Time Delay Curve Research Articles

RAU-Net-Based Imaging Method for Spatial-Variant Correction and Denoising in Multiple-Input Multiple-Output Radar

The conventional back projection (BP) algorithm is an accurate time-domain algorithm widely used for multiple-input multiple-output (MIMO) radar imaging, owing to its independence of antenna array configuration. The time-delay curve correction back projection (TCC-BP) algorithm greatly reduces the computational complexity of BP but suffers from spatial-variant correction, sidelobe interference and background noise due to the use of coherent superposition of echo time-delay curves. In this article, a residual attention U-Net-based (RAU-Net) MIMO radar imaging method that adapts complex noisy scenarios with spatial variation and sidelobe interference is proposed. On the basis of the U-Net underlying structure, we develop the RAU-Net with two modules: a residual unit with identity mapping and a dual attention module to obtain resolution spatial-variant correction and denoising on real-world MIMO radar images. The network realizes MIMO radar imaging based on the TCC-BP algorithm and substantially reduces the total computational time of the BP algorithm on the basis of improving the imaging resolution and denoising capability. Extensive experiments on the simulated and measured data demonstrate that the proposed method outperforms both the traditional methods and learning-imaging methods in terms of spatial-variant correction, denoising and computational complexity.

Analytical, simulation, and experimental verification of ultrasonic thermometry technique

When an ultrasonic wave travels through a material, such as a rod, the propagation and reflection characteristics are a function of the medium properties. When a material is heated, its mechanical properties, density, and volume change with respect to the medium, and so does the speed of sound. By using ultrasonic waves, the difference in speed can be used to estimate the temperature of a solid material. This technique is known as ultrasonic thermometry. The central hypothesis is that the wave travels slower as the temperature increases. To explain the underlying scientific principles of the technique, we developed analytical methods for estimating the time delays associated with varying temperatures. Time delay curves were developed by repeating the procedure at various temperature values using the corresponding mechanical and thermal properties at those values. That is, young’s modulus, Poisson’s ratio, and the thermal expansion coefficient were considered based on the temperature values. Additionally, this study outlines a numerical study on the temperature dependence of ultrasonic waves propagating through a 304L stainless steel rod using COMSOL software. Numerical results concur with analytically derived estimations, showing a decrease in the wave propagation speed and the wave amplitude as the temperature changes between 20 °C, 100 °C, 300 °C, and 500 °C. The simulated time delays agree well with the analytical calculations, and the displacement–time curve shift occurs due to the mechanical properties and thermal expansion effect. To confirm the accuracy of the technique, additional experiments were conducted on physical samples of 304L stainless steel. However, the frequency was modified to 2.25 MHz to increase spectral resolution given the limited temperature range possible of 25 °C–130 °C. We conclude by indicating that, due to the high accuracy of the analytically derived equations, the equations and technique developed has the potential to be utilized for time delay curves of other metals, in addition to 304L stainless steel.

Trend in risk of delay in diagnosis of new pulmonary tuberculosis in Northwest China from 2008 to 2017

BackgroundWith great changes over the past 10 years in China, especially the rapid economic development, population mobility, urbanization and aging, dynamic change on risk of delay, to our knowledge, has not been well studied in China. The study was to explore risk of delay in diagnosis of new pulmonary tuberculosis (PTB) and dynamic changes in risk of delay in Northwest China.MethodsFrom January 1, 2008 to December 31, 2017, a total of 13,603 people with new PTB registered in Yulin city of Shaanxi province were included. The median delay time was estimated by Kaplan-Meier survival curve. Time delay curves of year-, gender-year-, age-year- and smear-year specific were examined using log-rank test. Two-level mixed-effects survival model was used to calculate the hazard ratio (HR) and 95% confidence interval (95%CI) for factors associated with diagnostic delay. Time delay was defined as time interval between the onset of PTB symptoms and being diagnosed. The outcome variable of interest was defined as “being diagnosed” in survival analysis.ResultsThe 10-year delay time was 33 days (Interquartile Range, 16–65). Annual median delay time gradually decreased from 60 days to 33 days during the past 10 years. The probability that individuals were diagnosed since onset of PTB symptoms increased by 1.29 times in 2017 when compared to 2008. Female (Hazard Ratio (HR), 95%CI, 0.95(0.91–0.99)), age>45 years (HR, 95%CI, 0.87(0.82–0.93)) and smear positive (HR, 95%CI, 0.86(0.78–0.95)) were associated with increased risk of diagnostic delay over 10-year timespan. However, Age>45 years and smear positive showed trend to be protective factors in the past 5 years.ConclusionsTime and risk of delay in diagnosis of new PTB had declined over the past 10 years. However, more attentions should be paid to the fact that female still suffered from higher risk of diagnostic delay. We noted a potential reversal in traditional risk factors such as age>45 and smear positive. Those dynamic changes deserved further attention.

SRP-PHAR Combined Velocity Scanning for Locating the Shallow Underground Acoustic Source

Shallow underground acoustic source localization is a component of near-field source localization, which is involved in numerous application fields. The positioning accuracy is mainly limited by the accuracy of time of arrival (TOA)/time difference of arrival (TDOA) extraction and velocity extraction from noisy data. The steered response power with phase transform (SRP-PHAT) is one of the most robustness and high-precision acoustic source localization approaches, which avoids extracting the TDOA in advance. But SRP-PHAT is constrained for only using under known velocity. Furthermore, it is barely possible for shallow underground sound source localization to easily obtain high-quality velocity models. This paper proposes an improved SRP-PHAT with unknown velocity (SRP-PHAT-UNVEL), which avoids extracting the TDOA and velocity in advance. SRP-PHAT-UNVEL matches the calculated time delay curve with the actual time delay curve by scanning of the candidate spatial position and the candidate velocity simultaneously, so as to maximize the output energy to fulfill the positioning. However, SRP-PHAT-UNVEL has larger computational complexity as it proceeds with the optimization of space and velocity. Since the spatial position and velocity affect the shape and the curvature of the calculated delay curve respectively, these are two relatively independent processes. Therefore, the simultaneous optimization of space and velocity can be replaced by a two-stage optimization to improve the efficiency and accuracy of SRP-PHAT-UNVEL. Spatial optimization is equivalent to the optimization of SRP-PHAT, and the spatial optimization of the bat algorithm has faster convergence rate and higher location precision than traditional methods. Velocity optimization can be achieved by the common linear search technique since the function of velocity and energy is an ideal convex function. Simulation experiment results show that the proposed method is insensitive to noise, which can achieve high accuracy of the acoustic source position and velocity simultaneously. With grouping the measured data, the proposed method can further improve the robustness and accuracy by fusing the grouping location results with principal component analysis.

Spectral properties of nonlinearly chirped fiber Bragg gratings for optical communications

Numerical investigation of spectral properties of nonlinearly chirped grating under strain is made. Calculation is performed using Matlab code based on solving the coupled mode equations using transfer matrix method. Our findings show that, by optimizing the linear and higher-order nonlinear chirp coefficients, the reflection bandwidth, side lobes, and group delay could be tunable with the increment of the applied tension. Indeed, the fiber grating chirp is tunable by the applied tension represented by the increase of the reflection spectrum bandwidth and the decrease of the group delay ripples. Besides, the time delay curve typically exhibits two behaviors within the rejection bandwidth: a linear variation for large wavelengths and a quadratic variation for short wavelengths. Therefore, with such kind of grating, it is possible to compensate both linear and nonlinear dispersion in high speed optical networks.

Time-delay Curve Detection and Target Depth Estimation in Ground Penetrating Radar Multi-layer Medium Detection

GPR is a useful tool in non-destructive evaluation area. Time delay curve detection and target depth estimation are two key steps in GPR data processing procedure, as they can provide accurate target depth information, especially in multi-layer medium detection scenario. Traditional methods for time-delay curve are applicable to homogeneous medium and ideal environments. This paper presents a new time-delay curve extracting approximation hyperbola algorithm (TDC-AH) and target depth algorithm. By applying auto-detecting edge points criterion in detection scenario, an approximation hyperbola equation can be established and target depth can be estimated subsequently. Simulating experiment proves the proposed algorithm is suitable for multi-layer medium.

Finding non-eclipsing binaries through pulsational phase modulation

We present a method for finding binaries among pulsating stars that were observed by the Kepler Mission. We use entire four-year light curves to accurately mea- sure the frequencies of the strongest pulsation modes, then track the pulsation phases at those frequencies in 10-d segments. This produces a series of time-delay measurements in which binarity is apparent as a periodic modulation whose amplitude gives the projected light travel time across the orbit. Fourier analysis of this time-delay curve provides the pa- rameters of the orbit, including the period, eccentricity, angle of ascending node and time of periastron passage. Differentiating the time-delay curve yields the full radial-velocity curve directly from the Kepler photometry, without the need for spectroscopy. We show examples with delta Scuti stars having large numbers of pulsation modes, including one system in which both components of the binary are pulsating. The method is straightfor- ward to automate, thus radial velocity curves can be derived for hundreds of non-eclipsing binary stars from Kepler photometry alone. This contribution is based largely upon the work by Murphy et al. [1], describing the phase-modulation method in detail.

A Multi-Scale Weighted Back Projection Imaging Technique for Ground Penetrating Radar Applications

In this paper, we propose a new ground penetrating radar (GPR) imaging technique based on multi-scale weighted back projection (BP) processing. Firstly, the whole imaging region is discretized by large scale and low-resolution imaging result is obtained by using traditional BP imaging technique. Secondly, the potential targets regions (PTR) are delineated from low-resolution imaging result by using intensity detection method. In the PTR, small scale discretization is implemented and higher resolution imaging result is obtained by using weighted BP imaging technique. A weight factor is designed by analyzing the statistical characteristics of scattering data on the time-delay curve. The above “discretization-imaging-PTR delineation” processing continues until the imaging resolution reaches the specified requirement. In the multi-scale imaging result, the resolution in other regions is not as high as that in PTR. This algorithm can get higher resolution imaging results with much lower computation compared with traditional BP imaging algorithm. The simulation of this algorithm is processed and experimental results validate the feasibility of this method.

Finding binaries among Kepler pulsating stars from phase modulation of their pulsations

We present a method for finding binaries among pulsating stars that were observed by the Kepler Mission. We use entire four-year light curves to accurately measure the frequencies of the strongest pulsation modes, then track the pulsation phases at those frequencies in 10-d segments. This produces a series of time-delay measurements in which binarity is apparent as a periodic modulation whose amplitude gives the projected light travel time across the orbit. Fourier analysis of this time-delay curve provides the parameters of the orbit, including the period, eccentricity, angle of ascending node and time of periastron passage. Differentiating the time-delay curve yields the full radial-velocity curve directly from the Kepler photometry, without the need for spectroscopy. We show examples with $\delta$ Scuti stars having large numbers of pulsation modes, including one system in which both components of the binary are pulsating. The method is straightforward to automate, thus radial velocity curves can be derived for hundreds of non-eclipsing binary stars from Kepler photometry alone.

Control Algorithms and Circuit of Interactive Mechanical Bionic Intelligent Robot

According to the mechanical simulation intelligent control theory, and combining the character interaction principle, the use of genetic algorithm carries out an in-depth analysis and research for the process of PC MCU automatic control, and then the control algorithm of interactive genetic is established, finally we design the VGA structure circuit. In order to validate the validity and reliability of the model and control circuit, this paper uses the medical micro robot as the research object to the experimental analysis for the delay control circuit, so the delay characteristic curve will be obtained. By the control of time delay curve, we can be seen that the scanning delay of controllable voltage can control delay in the range of 22ps-60ps, it meets the design standards, to provide the theory reference for the mechanical bionic intelligence automatic control research.

Through-Wall Shape Estimation Based on UWB-SP Radar

This letter presents a new method for localizing and identifying a target through walls with known wall parameters. A time-delay difference curve (TDDC) is utilized in this method for target localization and identification. The characteristic of the TDDC can be applied to estimate the incident angle and offset the influences in propagation path and propagation time delay brought from the wall. This letter analyzes the method and gives out the theoretical TDDC. Extensive simulations and experiments show the effectiveness of the proposed method.

An improved back projection imaging algorithm for subsurface target detection

An improved back projection imaging algorithm for subsurface target detection is presented in this paper. Firstly, the characteristic of the scattering data at each time-delay curve in the traditional back projection imaging procedure is analyzed. Secondly, a weight factor is designed for each focal point and an improved back projection imaging algorithm is presented. Thirdly, the simulation of the improved imaging algorithm is processed. The imaging results of both the simulation data and the real ground penetrating radar data show the effectiveness of this imaging algorithm.

Virtual Instrument Applied in Seismic Time Delay Signal Process

It is very important to do some preliminary analysis and processing of the time delay signal before the time delay estimation for the target orientation of the multi-sensor network. In this paper, a virtual instrument time delay analysis system is designed, which contains: a virtual oscilloscope, a virtual spectrum analyzer, a virtual filter and a virtual time delay analyzer. By the use of this analysis system, the spectrum of the seismic target signal collected in the field is analyzed. Analysis shows the main frequency of the target signal: 13Hz, 85Hz, 170Hz, 125Hz. Distinctness of the time delay peak is proposed to describe the validation of the cross-correlation result. Based on the three main frequency components, signals were filtered by five filters and analyzed separately. Results were shown in figures of time delay vs. time, distinctness vs. time. Each curve in a figure corresponds to a certain number of points of cross correlation. According to the results, the frequency component from 8Hz to 30Hz is much more suitable for practical use. The regular pattern of the time delay curve is consistent with the target motion. Application reveals that the system is helpful in the research of time delay estimation.

Self-excited oscillation under nonlinear feedback with time-delay

Several important applications use nonlinear feedback methods for synthetically inducing self-excited oscillations in mechanical systems. The van der Pol and saturation function type feedback methods are widely used. The effects of time-delay on the self-excited oscillation of single and two degrees-of-freedom systems under nonlinear feedback have been studied in this paper. It is shown that a single degree-of-freedom oscillator with the van der Pol type nonlinear feedback can produce unbounded response in presence of time-delay. In general, an uncontrolled time-delay in the feedback changes the state of oscillations in an uncertain manner. Therefore, a bounded saturation type feedback with controllable time-delay is proposed for inducing self-excited oscillations. The feedback signal is essentially an infinite weighted sum of a nonlinear function of the state variables of the system measured at equal intervals in the past. More recent is the measurement, higher is the weight. Thus, the feedback signal uses a large amount of information about the past history of the dynamics. Such a control signal can be realized in practice by a recursive means. The control law allows three parameters to be varied namely, the time-delay, feedback and recursive gains. Multiple time scale analysis is used to plot amplitude vs. time-delay curves. Time-delay can be controlled to vary the amplitude of oscillation as well as to switch the oscillation from one mode to the other in a two degrees-of-freedom system. It is shown that a higher recursive gain can exercise a better and a more robust control on the amplitude of oscillation of the system. Analytical results are compared with the results of numerical simulations.

Application of Virtual Instrument in Time Delay Signal Analysis

Time delay estimation is the basis of target location of multi-sensor network, while the basic analysis of the signal is of key importance to the time delay estimation. In this paper, a time delay analysis system is designed by virtual instrument development tools. The analysis system contains: virtual oscilloscope, virtual spectrum analyzer, virtual filter and virtual time delay analyzer. Using this analysis system on a set of field collected acoustic target signal, spectrum analysis and filtering is made. Then the time delay estimation has been carried out for several sampling data segments selected by certain rules, and curve of the time delay vs. time is given. Analysis shows the main frequency of the target signal: 85Hz, 13Hz, 170Hz and 125Hz. The regular pattern of the time delay curve is consistent with the target motion. Application reveals that the system is helpful in the research of time delay estimation.

Improving the performance of chirped fiber grating with cladding being etched as sinusoidal function

A new grating structure of cladding being etched as sinusoidal function along the grating length is introduced to improve their performance. When a tension is applied to it, the fiber grating not only exhibits a flattop spectrum with steep edges and high reflectivity, but also has a smoothly time delay curve. The bandwidth utilization defined as the ratio of −1:−30 could be achieved a larger value (>0.90). The −3 dB bandwidth and the bandwidth utilization could be tunable with the increment of tension applied to the grating and the linearly chirped modulus.

New mathematical modeling approach for predicting microbial inactivation by high hydrostatic pressure.

A new primary model based on a thermodynamically consistent first-order kinetic approach was constructed to describe non-log-linear inactivation kinetics of pressure-treated bacteria. The model assumes a first-order process in which the specific inactivation rate changes inversely with the square root of time. The model gave reasonable fits to experimental data over six to seven orders of magnitude. It was also tested on 138 published data sets and provided good fits in about 70% of cases in which the shape of the curve followed the typical convex upward form. In the remainder of published examples, curves contained additional shoulder regions or extended tail regions. Curves with shoulders could be accommodated by including an additional time delay parameter and curves with tails shoulders could be accommodated by omitting points in the tail beyond the point at which survival levels remained more or less constant. The model parameters varied regularly with pressure, which may reflect a genuine mechanistic basis for the model. This property also allowed the calculation of (a) parameters analogous to the decimal reduction time D and z, the temperature increase needed to change the D value by a factor of 10, in thermal processing, and hence the processing conditions needed to attain a desired level of inactivation; and (b) the apparent thermodynamic volumes of activation associated with the lethal events. The hypothesis that inactivation rates changed as a function of the square root of time would be consistent with a diffusion-limited process.

Ultrasonic signal focusing method for ultrasonic imaging system

A focusing method plays a big role of determining a resolution of an ultrasonic image. Focusing is performed by controlling an arrival difference of a signal up to a focal point by an electronics delay circuit. Here, the focusing method for focusing an ultrasonic signal having emitted to a focal point of an object via an array transducer including a plurality of elements, obtains an optimal focusing time delay curve according to the ultrasonic signal travelling velocity to thereby obtain an optimal ultrasonic image. Using only data obtained without any modification of the structure of an existing ultrasonic imaging system, a focusing time delay curve is estimated. Thus, a resolution can be enhanced with only a simple calculation.

Stimulated emission and laser oscillation from light-hole excitonic state in a ZnSe-Zn0.8Cd0.2Se superlattice

At 77 K, stimulated emission from n=1 light-hole excitons in a ZnSe-Zn0.8Cd0.2Se superlattice is observed and the oscillation mode properties of n=1 light-hole and heavy-hole excitons are analyzed. It is noticed that the ZnSe-Zn0.8Cd0.2Se superlattice with the shorter Fabry–Pérot cavity length d has the larger threshold excitation. The threshold of each mode has been determined using its time delay curve.

Influence of Transverse Air or Inert‐Filled Gaps in HE Charges on the detonation velocity

AbstractGaps 0.8‐mm wide and transverse to the direction of detonation in high‐performance high explosive compositions, such as squeeze cast TNT/HMX (15/85) or pressed HMX/B (97/3), show no measurable time delay, or it must be less than 50 ns. As expected, delay times increase with the gap width. A surprising result, however, is the convex shape of the time delay curves, which begins at a gap width of about 1 mm. The delay time curves from air and plexiglass‐filled gaps resemble one another very much.