Sublayer Thickness Research Articles

Ablation resistance of HfC-TaC/HfC-SiC alternate coating for SiC-coated carbon/carbon composites under cyclic ablation

HfC-TaC/HfC-SiC alternate coatings with different sublayer thicknesses were fabricated on SiC-coated carbon/carbon composites by supersonic atmosphere plasma spraying. Their ablation resistance was studied under oxyacetylene torch and compared with monolayered HfC-TaC coating. The alternate coating with 6 spray cycles of HfC-TaC and 3 spray cycles of HfC-SiC sublayers exhibited the best ablation performance as confirmed by the integral coating morphology and the lowest ablation rates. A dense oxide layer acting as an oxygen insulator and the release of thermal stress induced by the formation of dendritic cracks are thought to be responsible for its great ablation resistance. For the alternate coating with 4 spray cycles of HfC-TaC and 2 spray cycles of HfC-SiC sublayers, exfoliation occurred at the interface of two adjacent sublayers, leading to violent evaporation of exposed HfC-SiC sublayer.

Association of ambient air pollution with age-related macular degeneration and retinal thickness in UK Biobank

AimTo examine the associations of air pollution with both self-reported age-related macular degeneration (AMD), and in vivo measures of retinal sublayer thicknesses.MethodsWe included 115 954 UK Biobank participants aged 40–69...

Effect on overall fatigue performance of varying thickness of an intermetallic sublayer within a soft multilayer coating

A series of 2IML multilayer coatings (composed of two hard intermetallic (IML) layers and two soft sublayers) with the different thickness of the first IML sublayer have been built to develop our mechanistic understanding of what controls its fatigue performance. Experimental investigations of these multilayer coatings reveal that decreasing the IML-Top layer’s thickness provides improved fatigue resistance. This improvement could be linked to: (1) the increased difficulty of surface crack initiation due to the limitation of the strain ranges experienced at the top surface and (2) the shorter crack propagation period in a thinner IML-Top layer.

Investigation of buoyancy influence on mixed convection in a vertical channel through PIV measurement

Buoyancy-aided mixed convection experiments were performed in a vertical rectangular channel heated on one side. Based on the heat/mass transfer analogy, mass transfer experiments were performed using a copper electroplating system. The Reynolds number ranged from 985 to 25,450 at a fixed Grashof number of 1.01 × 1010. We derived a local turbulent forced convection correlation following Petukhov et al. and Gnielinski. The heat transfer of turbulent mixed convective flow exhibited impairment and enhancement compared with the forced convection correlation affected by buoyancy at different axial position. Local heat transfer distributions were non-monotonous; five distinct flow regimes were apparent. Particle image velocimetry (PIV) was used to measure velocity profiles and turbulent shear stress. The effects of buoyancy on velocity profiles, turbulent shear stress, the thickness of the viscous sublayer, and heat transfer were identified.

Analytic formulas and numerical simulations for non-uniform AlxGa1-xN nanostructure on electro-optical properties for UV Photodetectors

In this paper, we numerically studied the influence of the geometry of gradient Al component AlxGa1-xN nanowires on their optical response. Based on the finite element simulation software COMSOL Multiphysics, we systematically studied the influence of geometric parameters of base radius (R), nanowires spacing and angle of incident light (AOI) on the optical response. To this end, we designed various gradient Al component AlxGa1-xN nano-trapped structure in the wavelength range of lambda (300–400 nm). The simulation results show that the optimal optical absorption spectra of hexagonal pyramid nanostructure arrays range from 300 to 400 nm and the average optical absorption efficiency is 97.87%, achieving omnidirectionality and unified broadband light absorption for AlxGa1-xN ultraviolet photocathode. In addition, we adjust the distribution and thickness of the Al component in the nanowires to achieve the optimization of the quantum efficiency and collection efficiency of the gradient Al component AlxGa1-xN. Using Spicer’s three-step emission theoretical model, the photoemission efficiency of variable Al component AlxGa1-xN nanowires array was calculated. As a result, when the Al component range is 0–0.19, the external electric field is 2.5 (V/μm) and the sublayer thickness is 60 nm, 120 nm, 180 nm, 240 nm, respectively, the optimal quantum efficiency of the AlGaN photocathode is 38.16% and the optimal collection efficiency is 31.12%. All these findings not only indicate that the gradient Al component AlxGa1-xN material has great potential advantages for UV band detection, but also provide theoretical support for the experiment and preparation of AlGaN photocathodes.

Optimization of transparent amorphous oxide-metal-amorphous oxide multilayer with high figure of merit for high transmittance and low resistivity

Highly transparent amorphous oxide-metal-amorphous oxide (OMO) multilayers were fabricated at room temperature using amorphous semiconducting Si–Zn–Sn–O (SZTO) metal oxide and metallic silver. Amorphous SZTO (a-SZTO) showed high refractive index of 2.04 which is comparable to crystalline ITO, and wide optical bandgap (E g ) of 3.26 eV, allowing transmitting of wavelength above 380 nm. SZTO based OMO showed low resistivity at the level of 10 −5 Ω cm by inserting an Ag layer. After optimizing the optical and electrical properties by changing Ag and SZTO sublayer thickness, a transparent conductive electrode with high average transmittance of 96.5% in visible region and low resistivity of 7.158 × 10 −5 Ω cm was fabricated at room temperature. The results show that SZTO is a promising sublayer for high performance transparent conducting oxides applications. • SZTO OMO multilayer is a transparent conductive electrode having high transmittance and low resistivity. • It was calculated that the optical bandgap has a wide bandgap. • The optical and electrical properties were optimized by changing the Ag and SZTO sub-layer thickness.

Titanium dioxide nanoparticles impair the inner blood-retinal barrier and retinal electrophysiology through rapid ADAM17 activation and claudin-5 degradation

BackgroundDepending on their distinct properties, titanium dioxide nanoparticles (TiO2-NPs) are manufactured extensively and widely present in our daily necessities, with growing environmental release and public concerns. In sunscreen formulations, supplementation of TiO2-NPs may reach up to 25% (w/w). Ocular contact with TiO2-NPs may occur accidentally in certain cases, allowing undesirable risks to human vision. This study aimed to understand the barrier integrity of retinal endothelial cells in response to TiO2-NP exposure. bEnd.3 cells and human retinal endothelial cells (HRECs) were exposed to TiO2-NP, followed by examination of their tight junction components and functions.ResultsTiO2-NP treatment apparently induced a broken structure of the junctional plaques, conferring decreased transendothelial electrical resistance, a permeable paracellular cleft, and improved cell migration in vitro. This might involve rapid activation of metalloproteinase, a disintegrin and metalloproteinase 17 (ADAM17), and ADAM17-mediated claudin-5 degradation. For the in vivo study, C57BL/6 mice were administered a single dose of TiO2-NP intravitreally and then subjected to a complete ophthalmology examination. Fluorescein leakage and reduced blood flow at the optical disc indicated a damaged inner blood-retinal barrier induced by TiO2-NPs. Inappreciable change in the thickness of retinal sublayers and alleviated electroretinography amplitude were observed in the TiO2-NP-treated eyes.ConclusionsOverall, our data demonstrate that TiO2-NP can damage endothelial cell function, thereby affecting retinal electrophysiology.

Relationship between corneal biomechanical parameters and corneal sublayer thickness measured by Corvis ST and UHR-OCT in keratoconus and normal eyes

BackgroundTo explore the relationship between corneal biomechanical parameters and corneal sublayer thickness using corneal visualization Scheimpflug technology (Corvis ST) and ultrahigh-resolution optical coherence tomography (UHR-OCT) in clinical and suspected keratoconus and normal eyes.MethodsCross-sectional prospective study. A total of 94 eyes of 70 participants were recruited. Twenty five eyes of 19 keratoconus patients, 52 eyes of 34 patients showing high risk of developing keratoconus according to the Belin/Ambrosio Enhanced Ectasia Display, and each eye of 17 normal subjects were enrolled. All participants underwent Corvis ST, Pentacam, and UHR-OCT examinations at the same time. Stiffness parameter A1 (SP-A1), deformation amplitude ratio (DA ratio), and other biomechanical parameters were recorded using Corvis ST. The vertical and horizontal thickness profiles of central 3 mm corneal epithelium, Bowman’s layer, and stroma as measured by the perpendicular distance between the neighboring interfaces were generated using UHR-OCT. The flat keratometry and steep keratometry were obtained using Pentacam. Analysis of correlation was applied to explore the association between variables.ResultsMost of the biomechanical parameters and corneal sublayer thickness profiles showed statistical differences among three groups. A statistically significant linear relationship was noted between SP-A1 and DA ratio in all three groups. SP-A1 was found to be positively correlated with epithelial and Bowman’s layer thickness in the keratoconus (KC) group, and with stromal thickness in all three groups. In the normal and suspected keratoconus (SKC) groups, only stromal thickness was included in the stepwise linear regression to predict SP-A1, whereas in the KC group, steep keratometry and Bowman’s layer thickness were included.ConclusionsSignificant and different correlations were noted between corneal stiffness and corneal sublayer thickness in different groups, indicating that corneal sublayers may play different roles in maintaining corneal biomechanical stability between keratoconus and normal eyes.

The Effect of a Ba0.2Sr0.8TiO3 Sublayer on the Structure and Electric Characteristics of Lead Zirconate Titanate Films on the Si(001) Substrate

Metal–ferroelectric–semiconductor Pb(ZrTi)O3/Ba0.2Sr0.8TiО3/Si(001) heterostructures have been synthesized by radiofrequency cathode sputtering. It has been established that the Pb(ZrTi)O3 films are single-phase and textured and the degree of predominance of one crystallographic orientation over another (110 or 001) is determined by the Ba0.2Sr0.8TiO3 sublayer thickness. It is shown that, by varying the sublayer thickness and/or the amplitude of one period of the external bipolar field effect, one can obtain different electric states of the structure, which can give rise to creating memory cells, including multilevel ones.

Direct numerical simulation of turbulent particle-laden flows: effects of Prandtl and Stokes numbers

The effect of molecular Prandtl number on the turbulent heat transfer of a non-isothermal turbulent channel flow laden with particles with four different Stokes number is investigated using direct numerical simulation coupled with a Lagrangian particle tracking. The flow configuration is a downward vertical channel with side walls kept at constant temperature. A total of 16 test cases with four different Prandtl numbers of Pr = 0.71, 1, 3, 7, and four particle sizes with the Stokes numbers of St= 40, 60, 100, 190 are considered. The mass loading, particle-to-fluid density ratio, and specific heat ratio are constant for all cases and they are equal to 0.57, 7298, and 0.39, respectively. It is shown that by the addition of particles, the heat transfer rate decreases and the thickness of the conductive sublayer thickness increases for all cases. The percentage of heat transfer modulation resulting from the addition of particles is almost independent of the Prandtl number but it slightly depends on the size of the particles, with the maximum being for smaller particles. The mean and rms values of temperature, temperature-velocity correlations, mean energy equation, and temperature variance budgets are presented. Contours of temperature in planes parallel to the wall and normal to the streamwise direction are also reported. At higher Prandtl numbers, the temperature contours clearly visualize the mushroom shaped structures formed as a result of the ejection of low-speed fluid from the wall.

Example of applied outcrop analysis and its significance as an analogue for surrounding giant gas-fields; Case study of Kuh-e-Surmeh region, southwestern Iran

Outcrops provide crucial information that can be used for the improvement of subsurface geological modeling. The present work provides a great example of such an application from a study on two well-known carbonate reservoirs uniquely exposed in the Kuh-e-Surmeh region, south-west Iran. Surface geology data were collected through extensive field study while the equivalent subsurface geology was reviewed based on bore reports available from the nearby giant gas-fields. Moreover, Schmidt hammer data were collected to investigate the variation in outcrop's uniaxial strength and detailed fracture analysis was carried out using Unmanned Aerial Vehicle (UAV) photography and direct field observations in selected stations. At the end, dolomite and limestone were identified as the dominant lithology of outcrops, greater apparent fracture intensity values were estimated for Kangan formation (P21=0.46) and the base of upper Dalan formation (P21=0.48). Moreover, fracture density (P20) was shown to be directly related to the formation uniaxial strength and the height of fractures was revealed to be inversely proportional to the thickness of sublayers. At the end, the collected surface and subsurface data were found to be in a general good agreement in terms of the stratigraphic location of fractured zones and mineralogy data, specifically, for the case of upper Dalan formation.

Effect of hydrodynamics on the formation and removal of microalgal biofilm in photobioreactors

To prevent the formation of biofilm or to remove already formed biofilm on the transparent walls of the closed cultivation systems, it is important to ensure that there are sufficient wall shear stresses to disrupt the stability of the biofilm. A pilot-scale flat-panel photobioreactor and laboratory tubular system were used to determine the critical value of the wall shear stress. The formation of biofilm on transparent walls of the cultivation systems reduces light penetration into the cultivation medium, which can subsequently reduce the production of microalgae, since light radiation a key parameter influencing the growth of microalgae. To study the influence of hydrodynamic conditions on the prevention of biofilm formation, a numerical model of a flat-panel photobioreactor was validated based on the experimental data. Using the validated model, a critical value of wall shear stress that above which avoids the formation of biofilm was defined to be 0.2 Pa. To refine the values from the numerical model, and to investigate the influence of hydrodynamic conditions on the process of disruption of the formed and stabilized biofilm, a simple experimental tubular system with the one-dimensional flow was developed. For one-dimensional flow, it is easier to describe the hydrodynamic behaviour and more precisely define the parameters influencing biofilm formation. The experiments in this simplified tubular system were focused on removing already formed biofilm. The formed biofilm on the transparent wall was completely removed from the surface when the wall shear stress reached a value of 53 Pa. However, the stability of the biofilm was already disturbed at a value of 6 Pa. The resulting values of critical wall shear stress could be used to select the operating conditions of the cultivation systems or to adjust their geometry affecting the hydrodynamic conditions. According to the velocity distribution based on the measured values, the thickness of the biofilm was less than the thickness of the viscous sublayer. Thus, the prevention of formation, disruption, or even removal of biofilm can be ensured by shear forces in the viscous sublayer.

Analysis of retinal sublayer thicknesses and rates of change in ABCA4-associated Stargardt disease

Stargardt disease, the most common inherited macular dystrophy, is characterized by vision loss due to central retinal atrophy. Although clinical trials for Stargardt are currently underway, the disease is typically slowly progressive, and objective, imaging-based biomarkers are critically needed. In this retrospective, observational study, we characterize the thicknesses of individual retinal sublayers by macular optical coherence tomography (OCT) in a large cohort of patients with molecularly-confirmed, ABCA4-associated Stargardt disease (STGD1) relative to normal controls. Automated segmentation of retinal sublayers was performed with manual correction as needed, and thicknesses in various macular regions were compared using mixed effects models. Relative to controls (42 eyes, 40 patients), STGD1 patients (107 eyes, 63 patients) had slight thickening of the nerve fiber layer and retinal pigment epithelium-Bruch’s membrane, with thinning in other sublayers, especially the outer nuclear layer (ONL) (p < 0.0015). When comparing the rate of retinal sublayer thickness change over time (mean follow-up 3.9 years for STGD1, 2.5 years for controls), STGD1 retinas thinned faster than controls in the outer retina (ONL to photoreceptor outer segments). OCT-based retinal sublayer thickness measurements are feasible in STGD1 patients and may provide objective measures of disease progression or treatment response.

Thickness-Dependent NIR LSPR of Curved Ag/TiS2 Bilayer Film.

We demonstrated that the localized surface plasmon resonance (LSPR) features of Ag/TiS2 nanostructures were dependent on the sublayer thickness. The Ag/TiS2 bilayer film was obtained by the self-assembly method and magnetron sputtering. The thickness was controlled by changing the sputtering time when the sputtering powers were the same. When the Ag thickness decreased from 50 nm to 5 nm, the LSPR was tuned from the visible region to the Near Infrared (NIR) region. When the TiS2 thickness decreased from 60 nm to 2 nm, the LSPR shifted from the IR to NIR region. Analysis showed the thickness changes of Ag and TiS2 resulted in the changed carrier density, which led to the thickness-dependent shift of the LSPR.

Improved corrosion resistance of reactive gas pulse sputtered (TiTaNbZrNi)N high entropy alloy coatings with a hybrid architecture of multilayered and compositionally graded structures

In an attempt to introduce a new coating structure design strategy to strengthen the high temperature water corrosion resistance or high temperature oxidation of the coating in the normal operation condition or event of a loss-of-coolant accident. (TiTaNbZrNi)N hybrid structure coatings with ν = 0.25, 0.5, 1, 2 sccm/min were prepared by the reactive gas pulse (RGP) sputtering technique. This hybrid structure consisted of a FCC (TiTaNbZrNi)N sublayer and an amorphous (TiTaNbZrNi)Nx sublayer with both N element concentration gradient, and .an amorphous TiTaNbZrNi sublayer. After autoclave test at a temperature of 360°C and a pressure of 18.6 MPa for 3, 14 and 50 days, the results indicated that the weight gain of the hybrid structure coating is approximately an order of magnitude lower than that of the uncoated N36 substrate, and it still has a stable FCC structure. The coating with ν = 2 sccm/min has a lower oxygen diffusion depth than the coating ν = 0.25, 2 sccm/min, which is due to the lower thickness of the (TiTaNbZrNi)Nx sublayer and the multilayer interface suppressing the diffusion of oxygen. Moreover, Corrosion resistance of the (TiTaNbZrNi)N hybrid coating can be well tuned by changing the undulation period number of N2 gas flow rate. Detailed analysis indicates that the corrosion resistance of hybrid structure coatings may be related to the combined effect of multilayer structure and composition gradient structures.

Determination of thermal parameters of a shell and tube heat exchanger with increased turbulization of the working fluid

Shell and tube heat exchangers are still widely used. This equipment is widely used in heat supply systems, food, chemical and petroleum industries. Therefore, conducting research to improve their performance is an important area. By changing the geometry of the heat exchange surface, the flow of the working fluid is further turbulated and the heat exchange area increases. The heat exchanger with a developed heat exchange surface is proposed, which differs from the serial device (with smooth tubes). Thus, a plate equipped with a cylindrical edge is installed on the heat exchange tube. The working fluid in the inter-tube space, flowing around the edges, is turbulated. This reduces the thickness of the laminar sublayer on the plate and edge. Accordingly, the heat transfer from the heat exchange surface to the streamlined fluid increases. When new elements appear in the design of the heat exchange surface, it is necessary to develop the calculation of temperature parameters for these surfaces. Formulas for calculating the average surface temperature of the edge and plate under conditions of turbulent flow around these surfaces are obtained analytically. The temperatures of the plate and edge will determine the Prandtl criterion Pr. In the future, this is necessary to find the main parameter of the heat exchanger – the heat transfer coefficient.

Comprehensive study on the optical properties of graded Al component AlxGA1-xn nanostructures for UV photocathode

In this paper, we numerically studied the effect of gradient Al component distribution on the optical capture performance of AlxGa1-xN nanowires with various geometrical structure. Based on the finite element method COMSOL multiphysics commercial software, this paper systematically studied the influence of geometric parameters such as base radius (R), nanorod height (H), period (P) and the filling factor (FR). The simulation results show that compared with other nanostructures, the multiradius cylinder can effectively couple photons into the nanoarray to achieve a wide-band and effective light absorption of the AlxGa1-xN UV photocathode. We change the distribution range of Al components (0–0.35 and 0–0.75) and the thickness of different sub-layers in the nanostructures to study their effects on the optical properties of AlxGa1-xN nanostructures. Consequently, Cylinder nanoarray achieves enhanced optical absorption and quantum efficiency with gradient Al component range at 0–0.35 and graded thickness of the sublayer. In addition, we also flexible adjusted geometry of AlxGa1-xN nanoarrays to obtain the most effective optical absorption for the ultraviolet detector optical system. All these findings not only indicate that the gradient Al component AlxGa1-xN material has great potential advantages for UV photocathodes, but also provide a wide-band enhanced light absorption for UV photocathode.

Gravity currents over fixed beds of monodisperse spheres

Abstract

Conductive and viscous sub-layers on forced convection and mechanism of critical heat flux during flow boiling of subcooled water in a platinum circular tube with 3 mm inner diameter and 32.7 mm heated length at high liquid Reynolds number

The turbulent heat transfer, the subcooled boiling heat transfer and the steady state CHF for a Pt-circular test tube of a 3 mm inner diameter and a 32.7 mm heated length are measured with a wide range of inlet subcooling and flow velocity at high liquid Reynolds number, i.e. Red = 2.35 × 104 to 1.12 × 105. For flow velocities ranging from 4.103 to 21.446 m/s, the inner surface temperature of the Pt circular test tube calculated by the steady one-dimensional heat conduction equation is compared with the value obtained from our turbulent heat transfer correlation equation and the numerical solution of the RANS equation (Reynolds mean Navier–Stokes simulation) of the k-ε turbulence model. The conduction sub-layer thicknesses from the non-boiling region to CHF are measured in the conduction sub-layer itself in the forced convection region and the thinner sub-layer dissipated by boiling evaporation in the nucleate boiling region. The nondimensional thicknesses of local and average conductive sub-layers and, the thicknesses and nondimensional thicknesses of local and average viscous sub-layers on forced convection are estimated from the thicknesses of local and average conductive sub-layers and Prandtl numbers evaluated at the calculated temperature of the first control volume on the heated surface. In addition, the thickness of the conductive sublayer at the CHF point is estimated from measurements at various flow velocities. The experimental values of the CHF are also compared with authors’ widely and precisely predictable correlations of critical heat flux during flow boiling of subcooled water and the corresponding theoretical values of the liquid sub-layer dry-out models suggested by other researchers, respectively. The authors’ correlations and other researchers’ theoretical values can represent the subcooled boiling CHFs obtained in this study within the ranges of −22.74 to −6.21% difference and −22.17 to 6.16% one, respectively. Proposals for the main mechanism of critical heat flux during flow boiling of subcooled water on vertical tubes are confirmed again at high liquid Reynolds numbers based on experimental data. The boiling transitions to film boiling at the subcooled water flow boiling in the Pt test tube of d = 3 mm and L = 32.7 mm is not due to heterogeneous spontaneous nucleation or hydro-dynamic instability, but to liquid sub-layer dry-out model at the steady-state CHF. It is similar to those for the Pt test tubes with d = 3 mm and L = 66.5 mm, and d = 3 mm and L = 100 mm.

Nanoscale stress distributions and microstructural changes at scratch track cross-sections of a deformed brittle-ductile CrN-Cr bilayer

In order to interpret the mechanical response of thin films subjected to scratch tests, it is necessary to elucidate local stress distributions and microstructural changes accompanying deformation across the scratch track area. Here, 50 nm synchrotron cross-sectional X-ray nanodiffraction and electron microscopy are used to characterize nanoscale multiaxial residual stress gradients and irreversible microstructural-morphological changes across a brittle-ductile film consisting of 1.2 and 2 μm thick CrN and Cr sublayers. The experimental results reveal a complex alternation of the original columnar grain microstructure and a formation of pronounced lateral and depth stress gradients, which are complemented by a finite element model. After scratching, steep gradients of in-plane, out-of-plane and shear stress distributions were revealed, ranging from −6 to 1.5 and − 1.5 to 1.5 GPa in CrN and Cr, respectively, which are furthermore correlated with microstructural changes and residual curvatures. The scratch test results in intergranular grain sliding and the formation of nanoscopic intragranular defects within CrN, while Cr sublayer's thickness reduction and pile-up formation are accompanied by a bending of columnar crystallites and localized plastic deformation. In summary, the quantitative stress data elucidate the stabilizing role of the Cr sublayer, which suppresses the bilayer's catastrophic fracture during scratch tests.