Composition of high frequency ambient noise from cross-correlation:A case study using a small aperture array

Long-time cross correlation of ambient noise has been proved as a powerful tool to extract Green＇s function between two receivers. The study of composition of ambient noise is important for a better understanding of this method. Previous studies confirm that ambient noise in the long period （3 s and longer） mostly consists of surface wave, and 0.25-2.5 s noise consists more of body waves. In this paper, we perform cross correlation processing at much higher frequency （30-70 Hz） using ambient noise recorded by a small aperture array. No surface waves emerge from noise correlation function （NCF）, but weak P waves emerge. The absence of surface wave in NCF is not due to high attenuation since surface waves are strong from active source, therefore probably the high ambient noise mostly consists of body wave and lacks surface wave. Origin of such high frequency body waves in ambient noise remains to be studied.

An Optimized Cross Correlation Power Attack of Message Blinding Exponentiation Algorithms

The message blinding method is the most efficient and secure countermeasure against first-order differential power analysis(DPA).Although cross correlation attacks(CCAs) were given for defeating message blinding methods,however searching for correlation points is difficult for noise,misalignment in practical environment.In this paper,we propose an optimized cross correlation power attack for message blinding exponentiation algorithms.The attack method can select the more correlative power points of share one operation in the modular multiplication by comparing variances between correlation coefficients.Further we demonstrate that the attack method is more efficient in experiments with hardware implementation of RSA on a crypto chip card.In addition to the proposed CCA method can recovery all 1024 bits secret key and recognition rate increases to 100%even when the recorded signals are noisy.

Teleseismic body waves extracted from ambient noise cross correlation between F-net and Chin Array phase Ⅱ

The vertical-vertical noise cross-correlation functions(NCFs)between two seismic arrays,the Japan F-net and Chin Array phase Ⅱ,are calculated using continuous recordings during 2013-2016.After array interferometry to obtain bin stacked NCFs,clear body waves are retrieved at different period bands.Teleseismic direct P waves for distance 15-40 degrees are observed between short period 3-10 s while core reflected PcP/ScS waves are more obvious for longer period 30-60 s.The signal-to-noise-ratio(SNR)of the short period P waves reaches its highest point with bin widths around 20 km while SNRs of PcP and ScS increase slowly with bin width.All those body waves demonstrate clear directivity with strong signals traveling from the east.The time-lapse SNR variations for the PcP and ScS show correlation with the occurrence of major earthquakes,while the P-wave SNR demonstrates seasonal variations with additional contribution from major earthquakes.The present results suggest teleseismic body waves can be retrieved through bin stacking,though further processing is still necessary to obtain finer waveforms such as P wave triplications.

Cross correlation mediated by distant Majorana zero modes with no overlap

Existing studies via shot noise calculation conclude that the cross correlation between the currents in the two leads connected by a pair of Majorana zero modes(MZMs)vanishes when their coupling energy𝜖∈_(M)→0.Motivated by the intrinsic nature of nonlocality of the MZMs,we revisit this important problem and propose an experimental scheme to demonstrate the nonvanishing cross correlation even at the limit𝜖∈_(M)→0.The proposed scheme employs the Andreevprocess-associated branch circuit currents,which are theoretically obtained by applying a decomposition analysis for the total currents while are accessible directly in practical measurement.For different bias voltage setup,we find intriguing results of both negative and positive correlations and carry out simple physical understanding using a quantum jump technique.Importantly,combining together with the evidence of the zero-bias-peak of conductance,the nonlocal cross correlation predicted in this work can help to confirm the existence of the nonlocal MZMs.

Automated Recovery of the 2012 Sumatera Aftershock Sequence Using Waveform Cross Correlation

We assess the performance of waveform cross correlation as applied to automatic and interactive processing of the aftershock sequence of the April 11, 2012 Sumatera Ms（IDC） = 8.2 earthquake. The XSEL （cross correlation standard event list） is compared to the REB （Reviewed Event Bulletin） issued by the IDC （International Data Centre）. The latter includes 1,181 aftershocks between April 11 and May 25. To automatically recover the sequence, sixteen aftershocks were selected from the IDC SEL3 （Standard Event List） available on April 13 and used as master events. Waveform templates from only seven IMS （International Monitoring System） array stations with the largest SNR （signal-to-noise ratio） for the main shock were used to calculate cross correlation coefficients. Approximately 620,000 arrivals were detected and then used to build events according to the IDC definition. After conflict resolution between event hypotheses with similar arrivals found by more than one master, all survived hypotheses populated the XSEL. The total number of distinct hypotheses was 4,924, with 2,763 hypotheses not matched by the REB, i.e. potentially new REB events. To evaluate the quality of the XSEL, we randomly selected a representative portion （-15%） from 2,763 hypotheses and reviewed them interactively according to standard IDC rules and guidelines. There were 119 new REB events built and 145 XSEL hypotheses rejected. Several frequency and probability density distributions have been constructed for all detections, the associated detections, the XSEL detections, the detections in the new REB, and rejected events.

A New Method For Mitigation Of Cross Correlation In GPS Receiver

An algorithm for GPS receiver performing to mitigate cross correlations between weak satellite signal and strong satellite signals is presented.By using the tracking result of strong signal,the cross-correlation and cross correlation sequence between weak signals and strong signal can be computed,further modifying the local generate C/A code to drive the cross correlation to zero. The advantage of this method is that it does not require estimation of the strong signal amplitude and it partially independent of the data bit value.Simulation result shows it can eliminate the interference of 75%,and this method is at the cost of sensitivity loss of 0.28dB.

A Practical Approach for Missing Wireless Sensor Networks Data Recovery

In wireless sensor networks(WSNs),the performance of related applications is highly dependent on the quality of data collected.Unfortunately,missing data is almost inevitable in the process of data acquisition and transmission.Existing methods often rely on prior information such as low-rank characteristics or spatiotemporal correlation when recovering missing WSNs data.However,in realistic application scenarios,it is very difficult to obtain these prior information from incomplete data sets.Therefore,we aim to recover the missing WSNs data effectively while getting rid of the perplexity of prior information.By designing the corresponding measurement matrix that can capture the position of missing data and sparse representation matrix,a compressive sensing(CS)based missing data recovery model is established.Then,we design a comparison standard to select the best sparse representation basis and introduce average cross-correlation to examine the rationality of the established model.Furthermore,an improved fast matching pursuit algorithm is proposed to solve the model.Simulation results show that the proposed method can effectively recover the missing WSNs data.

Coulomb-assisted nonlocal electron transport between two pairs of Majorana bound states in a superconducting island

We investigate the nonlocal transport modulated by Coulomb interactions in devices comprising two interacting Majorana wires,where both nanowires are in proximity to a mesoscopic superconducting(SC)island.Each Majorana bound state(MBS)is coupled to one lead via a quantum dot with resonant levels.In this device,the nonlocal correlations can be induced in the absence of Majorana energy splitting.We find that the negative differential conductance and giant current noise cross correlation could be induced,due to the interplay between nonlocality of MBSs and dynamical Coulomb blockade effect.This feature may provide a signature for the existence of the MBSs.

THE CORRELATED CROSS SECTION OF THE MANY-BODY SCATTERING

In this paper the tensor probability current and continuity equation is obtained, with this the correlated cross section of many particle scattering can be evaluation.

A Linear Interference Cancellation Multi-User Detector for Synchronous CDMA Communications

This paper describes a linear interference cancellation multi user detector for synchronous DS CDMA systems under the condition that all spread spectrum code waveforms have the constant cross correlating coefficients. The basic idea is to get the estimation for total multiple access interference (MAI) of all users using a reference code waveform, then subtract the total MAI from the received signal. The structure of such a detector is nearly similar to the conventional detector. The BER expression obtained in the paper shows significant performance improvement compared to the other detectors.

Ambient noise spectral properties in the north area of Xisha

Ambient noise is very important in the prediction system of a sonar performance, because it determines the detection ranges always in a passive sonar and usually in an active sonar. In the uncertainty issue for the so-nar performance, it is necessary to know this factor＇s statistical characteristics that are only obtained by data processing from the underwater ambient noise measurements. Broad-band ambient noise signals from 16 hydrophones were amplified and recorded for 2 min every 1 h. The results show that the ambient noise is essentially depth independent. The cross correlation of the ambient noise levels （1, 6 and 12 h average） with a wind speed is presented. It was found that the correlation is excellent on the upper frequency band and the noise levels correlate better with high wind speed than with low wind speed.

Efficient normalized cross correlation calculation method for stereo vision based robot navigation

Stereo vision systems are widely used for autonomous robot navigation. Most of them apply local window based methods for real-time purposes. Normalized cross correlation （NCC） is notorious for its high computational cost, though it is robust to different illumination conditions between two cameras. It is rarely used in real-time stereo vision systems. This paper proposes an efficient normalized cross correlation calculation method based on the integral image technique. Its computational complexity has no relationship to the size of the matching window. Experimental results show that our algorithm can generate the same results as traditional normalized cross correlation with a much lower computational cost. Our algorithm is suitable for planet rover navigation.

The Velocity Measurement of Two-phase Flow Based on Particle Swarm Optimization Algorithm and Nonlinear Blind Source Separation

In order to overcome the disturbance of noise,this paper presented a method to measure two-phase flow velocity using particle swarm optimization algorithm,nonlinear blind source separation and cross correlation method.Because of the nonlinear relationship between the output signals of capacitance sensors and fluid in pipeline,nonlinear blind source separation is applied.In nonlinear blind source separation,the odd polynomials of higher order are used to fit the nonlinear transformation function,and the mutual information of separation signals is used as the evaluation function.Then the parameters of polynomial and linear separation matrix can be estimated by mutual information of separation signals and particle swarm optimization algorithm,thus the source signals can be separated from the mixed signals.The two-phase flow signals with noise which are obtained from upstream and downstream sensors are respectively processed by nonlinear blind source separation method so that the noise can be effectively removed.Therefore,based on these noise-suppressed signals,the distinct curves of cross correlation function and the transit times are obtained,and then the velocities of two-phase flow can be accurately calculated.Finally,the simulation experimental results are given.The results have proved that this method can meet the measurement requirements of two-phase flow velocity.

Spatial pyramidal cross correlation for particle image velocimetry

A spatial pyramidal cross-correlation based on interrogation area sub-division is introduced to improve the measurement resolution in particle image velocimetry(PIV). The high-resolution velocity can be achieved with a velocity prediction model via coarse cross-correlation. The prediction formula is deduced from the frequency response of the moving average(MA). The performance of this method was assessed using synthetically generated images of sinusoidal shear flow, two-dimensional vortical cellular flow, and homogeneous turbulence. A real PIV experiment of turbulent boundary layer was used to evaluate the new method. The results indicate that the spatial pyramid cross-correlation can robustly increase the spatial resolution.

Theoretical analysis of stack gas emission velocity measurement by optical scintillation

Theoretical analysis for an online measurement of the stack gas flow velocity based on the optical scintillation method with a structure of two parallel optical paths is performed. The causes of optical scintillation in a stack are first introduced. Then, the principle of flow velocity measurement and its mathematical expression based on cross correlation of the optical scintillation are presented. The field test results show that the flow velocity measured by the proposed technique in this article is consistent with the value tested by the Pitot tube. It verifies the effectiveness of this method. Finally, by use of the structure function of logarithmic light intensity fluctuations, the theoretical explanation of optical scintillation spec- tral characteristic in low frequency is given. The analysis of the optical scintillation spectrum provides the basis for the measurement of the stack gas flow velocity and particle concentration simultaneously.

Analysis of the relationship between water level fluctuation and seismicity in the Three Gorges Reservoir(China)

The Three Gorges Reservoir is a good site for the further researches on reservoir induced seismicity due to decades＇ seismic monitoring. After the first water impounding in 2003, seismic activity becomes more frequent than that before water impoundment. In order to quantitatively study, the relationship between the water level fluctuation and earthquakes in TGR, we introduced statistical methods to attain the goal. First of all, we relocated the earthquakes in TGR region with double difference method and divided the earthquakes into 5 clusters with clustering analysis method. Secondly, to examine the impacts of water level fluctuation in different water filling stages on the seismic activity in the 5 clusters, a series of statistical analyses are applied. Pearson correlation results show that only the 175 m water level fluc- tuation has significantly positive impacts on the seismic activity in clusters I, II, III and V with correlation coefficients of 0.44, 0.38, 0.66 and 0.63. Cross-correlation analysis demonstrates that 0, ], 0 and 0 month time delay separately for the clusters I, II, III and V exists. It illustrated the influences of the water loading and pore pressure diffusion on induced earthquakes. Cointegration tests and impulse response analysis denoted that the 175 m water level only had long term and significant effects just on the seismic events in the intersection region of the Fairy Mount Fault and Nine-brook Fault. One standard deviation shock to 175 m water level increased the seismic activity in cluster V for the first 3 months, and then the negative influence was shown. After 7 months, the negative impulse response becomes stable. The long-term effect of the 175 m water impoundment also proved the important role of pore pressure diffusion in RIS with time.

Quantitative deconvolution of autocorrelations and cross correlations from two-dimensional lifetime decay maps in fluorescence lifetime correlation spectroscopy

Fluorescence correlation spectroscopy （FCS） is a widely used method for measuring molecular diffusion and chemical kinetics. However, when a mixture of fluorescent species is taken into account, the conven- tional FCS method has limitations in extracting autocorrelations for different species and cross correla- tions between different species. Recently developed fluorescence lifetime correlation spectroscopy （FLCS） based on time-tagged time-resolved （TITR） photon recording, which can record the global and micro arrival time for each individual photon, has been used to discriminate different species according to fluorescence lifetime. Here, based on two-dimensional lifetime decay maps constructed from TITR photon stream, we have developed a quantitative lifetime-deconvolution FCS model （LDFCS） to extract precise chemical rates for chemical conversions in multi-species systems. The key point of LDFCS model is separation of different species according to the global distribution of fluorescence lifetime and then deconvolution of autocorrelations and cross-correlations from the two-dimensional lifetime decay maps constructed bv the micro arrival times of photon pairs at each delay time.

Automatic onset phase picking for portable seismic array observation

Automatic phase picking is a critical procedure for seismic data processing, especially for a huge amount of seismic data recorded by a large-scale portable seismic array. In this study is presented a new method used for automatic accurate onset phase picking based on the proporty of dense seismic array observations. In our method, the Akaike＇s information criterion （AIC） for the single channel observation and the least-squares cross-correlation for the multi-channel observation are combined together. The tests by the seismic array observation data after triggering with the short-term average/long-term average （STA/LTA） technique show that the phase picking error is less than 0.3 s for local events by using the single channel AIC algorithm. In terms of multi-channel least-squares cross-correlation technique, the clear teleseismic P onset can be detected reliably. Even for the teleseismic records with high noise level, our algorithm is also able to effectually avoid manual misdetections.

Measuring Acoustic Wave Transit Time in Furnace Based on Active Acoustic Source Signal

Accurate measurement of transit time for acoustic wave between two sensors installed on two sides of a furnace is a key to implementing the temperature field measurement technique based on acoustical method. A new method for measuring transit time of acoustic wave based on active acoustic source signal is proposed in this paper, which includes the followings： the time when the acoustic source signal arrives at the two sensors is measured first; then, the difference of two arriving time arguments is computed, thereby we get the transit time of the acoustic wave between two sensors installed on the two sides of the furnace. Avoiding the restriction on acoustic source signal and background noise, the new method can get the transit time of acoustic wave with higher precision and stronger ability of resisting noise interference.

Stability of PAC(Psy-2A-Crt I) gene and agronomic traits in the F_(2:3) of IR36/PAC transgenic plants

This study was carried out to evaluate the expression of yellow endosperm color in the progeny of Psy-2A-Crt I（β-carotene gene, PAC） transgenic plants crossed with IR36. The selected 25 lines of F2 progeny exhibited stable expression of yellow endosperm color and high agronomic characteristics. IR36 and PAC transgenic plant of the grain length, width and ratio showed the same tendency of normal distribution. For progeny selection, colorimeters were as employed to distinguish differing visible colors. Correlation analysis was conducted to investigate the relationship between b＊ value and the expression of specific genes. b＊ value was associated with the relative expression of the PAC-Rev and MAR product by real-time PCR and t-test revealed significant difference. Based on this study, correlation between colorimetric values and real-time PCR was effective to detect gene expression. Yellow endosperm progenies represent a new genetic pool that might be useful to increase the genetic diversity of yellow endosperm rice.