Azimuthal distributions of final-state particles and fragments and transverse structure of emission source in high-energy nucleus-nucleus collisions

The azimuthal distributions of final-state particles and fragments produced in high-energy nucleus-nucleus collisions are described by a modified multisource ideal gas model which contains the expansions and movements of the emission sources. The transverse structures of the sources are given in the transverse plane by momentum components Px and Py, and described by parameters in the model. The results of the azimuthal distributions, calculated by the Monte Carlo method, are in good agreement with the experimental data in nucleus-nucleus collisions at high energies.

Collective Flows of 16O＋16O Collisions with α-Clustering Configurations

The main purpose of the present work is to discuss whether or not the collective flows in heavy-ion collision at the Fermi energy can be taken as a tool to investigate the cluster configuration in light nuclei. In practice, within an extended quantum molecular dynamics model, four a-clustering （linear chain, kite, square and tetrahedron） configurations of 16O are employed in the initialization, 16O＋16O around the Fermi energy （40-60 MeV/nucleon） with impact parameter 1-3fro are simulated, and the directed and elliptic flows are analyzed. It is found that collective flows are influenced by the different a-clustering configurations, and the directed flow of free protons is more sensitive to the initial cluster configuration than the elliptic flow. Nuclear reaction at the Fermi energy can be taken as a useful way to study cluster configuration in light nuclei.

Peripheral collisions of highly charged ions with metal clusters

Within the framework of the dynamical classical over-barrier model,the soft collisions between slow highly charged ions（SHCIs） Ar 17＋ and the large copper clusters under large impact parameters have been studied in this paper.We present the dominant mechanism of the electron transfer between SHCIs and a large metal cluster by computational simulation.The evolution of the occupation of projectile ions,KL x satellite lines,X-ray yields,Auger electron spectrum and scattering angles are provided.

Collision statistics of clusters:from Poisson model to Poisson mixtures

Clusters traverse a gas and collide with gas particles. The gas particles are absorbed, and the clusters become hosts. If the clusters are size-selected, the number of guests will be Poisson distributed. We review this by showcasing four laboratory procedures that all rely on the validity of the Poisson model. The effects of a statistical distribution of the clusters＇ sizes in a beam of clusters are discussed. We derive the average collision rates. Additionally, we present Poisson mixture models that also involve standard deviations. We derive the collision statistics for common size distributions of hosts and also for some generalizations thereof. The models can be applied to large noble gas clusters traversing doping gas. While outlining how to fit a generalized Poisson to the statistics, we still find even these Poisson models to be often insufficient.

A GPU-based general numerical framework for plasma simulations in terms of microscopic kinetic equations with full collision terms

We have proposed a general numerical framework for plasma simulations on graphics processing unit clusters based on microscopic kinetic equations with full collision terms.Our numerical algorithm consistently deals with both long-range(classical forces in the Vlasov term)and short-range(quantum processes in the collision term)interactions.Providing the relevant particle masses,charges and types(classical,fermionic or bosonic),as well as the external forces and the matrix elements(in the collisional integral),the algorithm consistently solves the coupled multi-particle kinetic equations.Currently,the framework is being tested and applied in the field of relativistic heavy-ion collisions;extensions to other plasma systems are straightforward.Our framework is a potential and competitive numerical platform for consistent plasma simulations.

Gas-Dust Protoplanetary Disc: Modeling Collisional Interaction of Primordial Bodies

One of the key problems in the concept of planetary systems origin and early evolution is solid bodies formation in the protoplanetary gas-dust disc around young stars. Dust particles interactions inside the original fluffy dust clusters of fractal nature resulted from gravitational instability and fragmentation in the disc’s central plane areassumed as the most plausible mechanism of primary bodies set up owing to particles integration within the clusters. Follow upcollisions are regarded to be responsible for eventual growth of primary bodies to the size of planetesimals. We discuss this scenario including chemical nature of particles depending on the disc’s radial temperature distribution and phase transitions. The mathematical model is developed based on the method of penetrating particles with the account for internal structure/properties of bodies involved, complicated patterns of their interaction, and phenomenological approach to describe energy distribution in the contact zone. The model is mainly addressed to the stage of formed solid bodies collisions. The results of numerical evaluation of the model are described involving some constraints for complete or partial destruction of colliding bodies followed by either scattering of collisional fragments orpartial back accumulation.

Collision of low energy Na+ ion with C_(60)

The collision-induced reaction of Na+ ion with neutral C6o vapour was investigated at the energy range of 10 to 150 eV. The deposited films were studied via laser desorption time-of-flight mass spectroscopy (TOFMS). The fragment products of C60 with even number of carbon atoms, such as Cn+ (n=58, 56, 54), and adduct products, such as Cn+ (n=62, 64, 66, 68) were obser.vcd in the positively charged TOF mass spectra. The endohedral fullerene ion of Na@C60+ was detected when collision energies are above 20 eV. Besides, no negative endohedral fullerene was detected, the products appearing in positively charged mass spectra were also observed in the negatively charged mass spectra. In addition, a series of products with odd number of carbon atoms, such as Cn- (n=53, 55, 57, 59, 61, 63, 65, 67), also appeared, but the intensities of their signals were not as high as that of even numbered. Finally, it is interesting to find that the deposited films are insoluable in toluene, benzene or water. Their Fourier transform infrared (FTIR) spectra seem like those photopolymerized ones. Some of the reaction schemes are proposed to explain the experimental results.

Collision Resolution MAC Protocols for Wireless Ad Hoc Networks

In wireless ad hoc networks, nodes cooperatively form a network without any infrastructure such as a BS/AP (base station or access point). The widely-used contention-based MAC protocol, IEEE 802.11b, is inefficient in multi-hop networks due to the hidden and exposed terminal problems. The most popular schedule-based MAC protocol, TDMA (time division multiple access), is difficult to implement in an ad hoc network due to the lack of infrastructure. The contribution of this paper is to provide the community novel and efficient MAC (medium access control) protocols (i.e., a collision resolution protocol) for a wireless ad hoc network without a centralized infrastructure. We propose two new MAC protocols (one distributed algorithm and one cluster-based algorithm) that use a collision resolution scheme for a network with a single BS/AP. We first compare the performance of our distributed algorithm with our cluster-based algorithm. Then, we compare our algorithm that performs better (i.e., our cluster-based algorithm) to TDMA in a two-hop network. The simulation results illustrate that our cluster-based algorithm provides higher throughput and lower delay than TDMA in a two-hop network.

基于级联碰撞缺陷数据库的源项对辐照微结构演化影响团簇动力学模拟研究

团簇动力学(CD)方法是模拟核材料在高能粒子辐照下微观结构演化的重要方法之一,源项是团簇动力学方法的关键输入。经典CD方法中源项通常采用经验拟合得到,未能充分利用原子尺度获得的初始缺陷信息。随着分子动力学等方法的发展,级联碰撞缺陷数据库大为丰富,结合初级离位原子(PKA)能谱足以得到更为合理的源项。由于级联碰撞缺陷数据库的能量值数量相对于准连续PKA能谱仍然偏少,本文提出了5种从准连续PKA能谱得到级联能量分立值的抽样算法,并基于团簇动力学方法模拟低剂量中子辐照纯钨实验对算法进行了验证和比较。

切入场景下基于碰撞风险聚类的改进车速预测方法

切入工况的高精度车速预测是保证自动驾驶切入安全的关键依据。为提高自动驾驶汽车切入工况安全,开展了基于车车耦合风险聚类的切入场景自车速度高精度预测方法的研究。首先,依据实验所得自然驾驶数据进行车辆切入切出片段提取,使用K-means方法依据碰撞风险与加速度关联特征进行聚类分析。其次,基于支持向量机(SVM)模型,对切入切出工况车车交互状态进行在线识别,对切入危险工况进行实时预测。最后,提出基于自回归综合移动平均(ARIMA)模型的改进车速预测方法,结合在线识别结果进行车速在线优化。仿真结果表明,所提出的基于碰撞风险聚类的改进ARIMA车速预测方法对提高切入安全效果明显,较传统的预测方法车辆的碰撞风险降低了10%~20%。研究结果表明,ARIMA模型的改进车速预测方法对提高自动驾驶车切入安全具有重要的研究意义。

基于改进DBSCAN的船舶会遇识别模型

为解决大数据下船舶会遇识别算法效率不高且存在误判等问题,提出一种融合国际海上避碰规则(International Regulations for Preventing Collisions at Sea,COLREGs)的带噪声的基于密度的空间聚类(density-based spatial clustering of applications with noise,DBSCAN)算法,建立船舶会遇识别模型。在DBSCAN算法对邻域内的船舶数量进行统计时,计算船舶间的最近会遇距离(distance to closest point of approach,DCPA)和最近会遇时间(time to closest point of approach,TCPA),初步筛选邻域内的噪声点;基于模糊综合评价模型计算船舶会遇风险,对邻域内的船舶进行二次筛选,实现船舶会遇态势的提取。结果表明:改进后的DBSCAN算法过滤掉传统DBSCAN算法识别到的非会遇局面,并且在同一会遇局面下的船舶数量均保持在4艘以内;输出的会遇船舶风险演变趋势对实际水域内高风险船舶的监控适用性较好,能有效辅助船舶避碰。所提识别模型对保障航行安全和提高海事监管效率具有重要意义。

碳纤维复合材料车门防撞梁多尺度高效变形模拟及实验验证

以碳纤维复合材料车门防撞梁为例,开发了一种面向工程零部件的多尺度高效变形模拟技术,建立了自洽聚类分析方法及多尺度渐进损伤本构模型,通过多尺度单元与唯象单元混合建模,有效降低了模型的求解成本,通过将有限的计算资源分配在恰当的位置,结果表明计算资源的利用效率得到显著提升,实现了工程零部件损伤行为的高效预测,实际计算时间缩短至原来的1/4。对三点弯状态下复合材料防撞梁的宏微观渐进损伤过程进行了分析。基于真空袋成形工艺进行了防撞梁样件试制以及三点弯破坏实验,验证了仿真结果的准确性。

宝钢湛江钢铁焦炉智能设备的应用

宝钢湛江钢铁厂三期新建了2×65孔炭化室高7 m、宽530 mm的复热式顶装焦炉,通过无人驾驶、智能防碰撞、区域防控、安全联锁、无线技术、集群操作模式、结次焦检查等技术的应用,实现焦炉机车自动化。结合焦炉本体的防爆液压交换机、炉底巡检机器人、上升管余热回收、上升管自动开闭和火落判定技术等功能相互配合,完成焦炉无人化生产作业,同时分析了焦炉机车无人驾驶的可行性。

Signals of α clusters in ^(16)O+^(16)O collisions at the LHC from relativistic hydrodynamic simulations

In relativistic heavy ion collisions,the fluctuations of initial entropy density convert to the correlations of final state hadrons in momentum space through the collective expansion of strongly interacting QCD matter.Using a(3+1)D viscous hydrodynamic program,CL Visc,we consider whether the nuclear structure,which provides initial state fluctuations as well as correlations,can affect the final state of heavy ion collisions,and whether one can find signals of α cluster structures in oxygen using final state observables in ^(16)O+ ^(16)O collisions at the CERN Large Hadron Collider.For the initial nucleon distributions in oxygen nuclei,we compare three different configurations,a tetrahedral structure with four-α clusters,the deformed Woods-Saxon distribution,and a spherical symmetric Woods-Saxon distribution.Our results show that the charged multiplicity as a function of centrality and the elliptic flow at the most central collisions using the four-α structure differs from those with the Woods-Saxon and deformed Woods-Saxon distributions,which may help to identify α clustering structures in oxygen nuclei.

路网级桥梁集群监测系统建设关键技术及实践

桥梁健康监测是防范结构运行风险、提升养护管理和应急处置水平的重要举措之一,国家和行业政策对于桥梁结构健康监测系统建设提出了明确的要求。以广东交通集团路网节点桥梁集群监测系统为例,介绍了路网级桥梁监测系统的技术路线、总体架构、关键技术和建设实践,可为地市级、路网级桥梁健康监测系统的构建提供参考。

Unimolecular Dissociation of H⁺<sub style="margin-left:-6px;">2n+1</sub>Hydrogen Clusters: Measured Cross Sections and Theoretically Calculated Rate Constants

In this paper, we studied the process of dissociation unimolecular of the evaporation of H+2n+1 hydrogen clusters according to size, using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The rate constants k(E) were determined with the use of statistical theory of unimolecular reactions using various approximations. In our work, we used the products frequencies instead of transitions frequencies in the calculation of unimolecular dissociation rates obtained by three models RRKM. The agreement between the experimental cross section ratio and calculated rate ratio with direct count approximation seems to be reasonable.

密集丛式井防碰技术研究现状及发展趋势

密集丛式井钻井密度大、井口间距小,钻进时受邻井轨迹数据不准确、仪器测量精度及井眼轨迹控制等因素影响,井眼碰撞风险较高,已成为制约密集丛式井安全优快钻进的主要因素之一。在对国内外密集丛式井防碰技术研究现状进行广泛调研的基础上,结合现场防碰监测作业经验,分析总结了井眼相碰的原因;对现有井眼轨道优化设计方法、井眼轨迹精确控制技术、井眼轨迹误差模型、井眼轨迹实时三维可视化、防碰风险评价指标、防碰作业要求及防碰监测技术等进行了分析;基于大数据及人工智能在油气田开发中的应用,探讨了未来密集丛式井防碰技术发展趋势。本文对密集丛式井防碰技术研究现状的调研分析,可为保障密集丛式井安全钻进提供指导。

基于视觉共享的多无人机协同防碰撞方法

现代复杂空域中,由于视觉遮挡的存在,无人机集群难以实现全局环境已知情况下的集群防碰撞。为此,借鉴人类相互协作完成整体目标的感知共享机制,通过将局部感知信息进行融合拼接形成对整体环境的认知,采用最近力-最远力模型构建无人机编队的防碰撞策略,提出基于视觉共享的多无人机协同防碰撞控制方法。仿真实验表明,该方法使无人机集群在部分视觉遮挡情况下仍然能够实现全局的协同防碰撞,提高了防碰撞行为的智能性。

子拦截弹拦截无人机集群防碰撞制导律

为解决子拦截弹拦截无人机集群过程中可能发生的碰撞问题,本文将虚拟排斥力与纯比例导引律结合,提出一种防碰撞纯比例导引制导律(Collision Avoidance-Pure Proportional Guidance Law,CA-PPN)。首先,提出一种子母导弹拦截无人机集群的作战构想,并分析了其中的子拦截弹制导问题。随后,针对子拦截弹制导中可能发生的碰撞问题,在子拦截弹之间设计了一种用于避碰的人工势场,分析了PPN的特性,在此基础上将人工势场下的虚拟排斥力与PPN结合,并加入视场角与过载约束,提出了CA-PPN。仿真结果表明,CA-PPN能在制导子拦截弹有效拦截目标的同时避免相互之间的碰撞。