Search

The characteristic timescale at which the variability of active galactic nuclei (AGNs) turns from red noise to white noise can probe the accretion physics around supermassive black holes (SMBHs). A number of works have studied the characteristic timescale of quasars and obtained quite different scaling relations between the timescale and quasar physical properties. One possible reason for the discrepancies is that the characteristic timescale can be easily underestimated if the light curves are not long enough. In this work, we construct well-defined AGN samples to observationally test the relationships between the characteristic timescale and AGN properties obtained by previous works. Our samples eliminate the effects of insufficient light-curve lengths. We confirm that the timescale predictions of the Corona Heated Accretion disk Reprocessing model are consistent with our timescale measurements. The timescale predictions by empirical relations are systematically smaller than our measured ones. Our results provide further evidence that AGN variability is driven by thermal fluctuations in SMBH accretion disks. Future flagship time-domain surveys can critically test our conclusions and reveal the physical nature of AGN variability. [ABSTRACT FROM AUTHOR]

The Cosmology Large Angular Scale Surveyor (CLASS) is a telescope array that observes the cosmic microwave background over 75% of the sky from the Atacama Desert, Chile, at frequency bands centered near 40, 90, 150, and 220 GHz. This paper describes the CLASS data pipeline and maps for 40 GHz observations conducted from 2016 August to 2022 May. We demonstrate how well the CLASS survey strategy, with rapid (∼10 Hz) front-end modulation, recovers the large-scale Galactic polarization signal from the ground: the mapping transfer function recovers ∼67% (85%) of EE and BB (VV) power at ℓ = 20 and ∼35% (47%) at ℓ = 10. We present linear and circular polarization maps over 75% of the sky. Simulations based on the data imply the maps have a white noise level of 110 μ K arcmin and correlated noise component rising at low- ℓ as ℓ −2.4. The transfer-function-corrected low- ℓ component is comparable to the white noise at the angular knee frequencies of ℓ ≈ 18 (linear polarization) and ℓ ≈ 12 (circular polarization). Finally, we present simulations of the level at which expected sources of systematic error bias the measurements, finding subpercent bias for the Λ cold dark matter EE power spectra. Bias from E -to- B leakage due to the data reduction pipeline and polarization angle uncertainty approaches the expected level for an r = 0.01 BB power spectrum. Improvements to the instrument calibration and the data pipeline will decrease this bias. [ABSTRACT FROM AUTHOR]

Objective. As an emerging diagnosis technology for gastrointestinal diseases, confocal laser endomicroscopy (CLE) is limited by the physical structure of the fiber bundle, leading to the inevitable production of various forms of noise during the imaging process. However, existing denoising methods based on hand-crafted features inefficiently deal with realistic noise in CLE images. To alleviate this challenge, we proposed context-aware kernel estimation and multi-scale dynamic fusion modules to remove realistic noise in CLE images, including multiplicative and additive white noise. Approach. Specifically, a realistic noise statistics model with random noise specific to CLE data is constructed and further used to develop a self-supervised denoised model without the participation of clean images. Secondly, context-aware kernel estimation, which improves the representation of features by similar learnable region weights, addresses the problem of the non-uniform distribution of noises in CLE images and proposes a lightweight denoised model (CLENet). Thirdly, we have developed a multi-scale dynamic fusion module that decouples and recalibrates features, providing a precise and contextually enriched representation of features. Finally, we integrated two developed modules into a U-shaped backbone to build an efficient denoising network named U-CLENet. Main Results. Both proposed methods achieve comparable or better performance with low computational complexity on two gastrointestinal disease CLE image datasets using the same training benchmark. Significance. The proposed approaches improve the visual quality of unclear CLE images for various stages of tumor development, helping to reduce the rate of misdiagnosis in clinical decision-making and achieve computer graphics-assisted diagnosis. [ABSTRACT FROM AUTHOR]

This study formulated and clarified the presentation of the noise-related error terms in the power spectral density (PSD) and height–height correlation function (HHCF) through a roughness analysis of self-affine fractals. Assuming the noise as white noise, this study simulated the PSD and HHCF of the noisy roughness profile in a typical situation: line-edge roughness measurements involved in semiconductor lithography technology. It was found that conventional noise-correction techniques can bias the PSD/HHCF from those of the true roughness profiles because they do not account for the residual noise-induced error. The findings obtained from the roughness analysis and simulation techniques are expected to benefit various applications, such as clarifying the quantitative residual error in specific situations, selecting the optimum analysis method (PSD or HHCF), estimating the required number of averaged profiles (measurements) that yields sufficiently small noise errors, and considering strategies for noise reduction. [ABSTRACT FROM AUTHOR]

We propose the use of a second surface mirror as a displacement plate-beamsplitter to provide significant simplification and cost reduction of time-of-flight anemometry (ToFA), without sacrificing precision and accuracy. These benefits are most pronounced for long-range applications. Our method's principle benefits are due to the few and simple components it requires as well as low sensitivity to both temperature effects and light source incoherence. We found that precise and accurate results are possible using a common consumer mirror as the main optical element and an inexpensive diode laser as the light source, which could broaden access to laser anemometry and make many industry applications economically feasible. The nature of the design also permits an increase in range for a given laser power since the method can utilize the entire optical area of the focusing lens/mirror independent of other design considerations and the cost of a flat second-surface mirror is usually negligible. To characterize the performance of this method, we develop a Cramer–Rao bound (CRB) for a general class of ToFA's with multiple Gaussian beams under signal-independent Gaussian white noise. For a given measurement volume, the lowest velocity uncertainty is achieved by creating a standard two-sheet geometry: power-matching the first two beams by adjusting the beamsplitter and blocking the rest of the beams is optimal. However, keeping the higher order beams permits determination of flow direction. Conditions to achieve beam power-matching are given. An anemometer is built using a diode laser with 12 mw 405 nm beam using a total of just three transmitting optical components. Our setup has an accuracy of 99.1%. The worst-case precision of 96.7% nearly achieves the CRB, although optimizing the setup more can lower the bound, and therefore allow increase in the performance by an order of magnitude or more. [ABSTRACT FROM AUTHOR]

We study the static and dynamic structure of thermally fluctuating elastic thin sheets by investigating a model known as the overdamped dynamic Föppl–von Kármán equation, in which the Föppl–von Kármán equation from elasticity theory is driven by white noise. The resulting nonlinear equation is governed by a single nondimensional coupling parameter g where large and small values of g correspond to weak and strong nonlinear coupling respectively. By analysing the weak coupling case with ordinary perturbation theory and the strong coupling case with a self-consistent methodology known as the self-consistent expansion, precise analytic predictions for the static and dynamic structure factors are obtained. Importantly, the maximum frequency n max supported by the system plays a role in determining which of three possible classes such sheets belong to: (1) when g ≫ 1 , the system is mostly linear with roughness exponent ζ = 1 and dynamic exponent z = 4, (2) when g ≪ 2 / n max , the system is extremely nonlinear with roughness exponent ζ = 1 / 2 and dynamic exponent z = 3, (3) between these regimes, an intermediate behaviour is obtained in which a crossover occurs such that the nonlinear behaviour is observed for small frequencies while the linear behaviour is observed for large frequencies, and thus the large frequency linear tail is found to have a significant impact on the small frequency behaviour of the sheet. Back-of-the-envelope calculations suggest that ultra-thin materials such as graphene lie in this intermediate regime. Despite the existence of these three distinct behaviours, the decay rate of the dynamic structure factor is related to the static structure factor as if the system were completely linear. This quasi-linearity occurs regardless of the size of g and at all length scales. Numerical simulations confirm the existence of the three classes of behaviour and the quasi-linearity of all classes. [ABSTRACT FROM AUTHOR]

Objective. The imaging photoplethysmography (IPPG), which is applied to heart rate measurement, is susceptible to interference caused by illumination variations during photography. To improve the accuracy, robustness, and real-time performance of IPPG, a new method combined with modified ensemble empirical mode decomposition (EEMD) and fast independent component analysis (FastICA) was proposed. Approach. On the modified EEMD, to reduce the error caused by the residual white noise of the algorithm, it was characterized by recurrently updating zero-mean white noise for ensemble averaging based on the standard deviation of the input signal. On the modified FastICA, its constructed nonlinear function was superseded by Huber's approximation function to improve the robustness and running speed. Main results. Comparison experiments were conducted between the MAHNOB-HCI database and own collected data. In the hybrid natural light and computer screen light scenario, the mean absolute error (MAE) of heart rate amounted to 0.93 beats per minute and the correlation coefficient r reached 0.85. In the experiments of MAHNOB-HCI database, the MAE amounted to 6.03 beats per minute and the correlation coefficient r reached 0.75. Furthermore, the modified method decreased the running time by approximately ten times compared to the original algorithms. Significance. Various experimental results demonstrated that the proposed method significantly improves the accuracy, timeliness, and interference resistance. [ABSTRACT FROM AUTHOR]

We consider the partition function Z ℓ (x ⃗ , 0 | y ⃗ , t) of ℓ non-intersecting continuous directed polymers of length t in dimension 1 + 1 , in a white noise environment, starting from positions x ⃗ and terminating at positions y ⃗ . When ℓ = 1 , it is well known that for fixed x, the field log Z 1 (x , 0 | y , t) solves the Kardar–Parisi–Zhang equation and admits the Brownian motion as a stationary measure. In particular, as t goes to infinity, Z 1 (x , 0 | y , t) / Z 1 (x , 0 | 0 , t) converges to the exponential of a Brownian motion B (y). In this article, we show an analogue of this result for any ℓ. We show that Z ℓ (x ⃗ , 0 | y ⃗ , t) / Z ℓ (x ⃗ , 0 | 0 ⃗ , t) converges as t goes to infinity to an explicit functional Z ℓ s t a t (y ⃗) of ℓ independent Brownian motions. This functional Z ℓ s t a t (y ⃗) admits a simple description as the partition sum for ℓ non-intersecting semi-discrete polymers on ℓ lines. We discuss applications to the endpoints and midpoints distribution for long non-crossing polymers and derive explicit formula in the case of two polymers. To obtain these results, we show that the stationary measure of the O'Connell–Warren multilayer stochastic heat equation is given by a collection of independent Brownian motions. This in turn is shown via analogous results in a discrete setup for the so-called log-gamma polymer and exploit the connection between non-intersecting log-gamma polymers and the geometric Robinson–Schensted–Knuth correspondence found in Corwin-O'Connell-Seppäläinen-Zygouras (2014 Duke Math. J. 163 513–63). [ABSTRACT FROM AUTHOR]

We study a Langevin-like model which describes an inertial particle in a one-dimensional harmonic potential and subjected to two heat baths and one athermal environment. The thermal noises are white and Gaussian, and the temperatures of heat reservoirs are different. The athermal medium act through an external non-Gaussian noise of Poisson type. We calculate exactly the time-dependent cumulant-generating function of position and velocity of the particle, as well as an expression of this generating function for stationary states. We discuss the long-time behavior of first cumulants of the energy injected by the athermal reservoir and the heat exchanged with thermal baths. In particular, we find that the covariance of stochastic heat due to distinct thermal reservoirs exhibits a complex dependence on properties of athermal noise. [ABSTRACT FROM AUTHOR]

Searching for periodic non-accelerated signals in the presence of ideal white noise using the fully phase-coherent fast-folding algorithm (FFA) is theoretically established as a more sensitive search method than the fast Fourier transform (FFT) search with incoherent harmonic summing. In this paper, we present a comparison of the performance of an FFA search implementation using RIPTIDE and an FFT search implementation using PRESTO, over a range of signal parameters with white noise and with real telescope noise from the Giant Meterwave Radio Telescope (GMRT) High Resolution Southern Sky (GHRSS) survey with the upgraded GMRT (uGMRT). We find that the FFA search with appropriate de-reddening of the time series performs better than the FFT search with spectral whitening for long-period pulsars under real GHRSS noise conditions. We describe an FFA-search pipeline implemented for the GHRSS survey looking for pulsars over a period of 0.1â€"100 s and up to a dispersion measure of 500 pc cmâˆ'3. We processed GHRSS survey data covering ∼1500 deg2 of the sky with this pipeline. We re-detected 43 known pulsars with a better signal-to-noise ratio in the FFA search than in the FFT search. We also report the discovery of two new pulsars, including a long-period pulsar with a short duty cycle, using this FFA-search pipeline. A population of long-period pulsars with periods of several seconds or higher could help constrain the pulsar death line. [ABSTRACT FROM AUTHOR]

We describe the first-season CO Mapping Array Project (COMAP) analysis pipeline that converts raw detector readouts to calibrated sky maps. This pipeline implements four main steps: gain calibration, filtering, data selection, and mapmaking. Absolute gain calibration relies on a combination of instrumental and astrophysical sources, while relative gain calibration exploits real-time total-power variations. High-efficiency filtering is achieved through spectroscopic common-mode rejection within and across receivers, resulting in nearly uncorrelated white noise within single-frequency channels. Consequently, near-optimal but biased maps are produced by binning the filtered time stream into pixelized maps; the corresponding signal bias transfer function is estimated through simulations. Data selection is performed automatically through a series of goodness-of-fit statistics, including χ 2 and multiscale correlation tests. Applying this pipeline to the first-season COMAP data, we produce a data set with very low levels of correlated noise. We find that one of our two scanning strategies (the Lissajous type) is sensitive to residual instrumental systematics. As a result, we no longer use this type of scan and exclude data taken this way from our Season 1 power spectrum estimates. We perform a careful analysis of our data processing and observing efficiencies and take account of planned improvements to estimate our future performance. Power spectrum results derived from the first-season COMAP maps are presented and discussed in companion papers. [ABSTRACT FROM AUTHOR]

In order to explore how the ubiquitous short-term stochastic variability in the photometric observations of Wolfâ€"Rayet (WR) stars is related to various stellar characteristics, we examined a sample of 50 Galactic WR stars using 122 lightcurves obtained by the BRIght Target Explorer-Constellation, Transiting Exoplanet Survey Satellite and Microvariability and Oscillations of Stars satellites. We found that the periodograms resulting from a discrete Fourier transform of all our detrended lightcurves are characterized by a forest of random peaks showing an increase in power starting from ∼0.5 dayâˆ'1 down to ∼0.1 dayâˆ'1. After fitting the periodograms with a semi-Lorentzian function representing a combination of white and red noise, we investigated possible correlations between the fitted parameters and various stellar and wind characteristics. Seven correlations were observed, the strongest and only significant one being between the amplitude of variability, α 0, observed for hydrogen-free WR stars, while WNh stars exhibit correlations between α 0 and the stellar temperature, T *, and also between the characteristic frequency of the variations, ν char, and both T * and v ∞. We report that stars observed more than once show significantly different variability parameters, indicating an epoch-dependent measurement. We also find that the observed characteristic frequencies for the variations generally lie between âˆ' 0.5 < log 10 ν char < 0.5 , and that the values of the steepness of the amplitude spectrum are typically found in the range âˆ' 0.1 < log 10 Îł < 0.5. We discuss various physical processes that can lead to this correlation. [ABSTRACT FROM AUTHOR]

We propose entanglement criteria for multipartite systems via symmetric informationally complete measurement and general symmetric informationally complete measurement. We apply these criteria to detect entanglement of multipartite states, such as the convex of Bell states, entangled states mixed with white noise. It is shown that these criteria are stronger than some existing ones. [ABSTRACT FROM AUTHOR]

BeiDou-3 global navigation satellite system (BDS-3) has officially provided positioning, navigation, and timing (PNT) services on 31 July 2020. The difference between BDS-2 and BDS-3 in signal modulation mode, signal characteristics, and satellite clock datum leads to the possible existence of inter-system bias (ISB) between BDS-2 and BDS-3, which becomes the key to affect the time-frequency transfer of BDS. In this contribution, taking the observations of BRUX, CEBR, USUD, WTZZ, and YEL2 stations as an example, five analysis centres (ACs) precise products (for instance, CNT, COM, ESA, GBM, and WUM) are used to evaluate the BDS-2 BII/B3I combined BDS-3 B1I/B3I, B1I/B2a, B1C/B2a, and B1C/B2a time-frequency transfer performance with ignore ISB (ISBNO), estimating ISB as constant (ISBCT), estimating ISB as a random walk (ISBRW) and estimating ISB as white noise (ISBWN) four kinds of estimation strategies. The results show that the ISBCT estimation strategy has the better performance than ISBNO, ISBRW, and ISBWN estimation strategies in BDS-2/BDS-3 combined time-frequency transfer; compared with ignoring ISB strategy, the standard deviation and frequency instability of ISBCT estimation strategy is decreased by 9.16% and 12.83% on average, respectively. Meanwhile, an ISBCT estimation strategy is recommended when using CNT, COM, ESA, and WUM precision products for BDS-2/BDS-3 combined time-frequency transfer. [ABSTRACT FROM AUTHOR]

We propose an algorithm, referred to as the pulsar phase and standard deviation (PPSD), to mitigate transient radio frequency interference (RFI) in pulsar observations. PPSD uses the model for pulsar time of arrival to identify pulsar phase and extract the pulse profile to protect the original pulsar profile. PPSD sets a threshold based on the statistics empirical rule to label the transient RFI in the off-pulse data until all unlabelled off-pulse data obeys the white Gaussian noise (WGN) distribution. The transient RFI data is then substituted with WGN. Finally, we use PPSD to process the pulsar observation data obtained from the NanShan 25 m Radio Telescope. Our results show that PPSD can effectively mitigate the transient RFI and improve the signal-to-noise ratio of the pulsar observations. [ABSTRACT FROM AUTHOR]

The Euclid satellite, to be launched by ESA in 2022, will be a major instrument for cosmology for the next decades. Euclid is composed of two instruments: the Visible instrument and the Near Infrared Spectrometer and Photometer (NISP). In this work, we estimate the implications of correlated readout noise in the NISP detectors for the final in-flight flux measurements. Considering the multiple accumulated readout mode, for which the UTR (Up The Ramp) exposure frames are averaged in groups, we derive an analytical expression for the noise covariance matrix between groups in the presence of correlated noise. We also characterize the correlated readout noise properties in the NISP engineering-grade detectors using long dark integrations. For this purpose, we assume a (1/f)α-like noise model and fit the model parameters to the data, obtaining typical values of e− Hz−0.5, and. Furthermore, via realistic simulations and using a maximum likelihood flux estimator we derive the bias between the input flux and the recovered one. We find that using our analytical expression for the covariance matrix of the correlated readout noise we diminish this bias by up to a factor of four with respect to the white noise approximation for the covariance matrix. Finally, we conclude that the final bias on the in-flight NISP flux measurements should still be negligible even in the white readout noise approximation, which is taken as a baseline for the Euclid on-board processing to estimate the on-sky flux. [ABSTRACT FROM AUTHOR]

We introduce two types of statistical quasi-separation between local observables to construct two-party Bell-type inequalities for an arbitrary dimensional systems and arbitrary number of measurement settings per site. Note that, the main difference between statistical quasi-separations and the usual statistical separations is that the former are not symmetric under exchange of the two local observables, whereas latter preserve the symmetry. We show that a variety of Bell inequalities can be derived by sequentially applying triangle inequalities which statistical quasi-separations satisfy. A sufficient condition is presented to show quantum violations of the Bell-type inequalities with infinitesimal values of critical visibility vc. [ABSTRACT FROM AUTHOR]

The magnetohydrodynamics system forced by space–time white noise has been proposed and investigated by physicists and engineers, although without rigorous mathematical proofs of its solution's fundamental properties. Applying the theory of regularity structures, we prove its well-posedness and strong Feller property. The proof requires a careful treatment of nonlinear terms which are sensitive to specific components of the solution that is a six-dimensional vector field, of which the first three and the last three are velocity and magnetic fields, respectively. [ABSTRACT FROM AUTHOR]

Relic gravitational waves (GWs) can be produced by primordial magnetic fields. However, not much is known about the resulting GW amplitudes and their dependence on the details of the generation mechanism. Here we treat magnetic field generation through the chiral magnetic effect (CME) as a generic mechanism and explore its dependence on the speed of generation (the product of magnetic diffusivity and characteristic wavenumber) and the speed characterizing the maximum magnetic field strength expected from the CME. When the latter exceeds the former (regime I), which is the regime applicable to the early universe, we obtain an inverse cascade with moderate GW energy that scales with the third power of the magnetic energy. When the generation speed exceeds the CME limit (regime II), the GW energy continues to increase without a corresponding increase of magnetic energy. In the early kinematic phase, the GW energy spectrum (per linear wavenumber interval) has opposite slopes in both regimes and is characterized by an inertial range spectrum in regime I and a white noise spectrum in regime II. The occurrence of these two slopes is shown to be a generic consequence of a nearly monochromatic exponential growth of the magnetic field. The resulting GW energy is found to be proportional to the fifth power of the limiting CME speed and the first power of the generation speed. [ABSTRACT FROM AUTHOR]

In this letter we report the existence of nondegenerate fundamental bright soliton solution for coupled multi-component nonlinear Schrödinger equations of Manakov type. To derive this class of nondegenerate vector soliton solutions, we adopt the Hirota bilinear method with appropriate general class of seed solutions. Very interestingly the obtained nondegenerate fundamental soliton solution of the N-coupled nonlinear Schrödinger (CNLS) system admits multi-hump natured intensity profiles. We explicitly demonstrate this specific property by considering the nondegenerate soliton (NDS) solutions for 3 and 4-CNLS systems. We also point out the existence of a special class of partially NDS solutions by imposing appropriate restrictions on the wavenumbers in the already obtained completely NDS solution. Such class of soliton solutions can also exhibit multi-hump profile structures. Finally, we present the stability analysis of nondegenerate fundamental soliton of the 3-CNLS system as an example. The numerical results confirm the stability of triple-humped profile nature against perturbations of 5% and 10% white noise. The multi-hump nature of nondegenerate fundamental soliton solution will be useful in multi-level optical communication applications with enhanced flow of data in multi-mode fibers. [ABSTRACT FROM AUTHOR]

We demonstrate wide-range linewidth-tuning of a narrow-linewidth laser in the C-band up to 40 GHz through cascaded four-wave mixing (CFWM) based phase modulation amplification. Stimulated Brillouin scattering (SBS) severely limits the power scaling of narrow-linewidth lasers. Continuous tuning of the linewidth or temporal coherence of the laser to mitigate SBS is conventionally achieved through external phase modulation with white noise or other RF waveforms. However, the range of linewidth tuning is limited by the bandwidth and power of the electro-optic modulator. We overcome this through the use of FWM as a linewidth multiplier. To achieve linewidth multiplication, two tunable pumps line-broadened in electro-optic phase modulators with white noise are power scaled and propagated through highly nonlinear fiber. We achieve linewidth tuning up to ∼4 GHz using control of the noise waveform, while CFWM achieves a 10× multiplication of linewidth up to 40 GHz at a fixed wavelength. Linewidth tuning can be further scaled through power scaling or cascading multiple nonlinear stages. The proposed technique would be useful in nonlinearity control in narrow-linewidth laser amplifiers, high-resolution optical imaging, LIDAR, and infrared spectroscopy. [ABSTRACT FROM AUTHOR]

Mode-interaction plays an important role in the dark soliton generation in the microcavity. It is beneficial to the excitation of dark solitons, but also facilitates a variety of dark soliton states. Based on the non-normalized Lugiato–Lefever equation, the evolution of dark soliton in the microcavity with mode-interaction is investigated. By means of mode-interaction, the initial continuous wave (CW) field evolves into a dark soliton gradually, and the spectrum expands from a single mode to a broadband comb. After changing the mode-interaction parameters, the original modes which result in dual circular dark solitons inside the microcavity, are separated from the resonant mode by 2 free spectral ranges (FSR). When the initial field is another feasible pattern of weak white Gaussian noise, the large frequency detuning leads to the amplification of the optical power in the microcavity, and the mode-interaction becomes stronger. Then, multiple dark solitons, which correspond to the spectra with multi-FSR, can be excited by selecting appropriate mode-interaction parameters. In addition, by turning the mode-interaction parameters, the dark soliton number can be regulated, and the comb tooth interval in the spectrum also changes accordingly. Theoretical analysis results are significant for studying the dark soliton in the microcavity with mode-interaction. [ABSTRACT FROM AUTHOR]

Precise web tension measurement is critical for web handling and process control in roll-to-roll (R2R) manufacturing systems. Calculating web tension by using out-of-plane vibration measurement offers a contactless solution to tension measurement during the R2R process, which is suitable for situations where contacting web tension measurement sensors cannot be applied. In this paper, a real-time prediction of web tension based on contactless sensing of out-of-plane web vibration is presented for the first time. We design and test a fast frequency estimation algorithm, based on the Fourier series, which solves the frequency resolution problem currently existing in real-time applications when conventional FFT is applied. Our simulation results show that the proposed method has an accurate estimation of frequency under harmonics and white Gaussian noise based on few observed cycles. A R2R testbed was built for testing the real-time performance of the proposed algorithm including accuracy, robustness, and computation speed. The experimental results on the testbed show that the proposed method can predict the web tension with an error less than 10% for various tension values and track the tension changes within one analysis window of 50 ms. [ABSTRACT FROM AUTHOR]

For the large-scale linear discrete ill-posed problem min‖Ax − b‖ or Ax = b with b contaminated by white noise, the Golub–Kahan bidiagonalization based LSQR method and its mathematically equivalent CGLS, the conjugate gradient (CG) method applied to ATAx = ATb, are most commonly used. They have intrinsic regularizing effects, where the iteration number k plays the role of regularization parameter. The long-standing fundamental question is: Can LSQR and CGLS find two-norm filtering best possible regularized solutions? The author has given definitive answers to this question for severely and moderately ill-posed problems when the singular values of A are simple. This paper extends the results to the multiple singular value case, and studies the approximation accuracy of Krylov subspaces, the quality of low rank approximations generated by Golub–Kahan bidiagonalization and the convergence properties of Ritz values. For the two kinds of problems, we prove that LSQR finds two-norm filtering best possible regularized solutions at semi-convergence. Particularly, we consider some important and untouched issues on best, near best and general rank k approximations to A for the ill-posed problems with the singular values with α > 0, and the relationships between them and their nonzero singular values. Numerical experiments confirm our theory. The results on general rank k approximations and the properties of their nonzero singular values apply to several Krylov solvers, including LSQR, CGME, MINRES, MR-II, GMRES and RRGMRES. [ABSTRACT FROM AUTHOR]

A feasible neuron model can be effective to estimate the mode transition in neural activities in a complex electromagnetic environment. When neurons are exposed to electromagnetic field, the continuous magnetization and polarization can generate nonlinear effect on the exchange and propagation of ions in the cell, and then the firing patterns can be regulated completely. The conductivity of ion channels can be affected by the temperature and the channel current is adjusted for regulating the excitability of neurons. In this paper, a phototube and a thermistor are used to the functions of neural circuit. The phototube is used to capture external illumination for energy injection, and a continuous signal source is obtained. The thermistor is used to percept the changes of temperature, and the channel current is changed to adjust the excitability of neuron. This functional neural circuit can encode the external heat (temperature) and illumination excitation, and the dynamics of neural activities is investigated in detail. The photocurrent generated in the phototube can be used as a signal source for the neural circuit, and the thermistor is used to estimate the conduction dependence on the temperature for neurons under heat effect. Bifurcation analysis and Hamilton energy are calculated to explore the mode selection. It is found that complete dynamical properties of biological neurons can be reproduced in spiking, bursting, and chaotic firing when the phototube is activated as voltage source. The functional neural circuit mainly presents spiking states when the photocurrent is handled as a stable current source. Gaussian white noise is imposed to detect the occurrence of coherence resonance. This neural circuit can provide possible guidance for investigating dynamics of neural networks and potential application in designing sensitive sensors. [ABSTRACT FROM AUTHOR]

Quantum sensing has been receiving researcher's attention these years due to its ultrahigh sensitivity and precision. However, the bandwidth of the sensors may be low, thus limiting the scope of their practical applications. The low-bandwidth problem is conquered by feedback control methods, which are widely utilized in classic control fields. Based on a quantum harmonic oscillator model operating near the resonant point, the bandwidth and sensitivity of the quantum sensor are analyzed. The results give two important conclusions: (a) the bandwidth and sensitivity are two incompatible performance parameters of the sensor, so there must be a trade-off between bandwidth and sensitivity in practical applications; (b) the quantum white noise affects the signal to be detected in a non-white form due to the feedback control. [ABSTRACT FROM AUTHOR]

TianQin is a Chinese space-based observatory concept with three drag-free spacecraft orbiting the earth to observe gravitational-waves in the millihertz range. Electrical charge is inevitably accumulating on its isolated test masses which are used as the mirrors for interferometers to measure gravity variation. Charge management system based on ultraviolet (UV) light is developed to reduce the charge-induced noises acting on the test mass in space gravitational experiments such as GP-B, LISA, LISA Pathfinder and TianQin mission. The UV LED is a new UV light source with some advantages relative to mercury lamps, such as smaller size, lighter weight, lower power consumption and higher efficiency. For these reasons, ground-based tests for the combination of UV LED and inertial sensor are essential. This paper presents the development of a charge management system based on a UV LED, its application to a torsion pendulum system with a TianQin-like test mass, and assesses the charge-management performance of the system. The experimental results indicate that the isolated test mass can be charged positively or negatively through UV illumination. It demonstrates that the charging and discharging rates can both reach higher than 105 e s−1, as well as spectral measurement of the pendulum charge resulting in a white noise level equivalent to ∼5 × 105 e Hz−1/2, satisfying the TianQin requirement. [ABSTRACT FROM AUTHOR]

In this work, we propose a new criterion for choosing the regularization parameter in Tikhonov regularization when the noise is white Gaussian. The criterion minimizes a lower bound of the predictive risk, when both data norm and noise variance are known, and the parameter choice involves minimizing a function whose solution depends only on the signal-to-noise ratio. Moreover, when neither noise variance nor data norm is given, we propose an iterative algorithm which alternates between a minimization step of finding the regularization parameter and an estimation step of estimating signal-to-noise ratio. Simulation studies on both small- and large-scale datasets suggest that the approach can provide very accurate and stable regularized inverse solutions and, for small sized samples, it outperforms discrepancy principle, balancing principle, unbiased predictive risk estimator, L-curve method, generalized cross validation, and quasi-optimality criterion, and achieves excellent stability hitherto unavailable. [ABSTRACT FROM AUTHOR]

The CSL model predicts a progressive breakdown of the quantum superposition principle, with a noise randomly driving the state of the system towards a localized one, thus accounting for the emergence of a classical world within a quantum framework. In the original model the noise is supposed to be white, but since white noises do not exist in nature, it becomes relevant to identify some of its spectral properties. Experimental data set an upper bound on its frequencies, while in this paper we bound it from below. We do so in two ways: by considering a 'minimal' measurement setup, requiring that the collapse is completed within the measurement time; and in a measurement modeling-independent way, by requiring that the fluctuations average to zero before the measurement time. [ABSTRACT FROM AUTHOR]

We demonstrate a 87Rb–129Xe/131Xe atom spin gyroscope, where two stage lock-in-amplifiers are applied to measure the shift of the NMR frequency. The NMR frequency shifts and their Allan deviation are analyzed during on- and off-resonance operation. The filter effects of the lock-in-amplifiers are investigated in terms of the Allan deviation. Based on the dual species operation, we achieve an angular random walk of 1.11 deg h–1/2 for the rotation rate. The slightly off-resonance operation reveals that the NMR insensitive white noise of the 131Xe signal limits the angular random walk of our system. [ABSTRACT FROM AUTHOR]

We introduce two types of statistical quasi-separation between local observables to construct two-party Bell-type inequalities for an arbitrary dimensional systems and arbitrary number of measurement settings per site. Note that, the main difference between statistical quasi-separations and the usual statistical separations is that the former are not symmetric under exchange of the two local observables, whereas latter preserve the symmetry. We show that a variety of Bell inequalities can be derived by sequentially applying triangle inequalities which statistical quasi-separations satisfy. A sufficient condition is presented to show quantum violations of the Bell-type inequalities with infinitesimal values of critical visibility v _c .

Weconsidered various types of potential noise in gates controlling non-adiabatic holonomic transformations of spin-qubits in one and two-dimensional systems with the Rashba interaction. It is shown how exact results can be derived for deviations of spin rotation angle and fidelity of the qubit transformation after a completed transformation. Errors in initial values of gate potentials and timedependent drivings are considered and exact results for white gate noise are derived and analysed in detail. It is demonstrated how the drivings can be tuned to optimise the final fidelity of the transformation and to minimise the variances of qubit transformations. [ABSTRACT FROM AUTHOR]

The simulated noise used to benchmark wavelet edge detection in this work was described incorrectly. The correct description is given here, and new results based on noise that matches the original description are provided. The results support our original conclusion, which is that wavelet edge detection outperforms thresholding in the presence of white noise and 1/ f noise. [ABSTRACT FROM AUTHOR]

We considered various types of potential noise in gates controlling non-adiabatic holonomic transformations of spin-qubits in one and two-dimensional systems with the Rashba interaction. It is shown how exact results can be derived for deviations of spin rotation angle and fidelity of the qubit transformation after a completed transformation. Errors in initial values of gate potentials and time-dependent drivings are considered and exact results for white gate noise are derived and analysed in detail. It is demonstrated how the drivings can be tuned to optimise the final fidelity of the transformation and to minimise the variances of qubit transformations.

This paper describes the near-infrared detector system noise generator (NG) that we wrote for the James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec). NG simulates many important noise components including: (1) white "read noise"; (2) residual bias drifts; (3) pink 1/f noise; (4) alternating column noise; and (5) picture frame noise. By adjusting the input parameters, NG can simulate noise for Teledyne's H1RG, H2RG, and H4RG detectors with and without Teledyne's SIDECAR ASIC IR array controller. NG can be used as a starting point for simulating astronomical scenes by adding dark current, scattered light, and astronomical sources into the results from NG. NG is written in Python-3.4. The source code is freely available for download from http://jwst.nasa.gov/publications.html. [ABSTRACT FROM AUTHOR]

We present the results of simulations on the detectability of O2 in the atmosphere of Earth twins around nearby low mass stars using high resolution transmission spectroscopy. We explore such detectability with each of the three upcoming Extremely Large Telescopes (ELTs), i.e., GMT, TMT, and E-ELT, and high resolution spectrographs, assuming such instruments will be available in all ELTs. With these simulations we extend previous studies by taking into account atmospheric refraction in the transmission spectrum of the exo-Earth and observational white and red noise contributions. Our studies reveal that the number of transits necessary to detect O2 in the atmosphere of an Earth twin around an M dwarf is by far higher than the number of transits estimated by Snellen et al. In addition, our simulations show that, when accounting for typical noise levels associated with observations in the optical and near-infrared, the O2A band at 760 nm is more favorable for detecting the exoplanetary signal than the O2 band at 1268 nm for all the spectral types, except M9V. We conclude that, unless unpredicted instrumental limitations arise, the implementation of pre-slit optics such as image slicers appears to be key to significantly improving the yield of this particular science case. However, even in the most optimistic cases, we conclude that the detection of O2 in the atmosphere of an Earth twin will only be feasible with the ELTs if the planet is orbiting a bright close by (d ⩽ 8 pc) M dwarf with a spectral type later than M3. [ABSTRACT FROM AUTHOR]

The us of stochastic resonance (SR) can effectively achieve the detection of weak signal in white noise and colored noise. However, SR in chaotic interference is seldom involved. In view of the requirements for the detection of weak signal in the actual project and the relationship between the signal, chaotic interference, and nonlinear system in the bistable system, a self-adaptive SR system based on genetic algorithm is designed in this paper. It regards the output signal-to-noise ratio (SNR) as a fitness function and the system parameters are jointly encoded to gain optimal bistable system parameters, then the input signal is processed in the SR system with the optimal system parameters. Experimental results show that the system can keep the best state of SR under the condition of low input SNR, which ensures the effective detection and process of weak signal in low input SNR. [ABSTRACT FROM AUTHOR]

The statistical properties of random cross-correlated sequences constructed by the convolution method (likewise referred to as the Rice or the inverse Fourier transformation) are examined. We clarify the meaning of the filtering function--the kernel of the convolution operator--and show that it is the value of the cross-correlation function which describes correlations between the initial white noise and constructed correlated sequences. The matrix generalization of this method for constructing a bunch of N cross-correlated sequences is presented. Algorithms for their generation are reduced to solving the problem of decomposition of the Fourier transform of the correlationmatrix into a product of two mutually conjugate matrices. Different decompositions are considered. The limits of weak and strong correlations for the one-point probability and pair correlation functions of sequences generated by themethod under consideration are studied. Special cases of heavy-tailed distributions of the generated sequences are analyzed. We show that, if the filtering function is rather smooth, the distribution function of generated variables has the Gaussian or L'evy form depending on the analytical properties of the distribution (or characteristic) functions of the initial white noise. Anisotropic properties of statistically homogeneous random sequences related to the asymmetry of a filtering function are revealed and studied. These asymmetry properties are expressed in terms of the third- or fourth-order correlation functions. Several examples of the construction of correlated chains with a predefined correlation matrix are given. [ABSTRACT FROM AUTHOR]

In the quantum metrology, applications of quantum techniques based on entanglement bring in some better performances than conventional approaches. We experimentally investigate an application of entanglement in accurate ranging based on the second-order coherence in the time domain. By a fitting algorithm in the data processing, the optimization results show a precision of ±200 μm at a distance of 1043.3m. In addition, the influence of jamming noise on the ranging scheme is studied. With some different fitting parameters, the result shows that the proposed scheme has a powerful anti-jamming capability for white noise. [ABSTRACT FROM AUTHOR]

Variable coefficients and Wick-type stochastic fractional coupled KdV equations are investigated. By using the modified fractional sub-equation method, Hermite transform, and white noise theory the exact travelling wave solutions and white noise functional solutions are obtained, including the generalized exponential, hyperbolic, and trigonometric types. [ABSTRACT FROM AUTHOR]

We reanalyze the problem of spontaneous photon emission in collapse models. We show that the extra term found by Bassi and Dürr is present for non-white (colored) noise, but its coefficient is proportional to the zero frequency Fourier component of the noise. This leads one to suspect that the extra term is an artifact. When the calculation is repeated with the final electron in a wave packet and with the noise confined to a bounded region, the extra term vanishes in the limit of continuum state normalization. The result obtained by Fu and by Adler and Ramazano?glu from application of the Golden Rule is then recovered. [ABSTRACT FROM AUTHOR]

The development of quantum technologies depends on the investigation of the behaviour of quantum systems in noisy environments, since complete isolation from its environment is impossible to achieve. In this paper, we show that the main features of a quantum delayed-choice experiment hold even if performed in a system with an arbitrary level of white noise. In light of our results, we analyse recent optical and NMR experiments and show that a loophole on non-locality is not fundamental. [ABSTRACT FROM AUTHOR]

In this paper, we consider the average-consensus problem with communication time delays and noisy links. We analyze two different cases of coupling topologies: fixed and switching topologies. By utilizing the stability theory of the stochastic differential equations, we analytically show that the average consensus could be achieved almost surely with the perturbation of noise and the communication time delays even if the time delay is time-varying. The theoretical results show that multi-agent systems can tolerate relatively large time delays if the noise is weak, and they can tolerate relatively strong noise if the time delays are low. The simulation results show that systems with strong noise intensities yield slow convergence. [ABSTRACT FROM AUTHOR]