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<jats:title>Abstract</jats:title><jats:p>The detection of deep reflected S waves on Mars inferred a core size of 1,830 ± 40 km (ref. <jats:sup>1</jats:sup>), requiring light-element contents that are incompatible with experimental petrological constraints. This estimate assumes a compositionally homogeneous Martian mantle, at odds with recent measurements of anomalously slow propagating P waves diffracted along the core–mantle boundary<jats:sup>2</jats:sup>. An alternative hypothesis is that Mars’s mantle is heterogeneous as a consequence of an early magma ocean that solidified to form a basal layer enriched in iron and heat-producing elements. Such enrichment results in the formation of a molten silicate layer above the core, overlain by a partially molten layer<jats:sup>3</jats:sup>. Here we show that this structure is compatible with all geophysical data, notably (1) deep reflected and diffracted mantle seismic phases, (2) weak shear attenuation at seismic frequency and (3) Mars’s dissipative nature at Phobos tides. The core size in this scenario is 1,650 ± 20 km, implying a density of 6.5 g cm<jats:sup>−3</jats:sup>, 5–8% larger than previous seismic estimates, and can be explained by fewer, and less abundant, alloying light elements than previously required, in amounts compatible with experimental and cosmochemical constraints. Finally, the layered mantle structure requires external sources to generate the magnetic signatures recorded in Mars’s crust.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Microfluidics have enabled notable advances in molecular biology<jats:sup>1,2</jats:sup>, synthetic chemistry<jats:sup>3,4</jats:sup>, diagnostics<jats:sup>5,6</jats:sup> and tissue engineering<jats:sup>7</jats:sup>. However, there has long been a critical need in the field to manipulate fluids and suspended matter with the precision, modularity and scalability of electronic circuits<jats:sup>8–10</jats:sup>. Just as the electronic transistor enabled unprecedented advances in the automatic control of electricity on an electronic chip, a microfluidic analogue to the transistor could enable improvements in the automatic control of reagents, droplets and single cells on a microfluidic chip. Previous works on creating a microfluidic analogue to the electronic transistor<jats:sup>11–13</jats:sup> did not replicate the transistor’s saturation behaviour, and could not achieve proportional amplification<jats:sup>14</jats:sup>, which is fundamental to modern circuit design<jats:sup>15</jats:sup>. Here we exploit the fluidic phenomenon of flow limitation<jats:sup>16</jats:sup> to develop a microfluidic element capable of proportional amplification with flow–pressure characteristics completely analogous to the current–voltage characteristics of the electronic transistor. We then use this microfluidic transistor to directly translate fundamental electronic circuits into the fluidic domain, including the amplifier, regulator, level shifter, logic gate and latch. We also combine these building blocks to create more complex fluidic controllers, such as timers and clocks. Finally, we demonstrate a particle dispenser circuit that senses single suspended particles, performs signal processing and accordingly controls the movement of each particle in a deterministic fashion without electronics. By leveraging the vast repertoire of electronic circuit design, microfluidic-transistor-based circuits enable fluidic automatic controllers to manipulate liquids and single suspended particles for lab-on-a-chip platforms.</jats:p>