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951.
Toshihiko Komatsuzaki Yoshio Iwata 《International Journal of Mechanics and Materials in Design》2017,13(3):407-417
A particle impact damper is a vibration absorber type that consists of a container attached to a primary vibrating structure. It also contains many particles that are constrained to move inside the container, whereby the damping effect can be obtained by collision between particles and the container. The discrete element method (DEM) has been developed for modeling granular systems, where the kinematics of each particle are calculated numerically using the equations of motion. However, the computational time is significant since the algorithm checks for particle contacts for all possible particle combinations. The use of a cellular automata (CA) modeling technique may provide increased computational efficiency due to the local updating of variables, and the discrete treatment of time and space. In this study, we propose a new approach combining DEM with CA for modeling a granular damper under a forced excitation. We use DEM to describe the particle motion according to the equations of motion, while CA is introduced for the particle contact checks in discrete space. We also investigate the effect of simplification in the contact force model, which allows the unit time step of numerical integration to become larger than that used in the strict model. It is shown that the suggested particle contact scanning method and the force approximation model contribute to the reduction of the computational time, and neither degenerates the calculation accuracy nor causes the numerical instability. 相似文献
952.
Tao Shen Hailong Dai Mingxin Song Hongchen Liu Xinlao Wei 《Journal of Superconductivity and Novel Magnetism》2017,30(4):937-941
Y3?xCe x Fe5 O 12 (CeYIG) ceramics, with x = 0, 0.15, 0.25, 0.35, 0.45, and 0.5, were fabricated by a conventional ceramic sintering technique. We studied the structures and magnetic fields of a series of CeYIG ceramics using X-ray powder diffraction, a scanning electron microscope, and a superconducting quantum interference device magnetometer. Findings showed that the substitution limit of the concentration of Ce3+ ions in the yttrium iron garnet structure was approximately x = 0.25. An extra CeO2 phase was detected in the ceramic when the addition of CeO2 content overtook the limit. The lattice constants and relative densities increased by increasing the Ce3+ contents in the ceramics. First, the saturation magnetization increased gradually with increases in the substitute concentration of Ce3+ ions and then decreased gradually when x = 0.35, 0.45, and 0.5. Overall, this study showed that the Y3?xCe x Fe5 O 12 material with x ≤ 0.15 exhibited excellent magnetic properties. Hence, the material show promise for magneto-optical and microwave communication applications. 相似文献
953.
Mohsen Yarmohammadi 《Journal of Superconductivity and Novel Magnetism》2017,30(4):943-949
In this paper, the effects of dilute charged impurity doping on electronic heat capacity (EHC) and magnetic susceptibility (MS) of a two-dimensional material ferromagnetic gapped graphene-like, MoS2, are investigated within the Green’s function approach by using the Kane-Mele Hamiltonian and self-consistent Born approximation (SCBA) at Dirac points. Our findings show that there is a critical impurity concentration (IC) and scattering strength (ISS) for each valley in EHC and MS curves. Also, we have found that the spin band gap decreases with impurity only for valley K, ↑ and \(K^{\prime }, \downarrow \) due to the existence of inversion symmetry between valleys. On the other hand, a magnetic phase transition from ferromagnetic to antiferromagnetic and paramagnetic has been observed. The increase of scattering rate of carriers in the presence of impurity is the main reason of these behaviors. 相似文献
954.
R. Kesavamoorthi C. Ramachandra Raja 《Journal of Superconductivity and Novel Magnetism》2017,30(5):1207-1212
Rare-earth ions (RE3+)-doped Ni-Zn ferrite nanoparticles with a structural formula of Ni0.5Zn0.5Fe1.8RE0.2O4 (RE3+ = Nd, Ce, La and Pr) were synthesized at room temperature by a sol-gel auto-combustion method. The structural and magnetic properties of Ni-Zn ferrite samples were carried out by XRD, vibrating sample magnetometer (VSM), field emission scanning electron microscopy (FE-SEM) and FT-IR spectroscopy. XRD pattern of Ni-Zn ferrite revealed that all the diffraction planes are in agreement with cubic spinel phase and the addition of Fe2O3 phase was also observed. In the case of RE ions-doped Ni-Zn ferrite in addition to the Fe2O3 phase, very low intensity peaks corresponding to some secondary phase are also present. The average crystallite sizes were found to be from 42 to 56 nm using the Scherer formula. The lattice constant (a) values are gradually decreased from 8.378 to 8.349 Å with different substitutions of RE3+ ions in the Ni-Zn ferrite samples. VSM analysis revealed that saturation magnetization values are decreased and coercivity values are increased with substitution of different RE3+ ions. FE-SEM images exhibits that particles are spherical in shape. FT-IR interpretation revealed that two main metal oxygen bands (564 and 411 cm?1) are observed in all the substituted Ni-Zn ferrite samples. 相似文献
955.
Daniele Di Gioacchino Nicola Poccia Martijn Lankhorst Claudio Gatti Bruno Buonomo Luca Foggetta Augusto Marcelli Hans Hilgenkamp 《Journal of Superconductivity and Novel Magnetism》2017,30(2):359-363
The current frontiers in the investigation of high-energy particles demand for new detection methods. Higher sensitivity to low-energy deposition, high-energy resolution to identify events and improve the background rejection, and large detector masses have to be developed to detect even an individual particle that weakly interacts with ordinary matter. Here, we will describe the concept and the layout of a novel superconducting proximity array which show dynamic vortex Mott insulator to metal transitions, as an ultra-sensitive compact radiation-particle detector. 相似文献
956.
We investigate the relationship between superconductivity and spin glasses, which were observed to be coexistent in heavy fermion superconductors (HFSs). We begin by explaining the phase of spin glass using concepts of finite-sized block spin. We then introduce the phase of superconductivity in HFSs as collective Cooper pairing, that is, the pairing of block spins with net spin = 1/2, each of which is comprised of a large number of random spins that together produce a majority spin direction. The superconducting Bardeen-Cooper-Schrieffer (BCS)-type phonon-mediated electron-electron interaction is substituted for the BCS-type electron-electron interaction mediated by phonon-enhanced spin flips previously suggested by us. An effective charge of any value stemming from an electron attached to the flux of an electric field can be referred to as a composite charge. The distinguished difference between ours and the original BCS model is the following: (i) another BCS-type interaction, (ii) bare electrons that are substituted for block spins with net spin = 1/2 and net charge = e in the presence of electric fields, and (iii) Fermi-Dirac distributions that are replaced by a new distribution called as Brillouin distribution. 相似文献
957.
Superconductivity and Unusual Magnetic Features in Amorphous Carbon and in Other Unrelated Materials
Israel Felner 《Journal of Superconductivity and Novel Magnetism》2017,30(1):55-61
Traces of superconductivity (SC) were observed in three different inhomogeneous sulfur-doped amorphous carbon (a-C) systems: (i) in old commercial powder, (ii) in fabricated (by pyrolytic decomposition of sucrose) powder, and (iii) in a-C thin films. (i) The commercial a-C powder contains 0.21 at% sulfur and reveals traces of two superconducting phases around T C ?34 and T C~65 K. (ii) The fabricated a-C powder is diamagnetic but not superconducting. However, mixtures of this powder with sulfur (a-CS) which were heated to 250 °C also show traces of SC up to T C~42 K. (iii) Non-superconducting a-C thin films were grown by electron-beam induced deposition. SC at T C~34 K emerged only after heat treatment with sulfur. It is proposed that the high SC states in a-CS (T C~65 K at ambient pressure) and in H3S materials (T C = 203 K under >200 GPa) has the same origin. In both sulfur-containing systems, SC is induced by the interaction between electrons and the high frequencies of low mass atom (H or C) vibrations a-CS products obtained by heating commercial and fabricated a-C powders at 400 °C show unusual magnetic features: (a) pronounced irreversible peaks around 55–80 K which appear in the first zero-field-cooled (ZFC) runs only. This temperature range is close to the highest T C observed. (b) These peaks are totally suppressed in the second ZFC sweeps measured a few minutes later. (c) The peaks reappear after 18 months. (d) Around the peak position, the field-cooled (FC) curves cross the ZFC plots (ZFC > FC). All these phenomena are intrinsic properties of the amorphous carbon materials and were not observed in crystalline graphite. The ZFC > FC state was also observed in chiral-based magnetic memory device and unexpectedly in the liver taken from a patient with mantle cell lymphoma. This peculiarity will be discussed. 相似文献
958.
Sanjeev K Srivastava Alireza Aghajamali 《Journal of Superconductivity and Novel Magnetism》2017,30(2):343-351
In the present work, reflectance properties of one-dimensional photonic crystal (1D PC) containing a metamaterial and high-temperature superconductor have been investigated theoretically and analyzed. The reflectance/transmittance spectrum of the proposed structure is obtained by using the characteristic or transfer-matrix method (TMM). The results show that by increasing the thickness of the metamaterial layer, the width of the second reflection band decreases while the width of the first reflection band remains almost the same though it shifts towards the higher frequency side. In addition to this, a new band gap arises in the lower side of frequency. But, when the thickness of the superconductor layer is increased, the width of both the bands increases and no additional band arises in this case. Moreover, the reflection band is also affected by varying the operating temperature of the superconducting layer and the results show that bands get narrower by increasing the operating temperature. Finally, the effect of incident angle on the reflection band has been discussed for both transverse electric (TE) and transverse magnetic (TM) polarizations. 相似文献
959.
Half-metallic ferromagnetism in the Ga1 ? xCr x N compound at different concentrations, x = 25, 12.5 and 6.25 %, have been investigated using density functional theory as implemented in code Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) using LDA + U as exchange-correlation (XC) potential, to find out the possibility of new diluted DMSs. The outcomes reveal that transition metal atom (Cr) doping in GaN induces ferromagnetism. The 3d levels of the TM ion originate a half-metallic gap at the Fermi level in the majority spin channel for all concentrations. Moreover, diluted magnetic semiconductor compounds retain the half-metallic nature at all concentrations, i.e., x = 0.25, 0.125 and 0.0625, with 100 % spin polarization at the Fermi level (E F). The total magnetic moment of these compounds is due to Cr-3d states, and the existence of a small magnetic moment on Ga and N, non-magnetic atoms, for all doping concentrations is a consequence of p-d hybridization of Cr-d and N-p states. The calculated values of s-d exchange constant N α and p-d exchange constant N βconfirm the ferromagnetic character of the Cr-doped GaN compound. 相似文献
960.
Ren Zhang Yunhua Zhou Yiyi Zhu Yangyang Li Liang Chu Yonggang Min Jian Zhang Jianping Yang Xing’ao Li 《Journal of Superconductivity and Novel Magnetism》2017,30(9):2471-2479
Tetragonal BiFeO3 (BFO), which has a giant spontaneous polarization, has attracted a great deal of attention recently. In this paper, we systematically study the structural, magnetic, electronic and optic properties of BFO, BiFe0.75Mn0.25 O 3 (BFMM), and BiFe0.75Ti0.125Mn0.125 O 3 (BFMT). Results show that doping Ti and Mn into the Fe sites increases the c/a ratio and enhances the magnetization of BiFeO3 from 0 to 5 μB. The crystal symmetry changes from orthogonality to tetragonality with half of the Mn atoms being replaced by Ti in BiFe0.75Mn0.25 O 3, which suppresses the energy splitting of the Mn 3d orbitals and thus enlarge the band gap to 1.21 eV for BiFe0.75Ti0.125Mn0.125 O 3. Our calculated Bader charge and charge density difference show that the smallest volume of BiFe0.75Mn0.25 O 3 arises from the strong Mn–O bonds in BiFe0.75Mn0.25 O 3. Further investigations indicate similar optical behaviors for BiFeO3 and BiFe0.75Ti0.125Mn0.125 O 3. However, BiFe0.75Mn0.25 O 3 exhibits strong absorption in the infrared region for the transition from O 2p to Mn \({e_{g}^{2}}\) and \(t_{2g}^{3}\). 相似文献