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关键词： quanta   Phase transtormations   Compressibility   particle-hole   Glass transition   Monte Carlo technique   Exponent   Bosons   gapless  

摘要： Systems of disordered interacting bosons with particle-hole symmetry can undergo a quantum phase transition between the superfluid phase and the Mott glass phase which is a gapless incompressible insulator. We employ large-scale Monte Carlo simulations of a two-dimensional site-diluted quantum rotor model to investigate the properties of the superfluid density and the compressibility at this transition. We find that both quantities feature power-law critical behavior with exponents governed by generalized Josephson relations.

关键词： internally circulating fluidized bed   solid circulation rate   Eulerian-Eulerian model   kinetic theory of granular flow  

摘要： In this paper, the hydrodynamic flow inside an internally circulating fluidized bed (ICFBG) was characterized using experimental and three-dimensional computational fluid dynamics (CFD) models. Eulerian-Eulerian model (EEM) incorporating the kinetic theory of granular flow was implemented in order to simulate the gas-solid flow. A full-scale plexiglass cold flow experimental model was built to verify simulation results prior to the fabrication of the gasifier. Six parameters were manipulated to achieve the optimum design geometry: fluidization flow rate of the draft tube (Q(dt)), aeration flow rate of the annulus (Q(an)), initial bed static height (H-bs), draft tube height (H-dt), draft tube diameter (D-dt), and orifice diameter (D-or). The investigated parameters showed strong effect on the particle flow characteristics in terms of the pressure difference (Delta p) and solid circulation rate (G(s)). The predicted results by simulation for the optimum case were in close agreement with experimental measurements with about 5% deviation. The results show that the ICFBG operated stably with the maximum G(s) value of 86.6 kg/h at Q(dt) of 350 LPM, Q(an) of 150 LPM, H-bs of 280 mm, H-dt of 320 mm, Ddt of 100 mm, and D-or of 20 mm.

关键词： Ba(Fe1-xCox)(2)As-2 superconductor   s-wave energy gap   d-wave energy gap   Two-gap model   Penetration depth   Optical conductivity  

摘要： The temperature and frequency dependence of complex dynamical conductivity sigma = sigma(1) + i sigma(2), penetration depth, and superfluid density of Ba(Fe1-xCox)(2)As-2 are calculated in the framework of one- and two-gap models at terahertz frequencies for a temperature range of 2 K < T < T-C (T-C = 22 K). In the single-gap model, an isotropic s-wave gap without any node and a d-wave gap with possible nodes are considered. In the two-gap model, one of the gaps was considered isotropic s-wave gap with amplitude Delta(A)=3 meV, while the other gap was supposed to be an anisotropic d-wave gap with possible nodes, and its rms amplitude was Delta(0) = 8 meV. The interaction between the gaps is waived, since it is small, and its description is problematic. Comparing the result with the experimental data proves that the two-gap model consistently describes the optical characteristics of Ba(Fe1-xCox)(2)As-2. In the two-gap model, the temperature dependence of sigma(1) demonstrated a coherence peak at frequencies below 15 cm(-1). The temperature dependence of the penetration depth calculated from sigma(2) shows power-law behavior at low temperatures, and the superfluid density varies steeply near T-C.

关键词： Friction factor   Explicit solutions   Moody diagram   Maximum deviation   Turbulent flow  

摘要： The Colebrook-white equation is widely used in many fields, like civil engineering for calculation of water distribution systems and in all fields of engineering where fluid flow can be occurred. Numerous formulas have been proposed since 1947 in order to simplify the computation of the friction factor, to avoid the iterative procedures methods and to alter the Colebrook-white equation in practice. most of the existing explicit formulas for computation of the friction factor for turbulent flow in rough pipes proposed are cited, where thirty three "33" equations have been inventoried. The goal of this paper is to assess the accuracy of each model and to propose an arrangement from the best to the lower accuracy according to a proposed method combined of three criteria which are: simplicity of the formula, maximum deviations and the coverage of the entire range of Moody diagram. (C) 2019 The Authors. Published by Elsevier B.V. on behalf of Faculty of Engineering, Ain Shams University.

关键词： Vibration gas-solid fluidized bed   Pressure signals   Energy transfer   Dynamics behavior  

摘要： The study explores the characteristics of non-linear fluidization of vibration gas-solid fluidized bed (VGFB) and the laws of wave energy transfer. A VGFB (phi 110 mm x 180 mm) with the -0.3 + 0.074 mm magnetite particle was adopted in the experiment. The Hilbert-Huang transform (HHT) analysis of the pressure signal was used to obtain the time-frequency-energy two-dimensional Hilbert-Huang spectrum of pressure fluctuation signals under different fluidized states, and this revealed that the pressure fluctuation signal was composed of complex inter- and intra-wave frequency modulation components, this verified the non-linearity and randomness of the pressure signal. The distribution of the empirical mode decompositions (IMFs) energy of pressure fluctuation signal under different operation conditions was analyzed, and the results indicated that the IMF4 energy increased with increases in the bubble size. Conversely, with decreases in the bubble size, the energy was gradually transferred from IMF4 to IMF3, this revealed that the energy distribution of IMF3 and IMF4 exhibited a good correspondence with the bubble phase behavior and was a quantitative reflection of the non-linear bed fluidization. Finally, the main frequency and energy of the pressure signal were used to describe the dynamic behavior of the VGFB under different fluidized states. The results indicated that the pressure fluctuation frequency of quasi-dispersive fluidization and bubbling fluidization were both lower than that of the frequency of turbulent fluidization. Additionally, the pressure signal energy of quasi-dispersive fluidization was the lowest, bubbling fluidization was intermediary, and turbulent fluidization was the highest. (C) 2018 Elsevier B.V. All rights reserved.

关键词： 载金黄铁矿   稀土与微量元素   成矿流体来源   蚀变岩型和石英脉型矿石   罗山金矿床   胶东  

摘要： 罗山金矿床是胶东玲珑金矿田最大的金矿床之一,同时发育蚀变岩型矿化和石英脉型矿化。本研究在系统的野外和镜下工作基础上,利用电感耦合等离子体质谱(ICP-MS)技术分析了载金黄铁矿的微量和稀土元素,对比了蚀变岩型和石英脉型矿石载金黄铁矿稀土和微量元素特征,探讨了成矿流体的性质与来源。黄铁矿稀土总含量较低,多呈较明显的"右倾"式稀土配分模式,总体表现出负Eu异常,基本无Ce异常; Hf/Sm、Th/La、Nb/La值均<1,推断成矿流体为富Cl的还原性流体。Co/Ni比值范围在0. 08～3. 77,平均值为1. 09; Co/Ni值以及Co、Ni、Bi、Cu和Zn含量均与变质热液型金矿平均含量相近; Y/Ho比值范围总体在21～32之间,与中国东部大陆地壳Y/Ho比值(20～35)基本重合;结合个别样品的弱正Eu异常以及前人的研究成果,推断成矿流体与变质热液类似,主要来源于古太平洋板块俯冲板片脱水和脱碳作用,且可能有长英质岩浆流体和地壳流体的混入。蚀变岩型和石英脉型矿石内的载金黄铁矿的稀土、微量元素组成没有明显区别,Y/Ho、Nb/Ta和Zr/Hf比值变化范围均很小,表明两类矿石的载金黄铁矿为同一期热液活动作用的产物。

关键词： Fluidized dense phase   Pulsatile   Wavelet   Pulse structures  

摘要： The objective of this paper is to report the experimental findings related to the pressure fluctuations in the fluidized dense phase pneumatic conveying of fine powders in the pipeline. Investigation has also been carried out to understand the relation between pressure pulse characteristics and specific power consumption and pneumatic conveying parameters. In addition, the transition in mode of flow along the downstream of flow of fine powders has been assessed and discussed. The wavelet analysis (Daubechies db4 wavelet) of signals of air pulses revealed that the moving bed flow possesses the transient feature and pulsatile phenomenon characterized by multiple amplitudes and random frequencies. Variations of pulse structures along the length of pipeline have been observed due to occurring of frequent aeration and de-aeration of dunes during the conveying. Substantial variations in pulse structures have also been found with different types of bulk materials. Pulse velocities of air between two data points are found higher at high solid loading ratios leading to low voidage in case of dense phase flow. (C) 2018 Elsevier B.V. All rights reserved.

关键词： 表面张力   自制教具   实验   创新  

摘要： 生活中的液体表面张力现象虽然丰富,但表面张力本身及其产生原因却比较抽象,并不像弹力和摩擦力那样容易被学生感受和认知,对学生的学习产生一定的困难。笔者对教材中的实验进行了改进,做到化静态为动态,变抽象为具体,教学中同时进行了实验创新和思维创新,旨在提升学生物理学科核心素养。

关键词： 风浪   波流分离   流函数  

摘要： 风作用于水面产生风浪,其中由于波流紊动产生的动量和能量的交换机制是一个很复杂的过程。风应力一般用来描述这种能量交换,可以分为3个部分:水面的剪切力、波生应力以及紊动应力。采用一种有效的非线性波流分离方法——NSFM(Nonlinear Stream Function Method)对波流运动的动量和能量输移进行定性描述。构造能够有效表达非线性波浪的解析流函数,摄动求解使其满足拉普拉斯方程、动力边界条件和运动边界条件,结合实验室风浪数据,分离出波生速度场。通过交叉谱分析,得到波生雷诺应力在不同风速下对风应力的贡献。结果表明:NSFM对不同工况条件下的风浪的处理具有较高的精度,模型适应性良好;且风速越大,波生应力沿着水深衰减得越快,且自由面波生应力在动量输移中的比重会逐渐减弱。

关键词： 弹性绳   流固耦合   速度修正   动量方程   动态模拟  

摘要： 研究柔性结构与流体间耦合作用,可以促进软体机器人的发展.通过速度快、精度高的数值模拟方法模拟水下机器人的实时运动轨迹,可以为真实实验提供测试方向与理论牵引,增大实验成功的可能性.本文研究有自主运动趋势的弹性绳在二维流场中的运动轨迹.首先,对弹性绳离散化建模并同时考虑拉压与扭转弹性力,从能量角度建立动力学方程,此模型可以较为真实地反映弹性绳内力对其运动产生的作用.然后基于半拉格朗日法建立流体求解器.最后,提出简化的基于动量方程的浸入边界法作为耦合算法,通过直接修正网格速度代替浸入边界力法中力源项的作用.使用这种算法求解耦合作用兼具简便性与快速性.对弹性绳模型、流体模型与简化耦合模型依次解算,模拟了正弦形式波动弹性绳在水中的运动轨迹.结果显示,弹性绳在弹性内力与流固相互作用力共同影响下,该种新的浸入边界法可以实现对水下弹性绳运动轨迹的模拟.数值实验显示弹性绳的自主运动参考模型的初相位改变时,其前进方向会发生改变.该仿真模拟算法与平台可以为细长形软体水生机器人的研发提供参考.