94 research outputs found
Development of a symplectic and phase error reducing perturbation finite-difference advection scheme
No full textThe aim of this work is to develop a new scheme for solving the pure advection equation. This scheme formulated within the perturbation finite-difference context not only conserves symplecticity but also preserves the numerical dispersion relation equation. The employed symplectic integrator of second-order accuracy in time enables calculation of a long-time accurate solution in the sense that the Hamiltonian is conserved at all times. The generalized high-order spatially accurate perturbation difference scheme optimizes numerical phase accuracy through the minimization of the difference between the numerical and exact dispersion relation equations. Our proposed new class of phase error reducing perturbation difference schemes can in addition locally capture discontinuities underlying the concept of applying a shope/flux limiter. The high-order spatial accuracy can be recovered in a smooth region. Besides the Fourier analysis of the discretization errors, anisotropy and dispersion analyses are both conducted on the dispersion-relation and symplecticity-preserving pure advection scheme to shed light on the distinguished nature of the proposed scheme. Numerical tests are carried out and the results compare well with the exact solutions, demonstrating the efficiency, accuracy, and the discontinuity-resolving ability using the proposed class of high-resolution perturbation finite-difference schemes
Effects of tissue relaxation and acoustic streaming on liver tumor ablation: Numerical simulation
No full text[[abstract]]Liver cancer is one of the leading causes of death in the world. High intensity focused ultrasound (HIFU) is a rapidly developing medical technology for conducting non-invasive tumor ablation therapy in various organs of the body. One of the major objectives of this study is to achieve a virtually complete necrosis of tumors close to major blood vessels and to avoid blood vessel damage. The three-dimensional (3D) acoustic-thermal-hydrodynamic coupling model is proposed to compute the pressure, temperature, and blood flow velocity in the patient specific geometry. At high frequencies propagation of ultrasound in the medium is a non-equilibrium process and relaxation effects should be taken into account. The nonlinear Westervelt equation with relaxation effects and bioheat equations in both the hepatic parenchyma and blood vessels are considered. The classical nonlinear Navier-Stokes equations related to mass and momentum conservations in large hepatic blood vessels are employed both for convective cooling and acoustic streaming. From this three-dimensional study it is found that relaxation effects can significantly affect the amount of ultrasound energy deposited to the tumor. In large blood vessels both convective cooling and acoustic streaming can change the temperature considerably near blood vessels
Geospatial analysis of Indonesia's bankable utility-scale solar PV potential using elements of project finance
No full textGeospatial analysis is useful for mapping the potential of renewables like solar PV. However, recent studies do not address PV’s bankable potential for which project financing can be secured. This paper proposes a framework that incorporates project finance into geospatial analyses to obtain the bankable potential of renewables. We demonstrate our framework for Indonesia, and compare the bankable potential with the socio-economic potential mostly used in literature. Using average inputs On average, the technical potential is 12,200 TWh/year and the socio-economic potential is 152.7 TWh/year if capped by 2030 demand (34% coverage). Considering PV’s financing risks, PV’s bankable potential is 16.0 TWh under current conditions if capped by 2030 demand (3.6% coverage). Both economic potentials are mainly in East Indonesia and absent on Java due to tariffs and land availability. For the bankable potential, the risk perception by banks and investors is another key influence. With a feed-in tariff of 11.5 US¢(2021)/kWh and temporary lift of import restrictions, the bankable potential is 23 TWh if capped by 2030 demand (5.2% coverage) and spreads to Java. For more widespread bankability, additional temporary measures are recommended until the PV’s costs have decreased further and trust by financial institutions has increased.Energie and IndustrieEconomics of Technology and InnovationPhotovoltaic Materials and Device
Investigating ion transport inside the pentameric ion channel encoded in COVID-19 e protein
No full text[[abstract]]Ion flow inside an ion channel can be described through continuum based Born-Poisson-Nernst-Planck (BPNP) equations in conjunction with the Lennard-Jones potential. Keeping in mind the ongoing pandemic, in this study, an attempt has been made to understand the selectivity and the current voltage relation of the COVID-19 E protein pentameric ion channel. Two ionic species, namely Na+ and Cl-, have been considered here. E protein is one of the smallest structural protein which is embedded in the outer membrane of the virus. Once the virus is inside the host cell, this protein is expressed abundantly and is responsible for activities such as replication and budding of the virus. In the literature, we can find a few experimental studies focusing on understanding the activity of the channel formed by E proteins of different viruses. Here, we attempt the same study for the COVID-19 E protein ion channel through mathematical modeling. The channel geometry is calculated from the protein data bank file which was provided by NARLabs, Taiwan, using the hole program. Further, it was used to obtain the charge distribution using the pdbtopqr online program. The immersed boundary-lattice Boltzmann method (IB-LBM) has been implemented to numerically solve the system of equations in the channel generated by the protein data bank file. Further, an in-house code which operates on multiple GPUs and uses the cuda platform has been developed to achieve the goal of performing the current investigation
The inertial cavitation threshold in soft tissue using a dual-frequency driving signal C3 - World Congress in Computational Mechanics and ECCOMAS Congress
No full text[[abstract]]High Intensity Focused Ultrasound (HIFU) is a non-invasive technology that can be applied for treatment of different diseases and ablation of tumours in different parts of the body. When high intensity ultrasound propagates through the medium bubbles can be formed, a phenomenon known as acoustic cavitation. There are two different regimes of acoustic cavitation: stable cavitation when a bubble just oscillates around an equilibrium state, and inertial cavitation which is accompanied by bubble collapse. These two different regimes can be used for different biomedical applications. However, in some cases it can also make the treatment less predictable. Therefore, fundamental understanding of these effects is very important. In the current study theoretical investigation of the bubble dynamics in viscoelastic medium is performed and inertial cavitation thresholds have been calculated. To describe the bubble dynamics, Gilmore-Akulichev-Zener model has been used, which is suitable for a large bubble oscillations and high ultrasound powers. The results showed that using the dual-frequency driving signal the threshold value of inertial cavitation can be significantly reduced compared to single-frequency signal mode. Large difference between frequencies in the dual-frequency signal leads to lower threshold values. Numerical simulations also showed the dependencies of the cavitation threshold on the bubble radius
Bubble dynamics in viscoelastic soft tissue in high-intensity focal ultrasound thermal therapy
No full text[[abstract]]The present study is aimed to investigate bubble dynamics in a soft tissue, to which HIFU's continuous harmonic pulse is applied by introducing a viscoelastic cavitation model. After a comparison of some existing cavitation models, we decided to employ Gilmore-Akulichev model. This chosen cavitation model should be coupled with the Zener viscoelastic model in order to be able to simulate soft tissue features such as elasticity and relaxation time. The proposed Gilmore-Akulichev-Zener model was investigated for exploring cavitation dynamics. The parametric study led us to the conclusion that the elasticity and viscosity both damp bubble oscillations, whereas the relaxation effect depends mainly on the period of the ultrasound wave. The similar influence of elasticity, viscosity and relaxation time on the temperature inside the bubble can be observed. Cavitation heat source terms (corresponding to viscous damping and pressure wave radiated by bubble collapse) were obtained based on the proposed model to examine the cavitation significance during the treatment process. Their maximum values both overdominate the acoustic ultrasound term in HIFU applications. Elasticity was revealed to damp a certain amount of deposited heat for both cavitation terms
Experimental and numerical study on the temperature elevation in tissue during moxibustion therapy
No full text[[abstract]]Moxibustion is a thermal therapy in traditional Chinese medicine that relies on the heat from burning moxa to be transferred beneath the skin surface. Although moxibustion has long been in widespread practice, the mechanism of heat transfer modality and temperature distribution during this treatment is not yet well understood. The current paper presents the first examination by magnetic resonance imaging (MRI) of the three-dimensional temperature elevation during moxibustion treatment. A mathematical model for the prediction of temperature elevation during moxibustion therapy has been constructed and compared with the experimental data. Good agreement between the measured temperature and the results of numerical calculations has been found. Tissue up to 3 cm deep can be heated during the treatment. It was revealed that both heat conduction and radiation heat transfer play important roles during the treatment. The results presented in the current paper can be used for understanding the mechanisms of Chinese medicine and developing useful guidelines for Chinese medicine doctors
Arbitrary lagrangian eulerian-type finite element methods formulation for pdes on time-dependent domains with vanishing discrete space conservation law
No full text[[abstract]]The aim of this paper is to introduce a finite element formulation within an arbitrary Lagrangian Eulerian (ALE) framework with a vanishing discrete space conservation law (SCL) for differential equations on time-dependent domains. The novelty of the formulation is the method for temporal integration which results in preserving the SCL property and retaining the higher order accuracy at the same time. Once the time derivative is discretized (based on an integration or differentiation formula), the common approach for terms in differential equation which do not involve temporal derivative is classified to be a kind of "time averaging" between time steps. In the spirit of classical approaches, this involves evaluating these terms at several points in time between the current and the previous time step ([t(n), t(n+1)]), and then averaging them in order to provide the satisfaction of discrete SCL. Here, we fully use the polynomial in time form of mapping through which the evolution of the domain is realized-the so-called ALE map-in order to avoid the problems arising due to the moving grids. We give a general recipe on temporal schemes that have to be employed once the discretization for the temporal derivative is chosen. Numerical investigations on stability, accuracy, and convergence are performed and the simulated results are compared with benchmark problems set up by other authors
Lattice Boltzmann method to simulate three-dimensional ion channel flow using fourth order Poisson-Nernst-Planck-Bikerman model
No full text[[abstract]]Over the past three decades, the lattice Boltzmann method (LBM) has been applied to a vast range of hydrodynamic and non-hydrodynamic (e.g., ion transport) systems. In conjunction with the immersed boundary method (IBM), the LBM has been successfully implemented to solve systems with complex geometries. In this study, the immersed boundary-lattice Boltzmann method (IB-LBM) is implemented to simulate nanoscale ion transport. Traditionally, ion transport is described through the Poisson-Nernst-Planck (PNP) equations where ionic interactions are included. In the current paper, the fourth order Poisson-Nernst-Planck-Bikerman (4PNPBik) model has been used. In addition to ionic interactions, the 4PNPBik model includes the effects of the finite size of particles (ions and water) and interactions between ions and its surrounding medium. Applicability of the 4PNPBik model is demonstrated through comparison of the experimental and predicted ion activity. Implementation of the 4PNPBik model has been validated by comparing the predicted current-voltage curve with the analytical result. The transient receptor potential (TRP) ion channel of the vanilloid group (TRPV4) is used to demonstrate the applicability of this approach. The TRPV4 is a nonselective cation channel that prefers divalent cationic species over monovalent cations. In this study, this selectivity is demonstrated by comparing the concentration profiles of calcium, sodium, and chloride ions. Further, the role of the finite size of particles and nonlocal electrostatics is discussed by comparing the results obtained from the PNP and 4PNPBik models under identical initial and boundary conditions
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