Equivalent Medium Research Articles

Impact of various iodine concentrations of iohexol and iodixanol contrast media on image reconstruction techniques in a vascular-specific contrast media phantom: quantitative and qualitative image quality assessment.

The aim of our study is to investigate the impact of iodine quantification on image reconstruction when employing a vascular-specific contrast media phantom with varying iodine concentrations. A 30-cm phantom simulating arterial and venous blood vessel diameters was manufactured. Small (9mm) and medium (12mm) cylinders contained iodine concentrations from 10 to 100% while large (21mm) cylinders were in quartiles from 25 to 100% diluted in blood equivalent medium. Each phantom was filled with either iohexol 350 mgI/mL (Group A) or iodixanol 320 mgI/mL (Group B) and then scanned separately. For each group, tube potential (80-140 kVp) and current (50-400mAs) were changed and all image series were reconstructed with filtered back projection (FBP), hybrid-based iterative reconstruction (HBIR) and model-based iterative reconstruction (MBIR). Mean opacification was measured in all groups. All data were compared employing an independent t test and Pearson's correlation. Visual grading characteristic (VGC) and Cohens' kappa analyses were performed. At 80 kVp, mean opacification using HBIR was significantly higher in Group B (2165 ± 1108 HU) than in Group A (2040 ± 1036 HU) (p < 0.009). At 140 kVp, MBIR and HBIR were greater in Group A (1704 ± 1033 HU and 1685 ± 1023 HU) versus Group B (1567 ± 1036 HU and 1567 ± 1034 HU) (p < 0.022). CNR using FBP, HBIR and MBIR was higher in Group B (46 ± 42 HU, 70 ± 163 HU and 83 ± 74 HU, respectively) than in Group A (43 ± 39 HU, 174 ± 130 HU and 80 ± 65 HU, respectively) (p < 0.0001-0.035). Qualitative image analysis demonstrated no difference in Cohen's kappa analysis. VGC was higher in Group A at all image reconstruction groups. Iohexol outperforms iodixanol in observer performance when assessing image reconstruction techniques and iodine concentrations in a vascular-specific contrast media phantom.

Reexamining the Necessity of Adding Water Curtain Borehole with Improved Understanding of Water Sealing Criterion

A water curtain system is widely adopted in the underground storage of gas/oil in unlined rock caverns to maintain a stable groundwater level and ensure a good water sealing condition for the storage facility. Hydrogeological tests were conventionally carried out in practice to assess the hydraulic conductivity of the surrounding rocks and evaluate the performance of the water curtain system. Among them, the hydraulic connectivity between adjacent boreholes is assessed using interconnectivity test, and it is commonly thought that, if the measured connectivity between two neighboring boreholes is low, a new borehole has to be added in the middle of them to improve the local efficiency of water curtain system. This paper reexamines the viewpoint of using interconnectivity test to determine the necessity of adding borehole. To this end, the conditions of water sealing were firstly discussed and the deficiency of existing water-sealing criterion was presented, with a new rigorous criterion proposed. The equivalent porous medium (EPM) flow model and fractured porous medium (FPM) flow model, two representative models for groundwater flow analysis, were then used to investigate the influences of borehole spacing and stored gas pressure on seepage field. These numerical results were employed to validate the proposed water-sealing criterion and suggested that, in terms of forming a stable water covering layer, the addition of borehole based on interconnectivity test is unnecessary and should be canceled for saving time and reducing cost.

Explication of absorbed dose defines radiotherapy – A study of unification

Radiotherapy is a branch of medicine which uses ionizing radiation for treatment of cancer. It can be described in two steps, viz. (I) dosimetry or the measurement of dose and (II) treatment or the delivery of dose to the patient in a planned manner. The foremost intention of this study is to unify the various steps involved in radiotherapy from the definition of dose. Considering the definition of dose as the central theme of argument, an elementary approach has been attempted to reveal the underlying string which connects all the branches in radiotherapy. Dose to the patient cannot be measured in the patient itself. The procedure is to measure it in an equivalent medium similar to the human body. Many changes were made from time to time in the field of dosimetry while choosing the medium for dose measurement experiments. With the advent of new devices and techniques, various changes and modifications have been made in the field of treatment with ionizing radiation. This study is an attempt to explain, relate and unify those changes and new advents in radiotherapy with the definition of dose.

Exploring impact of supersaturated lipid-based drug delivery systems of celecoxib on in vitro permeation across PermeapadⓇ membrane and in vivo absorption

Supersaturated lipid-based drug delivery systems have recently been investigated for oral administration for a variety of lipophilic drugs and have shown either equivalent or superior oral bioavailability compared to conventional non-supersaturated lipid-based drug delivery systems. The aim of the present work was to explore supersaturated versus non-supersaturated lipid-based systems at equivalent lipid doses, on in vivo bioavailability in rats and on in vitro permeation across a biomimetic PermeapadⓇ membrane to establish a potential in vivo - in vitro correlation. A secondary objective was to investigate the influence of lipid composition on in vitro and in vivo performance of lipid systems. Results obtained indicated that increasing the celecoxib load in the lipid-based formulations by thermally-induced supersaturation resulted in increased bioavailability for medium and long chain mono-/di-glycerides systems relative to their non-supersaturated (i.e. 85%) reference formulations, albeit only significant for the medium chain systems. Long chain systems displayed higher celecoxib bioavailability than equivalent medium chain systems, both at supersaturated and non-supersaturated drug loads. In vitro passive permeation of celecoxib was studied using both steady-state and dynamic conditions and correlated well with in vivo pharmacokinetic results with respect to compositional effects. In contrast, permeation studies indicated that flux and percentage permeated of supersaturated systems, either at steady-state or under dynamic conditions, decreased or were unchanged relative to non-supersaturated systems. This study has shown that by using two cell-free PermeapadⓇ permeation models coupled with rat-adapted gastro-intestinal conditions, bio-predictive in vitro tools can be developed to be reflective of in vivo scenarios. With further optimization, such models could be successfully used in pharmaceutical industry settings to rapidly screen various prototype formulations prior to animal studies.

철근 콘크리트 구조 내 포설 케이블의 HEMP 결합 근사 해석 방법

High-power electromagnetic fields, which are used as one of the core weapon systems in electronic warfare, can cause malfunctions in communication and power systems. Therefore, it is necessary to study their effects on civil and military facilities. In this paper, an approximated method for analyzing the voltage induced in a cable, placed inside a building, by HEMP was proposed. To calculate the electric field penetrating into the building, an equivalent medium for a multilayer reinforced concrete structure was implemented, and its transmission and reflection characteristics were obtained. The penetration level of the E1 pulse and the load voltage of the cable for unit voltage sources at each load were calculated. Subsequently, the coupling voltage was obtained and verified.

Evaluating the Clinical Outcomes of Three Medication Regimens for Treating a Sample of Iraqi Persistent Asthmatic patients

Abstract&#x0D; Asthma is a complex disease defined by chronic airway inflammation and airflow limitation causing variable respiratory symptoms which include shortness of breath (SOB), wheezing, chest tightness and cough. Asthma guidelines advocate adding a second long acting bronchodilator to medium doses of inhaled corticosteroids (ICS) rather using high doses of ICS alone to control moderate to severe persistent asthma. The aim of this study was to evaluate the clinical outcomes of three medication regimens indicated for Iraqi patients suffering from persistent asthma. &#x0D; This study was interventional randomized clinical study conducted on a sample of adult Iraqi asthmatic patients in Baghdad City. The study composed of three visits distributed over eight weeks; baseline visit followed by first follow up and second follow up visits after four and eight weeks respectively. The study enrolled 78 adult patients with moderate to severe persistent asthma as diagnosed by specialist physician according to patient history and baseline pulmonary function test (PFT) and allocated them randomly to three groups (each group included 26 patients) to receive equivalent medium doses of budesonide inhaler in addition to either formoterol inhaler, oral modified release aminophylline tablets or tiotropium inhaler (first, second and third group respectively). Sixty four patients completed this study. The mean ages of patients were above 35 years with slightly more male predominance.&#x0D; The study groups developed significant increase of peak expiratory flow rate (PEFR) and forced vital capacity (FVC) values at the first follow up visit compared to baseline values (p&lt;0.001). Thereafter, the first and third groups achieved significant higher values at the second follow up visit compared to first follow up visit (p&lt;0.001), while second group produced no change. All the groups developed significant improvement of Mini asthma quality of life questionnaire (MiniAQLQ) scores and percentage of symptom free days (SFD) at first follow up visit and continued further significant improvement at the second follow up visit (p&lt;0.001). Generally, between groups comparison according to extent of change of study parameters revealed that third group produced the greatest improvement over the entire study period followed by the first group, whereas the second group was associated with the least extent of improvement.&#x0D; This study concluded that all groups caused significant improvement in study parameters compared to baseline values and also concluded that the third group of inhaled [tiotropium/budesonide] was associated with the highest extent of improvement followed by first group, while the second group was the least. &#x0D;

Influence of frequency‐dependent anisotropy on seismic amplitude‐versus‐offset signatures for fractured poroelastic rocks

ABSTRACTFrequency‐dependent amplitude variation with offset offers an effective method for hydrocarbon detections and analysis of fluid flow during production of oil and natural gas within a fractured reservoir. An appropriate representation for the frequency dependency of seismic amplitude variation with offset signatures should incorporate influences of dispersive and attenuating properties of a reservoir and the layered structure for either isotropic or anisotropic dispersion analysis. In this study, we use an equivalent medium permeated with aligned fractures that simulates frequency‐dependent anisotropy, which is sensitive to the filled fluid of fractures. The model, where pores and fractures are filled with two different fluids, considers velocity dispersion and attenuation due to mesoscopic wave‐induced fluid flow. We have introduced an improved scheme seamlessly linking rock physics modelling and calculations for frequency‐dependent reflection coefficients based on the propagator matrix technique. The modelling scheme is performed in the frequency‐slowness domain and can properly incorporate effects of both bedded structure of the reservoir and velocity dispersion quantified with frequency‐dependent stiffness. Therefore, for a dispersive and attenuated layered model, seismic signatures represent a combined contribution of impedance contrast, layer thickness, anisotropic dispersion of the fractured media and tuning and interference of thin layers, which has been avoided by current conventional methods. Frequency‐dependent amplitude variation with offset responses was studied via considering the influences of fracture fills, layer thicknesses and fracture weaknesses for three classes amplitude variation with offset reservoirs. Modelling results show the applicability of the introduced procedure for interpretations of frequency‐dependent seismic anomalies associated with both layered structure and velocity dispersion of an equivalent anisotropic medium. The implications indicate that anisotropic velocity dispersion should be incorporated accurately to obtain enhanced amplitude variation with offset interpretations. The presented frequency‐dependent amplitude variation with offset modelling procedure offers a useful tool for fracture fluid detections in an anisotropic dispersive reservoir with layered structures.

Mathematical analysis and flux-based radius of influence for radon/VOC vapor intrusion mitigation systems

Volatile organic compounds (VOCs) and radon progeny pose potential health risks to occupants of certain buildings via subsurface vapor intrusion (VI) to indoor air. VI mitigation is usually performed using systems that extract gas from below the building, and the system performance is typically evaluated by measuring the distribution of applied vacuum below the floor. This article provides a new approach to assessing the radius of influence (ROI) for subslab venting systems based on mass flux instead of static vacuum distribution and includes an analyses of 121 pneumatic tests performed at 65 different suction points in 16 different buildings. The mathematical model represents a two-layer system with horizontal radial flow through transmissive material below the floor slab and vertical flow through discontinuities in the floor slab (which is simplified to approximate an equivalent porous medium). The analysis includes comparisons of the flux-based ROI to values calculated using the two-layer model for 1) vacuum, 2) velocity, and 3) travel time, which may be useful as alternative performance metrics for mitigation systems.

Homogenization of acoustic metamaterials using retrieval methods

The effective properties of two-dimensional acoustic metamaterials are here obtained by applying two retrieval methods, referred to as the direct inversion method and the differential method. They employ the scattering coefficients at the incidence and transmission sides of the global systems immersed in a fluid. A validation case study on a one-dimensional periodic design is first presented. A two-dimensional design comprising periodic cylindrical steel inclusions in a soft elastic matrix is then examined. Homogenization issues related to different underlying assumptions in the two retrieval methods are discussed. It is shown that one of the retrieval methods (the differential method) well describes the interior of the medium, away from the interfaces, while the other (the direct inversion method) captures the interface effects. The two retrieval methods are used to build homogeneous equivalent media which are used to predict scattering coefficients. A hybrid method is introduced which combines the two methods to create effective media that are accurate approximations of their 2D counterparts.

Estimating pore volume compressibility by spheroidal pore modeling of digital rocks

The real pores in digital cores were simplified into three abstractive types, including prolate ellipsoids, oblate ellipsoids and spheroids. The three-dimensional spheroidal-pore model of digital core was established based on mesoscopic mechanical theory. The constitutive relationship of different types of pore microstructure deformation was studied with Eshelby equivalent medium theory, and the effects of pore microstructure on pore volume compressibility under elastic deformation conditions of single and multiple pores of a single type and mixed types of pores were investigated. The results showed that the pore volume compressibility coefficient of digital core is closely related with porosity, pore aspect ratio and volumetric proportions of different types of pores. (1) The compressibility coefficient of prolate ellipsoidal pore is positively correlated with the pore aspect ratio, while that of oblate ellipsoidal pore is negatively correlated with the pore aspect ratio. (2) At the same mean value of pore aspect ratio satisfying Gaussian distribution, the more concentrated the range of pore aspect ratio, the higher the compressibility coefficient of both prolate and oblate ellipsoidal pores will be, and the larger the deformation under the same stress condition. (3) The pore compressibility coefficient increases with porosity. (4) At a constant porosity value, the higher the proportion of oblate ellipsoidal and spherical pores in the rock, the more easier for the rock to deform, and the higher the compressibility coefficient of the rock is, while the higher the proportion of prolate ellipsoidal pores in the rock, the more difficult it is for rock to deform, and the lower the compressibility coefficient of the rock is. By calculating pore compressibility coefficient of ten classical digital rock samples, the presented analytical elliptical-pore model based on real pore structure of digital rocks can be applied to calculation of pore volume compressibility coefficient of digital rock sample.

Research on the Response Relation of Acoustic Logging in Fractured Reservoirs

Based on Hudson equivalent medium model and Schoenberg linear sliding model theory, a fracture equivalent medium model suitable for sonic logging is proposed, and the equivalent elastic parameter expression of the inclined fracture is derived. Using the established equivalent medium model, the effects of fracture density, width, dip angle and fillings on formation P-wave velocity and anisotropy information obtained from sonic logging were studied, which provides a theoretical basis for evaluating fractured formations using acoustic logging data.

NUMERICAL STUDY OF PORE STRUCTURE EFFECTS ON ACOUSTIC LOGGING DATA IN THE BOREHOLE ENVIRONMENT

Existing methods of well-logging interpretation often contain errors in the exploration and evaluation of carbonate reservoirs due to the complex pore structures. The differences in frequency ranges and measurement methods deviated between the acoustic well logs and indoor ultrasonic tests cause inconsistent results. Based on the elastic wave equation and the principle of the control variable method, a 2D axisymmetric borehole model with complex pore structures was developed, and the numerical simulation method for acoustic log was constructed. The modeling results show that the power function can well describe the effects of pore structure on the acoustic waves, while the velocity of the Stoneley wave is not sensitive to the pore structure. Crack-like pores with pore aspect ratio (AR) less than 0.1 significantly affect the velocities of P- and S-waves, whereas “spherical” pores have fewer effects. The models with larger pore sizes have high velocities of P- and S-waves. The velocities calculated by the equivalent medium theory are always higher than the numerical simulation results. The velocity deviation caused by the difference in frequency is much smaller than the pore structure. A fractal approach to quantify the effects of pore structures is applied in the acoustic logging data. The fractal dimension increases with the pore AR or size when the porosity is constant, which can be described by a simple power function. This gives us new ideas and methods for pore structure evaluation in the lower frequency range than the conventional petrophysical model.

Optimal Design and Implementation of Inhomogeneous Planar Radome by Perforating the Host Material

An analytical expression for the reflection and transmission coefficients (TE and TM) for inhomogeneous planar layer (IPL) with variable inverse square relative permittivity is achieved. The correctness of derived expression is shown by comparison with Comsol numerical simulation. After choosing an appropriate material as the host medium, the transmission coefficient of inhomogeneous layer is calculated versus ${d} /{\lambda }_{{0}}$ . Then, the optimum profile of relative dielectric constant is obtained based on desired requirements. As an experimental prototype, IPL is discretized to seven different homogeneous layers. Equivalent medium theory (EMT) is used to realize necessary dielectric constant of each layer by using asymmetric Brugemans’s (ABG) formula. The radome layers are fabricated by perforating numerous holes in the host material with diameters sufficiently smaller than the wavelength. Properly sticking different layers together forms the final radome geometry. The designed radome is verified with free-space measurement setup. The measurement results are in good agreement with simulations and shows low insertion loss and high stability in wide aspect angle range for both TE and TM polarizations.

Broadband water-based metamaterial absorber with wide angle and thermal stability

In order to widen the absorption band of the metamaterial absorber to expand its application field, using the electromagnetic characteristics of water in the microwave band, a water-based metamaterial absorber with a structure different from the traditional “metal layer–dielectric layer–metal layer” one is proposed. The numerical simulation results show that its absorptivity of incident electromagnetic waves exceeds 90% in the ultra-wide operating band of 7.84–74.16 GHz and the absorption bandwidth can cover five bands including the X-band, Ku-band, K-band, Ka-band, and U-band. Based on the theories of equivalent medium and impedance matching, the mechanism of broadband absorption was explored by analyzing the electromagnetic field distribution and power loss density of the absorber. The designed absorber has the absorption performance of polarization independence, and it can work under a wide incident angle. In addition, the absorber has excellent thermal stability which can still maintain stable operation when the temperature changes from 0 °C to 100 °C. This water-based metamaterial absorber is of low cost, and its manufacturing process is relatively convenient, so it has broad application prospects in the fields of radar stealth, microwave darkroom, and prevention of electromagnetic radiation.

Computation of macroscopic permeability of doubly porous media with FFT based numerical homogenization method

In this paper we provide a FFT algorithm to compute the effective permeability of doubly porous solids constituted of two populations of pores which are different in size. The paper focuses on the resolution of the fluid flow at the intermediate scale, that of the macropores, that requires the resolution of the coupled Darcy/Stokes problem. The permeability associated with the first population of cavities is assumed to be known. A two-field FFT based iterative scheme is derived to compute the solution of the Darcy/Stokes problem. The principle is to reformulate the problem by considering a unique Brinkman equation with different coefficients for the Darcy and the Stokes regions. As a first application, we determine the macroscopic permeability of a porous solid containing circular macropores. The results are compared to analytic expressions and simplified modeling which use an equivalent Darcy medium in place of the macropores. Next, we apply the FFT method to a bi-porous polymer. The computations are performed on 2D and 3D cells extracted from X-ray computed microtomography.

Precise integration method for solving the seepage‐stress coupling problem in rock mass with singular possibilities of the coupling matrix

SummarySeepage‐stress coupling is a key problem in the field of geotechnical engineering, and the finite element method is one of the main methods to study seepage‐stress coupling in rock masses. However, the finite element method has issues of poor stability, low efficiency, and low accuracy in the simulation of the seepage‐stress coupling problem. In this paper, the homogeneous saturated rock mass is taken as the object to deduce the control equation based on the Biot's theory. Considering the singularity of the coupling matrix, the discrete equation is converted into a precise integral format, and the equation is solved by the precise integration method to avoid instability and low precision. The precise integration method in this paper has good numerical stability, fast convergence speed, and high simulation accuracy, which effectively facilitates the rapid and stable numerical simulation of the seepage‐stress coupling problem using the equivalent continuum medium model. The validity and accuracy of the precise integration method for seepage‐stress coupling problems are verified by numerical examples.

Wave propagation modeling in periodic elasto-thermo-diffusive materials via multifield asymptotic homogenization

A multifield asymptotic homogenization technique for periodic thermo-diffusive elastic materials is provided in the present study. Field equations for the first-order equivalent medium are derived and overall constitutive tensors are obtained in closed form. These lasts depend upon the micro constitutive properties of the different phases composing the composite material and upon periodic perturbation functions, which allow taking into account the effects of microstructural heterogeneities. Perturbation functions are determined as solutions of recursive non homogeneous cell problems emanated from the substitution of asymptotic expansions of the micro fields in powers of the microstructural characteristic size into local balance equations. Average field equations of infinite order are also provided, whose formal solution can be obtained through asymptotic expansions of the macrofields. With the aim of investigating dispersion properties of waves propagating inside the medium, proper integral transforms are applied to governing field equations of the homogenized medium. A quadratic generalized eigenvalue problem is thus obtained, whose solution characterizes the complex valued frequency spectrum of the first-order equivalent material. The validity of the proposed technique has been confirmed by the very good matching obtained between dispersion curves of the homogenized medium and the lowest frequency ones relative to the heterogeneous material. These lasts are computed from the resolution of a quadratic generalized eigenvalue problem over the periodic cell subjected to Floquet–Bloch boundary conditions. An illustrative benchmark is conducted referring to a Solid Oxide Fuel Cell (SOFC)-like material, whose microstructure can be modeled through the spatial tessellation of the domain with a periodic cell subjected to thermo-diffusive phenomena.

Modeling the impact of rainfall variations and management interventions on the groundwater regime of a hard-rock terrain in central India

Realistic assessment and prediction of groundwater resources, at appropriate scales, are crucial for proper management and systematic development of groundwater in India. An equivalent porous medium (EPM)-based groundwater flow model is implemented for a typical hard-rock aquifer in central India, to provide quantification, analysis and prediction of groundwater balance components. This research also provides refined estimates of aquifer parameters, recharge factors and newer insights into groundwater dynamics. It is observed that evaporative losses and effluent seepage of groundwater to rivers jointly account for ~20% of the annual recharge, which is significantly higher than most prior regional assessments. Evaluation of groundwater resource use under a business-as-usual scenario shows annual groundwater draft to exceed recharge by 13% in the year 2020–2021, and under a worst-case scenario (with prevailing drought conditions) this deficit is predicted to increase to 30%. However, with suitable recharge augmentation and demand control measures, in the best-case scenario, groundwater draft can be contained to ~90% of annual recharge, thereby ensuring long-term sustainability of groundwater resources. Importantly, this study reveals that demand control measures can be more effective than recharge augmentation measures.

An Experimental Study on Scale-Dependent Velocity and Anisotropy in Fractured Media Based on Artificial Rocks with Controlled Fracture Geometries

The scale of the fractures can vary, making the seismic velocity and anisotropy substantially scale dependent. Two mechanisms of the scale-dependent phenomenon may be considered: scattering and wave-induced fluid flow. In this study, we measure the scale-dependent velocity and anisotropy effects through laboratory experiments on porous and non-porous artificial rocks containing aligned fractures. This allows us to isolate the effects of these two mechanisms for the first time, yielding some insights into the scale-dependent phenomenon. For short-wavelength waves, scattering dominates with less wave-induced fluid flow effects. For intermediate- and long-wavelength waves, the P-wave is strongly scale dependent mainly due to wave-induced fluid flow mechanism, and the slow shear-wave is also strongly scale dependent but due to both scattering and wave-induced fluid flow. However, the fast shear-wave is almost scale independent. Moreover, a multi-scale equivalent medium theory can model the P-wave propagation accurately.

Transfer-matrix formulation of the scattering of electromagnetic waves and broadband invisibility in three dimensions

We develop a transfer-matrix formulation of the scattering of electromagnetic waves by a general isotropic medium which makes use of a notion of electromagnetic transfer matrix that does not involve slicing of the scattering medium or discretization of some of the position- or momentum-space variables. This is a linear operator that we can express as a matrix with operator entries and identify with the S-matrix of an effective nonunitary quantum system. We use this observation to establish the composition property of , obtain an exact solution of the scattering problem for a non-magnetic point scatterer that avoids the divergences of the Green’s function approaches, and prove a general invisibility theorem. The latter allows for an explicit characterization of a class of isotropic media displaying perfect broadband invisibility for electromagnetic waves of arbitrary polarization provided that their wavenumber k does not exceed a preassigned critical value , i.e. behaves exactly like vacuum for . Generalizing this phenomenon, we introduce and study -equivalent media that, by definition, have identical scattering features for .