Synthesis and nitrogen content regulation of diamond in a high-pressure hydrogen-rich environment

The regulating nitrogen content of diamond in a hydrogen-rich high-temperature and high-pressure(HPHT) growth environment was systematically investigated in this work by developing three growth systems,namely, "FeNi+Ti", "FeNi+G_(3)N_(6)H_(6)",and "FeNi+Ti+C_(3)N_(6)H_(6)".Optical microscopy,infrared spectroscopy,and photoluminescence(PL)spectroscopy measurements were conducted to analyze the spectroscopic characteristics of diamonds grown in these three systems.From our analysis,it was demonstrated that the presence of hydrogen in the sp^(3) hybrid C-H does not directly affect the color of the diamond and facilitates the increase of the nitrogen-vacancy(NV) center concentration in a highnitrogen-content diamond.In addition,titanium plays an important role in nitrogen removal,while its impact on hydrogen doping within the diamond lattice is insignificant.Most importantly,by regulating the ratio of nitrogen impurities that coexist in the nitrogen and hydrogen HPHT environment,the production of hydrogenous Ⅱa-type diamond,hydrogenous Ib-type diamond,and hydrogenous high-nitrogen-type diamonds was achieved with a nitrogen content of less than 1 ppm to 1600 ppm.

Optimal preparation of Bose and Fermi atomic gas mixtures of ^(87)Rb and ^(40)K in a crossed optical dipole trap

We report on the optimal production of the Bose and Fermi mixtures with ^(87) Rb and ^(40)K in a crossed optical dipole trap(ODT).We measure the atomic number and lifetime of the mixtures in combination of the spin state |F=9/2,m_(F)=9/2> of^(40)K and |1,1>of ^(87) Rb in the ODT,which is larger and longer compared with the combination of the spin state |9/2,9/2> of^(40)K and 12,2) of ^(87)Rb in the ODT.We observe the atomic numbers of ^(87)Rb and ^(40)K shown in each stage of the sympathetic cooling process while gradually reducing the depth of the optical trap.By optimizing the relative loading time of atomic mixtures in the MOT,we obtain the large atomic number of ^(40)K(~6 ×10^(6)) or the mixtures of atoms with an equal number(~1.6 × 10^(6)) at the end of evaporative cooling in the ODT.We experimentally investigate the evaporative cooling in an enlarged volume of the ODT via adding a third laser beam to the crossed ODT and found that more atoms(8 × 10^(6)) and higher degeneracy(T/T_(F)=0.25) of Fermi gases are obtained.The ultracold atomic gas mixtures pave the way to explore phenomena such as few-body collisions and the Bose-Fermi Hubbard model,as well as for creating ground-state molecules of ^(87)Rb^(40)K.

Strong electron correlation-induced Mott-insulating electrides of Ae_(5)X_(3)(Ae=Ca,Sr,and Ba;X=As and Sb)

The presence of interstitial electrons in electrides endows them with interesting attributes,such as low work function,high carrier concentration,and unique magnetic properties.Thorough knowledge and understanding of electrides are thus of both scientific and technological significance.Here,we employ first-principles calculations to investigate Mott-insulating Ae_(5)X_(3)(Ae=Ca,Sr,and Ba;X=As and Sb)electrides with Mn_(5)Si_(3)-type structure,in which half-filled interstitial electrons serve as ions and are spin-polarized.The Mott-insulating property is induced by strong electron correlation between the nearest interstitial electrons,resulting in spin splitting and a separation between occupied and unoccupied states.The half-filled antiferromagnetic configuration and localization of the interstitial electrons are critical for the Mott-insulating properties of these materials.Compared with that in intermetallic electrides,the orbital hybridization between the half-filled interstitial electrons and the surrounding atoms is weak,leading to highly localized magnetic centers and pronounced correlation effects.Therefore,the Mott-insulating electrides Ae_(5)X_(3)have very large indirect bandgaps(0.30 eV).In addition,high pressure is found to strengthen the strong correlation effects and enlarge the bandgap.The present results provide a deeper understanding of the formation mechanism of Mott-insulating electrides and provide guidance for the search for new strongly correlated electrides.

Diamond growth in a high temperature and high pressure Fe–Ni–C–Si system:Effect of synthesis pressure

Pressure is one of the necessary conditions for diamond growth.Exploring the influence of pressure on growth changes in silicon-doped diamonds is of great value for the production of high-quality diamonds.This work reports the morphology,impurity content and crystal quality characteristics of silicon-doped diamond crystals synthesized under different pressures.Fourier transform infrared spectroscopy shows that with the increase of pressure,the nitrogen content in the C-center inside the diamond crystal decreases.X-ray photoelectron spectroscopy test results show the presence of silicon in the diamond crystals synthesized by adding silicon powder.Raman spectroscopy data shows that the increase in pressure in the Fe-Ni-C-Si system shifts the Raman peak of diamonds from 1331.18 cm^(-1)to 1331.25 cm^(-1),resulting in a decrease in internal stress in the crystal.The half-peak width decreased from 5.41 cm^(-1)to 5.26 cm^(-1),and the crystallinity of the silicon-doped diamond crystals improved,resulting in improved quality.This work provides valuable data that can provide a reference for the synthesis of high-quality silicon-doped diamonds.

Achieving ultracold Bose–Fermi mixture of^(87)Rb and^(40)K with dual dark magnetic-optical-trap

We demonstrate that dual dark magnetic-optical-traps(MOTs)have great importance in the two-species^(87)Rb and^(40)K mixture compared with dual bright MOTs.The dark MOT has a little improvement in the trapping of single-species^(87)Rb or^(40)K gases compared with bright MOT.For the case of loading two-species^(87)Rb and^(40)K simultaneously,the improvement of^(40)K in the dual dark MOTs is mainly from the reduction of light-assisted collision losses.The dual dark MOTs employ a pair of conical lenses to produce the hollow beam for repump laser with high efficiency.The number and density of^(87)Rb and^(40)K atoms after evaporative cooling in the hybrid magnetic trap with dark MOT loading are compared with those in bright MOT.The atoms with large number and high density make it easier to realize the quantum degenerate of Bose-Fermi mixture.

Effect of the codoping of N-H-O on the growth characteristics and defects of diamonds under high temperature and high pressure

Diamond crystals were synthesized with different doping proportions of N-H-O at 5.5 GPa-7.1 GPa and 1370℃-1450℃. With the increase in the N-H-O doping ratio, the crystal growth rate decreased, the temperature and pressure conditions required for diamond nucleation became increasingly stringent, and the diamond crystallization process was affected. [111] became the dominant plane of diamonds;surface morphology became block-like;and growth texture,stacking faults, and etch pits increased. The diamond crystals had a two-dimensional growth habit. Increasing the doping concentration also increased the amount of N that entered the diamond crystals as confirmed via Fourier transform infrared spectroscopy. However, crystal quality gradually deteriorated as verified by the red-shifting of Raman peak positions and the widening of the Raman full width at half maximum. With the increase in the doping ratio, the photoluminescence property of the diamond crystals also drastically changed. The intensity of the N vacancy center of the diamond crystals changed, and several Ni-related defect centers, such as the NE1 and NE3 centers, appeared. Diamond synthesis in N-H-O-bearing fluid provides important information for deepening our understanding of the growth characteristics of diamonds in complex systems and the formation mechanism of natural diamonds, which are almost always N-rich and full of various defect centers. Meanwhile, this study proved that the type of defect centers in diamond crystals could be regulated by controlling the N-H-O impurity contents of the synthesis system.

Preparation of a two-state mixture of ultracold fermionic atoms with balanced population subject to the unstable magnetic field

We report a novel method to prepare a mixture of ^(40)K Fermi gas having an equal population of the two ground magnetic spin states confined in an optical dipole trap,in the presence of an noisy quantization(magnetic)field.We realize the equal population mixture by applying a series of RF pulses.We observe the dependence of the population distribution between two spin states on the number of the applied RF pulses and find that the decoherence effects leading to the population fluctuations are overcome by the high number of RF pules.Our demonstrated technique can be potentially used in the precision measurement experiments with ultracold gases in noisy environments.

Properties of B4C-TiB2 ceramics prepared by spark plasma sintering

By doping titanium hydride(TiH2) into boron carbide(B4C), a series of B4C + x wt% TiH2(x = 0, 5, 10, 15, and 20)composite ceramics were obtained through spark plasma sintering(SPS). The effects of the sintering temperature and the amount of TiH2 additive on the microstructure, mechanical and electrical properties of the sintered B4C-TiB2 composite ceramics were investigated. Powder mixtures of B4C with 0–20 wt% TiH2 were heated from 1400℃ to 1800℃ for 20 min under 50 MPa. The results indicated that higher sintering temperatures contributed to greater ceramic density. With increasing TiH2 content, titanium diboride(TiB2) formed between the TiH2 and B4C matrix. This effectively improved Young’s modulus and fracture toughness of the composite ceramics, significantly improving their electrical properties: the electrical conductivity reached 114.9 S·cm-1 at 1800℃ when x = 20. Optimum mechanical properties were obtained for the B4C ceramics sintered with 20 wt% TiH2, which had a relative density of 99.9±0.1%, Vickers hardness of 31.8 GPa,and fracture toughness of 8.5 MPa·m1/2. The results indicated that the doping of fine Ti particles into the B4C matrix increased the conductivity and the fracture toughness of B4C.

Experimental realization of two-dimensional single-layer ultracold gases of ^(87)Rb in an accordion lattice

We experimentally realize two-dimensional(2D) single-layer ultracold gases of ^(87)Rb by dynamically tuning the periodicity of a standing wave, known as accordion lattice. In order to load ^(87)Rb Bose-Einstein condensate into single dark fringe node of the blue detuning optical lattice, we reduce the lattice periodicity from 26.7 μm to 3.5 μm with the help of an acousto-optic deflector(AOD) to compress the three-dimensional BEC adiabatically into a flat and uniform quasi-2D single-layer. We describe the experimental procedure of the atoms loading into the accordion lattice in detail and present the characteristics of the quasi-2D ultracold gases. This setup provides an important platform for studying in-and out-of equilibrium physics, phase transition and 2D topological matter.

Atmospheric dispersion prediction of accidental release:A review

Modern industrial development is accompanied by the increasingly frequent occurrence of accidental release atmospheric dispersion events,causing extremely serious human and property losses and environmental pollution,in which rapid and accurate prediction of atmospheric dispersion is an important task to mitigate the unexpected consequences.In this paper,we take the case of previous years as the starting point,firstly,the occurred hazardous chemical atmospheric dispersion accidents in the past five years are shown,and the related concepts of hazardous chemical atmospheric dispersion are given.Then,the current state of atmospheric dispersion research is reviewed,well-known experiments on atmospheric dispersion of hazardous chemicals are summarized,and correspondingly the existing atmospheric dispersion prediction models are classified into simplified-experience models,mechanism-and rule-driven models and data-driven models.In particular,for the purpose of rapid atmospheric dispersion prediction,some research on atmospheric detection and identification are analyzed in detail.Moreover,the relevant professional software for atmospheric dispersion prediction are introduced,and also their calculation adaptabilities regarding time-consumption and output accuracy are discussed.Thereinafter,according to the shortcomings of existing atmospheric dispersion prediction models in research and application fields,the development trend of atmospheric dispersion prediction research and technology is foreseen,and some feasible future research directions are proposed as follows:(1)the fusion of image processing techniques,the establishment of a database of historical accident scene information and meteorological information,(2)new correction algorithms,and(3)an emergency response system for full-scene atmospheric dispersion prediction.

一种结构化的化工系统人因失误概率评估方法

化工生产系统高度非线性且复杂耦合化,使现有人因可靠性分析(HRA)技术难以直接应用,且分析结果的有效性和准确性差。为此,本工作将人因-危险和可操作性分析(人因HAZOP)与贝叶斯网络(BN)相融合,提出了一种结构化的化工系统人因失误概率评估方法。通过概述人因HAZOP的作业任务,筛选引导词和偏差,形成结构化的人因HAZOP报告,并据此构建BN模型,求解化工系统人因失误概率。以丙烯酸甲酯虚拟仿真工厂的酯化反应为例,人因失误概率的计算结果为0.0004,且主要人误行为是维护人员遗漏。对该化工系统进行传统CREAM分析,人因失误概率结果为0.0001~0.01。与传统CREAM相比,这种结构化方法能够高效且精确地评估化工系统人因失误概率。