共查询到20条相似文献,搜索用时 31 毫秒
1.
Tapered metal wires show a remarkable ability to ‘squeeze’ the lateral extent of a propagating surface-plasmon-polariton mode
as it travels toward the tip of the taper. The transformation can be continued well below the diffraction limit to terminate
at a nanoscale apex where intense near-fields are created. We perform the first full numerical simulations to investigate
and quantify this phenomenon. We find optimal angles for maximal tip-field enhancement on conical wires by considering absorption,
scattering to radiation and reflection. The optimal parameters we obtain contradict the conditions for adiabatic tapering,
thereby advocating the use of numerical simulations. Despite the influence of losses, nanofocusing is still highly efficient
for a broad range of practical metals, visible wavelengths and taper geometries. Diverse nano-optic applications can benefit
directly and significantly from the results. 相似文献
2.
Mir-Hossein Moosavi Hamid Katoozian Ali Pashaei Oscar Camara Alejandro F. Frangi 《Computer methods in biomechanics and biomedical engineering》2014,17(7):740-749
Understanding cardiac blood flow patterns has many applications in analysing haemodynamics and for the clinical assessment of heart function. In this study, numerical simulations of blood flow in a patient-specific anatomical model of the left ventricle (LV) and the aortic sinus are presented. The realistic 3D geometry of both LV and aortic sinus is extracted from the processing of magnetic resonance imaging (MRI). Furthermore, motion of inner walls of LV and aortic sinus is obtained from cine-MR image analysis and is used as a constraint to a numerical computational fluid dynamics (CFD) model based on the moving boundary approach. Arbitrary Lagrangian–Eulerian finite element method formulation is used for the numerical solution of the transient dynamic equations of the fluid domain. Simulation results include detailed flow characteristics such as velocity, pressure and wall shear stress for the whole domain. The aortic outflow is compared with data obtained by phase-contrast MRI. Good agreement was found between simulation results and these measurements. 相似文献
3.
The current paper accounts for the influence of intra-specific competition among predators in a prey dependent tri-trophic food chain model of interacting populations. We offer a detailed mathematical analysis of the proposed food chain model to illustrate some of the significant results that has arisen from the interplay of deterministic ecological phenomena and processes. Biologically feasible equilibria of the system are observed and the behaviours of the system around each of them are described. In particular, persistence, stability (local and global) and bifurcation (saddle-node, transcritical, Hopf–Andronov) analysis of this model are obtained. Relevant results from previous well known food chain models are compared with the current findings. Global stability analysis is also carried out by constructing appropriate Lyapunov functions. Numerical simulations show that the present system is capable enough to produce chaotic dynamics when the rate of self-interaction is very low. On the other hand such chaotic behaviour disappears for a certain value of the rate of self interaction. In addition, numerical simulations with experimented parameters values confirm the analytical results and shows that intra-specific competitions bears a potential role in controlling the chaotic dynamics of the system; and thus the role of self interactions in food chain model is illustrated first time. Finally, a discussion of the ecological applications of the analytical and numerical findings concludes the paper. 相似文献
4.
In this article, we aim at giving a non-technical overview of some mathematical models currently used in the numerical simulation of the cardiovascular system. A hierarchy of models for blood flows in large arteries is briefly described as well as an electromechanical model for the heart. We discuss some possible applications of the numerical simulations of such models, for example the optimization of prostheses. We also address the issue of the data assimilation for the calibration of the models. 相似文献
5.
A new design for the multilayer superlens, with the sub-wavelength imaging ability for various 2D objects in the visible range, is introduced and analyzed. The designed superlens will be more versatile for practical applications. A rigorous and efficient approach based on the method of moments is used to study the imaging performance of this structure. The imaging performance of the proposed superlens is evaluated using the correlation coefficient. In this work, the closed-form dyadic Green’s functions in spatial domain, needed for the method of moments solutions, are obtained by applying the complex image method. Besides, the numerical integration is exploited to verify this method. The imaging results obtained via our approach are examined by comparison with the finite element method simulations that reveal good efficiency and accuracy of the proposed method. 相似文献
6.
V. A. Koldanov A. M. Gorbachev A. L. Vikharev D. B. Radishchev 《Plasma Physics Reports》2005,31(11):965-977
Results are presented from numerical simulations of pulse-periodic and continuous microwave discharges in hydrogen that are used in CVD reactors for chemical vapor deposition of diamond films. Attention is focused on the processes that should be taken into account in order to construct the simplest possible adequate numerical model. It is shown that the processes of vibrational excitation of hydrogen molecules, as well as chemical reactions, play an important role in the establishment of energy balance within the discharges. The results of numerical simulations are compared to the experimental data. 相似文献
7.
DEM Numerical Simulation of Abrasive Wear Characteristics of a Bioinspired Ridged Surface 总被引:3,自引:0,他引:3
Jin Tong Mohammad Almagzoub Mohammad Jinbo Zhang Yunhai Ma Baojun Rong Donghui Chen Carlo Menon 《仿生工程学报(英文版)》2010,7(2):175-181
<正> This paper presents numerical investigations into a ridged surface whose design is inspired by the geometry of a Farrer'sscallop.The objective of the performed research is to assess if the proposed Bioinspired Ridged Surface (BRS) can potentiallyimprove wear resistance of soil-engaging components used in agricultural machinery and to validate numerical simulationsperformed using software based on the Discrete Element Method (DEM).The wear performance of the BRS is experimentallydetermined and also compared with a conventional flat surface.Different size of soil particles and relative velocities between theabrasive sand and the testing surfaces are used.Comparative results show that the numerical simulations are in agreement withthe experimental results and support the hypothesis that abrasive wear is greatly reduced by substituting a conventional flatsurface with the BRS. 相似文献
8.
9.
Finite element implementation of a generalized Fung-elastic constitutive model for planar soft tissues 总被引:1,自引:0,他引:1
Numerical simulations of the anisotropic mechanical properties of soft tissues and tissue-derived biomaterials using accurate constitutive models remain an important and challenging research area in biomechanics. While most constitutive modeling efforts have focused on the characterization of experimental data, only limited studies are available on the feasibility of utilizing those models in complex computational applications. An example is the widely utilized exponential constitutive model proposed by Fung. Although present in the biomechanics literature for several decades, implementation of this model into finite element (FE) simulations has been limited. A major reason for limited numerical implementations are problems associated with inherent numerical instability and convergence. To address this issue, we developed and applied two restrictions for a generalized Fung-elastic constitutive model necessary to achieve numerical stability. These are (1) convexity of the strain energy function, and (2) the condition number of material stiffness matrix set lower than a prescribed value. These constraints were implemented in the nonlinear regression used for constitutive model parameter estimation to the experimental biaxial mechanical data. We then implemented the generalized Fung-elastic model into a commercial FE code (ABAQUS, Pawtucket, RI, USA). Single element and multi-element planar biaxial test simulations were conducted to verify the accuracy and robustness of the implementation. Results indicated that numerical convergence and accurate FE implementation were consistently obtained. The present study thus presents an integrated framework for accurate and robust implementation of pseudo-elastic constitutive models for planar soft tissues. Moreover, since our approach is formulated within a general FE code, it can be straightforwardly adopted across multiple software platforms. 相似文献
10.
ABSTRACT: BACKGROUND: Stochastic biochemical reaction networks are commonly modelled by the chemical master equation, and can be simulated as first order linear differential equations through a finite state projection. Due to the very high state space dimension of these equations, numerical simulations are computationally expensive. This is a particular problem for analysis tasks requiring repeated simulations for different parameter values. Such tasks are computationally expensive to the point of infeasibility with the chemical master equation. RESULTS: In this article, we apply parametric model order reduction techniques in order to construct accurate low-dimensional parametric models of the chemical master equation. These surrogate models can be used in various parametric analysis task such as identifiability analysis, parameter estimation, or sensitivity analysis. As biological examples, we consider two models for gene regulation networks, a bistable switch and a network displaying stochastic oscillations. CONCLUSIONS: The results show that the parametric model reduction yields efficient models of stochastic biochemical reaction networks, and that these models can be useful for systems biology applications involving parametric analysis problems such as parameter exploration, optimization, estimation or sensitivity analysis. 相似文献
11.
Christian Schulze Danny Vogel Manuela Sander Rainer Bader 《Computer methods in biomechanics and biomedical engineering》2019,22(1):25-37
Polyurethane (PU) foam is a material often used in biomechanical experiments and demands for the definition of crushable foam plasticity (CFP) in numerical simulations of the primary stability and deformation of implants, to describe the crushing behaviour appropriately. Material data of PU foams with five different densities (10–40 pounds per cubic foot were ascertained experimentally in uniaxial compression test and used to calibrate CFP models for finite element modelling. Additionally, experimental and numerical deformation, push-out and lever-out tests of press-fit acetabular cups were carried out to assess the influence of the chosen material definition (linear elastic and CFP) on the numerical results. Comparison of the experimentally and numerically determined force–displacement curves of the uniaxial compression test showed a mean deviation of less than 3%. In primary stability testing, the deviation between the experimental and numerical results was in a range of 0%–27% for CFP modelling and 64%–341% for the linear elastic model. The material definition selected, highly influenced the numerical results in the current study. The use of a CFP model is recommended for further numerical simulations, when a deformation of the foam beyond the yield strength is likely to occur. 相似文献
12.
《Journal of Biomedical Engineering》1984,6(1):49-55
A finite element formulation of the Navier-Stokes equations for three dimensional flow is presented. The equations are solved using the finite element method. The model is constructed from a cast of a human aortic bifurcation. The numerical problems introduced by solving the equation system are discussed and special attention is paid to the selection of the linear equation solver. The simulations of the steady blood flow patterns in an aortic bifurcation is shown. The results of the numerical analysis are presented as three dimensional plots of velocity vectors, wall shear vectors, streamlines and pressure isobars. The flow simulations are done for Reynolds number 10. The flow patterns found in the bifurcation model are discussed in connection with proposed theories to explain the event of early atherosclerosis. 相似文献
13.
Advances in information technologies have made network data increasingly frequent in a spectrum of big data applications, which is often explored by probabilistic graphical models. To precisely estimate the precision matrix, we propose an optimal model averaging estimator for Gaussian graphs. We prove that the proposed estimator is asymptotically optimal when candidate models are misspecified. The consistency and the asymptotic distribution of model averaging estimator, and the weight convergence are also studied when at least one correct model is included in the candidate set. Furthermore, numerical simulations and a real data analysis on yeast genetic data are conducted to illustrate that the proposed method is promising. 相似文献
14.
Chia-Yang Tsai Che-Yao Wu Kai-Hau Chang Po-Tsung Lee 《Plasmonics (Norwell, Mass.)》2013,8(2):1011-1016
We present detailed experimental and numerical studies of plasmonic properties of gold nanoring (NR) arrays with different slab thicknesses from 15 to 125 nm. The hybrid plasmon resonances for the bonding and antibonding modes in gold NRs exhibit a high slab thickness dependence behavior in optical properties. For the thinner slab thickness below 50 nm, both hybrid modes show large spectral tunabilities by varying the slab thickness. Furthermore, for such hollow NR structure, the enhancements of electric field intensities at the inner and outer ring surfaces when reducing the slab thickness are investigated. We observe a significant transition of field distributions for the antibonding mode. All these features can be understood by surface charge distributions from our simulations. The results of this study offer a potential strategy to design a composite plasmonic nanostructure with large field enhancement for numerous applications. 相似文献
15.
It is known that surfactants can induce flow in unsaturated porous media due to the dependence of capillary pressure on surface tension. A commonly observed feature in systems with surfactant-induced flow is a transient wetting/drying/wetting sequence associated with the propagation of a surfactant solute front under monotonic flow conditions. Previous efforts to model surfactant-induced flow in relatively complex (e.g., two-dimensional systems) have not successfully incorporated hysteretic moisture retention properties. In this research, hysteretic, two-dimensional simulations of surfactant-induced flow were performed to assess the potential importance of considering hysteresis in such simulations. Hysteretic simulation results were compared to experimental data and to non-hysteretic simulations. The results suggest that the inclusion of hysteresis in numerical simulations can improve the match between simulated and experimental results in systems with surfactant-induced unsaturated flow. Furthermore, the inclusion of hysteresis in numerical simulations played a significant role in predicting the distribution of the contaminant and correct pressure head/moisture condition at the end of the experiment. 相似文献
16.
O. S. Vaulina 《Plasma Physics Reports》2009,35(5):385-393
An approximation is proposed for energy density in two-dimensional nonideal systems for a wide class of isotropic repulsive pair interparticle potentials. The approximation allows one to determine the main thermodynamic functions and characteristics of the system by using well-known thermodynamic formulas. The results obtained with the help of this approximation are compared with the data of numerical simulations of thermodynamic properties of the structures under study. The simulations were performed in a wide range of parameters typical of laboratory dusty plasmas. Main attention was paid to the screened Coulomb potential. 相似文献
17.
S. A. Maiorov 《Plasma Physics Reports》2001,27(4):293-302
Collisional heating of plasma electrons in the field of an ultraintense ultrashort laser pulse is studied. The numerical results obtained by the method of molecular dynamics are compared with the well-known results from kinetic simulations. A model is proposed that provides a good agreement with the results of calculations for both linearly and circularly polarized high-intensity laser pulses. 相似文献
18.
Applications of computational fluid dynamics (CFD) in the modelling and design of ventilation systems in the agricultural industry: a review 总被引:1,自引:0,他引:1
The application of computational fluid dynamics (CFD) in the agricultural industry is becoming ever more important. Over the years, the versatility, accuracy and user-friendliness offered by CFD has led to its increased take-up by the agricultural engineering community. Now CFD is regularly employed to solve environmental problems of greenhouses and animal production facilities. However, due to a combination of increased computer efficacy and advanced numerical techniques, the realism of these simulations has only been enhanced in recent years. This study provides a state-of-the-art review of CFD, its current applications in the design of ventilation systems for agricultural production systems, and the outstanding challenging issues that confront CFD modellers. The current status of greenhouse CFD modelling was found to be at a higher standard than that of animal housing, owing to the incorporation of user-defined routines that simulate crop biological responses as a function of local environmental conditions. Nevertheless, the most recent animal housing simulations have addressed this issue and in turn have become more physically realistic. 相似文献
19.
Currently, the growth in capacity demand is still increasing by the emergence of a large number of applications that dramatically increase bandwidth demand and generate a large number of resource requirements in the network. Since the emerging applications require increased bandwidth capacity, the vision of using optical technology in the communication channel, signal processing, and switching fabric is very promising. This article presents an overview of optical switching techniques currently under research investigations. It introduces enabling technologies that have been recently researched and then presents some newly proposed architectures. It describes the SKYLIGHT switch that has been recently developed by the author. The architecture design of the switch is based on a optical code division multiple access (OCDMA) technique. Performance evaluation of the switch fabric based on the analytical evaluation of the code and numerical simulations of the optical components used to implement the system is presented. 相似文献
20.
S. S. Ananyev G. A. Bagdasarov V. A. Gasilov S. A. Dan’ko B. A. Demidov E. D. Kazakov Yu. G. Kalinin A. A. Kurilo O. G. Ol’khovskaya M. G. Strizhakov S. I. Tkachenko 《Plasma Physics Reports》2017,43(7):726-732
Results are presented from experimental studies of plasma dynamics in a diode gap under the action of a high-current relativistic electron beam on epoxy resin at energy densities in the range of 170–860 J/cm2. The plasma expansion was studied by means of an optical streak camera. Three-dimensional numerical simulations in the one-temperature hydrodynamic approximation were also performed. The experimental data are compared with the results of numerical simulations. 相似文献