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Coronapod: the latest on COVID and sporting events

Nature - issue - So, 07/24/2021 - 00:00

Nature, Published online: 24 July 2021; doi:10.1038/d41586-021-02053-0

As the Olympics kick off, data on the impact of large sporting events is still limited, despite large research efforts

Toxic mercury rides rivers into the sea

Nature - issue - Pá, 07/23/2021 - 00:00

Nature, Published online: 23 July 2021; doi:10.1038/d41586-021-02026-3

Research suggests that rivers are a bigger source of mercury in coastal waters than is the atmosphere — a finding that contradicts some global models.

Single chip tests thousands of enzyme mutations at once

Nature - issue - Pá, 07/23/2021 - 00:00

Nature, Published online: 23 July 2021; doi:10.1038/d41586-021-02034-3

The technique vastly speeds up understanding of how the proteins function and how to target drugs.

NASA investigates renaming James Webb telescope after anti-LGBT+ claims

Nature - issue - Pá, 07/23/2021 - 00:00

Nature, Published online: 23 July 2021; doi:10.1038/d41586-021-02010-x

Some astronomers argue the flagship observatory — successor to the Hubble Space Telescope — will memorialize discrimination. Others are waiting for more evidence.

Bullying and harassment are rife in astronomy, poll suggests

Nature - issue - Pá, 07/23/2021 - 00:00

Nature, Published online: 23 July 2021; doi:10.1038/d41586-021-02024-5

Nearly half of researchers surveyed in the United Kingdom and elsewhere reported problems, with people from marginalized groups most likely to be mistreated.

The lessons I learnt supervising master’s students for the first time

Nature - issue - Pá, 07/23/2021 - 00:00

Nature, Published online: 23 July 2021; doi:10.1038/d41586-021-02028-1

PhD student Emilio Dorigatti supported three junior colleagues during their degrees.

China’s space station is preparing to host 1,000 scientific experiments

Nature - issue - Pá, 07/23/2021 - 00:00

Nature, Published online: 23 July 2021; doi:10.1038/d41586-021-02018-3

Researchers around the world are eagerly awaiting the completion of Tiangong, to study topics from dark matter and gravitational waves to the growth of cancer and pathogenic bacteria.

Coherent manipulation of an Andreev spin qubit

Science - issue - Čt, 07/22/2021 - 19:41

Two promising architectures for solid-state quantum information processing are based on electron spins electrostatically confined in semiconductor quantum dots and the collective electrodynamic modes of superconducting circuits. Superconducting electrodynamic qubits involve macroscopic numbers of electrons and offer the advantage of larger coupling, whereas semiconductor spin qubits involve individual electrons trapped in microscopic volumes but are more difficult to link. We combined beneficial aspects of both platforms in the Andreev spin qubit: the spin degree of freedom of an electronic quasiparticle trapped in the supercurrent-carrying Andreev levels of a Josephson semiconductor nanowire. We performed coherent spin manipulation by combining single-shot circuit–quantum-electrodynamics readout and spin-flipping Raman transitions and found a spin-flip time TS = 17 microseconds and a spin coherence time T2E = 52 nanoseconds. These results herald a regime of supercurrent-mediated coherent spin-photon coupling at the single-quantum level.

Upper mantle structure of Mars from InSight seismic data

Science - issue - Čt, 07/22/2021 - 19:41

For 2 years, the InSight lander has been recording seismic data on Mars that are vital to constrain the structure and thermochemical state of the planet. We used observations of direct (P and S) and surface-reflected (PP, PPP, SS, and SSS) body-wave phases from eight low-frequency marsquakes to constrain the interior structure to a depth of 800 kilometers. We found a structure compatible with a low-velocity zone associated with a thermal lithosphere much thicker than on Earth that is possibly related to a weak S-wave shadow zone at teleseismic distances. By combining the seismic constraints with geodynamic models, we predict that, relative to the primitive mantle, the crust is more enriched in heat-producing elements by a factor of 13 to 20. This enrichment is greater than suggested by gamma-ray surface mapping and has a moderate-to-elevated surface heat flow.

Thickness and structure of the martian crust from InSight seismic data

Science - issue - Čt, 07/22/2021 - 19:41

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.

Seismic detection of the martian core

Science - issue - Čt, 07/22/2021 - 19:41

Clues to a planet’s geologic history are contained in its interior structure, particularly its core. We detected reflections of seismic waves from the core-mantle boundary of Mars using InSight seismic data and inverted these together with geodetic data to constrain the radius of the liquid metal core to 1830 ± 40 kilometers. The large core implies a martian mantle mineralogically similar to the terrestrial upper mantle and transition zone but differing from Earth by not having a bridgmanite-dominated lower mantle. We inferred a mean core density of 5.7 to 6.3 grams per cubic centimeter, which requires a substantial complement of light elements dissolved in the iron-nickel core. The seismic core shadow as seen from InSight’s location covers half the surface of Mars, including the majority of potentially active regions—e.g., Tharsis—possibly limiting the number of detectable marsquakes.

Inhibited nonradiative decay at all exciton densities in monolayer semiconductors

Science - issue - Čt, 07/22/2021 - 19:41

Most optoelectronic devices operate at high photocarrier densities, where all semiconductors suffer from enhanced nonradiative recombination. Nonradiative processes proportionately reduce photoluminescence (PL) quantum yield (QY), a performance metric that directly dictates the maximum device efficiency. Although transition metal dichalcogenide (TMDC) monolayers exhibit near-unity PL QY at low exciton densities, nonradiative exciton-exciton annihilation (EEA) enhanced by van-Hove singularity (VHS) rapidly degrades their PL QY at high exciton densities and limits their utility in practical applications. Here, by applying small mechanical strain (less than 1%), we circumvented VHS resonance and markedly suppressed EEA in monolayer TMDCs, resulting in near-unity PL QY at all exciton densities despite the presence of a high native defect density. Our findings can enable light-emitting devices that retain high efficiency at all brightness levels.

Atomically resolved single-molecule triplet quenching

Science - issue - Čt, 07/22/2021 - 19:41

The nonequilibrium triplet state of molecules plays an important role in photocatalysis, organic photovoltaics, and photodynamic therapy. We report the direct measurement of the triplet lifetime of an individual pentacene molecule on an insulating surface with atomic resolution by introducing an electronic pump-probe method in atomic force microscopy. Strong quenching of the triplet lifetime is observed if oxygen molecules are coadsorbed in close proximity. By means of single-molecule manipulation techniques, different arrangements with oxygen molecules were created and characterized with atomic precision, allowing for the direct correlation of molecular arrangements with the lifetime of the quenched triplet. Such electrical addressing of long-lived triplets of single molecules, combined with atomic-scale manipulation, offers previously unexplored routes to control and study local spin-spin interactions.

Innovation and geographic spread of a complex foraging culture in an urban parrot

Science - issue - Čt, 07/22/2021 - 19:41

The emergence, spread, and establishment of innovations within cultures can promote adaptive responses to anthropogenic change. We describe a putative case of the development of a cultural adaptation to urban environments: opening of household waste bins by wild sulphur-crested cockatoos. A spatial network analysis of community science reports revealed the geographic spread of bin opening from three suburbs to 44 in Sydney, Australia, by means of social learning. Analysis of 160 direct observations revealed individual styles and site-specific differences. We describe a full pathway from the spread of innovation to emergence of geographic variation, evidencing foraging cultures in parrots and indicating the existence of cultural complexity in parrots. Bin opening is directly linked to human-provided opportunities, highlighting the potential for culture to facilitate behavioral responses to anthropogenic change.

For those we've lost

Science - issue - Čt, 07/22/2021 - 19:41

Retinal waves prime visual motion detection by simulating future optic flow

Science - issue - Čt, 07/22/2021 - 19:41

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.

Enterically derived high-density lipoprotein restrains liver injury through the portal vein

Science - issue - Čt, 07/22/2021 - 19:41

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.

Skull and vertebral bone marrow are myeloid cell reservoirs for the meninges and CNS parenchyma

Science - issue - Čt, 07/22/2021 - 19:41

The meninges are a membranous structure enveloping the central nervous system (CNS) that host a rich repertoire of immune cells mediating CNS immune surveillance. Here, we report that the mouse meninges contain a pool of monocytes and neutrophils supplied not from the blood but by adjacent skull and vertebral bone marrow. Under pathological conditions, including spinal cord injury and neuroinflammation, CNS-infiltrating myeloid cells can originate from brain borders and display transcriptional signatures distinct from their blood-derived counterparts. Thus, CNS borders are populated by myeloid cells from adjacent bone marrow niches, strategically placed to supply innate immune cells under homeostatic and pathological conditions. These findings call for a reinterpretation of immune-cell infiltration into the CNS during injury and autoimmunity and may inform future therapeutic approaches that harness meningeal immune cells.

Revealing enzyme functional architecture via high-throughput microfluidic enzyme kinetics

Science - issue - Čt, 07/22/2021 - 19:41

Systematic and extensive investigation of enzymes is needed to understand their extraordinary efficiency and meet current challenges in medicine and engineering. We present HT-MEK (High-Throughput Microfluidic Enzyme Kinetics), a microfluidic platform for high-throughput expression, purification, and characterization of more than 1500 enzyme variants per experiment. For 1036 mutants of the alkaline phosphatase PafA (phosphate-irrepressible alkaline phosphatase of Flavobacterium), we performed more than 670,000 reactions and determined more than 5000 kinetic and physical constants for multiple substrates and inhibitors. We uncovered extensive kinetic partitioning to a misfolded state and isolated catalytic effects, revealing spatially contiguous regions of residues linked to particular aspects of function. Regions included active-site proximal residues but extended to the enzyme surface, providing a map of underlying architecture not possible to derive from existing approaches. HT-MEK has applications that range from understanding molecular mechanisms to medicine, engineering, and design.

Heterogeneity of meningeal B cells reveals a lymphopoietic niche at the CNS borders

Science - issue - Čt, 07/22/2021 - 19:41

The meninges contain adaptive immune cells that provide immunosurveillance of the central nervous system (CNS). These cells are thought to derive from the systemic circulation. Through single-cell analyses, confocal imaging, bone marrow chimeras, and parabiosis experiments, we show that meningeal B cells derive locally from the calvaria, which harbors a bone marrow niche for hematopoiesis. B cells reach the meninges from the calvaria through specialized vascular connections. This calvarial–meningeal path of B cell development may provide the CNS with a constant supply of B cells educated by CNS antigens. Conversely, we show that a subset of antigen-experienced B cells that populate the meninges in aging mice are blood-borne. These results identify a private source for meningeal B cells, which may help maintain immune privilege within the CNS.


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