Porous polymeric films are promising materials for the production of ultralow-dielectric constant materials. A high porosity polyimide thin film was prepared via the phase separation of a polyimide precursor in an N,N-dimethylacetamide (solvent)/2-(diethylamino)ethyl methacrylate/photoinitiator system. A novel technique involving high-pressure CO 2 (5 MPa) gas injection was used to form CO 2 -2-(diethylamino)ethyl methacrylate zwitterion salt and induce the immediate phase separation and solvent droplet formation (within 60 s) of a wet precursor film on a metal substrate. The film was exposed to UV light through quartz windows for 30 s to polymerize the 2-(diethylamino)ethyl methacrylate while maintaining a constant CO 2 pressure. The cured thin film containing numerous pores with an average diameter of approximately 1 μm ± 1.0 μm was treated at 320 °C for 1 h under a continuous flow of nitrogen. The obtained film was 30 μm thick and exhibited pores with an average diameter of approximately 1 μm ± 0.9 μm. The ultralow-k level minimum relative dielectric constant for the optimal polyimide film was 1.536, and the porosity was 74% with open porous structure.
Our aim was to determine differences in thermal comfort during simulated one-day parcel
home delivery between summer and winter. Six young healthy males performed experiments in
summer (up to 31°C) and winter (up to 8°C). After baseline measurement in a chamber,
subjects drove a truck to a prespecified location for outside measurements. They performed
4 sets of 100-m walk with carrying 5-kg plate during the first 50-m walk at 100 m/min,
separated by 7-min driving in each of the morning and the afternoon. Subjects could ingest
water ad libitum in outside and set the cockpit temperature by themselves during driving.
Thermal sensation and comfort were recorded using a subjective scale at the first and the
last sets of each morning and afternoon session, while esophageal temperature
(Tes) was monitored (thermocouples). Body weight was measured before and the
end of experiment. We found that 1) whole-body comfort decreased in summer and the
decrease was greater than winter with higher Tes and 2) changes in body weight
were 0.7 and 0.3 kg through whole day in summer and winter, respectively. In summary,
thermal comfort during working worsened in summer, possibly related with higher core
temperature and greater decrease in body weight.
: Ground faults are major problems of power cable systems. Time-series data of voltage and current are available for diagnosis when a ground fault occurs. In the present work, a data-based fault diagnosis system of power cable systems was developed. In order to achieve the high fault diagnosis performance, new feature variables were generated by using wavelet analysis and cepstrum analysis. In addition, six classification techniques, i.e., k-nearest neighbor (k-NN), artificial neural network (ANN), boosted ANN (B-ANN), random forest (RF), classification and regression trees (CART), and boosted CART (B-CART), were compared. B-ANN and B-CART were combined with the naive Bayes classifier to cope with multiclass problems. The results of applying the proposed methods to real ground fault data show that B-ANN and B-CART with the naive Bayes classifier can achieve the best diagnosis performance, which satisfies the requirement for its industrial application.
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