributions to model the penetration of irradiance from a parallel source and the single and multiple scattering of that irradiance in the direction of an observer. The model applies to vegetation covers of discrete plant crowns that are randomly centered both on the plane and within a layer of variable thickness above it. Crowns assume a spheroidal shape with arbitrary height to width ratio. Geometric optics easily models the irradiance that penetrates the vegetation cover directly, is scattered by the soil, and exits without further scattering by the vegetation. Within a plant crown, the probability of scattering is a negative exponential function of path length. Within-crown scattering provides the source for singly-scattered radiation, which exits with probabilities proportional to further path-length distributions in the direction of exitance (including the hotspot effect). Single scattering provides the source for double scattering, and then higher order pairs of scattering are solved successively by a convolution function. As an early exercise in validation, the model is applied to an open jack pine canopy and ground-level irradiance is predicted with good accuracy.
3D Face Modeling Using the Multi-Deformable Method
Hwang, Jinkyu; Yu, Sunjin; Kim, Joongrock; Lee, Sangyoun
2012-01-01
In this paper, we focus on the problem of the accuracy performance of 3D face modeling techniques using corresponding features in multiple views, which is quite sensitive to feature extraction errors. To solve the problem, we adopt a statistical model-based 3D face modeling approach in a mirror system consisting of two mirrors and a camera. The overall procedure of our 3D facial modeling method has two primary steps: 3D facial shape estimation using a multiple 3D face deformable model and texture mapping using seamless cloning that is a type of gradient-domain blending. To evaluate our method's performance, we generate 3D faces of 30 individuals and then carry out two tests: accuracy test and robustness test. Our method shows not only highly accurate 3D face shape results when compared with the ground truth, but also robustness to feature extraction errors. Moreover, 3D face rendering results intuitively show that our method is more robust to feature extraction errors than other 3D face modeling methods. An additional contribution of our method is that a wide range of face textures can be acquired by the mirror system. By using this texture map, we generate realistic 3D face for individuals at the end of the paper. PMID:23201976
Unified constitutive model for single crystal deformation behavior with applications
NASA Technical Reports Server (NTRS)
Walker, K. P.; Meyer, T. G.; Jordan, E. H.
1988-01-01
Single crystal materials are being used in gas turbine airfoils and are candidates for other hot section components because of their increased temperature capabilities and resistance to thermal fatigue. Development of a constitutive model which assesses the inelastic behavior of these materials has been studied in 2 NASA programs: Life Prediction and Constitutive Models for Engine Hot Section Anisotropic Materials and Biaxial Constitutive Equation Development for Single Crystals. The model has been fit to a large body of constitutive data for single crystal PWA 1480 material. The model uses a unified approach for computing total inelastic strains (creep plus plasticity) on crystallographic slip systems reproducing observed directional and strain rate effects as a natural consequence of the summed slip system quantities. The model includes several of the effects that have been reported to influence deformation in single crystal materials, such as shear stress, latent hardening, and cross slip. The model is operational in a commercial Finite Element code and is being installed in a Boundary Element Method code.
Morphogenesis of the human palma arch using three-dimensional geometric modeling.
Durand, Sebastien; Marin, Frederic; Oberlin, Christophe; Ho Ba Tho, Marie-Christine
2011-10-01
The hand goes through complex morphological modifications during embryogenesis. The goal of this study was to use geometric modeling to study the morphometric modifications of the palmar arch. Five embryos were used for the study (sizes: 15, 17, 23, 30, and 44 mm). After digitalization of histologic sections (Sony DXC-930P 3CCD camera, Leica Qwin) and segmentation of the metacarpal cartilaginous matrices (Winsurf 4.3 software), geometric modeling and calculations were performed using MSC.Patran 2005r2 software. Correlations (r > 0.99) were found between embryo size and metacarpal volume, metacarpal surface, and the surface of the modeled palmar arch. The growth of the palmar arch is nonhomothetic. Significant reduction (P = 0.05) in the divergence of the 2nd, 3rd, 4th, and 5th metacarpals was observed. Deepening of the palmar arch is correlated with embryo size and age (r > 0.99). Geometric modeling allows 3D rendering of histologic sections and thus quantitative description of the morphogenesis. The results of this study support the hypothesis that opposition of the thumb in correlation with deepening of the palmar arch appears early in embryological development. It constitutes a specific morphological characteristic that appears very early in the human phylum. The fact that the human thumb is naturally in opposition in the resting position is a consequence of this morphogenesis. The thumb's resting position has received little attention in clinical settings and should be considered as the reference position for biomechanical analysis of the thumb column. PMID:21538563
NASA Technical Reports Server (NTRS)
Strahler, Alan H.; Li, Xiao-Wen; Jupp, David L. B.
1991-01-01
The bidirectional radiance or reflectance of a forest or woodland can be modeled using principles of geometric optics and Boolean models for random sets in a three dimensional space. This model may be defined at two levels, the scene includes four components; sunlight and shadowed canopy, and sunlit and shadowed background. The reflectance of the scene is modeled as the sum of the reflectances of the individual components as weighted by their areal proportions in the field of view. At the leaf level, the canopy envelope is an assemblage of leaves, and thus the reflectance is a function of the areal proportions of sunlit and shadowed leaf, and sunlit and shadowed background. Because the proportions of scene components are dependent upon the directions of irradiance and exitance, the model accounts for the hotspot that is well known in leaf and tree canopies.
The Beta-Geometric Model Applied to Fecundability in a Sample of Married Women
NASA Astrophysics Data System (ADS)
Adekanmbi, D. B.; Bamiduro, T. A.
2006-10-01
The time required to achieve pregnancy among married couples termed fecundability has been proposed to follow a beta-geometric distribution. The accuracy of the method used in estimating the parameters of the model has an implication on the goodness of fit of the model. In this study, the parameters of the model are estimated using the Method of Moments and Newton-Raphson estimation procedure. The goodness of fit of the model was considered, using estimates from the two methods of estimation, as well as the asymptotic relative efficiency of the estimates. A noticeable improvement in the fit of the model to the data on time to conception was observed, when the parameters are estimated by Newton-Raphson procedure, and thereby estimating reasonable expectations of fecundability for married female population in the country.
The Utility of Fisher’s Geometric Model in Evolutionary Genetics
Tenaillon, O.
2015-01-01
The accumulation of data on the genomic bases of adaptation has triggered renewed interest in theoretical models of adaptation. Among these models, Fisher Geometric Model (FGM) has received a lot of attention over the last two decades. FGM is based on a continuous multidimensional phenotypic landscape, but it is for the emerging properties of individual mutation effects that it is mostly used. Despite an apparent simplicity and a limited number of parameters, FGM integrates a full model of mutation and epistatic interactions that allows the study of both beneficial and deleterious mutations, and subsequently the fate of evolving populations. In this review, I present the different properties of FGM and the qualitative and quantitative support they have received from experimental evolution data. I later discuss how to estimate the different parameters of the model and outline some future directions to connect FGM and the molecular determinants of adaptation. PMID:26740803
A solution to the surface intersection problem. [Boolean functions in geometric modeling
NASA Technical Reports Server (NTRS)
Timer, H. G.
1977-01-01
An application-independent geometric model within a data base framework should support the use of Boolean operators which allow the user to construct a complex model by appropriately combining a series of simple models. The use of these operators leads to the concept of implicitly and explicitly defined surfaces. With an explicitly defined model, the surface area may be computed by simply summing the surface areas of the bounding surfaces. For an implicitly defined model, the surface area computation must deal with active and inactive regions. Because the surface intersection problem involves four unknowns and its solution is a space curve, the parametric coordinates of each surface must be determined as a function of the arc length. Various subproblems involved in the general intersection problem are discussed, and the mathematical basis for their solution is presented along with a program written in FORTRAN IV for implementation on the IBM 370 TSO system.
NASA Astrophysics Data System (ADS)
Kis, M.; Detzky, G.; Koppán, A.
2012-04-01
phenomenon in general. Authors calculated the deformations of a simple-geometry 3D cavity, which is caused by variable gravity loads. Dependence of the cavity effect on changing of distinct elastic properties in categorized models has been investigated. Authors introduced qualifying parameter fields calculated using the results of the FE modelling (nodal displacements as a model answer for the gravity load), in order to characterize the effect. Modelling results can be used as an estimation not only for the absolute cavity effect rate of the intended arrangement, furthermore the sensitivity of the given system against a particular geometric property. As an application example finite element modelling were carried out in order to estimate the influence of the complicated cavity system surrounding the "Budapest-Matyashegy" Gravity and Geodynamical Observatory of the Eotvos Lorand Geophysical Institute of Hungary.
NASA Astrophysics Data System (ADS)
Brasebin, M.; Perret, J.; Mustière, S.; Weber, C.
2012-10-01
The increased availability of 3D urban data reflects a growing interest in 3D spatial analysis. As 3D spatial analysis often uses complex 3D data, studies of the potential gains of using more detailed 3D urban databases for specific uses is an important issue. First, more complex data implies an increase in time and memory usage for the analysis (and calls for more research on the efficiency of the algorithms used). Second, detailed 3D urban data are complex to produce, expensive and it is important to be well informed in order to decide whether of not to invest in such data. Currently, many studies have been led about the fitness for use of 2D data but they are very scarce concerning 3D data. This article presents a method to determine the influence of 3D modeling on the results of 3D analysis by isolating the potential sources of errors (such as roof modeling and geometric accuracy). This method is applied on two 3D datasets (LOD1 and LOD2) and a 3D indicator (the sky view factor or SVF). The results show that the significant influence of roof modeling is globally compensated by the difference in geometric modeling but that important local variations are noticed. Nevertheless, for 75% of the SVF processed the difference between the results using these two databases is lower than 2%.
Video model deformation system for the National Transonic Facility
NASA Technical Reports Server (NTRS)
Burner, A. W.; Snow, W. L.; Goad, W. K.
1983-01-01
A photogrammetric closed circuit television system to measure model deformation at the National Transonic Facility is described. The photogrammetric approach was chosen because of its inherent rapid data recording of the entire object field. Video cameras are used to acquire data instead of film cameras due to the inaccessibility of cameras which must be housed within the cryogenic, high pressure plenum of this facility. A rudimentary theory section is followed by a description of the video-based system and control measures required to protect cameras from the hostile environment. Preliminary results obtained with the same camera placement as planned for NTF are presented and plans for facility testing with a specially designed test wing are discussed.
Geometric Context and Orientation Map Combination for Indoor Corridor Modeling Using a Single Image
NASA Astrophysics Data System (ADS)
Baligh Jahromi, Ali; Sohn, Gunho
2016-06-01
Since people spend most of their time indoors, their indoor activities and related issues in health, security and energy consumption have to be understood. Hence, gathering and representing spatial information of indoor spaces in form of 3D models become very important. Considering the available data gathering techniques with respect to the sensors cost and data processing time, single images proved to be one of the reliable sources. Many of the current single image based indoor space modeling methods are defining the scene as a single box primitive. This domain-specific knowledge is usually not applicable in various cases where multiple corridors are joined at one scene. Here, we addressed this issue by hypothesizing-verifying multiple box primitives which represents the indoor corridor layout. Middle-level perceptual organization is the foundation of the proposed method, which relies on finding corridor layout boundaries using both detected line segments and virtual rays created by orthogonal vanishing points. Due to the presence of objects, shadows and occlusions, a comprehensive interpretation of the edge relations is often concealed. This necessitates the utilization of virtual rays to create a physically valid layout hypothesis. Many of the former methods used Orientation Map or Geometric Context to evaluate their proposed layout hypotheses. Orientation map is a map that reveals the local belief of region orientations computed from line segments, and in a segmented image geometric context uses color, texture, edge, and vanishing point cues to estimate the likelihood of each possible label for all super-pixels. Here, the created layout hypotheses are evaluated by an objective function which considers the fusion of orientation map and geometric context with respect to the horizontal viewing angle at each image pixel. Finally, the best indoor corridor layout hypothesis which gets the highest score from the scoring function will be selected and converted to a 3D
Chi, Y.; Liang, J.; Yan, D.
2006-02-15
Model-based deformable organ registration techniques using the finite element method (FEM) have recently been investigated intensively and applied to image-guided adaptive radiotherapy (IGART). These techniques assume that human organs are linearly elastic material, and their mechanical properties are predetermined. Unfortunately, the accurate measurement of the tissue material properties is challenging and the properties usually vary between patients. A common issue is therefore the achievable accuracy of the calculation due to the limited access to tissue elastic material constants. In this study, we performed a systematic investigation on this subject based on tissue biomechanics and computer simulations to establish the relationships between achievable registration accuracy and tissue mechanical and organ geometrical properties. Primarily we focused on image registration for three organs: rectal wall, bladder wall, and prostate. The tissue anisotropy due to orientation preference in tissue fiber alignment is captured by using an orthotropic or a transversely isotropic elastic model. First we developed biomechanical models for the rectal wall, bladder wall, and prostate using simplified geometries and investigated the effect of varying material parameters on the resulting organ deformation. Then computer models based on patient image data were constructed, and image registrations were performed. The sensitivity of registration errors was studied by perturbating the tissue material properties from their mean values while fixing the boundary conditions. The simulation results demonstrated that registration error for a subvolume increases as its distance from the boundary increases. Also, a variable associated with material stability was found to be a dominant factor in registration accuracy in the context of material uncertainty. For hollow thin organs such as rectal walls and bladder walls, the registration errors are limited. Given 30% in material uncertainty
Matching Aerial Images to 3D Building Models Using Context-Based Geometric Hashing
Jung, Jaewook; Sohn, Gunho; Bang, Kiin; Wichmann, Andreas; Armenakis, Costas; Kada, Martin
2016-01-01
A city is a dynamic entity, which environment is continuously changing over time. Accordingly, its virtual city models also need to be regularly updated to support accurate model-based decisions for various applications, including urban planning, emergency response and autonomous navigation. A concept of continuous city modeling is to progressively reconstruct city models by accommodating their changes recognized in spatio-temporal domain, while preserving unchanged structures. A first critical step for continuous city modeling is to coherently register remotely sensed data taken at different epochs with existing building models. This paper presents a new model-to-image registration method using a context-based geometric hashing (CGH) method to align a single image with existing 3D building models. This model-to-image registration process consists of three steps: (1) feature extraction; (2) similarity measure; and matching, and (3) estimating exterior orientation parameters (EOPs) of a single image. For feature extraction, we propose two types of matching cues: edged corner features representing the saliency of building corner points with associated edges, and contextual relations among the edged corner features within an individual roof. A set of matched corners are found with given proximity measure through geometric hashing, and optimal matches are then finally determined by maximizing the matching cost encoding contextual similarity between matching candidates. Final matched corners are used for adjusting EOPs of the single airborne image by the least square method based on collinearity equations. The result shows that acceptable accuracy of EOPs of a single image can be achievable using the proposed registration approach as an alternative to a labor-intensive manual registration process. PMID:27338410
Matching Aerial Images to 3D Building Models Using Context-Based Geometric Hashing.
Jung, Jaewook; Sohn, Gunho; Bang, Kiin; Wichmann, Andreas; Armenakis, Costas; Kada, Martin
2016-01-01
A city is a dynamic entity, which environment is continuously changing over time. Accordingly, its virtual city models also need to be regularly updated to support accurate model-based decisions for various applications, including urban planning, emergency response and autonomous navigation. A concept of continuous city modeling is to progressively reconstruct city models by accommodating their changes recognized in spatio-temporal domain, while preserving unchanged structures. A first critical step for continuous city modeling is to coherently register remotely sensed data taken at different epochs with existing building models. This paper presents a new model-to-image registration method using a context-based geometric hashing (CGH) method to align a single image with existing 3D building models. This model-to-image registration process consists of three steps: (1) feature extraction; (2) similarity measure; and matching, and (3) estimating exterior orientation parameters (EOPs) of a single image. For feature extraction, we propose two types of matching cues: edged corner features representing the saliency of building corner points with associated edges, and contextual relations among the edged corner features within an individual roof. A set of matched corners are found with given proximity measure through geometric hashing, and optimal matches are then finally determined by maximizing the matching cost encoding contextual similarity between matching candidates. Final matched corners are used for adjusting EOPs of the single airborne image by the least square method based on collinearity equations. The result shows that acceptable accuracy of EOPs of a single image can be achievable using the proposed registration approach as an alternative to a labor-intensive manual registration process. PMID:27338410
Modeling of ductile deformation in anisotropic rocks with slip surfaces
NASA Astrophysics Data System (ADS)
Dabrowski, Marcin
2013-04-01
Flanking structures and sheath folds can develop in layered rocks due to flow perturbation around slip surfaces in shear zones (Exner and Dabrowski, 2010; Reber et al., submitted). Mechanical anisotropy of the host rock has been shown to play a major role in determining the slip rate and the flow pattern around it (Kocher and Mancktelow, 2006; Fletcher, 2011). In addition, anisotropic fluids such as ductile foliated rocks have a 'memory' of deformation due to evolving microstructure. For example, the rotation of a rigid circular inclusion embedded in a layered host in layer-parallel shear results in the structural reorganization around it, which leads to the modification of the flow pattern in the host and in consequence to a massive reduction of the inclusion rotation rate (Dabrowski and Schmid, 2011). Willis (1964) derived an analytical elastic solution for an elliptical inclusion in a homogeneous anisotropic matrix subject to a uniform load in the far field. The solution can be reduced to the case of an incompressible viscous medium. The case of an arbitrarily oriented inviscid slit under shear parallel to the principal axis of anisotropy can be obtained by reducing it even further. Although derived for the initial state of homogeneous planar anisotropy, the solution provides useful insights into the large deformation behavior of the system. In this study, I will use different models and numerical modeling techniques to assess the impact of mechanical anisotropy and structural development on the perturbing flow around an inviscid slit (slip surface) embedded in a host comprising discrete isotropic layers in layer-parallel simple shear. In the limit of thin layers (the number of layers intercepting the slit tends to infinity), the host is modeled as an anisotropic fluid. The anisotropic viscosity is determined by the bulk anisotropic viscosity of the layered system. The layering is initially planar or equivalently the anisotropy is initially homogeneous. Both non
Modelling of reactive fluid transport in deformable porous rocks
NASA Astrophysics Data System (ADS)
Yarushina, V. M.; Podladchikov, Y. Y.
2009-04-01
One outstanding challenge in geology today is the formulation of an understanding of the interaction between rocks and fluids. Advances in such knowledge are important for a broad range of geologic settings including partial melting and subsequent migration and emplacement of a melt into upper levels of the crust, or fluid flow during regional metamorphism and metasomatism. Rock-fluid interaction involves heat and mass transfer, deformation, hydrodynamic flow, and chemical reactions, thereby necessitating its consideration as a complex process coupling several simultaneous mechanisms. Deformation, chemical reactions, and fluid flow are coupled processes. Each affects the others. Special effort is required for accurate modelling of the porosity field through time. Mechanical compaction of porous rocks is usually treated under isothermal or isoentropic simplifying assumptions. However, joint consideration of both mechanical compaction and reactive porosity alteration requires somewhat greater than usual care about thermodynamic consistency. Here we consider the modelling of multi-component, multi-phase systems, which is fundamental to the study of fluid-rock interaction. Based on the conservation laws for mass, momentum, and energy in the form adopted in the theory of mixtures, we derive a thermodynamically admissible closed system of equations describing the coupling of heat and mass transfer, chemical reactions, and fluid flow in a deformable solid matrix. Geological environments where reactive transport is important are located at different depths and accordingly have different rheologies. In the near surface, elastic or elastoplastic properties would dominate, whereas viscoplasticity would have a profound effect deeper in the lithosphere. Poorly understood rheologies of heterogeneous porous rocks are derived from well understood processes (i.e., elasticity, viscosity, plastic flow, fracturing, and their combinations) on the microscale by considering a
NASA Astrophysics Data System (ADS)
Hilley, G. E.; Arrowsmith, R.
2011-12-01
cases in which the SAF fault friction is low, and the contrast in frictional properties between the simulated North American and Pacific Plate sediments is high. In these cases, the overall dimensions and rock uplift rates predicted by the simulations are, to first order, consistent with values measured or inferred based on field observations. Our results provide a mechanically plausible scenario to supplement the geometric explanation previously posed for this specific feature, and indicate that this type of numerical modeling may provide a useful basis for forming a mechanistic understanding these near-fault deformation features.
Morphing of geometric composites via residual swelling.
Pezzulla, Matteo; Shillig, Steven A; Nardinocchi, Paola; Holmes, Douglas P
2015-08-01
Understanding and controlling the shape of thin, soft objects has been the focus of significant research efforts among physicists, biologists, and engineers in the last decade. These studies aim to utilize advanced materials in novel, adaptive ways such as fabricating smart actuators or mimicking living tissues. Here, we present the controlled growth-like morphing of 2D sheets into 3D shapes by preparing geometric composite structures that deform by residual swelling. The morphing of these geometric composites is dictated by both swelling and geometry, with diffusion controlling the swelling-induced actuation, and geometric confinement dictating the structure's deformed shape. Building on a simple mechanical analog, we present an analytical model that quantitatively describes how the Gaussian and mean curvatures of a thin disk are affected by the interplay among geometry, mechanics, and swelling. This model is in excellent agreement with our experiments and numerics. We show that the dynamics of residual swelling is dictated by a competition between two characteristic diffusive length scales governed by geometry. Our results provide the first 2D analog of Timoshenko's classical formula for the thermal bending of bimetallic beams - our generalization explains how the Gaussian curvature of a 2D geometric composite is affected by geometry and elasticity. The understanding conferred by these results suggests that the controlled shaping of geometric composites may provide a simple complement to traditional manufacturing techniques. PMID:26076671
An atomistic geometrical model of the B-DNA configuration for DNA-radiation interaction simulations
NASA Astrophysics Data System (ADS)
Bernal, M. A.; Sikansi, D.; Cavalcante, F.; Incerti, S.; Champion, C.; Ivanchenko, V.; Francis, Z.
2013-12-01
In this paper, an atomistic geometrical model for the B-DNA configuration is explained. This model accounts for five organization levels of the DNA, up to the 30 nm chromatin fiber. However, fragments of this fiber can be used to construct the whole genome. The algorithm developed in this work is capable to determine which is the closest atom with respect to an arbitrary point in space. It can be used in any application in which a DNA geometrical model is needed, for instance, in investigations related to the effects of ionizing radiations on the human genetic material. Successful consistency checks were carried out to test the proposed model. Catalogue identifier: AEPZ_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEPZ_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 1245 No. of bytes in distributed program, including test data, etc.: 6574 Distribution format: tar.gz Programming language: FORTRAN. Computer: Any. Operating system: Multi-platform. RAM: 2 Gb Classification: 3. Nature of problem: The Monte Carlo method is used to simulate the interaction of ionizing radiation with the human genetic material in order to determine DNA damage yields per unit absorbed dose. To accomplish this task, an algorithm to determine if a given energy deposition lies within a given target is needed. This target can be an atom or any other structure of the genetic material. Solution method: This is a stand-alone subroutine describing an atomic-resolution geometrical model of the B-DNA configuration. It is able to determine the closest atom to an arbitrary point in space. This model accounts for five organization levels of the human genetic material, from the nucleotide pair up to the 30 nm chromatin fiber. This subroutine carries out a series of coordinate transformations
A simple geometrical model describing shapes of soap films suspended on two rings
NASA Astrophysics Data System (ADS)
Herrmann, Felix J.; Kilvington, Charles D.; Wildenberg, Rebekah L.; Camacho, Franco E.; Walecki, Wojciech J.; Walecki, Peter S.; Walecki, Eve S.
2016-09-01
We measured and analysed the stability of two types of soap films suspended on two rings using the simple conical frusta-based model, where we use common definition of conical frustum as a portion of a cone that lies between two parallel planes cutting it. Using frusta-based we reproduced very well-known results for catenoid surfaces with and without a central disk. We present for the first time a simple conical frusta based spreadsheet model of the soap surface. This very simple, elementary, geometrical model produces results surprisingly well matching the experimental data and known exact analytical solutions. The experiment and the spreadsheet model can be used as a powerful teaching tool for pre-calculus and geometry students.
An initial comparison of CFD with experiment for a geometrically simplified STOVL model
NASA Technical Reports Server (NTRS)
Roth, Karlin R.
1993-01-01
The transition flight performance of a representative Short Take-Off or Vertical Landing (STOVL) model is investigated using side-by-side experimental and numerical simulations. The model consists of a 60 deg cropped delta wing planform; a simple fuselage shape blended to the wing; and tandem, circular, high-pressure-air lift jets that exit perpendicular to the flat lower surface. The configuration was chosen to minimize the geometric modeling complexity while retaining the important flow physics of the lift-jet/aerodynamic surface interaction. Three-dimensional, turbulent Navier-Stokes computations are made using a multiple, overset grid scheme. Results are presented and compared with the measured forces and pressures for the model at a freestream Mach number of 0.14 and a 10 deg angle-of-attack without lift jets operating. Computed surface flow patterns and particle traces show that the simulation predicts primary and secondary wing leading edge vortices for these conditions.
Modeling Step-Strain Relaxation and Cyclic Deformations of Elastomers
NASA Technical Reports Server (NTRS)
Johnson, A.R.; Mead, J. L.
2000-01-01
Data for step-strain relaxation and cyclic compressive deformations of highly viscous short elastomer cylinders are modeled using a large strain rubber viscoelastic constitutive theory with a rate-independent friction stress term added. In the tests, both small and large amplitude cyclic compressive strains, in the range of 1% to 10%, were superimposed on steady state compressed strains, in the range of 5% to 20%, for frequencies of 1 and 10 Hz. The elastomer cylinders were conditioned prior to each test to soften them. The constants in the viscoclastic-friction constitutive theory are determined by employing a nonlinear least-squares method to fit the analytical stresses for a Maxwell model, which includes friction, to measured relaxation stresses obtained from a 20% step-strain compression test. The simulation of the relaxation data with the nonlinear model is successful at compressive strains of 5%, 10%, 15%, and 20%. Simulations of hysteresis stresses for enforced cyclic compressive strains of 20% +/- 5% are made with the model calibrated by the relaxation data. The predicted hysteresis stresses are lower than the measured stresses.
Model of plastic deformation for extreme loading conditions
NASA Astrophysics Data System (ADS)
Preston, Dean L.; Tonks, Davis L.; Wallace, Duane C.
2003-01-01
We present a model of metallic plastic flow suitable for numerical simulations of explosive loading and high velocity impacts. The dependence of the plastic strain rate on applied stress at low strain rates is of the Arrhenius form but with an activation energy that is singular at zero stress so that the deformation rate vanishes in that limit. Work hardening is modeled as a generalized Voce law. At strain rates exceeding 109s-1, work hardening is neglected, and the rate dependence of the flow stress is calculated using Wallace's theory of overdriven shocks in metals [D.C. Wallace, Phys. Rev. B 24, 5597 (1981); 24, 5607 (1981)]. The thermal-activation regime is continuously merged into the strong shock limit, yielding a model applicable over the 15 decades in strain rate from 10-3 to 1012 s-1. The model represents all aspects of constitutive behavior seen in Hopkinson bar and low-rate data, including a rapid increase in the constant-strain rate sensitivity, with 10% accuracy. High-pressure behavior is controlled by the shear modulus, G(ρ,T), and the melting temperature, Tm(ρ). There are eleven material parameters in addition to G(ρ,T) and Tm(ρ). Parameters for Cu, U, Ta, Mo, V, Be, 304 SS, and 21-6-9 SS are provided.
NASA Astrophysics Data System (ADS)
Rahmouni, A.; Beidouri, Z.; Benamar, R.
2013-09-01
The purpose of the present paper was the development of a physically discrete model for geometrically nonlinear free transverse constrained vibrations of beams, which may replace, if sufficient degrees of freedom are used, the previously developed continuous nonlinear beam constrained vibration models. The discrete model proposed is an N-Degrees of Freedom (N-dof) system made of N masses placed at the ends of solid bars connected by torsional springs, presenting the beam flexural rigidity. The large transverse displacements of the bar ends induce a variation in their lengths giving rise to axial forces modelled by longitudinal springs. The calculations made allowed application of the semi-analytical model developed previously for nonlinear structural vibration involving three tensors, namely the mass tensor mij, the linear rigidity tensor kij and the nonlinearity tensor bijkl. By application of Hamilton's principle and spectral analysis, the nonlinear vibration problem is reduced to a nonlinear algebraic system, examined for increasing numbers of dof. The results obtained by the physically discrete model showed a good agreement and a quick convergence to the equivalent continuous beam model, for various fixed boundary conditions, for both the linear frequencies and the nonlinear backbone curves, and also for the corresponding mode shapes. The model, validated here for the simply supported and clamped ends, may be used in further works to present the flexural linear and nonlinear constrained vibrations of beams with various types of discontinuities in the mass or in the elasticity distributions. The development of an adequate discrete model including the effect of the axial strains induced by large displacement amplitudes, which is predominant in geometrically nonlinear transverse constrained vibrations of beams [1]. The investigation of the results such a discrete model may lead to in the case of nonlinear free vibrations. The development of the analogy between the
Modeling Airflow Using Subject-Specific 4DCT-Based Deformable Volumetric Lung Models.
Ilegbusi, Olusegun J; Li, Zhiliang; Seyfi, Behnaz; Min, Yugang; Meeks, Sanford; Kupelian, Patrick; Santhanam, Anand P
2012-01-01
Lung radiotherapy is greatly benefitted when the tumor motion caused by breathing can be modeled. The aim of this paper is to present the importance of using anisotropic and subject-specific tissue elasticity for simulating the airflow inside the lungs. A computational-fluid-dynamics (CFD) based approach is presented to simulate airflow inside a subject-specific deformable lung for modeling lung tumor motion and the motion of the surrounding tissues during radiotherapy. A flow-structure interaction technique is employed that simultaneously models airflow and lung deformation. The lung is modeled as a poroelastic medium with subject-specific anisotropic poroelastic properties on a geometry, which was reconstructed from four-dimensional computed tomography (4DCT) scan datasets of humans with lung cancer. The results include the 3D anisotropic lung deformation for known airflow pattern inside the lungs. The effects of anisotropy are also presented on both the spatiotemporal volumetric lung displacement and the regional lung hysteresis. PMID:23365554
Modeling Airflow Using Subject-Specific 4DCT-Based Deformable Volumetric Lung Models
Ilegbusi, Olusegun J.; Li, Zhiliang; Seyfi, Behnaz; Min, Yugang; Meeks, Sanford; Kupelian, Patrick; Santhanam, Anand P.
2012-01-01
Lung radiotherapy is greatly benefitted when the tumor motion caused by breathing can be modeled. The aim of this paper is to present the importance of using anisotropic and subject-specific tissue elasticity for simulating the airflow inside the lungs. A computational-fluid-dynamics (CFD) based approach is presented to simulate airflow inside a subject-specific deformable lung for modeling lung tumor motion and the motion of the surrounding tissues during radiotherapy. A flow-structure interaction technique is employed that simultaneously models airflow and lung deformation. The lung is modeled as a poroelastic medium with subject-specific anisotropic poroelastic properties on a geometry, which was reconstructed from four-dimensional computed tomography (4DCT) scan datasets of humans with lung cancer. The results include the 3D anisotropic lung deformation for known airflow pattern inside the lungs. The effects of anisotropy are also presented on both the spatiotemporal volumetric lung displacement and the regional lung hysteresis. PMID:23365554
Stochastic Geometric Network Models for Groups of Functional and Structural Connectomes
Friedman, Eric J.; Landsberg, Adam S.; Owen, Julia P.; Li, Yi-Ou; Mukherjee, Pratik
2014-01-01
Structural and functional connectomes are emerging as important instruments in the study of normal brain function and in the development of new biomarkers for a variety of brain disorders. In contrast to single-network studies that presently dominate the (non-connectome) network literature, connectome analyses typically examine groups of empirical networks and then compare these against standard (stochastic) network models. Current practice in connectome studies is to employ stochastic network models derived from social science and engineering contexts as the basis for the comparison. However, these are not necessarily best suited for the analysis of connectomes, which often contain groups of very closely related networks, such as occurs with a set of controls or a set of patients with a specific disorder. This paper studies important extensions of standard stochastic models that make them better adapted for analysis of connectomes, and develops new statistical fitting methodologies that account for inter-subject variations. The extensions explicitly incorporate geometric information about a network based on distances and inter/intra hemispherical asymmetries (to supplement ordinary degree-distribution information), and utilize a stochastic choice of networks' density levels (for fixed threshold networks) to better capture the variance in average connectivity among subjects. The new statistical tools introduced here allow one to compare groups of networks by matching both their average characteristics and the variations among them. A notable finding is that connectomes have high “smallworldness” beyond that arising from geometric and degree considerations alone. PMID:25067815
Matching Aerial Images to 3d Building Models Based on Context-Based Geometric Hashing
NASA Astrophysics Data System (ADS)
Jung, J.; Bang, K.; Sohn, G.; Armenakis, C.
2016-06-01
In this paper, a new model-to-image framework to automatically align a single airborne image with existing 3D building models using geometric hashing is proposed. As a prerequisite process for various applications such as data fusion, object tracking, change detection and texture mapping, the proposed registration method is used for determining accurate exterior orientation parameters (EOPs) of a single image. This model-to-image matching process consists of three steps: 1) feature extraction, 2) similarity measure and matching, and 3) adjustment of EOPs of a single image. For feature extraction, we proposed two types of matching cues, edged corner points representing the saliency of building corner points with associated edges and contextual relations among the edged corner points within an individual roof. These matching features are extracted from both 3D building and a single airborne image. A set of matched corners are found with given proximity measure through geometric hashing and optimal matches are then finally determined by maximizing the matching cost encoding contextual similarity between matching candidates. Final matched corners are used for adjusting EOPs of the single airborne image by the least square method based on co-linearity equations. The result shows that acceptable accuracy of single image's EOP can be achievable by the proposed registration approach as an alternative to labour-intensive manual registration process.
NASA Astrophysics Data System (ADS)
Qianxiang, Zhou
2012-07-01
It is very important to clarify the geometric characteristic of human body segment and constitute analysis model for ergonomic design and the application of ergonomic virtual human. The typical anthropometric data of 1122 Chinese men aged 20-35 years were collected using three-dimensional laser scanner for human body. According to the correlation between different parameters, curve fitting were made between seven trunk parameters and ten body parameters with the SPSS 16.0 software. It can be concluded that hip circumference and shoulder breadth are the most important parameters in the models and the two parameters have high correlation with the others parameters of human body. By comparison with the conventional regressive curves, the present regression equation with the seven trunk parameters is more accurate to forecast the geometric dimensions of head, neck, height and the four limbs with high precision. Therefore, it is greatly valuable for ergonomic design and analysis of man-machine system.This result will be very useful to astronaut body model analysis and application.
Rate-State Modeling of Stress Relaxation in Geometrically Complex Fault Systems
NASA Astrophysics Data System (ADS)
Dieterich, J.; Smith, D. E.
2007-12-01
Slip of geometrically complex faults involves interactions and processes that do not occur in standard planar fault models. These include off-fault yielding and stress relaxation, which are required to prevent the development of pathological stress conditions on the fault (or in extreme cases fault lock-up). Nielsen and Knopoff [1988] introduced yielding through a simplified form of viscoelastic stress relaxation. However, the mechanical characteristics of the brittle seismogenic crust indicate that faulting processes will dominate the stress relaxation processes. The fractal-like character of fault systems and fault roughness, together with the finite strength of rocks, insures that slight movements of secondary faults, at all scales, will be necessary to accommodate slip of major through-going faults. To model the integrated effect of these processes, we employ an earthquake rate formulation [Dieterich, 1994], which incorporates laboratory-derived rate- and state-dependent frictional properties, on geometrically complex faults. With the rate-state formulation we find that stress relaxation occurs co-seismically during large earthquakes, as delayed stress relaxation in the form of aftershocks, and as spatially distributed background seismicity. During aftershocks the spatial mean of stresses decay at a rate proportional to 1/t. We find large spatial and temporal differences in models of slip of faults with relaxation compared to faults in purely elastic media. We conclude that that yielding and relaxation are important controlling processes that are the mechanics of slip on geometically complex faults
2D and 3D shape based segmentation using deformable models.
El-Baz, Ayman; Yuksel, Seniha E; Shi, Hongjian; Farag, Aly A; El-Ghar, Mohamed A; Eldiasty, Tarek; Ghoneim, Mohamed A
2005-01-01
A novel shape based segmentation approach is proposed by modifying the external energy component of a deformable model. The proposed external energy component depends not only on the gray level of the images but also on the shape information which is obtained from the signed distance maps of objects in a given data set. The gray level distribution and the signed distance map of the points inside and outside the object of interest are accurately estimated by modelling the empirical density function with a linear combination of discrete Gaussians (LCDG) with positive and negative components. Experimental results on the segmentation of the kidneys from low-contrast DCE-MRI and on the segmentation of the ventricles from brain MRI's show how the approach is accurate in segmenting 2-D and 3-D data sets. The 2D results for the kidney segmentation have been validated by a radiologist and the 3D results of the ventricle segmentation have been validated with a geometrical phantom. PMID:16686036
STATISTICAL MECHANICS MODELING OF MESOSCALE DEFORMATION IN METALS
Anter El-Azab
2013-04-08
The research under this project focused on a theoretical and computational modeling of dislocation dynamics of mesoscale deformation of metal single crystals. Specifically, the work aimed to implement a continuum statistical theory of dislocations to understand strain hardening and cell structure formation under monotonic loading. These aspects of crystal deformation are manifestations of the evolution of the underlying dislocation system under mechanical loading. The project had three research tasks: 1) Investigating the statistical characteristics of dislocation systems in deformed crystals. 2) Formulating kinetic equations of dislocations and coupling these kinetics equations and crystal mechanics. 3) Computational solution of coupled crystal mechanics and dislocation kinetics. Comparison of dislocation dynamics predictions with experimental results in the area of statistical properties of dislocations and their field was also a part of the proposed effort. In the first research task, the dislocation dynamics simulation method was used to investigate the spatial, orientation, velocity, and temporal statistics of dynamical dislocation systems, and on the use of the results from this investigation to complete the kinetic description of dislocations. The second task focused on completing the formulation of a kinetic theory of dislocations that respects the discrete nature of crystallographic slip and the physics of dislocation motion and dislocation interaction in the crystal. Part of this effort also targeted the theoretical basis for establishing the connection between discrete and continuum representation of dislocations and the analysis of discrete dislocation simulation results within the continuum framework. This part of the research enables the enrichment of the kinetic description with information representing the discrete dislocation systems behavior. The third task focused on the development of physics-inspired numerical methods of solution of the coupled
Representing geometric structures in 3D tomography soil images: Application to pore-space modeling
NASA Astrophysics Data System (ADS)
Monga, Olivier; Ndeye Ngom, Fatou; François Delerue, Jean
2007-09-01
Only in the last decade have geoscientists started to use 3D computed tomography (CT) images of soil for better understanding and modeling of soil properties. In this paper, we propose one of the first approaches to allow the definition and computation of stable (intrinsic) geometric representations of structures in 3D CT soil images. This addresses the open problem set by the description of volume shapes from discrete traces without any a priori information. The basic concept involves representing the volume shape by a piecewise approximation using simple volume primitives (bowls, cylinders, cones, etc.). This typical representation is assumed to optimize a criterion ensuring its stability. This criterion includes the representation scale, which characterizes the trade-off between the fitting error and the number of patches. We also take into account the preservation of topological properties of the initial shape: the number of connected components, adjacency relationships, etc. We propose an efficient computation method for this piecewise approximation using cylinders or bowls. For cylinders, we use optimal region growing in a valuated adjacency graph that represents the primitives and their adjacency relationships. For bowls, we compute a minimal set of Delaunay spheres recovering the skeleton. Our method is applied to modeling of a coarse pore space extracted from 3D CT soil images. The piecewise bowls approximation gives a geometric formalism corresponding to the intuitive notion of pores and also an efficient way to compute it. This geometric and topological representation of coarse pore space can be used, for instance, to simulate biological activity in soil.
NASA Astrophysics Data System (ADS)
Levia, D. F.; Michalzik, B.; Bischoff, S.; Näthe, K.; Gruselle, M.; Richter, S.
2013-12-01
Particulate matter (PM) is of great importance to the biogeochemistry of forest ecosystems. The geometric configuration and carbon content of PM can affect the physics, surface area, and biogeochemical reactivity of PM. To date, however, no known work has quantified the geometric size and shape of PM contained in bulk precipitation, throughfall, stemflow, and Oa soil solution. Seeking to fill this knowledge gap, this work quantifies the geometric configurations and carbon content of PM in bulk precipitation, throughfall, stemflow, and Oa soil solution from a European beech (Fagus sylvatica L.) in east-central Germany during the leafed and leafless periods. Scanning electron microscopy (SEM), image processing and analysis techniques, and loss on ignition (LOI) analyses were employed to quantify the geometry of PM in the above terrestrial solutions as well as the carbon content. Building upon the work of Levia et al. [2013] who quantified the diameter distributions of 43,278 individual particulates in bulk precipitation, throughfall, stemflow, and Oa soil solution, this work investigates various aspects of the size and shape of PM in different terrestrial solutions, including surface area, roundness, perimeter, and area/perimeter (A/P) ratios. These results are then modeled to provide cross-scale understanding of PM in terrestrial solutions. Preliminary results suggest notable differences in the geometric representations of PM as a function of season and type (e.g., stemflow, Oa soil solution). For instance, maximum A/P ratio values were different among solution type, with the smallest maximum being recorded for stemflow. Empirical and modeling results of this work will be useful in cross-scaling of findings from the particulate scale to forests and beyond. Levia, D.F.*, Michalzik, B.*, Bischoff, S., Näthe, K., Legates, D.R., Gruselle, M.C-. and Richter, S. 2013. Measurement and modeling of diameter distributions of particulate matter in terrestrial solutions
Chen, Hsin-Chen; Tan, Jun; Dolly, Steven; Kavanaugh, James; Harold Li, H.; Altman, Michael; Gay, Hiram; Thorstad, Wade L.; Mutic, Sasa; Li, Hua; Anastasio, Mark A.; Low, Daniel A.
2015-02-15
Purpose: One of the most critical steps in radiation therapy treatment is accurate tumor and critical organ-at-risk (OAR) contouring. Both manual and automated contouring processes are prone to errors and to a large degree of inter- and intraobserver variability. These are often due to the limitations of imaging techniques in visualizing human anatomy as well as to inherent anatomical variability among individuals. Physicians/physicists have to reverify all the radiation therapy contours of every patient before using them for treatment planning, which is tedious, laborious, and still not an error-free process. In this study, the authors developed a general strategy based on novel geometric attribute distribution (GAD) models to automatically detect radiation therapy OAR contouring errors and facilitate the current clinical workflow. Methods: Considering the radiation therapy structures’ geometric attributes (centroid, volume, and shape), the spatial relationship of neighboring structures, as well as anatomical similarity of individual contours among patients, the authors established GAD models to characterize the interstructural centroid and volume variations, and the intrastructural shape variations of each individual structure. The GAD models are scalable and deformable, and constrained by their respective principal attribute variations calculated from training sets with verified OAR contours. A new iterative weighted GAD model-fitting algorithm was developed for contouring error detection. Receiver operating characteristic (ROC) analysis was employed in a unique way to optimize the model parameters to satisfy clinical requirements. A total of forty-four head-and-neck patient cases, each of which includes nine critical OAR contours, were utilized to demonstrate the proposed strategy. Twenty-nine out of these forty-four patient cases were utilized to train the inter- and intrastructural GAD models. These training data and the remaining fifteen testing data sets
NASA Astrophysics Data System (ADS)
Dahmen, K.; Ben-Zion, Y.; Uhl, J.
2011-12-01
Slowly sheared solid or densely packed granular materials often deform in an intermittent way with slip avalanches. The distribution of sizes follows often a power law over a broad range of sizes. In these cases, universal (i.e. detail-independent) scaling behavior governs the statistics of the slip-avalanches. Under some conditions, there are also "characteristic" statistics associated with enhanced occurrence of system-size events, and long-term mode switching between power law and characteristic behavior. These dynamic regimes can be understood with basic micromechanical model for deformation of solids with only two tuning parameter: weakening and dissipation of elastic stress transfer. For granular materials the packing fraction plays the role of the dissipation parameter and it sets the size of the largest slip avalanche. The model can reproduce observed stress-strain curves, power spectra of acoustic emissions, statistics of slip avalanches, and geometrical properties of slip, with a continuous phase transition from brittle to ductile behavior. Exact universal predictions for the power law exponents of the avalanche size distributions, durations, power spectra of acoustic emissions, and scaling functions are extracted using an analytical mean field theory and renormalization group tools. For granular materials a dynamic phase diagram with solid-like behavior and large slip avalanches at large packing fractions, and fluid-like behavior at lower packing fractions is obtained. The results agree with recent experimental observations and simulations of the statistics of dislocation dynamics in sheared crystals such as ice [1], slip avalanches in sheared granular materials [2], and avalanches in magnetic and fault systems [3,4]. [1] K. A. Dahmen, Y. Ben-Zion, and J.T. Uhl, "A micromechanical model for deformation in solids with universal predictions for stress strain curves and slip avalanches", Physical Review Letters 102, 175501/1-4 (2009). [2] K. A. Dahmen, Y
Fluid-Structure interaction modeling in deformable porous arteries
NASA Astrophysics Data System (ADS)
Zakerzadeh, Rana; Zunino, Paolo
2015-11-01
A computational framework is developed to study the coupling of blood flow in arteries interacting with a poroelastic arterial wall featuring possibly large deformations. Blood is modeled as an incompressible, viscous, Newtonian fluid using the Navier-Stokes equations and the arterial wall consists of a thick material which is modeled as a Biot system that describes the mechanical behavior of a homogeneous and isotropic elastic skeleton, and connecting pores filled with fluid. Discretization via finite element method leads to the system of nonlinear equations and a Newton-Raphson scheme is adopted to solve the resulting nonlinear system through consistent linearization. Moreover, interface conditions are imposed on the discrete level via mortar finite elements or Nitsche's coupling. The discrete linearized coupled FSI system is solved by means of a splitting strategy, which allows solving the Navier-Stokes and Biot equations separately. The numerical results investigate the effects of proroelastic parameters on the pressure wave propagation in arteries, filtration of incompressible fluids through the porous media, and the structure displacement. The fellowship support from the Computational Modeling & Simulation PhD program at University of Pittsburgh for Rana Zakerzadeh is gratefully acknowledged.
Design and analysis of a multi-sensor deformation detection system
NASA Astrophysics Data System (ADS)
Szostak-Chrzanowski, Anna; Chrzanowski, Adam; Deng, Nianwu; Bazanowski, Maciej
2008-12-01
Development of new technologies for monitoring structural and ground deformations puts new demands on the design and analysis of the multi-sensor systems. Design and analysis of monitoring schemes require a good understanding of the physical process that leads to deformation. Deterministic modelling of the load-deformation relationship provides information on the magnitude and location of expected critical deformations as well as delineates the deformation zone. By combining results of deterministic modelling with geometrical analysis, one can find the deformation mechanism and explain the cause of deformation in case of irregular behaviour of the investigated object. The concept is illustrated by four practical examples.
Geometrical properties of avalanches in self-organized critical models of solar flares.
McIntosh, Scott W; Charbonneau, Paul; Bogdan, Thomas J; Liu, Han-Li; Norman, James P
2002-04-01
We investigate the geometrical properties of avalanches in self-organized critical models of solar flares. Traditionally, such models differ from the classical sandpile model in their formulation of stability criteria in terms of the curvature of the nodal field, and belong to a distinct universality class. With a view toward comparing these properties to those inferred from spatially and temporally resolved flare observations, we consider the properties of avalanche peak snapshots, time-integrated avalanches in two and three dimensions, and the two-dimensional projections of the latter. The nature of the relationship between the avalanching volume and its projected area is an issue of particular interest in the solar flare context. Using our simulation results we investigate this relationship, and demonstrate that proper accounting of the fractal nature of avalanches can bring into agreement hitherto discrepant results of observational analyses based on simple, nonfractal geometries for the flaring volume. PMID:12005944
A True-Stress Creep Model Based on Deformation Mechanisms for Polycrystalline Materials
NASA Astrophysics Data System (ADS)
Wu, Xijia; Williams, Steve; Gong, Diguang
2012-11-01
A true-stress creep model has been developed based on well-recognized deformation mechanisms, i.e., dislocation glide, dislocation climb, and grain boundary sliding. The model provides a physics-based description of the entire creep deformation process with regards to the strain-time history (primary, secondary, and tertiary creep), rupture strain and lifetime, which finds good agreement with experimental observations for Waspaloy. A deformation-mechanism map is constructed for Waspaloy, and a creep failure criterion is defined by the dominant deformation mechanisms leading to intergranular/transgranular fracture. Thus, the model is a self-consistent tool for creep life prediction.
Domain-size heterogeneity in the Ising model: Geometrical and thermal transitions.
de la Rocha, André R; de Oliveira, Paulo Murilo C; Arenzon, Jeferson J
2015-04-01
A measure of cluster size heterogeneity (H), introduced by Lee et al. [Phys. Rev. E 84, 020101 (2011)] in the context of explosive percolation, was recently applied to random percolation and to domains of parallel spins in the Ising and Potts models. It is defined as the average number of different domain sizes in a given configuration and a new exponent was introduced to explain its scaling with the size of the system. In thermal spin models, however, physical clusters take into account the temperature-dependent correlation between neighboring spins and encode the critical properties of the phase transition. We here extend the measure of H to these clusters and, moreover, present new results for the geometric domains for both d=2 and 3. We show that the heterogeneity associated with geometric domains has a previously unnoticed double peak, thus being able to detect both the thermal and percolative transitions. An alternative interpretation for the scaling of H that does not introduce a new exponent is also proposed. PMID:25974445
Domain-size heterogeneity in the Ising model: Geometrical and thermal transitions
NASA Astrophysics Data System (ADS)
de la Rocha, André R.; de Oliveira, Paulo Murilo C.; Arenzon, Jeferson J.
2015-04-01
A measure of cluster size heterogeneity (H ), introduced by Lee et al. [Phys. Rev. E 84, 020101 (2011), 10.1103/PhysRevE.84.020101] in the context of explosive percolation, was recently applied to random percolation and to domains of parallel spins in the Ising and Potts models. It is defined as the average number of different domain sizes in a given configuration and a new exponent was introduced to explain its scaling with the size of the system. In thermal spin models, however, physical clusters take into account the temperature-dependent correlation between neighboring spins and encode the critical properties of the phase transition. We here extend the measure of H to these clusters and, moreover, present new results for the geometric domains for both d =2 and 3. We show that the heterogeneity associated with geometric domains has a previously unnoticed double peak, thus being able to detect both the thermal and percolative transitions. An alternative interpretation for the scaling of H that does not introduce a new exponent is also proposed.
Capturing spiral radial growth of conifers using the superellipse to model tree-ring geometric shape
Shi, Pei-Jian; Huang, Jian-Guo; Hui, Cang; Grissino-Mayer, Henri D.; Tardif, Jacques C.; Zhai, Li-Hong; Wang, Fu-Sheng; Li, Bai-Lian
2015-01-01
Tree-rings are often assumed to approximate a circular shape when estimating forest productivity and carbon dynamics. However, tree rings are rarely, if ever, circular, thereby possibly resulting in under- or over-estimation in forest productivity and carbon sequestration. Given the crucial role played by tree ring data in assessing forest productivity and carbon storage within a context of global change, it is particularly important that mathematical models adequately render cross-sectional area increment derived from tree rings. We modeled the geometric shape of tree rings using the superellipse equation and checked its validation based on the theoretical simulation and six actual cross sections collected from three conifers. We found that the superellipse better describes the geometric shape of tree rings than the circle commonly used. We showed that a spiral growth trend exists on the radial section over time, which might be closely related to spiral grain along the longitudinal axis. The superellipse generally had higher accuracy than the circle in predicting the basal area increment, resulting in an improved estimate for the basal area. The superellipse may allow better assessing forest productivity and carbon storage in terrestrial forest ecosystems. PMID:26528316
Geometric models of the new diamond turning for large off-axis aspheric mirrors
NASA Astrophysics Data System (ADS)
Han, C. S.; Xu, P. M.; Zhang, L. J.; Dong, S.
2006-02-01
Demands on large off-axis aspheric mirrors with high precision have propelled innovations of new effective and economical fabrication techniques as well as ultra-precision machining systems. A new generation of forming method for large off-axis aspheric surface is introduced. Linear motion guides are employed in the tool feed systems on most of diamond turning machines. For a rotary spindle can be made easier and less expensive than a linear guide at the same accuracy level, especially in manufacturing of a large size component, a rotary arm that carries a diamond tool combined with fast tool servo is used to replace the straight line. Therefore a new structure of a rotary feed machine is developed. Combination of two rotating movement of workpiece and diamond tool, and the micro linear feed of the fast tool servo controlled by CNC system synchronously, ultra-precision large aspheric surfaces can be turned. The corresponding geometric models are presented based on constituting appropriate coordinate systems and giving equation of the off-axis aspheric surface. By computer simulation it is verified that the processing method for the large off-axis aspheric component is simple and feasible. According to the geometric models provided in this paper, the 3-D machining is achieved. This new fabrication method allows equipment investment be decreased.
NASA Astrophysics Data System (ADS)
De Lucas, Javier
2015-03-01
A simple geometrical model for calculating the effective emissivity in blackbody cylindrical cavities has been developed. The back ray tracing technique and the Monte Carlo method have been employed, making use of a suitable set of coordinates and auxiliary planes. In these planes, the trajectories of individual photons in the successive reflections between the cavity points are followed in detail. The theoretical model is implemented by using simple numerical tools, programmed in Microsoft Visual Basic for Application and Excel. The algorithm is applied to isothermal and non-isothermal diffuse cylindrical cavities with a lid; however, the basic geometrical structure can be generalized to a cylindro-conical shape and specular reflection. Additionally, the numerical algorithm and the program source code can be used, with minor changes, for determining the distribution of the cavity points, where photon absorption takes place. This distribution could be applied to the study of the influence of thermal gradients on the effective emissivity profiles, for example. Validation is performed by analyzing the convergence of the Monte Carlo method as a function of the number of trials and by comparison with published results of different authors.
Image Sensor Model Using Geometric Algebra: From Calibration to Motion Estimation
NASA Astrophysics Data System (ADS)
Debaecker, Thibaud; Benosman, Ryad; Ieng, Sio H.
In computer vision image sensors have universally been defined as the nonparametric association of projection rays in the 3D world to pixels in the images. If the pixels' physical topology can be often neglected in the case of perspective cameras, this approximation is no longer valid in the case of variant scale sensors, which are now widely used in robotics. Neglecting the nonnull pixel area and then the pixel volumic field of view implies that geometric reconstruction problems are solved by minimizing a cost function that combines the reprojection errors in the 2D images. This paper provides a complete and realistic cone-pixel camera model that equally fits constant or variant scale resolution together with a protocol to calibrate such a sensor. The proposed model involves a new characterization of pixel correspondences with 3D-cone intersections computed using convex hull and twists in Conformal Geometric Algebra. Simulated experiments show that standard methods and especially Bundle Adjustment are sometimes unable to reach the correct motion, because of their ray-pixel approach and the choice of reprojection error as a cost function which does not particularly fit the physical reality. This problem can be solved using a nonprojective cone intersection cost function as introduced below.
NASA Astrophysics Data System (ADS)
Papaioannou, G.; Loukas, Athanasios
2010-05-01
Floodplain modeling is a recently new and applied method in river engineering discipline and is essential for prediction of flood hazards. The issue of flood inundation of upland environments with topographically complex floodplains is an understudied subject. In most areas of the U.S.A., the use of topographic information derived from Light Detection and Ranging (LIDAR) has improved the quality of river flood inundation predictions. However, such high quality topographical data are not available in most countries and the necessary information is obtained by topographical survey and/or topographical maps. Furthermore, the optimum dimensionality of hydraulic models, cross-section configuration in one-dimensional (1D) models, mesh resolution in two-dimensional models (2D) and modeling approach is not well studied or documented. All these factors introduce significant uncertainty in the evaluation of the floodplain zoning. This study addresses some of these issues by comparing flood inundation maps developed using different topography, geometric description and modeling approach. The methodology involves use of topographic datasets with different horizontal resolutions, vertical accuracies and bathymetry details. Each topographic dataset is used to create a flood inundation map for different cross-section configurations using 1D (HEC-RAS) model, and different mesh resolutions using 2D models for steady state and unsteady state conditions. Comparison of resulting maps indicates the uncertainty introduced in floodplain modeling by the horizontal resolution and vertical accuracy of topographic data and the different modeling approaches.
Model Attitude and Deformation Measurements at the NASA Glenn Research Center
NASA Technical Reports Server (NTRS)
Woike, Mark R.
2008-01-01
The NASA Glenn Research Center is currently participating in an American Institute of Aeronautics and Astronautics (AIAA) sponsored Model Attitude and Deformation Working Group. This working group is chartered to develop a best practices document dealing with the measurement of two primary areas of wind tunnel measurements, 1) model attitude including alpha, beta and roll angle, and 2) model deformation. Model attitude is a principle variable in making aerodynamic and force measurements in a wind tunnel. Model deformation affects measured forces, moments and other measured aerodynamic parameters. The working group comprises of membership from industry, academia, and the Department of Defense (DoD). Each member of the working group gave a presentation on the methods and techniques that they are using to make model attitude and deformation measurements. This presentation covers the NASA Glenn Research Center s approach in making model attitude and deformation measurements.
Noncyclic geometric quantum computation and preservation of entanglement for a two-qubit Ising model
NASA Astrophysics Data System (ADS)
Rangani Jahromi, H.; Amniat-Talab, M.
2015-10-01
After presenting an exact analytical solution of time-dependent Schrödinger equation, we study the dynamics of entanglement for a two-qubit Ising model. One of the spin qubits is driven by a static magnetic field applied in the direction of the Ising interaction, while the other is coupled with a rotating magnetic field. We also investigate how the entanglement can be controlled by changing the external parameters. Because of the important role of maximally entangled Bell states in quantum communication, we focus on the generalized Bell states as the initial states of the system. It is found that the entanglement evolution is independent of the initial Bell states. Moreover, we can preserve the initial maximal entanglement by adjusting the angular frequency of the rotating field or controlling the exchange coupling between spin qubits. Besides, our calculation shows that the entanglement dynamics is unaffected by the static magnetic field imposed in the direction of the Ising interaction. This is an interesting result, because, as we shall show below, this driving field can be used to control and manipulate the noncyclic geometric phase without affecting the system entanglement. Besides, the nonadiabatic and noncyclic geometric phase for evolved states of the present system are calculated and described in detail. In order to identify the unusable states for quantum communication, completely deviated from the initial maximally entangled states, we also study the fidelity between the initial Bell state and the evolved state of the system. Interestingly, we find that these unusable states can be detected by geometric quantum computation.
NASA Astrophysics Data System (ADS)
Shibkov, A. A.; Zolotov, A. E.; Zheltov, M. A.; Denisov, A. A.; Gasanov, M. F.; Kochegarov, S. S.
2016-05-01
The effect of an electric current on the band formation and the serrated deformation of planar specimens made of an aluminum-magnesium AlMg5 alloy and weakened by holes is experimentally studied. It is found that the concentration of elastic stress fields and the self-localized unstable plastic deformation field near a hole decreases the critical strain of appearance of the first stress drop and hinders the currentinduced suppression of band formation and the serrated Portevin-Le Chatelier deformation. These results are shown not to be related to the concentration of Joule heat near a hole.
Model for deformation in Long Valley, California, 1980-1983
Rundle, J.B.; Whitcomb, J.H.
1984-10-10
Geodetic data collected in Long Valley, California, from 1975 through 1981 define a pattern of uplift and strain which is evidently associated with a sequence of earthquakes occuring in May 1980 and subsequent swarm activity continuing until the present. We have constructed a model to explain the deformation observed since May 1980 in terms of inflation of two subsurface magma chambers, faulting in the south most region of the caldera, and slip in the Hilton Creek fault. The most significant new feature of the model is the shallow magma chamber at 5 km depth, located a few hundred meters to the east of the Casa Diablo hot spring area. Inflation of this chamber cause stresses which show consistency with various aspects of the seismicity in the south moat of the calcers. Calculations of stress across vertical planes over the magma chambers can be used together with failure criteria to estimate the inflation volume at which the rock layers intervening between the chamber and the surface will fail by extensional fracture.
New geometric design consistency model based on operating speed profiles for road safety evaluation.
Camacho-Torregrosa, Francisco J; Pérez-Zuriaga, Ana M; Campoy-Ungría, J Manuel; García-García, Alfredo
2013-12-01
To assist in the on-going effort to reduce road fatalities as much as possible, this paper presents a new methodology to evaluate road safety in both the design and redesign stages of two-lane rural highways. This methodology is based on the analysis of road geometric design consistency, a value which will be a surrogate measure of the safety level of the two-lane rural road segment. The consistency model presented in this paper is based on the consideration of continuous operating speed profiles. The models used for their construction were obtained by using an innovative GPS-data collection method that is based on continuous operating speed profiles recorded from individual drivers. This new methodology allowed the researchers to observe the actual behavior of drivers and to develop more accurate operating speed models than was previously possible with spot-speed data collection, thereby enabling a more accurate approximation to the real phenomenon and thus a better consistency measurement. Operating speed profiles were built for 33 Spanish two-lane rural road segments, and several consistency measurements based on the global and local operating speed were checked. The final consistency model takes into account not only the global dispersion of the operating speed, but also some indexes that consider both local speed decelerations and speeds over posted speeds as well. For the development of the consistency model, the crash frequency for each study site was considered, which allowed estimating the number of crashes on a road segment by means of the calculation of its geometric design consistency. Consequently, the presented consistency evaluation method is a promising innovative tool that can be used as a surrogate measure to estimate the safety of a road segment. PMID:23176754
Packaged Fault Model for Geometric Segmentation of Active Faults Into Earthquake Source Faults
NASA Astrophysics Data System (ADS)
Nakata, T.; Kumamoto, T.
2004-12-01
In Japan, the empirical formula proposed by Matsuda (1975) mainly based on the length of the historical surface fault ruptures and magnitude, is generally applied to estimate the size of future earthquakes from the extent of existing active faults for seismic hazard assessment. Therefore validity of the active fault length and defining individual segment boundaries where propagating ruptures terminate are essential and crucial to the reliability for the accurate assessments. It is, however, not likely for us to clearly identify the behavioral earthquake segments from observation of surface faulting during the historical period, because most of the active faults have longer recurrence intervals than 1000 years in Japan. Besides uncertainties of the datasets obtained mainly from fault trenching studies are quite large for fault grouping/segmentation. This is why new methods or criteria should be applied for active fault grouping/segmentation, and one of the candidates may be geometric criterion of active faults. Matsuda (1990) used _gfive kilometer_h as a critical distance for grouping and separation of neighboring active faults. On the other hand, Nakata and Goto (1998) proposed the geometric criteria such as (1) branching features of active fault traces and (2) characteristic pattern of vertical-slip distribution along the fault traces as tools to predict rupture length of future earthquakes. The branching during the fault rupture propagation is regarded as an effective energy dissipation process and could result in final rupture termination. With respect to the characteristic pattern of vertical-slip distribution, especially with strike-slip components, the up-thrown sides along the faults are, in general, located on the fault blocks in the direction of relative strike-slip. Applying these new geometric criteria to the high-resolution active fault distribution maps, the fault grouping/segmentation could be more practically conducted. We tested this model
Numerical modeling on progressive internal deformation in down-built diapirs
NASA Astrophysics Data System (ADS)
Fuchs, Lukas; Koyi, Hemin; Schmeling, Harro
2014-09-01
A two-dimensional finite difference code (FDCON) is used to estimate the finite deformation within a down-built diapir. The geometry of the down-built diapir is fixed by using two rigid rectangular overburden units which sink into a source layer of a constant viscosity. Thus, the model refers to diapirs consisting of a source layer feeding a vertical stem, and not to other salt structures (e.g. salt sheets or pillows). With this setup we study the progressive strain in three different deformation regimes within the “salt” material: (I) a squeezed channel-flow deformation regime and (II) a corner-flow deformation regime within the source layer, and (III) a pure channel-flow deformation regime within the stem. We analyze the evolution of finite deformation in each regime individually, progressive strain for particles passing all three regimes, and total 2D finite deformation within the salt layer. Model results show that the material which enters the stem bears inherited strain accumulated from the other two domains. Therefore, finite deformation in the stem differs from the expected channel-flow deformation, due to the deformation accumulated within the source layer. The stem displays a high deformation zone within its center and areas of decreasing progressive strain between its center and its boundaries. High deformation zones within the stem could also be observed within natural diapirs (e.g. Klodowa, Polen). The location and structure of the high deformation zone (e.g. symmetric or asymmetric) could reveal information about different rates of salt supplies from the source layer. Thus, deformation pattern could directly be correlated to the evolution of the diapir.
Geometric continuum regularization of quantum field theory
Halpern, M.B. . Dept. of Physics)
1989-11-08
An overview of the continuum regularization program is given. The program is traced from its roots in stochastic quantization, with emphasis on the examples of regularized gauge theory, the regularized general nonlinear sigma model and regularized quantum gravity. In its coordinate-invariant form, the regularization is seen as entirely geometric: only the supermetric on field deformations is regularized, and the prescription provides universal nonperturbative invariant continuum regularization across all quantum field theory. 54 refs.
NASA Astrophysics Data System (ADS)
Mukherjee, A. B.; Kapoor, R.; Thota, M. K.; Chakravartty, J. K.
2016-05-01
Finite element analysis (FEA) was used to model the joining of titanium grade 2 (Ti) to AISI 321 stainless steel (SS) transition joint of lap configuration with grooves at the interface on SS side. The hot forming of Ti for filling the grooves without defects was simulated. FEA involving large plastic flow with sticking friction condition was initially validated using compression test on cylindrical specimen at 900 °C. The barreled shape and a no-deformation zone in the sample predicted by FEA matched with those of the compression experiments. For the joining process, FEA computed the distribution of strain and hydrostatic stress in Ti and the minimum ram load required for a defect-free joint. The hot forming parameters for Ti to fill the grooves without defects and any geometrical distortion of the die were found to be 0.001 s-1 at 900 °C. Using these conditions a defect-free Ti-SS joint was experimentally produced.
NASA Astrophysics Data System (ADS)
Mukherjee, A. B.; Kapoor, R.; Thota, M. K.; Chakravartty, J. K.
2016-07-01
Finite element analysis (FEA) was used to model the joining of titanium grade 2 (Ti) to AISI 321 stainless steel (SS) transition joint of lap configuration with grooves at the interface on SS side. The hot forming of Ti for filling the grooves without defects was simulated. FEA involving large plastic flow with sticking friction condition was initially validated using compression test on cylindrical specimen at 900 °C. The barreled shape and a no-deformation zone in the sample predicted by FEA matched with those of the compression experiments. For the joining process, FEA computed the distribution of strain and hydrostatic stress in Ti and the minimum ram load required for a defect-free joint. The hot forming parameters for Ti to fill the grooves without defects and any geometrical distortion of the die were found to be 0.001 s-1 at 900 °C. Using these conditions a defect-free Ti-SS joint was experimentally produced.
NASA Astrophysics Data System (ADS)
Lüdde, H. J.; Achenbach, A.; Kalkbrenner, T.; Jankowiak, H. C.; Kirchner, T.
2016-05-01
A recently introduced model to account for geometric screening corrections in an independent-atom-model description of ion-molecule collisions is applied to proton collisions from amino acids and DNA and RNA nucleobases. The correction coefficients are obtained from using a pixel counting method (PCM) for the exact calculation of the effective cross sectional area that emerges when the molecular cross section is pictured as a structure of (overlapping) atomic cross sections. This structure varies with the relative orientation of the molecule with respect to the projectile beam direction and, accordingly, orientation-independent total cross sections are obtained from averaging the pixel count over many orientations. We present net capture and net ionization cross sections over wide ranges of impact energy and analyze the strength of the screening effect by comparing the PCM results with Bragg additivity rule cross sections and with experimental data where available. Work supported by NSERC, Canada.
Mean-field dynamic criticality and geometric transition in the Gaussian core model
NASA Astrophysics Data System (ADS)
Coslovich, Daniele; Ikeda, Atsushi; Miyazaki, Kunimasa
2016-04-01
We use molecular dynamics simulations to investigate dynamic heterogeneities and the potential energy landscape of the Gaussian core model (GCM). Despite the nearly Gaussian statistics of particles' displacements, the GCM exhibits giant dynamic heterogeneities close to the dynamic transition temperature. The divergence of the four-point susceptibility is quantitatively well described by the inhomogeneous version of the mode-coupling theory. Furthermore, the potential energy landscape of the GCM is characterized by large energy barriers, as expected from the lack of activated, hopping dynamics, and display features compatible with a geometric transition. These observations demonstrate that all major features of mean-field dynamic criticality can be observed in a physically sound, three-dimensional model.
Mean-field dynamic criticality and geometric transition in the Gaussian core model.
Coslovich, Daniele; Ikeda, Atsushi; Miyazaki, Kunimasa
2016-04-01
We use molecular dynamics simulations to investigate dynamic heterogeneities and the potential energy landscape of the Gaussian core model (GCM). Despite the nearly Gaussian statistics of particles' displacements, the GCM exhibits giant dynamic heterogeneities close to the dynamic transition temperature. The divergence of the four-point susceptibility is quantitatively well described by the inhomogeneous version of the mode-coupling theory. Furthermore, the potential energy landscape of the GCM is characterized by large energy barriers, as expected from the lack of activated, hopping dynamics, and display features compatible with a geometric transition. These observations demonstrate that all major features of mean-field dynamic criticality can be observed in a physically sound, three-dimensional model. PMID:27176347
NASA Technical Reports Server (NTRS)
Goldberg, Robert K.; Stouffer, Donald C.
1998-01-01
Recently applications have exposed polymer matrix composite materials to very high strain rate loading conditions, requiring an ability to understand and predict the material behavior under these extreme conditions. In this second paper of a two part report, a three-dimensional composite micromechanical model is described which allows for the analysis of the rate dependent, nonlinear deformation response of a polymer matrix composite. Strain rate dependent inelastic constitutive equations utilized to model the deformation response of a polymer are implemented within the micromechanics method. The deformation response of two representative laminated carbon fiber reinforced composite materials with varying fiber orientation has been predicted using the described technique. The predicted results compare favorably to both experimental values and the response predicted by the Generalized Method of Cells, a well-established micromechanics analysis method.
A Method for Lung Boundary Correction Using Split Bregman Method and Geometric Active Contour Model.
Feng, Changli; Zhang, Jianxun; Liang, Rui
2015-01-01
In order to get the extracted lung region from CT images more accurately, a model that contains lung region extraction and edge boundary correction is proposed. Firstly, a new edge detection function is presented with the help of the classic structure tensor theory. Secondly, the initial lung mask is automatically extracted by an improved active contour model which combines the global intensity information, local intensity information, the new edge information, and an adaptive weight. It is worth noting that the objective function of the improved model is converted to a convex model, which makes the proposed model get the global minimum. Then, the central airway was excluded according to the spatial context messages and the position relationship between every segmented region and the rib. Thirdly, a mesh and the fractal theory are used to detect the boundary that surrounds the juxtapleural nodule. Finally, the geometric active contour model is employed to correct the detected boundary and reinclude juxtapleural nodules. We also evaluated the performance of the proposed segmentation and correction model by comparing with their popular counterparts. Efficient computing capability and robustness property prove that our model can correct the lung boundary reliably and reproducibly. PMID:26089976
NASA Technical Reports Server (NTRS)
Grebowsky, G. J.
1982-01-01
Present LANDSAT data formats are reviewed to clarify how the geodetic location and registration capabilities were defined for P-tape products and RBV data. Since there is only one geometric model used in the master data processor, geometric location accuracy of P-tape products depends on the absolute accuracy of the model and registration accuracy is determined by the stability of the model. Due primarily to inaccuracies in data provided by the LANDSAT attitude management system, desired accuracies are obtained only by using ground control points and a correlation process. The verification of system performance with regards to geodetic location requires the capability to determine pixel positions of map points in a P-tape array. Verification of registration performance requires the capability to determine pixel positions of common points (not necessarily map points) in 2 or more P-tape arrays for a given world reference system scene. Techniques for registration verification can be more varied and automated since map data are not required. The verification of LACIE extractions is used as an example.
Geometrical influence of pulmonary acinar models on respiratory flows and particle deposition
NASA Astrophysics Data System (ADS)
Hofemeier, Philipp; Sznitman, Josue
2012-11-01
Due to experimental challenges in assessing respiratory flows in the deep regions of the lungs, computational simulations are typically sought to quantify inhaled aerosol transport and deposition in the acinus. Most commonly, simulations are performed using generic geometries of alveoli, including spheres, toroids and polyhedra to mimic the acinar region. However, local respiratory flows and ensuing particle trajectories are anticipated to be highly influenced by the specific geometrical structures chosen. To date, geometrical influences have not yet been thoroughly quantified. Knowing beforehand how geometries affect acinar flows and particle transport is critical in translating simulated data to predictions of aerosol deposition in real lungs. Here, we conduct a systematic investigation on a number of generic acinar models. Simulations are conducted for simple alveolated airways featuring a selection of geometries. Deposition patterns and efficiencies are quantified both for massless particles, highlighting details of the local flow, and micron-scale aerosols. This latter group of particles represents an important class of inhaled aerosols known to reach and deposit in the acinus. Our work emphasizes the subtleties of acinar geometry in determining the fate of inhaled aerosols.
A geometric photography model for determining cloud top heights using MISR images
NASA Astrophysics Data System (ADS)
He, Yongjian; Qiu, Xinfa; Sun, Zhian; Li, Qiang
2015-10-01
Cloud top height (CTH) is an important factor in weather forecasting and monitoring. An accurate CTH has scientific significance for improving the quality of both weather analyses and numerical weather prediction. The three-dimensional geometric method has been widely recognized as a CTH calculation method that provides relatively high accuracy. In this paper, we used the theory of digital photogrammetry and remote sensing technology to establish a geometric photography model (GPM) that can simultaneously determine CTHs and cloud movement speed (CMS) by introducing the CMS into the collinearity equation of photogrammetry. The CTH is derived by constructing three-dimensional image pairs of multitemporal Multiangle Imaging Spectroradiometer (MISR) red spectral band images from three angles. Compared with CTHs observed by ground-based lidar at the United States Southern Great Plains, the difference of CTHs using the GPM relative to the reference value was less than 300 m. By analyzing the ground control points, the GPM error is estimated to be approximately 300 m. Compared with MISR CTH data, the CTHs calculated in this study were similar to that of MISR without wind.
Modeling Geometric-Temporal Context With Directional Pyramid Co-Occurrence for Action Recognition.
Yuan, Chunfeng; Li, Xi; Hu, Weiming; Ling, Haibin; Maybank, Stephen J
2014-02-01
In this paper, we present a new geometric-temporal representation for visual action recognition based on local spatio-temporal features. First, we propose a modified covariance descriptor under the log-Euclidean Riemannian metric to represent the spatio-temporal cuboids detected in the video sequences. Compared with previously proposed covariance descriptors, our descriptor can be measured and clustered in Euclidian space. Second, to capture the geometric-temporal contextual information, we construct a directional pyramid co-occurrence matrix (DPCM) to describe the spatio-temporal distribution of the vector-quantized local feature descriptors extracted from a video. DPCM characterizes the co-occurrence statistics of local features as well as the spatio-temporal positional relationships among the concurrent features. These statistics provide strong descriptive power for action recognition. To use DPCM for action recognition, we propose a directional pyramid co-occurrence matching kernel to measure the similarity of videos. The proposed method achieves the state-of-the-art performance and improves on the recognition performance of the bag-of-visual-words (BOVWs) models by a large margin on six public data sets. For example, on the KTH data set, it achieves 98.78% accuracy while the BOVW approach only achieves 88.06%. On both Weizmann and UCF CIL data sets, the highest possible accuracy of 100% is achieved. PMID:26270910
Geometric and number effect on damping capacity of Helmholtz resonators in a model chamber
NASA Astrophysics Data System (ADS)
Kim, H. J.; Cha, J.-P.; Song, J.-K.; Ko, Y. S.
2010-08-01
An acoustic cavity was selected as a stabilization device to control high-frequency combustion instabilities in gas turbines or liquid rocket engine combustors, and the acoustic damping capacity of the acoustic cavity was investigated for various geometric configurations under atmospheric non-reacting conditions. The tuning frequency of the acoustic cavity and the acoustic responses of a model chamber with a single acoustic cavity were studied first. Damping capacity was initially quantified through the frequency width of two split modes and the amplitude-damped ratio. The results showed that the cavity with the largest orifice area or the shortest orifice length was the most effective in acoustic damping of the harmful resonant mode. The effect of the number of cavities on acoustic damping capacity was also studied. Damping capacity was improved by increasing the number of cavities. For a better evaluation of acoustic damping capacity, two quantified parameters; the acoustic absorption, meaning the damping efficiency, and acoustic conductance, meaning the acoustic power loss, were introduced. The case was observed that has had insufficient loss of acoustic power in spite of having the highest absorption efficiency. As a result, fine geometric tuning for the acoustic cavity is required for the sufficient passive control. Also, the choice of the number of cavities is important to optimize the damping efficiency and absolute damping loss in consideration of the restriction of the cavity volume.
NASA Astrophysics Data System (ADS)
Zhu, Limin; He, Gaiyun; Song, Zhanjie
2016-03-01
Product variation reduction is critical to improve process efficiency and product quality, especially for multistage machining process (MMP). However, due to the variation accumulation and propagation, it becomes quite difficult to predict and reduce product variation for MMP. While the method of statistical process control can be used to control product quality, it is used mainly to monitor the process change rather than to analyze the cause of product variation. In this paper, based on a differential description of the contact kinematics of locators and part surfaces, and the geometric constraints equation defined by the locating scheme, an improved analytical variation propagation model for MMP is presented. In which the influence of both locator position and machining error on part quality is considered while, in traditional model, it usually focuses on datum error and fixture error. Coordinate transformation theory is used to reflect the generation and transmission laws of error in the establishment of the model. The concept of deviation matrix is heavily applied to establish an explicit mapping between the geometric deviation of part and the process error sources. In each machining stage, the part deviation is formulized as three separated components corresponding to three different kinds of error sources, which can be further applied to fault identification and design optimization for complicated machining process. An example part for MMP is given out to validate the effectiveness of the methodology. The experiment results show that the model prediction and the actual measurement match well. This paper provides a method to predict part deviation under the influence of fixture error, datum error and machining error, and it enriches the way of quality prediction for MMP.
Deformation-induced damage and recovery in model hydrogels - A molecular dynamics simulation
NASA Astrophysics Data System (ADS)
Zidek, Jan; Milchev, Andrey; Jancar, Josef; Vilgis, Thomas A.
2016-09-01
Using molecular dynamics simulation of a model hybrid cross-link hydrogel, we investigate the network damage evolution and the related structure transformations. We model the hydrogel structure as a network-connected assembly of crosslinked clusters whereby deformation-induced damage is considered along with network recovery. The two principal mechanisms involved in hydrogel recovery from deformation include segment hops of the building structure units (segments) between clusters and cluster shape modification. These mechanisms act either instantaneously, or with a certain time delay after the onset of deformation. By elucidating the conditions under which one of the mechanisms prevails, one may design hydrogel materials with a desired response to deformation.
HERMES: A Model to Describe Deformation, Burning, Explosion, and Detonation
Reaugh, J E
2011-11-22
performance, whether as a result of accident, hazard, or a fault in the detonation train. These models describe the build-up of detonation from a shock stimulus. They are generally consistent with the mesoscale picture of ignition at many small defects in the plane of the shock front and the growth of the resulting hot-spots, leading to detonation in heterogeneous explosives such as plastic-bonded explosives (PBX). The models included terms for ignition, and also for the growth of reaction as tracked by the local mass fraction of product gas, {lambda}. The growth of reaction in such models incorporates a form factor that describes the change of surface area per unit volume (specific surface area) as the reaction progresses. For unimolecular crystalline-based explosives, the form factor is consistent with the mesoscale picture of a galaxy of hot spots burning outward and eventually interacting with each other. For composite explosives and propellants, where the fuel and oxidizer are segregated, the diffusion flame at the fuel-oxidizer interface can be interpreted with a different form factor that corresponds to grains burning inward from their surfaces. The form factor influences the energy release rate, and the amount of energy released in the reaction zone. Since the 19th century, gun and cannon propellants have used perforated geometric shapes that produce an increasing surface area as the propellant burns. This helps maintain the pressure as burning continues while the projectile travels down the barrel, which thereby increases the volume of the hot gas. Interior ballistics calculations use a geometric form factor to describe the changing surface area precisely. As a result, with a suitably modified form factor, detonation models can represent burning and explosion in damaged and broken reactant. The disadvantage of such models in application to accidents is that the ignition term does not distinguish between a value of pressure that results from a shock, and the same
Towards Automatic Validation and Healing of Citygml Models for Geometric and Semantic Consistency
NASA Astrophysics Data System (ADS)
Alam, N.; Wagner, D.; Wewetzer, M.; von Falkenhausen, J.; Coors, V.; Pries, M.
2013-09-01
A steadily growing number of application fields for large 3D city models have emerged in recent years. Like in many other domains, data quality is recognized as a key factor for successful business. Quality management is mandatory in the production chain nowadays. Automated domain-specific tools are widely used for validation of business-critical data but still common standards defining correct geometric modeling are not precise enough to define a sound base for data validation of 3D city models. Although the workflow for 3D city models is well-established from data acquisition to processing, analysis and visualization, quality management is not yet a standard during this workflow. Processing data sets with unclear specification leads to erroneous results and application defects. We show that this problem persists even if data are standard compliant. Validation results of real-world city models are presented to demonstrate the potential of the approach. A tool to repair the errors detected during the validation process is under development; first results are presented and discussed. The goal is to heal defects of the models automatically and export a corrected CityGML model.
Geometric entanglement and quantum phase transitions in two-dimensional quantum lattice models
NASA Astrophysics Data System (ADS)
Shi, Qian-Qian; Wang, Hong-Lei; Li, Sheng-Hao; Cho, Sam Young; Batchelor, Murray T.; Zhou, Huan-Qiang
2016-06-01
Geometric entanglement (GE), as a measure of multipartite entanglement, has been investigated as a universal tool to detect phase transitions in quantum many-body lattice models. In this paper we outline a systematic method to compute GE for two-dimensional (2D) quantum many-body lattice models based on the translational invariant structure of infinite projected entangled pair state (iPEPS) representations. By employing this method, the q -state quantum Potts model on the square lattice with q ∈{2 ,3 ,4 ,5 } is investigated as a prototypical example. Further, we have explored three 2D Heisenberg models: the antiferromagnetic spin-1/2 X X X and anisotropic X Y X models in an external magnetic field, and the antiferromagnetic spin-1 X X Z model. We find that continuous GE does not guarantee a continuous phase transition across a phase transition point. We observe and thus classify three different types of continuous GE across a phase transition point: (i) GE is continuous with maximum value at the transition point and the phase transition is continuous, (ii) GE is continuous with maximum value at the transition point but the phase transition is discontinuous, and (iii) GE is continuous with nonmaximum value at the transition point and the phase transition is continuous. For the models under consideration, we find that the second and the third types are related to a point of dual symmetry and a fully polarized phase, respectively.
A Novel Method of Modeling the Deformation Resistance for Clad Sheet
Hu Jianliang; Yi Youping; Xie Mantang
2011-08-22
Because of the excellent thermal conductivity, the clad sheet (3003/4004/3003) of aluminum alloy is extensively used in various heat exchangers, such as radiator, motorcar air conditioning, evaporator, and so on. The deformation resistance model plays an important role in designing the process parameters of hot continuous rolling. However, the complex behaviors of the plastic deformation of the clad sheet make the modeling very difficult. In this work, a novel method for modeling the deformation resistance of clad sheet was proposed by combining the finite element analysis with experiments. The deformation resistance model of aluminum 3003 and 4004 was proposed through hot compression test on the Gleeble-1500 thermo-simulation machine. And the deformation resistance model of clad sheet was proposed through finite element analysis using DEFORM-2D software. The relationship between cladding ratio and the deformation resistance was discussed in detail. The results of hot compression simulation demonstrate that the cladding ratio has great effects on the resistance of the clad sheet. Taking the cladding ratio into consideration, the mathematical model of the deformation resistance for clad sheet has been proved to have perfect forecasting precision of different cladding ratio. Therefore, the presented model can be used to predict the rolling force of clad sheet during the hot continuous rolling process.
Dystrophic Spinal Deformities in a Neurofibromatosis Type 1 Murine Model
Yang, Dalong; Yang, Hao; Chen, Shi; Wu, Xiaohua; Li, Xiaohong; Yang, Xianlin; Mohammad, Khalid S.; Guise, Theresa A.; Bergner, Amanda L.; Stevenson, David A.; Yang, Feng-Chun
2015-01-01
Despite the high prevalence and significant morbidity of spinal anomalies in neurofibromatosis type 1 (NF1), the pathogenesis of these defects remains largely unknown. Here, we present two murine models: Nf1flox/−;PeriCre and Nf1flox/−;Col.2.3Cre mice, which recapitulate spinal deformities seen in the human disease. Dynamic histomorphometry and microtomographic studies show recalcitrant bone remodeling and distorted bone microarchitecture within the vertebral spine of Nf1flox/−;PeriCre and Nf1flox/−;Col2.3Cre mice, with analogous histological features present in a human patient with dystrophic scoliosis. Intriguingly, 36–60% of Nf1flox/−;PeriCre and Nf1flox/−;Col2.3Cre mice exhibit segmental vertebral fusion anomalies with boney obliteration of the intervertebral disc (IVD). While analogous findings have not yet been reported in the NF1 patient population, we herein present two case reports of IVD defects and interarticular vertebral fusion in patients with NF1. Collectively, these data provide novel insights regarding the pathophysiology of dystrophic spinal anomalies in NF1, and provide impetus for future radiographic analyses of larger patient cohorts to determine whether IVD and vertebral fusion defects may have been previously overlooked or underreported in the NF1 patient population. PMID:25786243
Dystrophic spinal deformities in a neurofibromatosis type 1 murine model.
Rhodes, Steven D; Zhang, Wei; Yang, Dalong; Yang, Hao; Chen, Shi; Wu, Xiaohua; Li, Xiaohong; Yang, Xianlin; Mohammad, Khalid S; Guise, Theresa A; Bergner, Amanda L; Stevenson, David A; Yang, Feng-Chun
2015-01-01
Despite the high prevalence and significant morbidity of spinal anomalies in neurofibromatosis type 1 (NF1), the pathogenesis of these defects remains largely unknown. Here, we present two murine models: Nf1flox/-;PeriCre and Nf1flox/-;Col.2.3Cre mice, which recapitulate spinal deformities seen in the human disease. Dynamic histomorphometry and microtomographic studies show recalcitrant bone remodeling and distorted bone microarchitecture within the vertebral spine of Nf1flox/-;PeriCre and Nf1flox/-;Col2.3Cre mice, with analogous histological features present in a human patient with dystrophic scoliosis. Intriguingly, 36-60% of Nf1flox/-;PeriCre and Nf1flox/-;Col2.3Cre mice exhibit segmental vertebral fusion anomalies with boney obliteration of the intervertebral disc (IVD). While analogous findings have not yet been reported in the NF1 patient population, we herein present two case reports of IVD defects and interarticular vertebral fusion in patients with NF1. Collectively, these data provide novel insights regarding the pathophysiology of dystrophic spinal anomalies in NF1, and provide impetus for future radiographic analyses of larger patient cohorts to determine whether IVD and vertebral fusion defects may have been previously overlooked or underreported in the NF1 patient population. PMID:25786243
Using transverse isotropy to model arbitrary deformation-induced anisotropy
Brannon, R.M.
1996-07-01
A unifying framework is developed for the analysis of brittle materials. Heretofore diverse classes of models result from different choices for unspecified coefficient and distribution functions in the unified theory. Material response is described in terms of expectation integrals of transverse symmetry tensors. First, a canonical body containing cracks of all the same orientation is argued to possess macroscopic transverse isotropy. An orthogonal basis for the linear subspace consisting of all double-symmetric transversely-isotropic fourth-order tensors associated with a given material vector is introduced and applied to deduce the explicit functional dependence of the compliance of such contrived materials on the shared crack orientation. A principle of superposition of strain rates is used to write the compliance for a more realistic material consisting of cracks of random size and orientation as an expectation integral of the transverse compliance for each orientation times the joint distribution function for the size and orientation. Utilizing an evolving (initially exponential) size- dependence in the joint distribution, the general theory gives unprecedented agreement with measurements of the dynamic response of alumina to impact loading, especially upon release where the calculations predict the development of considerable deformation- induced anisotropy, challenging the conventional notion of shocks as isotropic phenomena.
Four dimensional deformable image registration using trajectory modeling
Castillo, Edward; Castillo, Richard; Martinez, Josue; Shenoy, Maithili; Guerrero, Thomas
2013-01-01
A four-dimensional deformable image registration (4D DIR) algorithm, referred to as 4D local trajectory modeling (4DLTM), is presented and applied to thoracic 4D computed tomography (4DCT) image sets. The theoretical framework on which this algorithm is built exploits the incremental continuity present in 4DCT component images to calculate a dense set of parameterized voxel trajectories through space as functions of time. The spatial accuracy of the 4DLTM algorithm is compared with an alternative registration approach in which component phase to phase (CPP) DIR is utilized to determine the full displacement between maximum inhale and exhale images. A publically available DIR reference database (http://www.dir-lab.com) is utilized for the spatial accuracy assessment. The database consists of ten 4DCT image sets and corresponding manually identified landmark points between the maximum phases. A subset of points are propagated through the expiratory 4DCT component images. Cubic polynomials were found to provide sufficient flexibility and spatial accuracy for describing the point trajectories through the expiratory phases. The resulting average spatial error between the maximum phases was 1.25 mm for the 4DLTM and 1.44 mm for the CPP. The 4DLTM method captures the long-range motion between 4DCT extremes with high spatial accuracy. PMID:20009196
An asperity-deformation model for effective pressure
NASA Astrophysics Data System (ADS)
Gangi, Anthony F.; Carlson, Richard L.
1996-05-01
Variations of the mechanical and transport properties of cracked and/or porous rocks under isotropic stress depend on both the confining pressure ( Pc) and the pore-fluid pressure ( Pp). To a first approximation, these rock properties are functions of the differential pressure, Pd = Pc - Pp; at least for low differential pressures. However, at higher differential pressures, the properties depend in a more complicated way upon the two pressures. The concept of effective pressure, Pe, is used to denote this variation and it is defined as Pe( Pc, Pp) = Pc - n( Pc, Pp) Pp. If n = 1 (and therefore, is independent of Pc and Pp), the effective pressure is just the differential pressure. We have used an asperity-deformation model and a force-balance equation to derive expressions for the effective pressure. We equate the total external force (in one direction), Fc, to the total force on the asperities, Fa, and the force of the fluid, Fp, acting in that same direction. The fluid force, Fp, acts only on the parts of the crack (or pore-volume) faces which are not in contact. Then, the asperity pressure, Pa, is the average force per unit area acting on the crack (or grain) contacts P a = {F a}/{A} = {F c}/{A} - {F p}/{A} = P c - (1 - {A c}/{A})P p, where A is the total area over which Fc acts and Ac is the area of contact of the crack asperities or the grains. Thus, the asperity pressure, Pa, is greater than the differential pressure, Pd, because Pp acts on a smaller area, A- Ac, than the total area, A. For elastic asperities, the area of contact Ac and the strain (e.g., crack and pore openings) remain the same, to a high degree of approximation, at constant asperity pressure. Therefore, transport properties such as permeability, resistivity, thermal conductivity, etc. are constant, to the same degree of approximation, at constant asperity pressure. For these properties, the asperity pressure is, very accurately, the effective pressure, Pc. Using this model, we find that the
NASA Astrophysics Data System (ADS)
Yao, Yong Tao; Alderson, Andrew; Alderson, Kim Lesley
2012-04-01
Force field based simulation has been employed to predict the deformation mechanisms of auxetic nano-materials having tetrahedral framework. The structure of α-quartz was studied in detail for subjecting to uniaxial loading along the Z direction. The cooperative dilation and rotation of tetrahedra acting concurrently were demonstrated to be the main deformation mechanism of α-quartz, confirming previous analytical model. Slight tetrahedral distortion also existed for undeformed and deformed structure.
NASA Astrophysics Data System (ADS)
Yao, Yong Tao; Alderson, Andrew; Alderson, Kim Lesley
2011-11-01
Force field based simulation has been employed to predict the deformation mechanisms of auxetic nano-materials having tetrahedral framework. The structure of α-quartz was studied in detail for subjecting to uniaxial loading along the Z direction. The cooperative dilation and rotation of tetrahedra acting concurrently were demonstrated to be the main deformation mechanism of α-quartz, confirming previous analytical model. Slight tetrahedral distortion also existed for undeformed and deformed structure.
A geometrical model for the Monte Carlo simulation of the TrueBeam linac.
Rodriguez, M; Sempau, J; Fogliata, A; Cozzi, L; Sauerwein, W; Brualla, L
2015-06-01
Monte Carlo simulation of linear accelerators (linacs) depends on the accurate geometrical description of the linac head. The geometry of the Varian TrueBeam linac is not available to researchers. Instead, the company distributes phase-space files of the flattening-filter-free (FFF) beams tallied at a plane located just upstream of the jaws. Yet, Monte Carlo simulations based on third-party tallied phase spaces are subject to limitations. In this work, an experimentally based geometry developed for the simulation of the FFF beams of the Varian TrueBeam linac is presented. The Monte Carlo geometrical model of the TrueBeam linac uses information provided by Varian that reveals large similarities between the TrueBeam machine and the Clinac 2100 downstream of the jaws. Thus, the upper part of the TrueBeam linac was modeled by introducing modifications to the Varian Clinac 2100 linac geometry. The most important of these modifications is the replacement of the standard flattening filters by ad hoc thin filters. These filters were modeled by comparing dose measurements and simulations. The experimental dose profiles for the 6 MV and 10 MV FFF beams were obtained from the Varian Golden Data Set and from in-house measurements performed with a diode detector for radiation fields ranging from 3 × 3 to 40 × 40 cm(2) at depths of maximum dose of 5 and 10 cm. Indicators of agreement between the experimental data and the simulation results obtained with the proposed geometrical model were the dose differences, the root-mean-square error and the gamma index. The same comparisons were performed for dose profiles obtained from Monte Carlo simulations using the phase-space files distributed by Varian for the TrueBeam linac as the sources of particles. Results of comparisons show a good agreement of the dose for the ansatz geometry similar to that obtained for the simulations with the TrueBeam phase-space files for all fields and depths considered, except for
A geometrical model for the Monte Carlo simulation of the TrueBeam linac
NASA Astrophysics Data System (ADS)
Rodriguez, M.; Sempau, J.; Fogliata, A.; Cozzi, L.; Sauerwein, W.; Brualla, L.
2015-06-01
Monte Carlo simulation of linear accelerators (linacs) depends on the accurate geometrical description of the linac head. The geometry of the Varian TrueBeam linac is not available to researchers. Instead, the company distributes phase-space files of the flattening-filter-free (FFF) beams tallied at a plane located just upstream of the jaws. Yet, Monte Carlo simulations based on third-party tallied phase spaces are subject to limitations. In this work, an experimentally based geometry developed for the simulation of the FFF beams of the Varian TrueBeam linac is presented. The Monte Carlo geometrical model of the TrueBeam linac uses information provided by Varian that reveals large similarities between the TrueBeam machine and the Clinac 2100 downstream of the jaws. Thus, the upper part of the TrueBeam linac was modeled by introducing modifications to the Varian Clinac 2100 linac geometry. The most important of these modifications is the replacement of the standard flattening filters by ad hoc thin filters. These filters were modeled by comparing dose measurements and simulations. The experimental dose profiles for the 6 MV and 10 MV FFF beams were obtained from the Varian Golden Data Set and from in-house measurements performed with a diode detector for radiation fields ranging from 3 × 3 to 40 × 40 cm2 at depths of maximum dose of 5 and 10 cm. Indicators of agreement between the experimental data and the simulation results obtained with the proposed geometrical model were the dose differences, the root-mean-square error and the gamma index. The same comparisons were performed for dose profiles obtained from Monte Carlo simulations using the phase-space files distributed by Varian for the TrueBeam linac as the sources of particles. Results of comparisons show a good agreement of the dose for the ansatz geometry similar to that obtained for the simulations with the TrueBeam phase-space files for all fields and depths considered, except for the
Surrogate-driven deformable motion model for organ motion tracking in particle radiation therapy
NASA Astrophysics Data System (ADS)
Fassi, Aurora; Seregni, Matteo; Riboldi, Marco; Cerveri, Pietro; Sarrut, David; Battista Ivaldi, Giovanni; Tabarelli de Fatis, Paola; Liotta, Marco; Baroni, Guido
2015-02-01
The aim of this study is the development and experimental testing of a tumor tracking method for particle radiation therapy, providing the daily respiratory dynamics of the patient’s thoraco-abdominal anatomy as a function of an external surface surrogate combined with an a priori motion model. The proposed tracking approach is based on a patient-specific breathing motion model, estimated from the four-dimensional (4D) planning computed tomography (CT) through deformable image registration. The model is adapted to the interfraction baseline variations in the patient’s anatomical configuration. The driving amplitude and phase parameters are obtained intrafractionally from a respiratory surrogate signal derived from the external surface displacement. The developed technique was assessed on a dataset of seven lung cancer patients, who underwent two repeated 4D CT scans. The first 4D CT was used to build the respiratory motion model, which was tested on the second scan. The geometric accuracy in localizing lung lesions, mediated over all breathing phases, ranged between 0.6 and 1.7 mm across all patients. Errors in tracking the surrounding organs at risk, such as lungs, trachea and esophagus, were lower than 1.3 mm on average. The median absolute variation in water equivalent path length (WEL) within the target volume did not exceed 1.9 mm-WEL for simulated particle beams. A significant improvement was achieved compared with error compensation based on standard rigid alignment. The present work can be regarded as a feasibility study for the potential extension of tumor tracking techniques in particle treatments. Differently from current tracking methods applied in conventional radiotherapy, the proposed approach allows for the dynamic localization of all anatomical structures scanned in the planning CT, thus providing complete information on density and WEL variations required for particle beam range adaptation.
Proximity potential for heavy ion reactions on deformed nuclei
Baltz, A. J.; Bayman, B. F.
1982-01-01
The usual treatment of the deformed optical model for analysis of heavy ion induced inelastic scattering data involves a deformed (target) radius, a spherical (projectile) radius and a potential strength dependent on the surface separation along the line between the two centers. Several authors using various approaches have shown that this center line potential is geometrically inadequate especially for description of higher L deformation parameters probed in heavy ion induced inelastic scattering experiments. A quantitatively adequate form of the deformed proximity potential suitable for use with a coupled channels reaction code in the analysis of inelastic scattering data above the Coulomb barrier is described. A major objective is to be able to extract reliably higher deformed multipole moments from such data. The deformed potential calculated in the folding model will serve as a geometrically exact benchmark to evaluate the accuracy of the proximity potential prescriptions. (WHK)
Enhancement of Generic Building Models by Recognition and Enforcement of Geometric Constraints
NASA Astrophysics Data System (ADS)
Meidow, J.; Hammer, H.; Pohl, M.; Bulatov, D.
2016-06-01
Many buildings in 3D city models can be represented by generic models, e.g. boundary representations or polyhedrons, without expressing building-specific knowledge explicitly. Without additional constraints, the bounding faces of these building reconstructions do not feature expected structures such as orthogonality or parallelism. The recognition and enforcement of man-made structures within model instances is one way to enhance 3D city models. Since the reconstructions are derived from uncertain and imprecise data, crisp relations such as orthogonality or parallelism are rarely satisfied exactly. Furthermore, the uncertainty of geometric entities is usually not specified in 3D city models. Therefore, we propose a point sampling which simulates the initial point cloud acquisition by airborne laser scanning and provides estimates for the uncertainties. We present a complete workflow for recognition and enforcement of man-made structures in a given boundary representation. The recognition is performed by hypothesis testing and the enforcement of the detected constraints by a global adjustment of all bounding faces. Since the adjustment changes not only the geometry but also the topology of faces, we obtain improved building models which feature regular structures and a potentially reduced complexity. The feasibility and the usability of the approach are demonstrated with a real data set.
Parametric geometric model and shape optimization of an underwater glider with blended-wing-body
NASA Astrophysics Data System (ADS)
Sun, Chunya; Song, Baowei; Wang, Peng
2015-11-01
Underwater glider, as a new kind of autonomous underwater vehicles, has many merits such as long-range, extended-duration and low costs. The shape of underwater glider is an important factor in determining the hydrodynamic efficiency. In this paper, a high lift to drag ratio configuration, the Blended-Wing-Body (BWB), is used to design a small civilian under water glider. In the parametric geometric model of the BWB underwater glider, the planform is defined with Bezier curve and linear line, and the section is defined with symmetrical airfoil NACA 0012. Computational investigations are carried out to study the hydrodynamic performance of the glider using the commercial Computational Fluid Dynamics (CFD) code Fluent. The Kriging-based genetic algorithm, called Efficient Global Optimization (EGO), is applied to hydrodynamic design optimization. The result demonstrates that the BWB underwater glider has excellent hydrodynamic performance, and the lift to drag ratio of initial design is increased by 7% in the EGO process.
Computer-aided geometric modeling of the human eye and orbit.
Parshall, R F
1991-01-01
The author advocates, as a long-term development agenda for the profession, a shift in the working methods of medical illustrators from a two-dimensional image processing mode to a computer-aided design and drafting (CADD) mode. Existing CADD technology, which can make short work of the complex graphic construction problems of anatomical visualization, performs virtually all of its manipulations through systematic exercise of graphic geometry which illustrators tend to reduce to an intuitive, almost vestigial supplement to 2D image processing methods. The primary barrier to the immediate use of CADD is a lack of geometric database materials on anatomical component systems of the body. An on-going experimental project in modeling the human eye and orbit, utilizing a Silicon Graphics Iris workstation and Control Data Corporation's Integrated Computerized Engineering and Manufacturing (ICEM) software, exemplifies the preparatory work needed to create such database materials. PMID:1874709
A geometric model of a V-slit Sun sensor correcting for spacecraft wobble
NASA Technical Reports Server (NTRS)
Mcmartin, W. P.; Gambhir, S. S.
1994-01-01
A V-Slit sun sensor is body-mounted on a spin-stabilized spacecraft. During injection from a parking or transfer orbit to some final orbit, the spacecraft may not be dynamically balanced. This may result in wobble about the spacecraft spin axis as the spin axis may not be aligned with the spacecraft's axis of symmetry. While the widely used models in Spacecraft Attitude Determination and Control, edited by Wertz, correct for separation, elevation, and azimuthal mounting biases, spacecraft wobble is not taken into consideration. A geometric approach is used to develop a method for measurement of the sun angle which corrects for the magnitude and phase of spacecraft wobble. The algorithm was implemented using a set of standard mathematical routines for spherical geometry on a unit sphere.
On a geometric model of crystal growth on a flat substrate
NASA Astrophysics Data System (ADS)
Brednikhina, Anna; Debelov, Victor A.
2009-01-01
This paper is devoted to computer simulation of crystalline aggregates growth from a homogeneous solution. This process is considered from the geometric point of view, when crystals can be represented as a collection of flat faces, growing layer by layer with stable relative growth rates in the directions of their perpendiculars. Simply speaking, we extend Frank's model [H. Muller-Krumbhaar, Yu. Saito, Crystal Growth and Solidification, in: Surfactant Science Series, vol. 89, CRC Press, Boca Raton, FL, 2000, pp. 853-854] to the case of simultaneous growth of several individuals placed on a flat unbounded static substrate. Attention is given not only to finding the outer boundary of an aggregate but to determining the interfacing surfaces between individuals. In other words, our goal is to construct detailed bounding surfaces of all individuals included in an aggregate.
A Model for the Origin and Properties of Flicker-Induced Geometric Phosphenes
Rule, Michael; Stoffregen, Matthew; Ermentrout, Bard
2011-01-01
We present a model for flicker phosphenes, the spontaneous appearance of geometric patterns in the visual field when a subject is exposed to diffuse flickering light. We suggest that the phenomenon results from interaction of cortical lateral inhibition with resonant periodic stimuli. We find that the best temporal frequency for eliciting phosphenes is a multiple of intrinsic (damped) oscillatory rhythms in the cortex. We show how both the quantitative and qualitative aspects of the patterns change with frequency of stimulation and provide an explanation for these differences. We use Floquet theory combined with the theory of pattern formation to derive the parameter regimes where the phosphenes occur. We use symmetric bifurcation theory to show why low frequency flicker should produce hexagonal patterns while high frequency produces pinwheels, targets, and spirals. PMID:21980269
NASA Astrophysics Data System (ADS)
Mihalev, Mihail; Parvanov, Orlin; Pirgov, Peter S.
1996-12-01
We report the use of computer techniques for modeling and visualization of the laser monitoring of the inner surface of an operating Bessemer converter. The purpose of the study was to estimate the accuracy of the laser measurement technique, to determine the geometrical parameters necessary, and to establish the requirements to the accuracy of the scanning part of a laser meter when the pulse duration, beam divergence and defects size are pre-set. The following basic conclusions can be drawn: firstly, it is possible to use a laser meter as a device for monitoring the casing thickness based on the use of a pulsed solid-state laser; secondly, the process of non-uniform wear can be handled by means of additional measurements with off-axis sounding geometry; thirdly, the numerical experiment demonstrates that, based on the accuracy achieved of determining the casing thickness, the operating life-time of the converter can be extended.
NASA Astrophysics Data System (ADS)
Gentry, R. W.; Perfect, E.; Sukop, M. C.
2005-12-01
Recent analyses of field data suggest that the spatial variation of hydraulic conductivity, K, within an aquifer may be multifractal. We investigated the implications of this finding for the scaling of effective hydraulic conductivity,
Visualization of 3D geometric models of the breast created from contrast-enhanced MRI
NASA Astrophysics Data System (ADS)
Leader, J. Ken, III; Wang, Xiao Hui; Chang, Yuan-Hsiang; Chapman, Brian E.
2002-05-01
Contrast enhanced breast MRI is currently used as an adjuvant modality to x-ray mammography because of its ability to resolve ambiguities and determine the extent of malignancy. This study described techniques to create and visualize 3D geometric models of abnormal breast tissue. MRIs were performed on a General Electric 1.5 Tesla scanner using dual phased array breast coils. Image processing tasks included: 1) correction of image inhomogeneity caused by the coils, 2) segmentation of normal and abnormal tissue, and 3) modeling and visualization of the segmented tissue. The models were visualized using object-based surface rendering which revealed characteristics critical to differentiating benign from malignant tissue. Surface rendering illustrated the enhancement distribution and enhancement patterns. The modeling process condensed the multi-slice MRI data information and standardized its interpretation. Visualizing the 3D models should improve the radiologist's and/or surgeon's impression of the 3D shape, extent, and accessibility of the malignancy compared to viewing breast MRI data slice by slice.
t-LSE: A Novel Robust Geometric Approach for Modeling Protein-Protein Interaction Networks
Huang, De-Shuang; Wang, Bing
2013-01-01
Protein-protein interaction (PPI) networks provide insights into understanding of biological processes, function and the underlying complex evolutionary mechanisms of the cell. Modeling PPI network is an important and fundamental problem in system biology, where it is still of major concern to find a better fitting model that requires less structural assumptions and is more robust against the large fraction of noisy PPIs. In this paper, we propose a new approach called t-logistic semantic embedding (t-LSE) to model PPI networks. t-LSE tries to adaptively learn a metric embedding under the simple geometric assumption of PPI networks, and a non-convex cost function was adopted to deal with the noise in PPI networks. The experimental results show the superiority of the fit of t-LSE over other network models to PPI data. Furthermore, the robust loss function adopted here leads to big improvements for dealing with the noise in PPI network. The proposed model could thus facilitate further graph-based studies of PPIs and may help infer the hidden underlying biological knowledge. The Matlab code implementing the proposed method is freely available from the web site: http://home.ustc.edu.cn/~yzh33108/PPIModel.htm. PMID:23560036
Effect of Material Property Heterogeneity on Biomechanical Modeling of Prostate under Deformation
Samavati, Navid; McGrath, Deirdre M.; Jewett, Michael A.S.; van der Kwast, Theo; Ménard, Cynthia; Brock, Kristy K.
2015-01-01
Biomechanical model based deformable image registration has been widely used to account for prostate deformation in various medical imaging procedures. Biomechanical material properties are important components of a biomechanical model. In this study, the effect of incorporating tumor-specific material properties in the prostate biomechanical model was investigated to provide insight into the potential impact of material heterogeneity on the prostate deformation calculations First, a simple spherical prostate and tumor model was used to analytically describe the deformations and demonstrate the fundamental effect of changes in the tumor volume and stiffness in the modeled deformation. Next, using clinical prostate model, a parametric approach was used to describe the variations in the heterogeneous prostate model by changing tumor volume, stiffness, and location, to show the differences in the modeled deformation between heterogeneous and homogeneous prostate models. Finally, five clinical prostatectomy examples were used in separately performed homogeneous and heterogeneous biomechanical model based registrations to describe the deformations between 3D reconstructed histopathology images and ex vivo Magnetic Resonance Imaging (MRI), and examine the potential clinical impact of modeling biomechanical heterogeneity of the prostate. The analytical formulation showed that increasing the tumor volume and stiffness could significantly increase the impact of heterogeneous prostate model in the calculated displacement differences compared to homogeneous model. The parametric approach using a single prostate model indicated up to 4.8 mm of displacement difference at the tumor boundary compared to a homogeneous model. . Such differences in the deformation of prostate could bepotentially clinically significant given the voxel size of the ex vivo MR images (0.3×0.3×0.3 mm). However, no significant changes in the registration accuracy were observed using heterogeneous models
A theoretical model of grainsize evolution during deformation
NASA Astrophysics Data System (ADS)
Ricard, Y.; Bercovici, D.; Rozel, A.
2007-12-01
Lithospheric shear localization, as occurs in the formation of tectonic plate boundaries, is often associated with diminished grainsize (e.g., mylonites). Grainsize reduction is typically attributed to dynamic recrystallization; however, theoretical models of shear-localization arising from this hypothesis are problematic since (1) they require the simultaneous action of two exclusive creep mechanisms (diffusion and dislocation creep), and (2) the grain-growth ("healing") laws employed by these models are derived from static grain-growth or coarsening theory, although the shear-localization setting itself is far from static equilibrium. We present a new first-principles grained-continuum theory which accounts for both coarsening and damage-induced grainsize reduction. Damage per se is the generic process for generation of microcracks, defects, dislocations (including recrystallization), subgrains, nucleii and cataclastic breakdown of grains. The theory contains coupled statistical grain-scale and continuum macroscopic components. The grain-scale element of the theory prescribes both the evolution of the grainsize distribution, and a phenomenological grain-growth law derived from non-equilibrium thermodynamics; grain-growth thus incorporates the free energy differences between grains, including both grain-boundary surface energy (which controls coarsening) and the contribution of deformational work to these free energiesconservation and positivity of entropy production provide the phenomenological law for the statistical grain-growth law. We identify four potential mechanisms that affect the distribution of grainsize; two of them conserve the number of grains but change their relative masses and two of them change the number of grains by sticking them together or breaking them. In the limit of static equilibrium, only the two mechanisms that increase the average grainsize are allowed by the second law of thermodynamics. The first one is a diffusive mass transport
NASA Astrophysics Data System (ADS)
Samadi, Reza
Technical textiles are increasingly being engineered and used in challenging applications, in areas such as safety, biomedical devices, architecture and others, where they must meet stringent demands including excellent and predictable load bearing capabilities. They also form the bases for one of the most widespread group of composite materials, fibre reinforced polymer-matrix composites (PMCs), which comprise materials made of stiff and strong fibres generally available in textile form and selected for their structural potential, combined with a polymer matrix that gives parts their shape. Manufacturing processes for PMCs and technical textiles, as well as parts and advanced textile structures must be engineered, ideally through simulation, and therefore diverse properties of the textiles, textile reinforcements and PMC materials must be available for predictive simulation. Knowing the detailed geometry of technical textiles is essential to predicting accurately the processing and performance properties of textiles and PMC parts. In turn, the geometry taken by a textile or a reinforcement textile is linked in an intricate manner to its constitutive behaviour. This thesis proposes, investigates and validates a general numerical tool for the integrated and comprehensive analysis of textile geometry and constitutive behaviour as required toward engineering applications featuring technical textiles and textile reinforcements. The tool shall be general with regards to the textiles modelled and the loading cases applied. Specifically, the work aims at fulfilling the following objectives: 1) developing and implementing dedicated simulation software for modelling textiles subjected to various load cases; 2) providing, through simulation, geometric descriptions for different textiles subjected to different load cases namely compaction, relaxation and shear; 3) predicting the constitutive behaviour of the textiles undergoing said load cases; 4) identifying parameters
Watermarked cardiac CT image segmentation using deformable models and the Hermite transform
NASA Astrophysics Data System (ADS)
Gomez-Coronel, Sandra L.; Moya-Albor, Ernesto; Escalante-Ramírez, Boris; Brieva, Jorge
2015-01-01
Medical image watermarking is an open area for research and is a solution for the protection of copyright and intellectual property. One of the main challenges of this problem is that the marked images should not differ perceptually from the original images allowing a correct diagnosis and authentication. Furthermore, we also aim at obtaining watermarked images with very little numerical distortion so that computer vision tasks such as segmentation of important anatomical structures do not be impaired or affected. We propose a preliminary watermarking application in cardiac CT images based on a perceptive approach that includes a brightness model to generate a perceptive mask and identify the image regions where the watermark detection becomes a difficult task for the human eye. We propose a normalization scheme of the image in order to improve robustness against geometric attacks. We follow a spread spectrum technique to insert an alphanumeric code, such as patient's information, within the watermark. The watermark scheme is based on the Hermite transform as a bio-inspired image representation model. In order to evaluate the numerical integrity of the image data after watermarking, we perform a segmentation task based on deformable models. The segmentation technique is based on a vector-value level sets method such that, given a curve in a specific image, and subject to some constraints, the curve can evolve in order to detect objects. In order to stimulate the curve evolution we introduce simultaneously some image features like the gray level and the steered Hermite coefficients as texture descriptors. Segmentation performance was assessed by means of the Dice index and the Hausdorff distance. We tested different mark sizes and different insertion schemes on images that were later segmented either automatic or manual by physicians.
Neotectonic deformation models for probabilistic seismic hazard: a study in the External Dinarides
NASA Astrophysics Data System (ADS)
Kastelic, Vanja; Carafa, Michele M. C.; Visini, Francesco
2016-06-01
In Europe, common input data types for seismic hazard evaluation include earthquake catalogues, seismic zonation models and ground motion models, all with well-constrained epistemic uncertainties. In contrast, neotectonic deformation models and their related uncertainties are rarely considered in earthquake forecasting and seismic hazard studies. In this study, for the first time in Europe, we developed a seismic hazard model based exclusively on active fault and geodynamic deformation models. We applied it to the External Dinarides, a slow-deforming fold-and-thrust belt in the Central Mediterranean. The two deformation models furnish consistent long-term earthquake rates above the Mw 4.7 threshold on a latitude/longitude grid with 0.2° spacing. Results suggest that the use of deformation models is a valid alternative to empirical-statistical approaches in earthquake forecasting in slow-deforming regions of Europe. Furthermore, we show that the variability of different deformation models has a comparable effect on the peak ground motion acceleration uncertainty as do the ground motion prediction equations.
NASA Astrophysics Data System (ADS)
Vishwakarma, Vinod
Modified Modal Domain Analysis (MMDA) is a novel method for the development of a reduced-order model (ROM) of a bladed rotor. This method utilizes proper orthogonal decomposition (POD) of Coordinate Measurement Machine (CMM) data of blades' geometries and sector analyses using ANSYS. For the first time ROM of a geometrically mistuned industrial scale rotor (Transonic rotor) with large size of Finite Element (FE) model is generated using MMDA. Two methods for estimating mass and stiffness mistuning matrices are used a) exact computation from sector FE analysis, b) estimates based on POD mistuning parameters. Modal characteristics such as mistuned natural frequencies, mode shapes and forced harmonic response are obtained from ROM for various cases, and results are compared with full rotor ANSYS analysis and other ROM methods such as Subset of Nominal Modes (SNM) and Fundamental Model of Mistuning (FMM). Accuracy of MMDA ROM is demonstrated with variations in number of POD features and geometric mistuning parameters. It is shown for the aforementioned case b) that the high accuracy of ROM studied in previous work with Academic rotor does not directly translate to the Transonic rotor. Reasons for such mismatch in results are investigated and attributed to higher mistuning in Transonic rotor. Alternate solutions such as estimation of sensitivities via least squares, and interpolation of mass and stiffness matrices on manifolds are developed, and their results are discussed. Statistics such as mean and standard deviations of forced harmonic response peak amplitude are obtained from random permutations, and are shown to have similar results as those of Monte Carlo simulations. These statistics are obtained and compared for 3 degree of freedom (DOF) lumped parameter model (LPM) of rotor, Academic rotor and Transonic rotor. A state -- estimator based on MMDA ROM and Kalman filter is also developed for offline or online estimation of harmonic forcing function from
A new geometric-based model to accurately estimate arm and leg inertial estimates.
Wicke, Jason; Dumas, Geneviève A
2014-06-01
Segment estimates of mass, center of mass and moment of inertia are required input parameters to analyze the forces and moments acting across the joints. The objectives of this study were to propose a new geometric model for limb segments, to evaluate it against criterion values obtained from DXA, and to compare its performance to five other popular models. Twenty five female and 24 male college students participated in the study. For the criterion measures, the participants underwent a whole body DXA scan, and estimates for segment mass, center of mass location, and moment of inertia (frontal plane) were directly computed from the DXA mass units. For the new model, the volume was determined from two standing frontal and sagittal photographs. Each segment was modeled as a stack of slices, the sections of which were ellipses if they are not adjoining another segment and sectioned ellipses if they were adjoining another segment (e.g. upper arm and trunk). Length of axes of the ellipses was obtained from the photographs. In addition, a sex-specific, non-uniform density function was developed for each segment. A series of anthropometric measurements were also taken by directly following the definitions provided of the different body segment models tested, and the same parameters determined for each model. Comparison of models showed that estimates from the new model were consistently closer to the DXA criterion than those from the other models, with an error of less than 5% for mass and moment of inertia and less than about 6% for center of mass location. PMID:24735506
NASA Technical Reports Server (NTRS)
Miller, E. F.
1982-01-01
Mathematical models used in the software package developed for use at the 1983 Regional Administrative Radio Conference on broadcasting satellites. The models described are those used in the Spectrum Orbit Utilization Program (SOUP) analysis. The geometric relationships necessary to model broadcasting satellite systems are discussed. Antenna models represent copolarized and cross polarized performance as functions of the off axis angle. The protection ratio is modelled as a co-channel value and a template representing systems with frequency offsets.
Simple geometric model to describe self-folding of polymer sheets.
Liu, Ying; Mailen, Russell; Zhu, Yong; Dickey, Michael D; Genzer, Jan
2014-04-01
Self-folding is the autonomous folding of two-dimensional shapes into three-dimensional forms in response to an external stimulus. This paper focuses on light-induced self-folding of prestrained polymer sheets patterned with black ink. The ink absorbs the light and the resulting heat induces the polymer beneath the ink to relax faster than the rest of the sheet. A simple geometric model captures both the folding angle and folding kinetics associated with this localized shrinkage. The model assumes that (1) the polymer in contact with the ink shrinks at a rate determined by the temporal temperature profile of the hinge surface; (2) the bottom of the sheet, which is cooler, does not shrink considerably; and (3) a linear gradient of strain relaxation exists across the film between these two extremes. Although there are more complex approaches for modeling folding, the appeal of this model is its simplicity and ease of use. Measurements of the macroscopic, thermally driven shrinkage behavior of the sheets help predict the kinetics of folding by determining how fast the top of the hinge shrinks as a function of temperature and time. These measurements also provide information about the temperature required to induce folding and offer indirect measurement of the glass transition temperature of the polymer that comprises the sheet. PMID:24827268
Simple geometric model to describe self-folding of polymer sheets
NASA Astrophysics Data System (ADS)
Liu, Ying; Mailen, Russell; Zhu, Yong; Dickey, Michael D.; Genzer, Jan
2014-04-01
Self-folding is the autonomous folding of two-dimensional shapes into three-dimensional forms in response to an external stimulus. This paper focuses on light-induced self-folding of prestrained polymer sheets patterned with black ink. The ink absorbs the light and the resulting heat induces the polymer beneath the ink to relax faster than the rest of the sheet. A simple geometric model captures both the folding angle and folding kinetics associated with this localized shrinkage. The model assumes that (1) the polymer in contact with the ink shrinks at a rate determined by the temporal temperature profile of the hinge surface; (2) the bottom of the sheet, which is cooler, does not shrink considerably; and (3) a linear gradient of strain relaxation exists across the film between these two extremes. Although there are more complex approaches for modeling folding, the appeal of this model is its simplicity and ease of use. Measurements of the macroscopic, thermally driven shrinkage behavior of the sheets help predict the kinetics of folding by determining how fast the top of the hinge shrinks as a function of temperature and time. These measurements also provide information about the temperature required to induce folding and offer indirect measurement of the glass transition temperature of the polymer that comprises the sheet.
Forest crown closure retrieval and change detection using an inverted geometric-optical model
NASA Astrophysics Data System (ADS)
Zeng, Y.; Wu, B.
2012-12-01
The objective of this study is to use an inversion of the Li-Strahler geometric-optical model combined with a scaling-based endmember extraction method and a spatial interpolation technique to retrieve and detect the changes of a forest canopy structural property, crown closure (CC), in the Three Gorges reservoir region of China. A MODIS image covered the whole study area and a Landsat TM data located in the typical region are collected together for each year from 2001 to 2010. We firstly extract the viewed surface components endmembers from the MODIS data by the regional scaling-based linear unmixing model using the corresponding Landsat TM image; secondly, derive and map the forest structural variable CC by inverting the Li-Strahler model based on the extracted endmembers for each year; thirdly, complement prediction deficiencies of the inverted Li-Strahler model derived CC by using a spatial interpolation algorithm (regression kriging) in the infeasible regions; finally produce spatially continuous CC maps for the 10 years and representing CC changes between 2001 and 2010. The results show a decrease in CC in the eastern counties of the Three Gorges region located close to the Three Gorges Dam, which is the largest hydroelectric dam in the world. An increase in CC has been observed in other counties of the Three Gorges region, implying a preliminary positive feedback on certain policy measures taken safeguarding forest structure.
Competition and fixation of cohorts of adaptive mutations under Fisher geometrical model
Alpedrinha, João; Campos, Paulo R.A.; Gordo, Isabel
2016-01-01
One of the simplest models of adaptation to a new environment is Fisher’s Geometric Model (FGM), in which populations move on a multidimensional landscape defined by the traits under selection. The predictions of this model have been found to be consistent with current observations of patterns of fitness increase in experimentally evolved populations. Recent studies investigated the dynamics of allele frequency change along adaptation of microbes to simple laboratory conditions and unveiled a dramatic pattern of competition between cohorts of mutations, i.e., multiple mutations simultaneously segregating and ultimately reaching fixation. Here, using simulations, we study the dynamics of phenotypic and genetic change as asexual populations under clonal interference climb a Fisherian landscape, and ask about the conditions under which FGM can display the simultaneous increase and fixation of multiple mutations—mutation cohorts—along the adaptive walk. We find that FGM under clonal interference, and with varying levels of pleiotropy, can reproduce the experimentally observed competition between different cohorts of mutations, some of which have a high probability of fixation along the adaptive walk. Overall, our results show that the surprising dynamics of mutation cohorts recently observed during experimental adaptation of microbial populations can be expected under one of the oldest and simplest theoretical models of adaptation—FGM. PMID:27547562
NASA Astrophysics Data System (ADS)
Lucarini, Valerio; Vannitsem, Stephane
2016-04-01
We study a simplified coupled atmosphere-ocean model using the formalism of covariant Lyapunov vectors (CLVs), which link physically-based directions of perturbations to growth/decay rates. The model is obtained via a severe truncation of quasi-geostrophic equations for the two fluids, and includes a simple yet physically meaningful representation of their dynamical/thermodynamical coupling. The model has 36 degrees of freedom, and the parameters are chosen so that a chaotic behaviour is observed. One finds two positive Lyapunov exponents (LEs), sixteen negative LEs, and eighteen near-zero LEs. The presence of many near-zero LEs results from the vast time-scale separation between the characteristic time scales of the two fluids, and leads to nontrivial error growth properties in the tangent space spanned by the corresponding CLVs, which are geometrically very degenerate. Such CLVs correspond to two different classes of ocean/atmosphere coupled modes. The tangent space spanned by the CLVs corresponding to the positive and negative LEs has, instead, a non-pathological behaviour, and one can construct robust large deviations laws for the finite time LEs, thus providing a universal model for assessing predictability on long to ultra-long scales along such directions. Finally, it is somewhat surprising to find that the tangent space of the unstable manifold has strong projection on both atmospheric and oceanic components, thus giving evidence that coupled modes are responsible for the instability of the flow.
Competition and fixation of cohorts of adaptive mutations under Fisher geometrical model.
Moura de Sousa, Jorge A; Alpedrinha, João; Campos, Paulo R A; Gordo, Isabel
2016-01-01
One of the simplest models of adaptation to a new environment is Fisher's Geometric Model (FGM), in which populations move on a multidimensional landscape defined by the traits under selection. The predictions of this model have been found to be consistent with current observations of patterns of fitness increase in experimentally evolved populations. Recent studies investigated the dynamics of allele frequency change along adaptation of microbes to simple laboratory conditions and unveiled a dramatic pattern of competition between cohorts of mutations, i.e., multiple mutations simultaneously segregating and ultimately reaching fixation. Here, using simulations, we study the dynamics of phenotypic and genetic change as asexual populations under clonal interference climb a Fisherian landscape, and ask about the conditions under which FGM can display the simultaneous increase and fixation of multiple mutations-mutation cohorts-along the adaptive walk. We find that FGM under clonal interference, and with varying levels of pleiotropy, can reproduce the experimentally observed competition between different cohorts of mutations, some of which have a high probability of fixation along the adaptive walk. Overall, our results show that the surprising dynamics of mutation cohorts recently observed during experimental adaptation of microbial populations can be expected under one of the oldest and simplest theoretical models of adaptation-FGM. PMID:27547562
Fisher’s Geometrical Model Emerges as a Property of Complex Integrated Phenotypic Networks
Martin, Guillaume
2014-01-01
Models relating phenotype space to fitness (phenotype–fitness landscapes) have seen important developments recently. They can roughly be divided into mechanistic models (e.g., metabolic networks) and more heuristic models like Fisher’s geometrical model. Each has its own drawbacks, but both yield testable predictions on how the context (genomic background or environment) affects the distribution of mutation effects on fitness and thus adaptation. Both have received some empirical validation. This article aims at bridging the gap between these approaches. A derivation of the Fisher model “from first principles” is proposed, where the basic assumptions emerge from a more general model, inspired by mechanistic networks. I start from a general phenotypic network relating unspecified phenotypic traits and fitness. A limited set of qualitative assumptions is then imposed, mostly corresponding to known features of phenotypic networks: a large set of traits is pleiotropically affected by mutations and determines a much smaller set of traits under optimizing selection. Otherwise, the model remains fairly general regarding the phenotypic processes involved or the distribution of mutation effects affecting the network. A statistical treatment and a local approximation close to a fitness optimum yield a landscape that is effectively the isotropic Fisher model or its extension with a single dominant phenotypic direction. The fit of the resulting alternative distributions is illustrated in an empirical data set. These results bear implications on the validity of Fisher’s model’s assumptions and on which features of mutation fitness effects may vary (or not) across genomic or environmental contexts. PMID:24583582
Deformations in the Shoulder Tissues During Load Carriage: A Computational Model.
Hadid, Amir; Belzer, Noa; Shabshin, Nogah; Epstein, Yoram; Gefen, Amit
2015-11-01
Shoulder soft tissue deformations seem to be one of the limiting factors of load carriage among soldiers and recreational backpackers that are required to carry heavy loads. Yet, there are no loading limits related to the forces borne by the shoulders, and the backpacks designs are not consistent with providing pressure relief from this sensitive anatomical region. The aim of this study was to develop a model that will enable to study the biomechanical loads that develop in the shoulder under heavy loads and to help in optimizing load carriage systems design. A 3-dimensional, anatomically accurate finite element model of a human shoulder was constructed based on MRI scans. The model was developed to calculate the effective stresses on the skin below the shoulder strap (superficial loads) and the effective strain in the brachial plexus region (inner tissue deformation) for loads of up to 35 kg. The model successfully predicted deformations in the soft tissue surrounding the brachial plexus when compared with deformations measured from load-bearing MRI scans. The model yielded a skin pressure mapping, which showed pressure hotspots in the clavicle region. Inner tissue deformations mapping, as assessed by brachial plexus envelop strains, were found to peak at 30% effective strain at the lateral aspect below the pectoralis muscle. The newly developed model successfully predicted soft tissue deformations in the shoulder related to backpacks. This model can be used to optimize load carriage systems for better distribution of pressure over the shoulders and lower inner tissue deformations. PMID:26506178
DEFORMATION DEPENDENT TUL MULTI-STEP DIRECT MODEL
WIENKE,H.; CAPOTE, R.; HERMAN, M.; SIN, M.
2007-04-22
The Multi-Step Direct (MSD) module TRISTAN in the nuclear reaction code EMPIRE has been extended in order to account for nuclear deformation. The new formalism was tested in calculations of neutron emission spectra emitted from the {sup 232}Th(n,xn) reaction. These calculations include vibration-rotational Coupled Channels (CC) for the inelastic scattering to low-lying collective levels, ''deformed'' MSD with quadrupole deformation for inelastic scattering to the continuum, Multi-Step Compound (MSC) and Hauser-Feshbach with advanced treatment of the fission channel. Prompt fission neutrons were also calculated. The comparison with experimental data shows clear improvement over the ''spherical'' MSD calculations and JEFF-3.1 and JENDL-3.3 evaluations.
A Deformable Generic 3D Model of Haptoral Anchor of Monogenean
Teo, Bee Guan; Dhillon, Sarinder Kaur; Lim, Lee Hong Susan
2013-01-01
In this paper, a digital 3D model which allows for visualisation in three dimensions and interactive manipulation is explored as a tool to help us understand the structural morphology and elucidate the functions of morphological structures of fragile microorganisms which defy live studies. We developed a deformable generic 3D model of haptoral anchor of dactylogyridean monogeneans that can subsequently be deformed into different desired anchor shapes by using direct manipulation deformation technique. We used point primitives to construct the rectangular building blocks to develop our deformable 3D model. Point primitives are manually marked on a 2D illustration of an anchor on a Cartesian graph paper and a set of Cartesian coordinates for each point primitive is manually extracted from the graph paper. A Python script is then written in Blender to construct 3D rectangular building blocks based on the Cartesian coordinates. The rectangular building blocks are stacked on top or by the side of each other following their respective Cartesian coordinates of point primitive. More point primitives are added at the sites in the 3D model where more structural variations are likely to occur, in order to generate complex anchor structures. We used Catmull-Clark subdivision surface modifier to smoothen the surface and edge of the generic 3D model to obtain a smoother and more natural 3D shape and antialiasing option to reduce the jagged edges of the 3D model. This deformable generic 3D model can be deformed into different desired 3D anchor shapes through direct manipulation deformation technique by aligning the vertices (pilot points) of the newly developed deformable generic 3D model onto the 2D illustrations of the desired shapes and moving the vertices until the desire 3D shapes are formed. In this generic 3D model all the vertices present are deployed for displacement during deformation. PMID:24204903
A deformable generic 3D model of haptoral anchor of Monogenean.
Teo, Bee Guan; Dhillon, Sarinder Kaur; Lim, Lee Hong Susan
2013-01-01
In this paper, a digital 3D model which allows for visualisation in three dimensions and interactive manipulation is explored as a tool to help us understand the structural morphology and elucidate the functions of morphological structures of fragile microorganisms which defy live studies. We developed a deformable generic 3D model of haptoral anchor of dactylogyridean monogeneans that can subsequently be deformed into different desired anchor shapes by using direct manipulation deformation technique. We used point primitives to construct the rectangular building blocks to develop our deformable 3D model. Point primitives are manually marked on a 2D illustration of an anchor on a Cartesian graph paper and a set of Cartesian coordinates for each point primitive is manually extracted from the graph paper. A Python script is then written in Blender to construct 3D rectangular building blocks based on the Cartesian coordinates. The rectangular building blocks are stacked on top or by the side of each other following their respective Cartesian coordinates of point primitive. More point primitives are added at the sites in the 3D model where more structural variations are likely to occur, in order to generate complex anchor structures. We used Catmull-Clark subdivision surface modifier to smoothen the surface and edge of the generic 3D model to obtain a smoother and more natural 3D shape and antialiasing option to reduce the jagged edges of the 3D model. This deformable generic 3D model can be deformed into different desired 3D anchor shapes through direct manipulation deformation technique by aligning the vertices (pilot points) of the newly developed deformable generic 3D model onto the 2D illustrations of the desired shapes and moving the vertices until the desire 3D shapes are formed. In this generic 3D model all the vertices present are deployed for displacement during deformation. PMID:24204903
Is There a Geometric Module for Spatial Orientation? Insights from a Rodent Navigation Model
ERIC Educational Resources Information Center
Sheynikhovich, Denis; Chavarriaga, Ricardo; Strosslin, Thomas; Arleo, Angelo; Gerstner, Wulfram
2009-01-01
Modern psychological theories of spatial cognition postulate the existence of a geometric module for reorientation. This concept is derived from experimental data showing that in rectangular arenas with distinct landmarks in the corners, disoriented rats often make diagonal errors, suggesting their preference for the geometric (arena shape) over…
Borel-Cantelli lemmas and extreme value theory for geometric Lorenz models
NASA Astrophysics Data System (ADS)
Zhang, Licheng
2016-01-01
We establish dynamical Borel-Cantelli lemmas for nested balls and rectangles centered at generic points in the setting of geometric Lorenz maps. We also establish the convergence of rare events point processes to the standard Poisson process, which implies extreme value laws for observations maximised at generic points for geometric Lorenz maps. Further, we extend our extreme value laws to the associated flows.
Computer modeling of electromagnetic problems using the geometrical theory of diffraction
NASA Technical Reports Server (NTRS)
Burnside, W. D.
1976-01-01
Some applications of the geometrical theory of diffraction (GTD), a high frequency ray optical solution to electromagnetic problems, are presented. GTD extends geometric optics, which does not take into account the diffractions occurring at edges, vertices, and various other discontinuities. Diffraction solutions, analysis of basic structures, construction of more complex structures, and coupling using GTD are discussed.
Modelling MEMS deformable mirrors for astronomical adaptive optics
NASA Astrophysics Data System (ADS)
Blain, Celia
As of July 2012, 777 exoplanets have been discovered utilizing mainly indirect detection techniques. The direct imaging of exoplanets is the next goal for astronomers, because it will reveal the diversity of planets and planetary systems, and will give access to the exoplanet's chemical composition via spectroscopy. With this spectroscopic knowledge, astronomers will be able to know, if a planet is terrestrial and, possibly, even find evidence of life. With so much potential, this branch of astronomy has also captivated the general public attention. The direct imaging of exoplanets remains a challenging task, due to (i) the extremely high contrast between the parent star and the orbiting exoplanet and (ii) their small angular separation. For ground-based observatories, this task is made even more difficult, due to the presence of atmospheric turbulence. High Contrast Imaging (HCI) instruments have been designed to meet this challenge. HCI instruments are usually composed of a coronagraph coupled with the full onaxis corrective capability of an Extreme Adaptive Optics (ExAO) system. An efficient coronagraph separates the faint planet's light from the much brighter starlight, but the dynamic boiling speckles, created by the stellar image, make exoplanet detection impossible without the help of a wavefront correction device. The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system is a high performance HCI instrument developed at Subaru Telescope. The wavefront control system of SCExAO consists of three wavefront sensors (WFS) coupled with a 1024- actuator Micro-Electro-Mechanical-System (MEMS) deformable mirror (DM). MEMS DMs offer a large actuator density, allowing high count DMs to be deployed in small size beams. Therefore, MEMS DMs are an attractive technology for Adaptive Optics (AO) systems and are particularly well suited for HCI instruments employing ExAO technologies. SCExAO uses coherent light modulation in the focal plane introduced by the DM, for
NASA Technical Reports Server (NTRS)
Erickson, Gary E.
2013-01-01
A video-based photogrammetric model deformation system was established as a dedicated optical measurement technique at supersonic speeds in the NASA Langley Research Center Unitary Plan Wind Tunnel. This system was used to measure the wing twist due to aerodynamic loads of two supersonic commercial transport airplane models with identical outer mold lines but different aeroelastic properties. One model featured wings with deflectable leading- and trailing-edge flaps and internal channels to accommodate static pressure tube instrumentation. The wings of the second model were of single-piece construction without flaps or internal channels. The testing was performed at Mach numbers from 1.6 to 2.7, unit Reynolds numbers of 1.0 million to 5.0 million, and angles of attack from -4 degrees to +10 degrees. The video model deformation system quantified the wing aeroelastic response to changes in the Mach number, Reynolds number concurrent with dynamic pressure, and angle of attack and effectively captured the differences in the wing twist characteristics between the two test articles.
Wittek, Adam; Joldes, Grand; Couton, Mathieu; Warfield, Simon K; Miller, Karol
2010-12-01
Long computation times of non-linear (i.e. accounting for geometric and material non-linearity) biomechanical models have been regarded as one of the key factors preventing application of such models in predicting organ deformation for image-guided surgery. This contribution presents real-time patient-specific computation of the deformation field within the brain for six cases of brain shift induced by craniotomy (i.e. surgical opening of the skull) using specialised non-linear finite element procedures implemented on a graphics processing unit (GPU). In contrast to commercial finite element codes that rely on an updated Lagrangian formulation and implicit integration in time domain for steady state solutions, our procedures utilise the total Lagrangian formulation with explicit time stepping and dynamic relaxation. We used patient-specific finite element meshes consisting of hexahedral and non-locking tetrahedral elements, together with realistic material properties for the brain tissue and appropriate contact conditions at the boundaries. The loading was defined by prescribing deformations on the brain surface under the craniotomy. Application of the computed deformation fields to register (i.e. align) the preoperative and intraoperative images indicated that the models very accurately predict the intraoperative deformations within the brain. For each case, computing the brain deformation field took less than 4 s using an NVIDIA Tesla C870 GPU, which is two orders of magnitude reduction in computation time in comparison to our previous study in which the brain deformation was predicted using a commercial finite element solver executed on a personal computer. PMID:20868706
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. PMID:25485391
A geometric analysis of fast-slow models for stochastic gene expression.
Popović, Nikola; Marr, Carsten; Swain, Peter S
2016-01-01
Stochastic models for gene expression frequently exhibit dynamics on several different scales. One potential time-scale separation is caused by significant differences in the lifetimes of mRNA and protein; the ratio of the two degradation rates gives a natural small parameter in the resulting chemical master equation, allowing for the application of perturbation techniques. Here, we develop a framework for the analysis of a family of 'fast-slow' models for gene expression that is based on geometric singular perturbation theory. We illustrate our approach by giving a complete characterisation of a standard two-stage model which assumes transcription, translation, and degradation to be first-order reactions. In particular, we present a systematic expansion procedure for the probability-generating function that can in principle be taken to any order in the perturbation parameter, allowing for an approximation of the corresponding propagator probabilities to that same order. For illustrative purposes, we perform this expansion explicitly to first order, both on the fast and the slow time-scales; then, we combine the resulting asymptotics into a composite fast-slow expansion that is uniformly valid in time. In the process, we extend, and prove rigorously, results previously obtained by Shahrezaei and Swain (Proc Natl Acad Sci USA 105(45):17256-17261, 2008) and Bokes et al. (J Math Biol 64(5):829-854, 2012; J Math Biol 65(3):493-520, 2012). We verify our asymptotics by numerical simulation, and we explore its practical applicability and the effects of a variation in the system parameters and the time-scale separation. Focussing on biologically relevant parameter regimes that induce translational bursting, as well as those in which mRNA is frequently transcribed, we find that the first-order correction can significantly improve the steady-state probability distribution. Similarly, in the time-dependent scenario, inclusion of the first-order fast asymptotics results in a
Results of including geometric nonlinearities in an aeroelastic model of an F/A-18
NASA Technical Reports Server (NTRS)
Buttrill, Carey S.
1989-01-01
An integrated, nonlinear simulation model suitable for aeroelastic modeling of fixed-wing aircraft has been developed. While the author realizes that the subject of modeling rotating, elastic structures is not closed, it is believed that the equations of motion developed and applied herein are correct to second order and are suitable for use with typical aircraft structures. The equations are not suitable for large elastic deformation. In addition, the modeling framework generalizes both the methods and terminology of non-linear rigid-body airplane simulation and traditional linear aeroelastic modeling. Concerning the importance of angular/elastic inertial coupling in the dynamic analysis of fixed-wing aircraft, the following may be said. The rigorous inclusion of said coupling is not without peril and must be approached with care. In keeping with the same engineering judgment that guided the development of the traditional aeroelastic equations, the effect of non-linear inertial effects for most airplane applications is expected to be small. A parameter does not tell the whole story, however, and modes flagged by the parameter as significant also need to be checked to see if the coupling is not a one-way path, i.e., the inertially affected modes can influence other modes.
NASA Astrophysics Data System (ADS)
Likhachev, Dmitriy S.; Li, FengChen
2014-03-01
In this paper, a rotational supercavitating evaporator (RSCE) was at first modeled by means of theoretical analysis approach. The geometrical characteristics of supercavity in the modeled RSCE were then studied through numerical simulations. The current research objectives consist in determination of shape of the supercavitator (which in the plane of rotation generates supercavity occupying the most volume between blades), and location of the area suitable for steam extraction by revealing the inner structure of supercavity. Analytical analysis was performed by solving empirical equations for the shape of RSCE, through which an evaluation of two-dimensional relative position of supercavity trailing edge for different shapes of the supercavitator has been realized. Numerical simulation was then carried out, by numerically solving the unsteady Navier-Stokes equations in their conservation form coupled with the Rayleigh-Plesset cavitation and Shear-Stress Transport turbulence models, for verification of the results obtained from empirical equations. Despite unreliable assumption of applicability of empirical equations we have confirmed similarity of the supercavity shapes obtained by both methods for the same RSCE. Therefore, the shape of supercavitator calculated by using empirical equations is acceptable, which provides a simple but reliable approach for design of RSCE. The inner structure of supercavity obtained by numerical simulation has indicated position and parameters for steam extraction openings for further numerical and experimental studies on the performance of RSCE. Practical application of steam or gas extraction is suggested for solving of some problems associated with cavitating pumping of cryogenic liquid.
A Geometric Computational Model for Calculation of Longwall Face Effect on Gate Roadways
NASA Astrophysics Data System (ADS)
Mohammadi, Hamid; Ebrahimi Farsangi, Mohammad Ali; Jalalifar, Hossein; Ahmadi, Ali Reza
2016-01-01
In this paper a geometric computational model (GCM) has been developed for calculating the effect of longwall face on the extension of excavation-damaged zone (EDZ) above the gate roadways (main and tail gates), considering the advance longwall mining method. In this model, the stability of gate roadways are investigated based on loading effects due to EDZ and caving zone (CZ) above the longwall face, which can extend the EDZ size. The structure of GCM depends on four important factors: (1) geomechanical properties of hanging wall, (2) dip and thickness of coal seam, (3) CZ characteristics, and (4) pillar width. The investigations demonstrated that the extension of EDZ is a function of pillar width. Considering the effect of pillar width, new mathematical relationships were presented to calculate the face influence coefficient and characteristics of extended EDZ. Furthermore, taking GCM into account, a computational algorithm for stability analysis of gate roadways was suggested. Validation was carried out through instrumentation and monitoring results of a longwall face at Parvade-2 coal mine in Tabas, Iran, demonstrating good agreement between the new model and measured results. Finally, a sensitivity analysis was carried out on the effect of pillar width, bearing capacity of support system and coal seam dip.
Geometric analysis of the Goldbeter minimal model for the embryonic cell cycle.
Kosiuk, Ilona; Szmolyan, Peter
2016-04-01
A minimal model describing the embryonic cell division cycle at the molecular level in eukaryotes is analyzed mathematically. It is known from numerical simulations that the corresponding three-dimensional system of ODEs has periodic solutions in certain parameter regimes. We prove the existence of a stable limit cycle and provide a detailed description on how the limit cycle is generated. The limit cycle corresponds to a relaxation oscillation of an auxiliary system, which is singularly perturbed and has the same orbits as the original model. The singular perturbation character of the auxiliary problem is caused by the occurrence of small Michaelis constants in the model. Essential pieces of the limit cycle of the auxiliary problem consist of segments of slow motion close to several branches of a two dimensional critical manifold which are connected by fast jumps. In addition, a new phenomenon of exchange of stability occurs at lines, where the branches of the two-dimensional critical manifold intersect. This novel type of relaxation oscillations is studied by combining standard results from geometric singular perturbation with several suitable blow-up transformations. PMID:26100376
Automated Geometric Model Builder Using Range Image Sensor Data: Final Acquistion
Diegert, C.; Sackos, J.
1999-02-01
This report documents a data collection where we recorded redundant range image data from multiple views of a simple scene, and recorded accurate survey measurements of the same scene. Collecting these data was a focus of the research project Automated Geometric Model Builder Using Range Image Sensor Data (96-0384), supported by Sandia's Laboratory-Directed Research and Development (LDRD) Program during fiscal years 1996, 1997, and 1998. The data described here are available from the authors on CDROM, or electronically over the Internet. Included in this data distribution are Computer-Aided Design (CAD) models we constructed from the survey measurements. The CAD models are compatible with the SolidWorks 98 Plus system, the modern Computer-Aided Design software system that is central to Sandia's DeskTop Engineering Project (DTEP). Integration of our measurements (as built) with the constructive geometry process of the CAD system (as designed) delivers on a vision of the research project. This report on our final data collection will also serve as a final report on the project.
Progressive Conversion from B-rep to BSP for Streaming Geometric Modeling.
Bajaj, Chandrajit; Paoluzzi, Alberto; Scorzelli, Giorgio
2006-01-01
We introduce a novel progressive approach to generate a Binary Space Partition (BSP) tree and a convex cell decomposition for any input triangles boundary representation (B-rep), by utilizing a fast calculation of the surface inertia. We also generate a solid model at progressive levels of detail. This approach relies on a variation of standard BSP tree generation, allowing for labeling cells as in, out and fuzzy, and which permits a comprehensive representation of a solid as the Hasse diagram of a cell complex. Our new algorithm is embedded in a streaming computational framework, using four types of dataflow processes that continuously produce, transform, combine or consume subsets of cells depending on their number or input/output stream. A varied collection of geometric modeling techniques are integrated in this streaming framework, including polygonal, spline, solid and heterogeneous modeling with boundary and decompositive representations, Boolean set operations, Cartesian products and adaptive refinement. The real-time B-rep to BSP streaming results we report in this paper are a large step forward in the ultimate unification of rapid conceptual and detailed shape design methodologies. PMID:21499445
Tsukanaka, Masako; Röhrl, Stephan M; von Schewelov, Thord; Nordsletten, Lars
2016-02-01
Elementary geometrical shape (EGS) models are useful in radiostereometric analysis (RSA) on hip stems because tantalum markers attached to the stems can be omitted. In order to create an EGS model of a femoral stem, the center of the femoral head has to be identified. The contour of the femoral head is recommended to be used. However, the contour of the femoral head cannot be detected exclusively by computer if it is combined with a bipolar head or a metal cup. We therefore hypothesized that the contour of the outer head of bipolar hemiarthroplasty can be included in the EGS model as well as the femoral head contour. We calculated the time required for the detection of the contour, the precision of analysis and the stem micromotion at 2 years using the two different methods in the same picture set and compared the results. The detection of the bipolar head contour was 10 times faster than that of the femoral head contour. The precision for subsidence was 0.16 mm in EGS RSA with the femoral head contour, and 0.15 mm with the bipolar head contour (p=0.68). The precisions were comparable and clinically acceptable. There was no significant difference between the results of the 2-year micromotion with the two different methods. We conclude that this new method is applicable to measure stem micromotion of hemi-arthroplasty with EGS RSA and the method facilitates the Radiostereometric analysis. PMID:26705109
Volume Preserved Mass-Spring Model with Novel Constraints for Soft Tissue Deformation.
Duan, Yuping; Huang, Weimin; Chang, Huibin; Chen, Wenyu; Zhou, Jiayin; Teo, Soo Kng; Su, Yi; Chui, Chee Kong; Chang, Stephen
2016-01-01
An interactive surgical simulation system needs to meet three main requirements, speed, accuracy, and stability. In this paper, we present a stable and accurate method for animating mass-spring systems in real time. An integration scheme derived from explicit integration is used to obtain interactive realistic animation for a multiobject environment. We explore a predictor-corrector approach by correcting the estimation of the explicit integration in a poststep process. We introduce novel constraints on positions into the mass-spring model (MSM) to model the nonlinearity and preserve volume for the realistic simulation of the incompressibility. We verify the proposed MSM by comparing its deformations with the reference deformations of the nonlinear finite-element method. Moreover, experiments on porcine organs are designed for the evaluation of the multiobject deformation. Using a pair of freshly harvested porcine liver and gallbladder, the real organ deformations are acquired by computed tomography and used as the reference ground truth. Compared to the porcine model, our model achieves a 1.502 mm mean absolute error measured at landmark locations for cases with small deformation (the largest deformation is 49.109 mm) and a 3.639 mm mean absolute error for cases with large deformation (the largest deformation is 83.137 mm). The changes of volume for the two deformations are limited to 0.030% and 0.057%, respectively. Finally, an implementation in a virtual reality environment for laparoscopic cholecystectomy demonstrates that our model is capable to simulate large deformation and preserve volume in real-time calculations. PMID:25398184
Study of optical techniques for the Ames unitary wind tunnels. Part 4: Model deformation
NASA Technical Reports Server (NTRS)
Lee, George
1992-01-01
A survey of systems capable of model deformation measurements was conducted. The survey included stereo-cameras, scanners, and digitizers. Moire, holographic, and heterodyne interferometry techniques were also looked at. Stereo-cameras with passive or active targets are currently being deployed for model deformation measurements at NASA Ames and LaRC, Boeing, and ONERA. Scanners and digitizers are widely used in robotics, motion analysis, medicine, etc., and some of the scanner and digitizers can meet the model deformation requirements. Commercial stereo-cameras, scanners, and digitizers are being improved in accuracy, reliability, and ease of operation. A number of new systems are coming onto the market.
[Research progress on real-time deformable models of soft tissues for surgery simulation].
Xu, Shaoping; Liu, Xiaoping; Zhang, Hua; Luo, Jie
2010-04-01
Biological tissues generally exhibit nonlinearity, anisotropy, quasi-incompressibility and viscoelasticity about material properties. Simulating the behaviour of elastic objects in real time is one of the current objectives of virtual surgery simulation which is still a challenge for researchers to accurately depict the behaviour of human tissues. In this paper, we present a classification of the different deformable models that have been developed. We present the advantages and disadvantages of each one. Finally, we make a comparison of deformable models and perform an evaluation of the state of the art and the future of deformable models. PMID:20481334
NASA Astrophysics Data System (ADS)
Sablik, M. J.; Rios, S.; Landgraf, F. J. G.; Yonamine, T.; de Campos, M. F.
2005-05-01
In 2.2% Si electrical steel, the magnetic hysteresis behavior is sharply sheared by a rather small plastic deformation (0.5%). A modification to the Jiles-Atherton hysteresis model makes it possible to model magnetic effects of plastic deformation. In this paper, with this model, it is shown how a narrow hysteresis with an almost steplike hysteresis curve for an undeformed specimen is sharply sheared by plastic deformation. Computed coercivity and hysteresis loss show a sharp step to higher values at small strain due to an n =1/2 power law dependence on residual strain. The step is seen experimentally.
Sablik, M.J.; Rios, S.; Landgraf, F.J.G.; Yonamine, T.; Campos, M.F. de
2005-05-15
In 2.2% Si electrical steel, the magnetic hysteresis behavior is sharply sheared by a rather small plastic deformation (0.5%). A modification to the Jiles-Atherton hysteresis model makes it possible to model magnetic effects of plastic deformation. In this paper, with this model, it is shown how a narrow hysteresis with an almost steplike hysteresis curve for an undeformed specimen is sharply sheared by plastic deformation. Computed coercivity and hysteresis loss show a sharp step to higher values at small strain due to an n=1/2 power law dependence on residual strain. The step is seen experimentally.
Models for rupture mechanics of plate boundaries and crustal deformation
NASA Astrophysics Data System (ADS)
Nur, A.
1983-02-01
The role of pull aparts and pushups in transcurrent systems, the rotation of faults and blocks within transcurrent fault systems, the role of accretion tectonics in plate boundary deformation, and power law creep behavior and the yielding at plate boundaries were investigated.
A stochastic-geometric model of soil variation in Pleistocene patterned ground
NASA Astrophysics Data System (ADS)
Lark, Murray; Meerschman, Eef; Van Meirvenne, Marc
2013-04-01
In this paper we examine the spatial variability of soil in parent material with complex spatial structure which arises from complex non-linear geomorphic processes. We show that this variability can be better-modelled by a stochastic-geometric model than by a standard Gaussian random field. The benefits of the new model are seen in the reproduction of features of the target variable which influence processes like water movement and pollutant dispersal. Complex non-linear processes in the soil give rise to properties with non-Gaussian distributions. Even under a transformation to approximate marginal normality, such variables may have a more complex spatial structure than the Gaussian random field model of geostatistics can accommodate. In particular the extent to which extreme values of the variable are connected in spatially coherent regions may be misrepresented. As a result, for example, geostatistical simulation generally fails to reproduce the pathways for preferential flow in an environment where coarse infill of former fluvial channels or coarse alluvium of braided streams creates pathways for rapid movement of water. Multiple point geostatistics has been developed to deal with this problem. Multiple point methods proceed by sampling from a set of training images which can be assumed to reproduce the non-Gaussian behaviour of the target variable. The challenge is to identify appropriate sources of such images. In this paper we consider a mode of soil variation in which the soil varies continuously, exhibiting short-range lateral trends induced by local effects of the factors of soil formation which vary across the region of interest in an unpredictable way. The trends in soil variation are therefore only apparent locally, and the soil variation at regional scale appears random. We propose a stochastic-geometric model for this mode of soil variation called the Continuous Local Trend (CLT) model. We consider a case study of soil formed in relict patterned
NASA Astrophysics Data System (ADS)
Tang, Xiaoli; Jeong, Yongwon; Radke, Richard J.; Chen, George T. Y.
2004-01-01
We present a computer vision tool to improve the clinical outcome of patients undergoing radiation therapy for prostate cancer by improving irradiation technique. While intensity modulated radiotherapy (IMRT) allows one to irradiate a specific region in the body with high accuracy, it is still difficult to know exactly where to aim the radiation beam on every day of the 30~40 treatments that are necessary. This paper presents a geometric model-based technique to accurately segment the prostate and other surrounding structures in a daily serial CT image, compensating for daily motion and shape variation. We first acquire a collection of serial CT scans of patients undergoing external beam radiotherapy, and manual segmentation of the prostate and other nearby structures by radiation oncologists. Then we train shape and local appearance models for the structures of interest. When new images are available, an iterative algorithm is applied to locate the prostate and surrounding structures automatically. Our experimental results show that excellent matches can be given to the prostate and surrounding structure. Convergence is declared after 10 iterations. For 256 x 256 images, the mean distance between the hand-segmented contour and the automatically estimated contour is about 1.5 pixels (2.44 mm), with variance about 0.6 pixel (1.24 mm).
Complex defect in pyrite and its structure model derived from geometric phase analysis.
Németh, Péter; Dódony, István; Pósfai, Mihály; Buseck, Peter R
2013-10-01
New methods for defect analysis can lead to improved interpretation of experimental data and thus better understanding of material properties. Although transmission electronmicroscopy (TEM) has been used to study defects for many decades, interpretive ambiguities can arise for cases that seem simple or even trivial.Using geometric phase analysis (GPA), an image processing procedure, we show that an apparent simple line defect in pyrite has an entirely different character. It appears to be a b = ½[100] edge dislocation as viewed in a [001] high-resolution TEM (HRTEM) image, but the measured u(x) and u(y) displacements are asymmetric, which is inconsistent with a simple line dislocation. Instead, the defect is best understood as a terminating {101} marcasite slab in pyrite. The simulated HRTEM image based on this model reproduces the defect contrast and illustrates the power of GPA analysis for (1) avoiding potential pitfalls of misinterpreting apparently simple defects in HRTEM images, (2) detecting differences in elastic properties at the atomic scale, and (3) providing data for the positions of atom columns, thereby facilitating the construction of structure models for complex defects. PMID:23773546
Geometric structure and geodesic in a solvable model of nonequilibrium process
NASA Astrophysics Data System (ADS)
Kim, Eun-jin; Lee, UnJin; Heseltine, James; Hollerbach, Rainer
2016-06-01
We investigate the geometric structure of a nonequilibrium process and its geodesic solutions. By employing an exactly solvable model of a driven dissipative system (generalized nonautonomous Ornstein-Uhlenbeck process), we compute the time-dependent probability density functions (PDFs) and investigate the evolution of this system in a statistical metric space where the distance between two points (the so-called information length) quantifies the change in information along a trajectory of the PDFs. In this metric space, we find a geodesic for which the information propagates at constant speed, and demonstrate its utility as an optimal path to reduce the total time and total dissipated energy. In particular, through examples of physical realizations of such geodesic solutions satisfying boundary conditions, we present a resonance phenomenon in the geodesic solution and the discretization into cyclic geodesic solutions. Implications for controlling population growth are further discussed in a stochastic logistic model, where a periodic modulation of the diffusion coefficient and the deterministic force by a small amount is shown to have a significant controlling effect.
White Matter MS-Lesion Segmentation Using a Geometric Brain Model.
Strumia, Maddalena; Schmidt, Frank R; Anastasopoulos, Constantinos; Granziera, Cristina; Krueger, Gunnar; Brox, Thomas
2016-07-01
Brain magnetic resonance imaging (MRI) in patients with Multiple Sclerosis (MS) shows regions of signal abnormalities, named plaques or lesions. The spatial lesion distribution plays a major role for MS diagnosis. In this paper we present a 3D MS-lesion segmentation method based on an adaptive geometric brain model. We model the topological properties of the lesions and brain tissues in order to constrain the lesion segmentation to the white matter. As a result, the method is independent of an MRI atlas. We tested our method on the MICCAI MS grand challenge proposed in 2008 and achieved competitive results. In addition, we used an in-house dataset of 15 MS patients, for which we achieved best results in most distances in comparison to atlas based methods. Besides classical segmentation distances, we motivate and formulate a new distance to evaluate the quality of the lesion segmentation, while being robust with respect to minor inconsistencies at the boundary level of the ground truth annotation. PMID:26829786
NASA Astrophysics Data System (ADS)
Zhang, Youbing; Dalguer, Luis A.; Song, Seok Goo; Clinton, John; Giardini, Domenico
2015-01-01
The effect of network density and geometric distribution on kinematic non-linear source inversion is investigated by inverting synthetic ground motions from a buried strike-slip fault (Mw 6.5), that have been generated by dynamic spontaneous rupture modelling. For the inversion, we use a physics-based regularized Yoffe function as slip velocity function. We test three different cases of station network geometry: (i) single station, varying azimuth and epicentral distance; (ii) multistation circular configurations, that is stations at similar distances from the fault, and regularly spaced around the fault; (iii) irregular multistation configurations using different numbers of stations. Our results show: (1) single station tests suggest that it may be possible to obtain a relatively good source model even using a single station. The best source model using a single station is obtained with stations at which amplitude ratios between three components are not large. We infer that both azimuthal angle and source-to-station distance play an important role in the design of optimal seismic network for source inversion. (2) Multistation tests show that the quality of the inverted source systematically correlates neither with the number of stations, nor with waveform misfit. (3) Waveform misfit has a direct correlation with the number of stations, resulting in overfitting the observed data without any systematic improvement of the source. It suggests that the best source model is not necessarily derived from the model with minimum waveform misfit. (4) A seismic network with a small number of well-spaced stations around the fault may be sufficient to obtain acceptable source inversion.
Evolving Nutritional Strategies in the Presence of Competition: A Geometric Agent-Based Model
Senior, Alistair M.; Charleston, Michael A.; Lihoreau, Mathieu; Buhl, Jerome; Raubenheimer, David; Simpson, Stephen J.
2015-01-01
Access to nutrients is a key factor governing development, reproduction and ultimately fitness. Within social groups, contest-competition can fundamentally affect nutrient access, potentially leading to reproductive asymmetry among individuals. Previously, agent-based models have been combined with the Geometric Framework of nutrition to provide insight into how nutrition and social interactions affect one another. Here, we expand this modelling approach by incorporating evolutionary algorithms to explore how contest-competition over nutrient acquisition might affect the evolution of animal nutritional strategies. Specifically, we model tolerance of nutrient excesses and deficits when ingesting nutritionally imbalanced foods, which we term ‘nutritional latitude’; a higher degree of nutritional latitude constitutes a higher tolerance of nutritional excess and deficit. Our results indicate that a transition between two alternative strategies occurs at moderate to high levels of competition. When competition is low, individuals display a low level of nutritional latitude and regularly switch foods in search of an optimum. When food is scarce and contest-competition is intense, high nutritional latitude appears optimal, and individuals continue to consume an imbalanced food for longer periods before attempting to switch to an alternative. However, the relative balance of nutrients within available foods also strongly influences at what levels of competition, if any, transitions between these two strategies occur. Our models imply that competition combined with reproductive skew in social groups can play a role in the evolution of diet breadth. We discuss how the integration of agent-based, nutritional and evolutionary modelling may be applied in future studies to further understand the evolution of nutritional strategies across social and ecological contexts. PMID:25815976
NASA Astrophysics Data System (ADS)
Bibee, M. A.; Calantoni, J.; Sclater, J. G.
2005-05-01
Experiments on sandboxes provide a useful tool for understanding the deformation of both sedimentary sequences and the continental crust. Boerner and Sclater (1992) have shown that the deformation under extension of assemblies of steel balls can reproduce many of the basic features of these experiments. We use a discrete particle model (DPM) to simulate previously performed physical experiments, which consisted of extending close-packed assemblies of steel balls placed on a rubber sheet attached to moveable boundaries. Steel balls are modeled with spherical elements in the DPM where normal and tangential forces generated at contact points are modeled with springs and friction, respectively. The simulations allow for a quantitative examination of the displacement and rotation of each steel ball as well as provide estimates of the contact forces between them. We perform a suite of simulations to explore the behavior of the model due to variations in the material properties of the balls and rate of extension of the assembly. Qualitative visual analysis shows that the simulations reproduce the qualitative features from the physical experiments such as dilation, rotation, and fault formation. Our success in matching most of the major features of the experiment indicates that the DPM may have a real future in improving our understanding of the deformation of both sedimentary sequences and the continental crust.
Two-dimensional numerical modeling for separation of deformable cells using dielectrophoresis.
Ye, Ting; Li, Hua; Lam, K Y
2015-02-01
In this paper, we numerically explore the possibility of separating two groups of deformable cells, by a very small dielectrophoretic (DEP) microchip with the characteristic length of several cell diameters. A 2D two-fluid model is developed to describe the separation process, where three types of forces are considered, the aggregation force for cell-cell interaction, the deformation force for cell deformation, and the DEP force for cell dielectrophoresis. As a model validation, we calculate the levitation height of a cell subject to DEP force, and compare it with the experimental data. After that, we simulate the separation of two groups of cells with different dielectric properties at high and low frequencies, respectively. The simulation results show that the deformable cells can be separated successfully by a very small DEP microchip, according to not only their different permittivities at the high frequency, but also their different conductivities at the low frequency. In addition, both two groups of cells have a shape deformation from an original shape to a lopsided slipper shape during the separation process. It is found that the cell motion is mainly determined by the DEP force arising from the electric field, causing the cells to deviate from the centerline of microchannel. However, the cell deformation is mainly determined by the deformation force arising from the fluid flow, causing the deviated cells to undergo an asymmetric motion with the deformation of slipper shape. PMID:24981085
NASA Technical Reports Server (NTRS)
Goldberg, Robert K.; Stouffer, Donald C.
1998-01-01
Recently applications have exposed polymer matrix composite materials to very high strain rate loading conditions, requiring an ability to understand and predict the material behavior under these extreme conditions. In this first paper of a two part report, background information is presented, along with the constitutive equations which will be used to model the rate dependent nonlinear deformation response of the polymer matrix. Strain rate dependent inelastic constitutive models which were originally developed to model the viscoplastic deformation of metals have been adapted to model the nonlinear viscoelastic deformation of polymers. The modified equations were correlated by analyzing the tensile/ compressive response of both 977-2 toughened epoxy matrix and PEEK thermoplastic matrix over a variety of strain rates. For the cases examined, the modified constitutive equations appear to do an adequate job of modeling the polymer deformation response. A second follow-up paper will describe the implementation of the polymer deformation model into a composite micromechanical model, to allow for the modeling of the nonlinear, rate dependent deformation response of polymer matrix composites.
Can We Improve Estimates of Seismological Q Using a New ``Geometrical Spreading'' Model?
NASA Astrophysics Data System (ADS)
Xie, Jiakang
2010-10-01
Precise measurements of seismological Q are difficult because we lack detailed knowledge on how the Earth’s fine velocity structure affects the amplitude data. In a number of recent papers, Morozov (Geophys J Int 175:239-252, 2008; Seism Res Lett 80:5-7, 2009; Pure Appl Geophys, this volume, 2010) proposes a new procedure intended to improve Q determinations. The procedure relies on quantifying the structural effects using a new form of geometrical spreading (GS) model that has an exponentially decaying component with time, e -γt·γ is a free parameter and is measured together with Q. Morozov has refit many previously published sets of amplitude attenuation data. In general, the new Q estimates are much higher than previous estimates, and all of the previously estimated frequency-dependence values for Q disappear in the new estimates. In this paper I show that (1) the traditional modeling of seismic amplitudes is physically based, whereas the new model lacks a physical basis; (2) the method of measuring Q using the new model is effectively just a curve fitting procedure using a first-order Taylor series expansion; (3) previous high-frequency data that were fit by a power-law frequency dependence for Q are expected to be also fit by the first-order expansion in the limited frequency bands involved, because of the long tails of power-law functions; (4) recent laboratory measurements of intrinsic Q of mantle materials at seismic frequencies provide independent evidence that intrinsic Q is often frequency-dependent, which should lead to frequency-dependent total Q; (5) published long-period surface wave data that were used to derive several recent Q models inherently contradict the new GS model; and (6) previous modeling has already included a special case that is mathematically identical to the new GS model, but with physical assumptions and measured Q values that differ from those with the new GS model. Therefore, while individually the previous Q measurements
Learning deformation model for expression-robust 3D face recognition
NASA Astrophysics Data System (ADS)
Guo, Zhe; Liu, Shu; Wang, Yi; Lei, Tao
2015-12-01
Expression change is the major cause of local plastic deformation of the facial surface. The intra-class differences with large expression change somehow are larger than the inter-class differences as it's difficult to distinguish the same individual with facial expression change. In this paper, an expression-robust 3D face recognition method is proposed by learning expression deformation model. The expression of the individuals on the training set is modeled by principal component analysis, the main components are retained to construct the facial deformation model. For the test 3D face, the shape difference between the test and the neutral face in training set is used for reconstructing the expression change by the constructed deformation model. The reconstruction residual error is used for face recognition. The average recognition rate on GavabDB and self-built database reaches 85.1% and 83%, respectively, which shows strong robustness for expression changes.
Technology Transfer Automated Retrieval System (TEKTRAN)
A new method is described for the retrieval of fractional cover of large woody plants (shrubs) at the landscape scale using moderate resolution multiangle remote sensing data from the Multiangle Imaging SpectroRadiometer (MISR) and an hybrid geometric-optical (GO) canopy reflectance model. Remote se...
A low-dimensional deformation model for cancer cells in flow
NASA Astrophysics Data System (ADS)
Lee, A. M.; Berny-Lang, M. A.; Liao, S.; Kanso, E.; Kuhn, P.; McCarty, O. J. T.; Newton, P. K.
2012-08-01
A low-dimensional parametric deformation model of a cancer cell under shear flow is developed. The model is built around an experiment in which MDA-MB-231 adherent cells are subjected to flow with increasing shear. The cell surface deformation is imaged using differential interference contrast microscopy imaging techniques until the cell releases into the flow. We post-process the time sequence of images using an active shape model from which we obtain the principal components of deformation. These principal components are then used to obtain the parameters in an empirical constitutive equation determining the cell deformations as a function of the fluid normal and shear forces imparted. The cell surface is modeled as a 2D Gaussian interface which can be deformed with three active parameters: H (height), σx (x-width), and σy (y-width). Fluid forces are calculated on the cell surface by discretizing the surface with regularized Stokeslets, and the flow is driven by a stochastically fluctuating pressure gradient. The Stokeslet strengths are obtained so that viscous boundary conditions are enforced on the surface of the cell and the surrounding plate. We show that the low-dimensional model is able to capture the principal deformations of the cell reasonably well and argue that active shape models can be exploited further as a useful tool to bridge the gap between experiments, models, and numerical simulations in this biological setting.
NASA Technical Reports Server (NTRS)
Emery, J. D.
1985-01-01
Two topics in topology, the comparison of plane curves and faces on geometric models, are discussed. With regard to the first problem, a curve is defined to be a locus of points without any underlying parameterization. A metric on a class of plane curves is defined, a finite computation of this metric is given for the case of piecewise linear curves, and it is shown how to approximate curves that have bounded curvature by piecewise linear curves. In this way a bound on the distance between two curves can be computed. With regard to the second problem, the questions to be discussed are under what circumstances do geometrical faces make sense; how can they be explicity defined; and when are these geometrical faces homeomorphic to the realization of the abstract (topological) face.
Modeling for deformable mirrors and the adaptive optics optimization program
Henesian, M.A.; Haney, S.W.; Trenholme, J.B.; Thomas, M.
1997-03-18
We discuss aspects of adaptive optics optimization for large fusion laser systems such as the 192-arm National Ignition Facility (NIF) at LLNL. By way of example, we considered the discrete actuator deformable mirror and Hartmann sensor system used on the Beamlet laser. Beamlet is a single-aperture prototype of the 11-0-5 slab amplifier design for NIF, and so we expect similar optical distortion levels and deformable mirror correction requirements. We are now in the process of developing a numerically efficient object oriented C++ language implementation of our adaptive optics and wavefront sensor code, but this code is not yet operational. Results are based instead on the prototype algorithms, coded-up in an interpreted array processing computer language.
NASA Astrophysics Data System (ADS)
Zhang, Youbing; Song, Seok Goo; Dalguer, Luis; Clinton, John
2013-04-01
An essential element of understanding earthquake source processes is obtaining a reliable source model via geophysical data inversion. The most common procedure to determine the kinematic source parameters (final slip, peak slip velocity, rise time and rupture time) is to invert observed ground motions recorded at a number of different stations (typically strong motion accelerometers). Few studies have been dedicated to evaluate the effect of the number of stations and their geometrical distribution on earthquake source parameters. In this paper we investigate these effects by inverting ground motions from synthetic dynamic earthquake rupture models with heterogeneous stress distribution governed by the slip weakening friction law. Our first target model is a buried strike-slip event (Mw 6.5) in a layered half space. The Compsyn code (Spudich and Xu, 2002) was used in the inversion procedure to generate forward synthetic waveforms, and an Evolutionary Algorithm was used to search for the source parameters: peak slip velocity (PSV), rupture time, and rise time at low frequency (up to 1Hz). The regularized Yoffe function was applied as a single window slip velocity function, which is a flexible slip velocity function defined by three independent parameters: the final slip, the slip duration and the duration of the positive slip acceleration, Tacc (Tinti, et al. 2005). The same velocity structure was used for both the foward and inversion modeling and no noise was added to the synthetic ground motions before inversion. We applied the Tikhonov regularization to smooth the final slip on fault, which is controlled by PSV and rise time. Our preliminary results show that: First, we can capture large slip patches of the dynamic models with good ground velocity waveform fitting, using the regularized Yoffe function, which is consistent with the overall properties of dynamic rupture models. Second, the geometry of station distribution is important for finite kinematic source
Kao, Philip H; Lammers, Steven R; Hunter, Kendall; Stenmark, Kurt R; Shandas, Robin; Qi, H Jerry
2010-04-01
Many biological materials are composites composed of a soft matrix reinforced with stiffer fibers. These stiffer fibers may have a tortuous shape and wind through the soft matrix. At small material deformation, these fibers deform in a bending mode and contribute little to the material stiffness; at large material deformation, these fibers deform in a stretching mode and induce a stiffening effect in the material behavior. The transition from bending mode deformation to stretching mode deformation yields a characteristic J-shape stress-strain curve. In addition, the spatial distribution of these fibers may render the composite an anisotropic behavior. In this paper, we present an anisotropic finite-deformation hyperelastic constitutive model for such materials. Here, the matrix is modeled as an isotropic neo-Hookean material. "The behaviors of single tortuous fiber are represented by a crimped fiber model". The anisotropic behavior is introduced by a structure tensor representing the effective orientation distribution of crimped fibers. Parametric studies show the effect of fiber tortuosity and fiber orientation distribution on the overall stress-strain behaviors of the materials. PMID:21822502
Martin, Guillaume; Lenormand, Thomas
2015-06-01
When are mutations beneficial in one environment and deleterious in another? More generally, what is the relationship between mutation effects across environments? These questions are crucial to predict adaptation in heterogeneous conditions in a broad sense. Empirical evidence documents various patterns of fitness effects across environments but we still lack a framework to analyze these multivariate data. In this article, we extend Fisher's geometrical model to multiple environments determining distinct peaks. We derive the fitness distribution, in one environment, among mutants with a given fitness in another and the bivariate distribution of random mutants' fitnesses across two or more environments. The geometry of the phenotype-fitness landscape is naturally interpreted in terms of fitness trade-offs between environments. These results may be used to fit/predict empirical distributions or to predict the pattern of adaptation across heterogeneous conditions. As an example, we derive the genomic rate of substitution and of adaptation in a metapopulation divided into two distinct habitats in a high migration regime and show that they depend critically on the geometry of the phenotype-fitness landscape. PMID:25908434
Balancing Selection in Species with Separate Sexes: Insights from Fisher’s Geometric Model
Connallon, Tim; Clark, Andrew G.
2014-01-01
How common is balancing selection, and what fraction of phenotypic variance is attributable to balanced polymorphisms? Despite decades of research, answers to these questions remain elusive. Moreover, there is no clear theoretical prediction about the frequency with which balancing selection is expected to arise within a population. Here, we use an extension of Fisher’s geometric model of adaptation to predict the probability of balancing selection in a population with separate sexes, wherein polymorphism is potentially maintained by two forms of balancing selection: (1) heterozygote advantage, where heterozygous individuals at a locus have higher fitness than homozygous individuals, and (2) sexually antagonistic selection (a.k.a. intralocus sexual conflict), where the fitness of each sex is maximized by different genotypes at a locus. We show that balancing selection is common under biologically plausible conditions and that sex differences in selection or sex-by-genotype effects of mutations can each increase opportunities for balancing selection. Although heterozygote advantage and sexual antagonism represent alternative mechanisms for maintaining polymorphism, they mutually exist along a balancing selection continuum that depends on population and sex-specific parameters of selection and mutation. Sexual antagonism is the dominant mode of balancing selection across most of this continuum. PMID:24812306
Geometric factors affecting dentin bonding in root canals: a theoretical modeling approach.
Tay, Franklin R; Loushine, Robert J; Lambrechts, Paul; Weller, R Norman; Pashley, David H
2005-08-01
Cavity configuration factor (C-factor) is the ratio of the bonded surface area in a cavity to the unbonded surface area. In a box-like class I cavity, there may be five times more bonded surface area than the unbonded surface area. During polymerization, the volume of monomers is reduced, which creates sufficient shrinkage stresses to debond the material from dentin, thereby decreasing retention and increasing leakage. The important variables influencing bonding adhesive root-filling materials to canals was examined using a truncated inverted cone model. C-factors in bonded root canals exhibit a negative correlation with sealer thickness. For a 20 mm-long canal prepared with a size 25 file, calculated C-factors ranged from 46 to 23,461 with decreasing sealer thickness (500-1 microm), compared to a C-factor of 32 when the canal was filled only with sealer. As the thickness of the adhesive is reduced, the volummetric shrinkage is reduced, which results in a reduction in shrinkage stress (S-factor). C-factors above 954 calculated with sealer thickness smaller than 25 microm are partially compensated by increases in bonding area and decreases in shrinkage volume. However, the interaction of these two geometrically related factors (C- and S-factors) predicts that bonding of adhesive root-filling materials to root canals is highly unfavorable when compared with indirect intracoronal restorations with a similar resin film thickness. PMID:16044041
NASA Astrophysics Data System (ADS)
Pavlov, V. P.
2014-03-01
Faddeev and Vershik proposed the Hamiltonian and Lagrangian formulations of constrained mechanical systems that are invariant from the differential geometry standpoint. In both formulations, the description is based on a nondegenerate symplectic 2-form defined on a cotangent bundle T*Q (in the Hamiltonian formulation) or on a tangent bundle TQ (in the Lagrangian formulation), and constraints are sets of functions in involution on these manifolds. We demonstrate that this technique does not allow "invariantization" of the Dirac procedure of constraint "proliferation." We show this in an example of a typical quantum field model in which the original Lagrange function is a quadratic form in velocities with a degenerate coefficient matrix. We postulate that the initial phase space is a manifold where all arguments of the action functional including the Lagrange multipliers are defined. The Lagrange multipliers can then be naturally interpreted physically as velocities (in the Hamiltonian formulation) or momenta (in the Lagrangian formulation) related to "nonphysical" degrees of freedom. A quasisymplectic 2-form invariantly defined on such a manifold is degenerate. We propose new differential-geometric structures that allow formulating the Dirac procedure invariantly.
Fisher's geometric model predicts the effects of random mutations when tested in the wild.
Stearns, Frank W; Fenster, Charles B
2016-02-01
Fisher's geometric model of adaptation (FGM) has been the conceptual foundation for studies investigating the genetic basis of adaptation since the onset of the neo Darwinian synthesis. FGM describes adaptation as the movement of a genotype toward a fitness optimum due to beneficial mutations. To date, one prediction of FGM, the probability of improvement is related to the distance from the optimum, has only been tested in microorganisms under laboratory conditions. There is reason to believe that results might differ under natural conditions where more mutations likely affect fitness, and where environmental variance may obscure the expected pattern. We chemically induced mutations into a set of 19 Arabidopsis thaliana accessions from across the native range of A. thaliana and planted them alongside the premutated founder lines in two habitats in the mid-Atlantic region of the United States under field conditions. We show that FGM is able to predict the outcome of a set of random induced mutations on fitness in a set of A. thaliana accessions grown in the wild: mutations are more likely to be beneficial in relatively less fit genotypes. This finding suggests that FGM is an accurate approximation of the process of adaptation under more realistic ecological conditions. PMID:26768168
Geometrical mutual information at the tricritical point of the two-dimensional Blume–Capel model
NASA Astrophysics Data System (ADS)
Mandal, Ipsita; Inglis, Stephen; Melko, Roger G.
2016-07-01
The spin-1 classical Blume–Capel model on a square lattice is known to exhibit a finite-temperature phase transition described by the tricritical Ising CFT in 1 + 1 space-time dimensions. This phase transition can be accessed with classical Monte Carlo simulations, which, via a replica-trick calculation, can be used to study the shape-dependence of the classical Rényi entropies for a torus divided into two cylinders. From the second Rényi entropy, we calculate the geometrical mutual information (GMI) introduced by Stéphan et al (2014 Phys. Rev. Lett. 112 127204) and use it to extract a numerical estimate for the value of the central charge near the tricritical point. By comparing to the known CFT result, c = 7/10, we demonstrate how this type of GMI calculation can be used to estimate the position of the tricritical point in the phase diagram.
Predictive Model for Temperature-Induced Deformation of Robot Mechanical Systems
NASA Astrophysics Data System (ADS)
Poonyapak, Pranchalee
The positioning accuracy and repeatability of a robot are critical for many industrial applications. Drift in repeatability can occur with changes in environmental and internal conditions, such as those seen with temperature-induced deformation. Thermal instability causes dimensional deformation, and a warm-up cycle is typically required to bring the robot to a thermally stable working condition. The elimination of warm-up cycles will ultimately enhance the positioning accuracy of the robots, their productivity, and reduce unnecessary energy consumption. The main objective of this research was to develop a robot controller algorithm that would provide, a priori, compensation for temperature-induced deformation associated with warm-up in robot mechanical systems. The research started at the fundamental stage of gaining insight into the thermal behaviour and corresponding temperature-induced deformation of simplified, i.e., one-dimensional, robot mechanical systems consisting of slender links and heat sources. The systems were studied using concomitant experimental, numerical and analytical models to provide cross-checking of the results. For the experimental model, the deformation was measured by tracking the drift of a laser diode spot across a charge-coupled device (CCD) camera chip. A non-contact measurement system consisting of an infrared camera, a CCD camera and a laser diode was developed to provide high accuracy measurement for the deformation. The numerical model was generated with a coupled thermal-mechanical finite element analysis incorporating thermal effects due to conduction and convection. The models were tested with the analytical model that was further extended using a finite difference technique. Once the three models showed excellent agreement, it was possible to develop a controller algorithm. Deformations predicted by the finite difference model were used as input for a validation experiment of the compensation algorithm. Results