Effective Medium Research Articles

An effective medium theory-based unified model for estimating thermal conductivity of unfrozen and frozen soils

Soil thermal conductivity (STC) is a crucial parameter in modeling land surface processes. However, the current STC models are developed separately for unfrozen and frozen soils, leading to inconsistent understanding. In this study, we propose a unified model based on the work of Ghanbarian and Daigle (2016) originally developed for unfrozen soils. The unified model comprises three parameters: critical volume fraction (ϕc), scaling exponent (t), and a compensating factor (α), and considers dry soil as the low-conductivity component (weighted by air volume fraction) and saturated soil as the high-conductivity component (weighted by volumetric liquid content for unfrozen state and total water content for frozen state). Specifically, ϕc represents a critical point where high-conductivity component begins to govern the behavior of effective STC, characterized by t. α allows for accurate calibration of saturated STC. Using a dataset of 90 unfrozen samples (693 measurements) and 74 frozen samples (255 measurements), pedotransfer functions (PTFs) for the three parameters were trained. The unified model successfully reproduces the sharp rise in STC at low moisture conditions during wetting and the increase during freezing. Compared to an empirical model (Côté and Konrad, 2005a) and a theoretical model (Tian et al., 2016), the unified model demonstrates higher predictive skill for unfrozen and frozen soils, achieving Nash-Sutcliffe efficiency coefficients of 0.96 and 0.90, respectively. This work contributes to a more consistent and comprehensive understanding of STC in cold environments and has the potential to be integrated into land surface models.

The conductivity effect of the top coating on optical properties of thin Cu(Ag)-layered structures

This study examines the optical properties of thin Cu (Ag)-layered structures covered with protective layers based on graphene, titanium (TiO2), or aluminium (Al2O3) oxides. The objective is to investigate the impact of these coatings on the optical behaviors of underlying metallic layers, specifically in the spectral range of excitation of surface plasmon resonances. Combining the methods of spectroreflectometry and spectro-ellipsometry was used to analyze the optical characteristics of the hybrid metal-oxide-graphene films. The study shows that graphene, due to its exceptional electrical conductivity and unique optoelectronic properties, significantly modifies the optical behavior of investigated structures. It includes notable changes in refractive and absorption indices, and optical conductivity indicating potential for enhancing light-matter interactions in plasmonic-graphene layered structures with the aim to apply as biosensor. It is important that addition of TiO2 and Al2O3 layers has also strong effects on the optical properties, which are relevant to their respective applications in the fields of optoelectronics and microelectronics. Employing the effective medium approximation and the Tauc–Lorentz model promotes deeper understanding the interplay between interband and intraband electronic transitions at the nanoscale level. It was revealed that the layer thickness of constituted materials and their individual dielectric functions together with addition of a graphene monolayer commit the significance for altering the optical properties of hybrid layered structures. The obtained results are important for the fields of plasmonics and nanotechnology, providing insights for designing sensors and devices with improved optical characteristics.

Effective medium theory for second-gradient elasticity with chirality

We derive effective models for a heterogeneous second-gradient elastic material taking into account chiral scale-size effects. Our classification of the effective equations depends on the hierarchy of four characteristic lengths: The size of the heterogeneities ℓ, the intrinsic lengths of the constituents ℓ SG and ℓ chiral , and the overall characteristic length of the domain L. Depending on the different scale interactions between ℓ SG , ℓ chiral , ℓ, and L we obtain either an effective Cauchy continuum or an effective second-gradient continuum. The working technique combines scaling arguments with the periodic homogenization asymptotic procedure. Both the passage to the homogenization limit and the unveiling of the correctors’ structure rely on a suitable use of the periodic unfolding operator.

Wave scattering and radiation by a surface-piercing vertical truncated metamaterial cylinder

In this paper, we study wave scattering and radiation by a surface-piercing vertical truncated metamaterial cylinder composed of a closely spaced array of thin vertical barriers, between which fluid can flow. A theoretical model is developed under full depth-dependent linearised water wave theory, where an effective medium equation and effective boundary conditions are employed, respectively, to describe the fluid motion inside the cylinder and match the flow between the fluid regions in and outside the metamaterial cylinder. A damping mechanism is introduced at the surface of the fluid occupied by the metamaterial cylinder to consider the wave power dissipation in narrow gaps between the thin vertical plates. The wave excitation forces acting on the cylinder and the hydrodynamic coefficients can be calculated straightforwardly in terms of the velocity potential inside the cylinder. An alternative way is by using the velocity potential outside the cylinder, the expression of which has the reduction of the integral and an infinite accumulation that are included in the straightforward expression. The results highlight the patterns of the radiated waves induced by the oscillation of the cylinder and the characteristics of the hydrodynamic coefficients. The metamaterial cylinder when fixed in place and with a damping mechanism included is found to capture more wave power than that of a traditional axisymmetric heaving wave energy converter over a wide range of wave frequencies.

Fused Deposition Modeling of Isotactic Polypropylene/Graphene Nanoplatelets Composites: Achieving Enhanced Thermal Conductivity through Filler Orientation.

High-performance thermally conductive composites are increasingly vital due to the accelerated advancements in communication and electronics, driving the demand for efficient thermal management in electronic packaging, light-emitting diodes (LEDs), and energy storage applications. Controlling the orderly arrangement of fillers within a polymer matrix is acknowledged as an essential strategy for developing thermal conductive composites. In this study, isotactic polypropylene/GNP (iPP/GNP) composite filament tailored for fused deposition modeling (FDM) was achieved by combining ball milling with melt extrusion processing. The rheological properties of the composites were thoroughly studied. The shear field and pressure field distributions during the FDM extrusion process were simulated and examined using Polyflow, focusing on the influence of the 3D printing processing flow field on the orientation of GNP within the iPP matrix. Exploiting the unique capabilities of FDM and through strategic printing path design, thermally conductive composites with GNPs oriented in the through-plane direction were 3D printed. At a GNP content of 5 wt%, the as-printed sample demonstrated a thermal conductivity of 0.64 W/m · K, which was 1.5 times the in-plane thermal conductivity for 0.42 W/m · K and triple pure iPP for 0.22 W/m · K. Effective medium theory (EMT) model fitting results indicated a significantly reduced interface thermal resistance in the through-plane direction compared to the in-plane direction. This work shed brilliant light on developing PP-based thermal conductive composites with arbitrarily-customized structures.

A review of ultrasound contrast media

Efforts have been made over the last five decades to create effective ultrasonic contrast media (UCM) for cardiac and noncardiac applications. The initial UCM was established in the 1980s, following publications from the 1960s that detailed the discovery of ultrasonic contrast enhancement using small gaseous bubbles in echocardiographic examinations. An ideal contrast medium for echography should be nontoxic, capable of being injected intravenously, able to travel through pulmonary, cardiac, and capillary circulations, and stable for recirculation. Examples of current commercial contrast media include Definity, Optison, Sonazoid, and SonoVue, which have demonstrated potential for various clinical purposes, both on- and off-label. Several possible UCMs have been developed or are in progress. Advancements in comprehending the physical, chemical, and biological characteristics of microbubbles have significantly improved the visualization of tumor blood vessels, the identification of areas with reduced blood supply, and the enhanced detection of narrowed blood vessels. Innovative advances are expected to enhance future applications such as ultrasonic molecular imaging and therapeutic utilization of microbubbles.

Optical properties of yttria-stabilized zirconia from spectroscopic ellipsometry

Complex dielectric function (ɛ = ɛ1 + iɛ2) spectra of a heat treated single crystal yttria-stabilized zirconia (YSZ) have been determined over a spectral range of 0.03–8.5 eV using spectroscopic ellipsometry. Spectra are collected using three instruments covering different parts of the measured spectrum. The YSZ sample is modeled as a semi-infinite bulk crystal covered by a surface layer described by a Bruggeman effective medium approximation of equal parts YSZ and void.

On the Use of Foam Rubber for Sealing Applications

O-rings made from foam rubber are often used in sealing applications. Foam rubber have low (macroscopic) elastic modulus E0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E_0$$\\end{document} resulting in a low nominal contact pressure when squeezed against a countersurface. In most cases the foam rubber is covered by a thin surface film with the effective elastic modulus E1>E0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E_1 > E_0$$\\end{document}. We show that the nominal contact pressure may not be high enough for the contact area to percolate and the O-ring seal will leak. For the leakage calculations we use the Persson multiscale contact mechanics theory, and the (modified) Bruggeman effective medium theory for the fluid flow conductivity. The experimental input for the theory are surface roughness power spectrum, which was obtained from stylus topography measurements, and the elastic properties (E0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E_0$$\\end{document} and E1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E_1$$\\end{document}) of the rubber O-ring. As an application of this calculation method, we have used the preliminary as well as the final results of the laboratory gas tightness tests of the 136 New Small Wheel Micromegas Quadruplets performed at CERN, from February 2019 to May 2021, in the framework of the ATLAS Experiment upgrade. In the integration quality control, a novel method for gas tightness measurement, that we have called “Flow Rate Loss”, has been used as a baseline method.Graphical

Demonstration and Control of "Spoof-Plasmon" Scattering from 3D Spherical Metaparticles.

Geometries that replicate the behavior of metal nanostructures at much lower frequencies via texturing surfaces so they will support a surface wave have been a central pillar of metamaterials research. However, previous work has focused largely on geometries that can be reduced to symmetries in one or two dimensions, such as strips, flat planes, and cylinders. Shapes with isotropic responses in three dimensions are important for applications, such as radar scattering and the replication of certain nanoscale behaviors. This work presents a detailed exploration of the scattering behavior of 3D spherical "spoof plasmonic" metaparticles, based on the platonic solids. Their behavior is compared to an effective medium model through simulation and experiment, and the vast range of behaviors that can be produced from a metal sphere of a given radius via tuning its internal structure is explored in detail.

Online Scan of Campus Health Resources and HPV Vaccination Information on College and University Websites in the State of Oregon.

This study is the first to report the results of a scan of the official webpages of all public and private colleges and universities in the state of Oregon, including but not limited to student health services webpages and student handbooks, to identify available services, policies, and educational information on HPV vaccination. The purpose is to describe vaccination services (with a focus on the HPV vaccine), prevention efforts, and institutional policies on vaccination on college and university websites in Oregon. An online scan was conducted from September to November 2020 to collect and describe data from college/university websites across Oregon. Colleges/universities were obtained from the National Center for Education Statistics website. The final sample included 48 colleges/universities. Twenty colleges/universities have a health center with 11 providing the HPV vaccine on campus: most are large public universities and non-religious private colleges. A few religious private universities and one community college offer the vaccine on campus. More than half (n = 26) of Oregon colleges/universities had a webpage specifically designated for immunization information, but only 11 mentioned the HPV vaccine on their immunization webpage. Twelve colleges/universities recommend, and none require the vaccine. Information on HPV vaccination services and education was limited on college/university websites, especially on community college and religious private university websites. Most colleges/universities with a student health center recommend and offer the HPV vaccine on campus. College/university websites may be a low-cost and effective medium to increase HPV vaccination awareness, encourage immunizations, and prevent HPV-associated cancers.

Influence Technological Innovation, Social Media & Marketing Increasing Productivity And Growth Jakarta's UMKM

The growth and sustainability of DKI Jakarta's micro, small, and medium enterprises (UMKM) in the current digital era is greatly influenced by their ability to utilize technological innovation, social media, and effective, interactive, and creative marketing strategies. This research aims to study the effect of using technological innovation, social media and creative, interactive and effective marketing media on the productivity and growth rate of UMKM in DKI Jakarta. This case study was conducted on Jakarta residents, and data was collected through a questionnaire survey. The results of the analysis show that DKI Jakarta UMKM that are successful in utilizing the latest technology and integrating it into their daily operations experience a significant increase in productivity and business growth. The use of apps, interactive marketing on social media and product and service innovation are key factors that support the success of this study. This research makes an important contribution in understanding the role of technology, marketing media and social media in supporting DKI Jakarta UMKM. The implication of the findings of this research is the importance of training and mentoring in assisting DKI Jakarta UMKM in developing their digital skills. In addition, cooperation with e-commerce platforms and the use of interactive marketing strategies also need to be improved.

Modeling and analysis of discrete particle detection in wide-field surface plasmon resonance microscopy

Wide-field surface plasmon resonance microscopy (WF-SPRM), based on Kretschmann’s configuration, is a powerful technique for detecting nano-objects in solution. In this study, key parameters for building a highly sensitive WF-SPRM are optimized, including laser wavelength, prism refractive index, numerical aperture of the objective, and gold layer thickness. A medium model describes the surface plasmon resonance (SPR) sensor principle, treating molecules bound on the sensor surface as an effective medium with an effective refractive index and thickness. On the other hand, the SPR discrete particle model is introduced to describe the detection principle for discrete particles. Theoretical, numerical, and experimental analyses are conducted, and the calculated intensity profiles of single and double nanoparticles from the discrete particle model describe the experimental profiles well. Furthermore, the influence of coating the gold layer with a dielectric layer on the SPR sensitivity is investigated for varying refractive indices.

Impact of Western transmission of the Peking Gazette on Late-Qing China’s information security

The Peking Gazette, as a widespread and effective medium for the dissemination of important information from the Qing government, played a significant role in the internal governance of the empire. In the 19th century, Western missionaries, diplomats, and businessmen in China respected the authenticity and authority of the content in the Gazette, and carried out large-scale translations of political, social, cultural, economic, and military-diplomatic information into English. Western transmission of the Peking Gazette to some extent promoted cultural exchanges between China and the West and also provided the Western powers, which were in a period of expansion, with a wealth of political and military intelligence. The internally focused Qing dynasty was initially unaware of the Western transmission of the Peking Gazette and later took a series of doomed measures, leading to severe damage to national information security and political safety. The historical lessons of the Qing empire are enlightening for countries worldwide today: there is a need not only for openness and transparency but also for balancing the relationship between information disclosure and national security.

Modeling the Interface Between Phases in Dense Polymer‐Carbon Black Nanoparticle Composites by Dielectric Spectroscopy: Where Are We Now and What are the Opportunities?

AbstractThe macroscopic properties of polymer nanocomposites (PNC) rely largely on the interphase between the polymer chains and the filler particles. One significant difficulty to solve this issue is to quantitatively model the structure‐property correlations due to the interfacial region in these complex materials. While dielectric spectroscopy (DS) measurements are routinely used to characterize the effective permittivity of filled polymers, fitting standard effective medium models and mixing equations to these data remains notoriously difficult to interpret. This is due to the absence of explicit reference to internal length scales characterizing the interfaces in the PNC. As an illustrative example, a two‐level homogenization framework is proposed which enables the extraction of useful information on the impact of a thin interphase confined on a nanometer length scale based on broadband DS data. This model leads to new ways of tuning the interphase so as to optimize the material's response to electric field, a situation relevant for electromagnetic shielding. This approach provides guidance on how to observe directly and experimentally the actual properties of the interface between the phases (as opposed to model‐based inference). Aside from its secure physical foundation in the theory of effective medium, a significant advantage of this approach is that a genetic algorithm (GA) technique applied to this physics‐based model enables the uniqueness of the fit parameters to be considered, as the GA method is robust in terms of finding globally optimum solutions, therefore placing confidence in non‐universal values of the percolation exponents. Recent work in physics‐informed machine learning indicates that the effective dielectric properties of PNC with many degrees of freedom due to their complex morphology can be described by considering only a few degrees of freedom describing the interface features between the phases in these composites.

Absorption spectrum of magnetically structured emulsions in the centimeter range

The high degree of absorption of microwave radiation by composite materials with developed morphology can be significantly improved by directly changing the geometrical parameters of the subwavelength structure, which is difficult in the case of solid-state materials. In this work, a new composite liquid material with controlled absorption properties, a magnetodielectric emulsion, is investigated. The control of microgeometry parameters is accomplished through exposure to a magnetic field. The experimental studies have shown that the formation of chain structures from spherical water droplets in the composite leads to a significant change in the absorption coefficient. Thus, for an emulsion with 10% water content, exposure to a magnetic field of 25 kA m−1 increases the absorption coefficient by 400% at a radiation frequency of 10 GHz. It is noteworthy that the efficiency of the absorption properties control depends on the volume concentration of droplets in the sample and has a non-monotonic character. To interpret the obtained results, numerical modeling of the studied system in the effective medium approximation was carried out.

Evaluation of drying shrinkage effects on the elastic properties of porous sandstones using a modified micromechanical model

SUMMARY The effects of pore fluids on the elastic properties of sedimentary rocks can be broadly categorized into two mechanisms: variations in pore compressibility due to the physical properties of the fluids and alterations in the stiffness of the rock frame resulting from rock–fluid interactions. Particularly, as rock–fluid interactions alter the stiffness of contacts between mineral grains, changes in the fluid properties around grain contacts can induce volumetric deformation of the rock as well as in variations of the associated elastic coefficients. Even though many previous studies have explored the influence of swelling of clay minerals, the relationships between changes in elastic moduli and deformation in rocks, which hardly contain swellable minerals, remain to date enigmatic. In this paper, to evaluate quantitatively these effects, drying rates, strains and ultrasonic velocities of small cylindrical Berea sandstone samples were measured as their water saturation was decreased by evaporative drying. The measurements clearly showed drying shrinkage and drastic increases in shear and compressional moduli for all the samples under an almost fully dried condition. Previous studies considered that the alteration in surface energy of grain minerals between wet and dry states affected the contact stiffness between them. Some of them used micromechanical model, uniting the Digby grain contact model with the effective medium theory, to interpret the changes in elastic moduli observed in the non-swellable sandstones during water adsorption on the grain surface. The conventional micromechanical model assumes that a mineral grain is a pure sphere and that the number of contacts between the grains is one. However, grains in a sedimentary rock are generally not purely spherical, and the contact surface is composed of several adhesive asperities. We therefore modified the conventional model by introducing the curvature radius and the number of asperities per contact surface. The modified model well reproduced the shear moduli under wet conditions using the strain and moduli measured under dry conditions. On the other hand, the predictions of the compressional moduli using the model were partially in agreement with the experimental results. Therefore, we attempted to qualitatively interpret the relationship by combining the model with the viscoelastic effect associated with wave-induced fluid flow. The deformation and changes in the elastic moduli of rocks resulting from multiple pore fluids within them can be better understood by the present combined model.

Immersive Virtual Reality Serious Game Studies in Education: A Brief Review

Currently, immersive virtual reality environments(IVR) are providing interactive learning experiences in various fields including “education”. Especially after covid-19 pandemic, the popularity of the online learning environment has increased, and the IVR would be a possible alternative to other mediums in online learning. The previous reviews usually contain related literature before the pandemic. There is a need to better understand the current body of knowledge on IVR. The specific application contexts, research designs, and possible results of the current works needed to be clarified. To answer this question a literature review was conducted between 2013-2023 years on the “Web of Science” database for “IVR” and “serious games” keywords in the field of “education”. Then, 18 articles are reviewed and the main themes are provided. As a result, the majority of the articles were found as “applied studies” and the main research intent was to determine “cognitive effects” including knowledge improvement. Depending on literature analyses qualitative and quantitative study results can be listed as; “IVR in the form of serious game” in general was found and perceived as an effective medium for learning in various fields of education. In addition, some study results about instructional design decisions of IVR applications and the effectiveness of IVR comparing other types of mediums are provided. The study recommends taking into account educational theories behind the design of IVR and related multimedia design principles.

Design and mathematical modeling of DNG metamaterial having six-band capabilities with high effective medium ratio

ABSTRACT In this paper, six-band double negative (DNG) metamaterial with a substantially high effective medium ratio (EMR) under the S and C microwave band is designed and investigated for multiple microwave applications. The proposed metamaterial unit cell consists of four Plus Appended Split Ring Resonator (PASRR) cells, which are combined with variable sides and positions by plus (+) shape stubs at the centre. All four Plus Appended Split Ring Resonator (PASRR) cells are mutually coupled with each other to vary the electrical length to achieve hexa Bands DNG characteristics in a lossy FR-4 epoxy substrate with the thickness of 1.5748 mm. A parameter extraction method has been used to extract effective permittivity (ε eff), permeability (μ eff) and refractive index (n). Moreover, the equivalent circuit model is obtained. Ansys HFSSTM software & Keysight ADSTM software are used to obtain the simulated and theoretical results, respectively, which agree measured with simulated and theoretical results.

On the applicability of the Maxwell Garnett effective medium model to media with a high density of cylindrical pores

The optical properties of dielectric materials with subwavelength cylindrical pores are commonly described by effective medium models. We compare the Maxwell Garnett and the Bruggeman effective medium models for porous silicon with simulations and experiments for the case of polarization orthogonal to the pore axis. The Maxwell Garnett model matches the results of the simulations even up to very high porosities. An experimental study of the effective permittivity of macroporous and mesoporous silicon is conducted by analyzing the Fabry-Pérot oscillations in the long-wavelength limit. These experimental results are also consistent with the Maxwell Garnett model. We advocate using this model for media with cylindrical pores in the future.

INTERNET-BASED HOTEL MARKETING STRATEGY IN INDONESIA: EMPIRICAL STUDY WITH VECTOR AUTOREGRESSION MODEL

Purpose: The purpose of this study is to determine how the Indonesian hotel sector may use the internet as a productive and successful marketing tool. Theoretical Framework: The opportunities offered by the internet include ease of accessing and disseminating information about hotel products and services, the ability to reach a wider and more diverse market, and the opportunity to improve the quality and efficiency of services (Kapoor & Kapoor, 2021). However, the internet also poses challenges, such as increasingly fierce competition, changes in consumer preferences and behavior, and threats to data security and privacy (Bandara, Fernando, & Akter, 2020). Design/Methodology/Approach: This research uses secondary data from the World Bank and UNWTO regarding Internet users, Number of hotel rooms, Total guests, and Tourism arrivals from 2000 to 2022. This research applies a vector autoregression (VAR) model with two lags to test the relationship between five time variables. series, namely Total Guests, Tourism Arrivals, Room Rate, Number Of Rooms, and Internet Users. The VAR model was chosen because it has the lowest information criteria values, namely AIC, SC, and HQ, which shows a high fit to the data. Findings: Number of Rooms is the variable that has the most influence on other variables, which indicate the capacity and quality of hotel accommodation. Therefore, hotels are advised to increase the Number Of Rooms in order to attract more tourists and increase revenue. Apart from that, Total Guests, Tourism Arrivals, and Room Rate also have a significant effect on several other variables, which reflect the dynamics of market demand and supply, as well as hotel competitiveness. Therefore, hotels are advised to maintain and improve these variables with appropriate marketing strategies, such as promotions, distribution channels and social networks. Meanwhile, Internet User is the weakest variable in the VAR model, which has a negative relationship with Total Guests, Tourism Arrivals, and Room Rate, which reflects the influence of information technology on consumer behavior. Research, Practical & Social Implications: This research makes a practical contribution by providing solutions for the hotel industry in Indonesia to increase performance and income by utilizing the internet as an effective and efficient marketing medium. Originality/Value: This research provides a theoretical contribution by examining the influence of the internet as an effective and efficient marketing medium for the hotel industry in Indonesia, which is a topic that has rarely been researched before.