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排序方式: 共有894条查询结果,搜索用时 62 毫秒
61.
Roman Schuh Thomas Wriedt 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(11):1697-1704
The implementation of iterative methods as solvers for the Discrete Sources Method (DSM) is presented. In this method, light scattering computation linear systems with dense and relative small matrices are generated. The linear systems are traditionally solved using the QR-decomposition method. For large particles or particles with extreme geometries even this commonly stable solver can fail. In these cases, we expect that iterative methods can provide a satisfying solution nevertheless.We will present our investigation in two consecutive papers. Here, we study four different iterative solvers (RGMRES, BiCGStab, BiCGStab(l), and MinRes) considering the performance and the accuracy for typical light scattering problems. Using these iterative methods we increased the quality of a solution, especially for oblate spheroids with a higher aspect ratio. Preconditioning technique is considered in the following paper. 相似文献
62.
Pablo L. Saldanha 《Optics Communications》2011,284(12):2653-2657
We defend a natural division of the energy density, energy flux and momentum density of electromagnetic waves in linear media in electromagnetic and material parts. In this division, the electromagnetic part of these quantities have the same form as in vacuum when written in terms of the macroscopic electric and magnetic fields, the material momentum is calculated directly from the Lorentz force that acts on the charges of the medium, the material energy is the sum of the kinetic and potential energies of the charges of the medium and the material energy flux results from the interaction of the electric field with the magnetized medium. We present reasonable models for linear dispersive non-absorptive dielectric and magnetic media that agree with this division. We also argue that the electromagnetic momentum of our division can be associated with the electromagnetic relativistic momentum, inspired on the recent work of Barnett [Phys. Rev. Lett. 104 (2010) 070401] that showed that the Abraham momentum is associated with the kinetic momentum and the Minkowski momentum is associated with the canonical momentum. 相似文献
63.
Hu Jianjun Duan Yuping Zhang JiaJing Hui Liu ShunhuaLi Weiping 《Physica B: Condensed Matter》2011,406(10):1950-1955
MnO2/doped polyaniline (PANI) is prepared by an in situ polymerization method using γ-MnO2 as the addition agent and hydrochloric acid as the doping agent. Products are characterized by FT-IR, UV-vis, XRD, and TEM. Conductivity, electromagnetic properties, and microwave absorption properties are first discussed on the basis of structural characterization. The as-prepared products of MnO2/PANI are partially crystalline in nature and spherical in pattern with grain sizes of 50-70 nm. MnO2 particles are successfully decorated with doped PANI. MnO2/PANI displays moderate electric conduction, excellent dielectric losses, and microwave absorption capabilities. Compared to pure MnO2, the dielectric and reflection loss properties of MnO2/PANI composites exhibit significant improvements, with an effective absorption band at 5 GHz under −10 dB and maximum reflection loss of −21 dB at 13.56 GHz. Pure MnO2 shows an effective absorption band of 3 GHz under −10 dB and a maximum reflection loss of −14.20 dB at 11.5 GHz. Thus, MnO2/PANI composites are found to be a promising microwave absorption material. 相似文献
64.
Sensitization in 5XXX aluminum alloys is an insidious problem characterized by the gradual formation and growth of beta phase (Mg2Al3) at grain boundaries, which increases the susceptibility of alloys to intergranular corrosion (IGC) and intergranular stress-corrosion cracking (IGSCC). The degree of sensitization (DoS) is currently quantified by the ASTM G67 Nitric Acid Mass Loss Test, which is destructive and time consuming. A fast, reliable, and non-destructive method for rapid detection and the assessment of the condition of DoS in AA5XXX aluminum alloys in the field is highly desirable. In this paper, we describe a non-destructive method for measurements of DoS in aluminum alloys with an electromagnetic acoustic transducer (EMAT). AA5083 aluminum alloy samples were sensitized at 100 °C with processing times varying from 7 days to 30 days. The DoS of sensitized samples was first quantified with the ASTM 67 test in the laboratory. Both ultrasonic velocity and attenuation in sensitized specimens were then measured using EMAT and the results were correlated with the DoS data. We found that the longitudinal wave velocity was almost a constant, independent of the sensitization, which suggests that the longitudinal wave can be used to determine the sample thickness. The shear wave velocity and especially the shear wave attenuation are sensitive to DoS. Relationships between DoS and the shear velocity, as well as the shear attenuation have been established. Finally, we performed the data mining to evaluate and improve the accuracy in the measurements of DoS in aluminum alloys with EMAT. 相似文献
65.
Complex permittivity, complex permeability and microwave absorption properties of ferrite-paraffin polymer composites 总被引:1,自引:0,他引:1
Harun Bayrakdar 《Journal of magnetism and magnetic materials》2011,323(14):1882-1885
We have investigated the electromagnetic (EM) characteristics of CoxMn1−xFe2O4 spinel ferrite (where x=0.0, 0.5 and 1.0) nanoparticles (NPs)/paraffin nanocomposite material at 8-20 GHz. CoxMn1−xFe2O4 NPs have been synthesized by cetyltrimethylammonium assisted hydrothermal route using NaOH. A variation in complex dielectric permittivity and magnetic permeability at room temperature with frequency in the range 8-20 GHz has been studied. Particles showed phase purity and crystallinity in powder X-ray diffraction (XRD) analysis. At the same time, CoxMn1−xFe2O4 NPs demonstrated a spinel cubic structure from XRD results. A reflection loss of −46.60 dB was found at 10.5 GHz for an absorber thickness of 2 mm. CoxMn1−xFe2O4 may be attractive candidates for EM wave absorption materials. 相似文献
66.
Jijing XuGuijuan Ji Haifeng ZouYanhua Song Shucai Gan 《Journal of magnetism and magnetic materials》2011,323(1):156-161
Sm-substituted barium hexaferrites, Ba3−xSmxCo2Fe24O41 (x=0-0.25), were prepared by a conventional ceramic sintering method. The microstructure, complex permittivity, complex permeability and static magnetic properties of the samples were studied using powder X-ray diffraction, field emission scanning electron microscopy, vector network analyzer and vibrating sample magnetometry. The results reveal that by introducing a relatively small amount of Sm3+ instead of Ba2+ an important modification of both structure and high-frequency electromagnetic properties can be obtained. Doping of Sm3+ suppressed the grain growth and gave rise to a decrease of the grain size. As the Sm content increases, the static magnetic properties continuously increase. The real part and imaginary part of complex permittivity initially increase with Sm content, and then decreases when x>0.10. The imaginary part of complex permeability decreases after Sm3+ is doped. There is no obvious change in the real part of the complex permeability for different Sm contents. The reasons are discussed using electromagnetic theory. 相似文献
67.
Yang Rui-gang 《Journal of magnetism and magnetic materials》2011,323(13):1805-1810
BaTiO3 powders are prepared by sol-gel method. The carbonyl iron powder is prepared via thermal decomposition of iron pentacarbonyl. Then BaTiO3-carbonyl iron composite with different mixture ratios was prepared using the as-prepared material. The structure, morphology, and properties of the composites are characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, scanning electron microscopy (SEM), and a network analyzer. The complex permittivity and reflection loss of the composites have been measured at different microwave frequencies in S- and C-bands employing vector network analyzer model PNA 3629D vector. The effect of the mass ratio of BaTiO3/carbonyl iron on the microwave loss properties of the composites is investigated. A possible microwave absorbing mechanism of BaTiO3-carbonyl iron composite has been proposed. The BaTiO3-carbonyl iron composite can find applications in suppression of electromagnetic interference, and reduction of radar signature. 相似文献
68.
Jinying XuXiangdong Zhang 《Physics letters. A》2011,375(13):1524-1527
We present a rigorous multiple-scattering method to calculate the interaction energies due to electromagnetic field fluctuations in a cluster of parallel cylinders. Various kinds of cluster structure with both isotropic and anisotropic materials are considered. It is shown that Casimir interactions are sensitive to the positions of the cylinders in the cluster or the structure of the system. The sign of the interaction energy cannot only be changed by tuning the parameters of anisotropic materials, it can also be caused by changing the cylinders configuration of the system. 相似文献
69.
F. Gonzlez G. Videen P. J. Valle J. M. Saiz J. L. de la Pea F. Moreno 《Journal of Quantitative Spectroscopy & Radiative Transfer》2001,70(4-6):383-393
Four theoretical and computational methods to describe the scattering from simple particles on substrates are presented and discussed. These methods are based on the extinction theorem, image theory, the double-interaction model, and geometrical optics (ray-tracing). We compare the four methods with measurements of scattered light from gold metallic cylinders resting on a gold metallic substrate. In particular, we analyze the co-polarized (s and p polarization) full-scan and back-scattering intensities in the far field within the plane of incidence. Advantages and disadvantages of each method as a computational and reliable tool are discussed. 相似文献
70.
Lijun Jia Huaiwu Zhang Jun Luo Yingli Liu Qiye Wen 《Journal of magnetism and magnetic materials》2010,322(14):1934-1938
MgO was introduced into low-temperature sintered Z-type hexaferrites in order to improve their high-frequency electromagnetic properties. In the doped samples the major Z-type phase coexists with a small amount of W-type magnetoplumbite phase. The addition of MgO causes a decrease of the average grain size and an increase of the magnetocrystalline anisotropy (K1) and the saturation magnetization (Ms) with the increment of K1 being larger than that of Ms. These factors result in a reduce of the initial permeability. Also, the samples with MgO additive exhibit higher Q-factor and dc resistivity. Furthermore, the introduction of MgO can decrease the dielectric constant and improve the dielectric loss tangent of the samples by reducing the electronic transition in octahedral site (B-site) between Fe2+ and Fe3+ ions. 相似文献