装药不耦合系数对碳酸盐岩爆炸地震波能量的影响

针对碳酸盐岩中化学爆炸地震勘探激发地震波能量弱、频率高、信噪比低的现状,为对炮孔装药结构提出合理的改进措施,建立了耦合与不耦合装药孔壁爆炸载荷及透射波能量的计算模型,并借助MATLAB编程计算得到解析解.同时在灰岩场地进行了装药不耦合系数Kd对地震波能量影响的现场实验,应用基于功率谱的能量分析方法对实验数据进行了分析....     

Full-field calculation of hole drilling residual stresses from electronic speckle pattern interferometry data

A mathematical method is proposed for calculating residual stresses from hole drilling electronic speckle pattern interferometry (ESPI) data, independent of rigid-body motions. Even though the signal-to-noise ratio of typical ESPI data is modest, the method achieves good computational stability by averaging a large amount of data. It does this without excessive numerical effort by exploiting known trigonometric relationships among the data. The resulting stress calculations are very rapid, and are well suited for future application to non-uniform stress measurements.     

Photoelastometric recording of stress waves

A very sensitive, fast-responding photomultiplier tube and laser light source were used to record stress-optic data associated with a moving stress wave. By using a “gray-field” (which is halfway between a dark and light field) polariscope, optical-electrical recordings were obtained which were linearly proportional to strain. A discriminatory record results which exhibits a higher signal-to-noise ratio than semiconductor strain gages. Gage length can be varied from 0.005 in. upwards.     

Nonlinear dynamical analysis of noisy time series

Empirical time series in the life sciences are often nonstationary and have small signal-to-noise ratios, making it difficult to accurately detect and characterize dynamical structure. The usual response to high noise is averaging, but time domain averaging is inappropriate, especially when the dynamics are nonlinear. We review alternative delay-space averaging methods based on the topology and short-term predictability of nonlinear dynamics and illustrate their application using the TISEAN software (Hegger, Kantz & Schreiber, 1999). The methods were applied to a Lorenz series, which resembles the dynamics found by Kelly, Heathcote, Heath and Longstaff (2001) in series of decision times. The Lorenz series was corrupted with up to 80% additive Gaussian noise, a lower signal-to-noise ratio than has been used in any previous test of these methods, but consistent with Kelly et al.'s data. Prediction methods performed the best for detecting nonstationarity and nonlinear dynamics, and optimal predictability provided an objective criterion for setting the parameters required by the analyses. Local linear filtering methods performed best for characterization, producing informative plots that revealed the nature of the underlying dynamics. These results suggest that a methodology based on delay-space averaging and prediction could be useful with noisy empirical data series.     

脑科学中若干非线性动力学问题

对近年发展起来的脑科学中的非线性问题作一介绍.这些问题得到脑科学界的广泛注意.它们是同步, 混沌与混沌周游, 噪声与随机共振.在很多不同背景下的神经生理实验表明脑皮层的振荡活动都存在同步与去同步现象.混沌在人与动物的脑中扮演着重要的角色, 混沌周游与Freeman模型被认为与联想记忆或记忆的动态连接有关.适当噪声强度导致信噪比的极大提高------随机共振是脑神经系统能检测到极其微弱信号的工作机制.噪声也导致同步态并使之稳定.此外,噪声的一些其他作用也在本文中提及.      

与CRP相结合的SAFT在混凝土损伤检测成像中的研究

将传统合成孔径聚焦技术(Synthetic aperture focusing technique,SAFT)与共反射点(Common reflection point,CRP)信号叠加法相结合应用于混凝土损伤检测中,可提高在强噪声环境中拾取缺陷回波信号的能力。本文采用二维有限元仿真验证了该思想的合理性,通过混凝土实验检验了该方法在实际应用中的可行性和有效性。与传统SAFT成像结果相比,应用CRP信号叠加法的SAFT提高了成像横向分辨率和损伤定位精度,为工程应用提供了理论和实验参考。     

An improved laser-Rayleigh scattering photodetection system

An improved photodetection system for high resolution laser-Rayleigh scattering measurements has been developed that utilizes a solid state detector coupled to a custom-designed, low-noise, transimpedance amplifier. The resulting system, based on a PIN photodiode is less expensive, inherently safer, less delicate and, depending on the detected light level, may exhibit higher signal-to-noise ratios than photodetection systems based on photomultiplier tubes. The frequency response of the system was designed to be uniform (3% peak variation) from DC to nearly 100 kHz. Concentration fluctuation spectra of a high scattering cross-section label (jet fluid) gas discharging into a density-matched, low scattering cross-section quiescent reservoir gas were measured using this system. Spectral signal-to-noise ratios as high as 7 decades were achieved under some conditions in parts of the spectrum.     

High sensitivity Fourier-transform rheology

The application of oscillatory shear strain leads, in the non-linear regime, to the appearance of higher harmonic contributions in the shear stress response. These contributions can be analyzed as spectra in Fourier space with respect to their frequencies, amplitudes and phase angles. In this article, we present several theoretical and practical aspects of measuring Fourier rheology spectra with high sensitivity. Using the hardware of a conventional rheometer, Fourier rheology spectra with a signal-to-noise ratio of about 18,000:1 for a single acquisition were obtained. This allowed the observation of harmonics up to the 21st harmonic. Signal averaging can further increase the sensitivity. Received: 4 November 1998 Accepted: 28 April 1999     

Resolution enhancement of Doppler frequency measurements using a centroid technique

 A centroid-based technique for locating peaks in the frequency spectrum is demonstrated to have the potential for substantially enhancing the resolution of Fourier-based laser Doppler velocimetry measurements. The effect of data windowing and signal-to-noise ratio on the potential resolution improvement is also analyzed. Received: 10 January 2001/Accepted: 19 November 2001     

Inertialess Nonlinear Systems for Information Coding

Linear properties of primary information converters are mostly used in conventional information coding methods and devices. The more converters are considered suitable for information transmission purposes, the more linear their characteristics are. However, purely linear converters are usually unavailable. Therefore, the devices should operate only in a narrow range, where the converter characteristic is close to linear. Unfortunately, only a low signal-to-noise ratio can be thus obtained. When trying to increase the output level, nonlinear distortions are encountered. If nonlinear elements are employed for information transmission, they are only constituents of the entire conversion system. However, even in this case only linear properties of the system are used. The above conflict is characteristic not only of primary information converters, but also of converters operating on the basis of amplitude, phase, or frequency modulation. A new information coding method is proposed in this work that employs the nonlinear properties of a converter described by a monotonous conversion function f(x). It allows one to avoid the effect of nonlinear distortions and to increase the signal-to-noise ratio. Calculations are presented that concern application of the proposed method for measurements, in the transmission of analog and digital information. Possible applications of the method in analog-to-digital converters are discussed.     

Correlation of crack growth rate and stress ratio for fatigue damage containing very high cycle fatigue regime

A model is proposed to correlate the crack growth rate and stress ratio containing very high cycle fatigue regime. The model is verified by the experimental data in literature. Then a formula is derived for the effect of mean stress on fatigue strength, and it is used to estimate the fatigue strength of a bearing steel in very high cycle fatigue regime at different stress ratios. The estimated results are also compared with those by Goodman formula.     

Fence probe measurement of flow reversal in separating turbulent boundary layers

A small fence probe was evaluated for measurements in the time-dependent flow reversal region of the transition from boundary layer to separated flow. For moderate and high Reynolds numbers, the fence probe is demonstrated to be a usable tool for the measurement of the reverse flow associated with separation. Although the present probe pressure transducer system was limited to approximately 200?Hz, pulses of positive and negative shear stress were readily detected. At or near the location of zero surface shear stress, the measurements were limited by the signal-to-noise ratio. For the separated flow investigated, a marked reduction in the pressure gradient occurred when the fence probe indicated approximately 20?% reversal for the higher Reynolds numbers. The reversal increased to 24?% for the lower Reynolds numbers. The measurements indicate that flow reversal alone may not be adequate to identify the degree of separation. Upstream of turbulent boundary layer (intermittent) separation, the duration of the reversed shear stress was found to be very short (0.002?C0.007?s), suggesting a local, small-scale, impulse-type separation. At and beyond the location of intermittent separation, the shear stress reversal duration was an order of magnitude longer. Estimates of the maximum and minimum surface shear stress in the separation region were also obtained with the fence probe.     

Near-infrared emissive AIE nanoparticles for biomedical applications: From the perspective of different nanocarriers

Fluorescent imaging based on near-infrared (NIR) fluorophores has revolutionized the techniques employed for detecting biological events in depth owing to their advantages referring to diminished photon scattering, high signal-to-noise ratio and better light transparence through tissue. As for conventional luminogens, the nanofabrication of those innately hydrophobic π-conjugated architectures into water-dispersible nanoparticles (NPs) may result in attenuated fluorescent intensity deriving from the detrimental distribution of π-π interactions in the confined space. Oppositely, chromophores possessing aggregation-induced emission (AIE) characteristics emit boosted brightness at aggregate level according to the mechanism of restriction of intramolecular motion (RIM). In this review, we summarize the recent progresses of NIR emissive AIE NPs for multifarious biomedical applications from the viewpoint of different fabricated manners, mainly covering self-assembly and matrices assisted approaches. Furthermore, the current challenges and future research directions of NIR AIE NPs are briefly discussed.     

A calculating method of shock wave oscillating frequency due to turbulent shear layer fluctuations in supersonic flow

One of the more severe fluctuating pressure environments encountered in supersonic orhypersonic flows is the shock wave oscillation driven by interaction of a shock wave withboundary layer.The high intensity oscillating shock wave may induce structure resonanceof a high speed vehicle.The research for the shock oscillation used to adopt empirical orsemiempirical methods because the phenomenon is very complex.In this paper atheoretical solution on shock oscillating frequency due to turbulent shear layer fluctuationshas been obtained from basic conservation equations.Moreover,we have attained theregularity of the frequency of oscillating shock varying with incoming flow Mach numbersM_∞and turning angleθ.The calculating results indicate excellent agreement withmeasurements.This paper has supplied a valuable analytical method to study aeroelasticproblems produced by shock wave oscillation.     

Lamb波频域逆散射全聚焦成像方法研究

Lamb波因其传播距离远、衰减小常被用于板状结构的无损检测中,在基于Lamb波损伤检测的诸多成像技术中,全聚焦方法(Total Focus Method,TFM)方法因其成像分辨率高、信噪比高而受青睐.然而Lamb波的频散效应导致时域延时量不能被准确计算,进而影响传统TFM方法对损伤定位及成像的精度;此外,既有的TFM...     

Barkhausen noise in fluxgate magnetometers

Barkhausen noise is one of the limiting factors for the sensitivity of fluxgate magnetometers. In order to set up calculations about Barkhausen noise, the theory of Bittel and Storm [1] had to be modified. As a result an equation for the signal-to-noise ratio is given, which gives criteria to increase the sensitivity of fluxgate magnetometers.Dept. of PhysicsDept. of Electrical Eng.     

Experimental analysis of concrete behavior under high confinement: Effect of the saturation ratio

This study focuses on the identification of concrete behavior under severe triaxial loading in order to better evaluate the vulnerability of sensitive infrastructure to near-field detonations or ballistic impacts. For the purpose of reproducing high stress levels with well-controlled loading paths, static tests have been conducted on concrete samples using a triaxial press offering very high capacities (stress levels of around 1 GPa). It is a well-known fact that the concrete drying process is a slow phenomenon. Massive concrete structures, such as bridge piers, dams and nuclear reactors, could retain a quasi-saturated core throughout most of their lifetime, even though their facing dries very quickly. The objective of this article is to evaluate the effect of the saturation ratio on concrete behavior under high confinement; this article will present triaxial test results on concrete samples over a saturation ratio range extending from dried to quasi-saturated concretes. The subsequent analysis of results will show that the saturation ratio exerts a major influence on concrete behavior, particularly on both the concrete strength capacity and shape of the limit state curve for saturation ratios above 50%. This analysis also highlights that while the strength of dried concrete strongly increases with confining pressure, it remains constant over a given confining pressure range for either wet or saturated samples.     

地震检波器特性参数识别的一种新的正弦扫频恒流激励方法

提出一种新的正弦扫频恒流激励法,依此建立了适合不同动圈式地震检波器参数测量的8参数与9参数模型,并给出了检波器固有频率、灵敏度、阻尼比和线圈电感量的测量与识别方法。理论分析、参数识别和与振动台激励法测试的比较结果均显示,此方法测量的频响函数信噪比高,在较宽频率范围内曲线拟合精度较高,测试速度快,操作性好,现已应用于便携式检波器特性参数测试仪的研制与生产,此仪器适用于各种动圈式检波器在生产、维修和施工现场的特性参数测量。     

A reliable method for determining the measurement volume size and particle mass fluxes using phase-Doppler anemometry

A reliable method for the calibration of the measurement volume cross-section has been developed, in order to correct the particle size distribution measured by a phase-Doppler anemometer (PDA) with respect to the counting bias in favour of the large particles. Furthermore, this method allows the measurement of particle concentration or mass flux with high accuracy in two-dimensional two-phase flows. A comparison of the mass flow rate obtained by the integration of the mass flux measured in a water spray by applying this method with the global mass balance showed a difference of about 5%.The basis of the present method is the detection of the amplitude of the filtered Doppler signal in connection with the particle size measured by the PDA. The detection process is performed using an electronic circuit which validates the Doppler burst and has additionally the advantage that the highest amplitude portion of the burst can be selected for digitizing, acquisition and subsequent processing. Therefore, this method has the great advantage that the processed part of the burst has the highest signal-to-noise ratio which results in high accuracies for frequency and phase estimation.     

The surface hot wire as a means of measuring mean and fluctuating wall shear stress

 The paper describes some applications of a wall shear stress sensor technique which is based on hot-wire anemometry. The “surface hot wire” is a flush-mounted thermal resistive wire with a tiny slot underneath. The arrangement of this sensor guarantees an improved signal-to-noise ratio compared to a common surface hot film. The setup and the application of single sensors and of surface hot-wire arrays are shown. Some results are presented that were acquired in several experiments in the field of laminar-turbulent transition. Received: 26 May 2000/Accepted: 7 February 2001