Miracle-dz/UniFAR-FTUs huggingface dataset:
Nonlinearity in Structural Dynamics: Detection, Identification and Modelling

Summary chapter and guidelines on nonlinear procedures: Flow diagrams. Why not dynamical systems theory. Summary of linear system theory: Continuous-time. Discrete-time. Dynamic testing of linear and nonlinear structures: Simple procedures for detecting nonlinearity in dynamic testing. Sine, Chirp, Random, Impulse etc. Linearisation. Correlations-coherence. FRFs of linear and nonlinear systems: Harmonic balance. Averaging methods. Nyquist plots. Carpet plots. MDOF systems. Hilbert transform - a practical approach: Definition in terms of odd/even functions. Time-frequency domain definitions. Computation - fast method. Correction terms. Principal component analysis. Corehence. Damping estimation (Khalid's work). Linearisation from random testing. Spectral moments. Hilbert transform - a complex analytical approach: Contour integrals. Titchmarsh's theorem. Artificial noncausality. Correction for asymptotic behaviour. Viscous v. Hysteretic damping - exponential integrals. Pole-zero decomposition - estimation without truncation. Restoring force surfaces and direct parameter estimation: Masri/Caughey theory. Link models/Khalids approach. Application requirements - integration/differentiation of data. Least-squares estimation: Normal equations. Orthogonal estimator. SVD. Recursive LS. - forgetting factors. Discrete-time methods: NARMAX. AVD. Model validity. Functional series: Volterra series. Existence, uniqueness, convergence. Connection with Green's functions - calculation - symmetries. Fliess/Lamnabhi power series approach. Wiener series - high-dimensional correlations - Volterra limit. Higher order FRFs/Transfer functions: Harmonic probing. Interpretaton. SDOF/MDOF systems. Hypercurve fitting (S. Gifford). Convergence revisited (Dr Lee). Neural networks: Multi-layer perceptrons. Radial basis functions. Modelling nonlinear systems. Dynamics neurons. Networks as nonlinear dynamical systems. Classification of nonlinear systems: Pattern recognition/feature extraction. Wigner-Ville distribution. Wavelet transform. Neural networks. FRFs for classification SDOF/MDOF. Nonlinear least-squares: Piecewise-linear systems. Hysteretic systems. Yar/Hammond - GA parameter estimation. Gradient descent - shock absorber model.
Resonantly pumped optical pumping injection cavity lasers

An optical parametric oscillator is tuned to the resonance wavelength of the etalon in an optical pumping injection cavity (OPIC) laser with a type-II “W” active region, thereby minimizing the threshold pump intensity and maximizing the output slope efficiency. Previous OPIC experiments employed fixed-wavelength sources with only limited tuning available by adjusting the incident angle. Low threshold pump intensities of 330W∕cm2 at 100K and 14kW∕cm2 at 300K (where the output wavelength is 3200nm) were achieved. The energy conversion efficiency is found to decrease by over a factor of 100 when the pump wavelength is tuned from the resonance condition (1822nm at 300K) to only slightly off resonance (e.g., 1808nm).
A dynamic animation engine for generic spline objects

This paper introduces an accurate and efficient engine whose purpose is the dynamic animation of curvilinear objects which are modelled as successions of splines. At each time step the object shape conforms to its spline definitions, thus ensuring that each property implied by the chosen spline models is verified. This is achieved by animating spline control points. However, these control points are not considered as material points but rather as the degrees of freedom of the continuous object. The chosen dynamic equations (Lagrangian formalism) reflect this modelling scheme and yield an exact and very proficient linear system. In the chosen formalism, forces are introduced by either their potential energy or their power ratings in the virtual movements instilled by the degrees of freedom. Both methods are carried out in three cases: gravity, viscosity and generic force. Suitable and classical methods for constraint handling and numerical resolution are briefly discussed. Finally, this animation engine is applied to knitted patterns. Copyright © 2000 John Wiley & Sons, Ltd.
Effects of encounters with field stars on the evolution of low-mass semidetached binaries

Consequences of close encounters on the binary parameters and on the mass transfer rate and its stability are discussed. Thousands of numerical experiments have been performed in order to obtain accurate cross sections for inducing eccentricity in binaries with initially circular orbits. Analytic formulae are presented relating the radius excess of the secondary component over its Roche lobe to the mass transfer rate, for two extreme models of mass outflow: adiabatic and isothermal. Mass transfer is found to be stable even if there is no angular momentum transferred from the disk around the primary component back into binary orbit, provided the mass ratio M/sub 1//M/sub 2/>4.6. It is not likely that close encounters significantly affect the evolution of bright globular cluster X-ray sources, unless central densities in the cores of those clusters are much higher than commonly believed.
MAGNETIC FIELD LINE RANDOM WALK FOR DISTURBED FLUX SURFACES: TRAPPING EFFECTS AND MULTIPLE ROUTES TO BOHM DIFFUSION

The magnetic field line random walk (FLRW) is important for the transport of energetic particles in many astrophysical situations. While all authors agree on the quasilinear diffusion of field lines for fluctuations that mainly vary parallel to a large-scale field, for the opposite case of fluctuations that mainly vary in the perpendicular directions, there has been an apparent conflict between concepts of Bohm diffusion and percolation/trapping effects. Here computer simulation and non-perturbative analytic techniques are used to re-examine the FLRW in magnetic turbulence with slab and two-dimensional (2D) components, in which 2D flux surfaces are disturbed by the slab fluctuations. Previous non-perturbative theories for D⊥, based on Corrsin's hypothesis, have identified a slab contribution with quasilinear behavior and a 2D contribution due to Bohm diffusion with diffusive decorrelation (DD), combined in a quadratic formula. Here we present analytic theories for other routes to Bohm diffusion, with random ballistic decorrelation (RBD) either due to the 2D component itself (for a weak slab contribution) or the total fluctuation field (for a strong slab contribution), combined in a direct sum with the slab contribution. Computer simulations confirm the applicability of RBD routes for weak or strong slab contributions, while the DD route applies for a moderate slab contribution. For a very low slab contribution, interesting trapping effects are found, including a depressed diffusion coefficient and subdiffusive behavior. Thus quasilinear, Bohm, and trapping behaviors are all found in the same system, together with an overall viewpoint to explain these behaviors.
Design and finite-element analysis of an outer-rotor permanent-magnet generator for directly coupled wind turbines

This paper presents the design and finite-element analysis of a permanent-magnet generator using neodymium-iron-boron magnets for directly coupled wind turbines. For the sake of small size and light weight with extra low speed for direct coupling, the outer rotor structure is used. The simple magnetic equivalent circuit approach is used for initial design iteration, and the finite-element method is applied to analyze the detailed characteristics. Comprehensive experimental tests were conducted to verify the theoretical predictions. Agreement between the theoretical work and testing results was good.
Unknown transient detection using wavelets

We evaluate via numerical simulation the performance of a detection algorithm applicable to unknown transients in acoustic signals. This is a filter-then-detect scheme in which the filtering is accomplished by thresholding in the wavelet domain. The incoming time series is separated into 'signal' and 'noise' in the wavelet transform domain. The set of coefficients representing the 'signal' is inverse-transformed back to the time domain. An energy threshold is applied to the recovered signal time series. The performance of the wavelet filtering as a part of the detection process is determined by constructing the receiver-operating-characteristic curve, which displays the dependence of the probability of detection on the probability of false alarm as functions of an energy threshold.
Adjusting a Significance Test for Clustering in Designs With Two Levels of Nesting

A common mistake in analysis of cluster randomized experiments is to ignore the effect of clustering and analyze the data as if each treatment group were a simple random sample. This typically leads to an overstatement of the precision of results and anticonservative conclusions about precision and statistical significance of treatment effects. This article gives a simple adjustment to the t statistic that would be computed if clustering were (incorrectly) ignored in an experiment with two levels of nesting (e.g., classrooms and schools) where treatment assignment is made at the highest (e.g., school) level. The adjustment is a multiplicative factor depending on the number of clusters and subclusters, the cluster and subcluster sample sizes, and the cluster and subcluster intraclass correlations ρ S and ρ C . The adjusted t statistic has Student's t distribution with reduced degrees of freedom. The adjusted statistic reduces to the t statistic computed by ignoring clustering when ρ S = ρ C = 0. It reduces to the t statistic computed using cluster means when ρ S = 1. If ρ S and ρ C are between 0 and 1, the adjusted t statistic lies between these two and the degrees of freedom are in between those corresponding to these two extremes.
On the force fluctuations acting on a circular cylinder in crossflow from subcritical up to transcritical Reynolds numbers

Force measurements were conducted in a pressurized wind tunnel from subcritical up to transcritical Reynolds numbers 2.3 × 104 [les ] Re [les ] 7.1 × 106 without changing the experimental arrangement. The steady and unsteady forces were measured by means of a piezobalance, which features a high natural frequency, low interferences and a large dynamic range. In the critical Reynolds-number range, two discontinuous transitions were observed, which can be interpreted as bifurcations at two critical Reynolds numbers. In both cases, these transitions are accompanied by critical fluctuations, symmetry breaking (the occurrence of a steady lift) and hysteresis. In addition, both transitions were coupled with a drop of the CD value and a jump of the Strouhal number. Similar phenomena were observed in the upper transitional region between the super- and the transcritical Reynolds-number ranges. The transcritical range begins at about Re ≈ 5 × 106, where a narrow-band spectrum is formed with Sr(Re = 7.1 × 106) = 0.29.
Tropical Stationary Wave Response to ENSO: Diabatic Heating Influence on the Indian Summer Monsoon

AbstractThe atmospheric response to boreal summer tropical diabatic heating is studied in the atmospheric model component of the Community Atmosphere Model [CAM, version 3 (CAM3)] of the National Center for Atmospheric Research. An idealized heating function (with broad vertical but localized horizontal structure) is added to CAM3 near the equator; the circulation response is studied as a function of the sign of the heating and its longitude (Indian Ocean to eastern Pacific Ocean). The atmospheric circulation forced by the added heating interacts with all the physical and dynamical processes in CAM3; the total heating is the sum of the added heating and that produced by CAM3. In experiments using climatological sea surface temperature, added cooling (heating) over the Maritime Continent induces asymmetric anticyclonic (cyclonic) circulation extending toward India, opposing (reinforcing) the climatological monsoon flow and weakening (strengthening) the Indian monsoon. The anchoring of the anticyclonic (cyc.
The Neumann problem for nonlinear second order singular perturbation problems

Singularly perturbed second order elliptic partial differential equations with Neumann boundary conditions arise in many areas of application. These problems rarely have smooth limit solutions. In this paper, we characterize the limit solution for a wide class of such problems. We also give an abstract rate of convergence theorem and apply the abstract theorem to certain finite difference approximations.
Asymptotic Integration of Linear Differential Equations Subject to Integral Smallness Conditions Involving Ordinary Convergence

The problem of asymptotic behavior of solutions of an nth order linear differential equation is reconsidered, and a result obtained by Hartman under integral smallness conditions requiring absolute integrability is shown to hold with most of the conditions stated in terms of ordinary integrability. Results of Fubini and Halanay for linear perturbations of nonoscillatory second order equations are similarly extended.
GEOMETRICALLY NON-LINEAR FREE VIBRATION OF FULLY CLAMPED SYMMETRICALLY LAMINATED RECTANGULAR COMPOSITE PLATES

Abstract The geometrically non-linear free vibration of thin composite laminated plates is investigated by using a theoretical model based on Hamilton's principle and spectral analysis previously applied to obtain the non-linear mode shapes and resonance frequencies of thin straight structures, such as beams, plates and shells (Benamar et al. 1991Journal of Sound and Vibration149 , 179–195; 1993, 164, 295–316; 1990 Proceedings of the Fourth International Conference on Recent Advances in Structural Dynamics, Southampton; Moussaoui et al. 2000 Journal of Sound and Vibration232, 917–943 [1–4]). The von Karman non-linear strain–displacement relationships have been employed. In the formulation, the transverse displacement W of the plate mid-plane has been taken into account and the in-plane displacements U and V have been neglected in the non-linear strain energy expressions. This assumption, quite often made in the literature has been adopted in reference [2] and (El Kadiri et al. 1999 Journal of Sound and Vibration228, 333–358 [5]), in the isotropic case and has been mentioned here because the results obtained have been found to be in very good agreement with those based on the hierarchical finite element method (HFEM). In a previous study, it was assumed, based on the analogy with the isotropic case, that the fundamental carbon fibre reinforced plastic (CFRP) plate non-linear mode shape could be well estimated, by using nine plate functions, obtained as products of clamped–clamped beam functions in the x and y directions, symmetric in both the length U001and width directions [3]. In the present work, a convergence study has been performed and has shown that, although such an assumption may yield a good estimate for the non-linear resonance frequency, 18 plate functions should be taken into account instead of nine in the first non-linear mode shape and associated bending stress patterns calculations. This allows the anisotropy induced by the fibre orientations to be taken into account. Results are given for the fundamental mode of fully clamped CFRP rectangular plates, for various plate aspect ratios and vibration amplitudes. The non-linear mode shows a higher bending stress near the clamps at large deflection, compared with that predicted by linear theory. Some experimental measurements are presented which are in good qualitative agreement with the theory.
Impurity Transport in Alcator C-Mod Plasmas

Abstract Trace nonrecycling impurities (scandium and CaF2) have been injected into Alcator C-Mod plasmas in order to determine impurity transport coefficient profiles in a number of operating regimes. Recycling Ar has also been injected to characterize steady-state impurity density profiles. Subsequent impurity emission has been observed with spatially scanning X-ray and vacuum ultraviolet spectrometer systems, in addition to very high spatial resolution X-ray and bolometer arrays viewing the plasma edge. Measured time-resolved brightness profiles of helium-, lithium-, and beryllium-like transitions have been compared with those calculated from a transport code that includes impurity diffusion and convection, in conjunction with an atomic physics package for individual line emission. Similar modeling has been performed for the edge observations, which are unresolved in energy. The line time histories and the profile shapes put large constraints on the impurity diffusion coefficient and convection velocity profiles. In L-mode plasmas, impurity confinement times are short (~20 ms), with diffusivities in the range of 0.5 m2/s, anomalously large compared to neoclassical values. During Enhanced Dα (EDA) H-modes, the impurity confinement times are longer than in L-mode plasmas, and the modeling suggests that there exists inward convection (≤50 m/s) near the plasma edge, with greatly reduced diffusion (of order 0.1 m2/s), also in the region of the edge transport barrier. These edge values of the transport coefficients during EDA H-mode are qualitatively similar to the neoclassical values. In edge localized mode-free H-mode discharges, impurity accumulation occurs, dominated by large inward impurity convection in the pedestal region. A scaling of the impurity confinement time with H-factor reveals a very strong exponential dependence. In internal transport barrier discharges, there is significant impurity accumulation inside of the barrier foot, typically at r/a = 0.5. Steady-state impurity density profiles in L-mode plasmas have a large up-down asymmetry near the last closed flux surface. The impurity density enhancement, in the direction opposite to the ion B × ΔB drift, is consistent with modeling of neoclassical parallel impurity transport.
Weighted Norm Inequalities for Commutators of BMO Functions and Singular Integral Operators with Non-Smooth Kernels

The aim of this paper is to establish a sufficient condition for certain weighted norm inequalities for singular integral operators with non-smooth kernels and for the commutators of these singular integrals with BMO functions. Our condition is applicable to various singular integral operators, such as the second derivatives of Green operators associated with Dirichlet and Neumann problems on convex domains, the spectral multipliers of non-negative self-adjoint operators with Gaussian upper bounds, and the Riesz transforms associated with magnetic Schrödinger operators.
Domain-wall eddy-current loss in a stripe domain structure of Si-Fe crystals inclined slightly from the perfect

The fundamental relationship between the domain structure and the eddy current loss of a cube-on-edge Si-Fe single crystal whose angle of inclination of the [001] axis to a specimen surface is small is clarified. A model domain structure shows that the perpendicular component of magnetization which appears from this inclination affects the domain width, the permeability, and the eddy current loss. The dependence of iron losses on angle of inclination observed in specimens having some inclination from the ideal cube-on-edge orientation is elucidated by a newly proposed idea. This idea suggests the existence of the in-plane eddy current component due to a change of magnetization in the direction perpendicular to the specimen surface.
Destabilizing effects of confinement on homogeneous mixing layers

The absolute and convective instability properties of plane mixing layers are investigated for linearized inviscid disturbances. It is shown that confinement by plates parallel to the flow can enhance the absolute instability so much that even a co-flow plane mixing layer becomes absolutely unstable when the ratio of distances of the plates from the mixing layer lies in a certain range. Even when the plates are placed equidistantly from the mixing layer, a co-flow mixing layer can become absolutely unstable if the velocity profile has an asymmetry about its mid-plane. ‘Semiconfinement’, where a plate is only added to one side of the mixing layer, is also investigated. A substantial destabilization is possible when the plate is added on the side of the faster stream. Previous investigations seem only to have found absolute instability when the streams flow in opposite directions.
Sol-gel prepared β-Ga2O3 thin films for ultraviolet photodetectors

β-Ga2O3 thin films have been prepared on (0001) sapphire substrates by the sol-gel method. X-ray diffraction showed that β-Ga2O3 polycrystalline films were formed at heat-treatment temperatures above 600°C. With increasing heat-treatment temperature above 900°C, the lattice constants of the β-Ga2O3 films decreased, while the band gap increased. Planar geometry photoconductive detectors based on the sol-gel prepared β-Ga2O3 thin films have been fabricated. They showed the photoresponse only for the wavelengths shorter than 270nm, which correspond to the solar-blind region. The peak wavelength in the spectral response depended on the heat-treatment temperature in the sol-gel process.
Compressibility and cyclotron damping in the oblique Alfvén wave

Compressibility, magnetic compressibility, and damping rate are calculated for the obliquely propagating Alfven shear wave in high- and low-beta Vlasov plasmas. There is an overall increase in compressibility as beta is reduced from β = 1 to β≪1. For high obliquity θ and low frequency (ω≪Ωp) the compressibility C follows a k² wave number dependence; for high θ and low β the approximation C(k) ≈ kn² ≡ (kVA/Ωp)² holds for wave numbers up to the proton cyclotron resonance, where Ωp is the proton cyclotron frequency and VA is the Alfven velocity. Strong proton cyclotron damping sets in at kn of the order of unity; the precise kn position of the damping cutoff increases with decreasing β and increasing θ. Hence compressibility can exceed unity near the damping cutoff for high-θ waves in a low-β plasma. The magnetic compressibility of the oblique Alfven wave also has a k² dependence and can reach a maximum value of the order of 10% at high wave number. It is shown that Alfven compressibility could be the dominant contributor to the near-Sun solar wind density fluctuation spectrum for k>10−2 km−1 and hence might cause some of the flattening at high wave number seen in radio scintillation measurements. This would also be consistent with the notion that the observed density spectrum inner scale is a signature of cyclotron damping.
Functional separability within a quadratic inverse demand system

In this paper, a quadratic inverse (almost ideal) demand system (IQUAIDS) is derived, that generalizes the inverse (almost ideal) demand system (IAIDS). Starting from a flexible parameterization of the distance function, this model allows a more flexible specification by overcoming the potential restrictiveness of linear scale curves. However, at a point of normalization, the IQUAIDS boils down to the IAIDS, thus the additional flexibility pertains only to the specification of scale elasticities away from the point of approximation. Previous work on functional separability is extended to the case of inverse demands, and necessary and sufficient conditions for weak separability of the direct and indirect utility function derived, in terms of the Antonelli elasticities of complementarity and of the scale elasticities. Their proper parametric representation within the inverse specification is also derived. An empirical application to fish demand in Italy is provided, mainly for illustrative purposes.