Step Height Research Articles

Physical Modelling Of The Wave Field Around An Array Of Centrally Controlled Wave Energy Converters

Stepped revetments have shown to be effective in limiting wave overtopping and wave run-up compared to sloped revetments. However, literature on wave impact pressures and comprehensive design guidelines for these structures is scarce. Laboratory experiments support establishing design recommendations. So far, studies for wave impacts at stepped revetments were mainly performed at small scales. Results from these tests are likely to be subjected to scale effects and therefore inaccurately replicate the wave-structure interaction at full scale. This study quantifies scale effects of wave impact characteristics for design cases based on a comparison to small-scale tests (Kerpen et al., 2018). Full-scale flume experiments were studied with a slope of 1:3 and uniform step heights of 0.17 m and 0.50 m in the Large Wave Flume (GWK) in Hannover, Germany. Horizontal and vertical wave impacts were measured at 15 locations in the plunging region of the revetment for a range of wave steepnesses (). The results show that previous small-scale tests underestimate design wave impact pressures by a factor of up to 7.7. Impact loadings occur considerably faster than at small scale with relative peak rising times decreasing by a factor of up to 5.6. Prediction formulae are derived for the vertical distribution of horizontal impact pressures (Figure 1b) as well as for temporal characteristics of these pressures at stepped revetments.

Atomic scale mechanism of reorientation induced plasticity in titanium alloys - experimental and first principles investigation of the mobile [formula omitted] interfaces

Recent experiments identified a new type of stress induced structural transformation allowing to combine high strength, great work hardening and good ductility in multiphase Ti alloys. These properties are achieved through reorientation of the α′ martensite plates being in specific self accommodating 〈54‾1‾3〉 type II twin relation, i.e. under applied load one martensite variant reconfigure to its twinned configuration with visible motion of the {134‾1} twin boundary. This mechanism of plastic deformation was never observed before thus, its current understanding is fragmentary. In this article we present the results of experimental observations and ab initio calculations of 〈54‾1‾3〉 type II twins determining the crystallography of twin formation, structure and energy of the {134‾1} interface as well as mobility of the corresponding twinning disconnections. It was found that the investigated boundary has one of the lowest energies among known twinning modes in hexagonal Ti. Moreover, the 〈54‾1‾3〉{134‾1} disconnections have the smallest Burgers vector and step height in comparison to other active twinning systems. As a result, these disconnections are highly mobile which rationalize migration of the {134‾1} twin boundaries at straining. Furthermore, energy of the twin boundary and mobility of disconnections can be adjusted by particular alloying elements enabling the conscious development of new alloys exhibiting reorientation induced plasticity.

Deep ensemble learning for material removal rate prediction in chemical mechanical planarization with pad surface topography

Chemical mechanical planarization (CMP) stands as a critical process in semiconductor manufacturing, necessitating precise prediction of material removal rate (MRR) to achieve optimal global planarization of material surface step heights. A notable hurdle in MRR prediction lies in the nonlinear pad-wafer interaction stemming from variations in the polishing pad surface. Despite numerous extant studies examining the asperity of the pad surface and the wafer-pad contact, aspects such as slurry lubrication and micro-topographical structure of the pad surface remain unaddressed. This study firstly proposes a deep ensemble learning-based approach for MRR prediction, leveraging the intricate interactions between the overall features of the pad surface and the polishing pressure. We experimentally generated diverse pad surfaces by controlling the process variables governing pad surface topography. The Multi-TabNet model, constructed by independently training multiple TabNet instances with distinct initialization and hyperparameters, furnishes a framework for MRR prediction across a broad spectrum of pad surface features, encompassing pores and cores. The results demonstrate a root mean square error of 80 Å/min, with the error margin reduced by up to 70 % compared to predictions utilizing a single parameter of the pad surface. Furthermore, it exhibits an error improvement exceeding 17 % relative to the existing method solely considering asperity. This study not only imparts insights for addressing MRR variations contingent on pad condition but also facilitates dependable material removal even on variable pad surfaces due to conditioner wear.

Linearizing the vertical scale of an interferometric microscope and its effect on step-height measurement.

The vertical scale calibration of an interferometric microscope is important for establishing traceability of surface topography measurements to the International System of Units (SI) unit of length, the meter. Building on the calibration procedure for the amplification coefficient developed by de Groot and Beverage [Proc. SPIE 9526, 952610 (2015)], this paper describes a calibration procedure that yields the response curve for the entire vertical scan motion of a coherent scanning interferometric microscope. The method requires only a flat mirror as an artifact, a narrow band spectral filter, an aperture to reduce the effective numerical aperture, and the ability to raise and lower the microscope head so that the center of the interferogram can be varied within the scan range. The local frequency of the interferogram is determined by fitting sections of the interferogram to a sinusoidal function. The nonlinearity determined from the local frequency data can be used to estimate the uncertainty in uncorrected vertical height measurements. We describe how optical profile data can be corrected for nonlinearity due to dynamic effects in the scan motion and show that the correction improves the reproducibility of step height measurements by at least a factor of three and close to that of the repeatability.

Experimental investigation on local scour downstream of stepped chutes with a flip bucket

Stepped chutes and flip buckets are the most prevalent energy dissipators in emergency spillways at dams. Given the impact that scour depth has on the stability and safety of these structures, the effects of stepped and smooth chutes on the local scour process downstream of a flip bucket for various hydraulic and geometric conditions were experimentally investigated in the present study. Experiments were conducted for 1:1 and 1:2 chute slopes (V: H), bucket exit angles of 15° and 30°, and a ratio of critical flow depth to step height (yc/h) between 0.53 and 0.97. The comparison of results revealed that installing steps over the chute profile reduced the maximum scour depth downstream in range of 15–51 percent, compared to smooth chute. By changing chute slope from 1:1 to 1:2, the maximum scour depth was reduced by an average of 16 and 25 percent for smooth and stepped chutes, respectively.

Room-Temperature Antisymmetric Magnetoresistance in Van Der Waals Ferromagnet Fe3GaTe2 Nanosheets.

Van der Waals (vdW) ferromagnetic materials have emerged as a promising platform for the development of 2D spintronic devices. However, studies to date are restricted to vdW ferromagnetic materials with low Curie temperature (Tc) and small magnetic anisotropy. Here, a chemical vapor transport method is developed to synthesize a high-quality room-temperature ferromagnet, Fe3GaTe2 (c-Fe3GaTe2), which boasts a high Tc = 356 K and large perpendicular magnetic anisotropy. Due to the planar symmetry breaking, an unconventional room-temperature antisymmetric magnetoresistance (MR) is first observed in c-Fe3GaTe2 devices with step features, manifesting as three distinctive states of high, intermediate, and low resistance with the sweeping magnetic field. Moreover, the modulation of the antisymmetric MR is demonstrated by controlling the height of the surface steps. This work provides new routes to achieve magnetic random storage and logic devices by utilizing the room-temperature thickness-controlled antisymmetric MR and further design room-temperature 2D spintronic devices based on the vdW ferromagnet c-Fe3GaTe2.

Assessing cows' mobility to determine their comfort state

Milk production and breeding of highly productive cows using modern innovative technologies have led to specific unfavorable combinations of technological factors in how cows are kept, which has significantly increased their susceptibility to developing various pathological processes in the musculoskeletal system. Lameness is the most common pathology. It is important to note that this information is based on objective evaluations and scientific research. The article is devoted to developing methodological approaches to determine the comfort state of cows based on mobility assessment. When determining the comfort state of a cow, in particular, the detection of diseases of the musculoskeletal system, a three-dimensional image of the animal was used, the position of the specified points of the animal's body was determined (tracking), the kinematic indicators of the movement of these points were calculated, the degree of bending of the animal's back during movement was assessed, complex mobility indicators were calculated, and the calculated complex mobility indicator was compared with the reference one. Based on the research results, a structural and technological scheme of a system for determining the comfort state of an animal based on the assessment of its mobility was developed, and software for video recording of movement was created. The step length, maximum step height, step duration, posture, and free state, as well as the speed of movement of healthy animals, those with single lesions and hoof ulcers were determined, and, as a result, the dynamics of changes in the accelerations of nodal points in the joints for each body link of healthy cows was revealed. The key variables of the biomechanical model for assessing the limbs of cattle (cows) are substantiated. The value of the specific force of the support reaction acting on the hooves of cows was determined: the highest value (9.8 N/kg) was observed for the concrete surface, the lowest (5 N/kg) – for rubber mats. The practical examples of the complex relationship between welfare indicators (lameness), elements of physiology (mobility), and technology (floor type) presented in the publication are recommended to be effectively used in monitoring the results of detecting gait disorders in animals and evaluating its effectiveness even in the early stages of the disease. The prospect of further research is to determine the comfort state of animals depending on environmental and climatic conditions.

Effect of Step Height and Visual Feedback on the Lower Limb Kinematics Before and After Landing

Effect of Step Height and Visual Feedback on the Lower Limb Kinematics Before and After Landing

GAITBOOST: Boosting gait recognition performance with BAT-extreme learning machines algorithm

Gait analysis is a widely used technique for passive human identification and tracking, with potential applications in security and surveillance systems. However, existing gait recognition methods face challenges in handling changing angles and uncertain features. In this paper, we propose a novel gait recognition approach that leverages real-time spatio-temporal gait features, including step length, gait cycle, height, cadence, swing ratio, and foot length. We apply the Extreme Learning Machines (ELM) algorithm for classification, which has been shown to be effective in various applications due to its fast-learning speed and good generalization performance. To further enhance the recognition rate, we introduce an evolutionary BAT-optimized ELM algorithm that addresses the instability issue in ELM. The proposed BAT-ELM algorithm can optimize the hidden nodes and weights of ELM, which leads to improved efficiency in recognizing gait from multiple view angles ranging from 0° to 180°. Our comprehensive analysis of the proposed approach indicates that it outperforms other reported algorithms in terms of recognition rate and efficiency. Our work demonstrates the effectiveness of combining real-time spatio-temporal gait features with the BAT-ELM algorithm for gait recognition. The proposed approach has potential applications in various fields, including security and surveillance systems, healthcare, and robotics. Our findings highlight the importance of leveraging evolutionary algorithms to optimize machine learning models and achieve better performance in complex recognition tasks.

Novel Probability Density Function of Pad Asperity by Wear Effect over Time in Chemical Mechanical Planarization.

Chemical mechanical planarization (CMP) reduces film thickness, eliminates step height, and achieves high levels of planarity in semiconductor manufacturing. However, research into its mechanisms is still in progress, and there are many issues to be resolved. To solve problems in CMP, it is necessary to understand the contact phenomenon that occurs at the pad-wafer interface, especially pad asperity. Moreover, understanding the non-uniform distribution of pad asperity, such as height and radius, is essential for predicting the material removal rate (MRR). In this study, based on the existing Greenwood-Williamson (GW) theory and probability density function (PDF), a modified mathematical model that includes changes in asperity distribution was developed and validated experimentally. The contact model proposed in this study included functions that calculated the time-dependent height and radius wear of the pad asperities. Specifically, the experimentally obtained values were compared with the values obtained by the model, and the comparison results were analyzed. Thereby, it was found that the contact model and MRR model considering the change in asperity wear and distribution due to CMP proposed in this study are in better agreement with the experimental results than the existing model, which shows that the MRR can be predicted by a mathematical model using the change in asperity distribution.

Kinetic View of Enzyme Catalysis from Enhanced Sampling QM/MM Simulations.

The rate constants of enzyme-catalyzed reactions (kcat) are often approximated from the barrier height of the reactive step. We introduce an enhanced sampling QM/MM approach that directly calculates the kinetics of enzymatic reactions, without introducing the transition-state theory assumptions, and takes into account the dynamical equilibrium between the reactive and non-reactive conformations of the enzyme/substrate complex. Our computed kcat values are in order-of-magnitude agreement with the experimental data for two representative enzymatic reactions.

Gait-modifying effects of augmented-reality cueing in people with Parkinson's disease.

External cueing can improve gait in people with Parkinson's disease (PD), but there is a need for wearable, personalized and flexible cueing techniques that can exploit the power of action-relevant visual cues. Augmented Reality (AR) involving headsets or glasses represents a promising technology in those regards. This study examines the gait-modifying effects of real-world and AR cueing in people with PD. 21 people with PD performed walking tasks augmented with either real-world or AR cues, imposing changes in gait speed, step length, crossing step length, and step height. Two different AR headsets, differing in AR field of view (AR-FOV) size, were used to evaluate potential AR-FOV-size effects on the gait-modifying effects of AR cues as well as on the head orientation required for interacting with them. Participants modified their gait speed, step length, and crossing step length significantly to changes in both real-world and AR cues, with step lengths also being statistically equivalent to those imposed. Due to technical issues, step-height modulation could not be analyzed. AR-FOV size had no significant effect on gait modifications, although small differences in head orientation were observed when interacting with nearby objects between AR headsets. People with PD can modify their gait to AR cues as effectively as to real-world cues with state-of-the-art AR headsets, for which AR-FOV size is no longer a limiting factor. Future studies are warranted to explore the merit of a library of cue modalities and individually-tailored AR cueing for facilitating gait in real-world environments.

Numerical Investigation of Single and Double Steps in Planing Hulls

Incorporating steps into a hull reduces the wetted surface, promoting improved hydrodynamic lift and reduced resistance at high speeds, provided that the step is designed appropriately. Traditional hydrodynamics studies rely on scaled model testing in towing tanks, but numerical tools offer a more efficient alternative. This study focused on investigating the hydrodynamic performance of stepped hulls by modifying the parent hull of the Naples Systematic Series (C1). The Computational Fluid Dynamics (CFD) code SIEMENS PLM STAR CCM+ version 2302 was used for simulations, including four different beam Froude numbers (FrB = 1.13, 2.22, 2.56, and 2.96) and a total of 15 hull configurations with single and double steps. By employing a three-dimensional computational analysis of multiphase flow using Dynamic Fluid–Body Interaction (DFBI) and overset mesh, various performance parameters such as resistance coefficient, dimensionless wetted surface, sinkage, and dynamic trim were analyzed. The accuracy of the CFD results was confirmed through comparison with experimental data and grid uncertainty assessment. The study demonstrated that placing a single step near the transom decreased trim and increased resistance and wetted surface. Conversely, positioning a step in the forward section reduced the trim angle at lower step heights but increased trim at higher step heights in single-stepped hulls. The application of these findings contributes to the design optimization of stepped hulls for enhanced performance in high-speed maritime applications.

Silicon-based waveguide technology for millimeter-wave antennas

This paper describes a method for the preparation of complex structured waveguides that can be used for millimeter-wave antennas based on a bulk silicon MEMS process. In this paper, a millimeter-wave band array of ridge waveguide slit antennas with multilayer step-matched feeds is realized by this method. A bulk silicon MEMS process is used to realize the complex structure and the high precision and flatness requirements on the millimeter scale, which cannot be achieved by machining. And the step height difference of more than 100um is realized by combining multiple lithography and silicon oxide mask. The step difference is larger than that achievable by dry etching using the etching selection ratio of silicon oxide and silicon. The waveguide fabricated by this method can work well in the millimeter wave band and is used for antenna feeding, power distribution, etc. It is characterized by compact structure, high precision, and high performance.

Prediction of effect of small local surface irregularities on natural transition to turbulence based on Global Stability Analysis

Reliable prediction of the effect of surface irregularities on laminar-turbulent transition (LTT) is of great importance for many industrial applications. At low levels of free-stream turbulence typical of external aerodynamics, the primary mechanism of LTT is associated with the so-called convective instability of the Tollmien-Schlichting waves. In this paper, a non-empiric methodology based on Global Stability Analysis, which has been developed and validated previously to predict the evolution of these waves and the location of the LTT on a smooth flat plate, is applied to evaluation of this effect for backward- and forward- facing steps of different heights and locations. The results obtained are analyzed and compared with results of 2D time-accurate unsteady Navier-Stokes simulations, as well as with available experimental data and with the semi-empiric “variable N-factor” method.

Service performance evaluation of light-transmitting concrete lane markings on highways based on accelerated pavement testing

Applying light-transmitting concrete (LTC) to highway lane markings is a novel idea to increase the visual recognition distance and promote traffic safety. However, compared to its excellent visual recognition performance, its service performance has received little attention in the current research. This paper conducted an accelerated pavement test to investigate the behaviour of rutting depth, British Pendulum Number (BPN) and water permeability coefficient of the LTC lane markings. The results show that rutting depth of LTC is lower than that of asphalt pavement. As a result, small height steps appeared at the seam of the two parts. For the anti-sliding performance represented by the BPN, the BPN of LTC gradually exceeds asphalt pavement and maintains a slightly higher value. For the water permeability coefficient, the LTC is almost un-permeable, avoiding water damage during service. According to these findings, the LTC lane markings meet the requirements of highway service performance. .

Effects of channel structure at inlet region on temperature distribution of proton exchange membrane fuel cells

Enhancing the temperature distribution uniformity in membrane electrodes is crucial for improving the durability and performance stability of proton exchange membrane fuel cells. In this study, we discovered an entrance region in the cathode membrane electrode of proton exchange membrane fuel cells characterized by a rapid rise in temperature. This inlet region shows a notably higher temperature variation rate compared to other regions. This phenomenon is attributed to the temperature difference between the constant temperature fluid supplied by the channel inlet and the heat generation in the cathode catalyst layer. Thus, the impact of channel structure at the entrance region on the temperature distribution of the cathode catalyst layer is investigated, based on a three-dimensional, non-isothermal, two-phase model. Results show that boosting heat transfer in the inlet region is more effective for reducing the average temperature than in other regions. We proposed five kinds of step arrangement schemes and discovered that the step arrangement in the entrance region of the cathode flow channel can increase the temperature uniformity of the cathode catalyst layer by 9.71% without net power loss. Furthermore, this study examines the impact of length, height of entrance steps, and outlet channel height on heat transfer and identifies the optimum value. When severe water flooding occurs, the gas purge coupled with the step-fronted scheme is essential for improving temperature uniformity.

Magnetoelectric transport properties in topological nodal-line semimetals

We study the impact of the size effect and the varying perpendicular magnetic field B on the transport properties of topological nodal-line semimetals (TNLSMs) by using the Landauer–Büttiker formula combined with the nonequilibrium Green’s function. We theoretically calculate the band structure, conductance G and local density of states (LDOS) of TNLSMs nanowire. The results show that both the size effect and the application of varying magnetic field play a crucial role in the electron transport of TNLSMs. We find that both the step height and width of the conductance plateau in TNLSMs are closely related to the size effect of the system. For the system with a large TNLSMs, the low energy states are dominated by flat bands, leading to a series of quantized conductance plateaus. Furthermore, it has been observed that the presence of a magnetic field leads to the formation of the Landau levels in the TNLSMs, which exhibit sensitivity to the direction of the applied magnetic field. A perpendicular magnetic field parallel to the transport direction forms a linearly dispersed Landau level in the TNLSMs system, which leads to an increase in its conductance G and LDOS. At the same time, when the magnetic field perpendicular to the transport direction is applied, a series of the Landau levels with the flat bands are formed near the Fermi energy level EF of the system, resulting in a significant decrease of its conductance G and a rapid decay of LDOS. These unique physical properties of the TNLSMs nanowire offer a wide range of the applications in magnetoelectric transport.

Suppression of Mixing of Metastable Zincblende Phase in GaN Crystal Grown on ScAlMgO4 Substrates by Radio‐Frequency Plasma‐Assisted Molecular Beam Epitaxy

ScAlMgO4 (SAM) substrates have attracted significant attention as template substrates for fabricating bulk GaN crystals. Radio‐frequency plasma‐assisted molecular beam epitaxy (RF‐MBE) is preferred for the growth of the first GaN layer. However, the metastable zincblende (ZB) phase is mixed on the SAM substrate with a smaller terrace width, coupled with lower growth temperatures in MBE. Herein, the time evolution of GaN growth on SAM substrates is investigated to elucidate the mechanism underlying ZB mixing. ZB‐GaN is generated as stacking faults during the coalescence of the initially grown wurtzite‐ (WZ‐) GaN islands on adjacent SAM terraces, owing to the extraordinarily large step height close to three bilayers of WZ‐GaN. Therefore, high‐temperature growth on a SAM substrate with wider terraces suppresses the generation of the ZB phase in the initial growth stage. ZB‐GaN also decreases with an increase in the growth time. Based on these results, a 940 nm‐thick GaN layer is grown at 750 °C on the SAM substrate with a terrace width of 820 nm. A pure WZ‐GaN layer from the GaN/SAM interface with a flat surface with a root mean square value of below 1 nm and a dislocation density of 7.3 × 109 cm−2 is obtained.

Assessing lateral torsional buckling of stepped steel I beams using finite element method

The use of steel beams with variable sections along their length is getting more attention in recent years. These variable sections can vary gradually along the beam or change abruptly as a drop or a step. The current study investigates the lateral torsional buckling (LTB) of stepped steel beams with flanged I section subjected to uniformly distributed pressure on the top flange. The studied parameters are the step height, the step length, and the boundary conditions of the beam. The finite element method is used to carry out a linear buckling analysis of the beams’ models. The results show significant degradation in beams LTB strength due to the jump of the beam's section. Reducing the simply supported beam depth by 25 % reduces LTB strength by about 40–50 %, while reducing the fixed beam depth by 25 % reduces LTB strength by about 30–40 %. Further reduction in depth showed no significant additional reduction in simply supported beams strength, while the fixed beams showed another 30–40 % reduction in strength with another 25 % reduction in beam total depth. The step made the compressive stress transfer between the two flange parts through the web.