Non-isolated resonant link DC-DC converter for use with GaN devices

As new wide band-gap (WBG) devices are developed and improved, new topologies and control schemes are required to take advantage of the ultra-fast switching turn on/off speeds that are now available, without the limitations of switching losses and unacceptable EMI from fast switching transitions. This paper presents a non-isolated DC-DC resonant link converter that allows for soft switching over an extended load range that is particularly suited to GaN devices

Fossilized skin reveals coevolution with feathers and metabolism in feathered dinosaurs and early birds

Feathers are remarkable evolutionary innovations that are associated with complex adaptations of the skin in modern birds. Fossilised feathers in non-avian dinosaurs and basal birds provide insights into feather evolution, but how associated integumentary adaptations evolved is unclear. Here we report the discovery of fossil skin, preserved with remarkable nanoscale fidelity, in three non-avian maniraptoran dinosaurs and a basal bird from the Cretaceous Jehol biota (China). The skin comprises patches of desquamating epidermal corneocytes that preserve a cytoskeletal array of helically coiled α-keratin tonofibrils. This structure confirms that basal birds and non-avian dinosaurs shed small epidermal flakes as in modern mammals and birds, but structural differences imply that these Cretaceous taxa had lower body heat production than modern birds. Feathered epidermis acquired many, but not all, anatomically modern attributes close to the base of the Maniraptora by the Middle Jurassic

Fossilization of melanosomes via sulfurization

Fossil melanin granules (melanosomes) are an important resource for inferring the evolutionary history of colour and its functions in animals. The taphonomy of melanin and melanosomes, however, is incompletely understood. In particular, the chemical processes responsible for melanosome preservation have not been investigated. As a result, the origins of sulfur‐bearing compounds in fossil melanosomes are difficult to resolve. This has implications for interpretations of original colour in fossils based on potential sulfur‐rich phaeomelanosomes. Here we use pyrolysis gas chromatography mass spectrometry (Py‐GCMS), fourier transform infrared spectroscopy (FTIR) and time of flight secondary ion mass spectrometry (ToF‐SIMS) to assess the mode of preservation of fossil microstructures, confirmed as melanosomes based on the presence of melanin, preserved in frogs from the Late Miocene Libros biota (NE Spain). Our results reveal a high abundance of organosulfur compounds and non‐sulfurized fatty acid methyl esters in both the fossil tissues and host sediment; chemical signatures in the fossil tissues are inconsistent with preservation of phaeomelanin. Our results reflect preservation via the diagenetic incorporation of sulfur, i.e. sulfurization (natural vulcanization), and other polymerization processes. Organosulfur compounds and/or elevated concentrations of sulfur have been reported from melanosomes preserved in various invertebrate and vertebrate fossils and depositional settings, suggesting that preservation through sulfurization is likely to be widespread. Future studies of sulfur‐rich fossil melanosomes require that the geochemistry of the host sediment is tested for evidence of sulfurization in order to constrain interpretations of potential phaeomelanosomes and thus of original integumentary colour in fossils

Trifluoroacetic Acid::Toxicity, Sources, Sinks and Future Prospects

Trifluoroacetic acid (TFA) is a known persistent pollutant in the environment. Although several direct anthropogenic sources exist, production from the atmospheric degradation of fluorocarbons such as some hydrofluorocarbons (HFCs) has been a known source for some time. The current transition from HFCs to HFOs (hydrofluoroolefins) is beneficial from a global warming viewpoint, because HFOs are much shorter-lived and pose a much smaller threat to warming, but the fraction of HFO conversion to TFA is higher than for the corresponding HFCs and the region over which the TFA is produced is close to the source. Therefore, it is timely to review the role of TFA in the Earth’s environment. This review considers its toxicity, sources and removal processes, measurements in a variety of environments and future prospects. New global model integrations quantify the impacts on TFA levels of uncertainties in the Henry’s Law constant for TFA and the range of gas-phase kinetic parameters determined for the reaction of OH radicals with a representative HFO (HFO-1234yf). Model runs suggest that TFA surface concentrations vary by up to 10% based on Henry’s Law data, but could be up to 25% smaller than previously modelled values depending on the kinetic analysis adopted. Therefore, future estimates of TFA surface concentrations based on HFO removal re-quire updating and the kinetic analysis of TFA production warrants further investigation. The toxicity of TFA appears to be low but further studies of a much wider range of animal and plant types are required