随机多孔介质逾渗模型渗透率的临界标度性质

研究了一类非零键渗透率满足均匀分布的随机多孔介质逾渗模型-数值计算了该模型系统渗透率在临界点处的标度指数-结果表明该指数并不能看作是普适常数,而与均匀分布的参数有关-这意味着即使非零键渗透率值的概率密度函数满足负一阶矩存在条件,系统渗透率在逾渗临界点处的标度指数仍然依赖于分布函数的具体参数,并不是常数-这一数值结果与Sahimi对此问题的结论不同- 关键词： 逾渗 随机多孔介质 标度指数 渗透率     

摩擦颗粒体系各向同性压缩过程中的堵塞行为

利用分子动力学方法,模拟了5000个表面轻微摩擦(μ=1×10^-4)的弹性颗粒组成的体系在各向同性压缩过程中的堵塞(jamming)现象,研究了颗粒体系对边壁压强P和对关联函数第一个峰的高度g₁随体积分数φ的变化规律. 结果表明,当体系的体积分数φ大于临界体积分数φ_c时,P(φ)曲线表现出明显的黏滑(stick-slip)行为,法向的力-力关联函数、切向的力-力关联函数和颗粒的位置-位置关联函数同时发生跳变,说明宏观黏滑现象源自内部的力位形和几何构形的调整. 体系在φ缓慢增大过程中得到了不同的堵塞态,随着颗粒粒径的缓慢减小,体系得以松弛(unjamming),实现松弛过程并得到相应的φ_c. 对于不同堵塞态,其边壁压强P与φ-φ_c遵从幂律标度P∝(φ-φ_c)^0.964. 关键词： 堵塞相图 对关联函数 力-力关联函数 标度规律     

Breit夸克势的不同次正规化与ηc-J/ψ等的质量劈裂

用夸克势模型研究结构相同而自旋和轨道量子数不同的介子之间质量劈裂是检验势模型有效性的重要手段之一. 在以往的用各种夸克势模型计算质量劈裂工作中, 当轻介子和重介子一起计算时, π-ρ很容易劈裂, 而η_c-J/ψ等的劈裂都很 难达到实验值. 这里首先用正规化形状因子μ²/(q²+μ²), 对完整的动量空间中的Breit夸克势的第三项实施二次正规化, 除了第一项 库仑势和第七项常数项势, 对其余的项实施一次正规化, 然后用来计算 质量劈裂. 研究计算发现, 只有当屏蔽质量μ取为关于 折合质量μ_r=m_r m_j/(m_r+m_j) 的三阶多项式时, 轻介子π-ρ和重介子η_c-J/ψ, η_b-Υ(1s), 还有χ_c0-χ_c1-χ_c2 等的劈裂 精确达到实验值, 同时其他介子质量也都比以往得到较大的改善. 因此, 本文给出了一个有效的夸克势模型.     

传输线模型测量Au/Ti/p型金刚石薄膜的欧姆接触电阻率

采用传输线模型测量了重B掺杂p型金刚石薄膜(约10²⁰cm^-3)上Ti/A u欧姆接触电阻率ρ_c,测试了500℃退火前后及大电流情况下的I-V特性,研究 了退火对ρ_c的影响.结果表明,重掺杂和退火工艺是改善欧姆接触的有效手段. ρ_c随测试温度的变化表明金属/半导体接触界面载流子输运机制为隧道穿透.而 光照对ρ_c影响的分析表明金刚石可作为理想窗口材料.测试得到的最低ρ _c值约为10^-4Ωcm². 关键词： 金刚石薄膜 欧姆接触 接触电阻率     

吸附在活性炭、三氧化二铝和硅胶上分子的核弛豫研究

本文提出核与电子偶极相互作用和自旋扩散两种作用在被吸附到固体多电子表面上的分子弛豫起着重要作用,给出了自旋晶格弛豫时间(T_1e)和相关时间(τ_c)的关系:T_1e,-kτ_c/1+ω₀²τ_c²)^1/2,式中k对给定固体是常数。吸附在硅胶上甲苯的弛豫数据可用此式描述。得到了甲苯中甲基在不同温度下的τ_c。,它们在374K到240K间的相关时间在3.56×10^-9 s到5.76×10^-8 s范围。由此计算出其活化能为15.0kJ/mol。     

无规分形衬底上银膜逾渗系统的交流特性

通过对沉积在具有无规自相似结构的α-Al₂O₃断裂面上的银薄膜逾渗系统交流特性的测量,证明了在逾渗阈值p_c附近这一系统的交流电导率和介电常数满足指数临界规律和普适标度关系。还给出了这种逾渗系统的电容与直流电阻的关系,并对其意义作了讨论。 关键词：     

锐钛矿金红石的高温原位X射线衍射研究

对TiO₂粉末进行了空气和真空条件下从室温到1200℃的加热原位X射线衍射实验, 得到了空气和真空条件下微米级锐钛矿颗粒转变为金红石的起始温度分别为850℃ 和855℃; 分别修正了空气条件下锐钛矿在(27–850℃)范围和金红石在(900–1200℃) 范围内的晶胞参数和真空条件下锐钛矿在(27–850℃)范围和金红石在(950–1200℃) 范围的晶胞参数, 从而得到了晶胞参数随温度变化的关系, 得到了锐钛矿和金红石在空气中和真空中的热膨胀系数, 并总结了热膨胀系数随温度变化的规律. 室温下锐钛矿在空气条件下的热膨胀系数为 α_a=4.55063×10^-6/℃, α_c=7.7543×10^-6/℃, β=16.85836×10^-6/℃; 真空下为 α_a=4.69429×10^-6/℃, α_c=9.02850×10^-6/℃, β=18.69688×10^-6/℃. 室温下, 金红石在空气条件下的热膨胀系数为 α_a=6.81243×10^-6/℃, α_c=8.71644×10^-6/℃, β=22.22178×10^-6/℃; 真空条件下为 α_a=6.05834×10^-6/℃, α_c= 8.39280×10^-6/℃, β=20.52362×10^-6/℃. 关键词： 2')" href="#">TiO₂ 原位X射线衍射 相转变 热膨胀     

Co2+-Ti4+和Cu2+-Nb5+离子取代BaFe12O19单晶体中Fe3+离子的研究

本文对用Co²⁺-Ti⁴⁺和Cu²⁺-Nb⁵⁺离子取代BaFe₁₂O₁₉单晶体中Fe³⁺离子进行了研究,以Bi₂O₃作为助熔剂生长出了BaFe_12-2xCo_x²⁺Ti_x⁴⁺O₁₉(x=0;0.04;0.09;0.13;0.27和0.68)以及BaFe_12-x[Nb_1/3⁵⁺Cu_2/3²⁺]_xO₁₉(x=0;0.28;0.44和0.60)这两系列的单晶体,测定了100—300K温度范围内样品的磁化强度σ与单轴各向异性常数K₁,我们发现,对Co²⁺-Ti⁴⁺取代的样品,当x≤0.09时,其σ与K₁随x的增加而缓慢增加;当x>0.09时,其σ与K₁随x的增加而迅速降低,至x=1.1时,K₁变为零,对Nb⁵⁺-Cu²⁺取代的样品,其σ值在整个成份范围内基本保持不变,且有缓慢增加趋势;而K₁值则随x增加而单调下降,提出了取代离子在M型六角铁氧体中可能的分布模型来解释我们的结果。 关键词：     

2018年6期 电子期刊

研究了白光LED用K₂SiF₆：Mn⁴⁺红色荧光粉湿热环境下的发光性能劣化规律及机理。结果表明,环境中水汽的侵蚀可导致K₂SiF₆：Mn⁴⁺荧光粉发光性能劣化,且温度升高可加剧该劣化过程。85%湿度/70℃下处理6 h,K₂SiF₆：7%Mn⁴⁺荧光粉相对亮度降至初始值的25%。荧光粉中Mn⁴⁺含量越高,湿热条件下的性能劣化越显著。基于湿热处理前后荧光粉的XRD、表面形貌以及光学性能的对比分析,发现湿热环境下K₂SiF₆：Mn⁴⁺荧光粉的劣化主要是由于表面水汽侵蚀产物强吸收400~700 nm的可见光,降低荧光粉的激发效率以及再吸收荧光粉的发射光。水热后处理可使K₂SiF₆：Mn⁴⁺荧光粉颗粒尺寸增大,结晶性提高,从而显著改善其耐水性。85%湿度/70℃下处理6 h,水热后处理K₂SiF₆：7%Mn⁴⁺荧光粉的相对亮度仍可保持初始值的80%。     

K3[Cr(CN)6]中Cr3+电子跃迁几率(I)

本文首先计算了K₃[C_r(CN)₆]中C_r³⁺在外加直流磁场H绕晶体形态轴(a,b,c)情况下能级的分裂,然后计算相应的波函致,最后计算了电子极大受激相对跃迂几率。     

Modeling mobile ad hoc communication networks on two-dimensional square lattice

In this paper, we model the mobile ad hoc communication network on a two-dimensional square lattice. Both structure and function of it depend on transmission range and site-occupancy of nodes. Critical occupancies σ_c for different transmission ranges r to maintain global connection are found. Universal scaling function behaves as η~f(R^βσ), where R=(r−r₀)/r₀, and the scaling exponent β=−0.61, which distinguishes itself from percolation in previous lattice or network models. When the occupancy σ is near the threshold σ_c, individual nodes self-organize into a dynamic small world network relative to geometric distance. The network has a cut-off degree below which clustering coefficient keeps constant, which distinguish itself from other systems and has its potential application in technical designs.     

The Effective Mass of Nucleon in Asymmetric Nuclear Matter

The effective mass of nucleon in asymmetric nuclear matter is studied by the RHF approach.It is found that there exist critical densities ρ_c(δ). When ρ > ρ_c a phase transition from Fermi sphere to Fermi shell.pattern for ground state will occur.     

Gluonia and Charmonium Decays

We discuss the search for a 1^-- gluonium state, 0, in connection with a possible solution for the so-called ρπ, K^*K puzzle in the J/φ and φ' decays. Some issues are examined. In particular, we argue that the expected most favorable process φ → ππO can have an appreciable branching ratio (say 10^-3 ~ 10^-4) only if the O has a very narrow partial decay width to ρπ (say 1 ~ 10 MeV). For the 0^-+ system we deduce a relation that BR(η'_c → h) ≈ BR (η_c → h), where h denotes an exclusive light hadronic channel. This relation may be useful for the experimental search of the yet to be confirmed q: state, for which the branching ratios of φ' → η'_c → γKKπ, γηππ, γη'ππ are estimated to be about 1 × 10^-4 if the mass of η'_c is around 3600 MeV, and this relation may also serve as a criterion to determine whether there exist anomalous decays in the η_c and η'_c system, in particular in the VV decay channels, which might be related to the 0^-+ glueball-charmonium mixing. We emphasize that the bigluonium and the trigluonium may have very different effects on these decays.     

Multi-Type Directed Scale-Free Percolation

In this paper,we study a long-range percolation model on the lattice Z d with multi-type vertices and directed edges.Each vertex x ∈ Z d is independently assigned a non-negative weight Wx and a type ψx,where(Wx) x∈Z d are i.i.d.random variables,and(ψx) x∈Z d are also i.i.d.Conditionally on weights and types,and given λ,α 0,the edges are independent and the probability that there is a directed edge from x to y is given by pxy = 1 exp(λφψ x ψ y WxWy /| x-y | α),where φij 's are entries from a type matrix Φ.We show that,when the tail of the distribution of Wx is regularly varying with exponent τ-1,the tails of the out/in-degree distributions are both regularly varying with exponent γ = α(τ-1) /d.We formulate conditions under which there exist critical values λ WCC c ∈(0,∞) and λ SCC c ∈(0,∞) such that an infinite weak component and an infinite strong component emerge,respectively,when λ exceeds them.A phase transition is established for the shortest path lengths of directed and undirected edges in the infinite component at the point γ = 2,where the out/in-degrees switch from having finite to infinite variances.The random graph model studied here features some structures of multi-type vertices and directed edges which appear naturally in many real-world networks,such as the SNS networks and computer communication networks.     

Target-Searching on Percolation

We study target-searching processes on a percolation, on which a hunter tracks a target by smelling odors it emits. The odor intensity is supposed to be inversely proportional to the distance it propagates. The Monte Carlo simulation is performed on a 2-dimensional bond-percolation above the threshold. Having no idea of the location of the target, the hunter determines its moves only by random attempts in each direction. For lager percolation connectivity p 〉 0.90, it reveals a scaling law for the searching time versus the distance to the position of the target. The scaling exponent is dependent on the sensitivity of the hunter. For smaller p, the scaling law is broken and the probability of finding out the target significantly reduces. The hunter seems trapped in the cluster of the percolation and can hardly reach the goal.     

化学气相沉积中影蔽效应对硅薄膜表面形貌和微结构的影响

采用斜入射热丝化学气相沉积技术(OAD-HWCVD),研究了气流入射角度(θ)对氢化非晶硅(a-Si:H)薄膜表面和微结构的影响.实验发现,薄膜厚度为1μm时,均方根粗糙度与tanθ成指数关系;在入射角度为75°时,薄膜表面由自仿射表面转变为mound表面.采用拉曼谱和红外谱表征了硅薄膜的微结构随气流入射角度的变化.在薄膜转变为mound表面生长之前,随入射角度的增加,准局域的影蔽效应使得薄膜中微空洞的数目及尺寸增加,导致薄膜微结构因子升高、致密度下降、薄膜质量变差.在薄膜转变为mound表面生长之后,非局域的影蔽效应导致大尺度的空洞,同时薄膜中以Si-Hn(n 2)形式存在的氢增多.本文以非晶硅薄膜为例,结合标度理论,分析了薄膜生长过程中的表面形貌和微结构与影蔽效应的关系.     

Λc重子谱疑难(英文)

Λ_c+重子家族存在一个疑难,也就是重夸克有效理论预言的轨道角动量为L=2的多重态中JP=3/2+的态在实验上是缺失的,而且已发现的Λ_c（2765）+和Λ_c（2940）+的JP量子数仍然未知。在本工作中,我们使用双夸克图像计算了重子的质量,研究了Λ_c（2765）+和Λ_c（2940）+的可能归类以及仍缺失的具有L=2和JP=3/2+量子数的Λ_c+态,进而指出Λ_c（2880）+的峰结构中实际上已经包含了L=2、JP=3/2+这一缺失态,并建议Λ_c（2765）+和Λ_c（2940）+的量子数应分别为2S（1/2+）和2P（1/2-）。There is a puzzle in the Λ_c+ family, i.e., one member with JP=3/2+ is missing in a L=2 multiplet which the heavy quark effective theory predicts, and JP's of Λ_c(2765)+ and Λ_c(2940)+ are unknown. Using a light diquark picture to calculate baryon masses, we study possible assignments of two Λ_c's with unknown JP and the missing Λ_c+ with 3/2+ for L=2, and we find the most probable possibility that the peak corresponding to Λ_c(2880)+ actually includes a missing member with spin 3/2+ for L=2 and that quantum numbers of Λ_c(2765)+ and Λ_c(2940)+ are 2S(1/2+) and 2P (1/2-), respectively.     

Density profile and flow of miscible fluid with dissimilar constituent masses

A computer simulation model is used to study the density profile and flow of a miscible gaseous fluid mixture consisting of differing constituent masses (m_A=m_B/3) through an open matrix. The density profile is found to decay with the height ∝exp (−m_A(B)h), consistent with the barometric height law. The flux density shows a power-law increase ∝(p_c−p)^μ with μ2.3 at the porosity 1−p above the pore percolation threshold 1−p_c.     

Stress-induced ultrasonic wave velocity anisotropy in fractured rock

The closure of cracks in rock under an applied compressive stress can significantly affect the permeability of the rock. Crack closure may be monitored using ultrasonic wave velocities, since these are significantly reduced in the presence of open cracks. When a non-hydrostatic compressive stress is applied to a rock, an initially isotropic distribution of cracks will become anisotropic and the rock will display an elastic anisotropy determined by the orientation distribution of those cracks remaining open. The crack orientation distribution function gives the probability of a crack having a given orientation with respect to a set of axes fixed in the rock. The coefficients W_Imn of a series expansion of this function in generalized Legendre functions can be obtained to order I = 4 from the angular variation of the elastic wave velocity. This allows construction of microfracture pole figures, which specify the orientation distribution of open cracks. The theory is applied to the measurements of Nur and Simmons, who applied a uniaxial compressive stress to a sample of Barre granite. Cracks with normals aligned along the stress direction are closed preferentially in agreement with the theory of Walsh. However, for crack normals perpendicular to the applied stress there is some evidence of crack opening that is not predicted by the theory. This is also observed in the electron microscope study of Batzle et al. and a possible mechanism is discussed.