Bulk energy storage potential in the USA, current developments and future prospects

Stored energy can provide electricity during periods of high demand, as currently demonstrated with bulk storage systems such as pumped hydro storage (PHS), which accounts for only 2.5% of the current installed base load in the USA. Sites for future developments have become less available, and environmental siting issues, as well as high costs have stopped further prospects. This paper looks at the potential beyond PHS, with bulk storage systems such as compressed air energy storage (CAES) flow-batteries and 1 MW flywheel systems that can provide system stability/support at the grid, substations and distributed level. Current developments in bulk energy storage will be reviewed as well as some storage project developments incorporating wind energy and the impact on base-loaded coal and natural gas fired GT combined cycle plants. The large potential and the economic benefits for energy storage in the US will be examined.     

Antimicrobial activities of beta-lactam antibiotics and gentamicin against penicillin-susceptible and penicillin-resistant pneumococci

The MICs of penicillin and cefotaxime for a range of penicillin-susceptible and penicillin-resistant isolates of Streptococcus pneumoniae were unchanged by the addition of gentamicin. In time-kill studies the rate of killing was greater for 18 of 20 isolates in the presence of gentamicin. However, mean differences in killing after 6 h of incubation were modest, not exceeding 1 log10 unit.     

Psychosocial correlates of chronic fatigue syndrome in adolescent girls

Behavior problems and family functioning were investigated in a sample of 10 adolescent girls with chronic fatigue syndrome (CFS), 10 matched healthy adolescent girls, and 10 adolescents with childhood cancer in remission. Based on the adolescent girls' reports, the CFS group had significantly higher scores than the cancer and healthy comparison adolescent girls on somatic complaints and also significantly higher scores than the cancer controls on internalizing symptoms and depression. Parent reports resulted in significantly higher scores in the CFS group than the adolescent girls from the healthy comparison groups on internalizing scores and somatic complaints. There were no significant differences on any family variables.     

Simulation and Experimental Study of a Reactively Loaded PWM Converter as a Fast Source of Reactive Power

The question of eliminating distorted current waveforms from power networks by active power filters is investigated. If the active current is subtracted from the distorted current, the compensating equipment must be capable of generating the inverse of this difference. Addition of this compensating current to the distorted current then eliminates the distortion. This requires the capability to generate these currents with response times many times less than the fundamental power frequency cycle. This capability is presented by reactively loaded PWM converters. A system configuration with three single-phase PWM converters building a three-phase unit is investigated. The single-phase converter with PWM operation, inductive reactance as load, low-pass input filter, and representative system losses is simulated by state-space techniques. An experimental system of 1 kVA is also constructed for verification. Good correspondence between the simulation and experiment s shown. Starting up the system, compensating the system losses from the supply, and the influence of the control system on the compensating capabilities are investigated. It is concluded that a PWM converter with a reactive load can be used as a fast distortion compensator and that the present state of the art and future development of PWM converter technology will make this technique applicable at least up to 1 Mvar.