Adjacent Mesh Research Articles

A fine-grained orthodontics segmentation model for 3D intraoral scan data

With the widespread application of digital orthodontics in the diagnosis and treatment of oral diseases, more and more researchers focus on the accurate segmentation of teeth from intraoral scan data. The accuracy of the segmentation results will directly affect the follow-up diagnosis of dentists. Although the current research on tooth segmentation has achieved promising results, the 3D intraoral scan datasets they use are almost all indirect scans of plaster models, and only contain limited samples of abnormal teeth, so it is difficult to apply them to clinical scenarios under orthodontic treatment. The current issue is the lack of a unified and standardized dataset for analyzing and validating the effectiveness of tooth segmentation. In this work, we focus on deformed teeth segmentation and provide a fine-grained tooth segmentation dataset (3D-IOSSeg). The dataset consists of 3D intraoral scan data from more than 200 patients, with each sample labeled with a fine-grained mesh unit. Meanwhile, 3D-IOSSeg meticulously classified every tooth in the upper and lower jaws. In addition, we propose a fast graph convolutional network for 3D tooth segmentation named Fast-TGCN. In the model, the relationship between adjacent mesh cells is directly established by the naive adjacency matrix to better extract the local geometric features of the tooth. Extensive experiments show that Fast-TGCN can quickly and accurately segment teeth from the mouth with complex structures and outperforms other methods in various evaluation metrics. Moreover, we present the results of multiple classical tooth segmentation methods on this dataset, providing a comprehensive analysis of the field. All code and data will be available at https://github.com/MIVRC/Fast-TGCN.

Comparison of internal boundary conditions for optical diffusion calculations considering reflection and refraction

A method to treat the internal boundary condition in an optical diffusion calculation is proposed and is compared with the conventional methods. One of the existing internal boundary conditions is Haskel's method, which uses the effective reflection coefficient for partial currents. However, Haskel's method ignores incoming partial currents from the adjacent mesh in its derivation. As a result, the accuracy at the internal boundary is lower. This paper proposes a method to improve the accuracy by iteratively updating the effective reflection coefficient for partial current. The proposed method was applied to the benchmark calculations on a one-dimensional slab geometry and its accuracy was confirmed by comparing it with the reference solution obtained by the Monte Carlo code MCML, along with the previously proposed Haskel's method and Aronson's method. As a result, it was confirmed that the proposed method is more accurate than Haskel's method at the internal boundary and gives the same result as Aronson's method. The convergence of the effective reflection coefficient using iterative calculations in the proposed method was good.

An efficient model for predicting complex delamination front of elastic coupling laminates

This work proposes a simple and efficient model to predict the variable crack front with any shape. The model contains a propagation criterion which defines the local growth direction of the delamination crack front by the vector perpendicular to the connection line of two adjacent mesh points. The angle between this vector and the pre-crack direction is calculated by the coordinates of two delamination front points. Crack front can be obtained by the local direction changes of the historical crack front. This model avoids the computing time caused by a high-fidelity finite element model. Its applicability is verified for composite laminates without coupling and with different couplings. The predicted crack front shows good agreements with the numerical results obtained by a high-fidelity FE model with refined mesh. Factors controlling the crack front shape are further discussed by analyzing strain energy release rate and mode mixture distribution at the crack front.

Mesh Oversegmentation with Segmentation-Aware Loss

Superfacets are generated by clustering adjacent mesh faces that share similar characteristics, which can serve as processing units in downstream mesh applications. While there are existing deep neural networks that generate superpixels and superpoints/supervoxels from images and point clouds respectively, the current oversegmentation methods in 3D meshes mostly rely on hand-crafted features that are extracted using non-differentiable algorithms to generate superfacets. Nevertheless, these methods cannot leverage the feature extraction abilities of deep neural networks to generate superfacets in an end-to-end fashion. Therefore, we propose an end-to-end trainable deep neural network that learns to generate boundary-aware superfacets from 3D meshes. Specifically, our network learns a soft face-superfacet association map from faces and their adjacency relationships. Moreover, we develop a segmentation-aware loss on the faces that train the network to predict their labels in an end-to-end manner. We evaluate the performance of our method using mesh adaptations of two well-known superpixel evaluation metrics where experimental results demonstrate that the performance of our proposed network surpasses that of other state-of-the-art mesh oversegmentation methods, and in doing so simultaneously improves superfacet-based semantic segmentation.

Efficient reduced order model based on the proper orthogonal decomposition for time-dependent MOC calculations

ABSTRACT An efficient reduced order model (ROM) for time-dependent transport calculations using the method of characteristics (MOC) is proposed. In the present ROM, the flux distributions and the net neutron currents between the adjacent unstructured mesh regions are taken from the MOC solution. Then, the coefficient matrices for the MOC-equivalent diffusion equation are reconstructed from them. The proper orthogonal decomposition (POD) is applied for the MOC-equivalent diffusion equation to reduce the degree of freedoms (DOFs) using the orthogonal bases obtained by the singular value decomposition (SVD) for the sampled MOC solution. The accuracy and computation time of the present ROM are verified in the C5G7-TD 2D benchmark problem. The calculation results show that the present ROM enables us approximately 5000–6000 times faster computation than the full order model (FOM) for kinetic calculations itself in the present calculation condition. The present method can be substituted as real-time simulations without the spatial homogenization when typical flux distributions and the net neutron currents of a target problem can be precalculated.

Biocrust succession improves soil aggregate stability of subsurface after “Grain for Green” Project in the Hilly Loess Plateau, China

Soil aggregate stability is often used as the key indicate to evaluate soil degradation or soil erodibility. Numerous studies have indicated that biological soil crusts (biocrusts) can stabilise the soil surface by increasing the aggregate stability. In the end of the 20th century, the “Grain for Green” ecological project was implemented in most areas of the Loess Plateau, leading to the widespread distribution and succession of biocrusts in the open spaces between vascular plants in the abandoned farmlands. However, the effects of biocrust succession on the soil aggregate stability of subsurface remain poorly explored. Thus, to determine how biocrust succession affect subsurface soil aggregate stability, we investigated a cropland and 5 abandoned farmlands sites that have developed over three to 30 years in the Loess Plateau region of China. Then we measured the amounts of water stable aggregates of subsurface soil underlying different successional stage biocrusts (bare soil, cyanobacterial crust, cyanobacteria-moss mixed crust, and moss crust) by using wet-sieving method, and summed the mass fraction of soil remaining on each sieve after sieving multiplied by the mean aperture of the adjacent mesh (mean weight diameter) to characterise the soil aggregate stability. In addition, we analysed the complex correlations among age of farmland abandonment, biocrust succession, soil organic matter, clay fraction, and aggregate stability using structural equation modelling (SEM). The results are as follows: (1) the mean weight diameter (MWD) in the subsurface soil increased with the biocrust succession. The MWD in the 0–2-cm soil layer beneath moss crusts was 2.33 mm, 7.3 times as much as that of cropland sites. (2) The later successional stage biocrusts (mixed crust and moss crust) improved the deeper soil aggreggate stability compared with the early successional stage biocrusts. The MWD in 0–2-cm layer of the cyanobacterial crust was significantly higher than those of the lower layers, while MWDs in 0–2-cm and 0–5-cm layers of the later successional stage biocrust were significantly higher than that of 5–10-cm layer. (3) The SEM results confirmed that in the 0–5-cm layer, biocrust succession indirectly improved the stability of aggregates by increasing soil organic matter (SOM). There was a highly significant linear relationship between MWD of 0–5-cm layer and biocrust succession parameter (moss biomass) (R2 = 0.35, P = 0.002). In the 5–10-cm layer, the SOM still significantly influenced the aggregate stability, but the biocrusts had no significant effect on the SOM in this layer. The results suggest that biocrusts should be considered a crucial factor in soil stability and be used as an effective rehabilitative tool for restoring lands in dryland regions.

A micro electromagnetic actuator with high force density

In this paper, we propose a planar type micro electromagnetic actuator with high force density. The actuator is composed of a mover (8 mm*8 mm*0.5 mm) and a stator (14mm*10mm*0.2 mm). As the mover, a thick NdFeB permanent magnet film (300 μm) with a chessboard pattern (unit size is 0.8 mm*0.8 mm) is attached with a ferromagnetic back yoke to provide enhanced magnetic flux density. In the stator, 3D mesh type micro coil with multi-turn configuration is designed accordingly. The micro coil has a novel connection between adjacent mesh units, which enables easy fabrication. The thick film magnet with chessboard pattern as well as the multi-turn micro coil with novel connection constitute the originality of this actuator. The mover and the stator can be produced by batch fabrication. The magnetic flux density (B) generated by the magnet are simulated and experimentally measured. The magnitude of B at vertical direction attains around 40 m T at 770 μm plane above the surface. Due to delicate design, the MEMS-based micro coil can withstand as high as 0.4A constant current input for over 60 min on a thermal isolated ceramic plate. The long-time duration experiment testifies the practicality of this micro actuator. Both repulsive and attractive electromagnetic force can be generated on the mover by altering the current direction in the stator. The measured force is around 4.3 mN at 20 μm gap with 0.1A stable current input in the stator and the force density attains as high as 0.96 mN/A/mm3.

Facile fabrication of nonswellable and biocompatible hydrogels with cartilage-comparable performances

The preparation of high-performance hydrogels from biocompatible materials via a facile process has been increasingly studied but remains challenging. Herein, a nonswellable and biocompatible hydrogel was fabricated from polyvinyl alcohol and chitosan by multiple physical interactions without harmful crosslinkers. Owing to the synergy of salting-out effect and tridentate coordination, the network uniformity and stability were improved greatly. Compared with the precursor PVA-CS hydrogel, the crosslinking density increases from 76.9 to 157.8 mmol/cm3 accompanied by an increase in the gel fraction from 58.6 to 91.5%. In contrast, the average molecular weight between adjacent knots and mesh size decrease from 1650 to 1096 g/mol and from 6.1 to 4.8 nm, respectively. Benefited from the higher cross-linking density and more homogeneous gel framework, the obtained hydrogel exhibits cartilage-equivalent mechanical properties (tensile strength = 4.5 MPa, tensile strain = 299 %, elastic modulus = 1.2 MPa, toughness = 6.5 MJ m−3 and compressive stress = 8.4 MPa), combined with a high water content of 84.3 %. Remarkably, this hydrogel demonstrates excellent anti-swelling property due to the combination of high cross-linking density, water-resistant knots and dialysis process. The hydrogel barely expands after immersion in a PBS aqueous solution at 37 °C for 28 days. Moreover, both the tensile and compressive stresses remain exactly the same as their initial values, which is superior to most reported swelling-resistant hydrogels. Furthermore, the hydrogel shows good creep resistance upon external loading and cytocompatibility with HeLa cells, making it an ideal material for biotechnological applications. The full-fledged starting materials and facile methods of this hydrogel show its high potential for scale up and use in industrial applications.

Precise localization of neutron noise sources based on transport theory and comparison with diffusion theory

In an attempt to explore the significance of transport theory in neutron noise, localization of a noise source by Green’s function based on transport theory is investigated. There are considerable differences between Green’s functions based on diffusion and transport, such as small dimensions, near edges, high heterogeneity medium and high-frequency source of perturbation. These differences are expected to significantly impact unfolding, reconstruction, and identification of the neutron noise source. Improvement in noise source unfolding methods is essential in terms of safety aspects and reactor performance enhancement. Since gaining the ability to monitor nuclear reactor based on noise diagnostics principle using few numbers of detectors is a challenging problem, more accurate methods of calculation of neutron noise can help reduce the detectors in number and sensitivity to location. This study revealed that inverse Green’s function based on diffusion and transport is fundamentally different in concept. The inverse Green’s function based on diffusion theory requires applying complicated reconstruction methods to gain more accurate results. This means that a large number of detectors must be used for noise source reconstruction. In contrast, in the case of inverse Green’s function based on transport theory, each mesh's shape function is strongly correlated with the adjacent mesh. As a result, simple methods can be used to reconstruct the noise source. Therefore, the noise source can be identified and reconstructed with a smaller number of detectors in practical terms.

New hybrid FDTD algorithm for electromagnetic problem analysis**Project supported by the National Natural Science Foundation of China (Grant No. 61571348) and the Equipment Pre-Research Foundation of China (Grant No. 61405180202).

Since the time step of the traditional finite-difference time-domain (FDTD) method is limited by the small grid size, it is inefficient when dealing with the electromagnetic problems of multi-scale structures. Therefore, the explicit and unconditionally stable FDTD (US-FDTD) approach has been developed to break through the limitation of Courant–Friedrich–Levy (CFL) condition. However, the eigenvalues and eigenvectors of the system matrix must be calculated before the time iteration in the explicit US-FDTD. Moreover, the eigenvalue decomposition is also time consuming, especially for complex electromagnetic problems in practical application. In addition, compared with the traditional FDTD method, the explicit US-FDTD method is more difficult to introduce the absorbing boundary and plane wave. To solve the drawbacks of the traditional FDTD and the explicit US-FDTD, a new hybrid FDTD algorithm is proposed in this paper. This combines the explicit US-FDTD with the traditional FDTD, which not only overcomes the limitation of CFL condition but also reduces the system matrix dimension, and introduces the plane wave and the perfectly matched layer (PML) absorption boundary conveniently. With the hybrid algorithm, the calculation of the eigenvalues is only required in the fine mesh region and adjacent coarse mesh region. Therefore, the calculation efficiency is greatly enhanced. Furthermore, the plane wave and the absorption boundary introduction of the traditional FDTD method can be directly utilized. Numerical results demonstrate the effectiveness, accuracy, stability, and convenience of this hybrid algorithm.

A partition of unity approach to adaptivity and limiting in continuous finite element methods

The partition of unity finite element method (PUFEM) proposed in this paper makes it possible to blend space and time approximations of different orders in a continuous manner. The lack of abrupt changes in the local mesh size h and polynomial degree p simplifies implementation and eliminates the need for using sophisticated hierarchical data structures. In contrast to traditional hp-adaptivity for finite elements, the proposed approach preserves discrete conservation properties and the continuity of traces at common boundaries of adjacent mesh cells. In the context of space discretizations, a continuous blending function is used to combine finite element bases corresponding to high-order polynomials and piecewise-linear approximations based on the same set of nodes. In a similar vein, spatially partitioned time discretizations can be designed using weights that depend continuously on the space variable. The design of blending functions may be based on a priori knowledge (e.g., in applications to problems with singularities or boundary layers), local error estimates, smoothness indicators, and/or discrete maximum principles. In adaptive methods, changes of the finite element approximation exhibit continuous dependence on the data. The presented numerical examples illustrate the typical behavior of local H1 and L2 errors.

Dry separation using a fluidized Sink-Hole

Dry separation of heavy-mineral particles such as iron ore in the nominal size range of 1–10 mm is a significant challenge. This paper reports the findings of dry separation experiments conducted under batch conditions using a novel device referred to as the Sink-Hole fluidizer. The device utilizes a fluidized bed, with vibration applied as an additional energy source to disrupt the tendency of the excess air to pass through as bubbles. The fluidized bed is covered by a fine mesh containing holes with a nominal 1 mm square aperture. A much larger hole located at the centre acts as the “Sink-Hole”. When the system is fluidized the media expands, passing up through the Sink-Hole, spilling onto the adjacent mesh, and sifting back into the lower bed. For this work nominal 200 μm sand was used as the bed media. Tracer particles of density 2.4 to 4.8 RD, covering the size range from 2.0 to 8.0 mm, were added onto the mesh. The vibration caused the particles to repeatedly pass over the Sink-Hole, resulting in some sinking through the media, and others remaining on the mesh. By adjusting the mass of sand in the system and the superficial air velocity, it was possible to vary the separation density from 2.5 to 3.2 RD, whilst holding the Ep values in the range 0.1 to 0.2 RD.

Intensity control of individual DBD plasma filament. II. Fundamental physical mechanism

Filamentary volume dielectric barrier discharge (DBD) produces patterned plasma structures that are currently being explored for reconfigurable metamaterial applications. Previous work has demonstrated control of the presence and intensity of a single DBD plasma filament (within an array of filaments) by biasing a low voltage needle electrode. The results were attributed to redistributed charge inside the DBD due to the modified electric field created by the needle electrode. In the present work, results from a 3D electrodynamic field simulation bolster this argument. Results show that increasing needle bias voltage causes changes in the transverse electric field structure, resulting in redistribution and build-up of surface charge at the needle location. This reduces the needle plasma filament intensity and eventually extinguishes the filament. Specifically, extinguishment of the filament corresponds with the following transitions in the field profile: (1) the applied longitudinal electric field profile along the needle lies below that of the adjacent mesh filament; (2) the surface charge on the dielectric at the needle and adjacent mesh locations is equal; and (3) the transverse electric field reverses direction and forces charge toward the needle location. The calculated surface charge on the dielectric barrier agrees with experimentally measured filament light intensity to within 8%, in agreement with theoretical predictions. Analysis of the data and trends suggests a method for predicting filament pattern formation and reducing the necessary voltage bias.

Seamless images stitching for 3D human models.

Realistic 3D human model reconstruction is an important component in computer graphics and computer vision. In particular, texturing on the surface of models is a key stage of reconstruction. In this paper, we dispose the texture mapping on the model’s surface as an optimization of image stitching, and present an effective method to generate a seamless, integrated and smooth texture on the surface of 3D human model. First, we build a corresponding Markov Random Field model with respect to color images and triangular meshes of the surface. On the basis of alpha-expansion optimization for this Markov Random Field model, a 2D translation coordinate of color image, as an adaptive iterative factor, is introduced into the optimization to match the color content at the boundary of adjacent meshes. That compensates for the misalignment of adjacent color images, which caused by the inaccuracy of depth data and multi-view misregistration. Then we apply Poisson blending to a composite vector field in gradient domain, to resolve the small but noticeable illumination variations between different color images. To repair the blank regions, we parameterize the model’s surface and project it onto a 2D plane. Then the K-Nearest Neighbor algorithm is applied to fill up the blank regions with texture contents. Finally, we evaluate our method by comparison with another three advanced methods on some human models, and the results demonstrate that our method of images stitching creates a best texture on the surface of 3D human model both in visual effect and quantitative analysis.

Precise trajectory optimization for articulated wheeled vehicles in cluttered environments

Trajectory planning refers to planning a time-dependent path connecting the initial and final configurations with some special constraints simultaneously considered. It is a critical aspect in autonomously driving an articulated vehicle. In this paper, trajectory planning is formulated as a dynamic optimization problem that contains kinematic differential equations, mechanical/environmental constraints, boundary conditions and an optimization objective. The prevailing numerical methods for solving the formulated dynamic optimization problem commonly disregard the constraint satisfactions between every two adjacent discretized mesh points, thus resulting in failure when the planned motions are actually implemented. As a remedy for this limitation, the concept of minute mesh grid is proposed, which improves the constraint satisfactions between adjacent rough mesh points. On the basis of accurate penalty functions, large-scale constraints are successfully incorporated into the optimization criterion, thus transforming the dynamic optimization problem into a static one with simple bounds on the decision variables. Simulation results verify that our proposed methodology can provide accurate results and can deal with various optimization objectives uniformly.

A Boundary Condition-Implemented Immersed Boundary-Lattice Boltzmann Method and Its Application for Simulation of Flows Around a Circular Cylinder

A boundary condition-implemented immersed boundary-lattice Boltzmann method (IB-LBM) is presented in this work. The present approach is an improvement to the conventional IB-LBM. In the conventional IB-LBM, the no-slip boundary condition is only approximately satisfied. As a result, there is flow penetration to the solid boundary. Another drawback of conventional IB-LBM is the use of Dirac delta function interpolation, which only has the first order of accuracy. In this work, the no-slip boundary condition is directly implemented, and used to correct the velocity at two adjacent mesh points from both sides of the boundary point. The velocity correction is made through the second-order polynomial interpolation rather than the first-order delta function interpolation. Obviously, the two drawbacks of conventional IB-LBM are removed in the present study. Another important contribution of this paper is to present a simple way to compute the hydrodynamic forces on the boundary from Newton’s second law. To validate the proposed method, the two-dimensional vortex decaying problem and incompressible flow over a circular cylinder are simulated. As shown in the present results, the flow penetration problem is eliminated, and the obtained results compare very well with available data in the literature.

Adaptive mesh refinement method for optimal control using nonsmoothness detection and mesh size reduction

An adaptive mesh refinement method for solving optimal control problems is developed. The method employs orthogonal collocation at Legendre–Gauss–Radau points, and adjusts both the mesh size and the degree of the approximating polynomials in the refinement process. A previously derived convergence rate is used to guide the refinement process. The method brackets discontinuities and improves solution accuracy by checking for large increases in higher-order derivatives of the state. In regions between discontinuities, where the solution is smooth, the error in the approximation is reduced by increasing the degree of the approximating polynomial. On mesh intervals where the error tolerance has been met, mesh density may be reduced either by merging adjacent mesh intervals or lowering the degree of the approximating polynomial. Finally, the method is demonstrated on two examples from the open literature and its performance is compared against a previously developed adaptive method.

A Boundary Condition-Implemented Immersed Boundary-Lattice Boltzmann Method and Its Application for Simulation of Flows Around a Circular Cylinder

AbstractA boundary condition-implemented immersed boundary-lattice Boltzmann method (IB-LBM) is presented in this work. The present approach is an improvement to the conventional IB-LBM. In the conventional IB-LBM, the no-slip boundary condition is only approximately satisfied. As a result, there is flow penetration to the solid boundary. Another drawback of conventional IB-LBM is the use of Dirac delta function interpolation, which only has the first order of accuracy. In this work, the no-slip boundary condition is directly implemented, and used to correct the velocity at two adjacent mesh points from both sides of the boundary point. The velocity correction is made through the second-order polynomial interpolation rather than the first-order delta function interpolation. Obviously, the two drawbacks of conventional IB-LBM are removed in the present study. Another important contribution of this paper is to present a simple way to compute the hydrodynamic forces on the boundary from Newton’s second law. To validate the proposed method, the two-dimensional vortex decaying problem and incompressible flow over a circular cylinder are simulated. As shown in the present results, the flow penetration problem is eliminated, and the obtained results compare very well with available data in the literature.

VISUAL DESIGN TOOL FOR ELECTROSTATIC LELSES

Current research presents a visual-computational tool to design and investigate round electrostatic lenses in sense of analysis procedure. The finite elements methods is adopted to find the electrostatic potential in the lens region. Laplace’s equation is first replaced by a certain functional which physically represent the electric energy stored in the electric field. This functional is then minimized at each mesh point with respect to the nearest eight ones. This minimization process is proved to be entirely equivalent to solving Laplace’s equation. The requirement that the functional being minimized is then yields a set of nine point equations which inter relate the potentials at adjacent mesh points. Finally this set of equations is solved to find the electrostatic potential at each mesh point in the region of the lens under consideration. The procedure steps mention above are coded to program written in visual basic. Hence an interface tool for analyzing and designing electrostatic lenses has been built up. Designing results proved that the introduced tools has an excellent outputs in comparison with the others written in not visual programming languages. Furthermore it easier for researchers and designer to use such a tool over their counterpart ones.

Management of Urinary Fistulas Due to Midurethral Sling Surgery

We report our experience with the diagnosis and treatment of women with urinary fistula after mid urethral sling surgery. We retrospectively reviewed the records of patients with urinary fistula secondary to mid urethral sling surgery. Electronic medical records and billing records were searched. We analyzed sling type, presenting symptoms and interval from initial sling surgery to 1) symptom appearance, 2)fistula diagnosis and 3) fistula repair. Symptomatic outcomes were assessed byPGI-I. Surgical outcomes were based on history and examination. We identified 10 women with a mean age of 58 years (range 37 to 70). Mean interval from mid urethral sling surgery to symptom onset, diagnosis andfistula repair was 2, 16 and 18 months, respectively. Mean followup was 26months (range 4 to 96). There were 1 ureterovaginal, 1 enterovesical, 6 vesicovaginal and 7 urethrovaginal fistulas. Patients presented with stress urinary incontinence (70%), unaware incontinence (50%), overactive bladder (40%), pelvic pain (30%) and voiding symptoms (20%). Nine women underwent fistula repair and 1 underwent continent urinary diversion. A Martius flap was used in 6 of 9patients, an omental flap and a bladder wall flap were used in 2 each, urethral reconstruction and ureterocolovesicostomy were performed in 1 each and 7 received an autologous pubovaginal sling. Seven patients (78%) underwent successful fistula repair. A successful symptomatic outcome was achieved in 5 of 7women with stress urinary incontinence, 3 of 5 with unaware incontinence, 3 of 4 with overactive bladder, 2 of 3 with pelvic pain and 2 of 2 with voiding symptoms. With careful attention to surgical principles and technique, including removal of as much of the adjacent mesh as possible, a successful outcome can be achieved in most patients with a fistula secondary to mid urethral sling surgery.