Autocorrelation Technique Research Articles

PEMFCs flow microstructure analysis by advanced speckle technologies

An advanced optical technique based on digital version of μ-PIV and speckle technologies has been applied for flow microstructure analysis in a semi-transparent model of a PEM fuel cell. The line-of-sight speckle photography has been used for quantitative measurements of the instantaneous temperature fields in 3D unsteady flows. Using μ-PIV, the sequence of flow images has been visualised by micro-particles. The images obtained have been evaluated then by cross-correlation and autocorrelation techniques and instantaneous temperature, velocity and vorticity maps have been obtained with sub-millimeter spatial resolution. Up to 250,000 quantitative velocity vectors are reconstructed simultaneously using one digitally recorded specklogram.

Measurement of the effective nonlinear and dispersion coefficients in optical fibers by the induced grating autocorrelation technique

The induced grating autocorrelation technique, a technique based on temporally resolved two-beam coupling in a photorefractive crystal, was used to measure the nonlinear coefficient γ of three photonic crystal fibers (PCFs): a 30-cm long highly nonlinear PCF, and two large mode area PCFs of 4.5-m and 4.9-m lengths. The measurement used intense 2-ps, 800-nm (850-nm in one case) pulses from a Ti: sapphire laser that experienced self-phase modulation and group velocity dispersion as it travels inside the fibers. This technique was also expanded to measure γ and the dispersion coefficient β2 simultaneously.

An improved Markov chain model based on autocorrelation and entropy techniques and its application to state prediction of water resources

According to the relationships among state transition probability matrixes with different step lengths, an improved Markov chain model based on autocorrelation and entropy techniques was introduced. In the improved Markov chain model, the state transition probability matrixes can be adjusted. The steps of the historical state of the event, which was significantly related to the future state of the event, were determined by the autocorrelation technique, and the impact weights of the event historical state on the event future state were determined by the entropy technique. The presented model was applied to predicting annual precipitation and annual runoff states, showing that the improved model is of higher precision than those existing Markov chain models, and the determination of the state transition probability matrixes and the weights is more reasonable. The physical concepts of the improved model are distinct, and its computation process is simple and direct, thus, the presented model is sufficiently general to be applicable to the prediction problems in hydrology and water resources.

Application of a Simple Adaptive Estimator for an Atmospheric Doppler Radar

A simple method for estimating parameters of the Doppler spectrum of atmospheric signals is described. The method is based on an adaptive filter processing that has been widely used in telecommunications but rarely applied in measurements using atmospheric radars. The method has been tested using both synthetic and real data obtained by the radar profiler-Transportable Atmospheric Radar (TARA)-and the weather radar-International Research Centre for Telecommunications and Radar (IRCTR) Drizzle Radar (IDRA)-both developed by IRCTR. The method is compared with the traditional pulse-pair method and fast Fourier transform (FFT)-based methods, as well as with the IRCTR FFT-based method implemented in the TARA and IDRA processing including an additional noise clipping stage. The tests have demonstrated high efficiency of the adaptive filtering estimator under low signal-to-noise ratio conditions. The applicability of adaptive estimations in radar meteorology and the limitations associated with a sample length are discussed.

Improved Methods for Survey of Carabid Beetles (Coleoptera: Carabidae) Using Pitfall Trapping and Spatial Autocorrelation Techniques

Ground beetles (Coleoptera: Carabidae) inhabiting a peach orchard were collected using pitfall traps placed adjacent to plastic barriers that were perpendicular to each other and crossed each other at their midpoints. Each array of traps contained 5 traps with 1 at the midpoint of each barrier and the other 4 at the ends of each plastic barrier. The trap located at the center of each array captured about 40% of the total beetles trapped by each array, thus suggesting that a single trap located at the center of the array could be a more efficient means of sampling. Using spatial autocorrelation techniques, the range of spatial dependence for the two herbivorous carabids collected in this study - Harpalus tschiliensis Schauberger and Harpalus griseus Panzer - ranged from 136.7 - 210.3 m, whereas that of the predatory carabid Calathus halensi Schailer ranged from 330.1 - 412.4 m. Based upon our results, we suggest that pitfall traps used for monitoring or sampling carabid beetles be set no further than 210 m apart for herbivorous species and 412 m apart for carnivorous species.

Perceptual Harmonic Cepstral Coefficients As The Front-End For Speech Recognition

Pitch estimation and classification into voiced, unvoiced and transitional speech were performed by a spectro-temporal auto-correlation technique. A peak picking formula was then employed. A weighting function was then applied to the power spectrum. The harmonics weighted power spectrum underwent mel-scaled band-pass filtering, and the log-energy of the filter's output was discrete cosine transformed to produce cepstral coefficients. A within-filter cubic-root amplitude compression was applied to reduce amplitude variation without compromise of the gain invariance properties.

Extended Noninvasive Fetal Monitoring by Detailed Analysis of Data Measured With Phonocardiography

This paper presents a complex heuristic method for the evaluation of fetal heart sounds, applying simultaneously several algorithms, where the autocorrelation technique has been completed with the wavelet transform and the matching pursuit methods. In this way, a more reliable heart rate variability can be achieved and further parameters of the cardiac operation can be assessed in addition to the conventional cardiotocographic examination. This also comprises those parameters, which can be investigated only with long-term or continuous monitoring, and those, which rely on a very accurate estimation of the heart rate variability. The proposed method provides a way for assessing fetal heart murmurs, which is a completely new possibility for monitoring the well-being of the fetus.

Low power autocorrelation technique based on the degree-of-polarization measurement

Based on the degree-of-polarization (DOP) measurement, an autocorrelation technique to measure the pulse width of chirp-free optical short pulse with a very low optical power (<−60 dBm) is demonstrated. The impacts of chirp and misalignment of the input light are also discussed in detail. The pulse width measurement results are consistent with the conventional second-harmonic generation (SHG) autocorrelation, while our autocorrelation technique does not require high input power or rigid optical alignment.

Diagnostics of femtosecond laser pulses based on generation of nonlinear-dispersive similariton

We propose and test experimentally a method, alternative to the autocorrelation technique, for determination of the duration of femtosecond laser pulses. The method is based on generation of nonlinear-dispersive similariton in a passive optical fiber (without gain) and measuring its spectral width (or duration) determined by the power of the initial pulse.

Measurement of Ultrashort Laser Pulse Width in a Wide Spectrum Range Using Dimethyl Sulfoxide by Optical Kerr Effect Technique

We illustrate that applying the optical Kerr effect technique to dimethyl sulfoxide (DMSO) can determine the width of laser pulses in a wide spectrum range that is transparent. Different from many other simple molecular liquids, such CS2, and toluene, DMSO responds to both 130 fs 800nm laser pulses and 248 fs 400 nm laser pulses with electronic motions only. Therefore, the observed signal as a function of time reflects the temporal distribution of the intensity. We verify our illustration by both the autocorrelation technique and spectra analysis.

Research on multipoint layer-type laser Doppler self-velocimeter

An idea of using a multipoint layer-type laser Doppler self-velocimeter (LDV) to offer velocity for the vehicle navigation system was proposed because the accelerometer had the error term generated by overload. The principle of measuring its own velocity with laser Doppler was expounded while a multipoint layer-type LDV was designed, and the Doppler signal was processed by the technique of tracking filter and digital autocorrelation. The result of theory and experiment showed that the multipoint layer-type dual-beam LDV system was suitable for measuring on rough road surfaces when the individual dual-beam LDV was in the status of out of focus. Low-frequency disturbance and some noises were eliminated by the tracking filter, and the residual noise was removed by digital autocorrelator so that the signal-to-noise ratio and the detection sensibility of the system was greatly improved. Comparing to the global position system, the relative accuracy of LDV is ~1.95%.

Multiphoton Photoemission from a Copper Cathode Illuminated by Ultrashort Laser Pulses in an rf Photoinjector

In this Letter we report on the use of ultrashort infrared laser pulses to generate a copious amount of electrons by a copper cathode in an rf photoinjector. The charge yield verifies the generalized Fowler-Dubridge theory for multiphoton photoemission. The emission is verified to be prompt using a two pulse autocorrelation technique. The thermal emittance associated with the excess kinetic energy from the emission process is comparable with the one measured using frequency tripled uv laser pulses. In the high field of the rf gun, up to 50 pC of charge can be extracted from the cathode using a 80 fs long, 2 microJ, 800 nm pulse focused to a 140 mum rms spot size. Taking into account the efficiency of harmonic conversion, illuminating a cathode directly with ir laser pulses can be the most efficient way to employ the available laser power.

单发次皮秒脉冲对比度的三阶自相关法测试技术

单发次皮秒脉冲对比度的三阶自相关法测试技术

Temporal downscaling: a comparison between artificial neural network and autocorrelation techniques over the Amazon Basin in present and future climate change scenarios

Several studies have been devoted to dynamic and statistical downscaling for both climate variability and climate change. This paper introduces an application of temporal neural networks for downscaling global climate model output and autocorrelation functions. This method is proposed for downscaling daily precipitation time series for a region in the Amazon Basin. The downscaling models were developed and validated using IPCC AR4 model output and observed daily precipitation. In this paper, five AOGCMs for the twentieth century (20C3M; 1970–1999) and three SRES scenarios (A2, A1B, and B1) were used. The performance in downscaling of the temporal neural network was compared to that of an autocorrelation statistical downscaling model with emphasis on its ability to reproduce the observed climate variability and tendency for the period 1970–1999. The model test results indicate that the neural network model significantly outperforms the statistical models for the downscaling of daily precipitation variability.

Mode-locked pulses from mid-infrared Quantum Cascade Lasers

In this study, we report the unequivocal demonstration of midinfrared mode-locked pulses from quantum cascade lasers. The train of short pulses was generated by actively modulating the current and hence the gain of an edge-emitting quantum cascade laser (QCL). Pulses with duration of about 3 ps at full-width-at-half-maxima and energy of 0.5 pJ were characterized using a second-order interferometric autocorrelation technique based on a nonlinear quantum well infrared photodetector. The mode-locking dynamics in the QCLs was modeled based on the Maxwell-Bloch equations in an open two-level system. Our model reproduces the overall shape of the measured autocorrelation traces and predicts that the short pulses are accompanied by substantial wings as a result of strong spatial hole burning. The range of parameters where short mode-locked pulses can be formed is found.

Colour flow and motion imaging

Colour flow imaging (CFI) is an ultrasound imaging technique whereby colour-coded maps of tissue velocity are superimposed on grey-scale pulse-echo images of tissue anatomy. The most widespread use of the method is to image the movement of blood through arteries and veins, but it may also be used to image the motion of solid tissue. The production of velocity information is technically more demanding than the production of the anatomical information, partly because the target of interest is often blood, which backscatters significantly less power than solid tissues, and partly because several transmit-receive cycles are necessary for each velocity estimate. This review first describes the various components of basic CFI systems necessary to generate the velocity information and to combine it with anatomical information. It then describes a number of variations on the basic autocorrelation technique, including cross-correlation-based techniques, power Doppler, Doppler tissue imaging, and three-dimensional (3D) Doppler imaging. Finally, a number of limitations of current techniques and some potential solutions are reviewed.

Alternating-Site Mechanism of Kinesin-1 Characterized by Single-Molecule FRET Using Fluorescent ATP Analogues

Kinesin-1 motor proteins move along microtubules in repetitive steps of 8 nm at the expense of ATP. To determine nucleotide dwell times during these processive runs, we used a Förster resonance energy transfer method at the single-molecule level that detects nucleotide binding to kinesin motor heads. We show that the fluorescent ATP analog used produces processive motility with kinetic parameters altered <2.5-fold compared with normal ATP. Using our confocal fluorescence kinesin motility assay, we obtained fluorescence intensity time traces that we then analyzed using autocorrelation techniques, yielding a time resolution of ∼1 ms for the intensity fluctuations due to fluorescent nucleotide binding and release. To compare these experimental autocorrelation curves with kinetic models, we used Monte-Carlo simulations. We find that the experimental data can only be described satisfactorily on the basis of models assuming an alternating-site mechanism, thus supporting the view that kinesin's two motor domains hydrolyze ATP and step in a sequential way.

Ultrasonic device for real-time sewage velocity and suspended particles concentration measurements

In the frame of a technological research and innovation network in water and environment technologies (RITEAU, Réseau de Recherche et d'Innovation Technologique Eau et Environnement), our research group, in collaboration with industrial partners and other research institutions, has been in charge of the development of a suitable flowmeter: an ultrasonic device measuring simultaneously the water flow and the concentration of size classes of suspended particles. Working on the pulsed ultrasound principle, our multi-frequency device (1 to 14 MHz) allows flow velocity and water height measurement and estimation of suspended solids concentration. Velocity measurements rely on the coherent Doppler principle. A self developed frequency estimator, so called Spectral Identification method, was used and compared to the classical Pulse-Pair method. Several measurements campaigns on one wastewater collector of the French city of Strasbourg gave very satisfactory results and showed smaller standard deviation values for the Doppler frequency extracted by the Spectral Identification method. A specific algorithm was also developed for the water height measurements. It relies on the water surface acoustic impedance rupture and its peak localisation and behaviour in the collected backscattering data. This algorithm was positively tested on long time measurements on the same wastewater collector. A large part of the article is devoted to the measurements of the suspended solids concentrations. Our data analysis consists in the adaptation of the well described acoustic behaviour of sand to the behaviour of wastewater particles. Both acoustic attenuation and acoustic backscattering data over multiple frequencies are analyzed for the extrapolation of size classes and respective concentrations. Under dry weather conditions, the massic backscattering coefficient and the overall size distribution showed similar evolution whatever the measurement site was and were suggesting a global wastewater particles behaviour. By comparison to sampling data, our data analysis lead to the characterization of two particle groups: the ones occurring during rain events and the ones typical of wastewater under dry weather conditions. Even with already encouraging results on the several weeks of data recorded on several wastewater collectors, the validation of our data inversion method is still under progress.

Differentiating geology and tectonics using a spatial autocorrelation technique for the hypsometric integral

Hypsometry is thought to be sensitive to tectonic uplift rates and lithology differences. In this study we calculated hypsometric integrals (HIs) using as topographic sources two digital elevation models of 10 and 90 m of pixel resolution in the Granada basin (SE of Spain). The HI spatial distributions do not show clear spatial patterns and do not correlate with basin parameters as mean elevation or relief amplitude. However, when exploratory spatial data analysis is applied to the data distributions through local indices of spatial autocorrelation, clear hot spots are visible that improve the geologic meaning of the HI. The distributions are robust and independent of the model resolution but are scale influenced. The application of this new method to the Granada basin shows a strong correlation between the main distribution of active normal faults in the basin and the clusters of high or low HI values obtained in our analysis. Clusters with high HI values define the uplifted footwalls of these faults and regions uplifted in relation with rollover anticlines or where epeirogenic uplift has not been counteracted by local extension. Once the method was adjusted in the Granada basin, we tested its applicability in an area of known contractive tectonic activity, central Otago, New Zealand, showing that the meaning of HI values is improved by using the autocorrelation techniques.

Deconvolution of Three-Component Teleseismic Data from Southern Tibet Using the SVA Technique

In this study, the SV autocorrelation (SVA) technique of Dasgupta and Nowack (2006) is tested using three-component P-wave data from selected INDEPTH II and CDSN stations in southern Tibet. The SVA technique involves constructing an estimate of the source and distant Earth wavelet from the autocorrelation of the SV component and using this to deconvolve the data. The deconvolved vertical compo- nents are then used to infer the crustal P-velocity structure. Initial models for the in- version of the deconvolved vertical components were based on the S-velocity results obtained from the inversions of radial receiver functions by Mitra et al. (2005). The Moho depths obtained from inverting the vertical components deepen from the south to the north in the study area and are comparable to the depths obtained by Mitra et al. (2005) to the north and similar but somewhat shallower to the south. The crustal VP=VS ratios are obtained from the inverted VS models from Mitra et al. (2005) and the inferred VP speeds obtained from this study. Except for station BB18 with a some- what higher VP=VS ratio, the other stations to the north in the Tethyan Himalayas and the southern Lhasa terrane have VP=VS ratios between 1.75 and 1.80 with a mean of 1.77 (a Poisson's ratio of 0.265). The range of values could result from noise in the data as well as from lateral heterogeneity in the region with different piercing points at depth for the Ps and PpPp phases.