87 resultados para Equation of state
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An isospin-dependent quantum molecular dynamical model (IQMD) is developed, with the isospin degree of freedom in the momentum-dependent interaction(MDI) included in IQMD, to obtain an isospin- and momentum-dependent interaction (IMDI) in IQMD. We investigate the effect of IMDI on the isospin fractionation ratio and its dynamical mechanism in the intermediate energy heavy ion collisions. It is found that the IMDI induces the significant reductions in the isospin fractionation ratio for all of beam energies, impact parameters, neutron-proton ratios and mass number of colliding systems. However, the strong dependence of isospin fractionation ratio on the symmetrical potential is preserved, with the isospin degree of freedom included in the MDI, i.e. the isospin fractionation ratio is still a good probe for extracting the information about the equation of state of isospin asymmetrical nuclear matter.
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Based on the isospin-dependent transport model IBUU and on the scaling model according to nucleon effective mass, effects of elastic and inelastic NN scattering cross-sections on pi(-)/pi(+) in the neutron-rich reaction Ca-48 + Ca-48 at a beam energy of 400MeV/nucleon are studied. It is found that cross-section effects of both NN elastic and inelastic scatterings affect Delta(1232), pi(-) and pi(+) productions as well as the value of pi(-)/pi(+).
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Microscopic three-nucleon force consistent with the Bonn B two-nucleon potential is constructed, which includes Delta(1232), Roper, and nucleon-antinucleon excitation contributions. Recent results for the choice of the meson parameters are discussed. The forces are used in Brueckner calculations and the saturation properties of nuclear matter are determined. At the high densities,the nuclear equation of state and the symmetry energy are calculated. The corresponding neutron star mass-radius relations are presented.
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本论文介绍了放射性核束物理研究的现状以及当前常用的几种同位旋相关的重离子微观输运理论,系统描述了非对称核物质的状态方程、中能重离子碰撞中的同位旋效应以及中子星的性质。基于 Hartree-Fock 理论和扩展的 Skyrme 相互作用,在核物质近似下得到了一个非相对论性的密度、温度和同位旋相关的核物质状态方程 (IEOS)。系统研究了核物质状态方程的同位旋效应。讨论了核子的平均场、核物质的不可压缩系数、核子的有效质量以及核物质临界温度的同位旋相关性,并且给出了核物质饱笔点处的饱和密度、不可压缩系数以及单核子结合能的抛物线规律。同时,探讨了对称能的温度和密度相关性,给出了零温度时对称能的解析表达式,并提出了对称能温度相关性的抛物线规律,发现对称能随着温度的升高而减小。另外,基于以上的同位旋相关的核物质状态方程,对 ALADIN's Caloric Curve 给出了一种静态解释。在传统量子分子动力学 (QMD) 模型的基础上,通过在相互作用平均场、两体碰撞、泡利阻塞、初始化以及碎片构造过程中适当地考虑同位旋自由度,得到了一个同位旋相关的 QMD 模型 (IQMD 模型)。利用IQMD模型系统研究了中能重离子碰撞中的同位旋效应。例如,中能重离子碰撞中同位旋自由度的弛豫、重离子碰撞中核子前平衡发射的同位旋效应、重离子碰撞中的集体流(包括直接流、转动流、挤出流和径向流)及其同位旋相关性、原子核多重碎裂的同位旋效应及其消失、重离子碰撞中的化学不稳定性以及中能重离子碰撞中如何选取事件的碰撞参数及其同位旋效应等。同样,在传统的 Boltzmann-Langevin 方程中适当地考虑同位旋自由度,得到了同位旋相关的Boltzmann-Langevin方程 (IBLE),利用IBLE研究了 ~(19)Na的产生截面。另外,利用IQMD模型探讨了多重碎裂的"neck" 机制以及重离子碰撞中局域势的有限程效应。基于前面给出的非相对论的核物质状态方程,系统研究了中子星的性质,如中子星的化学组份、质量、结合能、半径、密度剖面、转动惯量及表面红移等。结果表明,使用一些常用的 Skyrme 势参数能够给出与天文学观测相一致的结果。
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本论文基于重离子输运理论模型对当前人们感兴趣的超重核合成及非对称核物质状态方程做了研究。基于双核系统概念建立了一个描述超重核合成的理论模型。这个模型中通过求解Fokker-Planck方程来描述重离子碰撞过程的能量、角动量以及形变等的弛豫过程,从而合理地包含了重离子熔合过程中的动力学效应。在求解弹靶的质量扩散时采用了数值求解主方程的方法,避免对势能面做任何近似,因此能够充分地体现重离子熔合过程中弹靶的结构效应。本文利用这一模型计算了重离子熔合形成超重元素的最佳激发能、熔合几率、复合核的存活几率以及蒸发剩余核截面等,并给出了合成超重核的最佳弹靶组合。计算了超重核形成的最佳激发能,在符合已有最佳激发能实验数据的基础上预言了基于冷熔合反应合成114,116和118号元素的最佳激发能。计算了重离子熔合反应的熔合几率。结果表明,随着反应系统变得越来越重,重离子的熔合几率呈指数规律下降,准裂变变得越来越严重。这解释了实验上观测到的超重剩余核截面随体系的变重而急剧下降的现象。研究了重离子熔合截面的弹靶相关性。结果表明弹靶的质量非对称度越高越有利于熔合生成复合核,同时重离子熔合截面还强烈地依赖于弹靶结构。重离子的熔合过程是合成超重元素的关键因素之一,另一个影响超重核合成的因素是超重复合核的存活几率。基于统计模型,系统的研究了超重复合核存活几率的质量、能量、角动量等相关性。计算了基于冷熔合反应的蒸发剩余截面,得到的结果与实验基本符合,并预言了基于冷熔合反应生成114,116和115号元素的截面。在研究超重核蒸发剩余截面的弹靶相关性的基础上给出了合成超重核的最佳弹靶组合。计算表明,在挑选弹靶组合时使得合成的超重复合核是奇A核则会得到更高的奇数中子蒸发剩余核截面。计算给出了超重复合核的自旋布居及其对裂变位垒和鞍点态形变的依赖性。发现超重复合核的自旋布居强烈地依赖于复合核的裂变位垒,高的裂变位垒会给出宽的自旋布居;而超重复合核的自旋布居对鞍点态形变不是很敏感。另外研究了多核子转移反应合成超重元素的可能性。结果表明基于多核子转移反应合成大于108号的元素是很困难的。非对称核物质状态方程由于其对天体物理及理解奇异核结构的重要性,因此是人们长期以来一直感兴趣的研究内容,然而直到现在人们对核物质状态方程特别是高密核物质和非对称核物质状态状态方程仍了解甚少。基于Skyrme-Hartree-Fock理论以及同位旋相关的量子分子动力学(IQMD)模型研究了非对称核物质的化学不稳定性,结果表明非对称核物质可以发生化学不稳定性,且化学不稳定性发生的条件依赖于单粒子势能的密度相关形式。同时计算表明化学不稳定性是可以发生在真实的重离子碰撞过程中的,且在入射能量较高时化学不稳定性会消失。另外首次研究了高密核物质的化学不稳定性及其发生的条件。由于实验室很难达到很高密度的核物质,而中子星是由致密的极丰中子物质组成,因此提供了研究高密非对称核物质的自然实验室。基于Skyrme-Hartree-Fock理论研究了两种典型的非对称核物质状态方程(软对称势和硬对称势)对中子星中质子百分比的影响。另外研究了热中子星中质子百分比的温度相关性,发现热中子星中质子百分比随温度的升高而减小。基于IQMD模型研究了同位旋相分化现象的产生机制。通过与MSU的实验数据比较指出核物质应该有软的对称势。研究了重离子碰撞过程中的径向流现象,及其同位旋效应。计算了径向流产生的能量闭,并给出了实验上利用径向流产生的能量闭来提取非对称核物质状态方程的方法。
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本论文介绍了极端条件下核物质研究的现状以及目前常用的几种核多体方法,系统描述了冷、热非对称核物质的状态方程和刀稳定中子星物质中的15。态中子和质子超流性,特别是微观三体核力对此所产生的影响。通过引入微观三体核力,扩展了有限温度的BI.tleclcller-Hal'tree-Fock(FTBHF)理论。利用这一扩展的理沦,详细研究了同位旋非对称热核物质的状态方程、液气相变临界现象以及三体核力对此所产生的影响。在不同的中质比条件下,重点讨论了热核物质液气相变的临界温度和动力学不稳定区域的温度、同位旋相关性。由此表明,三体核力的引入在一定程度上降低了液气相变的临界温度值,在固定的温度和密度下,非对称核物质的压弧随同位旋非对称度的增加而单调的增力日,而且随着核物质温度的升高和非对称度的增加,动力学不稳定区域逐渐缩小。通过与其它理论模型(特别是Di1'ac-BHF方法)所预言的结果相比较,就目前扩展的包含三体核力修正的FTBHF理论与Dilac-BHF方法所计算的临界温度的差异问题,文中给出一种可能的解释。通过计算热核物质的单粒子结合能,给出了有限温度条件下对称能的计算方式,并且细致研究了不同温度、密度下的对称能以及三体核力在高密度区域对对称能的影响。结果表明,微观三体核力强烈影响着高密度区域的对称能,使其对温度的变化更加明显。此外,其它重要物理量(例如中子和质子的单粒子势能、有效质量等)的同位旋依赖性和温度、密度相关性在文中也被详细的讨论。利用质量算子的空穴线展井,表明了在基态关联所导致的对单核子势的重排修正项影响下的HLlgenholtz-VanHove(HVH)定理的恢复程度,并且进一步计算了中子和质子化学势。并且以包含兰体核力的FTBI-方法为基础,研究了热核物质中重排项的密度和温度依赖性并讨论了三体核力对重排项的影响。通过计算不同温度和密度下的核物质中单核子势和核子有效质量,特别是研究和讨论了基态关联效应和三体核力贡献对热核物质中单核子势的影响,表明了基态关联和三体核力对单核子势修正的重要性。利用BHF和BCS的理论方法,计算了β稳定中子星物质中处于150态的中子和质子的对关联能隙,着重研究和讨论了三体核力的影响。结果表明,三体核力对刀稳定物质中{s0态中子超流性的影响相对较小,但是对,S0态质子超流性具有重要影响,其效应随核子数密度的增大而迅速增强。三体核力的主要作用是强烈地抑制了高密度区刀稳定中子星物质中的150态质子超流性,而且三体核力对中子星物质中,So态超流相的抑制效应主要是通过质子或中子的有效对相互作用而起作用的。
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相对于非对称核物质状态方程,对称核物质的状态方程己基本确定。然而不同的微观·唯象多体方法对非对称核物质状态方程(尤其是对称能)的预言很不一致。利用动量相关的标量势与矢量势(对称势)及介质修正的核子一核子散射截面,在工Buuo4输运模型框架下我们对重粒子碰撞产生的丰中子核物质的状态方程进行了研究。我们发现在低密情况下对称能E32(p/po),核物质同位旋依赖部分的等压不可压缩系数为K-55OMeF时能够较好地再现NSCL/MSU实验数据。在高密情况下π~-/π~+谱的横动量与动能分布,π~-谱的动能分布,π-的多重数,中快度前平衡核子发射的中一质比,中快度前平衡核子发射的同位旋非对称度,发射核子的中一质微分流,中一质微分椭圆流以及质子椭圆流是对对称能敏感的几个探针。其中对对称能最理想的探针是π-/π+谱的横动量与动能分布、中快度前平衡核子发射的同位旋非对称度以及发射核子的中一质微分流。利用这些对对称能敏感的观测量,通过与实验数据的对照我们就可以得出关于对称能的高密行为的重要信息。
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Natural fluids with water-salt-gas are often found in every sphere of the Earth, whose physicochemical properties and geochemical behaviors are complicated. To study these properties and behaviors turns out to be one of the challenging issues in geosciences. Traditional approaches mainly depend on experiments and observations. However, it is impossible to obtain a large number of data covering a large T-P space of the Earth by experimental methods in the near future, which will hinder the advance of the theoretical study. Therefore, it is important to model natural fluids by advanced theoretical methods, by which limited experimental data can be extended to a large temperature-pressure-composition space. Physicochemical models developed in this dissertation are not only more accurate, but also extend the applied T-P-m region of the experimental data of the multi-fluid systems by about two times. These models provide the new and accurate theoretical tools for the geochemical research, especially for the water-rock interactions and the study of the fluid inclusions. The main achievements can be summarized as follows: (1) A solubility model on components of natural gases is presented. The solubility model on the systems of CH4-H2O-NaCl, C2H6-H2O-NaCl or N2-H2O-NaCl takes advantage of modern physicochemical theory and methods, and is an improvement over previous models whose prediction and precision are relatively poor. The model can predict not only the gas solubility in liquid phase but also water content in the gas phase. In addition, it can predict gases (methane or nitrogen) solubility in seawater and brine. Isochores can be determined, which are very important in the interpretation of fluid inclusions. (2) A density model on common aqueous salt solutions is developed. The density models with high precision for common aqueous salt solutions (H2O-NaCl, H2O-LiCl, H2O-KCl, H2O-MgCl2, H2O-CaCl2, H2O-SrCl2 or H2O-BaCl2) are absent in the past. Previous density models are limited to the relatively small range of experimental data, and cannot meet the requirement of the study of natural fluids. So a general density model of the above systems is presented by us based on the international standard density model of the water. The model exceeds the other models in both precision and prediction. (3) A viscosity model on common aqueous alkali-chloride solutions is proposed. Dynamic viscosity of water-salt systems, an important physics variable, is widely used in three-dimension simulation of the fluids. But in most cases, due to the lack of viscosity models with a wide T-P range, the viscosity of aqueous salt solutions is replaced by that of the water, giving rise to a relatively large uncertainty. A viscosity model with good prediction for the systems (H2O-NaCl, H2O-LiCl or H2O-KCl) is presented on the base of the international standard viscosity model of water and the density model developed before. (4) Equation of State applied in fluid inclusions. The best Equations of State in the world developed by others or us recently are applied in the study of the fluid inclusions. Phase equilibria and isochores of unitary system (e.g. H2O, CO2, CH4, O2, N2, C2H6 or H2S), binary H2O-NaCl system and ternary H2O-CH4-NaCl system are finished. From these programs and thermodynamic equations of coexisting ores, the physicochemical conditions before or after the deposits form can be determined. To some extent, it is a better tool.
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Geological fluids are important components in the earth system. To study thephysical chemistry properties and the evolution of fluid system turns out to be one of the most challenging issues in geosciences. Besides the conventional experimental approaches and theoretical or semi-theoretical modeling, molecular level computer simulation(MLCS) emerges as an alternative tool to quantificationally study the physico-chemical properties of fluid under extreme conditions in order to find out the characteristics and interaction of geological fluids in and around earth. Based on our previous study of the intermolecular potential for pure H2O and thestrict evaluation of the competitive potential models for pure CH4 and the ab initio fitting potential surface across H2O-CH4 molecules in this study, we carried out more than two thousand molecular dynamics simulations for the PVTx properties of pure CH4 and the H2O-CH4 mixtures. Comparison of 1941 simulations with experimental PVT data for pure CH4 shows an average deviation of 0.96% and a maximum deviation of 2.82%. The comparison of the results of 519 simulations of the mixtures with the experimental measurements reveals that the PVTx properties of the H2O-CH4 mixtures generally agree with the extensive experimental data with an average deviation of 0.83% and 4% in maximum, which is equivalent to the experimental uncertainty. Moreover, the maximum deviation between the experimental data and the simulation results decreases to about 2% as temperature and pressure increase,indicating that the high accuracy of the simulation is well retained in the high temperature and pressure region. After the validation of the simulation method and the intermolecular potential models, we systematically simulated the PVTx properties of this binary system from 673 K and 0.05 GPa to 2573 K and 10 GPa. In order to integrate all the simulation results and the experimental data for the calculation of thermodynamic properties, an equation of state (EOS) is developed for the H2O-CH4 system covering 673 to 2573 K and 0.01 to 10 GPa. Isochores for compositions < 4 mol% CH4 up to 773 K and 600 MPa are also determined in this thesis.
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By first principle methods based on density functional theory (DFT),the equation of state(EOS) and elastic constants of both periclase and ferropericlase are calculated. The pressure and iron doping effects on the elastic constants of ferropericlase are investigated systematically. Firstly, we calculate the elastic constants of periclase and compare the obtained results with experimental data and other theoretical calculations, which shows a encouraging consistence and demonstrates the practicability of first-principle methods. Secondly, by adding iron into periclase crystal model, we build up ferropericlase with iron contents ranging from 0% to 25% mole percent. The corresponding elastic constants are calculated in a large pressure range(0~120GPa). Emphatically, the strong correlation of 3d electrons in transitional elements, such as iron, is difficult to treat in first-principle methods for a long time. The current solution is to make additional correction. During the initial stage of this study, the strong correlation of 3d electrons in iron is not considered, and we observed that addition of iron decreases the volume of ferropericlase, which is totally contradictory to the experimental data. By applying LDA+U approximation in order to solve the strongly correlated 3d electron of iron, we observed the expansion of volume by iron as expected. On the basis of the LDA+U approximation, the elastic constants of ferropericlase are calculated. After a detailed analysis of data obtained from theoretical calculations, we have reached the following conclusions:(1)pressure imposes positive effects on all elastic constants, and the degree of effects is C11>C12>C44. (2) Iron has no distinctive effects on C11 and C12, although some fluctuations are observed around 60GPa. However, iron has obvious softening effects on C44 The softening effects on C44 are intensified as pressure increases. Above the 100GPa, the effects increase greatly, even surpasses the pressure's positive effects in ferropericlase crystal models with iron mole percent of having 12.5%, 18.75% and 25% iron content. (3)As to the modulus deprived from elastic constants, iron has no effect on the adiabatic bulk module BS, only a little fluctuation around 60GPa. We find iron's softening effects on shear modulus G. (4)We find out that, compared with low iron content, elastic constants with iron content approaching 25mole% is consistently fluctuated,which may be caused by the limitations of the LDA+U approximation method itself. (5)We investigate the pressure and Fe doping effects on elastic anisotropy factor(A=(2C44+C12-C11)/C11) of ferropericlase and find out that iron contents will lower the critical isotropic pressure. At the same pressure, when the pressure is below the isotropic pressure, iron softens the anisotropy factor ; when pressure surpasses the isotropic pressure, iron increases the anisotropy factor.
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Geological fluids exist in every geosphere of the Earth and play important roles in many processes of material transformations, energetic interchanges and geochemical interactions. To study the physicochemical properties and geochemical behaviors of geological fluids turn Girt to be one of the challenging issues in geosciences. Compared with conventional approaches of experiments and semi-theoretical modeling, computer simulation on molecular level shows its advantages on quantitative predictions of the physicochemical properties of geological fluids under extreme conditions and emerges as a promising approach to find the characteristics of geological fluids and their interactions in different geospheres of the Earth interior.This dissertation systematically discusses the physicochemical properties of typical geological fluids with state-of-the-art computer simulation techniques. The main results can be summarized as follows: (1) The experimental phase behaviors of the systems CH4-C2H6 and. CO2 have been successfully reproduced with Monte Carlo simulations. (2) Through comprehensive isothermal-isobaric molecular dynamics simulations, the PVT data of water hia^e been extended beyond experimental range to about 2000 K and 20 GPa and an improved equation of state for water has been established. (3) Based on extensive computer simulations, am optimized molecular potential for carbon dioxide have been proposed, this model is expected to predict different properties of carbon dioxide (volumetric properties, phase equilibria, heat of vaporization, structural and dynamical properties) with improved accuracies. (4) On the basis of the above researches of the end-members, a set of parameters for unlike interactions has been proposed by non-linear fitting to the ab initio potential surface of CO2-H2O and is superior to the common used mixing rule and the results of prior workers vs/Ith remarkable accuracies, then a number of simulations of the mixture have been carried out to generate data under high temperatures and pressures as an important complement to the limited experiments. (5) With molecular dynamics simulations, various structural, dynamical and thermodynamical properties of ionic solvations and associations have been oomprehensively analyzed, these results not only agree well with experimental data and first principle calculation results, but also reveal some new insights into the microscopic ionic solvation and association processes.
Resumo:
矿物PVT状态方程是研究矿物在一定温压条件下的晶胞体积与温度、压力之间的关系,依据这个基本关系,可以了解矿物在高温高压下的密度、弹性、热膨胀等性质。矿物PVT状态方程的研究可以了解矿物在地球深部存在的结构状态,为进一步的理论计算提供基础的数据,其结果也可以与天然和人工地震的地震波反演的结果对比,对地球深部的地质作用过程、物质结构状态和组成进行限制。然而,目前矿物PVT状态方程的研究主要集中在氧化物矿物和上地幔主要矿物(橄榄石和辉石)及其高压相(瓦兹利石、林伍德石、方镁铁矿、Majorite、Mg-Perovskite、Ca-Perovskite)的研究上,对石榴石、尖晶石等地幔常见副矿物和硫化物矿物的PVT状态方程的研究很少。 作者在参与搭建并完善金刚石压腔外加温系统的基础上,利用北京同步辐射X射线衍射实验技术结合金刚石压腔外加温技术对天然铁铝榴石、锰铝榴石、铬尖晶石进行了PVT状态方程的研究,同时对闪锌矿、辰砂、方铅矿、辉钼矿、辉锑矿等硫化物矿物进行了相变及状态方程的研究。结合前人研究成果,讨论了类质同象置换对镁铝-铁铝系列石榴石、锰铝-铁铝系列石榴石、尖晶石和硫化物矿物相变及状态方程的影响。获得了以下研究结果: 1)镁铝-铁铝系列石榴石和锰铝-铁铝系列石榴石的体弹模量都随着铁铝榴石组分的增加而增大。其主要原因是在二价阳离子位置上Fe2+取代了Mg2+、Mn2+。在镁铝-铁铝榴石系列中Mg2+的共价键半径(1.36Å)要大于Fe2+的共价键半径(1.17Å),而Mg2+-O键长(2.270Å)与铁铝榴石中的Fe2+-O(2.299Å)键长基本相当。在锰铝-铁铝榴石系列中, 尽管Mn2+的共价键半径(1.17Å)与铁铝榴石中的Fe2+共价键半径(1.17Å)相等,但是Mn2+-O键长(2.326Å)大于Fe2+-O键长(2.299Å)。较小的键长和共价键半径将会增强离子间的结合力,从而具有较强的抗压缩能力,因此随铁铝榴石组分的增加,镁铝-铁铝榴石系列和锰铝-铁铝榴石系列具有较大的体弹模量。 2)首次获得了铬尖晶石((Mg0.6766Fe0.2808Na0.0073Ti0.0014)0.9661(Cr1.4874Al0.5367)2.0241O4)的体弹模量的温度导数。结合前人关于其他组分尖晶石的实验结果发现,尖晶石中在四面体位置上发生Fe2+-Mg2+置换对体弹模量的影响要大于在八面体位置上发生Cr3+-Al3+置换对体弹模量的影响。而造成铬尖晶石的体弹模量值比其他组分尖晶石的体弹模量值大的主要原因也是四面体位置上的Fe2+-Mg2+的类质置换。 3)依据获得的尖晶石和石榴石的状态方程计算了不同地幔岩模型(橄榄岩和榴辉岩模型)的密度值在上地幔温压条件下的变化情况。结果表明,在尖晶石二辉橄榄岩模型中尖晶石含量的改变(2%-10%)会引起较大的密度变化(2.2%);在石榴石二辉橄榄岩(石榴石含量14%-20%)和榴辉岩(石榴石含量37%-45%)模型中石榴石含量的变化几乎未引起其密度值的变化,但石榴石是这两种地幔岩模型中的重要组成矿物。 4)首次获得了辰砂的Cinnabar相、方铅矿的B33相、辉钼矿、辉锑矿体弹模量的温度导数和热膨胀系数。讨论了闪锌矿、辰砂、方铅矿的相变情况。 5)总结了锌的、汞的、铅的硫族化合物发生结构相变的规律。认为造成锌的、汞的、铅的硫族化合物的相变压力随阴离子原子序数的增加(S→Se→Te)而逐渐减小的原因是:元素周期表中相对较大原子序数的原子具有更多的核内电子,引起价电子及导带电子的有效位能相对变弱,引起电离能降低,因此在相对较低的压力下就容易发生结构相变。 6)分析了ZnS中Fe2+替代Zn2+、Sb2S3-Bi2S3、MoS2-WS2以及同族相同结构不同组分的简单硫化物矿物的阴、阳离子对体弹模量值的影响。认为简单硫化物矿物的体弹模量值取决于阴、阳离子的离子半径、电负性以及键长。