A humidity generator with a test chamber system

For the calibration of relative humidity hygrometers and dew-point hygrometers with an open sensor, a test chamber system was constructed and connected to a dew-point generator. The system includes several small chambers connected in series. By reversing the flow direction, humidity and temperature gradients in the test chamber system are monitored during calibration measurements. This paper reports the construction of the test chamber system and the improvements in the construction and the analysis of the dew-point generator. A full uncertainty analysis is presented. The expanded uncertainty of the dew-point temperature and the relative humidity with the coverage factor k=2 are from ±0.05°C to ±0.08°C and from ±0.1%rh to ±1.0%rh, respectively. Although the dew-point temperature range is from −40°C to +77°C, the limits for the temperature range of the test chamber system are −20°C and +60°C. The system was not tested with relative humidity values lower than 10% or higher than 95%.     

Improved description of base dynamics in the modelling of bipolar transistors

An improved non-linear high-frequency model for the bipolar transistor is presented, based on considerations of the dynamics of the charge stored in the base region. the model incorporates higher-order circuit elements in order to obtain increased accuracy in circuit simulation at high frequencies. the model is derived from device physics by solving the diffusion equation in the base region by means of a quasi-static expansion. the result is a more accurate circuit representation, which can be added to existing bipolar transistor models. Simulation examples are given and the possible convergence problems associated with the model are discussed.     

Compressibility of porous TiO2 nanoparticle coating on paperboard

Compressibility of liquid flame spray-deposited porous TiO₂ nanoparticle coating was studied on paperboard samples using a traditional calendering technique in which the paperboard is compressed between a metal and polymer roll. Surface superhydrophobicity is lost due to a smoothening effect when the number of successive calendering cycles is increased. Field emission scanning electron microscope surface and cross‒sectional images support the atomic force microscope roughness analysis that shows a significant compressibility of the deposited TiO₂ nanoparticle coating with decrease in the surface roughness and nanoscale porosity under external pressure.

PACS

61.46.-w; 68.08.Bc; 81.07.-b     

Investigations of the effects of temperature and initial sample pH on natural organic matter (NOM) removal with electrocoagulation using response surface method (RSM)

The removal of natural organic matter (NOM) from surface water by electrocoagulation (EC) was studied using response surface method (RSM). Factors used in the empirical model were electric charge per liter, initial pH and temperature. Relevant square and interaction terms of factors were studied. Based on analysis of variance (ANOVA), the model fitted well with dissolved organic carbon (DOC) reduction, aluminum dissolving and pH changes. UV 254 nm absorbance removal was moderately predicted. According to results, temperature affected significantly the dissolving rate of aluminum electrodes. Initial DOC concentration of the surface water was 18.35 mg/l. Maximum DOC removal of 80.4% was obtained when high electric charge per liter (144 C/l), low pH (4.3) and high temperature (295.15 K) were used. However, high DOC removal of 76.2% was predicted also when water temperature was only 275.15 K. Effect of temperature on NOM removal was minor as compared to the effects of electric charge per volume and the initial pH. EC neutralized pH during the EC treatment and had little impact on the conductivity of the water. According to the results, EC can be used for NOM removal during cold water period in Nordic countries.