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AbstractThe similarities between horizontal and vertical Optical Coherence Tomography (OCT) scans for the individual retinal layer thickness measurements in the macula was evaluated. Two volumetric scans (B-scans oriented horizontally and vertically) were performed in 64 multiple sclerosis subjects with history of unilateral optic neuritis and 64 healthy controls. The agreement between the thickness measurements with horizontal and vertical OCT scans was evaluated in 3 groups of eyes: healthy controls, eyes with history of optic neuritis and the fellow eyes. The mean difference in individual layer thickness between the scans was smaller than the instrument’s axial resolution in all 3 groups. The limit of agreement (LoA) varied among the different layers and sectors analyzed and this trend was similar in all the groups. For the inner retinal layers (retinal nerve fiber layer to inner nuclear layer), the inner macular sectors had a larger LoA compared to the corresponding outer sectors. In the outer plexiform and nuclear layers, the central and inner sectors (except inner temporal) had LoA larger than the other sectors and layers. The larger LoA seen for different layers and sectors suggests that the scan direction must be same for the follow-up OCT measurements and in clinical studies.

Abstract Understanding the relationship of interlayer interaction with mechanical properties and behaviors of two-dimensional layered materials (2DLMs) is critical in favoring the development of related nanodevices, nevertheless, still challenging due to the difficulties in experiments. In this work, nanoindentation simulations on few-layer WS2 were conducted by varying tip radius, suspended membrane radius and membrane size using molecular dynamics simulation. Consistent with our previous experimental results, few-layer WS2 exhibited layer-dependent reduction in fracture strength owing to the uneven stress distribution among individual layer induced by interlayer sliding under out-of-plane deformation. Besides, apparent curve hysteresis was observed due to interlayer sliding in the supported region when large tip radius and membrane radius were employed. However, instead of the supported part, the interlayer sliding within the suspended part resulted in the reduced fracture strength with the increase of layer number. These findings not only provide an in-depth comprehension on the influence of interlayer sliding on the fracture strength of few-layer WS2, but also suggest that the role of interlayer interaction should be seriously considered during nanodevice design.

Abstract Nitrides, carbides, and carbonitrides of transition metal elements like Zr, W, Ti, etc. are generally employed to produce hard coatings. Zirconium-based hard coatings have shown useful applications in the areas of tribology, biomedicine and electrical due to their high thermal stability, hardness, biocompatibility, good erosion, wear, and corrosion resistance. In this study, we created homogeneous and tenacious nanostructured hard coatings based on Zr with good mechanical properties. The magnetron sputter deposition technique was utilized to coat stainless steel 316L substrates with multilayers of Zr/ZrN and ZrN/ZrCN with individual layer thicknesses of 250 and 500 nm for each coating composition. The deposition conditions were adjusted to create two different coating thicknesses of 2 and 3 µm. The thickness of the coating was confirmed using Calotest and the coatings’ morphology and elemental composition were determined utilizing the atomic force microscope and scanning electron microscope equipped with energy dispersive x-ray spectrometer. Coating thickness and adhesion were measured using cross-sectional samples and XRD was utilized to analyze the coatings structure. Nanoindenter was employed to determine the instrumental nanoindentation hardness and elastic modulus. The influence of coating thickness on tribological behavior was further investigated using the ratio of nanohardness-to-elastic modulus (H/E). No evidence of decohesion was observed at the substrate/coatings interface, and the grains of all the coatings were observed to show columnar growth which were homogeneous, compact and dense. The grains of the ZrN/ZrCN coatings were observed to be denser, finer and more compact compared to those of the Zr/ZrN coatings. Correspondingly, higher hardness, modulus and H/E values were exhibited by ZrN/ZrCN than Zr/ZrN coatings. This suggests that the ZrN/ZrCN coatings are capable of exhibiting better wear resistance and fracture toughness. The coatings developed in this investigation are anticipated to be suitable for applications in tribology due to their excellent hardness and H/E properties.

Multilayer films with high-density layer interfaces have been studied widely because of the unique mechanical and functional properties. Magnetron sputtering is widely chosen to fabricate multilayer films because of the convenience in controlling the microstructure. Essentially, the properties of multilayer films are decided by the microstructure, which could be adjusted by manipulating the deposition parameters, such as deposition temperature, rate, bias, and target–substrate distance, during the sputter process. In this review, the influences of the deposition parameters on the microstructure evolution of the multilayer films have been summarized. Additionally, the impacts of individual layer thickness on the microstructure evolution as well as the irradiation behavior of various multilayer films have been discussed.

<p>In this thesis the magnetic response of a layered type-II superconducting system is explored across the entire range of fields, temperatures and currents where superconductivity exists, with the results providing valuable insight into the role of reduced dimensionality in determining the behaviour of type-II materials such as the new high temperature superconductors. The system in question consists of alternating layers of amorphous Ta or TaxGe1-x (x approximation 0.3) with amorphous Ge where the individual layer thicknesses vary between 17A [angstrom] and 210A [angstrom]. These multilayers were fabricated by vapour deposition in a high vacuum chamber which allowed the creation of samples with uniform layers of high purity. The resistive transport properties have been measured from Tc (approximation 1-3K) to temperatures as low as 50mK in some cases, and in fields of up to 15T. The upper critical fields have been determined from the fluctuation conductivity both with the field parallel and perpendicular to the layer plane of the samples. The results show clearly the dependence of the dimensionality on the superconducting layer thickness and the degree of coupling across the Ge layers. For the samples with the most two-dimensional properties the zero field resistive transition is governed by the unbinding of thermally created vortex-antivortex pairs as described by the Berezinskii-Kosterlitz-Thouless theory. A detailed investigation of the perpendicular field vortex states and dynamics has been performed, including measurement of the activation energies needed for thermally activated vortex motion. Qualitative difference are observed between the activation energies in two- and three-dimensional samples, with the barriers being generally higher in 3D. The non-linear current-voltage characteristics of the samples provide evidence for the existence of a vortex glass state which melts into a liquid below Hc2, although the divergence of the activation barriers in the glass can be restricted by the finite sample thickness. A brief investigation of the corresponding parallel field regime showed considerably less dissipation, due largely to the transparent nature of the Ge layers to the magnetic field. At the highest currents an instability is observed in the vortices which can drive the samples discontinuously back into the normal state. This instability is shown to be of the type predicted by Larkin and Ovchinnikov (LO), including quantitative agreement between the measured and predicted values of the critical vortex velocity. Several features of the instability are noted which are not specifically predicted by the LO theory, and comparisons are drawn between these and the prevailing vortex state at lower currents.</p>

<p>In this thesis the magnetic response of a layered type-II superconducting system is explored across the entire range of fields, temperatures and currents where superconductivity exists, with the results providing valuable insight into the role of reduced dimensionality in determining the behaviour of type-II materials such as the new high temperature superconductors. The system in question consists of alternating layers of amorphous Ta or TaxGe1-x (x approximation 0.3) with amorphous Ge where the individual layer thicknesses vary between 17A [angstrom] and 210A [angstrom]. These multilayers were fabricated by vapour deposition in a high vacuum chamber which allowed the creation of samples with uniform layers of high purity. The resistive transport properties have been measured from Tc (approximation 1-3K) to temperatures as low as 50mK in some cases, and in fields of up to 15T. The upper critical fields have been determined from the fluctuation conductivity both with the field parallel and perpendicular to the layer plane of the samples. The results show clearly the dependence of the dimensionality on the superconducting layer thickness and the degree of coupling across the Ge layers. For the samples with the most two-dimensional properties the zero field resistive transition is governed by the unbinding of thermally created vortex-antivortex pairs as described by the Berezinskii-Kosterlitz-Thouless theory. A detailed investigation of the perpendicular field vortex states and dynamics has been performed, including measurement of the activation energies needed for thermally activated vortex motion. Qualitative difference are observed between the activation energies in two- and three-dimensional samples, with the barriers being generally higher in 3D. The non-linear current-voltage characteristics of the samples provide evidence for the existence of a vortex glass state which melts into a liquid below Hc2, although the divergence of the activation barriers in the glass can be restricted by the finite sample thickness. A brief investigation of the corresponding parallel field regime showed considerably less dissipation, due largely to the transparent nature of the Ge layers to the magnetic field. At the highest currents an instability is observed in the vortices which can drive the samples discontinuously back into the normal state. This instability is shown to be of the type predicted by Larkin and Ovchinnikov (LO), including quantitative agreement between the measured and predicted values of the critical vortex velocity. Several features of the instability are noted which are not specifically predicted by the LO theory, and comparisons are drawn between these and the prevailing vortex state at lower currents.</p>

The renewable resource, wood, is becoming increasingly popular as a feedstock material for additive manufacturing (AM). It can help make those processes more affordable and reduce their environmental impact. Individual layer fabrication (ILF) is a novel AM process conceived for structural applications. In ILF, parts are formed by laminating thin, individually contoured panels of wood composites which are fabricated additively by binder jetting. The individual fabrication of single panels allows the application of mechanical pressure in manufacturing those board-like elements, leading to a reduction of binder contend and an increase of mechanical strength. In this paper, the ILF process is described in detail, geometric and processing limitations are identified, and the mechanical properties of the intermediate product (panels) are presented. It is shown that the thickness of panels significantly influences the geometric accuracy. Wood composite panels from spruce chips and pMDI adhesive showed flexural strengths between 24.00 and 52.45 MPa with adhesive contents between 6.98 and 17.00 wt %. Thus, the panels meet the mechanical requirements for usage in the European construction industry. Additionally, they have significantly lower binder contents than previously investigated additively manufactured wood composites.

Abstract This paper reports, the application of Taguchi Design of Experiments (DoE) and ANOVA (Analysis of Variance) for finding the optimal combinations and analysis of the effect of individual layer thickness on the performance of SMR sensor. The optimum combination of design parameters and its performance as a sensor have been predicted with DoE and validated through the finite element modeling (FEM) simulation. The optimization has been done to achieve enhancement in coupling coefficient of SMR sensor. The best optimized thickness of metal electrodes, piezoelectric, sensing, insulation low and high acoustic impedance layers have been found to be 0.2µm, 2µm, 0.68µm, 0.3µm, 1.028µm and 1.008µm, respectively. The results of the present study show that for the optimized dimension of SMR structure, simulated values of coupling coefficient (K2eff), Quality factor (Q) and figure of merit (FoM) are 0.075596 (or 7.5596%), 1171.6 and ≈ 88, respectively. Optimized structure performance has been compared with the existing SMR sensors and it is observed that proposed SMR exhibits performance enhancement in terms of FoM by ≈ 37 %.

Micro-perforated panel absorbers can typically achieve either visual transparency or broadband absorption, but not both. This paper assesses the potential of Multilayer Micro-Slit panels to maintain both of these characteristics simultaneously. Micro-slit panels are similar to micro-perforated panels, and can similarly achieve high absorption coefficients without fibrous backing materials. The arrangement of slits are better suited to visual transparency than perforated holes because it provides more unobstructed panel per perforated area. However, these types of absorbers are limited to a narrow frequency bandwidth of effective absorption. By combining several panels into a multilayer assembly, broadband absorption becomes possible. The inherent complexity stemming from optimizing the parameters for multiple layers to meet a given design criteria necessitates the use of the Bayesian framework. This probabilistic method rapidly hones in on the best parameters of each individual layer so that the overall composite meets the design goal. Furthermore, Bayesian inference implemented cyclically alongside panel fabrication and testing allows for corrections of fabrication tolerances while assessing visual transparency.