Preparation and characterization of diamond–silicon carbide–silicon composites by gaseous silicon vacuum infiltration process

Diamond–SiC–Si composites have been prepared using gaseous silicon vacuum infiltration. The evolution of the phases and microstructures of the composites have been analyzed using X-ray diffraction technique and scanning electron microscopy. It has been found that the diamond–SiC–Si composite is composed of β-SiC, diamond, and residual Si. The diamond particles were distributed homogeneously in the dense matrix of the composites. Besides, the effects of particle size and content of diamond on the properties of diamond–SiC–Si composites have been analyzed. The thermal conductivity of the composites increases with particle size and content of diamond. When the particle size and content of diamond are 300 µm and 80 wt %, respectively, the thermal conductivity of the composites approaches the value of 280 W·m⁻¹·K⁻¹.Проведен анализ эволюции фаз и микроструктуры композитов алмаз–SiC–Si, изготовленных с использованием процесса вакуумной инфильтрации газообразного кремния. Исследование выполнено с помощью дифракции рентгеновских лучей и сканирующей электронной микроскопии. Установлено, что композит алмаз–SiC–Si состоит из β-SiC, алмаза и остаточного Si. Алмазные частицы распределены однородно в плотной матрице композитов. Также проанализировано влияние размера частиц и содержания алмазов на свойства композитов алмаз–SiC–Si. Показано, что теплопроводность композитов возрастает с увеличением размера частиц и содержания алмазов. Теплопроводность композитов приближается к значению 280 Вт∙м⁻¹∙K⁻¹ при размере частиц и содержании алмаза 300 мкм и 80 % (по массе), соответственно.Проведено аналіз еволюції фаз і мікроструктури композитів алмаз–SiC–Si, виготовлених з використанням процесу вакуумної інфільтрації газоподібного кремнію. Дослідження виконано за допомогою дифракції рентгенівських променів і скануючої електронної мікроскопії. Встановлено, що композит алмаз–SiC–Si складається з β-SiC, алмазу і залишкового Si. Алмазні частки розподілені однорідно в щільній матриці композитів. Також проаналізовано вплив розміру частинок і вмісту алмазів на властивості композитів алмаз–SiC–Si. Показано, що теплопровідність композитів зростає зі збільшенням розміру частинок і вмісту алмазів. Теплопровідність композитів наближається до значення 280 Вт∙м⁻¹∙K⁻¹ при розмірі частинок і вмісту алмазу 300 мкм і 80 % (за масою) відповідно.This work was financially supported by the National Natural Science Foundation of China (grant no. 51102282) and Aid Program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province

Charmonium states in QCD-inspired quark potential model using Gaussian expansion method

We investigate the mass spectrum and electromagnetic processes of charmonium system with the nonperturbative treatment for the spin-dependent potentials, comparing the pure scalar and scalar-vector mixing linear confining potentials. It is revealed that the scalar-vector mixing confinement would be important for reproducing the mass spectrum and decay widths, and therein the vector component is predicted to be around 22%. With the state wave functions obtained via the full-potential Hamiltonian, the long-standing discrepancy in M1 radiative transitions of $J/\psi$ and $\psi^{\prime}$ are alleviated spontaneously. This work also intends to provide an inspection and suggestion for the possible $c\bar{c}$ among the copious higher charmonium-like states. Particularly, the newly observed X(4160) and X(4350) are found in the charmonium family mass spectrum as $M(2^1D_2)= 4164.9$ MeV and $M(3^3P_2)= 4352.4$ MeV, which strongly favor the $J^{PC}=2^{-+}, 2^{++}$ assignments respectively. The corresponding radiative transitions, leptonic and two-photon decay widths have been also predicted theoretically for the further experimental search.Comment: 16 pages,3 figure

Anomalous Heat Conduction and Anomalous Diffusion in Low Dimensional Nanoscale Systems

Thermal transport is an important energy transfer process in nature. Phonon is the major energy carrier for heat in semiconductor and dielectric materials. In analogy to Ohm's law for electrical conductivity, Fourier's law is a fundamental rule of heat transfer in solids. It states that the thermal conductivity is independent of sample scale and geometry. Although Fourier's law has received great success in describing macroscopic thermal transport in the past two hundreds years, its validity in low dimensional systems is still an open question. Here we give a brief review of the recent developments in experimental, theoretical and numerical studies of heat transport in low dimensional systems, include lattice models, nanowires, nanotubes and graphenes. We will demonstrate that the phonon transports in low dimensional systems super-diffusively, which leads to a size dependent thermal conductivity. In other words, Fourier's law is breakdown in low dimensional structures

Grain refinement of magnesium alloys: a review of recent research, theoretical developments and their application

This paper builds on the ‘‘Grain Refinement of Mg Alloys’’ published in 2005 and reviews the grain refinement research onMg alloys that has been undertaken since then with an emphasis on the theoretical and analytical methods that have been developed. Consideration of recent research results and current theoretical knowledge has highlighted two important factors that affect an alloy’s as-cast grain size. The first factor applies to commercial Mg-Al alloys where it is concluded that impurity and minor elements such as Fe and Mn have a substantially negative impact on grain size because, in combination with Al, intermetallic phases can be formed that tend to poison the more potent native or deliberately added nucleant particles present in the melt. This factor appears to explain the contradictory experimental outcomes reported in the literature and suggests that the search for a more potent and reliable grain refining technology may need to take a different approach. The second factor applies to all alloys and is related to the role of constitutional supercooling which, on the one hand, promotes grain nucleation and, on the other hand, forms a nucleation-free zone preventing further nucleation within this zone, consequently limiting the grain refinement achievable, particularly in low solute-containing alloys. Strategies to reduce the negative impact of these two factors are discussed. Further, the Interdependence model has been shown to apply to a broad range of casting methods from slow cooling gravity die casting to fast cooling high pressure die casting and dynamic methods such as ultrasonic treatment

Determination of the number of psi ' events at BESIII

The number of psi' events accumulated by the BESIII experiment from March 3 through April 14, 2009, is determined by counting inclusive hadronic events. The result is 106.41x(1.00+/-0.81%)x10(6). The error is systematic dominant; the statistical error is negligible

Search for strong gravity in multijet final states produced in pp collisions at √s=13 TeV using the ATLAS detector at the LHC

A search is conducted for new physics in multijet final states using 3.6 inverse femtobarns of data from proton-proton collisions at √s = 13TeV taken at the CERN Large Hadron Collider with the ATLAS detector. Events are selected containing at least three jets with scalar sum of jet transverse momenta (HT) greater than 1TeV. No excess is seen at large HT and limits are presented on new physics: models which produce final states containing at least three jets and having cross sections larger than 1.6 fb with HT > 5.8 TeV are excluded. Limits are also given in terms of new physics models of strong gravity that hypothesize additional space-time dimensions