计算多轴拌器的轴功率

对三种搅拌器：锚式、螺旋式、锯齿式，在不同的转速配比下进行了轴功率测试，搅拌雷诺数为０．８～３０００００，液体的粘度为０．００１～８４Ｐａ．ｓ。液体的性质属牛顿型流体，试验过程用计算机控制．通过测量轴的扭矩来确定搅拌器的轴功率。实验测定了不同情况下搅拌器相互之间的影响。实验数据由马跨特计算方法确定模型参数并给出层流至湍流范围内三种搅拌器轴功率的计算公式．     

Deformation-mediated superstructures and cavitation of poly (l-lactide): In-situ small-angle X-ray scattering study

Cavitation and superstructure evolution of polymers during stretching play crucial roles to influence the mechanical properties of materials. In this study, we investigated deformation-mediated superstructures and cavitation of poly (l-lactide) (PLA) as well as their dependence on stretching temperatures by in-situ small-angle X-ray (SAXS) analysis coupled with mechanical testing. It is found that the cavitation and crystalline deformation are strongly influenced by stretching stress during deformation, which significantly depends on the stretching temperature. At lower stretching temperature (70 °C), the cavitation is initiated before the yielding and then stimulates the crystallite shearing. At higher stretching temperature (90 °C), however, the crystallites shear firstly and then crystalline deformation promotes the formation of cavities orientated along the stretching direction. High stretching temperature benefits the formation of relatively perfect crystals with high orientation. The results provide the basic knowledge of how to adjust the mechanical properties of polymer materials by controlling their superstructure in the deformation process.     

Votum der Ethikkommission der Medizinischen Universität zu Lübeck zur Präimplantationsdiagnostik

Ethik in der Medizin -     

Untersuchungen zum Transfer pharmakologisch wirksamer Substanzen aus der Nutztierhaltung in Porree und Weißkohl

Investigation on the transfer of pharmacologically active substances used in animal husbandry into leek and cabbage. The potential of leek and cabbage for uptake of highly prescribed veterinary drugs (antibiotics) was tested in hydroponically grown plants. For this purpose the antibiotics sulfadiazine (SFD), enrofloxacine (ENR), tetracycline (TC), chlortetracycline (CTC) and monensine (MON) were chosen. A further aim was to gain data on the situation of vegetables grown in agricultural practise with regard to antibiotic residues. The evident effects of the antibiotics on plants grown hydroponically (each antibiotic was administered at 5 μmol/l nutrient solution) were greatly different: With regard to leek there were no visible effects (MON, SFD), a weak bleaching of the younger leaf sections (CTC), and strong effects of ENR. The (phytotoxic) effects of antibiotics on cabbage were much more distinct. CTC caused a yellowing of the plant vasculature in cabbage. MON induced lesions on some leaves and finally led to leaf wilting. With administration of ENR a nearly complete bleaching of young leaves was observed. Using LC-MS/MS-methods (low-resolution and high-resolution MS) the administered antibiotics, as well as conversion products and metabolites, were separately identified and quantified in various organs of leek (roots, young and old sections of leaves) and cabbage (roots, stalks, young and old leaves). Depending on the type of antibiotic, vegetable species, and plant organ, the detected concentrations of antibiotic residues comprised several orders of magnitude ranging from μg/kg to mg/kg of fresh weight (fw). The highest concentrations of antibiotics were found in roots of both vegetable species: CTC and TC were detected at approximately 10 mg/kg fw in cabbage roots and at approximately 20 mg/kg fw in leek roots and ENR was determined at approximately 12 mg/kg fw in cabbage roots. Low amounts of ENR were metabolised to ciprofloxacine (CIP). ENR occurred at similar concentrations of approximately 7 mg/kg fw in roots and old leaves of cabbage, indicating a high transport rate of this antibiotic in the cabbage plant. In stalks, young and old leaves of cabbage and in young and old leaf sections of leek all administered antibiotics were detected. Within these antibiotics, ENR and CTC and their conversion products, e. g. demeclocycline (DMC) and TC, occurred at the highest concentrations. SFD and MON were found in considerably lower concentrations (<100 μg/kg fw). The results of our experiments in hydroponic cultures, using defined concentrations of antibiotics in the nutrient solution, evidently demonstrate that cabbage and leek have a very high potential for uptake of a number of veterinary antibiotic drugs, especially for tetracycline and ENR.     

Low-cost direct writing lithography system for the sub-micron range

Abstract

We have developed a fixed beam direct writing laser lithography system with a minimum feature size of 400nm at 457nm wavelength and a writing speed of 4·2mm/s with total system costs of less than 100 000 US$.     

Modification of CaCO3 precipitation rates by water-soluble nacre proteins

Mineral growth in nacre and other CaCO₃-containing biominerals is controlled by biopolymers. Water-soluble proteins were extracted from nacre of the sea snail Haliotis laevigata by dissolving the mineral phase with 6% acetic acid. The influence of this protein mixture on CaCO₃ precipitation rates was investigated at different concentrations. A well-established assay for measuring the pH-value during CaCO₃ precipitation with and without protein additives was extended by calculating maximum precipitation rates from the pH-values. It could be shown that precipitation rates are greatly influenced by the mixtures of water-soluble nacre proteins. At very low protein concentrations (0.02 μg/ml) a rate enhancement in comparison to the pure supersaturated calcium carbonate solution by a factor of 1.4 was observed. At higher protein concentrations, a strong inhibitory effect occurred, with total inhibition at concentrations of 1.0 μg/ml and higher. Two unspecific proteins (bovine serum albumin and lysozyme) showed little or no modification of precipitation rates. In vivo, the function of the strong inhibition of CaCO₃ precipitation by nacre proteins at higher concentrations is presumably to prevent uncontrolled crystallization in the extrapallial fluid. The rate-enhancing capability of proteins at low concentrations may be explained by the presence of acidic and/or hydrophilic moieties.     

Polymerization of epoxy resins initiated by metal complexes

BACKGROUND: Processing parameters and material properties of epoxy resins can be vastly influenced by choice of curing agent. In this work, metal complexes were investigated as initiators for anionic and cationic epoxide polymerization. Systems for thermally induced and electron beam‐induced curing are described. RESULTS: Zinc or cobalt imidazole complexes of the type [M(imidazole)₂(anion)₂] are efficient initiators for anionic polymerization of glycidyl‐based epoxy resins. The complexes can be employed to prepare tailored resin systems ranging from fast curing systems at slightly elevated temperatures to systems with very high thermal latencies curable at temperatures far above 150 °C. Silver complexes [Ag(L)_n]SbF₆ (L = crown ether or alkene) are highly efficient initiators for cationic curing and low initiator contents of around 1% are sufficient to reach high degrees of crosslinking. The complexes are excellent initiators for both thermally induced and electron beam‐induced polymerizations. CONCLUSION: Metal complexes are powerful initiators for the homopolymerization of epoxy resins and can be designed not only for anionic and cationic polymerization but also for thermal and radiation curing. Based on this study and additional work, a library can be compiled which allows retrieval of optimized metal–ligand–anion combinations and adjustment of the initiators to the respective processing and material demands. Copyright © 2009 Society of Chemical Industry