The use of a mixing-sensitive chemical reaction for the study of pulp fibre suspension mixing

The competitive, consecutive chemical reactions between 1-naphthol and diazotized sulfanilic acid were utilized to study the mixing of a pulp fibre suspension in a 22 L stirred tank reactor. Mixing quality was determined from the distribution between the mono and bis substituted reaction products once a correlation was made for the adsorption of the product dyes onto the suspended fibres. The technique was found to be adequate for assessing micromixing and turbulence intensity within a fibre suspension provided the measured product distribution, Xs, was between 0.4 and 0.01. Thus the mixing conditions that could be assessed depended on both the energy dissipation within the mixer and the amount of the fibre present. For the experimental conditions chosen for this study energy dissipation rates would typically have to be less than 80 W/kg and the suspension mass concentration less than 2.5%. When compared with water, a reduction in turbulence levels at both the impeller zone and a remote zone in the stirred vessel was observed for fibre mass concentrations as low as 0.5%. The turbulence decreased as the suspension mass concentration was increased. This decrease is attributed to energy dissipation by friction at fibre-fibre contact points as the fibres move relative to one another in the flow. This sink removes energy from the turbulence cascade which never shows up as small-scale fluid deformations leading to better mixing.     

Acquired Predator Recognition by Fathead Minnows: Influence of Habitat Characteristics on Survival

In this study we conditioned fathead minnows (Pimephales promelas) to recognize the odor of a perch (Perca flavescens) by exposing them to perch odor coupled with minnow alarm cue. We then staged encounters between the predator and prey in order to assess whether the predator odor training had any effect on survival of the prey. We tested for a survival effect in the presence and absence of shelter. Our results indicate that fish trained with alarm signals to recognize predators gained a survival benefit during staged encounters with a predator and that habitat characteristics influenced the survival of conditioned fish.     

Chemical Composition Determination at the Bottom Region of a Recovery Boiler Furnace by Direct Minimization of Gibbs Free Energy

An optimization strategy has been applied to describe the chemical composition at the furnace bottom in the Kraft recovery boiler of a pulp production process. The concentrations of each involved chemical species were calculated through an optimization approach, minimizing the Gibbs free energy of the system. Various systems were proposed and tested, assuming different chemical species and phases number. Because serious initialization problems were found at this stage for some of the proposed systems, an optimization heuristic method (PSO) was used for the first approach to the problem. Once the appropriate phases number and chemical species in the system were determined, the initialization problems disappeared and the use of a deterministic optimization method (SQP) became viable. The proposed approach has shown to be satisfactory to reproduce industrial data and also data reported in the open scientific literature.     

Sex-identifying urine and molt signals in lobster (Homarus americanus)

During courtship, premolt female lobsters,Homarus americanus, choose a male and initiate a pair bond by repeated approaches to his shelter. The male allows such a female to share his shelter for about one week. This knowledge formed the basis to search for quantitative evidence for lobster sex pheromone(s) used in courtship: male cues to allow premolt females to identify a preferred male, and female cues to allow males to identify a premolt mature female. In each of four 1500-liter naturalistic aquaria, the behavioral responses of one female and two male lobsters to male and female lobster urine (0.5 ml) and body odor (20 ml) stimuli were observed. These stimuli were injected once or twice per day into a continuously flowing delivery tube attached to lobster shelters. Habituation to stimulus introduction—a serious problem in earlier experiments—was apparently avoided in the more natural social and physical environment we employed in these experiments. We demonstrated that male and female molt body odors contain different chemical substances: females responded to male molt body odor and males responded to female molt body odor but not vice versa. In general, male and female intermolt urine caused strong responses; however, females responded only weakly to male urine. This suggests that male and female urine are chemically different. Female urine and molt body odor caused a typically male high-on-legs response. These results show that molt body odors and intermolt urine contain sex-specific substances, which may be used in lobster courtship as well as other social interactions.     

纳米管合成研究进展

当今纳米科学技术飞速发展，其中纳米管已构成了纳米材料的一个非常重要的类别。本文介绍近几年来由化学键结合的纳米管以及由分子间力形成的一些纳米或具有中观尺度的管状结构材料的合成研究进展。     

国内外聚碳酸酯市场及需求分析

聚碳酸酯(PC)综合性能好,其消费与生产增长举世瞩目,在世界五大通用工程塑料中占有重要地位。国内PC生产及消费量虽不大,但潜在市场不可忽视,发展与开拓工程塑料,特别是PC的应用与生产的开发,是我国化学和石化工业发展需要之一。     

基于表面反应和扩散迁移控制的灰岩单裂隙渗流—溶解模型及其数值模拟

针对碳酸盐类可溶岩地区水电站坝址流场、化学场以及固相介质属性等随时间发生改变,从而对工程安全运行造成不利影响等问题,研究了灰岩地区地下水运移过程中各物理场间的相互作用,分析了影响灰岩溶解速率的两个因素,即表面反应控制和扩散迁移控制。在此基础上,建立了单裂隙中的渗流—溶解耦合模型,并进行数值求解。模拟结果表明,在垂直裂隙延伸方向,其溶蚀锋面为非齐整平面,而是呈似“虫洞”状非均一变化,而沿裂隙延伸方向即自上游侧向下游方向溶蚀程度逐渐减轻;而通过裂隙的流量呈现随时间逐渐增大的趋势,但变幅不大;根据流量求得的等效水力隙宽,其增幅和增长速率均小于实际平均隙宽;同时,化学场中Ca2+浓度的分布与裂隙开度变化具有相似性,不同时刻下上游侧反应速率R均大于下游侧。就反应机制而言,在初期均受表面反应控制,而随反应进行,位于上游补给区部位转为受扩散迁移控制,但在下游位置仍受表面反应控制。     

A computational fluid dynamic analysis of gas and particle flow in flame spraying

The flame spraying process, which is a common industrial thermal spraying application, has been analyzed by means of three-dimensional computational fluid dynamics (CFD) simulations. The process used at the Volvo Aero Corporation for the coating of fan and compressor housings has been modeled. The process uses the Metco 6P torch (Metco, Westbury, NY), which ejects a mixture of acetylene and oxygen at high speed through a ring of 16 orifices to form the flame. A stream of argon gas flowing through an orifice in the center of the ring carries a powder of nickel-covered bentonite through the flame to the spray substrate. The torch is cooled by a flow of air through an outer ring of 9 orifices. The simulation emulated reality closely by including the individual inlets for fuel, cooling air, and injected particles. The gas combustion was simulated as a turbulent, multicomponent chemically reacting flow. The standard, two-equation k-ε turbulence model was used. The chemical reaction rates appeared as source terms in the species transport equations. They were computed from the contributions of the Arrhenius rate expressions and the Magnussen and Hjertager eddy dissipation model. The first simulations included several intermediate chemical substances whose predicted concentration agreed favorably with measurements. Later, more simplified simulations incorporated only the global chemical reaction involving the initial and the final products, with corrections to the thermal properties being made to account for the missing intermediaries. The gas velocity and temperature fields predicted by the later simulations compared satisfactorily to those predicted by the earlier, more elaborate, ones. Therefore, the final simulations, which incorporated injected particles, were conducted employing the simplified model with only the global reaction. An in-house finite difference code was developed to calculate particle properties. Allowance was made for elliptical shapes, phase changes, and internal heat transfer with regard to the composite material. The particle velocities and temperatures predicted by the final simulations compared fairly well with experimental results obtained with the optical DPV2000 system.     

Formation and thermal stability of amorphous Ni-Mo-P alloys

The experimental researches on the chemical deposition of Ni-Mo-P amorphous alloys were carried out by adding Na2 MoO4 into acidic solutions. The optimum technology conditions were obtained by orthogonal design experiments. The structures and the relationship between compositions and their thermal stability were studied by energy spectrum (EC), scanning electron micrograph and X-ray diffraction spectrum. Compared with Ni-P amorphous alloys, the Ni-Mo-P amorphous alloys have high crystallization temperature and thermal stability, and the hardness reaches its peak when the annealing temperature is 500 ℃. With the increase of the heat treatment temperature, the surface morphology of the alloys changes.     

High-temperature oxidation of SiC in a glow-discharge oxygen plasma

The oxidation kinetics and structure of the oxide scales formed on high-density SiC were studied in molecular oxygen at 740 Torr and in a glow-discharge oxygen plasma at 0.1 Torr at temperatures of 1000, 1100, and 1200°C. The monatomic oxygen formed by the glow discharge markedly increased the reaction rate and the vaporization of some of the oxidation products. The marked differences in kinetics suggest that the rate-controlling step during oxidation in molecular oxygen is the dissociation of adsorbed diatomic oxygen to the monatomic species. Films formed in molecular oxygen were mostly amorphous SiO₂ with small inclusions of SiC and graphite, whereas films formed in dissociated oxygen were primarily amorphous SiO₂ containing SiO, S₂O₃, and the coesite form of SiO₂.