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"Gao, Xiang"
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Rheological separation of the megathrust seismogenic zone and episodic tremor and slip
A model of the conditions required for episodic tremor and accompanying slow slip to occur, near the megathrust seismogenic zone, reconciles seemingly contradictory observations.
Zone separation in subducting slabs
Xiang Gao and Kelin Wang propose a unifying model for the spatial separation between the seismogenic zone and the zone of episodic tremor and accompanying slow slip (ETS zone) that is observed in some subduction zones of young and warm subducting slabs. Using numerical thermal models, they infer that high temperatures in the warm-slab environment cause the megathrust seismogenic zone to terminate at a depth much shallower than that of the mantle wedge corner. They conclude that high pore-fluid pressures around the mantle wedge corner give rise to an isolated friction zone that is responsible for episodic tremor and slow slip, and that this friction zone is separated from the seismogenic zone by a segment of semi-frictional or viscous behaviour.
Episodic tremor and accompanying slow slip, together called ETS, is most often observed in subduction zones of young and warm subducting slabs
1
,
2
,
3
. ETS should help us to understand the mechanics of subduction megathrusts
3
,
4
, but its mechanism is still unclear. It is commonly assumed that ETS represents a transition from seismic to aseismic behaviour of the megathrust with increasing depth, but this assumption is in contradiction with an observed spatial separation between the seismogenic zone and the ETS zone
5
,
6
,
7
,
8
. Here we propose a unifying model for the necessary geological condition of ETS that explains the relationship between the two zones. By developing numerical thermal models, we examine the governing role of thermo-petrologically controlled fault zone rheology (frictional versus viscous shear). High temperatures in the warm-slab environment
9
cause the megathrust seismogenic zone to terminate before reaching the depth of the intersection of the continental Mohorovičić discontinuity (Moho) and the subduction interface, called the mantle wedge corner. High pore-fluid pressures around the mantle wedge corner
10
give rise to an isolated friction zone responsible for ETS. Separating the two zones is a segment of semi-frictional or viscous behaviour. The new model reconciles a wide range of seemingly disparate observations and defines a conceptual framework for the study of slip behaviour and the seismogenesis of major faults.
Journal Article
Precipitation strengthening of aluminum alloys by room-temperature cyclic plasticity
High-strength aluminum alloys are important for lightweighting vehicles and are extensively used in aircraft and, increasingly, in automobiles. The highest-strength aluminum alloys require a series of high-temperature “bakes” (120° to 200°C) to form a high number density of nanoparticles by solid-state precipitation. We found that a controlled, room-temperature cyclic deformation is sufficient to continuously inject vacancies into the material and to mediate the dynamic precipitation of a very fine (1- to 2-nanometer) distribution of solute clusters. This results in better material strength and elongation properties relative to traditional thermal treatments, despite a much shorter processing time. The microstructures formed are much more uniform than those characteristic of traditional thermal treatments and do not exhibit precipitate-free zones. These alloys are therefore likely to be more resistant to damage.
Journal Article
Carbon redirection via tunable Fenton-like reactions under nanoconfinement toward sustainable water treatment
The ongoing pattern shift in water treatment from pollution control to energy recovery challenges the energy-intensive chemical oxidation processes that have been developed for over a century. Redirecting the pathways of carbon evolution from molecular fragmentation to polymerization is critical for energy harvesting during chemical oxidation, yet the regulation means remain to be exploited. Herein, by confining the widely-studied oxidation system—Mn
3
O
4
catalytic activation of peroxymonosulfate—inside amorphous carbon nanotubes (ACNTs), we demonstrate that the pathways of contaminant conversion can be readily modulated by spatial nanoconfinement. Reducing the pore size of ACNTs from 120 to 20 nm monotonously improves the pathway selectivity toward oligomers, with the yield one order of magnitude higher under 20-nm nanoconfinement than in bulk. The interactions of Mn
3
O
4
with ACNTs, reactant enrichment, and pH lowering under nanoconfinement are evidenced to collectively account for the enhanced selectivity toward polymerization. This work provides an adaptive paradigm for carbon redirection in a variety of catalytic oxidation processes toward energy harvesting and sustainable water purification.
Regulating the carbon evolution pathway during chemical oxidation is critical, but challenging, for sustainable water treatment. Here, the authors report an adaptive approach to drive carbon redirection from molecular fragmentation to polymerization under tunable nanoconfinement.
Journal Article
Unsupervised learning to detect loops using deep neural networks for visual SLAM system
This paper is concerned of the loop closure detection problem for visual simultaneous localization and mapping systems. We propose a novel approach based on the stacked denoising auto-encoder (SDA), a multi-layer neural network that autonomously learns an compressed representation from the raw input data in an unsupervised way. Different with the traditional bag-of-words based methods, the deep network has the ability to learn the complex inner structures in image data, while no longer needs to manually design the visual features. Our approach employs the characteristics of the SDA to solve the loop detection problem. The workflow of training the network, utilizing the features and computing the similarity score is presented. The performance of SDA is evaluated by a comparison study with Fab-map 2.0 using data from open datasets and physical robots. The results show that SDA is feasible for detecting loops at a satisfactory precision and can therefore provide an alternative way for visual SLAM systems.
Journal Article
Strength of stick-slip and creeping subduction megathrusts from heat flow observations
Subduction faults, called megathrusts, can generate large and hazardous earthquakes. The mode of slip and seismicity of a megathrust is controlled by the structural complexity of the fault zone. However, the relative strength of a megathrust based on the mode of slip is far from clear. The fault strength affects surface heat flow by frictional heating during slip. We model heat-flow data for a number of subduction zones to determine the fault strength. We find that smooth megathrusts that produce great earthquakes tend to be weaker and therefore dissipate less heat than geometrically rough megathrusts that slip mainly by creeping.
Journal Article
Scytonemin Plays a Potential Role in Stabilizing the Exopolysaccharidic Matrix in Terrestrial Cyanobacteria
Cyanobacteria are photosynthetic oxygen-evolving prokaryotes that are distributed in diverse habitats. They synthesize the ultraviolet (UV)-screening pigments, scytonemin (SCY) and mycosporine-like amino acids (MAAs), located in the exopolysaccharide (EPS) matrix. Multiple roles for both pigments have gradually been recognized, such as sunscreen ability, antioxidant activity, and heat dissipation from absorbed UV radiation. In this study, a filamentous terrestrial cyanobacterium Nostoc flagelliforme was used to evaluate the potential stabilizing role of SCY on the EPS matrix. SCY (~3.7 %) was partially removed from N. flagelliforme filaments by rinsing with 100 % acetone for 5 s. The physiological damage to cells resulting from this treatment, in terms of photosystem II activity parameter Fv/Fm, was repaired after culturing the sample for 40 h. The physiologically recovered sample was further desiccated by natural or rapid drying and then allowed to recovery for 24 h. Compared with the normal sample, a relatively slower Fv/Fm recovery was observed in the SCY-partially removed sample, suggesting that the decreased SCY concentration in the EPS matrix caused cells to suffer further damage upon desiccation. In addition, the SCYpartially removed sample could allow the release of MAAs (~25 %) from the EPS matrix, while the normal sample did not. Therefore, damage caused by drying of the former resulted from at least the reduction of structural stability of the EPS matrix as well as the loss of partial antioxidant compounds. Considering that an approximately 4 % loss of SCY led to this significant effect, the structurally stabilizing potential of SCY on the EPS matrix is crucial for terrestrial cyanobacteria survival in complex environments.
Journal Article
Maximizing ion accessibility in MXene-knotted carbon nanotube composite electrodes for high-rate electrochemical energy storage
Improving the accessibility of ions in the electrodes of electrochemical energy storage devices is vital for charge storage and rate performance. In particular, the kinetics of ion transport in organic electrolytes is slow, especially at low operating temperatures. Herein, we report a new type of MXene-carbon nanotube (CNT) composite electrode that maximizes ion accessibility resulting in exceptional rate performance at low temperatures. The improved ion transport at low temperatures is made possible by breaking the conventional horizontal alignment of the two-dimensional layers of the MXene Ti
3
C
2
by using specially designed knotted CNTs. The large, knot-like structures in the knotted CNTs prevent the usual restacking of the Ti
3
C
2
flakes and create fast ion transport pathways. The MXene-knotted CNT composite electrodes achieve high capacitance (up to 130 F g
−1
(276 F cm
−3
)) in organic electrolytes with high capacitance retention over a wide scan rate range of 10 mV s
−1
to 10 V s
−1
. This study is also the first report utilizing MXene-based supercapacitors at low temperatures (down to −60 °C).
Improving the accessibility of ions in the electrodes of electrochemical energy storage devices is vital for charge storage and rate performance. Here, the authors report a new type of MXene-carbon nanotube composite electrode that maximizes ion accessibility, resulting in high rate performance at low temperatures.
Journal Article
Mesenchymal stem cell therapy induces FLT3L and CD1c+ dendritic cells in systemic lupus erythematosus patients
Allogeneic mesenchymal stem cells (MSCs) exhibit immunoregulatory function in human autoimmune diseases such as systemic lupus erythematosus (SLE), but the underlying mechanisms remain incompletely understood. Here we show that the number of peripheral tolerogenic CD1c
+
dendritic cells (DCs) and the levels of serum FLT3L are significantly decreased in SLE patients especially with lupus nephritis, compared to healthy controls. Transplantation of allogeneic umbilical cord-derived MSCs (UC-MSCs) significantly up-regulates peripheral blood CD1c
+
DCs and serum FLT3L. Mechanistically, UC-MSCs express FLT3L that binds to FLT3 on CD1c
+
DCs to promote the proliferation and inhibit the apoptosis of tolerogenic CD1c
+
DCs. Conversely, reduction of FLT3L with small interfering RNA in MSCs abolishes the up-regulation of tolerogenic CD1c
+
DCs in lupus patients treated with MSCs. Interferon-γ induces FLT3L expression in UC-MSCs through JAK/STAT signaling pathway. Thus, allogeneic MSCs might suppress inflammation in lupus through up-regulating tolerogenic DCs.
Promising pilot clinical trials of mesenchymal stem cells (MSCs) therapy of lupus await validation in larger, controlled trials. Here the authors show that MSCs expand CD1c
+
dendritic cells in cell culture by producing FLT3L, and that in lupus patients, circulating CD1c
+
dendritic cells and FLT3L are increased following MSCs therapy.
Journal Article