Design of high-efficiency series-resonant converters aboveresonance

Power losses in series-resonant converters (SRCs) operated above resonance are examined for the purpose of developing design guidelines leading to SRC designs with the highest possible operating efficiencies. Loss expressions are formulated and analyzed as functions of normalized voltage conversion ratio M and normalized output current J for the controlled transistor switches, antiparallel diodes, bridge diodes, and resonant capacitor. Overall losses range from a low of nearly 9% to a maximum of about 17%. Operating efficiencies corresponding to these losses range from a high of 92% to a low of 85%. Operation at the maximum efficiency of 92% occurs at values of M close to unity and is not highly dependent on J. However, in a practical closed-loop regulated SRC, operation with M too close to unity could provide an insufficient design margin, given component tolerances or other variations     

Chicxulub and climate: radiative perturbations of impact-produced S-bearing gases

We use one-dimensional (1D) atmospheric models coupled to a sulfate aerosol model to investigate climate forcing and short-term response to stratospheric sulfate aerosols produced by the reaction of S-bearing gases and water vapor released in the Chicxulub impact event. A 1D radiation model is used to assess the climate forcing due to the impact-related loading of S-bearing gases. The model suggests that a climate forcing 100 times larger than that from the Pinatubo volcanic eruption is associated with the Chicxulub impact event for at least 2 years after the impact. In particular, we find a saturation effect in the forcing, that is, there is no significant difference in the maximum forcing between the highest (approximately 300 Gt) and lowest (approximately 30 Gt) estimated stratospheric S-loading from the Chicxulub impact. However, higher S-loads increase the overall duration of the forcing by several months. We use a single column model for a preliminary investigation of the short-term climate response to the impact-related production of sulfate aerosols (the lack of horizontal feedbacks limits the usefulness of the single column model to the first few days after the impact). Compared with the present steady-state climate, the introduction of large amounts of sulfate aerosols in the stratosphere results in a significant cooling of the Earth's surface. A long-term climate response can only be investigated with the use of a three-dimensional atmospheric model, which allows for the atmospheric circulation to adjust to the perturbation. Overall, although the climate perturbation to the forcing appears to be relatively large, the geologic record shows no sign of a significant long-term climatic shift across the K/T boundary, which is indicative of a fast post-impact climatic recovery.