Circular Track Research Articles

Skyrmion-based JK flip–flop with a wedge-shaped circular track

Magnetic skyrmion can be used as information carrier of logic devices because of its nano size and topological properties. Here, we introduce a wedge-shaped circular track structure, in which the cycle motion of skyrmion in the ferromagnetic track is induced by the gradient of voltage-controlled magnetic anisotropy. Compared with the straight track, the process of generation and annihilation of skyrmion is avoided due to the recycling of skyrmion. Furthermore, the logic of the JK flip–flops is successfully implemented in the wedge-shaped circular track, which provides guidance for the design of skyrmion-based sequential logic devices.

SYNTHRSIS OF QUADROTOR ROBUST GUIDANCE AND CONTROL SYSTEM VIA PARAMETERIZATION OF ALL STABILIZING Н-INFINITY STATE-FEEDBACK GAINS

The main purpose of the research is to develop the quadrotor robust control system adapted to the rejection of external disturbances. The methodology of control system synthesis is based on the parameterization of all stabilizing H-infinity static state feedback gains with applications to output feedback design. The main feature of the article is the development of the above-mentioned method relative to the quadrotor. The main results of the article are synthesized control laws and simulation of the closed-loop dynamics. The basic practical implication is the usage of synthesized control laws in guidance of the quadrotor motion in path following of circular and linear-piecewise reference tracks. Originality and value of the article are caused by the necessity to improve the quality of control by quadrotor motion.

Y-Shaped Backbone-Rigidified Triangular DNA Scaffold-Directed Stepwise Movement of a DNAzyme Walker for Sensitive MicroRNA Imaging within Living Cells.

DNA as a programmable molecule shows great potential in a wide variety of applications, with the dynamic DNA nanodevices such as DNA motors and walkers holding the most promise in controlled functions for biosensing and nanomedicine. However, a motor or walker that consists of DNA exclusively has not been shown to function within cells because of its susceptibility to endogenous nuclease-mediated degradation. In this contribution, we demonstrate a Y-shaped backbone-rigidified triangular DNA scaffold (YTDS)-directed DNAzyme walker that functions inside living cells to detect microRNAs (miRNAs) with high sensitivity. A novel Y-shaped backbone offers access to geometrically well-defined configurations and increases the rigidity of DNA assemblies, providing a unique, circular, and rigid DNA track within living cells without non-nucleic acid auxiliary materials and enabling the stepwise movement of DNAzyme in an inchworm fashion. This strategy is extended to the construction of larger rigid planar geometric polygon-based DNA walkers, demonstrating unprecedented opportunities to build dynamic DNA nanostructures with precise geometry and versatile functionality.

A Phase Calibration Method Based on Phase Gradient Autofocus for Airborne Holographic SAR Imaging

Holographic synthetic aperture radar tomography can realize full 3-D reconstructions of objects over 360° with very high resolution, and thus becomes an interesting 3-D imaging technique. However, due to the uncompensated platform motion errors, phase errors among different tracks usually exist in this imaging mode, which will hinder the 3-D image focusing. In this letter, a phase calibration method based on phase gradient autofocus is proposed to mitigate the influence of these phase errors. It exploits the space-invariant characteristic of the phase errors in a limited scene and uses an efficient and robust multibaseline autofocus to calibrate the phase errors among the multiple circular tracks. Experimental results with the GOTCHA real data are carried out to demonstrate the validity and feasibility of the proposed method.

Three-dimensional integral imaging with circular non-uniform distribution

In this paper, we present the realization of three-dimensional integral imaging with circular non-uniform distribution. Due to circular non-uniform distributed cameras for the pickup configuration, more light information from a 3D scene can be collected. To achieve a flexible integral imaging system, a camera is moved along a circular track with random central angles to capture a set of elemental images. We develop a mathematical framework for error estimation of the camera positions. The experimental results are carried out to verify the proposed system. We also analyze voxel resolution for the performance evaluation of the proposed system, based on two point sources resolution criteria.

Observational characteristics of pedestrian flows under high-density conditions based on controlled experiments

High-density crowds are associated with high risks such as stampede accidents. Therefore, it is important to understand the dynamics of high-density crowds. We performed experiments in both a 1.5-m-wide ring corridor and a single-file circular track to study pedestrian flow dynamics under high-density conditions. For the wide-track experiment, we examined global densities as high as 9 ped/m2. Our main findings were as follows. (i) The middle section of our unidirectional fundamental diagram exhibited a clear similarity to that of a single-file pedestrian flow, which enabled us to distinguish two different kinds of congested pedestrian flow. (ii) The unidirectional fundamental diagram for a high-density situation was quantitatively nearly the same as that observed in the empirical data. (iii) In the absence of a bottleneck, typical stop-and-go patterns did not emerge in the unidirectional flow on the 1.5-m track. Instead, some high-density clusters propagating downstream can be observed. (iv) In the bidirectional flow experiments, three different lane formation processes were observed. The processes were quite quick, even under very dense conditions. (v) When three lanes formed, the bidirectional flow rate was much larger than the unidirectional flow rate due to the inhomogeneous distribution of pedestrians across different lanes. (vi) At high densities, the unidirectional and bidirectional flow rates were nearly the same. However, a bottleneck emerged in the bidirectional flow due to the variable width of the opposite streams. Our study helps to achieve a better understanding and modeling of the dynamics of high-density pedestrian flows.

Optimization of horizontally curved track in the alignment design of a high-speed maglev line

This paper presents an optimal solution for the alignment of horizontally curved track in a high-speed maglev line, in which the minimum length of the curved track is taken as a major objective function and the satisfaction of the minimum comfort level of passengers is considered as a boundary condition to constrain the selection of alignment parameters of the curved track. To verify the optimal solution provided by this study and assess the effects of viaduct subsystem and its interaction with train subsystem, the dynamic model of a coupled maglev train-curved viaduct system is numerically established, experimentally validated, and explicitly used to compute the responses of the train subsystem and viaduct subsystem. The computed results show that the comfort indexes computed from the dynamic model are comparable with those from the optimal solution. The parametric studies also show that with the increase of vehicle speed, the optimal radius of the circular track and the optimal length of the transitional track both increase but the cant and the cant deficiency remain constant.

Discovering Quantities of Circular Motion of a Light-Emitting Toy Train Using a Smartphone Light Sensor

In recent years, smartphone sensors have been frequently used in educational demonstrations to improve students’ understanding of certain physical kinematic topics. In particular, the sensors on modern smartphones enable students to use their phones as physics mini-laboratories, and they have been used to analyze objects’ speeds and accelerations and to investigate the conservation of energy and magnetic field properties. As a particular example, one of the sensors on smartphones capable of being used to measure the speed and acceleration of light-emitting objects, and the value of g and spring constant, is the smartphone’s light sensor. In similar fashion, we now outline how a smartphone’s light sensor may be used to find the angular velocity, linear velocity, and centripetal acceleration of a light-emitting toy train moving on a circular track.

Tribological Properties of High-Speed Uniform Femtosecond Laser Patterning on Stainless Steel

In this work, an analysis of the tribological performance of laser-induced periodic surface structures (LIPSS) treated X5CrNi1810 stainless steel was conducted. The approach followed by authors was to generate LIPSS-patterned circular tracks, composed of radial straight grooves with uniform angular periodicity. This permitted to measure the tribological properties in a pin-on-flat configuration, keeping fixed the orientation between the grooves and the sliding direction. A Stribeck curve was measured, as well as the consequent wear. A deep analysis of the sub-surface conditions after LIPSS generation was moreover performed using Focused Ion Beam (FIB) cross-section.

Optimal YBCO Bulk Size to Maximize Running Speed of the SS-HTS Maglev Circular Track System by Static Simulation Experiments

The constraints of experiment site and construction cost have increased difficulties in the high-speed and large-scale experiments of high- $T_{c}$ superconductor (HTS) maglev. At the beginning of this article, a side-suspension HTS (SS-HTS) maglev circular track was successfully built, which enabled the prototype vehicle to reach the maximum speed of 160 km/h. However, it is expected that with further increase in the running speed, the insufficient centripetal force caused thereby will destroy the dynamic stability of the circular track system. In order to improve the dynamic performance of circular track system with prototype vehicle running at a high speed, static experiments were carried out to simulate the free suspension and dynamic processes of the prototype vehicle. The levitation and guidance performance of bulk YBa 2 Cu 3 O7– x (YBCO) superconductors with different thickness and sectional area were tested during the simulation experiment, and the curve of $K_{l}$ and $K_{g}$ was obtained through calculation with the centrifugal force formula. The test and calculation results indicate that the maximum speed of prototype vehicle can rise by 19% compared to the earlier circular system in the case of 40 × 40 × 16 mm3 ( L × W × H ) bulk YBCO superconductors. The research findings can provide design reference for optimizing and constructing an SS-HTS maglev circular track system with higher performance and higher speed grade.

Dynamic response of vehicle and track in long downhill section of high-speed railway under braking condition

The dynamic behaviors of vehicle and track in long and downhill section of high-speed railway are studied under braking condition. A vehicle–track dynamic interaction model is constructed based on two longitudinal vehicle–track interaction models. In the model, the vehicle is considered as a 21-degree-of-freedom multi-rigid body system composed of a car body, two bogies, and four wheels; using the finite-element method, the track is modeled as a Euler beam; the “circular track” method is proposed to reduce the degree of freedom of the model for the simulation of long-distance track; two longitudinal wheel–rail interaction models are considered: the Polach creep theory (suitable for simulating condition of large creep resulting from heavy braking) and the longitudinal rigid-contact theory. The dynamic responses of the substructures during vehicle braking calculated by the models based on the Polach creep model and longitudinal contact model show little difference, but the Polach creep model can fully consider the motion of the wheels and large wheel–rail creep in the braking process and can accurately analyze the wheel–rail interface damage. The results of dynamic interaction between wheel and rail under different conditions suggest that large braking torque will cause some or all of the wheels to slide and then cause the damage of wheel–rail interface. The grade will lead to the increase in braking distance and time and also extend the sliding time of locked wheels, increasing the risk of damage of the wheel–rail interface. The braking torque should be kept below a reasonable value, so that the braking distance and braking time can be as short as possible without the occurrence of wheel sliding along the track. A reasonable braking torque under the dry track and wet track conditions should be 7 and 4 kN m respectively, according to the calculation in this article.

A New Adaptive System for Suppression of Transient Wind Disturbance in Large Antennas

Under transient wind disturbance, vibration deformation of the large antenna surface profile causes deterioration of pointing performance. This paper presents a new adaptive system to suppress unknown transient wind disturbance. First, to monitor the vibration, based on the acceleration measurement and a low-order flexible model considering equivalent identification of forces, the real-time estimation of the vibration state is obtained in an unbiased minimum-variance way. Next, a novel four-cable-actuator mechanism with a circular slide track is proposed for suppressing the vibration, in which the locations of the cable drivers on the slide track are determined according to the attitude of the antenna, and the expected tension distribution of the cables is found by the vibration state and the optimal gain of the linear quadratic regulator (LQR). In the end, the simulation implementation of a 7.3 m antenna under the transient wind disturbance is used to verify the effectiveness of the proposed method.

Maximum Entropy Derived Statistics of Sound-Speed Structure in a Fine-Grained Sediment Inferred From Sparse Broadband Acoustic Measurements on the New England Continental Shelf

Marginal probability distributions for parameters representing an effective sound-speed structure of a fine-grained sediment are inferred from a data ensemble maximum entropy method that utilizes a sparse spatially distributed set of received pressure time series resulting from multiple explosive sources in a shallow-water ocean environment possessing significant spatial variability of the seabed. A remote sensing seabed acoustics experiment undertaken in March 2017 off the New England Shelf was designed so that multiple independent analyses could infer the statistical properties of the seabed. The current analysis incorporates the measured horizontal variability from interpretations of a subbottom profiling survey of the experimental area. An idealized range- and azimuth-dependent parameterization of the seabed is derived from identification of horizons within the seabed that define multiple sediment layers. A sparse set of explosive charges were deployed on circular tracks with radii of about 2, 4, and 6.5 km with an acoustic array at the center to correlate a set of random measurements to physical acoustic processes that characterize the seabed. The mean values of a surface sound speed ratio and a linear sound speed gradient for the fine-grained sediment layer derived from 12 data samples processed in the 25-275-Hz band provide an estimate of the effective sound-speed structure in a 130-km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> area. The inferred sediment sound speed values are evaluated by predicting measured time series data not used in the statistical inference, and are also compared to historical measurements. Finally, the low-frequency maximum entropy estimate of the sediment sound speed along with physical measurements derived from piston core measurements are utilized to estimate the sediment grain bulk modulus.

A Compact and Repetitively Triggered, Field-Distortion Low-Jitter Spark-Gap Switch

This paper describes the development of a small field-distortion spark gap switch. Comprehensive experimental studies made with the switch revealed its self-breakdown characteristics, voltage operating range, time delay and jitter, repetition frequency, and finally the electrode erosion processes and duration of its service lifetime. A series of design improvements were required to be implemented in the switch design. For example, to reduce the structural inductance of the switch and to improve its working characteristics, the main electrode was designed as a circular track structure. Similarly, to increase the operation stability and reduce the self-breakdown probability, the trigger electrode was designed as a disk-like structure. Moreover, to balance the gas pressure in the discharge region and increase the stability during closure, a circular hole was added at the center of the trigger electrode. The compact switch has a small size of only 150 mm $\times42$ mm, a weight of 1.5 kg, and can be successfully operated at a voltage over 110 kV, at a repetition rate between 1 and 50 Hz and having a jitter of less than 4 ns. It was experimentally demonstrated that during normal operation conditions, the switch lifetime exceeds 100 000 shots.

Different Modes of Anion Response Cause Circulatory Phase Transfer of a Coordination Cage with Controlled Directionality.

Controlled directional transport of molecules is essential to complex natural systems, from cellular transport up to organismal circulatory systems. In contrast to these natural systems, synthetic systems that enable transport of molecules between several spatial locations on the macroscopic scale, when external stimuli are applied, remain to be explored. Now, the transfer of a supramolecular cage is reported with controlled directionality between three phases, based on a cage that responds reversibly in two distinct ways to different anions. Notably, circulatory phase transfer of the cage was demonstrated based on a system where the three layers of solvent are arranged within a circular track. The direction of circulation between solvent phases depended upon the order of addition of anions.

Different Modes of Anion Response Cause Circulatory Phase Transfer of a Coordination Cage with Controlled Directionality

AbstractControlled directional transport of molecules is essential to complex natural systems, from cellular transport up to organismal circulatory systems. In contrast to these natural systems, synthetic systems that enable transport of molecules between several spatial locations on the macroscopic scale, when external stimuli are applied, remain to be explored. Now, the transfer of a supramolecular cage is reported with controlled directionality between three phases, based on a cage that responds reversibly in two distinct ways to different anions. Notably, circulatory phase transfer of the cage was demonstrated based on a system where the three layers of solvent are arranged within a circular track. The direction of circulation between solvent phases depended upon the order of addition of anions.

Experimental Study of Laser Texturing Processes on the Lubricant Retention of Carbide (WC-Co) Surfaces

Machining process usually involves relevant wear effects on the cutting tool, producing undesirable surface features on the work-pieces. Lubricants and cooling fluids are used with the aim to minimize the wear phenomena as well as high temperatures produced during the cutting processes. However, the use of these fluids may have an adverse environmental impact. For this reason, the reduction of quantity of cutting fluids used in the machining process is a requirement in order to improve the performance and sustainability of the process. For this purpose, this work proposes an increase of the lubricant retention ability for cutting tools based on surface modification. In this research, micro-geometrical features of Carbide (WC-Co) surfaces have been modified by laser texturing techniques. A wide range of roughness topographies had been developed by changing the laser irradiation parameters of energy density of pulse (Ed) and scanning speed of the beam (Vs). Different geometries of the textured tracks (single spots, linear tracks, circular tracks) also were studied. Moreover, through specific roughness features conducted by texturing process, the retention ability of cutting fluids was modified. It was evaluated by the contact angle between liquid and solid phases. This modification allowed to increase the self-lubricant effect of the WC-Co surface. This methodology has been validated on carbide tools under lubricated machining processes. Wear effects on the cutting tool were reduced and the surface finish of the machined parts was remained at least in the same ranges as non-modified tools.

Range-Doppler Based CFAR Ship Detection with Automatic Training Data Selection

Ship detection is an essential maritime security requirement. Current state-of-the-art synthetic aperture radar (SAR) based ship detection methods employ fully focused images. The time-consuming processing efforts required to generate these images make them generally unsuitable for real time applications. This paper proposes a novel real time oriented ship detection strategy applicable to range-compressed (RC) radar data acquired by an airborne radar sensor during linear, circular and arbitrary flight tracks. A constant false alarm rate (CFAR) detection threshold is computed in the range-Doppler domain using suitable distribution functions. Detection in range-Doppler has the advantage that principally even small ships with a low radar cross section (RCS) can be detected if they are moving fast enough so that the ship signals are shifted to the exo-clutter region. In order to determine a robust threshold, the ocean statistics have to be described accurately. Bright target peaks in the background ocean data bias the statistics and lead to an erroneous threshold. Therefore, an automatic ocean training data extraction procedure is proposed in the paper. It includes (1) a novel target pre-detection module that removes the bright peaks from the data already in time domain, (2) clutter normalization in the Doppler domain using the remaining samples, (3) ocean statistics estimation and (4) threshold computation. Various sea clutter models are investigated and analyzed in the paper for finding the most suitable models for the RC data. The robustness and applicability of the proposed method is validated using real linearly and circularly acquired radar data from DLR’s (Deutsches Zentrum für Luft- und Raumfahrt) airborne F-SAR system.

Analysis and prediction of high‐speed train wheel wear based on SIMPACK and backpropagation neural networks

AbstractAs train running speeds increase, the wheel–rail interactions of high‐speed trains are becoming more complicated, and predicting and monitoring wheel wear are becoming increasingly important for the safe operation of high‐speed trains. Therefore, identifying the critical factors that affect the wear of wheel–rail interactions and developing novel methods to predict wheel wear are of great importance. In this work, SIMPACK is used to establish a dynamic model of a high‐speed train and to investigate the normal and lateral contact forces of the wheel–rail interfaces and the wear of the wheels for a train passing through a specially designed route that consists of straight‐line, smooth‐curved, and circular tracks. The wheel wear is predicted by means of the Archard wear model based on the SIMPACK analysis, and the wear is validated by a backpropagation neural network (BPNN) classification based on daily measured data provided by the Beijing Railway Administration. The results from the SIMPACK dynamic simulation and the BPNN classification show that the position of a wheel in a bogie has a significant effect on the wheel wear, but the position of a carriage in a train does not have a significant effect on the wheel wear. The findings from this study are very useful for the maintenance and safe operation of high‐speed trains.

Characterization and control of a bottleneck-induced traffic-jam transition for self-propelled particles in a track.

A collection of self-propelled elongated particles is circulating in a circular track. Due to the presence of a bottleneck, the flow transits to a congested state for a sufficient number of particles, even if the whole track is not saturated. Both experiments and simulations are used to identify the transition toward congestion. An intermediate regime of coexistence is characterized by intermittency between a free flow state and a jammed state. The range of the coexistence region is found to depend explicitly on fluctuating quantities such as the distribution of the escape times from a jam and the headway time distribution between free particles. Optimization strategies, such as the "slower is faster" effect, are tested in experiments and simulations, and an increase in the traffic performances is reported.