Articles de revues : « Newtonian noise »

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Trozzo, Lucia, et Francesca Badaracco. « Seismic and Newtonian Noise in the GW Detectors ». Galaxies 10, n^o 1 (22 janvier 2022) : 20. http://dx.doi.org/10.3390/galaxies10010020.

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Gravitational wave detectors aim to measure relative length variations of the order of ΔL/L≃10−21, or less. Thus, any mechanism that is able to reproduce such a tiny variation can, in principle, threaten the sensitivity of these instruments, representing a source of noise. There are many examples of such noise, and seismic and Newtonian noise are among these and will be the subject of this review. Seismic noise is generated by the incessant ground vibration that characterizes Earth. Newtonian noise is instead produced by the tiny fluctuations of the Earth’s gravitational field. These fluctuations are generated by variations of air and soil density near the detector test masses. Soil density variations are produced by the same seismic waves comprising seismic noise. Thus, it makes sense to address these two sources of noise in the same review. An overview of seismic and Newtonian noise is presented, together with a review of the strategies adopted to mitigate them.

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Badaracco, Francesca. « Environmental noises in current and future gravitational-wave detectors ». Journal of Physics : Conference Series 2156, n^o 1 (1 décembre 2021) : 012077. http://dx.doi.org/10.1088/1742-6596/2156/1/012077.

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Abstract Gravitational–wave (GW) detectors are very sensitive instruments that suffer from a huge number of noises. If we aim to observe gravitational waves with earthbound detectors, we need to take care of every source that can prevent the observation. Seismic noise poses a huge challenge to the sensitivity in the the low-frequency band and it is tackled with suspensions and active controls. The low–frequency band can also be threatened by the so–called Newtonian noise, generated by the fluctuations of the gravity field. If this has not been a problem in the first generation gravitational-wave detectors, it will be so in the next runs and especially in the third–generation detectors, like the Einstein Telescope. We need then to be prepared to suppress as much as possible these noises, otherwise they might become the last wall for the sensitivity of our detectors. This manuscript will explore environmental noises with a particular detail on Newtonian and seismic noise and the techniques that we can employ to reduce their effects.

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Tauviqirrahman, Mohammad, J. Jamari, S. Susilowati, Caecilia Pujiastuti, Budi Setiyana, Ahmad Hafil Pasaribu et Muhammad Imam Ammarullah. « Performance Comparison of Newtonian and Non-Newtonian Fluid on a Heterogeneous Slip/No-Slip Journal Bearing System Based on CFD-FSI Method ». Fluids 7, n^o 7 (2 juillet 2022) : 225. http://dx.doi.org/10.3390/fluids7070225.

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It is a well-known fact that incorporating a slip boundary into the contact surfaces improves bearing performance significantly. Regrettably, no research into the effect of slip on the behavior of journal bearing systems operating with non-Newtonian lubricants has been conducted thus far. The main purpose of this work is to explore the performance comparison of Newtonian and non-Newtonian fluid on a heterogeneous slip/no-slip journal bearing system. The tribological and acoustic behavior of journal bearing is investigated in this study using a rigorous program that combines CFD (computational fluid dynamics) and two-way FSI (fluid–structure interaction) procedures to simulate Newtonian vs. non-Newtonian conditions with and without slip boundary. The numerical results indicate that irrespective of the lubricant type (i.e., Newtonian or non-Newtonian), an engineered heterogeneous slip/no-slip pattern leads to the improvement of the bearing performance (i.e., increased load-carrying capacity, reduced coefficient of friction, and decreased noise) compared to conventional journal bearing. Furthermore, the influence of the eccentricity ratio is discussed, which confirms that the slip beneficial effect becomes stronger as the eccentricity ratio decreases. It has also been noticed that the Newtonian lubricant is preferable for improving tribological performance, whereas non-Newtonian fluid is recommended for lowering bearing noise.

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Paik, Ho Jung, et Jan Harms. « Newtonian noise cancellation in tensor gravitational wave detector ». Journal of Physics : Conference Series 716 (mai 2016) : 012025. http://dx.doi.org/10.1088/1742-6596/716/1/012025.

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Fenyvesi, Edit, József Molnár et Sándor Czellár. « Investigation of Infrasound Background Noise at Mátra Gravitational and Geophysical Laboratory (MGGL) ». Universe 6, n^o 1 (3 janvier 2020) : 10. http://dx.doi.org/10.3390/universe6010010.

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Infrasound and seismic waves are supposed to be the main contributors to the gravity-gradient noise (Newtonian noise) of the third-generation subterranean gravitational wave detectors. This noise will limit the sensitivity of the instrument at frequencies below 20 Hz. Investigation of its origin and the possible methods of mitigation have top priority during the designing period of the detectors. Therefore, long-term site characterizing measurements are needed at several subterranean sites. However, at some sites, mining activities can occur. These activities can cause sudden changes (transients) in the measured signal, and increase the continuous background noise, too. We have developed an algorithm based on discrete Haar transform to find these transients in the infrasound signal. We found that eliminating the transients decreases the variation of the noise spectra, and therefore results a more accurate characterization of the continuous background noise. We carried out experiments for controlling the continuous noise. Machines operating at the mine were turned on and off systematically in order to see their effect on the noise spectra. These experiments showed that the main contributor of the continuous noise is the ventilation system of the mine. We also estimated the contribution of infrasound Newtonian noise at MGGL to the strain noise of a subterranean GW detector similar to Einstein Telescope.

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Yue, Pengcheng, Hua Qu, Jihong Zhao et Meng Wang. « Newtonian-Type Adaptive Filtering Based on the Maximum Correntropy Criterion ». Entropy 22, n^o 9 (22 août 2020) : 922. http://dx.doi.org/10.3390/e22090922.

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This paper provides a novel Newtonian-type optimization method for robust adaptive filtering inspired by information theory learning. With the traditional minimum mean square error (MMSE) criterion replaced by criteria like the maximum correntropy criterion (MCC) or generalized maximum correntropy criterion (GMCC), adaptive filters assign less emphasis on the outlier data, thus become more robust against impulsive noises. The optimization methods adopted in current MCC-based LMS-type and RLS-type adaptive filters are gradient descent method and fixed point iteration, respectively. However, in this paper, a Newtonian-type method is introduced as a novel method for enhancing the existing body of knowledge of MCC-based adaptive filtering and providing a fast convergence rate. Theoretical analysis of the steady-state performance of the algorithm is carried out and verified by simulations. The experimental results show that, compared to the conventional MCC adaptive filter, the MCC-based Newtonian-type method converges faster and still maintains a good steady-state performance under impulsive noise. The practicability of the algorithm is also verified in the experiment of acoustic echo cancellation.

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Beker, M. G., J. F. J. van den Brand, E. Hennes et D. S. Rabeling. « Newtonian noise and ambient ground motion for gravitational wave detectors ». Journal of Physics : Conference Series 363 (1 juin 2012) : 012004. http://dx.doi.org/10.1088/1742-6596/363/1/012004.

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FRAEDRICH, KLAUS. « FICKIAN DIFFUSION AND NEWTONIAN COOLING : A CONCEPT FOR NOISE INDUCED CLIMATE VARIABILITY WITH LONG-TERM MEMORY ? » Stochastics and Dynamics 02, n^o 03 (septembre 2002) : 403–12. http://dx.doi.org/10.1142/s0219493702000492.

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Observed near surface air and soil temperature time series reveal a long-term memory, which is associated with a power-law scaling of the frequency spectra, S(ω) ~ ω- β with β ~ 0.6, lying between white and flicker noise, 0 < β < 1. As this power law scaling is not consistent with the Brownian motion concept of climate variability, Fickian diffusion is added to a Newtonian cooling relaxation to provide a more suitable analog of climatic fluctuations: (i) Diffusive plus random heat fluxes parametrise the turbulent mixing by synoptic scale eddy life cycles, affect tropospheric and near surface temperatures and excite a long-term memory regime with a β ~ 0.5 scaling. (ii) Newtonian cooling describes the near surface temperatures relaxing towards a global mean deep soil temperature and stabilises the system to a white noise response at very low frequencies. The long-term memory regime emerges from the high frequency scaling (β ~ 1.5), once temperatures become correlated in space due to diffusion, so that spatially averaged fluctuations correlate for times beyond the diffusion time scale. The long-term memory regime disappears into a white noise plateau (β ~ 0), when low frequencies exceed the damping time scale of Newtonian cooling. This system may be interpreted as a diffusive system relaxing towards the deep soil restoration temperature with an almost infinitely large time scale.

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Paik, Ho Jung, M. Vol Moody et Ronald S. Norton. « SOGRO — Terrestrial full-tensor detector for mid-frequency gravitational waves ». International Journal of Modern Physics D 29, n^o 04 (21 janvier 2019) : 1940001. http://dx.doi.org/10.1142/s0218271819400017.

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Laser interferometer gravitational-wave (GW) detectors are observing signals from merging black hole and neutron star binaries with a frequency window from 10[Formula: see text]Hz to several kHz. Future space-based laser interferometers will open a new window of 0.1[Formula: see text]mHz to 0.1[Formula: see text]Hz. In this paper, we discuss the possibility of constructing a terrestrial GW detector named Superconducting Omni-directional Gravitational Radiation Observatory (SOGRO), which can fill the missing frequency window, 0.1 to 10[Formula: see text]Hz, with astronomically interesting sensitivity. SOGRO measures all five tensor components of the spacetime metric, which results in uniform sensitivity for all-sky directions and enables identification of the source direction and wave polarization with a single detector. Seismic and Newtonian gravity noise pose the greatest challenges for constructing ground-based detectors below 10[Formula: see text]Hz. SOGRO utilizes enhanced mechanical and electrical stabilities of materials at cryogenic temperatures to reject common-mode seismic noise to a very high degree. Further, its full-tensor characteristic gives an advantage in the rejection of the Newtonian noise over conventional detectors.

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Carrillo, José A., Young-Pil Choi et Samir Salem. « Propagation of chaos for the Vlasov–Poisson–Fokker–Planck equation with a polynomial cut-off ». Communications in Contemporary Mathematics 21, n^o 04 (31 mai 2019) : 1850039. http://dx.doi.org/10.1142/s0219199718500396.

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We consider a [Formula: see text]-particle system interacting through the Newtonian potential with a polynomial cut-off in the presence of noise in velocity. We rigorously prove the propagation of chaos for this interacting stochastic particle system. Taking the cut-off like [Formula: see text] with [Formula: see text] in the force, we provide a quantitative error estimate between the empirical measure associated to that [Formula: see text]-particle system and the solutions of the [Formula: see text]-dimensional Vlasov–Poisson–Fokker–Planck (VPFP) system. We also study the propagation of chaos for the Vlasov–Fokker–Planck equation with less singular interaction forces than the Newtonian one.

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Mouro, João, Paolo Paoletti, Marco Sartore, Massimo Vassalli et Bruno Tiribilli. « Photothermal Self-Excitation of a Phase-Controlled Microcantilever for Viscosity or Viscoelasticity Sensing ». Sensors 22, n^o 21 (2 novembre 2022) : 8421. http://dx.doi.org/10.3390/s22218421.

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This work presents a feedback closed-loop platform to be used for viscosity or viscoelasticity sensing of Newtonian or non-Newtonian fluids. The system consists of a photothermally excited microcantilever working in a digital Phase-Locked Loop, in which the phase between the excitation signal to the cantilever and the reference demodulating signals is chosen and imposed in the loop. General analytical models to describe the frequency and amplitude of oscillation of the cantilever immersed in viscous and viscoelastic fluids are derived and validated against experiments. In particular, the sensitivity of the sensor to variations of viscosity of Newtonian fluids, or to variations of elastic/viscous modulus of non-Newtonian fluids, are studied. Interestingly, it is demonstrated the possibility of controlling the sensitivity of the system to variations of these parameters by choosing the appropriate imposed phase in the loop. A working point with maximum sensitivity can be used for real-time detection of small changes of rheological parameters with low-noise and fast-transient response. Conversely, a working point with zero sensitivity to variations of rheological parameters can be potentially used to decouple the effect of simultaneous external factors acting on the resonator.

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IORIO, L. « EFFECTS OF STANDARD AND MODIFIED GRAVITY ON INTERPLANETARY RANGES ». International Journal of Modern Physics D 20, n^o 02 (février 2011) : 181–232. http://dx.doi.org/10.1142/s0218271811018780.

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We numerically investigate the impact on the two-body range of several Newtonian and non-Newtonian dynamical effects for some Earth-planet (Mercury, Venus, Mars, Jupiter, Saturn) pairs, in view of the expected cm-level accuracy in some future planned or proposed interplanetary ranging operations. The general relativistic gravitomagnetic Lense–Thirring effect should be modeled and solved for in future accurate ranging tests of Newtonian and post-Newtonian gravity, because it falls within their measurability domain. It could a priori "imprint" the determination of some of the target parameters of the tests considered. Moreover, the ring of the minor asteroids, Ceres, Pallas, Vesta (and also many other asteroids if Mars is considered) and the trans-Neptunian objects (TNOs) act as sources of nonnegligible systematic uncertainty on the larger gravitoelectric post-Newtonian signals from which it is intended to determine the parameters γ and β of the parametrized post-Newtonian (PPN) formalism with very high precision (several orders of magnitude better than the current 10-4–10-5levels). Also, other putative, nonconventional gravitational effects, like a violation of the strong equivalence principle (SEP), a secular variation of the Newtonian constant of gravitation G, and the Pioneer anomaly, are considered. The presence of a hypothetical, distant planetary-sized body X could be detectable with future high-accuracy planetary ranging. Our analysis can, in principle, be extended to future interplanetary ranging scenarios in which one or more spacecrafts in heliocentric orbits are involved. The impact of fitting the initial conditions, and of the noise in the observations, on the actual detectability of the dynamical signatures investigated, which may be partly absorbed in the estimation process, should be quantitatively addressed in further studies.

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Mora, Marco, Fernando Córdova-Lepe et Rodrigo Del-Valle. « A non-Newtonian gradient for contour detection in images with multiplicative noise ». Pattern Recognition Letters 33, n^o 10 (juillet 2012) : 1245–56. http://dx.doi.org/10.1016/j.patrec.2012.02.012.

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Harms, Jan, et Krishna Venkateswara. « Newtonian-noise cancellation in large-scale interferometric GW detectors using seismic tiltmeters ». Classical and Quantum Gravity 33, n^o 23 (28 octobre 2016) : 234001. http://dx.doi.org/10.1088/0264-9381/33/23/234001.

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Guspí, Fernando, et Iván Novara. « Reduction to the pole and transformations of scattered magnetic data using Newtonian equivalent sources ». GEOPHYSICS 74, n^o 5 (septembre 2009) : L67—L73. http://dx.doi.org/10.1190/1.3170690.

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We have developed an equivalent-source method for performing reduction to the pole and related transforms from magnetic data measured on unevenly spaced stations at different elevations. The equivalent source is composed of points located vertically beneath the measurement stations, and their magnetic properties are chosen in such a way that the reduced-to-the-pole magnetic field generated by them is represented by an inverse-distance Newtonian potential. This function, which attenuates slowly with distance, provides better coverage for discrete data points. The magnetization intensity is determined iteratively until the observed field is fitted within a certain tolerance related to the level of noise; thus, advantages in computer time are gained over the resolution of large systems of equations. In the case of induced magnetization, the iteration converges well for verticalor horizontal inclinations, and results are stable if noise is taken into account properly. However, for a range of intermediate inclinations near 35°, a factor tending to zero makes it necessary to perform the reduction through a two-stage procedure, using an auxiliary magnetization direction, without significantly affecting the speed and stability of the method. The performance of the procedure was tested on a synthetic example based on a field generated on randomly scattered stations by a random set of magnetic dipoles, contaminated with noise, which is reduced to the pole for three different magnetization directions. Results provide a good approximation to the theoretical reduced-to-the-pole field using a one- or a two-stage reduction, showing minor noise artifacts when the direction is nearly horizontal. In a geophysical example with real data, the reduction to the pole was used to correct the estimated magnetization direction that originates an isolated anomaly over Sierra de San Luis, Argentina.

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Qvarfort, Sofia, Dennis Rätzel et Stephen Stopyra. « Constraining modified gravity with quantum optomechanics ». New Journal of Physics 24, n^o 3 (1 mars 2022) : 033009. http://dx.doi.org/10.1088/1367-2630/ac3e1b.

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Abstract We derive the best possible bounds that can be placed on Yukawa- and chameleon-like modifications to the Newtonian gravitational potential with a cavity optomechanical quantum sensor. By modelling the effects on an oscillating source-sphere on the optomechanical system from first-principles, we derive the fundamental sensitivity with which these modifications can be detected in the absence of environmental noise. In particular, we take into account the large size of the optomechanical probe compared with the range of the fifth forces that we wish to probe and quantify the resulting screening effect when both the source and probe are spherical. Our results show that optomechanical systems in high vacuum could, in principle, further constrain the parameters of chameleon-like modifications to Newtonian gravity.

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Singha, Ayatri, Stefan Hild et Jan Harms. « Newtonian-noise reassessment for the Virgo gravitational-wave observatory including local recess structures ». Classical and Quantum Gravity 37, n^o 10 (27 avril 2020) : 105007. http://dx.doi.org/10.1088/1361-6382/ab81cb.

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Caidi, Zhao, Li Yongsheng et Zhou Shengfan. « Random attractor for a two-dimensional incompressible non-Newtonian fluid with multiplicative noise ». Acta Mathematica Scientia 31, n^o 2 (mars 2011) : 567–75. http://dx.doi.org/10.1016/s0252-9602(11)60257-9.

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Guo, Chunxiao, et Boling Guo. « $H^1$-random attractors of stochastic monopolar non-Newtonian fluids with multiplicative noise ». Communications in Mathematical Sciences 12, n^o 8 (2014) : 1565–78. http://dx.doi.org/10.4310/cms.2014.v12.n8.a9.

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Coughlin, M., N. Mukund, J. Harms, J. Driggers, R. Adhikari et S. Mitra. « Towards a first design of a Newtonian-noise cancellation system for Advanced LIGO ». Classical and Quantum Gravity 33, n^o 24 (14 novembre 2016) : 244001. http://dx.doi.org/10.1088/0264-9381/33/24/244001.

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Guo, Chun-xiao, Bo-ling Guo et Hui Yang. « H 2-regularity random attractors of stochastic non-Newtonian fluids with multiplicative noise ». Applied Mathematics and Mechanics 35, n^o 1 (13 décembre 2013) : 105–16. http://dx.doi.org/10.1007/s10483-014-1776-7.

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Huang, Jianhua, Yan Zheng et Jin Li. « Martingale solution and Markov selection of stochastic non-Newtonian fluid driven by Lévy noise ». Stochastics and Dynamics 14, n^o 02 (24 mars 2014) : 1350017. http://dx.doi.org/10.1142/s0219493713500172.

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This paper is devoted to stochastic non-Newtonian fluid driven by Lévy noise. By the tight compactness of distribution of the solution for finite-dimensional approximate in a Hilbert space, Skorohod embedding theorem and representation of martingale, the existence of the martingale solution is shown. Moreover, the procedure of the proof for the Markov selection in [J. Differential Equations250 (2011) 2737–2778] are simplified to show the existence of Markov selection for the martingale solution.

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Badaracco, F., et J. Harms. « Optimization of seismometer arrays for the cancellation of Newtonian noise from seismic body waves ». Classical and Quantum Gravity 36, n^o 14 (25 juin 2019) : 145006. http://dx.doi.org/10.1088/1361-6382/ab28c1.

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Guo, Boling, et Chunxiao Guo. « Remark on random attractor for a two dimensional incompressible non-Newtonian fluid withmultiplicative noise ». Communications in Mathematical Sciences 10, n^o 3 (2012) : 821–33. http://dx.doi.org/10.4310/cms.2012.v10.n3.a5.

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Almeida, Adilson, et Fernanda Cipriano. « Weak Solution for 3D-Stochastic Third Grade Fluid Equations ». Water 12, n^o 11 (16 novembre 2020) : 3211. http://dx.doi.org/10.3390/w12113211.

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This article studies the stochastic evolution of incompressible non-Newtonian fluids of differential type. More precisely, we consider the equations governing the dynamic of a third grade fluid filling a three-dimensional bounded domain O, perturbed by a multiplicative white noise. Taking the initial condition in the Sobolev space H2(O), and supplementing the equations with a Navier slip boundary condition, we establish the existence of a global weak stochastic solution with sample paths in L∞(0,T;H2(O)).

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Harms, Jan, et Stefan Hild. « Passive Newtonian noise suppression for gravitational-wave observatories based on shaping of the local topography ». Classical and Quantum Gravity 31, n^o 18 (28 août 2014) : 185011. http://dx.doi.org/10.1088/0264-9381/31/18/185011.

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Singha, Ayatri, Stefan Hild, Jan Harms, Maria C. Tringali, Irene Fiori, Federico Paoletti, Tomasz Bulik et al. « Characterization of the seismic field at Virgo and improved estimates of Newtonian-noise suppression by recesses ». Classical and Quantum Gravity 38, n^o 24 (23 novembre 2021) : 245007. http://dx.doi.org/10.1088/1361-6382/ac348a.

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Abstract Fluctuations of gravitational forces cause so-called Newtonian noise (NN) in gravitational-wave detectors which is expected to limit their low-frequency sensitivity in upcoming observing runs. Seismic NN is produced by seismic waves passing near a detector’s suspended test masses. It is predicted to be the strongest contribution to NN. Modeling this contribution accurately is a major challenge. Arrays of seismometers were deployed at the Virgo site to characterize the seismic field near the four test masses. In this paper, we present results of a spectral analysis of the array data from one of Virgo’s end buildings to identify dominant modes of the seismic field. Some of the modes can be associated with known seismic sources. Analyzing the modes over a range of frequencies, we provide a dispersion curve of Rayleigh waves. We find that the Rayleigh speed in the NN frequency band 10–20 Hz is very low (≲100 m s−1), which has important consequences for Virgo’s seismic NN. Using the new speed estimate, we find that the recess formed under the suspended test masses by a basement level at the end buildings leads to a 10 fold reduction of seismic NN.

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Paik, Ho Jung. « SOGRO (Superconducting Omni-directional Gravitational Radiation Observatory) ». EPJ Web of Conferences 168 (2018) : 01005. http://dx.doi.org/10.1051/epjconf/201816801005.

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Detection of gravitational waves (GWs) from merging binary black holes (BHs) by Advanced LIGO has ushered in the new era of GW astronomy. Many conceivable sources such as intermediate-mass BH binaries and white dwarf binaries, as well as stellar-mass BH inspirals, would emit GWs below 10 Hz. It is highly desirable to open a new window for GW astronomy in the infrasound frequency band. A low-frequency tensor detector could be constructed by combining six magnetically levitated superconducting test masses. Such a detector would be equally sensitive to GWs coming from anywhere in the sky, and would be capable of resolving the source direction and wave polarization. I will present the design concept of a new terrestrial GW detector, named SOGRO, which could reach a strain sensitivity of 10−19-10−21 Hz−1/2 at 0.1-10 Hz. Seismic and Newtonian gravity noises are serious obstacles in constructing terrestrial GW detectors at frequencies below 10 Hz. I will explain how these noises are rejected in SOGRO. I will also report the progress made in designing the platform and modelling its thermal noise.

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Liu, M., et D. Bothe. « Numerical study of head-on droplet collisions at high Weber numbers ». Journal of Fluid Mechanics 789 (26 janvier 2016) : 785–805. http://dx.doi.org/10.1017/jfm.2015.725.

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Head-on collisions of binary water droplets at high Weber numbers are studied by means of direct numerical simulations (DNS). We modify the lamella stabilization method of Focke & Bothe (J. Non-Newtonian Fluid Mech., vol. 166 (14), 2011, pp. 799–810), which avoids the artificial rupture of the thin lamella arising in high-energy collisions, and validate it in the regime of high Weber numbers. The simulations are conducted with and without initial disturbances and the results are compared with the experimental work of Pan et al. (Phys. Rev. E, vol. 80 (3), 2009, 036301). The influence of initial white noise disturbance on the collision dynamics is identified and good agreement between the simulation results and the experimental results is obtained when the initial noise disturbances are properly exerted. In order to include the stochastic nature of the disturbance, we conduct several simulations with white noise disturbance of same strength and average the spectrum diagram for the unstably developing rim of the collision complex. We show that the magnification of rim perturbation can be predicted by Plateau–Rayleigh theory over a long time span.

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IORIO, LORENZO. « PERSPECTIVES ON MEASURING THE PPN PARAMETERS β AND γ IN EARTH'S GRAVITATIONAL FIELD TO HIGH ACCURACY WITH CHAMP/GRACE MODELS ». International Journal of Modern Physics D 17, n^o 05 (mai 2008) : 815–29. http://dx.doi.org/10.1142/s0218271808012516.

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The current bounds on the PPN parameters β and γ are on the order of 10-4–10-5. Many missions aimed at improving such limits by several orders of magnitude have been proposed, including LATOR, ASTROD, BepiColombo and GAIA. They involve the use of various spacecraft, to be launched along interplanetary trajectories, for measuring the post-Newtonian effects induced by solar gravity on the propagation of electromagnetic waves. In this paper, we investigate the requirements needed to measure the combination ν = (2 + 2γ - β)/3 entering the post-Newtonian Einstein pericenter precession [Formula: see text] of a test particle to an accuracy on the order of ~10-5 with a pair of drag-free spacecraft in Earth's gravitational field. It turns out that the latest gravity models from the dedicated CHAMP and GRACE missions would allow the reduction of the systematic errors of gravitational origin to just this demanding level of accuracy. With regard to the non-gravitational errors, the spectral noise density of the required drag-free sensors amounts to 10-8–10-9 cm s-2 Hz-½ over very low frequencies. Although not yet attainable with present technologies, such a level of compensation is much less demanding than those required for LISA, for instance. As a by-product, an independent measurement of the post-Newtonian gravitomagnetic Lense–Thirring effect with a ~1% accuracy will be possible as well. The forthcoming Earth gravity models from CHAMP and GRACE will further reduce the systematic bias of gravitational origin in both such tests.

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de Angelis, M., F. Greco, A. Pistorio, N. Poli, M. Prevedelli, G. Saccorotti, F. Sorrentino et G. M. Tino. « Measurement of absolute gravity acceleration in Firenze ». Solid Earth Discussions 3, n^o 1 (31 janvier 2011) : 43–64. http://dx.doi.org/10.5194/sed-3-43-2011.

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Abstract. This paper reports the results from the accurate measurement of the acceleration of gravity g taken at two separate premises in the Polo Scientifico of the University of Firenze (Italy). In these laboratories, two separate experiments aiming at measuring the Newtonian constant and testing the Newtonian law at short distances are in progress. Both experiments require an independent knowledge on the local value of g. The only available datum, pertaining to the italian zero-order gravity network, was taken more than 20 years ago at a distance of more than 60 km from the study site. Gravity measurements were conducted using an FG5 absolute gravimeter, and accompanied by seismic recordings for evaluating the noise condition at the site. The absolute accelerations of gravity at the two laboratories are (980 492 160.6 ± 4.0) μGal and (980 492 048.3 ± 3.0) μGal for the European Laboratory for Non-Linear Spectroscopy (LENS) and Dipartimento di Fisica e Astronomia, respectively. Other than for the two referenced experiments, the data here presented will serve as a benchmark for any future study requiring an accurate knowledge of the absolute value of the acceleration of gravity in the study region.

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PAIK, HO JUNG, VIOLETA A. PRIETO et M. VOL MOODY. « INVERSE-SQUARE LAW EXPERIMENT IN SPACE ». International Journal of Modern Physics D 16, n^o 12a (décembre 2007) : 2181–90. http://dx.doi.org/10.1142/s0218271807011619.

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The objective of ISLES (Inverse-Square Law Experiment in Space) is to perform a null test of Newton's law in space with a resolution of 10 ppm or better at a 100 μm distance. ISLES will be sensitive enough to detect the axion, a dark matter candidate, with the strongest allowed coupling and probe large extra dimensions of string theory down to a few micrometers. The experiment will be cooled to < 2 K , which permits superconducting magnetic levitation of the test masses. This soft, low-loss suspension, combined with a low-noise SQUID, leads to extremely low intrinsic noise in the detector. To minimize Newtonian errors, ISLES employs a near-null source, a circular disk of large diameter-to-thickness ratio. Two test masses, also disk-shaped, are suspended on the two sides of the source mass at a nominal distance of 100 μm. The signal is detected by a superconducting differential accelerometer.

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Tringali, Maria C., Tomasz Bulik, Jan Harms, Irene Fiori, Federico Paoletti, Neha Singh, Bartosz Idzkowski et al. « Seismic array measurements at Virgo’s west end building for the configuration of a Newtonian-noise cancellation system ». Classical and Quantum Gravity 37, n^o 2 (19 décembre 2019) : 025005. http://dx.doi.org/10.1088/1361-6382/ab5c43.

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Broeck, Chris Van Den, et Anand S. Sengupta. « Phenomenology of amplitude-corrected post-Newtonian gravitational waveforms for compact binary inspiral : I. Signal-to-noise ratios ». Classical and Quantum Gravity 24, n^o 1 (22 novembre 2006) : 155–76. http://dx.doi.org/10.1088/0264-9381/24/1/009.

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Beker, M. G., G. Cella, R. DeSalvo, M. Doets, H. Grote, J. Harms, E. Hennes et al. « Improving the sensitivity of future GW observatories in the 1–10 Hz band : Newtonian and seismic noise ». General Relativity and Gravitation 43, n^o 2 (23 mai 2010) : 623–56. http://dx.doi.org/10.1007/s10714-010-1011-7.

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Rembold, Christopher M., Ankit D. Tejani, Marcia L. Ripley et Shaojie Han. « Paxillin phosphorylation, actin polymerization, noise temperature, and the sustained phase of swine carotid artery contraction ». American Journal of Physiology-Cell Physiology 293, n^o 3 (septembre 2007) : C993—C1002. http://dx.doi.org/10.1152/ajpcell.00090.2007.

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Histamine stimulation of swine carotid artery induces both contraction and actin polymerization. The importance of stimulus-induced actin polymerization is not known. Tyrosine phosphorylation of the scaffolding protein paxillin is thought to be an important regulator of actin polymerization. Noise temperature, hysteresivity, and phase angle are rheological measures of the fluidity of a tissue, i.e., whether the muscle is more a “Hookean solid” or a “Newtonian liquid.” Y118 paxillin phosphorylation, crossbridge phosphorylation, actin polymerization, noise temperature, hysteresivity, phase angle, real stiffness, and stress were measured in intact swine carotid arteries that were depolarized with high K+ or stimulated with histamine. The initial rapid force development phase of high-K+ or histamine-induced contraction was associated with increased crossbridge phosphorylation but no significant change in Y118 paxillin phosphorylation, actin polymerization, noise temperature, hysteresivity, or phase angle. This suggests that the initial contraction was caused by the increase in crossbridge phosphorylation and did not alter the tissue's rheology. Only after full force development was there a significant increase in Y118 paxillin phosphorylation and actin polymerization associated with a significant decrease in noise temperature and hysteresivity. These data suggest that some part of the sustained contraction may depend on stimulated actin polymerization and/or a transition to a more “solid” rheology. Supporting this contention was the finding that an inhibitor of actin polymerization, latrunculin-A, reduced force while increasing noise temperature/hysteresivity. Further research is needed to determine whether Y118 paxillin phosphorylation, actin polymerization, and changes in rheology could have a role in arterial smooth muscle contraction.

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Mohammadpour, M., S. Theodossiades et H. Rahnejat. « Dynamics and efficiency of planetary gear sets for hybrid powertrains ». Proceedings of the Institution of Mechanical Engineers, Part C : Journal of Mechanical Engineering Science 230, n^o 7-8 (10 juin 2015) : 1359–68. http://dx.doi.org/10.1177/0954406215590644.

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The paper presents a tribo-dynamic model for planetary gear sets of hybrid-electric-vehicle configurations. The model comprises a six degree-of-freedom torsional multi-body dynamic system, as well as a tribological contact model in order to evaluate the lubricant film thickness, friction and efficiency of the meshing gear teeth contacts. The tribological model takes into account the non-Newtonian, thermal-mixed elastohydrodynamic regime of lubrication. Analysis is performed for a hybrid electric C-segment vehicle. The simulated conditions correspond to cases of power supplied by either the engine or the electric motor. The results illustrate that in the electric motor drive mode, improved noise, vibration and harshness refinement would be expected, whereas better transmission efficiency is achieved in the internal combustion engine drive mode.

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Amann, Florian, Francesca Badaracco, Riccardo DeSalvo, Luca Naticchioni, Andrea Paoli, Luca Paoli, Paolo Ruggi et Stefano Selleri. « Tunnel Configurations and Seismic Isolation Optimization in Underground Gravitational Wave Detectors ». Applied Sciences 12, n^o 17 (2 septembre 2022) : 8827. http://dx.doi.org/10.3390/app12178827.

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The Einstein Telescope will be a gravitational wave observatory comprising six nested detectors, three optimized to collect low-frequency signals, and three for high frequency. It will be built a few hundred meters under Earth’s surface to reduce direct seismic and Newtonian noise. A critical issue with the Einstein Telescope design are the three corner stations, each hosting at least one sensitive component of all six detectors in the same hall. Maintenance, commissioning, and upgrade activities on a detector will cause interruptions of the operation of the other five, in some cases for years, thus greatly reducing the Einstein Telescope observational duty cycle. This paper proposes a new topology that moves the recombination and input–output optics of the Michelson interferometers, the top stages of the seismic attenuation chains and noise-inducing equipment in separate excavations far from the tunnels where the test masses reside. This separation takes advantage of the shielding properties of the rock mass to allow continuing detection with most detectors even during maintenance and upgrade of others. This configuration drastically improves the observatory’s event detection efficiency. In addition, distributing the seismic attenuation chain components over multiple tunnel levels allows the use of effectively arbitrarily long seismic attenuation chains that relegate the seismic noise at frequencies farther from the present low-frequency noise budget, thus keeping the door open for future upgrades. Mechanical crowding around the test masses is eliminated allowing the use of smaller vacuum tanks and reduced cross section of excavations, which require less support measures.

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Faller, James E. « Precision measurement, scientific personalities and error budgets : the sine quibus non for big G determinations ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 372, n^o 2026 (13 octobre 2014) : 20140023. http://dx.doi.org/10.1098/rsta.2014.0023.

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Determinations of the Newtonian constant of gravitation (big G ) fit into the oftentimes-unappreciated area of physics called precision measurement—an area which includes precision measurements, null experiments and determinations of the fundamental constants. The determination of big G —a measurement which on the surface appears deceptively simple—continues to be one of Nature's greatest challenges to the skills and cunning of experimental physicists. In spite of the fact that, on the scale of the Universe, big G 's effects are so large as to single-handedly hold everything together, on the scale of an individual research laboratory, big G 's effects are so small that they go unnoticed…hidden in a background of much larger forces and noise sources. It is this ‘smallness’ that makes determining the precise value of this (seemingly unrelated to the rest of physics) fundamental constant so difficult.

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Koley, Soumen, Maria Bader, Jo van den Brand, Xander Campman, Henk Jan Bulten, Frank Linde et Bjorn Vink. « Surface and underground seismic characterization at Terziet in Limburg—the Euregio Meuse–Rhine candidate site for Einstein Telescope ». Classical and Quantum Gravity 39, n^o 2 (11 janvier 2022) : 025008. http://dx.doi.org/10.1088/1361-6382/ac2b08.

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Abstract We present a detailed characterization of surface and underground seismic noise measured at Limburg in the south of the Netherlands. This location is the Euregio Meuse–Rhine candidate for hosting Einstein Telescope, a future observatory for gravitational waves. Seismic noise measurements were performed with an array of seismometers installed on the surface. Passive seismic methods like beamforming were used to extract the propagation wave types of ambient seismic noise and the Rayleigh-wave dispersion in the region. Subsurface shear-wave models sensitive to depths of 300 m were derived by using the Rayleigh-wave dispersion and ellipticity. Subsurface P-wave velocities to depths of 200 m were obtained from an active seismic survey. Wavepath Eikonal tomography was used on the source-receiver refracted-wave travel-times to obtain a subsurface P-wave velocity model. Both the passive and the active seismic data analysis point to the presence of a layered geology with a soft-soil to hard-rock transition occurring at a shallow depth of about 25 to 40 m. The surface arrays are complemented by two permanent tri-axial seismometers installed on the surface and in a borehole at 250 m depth. Their data are used to interpret the surface-wave and body-wave contributions to the observed seismic noise. We use a cross-correlation analysis and compute the theoretical surface-wave eigenfunctions to understand the contributions of the different wave types at different frequencies. We observe that below 4 Hz in the horizontal component and 9 Hz in the vertical component, the seismic noise at depth is dominantly due to surface waves. Above these frequencies a significant contribution can be attributed to both nearby and far-away body-wave sources. At a depth of 250 m we find that the surface noise power has been damped by up to a factor 104 above about 2 Hz. The Limburg geology with soft-soil on top of hard-rock efficiently damps the anthropogenic noise produced at the surface. This implies that Einstein Telescope’s test masses are shielded from anthropogenic seismic noise and construction at greater depth will not bring significant further improvements in this regard. A body-wave background has been identified that contributes about half of the total underground seismic noise at 250 m depth for frequencies above 4 Hz. It remains to be studied if subtraction schemes for Newtonian noise originating from this body-wave background will be necessary. Finally, we estimate an interferometer downtime of about 3% due to regional and teleseismic earthquakes. We believe this is acceptable as it is comparable to current experience at the LIGO and Virgo interferometer sites.

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Alejandro, A. C. B., A. T. Ringler, D. C. Wilson, R. E. Anthony et S. V. Moore. « Towards understanding relationships between atmospheric pressure variations and long-period horizontal seismic data : a case study ». Geophysical Journal International 223, n^o 1 (16 juillet 2020) : 676–91. http://dx.doi.org/10.1093/gji/ggaa340.

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SUMMARY Variations in atmospheric pressure have long been known to introduce noise in long-period (>10 s) seismic records. This noise can overwhelm signals of interest such as normal modes and surface waves. Generally, this noise is most pronounced on the horizontal components where it arises due to tilting of the seismometer in response to changes in atmospheric pressure. Several studies have suggested methodologies for correcting unwanted pressure-induced noise using collocated microbarograph records. However, how applicable these corrections are to varying geologic settings and installation types (e.g. vault versus post-hole) is unclear. Using coefficients obtained by solving for the residuals of these corrections, we can empirically determine the sensitivity of instruments in a specific location to the influences of pressure. To better understand how long-period, pressure-induced noise changes with time and emplacement, we examine horizontal seismic records along with barometric pressure at five different Global Seismographic Network stations, all with multiple broadband seismometers. We also analyse three Streckeisen STS-2 broadband seismometers, which are collocated with a microbarograph, at the Albuquerque Seismological Laboratory. We observe periods of high magnitude-squared-coherence (γ2-coherence; γ2 > 0.8) between the seismic and pressure signals which fluctuate through time, frequency, and even between seismic instruments in the same vault. These observations suggest that these tilt-generated signals are highly sensitive to very local (<10 m) site effects. However, we find that in cases where instruments are not located at a large depth (<100 m), the pressure-induced noise is polarized in a nearly constant direction that is consistent with local topographic features or the geometry of the vault. We also find that borehole instruments at a large depth (>100 m) appear to be unaffected by pressure-loading mechanisms outlined by Sorrells (1971) but possibly by Newtonian attraction. Correlating the induced-noise polarization direction with times of high coherence, we work to identify sensors that are ultimately limited by pressure-induced horizontal noise as well as period bands that can benefit from pressure corrections. We find that while the situation is complex, each sensor appears to have its own unique response to pressure. Our findings suggest that we can determine empirical relationships between pressure and induced tilt on a case by case basis.

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Kunz, Torben, et Richard J. Greatbatch. « Effect of the Kinematic Lower Boundary Condition on the Spectral and Autocorrelation Structure of Annular Variability in the Troposphere ». Journal of the Atmospheric Sciences 71, n^o 6 (30 mai 2014) : 2264–79. http://dx.doi.org/10.1175/jas-d-13-0104.1.

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Abstract The dynamical origin of the spectral and autocorrelation structure of annular variability in the troposphere is investigated by a deductive approach. Specifically, the structure of the power spectrum and autocorrelation function of the zonal-mean geopotential is analyzed for the case of a quasigeostrophic spherical atmosphere subject to a white noise mechanical forcing applied in a single Hough mode and concentrated at a particular level in the vertical, with vertically uniform Newtonian cooling and Rayleigh drag concentrated at a rigid lower boundary. Analytic expressions for the power spectrum are presented together with expressions for an approximate red noise (i.e., a Lorentzian-shaped) power spectrum. It is found that for an infinitely deep atmosphere the power spectrum can be well approximated by a red noise process for the first few Hough modes (associated with large Rossby heights), provided the distance from the forcing is not larger than about one Rossby height. When a frictional rigid lower boundary is included, however, the approximation is generally bad. The high-frequency part of the power spectrum exhibits near-exponential behavior and the autocorrelation function shows a transition from a rapid decay at short lags to a much slower decay at longer lags, if the thermal and mechanical damping time scales are sufficiently well separated. Since observed annular variability exhibits the same characteristics, the above results lead to the hypothesis that these characteristics may, to some extent, be intrinsic to the linear zonal-mean response problem—although the need for an additional contribution from eddy feedbacks is also implied by the results.

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Badaracco, F., J. Harms, A. Bertolini, T. Bulik, I. Fiori, B. Idzkowski, A. Kutynia et al. « Machine learning for gravitational-wave detection : surrogate Wiener filtering for the prediction and optimized cancellation of Newtonian noise at Virgo ». Classical and Quantum Gravity 37, n^o 19 (12 septembre 2020) : 195016. http://dx.doi.org/10.1088/1361-6382/abab64.

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Alaruri, Sami D. « Practical Methods for Characterizing the Optical Performance of Digital Camera-Based Imaging Systems ». International Journal of Electronics, Communications, and Measurement Engineering 9, n^o 1 (janvier 2020) : 31–45. http://dx.doi.org/10.4018/ijecme.2020010103.

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In this paper, practical and simple methods for characterizing the optical performance of a digital CCD camera equipped with a zoom lens using test targets projected by a Newtonian collimator coupled to an integrating sphere and a halogen light source are presented. The presented methods include the evaluation of the CCD camera system modulation transfer function (MTF), uniformity, dynamic range, linearity, and signal-to-noise ratio (S/N) properties in the visible region of the spectrum. Through out this work image processing for the recorded target images is performed using ImageJ. In addition, the paper presents a comparison between MTF measurements collected with a 1951-USAF resolution test target and a slanted edge test target. Finally, simple mathematical expressions for the measured optical system performance properties are provided. The presented optical system characterization methods can provide researchers with the needed data when a CCD or CMOS digital camera is integrated with a lens system.

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Noordin, A., M. A. M. Basri et Z. Mohamed. « Simulation and experimental study on PID control of a quadrotor MAV with perturbation ». Bulletin of Electrical Engineering and Informatics 9, n^o 5 (1 octobre 2020) : 1811–18. http://dx.doi.org/10.11591/eei.v9i5.2158.

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This paper presents a proportional-integral-derivative (PID) flight controller for a quadrotor micro air vehicle (MAV). The MAV (Parrot Mambo minidrones) is small, therefore, a slight perturbation will affect its performance. Hence, for the actuated dynamics, roll (ϕ), pitch (θ), yaw (ψ), and z stabilization, a PID control scheme is proposed. Furthermore, the same controller technique is also applied for under-actuated dynamics x and y position control. The newtonian model is simulated using simulink with a normal Gaussian noise of force as external disturbances. using simulink support package for Parrot Minidrones by MATLAB and based on the simulation parameter, the algorithm is deployed using Bluetooth® Low energy connection via personal area network (PAN). A slight force by hand is applied as perturbation during hovering to investigation system performances. Finally, the simulation and experimental on this commercial MAV, Parrot Mambo minidrones shows good performance of the flight controller scheme in the presence of external disturbances.

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Barrera-Hinojosa, Cristian, Baojiu Li et Yan-Chuan Cai. « Looking for a twist : probing the cosmological gravitomagnetic effect via weak lensing-kSZ cross-correlations ». Monthly Notices of the Royal Astronomical Society 510, n^o 3 (20 décembre 2021) : 3589–604. http://dx.doi.org/10.1093/mnras/stab3657.

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ABSTRACT General relativity predicts that the rotational momentum flux of matter twists the space–time via a vector gravitomagnetic (frame-dragging) field, which remains undetected in cosmology. This vector field induces an additional gravitational lensing effect; at the same time, the momentum field sources the kinetic Sunyaev–Zel’dovich (kSZ) effect. The common origin of these two effects allows us to probe the gravitomagnetic signal via their cross-correlations. In this paper, we explore the possibility of detecting the gravitomagnetic field in Λ cold dark matter by cross-correlating the weak-lensing convergence field with the cosmic microwave background (CMB) temperature map, which is imprinted with the kSZ signal. This approach allows us to extract the gravitomagnetic effect because the cross-correlation between the standard Newtonian contribution to the weak-lensing convergence field, $\kappa _\Phi$, and the kSZ effect is expected to vanish. We study the cross-correlations with a suite of large-volume Newtonian N-body simulations and a small-volume, high-resolution, general-relativistic counterpart. We show that insufficient simulation resolution can introduce significant spurious correlations between $\kappa _\Phi$ and kSZ. From the high-resolution simulation, we find that the cumulative signal-to-noise ratio (SNR) of the kSZ-gravitomagnetic convergence field can reach almost 15 (30) at ℓ ≃ 5000 (104) for the lensing source redshift zs = 0.83, if only cosmic variance is considered. We make forecast for next-generation lensing surveys such as euclid and lsst, and CMB experiments such as Simons Observatory and cmb-s4, and find that, for zs = 1.4, the cumulative SNR can exceed 5 (9) at ℓ ≃ 5000 (104), indicating that the cosmological gravitomagnetic effect can be detected, if several foreground contaminations can be removed.

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HIRSA, A. H., J. M. LOPEZ et R. MIRAGHAIE. « Determination of surface shear viscosity via deep-channel flow with inertia ». Journal of Fluid Mechanics 470 (31 octobre 2002) : 135–49. http://dx.doi.org/10.1017/s002211200200191x.

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Results of an experimental and computational study of the flow in an annular region bounded by stationary inner and outer cylinders and driven by the rotation of the floor are presented. The top is a flat air/water interface, covered by an insoluble monolayer. We develop a technique to determine the surface shear viscosity from azimuthal velocity measurements at the interface which extends the range of surface shear viscosity that can be measured using a deep-channel viscometer in the usual Stokes flow regime by exploiting flow inertia. A Navier–Stokes-based model of bulk flow coupled to a Newtonian interface that has surface shear viscosity as the only interfacial property is developed. This is achieved by restricting the flow to regimes where the surface radial velocity vanishes. The use of inertia results in an improved signal-to-noise ratio of the azimuthal velocity measurements by an order of magnitude beyond that available in the Stokes flow limit. Measurements on vitamin K1 and stearic acid monolayers were performed, and their surface shear viscosities over a range of concentrations are determined and found to be in agreement with data in the literature.

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Wagg, T., K. Breivik et S. E. de Mink. « LEGWORK : A Python Package for Computing the Evolution and Detectability of Stellar-origin Gravitational-wave Sources with Space-based Detectors ». Astrophysical Journal Supplement Series 260, n^o 2 (1 juin 2022) : 52. http://dx.doi.org/10.3847/1538-4365/ac5c52.

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Abstract We present LEGWORK (LISA Evolution and Gravitational Wave Orbit Kit), an open-source Python package for making predictions about stellar-origin gravitational-wave sources and their detectability in LISA or other space-based gravitational-wave detectors. LEGWORK can be used to evolve the orbits of sources due to gravitational-wave emission, calculate gravitational-wave strains (using post-Newtonian approximations), compute signal-to-noise ratios, and visualize the results. It can be applied to a variety of potential sources, including binaries consisting of white dwarfs, neutron stars, and black holes. Although we focus on double compact objects, in principle LEGWORK can be used for any system with a user-specified orbital evolution, such as those affected by a third object or gas drag. We optimized the package to make it efficient for use in population studies, which can contain tens of millions of sources. This paper describes the package and presents several potential use cases. We explain in detail the derivations of the expressions behind the package as well as identify and clarify some discrepancies currently present in the literature. We hope that LEGWORK will enable and accelerate future studies triggered by the rapidly growing interest in gravitational-wave sources.

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LeDesma, C. K., M. P. Ross, B. E. Daly, C. D. Hoyle et M. M. Mola. « A modified Michelson interferometer to measure sub-milliradian changes in angle ». AIP Advances 12, n^o 8 (1 août 2022) : 085002. http://dx.doi.org/10.1063/5.0100720.

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Modern short-range gravity experiments that seek to test the Newtonian inverse-square law or weak equivalence principle of general relativity typically involve measuring the minute variations in the twist angle of a torsion pendulum. Motivated by various theoretical arguments, recent efforts largely focus on measurements with test mass separations in the sub-millimeter regime. To measure the twist, many experiments employ an optical autocollimator with a noise performance of ∼300 nrad[Formula: see text] in the 0.1–10 mHz band, enabling a measurement uncertainty of a few nanoradians in a typical integration time. We investigated an alternative method for measuring a small twist angle through the construction of a modified Michelson interferometer. The main modification is the introduction of two additional arms that allow for improved angular alignment. A series of detectors and LabView software routines were developed to determine the orientation of a mirror attached to a sinusoidally driven rotation stage that oscillated with an amplitude of 0.35 mrad and a period of 200 s. In these measurements, the resolution of the interferometer is 8.1 μrad per fringe, while its dynamic range spanned 0.962 mrad. We compare the performance of this interferometric optical system to existing autocollimator-based methods, discussing its implementation, possible advantages, and future potential, as well as disadvantages and limitations.

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Seoane, Lucía, Guillaume Ramillien, Benjamin Beirens, José Darrozes, Didier Rouxel, Thierry Schmitt, Corinne Salaün et Frédéric Frappart. « Regional Seafloor Topography by Extended Kalman Filtering of Marine Gravity Data without Ship-Track Information ». Remote Sensing 14, n^o 1 (31 décembre 2021) : 169. http://dx.doi.org/10.3390/rs14010169.

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An iterative Extended Kalman Filter (EKF) approach is proposed to recover a regional set of topographic heights composing an undersea volcanic mount by the successive combination of large numbers of gravity measurements at sea surface using altimetry satellite-derived grids and taking the error uncertainties into account. The integration of the non-linear Newtonian operators versus the radial and angular distances (and its first derivatives) enables the estimation process to accelerate and requires only few iterations, instead of summing Legendre polynomial series or using noise-degraded 2D-FFT decomposition. To show the effectiveness of the EKF approach, we apply it to the real case of the bathymetry around the Great Meteor seamount in the Atlantic Ocean by combining only geoid height/free-air anomaly datasets and using ship-track soundings as reference for validation. Topography of the Great Meteor seamounts structures are well-reconstructed, especially when regional compensation is considered. Best solution gives a RMS equal to 400 m with respect to the single beam depth observations and it is comparable to RMS obtained for ETOPO1 of about 365 m. Larger discrepancies are located in the seamount flanks due to missing high-resolution information for gradients. This approach can improve the knowledge of seafloor topography in regions where few echo-sounder measurements are available.

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