The associations of indoor environment and psychosocial factors on the subjective evaluation of Indoor Air Quality among lower secondary school students: a multilevel analysis

Subjective evaluation of Indoor Air Quality (subjective IAQ) reflects both building‐related and psychosocial factors, but their associations have rarely been studied other than on the individual level in occupational settings and their interactions have not been assessed. Therefore, we studied whether schools’ observed indoor air problems and psychosocial factors are associated with subjective IAQ and their potential interactions. The analysis was performed with a nationwide sample (N = 195 schools/26946 students) using multilevel modeling. Two datasets were merged: (i) survey data from students, including information on schools’ psychosocial environment and subjective IAQ, and (ii) data from school principals, including information on observed indoor air problems. On the student level, school‐related stress, poor teacher–student relationship, and whether the student did not easily receive help from school personnel, were significantly associated with poor subjective IAQ. On the school level, observed indoor air problem (standardized β = ?0.43) and poor teacher–student relationship (standardized β = ?0.22) were significant predictors of poor subjective IAQ. In addition, school‐related stress was associated with poor subjective IAQ, but only in schools without observed indoor air problem (standardized β = ?0.44).     

Spontaneous fracture of growing precipitates with large misfit strain

Precipitates that form as a result of phase transformation are studied with regard to mechanical behaviour and initiation of internal cracks. The focus is on precipitates occupying a larger volume than the surrounding matrix. Further the study is restricted to precipitates growing by incorporating material transformed from being matrix material to the phase of the precipitate. The phase transformation is here treated as a simple homogeneous swelling. The classical solutions for expanding inclusions predict that the inclusion becomes subjected to a constant homogeneous hydrostatic compression. During the process analysed here, added transformed material progressively relieve the compressive stress in the interior of the precipitate. As the process continues the stresses change from compression to tension in both radial and tangential directions in the centre of the precipitate. Further, growth of cracks in precipitates with poor fracture mechanical properties are studied. To simplify the analysis it is assumed that the fracture toughness is insignificant. The prediction is that around a third of the precipitate will fracture. The presence of a crack only has an insignificant effect on the load exerted by the swelling precipitate on the matrix.     

Assessment of mill lifter bar deflection measurements using wavelets and discrete element methods

This paper shows how Partial Least Square Regression (PLS) methods can be used to model sensor data of spectral character. The modelling approach has been applied on a tumbling mill where a strain gauge sensor measures the deflection of a lifter bar when it hits the charge. The deflection of the lifter bar during every mill revolution gives rise to a characteristic signal profile that is shown to contain information on both the charge position and grinding performance. As a signal pre-processing method the discrete wavelet transform is used. It distinctly shows a capability of signal feature extraction where both time and frequency are of interest. Its well-known ability to achieve good data compression without loss of information is also demonstrated, a data reduction ratio of 20:1 is obtained here. Modelling results demonstrate that different operating conditions are well distinguishable from each other and by that the finding of proper operating regimes are highly feasible. Grinding parameters that are normally measured in the laboratory are now readily modelled from the on-line signal. A further objective of this paper is to link the experimentally obtained strain gauge sensor data with computational data from a discrete element mill model (DEM). This enables to visualise the charge motion and helps to interpret the complex phenomena that take place inside a grinding mill measured by the strain gauge sensor. The approach taken is to simulate the behaviour of a rubber lifter when it is exposed to forces from the grinding charge in a two-dimensional DEM mill model using a particle flow code. The deflection profile obtained from the DEM simulation shows a reasonably good correspondence to pilot mill measurements.     

Characteristics of Ti‐Ce Complex Deoxidation Products in a Fe‐20mass%Cr Alloy

The particle characteristics such as size distribution, composition and morphology have been studied in an Fe‐20mass%Cr alloy as a function of holding time at 1600°C. The alloy was deoxidised with Ti and Ce, followed by holding at 1600°C and cooling to 1400°C and quenching. The inclusion particles were investigated on a surface of film filter with an open pore size of 0.05 or 5 μm after electrolytic extraction of the metal samples. Different electric charge and electrolytes (2%TEA and 10%AA) were compared for extraction of the Fe‐20mass%Cr alloy. 300 Coulombs with 10%AA was found most suitable for the electrolytic extraction of particles to determine the particle composition and size distribution. Most of the particles were found to be complex oxides containing Ti, Ce and Cr. Furthermore, the composition of the particles was found to change from a high Ce‐content to a high Cr‐content with longer holding time at 1600°C.     

Non-prejudiced Detection and Characterization of Genetic Modifications

The application of gene technology is becoming widespread much thanks to the rapid increase in technology, resource, and knowledge availability. Consequently, the diversity and number of genetically modified organisms (GMOs) that may find their way into the food chain or the environment, intended or unintended, is rapidly growing. From a safety point of view the ability to detect and characterize in detail any GMO, independent of publicly available information, is fundamental. Pre-release risk assessments of GMOs are required in most jurisdictions and are usually based on application of technologies with limited ability to detect unexpected rearrangements and insertions. We present an array-based approach to address these problems and show with three examples (GTS 40-3-2 Roundup Ready and event A5547-127 soybean as well as T25 Liberty Link Maize) that the method can detect and characterize GMOs with high accuracy while making very few prior assumptions about the actual genetic modifications or constructs in question. Based on the array results, a simple polymerase chain reaction-scheme is also described that will enable the user to characterize the inserted sequences to DNA sequence level. The method may provide the biotechnology developers and risk regulators with a useful tool to improve pre-market risk assessments as well as seed producers and other food chain and environmental stakeholders with a platform to improve their ability to detect and characterize GMOs.     

Investigation of Chocolate Surfaces Using Profilometry and Low Vacuum Scanning Electron Microscopy

In this study we establish the use of optical non-contact profilometry combined with low vacuum scanning electron microscopy (LV SEM) for the investigation of lipid surfaces. We illustrate, by using profilometry, a methodology for investigation of chocolate surface topology as a function of time, in the same area of interest. Both qualitative and quantitative data analysis has been performed for profilometry data. Further, relating these results to LV SEM images provides complementary topological information and hence a useful toolkit for the study of the chocolate surface prior and post fat bloom formation. For the demonstration of the successful combination of these two analytical techniques, white chocolate pralines were stored at two temperature-controlled conditions (at 18 °C, and cycled between 15 and 25 °C). Surface properties were then investigated during 36 weeks of storage. The surface images and the roughness parameters indicated distinct development of surface characteristics for the two storage conditions. From the results it is suggested that some imperfections, in the form of pores or protrusions, could play a role in fat bloom development and that there may be different main mechanisms of fat migration taking place for the different storage environments. In the present work, a positive correlation of profilometry data to chocolate surface characteristics and early bloom development has been established. There are indications that early prediction of fat bloom can be possible, however further work needs to be done to quantify prediction of fat bloom.     

Thermodynamic evolution of unsaturated polyester-styrene-hyperbranched polymers

Summary The free energy of mixing during cure has been modeled for different blends of linear unsaturated polyester, styrene and allyl ether functional hyperbranched polymers. The molecular weight of the blend components has been implemented as measured by gel permeation chromatography (GPC) into the Flory-Huggins equation. This approach enables the distinction to be made between the contributions of enthalpy and entropy of mixing, the latter being automatically followed during curing by the development of average molecular weights. The model allows gaining an idea of the factors acting as driving forces for chemically induced phase separation in these blends. Received: 24 January 2001/Revised version: 26 April 2001/Accepted: 6 May 2001