Compilation | Li Yan
Nature, 10 September 2020, Volume 585 Issue 7824
《Nature》September 10, 2020, Volume 585, Issue 7824
AstronomyAstronomy
The Magellanic Corona as the key to the formation of the Magellanic Stream
Magellan corona is the key to the formation of Magellan star flow
▲ Author: S. Lucchini, E. D’Onghia, A. J. Fox, C. Bustard, J. Bland-Hawthorn & E. Zweibel
▲ Link: https://www.nature.com/articles/s41586-020-2663-4
▲ Abstract
The main gas structure in the galaxy halo is the Magellan star flow.
Recent discoveries—including the discovery of dwarf galaxies associated with the Magellan constellation, the determination of LMC high-quality, detection of highly ionized gases near stars in LMC, and cosmological simulation predictions—all support the existence of a circle of warm (about 500,000 k) ionized gases near the LMC (Magellan corona).
Here we report that by simulating the Magellan cloud falls in the Milky Way Magellan corona, we can reproduce the Magellan star flow and its dominant arm. Our simulations explain the filamentous structure, spatial range, radial velocity gradient, and total ionized gas mass of the Magellan flow.
We predict that the Magellan corona will be clearly visible in the high ionization absorption line of the UV spectrum of the background quasar near LMC.
▲ Abstract 3
The dominant gaseous structure in the Galactic halo is the Magellanic Stream. Several recent developments—including the discovery of dwarf galaxies associated with the Magellanic group, determination of the high mass of the LMC, detection of highly ionized gas near stars in the LMC and predictions of cosmological simulations—support the existence of a halo of warm (roughly 500,000 kelvin) ionized gas around the LMC (the ‘Magellanic Corona’). Here we report that, by including this Magellanic Corona in hydrodynamic simulations of the Magellanic Clouds falling onto the Milky Way, we can reproduce the Magellanic Stream and its leading arm. Our simulations explain the filamentary structure, spatial extent, radial-velocity gradient and total ionized-gas mass of the Magellanic Stream. We predict that the Magellanic Corona will be unambiguously observable via high-ionization absorption lines in the ultraviolet spectra of background quasars lying near the LMC.
Quantum Physics
Experimental determination correction of qubit Loss
Experimental determination correction of qubit loss
▲ Author: Roman Stricker, Davide Vodola, Alexander Erhard, Lukas Postler, Michael Meth, Martin Ringbauer, et al.
▲ Link: https://www.nature.com/articles/s41586-020-2667-0
▲ Summary
The successful operation of a quantum computer relies on protecting qubits from decoherence and noise, which will lead to false results if not corrected.
Here, we implement a full-cycle quantum loss detection and correct the minimum instance of topological surface code in the capture ion quantum processor.
The key technique used for correction is quantum non-destructive measurements performed by assisting qubits, which act as a minimum intrusion probe, detecting missing qubits while passing the smallest possible interference of quantum mechanics to the remaining qubits. Once
detects a qubit loss, a recovery program is triggered in real time, which maps the logical information to the new encoding on the remaining qubits.
Although the current demonstration was performed in an ion-intercepting quantum processor, the protocol is suitable for other quantum computing architectures and error correction codes, including leading 2D and 3D topological codes.
▲ Abstract th 3
The successful operation of quantum computers relies on protecting qubits from decoherence and noise, which—if uncorrected—will lead to erroneous results. Here we experimentally implement a full cycle of qubit loss detection and correction on a minimum instance of a topological surface code in a trapped-ion quantum processor. The key technique used for this correction is a quantum non-demolition measurement performed via an ancillary qubit, which acts as a minimally invasive probe that detects absent qubits while imparting the smallest quantum mechanically possible disorder to the remaining qubits. Upon detecting qubit loss, a recovery procedure is triggered in real time that maps the logical information onto a new encoding on the remaining qubits. Although the current demonstration is performed in a trapped-ion quantum processor, the protocol is applicable to other quantum computing architectures and error correcting codes, including leading two- and three-dimensional topological codes.
Material ScienceMaterial Science
Co-designing electronics with microfluidics for more sustainable cooling
collaborates with microfluidics to design electronic devices to achieve more sustainable cooling
▲ Author: Remco van Erp, Reza Soleimanzadeh, Luca Nela, Georgios Kampitsis & Elison Matioli
▲ Link: https://www.nature.com/articles/s41586-020-2666-1
▲ Abstract
Cooling liquid directly into the chip is a promising and more effective thermal management method. However, even in state-of-the-art methods, electronics and cooling are processed separately, leaving full energy saving potential for embedded cooling untapped.
Here, we show that by co-designing microfluidics and electronic components within the same semiconductor substrate, we can produce an integrally integrated manifold microchannel cooling structure with efficiency exceeding that currently available. Our results show that heat flow over 1.7 kW per square centimeter can be extracted using only 0.57 watts per square centimeter of pumping power.
We observe that single-phase water cooling with heat flux exceeding 1 kW per square centimeter has unprecedented performance coefficient (more than 10,000), corresponding to a 50-fold increase in linear microchannels, and a very high average Nussel number of 16.
▲ Abstract th 3
Embedding liquid cooling directly inside the chip is a promising approach for more efficient thermal management. However, even in state-of-the-art approaches, the electronics and cooling are treated separately, leaving the full energy-saving potential of embedded cooling untapped. Here we show that by co-designing microfluidics and electronics within the same semiconductor substrate we can produce a monolithically integrated manifold microchannel cooling structure with efficiency beyond what is currently available. Our results show that heat fluxes exceeding 1.7 kilowatts per square centimetre can be extracted using only 0.57 watts per square centimetre of pumping power. We observed an unprecedented coefficient of performance (exceeding 10,000) for single-phase water-cooling of heat fluxes exceeding 1 kilowatt per square centimetre, corresponding to a 50-fold increase compared to straight microchannels, as well as a very high average Nusselt number of 16.
ChemstryChemstry
Evidence for supercritical behavior of high-pressure liquid hydrogen
Evidence of supercritical behavior of high-pressure liquid hydrogen
▲ Author: Bingqing Cheng, Guglielmo Mazzola, Chris J. Pickard & Michele Ceriotti
▲ Link: https://www.nature.com/articles/s41586-020-2677-y
▲ Abstract
Hydrogen is the simplest and richest element in the universe, and it will show very complex characteristics during the compression process.
Here, we propose a theoretical study of the phase graph of dense hydrogen using machine learning to “learn” the forces between potential energy surfaces and atoms from reference calculations, and then predict them at low computational costs, overcoming the limitations of length and time scales. We reproduce the behavior of reentrant melting points and the polymorphism of the solid phase.
uses machine learning-based simulations of potentials to provide evidence for continuous molecular to atomic transformations in liquids, with no primary transitions observed on the melting line. This shows that in the huge gas planet, there is a smooth transition between the insulating layer and the metal layer, while also harming the differences in supercritical phenomena present in the experiment.
▲ Abstract tml3
Hydrogen, the simplest and most abundant element in the Universe, develops a remarkably complex behavior upon compression. Here we present a theoretical study of the phase diagram of dense hydrogen that uses machine learning to ‘learn’ potential-energy surfaces and interatomic forces from reference calculations and then predict them at low computational cost, overcoming length- and timescale limitations. We reproduce both the re-entrant melting behavior and the polymorphism of the solid phase. Simulations using our machine-learning-based potentials provide evidence for a continuous molecular-to-atomic transition in the liquid, with no first-order transition observed above the melting line. This suggests a smooth transition between insulating and metallic layers in giant gas planets, and reconciles existing discrepancies between experiments as a manifestation of supercritical behaviour.
Rare-earth–platinum alloy nanoparticles in mesoporous zeolite for catalysingl4
Catalytic effects of rare earth-platinum alloy nanoparticles in mesoporous zeolite
▲ Author: Ryong Ryoo, Jaeheon Kim, Changbum Jo, Seung Won Han, Jeong-Chul Kim, Hongjun Park, Jongho Han, et al.
▲ Link: https://www.nature.com/articles/s41586-020-2671-4
▲ Abstract
In the petrochemical process, platinum is a commonly used catalyst, usually mixed with other metals to improve catalytic activity, selectivity and service life.
Here we use a mesoporous zeolite (called "silanol nest") with a surface frame defect in the pore wall as support, indicating that the zeolite forms an alloy between platinum and rare earth elements. We found that silanol nests allow rare earth elements to exist in single atoms at a much higher chemical potential than bulk oxides, making them possible to diffuse onto platinum.
High resolution transmission electron microscopy and hydrogen chemosorption measurements show that bimetallic nanoparticles supported on mesoporous zeolites are intermetallic compounds, which we find as a stable, highly active and selective catalyst for propane dehydrogenation reaction.
When used with = transition metal, the same preparation strategy can produce a platinum alloy catalyst containing a large amount of the second metal, for platinum carbon alloys, which exhibit high catalytic activity and selectivity when preferentially oxidizing carbon monoxide in H2.
▲ Abstract tml3
Platinum is a much used catalyst that, in petrochemical processes, is often allowed with other metals to improve catalytic activity, selectivity and longevity. Here we use as support a mesoporous zeolite that has pore walls with surface framework defects (called ‘silanol nests’) and show that the zeolite enables alloy formation between Pt and rare-earth elements. We find that the silanol nests enable the rare-earth elements to exist as single atomic species with a generally higher chemical potential compared with that of the bulk oxide, making it possible for them to diffuse onto Pt. High-resolution transmission electron microscopy and hydrogen chemistry measurements indicate that the resultant bimetallic nanoparticles supported on the mesoporous zeolite are intermetallic compounds, which we find to be stable, highly active and selective catalysts for the propane dehydrogenation reaction. When used with late transition metals, the same preparation strategy produces Pt alloy catalysts that incorporate an unusually large amount of the second metal and, in the case of the PtCo alloy, show high catalytic activity and selectivity in the preferential oxidation of carbon monooxide in H2.
Earth ScienceGeoscience
Satellite isoprene retrievals constrain emissions and atmospheric oxidation
Satellite isoprene recovery device limits emissions and atmospheric oxidation
▲ Author: Kelley C. Wells, Dylan B. Millet, Vivienne H. Payne, M. Julian Deventer, Kelvin H. Bates, Joost A. de Gouw, et al.
▲ Link: https://www.nature.com/articles/s41586-020-2664-3
▲ Abstract
isoprene is the main non-methane organic compound emitted into the atmosphere. It drives the production of ozone and aerosols, regulates atmospheric oxidation, and interacts with the global nitrogen cycle.
Here we show the global measurement of isoprene from space using cross-tracking infrared detectors. Together with observations on formaldehyde, an isoprene oxidation product, these measurements provide limitations on isoprene emissions and atmospheric oxidation.
We found that the isoprene-formaldehyde relationship measured from space is roughly consistent with the current understanding of isoprene-OH chemistry, with no indication of the lack of OH cycle at low nitrogen oxide concentrations. We analyzed the relationship between the four isoprene hotspot data sets around the world and model predictions, and gave a quantitative analysis of isoprene emissions based on satellite measurements of isoprene itself. A significant difference occurred in the Amazon region, where the current underestimation of natural nitrogen oxide emissions mimics OH and isoprene. In southern Africa, we found a significant isoprene hotspot disappearing in bottom-up predictions.
▲ Abstractt
Isoprene is the dominant non-methane organic compound emitted to the atmosphere. It drives ozone and aerosol production, modulates atmosphere oxidation and interacts with the global nitrogen cycle. Here we present global isoprene measures taken from space using the Cross-track Infrared Sounder. Together with observations of formaldehyde, an isoprene oxidation product, these measures provide constraints on isoprene emissions and atmosphere oxidation. We find that the isoprene–formaldehyde relationships measured from space are broadly consistent with the current understanding of isoprene–OH chemistry, with no indication of missing OH recycling at low nitrogen oxide concentrations. We analyze these datasets over four global isoprene hotspots in relation to model predictions, and present a quantification of isoprene emissions based directly on satellite measurements of isoprene itself. A major discrepancy emerges over Amazonia, where current underestimates of natural nitrogen oxide emissions biased OH and hence isoprene. Over southern Africa, we find that a prominent isoprene hotspot is missing from bottom-up predictions.
The lithospheric-to-lower-mantle carbon cycle recorded in superdeep diamonds
Carbon cycle from lithosphere to lower mantle
▲ Author: M. E. Regier, D. G. Pearson, T. Stachel, R. W. Luth, R. A. Stern & J. W. Harris
▲ Link: https://www.nature.com/articles/s41586-020-2676-z
▲ Abstract
carbon enters the mantle is an important way for the earth's carbon cycle, affecting the climate and redox conditions of the surface and mantle. Here we show the oxygen isotope measurements of mineral inclusions in diamonds from Guinea, derived from depths extending from the lithosphere to the lower mantle (over 660 km).
combines the carbon and nitrogen isotope content of diamond, and these data indicate that carbonized igneous ocean crusts, rather than sediments, are the main carbon-containing reservoirs in plates submerged to the depths of the lithosphere and deep in the transition zone (less than 660 km).
In this depth range, sublite lithosphere inclusions are significantly enriched with oxygen isotopes of the developmental lithosphere inclusions derived from crustal protostones. The increase in oxygen isotope content of these sublite lithosphere inclusions is due to melt crystallization of submerged crusts rich in carbonate.
In contrast, the isotope values range of lower mantle mineral inclusions and their host diamonds (deep over 660 km) is a typical feature of mantle with little or no crust interactions occurring.
Because carbon is present in metals, not in diamonds, in the reduced, poorly volatile lower mantle, carbon must be mobilized and concentrated to form lower mantle diamonds.
Our data support a model in which the submerged marine lithosphere causes the hydration of the upper and lower mantle to unstable carbon-containing metals, thus forming diamonds without disturbing the stable isotope characteristics of the middle mantle. This transition from melting of transition zone carbonate slabs to dehydration of the lower mantle plate provides a lower mantle barrier to carbon subduction.
▲ Abstract th 3
The transport of carbon into Earth’s mantle is a critical pathway in Earth’s carbon cycle, affecting both the climate and the redox conditions of the surface and mantle. Here we present oxygen isotope measurements of miner inclusions within diamonds from Kankan, Guinea that are derived from depths extending from the lithosphere to the lower mantle (greater than 660 kilometres). These data, combined with the carbon and nitrogen isotope contents of the diamonds, indicating that carbonated igneous oceanic crust, not sediment, is the primary carbon-bearing reserve in slabs subducted to deep-lithospheric and transition-zone depths (less than 660 kilometres). Within this depth regime, sublithospheric inclusions are distinctly enriched in 18O relative to eclogitic lithospheric inclusions derived from crustal protoliths. The increased 18O content of these sublithospheric inclusions results from their crystallization from melts of carbonate-rich subducted oceanic crust. In contrast, lower-mantle minerization and their host diamonds (deeper than 660 kilometres) have a narrow range of isotopic values that are typical of mantle that has experienced little or no crustal interaction. Because carbon is hosted in metals, rather than in diamond, in the reduced, volatile-poor lower mantle, carbon must be mobilized and concentrated to form lower-mantle diamonds. Our data supports a model in which the hydration of the uppermost lower mantle by subducted oceanic lithosphere destabilizes carbon-bearing metals to form diamond, without disturbing the ambient-mantle stable-isotope signatures. This transition from carbonate slab melting in the transition zone to slab dehydration in the lower mantle supports a lower-mantle barrier for carbon subscription.
