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• Impact of fractal dimension on aggregate scattering cross-section predicted by EMA was assessed. • Condition when EMA is more accurate than RDG-FA was proposed with reference to MSTM. • A critical aggregate size parameter value for which EMA is applicable was suggested. Particles within aggregates are commonly in a status of dependent scattering due to the near-field multiple scattering and far-field interferences from neighboring particles. The integral radiative characteristics of fractal aggregates are consequently not only influenced by the monomer size parameter x s , the refractive index n m , and the monomer number N s , but also tied to the fractal dimension D f. The effective-medium approximation (EMA) simplifies the calculation of aggregate radiative characteristics by treating an aggregate and its surrounding medium as a homogeneous sphere with an effective refractive index, and by applying the Lorenz-Mie theory to this equivalent sphere. The study aims to assess the applicability of EMA to predict the scattering cross-section of fractal aggregates consisting of non-absorbing monomers with x s , varying from 0.001 to 1.25, N s ranging from 10 to 500, under different fractal dimensions D f. The accurate results obtained using the multiple spheres T-matrix were used as a reference. In addition, the RDG-FA (Rayleigh-Deybe-Gans Fractal Aggregates) theory, which is widely used for aggregates with monomer size x s ≪ 1, was also evaluated for comparison. The finding reveals that both EMA and RDG-FA provide accurate predictions for aggregates satisfying the equivalent aggregate size parameter χ m less than D f , where the dependent scattering is limited. As the dependent scattering effect increases, the fractal dimension D f emerges as a critical factor influencing EMA's accuracy, with EMA excelling for aggregates with larger fractal dimensions close to 3. Furthermore, 2.1 is a critical value of D f above which EMA outperforms RDG-FA. [ABSTRACT FROM AUTHOR]

The effect of point-like lattice impurities on nanoparticle Raman spectra is studied using both numerical and analytical methods. Particular cases of replacement atoms of various masses, vacancies, and disorder in interatomic bonds are considered. It is shown that the disorder leads not only to the broadening of optical phonon lines but also to the shift of the corresponding Raman peak. The latter can be either positive (i.e., blueshift) or negative (redshift) depending on the type of impurities. Thus there is an additional contribution to the well-known redshift that occurs due to the size-quantization (confinement) effect. Considering nanometer-sized diamond particles as a representative example, we show that the broadening and the shift are, as a rule, of the same order of magnitude. The results are discussed in the framework of the self-consistent T-matrix approach. It is argued that both effects should be considered for accurate treatment of experimental Raman spectra. Simple recipes to do so are formulated for several important cases including NV centers in nanodiamonds. [Display omitted] [ABSTRACT FROM AUTHOR]

Relying on the time averaged Poynting vector expressed in terms of beam shape coefficients, dark and superdark theorems are discussed generalizing a previously published dark theorem. The superdark theorem allows one to characterize helical beams (that is to say beams possessing a topological charge) in terms of beam shape coefficients, and to demonstrate that beams with a topological charge equal to ± 2 are not necessarily vortex beams, although it is erroneously traditional to state that helical beams are all vortex beams. • Dark and superdark theorems are established in terms of beam shape coefficients of GLMT. • They allow one to decide on the properties of light intensities (null or not) on the axis of a beam. • And then to decide whether a beam with topological charge is a vortex beam or not. • We may then exhibit examples of beams with topological charges which are not vortex beams. [ABSTRACT FROM AUTHOR]

• A hybrid manipulator for optomechanical modules assembly in an inertial confinement fusion facility is presented. • The analytic inverse kinematics solution is obtained by decomposing the coupled kinematics model into two simple sub-models. • An improved back propagation neural network is proposed to increase the kinematic accuracy. A novel hybrid manipulator is proposed in this work, in order to assemble optomechanical modules in an inertial confinement fusion facility (SG-Ⅲ). Differ from general serial and parallel manipulators, both the inverse and forward kinematics problems of hybrid manipulators are difficult to be solved. Based on an analytic method, the position and orientation mapping functions between the optomechanical module and the parallel manipulators are established, and then the method of transformation matrix is employed to obtain the inverse kinematics solution. The forward kinematics of this hybrid manipulator is highly nonlinear and coupled, so a back propagation neural network using all class one network strategy is trained to approximate the mapping relation. Aiming to improve the accuracy, the network is split into two sub-networks corresponding to the natural property of the outputs. In the end, an improved back propagation neural network is proposed to optimize the network, results illustrate that the kinematic accuracy is increased significantly. [ABSTRACT FROM AUTHOR]

• We study the many-body t-matrix approximation for the weakly interacting bose gas. • We solved the coupled equation for the t-matrix and the condensate density. • This results lead to the correct order of the phase transition. We have proved in the many-body t-matrix approximation for the weakly interacting Bose gas the infrared divergences are exactly removed. We also show that this t-matrix becomes very temperature-dependent and, as the temperature approaches to T c it vanishes at the transition point. This leads to a smooth change of condensate density and compressibility at T c , implying the second order phase transition occurs at T c. [ABSTRACT FROM AUTHOR]

Previous works have been devoted to the symmetry properties of the Poynting vector for longitudinal axisymmetric beams expressed in terms of beam shape coefficients (BSCs). In the present paper, we examine the case of circularly axisymmetric beams. The former is defined as beams whose longitudinal component of the Poynting vector does not depend on the azimuthal angle. The latter is defined as beams whose all components of the Poynting vector do not depend on the azimuthal angle. We establish that two previously studied families of longitudinal axisymmetric beams are actually circularly axisymmetric beams as well. Examples are provided. • Symmetries of Poynting vector may be expressed in terms of beam shape coefficients of the GLMT. • Such symmetries are studied in the case of circularly symmetric beams. • Two families of such circularly symmetric beams are examined. • Examples and counter-examples are provided. [ABSTRACT FROM AUTHOR]

Currently, the majority of publicly raindrop scattering database are calculated with spherical particles. However, as the raindrop grows, the bottom of the raindrop gradually flattens out. The differences of raindrop shape will lead to a difference of the calculated scattering parameters from reality, and further influencing the accuracy of calculations in the fields of radar detection, microwave transmission and satellite remote sensing. In this regard, we developed a non-spherical raindrop scattering parameter database (RP database) with frequencies from 3GHz to 1000GHz. It has been published in an open-access repository. We compared the RP database with the database of Ekelund et al., and found that their difference is basically under 5%; Further the comparisons were also made between the scattering parameters of ellipsoids, spherical raindrops and the non-spherical raindrops, both spherical and ellipsoidal particles have clear difference from non-spherical particles. Finally, we analyzed the group particle attenuation at different frequencies. • A database of the Raindrop Scattering Properties covering the Millimeter and Sub-Millimeter band is established. • The actual shape of the rain droplet is considered in the scattering simulation. • The appicablity of different shape model of rain droplet is systematically analyzed. [ABSTRACT FROM AUTHOR]

• A new method for preparing non spherical particles (burning Ganoderma spores method) has been proposed. • A polarized light simulation transmission model based on T-matrix was established in a smoke simulation environment. • Conducted quantitative and qualitative model validation experiments. In order to deal with the problem of serious pollution caused by non-spherical particles, this study developed and obtained a non-spherical medium based on the theoretical basis of polarized optics and a new non-spherical particle preparation method (burning Ganoderma lucidum spores method). A polarized light simulation transport model based on the T-matrix was established by applying it to the smoke simulation environment. Using this polarization transmission model, simulation experiments were conducted to determine the effects of wavelength, polarization state, optical thickness and various transmission media on the Degree of Polarization (DOP). The simulation results show that both incoming linearly and circularly polarized light undergo depolarization as the optical thickness increases; however, the depolarization of circularly polarized light becomes more severe. In addition, the DOP in the non-spherical particle medium is always larger than that in the spherical particle medium, which indicates that the circularly polarized light is superior to the linearly polarized light in terms of deflection precession. [ABSTRACT FROM AUTHOR]

The T-matrix is a powerful tool that provides the complete description of the linear interaction between the electromagnetic field and a given object. In here, we generalize the usual monochromatic formalism to the case of polychromatic field-matter interaction. The group of transformations of special relativity provides the guidance for building the new formalism, which is inherently polychromatic. The polychromatic T-matrix affords the direct treatment of the interaction of electromagnetic pulses with objects, even when the objects move at constant relativistic speeds. • We expand the T-matrix method to the domain of polychromatic fields. • We put the T-matrix method in the framework of representations of the Poincare group. • We derive the matrix element of the Lorentz boost for the T-matrix in closed form. [ABSTRACT FROM AUTHOR]

Aerodynamic load is one of the important loads that must be considered for wind-wave energy hybrid devices. In this study, the effects of blade angle and foundation structure vibration on aerodynamic loads are considered, and the traditional blade element momentum (BEM) is dynamically modified by the method of coordinate matrix transformation and vibration function analysis, starting from the relative inflow angle and the instantaneous wind speed of the wind turbine, and the aerodynamic loads of the wind turbine were simulated by using the improved BEM theory. The correctness of the proposed method in this study is verified by comparing the data of a large number of researchers and the computational results of OpenFast. A simulation study has been carried out using AQWA, combining the modified aerodynamic load of the wind turbine and the hydrodynamic load of the wave energy device, to analyze the variation trend of the base structure response of the wind-wave hybrid device under general and extreme conditions. The results show that the method developed in this paper can provide theoretical reference for the development and stable operation of wind-wave hybrid device. • In this study, the classical BEM theory was modified based on the blade installation angle and foundation structure vibration. • The load fluctuation rules of the structure under the combined effect of blade angle and foundation vibration were revealed. • The distribution rules of the axial thrust of the blades were obtained by considered the effects of wind shear and fluctuating wind on the aerodynamic loads. • The response change rules of the foundation structure of hybrid devices under general and extreme conditions were analyzed. [ABSTRACT FROM AUTHOR]

Due to suffering the thermal and mechanical loadings simultaneously, metamaterials integrating with the customizable coefficient of thermal expansion (CTE) and high mechanical performances are desirable to ensure the thermal and structural stabilities in engineering devices. Hence, various multi-phase metamaterials with programmable CTEs and mechanical performances were developed. Specifically, inspired by the mixture of multiple phases in composites and the rigid rotations of framework structures in materials with negative CTE, a typical pyramid unit was introduced. Additionally, two series of metamaterials were systematically designed, which were constructed in batches from different units through the matrix transformation method. The CTEs of the metamaterials were theoretically established and analyzed. Besides, mechanical performances, including relative density, stiffness and strength were also calculated and discussed. The results suggest that the directionality and magnitude of CTEs are determined by the constructing principle of multi-fold rotations. In addition, the large ranges of programmable CTEs and high load-bearing capacity are available in the devised metamaterials by reasonably modulating the geometrical parameters. The thermal expansion and mechanical performances of the metamaterials could be synchronously programmed. The diversity of the phase configurations and geometrical architectures in the metamaterials offers the opportunity to satisfy manifold requirements in different applications. [ABSTRACT FROM AUTHOR]