Large Radius Of Curvature Research Articles

Fast measurement strategy for large radius of curvature

The method, based on searching the maximum or minimum of the metric function in the defined range that can be used to confirm the expected value, has been applied for measuring the large radius of curvature (ROC). The small step size is always needed in the searching range to ensure the measurement accuracy. But in the wide searching range, it will consume much time for finding the expected value. In order to improve the measurement efficiency, this paper proposes a fast measurement strategy for large ROC. This method uses a large step size to find a rough solution in a wide search range, and then constructs a shrunken range with a small step size based on the rough solution to quickly determine the high-precision measurement results. Simulation and experimental results show that the proposed method can be flexibly applied to different interference systems and greatly improve their measurement efficiency. For the tested spherical mirrors with ROC of 41400 mm and 1000 mm, high precision ROC can be obtained in just a few seconds.

Silicon Nitride Interferometers for Optical Sensing with Multi-micron Dimensions

Increasing the size of the smallest features of Photonic Integrated Circuits (PICs) to multi-micron dimensions can be advantageous to avoid expensive and complex lithographic steps in the fabrication process. In applications where extremely reduced chip size is not a requirement, the design of devices with multi-micron dimensions is potential interesting to avoid the need for e-beam lithography. Another benefit is that making the dimensions larger reduces the effect of lithographic imperfections such as waveguide surface roughness. However, the benefits do not come without limitations. Coupling the light in and out of the circuit is more challenging since diffraction gratings are not available when designing for such large dimensions. Circuit bends must have a larger radius of curvature and the existence of multimode propagation conditions can have detrimental impact in the performance of several devices, such as interferometers. In this study we perform simulations of the coupling between a lensed multimode optical fiber and a multi-micron a-SiN:H rib waveguide. Light coupling efficiency is analyzed as a function of distance variations using the FDTD method and compared with coupling to a strip waveguide. Moreover, we use numerical simulations to study the performance of a Mach-Zehnder interferometer sensitive to refractive index variations. Both the interferometer, splitters and combiners are designed with multi-micron dimensions.

A Silicon Migration Model Incorporating Anisotropic Surface Energy and Non-Uniform Diffusivity

Silicon migration is a process that can produce seamless, single-crystal silicon cavities in a single mask layer, greatly simplifying process flows for forming various cavity- and channel-based structures. However, controlling the dimensions of the final cavity and membrane thickness is complex and difficult to predict. To address this challenge, we present an efficient and accurate method of simulating silicon migration, which advances the state of art in three ways. First, it accounts for anisotropic surface energy. Second, it uniquely models selective migration. Third, the method is implemented in Python, an open source and highly pervasive programming language. We validate the model using experimental results from the literature, and we show that incorporating anisotropy is critical for simulating high aspect ratio, high density etch hole arrays. We also find indications in the simulations of selective migration that anisotropy may be less significant for very large curvature (radius less than 100 nm) features. Lastly, we use this new model to predict the relationship between layout and annealing time for a given set of final objective cavity and membrane dimensions. [2022-0128]

Factors affecting the radius of curvature of circular braids

Marudai is a tool for making traditional braids, Kumihimo. It can produce braids of various cross-sectional shapes. Most of the braids are straight braids, but in a previous study, a circular braid was manufactured for the first time using a traditional technique called Marugenji-gumi. In this study, the same manufacturing method was applied to other Marudai techniques and the effectiveness of this method was verified. In addition, the factors affecting the radius of curvature were elucidated by comparing the structure of the braids produced from each technique. As the results of examining the unit mass, flexural rigidity, cross-sectional shape, and crimp curvature, it was found that there are two forces that promote and interfere with curvature, thus affecting the radius of curvature. This insight makes it possible to predict and design the presence or absence of curving, or a large or small radius of curvature, depending on the characteristics of each technique.

Particle Dynamic Characteristics of the Vertical Tubes in a Horizontal-Vertical Pneumatic Conveying System with Different Curvature Radius Bends

To examine the flow characteristics of particles in the vertical tube corresponding to different curvature radius bends, the particle velocity is measured at the Minimum Pressure Drop (MPD) using a high-speed Particle Image Velocimeter (PIV). This experiment explores the effects of particle flow characteristics at different curvature radius bends and their corresponding vertical tubes with pressure drop, power consumption, the intensity of particle fluctuation velocity, power spectrum and time-frequency characteristics. It is observed that the pressure drop and power consumption can be reduced with the help of a large curvature radius bend. Besides, the reduction of particle velocity in the large curvature radius bend and its corresponding vertical tube is less, and the particle possesses a larger intensity of fluctuation velocity in its corresponding vertical tube. The particles in the vertical tube corresponding to the large curvature radius bend lead to large peaks of the power spectrum in the low-frequency region, which is closely linked to the pressure drop. Eventually, the dynamics of particles in a vertical tube are revealed from the perspective of time-frequency analysis by using a continuous wavelet transform.

The effect of low-viscosity sediments on the dynamics and accretionary style of subduction margins

Abstract. Observations of sediments at subduction margins appear to divide them into two classes: accretionary and erosive. Accretionary margins are dominated by accretion of thick piles of sediments (>1 km) from the subducting plate, while tectonic erosion is favored in regions with little or no sedimentary cover (<1 km). The consequences of the two styles of margins for subduction dynamics remain poorly resolved. In this study, we used 2-D numerical simulations of subduction to investigate how low-viscosity sediments influence subduction dynamics and margin type through plate coupling. We vary the thickness and viscosity of the sediment layer entering subduction, the thickness of the upper plate, and the driving velocity of the subducting plate (i.e., kinematic boundary conditions). Diagnostic parameters are extracted automatically from numerical simulations to analyze the dynamics and differentiate between modes of subduction margin. We identify three margin types based on the extent of viscous coupling in the sediment layer at the subduction interface: (a) tectonic coupling margin, (b) low-angle accretionary wedge margin, and (c) high-angle accretionary wedge margin. In the tectonic coupling case – analogous to an erosive margin – high-viscosity or thin-layer sediments increase coupling at the interface. On the other hand, when the viscous coupling is reduced, sediments are scrapped off the subducting slab to form an accretionary wedge. Models that develop tectonic coupling margins show small radii of curvature, slow convergence rates, and thin subduction interfaces, while models with accretionary margins show large radii of curvature, faster convergence rates, and dynamic accretionary wedges. These diagnostic parameters are then linked with observations of present-day subduction zones.

Analytic investigation on error of heat flux measurement and data processing for large curvature models in hypersonic shock tunnels

Due to short test time, heat conduction was considered as transient in hypersonic shock tunnels. The heat flux measurement and data processing were operated basing on one-dimensional semi-infinite heat conduction theory. However, for models with local large curvature or small radius, it resulted in significant compression or expansion of space for heat transfer, or lateral heat conduction, which made the hypothesis of one-dimensional unsatisfied and errors. In this paper, approximate solutions for the unsteady heat conduction in cylindrically convex and concave shells were established, and were used for further analysis of the errors, with forms of heating load, location and curvature radius of heated surface taken into consideration.

Numerical study on fire-induced smoke temperature characteristics in small curvature radius UTLT-like tunnels under emergency state

Extensive studies have usually focused on an ordinary single straight or large curvature radius tunnel fire. However, the curvature effect of small curvature radius curved tunnel on the fire-induced smoke temperature characteristics still needs to clarify. Therefore, a three-dimensional transient computational fluid dynamics (CFD) fire model for small curvature radius urban traffic link tunnel (UTLT)-like tunnel was established to understand the scope and extent of curvature effect on the fire-induced smoke under emergency state. The results show that, in the curved tunnel area, small curvature radius or large critical ventilation velocity results in stronger centrifugal force of the fire smoke, readily destabilizing the fire smoke downstream of the fire source. Compared with large radius of curvature and straight tunnels, due to the greater resistance of curved walls in small curvature radius tunnel, the length of smoke back-layering is longer. Simultaneously, the temperature of the high-temperature smoke on the outer wall of the ceiling cross section is higher than the inner wall. Prediction mathematical models for the maximum temperature and longitudinal temperature profiles were further developed by taking the curvature and ventilation velocity effect, which is basically consistent with experimental and simulated results.

Simulated Performance of Laser-Machined Metamaterial Anti-reflection Coatings

Lenslet-coupled antenna arrays have been used in CMB experiments and are the baseline technology for the next-generation satellite missions such as LiteBIRD and PICO. Lenslets are small hemispherical lenses mounted on the focal plane that couple light to the detectors and are typically made of silicon or alumina due to their high focusing power and low absorption loss. To minimize reflection at the vacuum-dielectric interface, lenslets require anti-reflection (AR) coatings. Metamaterials have been used in large microwave optical components because they avoid any mismatch on the thermal expansion between the lens and its coating, but so far they have only been machined on surfaces of comparatively large radius of curvature. As a first step to understand the feasibility of machining metamaterial AR layers in lenslets through laser-etching for the LiteBIRD mission, a model in ANSYS HFSS was developed. The goal of the simulation was to optimize transmission in three frequency bands while meeting assumed laser machinability constraints and optical requirements. Simulation results from flat silicon show that an AR metamaterial coating made under the assumed conditions is feasible, and the baseline parameters for further curved-surface studies are provided.

Influence of Adhesion on the Chemical Potential of Supported Nanoparticles as Modeled with Spherical Caps

The effect of adhesion on the chemical potential of supported nanoparticles is derived for the case of spherical caps. It is explicitly shown that for the minimum-energy particle shape (neglecting any anisotropy in surface energy), the chemical potential of a spherical cap attached to any flat support material reduces to μ = 2γVm/r, where r is the radius of curvature, γ is the surface energy, and Vm is the volume per mole of atoms. This is identical to the well-known Gibbs–Thomson relation derived instead for free-standing spherical particles. The chemical potential nevertheless depends on the adhesion energy Eadh because this radius r is a strong function of both adhesion (specifically, of Eadh/γ) and particle volume. The approximation of hemispherical particle shape, for which μ = (3γ – Eadh)Vm/r as proposed by Campbell and Hemmingson (ACS Nano 2017, 11, 1196) is exact for γ = Eadh, where it reduces to μ = 2γVm/r. Using hemispheres, or any fixed particle shape, is furthermore shown to be a linear approximation to the exact dependence of μ on Eadh for the minimum-energy particle shape, with error <10% for contact angles between 66 and 120° (i.e., for Eadh/γ = 0.5–1.4). Generally, these approaches only consider the limit of a large radius of curvature, where γ and Eadh are constant. It is known that both γ and Eadh increase with the decreasing r below 4 nm.

Evaluation of Blast Simulation Methods for Modeling Blast Wave Interaction With Human Head.

Blast-induced traumatic brain injury (bTBI) research is crucial in asymmetric warfare. The finite element analysis is an attractive option to simulate the blast wave interaction with the head. The popular blast simulation methods are ConWep-based pure Lagrangian, Arbitrary-Lagrangian-Eulerian, and coupling method. This study examines the accuracy and efficiency of ConWep and coupling methods in predicting the biomechanical response of the head. The simplified cylindrical, spherical surrogates and biofidelic human head models are subjected to field-relevant blast loads using these methods. The reflected overpressures at the surface and pressures inside the brain from the head models are qualitatively and quantitatively evaluated against the available experiments. Both methods capture the overall trends of experiments. Our results suggest that the accuracy of the ConWep method is mainly governed by the radius of curvature of the surrogate head. For the relatively smaller radius of curvature, such as cylindrical or spherical head surrogate, ConWep does not accurately capture decay of reflected blast overpressures and brain pressures. For the larger radius of curvature, such as the biofidelic human head, the predictions from ConWep match reasonably well with the experiment. For all the head surrogates considered, the reflected overpressure-time histories predicted by the coupling method match reasonably well with the experiment. Coupling method uniquely captures the shadowing and union of shock waves governed by the geometry-driven flow dynamics around the head. Overall, these findings will assist the bTBI modeling community to judiciously select an objective-driven modeling methodology.

Numerical study on the particle erosion of elbows mounted in series in the gas-solid flow

Solid particles in the fluid cause great damages to elbows. In particular, the erosion behavior of elbows mounted in series is more complicated than a single elbow. In the present study, the Eulerian-Lagrangian approach is applied to solve the gas-solid flow in the pipeline with four elbows mounted in series. Three erosion models are used for prediction and Zhang et al. model is finally selected for the development of the numerical model after comparison with the experimental data. Based on the numerical model, the effect of particle diameter, connection length between elbows, and curvature radius on the erosion behavior of four elbows are investigated through the particle trajectory analysis and particle impact characteristic at the elbows. Obtained results show that the erosion behavior of downstream elbows of the connecting pipe is considerably affected by the connection length. The sensitivity of four elbows to particle size is significantly different. Compared with small size particles, large size particles cause greater damage at the first elbow and less erosion at downstream elbows. Additionally, due to the secondary collision of particles, V-shaped erosion morphology appears at elbows and gradually evolves into the closed ring under a larger curvature radius.

Bright sources under the projection microscope: using an insulating crystal on a conductor as electron source

The development of bright sources is allowing technological breakthroughs, especially in the field of microscopy. This requires a very advanced control and understanding of the emission mechanisms. For bright electron sources, a projection microscope with a field emission tip provides an interference image that corresponds to a holographic recording. Image reconstruction can be performed digitally to form a “real” image of the object. However, interference images can only be obtained with a bright source that is small: often, an ultra-thin tip of tungsten whose radius of curvature is of the order of 10nm. The contrast and ultimate resolution of this image-projecting microscope depend only on the size of the apparent source. Thus, a projection microscope can be used to characterize source brightness: for example, analyzing the interference contrast enables the size of the source to be estimated. Ultra-thin W tips are not the only way to obtain bright sources: field emission can also be achieved by applying voltages leading to a weak macroscopic electric field (&lt; 1V∕μm) to insulating micron crystals deposited on conductors with a large radius of curvature (&gt; 10 μm). Moreover, analyzing the holograms reveals the source size, and the brightness of these new emitters equals that of traditional field emission sources.

Proximal femur anatomy-implant geometry discrepancies.

Objectives: Due to ongoing concern about femur anatomy-implant mismatches, this cross-sectional study aimed to create a geometric femur profile and used it to identify and quantify possible mismatches between femur anatomy and cephalomedullary nail dimensions. The work further aimed to assess whether patient demographics affect anatomy-implant coherence. Methods: One hundred skeletally mature complete femur computer tomography (CT) scans were collected and exported to software enabling landmark placement and measures with multiplanar reconstruction techniques. Results: Clinically relevant anatomy-implant discrepancies included the femur neck and shaft axis offset 6.1 ± 1.7 mm (95% CI [5.7–6.4]), femur radius of curvature 1.2 ± 0.3 m (95% CI [1.1–1.2]), femur anteversion 18.8 ± 9.2 (95% CI [16.9–20.6]). The implants reviewed in this study did not compensate for the femur neck and shaft axis offset and had a larger radius of curvature than the studied population. Clinically significant demographic geometry differences were not identified. Conclusion: There were discrepancies between femur anatomy and cephalomedullary nail implant design; however, no clinically significant femur feature inconsistency was identified among the demographic subgroups. Due to the identified anatomy-implant discrepancies, including the femur neck and shaft axis offset, we suggest that these measurements be considered for future implant design and surgical technique.

A three‐dimensional physical model for calculating the corona onset voltage of a large‐diameter alternating‐current shielding ball under different ambient conditions

For an alternating-current (AC) shielding ball with a large radius of curvature, a three-dimensional (3-d) physical model for the corona onset voltage (COV) of the large-diameter shielding ball under different ambient conditions was established according to numerical calculation in concert with the theory governing gas discharge. At first, distribution of the spatial 3-d electric field around the shielding ball was calculated by using the ring charge simulation method. Then, a calculation criterion suitable for the COV of the shielding ball was derived and the area factor of the geometric absorption function for photons applicable to such structures was proposed in detail based on the theory of secondary photoelectron emission. Moreover, tests on COVs of shielding balls with different diameters were conducted in an extra-high voltage (EHV) AC test-base. The test results show that the model was found to show a favourable effect in calculating the COV of a large-diameter shielding ball under different ambient conditions. Finally, in combination with the thickness of the ionosphere and effective ionization coefficient, the influence and mechanism of action of various parameters (such as atmospheric pressure, humidity, and temperature) on the COV of the shielding ball were investigated.

Narrow Divergence Emission from Blue GaN-based VCSELs with Curved Mirror

Recently, research to achieve narrow emission from GaN-based VCSELs has been of great interest. Sony's VCSELs with curved mirror has feature of strong lateral optical condiment, in which, causes wider emission angle. The authors obtained narrow emission angle of 3.9 degree by adopting concave mirror with large radius of curvature.

Multilayered recoverable sandwich composite structures with architected core

In this paper, we propose a novel design and fabrication strategy to produce architected structures for use as the core in composite sandwich structures. A traditional foam core or honeycomb structure is lightweight and stiff, but susceptible to permanent deformation when subjected to excessive loading. Here we propose the use of an architected structure composed of arrays of hollow truncated cone unit cells that dissipate energy and exhibit structural recovery. These structures, printed with a viscoelastic material, rely on buckling of their sidewalls to dissipate energy and snap-back to prevent permanent deformation. We explore the mechanical response of these conical unit cells in terms of their buckling strength and post-buckling stability condition and develop design maps for the same by relating them to non-dimensional geometric parameters α,β,γ where α represents the slenderness of the curved sidewalls, β is the angle of the sidewall to the base, and γ represents the curvature of the sidewall. A validated finite element model is developed and used to investigate the effect of these parameters. We show that the volume normalized peak buckling load is directly proportional to both α &β, but is independent of γ. The post-buckling stability is influenced by γ as a large radius of curvature makes the structure less likely to exhibit structural bistability. Due to viscoelastic dissipation, for certain geometric parameters, the structures exhibit pseudo-bistability which allows them to recover to their original configurations without the need for external stimuli or energy.

Lowering the reflection on curved flexible substrates over a broad wavelength range by the structure with Ag nanoparticles on SiO2 nanocolumns

A broadband antireflective structure with Ag nanoparticles on SiO2 nanocolumns for curved flexible substrates is presented. Experimental results show that the structure can lower effectively the light reflection on curved surfaces over a broad wavelength range. It is found that increasing incident angle leads to the blue-shift of position of the minimum light reflection due to the reduced travel distance of resonated electrons of Ag nanoparticles and the weakened mutual attraction between the resonated electrons in neighbouring Ag nanoparticles. The surfaces with smaller curvature radii have higher light reflection than those with larger curvature radii. The light reflection on a curved surface can be calculated through the weighted summation of the angle-dependent reflections on a flat surface, which agrees well with experimental results.

Numerical design studies of meander structures for self-expanding absorbable stents

Abstract Absorbable stents made of poly-L-lactic acid (PLLA) exhibit inferior mechanical properties compared with metal based devices. Therefore, design optimization by means of finite element analysis (FEA) plays an important role in development of high performance absorbable stents. In the present study, three different meander structures made of PLLA material were compared in terms of their radial resistive force (RRF) using FEA. Material tests were performed to obtain input parameters of PLLA for the simulation. FEA was carried out to simulate the RRF and the length change of the meander structures as a function of the diameter. In addition, the numerical results were compared to the experimental outcome using corresponding meander based stents performing radial testing with a segmented head mechanism. Comparable high stresses occurred in the Ubends of the examined stent designs. In designs with a large radius of curvature less stress was observed while crimping. One meander structure developed comparatively higher structural resistance against radially acting forces, due to its curved strut design. In general, FEA revealed consistent results compared to the experimental investigations.

Simulation and optimization of microlens hot-melting fabricating process based on finite element method

As an important optical element, the microlens array has received more and more attention. Due to the advantages of a short production cycle, low cost, high efficiency, and easy to transfer, the photoresist hot-melting method has been widely used to fabricate microlens. Fabricating microlenses with large aperture and curvature radius are the basic requirements to ensure image quality. However, due to the limitations of photoresist material properties and the hot-melting process, the shape of the microlens is not easy to control. In this paper, the finite element fluid simulation software Fluent was used to simulate the microlens hot-melting fabricating process. Through the simulation, we could understand the formation process of the microlens. By multiple groups of simulation comparison, the key parameter in the formation of microlens was discussed. Besides, the simulation result shows that when a layer of residual photoresist is left around the original photoresist cylinder, microlens with larger diameter can be easily obtained. The experimental results are in good agreement with the simulation results. The comparison imaging experiment also illustrates that the microlens fabricated by the improved process has better imaging ability. Through simulation, this paper not only explains the mechanism of the hot-melting method, but also optimizes its process. The related research could expand the application range of the hot-melting method in the fabrication of microlens.