Step Height Research Articles

A study of step defects on NiAl(110) using a curved single crystal surface

In contrast to common flat single crystal surfaces, curved surfaces provide the opportunity to study a large range of vicinals using only one single crystal. Here, we employ a curved NiAl single crystal surface to study step defects on the (110) plane using scanning tunneling microscopy under UHV conditions and at room temperature. The direction of curvature is chosen to align with the alternating Al and Ni atom rows, and we image the surface at various positions along its curvature. With very few exceptions, we find only monoatomic step heights to occur with local step densities consistent with the expected values along the macroscopically curved surface. We use our home-built Python-based analysis script to analyze STM images and obtain statistical information on step and kink distributions, a.o. it allows us to determine the kink formation energy.

Accuracy improvement of surface measurement through phase correction in spectrally resolved interferometer

The spectrally resolved interferometer (SRI) is used to measure the surface profile by the linear fitting line of its phase distribution of spectral interference signal. However, the noise existed in the phase cannot be ignored if the nano-scale measurement accuracy is required. In this paper, a novel algorithm is proposed to improve the measurement accuracy by using the constant term oflinear fitting line of phase distribution in wavenumber domain. The simulations indicate that the algorithm achieves the similar measurement accuracy under the influence of three kinds of noise. Even though the proposed algorithm has the possibility of 4% to bring the additional minor error, it provides a better performance on measurement of entire surface in different SNRs compared with the other two common algorithms. In experiments, the variations of surface less than 10 nm and 30 nm and the repeatability of 2.2 nm and 4.9 nm are obtained in the measurements of a protected aluminium mirror with and without proposed algorithm. A smooth profile with a step shape of nearly 3 μm height is tested, where the maximum repeatability of step height and maximum magnitude of variations of the surfaces reaches to 3.8 nm and 10 nm from the 15.3 nm and 30 nm by using this algorithm. Both the simulations and experimental results demonstrate that the proposed algorithm is feasible for high-precision measurement.

Bottom-Up Generated Height Gauges for Silicon-Based Nanometrology.

Steady progress in integrated circuit design has forced basic metrology to adopt silicon lattice parameter as a secondary realization of the SI meter that lacks convenient physical gauges for precise surface measurements at a nanoscale. To employ this fundamental shift in nanoscience and nanotechnology, we propose a set of self-organized silicon surface morphologies as a gauge for height measurements within the whole nanoscale (0.3-100 nm) range. Using 2 nm sharp atomic force microscopy (AFM) probes, we have measured the roughness of wide (up to 230 μm in diameter) singular terraces and the height of monatomic steps on the step-bunched and amphitheater-like Si(111) surfaces. For both types of self-organized surface morphology, the root-mean-square terrace roughness exceeds 70 pm but has a little effect on step height measurements having 10 pm accuracy for AFM technique in air. We implement a step-free 230-μm-wide singular terrace as a reference mirror in an optical interferometer to reduce the systematic error of height measurements from >5 nm to about 0.12 nm, which allows visualizing 136-pm-high monatomic steps on the Si(001) surface. Then, using a "pit-patterned" extremely wide terrace with dense but counted monatomic steps in a pit wall, we have optically measured mean Si(111) interplanar spacing (313.8 ± 0.4 pm) that agrees well with the most precise metrological data (313.56 pm). This opens up avenues for the creation of silicon-based height gauges using bottom-up approaches and advances optical interferometry among techniques for metrology-grade nanoscale height measurements.

Active and passive mechanics for rugose terrain traversal in centipedes.

Centipedes coordinate body and limb flexion to generate propulsion. On flat, solid surfaces, the limb-stepping patterns can be characterized according to the direction in which limb-aggregates propagate, opposite to (retrograde) or with the direction of motion (direct). It is unknown how limb and body dynamics are modified in terrain with terradynamic complexity more representative of these animal's natural heterogeneous environments. Here, we investigated how centipedes that use retrograde and direct limb-stepping patterns, Scolopendra polymorpha and Scolopocryptops sexspinosus, respectively, coordinate their body and limbs to navigate laboratory environments which present footstep challenges and terrain rugosity. We recorded the kinematics and measured the locomotive performance of these animals traversing two rugose terrains with randomly distributed step heights and compared the kinematics with those on a flat frictional surface. Scolopendra polymorpha exhibited similar body and limb dynamics across all terrains and a decrease in speed with increased terrain rugosity. Unexpectedly, when placed in a rugose terrain, S. sexspinosus changed the direction of the limb-stepping pattern from direct to retrograde. Further, for both species, traversal of these rugose terrains was facilitated by hypothesized passive mechanics: upon horizontal collision of a limb with a block, the limb bent and later continued the stepping pattern. Although centipedes have many degrees of freedom, our results suggest these animals negotiate limb-substrate interactions and navigate complex terrains leveraging the innate flexibility of their limbs to simplify control.

Development and Characterization of Low Temperature Wafer-Level Vacuum Packaging Using Cu-Sn Bonding and Nanomultilayer Getter.

Most microsensors are composed of devices and covers. Due to the complicated structure of the cover and various other requirements, it difficult to use wafer-level packaging with such microsensors. In particular, for monolithic microsensors combined with read-out ICs, the available process margins are further reduced due to the thermal and mechanical effects applied to IC wafers during the packaging process. This research proposes a low-temperature, wafer-level vacuum packaging technology based on Cu-Sn bonding and nano-multilayer getter materials for use with microbolometers. In Cu-Sn bonding, the Cu/Cu3Sn/Cu microstructure required to ensure reliability can be obtained by optimizing the bonding temperature, pressure, and time. The Zr-Ti-Ru based nanomultilayer getter coating inside the cap wafer with high step height has been improved by self-aligned shadow masking. The device pad, composed of bonded wafer, was opened by wafer grinding, and the thermoelectrical properties were evaluated at the wafer-level. The bonding strength and vacuum level were characterized by a shear test and thermoelectrical test using microbolometer test pixels. The vacuum level of the packaged samples showed very narrow distribution near 50 mTorr. This wafer-level packaging platform could be very useful for sensor development whereby high reliability and excellent mechanical/optical performance are both required. Due to its reliability and the low material cost and bonding temperature, this wafer-based packaging approach is suitable for commercial applications.

Improving Trunk Postural Control Facilitates Walking in Children With Cerebral Palsy: A Pilot Study.

The aim of this study is to determine the effects of bilateral trunk support during walking on trunk and leg kinematics and neuromuscular responses in children with cerebral palsy. Fourteen children with spastic cerebral palsy (Gross Motor Function Classification System level I to III) participated in this study. Children walked on a treadmill under four different conditions, that is, without support (Baseline), with bilateral support applied to the upper trunk (upper trunk support), the lower trunk (lower trunk support), and combined upper and lower trunk (combined trunk support). The trunk and leg kinematics and muscle activity were recorded. Providing bilateral support to the trunk had a significant impact on the displacement of the pelvis and trunk ( P < 0.003) during walking. Children's weaker leg showed greater step length ( P = 0.032) and step height ( P = 0.012) in combined trunk support compared with baseline and greater step length in upper trunk support ( P = 0.02) and combined trunk support ( P = 0.022) compared with lower trunk support. Changes in soleus electromyographic activity during stance phase of gait mirrored the changes in step length across all conditions. Providing bilateral upper or combined upper and lower trunk support during walking may induce improvements in gait performance, which may be due to improved pelvis kinematics. Improving trunk postural control may facilitate walking in children with cerebral palsy.

A Novel Three-Dimensional Positioning Method for Foot-Mounted Pedestrian Navigation System Using Low-Cost Inertial Sensor

Aiming at the problem that position errors accumulate rapidly in foot-mounted pedestrian navigation systems using a low-cost inertial sensor, a novel three-dimensional (3D) positioning method is proposed. First, when the foot is still, an improved zero velocity detection method that assigns different weights to each inertial measurement unit (IMU) data in a sliding window is designed to reduce positioning errors. When the foot is in swing, a lateral velocity restriction method is proposed by analyzing the gait characteristics of pedestrians. In addition, when pedestrians need altitude positioning in the building, the stair step height is also applied to the zero-velocity update (ZUPT)-aided inertial navigation system, which can effectively improve altitude positioning accuracy. Experiments under multi-gait modes show that the proposed zero velocity detection method can achieve smaller positioning errors compared with other traditional zero velocity detection methods. Moreover, the trajectory estimated by the proposed method has a higher coincidence with the real trajectories, the two-dimensional (2D) plane positioning error is less than 0.9% and the average altitude positioning error is only 0.12 m.

Deposition characteristics of particles in backward-facing step flow and a radiant syngas cooler

Investigation of the mechanism of particle transport and deposition in backward-facing step (BFS) flow is conducive to enhancing the understanding of the deposition characteristics of fly ash in the radiant syngas cooler (RSC). In this study, the regional characteristics of particle deposition in BFS and RSC are deeply studied by numerical simulation. The results show that the deposition of small particles in the recirculation (RC) zone and most particles in the reattachment and redevelopment (RR) zone is promoted while that of large particles in the RC zone is inhibited by the main flow. The variation curves of dimensionless deposition velocity gradually approach to that in straight channel with the increase in deposition length, but they are little affected by the step height and inlet velocity. The differences in particle deposition rates and size distributions between the two zones in RSC are analyzed. The average deposition rate in the RC zone is 21% lower than that in the RR zone, and the proportion of particles smaller than 45.03 μm in the RC zone is higher than that in the RR zone by 24%. This study can provide a basis for the establishment of ash deposition control strategies.

Research on development of aspheric diffractive optical element for mid-infrared imaging

The aspheric diffractive lens reduces chromatic aberration in precision infrared optical systems. With the advancement in micro-optics, conventional lenses are replaced by aspheric, diffractive and hybrid surfaces to fulfil the requirements of miniaturized design of optical devices. This paper covers the detailed aspects of hybrid aspheric diffractive optics from design to manufacturing by precision machining. The germanium aspheric diffractive lens is designed using Zemax OpticsStudio® for Medium Wave Infrared (MWIR) range to achieve an aberration-free and diffraction-limited surface. The designed surface is fabricated by the diamond turning process. The developed surface is characterized by profile and diffractive structure quality. The results demonstrate the fabricated lens with a diffractive structure step height error of 0.001 µm and radial position error of 1 µm. A high-quality aspheric diffractive lens is fabricated with 99.57 % diffraction efficiency.

Design Verification of a New Socket Partially Embedded Connection between Precast Rectangular Columns and Stepped Pile Caps

Socket connections are suggested to connect a precast column with adjacent members in accelerated bridge construction owing to their large construction tolerance. However, a typical socket-embedded connection always causes a heavy footing or pile cap due to the required embedment length, which is not preferable in the seismic design of a bridge system. In this paper, a new type of socket connection, namely, the partially embedded connection between a precast rectangular column and a stepped pile cap, is proposed to overcome this defect. Three half-scale specimens, that is, a cast-in-place specimen and two such designed socketed specimens with different step heights, were fabricated and tested to verify the new socket connection design concept. Experimental results showed that all specimens formed the approximate plastic hinges at the column bases and only minor damage occurred in the pile caps and the connecting regions; the hysteretic curves of the socketed specimens were approximately the same as that of the cast-in-place specimen, which proves that this new socket partially embedded connection is reliable to transfer the horizontal bending moment from columns to pile caps in a column–pile cap system and, meanwhile, can not only reduce the pile cap volume but also achieve the expected seismic performance.

The Dirac impenetrable barrier in the limit point of the Klein energy zone

We reanalyze the problem of a 1D Dirac single particle colliding with the electrostatic potential step of height V 0 with a positive incoming energy that tends to the limit point of the so-called Klein energy zone, i.e. E → V 0 − mc 2, for a given V 0. In such a case, the particle is actually colliding with an impenetrable barrier. In fact, V 0 → E + mc 2, for a given relativistic energy E( < V 0), is the maximum value that the height of the step can reach and that ensures the perfect impenetrability of the barrier. Nevertheless, we note that, unlike the nonrelativistic case, the entire eigensolution does not completely vanish, either at the barrier or in the region under the step, but its upper component does satisfy the Dirichlet boundary condition at the barrier. More importantly, by calculating the mean value of the force exerted by the impenetrable wall on the particle in this eigenstate and taking its nonrelativistic limit, we recover the required result. We use two different approaches to obtain the latter two results. In one of these approaches, the corresponding force on the particle is a type of boundary quantum force. Throughout the article, various issues related to the Klein energy zone, the transmitted solutions to this problem, and impenetrable barriers related to boundary conditions are also discussed. In particular, if the negative-energy transmitted solution is used, the lower component of the scattering solution satisfies the Dirichlet boundary condition at the barrier, but the mean value of the external force when V 0 → E + mc 2 does not seem to be compatible with the existence of the impenetrable barrier.

Standing waves of the stepped dropshaft in a deep tunnel stormwater system.

The deep tunnel stormwater system, consisting of dropshafts and underground tunnels, is used to alleviate or prevent urban water problems associated with extreme rainfall events. The stepped dropshaft can transport surface runoff to the tunnels with high energy dissipation, low risk of cavitation and good exhaust performance, which well meets the requirement of the deep tunnel stormwater system. In the present study, the characteristics of the standing wave were investigated by experiments and numerical simulations, including the peak, trough and length of the standing wave. The flow regimes were divided into the nappe flow, the transition flow and the skimming flow with the increase of discharge, in which the standing wave mainly occurs on the external wall under the nappe flow and the transition flow. Influences of inflow discharge and dropshaft geometries were analyzed, including step rotation angle, relative step height and dropshaft curvature. The relations of the characteristics of standing wave with these effect factors were obtained. The maximum discharge capacity of the stepped dropshaft was established by considering that the standing wave just reached the above steps, which could be useful for the design and safe operation of the stepped dropshaft.

Evaluation of a stepped, fixed-height magnification marker stand for use with a 100-mm marker in implant sizing prediction in 52 total hip replacement procedures in dogs.

To describe the use of a 100-millimeter marker placed on a stepped, fixed-height magnification marker stand to measure radiographic magnification on accuracy of implant size prediction when used for canine total hip replacement (THR) implant size selection. Retrospective study. Fifty-two hips in 45 dogs. This study evaluated 52 consecutive canine total hip replacement surgery pre-planning procedures involving 45 dogs with 7 undergoing staged bilateral THRs. Data collected included demographic information, measured radiographic magnification for magnification recalibration, implant size prediction of the cups (52) and the stems (52) based on digital templates superimposed on digital radiographs, and the actual implant sizes used during surgery. Use of the magnification marker stand (MMS) and template application system resulted in an accurate prediction of implant size of 98/104 implants (94.2%) implants. A 100-mm marker placed on a magnification marker stand was a viable method to measure and recalibrate for magnification on digital radiographs during the template process to predict the THR implant sizes that should be available when the surgery begins. This stepped calibration marker stand is helpful in determination of an accurate preoperative THR implant size prediction, lowering implant stock thresholds, operating time, and associated complications. Additionally, the radiographic documentation of the marker's step height allows for indefinite confirmation of the magnification marker height used and for accurate repeatability for all follow-up imaging examinations and contralateral procedure planning.

Modeling-Based Design of the Control Pattern for Uniform Macrostep Morphology in Solution Growth of SiC

In the solution growth of the SiC crystal, macrosteps with sufficient height on an off-axis substrate are required to reduce defects and achieve a high-quality grown layer. However, over-developed macrosteps can induce new defects and adversely affect the crystal quality. To better understand and control the behavior of macrosteps corresponding to the control parameters of the growth system, a simulation method that consists of a global two-dimensional computational fluid dynamic (CFD) model, a local three-dimensional CFD model near the growth front, and a kinetics model that describes the movement of macrosteps on the crystal surface is proposed. The simulation method is first applied to investigate the effect of the crystal rotation speed on macrostep morphology. Although the results indicate that a higher crystal rotation speed results in less step bunching, constantly rotating the crystal in one direction is demonstrated to be incapable of yielding a uniform macrostep distribution on the whole surface. Accordingly, a sophisticated control pattern is designed by periodically switching the flow direction underneath the crystal surface, where the proposed simulation method is critical to determine detailed control-parameter values. When the control pattern suggested by the simulation is used, a grown crystal with a uniform macrostep morphology and ideal step height on the whole surface is obtained in the practical experiment.

Effect of Medication and Deep Brain Stimulation on Gait in Parkinson's Disease and its Quantitative Analysis Using Mobishoe - A Comparative Study.

Movement abnormalities pertaining to balance, posture, and gait are observed in Parkinson's disease patients. Gait characteristics vary widely and their analysis has been performed traditionally in gait labs. Freezing and festination usually occur at an advanced stage of the disease and are associated with reduced quality of life. Therapeutic strategies and surgical interventions are often modulated by the physician depending upon the clinical manifestations. Introduction of accelerometers and wireless data transmission systems made quantitative gait analysis possible and cost-effective. To assess spatiotemporal gait parameters (step height, length (spatial), and swing support time of each foot and double support time (temporal)) in subjects who underwent deep brain stimulation surgery using a purpose-built instrument-Mobishoe. A simple footwear-based gait sensing device-Mobishoe was built in-house. Thirty-six participants were included in the study after obtaining consent. Participants were made to wear Mobishoe and walk an empty corridor of 30m before Deep Brain Stimulation (DBS) in the drug on and off stated and post DBS in DBS stimulation on and medication off state (B1M0), DBS stimulation off-medication off state (B0M0), DBS stimulation off-medication on (B0M1), and DBS stimulation on and on medication (B1M1). Data was electronically captured and analyzed offline in MATrix LABoratory (MATLAB). Various gait parameters were extracted and analyzed. Improvement in gait parameters was observed when the subject was on medication, on stimulation, or on both when compared to baseline. Improvement was similar with both medication and stimulation and was synergistic when both were used. Significant improvement was noted in spatial characteristics when the subjects were on both the treatments, which is the ideal treatment modality. Mobishoe is an affordable device which can measure spatiotemporal characteristics of gait. The best improvement was seen when the subjects were on both the treatment groups and the improvement can be justified as a synergistic effect of stimulation and medication.

Effect of a detached rib behind a backward-facing step on separated flow dynamics and heat transfer

Here, we present the experimental results on the influence of a detached rib behind a backward-facing step on the flow dynamics and heat transfer. The height of a slot between the lower edge of the rib and the channel wall was varied in the range dh/H = 0.7–1.3, and the distance between the rib and the step was varied within t/H = 0.2–3.2. The rib height was constant and equal to 0.3H, where H is the step height. The fields of static pressures were measured behind the point of flow separation at the step edge. The study was performed in the range of Reynolds numbers 14,200-42,500. The two-dimensional fields of velocities and their fluctuations were measured using the PIV method. Heat transfer was studied in the regime of constant heat flux on the channel surface, where the step was located. Behaviors of the pressure and velocity profiles, as well as heat transfer with varying the detached rib location relative to the step are shown.

Experimental study on aerodynamic sound generated from flow around a forward facing step

Aerodynamic noise in high frequency band related in the flows around A-pillar is easily propagated to the cabin of the automobile. Understanding of the characteristics of the aerodynamic noise is needed to reduce the cabin noise. Moreover, understanding of the separated shear layer which is strongly affected by the condition of the step hight H to the boundary layer thickness δ is needed. In this study, far field sound and correlation measurement of flow velocity are measured to investigate the characteristics of aerodynamic noise and the relationship between H/δ and turbulence length scale L as eddy scale for the forward facing step. As a result, multiple gradual peaks in more than 1 kHz are observed in the aerodynamic sound spectra. Furthermore, it is found that turbulence length scale L increases for increasing of H/δ and turbulence length scale to step height for H/δ = 2.0 is almost equal to that for H/δ = 3.0. Then, it is clear that spectral peaks are strongly affected by step height. And it is confirmed that H/δ = 2.0 and 3.0 are equal in turbulence length scale to the step height.

Collective excitations in even-even nuclei with a stepped infinite square well potential

A solution is worked out for a γ-unstable Bohr Hamiltonian with an infinite square well potential having an adjustable step. The evolution of the model’s spectral characteristics are investigated with varying height and width of the additional step, revealing shape coexisting an mixing features. The description of the dynamical shape phase transition in the collective bands of the Te even-even nuclei is offered as a numerical application.

Design optimization of one-dimensional aberration-free x-ray gradually focusing lenses

In our previous work, we proposed a new design method for an aberration-free x-ray refractive focusing lens based on an ideal Cartesian oval shape to solve the aberration problem in x-ray compound refractive focusing. In this paper, we propose an optimization method for this new lens. By reducing the aperture of each lens, we achieve the objective of increasing the effective aperture and improving the focusing performance of the lens. The simulation of the beam propagation method shows that the focusing performance of the optimized lenses is better in compound refractive lens shape but worse in the kinoform shape. This is different from the results obtained with the conventional kinoform lens. After further comparison, we found that this is because the step height of the kinoform lens is small when the lens aperture is very small, resulting in a strong diffraction effect that weakens the focusing performance of the lens. Further modifications to the structure of the kinoform lens are needed to improve this phenomenon.

Probing strongly exchange coupled magnetic behaviors in soft/hard Ni/CoFe2O4 core/shell nanoparticles.

Exchange coupling in a model core-shell system is demonstrated as a step on the path to 3d exchange spring magnets. Employing a model system of Ni@CoFe2O4, high quality core-shell nanoparticles were fabricated using a simple two-step method. The microstructural quality was validated using TEM, confirming a well-defined interface between the core and the shell. A strongly temperature dependent two-phase magnetic hysteresis loop was measured, wherein an analysis of step heights indicates coupling of roughly 50% between the core and the shell. Element-specific XMCD hysteresis confirms the presence of exchange coupling, suppressing the superparamagnetism of the Ni core at room temperature, and reaching a coercivity of >6 kOe at 80 K. These results provide a pathway to the development of heterostructured metal-oxide exchange coupled nanoparticles with improved maximum energy product.