WorldWideScience

Sample records for ambient noise correlation

  1. Horizontal Correlation of Ambient Noise near a Sea Route

    Institute of Scientific and Technical Information of China (English)

    HE Li; LI Zheng-Lin; ZHANG Ren-He; PENG Zhao-Hui

    2008-01-01

    Ambient noise data measured in an experiment conducted near the sea route are analysed.It is found that at low frequency,the measured horizontal correlation coeffients at different separations oscillate much larger than that predicted by the classical ambient noise model.The theoretical analyses show that the observed phenomenon is mainly caused by windy noise together with the discrete shipping noise nearby.An ambient noise model is proposed to include the effects caused by both the noise sources and can be used to forecast the ambient noise field neara sea route.

  2. Cross-correlations of ambient noise recorded by accelerometers.

    Science.gov (United States)

    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

  3. Passive defect localization in reverberating plates using ambient noise correlation

    OpenAIRE

    Chehami, Lynda

    2015-01-01

    Green’s functions retrieval from ambient noise correlation has recently drawn a new interestin structural health monitoring. In this manuscript, we propose an original methodbased on this approach to detect and locate defects (cracks, holes, grooves) in a reverberantthin plate with a limited number of sensors. Flexural waves that propagate on the plateare generated by either a set of sources distributed randomly on the surface or an ambientnoise. Covariance matrices are estimated from the spa...

  4. Estimating correlations of neighbouring frequencies in ambient seismic noise

    Science.gov (United States)

    Liu, Xin; Ben-Zion, Yehuda

    2016-08-01

    Extracting accurate empirical Green's functions from the ambient seismic noise field requires the noise to be fully diffuse and that different frequency components are not correlated. Calculating a matrix of correlation coefficients of power spectral samples can be used to estimate deviations from a fully diffuse random noise field in the analysed frequency range. A fully diffuse field has correlations only in a narrow region around the diagonal of the matrix, with frequency resolution inversely proportional to length of the used time window. Analysis of low-frequency data (0.005-0.6 Hz) recorded by three broad-band stations of the southern California seismic network reveals three common types of correlations, manifested in the correlation coefficient matrix as square, diagonal halo and correlated stripes. Synthetic calculations show that these types of signatures in the correlation coefficient matrix can result from certain combinations of cross-frequency correlated random components and diffuse field. The analysis of observed data indicates that the secondary microseismic peak around 0.15 Hz is correlated with its neighbouring frequencies, while the primary peak around 0.06 Hz is more diffuse. This suggests that the primary and secondary peaks may be associated with somewhat different physical origins. In addition, significant correlation of frequencies below that of the primary microseismic peak suggests that the very low frequencies noise is less scattered during propagation. The power spectra recorded by a station close to the edge of the Los Angeles basin is higher compared to data recorded by stations outside the basin perhaps because of enhanced basin reverberations and/or closer proximity to the ocean. This and other regional variations should be tested further using data from many more stations.

  5. Infrasonic ambient noise interferometry from correlations of microbaroms

    Science.gov (United States)

    Haney, M.M.

    2009-01-01

    We show that microbaroms, continuous infrasound fluctuations resulting from the interaction of the ocean with the atmosphere, have long-range correlation properties that make it possible to estimate the impulse response between two microphones from passive recordings. The processing is analogous to methods employed in the emerging field of ambient noise seismology, where the random noise source is the ocean coupling with the solid Earth (microseisms) instead of the atmosphere (microbaroms). We find that time-dependent temperature fields and temperature inversions determine the character of infrasonic impulse responses at Fourpeaked Volcano in Alaska. Applications include imaging and monitoring the gross structure of the Earth's atmospheric boundary layer. Copyright 2009 by the American Geophysical Union.

  6. Body Waves Revealed by Spatial Stacking on Long-Term Cross-Correlation of Ambient Noise

    Institute of Scientific and Technical Information of China (English)

    Kai Wang; Yinhe Luo; Kaifeng Zhao; Limeng Zhang

    2014-01-01

    ABSTRCT: Theoretical and experimental studies indicate that complete Green’s Function can be retrieved from cross-correlation in a diffuse field. High SNR (signal-to-noise ratio) surface waves have been extracted from cross-correlations of long-duration ambient noise across the globe. Body waves, not extracted in most of ambient noise studies, are thought to be more difficult to retrieve from regular ambient noise data processing. By stacking cross-correlations of ambient noise in 50 km inter-station distance bins in China, western United States and Europe, we observed coherent 20–100 s core phases (ScS, PKIKPPKIKP, PcPPKPPKP) and crustal-mantle phases (Pn, P, PL, Sn, S, SPL, SnSn, SS, SSPL) at distances ranging from 0 to 4 000 km. Our results show that these crustal-mantle phases show diverse characteristics due to different substructure and sources of body waves beneath different regions while the core phases are relatively robust and can be retrieved as long as stations are available. Further analysis indicates that the SNR of these body-wave phases depends on a compromise between stacking fold in spatial domain and the coherence of pre-stacked cross-correlations.Spatially stacked cross-correlations of seismic noise can provide new virtual seismograms for paths that complement earthquake data and that contain valuable information on the structure of the Earth. The extracted crustal-mantle phases can be used to study lithospheric heterogeneities and the robust core phases are significantly useful to study the deep structure of the Earth, such as detecting fine heterogeneities of the core-mantle boundary and constraining differential rotation of the inner core.

  7. Stability of Monitoring Weak Changes in Multiply Scattering Media with Ambient Noise Correlation: Laboratory Experiments

    CERN Document Server

    Hadziioannou, Céline; Coutant, Olivier; Roux, Philippe; Campillo, Michel

    2009-01-01

    Previous studies have shown that small changes can be monitored in a scattering medium by observing phase shifts in the coda. Passive monitoring of weak changes through ambient noise correlation has already been applied to seismology, acoustics and engineering. Usually, this is done under the assumption that a properly reconstructed Green function as well as stable background noise sources are necessary. In order to further develop this monitoring technique, a laboratory experiment was performed in the 2.5MHz range in a gel with scattering inclusions, comparing an active (pulse-echo) form of monitoring to a passive (correlation) one. Present results show that temperature changes in the medium can be observed even if the Green function (GF) of the medium is not reconstructed. Moreover, this article establishes that the GF reconstruction in the correlations is not a necessary condition: the only condition to monitoring with correlation (passive experiment) is the relative stability of the background noise struc...

  8. Waveform modeling and inversion of ambient noise cross-correlation functions in a coastal ocean environment.

    Science.gov (United States)

    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

  9. Detecting seasonal variations in seismic velocities within Los Angeles basin from correlations of ambient seismic noise.

    OpenAIRE

    Ueli, Meier; Brenguier, Florent; M. Shapiro, N.

    2010-01-01

    International audience We analyze 3 years of continuous seismic records from broadband stations of the Caltech Regional Seismic Network (CI) in vicinity of the Los Angeles basin. Using correlations of ambient seismic noise, relative velocity variations in the order of 0.1 % can be measured between all inter-station pairs. It is the first time that such an extensive study between 861 inter-station pairs over such a large area has been carried out. We perform these measurements using the 'st...

  10. Towards a global-scale ambient noise cross-correlation data base

    Science.gov (United States)

    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

  11. Extracting seismic attenuation coefficients from cross-correlations of ambient noise at linear triplets of stations

    Science.gov (United States)

    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.

  12. First results of cross-correlation analysis of ambient seismic noise from the Hellenic Unified Seismic Network

    NARCIS (Netherlands)

    Panou, Areti; Paulssen, Hanneke; Hatzidimitriou, Panagiotis

    2015-01-01

    In this study we present phase velocity maps that were obtained from the cross-correlation analysis of ambient seismic noise recorded in the region of Greece.We used one year (2013) of ambient seismic data obtained from the vertical component of 64 broadband permanent seismological stations that are

  13. Using auto-correlations from seismic ambient noise to monitor velocity changes at Villarrica Volcano, Chile

    Science.gov (United States)

    McKee, K. F.; Waite, G. P.; Richardson, J. P.

    2012-12-01

    We used the Green's functions from auto-correlations and cross-correlations of seismic ambient noise to monitor temporal velocity changes in the subsurface at Villarrica Volcano in the Southern Andes of Chile. Campaigns were conducted from March to October 2010 and February to April 2011 with 8 broadband and 6 short-period stations, respectively. We prepared the data by removing the instrument response, normalizing with a root-mean-square method, whitening the spectra, and filtering from 1 to 10 Hz. This frequency band was chosen based on the relatively high background noise level in that range. Hour-long auto- and cross-correlations were computed and the Green's functions stacked by day and total time. To track the temporal velocity changes we stretched a 24 hour moving window of correlation functions from 90% to 110% of the original and cross correlated them with the total stack. The average increase in velocity gleaned from the auto-correlations during the 2010 array was 0.13%, as seen in the figure. Cross-correlations from station V01, near the summit, to the other stations show comparable increases in velocity. We attribute this change to the closing of cracks in the subsurface due either to seasonal snow loading or regional tectonics. In addition to the common increase in velocity across the stations, there are excursions in velocity on the same order lasting several days. Amplitude decreases as the station's distance from the vent increases suggesting these excursions may be attributed to changes within the volcanic edifice. Two occurrences are highlighted in the figure in which it is seen that the amplitudes at stations V06 and V07, the stations farthest from the vent, are smaller. Similar short temporal excursions were seen in the auto-correlations from 2011, however, there was little to no increase in the overall velocity.ercent change in velocity at Villarrica Volcano, Chile from March to October 2010 (stations offset by 0.2%)

  14. Optimization of Ambient Noise Cross-Correlation Imaging Across Large Dense Array

    Science.gov (United States)

    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

  15. Ambient noise near the sea-route

    Institute of Scientific and Technical Information of China (English)

    HE Li; LI ZhengLin; PENG ZhaoHui

    2009-01-01

    Ambient noise data measured in an experiment conducted in shallow water near a sea-route were analyzed. It was observed that, at low frequency, the horizontal correlation has an obvious difference from that predicted by the classical ambient noise model. The theoretical analyses show that this phenomenon is caused by wind noise together with the discrete shipping noise nearby. An ambient noise model was proposed to include the effects caused by both the noise sources. Data measured at different times verify that the proposed model can be used to forecast the ambient noise field in shal-low water near the sea-route.

  16. Ambient noise near the sea-route

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Ambient noise data measured in an experiment conducted in shallow water near a sea-route were analyzed. It was observed that, at low frequency, the horizontal correlation has an obvious difference from that predicted by the classical ambient noise model. The theoretical analyses show that this phenomenon is caused by wind noise together with the discrete shipping noise nearby. An ambient noise model was proposed to include the effects caused by both the noise sources. Data measured at different times verify that the proposed model can be used to forecast the ambient noise field in shallow water near the sea-route.

  17. Temporal changes of surface wave velocity associated with major Sumatra earthquakes from ambient noise correlation.

    Science.gov (United States)

    Xu, Zhen J; Song, Xiaodong

    2009-08-25

    Detecting temporal changes of the medium associated with major earthquakes has implications for understanding earthquake genesis. Here we report temporal changes of surface wave velocity over a large area associated with 3 major Sumatra earthquakes in 2004, 2005, and 2007. We use ambient noise correlation to retrieve empirical Green's function (EGF) of surface waves between stations. Because the process is completely repeatable, the technique is powerful in detecting possible temporal change of medium. We find that 1 excellent station pair (PSI in Indonesia and CHTO in Thailand) shows significant time shifts (up to 1.44 s) after the 2004 and 2005 events in the Rayleigh waves at 10-20 s but not in the Love waves, suggesting that the Rayleigh time shifts are not from clock error. The time shifts are frequency dependent with the largest shifts at the period band of 11-16 s. We also observe an unusual excursion approximately 1 month before the 2004 event. We obtain a total of 17 pairs for June, 2007 to June, 2008, which allow us to examine the temporal and spatial variation of the time shifts. We observed strong anomalies (up to 0.68 s) near the epicenter after the 2007 event, but not in the region further away from the source or before the event or 3 months after the event. The observations are interpreted as stress changes and subsequent relaxation in upper-mid crust in the immediate vicinity of the rupture and the broad area near the fault zone. PMID:19667205

  18. First results of cross-correlation analysis of ambient seismic noise from the Hellenic Unified Seismic Network

    OpenAIRE

    Panou, Areti; Paulssen, Hanneke; Hatzidimitriou, Panagiotis

    2015-01-01

    In this study we present phase velocity maps that were obtained from the cross-correlation analysis of ambient seismic noise recorded in the region of Greece.We used one year (2013) of ambient seismic data obtained from the vertical component of 64 broadband permanent seismological stations that are part of the Hellenic Unified Seismic Network. Inter-station istances between these stations ranged from 60 to 840 km and the number of station pairs was 2054. All signals were corrected for instru...

  19. Extracting the Group Velocity of Rayleigh Waves from the Cross Correlation of the Ambient Seismic Noise Between Two Seismic Stations

    Institute of Scientific and Technical Information of China (English)

    Jin Xing; Li Jun; Lin Shu; Zhou Zhengrong; Kang Lanchi; Ou Yiping

    2008-01-01

    This paper uses the 8 broad-band stations' microseism data recorded by the Seismic Monitoring Network of Fujian Province to calculate the vertical correlation coefficient between two stationsat intervals of 5 minutes. According to the time intervals technique we obtain the different coefficients and then add the correlative coefficients. Depending on this, we extract the group velocity of Rayleigh waves from the cross correlation of the ambient seismic noise between two seismic stations and figure out the group velocity' spatial distribution. The results show that the signal noise ratio (SNR) increases proportionally to the superposition times, but the results from different days are similar to one another. Synchronously, the arrival-time is also stable and there is no obvious change when coming across typhoons. It is found the velocity of the surface wave is 2.9~3. 1km/s in Fujian Province, which is close to the observationally attained value.

  20. Imaging the Yellowstone Magmatic System Using Multi-Component Ambient Noise Cross-Correlation and Tomography

    Science.gov (United States)

    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.

  1. New Observations of Seismic Group Velocities in the Western Solomon Islands from Cross-Correlation of Ambient Seismic Noise

    Science.gov (United States)

    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.

  2. Ambient Noise Tomography of the British Isles

    Science.gov (United States)

    Nicolson, H. J.; Curtis, A.; Baptie, B.

    2009-12-01

    In recent years, surface wave tomography using empirical Green’s functions computed via the ambient noise interferometry method has become an established approach to lithospheric imaging problems. To date, ambient noise tomography has been successfully applied to seismometer arrays in the United States, Australia, Iceland, China, South Africa, Europe and the Tibetan Plateau. The basis of the ambient seismic interferometry method is that, by cross-correlating noise data between two seismic stations and stacking over a long enough time period, one can approximate the Green’s Function that would have been recorded at one of the stations if the other had actually been a source. Consequently, one of the main advantages of ambient noise interferometry is that traditional seismic sources such as earthquakes or ballistics are not required; therefore it is ideal for application to seismically quiescent areas such as the British Isles. The British Isles are an archipelago located adjacent to the Eurasian continental shelf in a typically intra-plate setting, formed by a complex amalgamation of several terranes. These range from Laurentian north of the Highland Boundary fault to Avalonian south of the Iapetus Suture and evidence of the regions turbulent geological past can be inferred from its lithospheric structure. Previous studies of the structure of the British Isles considered relatively few seismic stations and/or were limited to using offshore shots, quarry blasts or teleseismic earthquakes as seismic energy sources. We have applied the ambient noise tomography method to noise data recorded on approximately 100 broadband and short period seismometers, including many new stations, in the British Isles and mainland Europe. This dense coverage of the British Isles allows us to image the crust and upper mantle velocity structure with a horizontal resolution in the region of 100km across the North Sea and 30km in the mainland United Kingdom. Here we present the first

  3. Ambient noise spectral properties in the north area of Xisha

    Institute of Scientific and Technical Information of China (English)

    DA Lianglong; WANG Chao; HAN Mei; ZHANG Lin

    2014-01-01

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

  4. Ocean Ambient Noise Measurement and Theory

    CERN Document Server

    Carey, William M

    2011-01-01

    This book develops the theory of ocean ambient noise mechanisms and measurements, and also describes general noise characteristics and computational methods.  It concisely summarizes the vast ambient noise literature using theory combined with key representative results.  The air-sea boundary interaction zone is described in terms of non-dimensional variables requisite for future experiments.  Noise field coherency, rare directional measurements, and unique basin scale computations and methods are presented.  The use of satellite measurements in these basin scale models is demonstrated.  Finally, this book provides a series of appendices giving in-depth mathematical treatments.  With its complete and careful discussions of both theory and experimental results, this book will be of the greatest interest to graduate students and active researchers working in fields related to ambient noise in the ocean.

  5. Ambient noise levels and detection threshold in Norway

    Science.gov (United States)

    Demuth, Andrea; Ottemöller, Lars; Keers, Henk

    2016-07-01

    Ambient seismic noise is caused by a number of sources in specific frequency bands. The quantification of ambient noise makes it possible to evaluate station and network performance. We evaluate noise levels in Norway from the 2013 data set of the Norwegian National Seismic Network as well as two temporary deployments. Apart from the station performance, we studied the geographical and temporal variations, and developed a local noise model for Norway. The microseism peaks related to the ocean are significant in Norway. We, therefore, investigated the relationship between oceanic weather conditions and noise levels. We find a correlation of low-frequency noise (0.125-0.25 Hz) with wave heights up to 900 km offshore. High (2-10 Hz) and intermediate (0.5-5 Hz) frequency noise correlates only up to 450 km offshore with wave heights. From a geographic perspective, stations in southern Norway show lower noise levels for low frequencies due to a larger distance to the dominant noise sources in the North Atlantic. Finally, we studied the influence of high-frequency noise levels on earthquake detectability and found that a noise level increase of 10 dB decreases the detectability by 0.5 magnitude units. This method provides a practical way to consider noise variations in detection maps.

  6. Ambient noise levels and detection threshold in Norway

    Science.gov (United States)

    Demuth, Andrea; Ottemöller, Lars; Keers, Henk

    2016-03-01

    Ambient seismic noise is caused by a number of sources in specific frequency bands. The quantification of ambient noise makes it possible to evaluate station and network performance. We evaluate noise levels in Norway from the 2013 data set of the Norwegian National Seismic Network as well as two temporary deployments. Apart from the station performance, we studied the geographical and temporal variations, and developed a local noise model for Norway. The microseism peaks related to the ocean are significant in Norway. We, therefore, investigated the relationship between oceanic weather conditions and noise levels. We find a correlation of low-frequency noise (0.125-0.25 Hz) with wave heights up to 900 km offshore. High (2-10 Hz) and intermediate (0.5-5 Hz) frequency noise correlates only up to 450 km offshore with wave heights. From a geographic perspective, stations in southern Norway show lower noise levels for low frequencies due to a larger distance to the dominant noise sources in the North Atlantic. Finally, we studied the influence of high-frequency noise levels on earthquake detectability and found that a noise level increase of 10 dB decreases the detectability by 0.5 magnitude units. This method provides a practical way to consider noise variations in detection maps.

  7. 3-D Shear Wave Velocity Model of Mexico and South US: Bridging Seismic Networks with Ambient Noise Cross-Correlations (C1) and Correlation of Coda of Correlations (C3).

    Science.gov (United States)

    Spica, Zack; Perton, Mathieu; Calò, Marco; Legrand, Denis; Córdoba Montiel, Francisco; Iglesias, Arturo

    2016-07-01

    This work presents an innovative strategy to enhance the resolution of surface wave tomography obtained from ambient noise cross-correlation (C1) by bridging asynchronous seismic networks through the correlation of coda of correlations (C3). Rayleigh wave group dispersion curves show consistent results between synchronous and asynchronous stations. Rayleigh wave group travel times are inverted to construct velocity-period maps with unprecedented resolution for a region covering Mexico and the southern United States. The resulting period maps are then used to regionalize dispersion curves in order to obtain local 1-D shear velocity models (VS) of the crust and uppermost mantle in every cell of a grid of 0.4°. The 1-D structures are obtained by iteratively adding layers until reaching a given misfit, and a global tomography model is considered as an input for depths below 150 km. Finally, a high-resolution 3-D VS model is obtained from these inversions. The major structures observed in the 3-D model are in agreement with the tectonic-geodynamic features and with previous regional and local studies. It also offers new insights to understand the present and past tectonic evolution of the region.

  8. 3-D shear wave velocity model of Mexico and South US: bridging seismic networks with ambient noise cross-correlations (C1) and correlation of coda of correlations (C3)

    Science.gov (United States)

    Spica, Zack; Perton, Mathieu; Calò, Marco; Legrand, Denis; Córdoba-Montiel, Francisco; Iglesias, Arturo

    2016-09-01

    This work presents an innovative strategy to enhance the resolution of surface wave tomography obtained from ambient noise cross-correlation (C1) by bridging asynchronous seismic networks through the correlation of coda of correlations (C3). Rayleigh wave group dispersion curves show consistent results between synchronous and asynchronous stations. Rayleigh wave group traveltimes are inverted to construct velocity-period maps with unprecedented resolution for a region covering Mexico and the southern United States. The resulting period maps are then used to regionalize dispersion curves in order to obtain local 1-D shear velocity models (VS) of the crust and uppermost mantle in every cell of a grid of 0.4°. The 1-D structures are obtained by iteratively adding layers until reaching a given misfit, and a global tomography model is considered as an input for depths below 150 km. Finally, a high-resolution 3-D VS model is obtained from these inversions. The major structures observed in the 3-D model are in agreement with the tectonic-geodynamic features and with previous regional and local studies. It also offers new insights to understand the present and past tectonic evolution of the region.

  9. Low shear velocity in a normal fault system imaged by ambient noise cross correlation: The case of the Irpinia fault zone, Southern Italy

    Science.gov (United States)

    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.

  10. Ambient Noise in an Urbanized Tidal Channel

    Science.gov (United States)

    Bassett, Christopher

    In coastal environments, when topographic and bathymetric constrictions are combined with large tidal amplitudes, strong currents (> 2 m/s) can occur. Because such environments are relatively rare and difficult to study, until recently, they have received little attention from the scientific community. However, in recent years, interest in developing tidal hydrokinetic power projects in these environments has motivated studies to improve this understanding. In order to support an analysis of the acoustic effects of tidal power generation, a multi-year study was conducted at a proposed project site in Puget Sound (WA) are analyzed at a site where peak currents exceeded 3.5 m/s. From these analyses, three noise sources are shown to dominate the observed variability in ambient noise between 0.02-30 kHz: anthropogenic noise from vessel traffic, sediment-generated noise during periods of strong currents, and flow-noise resulting from turbulence advected over the hydrophones. To assess the contribution of vessel traffic noise, one calendar year of Automatic Identification System (AIS) ship-traffic data was paired with hydrophone recordings. The study region included inland waters of the Salish Sea within a 20 km radius of the hydrophone deployment site in northern Admiralty Inlet. The variability in spectra and hourly, daily, and monthly ambient noise statistics for unweighted broadband and M-weighted sound pressure levels is driven largely by vessel traffic. Within the one-year study period, at least one AIS transmitting vessel is present in the study area 90% of the time and over 1,363 unique vessels are recorded. A noise budget for vessels equipped with AIS transponders identifies cargo ships, tugs, and passenger vessels as the largest contributors to noise levels. A simple model to predict received levels at the site based on an incoherent summation of noise from different vessel types yields a cumulative probability density function of broadband sound pressure

  11. Event-driven approach to ambient-noise seismic interferometry

    Science.gov (United States)

    Draganov, Deyan; Campman, Xander; Thorbecke, Jan; Verdel, Arie; Wapenaar, Kees

    2010-05-01

    During the last decade, seismic interferometry, or SI, has gained rapidly in popularity among academia and the petroleum-exploration industry. One application of SI is the retrieval of the Earth's reflection response from cross-correlation of ambient seismic noise. In general, no information is available beforehand on the noise sources. For this reason, the ambient noise is assumed to originate from spatially uncorrelated, stationary noise sources that illuminate the recording array from all directions. To ensure this in the field, one wants to use recording times as long as possible. Correlating these long noise recordings would result in obtaining the best possible estimate of the complete Green's function including reflections and surface waves. The assumption of the spatially uncorrelated, stationary noise sources is not necessarily fulfilled, especially with measurements in the field taken during a limited time span. Results from different studies of ambient-noise SI for surface-wave tomography on global and regional scale have shown that when energy is used in the primary- and double-frequency-microseism bands, approximately between 0.07 Hz and 0.5 Hz, the majority of the recorded noise represents surface waves. After cross-correlation, such noise would result in the retrieval of only surface waves. For this reason one can choose to follow an alternative approach - to look in the ambient-noise data for parts of the noise that can be identified as body-wave arrivals (events). Such parts of the noise are then extracted and only they are used for SI. In this way, the correlated energy is manipulated to boost the contributions to the retrieval of body-wave reflections and, at the same time, minimize the contribution of those parts of the noise records that would retrieve surface waves. We apply the event-driven approach to about 11 hours of ambient seismic noise recorded by Shell in Libya. The noise, recorded by the vertical-component geophones, is stored in

  12. Shear velocity of the Rotokawa geothermal field using ambient noise

    Science.gov (United States)

    Civilini, F.; Savage, M. K.; Townend, J.

    2014-12-01

    Ambient noise correlation is an increasingly popular seismological technique that uses the ambient seismic noise recorded at two stations to construct an empirical Green's function. Applications of this technique include determining shear velocity structure and attenuation. An advantage of ambient noise is that it does not rely on external sources of seismic energy such as local or teleseismic earthquakes. This method has been used in the geothermal industry to determine the depths at which magmatic processes occur, to distinguish between production and non-production areas, and to observe seismic velocity perturbations associated with fluid extraction. We will present a velocity model for the Rotokawa geothermal field near Taupo, New Zealand, produced from ambient noise cross correlations. Production at Rotokawa is based on the "Rotokawa A" combined cycle power station established in 1997 and the "Nga Awa Purua" triple flash power plant established in 2010. Rotokawa Joint Venture, a partnership between Mighty River Power and Tauhara North No. 2 Trust currently operates 174 MW of generation at Rotokawa. An array of short period seismometers was installed in 2008 and occupies an area of roughly 5 square kilometers around the site. Although both cultural and natural noise sources are recorded at the stations, the instrument separation distance provides a unique challenge for analyzing cross correlations produced by both signal types. The inter-station spacing is on the order of a few kilometers, so waves from cultural sources generally are not coherent from one station to the other, while the wavelength produced by natural noise is greater than the station separation. Velocity models produced from these two source types will be compared to known geological models of the site. Depending on the amount of data needed to adequately construct cross-correlations, a time-dependent model of velocity will be established and compared with geothermal production processes.

  13. Ambient noise levels in the Taiwan region

    Science.gov (United States)

    Liang, W.; Liu, C.; Chen, R.; Huang, B.; Wu, F. T.; Wang, C.

    2008-12-01

    To characterize the island-wide background seismic noise in Taiwan, we estimate the power spectral density (PSD) at broadband stations of both the BATS (Broadband Array in Taiwan for Seismology) and the TAIGER experiment (Apr. 2006~Apr. 2008) for periods ranging from ~0.2 to 100 seconds. A new approach to calculate the probability density functions of noise power (PDFs, MaNamara and Buland, 2004) is used in this study. The results indicate that the cultural noise at higher frequencies is significant at populated area, which shows diurnal and weekly variation as what we expected. The noise power for microseisms centered at a period of ~5 seconds around the western costal plain show ~20dB higher than what observed at eastern Taiwan. This observation supports the inference that the coastal regions having narrow shelf with irregular coastlines are know to be especially efficient at radiating the predominat microseisms. Results from the linear array across central Taiwan demonstrate that the average noise power is quietest at the eastern Central Range. We have mapped the PDF mode for stations at various periods to see the spatial distribution of ambient noise levels, which could be used as the basic information for future station siting. Temporal variation of noise PSD is also present to provide a quantitative description of the seismic data quality collected by both BATS and TAIGER experiment. Some operational problems like base tilt, sensitivity change can be identified easily as well.

  14. Robust seismic velocity change estimation using ambient noise recordings

    CERN Document Server

    Daskalakis, E; Garnier, J; Melis, N S; Papanicolaou, G; Tsogka, C

    2016-01-01

    We consider the problem of seismic velocity change estimation using ambient noise recordings. Motivated by [23] we study how the velocity change estimation is affected by seasonal fluctuations in the noise sources. More precisely, we consider a numerical model and introduce spatio-temporal seasonal fluctuations in the noise sources. We show that indeed, as pointed out in [23], the stretching method is affected by these fluctuations and produces misleading apparent velocity variations which reduce dramatically the signal to noise ratio of the method. We also show that these apparent velocity variations can be eliminated by an adequate normalization of the cross-correlation functions. Theoretically we expect our approach to work as long as the seasonal fluctuations in the noise sources are uniform, an assumption which holds for closely located seismic stations. We illustrate with numerical simulations and real measurements that the proposed normalization significantly improves the accuracy of the velocity chang...

  15. Robust seismic velocity change estimation using ambient noise recordings

    Science.gov (United States)

    Daskalakis, E.; Evangelidis, C. P.; Garnier, J.; Melis, N. S.; Papanicolaou, G.; Tsogka, C.

    2016-06-01

    We consider the problem of seismic velocity change estimation using ambient noise recordings. Motivated by Zhan et al., we study how the velocity change estimation is affected by seasonal fluctuations in the noise sources. More precisely, we consider a numerical model and introduce spatio-temporal seasonal fluctuations in the noise sources. We show that indeed, as pointed out by Zhan et al., the stretching method is affected by these fluctuations and produces misleading apparent velocity variations which reduce dramatically the signal to noise ratio of the method. We also show that these apparent velocity variations can be eliminated by an adequate normalization of the cross-correlation functions. Theoretically we expect our approach to work as long as the seasonal fluctuations in the noise sources are uniform, an assumption which holds for closely located seismic stations. We illustrate with numerical simulations in homogeneous and scattering media that the proposed normalization significantly improves the accuracy of the velocity change estimation. Similar behaviour is also observed with real data recorded in the Aegean volcanic arc. We study in particular the volcano of Santorini during the seismic unrest of 2011-2012 and observe a decrease in the velocity of seismic waves which is correlated with GPS measured elevation.

  16. Constructing a global noise correlation database

    Science.gov (United States)

    Ermert, L. A.; Fichtner, A.; Sleeman, R.

    2013-12-01

    We report on the ongoing construction of an extensive global-scale database of ambient noise cross-correlation functions spanning a frequency range from seismic hum to oceanic microseisms (roughly 2 mHz to 0.2 Hz). The database - ultimately to be hosted by ORFEUS - will be used to study the distribution of microseismic and hum sources, and to perform multiscale full waveform inversion for crustal and mantle structure. To build the database, we acquire continuous time series data from permanent and temporary networks hosted mostly at IRIS and ORFEUS. We process and correlated the time series using a fully parallelised tool based on the Python package Obspy. Processing follows two main flows: We obtain both classical cross-correlation functions and phase cross-correlation functions. Phase cross-correlation is an amplitude-independent measure of waveform similarity. Either type of correlation can be used for the inversions. We stack individual time windows linearly. Additionally, we calculate the stack of instantaneous phases of the analytic cross-correlation signal, which can be included as optional processing step. Multiplying the linear stack by the phase stack downweights those parts of the linear stack that show little phase coherency. Thus, it accelerates the emergence of weak coherent signals, which is of particular importance for the processing of data from recently deployed or temporary stations that have only been recording for a short time. Obtaining and processing data for such a massive database requires considerable computational resources, offered by the Swiss National Supercomputing Centre (CSCS) in the form of HPC clusters specifically designed for large-scale data analysis. The data set will be made available to the scientific community via ORFEUS. By separately providing classical cross-correlation, phase cross-correlation and instantaneous phase stack, the database will offer relative flexibility for application in further studies. Many current

  17. Velocity variations associated with the large 2010 eruption of Merapi volcano, Java, retrieved from seismic multiplets and ambient noise cross-correlation

    Science.gov (United States)

    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

  18. Velocity variations associated with the large 2010 eruption of Merapi volcano, Java, retrieved from seismic multiplets and ambient noise cross-correlation

    Science.gov (United States)

    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

  19. Retrieving surface waves from ambient seismic noise using seismic interferometry by multidimensional deconvolution

    NARCIS (Netherlands)

    Van Dalen, Karel N.; Mikesell, T. Dylan; Ruigrok, Elmer N.; Wapenaar, Kees

    2015-01-01

    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 sam

  20. Application of the energy reassignment method to measure accurate Rayleigh and Love wave group velocities from ambient seismic noise cross-correlations

    Science.gov (United States)

    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

  1. Ambient noise levels in the chemotherapy clinic

    Directory of Open Access Journals (Sweden)

    Dana K Gladd

    2011-01-01

    Full Text Available Many of the drugs used for chemotherapy treatments are known to be ototoxic, and can result in permanent hearing threshold shifts. The degree of ototoxic damage can be influenced by many factors including dosage, duration of exposure, genetics, and coadministration with other ototoxic agents. Cisplatin is known for its ototoxic effects on hearing thresholds, particularly in the high frequencies. Recent studies have indicated a synergistic relationship between Cisplatin administration and moderate to high noise level exposure starting between 70-85 dB SPL. This study measured the noise levels in the Portland Veteran′s Affairs Medical Center′s outpatient chemotherapy clinic. Average (LAeq and peak (LCpeak noise measures were recorded every minute from 7 am until 6 pm on the two busiest clinic days. Patients, visitors, and staff members filled out anonymous surveys regarding their reactions to noise levels. Cumulative noise levels were not at levels known to interact with Cisplatin for a significant period of time. Noise measurement analysis indicated that levels were at or above 70 dB SPL for less than ten minutes during the 11-hour recording window. The patient and visitor surveys indicated that both groups were unbothered by noise in the clinic. However, most staff members were bothered by or concerned about noise levels, and many felt that it caused stress and difficulty communicating on the phone.

  2. Ambient noise tomography across the southern Alaskan Cordillera

    Science.gov (United States)

    Ward, Kevin M.

    2015-05-01

    I present the results of an extensive data mining effort integrating 197 permanent and temporary seismic stations into a Rayleigh wave ambient noise study across southern Alaska and westernmost Canada. Principal observations of my tomography model are largely consistent with mapped geology features and previous geophysical studies while providing previously unavailable, laterally continuous details of the southern Alaskan Cordillera lithosphere. At intermediate periods, a geophysically uniform crust is observed north of the Denali Fault and is consistent with a sharp transition in crustal thickness. Under the Wrangell volcanic belt, a prominent low-phase-velocity anomaly correlates well with the lateral extent of a relative low-gravity anomaly and Neogene surface volcanics. At longer periods, a low-phase-velocity anomaly bounds the inferred eastern extent of the subducted Yakutat microplate beneath the Wrangell volcanic belt.

  3. Regional Ambient Noise Tomography in the Eastern Alps of Europe

    Science.gov (United States)

    Behm, Michael; Nakata, Nori; Bokelmann, Götz

    2016-08-01

    We present results from ambient noise tomography applied to temporary seismological stations in the easternmost part of the Alps and their transition to the adjacent tectonic provinces (Vienna Basin, Bohemian Massif, Southern Alps, Dinarides). By turning each station into a virtual source, we recover surface waves in the frequency range between 0.1 and 0.6 Hz, which are sensitive to depths of approximately 2-15 km. The utilization of horizontal components allows for the analysis of both Rayleigh and Love waves with comparable signal-to-noise ratio. Measured group wave dispersion curves between stations are mapped to local cells by means of a simultaneous inverse reconstruction technique. The spatial reconstruction for Love-wave velocities fails in the central part of the investigated area, and we speculate that a heterogeneous noise source distribution is the cause for the failure. Otherwise, the obtained group velocity maps correlate well with surface geology. Inversion of Rayleigh-wave velocities for shear-wave velocities along a vertical N-S section stretching from the Bohemian Massif through the Central Alps to the Southern Alps and Dinarides reveals a mid-crustal low-velocity anomaly at the contact between the Bohemian Massif and the Alps, which shows a spatial correlation with the P-wave velocity structure and the low-frequency component of the magnetic anomaly map. Our study is validated by the analysis of resolution and accuracy, and we further compare the result to shear-wave velocity models estimated from other active and passive experiments in the area.

  4. Crustal Structure of the PARANÁ Basin from Ambient Noise Tomography

    Science.gov (United States)

    Collaço, B.; Assumpcao, M.; Rosa, M. L.; Sanchez, G.

    2013-12-01

    Previous surface-wave tomography in South America (SA) (e.g., Feng et al., 2004; 2007) mapped the main large-scale features of the continent, such as the high lithospheric velocities in cratonic areas and low velocities in the Patagonian province. However, more detailed features such as the Paraná Basin, have not been mapped with good resolution because of poor path coverage, i.e. classic surface- wave tomography has low resolution in low-seismicity areas, like Brazil and the Eastern Argentina. Crustal structure in Southern Brazil is poorly known. Most paths used by Feng et al. (2007) in this region are roughly parallel, which prevents good spatial resolution in tomographic inversions. This work is part of a major project that will increase knowledge of crustal structure in Southern Brazil and Eastern Argentina and is being carried out by IAG-USP (Brazil) in collaboration with UNLP and INPRES (Argentina). To improve resolution for the Paraná Basin we used inter-station dispersion curves derived from correlation of ambient noise for new stations deployed with the implementation of the Brazilian Seismic Network (Pirchiner et al. 2011). This technique, known as ambient noise tomography (ANT), was first applied by Shapiro et al. (2005) and is now expanding rapidly, especially in areas with high density of seismic stations (e.g. Bensen et al. 2007, Lin et al. 2008, Moschetti et al. 2010). ANT is a well-established method to estimate short period (Petrobras with additional support from CNPq and FAPESP.

  5. On the accuracy of long-period Rayleigh waves extracted from ambient noise

    Science.gov (United States)

    Xie, Jun; Yang, Yingjie; Ni, Sidao

    2016-04-01

    The aim of this paper is to assess the accuracy of the long-period (50-250 s) surface waves extracted from cross-correlation functions (CCF) of ambient noise. First, we compare the waveforms and travel times of a ground-truth earthquake and CCFs from ambient noise with those of synthetic seismograms from earthquake source parameters and a surface load of vertical force, and then quantify the accuracy using a double difference method. Second, we compare Rayleigh wave phase velocity dispersion measurements from ambient noise and those from earthquake data in both global and regional studies. Through these comparisons, we conclude that both the dispersion curves and waveforms from noise data are consistent with their counterparts from earthquake data in the long-period band. The long-period surface waves from ambient noise are as accurate as those from earthquake data, and can be included in both global and regional ambient noise tomography and provide complementary data to constrain the lithospheric and asthenospheric structures.

  6. Understanding the dynamics of a geyser using seismic ambient noise

    Science.gov (United States)

    Cros, Estelle; Roux, Philippe; Vandemeulebrouck, Jean; Kedar, Sharon

    2010-05-01

    Old Faithful Geyser in Yellowstone National Park, Wyoming, is one of the most studied geysers in the world. The predictability, the repeatability and the short time lag, ~1.5 hour, between 2 eruptions make the study convenient. The surface expression of the geyser is a 4m high, 60m wide mound with an approximately 2m x 1m opening at the top, which permits to deploy a dense network of sensors closed to the orifice. In 1992, Sharon Kedar deployed 96 vertical geophones in a tight grid over the geyser's dome. The geophones recorded the ambient seismic noise during an entire eruptive cycle, including a short period of quiet seismic activity. The survey was completed by seven shots carried out with a sledge hammer. The signal consists in a series of impulsive events, most likely due to bubble collapse in boiling water areas inside the geyser's plumbing system. The aim of this study is to locate the sources of these events. We revisited a 10 minutes-long data set from S. Kedar's records and processed the signal using a Matched Field Processing (MFP) algorithm derived from ocean acoustics. The cross-correlation of the signals recorded by the 96 geophones showed a great level of coherency between the sensors, which is a pre-requisite to use MFP. This method introduced in geophysics by Capon is based on comparing forward modelling solutions of the wave equation in a grid search with acquired data, measured on an array of motion sensors. The process consists in placing a test source at each point of the grid search, computing the acoustic field corresponding at all the elements of the array and then correlating this modelled field with the data. The correlation is maximum when the candidate point source is co-located with the true point source. We used both linear (Bartlett) and non linear (MVDR : Minimum Variance Distorsionless) processors. The MFP processor was performed either incoherently from the raw ambient noise data or coherently from the cross-correlated traces

  7. Masking of Wind Turbine Noise: Influence of wind turbulence on ambient noise fluctuations

    Energy Technology Data Exchange (ETDEWEB)

    Fegeant, Olivier

    2002-07-01

    In the issue of noise annoyance generated by wind turbines, masking by ambient noise is of great importance. At wind turbine sites, the main source of ambient noise arises from the wind blowing on the vegetation. However, natural wind can barely be described as a steady flow and 'lulls' and 'gusts' are words used to describe its unsteady component. This latter, also called wind turbulence, may affect the masking effect, as the wind turbine may become audible during short laps of time of low wind speed, that is of low ambient noise. The aim of the present report is to study the influence of wind turbulence on ambient noise fluctuations. It is shown that these latter are governed not only by the turbulence intensity, but also by its temporal and spatial structure. This report provides some elements of atmospheric turbulence as well as techniques for the simulation of turbulent wind fields. Simulation results are given that illustrate how the standard deviation of the vegetation noise can vary as function of the canopy size and turbulence spatial patterns. Finally, ambient noise fluctuations and their statistical descriptions are also discussed, based on both theoretical considerations and empirical results.

  8. Anisotropic Tomography of Portugal (West Iberia) from ambient seismic noise

    Science.gov (United States)

    Silveira, Graça; Stutzmann, Éléonore; Schimmel, Martin; Dias, Nuno; Kiselev, Sergey; Custódio, Susana; Dundar, Suleyman

    2016-04-01

    Located on the western Iberian Peninsula, Portugal constitutes a key area for accretionary terrane and basin research, providing the best opportunity to probe a crustal formation shaped by the Paleozoic Variscan orogeny followed by the Mesozoic-Cenozoic extensions. The geology of Portugal documents a protracted history from Paleozoic basement formation to the Mesozoic opening of the North Atlantic Ocean. The inheritance of such complex geologic history is yet to be fully determined, playing an important role in the current geodynamic framework influencing, for example, the observed regional seismicity. The physical properties of its crust have largely remained undetermined so far, with unevenly distributed knowledge on the spatial distributions of a detailed crustal structure. Also, the deep seismic reflection/refraction surveys conducted in Western Iberia do not provide a clear picture of the regional characteristics of the crust. Using Seismic Broad Band observations from a dense temporary deployment, conducted between 2010 and 2012 in the scope of the WILAS project and covering the entire Portuguese mainland, we computed a 3D anisotropic model from ambient seismic noise. The dispersion measurements were computed for each station pair using empirical Green's functions generated by cross-correlating one-day-length seismic ambient-noise records. After dispersion analysis, group velocity measurements were regionalized to obtain 2D anisotropic tomographic images. Afterwards, the dispersion curves, extracted from each cell of the 2D group velocity maps, were inverted as a function of depth to obtain a 3D shear wave anisotropic model, using a bayesian approach. A simulated annealing method, in which the number of splines that describes the model, is adapted within the inversion. The models are jointly interpreted with the models gathered from Ps receiver functions as well as with the regional seismicity, enabling to obtain a more detailed picture of the crustal

  9. When ambient noise impairs parent-offspring communication.

    Science.gov (United States)

    Lucass, Carsten; Eens, Marcel; Müller, Wendt

    2016-05-01

    Ambient noise has increased in extent, duration and intensity with significant implications for species' lives. Birds especially, because they heavily rely on vocal communication, are highly sensitive towards noise pollution. Noise can impair the quality of a territory or hamper the transmission of vocal signals such as song. The latter has significant fitness consequences as it may erode partner preferences in the context of mate choice. Additional fitness costs may arise if noise masks communication between soliciting offspring and providing parents during the period of parental care. Here, we experimentally manipulated the acoustic environment of blue tit (Cyanistes caeruleus) families within their nest boxes with playbacks of previously recorded highway noise and investigated the consequences on parent-offspring communication. We hypothesized that noise interferes with the acoustic cues of parental arrival and vocal components of offspring begging. As such we expected an increase in the frequency of missed detections, when nestlings fail to respond to the returning parent, and a decrease in parental provisioning rates. Parents significantly reduced their rate of provisioning in noisy conditions compared to a control treatment. This reduction is likely to be the consequence of a parental misinterpretation of the offspring hunger level, as we found that nestlings fail to respond to the returning parent more frequently in the presence of noise. Noise also potentially masks vocal begging components, again contributing to parental underestimation of offspring requirements. Either way, it appears that noise impaired parent-offspring communication is likely to reduce reproductive success. PMID:26986090

  10. Impact of wind on ambient noise recorded by seismic array in northern Poland

    Science.gov (United States)

    Lepore, Simone; Markowicz, Krzysztof; Grad, Marek

    2016-06-01

    Seismic interferometry and beam-forming techniques were applied to the ambient noise recorded during January 2014 at the `13 BB star' array composed of thirteen seismic stations located in northern Poland. The circular and symmetric geometry of the array allowed the evaluation of the azimuths of noise sources and the velocities of recovered surface waves with a good reliability. After having pre-processed the raw records of the ambient noise in time- and frequency-domain, we studied the associated power spectral density to identify the frequency bands suitable for the recovery of the surface waves. Then the cross-correlation was performed between all the station pairs of the array to retrieve the Green's function, from which the velocity range of the surface waves can be determined. Making use of that analysis, the direction of the noise wavefield was linked to the maximum amplitude of the beam-power, estimated by the mixing in the frequency-domain of all the corresponding noise records. The results were related day by day to the mean wind velocity around Europe at 10 m above ground level obtained from global surveys carried out during the same month. Significant correlation between the direction of maximum beam-power associated to the ambient noise recorded at `13 BB star' and the average wind velocity was found.

  11. Ambient noise during rough weather and cyclones in the shallow Bay of Bengal

    Science.gov (United States)

    Sanjana, M. C.; Latha, G.; Thirunavukkarasu, A.

    2014-07-01

    This paper presents ambient noise analysis during rough weather, using time series measurements from an automated noise measurement system in the shallow southwest Bay of Bengal during October-November 2010. The period witnessed low-pressure events including depressions and cyclones, with JAL cyclone passing close to the measurement site. The time series noise level shows a shift in mid-October, after which deep depressions and cyclones formed, with an average increase of 5-10 dB in the lower band and 2-3 dB in the higher band of frequencies. Furthermore, correlation between noise level and wave height (data from wave rider buoy deployed at the site) for sea state scale 3 and above shows good correlation with an increase in noise level with increase in wave height, the effect being most pronounced at 0.5 kHz. The noise captured during JAL was analysed to identify the spectrum components due to convective precipitation and heavy wind/wave activity and shows anomalously high levels during the crossing of the cyclone. Rain noise spectra from the rain bands associated with the wall of the cyclone are reported. This has been correlated with radar reflectivity measurements to ascertain the presence of rain, and discriminate between convective and stratiform types. Also, vertical directionality pattern of ambient noise during JAL showed clearly distinct surface contributions. On the whole, knowledge of ambient noise fields during high sea states and precipitation is useful in optimizing SONAR performance. The findings at the study site have been compared with measurements from other shallow water locations during rough weather.

  12. A high-resolution ambient seismic noise model for Europe

    Science.gov (United States)

    Kraft, Toni

    2014-05-01

    In the past several years, geological energy technologies receive growing attention and have been initiated in or close to urban areas. Some of these technologies involve injecting fluids into the subsurface (e.g., oil and gas development, waste disposal, and geothermal energy development) and have been found or suspected to cause small to moderate sized earthquakes. These earthquakes, which may have gone unnoticed in the past when they occurred in remote sparsely populated areas, are now posing a considerable risk for the public acceptance of these technologies in urban areas. The permanent termination of the EGS project in Basel, Switzerland after a number of induced ML~3 (minor) earthquakes in 2006 is one prominent example. It is therefore essential to the future development and success of these geological energy technologies to develop strategies for managing induced seismicity and keeping the size of induced earthquake at a level that is acceptable to all stakeholders. Most guidelines and recommendations on induced seismicity published since the 1970ies conclude that an indispensable component of such a strategy is the establishment of seismic monitoring in an early stage of a project. This is because an appropriate seismic monitoring is the only way to detect and locate induced microearthquakes with sufficient certainty to develop an understanding of the seismic and geomechanical response of the reservoir to the geotechnical operation. In addition, seismic monitoring lays the foundation for the establishment of advanced traffic light systems and is therefore an important confidence building measure towards the local population and authorities. Due to this development an increasing number of seismic monitoring networks are being installed in densely populated areas with strongly heterogeneous, and unfavorable ambient noise conditions. This poses a major challenge on the network design process, which aims to find the sensor geometry that optimizes the

  13. Random Correlation Matrix and De-Noising

    OpenAIRE

    Ken-ichi Mitsui; Yoshio Tabata

    2006-01-01

    In Finance, the modeling of a correlation matrix is one of the important problems. In particular, the correlation matrix obtained from market data has the noise. Here we apply the de-noising processing based on the wavelet analysis to the noisy correlation matrix, which is generated by a parametric function with random parameters. First of all, we show that two properties, i.e. symmetry and ones of all diagonal elements, of the correlation matrix preserve via the de-noising processing and the...

  14. On the accuracy of long-period Rayleigh waves extracted from ambient noise

    Science.gov (United States)

    Xie, Jun; Yang, Yingjie; Ni, Sidao

    2016-07-01

    The aim of this paper is to assess the accuracy of the long-period (50-250 s) surface waves extracted from cross-correlation functions (CCF) of ambient noise. First, we compare waveforms of Empirical Green's functions (EGF) converted from CCF with their synthetics, and also compare seismograms from a ground truth earthquake with their synthetics, through numerical simulations using a common 3-D model. We then quantify the accuracy of EGFs by comparing two sets of time-shifts between the observed waveforms and the synthetics: one set for the ground truth earthquake and the other set for EGFs. Second, we compare Rayleigh wave phase velocity dispersion measurements from ambient noise and those from earthquake data in both global and regional studies. Through these comparisons, we conclude that both the dispersion curves and waveforms from noise data are consistent with their counterparts from earthquake data in the long-period band. The long-period surface waves from ambient noise are as accurate as those from earthquake data, and can be included in both global and regional ambient noise tomography and provide complementary data to constrain the lithospheric and asthenospheric structures.

  15. Correlated Levy Noise in Linear Dynamical Systems

    International Nuclear Information System (INIS)

    Linear dynamical systems, driven by a non-white noise which has the Levy distribution, are analysed. Noise is modelled by a specific stochastic process which is defined by the Langevin equation with a linear force and the Levy distributed symmetric white noise. Correlation properties of the process are discussed. The Fokker-Planck equation driven by that noise is solved. Distributions have the Levy shape and their width, for a given time, is smaller than for processes in the white noise limit. Applicability of the adiabatic approximation in the case of the linear force is discussed. (author)

  16. Global examination of the wind-dependence of very low frequency underwater ambient noise.

    Science.gov (United States)

    Nichols, Stephen M; Bradley, David L

    2016-03-01

    Ocean surface winds play a key role in underwater ambient noise generation. One particular frequency band of interest is the infrasonic or very low frequency (VLF) band from 1 to 20 Hz. In this spectral band, wind generated ocean surface waves interact non-linearly to produce acoustic waves, which couple into the seafloor to generate microseisms, as explained by the theory developed by Longuet-Higgins. This study examines long term data sets in the VLF portion of the ambient noise spectrum, collected by the hydroacoustic systems of the Comprehensive Nuclear-Test Ban Treaty Organization in the Atlantic, Pacific, and Indian Oceans. Three properties of the noise field were examined: (a) the behavior of the acoustic spectrum slope from 1 to 5 Hz, (b) correlation of noise levels and wind speeds, and (c) the autocorrelation behavior of both the noise field and the wind. Analysis results indicate the spectrum slope is site dependent, and for both correlation methods, a high correlation between wind and the noise field in the 1-5 Hz band. PMID:27036248

  17. pSIN: A scalable, Parallel algorithm for Seismic INterferometry of large-N ambient-noise data

    Science.gov (United States)

    Chen, Po; Taylor, Nicholas J.; Dueker, Ken G.; Keifer, Ian S.; Wilson, Andra K.; McGuffy, Casey L.; Novitsky, Christopher G.; Spears, Alec J.; Holbrook, W. Steven

    2016-08-01

    Seismic interferometry is a technique for extracting deterministic signals (i.e., ambient-noise Green's functions) from recordings of ambient-noise wavefields through cross-correlation and other related signal processing techniques. The extracted ambient-noise Green's functions can be used in ambient-noise tomography for constructing seismic structure models of the Earth's interior. The amount of calculations involved in the seismic interferometry procedure can be significant, especially for ambient-noise datasets collected by large seismic sensor arrays (i.e., "large-N" data). We present an efficient parallel algorithm, named pSIN (Parallel Seismic INterferometry), for solving seismic interferometry problems on conventional distributed-memory computer clusters. The design of the algorithm is based on a two-dimensional partition of the ambient-noise data recorded by a seismic sensor array. We pay special attention to the balance of the computational load, inter-process communication overhead and memory usage across all MPI processes and we minimize the total number of I/O operations. We have tested the algorithm using a real ambient-noise dataset and obtained a significant amount of savings in processing time. Scaling tests have shown excellent strong scalability from 80 cores to over 2000 cores.

  18. Ambient noise and the design of begging signals

    OpenAIRE

    Marty L. Leonard; Horn, Andrew G

    2005-01-01

    The apparent extravagance of begging displays is usually attributed to selection for features, such as loud calls, that make the signal costly and hence reliable. An alternative explanation, however, is that these design features are needed for effective signal transmission and reception. Here, we test the latter hypothesis by examining how the begging calls of tree swallow (Tachycineta bicolor) nestlings and the response to these calls by parents are affected by ambient noise. In a field stu...

  19. Analysis of acoustic ambient noise in Monterey Bay, California.

    OpenAIRE

    Elles, Christopher Jacob.

    1982-01-01

    Approved for public release; distribution is unlimited Magnetic tape recordings, made in 1980 and 1981 by previous investigators using sonobuoys, of acoustic ambient noise in the south-eastern parts of Monterey Bay for various stations under various surf conditions, were analyzed. A computer program was developed and used with sonobuoy calibration data to correct :raw-data" to absolute sound pressure levels. The variation of omnidirectional levels with range from the beach as a function ...

  20. Analysis of the ambient seismic noise at Bulgarian seismic stations

    Science.gov (United States)

    Dimitrova, Liliya; Nikolova, Svetlana

    2010-05-01

    Modernization of Bulgarian National Seismological Network has been performed during a month in 2005. Broadband seismometers and 24-bits digital acquisition systems with dynamic range more than 132dB type DAS130-01 produced by RefTek Inc. were installed at the seismic stations from the existing analog network. In the present study the ambient seismic noise at Bulgarian National Digital Seismological Network (BNDSN) stations is evaluated. In order to compare the performance of the network against international standards the detail analysis of the seismic noise was performed using software and models that are applied in the international practice. The method of McNamara and Bulland was applied and the software code PDFSA was used to determine power spectral density function (PSD) of the background noise and to evaluate the probability density function (PDF). The levels of the ambient seismic noise were determined and the full range of the factors influencing the quality of the data and the performance of a seismic station was analyzed. The estimated PSD functions were compared against two models for high (NHNM) and low (NLNM) noise that are widely used in seismological practice for seismic station monitoring qualities assessment. The mode PDF are used to prepare annual, seasonal, diurnal and frequency analyses of the noise levels at BNDSN stations. The annual analysis shows that the noise levels at the Northern Bulgarian stations are higher than the ones at Central and Southern stations for the microseisms' periods (1sec -7sec). It is well observable at SS PRV and PSN located near Black sea. This is due to the different geological conditions of the seismic stations as well. For the periods of "cultural" noise the power distribution depends on the type of noise sources and as a rule is related to human activities at or near the Earth surface. Seismic stations MPE, VTS and MMB have least mode noise levels and the noisiest stations are PGB, PVL и JMB. The seasonal

  1. Antiferromagnetic noise correlations in optical lattices

    DEFF Research Database (Denmark)

    Bruun, Niels Bohr International Academy, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark, Georg Morten; Syljuåsen, F. T.; Pedersen, K. G. L.;

    2009-01-01

    We analyze how noise correlations probed by time-of-flight experiments reveal antiferromagnetic (AF) correlations of fermionic atoms in two-dimensional and three-dimensional optical lattices. Combining analytical and quantum Monte Carlo calculations using experimentally realistic parameters, we...... show that AF correlations can be detected for temperatures above and below the critical temperature for AF ordering. It is demonstrated that spin-resolved noise correlations yield important information about the spin ordering. Finally, we show how to extract the spin correlation length and the related...

  2. Extraction of triplicated PKP phases from noise correlations

    Science.gov (United States)

    Xia, Han H.; Song, Xiaodong; Wang, Tao

    2016-04-01

    Ambient noise correlation method has been widely used to extract surface waves and tomography. The extraction of body waves has been very limited, but recent reports have suggested promises for deep incident waves. Here we report our first observations of triplicated PKP phases (important phases for studying the Earth's core) and confirm observations of other body-wave core phases from noise correlations. We use dense seismic arrays in South America and China Regional Seismic Networks at distances from 145° to the antipode. We can clearly observe different PKP branches (df, bc and ab) in stacks of the station-station correlations. Both ambient noise and earthquake coda contribute to PKP phases. However, the contributions vary with frequency and with body-wave phases. At shorter periods (5-20 s), three branches of PKP (df, bc and ab) can be extracted from ambient noise and the ab phase from earthquake coda. At longer periods (15-50 s), earthquake coda are effective in generating the df branch, but not the ab branch. The generation of the PKIKP phase (df branch) from earthquake coda does not depend on earthquake focal mechanisms or focal depths. However, earthquakes far from the stations contribute more than events closer by. The best coda window is around 10 000-40 000 s and the best magnitude threshold is Mw greater than 6.8 or 6.9. The observation of triplicated PKP branches from noise correlations provides a new type of data for studying the Earth's deep interior, in particularly the inner core anisotropy, which overcomes some of the limitations of traditional earthquake-based studies (such as limited source distributions and source location errors).

  3. Correlated Noise Effects on Gene Expression

    Institute of Scientific and Technical Information of China (English)

    王先菊; 艾保全; 刘国涛; 刘良钢

    2003-01-01

    Based on the model describing the regulation of the PRM operator region of λ phage proposed by Hasty et al.[Proc. Nat. Acad. Sci. 97(2000)2075], we study the steady-state probability distribution properties of the model in the presence of correlated Gaussian white noise. We find that the degree of correlation of the noises can affect the form of the steady-state probability distribution. When the degree of correlation of the noises increases, the form of the steady-state probability distribution changes from a bimodal into a unimodal structure.The steady-state probability distribution extrema have also been investigated. We find that noise correlation can change the positions of the extreme value of the steady-state probability distribution of the model greatly.

  4. Source and processing effects on noise correlations

    Science.gov (United States)

    Fichtner, Andreas

    2014-05-01

    We quantify the effects of spatially heterogeneous noise sources and seismic processing on noise correlation measurements and their sensitivity to Earth structure. Our analysis is based on numerical wavefield simulations in heterogeneous media. This allows us to calculate inter-station correlations for arbitrarily distributed noise sources where - as in the real Earth - different frequencies are generated in different locations. Using adjoint methods, we compute the exact structural sensitivities for a given combination of source distribution, processing scheme, and measurement technique. The key results of our study are as follows: (1) Heterogeneous noise sources and subjective processing, such as the application of spectral whitening, have profound effects on noise correlation wave forms. (2) Nevertheless, narrow-band traveltime measurements are only weakly affected by heterogeneous noise sources and processing. This result is in accord with previous analytical studies, and it explains the similarity of noise and earthquake tomographies that only exploit traveltime information. (3) Spatially heterogeneous noise sources can lead to structural sensitivities that deviate strongly from the classical cigar-shaped sensitivities. Furthermore, the frequency dependence of sensitivity kernels can go far beyond the well-know dependence of the Fresnel zone width on frequency. Our results imply that a meaningful application of modern full waveform inversion methods to noise correlations is not possible unless both the noise source distribution and the processing scheme are properly taken into account. Failure to do so can lead to erroneous misfit quantifications, slow convergence of optimisation schemes, and to the appearance of tomographic artefacts that reflect the incorrect structural sensitivity. These aspects acquire special relevance in the monitoring of subtle changes of subsurface structure that may be polluted when the time dependence of heterogeneous noise sources

  5. Ambient noise tomography of the East African Rift in Mozambique

    Science.gov (United States)

    Domingues, Ana; Silveira, Graça; Ferreira, Ana M. G.; Chang, Sung-Joon; Custódio, Susana; Fonseca, João F. B. D.

    2016-03-01

    Seismic ambient noise tomography is applied to central and southern Mozambique, located in the tip of the East African Rift (EAR). The deployment of MOZART seismic network, with a total of 30 broad-band stations continuously recording for 26 months, allowed us to carry out the first tomographic study of the crust under this region, which until now remained largely unexplored at this scale. From cross-correlations extracted from coherent noise we obtained Rayleigh wave group velocity dispersion curves for the period range 5-40 s. These dispersion relations were inverted to produce group velocity maps, and 1-D shear wave velocity profiles at selected points. High group velocities are observed at all periods on the eastern edge of the Kaapvaal and Zimbabwe cratons, in agreement with the findings of previous studies. Further east, a pronounced slow anomaly is observed in central and southern Mozambique, where the rifting between southern Africa and Antarctica created a passive margin in the Mesozoic, and further rifting is currently happening as a result of the southward propagation of the EAR. In this study, we also addressed the question concerning the nature of the crust (continental versus oceanic) in the Mozambique Coastal Plains (MCP), still in debate. Our data do not support previous suggestions that the MCP are floored by oceanic crust since a shallow Moho could not be detected, and we discuss an alternative explanation for its ocean-like magnetic signature. Our velocity maps suggest that the crystalline basement of the Zimbabwe craton may extend further east well into Mozambique underneath the sediment cover, contrary to what is usually assumed, while further south the Kaapval craton passes into slow rifted crust at the Lebombo monocline as expected. The sharp passage from fast crust to slow crust on the northern part of the study area coincides with the seismically active NNE-SSW Urema rift, while further south the Mazenga graben adopts an N-S direction

  6. Shear-wave structure of the Lower-Tagus Valley region from ambient noise tomography

    Science.gov (United States)

    Silveira, Graça; Matos, Catarina; Dias, Nuno; Custódio, Susana; Morais, Iolanda

    2014-05-01

    The Lower Tagus Valley (LTV), located on Western Portugal, has a record of significant historical and instrumental seismicity. Knowledge of its subsurface structure is invaluable to better assess seismicity, earthquake source processes and associated risks. Ambient noise tomography is an efficient tool to illuminate crustal structure, providing a resolution which mainly depends of network coverage. Since 2006 the permanent Portuguese broadband (BB) seismic network expanded significantly. More recently a temporary dense BB network was deployed in Portugal, filling gaps between permanent stations and providing an excellent opportunity to study the shallow crustal structure beneath the LTV. Dispersion measurements were computed for each station pair using empirical Green's functions generated by cross-correlating one-day-length seismic ambient-noise records. To improve the seismic ambient noise signal extraction we apply a phase cross-correlation method, followed by time-frequency domain phase weighted stack. Group-velocities were inverted to obtain S-wave velocity profiles between station pairs. The models will be compared with models gathered from Ps receiver functions. The results obtained for the LTV will be integrated on a previous larger scale noise tomography performed on the entire Penisula. The models will be compared with models gathered from Ps receiver functions. The results obtained for the crust using both methods are consistent. This work is supported by project AQUAREL (PTDC/CTE-GIX/116819/2010) and a contribution to project QuakeLoc-PT (PTDC/GEO-FIQ/3522/2012).

  7. Inverting seismic noise cross-correlations for noise source distribution: A step towards reducing source-induced bias in seismic noise interferometry

    Science.gov (United States)

    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

  8. Retrieval of Moho-reflected shear wave arrivals from ambient seismic noise

    OpenAIRE

    Zhan, Zhongwen; Ni, Sidao; Helmberger, Don V.; Clayton, Robert W.

    2010-01-01

    Theoretical studies on ambient seismic noise (ASN) predict that complete Green's function between seismic stations can be retrieved from cross correlation. However, only fundamental mode surface waves emerge in most studies involving real data. Here we show that Moho-reflected body wave (SmS) and its multiples can be identified with ASN for station pairs near their critical distances in the short period band (1–5 s). We also show that an uneven distribution of noise sources, such as mining ac...

  9. 3-D surface wave tomography of the Piton de la Fournaise volcano using seismic noise correlations

    OpenAIRE

    Brenguier, Florent; M. Shapiro, Nikolai; Campillo, Michel; Nercessian, Alexandre; Ferrazzini, Valérie

    2007-01-01

    [1] We invert Rayleigh waves reconstructed from cross-correlations of 18 months of ambient seismic noise recorded by permanent seismological stations run by the Piton de la Fournaise Volcanological Observatory. By correlating noise records between 21 receivers, we reconstruct Rayleigh waves with sufficient signal-to-noise ratio for 210 inter-station paths. We use the reconstructed waveforms to measure group velocity dispersion curves at periods between 1.5 and 4.5 s. The obtained measurements...

  10. Origin of the chemical noise in ambient mass spectrometry

    International Nuclear Information System (INIS)

    The instrumental background of ambient mass spectrometry, (API-MS) is analyzed and the possible potential origins of the background noise is identified. According to the mass spectra obtained using the API-MS instruments by different manufacturers, the characteristic fragment ions all indicated that the background noise are resulted from the phthalates such as diethyl phthalate (DEP), dibutyl phthalate (DBP), benzyl butyl phthalate (BBP), bis (2-ethylhexyl) phthalate (DEHP), and silicones such as decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6). These chemicals are probably released from the polymeric materials used in the ionization sources, such as O-type sealing ring etc. In addition, the instrumental background has to be considered especially during the analysis of phthalate and peptide compounds. (authors)

  11. Correction of phase velocity bias caused by strong directional noise sources in high-frequency ambient noise tomography: a case study in Karamay, China

    Science.gov (United States)

    Wang, Kai; Luo, Yinhe; Yang, Yingjie

    2016-05-01

    We collect two months of ambient noise data recorded by 35 broad-band seismic stations in a 9 × 11 km area (1-3 km station interval) near Karamay, China, and do cross-correlation of noise data between all station pairs. Array beamforming analysis of the ambient noise data shows that ambient noise sources are unevenly distributed and the most energetic ambient noise mainly comes from azimuths of 40°-70°. As a consequence of the strong directional noise sources, surface wave components of the cross-correlations at 1-5 Hz show clearly azimuthal dependence, and direct dispersion measurements from cross-correlations are strongly biased by the dominant noise energy. This bias renders that the dispersion measurements from cross-correlations do not accurately reflect the interstation velocities of surface waves propagating directly from one station to the other, that is, the cross-correlation functions do not retrieve empirical Green's functions accurately. To correct the bias caused by unevenly distributed noise sources, we adopt an iterative inversion procedure. The iterative inversion procedure, based on plane-wave modeling, includes three steps: (1) surface wave tomography, (2) estimation of ambient noise energy and biases and (3) phase velocities correction. First, we use synthesized data to test the efficiency and stability of the iterative procedure for both homogeneous and heterogeneous media. The testing results show that: (1) the amplitudes of phase velocity bias caused by directional noise sources are significant, reaching ˜2 and ˜10 per cent for homogeneous and heterogeneous media, respectively; (2) phase velocity bias can be corrected by the iterative inversion procedure and the convergence of inversion depends on the starting phase velocity map and the complexity of the media. By applying the iterative approach to the real data in Karamay, we further show that phase velocity maps converge after 10 iterations and the phase velocity maps obtained using

  12. Correlation of Quantized Spectrally-Varying Noise

    CERN Document Server

    Gwinn, C R; Dougherty, S M; Rizzo, D D; Reynolds, J E; Jauncey, D L; Tzioumis, A K; Quick, J; McCulloch, P M; Hirabayashi, H; Kobayashi, H; Murata, Y

    2000-01-01

    We compute statistics for correlation of quantized, spectrally-varying,noise. We compare results with computer simulations and with radio-astronomicalobservations. We consider cross-correlation of two signals (or auto-correlationof one); we suppose that each signal is complex, and consists ofspectrally-varying Gaussian noise. We suppose that these signals are quantized,and then correlated. For many samples, the correlation is drawn from a Gaussiandistribution at each frequency, and is completely characterized by its averageand variance. The average is linearly related to the average correlation of theanalog signals. We present expressions for the variance, and compare resultswith computer simulations and with VLBI observations of the Vela pulsar. Wefind excellent agreement. These results are important for understanding thestatistics of radio-astronomical observations, particularly of sources thatvary with time and observing frequency.

  13. Correlated noise unfolding on a Hadronic Calorimeter

    CERN Document Server

    Fiolhais, M C N; The ATLAS collaboration

    2011-01-01

    The correlated noise component of TileCal, the barrel hadronic calorimeter of the ATLAS experiment at the Large Hadron Collider, is studied and an algorithm is used to parametrize and unfold it from the response of the photomultipliers. It is shown that the correlated noise component can be significantly reduced and mostly removed not only for pedestal runs, but also in the presence of physics signals like minimum bias events in 900 GeV collisions and 7 TeV simulated top quark pair production events.

  14. Physiologic correlates to background noise acceptance

    Science.gov (United States)

    Tampas, Joanna; Harkrider, Ashley; Nabelek, Anna

    2001-05-01

    Acceptance of background noise can be evaluated by having listeners indicate the highest background noise level (BNL) they are willing to accept while following the words of a story presented at their most comfortable listening level (MCL). The difference between the selected MCL and BNL is termed the acceptable noise level (ANL). One of the consistent findings in previous studies of ANL is large intersubject variability in acceptance of background noise. This variability is not related to age, gender, hearing sensitivity, personality, type of background noise, or speech perception in noise performance. The purpose of the current experiment was to determine if individual differences in physiological activity measured from the peripheral and central auditory systems of young female adults with normal hearing can account for the variability observed in ANL. Correlations between ANL and various physiological responses, including spontaneous, click-evoked, and distortion-product otoacoustic emissions, auditory brainstem and middle latency evoked potentials, and electroencephalography will be presented. Results may increase understanding of the regions of the auditory system that contribute to individual noise acceptance.

  15. Thirty years of progress in applications and modeling of ocean ambient noise

    Science.gov (United States)

    Siderius, Martin; Buckingham, Michael J.

    2012-11-01

    Ambient noise in the ocean is a stochastic process, which traditionally was considered to be a nuisance, since it reduced the detectability of sonar signals of interest. However, over the last thirty years, it has come to be recognized that the ambient noise itself contains useful information about the ocean and ocean processes. To extract the information, various inversion procedures have been developed, based upon which a number of practical applications of the ambient noise have evolved. Since naturally generated ambient noise is always present in the ocean, it has the advantage of being non-invasive and non-damaging to marine life, including marine mammals. In this article, a summary of the commonly encountered ambient noise models is offered, along with the associated inversion procedures, and some of the more recent applications of the ambient noise are highlighted.

  16. Ocean acoustic remote sensing using ambient noise: results from the Florida Straits

    Science.gov (United States)

    Brown, M. G.; Godin, O. A.; Zang, X.; Ball, J. S.; Zabotin, N. A.; Zabotina, L. Y.; Williams, N. J.

    2016-07-01

    Noise interferometry is the process by which approximations to acoustic Green's functions, which describe sound propagation between two locations, are estimated by cross-correlating time series of ambient noise measured at those locations. Noise-interferometry-based approximations to Green's functions can be used as the basis for a variety of inversion algorithms, thereby providing a purely passive alternative to active-source ocean acoustic remote sensing. In this paper we give an overview of results from noise interferometry experiments conducted in the Florida Straits at 100 m depth in December 2012, and at 600 m depth in September/October 2013. Under good conditions for noise interferometry, estimates of cross-correlation functions are shown to allow one to perform advanced phase-coherent signal processing techniques to perform waveform inversions, estimate currents by exploiting non-reciprocity, perform time-reversal/back-propagation calculations and investigate modal dispersion using time-warping techniques. Conditions which are favourable for noise interferometry are identified and discussed.

  17. Cross-correlation studies with seismic noise

    CERN Document Server

    Hoffmann, H; Cheng, Y; Blair, D G

    2002-01-01

    Ocean waves interacting in shallow water at the shore generate land waves propagating inland. To study these waves vertical, horizontal and tilt seismic noise were measured simultaneously at one location. Vibration isolators designed for gravitational wave research were used for detection. Cross-correlation between the above components was calculated. We found correlations between all of them. However, only the correlation between horizontal and vertical motions could be addressed to land waves, and other correlations are thought to be due to local rigid body motion of the large building in which the experiments were located.

  18. Shear wave velocities from noise correlation at local scale

    Science.gov (United States)

    De Nisco, G.; Nunziata, C.; Vaccari, F.; Panza, G. F.

    2008-07-01

    Cross correlations of ambient seismic noise recordings have been studied to infer shear seismic velocities with depth. Experiments have been done in the crowded and noisy historical centre of Napoli over inter-station distances from 50 m to about 400 m, whereas active seismic spreadings are prohibitive, even for just one receiver. Group velocity dispersion curves have been extracted with FTAN method from the noise cross correlations and then the non linear inversion of them has resulted in Vs profiles with depth. The information of near by stratigraphies and the range of Vs variability for samples of Neapolitan soils and rocks confirms the validity of results obtained with our expeditious procedure. Moreover, the good comparison of noise H/V frequency of the first main peak with 1D and 2D spectral amplifications encourages to continue experiments of noise cross-correlation. If confirmed in other geological settings, the proposed approach could reveal a low cost methodology to obtain reliable and detailed Vs velocity profiles.

  19. Ambient noise based monitoring of Piton de la Fournaise volcano

    OpenAIRE

    E. Pomponi; Christoph Sens-Schönfelder

    2012-01-01

    Exploiting the capability of the seismic noise correlation method to detect small velocity changes in the medium ( i.e. about 0.1%) we show that before the eruption of Piton de la Fournaise Volcano in October 2010 a clear variation (i.e. reduction) of this parameter is observed. Therefore its continuous monitoring could represent an important step ahead for our ability to forecast an eruption. This has been demonstrated previously. Moreover, through a simple inversion scheme based on a delta ...

  20. Ambient seismic noise monitoring of active landslides and rock columns prone to failure

    Science.gov (United States)

    Carrière, Simon; Valentin, Johann; Larose, Eric; Jongmans, Denis; Baillet, Laurent; Bottelin, Pierre; Franz, Martin; Michoud, Clément; Jaboyedoff, Michel

    2015-04-01

    Ambient seismic noise can be used to monitor the integrity of unstable slopes and rock columns prone to failure. To that end, we record continuously seismic waveforms in the fields using 1D or 3D short period seismic sensors together with autonomous and telemetered data loggers that can be operated in severe environmental conditions. When monitoring landslides made of unconsolidated materials (such as clay), we propose to monitor the relative seismic velocity changes using the Coda Wave Interferometry technique operated on the coda of daily ambient seismic noise correlations (Passive Image Interferometry). When monitoring the rupture of a rock column, we propose to track the evolution of the polarization and natural frequencies of the first resonant modes of the structures. In both cases, experimental results suggest potential precursory signals some days before the failure. We also observe a clear dependence of the seismic properties of the soil and environmental conditions such as temperature and hydrology. Bibliography : G. Mainsant, E. Larose, C. Brönnimann, D. Jongmans, C. Michoud, M. Jaboyedoff : Ambient seismic noise monitoring of a clay landslide : toward failure prediction, J. Geophys. Res. 117, F01030 (2012). P. Bottelin, C. Lévy, L. Baillet, D. Jongmans, P. Gueguen, Modal and thermal analysis of les arches unstable rock column (vercors massif, french alps), Geophys. J. Int. 194 (2013) 849-858.

  1. On the Use of Infrasonic Ambient Noise in Imaging the Atmosphere

    Science.gov (United States)

    Evers, L. G.; Fricke, J.; Smets, P. S. M.; Assink, J. D.

    2015-12-01

    To retrieve information on the wind and temperature in the (upper) atmosphere, determinsitic transient signals, like those from volcanoes, can be used. Both the traveltime and the slowness of the signals can be translated to variations in the wind and temperature structure along the source-receiver trajectory. In such a case, ground-truth about the source location and sometimes orgin time are necessary to restrict the analysis. However, sources with such a ground-truth are limited to certain geographical locations and have a sparse temporal availability. It is therefore attractive to use the ambient noise field, which is continuously present from a variety of directions. In theory, the cross correlation of the ambient noise field between two receivers should reveal the acoustic lag time between these receivers. With a known distance between the receivers, this lag time can be translated to the acoustic velocity which in turn is a function of the wind and temperature. In this presentation, the theory and results of this so-called ambient noise interferometry will be shown.

  2. 4-D imaging and monitoring of the Solfatara crater (Italy) by ambient noise tomography

    Science.gov (United States)

    Pilz, Marco; Parolai, Stefano; Woith, Heiko; Gresse, Marceau; Vandemeulebrouck, Jean

    2016-04-01

    Imaging shallow subsurface structures and monitoring related temporal variations are two of the main tasks for modern geosciences and seismology. Although many observations have reported temporal velocity changes, e.g., in volcanic areas and on landslides, new methods based on passive sources like ambient seismic noise can provide accurate spatially and temporally resolved information on the velocity structure and on velocity changes. The success of these passive applications is explained by the fact that these methods are based on surface waves which are always present in the ambient seismic noise wave field because they are excited preferentially by superficial sources. Such surface waves can easily be extracted because they dominate the Greeńs function between receivers located at the surface. For real-time monitoring of the shallow velocity structure of the Solfatara crater, one of the forty volcanoes in the Campi Flegrei area characterized by an intense hydrothermal activity due to the interaction of deep convection and meteoric water, we have installed a dense network of 50 seismological sensing units covering the whole surface area in the framework of the European project MED-SUV (The MED-SUV project has received funding from the European Union Seventh Framework Programme FP7 under Grant agreement no 308665). Continuous recordings of the ambient seismic noise over several days as well as signals of an active vibroseis source have been used. Based on a weighted inversion procedure for 3D-passive imaging using ambient noise cross-correlations of both Rayleigh and Love waves, we will present a high-resolution shear-wave velocity model of the structure beneath the Solfatara crater and its temporal changes. Results of seismic tomography are compared with a 3-D electrical resistivity model and CO2 flux map.

  3. Noise cross correlation functions in a noisy region

    Science.gov (United States)

    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

  4. Trans-dimensional ambient noise tomography of the northeast Asia

    Science.gov (United States)

    Kim, Seongryong; Tkalčić, Hrvoje; Rhie, Junkee; Chen, Youlin

    2016-04-01

    A trans-dimensional and hierarchical Bayesian tomography is performed to estimate spatial variations of shear wave velocity and provide the uncertainty in the northeast Asia region from the ambient noise data. The method accounts for irregular data distribution and sensitivity using adaptive partition property of Voronoi cells. Importantly, the number of basis functions used to parameterise the Earth model in the inversion and the level of data noise are implicitly balanced by the information contained in the data (and treated as free parameters in the inversions). Thereby more reliable models and their rigorous uncertainties are estimated by avoiding over- or under-estimation and explicit regularisation. We measure Rayleigh wave phase and group velocity (8-70 s) for available inter-station paths between more than 300 broadband stations. The obtained group and phase velocity maps reveal characteristic features beneath the former (East Sea also known as Japan Sea) and the current back-arc (Okinawa trough) regions, where relatively high and low velocities are estimated at intermediate (20-40 s) and longer periods (50-60 s), respectively. We observe that the low velocity anomalies extend to beneath intraplate volcanoes in the northeast China and the Korean Peninsula. Based on the depth sensitivity of surface wave dispersions and previous geological evidences, we argue that the intraplate volcanism in this region might be influenced by sub-lithospheric processes related to the subduction of the Pacific and Philippine Sea plates.

  5. Ambient Seismic Noise Monitoring for Stress-Induced Changes in Geysers Geothermal Field, California

    Science.gov (United States)

    Lai, V.; Taira, T.; Dreger, D. S.

    2013-12-01

    The Geysers Geothermal Field in California is one of the most seismically active zones in North America. We investigate the temporal change of the stress field within this region, by analyzing the small perturbations of the velocity structure through the correlations of ambient seismic noise. Vertical component of the continuous record of seismic noise for over 12 months are obtained from an array of seismic stations operated by the Lawrence Berkeley National Laboratory (LBNL). This network contains 30 seismic stations distributed over the entire Geysers geothermal field with an average station distance of 2 to 3 km. This translates into 435 possible combinations of the station pair in which some pairs have overlapping paths that allow us to verify the consistency of the Green's function along the same path. The procedure of the study includes computing hourly cross-correlations of the seismic noise of each station pair and stacking these hourly data into 1-day and subsequently 30-day stacks to obtain a reference Green's function (RGF) with high signal to noise ratio. Overlapping time windows are used to reduce any dependencies or effects of high amplitude transient signals. The relative travel time shift between the RGF and the 30-day stacked correlations in the frequency range from 0.1 to 0.9Hz is measured in which the value obtained is the opposite value of the relative velocity change of the structure. We are particularly interested in detecting temporal changes in seismic velocity structure accompanying tectonic events and fluid injections. To ensure the reliability of our correlations and to account for problematic data, we also perform a synthetic noise analysis by calculating the mean correlation coefficient (R-value) between the reference Green's function and data of varied durations. Correlations, which have an R-value below 0.9, are removed from the analysis.

  6. Imaging preeruptive and coeruptive structural and mechanical changes of a volcano with ambient seismic noise

    Science.gov (United States)

    Obermann, A.; Planès, T.; Larose, E.; Campillo, M.

    2013-12-01

    Forecasting the location of an eruption is of primary importance for risk management in volcanic regions. Locating the underground structural changes associated with a potential eruption is also a key issue to better understand the dynamics at work in a volcano. Using recent results in wave physics, we develop an imaging procedure that is based on the sensitivity of multiply scattered waves to weak changes in heterogeneous media. This procedure allows to locate changes in both mechanical and scattering properties of the studied medium. We study ambient seismic noise from 19 broadband stations at the active volcano Piton de la Fournaise on Reunion Island, recorded from June to December 2010. During this period, two volcanic eruptions occurred at two different locations. We calculate the noise cross correlations and study two types of changes in the coda: apparent velocity variations related to changes in the elastic properties of the medium; and, waveform decoherence associated with variations in the scattering, and thus the geological structures. We observe that the temporal variations of both of these parameters provide potential precursors of volcanic eruptions at Piton de la Fournaise. The locations determined from the preeruptive and coeruptive changes in both parameters are in good agreement with the actual eruptive activities. These data demonstrate that the coda of ambient noise correlations contains deterministic information on the locations of the eruptive processes in an active volcano. Our analysis offers an original and significant constraint for the localization of forthcoming volcanic eruptions.

  7. The preliminary results: Seismic ambient noise Rayleigh wave tomography around Merapi volcano, central Java, Indonesia

    Energy Technology Data Exchange (ETDEWEB)

    Trichandi, Rahmantara, E-mail: rachmantara.tri@gmail.com [Geophysical Engineering, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, 40132, Bandung (Indonesia); Yudistira, Tedi; Nugraha, Andri Dian [Global Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Bandung, 40132 (Indonesia); Zulhan, Zulfakriza [Earth Science Graduate Program, Faculty of Earth Science and Technology, Institut Teknologi Bandung, Bandung, 40132 (Indonesia); Saygin, Erdinc [Research School of Earth Sciences, The Australian National University, Canberra ACT 0200 (Australia)

    2015-04-24

    Ambient noise tomography is relatively a new method for imaging the shallow structure of the Earth subsurface. We presents the application of this method to produce a Rayleigh wave group velocity maps around the Merapi Volcano, Central Java. Rayleigh waves group velocity maps were reconstructed from the cross-correlation of ambient noise recorded by the DOMERAPI array which consists 43 broadband seismometers. In the processing stage, we first filtered the observation data to separatethe noise from the signal that dominated by the strong volcanic activities. Next, we cross-correlate the filtered data and stack to obtain the Green’s function for all possible station pairs. Then we carefully picked the peak of each Green’s function to estimate the dispersion trend and appliedMultiple Filter Technique to obtain the dispersion curve. Inter-station group velocity curvesare inverted to produceRayleigh wave group velocity maps for periods 1 to 10 s. The resulted Rayleigh group velocity maps show the interesting features around the Merapi Volcano which generally agree with the previous studies. Merapi-Lawu Anomaly (MLA) is emerged as a relatively low anomaly in our group velocity maps.

  8. The preliminary results: Seismic ambient noise Rayleigh wave tomography around Merapi volcano, central Java, Indonesia

    International Nuclear Information System (INIS)

    Ambient noise tomography is relatively a new method for imaging the shallow structure of the Earth subsurface. We presents the application of this method to produce a Rayleigh wave group velocity maps around the Merapi Volcano, Central Java. Rayleigh waves group velocity maps were reconstructed from the cross-correlation of ambient noise recorded by the DOMERAPI array which consists 43 broadband seismometers. In the processing stage, we first filtered the observation data to separatethe noise from the signal that dominated by the strong volcanic activities. Next, we cross-correlate the filtered data and stack to obtain the Green’s function for all possible station pairs. Then we carefully picked the peak of each Green’s function to estimate the dispersion trend and appliedMultiple Filter Technique to obtain the dispersion curve. Inter-station group velocity curvesare inverted to produceRayleigh wave group velocity maps for periods 1 to 10 s. The resulted Rayleigh group velocity maps show the interesting features around the Merapi Volcano which generally agree with the previous studies. Merapi-Lawu Anomaly (MLA) is emerged as a relatively low anomaly in our group velocity maps

  9. On measuring surface wave phase velocity from station-station cross-correlation of ambient signal

    OpenAIRE

    Boschi, Lapo; Weemstra, Cornelis; Verbeke, Julie; Ekström, Göran; Zunino, Andrea; Giardini, Domenico

    2013-01-01

    International audience We apply two different algorithms to measure surface wave phase velocity, as a function of frequency, from seismic ambient noise recorded at pairs of stations from a large European network. The two methods are based on consistent theoretical formulations, but differ in the implementation: one method involves the time-domain cross-correlation of signal recorded at different stations; the other is based on frequency-domain cross-correlation, and requires finding the ze...

  10. Body and surface wave reconstruction from seismic noise correlations between arrays at Piton de la Fournaise volcano

    Science.gov (United States)

    Nakata, Nori; Boué, Pierre; Brenguier, Florent; Roux, Philippe; Ferrazzini, Valérie; Campillo, Michel

    2016-02-01

    Body wave reconstruction from ambient seismic noise correlations is an important step toward improving volcano imaging and monitoring. Here we extract body and surface waves that propagate in Piton de la Fournaise volcano on La Réunion island using ambient noise cross correlation and array-processing techniques. Ambient noise was continuously recorded at three dense arrays, each comprising 49 geophones. To identify and enhance the Green's function from the ambient noise correlation, we apply a double beamforming (DBF) technique between the array pairs. The DBF allows us to separate surface and body waves, direct and reflected waves, and multipathing waves. Based on their azimuths and slownesses, we successfully extract body waves between all the combinations of arrays, including the wave that propagates through the active magmatic system of the volcano. Additionally, we identify the effects of uneven noise source distribution and interpret the surface wave reflections.

  11. Monitoring volcanoes using seismic noise correlations

    OpenAIRE

    Brenguier, Florent; Clarke, Daniel; Aoki, Yosuke; Shapiro, Nikolai M.; Campillo, Michel; Ferrazzini, Valérie

    2011-01-01

    In this article, we summarize some recent results of measurements of temporal changes of active volcanoes using seismic noise cross-correlations. We first present a novel approach to estimate volcano interior temporal seismic velocity changes. The proposed method allows to measure very small velocity changes (≈ 0.1%) with a time resolution as small as one day. The application of that method to Piton de la Fournaise Volcano (La Réunion Island) shows velocity decreases preceding eruptions. More...

  12. Crustal structure of Mexico and surrounding regions from seismic ambient noise tomography

    OpenAIRE

    Gaite, Beatriz; Iglesias, Arturo; Villaseñor, Antonio; Herraiz Sarachaga, Miguel; Pacheco, Javier F.

    2012-01-01

    Using continuous seismic data from newly available broadband stations in Mexico and Central America we have obtained group and phase velocity maps of fundamental mode Rayleigh wave for the region. These new maps have been calculated for periods between 8 and 60 s from cross-correlations of seismic ambient noise between 100 broadband stations, and stacked for 30 months from 2006 to 2008. The tomographic inversion of the obtained dispersion measurements has been carried out on a 1°× 1° grid, re...

  13. High-resolution surface-wave tomography from ambient seismic noise.

    Science.gov (United States)

    Shapiro, Nikolai M; Campillo, Michel; Stehly, Laurent; Ritzwoller, Michael H

    2005-03-11

    Cross-correlation of 1 month of ambient seismic noise recorded at USArray stations in California yields hundreds of short-period surface-wave group-speed measurements on interstation paths. We used these measurements to construct tomographic images of the principal geological units of California, with low-speed anomalies corresponding to the main sedimentary basins and high-speed anomalies corresponding to the igneous cores of the major mountain ranges. This method can improve the resolution and fidelity of crustal images obtained from surface-wave analyses. PMID:15761151

  14. Effect of earthquakes on ambient noise surface wave tomography in upper mantle studies

    Science.gov (United States)

    Yanovskaya, Tatiana; Koroleva, Tatiana; Lyskova, Eugenia

    2016-03-01

    Application of the ambient noise surface wave tomography method (ANT) for determination of the upper mantle structure requires data on long-periodic noise (T > 40 sec). The ANT technique implies that noise sources are distributed almost uniformly over the surface. This is practically true for short-periodic noise, however it is not so in the case of long periods. In this paper we show that the main contribution to noise at long periods is caused by signals from earthquakes. In some cases they may strongly distort noise cross-correlation. This leads to an incorrect determination of surface wave velocity dispersion curves. To minimize such a distortion we propose two means: (1) to use records of noise for the periods when there is no clustering of earthquakes, such as aftershocks of strong events; (2) to stack cross-correlation functions for a period of at least three years in order to achieve sufficient uniformity of earthquake locations. Validity of this approach is demonstrated by ANT results for Europe. Tomographic reconstruction of Rayleigh wave group velocities for 10-100 sec measured along interstation paths was carried out in a central part of Western Europe where resolving power of the data was the highest. Locally averaged dispersion curves were inverted to vertical S-wave velocity sections in this area. The results correspond closely to known features of the structure of the region, namely: strong difference of the crust and upper mantle structure at the opposite sides from the Tornquist-Teisseyre Line down to ˜ 250 km, penetration of high velocity material of EEP lithosphere under Carpathians, as well as penetration of low velocity asthenospheric layer from the Carpathian region toward the northeast.

  15. Effect of earthquakes on ambient noise surface wave tomography in upper-mantle studies

    Science.gov (United States)

    Yanovskaya, Tatiana; Koroleva, Tatiana; Lyskova, Eugenia

    2016-05-01

    Application of the ambient noise surface wave tomography method (ANT) for determination of the upper-mantle structure requires data on long-periodic noise (T > 40 s). The ANT technique implies that noise sources are distributed almost uniformly over the surface. This is practically true for short-periodic noise, however, it is not so in the case of long periods. In this paper we show that the main contribution to noise at long periods is caused by signals from earthquakes. In some cases, they may strongly distort noise cross-correlation. This leads to an incorrect determination of surface wave velocity dispersion curves. To minimize such a distortion we propose two means: (1) to use records of noise for the periods when there is no clustering of earthquakes, such as aftershocks of strong events; (2) to stack cross-correlation functions for a period of at least three years in order to achieve sufficient uniformity of earthquake locations. Validity of this approach is demonstrated by ANT results for Europe. Tomographic reconstruction of Rayleigh wave group velocities for 10-100 s measured along interstation paths was carried out in a central part of Western Europe where resolving power of the data was the highest. Locally averaged dispersion curves were inverted to vertical S-wave velocity sections in this area. The results correspond closely to known features of the structure of the region, namely: strong difference of the crust and upper-mantle structure at the opposite sides from the Tornquist-Teisseyre Line down to ˜ 250 km, penetration of high-velocity material of East European Platform lithosphere under Carpathians, as well as penetration of low-velocity asthenospheric layer from the Carpathian region towards the northeast.

  16. Ambient Seismic Noise Tomography of a Loess High Bank at Dunaszekcső (Hungary)

    Science.gov (United States)

    Szanyi, Gyöngyvér; Gráczer, Zoltán; Győri, Erzsébet; Kaláb, Zdeněk; Lednická, Markéta

    2016-08-01

    Loess high banks along the right side of the Danube in Hungary are potential subjects of landslides. Small scale ambient seismic noise tomography was used at the Dunaszekcső high bank. The aim of the study was to map near surface velocity anomalies since we assume that the formation of tension cracks—which precede landslides—are represented by low velocities. Mapping Rayleigh wave group velocity distribution can help to image intact and creviced areas and identify the most vulnerable sections. The study area lies at the top of the Castle Hill of Dunaszekcső, which was named after Castellum Lugio, a fortress of Roman origin. The presently active head scarp was formed in April 2011, and our study area was chosen to be at its surroundings. Cross-correlation functions of ambient noise recordings were used to retrieve the dispersion curves, which served as the input of the group velocity tomography. Phase cross-correlation and time-frequency phase weighted stacking was applied to calculate the cross-correlation functions. The average Rayleigh wave group velocity at the loess high bank was found to be 171 ms^{-1}. The group velocity map at a 0.1 s period revealed a low-velocity region, whose location coincides with a highly creviced area, where slope failure takes place along a several meter wide territory. Another low velocity region was found, which might indicate a previously unknown loosened domain. The highest velocities were observed at the supposed remnants of Castellum Lugio.

  17. Ambient Seismic Noise Tomography of a High Loess Bank at Dunaszekcső (Hungary)

    Science.gov (United States)

    Szanyi, Gyöngyvér; Gráczer, Zoltán; Győri, Erzsébet; Kaláb, Zdeněk; Lednická, Markéta

    2016-05-01

    High loess banks along the right side of the Danube in Hungary are potential subjects of landslides. Small scale ambient seismic noise tomography was used at the Dunaszekcső high bank. The aim of the study was to map near surface velocity anomalies since we assume that the formation of tension cracks—which precede landslides—are represented by low velocities. Mapping Rayleigh wave group velocity distribution can help to image intact and creviced areas and identify the most vulnerable sections. The study area lies at the top of the Castle Hill of Dunaszekcső, which was named after Castellum Lugio, a fortress of Roman origin. The presently active head scarp was formed in April 2011, and our study area was chosen to be at its surroundings. Cross-correlation functions of ambient noise recordings were used to retrieve the dispersion curves, which served as the input of the group velocity tomography. Phase cross-correlation and time-frequency phase weighted stacking was applied to calculate the cross-correlation functions. The average Rayleigh wave group velocity at the high loess bank was found to be 171 ms^{-1} . The group velocity map at a 0.1 s period revealed a low-velocity region, whose location coincides with a highly creviced area, where slope failure takes place along a several meter wide territory. Another low velocity region was found, which might indicate a previously unknown loosened domain. The highest velocities were observed at the supposed remnants of Castellum Lugio.

  18. Optimum deconvolution algorithm for system with multiplicative white noise and additive correlative noise

    Institute of Scientific and Technical Information of China (English)

    王会立; 陈希信

    2004-01-01

    The optimum state filter and fixed-interval smoother and the optimum deconvolution algorithm for system with multiplicative noise are derived upon the condition that the dynamic noise correlates itself in one-step and correlates with the measurement noise at the present step as well as one past step, and the multiplicative noise is white and statistically independent of the dynamic noise and the measurement noise. A simulation example demonstrates the effectiveness of the above-mentioned deconvolution algorithm.

  19. Seismic tomography and ambient noise reflection interferometry on Reykjanes, SW Iceland

    Science.gov (United States)

    Jousset, Philippe; Verdel, Arie; Ágústsson, Kristján; Blanck, Hanna; Franke, Steven; Metz, Malte; Ryberg, Trond; Weemstra, Cornelius; Hersir, Gylfi; Bruhn, David

    2016-04-01

    Recent advances in volcano-seismology and seismic noise interferometry have introduced new processing techniques for assessing subsurface structures and controls on fluid flow in geothermal systems. We present tomographic results obtained from seismic data recorded around geothermal reservoirs located both on-land Reykjanes, SW-Iceland and offshore along Reykjanes Ridge. We gathered records from a network of 234 seismic stations (including 24 Ocean Bottom Seismometers) deployed between April 2014 and August 2015. In order to determine the orientation of the OBS stations, we used Rayleigh waves planar particle motions from large magnitude earthquakes. This method proved suitable using the on-land stations: orientations determined using this method with the orientations measured using a giro-compass agreed. We obtain 3D velocity images from two fundamentally different tomography methods. First, we used local earthquakes to perform travel time tomography. The processing includes first arrival picking of P- and S- phases using an automatic detection and picking technique based on Akaike Information Criteria. We locate earthquakes by using a non-linear localization technique, as a priori information for deriving a 1D velocity model. We then computed 3D velocity models of velocities by joint inversion of each earthquake's location and lateral velocity anomalies with respect to the 1D model. Our models confirms previous models obtained in the area, with enhanced details. Second, we performed ambient noise cross-correlation techniques in order to derive an S velocity model, especially where earthquakes did not occur. Cross-correlation techniques involve the computation of cross- correlation between seismic records, from which Green's functions are estimated. Surface wave inversion of the Green's functions allows derivation of an S wave velocity model. Noise correlation theory furthermore shows that zero-offset P-wave reflectivity at selected station locations can be

  20. Highly noise resistant multiqubit quantum correlations

    International Nuclear Information System (INIS)

    We analyze robustness of correlations of the N-qubit GHZ and Dicke states against white noise admixture. For sufficiently large N, the Dicke states (for any number of excitations) lead to more robust violation of local realism than the GHZ states (e.g. for N > 8 for the W state). We also identify states that are the most resistant to white noise. Surprisingly, it turns out that these states are the GHZ states augmented with fully product states. Based on our numerical analysis conducted up to N = 8, and an analytical formula derived for any N parties, we conjecture that the three-qubit GHZ state augmented with a product of (N − 3) pure qubits is the most robust against white noise admixture among any N-qubit state. As a by-product, we derive a single Bell inequality and show that it is violated by all pure entangled states of a given number of parties. This gives an alternative proof of Gisin’s theorem. (paper)

  1. Potential of ambient noise techniques to monitor reservoir dynamics at the St. Gallen geothermal site

    Science.gov (United States)

    Obermann, A.; Larose, E. F.; Wiemer, S.

    2014-12-01

    In the last decade two large geothermal energy projects were launched in Switzerland (Basel 2006, St Gallen 2013). Both of them were stopped after the occurrence of strongly felt earthquakes (Ml3.4 and 3.5, respectively). This illustrates that one of the key challenges for the use of deep geothermal energy remains to control the risk of inducing felt and potentially hazardous seismic events during the development and operation of an underground heat exchangers. Current monitoring techniques of induced seismicity, e.g. traffic light systems, attempt to forecast seismic hazard during and after stimulation based on observed seismicity and hydraulic data. A limitation of these techniques is their focus on seismic processes. We demonstrate the potential of ambient seismic noise correlation techniques to monitor aseismic reservoir dynamics related to the 2013 geothermal project in St. Gallen. In St. Gallen, reservoir characterization tests lead to an unexpected leakage of methane gas into the well. Well-head pressure rose rapidly and operators decided to prevent a possible well blow-out with counter-pressure. The result was an immediate increase of induced seismicity with a maximum event of Ml3.5. While the reservoir characterization was not accompanied by any significant induced seismicity that could have given an indication for the ongoing processes in the reservoir, ambient noise cross-correlations reveal a significant aseismic perturbation in the system that can be clearly linked to the stimulation tests. These additional constraints may help to better understand reservoir dynamics. We also discuss the future role of noise correlation based techniques for monitoring/mitigation purposes.

  2. The Effects of Ambient Conditions on Helicopter Harmonic Noise Radiation: Theory and Experiment

    Science.gov (United States)

    Greenwood, Eric; Sim, Ben W.; Boyd, D. Douglas, Jr.

    2016-01-01

    The effects of ambient atmospheric conditions, air temperature and density, on rotor harmonic noise radiation are characterized using theoretical models and experimental measurements of helicopter noise collected at three different test sites at elevations ranging from sea level to 7000 ft above sea level. Significant changes in the thickness, loading, and blade-vortex interaction noise levels and radiation directions are observed across the different test sites for an AS350 helicopter flying at the same indicated airspeed and gross weight. However, the radiated noise is shown to scale with ambient pressure when the flight condition of the helicopter is defined in nondimensional terms. Although the effective tip Mach number is identified as the primary governing parameter for thickness noise, the nondimensional weight coefficient also impacts lower harmonic loading noise levels, which contribute strongly to low frequency harmonic noise radiation both in and out of the plane of the horizon. Strategies for maintaining the same nondimensional rotor operating condition under different ambient conditions are developed using an analytical model of single main rotor helicopter trim and confirmed using a CAMRAD II model of the AS350 helicopter. The ability of the Fundamental Rotorcraft Acoustics Modeling from Experiments (FRAME) technique to generalize noise measurements made under one set of ambient conditions to make accurate noise predictions under other ambient conditions is also validated.

  3. Ambient seismic noise tomography of Jeju Island, South Korea

    Science.gov (United States)

    Lee, S. J.; Rhie, J.; Kim, S.; Kang, T. S.; Kim, Y.

    2015-12-01

    Jeju Island, formed by Cenozoic basaltic eruptions, is an island off the southern coast of the Korean Peninsula. This volcanic island is far from the plate boundaries and the fundamental cause of the volcanic activity in this region is not understood well. To understand the origin of the island, resolving the detailed seismic velocity structures is crucial. Therefore, we applied ambient noise tomography to study the velocity structures of the island. Continuous waveform data recorded at 20 temporary and 3 permanent broad-band seismic stations are used. The group and phase velocity dispersion curves of the fundamental mode Rayleigh waves are extracted from cross-correlograms for 253 station pairs by adopting multiple filter technique. The fast marching method and the subspace method are jointly applied to construct 2-D group and phase velocity maps for periods ranging between 1 and 15 s. 1-D shear wave velocity models and their uncertainties are estimated by the Bayesian technique. The optimal number of the layers are determined at the end of the burn-in period based on the Bayesian Information Criteria (BIC). Final 3-D velocity model of the island is constructed by compiling 1-D models. In our 3-D model, a distinct low velocity anomaly appears beneath Mt. Halla from surface to about 6 km depth. The surficial extent of the anomaly is more or less consistent with the surface geologic feature of the third-stage basaltic eruption reported by previous studies but the vertical extension of the anomaly is not well constrained. To improve the velocity model, especially enhance the vertical resolution of the anomaly, we will apply joint analysis of the surface wave dispersions and teleseismic receiver functions. The improved model will provide more information to infer the tectonic or volcanic implications of the anomaly and unravel the origin of the strange volcanic island in South Korea.

  4. Real noise from the urban environment: how ambient community noise affects health and what can be done about it.

    Science.gov (United States)

    Moudon, Anne Vernez

    2009-08-01

    The increasing interest in the potential effects of the community environment on individual health has so far excluded those of the acoustic environment. Yet it has long been recognized that continued exposure to elevated sound levels leads to noise-induced hearing loss. Noise is defined as unwanted sound that disturbs communication and speech intelligibility and interferes with sleep and mental tasks. Evidence points to numerous psychophysiologic outcomes of sustained exposure, including annoyance, reduced performance, aggressive behavior, and increased risk of myocardial infarction. Populated areas have experienced a steady rise in outdoor ambient noise resulting from increases in vehicular traffic and the ubiquitous use of machinery. In 2000, the WHO produced guidelines on occupational and community noise. The European Union mandated noise surveillance and abatement programs in cities. In the U.S., a few cities have revised their noise ordinances, but proactive noise reduction initiatives remain confined to new transportation infrastructure projects, thus leaving a large portion of the population at risk. Adding community noise to the public health agenda seems timely. Research needs to measure population-wide health effects of involuntary long-term exposure to ambient noise. Further study of the range and severity of co-morbidities will help refine the thresholds used to protect health. Policies and interventions, including health impact assessments, will require detailed data on actual ambient noise levels. Reducing noise at the source will likely require new road standards and lower allowable engine noise levels. Finally, noise abatement programs have an environmental justice dimension and need to target the at-risk population. PMID:19589452

  5. Potential of ambient seismic noise techniques to monitor the St. Gallen geothermal site (Switzerland)

    Science.gov (United States)

    Obermann, A.; Kraft, T.; Larose, E.; Wiemer, S.

    2015-06-01

    The failures of two recent deep geothermal energy projects in Switzerland (Basel, 2006; St. Gallen, 2013) have again highlighted that one of the key challenges for the successful development and operation of deep underground heat exchangers is to control the risk of inducing potentially hazardous seismic events. In St. Gallen, after an injection test and two acid injections that were accompanied by a small number of micro-earthquakes (ML<0.2), operators were surprised by an uncontrolled gas release from the formation (gas kick). The "killing" procedures that had to be initiated following standard drilling procedures led to a ML3.5 earthquake. With ambient seismic noise cross correlations from nine stations, we observe a significant loss of waveform coherence that we can horizontally and vertically constrain to the injection location of the fluid. The loss of waveform coherence starts with the onset of the fluid injections 4 days prior to the gas kick. We interpret the loss of coherence as a local perturbation of the medium. We show how ambient seismic noise analysis can be used to assess the aseismic response of the subsurface to geomechanical well operations and how this method could have helped to recognize the unexpected reservoir dynamics at an earlier stage than the microseismic response alone, allowed.

  6. Adaptive ambient noise tomography and its application to the Garlock Fault, southern California

    Science.gov (United States)

    Li, Peng; Lin, Guoqing

    2014-05-01

    Traditional ambient noise tomography methods using regular grid nodes are often ill posed because the inversion grids do not always represent the distribution of ray paths. Large grid spacing is usually used to reduce the number of inversion parameters, which may not be able to solve for small-scale velocity structure. We present a new adaptive tomography method with irregular grids that provides a few advantages over the traditional methods. First, irregular grids with different sizes and shapes can fit the ray distribution better and the traditionally ill-posed problem can become more stable owing to the different parametrizations. Secondly, the data in the area with dense ray sampling will be sufficiently utilized so that the model resolution can be greatly improved. Both synthetic and real data are used to test the newly developed tomography algorithm. In synthetic data tests, we compare the resolution and stability of the traditional and adaptive methods. The results show that adaptive tomography is more stable and performs better in improving the resolution in the area with dense ray sampling. For real data, we extract the ambient noise signals of the seismic data near the Garlock Fault region, obtained from the Southern California Earthquake Data Center. The resulting group velocity of Rayleigh wave is well correlated with the geological structures. High-velocity anomalies are shown in the cold southern Sierra Nevada, the Tehachapi Mountains and the Western San Gabriel Mountains. In contrast, low velocity values are prominent in the southern San Joaquin Valley and western Mojave.

  7. Significance of geological units of the Bohemian Massif, Czech Republic, as seen by ambient noise interferometry

    Czech Academy of Sciences Publication Activity Database

    Růžek, Bohuslav; Valentová, L.; Gallovič, F.

    2016-01-01

    Roč. 173, - (2016). ISSN 0033-4553 Institutional support: RVO:67985530 Keywords : ambient noise * geological units * Bohemian Massif * velocity model Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 1.618, year: 2014

  8. Toward Understanding Crustal Body Wave Recovery with Ambient Noise Seismic Interferometry Applied to USArray

    Science.gov (United States)

    Labedz, C. R.; Mikesell, D.; Poli, P.; Prieto, G. A.

    2014-12-01

    Cross-correlation of the ambient seismic field is now widely applied for imaging and monitoring at many scales. This method has been quite successful in retrieving surface wave information, which can be used for estimating three-dimensional shear velocity structure, and in some cases estimating anisotropy or wave amplification and attenuation. However, the use of this approach to retrieve crustal body waves has seen less widespread use. While some studies (e.g., Zhan et al. 2010, Poli et al. 2012) have successfully recovered phases over a few hundred kilometers on continental shields, crustal body waves are not yet seen routinely over longer distances and in more structurally complex regions. In this study, we investigate the recovery of crustal body waves in the continental USA using stacked cross-correlations. The data for correlation was gathered over three to five years of continuous recording on an east-to-west line of USArray stations spanning the northern USA. Specifically, we study four parameters to determine which combination of processing produces the most robust crustal body wave estimates in this geologic setting: 1) the role of the total amount of data; 2) the influence of the length of the correlation time windows; 3) the effect of the geographic region of data collection; 4) the impact of different processes for selecting which noise windows go into the final stacks. In the last, we consider two methods to discriminate "good" and "bad" noise correlations: comparison of the amplitude of each correlation trace and matching the correlation window times with a global earthquake catalog. We are able to recover short period crustal S-wave phases at as far as 1300 kilometer interstation distances, which will provide unique information for future tomography models.

  9. Monitoring southwest Greenland's ice sheet melt with ambient seismic noise.

    Science.gov (United States)

    Mordret, Aurélien; Mikesell, T Dylan; Harig, Christopher; Lipovsky, Bradley P; Prieto, Germán A

    2016-05-01

    The Greenland ice sheet presently accounts for ~70% of global ice sheet mass loss. Because this mass loss is associated with sea-level rise at a rate of 0.7 mm/year, the development of improved monitoring techniques to observe ongoing changes in ice sheet mass balance is of paramount concern. Spaceborne mass balance techniques are commonly used; however, they are inadequate for many purposes because of their low spatial and/or temporal resolution. We demonstrate that small variations in seismic wave speed in Earth's crust, as measured with the correlation of seismic noise, may be used to infer seasonal ice sheet mass balance. Seasonal loading and unloading of glacial mass induces strain in the crust, and these strains then result in seismic velocity changes due to poroelastic processes. Our method provides a new and independent way of monitoring (in near real time) ice sheet mass balance, yielding new constraints on ice sheet evolution and its contribution to global sea-level changes. An increased number of seismic stations in the vicinity of ice sheets will enhance our ability to create detailed space-time records of ice mass variations. PMID:27386524

  10. Seismic Tomography Around the Eastern Edge of the Alps From Ambient-Noise-Based Rayleigh Waves

    Science.gov (United States)

    Zigone, Dimitri; Fuchs, Florian; Kolinsky, Petr; Gröschl, Gidera; Apoloner, Maria-Theresia; Qorbani, Ehsan; Schippkus, Sven; Löberich, Eric; Bokelmann, Götz; AlpArray Working Group

    2016-04-01

    Inspecting ambient noise Green's functions is an excellent tool for monitoring the quality of seismic data, and for swiftly detecting changes in the configuration of a seismological station. Those Green's functions readily provide stable information about structural variations near the Earth's surface. We apply the technique to a network consisting of about 40 broadband stations in the area of the Easternmost Alps, in particular those operated by the University of Vienna (AlpArrayAustria) and the Vienna University of Technology. Those data are used to estimate Green's functions between station pairs; the Green's function consist mainly of surface waves, and we use them to investigate crustal structure near the Eastern edge of the Alps. To obtain better signal-to-noise ratios in the noise correlation functions, we adopt a procedure using short time windows (2 hr). Energy tests are performed on the data to remove effects of transient sources and instrumental problems. The resulting 9-component correlation tensor is used to make travel time measurements on the vertical, radial and transverse components. Those measurements can be used to evaluate dispersion using frequency-time analysis for periods between 5-30 seconds. After rejecting paths without sufficient signal-to-noise ratio, we invert the velocity measurements using the Barmin et al. (2001) approach on a 10 km grid size. The obtained group velocity maps reveal complex structures with clear velocity contrasts between sedimentary basins and crystalline rocks. The Bohemian Massif and the Northern Calcareous Alps are associated with fast-velocity bodies. By contrast, the Vienna Basin presents clear low-velocity zones with group velocities down to 2 km/s at period of 7 s. The group velocities are then inverted to 3D images of shear wave speeds using the linear inversion method of Herrmann (2013). The results highlight the complex crustal structure and complement earthquake tomography studies in the region. Updated

  11. Crustal velocity structure of Central and Eastern Turkey from ambient noise tomography

    Science.gov (United States)

    Warren, Linda M.; Beck, Susan L.; Biryol, C. Berk; Zandt, George; Özacar, A. Arda; Yang, Yingjie

    2013-09-01

    In eastern Turkey, the ongoing convergence of the Arabian and African plates with Eurasia has resulted in the westward extrusion of the Anatolian Plate. To better understand the current state and the tectonic history of this region, we image crust and uppermost mantle structure with ambient noise tomography. Our study area extends from longitudes of 32° to 44°E. We use continuous data from two temporary seismic deployments, our 2006-2008 North Anatolian Fault Passive Seismic Experiment and the 1999-2001 Eastern Turkey Seismic Experiment, as well as from additional seismographs in the region. We compute daily cross-correlations of noise records between all station pairs and stack them over the entire time period for which they are available, as well as in seasonal subsets, to obtain interstation empirical Green's functions. After selecting interstation cross-correlations with high signal-to-noise ratios and measuring interstation phase velocities, we compute phase velocity maps at periods ranging from 8 to 40 s. At all periods, the phase velocity maps are similar for winter and summer subsets of the data, indicating that seasonal variations in noise sources do not bias our results. Across the study area, we invert the phase velocity estimates for shear velocity as a function of depth. The shear velocity model, which extends to 50 km depth, highlights tectonic features apparent at the surface: the Eastern Anatolian Plateau is a prominent low-velocity anomaly whereas the Kirşehir Massif has relatively fast velocities. There is a large velocity jump across the Inner Tauride Suture/Central Anataolian Fault Zone throughout the crust whereas the North Anatolian Fault does not have a consistent signature. In addition, in the southeastern part of our study area, we image a high velocity region below 20 km depth which may be the northern tip of the underthrusting Arabian Plate.

  12. Correlation function of an optical bistable system with cross-correlated additive white noise and multiplicative colored noise

    Institute of Scientific and Technical Information of China (English)

    Bing Wang; Shaoping Yan

    2009-01-01

    Considering an optical bistable system with cross-correlated additive white noise and multiplicative colored noise,we study the effects of correlation between the noises on the correlation function C(s)using the unified colored noise approximation and the Stratonovich decoupling ansatz formalism.The effects of the self-correlation time T of the multiplicative colored noise and the correlation intensity A between the two noises are studied with numerical calculation.It is found that C(s)increases with the increase of the self-correlation time r,but decreases with the increase of the correlation intensity A.At large value of T,there is almost no change for C(s)when T changes.

  13. The Correlation between Harmonica Indices and Noise Indicators

    Directory of Open Access Journals (Sweden)

    Momir Prascevic

    2015-09-01

    Full Text Available Environmental Noise Directive requires the use of common noise indicators in member countries of the European Union as physical quantities that describe the environment noise created by different sources of noise. The END noise indicators are expressed in decibel unit which is logarithmic in nature, and usually complicated to explain and relatively far-removed from perception of people. Two French organizations suggested a new environmental noise index called Harmonica index based on measurement data obtained by noise monitoring and take into account both the overall environmental noise load and noise peaks from sudden noise events. In order to determine adequacy of Harmonica indices and relationship between the Harmonica indices and the END noise indicators, the correlation analysis was carried out and the correlation coefficient was determined for different combination of the Harmonica indices and the END noise indicators. The results of the correlation analysis on the sample of noise monitoring data in the city of Niš are presented in this paper after overview the END noise indicators and Harmonica index.

  14. Synchronization in a Mutualism Ecosystem Induced by Noise Correlation

    Institute of Scientific and Technical Information of China (English)

    ZHONG Wei-Rong; SHAO Yuan-Zhi; BIE Meng-Jie; HE Zhen-Hui

    2008-01-01

    Understanding the cause of the synchronization of population evolution is an important issue for ecological improvement.Here we present a Lotka-Volterra-type model driven by two correlated environmental noises and show,via theoretical analysis and direct simulation,that noise correlation can induce a synchronization of the mutualists.The time series of mutual species exhibit a chaotic-like fluctuation,which is independent of the noise correlation,however,the chaotic fluctuation of mutual species ratio decreases with the noise correlation.A quantitative parameter defined for characterizing chaotic fluctuation provides a good approach to measure when the complete synchronization happens.

  15. System Driven by Correlated Gaussian Noises Related with Disorder

    Institute of Scientific and Technical Information of China (English)

    LI Jing-Hui

    2007-01-01

    A system driven by correlated Gaussian noises related with disorder is investigated. The Fokker-Planck equation (FPE) for the system is derived. Using the FPE derived, some systems driven by correlated Gaussian noises related with disorder can be investigated for Brownian motors, nonequilibrium transition, resonant activation,stochastic resonance, and so on. We only give one example: i.e., using the FPE derived, we study the resonant activation for a single motor protein model with correlated noises related to disorder. Since the correlated noise related to disorder usually exists with the friction, for the temperature, and so on, our results have generic physical meanings for physics, chemistry, biology and other sciences.

  16. Investigating Near Surface S-Wave Velocity Properties Using Ambient Noise in Southwestern Taiwan

    Directory of Open Access Journals (Sweden)

    Chun-Hsiang Kuo

    2015-01-01

    Full Text Available Ambient noise is typically used to estimate seismic site effects and velocity profiles instead of earthquake recordings, especially in areas with limited seismic data. The dominant Horizontal to Vertical Spectral Ratio (HVSR frequency of ambient noise is correlated to Vs30, which is the average S-wave velocity in the top 30 m. Vs30 is a widely used parameter for defining seismic amplification in earthquake engineering. HVSR can detect the vertical discontinuity of velocities, that is, the interfaces between hard bedrock and soft sediments. In southwestern Taiwan most strong motion stations are located in the plains and show a dominant frequency lower than 3 Hz. Several stations near the coast have low dominant frequencies of less than 1 Hz. The dominant frequencies are higher than 4 Hz at piedmont stations. The stations in the mountains with dominant frequencies over 8 Hz are typically located on very hard sites. This study analyzed the HVSR characteristics under different seismic site conditions considering the Vs30 from previous study (Kuo et al. 2012. The result implies that HVSRs are a better tool than Vs30 to classify the sites where bedrock is deeper than 30 m. Furthermore, we found a linear correlation between Vs30 and dominant HVSR frequency which could be used as a proxy of Vs30. The Vs30 map in this area was derived using the Engineering Geological Database for Taiwan Strong Motion Instrumentation Program (EGDT. The comparable distribution pattern between the dominant frequency and Vs30 demonstrate that HVSR can recognize S-wave velocity properties at the shallow subsurface.

  17. Developments in ambient noise analysis for the characterization of dynamic response of slopes to seismic shaking

    Science.gov (United States)

    Del Gaudio, Vincenzo; Wasowski, Janusz

    2016-04-01

    In the last few decades, we have witnessed a growing awareness of the role of site dynamic response to seismic shaking in slope failures during earthquakes. Considering the time and costs involved in acquiring accelerometer data on landslide prone slopes, the analysis of ambient noise offers a profitable investigative alternative. Standard procedures of ambient noise analysis, according to the technique known as HVNR or Nakamura's method, were originally devised to interpret data under simple site conditions similar to 1D layering (flat horizontal layering infinitely extended). In such cases, conditions of site amplification, characterized by a strong impedance contrast between a soft surface layer and a stiff bedrock, result in a single pronounced isotropic maximum of spectral ratios between horizontal and vertical component of ambient noise. However, previous studies have shown that the dynamic response of slopes affected by landslides is rather complex, being characterized by multiple resonance peaks with directional variability, thus, the use of standard techniques can encounter difficulties in providing reliable information. A new approach of data analysis has recently been proposed to exploit the potential of information content of Rayleigh waves present in ambient noise, with regard to the identification of frequency and orientation of directional resonance. By exploiting ground motion ellipticity this approach can also provide information on vertical distribution of S-wave velocity, which controls site amplification factors. The method, based on the identification of Rayleigh wave packets from instantaneous polarization properties of ambient noise, was first tested using synthetic signals in order to optimize the data processing system. Then the improved processing scheme is adopted to re-process and re-interpret the ambient noise data acquired on landslide prone slopes around Caramanico Terme (central Italy), at sites monitored also with accelerometer

  18. Partial removal of correlated noise in thermal imagery

    International Nuclear Information System (INIS)

    Correlated noise occurs in many imaging systems such as scanners and push-broom imagers. The sources of correlated noise can be from the detectors, pre-amplifiers and sampling circuits. Correlated noise appears as streaking along the scan direction of a scanner or in the along track direction of a push-broom imager. We have developed algorithms to simulate correlated noise and pre-filter to reduce the amount of streaking while not destroying the scene content. The pre- filter in the Fourier domain consists of the product of two filters. One filter models the correlated noise spectrum, the other is a windowing function e.g. Gaussian or Hanning window with variable width to block high frequency noise away from the origin of the Fourier Transform of the image data. We have optimized the filter parameters for various scenes and find improvements of the RMS error of the original minus the pre-filtered noisy image

  19. Newtonian noise and ambient ground motion for gravitational wave detectors

    International Nuclear Information System (INIS)

    Fluctuations of the local gravitational field as a result of seismic and atmospheric displacements will limit the sensitivity of ground based gravitational wave detectors at frequencies below 10 Hz. We discuss the implications of Newtonian noise for future third generation gravitational wave detectors. The relevant seismic wave fields are predominately of human origin and are dependent on local infrastructure and population density. Seismic studies presented here show that considerable seismic noise reduction is possible compared to current detector locations. A realistic seismic amplitude spectral density of a suitably quiet site should not exceed 0.5 nm/√Hz(Hz/f)2 above 1 Hz. Newtonian noise models have been developed both analytically and by finite element analysis. These show that the contribution to Newtonian noise from surface waves due to distance sources significantly reduces with depth. Seismic displacements from local sources and body waves then become the dominant contributors to the Newtonian fluctuations.

  20. Entropic noise induced stability and double entropic stochastic resonance induced by correlated noises

    Institute of Scientific and Technical Information of China (English)

    Zeng Chun-Hua; Wang Hua; Wang Hui-Tao

    2011-01-01

    For the activated dynamics of a Brownian particle moving in a confined system with the presence of entropic barriers, this paper investigates a periodic driving and correlations between two noises. Within the two-state approximation, the explicit expressions of the mean first passage time (MFPT) and the spectral power amplification (SPA)are obtained, respectively. Based on the numerical computations, it is found that: (i) The MFPT as a function of the noise intensity exhibits a maximum with the positive correlations between two noises (λ>0), this maximum for MFPT shows the characteristic of the entropic noise induced stability (ENIS) effect. The intensity λ of correlations between two noises can enhance the ENIS effect, (ii) The SPA as a function of the noise intensity exhibits a double-peak by tuning the noise correlation intensity λ, i.e., the existence of a double-peak behaviour is the identifying characteristic of the double entropic stochastic resonance phenomenon.

  1. High-sensitivity correlation spectrometer for shot noise measurements

    OpenAIRE

    Nieminen, Teemu

    2015-01-01

    Shot noise measurement is an important characterization method in nanophysics research, although shot noise correlation measurement setups have gained little attention in the literature. Most of the previous setups either utilize low frequencies around 1 MHz or rely on solely analog circuitry. This thesis presents a novel correlation spectrometer for low-temperature shot noise measurements. The setup utilizes a four-channel PCI-E digitizer card with a sample rate of 125 megasamples per se...

  2. Fluctuating Potential Barrier System with Correlated Spatial Noises

    Institute of Scientific and Technical Information of China (English)

    LI Jing-Hui

    2004-01-01

    In this paper, we study a fluctuating potential barrier system with correlated spatial noises. Study shows that for this system, there is the resonant activation over the fluctuating potential barrier, and that the correlation between the different spatial noises can enhance (or weaken) the resonant activation.

  3. Impact of correlated noise in an energy depot model.

    Science.gov (United States)

    Zeng, Chunhua; Zeng, Jiakui; Liu, Feng; Wang, Hua

    2016-01-01

    Based on the depot model of the motion of active Brownian particles (ABPs), the impact of cross-correlated multiplicative and additive noises has been investigated. Using a nonlinear Langevin approach, we discuss a new mechanism for the transport of ABPs in which the energy originates from correlated noise. It is shown that the correlation between two types of noise breaks the symmetry of the potential to generate motion of the ABPs with a net velocity. The absolute maximum value of the mean velocity depends on correlated noise or multiplicative noise, whereas a monotonic decrease in the mean velocity occurs with additive noise. In the case of no correlation, the ABPs undergo pure diffusion with zero mean velocity, whereas in the case of perfect correlation, the ABPs undergo pure drift with zero diffusion. This shows that the energy stemming from correlated noise is primarily converted to kinetic energy of the intrawell motion and is eventually dissipated in drift motion. A physical explanation of the mechanisms for noise-driven transport of ABPs is derived from the effective potential of the Fokker-Planck equation. PMID:26786478

  4. Ambient awareness: From random noise to digital closeness in online social networks

    OpenAIRE

    Levordashka, Ana; Utz, Sonja

    2016-01-01

    Ambient awareness refers to the awareness social media users develop of their online network in result of being constantly exposed to social information, such as microblogging updates. Although each individual bit of information can seem like random noise, their incessant reception can amass to a coherent representation of social others. Despite its growing popularity and important implications for social media research, ambient awareness on public social media has not been studied empiricall...

  5. On measuring surface wave phase velocity from station–station cross-correlation of ambient signal

    DEFF Research Database (Denmark)

    Boschi, Lapo; Weemstra, Cornelis; Verbeke, Julie;

    2012-01-01

    We apply two different algorithms to measure surface wave phase velocity, as a function of frequency, from seismic ambient noise recorded at pairs of stations from a large European network. The two methods are based on consistent theoretical formulations, but differ in the implementation: one...... method involves the time-domain cross-correlation of signal recorded at different stations; the other is based on frequency-domain cross-correlation, and requires finding the zero-crossings of the real part of the cross-correlation spectrum. Furthermore, the time-domain method, as implemented here and in...... the literature, practically involves the important approximation that interstation distance be large compared to seismic wavelength. In both cases, cross-correlations are ensemble-averaged over a relatively long period of time (1 yr). We verify that the two algorithms give consistent results, and...

  6. Intensity Correlation Function and Associated Relaxation Time of a Saturation Laser Model with Correlated Noises

    Institute of Scientific and Technical Information of China (English)

    ZHU Ping; CHEN Shi-Bo; MEI Dong-Cheng

    2006-01-01

    We investigate the intensity correlation function C(s) and its associated relaxation time Tc for a saturation model of single-mode laser with correlated noises.The expressions of C(s) and Tc are derived by means of the projection operator method,and effects of correlations between an additive noise and a multiplicative noise are discussed by numerical calculation.Based on the calculated results,it is found that the correlation strength λ between the additive noise and the multiplicative noise can enhance the fluctuation decay of the laser intensity.

  7. Spatial coherences of the sound pressure and the particle velocity in underwater ambient noise

    Institute of Scientific and Technical Information of China (English)

    YAN Jin; LUO Xianzhi; HOU Chaohuan

    2007-01-01

    The spatial coherences were investigated between the sound pressure and the three orthogonal components of the particle velocity in underwater ambient noise. Based on the ray theory, integral expression was derived for the spatial coherence matrix of the sound pressure and the particle velocity in a stratified ocean with dipole noise sources homogenously distributed on the surface. The integrand includes a multiplying factor of the vertical directivity of the noise intensity, and the layered ocean environment affects the spatial coherences via this directivity factor. For a shallow water environment and a semi-infinite homogenous medium, the coherence calculation results were given. It was showed that the sound speed profile and the sea bottom could not be neglected in determining the spatial coherences of the ambient noise vector field.

  8. Self-tuning measurement fusion white noise deconvolution estimator with correlated noises

    Institute of Scientific and Technical Information of China (English)

    Xiaojun Sun; Zili Deng

    2010-01-01

    For the multisensor linear discrete time-invadant stochastic systems with correlated noises and unknown noise statistics,an on-line noise statistics estimator is presented by using the correlation method.Substituting it into the steady-state Riccati equation,the self-tuning Riccati equation is obtained.Using the Kalman filtering method,based on the self-tuning Riccati equation,a self-tuning weighted measurement fusion white noise deconvolution estimator is presented.By the dynamic error system analysis(DESA)method,it is proved that the self-tuning fusion white noise deconvolution estimator converges to the optimal fusion steadystate white noise deconvolution estimator in a realization,so that it has the asymptotic global optimality.A simulation example for Bernoulli-Gaussian input white noise shows its effectiveness.

  9. Surface-wave array tomography in SE Tibet from ambient seismic noise and two-station analysis: I - Phase velocity maps

    NARCIS (Netherlands)

    Yao, H.; Hilst, R.D. van der; Hoop, M.V. de

    2006-01-01

    Empirical Green’s functions (EGFs) between pairs of seismographs can be estimated from the time derivative of the long-time cross-correlation of ambient seismic noise. These EGFs reveal velocity dispersion at relatively short periods, which can be used to resolve structures in the crust and uppermos

  10. Bandung seismic experiment: Towards tomographic imaging by using ambient seismic noise

    Science.gov (United States)

    Pranata, Bayu; Yudistira, Tedy; Saygin, Erdinc; Cummins, Phil R.; Widiyantoro, Sri; Zulfakriza, Nugraha, Andri D.

    2016-05-01

    Bandung is one of the most densely populated cities in Indonesia with vital infrastructures. On the other hand, this area is surrounded by potential sources of earthquakes that make Bandung vulnerable to earthquakes. Structure of seismic velocity and sediment thickness are crucially needed in the earthquake hazard reduction program for Bandung. Based on this consideration, we deployed 64 seismic stations over the Bandung basin to record seismic ambient noise. In this study, we employed a cross-correlation method to the simultaneously recorded data to retrieve interstation Green's functions. We measured group velocity of the retrieved Green's functions by using frequency-time analysis technique. By the end of this project, the set of interstation group velocity will be inverted to image the shallow seismic velocity structure of the Bandung basin and its surrounding areas including Mt. Tangkuban Parahu and Lembang fault. As the first stage of this work, currently we focus on Green ' s function calculation as well as the interstation group velocity measurements. The general characteristics of group velocity can be evaluated from the plot of cross-correlation function as a function of its interstation distance.

  11. Time correlation of noise pulses in a PMT

    International Nuclear Information System (INIS)

    Two types of time correlation of noise pulses caused by the PMT photocathode and dynodes are established using the autocorrelation delayed-coincidence time spectrometer. Time distributions of noise pulses in the XP2020, XP2232B, XP1021, FEU-85, FEU-87, FEU-93, and FEU-130 photomultiplier tubes are investigated. An exponential time component of noise pulses with a nanosecond scintillation time is found in some types of PMTs

  12. Noise correlations in a flux qubit with tunable tunnel coupling

    OpenAIRE

    Gustavsson, Simon; Bylander, Jonas; Yan, Fei; Oliver, William D.; Yoshihara, Fumiki; Nakamura, Yasunobu

    2011-01-01

    We have measured flux-noise correlations in a tunable superconducting flux qubit. The device consists of two loops that independently control the qubit's energy splitting and tunnel coupling. Low frequency flux noise in the loops causes fluctuations of the qubit frequency and leads to dephasing. Since the noises in the two loops couple to different terms of the qubit Hamiltonian, a measurement of the dephasing rate at different bias points provides a way to extract both the amplitude and the ...

  13. Directed transport induced by colored Lévy noise: Competition between long jumps and noise correlation

    Science.gov (United States)

    Lü, Yan; Bao, Jing-Dong

    2016-07-01

    Transport of overdamped particle driven by a colored Lévy noise in a static ratchet potential is investigated. We analyze the influence of the noise in the determination of the current and find that the direction of the current depends on the parameters characterizing the colored Lévy noise. In the present model, the long jumps and the noise correlation are two different factors that can break thermodynamical equilibrium and induce directional transport, the competition between the both leads to current inversion. This implies that an interesting non-equilibrium effect arises from long tail distribution of noise.

  14. The life cycle of a sudden stratospheric warming from infrasonic ambient noise observations

    NARCIS (Netherlands)

    Smets, P.S.M.; Evers, L.G.

    2014-01-01

    A method is presented to study the life cycle of a SSW using infrasonic ambient noise observations. The potential of infrasound is shown to provide the missing observations required by numerical weather prediction to better resolve the upper atmosphere. The 2009 major SSW is reanalyzed using the Eve

  15. Unscented Filtering from Delayed Observations with Correlated Noises

    OpenAIRE

    Hermoso-Carazo, A.; Linares-Pérez, J.

    2009-01-01

    A filtering algorithm based on the unscented transformation is proposed to estimate the state of a nonlinear system from noisy measurements which can be randomly delayed by one sampling time. The state and observation noises are perturbed by correlated nonadditive noises, and the delay is modeled by independent Bernoulli random variables.

  16. Unscented Filtering from Delayed Observations with Correlated Noises

    Directory of Open Access Journals (Sweden)

    A. Hermoso-Carazo

    2009-01-01

    Full Text Available A filtering algorithm based on the unscented transformation is proposed to estimate the state of a nonlinear system from noisy measurements which can be randomly delayed by one sampling time. The state and observation noises are perturbed by correlated nonadditive noises, and the delay is modeled by independent Bernoulli random variables.

  17. Microscopic realization of cross-correlated noise processes

    OpenAIRE

    Shit, Anindita; Chattopadhyay, Sudip; Banik, Suman Kumar; Chaudhuri, Jyotipratim Ray

    2010-01-01

    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.

  18. Microscopic realization of cross-correlated noise processes.

    Science.gov (United States)

    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

  19. Correlated Noises in a Prey-Predator Ecosystem

    Institute of Scientific and Technical Information of China (English)

    ZHONG Wei-Rong; SHAO Yuan-Zhi; HE Zhen-Hui

    2006-01-01

    @@ We investigate a Volterra ecosystem driven by correlated noises. The fluctuation in the death rate of the predator induces an increase of population density of the predators. The fluctuation in the growth rate of the prey, however,leads the predators to decay. It is reported that the predators undergo sensitivity to a random environment,whereas the preys exhibit a surprising endurance to the same stochastic factor. The predators are of better stability under strong correlation of noises.

  20. Impact of Correlated Noises on Additive Dynamical Systems

    Directory of Open Access Journals (Sweden)

    Chujin Li

    2014-01-01

    Full Text Available Impact of correlated noises on dynamical systems is investigated by considering Fokker-Planck type equations under the fractional white noise measure, which correspond to stochastic differential equations driven by fractional Brownian motions with the Hurst parameter H>1/2. Firstly, by constructing the fractional white noise framework, one small noise limit theorem is proved, which provides an estimate for the deviation of random solution orbits from the corresponding deterministic orbits. Secondly, numerical experiments are conducted to examine the probability density evolutions of two special dynamical systems, as the Hurst parameter H varies. Certain behaviors of the probability density functions are observed.

  1. Calibration of Correlation Radiometers Using Pseudo-Random Noise Signals

    Directory of Open Access Journals (Sweden)

    Sebastián Pantoja

    2009-08-01

    Full Text Available The calibration of correlation radiometers, and particularly aperture synthesis interferometric radiometers, is a critical issue to ensure their performance. Current calibration techniques are based on the measurement of the cross-correlation of receivers’ outputs when injecting noise from a common noise source requiring a very stable distribution network. For large interferometric radiometers this centralized noise injection approach is very complex from the point of view of mass, volume and phase/amplitude equalization. Distributed noise injection techniques have been proposed as a feasible alternative, but are unable to correct for the so-called “baseline errors” associated with the particular pair of receivers forming the baseline. In this work it is proposed the use of centralized Pseudo-Random Noise (PRN signals to calibrate correlation radiometers. PRNs are sequences of symbols with a long repetition period that have a flat spectrum over a bandwidth which is determined by the symbol rate. Since their spectrum resembles that of thermal noise, they can be used to calibrate correlation radiometers. At the same time, since these sequences are deterministic, new calibration schemes can be envisaged, such as the correlation of each receiver’s output with a baseband local replica of the PRN sequence, as well as new distribution schemes of calibration signals. This work analyzes the general requirements and performance of using PRN sequences for the calibration of microwave correlation radiometers, and particularizes the study to a potential implementation in a large aperture synthesis radiometer using an optical distribution network.

  2. Weighted Measurement Fusion White Noise Deconvolution Filter with Correlated Noise for Multisensor Stochastic Systems

    Directory of Open Access Journals (Sweden)

    Xin Wang

    2012-01-01

    Full Text Available For the multisensor linear discrete time-invariant stochastic control systems with different measurement matrices and correlated noises, the centralized measurement fusion white noise estimators are presented by the linear minimum variance criterion under the condition that noise input matrix is full column rank. They have the expensive computing burden due to the high-dimension extended measurement matrix. To reduce the computing burden, the weighted measurement fusion white noise estimators are presented. It is proved that weighted measurement fusion white noise estimators have the same accuracy as the centralized measurement fusion white noise estimators, so it has global optimality. It can be applied to signal processing in oil seismic exploration. A simulation example for Bernoulli-Gaussian white noise deconvolution filter verifies the effectiveness.

  3. Noise reduction algorithm for glueball correlators

    Energy Technology Data Exchange (ETDEWEB)

    Majumdar, Pushan, E-mail: tppm@iacs.res.in [Department of Theoretical Physics, Indian Association for the Cultivation of Science, Kolkata (India); Mathur, Nilmani, E-mail: nilmani@theory.tifr.res.in [Department of Theoretical Physics, Tata Institute of Fundamental Research, Mumbai (India); Mondal, Sourav, E-mail: tpsm5@iacs.res.in [Department of Theoretical Physics, Indian Association for the Cultivation of Science, Kolkata (India)

    2014-09-07

    We present an error reduction method for obtaining glueball correlators from Monte Carlo simulations of SU(3) lattice gauge theory. We explore the scalar and tensor channels at three different lattice spacings. Using this method we can follow glueball correlators to temporal separations even up to 1 fermi. We estimate the improvement over the naive method and compare our results with existing computations.

  4. Robust filtering: Correlated noise and multidimensional observation

    OpenAIRE

    Crisan, D.; Diehl, J.; Friz, P. K.; Oberhauser, H.

    2013-01-01

    In the late seventies, Clark [In Communication Systems and Random Process Theory (Proc. 2nd NATO Advanced Study Inst., Darlington, 1977) (1978) 721–734, Sijthoff & Noordhoff] pointed out that it would be natural for $\\pi_{t}$, the solution of the stochastic filtering problem, to depend continuously on the observed data $Y=\\{Y_{s},s\\in[0,t]\\}$. Indeed, if the signal and the observation noise are independent one can show that, for any suitably chosen test function $f$, there exists a continuous...

  5. Statistical fluctuations in a saturation laser model with correlated noises

    Institute of Scientific and Technical Information of China (English)

    Chen Shi-Bo; Mei Dong-Cheng

    2006-01-01

    We study the effects of correlations between quantum and pump noises on fluctuations of the laser intensity in a saturation laser model. An approximative Fokker-Planck equation and analytic expressions of the steady-state probability distribution function (SPD) of the laser system are derived. Based on the SPD, the normalized mean, the normalized variance, and the normalized skewness of the steady-state laser intensity are calculated numerically. The results indicate that (i) the correlation strength λ of correlated noises always enhances the fluctuation of laser intensity;(ii) the correlation time τ of correlated noises strengthens the fluctuation of laser intensity for the below-threshold case but τ weakens it for the above-threshold case.

  6. Noise reduction algorithm for glueball correlators

    Directory of Open Access Journals (Sweden)

    Pushan Majumdar

    2014-09-01

    Full Text Available We present an error reduction method for obtaining glueball correlators from Monte Carlo simulations of SU(3 lattice gauge theory. We explore the scalar and tensor channels at three different lattice spacings. Using this method we can follow glueball correlators to temporal separations even up to 1 fermi. We estimate the improvement over the naive method and compare our results with existing computations.

  7. Compressed Sensing with Linear Correlation Between Signal and Measurement Noise

    DEFF Research Database (Denmark)

    Arildsen, Thomas; Larsen, Torben

    2014-01-01

    Existing convex relaxation-based approaches to reconstruction in compressed sensing assume that noise in the measurements is independent of the signal of interest. We consider the case of noise being linearly correlated with the signal and introduce a simple technique for improving compressed...... sensing reconstruction from such measurements. The technique is based on a linear model of the correlation of additive noise with the signal. The modification of the reconstruction algorithm based on this model is very simple and has negligible additional computational cost compared to standard...... reconstruction algorithms, but is not known in existing literature. The proposed technique reduces reconstruction error considerably in the case of linearly correlated measurements and noise. Numerical experiments confirm the efficacy of the technique. The technique is demonstrated with application to low...

  8. High resolution Rayleigh wave group velocity tomography in North-China from ambient seismic noise

    International Nuclear Information System (INIS)

    This study presents the results of the Rayleigh wave group velocity tomography in North-China performed using ambient seismic noise observed at 190 broadband and 10 very broadband stations of the North-China Seismic Array. All available vertical component time-series for the 14 months span between January, 2007 and February, 2008 are cross-correlated to obtain empirical Rayleigh wave Green functions that are subsequently processed, with the multiple filter method, to isolate the group velocity dispersion curves of the fundamental mode of Rayleigh wave. Tomographic maps, with a grid spacing of 0.25 deg. x 0.25 deg., are computed at the periods of 4.5s, 12s, 20s, 28s. The maps at short periods reveal an evident lateral heterogeneity in the crust of North-China, quite well in agreement with known geological and tectonic features. The North China Basin is imaged as a broad low velocity area, while the Taihangshan and Yanshan uplifts and Ordos block are imaged as high velocity zones, and the Quaternary intermountain basins show up as small low-velocity anomalies. The group velocity contours at 4.5s, 12s and 20s are consistent with the Bouguer gravity anomalies measured in the area of the Taihangshan fault, that cuts through the lower crust at least. Most of the historical strong earthquakes (M≥6.0) are located where the tomographic maps show zones with moderate velocity gradient. (author)

  9. Upper crustal structure beneath East Java from ambient noise tomography: A preliminary result

    International Nuclear Information System (INIS)

    East Java has a fairly complex geological structure. Physiographically East Java can be divided into three zones, i.e. the Southern Mountains zone in the southern part, the Kendeng zone in the middle part, and the Rembang zone in the northern part. Most of the seismic hazards in this region are due to processes in the upper crust. In this study, the Ambient Noise Tomography (ANT) method is used to image the upper crustal structure beneath East Java. We have used seismic waveform data recorded by 8Meteorological, Climatological and Geophysical Agency (BMKG) stationary seismographic stations and 16 portable seismographs installed for 2 to 8 weeks. The data were processed to obtain waveforms fromnoise cross-correlation between pairs of seismographic stations. Our preliminary results indicate that the Kendeng zone, an area of low gravity anomaly, is associated with a low velocity zone. On the other hand, the southern mountain range, which has a high gravity anomaly, is related to a high velocity anomaly as shown by our tomographic images

  10. Upper crustal structure beneath East Java from ambient noise tomography: A preliminary result

    Energy Technology Data Exchange (ETDEWEB)

    Martha, Agustya Adi [Meteorological, Climatological and Geophysical Agency, Jakarta (Indonesia); Graduate Research on Earthquakes and Active Tectonics, Institut Teknologi Bandung, Bandung (Indonesia); Widiyantoro, Sri [Global Geophysics Group, Institut Teknologi Bandung, Bandung (Indonesia); Center for Disaster Mitigation, Institut Teknologi Bandung, Bandung (Indonesia); Cummins, Phil; Saygin, Erdinc [Research School of Earth Sciences, Australian National University, Canberra (Australia); Masturyono [Meteorological, Climatological and Geophysical Agency, Jakarta (Indonesia)

    2015-04-24

    East Java has a fairly complex geological structure. Physiographically East Java can be divided into three zones, i.e. the Southern Mountains zone in the southern part, the Kendeng zone in the middle part, and the Rembang zone in the northern part. Most of the seismic hazards in this region are due to processes in the upper crust. In this study, the Ambient Noise Tomography (ANT) method is used to image the upper crustal structure beneath East Java. We have used seismic waveform data recorded by 8Meteorological, Climatological and Geophysical Agency (BMKG) stationary seismographic stations and 16 portable seismographs installed for 2 to 8 weeks. The data were processed to obtain waveforms fromnoise cross-correlation between pairs of seismographic stations. Our preliminary results indicate that the Kendeng zone, an area of low gravity anomaly, is associated with a low velocity zone. On the other hand, the southern mountain range, which has a high gravity anomaly, is related to a high velocity anomaly as shown by our tomographic images.

  11. A perspective on 30 years of progress in ambient noise: Source mechanisms and the characteristics of the sound field

    Science.gov (United States)

    Cato, Douglas H.

    2012-11-01

    The last 30 years has seen substantial progress in ocean ambient noise research, particularly in understanding the mechanisms of sound generation by the sources of ambient noise, the way in which the noise field is affected by sound propagation, and improvements in quantifying the relationship between noise and environmental parameters. This has led to significant improvements in noise prediction. Activity was probably strongest in the 1980s and 1990s, as evident, for example, in the Sea Surface Sound conferences and their published proceedings (four over 10 years). Although much of the application has been to sonar, there has also been interest in using ambient noise to measure properties of the environment and in its significance to marine life. There have been significant changes in the ambient noise itself over the last 30 years. The contribution from human activities appears to have increased, particularly that due to increases in shipping numbers. Biological noise has also increased with the significant increases in populations of some whale species following the cessation of broad scale whaling in the 1960s and early 1970s. Concern about the effects of noise on marine animals as well as the way they exploit the noise has led to renewed interest in ambient noise.

  12. Surface-wave tomography of Ireland and surroundings using ambient noise and teleseismic data

    Science.gov (United States)

    Bonadio, Raffaele; Arroucau, Pierre; Lebedev, Sergei; Meier, Thomas; Schaeffer, Andrew; Licciardi, Andrea; Piana Agostinetti, Nicola

    2016-04-01

    Ireland's geology is dominated by northeast-southwest structural trends and suture zones, mostly inferred from geological mapping and a few active source seismic experiments. However, their geometry and extent at depth and their continuity across the Irish Sea are still poorly known. Important questions also remain unanswered regarding the thickness and bulk properties of the sedimentary cover at the regional scale, the deformation and flow of the deep crust during the formation of Ireland, the thickness of Ireland's lithosphere today, and the thermal structure and dynamics of the asthenosphere beneath Ireland. In this work, we take advantage of abundant, newly available broadband data from temporary array deployments and permanent seismic networks in Ireland and Great Britain to produce high-resolution models of seismic velocity structure and anisotropy of the lithosphere. We combine Rayleigh and Love phase velocity measurements from waveform cross-correlation using both ambient noise and teleseismic data in order to produce high-quality dispersion curves for periods ranging from 1 to 300 s. The phase velocity measurement procedures are adapted from Meier et al.[2], Lebedev et al.[1] and Soomro et al.[3] and are automated in order to deal with the large amount of data and ensure consistency and reproducibility. For the nearly 200 stations used in this study, we obtain a very large number of dispersion curves from both ambient noise and teleseimic data. Dispersion measurements are then inverted in a tomographic procedure for surface-wave phase velocity maps in a very broad period range. The maps constrain the 3D seismic-velocity structure of the crust and upper mantle underlying Ireland and the Irish Sea. {9} Lebedev, S., T. Meier, R. D. van der Hilst. Asthenospheric flow and origin of volcanism in the Baikal Rift area, Earth Planet. Sci. Lett., 249, 415-424, 2006. Meier, T., K. Dietrich, B. Stockhert, H.P. Harjes, One-dimensional models of shear wave velocity for

  13. Crustal Structure of the Paraná Basin from Ambient Noise Tomography

    Science.gov (United States)

    Collaco, B.; Rosa, M.; Sanchez, G.; Assumpcao, M.

    2013-05-01

    Previous surface-wave tomography in South America (e.g., Feng et al., 2004; 2007) mapped the main large-scale features of the continent, such as the high lithospheric velocities in cratonic areas and low velocities in the Patagonian province. However, more detailed features such as the Chaco and Paraná Basins have not been mapped with good resolution because of poor path coverage. This work is part of a major project to increase knowledge of crustal structure in Southern Brazil and Eastern Argentina, carried out by IAG-USP (Brazil) in collaboration with UNLP and INPRES (Argentina). To improve resolution for the Paraná Basin we used inter-station dispersion curves derived from correlation of ambient noise for new stations deployed with the implementation of the Brazilian Seismic Network (Pirchiner et al. 2011). Ambient noise tomography (ANT), was first applied by Shapiro et al. (2005) and is now expanding rapidly, especially in areas with high density of seismic stations (e.g. Bensen et al. 2007, Lin et al. 2008, Moschetti et al. 2010). ANT is a well-established method to estimate short period (Plata, CPUP in Paraguay, and the recently deployed Brazilian stations in southern Brazil. The dispersion curves were measured with a modified version of PGSWMFA (PGplot Surface Wave Multiple Filter Analysis) code, designed by Chuck Ammon (St. Louis University) and successfully applied by Pasyanos et al. (2001). Our modified version is no more event based and is working now with station pairs. For the tomographic group velocities maps, we used the conjugate gradient method with 2nd derivative smoothing (Pasyanos et al. 2001). The group velocity maps were generated with one-degree grid. For the tomographic inversion, we also added data from traditional dispersion measurements for earthquakes in South America. The velocity maps obtained for periods of 10 to 100s correspond generally well with data from previous studies (Feng et al, 2007), validating the use of ANT and

  14. Spatial variability of the ambient noise field associated with the Marginal Ice Zone and its relationship to environmental parameters

    OpenAIRE

    Biggs, Kristian Pedersen

    1988-01-01

    Approved for public release; distribution is unlimited During the month of July 1987 an acoustical experiment was conducted by the United States Naval Research Laboratory (NRL) in the East Greenland Sea Marginal Ice Zone (MIZ) . Ambient noise "hot spots" or concentrated areas of relatively high noise levels were found along the ice edge using a towed array. Ambient noise levels were obtained on 27 and 28 July using AN/SSQ-57A and AN/SSQ-57XN5 calibrated sonobuoys . The ...

  15. Extraction of Stoneley and acoustic Rayleigh waves from ambient noise on ocean bottom observations

    Science.gov (United States)

    Tonegawa, T.; Fukao, Y.; Takahashi, T.; Obana, K.; Kodaira, S.; Kaneda, Y.

    2013-12-01

    In the interferometry, the wavefield propagating between two positions can be retrieved by correlating ambient noise recorded on the two positions. This approach is useful for applying to various kinds of wavefield, such as ultrasonic, acoustic (ocean acoustic), and also seismology. Off the Kii Peninsula, Japan, more than 150 short-period (4.5 Hz) seismometers, in which hydrophone is also cosited, had been deployed for ~2 months on 2012 by Japan Agency for Marine-Earth Science and Technology (JAMSTEC) as a part of 'Research concerning Interaction Between the Tokai, Tonankai and Nankai Earthquakes' funded by Ministry of Education, Culture, Sports, Science and Technology, Japan. In this study, correlating ambient noise recorded on the sensors and hydrophones, we attempt to investigate characteristics of wavefield relative to the ocean, sediment, and solid-fluid boundary. The observation period is from Sep. 2012 to Dec. 2012. Station spacing is around 5 km. For 5 lines off the Kii Peninsula, the 30-40 seismometers are distributed at each line. Sampling interval is 200 Hz for both seismometer and hydrophone. The vertical component is just used in this study for correlation analysis. The instruments are located at 100-4800 m in water depth. In the processing for the both records, we applied a bandpass filter of 1-3 Hz, replaced the amplitude to zero if it exceeds a value that was set in this study, and took one-bit normalization. We calculated cross-correlation function (CCF) by using continuous records with a time length of 600 s, stacked the CCFs over the whole observation period. As a result of the analysis for hydrophone, a strong peak can be seen in the CCF for pairs of stations where the separation distance is ~5 km. Although the peak emerges in the CCFs for the separation distance up to 10 km, it disappears in the case that two stations are greater than 15 km separated. As a next approach, along a line off the Kii Peninsula, we aligned CCFs for two stations with

  16. Contribution of seasonal presence of cetaceans, earthquakes, drifting icebergs and anthropogenic activity to the ambient noise level in the Southern Indian Ocean

    Science.gov (United States)

    Tsang-Hin-Sun, Eve; Royer, Jean-Yves

    2015-04-01

    Assessing the ambient sound level in the oceans is essential for a better understanding of the interactions between the ecosystem and anthropogenic activities. Ambient noise studies conducted in the North Pacific and Atlantic oceans, have shown that since the 60's oceanic noise level increases with the ship traffic, even if potential impacts of shipping noise on the ecosystem is not yet fully understood. However long-term acoustic records for the Indian Ocean are still limited. Here we present long-term statistics on the ambient sound in the Southern Indian Ocean basin based on 2 years of data collected at 5 widely distributed autonomous hydrophones. The data consist of single hydrophone spectra (10-100 Hz in 1-Hz bins) averaged using Welch's method over 200 s. Spectral probability distributions of the ambient sound level are analyzed in order to identify the main sound sources and their geographical and time variability. The mean sound level within the array is 10 to 20 dB lower than in other oceans, revealing a weaker influence of shipping on the Southern Indian Ocean noise budget. Seismic events are evenly distributed in time and space and mostly contribute to the general low-frequency background noise. Periodic signals are mainly associated with the seasonal presence of 3 types of blue whales and fin whales whose signatures are easily identified at target frequencies. Winter lows and summer highs of the ambient noise levels are also well correlated with ice volume variations. Icebergs are found to be a major sound source, strongly contributing to seasonal variations even at northernmost sites of the array. Although anthropogenic factors do not seem to dominate the noise spectrum, shipping sounds are present north and east of the array. Observed higher sound levels are consistent with the proximity of major traffic lanes.

  17. Optimal filter design for shielded and unshielded ambient noise reduction in fetal magnetocardiography

    Energy Technology Data Exchange (ETDEWEB)

    Comani, S [Department of Clinical Sciences and Bio-imaging, Chieti University (Italy); Mantini, D [Department of Informatics and Automation Engineering, Marche Polytechnic University, Ancona (Italy); Alleva, G [ITAB-Institute of Advanced Biomedical Technologies, University Foundation ' G. D' Annunzio' , Chieti University (Italy); Luzio, S Di [Department of Clinical Sciences and Bio-imaging, Chieti University (Italy); Romani, G L [Department of Clinical Sciences and Bio-imaging, Chieti University (Italy)

    2005-12-07

    The greatest impediment to extracting high-quality fetal signals from fetal magnetocardiography (fMCG) is environmental magnetic noise, which may have peak-to-peak intensity comparable to fetal QRS amplitude. Being an unstructured Gaussian signal with large disturbances at specific frequencies, ambient field noise can be reduced with hardware-based approaches and/or with software algorithms that digitally filter magnetocardiographic recordings. At present, no systematic evaluation of filters' performances on shielded and unshielded fMCG is available. We designed high-pass and low-pass Chebychev II-type filters with zero-phase and stable impulse response; the most commonly used band-pass filters were implemented combining high-pass and low-pass filters. The achieved ambient noise reduction in shielded and unshielded recordings was quantified, and the corresponding signal-to-noise ratio (SNR) and signal-to-distortion ratio (SDR) of the retrieved fetal signals was evaluated. The study regarded 66 fMCG datasets at different gestational ages (22-37 weeks). Since the spectral structures of shielded and unshielded magnetic noise were very similar, we concluded that the same filter setting might be applied to both conditions. Band-pass filters (1.0-100 Hz) and (2.0-100 Hz) provided the best combinations of fetal signal detection rates, SNR and SDR; however, the former should be preferred in the case of arrhythmic fetuses, which might present spectral components below 2 Hz.

  18. Colored Correlated Noises in Growth Model of Tumor

    OpenAIRE

    Mirian, Najmeh Sadat

    2014-01-01

    Stochastic resonance induced by external factor is considering to investigate the complex dynamics of tumor. The surrounding environment and the treatment effects on the tumor growth are considered as additive and multiplicative noises in growth model. The adaptability of tumor to treatment is presented by correlation of these two noises. The Fokker-Plank equation is deduced to study the probability distribution function and mean number of tumor cells in different conditions. The mean number ...

  19. Effects of Perfectly Correlated and Anti-Correlated Noise in a Logistic Growth Model

    Institute of Scientific and Technical Information of China (English)

    ZHANG Li; CAO Li

    2011-01-01

    The logistic growth model with correlated additive and multipllcative Gaussian white noise is used to analyze tumor cell population. The effects of perfectly correlated and anti-correlated noise on the stationary properties of tumor cell population are studied. As in both cases the diffusion coefficient has zero point in real number field, some special features of the system are arisen. It is found that in both cases, the increase of the multiplicative noise intensity cause tumor cell extinction. In the perfectly anti-correlated case, the stationary probability distribution as a function of tumor cell population exhibit two extrema.

  20. Effects of Perfectly Correlated and Anti-Correlated Noise in a Logistic Growth Model

    International Nuclear Information System (INIS)

    The logistic growth model with correlated additive and multiplicative Gaussian white noise is used to analyze tumor cell population. The effects of perfectly correlated and anti-correlated noise on the stationary properties of tumor cell population are studied. As in both cases the diffusion coefficient has zero point in real number field, some special features of the system are arisen. It is found that in both cases, the increase of the multiplicative noise intensity cause tumor cell extinction. In the perfectly anti-correlated case, the stationary probability distribution as a function of tumor cell population exhibit two extrema. (general)

  1. New developments in ambient noise analysis to characterise the seismic response of landslide-prone slopes

    OpenAIRE

    V. Del Gaudio; J. Wasowski; S. Muscillo

    2013-01-01

    We report on new developments in the application of ambient noise analysis applied to investigate the dynamic response of landslide-prone slopes to seismic shaking, with special attention to the directional resonance phenomena recognised in previous studies. These phenomena can be relevant for seismic slope susceptibility, especially when maximum resonance orientation is close to potential sliding directions. Therefore, the implementation of an effective technique for site response directivit...

  2. Impact of wind on ambient noise recorded by the "13 BB star" seismic array in northern Poland

    Science.gov (United States)

    Lepore, Simone; Markowicz, Krzysztof; Grad, Marek

    2016-04-01

    corresponding to the best fit between phase slowness and back azimuth. The azimuth was mainly associated to the angle of the highest peak on the vertical component; however, if the related energy was not large enough, the angle of the main noise source on the horizontal component was employed. In some cases, the azimuth of the secondary peak was taken into account, if its energy was strong enough. The results were related to the daily mean wind speed around Europe recorded during the same month. A significant correlation between the daily average level of ambient noise and the mean wind speed was found. The main source of the ambient noise was located in the Atlantic Ocean and in the North Sea: some weaker sources, however, were identified as the Barents, Baltic, Mediterranean, and Black Seas. National Science Centre Poland provided financial support for this work by NCN grant DEC 2011/02/A/ST10/00284.

  3. Potential Misidentification of Love-Wave Phase Velocity Based on Three-Component Ambient Seismic Noise

    Science.gov (United States)

    Xu, Zongbo; Xia, Jianghai; Luo, Yinhe; Cheng, Feng; Pan, Yudi

    2016-04-01

    People have calculated Rayleigh-wave phase velocities from vertical component of ambient seismic noise for several years. Recently, researchers started to extract Love waves from transverse component recordings of ambient noise, where "transverse" is defined as the direction perpendicular to a great-circle path or a line in small scale through observation sensors. Most researches assumed Rayleigh waves could be negligible, but Rayleigh waves can exist in the transverse component when Rayleigh waves propagate in other directions besides radial direction. In study of data acquired in western Junggar Basin near Karamay city, China, after processing the transverse component recordings of ambient noise, we obtain two energy trends, which are distinguished with Rayleigh-wave and Love-wave phase velocities, in the frequency-velocity domain using multichannel analysis of surface waves (MASW). Rayleigh waves could be also extracted from the transverse component data. Because Rayleigh-wave and Love-wave phase velocities are close in high frequencies (>0.1 Hz), two kinds of surface waves might be merged in the frequency-velocity domain. Rayleigh-wave phase velocities may be misidentified as Love-wave phase velocities. To get accurate surface-wave phase velocities from the transverse component data using seismic interferometry in investigating the shallow geology, our results suggest using MASW to calculate real Love-wave phase velocities.

  4. Sensor Selection for Estimation with Correlated Measurement Noise

    Science.gov (United States)

    Liu, Sijia; Chepuri, Sundeep Prabhakar; Fardad, Makan; Masazade, Engin; Leus, Geert; Varshney, Pramod K.

    2016-07-01

    In this paper, we consider the problem of sensor selection for parameter estimation with correlated measurement noise. We seek optimal sensor activations by formulating an optimization problem, in which the estimation error, given by the trace of the inverse of the Bayesian Fisher information matrix, is minimized subject to energy constraints. Fisher information has been widely used as an effective sensor selection criterion. However, existing information-based sensor selection methods are limited to the case of uncorrelated noise or weakly correlated noise due to the use of approximate metrics. By contrast, here we derive the closed form of the Fisher information matrix with respect to sensor selection variables that is valid for any arbitrary noise correlation regime, and develop both a convex relaxation approach and a greedy algorithm to find near-optimal solutions. We further extend our framework of sensor selection to solve the problem of sensor scheduling, where a greedy algorithm is proposed to determine non-myopic (multi-time step ahead) sensor schedules. Lastly, numerical results are provided to illustrate the effectiveness of our approach, and to reveal the effect of noise correlation on estimation performance.

  5. The Effects of Ambient Conditions on Helicopter Rotor Source Noise Modeling

    Science.gov (United States)

    Schmitz, Frederic H.; Greenwood, Eric

    2011-01-01

    A new physics-based method called Fundamental Rotorcraft Acoustic Modeling from Experiments (FRAME) is used to demonstrate the change in rotor harmonic noise of a helicopter operating at different ambient conditions. FRAME is based upon a non-dimensional representation of the governing acoustic and performance equations of a single rotor helicopter. Measured external noise is used together with parameter identification techniques to develop a model of helicopter external noise that is a hybrid between theory and experiment. The FRAME method is used to evaluate the main rotor harmonic noise of a Bell 206B3 helicopter operating at different altitudes. The variation with altitude of Blade-Vortex Interaction (BVI) noise, known to be a strong function of the helicopter s advance ratio, is dependent upon which definition of airspeed is flown by the pilot. If normal flight procedures are followed and indicated airspeed (IAS) is held constant, the true airspeed (TAS) of the helicopter increases with altitude. This causes an increase in advance ratio and a decrease in the speed of sound which results in large changes to BVI noise levels. Results also show that thickness noise on this helicopter becomes more intense at high altitudes where advancing tip Mach number increases because the speed of sound is decreasing and advance ratio increasing for the same indicated airspeed. These results suggest that existing measurement-based empirically derived helicopter rotor noise source models may give incorrect noise estimates when they are used at conditions where data were not measured and may need to be corrected for mission land-use planning purposes.

  6. Effects of correlated Gaussian noise on the mean firing rate and correlations of an electrically coupled neuronal network

    OpenAIRE

    Sun, Xiaojuan; Perc, Matjaz; Lu, Qishao; Kurths, Jürgen

    2010-01-01

    In this paper, we examine the effects of correlated Gaussian noise on a two-dimensional neuronal network that is locally modeled by the Rulkov map. More precisely, we study the effects of the noise correlation on the variations of the mean firing rate and the correlations among neurons versus the noise intensity. Via numerical simulations, we show that the mean firing rate can always be optimized at an intermediate noise intensity, irrespective of the noise correlation. On the other hand, var...

  7. Ambient awareness: From random noise to digital closeness in online social networks

    Science.gov (United States)

    Levordashka, Ana; Utz, Sonja

    2016-01-01

    Ambient awareness refers to the awareness social media users develop of their online network in result of being constantly exposed to social information, such as microblogging updates. Although each individual bit of information can seem like random noise, their incessant reception can amass to a coherent representation of social others. Despite its growing popularity and important implications for social media research, ambient awareness on public social media has not been studied empirically. We provide evidence for the occurrence of ambient awareness and examine key questions related to its content and functions. A diverse sample of participants reported experiencing awareness, both as a general feeling towards their network as a whole, and as knowledge of individual members of the network, whom they had not met in real life. Our results indicate that ambient awareness can develop peripherally, from fragmented information and in the relative absence of extensive one-to-one communication. We report the effects of demographics, media use, and network variables and discuss the implications of ambient awareness for relational and informational processes online. PMID:27375343

  8. Jet engine noise and infrared plume correlation field campaign

    Science.gov (United States)

    Cunio, Phillip M.; Weber, Reed A.; Knobel, Kimberly R.; Smith, Christine; Draudt, Andy

    2015-09-01

    Jet engine noise can be a health hazard and environmental pollutant, particularly affecting personnel working in close proximity to jet engines, such as airline mechanics. Mitigating noise could reduce the potential for hearing loss in runway workers; however, there exists a very complex relationship between jet engine design parameters, operating conditions, and resultant noise power levels, and understanding and characterizing this relationship is a key step in mitigating jet engine noise effects. We demonstrate initial results highlighting the utility of high-speed imaging (hypertemporal imaging) in correlating the infrared signatures of jet engines with acoustic noise. This paper builds on prior theoretical analysis of jet engine infrared signatures and their potential relationships to jet engine acoustic emissions. This previous work identified the region of the jet plume most likely to emit both in infrared and in acoustic domains, and it prompted the investigation of wave packets as a physical construct tying together acoustic and infrared energy emissions. As a means of verifying these assertions, a field campaign to collect relevant data was proposed, and data collection was carried out with a bank of infrared instruments imaging a T700 turboshaft engine undergoing routine operational testing. The detection of hypertemporal signatures in association with acoustic signatures of jet engines enables the use of a new domain in characterizing jet engine noise. This may in turn enable new methods of predicting or mitigating jet engine noise, which could lead to socioeconomic benefits for airlines and other operators of large numbers of jet engines.

  9. Power Mapping and Noise Reduction for Financial Correlations

    International Nuclear Information System (INIS)

    The spectral properties of financial correlation matrices can show features known from completely random matrices. A major reason is noise originating from the finite lengths of the financial time series used to compute the correlation matrix elements. In recent years, various methods have been proposed to reduce this noise, i.e. to clean the correlation matrices. This is of direct practical relevance for risk management in portfolio optimization. In this contribution, we discuss in detail the power mapping, a new shrinkage method. We show that the relevant parameter is, to a certain extent, self-determined. Due to the 'hirality' and the normalization of the correlation matrix, the optimal shrinkage parameter is fixed. We apply the power mapping and the well-known filtering method to market data and compare them by optimizing stock portfolios. We address the role of constraints by excluding short selling in the optimization. (author)

  10. Experimental study of passive defect localization in plates using ambient noise.

    Science.gov (United States)

    Chehami, Lynda; de Rosny, Julien; Prada, Claire; Moulin, Emmanuel; Assaad, Jamal

    2015-08-01

    Passive listening methodology has been shown to be a practical and effective method for passive structural health monitoring. In this work, this approach is applied experimentally to monitor the occurrence of defects in thin aluminum plates. A correlation matrix is estimated from noise vibrations recorded on a transducer array. A defect is localized by applying a beamforming algorithm to the difference between the correlation matrices obtained with and without the defect. We successfully detect defects for different kinds of noise sources. Moreover, we show that this technique is robust to detect massive inclusions, holes, and cracks. With a vibrometer, we observe that the fidelity of the estimated transient responses strongly depends on the number of uncorrelated noise sources. Finally, we show that the defect is successfully localized even if the noise source distribution is not uniform, provided that it remains spatially stationary between the states with and without defect. A simple theoretical framework is proposed to interpret these results. PMID:26276962

  11. Investigations of Passive Seismic Body-Wave Interferometry Using Noise Auto-correlations for Crustal and Upper Mantle Structure

    Science.gov (United States)

    Oren, C.; Nowack, R. L.

    2015-12-01

    It is known that the positive lags of the auto-correlation for the seismic transmission response of a layered medium correspond to the reflection seismogram (Claerbout, 1968). In this study, we investigate the use of ambient seismic noise recorded at selected broadband USArray EarthScope Transportable Array (TA) stations to obtain effective reflection seismograms for frequencies up to 1 Hz. The goal is to determine the most suitable parameters used for the processing of ambient seismic noise for the identification of crustal and upper mantle reflections and to minimize unwanted artifacts in the noise correlations. In order to best retrieve the body-wave components of the Green's function beneath a station, a number of processing steps are required. We first remove the instrument response and apply a temporal normalization to remove the effects of the most energetic sources. Next we implement spectral whitening. We test several operators for the spectral whitening where the undulations of the power spectrum are related to the strengths of later arrivals in the auto-correlation. Different filters are then applied to the auto-correlation functions, including Gaussian and zero phase Butterworth filters, in order to reduce the effect of side lobes. Hourly auto-correlations are then stacked for up to one year. On the final stack, Automatic Gain Control (AGC) is applied to equalize the correlation amplitudes in the time domain. The robustness of the resulting ambient noise auto-correlation is first tested on selected TA stations in Nevada, where we are able to identify PmP and SmS arrivals similar to those found by Tibuleac and von Seggern (2012). We then investigate noise auto-correlations applied to selected USArray TA stations in the central US.

  12. Persistent Rabi oscillations probed via low-frequency noise correlation

    OpenAIRE

    Korotkov, Alexander N.

    2010-01-01

    The qubit Rabi oscillations are known to be non-decaying (though with a fluctuating phase) if the qubit is continuously monitored in the weak-coupling regime. In this paper we propose an experiment to demonstrate these persistent Rabi oscillations via low-frequency noise correlation. The idea is to measure a qubit by two detectors, biased stroboscopically at the Rabi frequency. The low-frequency noise depends on the relative phase between the two combs of biasing pulses, with a strong increas...

  13. Crustal structure of the Pannonian-Carpathian region, Central Europe, from ambient noise tomography

    Science.gov (United States)

    Ren, Y.; Stuart, G. W.; Houseman, G. A.; Carpathian Basins Project Working Group

    2010-12-01

    The Pannonian Basin of Central Europe is a major extensional basin surrounded by the Carpathian Mountains. During the evolution of the Carpathian-Pannonian region, extension of the crust and lithosphere created several inter-related basins of which the Pannonian basin is the largest. Imaging the seismic velocity structure of the crust and the upper mantle may help us understand the structure and geodynamic evolution of this part of central Europe. Here, we use ambient noise tomography to investigate the crust and uppermost mantle structure in the region. We have collected and processed continuous data from 56 temporary stations deployed in the Carpathian Basins Project (CBP) for 16 months (2005-2007) and 41 permanent broadband stations; this dataset enables the most well-resolved images of the S-wave structure of the region yet obtained. We computed the cross-correlation between vertical component seismograms from pairs of stations and stacked the correlated waveforms over 1-2 years to estimate the Rayleigh wave Green’s function. Frequency-time analysis is used to measure the group velocity dispersion curves, which are then inverted for the group velocity maps. Our 4-10 s group velocity maps exhibit low velocity anomalies which clearly defined the major sediment depo-centers in the Carpathian region. A broad low velocity anomaly in the center of the 5 s group velocity map can be associated with the Pannonian Basin, whereas an anomaly in the southeastern region is related to the Moesian platform. Further east, the Vienna Basin can also be seen on our maps. A fast anomaly in the central region can be associated with the Mid-Hungarian line. At periods from 18 to 24 seconds, group velocities become increasingly sensitive to crustal thickness. The maps also reveal low-velocity anomalies associated with the Carpathians. The low velocity anomalies are probably caused by deeper crustal roots beneath the mountain ranges which occur due to isostatic compensation. CBP

  14. Resolution for a local earthquake arrival time and ambient seismic noise tomography around the Eyjafjallajökull volcano

    Science.gov (United States)

    Benediktsdóttir, Á.; Gudmundsson, Ö.; Tryggvason, A.; Bödvarsson, R.; Brandsdóttir, B.; Vogfjörd; K.; Sigmundsson, F.

    2012-04-01

    The explosive summit eruption of Eyjafjallajökull volcano from 14 April to end of May 2010 was preceded by an effusive flank eruption of the volcano (at Fimmvörðuháls) March 20th - April 12th. These eruptions culminated 18 years of recurrent volcanic unrest in the area, with extensive seismicity and high deformation rates since beginning of January 2010. A national network of seismic stations in Iceland (the SIL network), operated by he Icelandic Meteorological Office, monitored the precursors and development of the eruptions, in real time. We analyse a seismic dataset available from SIL stations in the vicinity of the eruption area, as well as data from additional portable stations that were deployed during a period of unrest in 1999 and just before and during the eruptions in 2010. The SIL system detected and located 2328 events between early March and late May 2010 in the area around Eyjafjallajökull. Here we present a preliminary evaluation of resolution for a local earthquake arrival time tomography. Adding the portable stations to the pre-existing SIL data set is crucial in order to identify more seismic events and improve the data coverage for tomography. We also present a resolution analysis for Ambient Seismic Noise Tomography (ASNT) in the area. In this method ambient seismic noise, recorded at two seismic stations, is cross-correlated. This band-limited approximation of the Green's function between two stations is used to estimate surface wave velocities. The fundamental assumptions underlying this method is that the noise is constructed from a randomly distributed wavefield, but this may be violated by volcanic tremor during the eruptions. We evaluate the robustness of inter-station correlograms as a function of time during the unrest period as well as their frequency content for evaluation of depth resolution. The results can be compared to constraints on magma movements inside the volcano based on interpretation of crustal deformation and

  15. Italian and Alpine crustal structure imaged by ambient-noise surface-wave dispersion

    Science.gov (United States)

    Molinari, I.; Boschi, L.; Verbeke, J.; Morelli, A.; Kissling, E. H.

    2014-12-01

    Surface-wave dispersion measurements based on seismic background signal (ambient noise) are a very effective means to image S-wave velocity at crustal and lithospheric depths. The goal of our study is to integrate new ambient noise data for central Europe with more traditional models of crustal heterogeneity and discontinuity depths. We find that the reference crustal model EPcrust (Molinari and Morelli, 2011) is in good agreement with the large database of one-year-long records of European ambient noise compiled by Verbeke et al. (2012). We use the same data to further improve EPcrust, obtaining a new three-dimensional model of Italian and Alpine crustal structure. We first conduct a linear least squares inversion of the available phase-velocity observations, resulting in a set of Rayleigh-wave phase-velocity maps at periods between 5 and 37 s. At relatively short periods, these maps clearly reflect the surface geology of the region, e.g. low velocity zones at the Po Plain; longer-period maps reveal deeper structures such as Moho topography under Alps and Appennines, and lower crustal anomalies. The phase-velocity maps are next inverted via the Neighbourhood Algorithm to determine a set of one-dimensional shear-velocity models (one per phase-velocity pixel), which are in turn interpolated to build a new three-dimensional model and Moho depth. The reconstructed model shows the low velocity area beneath the Po Plain; the contrast between the low-velocity crust of the Adriatic domain and the high-velocity crust of the Tyrrhenian domain is clearly seen, as well as an almost uniform crystalline crust beneath the Alpine belt. Our results are physically consistent with the information for velocity structure and Moho depth independently obtained by other seismic methods.

  16. Ambient noise induces independent shifts in call frequency and amplitude within the Lombard effect in echolocating bats

    OpenAIRE

    Hage, Steffen R.; Jiang, Tinglei; Berquist, Sean W.; Feng, Jiang; Metzner, Walter

    2013-01-01

    The Lombard effect, an involuntary rise in call amplitude in response to masking ambient noise, represents one of the most efficient mechanisms to optimize signal-to-noise ratio. The Lombard effect occurs in birds and mammals, including humans, and is often associated with several other vocal changes, such as call frequency and duration. Most studies, however, have focused on noise-dependent changes in call amplitude. It is therefore still largely unknown how the adaptive changes in call ampl...

  17. Effects of noise from non-traffic-related ambient sources on sleep: Review of the literature of 1990-2010

    OpenAIRE

    Sarah Omlin; Bauer, Georg F.; Mark Brink

    2011-01-01

    This article reviews the literature about the effects of specific non-traffic-related ambient noise sources on sleep that appeared in the last two decades. Although everybody is faced with noise of non-traffic and non-industry origin (e.g. sounds made by neighbors, talk, laughter, music, slamming doors, structural equipment, ventilation, heat pumps, noise from animals, barking dogs, outdoor events etc.), little scientific knowledge exists about its effects on sleep. The findings of the presen...

  18. New developments in ambient noise analysis to characterise the seismic response of landslide prone slopes

    Directory of Open Access Journals (Sweden)

    V. Del Gaudio

    2013-04-01

    Full Text Available We report on new developments in the application of ambient noise analysis applied to investigate the dynamic response of landslide prone slopes to seismic shaking with special attention to the directional resonance phenomena recognised in previous studies. Investigations relying on the calculation of horizontal-to-vertical noise spectral ratio (HVNR were carried out in the area of Caramanico Terme (central Italy where an ongoing accelerometer monitoring on slopes with different characteristics offers the possibility of validation of HVNR analysis. The noise measurements, carried out in different times to test the result repeatability, revealed that sites affected by response directivity persistently show major peaks with a common orientation consistent with the resonance direction inferred from accelerometer data. At sites where directivity is absent, the HVNR peaks do not generally show a preferential orientation, with rare exceptions that could be linked to the presence of temporarily active sources of polarised noise. The observed spectral ratio amplitude variations can be related to temporal changes in site conditions, which can hinder the recognition of main resonance frequencies. Therefore, it is recommended to conduct simultaneous measurements at nearby sites within the same study area and to repeat measurements at different times in order to distinguish significant systematic polarisation caused by site specific response directivity from polarisation controlled by properties of noise sources. Furthermore, an analysis of persistence in noise recordings of signals with systematic directivity showed that only a~portion of recordings contains wave trains having a clear polarisation representative of site directional resonance. Thus a careful selection of signals for HVNR analysis is needed for a correct characterisation of site directional properties.

  19. Music and ambient operating room noise in patients undergoing spinal anesthesia.

    Science.gov (United States)

    Ayoub, Chakib M; Rizk, Laudi B; Yaacoub, Chadi I; Gaal, Dorothy; Kain, Zeev N

    2005-05-01

    Previous studies have indicated that music decreases intraoperative sedative requirements in patients undergoing surgical procedures under regional anesthesia. In this study we sought to determine whether this decrease in sedative requirements results from music or from eliminating operating room (OR) noise. A secondary aim of the study was to examine the relationship of response to intraoperative music and participants' culture (i.e., American versus Lebanese). Eighty adults (36 American and 54 Lebanese) undergoing urological procedures with spinal anesthesia and patient-controlled IV propofol sedation were randomly assigned to intraoperative music, white noise, or OR noise. We found that, controlling for ambient OR noise, intraoperative music decreases propofol requirements (0.004 +/- 0.002 mg . kg(-1) . min(-1) versus 0.014 +/- 0.004 mg . kg(-1) . min(-1) versus 0.012 +/- 0.002 mg . kg(-1) . min(-1); P = 0.026). We also found that, regardless of group assignment, Lebanese patients used less propofol as compared with American patients (0.005 +/- 0.001 mg . kg(-1) . min(-1) versus 0.017 +/- 0.003 mg . kg(-1) . min(-1); P = 0.001) and that, in both sites, patients in the music group required less propofol (P music decreases propofol requirements of both Lebanese and American patients who undergo urological surgery under spinal anesthesia. PMID:15845676

  20. Ambient Noise and Teleseismic Signals Recorded by Ocean-Bottom Seismometers Offshore Eastern Taiwan

    Directory of Open Access Journals (Sweden)

    Ching-Ren Lin

    2010-01-01

    Full Text Available Broadband records from ocean-bottom seismometers deployed in the Okinawa trough and the Huatung basin were analyzed to provide seafloor noise characteristics and the detection thresholds for teleseismic body and surface waves. Ambient noise levels on the horizontal components are 10 - 40 dB higher than on the vertical component, with the sensor seated on the surface of the sediment. On the vertical components, infragravity waves are 10 - 30 dB more energetic at the shallower Okinawa trough sites (≤ 2000 m depth than at the deeper Huatung basin site (~4700 m. From 0.03 to 0.2 Hz, the Huatung basin noise levels are comparable to that of the broadband stations in Taiwan on a quiet day. The microseism peaks (~0.2 - 0.5 Hz of OBSs reach or exceed the high noise model of continental stations. At regional distances Mw 6.5 is required for recording prominent Rayleigh waves if the source radiation is unfavorable, but 6.2 is sufficient for a favorable focal mecha¬nism.mecha¬nism. Several tens to over one hundred high-fidelity P, Pdiff and PKP waveforms have been recorded per year by OBSs at high corner frequency of 0.1 Hz with a minimum Mw 5.3 - 6.0. The number of recording drops to less than 5 per year at 1 Hz with Mw ≥ 6.4 and distances less than _

  1. The influence of noise sources on cross-correlation amplitudes

    CERN Document Server

    Hanasoge, Shravan M

    2012-01-01

    We use analytical examples and asymptotic forms to examine the mathematical structure and physical meaning of the seismic cross correlation measurement. We show that in general, cross correlations are not Green's functions of medium, and may be very different depending on the source distribution. The modeling of noise sources using spatial distributions as opposed to discrete collections of sources is emphasized. When stations are illuminated by spatially complex source distributions, cross correlations show arrivals at a variety of time lags, from zero to the maximum surface-wave arrival time. Here, we demonstrate the possibility of inverting for the source distribution using the energy of the full cross-correlation waveform. The interplay between the source distribution and wave attenuation in determining the functional dependence of cross correlation energies on station-pair distance is quantified. Without question, energies contain information about wave attenuation. However, the accurate interpretation o...

  2. Documenting and Assessing Dolphin Calls and Ambient and Anthropogenic Noise Levels via PAM and a SPL Meter.

    Science.gov (United States)

    Dudzinski, Kathleen M; Melillo-Sweeting, Kelly; Gregg, Justin D

    2016-01-01

    Song Meter SM2M marine recorders were deployed to document dolphin calls and ambient and anthropogenic noise. Recordings from Bimini were split into 2-h segments; no segment was without dolphin calls. At Dolphin Encounters, average noise levels ranged from 110 to 125 dB; the highest source level was 147.98 dB re 1 μPa at 1 m. Average ambient-noise levels documented at 4 sites in Guam were below 118 dB re 1 μPa at 1 m. These data were compared with values from a custom-built sound pressure level (SPL) meter and confirm that the SM2M recorder is a useful tool for assessing animal calls and ambient and anthropogenic noise levels. PMID:26610966

  3. Normalized intensity correlation function of single-mode laser system driven by colored cross-correlation noises

    Institute of Scientific and Technical Information of China (English)

    Bing Wang; Xiuqing Wu

    2008-01-01

    @@ Considering a single-mode laser system with cross-correlated additive colored noise and multiplicative colored noise, we study the effects of correlation among noises on the normalized intensity correlation function C(s).C(s) is derived by means of the projection operator method.

  4. Intensity Correlation Function of a Single-Mode Laser Driven by Two Colored Noises with Colored Cross-Correlation

    Institute of Scientific and Technical Information of China (English)

    HANLi-Bo; CAOLi; WUDa-Jin; WANGJun

    2004-01-01

    By using the linear approximation method, the intensity correlation function and the intensity correlation time are calculated in a gain-noise model of a single-mode laser driven by colored cross-correlated pump noise and quantum noise, each of which is colored. We detect that, when the cross-correlation between both noises is negative, the behavior of the intensity correlation function C(t) versus time t, in addition to decreasing monotonously, also exhibits several other cases, such as one maximum, one minimum, and two extrema (one maximum and one minimum), i.e., some parameters of the noises can greatly change the dependence of the intensity correlation function upon time. Moreover, we find that there is a minimum Tmin in the curve of the intensity correlation time versus the pump noise intensity, and the depth and position of Train strongly depend on the quantum noise self-correlation time T2 and cross-correlation time T3.

  5. Asymptotically Sufficient Statistics in Nonparametric Regression Experiments with Correlated Noise

    OpenAIRE

    Carter, Andrew V

    2009-01-01

    We find asymptotically sufficient statistics that could help simplify inference in nonparametric regression problems with correlated errors. These statistics are derived from a wavelet decomposition that is used to whiten the noise process and to effectively separate high-resolution and low-resolution components. The lower-resolution components contain nearly all the available information about the mean function, and the higher-resolution components can be used to estimate the error covarianc...

  6. Effects of noise from non-traffic-related ambient sources on sleep: Review of the literature of 1990-2010

    Directory of Open Access Journals (Sweden)

    Sarah Omlin

    2011-01-01

    Full Text Available This article reviews the literature about the effects of specific non-traffic-related ambient noise sources on sleep that appeared in the last two decades. Although everybody is faced with noise of non-traffic and non-industry origin (e.g. sounds made by neighbors, talk, laughter, music, slamming doors, structural equipment, ventilation, heat pumps, noise from animals, barking dogs, outdoor events etc., little scientific knowledge exists about its effects on sleep. The findings of the present extensive literature search and review are as follows: Only a small number of surveys, laboratory and field studies about mainly neighborhood, leisure and animal noise have been carried out. Most of them indicate that ambient noise has some effect on human sleep. However, a quantitative meta-analysis and comparison is not possible due to the small number of studies available and at times large differences in quality.

  7. Effects of noise from non-traffic-related ambient sources on sleep: review of the literature of 1990-2010.

    Science.gov (United States)

    Omlin, Sarah; Bauer, Georg F; Brink, Mark

    2011-01-01

    This article reviews the literature about the effects of specific non-traffic-related ambient noise sources on sleep that appeared in the last two decades. Although everybody is faced with noise of non-traffic and non-industry origin (e.g. sounds made by neighbors, talk, laughter, music, slamming doors, structural equipment, ventilation, heat pumps, noise from animals, barking dogs, outdoor events etc.), little scientific knowledge exists about its effects on sleep. The findings of the present extensive literature search and review are as follows: Only a small number of surveys, laboratory and field studies about mainly neighborhood, leisure and animal noise have been carried out. Most of them indicate that ambient noise has some effect on human sleep. However, a quantitative meta-analysis and comparison is not possible due to the small number of studies available and at times large differences in quality. PMID:21768734

  8. A 3D Seismic Velocity Model Offshore Southern California from Ambient Noise Tomography of the ALBACORE OBS Array

    Science.gov (United States)

    Kohler, M. D.; Bowden, D. C.; Tsai, V. C.; Weeraratne, D. S.

    2015-12-01

    The Pacific-North America plate boundary in Southern California extends far west of the coastline, and a 12-month ocean bottom seismometer (OBS) array spanned the western side of the plate boundary to image lithospheric seismic velocities. Velocities are modeled through stacked cross correlations of ambient noise data. Twelve months of continuous data were used from 22 OBS stations and ~30 coastal and island Southern California Seismic Network stations. Particular attention has been paid to improving signal-to-noise ratios in the noise correlations with OBS stations by removing the effects of instrument tilt and infragravity waves. Different applications of preprocessing techniques allow us to distinguish the fundamental and first higher order Rayleigh modes, especially in deep water OBS pairs where the water layer dominates crustal sensitivity of the fundamental mode. Standard time domain and frequency domain methods are used to examine surface wave dispersion curves for group and phase velocities between 5 and 50 second periods, and these are inverted for 3D velocity structure. The results define the transition in three dimensions from continental lithospheric structure in the near-shore region to oceanic structure west of the continental borderland. While the most prominent features of the model relate to thinning of the crust west of the Patton Escarpment, other notable anomalies are present north-to-south throughout the continental borderland and along the coast from the Los Angeles Basin to the Peninsular Ranges. The velocity model will help describe the region's tectonic history, as well as provide new constraints for determination of earthquake relocations and rupture styles.

  9. Metallic-thin-film instability with spatially correlated thermal noise.

    Science.gov (United States)

    Diez, Javier A; González, Alejandro G; Fernández, Roberto

    2016-01-01

    We study the effects of stochastic thermal fluctuations on the instability of the free surface of a flat liquid metallic film on a solid substrate. These fluctuations are represented by a stochastic noise term added to the deterministic equation for the film thickness within the long-wave approximation. Unlike the case of polymeric films, we find that this noise, while remaining white in time, must be colored in space, at least in some regimes. The corresponding noise term is characterized by a nonzero correlation length, ℓ_{c}, which, combined with the size of the system, leads to a dimensionless parameter β that accounts for the relative importance of the spatial correlation (β∼ℓ_{c}^{-1}). We perform the linear stability analysis (LSA) of the film both with and without the noise term and find that for ℓ_{c} larger than some critical value (depending on the system size), the wavelength of the peak of the spectrum is larger than that corresponding to the deterministic case, while for smaller ℓ_{c} this peak corresponds to smaller wavelength than the latter. Interestingly, whatever the value of ℓ_{c}, the peak always approaches the deterministic one for larger times. We compare LSA results with the numerical simulations of the complete nonlinear problem and find a good agreement in the power spectra for early times at different values of β. For late times, we find that the stochastic LSA predicts well the position of the dominant wavelength, showing that nonlinear interactions do not modify the trends of the early linear stages. Finally, we fit the theoretical spectra to experimental data from a nanometric laser-melted copper film and find that at later times, the adjustment requires smaller values of β (larger space correlations). PMID:26871167

  10. Quantum Stackelberg duopoly in the presence of correlated noise

    Energy Technology Data Exchange (ETDEWEB)

    Khan, Salman; Ramzan, M; Khan, M Khalid, E-mail: sksafi@phys.qau.edu.p, E-mail: mramzan@phys.qau.edu.p, E-mail: mkkhan@qau.edu.p [Department of Physics, Quaid-i-Azam University, Islamabad 45320 (Pakistan)

    2010-09-17

    We study the influence of entanglement and correlated noise using correlated amplitude damping, depolarizing and phase damping channels on the quantum Stackelberg duopoly. Our investigations show that under the influence of an amplitude damping channel a critical point exists for an unentangled initial state at which firms get equal payoffs. The game becomes a follower advantage game when the channel is highly decohered. Two critical points corresponding to two values of the entanglement angle are found in the presence of correlated noise. Within the range of these limits of the entanglement angle, the game is a follower advantage game. In the case of a depolarizing channel, the payoffs of the two firms are strongly influenced by the memory parameter. The presence of quantum memory ensures the existence of the Nash equilibrium for the entire range of decoherence and entanglement parameters for both the channels. A local maximum in the payoffs is observed which vanishes as the channel correlation increases. Moreover, under the influence of the depolarizing channel, the game is always a leader advantage game. Furthermore, it is seen that the phase damping channel does not affect the outcome of the game.

  11. Normal Mode Analysis of Ambient-Noise Induced Free Oscillations of a Slender Medieval Masonry Tower in Bologna (Italy)

    Science.gov (United States)

    Morelli, A.; Azzara, R. M.; Cavaliere, A.; Zaccarelli, L.

    2014-12-01

    Analysis of the oscillations of buildings — either excited by earthquakes or by ambient noise — has become an effective tool to evaluate the response of such structures to strong ground motion, and hence to assess their seismic vulnerability. Response to small-amplitude ground motion may also provide crucial information on the elastic and anelastic properties of a structure — essential in the case of historical buildings — and constrain numerical full dynamic structural analyses. We report about an analysis carried out for a tall medieval monumental building in the urban center of the Norther Italian city of Bologna. Seismic monitoring, carried on for six months using field seismic instrumentation, has revealed the response to ambient noise, and has allowed to reconstruct, with high detail, the free oscillation modes of the tower. At 97 meters, the XII-century tower of the Asinelli is the tallest masonry building in Europe, and the most slender. We measured the fundamental, and several higher-order, flexural normal modes of oscillation, as well as the fundamental torsional mode. Asymmetry due to non-coincidence of centers of mass and of stiffness produces slightly different modal frequencies of oscillation in two orthogonal directions, consistently with dynamical modeling. Horizontal particle-motion polarization plots show the cyclic energy transfer between two degrees of freedom of the system. The Asinelli spectral signature can also be easily recognized in the motion recorded at the base of nearby Garisenda. We verify that there is correlation of spectral amplitudes with time of the day — in agreement with expected time-variance of anthropic disturbance —- but also with wind velocity and, intriguingly, with temperature variations inside the buidings. We are using these data to adjust the numerical dynamical models of the buildings, to examine time variations of behavior, and to identify the origin of anthropogenic sources of vibration in view of their

  12. Laser-noise-induced correlations and anti-correlations in Electromagnetically Induced Transparency

    CERN Document Server

    Cruz, L S; Gómez, J G A; Lezama, A; Martinelliinst1, M; Nussenzveig, P; Valente, P

    2006-01-01

    High degrees of intensity correlation between two independent lasers were observed after propagation through a rubidium vapor cell in which they generate Electromagnetically Induced Transparency (EIT). As the optical field intensities are increased, the correlation changes sign (becoming anti-correlation). The experiment was performed in a room temperature rubidium cell, using two diode lasers tuned to the $^{85}$Rb $D_2$ line ($\\lambda = 780$nm). The cross-correlation spectral function for the pump and probe fields is numerically obtained by modeling the temporal dynamics of both field phases as diffusing processes. We explored the dependence of the atomic response on the atom-field Rabi frequencies, optical detuning and Doppler width. The results show that resonant phase-noise to amplitude-noise conversion is at the origin of the observed signal and the change in sign for the correlation coefficient can be explained as a consequence of the competition between EIT and Raman resonance processes.

  13. V S Profiles from Noise Cross Correlation at Local and Small Scale

    Science.gov (United States)

    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.

  14. Italian and Alpine crustal structure: results from ambient-noise surface-wave imaging.

    Science.gov (United States)

    Molinari, Irene; Boschi, Lapo; Verbeke, Julie; Morelli, Andrea; Kissling, Eduard

    2015-04-01

    Surface-wave dispersion measurements based on seismic background signal (ambient noise) are a very effective means to image S-wave velocity at crustal and lithospheric depths. The goal of our study is to integrate new ambient noise data for central Europe with more traditional models of crustal heterogeneity and discontinuity depths. We exploit the large database of one-year-long records of European ambient noise compiled by Verbeke et al. (2012) to test the surface wave dispersion predicted by the most recent crustal models, such as EPcrust (Molinari and Morelli, 2011), CRUST2.0 and LITHO1.0 (Pasyanos et al, 2014). We use the same data to further improve EPcrust, obtaining a new three-dimensional model of Italian and Alpine crustal structure (with a resolution of 0.25 degrees x 0.25 degrees). We obtain a set of Rayleigh-wave group and phase velocity maps at periods between 5 and 37 s as a resulting of a linear least squares inversion of the available phase and group-velocity measurements. At relatively short periods, these maps clearly reflect the surface geology of the region, e.g. low velocity zones at the Po Plain; longer-period maps reveal deeper structures such as Moho topography under Alps and Apennines, and lower crustal anomalies. The phase and group-velocity maps are next jointly inverted via the Neighborhood Algorithm to determine a set of one-dimensional shear-velocity models (one per surface wave velocity pixel), which are in turn interpolated to build a new three-dimensional model and Moho depth. The reconstructed model shows the low velocity area beneath the Po Plain; the contrast between the low-velocity crust of the Adriatic domain and the high-velocity crust of the Tyrrhenian domain is clearly seen, as well as an almost uniform crystalline crust beneath the Alpine belt. Our results are physically consistent with the information for velocity structure and Moho depth independently obtained by other seismic methods.

  15. New developments in ambient noise analysis to characterise the seismic response of landslide-prone slopes

    Directory of Open Access Journals (Sweden)

    V. Del Gaudio

    2013-08-01

    Full Text Available We report on new developments in the application of ambient noise analysis applied to investigate the dynamic response of landslide-prone slopes to seismic shaking, with special attention to the directional resonance phenomena recognised in previous studies. These phenomena can be relevant for seismic slope susceptibility, especially when maximum resonance orientation is close to potential sliding directions. Therefore, the implementation of an effective technique for site response directivity detection is of general interest. In this regard methods based on the calculation of horizontal-to-vertical noise spectral ratio (HVNR are promising. The applicability of such methods is investigated in the area of Caramanico Terme (central Italy, where ongoing accelerometer monitoring of slopes with different characteristics offers the possibility of validation of HVNR analysis. The noise measurements, carried out in different times to test the result repeatability, revealed that sites affected by response directivity persistently show major peaks with a common orientation, consistent with the resonance direction inferred from accelerometer data. In some cases such a directivity turned out parallel to maximum slope direction, but this cannot be considered a systematic feature of slope dynamic response. At sites where directivity is absent, the HVNR peaks do not generally show a preferential orientation, with rare exceptions that could be linked to the presence of temporarily active sources of polarised noise. The observed variations of spectral ratio amplitude can be related to temporal changes in site conditions (e.g. groundwater level/soil water content variations affecting P wave velocity and Poisson's ratio of surficial layer, which can hinder the recognition of main resonance frequencies. Therefore, we recommend conducting simultaneous measurements at nearby sites within the same study area and repeating measurements at different times in order to

  16. MSNoise: a Python Package for Monitoring Seismic Velocity Changes using Ambient Seismic Noise

    Science.gov (United States)

    Lecocq, Thomas; Caudron, Corentin; Brenguier, Florent

    2014-05-01

    We present MSNoise, a complete software suite to compute relative seismic velocity changes under a seismic network, using ambient seismic noise. The whole is written in Python, from the monitoring of data archives, to the production of high quality figures. All steps have been optimized to only compute the necessary steps and to use 'job'-based processing. All steps can be changed by matching the in/outs. MSNoise exposes an API for communication with the data archive and the database. We present a validation of the software on a dataset acquired during the UnderVolc project on the Piton de la Fournaise Volcano, La Réunion Island, France, for which precursory relative changes of seismic velocity are visible for three eruptions betwee 2009 and 2011. MSNoise is available on http://www.msnoise.org

  17. Environmental Resources of Selected Areas of Hawaii: Climate, Ambient Air Quality, and Noise (DRAFT)

    Energy Technology Data Exchange (ETDEWEB)

    Lombardi, D.A.; Blasing, T.J.; Easterly, C.E.; Hamilton, C.B.

    1994-06-01

    This report has been prepared to make available and archive background scientific data and related information on climate, ambient air quality, and ambient noise levels collected during the preparation of the environmental impact statement (EIS) for Phases 3 and 4 of the Hawaii Geothermal Project (HGP) as defined by the state of hawaii in its April 1989 proposal to Congress. The US Department of Energy (DOE) published a notice in the Federal Register on May 17, 1994 withdrawing its Notice of Intent of February 14, 1992, to prepare the HGP-EIS. Since the state of Hawaii is no longer pursuing or planning to pursue the HGP, DOE considers the project to be terminated. The report presents a general description of the climate and air quality for the islands of Hawaii (henceforth referred to as Hawaii), Maui, and Oahu. It also presents a literature review as baseline information on the health effects of hydrogen sulfide. the scientific background data and related information is being made available for use by others in conducting future scientific research in these areas. This report describes the environmental resources present in the areas studied (i.e., the affected environment) and does not represent an assessment of environmental impacts.

  18. Environmental resources of selected areas of Hawaii: Climate, ambient air quality, and noise

    Energy Technology Data Exchange (ETDEWEB)

    Lombardi, D.A.; Blasing, T.J.; Easterly, C.E.; Reed, R.M. [Oak Ridge National Lab., TN (United States); Hamilton, C.B. [Univ. of Tennessee, Knoxville, TN (United States)

    1995-03-01

    This report has been prepared to make available and archive background scientific data and related information on climate, ambient air quality, and ambient noise levels collected during the preparation of the environmental impact statement (EIS) for Phases 3 and 4 of the Hawaii Geothermal Project (HGP) as defined by the state of Hawaii in its April 1989 proposal to Congress. The US Department of Energy (DOE) published a notice withdrawing its Notice of Intent to prepare the HGP-EIS. Since the state of Hawaii is no longer pursuing or planning to pursue the HGP, DOE considers the project to be terminated. The report presents a general description of the climate add air quality for the islands of Hawaii (henceforth referred to as Hawaii), Maui and Oahu. It also presents a literature review as baseline information on the health effects of sulfide. The scientific background data and related information is being made available for use by others in conducting future scientific research in these areas. This report describes the environmental resources present in the areas studied (i.e., the affected environment) and does not represent an assessment of environmental impacts.

  19. Signal detection, modularity and the correlation between extrinsic and intrinsic noise in biochemical networks

    OpenAIRE

    Tanase-Nicola, Sorin; Warren, Patrick B.; Wolde, Pieter Rein ten

    2005-01-01

    Understanding cell function requires an accurate description of how noise is transmitted through biochemical networks. We present an analytical result for the power spectrum of the output signal of a biochemical network that takes into account the correlations between the noise in the input signal (the extrinsic noise) and the noise in the reactions that constitute the network (the intrinsic noise). These correlations arise from the fact that the reactions by which biochemical signals are det...

  20. Enhanced current noise correlations in a Coulomb-Majorana device

    Science.gov (United States)

    Lü, Hai-Feng; Lu, Hai-Zhou; Shen, Shun-Qing

    2016-06-01

    Majorana bound states (MBSs) nested in a topological nanowire are predicted to manifest nonlocal correlations in the presence of a finite energy splitting between the MBSs. However, the signal of the nonlocal correlations has not yet been detected in experiments. A possible reason is that the energy splitting is too weak and seriously affected by many system parameters. Here we investigate the charging energy induced nonlocal correlations in a hybrid device of MBSs and quantum dots. The nanowire that hosts the MBSs is assumed in proximity to a mesoscopic superconducting island with a finite charging energy. Each end of the nanowire is coupled to one lead via a quantum dot with resonant levels. With a floating superconducting island, the devices show a negative differential conductance and giant super-Poissonian shot noise, due to the interplay between the nonlocality of the MBSs and dynamical Coulomb blockade effect. When the island is strongly coupled to a bulk superconductor, the current cross correlations at small lead chemical potentials are negative by tuning the dot energy levels. In contrast, the cross correlation is always positive in a non-Majorana setup. This difference may provide a signature for the existence of the MBSs.

  1. Quantum correlations of identical particles subject to classical environmental noise

    Science.gov (United States)

    Beggi, Andrea; Buscemi, Fabrizio; Bordone, Paolo

    2016-06-01

    In this work, we propose a measure for the quantum discord of indistinguishable particles, based on the definition of entanglement of particles given in Wiseman and Vaccaro (Phys Rev Lett 91:097902, 2003. doi: 10.1103/PhysRevLett.91.097902). This discord of particles is then used to evaluate the quantum correlations in a system of two identical bosons (fermions), where the particles perform a quantum random walk described by the Hubbard Hamiltonian in a 1D lattice. The dynamics of the particles is either unperturbed or subject to a classical environmental noise—such as random telegraph, pink or brown noise. The observed results are consistent with those for the entanglement of particles, and we observe that on-site interaction between particles have an important protective effect on correlations against the decoherence of the system.

  2. Validation of S-wave Velocity beneath the Ise Bay, Central Japan, Using Continuous Short-period Ambient Noise Data

    Science.gov (United States)

    Hayashida, T.; Yoshimi, M.; Horikawa, H.

    2014-12-01

    We have applied seismic interferometry to three-component ambient noise data recorded around the Ise bay area, central Japan, to validate published three-dimensional S-wave velocity models. For the bay area, detailed seismic velocity structure models have been constructed based on P-wave reflection surveys. There is no direct information on the S-wave velocities beneath the bay and the parameters are assigned by reference to those in a land area. We used one-year continuous data from 20 permanent stations of the NIED Hi-net (High-sensitivity seismograph network) to obtain stacked cross-correlation functions (CCFs) of ambient noise between station pairs that cross the bay. The CCFs were calculated, using one-hour data in the radial-radial (R-R), transverse-transverse (T-T) and vertical-vertical (Z-Z) directions for time lags of ±500s. Horizontal distances between the stations range form 15 km to 103 km. Although the Hi-net stations deploy seismometers with the natural period of 1 s, we found that the yearly stacked CCFs for selected 101 Hi-net station pairs are comparable with those derived from neighboring broadband seismic stations in the frequency range between 0.1 and 0.5 Hz, by deconvolving the instrument response. The CCFs shows clear Rayleigh waves from all directions in the R-R and Z-Z components, and clear Love waves in the T-T component with reasonable signal-to-noise ratios. The derived group velocities and waveforms of the wave trains are variable in the higher frequency range (> 0.2 Hz), indicating deep sedimentary basin beneath the bay. We compared obtained group velocities with theoretical ones to find systematic differences between the expected structure model from the CCFs and the published models in the northwest part of the bay, while the agreements are generally good for many other station pairs. This result indicates that the seismic interferometry technique provides valuable information for validation and improvement of a velocity structure

  3. Effects of time delay and noise correlation on noise enhanced stability and resonant activation in a periodically modulated bistable system

    International Nuclear Information System (INIS)

    This work analyzes numerically the effects of delay time τ and cross-correlation strength between noises λ on the phenomena of noise enhanced stability (NES) and resonant activation (RA) in a periodically modulated bistable system. The simulation results indicate that: (i) multiplicative noise can produce the NES effect only for the larger λ, while additive noise always induces the NES effect; (ii) for the NES phenomenon induced by additive noise, there is a characteristic value of τ, below which the increasing of τ enhances it and above which the effect of τ reverses; however, the increasing of τ can only enhance the NES effect induced by multiplicative noise; (iii) increasing λ weakens the NES effect induced by additive noise and strengthens that induced by multiplicative noise; and (iv) the RA effect becomes more and more pronounced while the RA minimum of the mean first-passage time increases with the increase of λ or τ. (paper)

  4. Numerical Simulation of Target Range Estimation Using Ambient Noise Imaging with Acoustic Lens

    Science.gov (United States)

    Mori, Kazuyoshi; Ogasawara, Hanako; Nakamura, Toshiaki; Tsuchiya, Takenobu; Endoh, Nobuyuki

    2010-07-01

    In ambient noise imaging (ANI), each pixel of a target image is mapped by either monochrome or pseudo color to represent its acoustic intensity in each direction. This intensity is obtained by measuring the target object's reflecting or scattering wave, with ocean background noise serving as the sound source. In the case of using an acoustic lens, the ANI system creates a C-mode-like image, where receivers are arranged on a focal plane and each pixel's color corresponds to the intensity of each receiver output. There is no consideration for estimating a target range by this method, because it is impossible to measure the traveling time between a transducer and a target by a method like an active imaging sonar. In this study, we tried to estimate a target range using the ANI system with an acoustic lens. Here, we conducted a numerical simulation of sound propagation based on the principle of the time reversal mirror. First, instead of actual ocean measurements in the forward propagation, we calculated the scattering wave from a rigid target object in an acoustic noise field generated by a large number of point sources using the two-dimensional (2D) finite difference time domain (FDTD) method. The time series of the scattering wave converged by the lens was then recorded on each receiver. The sound pressure distribution assuming that the time-reversed wave of the scattering wave was reradiated from each receiver position was also calculated using the 2D FDTD method in the backward propagation. It was possible to estimate a target range using the ANI system with an acoustic lens, because the maximum position of the reradiated sound pressure field was close to the target position.

  5. Damage Detection of Structures for Ambient Loading Based on Cross Correlation Function Amplitude and SVM

    Directory of Open Access Journals (Sweden)

    Lin-sheng Huo

    2016-01-01

    Full Text Available An effective method for the damage detection of skeletal structures which combines the cross correlation function amplitude (CCFA with the support vector machine (SVM is presented in this paper. The proposed method consists of two stages. Firstly, the data features are extracted from the CCFA, which, calculated from dynamic responses and as a representation of the modal shapes of the structure, changes when damage occurs on the structure. The data features are then input into the SVM with the one-against-one (OAO algorithm to classify the damage status of the structure. The simulation data of IASC-ASCE benchmark model and a vibration experiment of truss structure are adopted to verify the feasibility of proposed method. The results show that the proposed method is suitable for the damage identification of skeletal structures with the limited sensors subjected to ambient excitation. As the CCFA based data features are sensitive to damage, the proposed method demonstrates its reliability in the diagnosis of structures with damage, especially for those with minor damage. In addition, the proposed method shows better noise robustness and is more suitable for noisy environments.

  6. Stochastic resonance in a bistable system with coloured correlation between additive and multiplicative noise

    Institute of Scientific and Technical Information of China (English)

    Luo Xiao-Qin; Zhu Shi-Qun

    2004-01-01

    The phenomenon of stochastic resonance (SR) in a bistable nonlinear system with coupling between additive and multiplicative noises is investigated when the correlation between two noise terms is coloured. It is found that the signal-to-noise ratio (SNR) of the system is affected not only by the coupling strength λ between two noise terms, but also by the noise correlation time . The SNR is changed from a single peak, to two peaks with a dip, and then to a monotonically decreasing function with noise strength. The dependence of the SR on the initial conditions is entirely caused by the coupling strength λ between two noise terms.

  7. Feasibility of retrieving time-lapse reflection signals using ambient-noise seismic interferometry at Ketzin, Germany

    NARCIS (Netherlands)

    Boullenger, B.; Verdel, A.; Paap, B.; Draganov, D.S.

    2015-01-01

    Ambient-noise seismic interferometry (ANSI) applied to passive body-wave measurements retrieves an estimate of the reflection response as if from a source at a receiver position. Often, the limited compliance with theoretical assumptions causes erroneous absolute amplitudes of the retrieved physical

  8. Studying CO2 storage with ambient-noise seismic interferometry: A combined numerical feasibility study and field-data example for Ketzin, Germany

    NARCIS (Netherlands)

    Boullenger, B.; Verdel, A.; Paap, B.; Thorbecke, J.W.; Draganov, D.S.

    2015-01-01

    Seismic interferometry applied to ambient-noise measurements allows the retrieval of the seismic response between pairs of receivers. We studied ambient-noise seismic interferometry (ANSI) to retrieve time-lapse reflection responses from a reservoir during CO2 geologic sequestration, using the case

  9. Seismic local site effects characterization in the Andarax River Valley (SE Spain) from ambient seismic noise

    Science.gov (United States)

    Carmona, Enrique; García-Jerez, Antonio; Luzón, Francisco; Sánchez-Martos, Francisco; Sánchez-Sesma, Francisco J.; Piña, José

    2014-05-01

    This work is focused on the characterization of seismic local effects in the Low Andarax River Valley (SE Spain). The Low Andarax River valley is located in an active seismic region, with the higher seismic hazard values in Spain. The landform is composed mainly by sedimentary materials which increase its seismic hazard due to the amplification of the seismic inputs and spectral resonances. We study seismic local effects in the Low Andarax River by analyzing the Horizontal-to-Vertical Spectral Ratio (HVSR) of ambient noise records. The noise data were recorded during two field campaigns in 2012 and 2013. There have been a total of 374 noise measurements with 15 and 30 minutes duration. The acquisition was performed with a Digital Broadband Seismometer Guralp CMG-6TD. The distance between measurements was about 200 meters, covering an area around 40 km2. There have been 6 significant peak frequencies between 0.3 Hz and 5 Hz. It was possible to find interesting areas with similar spectral peaks that coincide with zones with similar microgravimetric anomalies at the alluvial valley. It is also observed a decrease in the frequency peaks from West to East suggesting increased sediment layer. We also compute the soil models at those sites where geotechnical information is available, assuming that the seismic noise is diffuse. We invert the HVSR for these places using horizontally layered models and in the imaginary part the Green functions at the source. It is observed that the S wave velocity inverted models are consistent with the known geotechnical information obtained from drilled boreholes. We identify the elastodynamic properties of the limestone-dolomite materials with a formation of phyllites and quartzite that form the basement of the depression, and those properties of the Miocene and Pliocene detrital deposits (marls, sandy silts, sands and conglomerates) that fill the valley. These results together with the observed resonant frequencies along the Andarax

  10. Mutual Information of Pauli Channels with Correlated Noise

    Institute of Scientific and Technical Information of China (English)

    HOU Li-zhen; FANG Mao-Fa

    2007-01-01

    A general formula for the mutual information of the Pauli channels with memory modelled by correlated noise is derived.It is shown that the mutual information depends on the channel shrinking factor,the input state parameter and the channel memory coefficient.The analyses based on the general formula reveal that the entanglement is always a useful resource to enhance the mutual information of some.Pauli channels,such as the bit flip channel and the bit-phase flip channel.Our analyses also show that the entanglement is not advantageous to the reliable transmission of classical information for Borne Pauli channels at any time,such as the phase flip channel and the phase damping channel.

  11. Microseism source direction from noise cross-correlation

    Science.gov (United States)

    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.

  12. Ambient noise tomography of the Cameroon Volcanic Line and Northern Congo craton: new constraints on the structure of the lithosphere

    Science.gov (United States)

    Guidarelli, M.; Aoudia, A.

    2016-03-01

    We investigate the lithospheric structure of Cameroon inverting Rayleigh waves obtained from the cross-correlation of ambient seismic noise. We correlate seismic records between 32 broad-band stations and we obtain good quality Rayleigh waves for 310 interstation paths. We measure group velocity dispersion curves from the reconstructed Rayleigh waves in the period range 10-35 s and we invert the group velocities for tomographic images. After the tomography the group velocities are then inverted, together with longer period group velocity measurements from existing literature, to compute a 3-D S-wave velocity model of the Cameroon lithosphere down to 100 km depth. Our results provide an unprecedented mapping of the physical properties of the different crustal units and their correlations with surface geology, as well as with mantle lithospheric variations. The Cameroon Volcanic Line (CVL) appears as a segmented feature exhibiting different physical properties along strike. The active Mt Cameroon volcano is underlain by very low velocities, unlike the other segments of the CVL. The along-strike variations in crustal structure suggest that lateral heterogeneities in lithospheric thickness and physical properties have influenced the location and distribution of magmatism. The crust beneath the Central African Shear Zone exhibits a sizeable low velocity anomaly. The lithosphere beneath Cameroon is characterised by a heterogeneous crust with a relatively constant thickness and a low velocity uppermost mantle at the edge of the Congo Craton. Our results favour processes combining small-scale upwelling at the edge of a thick lithosphere and reactivation of Precambrian basement structures to explain the distribution of Holocene-Recent magmatism and plateau uplift. Our results also indicate that Mt Cameroon and surroundings areas are the most at risk zones for magmatic activity during this stage of CVL development.

  13. Intensity Correlation Function of a Single-Mode Laser Driven by Two Colored Noises with Colored Cross-Correlation

    Institute of Scientific and Technical Information of China (English)

    HAN Li-Bo; CAO Li; WU Da-Jin; WANG Jun

    2004-01-01

    By using the linear approximation method, the intensity correlation function and the intensity correlation time are calculated in a gain-noise model of a single-mode laser driven by colored cross-correlated pump noise and quantum noise, each of which is colored. We detect that, when the cross-correlation between both noises is negative, the behavior of the intensity correlation function C(t) versus time t, in addition to decreasing monotonously, also exhibits several other cases, such as one maximum, one minimum, and two extrema (one maximum and one minimum), i.e., some parameters of the noises can greatly change the dependence of the intensity correlation function upon time. T3.

  14. Column-Parallel Correlated Multiple Sampling Circuits for CMOS Image Sensors and Their Noise Reduction Effects

    OpenAIRE

    Shoji Kawahito; Shinya Itoh; Satoshi Aoyama; Sungho Suh

    2010-01-01

    For low-noise complementary metal-oxide-semiconductor (CMOS) image sensors, the reduction of pixel source follower noises is becoming very important. Column-parallel high-gain readout circuits are useful for low-noise CMOS image sensors. This paper presents column-parallel high-gain signal readout circuits, correlated multiple sampling (CMS) circuits and their noise reduction effects. In the CMS, the gain of the noise cancelling is controlled by the number of samplings. It has a similar effec...

  15. 3D shallow structures in the Baogutu area, Karamay, determined by eikonal tomography of short-period ambient noise surface waves

    Science.gov (United States)

    Xu, Hongrui; Luo, Yinhe; Chen, Chao; Xu, Yixian

    2016-06-01

    Eikonal tomography based on ambient noise data is one of the most effective methods to reveal shallow earth structures. By tracking surface wave phase fronts, constructing travel time surfaces, and computing the gradients of travel time surfaces to generate phase velocity maps, eikonal tomography avoids the ray tracing and matrix construction and inversion in the traditional surface wave tomography methods. In this study, we collect continuous ambient noise data recorded by a dense seismic array in Karamay, Xinjiang to construct a 3D model of shallow structures using eikonal tomography. The seismic array consists of 35 stations with shortest interstation distance close to 1 km. 890 empirical surface wave Green's functions (EGFs) between each station pair are retrieved by cross-correlating one or two months of continuous ambient noise data. From these EGFs, surface wave travel times in the frequency range of 1.8 to 4.0 Hz are measured by a frequency-time analysis technique (FTAN). Then, eikonal tomography is adopted to construct Rayleigh wave phase velocity maps and estimate the phase velocity uncertainties. Finally, we invert the obtained phase velocity dispersion curves for 1D shear velocity profiles and then assemble these 1D profiles to construct a 3D shear velocity model. Major velocity features of our 3D model are correlated well with the known geological features. A shallow east-west velocity discontinuity is observed, which clearly reflects the lithological change between Baogutu formation (C1b) and Xibeikulasi formation (C1x) of lower Carboniferous system. Low shear velocities are observed beneath the location of porphyry copper deposit (V), possibly related to stockwork fracture and hydrothermal brecciation developed during the intrusion of deep magma in forming the deposit.

  16. Crustal imaging of western Michoacán and the Jalisco Block, Mexico, from Ambient Seismic Noise

    Science.gov (United States)

    Spica, Zack; Cruz-Atienza, Víctor M.; Reyes-Alfaro, Gabriel; Legrand, Denis; Iglesias-Mendoza, Arturo

    2014-12-01

    Detailed crustal imaging of western Michoacán and the Jalisco Block is obtained from ambient noise tomography. Results show a deep and well-delineated volcanic system below the Colima volcano complex, rooting up to ~ 22 km depth, with a shallow magmatic chamber constrained to the first ~ 7 km. A shallow low-velocity system to the south of the Chapala rift and west of the Michoacán-Guanajuato volcanic field merges, underneath the Colima rift, with the Colima volcano system at about 20 km depth, honoring the geometry of the Trans-Mexican Volcanic Belt. For depths greater than ~30 km, low-velocity features become parallel to the slab strike, right beneath the Mascota, Ayutla and Tapalpa volcanic fields, suggesting the presence of the mantle wedge above the Rivera plate. All mentioned low-velocity bodies are spatially correlated with the superficial volcanic activity suggesting their magmatic origin so that, the shallower these bodies, the younger are the associated volcanic deposits. Along the coast, different depths of the uppermost layer of the Rivera and the Cocos plates suggest that the latter plate subducts with an angle ~ 9° steeper than the former.

  17. Effects of cross-correlated noises on the relaxation time of the bistable system

    Institute of Scientific and Technical Information of China (English)

    谢崇伟; 梅冬成

    2003-01-01

    The stationary correlation function and the associated relaxation time for a general system driven by crosscorrelated white noises are derived, by virtue of a Stratonovich-like ansatz. The effects of correlated noises on the relaxation time of a bistable kinetic model coupled to an additive and a multiplicative white noises are studied. It is proved that for small fluctuations the relaxation time Tc as a function of λ (the correlated intensity between noises)exhibits very different behaviours for α< D and for α> D (α and D, respectively, stand for the intensities of additive and multiplicative noises). When α> D, Tc increases with increasing λ. But when α< D, Tc increases with λ for the case of weak correlated noises and sharply decreases with λ for the case of strong correlated noises, and thus Tc-λ curve behaves with one extremum.

  18. Ground motion in the presence of complex topography: Earthquake and ambient noise sources

    Science.gov (United States)

    Hartzell, Stephen; Meremonte, Mark; Ramírez-Guzmán, Leonardo; McNamara, Daniel

    2014-01-01

    To study the influence of topography on ground motion, eight seismic recorders were deployed for a period of one year over Poverty Ridge on the east side of the San Francisco Bay Area, California. This location is desirable because of its proximity to local earthquake sources and the significant topographic relief of the array (439 m). Topographic amplification is evaluated as a function of frequency using a variety of methods, including reference‐site‐based spectral ratios and single‐station horizontal‐to‐vertical spectral ratios using both shear waves from earthquakes and ambient noise. Field observations are compared with the predicted ground motion from an accurate digital model of the topography and a 3D local velocity model. Amplification factors from the theoretical calculations are consistent with observations. The fundamental resonance of the ridge is prominently observed in the spectra of data and synthetics; however, higher‐frequency peaks are also seen primarily for sources in line with the major axis of the ridge, perhaps indicating higher resonant modes. Excitations of lateral ribs off of the main ridge are also seen at frequencies consistent with their dimensions. The favored directions of resonance are shown to be transverse to the major axes of the topographic features.

  19. Electromechanical Wave Green's Function Estimation from Ambient Electrical Grid Frequency Noise

    CERN Document Server

    Backhaus, Scott

    2011-01-01

    Many electrical grid transients can be described by the propagation of electromechanical (EM) waves that couple oscillations of power flows over transmission lines and the inertia of synchronous generators. These EM waves can take several forms: large-scale standing waves forming inter-area modes, localized oscillations of single or multi-machine modes, or traveling waves that spread quasi-circularly from major grid disturbances. The propagation speed and damping of these EM waves are potentially a powerful tool for assessing grid stability, e.g. small signal or rotor angle stability, however, EM wave properties have been mostly extracted from post-event analysis of major grid disturbances. Using a small set of data from the FNET sensor network, we show how the spatially resolved Green's function for EM wave propagation can be extracted from ambient frequency noise without the need for a major disturbance. If applied to an entire interconnection, an EM-wave Green's function map will enable a model-independent...

  20. ambiental

    Directory of Open Access Journals (Sweden)

    Roque Leal Salcedo

    2008-01-01

    Full Text Available El derecho internacional ambiental es un conocimiento de carácter transversal, que entre otras consideraciones refleja las preocupaciones de la sociedad por la implementación de un modelo de desarrollo sustentable para el respeto a las reglas del medio natural que garantizan la integridad y renovación de los sistemas naturales. El presente artículo enfoca esta visión a través del análisis de material documental revisado, entre ellos tratados internacionales que permiten distinguir el desarrollo del derecho internacional ambiental y el papel de Organización de las Naciones Unidas (ONU, en el propósito común del derecho individual y colectivo de disfrutar de una vida, un ambiente seguro, sano y ecológicamente equilibrado. En función a estas disertaciones las consideraciones finales exponen parte de la visión que ha estructurado la ONU y que representan un aporte considerable en el fomento de la conciencia mundial sobre la necesidad de establecer vínculos entre las naciones para el continuo desarrollo de esta rama del derecho.

  1. Steady-state analysis of a bistable system subject to a coloured multiplicative noise and a white additive noise with coloured cross-correlated noises

    Institute of Scientific and Technical Information of China (English)

    Wang Can-Jun; Chen Shi-Bo; Mei Dong-Cheng

    2006-01-01

    The steady-state properties of a bistable system are investigated when both the multiplicative noise and the coupling between additive and multiplicative noises are coloured with different values of noise correlation times τ1 and 72. After introducing a dimensionless parameter R(R = α/D, D is the intensity of the multiplicative noise and α is the intensity of the additive noise), and performing the numerical computations, we find the following points: (1) For the case ofR > 1, λ (the intensity of correlation between additive and multiplicative noises), τ1 and τ2 can induce the stationary probability distribution (SPD) transition from bimodal to unimodal in structure, but for the cases of R ≤ 1,the bimodal structure is preserved; (2) α can also induce the SPD transition from bimodal to unimodal in structure;(3) the bimodal structure of the SPD exhibits a symmetrical structure as D increases.

  2. Signal-to-noise ratio limitations for intensity correlation imaging.

    Science.gov (United States)

    Fried, David L; Riker, Jim; Agrawal, Brij

    2014-07-01

    Intensity correlation imaging (ICI) is a concept which has been considered for the task of providing images of satellites in geosynchronous orbit using ground-based equipment. This concept is based on the intensity interferometer principle first developed by Hanbury Brown and Twiss. It is the objective of this paper to establish that a sun-lit geosynchronous satellite is too faint a target object to allow intensity interferometry to be used in developing image information about it-at least not in a reasonable time and with a reasonable amount of equipment. An analytic treatment of the basic phenomena is presented. This is an analysis of one aspect of the statistics of the very high frequency random variations of a very narrow portion of the optical spectra of the incoherent (black-body like-actually reflected sunlight) radiation from the satellite, an analysis showing that the covariance of this radiation as measured by a pair of ground-based telescopes is directly proportional to the square of the magnitude of one component of the Fourier transform of the image of the satellite-the component being the one for a spatial frequency whose value is determined by the separation of the two telescopes. This analysis establishes the magnitude of the covariance. A second portion of the analysis considers shot-noise effects. It is shown that even with much less than one photodetection event (pde) per signal integration time an unbiased estimate of the covariance of the optical field's random variations can be developed. Also, a result is developed for the standard deviation to be associated with the estimated value of the covariance. From these results an expression is developed for what may be called the signal-to-noise ratio to be associated with an estimate of the covariance. This signal-to-noise ratio, it turns out, does not depend on the measurement's integration time, Δt (in seconds), or on the optical spectral bandwidth, Δν (in Hertz), utilized-so long as

  3. Full-3D waveform tomography of Southern California crustal structure by using earthquake recordings and ambient noise Green's functions based on adjoint and scattering-integral methods

    Science.gov (United States)

    Lee, E.; Chen, P.; Jordan, T. H.; Maechling, P. J.; Denolle, M.; Beroza, G. C.

    2013-12-01

    We apply a unified methodology for seismic waveform analysis and inversions to Southern California. To automate the waveform selection processes, we developed a semi-automatic seismic waveform analysis algorithm for full-wave earthquake source parameters and tomographic inversions. The algorithm is based on continuous wavelet transforms, a topological watershed method, and a set of user-adjustable criteria to select usable waveform windows for full-wave inversions. The algorithm takes advantages of time-frequency representations of seismograms and is able to separate seismic phases in both time and frequency domains. The selected wave packet pairs between observed and synthetic waveforms are then used for extracting frequency-dependent phase and amplitude misfit measurements, which are used in our seismic source and structural inversions. Our full-wave waveform tomography uses the 3D SCEC Community Velocity Model Version 4.0 as initial model, a staggered-grid finite-difference code to simulate seismic wave propagations. The sensitivity (Fréchet) kernels are calculated based on the scattering integral and adjoint methods to iteratively improve the model. We use both earthquake recordings and ambient noise Green's functions, stacking of station-to-station correlations of ambient seismic noise, in our full-3D waveform tomographic inversions. To reduce errors of earthquake sources, the epicenters and source parameters of earthquakes used in our tomographic inversion are inverted by our full-wave CMT inversion method. Our current model shows many features that relate to the geological structures at shallow depth and contrasting velocity values across faults. The velocity perturbations could up to 45% with respect to the initial model in some regions and relate to some structures that do not exist in the initial model, such as southern Great Valley. The earthquake waveform misfits reduce over 70% and the ambient noise Green's function group velocity delay time variance

  4. SPEECH ENHANCEMENT BASED ON DYNAMIC NOISE ESTIMATION WITHIN AUTO-CORRELATION DOMAIN

    Institute of Scientific and Technical Information of China (English)

    吴亚栋; 吴旭辉

    2002-01-01

    Most noise suppression algorithms of single channel use the mean of noisy segments to estimate the characteristics of noise spectrum, ignoring the estimation of noise in speech segments. Therefore, when the energy level of noise varies with the time, the performance of removing noise will be degraded. To solve this problem, a speech enhancement approach based on dynamic noise estimation within correlation domain was proposed. This method exploits the characteristics that noise energy mainly concentrates on 0 th-order correlation coefficients, signal is auto-correlated but signal and noise, noise and noise are uncorrelated, then estimates and decomposes the noise, thus helps to solve the above-mentioned problem. The results of recognition experiments on speech signals of 15 Chinese cities' names corrupted by noise of exhibition hall shows, this approach is better than SS (Spectral Subtraction) method, adapts better to the variances of energy levels of speech signal corrupted by noise, has some practicability to improve the robustness of recognition systems under noisy environment.

  5. Anisotropic Rayleigh wave tomography of Northeast China using ambient seismic noise

    Science.gov (United States)

    Liu, Zhikun; Huang, Jinli; Yao, Huajian

    2016-07-01

    The ambient noise data recorded by 249 seismic stations in the permanent and temporary networks in Northeast China are used to invert for the isotropic phase velocity and azimuthal anisotropy of Rayleigh waves in the period band 5-50 s. The inversion results reflect the structure from the shallow crust to upper mantle up to approximately 120 km depth. Beneath the Songliao basin, both the fast direction in shallow crust and strike of a low-velocity anomaly in the middle crust are NNE-SSW, which is coincident with the main tectonic trend of the (Paleo) Pacific tectonic domain. This indicates that the rifting of the Songliao basin is influenced by the subduction of (Paleo) Pacific plate. The upper mantle of Songliao block (except the central area of Songliao basin) to the west of Mudanjiang fault, and the east of the North-South Gravity Lineament, is characterized by high-velocity and weak anisotropy up to approximately ​120 km depth. We infer that there is delamination of lithospheric mantle beneath the Songliao block. Obvious N-S, NE-SW, and E-W trending fast directions are found in the lithospheric mantles of the east, west, and south sides of Songliao block, respectively, which coincide with the strikes of the Paleozoic tectonic in these areas. This suggests that the frozen-in anisotropic fabric in the lithospheric mantle can be used to indicate the historical deformation of the lithosphere. In the northern margin of the North China Craton, the spatial variations of phase velocity and azimuthal anisotropy are more dramatic than those in Northeast China blocks, which indicates that the lithosphere of the North China Craton has experienced more complicated tectonic evolution than that of the Northeast China blocks.

  6. Ice shelf structure derived from dispersion curve analysis of ambient seismic noise, Ross Ice Shelf, Antarctica

    Science.gov (United States)

    Diez, A.; Bromirski, P. D.; Gerstoft, P.; Stephen, R. A.; Anthony, R. E.; Aster, R. C.; Cai, C.; Nyblade, A.; Wiens, D. A.

    2016-05-01

    An L-configured, three-component short period seismic array was deployed on the Ross Ice Shelf, Antarctica during November 2014. Polarization analysis of ambient noise data from these stations shows linearly polarized waves for frequency bands between 0.2 and 2 Hz. A spectral peak at about 1.6 Hz is interpreted as the resonance frequency of the water column and is used to estimate the water layer thickness below the ice shelf. The frequency band from 4 to 18 Hz is dominated by Rayleigh and Love waves propagating from the north that, based on daily temporal variations, we conclude were generated by field camp activity. Frequency-slowness plots were calculated using beamforming. Resulting Love and Rayleigh wave dispersion curves were inverted for the shear wave velocity profile within the firn and ice to ˜150 m depth. The derived density profile allows estimation of the pore close-off depth and the firn-air content thickness. Separate inversions of Rayleigh and Love wave dispersion curves give different shear wave velocity profiles within the firn. We attribute this difference to an effective anisotropy due to fine layering. The layered structure of firn, ice, water and the seafloor results in a characteristic dispersion curve below 7 Hz. Forward modelling the observed Rayleigh wave dispersion curves using representative firn, ice, water and sediment structures indicates that Rayleigh waves are observed when wavelengths are long enough to span the distance from the ice shelf surface to the seafloor. The forward modelling shows that analysis of seismic data from an ice shelf provides the possibility of resolving ice shelf thickness, water column thickness and the physical properties of the ice shelf and underlying seafloor using passive-source seismic data.

  7. Dynamic characteristics of an active coastal spreading area using ambient noise measurements—Anchor Bay, Malta

    Science.gov (United States)

    Galea, Pauline; D'Amico, Sebastiano; Farrugia, Daniela

    2014-11-01

    Anchor Bay and surrounding regions are located on the northwest coast of the island of Malta, Central Mediterranean. The area is characterized by a coastal cliff environment having an outcropping layer of hard coralline limestone (UCL) resting on a thick (up to 50 m) layer of clays and marls (Blue Clay, BC). This configuration gives rise to coastal instability effects, in particular lateral spreading phenomena and rock falls. Previous and ongoing studies have identified both lateral spreading rates and vertical motions of several millimetres per year. The area is an interesting natural laboratory as coastal detachment processes in a number of different stages can be identified and are easily accessible. We investigate the site dynamic characteristics of this study area by recording ambient noise time-series at more than 30 points, over an area of 0.07 km2, using a portable three-component seismograph. The time-series are processed to give both horizontal-to-vertical spectral ratio graphs (H/V) as well as frequency-dependent polarisation analysis. The H/V graphs illustrate and quantify aspects of site resonance effects due both to underlying geology as well as to mechanical resonance of partly or wholly detached blocks. The polarization diagrams indicate the degree of linearity and predominant directions of vibrational effects. H/V curves closer to the cliff edge show complex responses at higher frequencies, characteristic of the dynamic behaviour of individual detached blocks. Particle motion associated with the higher frequencies shows strongly directional polarization and a high degree of linearity at well-defined frequencies, indicative of normal-mode vibration. The stable plateau areas, on the other hand, show simple, single-peak H/V curves representative of the underlying stratification and no predominant polarization direction. These results, which will be compared with those from other experiments in the area, have important implications for the

  8. Correlation-study about the ambient dose rate and the weather conditions

    Science.gov (United States)

    Furuya, Masato; Hatano, Yuko; Aoyama, Tomoo; Igarashi, Yasuhito; Kita, Kazuyuki; Ishizuka, Masahide

    2016-04-01

    The long-term radiation risks are believed to be heavily affected by the resuspension process. We therefore focus on the surface-atmosphere exchange process of released radioactive materials in this study. Radioactive materials were deposited on the soil and float in the air, and such complicated process are influenced by the weather conditions deeply. We need to reveal the correlation between the weather conditions and the ambient dose rate. In this study, we study the correlation between the weather conditions and the ambient dose rate with the correction of the decrease due to the radioactive decay. We found that there is a negative correlation between the ambient dose rate and the soil water content by the correlation coefficient. Using this result, we reconstruct the ambient dose rate from the weather conditions by the multiple regression analysis and found that the reconstructed data agree with the observation very well. Using Kalman filter, which can be sequentially updates the state estimate, we obtained such a good agreement.

  9. Stochastic resonance in the growth of a tumor induced by correlated noises

    Institute of Scientific and Technical Information of China (English)

    ZHONG Weirong; SHAO Yuanzhi; HE Zhenhui

    2005-01-01

    Multiplicative noise is found to divide the growth law of tumors into two parts in a logistic model, which is driven by additive and multiplicative noises simultaneously. The Fokker-Planck equation was also derived to explain the fact that the influence of the intensity of multiplicative noise on the growth of tumor cells has a stochastic resonance-like characteristic. An appropriate intensity of multiplicative noise is benefit to the growth of the tumor cells. The correlation between two sorts of noises weakens the stochastic resonance-like characteristic. Homologous noises promote the growth of the tumor cells.

  10. Ambient seismic noise levels: A survey of the permanent and temporary seismographic networks in Morocco, North Africa

    Science.gov (United States)

    El Fellah, Y.; Khairy Abd Ed-Aal, A.; El Moudnib, L.; Mimoun, H.; Villasenor, A.; Gallart, J.; Thomas, C.; Elouai, D.; Mimoun, C.; Himmi, M.

    2013-12-01

    Abstract The results, of a conducted study carried out to analyze variations in ambient seismic noise levels at sites of the installed broadband stations in Morocco, North Africa, are obtained. The permanent and the temporary seismic stations installed in Morocco of the Scientific Institute ( IS, Rabat, Morocco), institute de Ciencias de la Tierra Jaume almera (ICTJA, Barcelona, Spain) and Institut für Geophysik (Munster, Germany) were used in this study. In this work, we used 23 broadband seismic stations installed in different structural domains covering all Morocco from south to north. The main purposes of the current study are: 1) to present a catalog of seismic background noise spectra for Morocco obtained from recently installed broadband stations, 2) to assess the effects of experimental temporary seismic vault construction, 3) to determine the time needed for noise at sites to stabilize, 4) to establish characteristics and origin of seismic noise at those sites. We calculated power spectral densities of background noise for each component of each broadband seismometer deployed in the different investigated sites and then compared them with the high-noise model and low-noise Model of Peterson (1993). All segments from day and night local time windows were included in the calculation without parsing out earthquakes. The obtained results of the current study could be used forthcoming to evaluate permanent station quality. Moreover, this study could be considered as a first step to develop new seismic noise models in North Africa not included in Peterson (1993). Keywords Background noise; Power spectral density; Model of Peterson; Scientific Institute; Institute de Ciencias de la Tierra Jaume almera; Institut für Geophysik

  11. Escape over a potential barrier driven by colored noise: Large but finite correlation times

    International Nuclear Information System (INIS)

    The recent theory of Tsironis and Grigolini for the mean first-passage time from one metastable state to another of a bistable potential for long correlation times of the noise is extended to large but finite correlation times

  12. A methodological approach towards high-resolution surface wave imaging of the San Jacinto Fault Zone using ambient-noise recordings at a spatially dense array

    Science.gov (United States)

    Roux, Philippe; Moreau, Ludovic; Lecointre, Albanne; Hillers, Gregor; Campillo, Michel; Ben-Zion, Yehuda; Zigone, Dimitri; Vernon, Frank

    2016-08-01

    We present a new technique for deriving detailed information on seismic velocities of the subsurface material from continuous ambient noise recorded by spatially dense seismic arrays. This method uses iterative double beamforming between various subarrays to extract surface wave contributions from the ambient-noise data in complex environments with unfavourable noise-source distributions. The iterative double beamforming extraction makes it possible to retrieve large amounts of Rayleigh wave traveltime information in a wide frequency band. The method is applied to data recorded by a highly dense Nodal array with 1108 vertical geophones, centred on the damage zone of the Clark branch of the San Jacinto Fault Zone south of Anza, California. The array covers a region of ˜650 × 700 m2, with instrument spacing of 10-30 m, and continuous recording at 500 samples s-1 over 30 d in 2014. Using this iterative double beamforming on subarrays of 25 sensors and cross-correlations between all of the station pairs, we separate surface waves from body waves that are abundant in the raw cross-correlation data. Focusing solely on surface waves, maps of traveltimes are obtained at different frequencies with unprecedented accuracy at each point of a 15-m-spacing grid. Group velocity inversions at 2-4 Hz reveal depth and lateral variations in the structural properties within and around the San Jacinto Fault Zone in the study area. This method can be used over wider frequency ranges and can be combined with other imaging techniques, such as eikonal tomography, to provide unprecedented detailed structural images of the subsurface material.

  13. A methodological approach toward high-resolution surface wave imaging of the San Jacinto Fault Zone using ambient-noise recordings at a spatially dense array

    Science.gov (United States)

    Roux, Philippe; Moreau, Ludovic; Lecointre, Albanne; Hillers, Gregor; Campillo, Michel; Ben-Zion, Yehuda; Zigone, Dimitri; Vernon, Frank

    2016-05-01

    We present a new technique for deriving detailed information on seismic velocities of the sub-surface material from continuous ambient noise recorded by spatially dense seismic arrays. This method uses iterative double beamforming between various subarrays to extract surface-wave contributions from the ambient-noise data in complex environments with unfavorable noise-source distributions. The iterative double beamforming extraction makes it possible to retrieve large amounts of Rayleigh wave travel-time information in a wide frequency band. The method is applied to data recorded by a highly dense Nodal array with 1,108 vertical geophones, centered on the damage zone of the Clark branch of the San Jacinto Fault Zone south of Anza, California. The array covers a region of ˜650 m x 700 m, with instrument spacing of 10 m to 30 m, and continuous recording at 500 samples/s over 30 days in 2014. Using this iterative double beamforming on subarrays of 25 sensors and cross-correlations between all of the station pairs, we separate surface waves from body waves that are abundant in the raw cross-correlation data. Focusing solely on surface waves, maps of travel times are obtained at different frequencies with unprecedented accuracy at each point of a 15-m-spacing grid. Group velocity inversions at 2 Hz to 4 Hz reveal depth and lateral variations in the structural properties within and around the San Jacinto Fault Zone in the study area. This method can be used over wider frequency ranges and can be combined with other imaging techniques, such as eikonal tomography, to provide unprecedented detailed structural images of the sub-surface material.

  14. Assessment of ambient noise levels in the intensive care unit of a university hospital

    Directory of Open Access Journals (Sweden)

    Hatem O Qutub

    2009-01-01

    Conclusion : Some sources of environmental noise, such as the use of oxygen, suction equipment or respirators are unavoidable. Nevertheless, hospital ICUs should have measures to minimize the level of exposure to noise in the ICU. Further research in this area might focus on the noise level and other modifiable environmental stress factors in the ICU that affect patients as well as the staff.

  15. Noise-robust low-contrast retinal recognition using compression-based joint wavelet transform correlator

    Science.gov (United States)

    Widjaja, Joewono

    2015-11-01

    A new method is proposed for recognizing noise corrupted low-contrast retinal images that employs joint wavelet transform correlator with compressed reference and target. Noise robustness is achieved by correlating wavelet-transformed retinal target and reference images. Simulation results show that besides being robust to noise, its recognition performance can become independent upon compression qualities when low spatial-frequency components of joint power spectrum are enhanced by appropriately dilated wavelet filter.

  16. Probing Spatial Spin Correlations of Ultracold Gases by Quantum Noise Spectroscopy

    OpenAIRE

    Bruun, G.; Andersen, Brian; Sørensen, Anders; Demler, Eugene A.

    2009-01-01

    Spin noise spectroscopy with a single laser beam is demonstrated theoretically to provide a direct probe of the spatial correlations of cold fermionic gases. We show how the generic many-body phenomena of anti-bunching, pairing, antiferromagnetic, and algebraic spin liquid correlations can be revealed by measuring the spin noise as a function of laser width, temperature, and frequency.

  17. Shear velocity model for the westernmost Mediterranean from ambient noise and ballistic finite-frequency Rayleigh wave tomography

    Science.gov (United States)

    Palomeras, I.; Villasenor, A.; Thurner, S.; Levander, A.; Gallart, J.; Harnafi, M.

    2014-12-01

    The westernmost Mediterranean comprises the Iberian Peninsula and Morocco, separated by the Alboran Sea and the Algerian Basin. From north to south this region consists of the Pyrenees, resulting from Iberia-Eurasia collision; the Iberian Massif, which has been undeformed since the end of the Paleozoic; the Central System and Iberian Chain, regions with intracontinental Oligocene-Miocene deformation; the Gibraltar Arc (Betics, Rif and Alboran terranes), resulting from post-Oligocene subduction roll-back; and the Atlas Mountains. We analyzed data from recent broad-band array deployments and permanent stations in the area (IberArray and Siberia arrays, the PICASSO array, the University of Munster array, and the Spanish, Portuguese and Moroccan National Networks) to characterize its lithospheric structure. The combined array of 350 stations has an average interstation spacing of ~60 km. We calculated the Rayleigh waves phase velocities from ambient noise (periods 4 to 40 s) and teleseismic events (periods 20 to 167 s). We inverted the phase velocities to obtain a shear velocity model for the lithosphere to ~200 km depth. Our results correlate well with the surface expression of the main structural units with higher crustal velocity for the Iberian Massif than for the Alpine Iberia and Atlas Mountains. The Gibraltar Arc has lower crustal shear velocities than the regional average at all crustal depths. It also shows an arc shaped anomaly with high upper mantle velocities (>4.6 km/s) at shallow depths (Atlas, the northeastern end of the Betic Mountains and the Late Cenozoic volcanic fields in Iberia and Morocco, indicative of high temperatures at relatively shallow depths, and suggesting that the lithosphere has been removed beneath these areas.

  18. Perception of Health-Impacts of Environmental Noise in an Ambient Noise Context in Owerri -Urban , Imo State, Nigeria

    OpenAIRE

    Ubuoh Emmanuel Attah; S.M.O. Akhionbare; O.A. Onifade; Ogbuji S. I.

    2012-01-01

    This paper reports the results of the investigation of health impacts of environmental noise context in Owerri-urban, due to incessant complains of urban dwellers of noise pollution and their effects on the health. This was measured by the use of 210 questionnaires on urban dwellers along the major routes, in which 30 questionnaires  were randomly  administered  between sampled routes designated  NP1- NP7. The observed results indicate that , automobile  has 32.3%, church 3.3%, construction w...

  19. Noise enhanced stability effect in a metastable system with two different kinds of time delays and cross-correlated noises

    International Nuclear Information System (INIS)

    We numerically investigate the influences of the time delay τ simultaneously existing in both the deterministic and fluctuating forces, the time delay τr existing only in the fluctuating force and the cross-correlation strength λ on the enhancement of the mean first-passage time (MFPT) as a function of the additive D and the multiplicative α noise intensities in a metastable system. The results indicate that both the multiplicative and additive noises can induce the noise-enhanced stability (NES) effect. An increase of λ can enhance or weaken the NES effect induced by the additive noise, depending on the value of τ. However, it weakens the NES effect induced by the multiplicative noise with a suppression of the effect of λ caused by increasing τ. The τ-induced critical behavior on both NES effects can be observed, i.e. an increase of τ can enhance or restrain the NES effects induced by the two kinds of noises. With an increase of λ and τ, MFPT versus D shows a transition from one peak to two peaks and finally one peak, implying the multiple NES effect caused by λ and τ. An increase of τr can enhance the NES effect induced by the additive noise and weaken the NES effect induced by the multiplicative noise.

  20. Quantum metrology subject to spatially correlated Markovian noise: restoring the Heisenberg limit

    Science.gov (United States)

    Jeske, Jan; Cole, Jared H.; Huelga, Susana F.

    2014-07-01

    Environmental noise can hinder the metrological capabilities of entangled states. While the use of entanglement allows for Heisenberg-limited resolution, the largest permitted by quantum mechanics, deviations from strictly unitary dynamics quickly restore the standard scaling dictated by the central limit theorem. Product and maximally entangled states become asymptotically equivalent when the noisy evolution is both local and strictly Markovian. However, temporal correlations in the noise have been shown to lift this equivalence while fully (spatially) correlated noise allows for the identification of decoherence-free subspaces. Here we analyze precision limits in the presence of noise with finite correlation length and show that there exist robust entangled state preparations which display persistent Heisenberg scaling despite the environmental decoherence, even for small correlation length. Our results emphasize the relevance of noise correlations in the study of quantum advantage and could be relevant beyond metrological applications.

  1. Crustal thickness beneath the Chaco-Parana basin, NE Argentina, from surface waves and ambient noise tomography

    Science.gov (United States)

    Rosa, M.; Collaco, B.; Sanchez, G.; Assumpcao, M.; Sabbione, N.

    2013-05-01

    We present the results of a study of surface-wave dispersion data obtained by group velocity tomography, using seismic data and ambient seismic noise correlation, for the region of the Chaco-Parana basin, a Neopaleozoic intracratonic basin, formed by a complex history of different processes of subsidence. Previous surface waves analysis (e.g., Feng et al., 2004, 2007; Snokes and James, 1997) estimated Moho depth in the central Chaco basin and a low-velocity anomaly in the lithospheric mantle. However the seismic structure of the crust and upper mantle remains little characterized across the region due to the rather poor resolution, especially for the south region. The aim of this work is to improve the resolution and fidelity of crustal images obtained from traditional earthquake-based measurements. Hence, we have increased the number of group velocity measurements using data from regional earthquakes recorded at LPA (La Plata) station, Brazilian Seismic Network stations (BRASIS), permanent (GSN) and portable (BLSP) stations as well as inter-station dispersion curves derived from a dataset of seismic noise recordings from BRASIS, INPRES stations, LPA, CPUP and TRQA stations. The resulting path coverage is denser and displays a more uniform azimuthally distribution producing better tomographic images. The dispersion curves were obtained by a multiple filter technique (Dziewonski et al, 1969) using a phase-matched filter. A 2D group velocity tomographic inversion was performed, applying a conjugate-gradient method (Paige and Saunders, 1982). The group velocity maps for 10 to 120 seconds correspond very well to tectonic structures throughout the studied area and the resolution was improved in northern Argentina and southern Brazil by the better seismic ray coverage showing low-velocity anomalies in the upper-mantle beneath the Chaco basin, compatible with other dispersion results. The new group velocity maps were inverted for S velocity structures, using a

  2. Combined effects of road traffic noise and ambient air pollution in relation to risk for stroke?

    DEFF Research Database (Denmark)

    Sørensen, Mette; Lühdorf, Pernille; Ketzel, Matthias;

    2014-01-01

    Exposure to road traffic noise and air pollution have both been associated with risk for stroke. The few studies including both exposures show inconsistent results. We aimed to investigate potential mutual confounding and combined effects between road traffic noise and air pollution in association...... to 2009 were identified in national registers and road traffic noise and air pollution were modeled for all addresses. Analyses were done using Cox regression. A higher mean annual exposure at time of diagnosis of 10µg/m(3) nitrogen dioxide (NO2) and 10dB road traffic noise at the residential address...... was found for combination of high noise and high NO2 (IRR=1.28; 95% CI=1.09-1.52). Fatal stroke was positively associated with air pollution and not with traffic noise. In conclusion, in mutually adjusted models road traffic noise and not air pollution was associated ischemic stroke, while only air...

  3. Investigation of the spatial correlations of flow noise in vector hydrophone towed linear array

    Institute of Scientific and Technical Information of China (English)

    YANG Xiuting; SUN Guiqing; LI Mini; LI Qihu

    2008-01-01

    Following the wall pressure spectrum of the turbulent boundary layer developed by Corcos, a method in the frequency-wavenumber space was presented to analyze the flow noise in the vector hydrophone towed linear array. The general forms of the acoustic pressure and particle velocity in the flow noise field were obtained, and the spatial correlations of the flow noise were calculated. The numerical analysis results based on wavenumber integration show that: (1) The spatial correlations of flow noise drops rapidly with increasing axial separation between the elements, so the flow noise received by different vector hydrophones usually sampled in a half-wavelength rate can be considered as independent; (2) The flow noise is highly correlated in the radial direction at low frequency, and only those of high frequency componet can be neglected.

  4. Intensity and phase noise correlations in a dual-frequency VECSEL operating at telecom wavelength

    CERN Document Server

    De, Syamsundar; Bouchoule, Sophie; Alouini, Mehdi; Bretenaker, Fabien

    2015-01-01

    The amplitude and phase noises of a dual-frequency vertical-external-cavity surface-emitting laser (DF-VECSEL) operating at telecom wavelength are theoretically and experimentally investigated in detail. In particular, the spectral behavior of the correlation between the intensity noises of the two modes of the DF-VECSEL is measured. Moreover, the correlation between the phase noise of the radio-frequency (RF) beatnote generated by optical mixing of the two laser modes with the intensity noises of the two modes is investigated. All these spectral behaviors of noise correlations are analyzed for two different values of the nonlinear coupling between the laser modes. We find that to describe the spectral behavior of noise correlations between the laser modes, it is of utmost importance to have a precise knowledge about the spectral behavior of the pump noise, which is the dominant source of noise in the frequency range of our interest (10 kHz to 35 MHz). Moreover, it is found that the noise correlation also dep...

  5. Monitoring southwest Greenland’s ice sheet melt with ambient seismic noise

    Science.gov (United States)

    Mordret, Aurélien; Mikesell, T. Dylan; Harig, Christopher; Lipovsky, Bradley P.; Prieto, Germán A.

    2016-01-01

    The Greenland ice sheet presently accounts for ~70% of global ice sheet mass loss. Because this mass loss is associated with sea-level rise at a rate of 0.7 mm/year, the development of improved monitoring techniques to observe ongoing changes in ice sheet mass balance is of paramount concern. Spaceborne mass balance techniques are commonly used; however, they are inadequate for many purposes because of their low spatial and/or temporal resolution. We demonstrate that small variations in seismic wave speed in Earth’s crust, as measured with the correlation of seismic noise, may be used to infer seasonal ice sheet mass balance. Seasonal loading and unloading of glacial mass induces strain in the crust, and these strains then result in seismic velocity changes due to poroelastic processes. Our method provides a new and independent way of monitoring (in near real time) ice sheet mass balance, yielding new constraints on ice sheet evolution and its contribution to global sea-level changes. An increased number of seismic stations in the vicinity of ice sheets will enhance our ability to create detailed space-time records of ice mass variations. PMID:27386524

  6. Reorganization of auditory map and pitch discrimination in adult rats chronically exposed to low-level ambient noise

    Directory of Open Access Journals (Sweden)

    Weimin Zheng

    2012-09-01

    Full Text Available Behavioral adaption to a changing environment is critical for an animal’s survival. How well the brain can modify its functional properties based on experience essentially defines the limits of behavioral adaptation. In adult animals the extent to which experience shapes brain function has not been fully explored. Moreover, the perceptual consequences of experience-induced changes in the brains of adults remain unknown. Here we show that the tonotopic map in the primary auditory cortex of adult rats living with low-level ambient noise underwent a dramatic reorganization. Behaviorally, chronic noise-exposure impaired fine, but not coarse pitch discrimination. When tested in a noisy environment, the noise-exposed rats performed as well as in a quiet environment whereas the control rats performed poorly. This suggests that noise-exposed animals had adapted to living in a noisy environment. Behavioral pattern analyses revealed that stress or distraction engendered by the noisy background could not account for the poor performance of the control rats in a noisy environment. A reorganized auditory map may therefore have served as the neural substrate for the consistent performance of the noise-exposed rats in a noisy environment.

  7. Fast direction of arrival estimation of wideband sources in unknown correlated noise fields

    Institute of Scientific and Technical Information of China (English)

    DAI Zhengjian; LIU Yun; LI Zhishun

    2006-01-01

    A computational efficient wideband Direction of Arrival (DOA) estimation method in the presence of unknown correlated noise is presented. A fast Two-sided Correlation Transformation (TCT) focusing matrix that transforms only the signal subspace is developed firstly,and then the propagator method is utilized to compute the focusing matrix and noise correlation matrix. In contrast to conventional wideband DOA estimation method, the proposed method requires only linear operation but does not involve any eigenvelue-decomposition to estimate the focusing matrix; it has a lower computational load, especially when the sensor number is greater than the source number. Because noise correlation matrix is estimated and eliminated from the array correlation matrix, the accuracy of DOA estimation is improved even in the presence of unknown correlation noise. Computer simulation results verified the efficiency of the method.

  8. Determination of Ambient Noise Levels in the Main Commercial Area of Cape Coast, Ghana

    OpenAIRE

    Paul K. Essandoh; Frederick Ato Armah

    2011-01-01

    Noise pollution associated with urbanisation is an emerging environmental problem in many developing countries including Ghana. In comparison with other pollutants, the control of environmental noise has been hampered by insufficient knowledge of its effects on humans and of dose–response relationships, as well as by a lack of sufficient data. The study set to quantify noise and obtain the perceptions of residents in selected neighbourhoods in the main commercial area of Cape Coast, Ghana. Th...

  9. Moment Equations in a Lotka--Volterra Extended System with Time Correlated Noise

    Science.gov (United States)

    Valenti, D.; Schimansky-Geier, L.; Sailer, X.; Spagnolo, B.; Iacomi, M.

    2007-05-01

    A spatially extended Lotka--Volterra system of two competing species in the presence of two correlated noise sources is analyzed: (i) an external multiplicative time correlated noise, which mimics the interaction between the system and the environment; (ii) a dichotomous stochastic process, whose jump rate is a periodic function, which represents the interaction parameter between the species. The moment equations for the species densities are derived in Gaussian approximation, using a mean field approach. Within this formalism we study the effect of the external time correlated noise on the ecosystem dynamics. We find that the time behavior of the 1st order moments are independent on the multiplicative noise source. However, the behavior of the 2nd order moments is strongly affected both by the intensity and the correlation time of the multiplicative noise. Finally we compare our results with those obtained studying the system dynamics by a coupled map lattice model.

  10. Relaxation dynamics in the presence of pulse multiplicative noise sources with different correlation properties.

    Science.gov (United States)

    Kargovsky, A V; Chichigina, O A; Anashkina, E I; Valenti, D; Spagnolo, B

    2015-10-01

    The relaxation dynamics of a system described by a Langevin equation with pulse multiplicative noise sources with different correlation properties is considered. The solution of the corresponding Fokker-Planck equation is derived for Gaussian white noise. Moreover, two pulse processes with regulated periodicity are considered as a noise source: the dead-time-distorted Poisson process and the process with fixed time intervals, which is characterized by an infinite correlation time. We find that the steady state of the system is dependent on the correlation properties of the pulse noise. An increase of the noise correlation causes the decrease of the mean value of the solution at the steady state. The analytical results are in good agreement with the numerical ones. PMID:26565201

  11. The power spectrum and correlation of flow noise for an axisymmetric body in water

    Institute of Scientific and Technical Information of China (English)

    Li Xue-Gang; Yang Kun-De; Wang Yong

    2011-01-01

    Understanding the physical features of the flow noise for an axisymmetric body is important for improving the performance of a sonar mounted on an underwater platform. Analytical calculation and numerical analysis of the physical features of the flow noise for an axisymmetric body are presented and a simulation scheme for the noise correlation on the hydrophones is given. It is shown that the numerical values of the flow noise coincide well with the analytical values. The main physical features of flow noise are obtained. The flow noises of two different models are compared and a model with a rather optimal fore-body shape is given. The flow noise in horizontal symmetry profile of the axisymmetric body is non-uniform, but it is omni-directional and has little difference in the cross section of the body. The loss of noise diffraction has a great effect on the flow noise from boundary layer transition. Meanwhile, based on the simulation, the noise power level increases with velocity to approximately the fifth power at high frequencies,which is consistent with the experiment data reported in the literature. Furthermore, the flow noise received by the acoustic array has lower correlation at a designed central frequency, which is important for sonar system design.

  12. Possible Noncausal Bases for Correlations Between Low Concentrations of Ambient Particulate Matter and Daily Mortality

    OpenAIRE

    Valberg, Peter A

    2003-01-01

    Numerous studies of populations living in areas with good air quality have reported correlations between daily average levels of ambient particulate matter (PM) and daily mortality rates. These associations persist at PM levels below current air quality standards and are difficult to reconcile with the toxicology of PM chemical constituents. The unusual level of lethality per unit PM mass predicted by these associations may result from confounding by unmeasured societal, behavioral, or stress...

  13. TH-A-18C-03: Noise Correlation in CBCT Projection Data and Its Application for Noise Reduction in Low-Dose CBCT

    International Nuclear Information System (INIS)

    Purpose: To study the noise correlation properties of cone-beam CT (CBCT) projection data and to incorporate the noise correlation information to a statistics-based projection restoration algorithm for noise reduction in low-dose CBCT. Methods: In this study, we systematically investigated the noise correlation properties among detector bins of CBCT projection data by analyzing repeated projection measurements. The measurements were performed on a TrueBeam on-board CBCT imaging system with a 4030CB flat panel detector. An anthropomorphic male pelvis phantom was used to acquire 500 repeated projection data at six different dose levels from 0.1 mAs to 1.6 mAs per projection at three fixed angles. To minimize the influence of the lag effect, lag correction was performed on the consecutively acquired projection data. The noise correlation coefficient between detector bin pairs was calculated from the corrected projection data. The noise correlation among CBCT projection data was then incorporated into the covariance matrix of the penalized weighted least-squares (PWLS) criterion for noise reduction of low-dose CBCT. Results: The analyses of the repeated measurements show that noise correlation coefficients are non-zero between the nearest neighboring bins of CBCT projection data. The average noise correlation coefficients for the first- and second- order neighbors are about 0.20 and 0.06, respectively. The noise correlation coefficients are independent of the dose level. Reconstruction of the pelvis phantom shows that the PWLS criterion with consideration of noise correlation (PWLS-Cor) results in a lower noise level as compared to the PWLS criterion without considering the noise correlation (PWLS-Dia) at the matched resolution. Conclusion: Noise is correlated among nearest neighboring detector bins of CBCT projection data. An accurate noise model of CBCT projection data can improve the performance of the statistics-based projection restoration algorithm for low

  14. Offshore Southern California lithospheric velocity structure from noise cross-correlation functions

    Science.gov (United States)

    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.

  15. Stochastic Resonance in a Spatially Symmetric and Flashing Periodic Potential Subjected to Correlated Noises

    International Nuclear Information System (INIS)

    A Brownian particle in a spatially symmetric and Bashing periodic potential subjected to correlated noises is investigated. The exact expression of its current is analytically derived. The numerical results indicate that its current as a function of noise intensity exhibits two peaks in the case of positive correlations, and two vales in the case of negative correlations, i.e., a novel stochastic resonance (SR) phenomenon. The SR is attributed to the harmonic cooperation between the noises and the Bashing periodic potential. The conditions under which the SR occurs are also presented

  16. Noise and correlations in genes silenced by small RNA.

    Science.gov (United States)

    Hwa, Terence; Levine, Erel

    2006-03-01

    Many small regulatory RNAs have been identified in prokaryotes and eukaryotes in recent years. In many cases, RNA regulation is found in critical pathways. These include stress response and quorum sensing pathways in bacteria, and cell differentiation and programmed cell death in eukaryotes. In many cases, regulation by small RNA is used in switching off a response program as long as it is not required, allowing for a fast switching on when necessary. Clearly, accidental execution of such a program may bare grave consequences on the cell, and should be avoided. Here we analyze a stochastic model for gene regulation by the most abundant class of small RNA in bacteria. This class of small RNAs acts by base pairing with target mRNAs, silencing its translation and actively promoting its degradation. Importantly, the small RNA molecule is not recycled. Our model suggests that genes silenced by sRNA exhibits smooth noise, as opposed to the bursty noise characteristic to genes repressed at the level of transcription, with coupling between intrinsic noise and global, extrinsic fluctuations. In addition, we investigate how noise propagates through the indirect coupling between different targets of the same sRNA. These features are discussed in the context of circuits exhibiting multi-stability, where protein bursts have strong implications on spontaneous switching.

  17. The sign rule and beyond: boundary effects, flexibility, and noise correlations in neural population codes.

    Directory of Open Access Journals (Sweden)

    Yu Hu

    2014-02-01

    Full Text Available Over repeat presentations of the same stimulus, sensory neurons show variable responses. This "noise" is typically correlated between pairs of cells, and a question with rich history in neuroscience is how these noise correlations impact the population's ability to encode the stimulus. Here, we consider a very general setting for population coding, investigating how information varies as a function of noise correlations, with all other aspects of the problem - neural tuning curves, etc. - held fixed. This work yields unifying insights into the role of noise correlations. These are summarized in the form of theorems, and illustrated with numerical examples involving neurons with diverse tuning curves. Our main contributions are as follows. (1 We generalize previous results to prove a sign rule (SR - if noise correlations between pairs of neurons have opposite signs vs. their signal correlations, then coding performance will improve compared to the independent case. This holds for three different metrics of coding performance, and for arbitrary tuning curves and levels of heterogeneity. This generality is true for our other results as well. (2 As also pointed out in the literature, the SR does not provide a necessary condition for good coding. We show that a diverse set of correlation structures can improve coding. Many of these violate the SR, as do experimentally observed correlations. There is structure to this diversity: we prove that the optimal correlation structures must lie on boundaries of the possible set of noise correlations. (3 We provide a novel set of necessary and sufficient conditions, under which the coding performance (in the presence of noise will be as good as it would be if there were no noise present at all.

  18. Experimental verifications of noise suppression in retinal recognition by using compression-based joint transform correlator

    Science.gov (United States)

    Widjaja, Joewono; Kaewphaluk, Komin

    2014-03-01

    Noise suppression in retinal recognition by using a compression-based joint transform correlator (CBJTC) is experimentally studied. The experimental results show that the noise suppression can be done by compressing targets into a joint-photographic expert group (JPEG) format with appropriate image compression quality. In the case of the weak noise suppression, the improved recognition performance is as high as that of the classical JTC.

  19. Observer efficiency in free-localization tasks with correlated noise

    Directory of Open Access Journals (Sweden)

    Craig eAbbey

    2014-05-01

    Full Text Available The efficiency of visual tasks involving localization has traditionally been evaluated using forced choice experiments that capitalize on independence across locations to simplify the performance of the ideal observer. However, developments in ideal observer analysis have shown how an ideal observer can be defined for free-localization tasks, where a target can appear anywhere in a defined search region and subjects respond by localizing the target. Since these tasks are representative of many real-world search tasks, it is of interest to evaluate the efficiency of observer performance in them. The central question of this work is whether humans are able to effectively use the information in a free-localization task relative to a similar task where target location is fixed. We use a yes-no detection task at a cued location as the reference for this comparison. Each of the tasks is evaluated using a Gaussian target profile embedded in four different Gaussian noise backgrounds having power-law noise power spectra with exponents ranging from 0 to 3. The free localization task had a square 6.7° search region. We report on two follow-up studies investigating efficiency in a detect-and-localize task, and the effect of processing the white-noise backgrounds. In the fixed-location detection task, we find average observer efficiency ranges from 35% to 59% for the different noise backgrounds. Observer efficiency improves dramatically in the tasks involving localization, ranging from 63% to 82% in the forced localization tasks and from 78% to 92% in the detect-and- localize tasks. Performance in white noise, the lowest efficiency condition, was improved by filtering to give them a power-law exponent of 2. Classification images, used to examine spatial frequency weights for the tasks, show better tuning to ideal weights in the free-localization tasks. The high absolute levels of efficiency suggest that observers are well-adapted to free-localization tasks.

  20. Study of the normalized intensity correlation function of a single-mode laser system with colored cross-correlated noises

    Institute of Scientific and Technical Information of China (English)

    Bing Wang; Xiuqing Wu

    2007-01-01

    A single-mode laser system with colored cross-correlated additive and multiplicative noise terms is considered. By the means of projection operator method, we study the effects of the cross-correlation time τ and the cross-correlation intensity λ between noises on the normalized intensity correlation function C(s). It is found that if λ> 0 (λ< 0), the normalized intensity correlation function C(s) increases (decreases) with increasing the cross-correlation time τ, and at large value of τ, the variation of the normalized intensity correlation function C(s) becomes small. With the increase of the net gain a0, C(s) exhibits a maximum when λ is larger. However, a minimum and a maximum appear on C(s) curves with the increase of a0 when λ becomes smaller and smaller.

  1. Making sense of the noise: Replication difficulties of Correll's (2008) modulation of 1/f noise in a racial bias task.

    Science.gov (United States)

    Madurski, Christine; LeBel, Etienne P

    2015-08-01

    Correll (Journal of Personality and Social Psychology, 94, 48-59, 2008; Study 2) found that instructions to use or avoid race information decreased the emission of 1/f noise in a weapon identification task (WIT). These results suggested that 1/f noise in racial bias tasks reflected an effortful deliberative process, providing new insights regarding the mechanisms underlying implicit racial biases. Given the potential theoretical and applied importance of understanding the psychological processes underlying implicit racial biases - and in light of the growing demand for independent direct replications of findings to ensure the cumulative nature of our science - we attempted to replicate Correll's finding in two high-powered studies. Despite considerable effort to closely duplicate all procedural and methodological details of the original study (i.e., same cover story, experimental manipulation, implicit measure task, original stimuli, task instructions, sampling frame, population, and statistical analyses), both replication attempts were unsuccessful in replicating the original finding challenging the theoretical account that 1/f noise in racial bias tasks reflects a deliberative process. However, the emission of 1/f noise did consistently emerge across samples in each of our conditions. Hence, future research is needed to clarify the psychological significance of 1/f noise in racial bias tasks. PMID:25384891

  2. Direct correlation between strengthening mechanisms and electrical noise in strained copper wires

    OpenAIRE

    Bellido, Natalia; Pautrat, Alain; Keller, Clement; Hug, Eric

    2011-01-01

    We have measured the resistance noise of copper metallic wires during a tensile stress. The time variation of the main resistance is continuous up to the wire breakdown, but its fluctuations reveal the intermittent and heterogeneous character of plastic flow. We show in particular direct correlations between strengthening mechanisms and noise spectra characteristics.

  3. Passive elastography: shear-wave tomography from physiological-noise correlation in soft tissues.

    Science.gov (United States)

    Gallot, Thomas; Catheline, Stefan; Roux, Philippe; Brum, Javier; Benech, Nicolas; Negreira, Carlos

    2011-06-01

    Inspired by seismic-noise correlation and time reversal, a shear-wave tomography of soft tissues using an ultrafast ultrasonic scanner is presented here. Free from the need for controlled shear-wave sources, this passive elastography is based on Green's function retrieval and takes advantage of the permanent physiological noise of the human body. PMID:21693392

  4. When can Empirical Green Functions be computed from Noise Cross-Correlations? Hints from different Geographical and Tectonic environments

    Science.gov (United States)

    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

  5. Measurement of Barkhausen noise and its correlation with magnetic permeability

    Czech Academy of Sciences Publication Activity Database

    Stupakov, Oleksandr; Pal'a, J.; Yurchenko, Vitaliy; Tomáš, Ivan; Bydžovský, J.

    2008-01-01

    Roč. 320, 3-4 (2008), s. 204-209. ISSN 0304-8853 R&D Projects: GA AV ČR 1QS100100508 Grant ostatní: VEGA(SK) 1/3116/06 Institutional research plan: CEZ:AV0Z10100520 Keywords : Barkhausen noise * magnetic hysteresis * magnetic non-destructive testing Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.283, year: 2008

  6. New comfort index during combined conditions of moderate low ambient temperature and traffic noise

    Energy Technology Data Exchange (ETDEWEB)

    Nagano, K. [Kyushu University, Fukuoka (Japan). Dept. of Human Living System Design; Horikoshi, T. [Nagoya Institute of Technology (Japan). Graduate School of Engineering

    2005-03-01

    This study's aim is to propose a new comfort index for indicating the combined effect of cold and noise stress on the human state of mind. Twenty-two male students were exposed to twenty combined conditions involving four operative temperature levels and five noise levels. The subjects reported their sensations regarding each combined condition. The results show that the auditory condition significantly affected the hot sensation as well as the noise sensation, and that the thermal condition also significantly affected the noise sensation. Both temperature and noise affected obviously the universal comfort and discomfort sensations. Consequently, two kinds of equi-comfort charts were derived. One of the charts, which represents the equal universal comfort sensation derived from the combination of thermal and auditory comfort sensation, demonstrates the exclusivity of the combined effects. The other chart indicates temperature and noise levels in order to quantitatively evaluate the combined effect of cold and noisy conditions based on the experimental results. This chart can reasonably predict human comfort sensations within this experimental condition. (author)

  7. Electronic Correlated Noise Calibration Standard for Interferometric and Polarimetric Microwave Radiometers Project

    Data.gov (United States)

    National Aeronautics and Space Administration — A new type of calibration standard is proposed which produces a pair of microwave noise signals to aid in the characterization and calibration of correlating...

  8. Column-Parallel Correlated Multiple Sampling Circuits for CMOS Image Sensors and Their Noise Reduction Effects

    Directory of Open Access Journals (Sweden)

    Shoji Kawahito

    2010-10-01

    Full Text Available For low-noise complementary metal-oxide-semiconductor (CMOS image sensors, the reduction of pixel source follower noises is becoming very important. Column-parallel high-gain readout circuits are useful for low-noise CMOS image sensors. This paper presents column-parallel high-gain signal readout circuits, correlated multiple sampling (CMS circuits and their noise reduction effects. In the CMS, the gain of the noise cancelling is controlled by the number of samplings. It has a similar effect to that of an amplified CDS for the thermal noise but is a little more effective for 1/f and RTS noises. Two types of the CMS with simple integration and folding integration are proposed. In the folding integration, the output signal swing is suppressed by a negative feedback using a comparator and one-bit D-to-A converter. The CMS circuit using the folding integration technique allows to realize a very low-noise level while maintaining a wide dynamic range. The noise reduction effects of their circuits have been investigated with a noise analysis and an implementation of a 1Mpixel pinned photodiode CMOS image sensor. Using 16 samplings, dynamic range of 59.4 dB and noise level of 1.9 e- for the simple integration CMS and 75 dB and 2.2 e- for the folding integration CMS, respectively, are obtained.

  9. Determination of Ambient Noise Levels in the Main Commercial Area of Cape Coast, Ghana

    Directory of Open Access Journals (Sweden)

    Paul K. Essandoh

    2011-11-01

    Full Text Available Noise pollution associated with urbanisation is an emerging environmental problem in many developing countries including Ghana. In comparison with other pollutants, the control of environmental noise has been hampered by insufficient knowledge of its effects on humans and of dose–response relationships, as well as by a lack of sufficient data. The study set to quantify noise and obtain the perceptions of residents in selected neighbourhoods in the main commercial area of Cape Coast, Ghana. The focus was on five selected areas: commercial centres, road junctions/busy roads, passengers loading stations, high-density residential areas, and low-density residential areas. The range of noise pollution levels, LNP, at high-density residential areas is 58-68 dB (A, while that of low-density residential areas is 53-72 dB (A. The range of traffic noise index TNI at high-density residential areas is 34-107 dB (A, and that of low density residential areas is 27-65 dB (A. There is a wide disparity in the noise level exposure by the residents in high-density residential areas and that of low-density residential areas. At 90% confidence level, the Mean Square Ratio (MSR calculated for LNP is 65.02, while the tabulated value is 2.36. Similarly, at the same confidence level, the MSR calculated for TNI is 6.23 and the tabulated value remains as 2.36. Since, in the two cases, the calculated MSR is greater than the tabulated value, there is a significant difference (p<0.05 in the noise pollution level and TNI in the locations surveyed based on the data analyzed at 90% confidence level. About 82.1% of the respondents complained that the noise from the audio music shops and traffic is a nuisance. Noise levels at all the 10 measurement points exceeded the Ghana EPA recommended upper limit by values of 1-15 dB (A. This makes it imperative for the regulatory authority to enforce compliance on noise.

  10. Geographical correlation between ambient UVB level and mortality risk of leukemia in Japan

    International Nuclear Information System (INIS)

    As a preliminary epidemiological study, we evaluated the geographical correlation between estimated ambient ultraviolet B (UVB) levels and the mortality risk of leukemia in Japan. Ambient UVB levels were estimated from meteorological data for several successive periods. The standardized mortality ratio (SMR) was calculated for the 11 regions or 38 large cities and different times for nine types of leukemia [the International Classification of Diseases, ninth revision (ICD-9), ICD 200-208]. The ecological relationship was assessed by calculating Spearman's correlation coefficient. Among the nine types of leukemia, geographical correlation was found for two types of leukemia: 'other malignant neoplasms of lymphoid and histiocytic tissue' (ICD 202) and 'lymphoid leukemia' (ICD 204). The correlation coefficients between the SMR and UVB levels were statistically significant and ranged from 0.4 to 0.7 for the former and from 0.3 to 0.6 for the latter type of leukemia. This ecological study generated the hypothesis that UVB exposure may increase the risk of leukemias of lymphatic origin

  11. Intercomparison of tunable diode laser and gas filter correlation measurements of ambient carbon monoxide

    Science.gov (United States)

    Fried, Alan; Henry, Bruce; Parrish, David D.; Carpenter, James R.; Buhr, Martin P.

    An intercomparison that involved a standards intercomparison, interferant spiking tests and simultaneous ambient measurements was carried out between two CO measurement systems: a tunable diode laser absorption spectrometer (TDLAS) and a gas filter correlation, non-dispersive infrared absorption instrument (GFC). Both the TDLAS and the GFC techniques responded to CO. No major interferences were found for the TDLAS system; tested species included H 2O, O 3 and OCS. The GFC instrument exhibited no interference from H 2O or O 3, but only a relatively high upper limit could be placed on the O 3 interference. For CO measurements in ambient air at levels from 100 to 1500 ppbv, the results from the two instruments agreed within their combined uncertainties. On average the GFC technique was 6% higher than the TDLAS system, and there was no systematic, constant offset. The precision of the GFC instrument was about 10%, and the precision of the TDLAS system was better than 4%.

  12. Improving signal-to-noise ratio performance of compressive imaging based on spatial correlation

    Science.gov (United States)

    Mao, Tianyi; Chen, Qian; He, Weiji; Zou, Yunhao; Dai, Huidong; Gu, Guohua

    2016-07-01

    In this paper, compressive imaging based on spatial correlation (CISC), which uses second-order correlation with the measurement matrix, is introduced to improve the signal-to-noise ratio performance of compressive imaging (CI). Numerical simulations and experiments are performed as well. Referred to the results, it can be seen that CISC performs much better than CI in three common noise environments. This provides the great opportunity to pave the way for real applications.

  13. Correlation of Electrical Noise with Non-radiative Current for High Power QWLs

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The characteristics of low-frequency electrical noise, voltage-current (V-I) and electrical derivation for 980nm InGaAsP/InGaAs/GaAs high power double quantum well lasers(DQWLs) are measured under different conditions. The correlation of the low-frequency electrical noise with surface non-radiative current of devices is discussed. The results indicate the low-frequency electrical noise of 980nm DQWLs with high power is mainly 1/f noise and has good relation with the device surface current at low injection.

  14. A Noise-Correlated Cancellation Transmission Scheme for Cooperative MIMO Ad Hoc Networks

    Directory of Open Access Journals (Sweden)

    Wanni Liu

    2014-04-01

    Full Text Available A new transmission scheme based on noise-correlated cancellation (NCC is proposed, which absorbs the advantages of phase-inversion symmetric method and cooperative MIMO technology and makes full use of the correlation of noise in the adjacent channels to reduce channel noise. This paper firstly presents the implementation process of NCC transmission scheme in detail. Further, through theoretical analysis, it is showed that the signal-to-noise ratio gain which the proposed NCC transmission scheme gets is at least 4 times greater than the signal-to-noise ratio gain which the traditional cooperative MIMO transmission scheme gets. Finally, simulation experiment results also verify that the proposed NCC transmission scheme can make the channel capacity per bandwidth of cooperative MIMO Ad Hoc networks improve significantly and bit error rate (BER of the network reduce greatly, which will help to expand application scopes of cooperative MIMO Ad Hoc networks.

  15. The shot noise of a strongly correlated quantum dot coupled to the Luttinger liquid leads

    International Nuclear Information System (INIS)

    We study the shot noise of a strongly correlated quantum dot weakly coupled to Luttinger liquid leads in the Kondo regime by means of the extended equation of motion method. A general zero-frequency shot noise formula with good convergence is derived. The shot noise exhibits a non-monotonic dependence on voltage for weak intralead interaction. There is a peak around the Kondo temperature at low voltage when the interaction is very weak, and its height decreases rapidly with the intralead interaction increasing. When the interaction is moderately strong the peak disappears and the shot noise scales as a power law in bias voltage, indicating that the intralead electron interaction suppresses the shot noise. It is possible that the measurements of the shot noise spectrum can extract the information of the intralead interaction. - Highlights: • The shot noise of a dot coupled to Luttinger liquid leads in the Kondo regime. • A shot noise formula is derived. • Intralead interaction suppresses the shot noise. • The noise shows different voltage-dependence for different intralead interaction

  16. Shallow Velocity Structure of Tapachula Town (chiapas, Mexico) from Joint Inversion of Array and H/v Spectral Ratio of Ambient Noise

    Science.gov (United States)

    Navarro, M.; Vidal, F.; García-Jerez, A.; Alguacil, G.; Ruíz-Sibaja, A.; Aguirre, J.; Cárdenas, R.

    2013-05-01

    The shallow geological structure of Tapachula town has been estimated applying an association of the spatial autocorrelation (SPAC) method and the horizontal-to-vertical spectral ratio (HVSR, Nakamura 1989) method for ambient noise. Regular pentagonal arrays with radii up to 24 m have been employed for velocity computation. The measurements were carried out at six open spaces. Vertical components of ground motion, excited by ambient noise, were recorded at the surface. Five high-sensitivity sensors surrounding a sixth central sensor with same characteristics were used. All the records were analysed by using an implementation of the SPAC method (Aki, 1957). The phase-velocity of the Rg-wave was computed for each frequency from the correlation coefficient. The frequencies of the obtained curves ranged from 2.7 to 16.5 Hz and the phase velocity values varied between 226 and 594 m s-1. Nakamura's method was applied to determine the ground predominant period in the center of such arrays. The predominant period values vary in the 0.2-0.8 s range. Inversions of the S-wave velocity profiles corresponding to the six array sites have been achieved by using dispersion curves derived from SPAC and HVSR shapes. In order to classify the top shallow structure of Tapachula town, following the characterization of site adopted in several seismic codes (e.g. NEHRP 1994, Eurocode-8), the average shear-wave velocity of the upper 30 m (VS30) has been calculated. The results show differences between central part of the town and the peripheral zones close to both rivers rounding the city.

  17. Comparison of ground truth location of earthquake from InSAR and from ambient seismic noise: A case study of the 1998 Zhangbei earthquake

    Science.gov (United States)

    Xie, Jun; Zeng, Xiangfang; Chen, Weiwen; Zhan, Zhongwen

    2011-04-01

    Because ambient seismic noise provides estimated Green's function (EGF) between two sites with high accuracy, Rayleigh wave propagation along the path connecting the two sites is well resolved. Therefore, earthquakes which are close to one seismic station can be well located with calibration extracting from EGF. We test two algorithms in locating the 1998 Zhangbei earthquake, one algorithm is waveform-based, and the other is traveltime-based. We first compute EGF between station ZHB (a station about 40 km away from the epicenter) and five IC/IRIS stations. With the waveform-based approach, we calculate 1D synthetic single-force Green's functions between ZHB and other four stations, and obtain traveltime corrections by correlating synthetic Green's functions with EGFs in period band of 10-30 s. Then we locate the earthquake by minimizing the differential travel times between observed earthquake waveform and the 1D synthetic earthquake waveforms computed with focal mechanism provided by Global CMT after traveltime correction from EGFs. This waveform-based approach yields a location which error is about 13 km away from the location observed with InSAR. With the traveltime-based approach, we begin with measuring group velocity from EGFs as well as group arrival time on observed earthquake waveforms, and then locate the earthquake by minimizing the difference between observed group arrival time and arrival time measured on EGFs. This traveltime-based approach yields accuracy of 3 km, Therefore it is feasible to achieve GT5 (ground truth location with accuracy 5 km) with ambient seismic noises. The less accuracy of the waveform-based approach was mainly caused by uncertainty of focal mechanism.

  18. Broadband ocean bottom seismometer in the Gulf of Cadiz (offshore SW Iberia and NW of Moroccan margin): Characterization of ambient noise and tomographic model of the crustal structure.

    Science.gov (United States)

    Corela, C. J.; Silveira, G. M.; Matias, L. M.; Geissler, W. H.; Schimmel, M.

    2014-12-01

    In this study, we use the continuous data recorded by 24 broadband ocean bottom seismometers (OBS-BB) deployed in the Gulf of Cadiz, in the framework of the NEAREST project, from September 2007 to July of 2008. Our goals are: i) to understand the instrument and the environmental conditions that control the observed seismic noise; and ii) to obtain reliable broadband surface wave dispersion measurements.The noise sources are investigated through the probability density functions (PDFs) of power spectral density (PSDs), which provides insights on the generation and propagating of seismic noise in the Gulf of Cadiz.We show the results of the Rayleigh wave group velocity tomography performed using ambient seismic noise observed on the 24 broadband OBS and on 7 broadband land stations located in the south of Portugal. The time-series, for the 11 months, were cross-correlated to obtain the empirical Green's functions between all vertical sensors pairs, namely the OBS-vertical, the OBS-hydrophone and the vertical component of the land seismic stations. To improve the signal-to-noise ratio, the individual cross-correlograms were summed using a time-frequency domain phase weighted stack.The stacked cross-correlograms enabled us to compute short-period surface-wave group-velocity measurements for all the interstation paths. We used these measurements to construct maps of Rayleigh-wave group-velocity lateral perturbations, at different periods. Despite the great difference in the crustal structure below the OBS (thin continental or oceanic type) and the land stations (typical continental crust, 30 km thick) we were able to derive high S/N cross-correlations between these different types of sensors.This study was co-sponsored by several projects namely the QuakeLoc-PT (PTDC/GEO-FIQ/3522/2012), AQUAREL (PTDC/CTE-GIX/116819/2010), NEAREST FP6-2005-GLOBAL-4 (OJ 2005 C177/15), WILAS (PTDC/CTE-GIX/097946/2008), and PEST-OE/CTE/LA-0019/2013-2014.

  19. Particle image velocimetry correlation signal-to-noise ratio metrics and measurement uncertainty quantification

    CERN Document Server

    Xue, Zhenyu; Vlachos, Pavlos P

    2014-01-01

    In particle image velocimetry (PIV) the measurement signal is contained in the recorded intensity of the particle image pattern superimposed on a variety of noise sources. The signal-to-noise-ratio (SNR) strength governs the resulting PIV cross correlation and ultimately the accuracy and uncertainty of the resulting PIV measurement. Hence we posit that correlation SNR metrics calculated from the correlation plane can be used to quantify the quality of the correlation and the resulting uncertainty of an individual measurement. In this paper we present a framework for evaluating the correlation SNR using a set of different metrics, which in turn are used to develop models for uncertainty estimation. The SNR metrics and corresponding models presented herein are expanded to be applicable to both standard and filtered correlations. In addition, the notion of a valid measurement is redefined with respect to the correlation peak width in order to be consistent with uncertainty quantification principles and distinct ...

  20. Temporal Correlation-Based Spatial Filtering of Rician Noise for Functional MRIs

    Institute of Scientific and Technical Information of China (English)

    Amir. A. Khaliq; I. M. Qureshi; Jawad. A. Shah

    2012-01-01

    A novel correlation-based filter is presented for de-noising functional magnetic resonance imaging (fMRI) data. Temporal correlation-based exponential weights are defined for spatial smoothing of the data, with bias reduction using estimated noise variance. The proposed scheme is tested on simulated and real fMRI data. Finally, the results are compared with conventional filters. The method is found to be effectively suppressing the Rician noise in fMRI data, while improving the SNR.%A novel correlation-based filter is presented for de-noising functional magnetic resonance imaging (fMRI) data.Temporal correlation-based exponential weights are defined for spatial smoothing of the data,with bias reduction using estimated noise variance.The proposed scheme is tested on simulated and real fMRI data.Finally,the results are compared with conventional filters.The method is found to be effectively suppressing the Rician noise in fMRI data,while improving the SNR.

  1. Attofarad resolution capacitance-voltage measurement of nanometer scale field effect transistors utilizing ambient noise.

    Science.gov (United States)

    Gokirmak, Ali; Inaltekin, Hazer; Tiwari, Sandip

    2009-08-19

    A high resolution capacitance-voltage (C-V) characterization technique, enabling direct measurement of electronic properties at the nanoscale in devices such as nanowire field effect transistors (FETs) through the use of random fluctuations, is described. The minimum noise level required for achieving sub-aF (10(-18) F) resolution, the leveraging of stochastic resonance, and the effect of higher levels of noise are illustrated through simulations. The non-linear DeltaC(gate-source/drain)-V(gate) response of FETs is utilized to determine the inversion layer capacitance (C(inv)) and carrier mobility. The technique is demonstrated by extracting the carrier concentration and effective electron mobility in a nanoscale Si FET with C(inv) = 60 aF. PMID:19636094

  2. Low-frequency noise in high-transition-temperature superconducting multilayer magnetometers in ambient magnetic fields

    International Nuclear Information System (INIS)

    Each magnetometer consisted of a dc superconducting quantum interference device (SQUID), with the YBa2Cu3O7-x washer patterned into 4 μm lines, coupled to a multiturn, multilayer flux transformer containing flux dams. The noise at 1 Hz did not increase when bare SQUIDs or magnetometers were cooled and operated in fields up to values well above the magnetic field of the earth. When the magnetic field was changed, the noise in a bare SQUID was constant up to a threshold field of 12 μT. The addition of a flux transformer containing flux dams increased the magnetic field sensitivity by a factor of 43, while reducing the threshold field only moderately, to 5 μT

  3. Data analysis results of the second sea trial of ambient noise imaging with acoustic lens in 2014: Two-dimensional target images affected by direction of field of view and spatial noise distribution

    Science.gov (United States)

    Mori, Kazuyoshi; Ogasawara, Hanako; Tsuchiya, Takenobu; Endoh, Nobuyuki

    2016-07-01

    An aspherical lens with an aperture diameter of 1.0 m has been designed and fabricated to develop a prototype system for ambient noise imaging (ANI). A sea trial of silent target detection using the prototype ANI system was conducted under only natural ocean ambient noise at Uchiura Bay in November 2010. It was verified that targets are successfully detected under natural ocean ambient noise, mainly generated by snapping shrimps. Recently, we have built a second prototype ANI system using an acoustic lens with a two-dimensional (2D) receiver array with 127 elements corresponding to a field of view (FOV) spanning 15° horizontally by 9° vertically. In this study, we investigated the effects of the direction of the FOV and the spatial noise distribution on the 2D target image obtained by ANI. Here, the noise sources in front of the target are called “front light”, and those at the rear of the target are called “back light”. The second sea trial was conducted to image targets arranged in the FOV and measure the positions of noise sources at Uchiura Bay in November 10–14, 2014. For front light, the pixel values in the on-target directions were greater than those in other directions owing to the dominant target scatterings. Reversely, for back light, the pixel values in the on-target directions were lower than those in other directions owing to the dominant direct noises such as “silhouette”.

  4. Optimal filtering for uncertain systems with stochastic nonlinearities, correlated noises and missing measurements

    Institute of Scientific and Technical Information of China (English)

    Shuo Zhang,Yan Zhao,Min Li,; Jianhui Zhao

    2015-01-01

    The global y optimal recursive filtering problem is stu-died for a class of systems with random parameter matrices, stochastic nonlinearities, correlated noises and missing measure-ments. The stochastic nonlinearities are presented in the system model to reflect multiplicative random disturbances, and the addi-tive noises, process noise and measurement noise, are assumed to be one-step autocorrelated as wel as two-step cross-correlated. A series of random variables is introduced as the missing rates governing the intermittent measurement losses caused by un-favorable network conditions. The aim of the addressed filtering problem is to design an optimal recursive filter for the uncertain systems based on an innovation approach such that the filtering error is global y minimized at each sampling time. A numerical simulation example is provided to il ustrate the effectiveness and applicability of the proposed algorithm.

  5. The correlation between serum leptin and blood pressure after exposure to noise at work

    Directory of Open Access Journals (Sweden)

    Muayad S Rahma

    2013-01-01

    Full Text Available Several epidemiologic studies have reported that exposure to noise is associated with cardiovascular disease. The increased body weight is often associated with metabolic as well as increased blood pressure. The aim of this study is to investigate the correlation between the elevation of blood pressure and serum leptin hormones due to the effects of noise in the work place. A total of 80 volunteer males where included in this study with an age range between of 20 and 45 years, they were divided in two groups equally, the 1 st group were exposed to noise in the workplace while the 2 nd group were not. The individual noise exposure was determined by using a sound level meter. The range of noise was 80-100 dBA. Body Mass Index was also taken for each individual by a standard measure, blood pressure was measured by OMRON sphygmomanometer and serum leptin was measured through venous blood sample analysis enzyme linked immunosorbent assay. Spearman rank order correlation was used to examine the correlations between Blood pressure value (Systolic, Diastolic and Leptin. All the relationships between parameters showed a positive correlation. Systolic and diastolic blood pressure values had a significant correlation to leptin hormone level in comparison to the control. There was a significant relation between leptin and blood pressure. leptin effects on the sympathetic nervous system may provide a partial explanation. Therefore, Leptin might have diverse cardiovascular actions.

  6. A new method to estimate the noise in financial correlation matrices

    International Nuclear Information System (INIS)

    Companies belonging to the same industrial branch are subject to similar economical influences. Hence, the time series of their stocks can show similar trends implying a correlation. Financial correlation matrices measure the unsystematic correlations between time series of stocks. Such information is important for risk management. It has been found by Laloux et al that the correlation matrices are 'noise dressed', a major reason being the finiteness of the time series. We present a new and alternative method to estimate this noise. We introduce a power mapping of the elements in the correlation matrix which suppresses the noise and thereby effectively 'prolongs' the time series. Neither further data processing nor additional input is needed. To develop and test our method, we use a model suggested by Noh which can be viewed as a special case of a 'factor model' in economics. We perform numerical simulations for the time series and obtain correlation matrices. We support the numerics by a qualitative analytical discussion. With our approach, different correlation structures buried under this noise can be detected. Our method is general and can be applied to all systems in which time series are measured

  7. Shot noise of a quantum dot with non-Fermi liquid correlations

    OpenAIRE

    Braggio, A.; Fazio, R.; Sassetti, M.

    2003-01-01

    The shot noise of a one-dimensional wire interrupted by two barriers shows interesting features related to the interplay between Coulomb blockade effects, Luttinger correlations and discrete excitations. At small bias the Fano factor reaches the lowest attainable value, 1/2, irrespective of the ratio of the two junction resistances. At larger voltages this asymmetry is power-law renormalized by the interaction strength. We discuss how the measurement of current and these features of the noise...

  8. The connection between noise and quantum correlations in a double quantum dot

    OpenAIRE

    Bodoky, F.; Belzig, W.; Bruder, C.

    2007-01-01

    We investigate the current and noise characteristics of a double quantum dot system. The strong correlations induced by the Coulomb interaction create entangled two-electron states and lead to signatures in the transport properties. We show that the interaction parameter phi, which measures the admixture of the double-occupancy contribution to the singlet state and thus the degree of entanglement, can be directly accessed through the Fano factor of super-Poissonian shot noise.

  9. Noise-correlation-time-mediated localization in random nonlinear dynamical systems

    CERN Document Server

    Cabrera, J L; De la Rubia, F J; Cabrera, Juan L.

    1999-01-01

    We investigate the behavior of the residence times density function for different nonlinear dynamical systems with limit cycle behavior and perturbed parametrically with a colored noise. We present evidence that underlying the stochastic resonancelike behavior with the noise correlation time, there is an effect of optimal localization of the system trajectories in the phase space. This phenomenon is observed in systems with different nonlinearities, suggesting a degree of universality.

  10. On the loss-of-correlation due to PIV image noise

    Science.gov (United States)

    Scharnowski, Sven; Kähler, Christian J.

    2016-07-01

    The effect of image noise on the uncertainty of velocity fields measured with particle image velocimetry (PIV) is still an unsolved problem. Image noise reduces the correlation signal and thus affects the estimation of the particle image displacement. However, a systematic quantification of the effect of the noise level on the loss-of-correlation is missing. In this work, a new method is proposed to estimate the loss-of-correlation due to image noise F_{σ } from the autocorrelation function of PIV images. Furthermore, a new definition of the signal-to-noise ratio (SNR) for PIV images is suggested, which results in a bijective relation between F_{σ } and SNR. Based on the newly defined SNR, it becomes possible to estimate the signal level and the noise level itself. The presented method is very general because the estimation of F_{σ } and SNR works independently of various parameters, including the particle image intensity, the particle image density, the particle image size, the image noise distributions and the laser light-sheet profile. The findings lead to an extension of the fundamental PIV equation N=NI FI FO F_{Δ } and enable PIV users to optimize their measurement setup with respect to the image noise and not only based on the loss-of-correlation due to in-plane motion, out-of-plane motion and displacement gradients. Furthermore, the new definition of SNR allows for a characterization and comparison of PIV images. The new approaches are validated by using synthetic images, and the predictions are confirmed by using experimental data.

  11. Intensity Correlation Function of a Single-Mode Laser Driven by Colored Cross-Correlation Noises in Modulation of a Bias Signal

    Institute of Scientific and Technical Information of China (English)

    HAN Li-Bo; CAO Li; YANG Hong-Quan; WU Da-Jin

    2005-01-01

    By using the linear approximation method, the intensity correlation function is calculated for a single-mode laser modulated by a bias signal and driven by colored pump and quantum noises with colored cross-correlation. We found that, when the correlation time between the two noises is very short, the behavior of the intensity correlation function versus the time, in addition to decreasing monotonously, also exhibits several cases, such as one maximum, one minimum, and two extrema. When the correlation time between the two noises is very long, the behavior of the intensity correlation function exhibits oscillation and the envelope is similar to the case of short cross-correlation time.

  12. Noise-induced bias for convolution-based interpolation in digital image correlation.

    Science.gov (United States)

    Su, Yong; Zhang, Qingchuan; Gao, Zeren; Xu, Xiaohai

    2016-01-25

    In digital image correlation (DIC), the noise-induced bias is significant if the noise level is high or the contrast of the image is low. However, existing methods for the estimation of the noise-induced bias are merely applicable to traditional interpolation methods such as linear and cubic interpolation, but are not applicable to generalized interpolation methods such as BSpline and OMOMS. Both traditional interpolation and generalized interpolation belong to convolution-based interpolation. Considering the widely use of generalized interpolation, this paper presents a theoretical analysis of noise-induced bias for convolution-based interpolation. A sinusoidal approximate formula for noise-induced bias is derived; this formula motivates an estimating strategy which is with speed, ease, and accuracy; furthermore, based on this formula, the mechanism of sophisticated interpolation methods generally reducing noise-induced bias is revealed. The validity of the theoretical analysis is established by both numerical simulations and actual subpixel translation experiment. Compared to existing methods, formulae provided by this paper are simpler, briefer, and more general. In addition, a more intuitionistic explanation of the cause of noise-induced bias is provided by quantitatively characterized the position-dependence of noise variability in the spatial domain. PMID:26832501

  13. Seismic ambient noise around the South China Sea: seasonal and spatial variations, and implications for its climate and surface circulation

    Science.gov (United States)

    Huo, Da; Yang, Ting

    2013-12-01

    With its strong seasonal variation in wave climate and various bathymetric features due to the complex tectonics, the South China Sea (SCS) provides a natural laboratory to study the microseism. We collected data from seismic stations around the SCS and calculated their noise spectra, through which seasonal and spatial variations of microseism, as well as the general feature of seismic ambient noise in this marginal sea were revealed. Microseism seasonal variations in general reflect influences of the East Asian monsoon in winter and the Indian monsoon in summer, respectively. The two microseism components, the single frequency microseism (SFM) and the double frequency microseism (DFM), show striking alternating variation patterns both seasonally and spatially. These variation patterns, along with the bathymetric feature near the stations, indicate SFM and DFM are generated through different physical mechanisms. More interestingly, seasonal and spatial variations of DFM appear to be consistent with the basin-scale surface circulation model of the SCS, in which the upper SCS experiences cyclonic in winter and anti-cyclonic in summer. These consistencies provide observational evidence for the hypothesis that the cyclonic depression is a favorable condition to generate DFM.

  14. Understanding the Structure of the Subsurface of the El Tatio Geyser field: A Velocity Model of the El Jefe Geyser from Ambient Seismic Noise

    Science.gov (United States)

    LongJohn, T.; Kelly, C.; Seats, K.; Lawrence, J.

    2013-12-01

    Hydrothermal system studies are important for geothermal energy exploration and geysers are also believed to be functional analogues of volcanoes. However, the mechanism of eruption and the characteristics of the plumbing system of most geysers are poorly understood given their subsurface location and sparse global distribution. An accurate acoustic velocity model could yield important insight into subsurface density and thermal variations in a geyser system. Passive seismic data was collected at El Jefe geyser in El Tatio Geyser Field, northern Chile during October of 2012. An array of 6 broadband seismometers and 51 high frequency geophones were deployed for ~1 week in a grid array with station spacing of 2-10 meters (geophones) and 3-50 meters (broadbands) centered around El Jefe Geyser. Using ambient seismic noise generated by the geyser system, I constructed a preliminary subsurface velocity model for El Jefe Geyser. As a result of the close station spacing, the seismic signals sampled shallow depths corresponding to high frequency waves. Coherent seismic records from different seismic station pairs were cross correlated to produce noise correlation functions (NCF). Adaptive covariance filtering and stacking techniques were utilized to amplify the signal of the NCFs and one-dimensional velocities between station pairs at varying depths were determined. Next, a tomographic inversion was done to interpolate between the one-dimensional velocities and produce a three-dimensional velocity model for the entire geyser area. From the velocity model, we can identify regions of low and high acoustic velocity that potentially represent water reservoirs and bedrock respectively.

  15. Stochastic resonance in a gain-noise model of a single-mode laser driven by pump noise and quantum noise with cross-correlation between real and imaginary parts under direct signal modulation

    Institute of Scientific and Technical Information of China (English)

    Chen Li-Mei; Cao Li; Wu Da-Jin

    2007-01-01

    Stochastic resonance (SR) is studied in a gain-noise model of a single-mode laser driven by a coloured pump noise and a quantum noise with cross-correlation between real and imaginary parts under a direct signal modulation. By using a linear approximation method, we find that the SR appears during the variation of signal-to-noise ratio (SNR)separately with the pump noise self-correlation time τ, the noise correlation coefficient between the real part and the imaginary part of the quantum noise λq, the attenuation coefficient γ and the deterministic steady-state intensity I0.In addition, it is found that the SR can be characterized not only by the dependence of SNR on the noise variables of τand λq, but also by the dependence of SNR on the laser system variables of γ and I0. Thus our investigation extends the characteristic quantity of SR proposed before.

  16. Noise

    Science.gov (United States)

    Noise is all around you, from televisions and radios to lawn mowers and washing machines. Normally, you ... sensitive structures of the inner ear and cause noise-induced hearing loss. More than 30 million Americans ...

  17. Cross-correlation measurement of quantum shot noise using homemade transimpedance amplifiers.

    Science.gov (United States)

    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

  18. Cross-correlation measurement of quantum shot noise using homemade transimpedance amplifiers

    International Nuclear Information System (INIS)

    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

  19. The characteristic analysis of ambient sea noise spectrum based on submersible buoy%基于潜标测量的海洋环境噪声谱特性分析

    Institute of Scientific and Technical Information of China (English)

    笪良龙; 王超; 卢晓亭; 韩梅; 邓小花

    2014-01-01

    利用海洋环境噪声测量潜标系统对南海典型海域开展了为期3个月的海洋环境噪声测量,16通道海洋环境噪声测量系统每小时测量两分钟噪声信号。数据处理结果表明,800~5000 Hz范围内,噪声谱与风速相关性最好,且风速越大相关性越好,噪声谱与风速的相关性好于与浪高的相关性。风关噪声谱级在海水中部基本不随接收深度发生变化,但由于测量水听器阵长度未能覆盖整个水深,因此未给出海面和海底处谱级变化规律。在400 Hz以上的高频段整个风速范围内噪声谱级都随风速发生变化,且噪声谱级与对数风速具有很好的线性关系。%Ambient sea-noise data were collected for three month period ,using submersible buoy system in the South China Sea .Broad-band ambient-noise signals from the sixteen hydrophones were amplified and recorded for 2min every 1h .The results of data processing show a strong wind dependence in the upper frequency bands from ap-proximately 800 Hz to 5 kHz ,and the greater the wind speed ,the better the correlation .The noise is correlated more with wind speed than with wave height . The wind-generated spectrum level producing virtually constant noise intensity in the midwater ,however ,due to the length of the hydrophone failed to cover the entire depth ,the distribution of the noise at the near-surface and near-bottom unable to given .In the frequencies above 400 Hz am-bient-noise spectrum level ranged with the entire wind speeds .In addition it was found that the ambient-noise spec-trum shown to be linearly dependent upon the logarithm of wind speed .

  20. Interpreting Cross-correlations of One-bit Filtered Seismic Noise

    CERN Document Server

    Hanasoge, Shravan

    2013-01-01

    Seismic noise, generated by oceanic microseisms and other sources, illuminates the crust in a manner different from tectonic sources, and therefore provides independent information. The primary measurable is the two-point cross-correlation, evaluated using traces recorded at a pair of seismometers over a finite-time interval. However, raw seismic traces contain intermittent large-amplitude perturbations arising from tectonic activity and instrumental errors, which may corrupt the estimated cross-correlations of microseismic fluctuations. In order to diminish the impact of these perturbations, the recorded traces are filtered using the nonlinear one-bit digitizer, which replaces the measurement by its sign. Previous theory shows that for stationary Gaussian-distributed seismic noise fluctuations one-bit and raw correlation functions are related by a simple invertible transformation. Here we extend this to show that the simple correspondence between these two correlation techniques remains valid for {\\it non-st...

  1. Graphene thermal transport studies via radio-frequency, cross-correlated Johnson noise thermometry

    Science.gov (United States)

    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.

  2. Probability distributions for directed polymers in random media with correlated noise.

    Science.gov (United States)

    Chu, Sherry; Kardar, Mehran

    2016-07-01

    The probability distribution for the free energy of directed polymers in random media (DPRM) with uncorrelated noise in d=1+1 dimensions satisfies the Tracy-Widom distribution. We inquire if and how this universal distribution is modified in the presence of spatially correlated noise. The width of the distribution scales as the DPRM length to an exponent β, in good (but not full) agreement with previous renormalization group and numerical results. The scaled probability is well described by the Tracy-Widom form for uncorrelated noise, but becomes symmetric with increasing correlation exponent. We thus find a class of distributions that continuously interpolates between Tracy-Widom and Gaussian forms. PMID:27575059

  3. Experimental demonstration of sub-shot-noise intensity correlations in an intense twin beam

    Czech Academy of Sciences Publication Activity Database

    Bondani, M.; Allevi, A.; Zambra, G.; Andreoni, A.; Peřina, Jan; Křepelka, Jaromír; Peřina ml., Jan

    2008-01-01

    Roč. 160, č. 1 (2008), s. 33-41. ISSN 1951-6355 Institutional research plan: CEZ:AV0Z10100522 Keywords : sub- shot -noise * intensity correlation * twin beam Subject RIV: BH - Optics, Masers, Lasers Impact factor: 0.689, year: 2008

  4. Filtering for linear systems with noise correlation and its application to singular systems

    Institute of Scientific and Technical Information of China (English)

    Wu Jian-Rong; Song Shi-Ji

    2004-01-01

    In this paper, an optimal filter for a stochastic linear system with previous stage noise correlation is designed.Based on this result, together with the decomposition techniques of the stochastic singular linear system, the design of an optimal filter for a stochastic singular linear system is given.

  5. The buried shape of an alpine valley from gravity surveys, seismic and ambient noise analysis

    Science.gov (United States)

    Barnaba, C.; Marello, L.; Vuan, A.; Palmieri, F.; Romanelli, M.; Priolo, E.; Braitenberg, C.

    2010-02-01

    It has long been observed that damage due to earthquakes depends greatly on local geological conditions. Alpine valleys represent a typical populated environment where large amplifications can take place owing to the presence of surface soils with poor mechanical properties combined to complex topography of the rock basin. In the framework of the EU Interreg IIIB SISMOVALP Project `Seismic hazard and alpine valley response analysis', a stretch of the Tagliamento River Valley (TRV), located in the north-western part of the Friuli Region (Italy) and close to the epicentre of the 1976 Mw = 6.4 earthquake, has been investigated with the aim to define the buried shape of the valley itself. Two non-invasive, low cost, independent geophysical methods were used: (i) detailed gravity survey and (ii) H/V spectral ratio (HVSR) of microtremors. Because of structural geological complexity and active tectonics of the Friuli region, an irregular valley shape was expected in this area. The independent analysis performed by gravity and passive noise, and complemented with refraction seismic velocity profiles, confirms this hypothesis and leads to two models that were consistent, but for some small scale details. The maximum depth estimated is about 400-450 m in the southern part of the valley, while a mean value of 150-180 m is estimated in the northern part. The sediment thickness obtained for this stretch of the TRV is quite large if compared to eastern Alps Plio-Quaternary rates; therefore the valley shape imaged by this study better corresponds to the top of carbonate rocks. Finally, on the basis of the obtained morphology and some direct measurements, we conclude that the TRV features an overall 1-D seismic response (i.e. the resonance is related only to the sediment thickness rather than to the cross-section shape), but in its deepest part some limited 2-D effects could take place.

  6. Ambient Sensors

    OpenAIRE

    Börner, Dirk; Specht, Marcus

    2014-01-01

    This software sketches comprise two custom-built ambient sensors, i.e. a noise and a movement sensor. Both sensors measure an ambient value and process the values to a color gradient (green > yellow > red). The sensors were built using the Processing 1.5.1 development environment. Available under the GNU LGPL licence version 3 or higher.

  7. Ambient Sensors

    NARCIS (Netherlands)

    Börner, Dirk; Specht, Marcus

    2014-01-01

    This software sketches comprise two custom-built ambient sensors, i.e. a noise and a movement sensor. Both sensors measure an ambient value and process the values to a color gradient (green > yellow > red). The sensors were built using the Processing 1.5.1 development environment. Available under th

  8. Geophysical Investigations on Malta (Central Mediterranean) using Ambient Noise: Assessing Array Performance and Influence of a Thick Low Velocity Layer.

    Science.gov (United States)

    Farrugia, D.; Paolucci, E.; D'Amico, S.; Galea, P. M.

    2014-12-01

    The use of microtremors to obtain shear wave velocity (Vs) profiles of the subsurface is becoming a widespread approach due to its various advantages. Noise measurements were carried out at four sites on Malta (Central Mediterranean). Array techniques were first tested in an area where a ≈45 m layer of soft Blue Clay (BC) overlies the harder limestone. Three array configurations (two arrays of 17 geophones in an L-shape and circle respectively and one 42 geophone array in an L-shape) were tested and processed using the f-k and two SPAC techniques: Modified and Extended SPAC. No significant difference was observed in the dispersion curve from the two short arrays despite having different shapes. However, a significant variation was observed between the dispersion curve from the long and short arrays in the low frequency part. A joint inversion, using two direct search methods, of the dispersion and the H/V curve was then used to obtain the Vs profile for the site, with most of the profiles being in agreement both in terms of velocity and depth. A study was also conducted at three other sites on Malta where hard Upper Coralline Limestone (UCL) overlies the soft BC creating a velocity inversion in the soil profile. The shape of the effective dispersion curves obtained using ESAC show both an inverse dispersive trend and normal dispersion. This shape is tentatively explained in terms of the presence of higher mode Rayleigh waves. A Genetic Algorithm approach was then used to jointly invert the H/V and Rayleigh wave dispersion curve. It was observed that the BC velocity was higher when overlain by a large thickness of UCL. This could be linked to the effective pressure caused by the hard UCL, making the BC more compact, and having a higher velocity. The theoretical implications of a prominent low-velocity layer on site amplification and the interpretation of ambient noise data are investigated and discussed.

  9. Statistical properties of a filtered Poisson process with additive random noise: Distributions, correlations and moment estimation

    CERN Document Server

    Theodorsen, Audun; Rypdal, Martin

    2016-01-01

    The filtered Poisson process is often used as a reference model for intermittent fluctuations in physical systems. Here, this process is extended by adding a noise term, either as a purely additive term to the process or as a dynamical term in a stochastic differential equation. The moments, probability density function, auto- correlation function and power spectral density are derived and used to compare the effects of the different noise terms. Monte-Carlo studies of synthetic time series are used to investigate the accuracy of parameter estimation and to identify methods for separating the noise types. It is shown that the probability density function and the three lowest moments provide accurate estimations of the parameters, but are unable to separate the noise types. The auto-correlation function and the power spectral density also provide methods for estimating the model parameters, as well as being capable of determining the noise type. The number of times the signal passes a prescribed threshold in t...

  10. The anisotropic structure in the crust in the northern part of North China from ambient seismic noise tomography

    Science.gov (United States)

    Fu, Yuanyuan V.; Gao, Yuan; Li, Aibing; Lu, Laiyu; Shi, Yutao; Zhang, Yi

    2016-03-01

    We have measured radial anisotropy in the crust beneath the northern part of North China by jointly inverting Rayleigh and Love wave phase velocities at periods less than 35 s from 14 months of ambient noise data recorded by 222 broad-band seismic stations. We also estimate the azimuthal anisotropy of phase velocity from Rayleigh wave data. The fast direction of azimuthal anisotropy varies with periods, NE-SW orientation at short and intermediate periods (10-16 s) and NW-SE orientation at periods larger than 20 s. The NE-SW oriented fast direction of azimuthal anisotropy may be related to the fossilized structural fabrics due to the compression during the Indosinian orogeny from late Palaeozoic to middle Mesozoic. The NW-SE trend of anisotropic fabric in the lower crust and uppermost mantle is probably associated with the later lithospheric extension. The observed radial anisotropy also shows a two-layer feature, negative radial anisotropy (Vsh Vsv) in the middle-lower crust. The compressional tectonics from late Palaeozoic to middle Mesozoic may cause crustal materials align vertically throughout the crust. This vertical fabric could make Vsh slower than Vsv. However, the lithospheric extension in the late Mesozoic to Cenozoic time could overprint the older fabric in the middle and lower crust by magma intrusion and underplating. Horizontal alignment of the material or intruded melt sills due to the extension probably produce the observed strong positive radial anisotropy in the middle and lower crust.

  11. Inversion of ambient seismic noise HVSR to evaluate velocity and structural models of the Lower Tagus Basin, Portugal

    Science.gov (United States)

    Borges, J. F.; Silva, H. G.; Torres, R. J. G.; Caldeira, B.; Bezzeghoud, M.; Furtado, J. A.; Carvalho, J.

    2016-07-01

    During its history, several significant earthquakes have shaken the Lower Tagus Valley (Portugal). These earthquakes were destructive; some strong earthquakes were produced by large ruptures in offshore structures located southwest of the Portuguese coastline, and other moderate earthquakes were produced by local faults. In recent years, several studies have successfully obtained strong-ground motion syntheses for the Lower Tagus Valley using the finite difference method. To confirm the velocity model of this sedimentary basin obtained from geophysical and geological data, we analysed the ambient seismic noise measurements by applying the horizontal to vertical spectral ratio (HVSR) method. This study reveals the dependence of the frequency and amplitude of the low-frequency (HVSR) peaks (0.2-2 Hz) on the sediment thickness. We have obtained the depth of the Cenozoic basement along a profile transversal to the basin by the inversion of these ratios, imposing constraints from seismic reflection, boreholes, seismic sounding and gravimetric and magnetic potentials. This technique enables us to improve the existing three-dimensional model of the Lower Tagus Valley structure. The improved model will be decisive for the improvement of strong motion predictions in the earthquake hazard analysis of this highly populated basin. The methodology discussed can be applied to any other sedimentary basin.

  12. Surrogate testing of volatility series from long-range correlated noise

    CERN Document Server

    Nagarajan, R

    2006-01-01

    Detrended fluctuation analysis (DFA) [1] of the volatility series has been found to be useful in dentifying possible nonlinear/multifractal dynamics in the empirical sample [2-4]. Long-range volatile correlation can be an outcome of static as well as dynamical nonlinearity. In order to argue in favor of dynamical nonlinearity, surrogate testing is used in conjunction with volatility analysis [2-4]. In this brief communication, surrogate testing of volatility series from long-range correlated noise and their static, invertible nonlinear transforms is investigated. Long-range correlated monofractal noise is generated using FARIMA (0, d, 0) with Gaussian and non-Gaussian innovations. We show significant deviation in the scaling behavior between the empirical sample and the surrogate counterpart at large time-scales in the case of FARIMA (0, d, 0) with non-Gaussian innovations whereas no such discrepancy was observed in the case of Gaussian innovations. The results encourage cautious interpretation of surrogate t...

  13. A correlation polarimeter for noise-like signals. [optimum estimation of linearly polarized electromagnetic wave

    Science.gov (United States)

    Ohlson, J. E.

    1976-01-01

    Optimum estimation (tracking) of the polarization plane of a linearly polarized electromagnetic wave is determined when the signal is a narrow-band Gaussian random process with a polarization plane angle which is also a Gaussian random process. This model is compared to previous work and is applicable to space communication. The estimator performs a correlation operation similar to an amplitude-comparison monopulse angle tracker, giving the name correlation polarimeter. Under large signal-to-noise ratio (SNR), the estimator is causal. Performance of the causal correlation polarimeter is evaluated for arbitrary SNR. Optimum precorrelation filtering is determined. With low SNR, the performance of this system is far better than that of previously developed systems. Practical implementation is discussed. A scheme is given to reduce the effect of linearly polarized noise.

  14. Stochastic Bifurcations induced by correlated Noise in a Birhythmic van der Pol System

    CERN Document Server

    Yonkeu, R Mbakob; Filatrella, G; Tchawoua, C

    2015-01-01

    We investigate the effects of exponentially correlated noise on birhythmic van der Pol type oscillators. The analytical results are obtained applying the quasi-harmonic assumption to the Langevin equation to derive an approximated Fokker-Planck equation. This approach allows to analytically derive the probability distributions as well as the activation energies associated to switching between coexisting attractors. The stationary probability density function of the van der Pol oscillator reveals the influence of the correlation time on the dynamics. Stochastic bifurcations are discussed through a qualitative change of the stationary probability distribution, which indicates that noise intensity and correlation time can be treated as bifurcation parameters. Comparing the analytical and numerical results, we find good agreement both when the frequencies of the attractors are about equal or when they are markedly different.

  15. Depict noise-driven nonlinear dynamic networks from output data by using high-order correlations

    CERN Document Server

    Chen, Yang; Chen, Tianyu; Wang, Shihong; Hu, Gang

    2016-01-01

    Many practical systems can be described by dynamic networks, for which modern technique can measure their output signals, and accumulate extremely rich data. Nevertheless, the network structures producing these data are often deeply hidden in these data. Depicting network structures by analysing the available data turns to be significant inverse problems. On one hand, dynamics are often driven by various unknown facts, called noises. On the other hand, network structures of practical systems are commonly nonlinear, and different nonlinearities can provide rich dynamic features and meaningful functions of realistic networks. So far, no method, both theoretically or numerically, has been found to systematically treat the both difficulties together. Here we propose to use high-order correlation computations (HOCC) to treat nonlinear dynamics; use two-time correlations to treat noise effects; and use suitable basis and correlator vectors to unifiedly depict all dynamic nonlinearities and topological interaction l...

  16. Cross-correlation spin noise spectroscopy of heterogeneous interacting spin systems

    International Nuclear Information System (INIS)

    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

  17. An Optimal Energy Estimator to Reduce Correlated Noise for the EXO-200 Light Readout

    OpenAIRE

    Collaboration, EXO-200; :; Davis, C. G.; Hall, C; Albert, J. B.; Barbeau, P. S.; D. Beck; Belov, V.; Breidenbach, M.; Brunner, T.; Burenkov, A.; Cao, G. F.; Cen, W. R.; Chambers, C.; Cleveland, B.

    2016-01-01

    The energy resolution of the EXO-200 detector is limited by electronics noise in the measurement of the scintillation response. Here we present a new technique to extract optimal scintillation energy measurements for signals split across multiple channels in the presence of correlated noise. The implementation of these techniques improves the energy resolution of the detector at the neutrinoless double beta decay Q-value from $\\left[1.9641\\pm 0.0039\\right]\\%$ to $\\left[1.5820\\pm 0.0044\\right]...

  18. An Optimal Energy Estimator to Reduce Correlated Noise for the EXO-200 Light Readout

    CERN Document Server

    :,; Hall, C; Albert, J B; Barbeau, P S; Beck, D; Belov, V; Breidenbach, M; Brunner, T; Burenkov, A; Cao, G F; Cen, W R; Chambers, C; Cleveland, B; Coon, M; Craycraft, A; Daniels, T; Danilov, M; Daugherty, S J; Davis, J; Delaquis, S; Der Mesrobian-Kabakian, A; DeVoe, R; Didberidze, T; Dilling, J; Dolgolenko, A; Dolinski, M J; Dunford, M; Fairbank, W; Farine, J; Feldmeier, W; Feyzbakhsh, S; Fierlinger, P; Fudenberg, D; Gornea, R; Graham, K; Gratta, G; Hughes, M; Jewell, M J; Johnson, A; Johnson, T N; Johnston, S; Karelin, A; Kaufman, L J; Killick, R; Koffas, T; Kravitz, S; Krücken, R; Kuchenkov, A; Kumar, K S; Leonard, D S; Licciardi, C; Lin, Y H; Ling, J; MacLellan, R; Marino, M G; Mong, B; Moore, D; Njoya, O; Nelson, R; Odian, A; Ostrovskiy, I; Piepke, A; Pocar, A; Prescott, C Y; Retière, F; Rowson, P C; Russell, J J; Schubert, A; Sinclair, D; Smith, E; Stekhanov, V; Tarka, M; Tolba, T; Tsang, R; Twelker, K; Vuilleumier, J -L; Waite, A; Walton, J; Walton, T; Weber, M; Wen, L J; Wichoski, U; Wood, J; Yang, L; Yen, Y -R; Zeldovich, O Ya

    2016-01-01

    The energy resolution of the EXO-200 detector is limited by electronics noise in the measurement of the scintillation response. Here we present a new technique to extract optimal scintillation energy measurements for signals split across multiple channels in the presence of correlated noise. The implementation of these techniques improves the energy resolution of the detector at the neutrinoless double beta decay Q-value from $\\left[1.9641\\pm 0.0039\\right]\\%$ to $\\left[1.5820\\pm 0.0044\\right]\\%$.

  19. Significance of Geological Units of the Bohemian Massif, Czech Republic, as Seen by Ambient Noise Interferometry

    Science.gov (United States)

    Růžek, Bohuslav; Valentová, Lubica; Gallovič, František

    2016-05-01

    Broadband recordings of 88 seismic stations distributed in the Bohemian Massif, Czech Republic, and covering the time period of up to 12 years were processed by a cross-correlation technique. All correlograms were analyzed by a novel approach to get both group and phase dispersion of Rayleigh and Love waves. Individual dispersion curves were averaged in five distinct geological units which constitute the Bohemian Massif (Saxothuringian, Teplá-Barrandean, Sudetes, Moravo-Silesian, and Moldanubian). Estimated error of the averaged dispersion curves are by an order smaller than the inherent variability due to the 3D distribution of seismic velocities within the units. The averaged dispersion data were inverted for 1D layered velocity models including their uncertainty, which are characteristic for each of the geological unit. We found that, overall, the differences between the inverted velocity models are of similar order as the variability inside the geological units, suggesting that the geological specification of the units is not fully reflected into the S-wave propagation velocities on a regional scale. Nevertheless, careful treatment of the dispersion data allowed us to identify some robust characteristics of the area. The vp to vs ratio is anomalously low (~1.6) for all the units. The Moldanubian is the most rigid and most homogeneous part of the Bohemian Massif. Middle crust in the depth range of ~3-15 km is relatively homogeneous across the investigated region, while both uppermost horizon (0-3 km) and lower crust (>15 km) exhibit lower degree of homogeneity.

  20. Upper bound for the time derivative of entropy for a dynamical system driven by coloured cross-correlated white noises

    Institute of Scientific and Technical Information of China (English)

    Xie Wen-Xian; Xu Wei; Cai Li; Jin Yan-Fei

    2005-01-01

    It is shown how the cross-correlation time and strength of coloured cross-correlated white noises can set an upper bound for the time derivative of entropy in a nonequilibrium system. The value of upper bound can be calculateddirectly based on the Schwartz inequality principle and the Fokker-Planck equation of the dynamical system driven by coloured cross-correlated white noises. The present calculations can be used to interpret the interplay of the dissipative constant and cross-correlation time and strength of coloured cross-correlated white noises on the upper bound.

  1. Particle image velocimetry correlation signal-to-noise ratio metrics and measurement uncertainty quantification

    International Nuclear Information System (INIS)

    In particle image velocimetry (PIV) the measurement signal is contained in the recorded intensity of the particle image pattern superimposed on a variety of noise sources. The signal-to-noise-ratio (SNR) strength governs the resulting PIV cross correlation and ultimately the accuracy and uncertainty of the resulting PIV measurement. Hence we posit that correlation SNR metrics calculated from the correlation plane can be used to quantify the quality of the correlation and the resulting uncertainty of an individual measurement. In this paper we extend the original work by Charonko and Vlachos and present a framework for evaluating the correlation SNR using a set of different metrics, which in turn are used to develop models for uncertainty estimation. Several corrections have been applied in this work. The SNR metrics and corresponding models presented herein are expanded to be applicable to both standard and filtered correlations by applying a subtraction of the minimum correlation value to remove the effect of the background image noise. In addition, the notion of a ‘valid’ measurement is redefined with respect to the correlation peak width in order to be consistent with uncertainty quantification principles and distinct from an ‘outlier’ measurement. Finally the type and significance of the error distribution function is investigated. These advancements lead to more robust and reliable uncertainty estimation models compared with the original work by Charonko and Vlachos. The models are tested against both synthetic benchmark data as well as experimental measurements. In this work, U68.5 uncertainties are estimated at the 68.5% confidence level while U95 uncertainties are estimated at 95% confidence level. For all cases the resulting calculated coverage factors approximate the expected theoretical confidence intervals, thus demonstrating the applicability of these new models for estimation of uncertainty for individual PIV measurements. (paper)

  2. Mean first-passage time of an asymmetric bistable system driven by colour-correlated noise

    Institute of Scientific and Technical Information of China (English)

    Zhang Xiao-Yan; Xu Wei

    2007-01-01

    In this paper, the effect of every parameter (including p, q,r, λ,τ) on the mean first-passage time (MFPT) is investigated in an asymmetric bistable system driven by colour-correlated noise. The expression of MFPT has been obtained by applying the steepest-descent approximation. Numerical results show that (1) the intensity of multiplicative noise p and the intensity of additive noise q play different roles in the MFPT of the system, (2) suppression appears on the curve of the MFPT with small λ (e.g. λ< 0.5) but there is a peak on the curve of the MFPT when λ is big (e.g.λ> 0.5), and (3) with different values of r (e.g. r = 0.1, 0.5, 1.5), the effort of τ on the MFPT is diverse.

  3. Effects of Tropospheric Spatio-Temporal Correlated Noise on the Analysis of Space Geodetic Data

    Science.gov (United States)

    Romero-Wolf, A.; Jacobs, C. S.; Ratcliff, J. T.

    2012-01-01

    The standard VLBI analysis models the distribution of measurement noise as Gaussian. Because the price of recording bits is steadily decreasing, thermal errors will soon no longer dominate. As a result, it is expected that troposphere and instrumentation/clock errors will increasingly become more dominant. Given that both of these errors have correlated spectra, properly modeling the error distributions will become increasingly relevant for optimal analysis. We discuss the advantages of modeling the correlations between tropospheric delays using a Kolmogorov spectrum and the frozen flow assumption pioneered by Treuhaft and Lanyi. We then apply these correlated noise spectra to the weighting of VLBI data analysis for two case studies: X/Ka-band global astrometry and Earth orientation. In both cases we see improved results when the analyses are weighted with correlated noise models vs. the standard uncorrelated models. The X/Ka astrometric scatter improved by approx.10% and the systematic Delta delta vs. delta slope decreased by approx. 50%. The TEMPO Earth orientation results improved by 17% in baseline transverse and 27% in baseline vertical.

  4. Influence of the angular correlation of fission neutrons on noise signatures

    International Nuclear Information System (INIS)

    Noise signatures, the measurement of the correlation between the fluctuating parts of the signals coming from neutron detectors, are commonly used to measure nuclear parameters (reactivities, mean lives) and to monitor nuclear systems. Several techniques are used, such as the correlation or analog signals in time or frequency domains or the statistical analysis of detection events. Apart from the experimental method, the useful components of the stochastic descriptors is related to the detection of neutrons that have ancestors born in the same fission event. Despite an early work opened to the inclusion of the n - n angular correlations of neutrons coming from the same fission, practically all the theoretical applications ignore this additional complication by making the implicit or explicit hypothesis that fission neutrons are born uncorrelated. However, there are direct measurements that show angular and energy correlation for the two-fission-neutron distribution. The first attempt to include this experimental evidence into the theory of neutron noise was the calculation of the ratio of spectral densities related to the 252Cf method of measuring reactivities under the simplest condition: two neutron detectors monitoring a 252Cf-plated fission chamber. The objective of this communication is to show how noise signatures of more complex systems are sensitive to the joint distribution γ(v,v '), of two neutrons coming from the same fission with velocities v and v'

  5. On the dependence of the noise amplitude on the correlation length of inlet temperature fluctuations in PWRs

    International Nuclear Information System (INIS)

    Highlights: ► Significant increase of the noise amplitude was observed in PWRs. ► Coolant flow with more coherent characteristics could be an explanation. ► The dependence of the noise amplitude on radial correlation length was investigated. ► The noise amplitude increases with the increased spatial correlation length. - Abstract: The dependence of the amplitude of the neutron noise in PWRs on the radial correlation length of the noise source, that is the inlet temperature fluctuations, is investigated. The motivation for this work comes from the recent observation that the noise amplitude has increased significantly in certain Spanish PWRs. The reason of this increase has not yet been satisfactorily identified, although there are a few assumptions. One new hypothesis, put forward in this paper, is that a coolant flow with more coherent characteristics, which has actually been observed, could explain the increase of the noise amplitude. A more coherent flow leads to a longer spatial (radial) correlation length of the inlet temperature fluctuations, which in turn, in case the APSD of the temperature noise is unchanged, will lead to the increase of the neutron noise APSD. The mechanism behind this phenomenon is the same as the reason of the failure of the traditional noise based method for the determination of the Moderator Temperature Coefficient (MTC), and is related to the characteristics of the spatially randomly distributed noise sources. In this paper the relationship between the radial correlation length of the inlet temperature fluctuations and the neutron noise amplitude is investigated quantitatively and the increase of the noise amplitude with the increased spatial correlation of the inlet temperature fluctuations is demonstrated

  6. Measurement and Correlation of Ambient VOCs in Windsor, Ontario, Canada and Detroit, Michigan, USA

    Science.gov (United States)

    Miller, L. J.; You, H.; Xu, X.; Molaroni, S.; Lemke, L.; Weglicki, L.; Krouse, H.; Krajenta, R.

    2009-05-01

    An air quality study has been carried out in Windsor, Ontario, Canada and Detroit, Michigan, USA as part of a pilot research study undertaken by the Geospatial Determinants of Health Outcomes Consortium (GeoDHOC), a multidisciplinary, international effort aimed at understanding the health effects of air pollution in urban environments. Exposure to volatile organic compounds has long been associated with adverse health conditions such as atrophy of skeletal muscles, loss of coordination, neurological damage, dizziness, throat, nose, and eye irritation, nervous system depression, liver damage, and respiratory symptoms. Twenty-six species of ambient volatile organic compounds (VOCs) were monitored during a 2-week period in September, 2008 at 100 sites across Windsor and Detroit, using 3M # 3500 Organic Vapour Monitors. Ten species with highest concentrations were selected for further investigation; Toluene (mean concentration =4.14 μm/m3), (m+p)-Xylene (2.30 μm/m3), Hexane (1.87 μm/m3), Benzene (1.37 μm/m3), 1,2,4-Trimethylbenzene (0.87 μm/m3), Dichloromethane (0.77 μm/m3), Ethylbenzene (0.68 μm/m3), o-Xylene (0.63 μm/m3), n-Decane (0.42 μm/m3), and 1,3,5-Trimethylbenzene (0.39 μm/m3). Comparison to a similar investigation in Sarnia, Ontario in October 2005 revealed that the mean concentrations of VOCs were higher in Windsor-Detroit for all species by a significant margin (31-958%), indicating substantial impact of local industrial and vehicular emissions in the WindsorVDetroit area. For most VOCs, the concentrations were higher in Detroit than in Windsor. The mean concentration of total VOC was 9.7 μm/m3 in Windsor, which is slightly higher than that in Sarnia in 2005 (7.9 um/m3), whilst total VOC concentration in Detroit was much higher (16.5 μm/m3). There were strong correlations among several of the 10 species, with the highest Pearson correlation coefficients (r=0.78 - 0.99, p<0.05) amongst the BTEX (benzene, toluene, ethylbenzene, and xylenes) group

  7. Effects of cross-correlated noises on the intensity fluctuation of the single-mode laser system

    Institute of Scientific and Technical Information of China (English)

    Bing Wang; Shuwen Dai; Shuping Ge

    2006-01-01

    @@ A single-mode laser model with cross-correlated additive and multiplicative noise terms is considered, and the effects of correlation between noises on the relaxation time and the intensity correlation function are studied. Using the projection operator method and taking into account the effects of the memory kernels of the intensity correlation function, the analytic expressions for the relaxation time and the correlation function are derived. Based on numerical computations, it is found that the self-correlation time and the cross-correlation time have the same effects on the single-mode laser system.

  8. Coarse-Grained Theory of Biological Charge Transfer with Spatially and Temporally Correlated Noise.

    Science.gov (United States)

    Liu, Chaoren; Beratan, David N; Zhang, Peng

    2016-04-21

    System-environment interactions are essential in determining charge-transfer (CT) rates and mechanisms. We developed a computationally accessible method, suitable to simulate CT in flexible molecules (i.e., DNA) with hundreds of sites, where the system-environment interactions are explicitly treated with numerical noise modeling of time-dependent site energies and couplings. The properties of the noise are tunable, providing us a flexible tool to investigate the detailed effects of correlated thermal fluctuations on CT mechanisms. The noise is parametrizable by molecular simulation and quantum calculation results of specific molecular systems, giving us better molecular resolution in simulating the system-environment interactions than sampling fluctuations from generic spectral density functions. The spatially correlated thermal fluctuations among different sites are naturally built-in in our method but are not readily incorporated using approximate spectral densities. Our method has quantitative accuracy in systems with small redox potential differences (correlations of site energies are critical in determining the coherent-incoherent transition, while the role of spatial correlations depends on the nature of the systems. In a system with repeated bridge units of the same chemistry, spatially correlated fluctuations enhance the charge delocalization and charge-transfer rates; however, in a system of units with different site energies, spatial correlations slow the fluctuations to bring units into degeneracy, in turn, slowing the charge-transfer rates. The spatial and temporal correlations of condensed phase medium fluctuations provide another source to control and tune the kinetics and dynamics of charge-transfer systems. PMID:27008541

  9. Correlation between General Corrosion Behavior and Eddy Current Noise of Alloy 690 Steam Generator Tube

    International Nuclear Information System (INIS)

    Nickel and its oxides are released from the surface of steam generator tubes into the primary water. Released nickel and cobalt is activated to Co-58 and Co-60 in the reactor core by a neutron flux, respectively. These activated corrosion products are the main source of high radiation fields and occupational radiation exposure. In addition, some of the corrosion products redeposit on the fuel cladding, hinder the heat transfer, increase the corrosion rate of the fuel cladding, and finally induce an axial offset anomaly. This phenomenon can decrease core shutdown margin, and thus lead to a down-rating of a plant. Recently, many researchers have reported that the surface states of Alloy 690 tubes affect the corrosion product formation and its release in simulated primary water environments. Meanwhile, the surface states of steam generator tubes affect the noise level of eddy current testing. Noise signals arising from the tubes degrade the probability of detection and sizing accuracy of the defects. The corrosion behavior was closely correlated to the tube noise measured using a rotating probe, while it was not related to the noise measured using a bobbin probe. It is suggested that the tube noise value measured using a rotating pancake coil probe can be a decisive measure to estimate the corrosion behavior of tubing

  10. Correlation between General Corrosion Behavior and Eddy Current Noise of Alloy 690 Steam Generator Tube

    Energy Technology Data Exchange (ETDEWEB)

    Hur, Do Haeng; Choi, Myung Sik; Lee, Deok Hyun; Shim, Hee-Sang [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2015-05-15

    Nickel and its oxides are released from the surface of steam generator tubes into the primary water. Released nickel and cobalt is activated to Co-58 and Co-60 in the reactor core by a neutron flux, respectively. These activated corrosion products are the main source of high radiation fields and occupational radiation exposure. In addition, some of the corrosion products redeposit on the fuel cladding, hinder the heat transfer, increase the corrosion rate of the fuel cladding, and finally induce an axial offset anomaly. This phenomenon can decrease core shutdown margin, and thus lead to a down-rating of a plant. Recently, many researchers have reported that the surface states of Alloy 690 tubes affect the corrosion product formation and its release in simulated primary water environments. Meanwhile, the surface states of steam generator tubes affect the noise level of eddy current testing. Noise signals arising from the tubes degrade the probability of detection and sizing accuracy of the defects. The corrosion behavior was closely correlated to the tube noise measured using a rotating probe, while it was not related to the noise measured using a bobbin probe. It is suggested that the tube noise value measured using a rotating pancake coil probe can be a decisive measure to estimate the corrosion behavior of tubing.

  11. Spin correlations due to Dyakonov-Perel and spin noise spectroscopy in semicoductor quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Hartenstein, Tobias; Krauss, Michael; Schneider, Hans Christian [Department of Physics and Research Center OPTIMAS, Kaiserslautern University of Technology (Germany)

    2010-07-01

    We present a theoretical investigation of dynamical electronic spin-spin correlations in quantum wells resulting from the Dyakonov-Perel mechanism due to electron-impurity interactions in the presence of external magnetic fields. We set up the coupled equations of motion for the different spin-spin correlation functions, and solve them numerically. Since spin-noise measurements are sensitive to the spin-spin correlation functions, our results provide a microcscopic basis for this measurement technique, but also allow us to study how the Dyakonov-Perel relaxation mechanism affects non-trivial electronic spin correlations and correlation waves that can be induced by the absorption of non-classical polarization-squeezed light.

  12. Polarization controlled intensity noise correlation and squeezing of four-wave mixing processes in rubidium vapor

    Science.gov (United States)

    Li, Changbiao; Jiang, Zihai; Wang, Xiuxiu; Ahmed, Irfan; Raza, Faizan; Yang, Yiheng; Zhang, Yanpeng

    2016-05-01

    We observed four-wave mixing (FWM) processes in a double-Λ level of rubidium atomic system with electromagnetically induced transparency window having different polarization. The Autler-Townes splitting of FWM induced by the polarized multi-dark-state is observed. And the two-stage line shape of correlation that exhibits a sharp peak and a broad peak is also studied. The sharp peak and the broad peak are from the correlation of two spontaneous parametric FWMs and that of the vertical component and horizontal component of two coherent FWMs. Moreover we demonstrate that the intensity noise correlation and intensity-difference squeezing can be well modulated by the relative initial phase and nonlinear phase shift. Meanwhile, we also found the following of correlation (anti-correlation) by intensity-difference squeezing (anti-squeezing). The associated results may be applicable in all-optical communication and optical information processing on photonic chips.

  13. Stochastic resonance induced by a multiplicative periodic signal in the gene transcriptional regulatory system with correlated noises

    International Nuclear Information System (INIS)

    This paper investigates the stochastic resonance (SR) induced by a multiplicative periodic signal in the gene transcriptional regulatory system with correlated noises. The expression of the signal-to-noise ratio (SNR) is derived. The results indicate that the existence of a maximum in SNR vs. the additive noise intensity α, the multiplicative noise intensity D and the cross-correlated noise intensity λ is the identifying characteristic of the SR phenomenon and there is a critical phenomenon in the SNR as a function of λ, i.e., for the case of smaller values of noise intensity (α or D), the SNR decreases as λ increases; however, for the case of larger values of noise intensity (α or D), the SNR increases as λ increases. (general)

  14. Stationary Intensity Distribution of Single-Mode Laser Driven by Additive and Multiplicative Colored Noises with Colored Cross-Correlation

    Institute of Scientific and Technical Information of China (English)

    CAOLi; WANGJun; WuDa-Jin; LIANGGui-Yun

    2003-01-01

    Applying the approximate Fokker-Planck equation we derived, we obtain the analytic expression of the stationary laser intensity distribution Pst(l) by studying the single-mode laser cubic model subject to colored cross-correlation additive and multiplicative noise, each of which is colored. Based on it, we discuss the effects on the stationary laser intensity distribution Pot(I) by cross-correlation between noises and "color" of noises (non-Markovian effect) when the laser system is above the threshold. In detail, we analyze two cases: One is that the three correlation-times (i.e.the self-correlation and cross-correlation times of the additive and multiplicative noise) are chosen to be the same value(Tl=T2=T3=T). For this case, the effect of noise cross-correlation is investigated emphatically, and we detect that only when λ≠ 0 can the noise-induced transition occur in the Pst (I) curve, and only when T≠ 0 and λ≠0, can the "reentrant noise-induced transition" occur. The other case is that the three correlation times are not the same value,T1≠T2≠T3. For this case, we find that the noise-induced transition occurring in the Pst(I) curve is entirely different when the values of T1,T2, and T3 are changed respectively. In particular, when T2 (serf-correlation time of additive noise) is cha~g~g, the ratio of the two maximums of the Pst( I) curve R exhibits an interesting phenomenon,"reentrant noise-induced transition", which demonstrates the effect of noise "color" (non-Markovian effect).

  15. Enhancement of current commensurate with mutual noise–noise correlation in a symmetric periodic substrate: The benefits of noise and nonlinearity

    International Nuclear Information System (INIS)

    Highlights: ► Exploration of directed transport in stochastic systems with embedded nonlinearity. ► Formalism is valid for open system in the presence of arbitrary periodic potential. ► Effective temperature depends on correlation time and extent of correlation. ► Study of the directed motion in presence of external cross-correlated noises. ► Steady state current increases with increase in the extent of correlation. - Abstract: Starting from a Langevin description of a particle submerged in a heat bath that offers a state dependent dissipation, we examine the noise-induced transport of a Brownian particle in the presence of two external, mutually correlated noises and envisage that in a symmetric periodic potential, the steady state current increases with an increase in the extent of correlation. The study of inhomogeneous diffusion in the presence of colored noise makes the present development formally interesting since this brings in a direct implication that exercising control on the degree of correlation can enhance the current in a properly designed experiment. As an offshoot of this development, we also envisage an effective temperature that depends on the correlation time and the extent of correlation.

  16. Subtraction of correlated noise in global networks of gravitational-wave interferometers

    CERN Document Server

    Coughlin, Michael W; De Rosa, Rosario; Fiori, Irene; Gołkowski, Mark; Guidry, Melissa; Harms, Jan; Kubisz, Jerzy; Kulak, Andrzej; Mlynarczyk, Janusz; Paoletti, Federico; Thrane, Eric

    2016-01-01

    The recent discovery of merging black holes suggests that a stochastic gravitational-wave background is within reach of the advanced detector network operating at design sensitivity. However, correlated magnetic noise from Schumann resonances threatens to contaminate observation of a stochastic background. In this paper, we report on the first effort to eliminate intercontinental correlated noise from Schumann resonances using Wiener filtering. Using magnetometers as proxies for gravitational-wave detectors, we demonstrate as much as a factor of two reduction in the coherence between magnetometers on different continents. While much work remains to be done, our results constitute a proof-of-principle and motivate follow-up studies with a dedicated array of magnetometers.

  17. Shear-wave velocity model of the basin of Santiago de Chile derived from ambient noise measurements for the determination of seismic site conditions and amplification

    Science.gov (United States)

    Pilz, M.; Parolai, S.; Picozzi, M.; Wang, R.; Leyton, F.; Campos, J. A.; Zschau, J.

    2009-12-01

    Generally, the most intense shaking during an earthquake occurs near the rupture fault and decreases with distance away from the fault. However, in a single earthquake the shaking at one site can easily be several times stronger than at another site, even when their distance from the rupture fault is the same. Such site effects are mainly caused by the softness of the soil near the surface and by the thickness of the sediments above hard rock. Seismic site characterization therefore requires usually substantial investment both in time and money for geophysical data acquisition. On the other hand, the necessity of estimating seismic risk for large urban areas like Santiago de Chile wants for at least a first order classification of soil and building vulnerability and therefore needs the definition of proxies. Recently, Wald and Allen (2007) suggested that the slope of topography might serve as a suitable parameter for the estimation of site effects irrespective of the spatial resolution used. Measurements of seismic noise at 146 sites have been carried out in the northern part of Santiago de Chile to determine the fundamental resonance frequency of the sites. The spatial variation in the thickness of the sedimentary cover, known from previous gravimetric investigations, varies significantly over short scale and is roughly retrieved from the peak in the horizontal-to-vertical (H/V) ratios of ambient noise. We inverted the H/V spectra individually for receiving local S-wave velocity profiles. For the inversion procedure, we also used additional geological and geophysical information. The resulting 3D model was derived for a 26 km X 12 km area by interpolation between the single S-wave velocity profiles with a kriging technique and shows good agreement with the few existing velocity profiles but also allows to image the entire area as well as deeper parts of the basin in more detail. Significant variations in the S-wave velocity-depth gradient are found. The wealth of

  18. Intensity correlation time of a single-mode laser driven by two coloured noises with coloured cross-correlation with direct signal modulation

    Institute of Scientific and Technical Information of China (English)

    Chen Li-Mei; Cao Li; Wu Da-Jin; Wang Zhong-Long

    2005-01-01

    In this paper, the intensity correlation time T is studied for the gain-noise model of a single-mode laser driven by coloured pump noise and coloured quantum noise with coloured cross-correlation with a direct signal modulation.By using the linear approximation method, it is found that when the pump noise is modulated directly by a signal,the effects of the cross-correlation between the pump noise and the quantum noise will disappear. In addition, there exists a maximum (i.e. resonance) in the curve of the intensity correlation time T versus the pump noise self-correlation time τ1. Furthermore, when τ1 ≤τ2, the intensity correlation time T increases monotonically with the increase of D and decreases monotonically with the increase of Q, but when τ1 >τ2, the intensity correlation time T increases monotonically with the increase of Q and decreases monotonically with the increase of D.

  19. Complex Dynamics of Credit Risk Contagion with Time-Delay and Correlated Noises

    OpenAIRE

    2014-01-01

    The stochastic time-delayed system of credit risk contagion driven by correlated Gaussian white noises is investigated. Novikov’s theorem, the time-delay approximation, the path-integral approach, and first-order perturbation theory are used to derive time-delayed Fokker-Planck model and the stationary probability distribution function of the dynamical system of credit risk contagion in the financial market. Using the method of numerical simulation, the Hopf bifurcation and chaotic behaviors ...

  20. High-Resolution Algorithm for Image Segmentation in the Presence of Correlated Noise

    OpenAIRE

    Jiang, Haiping; Bourennane, Salah; Fossati, Caroline

    2010-01-01

    Multiple line characterization is a most common issue in image processing. A specific formalism turns the contour detection issue of image processing into a source localization issue of array processing. However, the existing methods do not address correlated noise. As a result, the detection performance is degraded. In this paper, we propose to improve the subspace-based high-resolution methods by computing the fourth-order slice cumulant matrix of the received signals instead of second-orde...

  1. The effects of correlated noise in intra-complex DSN arrays for S-band Galileo telemetry reception

    Science.gov (United States)

    Dewey, R. J.

    1992-01-01

    A number of the proposals for supporting a Galileo S-band (2.3-GHz) mission involve arraying several antennas to maximize the signal-to-noise ratio (and bit rate) obtainable from a given set of antennas. Arraying is no longer a new idea, having been used successfully during the Voyager encounters with Uranus and Neptune. However, arraying for Galileo's tour of Jupiter is complicated by Jupiter's strong radio emission, which produces correlated noise effects. This article discusses the general problem of correlated noise due to a planet, or other radio source, and applies the results to the specific case of an array of antennas at the DSN's Tidbinbilla, Australia, complex (DSS 42, DSS 43, DSS 45, and the yet-to-be-built DSS 34). The effects of correlated noise are highly dependent on the specific geometry of the array and on the spacecraft-planet configuration; in some cases, correlated noise effects produce an enhancement, rather than a degradation, of the signal-to-noise ratio. For the case considered here--an array of the DSN's Australian antennas observing Galileo and Jupiter--there are three regimes of interest. If the spacecraft-planet separation is approximately less than 75 arcsec, the average effect of correlated noise is a loss of signal to noise (approximately 0.2 dB as the spacecraft-planet separation approaches zero). For spacecraft-planet separations approximately greater than 75 arcsec, but approximately less than 400 arcsec, the effects of correlated noise cause signal-to-noise variations as large as several tenths of a decibel over time scales of hours or changes in spacecraft-planet separation of tens of arcseconds; however, on average its effects are small (less than 0.01 dB). When the spacecraft is more than 400 arcsec from Jupiter (as is the case for about half of Galileo's tour), correlated noise is a less than 0.05-dB effect.

  2. Seasonal changes of the ambient noise recorded by the "13 BB star" array in northern Poland within the Trans European Suture Zone

    Science.gov (United States)

    Lepore, Simone; Grad, Marek

    2016-04-01

    The variations in the azimuth of ambient noise sources, as well as the coherence of the average velocity of surface waves arrivals, were evaluated by applying beam forming and seismic interferometry techniques to the recordings carried out during 2014 at the "13 BB star" array composed of thirteen broadband seismic stations located in northern Poland within the Trans European Suture Zone. The evaluation of the beam power for the whole array each five days for the horizontal and vertical components led to the estimation of the azimuth variation of noise sources during the entire 2014. Fifty days represent a reasonable period to observe seasonal variations of the azimuth in time. The analysis of the azimuths makes evident the strongest beam power associated to noise does not show a preferred direction. The azimuth is predominantly fluctuating between the North Sea and the Baltic Sea: nevertheless, secondary sources like the Atlantic Sea, the Mediterranean Sea and the Black Sea were also noticed. To put in evidence the seasonal variations, the amplitude associated to the principal source was evaluated for the three components. It shows high values in January, March, April, July, August and November, whereas it is low in the remaining months. The analysis of the crosscorrelation between all the station pairs, obtained from the stacking of daily traces for January, April and September 2014 in the 0.1 1 Hz frequency band, allowed the estimation of precise values of velocities of surface waves. The best resolution to retrieve the surface waves is achieved in April, whereas in January and September several higher modes are still present in the traces. The fastest arrivals of surface waves are between ~7 s at ~20 km distance and ~40 s at ~120 km with an average velocity of ~3 km/s. The second group of arrivals is located between ~10 s at ~20 km distance and ~60 s at ~120 km: accordingly, the average velocity is ~2 km/s. The third group of arrivals, between ~13 s at 20 km

  3. Investigation of correlation characteristics for random array collaborative beamforming using noise signals

    Science.gov (United States)

    Alexander, David B.; Narayanan, Ram M.; Himed, Braham

    2016-05-01

    The performance of different random array geometries is analyzed and compared. Three phased array geometries are considered: linear arrays with non-uniform randomized spacing between elements, circular arrays with non-uniform element radii, and ad hoc sensor networks with elements located randomly within a circular area. For each of these array geometries, computer simulations modeled the transmission, reflection from an arbitrary target, and reception of signals. The effectiveness of each array's beamforming techniques was measured by taking the peak cross-correlation between the received signal and a time-delayed replica of the original transmitted signal. For each array type, the correlation performance was obtained for transmission and reception of both chirp waveforms and ultra-wideband noise signals. It was found that the non-uniform linear array generally produced the highest correlation between transmitted and reflected signals. The non-uniform circular and ad hoc arrays demonstrated the most consistent performance with respect to noise signal bandwidth. The effect of scan angle was found to have a significant impact on the correlation performance of the linear arrays, where the correlation performance declines as the scan angle moves away from broadside to the array.

  4. Experimental analysis of image noise and interpolation bias in digital image correlation

    Science.gov (United States)

    Gao, Zeren; Xu, Xiaohai; Su, Yong; Zhang, Qingchuan

    2016-06-01

    The popularization of the digital image correlation (DIC) method has raised urgent needs to evaluate the accuracy of this method. However, there are still some problems to be solved. Among the problems, the effects of various factors, such as the image noise caused by the camera sensors, the employed interpolation algorithm, and the structure of the speckle patterns, have become a major concern. To experimentally measure the position-dependent systematic error (i.e. interpolation bias) caused by non-ideal interpolation algorithm is an important way to evaluate the quality of the speckle patterns in the correlation method, and remains unsolved. In this work, a novel, simple and convenient method is proposed to measure the interpolation bias. In the new method which can avoid the out-of-plane displacements and the mechanical errors of translation stages, integral-pixel shifts are applied to the image shown on the screen so that sub-pixel displacements can be realized in the images captured by the camera via proper experimental settings. Besides, the fluctuations of the image noise and the sub-pixel displacement errors caused by the image noise are experimentally analyzed by employing three types of cameras commonly used in the DIC measurements. Experimental results indicate that the fluctuations of the image noise are not only proportional to the image gray value, but also dependent on the type of the employed camera. On the basis of eliminating the image noise via the image averaging technique, high-precision interpolation bias curves more than one period are experimentally obtained by the proposed method.

  5. The bulk of the stock market correlation matrix is not pure noise

    CERN Document Server

    Kwapien, J; Drozdz, S

    2006-01-01

    We analyse the structure of the distribution of eigenvalues of the stock market correlation matrix with increasing length of the time series representing the price changes. We use 100 highly-capitalized stocks from the American market and relate result to the corresponding ensemble of Wishart random matrices. It turns out that systematically more eigenvalues stay beyond the borders prescribed by this variant of the Random Matrix Theory (RMT). This may indicate that even the bulk of the spectrum of the stock market correlation matrix carries some sort of correlations that are masked by a measurement noise when the time series used to construct the matrix are short. We also study some other characteristics of the "noisy" eigensignals, like their return distributions, temporal correlations or their multifractal spectra and the results support the above conclusions.

  6. Correlation techniques for the improvement of signal-to-noise ratio in measurements with stochastic processes

    CERN Document Server

    Reddy, V R; Reddy, T G; Reddy, P Y; Reddy, K R

    2003-01-01

    An AC modulation technique is described to convert stochastic signal variations into an amplitude variation and its retrieval through Fourier analysis. It is shown that this AC detection of signals of stochastic processes when processed through auto- and cross-correlation techniques improve the signal-to-noise ratio; the correlation techniques serve a similar purpose of frequency and phase filtering as that of phase-sensitive detection. A few model calculations applied to nuclear spectroscopy measurements such as Angular Correlations, Mossbauer spectroscopy and Pulse Height Analysis reveal considerable improvement in the sensitivity of signal detection. Experimental implementation of the technique is presented in terms of amplitude variations of harmonics representing the derivatives of normal spectra. Improved detection sensitivity to spectral variations is shown to be significant. These correlation techniques are general and can be made applicable to all the fields of particle counting where measurements ar...

  7. Effects of correlated noise on the full-spectrum combining and complex-symbol combining arraying techniques

    Science.gov (United States)

    Vazirani, P.

    1995-01-01

    The process of combining telemetry signals received at multiple antennas, commonly referred to as arraying, can be used to improve communication link performance in the Deep Space Network (DSN). By coherently adding telemetry from multiple receiving sites, arraying produces an enhancement in signal-to-noise ratio (SNR) over that achievable with any single antenna in the array. A number of different techniques for arraying have been proposed and their performances analyzed in past literature. These analyses have compared different arraying schemes under the assumption that the signals contain additive white Gaussian noise (AWGN) and that the noise observed at distinct antennas is independent. In situations where an unwanted background body is visible to multiple antennas in the array, however, the assumption of independent noises is no longer applicable. A planet with significant radiation emissions in the frequency band of interest can be one such source of correlated noise. For example, during much of Galileo's tour of Jupiter, the planet will contribute significantly to the total system noise at various ground stations. This article analyzes the effects of correlated noise on two arraying schemes currently being considered for DSN applications: full-spectrum combining (FSC) and complex-symbol combining (CSC). A framework is presented for characterizing the correlated noise based on physical parameters, and the impact of the noise correlation on the array performance is assessed for each scheme.

  8. Dynamical properties of a tumor growth system in the presence of immunization and colored cross-correlated noises

    International Nuclear Information System (INIS)

    We investigate the effects of the noise parameters and immunization strength β on the dynamical properties of a tumor growth system with both immunization and colored cross-correlated noises. The analytical expressions for the associated relaxation time TC and the normalized correlation function C(s) are derived by means of the projection operator method. The results indicate that: (i) TC as a function of the multiplicative noise intensity α shows resonance-like behavior, i.e. the curves of TC versus α exhibit a single-peak structure and its peak position changes with increasing correlation strength between noises λ, the autocorrelation time of multiplicative noise τ1, the autocorrelation time of additive noise τ2 and the cross-correlation time τ3. This behavior can be understood in terms of the noise-enhanced stability effect and the influence of the memory effects on it. (ii) The increasing λ, τ1, τ2 and the additive noise intensity D slow down the fluctuation decay of the tumor population, whereas the increasing τ3 and β speed it up. (iii) C(s) increases as λ, τ1, τ2 and β increase, while it decreases with τ3 increasing. Our study shows that the effects of some noise parameters on tumor growth can be modified due to the presence of the immunization effect.

  9. Maternal and ambient environmental effects of light on germination in Plantago lanceolata: correlated responses to selection on leaf length

    International Nuclear Information System (INIS)

    1. Seeds from artificial selection lines were exposed to different maternal and ambient conditions, simulating sunlight and vegetation shade. 2. Lines selected for longer leaves also produced larger seeds, indicating a positive genetic correlation between leaf length and seed size. 3. Light conditions during maturation had no large effect on seed size. 4. Seed germination was reduced by a low ratio of red to far-red light (R/FR ratio) in the ambient environment. 5. Seeds maturated under simulated vegetation shade germinated less readily and were more inhibited by a low ambient R/FR ratio than seeds maturated under full sunlight or R/FR-neutral shade. Thus, low R/FR-ratios in the maternal and ambient environment operated synergistically. 6. Large genotypic variation in the germination responses to both maternal and ambient light conditions was found among and within selection lines, indicating that such responses might have the potential to evolve in response to natural selection. 7. Artificial selection for leaf length had affected seed germination characteristics but correlated responses and thus genetic correlations largely depended on light conditions in the selective environment. Selection for longer leaves under a low R/FR ratio increased seed dormancy and plasticity of germination in response to the R/FR ratio. However, in the opposite selective environment selection for longer leaves reduced seed dormancy and plasticity to the R/FR ratio. It is argued that leaf length and seed germination characteristics are somehow linked by shared physiological mechanisms, which may facilitate concerted changes in shade avoidance responses

  10. Quantum information tapping using a fiber optical parametric amplifier with noise figure improved by correlated inputs

    Science.gov (United States)

    Guo, Xueshi; Li, Xiaoying; Liu, Nannan; Ou, Z. Y.

    2016-01-01

    One of the important functions in a communication network is the distribution of information. It is not a problem to accomplish this in a classical system since classical information can be copied at will. However, challenges arise in quantum system because extra quantum noise is often added when the information content of a quantum state is distributed to various users. Here, we experimentally demonstrate a quantum information tap by using a fiber optical parametric amplifier (FOPA) with correlated inputs, whose noise is reduced by the destructive quantum interference through quantum entanglement between the signal and the idler input fields. By measuring the noise figure of the FOPA and comparing with a regular FOPA, we observe an improvement of 0.7 ± 0.1 dB and 0.84 ± 0.09 dB from the signal and idler outputs, respectively. When the low noise FOPA functions as an information splitter, the device has a total information transfer coefficient of Ts+Ti = 1.5 ± 0.2, which is greater than the classical limit of 1. Moreover, this fiber based device works at the 1550 nm telecom band, so it is compatible with the current fiber-optical network for quantum information distribution. PMID:27458089

  11. Steady-State Analysis of a Single-Mode Laser Driven by Colored Pump Noise with Cross-Correlation Between Real and Imaginary Parts of Quantum Noise

    Institute of Scientific and Technical Information of China (English)

    ZHANG Li; CAO Li; WU Da-Jin

    2003-01-01

    Applying the method of the unified colored noise approximation and phase lock, we study in this paper the stationary intensity distribution of the single-mode laser driven by colored pump noise with cross-correlation between the real and imaginary parts of the quantum noise. We present a thorough discussion of how the cross-correlation λq between the realand imaginary parts of the quantum noise and the self-correlation time τ of the pump noise determine the behaviors of the stationary distribution Qst(I), the mean (I), and the variance λ2(0) of the laser intensity. It is shown that cross-correlation intensity λq of the complex quantum noise can induce a first-order-like transition. When the pump noise is colored noise (τ≠ 0), improving the pump parameters monotonously will make the curves of Qst(I)exhibit reentrant phase transition. The fluctuations of laser intensity are strongly influenced by λq and τ when the laser is operated near or below threshold. Especially when τ≠ 0, the heights of the peaks of the curves of λ2(0)-a0 and λ3(0)-a0, (here a0 is the net gain coefficient) go up as λq increases. However the entire curves of λ2(0)-a0 and λ3(0)-a0are abruptly suppressed when λq = 1, in similarity to phase transition of stationary intensity distribution.

  12. Steady-State Analysis of a Single-Mode Laser Driven by Colored Pump Noise withCross-Correlation Between Real and Imaginary Parts of Quantum Noise

    Institute of Scientific and Technical Information of China (English)

    ZHANGLi; CAOLi; WUDa-Jin

    2003-01-01

    Applying the method of the unified colored noise approximation and phase lock, we study in this paper the stationary intensity distribution of the single-mode laser driven by colored pump noise with cross-correlation between the real and imaginary parts of the quantum noise. We present a thorough discussion of how the cross-correlation λq between the real and imaginary parts of the quantum noise and the self-correlation time τ of the pump noise determine the behaviors of the stationary distribution Qst(I), the mean (I), and the variance λ2(0) of the laser intensity. It is shown that cross-correlation intensity λq of the complex quantum noise can induce a first-order-like transition. When the pump noise is colored noise (τ≠0), improving the pump parameters monotonously will make the curves of Qst(I) exhibit reentrant phase transition. The fluctuations of laser intensity are strongly influenced by λq and τ when the laser is operated near or below threshold. Especially when τ≠0, the heights of the peaks of the curves of λ2(0)-α0 and α3(0)-α0, (here a0 is the net gain coefficient) go up as λq increases. However the entire curves λ2(0)-α0 and λ3(0)-α0 are abruptly suppressed when λq = 1, in similarity to phase transition of stationary intensity distribution.

  13. Effects of Time Delay on Stability of an Unstable State in a Bistable System with Correlated Noises

    International Nuclear Information System (INIS)

    Effects of time delay on stability of an unstable state in a time-delayed bistable system are investigated. The analytic expression of the transition rate W(xu, τ) from unstable state xu to stable state x+ is derived. The numerical calculation results of W(xu, τ) indicate that W(xu, τ) decreases with the increasing multiplicative noise intensity, the additive noise intensity and the strength of correlations between the multiplicative and the additive noise increase, but W(xu, τ) increases with increasing delay time. Namely, the multiplicative noise, the additive noise and the correlations between the multiplicative and the additive noises enhance the stability of the unstable state in the time-delayed bistable system but the stability is weakened by time delay. (general)

  14. Method of Removing the Cross-correlation Noise for Dual-input and Dual-output SAR

    Directory of Open Access Journals (Sweden)

    Huang Ping-ping

    2012-03-01

    Full Text Available According to analysis of separating the mixed echo by suppressing the cross-correlation noise in dual-input and dual-output SAR system, a new method based on threshold filter and inverse filter was proposed. The method can eliminate the most energy of cross-correlation noise by threshold filter, which can suppress the cross-correlation noise well. The principle and implementation steps are presented in detail. The computer simulation and account for the integrated sidelobe ratio showed the effectiveness of the proposed method.

  15. Approximate Fokker-Planck equation for a single-mode laser driven by quadratic pump noise and quantum noise with cross-correlation between real and imaginary parts of noise

    International Nuclear Information System (INIS)

    A single-mode laser noise model driven by quadratic pump noise and quantum noise with cross-correlation between the real and imaginary parts of the noises is proposed. The approximate Fokker-Planck equation (AFPE) of the model for the laser phase and the laser amplitude is derived. It is found that the laser phase is controlled intensively by the correlation between the real and imaginary parts of the pump noise and that of the quantum noise. The correlation between the real and imaginary parts of quantum noise λq tends to lead the laser phase to be locked at some values and the correlation between the real and imaginary parts of the pump noise λp tends to destroy or confine the laser phase lock. Quantitative results are presented and discussed in detail. As an important application of the above-mentioned results, we take a phase lock approximation to get a Langevin equation for the laser field amplitude and an AFPE of the laser intensity

  16. The correlation study of parallel feature extractor and noise reduction approaches

    Energy Technology Data Exchange (ETDEWEB)

    Dewi, Deshinta Arrova; Sundararajan, Elankovan; Prabuwono, Anton Satria [Industrial Computing Research Group, Centre for Artificial Intelligence Technology, Universiti Kebangsaan Malaysia, 43600 Bangi (Malaysia)

    2015-05-15

    This paper presents literature reviews that show variety of techniques to develop parallel feature extractor and finding its correlation with noise reduction approaches for low light intensity images. Low light intensity images are normally displayed as darker images and low contrast. Without proper handling techniques, those images regularly become evidences of misperception of objects and textures, the incapability to section them. The visual illusions regularly clues to disorientation, user fatigue, poor detection and classification performance of humans and computer algorithms. Noise reduction approaches (NR) therefore is an essential step for other image processing steps such as edge detection, image segmentation, image compression, etc. Parallel Feature Extractor (PFE) meant to capture visual contents of images involves partitioning images into segments, detecting image overlaps if any, and controlling distributed and redistributed segments to extract the features. Working on low light intensity images make the PFE face challenges and closely depend on the quality of its pre-processing steps. Some papers have suggested many well established NR as well as PFE strategies however only few resources have suggested or mentioned the correlation between them. This paper reviews best approaches of the NR and the PFE with detailed explanation on the suggested correlation. This finding may suggest relevant strategies of the PFE development. With the help of knowledge based reasoning, computational approaches and algorithms, we present the correlation study between the NR and the PFE that can be useful for the development and enhancement of other existing PFE.

  17. The correlation study of parallel feature extractor and noise reduction approaches

    International Nuclear Information System (INIS)

    This paper presents literature reviews that show variety of techniques to develop parallel feature extractor and finding its correlation with noise reduction approaches for low light intensity images. Low light intensity images are normally displayed as darker images and low contrast. Without proper handling techniques, those images regularly become evidences of misperception of objects and textures, the incapability to section them. The visual illusions regularly clues to disorientation, user fatigue, poor detection and classification performance of humans and computer algorithms. Noise reduction approaches (NR) therefore is an essential step for other image processing steps such as edge detection, image segmentation, image compression, etc. Parallel Feature Extractor (PFE) meant to capture visual contents of images involves partitioning images into segments, detecting image overlaps if any, and controlling distributed and redistributed segments to extract the features. Working on low light intensity images make the PFE face challenges and closely depend on the quality of its pre-processing steps. Some papers have suggested many well established NR as well as PFE strategies however only few resources have suggested or mentioned the correlation between them. This paper reviews best approaches of the NR and the PFE with detailed explanation on the suggested correlation. This finding may suggest relevant strategies of the PFE development. With the help of knowledge based reasoning, computational approaches and algorithms, we present the correlation study between the NR and the PFE that can be useful for the development and enhancement of other existing PFE

  18. Hanbury-Brown Twiss noise correlation with time controlled quasi-particles in ballistic quantum conductors

    Science.gov (United States)

    Glattli, D. C.; Roulleau, P.

    2016-02-01

    We study the Hanbury Brown and Twiss correlation of electronic quasi-particles injected in a quantum conductor using current noise correlations and we experimentally address the effect of finite temperature. By controlling the relative time of injection of two streams of electrons it is possible to probe the fermionic antibunching, performing the electron analog of the optical Hong Ou Mandel (HOM) experiment. The electrons are injected using voltage pulses with either sine-wave or Lorentzian shape. In the latter case, we propose a set of orthogonal wavefunctions, describing periodic trains of multiply charged electron pulses, which give a simple interpretation to the HOM shot noise. The effect of temperature is then discussed and experimentally investigated. We observe a perfect electron anti-bunching for a large range of temperature, showing that, as recently predicted, thermal mixing of the states does not affect anti-bunching properties, a feature qualitatively different from dephasing. For single charge Lorentzian pulses, we provide experimental evidence of the prediction that the HOM shot noise variation versus the emission time delay is remarkably independent of the temperature.

  19. Installation of the light tight cover for the SSD modules (the modules are behind the aluminium plate). The silicon sensors are sensitive to light tight, so ambient light will increase the noise and may even damage them.

    CERN Multimedia

    Nooren, G.

    2004-01-01

    Installation of the light tight cover for the SSD modules (the modules are behind the aluminium plate). The silicon sensors are sensitive to light tight , so ambient light will increase the noise and may even damage them.

  20. Effects of Time Delay on Stability of an Unstable State in a Bistable System with Correlated Noises

    Institute of Scientific and Technical Information of China (English)

    LI Chun; MEI Dong-Cheng

    2011-01-01

    @@ Effects of time delay on stability of an unstable state in a time-delayed bistable system are investigated.The analytic expression of the transition rate W(xu,τ)from unstable state xu to stable state x+ is derived.The numerical calculation results of W(xu,τ)indicate that W(xu,τ)decreases with the increasing multiplicative noise intensity, the additive noise intensi by and the strength of correlations between the multiplicative and the additive noise increase, but W(xu,τ)increases with increasing delay time.Namely, the multiplicative noise, the additive noise and the correlations between the multiplicative and the additive noises enhance the stability of the unstable state in the time-delayed bistable system but the stability is weakened by time delay.%Effects of time delay on stability of an unstable state in a time-delayed bistable system are investigated. The analytic expression of the transition rate W(xu, T) from unstable state xu to stable state x+ is derived. The numerical calculation results of W(xu, T) indicate that W(xu, T) decreases with the increasing multiplicative noise intensity, the additive noise intensity and the strength of correlations between the multiplicative and the additive noise increase, but W(xu, T) increases with increasing delay time. Namely, the multiplicative noise, the additive noise and the correlations between the multiplicative and the additive noises enhance the stability of the unstable state in the time-delayed bistable system but the stability is weakened by time delay.

  1. Stationary Intensity Distribution of Single-Mode Laser Driven by Additive and Multiplicative Colored Noises with Colored Cross-Correlation

    Institute of Scientific and Technical Information of China (English)

    LIANG Gui-Yun; CAO Li; WANG Jun; Wu Da-Jin

    2003-01-01

    Applying the approximate Fokker-Planck equation we derived, we obtain the analytic expression of thestationary laser intensity distribution Pst(Ⅰ) by studying the single-mode laser cubic model subject to colored cross-correlation additive and multiplicative noise, each of which is colored. Based on it, we discuss the effects on the stationarylaser intensity distribution Pst(Ⅰ) by cross-correlation between noises and "color" of noises (non-Markovian effect) whenthe laser system is above the threshold. In detail, we analyze two cases: One is that the three correlation-times (i.e.the self-correlation and cross-correlation times of the additive and multiplicative noise) are chosen to be the same value(τ1 = τ2 = τ3 = τ). For this case, the effect of noise cross-correlation is investigated emphatically, and we detect thatonly when λ≠ 0 can the noise-induced transition occur in the Pst(Ⅰ) curve, and only when τ≠ 0 and λ≠ 0, can the"reentrant noise-induced transition" occur. The other case is that the three correlation times are not the same value,τ1 ≠τ2 ≠τ3. For this case, we find that the noise-induced transition occurring in the Pst (Ⅰ) curve is entirely differentwhen the values of τ1, τ2, and τ3 are changed respectively. In particular, when τ2 (self-correlation time of additivenoise) is changing, the ratio of the two maximums of the Pst(Ⅰ) curve R exhibits an interesting phenomenon, "reentrantnoise-induced transition", which demonstrates the effect of noise "color" (non-Markovian effect).

  2. Influence of the angular correlation of fission neutrons on noise signatures

    International Nuclear Information System (INIS)

    Noise signatures, the measurement of the correlation between the fluctuating parts of the signals coming from neutron detectors, are commonly used to measure nuclear parameters (reactivities, mean lives) and to monitor nuclear systems. Several techniques are used, such as the correlation of analog signals in time or frequency domains or the statistical analysis of detection events. Independently of the experimental method, the useful component of the stochastic descriptors is related to the detection of neutrons that have ancestors born in the same fission event. Despite an early work, opened to the inclusion of the n-n angular correlations of neutrons coming from the same fission, practically all the theoretical applications ignore this additional complication by making the implicit or explicit hypothesis that fission neutrons are born uncorrelated. However, there are direct measurements that show angular and energy correlation for the two-fission-neutron distribution. The first attempt to include this experimental evidence into the theory of neutron noise was the calculation of the ratio of spectral densities related to the 252Cf method of measuring reactivities under the simplest condition: two neutron detectors monitoring a 252Cf plated fission chamber. The objective of this communication is to show how noise signatures of more complex systems are sensitive to the joint distribution of two neutrons coming from the same fission with velocities rvec v and rvec v'. To avoid mathematical complications, we are going to assume (1) that the system is monitored by two different detectors, Labels 2 and 3, distributed according to the fundamental kinetic mode, and (2) that the subcritical system contains only one fissile specie. The driver of the neutron flux is a 252Cf fission source. 5 refs

  3. Determination of local boiling in light water reactors by correlation of the neutron noise

    International Nuclear Information System (INIS)

    The power limit of swimming-pool type reactors depends on the phenomenon of the appearance of burn-out. In order to determine this limit we have attempted to detect the local boiling which usually occurs before the burn out. Local boiling has been simulated by an electrically heated plate placed in the core of the reactor Siloette. The study of local boiling, which is based on the properties of the correlation functions for the neutron noise of detectors placed in the core, shows that a privileged frequency occurs in the power spectrum of the noise. It is intended in the future to determine the influence of various parameters on this characteristic frequency. (author)

  4. Sub-shot-noise photon-number correlation in a mesoscopic twin beam of light

    International Nuclear Information System (INIS)

    We demonstrate sub-shot-noise photon-number correlations in a (temporal) multimode mesoscopic (∼103 detected photons) twin beam produced by picosecond-pulsed spontaneous nondegenerate parametric down-conversion. We have separately detected the signal and idler distributions of photons collected in twin coherence areas and found that the variance of the photon-count difference goes below the shot-noise limit by 3.25 dB. The number of temporal modes contained in the twin beam, as well as the size of the twin coherence areas, depends on the pump intensity. Our scheme is based on spontaneous down-conversion and thus does not suffer from limitations due to the finite gain of the parametric process. Twin beams are also used to demonstrate the conditional preparation of a nonclassical (sub-Poissonian) state

  5. S-wave velocities down to 1 km below the Peteroa volcano, Argentina, obtained from surface waves retrieved by means of ambient-noise seismic interferometry

    Science.gov (United States)

    Lepore, Simone; Gomez, Martin; Draganov, Deyan

    2015-04-01

    The main force driving the tectonics in South America is the subduction of the Nazca Plate below the South American plate. The subduction process generated numerous volcanoes in both Chile and Argentina, of which the majority is concentrated along the Chilean Argentine border. The recent explosive eruptions of some volcanoescaused concern of the population in both countries. At the beginning of 2012, a large temporary array was installed in the Malargüe region, Mendoza, Argentina, with the purpose of imaging the subsurface and monitoring the tectonic activity. The array was deployed until the end of 2012 to record continuously ambient noise and the local, regional, and global seismicity. It consisted of 38 seismic stations divided in two sub arrays, namely the PV array of six stations located on the east flank of the Peteroa volcano, and the T array of thirty two stations spread out on a plateau just north east of the town of Malargüe. Here,the focus will be on the PV array, which has a patch-like shape. Due to the intra-station distances, we chose to use for surface-wave retrieval the bands 0.8 Hz ÷ 4.0 Hz, 10 Hz ÷ 25 Hz. At the investigated area, most of the year there is little anthropogenic noise, which normally dominates frequencies above 1 Hz, meaning that the selected frequency bands can be used for surface-wave retrieval from noise. Using beamforming, we showed that for these bands, the noise is illuminating the stations from the west. This means that a correct surface-wave arrivals can be retrieved for station pairs oriented in that direction. Because of this, we used for retrieval only such station pairs. We cross-correlated the recordings on the vertical components and retrieved Rayleigh waves. By manual picking, we estimated for both bands velocity dispersion curves from the retrieved surface-wave arrivals. The curves were then inverted to obtain the velocity structure under the stations. The obtained S wave velocity depth profiles for the 10 Hz

  6. Stochastic noise reduction upon complexification: positively correlated birth-death type systems.

    Science.gov (United States)

    Rooman, Marianne; Albert, Jaroslav; Duerinckx, Mitia

    2014-08-01

    Cell systems consist of a huge number of various molecules that display specific patterns of interactions, which have a determining influence on the cell׳s functioning. In general, such complexity is seen to increase with the complexity of the organism, with a concomitant increase of the accuracy and specificity of the cellular processes. The question thus arises how the complexification of systems - modeled here by simple interacting birth-death type processes - can lead to a reduction of the noise - described by the variance of the number of molecules. To gain understanding of this issue, we investigated the difference between a single system containing molecules that are produced and degraded, and the same system - with the same average number of molecules - connected to a buffer. We modeled these systems using Itō stochastic differential equations in discrete time, as they allow straightforward analytical developments. In general, when the molecules in the system and the buffer are positively correlated, the variance on the number of molecules in the system is found to decrease compared to the equivalent system without a buffer. Only buffers that are too noisy themselves tend to increase the noise in the main system. We tested this result on two model cases, in which the system and the buffer contain proteins in their active and inactive state, or protein monomers and homodimers. We found that in the second test case, where the interconversion terms are non-linear in the number of molecules, the noise reduction is much more pronounced; it reaches up to 20% reduction of the Fano factor with the parameter values tested in numerical simulations on an unperturbed birth-death model. We extended our analysis to two arbitrary interconnected systems, and found that the sum of the noise levels in the two systems generally decreases upon interconnection if the molecules they contain are positively correlated. PMID:24632443

  7. Preliminary Results From the CAUGHT Experiment: Investigation of the North Central Andes Subsurface Using Receiver Functions and Ambient Noise Tomography

    Science.gov (United States)

    Ryan, J. C.; Ward, K. M.; Porter, R. C.; Beck, S. L.; Zandt, G.; Wagner, L. S.; Minaya, E.; Tavera, H.

    2011-12-01

    Altiplano and portions of the Eastern Cordillera, and at approximately 40 under the sub-Andes and westernmost edge of the Beni basin. Unlike previous studies farther south, we do not see an increased crustal thickness beneath the Eastern Cordillera. The CAUGHT station coverage is also ideal for Ambient Noise Tomography (ANT) to investigate the seismic shear wave velocities in the upper crust (McQuarrie, N., Barnes, J., and Ehlers, T.A., 2008, Geometric, kinematic and erosional history of the central Andean Plateau (15-17°S), northern Bolivia: Tectonics, v. 27, TC3007, doi:10.1029/2006TC002054.

  8. Background noise levels and correlation with ship traffic in the Gulf of Catania

    Science.gov (United States)

    Viola, Salvatore; Buscaino, Giuseppa; Caruso, Francesco; Chierici, Francesco; Embriaco, Davide; Favali, Paolo; Giovanetti, Gabriele; Grammauta, Roasario; Larosa, Giuseppina; Pavan, Gianni; Pellegrino, Carmelo; Pulvirenti, Sara; Riccobene, Giorgio; Sciacca, Virginia; Simeone, Francesco; Beranzoli, Laura; Marinaro, Giuditta

    2015-04-01

    In the last decades the growing interest in the evaluation of the underwater acoustic noise for studies in the fields of geology, biology and high-energy physics is driving the scientific community to collaborate towards a multidisciplinary approach to the topic. In June 2012 in the framework of the European project EMSO, a multidisciplinary underwater observatory, named NEMO-SN1, was installed 25 km off-shore the port of Catania, at a depth of 2100 m and operated until May 2013 by INFN (Istituto Nazionale di Fisica Nucleare) and INGV (Istituto Nazionale di Geofisica e Vulcanologia). NEMO-SN1 hosted aboard geophysical, oceanographic and acoustic sensors: among these a seismic hydrophone model SMID DT-405D(V). In this work, conducted within the activity of the SMO project, the results on the evaluation of the underwater acoustic pollution in the Gulf of Catania through SMID DT-405D(V) recordings are presented. The seismic hydrophone provided a data set of about 11 months of continuous (24/7) recordings. Underwater sounds have been continuously digitized at a sampling frequency of 2 kHz and the acquired data have been stored in 10min long files for off-line analysis. To describe one-year background noise levels, the mean integrated acoustic noise was measured every second (sampling frequency 2000, NFFT 2048) in the 1/3 octave bands with centre frequency 63 Hz and for each 10 minutes-long file the 5th, the 50th and the 98th percentiles were calculated. Measured noise was correlated with the shipping traffic in the area, thanks to the data provided by an AIS receiver installed at the INFN-Laboratori Nazionali del Sud. An acoustic noise increment was measured in coincidence with the passing of crafts in the area and it was possible to identify the characteristic spectrum of each ship. A simple model for the estimation of the acoustic noise induced by the ships passing through the area was developed. The model was applied by using AIS data acquired during the operation

  9. 3-D Anisotropic Ambient Noise Tomography of Piton De La Fournaise Volcano (La Réunion Island)

    Science.gov (United States)

    Mordret, A.; Rivet, D. N.; Landes, M.; Shapiro, N.

    2014-12-01

    We cross-correlate four years of seismic noise continuously recorded by the seismic monitoring network of the Piton de la Fournaise volcano (La Réunion Island). The network is composed of 40 stations 27 of which have 3-component sensors. We use Vertical-to-Vertical (ZZ) cross-correlation components from all stations and Radial-to-Radial (RR) and Transverse-to-Transverse (TT) cross-correlations computed from 3-component records. The group velocity dispersion curves for Rayleigh and Love waves are measured using a Frequency-Time Analysis. We average measurements from ZZ and RR components to finally obtain 577 Rayleigh-wave dispersion curves. 395 Love-wave dispersion curves are obtained from the TT cross-correlations. We then regionalize the group velocities measurements to construct 2D dispersion maps at a set of periods between 0.4 and 8 s. Finally, we construct a 3D shear-velocity model down to 3 km below the sea level by jointly inverting the Rayleigh and Love wave group velocity maps with a Neighborhood Algorithm and with taking into account the radial anisotropy. The distribution of 3-D Voigt averaged S-wave velocities shows three distinct high-velocity anomalies surrounded by a low-velocity ring. The most western high-velocity anomaly is located below the actual "Plaine des Sables" and could be attributed to an old intrusive body at the location of the former volcanic center before it migrated toward its present location. The second high-velocity body is located below the summit of the volcano and likely corresponds to the actual preferential dyke intrusion zone as highlighted by the seismicity. The third high-velocity anomaly is located below the "Grandes Pentes" and the "Grand Brûlé" areas and is thought to be an imprint of the solidified magma chamber of the ancient dismantled "Les Alizé" volcano. The distribution of the radial anisotropy shows two main anomalies: a positive anisotropy (Vsh>Vsv) above sea level highlighting the recent edifice of Piton de

  10. Crustal tomography of the Aegean-Anatolian domain using noise cross-correlations

    Science.gov (United States)

    Hubans, Fabien; Paul, Anne; Campillo, Michel; Karabulut, Hayrullah; Hatzidimitriou, Panagiotis

    2010-05-01

    Data of more than 150 temporary and permanent broadband seismological stations deployed in the Aegean-Anatolian domain between May 2007 and May 2009 are grouped in the SIMBAAD (Seismic Imaging of the Mantle Across the Anatolian Domain) dataset. We compute noise cross-correlations between all station pairs on a 1.5-yr duration. We obtain more than 11.000 correlations for each component of the cross-correlation tensor. We apply a MFA (Multiple Filter Analysis) method to measure group velocity dispersion curves of Rayleigh waves on 4 components of the correlation tensor (ZZ, ZR, RZ, RR) and of Love waves on the TT component, both in positive and negative times. According to the theory, a noise cross-correlation converges to the Green function if noise sources are randomly distributed around the station pair. If this condition is fulfilled, the cross-correlation should be symmetrical in time. We compare group velocity measurements between positive and negative times to evaluate the convergence of each cross-correlation to the Green function. The quality of the symmetry is used to weight the time measurements in the inversion for group velocity maps. In the last step, Rayleigh wave group velocity data are inverted for a 3-D model of S-wave velocity. This processing gives an image of the crustal structure in the area [37-41°N ; 23-33°E] with a horizontal resolution of 60 to 200 km depending on depth and station coverage. The shallowest layers clearly display the present-day thick sedimentary basins (Axios, Thrace, Marmara, Bay of Antalya, ...) and older sedimentary nappes (Lycian nappes, Miocene sediments in the Kirsehir block) as strong low velocity anomalies. At larger depth, Southwestern Anatolia is characterized by a broad low velocity anomaly which contrasts with the higher velocities of the Aegean Sea. We clearly image a West to East increase of Moho depth from 20-25 km in the Aegean Sea to 35 km in the Anatolian plateau. This increase located between 27°E and

  11. 3D-ambient noise Rayleigh wave tomography of Snæfellsjökull volcano, Iceland

    Science.gov (United States)

    Obermann, Anne; Lupi, Matteo; Mordret, Aurélien; Jakobsdóttir, Steinunn S.; Miller, Stephen A.

    2016-05-01

    From May to September 2013, 21 seismic stations were deployed around the Snæfellsjökull volcano, Iceland. We cross-correlate the five months of seismic noise and measure the Rayleigh wave group velocity dispersion curves to gain more information about the geological structure of the Snæfellsjökull volcano. In particular, we investigate the occurrence of seismic wave anomalies in the first 6 km of crust. We regionalize the group velocity dispersion curves into 2-D velocity maps between 0.9 and 4.8 s. With a neighborhood algorithm we then locally invert the velocity maps to obtain accurate shear-velocity models down to 6 km depth. Our study highlights three seismic wave anomalies. The deepest, located between approximately 3.3 and 5.5 km depth, is a high velocity anomaly, possibly representing a solidified magma chamber. The second anomaly is also a high velocity anomaly east of the central volcano that starts at the surface and reaches approximately 2.5 km depth. It may represent a gabbroic intrusion or a dense swarm of inclined magmatic sheets (similar to the dike swarms found in the ophiolites), typical of Icelandic volcanic systems. The third anomaly is a low velocity anomaly extending up to 1.5 km depth. This anomaly, located directly below the volcanic edifice, may be interpreted either as a shallow magmatic reservoir (typical of Icelandic central volcanoes), or alternatively as a shallow hydrothermal system developed above the cooling magmatic reservoir.

  12. A geometric Model for the Spatial Correlation of an Acoustic Vector Field in Surface-generated Noise

    Institute of Scientific and Technical Information of China (English)

    Yiwang Huang; Qunyan Ren; Ting Li

    2012-01-01

    Spatial correlation of sound pressure and particle velocity of the surface noise in horizontally stratified media was demonstrated,with directional noise sources uniformly distributed on the ocean surface.In the evaluation of particle velocity,plane wave approximation was applied to each incident ray.Due to the equivalence of the sound source correlation property and its directivity,solutions for the spatial correlation of the field were transformed into the integration of the coherent function generated by a single directional source.As a typical horizontally stratified media,surface noise in a perfect waveguide was investigated.Correlation coefficients given by normal mode and geometric models show satisfactory agreement.Also,the normalized covariance between sound pressure and the vertical component of particle velocity is proportional to acoustic absorption coefficient,while that of the surface noise in semi-infinitely homogeneous space is zero.

  13. Real time noise and wavelength correlations in octave-spanning supercontinuum generation

    CERN Document Server

    Godin, T; Sylvestre, T; Larger, L; Kudlinski, A; Mussot, A; Salem, A Ben; Zghal, M; Genty, G; Dias, F; Dudley, J M

    2013-01-01

    We use dispersive Fourier transformation to measure shot-to-shot spectral instabilities in femtosecond supercontinuum generation. We study both the onset phase of supercontinuum generation with distinct dispersive wave generation, as well as a highly-unstable supercontinuum regime spanning an octave in bandwidth. Wavelength correlation maps allow interactions between separated spectral components to be identified, even when such interactions are not apparent in shot-to-shot or average measurements. Experimental results are interpreted using numerical simulations. Our results show the clear advantages of dispersive Fourier transformation for studying spectral noise during supercontinuum generation.

  14. [Correlation of ear and extra-ear effects in workers exposed to industrial noise].

    Science.gov (United States)

    Chkannikov, A N

    1993-01-01

    A morbidity of 600 female twister operators was exposed to a long-standing (over 20 years) study and manifold statistic analysis, data of which are represented. The vascular disorders appeared to correlate with the occupational deafness formation. Cerebral resistance recording (CRR) and EEG in 120 workers with various deafness degrees demonstrated the different grades of impaired cerebral and peripheral blood flow. The manifold analysis and CRR produced basic data so as to classify the vasculogenic lesions caused by the exposure to noise and to evaluate the occupational disablement. PMID:8061961

  15. Waveform correlation and coherence of short-period seismic noise within Gauribidanur array with implications for event detection

    International Nuclear Information System (INIS)

    In continuation with our effort to model the short-period micro seismic noise at the seismic array at Gauribidanur (GBA), we have examined in detail time-correlation and spectral coherence of the noise field within the array space. This has implications of maximum possible improvement in signal-to-noise ratio (SNR) relevant to event detection. The basis of this study is about a hundred representative wide-band noise samples collected from GBA throughout the year 1992. Both time-structured correlation as well as coherence of the noise waveforms are found to be practically independent of the inter element distances within the array, and they exhibit strong temporal and spectral stability. It turns out that the noise is largely incoherent at frequencies ranging upwards from 2 Hz; the coherency coefficient tends to increase in the lower frequency range attaining a maximum of 0.6 close to 0.5 Hz. While the maximum absolute cross-correlation also diminishes with increasing frequency, the zero-lag cross-correlation is found to be insensitive to frequency filtering regardless of the pass band. An extremely small value of -0.01 of the zero-lag correlation and a comparatively higher year-round average estimate at 0.15 of the maximum absolute time-lagged correlation yields an SNR improvement varying between a probable high of 4.1 and a low of 2.3 for the full 20-element array. 19 refs., 6 figs

  16. Fault zone reverberations from cross-correlations of earthquake waveforms and seismic noise

    Science.gov (United States)

    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.

  17. Effects of signal modulation and coloured cross-correlation of coloured noises on the diffusion of a harmonic oscillator

    Institute of Scientific and Technical Information of China (English)

    Liu Li; Zhang Liang-Ying; Cao Li

    2009-01-01

    The diffusion in a harmonic oscillator driven by coloured noises ζ(t) and η(t) with coloured cross-correlation in which one of the noises is modulated by a biased periodic signal is investigated. The exact expression of diffusion coefficient d as a function of noise parameter, signal parameter, and oscillator frequency is derived. The findings in this paper are as follows. 1) The curves of d versus noise intensity D and d versus noises cross-correlation time τ_3 exist as two different phases. The transition between the two phases arises from the change of the cross-correlation coefficient λ of the two Orustein-Uhlenbeck (O-U) noises. 2) Changing the value of τ3, the curves of d versus Q, the intensity of colored noise that is modulated by the signal, can transform from a phase having a minimum to a monotonic phase. 3)Changing the value of signal amplitude A, d versus Q curves can transform from a phase having a minimum to a monotonic phase. The above-mentioned results demonstrate that a like noise-induced transition appears in the model.

  18. Associated relaxation time and the correlation function for a tumor cell growth system subjected to color noises

    International Nuclear Information System (INIS)

    The associated relaxation time Tc and the normalized correlation function C(s) for a tumor cell growth system subjected to color noises are investigated. Using the Novikov theorem and Fox approach, the steady probability distribution is obtained. Based on them, the expressions of Tc and C(s) are derived by means of projection operator method, in which the effects of the memory kernels of the correlation function are taken into account. Performing the numerical computations, it is found: (1) With the cross-correlation intensity |λ|, the additive noise intensity α and the multiplicative noise self-correlation time τ1 increasing, the tumor cell numbers can be restrained; And the cross-correlation time τ3, the multiplicative noise intensity D can induce the tumor cell numbers increasing; However, the additive noise self-correlation time τ2 cannot affect the tumor cell numbers; The relaxation time Tc is a stochastic resonant phenomenon, and the distribution curves exhibit a single-maximum structure with D increasing. (2) The cross-correlation strength λ weakens the related activity between two states of the tumor cell numbers at different time, and enhances the stability of the tumor cell growth system in the steady state; On the contrast, τ1 and τ3 enhance the related activity between two states at different time; However, τ2 has no effect on the related activity between two states at different time

  19. Dynamic characteristics of a coastal area of lateral spreading using ambient noise time series - Anchor Bay, Malta

    Science.gov (United States)

    Galea, Pauline; D'Amico, Sebastiano; Farrugia, Daniela

    2013-04-01

    Anchor Bay and surrounding regions are located on the northwest coast of the island of Malta, Central Mediterranean. The area is characterized by a coastal cliff environment having an outcropping layer of hard coralline limestone (UCL) resting on a thick (up to 50m) layer of clays and marls (Blue Clay, BC). This configuration gives rise to a number of processes leading to coastal instability, in particular lateral spreading phenomena and rock falls. Previous and ongoing studies have identified both lateral spreading rates and vertical motions of up to 27mm per year (Mantovani et al, 2012). The area is an interesting natural laboratory as coastal detachment processes in a number of different stages can be identified and are easily accessible. We investigate the site dynamic characteristics of this study area by recording ambient noise time series (20 minutes long) at over 20 points, over an area of 0.07 km2, using a portable 3-component seismograph (Tromino ) The time series are processed to give both horizontal-to-vertical spectral ratio graphs (HVSR) as well as frequency-dependent polarisation analysis as proposed by Burjanek (2011, 2012). The HVSR graphs illustrate and quantify aspects of site resonance effects due both to underlying geology as well as to mechanical resonance of partly or wholly detached boulders or blocks. The polarization diagrams indicate predominant directions of vibrational effects. Results from this study show an unambiguous distinction between the behavior of "stable" areas, away from the cliff edges, the region of the unstable cliff edge and the actual rockfall areas. Stable regions are characterized by a single and pronounced HVSR resonance peak at around 1.5Hz that are characteristic of all other areas in the Maltese islands having the same underlying geological sequence, while HVSR curves closer to the cliff edge show more complex responses at higher frequencies characteristic of the dynamic behavior of individual detached blocks

  20. Statistical propeties of a single-mode laser driven by additive and multiplicative coloured noises with a coloured cross-correlation for different correlation times

    Institute of Scientific and Technical Information of China (English)

    梁贵云; 曹力; 张莉; 吴大进

    2003-01-01

    We study a system for a single-mode laser driven by additive and multiplicative coloured noises with a coloured cross-correlation. The analytical expression of the stationary intensity distribution (SID) for the laser is derived in the case of three different correlation times. The influences of each stochastic parameter on the SID are discussed, the the skewness, λ3(O) of the single-mode laser are investigated. We find that there are colourful phase transitions for the SID above a threshold, and re-entrant transitions induced by the "colour" of the additive noises. Further research of the not only increases with the additive noise correlation time τ2 and the cross-correlation time τs, but also the quality of the output of laser beams is optimized.

  1. Correlations among factors of sulfide ores in oxidation process at ambient temperature

    Institute of Scientific and Technical Information of China (English)

    吴超; 李孜军; 周勃

    2004-01-01

    Spontaneous combustion is one of the serious problems in the mining of sulfide ore deposits. The relevant factors, e. G. Oxygen absorption quantity, mass increase, contents of water soluble iron ions and sulfate ion of sulfide ore samples in the oxidation process were investigated both in theory and experiment. The results from the investigation show that there is no general interpretation relation among the oxygen absorption quantity, the contents of sulfate ion and water soluble iron ions during the oxidation process of sulfide ores at ambient temperature.However, there is a linear relationship between the mass increase of the sulfide ore samples in the oxidation process at ambient temperature and the quantity of oxygen absorption. Therefore, the simple and cheap mass scaling method is suitable for predicting the oxygen absorption performance of sulfide ores at ambient temperature in place of the expensive and complicated chemical method used hitherto. Furthermore, combined with other items of breeding-fire test, the mass increase potential can also be used to predict the spontaneous combustion tendency of sulfide ores.

  2. Effects of correlations between the real and imaginary parts of quantum noise on intensity fluctuation for a saturation laser model

    Institute of Scientific and Technical Information of China (English)

    Li Yue-Hong; Mei Dong-Cheng

    2008-01-01

    This paper studies the effects of cross-correlations between the real and imaginary parts of quantum noise on the laser intensity in a saturation laser model.It derives the analytic expressions of the intensity correlation function C(Υ)and the associated relaxation time T(C) in the case of a stable locked phase resulting from the cross-correlation λq between the real and imaginary parts of quantum noise.Based on numerical computations it finds that the presence of cross correlations between the real and imaginary parts of quantum noise slow down the decay of intensity fluctuation,i.e.,it causes the increase of intensity fluctuation.

  3. The functions of sound production in the lined seahorse, Hippocampus erectus, and effects of loud ambient noise on its behavior and physiology in captive environments

    Science.gov (United States)

    Anderson, Paul August

    Loud noise in aquaria represents a cacophonous environment for captive fishes. I tested the effects of loud noise on acoustic communication, feeding behavior, courtship behavior, and the stress response of the lined seahorse, Hippocampus erectus. Total Root Mean Square (RMS) power of ambient noise to which seahorses are exposed in captivity varies widely but averages 126.1 +/- 0.8 deciBels with reference to one micropascal (dB re: 1 muPa) at the middle of the water column and 133.7 +/- 1.1 dB at the tank bottom, whereas ambient noise in the wild averages 119.6 +/- 3.5 dB. Hearing sensitivity of H. erectus, measured from auditory evoked potentials, demonstrated maximum spectrum-level sensitivities of 105.0 +/- 1.5 dB and 3.5 x 10-3 + 7.6 x 10-4 m/s2 at 200 Hz; which is characteristic of hearing generalists. H. erectus produces acoustic clicks with mean peak spectrum-level amplitudes of 94.3 +/- 0.9 dB at 232 +/- 16 Hz and 1.5 x 10 -3 +/- 1.9 x 10-4 m/s2 at 265 +/- 22 Hz. Frequency matching of clicks to best hearing sensitivity, and estimates of audition of broadband signals suggest that seahorses may hear conspecific clicks, especially in terms of particle motion. Behavioral investigations revealed that clicking did not improve prey capture proficiency. However, animals clicked more often as time progressed in a courtship sequence, and mates performed more courtship behaviors with control animals than with muted animals, lending additional evidence to the role of clicking as an acoustic signal during courtship. Despite loud noise and the role of clicking in communication, masking of the acoustic signal was not demonstrated. Seahorses exposed to loud noise in aquaria for one month demonstrated physiological, chronic stress responses: reduced weight and body condition, and increased heterophil to lymphocyte ratio. Behavioral alterations were characterized by greater mean and variance of activity among animals housed in loud tanks in the first week, followed by

  4. Arrival angle anomalies of Rayleigh waves observed at a broadband array: a systematic study based on earthquake data, full waveform simulations and noise correlations

    Science.gov (United States)

    Pedersen, H. A.; Boué, P.; Poli, P.; Colombi, A.

    2015-12-01

    Deviation of seismic surface waves from the great-circle between source and receiver is illustrated by the anomalies in the arrival angle, that is the difference between the observed backazimuth of the incident waves and the great-circle. Such arrival angle anomalies have been known for decades, but observations remain scattered. We present a systematic study of arrival angle anomalies of fundamental mode Rayleigh waves (20-100 s period interval) from 289 earthquakes and recorded by a broadband network LAPNET, located in northern Finland. These observations are compared with those of full waveform synthetic seismograms for the same events, calculated in a 3-D Earth and also compared with those of seismograms obtained by ambient noise correlation. The arrival angle anomalies for individual events are complex, and have significant variations with period. On average, the mean absolute deviation decreases from ˜9° at 20 s period to ˜3° at 100 s period. The synthetic seismograms show the same evolution, albeit with somewhat smaller deviations. While the arrival angle anomalies are fairly well simulated at long periods, the deviations at short periods are very poorly modelled, demonstrating the importance of the continuous improvement of global crustal models. At 20-30 s period, both event data and numerical simulations have strong multipathing, and relative amplitude changes between different waves will induced differences in deviations between very closely located events. The source mechanism has only limited influence on the deviations, demonstrating that they are directly linked to propagation effects, including near-field effects in the source area. This observation is confirmed by the comparison with seismic noise correlation records, that is where the surface waves correspond to those emitted by a point source at the surface, as the two types of observations are remarkably similar in the cases where earthquakes are located close to seismic stations. This

  5. Qualificação e quantificação da exposição sonora ambiental em uma unidade de terapia intensiva geral Qualification and quantification of ambient noise exposure in a general intensive care unit

    Directory of Open Access Journals (Sweden)

    Raquel Paganini Pereira

    2003-12-01

    Full Text Available Os níveis de ruído hospitalares encontram-se excessivamente elevados, especialmente no ambiente de UTI, em decorrência dos inúmeros alarmes e equipamentos, além da conversação da própria equipe hospitalar. Diante disso, esse ambiente, que deveria ser silencioso e tranqüilo, torna-se ruidoso, transformando-se em um grande fator de estresse e podendo gerar distúrbios fisiológicos e psicológicos tanto nos pacientes como nos funcionários dessa unidade. OBJETIVO: O objetivo deste estudo foi verificar o nível de pressão sonora equivalente em uma UTI geral, procurando estabelecer o período de maior exposição e comparando os resultados com as recomendações nacionais e internacionais. FORMA DE ESTUDO: Estudo observacional. MATERIAL E MÉTODO: Medição do ruído ambiental da UTI do Hospital São Paulo através do analisador de ruído modelo 2260 (Brüel & Kjaer, em período total de 6.000 minutos e aferições a cada 27 segundos, configurado da seguinte forma: tempo de resposta rápido (Fast, medindo em decibel o nível de pressão sonora e usando a ponderação em freqüência A, de setembro de 2001 a junho de 2002 e sem o conhecimento dos funcionários do setor. RESULTADOS: O nível de pressão sonora equivalente (Leq apresentou média de 65,36 dB(A variando de 62,9 a 69,3 dB(A. Durante o período diurno a média do Leq foi de 65,23 dB(A e para o período noturno, 63,89 dB(A. O L FMax encontrado foi de 108,4 dB(A e o L FMin de 40 dB(A. CONCLUSÕES: O nível de ruído encontrado nessa UTI está acima do recomendado pela literatura em todos os períodos analisados. Dessa forma, as fontes produtoras de ruído excessivo precisam ser melhor identificadas para que possam ser tomadas as devidas medidas para atenuação desse ruído e tornar esse ambiente um local mais silencioso, beneficiando a função laborativa dos profissionais e a recuperação dos pacientes.Noise levels in hospitals are excessively high, especially in the ICU

  6. Effects of Time Delay on the Bistable System Subjected to Correlated Noises

    Institute of Scientific and Technical Information of China (English)

    NIE Lin-Ru; Mei Dong-Cheng

    2007-01-01

    The time-delayed bistable system subjected to the multiplicative and additive noises is investigated. In the condition of small delay time, the stationary probability distribution function (SPDF) is derived, and under the condition of large delay time, the SPDF is stochastically simulated. The analytical and simulative results indicate that: (i) For the case of λ= 0λ denotes the strength of correlations between the multiplicative and additive noises), the time delay affects weakly the SPDF peak structure, and the symmetrical property of the SPDF two-peak structure does not change with the increasing delay time, (ii) For the case of λ≠0, the two-peak structure changes with the increasing delay time, i.e. one peak goes up and the other go down simultaneously as the delay time increases and along with further increase of the delay time, the lower peak disappears gradually while the higher one goes up, i.e. the structure of the SPDF changes from a bimodal to a unimodal and the system becomes monostable.

  7. Analytically exploiting noise correlations inside the feedback loop to improve locked-oscillator performance

    Science.gov (United States)

    Sastrawan, J.; Jones, C.; Akhalwaya, I.; Uys, H.; Biercuk, M. J.

    2016-08-01

    We introduce concepts from optimal estimation to the stabilization of precision frequency standards limited by noisy local oscillators. We develop a theoretical framework casting various measures for frequency standard variance in terms of frequency-domain transfer functions, capturing the effects of feedback stabilization via a time series of Ramsey measurements. Using this framework, we introduce an optimized hybrid predictive feedforward measurement protocol that employs results from multiple past measurements and transfer-function-based calculations of measurement covariance to improve the accuracy of corrections within the feedback loop. In the presence of common non-Markovian noise processes these measurements will be correlated in a calculable manner, providing a means to capture the stochastic evolution of the local oscillator frequency during the measurement cycle. We present analytic calculations and numerical simulations of oscillator performance under competing feedback schemes and demonstrate benefits in both correction accuracy and long-term oscillator stability using hybrid feedforward. Simulations verify that in the presence of uncompensated dead time and noise with significant spectral weight near the inverse cycle time predictive feedforward outperforms traditional feedback, providing a path towards developing a class of stabilization software routines for frequency standards limited by noisy local oscillators.

  8. Noise-Driven Phenotypic Heterogeneity with Finite Correlation Time in Clonal Populations.

    Directory of Open Access Journals (Sweden)

    UnJin Lee

    Full Text Available There has been increasing awareness in the wider biological community of the role of clonal phenotypic heterogeneity in playing key roles in phenomena such as cellular bet-hedging and decision making, as in the case of the phage-λ lysis/lysogeny and B. Subtilis competence/vegetative pathways. Here, we report on the effect of stochasticity in growth rate, cellular memory/intermittency, and its relation to phenotypic heterogeneity. We first present a linear stochastic differential model with finite auto-correlation time, where a randomly fluctuating growth rate with a negative average is shown to result in exponential growth for sufficiently large fluctuations in growth rate. We then present a non-linear stochastic self-regulation model where the loss of coherent self-regulation and an increase in noise can induce a shift from bounded to unbounded growth. An important consequence of these models is that while the average change in phenotype may not differ for various parameter sets, the variance of the resulting distributions may considerably change. This demonstrates the necessity of understanding the influence of variance and heterogeneity within seemingly identical clonal populations, while providing a mechanism for varying functional consequences of such heterogeneity. Our results highlight the importance of a paradigm shift from a deterministic to a probabilistic view of clonality in understanding selection as an optimization problem on noise-driven processes, resulting in a wide range of biological implications, from robustness to environmental stress to the development of drug resistance.

  9. Correlated low-frequency electric and magnetic noise along the auroral field lines

    Science.gov (United States)

    Gurnett, D. A.; Huff, R. L.; Menietti, J. D.; Burch, J. L.; Winningham, J. D.; Shawhan, S. D.

    1984-01-01

    Dynamics Explorer 1 measurements of intense low-frequency electric and magnetic noise observed at low altitudes over the auroral zone are described. The intensity of both the electric and magnetic fields decreases rapidly with increasing frequency. Most of the energy is at frequencies below the O(+) cyclotron frequency, and some evidence is found for a cutoff or change in spectral slope near that frequency. The magnetic to electric field ratio decreases rapidly with increasing radial distance and also decreases with increasing frequency. The polarization of the electric field in a plane perpendicular to the earth's magnetic field is essentially random. The transverse electric and magnetic fields are closely correlated, with the average Poynting flux directed toward the earth. The total electromagnetic power flow associated with the noise is substantial. Two general models are discussed to interpret these observations, one based on static electric and magnetic fields imbedded in the ionosphere and the other based on Alfven waves propagating along the auroral field lines.

  10. Kardar-Parisi-Zhang equation with spatially correlated noise: a unified picture from nonperturbative renormalization group.

    Science.gov (United States)

    Kloss, Thomas; Canet, Léonie; Delamotte, Bertrand; Wschebor, Nicolás

    2014-02-01

    We investigate the scaling regimes of the Kardar-Parisi-Zhang (KPZ) equation in the presence of spatially correlated noise with power-law decay D(p) ∼ p(-2ρ) in Fourier space, using a nonperturbative renormalization group approach. We determine the full phase diagram of the system as a function of ρ and the dimension d. In addition to the weak-coupling part of the diagram, which agrees with the results from Europhys. Lett. 47, 14 (1999) and Eur. Phys. J. B 9, 491 (1999), we find the two fixed points describing the short-range- (SR) and long-range- (LR) dominated strong-coupling phases. In contrast with a suggestion in the references cited above, we show that, for all values of ρ, there exists a unique strong-coupling SR fixed point that can be continuously followed as a function of d. We show in particular that the existence and the behavior of the LR fixed point do not provide any hint for 4 being the upper critical dimension of the KPZ equation with SR noise. PMID:25353423

  11. Noise and Correlations in a Spatial Population Model with Cyclic Competition

    CERN Document Server

    Reichenbach, Tobias; Frey, Erwin

    2007-01-01

    Noise and spatial degrees of freedom characterize most ecosystems. Some aspects of their influence on the coevolution of populations with cyclic interspecies competition have been demonstrated in recent experiments [e.g. B. Kerr et al., Nature {\\bf 418}, 171 (2002)]. To reach a better theoretical understanding of these phenomena, we consider a paradigmatic spatial model where three species exhibit cyclic dominance. Using an individual-based description, as well as stochastic partial differential and deterministic reaction-diffusion equations, we account for stochastic fluctuations and spatial diffusion at different levels, and show how fascinating patterns of entangled spirals emerge. We rationalize our analysis by computing the spatio-temporal correlation functions and provide analytical expressions for the front velocity and the wavelength of the propagating spiral waves.

  12. A system for ocean ambient noise measurement based on subsurface buoy%基于潜标的海洋环境噪声测量系统

    Institute of Scientific and Technical Information of China (English)

    吕云飞; 张殿伦; 邹吉武; 兰华林; 孙大军

    2009-01-01

    This paper aims to design the system of ocean ambient noise measurement, the system is deployed with subsurface buoy, low frequency ambient noise of shallow water is measured by vector hydrophone. Vector hydrophone measures pressure and all three orthogonal components of particle velocity at a single point in space,the measured signal is preprocessed and sampled, the sampled data can be self-stored in subsurface buoy or transmitted to shore station by buoy. The method of noise measurement is discussed, the results of the sea trials show that the system is feasible and reliable.%对海洋环境噪声测量系统技术进行了研究,设计和实现了一种基于潜标的海洋环境噪声测量系统,并进行了海上试验.该系统采用潜标的布放方式,利用矢量水听器测量浅海海洋环境噪声场的低频噪声.矢量水听器同步测量声场空间一点处的声压和质点振速三个正交分量, 测量信号经预处理后,对信号进行数模变换,得到的噪声数据可以在潜标中自记录或通过水面浮标传输到岸站存储.对噪声测量方法进行的分析和海上试验的结果表明,该系统稳定可靠,能正确地拾取海洋环境噪声.

  13. An Integrated Denoising Method for Sensor Mixed Noises Based on Wavelet Packet Transform and Energy-Correlation Analysis

    Directory of Open Access Journals (Sweden)

    Chao Tan

    2014-01-01

    Full Text Available In order to solve the problem of industrial sensor signal denoising, an integrated denoising method for sensor mixed noises based on wavelet packet transform and energy-correlation analysis is proposed. The architecture of proposed method is designed and the key technologies, such as wavelet packet transformation, energy-correlation analysis, and processing method of wavelet packet coefficients based on energy-correlation analysis, are presented. Finally, a simulation example for a specific signal and an application of shearer cutting current signal, which mainly contain white Gaussian noise and impact noise, are carried out, and the simulation and application results show that the proposed method is effective and is outperforming others.

  14. Unknown input and state estimation for linear discrete-time systems with missing measurements and correlated noises

    Science.gov (United States)

    Shu, Huisheng; Zhang, Sijing; Shen, Bo; Liu, Yurong

    2016-07-01

    This paper is concerned with the problem of simultaneous input and state estimation for a class of linear discrete-time systems with missing measurements and correlated noises. The missing measurements occur in a random way and are governed by a series of mutually independent random variables obeying a certain Bernoulli distribution. The process and measurement noises under consideration are correlated at the same time instant. Our attention is focused on the design of recursive estimators for both input and state such that, for all missing measurements and correlated noises, the estimators are unbiased and the estimation error covariances are minimized. This objective is achieved using direct algebraic operation and the design algorithm for the desired estimators is given. Finally, an illustrative example is presented to demonstrate the effectiveness of the proposed design scheme.

  15. Two-time correlation of heat release rate and spectrum of combustion noise from turbulent premixed flames

    Science.gov (United States)

    Liu, Yu

    2015-09-01

    The spectral characteristics of combustion noise are dictated by the temporal correlation of the overall change of heat release rate fluctuations which has not received sufficient attention in prior studies. In this work, the two-time correlation of the volumetric heat release rate fluctuations within the flame brush and its role in modeling combustion noise spectrum are investigated by analyzing direct numerical simulation (DNS) data of turbulent premixed V-flames. This two-time correlation can be well represented by Gaussian-type functions and it captures the slow global variation of the fluctuating heat release rate and hence the low-frequency noise sources of unsteady combustion. The resulting correlation model is applied to predict the far-field noise spectrum from test open flames, and different reference time scales are used to scale this correlation from the DNS data to the test flames. The comparison between predictions and measurements indicates that the correlation models of all reference time scales are capable of reproducing the essential spectral shape including the low- and high-frequency dependencies. Reasonable agreement in the peak frequency, peak sound pressure level, and the Strouhal number scaling of peak frequency is also achieved for two turbulent time scales. A promising convective time scale shows great potential for characterizing the spectral features, yet its predictive capabilities are to be further verified through a longer DNS signal of a bounded flame configuration.

  16. Tunable non-local entanglement of electrons probed by noise cross-correlation measurement

    Science.gov (United States)

    Wei, Jian

    2010-03-01

    Nonlocal entanglement is crucial for quantum information processes. While nonlocal entanglement has been realized for photons, it is much more difficult to demonstrate for electrons. One approach that has been proposed is to use hybrid superconducting/normal-metal devices. When the distance between two normal-metal electrodes connected to a superconductor is comparable to the superconducting coherence length, theory predicts that two electrons in the normal-metal electrodes with opposite spin are entangled by Cooper pairs, leading to non-local entanglement of electrons. Such entanglement can be understood by a non-local process called crossed Andreev reflection (CAR), in which a Cooper pair splits into two coherent electrons with one in each normal-metal electrode, generating instantaneous current of the same sign, and inducing a positive current correlation. Experimentally, CAR is indicated by a negative non-local resistance. However, another non-local process, elastic cotunneling (EC), in which one electron tunnels through the superconductor from one normal-metal electrode to the other, contributes to a positive non-local resistance that cancels the contribution due to CAR, preventing us from measuring and control of the CAR component. Fortunately, EC leads to a negative current correlation with bias dependence different from that of CAR. Thus, noise correlation measurement is expected to be able to distinguish these two non-local processes. By cross-correlation measurements as well as measurements of the local and nonlocal resistance, we present here experimental evidence showing that by independently controlling the energy of electrons at the superconductor/normal-metal interfaces, nonlocal Andreev reflection, the signature of spin-entanglement, can be maximized, qualitatively in agreement with theoretical predication.

  17. Your attention please: increasing ambient noise levels elicits a change in communication behaviour in humpback whales (Megaptera novaeangliae).

    Science.gov (United States)

    Dunlop, Rebecca A; Cato, Douglas H; Noad, Michael J

    2010-08-22

    High background noise is an important obstacle in successful signal detection and perception of an intended acoustic signal. To overcome this problem, many animals modify their acoustic signal by increasing the repetition rate, duration, amplitude or frequency range of the signal. An alternative method to ensure successful signal reception, yet to be tested in animals, involves the use of two different types of signal, where one signal type may enhance the other in periods of high background noise. Humpback whale communication signals comprise two different types: vocal signals, and surface-generated signals such as 'breaching' or 'pectoral slapping'. We found that humpback whales gradually switched from primarily vocal to primarily surface-generated communication in increasing wind speeds and background noise levels, though kept both signal types in their repertoire. Vocal signals have the advantage of having higher information content but may have the disadvantage of loosing this information in a noisy environment. Surface-generated sounds have energy distributed over a greater frequency range and may be less likely to become confused in periods of high wind-generated noise but have less information content when compared with vocal sounds. Therefore, surface-generated sounds may improve detection or enhance the perception of vocal signals in a noisy environment. PMID:20392731

  18. The relationship between noise correlation and the Green's function in the presence of degeneracy and the absence of equipartition

    Science.gov (United States)

    Tsai, V.C.

    2010-01-01

    Recent derivations have shown that when noise in a physical system has its energy equipartitioned into the modes of the system, there is a convenient relationship between the cross correlation of time-series recorded at two points and the Green's function of the system. Here, we show that even when energy is not fully equipartitioned and modes are allowed to be degenerate, a similar (though less general) property holds for equations with wave equation structure. This property can be used to understand why certain seismic noise correlation measurements are successful despite known degeneracy and lack of equipartition on the Earth. No claim to original US government works Journal compilation ?? 2010 RAS.

  19. Optimal CMB map-making in presence of cross-correlated noise

    CERN Document Server

    de Gasperis, Giancarlo; Cabella, Paolo; de Bernardis, Paolo; Vittorio, Nicola

    2016-01-01

    We present an extension of the ROMA map-making algorithm for the generation of optimal CMB temperature and polarization maps. The new code takes into account a possible cross-correlated noise component among the detectors of a CMB experiment. A promising application is the forthcoming LSPE balloon experiment, devoted to the observation of CMB polarization at large angular scales. To check the reliability of the code, we tested the extended ROMA algorithm on real and simulated data of the BOOMERanG(2003) mission, in order to compare our conclusions with already established results. Hence, we performed a preliminary forecast of the LSPE/SWIPE instrument. We found that considering the cross-correlation among the detectors results in a more realistic estimate of the angular power spectra. In particular, the extended ROMA map-making algorithm provides a strong reduction of the spectra error bars. We expect that this improvement will be crucial in constraining the B component of CMB polarization at the largest scal...

  20. Stochastic resonance induced by a multiplicative periodic signal in a bistable system with cross-correlated noises and time delay

    International Nuclear Information System (INIS)

    The stochastic resonance (SR) phenomenon induced by a multiplicative periodic signal in a bistable system with cross-correlated noises and time delay is studied. Two cases have been considered: the case of a system with no delay and the case of a system with time-delayed feedback. The expressions for the signal-to-noise ratio (SNR) are derived, for both cases. The effects of the cross-correlated noise intensity (λ) and the delay time (τ) on the SNR are discussed. It is found that the existence of a maximum in the SNR is the identifying characteristic of the SR phenomenon. In contrast with the case for the SR induced by an additive signal, here both λ and τ have critical values in SR when the SNR as a function of the noise intensities, i.e., λ (or τ), suppresses the SR for λ (or τ) below the critical value while it enhances the SR for λ (or τ) above the critical value. τ suppresses the SR in the SNR as a function of λ while it enhances the SR in the SNR as a function of the noise intensities. The SNR is not only dependent on λ, τ and the noise intensities, but also on the initial condition of the system

  1. Joint inversion of teleseismic P waveforms and surface-wave group velocities from ambient seismic noise in the Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Růžek, Bohuslav; Plomerová, Jaroslava; Babuška, Vladislav

    2012-01-01

    Roč. 56, č. 1 (2012), s. 107-140. ISSN 0039-3169 R&D Projects: GA ČR GA205/07/1088; GA AV ČR IAA300120709; GA MŠk LM2010008 Institutional research plan: CEZ:AV0Z30120515 Keywords : receiver function * seismic noise * joint inversion * Bohemian Massif * velocity structure Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 0.975, year: 2012

  2. Your attention please: increasing ambient noise levels elicits a change in communication behaviour in humpback whales (Megaptera novaeangliae)

    OpenAIRE

    Dunlop, Rebecca A.; Cato, Douglas H.; Noad, Michael J.

    2010-01-01

    High background noise is an important obstacle in successful signal detection and perception of an intended acoustic signal. To overcome this problem, many animals modify their acoustic signal by increasing the repetition rate, duration, amplitude or frequency range of the signal. An alternative method to ensure successful signal reception, yet to be tested in animals, involves the use of two different types of signal, where one signal type may enhance the other in periods of high background ...

  3. Thermal conductivity of silver loaded conductive epoxy from cryogenic to ambient temperature and its application for precision cryogenic noise measurements

    Science.gov (United States)

    Amils, Ricardo I.; Gallego, Juan Daniel; Sebastián, José Luis; Muñoz, Sagrario; Martín, Agustín; Leuther, Arnulf

    2016-06-01

    The pressure to increase the sensitivity of instrumentation has pushed the use of cryogenic Low Noise Amplifier (LNA) technology into a growing number of fields. These areas range from radio astronomy and deep space communications to fundamental physics. In this context manufacturing for cryogenic environments requires a proper thermal knowledge of the materials to be able to achieve adequate design behavior. In this work, we present experimental measurements of the thermal conductivity of a silver filled conductive epoxy (EPO-TEK H20E) which is widely used in cryogenic electronics applications. The characterization has been made using a sample preparation which mimics the practical use of this adhesive in the fabrication of cryogenic devices. We apply the data obtained to a detailed analysis of the effects of the conductive epoxy in a monolithic thermal noise source used for high accuracy cryogenic microwave noise measurements. In this application the epoxy plays a fundamental role since its limited thermal conductivity allows heating the chip with relatively low power. To our knowledge, the cryogenic thermal conductivity data of this epoxy has not been reported before in the literature in the 4-300 K temperature range. A second non-conductive epoxy (Gray Scotch-Weld 2216 B/A), also widely used in cryogenic applications, has been measured in order to validate the method by comparing with previous published data.

  4. Statistical-noise reduction in correlation analysis of high-energy nuclear collisions with event-mixing

    Science.gov (United States)

    Ray, R. L.; Bhattarai, P.

    2016-06-01

    The error propagation and statistical-noise reduction method of Reid and Trainor for two-point correlation applications in high-energy collisions is extended to include particle-pair references constructed by mixing two particles from all event-pair combinations within event subsets of arbitrary size. The Reid-Trainor method is also applied to other particle-pair mixing algorithms commonly used in correlation analysis of particle production from high-energy nuclear collisions. The statistical-noise reduction, inherent in the Reid-Trainor event-mixing procedure, is shown to occur for these other event-mixing algorithms as well. Monte Carlo simulation results are presented which verify the predicted degree of noise reduction. In each case the final errors are determined by the bin-wise particle-pair number, rather than by the bin-wise single-particle count.

  5. Statistical-noise reduction in correlation analysis of high-energy nuclear collisions with event-mixing

    CERN Document Server

    Ray, R L

    2016-01-01

    The error propagation and statistical-noise reduction method of Reid and Trainor for two-point correlation applications in high-energy collisions is extended to include particle-pair references constructed by mixing two particles from all event-pair combinations within event subsets of arbitrary size. The Reid-Trainor method is also applied to other particle-pair mixing algorithms commonly used in correlation analysis of particle production from high-energy nuclear collisions. The statistical-noise reduction, inherent in the Reid-Trainor event-mixing procedure, is shown to occur for these other event-mixing algorithms as well. Monte Carlo simulation results are presented which verify the predicted degree of noise reduction. In each case the final errors are determined by the bin-wise particle-pair number, rather than by the bin-wise single-particle count.

  6. Correlation between dark current RTS noise and defects for AlGaInP multiple-quantum-well laser diode

    International Nuclear Information System (INIS)

    The correlation model between dark current RTS noise and defects for AlGaInP multiple-quantum-well laser diode is derived. Experimental results show that dark current RTS noise caused carrier number fluctuations at the interface of the heterojunction in the active region. According to this correlation model, the defect types are determined, and the defects' energy levels are quantitatively determined. The corner frequency of RTS noise power spectral density is analyzed. The experimental results are in good agreement with the theoretical. This result provided an effective method for estimating the deep-level traps in the active region of AlGaInP multiple quantum well laser diode. (semiconductor devices)

  7. Column-Parallel Single Slope ADC with Digital Correlated Multiple Sampling for Low Noise CMOS Image Sensors

    NARCIS (Netherlands)

    Chen, Y.; Theuwissen, A.J.P.; Chae, Y.

    2011-01-01

    This paper presents a low noise CMOS image sensor (CIS) using 10/12 bit configurable column-parallel single slope ADCs (SS-ADCs) and digital correlated multiple sampling (CMS). The sensor used is a conventional 4T active pixel with a pinned-photodiode as photon detector. The test sensor was fabricat

  8. The effects of concomitant Ginkgo intake on noise induced Hippocampus injury. Possible auditory clinical correlate

    Directory of Open Access Journals (Sweden)

    Alaa Abousetta

    2014-11-01

    Full Text Available This study was conducted to determine the injurious effects of noise on the hippocampus, and to show whether Ginkgo biloba (Gb has any modulatory effect on hippocampal injury. Fifteen adult male albino rats were divided into three groups; control group, noise group and protected group. The noise group was exposed to 100 dB Sound pressure level (SPL white noise, six hours/day for four consecutive weeks. The protected group was exposed to the same noise level with the administration of Gb extract to the animals (50 mg/kg daily for 4 weeks. In the noise exposed group, both pyramidal cell layer and dentate gyrus (DG granular cell layer showed a decrease in thickness with loss and degeneration of many cells. The protected group showed preservation of many parameters as compared to the noise group i.e. increase in thickness of Cornu Ammonis area3 (CA3 & DG; increase in surface area of cells and increased vascularity. In conclusion, noise had detrimental effects on cells of Cornu Ammonis area1 (CA1, CA3 & DG of the hippocampus. In view of this finding, the clinical auditory hazardous effects in people exposed to harmful noise such as tinnitus, as well as memory disturbances and learning disabilities might have a new dimension. The administration of Gb protected the hippocampus against the injurious effect of noise. The probable mechanism and usefulness of Gb in reducing the previously mentioned effects are discussed.

  9. Small-Scale Trial for Evaluating Directional Resolution of Single Spherical Biconcave Acoustic Lens in Designing of Ambient Noise Imaging System

    Science.gov (United States)

    Mori, Kazuyoshi; Ogasawara, Hanako; Nakamura, Toshiaki

    2008-05-01

    Ambient noise imaging (ANI) is the revolutionary idea of detecting objects by using natural ocean background noise. From the analysis results obtained by the finite difference time domain (FDTD) method in our previous studies, it was supposed that a spherical biconcave lens with an aperture diameter of 2.0 m has a sufficient directional resolution (for example, the beam width is 1° at 60 kHz) for realizing an ANI system. In this study, to confirm the analysis results, we performed a small-scale trial of one-fifth space in a water tank. The lens, made of acrylic resin, has an aperture diameter of 400 mm and a radius of curvature of 500 mm. A burst pulse of 25 cycles at 300 kHz, whose frequency increases 5 times, was radiated from the sound source. The sound pressure after passage through the acoustic lens was measured by moving the receiver around the image point. Results show that the shapes of -3 dB areas are similar to the FDTD analysis results at small incidence angles. It was verified that this lens has a sufficient directional resolution for use in the ANI system, because -3 dB areas do not overlap each other.

  10. Annoyance Caused by Noise and Air Pollution during Pregnancy: Associated Factors and Correlation with Outdoor NO2 and Benzene Estimations

    Directory of Open Access Journals (Sweden)

    Ana Fernández-Somoano

    2015-06-01

    Full Text Available This study aimed to describe the degree of annoyance among pregnant women in a Spanish cohort and to examine associations with proximity to traffic, NO2 and benzene exposure. We included 2457 participants from the Spanish Childhood and Environment study. Individual exposures to outdoor NO2 and benzene were estimated, temporally adjusted for pregnancy. Interviews about sociodemographic variables, noise and air pollution were carried out. Levels of annoyance were assessed using a scale from 0 (none to 10 (strong and unbearable; a level of 8 to 10 was considered high. The reported prevalence of high annoyance levels from air pollution was 11.2% and 15.0% from noise; the two variables were moderately correlated (0.606. Significant correlations between NO2 and annoyance from air pollution (0.154 and that from noise (0.181 were observed. Annoyance owing to noise and air pollution had a low prevalence in our Spanish population compared with other European populations. Both factors were associated with proximity to traffic. In multivariate models, annoyance from air pollution was related to NO2, building age, and country of birth; annoyance from noise was only related to the first two. The health burden of these exposures can be increased by stress caused by the perception of pollution sources.

  11. Annoyance Caused by Noise and Air Pollution during Pregnancy: Associated Factors and Correlation with Outdoor NO2 and Benzene Estimations.

    Science.gov (United States)

    Fernández-Somoano, Ana; Llop, Sabrina; Aguilera, Inmaculada; Tamayo-Uria, Ibon; Martínez, María Dolores; Foraster, Maria; Ballester, Ferran; Tardón, Adonina

    2015-06-01

    This study aimed to describe the degree of annoyance among pregnant women in a Spanish cohort and to examine associations with proximity to traffic, NO2 and benzene exposure. We included 2457 participants from the Spanish Childhood and Environment study. Individual exposures to outdoor NO2 and benzene were estimated, temporally adjusted for pregnancy. Interviews about sociodemographic variables, noise and air pollution were carried out. Levels of annoyance were assessed using a scale from 0 (none) to 10 (strong and unbearable); a level of 8 to 10 was considered high. The reported prevalence of high annoyance levels from air pollution was 11.2% and 15.0% from noise; the two variables were moderately correlated (0.606). Significant correlations between NO2 and annoyance from air pollution (0.154) and that from noise (0.181) were observed. Annoyance owing to noise and air pollution had a low prevalence in our Spanish population compared with other European populations. Both factors were associated with proximity to traffic. In multivariate models, annoyance from air pollution was related to NO2, building age, and country of birth; annoyance from noise was only related to the first two. The health burden of these exposures can be increased by stress caused by the perception of pollution sources. PMID:26095869

  12. Bayesian analysis of radial velocity data of GJ667C with correlated noise: evidence for only two planets

    Science.gov (United States)

    Feroz, F.; Hobson, M. P.

    2014-02-01

    GJ667C is the least massive component of a triple star system which lies at a distance of about 6.8 pc (22.1 light-year) from the Earth. GJ667C has received much attention recently due to the claims that it hosts up to seven planets including three super-Earths inside the habitable zone. We present a Bayesian technique for the analysis of radial velocity (RV) data sets in the presence of correlated noise component (`red noise'), with unknown parameters. We also introduce hyper-parameters in our model in order to deal statistically with under- or overestimated error bars on measured RVs as well as inconsistencies between different data sets. By applying this method to the RV data set of GJ667C, we show that this data set contains a significant correlated (red) noise component with correlation time-scale for HARPS data of the order of 9 d. Our analysis shows that the data only provide strong evidence for the presence of two planets: GJ667Cb and c with periods 7.19 and 28.13 d, respectively, with some hints towards the presence of a third signal with period 91 d. The planetary nature of this third signal is not clear and additional RV observations are required for its confirmation. Previous claims of the detection of additional planets in this system are due the erroneous assumption of white noise. Using the standard white noise assumption, our method leads to the detection of up to five signals in this system. We also find that with the red noise model, the measurement uncertainties from HARPS for this system are underestimated at the level of ˜50 per cent.

  13. NOISE REGULATION

    OpenAIRE

    Cristina Voican; Constantin Stanescu

    2012-01-01

    Noise regulation includes statutes or guidelines relating to sound transmission established by national, state or provincial and municipal levels of government. After the watershed passage of the United States Noise Control Act of 1972, other local and state governments passed further regulations. Although the UK and Japan enacted national laws in 1960 and 1967 respectively, these laws were not at all comprehensive or fully enforceable as to address generally rising ambient noise, enforceable...

  14. Noise-immune complex correlation for optical coherence angiography based on standard and Jones matrix optical coherence tomography

    Science.gov (United States)

    Makita, Shuichi; Kurokawa, Kazuhiro; Hong, Young-Joo; Miura, Masahiro; Yasuno, Yoshiaki

    2016-01-01

    This paper describes a complex correlation mapping algorithm for optical coherence angiography (cmOCA). The proposed algorithm avoids the signal-to-noise ratio dependence and exhibits low noise in vasculature imaging. The complex correlation coefficient of the signals, rather than that of the measured data are estimated, and two-step averaging is introduced. Algorithms of motion artifact removal based on non perfusing tissue detection using correlation are developed. The algorithms are implemented with Jones-matrix OCT. Simultaneous imaging of pigmented tissue and vasculature is also achieved using degree of polarization uniformity imaging with cmOCA. An application of cmOCA to in vivo posterior human eyes is presented to demonstrate that high-contrast images of patients’ eyes can be obtained. PMID:27446673

  15. Seismic tomography of Basse-Terre volcanic island, Guadeloupe, Lesser Antilles, using earthquake travel times and noise correlations

    Science.gov (United States)

    Barnoud, Anne; Coutant, Olivier; Bouligand, Claire; Massin, Frédérick; Stehly, Laurent

    2015-04-01

    We image the volcanic island of Basse-Terre, Guadeloupe, Lesser Antilles, using both earthquake travel times and noise correlations. (1) A new earthquake catalog was recently compiled for the Lesser Antilles by the CDSA/OVSG/IPGP (Massin et al., EGU General Assembly 2014) and allows us to perform classical travel time tomography to obtain smooth 3D body wave velocity models. The geometrical configuration of the volcanic arc controls the resolution of the model in our zone of interest. (2) Surface wave tomography using noise correlations was successfully applied to volcanoes (Brenguier et al., Geophys. Res. Lett. 2007). We use seismic noise recorded at 16 broad-band stations and 9 short-period stations from Basse-Terre over a period of six years (2007-2012). For each station pair, we extract a dispersion curve from the noise correlation to get surface wave velocity models. The inversion of the dispersion curves produces a 3D S-wave velocity model of the island. The spatial distribution of seismic stations accross the island is highly heterogeneous, leading to higher resolution near the dome of the Soufrière of Guadeloupe volcano. Resulting velocity models are compared with densities obtained by 3D inversion of gravimetric data (Barnoud et al., AGU Fall Meeting 2013). Further work should include simultaneous inversion of seismic and gravimetric datasets to overcome resolution limitations.

  16. Noise correlation-based adaptive polarimetric image representation for contrast enhancement of a polarized beacon in fog

    Science.gov (United States)

    Panigrahi, Swapnesh; Fade, Julien; Alouini, Mehdi

    2015-10-01

    We show the use of a simplified snapshot polarimetric camera along with an adaptive image processing for optimal detection of a polarized light beacon through fog. The adaptive representation is derived using theoretical noise analysis of the data at hand and is shown to be optimal in the Maximum likelihood sense. We report that the contrast enhancing optimal representation that depends on the background noise correlation differs in general from standard representations like polarimetric difference image or polarization filtered image. Lastly, we discuss a detection strategy to reduce the false positive counts.

  17. Concise calculation of the scaling function, exponents, and probability functional of the Edwards-Wilkinson equation with correlated noise

    International Nuclear Information System (INIS)

    The linear Langevin equation proposed by Edwards and Wilkinson [Proc. R. Soc. London A 381, 17 (1982)] is solved in closed form for noise of arbitrary space and time correlation. Furthermore, the temporal development of the full probability functional describing the height fluctuations is derived exactly, exhibiting an interesting evolution between two distinct Gaussian forms. We determine explicitly the dynamic scaling function for the interfacial width for any given initial condition, isolate the early-time behavior, and discover an invariance that was unsuspected in this problem of arbitrary spatiotemporal noise

  18. Ranking of stimuli that evoked memories in significant others after exposure to circumcerebral magnetic fields: correlations with ambient geomagnetic activity.

    Science.gov (United States)

    Booth, J N; Charette, J C; Persinger, M A

    2002-10-01

    To identify means to enhance the laboratory production of alleged paranormal phenomena, 15 pairs of men and women involved emotionally were tested by male and female experimenters who were not familiar with the hypothesis that ambient (geomagnetic) activity could modulate this production. While the female of the pair was exposed to six different patterns of complex magnetic fields designed to affect states of consciousness, the male wrote his reminiscences about shared experiences evoked by a postcard randomly selected from a collection of five. Increased global geomagnetic activity (k values between 0 and 5) at the time of the experiments was significantly and moderately correlated with the more accurate ranking of the stimulus cards. These results were similar to those of a previous study. We suggest that alleged paranormal phenomena involve processes that might be produced by experimentally altering the electroencephalographic correlates of consciousness with circumcerebral applications of counterclockwise weak magnetic fields. However, these processes may be enhanced if global geomagnetic activity is increasing during the periods of exposure. PMID:12434850

  19. Localization of Narrow-Band Sources in Unknown Spatially Correlated Noise

    Directory of Open Access Journals (Sweden)

    Bourennane Salah

    2010-01-01

    Full Text Available In subspace-based method for direction-of-arrival (DOA estimation of signal wavefronts, the additive noise term is often assumed to be spatially white or known to within a multiplicative scalar. When the noise is nonwhite but has a known covariance matrix, we can still handle the problem through prewhitening. However, the problem turns to be complex when the noise field is completely unknown. In this paper, we study the localization of the sources, when the noise covariance matrix is one unknown band matrix. An iterative denoising algorithm based on the noise subspace spanned by the eigenvectors associated with the smallest eigenvalues is developed. The performance of the proposed algorithm is evaluated by computer simulations. We also test the proposed algorithm with some experimental data recorded during an underwater acoustic experiment.

  20. Ambiente urbano e percepção da poluição sonora Urban environment and perception to noise pollution

    Directory of Open Access Journals (Sweden)

    Adriana Bender Moreira de Lacerda

    2005-12-01

    Full Text Available A presente pesquisa avaliou a percepção da população de uma grande cidade em relação à poluição sonora (ruído urbano. Buscou-se identificar quais fontes sonoras são percebidas com maior freqüência pela população e quais reações psico-sociais relacionadas ao ruído urbano são identificados por ela. Foi utilizado um questionário composto de questões fechadas, abrangendo aspectos demográficos e aspectos psico-sociais referentes ao ruído ambiental. Oitocentos e noventa e dois (892 indivíduos participaram da pesquisa. As principais fontes de ruído citadas pelos moradores como causadoras de incômodo foram: 1 o tráfego de veículos (67 %, 2 os vizinhos (33%, 3 o barulho de sirenes (23%, 4 o barulho de animais (21% e 5 o barulho gerado pela construção civil (21 %. As principais reações psico-sociais foram: 1 irritabilidade (55%, 2 baixa concentração (28%, 3 insônia (20% e 4 dor de cabeça (19%. Os resultados obtidos coincidem com dados obtidos em pesquisas desenvolvidas na Europa, EUA e no Brasil, de que a poluição sonora ambiental influencia a qualidade de vida da população, gerando reações psico-sociais importantes, como: 1 irritabilidade e 2 insônia. Estes podem estar na base de outras doenças (disfunções cardiovasculares, podendo interferir na saúde e no bem estar dos indivíduos em particular e de uma população urbana como um todo, gerando um problema de saúde pública.The present study investigated the psychosocial complaints related to urban noise among the population of Curitiba. We used a questionnaire of closed-set questions to collect data on demographics and psychosocial reactions to environmental noise when subjects are at home. Eight hundred and ninety-two individuals (892 participated of the study. The main noise sources associated with discomfort or annoyance were traffic noise (67%, neighbors (33%, sirens (23%, animals (21%, and construction (21%. The main psychosocial complaints were

  1. Improving the signal-to-noise ratio of thermal ghost imaging based on positive-negative intensity correlation

    Science.gov (United States)

    Song, Shu-Chun; Sun, Ming-Jie; Wu, Ling-An

    2016-05-01

    Ghost imaging with thermal light is a topic in optical imaging that has aroused great interest in recent years. However, the imaging quality must be greatly improved before the technology can be transferred from the lab to engineering applications. By means of correspondence ghost imaging (CGI) with a pseudo-thermal light source and appropriate sorting of the intensity fluctuations of the signal and reference beams, we obtain the positive and negative Hanbury Brown and Twiss intensity correlation characteristics of the optical field. Then, for ghost imaging of a transmissive binary object, we find that by subtracting the negative from the positive fluctuation frames of the presorted reference detector signals, the signal-to-noise ratio can be effectively increased, with almost all the background noise eliminated. Our results show that, compared with the generic CGI technique, the signal-to-noise ratio can be increased by nearly 60%.

  2. Noise robustness and parallel computation of the inverse compositional Gauss-Newton algorithm in digital image correlation

    Science.gov (United States)

    Shao, Xinxing; Dai, Xiangjun; He, Xiaoyuan

    2015-08-01

    The inverse compositional Gauss-Newton (IC-GN) algorithm is one of the most popular sub-pixel registration algorithms in digital image correlation (DIC). The IC-GN algorithm, compared with the traditional forward additive Newton-Raphson (FA-NR) algorithm, can achieve the same accuracy in less time. However, there are no clear results regarding the noise robustness of IC-GN algorithm and the computational efficiency is still in need of further improvements. In this paper, a theoretical model of the IC-GN algorithm was derived based on the sum of squared differences correlation criterion and linear interpolation. The model indicates that the IC-GN algorithm has better noise robustness than the FA-NR algorithm, and shows no noise-induced bias if the gray gradient operator is chosen properly. Both numerical simulations and experiments show good agreements with the theoretical predictions. Furthermore, a seed point-based parallel method is proposed to improve the calculation speed. Compared with the recently proposed path-independent method, our model is feasible and practical, and it can maximize the computing speed using an improved initial guess. Moreover, we compared the computational efficiency of our method with that of the reliability-guided method using a four-point bending experiment, and the results show that the computational efficiency is greatly improved. This proposed parallel IC-GN algorithm has good noise robustness and is expected to be a practical option for real-time DIC.

  3. Ambient seismic noise tomography reveals a hidden caldera and its relation to the Tarutung pull-apart basin at the Sumatran Fault Zone, Indonesia

    Science.gov (United States)

    Ryberg, Trond; Muksin, Umar; Bauer, Klaus

    2016-07-01

    We analyzed the noise recordings of a short-period seismic network to derive a shallow crustal S-wave velocity model at the Sumatra Fault in Northern Sumatra, Indonesia. By correlating the noise of 40 seismic stations' recording for 9 months, we could recover Rayleigh waves from vertical component recordings with sufficient signal-to-noise ratio. Group velocities of the Rayleigh waves could be determined in the period range from 0.71 to 4.4 s. These group velocities were used to invert for 2D group velocity maps at specific periods. Finally, the derived group velocity maps were inverted for a 3D S-wave velocity model. This model shows a region of a strong velocity decrease off the Great Sumatran Fault Zone, at the northeastern margin of the young Tarutung pull-apart basin. This observed low velocity block coincides with a caldera-like morphological feature which is interpreted as the surface expression of a hidden volcanic caldera. Considering the surface manifestations of geothermal activity around this anomaly, we conclude that the caldera is still acting as a heat source. On the other hand, the weak morphological expression at the surface indicates a certain age of the caldera which might be older than the Tarutung pull-apart basin. The findings provide important constraints on general concepts for the formation of pull-apart basins along the Sumatran fault and their relation to volcanism.

  4. Spectral-Ripple Resolution Correlates with Speech Reception in Noise in Cochlear Implant Users

    OpenAIRE

    Won, Jong Ho; Drennan, Ward R.; Rubinstein, Jay T.

    2007-01-01

    Speech perception ability in noise is one of the most practical measures of success with a cochlear implant; however, with experience, this ability can change dramatically over time, making it a less than ideal tool for comparing performance among different processing strategies. This study examined performance on a spectral discrimination task and compared it to speech perception in noise. An adaptive procedure was used to determine the spectral-ripple density that subjects could discriminat...

  5. Bayesian analysis of radial velocity data of GJ667C with correlated noise: evidence for no more than 3 planets

    CERN Document Server

    Feroz, Farhan

    2013-01-01

    GJ667C is the least massive component of a triple star system which lies at a distance of about 6.8 pc (22.1 light-years) from Earth. GJ667C has received much attention recently due to the claims that it hosts up to seven planets including three super-Earths inside the habitable zone. We present a Bayesian technique for the analysis of radial velocity (RV) data-sets in the presence of correlated noise component ("red noise"), with unknown parameters. We also introduce hyper-parameters in our model in order to deal statistically with under or over-estimated error bars on measured RVs as well as inconsistencies between different data-sets. By applying this method to the RV data-set of GJ667C and show that this data-set contains a significant correlated (red) noise component with correlation timescale for HARPS data of order 9 days. Our analysis shows that the data only provides strong evidence for the presence of two planets: GJ667Cb and c with periods 7.19d and 28.13d respectively, with some hints towards the ...

  6. Performance evaluation of commercial short-oligonucleotide microarrays and the impact of noise in making cross-platform correlations

    Directory of Open Access Journals (Sweden)

    Kaysser-Kranich Tamma

    2004-09-01

    Full Text Available Abstract Background Despite the widespread use of microarrays, much ambiguity regarding data analysis, interpretation and correlation of the different technologies exists. There is a considerable amount of interest in correlating results obtained between different microarray platforms. To date, only a few cross-platform evaluations have been published and unfortunately, no guidelines have been established on the best methods of making such correlations. To address this issue we conducted a thorough evaluation of two commercial microarray platforms to determine an appropriate methodology for making cross-platform correlations. Results In this study, expression measurements for 10,763 genes uniquely represented on Affymetrix U133A/B GeneChips® and Amersham CodeLink™ UniSet Human 20 K microarrays were compared. For each microarray platform, five technical replicates, derived from the same total RNA samples, were labeled, hybridized, and quantified according to each manufacturers' standard protocols. The correlation coefficient (r of differential expression ratios for the entire set of 10,763 overlapping genes was 0.62 between platforms. However, the correlation improved significantly (r = 0.79 when genes within noise were excluded. In addition to levels of inter-platform correlation, we evaluated precision, statistical-significance profiles, power, and noise levels for each microarray platform. Accuracy of differential expression was measured against real-time PCR for 25 genes and both platforms correlated well with r values of 0.92 and 0.79 for CodeLink and GeneChip, respectively. Conclusions As a result of this study, we recommend using only genes called 'present' in cross-platform correlations. However, as in this study, a large number of genes may be lost from the correlation due to differing levels of noise between platforms. This is an important consideration given the apparent difference in sensitivity of the two platforms. Data from

  7. Imaging hydrothermal systems associated with oceanic ridge: ambient noise and travel-time tomographies in the Reykjanes high-temperature area, SW-Iceland.

    Science.gov (United States)

    Jousset, Philippe; Ágústsson, Kristjan; Verdel, Arie; Blanck, Hanna; Franke, Steven; Specht, Sebastian; Stefánsson, Stefán; Tryggvason, Hörður; Erbas, Kemal; Deon, Fiorenza; Erlendsson, Ögmundur; Guðnason, Egill; Hersir, Gylfi; Ryberg, Trond; Halldórsdóttir, Sæunn; Weemstra, Cornelius; Bruhn, David; Flovenz, Ólafur; Friðleifsson, Ómar

    2015-04-01

    Analogue outcrops of hydrothermal fossil systems and simulating pressure/temperature conditions in the laboratory are classical methods for assessing supercritical conditions in magmatic environments. Scientific drilling is used when Earth surface sampled rocks cannot sufficiently explain past geological processes and when geophysical imaging does not sufficiently explain observed phenomena. However, our understanding of structural and dynamic characteristics of geothermal systems can be improved through application of advanced and/or innovative exploration technologies. Unlike resistivity imaging, active and passive seismic techniques have rarely been used in volcanic geothermal areas, because processing techniques were not adapted to geothermal conditions. Recent advances in volcano-seismology have introduced new processing techniques for assessing subsurface structures and controls on fluid flow in geothermal systems. We present here preliminary analyses of seismic records around a geothermal reservoir located both on-land and offshore along the Reykjanes Ridge, SW-Iceland. We deployed 214 on-land stations and 24 Ocean Bottom Seismometers since April 2014. We analyse more than 6 months of part of those records. We present first results of both travel-time tomography and ambient noise tomography and we discuss briefly implications for geothermal exploration in volcanic contexts.

  8. Characterization of phosphorescent organic light-emitting diodes using current noise cross-correlated spectroscopy

    Science.gov (United States)

    Kamdem Djidjou, Thaddee; Li, Sergey; Rogachev, Andrey

    2014-03-01

    Carrier injection and transport mechanism in small-molecule phosphorescent organic light-emitting diodes (PhOLED) have been investigated using current noise spectroscopy. The PhOLED devices studied consist of multilayers having the structure ITO / NPB / NPB:Irphq / Balq / Bpen:CsCO3/ Al. We found that in high bias regime, the noise spectral density can be described by two terms, 1/ f1.3 and 1/f2.8. The first term disappears below 2.5 V, as does the luminance; this suggests that this term is related to bimolecular recombination in the devices. The second term is more pronounced al low frequencies and its magnitude is linearly proportional to the current in the device. This term, which exists in all bias range, is likely related to the presence of traps with a distributed time constant. For applied voltages greater than 2.4 V, the frequency-independent noise is dominated by the shot noise. The Fano factor is one in the range 2.4 - 2.5 V, and decreases to a constant value of 0.4 at higher biases. This indicates the presence of a barrier for carrier injection into the device. Our overall results confirm the utility of noise measurements for OLED characterization.

  9. The statistical fluctuation of a single-mode laser system driven by coloured pump noise with signal modulation and the quantum noise with cross-correlation between its real and imaginary parts

    Institute of Scientific and Technical Information of China (English)

    Xu Dai-Hai; Cheng Qing-Hua; Cao Li; Wu Da-Jin

    2006-01-01

    Using the linear approximation method, this paper studies the statistical property of a single-mode laser driven by both coloured pump noise with signal modulation and the quantum noise with cross-correlation between its real and imaginary parts, and calculates the steady-state mean normalized intensity fluctuation and intensity correlation time.It analyses the influences of the modulation signal, the net gain coefficient, the noise and its correlation form on the statistical fluctuation of the laser system respectively. It is found that the coloured pump noise modulated by the signal has a great suppressing action on the statistical fluctuation of the laser system; the pump noise self-correlation time and the specific frequency of modulation signal have the result that the statistical fluctuation tends to zero. Furthermore,the intensity of pump noise will augment the statistical fluctuation of the laser system, but the intensity of quantum noise and the coefficient of cross-correlation between its real and imaginary parts have less influence on the statistical fluctuation of the laser system. Therefore, from the conclusions of this paper the statistical property can be known and a theoretical basis for steady operation and output of the laser system can be provided.

  10. Arctic ocean long-term acoustic monitoring : ambient noise, environmental correlates, and transients north of Barrow, Alaska

    OpenAIRE

    Roth, Ethan H.

    2008-01-01

    The Arctic Ocean has experienced wide-spread decreases in sea ice concentrations that may impact various marine ecosystems. This study analyzes yearlong ocean acoustic recordings from north of Barrow, Alaska, to provide baseline measurements prior to possible increases in anthropogenic activities. In September 2006, two autonomous High-frequency Acoustic Recording Packages (HARPs) were deployed to the seafloor (250m), where sound was continuously recorded by hydrophones for nine months. Ice c...

  11. A Measure of the Signal-to-Noise Ratio of Microarray Samples and Studies Using Gene Correlations

    Science.gov (United States)

    Venet, David; Detours, Vincent; Bersini, Hugues

    2012-01-01

    Background The quality of gene expression data can vary dramatically from platform to platform, study to study, and sample to sample. As reliable statistical analysis rests on reliable data, determining such quality is of the utmost importance. Quality measures to spot problematic samples exist, but they are platform-specific, and cannot be used to compare studies. Results As a proxy for quality, we propose a signal-to-noise ratio for microarray data, the “Signal-to-Noise Applied to Gene Expression Experiments”, or SNAGEE. SNAGEE is based on the consistency of gene-gene correlations. We applied SNAGEE to a compendium of 80 large datasets on 37 platforms, for a total of 24,380 samples, and assessed the signal-to-noise ratio of studies and samples. This allowed us to discover serious issues with three studies. We show that signal-to-noise ratios of both studies and samples are linked to the statistical significance of the biological results. Conclusions We showed that SNAGEE is an effective way to measure data quality for most types of gene expression studies, and that it often outperforms existing techniques. Furthermore, SNAGEE is platform-independent and does not require raw data files. The SNAGEE R package is available in BioConductor. PMID:23251415

  12. Influences of noise correlation and time delay on stochastic resonance induced by multiplicative signal in a cancer growth system

    International Nuclear Information System (INIS)

    This paper investigates the stochastic resonance (SR) phenomenon induced by the multiplicative periodic signal in a cancer growth system with the cross-correlated noises and time delay. To describe the periodic change of the birth rate due to the periodic treatment, a multiplicative periodic signal is added to the system. Under the condition of small delay time, the analytical expression of the signal-to-noise ratio RSNR is derived in the adiabatic limit. By numerical calculation, the effects of the cross-correlation strength λ and the delay time τ on RSNR are respectively discussed. The existence of a peak in the curves of RSNR as a function of the noise intensities indicates the occurrence of the SR phenomenon. It is found that λ and τ play opposite role on the SR phenomenon, i.e., the SR is suppressed by increasing λ whereas it is enhanced with the increase of τ, which is different from the case where the periodic signal is additive. (general)

  13. Reprint of : Hanbury-Brown Twiss noise correlation with time controlled quasi-particles in ballistic quantum conductors

    Science.gov (United States)

    Glattli, D. C.; Roulleau, P.

    2016-08-01

    We study the Hanbury Brown and Twiss correlation of electronic quasi-particles injected in a quantum conductor using current noise correlations and we experimentally address the effect of finite temperature. By controlling the relative time of injection of two streams of electrons it is possible to probe the fermionic antibunching, performing the electron analog of the optical Hong Ou Mandel (HOM) experiment. The electrons are injected using voltage pulses with either sine-wave or Lorentzian shape. In the latter case, we propose a set of orthogonal wavefunctions, describing periodic trains of multiply charged electron pulses, which give a simple interpretation to the HOM shot noise. The effect of temperature is then discussed and experimentally investigated. We observe a perfect electron anti-bunching for a large range of temperature, showing that, as recently predicted, thermal mixing of the states does not affect anti-bunching properties, a feature qualitatively different from dephasing. For single charge Lorentzian pulses, we provide experimental evidence of the prediction that the HOM shot noise variation versus the emission time delay is remarkably independent of the temperature.

  14. Constraints on temporal velocity variations associated with an underground gas storage in the Gulf of Valencia using earthquake and seismic ambient noise data

    Science.gov (United States)

    Ugalde, Arantza; Gaite, Beatriz; Villaseñor, Antonio

    2016-04-01

    During September 2013, the injection of the base gas in a depleted oil reservoir used as an underground natural gas storage (CASTOR) caused a sudden seismic activity increase in the eastern coast of Spain. As a result, a compact cluster of more than 550 earthquakes with magnitudes mbLg > 0.7 were located in the shallow offshore area of the Gulf of Valencia during two months. The strongest event, having a magnitude of Mw=4.2, was followed by two Mw=4.1 events the day after and took place once the gas injection activities had finished. Using the seismic data recorded by permanent stations at more than 25 km from the injection well, we applied coda wave interferometry to monitor changes in seismic velocity structure between similar earthquakes. Then we solved for a continuous function of velocity changes with time by combining observations from all the closely located earthquake sources. The rate of repeating events allowed measurements of relative velocity variations for about 30 days on a daily scale. To extend the analysis in time, we also processed the continuous data using the autocorrelation of band-pass filtered ambient seismic noise. A 10-day average was required to achieve a sufficient signal-to-noise ratio in the 0.2-0.5 Hz and 0.5-1 Hz frequency bands. We quantified the time lags between two traces in the frequency and time domains by means of the Moving Window Cross Spectral Analysis and a Dynamic Time Warping technique, respectively. Injection of fluids in geologic formations causes variations in seismic velocities associated to changes in fluid saturation, increase in pore pressure or opening or enlargement of cracks due to the injection process. Time delays associated with stress changes caused by moderate to large earthquakes have also been established. In this work, we found no velocity changes during the gas injection period nor on the occasion of the Mw 4.2 earthquake. The sensitivity of the method is dependent on the seismic network geometry and

  15. Joint inversion of P-waveforms from teleseismic events and surface waves group velocities from ambient seismic noise in Bohemian Massif

    Science.gov (United States)

    Ruzek, Bohuslav

    2010-05-01

    Joint inversion of P-waveforms from distant earthquakes recorded by 41 broadband seismic stations located on the territory of Bohemian Massif and Rayleigh/Love group velocities gained by using cross-correlation technique applied to seismic noise recorded by the same set of broadband stations has been performed. Together with joint inversion also individual inversions using single data sets have been carried out. All computations were arranged inside isotropic, locally 1D layered models. Remarkable result is indication of horizons just above MOHO in the lower crust below some stations where low-velocity S-wave channel is needed in order to ensure correct modeling of measured events. This indication follows both from individual and joint inversions. P-waveform inversion is based on using a set of 271 well-recorded teleseismic events from epicentral distances 3000-10000 km. The inversion was originally based on the popular 'receiver function' methodology, but due to the instability of needed deconvolution it was modified. We search for optimum layered velocity model, which correctly projects radial to vertical components (and vice versa, deconvolution is no more needed). Regarding second source of data, both Rayleigh and Love surface waves were extracted from seismic noise by using cross-correlation. Long time series covering the period 2001-2009 were processed. Such measurements provide group velocities between arbitrary pairs of stations. Local group velocity dispersion curves were computed by using 2D tomography-like approach for periods 4-20 s. The subject of inversion (both individual and joint) were just group velocity dispersion curves. Inversion required exhaustive computations. We used HPC cluster nemo.ig.cas.cz and ANNI inversion software, capable to run in parallel regime.

  16. Novel algorithm on DOA estimation for correlated sources under complex symmetric Toeplitz noise

    Institute of Scientific and Technical Information of China (English)

    Wang Kai; Zhang Yongshun; Shi Dan

    2008-01-01

    To cope with the scenario where both uncorrelated sources and coherent sources coexist,a novel algorithm to direction of arrival (DOA) estimation for symmetric uniform linear array is presented.Under the condition of stationary colored noise field,the algorithm employs a spatial differencing method to eliminate the noise covariance matrix and uncorrelated sources,then a Toeplitz matrix is constructed for the remained coherent sources.After preprocessing,a propagator method (PM) is employed to find the DOAs without any eigendecomposition.The number of sources resolved by this approach can exceed the number of array elements at a lower computational complexity.Simulation results demonstrate the effectiveness and efficiency of the proposed method.

  17. Image Subtraction Noise Reduction Using Point Spread Function Cross-correlation

    CERN Document Server

    Hartung, Steven

    2013-01-01

    Image subtraction in astronomy is a tool for transient object discovery and characterization, particularly useful in wide fields, and is well suited for moving or photometrically varying objects such as asteroids, extra-solar planets and supernovae. A convolution technique is used to match point spread functions (PSFs) between images of the same field taken at different times prior to pixel-by-pixel subtraction. Particularly suitable for large-scale images is a spatially-varying kernel, where the convolution is allowed to adapt to PSF changes as a function of position within the images. The most versatile basis for fitting the spatially-varying kernel is the Dirac delta function. However, the convolution kernel based on the delta function does not discriminate between pixel scale noise variations and the intended stellar point spread function signals. The situation can frequently lead to reduced signal to noise ratios for variable objects detectable in the resulting subtraction. This work presents a cross-cor...

  18. Deriving dispersional and scaled windowed variance analyses using the correlation function of discrete fractional Gaussian noise

    OpenAIRE

    RAYMOND, GARY M.; Bassingthwaighte, James B.

    1999-01-01

    Methods for estimating the fractal dimension, D, or the related Hurst coefficient, H, for a one-dimensional fractal series include Hurst’s method of rescaled range analysis, spectral analysis, dispersional analysis, and scaled windowed variance analysis (which is related to detrended fluctuation analysis). Dispersional analysis estimates H by using the variance of the grouped means of discrete fractional Gaussian noise series (DfGn). Scaled windowed variance analysis estimates H using the mea...

  19. Column-Parallel Single Slope ADC with Digital Correlated Multiple Sampling for Low Noise CMOS Image Sensors

    OpenAIRE

    Chen, Y; Theuwissen, A.J.P.; Chae, Y

    2011-01-01

    This paper presents a low noise CMOS image sensor (CIS) using 10/12 bit configurable column-parallel single slope ADCs (SS-ADCs) and digital correlated multiple sampling (CMS). The sensor used is a conventional 4T active pixel with a pinned-photodiode as photon detector. The test sensor was fabricated in a 0.18 colonm CMOS image sensor process from TSMC. The ADC nonlinearity measurement result shows totally 0.58% nonlinearity. Using the proposed column-parallel SS-ADC with digital CMS techniq...

  20. Simulation study of the effects of time delay on the correlation function of a bistable system with correlated noises

    International Nuclear Information System (INIS)

    The effects of time delay on the fluctuation properties of a bistable system are investigated by simulating its normalised correlation function C(s). Three cases including linear delay, cubic delay and global delay in the system are considered respectively. The simulation results indicate that the linear delay enhances the fluctuation of the system (reduces the stability of the system) while the cubic delay and global delay weaken it (enforce the stability of the system), and the effect of cubic delay is more pronounced than the linear delay and global delay. (general)

  1. Nonlinear statistical reconstruction for flat-panel cone-beam CT with blur and correlated noise models

    Science.gov (United States)

    Tilley, Steven; Siewerdsen, Jeffrey H.; Zbijewski, Wojciech; Stayman, J. Webster

    2016-03-01

    Flat-panel cone-beam CT (FP-CBCT) is a promising imaging modality, partly due to its potential for high spatial resolution reconstructions in relatively compact scanners. Despite this potential, FP-CBCT can face difficulty resolving important fine scale structures (e.g, trabecular details in dedicated extremities scanners and microcalcifications in dedicated CBCT mammography). Model-based methods offer one opportunity to improve high-resolution performance without any hardware changes. Previous work, based on a linearized forward model, demonstrated improved performance when both system blur and spatial correlations characteristics of FP-CBCT systems are modeled. Unfortunately, the linearized model relies on a staged processing approach that complicates tuning parameter selection and can limit the finest achievable spatial resolution. In this work, we present an alternative scheme that leverages a full nonlinear forward model with both system blur and spatially correlated noise. A likelihood-based objective function is derived from this forward model and we derive an iterative optimization algorithm for its solution. The proposed approach is evaluated in simulation studies using a digital extremities phantom and resolution-noise trade-offs are quantitatively evaluated. The correlated nonlinear model outperformed both the uncorrelated nonlinear model and the staged linearized technique with up to a 86% reduction in variance at matched spatial resolution. Additionally, the nonlinear models could achieve finer spatial resolution (correlated: 0.10 mm, uncorrelated: 0.11 mm) than the linear correlated model (0.15 mm), and traditional FDK (0.40 mm). This suggests the proposed nonlinear approach may be an important tool in improving performance for high-resolution clinical applications.

  2. Nonlinear Statistical Reconstruction for Flat-Panel Cone-Beam CT with Blur and Correlated Noise Models

    Science.gov (United States)

    Tilley, Steven; Siewerdsen, Jeffrey H.; Zbijewski, Wojciech; Stayman, J. Webster

    2016-01-01

    Flat-panel cone-beam CT (FP-CBCT) is a promising imaging modality, partly due to its potential for high spatial resolution reconstructions in relatively compact scanners. Despite this potential, FP-CBCT can face difficulty resolving important fine scale structures (e.g, trabecular details in dedicated extremities scanners and microcalcifications in dedicated CBCT mammography). Model-based methods offer one opportunity to improve high-resolution performance without any hardware changes. Previous work, based on a linearized forward model, demonstrated improved performance when both system blur and spatial correlations characteristics of FP-CBCT systems are modeled. Unfortunately, the linearized model relies on a staged processing approach that complicates tuning parameter selection and can limit the finest achievable spatial resolution. In this work, we present an alternative scheme that leverages a full nonlinear forward model with both system blur and spatially correlated noise. A likelihood-based objective function is derived from this forward model and we derive an iterative optimization algorithm for its solution. The proposed approach is evaluated in simulation studies using a digital extremities phantom and resolution-noise trade-offs are quantitatively evaluated. The correlated nonlinear model outperformed both the uncorrelated nonlinear model and the staged linearized technique with up to a 86% reduction in variance at matched spatial resolution. Additionally, the nonlinear models could achieve finer spatial resolution (correlated: 0.10 mm, uncorrelated: 0.11 mm) than the linear correlated model (0.15 mm), and traditional FDK (0.40 mm). This suggests the proposed nonlinear approach may be an important tool in improving performance for high-resolution clinical applications. PMID:27110051

  3. State and parameter estimation of state-space model with entry-wise correlated uniform noise

    Czech Academy of Sciences Publication Activity Database

    Pavelková, Lenka; Kárný, Miroslav

    2014-01-01

    Roč. 28, č. 11 (2014), s. 1189-1205. ISSN 0890-6327 R&D Projects: GA TA ČR TA01030123; GA ČR GA13-13502S Institutional research plan: CEZ:AV0Z1075907 Keywords : state-space models * bounded noise * filtering problems * estimation algorithms * uncertain dynamic systems Subject RIV: BC - Control Systems Theory Impact factor: 1.346, year: 2014 http://library.utia.cas.cz/separaty/2014/AS/pavelkova-0422958.pdf

  4. Acoustic signal detection through the cross-correlation method in experiments with different signal to noise ratio and reverberation conditions

    CERN Document Server

    Adrián-Martínez, S; Bou-Cabo, M; Felis, I; Llorens, C; Martínez-Mora, J A; Saldaña, M

    2015-01-01

    The study and application of signal detection techniques based on cross-correlation method for acoustic transient signals in noisy and reverberant environments are presented. These techniques are shown to provide high signal to noise ratio, good signal discernment from very close echoes and accurate detection of signal arrival time. The proposed methodology has been tested on real data collected in environments and conditions where its benefits can be shown. This work focuses on the acoustic detection applied to tasks of positioning in underwater structures and calibration such those as ANTARES and KM3NeT deep-sea neutrino telescopes, as well as, in particle detection through acoustic events for the COUPP/PICO detectors. Moreover, a method for obtaining the real amplitude of the signal in time (voltage) by using cross correlation has been developed and tested and is described in this work.

  5. Robust Frame Synchronization for Low Signal-to-Noise Ratio Channels Using Energy-Corrected Differential Correlation

    Directory of Open Access Journals (Sweden)

    Kim Pansoo

    2009-01-01

    Full Text Available Recent standards for wireless transmission require reliable synchronization for channels with low signal-to-noise ratio (SNR as well as with a large amount of frequency offset, which necessitates a robust correlator structure for the initial frame synchronization process. In this paper, a new correlation strategy especially targeted for low SNR regions is proposed and its performance is analyzed. By utilizing a modified energy correction term, the proposed method effectively reduces the variance of the decision variable to enhance the detection performance. Most importantly, the method is demonstrated to outperform all previously reported schemes by a significant margin, for SNRs below 5 dB regardless of the existence of the frequency offsets. A variation of the proposed method is also presented for further enhancement over the channels with small frequency errors. The particular application considered for the performance verification is the second generation digital video broadcasting system for satellites (DVB-S2.

  6. Disambiguating the role of noise correlations when decoding neural populations together

    OpenAIRE

    Eyherabide, Hugo Gabriel

    2016-01-01

    Objective: Integrating information from populations of correlated neurons can become too complex even for the human brain. Ignoring correlations may simplify the process but also cause an information loss. This loss has been quantified using many methods, one of which has always been deemed exact due to its rigorous communication-theoretical foundations. However, we have recently shown that this method can overestimate the loss in real applications. Approach: To solve this problem, we disting...

  7. Mechanics of underwater noise

    CERN Document Server

    Ross, Donald

    1976-01-01

    Mechanics of Underwater Noise elucidates the basic mechanisms by which noise is generated, transmitted by structures and radiated into the sea. Organized into 10 chapters, this book begins with a description of noise, decibels and levels, significance of spectra, and passive sonar equation. Subsequent chapters discuss sound waves in liquids; acoustic radiation fundamentals; wind-generated ocean ambient noise; vibration isolation and structural damping; and radiation by plate flexural vibrations. Other chapters address cavitation, propeller cavitation noise, radiation by fluctuating-force (dipo

  8. Inelastic Cotunneling Current and Shot Noise of an Interacting Quantum Dot with Ferromagnetic Correlations

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    We explore inelastic cotunneling through a strongly Coulomb-blockaded quantum dot attached to two ferromagnetic leads in the weak coupling limit using a generic quantum Langevin equation approach. We first develop a Bloch-type equation microscopically to describe the cotunneling-induced spin relaxation dynamics, and then develop explicit analytical expressions for the local magnetization, current, and its fluctuations. On this basis, we predict a novel zero-bias anomaly of the differential conductance in the absence of a magnetic field for the anti-parallel configuration,and asymmetric peak splitting in a magnetic field. Also, for the same system with large polarization, we find a negative zero-frequency differential shot noise in the low positive bias-voltage region. All these effects are ascribed to rapid spin-reversal due to underlying spin-flip cotunneling.

  9. Phase-sensitive correlation optical time-domain reflectometer using quantum phase noise of laser light.

    Science.gov (United States)

    Arias, A; Shlyagin, M G; Miridonov, S V; Manuel, Rodolfo Martinez

    2015-11-16

    We propose and experimentally demonstrate a simple approach to realize a phase-sensitive correlation optical time-domain reflectometer (OTDR) suitable for detection and localization of dynamic perturbations along a single-mode optical fiber. It is based on the quantum phase fluctuations of a coherent light emitted by a telecom DFB diode laser. Truly random probe signals are generated by an interferometer with the optical path difference exceeding the coherence length of the laser light. Speckle-like OTDR traces were obtained by calculating cross-correlation functions between the probe light and the light intensity signals returned back from the sensing fiber. Perturbations are detected and localized by monitoring time variations of correlation amplitude along the fiber length. Results of proof-of-concept experimental testing are presented using an array of ultra-low-reflectivity fiber Bragg gratings as weak reflectors. PMID:26698514

  10. A method for the estimation of the significance of cross-correlations in unevenly sampled red-noise time series

    CERN Document Server

    Max-Moerbeck, W; Hovatta, T; Pavlidou, V; Pearson, T J; Readhead, A C S

    2014-01-01

    We present a practical implementation of a Monte Carlo method to estimate the significance of cross-correlations in unevenly sampled time series of data, whose statistical properties are modeled with a simple power-law power spectral density. This implementation builds on published methods, we introduce a number of improvements in the normalization of the cross-correlation function estimate and a bootstrap method for estimating the significance of the cross-correlations. A closely related matter is the estimation of a model for the light curves, which is critical for the significance estimates. We present a graphical and quantitative demonstration that uses simulations to show how common it is to get high cross-correlations for unrelated light curves with steep power spectral densities. This demonstration highlights the dangers of interpreting them as signs of a physical connection. We show that by using interpolation and the Hanning sampling window function we are able to reduce the effects of red-noise leak...

  11. Inversion of H/V in layered media from seismic ambient noise based on the diffuse field theory and on improved calculation of Green functions

    Science.gov (United States)

    Sánchez-Sesma, Francisco J.; Piña, José; García-Jerez, Antonio; Luzón, Francisco; Perton, Mathieu

    2014-05-01

    The microtremor H/V spectral ratio (MHVSR) is widely used to assess the dominant frequency of soil sites. Measurements are relatively simple as only one station is needed. It has been recently proposed a theoretical basis linking ambient noise vibrations with diffuse field theory. In this theory the directional energy density computed as the average spectral density of motion at a point, is proportional to the imaginary part of Green function at the observation point. Appropriate normalization is crucial to make the experimental spectral ratios closer to the theoretical counterpart. According to this theory the square of H/V is twice the ratio ImG11 / ImG33, where ImG11 and ImG33 are the imaginary part of Green functions at the load point for horizontal and vertical components, respectively. In order to efficiently compute the imaginary part of Green's functions in a layered medium we start from an integral on the complex k plane and, using Harkrider's nomenclature, separate formulae for body-, Rayleigh-, and Love-wave components to the spectral densities are obtained. Then the poles allow for integration using the Cauchy residue theorem plus some contributions from branch integrals. It is possible to isolate pseudo reflections from ImG11 and thus constrain the inversion of soil profile. We assess ImG11 removing the influence of illumination spectrum using the H/V spectral ratio and an estimate of ImG33 (from an a priori model) by means of ImG11=0.5(H/V )2*ImG33. It has been found that ImG33 is less sensitive to details of stratigraphy. In fact, the Poisson ratio of the uppermost layer controls the slope in high frequency. With the obtained model ImG33 can be updated and the estimate of ImG11 will be improved. ACKNOWLEDGEMENTS. This research has been partially supported by DGAPA-UNAM under Project IN104712, by the MINECO research project CGL2010-16250, Spain, by the EU with FEDER, and the AXA Research Fund.

  12. Observation of noise correlated by the Hawking effect in a water tank

    CERN Document Server

    Euvé, L -P; Parentani, R; Philbin, T G; Rousseaux, G

    2015-01-01

    We measure the power spectrum and two-point correlation function for the fluctuating free surface on the downstream side of a stationary flow above an obstacle with high Froude number $F \\approx 0.85$. On such a flow the scattering of incident long wavelength modes is analogous to that responsible for black hole radiation (the Hawking effect). Our measurements of the correlations clearly indicate a steady conversion of incident modes into pairs of modes of opposite energies. We then use a wave maker to measure the scattering coefficients responsible for this effect.

  13. Effects of Correlations Between the Real and Imaginary Parts of Quantum Noise on Intensity Fluctuation for a Single-Mode Laser

    Institute of Scientific and Technical Information of China (English)

    谢崇伟; 梅冬成

    2003-01-01

    We study the effects of correlations between the real and imaginary parts of quantum noise on the intensity fluctuation for a single-mode laser. The analytic expressions of the intensity correlation function C(τ) and the associated relaxation time Tc in the case of a stable locked phase resulting from the cross-correlation λq between the real and imaginary parts of quantum noise are derived by means of projection operator method. Based on numerical computations it is found that the presence of cross-correlations between the real and imaginary parts of quantum noise causes the intensity fluctuation to increase. A slowing-down phenomenon exists in the sense that Tc increases as a function of |λq|. Thus the decay of intensity fluctuation becomes slower.

  14. 环境噪音对鸟类鸣声的影响及鸟类的适应对策%Impacts of ambient noise on bird song and adaptation strategies of birds

    Institute of Scientific and Technical Information of China (English)

    季婷; 张雁云

    2011-01-01

    For the animals living in the areas with high level ambient noise, their call signals could be overlapped with the frequency, amplitude , and temporal characters of the noise , making the spread efficiency of the animals acoustic signals decreased. Birds mainly rely on their songs for communication. The lower level spread efficiency of their acoustic signal will impact their individual recognition, mate selection, territorial defense, population density, community structure, and so on. This paper summarized the impacts of ambient noise, including urban noise and natural noise, on bird song and the adaptation strategies of birds, pointed out the concerns of these impacts in urbanization, and prospected the possible hotspots in the future research.%在高噪音环境中生存的动物,发出的声信号会与噪声的频率、振幅和时间等重叠,使动物声信号的传播效率降低.鸟类主要靠鸣声通讯,鸣声传播效率下降会影响鸟类个体间识别、配偶关系、领域防卫、种群密度、群落结构等.本文综述了城市噪音、自然噪音等环境噪声对鸟类鸣声的影响以及鸟类的适应对策,提出在城市化进程中要关注噪音对鸟类的影响,并展望了本领域今后可能的研究热点.

  15. On the Capacity of Densely Packed Arrays with Mutual Coupling and Correlated Noise

    Directory of Open Access Journals (Sweden)

    Vahid Dehghanian

    2015-01-01

    Full Text Available Capacity of a wireless link can be enhanced by increasing the number of receive antennas. However, imposed receiver physical size constraints necessitate that the antenna elements be in close proximity, which typically reduces the overall link capacity of the wireless channel. Counterintuitively, under certain conditions the capacity of the overall link can be enhanced by decreasing antenna spacings. The focus of this paper is that of identifying the fundamental mechanisms and the conditions that give rise to this excess capacity. Closed-form expressions that directly quantify this capacity gain are derived based on a representative circuit theoretic model. Interesting insights are developed about the impact of different noise and interference sources and the limiting effect of heat losses in the antenna system. The capacity analysis is subsequently generalized to encompass the effect of antenna current deformation and load mismatch due to mutual coupling, based on the standard Method of Moments (MoM analysis, demonstrating similar capacity enhancement behavior as predicted by the closed-form expressions.

  16. Quantum noise of a Bose-Einstein condensate in an optical cavity, correlations and entanglement

    OpenAIRE

    Szirmai G.; Nagy D.; Domokos P.

    2010-01-01

    A Bose-Einstein condensate of ultracold atoms inside the field of a laser-driven optical cavity exhibits dispersive optical bistability. We describe this system by using mean-field approximation and by analyzing the correlation functions of the linearized quantum fluctuations around the mean-field solution. The entanglement and the statistics of the atom-field quadratures are given in the stationary state. It is shown that the mean-field solution, i.e. the Bose-Einstein condensate is robust a...

  17. Power spectral density function and spatial autocorrelation of the ambient vibration full-wavefield generated by a distribution of spatially correlated surface sources

    Science.gov (United States)

    Lunedei, Enrico; Albarello, Dario

    2016-03-01

    Synthetic dispersion curves are here computed in the frame of an ambient-vibration full-wavefield model, which relies on the description of both ambient-vibration ground displacement and its sources as stochastic fields defined on the Earth's surface, stationary in time and homogeneous in space. In this model, previously developed for computing synthetic Horizontal-to-Vertical Spectral Ratio curves, the power spectral density function and the spatial autocorrelation of the displacement are naturally described as functions of the power spectral density function of the generating forces and of the subsoil properties (via the relevant Green's function), by also accounting for spatial correlation of these forces. Dispersion curves are computed from the displacement power spectral density function and from the spatial autocorrelation according with the well-known f-k and SPAC techniques, respectively. Two examples illustrate the way this new ambient-vibration model works, showing its possible use in better understanding the role of the surface waves in forming the dispersion curves, as well as its capability to capture some remarkable experimental findings.

  18. Effects of imperfect noise correlations on decoherence-free subsystems: SU(2) diffusion model

    International Nuclear Information System (INIS)

    We present a model of an N-qubit channel where consecutive qubits experience correlated random rotations. Our model is an extension to the standard decoherence-free subsystems approach which assumes that all qubits experience the same disturbance. The variation of rotations acting on consecutive qubits is modeled as diffusion on the SU(2) group. The model may be applied to spins traveling in a varying magnetic field or to photons passing through a fiber whose birefringence fluctuates over the time separation between photons. We derive an explicit formula describing the action of the channel on an arbitrary N-qubit state. For N=3 we investigate the effects of diffusion on both the classical and quantum capacities of the channel. We observe that nonorthogonal states are necessary to achieve optimal classical capacity. Furthermore, we find the threshold for the diffusion parameter above which coherent information of the channel vanishes

  19. Three-dimensional shear velocity anisotropic model of Piton de la Fournaise Volcano (La Réunion Island) from ambient seismic noise

    Science.gov (United States)

    Mordret, Aurélien; Rivet, Diane; Landès, Matthieu; Shapiro, Nikolaï M.

    2015-01-01

    We cross correlate 4 years of seismic noise from the seismic network of Piton de la Fournaise Volcano (La Réunion Island) to measure the group velocity dispersion curves of Rayleigh and Love waves. We average measurements from vertical and radial components to obtain 577 Rayleigh wave dispersion curves. The transverse components provided 395 Love wave dispersion curves. We regionalize the group velocities measurements into 2-D velocity maps between 0.4 and 8 s. Finally, we locally inverted these maps for a pseudo 3-D anisotropic shear-velocity model down to 3 km below the sea level using a Neighborhood Algorithm. The 3-D isotropic shear-wave model shows three distinct high-velocity anomalies surrounded by a low-velocity ring. The anomaly located below the present "Plaine des Sables" could be related to an old intrusive body at the location of the former volcanic center before it migrated toward its present location. The second high-velocity body located below the summit of the volcano likely corresponds to the actual preferential dyke intrusion zone as highlighted by the seismicity. The third high-velocity anomaly located below the "Grandes Pentes" and the "Grand Brûlé" areas and is an imprint of the solidified magma chamber of the dismantled "Les Alizés" Volcano. Radial anisotropy shows two main anomalies: positive anisotropy above sea level highlighting the recent edifice of Piton de la Fournaise with an accumulation of horizontal lava flows and the second one below the sea level with a negative anisotropy corresponding to the ancient edifice of Piton de la Fournaise dominated by intrusions of vertical dykes.

  20. Inversion of seismic data: how to take the correlated nature of noise into account; Inversion de donnees sismiques: prise en compte de la nature correlee du bruit

    Energy Technology Data Exchange (ETDEWEB)

    Renard, F.

    2003-01-01

    The goal of seismic inversion is to recover an Earth model that best fits some observed data. To reach that goal, we have to minimize an objective function that measures the amplitude of the misfits according to a norm to be chosen in data space. In general, the used norm is the L2 norm. Unfortunately, such a norm is not adapted to data corrupted by correlated noise: the noise is in that case inverted as signal and the inversion results are unacceptable. The goal of this thesis is to obtain satisfactory results to the inverse problem in that situation. For this purpose, we study two inverse problems: reflection tomography and waveform inversion. In reflection tomography, we propose a new formulation of the continuum inverse problem which relies on a H1 norm in data space. This allows us to account for the correlated nature of the noise that corrupts the kinematic information. However, this norm does not give more satisfactory results than the ones obtained with the classical formalism. This is why, for sake of simplicity, we recommend to use this classical formalism. Then we try to understand how to properly sample the kinematic information so as to obtain an accurate approximation of the continuum inverse problem. In waveform inversion, we propose to directly invert data corrupted by some correlated noise. A first idea consists in rejecting the noise in the residues. In that goal, we can use a semi-norm to formulate the inverse problem. This technique gives very good results, except when the data are corrupted by random noise. Thus we propose a second method which consists in retrieving, by solving an inverse problem, the signal and the noise whose sum best fits the data. This technique gives very satisfactory results, even if some random noise pollutes the data, and is moreover solved, thanks to an original algorithm, in a very efficient way. (author)

  1. Effect's of Cross-Correlation Between Real and Imaginary Parts of Colored Pump Noise in Transient Process of Single-Mode Laser

    Institute of Scientific and Technical Information of China (English)

    ZHANG Li; CAO Li; WU Da-Jin

    2006-01-01

    A two-dimensional single-mode laser model with cross-correlation between the real and imaginary parts of the colored quadric pump noise is investigated. A novel laser amplitude Langevin equation is obtained, in which the cross-correlation λp between the real and imaginary parts of the pump noise appears. The mean, variance, and skewness of first-passage-time are calculated. It is shown that the mean, variance, and skewness of first-passage-time are strongly affected by λp.

  2. Chronic Release of Tritium from SS316 at Ambient Temperature: Correlation Between Depth Profile and Tritium Liberation

    International Nuclear Information System (INIS)

    One conceivable option for the disposal of tritium-contaminated stainless steel consists in its storage at ambient temperature in a purged containment. To assess this option several stainless steel 316 specimens, previously loaded at elevated temperatures with 0.8-8.5 MBq of tritium, were flushed continuously with dry argon (water partial pressure 0.073 Pa) for extended periods of time. The released tritium (more than 99 % in the form of tritiated water (HTO)) was collected in bubblers and monitored periodically by liquid scintillation counting. After an initial fast liberation a fairly constant rate of the order of 0.2 % per day established. Tritium depth profile in the SS specimens could be simulated by a diffusion limited desorption model. The rate determining step for tritium release appears to be bulk diffusion

  3. Noise exposure modulates cochlear inner hair cell ribbon volumes, correlating with changes in auditory measures in the FVB/nJ mouse

    Science.gov (United States)

    Paquette, Stephen T.; Gilels, Felicia; White, Patricia M.

    2016-01-01

    Cochlear neuropathy resulting from unsafe noise exposure is a life altering condition that affects many people. This hearing dysfunction follows a conserved mechanism where inner hair cell synapses are lost, termed cochlear synaptopathy. Here we investigate cochlear synaptopathy in the FVB/nJ mouse strain as a prelude for the investigation of candidate genetic mutations for noise damage susceptibility. We used measurements of auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAE) to assess hearing recovery in FVB/nJ mice exposed to two different noise levels. We also utilized confocal fluorescence microscopy in mapped whole mount cochlear tissue, in conjunction with deconvolution and three-dimensional modeling, to analyze numbers, volumes and positions of paired synaptic components. We find evidence for significant synapse reorganization in response to both synaptopathic and sub-synaptopathic noise exposures in FVB/nJ. Specifically, we find that the modulation in volume of very small synaptic ribbons correlates with the presence of reduced ABR peak one amplitudes in both levels of noise exposures. These experiments define the use of FVB/nJ mice for further genetic investigations into the mechanisms of noise damage. They further suggest that in the cochlea, neuronal-inner hair cell connections may dynamically reshape as part of the noise response. PMID:27162161

  4. A normalized data-reusing least-mean-square algorithm of noise cancellation for magnetocardiography

    Institute of Scientific and Technical Information of China (English)

    Kong Xiang-Yan; Wang Hui-Wu; Tian Ye; Huang Xu-Guang; Zhang Li-Hua; Ren Yu-Feng; Chen Geng-Hua; Yang Qian-Sheng

    2004-01-01

    An adaptive filter based on Data-Reusing Least-Mean-Square algorithm has been proposed and applied in magnetocardiography (MCG) to suppress ambient noise. Numerical simulation studies indicate that the adaptive filter is a powerful noise suppresser for correlated interferences, especially for those with amplitude changing and time delay.Also the filter has a wide frequency bandwidth. With this filter, the signal-to-noise ratio of an MCG is improved to the intrinsic noise level. The periodic average method for further improvement of the noise level in MCG is also discussed.

  5. Criteria for environmental noise assessment

    OpenAIRE

    Hadzi-Nikolova, Marija; Mirakovski, Dejan; Doneva, Nikolinka

    2015-01-01

    The noise assessment generally refers to the assessment of noise impact from a specific source, such as noise originating from certain industrial plants, road traffic, and this is not always an easy task. Practically in every surrounding, a number of different sources contribute to the ambiental noise at a certain point. Standardization of noise level includes recommendations for noise level prescribed by legislation, which are enabling stay in the environment without danger to human heal...

  6. Noise correlation in PET, CT, SPECT and PET/CT data evaluated using autocorrelation function: a phantom study on data, reconstructed using FBP and OSEM

    International Nuclear Information System (INIS)

    Positron Emission Tomography (PET), Computed Tomography (CT), PET/CT and Single Photon Emission Tomography (SPECT) are non-invasive imaging tools used for creating two dimensional (2D) cross section images of three dimensional (3D) objects. PET and SPECT have the potential of providing functional or biochemical information by measuring distribution and kinetics of radiolabelled molecules, whereas CT visualizes X-ray density in tissues in the body. PET/CT provides fused images representing both functional and anatomical information with better precision in localization than PET alone. Images generated by these types of techniques are generally noisy, thereby impairing the imaging potential and affecting the precision in quantitative values derived from the images. It is crucial to explore and understand the properties of noise in these imaging techniques. Here we used autocorrelation function (ACF) specifically to describe noise correlation and its non-isotropic behaviour in experimentally generated images of PET, CT, PET/CT and SPECT. Experiments were performed using phantoms with different shapes. In PET and PET/CT studies, data were acquired in 2D acquisition mode and reconstructed by both analytical filter back projection (FBP) and iterative, ordered subsets expectation maximisation (OSEM) methods. In the PET/CT studies, different magnitudes of X-ray dose in the transmission were employed by using different mA settings for the X-ray tube. In the CT studies, data were acquired using different slice thickness with and without applied dose reduction function and the images were reconstructed by FBP. SPECT studies were performed in 2D, reconstructed using FBP and OSEM, using post 3D filtering. ACF images were generated from the primary images, and profiles across the ACF images were used to describe the noise correlation in different directions. The variance of noise across the images was visualised as images and with profiles across these images. The most important

  7. Spectral ratios of ambient noise based on the diffuse field theory: Improved inversion of H/V in layered media using analytical properties of Green functions

    Science.gov (United States)

    Sanchez-Sesma, F. J.; Perton, M.; Piña, J.; Luzón, F.; Garcia-Jerez, A.; Rodriguez-Castellanos, A.

    2013-12-01

    It is well know the popularity of H/V spectral ratio to extract the dominant frequency of soil sites for microzonation studies (Nakamura, 1989). It is relatively easy to make measurements as only one station is needed. Despite its success, this approach had not solid theoretical basis until a proposal to link ambient noise vibrations with diffuse field theory was made (Sánchez-Sesma et al, 2011a). Based on this theory the average spectral density of a given motion of a point, also called directional energy density (Perton et al, 2009), is proportional to the imaginary part of Green function precisely at the observation point. The proportionality implies that vector components are all multiplied by the current spectral level of the diffuse illumination. Appropriate normalization is crucial to make the experimental spectral ratios closer to the theoretical counterpart. According to this theory the square of H/V is twice the ratio of ImG11 and ImG33, where ImG11 and ImG33 are the imaginary part of Green functions at the load point for horizontal and vertical components, respectively. From ImG11 it could be possible through Fourier analysis to extract pseudo reflections and thus constrain the inversion of soil profile. We propose to assess ImG11 removing the influence of illumination spectrum using the H/V spectral ratio and an estimate of ImG33 (obtained from a priori model) by means of ImG11=0.5(H/V)2*ImG33. It has been found that ImG33 is less sensitive to details of stratigraphy. In fact, the most relevant property is the Poisson ratio of the uppermost layer which controls the slope in high frequency (Sánchez-Sesma et al, 2011b). Pseudo-reflection seismograms are thus obtained from Fourier transform, back to time domain, of i{ImG11-ImG11HSS}, where ImG11HSS is the imaginary part of Green functions at the load point for horizontal load at the surface of a half-space with the properties of the uppermost layer. With the obtained model ImG33 can be updated and the

  8. Noise from wind turbines

    Energy Technology Data Exchange (ETDEWEB)

    Fegeant, Olivier [Royal Inst. of Tech., Stockholm (Sweden). Dept. of Building Sciences

    2002-02-01

    A rapid growth of installed wind power capacity is expected in the next few years. However, the siting of wind turbines on a large scale raises concerns about their environmental impact, notably with respect to noise. To this end, variable speed wind turbines offer a promising solution for applications in densely populated areas like the European countries, as this design would enable an efficient utilisation of the masking effect due to ambient noise. In rural and recreational areas where wind turbines are sited, the ambient noise originates from the action of wind on the vegetation and about the listener's ear (pseudo-noise). It shows a wind speed dependence similar to that of the noise from a variable speed wind turbine and can therefore mask the latter for a wide range of conditions. However, a problem inherent to the design of these machines is their proclivity to pure tone generation, because of the enhanced difficulty of avoiding structural resonances in the mechanical parts. Pure tones are deemed highly annoying and are severely regulated by most noise policies. In relation to this problem, the vibration transmission of structure-borne sound to the tower of the turbine is investigated, in particular when the tower is stiffened at its upper end. Furthermore, since noise annoyance due to wind turbine is mostly a masking issue, the wind-related sources of ambient noise are studied and their masking potentials assessed. With this aim, prediction models for wind-induced vegetation noise and pseudo-noise have been developed. Finally, closely related to the effect of masking, is the difficulty, regularly encountered by local authorities and wind farm developers, to measure noise immission from wind turbines. A new measurement technique has thus been developed in the course of this work. Through improving the signal-to-noise ratio between wind turbine noise and ambient noise, the new technique yields more accurate measurement results.

  9. Passive defect localization in reverberant plates using correlation of acoustic field

    OpenAIRE

    Chehami, Lynda

    2015-01-01

    Green’s functions retrieval from ambient noise correlation has recently drawn a new interest in structural health monitoring. In this manuscript, we propose an original method based on this approach to detect and locate defects (cracks, holes, grooves) in a reverberant thin plate with a limited number of sensors. Flexural waves that propagate on the plate are generated by either a set of sources distributed randomly on the surface or an ambient noise. Covariance matrices are estimated from th...

  10. Development and research of shallow water ambient noise database%潜水环境噪声数据库设计与开发

    Institute of Scientific and Technical Information of China (English)

    方鹏

    2015-01-01

    随着人类水下活动和实验行为的增多,越来越多的应用需要借助水声探测技术和水声通信技术,而在潜水环境中,环境噪声是以上技术的重要制约因素。因而,了解相应海域的环境噪声特性并建立环境噪声数据库,将有助于该海域的航运、测绘、通信等水声技术的应用与发展。本文针对以上需求,提出一种噪声建模方法,并根据该方法设计和研究相应的潜水环境噪声数据库。实验证明本文提出的方法具有一定的可行性。%Along with the increase in human activities and underwater experimental behavior, more and more applications need to use acoustic detection technology and underwater acoustic communication technology, and in the diving environment, environmental noise is one of the important restriction factor to the technology above. Therefore, to understand the corresponding environmental noise characteristics of waters and establishing database of environmental noise, would help surveying and mapping, navigation, communication etc. with application and development of underwater acoustic technology. In view of the above requirements, this paper puts forward a kind of noise modeling method, and research the method of design and research the corresponding diving database of environmental noise. Finally this paper gives the experimental verification, and demonstrates that the proposed method has certain feasibility.

  11. Nonequilibrium Spin Noise and Noise of Susceptibility

    OpenAIRE

    Schad, Pablo; Narozhny, Boris N.; Schön, Gerd; Shnirman, Alexander

    2014-01-01

    We analyze out-of-equilibrium fluctuations in a driven spin system and relate them to the noise of spin susceptibility. In the spirit of the linear response theory we further relate the noise of susceptibility to a $4$-spin correlation function in equilibrium. We show that, in contrast to the second noise (noise of noise), the noise of susceptibility is a direct measure of non-Gaussian fluctuations in the system. We develop a general framework for calculating the noise of susceptibility using...

  12. Noise in mesoscopic physics

    OpenAIRE

    Martin, Thierry

    2005-01-01

    This is a course on noise which covers some of the scattering theory for normal metals, Hanbury Brown and Twiss analogs for noise correlations with electrons, noise correlations in superconducting/normal metal junctions. Entanglement in such NS systems is described with a criterion for violating Bell inegalities. The last section is devoted to the perturbative derivation of noise in a particular one dimensional correlated electron system (Luttinger liquid): edge states in the fractional quant...

  13. Medición de los niveles de ruido ambiental en la ciudad de Santiago de Chile Environmental noise levels measurement of the city of Santiago, Chile

    OpenAIRE

    Usbeth Platzer M; Rodrigo Iñiguez C; Jimena Cevo E; Fernanda Ayala R

    2007-01-01

    Introducción. Un estudio realizado en Santiago en 1989, estimó que 1.300.000 personas estaban sometidas a niveles de ruido inaceptables por las normas internacionales. Considerando que no existen publicaciones sobre ruido ambiental realizadas por otorrinolaringólogos, y que el tema no ha sido revisado en los últimos 15 años, quisimos actualizar la información al respecto. Material y método. Se evaluó el ruido en lugares que afectan la rutina del ciudadano común, independiente de su profesión:...

  14. Electrical conduction noise and its correlation with structural properties of Cu2ZnSnS4 thin films

    Science.gov (United States)

    Zubair Ansari, Mohd; Munjal, Sandeep; Kumar, Vikram; Khare, Neeraj

    2016-07-01

    Cu2ZnSnS4 (CZTS) thin films have been deposited by ultrasonic assisted chemical vapor deposition in a single step process at different substrate temperatures and structural, morphological, electrical and conduction noise characteristics of the CZTS thin films have been studied. Single phase CZTS thin films are formed at 275 °C and 325 °C deposition temperatures, whereas the CZTS thin film deposited at 375 °C showed secondary phase also. The crystallinity of the films improves and resistivity decreases with the increases of the deposition temperature. The temperature dependent electrical conductivity of the films reveals that in the temperature range 300–250 K, thermally activated conduction is observed. The conduction noise in the CZTS thin films, exhibits 1/f noise in the low frequency region and found to be strongly dependent on the film deposition temperatures. The film deposited at 275 °C and 375 °C shows larger conduction noise, whereas the film deposited at 325 °C shows smaller noise. For the low frequency 1/f noise, the value of α is also found to be the minimum for the film deposited at 325 °C. The higher value of conduction noise in the film deposited at 275 °C is related to poor crystallinity and less compact morphology. For the film deposited at 375 °C, crystallinity and compactness improves, but the presence of the secondary phases seems to be responsible for generating higher noise. The smallest conduction noise of the film deposited at 325 °C is due to single phase film with better crystallinity and smaller trap density ∼5.1 × 1015 cm‑2 eV‑1.

  15. Bedrock topography of western Cape Cod, Massachusetts, based on bedrock altitudes from geologic borings and analysis of ambient seismic noise by the horizontal-to-vertical spectral-ratio method

    Science.gov (United States)

    Fairchild, Gillian M.; Lane, Jr., John W.; Voytek, Emily B.; LeBlanc, Denis R.

    2013-01-01

    This report presents a topographic map of the bedrock surface beneath western Cape Cod, Massachusetts, that was prepared for use in groundwater-flow models of the Sagamore lens of the Cape Cod aquifer. The bedrock surface of western Cape Cod had been characterized previously through seismic refraction surveys and borings drilled to bedrock. The borings were mostly on and near the Massachusetts Military Reservation (MMR). The bedrock surface was first mapped by Oldale (1969), and mapping was updated in 2006 by the Air Force Center for Environmental Excellence (AFCEE, 2006). This report updates the bedrock-surface map with new data points collected by using a passive seismic technique based on the horizontal-to-vertical spectral ratio (HVSR) of ambient seismic noise (Lane and others, 2008) and from borings drilled to bedrock since the 2006 map was prepared. The HVSR method is based on a relationship between the resonance frequency of ambient seismic noise as measured at land surface and the thickness of the unconsolidated sediments that overlie consolidated bedrock. The HVSR method was shown by Lane and others (2008) to be an effective method for determining sediment thickness on Cape Cod owing to the distinct difference in the acoustic impedance between the sediments and the underlying bedrock. The HVSR data for 164 sites were combined with data from 559 borings to bedrock in the study area to create a spatially distributed dataset that was manually contoured to prepare a topographic map of the bedrock surface. The interpreted bedrock surface generally slopes downward to the southeast as was shown on the earlier maps by Oldale (1969) and AFCEE (2006). The surface also has complex small-scale topography characteristic of a glacially eroded surface. More information about the methods used to prepare the map is given in the pamphlet that accompanies this plate.

  16. Ambiente urbano e percepção da poluição sonora Urban environment and perception to noise pollution

    OpenAIRE

    Adriana Bender Moreira de Lacerda; Cristiana Magni; Thais Catalani Morata; Jair Mendes Marques; Paulo Henrique Trombetta Zannin

    2005-01-01

    A presente pesquisa avaliou a percepção da população de uma grande cidade em relação à poluição sonora (ruído urbano). Buscou-se identificar quais fontes sonoras são percebidas com maior freqüência pela população e quais reações psico-sociais relacionadas ao ruído urbano são identificados por ela. Foi utilizado um questionário composto de questões fechadas, abrangendo aspectos demográficos e aspectos psico-sociais referentes ao ruído ambiental. Oitocentos e noventa e dois (892) indivíduos par...

  17. Ambient Space and Ambient Sensation

    DEFF Research Database (Denmark)

    Schmidt, Ulrik

    The ambient is the aesthetic production of the sensation of being surrounded. As a concept, 'ambient' is mostly used in relation to the music genre 'ambient music' and Brian Eno's idea of environmental background music. However, the production of ambient sensations must be regarded as a central...... aspect of the aesthetization of modern culture in general, from architecture, transport and urbanized lifeforms to film, sound art, installation art and digital environments. This presentation will discuss the key aspects of ambient aesthetization, including issues such as objectlessness...

  18. Non-Markovian noise

    International Nuclear Information System (INIS)

    The properties of non-Markovian noises with exponentially correlated memory are discussed. Considered are dichotomic noise, white shot noise, Gaussian white noise, and Gaussian colored noise. The stationary correlation functions of the non-Markovian versions of these noises are given by linear combinations of two or three exponential functions (colored noises) or of the δ function and exponential function (white noises). The non-Markovian white noises are well defined only when the kernel of the non-Markovian master equation contains a nonzero admixture of a Markovian term. Approximate equations governing the probability densities for processes driven by such non-Markovian noises are derived, including non-Markovian versions of the Fokker-Planck equation and the telegrapher's equation. As an example, it is shown how the non-Markovian nature changes the behavior of the driven linear process

  19. Quantum Computers: Noise Propagation and Adversarial Noise Models

    OpenAIRE

    Kalai, Gil

    2009-01-01

    In this paper we consider adversarial noise models that will fail quantum error correction and fault-tolerant quantum computation. We describe known results regarding high-rate noise, sequential computation, and reversible noisy computation. We continue by discussing highly correlated noise and the "boundary," in terms of correlation of errors, of the "threshold theorem." Next, we draw a picture of adversarial forms of noise called (collectively) "detrimental noise." Detrimental noise is mode...

  20. Noise suppression by noise

    OpenAIRE

    Vilar, J. M. G.; Rubí Capaceti, José Miguel

    2001-01-01

    We have analyzed the interplay between an externally added noise and the intrinsic noise of systems that relax fast towards a stationary state, and found that increasing the intensity of the external noise can reduce the total noise of the system. We have established a general criterion for the appearance of this phenomenon and discussed two examples in detail.

  1. Relativistic Noise

    OpenAIRE

    Kapusta, Joseph; Mueller, Berndt; Stephanov, Misha

    2012-01-01

    The relativistic theory of hydrodynamic fluctuations, or noise, is derived and applied to high energy heavy ion collisions. These fluctuations are inherent in any space-time varying system and are in addition to initial state fluctuations. We illustrate the effects with the boost-invariant Bjorken solution to the hydrodynamic equations. Long range correlations in rapidity are induced by propagation of sound modes. The magnitude of these correlations are directly proportional to the viscositie...

  2. Det ambiente

    DEFF Research Database (Denmark)

    Schmidt, Ulrik

    Om begrebet "det ambiente", der beskriver, hvad der sker, når vi fornemmer baggrundsmusikkens diskrete beats, betragter udsigten gennem panoramavinduet eller tager 3D-brillerne på og læner os tilbage i biografsædet. Bogen analyserer, hvorfan ambiente oplevelser skabes, og hvilke konsekvenser det...

  3. Correlações fenotípica, genética aditiva e ambiental em cenoura Phenotypic, additive genetic and environmental correlations in carrots

    Directory of Open Access Journals (Sweden)

    Walter José Siqueira

    1993-01-01

    ízes comerciáveis (PC e produção total (PT. Finalmente, discute-se a participação relativa dos efeitos de ambiente e genéticos na correlação fenotípica.Since development of commercial varieties involves simultaneous selection for various traits, previous knowledge of their interrelationships may also be fundamental to the breeder as the strategies to be adopted. The objective of this research was to estimate phenotypic, additive genetic and environmental correlations for a number of traits of agronomic interest in carrot (Daucus carota L. cultivar Campinas, grown during the fall-winter and spring-summer seasons at the Experiment Station of Monte Alegre do Sul, Instituto Agronômico de Campinas (IAC, State of São Paulo, Brazil. This germplasm, originated from the "Seção de Hortaliças" (IAC, presents, besides a high level of resistance to Alternaria dauci, a large variation for root shape and a tendency to early bolting, stimulated by low temperatures and/or long photoperiods during the crop vegetative stage. Data were obtained by evaluating 102 half-sib progenies on a randomized block design experiment with four and three replications, respectively, for the fall-winter and spring-summer planting dates. Phenotypic (rF, additive genetic (rA and environmental (rE correlations were estimated by covariance analyses between pairs of characters, in both planting dates. The phenotypic and additive genetic correlations were negative only for pairs of characters involving percentage of early flowering (EF or percentage of defective roots, while the correlations were high (>0.5 for most of the pairs of characters in both planting dates. Selection for percentage of cylindric marketable roots will lead to reduction in EF as well as increases in marketable root yield and total root yield in both planting. This research further presents a discussion of the relative participation of environmental and genetic effects in the phenotypic correlation.

  4. Ambient air pollution and annoyance responses from pregnant women

    Science.gov (United States)

    Llop, Sabrina; Ballester, Ferran; Estarlich, Marisa; Esplugues, Ana; Fernández-Patier, Rosalia; Ramón, Rosa; Marco, Alfredo; Aguirre, Amelia; Sunyer, Jordi; Iñiguez, Carmen; INMA-Valencia cohort

    ObjectivesTo describe the degree of annoyance caused by air pollution and noise in pregnant women in a birth cohort; to determine the modifying factors and their relation with exposure to ambient nitrogen dioxide (NO 2). MethodsThe study population was 855 pregnant women in Valencia, Spain. Annoyance caused by air pollution and noise, and explanatory factors were obtained from 786 pregnant women through a questionnaire. NO 2 levels were determined combining measurements at 93 points within the area of study and using geostatistical techniques (kriging). ResultsIn all 7.9% of the women reported high annoyance caused by air pollution and 13.1% high annoyance caused by noise. There was a significant difference in the degree of annoyance due to both air pollution and noise depending on the area where the women lived and their working status. The degree of annoyance correlated better with measured NO 2 at the municipality level (air pollution: r=0.53; noise: r=0.44) than at the individual level (air pollution and noise: r=0.21). On multivariate analysis, being a housewife, higher NO 2 levels and high traffic density were associated with higher degrees of annoyance. ConclusionsThere was a high percentage of women who perceived medium-high annoyance due to noise and air pollution. Annoyance caused by environmental pollutants could lead to some psychological effects, which impair the quality of life, or even physiological ones, which affect prenatal development.

  5. Annoyance Caused by Noise and Air Pollution during Pregnancy: Associated Factors and Correlation with Outdoor NO2 and Benzene Estimations.

    OpenAIRE

    Ana Fernández-Somoano; Sabrina Llop; Inmaculada Aguilera; Ibon Tamayo-Uria; María Dolores Martínez; Maria Foraster; Ferran Ballester; Adonina Tardón

    2015-01-01

    This study aimed to describe the degree of annoyance among pregnant women in a Spanish cohort and to examine associations with proximity to traffic, NO2 and benzene exposure. We included 2457 participants from the Spanish Childhood and Environment study. Individual exposures to outdoor NO2 and benzene were estimated, temporally adjusted for pregnancy. Interviews about sociodemographic variables, noise and air pollution were carried out. Levels of annoyance were assessed using a scale from 0 (...

  6. Det Ambiente

    DEFF Research Database (Denmark)

    Schmidt, Ulrik

    Det ambiente er iscenesættelsen af en karakteristisk sanseoplevelse, der er kendetegnet ved fornemmelsen af at være omgivet. I dag bliver begrebet om det ambiente mest anvendt i forbindelse med musikgenren ’ambient musik’. Det ambiente er dog ikke essentielt knyttet til det musikalske, men må...... forstås som et betydeligt bredere fænomen i den moderne æstetiske kultur, der spiller en væsentlig rolle i oplevelsen af moderne transportformer, arkitektur, film, lydkunst, installationskunst og digitale multimedieiscenesættelser. En forståelse af det ambiente er derfor centralt for forståelsen af en...... moderne æstetiseret oplevelseskultur i almindelighed. Da det ambiente ikke hidtil har været gjort til genstand for en mere indgående teoretisk behandling, er der dog stor usikkerhed omkring, hvad fænomenet overhovedet indebærer. Hovedformålet med Det ambiente – Sansning, medialisering, omgivelse er derfor...

  7. Noise-immune complex correlation for vasculature imaging based on standard and Jones-matrix optical coherence tomography

    Science.gov (United States)

    Makita, Shuichi; Kurokawa, Kazuhiro; Hong, Young-Joo; Li, En; Miura, Masahiro; Yasuno, Yoshiaki

    2016-03-01

    A new optical coherence angiography (OCA) method, called correlation mapping OCA (cmOCA), is presented by using the SNR-corrected complex correlation. An SNR-correction theory for the complex correlation calculation is presented. The method also integrates a motion-artifact-removal method for the sample motion induced decorrelation artifact. The theory is further extended to compute more reliable correlation by using multi- channel OCT systems, such as Jones-matrix OCT. The high contrast vasculature imaging of in vivo human posterior eye has been obtained. Composite imaging of cmOCA and degree of polarization uniformity indicates abnormalities of vasculature and pigmented tissues simultaneously.

  8. Smooth bumps in H/V curves over a broad area from single-station ambient noise recordings are meaningful and reveal the importance of Q in array processing: The Boumerdes (Algeria) case

    Science.gov (United States)

    Guillier, B.; Chatelain, J.-L.; Hellel, M.; Machane, D.; Mezouer, N.; Ben Salem, R.; Oubaiche, E. H.

    2005-12-01

    Single-station H/V curves from ambient noise recordings in Boumerdes (Algeria) show smooth bumps around 1 and 3 Hz. A complementary microtremor study, based on two 34 and 134-meter aperture arrays, evidences that these bumps are indeed real peaks produced by two strong VS contrasts at 37 and 118 meters depth, strongly smoothed by very high S-wave attenuation in the two sedimentary layers. These two H/V bumps, observed over a broad area, are meaningful and reveal the importance of Q in S-wave velocity modeling from microtremor array data processing. It also appears that Tertiary rocks should be, at least in some cases, taken into account, together with the Quaternary sediments, to explain single-station H/V frequency peaks, and therefore that considering only the first 30 m of soil for VS amplification evaluation, as usually recommended, sometimes leads to flaky results by artificially eliminating non-explained low-frequency peaks from the analysis.

  9. Determination of primary combustion source organic carbon-to-elemental carbon (OC / EC) ratio using ambient OC and EC measurements: secondary OC-EC correlation minimization method

    Science.gov (United States)

    Wu, Cheng; Zhen Yu, Jian

    2016-05-01

    Elemental carbon (EC) has been widely used as a tracer to track the portion of co-emitted primary organic carbon (OC) and, by extension, to estimate secondary OC (SOC) from ambient observations of EC and OC. Key to this EC tracer method is to determine an appropriate OC / EC ratio that represents primary combustion emission sources (i.e., (OC / EC)pri) at the observation site. The conventional approaches include regressing OC against EC within a fixed percentile of the lowest (OC / EC) ratio data (usually 5-20 %) or relying on a subset of sampling days with low photochemical activity and dominated by local emissions. The drawback of these approaches is rooted in its empirical nature, i.e., a lack of clear quantitative criteria in the selection of data subsets for the (OC / EC)pri determination. We examine here a method that derives (OC / EC)pri through calculating a hypothetical set of (OC / EC)pri and SOC followed by seeking the minimum of the coefficient of correlation (R2) between SOC and EC. The hypothetical (OC / EC)pri that generates the minimum R2(SOC,EC) then represents the actual (OC / EC)pri ratio if variations of EC and SOC are independent and (OC / EC)pri is relatively constant in the study period. This Minimum R Squared (MRS) method has a clear quantitative criterion for the (OC / EC)pri calculation. This work uses numerically simulated data to evaluate the accuracy of SOC estimation by the MRS method and to compare with two commonly used methods: minimum OC / EC (OC / ECmin) and OC / EC percentile (OC / EC10 %). Log-normally distributed EC and OC concentrations with known proportion of SOC are numerically produced through a pseudorandom number generator. Three scenarios are considered, including a single primary source, two independent primary sources, and two correlated primary sources. The MRS method consistently yields the most accurate SOC estimation. Unbiased SOC estimation by OC / ECmin and OC / EC10 % only occurs when the left tail of OC / EC

  10. Ambient Gestures

    OpenAIRE

    Karam, Maria; Hare, Jonathon; Lewis, Paul; schraefel, m.c.

    2006-01-01

    We present Ambient Gestures, a novel gesture-based system designed to support ubiquitous ‘in the environment’ interactions with everyday computing technology. Hand gestures and audio feedback allow users to control computer applications without reliance on a graphical user interface, and without having to switch from the context of a non-computer task to the context of the computer. The Ambient Gestures system is composed of a vision recognition software application, a set of gestures to be p...

  11. THE ACOUSTIC CONTAMINATION OF SCHOOL ENVIRONMENT DUE TO URBAN NOISES IN THE FEDERAL DISTRICT, BRASIL = A CONTAMINAÇÃO ACÚSTICA DE AMBIENTES ESCOLARES DEVIDO AOS RUÍDOS URBANOS NO DISTRITO FEDERAL, BRASIL

    Directory of Open Access Journals (Sweden)

    Alexandre Eniz

    2006-01-01

    Full Text Available Urban noises are more and more presents in our daily life, invading residences, work places, leisure locations, hospitals and schools, becoming a potential harm to social interaction, communication, behavior, school performance, health etc. The main objective of this work was to analyze and quantify the environmental noise in ten schools of the basic education in District Federal, Brazil. The adopted parameter was the equivalent sound pressure level Leq (A, which was evaluated according to the sound level measures following the standard established by Brazilian Association of echnical Regulations (ABNT. The background noise was measured during holidays and during regular class periods. The study detected that half of the schools researched are being “contaminated” with noise from aircraft, road traffic, trucks, advertising vehicles, motorcycles, buses among other sources, with limits outside the recommended by law. In 90% of the evaluated schools, the noise levels observed during the activities are above of the maximum values recommended for the acoustic comfort of a school. These are buildings ill-located in the city and therefore “exposed” to levels that are above of recommended by the norms. The results show a critical situation indicating the urgent need of actions with the objective of mitigating this severe type of pollution. = Os ruídos urbanos estão cada vez mais presentes em nosso cotidiano, invadindo residências, locais de trabalho, de lazer, hospitais e escolas, podendo prejudicar as relações sociais, a comunicação, o comportamento, o rendimento escolar, a saúde etc. O objetivo principal deste trabalho foi analisar e quantificar o ruído ambiental em dez escolas do Ensino Fundamental e Médio no Distrito Federal. O parâmetro adotado foi o nível de pressão sonora equivalente Leq (A, avaliado por medidores de pressão sonora, segundo as normas estabelecidas pela Associação Brasileira de NormasTécnicas (ABNT. O ru

  12. Correlation between the signal-to-noise ratio improvement factor (KSNR) and clinical image quality for chest imaging with a computed radiography system

    Science.gov (United States)

    Moore, C. S.; Wood, T. J.; Saunderson, J. R.; Beavis, A. W.

    2015-12-01

    This work assessed the appropriateness of the signal-to-noise ratio improvement factor (KSNR) as a metric for the optimisation of computed radiography (CR) of the chest. The results of a previous study in which four experienced image evaluators graded computer simulated chest images using a visual grading analysis scoring (VGAS) scheme to quantify the benefit of using an anti-scatter grid were used for the clinical image quality measurement (number of simulated patients  =  80). The KSNR was used to calculate the improvement in physical image quality measured in a physical chest phantom. KSNR correlation with VGAS was assessed as a function of chest region (lung, spine and diaphragm/retrodiaphragm), and as a function of x-ray tube voltage in a given chest region. The correlation of the latter was determined by the Pearson correlation coefficient. VGAS and KSNR image quality metrics demonstrated no correlation in the lung region but did show correlation in the spine and diaphragm/retrodiaphragmatic regions. However, there was no correlation as a function of tube voltage in any region; a Pearson correlation coefficient (R) of  -0.93 (p  =  0.015) was found for lung, a coefficient (R) of  -0.95 (p  =  0.46) was found for spine, and a coefficient (R) of  -0.85 (p  =  0.015) was found for diaphragm. All demonstrate strong negative correlations indicating conflicting results, i.e. KSNR increases with tube voltage but VGAS decreases. Medical physicists should use the KSNR metric with caution when assessing any potential improvement in clinical chest image quality when introducing an anti-scatter grid for CR imaging, especially in the lung region. This metric may also be a limited descriptor of clinical chest image quality as a function of tube voltage when a grid is used routinely.

  13. Correlation between the signal-to-noise ratio improvement factor (KSNR) and clinical image quality for chest imaging with a computed radiography system

    International Nuclear Information System (INIS)

    This work assessed the appropriateness of the signal-to-noise ratio improvement factor (KSNR) as a metric for the optimisation of computed radiography (CR) of the chest. The results of a previous study in which four experienced image evaluators graded computer simulated chest images using a visual grading analysis scoring (VGAS) scheme to quantify the benefit of using an anti-scatter grid were used for the clinical image quality measurement (number of simulated patients  =  80). The KSNR was used to calculate the improvement in physical image quality measured in a physical chest phantom. KSNR correlation with VGAS was assessed as a function of chest region (lung, spine and diaphragm/retrodiaphragm), and as a function of x-ray tube voltage in a given chest region. The correlation of the latter was determined by the Pearson correlation coefficient. VGAS and KSNR image quality metrics demonstrated no correlation in the lung region but did show correlation in the spine and diaphragm/retrodiaphragmatic regions. However, there was no correlation as a function of tube voltage in any region; a Pearson correlation coefficient (R) of  −0.93 (p  =  0.015) was found for lung, a coefficient (R) of  −0.95 (p  =  0.46) was found for spine, and a coefficient (R) of  −0.85 (p  =  0.015) was found for diaphragm. All demonstrate strong negative correlations indicating conflicting results, i.e. KSNR increases with tube voltage but VGAS decreases. Medical physicists should use the KSNR metric with caution when assessing any potential improvement in clinical chest image quality when introducing an anti-scatter grid for CR imaging, especially in the lung region. This metric may also be a limited descriptor of clinical chest image quality as a function of tube voltage when a grid is used routinely. (paper)

  14. Simulation study of neutrons time-correlated coincidence count for uranium components based on 252Cf source-driven noise analysis method

    International Nuclear Information System (INIS)

    Background: For the intensity of high-enriched uranium's neutrons from fission is weak, the active detection method is commonly adopted. Purpose: The quality attribute of uranium components is analysed. Methods: According to the theory of neutron source-driven noise analysis method and mass measurement problem of uranium material or uranium component, Monte Carlo simulation is used to study the mass measurement of metal uranium sphere components with the same geometry and enrichment and the different masses. The time-correlation coincidence count distributions to different uranium components are obtained. Results: The source-driven time correlation coincidence measurements can provide quantities, time-dependent coincidence distributions between two detectors, which can be related to the mass of uranium components. Conclusions: By studying on the sample (radius: 4.67 cm, mass: 8 kg), it realized mass measurement to metal uranium sphere components with different masses. (authors)

  15. Noise in electromigrated nanojunctions

    OpenAIRE

    Wheeler, P. J.; Chen, Ruoyu; Natelson, D.

    2013-01-01

    Noise measurements are a probe beyond simple electronic transport that can reveal additional information about electronic correlations and inelastic processes. Here we report noise measurements in individual electromigrated nanojunctions, examining the evolution from the many channel regime to the tunneling regime, using a radio frequency technique. While we generally observe the dependence of noise on bias expected for shot noise, in approximately 12% of junction configurations we find discr...

  16. Road traffic noise and incident myocardial infarction

    DEFF Research Database (Denmark)

    Sørensen, Mette; Andersen, Zorana Jovanovic; Nordsborg, Rikke B;

    2012-01-01

    Both road traffic noise and ambient air pollution have been associated with risk for ischemic heart disease, but only few inconsistent studies include both exposures.......Both road traffic noise and ambient air pollution have been associated with risk for ischemic heart disease, but only few inconsistent studies include both exposures....

  17. Noise blind test

    OpenAIRE

    H. Cadet

    2006-01-01

    In the aim of characterizing site condition for seismic risk, the microtremor or ambient noise studies have been developed. The main objective of this blind test is to check of the reliability of results, to observe the user subjectivity (array choice, parameters that are user depend) in the noise recordings analyze. Noise records were analysed on single-station with H/V method and with several sensors for array method to determine the dispersion characteristics of the surface-wave part of th...

  18. Ambient intelligence

    OpenAIRE

    Sanders, David; Gegov, Alexander

    2006-01-01

    This paper considers some history and the state of the art of Ambient Intelligence and from that seeks to identify new topics and future work. Ubiquitous computing, communications, human-centric computer interaction, embedded systems, context awareness, adaptive systems and distributed device networks are considered.

  19. Ambient intelligence

    CERN Document Server

    Weber, W; Aarts, E

    2005-01-01

    Addresses ambient intelligence used to support human contacts and accompany an individual''s path through the complicated modern world, from applications that are imminent, since they use essentially existing technologies, to ambitious ideas whose realization is still far away, due to major unsolved technical challenges.

  20. Ambient noise levels in the chemotherapy clinic

    OpenAIRE

    Dana K Gladd; Saunders, Gabrielle H.

    2011-01-01

    Many of the drugs used for chemotherapy treatments are known to be ototoxic, and can result in permanent hearing threshold shifts. The degree of ototoxic damage can be influenced by many factors including dosage, duration of exposure, genetics, and coadministration with other ototoxic agents. Cisplatin is known for its ototoxic effects on hearing thresholds, particularly in the high frequencies. Recent studies have indicated a synergistic relationship between Cisplatin administration and mode...