Ni/Ni3C Core-Shell Nanochains and Its Magnetic Properties: One-Step Synthesis at low temperature

One-dimensional Ni/Ni3C core-shell nanoball chains with an average diameter by around 30 nm were synthesized by means of a mild chemical solution method using a soft template of trioctylphosphineoxide (TOPO). It was revealed that the uniform Ni nanochains were capped with Ni3C thin shells by about 1 to 4 nm in thickness and each Ni core consists of polygrains. The coercivity of the core-shell nanochains is much enhanced (600 Oe at 5 K) and comparable with single Ni nanowires due to the one-dimensional shape anisotropy. Deriving from the distinctive structure of Ni core and Ni3C shell, this architecture may possess a possible bi-functionality. This unique architecture is also useful for the study on the magnetization reversal mechanism of one-dimensional magnetic nanostructure.Comment: 17 pages, 6 figur

Application and measurement of underwater acoustic reciprocity transfer functions with impulse sound sources

The underwater acoustic reciprocity transfer function measuring method with impulse underwater sound source is studied, and time gates are utilized to eliminate the reverberant field influences on the sound pressures which are used to compute the source volume velocity. The method is validated in a lake experiment. It is showed that, the reciprocity measurement results based on the impulse source is similar to the reciprocal measurements results based on the traditional electromagnetic source, meanwhile the time cost of the impulse-based measurement is less. Thereby the measuring efficiency is boosted with an impulse source. Moreover, the reverberant field influences on volume velocity obtainments can be eliminated with suitable time gates in impulse-based measurements. Aiming at representative problems of the experiments, some suggestions about impulse-based reciprocity measurements are provided. This work may be valuable for the study of underwater sound sources and reciprocal measuring techniques

Magnetic properties of undoped Cu2O fine powders with magnetic impurities and/or cation vacancies

Fine powders of micron- and submicron-sized particles of undoped Cu2O semiconductor, with three different sizes and morphologies have been synthesized by different chemical processes. These samples include nanospheres 200 nm in diameter, octahedra of size 1 micron, and polyhedra of size 800 nm. They exhibit a wide spectrum of magnetic properties. At low temperature, T = 5 K, the octahedron sample is diamagnetic. The nanosphere is paramagnetic. The other two polyhedron samples synthesized in different runs by the same process are found to show different magnetic properties. One of them exhibits weak ferromagnetism with T_C = 455 K and saturation magnetization, M_S = 0.19 emu/g at T = 5 K, while the other is paramagnetic. The total magnetic moment estimated from the detected impurity concentration of Fe, Co, and Ni, is too small to account for the observed magnetism by one to two orders of magnitude. Calculations by the density functional theory (DFT) reveal that cation vacancies in the Cu2O lattice are one of the possible causes of induced magnetic moments. The results further predict that the defect-induced magnetic moments favour a ferromagnetically coupled ground state if the local concentration of cation vacancies, n_C, exceeds 12.5%. This offers a possible scenario to explain the observed magnetic properties. The limitations of the investigations in the present work, in particular in the theoretical calculations, are discussed and possible areas for further study are suggested.Comment: 20 pages, 5 figures 2 tables, submitted to J Phys Condense Matte

Surface magnetic states of Ni nanochains modified by using different organic surfactants

Three powder samples of Ni nanochains formed of polycrystalline Ni nanoparticles with an estimated diameter of about 30 nm have been synthesized by a wet chemical method using different organic surfactants. These samples, having magnetically/structurally core-shell structures, all with a ferromagnetic Ni core, are Ni@Ni3C nanochains, Ni@NiSG nanochains with a spin glass (SG) surface layer, and Ni@NiNM nanochains with a nonmagnetic (NM) surface layer. The average thickness of the shell for these three samples is determined as about 2 nm. Magnetic properties tailored by the different surface magnetism are studied. In particular, suppression in saturation magnetization usually observed with magnetic nanoparticles is revealed to arise from the surface magnetic states with the present samples.Comment: 23 pages, 6 figures include

A review on conventional and nonconventional machining of SiC particle-reinforced aluminium matrix composites

AbstractAmong the various types of metal matrix composites, SiC particle-reinforced aluminum matrix composites (SiCp/Al) are finding increasing applications in many industrial fields such as aerospace, automotive, and electronics. However, SiCp/Al composites are considered as difficult-to-cut materials due to the hard ceramic reinforcement, which causes severe machinability degradation by increasing cutting tool wear, cutting force, etc. To improve the machinability of SiCp/Al composites, many techniques including conventional and nonconventional machining processes have been employed. The purpose of this study is to evaluate the machining performance of SiCp/Al composites using conventional machining, i.e., turning, milling, drilling, and grinding, and using nonconventional machining, namely electrical discharge machining (EDM), powder mixed EDM, wire EDM, electrochemical machining, and newly developed high-efficiency machining technologies, e.g., blasting erosion arc machining. This research not only presents an overview of the machining aspects of SiCp/Al composites using various processing technologies but also establishes optimization parameters as reference of industry applications

Analysis and optimization of a double-sided air-cored tubular generator

In this paper, the design and development of a double-sided air-cored tubular generator (DSTG) is presented. The characteristics of air-cored slot-less structures are investigated in terms of power density and efficiency. This is highly desirable for small- and medium-sized renewable energy conversion systems. In this paper, an analytical tool based on the magnetic vector potential method is built in order to achieve a fast but accurate method by which the machine is analyzed. The analytical model is validated by finite-element (FE) analysis. Further design improvements based on the analytical and FE models are then suggested in order to enhance the performance of the DSTG. The final design of the DSTG is validated by the test results from a developed prototype of the DSTG

The resource investigation and community structure characteristics of mycorrhizal fungi associated with Chinese fir

Chinese fir is one of the most important commercial timber species in south China. Mycorrhizal fungi has been applied in many trees and showed important effect on enhancing the productive forces and the soil activities, but there is little report about the mycorrhizal fungi on Chinese fir. So this paper investigated the mycorrhizal fungi resources of Chinese fir in Hunan province and analyzed the relation of community with the environment factors. The results showed that, abuscular mycorrhizal fungi (AMF) existed universally in the roots of Chinese fir. 75 specimen of AMF spores were isolated by wet-sieved method from this collection of the rhizosphere soils. They were identified by morphologic method to 4 genera and 9 species of AMF, which 5 species belong to Glomus, 1 of Gigaspora, 2 of Acaulospora and 1 of Scutellospora. In the isolated AMF, the importance value of Glomus mosseae, Glomus intraradices and Acaulospora laevis were more than 50% and the spore number of them was significantly higher than other species. These 3 species of AMF were considered as the dominate species in rhizosphere soil of Chinese fir in Hunan province. This research also indicated that, mycorrhiza forming was associated with the environment factors. The AMF spores density has the extremely remarkable correlational dependence with vegetation quantity in Chinese Fir forest (r2=0.943, p < 0.05). Mycorrhiza distribution also associated with seasons and forest age; the most active season of mycorrhiza was between spring and summer and the natural AMF infection rate was increased along with the increasing of forest age. The results will not only provide the theory basis for exploitation and using of mycorrhizal resource, but also enhance the survival rate of seedling and prevent the soil degradation and conserve of soil against erosion.Key words: Mycorrhizal fungi, vesicle-abuscular, Chinese fir, mycorrhizal inocula

Finite size effect on Neel temperature with Co3O4 nanoparticles

Finite size effect on the antiferromagnetic transition temperature, TN, of Co3O4 nanoparticles of 75, 35, and 16 nm in diameter, has been investigated. The AFM transition point, TN, reduces with the decreasing diameter, d. Along with the results from the previous experiments on the Co3O4 nanoparticles of 8 and 4.3 nm, the variation of TN with d appears to follow the finite size relation. According to the scaling behavior, the shift exponent is determined as \lambda = 1.4 \pm 0.4, the correlation length, \ksi_0 = 3.0 \pm 0.3 nm, and the bulk Neel temperature, TN(\infint) = 38.6 \pm 0.7 K.Comment: 12 pages, 6 figures, J Appl. Phys. In Pres