熔点和凝固点的准确测量

介绍了英国政府化学家研究所(IGC)和兵总第204所样品的熔点和凝固点的准确测量方法,熔点和凝固点的测量结果,并进行了讨论。     

过冷水滴碰撞结冰的实验与模拟研究

以宏观结冰/霜过程中过冷水滴的碰撞结冰现象为背景,实验对比了亲水和超疏水表面上常温水滴碰撞、常温水滴碰撞结冰和过冷水滴碰撞结冰的过程,建立了过冷水滴碰撞结冰过程的数值模型,研究了We数和接触角对碰撞结冰的影响。结果表明:相比于常温水滴的碰撞及其碰撞结冰过程,过冷水滴碰撞结冰过程的稳态铺展系数更大;随着过冷度和We数的增大以及接触角的减小,过冷水滴的碰撞结冰与常温水滴的碰撞在水滴形态和铺展系数上的差异逐渐增大。     

壁面静止水滴冻结过程形状变化

低温表面上的液滴冻结时会形成具有尖顶的形状。针对这一现象开展了理论与实验研究,建立了新的动态曲形相界面模型用来模拟水滴冻结过程中的形状变化。模型考虑重力和成核再辉效应的影响,将冻结过程中的冰水相界面近似为球冠形曲面,并在三相点处引入动态生长角和直角关系。对壁面上20μL静止水滴进行了冻结实验,记录水滴三相点高度的演化过程,以此拟合得到了其随时间变化的关联式,基于该关联式求解理论模型,得到了水滴最终冻结形状。模拟结果与实验结果在水滴初始轮廓、成核再辉轮廓和最终冻结轮廓以及冻结时间上均吻合良好。曲面模型的计算结果表明,固液相界面上不同位置处的冻结速率不同;随着相界面向上推移,冻结速率逐渐减小。     

Preparation and Characterization of Poly(L-lactide-co-glycolide-co-ε-caprolactone) Scaffolds by Thermally Induced Phase Separation

Abstract

The technique of thermally induced phase separation (TIPS) is favorable for the fabrication of a porous scaffold due to a number of advantages. In this work the poly(L-lactide-co-glycolide-co-ε-caprolactone) (PLLGC) terpolymer was synthesized by melt copolymerization and porous scaffolds thereof from its solution in 1,4-dioxane were fabricated by using the TIPS method. The effects of fabrication parameters, including polymer concentration and freezing temperature, on the morphology, pore size and mechanical properties were studied. The results showed that the average pore size of the PLLGC porous scaffold increased with a decrease in PLLGC concentration and the pore size resulting from freezing at 4?°C (about 20–100?μm) was significantly larger than for other samples (20–50?μm) frozen at lower temperatures. The porosity of the scaffolds decreased with increasing PLLGC concentration or decreasing freezing temperature. On the other hand, the compressive strength of the scaffolds increased with the increase of PLLGC concentration or the decrease of freezing temperature, as would be expected. The present results can be applied in design to control the processing parameters of TIPS for a scaffold with desired pore morphology.     

金属Ni纳米线凝固行为的分子动力学模拟

采用EAM镶嵌原子作用势，通过经典的分子动力学模拟方法研究了不同冷却速度下的金属Ni纳米线的凝固行为，并给出了纳米线在凝固区域的结构演变过程.利用键对分析技术研究了在不同冷却速度下体系中的原子团簇在降温过程中的变化情况.研究表明，纳米线的凝固起始于表面原子，并且随着冷却速度的降低，Ni纳米线的微观结构从非晶态过渡到多壳螺旋结构，最终达到稳定的面心立方结构.多壳螺旋结构同时具有确定的结晶温度和长程无序、短程有序的非晶结构的特征. 关键词： 纳米线 凝固行为 分子动力学 键对分析     

基于门冻结技术的无冒险RS触发器设计

数字电路中的冒险现象不仅会导致电路的误操作,而且消耗了很多能量、增加了操作时间,因此在电路设计中冒险的检测和消除非常重要．文章介绍了门冻结技术的基本思想,以此为基础给出了基于F门的CMOS与非门、或非门的逻辑单元电路设计,并将其应用到RS触发器的设计中,经PSPICE模拟显示,与传统的同步RS触发器相比,所设计的基于F门的同步RS触发器电路不仅具有正确的逻辑功能,消除了冒险,而且使电路的功耗也得到了有效地降低。     

Identification of the metabolites after oral administration of extract of ziziphi spinosae semen to rats or dogs by high‐performance liquid chromatography/linear ion trap FTICR hybrid mass spectrometry

Ziziphi spinosae semen (ZSS) is a traditional Chinese medicine that has been widely used to treat insomnia and anxiety. Modern pharmacological studies have demonstrated that flavonoids are the main active compounds in ZSS. However, the metabolites and the metabolic pathways of flavonoids in ZSS have not been investigated thoroughly. In this study, a method based on high‐performance liquid chromatography coupled with Fourier transform ion cyclotron resonance mass spectrometry (HPLC/FTICR‐MS) was established to identify the metabolites of flavonoids after oral administration of extract of ZSS to rats or dogs, using parent mass list‐triggered data‐dependent multiple‐stage mass analysis at a resolving power of 50,000 in the external calibration mode. The mass accuracies obtained for all full‐scan analyses were less than 4 ppm (<2 ppm in most cases). A total of 15 compounds were detected in biological samples of rats and dogs, and nine compounds were identified. The metabolic pathways of flavonoids of ZSS in rats and dogs were proposed. The results may help better understand the material basis and pharmacological mechanism of ZSS. Copyright © 2012 John Wiley & Sons, Ltd.     

Injection moulding of thermoplastics: Freezing during mould filling

The injection moulding of thermoplastic polymers involves, during mould filling, flows of hot melts into mould networks, the walls of which are so cold that frozen layers form on them. Theoretical analyses of such flows are presented here. Br Brinkman number - c _L polymer melt specific heat capacity - c _S frozen polymer specific heat capacity - e exponential function - erf() error function - Gz Graetz number in thermal entrance region - Gz ^* modified Graetz number in thermal entrance region - Gz overall Graetz number - h channel half-height - h ^* half-height of polymer melt region - H mean heat transfer coefficient - k _L polymer melt thermal conductivity - k _S frozen polymer thermal conductivity - ln( ) natural logarithm function - L length of thermal entrance region in pipe or channel - m viscosity shear rate exponent - M(,,) Kummer function - Nu Nusselt number - p pressure - P pressure drop in thermal entrance region - P _f pressure drop in melt front region - Pe Péclet number - Pr Prandtl number - Q volumetric flow rate - r radial coordinate in pipe - R pipe radius - R ^* radius of polymer melt region - Re Reynolds number - Sf Stefan number - t time - T temperature - T _i inlet polymer melt temperature - T _m melting temperature of polymer - T _w pipe or channel wall temperature - U(,,) Kummer function - u _r radial velocity in pipe - u _x axial velocity in channel - u _y cross-channel velocity - u _z axial velocity in pipe - V melt front velocity - w channel width - x axial coordinate in channel - x _f melt front position in channel - y cross-channel coordinate - z axial coordinate in pipe - z _f melt front position in pipe - () gamma function - dimensionless thickness of frozen polymer layer - _i i-th term (i = 1,2,3) in power series expansion of - dimensionless axial coordinate in pipe - _f dimensionless melt front position in pipe - dimensionless cross-channel coordinate - ^* dimensionless half-height of polymer melt region - dimensionless temperature - _i i-th term (i = 0, 1, 2, 3) in power series expansion of - _i first derivative of _i with respect toø - _i second derivative of _i with respect toø - ^* dimensionless wall temperature - thermal diffusivity ratio - - latent heat of fusion - µ viscosity - µ ^* unit shear rate viscosity - dimensionless axial coordinate in channel - _f dimensionless melt front position in channel - dimensionless pressure drop in thermal entrance region - _f dimensionless pressure drop in melt front region - _L polymer melt density - _s frozen polymer density - dimensionless radial coordinate in pipe - ^* dimensionless radius of polymer melt region - ø dimensionless similarity variable in thermal entrance region - dummy variable - dimensionless contracted axial coordinate in thermal entrance region - dimensionless similarity variable in melt front region - ^* constant     

Effect of rapid freezing–thawing techniques on the sperm parameters and ultrastructure of Chinese Taihang black goat spermatozoa

Supercooling sperm in liquid nitrogen vapour is a feasible and economic technique for the practical production. The study aimed to reveal the negative effects of this rapid freezing and thawing processes on Taihang black goat spermatozoa and to find out the changing of spermatozoa motility and ultrastructure by using CASA and TEM. Qualified semen samples, which collected from twenty Chinese Taihang black goats using artificial vagina were pooled and investigated the kinematics parameters and ultrastructural morphology. The results showed that freezing–thawing caused a significant reduction in the spermatozoon total motility (P < 0.001), in rapid and medium cell numbers (P < 0.001) and motility parameters (VAP, VSL, VCL, ALH and BCF) (P < 0.01). Immotile spermatozoa number was increased significantly after freezing–thawing (P < 0.001). In the ultrastructural analysis, the shape with a sperm nucleus characterized by ruptures, bend and deformity was observed. The plasma membranes were broken, and nucleoplasm erupted. The mitochondria in the middle piece were disturbed by partial absence or additional accumulations. Swelling, coiling, vacuolization and structural disorganization of mitochondria were also observed. In conclusion, Freezing–thawing procedure has a detrimental effect on motility, membrane integrity and mitochondria of goat spermatozoa. Transmission electron microscopy provides an intuitive observation to investigate deformity spermatozoa.     

Using the Ethoxylated Polyalkylphenol Formaldehyde Additives to Enhance the Physical Properties of Egyptian Jet Fuel A1

Nine ethoxylated polyalkyl phenol formaldehydes were prepared. From our results, it was found that the maximum (Ec) enhancement was obtained by DDP3 (20 pS/m) while it was (9 pS/m) for the blank jet fuel A1. On the other hand, the decreasing of freezing point was achieved by DDP3 (?70°C), while it was (?57°C) for the blank jet fuel. The gross and net calorific values (Cv) were ameliorated enhancement, compared with blank Cv of the jet fuel A1. The maximum net Cv was obtained by DDP3 (45.3 Mj/kg), while it was 43.7 Mj/kg for the blank sample. Also, the density increased for both molecular weight and the alkyl chain length of the prepared polymers. The minimum emulsion stability was marked for DDP3 (10 minutes), which exhibited the minimum droplet size (10 mm) at the same time the maximum reduction of surface tension (γ) for DDP3 was obtained in both jet and water (34 and 29 mNm^?1). This results means that the maximum atomization of fuel during injection should be obtained by the DDP3, which leads to complete ignition in the combustion chamber. These general enhancements of the physical properties gives the used fuel a marvelous industrial reflection and enables us to use it for military purposes.