Artykuły w czasopismach: „Coherence time”

1

Le, Thai-Hoa, i Dong-Anh Nguyen. "TEMPORO-SPECTRAL COHERENT STRUCTURE OF TURBULENCE AND PRESSURE USING FOURIER AND WAVELET TRANSFORMS". ASEAN Journal on Science and Technology for Development 25, nr 2 (22.11.2017): 405–17. http://dx.doi.org/10.29037/ajstd.271.

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Studying the spatial distribution in coherent fields such as turbulent and turbulent-induced force ones is important to model and evaluate turbulent-induced forces and response of structures on the turbulent flows. Turbulent field-based coherent function is commonly used for the spatial distribution characteristic of induced forces in the frequency domain. This paper will focus to study spectral coherent structure of turbulence and forces in not only the frequency domain using conventional Fourier transform-based coherence, but also temporo-spectral coherent one in the time-frequency plane thanks to wavelet transform-based coherence for more understanding of the turbulence and force coherences and their spatial distributions. Effects of spanwise separations, bluff body flow and flow conditions on coherent structures of turbulence and induced pressure, comparison between turbulence and pressure coherences as well as intermittency of coherent structure in the time-frequency plane will be investigated here.

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Kobayashi, Yuki, i Stephen R. Leone. "Characterizing coherences in chemical dynamics with attosecond time-resolved x-ray absorption spectroscopy". Journal of Chemical Physics 157, nr 18 (14.11.2022): 180901. http://dx.doi.org/10.1063/5.0119942.

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Coherence can drive wave-like motion of electrons and nuclei in photoexcited systems, which can yield fast and efficient ways to exert materials’ functionalities beyond the thermodynamic limit. The search for coherent phenomena has been a central topic in chemical physics although their direct characterization is often elusive. Here, we highlight recent advances in time-resolved x-ray absorption spectroscopy (tr-XAS) to investigate coherent phenomena, especially those that utilize the eminent light source of isolated attosecond pulses. The unparalleled time and state sensitivities of tr-XAS in tandem with the unique element specificity render the method suitable to study valence electronic dynamics in a wide variety of materials. The latest studies have demonstrated the capabilities of tr-XAS to characterize coupled electronic–structural coherence in small molecules and coherent light–matter interactions of core-excited excitons in solids. We address current opportunities and challenges in the exploration of coherent phenomena, with potential applications for energy- and bio-related systems, potential crossings, strongly driven solids, and quantum materials. With the ongoing developments in both theory and light sources, tr-XAS holds great promise for revealing the role of coherences in chemical dynamics.

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3

Ma, Tian, i Erik M. Bollt. "Shape Coherence and Finite-Time Curvature Evolution". International Journal of Bifurcation and Chaos 25, nr 05 (maj 2015): 1550076. http://dx.doi.org/10.1142/s0218127415500765.

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We introduce a definition of finite-time curvature evolution along with our recent study on shape coherence in nonautonomous dynamical systems. Comparing to slow evolving curvature preserving the shape, large curvature growth points reveal the dramatic change on shape such as the folding behaviors in a system. Closed trough curves of low finite-time curvature (FTC) evolution field indicate the existence of shape coherent sets, and troughs in the field indicate the most significant shape coherence. Here, we will demonstrate these properties of the FTC, as well as contrast to the popular Finite-Time Lyapunov Exponent (FTLE) computation, often used to indicate hyperbolic material curves as Lagrangian Coherent Structures (LCS). We show that often the FTC troughs are in close proximity to the FTLE ridges, but in other scenarios, the FTC indicates entirely different regions.

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GÜLERCE, MUSTAFA, i GAZANFER ÜNAL. "FORECASTING OF OIL AND AGRICULTURAL COMMODITY PRICES: VARMA VERSUS ARMA". Annals of Financial Economics 12, nr 03 (wrzesień 2017): 1750012. http://dx.doi.org/10.1142/s2010495217500129.

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The aim of this paper is to show that the estimates made with vector autoregressive–moving-average (ARMA) models based on the coherent time intervals of the multiple time series give more precise results than the univariate case. The previous literature on dynamic correlations (co-movement) in between food and energy prices has mixed results and mainly based on parametric approaches. Therefore, partial wavelet coherence (PWC) and multiple wavelet coherence (MWC) methods are used, respectively, to uncover the coherency simultaneously for time and frequency domains. In our study; world oil, corn, soybeans, wheat and sugar prices are examined instead of the return and volatility relationship between oil and agricultural commodities due to model-free approach of wavelet analysis.

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Naik, Dinesh N., Takahiro Ezawa, Yoko Miyamoto i Mitsuo Takeda. "Real-time coherence holography". Optics Express 18, nr 13 (11.06.2010): 13782. http://dx.doi.org/10.1364/oe.18.013782.

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Wang, L. J., X. Y. Zou i L. Mandel. "Time-varying induced coherence". Journal of the Optical Society of America B 9, nr 4 (1.04.1992): 605. http://dx.doi.org/10.1364/josab.9.000605.

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Kohles, N., P. Aechtner i A. Laubereau. "The “coherence peak” in time-resolved coherent Raman scattering". Optics Communications 65, nr 5 (marzec 1988): 391–96. http://dx.doi.org/10.1016/0030-4018(88)90110-1.

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Villarroya-Carpio, Arturo, i Juan M. Lopez-Sanchez. "Multi-Annual Evaluation of Time Series of Sentinel-1 Interferometric Coherence as a Tool for Crop Monitoring". Sensors 23, nr 4 (7.02.2023): 1833. http://dx.doi.org/10.3390/s23041833.

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Interferometric coherence from SAR data is a tool used in a variety of Earth observation applications. In the context of crop monitoring, vegetation indices are commonly used to describe crop dynamics. The most frequently used vegetation indices based on radar data are constructed using the backscattered intensity at different polarimetric channels. As coherence is sensitive to the changes in the scene caused by vegetation and its evolution, it may potentially be used as an alternative tool in this context. The objective of this work is to evaluate the potential of using Sentinel-1 interferometric coherence for this purpose. The study area is an agricultural region in Sevilla, Spain, mainly covered by 18 different crops. Time series of different backscatter-based radar vegetation indices and the coherence amplitude for both VV and VH channels from Sentinel-1 were compared to the NDVI derived from Sentinel-2 imagery for a 5-year period, from 2017 to 2021. The correlations between the series were studied both during and outside the growing season of the crops. Additionally, the use of the ratio of the two coherences measured at both polarimetric channels was explored. The results show that the coherence is generally well correlated with the NDVI across all seasons. The ratio between coherences at each channel is a potential alternative to the separate channels when the analysis is not restricted to the growing season of the crop, as its year-long temporal evolution more closely resembles that of the NDVI. Coherence and backscatter can be used as complementary sources of information, as backscatter-based indices describe the evolution of certain crops better than coherence.

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9

Schwickert, David, Marco Ruberti, Přemysl Kolorenč, Andreas Przystawik, Slawomir Skruszewicz, Malte Sumfleth, Markus Braune i in. "Charge-induced chemical dynamics in glycine probed with time-resolved Auger electron spectroscopy". Structural Dynamics 9, nr 6 (listopad 2022): 064301. http://dx.doi.org/10.1063/4.0000165.

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In the present contribution, we use x-rays to monitor charge-induced chemical dynamics in the photoionized amino acid glycine with femtosecond time resolution. The outgoing photoelectron leaves behind the cation in a coherent superposition of quantum mechanical eigenstates. Delayed x-ray pulses track the induced coherence through resonant x-ray absorption that induces Auger decay. Temporal modulation of the Auger electron signal correlated with specific ions is observed, which is governed by the initial electronic coherence and subsequent vibronic coupling to nuclear degrees of freedom. In the time-resolved x-ray absorption measurement, we monitor the time-frequency spectra of the resulting many-body quantum wave packets for a period of 175 fs along different reaction coordinates. Our experiment proves that by measuring specific fragments associated with the glycine dication as a function of the pump-probe delay, one can selectively probe electronic coherences at early times associated with a few distinguishable components of the broad electronic wave packet created initially by the pump pulse in the cation. The corresponding coherent superpositions formed by subsets of electronic eigenstates and evolving along parallel dynamical pathways show different phases and time periods in the range of [Formula: see text] and [Formula: see text] fs. Furthermore, for long delays, the data allow us to pinpoint the driving vibrational modes of chemical dynamics mediating charge-induced bond cleavage along different reaction coordinates.

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10

Xiang, Wei, Rui Zhang, Guoxiang Liu, Xiaowen Wang, Wenfei Mao, Bo Zhang, Yin Fu i Tingting Wu. "Saline-Soil Deformation Extraction Based on an Improved Time-Series InSAR Approach". ISPRS International Journal of Geo-Information 10, nr 3 (27.02.2021): 112. http://dx.doi.org/10.3390/ijgi10030112.

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Significant seasonal fluctuations could occur in the regional scattering characteristics and surface deformation of saline soil, and cause decorrelation, which limits the application of the conventional time-series InSAR (TS-InSAR). For extending the saline-soil deformation monitoring capability, this paper presents an improved TS-InSAR approach, based on the interferometric coherence statistics and high-coherence interferogram refinement. By constructing a network of the refined interferograms, high-accuracy ground deformation can be extracted through the weighted least square estimation and the coherent target refinement. To extract the high-accuracy deformation of a representative saline soil area in the Qarhan Salt Lake, 119 C-band Sentinel-1A images collected between May 2015 and May 2020 are selected as the data source. Subsequently, 845 refined interferograms are selected from all possible interferograms to conduct the network inversion, based on the related thresholds (the temporal baseline <49 days, the average spatial coherences >0.5, respectively). Compared with the conventional TS-InSAR measurements, both the accuracy and reliability of the extracted deformation results of the saline soil increased dramatically. Furthermore, the testing results indicate that the improved TS-InSAR method has advantages on the deformation extraction in the saline soil region, and is adaptive to reflecting the typical seasonal variations of the saline soil.

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11

Chen, Ziyang, Xudong Chen, Jixiong Pu i Sabino Chávez-Cerda. "Generation of partially coherent beams with controllable time-dependent coherence". Optical Engineering 56, nr 12 (26.12.2017): 1. http://dx.doi.org/10.1117/1.oe.56.12.124110.

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12

Privalsky, V. "On studying relations between time series in climatology". Earth System Dynamics 6, nr 1 (24.06.2015): 389–97. http://dx.doi.org/10.5194/esd-6-389-2015.

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Abstract. Relationships between time series are often studied on the basis of cross-correlation coefficients and regression equations. This approach is generally incorrect for time series, irrespective of the cross-correlation coefficient value, because relations between time series are frequency-dependent. Multivariate time series should be analyzed in both time and frequency domains, including fitting a parametric (preferably, autoregressive) stochastic difference equation to the time series and then calculating functions of frequency such as spectra and coherent spectra, coherences, and frequency response functions. The example with a bivariate time series "Atlantic Multidecadal Oscillation (AMO) – sea surface temperature in Niño area 3.4 (SST3.4)" proves that even when the cross correlation is low, the time series' components can be closely related to each other. A full time and frequency domain description of this bivariate time series is given. The AMO–SST3.4 time series is shown to form a closed-feedback loop system with a 2-year memory. The coherence between AMO and SST3.4 is statistically significant at intermediate frequencies where the coherent spectra amount up to 55 % of the total spectral densities. The gain factors are also described. Some recommendations are offered regarding time series analysis in climatology.

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13

Privalsky, V. "On studying relations between time series in climatology". Earth System Dynamics Discussions 6, nr 1 (1.04.2015): 699–718. http://dx.doi.org/10.5194/esdd-6-699-2015.

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Abstract. In climatology, relationships between time series are often studied on the basis of crosscorrelation coefficients and regression equations. This approach is generally incorrect for time series irrespective of the crosscorrelation coefficient value because relations between time series are frequency-dependent. Multivariate time series should be analyzed in both time and frequency domains, including fitting a parametric (preferably, autoregressive) stochastic difference equation to the time series and then calculating functions of frequency such as spectra and coherent spectra, coherences, and frequency response functions. The example with a bivariate time series "Atlantic Multidecadal Oscillation (AMO) – sea surface temperature in Niño area 3.4 (SST3.4)" proves that even when the crosscorrelation is low, the time series' components can be closely related to each other. A full time and frequency domain description of this bivariate time series is given. The AMO − SST3.4 time series is shown to form a closed feedback loop system. The coherence between AMO and SST3.4 is statistically significant at intermediate frequencies where the coherent spectra amount up to 55% of the total spectral densities. The gain factors are also described. Some recommendations are offered regarding time series analysis in climatology.

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14

Zhang, Xuan, Yahong Chen, Fei Wang i Yangjian Cai. "Scattering of Partially Coherent Vector Beams by a Deterministic Medium Having Parity-Time Symmetry". Photonics 9, nr 3 (27.02.2022): 140. http://dx.doi.org/10.3390/photonics9030140.

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We study the scattering properties of the partially coherent vector beams with the deterministic media having the classic symmetric and parity-time (PT) symmetric scattering potential functions. The closed-form expressions for the intensity and polarization matrix of the far-zone scattered field are obtained, under first-order Born approximation, when the partially coherent vector beams are taken to be radially polarized and the deterministic media are assumed as the four-point scatterers. We demonstrate both analytically and numerically that the far-zone scattered field becomes noncentrosymmetric and the directionality appears in the scattering pattern when the scattering potential function is switched from classic symmetry to PT symmetry. We show the effect of spatial coherence of the incident partially coherent vector beam on the directionality in scattering. We find that by turning the symmetry property of the spatial coherence function of the incident beam, i.e., into PT symmetry, the directionality in the far-zone scattering can be suppressed or enhanced, depending on the joint effect from the symmetry of the scattering potential and the symmetry of the spatial coherence. Our findings may be useful in the application of dynamic control of the directionality in light scattering.

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15

Jaeger, Gary. "Building Practical Coherence over Time". Southwest Philosophy Review 27, nr 1 (2011): 111–17. http://dx.doi.org/10.5840/swphilreview201127112.

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Carter, G. C. "Coherence and time delay estimation". Proceedings of the IEEE 75, nr 2 (1987): 236–55. http://dx.doi.org/10.1109/proc.1987.13723.

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17

Vidybida, A. K. "Neuron as time coherence discriminator". Biological Cybernetics 74, nr 6 (czerwiec 1996): 537–42. http://dx.doi.org/10.1007/bf00209424.

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Vidybida, A. K. "Neuron as time coherence discriminator". Biological Cybernetics 74, nr 6 (1.06.1996): 537–42. http://dx.doi.org/10.1007/s004220050264.

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Shen, Peng, Changcheng Wang i Jun Hu. "A Polarization Stacking Method for Optimizing Time-Series Interferometric Phases of Distributed Scatterers". Remote Sensing 14, nr 17 (25.08.2022): 4168. http://dx.doi.org/10.3390/rs14174168.

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For time-series interferometric phases optimization of distributed scatterers (DSs), the SqueeSAR technology used the phase linking (PL) to extract the equivalent single-master (ESM) interferometric phases from the multilooking time-series coherence matrix. The Cramer–Rao lower bound (CRLB) for the PL describes the highest achievable estimation accuracy of the ESM phases, which depends on the number of looks and the time-series coherence magnitude matrix. With the abundance of time-series polarimetric SAR data, many scholars have studied the coherence magnitude-based polarimetric optimization methods for optimizing the DS’s time-series interferometric phases, for example, the widely-used exhaustive search polarimetric optimization (ESPO) algorithm. However, the traditional polarimetric optimization methods select the boundary extremums of the coherence region (CR) as the optimized complex coherence, which is usually biased from the free-noise one. Currently, in the polarimetric InSAR (PolInSAR) technology, Shen et al. innovatively considered polarimetric information as statistical samples and proposed the total power (TP) coherency matrix construction method for increasing the number of looks and reducing the interferometric phase noise. Therefore, to optimize the time-series interferometric phases for DS, this paper proposes performing a polarization stacking and extending the PolInSAR TP construction to the time-series PolInSAR (TSPolInSAR) data configuration, called the time-series TP (TSTP) method. Simulated and real experiments prove that the new TSTP construction method has better performance and higher efficiency than the single polarimetric and the traditional ESPO algorithms.

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20

Yeo, Chang-Yeon, Mun-Hwan Choi, Byoung-Jin Kim i Sung-Hyun Choi. "Coherence Time Estimation for Performance Improvement of IEEE 802.11n Link Adaptation". Journal of Korean Institute of Communications and Information Sciences 36, nr 3A (31.03.2011): 232–39. http://dx.doi.org/10.7840/kics.2011.36a.3.232.

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21

Cohen, M. I., A. D. Miller, R. Barnhardt i C. F. Shaw. "Weakness of short-term synchronization among respiratory nerve activities during fictive vomiting". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 263, nr 2 (1.08.1992): R339—R347. http://dx.doi.org/10.1152/ajpregu.1992.263.2.r339.

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In decerebrate, paralyzed cats, phrenic (PHR) and lumbar abdominal (ABD) nerve discharges during both neural respiration and fictive vomiting (FV) were subjected to spectral and coherence analyses. During respiration, PHR discharge exhibited high-frequency oscillation (HFO), manifested as a narrow spectral peak (range 57-90 Hz) in autospectra and left-right coherence spectra. During FV, the following occurred: 1) the HFO peak disappeared and was replaced by a broad peak with higher modal frequency (range 84-120 Hz), indicating elimination of inputs from the medullary inspiratory pattern generator. 2) Left-right PHR coherence spectra had no distinct peaks, indicating that correlations between opposite PHR discharges were now not frequency specific. 3) Although ABD and PHR autospectra were similar, PHR-ABD coherences were near zero, indicating lack of common inputs on a short time scale. 4) Nonzero coherences between ABD nerves were confined to ipsilateral pairs. Thus coherence analysis indicates that the outputs of the vomiting pattern generator are temporally dispersed on a short time scale and are not necessarily common to different motoneuron populations.

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22

YAKOVLEV, D. R., A. GREILICH, M. BAYER i I. A. YUGOVA. "ELECTRON SPIN COHERENCE IN SINGLY CHARGED QUANTUM DOTS". International Journal of Modern Physics B 23, nr 12n13 (20.05.2009): 2813–25. http://dx.doi.org/10.1142/s0217979209062396.

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Electron spin coherence is examined experimentally and theoretically in singly charged ( In , Ga ) As / GaAs quantum dots. Time-resolved pump-probe Faraday rotation technique is used to examine fine structure and Zeeman splitting of excitons and resident electrons. Spin dephasing and spin coherence times of resident electrons have been measured in the regime of mode-locking of spin coherency.

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23

Graf, Robert N., i Adam Wax. "Temporal coherence and time-frequency distributions in spectroscopic optical coherence tomography". Journal of the Optical Society of America A 24, nr 8 (11.07.2007): 2186. http://dx.doi.org/10.1364/josaa.24.002186.

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24

Chaouachi, Nizar, i Sihem Jaziri. "Possibility of observation quantum beat coherent exciton states with time-resolved photoemission". Journal of Applied Physics 131, nr 15 (21.04.2022): 155704. http://dx.doi.org/10.1063/5.0086440.

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We develop a theoretical study to evaluate the dynamic of the time-resolved photoemission spectrum arising from the dissociation of exciton steady-states 1s, 2s in a monolayer transition metal dichlacogenides. We discuss the dielectric environment effect on the exciton binding energies. Quantum beat signatures in photoemission intensity demonstrate coherent coupling between 1s and 2s excitons. The beating contribution due to excitonic coherence is also discussed. The periodic oscillations arising from coherent superposition states and quantum beats enable exploration of novel coherent phenomena.

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25

Stajic, Jelena. "Extending the coherence time of molecules". Science 357, nr 6349 (27.07.2017): 366.10–368. http://dx.doi.org/10.1126/science.357.6349.366-j.

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Davis, John, i William Tango. "Measurement of the Atmospheric Coherence Time". Publications of the Astronomical Society of the Pacific 108 (maj 1996): 456. http://dx.doi.org/10.1086/133747.

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Wang, Xiu-qing. "The coherence time of polar slab". Canadian Journal of Physics 96, nr 2 (luty 2018): 213–15. http://dx.doi.org/10.1139/cjp-2017-0272.

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The relationship among the coherence time τ, variation frequency λ, slab thickness d, energy separation ΔE, and coupling constant α in polar slab was investigated using Pekar-type variational method. The results indicated that the τ is positively proportional to the λ, but the ΔE, d and α are negatively correlated with the τ. When ΔE is more than 10 eV, and d is less than 5 nm, τ decreases sharply.

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Zhao, Xiaowei, Shangxu Wang, Sanyi Yuan, Cuiyun Xu i Tieyi Wang. "An efficient and robust scheme for the implementation of eigenstructure-based coherency algorithms". GEOPHYSICS 85, nr 5 (31.08.2020): O97—O108. http://dx.doi.org/10.1190/geo2019-0623.1.

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The coherence attribute has been widely used to detect faults and channels as well as other structural and stratigraphic discontinuities since its introduction. Currently, the most commonly used algorithm for coherence computation is the eigenstructure-based coherence method (C3). When seismic data are of a low signal-to-noise ratio, more traces should be involved in coherence computation to improve the robustness to noise; thus, a larger analysis window shall be used. However, this will lead to increased time costs and blurred coherence images. To address these issues, we have adopted a modified eigenstructure-based coherency algorithm (C3m) based on an inverse distance weighting method and dimensionality reduction of the covariance matrix for eigendecomposition in the case of a large lateral analysis window whose size is larger than [Formula: see text] (nine traces). To further improve the computational efficiency, the add-drop algorithm is also used for covariance matrix construction. In the case of large analysis windows, the time cost by C3m is less than the time cost by C3 as demonstrated in synthetic and field data studies; also, the coherence results computed via C3m are superior to those computed via the traditional C3 method, and the new method is more favorable to seismic interpretation. Thus, our method shall be a potentially efficient and robust alternative to C3 for coherence attribute computation.

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Katz, Or, Roy Shaham i Ofer Firstenberg. "Coupling light to a nuclear spin gas with a two-photon linewidth of five millihertz". Science Advances 7, nr 14 (kwiecień 2021): eabe9164. http://dx.doi.org/10.1126/sciadv.abe9164.

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Nuclear spins of noble gases feature extremely long coherence times but are inaccessible to optical photons. Here, we realize a coherent interface between light and noble-gas spins that is mediated by alkali atoms. We demonstrate the optical excitation of the noble-gas spins and observe the coherent back action on the light in the form of high-contrast two-photon spectra. We report on a record two-photon linewidth of 5 ± 0.7 mHz above room temperature, corresponding to a 1-min coherence time. This experiment provides a demonstration of coherent bidirectional coupling between light and noble-gas spins, rendering their long-lived spin coherence accessible for manipulations in the optical domain.

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Li, Shuang, Jia-Dong Shi, Wen-Yang Sun, Dong Wang i Liu Ye. "Coherence of two-level atoms within cavity QED". Modern Physics Letters B 31, nr 35 (13.12.2017): 1750330. http://dx.doi.org/10.1142/s0217984917503304.

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In this work, we investigate the dynamics of the coherence of two atoms trapped in one cavity with resonance and large detuned characters, respectively. By means of tracing over the freedom of the cavity, the evolution coherent state can be obtained. Subsequently, the coherence within the two different scenarios is discussed. Remarkably, an interesting result is obtained as the coherence can be enhanced to a large extent in the framework of large detuning. Besides, we find that there exists a distinctive phenomenon of recovery of the coherence with the interaction time of atom–cavity.

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Vanaken, Lauranne, Patricia Bijttebier, Robyn Fivush i Dirk Hermans. "An investigation of the concurrent and longitudinal associations between narrative coherence and mental health mediated by social support". Journal of Experimental Psychopathology 13, nr 1 (styczeń 2022): 204380872110682. http://dx.doi.org/10.1177/20438087211068215.

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The coherence of autobiographical narratives is thought to be reflective of individuals’ psychological adjustment. However, results are not always replicable, the longitudinal nature of the relation has remained largely unaddressed, and there is limited research on mechanisms that may explain the relation between coherence and mental health. Therefore, in a large longitudinal study, we investigated the concurrent and prospective associations of narrative coherence with mental health, as well as mediational effects of perceived social support. Concurrently, correlations showed that total narrative coherence was associated with higher psychological well-being, fewer symptoms of depression and anxiety, and fewer negative social interactions. Cross-sectional regressions showed that total narrative coherence was predictive for better psychological well-being and fewer symptoms of depression and anxiety, and that chronological coherence predicted depressive symptomatology. These relations were all mediated by perceived negative social interactions. Prospectively, over a 5-month time interval, higher coherence of positive narratives predicted relative decreases in depressive and anxious symptoms. These relations were also mediated by the amount of perceived negative social interactions. Individuals who were more coherent about their past positive life events experienced a relative decrease in depressive and anxious symptoms over a 5-month time interval because they experienced fewer negative interactions with their social network over time.

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DOLAN, KEVIN T. "SURROGATE ANALYSIS OF MULTICHANNEL DATA WITH FREQUENCY DEPENDANT TIME LAG". Fluctuation and Noise Letters 04, nr 01 (marzec 2004): L75—L81. http://dx.doi.org/10.1142/s0219477504001677.

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Recently a new technique for generating linear surrogates of multichannel data was introduced. This technique, referred to as the coherent digitally filtered surrogate method, preserves both the individual power spectra, and the coherence function, of the original data. This method is somewhat limited in that it can only be applied to multichannel data in which the cross-spectrum is real. We present here an alteration to this algorithm that can be used to test any linear-correlation model, with arbitrary complex cross-spectra. This is of particular interest for experiments in which two channels are coupled with some time lag, and it is necessary to determine if the coupling is linear. We also demonstrate that this algorithm can be used along with the synchronization to provide a much better estimate for the degree of phase-locking between two signals than the coherence analysis techniques traditionally used in neuroscience.

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PUSEP, Y. A., M. B. RIBEIRO, H. ARAKAKI, C. A. DE SOUZA, S. MALZER i G. H. DÖHLER. "DISORDER INDUCED COHERENCE-INCOHERENCE CROSSOVER IN RANDOM GaAs/AlGaAs SUPERLATTICES". International Journal of Modern Physics B 18, nr 27n29 (30.11.2004): 3629–32. http://dx.doi.org/10.1142/s0217979204027165.

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The coherence of electrons was studied in intentionally disordered GaAs / AlGaAs superlattices as a function of the vertical interlayer coupling. Depending on the relation of the disorder energy and the Fermi energy the coherent and incoherent diffusive transport regimes were distinguished. New features of weakly coupled layered electron systems such as the vertical coupling energy and the in-plane phase-breaking time were observed by magnetoresistance measurements in the coherent and incoherent regimes respectively. Both of them were found to decrease with increasing disorder strength. This demonstrates the disorder induced break-down of the interlayer coherence of quasi-particles which drastically affected their intralayer coherence.

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Porter, Tim, i Jim Stasheff. "Homotopy Coherent Representations". Symmetry 14, nr 3 (9.03.2022): 553. http://dx.doi.org/10.3390/sym14030553.

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Homotopy coherence has a considerable history, albeit also by other names. For this volume highlighting symmetries, the appropriate use is homotopy coherence of representations, at one time known as representations up to homotopy/homotopy coherent representations. We present a brief semi-historical survey, providing some links that may not be common knowledge.

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Neupane, Sujaya, Daniel Guitton i Christopher C. Pack. "Coherent alpha oscillations link current and future receptive fields during saccades". Proceedings of the National Academy of Sciences 114, nr 29 (3.07.2017): E5979—E5985. http://dx.doi.org/10.1073/pnas.1701672114.

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Oscillations are ubiquitous in the brain, and they can powerfully influence neural coding. In particular, when oscillations at distinct sites are coherent, they provide a means of gating the flow of neural signals between different cortical regions. Coherent oscillations also occur within individual brain regions, although the purpose of this coherence is not well understood. Here, we report that within a single brain region, coherent alpha oscillations link stimulus representations as they change in space and time. Specifically, in primate cortical area V4, alpha coherence links sites that encode the retinal location of a visual stimulus before and after a saccade. These coherence changes exhibit properties similar to those of receptive field remapping, a phenomenon in which individual neurons change their receptive fields according to the metrics of each saccade. In particular, alpha coherence, like remapping, is highly dependent on the saccade vector and the spatial arrangement of current and future receptive fields. Moreover, although visual stimulation plays a modulatory role, it is neither necessary nor sufficient to elicit alpha coherence. Indeed, a similar pattern of coherence is observed even when saccades are made in darkness. Together, these results show that the pattern of alpha coherence across the retinotopic map in V4 matches many of the properties of receptive field remapping. Thus, oscillatory coherence might play a role in constructing the stable representation of visual space that is an essential aspect of conscious perception.

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Li, Qing, Kris Vasudevan i Frederick A. Cook. "3-D coherency filtering". GEOPHYSICS 62, nr 4 (lipiec 1997): 1310–14. http://dx.doi.org/10.1190/1.1444232.

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Coherency filtering is a tool used commonly in 2-D seismic processing to isolate desired events from noisy data. It assumes that phase‐coherent signal can be separated from background incoherent noise on the basis of coherency estimates, and coherent noise from coherent signal on the basis of different dips. It is achieved by searching for the maximum coherence direction for each data point of a seismic event and enhancing the event along this direction through stacking; it suppresses the incoherent events along other directions. Foundations for a 2-D coherency filtering algorithm were laid out by several researchers (Neidell and Taner, 1971; McMechan, 1983; Leven and Roy‐Chowdhury, 1984; Kong et al., 1985; Milkereit and Spencer, 1989). Milkereit and Spencer (1989) have applied 2-D coherency filtering successfully to 2-D deep crustal seismic data for the improvement of visualization and interpretation. Work on random noise attenuation using frequency‐space or time‐space prediction filters both in two or three dimensions to increase the signal‐to‐noise ratio of the data can be found in geophysical literature (Canales, 1984; Hornbostel, 1991; Abma and Claerbout, 1995).

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Palato, Samuel, Hélène Seiler, Parmeet Nijjar, Oleg Prezhdo i Patanjali Kambhampati. "Atomic fluctuations in electronic materials revealed by dephasing". Proceedings of the National Academy of Sciences 117, nr 22 (14.05.2020): 11940–46. http://dx.doi.org/10.1073/pnas.1916792117.

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The microscopic origin and timescale of the fluctuations of the energies of electronic states has a significant impact on the properties of interest of electronic materials, with implication in fields ranging from photovoltaic devices to quantum information processing. Spectroscopic investigations of coherent dynamics provide a direct measurement of electronic fluctuations. Modern multidimensional spectroscopy techniques allow the mapping of coherent processes along multiple time or frequency axes and thus allow unprecedented discrimination between different sources of electronic dephasing. Exploiting modern abilities in coherence mapping in both amplitude and phase, we unravel dissipative processes of electronic coherences in the model system of CdSe quantum dots (QDs). The method allows the assignment of the nature of the observed coherence as vibrational or electronic. The expected coherence maps are obtained for the coherent longitudinal optical (LO) phonon, which serves as an internal standard and confirms the sensitivity of the technique. Fast dephasing is observed between the first two exciton states, despite their shared electron state and common environment. This result is contrary to predictions of the standard effective mass model for these materials, in which the exciton levels are strongly correlated through a common size dependence. In contrast, the experiment is in agreement with ab initio molecular dynamics of a single QD. Electronic dephasing in these materials is thus dominated by the realistic electronic structure arising from fluctuations at the atomic level rather than static size distribution. The analysis of electronic dephasing thereby uniquely enables the study of electronic fluctuations in complex materials.

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Matsuya, Ryosuke, Junichi Ushiyama i Junichi Ushiba. "Prolonged reaction time during episodes of elevated β-band corticomuscular coupling and associated oscillatory muscle activity". Journal of Applied Physiology 114, nr 7 (1.04.2013): 896–904. http://dx.doi.org/10.1152/japplphysiol.00942.2012.

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Oscillatory activity in the sensorimotor cortex is coherent with 15–35 Hz band (β-band) muscle activity during tonic isometric voluntary contractions. In human subjects with higher corticomuscular coherence, prominent grouped discharge associated with a significant silent period was observed in electromyographic (EMG) signals. We examined the potential effects of β-band corticomuscular coupling on new ballistic movement as assessed by reaction time (RT). First, we quantified the coherence between electroencephalographic (EEG) signals over the sensorimotor cortex and rectified EMG signals from the tibialis anterior muscle during tonic isometric voluntary dorsiflexion at 30% of maximal effort in 15 healthy subjects. Subjects were divided into 2 groups [i.e., those with significant EEG-EMG coherence (COH+, n = 8) and those with no significant coherence (COH−, n = 7)]. Next, subjects performed ballistic contractions from a preliminary state of sustained contractions in reaction to auditory signals. RT was defined as the interval between the signal and the response onset measured by force. There were no intersubject differences in RT between COH+ and COH−. However, when the trials performed by COH+ subjects were divided into 2 groups depending on whether clear grouped discharge in the β-band was observed in the EMG (GD+ or GD−) just prior to the reaction, RT was significantly longer in the GD+ than in the GD− trials. We found that the magnitude of EEG-EMG coherence just before the reaction was significantly greater in the GD+ than in the GD− trials. These results suggest that generation of a new movement is delayed when corticomuscular coupling is elevated.

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Zhu, Chenyang, Sai Geetha Seri, Hamed Mohebbi-Kalkhoran i Purnima Ratilal. "Long-Range Automatic Detection, Acoustic Signature Characterization and Bearing-Time Estimation of Multiple Ships with Coherent Hydrophone Array". Remote Sensing 12, nr 22 (13.11.2020): 3731. http://dx.doi.org/10.3390/rs12223731.

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Three approaches for instantaneous wide-area analysis of ship-radiated underwater sound, each focusing on a different aspect of that sound, received on a large-aperture densely-sampled coherent hydrophone array have been developed. (i) Ship’s narrowband machinery tonal sound is analyzed via temporal coherence using Mean Magnitude-Squared Coherence (MMSC) calculations. (ii) Ship’s broadband amplitude-modulated cavitation noise is examined using Cyclic Spectral Coherence (CSC) analysis that provides estimates for propeller blade pass rotation frequency, shaft rotation frequency, and hence the number of propeller blades. (iii) Mean power spectral densities (PSD) averaged across broad bandwidths are calculated in order to detect acoustically energetic ships. Each of these techniques are applied after beamforming of the received acoustic signals on a coherent hydrophone array, leading to significantly enhanced signal-to-noise ratios for simultaneous detection, bearing-time estimation and acoustic signature characterization of multiple ships over continental-shelf scale regions. The approaches are illustrated with underwater recordings of a 160-element coherent hydrophone array for six ocean vessels, that are located at a variety of bearings and ranges out to 200 km from the array, in the Norwegian Sea in February 2014. The CSC approach is shown to also be useful for automatic detection and bearing-time estimation of repetitive marine mammal vocalizations, providing estimates for inter-pulse-train and inter-pulse intervals from CSC spectra cyclic fundamental and first recurring peak frequencies respectively.

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Кулаковский, В. Д., i А. А. Деменев. "Динамика когерентности экситон-поляритонной системы в GaAs-микрорезонаторах при импульсном резонансном фотовозбуждении". Физика и техника полупроводников 53, nr 10 (2019): 1343. http://dx.doi.org/10.21883/ftp.2019.10.48287.33.

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AbstractIt is found that exciton-polariton systems resonantly excited in GaAs semiconductor microcavities by coherent picosecond laser pulses inherit the high coherence of the laser beam and retain it for their lifetime (>100 ps), while the coherence-formation time in polariton systems resonantly excited by incoherent pulses without excitation of the exciton reservoir exceeds 200 ps.

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Kay, Leslie M., i Philip Lazzara. "How Global Are Olfactory Bulb Oscillations?" Journal of Neurophysiology 104, nr 3 (wrzesień 2010): 1768–73. http://dx.doi.org/10.1152/jn.00478.2010.

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Previous studies in waking animals have shown that the frequency structure of olfactory bulb (OB) local field potential oscillations is very similar across the OB, but large low-impedance surface electrodes may have favored highly coherent events, averaging out local inhomogeneities. We tested the hypothesis that OB oscillations represent spatially homogeneous phenomena at all scales. We used pairs of concentric electrodes (200 μm outer shaft surrounding an inner 2–3 μm recording site) beginning on the dorsal OB at anterior and medial locations in urethane-anesthetized rats and measured local field potential responses at successive 200 μm depths before and during odor stimulation. Within locations (outer vs. inner lead on a single probe), on the time scale of 0.5 s, coherence in all frequency bands was significant, but on larger time scales (10 s), only respiratory (1–4 Hz) and beta (15–30 Hz) oscillations showed prominent peaks. Across locations, coherence in all frequency bands was significantly lower for both sizes of electrodes at all depths but the most superficial 600 μm. Near the pial surface, coherence across outer (larger) electrodes at different sites was equal to coherence across outer and inner (small) electrodes within a single site and larger than coherence across inner electrodes at different sites. Overall, the beta band showed the largest coherence across bulbar sites and electrodes. Therefore larger electrodes at the surface of the OB favor globally coherent events, and at all depths, coherence depends on the type of oscillation (beta or gamma) and duration of the analysis window.

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Wang, W., M. Motagh, S. Plank, A. Orynbaikyzy i S. Roessner. "APPLICATION OF SAR TIME-SERIES AND DEEP LEARNING FOR ESTIMATING LANDSLIDE OCCURRENCE TIME". International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLIII-B3-2022 (31.05.2022): 1181–87. http://dx.doi.org/10.5194/isprs-archives-xliii-b3-2022-1181-2022.

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Abstract. The time series of normalized difference vegetation index (NDVI) and interferometric coherence extracted from optical and Synthetic Aperture Radar (SAR) images, respectively, have strong responses to sudden landslide failures in vegetated regions, which is expressed by a sudden increase or decrease in the values of NDVI and coherence. Compared with optical sensors, SAR sensors are not affected by cloud and daylight conditions and can detect the occurrence time of failure in near real-time. The purpose of this paper is to automatically determine the time of failure occurrence using time series coherence values. We propose, based on some existing anomaly detection algorithms, a deep neural network-based anomaly detection strategy that combines supervised and unsupervised learning without a priori knowledge about failure time. Our experiment using July 21, 2020 Shaziba landslide in China shows that in comparison to widely used unsupervised methodology, the use of our algorithm leads to a more accurate detection of the timing of the landslide failure.

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Yang, Xiao-Song, i Tiantian Wu. "A Note on Phase Coherence of Chaotic Sets". International Journal of Bifurcation and Chaos 26, nr 14 (30.12.2016): 1650243. http://dx.doi.org/10.1142/s0218127416502436.

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The phase coherence phenomenon of chaotic motion is unique to continuous time dynamical systems and of significance in many disciplines such as nonlinear physics and biology. In this paper, we present a geometric description of phase coherence of chaotic motion and show that chaotic sets near a homoclinic orbit or heteroclinic cycle are phase coherent in this geometric setting under a mild condition.

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Mustafa, Armin, i Adrian Hilton. "Semantically Coherent 4D Scene Flow of Dynamic Scenes". International Journal of Computer Vision 128, nr 2 (3.10.2019): 319–35. http://dx.doi.org/10.1007/s11263-019-01241-w.

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Abstract Simultaneous semantically coherent object-based long-term 4D scene flow estimation, co-segmentation and reconstruction is proposed exploiting the coherence in semantic class labels both spatially, between views at a single time instant, and temporally, between widely spaced time instants of dynamic objects with similar shape and appearance. In this paper we propose a framework for spatially and temporally coherent semantic 4D scene flow of general dynamic scenes from multiple view videos captured with a network of static or moving cameras. Semantic coherence results in improved 4D scene flow estimation, segmentation and reconstruction for complex dynamic scenes. Semantic tracklets are introduced to robustly initialize the scene flow in the joint estimation and enforce temporal coherence in 4D flow, semantic labelling and reconstruction between widely spaced instances of dynamic objects. Tracklets of dynamic objects enable unsupervised learning of long-term flow, appearance and shape priors that are exploited in semantically coherent 4D scene flow estimation, co-segmentation and reconstruction. Comprehensive performance evaluation against state-of-the-art techniques on challenging indoor and outdoor sequences with hand-held moving cameras shows improved accuracy in 4D scene flow, segmentation, temporally coherent semantic labelling, and reconstruction of dynamic scenes.

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Haug, Hartmut. "Quantum Coherence in Ultrafast Semiconductor Spectroscopy". Journal of Nonlinear Optical Physics & Materials 07, nr 02 (czerwiec 1998): 227–39. http://dx.doi.org/10.1142/s0218863598000193.

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Coherent optical phenomena such as the optical Stark effect, Rabi flopping, photon echo and quantum beating which are well-known in atomic spectroscopy can also be observed in semiconductors by using femtosecond laser pulses. On these short time scales, the quantum coherence of the optical excitations in the solid do not only influence the optical properties but change at the same time the relaxation and dephasing kinetics. The quasi-classical Boltzmann kinetics has to be replaced by quantum kinetics. Coherence leads to the appearance of memory in the scattering integrals. For femtosecond four-wave mixing and pump-and-probe spectroscopy the use of quantum kinetics for LO-phonon and for carrier-carrier scattering will be reviewed.

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Ahmadian, Azadeh, i Rasoul Malekfar. "Investigation of the Time Behavior of the Second-Order Coherence Function of a Tunable Single-Photon Source". Journal of Spectroscopy 2021 (2.06.2021): 1–7. http://dx.doi.org/10.1155/2021/8811424.

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Single-photon sources are critical optical components in quantum communication, in particular, for security applications. One of the essential parameters that define these sources is the magnitude of the second-order coherence function, whose investigation reveals the state of the emitted photon. In this study, we indicate that the second-order coherence function varies over time when using two lasers and preparing coherent population trapping. The calculation is based on solving the master equation to find the density matrix corresponding to the emission dynamics and provide the second-order coherence function. The changes of the second-order coherence function can be estimated and the system behavior regarding photon emission can be predicted by solving the master equation based on the parameters obtained from the experimental results of a nitrogen vacancy (NV) in a diamond. Here we report, for the first time to the best of our knowledge, that the state of the emitted photons persists in the strong interaction of the aforementioned process. As using two lasers is a familiar method for controlling the single-photon source and the stability of the source is an essential point in a quantum network, this study can be considered to develop quantum network components such as memory and on-demand single-photon sources. Also, it suggests a method for tuning photon statistics while controlling the photon states.

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Dong, Yao, Ai-Ling Ji i Guo-Feng Zhang. "Evolution of quantum coherence of qutrit-qutrit system under correlated depolarizing channels". Acta Physica Sinica 71, nr 7 (2022): 070303. http://dx.doi.org/10.7498/aps.71.20212067.

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In order to study the decoherence process of quantum system and find the ways to delay it, in this paper we investigate the decoherence process under correlated depolarizing channels by calculating the evolution of norm coherence, relative entropy coherence and basis-independent coherence of the three initial states: special initial state, maximum coherent state and isotropic state. From the analytic results, numerical results and evolution images, it can be found that 1) completely correlated channels can suppress decoherence to a greatest extent,. 2) the time point at which maximum decoherence occurs is irrelevant to the degree of correlation, but system’s decoherence evolution behavior depends on it. 3)the correlation of depolarizing channels can reinforce the collective quantum coherence between subsystems, and an inequality relation of basis-independent coherence is proved in this system.

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Lindsay, A. C., N. Viceconte i C. Di Mario. "Optical coherence tomography: has its time come?" Heart 97, nr 17 (5.07.2011): 1361–62. http://dx.doi.org/10.1136/hrt.2010.214825.

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Scherzer, Daniel, Lei Yang, Oliver Mattausch, Diego Nehab, Pedro V. Sander, Michael Wimmer i Elmar Eisemann. "Temporal Coherence Methods in Real-Time Rendering". Computer Graphics Forum 31, nr 8 (4.09.2012): 2378–408. http://dx.doi.org/10.1111/j.1467-8659.2012.03075.x.

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Park, B. Hyle, Mark C. Pierce, Barry Cense i Johannes F. de Boer. "Real-time multi-functional optical coherence tomography". Optics Express 11, nr 7 (7.04.2003): 782. http://dx.doi.org/10.1364/oe.11.000782.

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