•A deep neural network surrogate approach is developed for predicting dynamic contaminate tracing in complex hydro-geological models.•The model can be used to improve the result of the predicted ...water saturation and pressure.•An autoregressive strategy combined with a residual U-net model is introduced to get better predictions with fewer data.•Our results indicate a significant acceleration and accuracy compared to the physics-based modeling.
The inherent complexity of the fluid flow in subsurface systems brings potential inevitable uncertainty in their characterization. Computationally intensive high-dimensional inversion problems often emerge in solving the fluid flow problems of various scenarios, which required to be probed. To improve the efficiency of solving such problems, surrogate strategies are widely used to quantify the uncertainty of underground multiphase flow models. In this paper, a deep learning surrogate model is developed for predicting the time-dependent dynamic multiphase flow in a two-dimensional (2D) channelized geological system. The surrogate model is combined with a residual U-net and an autoregressive strategy, which considers the output at the previous time step as input and predict the output at the current time step. The residual U-net has a symmetric network structure similar to U-net and contains extra residual units. The rich skip connections in the network can promote information dissemination and achieve better prediction performance with fewer parameters. We demonstrated the performance of the autoregressive residual U-net (AR-Runet) for predicting the migration of solute transport in heterogeneous 2D binary model. The result shows the AR-Runet surrogate model can provide an accurate approximation of saturation and pressure fields at different times. We also have demonstrated that with the autoregressive strategy this network can achieve similar predict results with relatively less training data. The performance of the AR-Runet network is also compared with the autoregressive Dense net (AR-Dense). The findings indicate that the AR-Runet can provide effective measures for developing surrogate model and uncertainty analysis in dynamic multiphase flow predictions of subsurface systems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Weyl semimetals exhibit unusual surface states and anomalous transport phenomena. It is hard to manipulate the band structure topology of specific Weyl materials. Topological transport ...phenomena usually appear at very low temperatures, which sets challenges for applications. In this work, we demonstrate the band topology modification via a weak magnetic field in a ferromagnetic Weyl semimetal candidate, Co
2
MnAl, at room temperature. We observe a tunable, giant anomalous Hall effect (AHE) induced by the transition involving Weyl points and nodal rings. The AHE conductivity is as large as that of a 3D quantum AHE, with the Hall angle (
Θ
H
) reaching a record value (
$$\tan {\Theta }^{H}=0.21$$
tan
Θ
H
=
0.21
) at the room temperature among magnetic conductors. Furthermore, we propose a material recipe to generate large AHE by gaping nodal rings without requiring Weyl points. Our work reveals an intrinsically magnetic platform to explore the interplay between magnetic dynamics and topological physics for developing spintronic devices.
Abstract
The promise of high-density and low-energy-consumption devices motivates the search for layered structures that stabilize chiral spin textures such as topologically protected skyrmions. At ...the same time, recently discovered long-range intrinsic magnetic orders in the two-dimensional van der Waals materials provide a new platform for the discovery of novel physics and effects. Here we demonstrate the Dzyaloshinskii–Moriya interaction and Néel-type skyrmions are induced at the WTe
2
/Fe
3
GeTe
2
interface. Transport measurements show the topological Hall effect in this heterostructure for temperatures below 100 K. Furthermore, Lorentz transmission electron microscopy is used to directly image Néel-type skyrmion lattice and the stripe-like magnetic domain structures as well. The interfacial coupling induced Dzyaloshinskii–Moriya interaction is estimated to have a large energy of 1.0 mJ m
−2
. This work paves a path towards the skyrmionic devices based on van der Waals layered heterostructures.
Transport of Topological Semimetals Hu, Jin; Xu, Su-Yang; Ni, Ni ...
Annual review of materials research,
07/2019, Volume:
49, Issue:
1
Journal Article
Peer reviewed
Open access
Three-dimensional (3D) topological semimetals represent a new class of topological matters. The study of this family of materials has been at the frontiers of condensed matter physics, and many ...breakthroughs have been made. Several topological semimetal phases, including Dirac semimetals (DSMs), Weyl semimetals (WSMs), nodal-line semimetals (NLSMs), and triple-point semimetals, have been theoretically predicted and experimentally demonstrated. The low-energy excitation around the Dirac Weyl nodal points, nodal line, or triply degenerated nodal point can be viewed as emergent relativistic fermions. Experimental studies have shown that relativistic fermions can result in a rich variety of exotic transport properties, e.g., extremely large magnetoresistance, the chiral anomaly, and the intrinsic anomalous Hall effect. In this review, we first briefly introduce band structural characteristics of each topological semimetal phase, then review the current studies on quantum oscillations and exotic transport properties of various topological semimetals, and finally provide a perspective of this area.
A Dirac nodal-line semimetal phase, which represents a new quantum state of topological materials, has been experimentally realized only in a few systems, including PbTaSe_{2}, PtSn_{4}, and ZrSiS. ...In this Letter, we report evidence of nodal-line fermions in ZrSiSe and ZrSiTe probed in de Haas-van Alphen quantum oscillations. Although ZrSiSe and ZrSiTe share a similar layered structure with ZrSiS, our studies show the Fermi surface (FS) enclosing a Dirac nodal line has a 2D character in ZrSiTe, in contrast with 3D-like FS in ZrSiSe and ZrSiS. Another important property revealed in our experiment is that the nodal-line fermion density in this family of materials (∼10^{20} cm^{-3}) is much higher than the Dirac fermion density of other topological materials with discrete nodes. In addition, we have demonstrated ZrSiSe and ZrSiTe single crystals can be thinned down to 2D atomic thin layers through microexfoliation, which offers the first platform to explore exotic properties of topological nodal-line fermions in low dimensions.
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The studies of topological insulators (TI) and topological semimetals have been at frontiers of condensed matter physics and material science. Both classes of materials are characterized by robust ...surface states created by the topology of the bulk band structures and exhibit exotic transport properties. When magnetism is present in topological materials and breaks the time-reversal symmetry, more exotic quantum phenomena can be generated, e.g., quantum anomalous Hall effect (QAHE), axion insulator, and large intrinsic AHE. In this research update, we briefly summarize the recent research progress in magnetic topological materials, including intrinsic magnetic TI and magnetic Weyl semimetals.
Abstract
The discovery of 2-dimensional (2D) materials, such as CrI
3
, that retain magnetic ordering at monolayer thickness has resulted in a surge of both pure and applied research in 2D magnetism. ...Here, we report a magneto-Raman spectroscopy study on multilayered CrI
3
, focusing on two additional features in the spectra that appear below the magnetic ordering temperature and were previously assigned to high frequency magnons. Instead, we conclude these modes are actually zone-folded phonons. We observe a striking evolution of the Raman spectra with increasing magnetic field applied perpendicular to the atomic layers in which clear, sudden changes in intensities of the modes are attributed to the interlayer ordering changing from antiferromagnetic to ferromagnetic at a critical magnetic field. Our work highlights the sensitivity of the Raman modes to weak interlayer spin ordering in CrI
3
.
Hydrogen sulfide (H2S) is a kind of gaseous signalling molecule that plays pivotal role in various biological processes. So far, it is still a challenge to develop convenient and reliable methods for ...H2S detection in lysosomes. Herein, we developed a novel ratiometric two-photon fluorescent probe LR-H2S for imaging H2S in lysosomes. Upon the addition of H2S (using Na2S as a donor) to LR-H2S in buffer solution, the azide group is reduced to amino group and subsequently the carbamate ester is cleaved by 1,6-elimination, resulting in a fluorescence emission increase at 541nm and a concomitant emission decrease at 475nm. Under two-photon excitation of 840nm, an 80-fold fluorescence ratio (F541/F475) enhancement was observed with a wide linear range of 25–2500μM. The detection limit was calculated to be 0.70μM based on 3σ/k method, indicating that the probe can detect H2S with a high sensitivity. The probe also shows excellent selectivity toward H2S among other biological interference species and features with low cytotoxicity and favorable two-photon properties. Furthermore, LR-H2S can easily localize in lysosomes and vividly illuminate endogenous/exogenous H2S level and distribution in lysosomes of living SGC-7901 cells.
A ratiometric fluorescent probe was constructed for imaging hydrogen sulfide in lysosomes by two-photon microscopy. Display omitted
•A novel two-photon fluorescent probe for hydrogen sulfide was developed for cell imaging.•The probe can offer ratiometric fluorescence signal under one-photon or two-photon excitation.•Morpholine group was employed to provide lysosome targeting ability.•The probe could detect endogenous and exogenous H2S in lysosomes of living cells with high sensitivity and selectivity.
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Topological semimetals represent a new class of quantum materials hosting Dirac/Weyl fermions. The essential properties of topological fermions can be revealed by quantum oscillations. Here we ...present systematic de Haas–van Alphen (dHvA) oscillation studies on the recently discovered topological Dirac nodal-line semimetal ZrSiS. From the angular dependence of dHvA oscillations, we have revealed the anisotropic Dirac bands in ZrSiS and found surprisingly strong Zeeman splitting at low magnetic fields. The Landé g factor estimated from the separation of Zeeman splitting peaks is as large as 38. From the analyses of dHvA oscillations, we also revealed nearly zero effective mass and exceptionally high quantum mobility for Dirac fermions in ZrSiS. These results shed light on the nature of novel Dirac fermion physics of ZrSiS.
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The ambient environmental instability and degradation mechanism of single‐ and few‐layer WTe2 are investigated. Oxidation of W and Te atoms appears to be a main reason for degradation. Single‐layer ...samples' Raman signals disappear within 20 min in air. Few‐layer WTe2 exhibits saturating degradation behavior: only the top layer WTe2 is oxidized; the degraded layer can protect inner layers from further degradation.
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