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1 – 10 of over 95000Oleg Rybin, Konstantin Yemelyanov, Amjad Pitafi and Tahira Nawaz
The purpose of this paper is to study the microwave behaviour of effective magnetic permeability for two‐component ferrite like metamaterial medium in the direction of a biasing…
Abstract
Purpose
The purpose of this paper is to study the microwave behaviour of effective magnetic permeability for two‐component ferrite like metamaterial medium in the direction of a biasing magnetic field. The metamaterial medium is presented as an infinite host dielectric material (air) with periodically embedded ferric cylindrical and spherical inclusions saturated with an external dc magnetic field. The study is based on the effective medium theory developed for polycrystalline metaferrites. The simulations show that the presented metamaterial can exhibit the ultra‐low refractive index (ULI) phenomenon and the phenomenon of negative magnetic permeability for the case of microwave propagation in the direction of bias.
Design/methodology/approach
The obtained results are based on the wave long approximation of permeability tensor of the presented metamaterial media obtained earlier by the first author. Using the standard approach, the authors apply the above expressions for the microwave propagation in direction of biasing dc magnetic field considering different polarization of the incident microwave.
Findings
The considered artificial material media can become either material with a ULI or with negative values in the GHz frequencies.
Originality/value
The paper is concerned with part of the theory of a new generation of artificial ferrites.
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Keywords
Brent W. Ritchie and Yawei Jiang
This paper aims to summarize the current state of research on risk, crisis and disaster management in the generic field, and in tourism and hospitality. It identifies key themes…
Abstract
Purpose
This paper aims to summarize the current state of research on risk, crisis and disaster management in the generic field, and in tourism and hospitality. It identifies key themes and compares the main topics studied in both the tourism and hospitality management and marketing literature.
Design/methodology/approach
A narrative (thematic) review and synthesis was completed based on articles published in the top 20 tourism and hospitality management journals from 2011 to March 2021. A review was conducted of the generic literature from 2016 to 2020.
Findings
From 210 papers reviewed, only 47 are in the hospitality field. The authors found that 80% of papers were empirical with slightly more quantitative papers produced. The majority of the papers focused on crises. Three key themes were found from the review and future research proposed to address gaps based on these findings and a review of 26 papers from the generic risk, crisis and disaster management field.
Practical implications
Research is required into planning and preparedness, not just response and recovery to crises and disasters. Future research should consider hospitality rather than tourism, particularly focusing attention outside of the accommodation sector. Hospitality studies also need to go beyond the micro-organizational level to include more meso- and macro-level studies.
Originality/value
The review provides a number of future research directions for tourism and hospitality research in the field. The paper provides a comprehensive multi-dimensional framework to synthesize studies and identifies research gaps. It also provides recommendations on methodologies required to progress these research directions. Research in this field is likely to grow because of the impact of COVID-19.
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Lingyun Kong, Mehdi Ostadhassan, Ran Lin and Chunxiao Li
Evaluating mechanical properties of simply made samples by 3D printing technology at nanoscale provides a clear path to better understand larger-scale responses of complex natural…
Abstract
Purpose
Evaluating mechanical properties of simply made samples by 3D printing technology at nanoscale provides a clear path to better understand larger-scale responses of complex natural rocks. Therefore, to realize the similarity between synthetically manufactured materials and natural geomaterials, this study focused on nanoscale mechanical characterization of a 3D printed object with only two constituent components (gypsum powder and infiltrant).
Design/methodology/approach
The study method includes nanoindentation technique combined with numerical simulation via discrete element method (DEM).
Findings
Four typical load-displacement curves were identified from nanoindentation of total test points indicating a typical elastic-plastic behavior of the 3D printed gypsum rock sample. Mechanical parameters such as Young’s modulus and hardness were calculated by energy-based methods and a positive correlation was observed. The infiltrant was found to considerably be responsible for the majority of the sample nano-mechanical behavior rather than the gypsum particles, thus expected to control macroscale properties. This was decided from deconvolution and clustering of elastic modulus data. Particle flow modeling in DEM was used to simulate the nanoindentation process in a porous media yielding rock-alike mechanical behavior.
Originality/value
The results show a matching load-displacement response between experimental and simulation results, which verified the credibility of simulation modeling for mechanical behavior of 3D printed gypsum rock at nanoscale. Finally, differential effective medium theory was used to upscale the nanoindentation results to the macroscale mechanical properties, which provided an insight into the geomechanical modeling at multiscale.
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Oleg Rybin, Konstantin Yemelyanov and Tahira Nawaz
The purpose of this paper is to obtain the long‐wave approximations for the effective electromagnetic response of two‐dimensional sandwich composite structure, as infinite chain…
Abstract
Purpose
The purpose of this paper is to obtain the long‐wave approximations for the effective electromagnetic response of two‐dimensional sandwich composite structure, as infinite chain of infinitely long metal cylinders symmetrically immersed in an infinite metamaterial slab are obtained. The slab is an infinite magneto‐dielectric matrix with periodically imbedded infinitely long metal cylinders whose diameter is smaller than those of the chain cylinders. The case of ferrite‐like metallic saturated inclusions is considered in the study.
Design/methodology/approach
The result is presented as a generalized expression of the electromagnetic response of the infinite periodic chain of infinitely long metallic cylinders immersed into the flat magneto‐dielectric host medium. Those expressions were obtained utilizing S‐ and T‐matrices approaches.
Findings
A good coincidence between the results of analytical modeling and numerical simulations was found.
Research limitations/implications
Low values of the metal volume fraction; microwave frequency range.
Practical implications
An improving of directivity of patch antennas; a minimization of patch antennas.
Originality/value
The analytical characterization of new artificial substrate‐like structure to be utilized for designing patch antennas of a new generation.
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Christian Meiners and Arne F. Jacob
This paper aims at providing information on scattering in layers composed of periodic and non‐periodic arrangements of small metal helices. Metal helices exhibit a pronounced…
Abstract
Purpose
This paper aims at providing information on scattering in layers composed of periodic and non‐periodic arrangements of small metal helices. Metal helices exhibit a pronounced resonance and are thus very effective scatterers.
Design/methodology/approach
Scattering is expressed in terms of multipole moments. Non‐periodic layers are investigated using the combination of periodic boundary conditions for sample configurations and averaging many of these configurations. The results and the methodology are compared to the well‐known Clausius‐Mossotti (CM) mixing rule and the assumptions and concepts therein. This is done to deepen the understanding of the scattering behavior.
Findings
The investigations show that only few multipole contributions are necessary to model the interaction correctly.
Originality/value
A systematic comparison of a full‐wave scattering theory and the fast CM mixing theory is conducted, providing some physical insight. From this, conclusions on the validity of the mixing approach are drawn.
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Akash K. Gupta, Rahul Yadav, Malay K. Das and Pradipta K. Panigrahi
This paper aims to present the implementation of a multi-layer radiation propagation model in simulations of multi-phase flow and heat transfer, for a dissociating methane hydrate…
Abstract
Purpose
This paper aims to present the implementation of a multi-layer radiation propagation model in simulations of multi-phase flow and heat transfer, for a dissociating methane hydrate reservoir subjected to microwave heating.
Design/methodology/approach
To model the induced heterogeneity due to dissociation of hydrates in the reservoir, a multiple homogeneous layer approach, used in food processes modelling, is suggested. The multi-layer model is incorporated in an in-house, multi-phase, multi-component hydrate dissociation simulator based on the finite volume method. The modified simulator is validated with standard experimental results in the literature and subsequently applied to a hydrate reservoir to study the effect of water content and sand dielectric nature on radiation propagation and hydrate dissociation.
Findings
The comparison of the multi-layer model with experimental results show a maximum difference in temperature estimation to be less than 2.5 K. For reservoir scale simulations, three homogeneous layers are observed to be sufficient to model the induced heterogeneity. There is a significant contribution of dielectric properties of sediments and water content of the reservoir in microwave radiation attenuation and overall hydrate dissociation. A high saturation reservoir may not always provide high gas recovery by dissociation of hydrates in the case of microwave heating.
Originality/value
The multi-layer approach to model microwave radiation propagation is introduced and tested for the first time in dissociating hydrate reservoirs. The multi-layer model provides better control over reservoir heterogeneity and interface conditions compared to existing homogeneous models.
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Ayush Jain, Imbesat Hassan Rizvi, Subrata Kumar Ghosh and P.S. Mukherjee
Nanofluids exhibit enhanced heat transfer characteristics and are expected to be the future heat transfer fluids particularly the lubricants and transmission fluids used in heavy…
Abstract
Purpose
Nanofluids exhibit enhanced heat transfer characteristics and are expected to be the future heat transfer fluids particularly the lubricants and transmission fluids used in heavy machinery. For studying the heat transfer behaviour of the nanofluids, precise values of their thermal conductivity are required. For predicting the correct value of thermal conductivity of a nanofluid, mathematical models are necessary. In this paper, the effective thermal conductivity of various nanofluids has been reported by using both experimental and mathematical modelling. The paper aims to discuss these issues.
Design/methodology/approach
Hamilton and Crosser equation was used for predicting the thermal conductivities of nanofluids, and the obtained values were compared with the experimental findings. Nanofluid studied in this paper are Al2O3 in base fluid water, Al2O3 in base fluid ethylene glycol, CuO in base fluid water, CuO in base fluid ethylene glycol, TiO2 in base fluid ethylene glycol. In addition, studies have been made on nanofluids with CuO and Al2O3 in base fluid SAE 30 particularly for heavy machinery applications.
Findings
The study shows that increase in thermal conductivity of the nanofluid with particle concentration is in good agreement with that predicted by Hamilton and Crosser at typical lower concentrations.
Research limitations/implications
It has been observed that deviation between experimental and theoretical results increases as the volume concentration of nanoparticles increases. Therefore, the mathematical model cannot be used for predicting thermal conductivity at high concentration values.
Originality/value
Studies on nanoparticles with a standard mineral oil as base fluid have not been considered extensively as per the previous literatures available.
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Eric Monier-Vinard, Brice Rogie, Valentin Bissuel, Najib Laraqi, Olivier Daniel and Marie-Cécile Kotelon
Latest Computational Fluid Dynamics (CFDs) tools allow modeling more finely the conjugate thermo-fluidic behavior of a single electronic component mounted on a Printed Wiring…
Abstract
Purpose
Latest Computational Fluid Dynamics (CFDs) tools allow modeling more finely the conjugate thermo-fluidic behavior of a single electronic component mounted on a Printed Wiring Board (PWB). A realistic three-dimensional representation of a large set of electric copper traces of its composite structure is henceforth achievable. The purpose of this study is to confront the predictions of the fully detailed numerical model of an electronic board to a set of experiment results to assess their relevance.
Design/methodology/approach
The present study focuses on the case of a Ball Grid Array (BGA) package of 208 solder balls that connect the component electronic chip to the Printed Wiring Board. Its complete geometrical definition has to be coupled with a realistic board layers layout and a fine description of their numerous copper traces to appropriately predict the way the heat is spread throughout that multi-layer composite structure. The numerical model computations were conducted on four CFD software then compare to experiment results. The component thermal metrics for single-chip packages are based on the standard promoted by the Joint Electron Device Engineering Council (JEDEC), named JESD-51. The agreement of the numerical predictions and measurements has been done for free and forced convection.
Findings
The present work shows that the numerical model error is lower than 2 per cent for various convective boundary conditions. Moreover, the establishment of realistic numerical models of electronic components permits to properly apprehend multi-physics design issues, such as joule heating effect in copper traces. Moreover, the practical modeling assumptions, such as effective thermal conductivity calculation, used since decades, for characterizing the thermal performances of an electronic component were tested and appeared to be tricky. A new approach based on an effective thermal conductivity matrix is investigated to reduce computation time. The obtained numerical results highlight a good agreement with experimental data.
Research limitations/implications
The study highlights that the board three-dimensional modeling is mandatory to properly match the set of experiment results. The conventional approach based on a single homogenous layer using effective thermal conductivity calculation has to be banned.
Practical implications
The thermal design of complex electronic components is henceforth under increasing control. For instance, the impact of gold wire-bonds can now be investigated. The three-dimensional geometry of sophisticated packages, such as in BGA family, can be imported with all its internal details as well as those of its associated test board to build a realistic numerical model. The establishment of behavioral models such as DELPHI Compact Thermal Models can be performed on a consistent three-dimensional representation with the aim to minimize computation time.
Originality/value
The study highlights that multi-layer copper trace plane discretization could be used to strongly reduce computation time while conserving a high accuracy level.
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Kakanuti Malleswari and Sarojamma G.
This study aims to explore the thermal energy diffusion and flow features of a hybrid nanofluid in a thin film. In particular, the focus is to elicit the impact of shape factor in…
Abstract
Purpose
This study aims to explore the thermal energy diffusion and flow features of a hybrid nanofluid in a thin film. In particular, the focus is to elicit the impact of shape factor in the backdrop of a magnetic field. The hybrid nanofluid is the amalgamation of various shaped nanoscale particles of copper and alumina in water.
Design/methodology/approach
The equations of motion and energy are modeled using the Tiwari–Das model. The differential equations governing the physics of the designed model have been obtained by the application of scaling analysis. To achieve quantitative outcomes, Runge–Kutta–Fehlberg numerical code along with shooting techniques is used. Validation of the derived outcomes with available data in literature reveals a greater accuracy of the numerical procedure used in this investigation.
Findings
The dynamics of the slender nano liquid film is explored eliciting the impact of various flow parameters. The rate of energy transport of the Cu-Al2O3/ water with blade-shaped nanoparticle, at a fixed Prandtl number (=2) is enhanced by 14.7% compared to that evaluated with spherical particles. The presence of hybrid nanoparticles has an affirmative impact in boosting the rate of heat transfer (RHT). The temperature and the rate of thermal diffusion of the hybrid nanofluid are more prominent than those of the Cu-H2O case. The numerical outcomes of this investigation are collated with the already published works as a limiting case and are found to be in good agreement.
Originality/value
The adopted methodology helped to obtain the results of the present problem. To the best of authors’ knowledge, it can be shown that the originality of the work with the table of comparison. There is a good agreement between present outcomes with the existed results.
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