Velocity Changing Research Articles

Magnetometer-only attitude and angular velocity filtering estimation for attitude changing spacecraft

This paper presents an improved real-time sequential filter (IRTSF) for magnetometer-only attitude and angular velocity estimation of spacecraft during its attitude changing (including fast and large angular attitude maneuver, rapidly spinning or uncontrolled tumble). In this new magnetometer-only attitude determination technique, both attitude dynamics equation and first time derivative of measured magnetic field vector are directly leaded into filtering equations based on the traditional single vector attitude determination method of gyroless and real-time sequential filter (RTSF) of magnetometer-only attitude estimation. The process noise model of IRTSF includes attitude kinematics and dynamics equations, and its measurement model consists of magnetic field vector and its first time derivative. The observability of IRTSF for small or large angular velocity changing spacecraft is evaluated by an improved Lie-Differentiation, and the degrees of observability of IRTSF for different initial estimation errors are analyzed by the condition number and a solved covariance matrix. Numerical simulation results indicate that: (1) the attitude and angular velocity of spacecraft can be estimated with sufficient accuracy using IRTSF from magnetometer-only data; (2) compared with that of RTSF, the estimation accuracies and observability degrees of attitude and angular velocity using IRTSF from magnetometer-only data are both improved; and (3) universality: the IRTSF of magnetometer-only attitude and angular velocity estimation is observable for any different initial state estimation error vector.

Influences of Fracture Angle on the Ultrasonic Compressional Wave Velocity

In this article, we prepare the physical model with the high density epoxy resin and different sizes of coin shaped silicone pieces which can simulate the directional arrangement of fracture medium. On the basis of this, we analyze the influences of fracture angle on the ultrasonic compressional wave velocity using the pulse transmission method and compare the experimental results with the Hudson effective medium model. The experimental results show that, velocity decreases linearly with the increase of fracture angle within the interval of [0°~90°]. In a similar aspect ratio and same angle case, the increase of fracture porosity will result in the decrease of the velocity which is weakened by the increase of fracture porosity. At high fracture porosity, fracture angle becomes the important influence factor on the velocity changing. The calculation results of the Hudson model have a small deviation which is less than 5% compared with the experimental results but show a difference in different angle interval. The combination of the two methods will provide a certain basis for the indoor experiment and the measurement of the velocity in field.

Ultrasonic tissue characterization of skin tissue using doublet mechanics method

Doublet mechanics (DM) is applied to materials with dispersing property. The wave equation in multi-layered skin tissue is obtained through the method of DM in this article. By changing the Poisson ratio in melanoma skin tissue, the growth and spread of melanoma (Breslow thickness), the internode distance, the reflection coefficients of the longitudinal waves incident vertically in the multi-layered skin model are calculated. And the acoustic velocity and acoustic attenuation coefficient changing with tissue parameters are also calculated. The results show that we can synthesize the change of the number of the minimal reflection coefficient, acoustic velocity and attenuation coefficient to discriminate cancerous skin from normal skin within a certain frequency.

Left-Turning Vehicle Trajectory Modeling and Guide Line Setting at the Intersection

When left-turning vehicles are released from the multiple left-turning lanes at the signalized intersection, there will be conflicts among them, and the conflicts will affect the traffic operation and safety. In order to solve the problem, by extracting running trajectories of left-turning vehicles and analyzing distribution characteristics of trajectories, velocity changing characteristics, and flow changing characteristics, the left-turning vehicle’s trajectory model was established. On the basis of the above research, taking an example of quadruple left-turning lanes, the idea of setting left-turning guide line at the intersection was proposed. Through instance verification, we could get the conclusion that the method of using left-turning guide line to control vehicles’ turning process can effectively reduce traffic conflicts and delay and improve traffic efficiency.

Motion in depth cued by chromatic interocular velocity differences and changing disparity

Motion in depth cued by chromatic interocular velocity differences and changing disparity

An Investigation of Compressible Turbulent Forced Convection by an Implicit Turbulence Model for Large Eddy Simulation

An investigation of compressible turbulent forced convection in a three-dimensional channel flow is studied numerically by an implicit turbulence model for large eddy simulation (LES). Because of a high temperature difference between two walls and turbulent flow, the compressibility and viscosity of fluid should be taken into consideration simultaneously. Methods of the Roe scheme, preconditioning, and dual time stepping coordinating an implicit turbulence model for LES are used for resolving the effect of the compressibility of fluid on a low speed flow field. The magnitudes of Re τ based on the friction velocity changing from 180 to 940, with the high temperature difference of two walls of 500 k are conducted. The results of the mean velocity profiles and turbulent intensities are in good agreement with the benchmark DNS data obtained by spectral codes from a low Reynolds number (Re τ = 180) to a high Reynolds number (Re τ = 940). Besides, the larger the Re τ is, with the exception of acquirement of larger average Nusselt number, the more drastic variation of local instantaneous Nusselt number is observed.

Gait Transition of Quadruped Robot Using Time Sequence Control Based on Finite-State Machine

The adaptability of velocity changing of quadruped robot needs to be realized by gait transition. In this paper, a gait transition method of a quadruped robot based on changing the time sequence was investigated. The swing phase and the stance phase are separated by finite-state machine (FSM), and the locomotion gait involves breaking/enforcing synchronization or changing the order of leg liftoff events, it makes the duration time of liftoff and touchdown events variable. The gait transition from walk to trot is realized by the combination driving of time and event. The experiment is verified by interactive co-simulation among Matlab-Adams. The transition method satisfies the velocity changing of quadruped robot.

STEM TEMPERATURE INFLUENCE ON HEAT PULSE SAP FLUX DENSITY MEASUREMENTS

While natural temperature gradients between measurement needles have been thoroughly investigated for continuous heat based sap flow methods, the natural changes in stem temperature because of varying ambient temperature and radiation have, with exception of the Sapflow+ method, so far never been mentioned as a possible error-inducing factor for heat pulse based methods. By modelling both the theoretical equation for an ideal instantaneous and step pulse and applying a finite element model including actual needle dimensions and wound effects, the influence of varying stem temperature on heat pulse based methods was investigated. It was shown that the Heat Ratio method was clearly influenced, while for the Heat Pulse Velocity and Tmax method changing stem temperatures did not lead to significantly different results. For the Heat Ratio method, rising stem temperatures during measurements led to lower heat velocity values while descending stem temperatures led to higher heat velocities and highly erroneous or even imaginary results for high flows. These errors can, fortunately, easily be prevented by including a temperature correction in the data analysis procedure, calculating the slope of the natural temperature change based on the measured temperatures before application of the heat pulse. Results of a greenhouse and outside experiment show the influence of this correction for low and average sap flux densities.

Evidence for speed sensitivity to motion in depth from binocular cues

Motion in depth can be perceived from binocular cues alone, yet it is unclear whether these cues support speed sensitivity in the absence of the monocular cues that normally co-occur in natural viewing. We measure threshold contours in space-time for the discrimination of three-dimensional (3D) motion to determine whether observers use speed to discriminate a test 3D motion from two identical standards. We compare thresholds for random-dot stereograms (RDS) containing both binocular cues to 3D motion-interocular velocity difference and changing disparity over time-with performance for dynamic random-dot stereograms (DRDS), which contain only the second cue. Threshold contours are tilted along the axis of constant velocity in space-time for RDS stimuli at slow speeds (0.5 m/s), evidence for speed sensitivity. However, for higher speeds (1.5 m/s) and DRDS stimuli, observers rely on the component cues of duration and disparity. In a second experiment, noise of constant velocity is added to the standards to degrade the reliability of these separate components. Again there is evidence for speed tuning for RDS, but not for DRDS. Considerable variation is observed in the ability of individual observers to use the different cues in both experiments, however, in general the results emphasize the importance of interocular velocity difference as a critical cue for speed sensitivity to motion in depth, and suggest that speed sensitivity to stereomotion from binocular cues is restricted to relatively slow speeds.

Straight or curved? From deterministic to probabilistic models of 3D motion perception

Straight or curved? From deterministic to probabilistic models of 3D motion perception

Motion in depth cued by chromatic interocular velocity differences and changing disparity

Motion in depth cued by chromatic interocular velocity differences and changing disparity

Coulomb Broadening of Resonance Induced by Standing Wave

Coherent preparation of quantum states of atoms and ions by laser light can lead to electromagnetically induced transparency and related effects. In particular, the standing wave at the adjacent transition induces a new type of nonlinear resonance in the probe-field spectrum of a three-level system. The resonance is due to the effect of high-order harmonics of atomic coherence. However, the resonance is broadened and the reason of the broadening was unclear. The paper describes how the velocity changing collisions broaden the resonance. The analytic theory taking into account up to 4-th order of the perturbation theory is presented. The numerical calculations are described. The analytical formulas are shown to describe the experiment qualitatively while the numerical computation demonstrates quantitative agreement. The Coulomb dephasing is discussed as the physical mechanism of the broadening.

Mathematical model and computer simulation of end-inspiratory plateau ventilation

Objective To establish the mathematical model for ventilation of the physical process of end-inspiratory plateau (EIP) and identify the computer simulation. Methods The physical process of EIP was divided into inspiratory phase,EIP phase,expiratory phase and end-expiratory phase,which was analyzed to deduce mathematical functions by hydromechanics theory.Computer simulation was carried out on the mathematical model and the simulated curves were compared with those of clinical monitoring. Results The mathematical functions and simulated curves of the flow velocity (v),flow rate (Q),pulmonary volume (Vt),alveolar pressure (PA) and airway pressure (Paw) changing along with the time (t) during the mechanical ventilation process have been obtained.The simulated curves were similar to the working curves from clinical monitoring.Conclusions The mathematical model for ventilation of physical process of EIP was established successfully and the computer simulation can reproduce the clinical working curves of some kinds of ventilators. Key words: End-inspiratory plateau; Mechanical ventilation; Mathematical model; Computer simulation

Three dimensional model of the interplanetary magnetic field and 27-day variation of the galactic cosmic ray intensity

We present a model of the 27-day variation of the galactic cosmic ray (GCR) intensity for three dimensional (3-D) heliosphere with the heliolongitudinal and heliolati- tudinal dependent radial solar wind speed for the period of 1995 - minimum epoch of solar activity (A > 0). In the present model we implement heliolongitudinal asymmetry of solar wind velocity reproducing as the sum of first and sec- ond harmonics depending on the heliolatitudes and the reg- ular part of the solar wind velocity (V0) changing versus he- liolatitudes in accord to in situ measurements of the Ulysses spacecraft. We show that the range of changes of the sum of the first and second harmonics of the 27-day variation of the GCR intensity for Kiel neutron monitor is little less than expected from the modelling, however, they are comparable. equations with the heliolongitudinally dependent solar wind velocity reproducing in situ observations. In spite, in situ measurements are an unique information which should be considered as a basic data in any type of modelling. This paper is a continuation of study presented in Alania et al. (2010) tending to construct a 3-D model of the 27-day vari- ation of the GCR intensity being able in certain scope to

Video-based measurement and data analysis of traffic flow on urban expressways

A new video-based measurement is proposed to collect and investigate traffic flow parameters. The output of the measurement is velocity-headway distance data pairs. Because density can be directly acquired by the reciprocal of headway distance, the data pairs have the advantage of better simultaneity than those from common detectors. By now, over 33 000 pairs of data have been collected from two road sections in the cities of Shanghai and Zhengzhou. Through analyzing the video files recording traffic movements on urban expressways, the following issues are studied: laws of vehicle velocity changing with headway distance, proportions of different driving behaviors in the traffic system, and characteristics of traffic flow in snowy days. The results show that the real road traffic is very complex, and factors such as location and climate need to be taken into consideration in the formation of traffic flow models.

Isolation of Binocular Cues for Motion in Depth

There are two binocular cues of motion in depth: the interocular velocity difference (IOVD) and changing disparity over time (CDOT). Psychophysical evidence for the contribution to perceiving motion in depth has been accumulated for both of the two cues, using techniques to isolate each cue. However, no study estimated seriously how reliably each cue is isolated in the techniques. In this study, we apply a model of motion in depth to estimate how each type of stimuli isolates each of IOVD and CDOT cues. The model consists of the motion energy and the disparity energy detectors as subunits and adds their outputs to built the IOVD and CDOT detectors. Simulations show that some, but not all of stimuli used in the literature are appropriate for isolating cues. The temporally uncorrelated randomdot stereogram isolates CDOT cue and the binocularly uncorrelated randomdot kinematogram isolates IOVD cues. However, temporally anticorreated version of randomdot stereogram has influence of reverse motion components of IOVD and binocularly anticorreated version of randomdot kinematogram has influence of reverse motion components of CDOT. Gratings with opposite orientation between the eyes are also good for isolation of IOVD. We performed psychophysical experiments to examine the plausibility of the model prediction.

Velocity changing collisions in the laser saturation spectra of 87Rb D 2 F″ = 2

The saturation absorption technique is applied to the 87Rb 2S 1/2 F″ = 2 → 2P 3/2 F′ = 1, 2 and 3 transitions to study the effect of velocity changing collisions (VCC). The VCC caused Doppler pedestal increases with argon pressure from 0 to 110 mTorr and decreases with modulation frequencies of 700–3200 Hz. The resonances of the velocity selective, saturated optical pumping are washed out for pressure of 110 mTorr. The magnitude of the Doppler pedestal relative to the homogeneous features, yields a rate for velocity changing collisions of 6.5 ± 0.2 × 10 −10 cm 3 s −1.

A Collisional-Radiative Model for Hydrogen Atom Including Velocity Changing Collisions

We develop a collisional-radiative model for calculating the velocity distributions of excited hydrogen atoms. In the model, the velocity distributions are approximated using linear combinations of several basis functions which are treated as discrete velocity states, and only charge exchange collisions with proton are considered as velocity changing collisions. The populations in the velocity and excited states are calculated under an assumption of a quasi-stationary state. With the model we derive the velocity distribution of the ground state atoms from that of excited atoms in the n = 3 level observed for an LHD plasma, where n is the principal quantum number. The mean kinetic energy of the ground state atoms is estimated to be 5.6 eV, which is 0.05 eV less than that of the n = 3 atoms.

Experimental study on horizontal wellbore cleanout by rotating jets

Horizontal wellbore cleanout by rotating jets has been developed rapidly in the past decades. To improve the sand cleanout efficiency, the strength of helical flow as one of the most important factors is necessary to be investigated and optimized. The flow rate, nozzle size, nozzle orientation and annular size have the major influence on the arising, performing and attenuating of annular helical flow. This paper presents the experimental results of a horizontal wellbore cleanout with varying nozzle assemblies in orifice size and orientation, tubing size, solid size, and flow rate. The tests of stationary circulation and wiper trip were carried out respectively. In the stationary circulation stage, there exists a critical length between sand bed and cleaning tool which results the two kinds of mechanisms to transport the sand. When the distance is shorter than the critical length, the primary mechanism of sand suspend is annular helical flow. As the distance is longer than it, the mechanism turns into straight annular flow which results in lower cleanout efficiency. In this study, the critical length increases rapidly with the increase of flow rate, tubing size and sand size. The sand bed moving velocity changing with the distance was also investigated and it is beneficial to optimize the wiper trip speed of cleaning tool. For the wiper trip stage, there exists the maximum wiper speed which can fulfill the requirement of completely sand cleanout when the tool is pulled out of the hole(POOTH), and it increases with the increase of flow rate and tubing size, and the decrease of sand size. The nozzle assembly is one of the most important factors to affect the helical flow profile and sand cleanout efficiency. The optimum lateral nozzle size and nozzle orientation were also obtained to get a best performance in annular helical flow and wiper trip speed. This study can contribute to the optimum design of nozzle assemblies, operation procedures and hydraulic parameters so that the highest efficiency of horizontal wellbore cleanout can be achieved.

An investigation of collisional processes in a Dicke narrowed transition of water vapor in the 7.8 μm spectral region by frequency down-chirped quantum cascade laser spectroscopy

Information about intermolecular potentials is usually obtained through the analysis of the absorption line shapes recorded in the frequency domain. This approach is also adopted to study the effects of motional narrowing and speed dependence of the pressure broadening coefficients. On the other hand, time domain measurements are directly related to molecular collisions and are therefore frequently employed to study molecular relaxation rates, as well as the effects of velocity changing collisions and the speed dependence of the absorption cross sections. Intrapulse quantum cascade laser spectrometers are able to produce both saturation and molecular alignment of the gas sample. This is due to the rapid sweep of the radiation through the absorption features. In the present work the frequency down-chirped radiation emitted by an intrapulsed quantum cascade laser operating near 7.8 mum is employed to investigate the collisional relaxation processes, and the collisional narrowing, in the 15(0,15)<--16(1,16) and 15(1,15)<--16(0,16) doublet in the water vapor nu(2) band. The effects of He, Ne, Ar, N(2), and CO(2) as collisional partners are investigated. The experimental results clearly indicate the dependence of the collisional cross sections upon the chirp rate. They also demonstrate that by using different chirp rates it is possible to gain information about the intermolecular processes driving the molecular collisions and the related energy transfer.