ISSN / EISSN : 0193-4511 / 1095-9203
Published by: American Association for the Advancement of Science (AAAS) (10.1126)
Total articles ≅ 274,920
Latest articles in this journal
Science, Volume 373, pp 405.1-405; doi:10.1126/science.373.6553.405-a
Science, Volume 373; doi:10.1126/science.abd0830
The ability to perceive and respond to environmental stimuli emerges in the absence of sensory experience. Spontaneous retinal activity prior to eye opening guides the refinement of retinotopy and eye-specific segregation in mammals, but its role in the development of higher-order visual response properties remains unclear. Here, we describe a transient window in neonatal mouse development during which the spatial propagation of spontaneous retinal waves resembles the optic flow pattern generated by forward self-motion. We show that wave directionality requires the same circuit components that form the adult direction-selective retinal circuit and that chronic disruption of wave directionality alters the development of direction-selective responses of superior colliculus neurons. These data demonstrate how the developing visual system patterns spontaneous activity to simulate ethologically relevant features of the external world and thereby instruct self-organization.
Science, Volume 373, pp 406.4-407; doi:10.1126/science.373.6553.406-d
Science, Volume 373, pp 403.2-404; doi:10.1126/science.abk1981
Science, Volume 373, pp 403.1-403; doi:10.1126/science.abk1312
Science, Volume 373; doi:10.1126/science.abe6729
The biogenesis of high-density lipoprotein (HDL) requires apoA1 and the cholesterol transporter ABCA1. Although the liver generates most of the HDL in the blood, HDL synthesis also occurs in the small intestine. Here, we show that intestine-derived HDL traverses the portal vein in the HDL3 subspecies form, in complex with lipopolysaccharide (LPS)–binding protein (LBP). HDL3, but not HDL2 or low-density lipoprotein, prevented LPS binding to and inflammatory activation of liver macrophages and instead supported extracellular inactivation of LPS. In mouse models involving surgical, dietary, or alcoholic intestinal insult, loss of intestine-derived HDL worsened liver injury, whereas outcomes were improved by therapeutics that elevated and depended upon raising intestinal HDL. Thus, protection of the liver from injury in response to gut-derived LPS is a major function of intestinally synthesized HDL.
Science, Volume 373, pp 438-443; doi:10.1126/science.abf8966
A planet’s crust bears witness to the history of planetary formation and evolution, but for Mars, no absolute measurement of crustal thickness has been available. Here, we determine the structure of the crust beneath the InSight landing site on Mars using both marsquake recordings and the ambient wavefield. By analyzing seismic phases that are reflected and converted at subsurface interfaces, we find that the observations are consistent with models with at least two and possibly three interfaces. If the second interface is the boundary of the crust, the thickness is 20 ± 5 kilometers, whereas if the third interface is the boundary, the thickness is 39 ± 8 kilometers. Global maps of gravity and topography allow extrapolation of this point measurement to the whole planet, showing that the average thickness of the martian crust lies between 24 and 72 kilometers. Independent bulk composition and geodynamic constraints show that the thicker model is consistent with the abundances of crustal heat-producing elements observed for the shallow surface, whereas the thinner model requires greater concentration at depth.
Published: 15 July 2021
The thermal conductivity of crystalline materials cannot be arbitrarily low as the intrinsic limit depends on the phonon dispersion. We used complementary strategies to suppress the contribution of the longitudinal and transverse phonons to heat transport in layered materials containing different types of intrinsic chemical interface. BiOCl and Bi2O2Se encapsulate these design principles for longitudinal and transverse modes respectively, and the bulk superlattice material Bi4O4SeCl2 combines these effects by ordering both interface types within its unit cell to reach an extremely low thermal conductivity of 0.1 W K−1 m−1 at room temperature along its stacking direction. This value comes within a factor of four of air. We demonstrated that chemical control of the spatial arrangement of distinct interfaces can synergically modify vibrational modes to minimize thermal conductivity.
Published: 15 July 2021
Artificial spin ices are frustrated spin systems that can be engineered, wherein fine tuning of geometry and topology has allowed the design and characterization of exotic emergent phenomena at the constituent level. Here we report a realization of spin ice in a lattice of superconducting qubits. Unlike conventional artificial spin ice, our system is disordered by both quantum and thermal fluctuations. The ground state is classically described by the ice rule, and we achieve control over a fragile degeneracy point leading to a Coulomb phase. The ability to pin individual spins allows us to demonstrate Gauss's law for emergent effective monopoles in two dimensions. The demonstrated qubit control lays the groundwork for potential future study of topologically protected artificial quantum spin liquids.
Published: 12 July 2021