Force Noise Research Articles

Explicit analytical form for memory kernel in the generalized Langevin equation for end-to-end vector of Rouse chains.

The generalized Langevin equation (GLE) provides an attractive theoretical framework for investigating the dynamics of conformational fluctuations of polymeric systems. While the memory kernel is a central function in the GLE, explicit analytical forms for this function have been challenging to obtain, even for the simple models of polymer dynamics. Here, we achieve an explicit analytical expression for the memory kernel in the GLE for the end-to-end vector of Rouse chains in the overdamped limit. Our derivation takes advantage of the finding that the dynamics of the end-to-end vector of Rouse chains with both free ends are equivalent to those of Rouse chains with one free end and the other fixed. For the latter model, we first show that the equations of motion of the Rouse modes as well as their statistical properties can be obtained under the boundary conditions where the free end is held fixed temporarily. We then analytically solve the terms associated with intrachain interactions in the GLE. By formally comparing these terms with the GLE based on the Rouse modes, we obtain an explicit expression for the memory kernel, along with analytical forms for the potential field and the random colored noise force. Our analytical memory kernel is confirmed by numerical calculations in the Laplace space and is shown to yield asymptotic behaviors that are consistent with previous studies. Finally, we utilize our analytical result to simulate the cyclization dynamics of Rouse chains and discuss the scaling of the cyclization time with chain length.

Study on parameter optimization of noise-vibration-force-metal removal rate in TC4 titanium alloy milling

Aiming at the influence of noise, vibration, and force on machining efficiency and machining quality in the process of milling, this paper proposed an improved particle swarm optimization algorithm. The algorithm could optimize the multi-objective and multi-parameter integration model and obtain the optimal milling parameters under the specified milling conditions, so as to reduce milling noise, vibration, and force and improve machining efficiency. First, based on the theory of all factor experiment, the milling experiment of TC4 titanium alloy was carried out, and the relevant milling noise, vibration, and force signals were obtained. Then, based on the response surface analysis method, the influence of milling parameters on noise, vibration, and force was studied. Finally, a multi-objective optimization model based on maximum metal removal rate, minimum noise, minimum vibration, and minimum force was established, and the improved particle swarm optimization algorithm was used to solve the optimal milling parameters. The result shows that when the milling speed is 24.9588 m/min, the feed speed is 9.9324 mm/min, and the milling depth is 1 mm, the optimal milling state within the constraint conditions can be achieved.

Living biotechnical lives: noise, parasites, and relational practices

Life in the era of biotechnology opens up opportunities but also poses challenges related to our values ​​and questions regarding the way we want to see coexistence on our planet, which is inhabited by many species. The parasite is our case study and an interesting concept that we inherit from biology but which is also addressed in humanism and philosophy. As humans, we commonly understand the concept of a parasite as a negative one that suggests someone or something which benefits at our expense. However, French philosopher Michel Serres had a different view of the parasite. According to him, the parasite is based on relationships between different entities, and there is often noise in these relationships. Serres refers to biologist Henri Atlan, who has argued that said noise forces the system to reorganize itself in a way that incorporates the noise into the complex system. The idea of ​​noise as an integrated part of the system is quite far from today’s thought processes with the development of bio/technology that typically aims to be noiseless and error-free and have aesthetically attractive results. Therefore, although parasites are often associated with terms such as inhospitable, undesirable, and disgusting and are seen to be located outside of art and technology, in this paper, we argue that the concept of something parasitical is tightly intertwined with our contemporary biotechnical lives. The article relates Serres’ parasitic thinking to an artistic mediation of the biological parasite: the tick.

Towards the understanding of wheel-rail flange squeal: In-situ experiment and genuine 3D profile-enhanced transient modelling

Wheel-rail squeal noise during train turning has been a tricky problem influencing passengers and nearby residents. The tonal curve squeal that mainly occurs at the inner rail has been extensively studied, while the broadband flange squeal that takes place at the outer rail that can be equally annoying is seldom mentioned and hardly investigated. This paper presents a study aiming at understanding the mechanism of wheel-rail flange squeal from phenomenon to the underlying source. The study systematically demonstrates the connection between the observed wheel-rail flange squeal noise and contact force, with measurements taken from a series of well-controlled in-situ experiments on an operating metro line, and numerical simulations. An integrated transient model consisting of three submodels on train dynamics, rail dynamics, and wheel-rail contact incorporating genuine 3D surface irregularities is developed specifically for flange squeal analysis. The developed model can reproduce the characteristics of flange squeal and correlates wheel-rail contact force with the flange squeal noise with satisfactory performance. Features of flange squeal under four-speed levels corresponding to in-situ experiments are reappeared from global dynamics to local contact status. An explanation of the generation mechanism of flange squeal is proposed by measurement observation and confirmed through the proposed model with multiple influencing key factors, including train speed, contact position, shape of contact patch, contact creepages, and wheel and rail irregularities. The present study is expected to establish a footstone for the mechanism comprehension of flange squeal and inspire further research in this area.

Effects of Remote Boundary Conditions on Clamping Loss in Micromechanical Resonators

Clamping loss in micromechanical resonators can strongly depend on the boundary conditions far away from the actual vibrating structure because the acoustic wavelength greatly exceeds the device dimensions. We demonstrate a scheme for post-fabrication tuning of the clamping loss in flexural-mode and bulk-mode resonators by modifying the boundary conditions of the chip with the frame. The measured quality factor increases by more than an order-of-magnitude for the microcantilevers and more than a factor of three for the bulk-mode resonators when frame contact is minimized via suspension of the chip by wirebonds. We propose a two-degree-of-freedom fluctuation-dissipation model to describe the thermomechanical noise and forced response in the presence of this tunable anchor damping. By studying the thermomechanical displacement spectrum with tunable clamping loss, we show that variable clamping loss tunes the mechanical quality factor, modifying both the resonator transfer function and thermomechanical noise force. We delineate the dependence of the tunable clamping loss mechanism on microcantilever beam length and ambient temperature from 300 K down to 40 K, and observe potential temperature dependence to clamping loss with reducing temperature. [2021-0141]

Intensity changes of Indian Ocean dipole mode in a carbon dioxide removal scenario

The Indian Ocean Dipole/Zonal mode (IOD) is an interannual phenomenon over the tropical Indian Ocean, causing a pronounced impact worldwide. Here, we investigate the mechanism of the change in IOD characteristics in a CO2 removal simulation for an earth system model (ESM). As the CO2 concentration increases, the intensity of IOD tends to increase, but at high CO2 concentrations, further increases decrease the IOD intensity. The minimum IOD amplitude was recorded during the early decrease in CO2. First, we developed a conceptual model for IOD that is composed of local air-sea coupled feedback, delayed ocean dynamics, El Niño impact, and noise forcing. Then, by adopting ESM results into this simple IOD model, we revealed that the local air–sea coupled feedback is a major factor for changing IOD amplitude, while El Niño does not exert a change in IOD amplitude. The local air–sea coupled feedback including thermocline feedback, wind-evaporation feedback, and Ekman feedback is strongly modified by the air–sea coupling strength during progression of a global warming. Consequently, under the higher CO2 concentrations, IOD amplitude is reduced due to the weakening of air-sea coupling over tropical Indian Ocean.

Most probable transition paths in eutrophicated lake ecosystem under Gaussian white noise and periodic force

The effects of stochastic perturbations and periodic excitations on the eutrophicated lake ecosystem are explored. Unlike the existing work in detecting early warning signals, this paper presents the most probable transition paths to characterize the regime shifts. The most probable transition paths are obtained by minimizing the Freidlin–Wentzell (FW) action functional and Onsager–Machlup (OM) action functional, respectively. The most probable path shows the movement trend of the lake eutrophication system under noise excitation, and describes the global transition behavior of the system. Under the excitation of Gaussian noise, the results show that the stability of the eutrophic state and the oligotrophic state has different results from two perspectives of potential well and the most probable transition paths. Under the excitation of Gaussian white noise and periodic force, we find that the transition occurs near the nearest distance between the stable periodic solution and the unstable periodic solution.

Asymptotic analysis for a Vlasov–Fokker–Planck/Navier–Stokes system in a bounded domain

We study an asymptotic analysis of a coupled system of kinetic and fluid equations. More precisely, we deal with the nonlinear Vlasov–Fokker–Planck equation coupled with the compressible isentropic Navier–Stokes system through a drag force in a bounded domain with the specular reflection boundary condition for the kinetic equation and homogeneous Dirichlet boundary condition for the fluid system. We establish a rigorous hydrodynamic limit corresponding to strong noise and local alignment force. The limiting system is a type of two-phase fluid model consisting of the isothermal Euler system and the compressible Navier–Stokes system. Our main strategy relies on the relative entropy argument based on the weak–strong uniqueness principle. For this, we provide a global-in-time existence of weak solutions for the coupled kinetic-fluid system. We also show the existence and uniqueness of strong solutions to the limiting system in a bounded domain with the kinematic boundary condition for the Euler system and Dirichlet boundary condition for the Navier–Stokes system.

Quantum Entanglement and its Quantification in a Two-Mode Cascade Laser

In this paper, quantum entanglement of correlated two-mode light generated by a three-level laser coupled to a two-mode squeezed vacuum reservoir is thoroughly analyzed using different inseparability criteria, using the master equation, we obtain the stochastic dierential equation and the correlation properties of the noise forces associated with the normal ordering. Next, we study the photon entanglement by considering different inseparability criteria. In particular, the criteria applied are Duan-Giedke-Cirac-Zoller (DGCZ) criterion, logarithmic negativity, Hillery-Zubairy, and Cauchy-Schwartz inequality and we found that the presence of the squeezing parameter leads to an increase in the degree of entanglement. Moreover, the linear gain coecient significantly achieved the degree of entanglement for the cavity radiation

Global Dynamics for the Two-dimensional Stochastic Nonlinear Wave Equations

AbstractWe study global-in-time dynamics of the stochastic nonlinear wave equations (SNLW) with an additive space-time white noise forcing, posed on the two-dimensional torus. Our goal in this paper is two-fold. (1) By introducing a hybrid argument, combining the $I$-method in the stochastic setting with a Gronwall-type argument, we first prove global well-posedness of the (renormalized) cubic SNLW in the defocusing case. Our argument yields a double exponential growth bound on the Sobolev norm of a solution. (2) We then study the stochastic damped nonlinear wave equations (SdNLW) in the defocusing case. In particular, by applying Bourgain’s invariant measure argument, we prove almost sure global well-posedness of the (renormalized) defocusing SdNLW with respect to the Gibbs measure and invariance of the Gibbs measure.

Lateral Resistance Requirement of Girder-Sleeper Fastener for CWR Track on an Open-Deck Steel Plate Girder Bridge

For an open-deck steel plate girder railway bridge with rail joints, frequent damage to the bridge members and a high level of noise and vibration occur. By installing continuous welded rail (CWR) to the bridge, it is possible to reduce the noise and impact force of the bridge. However, current girder–sleeper fasteners have low lateral resistance in nature and track buckling can occur when CWR is used on such a bridge. Therefore, a new girder-sleeper fastener with proper lateral resistance to prevent CWR track buckling is needed. In this study, the lateral resistance requirements of a girder-sleeper fastener are investigated through a series of finite element (FE) analyses and parametric study. The effect of peak lateral resistance of the fastener, curve radius, girder length, and lateral displacement of girder are examined. From the analysis results, the peak lateral resistance criterion of the girder–sleeper fastener is proposed for the design of a new fastener for CWR tracks on an open-deck steel plate girder bridge.

Quasi-Markovian property of strong wave turbulence.

This paper is concerned with the reduced-order modeling of the strongly nonlinear wave turbulence system. The motivation for such an attempt comes from the utility of the probabilistic coarse-grained model in facilitating the theoretical and numerical analysis of the true dynamical system model. One typical practice of simplifying the complex physical model is, in the spirit of Brownian motion, to replace the nonlinear interactions by white noise forcing and linear dissipation. For the case of slowly varying longwave, the resulting Markov process is an accurate approximate model. However, this conventional scheme is highly inappropriate for the description of shortwaves because the rapidly varying turbulent signal acquires a significantly non-Markovian character resulting from the poor timescale separation between the relevant mode and the environmental wave field. To resolve the issue, we discuss a simplification technique for which the central concept is the quasi-Markovian property; a non-Markov stochastic process is referred to as quasi-Markovian if it can be represented as a component of Markovian system made by adding a finite number of auxiliary variables. Our contribution in this work is to single out the nontrivial and near resonances from the nonlinear interactions in search of the auxiliary variable. We perform a comparison analysis of the autocorrelation matrices of the true and approximate models, and numerically demonstrate the effectiveness of our Markovian formulation of the inherently non-Markov turbulent signal.

Experimental Verification of Acoustic Noise and Radial Force Sum Variation in Switched Reluctance Motor

Acoustic noise reduction is one of the main topics of switched reluctance motor (SRM) developments. One of the effective methods is flattening three-phase radial force sum. This method is verified in experiments by optimizing the current profile. Novel current waveforms have been proposed recently for acoustic noise reduction without sacrificing the efficiency in the 18/12 SRM, which has competitive power density, torque density, peak efficiency, and outer dimensions compared with the permanent magnet motor employed in hybrid electric vehicles. In this article, electro-mechanical analysis and acoustic analysis are carried out to verify acoustic noise reduction in the 18/12 SRM. The relationship between radial force sum F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rsum</sub> , torque ripple T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rip</sub> , and acoustic noise is investigated. Experimental confirmation is also included.

Stochastic modelling of a noise-driven global instability in a turbulent swirling jet

Abstract

Global well posedness of the two-dimensional stochastic nonlinear wave equation on an unbounded domain

We study the two-dimensional wave equation with cubic nonlinearity posed on R2 with space-time white noise forcing. After a suitable renormalisation of the nonlinearity, we prove global well-posedness for this equation for initial data in Hs, s>45.

Random pullback and uniform exponential attractors for stochastic non-autonomous Navier-Stokes equations

We first prove the existence of a random pullback exponential attractor for the 2D Navier-Stokes equation with additive noise and non-autonomous forcing. Then, we introduce the definition and existence conditions of a random uniform exponential attractor for a jointly continuous non-autonomous random dynamical system, and prove the existence of a random uniform exponential attractor for the 2D Navier-Stokes equation with additive noise and quasi-periodic external forces.

Deterministic force-free resonant activation

The combined action of noise and deterministic force in dynamical systems can induce resonant effects. Here, we demonstrate a minimal, deterministic force-free setup allowing for the occurrence of resonant, noise-induced effects. We show that in the archetypal problem of escape from finite intervals driven by α-stale noise with a periodically modulated stability index, depending on the initial direction of the modulation, resonant-activation-like or noise-enhanced-stability-like phenomena can be observed. Consequently, in comparison to traditional Lévy flights, Lévy flights with a time-dependent jump length exponent are capable of facilitating or slowing down the escape from finite intervals in an analogous way, such as the modulation of the potential in the resonant activation setup.

Pullback random attractors of stochastic strongly damped wave equations with variable delays on unbounded domains

&lt;abstract&gt;&lt;p&gt;In this paper, we consider the asymptotic behavior of solutions to stochastic strongly damped wave equations with variable delays on unbounded domains, which is driven by both additive noise and deterministic non-autonomous forcing. We first establish a continuous cocycle for the equations. Then we prove asymptotic compactness of the cocycle by tail-estimates and a decomposition technique of solutions. Finally, we obtain the existence of a tempered pullback random attractor.&lt;/p&gt;&lt;/abstract&gt;

On the Formation Mechanism of the Seasonal Persistence Barrier

AbstractThe mechanism of the seasonal persistence barrier (SPB) is studied in the framework of an autoregressive (AR) model. In contrast to the seasonal variance, whose minimum is modulated mainly by the minimum growth rate or noise forcing, the SPB is caused primarily by the declining growth rate or increasing noise forcing, instead of the minimum/maximum of the growth rate or noise forcing. In other words, the SPB is caused by the declining signal-to-noise ratio (SNR) rather than the weakest SNR. In a weakly damped system, the phase of the SPB is delayed from that of declining SNR by about a season. The mechanism is further applied to explain the observed SST variability in the tropical and North Pacific. For the tropical Pacific, the spring SPB could be caused by the decreasing growth rate from September to March and weak annual mean damping rate, instead of the minimum growth rate in spring. Over the North Pacific, the increasing noise forcing from March to June may lead to the summer SPB. Our mechanism provides a null hypothesis for understanding the SPB of climate variability.

Measurement instrumentation and selected signal processing techniques for anomalous diffusion analysis

Anomalous diffusion phenomena are ubiquitous in many areas, including physics, biology, medicine, climate and also financial markets. The description and analysis of this phenomena are challenging tasks. To fully define the anomalous diffusion and properly understand its nature there is need to combine the skills in advanced sensing techniques, mathematical and statistical knowledge of the corresponding theoretical processes and the experience in physical interpretation of this phenomena. The paper reviews on the measurement instrumentation and signal processing used for detection and description of anomalous diffusion regimes. What is more, estimation of the anomalous diffusion exponent is commented. We present here four methods based on the statistics commonly used in the analyzed problem. Finally the fractional Brownian motion (FBM) is proposed as an analog proper for reliable depiction of properties valid for observed anomalous diffusion phenomena. Simulation studies exhibit the scenario of Hurst exponent estimation in the FBM model when the additive noise of various amplitudes disturbance is added to a simulated trajectory of individual particle. Proposed algorithms have different efficiency depending on the model parameters. This implicates a need to provide more advanced analysis and introduce new methods that could be less sensitive to the measurement noise and/or external forces of noise character. This paper is the starting point for the complete description of the anomalous diffusive processes. It presents the areas for prospective applications of the original sensing techniques but also highlights the needs in a range of statistical and intelligent signal processing suitable for description of the small scale complex systems during the SPT experiment.