Simple Boundary Research Articles

Simplified wetting boundary scheme in phase-field lattice Boltzmann model for wetting phenomena on curved boundaries.

In this work, a simplified wetting boundary scheme in the phase-field lattice Boltzmann model is developed for wetting phenomena on curved boundaries. The proposed scheme combines the advantages of the fluid-solid interaction scheme and geometric scheme-easy to implement (no need to interpolate the values of parameters exactly on solid boundaries and find proper characteristic vectors), the value of contact angle can be directly prescribed, and no unphysical spurious mass layer-and avoids mass leakage. Different from previous works, the values of the order parameter gradient on fluid boundary nodes are directly determined according to the geometric formulation rather than indirectly regulated through the order parameters on ghost solid nodes (i.e., ghost contact-line region). For this purpose, two numerical approaches to evaluate the order parameter gradient on fluid boundary nodes are utilized, one with the prevalent isotropic central scheme and the other with a local gradient scheme that utilizes the distribution functions. The simplified wetting boundary schemes with both numerical approaches are validated and compared through several numerical simulations. The results demonstrate that the proposed model has good ability and satisfactory accuracy to simulate wetting phenomena on curved boundaries under large density ratios.

Solution of a Parabolic Hamilton–Jacobi Type Equation Determined by a Simple Boundary Singularity

Solution of a Parabolic Hamilton–Jacobi Type Equation Determined by a Simple Boundary Singularity

Sequential monitoring of stock market price changes

In 2016, Eugene Fama mentioned that he wanted a systematic way of identifying and predicting a stock market bubble. This paper develops a statistical method to sequentially monitor the stock market price changes. A new simple boundary function is proposed and asymptotic properties are established. In the empirical application, we successfully detect that the U.S. dot-com bubble occurred around June 1997 using the S&P 500 and Nasdaq indices.

Linear and conservative IMEX Runge–Kutta finite difference schemes with provable energy stability for the Cahn–Hilliard model in arbitrary domains

The Cahn–Hilliard (CH) equation is a classical mathematical equation which models the spinodal decomposition in binary fluid mixtures. In the real world, the phase change in a two-phase system usually occurs in irregular domains. To efficiently and accurately simulate this dynamics, we herein develop linear temporally first- and second-order accurate methods for the CH equation in arbitrary domains. The implicit-explicit (IMEX) Runge–Kutta method is adopted to construct discrete schemes in time. By introducing a simple boundary control function, we transform the original equations into equivalent forms in irregular domains and discretize the space by using the standard second-order finite difference stencil. In each temporal step, the proposed numerical schemes are highly efficient and easy to implement because we only need to solve several linear elliptic type equations. The mass conservation and unconditional energy stability of the proposed schemes are analytically proved. The multigrid algorithm is adopted for fast computation. The numerical results confirm the desired accuracy in time and space, mass conservation, and energy dissipation property. Moreover, the extensive calculations in two- and three-dimensional spaces indicate that the proposed method has good capability to simulate spinodal decomposition in arbitrarily irregular domains.

Dirichlet and Neumann boundary conditions in a lattice Boltzmann method for elastodynamics

AbstractRecently, Murthy et al. (Commun Comput Phys 2:23, 2017. http://dx.doi.org/10.4208/cicp.OA-2016-0259 ) and Escande et al. (Lattice Boltzmann method for wave propagation in elastic solids with a regular lattice: theoretical analysis and validation, 2020. arXiv.doi:1048550/ARXIV.2009.06404. arXiv:2009.06404) adopted the Lattice Boltzmann Method (LBM) to model the linear elastodynamic behaviour of isotropic solids. The LBM is attractive as an elastodynamic solver because it can be parallelised readily and lends itself to finely discretised simulations of dynamic effects in continua, allowing transient phenomena such as wave propagation to be modeled efficiently. This work proposes simple local boundary rules which approximate the behaviour of Dirichlet and Neumann boundary conditions with an LBM for elastic solids. The boundary rules are shown to be consistent with the target boundary values in the first order. An empirical convergence study is performed for the transient tension loading of a rectangular plate, with a Finite Element (FE) simulation being used as a reference. Additionally, we compare results produced by the LBM for the sudden loading of a stationary crack with an analytical solution from Freund (Dynamic fracture mechanics. Cambridge Monographs on Mechanics. Cambridge University Press, Cambridge, 1990. https://doi.org/10.1017/CBO9780511546761).

Static analysis of orthotropic nanoplates reinforced by defective graphene based on strain gradient theory using a simple boundary method

Static analysis of orthotropic nanoplates reinforced by defective graphene based on strain gradient theory using a simple boundary method

Alignment Integration Network for Salient Object Detection and Its Application for Optical Remote Sensing Images.

Salient object detection has made substantial progress due to the exploitation of multi-level convolutional features. The key point is how to combine these convolutional features effectively and efficiently. Due to the step by step down-sampling operations in almost all CNNs, multi-level features usually have different scales. Methods based on fully convolutional networks directly apply bilinear up-sampling to low-resolution deep features and then combine them with high-resolution shallow features by addition or concatenation, which neglects the compatibility of features, resulting in misalignment problems. In this paper, to solve the problem, we propose an alignment integration network (ALNet), which aligns adjacent level features progressively to generate powerful combinations. To capture long-range dependencies for high-level integrated features as well as maintain high computational efficiency, a strip attention module (SAM) is introduced into the alignment integration procedures. Benefiting from SAM, multi-level semantics can be selectively propagated to predict precise salient objects. Furthermore, although integrating multi-level convolutional features can alleviate the blur boundary problem to a certain extent, it is still unsatisfactory for the restoration of a real object boundary. Therefore, we design a simple but effective boundary enhancement module (BEM) to guide the network focus on boundaries and other error-prone parts. Based on BEM, an attention weighted loss is proposed to boost the network to generate sharper object boundaries. Experimental results on five benchmark datasets demonstrate that the proposed method can achieve state-of-the-art performance on salient object detection. Moreover, we extend the experiments on the remote sensing datasets, and the results further prove the universality and scalability of ALNet.

Characterizing and understanding galaxies with two parameters

ABSTRACT We report the discovery of a 2D Galaxy Manifold within the multidimensional luminosity space of local galaxies. The multidimensional luminosity space is constructed using 11 bands that span from far ultraviolet to near-infrared for redshift < 0.1 galaxies observed with GALEX, SDSS, and UKIDSS. The manifold captures the diversity of observed galaxies in terms of stellar-dominated emissions and ties the correlations of various physical properties to the manifold. We find that two latent parameters are sufficient to express 93.2 per cent of the variance in the galaxy sample, suggesting that this Galaxy Manifold is one of the most efficient representations of galaxies. The transformation between the observed luminosities and the manifold parameters as an analytic mapping is provided. The manifold representation provides accurate (precision = 0.85) morphological classifications with a simple linear boundary, and galaxy properties can be estimated with minimal scatter (0.12 and 0.04 dex for star formation rate and stellar mass, respectively) by calibrating with the 2D manifold location. Under the assumption that the manifold expresses the possible parameter space of galaxies, the evolution on the manifold is considered. We find that constant and exponentially decreasing star formation histories form almost orthogonal modes of evolution on the manifold. Through these simple models, we understand that the two modes are closely related to gas content, which suggests the close relationship of the manifold to gas accretion. Lastly, the found manifold suggests a paradigm where galaxies are characterized by their mass/scale and specific SFR, which agrees with previous studies of dimensionality reduction.

Target volume delineation for radiotherapy of meningiomas: an ANOCEF consensus guideline

PurposeRadiotherapy is, with surgery, one of the main therapeutic treatment strategies for meningiomas. No prospective study has defined a consensus for the delineation of target volumes for meningioma radiotherapy. Therefore, target volume definition is mainly based on information from retrospective studies that include heterogeneous patient populations. The aim is to describe delineation guidelines for meningioma radiotherapy as an adjuvant or definitive treatment with intensity-modulated radiation therapy and stereotactic radiation therapy techniques. This guideline is based on a consensus endorsed by a multidisciplinary group of brain tumor experts, members of the Association of French-speaking Neuro-oncologists (ANOCEF).Materials and methodsA 3-step procedure was used. First, the steering group carried out a comprehensive review to identify divergent issues on meningiomas target volume delineation. Second, an 84-item web-questionnaire has been developed to precisely define meningioma target volume delineation in the most common clinical situations. Third, experts members of the ANOCEF were requested to answer. The first two rounds were completed online. A third round was carried out by videoconference to allow experts to debate and discuss the remaining uncertain questions. All questions remained in a consensus.ResultsLimits of the target volume were defined using visible landmarks on computed tomography and magnetic resonance imaging, considering the pathways of tumor extension. The purpose was to develop clear and precise recommendations on meningiomas target volumes.ConclusionNew recommendations for meningiomas delineation based on simple anatomic boundaries are proposed by the ANOCEF. Improvement in uniformity in target volume definition is expected.

Closed-Form ZVS Boundaries for Three-Phase M-Level-to-N-Level DAB Converters With Different Winding Configurations

One of the essential characteristics of a three-phase dual-active-bridge (DAB) DC-DC converter is its inherent zero-voltage switching (ZVS) capability during the turn-on of the switches. This paper provides closed-form equations that identify the ZVS boundaries for an M-level-to-N-level DAB converter, where M and N can be any natural numbers. It is shown that the derived ZVS boundaries can be used for different converter topologies, including but not limited to: two-level full-bridge converter, three-level neutral-point-clamped converter, T-type converter, transition arm converter, modular multilevel converter, and controlled-transition-bridge converter. The effect of different winding configurations of the medium frequency transformer—YY, Y <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta$</tex-math></inline-formula> , and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta \Delta$</tex-math></inline-formula> —is also considered in the study. Additionally, easy-to-implement simplified ZVS boundaries are provided, and the effects of the different number of levels, transition times, and dead times on the ZVS operation are quantified. An important result shown is that the converters with the YY and the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta \Delta$</tex-math></inline-formula> windings lose ZVS at partial loads as soon as the transition time increases from zero, whereas the ones with the Y <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta$</tex-math></inline-formula> configuration retain ZVS at partial loads and DC ratios close to unity, without any advanced modulation techniques. The derived analytical models are validated with MATLAB simulations and experiments.

Natural vibration of elastic metamaterial beam under arbitrary elastic boundary conditions

Elastic metamaterial (EM) is a kind of new composite material/structure that provides a new feasible way of vibration control in many scenarios. Although some analytical means for solving the vibration behavior of EM components with simple shapes and classic boundary conditions (BCs) have been presented, the analyses of those with complex shapes or BCs that are common in reality remain to be studied further. In this paper, the natural vibration problem of a typical EM beam under arbitrary elastic boundary conditions (EBC) is investigated by using the effective medium theory (EMT) and the Rayleigh-Ritz method. The inherent correlations between the EM beam and corresponding modified matrix beam together with the modified static equivalent beam are disclosed for their modal behaviors. The extraordinary natural vibration properties of the EM beam under arbitrary EBC are revealed and some common features are concluded. This work may provide a useful reference for further investigations of many other similar EM structures.

Developing a Biomechanical Testing Setup of the Pelvis-Part II: Experimental Testing.

Biomechanical testbench emulating the physiological loading of the pelvis is crucial in developing reconstructive implants for fragility fractures of the pelvis. Additionally, it will help understand the influence of the common daily loading on the pelvic ring. However, most reported experimental studies were mainly comparative with simplified loading and boundary conditions. In Part I of our study, we described the concept of the computational experiment design to design and construct a biomechanical testbench emulating the gait movement of the pelvis. The 57 muscles and joints' contact forces were reduced to four force actuators and one support, producing a similar stress distribution. The experimental setup is explained in this paper and some experimental results are presented. In addition, a series of repeatability and reproducibility tests were conducted to assess the test stand capabilities of replicating the gait physiological loading. The calculated stresses and the experimentally recorded strains showed that the pelvic ring response to the loading always follows the loaded leg side during the gait cycle. Furthermore, the experimental results of the pelvis displacement and strain at selected locations match the numerical ones. The developed test stand and the concept of computational experiment design behind it provide guidelines on how to design biomechanical testing equipment with physiological relevance.

Reliable design of urban surface-underground integrated logistics system network with stochastic demand and social-environmental concern

Transforming urban goods movement from roads to underground is an emerging concept to improve supply chain performance and alleviate overcrowded environments. Existing literature merely discussed the underground logistics system (ULS) network design problem within a simplified boundary, whereas several critical system features (e.g., stochastic freight demand and co-modality) were omitted. To bridge the knowledge gaps, this paper proposes a reliable modeling approach to solve an urban surface-underground integrated logistics network (USUIL) design problem with a holistic consideration of cost-benefit objectives, road-ULS modal split, and demand uncertainties. To begin with, we introduce a city-wide hub-and-spoke USUIL network structure with a two-tier parallel distribution process. Five major external benefits of underground goods movement are formulated using real-world data. Next, a deterministic model is developed to optimize the network decisions including hub-satellite location-allocation, deployment of tunnels and pipelines, logistics service assignment, and flow routing. Then, to deal with the influences of case-wise demand uncertainties, the model is reformulated into a reliable one by incorporating the ideas of solution robustness and stochastic equivalents. A two-stage heuristic-based optimization tool that hybridizes the adaptive immune genetic algorithm, plant growth simulation algorithm, and Clarke-Wright saving algorithm was proposed to solve the problem. Finally, numerical experiments are conducted on the Beijing city case to validate the proposed method, and the best network schemes obtained from different models and scenarios are compared. Results show that a greater robust control factor in our model helps the network to lower the integrated freight transport cost while improving the social-environmental benefit at the expense of deploying more facilities. The reliable model performs well in balancing the conservativeness (i.e., less capacity insufficiency risk) and optimality (i.e., less cost due to redundant facilities) of the USUIL network design when faced with diverse demand cases.

New Laboratory Experiments to Study the Large-Scale Circulation and Climate Dynamics

The large-scale flows of the oceans and the atmosphere are driven by a non-uniform surface heating over latitude, and rotation. For many years scientists try to understand these flows by doing laboratory experiments. In the present paper we discuss two rather new laboratory experiments designed to study certain aspects of the atmospheric circulation. One of the experiments, the differentially heated rotating annulus at the Brandenburg University of Technology (BTU) Cottbus, has a cooled inner cylinder and a heated outer wall. However, the structure of the atmospheric meridional circulation motivates a variation of this “classical” design. In the second experiment described, operational at the Institute of Continuous Media Mechanics (ICMM) in Perm, heating and cooling is performed at different vertical levels that resembles more the atmospheric situation. Recent results of both experiments are presented and discussed. Differences and consistencies are highlighted. Though many issues are still open we conclude that both setups have their merits. The variation with heating and cooling at different levels might be more suited to study processes in the transition zone between pure rotating convection and the zone of westerly winds. On the other hand, the simpler boundary conditions of the BTU experiment make this experiment easier to control.

Structure and Migration Mechanisms of Small Vacancy Clusters in Cu: A Combined EAM and DFT Study.

Voids in face-centered cubic (fcc) metals are commonly assumed to form via the aggregation of vacancies; however, the mechanisms of vacancy clustering and diffusion are not fully understood. In this study, we use computational modeling to provide a detailed insight into the structures and formation energies of primary vacancy clusters, mechanisms and barriers for their migration in bulk copper, and how these properties are affected at simple grain boundaries. The calculations were carried out using embedded atom method (EAM) potentials and density functional theory (DFT) and employed the site-occupation disorder code (SOD), the activation relaxation technique nouveau (ARTn) and the knowledge led master code (KLMC). We investigate stable structures and migration paths and barriers for clusters of up to six vacancies. The migration of vacancy clusters occurs via hops of individual constituent vacancies with di-vacancies having a significantly smaller migration barrier than mono-vacancies and other clusters. This barrier is further reduced when di-vacancies interact with grain boundaries. This interaction leads to the formation of self-interstitial atoms and introduces significant changes into the boundary structure. Tetra-, penta-, and hexa-vacancy clusters exhibit increasingly complex migration paths and higher barriers than smaller clusters. Finally, a direct comparison with the DFT results shows that EAM can accurately describe the vacancy-induced relaxation effects in the Cu bulk and in grain boundaries. Significant discrepancies between the two methods were found in structures with a higher number of low-coordinated atoms, such as penta-vacancies and di-vacancy absortion by grain boundary. These results will be useful for modeling the mechanisms of diffusion of complex defect structures and provide further insights into the structural evolution of metal films under thermal and mechanical stress.

A Novel Sensing Feature Extraction Based on Mold Temperature and Melt Pressure for Plastic Injection Molding Quality Assessment

Injection molding is one of the polymer molding methods. Product quality mainly can be affected by temperature and pressure. To observe the process of the melt forming in the mold, it is required to monitor the signal with the sensor. To achieve the purpose of robust molding, this research provides a new design-process window architecture based on machine learning of the injection product quality assessment. The process window is also known as the forming area map. The monitored value for defective products will be above or below the variable limit. The process is set to the center of this window so that any variation within the window will still result in an acceptable product. There are some potential problems in the current process. First, the conventional process window uses a small number of process variables as monitoring indicators, and it cannot provide stronger monitoring indicators. Second, most of the conventional process windows are 2-D and there are many monitoring windows, so the information that can be monitored is limited. Therefore, product quality cannot be effectively monitored without proper selection of important factors. Finally, the current process window can only provide information in the process and cannot make product quality prediction. In order to solve the above problems, a machine learning method is proposed to design the process window. The random forest classifier and regressor are used to predict the product quality. In order to improve the usability of the factor, the design of the proposed new variable is derived from the classical formula of thermodynamics (heat conduction). Using existing factors and proposing time-based feature changes can better represent the molding process as a whole. Based on the experimental results, the proposed variables can effectively increase the predictive performance of random forest model for quality assessment. The research results make a satisfactory result to the quality assessment of industrial injection molding. The accuracy of the prediction results is 100%. Moreover, it can be found from the 3-D process window that the data are very concentrated and can be clearly classified by the hyperplane, which is defined as the shortest distance between two clusters, and this space is the boundary of the process window. Therefore, compared with the past, the judgment boundary based on the random forest process window is no longer a simple boundary. Random forests can provide more accurate visualization boundaries.

P–T Phase Diagram of Phosphorus Revisited

Melting and phase transitions of phosphorus allotropes have been studied in the 2–11 GPa pressure range using in situ electrical resistivity measurements and synchrotron X-ray diffraction. It was found that the melting curve of rhombohedral phosphorus exhibits a positive slope of 58(2) K/GPa and crosses the rhombohedral–simple cubic phase boundary (negative slope of −420(70) K/GPa) at about 8.3 GPa and 1490 K. The melting slope of simple cubic phosphorus can be estimated to be +300(90) K/GPa. Calculations of phosphorus phase equilibria have been performed using our experimental and literature data within the framework of the phenomenological thermodynamics. The constructed equilibrium p–T phase diagram accurately describes the experimentally observed phase relations in solid and liquid phosphorus up to 12 GPa and 2000 K.

Point cloud simplification for the boundary preservation based on extracted four features

This paper proposes a simplification algorithm based on four feature parameters, aiming at solving the problem that the edge features cannot be retained due to the incompletely extracted sharp features during point cloud simplification. Firstly, K neighborhood searching is carried out for point cloud, and K neighborhood points are quickly found by a dynamic grid method. Then, four features including: the curvature of the point, the average of the normal angle of a point from a neighborhood point, the average distance between the point and the neighborhood point and the distance between the point and the center of gravity of the neighborhood point, are calculated according to the K neighborhood of the data point. The four parameters are used to define the feature discrimination parameters and feature thresholds, to compare the size and extract the feature points; finally, the non-feature points are reduced twice by the method of the bounding box, and the reduced point cloud and feature points are spliced to achieve the purpose of simplification. The experimental results show that the distance between the point and the center of gravity of the neighborhood has a great influence on the simplified model boundary, which effectively guarantees the accuracy of the simplified model.

A New Hydrodynamic Spherical Accretion Exact Solution and Its Quasi-spherical Perturbations

We present an exact γ = 5/3 spherical accretion solution that modifies the Bondi boundary condition of as r → ∞ to ρ → 0 as r → ∞. This change allows for simple power-law solutions on the density and infall velocity fields, ranging from a cold empty freefall condition where pressure tends to zero, to a hot hydrostatic equilibrium limit with no infall velocity. As in the case of the Bondi solution, a maximum accretion rate appears. As in the γ = 5/3 case of the Bondi solution, no sonic radius appears, this time however, because the flow is always characterized by a constant Mach number. This number equals 1 for the case of the maximum accretion rate, diverges toward the cold empty state, and becomes subsonic toward the hydrostatic equilibrium limit. It can be shown that in the limit r → 0, the Bondi solution tends to the new solution presented, extending the validity of the Bondi accretion value to cases where the accretion density profile does not remain at a fixed constant value out to infinity. We then explore small deviations from sphericity and the presence of angular momentum through an analytic perturbative analysis. Such perturbed solutions yield a rich phenomenology through density and velocity fields in terms of Legendre polynomials, which we begin to explore for simple angular velocity boundary conditions having zeros on the plane and pole. The new solution presented provides complementary physical insight into accretion problems in general.

The influence of boundary scattering phase shift on melting behavior of nanoparticles

Based on the Lindemann melting criterion and the lattice dynamical approach, we analytically estimated the melting temperature of nanoparticles with emphasis on the influence of the boundary scattering phase shift parameter α . With the decrease of size, the estimated relation shows that the melting temperature of free standing like nanoparticles will decrease, and the melting temperature of embedded nanoparticles will increase. The increase or decrease of the melting temperature depends on the boundary scattering phase shift parameter. The gradual change of parameter α from − 1 to 1 corresponds to the transition of the surface or environment of nanoparticles from the free boundary condition to the fixed boundary condition. Our analytical estimation qualitatively explains the experimental data, and its predictive capability will help the design of nanoparticles. • Based on the Lindemann criterion, An analytical estimation for size-dependent melting temperature of nanoparticles by lattice dynamical method will be given. • Our theoretical result can fit experimental data of nanoparticles in different environments qualitatively. • A simple boundary scattering phase shift is used to characterize the environment of nanoparticles.