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1.
A Highly Scalable Boundary Integral Equation and Walk-on-Spheres (BIE-WOS) Method for the Laplace Equation with Dirichlet Data
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In this paper, we study a highly scalable communication-free parallel domain boundary decomposition algorithm for the Laplace equation based on a hybrid method combining boundary integral equations and walk-on-spheres (BIE-WOS)
method, which provides a numerical approximation of the Dirichlet-to-Neumann
(DtN) mapping for the Laplace equation. The BIE-WOS is a local method on the
boundary of the domain and does not require a structured mesh, and only needs a
covering of the domain boundary by patches and a local mesh for each patch for a local BIE. A new version of the BIE-WOS method with second kind integral equations is
introduced for better error controls. The effect of errors from the Feynman-Kac formula
based path integral WOS method on the overall accuracy of the BIE-WOS method is
analyzed for the BIEs, especially in the calculation of the right hand sides of the BIEs.
For the special case of flat patches, it is shown that the second kind integral equation
of BIE-WOS method can be simplified where the local BIE solutions can be given in
closed forms. A key advantage of the parallel BIE-WOS method is the absence of communications during the computation of the DtN mapping on individual patches of
the boundary, resulting in a complete independent computation using a large number
of cluster nodes. In addition, the BIE-WOS has an intrinsic capability of fault tolerance for exascale computations. The nearly linear scalability of the parallel BIE-WOS
method on a large-scale cluster with 6400 CPU cores is verified for computing the DtN
mapping of exterior Laplace problems with Dirichlet data for several domains. 相似文献
2.
Boundary Integral Modelling of Elastic Wave Propagation in Multi-Layered 2D Media with Irregular Interfaces
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Enru Liu Zhongjie Zhang Jianghua Yue & y Dobson 《Communications In Computational Physics》2008,3(1):52-62
We present a semi-analytic method based on the propagation matrix formulation of indirect boundary element method to compute response of elastic (and
acoustic) waves in multi-layered media with irregular interfaces. The method works
recursively starting from the top-most free surface at which a stress-free boundary
condition is applied, and the displacement-stress boundary conditions are then subsequently applied at each interface. The basic idea behind this method is the matrix
formulation of the propagation matrix (PM) or more recently the reflectivity method
as wide used in the geophysics community for the computation of synthetic seismograms in stratified media. The reflected and transmitted wave-fields between arbitrary
shapes of layers can be computed using the indirect boundary element method (BEM,
sometimes called IBEM). Like any standard BEM, the primary task of the BEM-based
propagation matrix method (thereafter called PM-BEM) is the evaluation of element
boundary integral of the Green's function, for which there are standard method that
can be adapted. In addition, effective absorbing boundary conditions as used in the
finite difference numerical method is adapted in our implementation to suppress the
spurious arrivals from the artificial boundaries due to limited model space. To our
knowledge, such implementation has not appeared in the literature. We present several examples in this paper to demonstrate the effectiveness of this proposed PM-BEM
for modelling elastic waves in media with complex structure. 相似文献
3.
N. Suhm M. H. Götz J. P. Fischer F. Loesel W. Schlegel V. Sturm J. Bille R. Schröder 《Acta neurochirurgica》1996,138(3):346-349
Summary The basis for most laser applications in neurosurgery is the conversion of laser light into heat when the incident laser beam is absorbed by the tissue. Irradiation of neural tissue with laser light therefore leads to its thermal damage. However, due to the diffusion of heat energy into the surrounding tissue, often there is thermal damage to neural tissue outside the area of the target volume. These are the characteristics of thermal laser/tissue interaction. In this paper we discuss how we used three different short-pulsed lasers to achieve non-thermal ablation of neural tissue.Three different short-pulsed lasers were used to generate ultrashort laser pulses in the picosecond to femtosecond range. The interaction of such laser pulses with tissue was predicted to be nonthermal. The short-pulsed lasers were used for the ablation of neural tissue using an in vitro calf brain model. The histopathological examination of the lesions revealed that the neural tissue had been removed very precisely without any sign of thermal damage to the surrounding tissue. 相似文献
4.
This paper presents a fourth-order Cartesian grid based boundary integral
method (BIM) for heterogeneous interface problems in two and three dimensional
space, where the problem interfaces are irregular and can be explicitly given by parametric curves or implicitly defined by level set functions. The method reformulates the
governing equation with interface conditions into boundary integral equations (BIEs)
and reinterprets the involved integrals as solutions to some simple interface problems
in an extended regular region. Solution of the simple equivalent interface problems for
integral evaluation relies on a fourth-order finite difference method with an FFT-based
fast elliptic solver. The structure of the coefficient matrix is preserved even with the
existence of the interface. In the whole calculation process, analytical expressions of
Green’s functions are never determined, formulated or computed. This is the novelty
of the proposed kernel-free boundary integral (KFBI) method. Numerical experiments
in both two and three dimensions are shown to demonstrate the algorithm efficiency
and solution accuracy even for problems with a large diffusion coefficient ratio. 相似文献
5.
Hualong Feng Amlan Barua Shuwang Li & Xiaofan Li 《Communications In Computational Physics》2014,15(2):365-387
The evolution of precipitates in stressed solids is modeled by coupling a
quasi-steady diffusion equation and a linear elasticity equation with dynamic boundary conditions. The governing equations are solved numerically using a boundary
integral method (BIM). A critical step in applying BIM is to develop fast algorithms to
reduce the arithmetic operation count of matrix-vector multiplications. In this paper,
we develop a fast adaptive treecode algorithm for the diffusion and elasticity problems
in two dimensions (2D). We present a novel source dividing strategy to parallelize the
treecode. Numerical results show that the speedup factor is nearly perfect up to a
moderate number of processors. This approach of parallelization can be readily implemented in other treecodes using either uniform or non-uniform point distribution. We
demonstrate the effectiveness of the treecode by computing the long-time evolution of
a complicated microstructure in elastic media, which would be extremely difficult with
a direct summation method due to CPU time constraint. The treecode speeds up computations dramatically while fulfilling the stringent precision requirement dictated by
the spectrally accurate BIM. 相似文献
6.
A two-layer model using different properties for the pathological tissue and the normal tissue was developed to describe the spatial photon, temperature and thermal damage distributions during laser-induced interstitial thermo-therapy (LITT). The photon distribution was simulated using the Monte Carlo method. The optical tissue parameters and the blood perfusion were derived based on the Arrhenius rate process formulation of thermal damage and kinetics of vasodilatation. The corresponding temperature distribution was numerically calculated using the Pennes bio-heat equation. The calculated results showed that the two-layer model predicted different results on the temperature variation and distribution, the thermal damage distribution and the thermal damage volume etc. from the one-layer model. As a more reasonable physical model, the two-layer model can be used to optimize the therapeutic parameters for improved LITT treatments. 相似文献
7.
B Zysset J G Fujimoto C A Puliafito R Birngruber T F Deutsch 《Lasers in surgery and medicine》1989,9(3):193-204
The effects of picosecond laser-induced optical breakdown on tissue were investigated using high-intensity 40 ps Nd:YAG laser pulses at 1.06 microns. Tissue damage was evaluated using the corneal endothelium in vitro as a model system. Systematic studies were performed to determine the scaling of the tissue damage and damage range with pulse energy. For suprathreshold lesions, the radius of the damage zone varies as the cube root of the pulse energy, in agreement with simple physical scaling laws. A minimum damage range of less than 100 microns was observed for pulse energies of 8 muJ. Damage morphology was investigated by scanning electron microscopy. Three different damage patterns were observed; cell damage, cell removal, and rupture of Descemet's membrane. Different irradiation geometries were used to study damage mediated by either the shock wave or the cavitation bubble. Comparative studies using 10 ns pulses demonstrated that picosecond pulses yielded a significant reduction in collateral tissue damage. 相似文献
8.
Marco Caliari & Simone Zuccher 《Communications In Computational Physics》2021,29(5):1336-1364
We propose an idea to solve the Gross–Pitaevskii equation for dark structures inside an infinite constant background density $ρ_∞$=${|ψ_∞|}^2$, without the introduction of artificial boundary conditions. We map the unbounded physical domain $\mathbb{R}^3$ into the bounded domain ${(−1,1)}^3$ and discretize the rescaled equation by equispaced
4th-order finite differences. This results in a free boundary approach, which can be
solved in time by the Strang splitting method. The linear part is solved by a new, fast
approximation of the action of the matrix exponential at machine precision accuracy,
while the nonlinear part can be solved exactly. Numerical results confirm existing
ones based on the Fourier pseudospectral method and point out some weaknesses of
the latter such as the need of a quite large computational domain, and thus a consequent critical computational effort, in order to provide reliable time evolution of the
vortical structures, of their reconnections, and of integral quantities like mass, energy,
and momentum. The free boundary approach reproduces them correctly, also in finite
subdomains, at low computational cost. We show the versatility of this method by
carrying out one- and three-dimensional simulations and by using it also in the case of
Bose–Einstein condensates, for which $ψ$→0 as the spatial variables tend to infinity. 相似文献
9.
Review of Feynman's Path Integral in Quantum Statistics: From the Molecular Schrödinger Equation to Kleinert's Variational Perturbation Theory
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Kin-Yiu Wong 《Communications In Computational Physics》2014,15(4):853-894
Feynman's path integral reformulates the quantum Schrödinger differential
equation to be an integral equation. It has been being widely used to compute internuclear
quantum-statistical effects on many-body molecular systems. In this Review,
the molecular Schrödinger equation will first be introduced, together with the Born-Oppenheimer
approximation that decouples electronic and internuclear motions. Some
effective semiclassical potentials, e.g., centroid potential, which are all formulated in
terms of Feynman's path integral, will be discussed and compared. These semiclassical
potentials can be used to directly calculate the quantum canonical partition function
without individual Schrödinger's energy eigenvalues. As a result, path integrations
are conventionally performed with Monte Carlo and molecular dynamics sampling
techniques. To complement these techniques, we will examine how Kleinert's variational
perturbation (KP) theory can provide a complete theoretical foundation for developing
non-sampling/non-stochastic methods to systematically calculate centroid
potential. To enable the powerful KP theory to be practical for many-body molecular
systems, we have proposed a new path-integral method: automated integration-free
path-integral (AIF-PI) method. Due to the integration-free and computationally
inexpensive characteristics of our AIF-PI method, we have used it to perform ab initio
path-integral calculations of kinetic isotope effects on proton-transfer and RNA-related
phosphoryl-transfer chemical reactions. The computational procedure of using our
AIF-PI method, along with the features of our new centroid path-integral theory at the
minimum of the absolute-zero energy (AMAZE), are also highlighted in this review. 相似文献
10.
Yunyun Ma & Jiguang Sun 《Communications In Computational Physics》2022,31(5):1546-1560
We propose a numerical method for a non-selfadjoint Steklov eigenvalue
problem of the Helmholtz equation. The problem is formulated using boundary integrals. The Nyström method is employed to discretize the integral operators, which
leads to a non-Hermitian generalized matrix eigenvalue problems. The spectral indicator method (SIM) is then applied to calculate the (complex) eigenvalues. The convergence is proved using the spectral approximation theory for (non-selfadjoint) compact
operators. Numerical examples are presented for validation. 相似文献
11.
BACKGROUND AND OBJECTIVE: Short-pulse solid-state lasers have recently received much attention as new coherent light sources for medical applications, but steady transmission of their high-energy output pulses through a solid quartz fiber is difficult because of the onset of laser-induced breakdown. We previously demonstrated that hollow waveguides could be used to deliver nanosecond laser pulses for tissue ablation. The aim of this study was to determine the optimum laser pulse energy and range of defocused distance for obtaining a deep and sharp ablation channel in myocardial tissue with laser pulses transmitted through a hollow waveguide. STUDY DESIGN/MATERIALS AND METHODS: Cyclic-olefin-polymer-coated silver hollow waveguides of 1 mm in inner diameter and 1 m in length were used. A vacuum-cored scheme was applied to the waveguides to suppress laser-induced air breakdown. Porcine myocardial tissue was irradiated with 300 laser pulses that were delivered through the waveguide in vitro at various laser energy levels and defocused distances, and depths and diameters of channels were measured. Histological analysis of the ablated tissues was also performed. RESULTS: At an ablation energy of approximately 60 mJ/pulse, deep (>4.5 mm) and sharp (depth-to-diameter ratio of > 6) channels were created in tissue in the range of defocused distances of -4 approximately + 0.5 mm. Under these conditions, waveguide bending did not cause a remarkable change in ablation characteristics. Histological analysis of ablated tissue showed limited thermal damage but suggested a certain extent of mechanical effects in the tissue. CONCLUSION: With near-infrared, nanosecond laser pulses delivered through a cyclic-olefin-polymer-coated silver hollow waveguide, efficient and sharp ablation of myocardial tissue can be achieved, suggesting the usefulness of the hollow waveguide as a new flexible delivery system for high-intensity laser pulses. 相似文献
12.
Fast Multipole Accelerated Boundary Integral Equation Method for Evaluating the Stress Field Associated with Dislocations in a Finite Medium
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Degang Zhao Jingfang Huang & Yang Xiang 《Communications In Computational Physics》2012,12(1):226-246
In this paper, we develop an efficient numerical method based on the boundary integral equation formulation and new version of fast multipole method to solve
the boundary value problem for the stress field associated with dislocations in a finite
medium. Numerical examples are presented to examine the influence from material
boundaries on dislocations. 相似文献
13.
This work proposes a generalized boundary integral method for variable coefficients
elliptic partial differential equations (PDEs), including both boundary value
and interface problems. The method is kernel-free in the sense that there is no need
to know analytical expressions for kernels of the boundary and volume integrals in
the solution of boundary integral equations. Evaluation of a boundary or volume integral
is replaced with interpolation of a Cartesian grid based solution, which satisfies
an equivalent discrete interface problem, while the interface problem is solved by a
fast solver in the Cartesian grid. The computational work involved with the generalized
boundary integral method is essentially linearly proportional to the number
of grid nodes in the domain. This paper gives implementation details for a second-order
version of the kernel-free boundary integral method in two space dimensions
and presents numerical experiments to demonstrate the efficiency and accuracy of
the method for both boundary value and interface problems. The interface problems
demonstrated include those with piecewise constant and large-ratio coefficients and
the heterogeneous interface problem, where the elliptic PDEs on two sides of the interface
are of different types. 相似文献
14.
R. Cubeddu C. Sozzi P. Taroni G. Valentini G. Bottiroli A. C. Croce 《Lasers in medical science》1997,12(1):21-30
This work studied the ablation of bovine brain tissue by free-running Erbium-YAG laser pulses. Single-shot interactions were
investigated by means of an ultra-fast imaging technique. Thin sections of the treated tissue were processed for histochemical
analysis of enzyme activity to assess the extent of thermal/mechanical damage. Thereafter, a scanning beam technique was employed
to deliver multiple pulses over a definite region of tissue. An analytical balance was used to measure the removed mass in
order to calculate the ablation efficiency. The present quantity has been compared to the amount of the tissue damaged, as
assessed by the histochemical analysis. The present work shows that the interaction of the Erbium-YAG laser pulses with a
soft tissue may cause a large amount of mechanical damage, while thermal damage is restricted within a thin layer around the
ablation crater. A precise control of fluence and operating conditions prevents overwhelming side-effects, and possibly allows
the use of the Erbium-YAG laser for the ablation of brain and other soft tissues. 相似文献
15.
In the design of surfaces which absorb waves, the impedance boundary condition is used as an effective means of diminishing the reflection. In this paper, we use the geometrical optics method to approximate the optimal impedance value which minimizes the reflected field for the scalar wave equation with a monochromatic source. Our treatment yields good results for optimal impedance in the asymptoticity region of the geometrical optics solution. 相似文献
16.
This article presents experimental and computational results of electroporation in rat liver. The experiments were performed using different forms of electrodes and waveforms of applied electric pulses. For the numerical simulation, the electroporation model proposed by Ramos and Weinert in a previous publication was used. Dynamic adjustments were used for obtaining a good modeling of the electric current. A single set of model parameters was obtained to fit the simulated current response for different waveforms and electrodes. These parameters were obtained with the use of a genetic algorithm that minimized the error between the simulated and experimental currents. The electroporation model with dynamic adjustment proved to be an appropriate simulation tool to predict the tissue conductivity during stimulation by intense electrical fields. 相似文献
17.
G. H. Pettit R. Sauerbrey F. K. Tittel D. Weilbacher P. D. Henry 《Lasers in surgery and medicine》1993,13(3):279-283
The temporal modification of XeCl laser pulses reflected from human aorta tissue immersed in saline has been studied. Dynamic tissue reflectivity of both normal and atherosclerotic tissues has been examined for various incident pulse fluences between 0.7 and 6.5 J/cm2. Changes in reflected pulse duration are observed for fluences at or above 2.6 J/cm2 with normal tissue targets and 3.0 J/cm2 with calcified plaque. Such reflected pulse analysis may prove useful in identifying tissue targets for ablation during laser angioplasty. © 1993 Wiley-Liss, Inc. 1 This article is a US Government work and, such, is in the public domain in the United States of America. 相似文献
18.
A Well-Conditioned Hypersingular Boundary Element Method for Electrostatic Potentials in the Presence of Inhomogeneities within Layered Media
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In this paper, we will present a high-order, well-conditioned boundary element
method (BEM) based on Müller's hypersingular second kind integral equation
formulation to accurately compute electrostatic potentials in the presence of inhomogeneity
embedded within layered media. We consider two types of inhomogeneities:
the first one is a simple model of an ion channel which consists of a finite height cylindrical
cavity embedded in a layered electrolytes/membrane environment, and the second
one is a Janus particle made of two different semi-spherical dielectric materials.
Both types of inhomogeneities have relevant applications in biology and colloidal material,
respectively. The proposed BEM gives$\mathcal{O}$(1) condition numbers, allowing fast
convergence of iterative solvers compared to previous work using first kind of integral
equations. We also show that the second order basis converges faster and is more
accurate than the first order basis for the BEM. 相似文献
19.
A.A. Serafetinides M.G. Khabbaz M.I. Makropoulou A.K. Kar 《Lasers in medical science》1999,14(3):168-174
. The interaction of picosecond laser radiation with human dental tissue was investigated in this study, in order to determine
the ablation rates and the surface characteristics of the dentine by using scanning electron microscopy (SEM). Dentine ablation
was performed by using tooth sections of different thicknesses (0.5–2.0 mm). Dental tissue samples were irradiated in air
with the fundamental wavelength and first harmonic of a regenerative amplifier Nd:YAG laser system, at 1064 nm and 532 nm,
respectively, with a pulse duration of 100 ps and a pulse repetition rate of 10 Hz. The results showed very clean craters
surrounded by minimum melting of the surface of dentine when the 1064 nm pulses were used. In contrast, when the first harmonic
532 nm pulses were used, the SEM examinations revealed cracks and melting of dentine with irregular surface modification.
Consequently, it seems that cleaning and shaping of the root canal walls during endodontic therapy with the picosecond Nd:YAG
laser application may be possible in the future. The, as yet unexplored, field of the picosecond laser interaction with hard
dental tissue is expected to be a potential alternative for powerful laser processing of biomedical structures.
Paper received 24 February 1998; accepted following revision 20 November 1998. 相似文献
20.
Boundary integral methods are naturally suited for the computation of harmonic functions on a region having inclusions or cells with different material properties. However, accuracy deteriorates when the cell boundaries are close to each other.
We present a boundary integral method in two dimensions which is specially designed
to maintain second order accuracy even if boundaries are arbitrarily close. The method
uses a regularization of the integral kernel which admits analytically determined corrections to maintain accuracy. For boundaries with many components we use the fast
multipole method for efficient summation. We compute electric potentials on a domain
with cells whose conductivity differs from that of the surrounding medium. We first
solve an integral equation for a source term on the cell interfaces and then find values
of the potential near the interfaces via integrals. Finally we use a Poisson solver to extend the potential to a regular grid covering the entire region. A number of examples
are presented. We demonstrate that increased refinement is not needed to maintain
accuracy as interfaces become very close. 相似文献