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This study investigates a bifunctional cloak composed of concentric metamaterials arranged in 4N thin layers, where N denotes the number of periodic layer pairs within the structure. The structure includes an inner circular domain, an outer domain, and alternating sequences of 2N layers between them. We explore two models: one using isotropic materials and another one using anisotropic materials. The anisotropic model demonstrates superior cloaking performance for both electrical and thermal fields. Analytical solutions based on the Effective Medium Theory and boundary-value problems reveal the structure’s response under quasi-static conditions. Numerical simulations using COMSOL validate these findings, highlighting the cloak’s and concentration’s ability to manipulate external thermal and electric fields efficiently. [ABSTRACT FROM AUTHOR]

Understanding the nanotransport properties of NH 3 and H 2 is critical for designing adsorption and separation materials. In this work, we develop a novel numerical model at the molecular level by incorporating the M − S approach and effective medium theory, and provide a rigorous and analyzable simulation implementation for a binary transport system of NH 3 and H 2. In addition, the effect of pore length nonuniformity is simultaneously incorporated. The results show that high temperatures and large radii are detrimental to adsorption but favorable for diffusion at the single-pore scale, while the greater conductance increase in large pores dominates the fluid transport property in the pore network. The existence of a pore length distribution can induce greater effective diffusivity and lower apparent tortuosity within the pore network. Moreover, we confirm that at 300 K, the equilibrium selectivity of NH 3 over H 2 reaches approximately 28 in a uniform pore network with a pore radius of 0.25 nm, indicating the feasibility of nanoporous silica materials for use in adsorption separation of NH 3 and H 2 mixtures. [Display omitted] • Numerical transport model of NH 3 /H 2 mixture is built based on the M − S theory. • Competitive effect of adsorption and diffusion of fluid in nanopore is analyzed. • Influence of pore length distribution on fluid transport is discussed. • Possible strategy of NH 3 /H 2 mixture separation by Nano-porous silica is proposed. [ABSTRACT FROM AUTHOR]

Although light‐matter interaction and topology of photonic systems have been extensively studied, the topology induced novel light‐matter interaction phenomena in deep‐subwavelength region remain unexplored. Here, based on the non‐trivial topological singularity of 1D photonic crystals (PhCs), novel photonic spin Hall effects and abnormal beam behaviors are revealed in deep‐subwavelength region for the beams with nearly normal incidence, which beyond effective medium theory. The huge photonic spin Hall shift (PSHS) is observed around the singularity in the deep‐subwavelength region. The shape of reflected beam undergoes dramatic changes near the singularity, especially at the singularity, the reflected field is split as dipole‐like distribution for both polarizations. Physically, such a phenomenon is resulted from the destructive interference between the spin‐maintained beam and spin‐flipped beam. Based on these theoretical researches, super‐subwavelength thickness detecting, in which the wavelength is six orders of magnitude larger than the detecting scale, can be designed. Such sensitive detecting can also be applied to dielectric permittivity of PhC and background. Further more, by tuning the distance between two singularities in the deep‐subwavelength region, multi‐frequency channels sensitive detection and broadband platform with huge PSHS can be achieved. This system could be a platform to explore nontrivial light‐mater interaction in deep‐subwavelength region and to design of extremely sensitive detection devices. [ABSTRACT FROM AUTHOR]

In this study, a rapid water content detection method for donkey-hide gelatin was established based on terahertz time-domain spectroscopy in reflection mode. Notably, the effective medium theory, informed by the double-Debye relaxation for free water, was employed to predict the water content in the sample. The water content obtained through effective medium theory was lower than that of the traditional thermogravimetric method due to the existence of bound water. Bound water is invisible in THz spectroscopy due to its slower dynamics. In the frequency range of 0.22–0.48 THz, the offset in measured values between the thermogravimetric method and the THz-based method was fitted by a polynomial function. The results of THz-based method calibrated by polynomial fitting were consistent with the findings of the thermogravimetric method. The water content detection results derived by these two methods demonstrated high correlation values (R2) of 0.9860, 0.9160, and 0.9784, and small root mean square errors (RMSE) of 4.5584, 4.4887, and 5.3657 for three samples, respectively. Moreover, the proposed water content detection method needs to be calibrated only once by the thermogravimetric method. Overall, this study provides a rapid water content detection method and demonstrates the potential of real-time water content detection in donkey-hide gelatin. [ABSTRACT FROM AUTHOR]

Directional control of thermal emission over its broad wavelength range is a fundamental challenge. Gradient epsilon-near-zero (ENZ) material supporting Berreman mode has been proposed as a promising approach. However, the bandwidth is still inherently limited due to the availability of ENZ materials covering a broad bandwidth and additional undesired omnidirectional modes in multilayer stacking with increased thickness. Here, we show that broadband directional thermal emission can be realized beyond the previously considered epsilon-near-zero and Berreman mode region. We then establish a universal approach based on effective medium theory to realizing ultra-broadband directional thermal emitter. We numerically demonstrate strong (emissivity >0.8) directional (80 ± 5°) thermal emission covering the entire thermal emission wavelength range (5–30 μm) by using only two materials. This approach offers a new capability for manipulating thermal emission with potential applications in high-efficiency information encryption, energy collection and utilization, thermal camouflaging, and infrared detection. [ABSTRACT FROM AUTHOR]

The severe climate and energy issues require more environmentally friendly and efficient cooling methods. Radiative cooling offers a cooling solution with significant advantages. However, current radiative cooling technologies focus primarily on seeking perfect materials to achieve complete wavelength absorption. However, numerous research studies have shown that achieving such a perfect scenario is not feasible. Here, inspired by the surface of the Cerambycini Latreille, the inherent mechanism of radiative cooling functionality in the unique structure of these hairs is revealed using effective medium theory and Finite Difference Time Domain (FDTD) optical simulation analysis. Through alkaline etching and template methods, a biomimetic radiative cooling film (BRCF) was successfully fabricated. The BRCF not only efficiently reflects solar radiation but also enhances absorption in the atmospheric window wavelength range. The radiative cooling mechanism proposed in this study and the BRCF presented here may inspire researchers to further explore the field of structural radiative cooling. [ABSTRACT FROM AUTHOR]

This paper presents a cross-scale prediction of the dielectric properties of long-term-cured tricalcium silicate (C3S) paste specimens and investigated the effect of different phase geometry models on the prediction results. Firstly, the dielectric properties of C3S paste specimens cured for 180 days were tested. Based on tests such as X-ray diffraction (XRD) and mercury intrusion porosity (MIP), the types of phases and the volume fractions of individual phases in the C3S paste specimens were determined. Subsequently, the dielectric performance of the phases was measured. The dielectric performance linkage between each phase and the C3S paste specimen was established based on the effective medium theory. The effects of three morphological models of the phase on the predicted results were dissected. The results showed that the volume fraction and dielectric constant of calcium silicate hydrates (C-S-H) gel were significantly higher than those of other phases in the C3S paste specimens. Among the three computational models of phase geometry, the standard spherical phase model produced the best prediction. The prediction results of the standard spherical model improved the accuracy by more than 45.8% compared with that of the oblate phase model and the prolate phase model. Among the phases, the trend of the dielectric constant of C-S-H gels with frequency was the most similar to the results obtained by the three prediction models. [ABSTRACT FROM AUTHOR]

In this paper, features of generation of two types of surface plasmon-polaritons (SPPs) in optical anisotropic hyperbolic metamaterials formed by a periodic lattice of metal nanocylinders embedded in a dielectric matrix are considered. The dependencies of the group velocity and the penetration depth inside metamaterial of the generated plasmon-polaritons on filling ratio are established and analyzed. Based on the effective medium theory, the surface plasmon-polaritons generation at interface of hyperbolic metamaterials is analytically calculated and discussed. [ABSTRACT FROM AUTHOR]

• A mixing rule for imaginary parts of refractive indices is derived. • This Rayleigh Mixing Rule is valid for small particles in the Rayleigh regime. • In certain limits, it is in good agreement with established mixing rules. • The Rayleigh Mixing Rule retrieves imaginary parts of refractive index spectra. • Retrieved imaginary parts of refractive indices are weakly dependent on morphology. A Rayleigh mixing rule that relates the effective imaginary part of the refractive index of a composite medium, such as an aerosol or colloid, to the complex refractive index of the Rayleigh particles is derived using Rayleigh scattering theory. The derivation is simple, straightforward, and only weakly dependent on particle morphology. The Rayleigh mixing rule offers an opportunity to derive the imaginary part of refractive index spectra of Rayleigh particles, suspended in a non-absorbing medium with known refractive index spectrum, from an extinction spectrum of the composite medium. However, for this application, the real refractive index spectrum of the particle must be known reasonably well and the imaginary part must be known well enough to decide between two mathematical solutions for it. The Rayleigh mixing rule is compared with widely used mixing rules (i.e., volume, Maxwell Garnett, and Bruggeman mixing rules) and we show that in the small volume fraction regime both the Maxwell Garnet and Bruggeman mixing rules agree with the Rayleigh mixing rule. [ABSTRACT FROM AUTHOR]

Carbonate rocks have a wide variety of pore shapes and different types of grains, which greatly affect the elastic properties and characteristics of the reservoir. This causes certain difficulties in petroelastic modeling. One of the problems is the scale of the input data, which is then used to build the rock physics model. The paper presents the results of studying three core samples of carbonate rocks of the Upper Devonian and Lower Carboniferous age, which are located in the South Tatar arch (Volga-Ural oil and gas basin (Russia)). To evaluate the structural characteristics of the pore space, the effective medium theory is used. The input data are the results of laboratory studies that include measurements of the velocities of longitudinal and transverse waves, porosity, and thin section and computed tomography analysis. When using the computed tomography, the core samples are analyzed at different resolution (12–37 µm/voxel). The tomography studies of pore space at different scales provide rather different values of porosity and pore aspect ratio. The tomography-based porosity estimations also differ from the experimentally measured porosity (up to 10%). The pore space characteristics provided by different datasets are used to build a rock physics model for the studied rocks that helps to estimate the elastic wave velocities with three different methods of effective medium theory (self-consistent approximation, differential effective medium (DEM), and the Kuster–Toksöz method). A comparison of the velocity estimations with their experimental analogs for dry rocks may indicate the presence of microcracks whose size is beyond the tomography resolution. Improved rock physics models incorporating both pores and microcracks are then used to predict the elastic wave velocities of fluid-saturated rock in a wide porosity range. It is demonstrated that the predicted values significantly differ (up to 30%) from those provided by the rock physics (RP) models constructed without the support of the tomography results. Moreover, other types of models are considered in which the difference in experimental and theoretical velocities is attributed to changes in the host matrix properties as compared to the calcite polycrystal, which are caused by various reasons. [ABSTRACT FROM AUTHOR]

A close solution to acoustic illusion, caused by layered acoustical concentrator, has been investigated in-depth theoretical analysis using acoustic wave scattering theory. Based on this theory, a precise expansion for the scattered pressure field in each layer has been calculated, which by comparing this expansion with scattered field expansion of a bare cylinder, the illusion perception has been illustrated clearly. To show more clear illusion perception, an angular scattering cross section has been provided for bare and layered media. The size and constitute parameters of bare and layered media have been calculated using both transformation acoustics theory and effective medium theory. It is noteworthy that the concentration effect of layered concentrator has been introduced before, but no close solution to illusion perception has ever been provided. [ABSTRACT FROM AUTHOR]

A wide‐scanning dual‐polarized Luneburg lens antenna based on the quasi‐pyramid structure is proposed. To achieve beam consistency, 18 identical quasi‐pyramid sections are employed to approximate a spherical lens antenna, and each section is divided into 12 layers. The 6‐stepped gradient permittivity index is achieved by the diced ring‐type periodic unit cells in accordance with the Effective Medium Theory. Each quasi‐pyramid is incorporated with the same connecting structure to form an integrity. And a dielectric rod is penetrated parallelly to the center axis of the lens, thus improving the robustness of the overall structure. The radius of the whole lens is merely 0.88λ0. The spherical Luneberg lens antenna is fabricated and measured, with an impedance bandwidth of 45.5%, a measured peak gain of 15.4/15.1 dBi and a cross‐polarization level of higher than 17/17.5 dB. Placing the feed antenna at different locations during the measurement, results attest that those beams possess an excellent consistency. The multibeams are able to achieve an ultra‐wide beam coverage of 165°, promising it a serviceable candidate for mobile communication base stations and wireless networking. [ABSTRACT FROM AUTHOR]

The modeling of fluid transport in nanoporous materials has long attracted attention because of the numerous industrial applications of such materials, particularly in membrane-based separations, and others such as adsorptive gas separation and storage, catalysis, and the emerging area of nanofluidics. While effective medium theory has been widely used in modelling this transport, a critical approximation that all pores have the same length is commonly made, whose adequacy is unknown. Here we apply effective medium theory to a randomly overlapping capillary model having an inherent pore length distribution related to the pore radius distribution, and compare the network transport properties with those of the commonly used uniform pore length random network. We find that the consideration of nonuniform pore length distribution leads to significantly higher effective diffusivity and lower associated apparent tortuosity, mediated by the lower mean pore length of large pores due to their higher probability of overlap. The decrease in pore length with an increase in pore radius and the competing effects of adsorption and diffusion, lead to more complex behaviour of the transport properties with variation in temperature and relative standard deviation of the pore radius distribution. Our results clearly demonstrate the importance of considering nonuniformity of pore length, as the conventional uniform pore length approximation leads to significantly different and therefore misleading results. [Display omitted] • Comparison of transport properties of two different pore networks using effective medium theory. • A network of overlapping randomly oriented long capillaries has an inherent pore length distribution. • Effective diffusivity and tortuosity of membranes is strongly affected by pore length nonuniformity. • Nonuniformity in pore length enhances effective diffusivity compared to uniform pore length. [ABSTRACT FROM AUTHOR]

We employed the p-type semiconductor InTe as an extrinsic phase mixing in the GeTe matrix for thermoelectric properties investigations on the (GeTe) 1-x (InTe) x (x=0, 0.02, 0.04, 0.06, and 0.08) composites. We observed notable phenomena that a small amount of InTe has a significant influence on the thermoelectric properties as the primary host matrix in the (GeTe) 1-x (InTe) x (x=0.02, 0.04, 0.06, and 0.08) composites. Even for small concentrations of InTe which possess lower thermal and electrical conductivities compared to those of GeTe, the thermoelectric properties of the (GeTe) 1-x (InTe) x (x=0.02, 0.04, 0.06, and 0.08) composites are primarily influenced by the properties of InTe. We systematically elucidated the electrical conductivity of the (GeTe) 1-x (InTe) x (x=0.02, 0.04, 0.06, and 0.08) composites through the application of effective medium theory (EMT). It is found that the effective media of the (GeTe) 1-x (InTe) x (x=0.02, 0.04, 0.06, and 0.08) composites is an asymmetric medium insulator. The addition of InTe into GeTe reveals a significant decrease in total thermal conductivity due to reductions in both electronic and lattice thermal conductivity. Particularly, the decrease in lattice thermal conductivity was attributed to an increase in internal strain within the lattice induced by the addition of InTe. Consequently, the ZT values of the composite significantly increase across all temperature ranges. This study suggests that developing composites is an effective approach for enhancing thermoelectric performance, comparable to elemental doping, and demonstrates the ability to analyze the electrical properties of composite materials using EMT. • We synthesized the extrinsic phase mixing composite of (GeTe)1-x(InTe)x. • Small InTe concentration significantly changes thermal and electrical transport properties. • Effective medium theory states that the composite follows an asymmetric medium insulator. • Decrease of lattice and electronic thermal conductivities enhances ZT value over a wide temperature range. [ABSTRACT FROM AUTHOR]

This research applies Effective Medium Theory and 3D Finite Element Analysis to model the transmissive loss through a waveguide fed additively manufactured Luneburg lens. New results are presented that provide rational function approximations for accurately modeling the aperture, beam, and radiation loss factors of the antenna. It introduces a normalized loss tangent and shows that the loss factors are dependent on the product of this parameter and the lens radius. Applying the constraint that the main beam of the radiation pattern contains 50% of accepted power, a maximum useful radius is tabulated for common polymers used in additive manufacturing. [ABSTRACT FROM AUTHOR]

Many models of damage or cracking of isotropic solids consider a single damage/crack density variable. Based on both continuum damage mechanics (CDM) and effective medium theory (EMT), we model the impact of isotropic damage in the form of microcracks on the elastic properties of an isotropic solid. For each approach, we consider the complete tensorial description of the elastic moduli involving two damage/crack density variables D 1 and D 2 , or α and β ; and possible scalar approximations involving a single variable (with either D 2 = 0, or β = 0). We assess the accuracy of scalar approximations commonly employed for each approach against laboratory measurements of ultrasonic wave velocities and density obtained on a dry and isotropic specimen of thermally cracked Carrara Marble (CM) subjected to an increasing confining pressure up to 50 MPa. Overall, this laboratory dataset and the CDM and EMT modelling and inversion results reported here suggest that: (i) irreversible thermal cracking and microcrack opening occur after heating and sudden cooling of the CM specimen, whereas reversible and progressive microcracks' closure occurs with increasing confining pressure; (ii) tensorial damage/cracking models involving either two damage variables (CDM) or two crack density variables (EMT) fit equally well and virtually perfectly the laboratory data for any confining pressure tested; (iii) single scalar approximation models commonly used in CDM or the EMT models give comparable results to their complete tensorial counterparts, which is particularly true for the CDM approach; (iv) single scalar approximations derived from the CDM approach, and assuming a constant Poisson's ratio of the cracked rock, reproduces all the elastic moduli more accurately than the corresponding scalar approximation derived from the EMT approach, where a constant ratio of Young's modulus to Poisson's ratio is assumed instead; and (v) it is more reliable to use a tensorial rather than a scalar description of the effect of reversible microcrack closure with pressure on all elastic parameters, including Poisson's ratio. If the impact of reversible microcrack closure is accounted for, then a single scalar description of irreversible thermal damage with the CDM approach is remarkably accurate. [ABSTRACT FROM AUTHOR]

The study is focused on the problem of using geophysical data to estimate brittleness of rock masses for the needs of petroleum industry. Three main developed ways to estimate brittleness—mineral-based, log-based, and elastic-based brittleness indices—are discussed from the perspective of scaling factor. The study highlights the contradictions between brittleness indices calculated from the same data using various ways of introducing brittleness. These contradictions are explained by scaling factor, as geophysical data used for brittleness estimation are typically obtained at different spatial and temporal scales. A model based on the effective medium theory is used to understand the relationships between inner structure of inhomogeneous rocks and their brittleness indices estimated from laboratory tests on core samples as well as log data analysis. [ABSTRACT FROM AUTHOR]

Macroscopic poroelasticity and effective medium theory are two independent approaches which can be used to analyze the role of pores, cracks, and fluid on elastic properties. Macroscopic poroelasticity belongs to the macroscopic framework of thermodynamics whereas effective medium theory expresses the medium properties in terms of microstructural characteristics (pore and crack shape, etc.) and component properties (fluid properties, solid grain properties, etc.). In this paper, we review the fundamental assumptions and results of both approaches, and show that they are complementary but do not apply over the same range of conditions. A compilation of data is reported, in various dry and saturated rocks, to show the validity of the Gassmann equation and the dispersion between unrelaxed modulus –where effective medium model applies- and relaxed modulus –where poroelasticity applies. [ABSTRACT FROM AUTHOR]

Theoretical guidance on the optical properties of plasmonic nanoparticles (NPs) is of significant importance in tremendous numbers of fields like photovoltaics. The incorporation of plasmonic NPs into photovoltaic material can promote optical absorption either via the excitation of localized surface plasmon resonance (LSPR) modes or due to multiple light scattering. Since most fabrication techniques for the incorporation of NPs into photovoltaic material result in a random array of NPs with various sizes, numerical simulations based on solving the Maxwell equations are computationally expensive and prohibitively slow for this large number of NPs. Therefore, in this paper, based on modified effective medium theories, taking into account finite size of NPs, size dispersion for NPs, extrinsic dynamic effect, and intrinsic confinement effect, fast and cost-effective analytical modeling, considering both LSPR and scattering effects, is presented to obtain the optical properties of photovoltaic material incorporated by spherical NPs with nonuniform size and random distribution. Then, by means of presented analytical modeling, considering reasonably low and high volume fractions of NPs in addition to small and large size of NPs, the effect of different parameters of embedded NPs into organic and inorganic photovoltaic materials is explored. [ABSTRACT FROM AUTHOR]

This review is dedicated to the Effective Medium Theory of two-component metamaterials in the broad frequency range from microwaves to visible region. The metamaterials are unbounded periodic 2-D lattice of infinitely long cylinders of circular cross section or unbounded periodic 3-D lattice of spherical particles embedded in a homogeneous isotropic host dielectric. Three types of inclusions are considered: 1) non-magnetic metal inclusions; 2) ferric inclusions; 3) ferromagnetic inclusions. It is assumed that ferric and ferromagnetic inclusions can be fully or partially magnetized by an external dc bias magnetic field. Two directions of wave propagation are considered for magnetized inclusions: 1) the direction of the bias field; 2) the direction transversal to the direction of magnetization. It has been shown that the metamaterials can exhibit the different properties depending on the material constituent and the direction of wave propagation. Antenna substrate application of the metamaterials is discussed in the review. [ABSTRACT FROM AUTHOR]

The following article is a critical review of the most popular hypotheses that have been used in the past to model analytically or numerically the thermal conductivity enhancement of nanofluids (Λ). This analysis starts first with the Effective Medium Theories (EMT), which have been used in the past to calculate the macroscopic properties of solid composites. Secondly, the hypotheses of a Λ due to Brownian movement are evaluated. All estimations and characteristic dimensions point to a negligible Λ due to Brownian motion. In third place, the hypotheses based on the agglomeration of nanoparticles provide a convincing explanation for the experimental measurements of Λ. Furthermore, the complicated dynamics of agglomeration could be the source of disparity between the published measurements of Λ. Lastly, the possible effect of liquid layering is briefly discussed. All in all, agglomeration as the principal mechanism for Λ might prove to be sufficient to explain the thermal behavior of nanofluids. [ABSTRACT FROM AUTHOR]

In this paper, the spectral properties of the triangular lattice of grana are investigated. By the finite difference time domain method, the transmittance spectra of the structure are calculated and the components of the scattering matrix are determined, which makes it possible to determine the effective parameters of the structure. As a result, it was shown that a two-dimensional lattice of grana can be represented as a homogeneous film with a thickness equal to the height of the grana. It is shown that the positions of the resonances before and after the homogenization of the structure coincide, which makes this method attractive for estimated calculations of the structure. [ABSTRACT FROM AUTHOR]

A novel strategy is proposed by using surface plasmon resonance technique to investigate the corrosion process of silver thin film within 100 nm thickness exposed to laboratory air. Specifically, we continuously test surface plasmon resonance curves of silver thin film for 40 days and calculate its permittivity and thickness. Measurements of energy dispersive spectrometer indicate that there are silver sulfide formations on the film surface in the corrosion process. By using Maxwell–Garnett effective medium theory, the volume fraction of silver sulfide was confirmed in the silver/silver sulfide composites film. The results reveal that the concentration of silver sulfide in the film sample increases exponentially during the corrosion process and increases rapidly in the initial stage. [ABSTRACT FROM AUTHOR]

Although parity-time (PT)-symmetric systems can exhibit real spectra in the exact PT-symmetry regime, PT-symmetry is actually not a necessary condition for the real spectra. Here, we show that non-PT-symmetric photonic crystals (PCs) carrying Dirac-like cone dispersions can always exhibit real spectra as long as the average non-Hermiticity strength within the unit cell for the eigenstates is zero. By building a non-Hermitian Hamiltonian model, we find that the real spectra of the non-PT-symmetric system can be explained using the concept of pseudo-Hermiticity. We demonstrate using effective medium theories that, in the long-wavelength limit, such non-PT-symmetric PCs behave like the so-called complex conjugate medium (CCM) whose refractive index is real but whose permittivity and permeability are complex numbers. The real refractive index for this effective CCM is guaranteed by the real spectrum of the PCs, and the complex permittivity and permeability come from non-PT-symmetric loss-gain distributions. We show some interesting phenomena associated with CCM, such as the lasing effect. [ABSTRACT FROM AUTHOR]

Thermal conductivity of nanocrystalline and ultra-nanocrystalline films is analyzed with effective medium theory (EMT) models. The existing EMT models use the spherical inclusion approximation. Although this approximation works quite well it is inconsistent, mostly with respect to the maximal packing of 74%, which may be unrealistic for polycrystalline films. To check the consistency of these models we devise an EMT model with arbitrarily shaped inclusions. We pick the EMT model with cubic inclusions and we compare its results with the results of the EMT model with spherical inclusions. It is found a very good agreement between both calculations. This agreement is explained by general geometrical arguments. We further employ these models to analyze thermal conductivity of nanocrystalline and ultra-nanocrystalline diamond films. It is noticed that the effective conductivity is strongly affected not only by the boundary Kapitza resistance but also by intra-grain scattering for grain sizes below 100 nm. Generally, both intra-grain conductivity and Kapitza resistance increase with grain size. However, the effect of Kapitza resistance increase is negligible due to the geometrical factor accompanying Kapitza resistance contribution to the effective conductivity. Unlabelled Image • An effective medium model with arbitrarily shaped inclusions is given for thermal conductivity of polycrystalline films • A more appropriate model with cubic crystallite gives similar results like the existing models with spherical crystallites • The theory is applied to model thermal conductivity of nanocrystalline and ultra-nanocrystalline diamond films • Thermal conductivity is strongly affected by Kapitza resistance and intra-grain scattering for grain sizes below 100 nm • Intra-grain conductivity and Kapitza resistance increase with grain size, but the effect of Kapitza resistance is small [ABSTRACT FROM AUTHOR]

A generalized course of action was proposed for determining the separation properties of the interphase between filler and polymer phases in various mixed matrix membranes (MMMs). Accordingly, the permeability and thickness of the interphase were estimated by using the modified form of effective medium theory (EMT) and CO2, N2 and CH4 permeability data at two different filler loadings obtained from the literature. In spite of the sensitivity of the estimations to experimental inconsistencies in the data used, significant information could generally be obtained about the interphase permeability and thickness. It was observed that the interphase in different types of MMMs could have dissimilar separation properties even when the polymer used was the same. The CO2/CH4 ideal selectivities of the interphase between graphene oxide and polyether block amide (Pebax) polymer and the interphase between zeolite Y and a polyimide polymer, Matrimid, were determined to be higher than the selectivities of the pure polymers. Tailoring the interphase by having good knowledge of its properties, is expected to provide significant means for further improvement of the performances of mixed matrix membranes. [ABSTRACT FROM AUTHOR]

Garnet Li 7 La 3 Zr 2 O 12 (LLZO) is a promising solid electrolyte candidate for solid-state Li-ion batteries, but at room temperature it crystallizes in a poorly Li-ion conductive tetragonal phase. To this end, partial substitution of Li+ by Al3+ ions is an effective way to stabilize the highly conductive cubic phase at room temperature. Yet, fundamental aspects regarding this aliovalent substitution remain poorly understood. In this work, we use molecular dynamics and advanced hybrid Monte Carlo methods for systematic study of the room temperature Li-ion diffusion in tetragonal and cubic LLZO to shed light on important open questions. We find that Al substitution in tetrahedral sites of the tetragonal LLZO allows previously inaccessible sites to become available, which enhances Li-ion conductivity. In contrast, in the cubic phase Li-ion diffusion paths become blocked in the vicinity of Al ions, resulting in a decrease of Li-ion conductivity. Moreover, combining the conductivities of individual phases through an effective medium approximation allowed us to estimate the conductivities of cubic/tetragonal phase mixtures that are in good agreement with those reported in several experimental works. This suggests that phase coexistence (due to phase equilibrium or gradients in Al content within a sample) could have a significant impact on the conductivity of Al-substituted LLZO, particularly at low contents of Al3+. Overall, by making a thorough comparison with reported experimental data, the theoretical study and simulations of this work advance our current understanding of Li-ion mobility in Al-substituted LLZO garnets and might guide future in-depth characterization experiments of this relevant energy storage material. Image 1 [ABSTRACT FROM AUTHOR]

Abstract In this paper, we first design a coordinate transformation and derive the anisotropic material parameters of the quadrilateral thermal cloak according to the transformation thermodynamics principle. Then, since the derived parameters are inherently anisotropic, we eliminate its anisotropy by considering the effective medium theory and use a layered structure of metamaterials composed of only two isotropic materials to design the cloak device. Finally, we simulate the performance of a perfect and layered thermal cloak by the finite element method. To the best of our knowledge, this is the first work to design and simulate the performance of this quadrilateral thermal cloak by the finite element method(FEM). [ABSTRACT FROM AUTHOR]

A reexamination of the Clausius–Mossotti relation in which material with both electric and magnetic responses yields surprising results. Materials with indices near zero and with real parts less than zero, that is the real part of both the permeability and permittivity are negative, are found to emerge from the interaction of electric and magnetic responses in a self-consistent theory. The new results point the way to artificial and natural materials with exotic responses. A simulation with ∼ 1 0 10 particles shows good agreement with the analytical results. • Clausius–Mossotti relation is revised for media with electric and magnetic responses • Simulations for a large ensemble of particles show an agreement with the theory • Revisited Clausius–Mossotti relation has a promise for the effective medium theories [ABSTRACT FROM AUTHOR]

• A modified effective medium theory (m-EMT) is established to predict thermal conductivity of random Si/Ge superlattices. • Combination of m-EMT and genetic algorithm achieves high-throughput screening of superlattices for minimum conductivity. • Thermal conductivities of aperiodic superlattices can be constantly reduced to 1.5 W/(m·K) regardless of the total thickness. • The intense Anderson localization occurs at interfaces sandwiched between the highly asymmetric thick and thin layers. Superlattices (SLs) have received great attention as thermoelectric materials because phonon transport in them can be tailored independently without changing the electronic properties to enhance the thermoelectric figure of merit and conversion efficiency. Heterogeneous aperiodic SLs (ap-SLs) have lower thermal conductivity than their periodic counterparts (p-SL) due to Anderson localization of coherent phonons. Due to enormous amounts of layered structure combinations in ap-SLs, it is challenging to efficiently screen through all the combinations for the structure with the minimum thermal conductivity. In this work, a modified effective medium theory (m-EMT) is established to predict the thermal conductivity of Si/Ge p-SLs and ap-SLs. The effects of Anderson localization and layer thickness distribution are considered using a correction function for the degree of randomization (DOR) in layer thickness. The combination of the m-EMT and the genetic algorithm enables high-throughput screening of enormous amounts (∼ 2 n , where n is the number of atomic layers) of SL structures with micron-scale total SL thickness. The thermal conductivities of ap-SLs can be constantly reduced to 1.5 W/(m·K) at average periodic layer thicknesses of 2.0 nm and a DOR of 0.8, regardless of the total SL thicknesses. Phonon spatial localization energy distribution further reflects the intense Anderson localization at interfaces, especially for those sandwiched between the highly asymmetric thick and thin layers. This work provides a high-throughput screening tool to theoretically design micron-scale and heterogeneous SLs, with detailed structural guidance for experimentally growing ap-SL with minimum thermal conductivities. [Display omitted] [ABSTRACT FROM AUTHOR]

• Nanoscale heat transport does not obey Fourier's law and, at the very least, the Boltzmann transport equation (BTE) must be employed. • The BTE is computationally expensive to compute since it entails tracking phonon trajectory both in real- and momentum-space. • We develop a new method that allows us to compute the effective thermal conductivity in porous materials using precomputed key parameters associated with the material's geometry and underlying bulk system. • Precomputed parameters are provided for several combinations of geometries and bulk materials and disseminated on GitHub. Nanostructured materials enable high thermal transport tunability, holding promises for thermal management and heat harvesting applications. Predicting the effect that nanostructuring has on thermal conductivity requires models, such as the Boltzmann transport equation (BTE), that capture the non-diffusive transport of phonons. Although the BTE has been well validated against several key experiments, notably those on nanoporous materials, its applicability is computationally expensive. Several effective model theories have been put forward to estimate the effective thermal conductivity; however, most of them are either based on simple geometries, e.g., thin films, or simplified material descriptions such as the gray-model approximation. To fill this gap, we propose a model that takes into account the whole mean-free-path (MFP) distribution as well as the complexity of the material's boundaries in infinitely thick films with extruded porosity using uniparameter logistic regression. We validate our approach, which is called the "Ballistic Correction Model" (BCM), against full BTE simulations of a selection of three base materials (GaAs, InAs, and Si) with nanoscale porosity, obtaining excellent agreement. While the key parameters of our method, associated with the geometry of the bulk material, are obtained from the BTE, they can be decoupled and used in arbitrary combinations and scales. We tabulated these parameters for a few cases, enabling the exploration of systems that are beyond those considered in this work. Providing a simple yet accurate estimation of thermal transport in nanostructures, our work sets out to accelerate the discovery of materials for thermal-related applications. [ABSTRACT FROM AUTHOR]

Nanoscale radiative thermal transport between a pair of metamaterial gratings is studied within this work. The effective medium theory (EMT), a traditional method to calculate the near-field radiative heat transfer (NFRHT) between nanograting structures, does not account for the surface pattern effects of nanostructures. Here, we introduce the effective approximation NFRHT method that considers the effects of surface patterns on the NFRHT. Meanwhile, we calculate the heat flux between a pair of silica (SiO2) nanogratings with various separation distances, lateral displacements, and grating heights with respect to one another. Numerical calculations show that when compared with the EMT method, here the effective approximation method is more suitable for analyzing the NFRHT between a pair of relatively displaced nanogratings. Furthermore, it is demonstrated that compared with the result based on the EMT method, it is possible to realize an inverse heat flux trend with respect to the nanograting height between nanogratings without modifying the vacuum gap calculated by this effective approximation NFRHT method, which verifies that the NFRHT between the side faces of gratings greatly affects the NFRHT between a pair of nanogratings. By taking advantage of this effective approximation NFRHT method, the NFRHT in complex micro/nano-electromechanical devices can be accurately predicted and analyzed. [ABSTRACT FROM AUTHOR]

This work focused on the application of the effective medium theory to describe the extinction coefficient (Qext) in molybdenum trioxide (MoO3) doped with different kinds of plasmonic nanoparticles, such as silver (Ag), gold (Au), and copper (Cu). Usually, in studies of these materials, it is normal to analyze the transmission or absorption spectra. However, the effect of this type or size of nanoparticles on the spectra is not as remarkable as the effect that is found by analyzing the Qext of MoO3. It was shown that the β-phase of MoO3 enhanced the intensity response of the Qext when compared to the α-phase of MoO3. With a nanoparticle size of 5 nm, the Ag-doped MoO3 was the configuration that presents the best response in Qext. On the other hand, Cu nanoparticles with a radius of 20 nm embedded in MoO3 was the configuration that presented intensities in Qext similar to the cases of Au and Ag nanoparticles. Therefore, implementing the effective medium theory can serve as a guide for experimental researchers for the application of these materials as an absorbing layer in photovoltaic cells. [ABSTRACT FROM AUTHOR]

This paper investigates the spontaneous decay rate of elliptical plasmonic nanostructures. The refractive index was analyzed using the effective medium theory (EMT). Then, the polarizability, spontaneous radiative, non-radiative decay rate, and electric field enhancement factor were characterized for the targeted elliptical nanostructures at different aspect ratios. All of the optical analyses were analyzed at different distances between the excited fluorescent coupled atom and the plasmonic nanostructure (down to 100 nm). This work is promising in selecting the optimum elliptical nanostructure according to the required decay rates for optical conversion efficiency control in energy harvesting for solar cells and optical sensing applications. [ABSTRACT FROM AUTHOR]

The recent approach for enhancing the thermal conductivity of polymer-composites is to generate an interconnecting network of thermally conductive fillers. However, the existing models for effective thermal conductivity of composites are, generally, based on effective medium theory and valid for dilute filler concentration (low volume fraction), which leads to inaccurate predictions with non-dilute and percolating filler concentrations. In this work, the model is developed focusing on non-dilute filler concentrations, which is more practical for the recent approach towards thermally conductive polymer-composites. The existing model for dilute filler concentrations is modified based on Bruggeman's differential scheme wherein the ' non-dilute concentrations' are obtained by integrating the effect of adding ' dilute concentrations ' in small increments. The proposed model can handle particulate fillers of variable geometry. The proposed model is validated by producing different polymer matrix composite systems with ceramic fillers. Using Al 2 O 3 or AlN as filler, and high-density polyethylene or polypropylene as matrix, different binary composite systems were processed with volume fractions up to 0.5. From the parametric studies, conducted to establish the understandings of the model, the aspect ratio of filler particles is found the most critical. The proposed model is expected to be the mathematical ground for the industry and researchers to produce computationally designed polymer composites with tailorable ultrahigh thermal conductivity in corrosive environment-heat transfer applications such as polymeric heat exchangers for seawater desalination. Image 1 • A more realistic effective thermal conductivity model for polymer composites with non-dilute filler concentrations is proposed. • The effect of filler attributes such as volume fraction, size, shape, and orientation are considered in the model. • The model is validated by a different series of polymer-composites with variable matrix and filler-attributes. • The aspect ratio of the fillers is found the most sensitive to alter the effective thermal conductivity. [ABSTRACT FROM AUTHOR]

• Numerically exact simulations of near-field thermal emission by quartz nanowire arrays is reported. • The Maxwell-Garnett and Bruggeman effective medium theories (EMTs) can only qualitatively predict near-field thermal emission by nanowire arrays when the array pitch over the observation distance is in the range of 1 and π. • The Maxwell-Garnett EMT is slightly more accurate than the Bruggeman EMT. • The EMT cannot capture the lateral variation of near-field thermal emission by nanowire arrays. Nanowire arrays are promising man-made materials for tuning the spectrum and the magnitude of near-field thermal radiation. Near-field radiative properties of nanowire arrays are often studied using the effective medium theory (EMT). In this paper, we inspect the validity of the Maxwell-Garnett (MG) and Bruggeman (BR) EMTs for predicting near-field thermal emission by quartz and indium tin oxide (ITO) nanowire arrays. The near-field energy density predicted using the EMTs is compared with numerical simulations obtained using the thermal discrete dipole approximation. For quartz nanowire arrays, which support localized surface phonons in the infrared region, neither MG nor BR EMT can accurately predict the spectrum and the magnitude of near-field thermal emission even at distances, z o , greater than the array pitch, L over π. Based on the performed simulations, the EMT agrees the best with the T-DDA when 1 < L z o < π. It is also shown that MG EMT is slightly more consistent with numerical simulations than the BR EMT. For the ITO array, which does not support localized surface plasmons in the infrared region, the MG EMT provides an acceptable estimations of near-field thermal radiation. Finally, it is observed that near-field emission can vary by a factor of two in lateral directions which cannot be captured in the EMT. [ABSTRACT FROM AUTHOR]

Reservoir simulations are performed with fine grid geological models as primary input into the reservoir simulators. These fine grid geological models contain ten million to one hundred million cells while current serial reservoir simulators can only handle one hundred thousand to one million cells. This disparity in scales prohibits direct input of fine grid geological models into serial simulators. However, traditional upscaling techniques are unable to reproduce the fine-scale dynamic flow behavior at the coarse-scale and up-scaled permeability values are dependent on the applied boundary conditions. The problem is exacerbated if isolated flow units are present. These problems motivated the need to couple the permeability thresholding and effective medium theory (EMT) approaches to develop a practical and accurate quasi-global single-phase permeability upscaling technique that uses the reservoir simulator in the upscaling process. The workflow involves identifying and making the no-flow cells slightly permeable. This is followed by defining two models for each region to be scaled up, one of which includes the heterogeneous permeability field in the region and the other the upscaled value. Also, a fine-scale gridded ring is constructed around the target region. Then the upscaled value of the permeability is resolved by minimizing the difference between the well water production rates (WWPR) of the two runs. The technique is shown to mimic the channel fine-scale permeability distribution at the coarse-scale. It is also shown to reproduce the physics of flow for two-phase flow problems as evident in the well oil production rate, injection well pressure and pressure distribution profile. Sensitivity analyses on different scale-up factors, well locations and sequentially active wells show the superiority of the novel technique over the upscaling and downscaling with effective medium theory (UDEMT) and local upscaling techniques - albeit at the cost of more CPU time. The new method takes more CPU time than local upscaling method but the accurate results justifies the extra CPU time. Our workflow should be extended to three dimensions and fractured reservoirs as well as coupled with existing upscaling techniques for near wellbore and relative permeability upscaling. • A quasi-global upscaling technique for highly heterogeneous reservoirs that also accounts for the presence of isolated flow cells. • Technique couples the permeability thresholding and effective medium theory upscaling approaches. • Novel technique reproduced the fine-scale permeability distribution and dynamic flow behavior at the coarse-scale well. • Upscaled permeability obtained are independent of boundary conditions and well locations. • Coarse-scale model perfectly mimicked the fine-scale solution when wells were coming on stream sequentially. [ABSTRACT FROM AUTHOR]

For biomedical applications in the terahertz band, composites such as macromolecule compounds, biotissues and phantoms are studied. A description of dielectric properties of composite materials using mathematical models has its own fundamental and technological importance. In this work, we present an iterative effective medium theory for multi-component materials. The model has good performance in describing composite materials with more than two components. The theory is evaluated by comparing with the complex permittivity of three different composite materials. A comparison with other commonly used models is given in the form of relative errors. [ABSTRACT FROM AUTHOR]

Laser-induced structuring in nanoporous glass composites is promising for numerous emerging applications in photonics and plasmonics. Local laser irradiation activates an interplay of photo-thermo-chemical mechanisms that are extremely difficult to control. The choice of optimum laser parameters to fabricate structures with desired properties remains extremely challenging. Another challenging issue is the investigation of the properties of laser-induced buried structures. In this paper, we propose a way to control the plasmonic structures formation inside a nanoporous glass composite with doped silver/copper ions that are induced by laser irradiation. Experimental and numerical investigations both demonstrate the capacities of the procedure proving its validity and application potential. In particular, we register transmitted laser power to analyse and control the modification process. Spectral micro-analysis of the irradiated region shows a multilayer plasmonic structure inside the glass composite. Subsequently, the effective medium theory connects the measured spectral data to the numerically estimated size, concentration, and chemical composition of the secondary phase across the initial GC sample and the fabricated structure. [ABSTRACT FROM AUTHOR]

A simple approach based on effective medium theory is proposed and applied to evaluate and design a polarization–insensitive antireflection metagrating for terahertz waves. The period of the grating is subwavelength such that there is only one propagating mode within the grating region and high–order diffraction orders do not exist. Thus, the grating region is treated as a homogeneous medium and the whole problem can be modelled as a Fabry–Perot resonator, whose thickness then determines the transmittance. The transmittances of the fabricated device for TE and TM waves at 0.87 THz are measured to be 84% and 95% for an air–silicon surface, respectively. This simple metagrating design will find important applications in antireflection scenarios in the terahertz frequency range. [ABSTRACT FROM AUTHOR]

We present a study of tunable thermal transport characteristics of nanocomposites by employing a combination of a full-scale semi-ab inito approach and a generalised and extended modification of the effective medium theory. Investigations are made for planar superlattices (PSLs) and nanodot superlattices (NDSLs) constructed from isotropic conductivity covalent materials Si and Ge, and NDSLs constructed from anisotropic conductivity covalent-van der Waals materials MoS 2 and WS 2 . It is found that difference in the conductivities of individual materials, period size, volume fraction of insertion, and atomic-level interface quality are the four main parameters to control phonon transport in nanocomposite structures. It is argued that the relative importance of these parameters is system dependent. The equal-layer thickness Si/Ge PSL shows a minimum in the room temperature conductivity for the period size of around 4 nm, and with a moderate amount of interface mass smudging this value lies below the conductivity of SiGe alloy. [ABSTRACT FROM AUTHOR]

Based on the multi-scattering Mie theory, the effective relative permittivity and permeability of metal-dielectric non-resonant artificial dielectric are derived in a closed form in this study for a quite broad frequency range. The artificial dielectric is a 3-D infinite isotropic homogenous dielectric medium with periodically imbedded non-magnetic metallic inclusions of spherical shape. The obtained effective medium theory is shown that belonging to a general class of non-resonant metamaterials, the considered composite medium exhibits an effective "ultra-low index behavior" at the THz frequencies. The results obtained for the case of non-magnetic metallic inclusions are compared with the Lewin's theory. The comparisons of results of the proposed theory with the experimental results of the authors are presented in the study from deep UV to visible region. [ABSTRACT FROM AUTHOR]