Method for detecting fatigue crack in gears

The most undesirable damage that can occur in gear units is crack in the tooth root as it often makes gear unit operation impossible. Monitoring vibrations can be used to detect defects. Time signals are acquired experimentally and afterwards. Different methods can be used to analyse them. The changes in tooth stiffness caused by a fatigue crack in the tooth root are of significance. The dynamic response of a gear unit with a damaged tooth differs from the one of an undamaged tooth. Amplitudes of time signal are, by time–frequency analysis, presented as a function of frequencies in spectrum.     

Charge sharing effect on 600 μm pitch pixelated CZT detector for imaging applications

We are currently investigating the spatial resolution of highly pixelated Cadmium Zinc Telluride(CZT)detector for imaging application. A 20 mm×20 mm×5 mm CZT substrate was fabricated with 600 μm pitch pixels(500 μm anode pixels with 100 μm gap) and coplanar cathode. Charge sharing between two pixels was studied using collimated a 122 keV gamma ray source. Experiments show a resolution of 125 μm FWHM for double-pixel charge sharing events when the 600 μm pixelated and 5 mm thick CZT detector biased at-1000V. In addition, we analyzed the energy response of the 600 μm pitch pixelated CZT detector.     

New technique to measure particle size using electrostatic sensor

A new technique is proposed to measure the particle mean size using an electrostatic sensor in frequency domain. This paper starts with a finite-element modeling simulator to model the induced electric charge of a ring electrode and to find the electrode sensitivity. The mathematical modeling was used to extract particle size information from the simulated signal in frequency domain. The method is applied in an experimental test where a low-noise signal conditioning was designed with a ring electrode as the electrostatic sensor. The method can be used to establish a cost effective size measurement system using electrostatic sensor.     

Superluminal propagation and information transfer: A statistical approach in the microwave domain

Signal velocity is calculated in a medium with negative group delay (NGD). By accounting for the medium and the detector noise sources, the time varying probability of error at the detector [Pe(t)$\mathit{Pe}(t)$] is evaluated in the NGD channel and a normal dispersion channel. The scheme in which Pe(t)$\mathit{Pe}(t)$ falls below a threshold at earlier time, implies faster information transfer. It is found that the signal velocity depends on the detector type and the relative noise strength of the detector with respect to the channel. Finally, it is shown that NGD channels can be useful in applications that are limited by the detector noise.     

Highly accelerated aortic 4D flow MR imaging with variable-density random undersampling

Purpose

To investigate an effective time-resolved variable-density random undersampling scheme combined with an efficient parallel image reconstruction method for highly accelerated aortic 4D flow MR imaging with high reconstruction accuracy.

Materials and Methods

Variable-density Poisson-disk sampling (vPDS) was applied in both the phase-slice encoding plane and the temporal domain to accelerate the time-resolved 3D Cartesian acquisition of flow imaging. In order to generate an improved initial solution for the iterative self-consistent parallel imaging method (SPIRiT), a sample-selective view sharing reconstruction for time-resolved random undersampling (STIRRUP) was introduced. The performance of different undersampling and image reconstruction schemes were evaluated by retrospectively applying those to fully sampled data sets obtained from three healthy subjects and a flow phantom.

Results

Undersampling pattern based on the combination of time-resolved vPDS, the temporal sharing scheme STIRRUP, and parallel imaging SPIRiT, were able to achieve 6-fold accelerated 4D flow MRI with high accuracy using a small number of coils (N = 5). The normalized root mean square error between aorta flow waveforms obtained with the acceleration method and the fully sampled data in three healthy subjects was 0.04 ± 0.02, and the difference in peak-systolic mean velocity was − 0.29 ± 2.56 cm/s.

Conclusion

Qualitative and quantitative evaluation of our preliminary results demonstrate that time-resolved variable-density random sampling is efficient for highly accelerating 4D flow imaging while maintaining image reconstruction accuracy.     

Effects of signal processing on the measurement of maximum sound pressure levels

Maximum sound pressure levels are commonly used for environmental noise and building acoustics measurements. This paper investigates the signal processing errors due to Fast or Slow time-weighting detectors when combined with octave band filters, one-third octave band filters or an A-weighting filter. For 6th order Butterworth CPB filters the inherent time delay caused by the phase response of filters is quantified using three different approaches to establish the following rules-of-thumb: (1) time-to-gradient/amplitude matching occurs when Bt ≈ 1, (2) time-to-peak matching occurs when Bt ≈ 2 and (3) time-to-settle matching occurs when Bt ≈ 4 for octave band filters, and when Bt ≈ 3 for one-third octave band filters. Four different commercially-available sound level meters are used to quantify the variation in measured maximum levels using tone bursts, half-sine pulses, ramped noise and recorded transients. Tone bursts indicate that Slow time-weighting is inappropriate for maximum level measurements due to the large bias error. The results also show that there is more variation between sound level meters when considering Fast time-weighted maximum levels in octave bands or one-third octave bands than with A-weighted levels. To reduce the variation between measurements with different sound level meters, it is proposed that limits could be prescribed on the phase response for CPB filters and A-weighting filters.     

基于N个有序纠缠光子对的量子机密共享方案

提出了一种基于N个有序纠缠光子对量子机密共享方案.用纠缠光子作为信息的载体,密钥管理者Alice将纠缠光子对分成两个序列,其中一个序列直接发送给合作者之一Bob,在确保第一个序列发送安全后,再对第二个序列进行编码,发送给另一个合作者Charlie.Bob和Charlie分别对他们所接收到的光子序列进行Bell基联合测量,从而得到Alice所发布的密钥,完整密钥的获得需要管理者和所有合作者共同实现.本方案采用两体纠缠态,相对三体纠缠态来说,在实验上更容易实现,仅需要线性光学元件和简单的纠缠源.     

降低OFDM系统峰均比的可恢复限幅技术(英文)

针对正交频分复用系统中峰值平均功率比过高的问题,提出了一种基于限幅技术的改进算法.该算法对限幅后的信号进行标记,并将标记序列发送到接收端,从而使得接收端能够正确的解调出输入信号.此外,本文还将该改进算法应用于光载无线通信系统中.仿真结果表明,与传统限幅算法相比,改进算法能够明显降低系统的误码率,同时保证良好的抑制峰均比的性能.     

一种基于光纤布喇格光栅振动传感器的光纤围栏入侵监测系统及其模式识别

基于高灵敏度光纤布喇格光栅振动传感器,提出了一种光纤围栏入侵监测系统及其模式识别方法.该方法通过具有自适应动态阈值的时域统计特征提取算法对异常事件信号进行特征提取,将特征矢量输入到一个基于三层BP神经网络而设计的分类器中对目标事件进行识别和分类.通过仿真目标信号和实际采样数据进行测试,对系统的报警识别率进行了验证,结果表明:对于仿真信号,系统的平均正确识别率达到了100%;对于实际采样数据,系统的平均正确识别率可以达到96.83%.     

Benchmarking JPEG 2000 implementations on modern CPU and GPU architectures

The use of graphics hardware for non-graphics applications has become popular among many scientific programmers and researchers as we have observed a higher rate of theoretical performance increase than the CPUs in recent years. However, performance gains may be easily lost in the context of a specific parallel application due to various both hardware and software factors. JPEG 2000 is a complex standard for data compression and coding, that provides many advanced capabilities demanded by more specialized applications. There are several JPEG 2000 implementations that utilize emerging parallel architectures with the built-in support for parallelism at different levels. Unfortunately, many available implementations are only optimized for a certain parallel architecture or they do not take advantage of recent capabilities provided by modern hardware and low level APIs. Thus, the main aim of this paper is to present a comprehensive real performance analysis of JPEG 2000. It consists of a chain of data and compute intensive tasks that can be treated as good examples of software benchmarks for modern parallel hardware architectures. In this paper we compare achieved performance results of various JPEG 2000 implementations executed on selected architectures for different data sets to identify possible bottlenecks. We discuss also best practices and advices for parallel software development to help users to evaluate in advance and then select appropriate solutions to accelerate the execution of their applications.