Vibrations of a plate on a two-parameter foundation subjected to moving rectangular loads of varying velocities

The vibrational characteristics of a plate on a two-parameter foundation under moving rectangular loads with variable velocities are investigated, and the general solution for the dynamic deflection of the plate is derived using the double Fourier transform. Employing the fast Fourier Transform, a rigid pavement is chosen to obtain numerical results, which are consistent with those from the classical solution. The effects of initial load velocity, load acceleration, load deceleration and horizontal resistance at the plate bottom on the dynamic deflection are discussed. An expression to predict the critical velocity is derived, and the results from this formula show very good agreement with those from the numerical analysis. The numerical analysis indicates that the maximum dynamic deflection occurs when the load velocity reaches the critical velocity for the plate. The initial velocity, the acceleration and the deceleration of the rectangular load influence the dynamic response, and the dynamic deflection of the plate at the critical velocity decreases significantly as they increases

Laser Pulse Bidirectional Reflectance from CALIPSO Mission

In this Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) study, we present a simple way of determining laser pulse bidirectional reflectance over snow/ice surface using the Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP) 532 nanometer polarization channels' measurements. The saturated laser pulse returns from snow and ice surfaces are recovered based on surface tail information. The method overview and initial assessment of the method performance will be presented. The retrieved snow surface bidirectional reflectance is compared with reflectance from both CALIOP cloud cover regions and Moderate Resolution Imaging Spectroradiometer (Earth Observing System (EOS)) (MODIS) Bi-directional Reflectance Distribution Function (BRDF) / Albedo model parameters. The comparisons show that the snow surface bidirectional reflectance over Antarctica for saturation region are generally reliable with a mean value of about 0.90 plus or minus 0.10, while the mean surface reflectance from cloud cover region is about 0.84 plus or minus 0.13 and the calculated MODIS reflectance at 555 nanometers from the BRDF / Albedo model with near nadir illumination and viewing angles is about 0.96 plus or minus 0.04. The comparisons here demonstrate that the snow surface reflectance underneath the cloud with cloud optical depth of about 1 is significantly lower than that for a clear sky condition

Scaling analysis of time series using empirical mode decomposition and Hilbert spectral analysis

Recently, Hilbert-Huang transform (HHT), or Empirical Mode Decomposition (EMD) have become a promising methodology to deal with nonlinear and nonstationary time series [1,2]. This corresponds to a data-driven method with very local ability, both in physical and spectral space [3]. In this work, we propose an extended version of Hilbert spectral analysis, namely arbitrary order Hilbert spectral analysis, to characterize the scale invariant properties in spectral space directly. The most innovative part of the Hilbert-Huang transform is the Empirical Mode Decomposition, which can separate the original time series into several Intrinsic Mode Functions, called IMF. The starting point of EMD is to consider the time series from real word as multi-component signal. The corresponding characteristic scale is defined as the distance between two successive maxima points (resp. minima points). The intrinsic mode function is proposed to approximate the mono-component signal, which satisfies the following two conditions : (i) the difference between the number of local extrema and the number of zero-crossings must be zero or one ; (ii) the running mean value of the envelope defined by the local maxima and the envelope defined by the local minima is zero [1,2]. Then the empirical mode decomposition algorithm is proposed to extract IMF modes from a given time series [1,2,16].Nous proposons ici une généralisation de l’analyse spectrale de Hilbert qui est effectuée dans le cadre des décompositions modales empiriques. Cette analyse spectrale de Hilbert d’ordre arbitraire permet de caractériser les propriétés d’intermittence des séries temporelles à invariance d’échelle multiple. La méthode est validée en utilisant des simulations de mouvement Brownien fractionnaire, avec différentes valeurs du paramètre H, et avec des simulations lognormales multifractales. Une application est effectuée sur des données « réelles » issues du domaine de la turbulence. La méthode proposée ici fonctionne dans l’espace amplitude-fréquence ; cette méthode est la première approche pouvant prendre en compte les exposants d’intermittence dans l’espace des fréquences. Nous montrons également que cette méthode est supérieure à l’approche utilisant les fonctions de structure lorsque la série à analyser présente une invariance d’échelle superposée à une forte composante périodique

Analysis of experimental homogeneous turbulence time series by Hilbert-Huang transform

The Empirical Mode Decomposition (EMD) method and Hilbert-Huang transform are used to analyse experimental homogeneous turbulence time series. With this method, one can decompose nonlinear timeseries into a sum of different modes, each narrow-banded. Here we consider experimental turbulent velocity time series with a large Reynolds number (Re_lambda = 720). The Fourier power spectrum reveals a wide inertial range with a classical -5/3 Kolmogorov power-law spectrum. We show that the EMD method applies very nicely to the turbulent velocity time series, with a dyadic filter bank in the inertial range. We estimate the Fourier power spectra of each mode, showing that adding more and more modes corresponds to including lower and lower frequencies. This filtering property can have interesting applications in the field of turbulence modelling. We estimate the Hilbert-Huang power spectrum of the turbulent time series and show its scaling properties, with an exponent different from -5/3

Anomalous Photovoltaic Effect in Centrosymmetric Ferroelastic BiVO4

The anomolous photovoltaic (APV) effect is an intriguing phenomenon and rarely observed in bulk materials that structurally have an inversion symmetry. Here, the discovery of such an APV effect in a centrosymmetric vanadate, BiVO4, where noticeable above‐bandgap photovoltage and a steady‐state photocurrent are observed in both ceramics and single crystals even when illuminated under visible light, is reported. Moreover, the photovoltaic voltage can be reversed by the stress modulation, and a sine‐function relationship between the photovoltage and stress directional angle is derived. Microstructure and strain‐field analysis reveal localized asymmetries that are caused by strain fluctuations in bulk centrosymmetric BiVO4. On the basis of the experimental results, a flexoelectric coupling via a strain‐induced local polarization mechanism is suggested to account for the APV effect observed. This work not only allows new applications for BiVO4 in optoelectronic devices but also deepens insights into the mechanisms underlying the APV effect.This work was financially supported by the National Key R&D Program of China (2016YFA0201103), the Natural Science Foundation of China (Grant Nos. 21577143, 51502289, 51872311, and 51502325), the Natural Science Foundation of Fujian Province (Grant Nos. 2017J05031 and 2018I0021), the Frontier Science Key Project of the Chinese Academy of Sciences (QYZDB-SSW-JSC027), and the Instrument Developing Project of Chinese Academy of Sciences (Grant No. ZDKYYQ20180004). Y.L. thanks the Australian Research Council for support in the form of an ARC discovery program grant

Coordinated day-ahead reactive power dispatch in distribution network based on real power forecast errors

Reactive power outputs of DGs are used along with capacitor banks to regulate distribution network voltage. However, reactive power capability of a DG is limited by the inverter ratings and real power outputs of the DG. In order to achieve optimal power flow, minimize power losses, and minimize switching of capacitor banks, a day-ahead coordinated dispatch method of reactive power is proposed. Forecast errors of DG real power in every period are used to estimate the probability distribution of DGs reactive power capacity. Considering different output characteristics and constraints of reactive power sources, a dynamic preliminary-coarse-fine adjustment method is designed to optimize DG and shunt compensator outputs, decrease the switching cost, and reduce loss. The preliminary optimization obtains initial values, and multiple iterations between the coarse and fine optimizations are used to achieve a coordinated result. Simulations studies are performed to verify the proposed method