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Mizuno, T., M. Oguma, T. Kitoh, Y. Inoue, and H. Takahashi. "Mach-Zehnder interferometer exactly aligned with ITU grid frequencies." IEEE Photonics Technology Letters 18, no. 2 (January 2006): 325–27. http://dx.doi.org/10.1109/lpt.2005.861980.
Повний текст джерела
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HORING, N. J. M., S. Y. LIU, V. V. POPOV, and H. L. CUI. "TUNABLE GRID GATED DOUBLE-QUANTUM-WELL FET TERAHERTZ DETECTOR." International Journal of High Speed Electronics and Systems 18, no. 01 (March 2008): 147–57. http://dx.doi.org/10.1142/s0129156408005229.
Повний текст джерелаАнотація:
Several aspects of the theory of plasmon resonant DC photoconduction are discussed here, in connection with recent observations involving a THz-irradiated grid-gated double-quantum-well FET.1 In this, we construct a classical model of nonlinear polarizability to second order in the THz field using a “hydrodynamic” type formulation including the roles of a stress-tensor and friction/viscosity. The resulting second order polarizability exhibits resonant behavior when the THz frequency matches plasmon frequencies of the system, sharply reducing the effectiveness of screened impurity scattering potentials which can admit resonant DC photoconduction. Furthermore, we also show that an asymmetric double-quantum-well system with lateral periodicity can mix optical and acoustic plasmons, giving rise to an interlayer THz field which becomes very strong when tuned by gate voltage into the “mode-mode-repulsion” regime wherein the optical and acoustic modes equally share amplitude. This can enhance interlayer electron tunneling and may contribute to photoconductivity.
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Kishimoto, Satoshi, Yoshihisa Tanaka, Yong Ming Xing, and Gyu Chang Lee. "Measurement of Strain and Stress Distribution of Composite Materials by Electron Moiré Method." Materials Science Forum 561-565 (October 2007): 717–20. http://dx.doi.org/10.4028/www.scientific.net/msf.561-565.717.
Повний текст джерелаАнотація:
A method for measuring the stress and strain distribution in the composite materials and residual stress at the interface in the fiber reinforced composite has been developed. The strains are measured using an electron Moiré method and then the stresses are calculated from these strains. A very fine model grid with frequencies up to 10,000lines/mm can be fabricated using the optical and electron lithography techniques on the surface of the specimen and an electron beam scan which spaces are almost same as that of model grid the can be used for master-grid. The difference of the amount of secondary electrons per a primary electron makes Moiré fringes that consists bright and dark parts. Micro-creep deformation and residual strain and stress near the fibers of composite materials were measured by this method.
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Mi, Da Hai, Rui Yang, Liang Zhou, Yang Liu, and Dong Ming Guo. "Frequency-Aimed Structural Optimal Design of Stiffened Plate." Advanced Materials Research 452-453 (January 2012): 1475–80. http://dx.doi.org/10.4028/www.scientific.net/amr.452-453.1475.
Повний текст джерелаАнотація:
Optimal structural design of stiffened plate structure with multi order modal frequencies objective is discussed. It is a structural reverse design problem for the first several order modal frequencies to reach a set of given value. A new method based on bi-directional evolutionary structural optimization (BESO) and size optimization is presented. To solve the porous and irregular shape problem in the optimized structure, a regular shaped grid-like frame structure optimization model is established. The bars in the frame structure are regarded as basic unites of structure modification. The bars’ sensitivity is discussed, and applied to optimization process based on frequency sensitivity. The structural optimal design process can be described as follows: the frequencies are used as the target, the volume is considered as constraint, adjacent sensitivity redistribution method is adopted to suppress numerical instability. Then size optimization method is adopted to conduct detailed design. Finally this method is applied to a stiffened plate structure. Results show that the proposed approach is feasible to achieve given multi order modal frequencies. The optimized structure consists of regular bars, so a clear structure is obtained.
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Jumani, Touqeer, Mohd Mustafa, Madihah Rasid, Nayyar Mirjat, Mazhar Baloch, and Sani Salisu. "Optimal Power Flow Controller for Grid-Connected Microgrids using Grasshopper Optimization Algorithm." Electronics 8, no. 1 (January 19, 2019): 111. http://dx.doi.org/10.3390/electronics8010111.
Повний текст джерелаАнотація:
Despite the vast benefits of integrating renewable energy sources (RES) with the utility grid, they pose stability and power quality problems when interconnected with the existing power system. This is due to the production of high voltages and current overshoots/undershoots during their injection or disconnection into/from the power system. In addition, the high harmonic distortion in the output voltage and current waveforms may also be observed due to the excessive inverter switching frequencies used for controlling distributed generator’s (DG) power output. Hence, the development of a robust and intelligent controller for the grid-connected microgrid (MG) is the need of the hour. As such, this paper aims to develop a robust and intelligent optimal power flow controller using a grasshopper optimization algorithm (GOA) to optimize the dynamic response and power quality of the grid-connected MG while sharing the desired amount of power with the grid. To validate the effectiveness of proposed GOA-based controller, its performance in achieving the desired power sharing ratio with optimal dynamic response and power quality is compared with that of its precedent particle swarm optimization (PSO)-based controller under MG injection and abrupt load change conditions. The proposed controller provides tremendous system’s dynamic response with minimum current harmonic distortion even at higher DG penetration levels.
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Ma, Shi Lei, Fang Yi Li, Yang He, and Qing Zhong Xu. "Multidisciplinary Design Optimization of Driving Axle Housing Using Sparse Grid Approach." Applied Mechanics and Materials 224 (November 2012): 82–86. http://dx.doi.org/10.4028/www.scientific.net/amm.224.82.
Повний текст джерелаАнотація:
In order to improve the engineering performance of lightweight design on the driving axle housing, lightweight, structural mechanics, fatigue strength and dynamics are applied in the multidisciplinary design optimization. Firstly, finite element model of driving axle housing was established and its accuracy was verified through bench tests. Secondly, driving axle housing system was divided into multiple sub-discipline systems and design variables of multidisciplinary lightweight design were determined, in order to solve the problems of large amount of data transmission and complex calculation, sparse grid approach was used to establish high accuracy approximate model of each discipline. Lastly, mass of driving axle housing and difference values of first six order modal frequencies before and after lightweight design were optimized through Non-dominated Sorted Genetic Algorithm-Ⅱ, the Pareto optimal solution set was obtained. In optimization results, masses of driving axle housing are all decreased compared to the initial design, meanwhile, the dynamic performance, structural static intensity and fatigue life are all ensured.
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Operto, Stéphane, Jean Virieux, Patrick Amestoy, Jean-Yves L’Excellent, Luc Giraud, and Hafedh Ben Hadj Ali. "3D finite-difference frequency-domain modeling of visco-acoustic wave propagation using a massively parallel direct solver: A feasibility study." GEOPHYSICS 72, no. 5 (September 2007): SM195—SM211. http://dx.doi.org/10.1190/1.2759835.
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We present a finite-difference frequency-domain method for 3D visco-acoustic wave propagation modeling. In the frequency domain, the underlying numerical problem is the resolution of a large sparse system of linear equations whose right-hand side term is the source. This system is solved with a massively parallel direct solver. We first present an optimal 3D finite-difference stencil for frequency-domain modeling. The method is based on a parsimonious staggered-grid method. Differential operators are discretized with second-order accurate staggered-grid stencils on different rotated coordinate systems to mitigate numerical anisotropy. An antilumped mass strategy is implemented to minimize numerical dispersion. The stencil incorporates 27 grid points and spans two grid intervals. Dispersion analysis showsthat four grid points per wavelength provide accurate simulations in the 3D domain. To assess the feasibility of the method for frequency-domain full-waveform inversion, we computed simulations in the 3D SEG/EAGE overthrust model for frequencies 5, 7, and [Formula: see text]. Results confirm the huge memory requirement of the factorization (several hundred Figabytes) but also the CPU efficiency of the resolution phase (few seconds per shot). Heuristic scalability analysis suggests that the memory complexity of the factorization is [Formula: see text] for a [Formula: see text] grid. Our method may provide a suitable tool to perform frequency-domain full-waveform inversion using a large distributed-memory platform. Further investigation is still necessary to assess more quantitatively the respective merits and drawbacks of time- and frequency-domain modeling of wave propagation to perform 3D full-waveform inversion.
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Stokholm, Amalie, Poul Erik Nissen, Víctor Silva Aguirre, Timothy R. White, Mikkel N. Lund, Jakob Rørsted Mosumgaard, Daniel Huber, and Jens Jessen-Hansen. "The subgiant HR 7322 as an asteroseismic benchmark star." Monthly Notices of the Royal Astronomical Society 489, no. 1 (August 12, 2019): 928–40. http://dx.doi.org/10.1093/mnras/stz2222.
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Abstract We present an in-depth analysis of the bright subgiant HR 7322 (KIC 10005473) using Kepler short-cadence photometry, optical interferometry from CHARA, high-resolution spectra from SONG, and stellar modelling using garstec grids, and the Bayesian grid-fitting algorithm basta. HR 7322 is only the second subgiant with high-quality Kepler asteroseismology for which we also have interferometric data. We find a limb-darkened angular diameter of 0.443 ± 0.007 mas, which, combined with a distance derived using the parallax from Gaia DR2 and a bolometric flux, yields a linear radius of 2.00 ± 0.03 R⊙ and an effective temperature of 6350 ± 90 K. HR 7322 exhibits solar-like oscillations, and using the asteroseismic scaling relations and revisions thereof, we find good agreement between asteroseismic and interferometric stellar radius. The level of precision reached by the careful modelling is to a great extent due to the presence of an avoided crossing in the dipole oscillation mode pattern of HR 7322. We find that the standard models predict a stellar radius systematically smaller than the observed interferometric one and that a sub-solar mixing length parameter is needed to achieve a good fit to individual oscillation frequencies, interferometric temperature, and spectroscopic metallicity.
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Jin, Daeho, Lazaros Oreopoulos, Dongmin Lee, Nayeong Cho, and Jackson Tan. "Contrasting the co-variability of daytime cloud and precipitation over tropical land and ocean." Atmospheric Chemistry and Physics 18, no. 4 (March 2, 2018): 3065–82. http://dx.doi.org/10.5194/acp-18-3065-2018.
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Abstract. The co-variability of cloud and precipitation in the extended tropics (35∘ N–35∘ S) is investigated using contemporaneous data sets for a 13-year period. The goal is to quantify potential relationships between cloud type fractions and precipitation events of particular strength. Particular attention is paid to whether the relationships exhibit different characteristics over tropical land and ocean. A primary analysis metric is the correlation coefficient between fractions of individual cloud types and frequencies within precipitation histogram bins that have been matched in time and space. The cloud type fractions are derived from Moderate Resolution Imaging Spectroradiometer (MODIS) joint histograms of cloud top pressure and cloud optical thickness in 1∘ grid cells, and the precipitation frequencies come from the Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) data set aggregated to the same grid. It is found that the strongest coupling (positive correlation) between clouds and precipitation occurs over ocean for cumulonimbus clouds and the heaviest rainfall. While the same cloud type and rainfall bin are also best correlated over land compared to other combinations, the correlation magnitude is weaker than over ocean. The difference is attributed to the greater size of convective systems over ocean. It is also found that both over ocean and land the anti-correlation of strong precipitation with “weak” (i.e., thin and/or low) cloud types is of greater absolute strength than positive correlations between weak cloud types and weak precipitation. Cloud type co-occurrence relationships explain some of the cloud–precipitation anti-correlations. Weak correlations between weaker rainfall and clouds indicate poor predictability for precipitation when cloud types are known, and this is even more true over land than over ocean.
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Wang, Xiashuang, Guanghong Gong, and Ni Li. "Automated Recognition of Epileptic EEG States Using a Combination of Symlet Wavelet Processing, Gradient Boosting Machine, and Grid Search Optimizer." Sensors 19, no. 2 (January 9, 2019): 219. http://dx.doi.org/10.3390/s19020219.
Повний текст джерелаАнотація:
Automatic recognition methods for non-stationary electroencephalogram (EEG) data collected from EEG sensors play an essential role in neurological detection. The integrated approaches proposed in this study consist of Symlet wavelet processing, a gradient boosting machine, and a grid search optimizer for a three-class classification scheme for normal subjects, intermittent epilepsy, and continuous epilepsy. Fourth-order Symlet wavelets are adopted to decompose the EEG data into five frequencies sub-bands, such as gamma, beta, alpha, theta, and delta, whose statistical features were computed and used as classification features. The grid search optimizer is used to automatically find the optimal parameters for training the classifier. The classification accuracy of the gradient boosting machine was compared with that of a conventional support vector machine and a random forest classifier constructed according to previous descriptions. Multiple performance indices were used to evaluate the proposed classification scheme, which provided better classification accuracy and detection effectiveness than has been recently reported in other studies on three-class classification of EEG data.
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Ye, Xijun, Yingfeng Wu, Liwen Zhang, Liu Mei, and Yunlai Zhou. "Ambient Effect Filtering Using NLPCA-SVR in High-Rise Buildings." Sensors 20, no. 4 (February 19, 2020): 1143. http://dx.doi.org/10.3390/s20041143.
Повний текст джерелаАнотація:
The modal frequencies of a structure are affected by continuous changes in ambient factors, such as temperature, wind speed etc. This study incorporates nonlinear principal component analysis (NLPCA) with support vector regression (SVR) to build a mathematical model to reflect the correlation between ambient factors and modal frequencies. NLPCA is first used to eliminate the high correlation among different ambient factors and extract the nonlinear principal components. The extracted nonlinear principal components are input into the SVR model for training and predicting. The proposed method is verified by the measured data provided in the Guangzhou New TV Tower (GNTVT) Benchmark. The grid search method (GSM), genetic algorithm (GA) and fruit fly optimization algorithm (FOA) are applied to determine the optimal hyperparameters for the SVR model. The optimized result of FOA is most suitable for the NLPCA-SVR model. As evaluated by the hypothesis test and goodness-of-fit test, the results show that the proposed method has a high generalization performance and the correlation between the ambient factor and modal frequency can be strongly reflected. The proposed method can effectively eliminate the effects of ambient factors on modal frequencies.
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Mi, Da Hai, Rui Yang, Liang Zhou, Yang Liu, and Dong Ming Guo. "Optimal Structural Frequency Design of Stiffened Shell." Applied Mechanics and Materials 157-158 (February 2012): 1636–39. http://dx.doi.org/10.4028/www.scientific.net/amm.157-158.1636.
Повний текст джерелаАнотація:
Frequency-aimed optimal structural design of stiffened shell is concerned. It is a reverse design problem for the first several modal frequencies to converge to a set of target value. A design method combined modified bi-directional evolutionary structural optimization (BESO) and size optimization is presented. Optimization model consists of skin and regular grid frame structure. To solve irregular branches and holes that often exist in ordinary topology optimization results, instead of elements, the existence states of ribs in the frame are used as design variables and sensitivity of the rib is discussed. Detailed design is conducted by size optimization. Example shows that frequency requirements are achieved. And the optimum structure is regular and clear, the localized modes problem is avoid. This is very suitable for designing airplane wind tunnel flutter test models.
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Toodesh, Reenu, and Sandra Verhagen. "Adaptive, variable resolution grids for bathymetric applications using a quadtree approach." Journal of Applied Geodesy 12, no. 4 (October 25, 2018): 311–22. http://dx.doi.org/10.1515/jag-2017-0043.
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Abstract The spatial sampling often used to process and represent bathymetric data are of fixed grid resolution where the least depth value is stored in each grid cell. This results in Digital Elevation Models (DEMs) that are used to depict the underlying features of the seafloor. With the discretion of the user, the resulting DEMs used may either be of coarse resolution or a very fine resolution surface which provides as many details as possible. However, depending on the resolution of the data collected and the variability of the seafloor, the arbitrary user defined grid resolution is not the best option. Hence we address the problem of finding an optimal grid resolution for representing and processing the bathymetric data for the application of bathymetric risk assessment whilst maintaining computational efficiency. Here we adopt the quadtree decomposition approach. In addition, the research suggests the optimal criteria and standard deviation threshold, {\sigma _{th}} values for this particular application. These suggestions are still flexible and can be optimized for this application depending on the end user requirements. Previous studies have focused only on the splitting criteria or the constrained criteria to ensure that there is homogeneous accuracy over the entire dataset. However, an investigation into the threshold selection for the standard deviation, {\sigma _{th}} which describes the variability in the dataset is one of the most important splitting criterion, that is still lacking. Also, a new approach to store the depths in the grid in a time ordered approach for each epoch is shown. By optimizing the criteria for the quadtree decomposition and time series algorithm, the approaches shown in this paper provide the adaptive, accurate DEM which makes optimal use of the available bathymetric data for the Netherlands Continental Shelf (NCS) as the study area. This data preparation step forms the basis for developing a probabilistic approach to assigning hydrographic resurvey frequencies in the NCS.
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Davelaar, Jordy, Hector Olivares, Oliver Porth, Thomas Bronzwaer, Michael Janssen, Freek Roelofs, Yosuke Mizuno, Christian M. Fromm, Heino Falcke, and Luciano Rezzolla. "Modeling non-thermal emission from the jet-launching region of M 87 with adaptive mesh refinement." Astronomy & Astrophysics 632 (November 21, 2019): A2. http://dx.doi.org/10.1051/0004-6361/201936150.
Повний текст джерелаАнотація:
Context. The galaxy M 87 harbors a kiloparsec-scale relativistic jet, whose origin coincides with a compact source thought to be a supermassive black hole. Observational millimeter very long baseline interferometry campaigns are capable of resolving the jet-launching region at the scale of the event horizon. In order to provide a context for interpreting these observations, realistic general-relativistic magnetohydrodynamical (GRMHD) models of the accretion flow are constructed. Aims. Electrons in the jet are responsible for the observed synchrotron radiation, which is emitted in frequencies ranging from radio to near-infrared (NIR) and optical. The characteristics of the emitted radiation depend on the shape of the electrons’ energy-distribution function (eDF). The dependency on the eDF is omitted in the modeling of the first Event Horizon Telescope results. In this work, we aim to model the M 87 spectral-energy distribution from radio up to optical frequencies using a thermal-relativistic Maxwell–Jüttner distribution, as well as a relativistic κ-distribution function. The power-law index of the eDF is modeled based on sub-grid, particle-in-cell parametrizations for sub-relativistic reconnection. Methods. A GRMHD simulation in Cartesian–Kerr–Schild coordinates, using eight levels of adaptive mesh refinement (AMR), forms the basis of our model. To obtain spectra and images, the GRMHD data was post-processed with the ray-tracing code RAPTOR, which is capable of ray tracing through GRMHD simulation data that is stored in multi-level AMR grids. The resulting spectra and images maps are compared with observations. Results. We obtain radio spectra in both the thermal-jet and κ-jet models consistent with radio observations. Additionally, the κ-jet models also recover the NIR and optical emission. The images show a more extended structure at 43 GHz and 86 GHz and more compact emission at 228 GHz. The models recover the observed source sizes and core shifts and obtain a jet power of ≈1043 ergs s−1. In the κ-jet models, both the accretion rates and jet powers are approximately two times lower than the thermal-jet model. The frequency cut-off observed at ν ≈ 1015 Hz is recovered when the accelerator size is 106 − 108 cm, this could potentially point to an upper limit for plasmoid sizes in the jet of M 87.
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Gospodinova, M., G. Nan, J. Thomas, R. Subraya, and J. Held. "Electrical Characterization of High Performance Memory FBGA BOC Package." Journal of Microelectronics and Electronic Packaging 3, no. 1 (January 1, 2006): 44–51. http://dx.doi.org/10.4071/1551-4897-3.1.44.
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A multilayer Fine-pitch Ball Grid Array (FBGA) Board-on-chip (BOC) memory package used for applications running at more than 1 Gbit/p/s has been characterized using S-(distributed) parameter measurements and three types of test chips made using state of the art technology. The low parasitics FBGA test board itself was characterized for frequencies up to 5 GHz (the frequency range of interest) with the transmission being greater than −0.12 dB below 5 GHz. S-parameter model simulation of the package itself indicated that the transmission was greater than −1.5 dB up to 5 GHz. Correlation between the S-parameter simulation and measurements for the package and fixture combined was acceptable - in the order of tenths of dB in the frequency range DC to 2.5 GHz. Comparison of the S-parameter model versus lumped (RLC) model in the frequency range from DC to 5 GHz showed that the lumped model can be used for frequencies up to 2.9 GHz. A high degree of correlation between simulation and measurement has been shown. The lumped model bandwidth has been assessed and its application limits for time domain signal integrity simulations have been evaluated.
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Granada-Torres, Jhon James, Ana María Cárdenas-Soto, and Neil Guerrero-González. "Redes ópticas elásticas: un nuevo paradigma en las futuras redes de telecomunicaciones." Respuestas 20, no. 2 (July 1, 2015): 6. http://dx.doi.org/10.22463/0122820x.350.
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ResumenEl tráfico en las redes de datos por fibra óptica ha tenido un crecimiento exponencial debido a la creciente demanda de información por parte de los usuarios finales, llevando a una saturación en la capacidad de las redes actuales. Proyectando los sistemas de transmisiones ópticos a tasas superiores a los 400 Gbps para redes de largo alcance, no será posible mantener la tecnología WDM de rejilla espectral fija de 50 GHz, la cual permite transmitir en la actualidad tasas hasta los 100 Gbps. Teniendo como limitación además del ancho espectral que ocuparía la información, la conmutación de los dispositivos para trabajar a altas frecuencias. En este contexto, surge el concepto de las redes ópticas elásticas, donde se emplea una rejilla de espectro flexible (flexi-grid) o sin rejilla (grid-less), con ancho espectral variable por canal según la demanda de ancho de banda, permitiendo una separación espectral flexible entre canales con el propósito de optimizar la eficiencia en el uso del espectro. Este artículo hace una revisión de los nuevos conceptos tecnológicos que conllevan el escenario de redes elásticas, y los posibles retos y limitaciones para el desarrollo de estas tecnologías. Recientes pruebas experimentales incorporan nuevos conceptos tecnológicos con relación a los ya comerciales sistemas de 100-G como: el diseño de transmisores multicanales, el uso de tecnologías como Nyquist-WDM y OFDM óptico flexible, receptores digitales coherentes reconfigurables, formatos de modulación m-arios e híbridos y asignación dinámica del espectro. No obstante, grandes limitantes como los efectos no lineales de la fibra óptica deben ser foco de investigación en este nuevo escenario, debido a sus efectos en la degradación de la señal. Finalmente, se muestra como las técnicas de procesamiento digital de señales desempeñarán un papel importante para lograr la reconfigurabilidad y elasticidad de las redes de alta capacidad.AbstractIn the last years, traffic on data optical networks has had an exponential growth due to the increasing demand of information by end users. This had lead to saturation of the current deployed networks in terms of capacity. Planning the optical transmission systems of long-reach to work with capacities above 400 Gbps, it will not be possible to keep the spectral fixed-grid of the WDM technology, which currently allows transmitting up to 100 Gbps. The principal limitation is due to the greater spectral bandwidth occupied by the data information and also due to the switching of electronics devices at high frequencies. In this context a new concept known as elastic optical network emerges, which proposes a flexible-grid or gridless, where the spectral width changes according to the bandwidth demand and allows optimizing the spectral efficiency with a minimum separation between adjacent channels. In this paper, we present a comprehensive survey of elastic optical networks, introducing new concepts and describing the challenges and the limitations in these networks. Recent experimental reports show new technological concepts related to the commercials 100-G systems such as: design of multichannels transmitters, gridless Nyquist-WDM and Optical-OFDM, reconfigurable digital coherent receivers, optical dynamic spectrum allocation and advanced modulation formats. Nevertheless, the nonlinearity effects of the optical fiber are a significant limitation that must be researched in detail in this new elastic scenario. Hence, it is shown how the digital signal processing techniques are going to play an important role in order to get high capacity in elastic and reconfigurable networksPalabras clave: Comunicaciones por Fibra Óptica, Enrutamiento, Interferencia Intercanal (ICI), Multiplexación por División de Longitud de Onda, Óptica No-Lineal, Procesamiento Digital de Señales (DSP), Redes Ópticas.
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Zhang, Kai, Chun Zhao, Hui Wan, Yun Qian, Richard C. Easter, Steven J. Ghan, Koichi Sakaguchi, and Xiaohong Liu. "Quantifying the impact of sub-grid surface wind variability on sea salt and dust emissions in CAM5." Geoscientific Model Development 9, no. 2 (February 12, 2016): 607–32. http://dx.doi.org/10.5194/gmd-9-607-2016.
Повний текст джерелаАнотація:
Abstract. This paper evaluates the impact of sub-grid variability of surface wind on sea salt and dust emissions in the Community Atmosphere Model version 5 (CAM5). The basic strategy is to calculate emission fluxes multiple times, using different wind speed samples of a Weibull probability distribution derived from model-predicted grid-box mean quantities. In order to derive the Weibull distribution, the sub-grid standard deviation of surface wind speed is estimated by taking into account four mechanisms: turbulence under neutral and stable conditions, dry convective eddies, moist convective eddies over the ocean, and air motions induced by mesoscale systems and fine-scale topography over land. The contributions of turbulence and dry convective eddy are parameterized using schemes from the literature. Wind variabilities caused by moist convective eddies and fine-scale topography are estimated using empirical relationships derived from an operational weather analysis data set at 15 km resolution. The estimated sub-grid standard deviations of surface wind speed agree well with reference results derived from 1 year of global weather analysis at 15 km resolution and from two regional model simulations with 3 km grid spacing.The wind-distribution-based emission calculations are implemented in CAM5. In terms of computational cost, the increase in total simulation time turns out to be less than 3 %. Simulations at 2° resolution indicate that sub-grid wind variability has relatively small impacts (about 7 % increase) on the global annual mean emission of sea salt aerosols, but considerable influence on the emission of dust. Among the considered mechanisms, dry convective eddies and mesoscale flows associated with topography are major causes of dust emission enhancement. With all the four mechanisms included and without additional adjustment of uncertain parameters in the model, the simulated global and annual mean dust emission increase by about 50 % compared to the default model. By tuning the globally constant dust emission scale factor, the global annual mean dust emission, aerosol optical depth, and top-of-atmosphere radiative fluxes can be adjusted to the level of the default model, but the frequency distribution of dust emission changes, with more contribution from weaker wind events and less contribution from stronger wind events. In Africa and Asia, the overall frequencies of occurrence of dust emissions increase, and the seasonal variations are enhanced, while the geographical patterns of the emission frequency show little change.
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Li, Chuan, Jianxin Liu, Bo Chen, and Ya Sun. "Optimal Third-Order Symplectic Integration Modeling of Seismic Acoustic Wave Propagation." Bulletin of the Seismological Society of America 110, no. 2 (March 10, 2020): 754–62. http://dx.doi.org/10.1785/0120190193.
Повний текст джерелаАнотація:
ABSTRACT Seismic wavefield modeling based on the wave equation is widely used in understanding and predicting the dynamic and kinematic characteristics of seismic wave propagation through media. This article presents an optimal numerical solution for the seismic acoustic wave equation in a Hamiltonian system based on the third-order symplectic integrator method. The least absolute truncation error analysis method is used to determine the optimal coefficients. The analysis of the third-order symplectic integrator shows that the proposed scheme exhibits high stability and minimal truncation error. To illustrate the accuracy of the algorithm, we compare the numerical solutions generated by the proposed method with the theoretical analysis solution for 2D and 3D seismic wave propagation tests. The results show that the proposed method reduced the phase error to the eighth-order magnitude accuracy relative to the exact solution. These simulations also demonstrated that the proposed third-order symplectic method can minimize numerical dispersion and preserve the waveforms during the simulation. In addition, comparing different central frequencies of the source and grid spaces (90, 60, and 20 m) for simulation of seismic wave propagation in 2D and 3D models using symplectic and nearly analytic discretization methods, we deduce that the suitable grid spaces are roughly equivalent to between one-fourth and one-fifth of the wavelength, which can provide a good compromise between accuracy and computational cost.
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Salajegheh, E., and G. N. Vanderplaats. "An Efficient Approximation Method for Structural Synthesis with Reference to Space Structures." International Journal of Space Structures 2, no. 3 (September 1987): 165–75. http://dx.doi.org/10.1177/026635118700200305.
Повний текст джерелаАнотація:
A method is presented for the optimum design of structures which is very robust and efficient in terms of the number of required analyses of the structure. Some explicit approximation expressions are generated for the structural response quantities such as nodal displacements, forces and frequencies as functions of the cross-sectional properties. By substituting these expressions into the constraint equations, the design task becomes a non-linear programming problem which is an explicit problem in terms of the design variables. The solution of this problem gives the actual cross-sectional dimensions. The method is an iterative technique and the results indicate that the convergence to the optimal solution results indicate that the convergence to the optimal solution is very rapid. The robustness of the proposed method is due to the generation of explicit approximate relations for the structural response quantities, as in the past the design constraints were approximated. Also a high quality approximation is obtained for the internal forces directly without using the approximate values of the displacements. The quality of approximations is enhanced by expressing the structural responses, in particular, the frequencies with respect to the cross-sectional areas and second moment of inertias instead of using the cross-sectional dimensions. A double-layer grid and a grillage are chosen as test cases, the results of which are presented.
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Naghizadeh, Mostafa, and Kristopher A. Innanen. "Seismic data interpolation using a fast generalized Fourier transform." GEOPHYSICS 76, no. 1 (January 2011): V1—V10. http://dx.doi.org/10.1190/1.3511525.
Повний текст джерелаАнотація:
We have found a fast and efficient method for the interpolation of nonstationary seismic data. The method uses the fast generalized Fourier transform (FGFT) to identify the space-wavenumber evolution of nonstationary spatial signals at each temporal frequency. The nonredundant nature of FGFT renders a big computational advantage to this interpolation method. A least-squares fitting scheme is used next to retrieve the optimal FGFT coefficients representative of the ideal interpolated data. For randomly sampled data on a regular grid, we seek a sparse representation of FGFT coefficients to retrieve the missing samples. In addition, to interpolate the regularly sampled seismic data at a given frequency, we use a mask function derived from the FGFT coefficients of the low frequencies. Synthetic and real data examples can be used to examine the performance of the method.
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Naghizadeh, Mostafa. "Seismic data interpolation and denoising in the frequency-wavenumber domain." GEOPHYSICS 77, no. 2 (March 2012): V71—V80. http://dx.doi.org/10.1190/geo2011-0172.1.
Повний текст джерелаАнотація:
I introduce a unified approach for denoising and interpolation of seismic data in the frequency-wavenumber ([Formula: see text]) domain. First, an angular search in the [Formula: see text] domain is carried out to identify a sparse number of dominant dips, not only using low frequencies but over the whole frequency range. Then, an angular mask function is designed based on the identified dominant dips. The mask function is utilized with the least-squares fitting principle for optimal denoising or interpolation of data. The least-squares fit is directly applied in the time-space domain. The proposed method can be used to interpolate regularly sampled data as well as randomly sampled data on a regular grid. Synthetic and real data examples are provided to examine the performance of the proposed method.
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Blazek, Vojtech, Zdenek Slanina, Michal Petruzela, Roman Hrbáč, Jan Vysocký, Lukas Prokop, Stanislav Misak, and Wojciech Walendziuk. "Error Analysis of Narrowband Power-Line Communication in the Off-Grid Electrical System." Sensors 22, no. 6 (March 15, 2022): 2265. http://dx.doi.org/10.3390/s22062265.
Повний текст джерелаАнотація:
Narrowband power-line communication seems to be a suitable communication technology designed for off-grid renewable energy solutions. Existing electrical installations can be designed both for the transmission of electricity and for the communication of electrical equipment operating inside such an installation. This study presents an implementation of the above-mentioned off-grid communication system and examines the basic problems related to its exploitation. The authors of this article focused their attention primarily on examining the disturbance of the communication channel caused by the use of typical electrical devices, such as: a light bulb, a kettle, etc. used in a household. The aim of the research was also to find the impact of switching on individual devices and their combinations on the disturbances during data transmission. Measurements of incorrectly transmitted data packets were carried out and then the test results were referred to the error measures. Moreover, the influence of the carrier frequencies on the signal attenuation and the method of eliminating the existing interferences were also discussed.
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Chen, Yeying, Enrico Mohns, Michael Seckelmann, and Soeren de Rose. "Precise Amplitude and Phase Determination Using Resampling Algorithms for Calibrating Sampled Value Instruments." Sensors 20, no. 24 (December 21, 2020): 7345. http://dx.doi.org/10.3390/s20247345.
Повний текст джерелаАнотація:
Sampling-based calibration systems for calibrating “Sampled Value” (SV)-based instruments for substation automation require synchronised and time-aligned sampling processes. As the signal frequency of the power grid is always asynchronous to the standardised sampling frequencies according to IEC 61869-9, the sampled waveforms of the calibration system and of the SV-based device under test can be resampled to be synchronised and to allow better accuracy in the following measurements based on the Discrete Fourier Transform (DFT) of the resampled waveforms. The paper presents simulations and results for different resampling algorithms. A modified sinc interpolation method with a finite impulse response (FIR) is presented. The deviation of the results for the root mean square (RMS) and phase angle is in the order of 10−8V/V (or rad) for normalised frequencies of up to 20% of the sampling frequency. No practical degradation in the presence of noise and harmonics could be observed. In addition, laboratory experiments demonstrate the realization of the proposed resampling process in the future SV-based calibration systems for SV-based instrumentation.
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Navratil, Jan, Miroslav Manas, Michal Stanek, David Manas, Martin Bednarik, Ales Mizera, and Tomas Gavenda. "Utilization of Terahertz Spectroscopy for Optical Behavior Determination of Recycled Modified HDPE." Advanced Materials Research 1025-1026 (September 2014): 547–50. http://dx.doi.org/10.4028/www.scientific.net/amr.1025-1026.547.
Повний текст джерелаАнотація:
Little research was done to investigate possible utilization of irradiated materials after the end of their lifetime. This research paper deals with the possible utilization of irradiated high-density polyethylene (HDPEx) after its service life. Irradiated HDPE was used as filler into the virgin low-density polyethylene (LDPE). Three material combinations were investigated (powder/powder, granules/powder and granules/grit) and influence of the filler on optical behavior was measured. Terahertz spectroscopy at wide range of frequencies was used for refractive index determination. According to measured data there is significant influence by the amount of the filler. Moreover influence of particle size was also observed. All three combinations have similar curve courses; however the most consistent results were achieved at the powder/powder combination. Behavior of virgin LDPE and virgin HDPE is in correlation with previous findings.
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Maisto, Maria Antonia, Mehdi Masoodi, Giovanni Leone, Raffaele Solimene, and Rocco Pierri. "Scattered Far-Field Sampling in Multi-Static Multi-Frequency Configuration." Sensors 21, no. 14 (July 10, 2021): 4724. http://dx.doi.org/10.3390/s21144724.
Повний текст джерелаАнотація:
This paper deals with an inverse scattering problem under a linearized scattering model for a multi-static/multi-frequency configuration. The focus is on the determination of a sampling strategy that allows the reduction of the number of measurement points and frequencies and at the same time keeping the same achievable performance in the reconstructions as for full data acquisition. For the sake of simplicity, a 2D scalar geometry is addressed, and the scattered far-field data are collected. The relevant scattering operator exhibits a singular value spectrum that abruptly decays (i.e., a step-like behavior) beyond a certain index, which identifies the so-called number of degrees of freedom (NDF) of the problem. Accordingly, the sampling strategy is derived by looking for a discrete finite set of data points for which the arising semi-discrete scattering operator approximation can reproduce the most significant part of the singular spectrum, i.e., the singular values preceding the abrupt decay. To this end, the observation variables are suitably transformed so that Fourier-based arguments can be used. The arising sampling grid returns several data that is close to the NDF. Unfortunately, the resulting data points (in the angle-frequency domain) leading to a complicated measurement configuration which requires collecting the data at different spatial positions for each different frequency. To simplify the measurement configuration, a suboptimal sampling strategy is then proposed which, by an iterative procedure, enforces the sampling points to belong to a rectangular grid in the angle-frequency domain. As a result of this procedure, the overall data points (i.e., the couples angle-frequency) actually increase but the number of different angles and frequencies reduce and lead to a measurement configuration that is more practical to implement. A few numerical examples are included to check the proposed sampling scheme.
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Quintana-Barcia, Pablo, Tomislav Dragicevic, Jorge Garcia, Javier Ribas, and Josep Guerrero. "A Distributed Control Strategy for Islanded Single-Phase Microgrids with Hybrid Energy Storage Systems Based on Power Line Signaling." Energies 12, no. 1 (December 28, 2018): 85. http://dx.doi.org/10.3390/en12010085.
Повний текст джерелаАнотація:
Energy management control is essential to microgrids (MGs), especially to single-phase ones. To handle the variety of distributed generators (DGs) that can be found in a MG, e.g., renewable energy sources (RESs) and energy storage systems (ESSs), a coordinated power regulation is required. The latter are generally battery-based systems whose lifetime is directly related to charge/discharge processes, whereas the most common RESs in a MG are photovoltaic (PV) units. Hybrid energy storage systems (HESS) extend batteries life expectancy, thanks to the effect of supercapacitors, but they also require more complex control strategies. Conventional droop methodologies are usually applied to provide autonomous and coordinated power control. This paper proposes a method for coordination of a single-phase MG composed by a number of sources (HESS, RES, etc.) using power line signaling (PLS). In this distributed control strategy, a signal whose frequency is higher than the grid is broadcasted to communicate with all DGs when the state of charge (SoC) of the batteries reaches a maximum value. This technique prevents batteries from overcharging and maximizes the power contribution of the RESs to the MG. Moreover, different commands apart from the SoC can be broadcasted, just by changing to other frequency bands. The HESS master unit operates as a grid-forming unit, whereas RESs act as grid followers. Supercapacitors in the HESS compensate for energy peaks, while batteries respond smoothly to changes in the load, also expanding its lifetime due to less aggressive power references. In this paper, a control structure that allows the implementation of this strategy in single-phase MGs is presented, with the analysis of the optimal range of PLS frequencies and the required self-adaptive proportional-resonant controllers.
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Zou, Ling, Sabine Griessbach, Lars Hoffmann, Bing Gong, and Lunche Wang. "Revisiting global satellite observations of stratospheric cirrus clouds." Atmospheric Chemistry and Physics 20, no. 16 (August 26, 2020): 9939–59. http://dx.doi.org/10.5194/acp-20-9939-2020.
Повний текст джерелаАнотація:
Abstract. As knowledge about the cirrus clouds in the lower stratosphere is limited, reliable long-term measurements are needed to assess their characteristics, radiative impact and important role in upper troposphere and lower stratosphere (UTLS) chemistry. We used 6 years (2006–2012) of Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) measurements to investigate the global and seasonal distribution of stratospheric cirrus clouds and compared the MIPAS results with results derived from the latest version (V4.x) of the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) data. For the identification of stratospheric cirrus clouds, precise information on both the cloud top height (CTH) and the tropopause height is crucial. Here, we used lapse rate tropopause heights estimated from the ERA-Interim global reanalysis. Considering the uncertainties of the tropopause heights and the vertical sampling grid, we define CTHs more than 0.5 km above the tropopause as stratospheric for CALIPSO data. For MIPAS data, we took into account the coarser vertical sampling grid and the broad field of view so that we considered cirrus CTHs detected more than 0.75 km above the tropopause as stratospheric. Further sensitivity tests were conducted to rule out sampling artefacts in MIPAS data. The global distribution of stratospheric cirrus clouds was derived from night-time measurements because of the higher detection sensitivity of CALIPSO. In both data sets, MIPAS and CALIPSO, the stratospheric cirrus cloud occurrence frequencies are significantly higher in the tropics than in the extra-tropics. Tropical hotspots of stratospheric cirrus clouds associated with deep convection are located over equatorial Africa, South and Southeast Asia, the western Pacific, and South America. Stratospheric cirrus clouds were more often detected in December–February (15 %) than June–August (8 %) in the tropics (±20∘). At northern and southern middle latitudes (40–60∘), MIPAS observed about twice as many stratospheric cirrus clouds (occurrence frequencies of 4 %–5 % for MIPAS rather than about 2 % for CALIPSO). We attribute more frequent observations of stratospheric cirrus clouds with MIPAS to the higher detection sensitivity of the instrument to optically thin clouds. In contrast to the difference between daytime and night-time occurrence frequencies of stratospheric cirrus clouds by a factor of about 2 in zonal means in the tropics (4 % and 10 %, respectively) and at middle latitudes for CALIPSO data, there is little diurnal cycle in MIPAS data, in which the difference of occurrence frequencies in the tropics is about 1 percentage point in zonal mean and about 0.5 percentage point at middle latitudes. The difference between CALIPSO day and night measurements can also be attributed to their differences in detection sensitivity. Future work should focus on better understanding the origin of the stratospheric cirrus clouds and their impact on radiative forcing and climate.
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Saravanan, S., M. I. Sakri, and P. V. Mohanram. "Fatigue Prediction of Electronic Packages Subjected to Random Vibrations." Journal of Microelectronics and Electronic Packaging 5, no. 1 (January 1, 2008): 31–35. http://dx.doi.org/10.4071/1551-4897-5.1.31.
Повний текст джерелаАнотація:
In modern automotive control modules, mechanical failures of surface-mounted electronic components such as microprocessors, crystals, capacitors, inductors, transformers, ball grid array packages (BGA), quad flat packages (QFP), and chip-scale packages (CSP) are major road blocks in the design cycle and reliability of the product. This paper presents a general approach for failure analysis and fatigue prediction of electronic component like QFPs under automotive vibration environments. The mechanical performance of this package was studied through a finite element modeling approach for a given vibration environment in an automotive application. The vibration simulation provides system characteristics such as modal shapes, modal frequencies, and dynamic responses, including displacements and stresses. By using the results of vibration simulation, fatigue life is predicted based on Miner's cumulative damage ratio and the three-band technique. Detailed (local) model of the lead wire joint is built to correlate the system level model to obtain solder stresses. On the test vehicle, a 160-pin gull-wing lead plastic QFP was chosen to illustrate this approach for failure analysis and fatigue life prediction. From the analysis, it was found that the life used up by the lead wires was 11.6% of the 4-h vibration test.
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Toba, Masaya, Shuji Nomoto, Nobuhito Komuro, Kazuyuki Mitsukura, Shinichiro Abe, Takashi Masuko, and Kazuhiko Kurafuchi. "Assembly of Cu Wirings with Ultrasmooth and High-Adhesive Electroless Cu Seed Layer by Using UV Modification and Low Attenuation of High-Frequency Transmission Property." Journal of Microelectronics and Electronic Packaging 17, no. 2 (April 1, 2020): 45–51. http://dx.doi.org/10.4071/imaps.1100914.
Повний текст джерелаАнотація:
Abstract Semiconductor packages for high-performance devices with printed circuit boards having multiwiring layers such as flip-chip ball grid array have been attracting the attention to realize ultrare-liable and low-latency communications in 5G networking. Cu wirings for the package are usually fabricated by via formation by laser for dielectric, desmear, electroless Cu seed formation, photoresist patterning, electrolytic Cu plating, resist stripping, and seed layer etching. Although a desmear process can obtain enough adhesion between dielectric and Cu seed layer by anchoring effect to secure reliabilities, the interface between dielectric and Cu seed layer should be smooth to achieve low attenuation of electric signals at high frequencies. Here, instead of a desmear process, we applied a UV modification for the surface of dielectric to realize a smooth and high-adhesive seed layer against dielectric. We obtained .8 kN/m of peel strength between dielectric and Cu seed layer in spite of surface roughness of the dielectric being 45 nm by a nanolevel anchoring effect at the UV-modified layer. Because of the smooth interface by UV modification, the S21 value of microstrip line was 26% improved compared with that assembled through the desmear process at 60 GHz.
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Gosselin-Cliche, Benjamin, and Bernard Giroux. "3D frequency-domain finite-difference viscoelastic-wave modeling using weighted average 27-point operators with optimal coefficients." GEOPHYSICS 79, no. 3 (May 1, 2014): T169—T188. http://dx.doi.org/10.1190/geo2013-0368.1.
Повний текст джерелаАнотація:
Experimental data suggest that the viscoelastic behavior of rocks is more easily and accurately described in the frequency domain than in the time domain, supporting the idea of simulating seismic wave propagation in the frequency domain. We evaluated weighted-averaged 27-point finite-difference operators for 3D viscoelastic wave modeling in the frequency domain. Within the proposed framework, we developed general equations for normalized phase velocities that can be used with arbitrary finite-difference operators. Three sets of weighting coefficients for second-order central finite-difference operators that minimize the numerical dispersion for up to five grid points per wavelength were found using a damped least-squares (LS) criterion as well as a global optimization scheme based on [Formula: see text]- and [Formula: see text]-norm criteria. The three sets produced very similar dispersion curves, and improvement provided by global optimization appeared marginal in this respect. We also evaluated a discrete form for the heterogeneous formulation of the 3D viscoelastic equations with a perfectly match layer (PML). Heuristic performance assessment of frequency-dependent PML absorption coefficients provided a simple rule giving good results for eight PMLs at all frequencies. The proposed formalism was implemented with a massively parallel direct solver. Modeling results were compared with an analytic solution and a time-domain finite-difference code, and they gave good agreement when using LS and [Formula: see text]-norm optimal coefficients. On the other hand, [Formula: see text]-norm coefficients produced noisy results, indicating that minimizing the difference between analytic and numerical phase velocities, although necessary, is not a sufficient condition to guarantee low-numerical noise. Finally, analysis of the computational resources required to factorize the impedance matrix revealed that the memory complexity of the factorization is [Formula: see text] for an [Formula: see text] grid, compared to [Formula: see text] for the viscoacoustic case.
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Kujanpää, J., and N. Kalakoski. "Operational surface UV radiation product from GOME-2 and AVHRR/3 data." Atmospheric Measurement Techniques 8, no. 10 (October 21, 2015): 4399–414. http://dx.doi.org/10.5194/amt-8-4399-2015.
Повний текст джерелаАнотація:
Abstract. The surface ultraviolet (UV) radiation product, version 1.20, generated operationally in the framework of the Satellite Application Facility on Ozone and Atmospheric Chemistry Monitoring (O3M SAF) of the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) is described. The product is based on the total ozone column derived from the measurements of the second Global Ozone Monitoring Experiment (GOME-2) instrument aboard EUMETSAT's polar orbiting meteorological operational (Metop) satellites. Cloud cover is taken into account by retrieving cloud optical depth from the channel 1 reflectance of the third Advanced Very High-Resolution Radiometer (AVHRR/3) instrument aboard both Metop in the morning orbit and Polar Orbiting Environmental Satellites (POES) of the National Oceanic and Atmospheric Administration (NOAA) in the afternoon orbit. In addition, more overpasses are used at high latitudes where the swaths of consecutive orbits overlap. The input satellite data are received from EUMETSAT's Multicast Distribution System (EUMETCast). The surface UV product includes daily maximum dose rates and integrated daily doses with different biological weighting functions, integrated ultraviolet B (UVB) and ultraviolet A (UVA) radiation, solar noon UV index and daily maximum photolysis frequencies of ozone and nitrogen dioxide at the surface level. The quantities are computed in a 0.5°×0.5° regular latitude–longitude grid and stored as daily files in the hierarchical data format (HDF5) within 2 weeks from sensing. The product files are archived in the O3M SAF distributed archive and can be ordered via the EUMETSAT Data Centre.
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Yoon, Inseop, Seongwoog Oh, and Jungsuek Oh. "Affordable Thin Lens Using Single Polarized Disparate Filter Arrays for Beyond 5G toward 6G." Sensors 19, no. 18 (September 14, 2019): 3982. http://dx.doi.org/10.3390/s19183982.
Повний текст джерелаАнотація:
This paper proposes a novel design approach for a thin lens with the aim of overcoming fineness limits in the commercial millimeter wave printed circuit board (PCB) manufacturing process. The PCB manufacturing process typically does not allow the fabrication of metallic patterns with a gap and width of less than 100 μm. This hampers expanding thin lens technology to 5G commercial applications, especially when such technology is considered for 60 GHz or higher frequency, which requires a finer gap and width of metallic traces. This paper proposes that problematic process conditions can be mitigated when a lens is designed by establishing single-polarized lumped element models where larger capacitance and inductance values can be obtained for the same patch and grid unit cells. While the proposed design technique is more advantageous at higher target frequencies, a 60 GHz application and a wireless backhaul system is selected because of a limited range of frequencies that can be measured by an available vector network analyzer. The required gap or width of metallic traces can be widened significantly by using the proposed single-polarized unit cells to acquire the same in-plane capacitance or inductance. This enables the lens operating at higher-frequency under the process limits in fabricable fine traces. Finally, the effectiveness of the simulated design procedure is demonstrated by fabricating a 60 GHz thin lens that can achieve a gain enhancement of 16 dB for a 4 × 4 patch antenna array with a gain of 16.5 dBi.
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Hu, Ruyun, Liang Wang, and Song Fu. "Investigation of the coherent structures in flow behind a backward-facing step." International Journal of Numerical Methods for Heat & Fluid Flow 26, no. 3/4 (May 3, 2016): 1050–68. http://dx.doi.org/10.1108/hff-09-2015-0403.
Повний текст джерелаАнотація:
Purpose – The purpose of this paper is to investigate the characteristic flow structures behind a backward-facing step. With better understanding of unsteady features, effective control practice with harmonic actuation is illustrated. Design/methodology/approach – The present study employs Improved Delayed Detached Eddy Simulation to resolve flow turbulence with a finite-volume approach on structured grid mesh. The coherent structure is displayed through temporal- and spatial-evolution of pressure fluctuations. Characteristic frequencies in different flow regions are extracted using fast Fourier transform. Dynamic mode decomposition method is applied to uncover the critical dynamic modes. Findings – The time- and spanwise-averaged quantities agree well with experimental data. It is observed that two distinct modes exist: shear layer mode and shedding mode. The former is related to Kelvin-Helmholtz instability mechanism, vortex pairing and step mode with non-dimensional frequency, Sth,st at around 0.2. The latter is of multi-scale, with a typical coherent structure shedding frequency, Sth,st at 0.074. Step mode interacts with shedding mode in the reattachment region, resulting in the low-frequency characteristics. Originality/value – An optimal excitation frequency to reduce recirculation bubble length is obtained at about Sth,st =0.2 with an explanation.
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Bouakoura, Mohamed, Mohamed-Said Naït-Saïd, and Nasreddine Nait-Said. "Incipient Inter-Turn Short Circuit Fault Estimation Based on a Faulty Model Observer and ANN-Method for Induction Motor Drives." Recent Advances in Electrical & Electronic Engineering (Formerly Recent Patents on Electrical & Electronic Engineering) 12, no. 4 (August 23, 2019): 374–83. http://dx.doi.org/10.2174/2352096511666180705113021.
Повний текст джерелаАнотація:
Background: According to statistics, short circuit faults are the second most frequent faults in induction motors. Thus, in this paper, we investigated inter turn short circuit faults in their early stage. Methods: A new equivalent model of the induction motor with turn to turn fault on one phase has been developed. This model has been used to establish two schemes to estimate the severity of the short circuit fault. In the first scheme, the faulty model is considered as an observer, where a correction of an error between the measured and the estimated currents is the kernel of the fault severity estimator. However, to develop the second method, the model was required only in the training process of an artificial neural network (ANN). Since stator faults have a signature on symmetrical components of phase currents, the magnitudes and angles of these components were used with the mean speed value as inputs of the ANN. A simulation on MATLAB of both techniques has been performed with various stator frequencies. Results: The suggested schemes prove a unique efficiency in the estimation of incipient turn to turn fault. Besides, the ANN based scheme is less complex which reduces its implementation cost. Conclusion: To monitor the stator of an induction motor, the choice of the appropriate algorithm should be done according to the system in which the motor will be installed. If the motor is directing connected to the grid or fed via an inverter with a variable DC bus voltage, the observer would be better, otherwise, the ANN algorithm is recommended.
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Misbakhov, Rin Sh, A. N. Vasev, A. Zh Sakhabutdinov, I. I. Nureev, O. G. Morozov, K. A. Lipatnikov, and A. A. Vasilets. "Address Fiber Optical Sensor for Relative Humidity Measuring in a Switchgear." Radio Engineering, no. 1 (March 5, 2020): 1–16. http://dx.doi.org/10.36027/rdeng.0120.0000157.
Повний текст джерелаАнотація:
A number of governing documents and by-laws of the Russian Federation, branch ministries, departments and companies have introduced the use of measuring relative air humidity, elements insulation, and SF6 into operation and maintenance process of complete switchgear. A wide range of high-precision laboratory instruments has been developed to implement these measurements. However, as a rule, these are scheduled measurements to be carried out once or twice a quarter, although the constant on-line monitoring of humidity is concerned in both the production and scientific circles of the energy industry. The possibility of on-line monitoring appeared with the advent of fiber-optic object-based passive networks for collecting information and the possibility of forming interrogation channels in them, which is provided for by the development of the Smart Grid Plus concept. Fiber optic sensors, single in their physical layer structure with passive optical networks, are highly robust and resistant to high electromagnetic fields, typical of those generated in a switchgear, and are designed to operate in harsh environments. Among their broad class, fiber optic sensors on Bragg gratings, which differ from others by direct measurement methods, have significant advantages. In particular, an increase or decrease in relative humidity will lead to a corresponding change in the wavelength of the sensing source reflected from the grating, which can be measured with an accuracy of sixth place from its absolute value.This paper proposes to consider a two-element sensor of relative humidity of a parallel structure, which differs from the existing ones by using address fiber Bragg gratings made in SMF-28 fiber. One of the gratings has a polyimide-replaced quartz shell, synthesized using a reductant fiber coating, and a completely multiplicative response to temperature and deformation caused by humidity. The second grating is recorded in a standard fiber and responds only to temperature. It is possible to include an additional third grating with a partially etched cladding, which can be used for refract metric measurements of the amount of condensed moisture on the elements of a complete switchgear. All the gratings are identical, have, as a rule, the same Bragg wavelength after manipulating their claddings, but they have differing unique addresses, which are formed by recording two transparency windows in each of the gratings with different difference frequency space. The transparency windows correspond to phase p-shifts symmetrically located at the same distance from the center of each grating. The structure obtained makes it possible to record information of the measurement conversion at the said difference frequencies in the radio range, which significantly increases the speed of relative humidity measurements and their accuracy by an order of magnitude more. In addition to what has been said, it is possible to note the capability for building a network of these sensors in series arranged in switchgear devices, with a different radiofrequency address group being used in each of them.
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Hannoun, Imad A., and E. John List. "Turbulent mixing at a shear-free density interface." Journal of Fluid Mechanics 189 (April 1988): 211–34. http://dx.doi.org/10.1017/s0022112088000977.
Повний текст джерелаАнотація:
The interaction of a sharp density interface with oscillating-grid-induced shear-free turbulence was experimentally investigated. A linear photodiode array was used in conjunction with laser-induced fluorescence to measure the concentration of dye that was initially only in the less dense layer. A laser-Doppler velocimeter was used to measure the vertical velocity in and above the density interface at a point where the dye concentration was also measured. Potential refractive-index-fluctuation problems were avoided using solutes that provided a homogeneous optical environment across the density interface. Internal wave spectra, amplitudes and velocities, as well as the vertical mass flux were measured. The results indicate that mixing occurs in intermittent bursts and that the gradient (local) Richardson number remains constant for a certain range of the overall Richardson number Rj, defined in terms of an integral lengthscale, buoyancy jump and turbulence intensity. The spectra of the internal waves decay as f−3 at frequencies below the maximum Brunt-Väisälä frequency. These findings give support to a model for oceanic mixing proposed by Phillips (1977) in which the internal waves are limited in their spectral density by sporadic local instabilities and breakdown to turbulence. The results also indicate that, for a certain Rj range, the thickness of the interfacial layer (normalized by the integral lengthscale of the turbulence) is a decreasing function of Rj. At sufficiently high Rj the interfacial thickness becomes limited by diffusive effects. Finally, we discuss a simple model for entrainment at a density interface in the presence of shear-free turbulence.
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Shoucri, Magdi. "Formation of electron holes in the long-time evolution of the bump-on-tail instability." Laser and Particle Beams 35, no. 4 (December 2017): 706–21. http://dx.doi.org/10.1017/s0263034617000775.
Повний текст джерелаАнотація:
AbstractAn Eulerian Vlasov code is applied for the numerical solution of the one-dimensional Vlasov–Poisson system of equations for electrons, and with ions forming an immobile background. We study the non-linear evolution of the bump-on-tail instability in the case when the system length L is greater than the wavelength λ of the unstable mode, with a beam density of 10% of the total density, nb = 0.1. We follow the growth and the saturation of an initially unstable wave perturbation, and the formation of a traveling Bernstein–Greene–Kruskal (BGK) mode, which evolves out of the instability. This first stage is followed by sidebands growing from round-off errors which develop and disrupt the BGK equilibrium. In the excited spectrum, mode coupling is mediated by the oscillating resonant particles and results in the electric energy of the system flowing to the longest wavelengths (inverse cascade), and reaching in the asymptotic state a steady state with constant amplitude oscillation modulated by the persistent oscillation of the trapped particles. Coherent phase-space electron holes are formed, which are localized phase-space regions of reduced density on trapped electron orbits, where the electron density is lower than the surrounding plasma electron density. The distribution function evolves to a shape with stationary inflection points of zero slope, at the phase velocities of the excited waves. The longest wavelengths show oscillations at frequencies below the plasma frequency, with phase velocities higher than that of the injected beam, which can accelerate electrons to energies in excess of the initial beam energy. The present work makes a connection between the formation of electron holes, the existence of inflection points of zero slopes in the electron distribution function at the phase velocities of the dominant waves, and at frequencies below the plasma frequency. A fine resolution grid is used in the Eulerian Vlasov code in the phase space and time to allow an accurate calculation of the time history of the system and of the dynamic and oscillation of the trapped particles in the low-density regions of the phase space, and of those particles at the separatrix regions of the vortex structures which evolve periodically between trapping and untrapping states and which can only be accurately studied using a fine-resolution phase-space grid.
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Ebrahimi Moghadam, Majid, Hamid Falaghi, and Mahdi Farhadi. "A Novel Method of Optimal Capacitor Placement in the Presence of Harmonics for Power Distribution Network Using NSGA-II Multi-Objective Genetic Optimization Algorithm." Mathematical and Computational Applications 25, no. 1 (March 19, 2020): 17. http://dx.doi.org/10.3390/mca25010017.
Повний текст джерелаАнотація:
One of the effective ways of reducing power system losses is local compensation of part of the reactive power consumption by deploying shunt capacitor banks. Since the capacitor’s impedance is frequency-dependent and it is possible to generate resonances at harmonic frequencies, it is important to provide an efficient method for the placement of capacitor banks in the presence of nonlinear loads which are the main cause of harmonic generation. This paper proposes a solution for a multi-objective optimization problem to address the optimal placement of capacitor banks in the presence of nonlinear loads, and it establishes a reasonable reconciliation between costs, along with improvement of harmonic distortion and a voltage index. In this paper, while using the harmonic power flow method to calculate the electrical quantities of the grid in terms of harmonic effects, the non-dominated sorting genetic (NSGA)-II multi-objective genetic optimization algorithm was used to obtain a set of solutions named the Pareto front for the problem. To evaluate the effectiveness of the proposed method, the problem was tested for an IEEE 18-bus system. The results were compared with the methods used in eight other studies. The simulation results show the considerable efficiency and superiority of the proposed flexible method over other methods.
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Anderson, David A., Michael C. Heilemann, and Mark F. Bocko. "Optimized Driver Placement for Array-Driven Flat-Panel Loudspeakers." Archives of Acoustics 42, no. 1 (March 1, 2017): 93–104. http://dx.doi.org/10.1515/aoa-2017-0010.
Повний текст джерелаАнотація:
Abstract The recently demonstrated ‘modal crossover network’ method for flat panel loudspeaker tuning employs an array of force drivers to selectively excite one or more panel bending modes from a spectrum of panel bending modes. A regularly spaced grid of drivers is a logical configuration for a two-dimensional driver array, and although this can be effective for exciting multiple panel modes it will not necessarily exhibit strong coupling to all of the modes within a given band of frequencies. In this paper a method is described to find optimal force driver array layouts to enable control of all the panel bending modes within a given frequency band. The optimization is carried out both for dynamic force actuators, treated as point forces, and for piezoelectric patch actuators. The optimized array layouts achieve similar maximum mode coupling efficiencies in comparison with regularly spaced driver arrays; however, in the optimized arrays all of the modes within a specified frequency band may be independently addressed, which is important for achieving a desired loudspeaker frequency response. Experiments on flat panel loudspeakers with optimized force actuator array layouts show that each of the panel modes within a selected frequency band may be addressed independently and that the inter-modal crosstalk is typically −30 dB or less with non-ideal drivers.
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Abdelmassih, Gorg, Mohammed Al-Numay, and Abdelali El Aroudi. "Map Optimization Fuzzy Logic Framework in Wind Turbine Site Selection with Application to the USA Wind Farms." Energies 14, no. 19 (September 26, 2021): 6127. http://dx.doi.org/10.3390/en14196127.
Повний текст джерелаАнотація:
In this study, we analyze observational and predicted wind energy datasets of the lower 48 states of the United States, and we intend to predict an optimal map for new turbines placement. Several approaches have been implemented to investigate the correlation between current wind power stations, power capacity, wind seasonality, and site selection. The correlation between stations is carried out according to Pearson correlation coefficient approach joined with the spherical law of cosines to calculate the distances. The high correlation values between the stations spaced within a distance of 100 km show that installing more turbines close to the current farms would assist the electrical grid. The total power capacity indicates that the current wind turbines are utilizing approximately 70% of the wind resources available in the turbine’s sites. The Power spectrum of Fourier’s spectral density indicates main, secondary, and harmonic frequencies correspond to yearly, semiyearly, and daily wind-speed periodic patterns. We propose and validate a numerical approach based on a novel fuzzy logic framework for wind turbines placement. Map optimizations are fitted considering different parameters presented in wind speed, land use, price, and elevation. Map optimization results show that suitable sites for turbines placement are in general agreement with the direction of the correlation approach.
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Harmanci, Yunus, Utku Gülan, Markus Holzner, and Eleni Chatzi. "A Novel Approach for 3D-Structural Identification through Video Recording: Magnified Tracking." Sensors 19, no. 5 (March 11, 2019): 1229. http://dx.doi.org/10.3390/s19051229.
Повний текст джерелаАнотація:
Advancements in optical imaging devices and computer vision algorithms allow the exploration of novel diagnostic techniques for use within engineering systems. A recent field of application lies in the adoption of such devices for non-contact vibrational response recordings of structures, allowing high spatial density measurements without the burden of heavy cabling associated with conventional technologies. This, however, is not a straightforward task due to the typically low-amplitude displacement response of structures under ambient operational conditions. A novel framework, namely Magnified Tracking (MT), is proposed herein to overcome this limitation through the synergistic use of two computer vision techniques. The recently proposed phase-based motion magnification (PBMM) framework, for amplifying motion in a video within a defined frequency band, is coupled with motion tracking by means of particle tracking velocimetry (PTV). An experimental campaign was conducted to validate a proof-of-concept, where the dynamic response of a shear frame was measured both by conventional sensors as well as a video camera setup, and cross-compared to prove the feasibility of the proposed non-contact approach. The methodology was explored both in 2D and 3D configurations, with PTV revealing a powerful tool for the measurement of perceptible motion. When MT is utilized for tracking “imperceptible” structural responses (i.e., below PTV sensitivity), via the use of PBMM around the resonant frequencies of the structure, the amplified motion reveals the operational deflection shapes, which are otherwise intractable. The modal results extracted from the magnified videos, using PTV, demonstrate MT to be a viable non-contact alternative for 3D modal identification with the benefit of a spatially dense measurement grid.
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Ristić, Aleksandar, Miro Govedarica, Lara Pajewski, Milan Vrtunski, and Željko Bugarinović. "Using Ground Penetrating Radar to Reveal Hidden Archaeology: The Case Study of the Württemberg-Stambol Gate in Belgrade (Serbia)." Sensors 20, no. 3 (January 22, 2020): 607. http://dx.doi.org/10.3390/s20030607.
Повний текст джерелаАнотація:
This paper presents the results of a research study where ground penetrating radar (GPR) was successfully used to reveal the remains of the Württemberg-Stambol Gate in the subsurface of Republic Square, in Belgrade, Serbia. GPR investigations were carried out in the context of renovation works in the square, which involved rearranging traffic control, expanding the pedestrian zone, renewing the surface layer, and valorising existing archaeological structures. The presence of the gate remains was suggested by historical documents and information from previous restoration works. A pulsed radar unit was used for the survey, with antennas having 200- and 400-MHz central frequencies. Data were recorded over a grid and two three-dimensional models were built, one for each set of antennas. The grid was the same for both sets of antennas, therefore the two models could be compared. Several horizontal cross sections of the models were plotted, corresponding to different depths; these images were carefully examined and interpreted, paying particular attention to signatures that could originate from the sought archaeological structures. Reflections coming from the gate remains were identified in both models, in the same region of the survey area and at the same depth; the geometry, size, and layout of the gate columns, as well as of other construction elements belonging to the gate, were determined with very good accuracy. Based on the GPR findings, archaeological excavation works were carried out in the region where the foundation remains were estimated to be. The presence of the remains was confirmed, with various columns and side walls. This case study demonstrates and further corroborates the effectiveness and reliability of GPR for the non-invasive prospection of archaeological structures hidden in the heterogeneous subsurface of urban environments. In the opinion of the authors, GPR should be incorporated as a routine field procedure in construction and renovation projects involving historical cities.
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Hou, Wanting, Li-Yun Fu, José M. Carcione, Zhiwei Wang, and Jia Wei. "Simulation of thermoelastic waves based on the Lord-Shulman theory." GEOPHYSICS 86, no. 3 (April 8, 2021): T155—T164. http://dx.doi.org/10.1190/geo2020-0515.1.
Повний текст джерелаАнотація:
Thermoelasticity is important in seismic propagation due to the effects related to wave attenuation and velocity dispersion. We have applied a novel finite-difference (FD) solver of the Lord-Shulman thermoelasticity equations to compute synthetic seismograms that include the effects of the thermal properties (expansion coefficient, thermal conductivity, and specific heat) compared with the classic forward-modeling codes. We use a time splitting method because the presence of a slow quasistatic mode (the thermal mode) makes the differential equations stiff and unstable for explicit time-stepping methods. The spatial derivatives are computed with a rotated staggered-grid FD method, and an unsplit convolutional perfectly matched layer is used to absorb the waves at the boundaries, with an optimal performance at the grazing incidence. The stability condition of the modeling algorithm is examined. The numerical experiments illustrate the effects of the thermoelasticity properties on the attenuation of the fast P-wave (or E-wave) and the slow thermal P-wave (or T-wave). These propagation modes have characteristics similar to the fast and slow P-waves of poroelasticity, respectively. The thermal expansion coefficient has a significant effect on the velocity dispersion and attenuation of the elastic waves, and the thermal conductivity affects the relaxation time of the thermal diffusion process, with the T mode becoming wave-like at high thermal conductivities and high frequencies.
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Beck, Rainer. "Magnetism in galaxies – Observational overview and next generation radio telescopes." Proceedings of the International Astronomical Union 6, S274 (September 2010): 325–32. http://dx.doi.org/10.1017/s1743921311007228.
Повний текст джерелаАнотація:
AbstractThe strength and structure of cosmic magnetic fields is best studied by observations of radio continuum emission, its polarization and its Faraday rotation. Fields with a well-ordered spiral structure exist in many types of galaxies. Total field strengths in spiral arms and bars are 20–30 μG and dynamically important. Strong fields in central regions can drive gas inflows towards an active nucleus. The strongest regular fields (10–15 μG) are found in interarm regions, sometimes forming “magnetic spiral arms” between the optical arms. The typical degree of polarization is a few % in spiral arms, but high (up to 50%) in interarm regions. The detailed field structures suggest interaction with gas flows. Faraday rotation measures of the polarization vectors reveals large-scale patterns in several spiral galaxies which are regarded as signatures of large-scale (coherent) fields generated by dynamos. – Polarization observations with the forthcoming large radio telescopes will open a new era in the observation of magnetic fields and should help to understand their origin. Low-frequency radio synchrotron emission traces low-energy cosmic ray electrons which can propagate further away from their origin. LOFAR (30–240 MHz) will allow us to map the structure of weak magnetic fields in the outer regions and halos of galaxies, in galaxy clusters and in the Milky Way. Polarization at higher frequencies (1–10 GHz), to be observed with the EVLA, MeerKAT, APERTIF and the SKA, will trace magnetic fields in the disks and central regions of galaxies in unprecedented detail. All-sky surveys of Faraday rotation measures towards a dense grid of polarized background sources with ASKAP and the SKA are dedicated to measure magnetic fields in distant intervening galaxies and clusters, and will be used to model the overall structure and strength of the magnetic field in the Milky Way.
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Gkikas, A., S. Basart, N. Hatzianastassiou, E. Marinou, V. Amiridis, S. Kazadzis, J. Pey, et al. "Mediterranean desert dust outbreaks and their vertical structure based on remote sensing data." Atmospheric Chemistry and Physics Discussions 15, no. 19 (October 14, 2015): 27675–748. http://dx.doi.org/10.5194/acpd-15-27675-2015.
Повний текст джерелаАнотація:
Abstract. The main aim of the present study is to describe the vertical structure of the intense Mediterranean dust outbreaks, based on the use of satellite and surface-based retrievals/measurements. Strong and extreme desert dust (DD) episodes are identified at 1° × 1° spatial resolution, over the period March 2000–February 2013, through the implementation of an updated objective and dynamic algorithm. According to the algorithm, strong DD episodes occurring at a specific place correspond to cases in which the daily aerosol optical depth at 550 nm (AOD550 nm) exceeds or equals the long-term mean AOD550 nm (Mean) plus two standard deviations (SD) value being smaller than Mean + 4 · SD. Extreme DD episodes correspond to cases in which the daily AOD550 nm value equals or exceeds Mean + 4 · SD. For the identification of DD episodes additional optical properties (Ångström exponent, fine fraction, effective radius and Aerosol Index) derived by the MODIS-Terra & Aqua (also AOD retrievals), OMI-Aura and EP-TOMS databases are used as inputs. According to the algorithm using MODIS-Terra data, over the period March 2000–February 2013, strong DD episodes occur more frequently (up to 9.9 episodes yr−1) over the western Mediterranean while the corresponding frequencies for the extreme ones are smaller (up to 3.3 episodes yr−1, central Mediterranean Sea). In contrast to their frequency, dust episodes are more intense (AODs up to 4.1), over the central and eastern Mediterranean Sea, off the northern African coasts. Slightly lower frequencies and higher intensities are found when the satellite algorithm operates based on MODIS-Aqua retrievals, for the period 2003–2012. The performance of the satellite algorithm is assessed against surface-based daily data from 109 sun-photometric (AERONET) and 22 PM10 stations. The agreement between AERONET and MODIS AOD is satisfactory (R = 0.505 – 0.75) improving considerably when MODIS level 3 retrievals with higher sub-grid spatial representativeness and homogeneity are considered. Moreover, the evaluation analysis using other AERONET spectral optical and microphysical properties during the days of episodes as well as surface PM10 concentrations also provides strong support of the successful performance of the satellite algorithm. The CALIOP vertical profiles of pure and polluted dust observations and the associated total backscatter coefficient at 532 nm (β532 nm), indicate that dust particles are mainly detected between 0.5 and 6 km, though they can reach 8 km between the parallels 32 and 38° N in warm seasons, while an increased number of CALIOP dust records at higher altitudes is observed with increased latitude, northwards to 40° N, revealing an ascending mode of the dust transport. However, the overall intensity of DD episodes is maximum (up to 0.006 km−1 sr−1) below 2 km and at the southern parts of the study region (30–34° N). Additionally, the average thickness of dust layers gradually decreases from 4 to 2 km moving from south to north. In spring, dust layers of moderate-to-high β532 nm values (~ 0.004 km−1 sr−1) are detected over the Mediterranean (35–42° N), extending from 2 to 4 km. Over the western Mediterranean, dust layers are observed between 2 and 6 km, while their base height is decreased down to 0.5 km for increasing longitudes underlying the role of topography and thermal convection. The vertical profiles of CALIOP β532 nm confirm the multilayered structure of the Mediterranean desert dust outbreaks on both annual and seasonal basis, with several dust layers of variable geometrical characteristics and intensities.
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Doliński, Łukasz, Marek Krawczuk, Magdalena Palacz, Wiktor Waszkowiak, and Arkadiusz Żak. "The Influence of the Grid Density of Measurement Points on Damage Detection in an Isotropic Plate by the Use of Elastic Waves and Laser Scanning Doppler Vibrometry." Sensors 21, no. 21 (November 7, 2021): 7394. http://dx.doi.org/10.3390/s21217394.
Повний текст джерелаАнотація:
Damage detection in structural components, especially in mechanical engineering, is an important element of engineering practice. There are many methods of damage detection, in which changes in various parameters caused by the presence of damage are analysed. Recently, methods based on the analysis of changes in dynamic parameters of structures, that is, frequencies or mode shapes of natural vibrations, as well as changes in propagating elastic waves, have been developed at the highest rate. Diagnostic methods based on the elastic wave propagation phenomenon are becoming more and more popular, therefore it is worth focusing on the improvement of the efficiency of these methods. Hence, a question arises about whether it is possible to shorten the required measurement time without affecting the sensitivity of the diagnostic method used. This paper discusses the results of research carried out by the authors in this regard both numerically and experimentally. The numerical analysis has been carried out by the use of the Time-domain Spectral Finite Element Method (TD-SFEM), whereas the experimental part has been based on the measurement performed by 1-D Laser Doppler Scanning Vibrometery (LDSV).
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Gadgil, Krutuja S., Prabodh Khampariya, and Shashikant M. Bakre. "An Overview on the Investigation of Power Quality Problems and Harmonic Exclusion in the Power System Using Frequency Estimation Techniques." NeuroQuantology 20, no. 5 (April 30, 2022): 38–52. http://dx.doi.org/10.14704/nq.2022.20.5.nq22147.
Повний текст джерелаАнотація:
The present research paper is based on a survey on the Investigation of Power Quality Problems and Harmonic Exclusion in the Power System using the Frequency Estimation Technique. The majority of FD approaches are openloop, and they are based on Fourier series analysis in most cases. When applied to frequency domain approaches, Fourier series analysis is a powerful mathematical tool that allows users to acquire a wide range of frequency components by multiplying the input by a set of trigonometric functions (sine/cosine) at various frequencies. Typically, the discrete implementation of the Fourier series, also known as the Discrete Fourier Transform, is used to compute results. DFT can be done quickly and simply using computer technology, and it can be used to estimate the grid signal parameters with improved selectivity and greater steady-state accuracy than other methods. The A/D conversion process of the input signals is required for the real-time implementation of the DFT, which necessitates the repeated sampling and updating of the input signals. However, in order to compute the N samples, this approach necessitates the use of N2 complex multiplication and N2–N complex addition. As a result, it was not extensively used prior to the introduction of the microprocessor.
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Zhang, Min, Shouhua Dong, Yaping Huang, Haibo Wu, Guiwu Chen, Mingdi Wei, and Wenqiang Yang. "Enhanced Difference Algorithm for Seismic Modeling Based on Fruit Fly Optimization." Journal of Environmental and Engineering Geophysics 22, no. 4 (December 2017): 353–64. http://dx.doi.org/10.2113/jeeg22.4.353.
Повний текст джерелаАнотація:
The acoustic wave equation is an important basis for seismic wave propagation, imaging, and migration. This equation has led to the development of finite difference methods, but these methods are prone to numerical instability and grid dispersion problems, with the issue of dispersion being the most vital. Optimization methods can improve the accuracy across a large range of wavenumbers or frequencies. In this paper, we present a novel evolutionary optimization scheme for the acoustic wave equation. Our approach involves combining the fruit fly optimization algorithm (FOA) and sampling approximation (SA) to obtain the optimal difference operator for a wide range of wavenumbers. The difference coefficients are optimized to be extracted by the FOA, and the function of fitness, which is used to introduce an iterative process to determine the best smells, is evaluated by acoustic wave simulations. Based on the space-domain dispersion relation, we prove that the accuracy with which the absolute error is minimized is the same as that of the relative error. Within a given range of wavenumbers, we propose a fitness function by minimizing the absolute errors of the space-domain dispersion relation, and the dispersion analysis reveals that this scheme is superior to the Taylor-expansion scheme. We conduct two experiments by applying homogeneous and complex models, respectively. Further, the modeling results indicate that the fruit fly optimization approach in conjunction with sampling approximation preserve a higher accuracy for a small operator length and reduce the numerical artifacts.
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Estrada, Elsa, Martha Patricia Martínez Vargas, Judith Gómez, Adriana Peña Pérez Negron, Graciela Lara López, and Rocío Maciel. "Smart Cities Big Data Algorithms for Sensors Location." Applied Sciences 9, no. 19 (October 8, 2019): 4196. http://dx.doi.org/10.3390/app9194196.
Повний текст джерелаАнотація:
A significant and very extended approach for Smart Cities is the use of sensors and the analysis of the data generated for the interpretation of phenomena. The proper sensor location represents a key factor for suitable data collection, especially for big data. There are different methodologies to select the places to install sensors. Such methodologies range from a simple grid of the area to the use of complex statistical models to provide their optimal number and distribution, or even the use of a random function within a set of defined positions. We propose the use of the same data generated by the sensor to locate or relocate them in real-time, through what we denominate as a ‘hot-zone’, a perimeter with significant data related to the observed phenomenon. In this paper, we present a process with four phases to calculate the best georeferenced locations for sensors and their visualization on a map. The process was applied to the Guadalajara Metropolitan Zone in Mexico where, during the last twenty years, air quality has been monitored through sensors in ten different locations. As a result, two algorithms were developed. The first one classifies data inputs in order to generate a matrix with frequencies that works along with a matrix of territorial adjacencies. The second algorithm uses training data with machine learning techniques, both running in parallel modes, in order to diagnose the installation of new sensors within the detected hot-zones.
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Sun, Weiwei, Jun Ma, Gang Yang, and Weiyue Li. "Statistical and Hydrological Evaluations of Multi-Satellite Precipitation Products over Fujiang River Basin in Humid Southeast China." Remote Sensing 10, no. 12 (November 28, 2018): 1898. http://dx.doi.org/10.3390/rs10121898.
Повний текст джерелаАнотація:
The purpose of the paper is to evaluate the quality and hydrological utility of four popular satellite precipitation products, including the Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) product (3B42V7), near real-time product (3B42RT), and the Climate Prediction Center (CPC) MORPHing technique (CMORPH) satellite–gauge merged product (CMORPH BLD) and bias-corrected product (CMORPH CRT) over Fujiang River basin, China. First, we provided a statistical assessment of the four precipitation products at multiple spatiotemporal scales. The results show that: (1) all the products except 3B42RT capture the spatial pattern of annual precipitation fairly well; (2) in general, CMORPH BLD benefits from the application of the probability density function-optimal interpolation (PDF-OI) gauge adjustment algorithm and performs best among all the products with Pearson correlation coefficients (CC) of 0.84 and 0.94, equitable threat score (ETS) of 0.56 and 0.63 in grid and basin scales, respectively, followed by 3B42V7 and CMORPH CRT; whereas 3B42RT performs worst across all the metrics; (3) according to the occurrence frequencies of rainfall, satellite estimates mainly fall into the bin of 0–1 mm/day and tend to underestimate light precipitation. In addition, the performance of all the products in warm season is much better than in cold season in both grid and basin scales. Subsequently, a physically based distributed model is established to further evaluate the hydrological utility of different precipitation products. The results reveal that: (1) the errors in precipitation products mainly propagate into hydrological simulations, resulting in the best hydrological performance in CMORPH BLD in both daily and monthly scales after recalibrating the model, while 3B42RT shows limited skills in reproducing the daily observed hydrograph; (2) after recalibrating the model with the respective satellite data, significant improvements are observed for all the products; (3) CMORPH BLD no longer shows its superiority during near-real-time monitoring of floods. There is still a great challenge for the application of current satellite-based estimates into local flood monitoring. This study could be used as guidance for choosing alternative satellite precipitation products for hydrological applications in a local community, particularly in basins in which rainfall gauges are scarce.