Energy Difference Method Research Articles

VMD-HPCA-GRU ultra-short-term wind power forecasting based on COOT algorithm

In order to improve the prediction accuracy of ultra-short-term wind power, a combined prediction model of variational mode decomposition (VMD), hierarchical principal component analysis (HPCA) and gated recurrent unit neural network (GRU) based on COOT algorithm optimization is proposed. Firstly, the energy difference method is used to determine the number of sub-modes of variational mode decomposition, so that the original power sequence with strong nonlinearity is decomposed into a group of relatively stable sub-modes. Secondly, the correlation value between high-dimensional meteorological characteristics and power sequence is calculated by grey correlation analysis and sorted and layered. The first principal component of each layered characteristic variable is extracted by principal component analysis to achieve dimensionality reduction of high-dimensional meteorological characteristics. Finally, the COOT algorithm is introduced to optimize the hyperparameters of the gated recurrent unit prediction model, accelerate the model convergence speed, and improve the prediction accuracy of the model. The measured data of a wind farm in Guizhou are simulated and analyzed. The results show that compared with the prediction results of the traditional GRU model, the root mean square error, mean absolute error, and mean absolute percentage error of the proposed method are reduced 67.41%、72.25%、45.69%, and the prediction accuracy is higher than that of the other four combined prediction models, which effectively improves the prediction accuracy of ultra-short-term wind power.

Determination of the softening point and temperature interval of asphalt mixture for the healing process based on the contactless nonlinear ultrasonic method

The softening point and gradient healing have significant engineering significance for the self-healing of asphalt mixtures. This study introduces a novel approach utilizing a contactless ultrasonic system in conjunction with the Second Harmonic Generation (SHG) technique to determine the softening point and monitor the gradient healing process of asphalt mixtures. Three distinct fracture patterns resulting from temperature variations are accurately characterized through simulation using the Discrete Element Method (DEM). The ultrasonic nonlinear parameter β, reflecting different crack interfaces, proves to be a highly effective alternative for characterizing asphalt fractures, outperforming traditional methods such as bearing force and wave velocity. In experimental analysis, variations in the healing index highlight the significant influence of asphalt mixture fracture patterns on healing efficiency. The observed decrease in ultrasound amplitude signifies the transition of the asphalt binder from a solid to a liquefied state, accompanied by an increase in the nonlinear parameter indicating enhanced plasticity. The softening point is precisely determined when the Rayleigh surface wave disappears. The cumulative healing process is visualized through the continuous decrease in the nonlinear parameter. To further enhance the understanding of the asphalt self-healing process, the internal temperature gradient field is characterized using the proposed energy difference method. A correlation between the nonlinear parameter and the depth of the temperature interval is established, providing a non-destructive method for evaluating the distribution of the temperature interval. This innovative approach significantly accelerates the development of non-destructive testing in the field of asphalt self-healing.

An indentation method for measuring welding residual stress: Estimation of stress-free indentation curve using BP neural network prediction model

The measurement of welding residual stress (WRS) is necessary to formulate the stress control strategies, in order to ensure the reliability of engineering structures during their service life. The instrumented indentation technique can detect surface residual stress nondestructively with an acceptable accuracy, making it a desirable option for in-situ applications. However, it is difficult to meet the requirement for stress-free samples, particularly in the case of welded joints with non-uniform mechanical properties. In this work, the impact of stress-free indentation curves on determining WRS is furtherly studied based on the previously proposed indentation energy difference method. The WRS in a mismatched welded plate is measured using single reference method and distributed reference method, respectively. The study suggests that using the single reference method can lead to significant errors in determining the sign and magnitude of WRS in the weld zone. A prediction model combining the continuous spherical indentation (CSI) method and Back Propagation (BP) neural network is proposed to obtain the stress-free indentation curves of local positions nondestructively. And the CSI-BP method is verified through reverse finite element analysis and experiments.

An empirical analysis of the evolution of piano performance skills based on big data

Abstract The current hotspots of empirical analysis of piano performance skills mainly focus on the recognition of single notes, and there are some limitations in recognition accuracy and noise resistance performance. In this paper, to address this problem, firstly, on the basis of big data, we propose to realize the segmentation of the music section and noise section based on the single-port limit energy difference method and perform note onset and stop detection for the music section based on LMS adaptive filtering algorithm, using the musical characteristics of piano to identify the energy jumping point, which effectively improves the accuracy of note onset and stop detection and avoids the situation of missing and wrong diagnosis. Then the piano piece was played as an example, and the scientific evaluation of the piano performance skills was made based on the results of the determination of note types. The results showed that the errors of the eight notes of the piece were 0.9%, 0.30%, 0.24%, 0.28%, 0.34%, 0.11%, 0.63% and 0.28%. The correct rate of determining the types of notes in the performance technique of the music was 100%, and the error of determining all notes was controlled within 1%. This study provides a reference standard for evaluating the quality of music performance and has broad application prospects in the fields of family leisure, music tutoring, etc.

Combining the Δ-Self-Consistent-Field and GW Methods for Predicting Core Electron Binding Energies in Periodic Solids.

For the computational prediction of core electron binding energies in solids, two distinct kinds of modeling strategies have been pursued: the Δ-Self-Consistent-Field method based on density functional theory (DFT), and the GW method. In this study, we examine the formal relationship between these two approaches and establish a link between them. The link arises from the equivalence, in DFT, between the total energy difference result for the first ionization energy, and the eigenvalue of the highest occupied state, in the limit of infinite supercell size. This link allows us to introduce a new formalism, which highlights how in DFT─even if the total energy difference method is used to calculate core electron binding energies─the accuracy of the results still implicitly depends on the accuracy of the eigenvalue at the valence band maximum in insulators, or at the Fermi level in metals. We examine whether incorporating a quasiparticle correction for this eigenvalue from GW theory improves the accuracy of the calculated core electron binding energies, and find that the inclusion of vertex corrections is required for achieving quantitative agreement with experiment.

Wideband Waveform Design for Distributed Precision Jamming.

Precision electronic warfare is a hot direction for future jamming technology development, and distributed precision jamming (DIPJ) is one of its typical application scenarios. The task objective of DIPJ is to design jamming waveforms so that the jamming energy generated by a set of ultra-sparse array transmitters can be focused in the jamming region of interest while being suppressed in other specific protected regions, which can be viewed as a distributed multiple-input and multiple-output system waveform design problem under a three-dimensional scenario. This paper extends the jamming signal model in DIPJ from narrowband to wideband based on previous work to address a broader range of jamming tasks. After extending the model to wideband signals, a method based on the traditional maximum total energy difference optimization objective is first given for comparison. A wideband jamming waveform design method based on the majorization minimization algorithm with the desired power spectrum matching as the optimization target is designed for the problem that the maximum energy difference method cannot focus energy well in the jamming region. The simulation results show that the presented method can make the jamming energy well concentrated in the target region and evenly distributed over the whole bandwidth, while the energy in the whole bandwidth is suppressed in the protected region.

Determination of biaxial residual stresses via indentation energy difference method

<p indent="0mm">In this study, a novel method is proposed to estimate biaxial residual stress (RS) by using the indentation energy difference between the stressed and the stress-free samples. A Knoop indenter is applied along the directions of principal stresses, and the indentation energy obtained from the load-depth (<italic>F</italic>-<italic>h</italic>) curves is used as the calculation parameter without observing the indentation morphology. A work-energy transformation model is constructed to explain the change in the <italic>F</italic>-<italic>h</italic> curve with the RS in terms of energy. Then, the finite element analysis of different power-law hardening materials under different RS combinations is implemented to study the energy evolution. Consequently, the formula for calculating the indentation energy difference under a uniaxial RS is established. Meanwhile, the indentation energy difference of the Knoop indenter exhibits superposition and direction characteristics, which can be used to convert the indentation energy difference under a biaxial RS into the sum of that under two equivalent uniaxial stresses. Through this conversion, the two stress components can be calculated from the two indentation energy difference formulas. An indentation testing device is developed to verify the proposed method. The results obtained using the proposed method agree well with those obtained using the indentation strain-gage method.

Validation of the Green's Function Approximation for the Calculation of Magnetic Exchange Couplings.

In this work, we assess the potential of the Green's function approximation to predict isotropic magnetic exchange couplings and to reproduce the standard broken-symmetry energy difference approach for transition metal complexes. To this end, we have selected a variety of heterodinuclear, homodinuclear, and polynuclear systems containing 3d transition metal centers and computed the couplings using both the Green's function and energy difference methods. The Green's function approach is shown to have mixed results for the cases tested. For dinuclear complexes with large strength couplings (≳50 cm-1), the Green's function method is unable to reliably reproduce the energy difference values. However, for weaker dinuclear couplings, the Green's function approach acceptably reproduces broken-symmetry energy difference couplings. In polynuclear cases, the Green's function approximation worked remarkably well, especially for FeIII complexes. On the other hand, for a NiII polynuclear complex, qualitatively wrong couplings are predicted. Overall, the evaluation of exchange couplings from local rigid magnetization rotations offers a powerful alternative to time-consuming energy differences methods for large polynuclear transition metal complexes, but to achieve a quantitative agreement, some improvements to the method are needed.

The Mechanics of Forming Ideal Polymer-Solvent Combinations for Open-Loop Chemical Recycling of Solvents and Plastics.

The inherent value and use of hydrocarbons from waste plastics and solvents can be extended through open-loop chemical recycling, as this process converts plastic to a range of non-plastic materials. This process is enhanced by first creating plastic–solvent combinations from multiple sources, which then are streamlined through a single process stream. We report on the relevant mechanics for streamlining industrially relevant polymers such as polystyrene (PS), polypropylene (PP), high-density polyethylene (HDPE), and acrylonitrile butadiene styrene (ABS) into chemical slurries mixed with various organic solvents such as toluene, xylene, and cyclohexane. The miscibility of the polymer feedstock within the solvent was evaluated using the Relative Energy Difference method, and the dissolution process was evaluated using the “Molecular theories in a continuum framework” model. These models were used to design a batch process yielding 1 tonne/h slurry by setting appropriate assumptions including constant viscosity of solvents, disentanglement-controlled dissolution mechanism, and linear increase in the dissolved polymer’s mass fraction over time. Solvent selection was found to be the most critical parameter for the dissolution process. The characteristics of the ideal solvent are high affinity to the desired polymer and low viscosity. This work serves as a universal technical guideline for the open-loop chemical recycling of plastics, avoiding the growth of waste plastic by utilising them as a carbon feedstock towards a circular economy framework.

Biaxial residual stress measurement by indentation energy difference method: Theoretical and experimental study

In this paper, an energy difference method is proposed to estimate biaxial stress components based on indentation technique. The indentation energy is chosen as an analytical parameter, which can be calculated directly from the load-depth curve. The presence of residual stress in a material causes the change of indentation energy. The mapping relationship between uniaxial stress and indentation energy difference was established by finite element analysis. Meanwhile, the Knoop tip was applied since the indentation response varies according to the indenter orientation. Using this feature, a biaxial stress state can be transformed into two equivalent uniaxial stress states by indentation energy conversion. Finally, the biaxial residual stress components can be solved by the energy difference functions of two orthogonal indentations. A portable indentation instrument was developed to implement this approach, which is suitable for in-site measurement. The obtained results show good agreements with the artificial stresses applied by cross-shape sample experiment.

Free energy of micellization of dodecyl phosphocholine (DPC) from molecular simulation: Hybrid PEACH-BAR method.

A new method to extract the free energy of aggregation versus aggregate size from molecular simulation data is proposed and applied to a united atom model of the zwitterionic surfactant dodecyl phosphocholine in water. This system's slow dissociation rate and low critical micelle concentration (CMC of approximately 1-2 mM) make extraction of cluster free energies directly from simulation results using the "partition-enabled analysis of cluster histogram" (PEACH) method impractical. The new approach applies PEACH to a model with weakened attractions between aggregants, which allows sampling of a continuous range of cluster sizes, then recovers the free energy of aggregation under the original fully-attractive force field using the BAR free energy difference method. PEACH-BAR results are compared with free energy differences calculated via umbrella sampling, and are used to make predictions of CMC, average cluster size, and SAXS scattering profiles that are in fair agreement with experiment.

Параметры контура линий водяного пара при уширении гелием

The averaged energy difference method has been applied to calculate the broadening coefficients of rotation vibration water vapor lines induced by helium pressure. The calculations have been performed for a wide range of rotational quantum numbers (the averaged energy difference method have been applied for J from 0 to 20, interpolation of the J-dependence have been used for J from 20 to 50) in the spectral range from 500 to 10000 cm-1. We compared the calculated H2O-He line broadening coefficients with the literature data, and a good agreement have been obtained. The temperature dependence for linewidths are calculated.

Theoretical estimation of SO2 line broadening coefficients induced by carbon dioxide in the 150–300 K temperature range

Carbon dioxide broadened line widths of sulfur dioxide molecule have been obtained at the room temperature for ∼40 lines, rotational quantum numbers vary in the range: J from 14 to 51 and Ka from 2 to 18. The temperature exponents for every line were calculated. The data have been evaluated theoretically in the frame of two methods: the semi-empirical approach based on analytical expressions and including a few-parameter correction and the averaged energy difference method. Being validated by comparison with measurements, the first approach was used to compute line broadening values with their temperature exponents. Obtained data could be useful for atmospheric, astrophysical applications and spectroscopic databases.

Line broadening of SO2 and CO2 volcanic activity gases in the Earth’s atmosphere

Calculations of the CO2-broadening coefficients of sulfur oxide lines by the semi-empirical method [Mol. Phys. 102 (2004) 1653] and averaged energy difference method [Atmosph. Ocean. Optics 28 (2015) 403] are presented. In this work, 41 lines are considered, the rotational quantum number J varies from 14 to 51. Calculations of the line widths are carried out for room temperature (296 K), and also for the temperature range typical for the Ears atmosphere. There is good agreement with the literature data. The carbon dioxide lines broadening coefficients induced by nitrogen, nitrogen oxide, carbon monoxide and carbon dioxide at room temperature (T = 296 K) are obtained for a wide range of the rotational quantum number J (up to 100). The temperature exponents are calculated for every line widths. The calculations were performed by a semi-empirical method, based on the semiclassical impact theory of line broadening and modified by introducing additional correction factor whose parameters can be determined by fitting the broadening or shifting coefficients to the experimental data.

Pressure-dependent water absorption cross sections for exoplanets and other atmospheres

Many atmospheres (cool stars, brown dwarfs, giant planets, extrasolar planets) are predominately composed of molecular hydrogen and helium. H216O is one of the best measured molecules in extrasolar planetary atmospheres to date and a major compound in the atmospheres of brown-dwarfs and oxygen-rich cool stars, yet the scope of experimental and theoretical studies on the pressure broadening of water vapour lines by collision with hydrogen and helium remains limited. Theoretical H2- and He-broadening parameters of water vapour lines (rotational quantum number J up to 50) are obtained for temperatures in the range 300–2000K. Two approaches for calculation of line widths were used: (i) the averaged energy difference method and (ii) the empirical expression for J′J″-dependence. Voigt profiles based on these widths and the BT2 line list are used to generate high resolution (Δν˜=0.01cm−1) pressure broadened cross sections for a fixed range of temperatures and pressures between 300 and 2000K and 0.001–10bar. An interpolation procedure which can be used to determine cross sections at intermediate temperature and pressure is described. Pressure broadening parameters and cross sections are presented in new ExoMol format.

Magnetic Exchange Couplings in Heterodinuclear Complexes Based on Differential Local Spin Rotations.

We analyze the performance of a new method for the calculation of magnetic exchange coupling parameters for the particular case of heterodinuclear transition metals complexes of Cu, Ni, and V. This method is based on a generalized perturbative approach which uses differential local spin rotations via formal Lagrange multipiers (Phillips, J. J.; Peralta, J. E. J. Chem. Phys. 2013, 138, 174115). The reliability of the calculated couplings has been assessed by comparing with results from traditional energy differences with different density functional approximations and with experimental values. Our results show that this method to calculate magnetic exchange couplings can be reliably used for heteronuclear transition metal complexes, and at the same time, that it is independent from the different mapping schemes used in energy difference methods.

The average energy difference method for calculation of line broadening of asymmetric tops

A new method for estimation of broadening coefficients of vibrational-rotational lines of asymmetric tops is presented. The method allows finding line widths on the basis of a few empiric data without complicated calculations. Based on the analysis of experimental data, the dependence of the average energy difference on vibrational quantum numbers is found. The approach has been tested by the example of calculation of line broadening of asymmetric tops H2O and HDO. Calculated parameters of line profiles were compared with experimental data in different absorption bands.

Structural, electronic and magnetic properties of Ru2CrGe and Ru2MnGe: FP-LAPW calculations

Structural and magnetic properties as well as the electronic structures of [Formula: see text] Heusler alloys were investigated in the framework of first principle calculation. Using the full-potential linearized augmented plane wave (FP-LAPW) in connection with the generalized gradient approximation (GGA) treatment of exchange-correlation energy, we have performed the structural optimization in the non-magnetic (NM) and three different magnetic configurations: FM, AFM-I and AFM-II. We have found that our two compounds are stable for the AFM-II state, which agree with the available experimental and theoretical results. The exchange constants [Formula: see text] and [Formula: see text] as well as the temperature of transition to the paramagnetic state [Formula: see text] were estimated here by the use of the energy difference method and the mean field approximation. The electronic structure of our compounds in their magnetic state was also studied. The GGA [Formula: see text]+ [Formula: see text]U method has also been used to take into account the strong correlations among the d orbitals of [Formula: see text] and [Formula: see text] atoms. This has considerably improved both the electronic and magnetic results which became close to the corresponding experimental data. We have finally studied the thermodynamic properties using the quasi-harmonic Debye model as implemented in the Gibbs Program.

Метод средних частот для расчета полуширин линий молекул типа асимметричного волчка

Метод средних частот для расчета полуширин линий молекул типа асимметричного волчка

Migration of surface correlated multiples based on one-way wave equation

In conventional seismic data processing, multiple reflection waves are regarded as noise which should be removed from seismic data in order to avoid misunderstanding. In fact, multiples are also signals which contribute to part of subsurface structure illumination and imaging. In this paper, we analyzed the artifact generating mechanism and phenomenon caused by multiples in conventional one-way equation based pre-stack depth migration. In order to realize multiple imaging based on one-way wave equation, the boundary condition of one-way wave-equation based pre-stack depth migration was modified. It means that the input source wave field and recorded wave field are replaced by the record containing multiples and predicted surface correlated multiples, respectively. Then we stacked the pre-stack depth migration results from primaries and multiples based on the matching operator which is obtained from the norm II least-square energy difference methods. Imaging with multiples is a good compensation to imaging to that with primaries. The test on a simple model shows the validity of our method. Finally, jointed imaging with primaries and multiples was performed on the Sigsbee2B model. The results show that the imaging of the steep salt boundary was improved dramatically.