Determining creep ratio in buried pipes for applications without pressure. Accuracy of experimental results

A buried plastic pipe undergoes deformation, but it stabilizes at the end of a certain time not exceeding two years.Thus, there is an interest in determining the extrapolated creep of structured wall plastic pipes at 2 years.The main goal of this work is to present information regarding the assessment of results and their accuracy, based both on the requirements of the product standard [3] and on the uncertainty of the tests.     

Effects of temperature and stress on creep properties of ethylene tetrafluoroethylene (ETFE) foils for transparent buildings

Creep properties of ethylene tetrafluoroethylene (ETFE) foils are indispensable for evaluating serviceability limit state, especially under high temperature and high stress. This paper concerned temperature and stress effects on creep properties of ETFE foils with experimental and theoretical studies. Experimental results showed that dimensionless stress effect on creep properties could be higher than that of temperature effect. A unified equation incorporating temperature, stress and time based on experimental results was determined and could be utilized to calculate the stress limits and long-term creep strains. The stress limits in response to creep strain of 10% were less than 5 MPa, 4 MPa and 3 MPa for temperature ranges of 40–50 °C, 50–60 °C and 70–80 °C, respectively. The long-term creep strain of ETFE foils under 40 °C was 5.96% concerning 50-year working time.Master curves of ETFE foils were evaluated considering time-temperature superposition (TTSP) and time-stress superposition (TSSP). Long-term creep strains with these master curves were identified and compared with experimental creep strains. It is found that TTSP could be a little underestimation of creep strains while TSSP could overestimate creep strains to some extent. Moreover, the maximum creep strain difference was only 0.48%, which justified the feasibility and suitability of using the unified equation to predict creep strains of ETFE foils.     

Constitutive Expression and Optimization of Nutrients for Streptokinase Production by <Emphasis Type="Italic">Pichia pastoris</Emphasis> Using Statistical Methods

The Pichia pastoris clone producing streptokinase (SK) was optimized for its nutritional requirements to improve intracellular expression using statistical experimental designs and response surface methodology. The skc gene was ligated downstream of the native glyceraldehyde 3-phosphate dehydrogenase promoter and cloned in P. pastoris. Toxicity to the host was not observed by SK expression using YPD medium. The transformant producing SK at level of 1,120 IU/ml was selected, and the medium composition was investigated with the aim of achieving high expression levels. The effect of various carbon and nitrogen sources on SK production was tested by using Plackett–Burman statistical design and it was found that dextrose and peptone are the effective carbon and nitrogen sources among all the tested. The optimum conditions of selected production medium parameters were predicted using response surface methodology and the maximum predicted SK production of 2,136.23 IU/ml could be achieved with the production medium conditions of dextrose (x1), 2.90%; peptone (x2), 2.49%; pH, 7.2 (x3), and temperature, 30.4 (x4). Validation studies showed a 95% increase in SK production as compared to that before optimization at 2,089 IU/ml. SK produced by constitutive expression was found to be functionally active by plasminogen activation assay and fibrin clot lysis assay. The current recombinant expression system and medium composition may enable maximum production of recombinant streptokinase at bioreactor level.     

Response surface methodology based on central composite design accompanied by multivariate curve resolution to model gradient hydrophilic interaction liquid chromatography: Prediction of separation for five major opium alkaloids

Hydrophilic interaction liquid chromatography on bare silica presents some benefits for analysis and purification of ionizable basic alkaloids. This mode was used to separate five major opium alkaloids: morphine, codeine, thebaine, papaverine, and noscapine. Central composite design based on response surface methodology was applied for experimental design, modeling, and optimization in a single‐step gradient method. The main effects and their interactions (initial percentage of modifier, changing range of modifier in run time, pH of buffer, and its concentration) were investigated in 30 experiments. Multivariate curve resolution‐alternating least squares, by resolving overlapped curves, helped in the accurate calculation of baseline resolution factors to be modeled and optimized more accurately. Then three crucial resolution factors besides elution time were modeled in quadratic and cubic equations and optimized. In addition to the four factors, five extra logarithmic, and nonlogarithmic factors extracted from the four factors to give nine factors overall were inspected on mechanism of retention. It was shown that a linear combination consist of four independence variables successfully describes morphinans retentivity in a single‐step gradient method.