Step Height Research Articles

Numerical simulation of the effect of inclination angle and height of step in a backward facing step filled with nanofluid

Numerical simulation of the effect of inclination angle and height of step in a backward facing step filled with nanofluid

Performance of YBCO Step Edge Josephson Junctions for Different Film Thickness to Step Height Ratio

Step edge Josephson junction devices of YBa2Cu3O7‐x films on SrTiO3 substrates are fabricated, and the device performance is studied for different t/h (t: the thickness of the film, h: step height) ratios. After depositing YBCO films on the step etched substrates, photolithography, and ion beam etching techniques are used to fabricate three devices with t/h ratios of ≈0.4, 0.7, and 1.2. The critical temperatures (Tc) of the devices are ≈82, 85, and 88 K, respectively. The critical current (Ic) and normal state resistance (Rn) are observed to be t/h ratio dependent. The critical current values at 70 K for the devices with t/h ratios of 0.4, 0.7, and 1.2 are ≈425, 550, and 820 μA, respectively. The IcRn product at 70 K is ≈2.06, 2.76, and 0.43 mV for t/h ratios 0.4, 0.7, and 1.2, respectively, which indicates that the t/h ratio of 0.7 is optimum for the device performance. The current versus voltage curves at 68 K are fitted using the resistively shunted junction model using the Portable Superconducting Circuit Analyzer (PSCAN2) simulator, which suggests that there can be normal conducting links present across the microbridge, and it becomes effective for I > Ic, contributing to excess current.

Experimental study of hydrodynamic effect of loading and longitudinal variations of the center of gravity on the performance of a single-step craft in calm water

Performance of stepped planing vessels is notably influenced by loading and longitudinal position of the center of gravity. These factors directly affect trim angle, rise, total resistance due to motion, and overall hydrodynamic efficiency. This study experimentally investigates a 2.5 m Fridsma series model with 20° deadrise angle, length-to-width ratio of 5, step distance of 28% of the overall length from the transom, and step height of 4% of the model's width. It involves testing the model with two different weights: 63 and 76.6 kg, corresponding to load coefficients of CΔ=0.5 and CΔ=0.61. Center of gravity is placed at 0.8 m (32%), 0.85 m (34%), and 0.9 m (36%) from the transom. Experiments are conducted at speeds of 1, 2, 3, 4, 5, 6.5, and 8 m/s, which correspond to beam Froude numbers of 0.45, 0.9, 1.35, 1.8, 2.26, 2.9, and 3.6, respectively. The results indicate that increasing the load from 63 to 76.6 kg leads to approximately 12% increase in static trim across all center of gravity positions. The final trim is shown to increase by around 15% at all tested speeds. Additionally, load variations result in 20% rise in the rise up and total resistance. The model achieves optimal performance with load coefficient CΔ=0.61 and center of gravity at 36% of the overall length from the transom, showing the lowest resistance to weight ratio. Overall, the findings reveal that optimizing internal load distribution and LCG placement can enhance the boat's hydrodynamic efficiency, resulting in improved speed, stability, and fuel economy under different operational conditions.

Effect of backward-facing step heights in vegetation-step model on reducing the velocity of a tsunami inundation and increasing the energy dissipation efficiency

Effect of backward-facing step heights in vegetation-step model on reducing the velocity of a tsunami inundation and increasing the energy dissipation efficiency

Airflow characteristics of the stepped dropshaft in the deep tunnel storage system

ABSTRACT The deep tunnel storage system, mainly consisting of underground tunnels and dropshafts, is effective for dealing with urban waterlogging. A stepped dropshaft is suitable for the system to safely transport water to underground tunnels and efficiently release air carried by water. In this study, the air inflow discharge, air vent discharge, and air discharge into the underground tunnel are investigated experimentally. As the dimensionless water flow discharge increases to 0.56, the water flow successively forms the nappe flow, transition flow, and skimming flow regimes, the relative air inflow discharge decreases from 0.97 to 0.32, the relative air vent discharge decreases from 0.85 to 0.22, and the relative air discharge into the underground tunnel fluctuates below 0.20. The exhaust capacity (the ratio of the air vent discharge to the air inflow discharge) reaches a maximum of 0.87 at the threshold between the nappe flow and the transition flow. Influences of flow discharge, step height, step rotation angle, outlet diameter of the central exhaust pipe, and underground tunnel blockage on airflow characteristics are revealed. The prediction formulas for air inflow discharge, air vent discharge, and exhaust capacity are obtained with accuracies over 80%, providing a guide to the practical design and operation of stepped dropshafts.

Step recognition using LiDAR and navigation considering step entry direction for skid-steer robots

In recent years, studies on autonomous mobile robots for outdoor use have been actively conducted. In these studies, skid-steer robots such as crawler robots are often used. These mechanisms are not good at diagonally entering steps such as curbs, so it is necessary to consider the step entry direction for navigation of these robots. However, there are few previous studies that deal with detection of low height steps on the ground, path planning that considers the step entry direction, and tracking control, in a unified manner. In this study, we present a ground surface classification using LiDAR scan characteristics, a path optimization using quadratic programming with the step entry direction constraint, and a tracking control using TOPP to accurately follow the path. As a result of the experiment, we confirmed that it was able to detect 0.1 m height steps and climb over them by entering perpendicularly to the steps.

Flapping dynamics of a flexible membrane attached to the leading edge of a forward-facing step

An experimental investigation of velocity fields over and wall pressure fluctuations on a forward-facing step (FFS) disturbed by a flexible membrane has been conducted. A two-dimensional flexible membrane of 40mm length and 0.15mm thickness attached to a FFS of 40mm height was tested with oncoming velocity in the range of 7.3 < U < 12.9 m/s, corresponding to Reynolds numbers of 20391 < ReH < 35312 based on the step height. A high-speed camera was used to reconstruct the configuration of the flapping membrane. The flow field velocity dataset in the horizontal-vertical plane and the pressure fluctuation on the step surface were measured by planar particle image velocimetry and pressure sensors, respectively. The flexible membrane displayed two distinct modes, viz. a bending mode or flapping mode. In the bending mode, the membrane elevates the shear layer, thereby delaying the reattachment of separation flow generated by a FFS. In the flapping mode, the membrane periodically generates flapping-induced vortices (FIVs) of different scales with varying Reynolds numbers. The pressure on the FFS also undergoes periodic fluctuations corresponding to these FIVs.

Constructing a Semantic System of Facade Elements for Religious Architecture from a Regional Perspective: A Case Study of Jingzhou

The application of semantics in facade elements mainly involves the association between architectural elements and their cultural, historical, or functional significance. By analyzing the shape, layout, and decoration of various elements (such as windows, doors, decorative patterns) in facades, semantics helps us understand the symbolic meanings and cultural implications behind these design choices. This study selects twenty-eight pavilions and buildings from five temples and Taoist sites in Jingzhou City as the research objects, exploring the composition and patterns of religious architectural facades in Jingzhou through the extraction of structural and decorative elements. The study establishes the “Semantic System of Façade Elements in Jingzhou Religious Architecture”, from which the distinctive characteristics of Jingzhou religious building façades are identified. The study finds that side halls predominantly feature hard gable roofs, while the main halls use double-eave hip-and-gable roofs, reflecting differences in architectural hierarchy. The sack with three arrows pattern is the most widely used in door and window decorations, demonstrating the aesthetic preferences of the Jingchu region. Both side halls and main halls commonly adopt high podiums, with the main hall podiums typically exceeding twenty steps in height, which is closely related to Jingzhou’s climatic conditions and architectural hierarchy. This study provides scientific evidence for the preservation, new design, and harmonious integration of traditional culture and architectural features in regional religious architecture.

Perspective: imaging atomic step geometry to determine surface terminations of kagome materials and beyond

Here we review scanning tunneling microscopy research on the surface determination for various types of kagome materials, including 11-type (CoSn, FeSn, FeGe), 32-type (Fe3Sn2), 13-type (Mn3Sn), 135-type (AV3Sb5, A = K, Rb, Cs), 166-type (TbMn6Sn6, YMn6Sn6 and ScV6Sn6), and 322-type (Co3Sn2S2 and Ni3In2Se2). We first demonstrate that the measured step height between different surfaces typically deviates from the expected value of ±0.4 ∼0.8Å, which is owing to the tunneling convolution effect with electronic states and becomes a serious issue for Co3Sn2S2 where the expected Sn-S interlayer distance is 0.6Å. Hence, we put forward a general methodology for surface determination as atomic step geometry imaging, which is fundamental but also experimentally challenging to locate the step and to image with atomic precision. We discuss how this method can be used to resolve the surface termination puzzle in Co3Sn2S2. This method provides a natural explanation for the existence of adatoms and vacancies, and beyond using unknown impurity states, we propose and use designer layer-selective substitutional chemical markers to confirm the validity of this method. Finally, we apply this method to determine the surface of a new kagome material Ni3In2Se2, as a cousin of Co3Sn2S2, and we image the underlying kagome geometry on the determined Se surface above the kagome layer, which directly visualizes the p-d hybridization physics. We emphasize that this general method does not rely on theory, but the determined surface identity can provide guidelines for first-principles calculations with adjustable parameters on the surface-dependent local density of states and quasi-particle interference patterns.

Vibration disturbance compensation in in situ confocal microscopy.

In situ microscopic measurement, conducted within the natural environment of a material or device, offers precise observations directly at the sample location, mitigating potential damage or deformation during transport. However, the inherent vibration of microscopic measurement equipment can introduce blurring and distortion to images, compromising measurement accuracy. This study proposes employing an acceleration sensor to detect microprobe vibrations and subsequently calculates three-dimensional coordinate displacements to compensate for measurement discrepancies. This approach can diminish the adverse effects of vibration on measurement outcomes within the order of hundreds of nanometers. Experimental results demonstrated the efficacy of this method in mitigating vibration artifact stripes or irregularities with a displacement amplitude I = sinc2[a(z - b)] ranging from ∼0.2 to 5.2 μm and a frequency spanning ∼7.9-18.8 Hz. Moreover, the lateral resolution of the probe attained 212 nm. Notably, the measurement error associated with the standard step height was decreased from 2.32 to 0.03 μm.

Chromatic focus variation microscopy for surface metrology

Optical metrology plays a vital role in a wide range of research and inspection areas in the industry. At present, the market offers a variety of optical metrology instruments, among which the focus variation microscope stands out for its capability of measuring steep surfaces with high slopes. The traditional focus variation (FV) instrument mechanically scans the surface by sweeping the focal plane of the objective lens using linear motion stages and simultaneously capturing images at different scanning positions, forming a stack of images. The mechanical motion stages require regular maintenance and calibration to ensure accuracy over time. Another issue associated with the mechanical scanning methods is their physical size, which creates a limiting factor to compactness for in-situ measurement applications. This work proposes a chromatic focus variation (CFV) method that replaces mechanical scanning with a wavelength scanning mechanism to overcome the above limitations. Unlike traditional focus variation, the CFV system employs a dispersive objective lens (i.e. chromatically aberrated objective lens) to axially shift the focus along the optical axis to provide vertical/depth scanning. This approach brings significant enhancements in measurement speed and reduces the instrument size for on-machine metrology tasks. In this paper, a detailed analysis of the optical performance of the dispersive objective lens is conducted, and then the measurement performance of the proposed CFV system is validated using samples including a step height of 30 µm and a sine wave shape with a peak-to-valley amplitude of 19 µm. The experiment results were compared to those from the state-of-the-art commercial instrument (Alicona G5), which showed a good agreement between the two. Furthermore, a detailed analysis and discussions are provided to investigate the measurement’s accuracy.

Imaging of micro-steps on as-grown surface of sapphire with X-ray phase contrast technique

Basal-faceted sapphire ribbons grown using the Stepanov–LaBelle technology have a low density of surface steps. We present our results on a study of steps on the surface of a ribbon, misoriented relative to the singular face (0001) by several arc minutes. The ribbon has been characterized by means of in-line phase contrast imaging technique at Pohang Light Source, South Korea. It was shown for the first time that a step height of about 1 μm can be determined directly from an image. The step height obtained using the phase contrast method was confirmed by atomic force microscopy measurements. We have found that the experimental contrast matches the theoretical simulations only if the calculated intensity profile has been convolved with a Gaussian function. The full width at half maximum of the Gaussian was independently got from previous measurements. We have obtained an analytical solution in the case of theoretical fully coherent phase contrast image. The inverse problem is easy to solve, since there is a direct proportionality between the contrast and the step height.

Characteristic analysis of tunnel collapse arch in weak rock mass

The stress of surrounding rock and supporting structure is very complicated during the construction of a loose rock tunnel. The characteristics analysis of collapse arch is very important for the construction safety. This paper compares and analyzes the applicability of the full section method and the three-step method under shallow buried loose surrounding rock, reveals the influence law of tunnel excavation height span ratio on the stability of a pseudo-collapse arch of surrounding rock under shallow buried loose surrounding rock, and rationally chooses the three-step method as the dominant construction method of tunnel construction under this geological condition. For the three-step construction method, the optimization study of the excavation height of the upper step is carried out, the relationship between the excavation height of the tunnel and the stress concentration area under the condition of shallow buried loose surrounding rock is revealed, the influence of surrounding rock stress release on the stability of the tunnel surrounding rock is explored, and the damage of tunnel rock mass caused by the stress concentration phenomenon is analyzed. It is determined that the optimal excavation height of the upper step is 0.4H under the geological conditions of the DS project in Sichuan province, China, under construction. This paper analyzes the influence of structural plane spacing on the stability of a tunnel collapse arch under shallow buried loose conditions and reveals the law that the smaller the structural plane spacing, the worse the self-bearing capacity of the collapse arch, and the higher the risk of engineering accidents such as rock collapse or even collapse in the tunnel, which effectively guides the safe construction of the tunnel under shallow buried loose geological conditions.

In-situ momentum dispersion in a single crystal of MoS2

In this letter, we investigate the momentum dispersion in a MoS2 flake as a function of the thickness in a single crystal with several height steps. The outcomes of our study rely on the utilization of near-field microscopy and an excitation field in the strong-coupling regime. The observed propagating modes have characteristics that are consistent with transverse magnetic (TM) modes, which can be attributed to the investigated thicknesses. Numerical simulations support our experimental findings and correspond with previously reported studies.

Evaluation of hair surface structure and morphology of patients with lichen planopilaris (LPP) by atomic force microscopy (AFM).

Lichen planopilaris (LPP) is a chronic lymphocytic skin disease manifested by progressive scarring alopecia. The diagnosis of LPP is made based on histopathological examination, although it is not always definite. The current study evaluates the effectiveness of non-invasive atomic force microscopy (AFM) hair examination in detecting morphological differences between healthy and diseased hair. Here, three to five hairs from lesional skin of 10 LPP patients were collected and examined at nine locations using AFM. At least four images were taken at each of the nine sites. Metric measurements were taken and metric (length, width, and scale step height) and morphological features (striated and smooth surface of scales, the presence of endocuticle and cortex, shape of scales edges, scratches, pitting, cracks, globules, and wavy edge) were compared with hair from healthy controls. In addition, areas on diseased hair where the process of pathological, unnatural delamination of the hair fiber occurs are described. There was a statistically significant difference in the number of scratches in the initial sections of the LPP hair, in the intensity of wavy edges along the entire length of the tested hair, and in the number of scales with pitting in the middle section of the hair. In addition, a statistically significant higher number of scales with striated surface was found in LPP group starting at 3.5cm from the root continuing towards the free end of the hair. Other morphological changes such as presence of cortex, globules, oval indentations, and rod-like macrofibrillar elements were also assessed, however, detailed results are not presented, as the differences shown in the number of these morphological changes were not significantly different. This publication outlines the differences between virgin, healthy Caucasian hair, and the hair of LPP patients. The results of this study can be used for further research and work related to LPP. This is the first attempt to characterize the hair of LPP patients using AFM.

New insights on cavitating flows over a microscale backward-facing step

This study introduces the first experimental analysis of shear cavitation in a microscale backward-facing step (BFS) configuration. It explores shear layer cavitation under various flow conditions in a microfluidic device with a depth of 60 μm and a step height of 400 μm. The BFS configuration, with its unique characteristics of upstream turbulence and post-reattachment pressure recovery, provides a controlled environment for studying shear-induced cavitation without the complexities of other microfluidic geometries. Experiments were conducted across four flow patterns: inception, developing, shedding, and intense shedding, by varying upstream pressure and the Reynolds number. The study highlights key differences between microscale and macroscale shear cavitation, such as the dominant role of surface forces on nuclei distribution, vapor formation, and distinct timescales for phenomena like shedding and shockwave propagation. It is hypothesized that vortex strength in the shear layer plays a significant role in cavity shedding during upstream shockwave propagation. Results indicate that increased pressure notably elevates the mean thickness, length, and intensity within the shear layer. Instantaneous data analysis identified two vortex modes (shedding and wake modes) at the reattachment zone, which significantly affect cavitation shedding frequency and downstream penetration. The wake mode, characterized by stronger and lower-frequency vortices, transports cavities deeper into the channel compared to the shedding mode. Additionally, vortex strength, proportional to the Reynolds number, affects condensation caused by shockwaves. The study confirms that nuclei concentration peaks in the latter half of the shear layer during cavitation inception, aligning with the peak void fraction region.

Gait planning based on bionic quadruped robot

Based on the ankylosaurus, a four-legged robot structure with 14 degrees of freedom was designed in this study. The kinematic model was established using the Denavit-Hartenberg (D-H) method. The inverse kinematics of the robot was analyzed, and the angle equations of each leg joint were obtained. In order to reduce the kinetic energy generated when leaving the ground and landing, the compound cycloid was modified. The modified foot curve effectively reduces energy and meets the kinematic requirements. On the basis of the foot trajectory, the diagonal leg phase difference was set to 0.5, and the diagonal gait was adopted as the gait of the bionic quadrupled robot. Simulink software was used to construct the simulation environment, and the maximum error of the simulation results and the theoretical step height was 2.05%, and the step length maximum error was 2.39%. During walking, the thigh joint angle was −92.82° to −80.21°, and the hip joint angle was 22.23° to 43.83°. Compared with the simulation trajectory and the theoretical curve, because the experiment did not consider the balance of the fuselage, there was a certain error when the leg was raised to the highest point. Overall, the gait planning strategy designed in this study basically achieves the expected effect, lays a certain foundation for the practical application of the bionic quadruped dinosaur robot, and also provides a reference for the subsequent research.

Noise and flow characteristics of variable backwards- and forward-facing steps and gaps in laminar boundary layer

The noise and flow characteristics of combined backwards-facing and forward-facing steps (BFS and FFS) are experimentally investigated in an acoustic wind tunnel using a far-field microphone array and Particle Image Velocimetry (PIV), respectively. The step models considered have a step height H of 10∼40 mm and a step gap L of 10∼100 mm, and the Reynolds number is ( Re H=) 2.1 × 105∼1.1 × 106. The incoming flow boundary layer is laminar, and the step height is approximately 3∼28 of the boundary layer thickness. The results show that the noise is closely related to the step type, step height H and the gap L. In the step-only configuration, the BFS noise does not vary with the step height H 1 and is much lower than the FFS noise, of which the sound pressure level depends on U 0 5.8∼ U 0 6.2 within the height range H 2. As for the combined step model (BFS&FFS), the noise spectrum changes significantly with the step heights and gaps. When H 1> H 2, the noise spectrum resembles the BFS-only due to the flow shield of the FFS from the upstream BFS. When H 1< H 2, the noise spectrum is dominated by the FFS, especially at higher H 2 or longer gap L due to more face area of the FFS exposed to the incoming flow. As H 1= H 2, the noise resembles the BFS in the low-frequency range and the FFS at high frequencies, respectively. Generally, the step-only and BFS&FFS have broadband noise characteristics, except when the ratio L/H is small, the noise spectrum has the characteristics of a typical cavity dominated by tonal peaks.

Computerized simulation of 2-dimensional phase contrast images using spiral phase plates in neutron interferometry

Abstract We present calculations of interferograms (interference patterns) of one or multiple spiral phase plates that would be observed with a perfect crystal neutron interferometer of Mach–Zehnder type. A spiral phase plate (SPP) in one of the two coherent beam paths produces a twist in the phase front and thus a vortex beam with intrinsic angular momentum, which in the case of neutrons should be observed as a characteristic interference pattern that appears complementary to each other in both detectors behind the interferometer. Adding additional SPPs in one beam path of the interferometer yield interference patterns similar to that of a single SPP but only due to the cumulative step height. All simulated interferograms have been calculated on the basis of dynamical neutron diffraction without any assumption of a neutron orbital angular momentum and show very convincing agreement with experimental results from the literature, see e.g. (C. W. Clark, R. Barankov, M. G. Huber, M. Arif, D. G. Cory, and D. A. Pushin, “Controlling neutron orbital angular momentum,” Nature, vol. 525, pp. 504–506, 2015). In particular, this clarifies, that the cited experiments do not give evidence of the quantization of interactions caused by a twist of the phase front of a neutron wave in the interferometer and thus no evidence for the effect of a neutron orbital angular momentum.

Evaluating plantar biomechanics while descending a single step with different heights.

This study aims to investigate the plantar biomechanics of healthy young males as they descend a single transition step from varying heights. Thirty healthy young males participated the experiment using the F-scan insole plantar pressure system in which participants made single transition steps descent from four step heights (5, 15, 25, and 35cm), leading with their dominant or non-dominant foot. Plantar pressure data were collected for 5s during the period between landing touchdown and standing on the ground. Landing at each step height was repeated three times, with a five-minute rest between different height trials. At 5cm and 15cm steps, participants demonstrated a rearfoot landing strategy on both sides. However, forefoot contact was observed at heights of 25cm and 35cm. Parameters related to center of plantar pressure (COP) of the leading foot were significantly larger compared to the trailing foot (P < 0.001), increased with higher step heights. Vertical ground reaction forces for the biped, leading and trailing feet decreased with increasing step height (all P < 0.05). The leading foot had a higher proportion of overall and forefoot loads, and a lower proportion of rearfoot load compared to the trailing foot (P < 0.001). The overall load on the dominant side was lower than that on the non-dominant side for both the leading and trailing feet (P < 0.001). For the trailing foot, forefoot load on the dominant side was lower than that on the non-dominant side, however, the opposite result appeared in rearfoot load (P < 0.001). Upon the leading foot landing, forefoot load exceeded the rearfoot load for the dominant (P < 0.001) and non-dominant sides (P < 0.001). Upon the trailing foot landing, forefoot load was lower than the rearfoot load for the dominant (P < 0.001) and non-dominant sides (P = 0.019). When the characteristics of biomechanical stability are compromised by step height, landing foot, and footedness factors - due to altered foot landing strategies, changing COP, or uneven force distribution - ability to control motion efficiently and respond adaptively to the forces experienced during movement is challenged, increasing the likelihood of loss of dynamic balance, with a consequent increased risk of ankle sprains and falls.