INTEGRATED LINEAR AND NONLINEAR VISCOELASTICITY OF DISCOTIC LIQUID CRYSTALS

Theory and simulation of steady, small-amplitude, and large-amplitude oscillatory capillary Poiseuille flow of discotic mesophases are presented, discussed, and used to provide an integrated framework to characterize the rheology of precursors used in the manufacturing of carbon super-fibers. The underlying microstructural changes responsible for the non-Newtonian rheology are presented and discussed, taking into account dynamic couplings between orientation and velocity fields. Proper scaling of viscoelastic material functions leads to superposition and hence provides a better fundamental understanding of flow processes in steady and oscillatory flows. The relations between shear-thinning behavior in steady flow, elastic storage in small-amplitude oscillatory shear, and flow enhancement in pulsatile flow are established.     

EFFECT OF TEMPERATURE ON THE RHEOLOGY OF POLYMERIC LIQUID CRYSTALS

As part of a more general effort to elucidate the flow of polymeric liquid crystals, the effect of temperature on the rheological properties has been investigated. A lyotropic sample of poly(γ-benzyl-L-glutamate) in m-cresol has been used throughout the measurements. Under steady state shear flow the viscosity and the first normal stress difference have been measured. Oscillatory flow after cessation of steady shear flow reveals a time effect which led to the determination of initial and final moduli; both have been measured as a function of temperature. Finally some transients have been considered as well.

The limiting zero frequency value of the dynamic viscosity and the zero shear value of the steady state viscosity have different activation energies. The dynamic moduli can be scaled for temperature effects by means of the zero frequency viscosity. Because of the difference in activation energies this scaling does not hold for the steady state properties. An alternative scaling procedure is suggested. The time scale of the transients is nearly independent of temperature. None of the available theoretical models describes the measured phenomena.     

纤维素衍生物液晶相转变和织态结构

本文综述了纤维素衍生物液晶态相转变和织态结构。描述了纤维素衍生物从各向同性态向液晶态的转变过程和液晶态的织构特征。讨论了溶液浓度和温度对液晶相织构的影响。探讨了各种因素,如溶剂、取代基含量、外加力场和外加磁场等对液晶相的形成及织态结构的影响。     

ORDERING TRANSITIONS IN LIQUID CRYSTALS PERMIT IMAGING OF SPATIAL AND TEMPORAL PATTERNS FORMED BY PROTEINS PENETRATING INTO LIPID-LADEN INTERFACES

Recent studies have reported that full monolayers of L-α-dilaurylphosphatidylcholine (L-DLPC) and D-α-dipalmitoylphosphatidylcholine (D-DPPC) formed at interfaces between thermotropic liquid crystals (LCs) and aqueous phases lead to homeotropic (perpendicular) orientations of nematic LCs and that specific binding of proteins to these interfaces (such as phospholipase A ₂ binding to D-DPPC) can trigger orientational ordering transitions in the liquid crystals. We report on the nonspecific interactions of proteins with aqueous-LC interfaces decorated with partial monolayer coverage of L-DLPC. Whereas nonspecific interactions of four proteins (cytochrome c, bovine serum albumin, immunoglobulins, and neutravidin) do not perturb the ordering of the LC when a full monolayer of L-DLPC is assembled at the aqueous-LC interface, we observe patterned orientational transitions in the LC that reflect penetration of proteins into the interface of the LC with partial monolayer coverage of L-DLPC. The spatial patterns formed by the proteins and lipids at the interface are surprisingly complex, and in some cases the protein domains are found to compartmentalize lipid within the interfaces. These results suggest that phospholipid-decorated interfaces between thermotropic liquid crystals and aqueous phases offer the basis of a simple and versatile tool to study the spatial organization and dynamics of protein networks formed at mobile, lipid-decorated interfaces.     

深紫外非线性光学晶体及其应用

系统的介绍了我国深紫外非线性光学晶体的发展,主要以KBe_2BO_3F_2(KBBF)以及Sr_2Be_2B_2O_7(SBBO)族晶体为代表。通过晶体生长、确定结构以及各种光学性能的测定,发现KBBF晶体是目前唯一能采用直接倍频方法实现深紫外谐波光输出的非线性光学晶体。SBBO族晶体由于存在畴结构,目前还不能用于深紫外相干光输出。讨论了KBBF晶体的基本光学性质以及产生深紫外相干光源的能力和效率。介绍了这些深紫外相干光源的应用,并着重介绍了这些光源在先进能谱仪方面的应用及取得的重要成果。     

我国人工晶体的发展与展望

叙述了我国人工晶体的历史，现状和发展中的问题，在此基础上提出了进一步发展我国人工晶体的战略问题。     

GAS INDUCTION AND HOLD-UP CHARACTERISTICS OF LIQUID JET LOOP REACTORS

Gas induction and hold-up characteristics of liquid jet loop reactors (LJLR) have been studied. From the results of these investigations with various diffuser geometries the effect of various parts of the diffuser on the rate of induction, Q_G, and the gas hold-up, E_G, have been discerned. Two different diffuser designs yield highest E_G and Q_G, respectively. The use of draft tube has been found to increase the gas hold-up by 25-60% over those in its absence. Correlations for Q_G and E_G involving the main geometrical parameters of the nozzle-diffuser combinations and the liquid jet power input have been developed.     

LINEAR FEEDBACK EQUIVALENCE AND NONLINEAR CONTROL OF A CLASS OF TWO-DIMENSIONAL SYSTEMS

This paper applies the concept of linear feedback equivalence to two-dimensional nonlinear control systems of a certain model structure. Uniqueness and stability characteristics of the system are investigated. It is shown that global asymptotic stability can in general be achieved. A simple mathematical expression for a component of the unique steady-state is derived which provides a guide for the choice of the control parameters to obtain desirable dynamic properties and minimize steady-state offset. Numerical experiments in the phase plane of a model of an exothermic CSTR are employed to verify the analysis.     

炭纤维的导电性与炭化温度的关系

分析了炭纤维导电性能与炭化温度的关系,解释了炭纤维导电性的宏观表现与微观结构之间的联系。     

掺Nd系LiNbO3晶体的生长及外泵浦位相共轭激光器的特性

用提拉法生长Nd:LiNbO3(Nd:LN),In:Nd:LN和Ce:Nd:LN晶体.测试晶体的紫外-可见吸收光谱和抗光损伤能力.结果表明:Nd:LN晶体的吸收边相对同成分纯LN晶体向长波方向移动;In:Nd:LN晶体的吸收边相对Nd:LN晶体向短波方向移动;Ce:Nd:LN晶体的吸收边向长波方向移动.In:Nd:LN晶体的抗光损伤能力比Nd:LN晶体的提高1个数量级以上.以掺Nd系LN光折变晶体为位相共轭镜,He-Ne气体为激活介质,构成外泵浦位相共轭激光器.实验表明:掺Nd系LN晶体外泵浦位相共轭激光器的输出特性稳定,In:Nd:LN晶体的输出光强比Fe:LN晶体的提高了近1个数量级.     

ZnO单晶的KOH碱液法生长和表征(英文)

采用自发成核方法,以KOH碱液作助熔剂,在银、镍和铁坩埚中分别生长了透明、棕绿色和棕色的纤维锌矿氧化锌单晶。X射线衍射和电感耦合等离子体原子发射光谱分析表明:晶体的颜色与所含的杂质有关,这些杂质来源于所使用的坩埚。采用光致发光(photoluminescence,PL)光谱对所生长的晶体进行了表征,结果显示,从银坩埚中生长的氧化锌晶体质量较高,其室温下用325nm波长光激发的PL光谱显示381nm强的紫外发射峰。在此基础上,从200mL银坩埚中生长出了尺寸为φ3mm×34mm氧化锌晶体。     

广义线性模型与非线性模型参数的统计推断

概述了广义线性模型(含半参数广义线性模型)与非线性模型研究的新进展,着重讨论了它们参数估计的统计推断。近年来,广义线性模型与非线性模型的研究发展迅速,有着广泛的应用前景。     

空分装置工艺空气冷却器液位波动事故分析与处理

本文针对空分装置工艺冷却器在分子筛切换时液位波动冷却水进入分子筛事故的现象进行阐述,分析造成事故的原因,提出预防措施。     

HYDRODYNAMICS OF LAMINAR LIQUID JETS. EXPERIMENTAL STUDY AND COMPARISON WITH TWO MODELS

Laminar jets of Newtonian liquids issuing from long vertical cylindrical nozzles and falling freely through stagnant air were studied experimentally for Reynolds numbers between 300 and 1000. Jet diameters were measured from still photographs, and radial distributions of axial velocity were obtained by laser Doppler anemometry. The effect of nozzle diameter, fluid viscosity and surface tension was investigated.

The experimental results were compared with numerical solutions of the Protean coordinate model developed by Duda and Vrentas. The boundary layer simplifications were confirmed to be valid only for the downstream region of the jet and for Reynolds numbers greater than 1000.

The experimental diameters were also compared with predictions from a form of the Bernoulli equation with a surface tension term. The asymptotic validity of the model was confirmed, provided that the dissipation term arising from fluid viscosity could be neglected.

Neither model correlated the jet formation region satisfactorily. For this region, an empirical correlation was developed which improves the diameter prediction and is complementary of either model.     

掺镁铌酸锂晶体吸收边紫移及占位离子的离子极化模型

测量了系列Mg~(2+):LiNbO_3晶体的吸收边,根据晶体吸收边紫移和离子极化理论,提出:Mg~(2+)将首先取代位于Li~+位的Nb~(5+),当浓度超过5mol％后,才开始进入正常Li~+位。此模型可解释Mg~(2+):LiNbO_3抗光折变增强和光电导增大的机制。     

PREDICTION OF PRESSURE DROP IN A VENTURI SCRUBBER: EFFECT OF LIQUID FILM AND RE-ENTRAINMENT

A mathematical model has been developed for prediction of pressure drop in a Venturi scrubber. This model includes the effect of the amount of liquid film and re-entrainment of liquid droplets from liquid film. The result of the present model is compared with experimental data of Viswanathan et al. (1985) Viswanathan, S., Gnyp, W. A. and Pierre, St., C. 1985. Annular flow pressure drop model for pease-Anthony-type Venturi scrubbers. AIChE. J., 31(12): 1947–1958.  [Google Scholar] as well as with the other models (Viswanathan et al., 1985 Viswanathan, S., Gnyp, W. A. and Pierre, St., C. 1985. Annular flow pressure drop model for pease-Anthony-type Venturi scrubbers. AIChE. J., 31(12): 1947–1958.  [Google Scholar]; Boll, 1973 Boll, R. H. 1973. Particle collection and pressure drop in Venturi scrubbers. Ind. Eng. Chem. Fundam., 12: 40[Crossref], [Web of Science ®] , [Google Scholar]). Results of this study indicate that at high liquid to gas ratios prediction of pressure drop can be improved by considering re-entrainment and liquid film effects. Also the effects of gas velocity and liquid to gas ratio were investigated on the rate of droplet re-entrainment and pressure drop.     

PREDICTION OF PRESSURE DROP IN A VENTURI SCRUBBER: EFFECT OF LIQUID FILM AND RE-ENTRAINMENT

A mathematical model has been developed for prediction of pressure drop in a Venturi scrubber. This model includes the effect of the amount of liquid film and re-entrainment of liquid droplets from liquid film. The result of the present model is compared with experimental data of Viswanathan et al. (1985) as well as with the other models (Viswanathan et al., 1985; Boll, 1973). Results of this study indicate that at high liquid to gas ratios prediction of pressure drop can be improved by considering re-entrainment and liquid film effects. Also the effects of gas velocity and liquid to gas ratio were investigated on the rate of droplet re-entrainment and pressure drop.     

LIQUID CRYSTALLINE POLYMERS: 10: SYNTHESIS AND THERMAL BEHAVIOR OF SOME POLYETHERS CONTAINING A HEXAMETHYLENIC SPACER

The paper presents the synthesis and thermal behavior of some copolyethers containing a hexamethylenic spacer. The polymers were obtained using a phase transfer catalysis technique, starting from 1,6-dichlorohexane and various bisphenols as follows: 4,4′-dihydroxyazobenzene (DHAB), 4,4′-dihydroxydiphenyl (DHD), bisphenol A (BPA), 2,7-dihydroxynaphtyl (DN) and 4-hydroxydiphenyl sulfide (BPS). The synthesized polyethers have low molecular weights, being situated in the oligomeric domain. The polymers were characterized by ¹H-NMR spectroscopy, DSC calorimetry and optical microscopy in polarized light. Only the polyethers containing DHAB, DHD and BPA units exhibited liquid crystalline phase. All liquid crystalline oligomers evidenced enantiotropic behavior.     

THE SPLIT OF THE LIQUID PHASE IN DROPS AND FILM IN AN EJECTOR-VENTURI SCRUBBER

Liquid distribution along an ejector-Venturi scrubber was determined experimentally in an industrial-scale pilot plant. The effects of geometry as well as flow rates were studied. The results showed that a significant fraction of the liquid travels as a film. Therefore, it should be taken into consideration in mass transfer studies, where usually it is neglected. The data were used to test a model, that allows for interchange of liquid between drops and film flowing on the Venturi walls. There was good agreement between experiment and predictions.     

EFFECT OF A MAGNETIC FIELD ON TWO-PHASE LIQUID METAL FLOW AND CAVITATION OCCURRENCE

To clarify the effect of a magetic field on two-phase bubble flow characteristics and cavitation occurrence, an analytical study of two-phase MHD flow with low quality is developed, taking into account slip and bubble expansion. Numerical calculation shows that the application of a magnetic field causes a decrease in pressure in the diverging passage and an increase in the incipient cavitation number.