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21.
利用X-射线衍射,扫描电镜,拉曼光谱,等离子发射光谱和比表面测定等方法研究了不同状态下失活及新鲜催化剂的结构,杂种类及含量。结果表明,超温使催化剂晶化明显,制备方法对催化剂结构有直接影响,再生使其强度降低,条形催化剂比较容易粉化,无机杂质是次要的失活原因。 相似文献
22.
Maria A. Davidovich V.M. Apel E.V. Anda G. Chiappe 《Journal of magnetism and magnetic materials》2008,320(14):e246-e248
Transport properties of a double-dot system in a ring structure threaded by a magnetic flux are studied. The Aharonov–Bohm effect combined with the charging effects of the dots in the Kondo regime determines the phases of the currents going through each arm of the ring. Depending upon the magnetic flux and the state of charge of the dots, controlled by gate potentials, current circulates around the ring. 相似文献
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An extension of a recently published [Gyergyek T., ?er?ek M. Contrib. Plasma Phys., 45 , (2005), 89] one dimensional fluid model of the sheath formation in front of a floating electrode (collector) that emits secondary electrons and is immersed in a two‐electron temperature nonmagnetized, collisionless plasma is presented. The electron velocity distribution function is assumed to be a two‐temperature maxwellian, while the singly charged positive ions and the emitted electrons are assumed to be monoenergetic. It is assumed that the electrons in the pre‐sheath potential drop obey the Boltzmann relation, so that a larger fraction of the hot than of the cool electrons can penetrate to the sheath edge. Our model predicts that the collector can in some cases have 3 and in some cases, when the emission of electrons from the collector is critical, even 5 different floating potentials at the same hot to cool electron temperature and density ratios very far away from the collector. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
26.
Franco Carillo Giorgio Biasiol Diego Frustaglia Francesco Giazotto Lucia Sorba Fabio Beltram 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):53
Electron-phase modulation in magnetic and electric fields will be presented in In0.75Ga0.25As Aharonov–Bohm (AB) rings. The zero Schottky barrier of this material made it possible to nanofabricate devices with radii down to below 200 nm without carrier depletion. We shall present a fabrication scheme based on wet and dry etching that yielded excellent reproducibility, very high contrast of the oscillations and good electrical gating. The operation of these structures is compatible with closed-cycle refrigeration and suggests that this process can yield coherent electronic circuits that do not require cryogenic liquids. The InGaAs/AlInAs heterostructure was grown by MBE on a GaAs substrate [F. Capotondi, G. Biasiol, D. Ercolani, V. Grillo, E. Carlino, F. Romanato, L. Sorba, Thin Solid Films 484 (2005) 400], and in light of the large effective g-factor and the absence of the Schottky barrier is a material system of interest for the investigation of spin-related effects [W. Desrat, F. Giazotto, V. Pellegrini, F. Beltram, F. Capotondi, G. Biasiol, L. Sorba, D.K. Maude, Phys. Rev. B 69 (2004) 245324; W. Desrat, F. Giazotto, V. Pellegrini, M. Governale, F. Beltram, F. Capotondi, G. Biasiol, L. Sorba, Phys. Rev. B 71 (2005) 153314; J. Nitta, T. Akazaki, H. Takayanagi, T. Enoki, Phys. Rev. Lett. 78 (1997) 1335] and the realization of hybrid superconductor/semiconductor devices [Th. Schäpers, A. Kaluza, K. Neurohr, J. Malindretos, G. Crecelius, A. van der Hart, H. Hardtdegen, H. Lüth, Appl. Phys. Lett. 71 (1997) 3575]. 相似文献
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J. des Cloizeaux 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):439-443
Dirac equation is reformulated in terms of real local observables, which are mean values of the wave function . The quadrivector current is shown to be a function of the potential vector and of other local observables. The equations
describe the evolution of a four dimensional system T, X, Y, Z, and of two scalars, in the coordinate system ct, x, y, z. The current is proportional to the T vector. The Z vector is associated with the spin of the electron. Energy and gauge transformations correspond to rotations in the plane
(X, Y). In the presence of a static field, the (real) solutions of the equations appear as eigenfunctions associated with energy
eigenvalues.
Received 7 September 1998 相似文献
29.
J.D. Salazar-Santa D. Fonnegra Y.A. Suaza M.E. Mora-Ramos J.H. Marin 《Physics letters. A》2018,382(40):2927-2937
The theoretical study of the energy spectrum and optical response of off-axis donor in a GaAs quantum ribbon with anisotropic rim height under the presence of constant crossed electric and magnetic fields is presented. The calculations are carried out within the effective mass and parabolic approximation, using an adiabatic approach combined with a diagonalization scheme. The rim height of the quantum ribbon has been modeled by including a phenomenological two-parametric function that accounts for realistic features of multi-hilled semiconductor nanostructure obtained from atomic force microscopy images. The first phenomenological parameter is introduced to control the number of quantum ribbon structural hills and the second one to deal with the height of the hills. It is shown that both the depth and the number of structural hills tend to substantially affect the Aharonov–Bohm oscillation pattern which can be quenched or restored by applying an electric field in an appropriate direction. The effect of the changes in the geometry and in the applied electric field onto the optical absorption and refractive index change are discussed. The phenomenon of electric-field-induced optical transparency in the system is particularly highlighted. 相似文献
30.
Spin-polarized transport through an Aharonov–Bohm (AB) semiconductor mesoscopic ring is investigated in the presence of both the Rashba spin–orbit interaction (RSOI) and the Dresselhaus spin–orbit interaction (DSOI). The ring symmetrically bridges two input and output electrodes. Based on tight-binding model and Green?s function formalism, we find that for AB fluxes other than integer or half-integer multiples of the flux quanta the ring acts as a spin selective device with unit efficiency only when the difference between strengths of RSOI and DSOI is nonzero and small. Results of this study can be used to design a nonmagnetic-material-based perfect spin filter. 相似文献