Multilayer Slab Research Articles

A multi-layered poroelastic slab model under cyclic loading for a single osteon

BackgroundAn osteon consists of a multi-layered bone matrix and interstitial fluid flow in the lacunar–canalicular system. Loading-induced interstitial fluid flow in the lacunar–canalicular system is critical for osteocyte mechanotransduction and bone remodelling.MethodsTo investigate the effects of the lamellar structure and heterogeneous material properties of the osteon on the distributions of interstitial fluid flow and seepage velocity, an osteon is idealized as a hollow two-dimensional poroelastic multi-layered slab model subjected to cyclic loading. Based on poroelastic theory, the analytical solutions of interstitial fluid pressure and seepage velocity in lacunar–canalicular pores were obtained.ResultsThe results show that strain magnitude has a greater influence on interstitial fluid pressure than loading frequency. Interestingly, the heterogeneous distribution of permeability produces remarkable variations in interstitial fluid pressure and seepage velocity in the cross-section of cortical bone. In addition, interstitial fluid flow stimuli to osteocytes are mostly controlled by the value of permeability at the surface of the osteon rather than at the inner wall of the osteon.ConclusionInterstitial fluid flow induced by cycling loading stimuli to an osteocyte housed in a lacunar–canalicular pore is not only correlated with strain amplitude and loading frequency, but also closely correlated with the spatial gradient distribution of permeability. This model can help us better understand the fluid flow stimuli to osteocytes during bone remodelling.

Calculation and evaluation of the effectiveness of multilayer and monocoque slabs

The search for rational and effective design options is a very good motivation for research in the construction industry. In particular, the construction of inter-floor ceiling is one of the most important elements of any building or structure, and its cost is approximately 20-30% of the total volume of all construction and installation work. Therefore, one of the problems faced by the designer is the choice of the most efficient floor covering, including in terms of efficiency. The vast majority of loads are transmitted to the framework, walls and foundations through the overlap, the actual weight of which can reach up to 70% of the total vertical static load, therefore the search for new constructive solutions for the creation and study of lightweight types of overlays, which will reduce the constant component of the load, remains relevant. Given the constructive complexity of the facilitated effective forms of overlap, the question of adapting existing methods for assessing the bearing capacity for the engineering calculation of such structures is important. The article describes a brief overview of existing studies of multilayer structures and ceilings with void inserts. The engineering methodology for calculation of bearing capacity of multilayer and claydite monocoque (with void-forming inserts) of slabs of overlappings, with their bullying in four corners is given. The bearing capacity of multilayer boards was checked for strips 250 mm wide in the middle of the extreme contour, where the maximum moments are in operation. To determine the bearing capacity of monocoque floor slabs, their calculated section was reduced to a tread section. The calculation of the considered slabs is based on the deformation technique, taking into account the nonlinear diagram of tension-deformation for concrete and two-line for reinforcement based on the actual physical and mechanical characteristics of materials, in accordance with the current normative documents, in particular DSTU B V.2.6-156: 2010. The comparison of theoretical calculation results with the performed experimental researches of multilayer and monocoque floor slabs is given. Graphically depicted designs and design schemes for the obstruction of prototype samples. It is suggested to use a coefficient of efficiency Kef, which allows to evaluate the efficiency of such structures compared with the classical reinforced concrete and choose the most optimal variant, which is reflected on the example of the test plates.

The surface energy and stress of metals

We investigated surface properties of metals by performing first-principles calculations. A systematic database was established for the surface relaxation, surface energy (γ), and surface stress (τ) for metallic elements in the periodic table. The surfaces were modeled by multi-layered slab structures along the direction of low-index surfaces. The surface energy γ of simple metals decreases as the atomic number increases in a given group, while the surface stress τ has its minimum in the middle. The transition metal series show parabolic trends for both γ and τ with a dip in the middle. The dip occurs at half-band filling due to a long-range Friedel oscillation of the surface charge density, which induces a strong stability to the Peierls-like transition. In addition, due to magnetic effects, the dips in the 3d metal series are shallower and deeper for γ and τ, respectively, than those of the 4d and 5d metals. The surface stress of the transition metals is typically positive, only Cr and Mn have a negative τ for the (100) surface facet, indicating that they are under compression. The light actinides have an increasing γ trend according to the atomic number. The present work provides a useful and consistent database for the theoretical modelling of surface phenomena.

The gaseous plasmonic response of a one-dimensional photonic crystal composed of striated plasma layers

We present simulations of the response of a one-dimensional striated plasma slab to incident electromagnetic waves that span regions both above and below the plasma frequency, ωp. Photonic bandgap modes are present throughout these regions, and volume and surface plasmon modes facilitate the response below ωp, where the dielectric constant, εp < 0. In the vicinity of ωp, most apparently, when ωp is in proximity of the lattice frequency, there is a feature for transverse magnetic (TM) polarization that is associated with the emergence of new dispersion branches. Also for TM polarization, a very low frequency mode emerges outside of the light line. Both these features are plasmonic and are attributed to the excitation of symmetric and asymmetric surface plasmon polaritons (SPPs) at the plasma-dielectric interface of the multi-layer plasma slabs. The features seen in the bandgap maps near ωp reveal the possible presence of Fano resonances between the symmetric branch of the SPP and the Bragg resonance as a narrow stop band (anti-node) is superimposed on the otherwise broad transmission band seen for transverse-electric polarization. We provide renderings that allow the visualization of where the transmission bands are and compute the transmittance and reflectance to facilitate the design and interpretation of experiments. The transmission bands associated with photonic bandgap modes above the plasma frequency are rather broad. The plasmonic modes, i.e., those associated with εp ≤ 0, can be quite narrow and are tuned by varying the plasma density, affording an opportunity for the application of these structures as ultra-narrow tunable microwave transmission filters.

Formation Mechanisms for Entry and Exit Defects in Bobbin Friction Stir Welding

Bobbin friction stir welding (BFSW) is an innovative variant for the solid state welding process whereby a rotating symmetrical tool causes a fully penetrated bond. Despite the process development, there are still unknown variables in the characterization of the process parameters which can cause uncontrolled weld defects. The entry zone and the exit zone consist of two discontinuity-defects and removing them is one of the current challenges for improving the weld quality. In the present research, the characteristic features of the entry and exit defects in the weld structure and formation mechanism of them during the BFSW processing was investigated. Using stacked layers of multi-colour plasticine the material flow, analogous to metal flow, can be visualised. By using different colours as the path markers of the analogue model, the streamline flow can be easily delineated in the discontinuity defects compared with the metal welds. AA6082-T6 aluminium plates and multi-layered plasticine slabs were employed to replicate the entry-exit defects in the metal weld and analogue samples. The fixed-bobbin tool utilized for this research was optimized by adding a thread feature and tri-flat geometry to the pin and closed-end spiral scrolls on both shoulder surfaces. Samples were processed at different rotating and longitudinal speeds to show the degree of dependency on the welding parameters for the defects. The analogue models showed that the entry zone and the exit zone of the BFSW are affected by the inhomogeneity of the material flow regime which causes the ejection or disruption of the plastic flow in the gap between the bobbin shoulders. The trial aluminium welds showed that the elimination of entry-exit defects in the weld body is not completely possible but the size of the defects can be minimized by modification of the welding parameters. For the entry zone, the flow pattern evolution suggested formation mechanisms for a sprayed tail, island zone and discontinuity-channel. For the exit zone a keyhole-shaped discontinuity is discussed as a structural defect.

Entropy generation analysis of multilayer PCM slabs integrated with fins

Entropy generation analysis of multilayer PCM slabs integrated with fins

Entropy generation analysis of multilayer PCM slabs integrated with fins

In this study, the utilisation of composite phase change materials (PCMs) slabs with fins in a thermal energy storage (TES) system is numerically analysed. The storage system consists of three PCM layers at different melting temperatures. First, the predicted results are verified against the analytical solution that is taken from literature. Afterwards, the influence of the design parameters such as fin length and fin spacing on time for complete melting of the multi-layer TES are examined. Custom field functions are integrated into the ANSYS-FLUENT software to assess the local and volume averaged entropy generation within the system. The results show that at constant fin spacing, that increasing fin length from 20 mm to 80 mm enhances the melting rate up to 50%. In addition, when the fin spacing is doubled, the elapsed time for complete melting decreased about 37%. Moreover, the fin arrangement has a considerable effect on entropy generation.

Quantitative evaluation of functional Near Infrared Spectroscopy measurements with different source-detector separations using Monte Carlo simulation

Quantitative evaluation of functional Near Infrared Spectroscopy measurements with different source-detector separations using Monte Carlo simulation

Transfer matrix method for four-flux radiative transfer.

We develop a transfer matrix method for four-flux radiative transfer, which is ideally suited for studying transport through multiple scattering layers. The model predicts the specular and diffuse reflection and transmission of multilayer composite films, including interface reflections, for diffuse or collimated incidence. For spherical particles in the diffusion approximation, we derive closed-form expressions for the matrix coefficients and show remarkable agreement with numerical Monte Carlo simulations for a range of absorption values and film thicknesses, and for an example multilayer slab.

Analysis of Rigid Pavement Built with Multi-layer Concrete Slabs Resting on Pasternak Foundation

Rigid pavement construction is emerging due to its long term performance and less maintenance cost. Its rigidity and high modulus of elasticity tend to distribute load over a wide area of foundation, resulting in very low deflections under traffic and environmental loading. Thus a major portion of the structure capacity is imparted by slab itself. Multi-layer slab is the composition of several superposed concrete layers of different quality. An idea is that lower quality material can be sandwiched in the neutral axis zone. This paper deals a structural analysis of the three layered structure resting on the Pasternak foundation subjected to traffic loading. The three layered structure is replaced by an equivalent single layered structure. An assumption was taken that the deflection at the surface of the upper layer may be considered to be equal with the deflection at the bottom of the lower layer. The mechanical characteristics of the equivalent structure depend on the mechanical characteristics of the different layers and the various adhesion conditions at the interfaces. Adhesion condition are full slip at each of the interface, full friction at the first interface as well second interface, full friction at both interfaces and partial friction at all interfaces. Analytical solutions are arrived and structural responses are investigated. It has been found that the structural responses for full friction case showed significant results. This study is made towards enhancing current design method and economic construction.

Fracture characterization of multi-layer wire mesh rubberized ferrocement composite slabs by means of acoustic emission

This study investigated the fracture behaviour of multi-layer ferrocement composite slabs with partial replacement of tire rubber powder as filler utilizing acoustic emission (AE) technique for characterization. Ferrocement slab specimens prepared using normal-compact cement mortar, self-compact cement mortar, fly ash, and rubberized self-compact cement mortar –with varying steel mesh reinforcement layers– were statically loaded to failure. The inclusion of 10% rubber powder (by weight) was found capable of altering the failure mode of composite slabs from brittle to ductile with a slight reduction in the ultimate flexural strength. Fracture development of the specimens was closely monitored using AE for enhanced characterization. It is seemingly evident that the measured AE parameters could be effectively processed to distinguish different modes of fracture. The collected AE data was utilized to quantify stiffness reduction in the specimens due to progressive damage.

On the solution of the SN multigroup kinetics equations in multilayer slabs

Presented in this paper is an analytical representation for the solution of the slab-geometry neutron kinetics equations in energy-multigroup discrete ordinates (SN) transport formulation with an arbitrary number of delayed neutron precursors. The basic idea involves: (i) the group neutron angular fluxes and the concentrations of delayed neutron precursors are expanded in truncated series of analytic functions; (ii) by substituting these expansion representations into the multigroup SN kinetics equations, a set of recursive systems of first-order ordinary differential equations results. It is assumed that the first equation of the system is source free and is the only one which satisfies the initial conditions. The remaining equations of the recursive system satisfy zero initial condition and the source term is written in terms of the solution of the previous step. At each step of the recursive system, the multigroup SN equations are solved by using the TLTSN method, which is based on applying the double Laplace transform technique: first in the time variable and then in the space variable. Numerical results are given to two model problems which consist of a subcritical slab stabilized by a time-independent neutron source distribution.

Ka-Band Linear to Circular Polarization Converter Based on Multilayer Slab With Broadband Performance

In this paper, a Ka-band polarization converter is presented, which is based on multilayer slab. In order to improve impedance matching, metallic circular traces are printed periodically on each dielectric multilayer slab. Simulated results of the polarizer show that it can transform linearly polarized (LP) to circularly polarized (CP) fields over a frequency band from 23 to 35GHz (42%) with an insertion loss less than 0.5 dB. The transmitted CP wave by the polarizer is approximately robust under oblique illuminations. The polarizer is fabricated and measured by a wideband horn antenna satisfying the simulated results. Next, in order to design a high-gain CP structure around 30 GHz, an 8-element LP array antenna with Chebyshev tapered distribution is designed and integrated with the polarizer. Obviously, the antenna limits the overall bandwidth (nearly 28 to 31.5 GHz) due to the narrowband nature of the LP antenna array. When the polarizer is illuminated by an incident LP wave, the two linear components of the transmitted wave with approximately equal amplitudes and 90° phase difference on the frequency band of interest are produced. Experimental results of the proposed structure show a pure CP with a gain of 13 dBi at 30 GHz, which can be suitable for millimeter wave communication.

Near-Field Heat Transfer between Multilayer Hyperbolic Metamaterials

Abstract We review the near-field radiative heat flux between hyperbolic materials focusing on multilayer hyperbolic meta-materials. We discuss the formation of the hyperbolic bands, the impact of ordering of the multilayer slabs, as well as the impact of the first single layer on the heat transfer. Furthermore, we compare the contribution of surface modes to that of hyperbolic modes. Finally, we also compare the exact results with predictions from effective medium theory.

Ultrasensitive biosensors based on long-range surface plasmon polariton and dielectric waveguide modes

An ultrasensitive biosensor based on hybrid structure and composed of long-range surface plasmon polariton (LRSPP) and dielectric planar waveguide (PWG) modes is proposed. Both PWG and LRSPP modes have strong resonances to form strong coupling between the two modes, and the two modes can couple to enhance sensitivity of sensors. In the hybrid structure, PWG is composed of cytop–Si–cytop multilayers and the LRSPP configuration is composed of cytop–metal–sensing medium multilayer slabs. The highest imaging sensitivities of 2264 and 3619 RIU−1 were realized in the proposed sensors based on Au and Al-monolayer graphene, respectively, which are nearly 1.2 and 1.9 times larger than the 1910 RIU−1 sensitivity of the conventional LRSPR sensor (LRSPP sensor). Moreover, it is demonstrated that the PWG-coupled LRSPP biosensor is applicable to the sensing medium, with refractive index in the vicinity of 1.34.

NiMoS HDS catalysts – The effect of the Ti and Zr incorporation into the silica support and of the catalyst preparation methodology on the orientation and activity of the formed MoS2 slabs

HDS NiMo catalyst precursors supported on SiO2, SiO2-TiO2 or SiO2-ZrO2, having high specific surface areas and highly dispersed Mo species were prepared using a one-pot sol-gel methodology or by wet impregnation. After the catalyst precursor sulfidation, HRTEM and Raman analyses evidenced the effective formation of MoS2 slabs on the support. For the NiMoS-Si catalyst (precursor one-pot synthesized), there was a high formation of edge-bonded oriented MoS2 slabs, whereas for the NiMoS/Si prepared by impregnation, basal-bonded MoS2 slabs were more abundant. Coherent with the formation of MoS2 slabs and the promoting effect of Ni, all of the prepared NiMoS catalysts were active in the HDS of thiophene, with those one-pot supported on SiO2 or SiO2-ZrO2 being the most active. Due to the strong interaction between Mo and Ti, the NiMoS-SiTi catalyst did not show consistent formation of MoS2 slabs and consequently it presented the lowest activity. No observable effect in the HDS activity of the Zr incorporation into the SiO2 framework was noticed. The considerable specific activity (SA) of the catalysts NiMoS-Si and NiMoS/Si, was respectively related to the formation of the most active edge-bonded MoS2 slabs and to the well-active Type II HDS catalysts on multilayer basal-bonded MoS2 slabs. The studied NiMoS-Si and NiMo-SiZr with high SA values evidences that the one-pot sol-gel synthesis methodology used to prepare the catalyst precursor leads to highly active HDS catalysts with the important advantages of reducing the preparation time, energy consumption, and consequently diminishing the catalyst production cost.

A Response Matrix Method for One-Speed Slab-Geometry Discrete Ordinates Adjoint Calculations in Source-Detector Problems

ABSTRACTPresented here is an application of the one-speed Response Matrix (RM) method for adjoint discrete ordinates (SN) problems in slab geometry applied to source-detector problems. The adjoint RM method is free from spatial truncation errors, as it generates numerical results for the adjoint angular fluxes in multilayer slabs that agree with the numerical values obtained from the analytical solution of the adjoint SN equations. Numerical results are given for two typical source-detector problems to illustrate the accuracy and the efficiency of the offered RM computer code.

Van der Waals torque and force between dielectrically anisotropic layered media.

We analyse van der Waals interactions between a pair of dielectrically anisotropic plane-layered media interacting across a dielectrically isotropic solvent medium. We develop a general formalism based on transfer matrices to investigate the van der Waals torque and force in the limit of weak birefringence and dielectric matching between the ordinary axes of the anisotropic layers and the solvent. We apply this formalism to study the following systems: (i) a pair of single anisotropic layers, (ii) a single anisotropic layer interacting with a multilayered slab consisting of alternating anisotropic and isotropic layers, and (iii) a pair of multilayered slabs each consisting of alternating anisotropic and isotropic layers, looking at the cases where the optic axes lie parallel and/or perpendicular to the plane of the layers. For the first case, the optic axes of the oppositely facing anisotropic layers of the two interacting slabs generally possess an angular mismatch, and within each multilayered slab the optic axes may either be the same or undergo constant angular increments across the anisotropic layers. In particular, we examine how the behaviors of the van der Waals torque and force can be "tuned" by adjusting the layer thicknesses, the relative angular increment within each slab, and the angular mismatch between the slabs.

Improved homogenization procedure based on a Drude-Lorentz dispersive model for metamaterials

The extraction of constitutive parameters of metamaterials, i.e., electrical permittivity (e) and magnetic permeability (μ), is quite challenging. Usually, two techniques are used for this purpose, namely, the Nicolson-Ross-Weir technique and the dispersive models technique (Lorentz and Drude). However, these techniques fail to produce accurate results when the operating frequency is near the cell resonance frequency. In this article, an improved transition layer-based homogenization procedure is proposed where the metamaterial cell is homogenized as a Drude–Lorentz multilayer slab. This assumption considerably improves the scattering parameters approach, as demonstrated for a metamaterial slab with a thickness of three Omega cells. In addition, the proposed technique is more suitable for implementation in finite difference time domain (FDTD) methods. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1490–1494, 2016

General Boundary-Value Problems for the Heat Conduction Equation with Piecewise-Continuous Coefficients

A constructive scheme for the construction of a solution of a mixed problem for the heat conduction equation with piecewise-continuous coefficients coordinate-dependent in the final interval is suggested and validated in the present work. The boundary conditions are assumed to be most general. The scheme is based on: the reduction method, the concept of quasi-derivatives, the currently accepted theory of the systems of linear differential equations, the Fourier method, and the modified method of eigenfunctions. The method based on this scheme should be related to direct exact methods of solving mixed problems that do not employ the procedures of constructing Green′s functions or integral transformations. Here the theorem of eigenfunction expansion is adapted for the case of coefficients that have discontinuity points of the 1st kind. The results obtained can be used, for example, in investigating the process of heat transfer in a multilayer slab under conditions of ideal thermal contact between the layers. A particular case of piecewise-continuous coefficients is considered. A numerical example of calculation of a temperature field in a real four-layer building slab under boundary conditions of the 3rd kind (conditions of convective heat transfer) that model the phenomenon of fire near one of the external surfaces is given.