Non-rigid Structure Research Articles

Analysis of wavelet basis selection in optimal trajectory space finding for 3D non-rigid structure from motion

Trajectory representation model has been proposed to describe non-rigid deformation. An optimal trajectory space finding algorithm for 3D non-rigid structure from motion (OTSF-NRSFM) based on this model also has been proposed. However, the influence of the wavelet basis selection on the OTSF-NRSFM algorithm has still not been studied. To help OTSF-NRSFM researchers select wavelet basis properly, we investigated the influences of wavelet basis selection. Two typical wavelet bases, DCT basis and WHT basis, are discussed in this paper. The spectrum properties of wavelet basis and feature point trajectory, trajectory representation results on synthetic shark data, OTSF-NRSFM reconstruction results on synthetic data and real data are analyzed. The results show that the wavelet selection has much influence on OTSF-NRSFM reconstruction results of some non-rigid feature points, which have complicated trajectory. This paper gives researchers some inspiration about wavelet basis selection in OTSF-NRSFM algorithm.

Misperception of rigidity from actively generated optic flow

It is conventionally assumed that the goal of the visual system is to derive a perceptual representation that is a veridical reconstruction of the external world: a reconstruction that leads to optimal accuracy and precision of metric estimates, given sensory information. For example, 3-D structure is thought to be veridically recovered from optic flow signals in combination with egocentric motion information and assumptions of the stationarity and rigidity of the external world. This theory predicts veridical perceptual judgments under conditions that mimic natural viewing, while ascribing nonoptimality under laboratory conditions to unreliable or insufficient sensory information--for example, the lack of natural and measurable observer motion. In two experiments, we contrasted this optimal theory with a heuristic theory that predicts the derivation of perceived 3-D structure based on the velocity gradients of the retinal flow field without the use of egomotion signals or a rigidity prior. Observers viewed optic flow patterns generated by their own motions relative to two surfaces and later viewed the same patterns while stationary. When the surfaces were part of a rigid structure, static observers systematically perceived a nonrigid structure, consistent with the predictions of both an optimal and a heuristic model. Contrary to the optimal model, moving observers also perceived nonrigid structures in situations where retinal and extraretinal signals, combined with a rigidity assumption, should have yielded a veridical rigid estimate. The perceptual biases were, however, consistent with a heuristic model which is only based on an analysis of the optic flow.

Reconstruction of coronary trees from 3DRA using a 3D+t statistical cardiac prior.

A 3D+t description of the coronary tree is important for diagnosis of coronary artery disease and therapy planning. In this paper, we propose a method for finding 3D+t points on coronary artery tree given tracked 2D+t point locations in X-ray rotational angiography images. In order to cope with the ill-posedness of the problem, we use a bilinear model of ventricle as a spatio-temporal constraint on the nonrigid structure of the coronary artery. Based on an energy minimization formulation, we estimate i) bilinear model parameters, ii) global rigid transformation between model and X-ray coordinate systems, and iii) correspondences between 2D coronary artery points on X-ray images and 3D points on bilinear model. We validated the algorithm using a software coronary artery phantom.

A Simple Prior-Free Method for Non-rigid Structure-from-Motion Factorization

This paper proposes a simple "prior-free" method for solving the non-rigid structure-from-motion (NRSfM) factorization problem. Other than using the fundamental low-order linear combination model assumption, our method does not assume any extra prior knowledge either about the non-rigid structure or about the camera motions. Yet, it works effectively and reliably, producing optimal results, and not suffering from the inherent basis ambiguity issue which plagued most conventional NRSfM factorization methods. Our method is very simple to implement, which involves solving a very small SDP (semi-definite programming) of fixed size, and a nuclear-norm minimization problem. We also present theoretical analysis on the uniqueness and the relaxation gap of our solutions. Extensive experiments on both synthetic and real motion capture data (assuming following the low-order linear combination model) are conducted, which demonstrate that our method indeed outperforms most of the existing non-rigid factorization methods. This work offers not only new theoretical insight, but also a practical, everyday solution to NRSfM.

Modeling of porous scaffold deformation induced by medium perfusion

In this study, we tested the possibility of calculating permeability of porous scaffolds utilized in soft tissue engineering using pore size and shape. We validated the results using experimental measured pressure drop and simulations with the inclusion of structural deformation. We prepared Polycaprolactone (PCL) and Chitosan-Gelatin (CG) scaffolds by salt leaching and freeze drying technique, respectively. Micrographs were assessed for pore characteristics and mechanical properties. Porosity for both scaffolds was nearly same but the permeability varied 10-fold. Elastic moduli were 600 and 9 kPa for PCL and CG scaffolds, respectively, while Poisson's ratio was 0.3 for PCL scaffolds and ∼1.0 for CG scaffolds. A flow-through bioreactor accommodating a 10 cm diameter and 0.2 cm thick scaffold was used to determine the pressure-drop at various flow rates. Additionally, computational fluid dynamic (CFD) simulations were performed by coupling fluid flow, described by Brinkman equation, with structural mechanics using a dynamic mesh. The experimentally obtained pressure drop matched the simulation results of PCL scaffolds. Simulations were extended to a broad range of permeabilities (10(-10) m(2) to 10(-14) m(2) ), elastic moduli (10-100,000 kPa) and Poisson's ratio (0.1-0.49). The results showed significant deviation in pressure drop due to scaffold deformation compared to rigid scaffold at permeabilities near healthy tissues. Also, considering the scaffold as a nonrigid structure altered the shear stress profile. In summary, scaffold permeability can be calculated using scaffold pore characteristics and deformation could be predicted using CFD simulation. These relationships could potentially be used in monitoring tissue regeneration noninvasively via pressure drop.

Recursive non-rigid structure from motion with online learned shape prior

Most existing approaches in structure from motion for deformable objects focus on non-incremental solutions utilizing batch type algorithms. All data is collected before shape and motion reconstruction take place. This methodology is inherently unsuitable for applications that require real-time learning. Ideally the online system is capable of incrementally learning and building accurate shapes using current measurement data and past reconstructed shapes. Estimation of 3D structure and camera position is done online. To rely only on the measurements up until that moment is still a challenging problem.In this paper, a novel approach is proposed for recursive recovery of non-rigid structures from image sequences captured by a single camera. The main novelty in the proposed method is an adaptive algorithm for construction of shape constraints imposing stability on the online reconstructed shapes. The proposed, adaptively learned constraints have two aspects: constraints imposed on the basis shapes, the basic “building blocks” from which shapes are reconstructed; as well as constraints imposed on the mixing coefficients in the form of their probability distribution. Constraints are updated when the current model no longer adequately represents new shapes. This is achieved by means of Incremental Principal Component Analysis (IPCA). The proposed technique is also capable to handle missing data. Results are presented for motion capture based data of articulated face and simple human full-body movement.

Adaptive Non-rigid Registration and Structure from Motion from Image Trajectories

This paper addresses the problem of registering a known 3D model to a set of 2D deforming image trajectories. The proposed approach can adapt to a scenario where the 3D model to register is not an exact description of the measured image data. This results in finding a 2D---3D registration, given the complexity of having both 2D deforming data and a coarse description of the image observations. The method acts in two distinct phases. First, an affine step computes a factorization for both the 2D image data and the 3D model using a joint subspace decomposition. This initial solution is then upgraded by finding the best projection to the image plane complying with the metric constraints given by a scaled orthographic camera. Both steps are computed efficiently in closed-form with the additional feature of being robust to degenerate motions which may possibly affect the 2D image data (i.e. lack of relevant rigid motion). A further extension of the approach allows to compute the full 3D deformations of the shape given the first initial (rigid) registration. This step results in solving a Non-rigid Structure from Motion (NRSfM) problem using the 3D known shape as a prior. Experimental results show the robustness of the method in registration tasks such as pose estimation and 3D reconstruction when degenerate image motion is present.

A New-Type Packaging Protection Model of Moulded Pulp on Electron Gun

Electron gun is a kind of fragile and irregular-shape electronic product with multi-material, slender and similarly tube, non-rigid connection structure, which highly demand packaging protection during distribution. In this research work the moulded pulp of inexpensive and environmental-friendly advantages over plastic foams, and excellent machining technique is applied into the transport packaging of electron gun. Firstly, three packaging protection models of moulded pulp (one layer, two layers, and three layers) on electron gun are developed on account of the structural characteristics of electron gun, which have the advantages of compact structure with placement, orientation and fixation, favorable stability, count, and dustproof function for electron gun. Secondly, the package cushioning and vibration-proof performances of these packaging protection models are respectively studied by six groups of drop shock experiments and sine vibration tests of comparison. All results show that, the three packaging protection models of moulded pulp have favorable packaging function, and can provide effective protection for the products of electron gun during storage and transportation.

The Chimeric Genome of Sphaerochaeta : Nonspiral Spirochetes That Break with the Prevalent Dogma in Spirochete Biology

ABSTRACTSpirochaetes is one of a few bacterial phyla that are characterized by a unifying diagnostic feature, namely, the helical morphology and motility conferred by axial periplasmic flagella. Their unique morphology and mode of propulsion also represent major pathogenicity factors of clinical spirochetes. Here we describe the genome sequences of two coccoid isolates of the recently described genus Sphaerochaeta which are members of the phylum Spirochaetes based on 16S rRNA gene and whole-genome phylogenies. Interestingly, the Sphaerochaeta genomes completely lack the motility and associated signal transduction genes present in all sequenced spirochete genomes. Additional analyses revealed that the lack of flagella is associated with a unique, nonrigid cell wall structure hallmarked by a lack of transpeptidase and transglycosylase genes, which is also unprecedented in spirochetes. The Sphaerochaeta genomes are highly enriched in fermentation and carbohydrate metabolism genes relative to other spirochetes, indicating a fermentative lifestyle. Remarkably, most of the enriched genes appear to have been acquired from nonspirochetes, particularly clostridia, in several massive horizontal gene transfer events (>40% of the total number of genes in each genome). Such a high level of direct interphylum genetic exchange is extremely rare among mesophilic organisms and has important implications for the assembly of the prokaryotic tree of life.

Kernel Non-Rigid Structure from Motion.

Non-rigid structure from motion (NRSFM) is a difficult, underconstrained problem in computer vision. The standard approach in NRSFM constrains 3D shape deformation using a linear combination of K basis shapes; the solution is then obtained as the low-rank factorization of an input observation matrix. An important but overlooked problem with this approach is that non-linear deformations are often observed; these deformations lead to a weakened low-rank constraint due to the need to use additional basis shapes to linearly model points that move along curves. Here, we demonstrate how the kernel trick can be applied in standard NRSFM. As a result, we model complex, deformable 3D shapes as the outputs of a non-linear mapping whose inputs are points within a low-dimensional shape space. This approach is flexible and can use different kernels to build different non-linear models. Using the kernel trick, our model complements the low-rank constraint by capturing non-linear relationships in the shape coefficients of the linear model. The net effect can be seen as using non-linear dimensionality reduction to further compress the (shape) space of possible solutions.

The impact of flow induced loads on snap-through behavior of acoustically excited, thermally buckled panels

The analysis, and ultimately the design, of air-breathing hypersonic cruise-type vehicles is hampered by the inability to accurately capture the coupled fluid–thermal–structure interactions. There are few laboratory experiments that have investigated the interactions of compliant surface panels and hypersonic flow. The vast majority of experimental studies are limited to replicating only parts of the physical mechanisms and couplings because of the difficulty in imposing the complete transient, hypersonic environment. Studies of hot-structures, thermal protection systems, or exotic material and structural configurations, typically neglect vibration induced fluctuating pressures, shock-boundary layer interaction, the effect of transition, and separated flow. Conversely, hypersonic wind-tunnel experiments purposely neglect the influence of non-rigid structure on the aforementioned high-speed flow effects in an effort to better understand the nature of the high-speed effects. The goal of this study is to implement a simple computational model that seeks to incorporate many of the fluid–thermal–structure interactions inherent in hypersonic flow. This is accomplished using simplified aerothermal and aerodynamic theories in conjunction with a simply supported von Kármán panel in cylindrical bending. Comparisons are made between the inclusion and exclusion of self-induced and forced fluctuating pressures, as well as the fidelity required in computing the temperature distributions. Results indicate that self-induced pressure fluctuations, which arise from interactions of a vibrating structure with an ambient mean flow, significantly impact the response of panels to random acoustic loadings. Additionally, the inclusion of forced fluctuating pressure loadings can significantly reduce the onset time of panel flutter. It is surmised that experimental investigations must combine thermal loads, as well as both forced and self-induced fluctuating pressures.

The Contribution of Leonardo Torres Quevedo to Lighter-Than-Air Science and Technology

On 5 May 1902, Leonardo Torres Quevedo applied for a patent in France for 'Improvements in dirigible aerostats'. He had conceived a complex triangular inner structure for airships: a longitudinal frame made up of non-rigid ropes, permeable curtains and metal cables, joined to a metal articulated plane keel and two metal longerons, which rigidify altogether through the excess of pressure level of the gas. The initial system evolved to the design of an auto-rigid airship with a trefoil shape based upon a triangular non-rigid inner structure. After trials with two small models in Spain and France between 1906 and 1909, more than thirty units were manufactured in France between 1911 and 1936, and more than sixty in the UK between 1915 and 1919. But the number of different possible systems for the construction of dirigible balloons included in Torresquevedian contribution would cover more than one hundred years in airship designs.

Computing Smooth Time Trajectories for Camera and Deformable Shape in Structure from Motion with Occlusion

We address the classical computer vision problems of rigid and nonrigid structure from motion (SFM) with occlusion. We assume that the columns of the input observation matrix W describe smooth 2D point trajectories over time. We then derive a family of efficient methods that estimate the column space of W using compact parameterizations in the Discrete Cosine Transform (DCT) domain. Our methods tolerate high percentages of missing data and incorporate new models for the smooth time trajectories of 2D-points, affine and weak-perspective cameras, and 3D deformable shape. We solve a rigid SFM problem by estimating the smooth time trajectory of a single camera moving around the structure of interest. By considering a weak-perspective camera model from the outset, we directly compute euclidean 3D shape reconstructions without requiring postprocessing steps such as euclidean upgrade and bundle adjustment. Our results on real SFM data sets with high percentages of missing data compared positively to those in the literature. In nonrigid SFM, we propose a novel 3D shape trajectory approach that solves for the deformable structure as the smooth time trajectory of a single point in a linear shape space. A key result shows that, compared to state-of-the-art algorithms, our nonrigid SFM method can better model complex articulated deformation with higher frequency DCT components while still maintaining the low-rank factorization constraint. Finally, we also offer an approach for nonrigid SFM when W is presented with missing data.

Reconstruction of non-rigid 3D shapes from stereo-motion

Several non-rigid structure from motion methods have been proposed so far in order to recover both the motion and the non-rigid structure of an object. However, these monocular algorithms fail to give reliable 3D shape estimates when the overall rigid motion of the sequence is small. Aiming to overcome this limitation, in this paper we propose a novel approach for the 3D Euclidean reconstruction of deformable objects observed by an uncalibrated stereo rig. Using a stereo setup drastically improves the 3D model estimation when the observed 3D shape is mostly deforming without undergoing strong rigid motion. Our approach is based on the following steps. Firstly, the stereo system is automatically calibrated and used to compute metric rigid structures from pairs of views. Afterwards, these 3D shapes are aligned to a reference view using a RANSAC method in order to compute the mean shape of the object and to select the subset of points which have remained rigid throughout the sequence. The selected rigid points are then used to compute frame-wise shape registration and to robustly extract the motion parameters from frame to frame. Finally, all this information is used as initial estimates of a non-linear optimization which allows us to refine the initial solution and also to recover the non-rigid 3D model. Exhaustive results on synthetic and real data prove the performance of our proposal estimating motion, non-rigid models and stereo camera parameters even when there is no rigid motion in the original sequence.

Trajectory Space: A Dual Representation for Nonrigid Structure from Motion

Existing approaches to nonrigid structure from motion assume that the instantaneous 3D shape of a deforming object is a linear combination of basis shapes. These bases are object dependent and therefore have to be estimated anew for each video sequence. In contrast, we propose a dual approach to describe the evolving 3D structure in trajectory space by a linear combination of basis trajectories. We describe the dual relationship between the two approaches, showing that they both have equal power for representing 3D structure. We further show that the temporal smoothness in 3D trajectories alone can be used for recovering nonrigid structure from a moving camera. The principal advantage of expressing deforming 3D structure in trajectory space is that we can define an object independent basis. This results in a significant reduction in unknowns and corresponding stability in estimation. We propose the use of the Discrete Cosine Transform (DCT) as the object independent basis and empirically demonstrate that it approaches Principal Component Analysis (PCA) for natural motions. We report the performance of the proposed method, quantitatively using motion capture data, and qualitatively on several video sequences exhibiting nonrigid motions, including piecewise rigid motion, partially nonrigid motion (such as a facial expressions), and highly nonrigid motion (such as a person walking or dancing).

Objective 3D face recognition: Evolution, approaches and challenges

Face recognition is a natural human ability and a widely accepted identification and authentication method. In modern legal settings, a lot of credence is placed on identifications made by eyewitnesses. Consequently these are based on human perception which is often flawed and can lead to situations where identity is disputed. Therefore, there is a clear need to secure identifications in an objective way based on anthropometric measures. Anthropometry has existed for many years and has evolved with each advent of new technology and computing power. As a result of this, face recognition methodology has shifted from a purely 2D image-based approach to the use of 3D facial shape. However, one of the main challenges still remaining is the non-rigid structure of the face, which can change permanently over varying time-scales and briefly with facial expressions. The majority of face recognition methods have been developed by scientists with a very technical background such as biometry, pattern recognition and computer vision. This article strives to bridge the gap between these communities and the forensic science end-users. A concise review of face recognition using 3D shape is given. Methods using 3D shape applied to data embodying facial expressions are tabulated for reference. From this list a categorization of different strategies to deal with expressions is presented. The underlying concepts and practical issues relating to the application of each strategy are given, without going into technical details. The discussion clearly articulates the justification to establish archival, reference databases to compare and evaluate different strategies.

Case Scenario: Perioperative Airway Management of a Patient with Tracheal Stenosis

TRACHEAL stenosis is a rare but a life-threatening condition and is caused by congenital problems, postintubation injury, trauma, tracheal tumor, and compression of the trachea by tumor. Although accurate prevalence of this condition is unknown, an incidence of 4.9 cases per million per year is estimated for postintubation tracheal stenosis. A stenosis commonly occurs at the cuff of the tube (intrathoracic trachea) or at the level of the tracheostomy stoma (extrathoracic trachea). Anesthesia of a patient with tracheal stenosis is challenging for anesthesiologists. Depending on the severity and location of the stenosis and the type of surgical procedure, there may be a variety of choices for perioperative airway management such as a facemask, laryngeal mask airway, an tracheal intubation tube, cardiopulmonary bypass, and extracorporeal membrane oxygenation. The American Society of Anesthesiologists practice guidelines for management of the difficult airway primarily focus airway problems caused at the extrathoracic airway and may not be helpful, particularly for managing patients with intrathoracic tracheal stenosis. In this case scenario, we present a patient with severe intrathoracic tracheal stenosis, who required surgery for a lumbar fracture in the prone position. Various airway management strategies and the actual management used are discussed.

Iron−Ceria Aerogels Doped with Palladium as Water−Gas Shift Catalysts for the Production of Hydrogen

Mixed 4.5% iron oxide−95.5% cerium oxide aerogels doped with 1% and 2% palladium (Pd) by weight have been synthesized, and their activities for the catalysis of water−gas shift (WGS) reaction have been determined. The aerogels were synthesized using propylene oxide as the proton scavenger for the initiation of hydrolysis and polycondensation of a homogeneous alcoholic solution of cerium(III) chloride heptahydrate and iron(III) chloride hexahydrate precursor. Palladium was doped onto some of these materials by gas-phase incorporation (GPI) using (η3-allyl)(η5-cyclopentadienyl)palladium as the volatile Pd precursor. Water−gas shift catalytic activities were evaluated in a six-channel fixed-bed reactor at atmospheric pressure and reaction temperatures ranging from 150 to 350 °C. Both 1% and 2% Pd-doped 4.5% iron oxide−95.5% cerium oxide aerogels showed WGS activities that increased significantly from 150 to 350 °C. The activities of 1% Pd-doped 4.5% iron oxide−95.5% cerium oxide aerogels were also compared with that of the 1% Pd-doped ceria aerogel without iron. The WGS activity of 1% Pd on 4.5% iron oxide−95.5% cerium oxide aerogels is substantially higher (∼5 times) than the activity of 1% Pd-doped ceria aerogel without iron. The gas-phase incorporation results in a better Pd dispersion. Ceria aerogel provides a nonrigid structure wherein iron is not significantly incorporated inside the matrix, thereby resulting in better contact between the Fe and Pd and thus enhancing the WGS activity. Further, neither Fe nor Pd is reduced during the ceria-aerogel-catalyzed WGS reaction. This behavior contrasts with that noted for other Fe-based WGS catalysts, in which the original ferric oxide is typically reduced to a nonstoichiometric magnetite form.

Convex Optimization for Nonrigid Stereo Reconstruction

We present a method for recovering 3-D nonrigid structure from an image pair taken with a stereo rig. More specifically, we dedicate to recover shapes of nearly inextensible deformable surfaces. In our approach, we represent the surface as a 3-D triangulated mesh and formulate the reconstruction problem as an optimization problem consisting of data terms and shape terms. The data terms are model to image keypoint correspondences which can be formulated as second-order cone programming (SOCP) constraints using L(infinity) norm. The shape terms are designed to retaining original lengths of mesh edges which are typically nonconvex constraints. We will show that this optimization problem can be turned into a sequence of SOCP feasibility problems in which the nonconvex constraints are approximated as a set of convex constraints. Thanks to the efficient SOCP solver, the reconstruction problem can then be solved reliably and efficiently. As opposed to previous methods, ours neither involves smoothness constraints nor need an initial estimation, which enables us to recover shapes of surfaces with smooth, sharp and other complex deformations from a single image pair. The robustness and accuracy of our approach are evaluated quantitatively on synthetic data and qualitatively on real data.

Nearly automatic motion capture system for tracking octopus arm movements in 3D space

Tracking animal movements in 3D space is an essential part of many biomechanical studies. The most popular technique for human motion capture uses markers placed on the skin which are tracked by a dedicated system. However, this technique may be inadequate for tracking animal movements, especially when it is impossible to attach markers to the animal's body either because of its size or shape or because of the environment in which the animal performs its movements. Attaching markers to an animal's body may also alter its behavior. Here we present a nearly automatic markerless motion capture system that overcomes these problems and successfully tracks octopus arm movements in 3D space. The system is based on three successive tracking and processing stages. The first stage uses a recently presented segmentation algorithm to detect the movement in a pair of video sequences recorded by two calibrated cameras. In the second stage, the results of the first stage are processed to produce 2D skeletal representations of the moving arm. Finally, the 2D skeletons are used to reconstruct the octopus arm movement as a sequence of 3D curves varying in time. Motion tracking, segmentation and reconstruction are especially difficult problems in the case of octopus arm movements because of the deformable, non-rigid structure of the octopus arm and the underwater environment in which it moves. Our successful results suggest that the motion-tracking system presented here may be used for tracking other elongated objects.