Autocorrelation Technique Research Articles

Autocorrelation aided rough set based contamination level prediction of high voltage insulator at different environmental condition

This paper presents a Rough Set Theory (RST) based approach for predicting the surface contamination level of porcelain type insulators at different environmental condition. The sample insulators have been contaminated by Solid layer Method (SLM) according to IEC60507. Leakage current of the insulators are recorded at different contamination level and at different humidity conditions. In the proposed method, autocorrelation technique is used for feature selection from leakage current because it is well suited for non-stationary leakage current signals and cancels out the effect of noise present in the signal. Rough Set Theory is used for classification of extracted features as it suits well with the correlation technique. Result shows that the proposed method is able to detect the contamination level with acceptable range of accuracy.

Polarization dependence of phase-sensitive optical time-domain reflectometry and its suppression method based on orthogonal-state of polarization pulse pair

Phase-sensitive optical time-domain reflectometry (Φ-OTDR) has been widely used in various applications for its distributed measurement capability of dynamic disturbance along the entire sensing fiber. Commonly, the sensing system is considered to be only sensitive to the phase change and capable of detecting multiple vibration events. In application, once any of the vibration events leads to a local birefringence change, the polarization evolution of the signal will be disturbed along the following fiber, which will result in the generation of polarization-related noise and the failure of identification for multipoint vibration events. We will reveal the polarization-dependence of Φ-OTDR both theoretically and experimentally. To suppress the polarization-dependence of Φ-OTDR, an orthogonal-state of polarization pulse pair method has been proposed, making the sensing system purely phase-sensitive. The experiment result has shown that maximum noise suppression ratio of 11.2 dB and mean noise suppression ratio of 4.9 dB could be achieved, which confirmed the validity of the proposed method.

Assessing 3D metric data of digital surface models for extracting archaeological data from archive stereo-aerial photographs

Archaeological remains are under increasing threat of attrition from natural processes and the continued mechanisation of anthropogenic activities. This research analyses the ability of digital photogrammetry software to reconstruct extant, damaged, and destroyed archaeological earthworks from archive stereo-aerial photographs. Case studies of Flower’s Barrow and Eggardon hillforts, both situated in Dorset, UK, are examined using a range of imagery dating from the 1940s to 2010. Specialist photogrammetric software SocetGXP® is used to extract digital surface models, and the results compared with airborne and terrestrial laser scanning data to assess their accuracy. Global summary statistics and spatial autocorrelation techniques are used to examine error scales and distributions. Extracted earthwork profiles are compared to both current and historical surveys of each study site. The results demonstrate that metric information relating to earthwork form can be successfully obtained from archival photography. In some instances, these data out-perform airborne laser scanning in the provision of digital surface models with minimal error. The role of archival photography in regaining metric data from upstanding archaeology and the consequent place for this approach to impact heritage management strategies is demonstrated.

Ultrasonic Doppler Velocity Profile Measurement of Single-and Two-Phase Flows Using Spike Excitation

In the article, the application of the electrical spike, instead of the tone-burst, to the ultrasonic pulsed-Doppler velocity profiling the first time is presented. To generate ultrasound, the ultrasonic sensor is excited by the spike. For the Doppler method, the spike excitation was not used previously. It has been used with wideband signal processing methods. In our study, first, the fluid-velocity profile measurement using spike excitation has been carried out for single-phase pipe flow. The received data have been validated by the logarithmic law of the wall, for turbulent flow regime. The flow rate calculated by using the mean velocity profile well coincides with the flow-meter data. Furthermore, the spike signal and the Doppler method are used in the multiwave ultrasonic velocity profile (UVP) method, for the bubbly flow measurement. The experiments show that, if the spike signal is slowly damped, the generated ultrasonic wave is similar to the tone-burst that is required for the Doppler method, but in this case, usually the pulse length is smaller and depends on the damping and sensor characteristics. The autocorrelation technique is used for echo signal processing. The derived UVP systems inherit the advantages from both the spike excitation and Doppler method.

Detecting “Hot Spots” of Facility POIs Based on Kernel Density Estimation and Spatial Autocorrelation Technique

The distribution pattern of urban facility POIs usually forms clusters (i.e. spots) in local geographic space. The kernel density estimation (KDE), which has been usually utilized for expressing these spatial characteristics, is one of the most popular visualization tools. Considering the missing of quantitative statistical inference assessment in KDE, this paper proposes a novel method to detect the hot spots of urban facility POIs. First, this method computes the attribute value of geographic unit with the distance decay effect, then by adopting the statistical index of Getis-Ord Gi*, we analysis the local spatial cluster characteristics of urban facilities. Comparing this method with the conventional spatial autocorrelation based on the Quadrat clustering, the attribute value of kernel density computing can preserve the local information of data, and the spatial cluster characteristics of urban facilities can reflect the continuity characteristics of urban services, for that the KDE considers the regional impact based on the First Law of Geography. The actual data experiment for analyzing the financial POIs' distribution patterns indicates that this approach is effective to extract the hot spots of urban facility POIs in city areas.

The effect of deadtime and electronic transients on the predelay bias in neutron coincidence counting

In neutron coincidence counting using the shift register autocorrelation technique, a predelay is inserted before the opening of the (R+A)-gate. Operationally the purpose of the predelay is to ensure that the (R+A)- and A-gates have matched effectiveness, otherwise a bias will result when the difference between the gates is used to calculate the accidentals corrected net reals coincidence rate. The necessity for the predelay was established experimentally in the early practical development and deployment of the coincidence counting method. The choice of predelay for a given detection system is usually made experimentally, but even today long standing traditional values (e.g., 4.5µs) are often used. This, at least in part, reflects the fact that a deep understanding of why a finite predelay setting is needed and how to control the underlying influences has not been fully worked out. In this paper we attempt to gain some insight into the problem. One aspect we consider is the slowing down, thermalization, and diffusion of neutrons in the detector moderator. The other is the influence of deadtime and electronic transients. These may be classified as non-ideal detector behaviors because they are not included in the conventional model used to interpret measurement data. From improved understanding of the effect of deadtime and electronic transients on the predelay bias in neutron coincidence counting, the performance of both future and current coincidence counters may be improved.

Spatiotemporal Patterns and Social Risk Factors of Meningitis in Nigeria

This study aimed at characterising the spatiotemporal pattern of meningitis in Nigeria, in order to detect vulnerable areas. Stratified sampling was deployed in research inquiry based on the following variables: geographic location; population density; poverty status; and adult literacy level in accordance to diseases incidence rate. Population-based ratios were then computed for each stratum for the identification of high risk areas. Global Moran’s Index spatial autocorrelation technique was additionally used to investigate the extent to which neighbouring values of incidence rate are correlated and to determine meningitis demographic risk factors. A significant spatial clustering of meningitis incidence rate has been found in northern Nigeria, with less or no clustering in the southern part of the country. A significant correlation of disease, with geographical location and poverty was perceived. The study commends that improving the socioeconomic status of the affected population may reduce the incidents of meningitis in the high risk area in Nigeria.

Spatial Pattern Detection of Tuberculosis: A Case Study of Si Sa Ket Province, Thailand.

This retrospective population-based study was conducted to analyze spatial patterns of tuberculosis (TB) incidence in Si Sa Ket province, Thailand. TB notification data from 2004 to 2008 collected from TB clinics throughout the province was used along with population data to reveal a descriptive epidemiology of TB incidences. Global clustering patterns of the occurrence were assessed by using global spatial autocorrelation techniques. Additionally, local spatial pattern detection was performed by using local spatial autocorrelation and spatial scan statistic methods. The findings indicated clusters of the disease occurred in the study area. More specifically, significantly high-rate clusters were mostly detected in Mueang Si Sa Ket and Khukhan districts, which are located in the northwestern part of the province, while significantly low-rate clusters were persistent in Kantharalak and Benchalak districts, which are located at the southeastern area.

A MULTI-PERIOD OSCILLATION IN A STELLAR SUPERFLARE

Flares that are orders of magnitude larger than the most energetic solar flares are routinely observed on Sun-like stars, raising the question of whether the same physical processes are responsible for both solar and stellar flares. In this letter we present a white-light stellar superflare on the star KIC9655129, observed by NASA's Kepler mission, with a rare multi-period quasi-periodic pulsation (QPP) pattern. Two significant periodic processes were detected using the wavelet and autocorrelation techniques, with periods of 78 +/- 12 min and 32 +/- 2 min. By comparing the phases and decay times of the two periodicities, the QPP signal was found to most likely be linear, suggesting that the two periodicities are independent, possibly corresponding either to different magnetohydrodynamic modes of the flaring region, or different spatial harmonics of the same mode. The presence of multiple periodicities is a good indication that the QPPs were caused by magnetohydrodynamic oscillations, and suggests that the physical processes in operation during stellar flares could be the same as those in solar flares.

Remote sensing of chlorophyll-a as a measure of red tide in Tokyo Bay using hotspot analysis

Tokyo Bay plays significant roles in Japan׳s economic and social development; however, the bay is facing the threat on water quality degradation due to harmful algal productions. Water quality parameters are measured at few stations in Tokyo Bay by respective agencies but is limited in time and space. This paper presents empirical models for continual Chl-a retrieval and red tide detection in Tokyo Bay water using satellite reflectance data derived from Landsat OLI sensor. The models use regression results from 38 samples, which obtained for a period between January and December of 2014. Based on the model fit, band ratios of blue and green were used to retrieve the Chl-a (R2=0.63, p-value<0.05). Seasonal pattern of Chl-a were then studied using the images obtained for the study period. Results shows that Chl-a concentrations during summer months are associated with high phytoplankton activity, and that for winter months are accompanying with low phytoplankton activity in Tokyo Bay. A simple hotspot model based on Getis-Ord Gi* were then proposed to detect the red tide events. Based on the hotspot analysis, z score for the dates of Landsat images were calculated and mapped. The high z scores obtained from Chl-a maps often corresponds with the measured red tide events. Results confirm the potential of spatial autocorrelation techniques for the detection of red tide breakouts from Chl-a retrieved Landsat 8 OLI.

AN IMPROVED PREAMBLE AIDED TIMING ESTIMATION METHOD FOR OFDM SYSTEMS

This paper presents an improved robust method for timing offset estimation in preamble-aided OFDM system. The proposed method is aimed to provide low complexity, high performance timing estimator under the high frequency offset conditions. It uses a modified preamble structure and utilizes double autocorrelation technique to achieve robust timing estimation performance with only moderate increase in complexity. We finally evaluated and compared the performance of the proposed method in terms of mean square error (MSE) in AWGN, Rayleigh fading ISI channels and HIPERLAN/2 indoor channel A. The results indicate that the new method has a significantly smaller estimator MSE than the previously presented methods.

Identifying low-frequency earthquakes in central Cascadia using cross-station correlation

We use stations in the Willamette valley and Oregon coast ranges to identify low-frequency earthquakes that occurred during the August–September 2009 episodic tremor and slip event. While autocorrelation techniques are often successful at identifying LFE templates, in central Cascadia, this technique systematically fails due to the lack of densely spaced, high-quality stations. Instead, we use cross-station methods that have been successful at identifying LFEs in northern Cascadia to register initial candidate templates, network cross-correlation to register additional LFE detections, and stacking to refine the identified templates. Using this procedure, we detect nearly 16 thousand events comprising a total of 18 LFE families located in central Oregon between 30 and 40km depth either at or near the plate boundary. The time history of detections between families is consistent with the slip front in the 2009 SSE migrating from north to south at a velocity of 5km/day. The templates we identify have more complicated waveforms than those previously identified in northern Cascadia. These differences in waveform character likely a consequence of the small number of contributing stations.

Digital grain-size analysis based on autocorrelation algorithm

Grain size is one of the most important parameters in geology and coastal engineering. However, all traditional methods are time consuming, laborious, and expensive. In this study, the autocorrelation technique, which was first expounded by Rubin (2004), was extended to estimate the size of well-sorted sediments and the grain-size distribution of mixed-size sediments. Long and intermediate axes of well-sorted sediments ranging from 1 to 20mm obtained from applying the autocorrelation method are compared with the corresponding results measured using a vernier caliper. Using the autocorrelation technique, the sediment mean size was calculated and was found to compare better with point counts than sieving. Regarding the mixed-size sediment, a nonlinear programming method, which is different from the conventional ‘least-squares with non-negativity’ method, the kernel density method, and the maximum entropy method, was used to obtain the representative grain sizes and associated sediment inherent parameters, such as mean diameter, median diameter, sorting, skewness, and kurtosis. Image pre-processing was used in the present analysis to enhance the contrast of the recorded image, and a conversion method applied to take into account the difference between the two-dimensional digital image method and the three-dimensional sieving method. Using the modified fitting points and the improved Gaussian function fitting method, the cumulative grain-size distribution curve and the probability density curve of the mixed-size sediments were obtained. The enhanced autocorrelation technique that was developed from the traditional ‘look-up-catalogue’ approach provided a more accurate estimation of the grain-size distribution, as well as the relevant physical parameters of the mixed-size sediment.

Determination of the nonlinear refractive index of multimode silica fiber with a dual-line ultra-short pulse laser source by using the induced grating autocorrelation technique.

We measured, within 6% accuracy, the nonlinear refractive index (n2) of 10 meter long multimode silica fiber of 17μm core diameter, using a modified induced grating autocorrelation technique (IGA). This measurement technique, based on time-delayed two beam coupling in a photorefractive crystal has been used to accurately measure n2 in short lengths of single mode fibers. For the first time to our knowledge, IGA is used to measure n2 of multimode fiber with a passively modelocked Nd:YVO4 laser operating with a dual-line near 1342 nm.

Spatial distribution of unconventional gas wells and human populations in the Marcellus Shale in the United States: Vulnerability analysis

Modern forms of drilling and extraction have recently led to a boom in oil and gas production in the U.S. and stimulated a controversy around its economic benefits and environmental and human health impacts. Using an environmental justice paradigm this study applies Geographic Information Systems (GIS) and spatial analysis to determine whether certain vulnerable human populations are unequally exposed to pollution from unconventional gas wells in Pennsylvania, West Virginia, and Ohio. Several GIS-based approaches were used to identify exposed areas, and a t-test was used to find statistically significant differences between rural populations living close to wells and rural populations living farther away. Sociodemographic indicators include age (children and the elderly), poverty level, education level, and race at the census tract level. Local Indicators of Spatial Autocorrelation (LISA) technique was applied to find spatial clusters where both high well density and high proportions of vulnerable populations occur. The results demonstrate that the environmental injustice occurs in areas with unconventional wells in Pennsylvania with respect to the poor population. There are also localized clusters of vulnerable populations in exposed areas in all three states: Pennsylvania (for poverty and elderly population), West Virginia (for poverty, elderly population, and education level) and Ohio (for children).

Investigation of Aggregative Properties of the Antimicrobial Peptide LL‐37 by Dynamic Light Scattering (DLS) and Electrophoretic Shift Mobility Assay (EMSA)

The antimicrobial peptide LL‐37 is a member the cathelicidin family of antimicrobial peptides that play a role in mammalian innate immune defense and have potential for combating bacterial infection and antibiotic resistance. LL‐37 is known to induce cell death by disrupting the cell membrane, but the mechanism for membrane disruption is still unknown. By studying peptide properties, such as aggregation, we may better understand how LL‐37 induces cell death. We have used dynamic light scattering (DLS) and electrophoretic mobility shift assays (EMSA) to investigate the aggregative properties of LL‐37. DLS monitors diffusion and thus the hydrodynamic radius of scattering centers by analyzing temporal fluctuations in scattered light intensity using the autocorrelation technique. In the concentration range of 150 to 37 μM, we observe by DLS that LL‐37 shows decreasing mobility as concentration increases, indicative of particle size transition from a hydrodynamic radius on the order of 1 to 1,000 nm. EMSA with peptide detection by western blotting provides information about aggregate size at lower concentrations, ranging from 0.8 to 50 μM. As a result, the particle size distribution shifts decisively in favor of relatively small aggregates as the concentration falls below 50 μM, indicated by the decrease in hydrodynamic radius in DLS and increased protein migration in EMSA.

Ultra-short pulse reconstruction software in high power laser system

An ultra-short pulse reconstruction software, validated through a set of experimental measurements on the front-end of the Vulcan laser at the RAL Central Laser Facility is presented. The measurements were acquired in Target Area Petawatt of the Vulcan laser, both using a conventional autocorrelation technique and the GRENOUILLE technique in order to compare the results. The FWHM of the laser pulses considered came out to be comparable for the two techniques. In this experimental campaign for the first time a technique different from the autocorrelation one has been used for a PW class laser as Vulcan.

Multivariate spatial hierarchical Bayesian empirical likelihood methods for small area estimation

Recent advances in small area estimation incorporating both explicit spatial autocorrelation and empirical likelihood techniques have produced estimates with greater precision. Furthermore, the multivariate Fay–Herriot models take advantage of within‐location correlation between multiple outcomes for a set of small areas. We extend the Fay–Herriot model by utilizing empirical likelihood techniques to the spatially explicit multivariate setting. We then model the five‐year period estimates from the American Community Survey (2006–10) of percent of unemployed individuals and percent of families in poverty for the counties of Missouri. We demonstrate bivariate reduction in leave‐one‐out median absolute deviation over an approximately equivalently specified parametric model. Copyright © 2015 John Wiley &amp; Sons, Ltd.

A GIS Based Integrated Approach to Measure the Spatial Equity of Community Facilities of Bangladesh

The distribution of public facilities and their spatial equity is an important matter to be considered while planning public facilities. However, most of the studies in the literature have taken into consideration only a single type of facility while leaving other facilities unconsidered. In this paper an integrated spatial index for public facilities has been developed integrating GIS and spatial analysis models. The index measures the spatial equity based on the accessibility of 6 different types of public facilities for 5247 unions and 476 sub-districts of Bangladesh. Spatial autocorrelation techniques have been applied to understand the spatial pattern of accessibility. In fact it helps to understand the characteristics of spatial equity both for disaggregated and aggregated levels. It has been found that variation accessibilities to the facilities across the space are significant. Distribution of some facilities are spatially clustered to some particular areas means those areas are in an advantageous position in terms of accessibility while other areas are in a backward condition. The proposed index and the spatial autocorrelation will help to identify which areas should receive more priority in allocating particular types of public facilities in the future.

Development of experimental techniques for the characterization of ultrashort photon pulses of extreme ultraviolet free-electron lasers

One of the most challenging tasks for extreme ultraviolet, soft and hard x-ray free-electron laser photon diagnostics is the precise determination of the photon pulse duration, which is typically in the sub 100 fs range. Nine different methods, able to determine such ultrashort photon pulse durations, were compared experimentally at FLASH, the self-amplified spontaneous emission free-electron laser at DESY in Hamburg, in order to identify advantages and disadvantages of different methods. Radiation pulses at a wavelength of 13.5 and 24.0 nm together with the corresponding electron bunch duration were measured by indirect methods like analyzing spectral correlations, statistical fluctuations, and energy modulations of the electron bunch and also by direct methods like autocorrelation techniques, terahertz streaking, or reflectivity changes of solid state samples. In this paper, we present a comprehensive overview of the various techniques and a comparison of the individual experimental results. The information gained is of utmost importance for the future development of reliable pulse duration monitors indispensable for successful experiments with ultrashort extreme ultraviolet pulses.9 MoreReceived 16 July 2014DOI:https://doi.org/10.1103/PhysRevSTAB.17.120702This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical Society