核物质对称能的高密行为研究

同位旋物理的主要任务之一是通过放射性核束引起的核反应来探索介质中有效核子-核子相互作用的同位旋依赖性,尤其是同位旋相关的核物质状态方程, 即密度依赖的核物质对称能。由于对称能,尤其是其高密行为,对核物理学和天体物理学具有重要意义,密度依赖的对称能在过去10年一直是中能重离子物理研究领域的主要焦点之一。近年来,低密对称能的研究已经取得了重要进展, 而对称能的高密行为仍然很不确定。在理论方面,人们提出了许多对高密对称能敏感的观测量。 实验方面, 关于对称能高密行为研究的实验计划已经展开,世界各地正在建造的放射性核束装置为对称能的高密行为研究提供了新的机遇。基于IBUU输运模型综述了研究对称能高密行为的一些敏感观测量及其最新进展, 以及所面临的挑战与机遇。One of the major tasks of studying isospin physics via heavy ion collisions with neutron rich nuclei, is to explore the isospin dependence of in medium nuclear effective interactions and the equation of state of neutron rich nuclear matter, i.e., the density dependence of nuclear symmetry energy. Because of its great importance for understanding many phenomena in both nuclear physics and astrophysics, the study of the density dependence of nuclear symmetry energy has been the main focus of the intermediate energy heavy ion physics community during the last decade. Nowadays significant progress has been achieved in studying the low density behavior of nuclear symmetry energy, but the high density behavior of nuclear symmetry energy is still very uncertain. Theoretically, a number of observables have been proposed as sensitive probes to the high density behavior of nuclear symmetry energy. With new opportunities provided by the various radioactive beam facilities being constructed around the world, studies of the high density behavior of nuclear symmetry energy is expected to be one of the main forefront research areas in nuclear physics in the near future. In this report, based on the transport model IBUU we have reviewed the major progress achieved in studying the high density behavior of nuclear symmetry energy and discussed future challenges in this field.     

Nuclear Level Density at High Spin and Excitation Energy

The intensive studies of equilibrium processes in heavy-ion reaction have produced a need for information on nuclear level densities at high energies and spins. The Fermi gas level density is often used in investigation of heavy-ion reaction studies. Some papers have claimed that nuclear level densities might deviate substantially from the Fermi gas predications at excitations related to heavy-ion reactions. The formulae of calculation of the nuclear level density based on the theory of superconductivity are presented, special attention is paid to the dependence of the level density on the angular momentum. The spin-dependent nuclear level density is evaluated using the pairing interaction. The resulting level density for an average spin of 52 ħ is evaluated for ¹⁵⁵Er and compared with experimental data. Excellent agreement between experiment and theory is obtained.     

High Energy Density Polymeric Nitrogen Nanotubes inside Carbon Nanotubes

Polymeric nitrogen as a new class of high energy density materials has promising applications. We develop a new scheme of crystal structure searching in a confined space using external confining potentials fitted from firstprinciples calculations. As a showcase, this method is employed to systematically explore novel polymeric nitrogen structures confined in single-walled carbon nanotubes. Several quasi-one-dimensional single-bonded polymeric nitrogen structures are realized, two of them are com...     

Superhard Pseudocubic BC2N superlattices

It is currently under debate whether diamondlike BC2N may be harder than cubic BN (c-BN). Using the bond counting rule, we have performed an unconstrained search and identified a series of short period (111) superlattices that have much lower total energy than previously proposed structures. By examining the ideal strength of these pseudocubic boron-carbonitrides, we show that they are harder than c-BN. Our results are consistent with experimental findings, but in contrast with a recent theoretical study, which claimed that the BC2N is less hard than c-BN.     

高功率脉冲激光的远场能量密度分布测试方法研究

在分析现有的激光远场能量密度分布测试方法的基础上提出了一种新的测试方法.采用激光束照射漫反射靶,CCD相机对靶上激光光斑成像并在靶面上布置能量计探头以获取能量抽样绝对值的方法进行激光束远场大气传输后空域分布测试.从基本组成、测试原理、试验结果等方面对新测试方法进行了分析研究,并通过采用532nm脉冲激光照射1Km外的漫反射靶的实验对新测试方法进行了可行性验证,获得了远场激光光斑的图像和能量抽样值.     

Computational Prediction of a Novel Superhard SP~3 Trigonal Carbon Allotrope with Bandgap Larger than Diamond

Searching for new carbon allotropes with superior properties has been a longstanding interest in material sciences and condensed matter physics.Here we identify a novel superhard carbon phase with an 18-atom trigonal unit cell in a full-sp~3 bonding network,termed tri-C_(18) carbon,by first-principles calculations.Its structural stability has been verified by total energy,phonon spectra,elastic constants,and molecular dynamics simulations.Furthermore,tri-C_(18) carbon has a high bulk modulus of 400 GPa and Vickers hardness of 79.0 GPa,comparable to those of diamond.Meanwhile,the simulated x-ray diffraction pattern of tri-C_(18) carbon matches well with the previously unexplained diffraction peaks found in chimney soot,indicating the possible presence of tri-C_(18)carbon.Remarkably,electronic band structure calculations reveal that tri-C_(18) carbon has a wide indirect bandgap of 6.32 eV,larger than that of cubic diamond,indicating its great potential in electronic or optoelectronic devices working in the deep ultraviolet region.     

高功率脉冲激光的远场能量密度分布测试方法研究

在分析现有的激光远场能量密度分布测试方法的基础上提出了一种新的测试方法.采用激光束照射漫反射靶,CCD相机对靶上激光光斑成像并在靶面上布置能量计探头以获取能量抽样绝对值的方法进行激光束远场大气传输后空域分布测试.从基本组成、测试原理、试验结果等方面对新测试方法进行了分析研究,并通过采用532nm脉冲激光照射1Km外的漫反射靶的实验对新测试方法进行了可行性验证,获得了远场激光光斑的图像和能量抽样值.     

Pressure-Driven Ne-Bearing Polynitrides with Ultrahigh Energy Density

Neon（Ne） can reveal the evolution of planets,and nitrogen（N） is the most abundant element in the Earth’s atmosphere.Considering the inertness of neon,whether nitrogen and neon can react has aroused great interest in condensed matter physics and space science.Here,we identify three new Ne-N compounds(i.e.,NeN₆,NeN₁₀,and NeN₂₂) under pressure by first-principles calculations.We find that inserting Ne into N₂ substantially decreases the polymeric pressure...     

The Ground State Energy of the Weakly Interacting Bose Gas at High Density

We prove the Lee-Huang-Yang formula for the ground state energy of the 3D Bose gas with repulsive interactions described by the exponential function, in a simultaneous limit of weak coupling and high density. In particular, we show that the Bogoliubov approximation is exact in an appropriate parameter regime, as far as the ground state energy is concerned.     

超硬立方BC2N材料与金刚石的比较

最近有实验称成功合成超硬立方BC2N材料,其硬度仅次于金刚石.文章采用第一性原理计算方法,研究立方BC2N晶体材料的理想强度.计算结果显示,虽然立方BC2N晶体具有很大的弹性系数,但材料中化学成分的各向异性和原子键特性随外加应力变化的非线性性质限制了立方BC2N晶体的强度.最硬的立方BC2N晶体结构的硬度应低于立方BN,后者为目前已知的第二硬材料.实验中观测到的立方BC2N材料的超硬特性应源自材料中的纳米颗粒效应.制备立方BC2N纳米复合材料将是合成新型超硬材料的新方法.     

Superhard cubic BC2N compared to diamond

Recent experiments claimed successful synthesis of cubic boron-carbonitride compounds BC2N with an extreme hardness second only to diamond. In the present Letter, we examine the ideal strength of cubic BC2N using first-principles calculations. Our results reveal that, despite the large elastic parameters, compositional anisotropy and strain dependent bonding character impose limitation on their strength. Consequently, the hardness of the optimal BC2N structure is predicted to be lower than that of cubic BN, the second hardest material known. The measured extreme hardness of BC2N nanocomposites is most likely due to the nanocrystalline size effect and the bonding to the surrounding amorphous carbon matrix. This may prove to be a general rule useful in the quest for new superhard covalent materials.     

超硬立方BC2N材料与金刚石的比较

摘要最近有实验称成功合成超硬立方BC2N材料，其硬度仅次于金刚石．文章采用第一性原理计算方法，研究立方BC2N晶体材料的理想强度．计算结果显示，虽然立方BC2N晶体具有很大的弹性系数，但材料中化学成分的各向异性和原子键特性随外加应力变化的非线性性质限制了立方BC2N晶体的强度．最硬的立方BC2N晶体结构的硬度应低于立方BN，后者为目前已知的第二硬材料．实验中观测到的立方BC2N材料的超硬特性应源自材料中的纳米颗粒效应．制备立方BC2N纳米复合材料将是合成新型超硬材料的新方法．     

Holographic Dark Energy Density

In this article we consider the cosmological model based on the holographic dark energy. We study dark energy density in Universe with arbitrary spatially curvature described by the Friedmann-Robertson-Walker metric. We use Chevallier-Polarski-Linder parametrization to specify dark energy density.     

Estimate of the Maximal Energy Density and Space-Time Region of the Quark Matter in High Energy Heavy Ion Collisions

The Bjorken formula about maximal energy density in heavy ion collisions is modified,the effective way to increase the energy density is also analysed.The hydrodynamic equations and the equations of state in central and fragmental regions are discussed.It is pointed out that because of the energy diffusion caused by expansion of the system,it is lifficult to produce quark matter in fragmental region.For Au-Au collisions on the RHIC to be buict at BNL,the space-time region where phase transition occur d and the corresponding extent of impact parameter are predicted.     

质子椭圆流与对称能的密度依赖性

基于同位旋和动量依赖的强子输运IBUU04模型, 研究了¹³²Sn+¹²⁴Sn碰撞系统中的质子椭圆流对对称能的敏感关系. 研究发现入射能量从每核子400MeV到800MeV时质子椭圆流在低横动量端对对称能的敏感性高于高横动量端, 同时发现随着入射能量的增大, 质子椭圆流对对称能的敏感性在降低. 在研究入射能量范围内, 当入射能量为每核子400MeV左右时质子椭圆流对对称能最为敏感.     

高能中微子与核乳胶碰撞中的相对赝快度和簇射粒子数密度研究

论述了高能中微子与核乳胶碰撞中,归一化的两粒子相对赝快度分布,和平均最大簇射粒子数密度与多重数的关联. In high energy neutrino emulsion collisions, the normalized distribution of two particle relative pseudorapidity and the correlation between the mean maximum number density of shower particles and multiplicity are investigated.     

Microstructure and Wear Behaviour of WC Film Prepared by Pulsed High Energy Density Plasma

A super hard and wear resistant WC film is in-situ prepared on a 0.45%C steel substrate by pulsed high energy density plasma technique at ambient temperature. The microstructure and composition of the film are analysed by x-ray diffraction, x-ray photoelectron spectroscopy, Auger electron spectroscopy and scanning electron microscopy. The hardness profile and tribological behaviour of the film are determined with nano-indenter and wear tester, respectively. The results show that the microstructure of the film was dense and uniform and mainly composed of WC and a small amount of W2 C. A wide mixing interface exists between the film and the 0.45%C steel substrate. The thickness of the film is about 2μm. The hardness and Yang＇s modulus of the film are very high. The film has excellent wear resistance and low friction coefficient under dry sliding wear test conditions.     

脉冲放电脱硫反应器中高能电子密度分布的光谱研究

脉冲流光放电产生的大于等于11.2 eV的高能电子能将处于基态的氮分子激发到N₂(C3Π_u)态,测试脉冲流光放电时的N₂(C3Π_u→B3Πg)发射光谱相对强度可以得出脉冲流光放电产生的高能电子的密度。实验在室温常压下研究了空气中线-板式脉冲流光放电脱硫反应器内高能电子密度分布情况,并研究了脉冲电压、反应器的线线间距对反应器内高能电子密度分布的影响。实验结果表明,反应器内的高能电子主要集中在放电线附近高电场区内,随着离放电线的距离增大,高能电子密度减小;脉冲电压对高能电子密度有很大影响,随着电压的升高,高能电子密度基本呈线性增大;线板间距固定,线线间距为线板间距的0.6～1倍时,反应器内高能电子密度分布较为均匀。