A differential microphone is described that has been designed to employ similar operating principles to that of the ears of the parasitoid fly, Ormia ochracea. The ears of this fly have been shown to be highly directional even though they are only about 1 mm across [R. N. Miles, D. Robert, and R. R. Hoy, J. Acoust. Soc. Am. 98, 3059–3070 (1995)]. Analyses of the mechanics of this biological system suggest novel approaches to the design of miniature directional microphones. Finite element analysis results for the acoustic resonse of a 1 mm by 2 mm silicon nitride microphone diaphragm are presented. The diaphragm responds to pressure gradients in a manner that is inspired by Ormia’s ears. Predicted results for the natural frequencies, mode shapes, frequency response and directivity of our design are shown to compare closely with measured data obtained for a prototype silicon nitride diaphragm. [Work supported by NIH and DARPA.]

Aberrant amino acid metabolism is a common event in obesity. Particularly, subjects with obesity are characterized by the excessive plasma kynurenine (Kyn). However, the primary source of Kyn and its impact on metabolic syndrome are yet to be fully addressed. Herein, we show that the overexpressed indoleamine 2,3-dioxygenase 1 (IDO1) in adipocytes predominantly contributes to the excessive Kyn, indicating a central role of adipocytes in Kyn metabolism. Depletion of Ido1 in adipocytes abrogates Kyn accumulation, protecting mice against obesity. Mechanistically, Kyn impairs lipid homeostasis in adipocytes via activating the aryl hydrocarbon receptor (AhR)/Signal transducer and activator of transcription 3 /interleukin-6 signaling. Genetic ablation of AhR in adipocytes abolishes the effect of Kyn. Moreover, supplementation of vitamin B6 ameliorated Kyn accumulation, protecting mice from obesity. Collectively, our data support that adipocytes are the primary source of increased circulating Kyn, while elimination of accumulated Kyn could be a viable strategy against obesity.

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