Cylindrical Medium Research Articles

Radiation-induced double-strand breaks by internal ex vivo irradiation of lymphocytes: Validation of a Monte Carlo simulation model using GATE and Geant4-DNA

This study describes a method to validate a radiation transport model that quantifies the number of DNA double-strand breaks (DSB) produced in the lymphocyte nucleus by internal ex vivo irradiation of whole blood with the radionuclides 90Y, 99mTc, 123I, 131I, 177Lu, 223Ra, and 225Ac in a test vial using the GATE/Geant4 code at the macroscopic level and the Geant4-DNA code at the microscopic level. MethodsThe simulation at the macroscopic level reproduces an 8 mL cylindrical water-equivalent medium contained in a vial that mimics the geometry for internal ex vivo blood irradiation. The lymphocytes were simulated as spheres of 3.75 µm radius randomly distributed, with a concentration of 125 spheres/mL. A phase-space actor was attached to each sphere to register all the entering particles. The simulation at the microscopic level for each radionuclide was performed using the Geant4-DNA tool kit, which includes the clustering example centered on a density-based spatial clustering of applications with noise (DBSCAN) algorithm. The irradiation source was constructed by generating a single phase space from the sum of all phase spaces. The lymphocyte nucleus was defined as a water sphere of a 3.1 µm radius. The absorbed dose coefficients for lymphocyte nuclei (dLymph) were calculated and compared with macroscopic whole blood absorbed dose coefficients (dBlood). The DBSCAN algorithm was used to calculate the number of DSBs. Lastly, the number of DSB∙cell−1∙mGy−1 (simulation) was compared with the number of radiation-induced foci per cell and absorbed dose (RIF∙cell−1∙mGy−1) provided by experimental data for gamma and beta emitting radionuclides. For alpha emitters, dLymph and the number of α-tracks∙100 cell−1∙mGy−1 and DBSs∙µm−1 were calculated using experiment-based thresholds for the α-track lengths and DBSs/track values. The results were compared with the results of an ex vivo study with 223Ra. ResultsThe dLymph values differed from the dBlood values by −1.0% (90Y), −5.2% (99mTc), −22.3% (123I), 0.35% (131I), 2.4% (177Lu), −5.6% (223Ra) and −6.1% (225Ac). The number of DSB∙cell−1∙mGy−1 for each radionuclide was 0.015 DSB∙cell−1∙mGy−1 (90Y), 0.012 DSB∙cell−1∙mGy−1 (99mTc), 0.014DSB∙cell−1∙mGy−1 (123I), 0.012 DSB∙cell−1∙mGy−1 (131I), and 0.016 DSB∙cell−1∙mGy−1 (177Lu). These values agree very well with experimental data. The number of α-tracks∙100 cells−1∙mGy−1 for 223Ra and 225Ac where 0.144 α-tracks∙100 cells−1∙mGy−1 and 0.151 α-tracks∙100 cells−1∙mGy−1, respectively. These values agree very well with experimental data. Moreover, the linear density of DSBs per micrometer α-track length were 11.13 ± 0.04 DSB/µm and 10.86 ± 0.06 DSB/µm for 223Ra and 225Ac, respectively. ConclusionThis study describes a model to simulate the DNA DSB damage in lymphocyte nuclei validated by experimental data obtained from internal ex vivo blood irradiation with radionuclides frequently used in diagnostic and therapeutic procedures in nuclear medicine.

Rheology of a Viscous-Plastic Liquid in a Porous Medium

The hydrodynamics of the capillary flow of a viscous-plastic liquid in cylindrical rectilinear pores is considered, as a result of which the structural velocity distribution over the pore cross section is obtained. Analytical solutions are proposed for the equations of hydraulic diffusion and nonlinear filtration for a non-Newtonian fluid in a cylindrical porous medium. It is noted that when a non-Newtonian fluid flows in a porous medium, the filtration equations take a nonlinear form due to the effective viscosity, shear, and yield stresses taken into account in its structure. The proposed solutions make it possible to evaluate the state of the porous medium and its main parameters (permeability, hydraulic diffusion, and effective viscosity coefficients). The obtained solutions are compared with existing experimental data for non-Newtonian oils.

Decomposing stress wave interference in a cylindrical wooden medium using an inverse deconvolution filter.

Excitation of an embedded waveguide in the cross section plane of a cylindrical structure produces Rayleigh modes propagating primarily in circumferential regions of the propagating medium. In many applications, this region is critical to the overall strength of the structure. Using the through-transmission technique, the Rayleigh mode in cylindrical symmetry produces clockwise and counterclockwise trajectories that interfere with each other at the receiver, producing a composite energy response in the temporal domain that hinders the accurate mode characterization. This work presents a decomposition algorithm consisting of three processing steps: (1) analytical continuous wavelet transforms of the raw waveform; (2) frequency polynomial approximation of the inverse point spread function using L2 norm optimization; and (3) derivation of the inverse deconvolution filter via the dual derivative operator. This work demonstrates the mathematical formulation and algorithm implementation with numerical and empirical validations. The proposed decomposition filter can achieve the overall time and energy estimation accuracy with a relative root mean square error of 0.07. Its broader impact will enhance the parametric estimation of the diagnostic stress wave for material characterization.

A simplified model of low Re, immiscible, gas–liquid flow, and heat transfer in porous media numerical solution with experimental validation

ABSTRACT This study investigates the thermohydraulic characteristics of immiscible two-phase downward flow and heat transfer through porous media in a vertical, cylindrical, and homogeneous porous medium numerically and experimentally. The test section is exposed to a constant wall temperature after filled with spherical beads. Numerical solution of the model is achieved by the finite volume method and applied to a single-phase flow model. The numerical results are experimentally validated according to air/water downward flow, spherical beads, a ratio of particle diameter to pipe radius is 0.412, 0.396 porosity, 0.01 ≤ Re ≤ 500, water to air volume ratio range from 0 to ∞, and saturation ratio from 0 to 1. The results show that the average Nu is nearly constant up to Re = 40. At Re > 100, it is recommended to take inertia and friction effects into account by means of Forchheimer–Brinkman’s equation. For single-phase flow (water or air) and two-phase flow mixtures, the local Nu has higher values at the entrance section and decreases as the axial distance increases until it reaches its fully developed value of 4.37 at the end of the thermal entrance length. The comparison between numerical, experimental, and other available previous results shows good agreement and validates the numerical model.

Heat Transfer Study in Cylindrical Cavity with Heat Absorption or Generation

Lattice Boltzmann mesoscopic (LBM) is applied to solve energy equation of a transient conduction radiation heat transfer problem in a two-dimensional cylindrical participating (absorbing, emitting and scattering) medium in the presence of heat generation/absorption coefficient. Control volume finite element method (CVFEM) formulation is used to obtain the radiative information. To study the effectiveness of the LBM-CVFEM combination on unsteady conduction-radiation problems in cylindrical media, the energy equation of the problem is also solved using the finite difference method (FDM) in which the CVFEM is used to compute radiative information. The effects of heat generation/absorption coefficient on temperature distributions in the medium are studied. Results of the present work are benchmarked against those available in the literature. The hybrid numerical model’s results are also compared with those obtained by the FDM-CVFEM combination. All the results presented in this work show that the present method is accurate and valuable for the analysis of cylindrically axisymmetric radiative heat transfer problems .

Features of Casson liquid in non-linear radiative magnetized cylindrical media: a numerical solution

The numerical study is carried out to examine the flow field aspects of Casson fluid in magnetized cylindrical media. To be more specific, we considered a Casson fluid flow due to magnetized inclined cylindrical surface along with the thermal radiations, mixed convection, heat generation or absorption, variable thermal conductivity, and viscous dissipation effects. The obtained non-linear flow equations are reduced into ordinary differential equations by use of the suitable transformations. The said boundary value problem is further reduced to the initial value problem and then the shooting method with Runge–Kutta-scheme of fourth-order has been used to obtain the numerical results. Both tabular and line graphs trends are used to conclude the examination of the effects of flow parameters on non-dimensional temperature and velocity distributions. From the outcomes, we noticed Casson fluid temperature reflects inciting nature towards thermal radiation parameter, variable-thermal-conductivity parameter, and Eckert number. The Nusselt number is noticed as a decreasing function of both the Eckert number and variable thermal-conductivity parameter. In the presence of a magnetic field, the Casson fluid velocity and Casson fluid temperature show a direct relation to the curvature parameter.

Kelvin equation-based scaling model for pore-size estimation in mesoporous materials

In this paper we consider the phase equilibrium state of a fluid confined within a mesoporous controlled cylindrical pore medium. We begin with finding a meniscus shape in the limit of the smoothest curvature variation, for which the curvature radius is the only parameter to define the meniscus dimensions. Then the scaling law is established connecting the meniscus curvature and the pore radius, thus allowing us to create a one-parameter model for finding a pore radius when a meniscus curvature radius is known. Simultaneous use of the model with our previously developed one makes it possible to calculate the pore size on the basis of P/P 0 information from the adsorption isotherm.

A thermodynamic two-temperature model with distinct fractional derivative operators for an infinite body with a cylindrical cavity and varying properties

The current work presents a novel model in the field of thermoelasticity to study an infinitely cylindrical cavity solid medium with variable thermal properties. The governing equations are based on a two-temperature heat conduction model with local and non-local fractional differential operators (Caputo-Fabrizio (CF) and Atangana-Baleanu (AB)). The surface surrounding the cylindrical cavity is due to decreasing heat flow and transport at a constant speed. The effects of different fractional differential operators have been shown and analyzed by making some comparisons and presenting them in tables. The numerical results and figures show the effects of the fractional arrangement parameter and the heat flux velocity significantly on the stress and deformation patterns, but they have little effect on the dynamic temperature and conductivity changes. The thermoelastic model with two temperatures and fractional operators is suitable for describing the phenomenon of heat transfer within elastic and viscous media.

On the direct and inverse electromagnetic scattering by chiral media

Consider the direct and inverse electromagnetic scattering problems by a penetrable cylindrical chiral medium in a homogeneous achiral background medium. The scattering problem can be modeled by a pair of the two-dimensional Helmholtz equations with coupled transmission boundary conditions. The boundary integral equation method is applied to solve the direct scattering problem in a suitable Sobolev space. Then we investigate the linear sampling method for recovering the unknown scatterer from far-field pattern of the scattered field. The coupled boundary conditions bring new challenges during the procedure, and some novel techniques are needed in the theoretical analysis. Finally, we perform several numerical experiments to demonstrate the efficiency and effectiveness of this method.

Numerical results for radiative heat transfer in finite cylindrical medium with isotropic scattering

In recent years, the interest in radiative heat transfer in cylindrical media has increased primarily because of its several applications related to combustion chambers, furnaces, and high temperature heat exchangers. Although there are many papers dealing with the radiative transfer in such geometry, there is lack of high precision benchmarks. Such scarcity is related to the fact that some researches present inaccurate results and most published works are limited to presenting results only in graphics. The shortage is more evident in the case of multidimensional problems, like those in which incident radiation and radiative heat fluxes vary in the axial direction. These problems can be approached in many ways; in the integral formulation, the angular variables are completely eliminated by integration over the solid angle, which allows the elimination of the ray effect and the consequent obtainment of more accurate numerical results. A strategy that can be used simultaneously with the integral formulation is the use of the singularity-subtraction technique with the Nyström method, which provides high quality numerical results with relatively low computational times if combined with mathematical refinements. Following this methodology, in the present research, radiative heat transfer problems in finite cylindrical media with isotropic scattering are solved. High precision numerical results for incident radiation and radiative heat fluxes in the radial and axial directions are provided and validated by comparing with results available in the literature.

Investigation of transient coupled conduction and radiation heat transfer in the linearly anisotropic scattering cylindrical medium by spectral collocation method

In this paper, a spectral collocation method (SCM) is developed to solve transient conduction and radiation heat transfer problems in infinitely long annular cylinders with participating medium. The participating medium is an absorbing, emitting and linearly anisotropic scattering medium. To avoid the complex calculation of ray tracing, the radiative transfer equation and the transient heat conduction equation are expressed in eulerian coordinates. In the solving process, for the radiative transfer equation, both spatial and angular domains are discretized by the SCM; for the transient heat conduction equation, the spatial domain is discretized by the SCM, and the time domain is discretized by the fully implicit Euler scheme. The spatial derivative term, angular derivative term and scattering source integral term are approximated by the high order spectral collocation scheme. Compared with available data in references, the SCM can achieve very good accuracy even using few nodes. Thus, the SCM is a very effective method to achieve high order accuracy for transient coupled conduction and radiation heat transfer in an anisotropic scattering cylindrical medium. Moreover, the effects of conduction-radiation parameter, optical thickness, and wall emissivity on the transient temperature distribution and energy flow rate have also been comprehensively investigated.

Hyperbolic two-temperature generalized thermoelasticity with fractional order strain of solid cylinder

A novel mathematical model of thermoelastic of a homogenous isotropic solid cylindrical infinite medium has been constructed in this paper. Thermally shocked is the bounding surface of the cylinder. In the sense of the hyperbolic two-temperature generalized thermoelasticity with fractional stress theory, the governing equations have been taken. Different values of the fractional order and two-temperature parameters have shown numerical results for the dynamical and conductive temperature increment, strain, displacement, and average stress, which are graphically applicable to all the functions studied. The fractional-order parameter has significant effects on stress and displacement distributions, while it has little effect on the dynamical and conductive temperatures increment and significant effects on all studied functions as well as on the two-temperature parameter. The two-temperature hyperbolic model is precious and effective.

Gear-generalized differential quadrature analysis of oscillatory convective Taylor-Couette flows of second-grade fluids subject to Lorentz and Darcy-Forchheimer quadratic drag forces

Neglet of further analysis of Taylor-Couette flow problem is associated to the difficulty in research methodology for the examination of such transport phenomenon. However, little is known on the efficiency of Gear-Generalized Differential Quadrature Method (GGDQM) and thermal analysis across Taylor-Couette flow of second-grade fluid through Darcy-Forchheimer porous cylindrical medium subject to Lorentz force. The aforementioned research methodology was used to explore oscillatory magnetohydrodynamic (MHD) convective laminar flow of a second-grade fluid. The governing equations for the proposed fluid flow model are derived and simplified with the aid of suitable transformations in order to obtain nonlinear dimensionless set of partial differential equations (PDEs). The numerical solution of the corresponding problem was obtained using Gear-Generalized Differential Quadrature Method to provide appropriate graphical and tabular results in terms of velocity and temperature profiles, as well as the skin friction coefficient and Nusselet number on the surface of the inner cylinder. It is worth concluding that the elasticity of the fluidic medium has an enhancing influence on the dynamical and thermal features of the dynamics. However, the porosity characteristics of the medium together with the strength of the applied magnetic field exhibit a revere trend towards the velocity and temperature distributions.

Investigation on the nonreciprocal properties of one-dimensional cylindrical magnetized plasma photonic crystals.

In this paper, the equations for the transfer matrix method of one-dimensional cylindrical magnetized plasma photonic crystals are proposed, and its nonreciprocal properties based on the Thue-Morse sequence are also studied. By adding the influence of the magnetic field into Maxwell's equations in the cylindrical coordinate system, the transmission matrix equation of cylindrical wave propagation in the cylindrical medium is obtained and a quasi-periodic structure with the Thue-Morse sequence is designed to study its nonreciprocal features. By considering Maxwell's equations and the equations of motion of charged particles, the relative dielectric function of plasma under the $z$-axis magnetic field is achieved. Considering the influences of this dielectric function in the cylindrical coordinate system, the transmission matrix equations of cylindrical wave propagation in the cylindrical medium are derived, and those equations are used to design a cylindrical structure with two layers of ordinary medium and one layer of plasma satisfying the Thue-Morse sequence. It is concluded that the nonreciprocal phenomenon becomes more and more obvious with the increase of the plasma frequency, the relative dielectric constant of the medium, and the incident angle. But with the increase of ${\omega _c}$, the nonreciprocal propagation is attenuated, and there is no significant change when the collision frequency is enlarging.

Nonreciprocal absorption characteristics of one-dimensional cylindrical magnetized plasma photonic crystals

By combining the propagation matrix of planar magnetized plasma photonic crystals with that of the cylindrical non-magnetized medium, the transfer matrix equation of the cylindrical magnetized plasma photonic crystals is obtained. Applying this equation to the cylindrical structure, a quasi-periodic structure conforming to the Pell sequence is designed, which has good nonreciprocal property. Therefore, the absorptance of light propagating forward and backward in this structure are studied respectively. The concept of contrast ratio (D C ), calculated from the absorption of the forward and backward propagation of electromagnetic waves in the structure, is used to compare the degree of difference between the two. It is found that the nonreciprocal propagation becomes larger with the increase of the azimuth modulus and the relative dielectric constant of the medium, increases first, and then decreases with the increase of the incident angle, but does not change obviously when the plasma collision frequency and the cyclotron frequency of the plasma are getting larger. The absorptance decreases with the increase of azimuth modulus, relative dielectric constant, and plasma cyclotron frequency, and becomes better with the increase of the plasma collision frequency. However, when the incident angle gets larger, the absorptance becomes better at first and then gets worse.

Turbulence characteristics of turbulent pipe flow with porous wall

We report on the experiments of turbulent pipe flow with a porous wall. The pipe wall consists of a cylindrical porous medium in which there are many radial fine through-holes connected with a plenum chamber. We have investigated the dependence of friction factor f on Reynolds number Re up to Re~105 in porous pipe flow with a chamber, porous pipe flow without a chamber, and a smooth pipe flow. In the non-porous case, turbulent flow exhibits the Blasius law f = 0.3164Re-1/4 in the range of 3 × 103 ≲ Re ≲ 105. In porous pipe flow with chamber, on the other hand, we have found the scaling f~Re0 at higher Re ≳ 2 × 104, implying the Taylor dissipation law. In porous pipe flow without chamber, the friction drag increases compared to the non-porous case, but f decreases with increasing Re at Re ≲ 105. The significant difference in porous pipe flows with and without chamber suggests that the scaling f~Re0 in porous pipe flow with chamber is attributed to the fluid motion through the porous wall.

Methods to optimize conformal dynamic arcs in radiation therapy treatment planning

Conformal Dynamic Arcs (CDA) can provide a useful alternative in certain clinical situations which require a higher level of 3-dimensional (3D) conformation than shaped static fields but for which modulated fields (fixed or arc) are inappropriate. Due to lack of modulation, the quality of the dose distribution produced by a CDA is highly dependent on the specific patient geometry. The ideal geometry for a CDA, in terms of achievable conformation and uniformity, is a spherical target perfectly centered in a cylindrical medium or body and utilizing a full 360 degree of rotation. This manuscript will provide or review several methods a treatment planner may employ to improve dose distributions produced by CDA as the patient and/or target geometry or degrees of arc rotation vary from the ideal. These include:1. Weighting arc segments to improve homogeneity.2. Defining asymmetric margins for fitting leaves.3. Hybrid static/CDA compensating for CDA with limited degrees of rotations.4. Improving conformation in irregular target via use of pseudo-PTV.5. Creating concave features via the use of avoidance structures.6. Editing CDA multi-leaf collimator (MLC) to remove irregular hot spots.

Predicting radiative heat transfer in axisymmetric cylindrical enclosures using the collocation spectral method

In this paper, the collocation spectral method (CSM) is extended to solve the radiative transfer equation (RTE) in two-dimensional axisymmetric cylindrical medium, and an iterative solver based on Schur decomposition is developed for the spectral discretized equations. Then the performance of CSM is assessed by comparing with the semi-analytic solutions and the discrete ordinates method (DOM). The results show that the layout of angular grid points has great influence on the accuracy of CSM, and rearranging the angular grid can even reduce the ray effect. But a more reliable method to alleviate the ray effect is to decompose the radiative intensity into two components with separate treatments as the modified DOM proposed by Ramankutty and Crosbie (JQSRT, 57(1997) 107–140). Besides, the CSM can offer more accurate results than the DOM with acceptable computational cost and memory consumption, thus can be an alternative for the solution of RTE in cylindrical coordinates. However, the CSM loses its high order convergence accuracy for the two-dimensional problems due to the unavoidable non-smooth distribution of radiative intensity in both spatial and angular domains. Further treatments should be applied to improve the performance of CSM.

Anomalous Solute Transport in a Cylindrical Two-Zone Medium with Fractal Structure

In this paper, a problem of anomalous solute transport in a coaxial cylindrical two-zone porous medium with fractal structure is posed and numerically solved. The porous medium is studied in the form of cylinder with two parts: macropore—with high permeability characteristics in the central part and micropore—with low permeability around it. Anomalous solute transport is modeled by differential equations with a fractional derivative. The solute concentration and pressure fields are determined. Based on numerical results, the influence of the fractional derivatives order on the solute transport process is analysed. It was shown that with a decrease in the order of the derivatives in the diffusion term of the transport equation in the macropore leads to a “fast diffusion” in both zones. Characteristics of the solute transport in both zones mainly depend on the concentration distribution and other hydrodynamic parameters in the macropore.

Temperature distribution and stress analysis of end pumped lasers under Gaussian pump profile

Modified modeling of thermal effects within a dual end-pumped cylindrical shape laser medium was presented. The temperature distribution and the maximum hoop stress were determined by solving the heat conductance equation in a cylindrical medium. Two different incident beams of 0.6 mm waist radii were suggested, namely, effective and the Gaussian beam radii, where the effective beam radius is smaller by a factor of $$\sqrt 2$$ than the Gaussian beam radius. Under these considerations, the radial temperature difference due to an effective beam radius was found to be 23% higher than that for a Gaussian beam radius. The calculations show that the pump power does not affect the location of the maximum hoop stress as the spot does. A discrepancy within 1% was obtained by comparing the obtained results with the experimental work in the literature.