Dispersion polymerization of anionic polyacrylamide in an aqueous salt medium

Anionic polyacrylamide dispersions were prepared by dispersion polymerization in an aqueous salt medium, using acrylamide（AM） and acrylic acid（AA） as monomers and anionic polyelectrolytes as stabilizer. Effects of salt concentration, and molecular weight and concentration of stabilizers on the stability of the dispersions were investigated using a HAAKE rheometer and optical microscopy. The results showed that stable anionic polyacrylamide dispersions, consisting of smooth, spherical, polydisperse particles, could be obtained under the conditions of salt concentration ranging from 26 wt% to 30 wt%, concentration of stabilizers from 1.2 wt% to 1.8 wt%, and intrinsic viscosity of stabilizers from 2.98 dL·g^-1 to 3.74 dL·g^-1. The apparent viscosity of the stable dispersions changed very little with the shear rate, showing Newton fluid behavior.

Zinc Oxide Nanoparticles in Bacterial Growth Medium: Optimized Dispersion and Growth Inhibition of <i>Pseudomonas putida</i>

The majority of nanoparticles tend to agglomerate in bacterial growth media. Thus, nanoparticle-specific characteristics can get lost. To investigate the influence of nanoparticles on bacteria, these particles should remain in their nanoparticulate state. The present study demonstrates the stabilization of commercially available zinc oxide (ZnO) with sodiumhexametaphosphate (SHMP) in bacterial growth medium (LB) to avoid agglomeration of these particles after the addition to LB. This established method is appropriate to stabilize ZnO agglomerates as small as 43 nm. The method of fractionated centrifugation was used to obtain stable agglomerates (also stable in the presence of bacteria) with different mean diameters. The SHMP-stabilized ZnO inhibits the growth of Pseudomonas putida with increasing concentration (up to 500 mg/L) and decreasing agglomerate size (43 - 450 nm).

Efect of double dispersion on non-Darcy mixed convective flow over vertical surface embedded in porous medium

A numerical study of a non-Darcy mixed convective heat and mass transfer flow over a vertical surface embedded in a dispersion, melting, and thermal radiation is porous medium under the effects of double investigated. The set of governing boundary layer equations and the boundary conditions is transformed into a set of coupled nonlinear ordinary differential equations with the relevant boundary conditions. The transformed equations are solved numerically by using the Chebyshev pseudospectral method. Comparisons of the present results with the existing results in the literature are made, and good agreement is found. Numerical results for the velocity, temperature, concentration profiles, and local Nusselt and Sherwood numbers are discussed for various values of physical parameters.

Electrophoretic Coating of Hydroxyapatite on Pyrolytic Carbon Using Glycol as Dispersion Medium

Hydroxyapatite （HA） coatings on pyrolytic carbon were produced via electrophoretic deposition （EPD） using glycol and ethanol as dispersion medium respectively. The effect of the solubility of HA in the dispersion medium on crack occurrence and adherence of the coating was investigated by means of scanning electronic microscope （SEM） and atomic absorption spectrometer （AAS）. The results show that the solubility of HA in glycol is higher than that in ethanol. The usage of glycol as a dispersion medium can reduce the possibility of crack formation and enhance the adhesive strength between the coating and the carbon substrate. The green coatings can be sintered under vacuum at 1 000 ℃ whether the coatings are obtained using ethanol or glycol as dispersion medium. No HA decomposition was observed up to 1 000 ℃ by vacuum sintering by X-ray diffraction （XRD） analysis.

Propagation of a Rectangular Pulse in an Anomalous Dispersive Medium

The pulse with a rectangular envelop propagating through the caesium vapour with two gain lines used inthe Wang, Kuzmich, and Dogariu [Nature (London) 406 (2000) 277] experiment is studied. It is shown that there existsan obvious distortion for the pulse.

An optical rotation sensor based on dispersive slow-light medium

Slow light supported by electromagnetically induced transparency effect in dispersive medium is extremely susceptible with respect to Doppler detuning. In this paper, the Doppler effect induced by rotating dispersive medium was considered and the effect of the velocity of rotating dispersive medium on the group velocity was studied. Based on a dispersive slow-light medium, a high sensitive optical rotation sensor for measuring absolute rotation is proposed and analysed. The sensitivity of the rotation sensor is the group delay between the counterpropagationed wave packets in the device, and scales directly with square of the group index which can reach 102-10s orders of magnitude by selecting a proper dispersive medium.

海水基纳米流体分散稳定性和黏度特性研究

以海水为基础液的纳米流体,可作液压介质应用于海洋液压设备,解决传统液压油因海水侵入引起的油液变质问题。以天然海水为基础液,通过两步法制备海水基SiC纳米流体,采用单一变量法探究不同组分配比纳米流体的分散稳定性和黏度特性。结果表明,NaCl会破坏颗粒双电层,降低纳米流体稳定系数,但表面活性剂CMC可吸附在SiC颗粒表面提供空间位阻,使稳定系数在10 d内维持在0.9左右。同时,验证了SiC粒径在40 nm,质量分数在1%左右,CMC质量分数在2%左右,纳米流体分散稳定性最佳。海水基纳米流体的黏度随颗粒添加量的增加而增大,在质量分数>1%时,上升趋势减缓;随着CMC添加量的增多,影响了纳米流体中的微结构,使海水基纳米流体的黏度随CMC质量分数增加而上升,上升趋势为平缓-急剧-平缓;受布朗运动的影响,黏度与温度呈负相关;纳米流体黏度随NaCl质量分数的增加而下降,下降趋势先快后慢。制备的海水基纳米流体具有较好的分散稳定性,可通过调控组分配比得到所需黏度,有助于纳米流体技术的进一步发展。

LINEAR THEORY OF GRAVITY WAVES ON A VOIGT VISCOELASTIC MEDIUM

Linear surface gravity waves on a semi-infinite incompressible Voigt medium are studied in this paper.Three dimensionless parameters,the dimensionless viscoelastic parameter (?),the dimensionless wave number and the dimensionless sur- face tension are introduced.A dimensionless characteristic equation describing the waves is derived.This is a sixth order complex algebraic equation which is solved to give the complex dispersion relation.Based on the numerical solution, two critical values of (?),(?)_A=0.607 and (?)_R=2.380,which represent the appearance of the cutoff region and the disappearance of the strong dispersion region,are found.The effects of (?) on the characteristic equation and the properties of the waves are discussed.

Nonlinear convection in a non-Darcy porous medium

In this paper, the natural convection in a non-Darcy porous medium is studied using a temperature-concentration-dependent density relation. The effect of the two parameters responsible for the nonlinear convection is analyzed for different values of the inertial parameter, dispersion parameters, Rayleigh number, Lewis number, Soret number, and Dufour number. In the aiding buoyancy, the tangential velocity increases steeply with an increase in the nonlinear temperature parameter and the nonlinear concentration parameter when the inertial effect is zero. However, when the inertial effect is non-zero, the effect of the nonlinear temperature parameter and the nonlinear concentration parameter on the tangential velocity is marginal. The concentration distribution varies appreciably and spreads in different ranges for different values of the double dispersion parameters, the inertial effect parameter, and also for the parameters which control the nonlinear temperature and the nonlinear concentration. Heat and mass transfer varies extensively with an increase in the nonlinear temperature parameter and the nonlinear concentration parameter depending on Dacry and non-Darcy porous media. The variation in heat and mass transfer when all the effects, i.e., the inertial effect, double dispersion ef- fects, and Soret and Dufour effects, are simultaneously zero and non-zero. The combined effects of the nonlinear temperature parameter, the nonlinear concentration parameter and buoyancy are analyzed. The effect of the nonlinear temperature parameter and the nonlinear concentration parameter and also the cross diffusion effects on heat and mass transfer are observed to be more in Darcy porous media compared with those in non- Darcy porous media. In the opposing buoyancy, the effect of the temperature parameter is to increase the heat and mass transfer rate, whereas that of the concentration parameter is to decrease.

Reflection of thermoelastic wave on the interface of isotropic half-space and tetragonal syngony anisotropic medium of classes 4, 4/m with thermomechanical effect

The thermoelastic wave propagation in a tetragonal syngony anisotropic medium of classes 4, 4/m having heterogeneity along z axis has been investigated by employing matrizant method. This medium has an axis of second-order symmetry parallel to z axis. In the case of the fourth-order matrix coefficients, the problems of wave refraction and reflection on the interface of homogeneous anisotropic thermoelastic mediums are solved analytically.

Spectral anomalies of diffracted pulsed Hermite-Gaussian beams in dispersive media

This paper derives and uses the recurrence expressions for the power spectra of diffracted pulsed Hermite-Gaussian （HG） beams in dispersive media to study the spectral anomalies of pulsed HG beams in the far field. Numerical results are given to illustrate the dependence of spectral switches on the pulse parameters, truncation parameter and dispersive property of the medium. The potential application of spectral anomalies of ultrashort pulsed beams in information encoding and transmission is discussed.

P-wave velocity prediction in porous medium with liquid-pocket patchy saturation

It becomes increasingly clear that non-uniform distribution of immiscible fluids in porous rock is particularly relevant to seismic wave dispersion. White proposed a patchy saturation model in 1975, in which spherical gas pockets were located at the center of a liquid saturated cube. For an extremely light and compressible inner gas, the physical properties can be approximated by a vacuum with White＇s model. The model successfully analyzes the dispersion phenomena of a P-wave velocity in gas-water- saturated rocks. In the case of liquid pocket saturation, e.g., an oil-pocket surrounded by a water saturated host matrix, the light fluid-pocket assumption is doubtful, and few works have been reported in White＇s framework. In this work, Poisson＇s ratio, the bulk modulus, and the effective density of a dual-liquid saturated medium are formulated for the heterogeneous porous rocks containing liquid-pockets. The analysis of the difference between the newly derived bulk modulus and that of White＇s model shows that the effects of liquid-pocket saturation do not disappear unless the porosity approaches zero. The inner pocket fluid can no longer be ignored. The improvements of the P-wave velocity predictions are illustrated with two examples taken from experiments, i.e., the P-wave velocity in the sandstone saturated by oil and brine and the P-wave velocity for heavy oils and stones at different temperatures.

Nonlinear Propagation of Coupling Optical Pulse under Compton Scattering in Laser Medium

After considering Kerr nonlinear effect, group velocity dispersion of host and gain distribution of active particle in laser amplifying medium, a basic equation describing propagation of the coupling optical pulse under the multi-photon nonlinear Compton scattering in the laser amplifying medium has been deduced. Besides, the profile and power spectrum of a picosecond-level super-Gaussian coupling pulse in the laser amplifying medium have been discussed when its central frequency coincides with the gain peak frequency of the laser amplifying medium.

多孔介质气体弥散系数测试实验系统开发

为将流体力学的弥散理论教学融入实际应用,研发了多孔介质气体弥散系数测试实验系统。通过该系统可向学生直观地演示弥散系数测定方法,以及无因次气体浓度与无因次弥散系数之间的变化规律。自主开发了多孔介质气体弥散模拟程序,通过对模拟结果进行拟合来确定弥散系数反演解析式,并结合实验测试数据,反演得到弥散系数具体数值。实验结果表明:注气点附近的无因次气体浓度最高,从注气点开始沿测定容器深部和两侧延伸的方向,无因次气体浓度递减;随着无因次弥散系数的增大,气体混合均匀所需要的距离逐渐缩短;通过反演计算得到实验装置内多孔介质气体弥散系数为0.001647。

基于FOSC型的宽波段高效率中低色散光谱仪设计(特邀)

为实现各类暂现源及暗弱目标的宽波段、高效率光谱后随观测,以1.9 m光学望远镜为例,设计了一种基于Faint Object Spectrograph and Camera型的双通道中低色散光谱仪,可实现三种光谱分辨率(R=500、2000和5500),工作波段覆盖紫外-近红外(310~1000 nm)。根据光栅方程和光谱分辨率等各项指标,确定光谱仪的初始结构参数,针对光谱仪在全波段的高效率需求以及仪器随动的包络限制,确定光学系统采用双通道设计并近似对称分布:准直系统采用了不同于传统Faint Object Spectrograph and Camera型光谱仪的折反射式系统,在提高了系统效率的同时压缩了空间。色散系统根据直视棱栅的不同工艺,通过棱镜材料和角度的调整对工作波段的光栅效率进行优化并得到8种棱栅参数;红蓝通道相机系统在设计过程中优化选取光学材料,同时结合二次非球面和单透镜的主动调焦补偿,实现大动态温度范围(-30℃~20℃)全视场(φ16°)最大弥散斑半径均方根小于5μm的优良像质。该系统结构紧凑、分布对称,设计结果满足各项指标,光谱仪全波段峰值效率优于60%,最低效率优于20%,具有较高的可实现性。基于曲面芯片工艺,以红通道为例,简化的相机系统至少可提高整体光谱效率约4%,可以为未来光谱仪相机系统的设计提供参考。

磨料形貌及分散介质对4H碳化硅晶片研磨质量的影响研究

研磨作为4H碳化硅(4H-SiC)晶片加工的重要工序之一,对4H-SiC衬底晶圆的质量具有重要影响。本文研究了金刚石磨料形貌和分散介质对4H-SiC晶片研磨过程中材料去除速率和面型参数的影响,基于研磨过程中金刚石磨料与4H-SiC晶片表面的接触情况,推导出简易的晶片材料去除速率模型。研究结果表明,磨料形貌显著影响4H-SiC晶片的材料去除速率,材料去除速率越高,晶片的总厚度变化(TTV)越小。由于4H-SiC中C面和Si面的各向异性,4H-SiC晶片研磨过程中C面的材料去除速率高于Si面。在分散介质的影响方面:水基体系研磨液的Zeta电位绝对值较高,磨料分散均匀,水的高导热系数有利于控制研磨过程中的盘面温度;乙二醇体系研磨液的Zeta电位绝对值小,磨料易发生团聚,增大研磨过程的磨料切入深度,晶片的材料去除速率提高,晶片最大划痕深度随之增大。

适用于有耗型德拜色散媒质电磁特性仿真的RI-CDI-FDTD方法及程序实现

提出了一种新的处理有耗型德拜色散媒质的单步蛙跳遵从发散隐式-时域有限差分(complying divergence implicit FDTD,CDI-FDTD)方法.从频域下的Maxwell方程出发,利用傅里叶变换将电磁场分量从频域转换到时域,并采用递归积分(recursive integration,RI)方法对频域-时域转换过程中存在的积分项进行近似处理.然后应用单步蛙跳隐式格式对时域Maxwell方程和辅助变量进行差分离散,推导出有耗型德拜色散媒质的RI-CDI-FDTD算法的迭代公式.接着利用von Neumann方法验证了基于RI方法的CDI-FDTD算法的无条件稳定特性,最后通过数值算例验证了本文所提方法的正确性和有效性.

液体石蜡非水介质体系中涤纶织物的分散染料染色性能

为了促进节水低碳的涤纶分散染料非水介质染色技术的发展,研究液体石蜡非水介质体系中涤纶织物的分散染料染色性能。结果表明,分散染料在液体石蜡(LP)介质中的溶解度大于十甲基环五硅氧烷(D5)介质,以致分散染料在LP非水介质体系中染色的得色量不及在D5非水介质体系中的得色量;微量水能够显著提高分散染料非水介质体系染色的得色量,当加水量为50%(omf)时,增效作用最显著,过多的水量对匀染性不利;LP非水介质体系染色织物的色牢度与常规水浴染色和D5非水介质体系染色织物的色牢度相仿。

水基干压成型高导热氮化硅陶瓷的结构和性能

以α-Si_(3)N_(4)、β-Si_(3)N_(4)、MgO、Y_(2)O_(3)为原材料,利用以水为分散介质的水基干压成型工艺在不同温度(1 750,1 850℃)下烧结制备高导热氮化硅陶瓷,研究了不同烧结温度下陶瓷的结构、力学性能和热导率,并与以无水乙醇作为分散介质的非水基干压成型氮化硅陶瓷进行对比。结果表明:陶瓷的晶粒均呈长柱状,并且零散的粗大晶粒周围分布着较多的细长晶粒,呈双模式组织结构;1 750,1 850℃烧结温度下水基干压成型陶瓷的抗弯强度分别为555.7,747.5 MPa,断裂韧度分别为8.14,8.25 MPa·m^(1/2),均略低于非水基干压成型陶瓷,相对密度分别为99.00%,99.58%,平均晶粒尺寸分别为1.06,1.27μm,热导率分别为65.70,75.54 W·m^(-1)·K^(-1),均略高于非水基干压成型陶瓷。

涤纶分散染料无水染色研究进展

涤纶传统水浴染色存在高耗水、高排放、高污染的技术难题,严重制约了纺织行业的可持续发展。文中着眼于涤纶分散染料的无水染色方法,着重介绍有机溶剂染色、超临界二氧化碳流体染色、硅基介质染色等技术,分析各个新型染色技术的优点与不足,以期能够改变涤纶传统水浴染色的三高现状,为涤纶分散染料生态染色技术的发展提供新思路。