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result(s) for
"Zheng Sun"
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ENSO Asymmetry in CMIP5 Models
The El Niño–La Niña asymmetry is evaluated in 14 coupled models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). The results show that an underestimate of ENSO asymmetry, a common problem noted in CMIP3 models, remains a common problem in CMIP5 coupled models. The weaker ENSO asymmetry in the models primarily results from a weaker SST warm anomaly over the eastern Pacific and a westward shift of the center of the anomaly. In contrast, SST anomalies for the La Niña phase are close to observations.
Corresponding Atmospheric Model Intercomparison Project (AMIP) runs are analyzed to understand the causes of the underestimate of ENSO asymmetry in coupled models. The analysis reveals that during the warm phase, precipitation anomalies are weaker over the eastern Pacific, and westerly wind anomalies are confined more to the west in most models. The time-mean zonal winds are stronger over the equatorial central and eastern Pacific for most models. Wind-forced ocean GCM experiments suggest that the stronger time-mean zonal winds and weaker asymmetry in the interannual anomalies of the zonal winds in AMIP models can both be a contributing factor to a weaker ENSO asymmetry in the corresponding coupled models, but the former appears to be a more fundamental factor, possibly through its impact on the mean state. The study suggests that the underestimate of ENSO asymmetry in the CMIP5 coupled models is at least in part of atmospheric origin.
Journal Article
Observation of energy-resolved many-body localization
Many-body localization (MBL) describes a quantum phase where an isolated interacting system subject to sufficient disorder displays non-ergodic behaviour, evading thermal equilibrium that occurs under its own dynamics. Previously, the thermalization–MBL transition has been largely characterized with the growth of disorder. Here, we explore a new axis, reporting on an energy-resolved MBL transition using a 19-qubit programmable superconducting processor, which enables precise control and flexibility of both disorder strength and initial state preparation. We observe that the onset of localization occurs at different disorder strengths, with distinguishable energy scales, by measuring time-evolved observables and quantities related to many-body wave functions. Our results open avenues for the experimental exploration of many-body mobility edges in MBL systems, whose existence is widely debated due to the finiteness of the system size, and where exact simulations in classical computers become unfeasible.Many-body localization—a phenomenon where an isolated system fails to reach thermal equilibrium—has been studied with a programmable quantum processor, which reveals the crucial role played by the initial energy on the onset of localization.
Journal Article
ENSO Asymmetry in CMIP6 Models
An interesting aspect of the El Niño–Southern Oscillation (ENSO) phenomenon is the asymmetry between its two phases. This paper evaluates the simulations of this property of ENSO by the Coupled Model Intercomparison Project phase 6 (CMIP6) models. Both the surface and subsurface signals of ENSO are examined for this purpose. The results show that the models still underestimate ENSO asymmetry as shown in the SST field, but do a better job in the subsurface. A much weaker negative feedback from the net surface heat flux during La Niña in the models is identified as a factor causing the degradation of the ENSO asymmetry at the surface. The simulated asymmetry in the subsurface is still weaker than the observations owing to a weaker dynamic coupling between the atmosphere and ocean. Consistent with the finding of a weaker dynamic coupling strength, the precipitation response to the SST changes is also found to be weaker in the models. The results underscore that a more objective assessment of the simulation of ENSO by climate models may have to involve the examination of the subsurface signals. Future improvements in simulating ENSO will likely require a better simulation of the surface heat flux feedback from the atmosphere as well as the dynamical coupling strength between the atmosphere and ocean.
Journal Article
Photo-generated dinuclear {Eu(II)}2 active sites for selective CO2 reduction in a photosensitizing metal-organic framework
Photocatalytic reduction of CO
2
is a promising approach to achieve solar-to-chemical energy conversion. However, traditional catalysts usually suffer from low efficiency, poor stability, and selectivity. Here we demonstrate that a large porous and stable metal-organic framework featuring dinuclear Eu(III)
2
clusters as connecting nodes and Ru(phen)
3
-derived ligands as linkers is constructed to catalyze visible-light-driven CO
2
reduction. Photo-excitation of the metalloligands initiates electron injection into the nodes to generate dinuclear {Eu(II)}
2
active sites, which can selectively reduce CO
2
to formate in a two-electron process with a remarkable rate of 321.9 μmol h
−1
mmol
MOF
−1
. The electron transfer from Ru metalloligands to Eu(III)
2
catalytic centers are studied via transient absorption and theoretical calculations, shedding light on the photocatalytic mechanism. This work highlights opportunities in photo-generation of highly active lanthanide clusters stabilized in MOFs, which not only enables efficient photocatalysis but also facilitates mechanistic investigation of photo-driven charge separation processes.
Solar-to-chemical CO
2
reduction provides a means to use light’s energy for CO
2
removal and upgrading to useful products, although this photochemical conversion is challenging. Here, authors construct a Europium-containing metal-organic framework that selectively converts CO
2
to formate with light.
Journal Article
Deciphering synergetic core-shell transformation from Mo6O22@Ag44 to Mo8O28@Ag50
The structural transformation of high-nuclearity silver clusters from one to another induced by specific stimuli is of scientific significance in terms of both cluster synthesis and reactivity. Herein, we report two silver-thiolate clusters, [Mo
6
O
22
@Ag
44
] and [Mo
8
O
28
@Ag
50
], which are templated by isopolymolybdates inside and covered by
i
PrS
−
and PhCOO
−
ligands on the surfaces. Amazingly, the [Mo
8
O
28
@Ag
50
] can be transformed from [Mo
6
O
22
@Ag
44
] by adding PhCOOH which increases the degree of condensation of molybdates template from Mo
6
O
22
8-
to Mo
8
O
28
8-
, then enlarging the outer silver shell from Ag
44
to Ag
50
. The evolution of solution species revealed by time-dependent electrospray ionization mass spectrometry (ESI-MS) suggests a breakage-growth-reassembly (BGR) transformation mechanism. These results not only provide a combined assembly strategy (anion-template + induced transformation) for the synthesis of silver-thiolate clusters but also help us to better understand the complex transformation process underpinning the assembly system.
Understanding how one metal nanocluster transforms into another is of synthetic and fundamental importance. Here, the authors use mass spectrometry to reveal an acid-induced structural transformation between two Ag clusters that proceeds via a breakage-growth-reassembly mechanism.
Journal Article
Trapping an octahedral Ag6 kernel in a seven-fold symmetric Ag56 nanowheel
High-nuclearity silver clusters are appealing synthetic targets for their remarkable structures, but most are isolated serendipitously. We report here six giant silver-thiolate clusters mediated by solvents, which not only dictate the formation of an octahedral Ag
6
4+
kernel, but also influence the in situ-generated Mo-based anion templates. The typical sevenfold symmetric silver nanowheels show a hierarchical cluster-in-cluster structure that comprises an outermost Ag
56
shell and an inner Ag
6
4+
kernel in the centre with seven MoO
4
2−
anion templates around it. Electrospray ionization mass spectrometry analyses reveal the underlying rule for the formation of such unique silver nanowheels. This work establishes a solvent–intervention approach to construct high-nuclearity silver clusters in which both the formation of octahedral Ag
6
4+
kernel and in situ generation of various Mo-based anion templates can be simultaneously controlled.
High-nuclearity silver clusters are appealing synthetic targets for their remarkable structures, but most are isolated serendipitously. Here, the authors describe the rational use of solvents to form cluster-in-cluster silver nanowheels, which comprise an octahedral Ag
6
4+
core surrounded by a Ag
56
cage of unusual seven-fold symmetry.
Journal Article
Surface coordination layer passivates oxidation of copper
Owing to its high thermal and electrical conductivities, its ductility and its overall non-toxicity
1
–
3
, copper is widely used in daily applications and in industry, particularly in anti-oxidation technologies. However, many widespread anti-oxidation techniques, such as alloying and electroplating
1
,
2
, often degrade some physical properties (for example, thermal and electrical conductivities and colour) and introduce harmful elements such as chromium and nickel. Although efforts have been made to develop surface passivation technologies using organic molecules, inorganic materials or carbon-based materials as oxidation inhibitors
4
–
12
, their large-scale application has had limited success. We have previously reported the solvothermal synthesis of highly air-stable copper nanosheets using formate as a reducing agent
13
. Here we report that a solvothermal treatment of copper in the presence of sodium formate leads to crystallographic reconstruction of the copper surface and formation of an ultrathin surface coordination layer. We reveal that the surface modification does not affect the electrical or thermal conductivities of the bulk copper, but introduces high oxidation resistance in air, salt spray and alkaline conditions. We also develop a rapid room-temperature electrochemical synthesis protocol, with the resulting materials demonstrating similarly strong passivation performance. We further improve the oxidation resistance of the copper surfaces by introducing alkanethiol ligands to coordinate with steps or defect sites that are not protected by the passivation layer. We demonstrate that the mild treatment conditions make this technology applicable to the preparation of air-stable copper materials in different forms, including foils, nanowires, nanoparticles and bulk pastes. We expect that the technology developed in this work will help to expand the industrial applications of copper.
High oxidation resistance, without degradation of thermal or electrical conductivity, is achieved in copper using surface modification by a solvothermal or electrochemical treatment with sodium formate and formation of a thin surface coordination layer.
Journal Article
A hierarchically assembled 88-nuclei silver-thiacalix4arene nanocluster
Thiacalix[4]arenes as a family of promising ligands have been widely used to construct polynuclear metal clusters, but scarcely employed in silver nanoclusters. Herein, an anion-templated Ag
88
nanocluster (SD/Ag88a) built from
p
-tert-butylthiacalix[4]arene (H
4
TC4A) is reported. Single-crystal X-ray diffraction reveals that
C
4
-symmetric SD/Ag88a resembles a metal-organic super calix comprised of eight TC4A
4−
as walls and 88 silver atoms as base, which can be deconstructed to eight [CrO
4
@Ag
11
(TC4A)(EtS)
4
(OAc)] secondary building units arranged in an annulus encircling a CrO
4
2−
in the center. Local and global anion template effects from chromates are individually manifested in SD/Ag88a. The solution stability and hierarchical assembly mechanism of SD/Ag88a are studied by using electrospray mass spectrometry. The Ag
88
nanocluster represents the highest nuclearity metal cluster capped by TC4A
4−
. This work not only exemplify the specific macrocyclic effects of TC4A
4−
in the construction of silver nanocluster but also realize the shape heredity of TC4A
4−
to overall silver super calix.
The assembly of giant silver clusters by using macrocylic multidentate ligand remains a challenge. Here, the authors synthesize a chromate-templated 88-nuclei silver super calix and reveal the role of anion templating effects and a hierarchical assembly mechanism.
Journal Article
Probing spin hydrodynamics on a superconducting quantum simulator
Characterizing the nature of hydrodynamical transport properties in quantum dynamics provides valuable insights into the fundamental understanding of exotic non-equilibrium phases of matter. Experimentally simulating infinite-temperature transport on large-scale complex quantum systems is of considerable interest. Here, using a controllable and coherent superconducting quantum simulator, we experimentally realize the analog quantum circuit, which can efficiently prepare the Haar-random states, and probe spin transport at infinite temperature. We observe diffusive spin transport during the unitary evolution of the ladder-type quantum simulator with ergodic dynamics. Moreover, we explore the transport properties of the systems subjected to strong disorder or a tilted potential, revealing signatures of anomalous subdiffusion in accompany with the breakdown of thermalization. Our work demonstrates a scalable method of probing infinite-temperature spin transport on analog quantum simulators, which paves the way to study other intriguing out-of-equilibrium phenomena from the perspective of transport.
Quantum devices offer the potential to simulate quantum phenomena, which are otherwise computationally intractable. Here, Shi, Sun, Wang and coauthors use a superconducting quantum simulator to study spin-transport at infinite temperature.
Journal Article