Photoinitiated crosslinking of low density polyethylene. III: Degradation and stabilization of photocrosslinked polyethylene

Electron spectroscopy (ESCA) and reflectance infrared spectroscopy (ATR) were used to measure surface oxidation of photocrosslinked polyethylene. The deterioration of bulk properties during an artificial weathering test was also measured. It was found that the UV-irradiation during crosslinking process decreases the stability of the material considerably. Three kinds of antioxidants and photostabilizers (hindered phenols, hindered amines, and organic sulfides) which have no absorption in the UV region of 300 to 400 nm were added before crosslinking to improve the stability of the crosslinked material. Neither the rate nor the degree of photocrosslinking at different depths of the sample were affected significantly by these additives. It was found possible to prevent the decrease in stability due to the photocrosslinking by using small amounts of a stabilizer, e.g. 0.05% Tinuvin 770 (hindered amine).     

Induced low temperature catalytic ignition by transient changes in the gas composition

The effect of gas composition changes on the low temperature activity for supported platinum model catalysts has been studied. By introducing well-controlled periodic O₂ pulses to a simple diluted gas mixture of CO and O₂, a substantial improvement of the low temperature oxidation activity was observed. The reason for low activity on noble metals at low temperatures is often attributed to self-poisoning by CO. The improved catalytic performance observed is proposed to origin from the transients causing a surface reactant composition that is favourable for the reaction rate, i.e. lower degree of self-poisoning. This was also confirmed by in situ Fourier transform infrared (FT-IR) spectroscopy in combination with mass spectrometry (MS) measurements, which gave evidence for the existence of a strong interplay between the gas phase concentration and the adsorbate composition for these catalysts.     

Reliability analysis of hydraulic systems of LHD machines using the power law process model

Earlier, a preliminary study of the reliability characteristics of a fleet of load-haul-dump (LHD) machines deployed at Kiruna mine showed that the engine and the hydraulics are the two most critical subsystems. Hydraulic systems are selected for further study because such systems are still under a development phase. Maintenance data for two years for these machines are analyzed. The tests for trends and serial correlation showed that times between successive failures for the hydraulic systems are in most cases not independent and identically distributed. Goodness-of-fit tests showed that the power law process model provides a good fit to the failure data of the hydraulic systems. Methods for parameter estimation in the power law process model and estimation of optimal maintenance intervals for such systems are presented. Emphasis is on the use of graphical methods for data analysis.     

Measuring psychosocial work quality and health: Development of health care measures of measurement.

Demands on workload and work efficiency have increased because of ongoing global changes in health care organizations. Assessing and evaluating effects of changes on organizational and individual well-being require valid and reliable methods. Questionnaires from 3 large health care studies were used to develop instruments for work quality and health. Study 1 included 2,935 participants from all occupational groups. Study 2 sampled 3,545 nurses and midwives. Participants in Study 3 consisted of 3,506 employees at a large hospital. Variable fields of work quality, health and well-being, and modifying factors were factor analyzed with replicated structures in new samples, including 6 factors of work quality, 5 health factors, and 2 modifying factors. All except 2 factors had high internal consistency (Cronbach's α?=?.69–84) and low factor intercorrelations within areas. Social climate (but not individual resources) had, according to our model, a modifying effect on the work-health interaction (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Wind energy potential in southern Sweden-Example of planning methodology

This study presents a planning model for Swedish activities in the field of wind power. Models and results of calculations of the land-based wind energy potential with the Wind Atlas Analysis and Application Programme, WA^sP, are described and analysed in a geographical information systems (GIS) called the ArcView^® GIS system. One county in southern Sweden was chosen as a case study to present the methods used. The results from that case study indicate a great wind energy potential but there are nevertheless many factors limiting that potential. The study calls for a further development of planning tools in the field. Important areas for the future are the development of knowledge in market issues, wind power technology, environmental issues, and public opinion on constructing wind turbines.     

An improved dynamic solar collector test method for determination of non-linear optical and thermal characteristics with multiple regression

The objective is to characterise the solar collector during a relatively short testing period with no requirement for steady state climatic conditions. This information is then used for predicting annual performance of the collector. A standard collector model that is compatible with the ISO 9806-1 test standard is used with correction terms for beam and diffuse incidence angle modifiers, thermal capacitance, wind speed and sky temperature. This results in a more complete characterisation of the collector. The collector parameters are identified by multiple linear regression, MLR. The method has been tested for characterisation of unglazed collectors, glazed flat plate collectors, evacuated tubular collectors, CPC collectors and concentrating collectors with satisfying results. Typically the correlation coefficient R² is better than 0.99 and the standard deviation of the difference between model and measurement is in the range 3–10 W/m².

In the original method the angular dependence of the optical efficiency and the temperature dependence of the heat losses are supposed to be adjusted to a predetermined function. The most recent development is a routine that makes it possible to accurately identify non-linear optical and thermal performance. This extended MLR method can identify the zero loss efficiency for every angle of incidence interval and the temperature dependent heat losses for every temperature interval. This opens the application of the method to collectors with special incidence angle and heat loss effects that cannot be described easily with a combination of elementary functions. Instead a table of parameter values is determined, which is used directly in standard simulation programmes. This method will further increase the accuracy when comparing different collector designs. It has been used for comparing different glazings and for comparison with spectrophotometric measurements. It has also been used for analysing the heat loss factors for Teflon and honeycomb glazings. Since the total power output of the collector is less dependent on the heat loss coefficient than on the optical efficiency the scattering in this data is larger than for the incidence angle curves.

The reflectance of booster mirrors cannot be derived with the MLR-method with acceptable accuracy. The correlation between direct irradiance and irradiance from the reflector exhibit a very strong correlation. Instead the effective reflectance of the mirror can be estimated by comparison of the measured output with calculation by the complete collector and reflector model. This effective reflectance is not compatible with the specular reflectance obtained from spectrophotometric measurements caused by large differences in acceptance angles.

Standard multiple linear regression available in most spread sheet and statistical programs can be used for the parameter identification in the extended MLR-procedure. The identification takes only a few seconds. At the Älvkarleby Laboratory the test method is now used as a routine tool for the evaluation of new collector materials and designs. The Swedish National testing institute has evaluated the methods with the conclusion that they have a potential for being used in standardised collector testing.     

Influence of molecular tilt angle on the SHG response of pyroelectric liquid crystal polymers

Second harmonic generation in novel pyroelectric liquid crystal polymers (PLCP) made from a series binary mixtures, was studied using 1100 nm as the fundamental wavelength. The PLCPs were prepared by photo-polymerization of binary mixtures of two monomers which exhibit a smectic C^* phase, A2c (4″-(R)-(−)-2-[(10-acrylo-yloxy)decyl]oxy-3-nitrophenyl 4-{4′-[(11-acryloyloxy)-undecyloxy]phenyl}benzoate) and Alb (4″-((R)-(+)-2-octyloxy)-3″-nitrophenyl 4-(4′-(11-acryloyloxy)undecyloxy)-phenyl)-benzoate). The highest d₁₆ and d₂₃ coefficients were found to be in the range 0.65–0.8 pm/V, and differed depending on the detailed preparation of the sample. All cases of polymers formed from the chiral smectic C* phase showed an SHG-signal with no external field present, indicating that polar order became fixed. The SHG-signal was found to increase with the tilt angle of the FLC molecules.     

General longitudinal modeling of individual differences in experimental designs: A latent variable framework for analysis and power estimation.

The generality of latent variable modeling of individual differences in development over time is demonstrated with a particular emphasis on randomized intervention studies. First, a brief overview is given of biostatistical and psychometric approaches to repeated measures analysis. Second, the generality of the psychometric approach is indicated by some nonstandard models. Third, a multiple-population analysis approach is proposed for the estimation of treatment effects. The approach clearly describes the treatment effect as development that differs from normative, control-group development. This framework allows for interactions between treatment and initial status in their effects on development. Finally, an approach for the estimation of power to detect treatment effects in this framework is demonstrated. Illustrations of power calculations are carried out with artificial data, varying the sample sizes, number of timepoints, and treatment effect sizes. Real data are used to illustrate analysis strategies and power calculations. Further modeling extensions are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)