Miniemulsion polymerization of styrene. I. Preparation by redox initiator and new agitation mixer

Miniemulsion polymerization is usually conducted by a two-stage process, miniemulsion and polymerization, where the reactants are first processed using a high shearing machine, then transferred to a reactor to polymerize with magnetic stirring. However, the particles size distributions obtained usually are broad and skewed to small sizes owing to micelle and homogeneous nucleation in the aqueous solution. In this study, a saw-toothed blade mixer was successfully used for miniemulsion polymerization with a rotating rate over 500 rpm. The addition sequence of the components also affected the miniemulsion process in this system. The best result was obtained when the surfactant and cetyl alcohol were first dissolved in water and then the styrene was mixed in. Furthermore, a fast dissociated redox initiator system (cumene hydroperoxide/Fe²⁺/ethylenediaminetetraacetic acid-disodium salt/sodium formaldehyde sulfoxylate) was used to prepare miniemulsion polymer and monodisperse polystyrene. © 1996 John Wiley & Sons, Inc.     

锅炉异种钢管焊接接头焊缝稀释率试验

异种钢焊接的稀释率对焊接质量有影响,通过焊缝的稀释率与接头坡口形式、焊接工艺关系试验与分析,采用试验推荐的坡口形式及焊接参数可将焊缝稀释率控制在所要求的范围内.     

Salmonellosis in finishing pigs in Spain: prevalence, antimicrobial agent susceptibilities, and risk factor analysis

A herd-based survey of Salmonella in pigs was carried in a major pig producing region of Spain. Mesenteric lymph nodes were collected from the carcasses of 25 pigs from each of 80 herds at time of slaughter. Salmonella spp. were isolated from 31% of animals and 94% of herds. Within-herd prevalence ranged from 4 to 88%, with the prevalence in most herds being greater than 10%. A large diversity of Salmonella serotypes was found, with Typhimurium, 4,[5],12:i:-, and Rissen being the most prevalent. Two or more serotypes coexisted in 73% of the herds. Salmonella Typhimurium was present in 68% of the herds. Most (82%) of the Salmonella isolates belonged to serogroups targeted by enzyme-linked immunosorbent assay tests for pig salmonellosis. Resistance to at least one antimicrobial agent was detected in 73% of the strains, and one or more resistant strains were recovered from pigs in 93% of the herds. Antimicrobial agent resistance (AR) was more frequent among the most prevalent than it was among the rarer serotypes. Twenty-five multi-AR patterns were found. Resistance to three or more families of antimicrobial agents was found in 75% of AR strains. The finding that many of the herds yielded isolates of several multi-AR patterns indicates that Salmonella infections were acquired from multiple sources. High prevalence of Salmonella in herds was associated with lack of rodent control programs, herds from farms with only finishing pigs, herds managed by more than one full-time worker, herds for which the source of drinking water was not a city supply, and relatively long fattening times.     

Analysis of Water-Soluble Vitamins in Honey by Isocratic RP-HPLC

An isocratic RP-HPLC method has been developed for the identification and quantification of water-soluble vitamins in honey. The mobile phase tested was an aqueous solution of sulphuric acid and the detection was carried out simultaneously by UV and fluorescence. The separation of vitamins C (l-ascorbic acid), B₁ (thiamine), B₃N (nicotinamide), B₃H (nicotinic acid), B₅ (d-pantothenic acid) and B₆ (pyridoxine) is achieved in these conditions in 15 min. The addition to the mobile phase of methanol 2 %?v/v reduced significantly the analysis time in the separation of these vitamins up to 10 min. Moreover, in presence of a cationic surfactant hexadecyltrimethylammonium bromide (CTAB) in the mobile phase, the separation of vitamin C, B₁, B₃N, B₃H, B₂ (riboflavin) and B₆ is possible in 6 min. The combination of both mobile phases, H₂SO₄/methanol and H₂SO₄/methanol/CTAB, has been applied to the analysis, in isocratic mode, of several monofloral honeys (rosemary, thyme, lavender, chestnut, echium) and a honeydew honey in a short time analysis.     

Blends of amorphous and crystalline polylactides with poly(methyl methacrylate) and poly(methyl acrylate): a miscibility study

Blends of amorphous and crystalline polylactides (PDLA and PLLA) with poly(methyl methacrylate) (PMMA) and poly(methyl acrylate) (PMA) have been prepared. Thermal behaviour and miscibility of these blends along the entire composition interval were studied by differential scanning calorimetry (d.s.c.). The results were compared with those obtained by dynamic mechanical analysis (DMTA). Only one T_g was found in PDLA/PMA and PDLA/PMMA blends, indicating a high degree of miscibility in both systems. Nevertheless, the PDLA/PMMA blend presented enlargements of the T_g width at high PMMA contents. In this case, additional evidence of complete miscibility was obtained by studying the evolution of the enthalpic recovery peaks which appear after different thermal annealing treatments. When the polylactide used was semicrystalline (PLLA), once the thermal history of the blends had been destroyed, crystallization of PLLA was disturbed in both blends PLLA/PMMA and PLLA/PMA, but in a rather different fashion: in the first case crystallization was almost prevented while in the second one it was favoured. This behaviour was explained in terms of the effect of the higher stiffness as indicated by the value of T_g for PMMA compared to that for PMA.     

基于PLC的皮革感官特性测试仪

简要叙述了皮革感官参数的测定方法,构建了一种基于PLC的皮革感官特性参数测试仪器.以Visual Basic编程语言程序为开发平台,以PLC为基础硬件,实现对皮革力学性能控制参数的可视化设定,并将设定的参数通过PLC送给步进电机驱动器,控制步进电机;然后通过载荷传感器和位移传感器实时采集位移和载荷参数,并在人机界面上进行显示.     

崂山产黄精总皂苷提取工艺的响应面优化

目的优化崂山产黄精的总皂苷提取工艺。方法香草醛-高氯酸显色法测定黄精总皂苷含量;以黄精总皂苷提取率为指标,在单因素实验基础上,通过Box-Benhnken响应面法考察乙醇浓度、料液比、提取温度、提取时间和提取次数对提取工艺的影响。结果建立了崂山产黄精的总皂苷提取方法,其最佳提取工艺条件为:乙醇浓度73%、料液比1:15、提取温度56℃、提取时间45 min、二次提取。在此工艺条件下,黄精总皂苷提取得率可达2.87 mg/g,比单因素实验最高提取率高6.3%。结论优化了黄精总皂苷的提取工艺,为崂山产黄精的深度开发和综合利用奠定了基础。     

Effect of Sr and Al or Fe co-doping on the sinterability and conductivity of lanthanum silicate oxyapatite electrolytes for solid oxide fuel cells

The effect of co-doping of Sr and Al or Fe on the microstructure, sinterability and oxide-ion conductivity of lanthanum silicate oxyapatites is investigated in detail at 300–800 °C by the electrochemical impedance spectroscopy. The oxide-ion conductivity is 1.46 × 10⁻² S cm⁻¹ for La_9.5Sr_0.5Si_5.5Fe_0.5O_26.5 (LSSFO) and 1.34 × 10⁻² S cm⁻¹ at 800 °C for La_9.5Sr_0.5Si_5.5Al_0.5O_26.5 (LSSAO), respectively, which is one order of magnitude higher than 6.16 × 10⁻³ S cm⁻¹ measured on La_9.67Si₆O_26.5 (LSO) oxyapatite under the identical test conditions. The grain bulk and grain boundary resistances of co-doped oxyapatite are significantly smaller than that of LSO oxyapatite, and decrease significantly with the increase of the sintering temperature. LSSFO and LSSAO also show significantly higher density as compared to that of LSO. The results indicate that co-doping of Sr and Al or Fe significantly improves the densification, sinterability and oxide-ion conductivity of lanthanum silicate oxyapatites.     

Global sensitivity analysis of the blade geometry variables on the wind turbine performance

The need for implementing efficient blade designs gains relevance as wind turbine developments require longer blades. The design of blade geometry, traditionally divided in 2D airfoils and spanwise distributions, is usually addressed as an optimization problem. A correct identification of the design variables is crucial to avoid unnecessary computational cost or insufficient exploration of the design space. This paper deals with the identification of the design variables that affect the wind turbine performance. First, the number of design variables for an accurate airfoil representation is resolved. A methodology, based on statistical hypothesis testing applied to the airfoil approximation errors, is presented to assess the accuracy of types of B‐splines. Second, the study is extended to chord and twist distributions besides airfoil geometry with the purpose of assessing the sensitive blade variables in the wind turbine performance. Global sensitivity analysis as multi‐variable linear regressions and variance‐based methods are used. Latin hypercube sampling is applied to generate efficient inputs. MATLAB‐based code is developed to obtain outputs: annual energy production, maximum blade tip deflection, overall sound power level and blade mass. As result of the study, a list of non‐affecting variables is deduced. These variables can be avoided in the optimization without loss of gain in the performance. The method is a powerful tool to analyse in a preliminary phase a design problem involving a high amount of variables and complex physical relations by means of combining different multi‐disciplinar calculation codes and performing statistical treatments. Copyright © 2017 John Wiley & Sons, Ltd.