Slab Layer Research Articles

Zinc oxide aluminum doped slabs for heat-eliminating coatings of spacecrafts

This paper discuss a possibility for using a thin-film functional coating based on transparent conducting thin films of aluminum doped zinc oxide (AZO) as a heat-eliminating material on the surface of a spacecraft. The structure of the functional coating has been chosen taking into account the plasmonic properties of AZO and silver and represents the AZO slabs with embedded silver nanoparticles deposited on AZO layer and AZO slabs with embedded silver nanoparticles deposited on thin film fused quartz layer. The paper contains COMSOL finite element simulations of the scattering cross section for thermal radiation in the IR band in the case the investigated coating deposited on a reflective aluminum film, and absorption cross section in the near UV and visible spectral bands when the coating deposited on silicon solar panels. The calculations demonstrate an increase in the scattering cross-section in the spectral band of blackbody radiation by several orders of magnitude, with the maximum in the scattering spectrum of the AZO slabs/ AZO /Al structure corresponding to the maximum intensity of the blackbody thermal radiation, which has been heated to 100 °C in the case the lattice period of the AZO slabs is equal to the resonance wavelength for AZO. Also an increase in the absorption cross-section of AZO slabs/ AZO /Si structure in visible spectral band is observed corresponding to plasmon absorption of embedded silver nanoparticles.

Structural, surface morphology and magneto-transport properties of self flux grown Eu doped Bi2Se3 single crystal

Here, we report the effect of europium (Eu) doping in Bi2Se3 topological insulator (TI) by using different characterization techniques viz. X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive x-ray analysis (EDXA) and magneto-transport measurements. Good quality Eu doped Bi2Se3 (Eu0.1Bi1.9Se3) single crystal is grown by the self flux method through the solid state reaction route. Single crystal XRD pattern displayed the high crystalline quality of the Eu0.1Bi1.9Se3 sample along (00l) alignment whereas; the powder XRD confirmed the rhombohedral crystal structure without any impurity phases. SEM images exhibited a layered slab like structure stacked one over the other whereas; EDXA measurements confirmed the chemical composition of Eu0.1Bi1.9Se3 sample. Further, the EDXA mapping showed the homogeneous distribution of Bi, Se and Eu elements. Temperature dependent electrical resistivity curves revealed a metallic behaviour both in the presence and absence of applied magnetic field. Magneto-transport measurements showed a decrease in the magneto-resistance (MR) value of the Eu0.1Bi1.9Se3 sample (∼32% at 5 K) in comparison to the pure Bi2Se3 sample (∼80% at 5 K). For, Eu0.1Bi1.9Se3 sample, a complex crossover between WL and WAL phenomenon was observed at lower applied magnetic fields, whereas the same was absent in case of the pristine one. Further, HLN (Hikami Larkin Nagaoka) fitted magneto-conductivity (MC) analysis revealed a competing weak anti localization (WAL) and weak localization (WL) behaviour. Summarily, in the present work we study the structural, surface morphology and magneto-transport properties of as grown Eu0.1Bi1.9Se3 single crystals.

DFT STUDY OF METHYL (CH3) AND HYDROXYL (OH) ADSORPTION ON A GOLD (001) SURFACE

We used the DACAPO code with the GGA-PW91 approximation to study the adsorption of methyl (CH3) and hydroxyl (OH) for four- and five-layer gold (Au) (001) slabs. We have determined for each species the best binding site, adsorption energy, the change in the work function, surface energy, surface dipole moment, geometrical parameters and projected density of states (PDOS). We performed spin-unpolarized and spin-polarized DFT calculations for free and adsorbed CH3 and OH species. The most important point is that the spin polarization diminishes the adsorption energies but does not change the geometrical parameters. For the CH3 species, only the top site was found to be stable for different coverages. We found that during the optimization phase, the hollow and bridge sites were found to be unstable. In both cases the CH3 species moves toward the top site. We observe that the adsorption energy decreases when increasing the coverage. However, the OH species was stable in all investigated sites (top, bridge and hollow). We notice that the adsorption energy is dependent on the number of slab layers and the bridge is the best site in adsorption energy. The analysis of the calculated O PDOS of OH radical shows a mixing between the O orbitals and the Au bands.

Head model based on the shape of the subject’s head for optical brain imaging

Optical imaging methods such as near-infrared spectroscopy and diffuse optical tomography rely on models to solve the inverse problem. Imaging an adult human head also requires a head model. Using a model, which makes describing the structure of the head better, leads to acquiring a more accurate absorption map. Here, by combining the key features of layered slab models and head atlases, we introduce a new two-layered head model that is based on the surface geometry of the subject's head with variable thickness of the superficial layer. Using the Monte Carlo approach, we assess the performance of our model for fitting the optical properties from simulated time-resolved data of the adult head in a null distance source-detector configuration. Using our model, we observed improved results at 70 percent of the locations on the head and an overall 20 percent reduction in relative error compared to layered slab model.

Graphene based photonic crystal optical filter: Design and exploration of the tunability

Optical characteristics of two new graphene based photonic crystals are studied in detail. A structure containing alternating layers of graphene and SiO2 slabs is considered as the ideal crystal. The dependency of the photonic band gaps (PBGs) to the dielectric layer thickness and the period number is explored at first step. Potential of the proposed crystal to be used as an optical filter is then investigated. Adding a nonlinear electro-optic polymer as a defect layer, the alterations of the optical features are inspected. Results show that the defect layer insertion causes a resonant mode inside the PBGs. However, the location of the defect layer inside the crystal is very effective on both the frequency and width of the resonant mode. Tunability of the optical features is probed by taking into account of the dependencies to the wave incident angle, graphene chemical potential and the applied external voltage to the defect layer.

Transition Metal Cations Stabilized Layered Vanadate Cathodes for Zinc-Ion Batteries

A general strategy is explored to design and synthesize a series of layered vanadate hydrates. Structural analysis found a small amount of cations entered into the VO layers to form a chemical bonding and lock the layer slabs with a stable structure. The stabilized vanadate hydrates have the expanded layer spacing and the robust layered structures that provide a fast ion migration channel and stand the volume change in the intercalation/de-intercalation of Zinc-ion during the electrochemical reaction, rendering an excellent rate capability and stable cycling performance. Specifically, Mn-stabilized vanadium pentoxide hydrate delivers a specific capacity of 400 mAh/g at a current density of 50 mA/g and 260 mAh/g at 4 A/g with capacity retention of 92% over 2,000 cycles. Several transition metal cations can also play the same role in enhancing Zn-ion storage in layered vanadate hydrates, suggesting a general strategy for exploiting the high-performances cathodes for multi-valent ion batteries.

STRENGTH ANALYSIS OF VARIABLE RIGIDITY SLABS ON ELASTIC SUPPORT WITH VARIABLE SUBGRADE RATIO

The paper presents the strength analysis of variable rigidity slabs on elastic support with the variable subgrade ratio. The analysis is based on a solution of the differential equation of the slab flexure using the finite element method. The results are obtained for different slabs on the elastic support. The results are presented for the different thickness of the upper layer of the two-layer slab on the elastic support with the variable subgrade ratio.

Arching mechanism of the slab joints in CRTSII slab track under high temperature conditions

China Railway Track System II slab track is widely applied to China high-speed railway. Under the high temperature conditions, it tends to produce different degrees of arch at the joints between prefabricated slabs, which will affect the track irregularity and safe operation of high-speed trains. In this paper, considering the buckling instability of track structure, the arching mechanism of the slab joints was investigated by establishing a 3D finite element model of the CRTSII slab track. Combined with the field investigation, the damage process of joint concrete and its effects on the arching instability were analyzed. The results show: 1) The construction of joint concrete is difficult to control on site, which leads to inferior quality compared to prefabricated slab. The worse quality of joint concrete corresponds to a smaller amplitude of temperature rise causing joints damage and a greater damage area. 2) When the amplitude of temperature rise of the slab is over 37 °C, various damage emerges in the narrow joint and the middle of wide joint, resulting in the eccentric compression. 3) The temperature gradient load will cause the propagation of interface gap between slab and CA mortar layer, which aggravates the arching instability of slab, especially when the height of gap exceeds 1.5 mm. This research is expected to provide guidance for the optimization design, maintenance and damage control of slab track.

Analysis of the causes of damage to the RC floor slab in the underground garage

The article presents the results of testing a damaged reinforced concrete slab, which is located in the underground garage constituting the two lowest floors of a residential and service building. During the tests numerous cracks in the slab were inventoried. Some cracks covered the entire thickness of the RC slab and floor layers made of synthetic resin. The result of these damages was penetration through the slab of water from molten slush and the need to limit the parking places on the lower level of the garage. Conducted analysis of technical documentation, analysis of damage morphology, control material tests and structure computations allowed assessment of the causes of existing damages to the floor slab and ability to develop recommendations regarding the methods of its repair.

Modal analysis of metallic screen with finite conductivity perforated by array of subwavelength rectangular flared holes.

An array of flared rectangular holes pierced through a conducting screen is treated herein by a rigorous full-wave modal analysis using the moment method entailing Green's functions for rectangular cavities and planar multilayer structures in the spectral domain as well as classical Floquet theorem and the mode-matching technique. In this way, flared holes with arbitrary taper profile that may each even be composed of different dielectric sections and which perforated metal films that may be sandwiched between multiple layers of dielectric slabs on both sides is herein treated. The eclectic permutations of geometrical, structural, and material attributes thus afforded by this generic topology facilitate correspondingly diverse investigations that may prove pivotal to the success of future explorations in search for new breakthrough discoveries and innovations in the subject of extraordinary transmission through subwavelength hole arrays, to which the herein-analyzed configuration is central. Oblique angles of incidence for both principal polarizations and metal losses incurred by imperfect conducting screens are also investigated in this work, all constituting crucial aspects that may often be neglected.

Bound states in the continuum in the double-period rectangular hole arrays perforated in one layer of photonic crystal slab in the visible wavelength region

Abstract We investigate optical bound states in the continuum (BICs) supported by a photonic crystal (PhC) slab penetrated with two periodic rectangular hole arrays embedded each other parallelly and vertically. It proves that the tunable off- Γ BICs can be found in the structure of both types, but the at- Γ BICs can only be obtained in the parallel structure. Quality factors (Q-factor) are obtained extremely high exceeding 105 for both types of structures. The tunable off- Γ BICs can be modulated by the structure parameters. Especially, the sensitivity of the resonant wavelength on the surrounding medium refractive index change is very large for the structure in both types, and tunable off- Γ BICs can be tuned by varying the environmental index. The results above accord well from the finite difference time domain method (FDTD) and the temporal coupled mode theory (CMT), which are beneficial to design practical resonance elements based on optical BICs in various new optical applications.

Temporal changes in the mechanical properties of snow related to crack propagation after loading

Most dry slab avalanches occur during or immediately following loading by snowfall or wind deposition. In the absence of further loading avalanche activity decreases over time. This suggests that loading favorably changes snow cover properties for avalanche release over short time scales (e.g., minutes and hours), and that changes over longer time scales (days or longer) help to stabilize the snowpack. This study quantifies both: 1) the effect of increasing load on the interaction of the slab and weak layer over short time scales, and 2) the longer term stabilizing changes following loading. We developed a field method to rapidly increase the load on existing weak layers, and conducted two different sets of experiments. For the first set of experiments we used a cardboard frame the dimensions of a standard Propagation Saw Test (PST) and added 5, 10, 15, or 20 cm of disaggregated snow on top of PST columns on 11 sampling days. We allowed the added snow to sinter for approximately 30 to 60 min before completely isolating the block and performing a PST. In the second set of experiments we used the same technique to add 10 cm of disaggregated snow on over 30 isolated columns. We then conducted PSTs in the minutes, hours and days following isolation, with tests ranging from 15 min to 4 days. For both experiments we filmed each test at 120 fps for particle tracking velocimetry analysis. We also utilized a model simulating the experiments to better interpret our results. In the first set of experiments, critical crack lengths dramatically decreased with increasing load while crack propagation speed increased, a finding consistent with previous work. In the second set of experiments, we found that critical crack lengths increased rapidly at first and then more slowly over time. Simulations of the experiments suggest that changes in critical crack length over time are caused by an increase in slab elastic modulus in the first hours following loading, and then caused by both increasing slab elastic modulus and weak layer specific fracture energy in days following loading. Overall, our results help to illustrate changes in critical crack lengths immediately after and in the days following loading. Our results are consistent with field observations of increasing avalanche activity during and immediately following loading events and decreasing avalanche activity afterwards.

THz Sensing With Anomalous Extraordinary Optical Transmission Hole Arrays.

Subwavelength hole array (HA) metasurfaces support the so-called extraordinary optical transmission (EOT) resonance that has already been exploited for sensing. In this work, we demonstrate the superior performance of a different resonant regime of HA metasurfaces called anomalous EOT, by doing a thorough numerical and experimental study of its ability in thin-film label-free sensing applications in the terahertz (THz) band. A comprehensive analysis using both the regular and anomalous EOT resonances is done by depositing thin layers of dielectric analyte slabs of different thicknesses on the structures in different scenarios. We carry out a detailed comparison and demonstrate that the best sensing performance is achieved when the structure operates in the anomalous EOT resonance and the analyte is deposited on the non-patterned side of the metasurface, improving by a factor between 2 and 3 the results of the EOT resonance in any of the considered scenarios. This can be explained by the comparatively narrower linewidth of the anomalous EOT resonance. The results presented expand the reach of subwavelength HAs for sensing applications by considering the anomalous EOT regime that is usually overlooked in the literature.

Kinetic bandgap analysis of plasma photonic crystals

The dispersion relation of plasma and plasma-dielectric photonic multilayer structures is approached in terms of a one-dimensional Particle-in-Cell simulation. For several plasma-dielectric configurations, the system response is obtained using a pulsed excitation and a subsequent two-dimensional frequency analysis. It is first shown that the dispersion relation of a single, homogeneous plasma slab is well described by the cold-plasma model even at a low pressure of 1 Pa. The study is extended to the simulation of plasma photonic crystals with a variety of configurations based on the work of Hojo and Mase [J. Plasma Fusion Res. 80, 89 (2004)]. Considering a one-dimensional plasma photonic crystal made from alternating layers of dielectric and homogeneous plasma slabs, it is shown that the assumption of a cold-plasma description is well justified also in this case. Moreover, in this work, the results are reformatted and analyzed in a band diagram representation, in particular, based on the lattice constant a. Based on these considerations, a scaling invariant representation is presented, utilizing a generalized set of parameters. The study is completed with an exemplary comparison of three plasma-dielectric photonic crystal configurations and their corresponding band diagrams.

Calculation of Reasonable Tension Value for Longitudinal Connecting Reinforcement of CRTSII Slab Ballastless Track

There is confusion in the original design concept for the tensioning of longitudinally connected reinforcement of the CRTSII (China Railway Track System) slab ballastless track. In order to clarify the effect of tension value of longitudinal reinforcement on the mechanical characteristics of the ballastless track, a three-dimensional finite element model, considering the nonlinear interaction between the track slab and cement-emulsified asphalt (CA) mortar of the CRTSII slab ballastless track, was established. The mechanical characteristics of the track structure under longitudinal tension load and temperature gradient load of the longitudinal joint were calculated. A method of applying prestress to post-pouring concrete was proposed according to the concept of prestress loss of pretensioning prestressed concrete, a reasonable tensile force value was proposed after the crack width, and the reinforcement stress of the ballastless track in the operation stage was checked and calculated according to the concrete design principle. When the tension force is greater than 300 kN, it is harmful to the bonding between the slab and mortar layer, which is prone to interlayer damage. In order to add prestress to concrete with wide joints to ensure the longitudinal stability of the ballastless track, and that the reinforcement stress and crack width meet design requirements, it is suggested that the tension force value should be 230 kN. Further, the temperature difference between reinforcement and concrete should be 30 °C before the initial curdle of wide joint concrete.

Transverse magnetic mode slab waveguide optical sensor in the presence of conducting interfaces

In this paper, three –layer slab waveguide is considered for the p-polarization whose free charge layer with a surface conductivity is assumed to exist at the two interfaces. The structure is then enhanced for sensing process by considering the different refractive index analytes in its proposed cladding structures. The sensitivity of the proposed sensor is investigated in details. Positive as well as negative surface conductivities are considered. It is found that utilizing negative surface conductivity at the interfaces can significantly enhance the sensitivity.

First-principles calculations on wetting interface between Ag-Cu-Ti filler metal and SiC ceramic: Ag (1 1 1)/SiC (1 1 1) interface and Ag (1 1 1)/TiC (1 1 1) interface

Interfacial properties of Ag (1 1 1)/SiC (1 1 1) interface and Ag (1 1 1)/TiC (1 1 1) interface were researched by first-principles calculations to investigate the reason that Ag-Cu-Ti filler metal shows the superior reactive wettability on SiC ceramic. The calculated results show that, 7 atom-layers Ag (1 1 1) surface, 11 atom-layer SiC (1 1 1) surface and 9 atom-layer TiC (1 1 1) surface can represent the Ag bulk, SiC bulk and TiC bulk, effectively. Ag (1 1 1)/SiC (1 1 1) interface and Ag (1 1 1)/TiC (1 1 1) interface with C-terminated structure and TL stacking sequence show the highest interfacial stability. Chemical bonds at Ag (1 1 1)/SiC (1 1 1) interface and Ag (1 1 1)/TiC (1 1 1) interface are mainly formed by the interaction between 1st layer C atoms in SiC (or TiC) slab and 1st layer Ag atoms in Ag slab. Interfacial energy of Ag (1 1 1)/SiC (1 1 1) interface is much larger than that of Ag (1 1 1)/TiC (1 1 1) interface, which indicates that the formed TiC reaction layer between Ag-Cu-Ti filler metal and SiC ceramic indeed plays the positive role on improving the wettability of Ag-Cu-Ti filler metal on SiC ceramic.

Hydrodesulfurization of dibenzothiophene over NiW/(SnAlPO4-5+Al2O3) catalyst, the tuning effect of SnAlPO4-5 to the desulfurization reaction pathway

SnAlPO4-5 molecular sieves were hydrothermally synthesized using SnCl2·2H2O as the tin source, and were verified that divalent tin was incorporated into the framework by isomorphous substitution of trivalent aluminum, and increasing the numbers of Brønsted and Lewis acid sites relative to those in AlPO4-5. The molecular sieves were used to fabricate hybrid supports with alumina and then were loaded with active metals to obtain NiW catalysts. The hydrodesulfurization (HDS) of dibenzothiophene (DBT) were evaluated for the catalytic activity of the catalysts. Because of the higher number of weak acid sites, much greater average number of slab layers and higher dispersion of WS2, the HDS rate of DBT at 280 °C is improved from 49.6% for the NiW/(AlPO4-5+Al2O3) catalyst to 82.2% for the NiW/(Sn0.12AlPO4-5+Al2O3) catalyst. Moreover, the highly active NiW/(Sn0.12AlPO4-5+Al2O3) catalyst obviously increases the product of the direct desulfurization route in the DBT HDS, which is beneficial for reducing hydrogen consumption in the industrial applications.

Influence of molecular dissociation on blob-induced atom density perturbations

The effects of enhanced electron and ion pressure perturbations mediated in filamentary structures (blobs) on the densities of neutral atoms and molecules are investigated through a self-consistent dynamical fluid model for plasma and neutral fields. The electron and ion densities and pressures, and the generalized vorticity, are simulated by a 2D drift-fluid model in an edge and scrape-off layer slab domain of a toroidally magnetically confined plasma. The plasma dynamics are coupled with a diffusion model for densities of neutral atoms and molecules. The combined model allows for determining the response of the density of neutrals with various temperatures to blobs. It is found that blobs locally deplete densities of molecules and atoms that do not originate from dissociation of molecules, whereas the density of atoms created by dissociation may increase during blob events. The neutral species, their temperature, and origin should thus be taken into consideration when estimating the effect of blobs on neutral density perturbations when calculating emission rates, e.g. for gas puff imaging.

Experimental study of the gap between track slab and cement asphalt mortar layer in CRTS I slab track

Gap exists in the interface of cement asphalt emulsion mortar and CRTS I track slab universally, which is more severe at four corners than other parts of the track slab. In this work, the temperature and elevation of CRTS I slab track with and without rail were measured continuously to study the influence mechanism of rail on the gap. The results show that the alternating temperature gradient of track slab is the main reason that causes the gap, and laying rail can efficiently decrease the gap size in the slab track without rail. Compared with the slab track without rail, the maximum elevation occurred at the corner, the maximum gap width and the maximum gap depth of the slab track with rail laid were decreased by 0.45 mm (25.7%), 0.75 mm (46.6%) and 9.5 mm (59.4%), respectively; meanwhile, the disqualification ratio at corners was reduced to 5.9%, which is 50% less than that of the track without rail. When elevation mismatch occurs in adjacent track slabs, a gasket should be placed at rail-bearing bed below the track slab in order to avoid the lower slab being dragged up by the higher slab and the further occurrence of new gap.