Centroid Fluctuation Research Articles

Experimental study on the flash boiling spray characteristics and jet fluctuation of high-pressure direct injection liquid ammonia

The high-temperature environment of actual engines significantly influences the characteristics of high-pressure liquid ammonia flash boiling spray and leads to jet instability. Therefore, this study investigated the influence mechanisms of different ambient temperatures on the high-pressure liquid ammonia flash boiling spray characteristics in a constant volume chamber. Simultaneously, it conducted the first exploration of the fluctuation characteristics of liquid ammonia jets, laying a foundation for achieving the stable and efficient combustion. The results indicate that the spray exhibits a three-stage axial development process at different ambient temperatures and ambient pressures, and the non-dimensional empirical formulas for describing the different stages of ammonia were proposed. In high-temperature conditions, the spray area is subject to the synergistic effects of flash boiling and evaporation. During the early stages, the spray development is dominated by flash boiling, leading to a rapid increase in the change rate of the spray area. However, during the later stages, the spray development is dominated by high-temperature evaporation, resulting in a rapid decrease in the change rate of spray area. Therefore, with increasing ambient temperature, the spray area experiences a significant reduction during the later stages. Through an analysis of spray centroid fluctuations at different ambient temperatures, it is evident that with rising ambient temperature, thermal disturbances intensify, leading to an increase in the oscillations deviation of the near-nozzle local region, and the maximum growth rate reaches 59.16%. Regarding different flash boiling stages, the spray centroid fluctuation is more stable during the transition flash boiling stage, with oscillation deviations below 0.02 at all ambient temperatures.

High–Speed Laser Modulation for Low–Noise Micro–Cantilever Array Deflection Measurement

In this paper, an innovative approach is introduced to address the noise issues associated with micro–cantilever array deflection measurement systems employing multiple lasers. Conventional systems are affected by laser mode hopping during switching, resulting in wavelength instability and beam spot fluctuations that take several hundred milliseconds to stabilize. To mitigate these limitations, a high–speed laser modulation technique is utilized, leveraging the averaging effect over multiple modulation cycles within the sampling window. By driving the lasers with a high–frequency carrier signal, a low–noise and stable output suitable for micro–cantilever beam deflection measurement is achieved. The effectiveness of this approach is demonstrated by simultaneously modulating the lasers and rapidly observing the spectral and centroid variations during high–speed switching using a custom–built high–speed spectrometer. The centroid fluctuations are also analyzed under different modulation frequencies. The experimental results confirm that the high–speed modulation method can reduce the standard deviation of beam spot fluctuations by more than 90%, leading to significant improvements in noise reduction compared to traditional laser switching methods. The proposed high–speed laser modulation approach offers a promising solution for enhancing the precision and stability of multi–laser micro–cantilever array deflection measurement systems.

Integrated Wheel–Foot–Arm Design of a Mobile Platform With Linkage Mechanisms

Abstract Inspired by lizards, a novel mobile platform with revolving linkage legs is proposed. The platform consists of four six-bar bipedal modules, and it is designed for heavy transportation on unstructured terrain. The platform possesses smooth-wheeled locomotion and obstacle-adaptive legged locomotion to enhance maneuverability. The kinematics of the six-bar bipedal modules is analyzed using the vector loop method, subsequently ascertaining the drive scheme. The foot trajectory compensation curve is generated using the fixed-axis rotation contour algorithm, which effectively reduces the centroid fluctuation and enables seamless switching between wheels and legs. When encountering obstacles, the revolving linkage legs act as climbing arms, facilitating seamless integration of wheel, foot, and arm. A physical prototype is developed to test the platform on three typical terrains: flat terrain, slope, and vertical obstacle. The experimental results demonstrated the feasibility of the platform structure. The platform can climb obstacles higher than its own height without adding extra actuation.

Involute-arc-leg for Multi-legged Robot: High Stability and Low Energy Consumption

A novel involute-arc-leg (IAL) which could be applied to multi-legged robots has been presented in this paper. The IAL is composed of the involute-segment and arc-segment. Compared with the common curved leg, the IAL has two advantages: Firstly, the centroid fluctuation and body capsizing can be reduced to improve motion stability; secondly, the torque can be decreased to reduce the energy consumption. With these characteristics, the robot can achieve more efficient and stable motion. Multi-legged robots which are useful for carrying curved legs have been developed, and the stability and energy consumption of the robot with different curved legs have been compared. As verified by experiments, the centroid fluctuation and attitude angle of Quadruped Robot can be reduced to zero with IAL, comparing to arc-legs, in which the energy consumption in standing and walking phase is decreased by 14.1% and 28.71%, respectively. The results prove that the motion stability and energy efficiency of robot can be improved with the curved leg design method based on splicing involute and arc, which provides a useful reference for the design of other robots.

Identity authentication based on keystroke dynamics for mobile device users

• A valid user modeling method which combines stable centroids and centroid fluctuation ranges. • A data cleaning algorithm in order to remove abnormal data. • A fixed centroid clustering algorithm by using the stable cluster centroids as the initial centroids. • An authentication method based on fluctuation ranges of centroid positions. User authentication of mobile devices is an important means to protect data security and user privacy. Low overhead, high accuracy and continuous authentication are challenging problems in user authentication. Aiming at the disadvantages of current authentication methods based on keystroke dynamics such as low accuracy and one-time authentication, this paper proposes a new authentication method named UIKI (User Identity authentication method based on clusters of Keystroke time Intervals). UIKI consists of the valid user modeling phase and the runtime user authentication phase. In the valid user modeling phase, UIKI uses a clustering algorithm to find the stable centroids and the fluctuation range of a valid user's centroid positions. In the runtime user authentication phase, UIKI clusters the data to be authenticated with the stable centroids as the initial centroids, and compares the results of clustering with the stable centroids and the centroid fluctuation range of the valid user to determine whether the input data are from the valid user. Experimental results prove that UIKI has the average FAR (False Accept Rate) of 0.082 and the average FRR (False Reject Rate) of 0.052, which can effectively authenticate a user's identity. UIKI has the advantages of high accuracy, low overhead and continuous authentication, which is suitable for the user authentication of mobile devices.

Planning and Analysis of Centroid Fluctuation Gait for Hydraulic Hexapod Robot[−2pt

Energy consumption is an important comprehensive index of the hydraulic hexapod robot (HHR). In this paper, the kinematics model and the hydraulic system energy consumption model of HHR are established. In order to reduce the energy consumption, a centroid fluctuation gait that adds the movement of the centroid in the vertical direction is proposed. Then the gait parameters such as step length, gait cycle, average centroid height, centroid fluctuation height, and phase that influence the energy consumption are studied which could provide a theoretical basis for parameter optimization. In the same gait parameters, compared with using constant height gait, the energy consumption of HHR using centroid fluctuation gait is generally reduced, and the maximum energy saving can be more than 10%. Finally, a virtual prototype is used to verify the effectiveness of the proposed methods.

Comfortability and Centroid Fluctuation of Wheelchair Users during Movements

Comfortability and Centroid Fluctuation of Wheelchair Users during Movements

Property of a CZT Semiconductor Detector for Radionuclide Identification

Compound semiconductors of high Z value material have been studied intensively for X-ray and γ -ray spectroscopy at room temperature. CdZnTe has wide band gap energy as 1.6 eV and can provide high quantum efficiency with reasonably good energy resolution at room temperature. This study is aimed at determining radionuclide analysis ability by measuring energy resolution of CZT detector which will be applied at nuclear material identification purpose. For experiment we used a CZT detector (5 × 5 × 5 mm3) which is manufactured by eV Products. We have performed our measurement at varied temperatures similar to the outdoor environment for the investigation about temperature dependence of energy resolution and peak centroid fluctuation of CZT detector by using gas cooling and Peltier cooling methods. In order to test radionuclide identification we used various radionuclide samples; plutonium, europium and other standard sources. Pulse height spectra were obtained by standard electronics which consists of a preamplifier, a shaping amplifier, and a multi-channel analyzer.

Modification of Projected Velocity Power Spectra by Density Inhomogeneities in Compressible Supersonic Turbulence

The scaling of velocity fluctuation ?v as a function of spatial scale L in molecular clouds can be measured from size-line width relations, principal component analysis, or line centroid variation. Differing values of the power-law index of the scaling relation ?v21/2 L in three dimensions are given by these different methods: the first two give ?3D 0.5, while line centroid analysis gives ?3D 0. This discrepancy has previously not been fully appreciated, as the variation of projected velocity line centroid fluctuations (?v1/2 L) is indeed described, in two dimensions, by ?2D ? 0.5. However, if projection smoothing is accounted for, this implies, in three dimensions, that ?3D ? 0. We suggest that a resolution of this discrepancy can be achieved by accounting for the effect of density inhomogeneity on the observed ?2D obtained from velocity line centroid analysis. Numerical simulations of compressible turbulence are used to show that the effect of density inhomogeneity statistically, but not identically, reverses the effect of projection smoothing in the case of driven turbulence, so that velocity line centroid analysis does indeed predict that ?2D ? ?3D ? 0.5. For decaying turbulence, the effect of density inhomogeneity on the velocity line centroids diminishes with time so that at late times, ?2D ? ?3D + 0.5 as a result of projection smoothing alone. Deprojecting the observed line centroid statistics thus requires some knowledge of the state of the flow. This information can be inferred from the spectral slope of the column density power spectrum and a measure of the standard deviation in column density relative to the mean. Using our numerical results, we can restore consistency between line centroid analysis, principal component analysis, and size-line width relations, and we derive ?3D ? 0.5, corresponding to shock-dominated (Burgers) turbulence, which also describes the simulations of driven turbulence at scales on which numerical dissipation is negligible. We find that this consistency requires that molecular clouds are continually driven on large scales or are only recently formed.

Velocity Field Statistics in Star‐forming Regions. I. Centroid Velocity Observations

The probability density functions (pdfs) of molecular line centroid velocity fluctuations, and of line centroid velocity fluctuation differences at different spatial lags, are estimated for several nearby molecular clouds with active internal star formation. The data consist of over 75,000 13CO line profiles divided among 12 spatially and/or kinematically distinct regions. These regions range in size from less than 1 to more than 40 pc and are all substantially supersonic, with centroid fluctuation Mach numbers ranging from about 1.5 to 7. The centroid pdfs are constructed using three different types of estimators. Although three regions (all in Mon R2) exhibit nearly Gaussian centroid pdfs, the other regions show strong evidence for non-Gaussian pdfs, often nearly exponential, with possible evidence for power-law contributions in the far tails. Evidence for nearly exponential centroid pdfs in the neutral H I component of the interstellar medium is also presented, based on older published data for optical absorption lines and H I emission and absorption lines. These strongly non-Gaussian pdfs disagree with the nearly Gaussian behavior found for incompressible turbulence (except possibly shear flow turbulence) and simulations of decaying mildly supersonic turbulence. Spatial images of the largest magnitude centroid velocity differences for the star-forming regions appear less filamentary than predicted by decay simulations dominated by vortical interactions. No evidence for the scaling of difference pdf kurtosis with Reynolds number, as found in incompressible turbulence experiments and simulations, is found. We conclude that turbulence in both star-forming molecular clouds and diffuse H I regions involves physical processes that are not adequately captured by incompressible turbulence or by mildly supersonic decay simulations. The variation with lag of the variance and kurtosis of the difference pdfs is presented as a constraint on future simulations, and we evaluate and discuss the implications of the large scale and Taylor scale Reynolds numbers for the regions studied here.

High-resolution HCO+ and HCN observations of M17SW: clumps, turbulence and cloud support

The M17SW molecular cloud core has been mapped with a linear resolution of 0.2 pc in the J=3→2 lines of HCO + and HCN, using the JCMT. The HCO + and HCN maps are very similar in large-scale structure, with both molecules tracing the clumpy nature of the cloud core, but a detailed comparison reveals an anticorrelation of these clumps indicative of the different excitation of the two molecules. Analysis of the intensity distributions, using power spectrum and autocorrelation function techniques, indicates the presence of structure in both lines, on all scales down to the resolution limit of the telescope. The ACF of the velocity centroid fluctuations closely reproduces the ACF of turbulent gas motions in the cloud and reveals a correlation length ≤0.25 pc. The turbulent pressure and maximum energy dissipation rate are derived as functions of scalesize, and the relationship is markedly different from that assumed in standard turbulent cascade models

Centroid fluctuations of speckled targets

We present a statistical description of the centroid fluctuations of imaged targets under coherent illumination. We derive analytic expressions that take into account the illumination and imaging geometries. The fluctuations are shown to be insensitive to linear filtering and constitute a physical limitation to remote sensing devices making use of lasers.

X-ray position detection in the region of 6 μm RMS with wire proportional chambers

We have developed a MWPC system for X-ray detection with a position resolution in the region of 6 μm rms (14 μm fwhm). The performance with argon, krypton or xenon at pressures from 1 to 10 atm is explored for the X-ray energy range 5–25 keV. At a resolution of 6 μm rms the effects of photoelectron and Auger electron range, electronic noise, avalanche spread, lateral electron diffusion, as well as X-ray beam collimation, become of comparable magnitude. Their limiting effects on avalanche centroid fluctuation, and hence on position resolution, are investigated. The position resolution achieved in this work compares favorably with that of solid state devices.

Large-scale structure of the Taurus molecular complex. II - Analysis of velocity fluctuations and turbulence. III - Methods for turbulence

The velocity autocorrelation function (ACF) of observed spectral line centroid fluctuations is noted to effectively reproduce the actual ACF of turbulent gas motions within an interstellar cloud, thereby furnishing a framework for the study of the large scale velocity structure of the Taurus dark cloud complex traced by the present C-13O J = 1-0 observations of this region. The results obtained are discussed in the context of recent suggestions that widely observed correlations between molecular cloud widths and cloud sizes indicate the presence of a continuum of turbulent motions within the dense interstellar medium. Attention is then given to a method for the quantitative study of these turbulent motions, involving the mapping of a source in an optically thin spectral line and studying the spatial correlation properties of the resulting velocity centroid map. 61 references.