随机取向纳米石墨椭球粒子的红外消光特性

利用离散偶极子近似(DDA)方法研究了椭球形的纳米石墨粒子的红外消光特性。计算了不同形状的椭球粒子红外消光截面随波长变化规律,并与等效球形粒子的消光性能进行了比较,分析了不同入射波长时,椭球粒子形状和粒径对消光的影响。结果表明,椭球状的纳米石墨粒子红外消光性能好于等效球粒子的消光性能,椭球粒子的最佳消光等效粒径与轴长比和入射波长有关。     

Yolk–Shell‐Structured Cu/Fe@γ‐Fe2O3 Nanoparticles Loaded Graphitic Porous Carbon for the Oxygen Reduction Reaction

Core–shell Cu/γ‐Fe₂O₃@C and yolk–shell‐structured Cu/Fe@γ‐Fe₂O₃@C particles are prepared by a facile synthesis method using copper oxide as template particles, resorcinol‐formaldehyde as the carbon precursor, and iron nitrate solution as the iron source via pyrolysis. With increasing carbonization temperature and time, solid γ‐Fe₂O₃ cores are formed and then transformed into Fe@γ‐Fe₂O₃ yolk–shell‐structured particles via Ostwald ripening under nitrogen gas flow. The composition variations are studied, and the formation mechanism is proposed for the generation of the hollow and yolk–shell‐structured metal and metal oxides. Moreover, highly graphitic carbons can be obtained by etching the metal and metal oxide nanoparticles through an acid treatment. The electrocatalytic activity for oxygen reduction reaction is investigated on Cu/γ‐Fe₂O₃@C, Cu/Fe@γ‐Fe₂O₃@C, and graphitic carbons, indicating comparable or even superior performance to other Fe‐based nanocatalysts.     

Granular flows in a rotating drum: the scaling law between velocity and thickness of the flow

The flow of dry granular material in a half-filled rotating drum is studied. The thickness of the flowing zone is measured for several rotation speeds, drum sizes and beads sizes (size ratio between drum and beads ranging from 47 to 7400). Varying the rotation speed, a scaling law linking mean velocity vs. thickness of the flow, v∼h^m, is deduced for each couple (beads, drum). The obtained exponent m is not always equal to 1, the value previously reported for a drum in litterature, but varies with the geometry of the system. For small size ratios, exponents higher than 1 are obtained due to a saturation of the flowing zone thickness. The exponent of the power law decreases with the size ratio, leading to exponents lower than 1 for high size ratios. These exponents imply that the velocity gradient of a dry granular flow in a rotating drum is not constant. More fundamentally, these results show that the flow of a granular material in a rotating drum is very sensible to the geometry, and that the deduction of the “rheology” of a granular medium flowing in such a geometry is not obvious.     

Probabilistic Teleportation of a Three-Particle State

A scheme for teleporting a three-particle state is proposed when three pairs of entangled particles are used as quantum channels. Quantum teleportation can be successfully realized with a certain probability if the receiver adopts an appropriate unitary-reduction strategy. The probability of successful teleportation is determined by the smaller coetficients of the three entangled pairs.     

Preparation of hybrid film with superhydrophobic surfaces based on irregularly structure by emulsion polymerization

A superhydrophobic surface originated from quincunx-shape composite particles was obtained by utilizing the encapsulation and graft of silica particles to control the surface chemistry and morphology of the hybrid film. The composite particles make the surface of film form a composite interface with irregular binary structure to trap air between the substrate surface and the liquid droplets which plays an essential role in obtaining high water contact angle and low water contact angle hysteresis. The water contact angle on the hybrid film is determined to be 154 ± 2° and the contact angle hysteresis is less than 5°. This is expected to be a simple and practical method for preparing self-cleaning hydrophobic surfaces on large area.     

Microwave backscattering by nonspherical ice particles at 5.6 GHz using second-order perturbation series

Scattering of microwaves by an ensemble of nonspherical ice particles is studied using a scattering model based on a second-order perturbation series at 5.6 GHz (C-band). Particle shapes are defined using a Gaussian random sphere geometry. Particle inhomogeneity is taken into account using three different effective-medium approximations: Maxwell–Garnett, Bruggeman, and Coherent Potential mixing rules. By systematically varying particle size, liquid water content, Gaussian shape parameters, and internal structure, it is found that liquid water content is the most important factor for the co-polarized backscattering; the shape is relatively unimportant. For depolarized backscattering, the shape is of fundamental importance, although the other factors are significant too. Surprisingly, the type of nonsphericity is found to be important for depolarization even for scatterers that are in the Rayleigh region: elongated targets depolarize clearly stronger than more irregular shapes. This finding seems not to be strongly size dependent, at least for size parameters from 0.0059 to 0.47, and indicates that the accurate modeling of shape is important for polarization quantities even in the Rayleigh region.     

Al_2O_3和MgO多粒子体系光学截面的计算

本文利用微粒子 Mie散射理论建立了混合多粒子体系的光散射模型 ,计算了相应模型下 Al2 O3和 Mg O的光学截面     

4He-stopping power measurements by using ion implantation and backscattering techniques

Experimental results on changes in conductivity of N₂+ and Ar⁺ bombarded thin copper, aluminium and bismuth films are given along with the preliminary observations on photoconductivity of N₂+ bombarded Bi₂O₃ thin films. The performance of a low cost, medium resolution 200 keV ion implantation system, used in the above experiments is also discussed.     

Surface pressure in clusters and small particles—is it real?

Using the methods of statistical mechanics and applying the conditions of thermal equilibrium for an ensemble of interacting molecules, it is proved that there is no excess pressure, nor internal and surface stresses, in clusters and small particles that are not subjected to the action of external forces. With this premise taken into account the thermodynamics of spherical and faceted small particles is developed. In a particle-vapour system surrounded by a rigid impervious shell, Kelvin's and Thomson's formulae and Wulff's rule are derived. For a particle-melt system at a constant external pressure it is expected that the melting points of a particle and a bulk solid should be equal. It is noted that, if a particle is not subjected to the action of external fields or bodies, its molecules occupy their natural equilibrium positions, and it is from them that deformations and internal stresses should be counted off. These equilibrium positions differ from those occupied by the same molecules in a bulk solid, which is what usually gives rise to the illusions of the stressed state of a small particle and its deformation caused by the “uncompensated” surface forces.     

Mössbauer spectroscopy of magnetic small particles with emphasis on barium ferrite

Ferromagnetic and ferrimagnetic particles have been of scientific and technological interest for several decades. The study of nanometer clusters or particles is currently a developing subject. Such materials may be in a non-equilibrium or quasi-equilibrium phase; different properties as compared to the bulk and indeed even new physical phenomena may be expected. Some ways to synthesize clusters and fine particles are described. Mössbauer spectroscopy is shown to be particularly useful for the study of nanometer particles; an outline of how it actually works is given. As an illustration, barium ferrite small particles, a material of topical interest, is considered in detail. In particular, methods of preparation, the crystal and magnetic structure, the magnetic characteristics, recently obtained Mössbauer results, and potential and realized applications are reviewed.