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The two most common types of supply for mass transit systems are 1.5 kV dc and 25 kV ac. This paper will firstly brief the relative merits of dc and ac traction systems. As the ac traction system is of single phase, imbalance in three-phase supply is inevitable and is an universal problem. With reference to the local 25 kV traction system, the paper will assess the degree of imbalances and the corresponding impacts at different phase connection scenarios. Cost-effective and pragmatic measures to reduce degree of imbalance by minor but appropriate modification of existing phase connections of traction transformers 132 kV will be proposed in this paper. Consequently, generation performance and efficiency are improved, unnecessary fuel consumption is reduced as much as possible, and the extra cost imposed to consumers at large would also be reduced.

ABSTRACTThis study presents an analytical model for describing propagation of Rayleigh waves along the impermeable surface of an unsaturated poroelastic half-space. This model is based on the existence of the three modes of dilatational waves which employ the poroelastic equations developed for a porous medium containing two immiscible viscous compressible fluids (Lo, Sposito and Majer, [13]). In a two-fluid saturated medium, the three Rayleigh waves induced by the three dilatational waves can be expressed as R1, R2, and R3 waves in descending order of phase speed magnitude. As the excitation frequency and water saturation are given, the dispersion equation of a cubic polynomial can be solved numerically to obtain the phase speeds and attenuation coefficients of the R1, R2, and R3 waves. The numerical results show the phase speed of the R1 wave is frequency independent (non-dispersive). Comparatively, the R1 wave speed is 93 ∼ 95% of the shear wave speed, and 28% to 49% of the first dilatational wave speed for selected frequencies between 50Hz & 200Hz and relative water saturation ranging from 0.01 to 0.99. However, the R2 and R3 waves are dispersive at the frequencies examined. The ratios of R2 and R3 wave phase speeds to the second and third dilatational wave speeds fall between 56% and 90%. The R1 wave attenuates the least while the R3 wave has the highest attenuation coefficient. Furthermore, the phase speed of the R1 wave under an impermeable surface approaches 1.01 ∼ 1.37 times of the R1 wave under a permeable boundary. Impermeability has significant influence on the phase speeds and attenuation coefficients of the R1 and R2 waves at high water saturation due to the existence of confined fluids.

De novo antimicrobial peptides with the sequences:  (KLAKKLA)n, (KLAKLAK)n (where n = 1, 2, 3), (KALKALK)3, (KLGKKLG)n, and (KAAKKAA)n (where n = 2, 3), were prepared as the C-terminus amides. These peptides were designed to be perfectly amphipathic in helical conformations. Peptide antibacterial activity was tested against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. Peptide cytotoxicity was tested against human erythrocytes and 3T3 mouse fibroblasts. The 3T3 cell testing was a much more sensitive test of cytotoxicity. The peptides were much less lytic toward human erythrocytes than 3T3 cells. Peptide secondary structure in aqueous solution, sodium dodecylsulfate micelles, and phospholipid vesicles was estimated using circular dichroism spectroscopy. The leucine/alanine-containing 21-mers were bacteriostatic at 3−8 μM and cytotoxic to 3T3 cells at about 10 μM concentrations. The leucine/alanine- or leucine/glycine-containing 14-mers and the leucine/glycine 21-mer were bacteriostatic at 6−22 μM but had much lower cytotoxicity toward 3T3 cells and higher selectivities than the natural antimicrobial peptides magainin 2 amide and cecropin B amide. The 7-mer peptides are devoid of biological activity and of secondary structure in membrane mimetic environments. The 14-mer peptides and the glycine-containing 21-mer show modest levels of helicity in model membranes. The leucine/alanine-containing 21-mer peptides have substantial helicity in model membranes. The propensity to α-helical conformation of the peptides in amphipathic media is proportional to their 3T3 cell cytotoxicity.

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