Relativistic Continuum Random Phase Approximation and Applications I. Formalism

A fully consistent relativistic continuum random phase approximation (RCRPA) is constructed in terms of the Green's function technique. In this method the contribution of the continuum spectrum to nuclear excitations is treated exactly by the single particle Green's function, which includes also the negative states in the Dirac sea in the nose aapproximation. The theoretical formalism of RCRPA and numerical details are presented. The single particle Green's function is calculated numerically by a proper product of regular and irregular solutions of the Dirac equation. The numerical details and the formalism of RCRPA in the momentum representation are presented.

重核性质的相对论平均场理论研究

本论文主要包括两部分内容，一部分是运用相对论平均场理论对超重核基态性质的研究以及Pb同位素位移微观机制的研究，第二部分是在相对论平均场框架下对BCS型对关联的改进及其在有限核性质研究中的应用。基于核子与介子自由度的量子强子动力学(QHD)， 从有效拉氏密度出发, 采取平均场近似, 已经成为当前最为成功的原子核理论之一，相对论平均理论。本文比较详细地介绍该理论模型, 并系统地探讨了新核素287115及其 衰变链上核的基态性质。结果发现所计算的结合能和四极形变符合了有限力程小液滴模型的结果，计算表明研究的 衰变链具有中等大小的长椭球形变；且计算的 衰变能 成功地与实验符合，说明相对平均场理论在原子核的超重区是有成功的。在此基础上进一步研究了新核素的单粒子能级，从而发现了超重核的一些新特点。通过分析Z=108到Z=114这四条同位素链的平均结合能，说明在这些同位素链中，对中子分离能的分析则可以看到N=162与N=184是壳效应的存在。研究了Pb同位素链的基态性质，从原子核的微观结构出发，比较详细地研究了Pb链同位素位移出现反常扭折这一重要性质的物理机制，由于满壳外额外中子会排布在距离满壳稍远一些的下一能级上，这自然会导致中子半径的增加．由于中子在核内的分布对质子分布的影响，将必然使原子核的电荷半径会在中子满壳后增加得更快。相对论平均场理论能够自然地给出原子核的自旋和轨道耦合，从而能给出合理的单粒子能级序列和间距，这为定量描述原子核的同位素位移提供了有力的理论基础。在论文的第二部分，通过引进密度相关的Delta力来改进传统的处理对关联的BCS方法，假定核子之间的作用为Delta力，计算得到状态相关的对能隙。相对于传统的常数对能隙是一个很重要的改进。接着我们用改进的理论研究了Sr同位素链的基态性质，得到了一些很有意义的结果。

黄土旱塬麦田生态系统物质平衡及评价

根据长武试区 1986～ 1995年的统计资料并结合田间试验 ,对黄土旱塬麦田生态系统的主要物质 (氮、磷、钾 )循环及平衡特征进行了较为系统的分析。结果表明 ,农田中养分的流动量大 ,流通途径少 ,养分循环的开放性大 ,外循环规模大 ,内循环率小 ;系统养分平衡中 N基本保持收支平衡 ,K2 O入不敷出 ,P2 O5 输入大于输出 ;养分输入中 ,人工投入的化肥与有机肥是养分的主要来源 ,输出中 N主要集中于籽粒 ,K2 O主要集中于秸秆 ,P2 O5 主要残留于土壤中。指出在农业生产中 ,应采用秸秆还田以增加钾的投入 ,同时要增加氮肥投入尤其是有机肥的投入 ,而磷应以提高其有效性为主。

黄土旱塬麦田生态系统能流特征及评价

根据长武试区 1 986年～ 1 995年连续 1 0年的统计资料并结合田间试验 ,对黄土旱塬典型农田生态系统——冬小麦农田系统能量的投入产出、流向、流量与转化效率进行了较为系统的研究。结果表明 ,能量平衡中人工辅助能的投入逐渐增加 ,化肥能投入比例逐渐超过有机肥能 ;该区农业已发展到无机—有机复合阶段 ,农业生产中机械化程度有所提高。通过统计分析 ,得出提高无机能的投入比例可提高能量的产投比 ,增加化肥能投入水平则可提高能量的总产出 ,指出应在机械化条件下实行秸秆还田和多途径增加有机肥投入 ,调整能量投入结构 ,提高能量转化效率 ,提高光能利用率

Self-Assembly of Rod-Terminally Tethered Three-Armed Star-Shaped Coil Block Copolymer: Investigation of the Presence of the Branching in the Coil to the Self-Assembled Behavior

Self-assembled behavior of rod-terminally tethered three-armed star-shaped coil block copolymer melts was studied by applying self-consistent-field lattice techniques in three-dimensional (3D) space. Similar to rod-coil diblock copolymers, five morphologies were observed, i.e., lamellar, perforated lamellar, gyroidlike, cylindrical and sphericallike structures, while the distribution of the morphologies in the phase diagram was dramatically changed with respect to that Of rod-coil diblock copolymers.

Lattice Boltzmann study of hydrodynamic effects in lamellar ordering process of two-dimensional quenched block copolymers

By incorporating self-consistent field theory with lattice Boltzmann method, a model for polymer melts is proposed. Compared with models based on Ginzburg-Landau free energy, our model does not employ phenomenological free energies to describe systems and can consider the chain topological details of polymers. We use this model to study the effects of hydrodynamic interactions on the dynamics of microphase separation for block copolymers. In the early stage of phase separation, an exponential growth predicted by Cahn-Hilliard treatment is found. Simulation results also show that the effect of hydrodynamic interactions can be neglected in the early stage.

The phase behavior of comblike block copolymer A(m+1)B(m)/homopolymer A mixtures

The phase behaviors of comblike block copolymer A(m+1)B(m)/homopolymer A mixtures are studied by using the random phase approximation method and real-space self-consistent field theory. From the spinodals of macrophase separation and microphase separation, we can find that the number of graft and the length of the homopolymer A have great effects on the phase behavior of the blend. For a given composition of comblike block copolymer, increasing the number of graft does not change the macrophase separation spinodal curve but decreases the microphase separation region. The addition of a small quantity of long-chain homopolymer A increases the microphase separation of comblike block copolymer/homopolymer A mixture.

Defect evolution and hydrodynamic effects in lamellar ordering process of two-dimensional quenched block copolymers

The effects of hydrodynamic interactions on the lamellar ordering process for two-dimensional quenched block copolymers in the presence of extended defects and the topological defect evolutions in lamellar ordering process are numerically investigated by means of a model based on lattice Boltzmann method and self-consistent field theory. By observing the evolution of the average size of domains, it is found that the domain growth is faster with stronger hydrodynamic effects. The morphological patterns formed also appear different. To study the defect evolution, a defect density is defined and is used to explore the defect evolutions in lamellar ordering process. Our simulation results show that the hydrodynamics effects can reduce the density of defects. With our model, the relations between the Flory-Huggins interaction parameter chi, the length of the polymer chains N, and the defect evolutions are studied.

STUDY OF COARSENING OF MICRODOMAINS IN BLOCK COPOLYMERS BY LATTICE BOLTZMANN METHODS

In order to understand the coarsening of microdomains in symmetric diblock copolymers at the late stage, a model for block copolymers is proposed. By incorporating the self consistent field theory with the free energy approach Lattice Boltzmann model, hydrodynamic interactions can be considered. Compared with models based on Ginzburg-Landau free energy, this model does not employ phenomenological free energies to describe systems. The model is verified by comparing the simulation results obtained using this method with those of a dynamical version of the self consistent mean field theory. After that,the growth exponents of the characteristic domain size for symmetric block copolymers at late stage are studied. It is found that the viscosity of the system affects the growth exponents greatly, although the growth exponents are all less than 1/3 Furthermore, the relations between the growth exponent, the interaction parameter and the chain length are studied.

Nucleation in A/B/AB blends: Interplay between microphase assembly and macrophase separation

We study the interplay between microphase assembly and macrophase separation in A/B/AB ternary polymer blends by examining the free energy of localized fluctuation structures (micelles or droplets), with emphasis on the thermodynamic relationship between swollen micelles (microemulsion) and the macrophase-separated state, using self-consistent field theory and an extended capillary model. Upon introducing homopolymer B into a micelle-forming binary polymer blend A/AB, micelles can be swollen by B. A small amount of component B (below the A-rich binodal of macrophase coexistence) will not affect the stability of the swollen micelles. A large excess of homopolymer, B, will induce a microemulsion failure and lead to a macrophase separation.

Bump-Surface Multicompartment Micelles from a Linear ABC Triblock Copolymer: A Combination Study by Experiment and Computer Simulation

Novel bump-surface multicompartment micelles formed by a linear amphiphilic ABC triblock copolymer via self-assembly in selective solvent were successfully observed both in simulation and experiment. The results revealed that the block A forms the most inner core, and the blocks B and C form the inner and outer layers, respectively, and the bumps were formed by block A and more likely to be born on curving surfaces. Moreover, the micelle shape could be controlled by changing the solvent selectivity of the blocks A and B. Spherical, cylindrical, and discoidal micelles with bumpy surfaces were obtained both in experiment and simulation.

Effect of Solvent Molecular Size on the Self-Assembly of Amphiphilic Diblock Copolymer in Selective Solvent

Real-space self-consistent field theory (SCFT) is employed to study the effect of solvent molecular size on the self-assembly of amphiphilic diblock copolymer in selective solvent. The phase diagrams in wide ranges of interaction parameters and solvent molecular size were obtained in present study. The results indicate that the solvent molecular size is a key factor that determines the self-assembly of amphiphilic diblock copolymer. The self-assembled morphology changes from circle-like micelle to line-like micelle, then to loop-like micelle by decreasing the solvent molecular size in a wide range of solvent selectivity. We analyze and discuss this change in terms of the solvent solubility and the entropy contribution.

Comparing the morphology and phase diagram of H-shaped ABC block copolymers and linear ABC block copolymers

By using a combinatorial screening method based on the self-consistent field theory (SCFT) for polymers, we have investigated the morphology of H-shaped ABC block copolymers (A(2)BC(2)) and compared them with those of the linear ABC block copolymers. By changing the ratios of the volume fractions of two A arms and two C arms, one can obtain block copolymers with different architectures ranging from linear block copolymer to H-shaped block copolymer. By systematically varying the volume fractions of block A, B, and C, the triangle phase diagrams of the H-shaped ABC block copolymer with equal interactions among the three species are constructed. In this study, we find four different morphologies ( lamellar phase ( LAM), hexagonal lattice phase ( HEX), core-shell hexagonal lattice phase (CSH), and two interpenetrating tetragonal lattice (TET2)). Furthermore, the order-order transitions driven by architectural change are discussed.

Inverted to normal phase transition in solution-cast polystyrene-poly(methyl methacrylate) block copolymer thin films

We have investigated the inverted phase formation and the transition from inverted to normal phase for a cylinder-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer in solution-cast films with thickness about 300 nm during the process of the solution concentrating by slow solvent evaporation. The cast solvent is 1, 1,2,2-tetrachloroethane (Tetra-CE), a good solvent for both blocks but having preferential affinity for the minority PMMA block. During such solution concentrating process, the phase behavior was examined by freeze-drying the samples at different evaporation time, corresponding to at different block copolymer concentrations, phi. As phi increases from similar to 0.1 % (nu/nu), the phase structure evolved from the disordered sphere phase (DS), consisting of random arranged spheres with the majority PS block as I core and the minority PMMA block as a corona, to ordered inverted phases including inverted spheres (IS), inverted cylinders (IC), and inverted hexagonally perforated lamellae (IHPL) with the minority PMMA block comprising the continuum phase, and then to the lamellar (LAM) phase with alternate layers of the two blocks, and finally to the normal cylinder (NC) phase with the majority PS block comprising the continuum phase. The solvent nature and the copolymer solution concentration are shown to be mainly responsible for the inverted phase formation and the phase transition process.

Predicting the position of the spin-forbidden band for Tb3+ ions in crystal hosts

The energy difference DeltaE between the spin-allowed and spin-forbidden states of Tb3+ in crystals is studied. The environmental factor he representing the character of the host is redefined by using the chemical band of complex crystals. The relationship between h(e) and DeltaE is found to be a linear relation. The results show that the energy difference between the spin-forbidden and spin-allowed states for Tb3+ ions in crystals can be predicted from the environmental factor.