NASA Astrophysics Data System (ADS)
Alejos, Ana Vazques; Dawood, Muhammad
2012-06-01
In this contribution we examine the propagation of an ultrawideband (UWB) random noise signal through dispersive media such as soil, vegetation, and water, using Fourier-based analysis. For such media, the propagated signal undergoes medium-specific impairments which degrade the received signal in a different way than the non-dispersive propagation media. Theoretically, larger penetration depths into a dispersive medium can be achieved by identifying and detecting the precursors, thereby offering significantly better signal-to-noise ratio and enhanced imaging. For a random noise signal, well defined precursors in term of peak-amplitude don't occur. The phenomenon must therefore be studied in terms of energy evolution. Additionally, the distortion undergone by the UWB random noise signal through a dispersive medium can introduce frequency-dependent uncertainty or noise in the received signal. This leads to larger degradation of the cross-correlation function (CCF), mainly in terms of sidelobe levels and main peak deformation, and consequently making the information retrieval difficult. We would further analyze one method to restore the shape and carrier frequency of the input UWB random noise signal, thereby, improving the CCF estimation.
Colombi, Andrea; Boschi, Lapo; Roux, Philippe; Campillo, Michel
2014-03-01
Cross-correlations of ambient noise averaged at two receivers lead to the reconstruction of the two-point Green's function, provided that the wave-field is uniform azimuthally, and also temporally and spatially uncorrelated. This condition depends on the spatial distribution of the sources and the presence of heterogeneities that act as uncorrelated secondary sources. This study aims to evaluate the relative contributions of source distribution and medium complexity in the two-point cross-correlations by means of numerical simulations and laboratory experiments in a finite-size reverberant two-dimensional (2D) plate. The experiments show that the fit between the cross-correlation and the 2D Green's function depends strongly on the nature of the source used to excite the plate. A turbulent air-jet produces a spatially uncorrelated acoustic field that rapidly builds up the Green's function. On the other hand, extracting the Green's function from cross-correlations of point-like sources requires more realizations and long recordings to balance the effect of the most energetic first arrivals. When the Green's function involves other arrivals than the direct wave, numerical simulations confirm the better Green's function reconstruction with a spatially uniform source distribution than the typical contour-like source distribution surrounding the receivers that systematically gives rise to spurious phases. PMID:24606247
Retrieving the Green's Function by Cross-correlation: a Comparison of Approaches
NASA Astrophysics Data System (ADS)
Wapenaar, K.; Draganov, D.
2004-12-01
Recently it has been shown by various authors that the Green's function of a random medium can be obtained by cross-correlating the recordings of a diffuse wave field at two receiver positions (Weaver and Lobkis, 2001; van Tiggelen, 2003; Snieder, 2004). The resulting Green's function is the wave field that would be observed at one of these receiver positions if there were an impulsive source at the other. This theoretical result has first been demonstrated with ultrasonic measurements and later with seismic surface waves (Campillo and Paul, 2003). The accuracy of the reconstructed Green's function depends on the amount of disorder of the medium parameters and the duration of the signal. Ideally the cross-correlations should be done in the equipartitioned regime (where the net energy flux is equal to zero), which takes place after sufficiently long multiple scattering of the wave field between the heterogeneities in the disordered medium (Malcolm, Scales and van Tiggelen, 2004). An initially independent line of research, developed by exploration seismologists, deals with the reconstruction of the seismic reflection response of a deterministic medium from (passive) recordings of the transmission response. Already in 1968 Claerbout showed that the autocorrelation of the transmission response of a horizontally layered earth yields the superposition of the reflection response and its time-reversed version. The source in the subsurface may be a transient or a noise signal; in both cases the source signature in the reconstructed reflection response is the autocorrelation of the source signal in the subsurface. Claerbout's derivation was strictly one-dimensional. Later he conjectured for the 3-D situation that `by cross-correlating noise traces recorded at two locations on the surface, we can construct the wave field that would be recorded at one of the locations if there was a source at the other'. Although it was not explicitly stated, this conjecture applies to
NASA Astrophysics Data System (ADS)
Kwak, S.; Song, S. G.; Kim, G.; Shin, J. S.
2015-12-01
Recently many seismologists have paid attention to ambient seismic field, which is no more referred as noise and called as Earth's hum, but as useful signal to understand subsurface seismic velocity structure. It has also been demonstrated that empirical Green's functions can be constructed by retrieving both phase and amplitude information from ambient seismic field (Prieto and Beroza 2008). The constructed empirical Green's functions can be used to predict strong ground motions after focal depth and double-couple mechanism corrections (Denolle et al. 2013). They do not require detailed subsurface velocity model and intensive computation for ground motion simulation. In this study, we investigate the capability of predicting long period surface waves by the ambient seismic wave field with a seismic event of Mw 4.0, which occurred with a limestone mine collapse in South Korea on January 31, 2015. This limestone-mine event provides an excellent opportunity to test the efficiency of the ambient seismic wave field in retrieving both phase and amplitude information of Green's functions due to the single force mechanism of the collapse event. In other words, both focal depth and double-couple mechanism corrections are not required for this event. A broadband seismic station, which is about 5.4 km away from the mine event, is selected as a source station. Then surface waves retrieved from the ambient seismic wave field cross-correlation are compared with those generated by the event. Our preliminary results show some potential of the ambient seismic wave field in retrieving both phase and amplitude of Green's functions from a single force impulse source at the Earth's surface. More comprehensive analysis by increasing the time length of stacking may improve the results in further studies. We also aim to investigate the efficiency of retrieving the full empirical Green's functions with the 2007 Mw 4.6 Odaesan earthquake, which is one of the strongest earthquakes occurred
Benech, N; Brum, J; Catheline, S; Gallot, T; Negreira, C
2013-05-01
In a lossless system, the causal and acausal Green's function for elastic waves can be retrieved by cross-correlating the elastic field at two positions. This field, composed of converging and diverging waves, is interpreted in the frame of a time-reversal process. In this work, the near-field effects on the spatio-temporal focusing of elastic waves are analyzed through the elastodynamic Green's function. Contrary to the scalar field case, the spatial focusing is not symmetric preserving the directivity pattern of a simple source. One important feature of the spatial asymmetry is its dependency on the Poisson ratio of the solid. Additionally, it is shown that the retrieval of the bulk wave speed values is affected by diffraction. The correction factor depends on the relative direction between the source and the observed field. Experimental verification of the analysis is carried out on the volume of a soft-solid. A low-frequency diffuse-like field is generated by random impacts at the sample's free surface. The displacement field is imaged using ultrasound by a standard speckle tracking technique. One important application of this work is in the estimation of the shear elastic modulus in soft biological tissues, whose quantification can be useful in non-invasive diagnosis of various diseases. PMID:23654383
NASA Astrophysics Data System (ADS)
Sato, Haruo
2009-10-01
The peak lag time of the cross-correlation function (CCF) of random noise at two receivers give the wave propagation velocity. This idea has been widely used for the velocity tomography analysis. Recently, there were reports on the temporal change in the coda portion of CCF or autocorrelation function of ambient noise as a measure of the medium property. Here, we propose a simple concrete model for the retrieval of Green's function having a coda tail in a scattering medium without dissipation from the CCF of noise. The scattering medium is mathematically given by a distribution of velocity anomalies represented by delta functions. We suppose that waves are radiated from stationary noise sources, which are randomly distributed on a surrounding spherical shell with a large radius compared with the dimension of the scattering medium. Using the first order Born approximation, we show that the derivative of CCF with respect to lag time gives the antisymmetrized Green's function having a coda tail in the framework of the single scattering approximation.
Analog computation of auto and cross-correlation functions
NASA Technical Reports Server (NTRS)
1974-01-01
For analysis of the data obtained from the cross beam systems it was deemed desirable to compute the auto- and cross-correlation functions by both digital and analog methods to provide a cross-check of the analysis methods and an indication as to which of the two methods would be most suitable for routine use in the analysis of such data. It is the purpose of this appendix to provide a concise description of the equipment and procedures used for the electronic analog analysis of the cross beam data. A block diagram showing the signal processing and computation set-up used for most of the analog data analysis is provided. The data obtained at the field test sites were recorded on magnetic tape using wide-band FM recording techniques. The data as recorded were band-pass filtered by electronic signal processing in the data acquisition systems.
Noise cross correlation functions in a noisy region
NASA Astrophysics Data System (ADS)
Gaudot, I.; Beucler, E.; Mocquet, A.; Schimmel, M.; Le Feuvre, M.; Leparoux, D.; Côte, P.
2013-12-01
The geology of the western France can be roughly split into two main domains: the Armorican massif that contains imprints of the old Cadomian and Variscan orogens; and the Bay of Biscay which present signatures of more recent tectonic events closely related to the opening of North Atlantic ocean. Due to the lack of seismic stations deployment, it exists very few pictures of the deep structures below the Armorican Massif and the Bay of Biscay. Recently, a broadband array of seismometers has been deployed over the south and west of France, providing a good opportunity to get reliable images at depth. Since the region is surrounded by the seas, the seismic ambient noise tomography technique has been proposed to reveal the crustal and uppermost mantle features beneath this area. The first step consists in the computation of noise correlation functions (NCFs) between each station pairs. The ability to obtain empirical Green's functions from NCFs relies on the efficiency of the randomization. Classic ambient noise tomography studies use long-time series (typically several months) to help the randomization including all the scattering effects due to Earth's heterogeneities. However, additionnal signal processing steps such as temporal and/or spectral whitening are most often required for the signals to be representative of a random wavefield. These techniques rely on nonlinear operations which corrupt the integrity of the original record. In the literature, alternatives have been proposed to avoid, at least partially, such non linear operations. One of them is the instantaneous phase cross correlation (PCC). This correlation technique is intrinsically little sensitive to large amplitude transient signals. Using a set of data from a temporary broad band array, we explore the features of the PCC as compared to the time domain geometrically normalized cross correlation (CCGN). In the 0.02Hz-1Hz frequency band, different time series are extracted to investigate the effects of
Experimental Study of the Convergence of Two-Point Cross-Correlation Toward the Green's Function
NASA Astrophysics Data System (ADS)
Gouedard, P.; Roux, P.; Campillo, M.; Verdel, A.; Campman, X.
2007-12-01
It has been shown theoretically by several authors that cross-correlation of the seismic motion recorded at two points could yield the Green's Function (GF) between these points. Convergence of cross-correlations toward the GF depends on sources positions and/or the nature of the wavefield. Direct waves from an even distribution of sources can be used to retrieve the GF. On the other hand, in an inhomogeneous medium, recording the diffuse field (coda) is theoretically sufficient to retrieve the GF whatever the sources distribution is. Since none of these two conditions (even distribution of sources or a perfectly diffuse field) is satisfied in practice, the question of convergence toward the GF has to be investigated with real data. A 3D exploration survey with sources and receivers on a dense grid offers such an opportunity. We used a high- resolution survey recorded by Petroleum Development Oman in North Oman. The data have been obtained in a 1x1~km area covered with 1600 geophones located on a 25x25~m-cell grid. Records are 4-seconds long. A unique feature of this survey is that vibrators (working in the [8-120~Hz] frequency band), were located on a similar grid shifted with respect to the receiver grid by half a cell (12.5~m) in both directions. This allows us to compare estimated GF's with measured direct waves (GF's) between the geophones. The shallow subsurface is highly heterogeneous and records include seismic coda. From this dataset, we selected two receiver locations (Ra and Rb) distant from d=158~m. We used both different sets of source locations and time windows to compute the cross-correlation between these two receivers. Then we compared the derivatives of correlation functions with the actual GF measured in Rb (resp.~Ra) for a source close to Ra (resp.~Rb). By doing so, we show the actual influence of source locations and scattering (governed by the records' selected time window) on the Signal-to-Noise Ratio (SNR) of the reconstructed GF. When using
On the Noise Level of the Ambient Noise Cross-Correlation Function and Its Application
NASA Astrophysics Data System (ADS)
Chen, Y. N.; Gung, Y.; Chiao, L. Y.
2014-12-01
Retrieving the Empirical Green's function (EGF) between two receivers by cross-correlating continuous records is now a well-recognized technique and the derived EGFs have been applied to various fields in seismology. However, little attention has been given to a more quantitative description on the noise behavior of the noise-derived cross-correlation functions (CCF), for its signal-to-noise ratio (SNR) can be improved easily by increasing the total correlation time. In our early work, using data recorded from Taiwan and Korea, we have designed a procedure to quantify the noises within the noise-derived CCFs and their spatial/directional properties. Because the effective amplitudes and the noise levels of CCFs are closely related to the distribution of the ambient sources and the population of the uncorrelated noises, respectively, here we move forward to further investigate the source mechanisms of the ambient noises by using their distinctive sensitivities to the surrounding sources. It is known that the short period (3~5 seconds) secondary microseisms (SPSM) are much more active in Taiwan Straight and such asymmetric energy excitations are well demonstrated in the amplitude asymmetry of CCFs. Interestingly, we find that, there is nearly no directional dependence of the noise levels of CCFs, namely, the effects of uncorrelated sources in the CCFs are essentially isotropic. With the same data set, we also investigate the excitation mechanisms of (1) the intermediate period (7-9 seconds) microseisms, which are one of the spectral peaks in the ambient noises, and (2) the coda train in the noise-derived CCFs. Based upon our analysis, we argue that (1) the 7~9 period ambient noises are contributed mainly by the near-coast primary microseisms rather than the far-field long period secondary microseisms, and (2) instead of the distant ocean waves, local scatter effects are the major sources of the CCF coda train.
Asymmetry of coda cross-correlation function: dependence of the epicentre location
NASA Astrophysics Data System (ADS)
Emoto, K.; Campillo, M.; Brenguier, F.; Briand, X.; Takeda, T.
2015-06-01
We analyze the cross-correlation function (CCF) of coda of earthquakes, which is used to retrieve the Green's function between two stations as well as the CCF of ambient noise. We select 74 Hi-net stations located in eastern Japan and 66 earthquakes to calculate the CCF. For each earthquake, we calculate the CCFs between possible pairs for the frequency bands of 0.1-0.2 Hz, 0.2-0.4 Hz and 0.4-0.8 Hz. Then we stack the CCFs for different earthquakes at each pair to obtain the average CCF. Although the correlation coefficients between the average and each CCFs are lower than 0.5 for most of the earthquakes, we obtain the propagating Rayleigh wave trace from average CCFs. We focus on the ratio of the amplitude in the positive lag time of the CCF to that in the negative lag time. CCFs for different earthquakes show different ratios which depend on the angle between the path of two stations and the epicentre. The amplitude in the lag time corresponding to the signal travelling from the near source station to the far source station is larger than that in the opposite lag time. Therefore the energy flux is not isotropic even in the coda and the energy from the source side is dominant. We average the ratios of pairs whose absolute values of angles are less than 45°. The average ratios are 0.5 at 0.1-0.2 Hz. For higher frequencies, the ratio is not clear because of the bad signal-to-noise ratio. According to the diffusion model, the ratio is predicted as 0.6. Therefore, the coda is represented as the diffusion state in 0.1-0.2 Hz with our observation setting.
Using the Cross-Correlation Function to Evaluate the Quality of Eddy-Covariance Data
NASA Astrophysics Data System (ADS)
Qi, Yongfeng; Shang, Xiaodong; Chen, Guiying; Gao, Zhiqiu; Bi, Xueyan
2015-11-01
A cross-correlation test is proposed for evaluating the quality of 30-min eddy-covariance data. Cross-correlation as a function of time lag is computed for vertical velocity paired with temperature, humidity, and carbon dioxide concentration. High quality data have a dominant peak at zero time lag and approach zero within a time lag of 20 s. Poor quality data have erratic cross-correlation functions, which indicates that the eddy flux may no longer represent the energy and mass exchange between the atmospheric surface layer and the canopy, and such data should be rejected in post-data analyses. Eddy-covariance data over grassland in July 2004 are used to evaluate the proposed test. The results show that 17, 29, and 36 % of the available data should be rejected because of poor quality measurements of sensible heat, latent heat, and CO2 fluxes, respectively. The rejected data mainly occurred on calm nights and day/night transitions when the atmospheric surface layer became stable or neutrally stratified. We found no friction velocity (u_*) threshold below which all data should be rejected, a test that many other studies have implemented for rejecting questionable data. We instead found that some data with low u_* were reliable, whereas other data with higher u_* were not. The poor quality measurements collected under less than ideal conditions were replaced by using the mean diurnal variation gap-filling method. The correction for poor quality data shifted the daily average CO2 flux by +0.34 g C m^{-2} day^{-1}. After applying the quality-control test, the eddy CO2 fluxes did not display a clear dependence on u_*. The results suggest that the cross-correlation test is a potentially valuable step in evaluating the quality of eddy-covariance data.
Passive localization in the deep ocean based on cross-correlation function matching.
Lei, Zhixiong; Yang, Kunde; Ma, Yuanliang
2016-06-01
Passive localization of a sound source in the deep ocean is investigated in this study. The source can be localized by taking advantage of a cross-correlation function matching technique. When a two-sensor vertical array is used in the deep ocean, two types of side lobe curves appear in the ambiguity surface of the localization. The side lobe curves are analytically expressed and they are then used as indicators of the localization result instead of the scanning point with the maximum power. Simulation and experiment demonstrate the performance of the proposed passive localization method. PMID:27369172
NASA Astrophysics Data System (ADS)
Yang, Zhichun; Yu, Zhefeng; Sun, Hao
2007-10-01
A new approach to detecting structure damage using the cross correlation function amplitude vector (CorV) of the measured vibration responses is proposed. It is verified that under a steady random excitation with specific frequency spectrum, the CorV of a structure only depends on the frequency response function matrix of the structure, and it is also found that the normalized CorV has a specific shape. Thus the damage can be detected and located with the correlation and the relative difference between the CorVs obtained from intact and damaged structures. The Cross Correlation Function Amplitude Vector Assurance Criterion (CVAC) is then defined and can be used to quantify the variation of CorV. It is found that the CVAC decreases monotonously with the increasing of damage factor, which indicates the change of CorV is related to the damage severity. The methods of damage locating with CorV are then proposed and demonstrated by the experiments. Finally, the experiment on detection in the fasteners loosing of an aircraft panel model are presented to illustrate the application of the CorV. The feature of this approach lies in that the CorV is obtained from the time domain vibration responses of the structure under steady random excitation, and it has the advantages of simplicity in calculation and the damage detection, so it is possible that the presented approach applies to the structural health monitoring (SHM) with steady ambient excitations.
Zang, Xiaoqin; Brown, Michael G; Godin, Oleg A
2015-09-01
Theoretical studies have shown that cross-correlation functions (CFs) of time series of ambient noise measured at two locations yield approximations to the Green's functions (GFs) that describe propagation between those locations. Specifically, CFs are estimates of weighted GFs. In this paper, it is demonstrated that measured CFs in the 20-70 Hz band can be accurately modeled as weighted GFs using ambient noise data collected in the Florida Straits at ∼100 m depth with horizontal separations of 5 and 10 km. Two weighting functions are employed. These account for (1) the dipole radiation pattern produced by a near-surface source, and (2) coherence loss of surface-reflecting energy in time-averaged CFs resulting from tidal fluctuations. After describing the relationship between CFs and GFs, the inverse problem is considered and is shown to result in an environmental model for which agreement between computed and simulated CFs is good. PMID:26428771
Clustering of ROSAT All-Sky Survey AGNs Through Cross-Correlation Functions
NASA Astrophysics Data System (ADS)
Krumpe, Mirko; Miyaji, Takamitsu; Coil, Alison
2010-07-01
We investigate the clustering propertiesof ~1550 low-redshift broad-line AGNs detected in the ROSAT All-Sky Survey (RASS) through a cross-correlation function (CCF) with ~46000 Luminous Red Galaxies (LRGs) in the Sloan Digital Sky Survey (SDSS). Using this approach, we avoid small-number statistics and systematic errors caused by the variation of the Galactic absorption compared to a direct measurement of the AGN auto-correlation function (ACF). We compute the ACF of low-z RASS-AGN based on the CCF for the total X-ray sample (
Matthews, Daniel J.; Newman, Jeffrey A. E-mail: janewman@pitt.edu
2012-02-01
Cross-correlation techniques provide a promising avenue for calibrating photometric redshifts and determining redshift distributions using spectroscopy which is systematically incomplete (e.g., current deep spectroscopic surveys fail to obtain secure redshifts for 30%-50% or more of the galaxies targeted). In this paper, we improve on the redshift distribution reconstruction methods from our previous work by incorporating full covariance information into our correlation function fits. Correlation function measurements are strongly covariant between angular or spatial bins, and accounting for this in fitting can yield substantial reduction in errors. However, frequently the covariance matrices used in these calculations are determined from a relatively small set (dozens rather than hundreds) of subsamples or mock catalogs, resulting in noisy covariance matrices whose inversion is ill-conditioned and numerically unstable. We present here a method of conditioning the covariance matrix known as ridge regression which results in a more well behaved inversion than other techniques common in large-scale structure studies. We demonstrate that ridge regression significantly improves the determination of correlation function parameters. We then apply these improved techniques to the problem of reconstructing redshift distributions. By incorporating full covariance information, applying ridge regression, and changing the weighting of fields in obtaining average correlation functions, we obtain reductions in the mean redshift distribution reconstruction error of as much as {approx}40% compared to previous methods. We provide a description of POWERFIT, an IDL code for performing power-law fits to correlation functions with ridge regression conditioning that we are making publicly available.
NASA Astrophysics Data System (ADS)
Tahmasebi, Pejman; Sahimi, Muhammad
2015-03-01
Nonstationary disordered materials and media, those for which the probability distribution function of any property varies spatially when shifted in space, are abundant and encountered in astrophysics, oceanography, air pollution patterns, large-scale porous media, biological tissues and organs, and composite materials. Their reconstruction and modeling is a notoriously difficult and largely unsolved problem. We propose a method for reconstructing a broad class of such media based on partitioning them into locally stationary zones. Two methods are used for the partitioning. One is based on the Shannon entropy, while the second method utilizes a watershed transform. The locally stationary zones are then reconstructed based on a cross-correlation function and one-dimensional raster path that we recently introduced [P. Tahmasebi and M. Sahimi, Phys. Rev. Lett. 110, 078002 (2013), 10.1103/PhysRevLett.110.078002], with overlaps between the zones to ensure seamless transition from one zone to another. A large number of examples, including porous media, ecological systems, disordered materials, and biological tissues and organs, are reconstructed and analyzed to demonstrate the accuracy of the method.
NASA Technical Reports Server (NTRS)
Scargle, Jeffrey D.
1989-01-01
This paper develops techniques to evaluate the discrete Fourier transform (DFT), the autocorrelation function (ACF), and the cross-correlation function (CCF) of time series which are not evenly sampled. The series may consist of quantized point data (e.g., yes/no processes such as photon arrival). The DFT, which can be inverted to recover the original data and the sampling, is used to compute correlation functions by means of a procedure which is effectively, but not explicitly, an interpolation. The CCF can be computed for two time series not even sampled at the same set of times. Techniques for removing the distortion of the correlation functions caused by the sampling, determining the value of a constant component to the data, and treating unequally weighted data are also discussed. FORTRAN code for the Fourier transform algorithm and numerical examples of the techniques are given.
NASA Astrophysics Data System (ADS)
Sato, Shin-ichi; Kitamura, Toshihiro; Ando, Yochi
2004-10-01
While considering auditory-brain model for subjective responses, effects of spatial factors extracted from the interaural cross-correlation function (IACF) on annoyance of noise stimuli are examined. The previously developed indices to measure sound pressure levels (SPL) and frequency characteristics cannot fully explain the psychological effects of noise. In the first experiment, subjects judged their annoyance by changing fluctuations in the magnitude of interaural cross-correlation function (IACC) and the SPL. In the second, they judged their annoyance by changing fluctuations in the interaural time delay (τIACC) and the SPL. Results show that: (1) annoyance increased by increasing the fluctuations of IACC as well as the SPL, (2) annoyance increased by increasing the fluctuations of τIACC as well as the SPL.
Sabra, Karim G
2010-06-01
It has been demonstrated theoretically and experimentally that an estimate of the Green's function between two receivers can be obtained by cross-correlating acoustic (or elastic) ambient noise recorded at these two receivers. Coherent wavefronts emerge from the noise cross-correlation time function due to the accumulated contributions over time from noise sources whose propagation path pass through both receivers. Previous theoretical studies of the performance of this passive imaging technique have assumed that no relative motion between noise sources and receivers occurs. In this article, the influence of noise sources motion (e.g., aircraft or ship) on this passive imaging technique was investigated theoretically in free space, using a stationary phase approximation, for stationary receivers. The theoretical results were extended to more complex environments, in the high-frequency regime, using first-order expansions of the Green's function. Although sources motion typically degrades the performance of wideband coherent processing schemes, such as time-delay beamforming, it was found that the Green's function estimated from ambient noise cross-correlations are not expected to be significantly affected by the Doppler effect, even for supersonic sources. Numerical Monte-Carlo simulations were conducted to confirm these theoretical predictions for both cases of subsonic and supersonic moving sources. PMID:20550258
A GROUP-GALAXY CROSS-CORRELATION FUNCTION ANALYSIS IN zCOSMOS
Knobel, C.; Lilly, S. J.; Carollo, C. M.; Caputi, K.; Contini, T.; Kneib, J.-P.; Le Fevre, O.; Renzini, A.; Scodeggio, M.; Franzetti, P.; Garilli, B.; Zamorani, G.; Bardelli, S.; Bolzonella, M.; Bongiorno, A.; Cucciati, O.; Iovino, A.; De la Torre, S.; De Ravel, L.; and others
2012-08-10
We present a group-galaxy cross-correlation analysis using a group catalog produced from the 16,500 spectra from the optical zCOSMOS galaxy survey. Our aim is to perform a consistency test in the redshift range 0.2 {<=} z {<=} 0.8 between the clustering strength of the groups and mass estimates that are based on the richness of the groups. We measure the linear bias of the groups by means of a group-galaxy cross-correlation analysis and convert it into mass using the bias-mass relation for a given cosmology, checking the systematic errors using realistic group and galaxy mock catalogs. The measured bias for the zCOSMOS groups increases with group richness as expected by the theory of cosmic structure formation and yields masses that are reasonably consistent with the masses estimated from the richness directly, considering the scatter that is obtained from the 24 mock catalogs. Some exceptions are the richest groups at high redshift (estimated to be more massive than 10{sup 13.5} M{sub Sun }), for which the measured bias is significantly larger than for any of the 24 mock catalogs (corresponding to a 3{sigma} effect), which is attributed to the extremely large structure that is present in the COSMOS field at z {approx} 0.7. Our results are in general agreement with previous studies that reported unusually strong clustering in the COSMOS field.
NASA Astrophysics Data System (ADS)
Matos, Catarina; Silveira, Graça; Custódio, Susana; Domingues, Ana; Dias, Nuno; Fonseca, João F. B.; Matias, Luís; Krueger, Frank; Carrilho, Fernando
2014-05-01
Noise cross-correlations are now widely used to extract Green functions between station pairs. But, do all the cross-correlations routinely computed produce successful Green Functions? What is the relationship between noise recorded in a couple of stations and the cross-correlation between them? During the last decade, we have been involved in the deployment of several temporary dense broadband (BB) networks within the scope of both national projects and international collaborations. From 2000 to 2002, a pool of 8 BB stations continuously operated in the Azores in the scope of the Memorandum of Understanding COSEA (COordinated Seismic Experiment in the Azores). Thanks to the Project WILAS (West Iberia Lithosphere and Astenosphere Structure, PTDC/CTE-GIX/097946/2008) we temporarily increased the number of BB deployed in mainland Portugal to more than 50 (permanent + temporary) during the period 2010 - 2012. In 2011/12 a temporary pool of 12 seismometers continuously recorded BB data in the Madeira archipelago, as part of the DOCTAR (Deep Ocean Test Array Experiment) project. Project CV-PLUME (Investigation on the geometry and deep signature of the Cape Verde mantle plume, PTDC/CTE-GIN/64330/2006) covered the archipelago of Cape Verde, North Atlantic, with 40 temporary BB stations in 2007/08. Project MOZART (Mozambique African Rift Tomography, PTDC/CTE-GIX/103249/2008), covered Mozambique, East Africa, with 30 temporary BB stations in the period 2011 - 2013. These networks, located in very distinct geographical and tectonic environments, offer an interesting opportunity to study seasonal and spatial variations of noise sources and their impact on Empirical Green functions computed from noise cross-correlation. Seismic noise recorded at different seismic stations is evaluated by computation of the probability density functions of power spectral density (PSD) of continuous data. To assess seasonal variations of ambient noise sources in frequency content, time-series of
Green's function approximation from cross-correlations of 20-100 Hz noise during a tropical storm.
Brooks, Laura A; Gerstoft, Peter
2009-02-01
Approximation of Green's functions through cross-correlation of acoustic signals in the ocean, a method referred to as ocean acoustic interferometry, is potentially useful for estimating parameters in the ocean environment. Travel times of the main propagation paths between hydrophone pairs were estimated from interferometry of ocean noise data that were collected on three L-shaped arrays off the New Jersey coast while Tropical Storm Ernesto passed nearby. Examination of the individual noise spectra and their mutual coherence reveals that the coherently propagating noise is dominated by signals of less than 100 Hz. Several time and frequency noise normalization techniques were applied to the low frequency data in order to determine the effectiveness of each technique for ocean acoustic applications. Travel times corresponding to the envelope peaks of the noise cross-correlation time derivatives of data were extracted from all three arrays, and are shown to be in agreement with the expected direct, surface-reflected, and surface-bottom-reflected interarray hydrophone travel times. The extracted Green's function depends on the propagating noise. The Green's function paths that propagate horizontally are extracted from long distance shipping noise, and during the storm the more vertical paths are extracted from breaking waves. PMID:19206850
NASA Astrophysics Data System (ADS)
Feng, Lei; Yi, Xiaohua; Zhu, Dapeng; Xie, Xiongyao; Wang, Yang
2015-08-01
In a modern metropolis, metro rail systems have become a dominant mode for mass transportation. The structural health of a metro tunnel is closely related to public safety. Many vibration-based techniques for detecting and locating structural damage have been developed in the past several decades. However, most damage detection techniques and validation tests are focused on bridge and building structures; very few studies have been reported on tunnel structures. Among these techniques, transmissibility function and cross correlation analysis are two well-known diagnostic approaches. The former operates in frequency domain and the latter in time domain. Both approaches can be applied to detect and locate damage through acceleration data obtained from sensor arrays. Furthermore, the two approaches can directly utilize structural response data without requiring excitation measurement, which offers advantages in field testing on a large structure. In this research, a numerical finite element model of a metro tunnel is built and different types of structural defects are introduced at multiple locations of the tunnel. Transmissibility function and cross correlation analysis are applied to perform structural damage detection and localization, based on simulated structural vibration data. Numerical results demonstrate that the introduced defects can be successfully identified and located. The sensitivity and feasibility of the two approaches have been verified when sufficient distribution of measurement locations is available. Damage detection results of the two different approaches are compared and discussed.
Green's Function Retrieval with Absorbing Probes in Reverberating Cavities.
Davy, Matthieu; de Rosny, Julien; Besnier, Philippe
2016-05-27
The cross-correlation of a diffuse wave field converges toward the difference between the anticausal and causal Green's functions between two points. This property has paved the way to passive imaging using ambient noise sources. In this Letter, we investigate Green's function retrieval in electromagnetism. Using a model based on the fluctuation dissipation theorem, we demonstrate theoretically that the cross-correlation function strongly depends on the absorption properties of the receivers. This is confirmed in measurements within a reverberation chamber. In contrast to measurements with noninvasive probes, we show that only the anticausal Green's function can be retrieved with a matched antenna. Finally, we interpret this result as an equivalent time-reversal experiment with an electromagnetic sink. PMID:27284658
NASA Technical Reports Server (NTRS)
Shibazaki, N.; Elsner, R. F.; Bussard, R. W.; Ebisuzaki, T.; Weisskopf, M. C.
1988-01-01
The cross-correlation functions (CCFs) and cross spectra expected for quasi-periodic oscillation (QPO) shot noise models are calculated under various assumptions, and the results are compared to observations. Effects due to possible coherence of the QPO oscillations are included. General formulas for the cross spectrum, the cross-phase spectrum, and the time-delay spectrum for QPO shot models are calculated and discussed. It is shown that the CCFs, cross spectra, and power spectra observed for Cyg X-e2 imply that the spectrum of the shots evolves with time, with important implications for the interpretation of these functions as well as of observed average energy spectra. The possible origins for the observed hard lags are discussed, and some physical difficulties for the Comptonization model are described. Classes of physical models for QPO sources are briefly addressed, and it is concluded that models involving shot formation at the surface of neutron stars are favored by observation.
Understanding volatility correlation behavior with a magnitude cross-correlation function
NASA Astrophysics Data System (ADS)
Jun, Woo Cheol; Oh, Gabjin; Kim, Seunghwan
2006-06-01
We propose an approach for analyzing the basic relation between correlation properties of the original signal and its magnitude fluctuations by decomposing the original signal into its positive and negative fluctuation components. We use this relation to understand the following phenomenon found in many naturally occurring time series: the magnitude of the signal exhibits long-range correlation, whereas the original signal is short-range correlated. The applications of our approach to heart rate variability signals and high-frequency foreign exchange rates reveal that the difference between the correlation properties of the original signal and its magnitude fluctuations is induced by the time organization structure of the correlation function between the magnitude fluctuations of positive and negative components. We show that this correlation function can be described well by a stretched-exponential function and is related to the nonlinearity and the multifractal structure of the signals.
Computing exact p-values for a cross-correlation shotgun proteomics score function.
Howbert, J Jeffry; Noble, William Stafford
2014-09-01
The core of every protein mass spectrometry analysis pipeline is a function that assesses the quality of a match between an observed spectrum and a candidate peptide. We describe a procedure for computing exact p-values for the oldest and still widely used score function, SEQUEST XCorr. The procedure uses dynamic programming to enumerate efficiently the full distribution of scores for all possible peptides whose masses are close to that of the spectrum precursor mass. Ranking identified spectra by p-value rather than XCorr significantly reduces variance because of spectrum-specific effects on the score. In combination with the Percolator postprocessor, the XCorr p-value yields more spectrum and peptide identifications at a fixed false discovery rate than Mascot, X!Tandem, Comet, and MS-GF+ across a variety of data sets. PMID:24895379
Dean, Roger T; Dunsmuir, William T M
2016-06-01
Many articles on perception, performance, psychophysiology, and neuroscience seek to relate pairs of time series through assessments of their cross-correlations. Most such series are individually autocorrelated: they do not comprise independent values. Given this situation, an unfounded reliance is often placed on cross-correlation as an indicator of relationships (e.g., referent vs. response, leading vs. following). Such cross-correlations can indicate spurious relationships, because of autocorrelation. Given these dangers, we here simulated how and why such spurious conclusions can arise, to provide an approach to resolving them. We show that when multiple pairs of series are aggregated in several different ways for a cross-correlation analysis, problems remain. Finally, even a genuine cross-correlation function does not answer key motivating questions, such as whether there are likely causal relationships between the series. Thus, we illustrate how to obtain a transfer function describing such relationships, informed by any genuine cross-correlations. We illustrate the confounds and the meaningful transfer functions by two concrete examples, one each in perception and performance, together with key elements of the R software code needed. The approach involves autocorrelation functions, the establishment of stationarity, prewhitening, the determination of cross-correlation functions, the assessment of Granger causality, and autoregressive model development. Autocorrelation also limits the interpretability of other measures of possible relationships between pairs of time series, such as mutual information. We emphasize that further complexity may be required as the appropriate analysis is pursued fully, and that causal intervention experiments will likely also be needed. PMID:26100765
Offshore Southern California lithospheric velocity structure from noise cross-correlation functions
NASA Astrophysics Data System (ADS)
Bowden, D. C.; Kohler, M. D.; Tsai, V. C.; Weeraratne, D. S.
2016-05-01
A new shear wave velocity model offshore Southern California is presented that images plate boundary deformation including both thickening and thinning of the crustal and mantle lithosphere at the westernmost edge of the North American continent. The Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment (ALBACORE) ocean bottom seismometer array, together with 65 stations of the onshore Southern California Seismic Network, is used to measure ambient noise correlation functions and Rayleigh wave dispersion curves which are inverted for 3-D shear wave velocities. The resulting velocity model defines the transition from continental lithosphere to oceanic, illuminating the complex history and deformation in the region. A transition to the present-day strike-slip regime between the Pacific and North American Plates resulted in broad deformation and capture of the now >200 km wide continental shelf. Our velocity model suggests the persistence of the uppermost mantle volcanic processes associated with East Pacific Rise spreading adjacent to the Patton Escarpment, which marks the former subduction of Farallon Plate underneath North America. The most prominent of these seismic structures is a low-velocity anomaly underlying the San Juan Seamount, suggesting ponding of magma at the base of the crust, resulting in thickening and ongoing adjustment of the lithosphere due to the localized loading. The velocity model also provides a robust framework for future earthquake location determinations and ground-shaking simulations for risk estimates.
NASA Astrophysics Data System (ADS)
Martins, J. H. C.; Santos, N. C.; Figueira, P.; Melo, C.
2016-03-01
The direct detection of reflected light from exoplanets is an excellent probe for the characterization of their atmospheres. The greatest challenge for this task is the low planet-to-star flux ratio, which even in the most favourable case is of the order of 10-4 in the optical. This ratio decreases even more for planets in their host's habitable zone, typically lower than 10-7. To reach the signal-to-noise level required for such detections, we propose to unleash the power of the Cross Correlation Function in combination with the collecting power of next generation observing facilities. The technique we propose has already yielded positive results by detecting the reflected spectral signature of 51 Pegasi b (see Martins et al. 2015). In this work, we attempted to infer the number of hours required for the detection of several planets in their host's habitable zone using the aforementioned technique from theoretical EELT observations. Our results show that for 5 of the selected planets it should be possible to directly recover their reflected spectral signature.
Zhuang, Katie Z.; Lebedev, Mikhail A.
2014-01-01
Correlation between cortical activity and electromyographic (EMG) activity of limb muscles has long been a subject of neurophysiological studies, especially in terms of corticospinal connectivity. Interest in this issue has recently increased due to the development of brain-machine interfaces with output signals that mimic muscle force. For this study, three monkeys were implanted with multielectrode arrays in multiple cortical areas. One monkey performed self-timed touch pad presses, whereas the other two executed arm reaching movements. We analyzed the dynamic relationship between cortical neuronal activity and arm EMGs using a joint cross-correlation (JCC) analysis that evaluated trial-by-trial correlation as a function of time intervals within a trial. JCCs revealed transient correlations between the EMGs of multiple muscles and neural activity in motor, premotor and somatosensory cortical areas. Matching results were obtained using spike-triggered averages corrected by subtracting trial-shuffled data. Compared with spike-triggered averages, JCCs more readily revealed dynamic changes in cortico-EMG correlations. JCCs showed that correlation peaks often sharpened around movement times and broadened during delay intervals. Furthermore, JCC patterns were directionally selective for the arm-reaching task. We propose that such highly dynamic, task-dependent and distributed relationships between cortical activity and EMGs should be taken into consideration for future brain-machine interfaces that generate EMG-like signals. PMID:25210153
NASA Astrophysics Data System (ADS)
Budi-Santoso, Agus; Lesage, Philippe
2016-04-01
We present a study of the seismic velocity variations that occurred in the structure before the large 2010 eruption of Merapi volcano. For the first time to our knowledge, the technique of Coda Wave Interferometry is applied to both families of similar events (multiplets) and to correlation functions of seismic noise. About half of the seismic events recorded at the summit stations belong to one of the ten multiplets identified, including 120 similar events that occurred in the last 20 hours preceding the eruption onset. Daily noise cross-correlation functions (NCF) were calculated for the six pairs of short-period stations available. Using the stretching method, we estimate time series of apparent velocity variation (AVV) for each multiplet and each pair of stations. No significant velocity change is detected until September 2010. From 10 October to the beginning of the eruption on 26 October, a complex pattern of AVV is observed with amplitude of up to ±1.5%. Velocity decrease is first observed from families of deep events and then from shallow earthquakes. In the same period, AVV with different signs and chronologies are estimated from NCF calculated for various station pairs. The location in the horizontal plane of the velocity perturbations related with the AVV obtained from NCF is estimated by using an approach based on the radiative transfer approximation. Although their spatial resolution is limited, the resulting maps display velocity decrease in the upper part of the edifice in the period 12-25 October. After the eruption onset, the pattern of velocity perturbations is significantly modified with respect to the previous one. We interpret these velocity variations in the framework of a scenario of magmatic intrusion that integrates most observations. The perturbation of the stress field associated with the magma migration can induce both decrease and increase of the seismic velocity of rocks. Thus the detected apparent velocity variations can be
NASA Astrophysics Data System (ADS)
Budi-Santoso, Agus; Lesage, Philippe
2016-07-01
We present a study of the seismic velocity variations that occurred in the structure before the large 2010 eruption of Merapi volcano. For the first time to our knowledge, the technique of coda wave interferometry is applied to both families of similar events (multiplets) and to correlation functions of seismic noise. About half of the seismic events recorded at the summit stations belong to one of the ten multiplets identified, including 120 similar events that occurred in the last 20 hr preceding the eruption onset. Daily noise cross-correlation functions (NCF) were calculated for the six pairs of short-period stations available. Using the stretching method, we estimate time-series of apparent velocity variation (AVV) for each multiplet and each pair of stations. No significant velocity change is detected until September 2010. From 10 October to the beginning of the eruption on 26 October, a complex pattern of AVV is observed with amplitude of up to ±1.5 per cent. Velocity decrease is first observed from families of deep events and then from shallow earthquakes. In the same period, AVV with different signs and chronologies are estimated from NCF calculated for various station pairs. The location in the horizontal plane of the velocity perturbations related with the AVV obtained from NCF is estimated by using an approach based on the radiative transfer approximation. Although their spatial resolution is limited, the resulting maps display velocity decrease in the upper part of the edifice in the period 12-25 October. After the eruption onset, the pattern of velocity perturbations is significantly modified with respect to the previous one. We interpret these velocity variations in the framework of a scenario of magmatic intrusion that integrates most observations. The perturbation of the stress field associated with the magma migration can induce both decrease and increase of the seismic velocity of rocks. Thus the detected AVVs can be considered as precursors of
NASA Astrophysics Data System (ADS)
Zeng, X.; Lancelle, C.; Thurber, C. H.; Fratta, D.; Wang, H. F.; Chalari, A.; Clarke, A.
2015-12-01
The field test of Distributed Acoustic Sensing (DAS) conducted at Garner Valley, California on September 11-12, 2013 provided a continuous overnight record of ambient noise. The DAS array recorded ground motions every one meter of optical cable that was arranged approximately in the shape of a rectangle with dimensions of 160 m by 80 m. The long dimension of the array was adjacent to a state highway. Three hours of record were used to compute noise cross-correlation functions (NCFs) in one-minute windows. The trace from each sensor channel was pre-processed by downsampling to 200 Hz, followed by normalization in the time-domain and bandpass filtering between 2 and 20 Hz (Bensen et al., 2007). The one-minute NCFs were then stacked using the time-frequency domain phase-weighted stacking method (Schimmel & Gallart, 2007). The NCFs between channels were asymmetrical reflecting the direction of traffic noise. The group velocities were found using the frequency-time analysis method. The energy was concentrated between 5 and 15 Hz, which falls into the typical traffic noise frequency band. The resulting velocities were between 100 and 300 m/s for frequencies between 10 and 20 Hz, which are in the same range as described in the results for surface-wave dispersion obtained using an active source for the same site (Lancelle et al., 2015). The group velocity starts to decrease for frequencies greater than ~10 Hz, which was expected on the basis of a previous shear-wave velocity model (Steidl et al., 1996). Then, the phase velocity was calculated using the multichannel analysis of surface wave technique (MASW - Park et al., 1999) with 114 NCFs spaced one meter apart. The resulting dispersion curve between 5 and 15 Hz gave phase velocities that ranged from approximately 170 m/s at 15 Hz to 250 m/s at 5 Hz. These results are consistent with other results of active-source DAS and seismometer records obtained at the Garner Valley site (e.g., Stokoe et al. 2004). This analysis is
A fast SEQUEST cross correlation algorithm.
Eng, Jimmy K; Fischer, Bernd; Grossmann, Jonas; Maccoss, Michael J
2008-10-01
The SEQUEST program was the first and remains one of the most widely used tools for assigning a peptide sequence within a database to a tandem mass spectrum. The cross correlation score is the primary score function implemented within SEQUEST and it is this score that makes the tool particularly sensitive. Unfortunately, this score is computationally expensive to calculate, and thus, to make the score manageable, SEQUEST uses a less sensitive but fast preliminary score and restricts the cross correlation to just the top 500 peptides returned by the preliminary score. Classically, the cross correlation score has been calculated using Fast Fourier Transforms (FFT) to generate the full correlation function. We describe an alternate method of calculating the cross correlation score that does not require FFTs and can be computed efficiently in a fraction of the time. The fast calculation allows all candidate peptides to be scored by the cross correlation function, potentially mitigating the need for the preliminary score, and enables an E-value significance calculation based on the cross correlation score distribution calculated on all candidate peptide sequences obtained from a sequence database. PMID:18774840
Identifying apparent velocity changes in cross correlated microseism noise data
NASA Astrophysics Data System (ADS)
Friderike Volk, Meike; Bean, Christopher; Lokmer, Ivan; Pérez, Nemesio; Ibáñez, Jesús
2015-04-01
Currently there is a strong interest of using cross correlation of ambient noise to retrieve Green's functions. These are usually used to calculate the seismic wave velocity of the subsurface and therefore can be used for subsurface imaging or monitoring of various geological settings where we expect rapid velocity changes (e.g. reservoirs or volcanoes). The assumption of this method is that the wavefields which are correlated must be diffuse. This criterion is fulfilled if the ambient noise sources are uniformly distributed or the scattering in the medium is high enough to mitigate any source directivity. The location of the sources is usually unknown and it can change in time. These temporal and spatial variations of the microseism noise sources may lead to changes in the retrieved Green's functions, and so, to the apparent changes in seismic wave velocities. To further investigate the apparent changes in Green's functions we undertook an active seismic experiment in Tenerife lasting three months. A small airgun was used as an active source and was shooting repeatedly every 15 minutes. The shots and the microseism noise were recorded at several seismic stations at the same time. That data set gives us the opportunity to compare the changes in seismic wave velocity recovered through cross correlation of ambient noise and changes we measure through active shots from the airgun. The aim is to distinguish between apparent seismic velocity changes and seismic velocity changes caused by changes in the medium. We also use the data set to track the direction of the microseism noise sources to see if changes which are only recovered through cross correlation can be related to temporal and spatial variations of the microseism noise sources.
Crustal anisotropy viewed by noise cross-correlations
NASA Astrophysics Data System (ADS)
Zaccarelli, L.; Saadé, M.; Cupillard, P.; Roux, P.; Montagner, J.; Brenguier, F.
2012-12-01
The cross-correlation (CC) of the vertical component of the ambient seismic noise records at 2 stations has been related to the Green function, i.e. the impulse response of the medium between the two stations. Therefore by considering the 3-cmp signal we obtain a tensor of noise CC which may provide interesting information on both Rayleigh and Love surface waves. An intriguing aspect that may emerge from the analysis of the CC tensor is the crustal anisotropy, with a special regard to its main direction, highlighted by the surface wave polarization. The behavior of an S-wave entering an anisotropic volume is well known and modeled, and the shear-wave splitting phenomenon has been exploited both for quantifying the crustal anisotropy and monitoring its evolution with time. But the same is not completely understood in the case of surface waves. In this framework we aim to a better comprehension on how anisotropy can modify Rayleigh and Love waves: we set up an experiment based on synthetics signals generated through the Spectral Element Method simulating a 3-D anisotropic medium. We firstly test the shear-wave splitting as retrieved from signal recordings of a deep source on a circle of stations. Then we generate double couple sources all along an outer circle on the surface. Finally we construct the cross-correlation tensor and we retrieve the polarization angles for all couples of stations and all sources, to analyze their reciprocal dependence.
NASA Astrophysics Data System (ADS)
Ławniczak, Michał; Bauch, Szymon; Hul, Oleh; Sirko, Leszek
2011-02-01
We present the results of an experimental study of the enhancement factor WS,β of the two-port scattering matrix \\skew3\\hat{S} and the cross-correlation function c12(ν) for microwave irregular networks simulating quantum graphs with time-reversal symmetry (TRS), symmetry index β=1, and without TRS, β=2, in the presence of absorption. We show that even for systems with notable losses the elastic enhancement factor WS,β remains a statistical measure that allows the determination of a symmetry class of the chaotic quantum systems under investigation. Therefore, the enhancement factor WS,β may be contrasted with many others statistical measures such as, for example, the nearest neighbor spacing distribution or the spectral rigidity, which are not directly applicable in the presence of strong absorption. The quantum graphs with TRS were simulated by the microwave networks built of coaxial cables connected by joints and attenuators, which allowed us to control absorption. The microwave circulators were added to the networks to simulate graphs with broken TRS. The experimental results are compared to the ones obtained within the framework of random matrix theory.
NASA Astrophysics Data System (ADS)
Costanzo, M. R.; Nunziata, C.
2014-09-01
Cross-correlation functions of long noise recordings with two broadband stations and earthquake recordings in the Campanian Plain have been processed with frequency time analysis to extract the fundamental mode of Rayleigh waves. Group velocities have been combined with regional group and phase velocity data in the non-linear inversion, with Hedgehog method, in order to get average shear wave velocity models for lithospheric structures extending to 73 km of depth. The structural model below the central part of the Campanian Plain is characterized by a covering of pyroclastics and alluvial sediments, about 2 km thick, on the carbonate platform with VS ranging from 2.30-2.40 to 2.85-3.15 km/s. However, the presence of lava bodies within the carbonates cannot be excluded in the light of the same density and seismic velocities. At greater depths, a main feature is represented by a sharp increment of velocity around 8-9 km of depth (VS of 3.85 km/s), which can be attributed to the presence of metamorphic rocks, overlying a low VS layer (5% velocity reduction), at about 14-15 km of depth. Such structural model resembles those found below the quiescent Roccamonfina and Colli Albani volcanoes, and can be interpreted as the signature of a cooling magma chamber. Moreover, a low VS layer is detected at 8-9 km of depth towards the Apennines and at 6 km of depth in the southernmost part of the Campanian Plain, nearby Mt. Vesuvius. Such low velocity layer seems to be a regional feature since it has been found below Roccamonfina in the North, Campi Flegrei, bay of Napoli and Mt. Vesuvius in the South, and can be explained by the widespread presence of partially melted material below the whole Campanian area.
Representation theorems and Green's function retrieval for scattering in acoustic media.
Vasconcelos, Ivan; Snieder, Roel; Douma, Huub
2009-09-01
Reciprocity theorems for perturbed acoustic media are provided in the form of convolution- and correlation-type theorems. These reciprocity relations are particularly useful in the general treatment of both forward and inverse-scattering problems. Using Green's functions to describe perturbed and unperturbed waves in two distinct wave states, representation theorems for scattered waves are derived from the reciprocity relations. While the convolution-type theorems can be manipulated to obtain scattering integrals that are analogous to the Lippmann-Schwinger equation, the correlation-type theorems can be used to retrieve the scattering response of the medium by cross correlations. Unlike previous formulations of Green's function retrieval, the extraction of scattered-wave responses by cross correlations does not require energy equipartitioning. Allowing for uneven energy radiation brings experimental advantages to the retrieval of fields scattered by remote lossless and/or attenuative scatterers. These concepts are illustrated with a number of examples, including analytic solutions to a one-dimensional scattering problem, and a numerical example in the context of seismic waves recorded on the ocean bottom. PMID:19905236
Retrieving the Green's function of attenuating heterogeneous media by time-reversal modeling
NASA Astrophysics Data System (ADS)
Zhu, T.
2014-12-01
The Green's function between two locations within which seismograms that were not physically recorded, are retrieved by cross-correlation, convolution or deconvolution and summation of other recorded wavefields (also known as seismic interferometry). More recently seismic interferometry was applied in exploration seismology by Bakulin and Calvert (2006) and Schuster et al. (2004), in ultrasound by Weaver and Lobkis (2001), in crustal seismology by Campillo and Paul (2003), Sabra et al. (2005a, b), Roux et al. (2005) and Shapiro et al. (2005), and in helioseismology by Rickett and Claerbout (1999). Theory of the retrieval of Green's function can also be represented by time-reversal propagation because of time invariance of wave equations in the lossless media. In the presence of intrinsic attenuation in the media, however, the time invariance of wave equations is invalid. My previous work present methods of using novel viscoacoustic and viscoelastic wave equations to recover the time invariance property of such wave equations for viscoacoustic and viscoelastic time-reversal modeling. More importantly, attenuation effects are compensated for during time-reversal wave propagation. In this paper, I investigate the possibility of retrieving the Green's function through time-reversal modeling techniques in attenuating media. I consider two different models to illustrate the feasibility of Green's function retrieval in attenuating media. I consider the viscoacoustic as well as the viscoelastic situation. Numerical results show that the Green's function can be retrieved in the correct amplitude and phase by time-reversal modeling with compensating both amplitude loss and dispersion effects.
Study of cross-correlation in a self-affine time series of taxi accidents
NASA Astrophysics Data System (ADS)
Zebende, G. F.; da Silva, P. A.; Machado Filho, A.
2011-05-01
We study in this paper the cross-correlation between self-affine time series of real variables recorded simultaneously in cases of taxi accidents. For this purpose, we apply the DCCA method and show that the cross-correlation can be divided into three distinct groups, if we look for the detrended covariance function, i.e., long-range cross-correlations, short-range cross-correlations and no cross-correlations. Finally, it will be seen that the detrended covariance function is robust, if compared with other methods, in identifying these types of cross-correlations.
Petascale cross correlation in software
NASA Astrophysics Data System (ADS)
Barsdell, Benjamin R.; Clark, M. A.; Greenhill, L. J.
2014-04-01
The exascale computational demands of back-end processing in the era of the SKA and HERA, headlined by the needs of cross-correlation, are likely to require solutions that differ significantly from traditional approaches on smaller arrays. The rapid growth of massively-parallel general-purpose computing hardware presents an alternative to ASIC- or FPGA-based designs and promises several advantages. In this talk we present strong scaling results for an FX correlator that runs entirely in software on GPU-based off-the-shelf HPC clusters.
NASA Astrophysics Data System (ADS)
Liu, C.; Liu, X.; Kowalewski, M. G.; Janz, S. J.; González Abad, G.; Pickering, K. E.; Chance, K.; Lamsal, L. N.
2015-02-01
The Airborne Compact Atmospheric Mapper (ACAM), an ultraviolet/visible/near-infrared spectrometer, has been flown on board the NASA UC-12 aircraft during the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) campaigns to provide remote sensing observations of tropospheric and boundary-layer pollutants from its radiance measurements. To assure the trace-gas retrieval from ACAM measurements we perform detailed characterization and verification of ACAM slit functions. The wavelengths and slit functions of ACAM measurements are characterized for the air-quality channel (~304-500 nm) through cross-correlation with a high-resolution solar irradiance reference spectrum after necessarily accounting for atmospheric gas absorption and the ring effect in the calibration process. The derived slit functions, assuming a hybrid combination of asymmetric Gaussian and top-hat slit functions, agree very well with the laboratory-measured slit functions. Comparisons of trace-gas retrievals between using derived and measured slit functions demonstrate that the cross-correlation technique can be reliably used to characterize slit functions for trace-gas retrievals.
NASA Astrophysics Data System (ADS)
Liu, C.; Liu, X.; Kowalewski, M. G.; Janz, S. J.; González Abad, G.; Pickering, K. E.; Chance, K.; Lamsal, L. N.
2014-11-01
The Airborne Compact Atmospheric Mapper (ACAM), an ultraviolet/visible/near-infrared spectrometer, has been flown on board the NASA UC-12 aircraft during the DISCOVER-AQ (Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality) campaigns to provide remote sensing observations of tropospheric and boundary layer pollutants from its radiance measurements. To improve the trace gas retrieval from ACAM measurements, we perform detailed characterization and verification of ACAM slit functions. The wavelengths and slit functions of ACAM measurements are characterized for the air quality channel (~304-500 nm) through cross-correlation with a high-resolution solar irradiance reference spectrum after necessarily accounting for atmospheric gas absorption and the Ring effect in the calibration process. The derived slit functions, assuming a hybrid combination of asymmetric Gaussian and top-hat slit functions, agree very well with the laboratory-measured slit functions. Comparisons of trace gas retrievals between using derived and measured slit functions demonstrate that the cross-correlation technique can be reliably used to characterize slit functions for trace gas retrievals.
Cross-correlation in the auditory coincidence detectors of owls.
Fischer, Brian J; Christianson, G Björn; Peña, José Luis
2008-08-01
Interaural time difference (ITD) plays a central role in many auditory functions, most importantly in sound localization. The classic model for how ITD is computed was put forth by Jeffress (1948). One of the predictions of the Jeffress model is that the neurons that compute ITD should behave as cross-correlators. Whereas cross-correlation-like properties of the ITD-computing neurons have been reported, attempts to show that the shape of the ITD response function is determined by the spectral tuning of the neuron, a core prediction of cross-correlation, have been unsuccessful. Using reverse correlation analysis, we demonstrate in the barn owl that the relationship between the spectral tuning and the ITD response of the ITD-computing neurons is that predicted by cross-correlation. Moreover, we show that a model of coincidence detector responses derived from responses to binaurally uncorrelated noise is consistent with binaural interaction based on cross-correlation. These results are thus consistent with one of the key tenets of the Jeffress model. Our work sets forth both the methodology to answer whether cross-correlation describes coincidence detector responses and a demonstration that in the barn owl, the result is that expected by theory. PMID:18685035
Recirculating cross-correlation detector
Andrews, W.H. Jr.; Roberts, M.J.
1985-01-18
A digital cross-correlation detector is provided in which two time-varying signals are correlated by repetitively comparing data samples stored in digital form to detect correlation between the two signals. The signals are sampled at a selected rate converted to digital form, and stored in separate locations in separate memories. When the memories are filled, the data samples from each memory are first fed word-by-word through a multiplier and summing circuit and each result is compared to the last in a peak memory circuit and if larger than the last is retained in the peak memory. Then the address line to leading signal memory is offset by one byte to affect one sample period delay of a known amount in that memory and the data in the two memories are then multiplied word-by-word once again and summed. If a new result is larger than a former sum, it is saved in the peak memory together with the time delay. The recirculating process continues with the address of the one memory being offset one additional byte each cycle until the address is shifted through the length of the memory. The correlation between the two signals is indicated by the peak signal stored in the peak memory together with the delay time at which the peak occurred. The circuit is faster and considerably less expensive than comparable accuracy correlation detectors.
Statistical tests for power-law cross-correlated processes
NASA Astrophysics Data System (ADS)
Podobnik, Boris; Jiang, Zhi-Qiang; Zhou, Wei-Xing; Stanley, H. Eugene
2011-12-01
For stationary time series, the cross-covariance and the cross-correlation as functions of time lag n serve to quantify the similarity of two time series. The latter measure is also used to assess whether the cross-correlations are statistically significant. For nonstationary time series, the analogous measures are detrended cross-correlations analysis (DCCA) and the recently proposed detrended cross-correlation coefficient, ρDCCA(T,n), where T is the total length of the time series and n the window size. For ρDCCA(T,n), we numerically calculated the Cauchy inequality -1≤ρDCCA(T,n)≤1. Here we derive -1≤ρDCCA(T,n)≤1 for a standard variance-covariance approach and for a detrending approach. For overlapping windows, we find the range of ρDCCA within which the cross-correlations become statistically significant. For overlapping windows we numerically determine—and for nonoverlapping windows we derive—that the standard deviation of ρDCCA(T,n) tends with increasing T to 1/T. Using ρDCCA(T,n) we show that the Chinese financial market's tendency to follow the U.S. market is extremely weak. We also propose an additional statistical test that can be used to quantify the existence of cross-correlations between two power-law correlated time series.
Statistical tests for power-law cross-correlated processes.
Podobnik, Boris; Jiang, Zhi-Qiang; Zhou, Wei-Xing; Stanley, H Eugene
2011-12-01
For stationary time series, the cross-covariance and the cross-correlation as functions of time lag n serve to quantify the similarity of two time series. The latter measure is also used to assess whether the cross-correlations are statistically significant. For nonstationary time series, the analogous measures are detrended cross-correlations analysis (DCCA) and the recently proposed detrended cross-correlation coefficient, ρ(DCCA)(T,n), where T is the total length of the time series and n the window size. For ρ(DCCA)(T,n), we numerically calculated the Cauchy inequality -1 ≤ ρ(DCCA)(T,n) ≤ 1. Here we derive -1 ≤ ρ DCCA)(T,n) ≤ 1 for a standard variance-covariance approach and for a detrending approach. For overlapping windows, we find the range of ρ(DCCA) within which the cross-correlations become statistically significant. For overlapping windows we numerically determine-and for nonoverlapping windows we derive--that the standard deviation of ρ(DCCA)(T,n) tends with increasing T to 1/T. Using ρ(DCCA)(T,n) we show that the Chinese financial market's tendency to follow the U.S. market is extremely weak. We also propose an additional statistical test that can be used to quantify the existence of cross-correlations between two power-law correlated time series. PMID:22304166
A detrended cross-correlation analysis of meteorological and API data in Nanjing, China
NASA Astrophysics Data System (ADS)
Shen, Chen-hua; Li, Chao-ling; Si, Ya-li
2015-02-01
The cross correlation between daily meteorological data and air pollution index (API) records in Nanjing during the past 12 years is studied by means of a detrended cross-correlation analysis (DCCA). In this study, we use statistical significance tests and power-law statistical tests to verify cross correlation between meteorological data and the API. Through calculating the DCCA cross correlation coefficient ρDCCA, we intend to obtain a range of cross correlation levels between the meteorological data and the API at different time scales. Utilizing the multifractal detrended cross correlation analysis (MF-DCCA) and algorithm-multifractal cross correlation analysis (MF-CCA) proposed by Oświecimka, we observe multifractal cross-correlation behavior between meteorological factors and the API. Our results show a cross correlation between meteorological factors and the API in Nanjing. The cross-correlation between diurnal temperature ranges and the API is persistent at studied time scales, while the cross correlations of wind speed, relative humidity, and precipitation with the API are anti-persistent at studied time scales. Next, a cross correlation of temperature with the API finds persistent cross correlation at smaller time scales, and anti-persistent cross-correlation at larger time scales; the cross correlation of atmospheric pressure with the API, however, results in anti-persistent cross correlation at smaller time scales, and persistent cross correlation at larger time scales. The MF-DCCA demonstrates that all underlying fluctuations have a weak multifractal nature where one scaling exponent is obtained. However, the MF-CCA suggests that some crossovers exist in the cross-correlation fluctuation function in terms of time scales of temperature and atmospheric pressure versus the API. The MF-CCA method is more subtle and suitable for reflecting the cross correlation of the two given time series. Compared with a traditional correlation analysis, the DCCA can
Attribute-Based Time Series Cross-Correlation Measures
NASA Astrophysics Data System (ADS)
Cooper, G. R. J.
2016-05-01
Datasets are usually compared using cross-correlation, often using a moving window to calculate the correlation as a function of time or space. However, signals can be considered as being composed of sinusoids which possess amplitudes, frequencies and phases. All these three attributes can be computed at each point in time, and then used as the basis of a cross-correlation method. By using all the three measures of correlation together, their individual disadvantages can be minimised. By combining these measures with the continuous wavelet transform, information on the correlation as a function of wavelength can be obtained.
Garofalo, Matteo; Nieus, Thierry; Massobrio, Paolo; Martinoia, Sergio
2009-01-01
Functional connectivity of in vitro neuronal networks was estimated by applying different statistical algorithms on data collected by Micro-Electrode Arrays (MEAs). First we tested these "connectivity methods" on neuronal network models at an increasing level of complexity and evaluated the performance in terms of ROC (Receiver Operating Characteristic) and PPC (Positive Precision Curve), a new defined complementary method specifically developed for functional links identification. Then, the algorithms better estimated the actual connectivity of the network models, were used to extract functional connectivity from cultured cortical networks coupled to MEAs. Among the proposed approaches, Transfer Entropy and Joint-Entropy showed the best results suggesting those methods as good candidates to extract functional links in actual neuronal networks from multi-site recordings. PMID:19652720
CROSS-CORRELATIONS AS A COSMOLOGICAL CARBON MONOXIDE DETECTOR
Pullen, Anthony R.; Dore, Olivier; Chang, Tzu-Ching; Lidz, Adam
2013-05-01
We present a new procedure to measure the large-scale carbon monoxide (CO) emissions across cosmic history. As a tracer of large-scale structure (LSS), the CO gas content as a function of redshift can be quantified by its three-dimensional fluctuation power spectra. Furthermore, cross-correlating CO emission with other LSS tracers offers a way to measure the emission as a function of scale and redshift. Here we introduce the model relevant for such a cross-correlation measurement between CO and other LSS tracers, and between different CO rotational lines. We propose a novel use of cosmic microwave background (CMB) data and attempt to extract redshifted CO emissions embedded in the Wilkinson Microwave Anisotropy Probe (WMAP) data set. We cross-correlate the all-sky WMAP7 data with LSS data sets, namely, the photometric quasar sample and the luminous red galaxy sample from the Sloan Digital Sky Survey Data Releases 6 and 7, respectively. We are unable to detect a cross-correlation signal with either CO(1-0) or CO(2-1) lines, mainly due to the instrumental noise in the WMAP data. However, we are able to rule out models more than three times greater than our more optimistic model. We discuss the cross-correlation signal from the thermal Sunyaev-Zeldovich effect and dust as potential contaminants, and quantify their impact for our CO measurements. We discuss forecasts for current CMB experiments and a hypothetical future CO-focused experiment, and propose to cross-correlate CO temperature data with the Hobby-Eberly Telescope Dark Energy Experiment Ly{alpha}-emitter sample, for which a signal-to-noise ratio of 58 is possible.
Image Cross-Correlation Analysis of Time Varying Flows.
Marquezin, Cassia A; Ceffa, Nicolò G; Cotelli, Franco; Collini, Maddalena; Sironi, Laura; Chirico, Giuseppe
2016-07-19
In vivo studies of blood circulation pathologies have great medical relevance and need methods for the characterization of time varying flows at high spatial and time resolution in small animal models. We test here the efficacy of the combination of image correlation techniques and single plane illumination microscopy (SPIM) in characterizing time varying flows in vitro and in vivo. As indicated by numerical simulations and by in vitro experiments on straight capillaries, the complex analytical form of the cross-correlation function for SPIM detection can be simplified, in conditions of interest for hemodynamics, to a superposition of Gaussian components, easily amenable to the analysis of variable flows. The possibility to select a wide field of view with a good spatial resolution along the collection optical axis and to compute the cross-correlation between regions of interest at varying distances on a single time stack of images allows one to single out periodic flow components from spurious peaks on the cross-correlation functions and to infer the duration of each flow component. We apply this cross-correlation analysis to the blood flow in Zebrafish embryos at 4 days after fertilization, measuring the average speed and the duration of the systolic and diastolic phases. PMID:27348197
Effective intermittency and cross correlations in the standard map
NASA Astrophysics Data System (ADS)
Datseris, G.; Diakonos, F. K.; Schmelcher, P.
2015-07-01
We define auto- and cross-correlation functions capable of capturing dynamical characteristics induced by local phase-space structures in a general dynamical system. These correlation functions are calculated in the standard map for a range of values of the nonlinearity parameter k . Using a model of noninteracting particles, each evolving according to the same standard map dynamics and located initially at specific phase-space regions, we show that for 0.6
Cross correlation of thermal flux noise in layered superconductors
Ashkenazy, V.D.; Jung, G. |; Shapiro, B.Y. |
1996-10-01
Cross correlation in the magnetic flux noise due to thermally activated movements of pancake vortices in strongly anisotropic layered superconductors has been investigated theoretically. It has been shown that there exists a crossover frequency, inversely proportional to the sample thickness, below which vortices behave as rigid rods and their ends move coherently on the opposite sides of the sample. At low frequencies, the cross-correlation spectrum is identical to the spectrum measured at each side of the sample. The cross-correlation spectrum demonstrates two regimes of behavior, separated by a characteristic frequency which depends on the geometry of the flux measuring loop. At high frequencies above the crossover frequency, the excitations of the elastic lattice modes lead to exponentially vanishing oscillations of the cross-correlation spectra. Pancake movements became incoherent and the correlation function decays, accompanied by the oscillations. The oscillations are most pronounced for the separation between pickup loops smaller than the sample thickness. In a typical experimental configuration with pickup loops located on the sample surface, the oscillations constitute only small perturbations to the dominating powerlike decay of the correlation function. {copyright} {ital 1996 The American Physical Society.}
Antisymmetric galaxy cross-correlations as a cosmological probe
NASA Astrophysics Data System (ADS)
Dai, Liang; Kamionkowski, Marc; Kovetz, Ely D.; Raccanelli, Alvise; Shiraishi, Maresuke
2016-01-01
The autocorrelation between two members of a galaxy population is symmetric under the interchange of the two galaxies being correlated. The cross-correlation between two different types of galaxies, separated by a vector r , is not necessarily the same as that for a pair separated by -r . Local anisotropies in the two-point cross-correlation function may thus indicate a specific direction which when mapped as a function of position trace out a vector field. This vector field can then be decomposed into longitudinal and transverse components, and those transverse components written as positive- and negative-helicity components. A locally asymmetric cross-correlation of the longitudinal type arises naturally in halo clustering, even with Gaussian initial conditions, and could be enhanced with local-type non-Gaussianity. Early-Universe scenarios that introduce a vector field may also give rise to such effects. These antisymmetric cross-correlations also provide a new possibility to seek a preferred cosmic direction correlated with the hemispherical power asymmetry in the cosmic microwave background and to seek a preferred location associated with the cosmic microwave background cold spot. New ways to seek cosmic parity breaking are also possible.
Using SVD for improved interferometric Green's function retrieval
NASA Astrophysics Data System (ADS)
Melo, Gabriela; Malcolm, Alison; Mikesell, Dylan; van Wijk, Kasper
2013-09-01
Seismic interferometry (SI) is a technique used to estimate the Green's function (GF) between two receiver locations, as if there were a source at one of the receiver locations. However, in many applications, the requirements to recover the exact GF are not satisfied and SI yields a poor estimate of the GF. For these non-ideal cases, we improve the interferometric GFs, by applying singular value decomposition (SVD) to the cross-correlations before stacking. The SVD approach preserves energy that is stationary in the cross-correlations, which is the energy that contributes most to the GF recovery, and attenuates non-stationary energy, which leads to artefacts in the interferometric GF. We apply this method to construct virtual shot gathers (for both synthetic and field data) and demonstrate how using SVD enhances physical arrivals in these gathers. We also find that SVD is robust with respect to weakly correlated random noise, allowing a better recovery of events from noisy data, in some cases recovering energy that would otherwise be completely lost in the noise and that the standard SI technique fails to recover.
Absence of significant cross-correlation between WMAP and SDSS
NASA Astrophysics Data System (ADS)
López-Corredoira, M.; Sylos Labini, F.; Betancort-Rijo, J.
2010-04-01
Aims: Several authors have claimed to detect a significant cross-correlation between microwave WMAP anisotropies and the SDSS galaxy distribution. We repeat these analyses to determine the different cross-correlation uncertainties caused by re-sampling errors and field-to-field fluctuations. The first type of error concerns overlapping sky regions, while the second type concerns non-overlapping sky regions. Methods: To measure the re-sampling errors, we use bootstrap and jack-knife techniques. For the field-to-field fluctuations, we use three methods: 1) evaluation of the dispersion in the cross-correlation when correlating separated regions of WMAP with the original region of SDSS; 2) use of mock Monte Carlo WMAP maps; 3) a new method (developed in this article), which measures the error as a function of the integral of the product of the self-correlations for each map. Results: The average cross-correlation for b > 30 deg is significantly stronger than the re-sampling errors - both the jack-knife and bootstrap techniques provide similar results - but it is of the order of the field-to-field fluctuations. This is confirmed by the cross-correlation between anisotropies and galaxies in more than the half of the sample being null within re-sampling errors. Conclusions: Re-sampling methods underestimate the errors. Field-to-field fluctuations dominate the detected signals. The ratio of signal to re-sampling errors is larger than unity in a way that strongly depends on the selected sky region. We therefore conclude that there is no evidence yet of a significant detection of the integrated Sachs-Wolfe (ISW) effect. Hence, the value of Ω_Λ ≈ 0.8 obtained by the authors who assumed they were observing the ISW effect would appear to have originated from noise analysis.
V S Profiles from Noise Cross Correlation at Local and Small Scale
NASA Astrophysics Data System (ADS)
de Nisco, G.; Nunziata, C.
2011-03-01
Ambient noise measurements have been performed at local and small scales in the Neapolitan and surrounding areas (Campania, southern Italy) by employing two broad-band Kinemetrics Q330 stations, equipped with Episensor ES-T three component accelerometers. In both experiments frequency time analysis (FTAN method) has been performed on the vertical and radial components of noise cross correlations to retrieve the Rayleigh wave dispersion (Green's function). At local scale, over an interstation distance of about 26 km, the group velocity dispersion values have been compared with those obtained from FTAN analysis on recordings of two earthquakes with similar path. At small scale, measurements have been carried out over an interstation distance of about 440 m in the public gardens of Scampia, the northernmost quarter of Naples. The Rayleigh wave group velocity dispersion data obtained from noise cross correlation, have been combined with those from active seismic experiment along the same alignment, but shorter (120 m offset). The non linear inversion of such a dispersion curve has allowed the definition of V S models to depths of 100 m, in agreement with nearby stratigraphy. Moreover, a good agreement has resulted for the resonance frequency among the H/V ratio, the ellipticity of the fundamental mode computed for the chosen V S model, and the average two-dimensional (2D) spectral amplification computed along a cross section representative of the Scampia quarter.
Background-free balanced optical cross correlator
Nejadmalayeri, Amir Hossein; Kaertner, Franz X
2014-12-23
A balanced optical cross correlator includes an optical waveguide, a first photodiode including a first n-type semiconductor and a first p-type semiconductor positioned about the optical waveguide on a first side of the optical waveguide's point of symmetry, and a second photodiode including a second n-type semiconductor and a second p-type semiconductor positioned about the optical waveguide on a second side of the optical waveguide's point of symmetry. A balanced receiver including first and second inputs is configured to produce an output current or voltage that reflects a difference in currents or voltages, originating from the first and the second photodiodes of the balanced cross correlator and fed to the first input and to the second input of the balanced receiver.
Ambient seismic noise cross-correlations at Romanian broadband stations
NASA Astrophysics Data System (ADS)
Grecu, Bogdan; Tataru, Dragos; Neagoe, Cristian; Panza, Giuliano; Raileanu, Victor; Radulian, Mircea; Popa, Mihaela; Ionescu, Constantin
2010-05-01
In the last years the National Institute for Earth Physics (NIEP), Romania, has developed its real-time broadband seismic network. At present, NIEP operates 34 stations with both broadband velocity sensors (CMG3ESP, CMG40T, KS2000, STS2) and accelerometer sensors (2gEpi). The data are continuously recorded and transmitted to the Romanian Data Centre where Antelope 4.11 is running for acquisition and processing. The density of the stations produces 560 inter-station pairs for ambient noise cross-correlation analysis. In this study, we used seismic data recorded during a period of 12 months, between January 2009 and December 2009. A nonlinear procedure is applied to lower the influence of the earthquake-related signals and to obtain a symmetric noise cross-correlation function (for details see Cho et al., 2007). The results show good cross-correlation functions for almost all pair of stations. As the vertical components of ambient noise are cross-correlated, only the fundamental mode of the Rayleigh wave is obtained. The FTAN analysis is used to extract the group velocities from the estimated dispersive waves at periods between 6 and 30 sec. This work provides very useful data for future tomographic studies in Romania at crustal level, considering that new data from other broadband stations deployed on the Romanian territory will become available. References: Cho, K.H., R. B. Herrmann, C. J. Ammon and K. Lee. Imaging the Upper Crust of the Korean Peninsula by Surface-Wave Tomography, Bulletin of the Seismological Society of America (2007) 97, 198-207.
Cross-correlations between volume change and price change.
Podobnik, Boris; Horvatic, Davor; Petersen, Alexander M; Stanley, H Eugene
2009-12-29
In finance, one usually deals not with prices but with growth rates R, defined as the difference in logarithm between two consecutive prices. Here we consider not the trading volume, but rather the volume growth rate R, the difference in logarithm between two consecutive values of trading volume. To this end, we use several methods to analyze the properties of volume changes |R|, and their relationship to price changes |R|. We analyze 14,981 daily recordings of the Standard and Poor's (S & P) 500 Index over the 59-year period 1950-2009, and find power-law cross-correlations between |R| and |R| by using detrended cross-correlation analysis (DCCA). We introduce a joint stochastic process that models these cross-correlations. Motivated by the relationship between |R| and |R|, we estimate the tail exponent alpha of the probability density function P(|R|) approximately |R|(-1-alpha) for both the S & P 500 Index as well as the collection of 1819 constituents of the New York Stock Exchange Composite Index on 17 July 2009. As a new method to estimate alpha, we calculate the time intervals tau(q) between events where R > q. We demonstrate that tau(q), the average of tau(q), obeys tau(q) approximately q(alpha). We find alpha approximately 3. Furthermore, by aggregating all tau(q) values of 28 global financial indices, we also observe an approximate inverse cubic law. PMID:20018772
Precise Relative Earthquake Magnitudes from Cross Correlation
Cleveland, K. Michael; Ammon, Charles J.
2015-04-21
We present a method to estimate precise relative magnitudes using cross correlation of seismic waveforms. Our method incorporates the intercorrelation of all events in a group of earthquakes, as opposed to individual event pairings relative to a reference event. This method works well when a reliable reference event does not exist. We illustrate the method using vertical strike-slip earthquakes located in the northeast Pacific and Panama fracture zone regions. Our results are generally consistent with the Global Centroid Moment Tensor catalog, which we use to establish a baseline for the relative event sizes.
HEALPix Based Cross-Correlation in Astronomy
NASA Astrophysics Data System (ADS)
Fernique, P.; Durand, D.; Boch, T.; Oberto, A.; Pineau, F.
2013-10-01
We are presenting our work on a cross correlation system based on HEALPix cells indexing. The system allows users to answer scientific questions like “please find all HST images on which there is an observation of a radio quiet quasar” in a single query. The baseline of this system is the creation of the HEALPix indexes grouped hierarchically and organized in a special format file called MOC (see http://ivoa.net/Documents/Notes/MOC) developed by the CDS. Using the MOC files, the cross correlation between images and or catalogues is reduced to searches only in meaningful areas. Under the condition that the survey database also internally uses a HEALPix positional index, the search result comes back almost immediately (typically a few seconds). We have started building the index for some surveys, catalogues (VizieR catalogues, Simbad, etc.) and some pointed mode archives (like HST at CADC) and are developing an elementary library to support basic operations on any input MOC files. The usage of the MOC files is starting to be used throughout the VO community as a general indexing method and tools such as Aladin and TOPCAT are starting to make use of them.
A New Methodology of Spatial Cross-Correlation Analysis
Chen, Yanguang
2015-01-01
Spatial correlation modeling comprises both spatial autocorrelation and spatial cross-correlation processes. The spatial autocorrelation theory has been well-developed. It is necessary to advance the method of spatial cross-correlation analysis to supplement the autocorrelation analysis. This paper presents a set of models and analytical procedures for spatial cross-correlation analysis. By analogy with Moran’s index newly expressed in a spatial quadratic form, a theoretical framework is derived for geographical cross-correlation modeling. First, two sets of spatial cross-correlation coefficients are defined, including a global spatial cross-correlation coefficient and local spatial cross-correlation coefficients. Second, a pair of scatterplots of spatial cross-correlation is proposed, and the plots can be used to visually reveal the causality behind spatial systems. Based on the global cross-correlation coefficient, Pearson’s correlation coefficient can be decomposed into two parts: direct correlation (partial correlation) and indirect correlation (spatial cross-correlation). As an example, the methodology is applied to the relationships between China’s urbanization and economic development to illustrate how to model spatial cross-correlation phenomena. This study is an introduction to developing the theory of spatial cross-correlation, and future geographical spatial analysis might benefit from these models and indexes. PMID:25993120
Failure of the Cross Correlation Measurement Technique
NASA Astrophysics Data System (ADS)
McGill, Ken; Ham, Katie; Schock, Kris
2014-03-01
The experiment involves creating a sound wave that propagates down a pipe with 8 transducers attached at equally spaced intervals of 0.01016 meters. The numerical method used to solve for the phase component, the Cross Correlation Method, creates a high correlation value, but the speed of sound varies immensely. The method involves a Fast Fourier Transform of the collected data, which is used to find the phase of the sound wave, and the slope of the position versus time graph, which is used to calculate the speed of sound. This high correlation values shows that the data is correct, but the numerical method for analyzing the data is incorrect. We would like to thank Dr. Ken McGill for all of his time, help, and guidance with this research project. We would also like to thank Georgia College and State University for both the resources and space necessary for this experiment.
Temporal and Cross Correlations in Business News
NASA Astrophysics Data System (ADS)
Mizuno, T.; Takei, K.; Ohnishi, T.; Watanabe, T.
We empirically investigate temporal and cross correlations inthe frequency of news reports on companies, using a dataset of more than 100 million news articles reported in English by around 500 press agencies worldwide for the period 2003--2009. Our first finding is that the frequency of news reports on a company does not follow a Poisson process, but instead exhibits long memory with a positive autocorrelation for longer than one year. The second finding is that there exist significant correlations in the frequency of news across companies. Specifically, on a daily time scale or longer the frequency of news is governed by external dynamics, while on a time scale of minutes it is governed by internal dynamics. These two findings indicate that the frequency of news reports on companies has statistical properties similar to trading volume or price volatility in stock markets, suggesting that the flow of information through company news plays an important role in price dynamics in stock markets.
Investigating hum sources using cross-correlation asymmetry
NASA Astrophysics Data System (ADS)
Ermert, L. A.; Fichtner, A.; Schimmel, M.
2014-12-01
The sources and excitation of the Earth's hum are current subjects of debate. Here, we propose an alternative approach to map power spectral density of hum sources. We are currently processing IRIS continuous seismic data spanning the last 10 years to obtain a cross-correlation dataset. The amplitude-independent phase cross-correlation provides correlation stacks that converge relatively rapidly and without the application of additional preprocessing such as spectral whitening. We calculate monthly stacks of approx. daily broadband geometrically normalized 'classic' and phase cross-correlations. These can be recombined into 'seasonal' stacks of several months. Also, they can be restacked by month over several years, so as to investigate long-term average behavior during different months. Although these correlation functions retain no absolute amplitude information, observational evidence from our data shows that the relative amplitudes of the causal and acausal branch differ between certain station pairs, indicating a preferential direction of wave propagation. We intend to use this directional characteristic to investigate source distribution of continuous seismic motions. In a first step, we project the measurements of amplitude asymmetry back along the station-station path using very simplified sensitivity kernels. These kernels can be obtained numerically or by using analytical 2-D Green's functions for homogeneous media. We expect to obtain global maps of source regions for different seasons. In a further step (not to be presented here), the observations will be inverted for the geographical distribution of source power spectral density. We target hum as first example application, while the method could also be applied to other types of continuous seismic motion. The goal of our study is to obtain a global hum source map, which might benefit our understanding of the excitation mechanisms of hum.
Cross-correlation between interest rates and commodity prices
NASA Astrophysics Data System (ADS)
Wang, Qing; Hu, Yiming
2015-06-01
In this paper, we investigate cross-correlations between interest rate and agricultural commodity markets. Based on a statistic of Podobnik et al. (2009), we find that the cross-correlations are all significant. Using the MF-DFA and MF-DXA methods, we find strong multifractality in both auto-correlations and cross-correlations. Moreover, the cross-correlations are persistent. Finally, based on the technique of rolling window, the time-variation property of cross-correlations is also revealed.
Multifractal detrended cross-correlation analysis in the MENA area
NASA Astrophysics Data System (ADS)
El Alaoui, Marwane; Benbachir, Saâd
2013-12-01
In this paper, we investigated multifractal cross-correlations qualitatively and quantitatively using a cross-correlation test and the Multifractal detrended cross-correlation analysis method (MF-DCCA) for markets in the MENA area. We used cross-correlation coefficients to measure the level of this correlation. The analysis concerns four stock market indices of Morocco, Tunisia, Egypt and Jordan. The countries chosen are signatory of the Agadir agreement concerning the establishment of a free trade area comprising Arab Mediterranean countries. We computed the bivariate generalized Hurst exponent, Rényi exponent and spectrum of singularity for each pair of indices to measure quantitatively the cross-correlations. By analyzing the results, we found the existence of multifractal cross-correlations between all of these markets. We compared the spectrum width of these indices; we also found which pair of indices has a strong multifractal cross-correlation.
Long-range cross-correlation between urban impervious surfaces and land surface temperatures
NASA Astrophysics Data System (ADS)
Nie, Qin; Xu, Jianhua; Man, Wang
2016-03-01
The thermal effect of urban impervious surfaces (UIS) is a complex problem. It is thus necessary to study the relationship between UIS and land surface temperatures (LST) using complexity science theory and methods. This paper investigates the long-range cross-correlation between UIS and LST with detrended cross-correlation analysis and multifractal detrended cross-correlation analysis, utilizing data from downtown Shanghai, China. UIS estimates were obtained from linear spectral mixture analysis, and LST was retrieved through application of the mono-window algorithm, using Landsat Thematic Mapper and Enhanced Thematic Mapper Plus data for 1997-2010. These results highlight a positive long-range cross-correlation between UIS and LST across People's Square in Shanghai. LST has a long memory for a certain spatial range of UIS values, such that a large increment in UIS is likely to be followed by a large increment in LST. While the multifractal long-range cross-correlation between UIS and LST was observed over a longer time period in the W-E direction (2002-2010) than in the N-S (2007-2010), these observed correlations show a weakening during the study period as urbanization increased.
Cross-correlations between volume change and price change
Podobnik, Boris; Horvatic, Davor; Petersen, Alexander M.; Stanley, H. Eugene
2009-01-01
In finance, one usually deals not with prices but with growth rates R, defined as the difference in logarithm between two consecutive prices. Here we consider not the trading volume, but rather the volume growth rate R̃, the difference in logarithm between two consecutive values of trading volume. To this end, we use several methods to analyze the properties of volume changes |R̃|, and their relationship to price changes |R|. We analyze 14,981 daily recordings of the Standard and Poor's (S & P) 500 Index over the 59-year period 1950–2009, and find power-law cross-correlations between |R| and |R̃| by using detrended cross-correlation analysis (DCCA). We introduce a joint stochastic process that models these cross-correlations. Motivated by the relationship between |R| and |R̃|, we estimate the tail exponent α̃ of the probability density function P(|R̃|) ∼ |R̃|−1−α̃ for both the S & P 500 Index as well as the collection of 1819 constituents of the New York Stock Exchange Composite Index on 17 July 2009. As a new method to estimate α̃, we calculate the time intervals τq between events where R̃ > q. We demonstrate that τ̃q, the average of τq, obeys τ̃q ∼ qα̃. We find α̃ ≈ 3. Furthermore, by aggregating all τq values of 28 global financial indices, we also observe an approximate inverse cubic law. PMID:20018772
Estimating error cross-correlations in soil moisture data sets using extended collocation analysis
NASA Astrophysics Data System (ADS)
Gruber, A.; Su, C.-H.; Crow, W. T.; Zwieback, S.; Dorigo, W. A.; Wagner, W.
2016-02-01
Global soil moisture records are essential for studying the role of hydrologic processes within the larger earth system. Various studies have shown the benefit of assimilating satellite-based soil moisture data into water balance models or merging multisource soil moisture retrievals into a unified data set. However, this requires an appropriate parameterization of the error structures of the underlying data sets. While triple collocation (TC) analysis has been widely recognized as a powerful tool for estimating random error variances of coarse-resolution soil moisture data sets, the estimation of error cross covariances remains an unresolved challenge. Here we propose a method—referred to as extended collocation (EC) analysis—for estimating error cross-correlations by generalizing the TC method to an arbitrary number of data sets and relaxing the therein made assumption of zero error cross-correlation for certain data set combinations. A synthetic experiment shows that EC analysis is able to reliably recover true error cross-correlation levels. Applied to real soil moisture retrievals from Advanced Microwave Scanning Radiometer-EOS (AMSR-E) C-band and X-band observations together with advanced scatterometer (ASCAT) retrievals, modeled data from Global Land Data Assimilation System (GLDAS)-Noah and in situ measurements drawn from the International Soil Moisture Network, EC yields reasonable and strong nonzero error cross-correlations between the two AMSR-E products. Against expectation, nonzero error cross-correlations are also found between ASCAT and AMSR-E. We conclude that the proposed EC method represents an important step toward a fully parameterized error covariance matrix for coarse-resolution soil moisture data sets, which is vital for any rigorous data assimilation framework or data merging scheme.
Cross-Correlations in Quasar Radio Emission
NASA Astrophysics Data System (ADS)
Nefedyev, Yuri; Panischev, Oleg; Demin, Sergey
The main factors forming the complex evolution of the accretive astrophysical systems are nonlinearity, intermittency, nonstationarity and also collective phenomena. To discover the dynamic processes in these objects and to detain understanding their properties we need to use all the applicable analyzing methods. Here we use the Flicker-Noise Spectroscopy (FNS) as a phenomenological approach to analyzing and parameterizing the auto- and cross-correlations in time series of astrophysical objects dynamics. As an example we consider the quasar flux radio spectral density at frequencies 2.7 GHz and 8.1 GHz. Data have been observed by Dr. N. Tanizuka (Laboratory for Complex Systems Analysis, Osaka Prefecture University) in a period of 1979 to 1988 (3 309 days). According to mental habits quasar is a very energetic and distant active galactic nucleus containing a supermassive black hole by size 10-10,000 times the Schwarzschild radius. The quasar is powered by an accretion disc around the black hole. The accretion disc material layers, moving around the black hole, are under the influence of gravitational and frictional forces. It results in raising the high temperature and arising the resonant and collective phenomena reflected in quasar emission dynamics. Radio emission dynamics of the quasar 0215p015 is characterized by three quasi-periodic processes, which are prevalent in considering dynamics. By contrast the 1641p399's emission dynamics have not any distinguish processes. It means the presence of high intermittency in accretive modes. The second difference moment allows comparing the degree of manifesting of resonant and chaotic components in initial time series of the quasar radio emission. The comparative analysis shows the dominating of chaotic part of 1641p399's dynamics whereas the radio emission of 0215p015 has the predominance of resonant component. Analyzing the collective features of the quasar radio emission intensity demonstrates the significant
NASA Astrophysics Data System (ADS)
Bakirci, Taciser; Kaslilar, Ayse; Kocaoglu, Argun
2014-05-01
Records of ambient seismic noise (ASN) field are widely used to obtain seismic velocity structures at both engineering and global scales. Two well-known methods commonly employed to obtain shear-wave velocity profiles, in engineering seismology, are the frequency-wavenumber (FK) transform and spatial auto-correlation (SPAC) methods that are based on the analysis of ASN field recorded by 2D sensor arrays. At global scale on the other hand, seismic velocity structure is determined by the Green's function retrieved from cross-correlation of the ASN recorded between two seismic stations. In the last decade, this approach has become complementary or almost alternative to the conventional methods of surface wave tomography used to investigate the velocity structure of the crust and upper mantle. Similarly, in recent years, the Green's functions estimated from ASN have also been used to investigate the shear-wave velocity structure of basins and their site amplification properties. This work presents the Rayleigh wave Green's functions retrieved from the vertical-component ASN data recorded in the Bursa and Adana basins of Turkey. This constitutes the first stage of our research whose objective is to investigate whether velocity structures of these basins can reliably be obtained from tomographic inversion. The continuous data used in our study were recorded between 2010 and 2013 by the national seismic networks operated by Kandilli Observatory and Earthquake Research Institute (KOERI) of Bosphorus University and Earthquake Research Department (ERD) of Disaster and Emergency Management Presidency of Turkey. For both basins, distances between station pairs are in the range of 30-200 km. In this distance range, the Green's functions reveal Rayleigh waves with the periods of 6 to 30 s. Group velocity dispersion analysis carried out by the multiple filtering technique show that the group velocities are estimated to be in the range of 2.5-4.0 km/s. Observed variation of group
Multiscale Detrended Cross-Correlation Analysis of STOCK Markets
NASA Astrophysics Data System (ADS)
Yin, Yi; Shang, Pengjian
2014-06-01
In this paper, we employ the detrended cross-correlation analysis (DCCA) to investigate the cross-correlations between different stock markets. We report the results of cross-correlated behaviors in US, Chinese and European stock markets in period 1997-2012 by using DCCA method. The DCCA shows the cross-correlated behaviors of intra-regional and inter-regional stock markets in the short and long term which display the similarities and differences of cross-correlated behaviors simply and roughly and the persistence of cross-correlated behaviors of fluctuations. Then, because of the limitation and inapplicability of DCCA method, we propose multiscale detrended cross-correlation analysis (MSDCCA) method to avoid "a priori" selecting the ranges of scales over which two coefficients of the classical DCCA method are identified, and employ MSDCCA to reanalyze these cross-correlations to exhibit some important details such as the existence and position of minimum, maximum and bimodal distribution which are lost if the scale structure is described by two coefficients only and essential differences and similarities in the scale structures of cross-correlation of intra-regional and inter-regional markets. More statistical characteristics of cross-correlation obtained by MSDCCA method help us to understand how two different stock markets influence each other and to analyze the influence from thus two inter-regional markets on the cross-correlation in detail, thus we get a richer and more detailed knowledge of the complex evolutions of dynamics of the cross-correlations between stock markets. The application of MSDCCA is important to promote our understanding of the internal mechanisms and structures of financial markets and helps to forecast the stock indices based on our current results demonstrated the cross-correlations between stock indices. We also discuss the MSDCCA methods of secant rolling window with different sizes and, lastly, provide some relevant implications and
Robust Statistical Detection of Power-Law Cross-Correlation
NASA Astrophysics Data System (ADS)
Blythe, Duncan A. J.; Nikulin, Vadim V.; Müller, Klaus-Robert
2016-06-01
We show that widely used approaches in statistical physics incorrectly indicate the existence of power-law cross-correlations between financial stock market fluctuations measured over several years and the neuronal activity of the human brain lasting for only a few minutes. While such cross-correlations are nonsensical, no current methodology allows them to be reliably discarded, leaving researchers at greater risk when the spurious nature of cross-correlations is not clear from the unrelated origin of the time series and rather requires careful statistical estimation. Here we propose a theory and method (PLCC-test) which allows us to rigorously and robustly test for power-law cross-correlations, correctly detecting genuine and discarding spurious cross-correlations, thus establishing meaningful relationships between processes in complex physical systems. Our method reveals for the first time the presence of power-law cross-correlations between amplitudes of the alpha and beta frequency ranges of the human electroencephalogram.
Extraction of low frequency signals from cross-correlations of the infrasonic ambient noise
NASA Astrophysics Data System (ADS)
Landès, Matthieu; Shapiro, Nikolaï; Le Pichon, Alexis
2015-04-01
Cross-correlation of ambient noise are widely used in seismology for imaging and monitoring purposes. The underlying result is the possibility to extract the Green Function between two locations on the Earth by correlating the noise recorded at these two points during long period of time. However, the applicability of this approach in atmospheric infrasound is not yet well established. We present cross-correlations of the infrasonic dataset of the USArray for the year 2012 filtered between 3 and 330 seconds. All cross-correlations were computed daily with a moving window of 3 hours. Only the amplitude normalization has been applied. We observe clear signals on the stacked cross-correlations for inter-station distances smaller than 400 km. The dominant period of this signal is around 60-100 s and its propagation velocity is approximately 320 m/s. We then use the daily cross-correlations to get information on the location of corresponding noise sources. Daily cross-correlations are asymmetric and show seasonal variations. These observations are due to the inhomogeneous noise sources distribution that can be inferred from a beamforming analysis. Our results show the seasonal variations of the back-azimuth of dominant infrasound noise sources generating this low frequency signal. This is a new opportunity to characterize the composition of the infrasonic ambient noise and to promote the application of passive approaches in atmospheric infrasound.
Multifractal cross-correlation analysis in electricity spot market
NASA Astrophysics Data System (ADS)
Fan, Qingju; Li, Dan
2015-07-01
In this paper, we investigate the multiscale cross-correlations between electricity price and trading volume in Czech market based on a newly developed algorithm, called Multifractal Cross-Correlation Analysis (MFCCA). The new algorithm is a natural multifractal generalization of the Detrended Cross-Correlation Analysis (DCCA), and is sensitive to cross-correlation structure and free from limitations of other algorithms. By considering the original sign of the cross-covariance, it allows us to properly quantify and detect the subtle characteristics of two simultaneous recorded time series. First, the multifractality and the long range anti-persistent auto-correlations of price return and trading volume variation are confirmed using Multifractal Detrended Fluctuation Analysis (MF-DFA). Furthermore, we show that there exist long-range anti-persistent cross-correlations between price return and trading volume variation by MFCCA. And we also identify that the cross-correlations disappear on the level of relative small fluctuations. In order to obtain deeper insight into the dynamics of the electricity market, we analyze the relation between generalized Hurst exponent and the multifractal cross-correlation scaling exponent λq. We find that the difference between the generalized Hurst exponent and the multifractal cross-correlation scaling exponent is significantly different for smaller fluctuation, which indicates that the multifractal character of cross-correlations resembles more each other for electricity price and trading volume on the level of large fluctuations and weakens for the smaller ones.
Multifractal cross-correlation spectra analysis on Chinese stock markets
NASA Astrophysics Data System (ADS)
Zhao, Xiaojun; Shang, Pengjian; Shi, Wenbin
2014-05-01
In this paper, the long-range cross-correlation of Chinese stock indices is systematically studied. The multifractal detrended cross-correlation analysis (MF-DXA) appears to be one of the most effective methods in detecting long-range cross-correlation of two non-stationary variables. The Legendre spectrum and the large deviations spectrum are extended to the cross-correlation case, so as to present multifractal structure of stock return and volatility series. It is characterized of the multifractality in Chinese stock markets, partly due to clusters of local detrended covariance with large and small magnitudes.
Microseism Source Direction from Noise Cross-correlation
NASA Astrophysics Data System (ADS)
Chen, Zhao; Gerstoft, Peter; Bromirski, Peter D.
2016-02-01
Inhomogeneous noise sources surrounding stations produce asymmetric amplitudes in cross-correlation functions that yield preferential source directions. Here we show that preprocessing biases the dominant source direction estimate towards the source producing long-duration signals by down-weighting high-amplitude signals. Tests with both synthetic data and observations show that conventional preprocessing, where only earthquakes and local transients (e.g. trawling, fish impacts) are removed, is more sensitive to coherent energy, while one-bit preprocessing and running-absolute-mean (RAM) preprocessing are more influenced by signal duration. Comparisons between different preprocessing methods are made on data from the Cascadia Initiative (CI) ocean bottom seismometer (OBS) array, where we find that the total energy arriving from pelagic and coastal areas is similar. Moreover, pelagic-generated signals tend to be weaker but have longer duration, in contrast to coastal-generated signals that tend to be stronger but have shorter duration.
Microseism source direction from noise cross-correlation
NASA Astrophysics Data System (ADS)
Chen, Zhao; Gerstoft, Peter; Bromirski, Peter D.
2016-05-01
Inhomogeneous noise sources surrounding stations produce asymmetric amplitudes in cross-correlation functions that yield preferential source directions. Here we show that preprocessing biases the dominant source direction estimate towards the source producing long-duration signals by down-weighting high-amplitude signals. Tests with both synthetic data and observations show that conventional preprocessing, where only earthquakes and local transients (e.g. trawling, fish impacts) are removed, is more sensitive to coherent energy, while one-bit preprocessing and running-absolute-mean preprocessing are more influenced by signal duration. Comparisons between different preprocessing methods are made on data from the Cascadia Initiative ocean bottom seismometer array, where we find that the total energy arriving from pelagic and coastal areas is similar. Moreover, pelagic-generated signals tend to be weaker but have longer duration, in contrast to coastal-generated signals that tend to be stronger but have shorter duration.
Bringing the cross-correlation method up to date
NASA Technical Reports Server (NTRS)
Statler, Thomas
1995-01-01
The cross-correlation (XC) method of Tonry & Davis (1979, AJ, 84, 1511) is generalized to arbitrary parametrized line profiles. In the new algorithm the correlation function itself, rather than the observed galaxy spectrum, is fitted by the model line profile: this removes much of the complication in the error analysis caused by template mismatch. Like the Fourier correlation quotient (FCQ) method of Bender (1990, A&A, 229, 441), the inferred line profiles are, up to a normalization constant, independent of template mismatch as long as there are no blended lines. The standard reduced chi(exp 2) is a good measure of the fit of the inferred velocity distribution, largely decoupled from the fit of the spectral template. The updated XC method performs as well as other recently developed methods, with the added virtue of conceptual simplicity.
Cross-correlations of ambient noise recorded by accelerometers.
NASA Astrophysics Data System (ADS)
Rábade García, S. E.; Ramirez-Guzman, L.
2014-12-01
We investigate the ambient noise cross-correlations obtained by using properly corrected accelerometric recordings, and determine velocity structure in central Mexico based on a dispersion analysis. The data used comprise ten months of continuous recordings - from April 2013 to January 2014 - of ambient seismic noise at stations operated by the National Seismological Service of Mexico and the Engineering Strong Ground Motion Network of the National Autonomous University of Mexico (UNAM). The vertical component of ambient noise was base-line corrected, filtered, and properly integrated before extracting Green's functions (GF), which were compared successfully against GF obtained using recordings from broadband velocity sensors. In order to obtain dispersion curves, we estimated group and phase velocities applying the FTAN analysis technique and obtained s-wave velocity profiles at selected regions. We conclude and highlight that the use of widely deployed accelerographs to conduct regional studies using ambient noise tomography is feasible
(abstract) Cross with Your Spectra? Cross-Correlate Instead!
NASA Technical Reports Server (NTRS)
Beer, Reinhard
1994-01-01
The use of cross-correlation for certain types of spectral analysis is discussed. Under certain circumstances, the use of cross-correlation between a real spectrum and either a model or another spectrum can provide a very powerful tool for spectral analysis. The method (and its limitations) will be described with concrete examples using ATMOS data.
Cross-correlation-aided transport in stochastically driven accretion flows
NASA Astrophysics Data System (ADS)
Nath, Sujit Kumar; Chattopadhyay, Amit K.
2014-12-01
The origin of linear instability resulting in rotating sheared accretion flows has remained a controversial subject for a long time. While some explanations of such non-normal transient growth of disturbances in the Rayleigh stable limit were available for magnetized accretion flows, similar instabilities in the absence of magnetic perturbations remained unexplained. This dichotomy was resolved in two recent publications by Chattopadhyay and co-workers [Mukhopadhyay and Chattopadhyay, J. Phys. A 46, 035501 (2013), 10.1088/1751-8113/46/3/035501; Nath et al., Phys. Rev. E 88, 013010 (2013), 10.1103/PhysRevE.88.013010] where it was shown that such instabilities, especially for nonmagnetized accretion flows, were introduced through interaction of the inherent stochastic noise in the system (even a "cold" accretion flow at 3000 K is too "hot" in the statistical parlance and is capable of inducing strong thermal modes) with the underlying Taylor-Couette flow profiles. Both studies, however, excluded the additional energy influx (or efflux) that could result from nonzero cross correlation of a noise perturbing the velocity flow, say, with the noise that is driving the vorticity flow (or equivalently the magnetic field and magnetic vorticity flow dynamics). Through the introduction of such a time symmetry violating effect, in this article we show that nonzero noise cross correlations essentially renormalize the strength of temporal correlations. Apart from an overall boost in the energy rate (both for spatial and temporal correlations, and hence in the ensemble averaged energy spectra), this results in mutual competition in growth rates of affected variables often resulting in suppression of oscillating Alfven waves at small times while leading to faster saturations at relatively longer time scales. The effects are seen to be more pronounced with magnetic field fluxes where the noise cross correlation magnifies the strength of the field concerned. Another remarkable
Non-Stationary Effects and Cross Correlations in Solar Activity
NASA Astrophysics Data System (ADS)
Nefedyev, Yuri; Panischev, Oleg; Demin, Sergey
2016-07-01
In this paper within the framework of the Flicker-Noise Spectroscopy (FNS) we consider the dynamic properties of the solar activity by analyzing the Zurich sunspot numbers. As is well-known astrophysics objects are the non-stationary open systems, whose evolution are the quite individual and have the alternation effects. The main difference of FNS compared to other related methods is the separation of the original signal reflecting the dynamics of solar activity into three frequency bands: system-specific "resonances" and their interferential contributions at lower frequencies, chaotic "random walk" ("irregularity-jump") components at larger frequencies, and chaotic "irregularity-spike" (inertial) components in the highest frequency range. Specific parameters corresponding to each of the bands are introduced and calculated. These irregularities as well as specific resonance frequencies are considered as the information carriers on every hierarchical level of the evolution of a complex natural system with intermittent behavior, consecutive alternation of rapid chaotic changes in the values of dynamic variables on small time intervals with small variations of the values on longer time intervals ("laminar" phases). The jump and spike irregularities are described by power spectra and difference moments (transient structural functions) of the second order. FNS allows revealing the most crucial points of the solar activity dynamics by means of "spikiness" factor. It is shown that this variable behaves as the predictor of crucial changes of the sunspot number dynamics, particularly when the number comes up to maximum value. The change of averaging interval allows revealing the non-stationary effects depending by 11-year cycle and by inside processes in a cycle. To consider the cross correlations between the different variables of solar activity we use the Zurich sunspot numbers and the sequence of corona's radiation energy. The FNS-approach allows extracting the
Temporal cross-correlation asymmetry and departure from equilibrium in a bistable chemical system
NASA Astrophysics Data System (ADS)
Bianca, C.; Lemarchand, A.
2014-06-01
This paper aims at determining sustained reaction fluxes in a nonlinear chemical system driven in a nonequilibrium steady state. The method relies on the computation of cross-correlation functions for the internal fluctuations of chemical species concentrations. By employing Langevin-type equations, we derive approximate analytical formulas for the cross-correlation functions associated with nonlinear dynamics. Kinetic Monte Carlo simulations of the chemical master equation are performed in order to check the validity of the Langevin equations for a bistable chemical system. The two approaches are found in excellent agreement, except for critical parameter values where the bifurcation between monostability and bistability occurs. From the theoretical point of view, the results imply that the behavior of cross-correlation functions cannot be exploited to measure sustained reaction fluxes in a specific nonlinear system without the prior knowledge of the associated chemical mechanism and the rate constants.
Time reversal imaging and cross-correlations techniques by normal mode theory
NASA Astrophysics Data System (ADS)
Montagner, J.; Fink, M.; Capdeville, Y.; Phung, H.; Larmat, C.
2007-12-01
Time-reversal methods were successfully applied in the past to acoustic waves in many fields such as medical imaging, underwater acoustics, non destructive testing and recently to seismic waves in seismology for earthquake imaging. The increasing power of computers and numerical methods (such as spectral element methods) enables one to simulate more and more accurately the propagation of seismic waves in heterogeneous media and to develop new applications, in particular time reversal in the three-dimensional Earth. Generalizing the scalar approach of Draeger and Fink (1999), the theoretical understanding of time-reversal method can be addressed for the 3D- elastic Earth by using normal mode theory. It is shown how to relate time- reversal methods on one hand, with auto-correlation of seismograms for source imaging and on the other hand, with cross-correlation between receivers for structural imaging and retrieving Green function. The loss of information will be discussed. In the case of source imaging, automatic location in time and space of earthquakes and unknown sources is obtained by time reversal technique. In the case of big earthquakes such as the Sumatra-Andaman earthquake of december 2004, we were able to reconstruct the spatio-temporal history of the rupture. We present here some new applications at the global scale of these techniques on synthetic tests and on real data.
NASA Astrophysics Data System (ADS)
Sato, Haruo
2013-05-01
For imaging the earth structure, the cross-correlation function (CCF) of random waves as ambient noise or coda waves has been widely used for the estimation of the Green's function. We precisely study the condition for the Green's function retrieval in relation to the energy conservation for a single obstacle of arbitrary shape. When an obstacle is placed in a 2-D homogeneous medium, the Green's function is written by a double series expansion using Hankel functions of the first kind which represent outgoing waves. When two receivers and the scattering obstacle are illuminated by uncorrelated noise sources randomly and uniformly distributed on a closed circle of a large radius surrounding them, the lag-time derivative of the CCF of random waves at the two receivers can be written by a convolution of the antisymmetrized Green's function and the autocorrelation function of the noise source time function. We explicitly derive the constraint for the Hankel function expansion coefficients as the sufficient condition for the Green's function retrieval. We show that the constraint is equal to the generalized optical theorem derived from the energy conservation principle. Physical meaning of the generalized optical theorem becomes clear when the Hankel function expansion coefficients are transformed into scattering amplitudes in the framework of the conventional scattering theory. In the 3-D case, the Green's function is written by a double series expansion using spherical Hankel functions of the first kind and spherical harmonic functions. When two receivers and the scattering obstacle are illuminated by noise sources randomly and uniformly distributed on a closed spherical shell of a large radius surrounding them, we explicitly derive the constraint for the spherical Hankel function expansion coefficients for the Green's function retrieval and the energy conservation. We note that the derivation of the constraint does not assume that two receivers are in the far field of
Reprint of : Cross-correlations of coherent multiple Andreev reflections
NASA Astrophysics Data System (ADS)
Riwar, Roman-Pascal; Badiane, Driss M.; Houzet, Manuel; Meyer, Julia S.; Nazarov, Yuli V.
2016-08-01
We use the Landauer-Büttiker scattering theory for electronic transport to calculate the current cross-correlations in a voltage-biased three-terminal junction with all superconducting leads. At low bias voltage, when charge transport is due to coherent multiple Andreev reflections, we find large cross-correlations compared with their normal-state value. Furthermore, depending on the parameters that characterize the properties of the scattering region between the leads, the cross-correlations can reverse their sign with respect to the case of non-interacting fermionic systems.
Cross-correlation analysis of stock markets using EMD and EEMD
NASA Astrophysics Data System (ADS)
Xu, Mengjia; Shang, Pengjian; Lin, Aijing
2016-01-01
Empirical mode decomposition (EMD) is a data-driven signal analysis method for nonlinear and nonstationary data. Since it is intuitive, direct, posterior and adaptive, EMD is widely applied to various fields of study. In this paper, EMD and ensemble empirical mode decomposition (EEMD), a modified method of EMD, are applied to financial time series. Through analyzing the intrinsic mode functions (IMFs) of EMD and EEMD, we find EEMD method performs better on the orthogonality of IMFs than EMD. With clustering the ordered frequencies of IMFs, the IMFs obtained from EEMD method are grouped into high-, medium-, and low-frequency components, representing the short-, medium-, and long-term volatilities of the index sequences, respectively. With the cross-correlation analysis of DCCA cross-correlation coefficient, our findings allow us to gain further and detailed insight into the cross-correlations of stock markets.
Luminosity and Color Dependence in Galaxy Cross-Correlations since z = 1 in PRIMUS
NASA Astrophysics Data System (ADS)
Bray, Aaron; Blanton, M. R.; Coil, A. L.; Cool, R. J.; Eisenstein, D.; Moustakas, J.; Skibba, R. A.; Zhu, G.
2014-01-01
I present small-scale galaxy cross-correlation measurements from the PRIsm MUlti-object Survey (PRIMUS) as a function of color, luminosity, and redshift. We measure the real-space clustering of ~50,000 galaxies from PRIMUS, over a redshift range 0.2 < z < 1, by cross-correlating spectroscopic PRIMUS galaxies with a tracer population of galaxies selected from imaging catalogs. In agreement with previous work, we find strong clustering differences between blue and red galaxy populations. Our results indicate luminosity-dependent clustering, but this luminosity dependence further varies depending on color and physical scale. We interpret our results using a halo abundance model.
Romodina, Maria N.; Khokhlova, Maria D.; Lyubin, Evgeny V.; Fedyanin, Andrey A.
2015-01-01
The effect of magnetic interactions on the Brownian motion of two magnetic microparticles is investigated. The cross-correlations of the thermal fluctuations of the two magnetic microbeads are directly measured using double-trap optical tweezers. It is experimentally demonstrated that the cross-correlation function is governed by the gradient of the magnetic force between the microparticles. The magnetic forces are measured with femtonewton precision, and the magnetic dipole moments of individual microparticles are determined within an accuracy on the order of fA-m2. PMID:26035153
NASA Technical Reports Server (NTRS)
Lee, L. C.
1976-01-01
The cross correlation of the intensity fluctuations between different frequencies and finite bandwidth effects on the intensity correlations based on the Markov approximation were calculated. Results may be applied to quite general turbulence spectra for an extended turbulent medium. Calculations of the cross-correlation function and of finite bandwidth effects are explicitly carried out for both Gaussian and Kolmogorov turbulence spectra. The increases of the correlation scale of intensity fluctuations are different for these two spectra and the difference can be used to determine whether the interstellar turbulent medium has a Gaussian or a Kolmogorov spectrum.
Acoustic ship signature measurements by cross-correlation method.
Fillinger, Laurent; Sutin, Alexander; Sedunov, Alexander
2011-02-01
Cross-correlation methods were applied for the estimation of the power spectral density and modulation spectrum of underwater noise generated by moving vessels. The cross-correlation of the signal from two hydrophones allows the separation of vessel acoustic signatures in a busy estuary. Experimental data recorded in the Hudson River are used for demonstration that cross-correlation method measured the same ship noise and ship noise modulation spectra as conventional methods. The cross-correlation method was then applied for the separation of the acoustic signatures of two ships present simultaneously. Presented methods can be useful for ship traffic monitoring and small ship classification, even in noisy harbor environments. PMID:21361436
Forest Height Retrieval Algorithm Using a Complex Visibility Function Approach
NASA Astrophysics Data System (ADS)
Chu, T.; Zebker, H. A.
2011-12-01
reconstruct the vertical vegetated scene given a sufficient number of baseline pairs in the region. The phase and amplitude is measured by the interferometer as a function of frequency domain spatial coordinate system, it is known as the complex visibility function. The observed brightness distribution is directly the two-dimensional Fourier transform of the complex visibility function. The objective of this study is to demonstrate vegetation structure retrieval capabilities through computer simulations. We hope to apply this technique towards operation data of air-borne instruments such as UAVSAR and space-borne instruments such as ALOS and Terrasar-X.
Microscopic realization of cross-correlated noise processes.
Shit, Anindita; Chattopadhyay, Sudip; Banik, Suman Kumar; Chaudhuri, Jyotipratim Ray
2010-06-01
We present a microscopic theory of cross-correlated noise processes, starting from a Hamiltonian system-reservoir description. In the proposed model, the system is nonlinearly coupled to a reservoir composed of harmonic oscillators, which in turn is driven by an external fluctuating force. We show that the resultant Langevin equation derived from the composite system (system+reservoir+external modulation) contains the essential features of cross-correlated noise processes. PMID:20590326
Cross-correlation search for periodic gravitational waves
Dhurandhar, Sanjeev; Mukhopadhyay, Himan; Krishnan, Badri; Whelan, John T.
2008-04-15
In this paper we study the use of cross correlations between multiple gravitational wave (GW) data streams for detecting long-lived periodic signals. Cross-correlation searches between data from multiple detectors have traditionally been used to search for stochastic GW signals, but recently they have also been used in directed searches for periodic GWs. Here we further adapt the cross-correlation statistic for periodic GW searches by taking into account both the nonstationarity and the long-term-phase coherence of the signal. We study the statistical properties and sensitivity of this search and its relation to existing periodic wave searches, and describe the precise way in which the cross-correlation statistic interpolates between semicoherent and fully coherent methods. Depending on the maximum duration over which we wish to preserve phase coherence, the cross-correlation statistic can be tuned to go from a standard cross-correlation statistic using data from distinct detectors, to the semicoherent time-frequency methods with increasing coherent time baselines, and all the way to a full coherent search. This leads to a unified framework for studying periodic wave searches and can be used to make informed trade-offs between computational cost, sensitivity, and robustness against signal uncertainties.
Robust Statistical Detection of Power-Law Cross-Correlation
Blythe, Duncan A. J.; Nikulin, Vadim V.; Müller, Klaus-Robert
2016-01-01
We show that widely used approaches in statistical physics incorrectly indicate the existence of power-law cross-correlations between financial stock market fluctuations measured over several years and the neuronal activity of the human brain lasting for only a few minutes. While such cross-correlations are nonsensical, no current methodology allows them to be reliably discarded, leaving researchers at greater risk when the spurious nature of cross-correlations is not clear from the unrelated origin of the time series and rather requires careful statistical estimation. Here we propose a theory and method (PLCC-test) which allows us to rigorously and robustly test for power-law cross-correlations, correctly detecting genuine and discarding spurious cross-correlations, thus establishing meaningful relationships between processes in complex physical systems. Our method reveals for the first time the presence of power-law cross-correlations between amplitudes of the alpha and beta frequency ranges of the human electroencephalogram. PMID:27250630
Robust Statistical Detection of Power-Law Cross-Correlation.
Blythe, Duncan A J; Nikulin, Vadim V; Müller, Klaus-Robert
2016-01-01
We show that widely used approaches in statistical physics incorrectly indicate the existence of power-law cross-correlations between financial stock market fluctuations measured over several years and the neuronal activity of the human brain lasting for only a few minutes. While such cross-correlations are nonsensical, no current methodology allows them to be reliably discarded, leaving researchers at greater risk when the spurious nature of cross-correlations is not clear from the unrelated origin of the time series and rather requires careful statistical estimation. Here we propose a theory and method (PLCC-test) which allows us to rigorously and robustly test for power-law cross-correlations, correctly detecting genuine and discarding spurious cross-correlations, thus establishing meaningful relationships between processes in complex physical systems. Our method reveals for the first time the presence of power-law cross-correlations between amplitudes of the alpha and beta frequency ranges of the human electroencephalogram. PMID:27250630
Cross correlation and length scales in turbulent flows near surfaces
NASA Technical Reports Server (NTRS)
Hunt, J. C. R.; Moin, P.; Lee, M.; Moser, R. D.; Spalart, P.; Mansour, N. N.; Kaimal, J. C.; Gaynor, E.
1989-01-01
Two kinds of length scales are used in turbulent flows; 'functional length scales' such as mixing length, dissipation length L(sub epsilon), etc., and 'flow-field length scales' derived from cross correlations of velocity, pressure, etc. in the flow. Some connection between these scales are derived here. We first consider the cross correlation R(sub vv)(y,y(sub 1)) of the normal components u at two heights y, y(sub 1) above a rigid surface, normalized by the velocity y(sub 1) (greater than y). For shear-free boundary layers it is found theoretically, and in field and numerical experiments that R(sub vv) approximately equals y/y(sub 1). For shear layers it is also found that R(sub vv) approximately equals f(y/y(sub 1)) less than or equal to y,y(sub 1). This function f differs slightly between low Reynolds number numerical simulations and field experiments. The lateral structure defined by R(sub vv)(y,r(sub 3); y(sub 1),0) is also self similar and shows that the eddies centered at about y(sub 1) appear to have constant lateral width a(sub 3) above and below y(sub 1), where a(sub 3, sup +) approximately equals 7+1/(1.4dU(sup +)/dy(sup +)), when normalized on u(sub *) and v, where U is the mean velocity. Results for L(sub epsilon, sup -1) from direct numerical simulation are found to compare well with the formula L(sub epsilon, sup -1) = A(sub B)/y + A(sub S)dU/dy/v, for unidirectional and reversing turbulent boundary layers and channel flow, except near where dU/dy approximately equals 0. The conclusion is that the large-scale eddy structure and length scales in these flows are determined by a combination of shear and blocking, and that the vertical component of turbulence has a self-similar structure in both kinds of boundary layer.
Global tomography from ambient seismic noise cross-correlation
NASA Astrophysics Data System (ADS)
Haned, A.; Stutzmann, E.; Yelles-Chaouche, A.; Schimmel, M.; Kiselev, A. A.
2013-12-01
Ambient seismic noise is generated in the ocean and recorded worldwide. In order to extract Green function between stations from seismic noise records, we consider the analytical signal and compute the phase correlation to to extract phase coherent signals which after stacking build up the empirical Green function. The ambient noise phase cross-correlations are stacked using the time-frequency domain phase weighted stack (Schimmel et al. 2011). This method is applied to noise data in the period band 30 to 250sec. A bootstrap approach is used to measure group velocity between pairs of stations and to estimate the corresponding error. We show that it is necessary to stack 2 years of data in order to determine reliable group velocity measurements. It is observed by analyzing the convergence that less data are required to extract reliable group velocities at short period than at long periods. This data processing is applied to 150 stations of the global networks GEOSCOPE and GSN. Global maps of group velocities and the corresponding errors are then estimated and inverted to obtain the 3D S-wave model. CRUST2.0 model is used and the S-wave model below the crust is determined using a simulated annealing method in which the number of splines that describes the model is adapted within the inversion. This model is the first global S-wave velocity model derived from seismic noise recordings in the wide period band 30-250sec.
Cross-Correlation: An fMRI Signal-Processing Strategy
Hyde, James S.; Jesmanowicz, Andrzej
2011-01-01
The discovery of functional MRI (fMRI), with the first papers appearing in 1992, gave rise to new categories of data that drove the development of new signal-processing strategies. Workers in the field were confronted with image time courses, which could be reshuffled to form pixel time courses. The waveform in an active pixel time-course was determined not only by the task sequence but also by the hemodynamic response function. Reference waveforms could be cross-correlated with pixel time courses to form an array of cross-correlation coefficients. From this array of numbers, colorized images could be created and overlaid on anatomical images. An early paper from the authors’ laboratory is extensively reviewed here (Bandettini et al. 1993. Magn. Reson. Med. 30:161–173). That work was carried out using the vocabulary of vector algebra. Cross-correlation methodology was central to the discovery of functional connectivity MRI (fcMRI) by Biswal et al. (1995. Magn. Reson. Med. 34:537–541). In this method, a whole volume time course of images is collected while the brain is nominally at rest and connectivity is studied by cross-correlation of pixel time courses. PMID:22051223
The use of synthetic master events for waveform cross correlation
NASA Astrophysics Data System (ADS)
Rozhkov, Mikhail; Bobrov, Dmitry; Kitov, Ivan
2013-04-01
It has been clearly demonstrated that waveform cross correlation substantially improves signal detection, phase association and event building. These processes are inherently related to the Comprehensive Nuclear-Test-Ban Treaty (CTBT) monitoring. The workhorse of cross correlation is the set of seismic master events (earthquakes or explosions) with high quality waveform templates recorded at array stations of the International Monitoring System (IMS). For the monitoring to be globally uniform, these master events have to be evenly distributed and their template waveforms should be representative and pure. However, global seismicity is characterized by a non-uniform distribution. Therefore, the master events selected from the Reviewed Event Bulletin (REB) produced by the International Data Centre (IDC) can be found in the areas constrained by the global seismicity. There are two principal possibilities to populate the globe with master events: to replicate real REB events or to build synthetic events. Here we compare the performance of these two approaches as applied to the aftershock sequence of the April 11, 2012 Sumatera earthquake. To compute synthetic waveforms, we use AK135 teleseismic velocity model and local CRUST-2 models for source and receiver, and four different source functions representing three different source mechanisms for earthquakes and one for explosion. The synthetic modeling is performed for teleseismic events and based on the stationary phase approximation to a wave equation solution developed by J. Hudson. The grid covering the aftershock area consists of 16 points. For each grid point, we find detections associated with real, replicated, and four versions of synthetic master events at seven IMS array stations, and then build event hypothesis using the Local Association (LA) procedure based on the clustering of origin times as estimated by back projection of the relevant arrival times with known master/station travel times. Then all
Stationary-phase integrals in the cross correlation of ambient noise
NASA Astrophysics Data System (ADS)
Boschi, Lapo; Weemstra, Cornelis
2015-06-01
The cross correlation of ambient signal allows seismologists to collect data even in the absence of seismic events. "Seismic interferometry" shows that the cross correlation of simultaneous recordings of a random wavefield made at two locations is formally related to the impulse response between those locations. This idea has found many applications in seismology, as a growing number of dense seismic networks become available: cross-correlating long seismic records, the Green's function between instrument pairs is "reconstructed" and used, just like the seismic recording of an explosion, in tomography, monitoring, etc. These applications have been accompanied by theoretical investigations of the relationship between noise cross correlation and the Green's function; numerous formulations of "ambient noise" theory have emerged, each based on different hypotheses and/or analytical approaches. The purpose of this study is to present most of those approaches together, providing a comprehensive overview of the theory. Understanding the specific hypotheses behind each Green's function recipe is critical to its correct application. Hoping to guide nonspecialists who approach ambient noise theory for the first time, we treat the simplest formulation (the stationary-phase approximation applied to smooth unbounded media) in detail. We then move on to more general treatments, illustrating that the "stationary-phase" and "reciprocity theorem" approaches lead to the same formulae when applied to the same scenario. We show that a formal cross correlation/Green's function relationship can be found in complex, bounded media and for nonuniform source distributions. We finally provide the bases for understanding how the Green's function is reconstructed in the presence of scattering obstacles.
Exploring the distant universe with cross-correlation statistics
NASA Astrophysics Data System (ADS)
Matthews, Daniel J.
Future cosmological surveys will require distance information for an extremely large number of galaxies in order to gain insight into the structure and history of our Universe. Current methods of obtaining accurate distance information such as measuring the redshifts of galaxies via spectroscopy are not feasible for such enormous datasets, mainly due to the long exposure times required. Photometric redshifts, where the redshift is measured using broadband imaging through only a few Filters, are a promising avenue of study, although there are inherent limitations to this method making them less understood than spectroscopic redshifts. Understanding these limitations and improving the calibration of photometric redshifts will be very important for future cosmological measurements. This thesis presents tests of a new technique for calibrating photometric redshifts that exploits the clustering of galaxies due to gravitational interaction. This cross-correlation technique uses the measured spatial clustering on the sky of a photometric sample that has only imaging information, with a spectroscopic sample that has secure and accurate redshifts. These tests shows that measurements of this clustering as a function of redshift can be used to accurately reconstruct the true redshift distribution of the photometric sample. In addition, this thesis shows how similar clustering measurements can be used to constrain the contamination of a high redshift candidate sample by low redshift interlopers. Finally it describes a new catalog that combines spectroscopic redshifts and deep photometry that can be used as a testbed for future photo-z studies.
Estimation of the Mean Free Path using Cross-Correlations in the Seismic Coda
NASA Astrophysics Data System (ADS)
Clerc, V.; Roux, P.; Campillo, M.; Maynard, R.; Chaput, J. A.
2014-12-01
We present recent results concerning the extraction of Green's functions from coda waves. Campillo and Paul 2003 used earthquakes codas and found that the causal and anticausal parts of the cross-correlation are asymmetrical for some stations, depending on the earthquake source region. The lapse time in the coda window is a key parameter to understand causal to anticausal amplitude ratio. We show that this ratio result from the competition between the source signature (non-symmetric cross-correlations when the distribution of sources is non-isotropic around the receivers) and the scattering processes which tend to restore the time symmetry of the correlations. The theoretical analysis is derived from wave propagation theory for single scattering and multiple scattering as initiated by Roux 2005. We propose to use the temporal evolution of cross-correlation function amplitude in coda waves to estimate the value of the mean free path in the propagation medium. The equipartition of the energy is clearly observed in the numerical simulations conducted in a two-dimensional acoustic medium. The cross-correlations between the distinct time windows in synthetic coda records at two points are measured for a set of events for which we obtain a good estimate of the medium mean free path. We perform the same analysis on a set of icequakes recorded at Mount Erebus. The correlations averaged over sources and time exhibit a temporal evolution that obeys to convergence patterns similar to those observed in numerical studies.
A proposal of fuzzy connective with learning function and its application to fuzzy retrieval system
NASA Technical Reports Server (NTRS)
Hayashi, Isao; Naito, Eiichi; Ozawa, Jun; Wakami, Noboru
1993-01-01
A new fuzzy connective and a structure of network constructed by fuzzy connectives are proposed to overcome a drawback of conventional fuzzy retrieval systems. This network represents a retrieval query and the fuzzy connectives in networks have a learning function to adjust its parameters by data from a database and outputs of a user. The fuzzy retrieval systems employing this network are also constructed. Users can retrieve results even with a query whose attributes do not exist in a database schema and can get satisfactory results for variety of thinkings by learning function.
Magnified Weak Lensing Cross Correlation Tomography
Ulmer, Melville P., Clowe, Douglas I.
2010-11-30
nights on 4-m class telescopes, which gives concrete evidence of strong community support for this project. The WLT technique is based on the dependence of the gravitational shear signal on the angular diameter distances between the observer, the lens, and the lensed galaxy to measure cosmological parameters. By taking the ratio of measured shears of galaxies with different redshifts around the same lens, one obtains a measurement of the ratios of the angular diameter distances involved. Making these observations over a large range of lenses and background galaxy redshifts will measure the history of the expansion rate of the universe. Because this is a purely geometric measurement, it is insensitive to any form of evolution of objects or the necessity to understand the physics in the early universe. Thus, WLT was identified by the Dark Energy Task Force as perhaps the best method to measure the evolution of DE. To date, however, the conjecture of the DETF has not been experimentally verified, but will be by the proposed project. The primary reason for the lack of tomography measurements is that one must have an exceptional data-set to attempt the measurement. One needs both extremely good seeing (or space observations) in order to minimize the point spread function smearing corrections on weak lensing shear measurements and deep, multi-color data, from B to z, to measure reliable photometric redshifts of the background galaxies being lensed (which are typically too faint to obtain spectroscopic redshifts). Because the entire process from multi-drizzling the HST images, and then creating shear maps, to gathering the necessary ground based observations, to generating photo-zs and then carrying out the tomography is a complicated task, until the creation of our team, nobody has taken the time to connect all the levels of expertise necessary to carry out this project based on HST archival data. Our data are being used in 2 Ph.D. theses. Kellen Murphy, at Ohio University, is
Annotation and retrieval system of CAD models based on functional semantics
NASA Astrophysics Data System (ADS)
Wang, Zhansong; Tian, Ling; Duan, Wenrui
2014-11-01
CAD model retrieval based on functional semantics is more significant than content-based 3D model retrieval during the mechanical conceptual design phase. However, relevant research is still not fully discussed. Therefore, a functional semantic-based CAD model annotation and retrieval method is proposed to support mechanical conceptual design and design reuse, inspire designer creativity through existing CAD models, shorten design cycle, and reduce costs. Firstly, the CAD model functional semantic ontology is constructed to formally represent the functional semantics of CAD models and describe the mechanical conceptual design space comprehensively and consistently. Secondly, an approach to represent CAD models as attributed adjacency graphs(AAG) is proposed. In this method, the geometry and topology data are extracted from STEP models. On the basis of AAG, the functional semantics of CAD models are annotated semi-automatically by matching CAD models that contain the partial features of which functional semantics have been annotated manually, thereby constructing CAD Model Repository that supports model retrieval based on functional semantics. Thirdly, a CAD model retrieval algorithm that supports multi-function extended retrieval is proposed to explore more potential creative design knowledge in the semantic level. Finally, a prototype system, called Functional Semantic-based CAD Model Annotation and Retrieval System(FSMARS), is implemented. A case demonstrates that FSMARS can successfully botain multiple potential CAD models that conform to the desired function. The proposed research addresses actual needs and presents a new way to acquire CAD models in the mechanical conceptual design phase.
Nadel, Lynn; Campbell, Jenna; Ryan, Lee
2007-01-01
Multiple trace theory (MTT) predicts that hippocampal memory traces expand and strengthen as a function of repeated memory retrievals. We tested this hypothesis utilizing fMRI, comparing the effect of memory retrieval versus the mere passage of time on hippocampal activation. While undergoing fMRI scanning, participants retrieved remote autobiographical memories that had been previously retrieved either one month earlier, two days earlier, or multiple times during the preceding month. Behavioral analyses revealed that the number and consistency of memory details retrieved increased with multiple retrievals but not with the passage of time. While all three retrieval conditions activated a similar set of brain regions normally associated with autobiographical memory retrieval including medial temporal lobe structures, hippocampal activation did not change as a function of either multiple retrievals or the passage of time. However, activation in other brain regions, including the precuneus, lateral prefrontal cortex, parietal cortex, lateral temporal lobe, and perirhinal cortex increased after multiple retrievals, but was not influenced by the passage of time. These results have important implications for existing theories of long-term memory consolidation. PMID:18274617
Dynamics of cross-correlations in the stock market
NASA Astrophysics Data System (ADS)
Rosenow, Bernd; Gopikrishnan, Parameswaran; Plerou, Vasiliki; Eugene Stanley, H.
2003-06-01
Co-movements of stock price fluctuations are described by the cross-correlation matrix C. The application of random matrix theory (RMT) allows to distinguish between spurious correlations in C due to measurement noise and true correlations containing economically meaningful information. By calculating cross-correlations for different time windows, we study the time dependence of eigenvectors of C, which are related to economic sectors, and the time evolution of the largest eigenvalue, which describes the average correlation strength. We use these results to forecast cross-correlations, and test the quality of our forecast by constructing investments in the stock market which expose the invested capital to a minimum level of risk only.
NASA Astrophysics Data System (ADS)
Ku, C. S.; You, S. H.; Kuo, Y. T.; Huang, B. S.; Wu, Y. M.; Chen, Y. G.; Taylor, F. W.
2015-12-01
A MW 8.1 earthquake occurred on 1 April 2007 in the western Solomon Islands. Following this event, a damaging tsunami was induced and hit the Island Gizo where the capital city of Western Province of Solomon Islands located. Several buildings of this city were destroyed and several peoples lost their lives during this earthquake. However, during this earthquake, no near source seismic instrument has been installed in this region. The seismic evaluations for the aftershock sequence, the possible earthquake early warning and tsunami warning were unavailable. For the purpose of knowing more detailed information about seismic activity in this region, we have installed 9 seismic stations (with Trillium 120PA broadband seismometer and Q330S 24bit digitizer) around the rupture zone of the 2007 earthquake since September of 2009. Within a decade, it has been demonstrated both theoretically and experimentally that the Green's function or impulse response between two seismic stations can be retrieved from the cross-correlation of ambient noise. In this study, 6 stations' observations which are more complete during 2011/10 ~ 2012/12 period, were selected for the purpose of the cross-correlation analysis of ambient seismic noise. The group velocities at period 2-20 seconds of 15 station-pairs were extracted by using multiple filter technique (MFT) method. The analyzed results of this study presented significant results of group velocities with higher frequency contents than other studies (20-60 seconds in usually cases) and opened new opportunities to study the shallow crustal structure of the western Solomon Islands.
NASA Astrophysics Data System (ADS)
Schroer, M. A.; Gutt, C.; Grübel, G.
2014-07-01
Recently the analysis of scattering patterns by angular cross-correlation analysis (CCA) was introduced to reveal the orientational order in disordered samples with special focus to future applications on x-ray free-electron laser facilities. We apply this CCA approach to ultra-small-angle light-scattering data obtained from two-dimensional monolayers of microspheres. The films were studied in addition by optical microscopy. This combined approach allows to calculate the cross-correlations of the scattering patterns, characterized by the orientational correlation function Ψl(q), as well as to obtain the real-space structure of the monolayers. We show that CCA is sensitive to the orientational order of monolayers formed by the microspheres which are not directly visible from the scattering patterns. By mixing microspheres of different radii the sizes of ordered monolayer domains is reduced. For these samples it is shown that Ψl(q) quantitatively describes the degree of hexagonal order of the two-dimensional films. The experimental CCA results are compared with calculations based on the microscopy images. Both techniques show qualitatively similar features. Differences can be attributed to the wave-front distortion of the laser beam in the experiment. This effect is discussed by investigating the effect of different wave fronts on the cross-correlation analysis results. The so-determined characteristics of the cross-correlation analysis will be also relevant for future x-ray-based studies.
NASA Astrophysics Data System (ADS)
Chen, Zhi; Hu, Kun; Stanley, H. Eugene; Novak, Vera; Ivanov, Plamen Ch.
2006-03-01
We investigate the relationship between the blood flow velocities (BFV) in the middle cerebral arteries and beat-to-beat blood pressure (BP) recorded from a finger in healthy and post-stroke subjects during the quasisteady state after perturbation for four different physiologic conditions: supine rest, head-up tilt, hyperventilation, and CO2 rebreathing in upright position. To evaluate whether instantaneous BP changes in the steady state are coupled with instantaneous changes in the BFV, we compare dynamical patterns in the instantaneous phases of these signals, obtained from the Hilbert transform, as a function of time. We find that in post-stroke subjects the instantaneous phase increments of BP and BFV exhibit well-pronounced patterns that remain stable in time for all four physiologic conditions, while in healthy subjects these patterns are different, less pronounced, and more variable. We propose an approach based on the cross-correlation of the instantaneous phase increments to quantify the coupling between BP and BFV signals. We find that the maximum correlation strength is different for the two groups and for the different conditions. For healthy subjects the amplitude of the cross-correlation between the instantaneous phase increments of BP and BFV is small and attenuates within 3-5 heartbeats. In contrast, for post-stroke subjects, this amplitude is significantly larger and cross-correlations persist up to 20 heartbeats. Further, we show that the instantaneous phase increments of BP and BFV are cross-correlated even within a single heartbeat cycle. We compare the results of our approach with three complementary methods: direct BP-BFV cross-correlation, transfer function analysis, and phase synchronization analysis. Our findings provide insight into the mechanism of cerebral vascular control in healthy subjects, suggesting that this control mechanism may involve rapid adjustments (within a heartbeat) of the cerebral vessels, so that BFV remains steady in
Polarization-assisted WMAP-NVSS Cross Correlation
Liu, G.-C.
2008-10-10
Cross-correlation of Cosmic Microwave Background (CMB) and large scale structure survey is one of the powerful tools for constraining the nature of dark energy through the so-called Integrated Sachs-Wolfe effect. However, CMB from higher redshift is the dominated noise of this effect. Here, we present the CMB polarization-assisted method to suppress this noise. We apply this method to cross-correlation of the microwave sky observed by Wilkinson Microwave Anisotropy Probe (WMAP) with the radio source catalog compiled by NRAO VLA Sky Survey (NVSS) to study the efficiency of the noise suppression. We find that the spurious correlation is reduced about 2-7%.
Weak lensing corrections to tSZ-lensing cross correlation
NASA Astrophysics Data System (ADS)
Tröster, Tilman; Van Waerbeke, Ludovic
2014-11-01
The cross correlation between the thermal Sunyaev-Zeldovich (tSZ) effect and gravitational lensing in wide field has recently been measured. It can be used to probe the distribution of the diffuse gas in large scale structure, as well as inform us about the missing baryons. As for any lensing-based quantity, higher order lensing effects can potentially affect the signal. Here, we extend previous higher order lensing calculations to the case of tSZ-lensing cross correlations. We derive terms analogous to corrections due to the Born approximation, lens-lens coupling, and reduced shear up to order l gtrsim 3000.
Optical cross-correlator based on supercontinuum generation
Filip, Catalin V.; Toth, Csaba; Leemans, Wim P.
2006-03-20
A novel cross-correlator that can be used for temporal characterization of femtosecond laser pulses has been developed. The correlation trace is obtained by ''sampling'' the structure of the laser pulse with a single, high-contrast pulse produced through femtosecond white-light generation in a line focus. This correlator has, therefore, fewer ''ghosts'' than a conventional third-order cross-correlator and it can be used with laser pulses that span across a wide wavelength range. Both scanning and single-shot experimental arrangements are described.
2012-01-01
Background In spite of numerous non-invasive examinations the “gold clinical standard” of cardiac output measurements is the invasive pulmonary artery catheterization by means of the Swan-Ganz catheter and the application of the thermodilution method to estimate the blood flow. The results obtained by means of thermodilution are sensitive to many physical and biological disturbances. The unreliability of this method amounts to 20-45% and depends on the given variant of the method. Therefore some other method, more accurate and resistant to disturbances, was looked for. This paper presents a new approach to cardiac output measurements, based on cross-correlation signal analysis. The goal of investigations was to verify experimentally the application of the cross-correlation method of cardiac output measurements. Results In 99.2% of the examined cases the extreme of the cross-correlation function was easy to be estimated by numerical algorithms. In 0,8% of the remaining cases (with a plateau region adjacent to the maximum point) numerical detection of the extreme was inaccurate. The typical unreliability of the investigated method amounted o 5.1% (9.8% in the worst case). Investigations performed on a physical model revealed that the unreliability of cardiac output measurements by means of the cross-correlation method is 3–5 times better than in the case of thermodilution. Conclusions The performed investigations and theoretical analysis have shown, that the cross-correlation method may be applied in cardiac output measurements. This kind of measurements seems to be more accurate and disturbance-resistant than clinically applied thermodilution. PMID:22607380
Atmospheric pollution measurement by optical cross correlation methods - A concept
NASA Technical Reports Server (NTRS)
Fisher, M. J.; Krause, F. R.
1971-01-01
Method combines standard spectroscopy with statistical cross correlation analysis of two narrow light beams for remote sensing to detect foreign matter of given particulate size and consistency. Method is applicable in studies of generation and motion of clouds, nuclear debris, ozone, and radiation belts.
Optical periodic code matching by single-shot broadband frequency-domain cross-correlation.
Chuntonov, Lev; Amitay, Zohar
2010-08-16
We introduce and experimentally demonstrate a simple and reliable optical technique for matching between two periodic numerical sequences based on optical single-shot measurement of their broadband cross-correlation function in the frequency domain. Each sequence is optically encoded into the shape of the different broadband femtosecond pulse using pulse-shaping techniques. The two corresponding shaped pulses are mixed in a nonlinear medium together with an additional (amplitude-shaped) narrowband pulse. The spectrum of the resulting four-wave mixing signal is measured to provide the cross-correlation function of the two encoded sequences. For identical sequences it is the auto-correlation function that is being measured, allowing also the identification of the sequence period. The high contrast achieved here between cross-correlation and auto-correlation functions allows to determine with a very high reliability whether the two encoded sequences are identical or not. The demonstrated technique might be employed in an optical implementation of CDMA communication protocol. PMID:20721163
Functions and requirements for 105-KE Basin sludge retrieval and packaging
Feigenbutz, L.V.
1994-12-16
Sludge, and the clouding due to sludge, interferes with basin operation and maintenance activities. This document defines the overall functions and requirements for sludge retrieval and packaging activities to be performed in the 105-KE Basin.
NASA Astrophysics Data System (ADS)
Wang, Fang
2016-06-01
In order to detect and quantify asymmetry of two time series, a novel cross-correlation coefficient is proposed based on recent asymmetric detrended cross-correlation analysis (A-DXA), which we called A-DXA coefficient. The A-DXA coefficient, as an important extension of DXA coefficient ρ D X A , contains two directional asymmetric cross-correlated indexes, describing upwards and downwards asymmetric cross-correlations, respectively. By using the information of directional covariance function of two time series and directional variance function of each series itself instead of power-law between the covariance function and time scale, the proposed A-DXA coefficient can well detect asymmetry between the two series no matter whether the cross-correlation is significant or not. By means of the proposed A-DXA coefficient conducted over the asymmetry for California electricity market, we found that the asymmetry between the prices and loads is not significant for daily average data in 1999 yr market (before electricity crisis) but extremely significant for those in 2000 yr market (during the crisis). To further uncover the difference of asymmetry between the years 1999 and 2000, a modified H statistic (MH) and ΔMH statistic are proposed. One of the present contributions is that the high MH values calculated for hourly data exist in majority months in 2000 market. Another important conclusion is that the cross-correlation with downwards dominates over the whole 1999 yr in contrast to the cross-correlation with upwards dominates over the 2000 yr.
Wang, Fang
2016-06-01
In order to detect and quantify asymmetry of two time series, a novel cross-correlation coefficient is proposed based on recent asymmetric detrended cross-correlation analysis (A-DXA), which we called A-DXA coefficient. The A-DXA coefficient, as an important extension of DXA coefficient ρDXA, contains two directional asymmetric cross-correlated indexes, describing upwards and downwards asymmetric cross-correlations, respectively. By using the information of directional covariance function of two time series and directional variance function of each series itself instead of power-law between the covariance function and time scale, the proposed A-DXA coefficient can well detect asymmetry between the two series no matter whether the cross-correlation is significant or not. By means of the proposed A-DXA coefficient conducted over the asymmetry for California electricity market, we found that the asymmetry between the prices and loads is not significant for daily average data in 1999 yr market (before electricity crisis) but extremely significant for those in 2000 yr market (during the crisis). To further uncover the difference of asymmetry between the years 1999 and 2000, a modified H statistic (MH) and ΔMH statistic are proposed. One of the present contributions is that the high MH values calculated for hourly data exist in majority months in 2000 market. Another important conclusion is that the cross-correlation with downwards dominates over the whole 1999 yr in contrast to the cross-correlation with upwards dominates over the 2000 yr. PMID:27368774
Cross-correlation asymmetries and causal relationships between stock and market risk.
Borysov, Stanislav S; Balatsky, Alexander V
2014-01-01
We study historical correlations and lead-lag relationships between individual stock risk (volatility of daily stock returns) and market risk (volatility of daily returns of a market-representative portfolio) in the US stock market. We consider the cross-correlation functions averaged over all stocks, using 71 stock prices from the Standard & Poor's 500 index for 1994-2013. We focus on the behavior of the cross-correlations at the times of financial crises with significant jumps of market volatility. The observed historical dynamics showed that the dependence between the risks was almost linear during the US stock market downturn of 2002 and after the US housing bubble in 2007, remaining at that level until 2013. Moreover, the averaged cross-correlation function often had an asymmetric shape with respect to zero lag in the periods of high correlation. We develop the analysis by the application of the linear response formalism to study underlying causal relations. The calculated response functions suggest the presence of characteristic regimes near financial crashes, when the volatility of an individual stock follows the market volatility and vice versa. PMID:25162697
Cross-Correlation Asymmetries and Causal Relationships between Stock and Market Risk
Borysov, Stanislav S.; Balatsky, Alexander V.
2014-01-01
We study historical correlations and lead-lag relationships between individual stock risk (volatility of daily stock returns) and market risk (volatility of daily returns of a market-representative portfolio) in the US stock market. We consider the cross-correlation functions averaged over all stocks, using 71 stock prices from the Standard & Poor's 500 index for 1994–2013. We focus on the behavior of the cross-correlations at the times of financial crises with significant jumps of market volatility. The observed historical dynamics showed that the dependence between the risks was almost linear during the US stock market downturn of 2002 and after the US housing bubble in 2007, remaining at that level until 2013. Moreover, the averaged cross-correlation function often had an asymmetric shape with respect to zero lag in the periods of high correlation. We develop the analysis by the application of the linear response formalism to study underlying causal relations. The calculated response functions suggest the presence of characteristic regimes near financial crashes, when the volatility of an individual stock follows the market volatility and vice versa. PMID:25162697
Yoritomo, John Y; Weaver, Richard L
2016-07-01
Inasmuch as ambient noise fields are often not fully diffuse the question arises as to how, or whether, noise cross-correlations converge to Green's function in practice. Well-known theoretical estimates suggest that the quality of convergence scales with the square root of the product of integration time and bandwidth. However, correlations from natural environments often show random features too large to be consistent with fluctuations from insufficient integration time. Here it is argued that empirical seismic correlations suffer in practice from spurious arrivals due to scatterers, and not from insufficient integration time. Estimates are sought for differences by considering a related problem consisting of waves from a finite density of point sources. The resulting cross-correlations are analyzed for their mean and variance. The mean is, as expected, Green's function with amplitude dependent on noise strength. The variance is found to have support for all times up to its maximum at the main arrival. The signal-to-noise ratio there scales with the square root of source density. Numerical simulations support the theoretical estimates. The result permits estimates of spurious arrivals' impact on identification of cross-correlations with Green's function and indicates that spurious arrivals may affect estimates of amplitudes, complicating efforts to infer attenuation. PMID:27475191
On the linearity of cross-correlation delay times
NASA Astrophysics Data System (ADS)
Mercerat, E. D.; Nolet, G.
2012-12-01
We investigate the question whether a P-wave delay time Δ T estimated by locating the maximum of the cross-correlation function between data d(t) and a predicted test function s(t): γ (t) = ∫ t1t_2 s(τ ) d(τ -t) \\ {d}τ, provides an estimate of the Delta T that is (quasi-)linear with the relative velocity perturbation deltaln V_P}. Such linearity is intuitive if the data d(t) is an undeformed but delayed replica of the test signal, i.e. if d(t)=s(t-Delta T). Then the maximum of gamma (t) is shifted exactly by the delay Delta T, and linearity holds even for Delta T very large. In this case, we say that the body waves are in the ray theoretical regime and their delays, because of Fermat's Principle, depend quasi-linearly on the relative velocity (or slowness) perturbations deltaln V_P in the model. However, even if we correct for dispersion induced by the instrument response and by attenuation, body waves may show frequency dependent delay times that are caused by diffraction effects around lateral heterogeneities. It is not a-priori clear that linearity holds for Delta T, as is assumed in finite-frequency theory, if the waveforms of d(t) and s(t) differ substantially because of such dispersion. To test the linearity, we generate synthetic seismograms between two boreholes, and between the boreholes and the surface, in a 3D box of 200 × 120 × 120 m. The heterogeneity is a checkerboard with cubic anomalies of size 12 × 12 × 12 m. We test two different anomaly amplitudes: ± 2% and ± 5%, and measure Delta T using a test seismogram s(t) computed for an homogeneous medium. We also predict the delays for the 5% model from those in the 2% model by multiplying with 5/2. These predictions are in error by 10-20% of the delay, which is usually acceptable for tomography when compared with actual data errors. A slight bias in the prediction indicates that the Wielandt effect - the fact that negative delays suffer less wavefront healing than positive delays - is a
Intensity Mapping During Reionization: 21 cm and Cross-correlations
NASA Astrophysics Data System (ADS)
Aguirre, James E.; HERA Collaboration
2016-01-01
The first generation of 21 cm epoch of reionization (EoR) experiments are now reaching the sensitivities necessary for a detection of the power spectrum of plausible reionization models, and with the advent of next-generation capabilities (e.g. the Hydrogen Epoch of Reionization Array (HERA) and the Square Kilometer Array Phase I Low) will move beyond the power spectrum to imaging of the EoR intergalactic medium. Such datasets provide context to galaxy evolution studies for the earliest galaxies on scales of tens of Mpc, but at present wide, deep galaxy surveys are lacking, and attaining the depth to survey the bulk of galaxies responsible for reionization will be challenging even for JWST. Thus we seek useful cross-correlations with other more direct tracers of the galaxy population. I review near-term prospects for cross-correlation studies with 21 cm and CO and CII emission, as well as future far-infrared misions suchas CALISTO.
The Atacama Cosmology Telescope: cross correlation with Planck maps
Louis, Thibaut; Calabrese, Erminia; Dunkley, Joanna; Næss, Sigurd; Addison, Graeme E.; Hincks, Adam D.; Hasselfield, Matthew; Hlozek, Renée; Bond, J. Richard; Hajian, Amir; Das, Sudeep; Devlin, Mark J.; Dünner, Rolando; Infante, Leopoldo; Gralla, Megan; Marriage, Tobias A.; Huffenberger, Kevin; Kosowsky, Arthur; Moodley, Kavilan; Niemack, Michael D.; and others
2014-07-01
We present the temperature power spectrum of the Cosmic Microwave Background obtained by cross-correlating maps from the Atacama Cosmology Telescope (ACT) at 148 and 218 GHz with maps from the Planck satellite at 143 and 217 GHz, in two overlapping regions covering 592 square degrees. We find excellent agreement between the two datasets at both frequencies, quantified using the variance of the residuals between the ACT power spectra and the ACT × Planck cross-spectra. We use these cross-correlations to measure the calibration of the ACT data at 148 and 218 GHz relative to Planck, to 0.7% and 2% precision respectively. We find no evidence for anisotropy in the calibration parameter. We compare the Planck 353 GHz power spectrum with the measured amplitudes of dust and cosmic infrared background (CIB) of ACT data at 148 and 218 GHz. We also compare planet and point source measurements from the two experiments.
Cross-Correlation Effects Involving Curie Spin Relaxation in Methyl Groups
NASA Astrophysics Data System (ADS)
Madhu, P. K.; Mandal, Pravat K.; Müller, Norbert
2002-03-01
Cross-correlation effects arising in methyl protons due to the simultaneous presence of dipole-dipole, chemical shift anisotropy, and Curie spin relaxation mechanisms in paramagnetic systems are analyzed. We assess the potential of obtaining structural constraints from the cross-correlation of Curie spin relaxation with dipolar relaxation mechanisms among methyl proton spins. By theoretical analysis and numerical simulations we characterize the transfer functions describing the interconversion processes of different ranks of multispin order. The time dependence of these processes contains a new type of structural information, the orientation of the methyl C3-axis with respect to the electron center. Experimental confirmation is found for selected methyl groups in low spin Fe3+ sperm whale myoglobin.
Three dimensional winds: A maximum cross-correlation application to elastic lidar data
Buttler, W.T.
1996-05-01
Maximum cross-correlation techniques have been used with satellite data to estimate winds and sea surface velocities for several years. Los Alamos National Laboratory (LANL) is currently using a variation of the basic maximum cross-correlation technique, coupled with a deterministic application of a vector median filter, to measure transverse winds as a function of range and altitude from incoherent elastic backscatter lidar (light detection and ranging) data taken throughout large volumes within the atmospheric boundary layer. Hourly representations of three-dimensional wind fields, derived from elastic lidar data taken during an air-quality study performed in a region of complex terrain near Sunland Park, New Mexico, are presented and compared with results from an Environmental Protection Agency (EPA) approved laser doppler velocimeter. The wind fields showed persistent large scale eddies as well as general terrain-following winds in the Rio Grande valley.
Active ultrasonic cross-correlation flowmeters for mixed-phase pipe flows
NASA Astrophysics Data System (ADS)
Sheen, S. H.; Raptis, A. C.
Two ultrasonic flowmeters which employ the active cross-correlation technique and use a simple clamp-on transducer arrangement are discussed. The flowmeter for solid/liquid flows was tested over a wide range of coal concentration in water and oil. The measured velocity based on the peak position of the cross-correlation function is consistently higher by about 15% than the average velocity measured by flow diversion. The origin of the difference results mainly from the flow velocity profiles and the transit-time probability distribution. The flowmeter that can measure particle velocity in a solid/gas flow requires acoustic decoupling arrangement between two sensing stations. The measured velocity is mainly associated with the particles near the wall. Performance of both flowmeters is presented.
Time-lag cross-correlations in collective phenomena
NASA Astrophysics Data System (ADS)
Podobnik, B.; Wang, D.; Horvatic, D.; Grosse, I.; Stanley, H. E.
2010-06-01
We study long-range magnitude cross-correlations in collective modes of real-world data from finance, physiology, and genomics using time-lag random matrix theory. We find long-range magnitude cross-correlations i) in time series of price fluctuations, ii) in physiological time series, both healthy and pathological, indicating scale-invariant interactions between different physiological time series, and iii) in ChIP-seq data of the mouse genome, where we uncover a complex interplay of different DNA-binding proteins, resulting in power-law cross-correlations in xij, the probability that protein i binds to gene j, ranging up to 10 million base pairs. In finance, we find that the changes in singular vectors and singular values are largest in times of crisis. We find that the largest 500 singular values of the NYSE Composite members follow a Zipf distribution with exponent ≈2. In physiology, we find statistically significant differences between alcoholic and control subjects.
Waveform Cross-Correlation for Improved North Texas Earthquake Locations
NASA Astrophysics Data System (ADS)
Phillips, M.; DeShon, H. R.; Oldham, H. R.; Hayward, C.
2014-12-01
In November 2013, a sequence of earthquakes began in Reno and Azle, TX, two communities located northwest of Fort Worth in an area of active oil and gas extraction. Only one felt earthquake had been reported within the area before the occurrence of probable injection-induced earthquakes at the Dallas-Fort Worth airport in 2008. The USGS National Earthquakes Information Center (NEIC) has reported 27 felt earthquakes in the Reno-Azle area through January 28, 2014. A temporary seismic network was installed beginning in December 2013 to acquire data to improve location and magnitude estimates and characterize the earthquake sequence. Here, we present high-resolution relative earthquake locations derived using differential time data from waveform cross-correlation. Cross-correlation is computed using the GISMO software suite and event relocation is done using double difference relocation techniques. Waveform cross-correlation of the local data indicates high (>70%) similarity between 4 major swarms of events lasting between 18 and 24 hours. These swarms are temporal zones of high event frequency; 1.4% of the time series data accounts for 42.1% of the identified local earthquakes. Local earthquakes are occurring along the Newark East Fault System, a NE-SW striking normal fault system previously thought inactive at depths between 2 and 8 km in the Ellenburger limestone formation and underlying Precambrian basement. Data analysis is ongoing and continued characterization of the associated fault will provide improved location estimates.
Functional design criteria, Project W-211, Initial Tank Retrieval Systems. Revision 1
Rieck, C.A.
1995-02-07
This document provides the technical baseline for retrieval of waste from ten double-shell tanks in the SY, AN, AP, AW, AY, and AZ tank farms. In order to retrieve waste from these tanks, systems are needed to mix the sludge with the supernate and pump the waste mixture from the tank. For 101-SY, the existing mitigation pump will be used to mix the waste and Project W-211 will provide for waste removal. The retrieval scope for the other nine tanks includes both the waste mixing and removal functions.
Near-Field Fluorescence Cross-Correlation Spectroscopy on Planar Membranes
2015-01-01
The organization and dynamics of plasma membrane components at the nanometer scale are essential for biological functions such as transmembrane signaling and endocytosis. Planarized nanoscale apertures in a metallic film are demonstrated as a means of confining the excitation light for multicolor fluorescence spectroscopy to a 55 ± 10 nm beam waist. This technique provides simultaneous two-color, subdiffraction-limited fluorescence correlation spectroscopy and fluorescence cross-correlation spectroscopy on planar membranes. The fabrication and implementation of this technique are demonstrated for both model membranes and live cells. Membrane-bound proteins were observed to cluster upon the addition of a multivalent cross-linker: On supported lipid bilayers, clusters of cholera toxin subunit B were formed upon cross-linking by an antibody specific for this protein; on living cells, immunoglobulin E bound to its receptor (FcεRI) on the plasma membranes of RBL mast cells was observed to form clusters upon exposure to a trivalent antigen. The formation of membrane clusters was quantified via fluorescence intensity vs time and changes in the temporal auto- and cross-correlations above a single nanoscale aperture. The illumination profile from a single aperture is analyzed experimentally and computationally with a rim-dominated illumination profile, yielding no change in the autocorrelation dwell time with changes in aperture diameter from 60 to 250 nm. This near-field fluorescence cross-correlation methodology provides access to nanoscale details of dynamic membrane interactions and motivates further development of near-field optical methods. PMID:25004429
Cross-correlation of the cosmic 21-cm signal and Lyman α emitters during reionization
NASA Astrophysics Data System (ADS)
Sobacchi, Emanuele; Mesinger, Andrei; Greig, Bradley
2016-07-01
Interferometry of the cosmic 21-cm signal is set to revolutionize our understanding of the Epoch of Reionization (EoR), eventually providing 3D maps of the early Universe. Initial detections however will be low signal to noise, limited by systematics. To confirm a putative 21-cm detection, and check the accuracy of 21-cm data analysis pipelines, it would be very useful to cross-correlate against a genuine cosmological signal. The most promising cosmological signals are wide-field maps of Lyman α emitting galaxies (LAEs), expected from the Subaru Hyper-Suprime Cam ultradeep field (UDF). Here we present estimates of the correlation between LAE maps at z ˜ 7 and the 21-cm signal observed by both the Low Frequency Array (LOFAR) and the planned Square Kilometre Array Phase 1 (SKA1). We adopt a systematic approach, varying both: (i) the prescription of assigning LAEs to host haloes; and (ii) the large-scale structure of neutral and ionized regions (i.e. EoR morphology). We find that the LAE-21cm cross-correlation is insensitive to (i), thus making it a robust probe of the EoR. A 1000 h observation with LOFAR would be sufficient to discriminate at ≳ 1σ a fully ionized Universe from one with a mean neutral fraction of bar{x}_{H I}≈ 0.50, using the LAE-21 cm cross-correlation function on scales of R ≈ 3-10 Mpc. Unlike LOFAR, whose detection of the LAE-21 cm cross-correlation is limited by noise, SKA1 is mostly limited by ignorance of the EoR morphology. However, the planned 100 h wide-field SKA1-Low survey will be sufficient to discriminate an ionized Universe from one with bar{x}_{H I}=0.25, even with maximally pessimistic assumptions.
NASA Astrophysics Data System (ADS)
Rak, Rafał; Drożdż, Stanisław; Kwapień, Jarosław; Oświȩcimka, Paweł
2015-11-01
We consider a few quantities that characterize trading on a stock market in a fixed time interval: logarithmic returns, volatility, trading activity (i.e., the number of transactions), and volume traded. We search for the power-law cross-correlations among these quantities aggregated over different time units from 1 min to 10 min. Our study is based on empirical data from the American stock market consisting of tick-by-tick recordings of 31 stocks listed in Dow Jones Industrial Average during the years 2008-2011. Since all the considered quantities except the returns show strong daily patterns related to the variable trading activity in different parts of a day, which are the most evident in the autocorrelation function, we remove these patterns by detrending before we proceed further with our study. We apply the multifractal detrended cross-correlation analysis with sign preserving (MFCCA) and show that the strongest power-law cross-correlations exist between trading activity and volume traded, while the weakest ones exist (or even do not exist) between the returns and the remaining quantities. We also show that the strongest cross-correlations are carried by those parts of the signals that are characterized by large and medium variance. Our observation that the most convincing power-law cross-correlations occur between trading activity and volume traded reveals the existence of strong fractal-like coupling between these quantities.
Bunch Length Measurements With Laser/SR Cross-Correlation
Miller, Timothy; Daranciang, Dan; Lindenberg, Aaron; Corbett, Jeff; Fisher, Alan; Goodfellow, John; Huang, Xiaobiao; Mok, Walter; Safranek, James; Wen, Haidan; /SLAC
2012-07-06
By operating SPEAR3 in low-{alpha} mode the storage ring can generate synchrotron radiation pulses of order 1ps. Applications include pump-probe x-ray science and the production of THz radiation in the CSR regime. Measurements of the bunch length are difficult, however, because the light intensity is low and streak cameras typically provide resolution of only a few ps. Tests are now underway to resolve the short bunch length using cross-correlation between a 60-fs Ti:Sapphire laser and the visible SR beam in a BBO crystal. In this paper we report on the experimental setup, preliminary measurements and prospects for further improvement.
Acoustic cross-correlation flowmeter for solid-gas flow
Sheen, Shuh-Haw; Raptis, Apostolos C.
1986-01-01
Apparatus for measuring particle velocity in a solid-gas flow within a pipe includes: first and second transmitting transducers for transmitting first and second ultrasonic signals into the pipe at first and second locations, respectively, along the pipe; an acoustic decoupler, positioned between said first and second transmitting transducers, for acoustically isolating said first and second signals from one another; first and second detecting transducers for detecting said first and second signals and for generating first and second detected signals in response to said first and second detected signals; and means for cross-correlating said first and second output signals.
Galaxy Velocity Dispersions Using a Cross-Correlation Method: Erratum
NASA Astrophysics Data System (ADS)
Dalle Ore, Cristina; Faber, S. M.; Gonzalez, J. Jesus; Stoughton, Roland; Burstein, David
1991-07-01
In the paper "Galaxy Velocity Dispersions Using a Cross-Correlation Method" by Cristina Dalle Ore, S. M. Faber, J. Jesus Gonzalez, Roland Stoughton, and David Burstein (ApJ, 366,38 [1991]), the following corrections should be made: 1. The full name of the third author is J. Jesus Gonzalez. 2. The last line of equation (3) should read: [(t x t)*v|d], instead of [(t x t) * v|]. 3. Line 7 of the second paragraph on page 40 should read "...matches the observed FWHM of t x g. Equation (3) is more..."
Axion inflation with cross-correlated axion isocurvature perturbations
NASA Astrophysics Data System (ADS)
Kadota, Kenji; Kobayashi, Tatsuo; Otsuka, Hajime
2016-01-01
We study the inflation scenarios, in the framework of superstring theory, where the inflaton is an axion producing the adiabatic curvature perturbations while there exists another light axion producing the isocurvature perturbations. We discuss how the non-trivial couplings among string axions can generically arise, and calculate the consequent cross-correlations between the adiabatic and isocurvature modes through concrete examples. Based on the Planck analysis on the generally correlated isocurvature perturbations, we show that there is a preference for the existence of the correlated isocurvature modes for the axion monodromy inflation while the natural inflation disfavors such isocurvature modes.
Acoustic cross-correlation flowmeter for solid-gas flow
NASA Astrophysics Data System (ADS)
Sheen, S. H.; Raptis, A. C.
1984-05-01
An apparatus for measuring particle velocity in a solid-gas flow within a pipe is described. It includes: first and second transmitting transducers for transmitting first and second ultrasonic signals into the pipe at first and second locations, respectively, along the pipe; an acoustic decoupler, positioned between said first and second transmitting transducers, for acoustically isolating said first and second signals from one another; first and second detecting transducers for detecting said first and second signals and for generating first and second detected signals; and means for cross-correlating said first and second output signals.
Acoustic cross-correlation flowmeter for solid-gas flow
Sheen, S.H.; Raptis, A.C.
1984-05-14
Apparatus for measuring particle velocity in a solid-gas flow within a pipe includes: first and second transmitting transducers for transmitting first and second ultrasonic signals into the pipe at first and second locations, respectively, along the pipe; an acoustic decoupler, positioned between said first and second transmitting transducers, for acoustically isolating said first and second signals from one another; first and second detecting transducers for detecting said first and second signals and for generating first and second detected signals; and means for cross-correlating said first and second output signals.
Deterministic retrieval of complex Green's functions using hard X rays.
Vine, D J; Paganin, D M; Pavlov, K M; Uesugi, K; Takeuchi, A; Suzuki, Y; Yagi, N; Kämpfe, T; Kley, E-B; Förster, E
2009-01-30
A massively parallel deterministic method is described for reconstructing shift-invariant complex Green's functions. As a first experimental implementation, we use a single phase contrast x-ray image to reconstruct the complex Green's function associated with Bragg reflection from a thick perfect crystal. The reconstruction is in excellent agreement with a classic prediction of dynamical diffraction theory. PMID:19257417
NASA Astrophysics Data System (ADS)
Li, Y. H.; Ma, C. S.; Mei, D. C.
We study the effects of cross-correlations between the real and imaginary parts of quantum noise on the intensity fluctuation of a saturation laser model. By virtue of the locked phase method,we derived an approximate Fokker-Planck equation and analytic expressions of the stationary probability distribution function (SPD) of the laser system. Based on the SPD, the mean, the normalized variance, and the normalized skewness of the steady-state laser intensity are calculated numerically. The results indicate that the correlation strength of the cross-correlations between the real and imaginary parts of quantum noise increases the intensity fluctuations.
Cross-correlations between Renminbi and four major currencies in the Renminbi currency basket
NASA Astrophysics Data System (ADS)
Wang, Gang-Jin; Xie, Chi
2013-03-01
We investigate the cross-correlations between Renminbi (CNY) and four major currencies (USD, EUR, JPY, and KRW) in the Renminbi currency basket, i.e., the cross-correlations of CNY-USD, CNY-EUR, CNY-JPY, and CNY-KRW. Qualitatively, using a statistical test in analogy to the Ljung-Box test, we find that cross-correlations significantly exist in CNY-USD, CNY-EUR, CNY-JPY, and CNY-KRW. Quantitatively, employing the detrended cross-correlation analysis (DCCA) method, we find that the cross-correlations of CNY-USD, CNY-EUR, CNY-JPY, and CNY-KRW are weakly persistent. We use the DCCA cross-correlation coefficient ρ to quantify the level of cross-correlations and find the currency weight in the Renminbi currency basket is arranged in the order of USD>EUR>JPY >KRW. Using the method of rolling windows, which can capture the time-varying cross-correlation scaling exponents, we find that: (i) CNY and USD are positively cross-correlated over time, but the cross-correlations of CNY-USD are anti-persistent during the US sub-prime crisis and the European debt crisis. (ii) The cross-correlation scaling exponents of CNY-EUR have the cyclical fluctuation with a nearly two-year cycle. (iii) CNY-JPY has long-term negative cross-correlations, during the European debt crisis, but CNY and KRW are positively cross-correlated.
Hirose, Satoshi; Kimura, Hiroko M.; Jimura, Koji; Kunimatsu, Akira; Abe, Osamu; Ohtomo, Kuni; Miyashita, Yasushi; Konishi, Seiki
2013-01-01
Episodic memory retrieval most often recruits multiple separate processes that are thought to involve different temporal regions. Previous studies suggest dissociable regions in the left lateral parietal cortex that are associated with the retrieval processes. Moreover, studies using resting-state functional connectivity (RSFC) have provided evidence for the temporo-parietal memory networks that may support the retrieval processes. In this functional MRI study, we tested functional significance of the memory networks by examining functional connectivity of brain activity during episodic retrieval in the temporal and parietal regions of the memory networks. Recency judgments, judgments of the temporal order of past events, can be achieved by at least two retrieval processes, relational and item-based. Neuroimaging results revealed several temporal and parietal activations associated with relational/item-based recency judgments. Significant RSFC was observed between one parahippocampal region and one left lateral parietal region associated with relational recency judgments, and between four lateral temporal regions and another left lateral parietal region associated with item-based recency judgments. Functional connectivity during task was found to be significant between the parahippocampal region and the parietal region in the RSFC network associated with relational recency judgments. However, out of the four tempo-parietal RSFC networks associated with item-based recency judgments, only one of them (between the left posterior lateral temporal region and the left lateral parietal region) showed significant functional connectivity during task. These results highlight the contrasting roles of the parahippocampal and the lateral temporal regions in recency judgments, and suggest that only a part of the tempo-parietal RSFC networks are recruited to support particular retrieval processes. PMID:24009657
Structure of a financial cross-correlation matrix under attack
NASA Astrophysics Data System (ADS)
Lim, Gyuchang; Kim, SooYong; Kim, Junghwan; Kim, Pyungsoo; Kang, Yoonjong; Park, Sanghoon; Park, Inho; Park, Sang-Bum; Kim, Kyungsik
2009-09-01
We investigate the structure of a perturbed stock market in terms of correlation matrices. For the purpose of perturbing a stock market, two distinct methods are used, namely local and global perturbation. The former involves replacing a correlation coefficient of the cross-correlation matrix with one calculated from two Gaussian-distributed time series while the latter reconstructs the cross-correlation matrix just after replacing the original return series with Gaussian-distributed time series. Concerning the local case, it is a technical study only and there is no attempt to model reality. The term ‘global’ means the overall effect of the replacement on other untouched returns. Through statistical analyses such as random matrix theory (RMT), network theory, and the correlation coefficient distributions, we show that the global structure of a stock market is vulnerable to perturbation. However, apart from in the analysis of inverse participation ratios (IPRs), the vulnerability becomes dull under a small-scale perturbation. This means that these analysis tools are inappropriate for monitoring the whole stock market due to the low sensitivity of a stock market to a small-scale perturbation. In contrast, when going down to the structure of business sectors, we confirm that correlation-based business sectors are regrouped in terms of IPRs. This result gives a clue about monitoring the effect of hidden intentions, which are revealed via portfolios taken mostly by large investors.
In Vivo Fluorescence Correlation and Cross-Correlation Spectroscopy
NASA Astrophysics Data System (ADS)
Mütze, Jörg; Ohrt, Thomas; Petrášek, Zdeněk; Schwille, Petra
In this manuscript, we describe the application of Fluorescence Correlation Spectroscopy (FCS), Fluorescence Cross-Correlation Spectroscopy (FCCS), and scanning FCS (sFCS) to two in vivo systems. In the first part, we describe the application of two-photon standard and scanning FCS in Caenorhabditis elegans embryos. The differentiation of a single fertilized egg into a complex organism in C. elegans is regulated by a number of protein-dependent processes. The oocyte divides asymmetrically into two daughter cells of different developmental fate. Two of the involved proteins, PAR-2 and NMY-2, are studied. The second investigated system is the mechanism of RNA interference in human cells. An EGFP based cell line that allows to study the dynamics and localization of the RNA-induced silencing complex (RISC) with FCS in vivo is created, which has so far been inaccessible with other experimental methods. Furthermore, Fluorescence Cross-Correlation Spectroscopy is employed to highlight the asymmetric incorporation of labeled siRNAs into RISC.
Phases of scaling and cross-correlation behavior in traffic
NASA Astrophysics Data System (ADS)
Kantelhardt, Jan W.; Fullerton, Matthew; Kämpf, Mirko; Beltran-Ruiz, Cristina; Busch, Fritz
2013-11-01
While many microscopic models of traffic flow describe transitions between different traffic phases, such transitions are difficult to quantify in measured traffic data. Here we study long-term traffic recordings consisting of ≈2900 days of flow, density, and velocity time series with minute resolution from a Spanish motorway. We calculate fluctuations, cross-correlations, and long-term persistence properties of these quantities in the flow-density diagram. This leads to a data-driven definition of (local) traffic states based on the dynamical properties of the data, which differ from those given in standard guidelines. We find that detrending techniques must be used for persistence analysis because of non-stationary daily and weekly traffic flow patterns. We compare our results for the measured data with analysis results for a microscopic traffic model, finding good agreement in most quantities. However, the simulations cannot easily reproduce the congested traffic states observed in the data. We show how fluctuations and cross-correlations in traffic data may be used for prediction, i.e., as indications of increasing or decreasing velocities.
Random matrix theory analysis of cross correlations in financial markets
NASA Astrophysics Data System (ADS)
Utsugi, Akihiko; Ino, Kazusumi; Oshikawa, Masaki
2004-08-01
We confirm universal behaviors such as eigenvalue distribution and spacings predicted by random matrix theory (RMT) for the cross correlation matrix of the daily stock prices of Tokyo Stock Exchange from 1993 to 2001, which have been reported for New York Stock Exchange in previous studies. It is shown that the random part of the eigenvalue distribution of the cross correlation matrix is stable even when deterministic correlations are present. Some deviations in the small eigenvalue statistics outside the bounds of the universality class of RMT are not completely explained with the deterministic correlations as proposed in previous studies. We study the effect of randomness on deterministic correlations and find that randomness causes a repulsion between deterministic eigenvalues and the random eigenvalues. This is interpreted as a reminiscent of “level repulsion” in RMT and explains some deviations from the previous studies observed in the market data. We also study correlated groups of issues in these markets and propose a refined method to identify correlated groups based on RMT. Some characteristic differences between properties of Tokyo Stock Exchange and New York Stock Exchange are found.
Functional anatomy of temporal organisation and domain-specificity of episodic memory retrieval
Kwok, Sze Chai; Shallice, Tim; Macaluso, Emiliano
2013-01-01
Episodic memory provides information about the “when” of events as well as “what” and “where” they happened. Using functional imaging, we investigated the domain specificity of retrieval-related processes following encoding of complex, naturalistic events. Subjects watched a 42-min TV episode, and 24 h later, made discriminative choices of scenes from the clip during fMRI. Subjects were presented with two scenes and required to either choose the scene that happened earlier in the film (Temporal), or the scene with a correct spatial arrangement (Spatial), or the scene that had been shown (Object). We identified a retrieval network comprising the precuneus, lateral and dorsal parietal cortex, middle frontal and medial temporal areas. The precuneus and angular gyrus are associated with temporal retrieval, with precuneal activity correlating negatively with temporal distance between two happenings at encoding. A dorsal fronto-parietal network engages during spatial retrieval, while antero-medial temporal regions activate during object-related retrieval. We propose that access to episodic memory traces involves different processes depending on task requirements. These include memory-searching within an organised knowledge structure in the precuneus (Temporal task), online maintenance of spatial information in dorsal fronto-parietal cortices (Spatial task) and combining scene-related spatial and non-spatial information in the hippocampus (Object task). Our findings support the proposal of process-specific dissociations of retrieval. PMID:22877840
Cross-correlations between Baltic Dry Index and crude oil prices
NASA Astrophysics Data System (ADS)
Ruan, Qingsong; Wang, Yao; Lu, Xinsheng; Qin, Jing
2016-07-01
This paper examines the cross-correlation properties of Baltic Dry Index (BDI) and crude oil prices using cross-correlation statistics test and multifractal detrended cross-correlation analysis (MF-DCCA). The empirical results show that the cross-correlations between BDI and crude oil prices are significantly multifractal. By introducing the concept of a "crossover", we find that the cross-correlations are strongly persistent in the short term and weakly anti-persistent in the long term. Moreover, cross-correlations of all kinds of fluctuations are persistent in the short time while cross-correlations of small fluctuations are persistent and those of large fluctuations are anti-persistent in the long term. We have also verified that the multifractality of the cross-correlations of BDI and crude oil prices is both attributable to the persistence of fluctuations of time series and fat-tailed distributions.
Multifractal detrended cross-correlation analysis between PM2.5 and meteorological factors
NASA Astrophysics Data System (ADS)
Zhang, Chen; Ni, Zhiwei; Ni, Liping
2015-11-01
PM2.5 pollution has become one of the most serious air pollution in China. The cross-correlations between PM2.5 concentration and meteorological factors (i.e., temperature, air pressure, relative humidity and wind speed) in Beijing and Hong Kong are discussed in this paper. We use the multifractal detrended cross-correlation analysis (MF-DCCA) to analyze the cross-correlations, and study further the asymmetric characteristics of cross-correlations by multifractal asymmetric detrended cross-correlation analysis (MF-ADCCA). The experimental results show that the cross-correlations between PM2.5 concentration and four meteorological factors are multifractal and anti-persistent, and the strength of multifractality of Beijing is stronger than that of Hong Kong. Meanwhile, the cross-correlations between PM2.5 concentration and meteorological factors are asymmetric, and the asymmetric cross-correlations are multifractal.
Méndez-Couz, M; Conejo, N M; González-Pardo, H; Arias, J L
2015-04-24
The standard model of memory system consolidation supports the temporal reorganization of brain circuits underlying long-term memory storage, including interactions between the dorsal hippocampus and extra-hippocampal structures. In addition, several brain regions have been suggested to be involved in the retrieval of spatial memory. In particular, several authors reported a possible role of the ventral portion of the hippocampus together with the thalamus or the striatum in the persistence of this type of memory. Accordingly, the present study aimed to evaluate the contribution of different cortical and subcortical brain regions, and neural networks involved in spatial memory retrieval. For this purpose, we used cytochrome c oxidase quantitative histochemistry as a reliable method to measure brain oxidative metabolism. Animals were trained in a hidden platform task and tested for memory retention immediately after the last training session; one week after completing the task, they were also tested in a memory retrieval probe. Results showed that retrieval of the previously learned task was associated with increased levels of oxidative metabolism in the prefrontal cortex, the dorsal and ventral striatum, the anterodorsal thalamic nucleus and the dentate gyrus of the dorsal and ventral hippocampus. The analysis of functional interactions between brain regions suggest that the dorsal and ventral dentate gyrus could be involved in spatial memory retrieval. In addition, the results highlight the key role of the extended hippocampal system, thalamus and striatum in this process. Our study agrees with previous ones reporting interactions between the dorsal hippocampus and the prefrontal cortex during spatial memory retrieval. Furthermore, novel activation patterns of brain networks involving the aforementioned regions were found. These functional brain networks could underlie spatial memory retrieval evaluated in the Morris water maze task. PMID:25680583
Probing the circumgalactic baryons through cross-correlations
NASA Astrophysics Data System (ADS)
Singh, Priyanka; Majumdar, Subhabrata; Nath, Biman B.; Refregier, Alexandre; Silk, Joseph
2016-02-01
We study the cross-correlation of distribution of galaxies, the Sunyaev-Zel'dovich (SZ) and X-ray power spectra of galaxies from current and upcoming surveys and show these to be excellent probes of the nature, i.e. extent, evolution and energetics, of the circumgalactic medium (CGM). The SZ-galaxy cross-power spectrum, especially at large multipoles, depends on the steepness of the pressure profile of the CGM. This property of the SZ signal can, thus, be used to constrain the pressure profile of the CGM. The X-ray cross-power spectrum also has a similar shape. However, it is much more sensitive to the underlying density profile. We forecast the detectability of the cross-correlated galaxy distribution, SZ and X-ray signals by combining South Pole Telescope-Dark Energy Survey (SPT-DES) and eROSITA-DES/eROSITA-LSST (extended ROentgen Survey with an Imaging Telescope Array-Large Synoptic Survey Telescope) surveys, respectively. We find that, for the SPT-DES survey, the signal-to-noise ratio peaks at high mass and redshift with signal-to-noise ratio ˜9 around Mh ˜ 1013 h-1 M⊙ and z ˜ 1.5-2 for flat density and temperature profiles. The signal-to-noise ratio peaks at ˜6(12) for the eROSITA-DES (eROSITA-LSST) surveys. We also perform a Fisher matrix analysis to find the constraint on the gas fraction in the CGM in the presence or absence of an unknown redshift evolution of the gas fraction. Finally, we demonstrate that the cross-correlated SZ-galaxy and X-ray-galaxy power spectrum can be used as powerful probes of the CGM energetics and potentially discriminate between different feedback models recently proposed in the literature; for example, one can distinguish a `no active galactic nuclei feedback' scenario from a CGM energized by `fixed-velocity hot winds' at greater than 3σ.
Retrieving time-dependent Green's functions in optics with low-coherence interferometry.
Badon, Amaury; Lerosey, Geoffroy; Boccara, Albert C; Fink, Mathias; Aubry, Alexandre
2015-01-16
We report on the passive measurement of time-dependent Green's functions in the optical frequency domain with low-coherence interferometry. Inspired by previous studies in acoustics and seismology, we show how the correlations of a broadband and incoherent wave field can directly yield the Green's functions between scatterers of a complex medium. Both the ballistic and multiple scattering components of the Green's function are retrieved. This approach opens important perspectives for optical imaging and characterization in complex scattering media. PMID:25635547
NASA Astrophysics Data System (ADS)
Quaegebeur, Nicolas; Padois, Thomas; Gauthier, Philippe-Aubert; Masson, Patrice
2016-06-01
In this paper, an alternative formulation of the time-domain beamforming is proposed using the generalized cross-correlation of measured signals. This formulation uses spatial weighting functions adapted to microphone positions and imaging points. The proposed approach is demonstrated for acoustic source localization using a microphone array, both theoretically and experimentally. An increase in accuracy of acoustic imaging results is shown for both narrow and broadband sources, while a factor of reduction up to 20 in the computation time can be achieved, allowing real-time or volumetric source localization over very large grids.
Near Noise Field of a Jet-engine Exhaust II : Cross Correlation of Sound Pressures
NASA Technical Reports Server (NTRS)
Callaghan, Edmund E; Howes, Walton L; Coles, Willard D
1956-01-01
Pressure cross correlations were obtained over a range of jet velocities both longitudinally and laterally for the overall sound pressure and for several frequency bands. The region of positive correlation was found to increase with distance downstream of the nozzle exit and was greater for lateral than for longitudinal correlations. In general, little change in the correlation curves was found as a function of jet velocity or frequency band width. Measurements made with a fixed and a movable microphone in a plate showed correlations similar to the free-field results. The results are interpreted in terms of pressure loads on surfaces.
Cross correlation method application to prompt fission neutron investigation
NASA Astrophysics Data System (ADS)
Zeynalova, O. V.; Zeynalov, Sh.; Nazarenko, M. A.; Hambsch, F.-J.; Oberstedt, S.
2012-10-01
Do The prompt neutron emission in spontaneous fission of 252Cf has been investigated applying cross correlation method and digital signal processing algorithms. A new mathematical approach for neutron/gamma pulse shape separation was developed and implemented for prompt fission neutron (PFN) time-of-flight measurement. The main goal was development of automated data analysis algorithms and procedures for data analysis with minimum human intervention. Experimental data was taken with a twin Frisch-grid ionization chamber and a NE213-equivalent neutron detector in an experimental setup similar to well work of C. Budtz-Jorgensen and H.-H. Knitter [1]. About 2*107 fission events were registered with 2*105 neutron/gamma detection in coincidence with fission fragments. Fission fragment kinetic energy, mass and angular distribution, neutron time-of-flight and pulse shape have been investigated using a 12 bit waveform digitizer.
Complex cross correlators with three-level quantization Design tolerances
NASA Astrophysics Data System (ADS)
D'Addario, L. R.; Thompson, A. R.; Schwab, F. R.; Granlund, J.
1984-06-01
It is noted that for cases in which the components behave ideally, digital correlators have been analyzed in considerable detail. Consideration is given here to the effects of the major deviations from ideal behavior that are encountered in practice. Even though attention is restricted to the three-level quantization, the fairly general case of the complex cross correlator is investigated. Among the errors analyzed are quantization threshold errors, quantizer indecision regions, sampler timing skews, quadrature network errors, and numerical errors in algorithms for converting digital measurements to equivalent analog correlations. It is assumed that all the digital operations, including delay, multiplication, summing, and storage, can be implemented without errors. The study is prompted by the requirement for cross-power measurements in Fourier synthesis radio telescopes.
Investigation Of The Diffuse IGM By Cross-Correlation Studies
Farnsworth, Damon; Brown, Shea; Rudnick, Lawrence
2009-12-18
We present results from the first cross-correlation search for the synchrotron component of the diffuse intergalactic medium (IGM) in filamentary large scale structure (LSS). We used the low resolution (36') Bonn survey at 21cm, with the infrared 2MASS catalog as a tracer of the LSS. Synchrotron emission likely results from LSS formation shocks and feedback from AGN and galactic winds [2]. We determined 3{sigma} upper limits to the diffuse emission in units of flux per galaxy; these correspond to filament equipartition magnetic fields as low as 0.2 {mu}G. The detection threshold for the average (peak) filament brightness is 1 (7) mK for 0.03
Cross-correlation analysis for live-cell image trajectory
NASA Astrophysics Data System (ADS)
Cheng, Chih-Ming; Chang, Yu-Fen; Wu, Chien-ming
2013-08-01
In cell motility, researchers are usually used fluorescence microscopy, confocal microscopy, or total internal reflection microscopy to track a fluorescent labeled particle and reveal the dynamic trajectory in living. Because all fluorescent dyes have cell toxicity, quantum dots and gold nanoparticles can influence the structures and physical properties of biomolecules which they have labeled, to develop another label-free image approach becomes an important issue. We present here a Fourier-based cross-correlation process to analyze images of adhering living cell, including cell motility and single vesicle trajectory. We treated adhering MG-63 cell with 66 nM Epidermal growth factor (EGF) and observed its dynamic effect on cell motility based on the velocity fields of consecutive cell images. We also used crosscorrelation to track single vesicles in living cells. We found that EGF could rapidly activate the motility of adhering MG- 63 cell, and the vesicle exhibits either directed or diffusive motion.
Cross-correlation analysis of CMB with foregrounds for residuals
NASA Astrophysics Data System (ADS)
Aluri, Pavan K.; Rath, Pranati K.
2016-06-01
In this paper, we try to probe whether a clean cosmic microwave background (CMB) map obtained from the raw satellite data using a cleaning procedure is sufficiently clean. Specifically, we study if there are any foreground residuals still present in the cleaned data using a cross-correlation statistic. Residual contamination is expected to be present, primarily, in the Galactic plane due to the high emission from our own Galaxy. A foreground mask is applied conventionally to avoid biases in the estimated quantities of interest due to foreground leakage. Here, we map foreground residuals, if present, in the unmasked region i.e. outside a CMB analysis mask. Further locally extended foreground-contaminated regions, found eventually, are studied to understand them better. The few contaminated regions thus identified may be used to slightly extend the available masks to make them more stringent.
Cross-correlating Sunyaev-Zel'dovich and weak lensing maps
NASA Astrophysics Data System (ADS)
Munshi, Dipak; Joudaki, Shahab; Coles, Peter; Smidt, Joseph; Kay, Scott T.
2014-07-01
We present novel statistical tools to cross-correlate frequency cleaned thermal Sunyaev-Zel'dovich (tSZ) maps and tomographic weak lensing (wl) convergence maps. Moving beyond the lowest order cross-correlation, we introduce a hierarchy of mixed higher order statistics, the cumulants and cumulant correlators, to analyse non-Gaussianity in real space, as well as corresponding polyspectra in the harmonic domain. Using these moments, we derive analytical expressions for the joint two-point probability distribution function for smoothed tSZ (y) and convergence (κ) maps. The presence of tomographic information allows us to study the evolution of higher order mixed tSZ-wl statistics with redshift. We express the joint PDFs pκy(κ, y) in terms of individual one-point PDFs [pκ(κ), py(y)] and the relevant bias functions [bκ(κ), by(y)]. Analytical results for two different regimes are presented that correspond to the small and large angular smoothing scales. Results are also obtained for corresponding hotspots in the tSZ and convergence maps. In addition to results based on hierarchical techniques and perturbative methods, we present results of calculations based on the lognormal approximation. The analytical expressions derived here are generic and applicable to cross-correlation studies of arbitrary tracers of large-scale structure including, e.g., that of tSZ and soft X-ray background. We provide detailed comparison of our analytical results against state of the art Millennium Gas Simulations with and without non-gravitational effects such as pre-heating and cooling. Comparison of these results with gravity only simulations, shows reasonable agreement and can be used to isolate effect of non-gravitational physics from observational data.
Cross-correlations between three units in cat primary auditory cortex.
Eggermont, Jos J; Munguia, Raymundo; Shaw, Gregory
2013-10-01
Here we use a modification of the Joint-Peri-Stimulus-Time histogram (JPSTH) to investigate triple correlations between cat auditory cortex neurons. The modified procedure allowed the decomposition of the xy-pair correlation into a part that is due to the correlation of the x and y units with the trigger unit, and a remaining 'pair correlation'. We analyzed 16 sets of 15-minute duration stationary spontaneous recordings in primary auditory cortex (AI) with between 11 and 14 electrodes from 2 arrays of 8 electrodes each that provided spontaneous firing rates above 0.22 sp/s and for which reliable frequency-tuning curves could be obtained and the characteristic frequency (CF) was estimated. Thus we evaluated 11,282 conditional cross-correlation functions. The predictor for the conditional cross-correlation, calculated on the assumption that the trigger unit had no effect on the xy-pair correlation but using the same fraction of xy spikes, was equal to the conventional pair-wise correlation function between units xy. The conditional correlation of the xy-pair due to correlation of the x and/or y unit with the trigger unit decreased with the geometric mean distance of the xy pair to the trigger unit, but was independent of the pair cross-correlation coefficient. The conditional pair correlation coefficient was estimated at 78% of the measured pair correlation coefficient. Assuming a geometric decreasing effect of activities of units on other electrodes on the conditional correlation, we estimated the potential contribution of a large number of contributing units on the measured pair correlation at 35-50 of that correlation. This suggests that conventionally measured pair correlations in auditory cortex under ketamine anesthesia overestimate the 'true pair correlation', likely resulting from massive common input, by potentially up to a factor 2. PMID:23933479
Effect of Cross-Correlation on Geomagnetic Forecast Accuracies
NASA Technical Reports Server (NTRS)
Kuang, Weijia; Wei, Zigang; Tangborn, Andrew
2011-01-01
Surface geomagnetic observation can determine up to degree L = 14 time-varying spherical harmonic coefficients of the poloidal magnetic field. Assimilation of these coefficients to numerical dynamo simulation could help us understand better the dynamical processes in the Earth's outer core, and to provide more accurate forecast of geomagnetic secular variations (SV). In our previous assimilation studies, only the poloidal magnetic field in the core is corrected by the observations in the analysis. Unobservable core state variables (the toroidal magnetic field and the core velocity field) are corrected via the dynamical equations of the geodynamo. Our assimilation experiments show that the assimilated core state converges near the CMB, implying that the dynamo state is strongly constrained by surface geomagnetic observations, and is pulled closer to the truth by the data. We are now carrying out an ensemble of assimilation runs with 1000 years of geomagnetic and archeo/paleo magnetic record. In these runs the cross correlation between the toroidal and the poloidal magnetic fields is incorporated into the analysis. This correlation is derived from the physical boundary conditions of the toroidal field at the core-mantle boundary (CMB). The assimilation results are then compared with those of the ensemble runs without the cross-correlation, aiming at understanding two fundamental issues: the effect of the crosscorrelation on (1) the convergence of the core state, and (2) the SV prediction accuracies. The constrained dynamo solutions will provide valuable insights on interpreting the observed SV, e.g. the near-equator magnetic flux patches, the core-mantle interactions, and possibly other geodynamic observables.
Cross-correlation Doppler global velocimetry (CC-DGV)
NASA Astrophysics Data System (ADS)
Cadel, Daniel R.; Lowe, K. Todd
2015-08-01
A flow velocimetry method, cross-correlation Doppler global velocimetry (CC-DGV), is presented as a robust, simplified, and high dynamic range implementation of the Doppler global/planar Doppler velocimetry technique. A sweep of several gigahertz of the vapor absorption spectrum is used for each velocity sample, with signals acquired from both Doppler-shifted scattered light within the flow and a non-Doppler shifted reference beam. Cross-correlation of these signals yields the Doppler shift between them, averaged over the duration of the scan. With presently available equipment, velocities from 0 ms-1 to over 3000 ms-1 can notionally be measured simultaneously, making the technique ideal for high speed flows. The processing routine is shown to be robust against large changes in the vapor pressure of the iodine cell, benefiting performance of the system in facilities where ambient conditions cannot be easily regulated. Validation of the system was performed with measurements of a model wind turbine blade boundary layer made in a 1.83 m by 1.83 m subsonic wind tunnel for which laser Doppler velocimetry (LDV) measurements were acquired alongside the CC-DGV results. CC-DGV uncertainties of ±1.30 ms-1, ±0.64 ms-1, and ±1.11 ms-1 were determined for the orthogonal stream-wise, transverse-horizontal, and transverse-vertical velocity components, and root-mean-square deviations of 2.77 ms-1 and 1.34 ms-1 from the LDV validation results were observed for Reynolds numbers of 1.5 million and 2 million, respectively. Volumetric mean velocity measurements are also presented for a supersonic jet, with velocity uncertainties of ±4.48 ms-1, ±16.93 ms-1, and ±0.50 ms-1 for the orthogonal components, and self-validation done by collapsing the data with a physical scaling.
NASA Astrophysics Data System (ADS)
Cao, Guangxi; Cao, Jie; Xu, Longbing; He, LingYun
2014-01-01
We propose a new method called the multifractal asymmetric detrended cross-correlation analysis method (MF-ADCCA) to investigate the asymmetric cross-correlations in nonstationary time series that combine the multifractal detrended cross-correlation analysis (MF-DCCA) and asymmetric detrended fluctuation analysis (A-DFA). The study aims to determine whether different scaling properties of the cross-correlations are obtained if a one-time series trending is either positive or negative. We apply MF-ADCCA to analyze empirically the scaling behavior of the cross-correlations among the Chinese stock market, the RMB exchange market, and the US stock market. Empirical results indicate that the cross-correlations between the Chinese stock market and the RMB/USD exchange market are more persistent when any one of the markets is falling. On the contrary, the cross-correlations between the Chinese stock market and the RMB/EU, RMB/GBP, RMB/JPY exchange markets and the US stock market are more persistent when one of the markets is rising. Moreover, asymmetric cross-correlations between any two of the selected financial markets are multifractal.
NASA Astrophysics Data System (ADS)
Dalen, Karel N.; Mikesell, T. Dylan; Ruigrok, Elmer N.; Wapenaar, Kees
2015-02-01
Retrieving virtual source surface waves from ambient seismic noise by cross correlation assumes, among others, that the noise field is equipartitioned and the medium is lossless. Violation of these assumptions reduces the accuracy of the retrieved waves. A point-spread function computed from the same ambient noise quantifies the associated virtual source's spatial and temporal smearing. Multidimensional deconvolution (MDD) of the retrieved surface waves by this function has been shown to improve the virtual source's focusing and the accuracy of the retrieved waves using synthetic data. We tested MDD on data recorded during the Batholiths experiment, a passive deployment of broadband seismic sensors in British Columbia, Canada. The array consisted of two approximately linear station lines. Using 4 months of recordings, we retrieved fundamental-mode Rayleigh waves (0.05-0.27 Hz). We only used noise time windows dominated by waves that traverse the northern line before reaching the southern (2.5% of all data). Compared to the conventional cross-correlation result based on this subset, the MDD waveforms are better localized and have significantly higher signal-to-noise ratio. Furthermore, MDD corrects the phase, and the spatial deconvolution fills in a spectral (f, k domain) gap between the single-frequency and double-frequency microseism bands. Frequency whitening of the noise also fills the gap in the cross-correlation result, but the signal-to-noise ratio of the MDD result remains higher. Comparison of the extracted phase velocities shows some differences between the methods, also when all data are included in the conventional cross correlation.
Towards a global-scale ambient noise cross-correlation data base
NASA Astrophysics Data System (ADS)
Ermert, Laura; Fichtner, Andreas; Sleeman, Reinoud
2014-05-01
We aim to obtain a global-scale data base of ambient seismic noise correlations. This database - to be made publicly available at ORFEUS - will enable us to study the distribution of microseismic and hum sources, and to perform multi-scale full waveform inversion for crustal and mantle structure. Ambient noise tomography has developed into a standard technique. According to theory, cross-correlations equal inter-station Green's functions only if the wave field is equipartitioned or the sources are isotropically distributed. In an attempt to circumvent these assumptions, we aim to investigate possibilities to directly model noise cross-correlations and invert for their sources using adjoint techniques. A data base containing correlations of 'gently' preprocessed noise, excluding preprocessing steps which are explicitly taken to reduce the influence of a non-isotropic source distribution like spectral whitening, is a key ingredient in this undertaking. Raw data are acquired from IRIS/FDSN and ORFEUS. We preprocess and correlate the time series using a tool based on the Python package Obspy which is run in parallel on a cluster of the Swiss National Supercomputing Centre. Correlation is done in two ways: Besides the classical cross-correlation function, the phase cross-correlation is calculated, which is an amplitude-independent measure of waveform similarity and therefore insensitive to high-energy events. Besides linear stacks of these correlations, instantaneous phase stacks are calculated which can be applied as optional weight, enhancing coherent portions of the traces and facilitating the emergence of a meaningful signal. The _STS1 virtual network by IRIS contains about 250 globally distributed stations, several of which have been operating for more than 20 years. It is the first data collection we will use for correlations in the hum frequency range, as the STS-1 instrument response is flat in the largest part of the period range where hum is observed, up to a
NASA Astrophysics Data System (ADS)
Pal, Mayukha; Madhusudana Rao, P.; Manimaran, P.
2014-12-01
We apply the recently developed multifractal detrended cross-correlation analysis method to investigate the cross-correlation behavior and fractal nature between two non-stationary time series. We analyze the daily return price of gold, West Texas Intermediate and Brent crude oil, foreign exchange rate data, over a period of 18 years. The cross correlation has been measured from the Hurst scaling exponents and the singularity spectrum quantitatively. From the results, the existence of multifractal cross-correlation between all of these time series is found. We also found that the cross correlation between gold and oil prices possess uncorrelated behavior and the remaining bivariate time series possess persistent behavior. It was observed for five bivariate series that the cross-correlation exponents are less than the calculated average generalized Hurst exponents (GHE) for q<0 and greater than GHE when q>0 and for one bivariate series the cross-correlation exponent is greater than GHE for all q values.
Cross-correlation of the extragalactic gamma-ray background with luminous red galaxies
NASA Astrophysics Data System (ADS)
Shirasaki, Masato; Horiuchi, Shunsaku; Yoshida, Naoki
2015-12-01
Measurements of the cross-correlation between the extragalactic gamma-ray background (EGB) and large-scale structure provide a novel probe of dark matter on extragalactic scales. We focus on luminous red galaxies (LRGs) as optimal targets to search for the signal of dark matter annihilation. We measure the cross-correlation function of the EGB taken from the Fermi Large Area Telescope with the LRGs from the Sloan Digital Sky Survey. Statistical errors are calculated using a large set of realistic mock LRG catalogs. The amplitude of the measured cross-correlation is consistent with null detection. Based on an accurate theoretical model of the distribution of dark matter associated with LRGs, we exclude dark matter annihilation cross-sections over ⟨σ v ⟩=3 ×10-25- 1 0-26 cm3 s-1 for a 10 GeV dark matter. We further investigate systematic effects due to uncertainties in the Galactic gamma-ray foreground emission, which we find to be an order of magnitude smaller than the current statistical uncertainty. We also estimate the contamination from astrophysical sources in the LRGs by using known scaling relations between gamma-ray luminosity and star-formation rate, finding them to be negligibly small. Based on these results, we suggest that LRGs remain ideal targets for probing dark matter annihilation with future EGB measurement and galaxy surveys. Increasing the number of LRGs in upcoming galaxy surveys such as LSST would lead to big improvements of factors of several in sensitivity.
Measuring distance ratios with CMB-galaxy lensing cross-correlations
Das, Sudeep; Spergel, David N.
2009-02-15
We propose a method for cosmographic measurements by combining gravitational lensing of the cosmic microwave background (CMB) with cosmic shear surveys. We cross-correlate the galaxy counts in the lens plane with two different source planes: the CMB at z{approx}1100 and galaxies at an intermediate redshift. The ratio of the galaxy count/CMB lensing cross-correlation to the galaxy count/galaxy lensing cross-correlation is shown to be a purely geometric quantity, depending only on the distribution function of the source galaxies. By combining Planck, the Advanced Dark Energy Physics Telescope, and the Large Synoptic Survey Telescope, the ratio can be measured to {approx}4% accuracy, whereas a future polarization-based experiment like CMBPOL can make a more precise ({approx}1%) measurement. For cosmological models where the curvature and the equation of state parameter are allowed to vary, the direction of degeneracy defined by the measurement of this ratio is different from that traced out by baryon acoustic oscillation measurements. Combining this method with the stacked cluster mass reconstruction cosmography technique as proposed by Hu, Holz, and Vale (2007), the uncertainty in the ratio can be further reduced, improving the constraints on cosmological parameters. We also study the implications of the lensing-ratio measurement for early dark energy models, in the context of the parametrization proposed by Doran and Robbers (2006). For models which are degenerate with respect to the CMB, we find both baryon acoustic oscillation and lensing-ratio measurements to be insensitive to the early component of the dark energy density.
NASA Astrophysics Data System (ADS)
Liu, Xin; Ben-Zion, Yehuda; Zigone, Dimitri
2015-11-01
We develop and apply an algorithm for deriving interstation seismic attenuation from cross-correlations of ambient noise recorded by linear arrays. Theoretical results on amplitude decay due to attenuation are used to form a linear least-square inversion for interstation QR values of Rayleigh surface waves propagating along linear arrays having three or more stations. The noise wave field is assumed stationary within each day and the interstation distances should be greater than the employed wavelength. The inversion uses differences of logarithmic amplitude decay curves measured at different stations from cross-correlation functions within a given frequency band. The background attenuation between noise sources and receivers is effectively cancelled with this method. The site amplification factors are assumed constant (or following similar patterns) in the frequency band of interest. The inversion scheme is validated with synthetic tests using ambient noise generated by ray-theory-based calculations with heterogeneous attenuation and homogenous velocity structure. The interstation attenuation and phase velocity dispersion curves are inverted from cross-correlations of the synthetic data. The method is then applied to triplets of stations from the regional southern California seismic network crossing the Mojave section of the San Andreas fault, and a dense linear array crossing the southern San Jacinto Fault zone. Bootstrap technique is used to derive empirical mean and confidence interval for the obtained inverse Q values. The results for the regional stations yield QR values around 25 for a frequency band 0.2-0.36 Hz. The results for the San Jacinto fault zone array give QR values of about 6-30 for frequencies in the range 15-25 Hz.
NASA Astrophysics Data System (ADS)
Katahira, Kentaro; Kawamura, Masaki; Okanoya, Kazuo; Okada, Masato
2007-04-01
We investigate a recurrent neural network model with common external and bias inputs that can retrieve branching sequences. Retrieval of memory sequences is one of the most important functions of the brain. A lot of research has been done on neural networks that process memory sequences. Most of it has focused on fixed memory sequences. However, many animals can remember and recall branching sequences. Therefore, we propose an associative memory model that can retrieve branching sequences. Our model has bias input and common external input. Kawamura and Okada reported that common external input enables sequential memory retrieval in an associative memory model with auto- and weak cross-correlation connections. We show that retrieval processes along branching sequences are controllable with both the bias input and the common external input. To analyze the behaviors of our model, we derived the macroscopic dynamical description as a probability density function. The results obtained by our theory agree with those obtained by computer simulations.
NASA Astrophysics Data System (ADS)
Schaff, David P.; Richards, Paul G.
2014-04-01
Standard processing of seismic events for reporting in bulletins is usually done one-at-a time. State-of-the-art relative event methods, often involving cross correlation, are increasingly used and have improved estimates of event parameters for event detection, location and magnitude. This is because relative event techniques can simultaneously reduce measurement error and effects of model error. We show how cross correlation can be used to assign relative magnitudes for neighbouring seismic events distributed over a large region in east Asia and quantify to what extent the uncertainty in these values increases as waveform similarity breaks down. We find that cross correlation works well for magnitude comparison of two events when it is expected that they generate very similar signals even if these may be almost buried in large amounts of noise. This may be the case when investigating repeating earthquakes or nuclear explosions within a few kilometres of each other. Cross correlation is the optimal detector in these cases assuming noise is white and Gaussian, and also provides the least-squares solution for the relative amplitudes. However, when the waveform similarity of the underlying signals breaks down, due to interevent separation distance, source time function differences or focal mechanism differences, these assumptions are no longer valid and a bias is introduced into the relative magnitude measurement. This bias due to degradation of waveform similarity is modelled here with synthetics and an analytic expression for it is derived based on three terms-the cross-correlation coefficient (CC), and the signal-to-noise ratio (SNR) of the larger and smaller events. The analytic expression is a good match to the observed bias in the data. If the equation for relative magnitude is rewritten to correct for the bias due to the CC, a new equation results which is simply the log of the ratio of the L2 norms. The bias due to SNRs is still present because the observed
Flap noise characteristics measured by pressure cross correlation techniques
NASA Astrophysics Data System (ADS)
Miller, W. R.
1980-03-01
The aerodynamic sound generated by a realistic aircraft flap system was investigated through the use of cross correlations between surface pressure fluctuations and far field sound. Measurements were conducted in two subsonic wind tunnel studies to determine the strength, distribution, and directivity of the major sources of flap noise at speeds up to 79.0 m/sec. A pilot study was performed on a single flap model to test the measurement technique and provide initial data on the characteristics of flap noise. The major portion of this investigation studied the sound radiated by a realistic large scale model of a triple slotted flap system mounted on a sweptback 6.7 meter semispan model wing. The results of this investigation have identified the major sources of flap generated noise and their dependence of flow defining parameters. In addition, a possible avenue toward the reduction of flap generated noise has been identified via the placement of the flap actuator fairings on the flap system.
Accelerating radio astronomy cross-correlation with graphics processing units
NASA Astrophysics Data System (ADS)
Clark, M. A.; LaPlante, P. C.; Greenhill, L. J.
2013-05-01
We present a highly parallel implementation of the cross-correlation of time-series data using graphics processing units (GPUs), which is scalable to hundreds of independent inputs and suitable for the processing of signals from 'large-Formula' arrays of many radio antennas. The computational part of the algorithm, the X-engine, is implemented efficiently on NVIDIA's Fermi architecture, sustaining up to 79% of the peak single-precision floating-point throughput. We compare performance obtained for hardware- and software-managed caches, observing significantly better performance for the latter. The high performance reported involves use of a multi-level data tiling strategy in memory and use of a pipelined algorithm with simultaneous computation and transfer of data from host to device memory. The speed of code development, flexibility, and low cost of the GPU implementations compared with application-specific integrated circuit (ASIC) and field programmable gate array (FPGA) implementations have the potential to greatly shorten the cycle of correlator development and deployment, for cases where some power-consumption penalty can be tolerated.
Pulsed photoacoustic Doppler flowmetry using a cross correlation method
NASA Astrophysics Data System (ADS)
Brunker, J.; Beard, P.
2010-02-01
The feasibility of making spatially resolved measurements of blood flow using pulsed photoacoustic Doppler techniques has been explored. Doppler time shifts were quantified via cross-correlation of pairs of photoacoustic waveforms generated within a blood-simulating phantom using pairs of laser light pulses. The photoacoustic waves were detected using a focussed or planar PZT ultrasound transducer. This approach was found to be effective for quantifying the linear motion of micron-scale absorbers imprinted on an acetate sheet moving with velocities in the range 0.15 to 1.50 ms-1. The effect of the acoustic spot diameter and the time separation between the laser pulses on measurement resolution and the maximum measurable velocity is discussed. The distinguishing advantage of pulsed rather than continuous-wave excitation is that spatially resolved velocity measurements can be made. This offers the prospect of mapping flow within the microcirculation and thus providing insights into the perfusion of tumours and other pathologies characterised by abnormalities in flow status.
Investigation of cosmic ray penetration with wavelet cross-correlation analysis
NASA Astrophysics Data System (ADS)
Yang, Rui-zhi
2016-07-01
Aims: We use Fermi-LATand Planck data to calculate the cross correlation between γ-ray signal and gas distribution in different scales in giant molecular clouds (GMCs). Then we investigate the cosmic rays (CRs) penetration in GMCs with these informations. Methods: We use the wavelet technique to decompose both the γ-ray and dust opacity maps in different scales, then we calculate the wavelet cross correlation functions in these scales. We also define wavelet response as an analog to the impulsive response in Fourier transform and calculate that in different scales down to Fermi-LATangular resolution. Results: The γ-ray maps above 2 GeV show strong correlation with the dust opacity maps, the correlation coefficient is larger than 0.9 above a scale of 0.4 degree.The derived wavelet response is uniform in different scales. Conclusions: We argue that the CR above 10 GeV can penetrate the GMC freely and the CRs distributions in the same energy range are uniform down to parsec scale.
Evidence of Cross-correlation between the CMB Lensing and the γ-Ray Sky
NASA Astrophysics Data System (ADS)
Fornengo, Nicolao; Perotto, Laurence; Regis, Marco; Camera, Stefano
2015-03-01
We report the measurement of the angular power spectrum of cross-correlation between the unresolved component of the Fermi-LAT γ-ray sky maps and the cosmic microwave background lensing potential map reconstructed by the Planck satellite. The matter distribution in the universe determines the bending of light coming from the last scattering surface. At the same time, the matter density drives the growth history of astrophysical objects, including their capability at generating non-thermal phenomena, which in turn give rise to γ-ray emissions. The Planck lensing map provides information on the integrated distribution of matter, while the integrated history of γ-ray emitters is imprinted in the Fermi-LAT sky maps. We report here the first evidence of their correlation. We find that the multipole dependence of the cross-correlation measurement is in agreement with current models of the γ-ray luminosity function for active galactic nuclei and star-forming galaxies, with a statistical evidence of 3.0σ. Moreover, its amplitude can in general be matched only assuming that these extragalactic emitters are also the bulk contribution of the measured isotopic γ-ray background (IGRB) intensity. This leaves little room for a big contribution from galactic sources to the IGRB measured by Fermi-LAT, pointing toward direct evidence of the extragalactic origin of the IGRB.
Quasar-Lyman α forest cross-correlation from BOSS DR11: Baryon Acoustic Oscillations
Font-Ribera, Andreu; Kirkby, David; Blomqvist, Michael; Busca, Nicolas; Aubourg, Éric; Bautista, Julian; Ross, Nicholas P.; Bailey, Stephen; Beutler, Florian; Carithers, Bill; Slosar, Anže; Rich, James; Delubac, Timothée; Bhardwaj, Vaishali; Bizyaev, Dmitry; Brewington, Howard; Brinkmann, Jon; Brownstein, Joel R.; Dawson, Kyle S.; and others
2014-05-01
We measure the large-scale cross-correlation of quasars with the Lyα forest absorption, using over 164,000 quasars from Data Release 11 of the SDSS-III Baryon Oscillation Spectroscopic Survey. We extend the previous study of roughly 60,000 quasars from Data Release 9 to larger separations, allowing a measurement of the Baryonic Acoustic Oscillation (BAO) scale along the line of sight c/(H(z = 2.36)r{sub s}) = 9.0±0.3 and across the line of sight D{sub A}(z = 2.36)/r{sub s} = 10.8±0.4, consistent with CMB and other BAO data. Using the best fit value of the sound horizon from Planck data (r{sub s} = 147.49 Mpc), we can translate these results to a measurement of the Hubble parameter of H(z = 2.36) = 226±8 km s{sup −1} Mpc{sup −1} and of the angular diameter distance of D{sub A}(z = 2.36) = 1590±60 Mpc. The measured cross-correlation function and an update of the code to fit the BAO scale (baofit) are made publicly available.
McCormick, Cornelia; St-Laurent, Marie; Ty, Ambrose; Valiante, Taufik A; McAndrews, Mary Pat
2015-05-01
Autobiographical memory (AM) provides the opportunity to study interactions among brain areas that support the search for a specific episodic memory (construction), and the later experience of mentally reliving it (elaboration). While the hippocampus supports both construction and elaboration, it is unclear how hippocampal-neocortical connectivity differs between these stages, and how this connectivity involves the anterior and posterior segments of the hippocampus, as these have been considered to support the retrieval of general concepts and recollection processes, respectively. We acquired fMRI data in 18 healthy participants during an AM retrieval task in which participants were asked to access a specific AM (construction) and then to recollect it by recovering as many episodic details as possible (elaboration). Using multivariate analytic techniques, we examined changes in functional and effective connectivity of hippocampal-neocortical interactions during these phases of AM retrieval. We found that the left anterior hippocampus interacted with frontal areas during construction and bilateral posterior hippocampi with visual perceptual areas during elaboration, indicating key roles for both hippocampi in coordinating transient neocortical networks at both AM stages. Our findings demonstrate the importance of direct interrogation of hippocampal-neocortical interactions to better illuminate the neural dynamics underlying complex cognitive tasks such as AM retrieval. PMID:24275829
Multifractal detrended cross-correlation analysis of carbon and crude oil markets
NASA Astrophysics Data System (ADS)
Zhuang, Xiaoyang; Wei, Yu; Zhang, Bangzheng
2014-04-01
The complex dynamics between carbon and crude oil markets have been an increasingly interesting area of research. In this paper, we try to take a fresh look at the cross-correlations between carbon and crude oil markets as well as their dynamic behavior employing multifractal detrended cross-correlation analysis. First, we find that the return series of carbon and crude oil markets are significantly cross-correlated. Second, we confirm the existence of multifractality for the return series of carbon and crude oil markets by the multifractal detrended fluctuation analysis. Third, based on the multifractal detrended cross-correlation analysis, we find the existence of power-law cross-correlations between carbon and crude oil markets. The cross-correlated behavior of small fluctuations is found to be more persistent than that of large fluctuations. At last, some relevant discussions and implications of the empirical results are presented.
Lowe, S.S.
1993-11-16
The mission of the Tank Waste Remediation System (TWRS) Program is to store, treat, and immobilize highly radioactive Hanford waste in an environmentally sound, safe, and cost-effective manner. The scope of the TWRS Program includes project and program activities for receiving, storing, maintaining, treating, and disposing onsite, or packaging for offsite disposal, all Hanford tank waste. Hanford tank waste includes the contents of 149 single-shell tanks (SSTs) and 28 double-shell tanks (DSTs), plus any new waste added to these facilities, and all encapsulated cesium and strontium stored onsite and returned from offsite users. A key element of the TWRS Program is retrieval of the waste in the SSTs. The waste stored in these underground tanks must be removed in order to minimize environmental, safety, and health risks associated with continuing waste storage. Subsurface barriers are being considered as a means to mitigate the effects of tank leaks including those occurring during SST waste retrieval. The functions to be performed by subsurface barriers based on their role in retrieving waste from the SSTs are described, and the requirements which constrain their application are identified. These functions and requirements together define the functional baseline for subsurface barriers.
NASA Astrophysics Data System (ADS)
Ma, Feng; Zhang, Qian; Peng, Chen; Wei, Yu
2014-09-01
In this paper, we firstly investigate the cross-correlations between the crude oil market and the six GCC stock markets. Based on the analysis of the significant statistic Qcc(m) and the cross-correlation coefficient, we find that the cross-correlations between the crude oil market and the six GCC stock markets are all significant. Employing the method of the MF-DFA and MF-DXA, we further find that the auto-correlations of the crude oil market and the six GCC stock markets and cross-correlations between them are all the multifractality. Moreover, using the multifractal spectrum, we can also verify the multifractal characteristics between the crude oil market and the six GCC stock markets. Furthermore, we use the penalized contrast function to detect the structural break points of the WTI-Oil return series and its conditional volatility, and then discuss the cross-correlations between the crude oil and the six GCC stock markets in the different phases according to these break points. At last, we employ the technique of the rolling window to investigate the dynamic of the scaling exponent Hxy(q). In addition, we explore the relationship between the cross-correlation exponents Hxy(q) and the average scaling exponents [Hxx(q)+Hyy(q)]/2].
Dynamic cross correlation studies of wave particle interactions in ULF phenomena
NASA Technical Reports Server (NTRS)
Mcpherron, R. L.
1979-01-01
Magnetic field observations made by satellites in the earth's magnetic field reveal a wide variety of ULF waves. These waves interact with the ambient particle populations in complex ways, causing modulation of the observed particle fluxes. This modulation is found to be a function of species, pitch angle, energy and time. The characteristics of this modulation provide information concerning the wave mode and interaction process. One important characteristic of wave-particle interactions is the phase of the particle flux modulation relative to the magnetic field variations. To display this phase as a function of time a dynamic cross spectrum program has been developed. The program produces contour maps in the frequency time plane of the cross correlation coefficient between any particle flux time series and the magnetic field vector. This program has been utilized in several studies of ULF wave-particle interactions at synchronous orbit.
Hypo-retrieval and hyper-suppression mechanisms in functional amnesia.
Tramoni, Eve; Aubert-Khalfa, Stéphanie; Guye, Maxime; Ranjeva, Jean P; Felician, Olivier; Ceccaldi, Mathieu
2009-02-01
Functional amnesia (FA) is characterized by an extensive retrograde memory loss in the absence of detectable structural brain damage. The two main hypotheses put forward to explain this disturbance involve a global retrieval deficit (affecting both pre- and post-onset memories) and a selective inability to explicitly retrieve pre-onset memories. Here, we extensively examined P.P., a patient with FA, with a view to obtaining additional insights into the cognitive and neural mechanisms underlying this disorder. In Experiments 1 and 2, post-onset memories were assessed using tasks focusing on the state of consciousness associated with their retrieval. Although subtle deficits in the ability to recollect post-onset personal events were detected, P.P.'s performances were normal when the encoding of the event was monitored in a laboratory setting. In Experiment 3, implicit recognition of pre-onset memories was tested using skin conductance responses. Results showed that P.P. responded implicitly to photographs of personal pre-onset events that were not explicitly recognized. In Experiment 4, designed to assess the patient's ability to suppress newly acquired information, P.P. suppressed more items than controls. Additionally, while no grey matter loss was evidenced with voxel-based morphometry, magnetic resonance spectroscopy and magnetization transfer imaging showed significant metabolic and structural changes within the white matter of the right prefrontal lobe. In conclusion, our results suggest that FA may result from a combination between two processes, a "hypo-retrieval" of pre-onset memories, tentatively due to white matter tract damage, and a "hyper-suppression" mechanism, concomitantly preventing the retrieval of pre-onset memories. PMID:19071144
NASA Astrophysics Data System (ADS)
Li, Jing; Zeng, Zhaofa; Slob, Evert; Chen, Xiong; Liu, Fengshan
2014-12-01
Passive interferometry technology is based on the relation between the reflection and the transmission responses of the subsurface. The transmission response can be received at surface in the presence of the ambient noise source in the subsurface with the cross-correlation (CC) or multidimensional deconvolution methods. We investigate the feasibility of electromagnetic (EM) wave passive interferometry with CC method. We design a 2-D finite-difference time domain (FDTD) algorithm to simulate the long-duration ground penetrating radar (GPR) measurements with random distribution of passive EM sources. The noise sources have random duration time, waveform and spatial distribution. We test the FDTD GPR passive interferometry code with above source characteristics and apply the method to light non-aqueous phase liquid (LNAPL) monitoring. Based on the model simulation data, by using common midpoint velocity analysis and normal move out correction to process the interferometry retrieve record, we can accurately obtain the dynamic changing characteristics of the target's permittivity. The LNAPL dynamic leakage model can be imaged as well. The synthetic results demonstrate that the GPR passive interferometry is feasible in subsurface LNAPL monitoring. Our work provides a foundation for a passive interferometry field application using GPR.
NASA Astrophysics Data System (ADS)
Wang, Gang-Jin; Xie, Chi; Chen, Shou; Yang, Jiao-Jiao; Yang, Ming-Yan
2013-09-01
In this study, we first build two empirical cross-correlation matrices in the US stock market by two different methods, namely the Pearson’s correlation coefficient and the detrended cross-correlation coefficient (DCCA coefficient). Then, combining the two matrices with the method of random matrix theory (RMT), we mainly investigate the statistical properties of cross-correlations in the US stock market. We choose the daily closing prices of 462 constituent stocks of S&P 500 index as the research objects and select the sample data from January 3, 2005 to August 31, 2012. In the empirical analysis, we examine the statistical properties of cross-correlation coefficients, the distribution of eigenvalues, the distribution of eigenvector components, and the inverse participation ratio. From the two methods, we find some new results of the cross-correlations in the US stock market in our study, which are different from the conclusions reached by previous studies. The empirical cross-correlation matrices constructed by the DCCA coefficient show several interesting properties at different time scales in the US stock market, which are useful to the risk management and optimal portfolio selection, especially to the diversity of the asset portfolio. It will be an interesting and meaningful work to find the theoretical eigenvalue distribution of a completely random matrix R for the DCCA coefficient because it does not obey the Marčenko-Pastur distribution.
Surface wave phase-velocity tomography based on multichannel cross-correlation
NASA Astrophysics Data System (ADS)
Jin, Ge; Gaherty, James B.
2015-06-01
We have developed a new method to retrieve seismic surface wave phase velocity using dense seismic arrays. The method measures phase variations between nearby stations based on waveform cross-correlation. The coherence in waveforms between adjacent stations results in highly precise relative phase estimates. Frequency-dependent phase variations are then inverted for spatial variations in apparent phase velocity via the Eikonal equation. Frequency-dependent surface wave amplitudes measured on individual stations are used to correct the apparent phase velocity to account for multipathing via the Helmholtz equation. By using coherence and other data selection criteria, we construct an automated system that retrieves structural phase-velocity maps directly from raw seismic waveforms for individual earthquakes without human intervention. The system is applied to broad-band seismic data from over 800 events recorded on EarthScope's USArray from 2006 to 2014, systematically building up Rayleigh-wave phase-velocity maps between the periods of 20 and 100 s for the entire continental United States. At the highest frequencies, the resulting maps are highly correlated with phase-velocity maps derived from ambient noise tomography. At all frequencies, we observe a significant contrast in Rayleigh-wave phase velocity between the tectonically active western US and the stable eastern US, with the phase velocity variations in the western US being 1-2 times greater. The Love wave phase-velocity maps are also calculated. We find that overtone contamination may produce systemic bias for the Love-wave phase-velocity measurements.
Functional MRI evidence for the decline of word retrieval and generation during normal aging.
Baciu, M; Boudiaf, N; Cousin, E; Perrone-Bertolotti, M; Pichat, C; Fournet, N; Chainay, H; Lamalle, L; Krainik, A
2016-02-01
This fMRI study aimed to explore the effect of normal aging on word retrieval and generation. The question addressed is whether lexical production decline is determined by a direct mechanism, which concerns the language operations or is rather indirectly induced by a decline of executive functions. Indeed, the main hypothesis was that normal aging does not induce loss of lexical knowledge, but there is only a general slowdown in retrieval mechanisms involved in lexical processing, due to possible decline of the executive functions. We used three tasks (verbal fluency, object naming, and semantic categorization). Two groups of participants were tested (Young, Y and Aged, A), without cognitive and psychiatric impairment and showing similar levels of vocabulary. Neuropsychological testing revealed that older participants had lower executive function scores, longer processing speeds, and tended to have lower verbal fluency scores. Additionally, older participants showed higher scores for verbal automatisms and overlearned information. In terms of behavioral data, older participants performed as accurate as younger adults, but they were significantly slower for the semantic categorization and were less fluent for verbal fluency task. Functional MRI analyses suggested that older adults did not simply activate fewer brain regions involved in word production, but they actually showed an atypical pattern of activation. Significant correlations between the BOLD (Blood Oxygen Level Dependent) signal of aging-related (A > Y) regions and cognitive scores suggested that this atypical pattern of the activation may reveal several compensatory mechanisms (a) to overcome the slowdown in retrieval, due to the decline of executive functions and processing speed and (b) to inhibit verbal automatic processes. The BOLD signal measured in some other aging-dependent regions did not correlate with the behavioral and neuropsychological scores, and the overactivation of these uncorrelated
Retrieving the Hemodynamic Response Function in resting state fMRI: Methodology and application.
Wu, Guo-Rong; Deshpande, Gopikhrishna; Laureys, Steven; Marinazzo, Daniele
2015-08-01
In this paper we present a procedure to retrieve the hemodynamic response function (HRF) from resting state functional magnetic resonance imaging (fMRI) data. The fundamentals of the procedures are further validated by considering simultaneous electroencephalographic (EEG) recordings. The typical HRF shape at rest for a group of healthy subject is presented. Then we present the modifications to the shape of the HRF at rest following two physiological modulations: eyes open versus eyes closed and propofol-induced modulations of consciousness. PMID:26737671
NASA Astrophysics Data System (ADS)
Greig, D. W.; Spriggs, N.
2014-12-01
Waveform cross correlation, or template matching as it is sometimes called, has long been known to be an effective method for finding occurrences of a known repeating signal within a waveform. Because seismic signals are rarely known a priori, waveform cross correlation is not often used as a detection method for seismic networks. However, past studies (e.g. Gibbons and Ringdal, 2006) have shown that cross correlation can be effective in identifying events with similar locations and focal mechanisms (and thus waveforms) to a pre-existing template. Because induced seismicity often satisfies these requirements the method is well-suited to induced seismicity monitoring. We apply the method of waveform cross correlation to a sequence of events between Nov. 29, 2013 and Dec. 13, 2013 occurring at Crooked Lake near Fox Creek, Alberta. These events are believed to be attributable to injection activities in the area. A total of 24 events were detected using traditional STA/LTA triggering methods. The largest event, measured at local magnitude 3.9, is used as a template to identify other events. We compare the effectiveness of the traditional STA/LTA detection method to the cross correlation technique. With a modest correlation threshold we identify all 24 of the original events and an additional 89 new events for a total of 113 events identified by waveform cross correlation. We estimate the magnitude of completeness using the maximum curvature method (Wiemer and Wyss, 2000) and compare the result for the STA/LTA catalogue and the cross correlation catalogue. We find that the magnitude of completeness is about 0.8 magnitude units lower for the cross correlation catalogue. We explore the possibility of determining a probability density function to describe the values of observed correlation between a template and a seismic signal and reconcile theoretical expectations with empirical data. We further suggest a trigger threshold for cross correlation detection algorithms
Big Data Solution for CTBT Monitoring Using Global Cross Correlation
NASA Astrophysics Data System (ADS)
Gaillard, P.; Bobrov, D.; Dupont, A.; Grenouille, A.; Kitov, I. O.; Rozhkov, M.
2014-12-01
Due to the mismatch between data volume and the performance of the Information Technology infrastructure used in seismic data centers, it becomes more and more difficult to process all the data with traditional applications in a reasonable elapsed time. To fulfill their missions, the International Data Centre of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO/IDC) and the Département Analyse Surveillance Environnement of Commissariat à l'Energie atomique et aux énergies alternatives (CEA/DASE) collect, process and produce complex data sets whose volume is growing exponentially. In the medium term, computer architectures, data management systems and application algorithms will require fundamental changes to meet the needs. This problem is well known and identified as a "Big Data" challenge. To tackle this major task, the CEA/DASE takes part during two years to the "DataScale" project. Started in September 2013, DataScale gathers a large set of partners (research laboratories, SMEs and big companies). The common objective is to design efficient solutions using the synergy between Big Data solutions and the High Performance Computing (HPC). The project will evaluate the relevance of these technological solutions by implementing a demonstrator for seismic event detections thanks to massive waveform correlations. The IDC has developed an expertise on such techniques leading to an algorithm called "Master Event" and provides a high-quality dataset for an extensive cross correlation study. The objective of the project is to enhance the Master Event algorithm and to reanalyze 10 years of waveform data from the International Monitoring System (IMS) network thanks to a dedicated HPC infrastructure operated by the "Centre de Calcul Recherche et Technologie" at the CEA of Bruyères-le-Châtel. The dataset used for the demonstrator includes more than 300,000 seismic events, tens of millions of raw detections and more than 30 terabytes of continuous seismic data
Multi-scale Analysis of DSCOVR Data Using Wavelet Cross Correlation
NASA Astrophysics Data System (ADS)
Hegedus, A. M.; Kasper, J. C.; Stevens, M. L.; Alterman, B. L.; Case, A. W.; Szabo, A.; Koval, A.
2015-12-01
The Deep Space Climate Observatory (DSCOVR), launched February 11th 2015, makes the fastest combined measurements of solar wind magnetic field vectors and ion velocity distribution functions ever. These data allow us to search for correlation between ion and magnetic field fluctuations at kinetic ion scales for the first time. We present first results of a wavelet correlation analysis, which allows us to search for wave-particle interactions while accounting for different sampling cadences and data gaps. Using different wavelet algorithms we circumvent these issues and decompose the covariance and correlation between these two data streams on a scale by scale basis. We then generalize these quantities to wavelet cross-correlation and cross-covariance to identify interactions between charged particles and magnetic fields on kinetic scales. The techniques developed in this work will be directly applicable to plasma and magnetic field observations in the corona on the upcoming Solar Probe Plus mission.
NASA Technical Reports Server (NTRS)
Kaufman, Y. J.; Gitelson, A.; Karnieli, A.; Ganor, E. (Editor); Fraser, R. S.; Nakajima, T.; Mattoo, S.; Holben, B. N.
1994-01-01
Ground-based measurements of the solar transmission and sky radiance in a horizontal plane through the Sun are taken in several geographical regions and aerosol types: dust in a desert transition zone in Israel, sulfate particles in Eastern and Western Europe, tropical aerosol in Brazil, and mixed continental/maritime aerosol in California. Stratospheric aerosol was introduced after the eruption of Mount Pinatubo in June 1991. Therefore measurements taken before the eruption are used to analyze the properties of tropospheric aerosol; measurements from 1992 are also used to detect the particle size and concentration of stratospheric aerosol. The measurements are used to retrieve the size distribution and the scattering phase function at large scattering angles of the undisturbed aerosol particles. The retrieved properties represent an average on the entire atmospheric column. A comparison between the retrieved phase function for a scattering angle of 120 deg, with phase function predicted from the retrieved size distribution, is used to test the assumption of particle homogeneity and sphericity in radiative transfer models (Mie theory). The effect was found to be small (20% +/- 15%). For the stratospheric aerosol (sulfates), as expected, the phase function was very well predicted using the Mie theory. A model with a power law distribution, based on the spectral dependence of the optical thickness, alpha, cannot estimate accurately the phase function (up to 50% error for lambda = 0.87 microns). Before the Pinatubo eruption the ratio between the volumes of sulfate and coarse particles was very well correlated with alpha. The Pinatubo stratospheric aerosol destroyed this correlation. The aerosol optical properties are compared with analysis of the size, shape, and composition of the individual particles by electron microscopy of in situ samples. The measured volume size distribution before the injection of stratospheric aerosol consistently show two modes, sulfate
Siegle, Joshua H; Wilson, Matthew A
2014-01-01
Assessing the behavioral relevance of the hippocampal theta rhythm has proven difficult, due to a shortage of experiments that selectively manipulate phase-specific information processing. Using closed-loop stimulation, we triggered inhibition of dorsal CA1 at specific phases of the endogenous theta rhythm in freely behaving mice. This intervention enhanced performance on a spatial navigation task that requires the encoding and retrieval of information related to reward location on every trial. In agreement with prior models of hippocampal function, the behavioral effects depended on both the phase of theta and the task segment at which we stimulated. Stimulation in the encoding segment enhanced performance when inhibition was triggered by the peak of theta. Conversely, stimulation in the retrieval segment enhanced performance when inhibition was triggered by the trough of theta. These results suggest that processes related to the encoding and retrieval of task-relevant information are preferentially active at distinct phases of theta.DOI: http://dx.doi.org/10.7554/eLife.03061.001. PMID:25073927
NASA Astrophysics Data System (ADS)
Yueh, Simon; Tang, Wenqing; Fore, Alexander; Hayashi, Akiko; Song, Yuhe T.; Lagerloef, Gary
2014-08-01
This paper describes the updated Combined Active-Passive (CAP) retrieval algorithm for simultaneous retrieval of surface salinity and wind from Aquarius' brightness temperature and radar backscatter. Unlike the algorithm developed by Remote Sensing Systems (RSS), implemented in the Aquarius Data Processing System (ADPS) to produce Aquarius standard products, the Jet Propulsion Laboratory's CAP algorithm does not require monthly climatology SSS maps for the salinity retrieval. Furthermore, the ADPS-RSS algorithm fully uses the National Center for Environmental Predictions (NCEP) wind for data correction, while the CAP algorithm uses the NCEP wind only as a constraint. The major updates to the CAP algorithm include the galactic reflection correction, Faraday rotation, Antenna Pattern Correction, and geophysical model functions of wind or wave impacts. Recognizing the limitation of geometric optics scattering, we improve the modeling of the reflection of galactic radiation; the results are better salinity accuracy and significantly reduced ascending-descending bias. We assess the accuracy of CAP's salinity by comparison with ARGO monthly gridded salinity products provided by the Asia-Pacific Data-Research Center (APDRC) and Japan Agency for Marine-Earth Science and Technology (JAMSTEC). The RMS differences between Aquarius CAP and APDRC's or JAMSTEC's ARGO salinities are less than 0.2 psu for most parts of the ocean, except for the regions in the Intertropical Convergence Zone, near the outflow of major rivers and at high latitudes.
Siegle, Joshua H; Wilson, Matthew A
2014-01-01
Assessing the behavioral relevance of the hippocampal theta rhythm has proven difficult, due to a shortage of experiments that selectively manipulate phase-specific information processing. Using closed-loop stimulation, we triggered inhibition of dorsal CA1 at specific phases of the endogenous theta rhythm in freely behaving mice. This intervention enhanced performance on a spatial navigation task that requires the encoding and retrieval of information related to reward location on every trial. In agreement with prior models of hippocampal function, the behavioral effects depended on both the phase of theta and the task segment at which we stimulated. Stimulation in the encoding segment enhanced performance when inhibition was triggered by the peak of theta. Conversely, stimulation in the retrieval segment enhanced performance when inhibition was triggered by the trough of theta. These results suggest that processes related to the encoding and retrieval of task-relevant information are preferentially active at distinct phases of theta. DOI: http://dx.doi.org/10.7554/eLife.03061.001 PMID:25073927
Cross-correlations between price and volume in Chinese gold markets
NASA Astrophysics Data System (ADS)
Ruan, Qingsong; Jiang, Wei; Ma, Guofeng
2016-06-01
We apply the multifractal detrended cross-correlation analysis (MF-DCCA) method to investigate the cross-correlation behaviors between price and volume in Chinese gold spot and futures markets. Qualitatively, we find that the price and volume series are significantly cross-correlated using the cross-correlation test statistics Qcc(m) and the ρDCCA coefficients. Quantitatively, by employing the MF-DCCA analysis, we find that there is a power-law cross-correlation and significant multifractal features between price and volume in gold spot and futures markets. Furthermore, by comparing the multifractality of the original series to the shuffled and surrogated series, we find that, for the gold spot market, the main contribution of multifractality is fat-tail distribution; for the gold futures market, both long-range correlations and fat-tail distributions play important roles in the contribution of multifractality. Finally, by employing the method of rolling windows, we undertake further investigation into the time-varying features of the cross-correlations between price and volume. We find that for both spot and futures markets, the cross-correlations are anti-persistent in general. In the short term, the cross-correlation shows obvious fluctuations due to exogenous shocks while, in the long term, the relationship tends to be at a metastable level due to the dynamic mechanism.
An analysis of the intrinsic cross-correlations between API and meteorological elements using DPCCA
NASA Astrophysics Data System (ADS)
Shen, Chen-hua; Li, Cao-ling
2016-03-01
In order to reveal the intrinsic cross-correlations between air pollution index (API) records and synchronously meteorological elements data, the detrended partial cross-correlation (DPCC) coefficients are analyzed using a detrended partial cross-correlation analysis (DPCCA). DPCC coefficients for different spatial locations and seasons are calculated and compared. The results show that DPCCA can uncover intrinsic cross-correlations between API and meteorological elements, and most of their interactional mechanisms can be explained. DPCC coefficients are either positive or negative, and vary with spatial locations and seasons, with consistently interactional mechanisms. More remarkable, we find that detrended cross-correlation analysis can present the cross-correlations between the fluctuations in two nonstationary time series, but this cross-correlation does not always fully reflect the interactional mechanism for the original time series. Despite this, DPCCA is recommended as a comparatively reliable method for revealing intrinsic cross-correlations between API and meteorological elements, and it can also be useful for our understanding of their interactional mechanisms.
Multifractal detrended cross-correlations between the Chinese exchange market and stock market
NASA Astrophysics Data System (ADS)
Cao, Guangxi; Xu, Longbing; Cao, Jie
2012-10-01
Based on the daily price data of the Chinese Yuan (RMB)/US dollar exchange rate and the Shanghai Stock Composite Index, we conducted an empirical analysis of the cross-correlations between the Chinese exchange market and stock market using the multifractal cross-correlation analysis method. The results demonstrate the overall significance of the cross-correlation based on the analysis of a statistic. Multifractality exists in cross-correlations, and the cross-correlated behavior of small fluctuations is more persistent than that of large fluctuations. Moreover, using the rolling windows method, we find that the cross-correlations between the Chinese exchange market and stock market vary with time and are especially sensitive to the reform of the RMB exchange rate regime. The previous reduction in the flexibility of the RMB exchange rate in July 2008 strengthened the persistence of cross-correlations and decreased the degree of multifractality, whereas the enhancement of the flexibility of the RMB exchange rate in June 2010 weakened the persistence of cross-correlations and increased the multifractality. Finally, several relevant discussions are provided to verify the robustness of our empirical analysis.
Cross-correlations between crude oil and exchange markets for selected oil rich economies
NASA Astrophysics Data System (ADS)
Li, Jianfeng; Lu, Xinsheng; Zhou, Ying
2016-07-01
Using multifractal detrended cross-correlation analysis (MF-DCCA), this paper studies the cross-correlation behavior between crude oil market and five selected exchange rate markets. The dataset covers the period of January 1,1996-December 31,2014, and contains 4,633 observations for each of the series, including daily closing prices of crude oil, Australian Dollars, Canadian Dollars, Mexican Pesos, Russian Rubles, and South African Rand. Our empirical results obtained from cross-correlation statistic and cross-correlation coefficient have confirmed the existence of cross-correlations, and the MF-DCCA results have demonstrated a strong multifractality between cross-correlated crude oil market and exchange rate markets in both short term and long term. Using rolling window analysis, we have also found the persistent cross-correlations between the exchange rates and crude oil returns, and the cross-correlation scaling exponents exhibit volatility during some time periods due to its sensitivity to sudden events.
Gong, S.; Labanca, I.; Rech, I.; Ghioni, M.
2014-10-15
Fluorescence correlation spectroscopy (FCS) is a well-established technique to study binding interactions or the diffusion of fluorescently labeled biomolecules in vitro and in vivo. Fast FCS experiments require parallel data acquisition and analysis which can be achieved by exploiting a multi-channel Single Photon Avalanche Diode (SPAD) array and a corresponding multi-input correlator. This paper reports a 32-channel FPGA based correlator able to perform 32 auto/cross-correlations simultaneously over a lag-time ranging from 10 ns up to 150 ms. The correlator is included in a 32 × 1 SPAD array module, providing a compact and flexible instrument for high throughput FCS experiments. However, some inherent features of SPAD arrays, namely afterpulsing and optical crosstalk effects, may introduce distortions in the measurement of auto- and cross-correlation functions. We investigated these limitations to assess their impact on the module and evaluate possible workarounds.
Gong, S.; Labanca, I.; Rech, I.; Ghioni, M.
2014-01-01
Fluorescence correlation spectroscopy (FCS) is a well-established technique to study binding interactions or the diffusion of fluorescently labeled biomolecules in vitro and in vivo. Fast FCS experiments require parallel data acquisition and analysis which can be achieved by exploiting a multi-channel Single Photon Avalanche Diode (SPAD) array and a corresponding multi-input correlator. This paper reports a 32-channel FPGA based correlator able to perform 32 auto/cross-correlations simultaneously over a lag-time ranging from 10 ns up to 150 ms. The correlator is included in a 32 × 1 SPAD array module, providing a compact and flexible instrument for high throughput FCS experiments. However, some inherent features of SPAD arrays, namely afterpulsing and optical crosstalk effects, may introduce distortions in the measurement of auto- and cross-correlation functions. We investigated these limitations to assess their impact on the module and evaluate possible workarounds. PMID:25362365
Model-based cross-correlation search for gravitational waves from Scorpius X-1
NASA Astrophysics Data System (ADS)
Whelan, John T.; Sundaresan, Santosh; Zhang, Yuanhao; Peiris, Prabath
2015-05-01
We consider the cross-correlation search for periodic gravitational waves and its potential application to the low-mass x-ray binary Sco X-1. This method coherently combines data not only from different detectors at the same time, but also data taken at different times from the same or different detectors. By adjusting the maximum allowed time offset between a pair of data segments to be coherently combined, one can tune the method to trade off sensitivity and computing costs. In particular, the detectable signal amplitude scales as the inverse fourth root of this coherence time. The improvement in amplitude sensitivity for a search with a maximum time offset of one hour, compared with a directed stochastic background search with 0.25-Hz-wide bins, is about a factor of 5.4. We show that a search of one year of data from the Advanced LIGO and Advanced Virgo detectors with a coherence time of one hour would be able to detect gravitational waves from Sco X-1 at the level predicted by torque balance over a range of signal frequencies from 30 to 300 Hz; if the coherence time could be increased to ten hours, the range would be 20 to 500 Hz. In addition, we consider several technical aspects of the cross-correlation method: We quantify the effects of spectral leakage and show that nearly rectangular windows still lead to the most sensitive search. We produce an explicit parameter-space metric for the cross-correlation search, in general, and as applied to a neutron star in a circular binary system. We consider the effects of using a signal template averaged over unknown amplitude parameters: The quantity to which the search is sensitive is a given function of the intrinsic signal amplitude and the inclination of the neutron-star rotation axis to the line of sight, and the peak of the expected detection statistic is systematically offset from the true signal parameters. Finally, we describe the potential loss of signal-to-noise ratio due to unmodeled effects such as signal
RECONSTRUCTING REDSHIFT DISTRIBUTIONS WITH CROSS-CORRELATIONS: TESTS AND AN OPTIMIZED RECIPE
Matthews, Daniel J.; Newman, Jeffrey A. E-mail: janewman@pitt.ed
2010-09-20
Many of the cosmological tests to be performed by planned dark energy experiments will require extremely well-characterized photometric redshift measurements. Current estimates for cosmic shear are that the true mean redshift of the objects in each photo-z bin must be known to better than 0.002(1 + z), and the width of the bin must be known to {approx}0.003(1 + z) if errors in cosmological measurements are not to be degraded significantly. A conventional approach is to calibrate these photometric redshifts with large sets of spectroscopic redshifts. However, at the depths probed by Stage III surveys (such as DES), let alone Stage IV (LSST, JDEM, and Euclid), existing large redshift samples have all been highly (25%-60%) incomplete, with a strong dependence of success rate on both redshift and galaxy properties. A powerful alternative approach is to exploit the clustering of galaxies to perform photometric redshift calibrations. Measuring the two-point angular cross-correlation between objects in some photometric redshift bin and objects with known spectroscopic redshift, as a function of the spectroscopic z, allows the true redshift distribution of a photometric sample to be reconstructed in detail, even if it includes objects too faint for spectroscopy or if spectroscopic samples are highly incomplete. We test this technique using mock DEEP2 Galaxy Redshift survey light cones constructed from the Millennium Simulation semi-analytic galaxy catalogs. From this realistic test, which incorporates the effects of galaxy bias evolution and cosmic variance, we find that the true redshift distribution of a photometric sample can, in fact, be determined accurately with cross-correlation techniques. We also compare the empirical error in the reconstruction of redshift distributions to previous analytic predictions, finding that additional components must be included in error budgets to match the simulation results. This extra error contribution is small for surveys that
On the Balancing of the SMOS Ocean Salinity Retrieval Cost Function
NASA Astrophysics Data System (ADS)
Sabia, R.; Camps, A.; Portabella, M.; Talone, M.; Ballabrera, J.; Gourrion, J.; Gabarró, C.; Aretxabaleta, A. L.; Font, J.
2009-04-01
The Soil Moisture and Ocean Salinity (SMOS) mission will be launched in mid 2009 to provide synoptic sea surface salinity (SSS) measurements with good temporal resolution [1]. To obtain a proper estimation of the SSS fields derived from the multi-angular brightness temperatures (TB) measured by the Microwave Interferometric Radiometer by Aperture Synthesis (MIRAS) sensor, a comprehensive inversion procedure has been defined [2]. Nevertheless, several salinity retrieval issues remain critical, namely: 1) Scene-dependent bias in the simulated TBs, 2) L-band forward geophysical model function definition, 3) Auxiliary data uncertainties, 4) Constraints in the cost function (inversion), especially in salinity term, and 5) Adequate spatio-temporal averaging. These issues will have to be properly addressed in order to meet the proposed accuracy requirement of the mission: a demanding 0.1 psu (practical salinity units) after averaging in a 30-day and 2°x2° spatio-temporal boxes. The salinity retrieval cost function minimizes the difference between the multi-angular measured SMOS TBs (yet simulated, so far) and the modeled TBs, weighted by the corresponding radiometric noise of the measurements. Furthermore, due to the fact that the minimization problem is both non-linear and ill-posed, background reference terms are needed to nudge the solution and ensuring convergence at the same time [3]. Constraining terms in SSS, sea surface temperature (SST) and wind speed are considered with their respective uncertainties. Moreover, whether SSS constraints have to be included or not as part of the retrieval procedure is still a matter of debate. On one hand, neglecting background reference information on SSS might prevent from retrieving salinity with the prescribed accuracy or at least within reasonable error. Conversely, including constraints in SSS, relying for instance on the climatology, may force the retrieved value to be too close to the reference prior values, thus
Pozzi, Paolo; Sironi, Laura; D'Alfonso, Laura; Bouzin, Margaux; Collini, Maddalena; Chirico, Giuseppe; Pallavicini, Piersandro; Cotelli, Franco; Foglia, Efrem A
2014-06-01
Biomedical issues in vasculogenesis and cardiogenesis require methods to follow hemodynamics with high spatial (micrometers) and time (milliseconds) resolution. At the same time, we need to follow relevant morphogenetic processes on large fields of view. Fluorescence cross-correlation spectroscopy coupled to scanning or wide-field microscopy meets these needs but has limited flexibility in the excitation pattern. To overcome this limitation, we develop here a two-photon two-spots setup coupled to an all-reflective near-infrared (NIR) optimized scanning system and to an electron multiplying charge-coupled device. Two NIR laser spots are spaced at adjustable micron-size distances (1 to 50 μm) by means of a Twyman-Green interferometer and repeatedly scanned on the sample, allowing acquisition of information on flows at 4 ms-3 μm time-space resolution in parallel on an extended field of view. We analyze the effect of nonhomogeneous and variable flow on the cross-correlation function by numerical simulations and show exemplary application of this setup in studies of blood flow in zebrafish embryos in vivo. By coupling the interferometer with the scanning mirrors and by computing the cross-correlation function of fluorescent red blood cells, we are able to map speed patterns in embryos' vessels. PMID:24946713
NASA Astrophysics Data System (ADS)
Wang, Fang; Liao, Gui-ping; Li, Jian-hui; Zou, Rui-biao; Shi, Wen
2013-03-01
A novel method, which we called the analogous multifractal cross-correlation analysis, is proposed in this paper to study the multifractal behavior in the power-law cross-correlation between price and load in California electricity market. In addition, a statistic ρAMF -XA, which we call the analogous multifractal cross-correlation coefficient, is defined to test whether the cross-correlation between two given signals is genuine or not. Our analysis finds that both the price and load time series in California electricity market express multifractal nature. While, as indicated by the ρAMF -XA statistical test, there is a huge difference in the cross-correlation behavior between the years 1999 and 2000 in California electricity markets.
Asymmetric multiscale detrended cross-correlation analysis of financial time series.
Yin, Yi; Shang, Pengjian
2014-09-01
We propose the asymmetric multiscale detrended cross-correlation analysis (MS-ADCCA) method and apply MS-ADCCA method to explore the existence of asymmetric cross-correlation for daily price returns in US and Chinese stock markets and to assess the properties of these asymmetric cross-correlations. The results all show the existences of asymmetric cross-correlations, while small asymmetries at small scales and larger asymmetries at larger scales are also displayed. There is a strong similarity between S&P500 and DJI, and we reveal that the asymmetries depend more on the cross-correlations of S&P500 vs. DJI, S&P500 vs. NQCI, DJI vs. NQCI, and ShangZheng vs. ShenCheng when the market is falling than rising, respectively. By comparing the spectra of S&P500 vs. NQCI and DJI vs. NQCI with uptrends and downtrends, we detect some new characteristics which lead to some new conclusions. Likewise, some new conclusions also can be drawn by the new characteristics displayed through the comparison between the spectra of ShangZheng vs. HSI and ShenCheng vs. HSI. Obviously, we conclude that although the overall spectra are similar and one market has the same effect when it is rising and falling in the study of asymmetric cross-correlations between it and different markets, the cross-correlations and asymmetries on the trends of the different markets are all different. MS-ADCCA method can detect the differences on the asymmetric cross-correlations by different trends of markets. Moreover, the uniqueness of cross-correlation between NQCI and HSI can be detected in the study of the asymmetric cross-correlations, which confirms that HSI is unique in the Chinese stock markets and NQCI is unique in the US stock markets further. PMID:25273179
Asymmetric multiscale detrended cross-correlation analysis of financial time series
NASA Astrophysics Data System (ADS)
Yin, Yi; Shang, Pengjian
2014-09-01
We propose the asymmetric multiscale detrended cross-correlation analysis (MS-ADCCA) method and apply MS-ADCCA method to explore the existence of asymmetric cross-correlation for daily price returns in US and Chinese stock markets and to assess the properties of these asymmetric cross-correlations. The results all show the existences of asymmetric cross-correlations, while small asymmetries at small scales and larger asymmetries at larger scales are also displayed. There is a strong similarity between S&P500 and DJI, and we reveal that the asymmetries depend more on the cross-correlations of S&P500 vs. DJI, S&P500 vs. NQCI, DJI vs. NQCI, and ShangZheng vs. ShenCheng when the market is falling than rising, respectively. By comparing the spectra of S&P500 vs. NQCI and DJI vs. NQCI with uptrends and downtrends, we detect some new characteristics which lead to some new conclusions. Likewise, some new conclusions also can be drawn by the new characteristics displayed through the comparison between the spectra of ShangZheng vs. HSI and ShenCheng vs. HSI. Obviously, we conclude that although the overall spectra are similar and one market has the same effect when it is rising and falling in the study of asymmetric cross-correlations between it and different markets, the cross-correlations and asymmetries on the trends of the different markets are all different. MS-ADCCA method can detect the differences on the asymmetric cross-correlations by different trends of markets. Moreover, the uniqueness of cross-correlation between NQCI and HSI can be detected in the study of the asymmetric cross-correlations, which confirms that HSI is unique in the Chinese stock markets and NQCI is unique in the US stock markets further.
NASA Technical Reports Server (NTRS)
Wang, Menghua; Gordon, Howard R.
1993-01-01
Based on the fact that the part of downward radiance that depends on the optical properties of the aerosol in the atmosphere can be extracted from the measured sky radiance, a new scheme for retrieval of the aerosol phase function and the single-scattering albedo over the ocean is developed. This retrieval algorithm is tested with simulations for several cases. It is found that the retrieved aerosol phase function and the single-scattering albedo are virtually error-free if the vertical structure of the atmosphere is known and if the sky radiance and the aerosol optical thickness can be measured accurately. The robustness of the algorithm in realistic situations, in which the measurements are contaminated by calibration errors or noise, is examined. It is found that the retrieved value of omega(0) is usually in error by less than about 10 percent, and the phase function is accurately retrieved for theta less than about 90 deg. However, as the aerosol optical thickness becomes small, e.g., less than about 0.1, errors in the sky radiance measurement can lead to serious problems with the retrieval algorithm, especially in the blue. The use of the retrieval scheme should be limited to the red and near IR when the aerosol optical thickness is small.
NASA Astrophysics Data System (ADS)
Vassallo, Maurizio; Festa, Gaetano; Bobbio, Antonella; Serra, Marcello
2016-06-01
We extracted the Green's functions from cross correlation of ambient noise recorded at broadband stations located across the Apennine belt, Southern Italy. Continuous records at 26 seismic stations acquired for 3 years were analyzed. We found the emergence of surface waves in the whole range of the investigated distances (10-140 km) with energy confined in the frequency band 0.04-0.09 Hz. This phase reproduces Rayleigh waves generated by earthquakes in the same frequency range. Arrival time of Rayleigh waves was picked at all the couples of stations to obtain the average group velocity along the path connecting the two stations. The picks were inverted in separated frequency bands to get group velocity maps then used to obtain an S wave velocity model. Penetration depth of the model ranges between 12 and 25 km, depending on the velocity values and on the depth of the interfaces, here associated to strong velocity gradients. We found a low-velocity anomaly in the region bounded by the two main faults that generated the 1980, M 6.9 Irpinia earthquake. A second anomaly was retrieved in the southeast part of the region and can be ascribed to a reminiscence of the Adria slab under the Apennine Chain.
Skyglow: a retrieval of the approximate radiant intensity function of ground-based light sources
NASA Astrophysics Data System (ADS)
Kocifaj, M.; Solano Lamphar, H. A.
2014-04-01
The angular distribution of the light emitted from a city is an important source of information about public lighting systems and it also plays a key role in modelling the skyglow. Usually, the upwardly directed radiation is characterized through a parametrized emission function - a semi-empirical approach as a reasonable approximation that allows for fast computations. However, theoretical or experimental retrievals of emission characteristics are extremely difficult to obtain because of both the complexity of radiative transfer methods and/or the lack of highly specialized measuring devices. Our research has been conducted with the specific objective to identify an efficient theoretical technique for retrieval of the emission pattern of ground-based light sources in order to determine the optimum values of the scaling parameters of the Garstang function. In particular, the input data involve the zenith luminance or radiance with horizontal illuminance or irradiance. Theoretical ratios of zenith luminance LV(0) to horizontal illuminance DV are calculated for a set of distances d that separate a hypothetical observer from the light source (a city or town). This approach is advantageous because inexpensive traditional equipment can be used to obtain the mean values of the Garstang parameters. Furthermore, it can also be applied to other parametrizable emission functions and to any measuring site, even one with a masked horizon.
Smart Polyacrylonitrile (PAN) Nanofibers with Thermal Energy Storage and Retrieval Functionality
NASA Astrophysics Data System (ADS)
Cherry, De'Andre James
Phase change materials (PCMs) are generally substances with a high heat of fusion in the process of solid to liquid phase change. The nature of PCMs make them efficient materials to store and retrieve large amounts of thermal energy. Presently, high efficiency thermal energy storage/retrieval in applications where flexibility and space saving are required, such as smart textiles, still remains as a challenge. In this study, lauric acid (LA) and myristic acid (MA) were combined to prepare a specific binary fatty acid eutectic (LA-MA) with a melting point near the operating body temperature of a human being and then encapsulated in polyacrylonitrile (PAN) nanofibers through the electrospinning technique. Functionalized PCM-enhanced PAN nanofibers containing LA-MA at 30%, 50%, 70% and 100% of the weight of the PAN were successfully synthesized. The morphological structures and thermal energy storage capacity of the PCM-enhanced PAN nanofibers were characterized by electron microscopy (EM) and differential scanning calorimetry (DSC). The novel PCM-enhanced PAN nanofibers maintained their cylindrical fiber morphology after multiple heating-cooling cycles and retained their latent heat storage functionality. Thus, it is envisioned that the prepared PCM-enhanced PAN nanofibers will find use in applications such as smart textiles where temperature regulation functionality is required.
NASA Astrophysics Data System (ADS)
Timashev, Serge F.; Panischev, Oleg Yu.; Polyakov, Yuriy S.; Demin, Sergey A.; Kaplan, Alexander Ya.
2012-02-01
We apply flicker-noise spectroscopy (FNS), a time series analysis method operating on structure functions and power spectrum estimates, to study the clinical electroencephalogram (EEG) signals recorded in children/adolescents (11 to 14 years of age) with diagnosed schizophrenia-spectrum symptoms at the National Center for Psychiatric Health (NCPH) of the Russian Academy of Medical Sciences. The EEG signals for these subjects were compared with the signals for a control sample of chronically depressed children/adolescents. The purpose of the study is to look for diagnostic signs of subjects' susceptibility to schizophrenia in the FNS parameters for specific electrodes and cross-correlations between the signals simultaneously measured at different points on the scalp. Our analysis of EEG signals from scalp-mounted electrodes at locations F3 and F4, which are symmetrically positioned in the left and right frontal areas of cerebral cortex, respectively, demonstrates an essential role of frequency-phase synchronization, a phenomenon representing specific correlations between the characteristic frequencies and phases of excitations in the brain. We introduce quantitative measures of frequency-phase synchronization and systematize the values of FNS parameters for the EEG data. The comparison of our results with the medical diagnoses for 84 subjects performed at NCPH makes it possible to group the EEG signals into 4 categories corresponding to different risk levels of subjects' susceptibility to schizophrenia. We suggest that the introduced quantitative characteristics and classification of cross-correlations may be used for the diagnosis of schizophrenia at the early stages of its development.
Wavelet-based cross-correlation analysis of structure scaling in turbulent clouds
NASA Astrophysics Data System (ADS)
Arshakian, Tigran G.; Ossenkopf, Volker
2016-01-01
Aims: We propose a statistical tool to compare the scaling behaviour of turbulence in pairs of molecular cloud maps. Using artificial maps with well-defined spatial properties, we calibrate the method and test its limitations to apply it ultimately to a set of observed maps. Methods: We develop the wavelet-based weighted cross-correlation (WWCC) method to study the relative contribution of structures of different sizes and their degree of correlation in two maps as a function of spatial scale, and the mutual displacement of structures in the molecular cloud maps. Results: We test the WWCC for circular structures having a single prominent scale and fractal structures showing a self-similar behaviour without prominent scales. Observational noise and a finite map size limit the scales on which the cross-correlation coefficients and displacement vectors can be reliably measured. For fractal maps containing many structures on all scales, the limitation from observational noise is negligible for signal-to-noise ratios ≳5. We propose an approach for the identification of correlated structures in the maps, which allows us to localize individual correlated structures and recognize their shapes and suggest a recipe for recovering enhanced scales in self-similar structures. The application of the WWCC to the observed line maps of the giant molecular cloud G 333 allows us to add specific scale information to the results obtained earlier using the principal component analysis. The WWCC confirms the chemical and excitation similarity of 13CO and C18O on all scales, but shows a deviation of HCN at scales of up to 7 pc. This can be interpreted as a chemical transition scale. The largest structures also show a systematic offset along the filament, probably due to a large-scale density gradient. Conclusions: The WWCC can compare correlated structures in different maps of molecular clouds identifying scales that represent structural changes, such as chemical and phase transitions
Wang, Zhuo; Bradesi, Sylvie; Charles, Jonathan R; Pang, Raina D; Maarek, Jean-Michel I; Mayer, Emeran A; Holschneider, Daniel P
2011-12-01
This study assessed functional brain activation in rats during expectation of visceral pain. Male rats were trained in step-down passive avoidance (PA) for 2 days. Upon stepping down from a platform, conditioned animals received noxious colorectal distension delivered through a colorectal balloon, whereas the balloon in control rats remained uninflated. On day 3, PA behavior was assessed while [(14)C]-iodoantipyrine was infused intravenously, followed by immediate euthanasia. Regional cerebral blood flow-related tissue radioactivity (rCBF) was analyzed by statistical parametric mapping using 3-dimensional brains reconstructed from autoradiographic brain slice images. Associated with retrieved PA behavior, conditioned rats compared with control subjects showed increases in rCBF in sensory (anterior insula, somatosensory cortex), limbic/paralimbic regions (anterior cingulate, prelimbic cortex, amygdala), all regions previously reported to show activation during acute visceral pain. Increases in rCBF were also noted in the dorsal hippocampus, nucleus accumbens, and caudate putamen, regions associated with retrieval of PA. Organization of the underlying brain network was further delineated by functional connectivity analysis. This revealed in conditioned rats a strongly and positively connected corticostriatal cluster (cingulate, prelimbic cortex, caudate putamen). The amygdala and cerebellar hemispheres formed another positively connected cluster, which was negatively connected with the corticostriatal cluster, suggesting corticolimbic modulation. Prelimbic cortex, nucleus accumbens, and anterior insula emerged in conditioned animals as hubs. Our results show that during retrieval of PA, brain areas implicated in PA expression as well as those implicated in acute visceral pain processing were recruited, in line with findings from human brain imaging studies on pain expectation. PMID:21944154
NASA Astrophysics Data System (ADS)
Schaff, D. P.; Waldhauser, F.; Richards, P. G.
2003-12-01
In recent years substantial advances in earthquake location have realized one to two orders of magnitude improvement over seismically broad areas due to the complementary benefits of waveform cross correlation and double-difference (DD) relative location in reducing both measurement and velocity model errors respectively. We report on results from applying these techniques on a massive scale to locally recorded seismic data across all of Northern California and to regional and teleseismic data in China. We are in the process of performing 2.5 billion correlation measurements on 280,000 events in Northern California from 1984 to present. The waveforms comprise the entire digital archive at the NCEDC recorded by 900 short period vertical component stations totaling 225 GB of data. We use a correlation detector instead of a correlation function to allow lags greater than 1/2 of the window length (typically 1 to 2 s) to be searched. At station JST, which includes 35,000 events from Bay area faults such as the Hayward, the Calaveras, and the San Andreas faults, 40% of the events have at least one other event with cross correlation coefficients (CC) greater than 0.9 (62% for CC > 0.8, 77% for CC > 0.7). These percentages of similar events are surprisingly high, but they include known areas of repeating events on the Calaveras and San Andreas Faults. For a station in Long Valley Caldera recording 72,000 events, the distribution is 18% for CC > 0.9, 43% for CC > 0.8, and 67% for CC > 0.7. A station including 20,000 events in the different tectonic settings of Mendocino Triple Junction and Geysers Geothermal Fields has 16% of the events with CC > 0.9 with at least one other event, 32% have CC > 0.8, and 49% have CC > 0.7. The lower numbers of correlated events observed at the latter two stations most likely reflect the different faulting processes that take place in these areas, compared to the (mostly) strike-slip events recorded at JST. To improve the accuracy of inter
NASA Astrophysics Data System (ADS)
Bao, Pengyu; Yuan, Mei; Dong, Shaopeng; Song, Hao; Xue, Jingfeng
2013-01-01
As one of the most critical tasks in structural damage monitoring, real-time fatigue crack monitoring plays an important role in improving the durability of a structure. In this paper, an online fatigue crack detection method is investigated based on the fiber Bragg grating (FBG) crack monitoring test bed (FBG-CMTB). Aiming at detecting ultrasonic spread in the structure when the crack is growing, the spectrum cross-correlation analysis algorithm and the cross-correlation function sequence are two methods that we will investigate in detail. Considering the singularity characteristic of the crack detecting signals when crack initiates, the wavelet packet analysis method is applied for feature extraction and two damage factors, crack initiation factor (CIF) and crack propagation factor (CPF), are constructed for damage initiation and propagation degree identification. To analyze the efficiency of this method, this paper presents the comparison tests based on different sensors array, FBG and acoustic emission (AE). Experimental results shows a satisfactory performance of the proposed spectrum cross-correlation analysis (SCCA) and damage feature factors on the fatigue crack online monitoring.
NASA Technical Reports Server (NTRS)
Cattrall, Christopher; Carder, Kendall L.; Gordon, Howard R.
2001-01-01
The single-scattering albedo and phase function of African mineral dust are retrieved from ground-based measurements of sky radiance collected in the Florida Keys. The retrieval algorithm employs the radiative transfer equation to solve by iteration for these two properties which best reproduce the observed sky radiance using an assumed aerosol vertical structure and measured aerosol optical depth. Thus, no assumptions regarding particle size, shape, or composition are required. The single-scattering albedo, presented at fourteen wavelengths between 380 and 870 nm, displays a spectral shape expected of iron-bearing minerals but is much higher than current dust models allow. This indicates the absorption of light by mineral dust is significantly overestimated in climate studies. Uncertainty in the retrieved albedo is less than 0.02 due to the small uncertainty in the solar-reflectance-based calibration (12.2%) method employed. The phase function retrieved at 860 nm is very robust under simulations of expected experimental errors, indicating retrieved phase functions at this wavelength may be confidently used to describe aerosol scattering characteristics. The phase function retrieved at 443 nm is very sensitive to expected experimental errors and should not be used to describe aerosol scattering. Radiative forcing by aerosol is the greatest source of uncertainty in current climate models. These results will help reduce uncertainty in the absorption of light by mineral dust. Assessment of the radiative impact of aerosol species is a key component to NASA's Earth System Enterprise.
NASA Astrophysics Data System (ADS)
Qian, Xi-Yuan; Liu, Ya-Min; Jiang, Zhi-Qiang; Podobnik, Boris; Zhou, Wei-Xing; Stanley, H. Eugene
2015-06-01
When common factors strongly influence two power-law cross-correlated time series recorded in complex natural or social systems, using detrended cross-correlation analysis (DCCA) without considering these common factors will bias the results. We use detrended partial cross-correlation analysis (DPXA) to uncover the intrinsic power-law cross correlations between two simultaneously recorded time series in the presence of nonstationarity after removing the effects of other time series acting as common forces. The DPXA method is a generalization of the detrended cross-correlation analysis that takes into account partial correlation analysis. We demonstrate the method by using bivariate fractional Brownian motions contaminated with a fractional Brownian motion. We find that the DPXA is able to recover the analytical cross Hurst indices, and thus the multiscale DPXA coefficients are a viable alternative to the conventional cross-correlation coefficient. We demonstrate the advantage of the DPXA coefficients over the DCCA coefficients by analyzing contaminated bivariate fractional Brownian motions. We calculate the DPXA coefficients and use them to extract the intrinsic cross correlation between crude oil and gold futures by taking into consideration the impact of the U.S. dollar index. We develop the multifractal DPXA (MF-DPXA) method in order to generalize the DPXA method and investigate multifractal time series. We analyze multifractal binomial measures masked with strong white noises and find that the MF-DPXA method quantifies the hidden multifractal nature while the multifractal DCCA method fails.
Qian, Xi-Yuan; Liu, Ya-Min; Jiang, Zhi-Qiang; Podobnik, Boris; Zhou, Wei-Xing; Stanley, H Eugene
2015-06-01
When common factors strongly influence two power-law cross-correlated time series recorded in complex natural or social systems, using detrended cross-correlation analysis (DCCA) without considering these common factors will bias the results. We use detrended partial cross-correlation analysis (DPXA) to uncover the intrinsic power-law cross correlations between two simultaneously recorded time series in the presence of nonstationarity after removing the effects of other time series acting as common forces. The DPXA method is a generalization of the detrended cross-correlation analysis that takes into account partial correlation analysis. We demonstrate the method by using bivariate fractional Brownian motions contaminated with a fractional Brownian motion. We find that the DPXA is able to recover the analytical cross Hurst indices, and thus the multiscale DPXA coefficients are a viable alternative to the conventional cross-correlation coefficient. We demonstrate the advantage of the DPXA coefficients over the DCCA coefficients by analyzing contaminated bivariate fractional Brownian motions. We calculate the DPXA coefficients and use them to extract the intrinsic cross correlation between crude oil and gold futures by taking into consideration the impact of the U.S. dollar index. We develop the multifractal DPXA (MF-DPXA) method in order to generalize the DPXA method and investigate multifractal time series. We analyze multifractal binomial measures masked with strong white noises and find that the MF-DPXA method quantifies the hidden multifractal nature while the multifractal DCCA method fails. PMID:26172763
X-ray cross-correlation analysis of the low-mass X-ray binary 4U 1636-53
NASA Astrophysics Data System (ADS)
Lei, Ya-Juan
2014-05-01
We analyze the cross-correlation function of the soft and hard X-rays of the atoll source 4U 1636-53 with RXTE data. The results show that the cross-correlations evolve along the different branches of the color-color diagram. At the lower left banana states, we have both positive and ambiguous correlations, and positive correlations are dominant for the lower banana and the upper banana states. The anti-correlation is detected at the top of the upper banana states. The cross-correlations of two atoll sources 4U 1735-44 and 4U 1608-52 have been studied in previous work, and the anti-correlations are detected at the lower left banana or the top of the upper banana states. Our results show that, in the 4U 1636-53, the distribution of the cross-correlations in the color-color diagram is similar to those of 4U 1735-44 and 4U 1608-52, and confirm further that the distribution of cross-correlations in color-color diagram could be correlated with the luminosity of the source.
NASA Astrophysics Data System (ADS)
Li, Junfeng; Xing, Da; Chen, Tongsheng; Liu, Jinfeng
2006-09-01
In this study, a novel method for the direct detection of GMP without amplified by the general method of PCR is firstly presented and proved by experiments. In our method, fluorescence correlation spectroscopy, cleaving nucleic acid by restriction endonuclease and two nucleic acid probe hybridization techniques are combined to distinguish the caulifiower mosaic virus (CaMV) 35S promoter and determine whether samples contain genetically modified components. The detection principle is as follows: firstly two restriction endonucleases FOKI and BsrDlare used to cleave the genomic DNA and the 169bp fragments of CaMV 35S promoter are retrieved; secondly, two nucleic acid probes labeled by Rhodamine Green and y5 dyes respectively hybridize with cleaved 169bp fragments of CaMV 35S promoter; thirdly, the hybridization products simultaneously with two dye-labeled probes are detected by fluorescence cross-correlation spectroscopy and GMP is distinguished. As the detection and analysis by FCS can be performed at the level of single molecule, there is no need for any type of amplification. Genetically modified tobaccos are measured by this method. The results indicate this method can detect CaMV 35S promoter of GMP exactly and the sensitivity can be down to 3.47X10 -10M. Because no any type of amplification is involved, this method can avoid the non-specffic amplification and false-positive problems of PCR, Due to its high-sensitivity, simplicity, reliability and little need for sample amounts, this method promises to be a highly effective detection method for GMP.
Electrical cross-correlation spectroscopy: measuring picoliter-per-minute flows in nanochannels.
Mathwig, Klaus; Mampallil, Dileep; Kang, Shuo; Lemay, Serge G
2012-09-14
We introduce all-electrical cross-correlation spectroscopy of molecular number fluctuations in nanofluidic channels. Our approach is based on a pair of nanogap electrochemical transducers located downstream from each other in the channel. When liquid is driven through this device, mesoscopic fluctuations in the local density of molecules are transported along the channel. We perform a time-of-flight measurement of these fluctuations by cross-correlating current-time traces obtained at the two detectors. Thereby we are able to detect ultralow liquid flow rates below 10 pL/min. This method constitutes the electrical equivalent of fluorescence cross-correlation spectroscopy. PMID:23005685
NASA Astrophysics Data System (ADS)
Ghosh, Dipak; Dutta, Srimonti; Chakraborty, Sayantan
2015-09-01
This paper reports a study on the cross-correlation between the electric bid price and SENSEX using Multifractal Detrended Cross-correlation Analysis (MF-DXA). MF-DXA is a very rigorous and robust technique for assessment of cross-correction between two non-linear time series. The study reveals power law cross-correlation between Market Clearing Price (MCP) and SENSEX which suggests that a change in the value of one can create a subjective change in the value of the other.
NASA Astrophysics Data System (ADS)
Krasnopolsky, V. M.; Breaker, L. C.; Gemmill, W. H.
1995-06-01
A single, extended-range neural network (SER NN) has been developed to model the transfer function for special sensor microwave imager (SSM/I) surface wind speed retrievals. Applied to data sets used in previous SSM/I wind speed retrieval studies, this algorithm yields a bias of 0.05 m/s and an rms difference of 1.65 m/s, compared to buoy observations. The accuracy of the SER NN for clear (low moisture) and cloudy (higher moisture/light rain) conditions equals the accuracy of NNs trained separately for each of these cases. A new moisture retrieval criterion based on a single, physically interpretable parameter, cloud liquid water, is proposed in conjunction with the SER NN. Using this retrieval criterion, (1) a moisture retrieval threshold for cloud liquid water of 0.5 kg/m2 was estimated, and (2) 40% of the data rejected by previous rain flags could be recovered. When the SER NN was trained using this retrieval criterion, a bias of 0.03 m/s and an rms value of 1.58 m/s were obtained and only 2% of the data were rejected. Also, a slight improvement in retrieval accuracy for cloudy conditions was achieved (˜10%) by including SSM/I brightness temperatures at 85 GHz. Finally, the limitations of NN algorithms are discussed in light of the present application.
Functional TCR retrieval from single antigen-specific human T cells reveals multiple novel epitopes.
Simon, Petra; Omokoko, Tana A; Breitkreuz, Andrea; Hebich, Lisa; Kreiter, Sebastian; Attig, Sebastian; Konur, Abdo; Britten, Cedrik M; Paret, Claudia; Dhaene, Karl; Türeci, Özlem; Sahin, Ugur
2014-12-01
The determination of the epitope specificity of disease-associated T-cell responses is relevant for the development of biomarkers and targeted immunotherapies against cancer, autoimmune, and infectious diseases. The lack of known T-cell epitopes and corresponding T-cell receptors (TCR) for novel antigens hinders the efficient development and monitoring of new therapies. We developed an integrated approach for the systematic retrieval and functional characterization of TCRs from single antigen-reactive T cells that includes the identification of epitope specificity. This is accomplished through the rapid cloning of full-length TCR-α and TCR-β chains directly from single antigen-specific CD8(+) or CD4(+) T lymphocytes. The functional validation of cloned TCRs is conducted using in vitro-transcribed RNA transfer for expression of TCRs in T cells and HLA molecules in antigen-presenting cells. This method avoids the work and bias associated with repetitive cycles of in vitro T-cell stimulation, and enables fast characterization of antigen-specific T-cell responses. We applied this strategy to viral and tumor-associated antigens (TAA), resulting in the retrieval of 56 unique functional antigen-specific TCRs from human CD8(+) and CD4(+) T cells (13 specific for CMV-pp65, 16 specific for the well-known TAA NY-ESO-1, and 27 for the novel TAA TPTE), which are directed against 39 different epitopes. The proof-of-concept studies with TAAs NY-ESO-1 and TPTE revealed multiple novel TCR specificities. Our approach enables the rational development of immunotherapy strategies by providing antigen-specific TCRs and immunogenic epitopes. PMID:25245536
Development of a New Class of Zero Cross Correlation Codes for Optical CDMA Systems
NASA Astrophysics Data System (ADS)
Rashidi, Che Bin Mohd; Aljunid, S. A.; Ghani, F.; Anuar, M. S.
2012-03-01
The paper presents a method for the development of a new class of zero cross correlation optical code for Optical Code Division Multiple Access (OCDMA) system using
NASA Astrophysics Data System (ADS)
Dong, Keqiang; Gao, You; Jing, Liming
2015-02-01
The presence of cross-correlation in complex systems has long been noted and studied in a broad range of physical applications. We here focus on an aero-engine system as an example of a complex system. By applying the detrended cross-correlation (DCCA) coefficient method to aero-engine time series, we investigate the effects of the data length and the time scale on the detrended cross-correlation coefficients ρ DCCA ( T, s). We then show, for a twin-engine aircraft, that the engine fuel flow time series derived from the left engine and the right engine exhibit much stronger cross-correlations than the engine exhaust-gas temperature series derived from the left engine and the right engine do.
NASA Astrophysics Data System (ADS)
Yin, Yi; Shang, Pengjian
2015-04-01
In this paper, we propose multiscale detrended cross-correlation analysis (MSDCCA) to detect the long-range power-law cross-correlation of considered signals in the presence of nonstationarity. For improving the performance and getting better robustness, we further introduce the empirical mode decomposition (EMD) to eliminate the noise effects and propose MSDCCA method combined with EMD, which is called MS-EDXA method, then systematically investigate the multiscale cross-correlation structure of the real traffic signals. We apply the MSDCCA and MS-EDXA methods to study the cross-correlations in three situations: velocity and volume on one lane, velocities on the present and the next moment and velocities on the adjacent lanes, and further compare their spectrums respectively. When the difference between the spectrums of MSDCCA and MS-EDXA becomes unobvious, there is a crossover which denotes the turning point of difference. The crossover results from the competition between the noise effects in the original signals and the intrinsic fluctuation of traffic signals and divides the plot of spectrums into two regions. In all the three case, MS-EDXA method makes the average of local scaling exponents increased and the standard deviation decreased and provides a relative stable persistent scaling cross-correlated behavior which gets the analysis more precise and more robust and improves the performance after noises being removed. Applying MS-EDXA method avoids the inaccurate characteristics of multiscale cross-correlation structure at the short scale including the spectrum minimum, the range for the spectrum fluctuation and general trend, which are caused by the noise in the original signals. We get the conclusions that the traffic velocity and volume are long-range cross-correlated, which is accordant to their actual evolution, while velocities on the present and the next moment and velocities on adjacent lanes reflect the strong cross-correlations both in temporal and
Multifractal Detrended Cross-Correlation Analysis for Large-Scale Warehouse-Out Behaviors
NASA Astrophysics Data System (ADS)
Yao, Can-Zhong; Lin, Ji-Nan; Zheng, Xu-Zhou
2015-09-01
Based on cross-correlation algorithm, we analyze the correlation property of warehouse-out quantity of different warehouses, respectively, and different products of each warehouse. Our study identifies that significant cross-correlation relationship for warehouse-out quantity exists among different warehouses and different products of a warehouse. Further, we take multifractal detrended cross-correlation analysis for warehouse-out quantity among different warehouses and different products of a warehouse. The results show that for the warehouse-out behaviors of total amount, different warehouses and different products of a warehouse significantly follow multifractal property. Specifically for each warehouse, the coupling relationships of rebar and wire rod reveal long-term memory characteristics, no matter for large fluctuation or small one. The cross-correlation effect on long-range memory property among warehouses probably has less to do with product types,and the long-term memory of YZ warehouse is greater than others especially in total amount and wire rod product. Finally, we shuffle and surrogate data to explore the source of multifractal cross-correlation property in logistics system. Taking the total amount of warehouse-out quantity as example, we confirm that the fat-tail distribution of warehouse-out quantity sequences is the main factor for multifractal cross-correlation. Through comparing the performance of the multifractal detrended cross-correlation analysis (MF-DCCA), centered multifractal detrending moving average cross-correlation analysis (MF-X-DMA) algorithms, the forward and backward MF-X-DMA algorithms, we find that the forward and backward MF-X-DMA algorithms exhibit a better performance than the other ones.
NASA Astrophysics Data System (ADS)
Voigt, Ingmar; Vitanovski, Dime; Ionasec, Razvan I.; Tsymal, Alexey; Georgescu, Bogdan; Zhou, Shaohua K.; Huber, Martin; Navab, Nassir; Hornegger, Joachim; Comaniciu, Dorin
2010-03-01
Disorders of the heart valves constitute a considerable health problem and often require surgical intervention. Recently various approaches were published seeking to overcome the shortcomings of current clinical practice,that still relies on manually performed measurements for performance assessment. Clinical decisions are still based on generic information from clinical guidelines and publications and personal experience of clinicians. We present a framework for retrieval and decision support using learning based discriminative distance functions and visualization of patient similarity with relative neighborhood graphsbased on shape and derived features. We considered two learning based techniques, namely learning from equivalence constraints and the intrinsic Random Forest distance. The generic approach enables for learning arbitrary user-defined concepts of similarity depending on the application. This is demonstrated with the proposed applications, including automated diagnosis and interventional suitability classification, where classification rates of up to 88.9% and 85.9% could be observed on a set of valve models from 288 and 102 patients respectively.
Fault zone reverberations from cross-correlations of earthquake waveforms and seismic noise
NASA Astrophysics Data System (ADS)
Hillers, Gregor; Campillo, Michel
2016-03-01
Seismic wavefields interact with low-velocity fault damage zones. Waveforms of ballistic fault zone head waves, trapped waves, reflected waves and signatures of trapped noise can provide important information on structural and mechanical fault zone properties. Here we extend the class of observable fault zone waves and reconstruct in-fault reverberations or multiples in a strike-slip faulting environment. Manifestations of the reverberations are significant, consistent wave fronts in the coda of cross-correlation functions that are obtained from scattered earthquake waveforms and seismic noise recorded by a linear fault zone array. The physical reconstruction of Green's functions is evident from the high similarity between the signals obtained from the two different scattered wavefields. Modal partitioning of the reverberation wavefield can be tuned using different data normalization techniques. The results imply that fault zones create their own ambiance, and that the here reconstructed reverberations are a key seismic signature of wear zones. Using synthetic waveform modelling we show that reverberations can be used for the imaging of structural units by estimating the location, extend and magnitude of lateral velocity contrasts. The robust reconstruction of the reverberations from noise records suggests the possibility to resolve the response of the damage zone material to various external and internal loading mechanisms.
Local-scale cross-correlation of seismic noise from the Calico fault experiment
NASA Astrophysics Data System (ADS)
Zhang, Jian; Gerstoft, Peter
2014-06-01
Most studies of seismic noise cross-correlation (NCC) have focused on regional/continental scale imaging using empirical surface-wave Green's functions extracted from primary (0.05-0.08 Hz) and secondary (0.1-0.16 Hz) microseisms. In this work, we present the NCC results at higher frequencies (>0.5 Hz) from 6 months seismic noise recorded by a local array (~4 km aperture) deployed along the Calico fault in the Mojave Desert, California. Both fast and slow propagating waves are observed from the NCC record-sections. We compare the NCCs from sensor pairs that share a common sensor with the records of a borehole shot located very close to this common sensor. The result shows a good match of the slow surface-wave arrivals, indicating that the NCC method is able to recover unbiased surface-wave Green's functions at local scales. The strong body-wave NCC component is caused by the P waves generated offshore California. Along a SW-NE profile across the fault, we observe apparent P-wave arrivals and their reflections, which can be explained by a low-velocity-zone (LVZ) along the Calico fault. We calculate the LVZ width to be ~ 2.3 km, and the P-wave velocity reduction within the LVZ to be ~35 %. These estimates are consistent with other evidence for a relatively wide LVZ along the Calico fault.
NASA Astrophysics Data System (ADS)
Zhang, Hui; Wang, Deqing; Wu, Wenjun; Hu, Hongping
2012-11-01
In today's business environment, enterprises are increasingly under pressure to process the vast amount of data produced everyday within enterprises. One method is to focus on the business intelligence (BI) applications and increasing the commercial added-value through such business analytics activities. Term weighting scheme, which has been used to convert the documents as vectors in the term space, is a vital task in enterprise Information Retrieval (IR), text categorisation, text analytics, etc. When determining term weight in a document, the traditional TF-IDF scheme sets weight value for the term considering only its occurrence frequency within the document and in the entire set of documents, which leads to some meaningful terms that cannot get the appropriate weight. In this article, we propose a new term weighting scheme called Term Frequency - Function of Document Frequency (TF-FDF) to address this issue. Instead of using monotonically decreasing function such as Inverse Document Frequency, FDF presents a convex function that dynamically adjusts weights according to the significance of the words in a document set. This function can be manually tuned based on the distribution of the most meaningful words which semantically represent the document set. Our experiments show that the TF-FDF can achieve higher value of Normalised Discounted Cumulative Gain in IR than that of TF-IDF and its variants, and improving the accuracy of relevance ranking of the IR results.
Baldissarro, Eleonora; Aquilani, Roberto; Boschi, Federica; Baiardi, Paola; Iadarola, Paolo; Fumagalli, Marco; Pasini, Evasio; Verri, Manuela; Dossena, Maurizia; Gambino, Arianna; Cammisuli, Sharon; Viglio, Simona
2016-01-01
It is not known whether postsurgery systemic inflammation and plasma amino acid abnormalities are still present during rehabilitation of individuals after elective hip arthroplasty (EHA). Sixty subjects (36 females; age 66.58 ± 8.37 years) were randomized to receive 14-day oral EAAs (8 g/day) or a placebo (maltodextrin). At admission to and discharge from the rehabilitation center, serum C-reactive protein (CRP) and venous plasma amino acid concentrations were determined. Post-EHA hip function was evaluated by Harris hip score (HHS) test. Ten matched healthy subjects served as controls. At baseline, all patients had high CRP levels, considerable reduction in several amino acids, and severely reduced hip function (HHS 40.78 ± 2.70 scores). After treatment, inflammation decreased both in the EAA group and in the placebo group. Only EAA patients significantly improved their levels of glycine, alanine, tyrosine, and total amino acids. In addition, they enhanced the rate of hip function recovery (HHS) (from baseline 41.8 ± 1.15 to 76.37 ± 6.6 versus baseline 39.78 ± 4.89 to 70.0 ± 7.1 in placebo one; p = 0.006). The study documents the persistence of inflammation and plasma amino acid abnormalities in post-EHA rehabilitation phase. EAAs enhance hip function retrieval and improve plasma amino acid abnormalities. PMID:27110573
Monje, Alberto; González-García, Raúl; Fernández-Calderón, María Coronada; Hierro-Oliva, Margarita; González-Martín, María Luisa; Del Amo, Fernando Suarez-Lopez; Galindo-Moreno, Pablo; Wang, Hom-Lay; Monje, Florencio
2016-02-01
The aim of the present study was to report the main topographical and chemical changes of a failing 18-year in function retrieved acid-etching implant in the micro- and nanoscales. A partially edentulous 45 year old rehabilitated with a dental implant at 18 years of age exhibited mobility. After careful examination, a 3.25 × 13-mm press-fit dental implant was retrieved. Scanning electron microscope (SEM) analysis was carried out to study topographical changes of the retrieved implant compared with an unused implant with similar topographical characteristics. Moreover, X-ray photoelectron spectroscopy (XPS) analysis was used to study the surface composition of the retrieved failing implant. Clear changes related to the dual dioxide layer are present as visible in ≥×500 magnification. In addition, it was found that, for the retrieved implant, the surface composition consisted mainly of Ti2p, O1s, C1s, and Al2p. Also, a meaningful decrease of N and C was noticed, whereas the peaks of Ti2p, Al2p, and O1s increased when analyzing deeper (up to ×2000s) in the sample. It was shown that the superficial surface of a retrieved press-fit dual acid-etched implant 18 years after placement is impaired. However, the causes and consequences for these changes cannot be determined. PMID:25642739
Receiver structure from teleseisms: Autocorrelation and cross correlation
NASA Astrophysics Data System (ADS)
Sun, Weijia; Kennett, B. L. N.
2016-06-01
We present a way of characterizing the structure beneath a seismic station, by exploiting stacked correlograms of three-component records from teleseismic events. This seismic daylight imaging approach exploits the extraction of reflection and conversion information from teleseismic coda via tensor autocorrelation. The approach is illustrated for a number of Australian stations in a variety of tectonic environments using hundreds of teleseismic events, to extract P and S reflectivity and converted Ps and Sp information. The results show a very good agreement with prior knowledge across Australia. Compared with the classical receiver function, the broader-frequency band of 0.5-4.0 Hz provides additional information on finer-scale structure.
Retrieval of Garstang's emission function from all-sky camera images
NASA Astrophysics Data System (ADS)
Kocifaj, Miroslav; Solano Lamphar, Héctor Antonio; Kundracik, František
2015-10-01
The emission function from ground-based light sources predetermines the skyglow features to a large extent, while most mathematical models that are used to predict the night sky brightness require the information on this function. The radiant intensity distribution on a clear sky is experimentally determined as a function of zenith angle using the theoretical approach published only recently in MNRAS, 439, 3405-3413. We have made the experiments in two localities in Slovakia and Mexico by means of two digital single lens reflex professional cameras operating with different lenses that limit the system's field-of-view to either 180º or 167º. The purpose of using two cameras was to identify variances between two different apertures. Images are taken at different distances from an artificial light source (a city) with intention to determine the ratio of zenith radiance relative to horizontal irradiance. Subsequently, the information on the fraction of the light radiated directly into the upward hemisphere (F) is extracted. The results show that inexpensive devices can properly identify the upward emissions with adequate reliability as long as the clear sky radiance distribution is dominated by a largest ground-based light source. Highly unstable turbidity conditions can also make the parameter F difficult to find or even impossible to retrieve. The measurements at low elevation angles should be avoided due to a potentially parasitic effect of direct light emissions from luminaires surrounding the measuring site.
Research on the measurement of bubble velocity based on cross-correlation algorithm
NASA Astrophysics Data System (ADS)
Chen, Min; He, Junhua; Chen, Liangyi
2006-06-01
Cross-correlation algorithm is based on information theory and stochastic process theory. It has been widely used in many research fields, such as, medical ultrasound, ocean engineering, signal detection, modal parameters under ambient excitation, etc., but its applications in research of bubble curtains are seldom seen in domestic released periodicals, so our work is attempting to use cross-correlation algorithm. Through computing the velocity vector of bubble curtains, the bubble movement character can be known, i.e. the details of the bubble curtains can also be known. After comparing the differences between it and Doppler method, the cross-correlation algorithm has been applied to the measurement of bubble curtains parameters from a new aspect. The He-Ne laser and high-speed CCD camera are used to acquire the images of dancing bubbles, the velocities of bubbles are computed from image post-processed. Through improving conventional cross-correlation algorithm commonly used for analysis of flow field, the Fast Fourier Transform (FFT) has been used to implement the cross-correlation algorithm rapidly. In order to enhance the computing accuracy, Gaussian curve fitting is used to modify the correlation peak location and the fitting equations are listed, so the bubbles displacement with subpixel accuracy is obtained. Noises are stochastically added from hardware when acquiring images and the cross-correlation algorithm may also introduce errors. The character of velocity vectors result can be entirely wrong with ambient vectors, so they must be corrected. In order to calibrate the cross-correlation algorithm, images with universal displacement are used to validate its feasibility and reliability. The algorithm is applied to the computation of parameters in bubble curtains, yielding the vector graph of bubble motion. The algorithm is expected to be a valuable tool in acquiring the real-time velocity information in bubble curtains.
Temporal Variability of Surface Solar Irradiance as a Function of Satellite-retrieved Cloud
NASA Astrophysics Data System (ADS)
Hinkelman, L. M.; Sengupta, M.; Habte, A.
2014-12-01
Studies of the impact of renewables on the electrical transmission grid are needed as power production from renewable energy resources increases. These studies require estimates of high temporal and spatial resolution power output under various scenarios. Satellite-based solar resource estimates are the best source of long-term irradiance data but are generally of lower temporal and spatial resolution than needed and thus require downscaling. Likewise, weather forecast models cannot provide high spatial or temporal irradiance predictions. Downscaling requires information about solar irradiance variability in both space and time, which is primarily a function of cloud properties. In this study, we analyze the relationships between the temporal variability of surface solar irradiance and satellite-based cloud properties. One-minute resolution surface solar irradiance data were obtained from the National Oceanic and Atmospheric Administration's Surface Radiation (SURFRAD) network. These sites are distributed across the United States to cover a range of meteorological conditions. Cloud information at a nominal 4 km resolution and half hour intervals was retrieved from NOAA's Geostationary Operation Environmental Satellites (GOES). The retrieved cloud properties were then used to select and composite irradiance data from the measurement sites in order to identify the cloud properties that exert the strongest control over short-term irradiance variability. The irradiance variability was characterized using statistics of both the irradiances themselves and of irradiance differences computed for short time scales (minutes). The relationships derived using this method will be presented, comparing and contrasting the statistics computed for the different cloud properties. The implications for downscaling irradiance from satellites or forecast models will also be discussed.
Experimental cross-correlation nitrogen Q-branch CARS thermometry in a spark ignition engine
NASA Astrophysics Data System (ADS)
Lockett, R. D.; Ball, D.; Robertson, G. N.
2013-07-01
A purely experimental technique was employed to derive temperatures from nitrogen Q-branch Coherent Anti-Stokes Raman Scattering (CARS) spectra, obtained in a high pressure, high temperature environment (spark ignition Otto engine). This was in order to obviate any errors arising from deficiencies in the spectral scaling laws which are commonly used to represent nitrogen Q-branch CARS spectra at high pressure. The spectra obtained in the engine were compared with spectra obtained in a calibrated high pressure, high temperature cell, using direct cross-correlation in place of the minimisation of sums of squares of residuals. The technique is demonstrated through the measurement of air temperature as a function of crankshaft angle inside the cylinder of a motored single-cylinder Ricardo E6 research engine, followed by the measurement of fuel-air mixture temperatures obtained during the compression stroke in a knocking Ricardo E6 engine. A standard CARS programme (SANDIA's CARSFIT) was employed to calibrate the altered non-resonant background contribution to the CARS spectra that was caused by the alteration to the mole fraction of nitrogen in the unburned fuel-air mixture. The compression temperature profiles were extrapolated in order to predict the auto-ignition temperatures.
Dispersion Curve Analyis with Ambient Noise Cross Correlation in Case of Onshore-Offshore Networks
NASA Astrophysics Data System (ADS)
Schmidt, Andreas
2010-05-01
The determination of surface wave Green's functions between two seismic stations by cross correlating seismic noise has become a promising approach to tomography. In this study we emphasise the special application of this method for the case of onshore-offshore networks. The seismic records of 65 three-component land stations (Guralp, Mark, STS-2) and 22 ocean bottom seismographs (OBS, only Hydrophone component) are available for this study. The EGELADOS network was deployed in the southern Aegean from October 2005 to April 2007. Dispersion analysis of resulting seismograms provides group velocity curves which give information about the crustal and uppermost mantle structure that cannot be obtained from earthquake data. For the Aegean region considerable regional differences in crustal structure can be expected. Particular attention is paid to the determination and analysis of dispersive signals in case of Ocean Bottom Seismographs and hydrophones. At land stations we extract clear dispersion curves but OBS seismograms show multiple signals of different velocities. The frequency range and characteristics are dependent on surface structures between the two stations as well as their location. Ray path profiles between two hydrophones with no elevation have a strong acoustic phase with a faint surface wave signal.
Measuring time-of-flight in an ultrasonic LPS system using generalized cross-correlation.
Villladangos, José Manuel; Ureña, Jesús; García, Juan Jesús; Mazo, Manuel; Hernández, Alvaro; Jiménez, Ana; Ruíz, Daniel; De Marziani, Carlos
2011-01-01
In this article, a time-of-flight detection technique in the frequency domain is described for an ultrasonic local positioning system (LPS) based on encoded beacons. Beacon transmissions have been synchronized and become simultaneous by means of the DS-CDMA (direct-sequence code Division multiple access) technique. Every beacon has been associated to a 255-bit Kasami code. The detection of signal arrival instant at the receiver, from which the distance to each beacon can be obtained, is based on the application of the generalized cross-correlation (GCC), by using the cross-spectral density between the received signal and the sequence to be detected. Prior filtering to enhance the frequency components around the carrier frequency (40 kHz) has improved estimations when obtaining the correlation function maximum, which implies an improvement in distance measurement precision. Positioning has been achieved by using hyperbolic trilateration, based on the time differences of arrival (TDOA) between a reference beacon and the others. PMID:22346645
Fluorescence cross-correlation spectroscopy for time dependent flows: a numerical investigation
NASA Astrophysics Data System (ADS)
Ceffa, Nicolo'G.; Pozzi, Paolo; Bouzin, Margaux; Marquezin, Cassia A.; Sironi, Laura; D'Alfonso, Laura; Collini, Maddalena; Chirico, Giuseppe
2015-03-01
We have previously addressed experimentally blood fluidodynamics in microcapillaries by coupling optical microscopy to pixelated detection. By computing the Cross-Correlation Function (CCF) of signals coming from pixels at a distance along the flow we obtained information on the flow speed and direction. The extension of these experiments to more complex systems with high branching of capillaries and/or inverted flows needs a theoretical investigation that we present here. We focus first on straight capillaries and harmonic flows between a minimum Vmin ≠ 0 and a maximum Vmax flow speed. The CCF shows multiple peaks at lag times that correspond closely to the maximum and minimum flow speeds. The general analytical expression of the CCF is given, the position of its maxima are discussed by means of geometrical considerations and numerical analysis and an experimental validation are presented. The second case that we study is the flow in the branches of a y-shaped junction in a microcapillary. By simply modeling the branching in laminar flow (low Reynold numbers) and assuming a smooth transition of speeds along the branches we derive a simple numerical model to compute the trajectories of micro-beads. We estimate the flow speed in the branches by computing the CCFs between linear regions of interest set perpendicular to the axes of the branches.
Two-dimensional structure from random multiparticle X-ray scattering images using cross-correlations
NASA Astrophysics Data System (ADS)
Pedrini, B.; Menzel, A.; Guizar-Sicairos, M.; Guzenko, V. A.; Gorelick, S.; David, C.; Patterson, B. D.; Abela, R.
2013-04-01
Knowledge of the structure of biological macromolecules, especially in their native environment, is crucial because of the close structure-function relationship. X-ray small-angle scattering is used to determine the shape of particles in solution, but the achievable resolution is limited owing to averaging over particle orientations. In 1977, Kam proposed to obtain additional structural information from the cross-correlation of the scattering intensities. Here we develop the method in two dimensions, and give a procedure by which the single-particle diffraction pattern is extracted in a model-independent way from the correlations. We demonstrate its application to a large set of synchrotron X-ray scattering images on ensembles of identical, randomly oriented particles of 350 or 200 nm in size. The obtained 15 nm resolution in the reconstructed shape is independent of the number of scatterers. The results are discussed in view of proposed ‘snapshot’ scattering by molecules in the liquid phase at X-ray free-electron lasers.
Pedrini, B; Menzel, A; Guizar-Sicairos, M; Guzenko, V A; Gorelick, S; David, C; Patterson, B D; Abela, R
2013-01-01
Knowledge of the structure of biological macromolecules, especially in their native environment, is crucial because of the close structure-function relationship. X-ray small-angle scattering is used to determine the shape of particles in solution, but the achievable resolution is limited owing to averaging over particle orientations. In 1977, Kam proposed to obtain additional structural information from the cross-correlation of the scattering intensities. Here we develop the method in two dimensions, and give a procedure by which the single-particle diffraction pattern is extracted in a model-independent way from the correlations. We demonstrate its application to a large set of synchrotron X-ray scattering images on ensembles of identical, randomly oriented particles of 350 or 200 nm in size. The obtained 15 nm resolution in the reconstructed shape is independent of the number of scatterers. The results are discussed in view of proposed 'snapshot' scattering by molecules in the liquid phase at X-ray free-electron lasers. PMID:23552062
Pipeline Implementation of Real Time Event Cross Correlation for Nuclear Treaty Monitoring
NASA Astrophysics Data System (ADS)
Junek, W. N.; Wehlen, J. A., III
2014-12-01
The United States National Data Center (US NDC) is responsible for monitoring international compliance to nuclear test ban treaties. This mission is performed through real time acquisition, processing, and evaluation of data acquired by a global network of seismic, hydroacoustic, and infrasonic sensors. Automatic and human reviewed event solutions are stored in a data warehouse which contains over 15 years of alphanumeric information and waveform data. A significant effort is underway to employ the data warehouse in real time processing to improve the quality of automatic event solutions, reduce analyst burden, and supply decision makers with information regarding relevant historic events. To this end, the US NDC processing pipeline has been modified to automatically recognize events built in the past. Event similarity information and the most relevant historic solution are passed to the human analyst to assist their evaluation of automatically formed events. This is achieved through real time cross correlation of selected seismograms from automatically formed events against those stored in the data warehouse. Historic events used in correlation analysis are selected based on a set of user defined parameters, which are tuned to maintain pipeline timeliness requirements. Software architecture and database infrastructure were modified using a multithreaded design for increased processing speed, database connection pools for parallel queries, and Oracle spatial indexing to enhance query efficiency. This functionality allows the human analyst to spend more time studying anomalous events and less time rebuilding routine events.
Sensitivity of power functions to aggregation: Bias and uncertainty in radar rainfall retrieval
NASA Astrophysics Data System (ADS)
Sassi, M. G.; Leijnse, H.; Uijlenhoet, R.
2014-10-01
Rainfall retrieval using weather radar relies on power functions between radar reflectivity Z and rain rate R. The nonlinear nature of these relations complicates the comparison of rainfall estimates employing reflectivities measured at different scales. Transforming Z into R using relations that have been derived for other scales results in a bias and added uncertainty. We investigate the sensitivity of Z-R relations to spatial and temporal aggregation using high-resolution reflectivity fields for five rainfall events. Existing Z-R relations were employed to investigate the behavior of aggregated Z-R relations with scale, the aggregation bias, and the variability of the estimated rain rate. The prefactor and the exponent of aggregated Z-R relations systematically diverge with scale, showing a break that is event-dependent in the temporal domain and nearly constant in space. The systematic error associated with the aggregation bias at a given scale can become of the same order as the corresponding random error associated with intermittent sampling. The bias can be constrained by including information about the variability of Z within a certain scale of aggregation, and is largely captured by simple functions of the coefficient of variation of Z. Several descriptors of spatial and temporal variability of the reflectivity field are presented, to establish the links between variability descriptors and resulting aggregation bias. Prefactors in Z-R relations can be related to multifractal properties of the rainfall field. We find evidence of scaling breaks in the structural analysis of spatial rainfall with aggregation.
Cross-correlations between West Texas Intermediate crude oil and the stock markets of the BRIC
NASA Astrophysics Data System (ADS)
Ma, Feng; Wei, Yu; Huang, Dengshi; Zhao, Lin
2013-11-01
In this paper, we investigate the cross-correlation properties between West Texas Intermediate crude oil and the stock markets of the BRIC. We use not only the qualitative analysis of the cross-correlation test, but also take the quantitative analysis of the MF-DXA, confirming the cross-correlation relationship between West Texas Intermediate crude oil and the stock markets of the BRIC (Brazil, Russia, India and China) respectively, which have strongly multifractal features, and the cross-correlations are more strongly multifractal in the short term than in the long term. Furthermore, based on the multifractal spectrum, we also find the multifractality strength between the crude oil WTI and Chinese stock market is stronger than the multifractality strength of other pairs. Based on the Iraq war (Mar 20, 2003) and the Financial crisis in 2008, we divide sample period into four segments to research the degree of the multifractal (ΔH) and the market efficiency (and the risk). Finally, we employ the technique of the rolling window to calculate the time-varying EI (efficiency index) and dependent on the EI, we can easily observe the change of stock markets. Furthermore, we explore the relationship between bivariate cross-correlation exponents (Hxy(q)) and the generalized Hurst exponents.
NASA Astrophysics Data System (ADS)
Boué, Pierre; Roux, Philippe; Campillo, Michel; Briand, Xavier
2014-01-01
Continuous recordings of ambient seismic noise across large seismic arrays allows a new type of processing using the cross-correlation technique on broadband data. We propose to apply double beamforming (DBF) to cross correlations to extract a particular wave component of the reconstructed signals. We focus here on the extraction of the surface waves to measure phase velocity variations with great accuracy. DBF acts as a spatial filter between two distant subarrays after cross correlation of the wavefield between each single receiver pair. During the DBF process, horizontal slowness and azimuth are used to select the wavefront on both subarray sides. DBF increases the signal-to-noise ratio, which improves the extraction of the dispersive wave packets. This combination of cross correlation and DBF is used on the Transportable Array (USArray), for the central U.S. region. A standard model of surface wave propagation is constructed from a combination of the DBF and cross correlations at different offsets and for different frequency bands. The perturbation (phase shift) between each beam and the standard model is inverted. High-resolution maps of the phase velocity of Rayleigh and Love waves are then constructed. Finally, the addition of azimuthal information provided by DBF is discussed, to construct curved rays that replace the classical great-circle path assumption.
Cross-correlation measurements with the EJ-299-33 plastic scintillator
NASA Astrophysics Data System (ADS)
Bourne, Mark M.; Whaley, Jeff; Dolan, Jennifer L.; Polack, John K.; Flaska, Marek; Clarke, Shaun D.; Tomanin, Alice; Peerani, Paolo; Pozzi, Sara A.
2015-06-01
New organic-plastic scintillation compositions have demonstrated pulse-shape discrimination (PSD) of neutrons and gamma rays. We present cross-correlation measurements of 252Cf and mixed uranium-plutonium oxide (MOX) with the EJ-299-33 plastic scintillator. For comparison, equivalent measurements were performed with an EJ-309 liquid scintillator. Offline, digital PSD was applied to each detector. These measurements show that EJ-299-33 sacrifices a factor of 5 in neutron-neutron efficiency relative to EJ-309, but could still utilize the difference in neutron-neutron efficiency and neutron single-to-double ratio to distinguish 252Cf from MOX. These measurements were modeled with MCNPX-PoliMi, and MPPost was used to convert the detailed collision history into simulated cross-correlation distributions. MCNPX-PoliMi predicted the measured 252Cf cross-correlation distribution for EJ-309 to within 10%. Greater photon uncertainty in the MOX sample led to larger discrepancy in the simulated MOX cross-correlation distribution. The modeled EJ-299-33 plastic also gives reasonable agreement with measured cross-correlation distributions, although the MCNPX-PoliMi model appears to under-predict the neutron detection efficiency.
Children's Word Recognition and Retrieval as a Function of Reading Ability.
ERIC Educational Resources Information Center
Hackbarth, Steven L.; Rundle, Sarah A.
This study investigated fourth-grade children's ability to identify and retrieve tachistoscopically presented words in relation to their rated ability on both reading speed and comprehension. No significant difference was found between fast and slow readers in either recognition or retrieval. High comprehension children had significantly lower…
The role of executive function in children's source monitoring with varying retrieval strategies
Earhart, Becky; Roberts, Kim P.
2014-01-01
Previous research on the relationship between executive function and source monitoring in young children has been inconclusive, with studies finding conflicting results about whether working memory and inhibitory control are related to source-monitoring ability. In this study, the role of working memory and inhibitory control in recognition memory and source monitoring with two different retrieval strategies were examined. Children (N = 263) aged 4–8 participated in science activities with two sources. They were later given a recognition and source-monitoring test, and completed measures of working memory and inhibitory control. During the source-monitoring test, half of the participants were asked about sources serially (one after the other) whereas the other half of the children were asked about sources in parallel (considering both sources simultaneously). Results demonstrated that working memory was a predictor of source-monitoring accuracy in both conditions, but inhibitory control was only related to source accuracy in the parallel condition. When age was controlled these relationships were no longer significant, suggesting that a more general cognitive development factor is a stronger predictor of source monitoring than executive function alone. Interestingly, the children aged 4–6 years made more accurate source decisions in the parallel condition than in the serial condition. The older children (aged 7–8) were overall more accurate than the younger children, and their accuracy did not differ as a function of interview condition. Suggestions are provided to guide further research in this area that will clarify the diverse results of previous studies examining whether executive function is a cognitive prerequisite for effective source monitoring. PMID:24847302
Cross-correlations of X-ray and optically selected clusters with near-infrared and optical galaxies
NASA Astrophysics Data System (ADS)
Sánchez, Ariel G.; Lambas, Diego G.; Böhringer, Hans; Schuecker, Peter
2005-10-01
We compute the real-space cluster-galaxy cross-correlation ξcg(r) using the ROSAT-ESO Flux Limited X-ray (REFLEX) cluster survey, a group catalogue (2dFGGC) constructed from the final version of the Two-degree Field Galaxy Redshift Survey (2dFGRS), and galaxies extracted from the Two Micron All Sky Survey (2MASS) and Automated Plate Measurement (APM) surveys. This first detailed calculation of the cross-correlation for X-ray clusters and groups is consistent with previous works and shows that ξcg(r) cannot be described by a single power law. We analyse the clustering dependence on the cluster X-ray luminosity LX and virial mass Mvir thresholds as well as on the galaxy limiting magnitude. We also make a comparison of our results with those obtained for the halo-mass cross-correlation function in a ΛCDM N-body simulation to infer the scale dependence of galaxy bias around clusters. Our results indicate that the distribution of galaxies shows a significant anti-bias at highly non-linear small cluster-centric distances, bcg(r) ~= 0.7, irrespective of the group/cluster virial mass or X-ray luminosity and galaxy characteristics. This shows that a generic process controls the efficiency of galaxy formation and evolution in high-density regions. On larger scales, bcg(r) rises to a nearly constant value of the order of unity, the transition occurring at approximately 2 h-1 Mpc for 2dF groups and 5 h-1 Mpc for REFLEX clusters.
NASA Astrophysics Data System (ADS)
Choi, A.; Heymans, C.; Blake, C.; Hildebrandt, H.; Duncan, C. A. J.; Erben, T.; Nakajima, R.; Van Waerbeke, L.; Viola, M.
2016-09-01
We determine the accuracy of galaxy redshift distributions as estimated from photometric redshift probability distributions p(z). Our method utilises measurements of the angular cross-correlation between photometric galaxies and an overlapping sample of galaxies with spectroscopic redshifts. We describe the redshift leakage from a galaxy photometric redshift bin j into a spectroscopic redshift bin i using the sum of the p(z) for the galaxies residing in bin j. We can then predict the angular cross-correlation between photometric and spectroscopic galaxies due to intrinsic galaxy clustering when i ≠ j as a function of the measured angular cross-correlation when i = j. We also account for enhanced clustering arising from lensing magnification using a halo model. The comparison of this prediction with the measured signal provides a consistency check on the validity of using the summed p(z) to determine galaxy redshift distributions in cosmological analyses, as advocated by the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). We present an analysis of the photometric redshifts measured by CFHTLenS, which overlaps the Baryon Oscillation Spectroscopic Survey (BOSS). We also analyse the Red-sequence Cluster Lensing Survey (RCSLenS), which overlaps both BOSS and the WiggleZ Dark Energy Survey. We find that the summed p(z) from both surveys are generally biased with respect to the true underlying distributions. If unaccounted for, this bias would lead to errors in cosmological parameter estimation from CFHTLenS by less than ˜4%. For photometric redshift bins which spatially overlap in 3-D with our spectroscopic sample, we determine redshift bias corrections which can be used in future cosmological analyses that rely on accurate galaxy redshift distributions.
ERIC Educational Resources Information Center
Taconnat, Laurence; Clarys, David; Vanneste, Sandrine; Bouazzaoui, Badiaa; Isingrini, Michel
2007-01-01
Cued-recall in episodic memory was investigated in relation to low and high cognitive support at retrieval, executive function level and fluid intelligence level in 81 healthy adults divided first into two age groups (young and elderly adults). The first analyses showed that age-related differences were greater when a low cognitive support was…
NASA Technical Reports Server (NTRS)
Lee, T.; Boland, D. F., Jr.
1980-01-01
This document presents the results of an extensive survey and comparative evaluation of current atmosphere and wind models for inclusion in the Langley Atmospheric Information Retrieval System (LAIRS). It includes recommended models for use in LAIRS, estimated accuracies for the recommended models, and functional specifications for the development of LAIRS.
NASA Astrophysics Data System (ADS)
Wiseman, Paul W.; Squier, Jeffrey A.; Wilson, Kent R.
2000-05-01
The interaction of macromolecules in space and time are known to be important for the regulation of many biochemical reactions. Image correlation spectroscopy (ICS) was recently introduced as an imaging analog of fluorescence correlation spectroscopy optimized for measuring the aggregation state of fluorescently labeled macromolecules on the surface of biological cells. We present two novel developments of dynamic ICS that will greatly enhance our abilities to measure molecular interactions as a function of time and space in living cells. We illustrate the use of a rapid scan two-photon microscope system to collect image series at high time resolution (30 frames/s) for dynamic ICS analysis. Secondly, we demonstrate the implementation of two-color image cross-correlation spectroscopy (ICCS) with a CLSM using multiple wavelength excitation, and with two-photon excitation of samples containing two different fluorescent species. Cross-correlation analysis allows the degree of co- localization of two different fluorophores to be measured directly. By performing two-color ICCS, we can monitor the interactions of non-identical labeled macromolecules as a function of time and space. We describe the experimental setup for both methods and illustrate the application for measurements of the diffusion coefficients of singly and doubly labeled fluorescent microspheres in aqueous solutions.
NASA Technical Reports Server (NTRS)
Ganga, Ken; Cheng, ED; Meyer, Stephan; Page, Lyman
1993-01-01
This letter describes results of a cross-correlation between the 170 GHz partial-sky survey, made with a 3.8 deg beam balloon-borne instrument, and the COBE DMR 'Fit Technique' reduced galaxy all-sky map with a beam of 7 deg. The strong correlation between the data sets implies that the observed structure is consistent with thermal variations in a 2.7 K emitter. A chi-square analysis applied to the correlation function rules out the assumption that there is no structure in either of the two maps. A second test shows that if the DMR map has structure but the 170 GHz map does not, the probability of obtaining the observed correlation is small. Further analyses support the assumption that both maps have structure and that the 170 GHz-DMR cross-correlation is consistent with the analogous DMR correlation function. Maps containing various combinations of noise and Harrison-Zel'dovich power spectra are simulated and correlated to reinforce the result. The correlation provides compelling evidence that both instruments have observed fluctuations consistent with anisotropies in the cosmic microwave background.
NASA Astrophysics Data System (ADS)
Deng, Wei; Wang, Jun
2015-06-01
We investigate and quantify the multifractal detrended cross-correlation of return interval series for Chinese stock markets and a proposed price model, the price model is established by oriented percolation. The return interval describes the waiting time between two successive price volatilities which are above some threshold, the present work is an attempt to quantify the level of multifractal detrended cross-correlation for the return intervals. Further, the concept of MF-DCCA coefficient of return intervals is introduced, and the corresponding empirical research is performed. The empirical results show that the return intervals of SSE and SZSE are weakly positive multifractal power-law cross-correlated, and exhibit the fluctuation patterns of MF-DCCA coefficients. The similar behaviors of return intervals for the price model is also demonstrated.
One-factor model for the cross-correlation matrix in the Vietnamese stock market
NASA Astrophysics Data System (ADS)
Nguyen, Quang
2013-07-01
Random matrix theory (RMT) has been applied to the analysis of the cross-correlation matrix of a financial time series. The most important findings of previous studies using this method are that the eigenvalue spectrum largely follows that of random matrices but the largest eigenvalue is at least one order of magnitude higher than the maximum eigenvalue predicted by RMT. In this work, we investigate the cross-correlation matrix in the Vietnamese stock market using RMT and find similar results to those of studies realized in developed markets (US, Europe, Japan) [9-18] as well as in other emerging markets[20,21,19,22]. Importantly, we found that the largest eigenvalue could be approximated by the product of the average cross-correlation coefficient and the number of stocks studied. We demonstrate this dependence using a simple one-factor model. The model could be extended to describe other characteristics of the realistic data.
Nonlinear Analysis on Cross-Correlation of Financial Time Series by Continuum Percolation System
NASA Astrophysics Data System (ADS)
Niu, Hongli; Wang, Jun
We establish a financial price process by continuum percolation system, in which we attribute price fluctuations to the investors’ attitudes towards the financial market, and consider the clusters in continuum percolation as the investors share the same investment opinion. We investigate the cross-correlations in two return time series, and analyze the multifractal behaviors in this relationship. Further, we study the corresponding behaviors for the real stock indexes of SSE and HSI as well as the liquid stocks pair of SPD and PAB by comparison. To quantify the multifractality in cross-correlation relationship, we employ multifractal detrended cross-correlation analysis method to perform an empirical research for the simulation data and the real markets data.
NASA Astrophysics Data System (ADS)
Pal, Mayukha; Kiran, V. Satya; Rao, P. Madhusudana; Manimaran, P.
2016-08-01
We characterized the multifractal nature and power law cross-correlation between any pair of genome sequence through an integrative approach combining 2D multifractal detrended cross-correlation analysis and chaos game representation. In this paper, we have analyzed genomes of some prokaryotes and calculated fractal spectra h(q) and f(α) . From our analysis, we observed existence of multifractal nature and power law cross-correlation behavior between any pair of genome sequences. Cluster analysis was performed on the calculated scaling exponents to identify the class affiliation and the same is represented as a dendrogram. We suggest this approach may find applications in next generation sequence analysis, big data analytics etc.
Bilateral matching of frequency tuning in neural cross-correlators of the owl.
Fischer, Brian J; Peña, José Luis
2009-06-01
Sound localization requires comparison between the inputs to the left and right ears. One important aspect of this comparison is the differences in arrival time to each side, also called interaural time difference (ITD). A prevalent model of ITD detection, consisting of delay lines and coincidence-detector neurons, was proposed by Jeffress (J Comp Physiol Psychol 41:35-39, 1948). As an extension of the Jeffress model, the process of detecting and encoding ITD has been compared to an effective cross-correlation between the input signals to the two ears. Because the cochlea performs a spectrotemporal decomposition of the input signal, this cross-correlation takes place over narrow frequency bands. Since the cochlear tonotopy is arranged in series, sounds of different frequencies will trigger neural activity with different temporal delays. Thus, the matching of the frequency tuning of the left and right inputs to the cross-correlator units becomes a 'timing' issue. These properties of auditory transduction gave theoretical support to an alternative model of ITD-detection based on a bilateral mismatch in frequency tuning, called the 'stereausis' model. Here we first review the current literature on the owl's nucleus laminaris, the equivalent to the medial superior olive of mammals, which is the site where ITD is detected. Subsequently, we use reverse correlation analysis and stimulation with uncorrelated sounds to extract the effective monaural inputs to the cross-correlator neurons. We show that when the left and right inputs to the cross-correlators are defined in this manner, the computation performed by coincidence-detector neurons satisfies conditions of cross-correlation theory. We also show that the spectra of left and right inputs are matched, which is consistent with predictions made by the classic model put forth by Jeffress. PMID:19396457
Detrended fluctuation analysis made flexible to detect range of cross-correlated fluctuations
NASA Astrophysics Data System (ADS)
Kwapień, Jarosław; Oświecimka, Paweł; DroŻdŻ, Stanisław
2015-11-01
The detrended cross-correlation coefficient ρDCCA has recently been proposed to quantify the strength of cross-correlations on different temporal scales in bivariate, nonstationary time series. It is based on the detrended cross-correlation and detrended fluctuation analyses (DCCA and DFA, respectively) and can be viewed as an analog of the Pearson coefficient in the case of the fluctuation analysis. The coefficient ρDCCA works well in many practical situations but by construction its applicability is limited to detection of whether two signals are generally cross-correlated, without the possibility to obtain information on the amplitude of fluctuations that are responsible for those cross-correlations. In order to introduce some related flexibility, here we propose an extension of ρDCCA that exploits the multifractal versions of DFA and DCCA: multifractal detrended fluctuation analysis and multifractal detrended cross-correlation analysis, respectively. The resulting new coefficient ρq not only is able to quantify the strength of correlations but also allows one to identify the range of detrended fluctuation amplitudes that are correlated in two signals under study. We show how the coefficient ρq works in practical situations by applying it to stochastic time series representing processes with long memory: autoregressive and multiplicative ones. Such processes are often used to model signals recorded from complex systems and complex physical phenomena like turbulence, so we are convinced that this new measure can successfully be applied in time-series analysis. In particular, we present an example of such application to highly complex empirical data from financial markets. The present formulation can straightforwardly be extended to multivariate data in terms of the q -dependent counterpart of the correlation matrices and then to the network representation.
Detrended fluctuation analysis made flexible to detect range of cross-correlated fluctuations.
Kwapień, Jarosław; Oświęcimka, Paweł; Drożdż, Stanisław
2015-11-01
The detrended cross-correlation coefficient ρ(DCCA) has recently been proposed to quantify the strength of cross-correlations on different temporal scales in bivariate, nonstationary time series. It is based on the detrended cross-correlation and detrended fluctuation analyses (DCCA and DFA, respectively) and can be viewed as an analog of the Pearson coefficient in the case of the fluctuation analysis. The coefficient ρ(DCCA) works well in many practical situations but by construction its applicability is limited to detection of whether two signals are generally cross-correlated, without the possibility to obtain information on the amplitude of fluctuations that are responsible for those cross-correlations. In order to introduce some related flexibility, here we propose an extension of ρ(DCCA) that exploits the multifractal versions of DFA and DCCA: multifractal detrended fluctuation analysis and multifractal detrended cross-correlation analysis, respectively. The resulting new coefficient ρ(q) not only is able to quantify the strength of correlations but also allows one to identify the range of detrended fluctuation amplitudes that are correlated in two signals under study. We show how the coefficient ρ(q) works in practical situations by applying it to stochastic time series representing processes with long memory: autoregressive and multiplicative ones. Such processes are often used to model signals recorded from complex systems and complex physical phenomena like turbulence, so we are convinced that this new measure can successfully be applied in time-series analysis. In particular, we present an example of such application to highly complex empirical data from financial markets. The present formulation can straightforwardly be extended to multivariate data in terms of the q-dependent counterpart of the correlation matrices and then to the network representation. PMID:26651752
NASA Technical Reports Server (NTRS)
Dean, Bruce H. (Inventor); Smith, Jeffrey Scott (Inventor); Aronstein, David L. (Inventor)
2012-01-01
Disclosed herein are systems, methods, and non-transitory computer-readable storage media for simulating propagation of an electromagnetic field, performing phase retrieval, or sampling a band-limited function. A system practicing the method generates transformed data using a discrete Fourier transform which samples a band-limited function f(x) without interpolating or modifying received data associated with the function f(x), wherein an interval between repeated copies in a periodic extension of the function f(x) obtained from the discrete Fourier transform is associated with a sampling ratio Q, defined as a ratio of a sampling frequency to a band-limited frequency, and wherein Q is assigned a value between 1 and 2 such that substantially no aliasing occurs in the transformed data, and retrieves a phase in the received data based on the transformed data, wherein the phase is used as feedback to an optical system.
Influence of cross correlations on interdiffusion in Al-rich Al-Ni melts
NASA Astrophysics Data System (ADS)
Sondermann, Elke; Kargl, Florian; Meyer, Andreas
2016-05-01
The relation of self- and interdiffusion in a liquid metal, particularly the influence of cross correlations at low concentrations, is studied experimentally. Accurate interdiffusion data are obtained by a combination of x-ray radiography with the shear-cell method on the ground and on the sounding rocket MAPHEUS under microgravity conditions. Self-diffusion coefficients, measured by quasielastic neutron scattering, increase with decreasing Ni concentration, whereas interdiffusion coefficients are about constant. We show that cross correlations influence interdiffusion even at concentrations as low as 2 at. % Ni. Consequently, Darken's equation is not valid in this case.
NASA Astrophysics Data System (ADS)
Singh, Jaswinder
2013-12-01
The analysis of a three-dimensional (3-D) wavelength/time/space (W-T-S) asynchronous optical CDMA code family is presented considering MAI only under relaxed cross-correlation (λc ⩾ 1). Based on the code performance, it is shown that for code-limited systems (when W and/or T are non-prime), the number of generated codes and hence the supported users can be significantly increased by relaxing the cross-correlation constraint if a slight degradation in code performance can be tolerated.
Cross-correlation analysis of the AE index and the interplanetary magnetic field Bz component.
NASA Technical Reports Server (NTRS)
Meng, C.-I.; Tsurutani, B.; Kawasaki, K.; Akasofu, S.-I.
1973-01-01
A cross-correlation study between magnetospheric activity (the AE index) and the southward-directed component of the interplanetary magnetic field (IMF) is made for a total of 792 hours (33 days) with a time resolution of about 5.5 min. The peak correlation tends to occur when the interplanetary data are shifted approximately 40 min later with respect to the AE index data. Cross-correlation analysis is conducted on some idealized wave forms to illustrate that this delay between southward turning of the IMF and the AE index should not be interpreted as being the duration of the growth phase.
NASA Technical Reports Server (NTRS)
Cragin, B. L.; Hanson, W. B.; Mcclure, J. P.; Valladares, C. E.
1985-01-01
Equatorial bottomside sinusoidal (BSS) irregularities have been studied by applying techniques of cross-correlation and spectral analysis to the Atmosphere Explorer data set. The phase of the cross-correlations of the plasma number density is discussed and the two drift velocity components observed using the retarding potential analyzer and ion drift meter on the satellite are discussed. Morphology is addressed, presenting the geographical distributions of the occurrence of BSS events for the equinoxes and solstices. Physical processes including the ion Larmor flux, interhemispheric plasma flows, and variations in the lower F region Pedersen conductivity are invoked to explain the findings.
Scanning cross-correlator for monitoring uniform 3D ellipsoidal laser beams
Zelenogorskii, V V; Andrianov, A V; Gacheva, E I; Gelikonov, G V; Mironov, S Yu; Potemkin, A K; Khazanov, E A; Krasilnikov, M; Stephan, F; Mart'yanov, M A; Syresin, E M
2014-01-31
The specific features of experimental implementation of a cross-correlator with a scan rate above 1600 cm s{sup -1} and a spatial delay amplitude of more than 15 mm are considered. The possibility of measuring the width of femtosecond pulses propagating in a train 300 μs in duration with a repetition rate of 1 MHz is demonstrated. A time resolution of 300 fs for the maximum time window of 50 ps is attained. The cross-correlator is aimed at testing 3D pulses of a laser driver of an electron photo-injector. (laser applications and other topics in quantum electronics)
High-Dynamic-Range Single-Shot Cross-Correlator Based on an Optical Pulse Replicator
Dorrer, C.; Bromage, J.; Zuegel, J.D.
2008-09-05
The operation of a single-shot cross-correlator based on a pulse replicator is described. The correlator uses a discrete sequence of sampling pulses that are nonlinearly mixed with the pulse under test. The combination of a high reflector and partial reflector replicates an optical pulse by multiple internal reflections and generates a sequence of spatially displaced and temporally delayed sampling pulses. This principle is used in a cross-correlator characterizing optical pulses at 1053 nm. A dynamic range higher than 60 dB is obtained over a temporal range larger than 200 ps.
Cross-correlation of X-rays for 4U 1608-52
NASA Astrophysics Data System (ADS)
Lei, Y. J.; Zhang, H. T.; Luo, A. L.; Zhao, Y. H.
2013-02-01
We study the cross-correlation between X-rays of different energies for the atoll-type source 4U 1608-52 with RXTE, and find the cross-correlation evolutes along the different branches. The anti-correlation is reported from the Galactic black hole candidates and Z-type luminous sources in their hard states. Our results are a little different from the Z-type sources. Here we provide the first evidence that a similar anti-correlated feature can also be found in atoll-type source, and it is not corresponding to the lowest accretion rate.
NASA Astrophysics Data System (ADS)
Given, J. W.; Bobrov, D.; Kitov, I. O.; Spiliopoulos, S.
2012-12-01
The Technical Secretariat (TS) of the Comprehensive Nuclear Test-Ban Treaty Organization (CTBTO) will carry out the verification of the CTBT which obligates each State Party not to carry out any nuclear explosions, independently of their size and purpose. The International Data Centre (IDC) receives, collects, processes, analyses, reports on and archives data from the International Monitoring System(IMS). The IDC is responsible for automatic and interactive processing of the IMS data and for standard IDC products. The IDC is also required by the Treaty to progressively enhance its technical capabilities. In this study, we use waveform cross correlation as a technique to improve the detection capability and reliability of the seismic part of the IMS. In order to quantitatively estimate the gain obtained by cross correlation on the current sensitivity of automatic and interactive processing we compared seismic bulletins built for the North Atlantic (NA), which is an isolated region with earthquakes concentrating around the Mid-Atlantic Ridge. This avoids the influence of adjacent seismic regions on the final bulletins: the Reviewed Event Bulletin (REB) issued by the International Data Centre and the cross correlation Standard Event List (XSEL). We have cross correlated waveforms from ~1500 events reported in the REB since 2009. The resulting cross correlation matrix revealed the best candidates for master events. High-quality signals (SNR>5.0) recorded at eighteen array stations from approximately 50 master events evenly distributed over the seismically active zone in the NA were selected as templates. These templates are used for a continuous calculation of cross correlation coefficients since 2011. All detections obtained by cross-correlation are then used to build events according to the current IDC definition, i.e. at least three primary stations with accurate arrival times, azimuth and slowness estimates. The qualified event hypotheses populated the XSEL. In
NASA Astrophysics Data System (ADS)
Kitov, Ivan; Bobrov, Dmitry; Rozhkov, Mikhail
2013-04-01
The Technical Secretariat (TS) of the Comprehensive Nuclear Test-Ban Treaty Organization (CTBTO) will carry out the verification of the CTBT which obligates each State Party not to carry out nuclear explosions. The International Data Centre (IDC) receives, collects, processes, analyses, reports on and archives data from the International Monitoring System. The IDC is responsible for automatic and interactive processing of the International Monitoring System (IMS) data and for standard IDC products. The IDC is also required by the Treaty to progressively enhance its technical capabilities. In this study, we use waveform cross correlation as a technique to improve the detection capability and reliability of the seismic part of the IMS. In order to quantitatively estimate the gain obtained by cross correlation on the current sensitivity of automatic and interactive processing we compared seismic bulletins built for the North Atlantic (NA), which is a seismically isolated region with earthquakes concentrating around the Mid-Atlantic Ridge. This allows avoiding the spill-over of mislocated events between adjacent seismic regions and biases in the final bulletins: the Reviewed Event Bulletin (REB) issued by the IDC and the cross correlation Standard Event List (XSEL). To begin with, we cross correlated waveforms recorded at 18 IMS array stations from ~1500 events reported in the REB between 2009 and 2011. The resulting cross correlation matrix revealed the best candidates for master events. We have selected 60 master events evenly distributed over the seismically active zone in the NA. High-quality signals (SNR>5.0) recorded by 10 most sensitive array stations were used as waveform templates. These templates are used for a continuous calculation of cross correlation coefficients in the first half of 2012. All detections obtained by cross-correlation are then used to build events according to the current IDC definition: at least three primary stations with accurate
NASA Astrophysics Data System (ADS)
Minato, Shohei; Ghose, Ranajit
2016-04-01
The spatial heterogeneity along a fracture is a key determinant for fracture-associated mechanical and hydraulic properties of the subsurface. Laboratory experiments have been performed to test the applicability of the nonwelded interface representation to predict the frequency- and angle-dependent elastic response of a single fracture. The observation that nonwelded interface model can represent quite well the frequency- and angle-dependent reflection response of a fracture has led us to develop a new methodology for estimating the spatially heterogeneous fracture compliance from the reflection response along a fracture surface. A data-driven approach based on Marchenko equation coupled with inverse scattering to solve the nonwelded interface boundary condition has been formulated. The approach estimates the elastic wavefield along a fracture accurately, including the multiple reflections. As an extension, it offers the possibility to estimate fracture compliance using the multiple reflections. We illustrate the concept by numerically modeling 2-D SH waves sensing the heterogeneous tangential compliance of a fracture. The stationary phase method is applied to single and double spatial integrals to analyze the effect of source and receiver aperture on the Green's function retrieval. Our results show that the use of multiple reflections allows a better estimation of the heterogeneous fracture compliance than using primary reflections alone, especially for the far offsets on the fracture plane.
NASA Astrophysics Data System (ADS)
Nandy, P.; Thome, K.; Biggar, S.
2001-06-01
Vicarious calibration and field validation is a critical aspect of NASA's Earth Observing System program. As part of calibration and validation research related to this project, the Remote Sensing Group (RSG) of the Optical Science Center at the University of Arizona has developed an imaging radiometer for ground-based measurements of directional reflectance. The system relies on a commercially available 1024×1024 pixel, silicon CCD array. Angular measurements are accomplished using a fish-eye lens that has a full 180° field of view with each pixel on the CCD array having a nominal 0.2° field of view. Spectral selection is through four interference filters centered at 470, 575, 660, and 835 nm. The system is designed such that the entire 180° field is collected at one time with a complete multispectral data set collected in under 2 min. The results of laboratory experiments have been used to determine the gain and offset of each detector element as well as the effects of the lens on the system response. Measurements of a stable source using multiple integration times and at multiple distances for a set integration time indicate the system is linear to better than 0.5% over the upper 88% of the dynamic range of the system. The point spread function (PSF) of the lens system was measured for several field angles, and the signal level was found to fall to less than 1% of the peak signal within 1.5° for the on-axis case. The effect of this PSF on the retrieval of modeled BRDFs is shown to be less than 0.2% out to view angles of 70°. The degree of polarization of the system is shown to be negligible for on-axis imaging but to have up to a 20% effect at a field angle of 70°. The effect of the system polarization on the retrieval of modeled BRDFs is shown to be up to 3% for field angles of 70° off nadir and with a solar zenith angle of 70°. Field measurements are made by mounting the camera to a boom mounted to a large tripod that is aligned toward south. This
Dissociating word stem completion and cued recall as a function of divided attention at retrieval.
Clarke, A J Benjamin; Butler, Laurie T
2008-10-01
The aim of this study was to investigate the widely held, but largely untested, view that implicit memory (repetition priming) reflects an automatic form of retrieval. Specifically, in Experiment 1 we explored whether a secondary task (syllable monitoring), performed during retrieval, would disrupt performance on explicit (cued recall) and implicit (stem completion) memory tasks equally. Surprisingly, despite substantial memory and secondary costs to cued recall when performed with a syllable-monitoring task, the same manipulation had no effect on stem completion priming or on secondary task performance. In Experiment 2 we demonstrated that even when using a particularly demanding version of the stem completion task that incurred secondary task costs, the corresponding disruption to implicit memory performance was minimal. Collectively, the results are consistent with the view that implicit memory retrieval requires little or no processing capacity and is not seemingly susceptible to the effects of dividing attention at retrieval. PMID:18720222
Angular Cross-correlation of Spitzer IRAC and Herschel Spire Sources
NASA Astrophysics Data System (ADS)
Mitchell-Wynne, Ketron; Cooray, A.; Wang, L.; HerMES Consortium
2011-01-01
The Spitzer Deep Wide-Field Survey (SDWFS) and the Herschel Multi-tiered Extragalactic Survey (HerMES) each provide deep and wide coverage, centered on the Bootes field, at infrared and sub-millimeter wavelengths. The SDWFS covers approximately 8.5 square degrees with sensitivities of galaxies out to z 3. From the public SDWFS source catalog, we remove stars and contaminants by concentration, using selection methods based on IRAC and optical colors; optical photometry is provided by the NOAO Deep Wide-Field Survey. Photometric redshifts of detected IRAC sources are then determined using the 1.6 micron spectral feature (or 'bump'). We classify three different kinds of bumps, (bump 1- bump 3), with redshifts ranging approximately from 0-1.3, 1.3-2, and 2-3 respectively. The number of bump 1 sources in the SDWFS catalogs were found to be in excess of 25,000 at the 5 sigma detection limit of the 3.6 micron channel of the IRAC instrument. Bump 2 and bump 3 source identification yielded similar, but slightly fewer counts. We also extract a separate catalog of 2500 or so dust-obscured galaxies (DOGs) at z 2 using 24 micron and r-band fluxes. As part of HerMES observations with SPIRE, the Bootes field contain more than 15,000 clearly detected SPIRE sources at 250 microns, In this paper we report on the cross correlation function of these bump sources with the source catalogs from three bands of the SPIRE instrument onboard Herschel. The aim is to broadly reconstruct the redshift distribution of SPIRE sources using redshift distributions of bump and DOGs in the bootes field and the relative clustering strengths.
Cross-correlative 3D micro-structural investigation of human bone processed into bone allografts.
Singh, Atul Kumar; Gajiwala, Astrid Lobo; Rai, Ratan Kumar; Khan, Mohd Parvez; Singh, Chandan; Barbhuyan, Tarun; Vijayalakshmi, S; Chattopadhyay, Naibedya; Sinha, Neeraj; Kumar, Ashutosh; Bellare, Jayesh R
2016-05-01
Bone allografts (BA) are a cost-effective and sustainable alternative in orthopedic practice as they provide a permanent solution for preserving skeletal architecture and function. Such BA however, must be processed to be disease free and immunologically safe as well as biologically and clinically useful. Here, we have demonstrated a processing protocol for bone allografts and investigated the micro-structural properties of bone collected from osteoporotic and normal human donor samples. In order to characterize BA at different microscopic levels, a combination of techniques such as Solid State Nuclear Magnetic Resonance (ssNMR), Scanning Electron Microscope (SEM), micro-computed tomography (μCT) and Thermal Gravimetric Analysis (TGA) were used for delineating the ultra-structural property of bone. ssNMR revealed the extent of water, collagen fine structure and crystalline order in the bone. These were greatly perturbed in the bone taken from osteoporotic bone donor. Among the processing methods analyzed, pasteurization at 60 °C and radiation treatment appeared to substantially alter the bone integrity. SEM study showed a reduction in Ca/P ratio and non-uniform distribution of elements in osteoporotic bones. μ-CT and MIMICS (Materialize Interactive Medical Image Control System) demonstrated that pasteurization and radiation treatment affects the BA morphology and cause a shift in the HU unit. However, the combination of all these processes restored all-important parameters that are critical for BA integrity and sustainability. Cross-correlation between the various probes we used quantitatively demonstrated differences in morphological and micro-structural properties between BA taken from normal and osteoporotic human donor. Such details could also be instrumental in designing an appropriate bone scaffold. For the best restoration of bone microstructure and to be used as a biomaterial allograft, a step-wise processing method is recommended that preserves all
Tal, Balazs; Bencze, Attila; Zoletnik, Sandor; Veres, Gabor; Por, Gabor
2011-12-15
Time delay estimation methods (TDE) are well-known techniques to investigate poloidal flows in hot magnetized plasmas through the propagation properties of turbulent structures in the medium. One of these methods is based on the estimation of the time lag at which the cross-correlation function (CCF) estimation reaches its maximum value. The uncertainty of the peak location refers to the smallest determinable flow velocity modulation, and therefore the standard deviation of the time delay imposes important limitation to the measurements. In this article, the relative standard deviation of the CCF estimation and the standard deviation of its peak location are calculated analytically using a simple model of turbulent signals. This model assumes independent (non interacting) overlapping events (coherent structures) with randomly distributed spatio-temporal origins moving with background flow. The result of our calculations is the derivation of a general formula for the CCF variance, which is valid not exclusively in the high event density limit, but also for arbitrary event densities. Our formula reproduces the well known expression for high event densities previously published in the literature. In this paper we also present a derivation of the variance of time delay estimation that turns out to be inversely proportional to the applied time window. The derived formulas were tested in real plasma measurements. The calculations are an extension of the earlier work of Bencze and Zoletnik [Phys. Plasmas 12, 052323 (2005)] where the autocorrelation-width technique was developed. Additionally, we show that velocities calculated by a TDE method possess a broadband noise which originates from this variance, its power spectral density cannot be decreased by worsening the time resolution and can be coherent with noises of other velocity measurements where the same turbulent structures are used. This noise should not be confused with the impact of zero mean frequency zonal flow
Delay Times From Clustered Multi-Channel Cross Correlation and Simulated Annealing
NASA Astrophysics Data System (ADS)
Creager, K. C.; Sambridge, M. S.
2004-12-01
Several techniques exist to estimate relative delay times of seismic phases based on the assumption that the waveforms observed at several stations can be expressed as a common waveform that has been time shifted and distorted by random uncorrelated noise. We explore the more general problem of estimating the relative delay times for regional or even global distributions of seismometers in cases where waveforms vary systematically across the array. The estimation of relative delay times is formulated as a global optimization of the weighted sum of squares of cross correlations of each seismogram pair evaluated at the corresponding difference in their relative delay times. As there are many local minima in this penalty function, a simulated annealing algorithm is used to obtain a solution. The weights depend strongly on the separation distance among seismogram pairs as well as a measure of the similarity of waveforms. Thus, seismograph pairs that are physically close to each other and have similar waveforms are expected to be well aligned while those with dissimilar waveforms or large separation distances are severely down-weighted and thus need not be well aligned. As a result noisy seismograms, which are not similar to other seismograms, are down-weighted so they do not adversely effect the relative delay times of other seismograms. Finally, natural clusters of seismograms are determined from the weight matrix. Examples of aligning a few hundred P and PKP waveforms from a broadband global array and from a mixed broadband and short-period continental-scale array will be shown. While this method has applications in many situations, it may be especially useful for arrays such as the EarthScope Bigfoot Array.
Reimus, Paul W
2011-01-03
Transport parameter cross correlations are rarely considered in models used to predict radionuclide transport in natural systems. In this paper, it is shown that parameter cross correlations could have a significant impact on radionuclide transport predictions in saturated media. In fractured rock, the positive correlation between fracture apertures and groundwater residence times is shown to result in significantly less retardation due to matrix diffusion than is predicted without the correlation. The suppression of matrix diffusion is further amplified by a tendency toward larger apertures, smaller matrix diffusion coefficients, and less sorption capacity in rocks of lower matrix porosity. In a hypothetical example, strong cross correlations between these parameters result in a decrease in predicted radionuclide travel times of an order of magnitude or more relative to travel times calculated with uncorrelated parameters. In porous media, expected correlations between permeability, porosity, and sorption capacity also result in shorter predicted travel times than when the parameters are assumed to be uncorrelated. Individual parameter standard deviations can also have a significant influence on predicted radionuclide travel times, particularly when cross correlations are considered.
Lenses in the forest: cross--correlation of the Lyman-alpha flux with CMB lensing
Vallinotto, Alberto; Das, Sudeep; Spergel, David N.; Viel, Matteo; /Trieste Observ. /INFN, Trieste
2009-03-01
We present a theoretical estimate for a new observable: the cross-correlation between the Lyman-{alpha}-flux fluctuations in quasar (QSO) spectra and the convergence of the cosmic microwave background (CMB) as measured along the same line-of-sight. As a first step toward the assessment of its detectability, we estimate the signal-to-noise ratio using linear theory. Although the signal-to-noise is small for a single line-of-sight and peaks at somewhat smaller redshifts than those probed by the Lyman-{alpha} forest, we estimate a total signal-to-noise of 9 for cross-correlating QSO spectra of SDSSIII with Planck and 20 for cross-correlating with a future polarization based CMB experiment. The detection of this effect would be a direct measure of the neutral hydrogen-matter cross-correlation and could provide important information on the growth of structures at large scales in a redshift range which is still poorly probed by observations.
NASA Astrophysics Data System (ADS)
Kahbasi, A.; Moradi, A.
2016-04-01
The presence of man-made explosions in a seismic catalogue leads to errors in statistical analyses of seismicity. Recently, the need to monitor man-made explosions used for mining, road excavating, and other constructional applications has been become a demanding challenge for the seismologists. In this way, we gain new insight into the cross-correlation technique and conduct this approach to discriminate explosions from seismic datasets. Following this, improved P-wave arrival times are used for more precise relocation. In this study, the waveform cross-correlation technique provides a reliable means for discriminating explosions which have cross-correlation coefficients (CC) of 0.6 or greater with their own corresponding stacked waveforms. The results illustrate that approximately 80 % of seismicity of southeast of Tehran, recorded by the Iranian Seismological Center (IRSC), includes events which have cross-correlation coefficients of ≥0.6 with their corresponding stacked waveforms. Furthermore, with improved P-wave arrival time, there is a better chance to relocate explosions precisely in the region under study.
NASA Astrophysics Data System (ADS)
Cao, Guangxi; Han, Yan; Chen, Yuemeng; Yang, Chunxia
2014-05-01
Based on the daily price data of Shanghai and London gold spot markets, we applied detrended cross-correlation analysis (DCCA) and detrended moving average cross-correlation analysis (DMCA) methods to quantify power-law cross-correlation between domestic and international gold markets. Results show that the cross-correlations between the Chinese domestic and international gold spot markets are multifractal. Furthermore, forward DMCA and backward DMCA seems to outperform DCCA and centered DMCA for short-range gold series, which confirms the comparison results of short-range artificial data in L. Y. He and S. P. Chen [Physica A 390 (2011) 3806-3814]. Finally, we analyzed the local multifractal characteristics of the cross-correlation between Chinese domestic and international gold markets. We show that multifractal characteristics of the cross-correlation between the Chinese domestic and international gold markets are time-varying and that multifractal characteristics were strengthened by the financial crisis in 2007-2008.
Waveform cross-correlation and relocations for seismic events in the San Jacinto Fault Zone
NASA Astrophysics Data System (ADS)
Galipchak, E.; Kurzon, I.; Vernon, F.; Pavlis, G. L.; Ben-Zion, Y.
2012-12-01
We introduce a new approach for the relocation of local seismic events using waveform cross-correlation and automatic detection algorithm. This approach is developed and implemented for the San Jacinto Fault Zone (SJFZ), where recent cross-correlation and double-difference relocation methods (e.g., Hauksson et al. 2011) account up to ~75% of the seismic events, due to the complex nature of the SJFZ. The fault zone complexity features include a mismatch between the fault traces and seismicity clusters and strong heterogeneity of focal mechanisms. Our goal is to develop an efficient relocation method in which ~90% of the seismic events would be considered. The 'dbxcor' tool of the Antelope software package (e.g., Pavlis & Vernon 2010) is a graphic cross-correlation method involving an active reviewing of the cross-correlation process by a seismic analyst. The method is adjusted here for the analysis of local events from the original algorithm developed mainly for the processing of teleseismic events. The advantage of this approach is that the analyst may keep many of the waveforms that would have been dropped out due to the cross-correlation threshold, thereby increasing the percentage of events considered in the process. Moreover, the method allows an interactive demonstration and identification of different nearby source mechanisms, thus helping to examine the heterogeneity of the fault zone. A pre-request of the cross-correlation algorithm is the existence of arrivals for each waveform in the process. This required tuning a set of efficient automated detectors for grasping the specific nature of seismicity in the SJFZ. Applying such detectors we manage to increase the catalogue by up to 40% of additional events not reviewed previously by analysts. This improvement allows incorporating not only more events into the relocation process, but also additional stations, which were missed by previous automatic or manual picking of P and S arrivals. The relocated events
Using the CARDAMOM framework to retrieve global terrestrial ecosystem functioning properties
NASA Astrophysics Data System (ADS)
Exbrayat, Jean-François; Bloom, A. Anthony; Smallman, T. Luke; van der Velde, Ivar R.; Feng, Liang; Williams, Mathew
2016-04-01
Terrestrial ecosystems act as a sink for anthropogenic emissions of fossil-fuel and thereby partially offset the ongoing global warming. However, recent model benchmarking and intercomparison studies have highlighted the non-trivial uncertainties that exist in our understanding of key ecosystem properties like plant carbon allocation and residence times. It leads to worrisome differences in terrestrial carbon stocks simulated by Earth system models, and their evolution in a warming future. In this presentation we attempt to provide global insights on these properties by merging an ecosystem model with remotely-sensed global observations of leaf area and biomass through a data-assimilation system: the CARbon Data MOdel fraMework (CARDAMOM). CARDAMOM relies on a Markov Chain Monte Carlo algorithm to retrieve confidence intervals of model parameters that regulate ecosystem properties independently of any prior land-cover information. The MCMC method thereby enables an explicit representation of the uncertainty in land-atmosphere fluxes and the evolution of terrestrial carbon stocks through time. Global experiments are performed for the first decade of the 21st century using a 1°×1° spatial resolution. Relationships emerge globally between key ecosystem properties. For example, our analyses indicate that leaf lifespan and leaf mass per area are highly correlated. Furthermore, there exists a latitudinal gradient in allocation patterns: high latitude ecosystems allocate more carbon to photosynthetic carbon (leaves) while plants invest more carbon in their structural parts (wood and root) in the wet tropics. Overall, the spatial distribution of these ecosystem properties does not correspond to usual land-cover maps and are also partially correlated with disturbance regimes. For example, fire-prone ecosystems present statistically significant higher values of carbon use efficiency than less disturbed ecosystems experiencing similar climatic conditions. These results
Intensity mapping cross-correlations: connecting the largest scales to galaxy evolution
NASA Astrophysics Data System (ADS)
Wolz, L.; Tonini, C.; Blake, C.; Wyithe, J. S. B.
2016-05-01
Intensity mapping of the neutral hydrogen (H I) is a new observational tool to efficiently map the large-scale structure over wide redshift ranges. The cross-correlation of intensity maps with galaxy surveys is a robust measure of the cosmological power spectrum and the H I content of galaxies which diminishes systematics caused by instrumental effects and foreground removal. We examine the cross-correlation signature at redshift 0.9 using a semi-analytical galaxy formation model in order to model the H I gas of galaxies as well as their optical magnitudes. We determine the scale-dependent clustering of the cross-correlation power for different types of galaxies determined by their colours, which act as a proxy for their star formation activity. We find that the cross-correlation coefficient with H I density for red quiescent galaxies falls off more quickly on smaller scales k > 0.2 h Mpc-1 than for blue star-forming galaxies. Additionally, we create a mock catalogue of highly star-forming galaxies to mimic the WiggleZ Dark Energy Survey, and use this to predict existing and future measurements using data from the Green Bank telescope and Parkes telescope. We find that the cross-power of highly star-forming galaxies shows a higher clustering on small scales than any other galaxy type and that this significantly alters the power spectrum shape on scales k > 0.2 h Mpc-1. We show that the cross-correlation coefficient is not negligible when interpreting the cosmological cross-power spectrum and additionally contains information about the H I content of the optically selected galaxies.
NASA Astrophysics Data System (ADS)
Atkinson, Malcolm; Bell, Andrew; Curtis, Andrew; Entwistle, Elizabeth; Filgueira, Rosa; Krause, Amrey; Main, Ian; Meles, Giovani; Miniter, Mike; Zhao, Youqian
2015-04-01
Earthquakes and volcanic eruptions may in some instances be preceded or accompanied by changes in the geophysical properties of the Earth, such as seismic velocities or event rates. The development of reliable probabilistic forecasting methods for these hazards requires real-time analysis of seismic data and truly prospective forecasting and testing to reduce bias. However, potential forecasting techniques, including seismic interferometry and earthquake "repeater" analysis, require a large number of waveform cross-correlations; this is computationally intensive, and is particularly challenging in real-time. Here we describe the "Terracorrelator", a new high performance computing facility at the University of Edinburgh designed for real-time cross-correlational analyses. The machine consists of two 2TB shared memory nodes for cross-correlation and post-processing, and two Intel Xeon Phi nodes for pre-processing. The Terracorrelator has been tested on a seismic interferometry case study using ObsPy for seismic operations and processing, and Dispel4Py for writing and executing the workflow. The workflow is distributed automatically for parallel processing in a shared memory multicore environment. Preliminary results have demonstrated that data from 1000 seismic stations can be pre-processed, and each station cross-correlated with all others (499500 cross-correlations) in hourly or daily intervals sufficiently quickly to keep ahead of new data arriving, on one of the shared memory nodes. The second node is therefore free to perform interpretative analysis on the outputs, for example to look at changes in the resulting correlations. These promising results suggest that it will be possible to undertake real-time interferometric analysis using Sure~1000 stations, and to test the predictive power of current seismic velocity changes for future hazard occurrence.
NASA Astrophysics Data System (ADS)
Probst, Line; Caricchi, Luca; Gander, Martin; Wallace, Glenn
2016-04-01
Analysis of chemical zoning in minerals offers the opportunity to reconstruct the pre-eruptive conditions and the temporal evolution of magmatic reservoirs. The chemical composition of minerals is a function of the thermodynamic conditions of the reservoir from which they grow and therefore minerals record the evolution and variation of residual melt chemistry and intensive parameters within the magmatic system. A quantitative approach is required to determine if similar crystals actually shared a portion of their crystallisation history. These analyses are in many cases extremely time consuming and rather expensive. Therefore, it is not always possible to analyse a statically significant number of crystals, especially within their textural context in thin sections and that is the main reason to build automated methods. We are presenting a numerical cross-correlation method that compares the zonation pattern of minerals to identify if they share the totality or part of their growth history. We modified the method first developed by Wallace and Bergantz (2004) to compare profiles in minerals also from samples collected in different outcrops and that can be used for any dataset (i.e. geochemical proxies in stratigraphic sections). The main purpose of this method is to objectively compare chemical profiles in minerals (collected by electron microprobe, LA-ICP-MS or cathodoluminescence images) and quantify their degree of similarity. For this purpose, we use a well-known mathematical tool: the cross correlation which is a way of quantifying the difference between two given signals at a given position. Once our program was built, we performed tests using a set of synthetic profiles, profiles acquired along different transects of the same mineral and also on different minerals. Finally we applied our program to about 100 zircons from Kilgore Tuff, Heise Volcanic Field (USA) collected at different stratigraphic levels in two different outcrops. The correlation shows that
NASA Technical Reports Server (NTRS)
Remer, Lorraine A.; Mattoo, Shana; Levy, Robert C.; Heidinger, Andrew; Pierce, R. Bradley; Chin, Mian
2011-01-01
The challenge of using satellite observations to retrieve aerosol properties in a cloudy environment is to prevent contamination of the aerosol signal from clouds, while maintaining sufficient aerosol product yield to satisfy specific applications. We investigate aerosol retrieval availability at different instrument pixel resolutions, using the standard MODIS aerosol cloud mask applied to MODIS data and a new GOES-R cloud mask applied to GOES data for a domain covering North America and surrounding oceans. Aerosol availability is not the same as the cloud free fraction and takes into account the technqiues used in the MODIS algorithm to avoid clouds, reduce noise and maintain sufficient numbers of aerosol retrievals. The inherent spatial resolution of each instrument, 0.5x0.5 km for MODIS and 1x1 km for GOES, is systematically degraded to 1x1 km, 2x2 km, 4x4 km and 8x8 km resolutions and then analyzed as to how that degradation would affect the availability of an aerosol retrieval, assuming an aerosol product resolution at 8x8 km. The results show that as pixel size increases, availability decreases until at 8x8 km 70% to 85% of the retrievals available at 0.5 km have been lost. The diurnal pattern of aerosol retrieval availability examined for one day in the summer suggests that coarse resolution sensors (i.e., 4x4 km or 8x8 km) may be able to retrieve aerosol early in the morning that would otherwise be missed at the time of current polar orbiting satellites, but not the diurnal aerosol properties due to cloud cover developed during the day. In contrast finer resolution sensors (i.e., 1x1 km or 2x2 km) have much better opportunity to retrieve aerosols in the partly cloudy scenes and better chance of returning the diurnal aerosol properties. Large differences in the results of the two cloud masks designed for MODIS aerosol and GOES cloud products strongly reinforce that cloud masks must be developed with specific purposes in mind and that a generic cloud mask
Antoine, Thomas; Ott, David; Ebell, Katharina; Hansen, Kerrin; Henry, Luc; Becker, Frank; Hannus, Stefan
2016-06-01
G protein-coupled receptors (GPCRs) mediate many important physiological functions and are considered as one of the most successful therapeutic target classes for a wide spectrum of diseases. Drug discovery projects generally benefit from a broad range of experimental approaches for screening compound libraries and for the characterization of binding modes of drug candidates. Owing to the difficulties in solubilizing and purifying GPCRs, assay formats have been so far mainly limited to cell-based functional assays and radioligand binding assays. In this study, we used fluorescence cross-correlation spectroscopy (FCCS) to analyze the interaction of detergent-solubilized receptors to various types of GPCR ligands: endogenous peptides, small molecules, and a large surrogate antagonist represented by a blocking monoclonal antibody. Our work demonstrates the suitability of the homogeneous and time-resolved FCCS assay format for a robust, high-throughput determination of receptor-ligand binding affinities and kinetic rate constants for various therapeutically relevant GPCRs. PMID:26954998
NASA Astrophysics Data System (ADS)
Yin, Yin; Fotin, Sergei V.; Periaswamy, Senthil; Kunz, Justin; Haldankar, Hrishikesh; Muradyan, Naira; Cornud, François; Turkbey, Baris; Choyke, Peter
2012-02-01
Manual delineation of the prostate is a challenging task for a clinician due to its complex and irregular shape. Furthermore, the need for precisely targeting the prostate boundary continues to grow. Planning for radiation therapy, MR-ultrasound fusion for image-guided biopsy, multi-parametric MRI tissue characterization, and context-based organ retrieval are examples where accurate prostate delineation can play a critical role in a successful patient outcome. Therefore, a robust automated full prostate segmentation system is desired. In this paper, we present an automated prostate segmentation system for 3D MR images. In this system, the prostate is segmented in two steps: the prostate displacement and size are first detected, and then the boundary is refined by a shape model. The detection approach is based on normalized gradient fields cross-correlation. This approach is fast, robust to intensity variation and provides good accuracy to initialize a prostate mean shape model. The refinement model is based on a graph-search based framework, which contains both shape and topology information during deformation. We generated the graph cost using trained classifiers and used coarse-to-fine search and region-specific classifier training. The proposed algorithm was developed using 261 training images and tested on another 290 cases. The segmentation performance using mean DSC ranging from 0.89 to 0.91 depending on the evaluation subset demonstrates state of the art performance. Running time for the system is about 20 to 40 seconds depending on image size and resolution.
Jerger, James; Martin, Jeffrey; McColl, Roderick
2004-01-01
In a previous publication (Jerger et al, 2002), we presented event-related potential (ERP) data on a pair of 10-year-old twin girls (Twins C and E), one of whom (Twin E) showed strong evidence of auditory processing disorder. For the present paper, we analyzed cross-correlation functions of ERP waveforms generated in response to the presentation of target stimuli to either the right or left ears in a dichotic paradigm. There were four conditions; three involved the processing of real words for either phonemic, semantic, or spectral targets; one involved the processing of a nonword acoustic signal. Marked differences in the cross-correlation functions were observed. In the case of Twin C, cross-correlation functions were uniformly normal across both hemispheres. The functions for Twin E, however, suggest poorly correlated neural activity over the left parietal region during the three word processing conditions, and over the right parietal area in the nonword acoustic condition. Differences between the twins' brains were evaluated using diffusion tensor magnetic resonance imaging (DTI). For Twin E, results showed reduced anisotropy over the length of the midline corpus callosum and adjacent lateral structures, implying reduced myelin integrity. Taken together, these findings suggest that failure to achieve appropriate temporally correlated bihemispheric brain activity in response to auditory stimulation, perhaps as a result of faulty interhemispheric communication via corpus callosum, may be a factor in at least some children with auditory processing disorder. PMID:15030103
Omokoko, Tana; Simon, Petra; Türeci, Özlem; Sahin, Ugur
2015-01-01
We have developed a highly versatile platform for the systematic retrieval of T-cell receptors (TCRs) from single-antigen-reactive T cells and for characterization of their function and specificity. This approach enables rapid extraction of multiple TCRs from repertoires in individuals and not only broadens the diversity of TCRs suitable for clinical use, but also sets the stage for actively personalized immunotherapeutic strategies. PMID:26140230
Siekmeier, Peter J; Hasselmo, Michael E; Howard, Marc W; Coyle, Joseph
2007-01-01
The symptoms of schizophrenia may be associated with reductions in NMDA receptor (NMDAR) function. This is suggested by the psychotomimetic effects of NMDA antagonists, the ameliorative effects of NMDAR indirect agonists, elevated levels of the NMDA antagonist N-acetyl-aspartyl-glutamate (NAAG) in schizophrenic brain, and findings from recent genetic studies. However, the link between reduced NMDAR function and the behavioral features of schizophrenics has not been made explicit. Here we present a network simulation of hippocampal function, focused on retrieval of verbal stimuli in human memory tasks. Specifically, we trained a computational model of the hippocampal complex to perform a context-dependent paired associate task, a free recall task with category clustering, and the transitive inference (TI) task. In this network, direct perforant pathway input from entorhinal cortex to region CA1 provides the basis for semantic context cueing during initial encoding and retrieval, allowing selective retrieval on the basis of category cues. Alterations in the magnitude of this direct perforant pathway input to region CA1 causes impairments in use of organizational strategies for memory, accounting for specific features of memory dysfunction in schizophrenics and in normals treated with ketamine. This model provides a theoretical link between cellular physiological changes and specific cognitive symptoms. As such, it can shed light on the etiology of schizophrenia in a fundamental way, and also holds the promise of pointing the way to more effective treatments. PMID:17055702
Quiroga-Lombard, Claudio S; Hass, Joachim; Durstewitz, Daniel
2013-07-01
Correlations among neurons are supposed to play an important role in computation and information coding in the nervous system. Empirically, functional interactions between neurons are most commonly assessed by cross-correlation functions. Recent studies have suggested that pairwise correlations may indeed be sufficient to capture most of the information present in neural interactions. Many applications of correlation functions, however, implicitly tend to assume that the underlying processes are stationary. This assumption will usually fail for real neurons recorded in vivo since their activity during behavioral tasks is heavily influenced by stimulus-, movement-, or cognition-related processes as well as by more general processes like slow oscillations or changes in state of alertness. To address the problem of nonstationarity, we introduce a method for assessing stationarity empirically and then "slicing" spike trains into stationary segments according to the statistical definition of weak-sense stationarity. We examine pairwise Pearson cross-correlations (PCCs) under both stationary and nonstationary conditions and identify another source of covariance that can be differentiated from the covariance of the spike times and emerges as a consequence of residual nonstationarities after the slicing process: the covariance of the firing rates defined on each segment. Based on this, a correction of the PCC is introduced that accounts for the effect of segmentation. We probe these methods both on simulated data sets and on in vivo recordings from the prefrontal cortex of behaving rats. Rather than for removing nonstationarities, the present method may also be used for detecting significant events in spike trains. PMID:23636729
ERIC Educational Resources Information Center
Ekstrom, Arne D.; Bookheimer, Susan Y.
2007-01-01
Imaging, electrophysiological studies, and lesion work have shown that the medial temporal lobe (MTL) is important for episodic memory; however, it is unclear whether different MTL regions support the spatial, temporal, and item elements of episodic memory. In this study we used fMRI to examine retrieval performance emphasizing different aspects…
Cross-correlation Weak Lensing of SDSS Galaxy Clusters III: Mass-to-light Ratios
Sheldon, Erin S.; Johnston, David E.; Masjedi, Morad; McKay, Timothy A.; Blanton, Michael R.; Scranton, Ryan; Wechsler, Risa H.; Koester, Ben P.; Hansen, Sarah M.; Frieman, Joshua A.; Annis, James
2007-09-28
We present measurements of the excess mass-to-light ratio measured around MaxBCG galaxy clusters observed in the SDSS. This red sequence cluster sample includes objects from small groups with M{sub 200} {approx} 5 x 10{sup 12}h{sup -1}M{sub {circle_dot}} to clusters with M{sub 200} {approx} 5 x 10{sup 15}h{sup -1}M{sub {circle_dot}}. Using cross-correlation weak lensing, we measure the excess mass density profile above the universal mean {Delta}{yields}(r) = {rho}(r) -- {bar {rho}} for clusters in bins of richness and optical luminosity. We also measure the excess {sup 0.25}i-band luminosity density {Delta}{ell}(r) = {ell}(r) -- {bar {ell}}. For both mass and light, we de-project the profiles to produce 3D mass and light profiles over scales from 25h{sup -1} kpc to 22h{sup -1} Mpc. From these profiles we calculate the cumulative excess mass {Delta}M(r) and excess light {Delta}L(r) as a function of separation from the BCG. On small scales, where {rho}(r) >> {bar {rho}}, the integrated mass-to-light profile ({Delta}M/{Delta}L)(r) may be interpreted as the cluster mass-to-light ratio. We find the ({Delta}M/{Delta}L){sub 200}, the mass-to-light ratio within r{sub 200}, scales with cluster mass as a power law with index 0.33{+-}0.02. On large scales, where {rho}(r) {approx} {bar {rho}}, the {Delta}M/{Delta}L approaches an asymptotic value independent of scale or cluster richness. For small groups, the mean ({Delta}M/{Delta}L){sub 200} is much smaller than the asymptotic value, while for large clusters ({Delta}M/{Delta}L)200 is consistent with the asymptotic value. This asymptotic value should be proportional to the mean mass-to-light ratio of the universe {l_angle}M/L{r_angle}. We find {l_angle}M/L{r_angle} b{sup -2}{sub M/L} = 362 {+-} 54h measured in the {sup 0.25}i-bandpass. The parameter b{sup 2}{sub M/L} is primarily a function of the bias of the L {approx}< L* galaxies used as light tracers, and should be of order unity. Multiplying by the luminosity density in
Covariance of cross-correlations: towards efficient measures for large-scale structure
NASA Astrophysics Data System (ADS)
Smith, Robert E.
2009-12-01
We study the covariance of the cross-power spectrum of different tracers for the large-scale structure. We develop the counts-in-cells framework for the multitracer approach, and use this to derive expressions for the full non-Gaussian covariance matrix. We show that for the usual autopower statistic, besides the off-diagonal covariance generated through gravitational mode-coupling, the discreteness of the tracers and their associated sampling distribution can generate strong off-diagonal covariance, and that this becomes the dominant source of covariance as spatial frequencies become larger than the fundamental mode of the survey volume. On comparison with the derived expressions for the cross-power covariance, we show that the off-diagonal terms can be suppressed, if one cross-correlates a high tracer-density sample with a low one. Taking the effective estimator efficiency to be proportional to the signal-to-noise ratio (S/N), we show that, to probe clustering as a function of physical properties of the sample, i.e. cluster mass or galaxy luminosity, the cross-power approach can outperform the autopower one by factors of a few. We confront the theory with measurements of the mass-mass, halo-mass and halo-halo power spectra from a large ensemble of N-body simulations. We show that there is a significant S/N advantage to be gained from using the cross-power approach when studying the bias of rare haloes. The analysis is repeated in configuration space and again S/N improvement is found. We estimate the covariance matrix for these samples, and find strong off-diagonal contributions. The covariance depends on halo mass, with higher mass samples having stronger covariance. In agreement with theory, we show that the covariance is suppressed for the cross-power. This work points the way towards improved estimators for studying the clustering of tracers as a function of their physical properties.
NASA Astrophysics Data System (ADS)
Safar, Anuar Mat; Aljunid, Syed Alwee; Arief, Amir Razif; Nordin, Junita; Saad, Naufal
2012-01-01
The use of minimal multiple access interference (MAI) in code design is investigated. Applying a projection and mapping techniques, a code that has a zero cross correlation (ZCC) between users in optical code division multiple access (OCDMA) is presented in this paper. The system is based on an incoherent light source—LED, spectral amplitude coding (SAC), and direct detection techniques at the receiver. Using power spectral density (PSD) function and Gaussian approximation, we obtain the signal-to-noise ratio (SNR) and the bit-error rate (BER) to measure the code performance. Making a comparison with other existing codes, e.g., Hadamard, MFH and MDW codes, we show that our code performs better at BER 10-9 in terms of number of simultaneous users. We also demonstrate the comparison between the theoretical and simulation analyses, where the results are close to one another.
NASA Technical Reports Server (NTRS)
Pan, Y. S.
1975-01-01
Systematic methods based on cross-correlation techniques are presented for experimental studies of near- and farfield noise characteristics in airflow-surface interaction problems. Analyses show that, in near- and farfields, the noise characteristics due to the surface contribution of fluctuating pressures and velocities and due to the volume contribution of the turbulence in the flow can be determined separately. Both farfield noise intensities and nearfield acoustic energy fluxes can be expressed in terms of appropriate cross correlations. These correlations can be obtained by making microphone measurements in the farfield, in the nearfield, and on the surface. Examples of the applications to the noise field generated by impinging jets, by surface blowing jets, and by turbulent flow over trailing edges are presented. Advantages of the present method over conventional methods are also discussed.
NASA Astrophysics Data System (ADS)
Kitov, Ivan; Turuntaev, Sergey; Konovalov, Alexei; Stepnov, Andrey
2016-04-01
Unusually long duration of seismic activity (more than 20 years) was observed in the aftershock area of the 1995 Neftegorsk, Sakhalin, Russia catastrophic earthquake (Ms=7.6). To study the phenomena, we have processed seismic data from 130 events occurred within that area as measured between 2006 and 2015. In order to improve the accuracy of relative location and magnitude estimation of these events we have applied new techniques based on waveform cross correlation. We use 7 three-component (3-C) seismic stations which detected most of these events. Three-component waveform templates were prepared for these stations from those events which had signals with SNR>5 at vertical channels. The events with 3 and more templates are used as master-events for waveform cross correlation. Overall, the re-estimated location and magnitudes demonstrate higher precisions and are used for the statistical analysis and numerical modelling of seismo-tectonic regime within the studied zone.
Acoustic source location in a jet-blown flap using a cross-correlation technique
NASA Technical Reports Server (NTRS)
Becker, R. S.; Maus, J. R.
1977-01-01
The acoustic source strength distribution in a turbulent flow field was measured for two far field microphones at 45 deg above and below the plane of the flap surface. A processed signal from an inclined hot-film anemometry probe was cross correlated with the signal from the appropriate far field microphone. The contribution made by the sources associated with the fluctuating pressure on the flap surface to the sound received at far field microphone was estimated by cross correlating the processed signals of microphones which were embedded in the flap surface with the far field microphone signals. In addition, detailed fluid dynamic measurements were made in the flow field of the jet flap using dual sensor hot-film anemometry probes.
Background Noise Reduction Using Adaptive Noise Cancellation Determined by the Cross-Correlation
NASA Technical Reports Server (NTRS)
Spalt, Taylor B.; Brooks, Thomas F.; Fuller, Christopher R.
2012-01-01
Background noise due to flow in wind tunnels contaminates desired data by decreasing the Signal-to-Noise Ratio. The use of Adaptive Noise Cancellation to remove background noise at measurement microphones is compromised when the reference sensor measures both background and desired noise. The technique proposed modifies the classical processing configuration based on the cross-correlation between the reference and primary microphone. Background noise attenuation is achieved using a cross-correlation sample width that encompasses only the background noise and a matched delay for the adaptive processing. A present limitation of the method is that a minimum time delay between the background noise and desired signal must exist in order for the correlated parts of the desired signal to be separated from the background noise in the crosscorrelation. A simulation yields primary signal recovery which can be predicted from the coherence of the background noise between the channels. Results are compared with two existing methods.
Time Evolution of Financial Cross-Correlation Coefficients across Market Crisis
NASA Astrophysics Data System (ADS)
Tacchella, Andrea; Cristelli, Matthieu; Zaccaria, Andrea; Pietronero, Luciano
We investigate the time evolution of financial cross-correlation coefficients during financial crises and compare them to what is observed in periods of stability. We choose three main events, the Dot.Com Bubble, the market crisis which followed the attacks at the Twin Towers in 2001 and the recent subprime crisis. Each of them has a different nature and a different impact on the market, which we analyze by studying separately different economic sectors. As a general trend, we observe an increase of correlation during these high volatility periods and a broadening of the distributions of correlation coefficients. We then compare the spectra of the cross-correlation matrices, calculated in different periods of three years, with the distribution of eigenvalues predicted by the Random Matrix Theory. We find that these spectra are markedly perturbated during crisis periods. Finally we show how a simple stochastic model can produce similar results.
NASA Astrophysics Data System (ADS)
Ma, Pengcheng; Li, Daye; Li, Shuo
2016-02-01
Using one minute high-frequency data of the Shanghai Composite Index (SHCI) and the Shenzhen Composite Index (SZCI) (2007-2008), we employ the detrended fluctuation analysis (DFA) and the detrended cross correlation analysis (DCCA) with rolling window approach to observe the evolution of market efficiency and cross-correlation in pre-crisis and crisis period. Considering the fat-tail distribution of return time series, statistical test based on shuffling method is conducted to verify the null hypothesis of no long-term dependence. Our empirical research displays three main findings. First Shanghai equity market efficiency deteriorated while Shenzhen equity market efficiency improved with the advent of financial crisis. Second the highly positive dependence between SHCI and SZCI varies with time scale. Third financial crisis saw a significant increase of dependence between SHCI and SZCI at shorter time scales but a lack of significant change at longer time scales, providing evidence of contagion and absence of interdependence during crisis.
NASA Astrophysics Data System (ADS)
Shen, Chen-Hua
2015-12-01
To analyze the unique contribution of meteorological factors to the air pollution index (API), a new method, the detrended semipartial cross-correlation analysis (DSPCCA), is proposed. Based on both a detrended cross-correlation analysis and a DFA-based multivariate-linear-regression (DMLR), this method is improved by including a semipartial correlation technique, which is used to indicate the unique contribution of an explanatory variable to multiple correlation coefficients. The advantages of this method in handling nonstationary time series are illustrated by numerical tests. To further demonstrate the utility of this method in environmental systems, new evidence of the primary contribution of meteorological factors to API is provided through DMLR. Results show that the most important meteorological factors affecting API are wind speed and diurnal temperature range, and the explanatory ability of meteorological factors to API gradually strengthens with increasing time scales. The results suggest that DSPCCA is a useful method for addressing environmental systems.
Spectroscopy of cross-correlations of environmental noises with two qubits
NASA Astrophysics Data System (ADS)
Cywinski, Lukasz; Szankowski, Piotr; Trippenbach, Marek
A single qubit driven by an appropriate sequence of control pulses can serve as a spectrometer of local noise affecting its energy splitting. We show that by driving and observing two spatially separated qubits, it is possible to reconstruct the spectrum of cross-correlations of noises acting at various locations. When the qubits are driven by the same sequence of pulses, real part of cross-correlation spectrum can be reconstructed, while applying two distinct sequence to the two qubits allows for reconstruction of imaginary part of this spectrum. The latter quantity contains information on either causal correlations between environmental dynamics at distinct locations, or on the occurrence of propagation of noisy signals through the environment. While entanglement between the qubits is not necessary, its presence enhances the signal from which the spectroscopic information is reconstructed. This work is supported by funds of Polish National Science Center (NCN) under decision no. DEC- 2012/07/B/ST3/03616.
Sasaki, Akira; Yamamoto, Johtaro; Jin, Takashi; Kinjo, Masataka
2015-01-01
Reducing intracellular DNA degradation is critical to enhance the efficiency of gene therapy. Exogenous DNA incorporation into cells is strictly blocked by the defense machinery of intracellular nuclease activity. Raster image correlation spectroscopy (RICS) and raster image cross-correlation spectroscopy (cross-correlation RICS; ccRICS) are image-based correlation methods. These powerful tools allow the study of spatiotemporal molecular dynamics. Here we performed spatiotemporal ccRICS analyses of fluorescent DNA and directly monitored the process of exogenous DNA degradation in living cell cytoplasm. Such direct monitors of DNA degradation allow us to determine the fate of the exogenous DNA in living cells. On comparing the process in living cells, our study shows that cytoplasmic nuclease activity differs between cell lines; therefore, we propose that the difference of nuclease activity in cytoplasm dictates a different resistance to exogenous DNA incorporation. New insight on efficient gene delivery can be provided with our study. PMID:26400011
Cross correlation analysis of plasma perturbation in amplitude modulated reactive dusty plasmas
NASA Astrophysics Data System (ADS)
Ito, Teppei; Soejima, Masahiro; Yamashita, Daisuke; Seo, Hyunwoong; Itagaki, Naho; Koga, Kazunori; Shiratani, Masaharu; Kobayashi, Tatsuya; Inagaki, Shigeru
2015-09-01
Interactions between plasmas and nano-interface are one of the most important issues in plasma processing. We have studied effects of plasma perturbation on growth of nanoparticles in amplitude modulated reactive dusty plasmas and have clarified that amplitude modulation (AM) leads to suppression of growth of nanoparticles [1]. Here we report results of cross correlation analysis of time evolution of laser light scattering intensity from nanoparticles in reactive plasmas. Experiments were carried out using a capacitively-coupled rf discharge reactor with a two-dimensional laser light scattering (LLS) system. We employed Ar +DM-DMOS discharge plasmas to generate nanoparticles. The peaks at higher harmonics and subharmonics in spectra of laser light scattering intensity were detected, suggesting nonlinear coupling between plasma and nanoparticle amount. We found high cross correlation t between waves at AM frequency and its higher harmonics. Namely, perturbation at fAM closely correlates with those at higher harmonics.
Cross-correlation and image alignment for multi-band IR sensors
NASA Astrophysics Data System (ADS)
Lu, Thomas; Chao, Tien-Hsin; Chen, Kang (Frank); Luong, Andrew; Dewees, Mallory; Yan, Xinyi; Chow, Edward; Torres, Gilbert
2016-04-01
We present the development of a cross-correlation algorithm for correlating objects in the long wave, mid wave and short wave Infrared sensor arrays. The goal is to align the images in the multisensor suite by correlating multiple key features in the images. Due to the wavelength differences, the object appears very differently in the sensor images even the sensors focus on the same object. In order to perform accurate correlation of the same object in the multi-band images, we perform image processing on the images so that the features of the object become similar to each other. Fourier domain band pass filters are used to enhance the images. Mexican Hat and Gaussian Derivative Wavelets are used to further enhance the features of the object. A Python based QT graphical user interface has been implemented to carry out the process. We show reliable results of the cross-correlation of the objects in multiple band videos.
NASA Astrophysics Data System (ADS)
Falsone, G.; Settineri, D.
2011-06-01
A procedure for evaluating the response cross-correlation of a linear structural system subjected to the action of stationary random multi-correlated processes is presented in this work. It is based on the definition of the fourth-order differential equation governing the modal response cross-correlation and of the corresponding solution. This is expressed in terms of the corresponding fundamental matrix, whose expression is related to the fundamental matrices of the differential equations governing the modal responses. The properties of this matrix allows to define a particular unconditionally stable numerical integration approach, which is composed of two independent step-by-step procedures, a progressive one and a regressive one. The applications have shown a level of accuracy comparable to that corresponding to the numerical solution of the double convolution integral, but the presented approach is characterised by a reduced computational effort.
Sasaki, Akira; Yamamoto, Johtaro; Jin, Takashi; Kinjo, Masataka
2015-01-01
Reducing intracellular DNA degradation is critical to enhance the efficiency of gene therapy. Exogenous DNA incorporation into cells is strictly blocked by the defense machinery of intracellular nuclease activity. Raster image correlation spectroscopy (RICS) and raster image cross-correlation spectroscopy (cross-correlation RICS; ccRICS) are image-based correlation methods. These powerful tools allow the study of spatiotemporal molecular dynamics. Here we performed spatiotemporal ccRICS analyses of fluorescent DNA and directly monitored the process of exogenous DNA degradation in living cell cytoplasm. Such direct monitors of DNA degradation allow us to determine the fate of the exogenous DNA in living cells. On comparing the process in living cells, our study shows that cytoplasmic nuclease activity differs between cell lines; therefore, we propose that the difference of nuclease activity in cytoplasm dictates a different resistance to exogenous DNA incorporation. New insight on efficient gene delivery can be provided with our study. PMID:26400011
Perspectives of Cross-Correlation in Seismic Monitoring at the International Data Centre
NASA Astrophysics Data System (ADS)
Bobrov, Dmitry; Kitov, Ivan; Zerbo, Lassina
2014-03-01
We demonstrate that several techniques based on waveform cross-correlation are able to significantly reduce the detection threshold of seismic sources worldwide and to improve the reliability of arrivals by a more accurate estimation of their defining parameters. A master event and the events it can find using waveform cross-correlation at array stations of the International Monitoring System (IMS) have to be close. For the purposes of the International Data Centre (IDC), one can use the spatial closeness of the master and slave events in order to construct a new automatic processing pipeline: all qualified arrivals detected using cross-correlation are associated with events matching the current IDC event definition criteria (EDC) in a local association procedure. Considering the repeating character of global seismicity, more than 90 % of events in the reviewed event bulletin (REB) can be built in this automatic processing. Due to the reduced detection threshold, waveform cross-correlation may increase the number of valid REB events by a factor of 1.5-2.0. Therefore, the new pipeline may produce a more comprehensive bulletin than the current pipeline—the goal of seismic monitoring. The analysts' experience with the cross correlation event list (XSEL) shows that the workload of interactive processing might be reduced by a factor of two or even more. Since cross-correlation produces a comprehensive list of detections for a given master event, no additional arrivals from primary stations are expected to be associated with the XSEL events. The number of false alarms, relative to the number of events rejected from the standard event list 3 (SEL3) in the current interactive processing—can also be reduced by the use of several powerful filters. The principal filter is the difference between the arrival times of the master and newly built events at three or more primary stations, which should lie in a narrow range of a few seconds. In this study, one event at a
Draper, J.V.
1993-08-01
This document lists the functions likely to be performed by each proposed component of the Tank Waste Retrieval Manipulator System (TWRMS) and the user functions that must be performed to operate each component. While the information contained in this document is tentative because the systems are still evolving, it provides a foundation for task analysis and control room design efforts. These efforts will support the design of a test-bed control room in the near future and an operational control room later. The information in this document is based on specifications published for the TWRMS.
Cross-correlation cosmic shear with the SDSS and VLA FIRST surveys
NASA Astrophysics Data System (ADS)
Demetroullas, C.; Brown, M. L.
2016-03-01
We measure the cosmic shear power spectrum on large angular scales by cross-correlating the shapes of ˜9 million galaxies measured in the optical Sloan Digital Sky Survey (SDSS) with the shapes of ˜2.7 × 105 radio galaxies measured by the overlapping Very Large Array FIRST (Faint Images of the Radio Sky at Twenty centimetres) survey. Our measurements span the multipole range 10 < ℓ < 130, corresponding to angular scales 2° < θ < 20°. On these scales, the shear maps from both surveys suffer from significant systematic effects that prohibit a measurement of the shear power spectrum from either survey alone. Conversely, we demonstrate that a power spectrum measured by cross-correlating the two surveys is unbiased, reducing the impact of the systematics by at least an order of magnitude. We measure an E-mode power spectrum from the data that is inconsistent with zero signal at the 99 per cent confidence (˜2.7σ) level. The B-mode and EB cross-correlations are both found to be consistent with zero (within 1σ). These constraints are obtained after a careful error analysis that accounts for uncertainties due to cosmic variance, random galaxy shape noise and shape measurement errors, as well as additional errors associated with the observed large-scale systematic effects in the two surveys. Our constraints are consistent with the expected signal in the concordance cosmological model assuming recent estimates of the cosmological parameters from the Planck satellite, and literature values for the median redshifts of the SDSS and FIRST galaxy populations. The cross-correlation approach will be ideal for extracting robust results, with the exquisite control of systematics required, from future cosmic shear surveys with the Square Kilometre Array, Large Synoptic Survey Telescope, Euclid and WFIRST-AFTA.
NASA Astrophysics Data System (ADS)
Kirk, D.; Omori, Y.; Benoit-Lévy, A.; Cawthon, R.; Chang, C.; Larsen, P.; Amara, A.; Bacon, D.; Crawford, T. M.; Dodelson, S.; Fosalba, P.; Giannantonio, T.; Holder, G.; Jain, B.; Kacprzak, T.; Lahav, O.; MacCrann, N.; Nicola, A.; Refregier, A.; Sheldon, E.; Story, K. T.; Troxel, M. A.; Vieira, J. D.; Vikram, V.; Zuntz, J.; Abbott, T. M. C.; Abdalla, F. B.; Becker, M. R.; Benson, B. A.; Bernstein, G. M.; Bernstein, R. A.; Bleem, L. E.; Bonnett, C.; Bridle, S. L.; Brooks, D.; Buckley-Geer, E.; Burke, D. L.; Capozzi, D.; Carlstrom, J. E.; Rosell, A. Carnero; Kind, M. Carrasco; Carretero, J.; Crocce, M.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; Desai, S.; Diehl, H. T.; Dietrich, J. P.; Doel, P.; Eifler, T. F.; Evrard, A. E.; Flaugher, B.; Frieman, J.; Gerdes, D. W.; Goldstein, D. A.; Gruen, D.; Gruendl, R. A.; Honscheid, K.; James, D. J.; Jarvis, M.; Kent, S.; Kuehn, K.; Kuropatkin, N.; Lima, M.; March, M.; Martini, P.; Melchior, P.; Miller, C. J.; Miquel, R.; Nichol, R. C.; Ogando, R.; Plazas, A. A.; Reichardt, C. L.; Roodman, A.; Rozo, E.; Rykoff, E. S.; Sako, M.; Sanchez, E.; Scarpine, V.; Schubnell, M.; Sevilla-Noarbe, I.; Simard, G.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thomas, D.; Wechsler, R. H.; Weller, J.
2016-06-01
We measure the cross-correlation between weak lensing of galaxy images and of the cosmic microwave background (CMB). The effects of gravitational lensing on different sources will be correlated if the lensing is caused by the same mass fluctuations. We use galaxy shape measurements from 139 deg2 of the Dark Energy Survey (DES) Science Verification data and overlapping CMB lensing from the South Pole Telescope (SPT) and Planck. The DES source galaxies have a median redshift of zmed ˜ 0.7, while the CMB lensing kernel is broad and peaks at z ˜ 2. The resulting cross-correlation is maximally sensitive to mass fluctuations at z ˜ 0.44. Assuming the Planck 2015 best-fitting cosmology, the amplitude of the DES×SPT cross-power is found to be ASPT = 0.88 ± 0.30 and that from DES×Planck to be APlanck = 0.86 ± 0.39, where A = 1 corresponds to the theoretical prediction. These are consistent with the expected signal and correspond to significances of 2.9σ and 2.2σ, respectively. We demonstrate that our results are robust to a number of important systematic effects including the shear measurement method, estimator choice, photo-z uncertainty and CMB lensing systematics. We calculate a value of A = 1.08 ± 0.36 for DES×SPT when we correct the observations with a simple intrinsic alignment model. With three measurements of this cross-correlation now existing in the literature, there is not yet reliable evidence for any deviation from the expected LCDM level of cross-correlation. We provide forecasts for the expected signal-to-noise ratio of the combination of the five-year DES survey and SPT-3G.
Global grid of master events for waveform cross-correlation: from testing to real time processing
NASA Astrophysics Data System (ADS)
Bobrov, Dmitry; Rozhkov, Mikhail; Kitov, Ivan
2014-05-01
Seismic monitoring of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) requires a globally uniform detection threshold, which is provided by geographical distribution of the Primary Seismic Network of the International Monitoring System (IMS). This detection threshold has to be as low as allowed by the entire set of real time and historical data recorded by the IMS. The International Data Centre (IDC) analyzes all relevant data in automatic processing and interactive review to issue a Reviewed Event Bulletin (REB), which includes all qualified events as obtained for the purpose of nuclear test monitoring. Since 2000, raw data, individual detections, and created events are saved in the IDC archive currently reaching tens of terabyte. In order to effectively use this archive in global monitoring we introduced the waveform cross correlation (matched filter) technique. Cross correlation between real time records at IMS stations and template waveforms is calculated for a dense (spacing of ~ 140 km) and regular grid of master events uniformly covering the globe. There are approximately 25,000 master events with 3 to 10 templates at IMS stations. In seismically active zones, we populate masters with real waveforms. For aseismic zones, we develop an extended set of synthetic templates for virtual master events. For optimal performance of cross correlation, the Principal and Independent Component Analysis are applied to the historical (from earthquakes and underground nuclear tests) and synthetic waveforms. Real waveform templates and selected PCA/ICA components are used in automatic processing for the production of a tentative cross-correlation standard event list (XSEL).
New geo-portal for MODIS/SEVIRI image products with geolocation-based retrieval functionality
NASA Astrophysics Data System (ADS)
Sevilla, Jorge; Julien, Yves; Sória, Guillem; Sobrino, José A.; Plaza, Antonio
2015-01-01
A large number of remote sensing data sets have been collected in recent years by Earth observation instruments such as the moderate resolution imaging spectroradiometer (MODIS) aboard the Terra/Aqua satellite and the spinning enhanced visible and infrared imager (SEVIRI) aboard the geostationary platform Meteosat Second Generation. The advanced remote sensing products resulting from the analysis of these data are useful in a wide variety of applications but require significant resources in terms of storage, retrieval, and analysis. Despite the wide availability of these MODIS/SEVIRI products, the data coming from these instruments are spread among different locations and retrieved from different sources, and there is no common data repository from which the data or the associated products can be retrieved. We take a first step toward the development of a geo-portal for storing and efficiently retrieving MODIS/SEVIRI remote sensing products. The products are obtained using an automatic system that processes the data as soon as they are provided by the collecting antennas, and then the final products are uploaded with a one day delay in the geo-portal. Our focus in this work is on describing the design and efficient implementation of the geo-portal, which allows for a user-friendly and effective access to a full repository of MODIS/SEVIRI advanced products (comprising tens of terabytes of data) using geolocation retrieval capabilities. The geo-portal has been implemented as a web application composed of different layers. Its modular design provides quality of service and scalability (capacity for growth without any quality losing), allowing for the addition of components without the need to modify the entire system. On the client layer, an intuitive web browser interface provides users with remote access to the system. On the server layer, the system provides advanced data management and storage capabilities. On the storage layer, the system provides a secure
Passive dispersion analysis on a sea dike using cross-correlations and beamforming
NASA Astrophysics Data System (ADS)
Le Feuvre, Mathieu; Joubert, Anaëlle; Leparoux, Donatienne; Côte, Philippe
2014-05-01
In order to passively infer the velocities of surface waves beneath a receiver array, we propose to apply beamforming on cross-correlated noise records. We test the method with synthetic signals generated for a variety of array geometries and noise distributions. We show that the use of cross-correlations cleans the dispersion diagram that would be obtained from a phase-shift analysis alone, by resolving ambiguities between the location of noise sources and the wave velocities. In particular, when nearby noise sources are present, accurate dispersion curves can be inferred from arrays possessing poor azimuthal coverages. This passive method is therefore appropriate for the monitoring of stiffness at the civil-engineering scale, where multiple isolated noise sources may be present and where the field geometry does not always allow to deploy circular arrays. We apply the method to field data obtained from a linear array installed on top of a sea dike. The seismic noise, recorded at high tide during 8 minutes, is essentially generated by impacts of sea waves. In contrast to a phase-shift analysis performed on the noise itself, we show that the use of cross-correlations allow to infer a dispersion curve consistent with an active hammer-shot measurement, in a larger frequency band, ranging from 5 to 55 Hz. This result opens the possibility of following passively the mechanical evolution of embankments on a daily basis.
Spatial cross-correlation of Antarctic Sea ice and seabed topography
NASA Technical Reports Server (NTRS)
Deveaux, Richard D.; Phelan, Michael J.
1990-01-01
A time series of derived sea ice concentrations as observed about Antarctica by the Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) satellite in 1983 is considered. The degree of spatial cross correlation between these data and seabed topography is quantified. The approach is to implement a statistical image processing filter designed to extract local patterns of spatial cross correlation over the entire sea ice field as it undergoes daily changes. Throughout the sea ice, it was found that large scale variations in sea ice concentration correlate systematically with variations in the topography of the seabed. Generally speaking, high concentrations of sea ice occur over deep ocean, whereas areas of encavement, early dissipation and polynya formation develop over topographic features of high elevation. The latter was studied in detail with respect to the features Maud Rise, Astrid Ridge and the continental shelf in the Cosmonaut and Ross Seas. In each case, it is shown that an encavement in sea ice, a polynya, or both develops in the vicinity of the feature in question. As these results are quantified in terms of spatial cross correlation, a potential role is inferred for seabed topography in such fluctuations in the sea ice about Antarctica.
NASA Technical Reports Server (NTRS)
Serafini, J. S.; Terdan, F. F.
1973-01-01
Measurements of the RMS magnitude, spectra and cross-correlations for the fluctuations in the beam, discharge and neutralizer keeper currents are presented for a 30-cm diameter dished grid ion thrustor for a range of magnetic baffle currents and up to 2.0 amperes beam current. The ratio of RMS to mean ion beam current varied from 0.04 to 0.23. The spectra of the amplitudes of the beam and discharge current fluctuations were taken up to 9 MHz and show that the predominant amplitudes occur at frequencies of 10 kHz or below. The fall-off with increasing frequency is rapid. Frequencies above 100 kHz the spectral levels are 45 kb or more below the maximum peak amplitudes. The cross-correlations revealed the ion beam fluctuations to have large radial and axial scales which implied that the beam fluctuates as a whole or 'in-phase.' The cross-correlations of the beam and neutralizer keeper current fluctuations indicated the neutralizer contributions to the beam fluctuations to be small, but not negligible. The mode of operation of the thrustor (values of beam and magnetic baffle currents) was significant in determining the RMS magnitude and spectral shape of the beam fluctuations. The major oscillations were not found to be directly dependent on the power conditioner inverter frequencies.
NASA Astrophysics Data System (ADS)
Kim, Sungyoung; Martens, William L.
2005-04-01
By industry standard (ITU-R. Recommendation BS.775-1), multichannel stereophonic signals within the frequency range of up to 80 or 120 Hz may be mixed and delivered via a single driver (e.g., a subwoofer) without significant impairment of stereophonic sound quality. The assumption that stereophonic information within such low-frequency content is not significant was tested by measuring discrimination thresholds for changes in interaural cross-correlation (IACC) within spectral bands containing the lowest frequency components of low-pitch musical tones. Performances were recorded for three different musical instruments playing single notes ranging in fundamental frequency from 41 Hz to 110 Hz. The recordings, made using a multichannel microphone array composed of five DPA 4006 pressure microphones, were processed to produce a set of stimuli that varied in interaural cross-correlation (IACC) within a low-frequency band, but were otherwise identical in a higher-frequency band. This correlation processing was designed to have minimal effect upon other psychoacoustic variables such as loudness and timbre. The results show that changes in interaural cross correlation (IACC) within low-frequency bands of low-pitch musical tones are most easily discriminated when decorrelated signals are presented via subwoofers positioned at extreme lateral angles (far from the median plane). [Work supported by VRQ.
A new 'Implicit correlation' method for cross-correlation sampling in MCNPX-PoliMi
Marcath, M. J.; Larsen, E. W.; Clarke, S. D.; Pozzi, S. A.
2013-07-01
Monte Carlo particle transport codes used to accurately model detector response are traditionally run in fully analog mode. Analog simulations of cross-correlation measurements with these codes are extremely time-consuming because the probability of correlated detection is extremely small, approximately equal to the product of the probabilities of a single detection in each detector. The new 'implicit correlation' method described here increases the number of correlation event scores thereby reducing variance and required computation times. The cost of the implicit correlation method is comparable to the cost of simulating single event detection for the lowest absolute detector efficiency in the problem. This method is especially useful in the nuclear non-proliferation and safeguards fields for simulating correlation measurements of shielded special nuclear material. The new method was implemented in MCNPX-PoliMi for neutron-neutron cross-correlations with a Cf-252 spontaneous fission source measured by two detectors of variable stand-offs. The method demonstrated good agreement with analog simulation results for multiple measurement geometries. Small differences between non-analog and analog cross-correlation distributions are attributed to known features of the specific problem simulated that will not be present in practical applications. (authors)
Dynamic evolution of cross-correlations in the Chinese stock market.
Ren, Fei; Zhou, Wei-Xing
2014-01-01
The analysis of cross-correlations is extensively applied for the understanding of interconnections in stock markets and the portfolio risk estimation. Current studies of correlations in Chinese market mainly focus on the static correlations between return series, and this calls for an urgent need to investigate their dynamic correlations. Our study aims to reveal the dynamic evolution of cross-correlations in the Chinese stock market, and offer an exact interpretation for the evolution behavior. The correlation matrices constructed from the return series of 367 A-share stocks traded on the Shanghai Stock Exchange from January 4, 1999 to December 30, 2011 are calculated over a moving window with a size of 400 days. The evolutions of the statistical properties of the correlation coefficients, eigenvalues, and eigenvectors of the correlation matrices are carefully analyzed. We find that the stock correlations are significantly increased in the periods of two market crashes in 2001 and 2008, during which only five eigenvalues significantly deviate from the random correlation matrix, and the systemic risk is higher in these volatile periods than calm periods. By investigating the significant contributors of the deviating eigenvectors in different time periods, we observe a dynamic evolution behavior in business sectors such as IT, electronics, and real estate, which lead the rise (drop) before (after) the crashes. Our results provide new perspectives for the understanding of the dynamic evolution of cross-correlations in the Chines stock markets, and the result of risk estimation is valuable for the application of risk management. PMID:24867071
Dynamic Evolution of Cross-Correlations in the Chinese Stock Market
Ren, Fei; Zhou, Wei-Xing
2014-01-01
The analysis of cross-correlations is extensively applied for the understanding of interconnections in stock markets and the portfolio risk estimation. Current studies of correlations in Chinese market mainly focus on the static correlations between return series, and this calls for an urgent need to investigate their dynamic correlations. Our study aims to reveal the dynamic evolution of cross-correlations in the Chinese stock market, and offer an exact interpretation for the evolution behavior. The correlation matrices constructed from the return series of 367 A-share stocks traded on the Shanghai Stock Exchange from January 4, 1999 to December 30, 2011 are calculated over a moving window with a size of 400 days. The evolutions of the statistical properties of the correlation coefficients, eigenvalues, and eigenvectors of the correlation matrices are carefully analyzed. We find that the stock correlations are significantly increased in the periods of two market crashes in 2001 and 2008, during which only five eigenvalues significantly deviate from the random correlation matrix, and the systemic risk is higher in these volatile periods than calm periods. By investigating the significant contributors of the deviating eigenvectors in different time periods, we observe a dynamic evolution behavior in business sectors such as IT, electronics, and real estate, which lead the rise (drop) before (after) the crashes. Our results provide new perspectives for the understanding of the dynamic evolution of cross-correlations in the Chines stock markets, and the result of risk estimation is valuable for the application of risk management. PMID:24867071
MEASUREMENT OF 21 cm BRIGHTNESS FLUCTUATIONS AT z {approx} 0.8 IN CROSS-CORRELATION
Masui, K. W.; Switzer, E. R.; Calin, L.-M.; Pen, U.-L.; Shaw, J. R.; Banavar, N.; Bandura, K.; Blake, C.; Chang, T.-C.; Liao, Y.-W.; Chen, X.; Li, Y.-C.; Natarajan, A.; Peterson, J. B.; Voytek, T. C.
2013-01-20
In this Letter, 21 cm intensity maps acquired at the Green Bank Telescope are cross-correlated with large-scale structure traced by galaxies in the WiggleZ Dark Energy Survey. The data span the redshift range 0.6 < z < 1 over two fields totaling {approx}41 deg. sq. and 190 hr of radio integration time. The cross-correlation constrains {Omega}{sub HI} b{sub HI} r = [0.43 {+-} 0.07(stat.) {+-} 0.04(sys.)] Multiplication-Sign 10{sup -3}, where {Omega}{sub HI} is the neutral hydrogen (H I) fraction, r is the galaxy-hydrogen correlation coefficient, and b{sub HI} is the H I bias parameter. This is the most precise constraint on neutral hydrogen density fluctuations in a challenging redshift range. Our measurement improves the previous 21 cm cross-correlation at z {approx} 0.8 both in its precision and in the range of scales probed.
Contamination of early-type galaxy alignments to galaxy lensing-CMB lensing cross-correlation
NASA Astrophysics Data System (ADS)
Chisari, Nora Elisa; Dunkley, Joanna; Miller, Lance; Allison, Rupert
2015-10-01
Galaxy shapes are subject to distortions due to the tidal field of the Universe. The cross-correlation of galaxy lensing with the lensing of the cosmic microwave background (CMB) cannot easily be separated from the cross-correlation of galaxy intrinsic shapes with CMB lensing. Previous work suggested that the intrinsic alignment contamination can be 15 per cent of this cross-spectrum for the CFHT Stripe 82 (CS82) and Atacama Cosmology Telescope surveys. Here we re-examine these estimates using up-to-date observational constraints of intrinsic alignments at a redshift more similar to that of CS82 galaxies. We find an ≈10 per cent contamination of the cross-spectrum from red galaxies, with ≈3 per cent uncertainty due to uncertainties in the redshift distribution of source galaxies and the modelling of the spectral energy distribution. Blue galaxies are consistent with being unaligned, but could contaminate the cross-spectrum by an additional 9.5 per cent within current 95 per cent confidence levels. While our fiducial estimate of alignment contamination is similar to previous work, our work suggests that the relevance of alignments for CMB lensing-galaxy lensing cross-correlation remains largely unconstrained. Little information is currently available about alignments at z > 1.2. We consider the upper limiting case where all z > 1.2 galaxies are aligned with the same strength as low-redshift luminous red galaxies, finding as much as ≈60 per cent contamination.
NASA Astrophysics Data System (ADS)
Sun, Hong-Mei; Jia, Rui-Sheng; Du, Qian-Qian; Fu, You
2016-06-01
A micro-seismic signal's transient features are non-stationary. The traditional weighted generalized cross-correlation (GCC) algorithm is based on the cross-power spectrum density. This algorithm diminishes the performance of the time delay estimation for homologous micro-seismic signals. This paper analyzed the influence of calculation error on the cross-power spectrum density of a non-stationary signal and proposed a new cross-correlation analysis and time delay estimation method for homologous micro-seismic signals based on the Hilbert-Huang transform (HHT). First, the original signals are decomposed into intrinsic mode function (IMF) components using empirical mode decomposition (EMD) for de-noising. Subsequently, the IMF components and the original signals are analyzed using a cross-correlation analysis. The IMF components are subsequently remodeled at different scales using the Hilbert transform. The marginal spectrum density is obtained via a time integration of the remodeled components. The cross-marginal spectrum density of the two signals can also be obtained. Finally, the cross-marginal spectrum density is used in the weighted GCC algorithm for time delay estimation instead of the cross-power spectrum density. The time delay estimation is determined by searching for the weighted GCC function peak. The experiments demonstrated the superior time delay estimation performance of the new method for non-stationary transient signals. Therefore, a new time delay estimation method for non-stationary random signals is presented in this paper.
Optimization of Ambient Noise Cross-Correlation Imaging Across Large Dense Array
NASA Astrophysics Data System (ADS)
Sufri, O.; Xie, Y.; Lin, F. C.; Song, W.
2015-12-01
Ambient Noise Tomography is currently one of the most studied topics of seismology. It gives possibility of studying physical properties of rocks from the depths of subsurface to the upper mantle depths using recorded noise sources. A network of new seismic sensors, which are capable of recording continuous seismic noise and doing the processing at the same time on-site, could help to assess possible risk of volcanic activity on a volcano and help to understand the changes in physical properties of a fault before and after an earthquake occurs. This new seismic sensor technology could also be used in oil and gas industry to figure out depletion rate of a reservoir and help to improve velocity models for obtaining better seismic reflection cross-sections. Our recent NSF funded project is bringing seismologists, signal processors, and computer scientists together to develop a new ambient noise seismic imaging system which could record continuous seismic noise and process it on-site and send Green's functions and/or tomography images to the network. Such an imaging system requires optimum amount of sensors, sensor communication, and processing of the recorded data. In order to solve these problems, we first started working on the problem of optimum amount of sensors and the communication between these sensors by using small aperture dense network called Sweetwater Array, deployed by Nodal Seismic in 2014. We downloaded ~17 day of continuous data from 2268 one-component stations between March 30-April 16 2015 from IRIS DMC and performed cross-correlation to determine the lag times between station pairs. The lag times were then entered in matrix form. Our goal is to selecting random lag time values in the matrix and assuming all other elements of the matrix either missing or unknown and performing matrix completion technique to find out how close the results from matrix completion technique would be close to the real calculated values. This would give us better idea
Kernel Feature Cross-Correlation for Unsupervised Quantification of Damage from Windthrow in Forests
NASA Astrophysics Data System (ADS)
Pirotti, F.; Travaglini, D.; Giannetti, F.; Kutchartt, E.; Bottalico, F.; Chirici, G.
2016-06-01
In this study estimation of tree damage from a windthrow event using feature detection on RGB high resolution imagery is assessed. An accurate quantitative assessment of the damage in terms of volume is important and can be done by ground sampling, which is notably expensive and time-consuming, or by manual interpretation and analyses of aerial images. This latter manual method also requires an expert operator investing time to manually detect damaged trees and apply relation functions between measures and volume which are also error-prone. In the proposed method RGB images with 0.2 m ground sample distance are analysed using an adaptive template matching method. Ten images corresponding to ten separate study areas are tested. A 13x13 pixels kernel with a simplified linear-feature representation of a cylinder is applied at different rotation angles (from 0° to 170° at 10° steps). The higher values of the normalized cross-correlation (NCC) of all angles are recorded for each pixel for each image. Several features are tested: percentiles (75, 80, 85, 90, 95, 99, max) and sum and number of pixels with NCC above 0.55. Three regression methods are tested, multiple regression (mr), support vector machines (svm) with linear kernel and random forests. The first two methods gave the best results. The ground-truth was acquired by ground sampling, and total volumes of damaged trees are estimated for each of the 10 areas. Damaged volumes in the ten areas range from ~1.8 x102 m3 to ~1.2x104 m3. Regression results show that smv regression method over the sum gives an R-squared of 0.92, a mean of absolute errors (MAE) of 255 m3 and a relative absolute error (RAE) of 34% using leave-one-out cross validation from the 10 observations. These initial results are encouraging and support further investigations on more finely tuned kernel template metrics to define an unsupervised image analysis process to automatically assess forest damage from windthrow.
NASA Astrophysics Data System (ADS)
Cao, Guangxi; He, Cuiting; Xu, Wei
2016-03-01
This study investigates the correlation between weather and agricultural futures markets on the basis of detrended cross-correlation analysis (DCCA) cross-correlation coefficients and q-dependent cross-correlation coefficients. In addition, detrended fluctuation analysis (DFA) is used to measure extreme weather and thus analyze further the effect of this condition on agricultural futures markets. Cross-correlation exists between weather and agricultural futures markets on certain time scales. There are some correlations between temperature and soybean return associated with medium amplitudes. Under extreme weather conditions, weather exerts different influences on different agricultural products; for instance, soybean return is greatly influenced by temperature, and weather variables exhibit no effect on corn return. Based on the detrending moving-average cross-correlation analysis (DMCA) coefficient and DFA regression results are similar to that of DCCA coefficient.
Hirata, Shinnosuke; Kurosawa, Minoru Kuribayashi
2012-09-01
Real-time distance measurement of a moving object with high accuracy and high resolution using an ultrasonic wave is difficult due to the influence of the Doppler effect or the limit of the calculation cost of signal processing. An over-sampling signal processing method using a pair of LPM signals has been proposed for ultrasonic distance and velocity measurement of moving objects with high accuracy and high resolution. The proposed method consists of cross correlation by single-bit signal processing, high-resolution Doppler velocity estimation with wide measurement range and low-calculation-cost Doppler-shift compensation. The over-sampling cross-correlation function is obtained from cross correlation by single-bit signal processing with low calculation cost. The Doppler velocity and distance of the object are determined from the peak interval and peak form in the cross-correlation function by the proposed method of Doppler velocity estimation and Doppler-shift compensation. In this paper, the proposed method of Doppler-shift compensation is improved. Accuracy of the determined distance was improved from approximately within ±140μm in the previous method to approximately within ±10μm in computer simulations. Then, the proposed method of Doppler velocity estimation is evaluated. In computer simulations, accuracy of the determined Doppler velocity and distance were demonstrated within ±8.471mm/s and ±13.87μm. In experiments, Doppler velocities of the motorized stage could be determined within ±27.9mm/s. PMID:22560801
Kirk, D.; et al.
2015-12-14
We measure the cross-correlation between weak lensing of galaxy images and of the cosmic microwave background (CMB). The effects of gravitational lensing on different sources will be correlated if the lensing is caused by the same mass fluctuations. We use galaxy shape measurements from 139 deg$^{2}$ of the Dark Energy Survey (DES) Science Verification data and overlapping CMB lensing from the South Pole Telescope (SPT) and Planck. The DES source galaxies have a median redshift of $z_{\\rm med} {\\sim} 0.7$, while the CMB lensing kernel is broad and peaks at $z{\\sim}2$. The resulting cross-correlation is maximally sensitive to mass fluctuations at $z{\\sim}0.44$. Assuming the Planck 2015 best-fit cosmology, the amplitude of the DES$\\times$SPT cross-power is found to be $A = 0.88 \\pm 0.30$ and that from DES$\\times$Planck to be $A = 0.86 \\pm 0.39$, where $A=1$ corresponds to the theoretical prediction. These are consistent with the expected signal and correspond to significances of $2.9 \\sigma$ and $2.2 \\sigma$ respectively. We demonstrate that our results are robust to a number of important systematic effects including the shear measurement method, estimator choice, photometric redshift uncertainty and CMB lensing systematics. Significant intrinsic alignment of galaxy shapes would increase the cross-correlation signal inferred from the data; we calculate a value of $A = 1.08 \\pm 0.36$ for DES$\\times$SPT when we correct the observations with a simple IA model. With three measurements of this cross-correlation now existing in the literature, there is not yet reliable evidence for any deviation from the expected LCDM level of cross-correlation, given the size of the statistical uncertainties and the significant impact of systematic errors, particularly IAs. We provide forecasts for the expected signal-to-noise of the combination of the five-year DES survey and SPT-3G.
Detection of thermal SZ-CMB lensing cross-correlation in Planck nominal mission data
Hill, J. Colin; Spergel, David N. E-mail: dns@astro.princeton.edu
2014-02-01
The nominal mission maps from the Planck satellite contain a wealth of information about secondary anisotropies in the cosmic microwave background (CMB), including those induced by the thermal Sunyaev-Zel'dovich (tSZ) effect and gravitational lensing. As both the tSZ and CMB lensing signals trace the large-scale matter density field, the anisotropies sourced by these processes are expected to be correlated. We report the first detection of this cross-correlation signal, which we measure at 6.2σ significance using the Planck data. We take advantage of Planck's multifrequency coverage to construct a tSZ map using internal linear combination techniques, which we subsequently cross-correlate with the publicly-released Planck CMB lensing potential map. The cross-correlation is subject to contamination from the cosmic infrared background (CIB), which is known to correlate strongly with CMB lensing. We correct for this contamination via cross-correlating our tSZ map with the Planck 857 GHz map and confirm the robustness of our measurement using several null tests. We interpret the signal using halo model calculations, which indicate that the tSZ-CMB lensing cross-correlation is a unique probe of the physics of intracluster gas in high-redshift, low-mass groups and clusters. Our results are consistent with extrapolations of existing gas physics models to this previously unexplored regime and show clear evidence for contributions from both the one- and two-halo terms, but no statistically significant evidence for contributions from diffuse, unbound gas outside of collapsed halos. We also show that the amplitude of the signal depends rather sensitively on the amplitude of fluctuations (σ{sub 8}) and the matter density (Ω{sub m}), scaling as σ{sub 8}{sup 6.1}Ω{sub m}{sup 1.5} at ℓ = 1000. We constrain the degenerate combination σ{sub 8}(Ω{sub m}/0.282){sup 0.26} = 0.824±0.029, a result that is in less tension with primordial CMB constraints than some recent t
A novel pitch evaluation of one-dimensional gratings based on a cross-correlation filter
NASA Astrophysics Data System (ADS)
Chen, Xiaomei; Koenders, Ludger
2014-04-01
If one-dimensional (1D), p-period and arbitrarily structured grating position-related topographical signals coexist with noise, it is difficult to evaluate the pitch practically using the center-of-gravity (CG) method. The Fourier-transform-based (FT) method is the most precise to evaluate pitches; nevertheless, it cannot give the uniformity of pitches. If a cross-correlation filter—a half period of sinusoidal waveform sequence (pT period), cross-correlates with the signals, the noise can be eliminated if pT ≈ p. After cross-correlation filtering, the distance between any two adjacent waveform peaks along the direction perpendicular to 1D grating lines is one pitch value. The pitch evaluation based on the cross-correlation filtering together with the detection of the peak's position is described as the peak detection (PD) method in this paper. The pitch average and uniformity can be calculated by using the PD method. The computer simulation has indicated that the average of pitch deviations from the true pitch and the pitch variations are less than 0.2% and 0.2% for the sinusoidal and rectangular waveform signals with up to 50% uniform white noise, less than 0.1% and 1% for the sinusoidal and rectangular waveform signals and 0.6% and 2.5% for the triangular waveform signal if three waveform signals are mixed with Gaussian white, binomial and Bernoulli noise up to 50% in standard deviation, one probability and trial probability, respectively. As examples, a highly oriented pyrolytic graphite (HOPG) with a 0.246 nm distance between second nearest neighbour atoms and a 1D grating with 3000 nm nominal pitch are measured by a ultra-high vacuum scanning tunneling microscope (UHV STM) and a metrological atomic force microscope (AFM), respectively. After the position-related topographical signals are cross-correlation filtered, the 0.240 and 3004.11 nm pitches calculated by using the PD method are very close to the 0.240 and 3003.34 nm results evaluated by the FT
F2DPR: a fast and robust cross-correlation technique for volumetric PIV
NASA Astrophysics Data System (ADS)
Earl, Thomas; Jeon, Young Jin; Lecordier, Bertrand; David, Laurent
2016-08-01
The current state-of-the-art in cross-correlation based time-resolved particle image velocimetry (PIV) techniques are the fluid trajectory correlation, FTC (Lynch and Scarano 2013) and the fluid trajectory evaluation based on an ensemble-averaged cross-correlation, FTEE (Jeon et al 2014a). These techniques compute the velocity vector as a polynomial trajectory Γ in space and time, enabling the extraction of beneficial quantities such as material acceleration whilst significantly increasing the accuracy of the particle displacement prediction achieved by standard two-frame PIV. In the context of time-resolved volumetric PIV, the drawback of trajectory computation is the computational expense of the three-dimensional (3D) cross-correlation, exacerbated by the requirement to perform N ‑ 1 cross-correlations, where N (for typically 5≤slant N≤slant 9 ) is the number of sequential particle volumes, for each velocity field. Therefore, the acceleration of this calculation is highly desirable. This paper re-examines the application of two-dimensional (2D) cross-correlation methods to three-dimensional (3D) datasets by Bilsky et al (2011) and the binning techniques of Discetti and Astarita (2012). A new and robust version of the 2D methods is proposed and described, called fast 2D projection—re-projection (f2dpr). Performance tests based on computational time and accuracy for both two-frame and multi-frame PIV are carried out on synthetically generated data. The cases presented herein include uniaxial uniform linear displacements and shear, and simulated turbulence data. The proposed algorithm is shown to be in the order of 10 times faster than a standard 3D FFT without loss of precision for a wide range of synthetic test cases, while combining with the binning technique can yield 50 times faster computation. The algorithm is also applied to reconstructed synthetic turbulent particle fields to investigate reconstruction noise on its performance and no
FAST X-RAY/IR CROSS-CORRELATIONS AND RELATIVISTIC JET FORMATION IN GRS 1915+105
Lasso-Cabrera, N. M.; Eikenberry, S. S.
2013-10-01
We present cross-correlation analyses of simultaneous X-ray and near-infrared (near-IR) observations of the microquasar GRS 1915+105 during relativistic jet-producing epochs (X-ray class α and β). While previous studies have linked the large amplitude IR flares and X-ray behaviors to jet formation in these states, our new analyses are sensitive to much lower amplitude IR variability, providing more sensitive probes of the jet formation process. The X-ray to IR cross-correlation function (CCF) shows significant correlations that vary in form between the different X-ray states. During low/hard dips in both classes, we find no significant X-ray/IR correlation. During high-variability epochs, we find consistently significant correlations in both α and β classes, but with strong differences in the CCF structure. The high variability α CCF shows strong anti-correlation between X-ray/IR, with the X-ray preceding the IR by ∼13 ± 2 s. The high variability β state shows a time-variable CCF structure, which is statistically significant but without a clearly consistent lag. Our simulated IR light curves, designed to match the observed CCFs, show variably flickering IR emission during the class β high-variability epoch, while class α can be fit by IR flickering with frequencies in the range 0.1-0.3 Hz, strengthening ∼10 s after every X-ray subflare. We interpret these features in the context of the X-ray-emitting accretion disk and IR emission from relativistic jet formation in GRS 1915+105, concluding that the CCF analysis places the origin in a synchrotron-emitting relativistic compact jet at a distance from the compact object of ∼0.02 AU.
Visbal, Eli; Loeb, Abraham E-mail: aloeb@cfa.harvard.edu
2010-11-01
We discuss a method for detecting the emission from high redshift galaxies by cross correlating flux fluctuations from multiple spectral lines. If one can fit and subtract away the continuum emission with a smooth function of frequency, the remaining signal contains fluctuations of flux with frequency and angle from line emitting galaxies. Over a particular small range of observed frequencies, these fluctuations will originate from sources corresponding to a series of different redshifts, one for each emission line. It is possible to statistically isolate the fluctuations at a particular redshift by cross correlating emission originating from the same redshift, but in different emission lines. This technique will allow detection of clustering fluctuations from the faintest galaxies which individually cannot be detected, but which contribute substantially to the total signal due to their large numbers. We describe these fluctuations quantitatively through the line cross power spectrum. As an example of a particular application of this technique, we calculate the signal-to-noise ratio for a measurement of the cross power spectrum of the OI(63 μm) and OIII(52 μm) fine structure lines with the proposed Space Infrared Telescope for Cosmology and Astrophysics (SPICA). We find that the cross power spectrum can be measured beyond a redshift of z = 8. Such observations could constrain the evolution of the metallicity, bias, and duty cycle of faint galaxies at high redshifts and may also be sensitive to the reionization history through its effect on the minimum mass of galaxies. As another example of this technique, we calculate the signal-to-noise ratio for the cross power spectrum of CO line emission measured with a large ground based telescope like the Cornell Caltech Atacama Telescope (CCAT) and 21-cm radiation originating from hydrogen in galaxies after reionization with an interferometer similar in scale to the Murchison Widefield Array (MWA), but optimized for post
Word-to-picture recognition is a function of motor components mappings at the stage of retrieval.
Brouillet, Denis; Brouillet, Thibaut; Milhau, Audrey; Heurley, Loïc; Vagnot, Caroline; Brunel, Lionel
2016-10-01
Embodied approaches of cognition argue that retrieval involves the re-enactment of both sensory and motor components of the desired remembering. In this study, we investigated the effect of motor action performed to produce the response in a recognition task when this action is compatible with the affordance of the objects that have to be recognised. In our experiment, participants were first asked to learn a list of words referring to graspable objects, and then told to make recognition judgements on pictures. The pictures represented objects where the graspable part was either pointing to the same or to the opposite side of the "Yes" response key. Results show a robust effect of compatibility between objects affordance and response hand. Moreover, this compatibility improves participants' ability of discrimination, suggesting that motor components are relevant cue for memory judgement at the stage of retrieval in a recognition task. More broadly, our data highlight that memory judgements are a function of motor components mappings at the stage of retrieval. PMID:27585735
A General Uncertainty Quantification Methodology for Cloud Microphysical Property Retrievals
NASA Astrophysics Data System (ADS)
Tang, Q.; Xie, S.; Chen, X.; Zhao, C.
2014-12-01
The US Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program provides long-term (~20 years) ground-based cloud remote sensing observations. However, there are large uncertainties in the retrieval products of cloud microphysical properties based on the active and/or passive remote-sensing measurements. To address this uncertainty issue, a DOE Atmospheric System Research scientific focus study, Quantification of Uncertainties in Cloud Retrievals (QUICR), has been formed. In addition to an overview of recent progress of QUICR, we will demonstrate the capacity of an observation-based general uncertainty quantification (UQ) methodology via the ARM Climate Research Facility baseline cloud microphysical properties (MICROBASE) product. This UQ method utilizes the Karhunen-Loéve expansion (KLE) and Central Limit Theorems (CLT) to quantify the retrieval uncertainties from observations and algorithm parameters. The input perturbations are imposed on major modes to take into account the cross correlations between input data, which greatly reduces the dimension of random variables (up to a factor of 50) and quantifies vertically resolved full probability distribution functions of retrieved quantities. Moreover, this KLE/CLT approach has the capability of attributing the uncertainties in the retrieval output to individual uncertainty source and thus sheds light on improving the retrieval algorithm and observations. We will present the results of a case study for the ice water content at the Southern Great Plains during an intensive observing period on March 9, 2000. This work is performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Vallinotto, Alberto; Viel, Matteo; Das, Sudeep; Spergel, David N.
2009-10-01
We expect a detectable correlation between two seemingly unrelated quantities: the four point function of the cosmic microwave background (CMB) and the amplitude of flux decrements in quasar (QSO) spectra. The amplitude of CMB convergence in a given direction measures the projected surface density of matter. Measurements of QSO flux decrements trace the small-scale distribution of gas along a given line-of-sight. While the cross-correlation between these two measurements is small for a single line-of-sight, upcoming large surveys should enable its detection. This paper presents analytical estimates for the signal to noise (S/N) for measurements of the cross-correlation between the flux decrement and the convergence, {delta}F{kappa}, and for measurements of the cross-correlation between the variance in flux decrement and the convergence, <({delta}F){sup 2}{kappa}>. For the ongoing BOSS (SDSS III) and Planck surveys, we estimate an S/N of 30 and 9.6 for these two correlations. For the proposed BigBOSS and ACTPOL surveys, we estimate an S/N of 130 and 50 respectively. Since <({delta}F){sup 2}{kappa}> {proportional_to} {delta}{sub s}{sup 4}, the amplitude of these cross-correlations can potentially be used to measure the amplitude of {delta}{sub 8} at z {approx} 2 to 2.5% with BOSS and Planck and even better with future data sets. These measurements have the potential to test alternative theories for dark energy and to constrain the mass of the neutrino. The large potential signal estimated in our analytical calculations motivate tests with non-linear hydrodynamical simulations and analyses of upcoming data sets.
A new approach to quantify power-law cross-correlation and its application to commodity markets
NASA Astrophysics Data System (ADS)
He, Ling-Yun; Chen, Shu-Peng
2011-10-01
We proposed a new method: Detrended Moving-average Cross-correlation Analysis (DMCA) to detect the power-law cross-correlation between two correlated non-stationary time series by combining Detrended Cross-Correlation Analysis (DCCA) and Detrended Moving Average (DMA). In order to compare the performance of DMCA and DCCA in the detection of cross-correlation, and to estimate the influence of periodic trend, we generate two cross-correlated time series x(i) and y(i) by a periodic two-component fractionally autoregressive integrated moving average (ARFIMA) process. Then we apply both methods to quantify the cross-correlations of the generated series, whose theoretical values are already known to us. By comparing the results we obtained, we find that the performance of this new approach is comparable to DCCA with less calculating amounts; our method can also reduce the impact of trends; furthermore, DMCA (for background and forward moving average case) outperforms DCCA in more accurate estimation when the analyzed times series are short in length. To provide an example, we also apply this new method to the time series of the real-world data from Brent and WTI crude oil spot markets, to investigate the complex cross-market correlation between these commodity markets. In all, our method is another practical choice to detect the cross-correlation between two short period non-stationary time series, and has potential application to real world problems.
Cruse, Damian; Wilding, Edward L
2011-06-01
In a pair of recent studies, frontally distributed event-related potential (ERP) indices of two distinct post-retrieval processes were identified. It has been proposed that one of these processes operates over any kinds of task relevant information in service of task demands, while the other operates selectively over recovered contextual (episodic) information. The experiment described here was designed to test this account, by requiring retrieval of different kinds of contextual information to that required in previous relevant studies. Participants heard words spoken in either a male or female voice at study and ERPs were acquired at test where all words were presented visually. Half of the test words had been spoken at study. Participants first made an old/new judgment, distinguishing via key press between studied and unstudied words. For words judged 'old', participants indicated the voice in which the word had been spoken at study, and their confidence (high/low) in the voice judgment. There was evidence for only one of the two frontal old/new effects that had been identified in the previous studies. One possibility is that the ERP effect in previous studies that was tied specifically to recollection reflects processes operating over only some kinds of contextual information. An alternative is that the index reflects processes that are engaged primarily when there are few contextual features that distinguish between studied stimuli. PMID:21382387
NASA Astrophysics Data System (ADS)
Zhou, Yu; Chen, Shi
2016-02-01
In this paper, we investigate the high-frequency cross-correlation relationship between Chinese treasury futures contracts and treasury ETF. We analyze the logarithmic return of these two price series, from which we can conclude that both return series are not normally distributed and the futures markets have greater volatility. We find significant cross-correlation between these two series. We further confirm the relationship using the DCCA coefficient and the DMCA coefficient. We quantify the long-range cross-correlation with DCCA method, and we further show that the relationship is multifractal. An arbitrage algorithm based on DFA regression with stable return is proposed in the last part.
The large-scale quasar-Lyman α forest cross-correlation from BOSS
Font-Ribera, Andreu; Arnau, Eduard; Miralda-Escudé, Jordi E-mail: edu.arnau.lazaro@gmail.com; and others
2013-05-01
We measure the large-scale cross-correlation of quasars with the Lyα forest absorption in redshift space, using ∼ 60000 quasar spectra from Data Release 9 (DR9) of the Baryon Oscillation Spectroscopic Survey (BOSS). The cross-correlation is detected over a wide range of scales, up to comoving separations r of 80 h{sup −1}Mpc. For r > 15 h{sup −1}Mpc, we show that the cross-correlation is well fitted by the linear theory prediction for the mean overdensity around a quasar host halo in the standard ΛCDM model, with the redshift distortions indicative of gravitational evolution detected at high confidence. Using previous determinations of the Lyα forest bias factor obtained from the Lyα autocorrelation, we infer the quasar bias factor to be b{sub q} = 3.64{sup +0.13}{sub −0.15} at a mean redshift z = 2.38, in agreement with previous measurements from the quasar auto-correlation. We also obtain a new estimate of the Lyα forest redshift distortion factor, β{sub F} = 1.1±0.15, slightly larger than but consistent with the previous measurement from the Lyα forest autocorrelation. The simple linear model we use fails at separations r < 15h{sup −1}Mpc, and we show that this may reasonably be due to the enhanced ionization due to radiation from the quasars. We also provide the expected correction that the mass overdensity around the quasar implies for measurements of the ionizing radiation background from the line-of-sight proximity effect.
NASA Astrophysics Data System (ADS)
Hojjati, Alireza; McCarthy, Ian G.; Harnois-Deraps, Joachim; Ma, Yin-Zhe; Van Waerbeke, Ludovic; Hinshaw, Gary; Le Brun, Amandine M. C.
2015-10-01
We use the cosmo-OWLS suite of cosmological hydrodynamical simulations, which includes different galactic feedback models, to predict the cross-correlation signal between weak gravitational lensing and the thermal Sunyaev-Zeldovich (tSZ) y-parameter. The predictions are compared to the recent detection reported by van Waerbeke and collaborators. The simulations reproduce the weak lensing-tSZ cross-correlation, ξyκ(θ), well. The uncertainty arising from different possible feedback models appears to be important on small scales only (0θ lesssim 1 arcmin), while the amplitude of the correlation on all scales is sensitive to cosmological parameters that control the growth rate of structure (such as σ8, Ωm and Ωb). This study confirms our previous claim (in Ma et al.) that a significant proportion of the signal originates from the diffuse gas component in low-mass (Mhalo lesssim 1014 Msolar) clusters as well as from the region beyond the virial radius. We estimate that approximately 20% of the detected signal comes from low-mass clusters, which corresponds to about 30% of the baryon density of the Universe. The simulations also suggest that more than half of the baryons in the Universe are in the form of diffuse gas outside halos (gtrsim 5 times the virial radius) which is not hot or dense enough to produce a significant tSZ signal or be observed by X-ray experiments. Finally, we show that future high-resolution tSZ-lensing cross-correlation observations will serve as a powerful tool for discriminating between different galactic feedback models.
Sweeney, F.J.; Upadhyaya, B.R.
1982-01-01
To study the relationship between the time delay inferred from this phase angle and core coolant flow velocities, noise measurements were performed at the Loss of Fluid Test Facility (LOFT) reactor and at a commercial PWR. In-core, self-powered neutron detector (SPND) noise at LOFT and ex-core ionization chamber noise at the commercial PWR were cross correlated with core exit temperature noise. Time delays were inferred from the slope of the phase angle versus frequency plots over the frequency range from 0.05 to 2.0 Hz.
Detecting particle dark matter signatures by cross-correlating γ-ray anisotropies with weak lensing
NASA Astrophysics Data System (ADS)
Camera, S.; Fornasa, M.; Fornengo, N.; Regis, M.
2016-05-01
The underlying nature of dark matter still represents one of the fundamental questions in contemporary cosmology. Although observations well agree with its description in terms of a new fundamental particle, neither direct nor indirect signatures of its particle nature have been detected so far, despite a strong experimental effort. Similarly, particle accelerators have hitherto failed at producing dark matter particles in collider physics experiments. Here, we illustrate how the cross-correlation between anisotropies in the diffuse γ-ray background and weak gravitational lensing effects represents a novel promising way in the quest of detecting particle dark matter signatures.
A simple cross-correlation technique between infrared and hard x-ray pulses.
Kraessig, B.; Dunford, R. W.; Kanter, E. P.; Landahl, E. C.; Southworth, S. H.; Young, L.; Chemical Sciences and Engineering Division
2009-04-27
We report a gas phase technique to establish the temporal overlap of ultrafast infrared laser and hard x-ray pulses. We use tunnel ionization of a closed shell atom in the strong field at the focus of an infrared laser beam to open a distinct x-ray absorption resonance channel with a clear fluorescence signature. The technique has an intrinsic response of a few femtoseconds and is nondestructive to the two beams. It provides a step-functionlike cross-correlation result. The details of the transient provide a diagnostic of the temporal overlap of the two pulses.
Cross-correlation of Planck CMB lensing and CFHTLenS galaxy weak lensing maps
NASA Astrophysics Data System (ADS)
Liu, Jia; Hill, J. Colin
2015-09-01
We cross-correlate cosmic microwave background (CMB) lensing and galaxy weak lensing maps using the Planck 2013 and 2015 data and the 154 deg2 Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). This measurement probes large-scale structure at intermediate redshifts ≈0.9 , between the high- and low-redshift peaks of the CMB and CFHTLenS lensing kernels, respectively. Using the noise properties of these data sets and standard Planck 2015 Λ CDM cosmological parameters, we forecast a signal-to-noise ratio ≈4.6 for the cross-correlation. We find that the noise level of our actual measurement agrees well with this estimate, but the amplitude of the signal lies well below the theoretical prediction. The best-fit amplitudes of our measured cross-correlations are A2013=0.48 ±0.26 and A2015=0.44 ±0.22 , using the 2013 and 2015 Planck CMB lensing maps, respectively, where A =1 corresponds to the fiducial Planck 2015 Λ CDM prediction. Due to the low measured amplitude, the detection significance is moderate (≈2 σ ) and the data are in tension with the theoretical prediction (≈2 - 2.5 σ ) . The tension is reduced somewhat when compared to predictions using WMAP9 parameters, for which we find A2013=0.56 ±0.30 and A2015=0.52 ±0.26 . We consider various systematic effects, finding that photometric redshift uncertainties, contamination by intrinsic alignments, and effects due to the masking of galaxy clusters in the Planck 2015 CMB lensing reconstruction are able to help resolve the tension at a significant level (≈10 % each). An overall multiplicative bias in the CFHTLenS shear data could also play a role, which can be tested with existing data. We close with forecasts for measurements of the CMB lensing—galaxy lensing cross-correlation using ongoing and future weak lensing surveys, which will definitively test the significance of the tension in our results with respect to Λ CDM .
NASA Astrophysics Data System (ADS)
Feng, Lei; Li, Pengxiong; Zhang, Mengzhen; Wang, Tun; Xiao, Yanhong
2014-01-01
It is known that cross correlation between the random intensity fluctuations of two lasers forming electromagnetically induced transparency (EIT) exhibits a transition from correlation to anticorrelation. We study the linewidth behavior of this transition and have found the linewidth is below the (effective) coherence lifetime limit and is limited only by competing noises. We established a numerical model which reveals the linewidth dependence on laser linewidth and laser power. Our experiments using lasers with different linewidth showed results in qualitative agreement with the model. This result is useful for quantum optics using EIT and may also have applications in spectroscopy and precision measurements.
Carriage Error Identification Based on Cross-Correlation Analysis and Wavelet Transformation
Mu, Donghui; Chen, Dongju; Fan, Jinwei; Wang, Xiaofeng; Zhang, Feihu
2012-01-01
This paper proposes a novel method for identifying carriage errors. A general mathematical model of a guideway system is developed, based on the multi-body system method. Based on the proposed model, most error sources in the guideway system can be measured. The flatness of a workpiece measured by the PGI1240 profilometer is represented by a wavelet. Cross-correlation analysis performed to identify the error source of the carriage. The error model is developed based on experimental results on the low frequency components of the signals. With the use of wavelets, the identification precision of test signals is very high. PMID:23012558
Cross-Correlations and Joint Gaussianity in Multivariate Level Crossing Models
2014-01-01
A variety of phenomena in physical and biological sciences can be mathematically understood by considering the statistical properties of level crossings of random Gaussian processes. Notably, a growing number of these phenomena demand a consideration of correlated level crossings emerging from multiple correlated processes. While many theoretical results have been obtained in the last decades for individual Gaussian level-crossing processes, few results are available for multivariate, jointly correlated threshold crossings. Here, we address bivariate upward crossing processes and derive the corresponding bivariate Central Limit Theorem as well as provide closed-form expressions for their joint level-crossing correlations. PMID:24742344
NASA Astrophysics Data System (ADS)
Witek, M.; Kang, T. S.; van der Lee, S.
2015-12-01
We have collected three-component data from 122 Korean accelerometer stations for the month of December in 2014. We apply similar techniques described by Zha et al. (2013) to retrieve accurate station orientation angles, in order to rotate the horizontal component data into the radial and transverse frame of reference, and for subsequent measurement of Love wave group velocity dispersion. We simultaneously normalize all three components of a daily noise record via the frequency-time normalization (FTN) method. Each component is divided by the average signal envelope in an effort to retain relative amplitude information between all three components. Station orientations are found by a grid search for the orientation azimuth which maximizes the coherency between the radial-vertical cross-correlation and the Hilbert transformed vertical-vertical cross-correlation. After measuring orientation angles, we cross-correlate and rotate the data. Typically, the group velocity dispersion curves are measured using the frequency time analysis technique (FTAN), effectively producing spectrograms with significant uncertainty in the time-frequency plane. The spectrogram approach retains only the amplitude information of the short-time Fourier transform (STFT). However, Kodera et al (1976) show that by taking into account the phase information, the concepts of instantaneous frequency and group-time delay can be used to compute the first moment of the signal power in the frequency and time domains. During energy reassignment, the signal power calculated using the STFT at a point (t0,f0t_0, f_0) is reassigned to the location of the first moment (t^g,f^ihat{t}_g,hat{f}_i), where t^ghat{t}_g is the group-time delay and f^ihat{f}_i is the instantaneous frequency. We apply the method of energy reassignment to produce precise Rayleigh and Love wave group velocity measurements in the frequency range 0.1 - 1.0 Hz. Tests on synthetic data show more accurate retrieval of group velocities at
NASA Astrophysics Data System (ADS)
Likova, Lora T.
2015-03-01
This study is based on the recent discovery of massive and well-structured cross-modal memory activation generated in the primary visual cortex (V1) of totally blind people as a result of novel training in drawing without any vision (Likova, 2012). This unexpected functional reorganization of primary visual cortex was obtained after undergoing only a week of training by the novel Cognitive-Kinesthetic Method, and was consistent across pilot groups of different categories of visual deprivation: congenitally blind, late-onset blind and blindfolded (Likova, 2014). These findings led us to implicate V1 as the implementation of the theoretical visuo-spatial 'sketchpad' for working memory in the human brain. Since neither the source nor the subsequent 'recipient' of this non-visual memory information in V1 is known, these results raise a number of important questions about the underlying functional organization of the respective encoding and retrieval networks in the brain. To address these questions, an individual totally blind from birth was given a week of Cognitive-Kinesthetic training, accompanied by functional magnetic resonance imaging (fMRI) both before and just after training, and again after a two-month consolidation period. The results revealed a remarkable temporal sequence of training-based response reorganization in both the hippocampal complex and the temporal-lobe object processing hierarchy over the prolonged consolidation period. In particular, a pattern of profound learning-based transformations in the hippocampus was strongly reflected in V1, with the retrieval function showing massive growth as result of the Cognitive-Kinesthetic memory training and consolidation, while the initially strong hippocampal response during tactile exploration and encoding became non-existent. Furthermore, after training, an alternating patch structure in the form of a cascade of discrete ventral regions underwent radical transformations to reach complete functional
Squizzato, Silvano; Park, Young Mi; Buso, Nicola; Gur, Tamer; Cowley, Andrew; Li, Weizhong; Uludag, Mahmut; Pundir, Sangya; Cham, Jennifer A; McWilliam, Hamish; Lopez, Rodrigo
2015-07-01
The European Bioinformatics Institute (EMBL-EBI-https://www.ebi.ac.uk) provides free and unrestricted access to data across all major areas of biology and biomedicine. Searching and extracting knowledge across these domains requires a fast and scalable solution that addresses the requirements of domain experts as well as casual users. We present the EBI Search engine, referred to here as 'EBI Search', an easy-to-use fast text search and indexing system with powerful data navigation and retrieval capabilities. API integration provides access to analytical tools, allowing users to further investigate the results of their search. The interconnectivity that exists between data resources at EMBL-EBI provides easy, quick and precise navigation and a better understanding of the relationship between different data types including sequences, genes, gene products, proteins, protein domains, protein families, enzymes and macromolecular structures, together with relevant life science literature. PMID:25855807
Squizzato, Silvano; Park, Young Mi; Buso, Nicola; Gur, Tamer; Cowley, Andrew; Li, Weizhong; Uludag, Mahmut; Pundir, Sangya; Cham, Jennifer A.; McWilliam, Hamish; Lopez, Rodrigo
2015-01-01
The European Bioinformatics Institute (EMBL-EBI—https://www.ebi.ac.uk) provides free and unrestricted access to data across all major areas of biology and biomedicine. Searching and extracting knowledge across these domains requires a fast and scalable solution that addresses the requirements of domain experts as well as casual users. We present the EBI Search engine, referred to here as ‘EBI Search’, an easy-to-use fast text search and indexing system with powerful data navigation and retrieval capabilities. API integration provides access to analytical tools, allowing users to further investigate the results of their search. The interconnectivity that exists between data resources at EMBL-EBI provides easy, quick and precise navigation and a better understanding of the relationship between different data types including sequences, genes, gene products, proteins, protein domains, protein families, enzymes and macromolecular structures, together with relevant life science literature. PMID:25855807
A similarity retrieval method for functional magnetic resonance imaging (fMRI) statistical maps
NASA Astrophysics Data System (ADS)
Tungaraza, R. F.; Guan, J.; Rolfe, S.; Atmosukarto, I.; Poliakov, A.; Kleinhans, N. M.; Aylward, E.; Ojemann, J.; Brinkley, J. F.; Shapiro, L. G.
2009-02-01
We propose a method for retrieving similar fMRI statistical images given a query fMRI statistical image. Our method thresholds the voxels within those images and extracts spatially distinct regions from the voxels that remain. Each region is defined by a feature vector that contains the region centroid, the region area, the average activation value for all the voxels within that region, the variance of those activation values, the average distance of each voxel within that region to the region's centroid, and the variance of the voxel's distance to the region's centroid. The similarity between two images is obtained by the summed minimum distance of their constituent feature vectors. Results on a dataset of fMRI statistical images from experiments involving distinct cognitive tasks are shown.
NASA Astrophysics Data System (ADS)
Kitov, Ivan; Sanina, Irina
2016-04-01
Using the waveform cross-correlation technique, we have re-estimated relative locations and magnitudes of 200 events detected by an array consisting of seven 3-C sensors. All these events were quarry blasts conducted at several local/regional mines, which were detected and identified in the course of regional seismotectonic monitoring. From all detected signals we selected those having the highest quality and created a set of three-component templates for further cross correlation study. By changing the length of correlation window and the frequency band of the templates we selected optimal parameters for robust estimates of cross correlation coefficients and relative amplitudes/magnitudes of all signals. The relative locations and magnitude estimates obtained by cross correlation are compared to those in the catalog created in standard interactive analysis.
Avants, B B; Epstein, C L; Grossman, M; Gee, J C
2008-02-01
One of the most challenging problems in modern neuroimaging is detailed characterization of neurodegeneration. Quantifying spatial and longitudinal atrophy patterns is an important component of this process. These spatiotemporal signals will aid in discriminating between related diseases, such as frontotemporal dementia (FTD) and Alzheimer's disease (AD), which manifest themselves in the same at-risk population. Here, we develop a novel symmetric image normalization method (SyN) for maximizing the cross-correlation within the space of diffeomorphic maps and provide the Euler-Lagrange equations necessary for this optimization. We then turn to a careful evaluation of our method. Our evaluation uses gold standard, human cortical segmentation to contrast SyN's performance with a related elastic method and with the standard ITK implementation of Thirion's Demons algorithm. The new method compares favorably with both approaches, in particular when the distance between the template brain and the target brain is large. We then report the correlation of volumes gained by algorithmic cortical labelings of FTD and control subjects with those gained by the manual rater. This comparison shows that, of the three methods tested, SyN's volume measurements are the most strongly correlated with volume measurements gained by expert labeling. This study indicates that SyN, with cross-correlation, is a reliable method for normalizing and making anatomical measurements in volumetric MRI of patients and at-risk elderly individuals. PMID:17659998
Cross-correlation spin noise spectroscopy of heterogeneous interacting spin systems
Roy, Dibyendu; Yang, Luyi; Crooker, Scott A.; Sinitsyn, Nikolai A.
2015-04-30
Interacting multi-component spin systems are ubiquitous in nature and in the laboratory. As such, investigations of inter-species spin interactions are of vital importance. Traditionally, they are studied by experimental methods that are necessarily perturbative: e.g., by intentionally polarizing or depolarizing one spin species while detecting the response of the other(s). Here, we describe and demonstrate an alternative approach based on multi-probe spin noise spectroscopy, which can reveal inter-species spin interactions - under conditions of strict thermal equilibrium - by detecting and cross-correlating the stochastic fluctuation signals exhibited by each of the constituent spin species. Specifically, we consider a two-component spinmore » ensemble that interacts via exchange coupling, and we determine cross-correlations between their intrinsic spin fluctuations. The model is experimentally confirmed using “two-color” optical spin noise spectroscopy on a mixture of interacting Rb and Cs vapors. Noise correlations directly reveal the presence of inter-species spin exchange, without ever perturbing the system away from thermal equilibrium. These non-invasive and noise-based techniques should be generally applicable to any heterogeneous spin system in which the fluctuations of the constituent components are detectable.« less
Cross-correlation spin noise spectroscopy of heterogeneous interacting spin systems
Roy, Dibyendu; Yang, Luyi; Crooker, Scott A.; Sinitsyn, Nikolai A.
2015-04-30
Interacting multi-component spin systems are ubiquitous in nature and in the laboratory. As such, investigations of inter-species spin interactions are of vital importance. Traditionally, they are studied by experimental methods that are necessarily perturbative: e.g., by intentionally polarizing or depolarizing one spin species while detecting the response of the other(s). Here, we describe and demonstrate an alternative approach based on multi-probe spin noise spectroscopy, which can reveal inter-species spin interactions - under conditions of strict thermal equilibrium - by detecting and cross-correlating the stochastic fluctuation signals exhibited by each of the constituent spin species. Specifically, we consider a two-component spin ensemble that interacts via exchange coupling, and we determine cross-correlations between their intrinsic spin fluctuations. The model is experimentally confirmed using “two-color” optical spin noise spectroscopy on a mixture of interacting Rb and Cs vapors. Noise correlations directly reveal the presence of inter-species spin exchange, without ever perturbing the system away from thermal equilibrium. These non-invasive and noise-based techniques should be generally applicable to any heterogeneous spin system in which the fluctuations of the constituent components are detectable.
Cross-correlation measurement of quantum shot noise using homemade transimpedance amplifiers.
Hashisaka, Masayuki; Ota, Tomoaki; Yamagishi, Masakazu; Fujisawa, Toshimasa; Muraki, Koji
2014-05-01
We report a cross-correlation measurement system, based on a new approach, which can be used to measure shot noise in a mesoscopic conductor at milliKelvin temperatures. In contrast to other measurement systems in which high-speed low-noise voltage amplifiers are commonly used, our system employs homemade transimpedance amplifiers (TAs). The low input impedance of the TAs significantly reduces the crosstalk caused by unavoidable parasitic capacitance between wires. The TAs are designed to have a flat gain over a frequency band from 2 kHz to 1 MHz. Low-noise performance is attained by installing the TAs at a 4 K stage of a dilution refrigerator. Our system thus fulfills the technical requirements for cross-correlation measurements: low noise floor, high frequency band, and negligible crosstalk between two signal lines. Using our system, shot noise generated at a quantum point contact embedded in a quantum Hall system is measured. The good agreement between the obtained shot-noise data and theoretical predictions demonstrates the accuracy of the measurements. PMID:24880392
In-vessel fluid flow measurements using thermocouples cross-correlation.
NguyenLe, Q.
1998-05-08
Fluid flow rate in high temperature and pressure vessels can be difficult to measure due to the associated harsh environment, inaccessible locations and pressure boundary integrity concerns. However, by using quick response miniature thermocouples to measure the naturally occurring temperature variations within the flow, the fluid velocity can be inferred from the transit time analysis. This flow measurement technique has other advantages such as the flow profile is not significantly disturbed, no additional flow restrictions introduced and the system fiction factor is not increased. Furthermore, since the measured flow rate is generally unaffected by the global system dynamics, such as heat increases or losses, as well as changes in the flow regimes, the location of the thermocouple pairs is extremely flexible. Due to the mentioned advantages, the thermocouple cross-correlation flow measurement method has been developed for use at the Purdue University Multi-Dimensional Integral Test Assembly (PUMA). Currently, thermocouple cross-correlation technique is used to measure the Reactor Pressure Vessel downcomer fluid velocity and the suppression pool in-vessel natural circulation velocity.
Cross-correlation measurement of quantum shot noise using homemade transimpedance amplifiers
Hashisaka, Masayuki Ota, Tomoaki; Yamagishi, Masakazu; Fujisawa, Toshimasa; Muraki, Koji
2014-05-15
We report a cross-correlation measurement system, based on a new approach, which can be used to measure shot noise in a mesoscopic conductor at milliKelvin temperatures. In contrast to other measurement systems in which high-speed low-noise voltage amplifiers are commonly used, our system employs homemade transimpedance amplifiers (TAs). The low input impedance of the TAs significantly reduces the crosstalk caused by unavoidable parasitic capacitance between wires. The TAs are designed to have a flat gain over a frequency band from 2 kHz to 1 MHz. Low-noise performance is attained by installing the TAs at a 4 K stage of a dilution refrigerator. Our system thus fulfills the technical requirements for cross-correlation measurements: low noise floor, high frequency band, and negligible crosstalk between two signal lines. Using our system, shot noise generated at a quantum point contact embedded in a quantum Hall system is measured. The good agreement between the obtained shot-noise data and theoretical predictions demonstrates the accuracy of the measurements.
Measuring two phase flow parameters using impedance cross-correlation flow meter
NASA Astrophysics Data System (ADS)
Muhamedsalih, Y.; Lucas, G.
2012-03-01
This paper describes the design and implementation of an impedance cross correlation flow meter which can be used in solids-water pipe flows to measure the local solids volume fraction distribution and the local solids velocity distribution. The system is composed of two arrays of electrodes, separated by an axial distance of 50 mm and each array contains eights electrodes mounted over the internal circumference of the pipe carrying the flow. Furthermore every electrode in each array can be selected to be either"excitation", "measurement" or "earth". Changing the electrode configuration leads to a change in the electric field, and hence in the region of the flow cross section which is interrogated. The local flow velocity in the interrogated region is obtained by cross correlation between the two electrode arrays. Additionally, the local solids volume fraction can be obtained from the mean mixture conductivity in the region under interrogation. The system is being integrated with a microcontroller to measure the velocity distribution of the solids and the volume fraction distribution of the solids in order to create a portable flow meter capable of measuring the multi-phase flow parameters without the need of a PC to control it. Integration of the product of the local solids volume fraction and the local solids velocity in the flow cross section enables the solids volumetric flow rate to be determined.
Yuan, Naiming; Fu, Zuntao; Zhang, Huan; Piao, Lin; Xoplaki, Elena; Luterbacher, Juerg
2015-01-01
In this paper, a new method, detrended partial-cross-correlation analysis (DPCCA), is proposed. Based on detrended cross-correlation analysis (DCCA), this method is improved by including partial-correlation technique, which can be applied to quantify the relations of two non-stationary signals (with influences of other signals removed) on different time scales. We illustrate the advantages of this method by performing two numerical tests. Test I shows the advantages of DPCCA in handling non-stationary signals, while Test II reveals the “intrinsic” relations between two considered time series with potential influences of other unconsidered signals removed. To further show the utility of DPCCA in natural complex systems, we provide new evidence on the winter-time Pacific Decadal Oscillation (PDO) and the winter-time Nino3 Sea Surface Temperature Anomaly (Nino3-SSTA) affecting the Summer Rainfall over the middle-lower reaches of the Yangtze River (SRYR). By applying DPCCA, better significant correlations between SRYR and Nino3-SSTA on time scales of 6 ~ 8 years are found over the period 1951 ~ 2012, while significant correlations between SRYR and PDO on time scales of 35 years arise. With these physically explainable results, we have confidence that DPCCA is an useful method in addressing complex systems. PMID:25634341
NASA Astrophysics Data System (ADS)
Nobi, Ashadun; Maeng, Seong Eun; Ha, Gyeong Gyun; Lee, Jae Woo
2013-02-01
We analyzed cross-correlations between price fluctuations of global financial indices (20 daily stock indices over the world) and local indices (daily indices of 200 companies in the Korean stock market) by using random matrix theory (RMT). We compared eigenvalues and components of the largest and the second largest eigenvectors of the cross-correlation matrix before, during, and after the global financial the crisis in the year 2008. We find that the majority of its eigenvalues fall within the RMT bounds [ λ -, λ +], where λ - and λ + are the lower and the upper bounds of the eigenvalues of random correlation matrices. The components of the eigenvectors for the largest positive eigenvalues indicate the identical financial market mode dominating the global and local indices. On the other hand, the components of the eigenvector corresponding to the second largest eigenvalue are positive and negative values alternatively. The components before the crisis change sign during the crisis, and those during the crisis change sign after the crisis. The largest inverse participation ratio (IPR) corresponding to the smallest eigenvector is higher after the crisis than during any other periods in the global and local indices. During the global financial the crisis, the correlations among the global indices and among the local stock indices are perturbed significantly. However, the correlations between indices quickly recover the trends before the crisis.
Analysis of cross-correlations between financial markets after the 2008 crisis
NASA Astrophysics Data System (ADS)
Sensoy, A.; Yuksel, S.; Erturk, M.
2013-10-01
We analyze the cross-correlation matrix C of the index returns of the main financial markets after the 2008 crisis using methods of random matrix theory. We test the eigenvalues of C for universal properties of random matrices and find that the majority of the cross-correlation coefficients arise from randomness. We show that the eigenvector of the largest deviating eigenvalue of C represents a global market itself. We reveal that high volatility of financial markets is observed at the same times with high correlations between them which lowers the risk diversification potential even if one constructs a widely internationally diversified portfolio of stocks. We identify and compare the connection and cluster structure of markets before and after the crisis using minimal spanning and ultrametric hierarchical trees. We find that after the crisis, the co-movement degree of the markets increases. We also highlight the key financial markets of pre and post crisis using main centrality measures and analyze the changes. We repeat the study using rank correlation and compare the differences. Further implications are discussed.
The cross-correlation between 3D cosmic shear and the integrated Sachs-Wolfe effect
NASA Astrophysics Data System (ADS)
Zieser, Britta; Merkel, Philipp M.
2016-06-01
We present the first calculation of the cross-correlation between 3D cosmic shear and the integrated Sachs-Wolfe (iSW) effect. Both signals are combined in a single formalism, which permits the computation of the full covariance matrix. In order to avoid the uncertainties presented by the non-linear evolution of the matter power spectrum and intrinsic alignments of galaxies, our analysis is restricted to large scales, i.e. multipoles below ℓ = 1000. We demonstrate in a Fisher analysis that this reduction compared to other studies of 3D weak lensing extending to smaller scales is compensated by the information that is gained if the additional iSW signal and in particular its cross-correlation with lensing data are considered. Given the observational standards of upcoming weak-lensing surveys like Euclid, marginal errors on cosmological parameters decrease by 10 per cent compared to a cosmic shear experiment if both types of information are combined without a cosmic wave background (CMB) prior. Once the constraining power of CMB data is added, the improvement becomes marginal.
Improving the analysis of well-logs by wavelet cross-correlation
NASA Astrophysics Data System (ADS)
Henriques, M. V. C.; Leite, F. E. A.; Andrade, R. F. S.; Andrade, J. S.; Lucena, L. S.; Neto, M. Lucena
2015-01-01
The concept of wavelet cross-correlation is used to provide a new approach to identify similar patterns in related data sets, which largely improves the confidence of the results. The method amounts to decompose the data sets in the wavelet space so that correlations between wavelet coefficients can be analyzed in every scale. Besides the identification of the scales in which two independent measures are correlated, the method makes it possible to find patches of data sets where correlations exist simultaneously in all scales. This allows to extend the information of a small number of spots to larger regions. Well-log data sets from two neighboring oil wells are used. We compare similar measures at different probe sites, and also measurements of different physical quantities taken on the same place. Although this is a typical scenario for the application of classical geostatistical methods, it is well known that such methods erase out local differences in favor of smoother variability. In contraposition, this wavelet cross-correlation takes advantage of the fluctuations to give information about the continuity of the geological structures in space. It works even better if no filtering procedure has been applied to the original raw data.
The cross-correlation analysis in Z source GX 349+2
NASA Astrophysics Data System (ADS)
Ding, G. Q.; Zhang, W. Y.; Wang, Y. N.; Li, Z. B.; Qu, J. L.; Huang, C. P.
2016-01-01
Using all the observations from Rossi X-ray Timing Explorer for Z source GX 349+2, we systematically carry out cross-correlation analysis between its soft and hard X-ray light curves. During the observations from 1998 January 9 to January 29, GX 349+2 traced out the most extensive Z track on its hardness-intensity diagram, making a comprehensive study of cross-correlation on the track. The positive correlations and positively correlated time lags are detected throughout the Z track. Outside the Z track, anti-correlations and anti-correlated time lags are found, but the anti-correlated time lags are much longer than the positively correlated time lags, which might indicate different mechanisms for producing the two types of time lags. We argue that neither the short-term time lag models nor the truncated accretion disc model can account for the long-term time lags in neutron star low-mass X-ray binaries (NS-LMXBs). We suggest that the extended accretion disc corona model could be an alternative model to explain the long-term time lags detected in NS-LMXBs.
Burden, D L; Hobbs, S E; Hieftje, G M
1997-05-15
beta-Emitting 90Sr is used with a plastic scintillator to produce excitation-light pulses for fluorescence lifetime analysis. This light source is less expensive, more compact, and much more reliable than traditionally employed excitation sources such as lasers or pulsed flash lamps. The pulse train from this light source varies randomly in amplitude and time. Cross-correlation signal analysis is ideal for such a source because, unlike other time domain techniques, cross correlation takes complete advantage of its random nature. Here we report on the construction of an instrument and the methods employed to make fluorescence lifetime measurements via the new source and an analog correlation processor. Although the light intensity of the scintillator-based excitation source is comparatively low, an adequate signal level can be generated. The fluorescence lifetimes of three fluorophores are measured with a 1-mCi radionuclide to demonstrate a lifetime range from less than 1.5 to 28 ns. Long-lifetime measurements require an extra calibration step in order to compensate for delay cable energy loss. The light collection efficiency of the current instrument was found to be undesirably low; improvements in the instrument optics are suggested that will increase the collection efficiency and enhance the detection capability. PMID:9164162
Cross-correlation spin noise spectroscopy of heterogeneous interacting spin systems
NASA Astrophysics Data System (ADS)
Roy, Dibyendu; Yang, Luyi; Crooker, Scott A.; Sinitsyn, Nikolai A.
2015-04-01
Interacting multi-component spin systems are ubiquitous in nature and in the laboratory. As such, investigations of inter-species spin interactions are of vital importance. Traditionally, they are studied by experimental methods that are necessarily perturbative: e.g., by intentionally polarizing or depolarizing one spin species while detecting the response of the other(s). Here, we describe and demonstrate an alternative approach based on multi-probe spin noise spectroscopy, which can reveal inter-species spin interactions - under conditions of strict thermal equilibrium - by detecting and cross-correlating the stochastic fluctuation signals exhibited by each of the constituent spin species. Specifically, we consider a two-component spin ensemble that interacts via exchange coupling, and we determine cross-correlations between their intrinsic spin fluctuations. The model is experimentally confirmed using ``two-color'' optical spin noise spectroscopy on a mixture of interacting Rb and Cs vapors. Noise correlations directly reveal the presence of inter-species spin exchange, without ever perturbing the system away from thermal equilibrium. These non-invasive and noise-based techniques should be generally applicable to any heterogeneous spin system in which the fluctuations of the constituent components are detectable.
Steady-state cross-correlations for live two-colour super-resolution localization data sets
Stone, Matthew B.; Veatch, Sarah L.
2015-01-01
Cross-correlation of super-resolution images gathered from point localizations allows for robust quantification of protein co-distributions in chemically fixed cells. Here this is extended to dynamic systems through an analysis that quantifies the steady-state cross-correlation between spectrally distinguishable probes. This methodology is used to quantify the co-distribution of several mobile membrane proteins in both vesicles and live cells, including Lyn kinase and the B-cell receptor during antigen stimulation. PMID:26066572
Eckert, S. E-mail: martin.beye@helmholtz-berlin.de; Beye, M. E-mail: martin.beye@helmholtz-berlin.de; Pietzsch, A.; Quevedo, W.; Hantschmann, M.; Ochmann, M.; Huse, N.; Ross, M.; Khalil, M.; Minitti, M. P.; Turner, J. J.; Moeller, S. P.; Schlotter, W. F.; Dakovski, G. L.; Föhlisch, A.
2015-02-09
The discovery of ultrafast X-ray induced optical reflectivity changes enabled the development of X-ray/optical cross correlation techniques at X-ray free electron lasers worldwide. We have now linked through experiment and theory the fundamental excitation and relaxation steps with the transient optical properties in finite solid samples. Therefore, we gain a thorough interpretation and an optimized detection scheme of X-ray induced changes to the refractive index and the X-ray/optical cross correlation response.
NASA Astrophysics Data System (ADS)
Nishida, Kiwamu; Ichihara, Mie
2016-02-01
On 2013 November 20, a submarine eruption started close to Nishinoshima island, which lies ˜1000 km south of Tokyo. Real-time monitoring of the eruption is crucial for understanding the formation processes of the new volcano island and related disaster prevention. In situ monitoring, however, is difficult in practice because the closest inhabited island, Chichijima, is 130 km away from Nishinoshima. This study presents an infrasonic monitoring method that uses cross-correlating records at a pair of online stations on Chichijima. One is the horizontal ground velocity recorded at a permanent seismic station operated by the Japan Meteorological Agency (JMA). The seismic records were corrected for atmospheric pressure using an empirical ground response to infrasound. The other is the air pressure recorded at the JMA Meteorological Observatory. For each station, we divided the whole records into 3600-s segments. To suppress outliers, each segment was normalized by the envelope function. We then calculated cross-correlation functions between the pair of stations using the fast Fourier transform. They present clear successive arrivals of infrasound coming from Nishinoshima. We also conducted an offline tripartite-array observation using three low-frequency microphones with a station spacing of ˜50 m installed in 2013 May. The array analysis supports the results obtained from the online stations. The typical root-mean-squared amplitude is on the order of 0.01 Pa, and the typical duration is several days. The amplitudes were primarily controlled by the effective sound velocity structure from Nishinoshima to Chichijima. The infrasonic observations together with the meteorological observation at Chichijima suggest that infrasonic activity was not present in the first two weeks in 2015 January. With the help of a more quantitative estimation of the meteorological effect, we could infer eruptive activity in real time. Now many online seismic stations are available worldwide
NASA Astrophysics Data System (ADS)
Qorbani, Ehsan; Zigone, Dimitri; Kolinsky, Petr; Fuchs, Florian; Bokelmann, Götz; AlpArray-EASI Working Group
2016-04-01
The eastern part of the Alpine chain is considered as an area of complex tectonics and lithospheric structure. Having a relatively dense network of stations in this region provides an opportunity to study the crustal and lithospheric velocity structure using ambient-noise correlations methods. We used continuous data recorded during 2014 at 50 permanent stations located in Austria, Germany, northern Italy, and Slovenia, along with data from 8 temporary stations of the Eastern Alpine Seismic Investigation (EASI) profile. Cross correlation of ambient noise are performed in order to estimate the Green's functions of surface waves propagating between station pairs. Dispersion curves of Rayleigh and Love waves are constructed between 2 and 30 seconds and are then inverted to obtain group velocity maps at different frequency (depth) levels. We present here a new crustal-lithospheric velocity model for the Southern and Eastern Alps, which reveals clear spatial velocity variation and contrasts, associated with major faults, deformed and damaged zones. In this study, we also assess the azimuthal anisotropy from the group velocity measurements. The new finding together with the previous results from SKS splitting and receiver function provides 3D images of anisotropy at scales ranging from crust to upper mantle. This allows us to discuss the strain field and deformation pattern within both shallow and lithospheric-asthenospheric depth, in relation with the most prominent tectonic processes in the region, such as eastward extrusion of the ALCAPA block (Eastern Alps, Western Carpathian, and Pannonian Basin).
Numerical evaluation of the three-point scalar-tensor cross-correlations and the tensor bi-spectrum
NASA Astrophysics Data System (ADS)
Sreenath, V.; Tibrewala, Rakesh; Sriramkumar, L.
2013-12-01
Utilizing the Maldacena formalism and extending the earlier efforts to compute the scalar bi-spectrum, we construct a numerical procedure to evaluate the three-point scalar-tensor cross-correlations as well as the tensor bi-spectrum in single field inflationary models involving the canonical scalar field. We illustrate the accuracy of the adopted procedure by comparing the numerical results with the analytical results that can be obtained in the simpler cases of power law and slow roll inflation. We also carry out such a comparison in the case of the Starobinsky model described by a linear potential with a sudden change in the slope, which provides a non-trivial and interesting (but, nevertheless, analytically tractable) scenario involving a brief period of deviation from slow roll. We then utilize the code we have developed to evaluate the three-point correlation functions of interest (and the corresponding non-Gaussianity parameters that we introduce) for an arbitrary triangular configuration of the wavenumbers in three different classes of inflationary models which lead to features in the scalar power spectrum, as have been recently considered by the Planck team. We also discuss the contributions to the three-point functions during preheating in inflationary models with a quadratic minimum. We conclude with a summary of the main results we have obtained.
NASA Astrophysics Data System (ADS)
Beirle, Steffen; Lampel, Johannes; Wagner, Thomas
2016-04-01
The instrumental spectral response function (ISRF) is a key quantity in spectroscopy. Within DOAS retrievals, the ISRF is needed for an accurate wavelength calibration and for the convolution of trace gas cross-sections to instrumental resolution. DOAS analysis software like QDOAS or DOASIS allow the fitting of a high resolution solar spectrum to a measured spectrum based on a parameterized ISRF with predefined shape (e.g. Gauss, Lorentz, Voigt). For OMI, a more advanced ISRF ("broadened Gauss") was determined which allows for flat-top and asymmetric ISRF; however, this ISRF model is computationally expensive due to the high number of parameters. Here we propose a "Super Gaussian" as further model function for the ISRF, which is similar to a Gaussian, but with the exponent ξ as additional free parameter: F(x) = A ∗ exp(‑(|x|/w)ξ) The parameter w determines the width of F , while ξ basically determines the shape. Optionally, different values for ξ and w can be allowed for the left vs. right branch of F to construct asymmetric ISRFs. This model function was found to be a good compromise between good fit results (i.e., F represents the actual ISRF much better than a Gaussian) for a wide range of tested ISRF shapes on the one hand, and robustness of the fit and low computation time on the other hand due to the low number of free parameters. A further advantage of this description of the ISRF is that the two partial derivatives, representing changes of shape and width, respectively, allow to mimic potential spectral structures caused by temporal changes of the ISRF (e.g. due to changes of the detector temperature) by adding pseudo-absorbers in the DOAS analysis. We investigate how far this affects different trace gas retrievals from satellite measurements.
Using glacier seismicity for phase velocity measurements and Green's function retrieval
NASA Astrophysics Data System (ADS)
Walter, Fabian; Roux, Philippe; Roeoesli, Claudia; Lecointre, Albanne; Kilb, Debi; Roux, Pierre-François
2015-06-01
High-melt areas of glaciers and ice sheets foster a rich spectrum of ambient seismicity. These signals not only shed light on source mechanisms (e.g. englacial fracturing, water flow, iceberg detachment, basal motion) but also carry information about seismic wave propagation within glacier ice. Here, we present two approaches to measure and potentially monitor phase velocities of high-frequency seismic waves (≥1 Hz) using naturally occurring glacier seismicity. These two approaches were developed for data recorded by on-ice seasonal seismic networks on the Greenland Ice Sheet and a Swiss Alpine glacier. The Greenland data set consists of continuous seismograms, dominated by long-term tremor-like signals of englacial water flow, whereas the Alpine data were collected in triggered mode producing 1-2 s long records that include fracture events within the ice (`icequakes'). We use a matched-field processing technique to retrieve frequency-dependent phase velocity measurements for the Greenland data. In principle, this phase dispersion relationship can be inverted for ice sheet thickness and bed properties. For these Greenland data, inversion of the dispersion curve yields a bedrock depth of 541 m, which may be too small by as much as 35 per cent. We suggest that the discrepancy is due to lateral changes in ice sheet depth and bed properties beneath the network, which may cause unaccounted mixing of surface wave modes in the dispersion curve. The Swiss Alpine icequake records, on the other hand, allow for reconstruction of the impulse response between two seismometers. The direct and scattered wave fields from the vast numbers of icequake records (tens of thousands per month) can be used to measure small changes in englacial velocities and thus monitor structural changes within the ice.
Hajian, Amir; Bond, John R.; Acquaviva, Viviana; Das, Sudeep; Dunkley, Joanna; Ade, Peter A. R.; Aguirre, Paula; Barrientos, L. Felipe; Amiri, Mandana; Battistelli, Elia S.; Burger, Bryce; Appel, John William; Duenner, Rolando; Essinger-Hileman, Thomas; Fisher, Ryan P.; Brown, Ben; Chervenak, Jay; Doriese, W. Bertrand
2011-10-20
We present a new calibration method based on cross-correlations with the Wilkinson Microwave Anisotropy Probe (WMAP) and apply it to data from the Atacama Cosmology Telescope (ACT). ACT's observing strategy and map-making procedure allows an unbiased reconstruction of the modes in the maps over a wide range of multipoles. By directly matching the ACT maps to WMAP observations in the multipole range of 400 < l < 1000, we determine the absolute calibration with an uncertainty of 2% in temperature. The precise measurement of the calibration error directly impacts the uncertainties in the cosmological parameters estimated from the ACT power spectra. We also present a combined map based on ACT and WMAP data that has a high signal-to-noise ratio over a wide range of multipoles.
Changes in Cross-Correlations as an Indicator for Systemic Risk
Zheng, Zeyu; Podobnik, Boris; Feng, Ling; Li, Baowen
2012-01-01
The 2008–2012 global financial crisis began with the global recession in December 2007 and exacerbated in September 2008, during which the U.S. stock markets lost 20% of value from its October 11 2007 peak. Various studies reported that financial crisis are associated with increase in both cross-correlations among stocks and stock indices and the level of systemic risk. In this paper, we study 10 different Dow Jones economic sector indexes, and applying principle component analysis (PCA) we demonstrate that the rate of increase in principle components with short 12-month time windows can be effectively used as an indicator of systemic risk—the larger the change of PC1, the higher the increase of systemic risk. Clearly, the higher the level of systemic risk, the more likely a financial crisis would occur in the near future. PMID:23185692
Changes in Cross-Correlations as an Indicator for Systemic Risk
NASA Astrophysics Data System (ADS)
Zheng, Zeyu; Podobnik, Boris; Feng, Ling; Li, Baowen
2012-11-01
The 2008-2012 global financial crisis began with the global recession in December 2007 and exacerbated in September 2008, during which the U.S. stock markets lost 20% of value from its October 11 2007 peak. Various studies reported that financial crisis are associated with increase in both cross-correlations among stocks and stock indices and the level of systemic risk. In this paper, we study 10 different Dow Jones economic sector indexes, and applying principle component analysis (PCA) we demonstrate that the rate of increase in principle components with short 12-month time windows can be effectively used as an indicator of systemic risk--the larger the change of PC1, the higher the increase of systemic risk. Clearly, the higher the level of systemic risk, the more likely a financial crisis would occur in the near future.
Auto- and cross-correlation analysis of the QSOs radio wave intensity
NASA Astrophysics Data System (ADS)
Demin, S. A.; Panischev, O. Yu; Nefedyev, Yu A.
2015-12-01
We discuss here the Flicker-Noise Spectroscopy approach to studying astrophysical systems, for example the radio wave intensity of quasi-stellar object (QSO) 1641+399 and BL Lacertae (BL Lac) 0215+015 in different frequency ranges. The presented method allows to parameterize the study dynamics using a short set of characteristics. The considering sources have a significant differences in manifesting the non-stationary effects, dynamical intermittency and synchronization. The radio wave intensity dynamics of the BL Lac 0215+015 is characterized by well-defined set of natural frequencies, persistent behavior with low effects of non-stationarity and high level of frequency-phase synchronization. For dynamics of the QSO 1641+399 reverse occurs including the asymmetrical structure of cross-correlator. Our findings show that using the flicker-noise spectroscopy approach to studying astrophysical objects allows to carry out the more detail analysis of their behavior and evolution.
Graphene thermal transport studies via radio-frequency, cross-correlated Johnson noise thermometry
NASA Astrophysics Data System (ADS)
Crossno, Jesse; Liu, Xiaomeng; Wang, Ke; Harzheim, Achim; Watanabe, Kenji; Taniguchi, Takashi; Ohki, Thomas; Fong, Kin Chung; Kim, Philip
2015-03-01
The electronic temperature of a dissipative, mesoscale device can be determined by monitoring the Johnson noise power emitted over a wide frequency range. Using radiometry techniques, we have developed a high-frequency, wide bandwidth, cross-correlation Johnson noise thermometer operating from room temperature to cryogenic levels that is compatible with strong magnetic fields. Precisions ranging from 2 to 25 mK are demonstrated over the temperature range of 3 to 300 K with 1 second of integration time. This non-invasive thermometer has enabled us to perform sensitive electronic thermal transport studies in boron nitride encapsulated monolayer graphene over two orders of magnitude in temperature. This versatile technique also enables precision Fano factor measurements as well as studies of correlated noise phenomena, such as those found in layered Van der Waals heterostructures.
NASA Technical Reports Server (NTRS)
Hajian, Amir; Acquaviva, Viviana; Ade, Peter A. R.; Aguirre, Paula; Amiri, Mandana; Appel, John William; Barrientos, L. Felipe; Battistelli, Elia S.; Bond, John R.; Brown, Ben; Burger, Bryce; Chervenak, Jay; Das, Sudeep; Devlin, Mark J.; Dicker, Simon R.; Bertrand Doriese, W.; Dunkley, Joanna; Dunner, Rolando; Essinger-Hileman, Thomas; Fisher, Ryan P.; Fowler, Joseph W.; Halpern, Mark; Hasselfield, Matthew; Moseley, Harvey; Wollack, Ed
2011-01-01
We present a new calibration method based on cross-correlations with the Wilkinson Microwave Anisotropy Probe (WMAP) and apply it to data from the Atacama Cosmology Telescope (ACT). ACT's observing strategy and mapmaking procedure allows an unbiased reconstruction of the modes in the maps over a wide range of multipoles. By directly matching the ACT maps to WMAP observations in the multipole range of 400 < I < 1000, we determine the absolute calibration with an uncertainty of 2% in temperature. The precise measurement of the calibration error directly impacts the uncertainties in the cosmological parameters estimated from the ACT power spectra. We also present a combined map based on ACT and WMAP data that has a high signal-to-noise ratio over a wide range of multipoles.
First measurement of the cross-correlation of CMB lensing and galaxy lensing
NASA Astrophysics Data System (ADS)
Hand, Nick; Leauthaud, Alexie; Das, Sudeep; Sherwin, Blake D.; Addison, Graeme E.; Bond, J. Richard; Calabrese, Erminia; Charbonnier, Aldée; Devlin, Mark J.; Dunkley, Joanna; Erben, Thomas; Hajian, Amir; Halpern, Mark; Harnois-Déraps, Joachim; Heymans, Catherine; Hildebrandt, Hendrik; Hincks, Adam D.; Kneib, Jean-Paul; Kosowsky, Arthur; Makler, Martin; Miller, Lance; Moodley, Kavilan; Moraes, Bruno; Niemack, Michael D.; Page, Lyman A.; Partridge, Bruce; Sehgal, Neelima; Shan, Huanyuan; Sievers, Jonathan L.; Spergel, David N.; Staggs, Suzanne T.; Switzer, Eric R.; Taylor, James E.; Van Waerbeke, Ludovic; Welker, Charlotte; Wollack, Edward J.
2015-03-01
We measure the cross-correlation of cosmic microwave background (CMB) lensing convergence maps derived from Atacama Cosmology Telescope data with galaxy lensing convergence maps as measured by the Canada-France-Hawaii Telescope Stripe 82 Survey. The CMB-galaxy lensing cross power spectrum is measured for the first time with a significance of 4.2 σ , which corresponds to a 12% constraint on the amplitude of density fluctuations at redshifts ˜0.9 . With upcoming improved lensing data, this novel type of measurement will become a powerful cosmological probe, providing a precise measurement of the mass distribution at intermediate redshifts and serving as a calibrator for systematic biases in weak lensing measurements.
Automatic counting of fungiform papillae by shape using cross-correlation.
Valencia, Eréndira; Ríos, Homero V; Verdalet, Iñigo; Hernández, Jesús; Juárez, Sergio; Herrera, Rosa; Silva, Erik R
2016-09-01
The determination of the number of fungiform papillae (FP) on the human tongue is important for taste sensitivity studies. Most of the time, the counting of the FP is done manually. In this paper we propose a novel algorithm to count the FP using shape characteristics measured by cross-correlation. The accuracy of the algorithm is evaluated by counting the FP manually on the same images and then doing a statistical analysis. A Poisson regression model is fitted using maximum likelihood. The result is that the algorithm counts are very similar to the human experts. Another advantage of the algorithm is its facility of use, velocity and that it can work on a plain tongue image, without the need to stain the tongue as is usual in manual counting. PMID:27468169
NASA Astrophysics Data System (ADS)
Ermert, Laura; Afanasiev, Michael; Sager, Korbinian; Gokhberg, Alexey; Fichtner, Andreas
2016-04-01
We report on the ongoing development of a new inversion method for the space- and time-dependent power spectral density distribution of ambient seismic noise sources. The method, once complete, will mainly serve two purposes: First, it will allow us to construct more realistic forward models for noise cross-correlation waveforms, thereby opening new possibilities for waveform imaging by ambient noise tomography. Second, it may provide new insights about the properties of ambient noise sources, complementing studies based on beamforming or numerical modeling of noise based on oceanographic observations. To invert for noise sources, we consider surface wave signal energy measurements on the 'causal' (station A to B) and on the 'acausal' (station B to A) correlation branch, and the ratio between them. These and similar measurements have proven useful for locating noise sources using cross-correlations in several past studies. The inversion procedure is the following: We construct correlation forward models based on Green's functions from a spectral element wave propagation code. To construct these models efficiently, we use source-receiver reciprocity and assume spatial uncorrelation of noise sources. In such a setting, correlations can be calculated from a pre-computed set of Green's functions between the seismic receivers and sources located at the Earth's surface. We then calculate spatial sensitivity kernels for the noise source distribution with respect to the correlation signal energy measurements. These in turn allow us to construct a misfit gradient and optimize the source distribution model to fit our observed cross-correlation signal energies or energy ratios. We will present the workflow for calculation of the forward model and sensitivity kernels, as well as results for both forward modeling and kernels for an example data set of long-period noise or 'hum' at a global scale. We will also provide an outlook on the noise source inversion considering the
NASA Astrophysics Data System (ADS)
Wang, Duan; Podobnik, Boris; Horvatić, Davor; Stanley, H. Eugene
2011-04-01
We propose a modified time lag random matrix theory in order to study time-lag cross correlations in multiple time series. We apply the method to 48 world indices, one for each of 48 different countries. We find long-range power-law cross correlations in the absolute values of returns that quantify risk, and find that they decay much more slowly than cross correlations between the returns. The magnitude of the cross correlations constitutes “bad news” for international investment managers who may believe that risk is reduced by diversifying across countries. We find that when a market shock is transmitted around the world, the risk decays very slowly. We explain these time-lag cross correlations by introducing a global factor model (GFM) in which all index returns fluctuate in response to a single global factor. For each pair of individual time series of returns, the cross correlations between returns (or magnitudes) can be modeled with the autocorrelations of the global factor returns (or magnitudes). We estimate the global factor using principal component analysis, which minimizes the variance of the residuals after removing the global trend. Using random matrix theory, a significant fraction of the world index cross correlations can be explained by the global factor, which supports the utility of the GFM. We demonstrate applications of the GFM in forecasting risks at the world level, and in finding uncorrelated individual indices. We find ten indices that are practically uncorrelated with the global factor and with the remainder of the world indices, which is relevant information for world managers in reducing their portfolio risk. Finally, we argue that this general method can be applied to a wide range of phenomena in which time series are measured, ranging from seismology and physiology to atmospheric geophysics.
Wang, Duan; Podobnik, Boris; Horvatić, Davor; Stanley, H Eugene
2011-04-01
We propose a modified time lag random matrix theory in order to study time-lag cross correlations in multiple time series. We apply the method to 48 world indices, one for each of 48 different countries. We find long-range power-law cross correlations in the absolute values of returns that quantify risk, and find that they decay much more slowly than cross correlations between the returns. The magnitude of the cross correlations constitutes "bad news" for international investment managers who may believe that risk is reduced by diversifying across countries. We find that when a market shock is transmitted around the world, the risk decays very slowly. We explain these time-lag cross correlations by introducing a global factor model (GFM) in which all index returns fluctuate in response to a single global factor. For each pair of individual time series of returns, the cross correlations between returns (or magnitudes) can be modeled with the autocorrelations of the global factor returns (or magnitudes). We estimate the global factor using principal component analysis, which minimizes the variance of the residuals after removing the global trend. Using random matrix theory, a significant fraction of the world index cross correlations can be explained by the global factor, which supports the utility of the GFM. We demonstrate applications of the GFM in forecasting risks at the world level, and in finding uncorrelated individual indices. We find ten indices that are practically uncorrelated with the global factor and with the remainder of the world indices, which is relevant information for world managers in reducing their portfolio risk. Finally, we argue that this general method can be applied to a wide range of phenomena in which time series are measured, ranging from seismology and physiology to atmospheric geophysics. PMID:21599254
NASA Astrophysics Data System (ADS)
Farrell, J.; Lin, F. C.
2015-12-01
We present a new S-wave velocity model for the Yellowstone magmatic system derived from the inversion of Rayleigh- and Love-wave phase velocity measurements from periods from 6 to 35 s. All available data from 2007-2014 within and near the Yellowstone region was downloaded for the USArray TA network (TA), the Yellowstone Seismic Network (WY), the NOISY array (Z2), the USGS Intermountain West network (IW), the Plate Boundary Observatory Borehole Seismic Network (PB), and the USGS National Seismic Network (US). For each station, we perform daily noise pre-processing (temporal normalization and spectrum whitening) simultaneously for all three components before multi-component noise cross-correlations are calculated. Results for both Rayleigh- and Love-wave phase velocity inversions clearly show the low velocity anomaly associated with the upper-crustal magma reservoir seen previously using body wave tomography. In addition, low-velocity anomalies associated with sediment-filled basins are visible in Wyoming. Short period low Love-wave velocities are seen along the Snake River Plain, the track of the Yellowstone hotspot likely related to the shallow sediment layer. Based on the surface wave phase velocity maps, we invert for a 3D S-wave crustal model. The resulting model will be compared to previous, but spatially limited, body wave S-wave models as well as recent body wave P-wave velocity models to better constrain Vp/Vs ratios as well as the melt fraction of the magma chamber. Preliminary results using amplitude information of noise cross-correlations to calculate Rayleigh-wave ellipticity, or Rayleigh-wave H/V (horizontal to vertical) amplitude ratios to better constrain the shallow velocity structure will also be discussed.
Multi-channel analysis of passive surface waves based on cross-correlations
NASA Astrophysics Data System (ADS)
Cheng, F.; Xia, J.; Xu, Z.; Hu, Y.
2015-12-01
Traditional active seismic survey can no longer be properly applied in highly populated urban areas due to restrictions in modern civilian life styles. Passive seismic methods, however, have gained much more attention from the engineering geophysics community because of their environmental friendly and deeper investigation depth. Due to extracting signal from noise has never been as comfortable as that in active seismic survey, how to make it more efficiently and accurately has been emphasized. We propose a multi-channel analysis of passive surface waves (MAPW) based on long noise sequences cross-correlations to meet the demand for increasing investigation depth by acquiring surface-wave data at a relative low-frequency range (1 Hz ≤ f ≤ 10 Hz) in urban areas. We utilize seismic interferometry to produce common virtual source gathers from one-hour-long noise records and do dispersion measurements by using the classic passive multi-channel analysis of surface waves (PMASW). We used synthetic tests to demonstrate the advantages of MAPW for various noise distributions. Results show that our method has the superiority of maximizing the analysis accuracy. Finally, we used two field data applications to demonstrate the advantages of our MAPW over the classic PMASW on isolating azimuth of the predominant noise sources and the effectivity of combined survey of active multi-channel analysis of surface waves (MASW) and MAPW. We suggest, for the field operation using MAPW, that a parallel receiver line which is close to a main road or river, if any, with one or two hours noise observation will be an effective means for an unbiased dispersion image. Keywords: passive seismic method, MAPW, MASW, cross-correlation, directional noise source, spatial-aliasing effects, inversion
Sander, Tilmann H; Leistner, Stefanie; Wabnitz, Heidrun; Mackert, Bruno-Marcel; Macdonald, Rainer; Trahms, Lutz
2010-01-01
Neuronal and vascular responses due to finger movements were synchronously measured using dc-magnetoencephalography (dcMEG) and time-resolved near-infrared spectroscopy (trNIRS). The finger movements were monitored with electromyography (EMG). Cortical responses related to the finger movement sequence were extracted by independent component analysis from both the dcMEG and the trNIRS data. The temporal relations between EMG rate, dcMEG, and trNIRS responses were assessed pairwise using the cross-correlation function (CCF), which does not require epoch averaging. A positive lag on a scale of seconds was found for the maximum of the CCF between dcMEG and trNIRS. A zero lag is observed for the CCF between dcMEG and EMG. Additionally this CCF exhibits oscillations at the frequency of individual finger movements. These findings show that the dcMEG with a bandwidth up to 8 Hz records both slow and faster neuronal responses, whereas the vascular response is confirmed to change on a scale of seconds. PMID:20145717
Sander, Tilmann H.; Leistner, Stefanie; Wabnitz, Heidrun; Mackert, Bruno-Marcel; Macdonald, Rainer; Trahms, Lutz
2010-01-01
Neuronal and vascular responses due to finger movements were synchronously measured using dc-magnetoencephalography (dcMEG) and time-resolved near-infrared spectroscopy (trNIRS). The finger movements were monitored with electromyography (EMG). Cortical responses related to the finger movement sequence were extracted by independent component analysis from both the dcMEG and the trNIRS data. The temporal relations between EMG rate, dcMEG, and trNIRS responses were assessed pairwise using the cross-correlation function (CCF), which does not require epoch averaging. A positive lag on a scale of seconds was found for the maximum of the CCF between dcMEG and trNIRS. A zero lag is observed for the CCF between dcMEG and EMG. Additionally this CCF exhibits oscillations at the frequency of individual finger movements. These findings show that the dcMEG with a bandwidth up to 8 Hz records both slow and faster neuronal responses, whereas the vascular response is confirmed to change on a scale of seconds. PMID:20145717
NASA Astrophysics Data System (ADS)
Latham, D. W.; Nordstroem, B.; Andersen, J.; Torres, G.; Stefanik, R. P.; Thaller, M.; Bester, M. J.
1996-10-01
Fundamental mass determinations in eclipsing binaries rely on radial velocities derived from double-lined spectra. We evaluate the performance of the CfA Digital Speedometers for deriving radial velocities of double-lined systems, using simulated observations of composite spectra. When XCSAO (Kurtz et al. 1992) is used to calculate a one-dimensional cross-correlation, simple fits to the double peaks in the correlation function can lead to systematic errors as large as 3km/s due to the effects of line blending. The two-dimensional correlation scheme TODCOR (Zucker & Mazeh 1994ApJ...420..806Z) can reduce the systematic errors by an order of magnitude. We apply TODCOR to a new mass determination for the F-type eclipsing binary DM Vir, achieving an accuracy of 0.6%. The improved physical properties of DM Vir agree very well with stellar evolution models incorporating the most recent opacity data, both with and without convective core overshooting, and for reasonable assumptions about the chemical composition. The age of DM Vir is found to be 1.75+/-0.20x10^9^yr, metallicity being the dominant source of uncertainty.
Martinelli, Pénélope; Sperduti, Marco; Devauchelle, Anne-Dominique; Kalenzaga, Sandrine; Gallarda, Thierry; Lion, Stéphanie; Delhommeau, Marion; Anssens, Adèle; Amado, Isabelle; Meder, Jean François; Krebs, Marie-Odile; Oppenheim, Catherine; Piolino, Pascale
2013-01-01
Age-related changes in autobiographical memory (AM) recall are characterized by a decline in episodic details, while semantic aspects are spared. This deleterious effect is supposed to be mediated by an inefficient recruitment of executive processes during AM retrieval. To date, contrasting evidence has been reported on the neural underpinning of this decline, and none of the previous studies has directly compared the episodic and semantic aspects of AM in elderly. We asked 20 young and 17 older participants to recall specific and general autobiographical events (i.e., episodic and semantic AM) elicited by personalized cues while recording their brain activity by means of fMRI. At the behavioral level, we confirmed that the richness of episodic AM retrieval is specifically impoverished in aging and that this decline is related to the reduction of executive functions. At the neural level, in both age groups, we showed the recruitment of a large network during episodic AM retrieval encompassing prefrontal, cortical midline and posterior regions, and medial temporal structures, including the hippocampus. This network was very similar, but less extended, during semantic AM retrieval. Nevertheless, a greater activity was evidenced in the dorsal anterior cingulate cortex (dACC) during episodic, compared to semantic AM retrieval in young participants, and a reversed pattern in the elderly. Moreover, activity in dACC during episodic AM retrieval was correlated with inhibition and richness of memories in both groups. Our findings shed light on the direct link between episodic AM retrieval, executive control, and their decline in aging, proposing a possible neuronal signature. They also suggest that increased activity in dACC during semantic AM retrieval in the elderly could be seen as a compensatory mechanism underpinning successful AM performance observed in aging. These results are discussed in the framework of recently proposed models of neural reorganization in aging
The proper weighting function for retrieving temperatures from satellite measured radiances
NASA Technical Reports Server (NTRS)
Arking, A.
1976-01-01
One class of methods for converting satellite measured radiances into atmospheric temperature profiles, involves a linearization of the radiative transfer equation: delta r = the sum of (W sub i) (delta T sub i) where (i=1...s) and where delta T sub i is the deviation of the temperature in layer i from that of a reference atmosphere, delta R is the difference in the radiance at satellite altitude from the corresponding radiance for the reference atmosphere, and W sub i is the discrete (or vector) form of the T-weighting (i.e., temperature weighting) function W(P), where P is pressure. The top layer of the atmosphere corresponds to i = 1, the bottom layer to i = s - 1, and i = s refers to the surface. Linearization in temperature (or some function of temperature) is at the heart of all linear or matrix methods. The weighting function that should be used is developed.
NASA Technical Reports Server (NTRS)
Ni, Jianjun (David)
2012-01-01
This presentation discusses an analysis approach to evaluate the interuser interference for Direct-Sequence Spread-Spectrum (DSSS) Systems for Space Network (SN) Users. Part I of this analysis shows that the correlation property of pseudo noise (PN) sequences is the critical factor which determines the interuser interference performance of the DSSS system. For non-standard DSSS systems in which PN sequence s period is much larger than one data symbol duration, it is the partial-period cross-correlation that determines the system performance. This study reveals through an example that a well-designed PN sequence set (e.g. Gold Sequence, in which the cross-correlation for a whole-period is well controlled) may have non-controlled partial-period cross-correlation which could cause severe interuser interference for a DSSS system. Since the analytical derivation of performance metric (bit error rate or signal-to-noise ratio) based on partial-period cross-correlation is prohibitive, the performance degradation due to partial-period cross-correlation will be evaluated using simulation in Part II of this analysis in the future.
Hall, Katie; Oram, Mike W.; Campbell, Matthew W.; Eppley, Timothy M.; Byrne, Richard W.; de Waal, Frans B.M.
2014-01-01
In a dyadic informed forager task, chimpanzees (Pan troglodytes) are known to exploit the knowledge of informed subordinates; however, the behavioral mechanisms they employ are unknown. It is tempting to interpret outcome measures, such as which individual obtained the food, in a cognitively richer way than the outcomes may justify. We employed a different approach from prior research, asking how chimpanzees compete by maneuvering around each other, whether they use gaze cues to acquire information from others, and what information they use in moment-to-moment decision-making. We used cross correlations, which plot the correlation between two variables as a function of time, systematically to examine chimpanzee interactions in a series of dyadic informed forager contests. We used cross correlations as a “proof of concept” so as to determine whether the target actions were contingent on, or occurred in a time-locked pattern relative to, the referent actions. A subordinate individual was given privileged knowledge of food location. As expected, an ignorant dominant followed the informed subordinate’s movement in the enclosure. The dominant also followed the subordinate’s gaze direction: after she looked at the subordinate, she was more likely to gaze towards this same direction within one second. In contrast, the subordinate only occasionally followed the dominant’s movement and gaze. The dominant also changed her own direction of movement to converge on the location to which the subordinate directed her gaze and movement. Cross correlation proves an effective technique for charting contingencies in social interactions, an important step in understanding the use of cognition in natural situations. PMID:24710756
Hall, Katie; Oram, Mike W; Campbell, Matthew W; Eppley, Timothy M; Byrne, Richard W; De Waal, Frans B M
2014-10-01
In a dyadic informed forager task, chimpanzees (Pan troglodytes) are known to exploit the knowledge of informed subordinates; however, the behavioral mechanisms they employ are unknown. It is tempting to interpret outcome measures, such as which individual obtained the food, in a cognitively richer way than the outcomes may justify. We employed a different approach from prior research, asking how chimpanzees compete by maneuvering around each other, whether they use gaze cues to acquire information from others, and what information they use in moment-to-moment decision-making. We used cross correlations, which plot the correlation between two variables as a function of time, systematically to examine chimpanzee interactions in a series of dyadic informed forager contests. We used cross correlations as a "proof of concept" so as to determine whether the target actions were contingent on, or occurred in a time-locked pattern relative to, the referent actions. A subordinate individual was given privileged knowledge of food location. As expected, an ignorant dominant followed the informed subordinate's movement in the enclosure. The dominant also followed the subordinate's gaze direction: after she looked at the subordinate, she was more likely to gaze toward this same direction within one second. In contrast, the subordinate only occasionally followed the dominant's movement and gaze. The dominant also changed her own direction of movement to converge on the location to which the subordinate directed her gaze and movement. Cross correlation proves an effective technique for charting contingencies in social interactions, an important step in understanding the use of cognition in natural situations. PMID:24710756
Basso Moro, Sara; Cutini, Simone; Ursini, Maria Laura; Ferrari, Marco; Quaresima, Valentina
2013-01-01
Encoding, storage and retrieval constitute three fundamental stages in information processing and memory. They allow for the creation of new memory traces, the maintenance and the consolidation of these traces over time, and the access and recover of the stored information from short or long-term memory. Functional near-infrared spectroscopy (fNIRS) is a non-invasive neuroimaging technique that measures concentration changes of oxygenated-hemoglobin (O2Hb) and deoxygenated-hemoglobin (HHb) in cortical microcirculation blood vessels by means of the characteristic absorption spectra of hemoglobin in the near-infrared range. In the present study, we monitored, using a 16-channel fNIRS system, the hemodynamic response during the encoding and retrieval processes (EP and RP, respectively) over the prefrontal cortex (PFC) of 13 healthy subjects (27.2 ± 2.6 years) while were performing the “Logical Memory Test” (LMT) of the Wechsler Memory Scale. A LMT-related PFC activation was expected; specifically, it was hypothesized a neural dissociation between EP and RP. The results showed a heterogeneous O2Hb/HHb response over the mapped area during the EP and the RP, with a O2Hb progressive and prominent increment in ventrolateral PFC (VLPFC) since the beginning of the EP. During the RP a broader activation, including the VLPFC, the dorsolateral PFC and the frontopolar cortex, was observed. This could be explained by the different contributions of the PFC regions in the EP and the RP. Considering the fNIRS applicability for the hemodynamic monitoring during the LMT performance, this study has demonstrated that fNIRS could be utilized as a valuable clinical diagnostic tool, and that it has the potential to be adopted in patients with cognitive disorders or slight working memory deficits. PMID:24427131
Basso Moro, Sara; Cutini, Simone; Ursini, Maria Laura; Ferrari, Marco; Quaresima, Valentina
2013-01-01
Encoding, storage and retrieval constitute three fundamental stages in information processing and memory. They allow for the creation of new memory traces, the maintenance and the consolidation of these traces over time, and the access and recover of the stored information from short or long-term memory. Functional near-infrared spectroscopy (fNIRS) is a non-invasive neuroimaging technique that measures concentration changes of oxygenated-hemoglobin (O2Hb) and deoxygenated-hemoglobin (HHb) in cortical microcirculation blood vessels by means of the characteristic absorption spectra of hemoglobin in the near-infrared range. In the present study, we monitored, using a 16-channel fNIRS system, the hemodynamic response during the encoding and retrieval processes (EP and RP, respectively) over the prefrontal cortex (PFC) of 13 healthy subjects (27.2 ± 2.6 years) while were performing the "Logical Memory Test" (LMT) of the Wechsler Memory Scale. A LMT-related PFC activation was expected; specifically, it was hypothesized a neural dissociation between EP and RP. The results showed a heterogeneous O2Hb/HHb response over the mapped area during the EP and the RP, with a O2Hb progressive and prominent increment in ventrolateral PFC (VLPFC) since the beginning of the EP. During the RP a broader activation, including the VLPFC, the dorsolateral PFC and the frontopolar cortex, was observed. This could be explained by the different contributions of the PFC regions in the EP and the RP. Considering the fNIRS applicability for the hemodynamic monitoring during the LMT performance, this study has demonstrated that fNIRS could be utilized as a valuable clinical diagnostic tool, and that it has the potential to be adopted in patients with cognitive disorders or slight working memory deficits. PMID:24427131
Foulis, P R; Norbut, A M; Mendelow, H; Kessler, G F
1980-06-01
A pathology accessioning and retrieval system with encoding by computer (PARSEC) has been developed, employing a relatively inexpensive microcomputer. PARSEC performs a variety of administrative functions for anatomic pathology, including accessioning of surgical specimens, storage of patient demographic information, editing, retrieval, and archiving of patient data, as well as CAP (college of American Pathologists) workload units, billing, and inventory functions for histopathology. In addition, appropriate gross and microscopic descriptions and pathologic diagnoses can be entered into the system by a text editor. Automatic assignment of SNOP (Systematized Nomenclature of Pathology) codes, is accomplished via an online SNOP lexicon, allowing the ultimate generation of completed surgical pathology reports. The data base management system employed makes optimum use of disk storage space, while permitting rapid data retrieval. Data file maintenance is automatically accomplished by the system, requiring no user intervention. PMID:7395803
Green's Function Retrieval and Marchenko Imaging in a Dissipative Acoustic Medium.
Slob, Evert
2016-04-22
Single-sided Marchenko equations for Green's function construction and imaging relate the measured reflection response of a lossless heterogeneous medium to an acoustic wave field inside this medium. I derive two sets of single-sided Marchenko equations for the same purpose, each in a heterogeneous medium, with one medium being dissipative and the other a corresponding medium with negative dissipation. Double-sided scattering data of the dissipative medium are required as input to compute the surface reflection response in the corresponding medium with negative dissipation. I show that each set of single-sided Marchenko equations leads to Green's functions with a virtual receiver inside the medium: one exists inside the dissipative medium and one in the medium with negative dissipation. This forms the basis of imaging inside a dissipative heterogeneous medium. I relate the Green's functions to the reflection response inside each medium, from which the image can be constructed. I illustrate the method with a one-dimensional example that shows the image quality. The method has a potentially wide range of imaging applications where the material under test is accessible from two sides. PMID:27152808
Green's Function Retrieval and Marchenko Imaging in a Dissipative Acoustic Medium
NASA Astrophysics Data System (ADS)
Slob, Evert
2016-04-01
Single-sided Marchenko equations for Green's function construction and imaging relate the measured reflection response of a lossless heterogeneous medium to an acoustic wave field inside this medium. I derive two sets of single-sided Marchenko equations for the same purpose, each in a heterogeneous medium, with one medium being dissipative and the other a corresponding medium with negative dissipation. Double-sided scattering data of the dissipative medium are required as input to compute the surface reflection response in the corresponding medium with negative dissipation. I show that each set of single-sided Marchenko equations leads to Green's functions with a virtual receiver inside the medium: one exists inside the dissipative medium and one in the medium with negative dissipation. This forms the basis of imaging inside a dissipative heterogeneous medium. I relate the Green's functions to the reflection response inside each medium, from which the image can be constructed. I illustrate the method with a one-dimensional example that shows the image quality. The method has a potentially wide range of imaging applications where the material under test is accessible from two sides.
Chen, Yu-Wen; Guo, Jun-Yen; Tzeng, Shih-Yu; Chou, Ting-Chun; Lin, Ming-Jen; Huang, Lynn Ling-Huei; Yang, Chao-Chun; Hsu, Chao-Kai; Tseng, Sheng-Hao
2016-02-01
Spatially resolved diffuse reflectance spectroscopy (SRDRS) has been employed to quantify tissue optical properties and its interrogation volume is majorly controlled by the source-to-detector separations (SDSs). To noninvasively quantify properties of dermis, a SRDRS setup that includes SDS shorter than 1 mm is required. It will be demonstrated in this study that Monte Carlo simulations employing the Henyey-Greenstein phase function cannot always precisely predict experimentally measured diffuse reflectance at such short SDSs, and we speculated this could be caused by the non-negligible backward light scattering at short SDSs that cannot be properly modeled by the Henyey-Greenstein phase function. To accurately recover the optical properties and functional information of dermis using SRDRS, we proposed the use of the modified two-layer (MTL) geometry. Monte Carlo simulations and phantom experiment results revealed that the MTL probing geometry was capable of faithfully recovering the optical properties of upper dermis. The capability of the MTL geometry in probing the upper dermis properties was further verified through a swine study, and it was found that the measurement results were reasonably linked to histological findings. Finally, the MTL probe was utilized to study psoriatic lesions. Our results showed that the MTL probe was sensitive to the physiological condition of tissue volumes within the papillary dermis and could be used in studying the physiology of psoriasis. PMID:26977361
Chen, Yu-Wen; Guo, Jun-Yen; Tzeng, Shih-Yu; Chou, Ting-Chun; Lin, Ming-Jen; Huang, Lynn Ling-Huei; Yang, Chao-Chun; Hsu, Chao-Kai; Tseng, Sheng-Hao
2016-01-01
Spatially resolved diffuse reflectance spectroscopy (SRDRS) has been employed to quantify tissue optical properties and its interrogation volume is majorly controlled by the source-to-detector separations (SDSs). To noninvasively quantify properties of dermis, a SRDRS setup that includes SDS shorter than 1 mm is required. It will be demonstrated in this study that Monte Carlo simulations employing the Henyey-Greenstein phase function cannot always precisely predict experimentally measured diffuse reflectance at such short SDSs, and we speculated this could be caused by the non-negligible backward light scattering at short SDSs that cannot be properly modeled by the Henyey-Greenstein phase function. To accurately recover the optical properties and functional information of dermis using SRDRS, we proposed the use of the modified two-layer (MTL) geometry. Monte Carlo simulations and phantom experiment results revealed that the MTL probing geometry was capable of faithfully recovering the optical properties of upper dermis. The capability of the MTL geometry in probing the upper dermis properties was further verified through a swine study, and it was found that the measurement results were reasonably linked to histological findings. Finally, the MTL probe was utilized to study psoriatic lesions. Our results showed that the MTL probe was sensitive to the physiological condition of tissue volumes within the papillary dermis and could be used in studying the physiology of psoriasis. PMID:26977361
Theiler, J.; Henderson, B.G.; Smith, B.W.
1997-11-01
We present two algorithms for determining sensor motion of a multi-spectral push-broom imager for use in subsequent image registration. The first algorithm, termed the {open_quotes}pairwise{close_quotes} method, performs cross-correlations between individual pairs of channels. The offsets of maximum correlation are formulated into a system of linear equations whose solution gives an estimate of the jitter function. The second algorithm performs cross-correlations between channels and a reference image called the {open_quotes}baseline{close_quotes} which is constructed by averaging together all the channels in the image cube. An estimated jitter time series is computed for each channel, all of which are overlapped and averaged to obtain a best estimate of the jitter function. The pairwise method is more general in that it can handle a wider range of jitter scenarios. The baseline method, although more restricted, is very simple to implement, and its accuracy can be improved substantially through iteration. In this paper, we describe both methods in detail and present results of simulations performed on thermal-infrared data cubes.
Young, Laura K; Love, Gordon D; Smithson, Hannah E
2013-01-01
We previously showed that different types of aberration defocus, coma, and secondary astigmatism affect reading performance via different mechanisms. In this paper, we show the contrary result that, for identification of isolated letters, the effects of rendering different types of aberration can be described by a single cross-correlation-based metric. Aberrations reduce the effective resolution of an optical system, quantified by the high-frequency fall-off of the modulation transfer function. They additionally cause spatial-frequency-dependent phase and contrast changes, which have a size-dependent effect on letter forms. We used contrast threshold as our performance measure, instead of distance acuity, to separate the effects of form alterations from those of resolution limits. This measure is additionally appropriate in comparing single-letter-based performance to reading at a fixed distance. The relationship between a cross-correlation-based measure of letter confusability and performance was the same for all three types of aberration. For reading, we had found a different relationship for coma than for defocus and secondary astigmatism. We conclude that even when two tasks--letter identification and reading--use the same component stimulus set, the combination of multiple letters in a reading task produces functional differences between the effects of these aberrations that are not present for isolated letters. PMID:23788460
Sabra, Karim G; Winkel, Eric S; Bourgoyne, Dwayne A; Elbing, Brian R; Ceccio, Steve L; Perlin, Marc; Dowling, David R
2007-04-01
It has been demonstrated theoretically and experimentally that an estimate of the impulse response (or Green's function) between two receivers can be obtained from the cross correlation of diffuse wave fields at these two receivers in various environments and frequency ranges: ultrasonics, civil engineering, underwater acoustics, and seismology. This result provides a means for structural monitoring using ambient structure-borne noise only, without the use of active sources. This paper presents experimental results obtained from flow-induced random vibration data recorded by pairs of accelerometers mounted within a flat plate or hydrofoil in the test section of the U.S. Navy's William B. Morgan Large Cavitation Channel. The experiments were conducted at high Reynolds number (Re > 50 million) with the primary excitation source being turbulent boundary layer pressure fluctuations on the upper and lower surfaces of the plate or foil. Identical deterministic time signatures emerge from the noise cross-correlation function computed via robust and simple processing of noise measured on different days by a pair of passive sensors. These time signatures are used to determine and/or monitor the structural response of the test models from a few hundred to a few thousand Hertz. PMID:17471715
Liu, Guo-Chin; Ng, Kin-Wang; Pen, Ue-Li
2011-03-15
Integrated Sachs-Wolfe (ISW) effect can be estimated by cross-correlating the cosmic microwave background (CMB) sky with tracers of the local matter distribution. At late cosmic time, the dark energy-induced decay of gravitation potential generates a cross correlation signal on large angular scales. The dominant noise is the intrinsic CMB anisotropies from the inflationary epoch. In this paper we use CMB polarization to reduce this intrinsic noise. We cross-correlate the microwave sky observed by Wilkinson Microwave Anisotropy Probe (WMAP) with the radio source catalog compiled by NRAO VLA Sky Survey (NVSS) to study the efficiency of the noise suppression. We find that the error bars are reduced by about 4 to 14% and the statistical power in the signal is improved.
Automatic tremor detection with a combined cross-correlation and neural network approach
NASA Astrophysics Data System (ADS)
Horstmann, T.; Harrington, R. M.; Cochran, E. S.
2011-12-01
Low-amplitude, long-duration, and ambiguous phase arrivals associated with crustal tremor make automatic detection difficult. We present a new detection method that combines cross-correlation with a neural network clustering algorithm. The approach is independent of any a priori assumptions regarding tremor event duration; instead, it examines frequency content, amplitude, and motion products of continuous data to distinguish tremor from earthquakes and background noise in an automated fashion. Because no assumptions regarding event duration are required, the clustering algorithm is therefore able to detect short, burst-like events which may be missed by many current methods. We detect roughly 130 seismic events occurring over 100 minutes, including earthquakes and tremor, in a three-week long test data set of waveforms recorded near Cholame, California. The detection has a success rate of over 90% when compared to visually selected events. We use continuous broadband data from 13 STS-2 seismometers deployed from May 2010 to July 2011 along the Cholame segment of the San Andreas Fault, as well as stations from the HRSN network. The large volume of waveforms requires first reducing the amount of data before applying the neural network algorithm. First, we filter the data between 2 Hz and 8 Hz, calculate envelopes, and decimate them to 0.2 Hz. We cross-correlate signals at each station with two master stations using a moving 520-second time window with a 5-sec time step. We calculate a mean cross-correlation coefficient value between all station pairs for each time window and each master station, and select the master station with the highest mean value. Time windows with mean coefficients exceeding 0.3 are used in the neural network approach, and windows separated by less than 300 seconds are grouped together. In the second step, we apply the neural network algorithm, i.e., Self Organized Map (SOM), to classify the reduced data set. We first calculate feature
Fluid trajectory evaluation based on an ensemble-averaged cross-correlation in time-resolved PIV
NASA Astrophysics Data System (ADS)
Jeon, Young Jin; Chatellier, Ludovic; David, Laurent
2014-07-01
A novel multi-frame particle image velocimetry (PIV) method, able to evaluate a fluid trajectory by means of an ensemble-averaged cross-correlation, is introduced. The method integrates the advantages of the state-of-art time-resolved PIV (TR-PIV) methods to further enhance both robustness and dynamic range. The fluid trajectory follows a polynomial model with a prescribed order. A set of polynomial coefficients, which maximizes the ensemble-averaged cross-correlation value across the frames, is regarded as the most appropriate solution. To achieve a convergence of the trajectory in terms of polynomial coefficients, an ensemble-averaged cross-correlation map is constructed by sampling cross-correlation values near the predictor trajectory with respect to an imposed change of each polynomial coefficient. A relation between the given change and corresponding cross-correlation maps, which could be calculated from the ordinary cross-correlation, is derived. A disagreement between computational domain and corresponding physical domain is compensated by introducing the Jacobian matrix based on the image deformation scheme in accordance with the trajectory. An increased cost of the convergence calculation, associated with the nonlinearity of the fluid trajectory, is moderated by means of a V-cycle iteration. To validate enhancements of the present method, quantitative comparisons with the state-of-arts TR-PIV methods, e.g., the adaptive temporal interval, the multi-frame pyramid correlation and the fluid trajectory correlation, were carried out by using synthetically generated particle image sequences. The performances of the tested methods are discussed in algorithmic terms. A high-rate TR-PIV experiment of a flow over an airfoil demonstrates the effectiveness of the present method. It is shown that the present method is capable of reducing random errors in both velocity and material acceleration while suppressing spurious temporal fluctuations due to measurement noise.
Measuring water velocity using DIDSON and image cross-correlation techniques
Deng, Zhiqun; Mueller, Robert P.; Richmond, Marshall C.
2009-08-01
To design or operate hydroelectric facilities for maximum power generation and minimum ecological impact, it is critical to understand the biological responses of fish to different flow structures. However, information is still lacking on the relationship between fish behavior and flow structures despite many years of research. Existing field characterization approaches conduct fish behavior studies and flow measurements separately and coupled later using statistical analysis. These types of studies, however, lack a way to determine the specific hydraulic conditions or the specific causes of the biological response. The Dual-Frequency Identification Sonar (DIDSON) has been in wide use for fish behavior studies since 1999. The DIDSON can detect acoustic targets at long ranges in dark or turbid dark water. PIV is a state-of-the-art, non-intrusive, whole-flow-field technique, providing instantaneous velocity vector measurements in a whole plane using image cross-correlating techniques. There has been considerable research in the development of image processing techniques associated with PIV. This existing body of knowledge is applicable and can be used to process the images taken by the DIDSON. This study was conducted in a water flume which is 9 m long, 1.2 m wide, and 1.2 m deep when filled with water. A lab jet flow was setup as the benchmark flow to calibrate DIDSON images. The jet nozzle was 6.35 cm in diameter and core jet velocity was 1.52 m/s. Different particles were used to seed the flow. The flow was characterized based on the results using Laser Doppler Velocimetry (LDV). A DIDSON was mounted about 5 meters away from the jet nozzle. Consecutive DIDSON images with known time delay were divided into small interrogation spots after background was subtracted. Across-correlation was then performed to estimate the velocity vector for each interrogation spot. The estimated average velocity in the core zone was comparable to that obtained using a LDV. This proof
Satellite services and orbital retrieval
NASA Technical Reports Server (NTRS)
Adornato, R. J.
1985-01-01
Within the capabilities of the Space Shuttle Orbiter, a broad range of services which can be made available to the satellite user community as summarized. Payload deployment, close proximity retrieval, and a number of other mission related functions are discussed. The focus here is on close proximity retrieval and retrieval of payloads in higher energy low Earth orbits.
Language Processing in Information Retrieval.
ERIC Educational Resources Information Center
Doszkocs, Tamase
1986-01-01
Examines role and contributions of natural-language processing in information retrieval and artificial intelligence research in context of large operational information retrieval systems and services. State-of-the-art information retrieval systems combining the functional capabilities of conventional inverted file term adjacency approach with…
NASA Astrophysics Data System (ADS)
Quine, Brendan M.; Abrarov, Sanjar M.; Jagpal, Raj K.
2014-06-01
In our recent publication, we proposed the application of the spectrally integrated Voigt function (SIVF) to a line-by-line (LBL) radiative transfer modelling1. We applied the GENSPECT LBL radiative transfer model that utilizes the HITRAN database to generate synthetic spectral data due to thermal or solar radiation of the Earth or planetary atmosphere2. It has been shown that the SIVF methodology enables the computation of a LBL radiative transfer at reduced spectral resolution model without loss in accuracy. In contrast to the traditional method of computation, the SIVF implementation accounts for the area under the Voigt function between adjacent grid points resulting in well-preserved shape of a spectral radiance even at low spectral resolution. This significant advantage of the SIVF methodology can be applied in the rapid retrieval of the space observation data, required for real-time control and decision making in future generation of the Argus3 remote-sensing microspectrometers. The spectrally integrated methodology can be generalized to other linebroadening profiles, such as Galatry, Rautian-Sobelman or speed dependent profiles, to prevent underestimation of the spectral radiance that always occurs at reduced spectral resolution1 in any LBL radiative transfer model using a traditional method of computation.
NASA Astrophysics Data System (ADS)
Pal, Mayukha; Satish, B.; Srinivas, K.; Rao, P. Madhusudana; Manimaran, P.
2015-10-01
We propose a new approach combining the chaos game representation and the two dimensional multifractal detrended cross correlation analysis methods to examine multifractal behavior in power law cross correlation between any pair of nucleotide sequences of unequal lengths. In this work, we analyzed the characteristic behavior of coding and non-coding DNA sequences of eight prokaryotes. The results show the presence of strong multifractal nature between coding and non-coding sequences of all data sets. We found that this integrative approach helps us to consider complete DNA sequences for characterization, and further it may be useful for classification, clustering, identification of class affiliation of nucleotide sequences etc. with high precision.
NASA Astrophysics Data System (ADS)
Wapenaar, Kees; Thorbecke, Jan; van der Neut, Joost
2016-04-01
Green's theorem plays a fundamental role in a diverse range of wavefield imaging applications, such as holographic imaging, inverse scattering, time-reversal acoustics and interferometric Green's function retrieval. In many of those applications, the homogeneous Green's function (i.e. the Green's function of the wave equation without a singularity on the right-hand side) is represented by a closed boundary integral. In practical applications, sources and/or receivers are usually present only on an open surface, which implies that a significant part of the closed boundary integral is by necessity ignored. Here we derive a homogeneous Green's function representation for the common situation that sources and/or receivers are present on an open surface only. We modify the integrand in such a way that it vanishes on the part of the boundary where no sources and receivers are present. As a consequence, the remaining integral along the open surface is an accurate single-sided representation of the homogeneous Green's function. This single-sided representation accounts for all orders of multiple scattering. The new representation significantly improves the aforementioned wavefield imaging applications, particularly in situations where the first-order scattering approximation breaks down.
NASA Astrophysics Data System (ADS)
Finn, Charles W.; Morris, Simon L.; Tejos, Nicolas; Crighton, Neil H. M.; Perry, Robert; Fumagalli, Michele; Bielby, Rich; Theuns, Tom; Schaye, Joop; Shanks, Tom; Liske, Jochen; Gunawardhana, Madusha L. P.; Bartle, Stephanie
2016-04-01
We present new results on the auto- and cross-correlation functions of galaxies and O VI absorbers in a ˜18~Gpc3 comoving volume at z < 1. We use a sample of 51 296 galaxies and 140 O VIabsorbers in the column density range 13 ≲ log N ≲ 15 to measure two-point correlation functions in the two dimensions transverse and orthogonal to the line-of-sight ξ(r⊥, r∥). We furthermore infer the corresponding `real-space' correlation functions, ξ(r), by projecting ξ(r⊥, r∥) along r∥, and assuming a power-law form, ξ(r) = (r/r0)-γ. Comparing the results from the absorber-galaxy cross-correlation function, ξag, the galaxy auto-correlation function, ξgg, and the absorber auto-correlation function, ξaa, we constrain the statistical connection between galaxies and the metal-enriched intergalactic medium as a function of star-formation activity. We also compare these results to predictions from the EAGLE cosmological hydrodynamical simulation and find a reasonable agreement. We find that: (i) O VI absorbers show very little velocity dispersion with respect to galaxies on ˜ Mpc scales, likely ≲ 100 km s-1; (ii) O VI absorbers are less clustered, and potentially more extended around galaxies than galaxies are around themselves; (iii) On ≳ 100 kpc scales, the likelihood of finding O VI absorbers around star-forming galaxies is similar to the likelihood of finding O VI absorbers around non star-forming galaxies; and (iv) O VI absorbers are either not ubiquitous to galaxies in our sample, or their distribution around them is patchy on scales ≳ 100 kpc (or both), at least for the column densities at which most are currently detected.
NASA Astrophysics Data System (ADS)
Finn, Charles W.; Morris, Simon L.; Tejos, Nicolas; Crighton, Neil H. M.; Perry, Robert; Fumagalli, Michele; Bielby, Rich; Theuns, Tom; Schaye, Joop; Shanks, Tom; Liske, Jochen; Gunawardhana, Madusha L. P.; Bartle, Stephanie
2016-07-01
We present new results on the auto- and cross-correlation functions of galaxies and O VI absorbers in a ˜18 Gpc3 comoving volume at z < 1. We use a sample of 51 296 galaxies and 140 O VI absorbers in the column density range 13 ≲ log N ≲ 15 to measure two-point correlation functions in the two dimensions transverse and orthogonal to the line of sight ξ(r⊥, r∥). We furthermore infer the corresponding `real-space' correlation functions, ξ(r), by projecting ξ(r⊥, r∥) along r∥, and assuming a power-law form, ξ(r) = (r/r0)-γ. Comparing the results from the absorber-galaxy cross-correlation function, ξag, the galaxy autocorrelation function, ξgg, and the absorber autocorrelation function, ξaa, we constrain the statistical connection between galaxies and the metal-enriched intergalactic medium as a function of star formation activity. We also compare these results to predictions from the EAGLE cosmological hydrodynamical simulation and find a reasonable agreement. We find that: (i) O VI absorbers show very little velocity dispersion with respect to galaxies on ˜ Mpc scales, likely ≲100 km s-1; (ii) O VI absorbers are less clustered, and potentially more extended around galaxies than galaxies are around themselves; (iii) on ≳100 kpc scales, the likelihood of finding O VI absorbers around star-forming galaxies is similar to the likelihood of finding O VI absorbers around non-star-forming galaxies; and (iv) O VI absorbers are either not ubiquitous to galaxies in our sample, or their distribution around them is patchy on scales ≳100 kpc (or both), at least for the column densities at which most are currently detected.
Parametric instability in a helicon discharge observed by Cross-Correlation Enhanced-Scattering
NASA Astrophysics Data System (ADS)
Selenin, Valeriy L.; Kaganskaya, Nina M.; Krämer, Michael
2001-10-01
Enhanced scattering (ES) of microwaves close to the Upper Hybrid Resonance layer is a relatively new method for detecting small-scale fluctuations or waves in non-uniform magnetized plasmas. By applying the cross-correlation scheme of this diagnostic, we measured the frequency and wave number spectra of the fluctuations excited in the helicon discharge HE-L (ne <= 2\\cdot 10^19m-3,P_HF ≈ 2 kW, f=13.56 MHz, T_e≈ 4 eV, B<0.2 T, p≈ 1 Pa argon, r_p=7.4 cm, L_p=110 cm). Part of the spectrum can be attributed to ion-sound turbulence. The ES signal reveals a threshold at a certain RF power thus proving the nonlinear nature of the fluctuations. Features of their dispersion perpendicular to the magnetic field suggest that the turbulence originates from a parametric decay of helicon modes into ion-sound waves and, possibly, Trivelpiece-Gould (or Lower-Hybrid) waves. The growth rates and the saturation of the observed fluctuation amplitude are discussed in terms of the RF power absorption. (Supported by the DFG, SFB 191, Project A12 & Russian-German Contract 146 RUS 590, and the Grant supporting Scientific Schools 96-15-96367.)
NASA Astrophysics Data System (ADS)
Bee Cheng, Sew
Synthetic Aperture Radar (SAR) is one of the widely used remote sensing sensors which produces high resolution image by using advance signal processing technique. SAR managed to operate in all sorts of weather and cover wide range of area. To produce a high-quality image, accurate parameters such as Doppler centroid are required for precise SAR signal processing. In the azimuth matched filtering of SAR signal processing, Doppler centroid is an important azimuth parameter that helps to focus the image pixels. Doppler centroid has always been overlooked during SAR signal processing. It is due to the fact that estimation of Doppler centroid involved complicated calculation and increased computational load. Therefore, researcher used to apply only the approximate Doppler value which is not precise and cause defocus effort in the generated SAR image. In this study, several conventional Doppler centroid estimation algorithms are reviewed and developed using Matlab software program to extract the Doppler parameter from received SAR data, namely Spectrum Fit Algorithm, Wavelength Diversity Algorithm (WDA), Multilook Cross Correlation Algorithm (MLCC), and Multilook Beat Frequency Algorithm (MLBF). Two sets of SAR data are employed to evaluate the performance of each estimator, i.e. simulated point target data and RADARSAT-1 Vancouver scene raw data. These experiments gave a sense of accuracy for the estimated results together with computational time consumption. Point target is simulated to generate ideal case SAR data with pre-defined SAR system parameters.
Dependence of Adaptive Cross-correlation Algorithm Performance on the Extended Scene Image Quality
NASA Technical Reports Server (NTRS)
Sidick, Erkin
2008-01-01
Recently, we reported an adaptive cross-correlation (ACC) algorithm to estimate with high accuracy the shift as large as several pixels between two extended-scene sub-images captured by a Shack-Hartmann wavefront sensor. It determines the positions of all extended-scene image cells relative to a reference cell in the same frame using an FFT-based iterative image-shifting algorithm. It works with both point-source spot images as well as extended scene images. We have demonstrated previously based on some measured images that the ACC algorithm can determine image shifts with as high an accuracy as 0.01 pixel for shifts as large 3 pixels, and yield similar results for both point source spot images and extended scene images. The shift estimate accuracy of the ACC algorithm depends on illumination level, background, and scene content in addition to the amount of the shift between two image cells. In this paper we investigate how the performance of the ACC algorithm depends on the quality and the frequency content of extended scene images captured by a Shack-Hatmann camera. We also compare the performance of the ACC algorithm with those of several other approaches, and introduce a failsafe criterion for the ACC algorithm-based extended scene Shack-Hatmann sensors.
Auditory-evoked magnetic fields in relation to the interaural cross correlation
NASA Astrophysics Data System (ADS)
Soeta, Yoshiharu; Nakagawa, Seiji; Tonoike, Mitsuo; Hotehama, Takuya; Ando, Yoichi
2001-05-01
Noninvasive measurements utilizing magnetoencephalography (MEG) have been used to study how sound stimulus features are represented in the human brain. These measurements have successfully revealed how, for example, tone frequency, periodicity, and intensity are encoded. Here, the auditory-evoked magnetic fields in change of the magnitude of the interaural cross correlation (IACC) were analyzed. The IACC of the stimuli was controlled by mixing two independent bandpass noises in appropriate ratios. The auditory stimuli were binaurally delivered through silicon tubes and earpieces inserted into the ear canals. All source signals had the same sound-pressure level. Nine volunteers with normal hearing took part in this study. The auditory-evoked fields were recorded using a neuromagnetometer in a magnetically shielded room. Combinations of a reference stimulus (IACC=1.0) and test stimuli (IACC=0.2,0.6,0.85) were presented alternately at a constant 0.5-s interstimulus interval, and the MEGs were recorded and averaged more than 50 times. The results showed that the peak amplitude of N1m, which was found above left and right temporal lobes around 100 ms after the stimulus onset, significantly decreased with increasing IACC. The N1m latencies were not affected by IACC.
Dependence of adaptive cross-correlation algorithm performance on the extended scene image quality
NASA Astrophysics Data System (ADS)
Sidick, Erkin
2008-08-01
Recently, we reported an adaptive cross-correlation (ACC) algorithm to estimate with high accuracy the shift as large as several pixels between two extended-scene sub-images captured by a Shack-Hartmann wavefront sensor. It determines the positions of all extended-scene image cells relative to a reference cell in the same frame using an FFT-based iterative image-shifting algorithm. It works with both point-source spot images as well as extended scene images. We have demonstrated previously based on some measured images that the ACC algorithm can determine image shifts with as high an accuracy as 0.01 pixel for shifts as large 3 pixels, and yield similar results for both point source spot images and extended scene images. The shift estimate accuracy of the ACC algorithm depends on illumination level, background, and scene content in addition to the amount of the shift between two image cells. In this paper we investigate how the performance of the ACC algorithm depends on the quality and the frequency content of extended scene images captured by a Shack-Hatmann camera. We also compare the performance of the ACC algorithm with those of several other approaches, and introduce a failsafe criterion for the ACC algorithm-based extended scene Shack-Hatmann sensors.
NASA Astrophysics Data System (ADS)
Jammazi, Rania; Aloui, Chaker
2015-10-01
This paper analyzes the interactive linkages between carbon dioxide (CO2) emissions, energy consumption (EC) and economic growth (EG) using a novel approach namely wavelet windowed cross correlation (WWCC) for six oil-exporting countries from the GCC (Gulf Cooperation Council) region over the period 1980-2012. Our empirical results show that there exists a bidirectional causal relationship between EC and EG. However, the results support the occurrence of unidirectional causality from EC to CO2 emissions without any feedback effects, and there exists a bidirectional causal relationship between EG and CO2 emissions for the region as a whole. The study suggests that environmental and energy policies should recognize the differences in the nexus between EC and EG in order to maintain sustainable EG in the GCC region. Our findings will be useful for GCC countries to better evaluate its situation in the future climate negotiations. The overall findings will help GCC countries assess its position better in future climate change negotiations.
Cross-correlation matrix analysis of Chinese and American bank stocks in subprime crisis
NASA Astrophysics Data System (ADS)
Zhu, Shi-Zhao; Li, Xin-Li; Nie, Sen; Zhang, Wen-Qing; Yu, Gao-Feng; Han, Xiao-Pu; Wang, Bing-Hong
2015-05-01
In order to study the universality of the interactions among different markets, we analyze the cross-correlation matrix of the price of the Chinese and American bank stocks. We then find that the stock prices of the emerging market are more correlated than that of the developed market. Considering that the values of the components for the eigenvector may be positive or negative, we analyze the differences between two markets in combination with the endogenous and exogenous events which influence the financial markets. We find that the sparse pattern of components of eigenvectors out of the threshold value has no change in American bank stocks before and after the subprime crisis. However, it changes from sparse to dense for Chinese bank stocks. By using the threshold value to exclude the external factors, we simulate the interactions in financial markets. Project supported by the National Natural Science Foundation of China (Grant Nos. 11275186, 91024026, and FOM2014OF001) and the University of Shanghai for Science and Technology (USST) of Humanities and Social Sciences, China (Grant Nos. USST13XSZ05 and 11YJA790231).
NASA Astrophysics Data System (ADS)
Muñoz-Diosdado, A.
2005-01-01
We analyzed databases with gait time series of adults and persons with Parkinson, Huntington and amyotrophic lateral sclerosis (ALS) diseases. We obtained the staircase graphs of accumulated events that can be bounded by a straight line whose slope can be used to distinguish between gait time series from healthy and ill persons. The global Hurst exponent of these series do not show tendencies, we intend that this is because some gait time series have monofractal behavior and others have multifractal behavior so they cannot be characterized with a single Hurst exponent. We calculated the multifractal spectra, obtained the spectra width and found that the spectra of the healthy young persons are almost monofractal. The spectra of ill persons are wider than the spectra of healthy persons. In opposition to the interbeat time series where the pathology implies loss of multifractality, in the gait time series the multifractal behavior emerges with the pathology. Data were collected from healthy and ill subjects as they walked in a roughly circular path and they have sensors in both feet, so we have one time series for the left foot and other for the right foot. First, we analyzed these time series separately, and then we compared both results, with direct comparison and with a cross correlation analysis. We tried to find differences in both time series that can be used as indicators of equilibrium problems.
A cross-correlation search for intermediate-duration gravitational waves from GRB magnetars
NASA Astrophysics Data System (ADS)
Coyne, Robert
2015-04-01
Since the discovery of the afterglow in 1997, the progress made in our understanding of gamma-ray bursts (GRBs) has been spectacular. Yet a direct proof of GRB progenitors is still missing. In the last few years, evidence for a long-lived and sustained central engine in GRBs has mounted. This has called attention to the so-called millisecond-magnetar model, which proposes that a highly magnetized, rapidly-rotating neutron star may exist at the heart of some of these events. The advent of advanced gravitational wave detectors such as LIGO and Virgo may enable us to probe directly, for the first time, the nature of GRB progenitors and their byproducts. In this context, we describe a novel application of a generalized cross-correlation technique optimized for the detection of long-duration gravitational wave signals that may be associated with bar-like deformations of GRB magnetars. The detection of these signals would allow us to answer some of the most intriguing questions on the nature of GRB progenitors, and serve as a starting point for a new class of intermediate-duration gravitational wave searches.
Pack, Chan-Gi; Ahn, Sang-Gun
2015-07-31
The cellular response to stress is primarily controlled in cells via transcriptional activation by heat shock factor 1 (HSF1). HSF1 is well-known to form homotrimers for activation upon heat shock and subsequently bind to target DNAs, such as heat-shock elements, by forming stress granules. A previous study demonstrated that nuclear HSF1 and HSF2 molecules in live cells interacted with target DNAs on the stress granules. However, the process underlying the binding interactions of HSF family in cells upon heat shock remains unclear. This study demonstrate for the first time that the interaction kinetics among nuclear HSF1, HSF2, and HSF4 upon heat shock can be detected directly in live cells using dual color fluorescence cross-correlation spectroscopy (FCCS). FCCS analyses indicated that the binding between HSFs was dramatically changed by heat shock. Interestingly, the recovery kinetics of interaction between HSF1 molecules after heat shock could be represented by changes in the relative interaction amplitude and mobility. - Highlights: • The binding interactions among nuclear HSFs were successfully detected. • The binding kinetics between HSF1s during recovery was quantified. • HSF2 and HSF4 strongly formed hetero-complex, even before heat shock. • Nuclear HSF2 and HSF4 bound to HSF1 only after heat shock.
Cross-correlation analysis and interpretation of spaced-receiver measurements
Costa, E.; Fougere, P.F.; Basu, S.
1988-04-01
Two algorithms that provide a statistical treatment to the estimation of the parameters of the cross-correlation analysis of spaced-receiver data are reviewed. Their results are compared using signals transmitted by a quasi-stationary polar beacon and received at Goose Bay, Labrador; and transmitted by the orbiting Hilat satellite and received at Tromso, Norway. A good general agreement is displayed in this comparison. The former experiment indicates the possibility of extreme daily variations in the anisotropy of the ground diffraction pattern and in the true drift velocity of the in-situ irregularities. The latter experiment displays geometrical enhancements in the intensity scintillation index S sub 4, in the rms phase fluctuation sigma/sub phi/ and in the axial ration of the ellipse which characterizes the anisotropy of the ground-diffraction pattern, around the region of local L shell alignment of the ray paths. Increases of these parameters also are observed northward of Tromso. These observations are thus consistent with a morphological model for anisotropy of high-latitude nighttime F-region irregularities proposed in the literature. A possible dependence of the results of the spaced-receiver measurements on the receiver baselines is discussed. It is argued that this mechanism could be responsible for the relatively small values of the anisotropy of the diffraction pattern obtained from the Hilat measurements at Tromso.
Cross-correlation cosmography with intensity mapping of the neutral hydrogen 21 cm emission
NASA Astrophysics Data System (ADS)
Pourtsidou, A.; Bacon, D.; Crittenden, R.
2015-11-01
The cross-correlation of a foreground density field with two different background convergence fields can be used to measure cosmographic distance ratios and constrain dark energy parameters. We investigate the possibility of performing such measurements using a combination of optical galaxy surveys and neutral hydrogen (HI) intensity mapping surveys, with emphasis on the performance of the planned Square Kilometre Array (SKA). Using HI intensity mapping to probe the foreground density tracer field and/or the background source fields has the advantage of excellent redshift resolution and a longer lever arm achieved by using the lensing signal from high redshift background sources. Our results show that, for our best SKA-optical configuration of surveys, a constant equation of state for dark energy can be constrained to ≃8 % for a sky coverage fsky=0.5 and assuming a σ (ΩDE)=0.03 prior for the dark energy density parameter. We also show that using the cosmic microwave background as the second source plane is not competitive, even when considering a COrE-like satellite.
X-ray pump optical probe cross-correlation study of GaAs
Durbin, S.M.; Clevenger, T.; Graber, T.; Henning, R.
2012-09-10
Ultrafast dynamics in atomic, molecular and condensed-matter systems are increasingly being studied using optical-pump, X-ray probe techniques where subpicosecond laser pulses excite the system and X-rays detect changes in absorption spectra and local atomic structure. New opportunities are appearing as a result of improved synchrotron capabilities and the advent of X-ray free-electron lasers. These source improvements also allow for the reverse measurement: X-ray pump followed by optical probe. We describe here how an X-ray pump beam transforms a thin GaAs specimen from a strong absorber into a nearly transparent window in less than 100 ps, for laser photon energies just above the bandgap. We find the opposite effect - X-ray induced optical opacity - for photon energies just below the bandgap. This raises interesting questions about the ultrafast many-body response of semiconductors to X-ray absorption, and provides a new approach for an X-ray/optical cross-correlator for synchrotron and X-ray free-electron laser applications.
NASA Technical Reports Server (NTRS)
Sherwin, Blake D; Das, Sudeep; Haijian, Amir; Addison, Graeme; Bond, Richard; Crichton, Devin; Devlin, Mark J.; Dunkley, Joanna; Gralla, Megan B.; Halpern, Mark; Hill, J. Colin; Hincks, Adam D.; Hughes, John P.; Huffenberger, Kevin; Hlozek, Renee; Kosowsky, Arthur; Louis, Thibaut; Marriage, Tobias A.; Marsden, Danica; Menanteau, Felipe; Moodley, Kavilan; Niemack, Michael D.; Page, Lyman A.; Reese. Erik D.; Sehgal, Neelima; Sievers, Jon; Sifon, Cristobal; Spergel, David N.; Staggs, Suzanne T.; Switzer, Eric R.; Wollack, Ed.
2012-01-01
We measure the cross-correlation of Atacama cosmology telescope cosmic microwave background (CMB) lensing convergence maps with quasar maps made from the Sloan Digital Sky Survey DR8 SDSS-XDQSO photometric catalog. The CMB lensing quasar cross-power spectrum is detected for the first time at a significance of 3.8 sigma, which directly confirms that the quasar distribution traces the mass distribution at high redshifts z > 1. Our detection passes a number of null tests and systematic checks. Using this cross-power spectrum, we measure the amplitude of the linear quasar bias assuming a template for its redshift dependence, and find the amplitude to be consistent with an earlier measurement from clustering; at redshift z ap 1.4, the peak of the distribution of quasars in our maps, our measurement corresponds to a bias of b = 2.5 +/- 0.6. With the signal-to-noise ratio on CMB lensing measurements likely to improve by an order of magnitude over the next few years, our results demonstrate the potential of CMB lensing crosscorrelations to probe astrophysics at high redshifts.
Performance of waveform cross correlation using a global and regular grid of master events
NASA Astrophysics Data System (ADS)
Kitov, I. O.; Bobrov, D.; Rozhkov, M.
2013-12-01
Seismic monitoring of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) requires a uniform distribution of detection threshold over the earth. By design, the Primary Seismic Network of the International Monitoring System (IMS) provides an appropriate coverage. In order to effectively use the cross correlation technique and the archive waveforms from the International Data Centre (IDC) in global monitoring we have introduced a dense (spacing of ~ 140 km) and regular grid of master events with high quality templates at IMS array stations. In seismically active zones, we populated the grid with real masters. For aseismic zones, we developed an extended set of synthetic templates for virtual master events. This set includes a few simple double-couple source mechanisms in 1D and 2D velocity structures as well as explosion sources of varying size and at different depths of burial. All synthetics were first tested in seismic areas and showed the detection threshold similar to that demonstrated by real templates. We have designed three versions of the grid: V1.0 with only synthetic templates, V2.0 with real masters added where possible, and V3.0 with grand masters added. Their performance has been assessed by full processing of a few data days and a direct comparison with the Reviewed Event Bulletin issued by the IDC.
Sankaran, Jagadish; Manna, Manoj; Guo, Lin; Kraut, Rachel; Wohland, Thorsten
2009-11-01
Cell membrane organization is dynamic and is assumed to have different characteristic length scales. These length scales, which are influenced by lipid and protein composition as well as by the cytoskeleton, can range from below the optical resolution limit (as with rafts or microdomains) to far above the resolution limit (as with capping phenomena or the formation of lipid "platforms"). The measurement of these membrane features poses a significant problem because membrane dynamics are on the millisecond timescale and are thus beyond the time resolution of conventional imaging approaches. Fluorescence correlation spectroscopy (FCS), a widely used spectroscopic technique to measure membrane dynamics, has the required time resolution but lacks imaging capabilities. A promising solution is the recently introduced method known as imaging total internal reflection (ITIR)-FCS, which can probe diffusion phenomena in lipid membranes with good temporal and spatial resolution. In this work, we extend ITIR-FCS to perform ITIR fluorescence cross-correlation spectroscopy (ITIR-FCCS) between pixel areas of arbitrary shape and derive a generalized expression that is applicable to active transport and diffusion. ITIR-FCCS is applied to model systems exhibiting diffusion, active transport, or a combination of the two. To demonstrate its applicability to live cells, we observe the diffusion of a marker, the sphingolipid-binding domain (SBD) derived from the amyloid peptide Abeta, on live neuroblastoma cells. We investigate the organization and dynamics of SBD-bound lipid microdomains under the conditions of cholesterol removal and cytoskeleton disruption. PMID:19883607
Constraints on primordial non-Gaussianity from galaxy-CMB lensing cross correlation
Takeuchi, Yoshitaka; Ichiki, Kiyotomo; Matsubara, Takahiko
2010-07-15
Recent studies have shown that the primordial non-Gaussianity affects the clustering of dark matter halos through a scale-dependent bias, and various constraints on the non-Gaussianity through this scale-dependent bias have been placed. Here, we introduce the cross correlation between the CMB lensing potential and the galaxy angular distribution to effectively extract information about the bias from the galaxy distribution. Then, we estimate the error of the nonlinear parameter, f{sub NL}, for the ongoing CMB experiments and galaxy surveys, such as Planck and Hyper Suprime-Cam. We found that for the constraint on f{sub NL} with Planck and Hyper Suprime-Cam, the wide field galaxy survey is preferable to the deep one, and the expected error on f{sub NL} can be as small as {Delta}f{sub NL{approx}}80 for b{sub 0}=2 and {Delta}f{sub NL{approx}}30 for b{sub 0}=4, where b{sub 0} is the linear bias parameter. It is also found that a future wide field galaxy survey could achieve {Delta}f{sub NL{approx}}5 with cosmic microwave background prior to Planck, if one could observe highly biased objects at higher redshift (z{approx}2).
Estimating error cross-correlations in soil moisture data sets using extended collocation analysis
Technology Transfer Automated Retrieval System (TEKTRAN)
Consistent global soil moisture records are essential for studying the role of hydrologic processes within the larger earth system. Various studies have shown the benefit of assimilating satellite-based soil moisture data into water balance models or merging multi-source soil moisture retrievals int...
NASA Astrophysics Data System (ADS)
Taira, T.; Kato, A.
2013-12-01
A high-resolution Vp/Vs ratio estimate is one of the key parameters to understand spatial variations of composition and physical state within the Earth. Lin and Shearer (2007, BSSA) recently developed a methodology to obtain local Vp/Vs ratios in individual similar earthquake clusters, based on P- and S-wave differential times. A waveform cross-correlation approach is typically employed to measure those differential times for pairs of seismograms from similar earthquakes clusters, at narrow time windows around the direct P and S waves. This approach effectively collects P- and S-wave differential times and however requires the robust P- and S-wave time windows that are extracted based on either manually or automatically picked P- and S-phases. We present another technique to estimate P- and S-wave differential times by exploiting temporal properties of delayed time as a function of elapsed time on the seismograms with a moving-window cross-correlation analysis (e.g., Snieder, 2002, Phys. Rev. E; Niu et al. 2003, Nature). Our approach is based on the principle that the delayed time for the direct S wave differs from that for the direct P wave. Two seismograms aligned by the direct P waves from a pair of similar earthquakes yield that delayed times become zero around the direct P wave. In contrast, delayed times obtained from time windows including the direct S wave have non-zero value. Our approach, in principle, is capable of measuring both P- and S-wave differential times from single-component seismograms. In an ideal case, the temporal evolution of delayed time becomes a step function with its discontinuity at the onset of the direct S wave. The offset in the resulting step function would be the S-wave differential time, relative to the P-wave differential time as the two waveforms are aligned by the direct P wave. We apply our moving-window cross-correlation technique to the two different data sets collected at: 1) the Wakayama district, Japan and 2) the Geysers
NASA Astrophysics Data System (ADS)
Bray, Aaron D.; Eisenstein, Daniel J.; Skibba, Ramin A.; Blanton, Michael R.; Coil, Alison L.; Cool, Richard J.; Mendez, Alexander J.; Moustakas, John; Zhu, Guangtun
2015-10-01
We report small-scale clustering measurements from the PRIsm MUlti-object Survey (PRIMUS) spectroscopic redshift survey as a function of color and luminosity. We measure the real-space cross-correlations between 62,106 primary galaxies with PRIMUS redshifts and a tracer population of ∼545,000 photometric galaxies over redshifts from z = 0.2 to z = 1. We separately fit a power-law model in redshift and luminosity to each of three independent color-selected samples of galaxies. We report clustering amplitudes at fiducial values of z = 0.5 and L=1.5{L}*. The clustering of the red galaxies is ∼ 3 times as strong as that of the blue galaxies and ∼ 1.5 as strong as that of the green galaxies. We also find that the luminosity dependence of the clustering is strongly dependent on physical scale, with greater luminosity dependence being found between r=0.0625 {h}-1 {Mpc} and r=0.25 {h}-1 {Mpc}, compared to the r=0.5 {h}-1 {Mpc} to r=2 {h}-1 {Mpc} range. Moreover, over a range of two orders of magnitude in luminosity, a single power-law fit to the luminosity dependence is not sufficient to explain the increase in clustering at both the bright and faint ends at the smaller scales. We argue that luminosity-dependent clustering at small scales is a necessary component of galaxy-halo occupation models for blue, star-forming galaxies as well as for red, quenched galaxies.
EVOLUTION OF THE CROSS-CORRELATION AND TIME LAG OF 4U 1735-44 ALONG THE BRANCHES
Lei Yajuan; Zhang Haotong; Zhang Chengmin; Yuan Hailong; Dong Yiqiao; Zhao Yongheng; Zhang Yanxia; Qu Jinlu; Song Liming; Wang Dehua; Yin Hongxing
2013-09-15
We analyze the cross-correlation function between the soft and hard X-rays of atoll source 4U 1735-44 with RXTE data, and find anti-correlated soft and hard time lags of about a hecto-second. In the island state, the observations do not show any obvious correlations, and most observations of the banana branch show a positive correlation. However, anti-correlations are detected in the upper banana branch. These results are different from those of Z-sources (Cyg X-2, GX 5-1), where anti-correlations are detected in the horizontal branch and upper normal branch. In this case, the lag timescales of both this atoll and Z-sources are found to be similar, at a magnitude of several tens to hundreds of seconds. As a comparison, it is noted that anti-correlated lags lasting thousands of seconds have been reported from several black hole candidates in their intermediate states. In addition, for an observation containing four segments that show positive or anti-correlation, we analyze the spectral evolution with the hybrid model. In the observation, the anti-correlation is detected at the highest flux. The fitting results show that the Comptonized component is not the lowest at the highest flux, which suggests that the anti-correlation corresponds to the transition between the soft and hard states. Finally, we compare the corresponding results of atoll source 4U 1735-44 with those observed in Z-sources and black hole candidates, and the possible origins of the anti-correlated time lags are discussed.
NASA Astrophysics Data System (ADS)
Le Feuvre, M.; Joubert, A.; Leparoux, D.; Côte, P.
2015-03-01
We introduce the use of cross-correlations in the passive multi-channel analysis of surface waves (MASW), and report an improvement in the determination of subsurface shear velocities from ambient seismic noise. Velocities are measured from phase-shifts that are also related to the source location. Consequently, the accuracy with which velocities can be inferred depends on the ability of the array to locate noise sources. The computation of cross-correlations for each receiver pair allows increasing the effective spatial sampling of the array. For this reason, we show that beamforming is more efficient with cross-correlated signals. Consequently, MASW performed with cross-correlations produces a dispersion diagram where aliasing is reduced and signal-to-noise ratio increased. The proposed method is validated with synthetic records. It is then applied on passive recordings obtained on top of a sea dike at high tide, where sea waves were acting as continuous seismic sources. Surface wave velocities that favorably compare with hammer shot measurements are inferred.
Vallinotto, Alberto; Das, Sudeep; Spergel, David N; Viel, Matteo
2009-08-28
We present a theoretical estimate for a new observable: the cross correlation between the Lyman-alpha flux fluctuations in quasar spectra and the convergence of the cosmic microwave background as measured along the same line of sight. As a first step toward the assessment of its detectability, we estimate the signal-to-noise ratio using linear theory. Although the signal-to-noise is small for a single line of sight and peaks at somewhat smaller redshifts than those probed by the Lyman-alpha forest, we estimate a total signal-to-noise of 9 for cross correlating quasar spectra of SDSS-III with Planck and 20 for cross correlating with a future polarization based cosmic microwave background experiment. The detection of this effect would be a direct measure of the neutral hydrogen-matter cross correlation and could provide important information on the growth of structures at large scales in a redshift range which is still poorly probed. PMID:19792781
NASA Astrophysics Data System (ADS)
Ganilova, Yulia; Li, Pengcheng; Zhu, Dan; Lin, Nisong; Chen, Haiying; Luo, Qingming; Ulyanov, Sergey
2006-08-01
Different methods of speckle-metrology, which may be used in biomedical diagnostics, are considered in this paper. Cross-correlation technique, digital speckle-photography, LASCA are compared. Advantages and disadvantages of these methods are demonstrated; the limits for minimal resolution are studied.
Baheza, Richard A.; Welch, E. Brian; Gochberg, Daniel F.; Sanders, Melinda; Harvey, Sara; Gore, John C.; Yankeelov, Thomas E.
2015-03-15
Purpose: To develop and evaluate a new method for detecting calcium deposits using their characteristic magnetic susceptibility effects on magnetic resonance (MR) images at high fields and demonstrate its potential in practice for detecting breast microcalcifications. Methods: Characteristic dipole signatures of calcium deposits were detected in magnetic resonance phase images by computing the cross-correlation between the acquired data and a library of templates containing simulated phase patterns of spherical deposits. The influence of signal-to-noise ratio and various other MR parameters on the results were assessed using simulations and validated experimentally. The method was tested experimentally for detection of calcium fragments within gel phantoms and calcium-like inhomogeneities within chicken tissue at 7 T with optimized MR acquisition parameters. The method was also evaluated for detection of simulated microcalcifications, modeled from biopsy samples of malignant breast cancer, inserted in silico into breast magnetic resonance imaging (MRIs) of healthy subjects at 7 T. For both assessments of calcium fragments in phantoms and biopsy-based simulated microcalcifications in breast MRIs, receiver operator characteristic curve analyses were performed to determine the cross-correlation index cutoff, for achieving optimal sensitivity and specificity, and the area under the curve (AUC), for measuring the method’s performance. Results: The method detected calcium fragments with sizes of 0.14–0.79 mm, 1 mm calcium-like deposits, and simulated microcalcifications with sizes of 0.4–1.0 mm in images with voxel sizes between (0.2 mm){sup 3} and (0.6 mm){sup 3}. In images acquired at 7 T with voxel sizes of (0.2 mm){sup 3}–(0.4 mm){sup 3}, calcium fragments (size 0.3–0.4 mm) were detected with a sensitivity, specificity, and AUC of 78%–90%, 51%–68%, and 0.77%–0.88%, respectively. In images acquired with a human 7 T scanner, acquisition times below 12
Baheza, Richard A.; Welch, E. Brian; Gochberg, Daniel F.; Sanders, Melinda; Harvey, Sara; Gore, John C.; Yankeelov, Thomas E.
2015-01-01
Purpose: To develop and evaluate a new method for detecting calcium deposits using their characteristic magnetic susceptibility effects on magnetic resonance (MR) images at high fields and demonstrate its potential in practice for detecting breast microcalcifications. Methods: Characteristic dipole signatures of calcium deposits were detected in magnetic resonance phase images by computing the cross-correlation between the acquired data and a library of templates containing simulated phase patterns of spherical deposits. The influence of signal-to-noise ratio and various other MR parameters on the results were assessed using simulations and validated experimentally. The method was tested experimentally for detection of calcium fragments within gel phantoms and calcium-like inhomogeneities within chicken tissue at 7 T with optimized MR acquisition parameters. The method was also evaluated for detection of simulated microcalcifications, modeled from biopsy samples of malignant breast cancer, inserted in silico into breast magnetic resonance imaging (MRIs) of healthy subjects at 7 T. For both assessments of calcium fragments in phantoms and biopsy-based simulated microcalcifications in breast MRIs, receiver operator characteristic curve analyses were performed to determine the cross-correlation index cutoff, for achieving optimal sensitivity and specificity, and the area under the curve (AUC), for measuring the method’s performance. Results: The method detected calcium fragments with sizes of 0.14–0.79 mm, 1 mm calcium-like deposits, and simulated microcalcifications with sizes of 0.4–1.0 mm in images with voxel sizes between (0.2 mm)3 and (0.6 mm)3. In images acquired at 7 T with voxel sizes of (0.2 mm)3–(0.4 mm)3, calcium fragments (size 0.3–0.4 mm) were detected with a sensitivity, specificity, and AUC of 78%–90%, 51%–68%, and 0.77%–0.88%, respectively. In images acquired with a human 7 T scanner, acquisition times below 12 min, and voxel sizes of
NASA Astrophysics Data System (ADS)
Vasterling, Margarete; Wegler, Ulrich; Becker, Jan; Brüstle, Andrea; Bischoff, Monika
2016-08-01
We develop and test a real-time envelope cross-correlation detector for use in seismic response plans to mitigate hazard of induced seismicity. The incoming seismological data are cross-correlated in real-time with a set of previously recorded master events. For robustness against small changes in the earthquake source locations or in the focal mechanisms we cross-correlate the envelopes of the seismograms rather than the seismograms themselves. Two sequenced detection conditions are implemented: After passing a single trace cross-correlation condition, a network cross-correlation is calculated taking amplitude ratios between stations into account. Besides detecting the earthquake and assigning it to the respective reservoir, real-time magnitudes are important for seismic response plans. We estimate the magnitudes of induced microseismicity using the relative amplitudes between master event and detected event. The real-time detector is implemented as a SeisComP3 module. We carry out offline and online performance tests using seismic monitoring data of the Insheim and Landau geothermal power plants (Upper Rhine Graben, Germany), also including blasts from a nearby quarry. The comparison of the automatic real-time catalogue with a manually processed catalogue shows, that with the implemented parameters events are always correctly assigned to the respective reservoir (4 km distance between reservoirs) or the quarry (8 km and 10 km distance, respectively, from the reservoirs). The real-time catalogue achieves a magnitude of completeness around 0.0. Four per cent of the events assigned to the Insheim reservoir and zero per cent of the Landau events are misdetections. All wrong detections are local tectonic events, whereas none are caused by seismic noise.
NASA Astrophysics Data System (ADS)
Kitov, Ivan; Bobrov, Dmitry; Rozhkov, Mikhail
2016-04-01
We built an automatic seismic event bulletin for the whole globe using waveform cross correlation at array stations of the International Monitoring System (IMS). To detect signals and associate them into robust event hypotheses in an automatic pipeline we created a global grid (GG) of master events with a diversity of waveform templates. For the Comprehensive Nuclear-Test-Ban Treaty (CTBT), the GG provide an almost uniform distribution of monitoring capabilities and adjustable templates. For seismic areas, we select high quality signals at IMS stations from earthquakes. For test sites, signals from UNEs are best templates. Global detection and association with cross correlation technique for research and monitoring purposes demands templates from master events outside the regions of natural seismicity and test sites. We populate aseismic areas with masters having synthetic templates calculated for predefined sets of IMS array stations. We applied various technologies to synthesize most representative signals for cross correlation and tested them using the Reviewed Event Bulletin (REB) issued by the International Data Centre (IDC). At first, we tested these global sets of master events and synthetic templates using IMS seismic data for February 13, 2013 and demonstrated excellent detection and location capability. Then, using the REB and cross correlation bulletins (XSELs) experienced analysts from the IDC compared the relative performance of various templates and built reliable sets of events and detections for machine learning. In this study, we carefully compile global training sets for machine learning in order to establish statistical decision lines between reliable and unreliable event hypotheses, then apply classification procedures to the intermediate automatic cross correlation bulletin based on the GG, and compile the final XSEL, which is more accurate and has lower detection threshold than the REB.
STATISTICAL STUDY OF 2XMMi-DR3/SDSS-DR8 CROSS-CORRELATION SAMPLE
Zhang Yanxia; Zhou Xinlin; Zhao Yongheng; Wu Xuebing
2013-02-01
Cross-correlating the XMM-Newton 2XMMi-DR3 catalog with the Sloan Digital Sky Survey (SDSS) Data Release 8, we obtain one of the largest X-ray/optical catalogs and explore the distribution of various classes of X-ray emitters in the multidimensional photometric parameter space. Quasars and galaxies occupy different zones while stars scatter in them. However, X-ray active stars have a certain distributing rule according to spectral types. The earlier the type of stars, the stronger its X-ray emitting. X-ray active stars have a similar distribution to most stars in the g - r versus r - i diagram. Based on the identified samples with SDSS spectral classification, a random forest algorithm for automatic classification is performed. The result shows that the classification accuracy of quasars and galaxies adds up to more than 93.0% while that of X-ray emitting stars only amounts to 45.3%. In other words, it is easy to separate quasars and galaxies, but it is difficult to discriminate X-ray active stars from quasars and galaxies. If we want to improve the accuracy of automatic classification, it is necessary to increase the number of X-ray emitting stars, since the majority of X-ray emitting sources are quasars and galaxies. The results obtained here will be used for the optical spectral survey performed by the Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST, also named the Guo Shou Jing Telescope), which is a Chinese national scientific research facility operated by the National Astronomical Observatories, Chinese Academy of Sciences.
High-resolution Imaging of Rapid Tremor Reversals Using Cross-Station Cross-Correlations
NASA Astrophysics Data System (ADS)
Peng, Y.; Rubin, A. M.; Bostock, M. G.
2013-12-01
Tectonic tremor is assumed to be a proxy for slow slip, and together they provide unique observational constraints on the rheology and deformation styles operating near the base of the seismogenic zone. Several techniques have been used to locate tremor/LFE sources, including well-established "cross-time" methods that compare waveforms from different time windows at the same station (e.g., work by Shelly, Brown, Bostock and others). We have been developing a "cross-station" method, based on the original work of Armbruster and Kim [AGU 2010], that instead compares waveforms from the same time window at widely separated stations. We compare 4-second windows at 3 stations after rotating the horizontal component into the empirical shear wave particle motion direction for the particular source-station geometry. The large-scale "rapid tremor reversals" described by Houston et al. [2011] beneath southern Vancouver Island are best recorded by stations that exhibit pronounced shear wave splitting, which obscures this optimal direction. We correct for splitting using the stacked templates of about 90 LFE families obtained by Bostock et al. [2012] in this region. These empirical corrections significantly increase the cross-correlation coefficients between templates from a given family at stations separated by tens of kilometers, and significantly increase the number (and presumably location accuracy) of our cross-station detections. Requiring a large ratio of the amplitude of the (split-corrected) optimal horizontal component to that of the orthogonal component helps weed out false detections. We find numerous large-scale reversals, with propagation speeds similar to those of the smaller-scale reversals imaged further down-dip by Rubin and Armbruster [AGU2012]. However, the recurrence intervals of the larger reversals are longer, perhaps consistent with loading a larger patch by creep of the surroundings, and they progress from being too short to be tidally-modulated to
NASA Astrophysics Data System (ADS)
Fotin, Sergei V.; Yin, Yin; Periaswamy, Senthil; Kunz, Justin; Haldankar, Hrishikesh; Muradyan, Naira; Cornud, François; Turkbey, Baris; Choyke, Peter L.
2012-02-01
Fully automated prostate segmentation helps to address several problems in prostate cancer diagnosis and treatment: it can assist in objective evaluation of multiparametric MR imagery, provides a prostate contour for MR-ultrasound (or CT) image fusion for computer-assisted image-guided biopsy or therapy planning, may facilitate reporting and enables direct prostate volume calculation. Among the challenges in automated analysis of MR images of the prostate are the variations of overall image intensities across scanners, the presence of nonuniform multiplicative bias field within scans and differences in acquisition setup. Furthermore, images acquired with the presence of an endorectal coil suffer from localized high-intensity artifacts at the posterior part of the prostate. In this work, a three-dimensional method for fast automated prostate detection based on normalized gradient fields cross-correlation, insensitive to intensity variations and coil-induced artifacts, is presented and evaluated. The components of the method, offline template learning and the localization algorithm, are described in detail. The method was validated on a dataset of 522 T2-weighted MR images acquired at the National Cancer Institute, USA that was split in two halves for development and testing. In addition, second dataset of 29 MR exams from Centre d'Imagerie Médicale Tourville, France were used to test the algorithm. The 95% confidence intervals for the mean Euclidean distance between automatically and manually identified prostate centroids were 4.06 +/- 0.33 mm and 3.10 +/- 0.43 mm for the first and second test datasets respectively. Moreover, the algorithm provided the centroid within the true prostate volume in 100% of images from both datasets. Obtained results demonstrate high utility of the detection method for a fully automated prostate segmentation.
Influence of seismic anisotropy on the cross correlation tensor: numerical investigations
NASA Astrophysics Data System (ADS)
Saade, M.; Montagner, J. P.; Roux, P.; Cupillard, P.; Durand, S.; Brenguier, F.
2015-05-01
Temporal changes in seismic anisotropy can be interpreted as variations in the orientation of cracks in seismogenic zones, and thus as variations in the stress field. Such temporal changes have been observed in seismogenic zones before and after earthquakes, although they are still not well understood. In this study, we investigate the azimuthal polarization of surface waves in anisotropic media with respect to the orientation of anisotropy, from a numerical point of view. This technique is based on the observation of the signature of anisotropy on the nine-component cross-correlation tensor (CCT) computed from seismic ambient noise recorded on pairs of three-component sensors. If noise sources are spatially distributed in a homogeneous medium, the CCT allows the reconstruction of the surface wave Green's tensor between the station pairs. In homogeneous, isotropic medium, four off-diagonal terms of the surface wave Green's tensor are null, but not in anisotropic medium. This technique is applied to three-component synthetic seismograms computed in a transversely isotropic medium with a horizontal symmetry axis, using a spectral element code. The CCT is computed between each pair of stations and then rotated, to approximate the surface wave Green's tensor by minimizing the off-diagonal components. This procedure allows the calculation of the azimuthal variation of quasi-Rayleigh and quasi-Love waves. In an anisotropic medium, in some cases, the azimuth of seismic anisotropy can induce a large variation in the horizontal polarization of surface waves. This variation depends on the relative angle between a pair of stations and the direction of anisotropy, the amplitude of the anisotropy, the frequency band of the signal and the depth of the anisotropic layer.
Monitoring volcanic systems through cross-correlation of coincident A-Train satellite data.
NASA Astrophysics Data System (ADS)
Flower, V. J. B.; Carn, S. A.; Wright, R.
2014-12-01
The remote location and inaccessibility of many active volcanic systems around the world hinders detailed investigation of their eruptive dynamics. One methodology for monitoring such locations is through the utilisation of multiple satellite datasets to elucidate underlying eruption dynamics and aid volcanic hazard mitigation. Whilst satellite datasets are often analysed individually, here we exploit the multi-platform NASA A-Train satellite constellation, including the Ozone Monitoring Instrument (OMI) on Aura and Moderate Resolution Imaging Spectroradiometer (MODIS) on Aqua. OMI measures volcanic emissions (e.g. sulphur dioxide, ash) whilst MODIS enables monitoring of thermal anomalies (e.g. lava flows, lava lakes, pyroclastic deposits), allowing analysis of a more diverse range of volcanic unrest than is possible using a single measurement technique alone, and permitting cross-correlation between datasets for specific locations to assess cyclic activity. A Multi-taper (MTM) Fast Fourier Transform (FFT) analysis was implemented at an initial sample site (Soufriere Hills volcano [SHV], Montserrat) facilitating cycle identification and subsequent comparison with existing ground-based data. Corresponding cycles at intervals of 8, 12 and ~50 days were identified in both the satellite-based SO2 and thermal infrared signals and ground-based SO2 measurements (Nicholson et al. 2013), validating the methodology. Our analysis confirms the potential for identification of cyclical volcanic activity through synergistic analysis of satellite data, which would be of particular value at poorly monitored volcanic systems. Following our initial test at SHV, further sample sites have been selected in locations with varied eruption dynamics and monitoring capabilities including Ambrym (Vanuatu), Kilauea (Hawaii), Nyiragongo (DR Congo) and Etna (Italy) with the intention of identifying not only cyclic signals that can be attributed to volcanic systems but also those which are
Full relaxation matrix analysis of apparent cross-correlated relaxation rates in four-spin systems.
Vögeli, Beat
2013-01-01
Cross-correlated relaxation (CCR) rates are an established tool for the extraction of relative bond orientations in biomolecules in solution. CCR between dipolar interactions in four-spin systems is a particularly well-suited mechanism. In this paper, a simple approach to analyze systematic experimental errors is formulated in a subspace of the complete four-spin Hilbert space. It is shown that, contrary to the common assumption, the secular approximation of the relaxation matrix is marginal for the most prominent spin systems. With the main focus on the model protein GB3 at room temperature, it is shown that the apparent experimental CCR rates have errors between -12% and +4% for molecules with a molecular tumbling time of 3.5 ns. Although depending on the specific pulse sequence used, the following rule-of-thumb can be established: Judged by absolute values, the errors for H(α)-C(α)/H(α)-C(α), H(N)-N/C(α)-C', H(N)-N/C(γ)-C(β) and H(N)-N/H(β)-C(β) CCR rates can safely be neglected. However, errors for H(N)-N/H(N)-N and H(N)-N/H(α)-C(α) CCR rates are on the order of 0.1-0.3s(-1) and must be considered. Tabulated correction factors may be used for their extraction. If larger systems are studied, in most cases the errors cannot be neglected anymore. On the other hand, well-calibrated pulses can safely be assumed to be perfect. PMID:23207177
NASA Astrophysics Data System (ADS)
Brunker, J.; Beard, P.
2013-03-01
Blood flow measurements have been demonstrated using the acoustic resolution mode of photoacoustic sensing. This is unlike previous flowmetry methods using the optical resolution mode, which limits the maximum penetration depth to approximately 1mm. Here we describe a pulsed time correlation photoacoustic Doppler technique that is inherently flexible, lending itself to both resolution modes. Doppler time shifts are quantified via cross-correlation of pairs of photoacoustic waveforms generated in moving absorbers using pairs of laser light pulses, and the photoacoustic waves detected using an ultrasound transducer. The acoustic resolution mode is employed by using the transducer focal width, rather than the large illuminated volume, to define the lateral spatial resolution. The use of short laser pulses allows depth-resolved measurements to be obtained with high spatial resolution, offering the prospect of mapping flow within microcirculation. Whilst our previous work has been limited to a non-fluid phantom, we now demonstrate measurements in more realistic blood-mimicking phantoms incorporating fluid suspensions of microspheres flowing along an optically transparent tube. Velocities up to 110 mm/s were measured with accuracies approaching 1% of the known velocities, and resolutions of a few mm/s. The velocity range and resolution are scalable with excitation pulse separation, but the maximum measurable velocity was considerably smaller than the value expected from the detector focal beam width. Measurements were also made for blood flowing at velocities up to 13.5 mm/s. This was for a sample reduced to 5% of the normal haematocrit; increasing the red blood cell concentration limited the maximum measurable velocity so that no results were obtained for concentrations greater than 20% of a physiologically realistic haematocrit. There are several possible causes for this limitation; these include the detector bandwidth and irregularities in the flow pattern. Better
A Bayesian Estimate of the CMB–Large-scale Structure Cross-correlation
NASA Astrophysics Data System (ADS)
Moura-Santos, E.; Carvalho, F. C.; Penna-Lima, M.; Novaes, C. P.; Wuensche, C. A.
2016-08-01
Evidences for late-time acceleration of the universe are provided by multiple probes, such as Type Ia supernovae, the cosmic microwave background (CMB), and large-scale structure (LSS). In this work, we focus on the integrated Sachs–Wolfe (ISW) effect, i.e., secondary CMB fluctuations generated by evolving gravitational potentials due to the transition between, e.g., the matter and dark energy (DE) dominated phases. Therefore, assuming a flat universe, DE properties can be inferred from ISW detections. We present a Bayesian approach to compute the CMB–LSS cross-correlation signal. The method is based on the estimate of the likelihood for measuring a combined set consisting of a CMB temperature and galaxy contrast maps, provided that we have some information on the statistical properties of the fluctuations affecting these maps. The likelihood is estimated by a sampling algorithm, therefore avoiding the computationally demanding techniques of direct evaluation in either pixel or harmonic space. As local tracers of the matter distribution at large scales, we used the Two Micron All Sky Survey galaxy catalog and, for the CMB temperature fluctuations, the ninth-year data release of the Wilkinson Microwave Anisotropy Probe (WMAP9). The results show a dominance of cosmic variance over the weak recovered signal, due mainly to the shallowness of the catalog used, with systematics associated with the sampling algorithm playing a secondary role as sources of uncertainty. When combined with other complementary probes, the method presented in this paper is expected to be a useful tool to late-time acceleration studies in cosmology.
Vannini, Patrizia; Hedden, Trey; Huijbers, Willem; Ward, Andrew; Johnson, Keith A; Sperling, Reisa A
2013-06-01
Neural networks supporting memory function decline with increasing age. Accumulation of amyloid-β, a histopathological finding in Alzheimer's disease, is a likely contributor. Posteromedial cortices (PMCs) are particularly vulnerable to early amyloid pathology and play a role in both encoding and retrieval processes. The extent to which aging and amyloid influence the ability to modulate activity between these processes within the PMC was investigated by combining positron emission tomography-amyloid imaging with functional magnetic resonance imaging in cognitively normal older and young adults. Young subjects exhibited a marked decrease in activity during encoding and an increase during retrieval (also known as encoding/retrieval "flip"). Impaired ability to modulate activity was associated with increasing age, greater amyloid burden, and worse memory performance. In contrast, the hippocampus showed increased activity during both encoding and retrieval, which was not related to these variables. These findings support a specific link between amyloid pathology and neural dysfunction in PMC and elucidate the underpinnings of age-related memory dysfunction. PMID:22586140
NASA Astrophysics Data System (ADS)
Kim, Kyungsik; Lee, Dong-In
2013-04-01
There is considerable interest in cross-correlations in collective modes of real data from atmospheric geophysics, seismology, finance, physiology, genomics, and nanodevices. If two systems interact mutually, that interaction gives rise to collective modes. This phenomenon is able to be analyzed using the cross-correlation of traditional methods, random matrix theory, and the detrended cross-correlation analysis method. The detrended cross-correlation analysis method was used in the past to analyze several models such as autoregressive fractionally integrated moving average processes, stock prices and their trading volumes, and taxi accidents. Particulate matter is composed of the organic and inorganic mixtures such as the natural sea salt, soil particle, vehicles exhaust, construction dust, and soot. The PM10 is known as the particle with the aerodynamic diameter (less than 10 microns) that is able to enter the human respiratory system. The PM10 concentration has an effect on the climate change by causing an unbalance of the global radiative equilibrium through the direct effect that blocks the stoma of plants and cuts off the solar radiation, different from the indirect effect that changes the optical property of clouds, cloudiness, and lifetime of clouds. Various factors contribute to the degree of the PM10 concentration. Notable among these are the land-use types, surface vegetation coverage, as well as meteorological factors. In this study, we analyze and simulate cross-correlations in time scales between the PM10 concentration and the meteorological factor (among temperature, wind speed and humidity) using the detrended cross-correlation analysis method through the removal of specific trends at eight cities in the Korean peninsula. We divide time series data into Asian dust events and non-Asian dust events to analyze the change of meteorological factors on the fluctuation of PM10 the concentration during Asian dust events. In particular, our result is
Detailed Tremor Migration Styles in Guerrero, Mexico Imaged with Cross-station Cross-correlations
NASA Astrophysics Data System (ADS)
Peng, Y.; Rubin, A. M.
2015-12-01
Tremor occurred downdip of the area that slipped the most during the 2006 slow slip event (SSE) in Guerrero, Mexico, as opposed to Cascadia, where tremor locations and rupture zones of SSEs largely overlap. Here we obtain high resolution tremor locations by applying cross-station cross-correlations [Armbruster et al., 2014] to seismic data from the Meso-America Subduction Experiment deployment. A few 3-station detectors are adopted to capture detailed deformation styles in the tremor "transient zone" and the downdip "sweet spot" as defined in Frank et al., 2014. Similar to Cascadia, tremor activities in our study region were comprised mostly of short tremor bursts lasting minutes to hours. Many of these bursts show clear migration patterns with propagation velocities of hundreds of km/day, comparable to those in Cascadia. However, the propagation of the main tremor front was often not in a simple unilateral fashion. Before the 2006 SSE, we observe 4 large tremor episodes during which both the transient zone and the sweet spot participated, consistent with previous findings [Frank et al., 2014]. The transient zone usually became active a few days after the sweet spot. We find many along-dip migrations with recurrence intervals of about a half day within a region about 10 km along strike and 35 km along dip in the sweet spot, suggesting possible tidal modulation, after the main front moved beyond this region. These migrations appear not to originate at the main front, in contrast to tremor migrations from a few km to tens of km across observed in Cascadia [Rubin and Armbruster, 2013; Peng et al., 2015; Peng and Rubin, submitted], but possibly similar to Shikoku, Japan [Shelly et al., 2007]. We do not observe obvious half-day periodicity for the migrations farther downdip within the sweet spot. During the SSE, the recurrence interval of tremor episodes decreased significantly in both the transient zone and the sweet spot, with that of the former being much shorter
NASA Technical Reports Server (NTRS)
Wernet, Mark P.
1995-01-01
Particle Image Velocimetry provides a means of measuring the instantaneous 2-component velocity field across a planar region of a seeded flowfield. In this work only two camera, single exposure images are considered where both cameras have the same view of the illumination plane. Two competing techniques which yield unambiguous velocity vector direction information have been widely used for reducing the single exposure, multiple image data: cross-correlation and particle tracking. Correlation techniques yield averaged velocity estimates over subregions of the flow, whereas particle tracking techniques give individual particle velocity estimates. The correlation technique requires identification of the correlation peak on the correlation plane corresponding to the average displacement of particles across the subregion. Noise on the images and particle dropout contribute to spurious peaks on the correlation plane, leading to misidentification of the true correlation peak. The subsequent velocity vector maps contain spurious vectors where the displacement peaks have been improperly identified. Typically these spurious vectors are replaced by a weighted average of the neighboring vectors, thereby decreasing the independence of the measurements. In this work fuzzy logic techniques are used to determine the true correlation displacement peak even when it is not the maximum peak on the correlation plane, hence maximizing the information recovery from the correlation operation, maintaining the number of independent measurements and minimizing the number of spurious velocity vectors. Correlation peaks are correctly identified in both high and low seed density cases. The correlation velocity vector map can then be used as a guide for the particle tracking operation. Again fuzzy logic techniques are used, this time to identify the correct particle image pairings between exposures to determine particle displacements, and thus velocity. The advantage of this technique is the
Lg-Wave Cross Correlation and Epicentral Double-Difference Relative Locations in China
NASA Astrophysics Data System (ADS)
Schaff, D. P.; Richards, P. G.; Slinkard, M.; Heck, S.; Young, C. J.
2014-12-01
In prior work we presented high-resolution locations of 28 events in the 1999 Xiuyan sequence in China using only cross correlation measurements of Lg-waves and a double-difference technique solving for the epicenter. Only five regional stations 500 to 1000 km away were used. The resulting locations revealed a 4 km stretch of fault with 95% location errors ~150 m and 7 ms residuals from internal consistency. Based on this success, we now attempt to extend this work on a broader scale to all of China to see if similar results can be obtained for a significant fraction of the seismicity. We first examine in detail three other clusters. The first has 9 events, and has relocations in a 1 km box with location errors on the order of tens of m. The second has 10 events, and relocates in a 10 km box with location errors on the order of hundreds of m. The third cluster, relocates in a 25 km box, and has ~1 km location errors. From this we see that the location errors increase with increasing event separation. The Annual Bulletin of Chinese Earthquakes we have determined from a repeating event catalog has average errors of 16 km. Therefore we are able to demonstrate one to two orders of magnitude improvement in the location errors as compared to the bulletin. Then we apply a pair-wise location procedure for the repeating event catalog we have identified for China in earlier work. 13% of the events are classified as repeating events (2,379 out of 17,898). Of these there are 1,123 events (1,710 pairs and 6% of the catalog) that have two or more stations from which we can estimate the locations by the same procedure. 81% of these events are demonstrated to have locations separated by less than 1 km with another event. There are 677 events in the repeating event catalog that have observations at four or more stations which enables an estimate of the location errors for these high quality events to be about 200 m.
Ade, P A R; Akiba, Y; Anthony, A E; Arnold, K; Atlas, M; Barron, D; Boettger, D; Borrill, J; Borys, C; Chapman, S; Chinone, Y; Dobbs, M; Elleflot, T; Errard, J; Fabbian, G; Feng, C; Flanigan, D; Gilbert, A; Grainger, W; Halverson, N W; Hasegawa, M; Hattori, K; Hazumi, M; Holzapfel, W L; Hori, Y; Howard, J; Hyland, P; Inoue, Y; Jaehnig, G C; Jaffe, A; Keating, B; Kermish, Z; Keskitalo, R; Kisner, T; Le Jeune, M; Lee, A T; Leitch, E M; Linder, E; Lungu, M; Matsuda, F; Matsumura, T; Meng, X; Miller, N J; Morii, H; Moyerman, S; Myers, M J; Navaroli, M; Nishino, H; Paar, H; Peloton, J; Poletti, D; Quealy, E; Rebeiz, G; Reichardt, C L; Richards, P L; Ross, C; Rotermund, K; Schanning, I; Schenck, D E; Sherwin, B D; Shimizu, A; Shimmin, C; Shimon, M; Siritanasak, P; Smecher, G; Spieler, H; Stebor, N; Steinbach, B; Stompor, R; Suzuki, A; Takakura, S; Tikhomirov, A; Tomaru, T; Wilson, B; Yadav, A; Zahn, O
2014-04-01
We reconstruct the gravitational lensing convergence signal from cosmic microwave background (CMB) polarization data taken by the Polarbear experiment and cross-correlate it with cosmic infrared background maps from the Herschel satellite. From the cross spectra, we obtain evidence for gravitational lensing of the CMB polarization at a statistical significance of 4.0σ and indication of the presence of a lensing B-mode signal at a significance of 2.3σ. We demonstrate that our results are not biased by instrumental and astrophysical systematic errors by performing null tests, checks with simulated and real data, and analytical calculations. This measurement of polarization lensing, made via the robust cross-correlation channel, not only reinforces POLARBEAR auto-correlation measurements, but also represents one of the early steps towards establishing CMB polarization lensing as a powerful new probe of cosmology and astrophysics. PMID:24745402
NASA Astrophysics Data System (ADS)
Ade, P. A. R.; Akiba, Y.; Anthony, A. E.; Arnold, K.; Atlas, M.; Barron, D.; Boettger, D.; Borrill, J.; Borys, C.; Chapman, S.; Chinone, Y.; Dobbs, M.; Elleflot, T.; Errard, J.; Fabbian, G.; Feng, C.; Flanigan, D.; Gilbert, A.; Grainger, W.; Halverson, N. W.; Hasegawa, M.; Hattori, K.; Hazumi, M.; Holzapfel, W. L.; Hori, Y.; Howard, J.; Hyland, P.; Inoue, Y.; Jaehnig, G. C.; Jaffe, A.; Keating, B.; Kermish, Z.; Keskitalo, R.; Kisner, T.; Le Jeune, M.; Lee, A. T.; Leitch, E. M.; Linder, E.; Lungu, M.; Matsuda, F.; Matsumura, T.; Meng, X.; Miller, N. J.; Morii, H.; Moyerman, S.; Myers, M. J.; Navaroli, M.; Nishino, H.; Paar, H.; Peloton, J.; Poletti, D.; Quealy, E.; Rebeiz, G.; Reichardt, C. L.; Richards, P. L.; Ross, C.; Rotermund, K.; Schanning, I.; Schenck, D. E.; Sherwin, B. D.; Shimizu, A.; Shimmin, C.; Shimon, M.; Siritanasak, P.; Smecher, G.; Spieler, H.; Stebor, N.; Steinbach, B.; Stompor, R.; Suzuki, A.; Takakura, S.; Tikhomirov, A.; Tomaru, T.; Wilson, B.; Yadav, A.; Zahn, O.; Polarbear Collaboration
2014-04-01
We reconstruct the gravitational lensing convergence signal from cosmic microwave background (CMB) polarization data taken by the Polarbear experiment and cross-correlate it with cosmic infrared background maps from the Herschel satellite. From the cross spectra, we obtain evidence for gravitational lensing of the CMB polarization at a statistical significance of 4.0σ and indication of the presence of a lensing B-mode signal at a significance of 2.3σ. We demonstrate that our results are not biased by instrumental and astrophysical systematic errors by performing null tests, checks with simulated and real data, and analytical calculations. This measurement of polarization lensing, made via the robust cross-correlation channel, not only reinforces POLARBEAR auto-correlation measurements, but also represents one of the early steps towards establishing CMB polarization lensing as a powerful new probe of cosmology and astrophysics.
NASA Astrophysics Data System (ADS)
Camacho-Navarro, Jhonatan; Ruiz, Magda; Villamizar, Rodolfo; Mujica, Luis; Güemes, Alfredo; González-Requema, Ignacio
2015-07-01
This paper discusses, experimental results of classifying several mass adding in a wing aircraft structure, using cross-correlated piezoelectric signals, represented by principal components. Piezoelectric signals are applied and recorded at specific points of the structure under analysis. Then, statistical features are obtained by means of principal component analysis to the correlation between excitation and response signals. Unsupervised learning is implemented to the reduced feature space, in order to identify clusters of damaged cases. The main result of this paper is the advantage resulting from using cross-correlated signals, evaluated through the performance of clustering indexes. Experimental data are collected from two test structures: i.) A turbine blade of a commercial aircraft and ii.) The skin panel of the torsion box of a wing. Damages are induced adding masses at different locations of the wing section surface. The results obtained show the effectiveness of the methodology to distinguish between different damage cases.
NASA Astrophysics Data System (ADS)
Sun, Xuelian; Liu, Zixian
2016-02-01
In this paper, a new estimator of correlation matrix is proposed, which is composed of the detrended cross-correlation coefficients (DCCA coefficients), to improve portfolio optimization. In contrast to Pearson's correlation coefficients (PCC), DCCA coefficients acquired by the detrended cross-correlation analysis (DCCA) method can describe the nonlinear correlation between assets, and can be decomposed in different time scales. These properties of DCCA make it possible to improve the investment effect and more valuable to investigate the scale behaviors of portfolios. The minimum variance portfolio (MVP) model and the Mean-Variance (MV) model are used to evaluate the effectiveness of this improvement. Stability analysis shows the effect of two kinds of correlation matrices on the estimation error of portfolio weights. The observed scale behaviors are significant to risk management and could be used to optimize the portfolio selection.