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1.
The present paper studies nonreflecting boundary-conditions for the 2-D unsteady nonlinear Euler equations, applied to the propagation of monochromatic pressure-waves in a uniform mean flow. Various boundary-conditions (1-D nonlinear, approximate linearized 2-D, and exact linearized 2-D) are compared for a wide range of both propagating and decaying waves. An original methodology, based on a moving-averages technique, is developed for the application of the exact linearized boundary-conditions, which requires the computation of 2-D (space–time) Fourier coefficients. It is shown that the exact linearized boundary-conditions yield very low reflection, and also that the approximate conditions may perform poorly in difficult cases. The reflection-coefficient shows some correlation with the group-velocity (direction and Mach-number) of the reflected waves, suggesting that proposed nonreflecting boundary-conditions should always be validated against the entire range of group-velocities.  相似文献   

2.
Through theoretical investigation on the nonvolatile holographic storage in photochromic LiNbO3∶Fe∶Mn, we have found self-enhancement effect caused by beam-coupling effect during both recording and optical fixing phases, and proceeded a steady-state analysis and a numerical simulation about the effect. The experimental results obtained by self-enhancement and self-depletion are consistent with the theoretical analysis. From the theoretical and experimental studies, it is seen that the highest diffraction efficiency available from the self-enhancement during both the recording and fixing phases may be twice as large as the lowest one from the self-depletion. It demonstrates that self-enhancement effect has to be considered and utilized in practical applications for nonvolatile holographic storage. To the best of our knowledge, it is the first time to report the relevant results.  相似文献   

3.
Efficient weapon threat assignment reflects military proficiency and requires prompt decision while managing the available resources. An important problem which commanders/decision makers face is to optimally utilize the resources in complex and time constraints situations. Several solutions have been proposed in the literature. In this paper, an innovative approach is proposed for threat evaluation and weapon assignment (TEWA) by following 3-dimensional stable marriage algorithm (3-D SMA). This proposed model incorporates new parameters and constraints i.e. supply chain, inventory of resources and multiple threats-weapons assignments that outperforms the previous techniques. This suggested model is based on threat perception followed by an integration of parametric based automatic threat evaluation technique for further weapon scheduling and assignment problem keeping in view that the threat with greater threat index has higher priority to be intercepted and weapons’ kill probability. The experimental section shows that our proposed approach has greatly improved in comparison with other approaches. The results showed that the threat neutralization is improved up to 25% reducing the usage of ammunition till 31.1%. The damage of assets abridged to 28.5% in comparison with existing approaches. The proposed approach elucidates that TEWA is an efficient real-time threat perception and optimal multi-threat scheduling problem at weapons’ resolution. It is a three-stage process, where the first stage perceives the threat, the second stage works on threat evaluation and the final stage focuses on weapon scheduling and assignment problem. The addition of new parameters and constraints in the new proposed model makes it a unique approach in which more accurate results, in neutralizing the threats, are obtained with less use of ammunition and damage of assets that makes TEWA more effective and efficient tool for optimum decision making in time critical situations.  相似文献   

4.
Recently, meshfree-based computational modelling approaches have become popular in modelling biological phenomena due to their superior ability to simulate large deformations, multiphase phenomena and complex physics compared to the conventional grid-based methods. In this article, small plant cell aggregates were simulated using a three dimensional (3-D) Smoothed Particle Hydrodynamics (SPH) and Coarse-Grained (CG) coupled computational approach to predict the morphological behaviour during drying. The model predictions of these cell aggregate models have been compared qualitatively and quantitatively through comparisons with experimental findings. The results show that the shrinkage and wrinkling behaviour of cell cluster models are in fairly good agreement with real cellular structures. The agreement between the cell aggregate model predictions and the experimental findings are closer in the high and medium moisture content values (X/X0 ≥ 0.3), than highly dried stages (X/X0 < 0.3). Further, optimisation and sensitivity studies have been conducted on model parameters such as particle resolution, smoothing length, mass transfer characteristics and wall forces. Overall, the 3-D nature of this model allows it to predict real 3-D morphological changes more realistically compared to the previous meshfree based 2-D cellular drying models. The proposed 3-D modelling approach has a higher potential to be used to model larger plant tissues with complicated physical and mechanical interactions as well as their multiscale interactions.  相似文献   

5.
A new method to compute the first derivative of 3-D Radon transform is given for cone-beam data taken from any orbit. Smith [Ⅰ1] and Grangeat [5] even derived cone-beam inversion formulas which are the basic work in fully 3-D image reconstruction algorithm and are used extensively now. In this paper we will give a new inversion formula and a simple necessary and sufficient condition which guarantees the complete reconstruction algorithm.  相似文献   

6.
Open cell foams are a class of modern materials which is interesting for a wide variety of applications and which is not accessible to classical materialography based on 2d images. 3d imaging by micro computed tomography is a practicable alternative. Analysis of the resulting volume images is either based on a simple binarisation of the image or on so-called cell reconstruction by image processing. The first approach allows to estimate mean characteristics like the mean cell volume using the typical cell of a random spatial tessellation as model for the cell shape. The cell reconstruction allows estimation of empirical distributions of cell characteristics. This paper summarises the theoretical background for the first method, in particular estimation of the intrinsic volumes and their densities from discretized data and models for random spatial tessellations. The accuracy of the estimation method is assessed using the dilated edge systems of simulated random spatial tessellations.  相似文献   

7.
We present a method for compressing binary images via monochromatic pattern substitution. Such method has no relevant loss of compression effectiveness if the image is partitioned into up to a thousand blocks, approximately, and each block is compressed independently. Therefore, it can be implemented on a distributed system with no interprocessor communication. In the theoretical context of unbounded parallelism, interprocessor communication is needed. Compression effectiveness has a bell-shaped behaviour which is again competitive with the sequential performance when the highest degree of parallelism is reached. Finally, the method has a speed-up if applied sequentially to an image partitioned into up to 256 blocks. It follows that such speed-up can be applied to a parallel implementation on a small scale system.  相似文献   

8.
The paper presents numerical algorithms leading to an automated cell tracking and reconstruction of the cell lineage tree during the first hours of animal embryogenesis. We present results obtained for large-scale 3D+time two-photon laser scanning microscopy images of early stages of zebrafish (Danio rerio) embryo development. Our approach consists of three basic steps – the image filtering, the cell centers detection and the cell trajectories extraction yielding the lineage tree reconstruction. In all three steps we use nonlinear partial differential equations. For the filtering the geodesic mean curvature flow in level set formulation is used, for the cell center detection the motion of level sets by a constant speed regularized by mean curvature flow is used and the solution of the eikonal equation is essential for the cell trajectories extraction. The core of our new tracking method is an original approach to cell trajectories extraction based on finding a continuous centered paths inside the spatio-temporal tree structures representing cell movement and divisions. Such paths are found by using a suitably designed distance function from cell centers detected in all time steps of the 3D+time image sequence and by a backtracking in the steepest descent direction of a potential field based on this distance function. We also present efficient and naturally parallelizable discretizations of the aforementioned nonlinear PDEs and discuss properties and results of our new tracking method on artificial and real 4D data.  相似文献   

9.
In this paper, we discuss a class of nonlinear parabolic-hyperbolic equations which could be applied to image restoration. After theoretical analysis, we give an experimental approach to show the efficiency of this kind of model.  相似文献   

10.
Explicit exponential lower bounds for the chromatic numbers of spaces with forbidden monochromatic regular simplexes are found for the first time.  相似文献   

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