A second-order topological insulator (SOTI) in d spatial dimensions features topologically protected gapless states at its (d-2)-dimensional boundary at the intersection of two crystal faces, but is ...gapped otherwise. As a novel topological state, it has been attracting great interest, but it remains a challenge to identify a realistic SOTI material in two dimensions (2D). Here, based on combined first-principles calculations and theoretical analysis, we reveal the already experimentally synthesized 2D material graphdiyne as the first realistic example of a 2D SOTI, with topologically protected 0D corner states. The role of crystalline symmetry, the robustness against symmetry breaking, and the possible experimental characterization are discussed. Our results uncover a hidden topological character of graphdiyne and promote it as a concrete material platform for exploring the intriguing physics of higher-order topological phases.
In this work, conducting polymers poly(3,4-ethylenedioxythiophene) (PEDOT), polyaniline (PANi), and polypyrrole (PPy) were directly coated on the surface of reduced graphene oxide (RGO) sheets via ...an in situ polymerization process to prepare conducting-polymer-RGO nanocomposites with different loadings of the conducting polymers. Experiment results showed that ethanol played an important role in achieving a uniform coating of the polymers on RGO sheets. The electrochemical capacitive properties of the composite materials were investigated by using cycle voltammetry and charge/discharge techniques. The composite consisting of RGO and PANi (RGO-PANi) exhibited a specific capacitance of 361 F/g at a current density of 0.3 A/g. The composites consisting of RGO and PPy (RGO-PPy) and PEDOT (RGO-PEDOT) displayed specific capacitances of 248 and 108 F/g, respectively, at the same current density. More than 80% of initial capacitance retained after 1000 charge/discharge cycles, suggesting a good cycling stability of the composite electrodes. The good capacitive performance of the conducting–polymer-RGO composites is contributed to the synergic effect of the two components.
The impact of central Asian aridification on the low latitude North Pacific Ocean since the late Miocene remains unclear. To address this question, we systematically studied an abyssal manganese ...nodule from the northwestern Pacific Ocean, which is expected to be sensitive to eolian dust sourced from central Asia. Geochemical variations and the fossilized remains of magnetotactic bacteria within the studied nodule manifest two prominent Asian aridification events at ∼8–7 Ma and 3.6–0 Ma. These results suggest that central Asian aridification impacted both primary productivity and abyssal microbial activity in the NW Pacific Ocean via eolian dust inputs. In contrast to the Pliocene aridification event, the late Miocene event was associated with a primary productivity bloom that is not evident in coeval global primary productivity records, which indicates that the ∼8–7 Asian aridification event was likely due to NE Tibetan Plateau uplift rather than to global cooling.
Plain Language Summary
Central Asian aridification since the late Miocene has had a significant influence on climate, temperature, and North Pacific Ocean productivity through eolian dust inputs transported by westerlies. However, it is unclear whether the low latitude of NW Pacific Ocean responded to this aridification. We systematically analyzed the geochemistry and magnetism of a NW Pacific manganese nodule, and find that Asian aridification since, the late Miocene impacted biogeochemical cycling and abyssal microbial activity in the NW Pacific Ocean via eolian dust input. Our results imply that these two prominent Asian aridification events at around 8–7 Ma and ca. 3.6 Ma can be attributed to the NE Tibetan Plateau uplift and global cooling, respectively.
Key Points
A manganese nodule from the NW Pacific carries a paleoclimatic record of Asian aridification since the Late Miocene
Asian aridification impacted biogeochemical cycling and abyssal microbial activity in the NW Pacific Ocean
Major Asian aridification events at ∼8–7 Ma and ∼3.6–0 Ma may be attributed to NE Tibetan Plateau uplift and global cooling, respectively
Supercapacitors, which are attracting rapidly growing interest from both academia and industry, are important energy‐storage devices for acquiring sustainable energy. Recent years have seen a number ...of significant breakthroughs in the research and development of supercapacitors. The emergence of innovative electrode materials (e.g., graphene) has clearly provided great opportunities for advancing the science in the field of electrochemical energy storage. Conversely, smart configurations of electrode materials and new designs of supercapacitor devices have, in many cases, boosted the electrochemical performance of the materials. We attempt to summarize recent research progress towards the design and configuration of electrode materials to maximize supercapacitor performance in terms of energy density, power density, and cycle stability. With a brief description of the structure, energy‐storage mechanism, and electrode configuration of supercapacitor devices, the design and configuration of symmetric supercapacitors are discussed, followed by that of asymmetric and hybrid supercapacitors. Emphasis is placed on the rational design and configuration of supercapacitor electrodes to maximize the electrochemical performance of the device.
Charged and ready to go: In the past few years, significant breakthroughs in the development of supercapacitors as energy‐storage devices is promoted by the emergence of innovative electrode materials (e.g., graphene) and driven by rapidly increasing demands for high‐performance energy‐storage devices (see picture; ASC/SSC=asymmetric/symmetric supercapacitor.
•The article models ridership impacts of integrating ridesourcing with public transit.•Ridesourcing can help promote transit ridership and reduce operation costs.•Ridesourcing complements public ...transit by enhancing last-mile transit access.•Ridesourcing significantly reduces the wait time and travel time of a transit trip.•Transfers and additional pickups deter the integration of ridesourcing and transit.
Inspired by the success of private ridesourcing companies such as Uber and Lyft, transit agencies have started to consider integrating ridesourcing services (i.e. on-demand, app-driven ridesharing services) with public transit. Ridesourcing services may enhance the transit system in two major ways: replacing underutilized routes to improve operational efficiency, and providing last-mile connectivity to extend transit’s catchment area. While an integrated system of ridesourcing services and public transit is conceptually appealing, little is known regarding whether and how consumers might use a system like this and what key service attributes matter the most to them. This article investigates traveler responses to a proposed integrated transit system, named MTransit, at the University of Michigan Ann Arbor campus. We conducted a large-sample survey to collect both revealed preference (RP) and stated preference (SP) data and fit a RP-SP mixed logit model to examine the main determinants of commuting mode choice. The model results show that transfers and additional pickups are major deterrents for MTransit use. We further applied the model outputs to forecast the demand for MTransit under different deployment scenarios. We find that replacing low-ridership bus lines with ridesourcing services could slightly increase transit ridership while reducing operations costs. The service improvements offered by ridesourcing mainly come from reductions in wait time. Though relatively small in our study, another source of improvement is the decrease of in-vehicle travel time. Moreover, we find that when used to provide convenient last-mile connections, ridesourcing could provide a significant boost to transit. This finding verifies a popular notion among transit professionals that ridesourcing services can serve as a complement to public transit by enhancing last-mile transit access.
Vasculogenic mimicry (VM) refers to the unique capability of aggressive tumor cells to mimic the pattern of embryonic vasculogenic networks. In the study we demonstrated that CD133 expression was the ...highest in triple-negative (TN) breast cancer specimens. Importantly, VM showed statistical correlation with CD133(+) expression. The presence of the close relationship between VM and CD133(+) expression might be central for TN tumor relapse and progression. The TN breast cancer cell line, MDA-MB-231 cells developed a range of colony morphologies paralleling the holoclone, meroclone and paraclone morphologies produced by normal keratinocytes and other epithelial cancer cell lines when plated at clonal densities. Holoclone cells were capable of forming more colonies on soft agar than meroclone cells and paraclone cells, suggesting that holoclone cells had higher self-renew potential and might harbors cancer stem cells (CSCs) subpopulation. Strikingly, it was holoclone that displayed CD133(+) phenotype and formed VM. In addition, holoclone acquired endothelial cell marker vascular endothelial-cadherin expression and upregulated VM mediators matrix metalloproteinase (MMP)-2 and MMP-9 expression. The subpopulation with holoclone morphology, CD133(+) phenotype and CSCs characteristics might have the capacity of transdifferentiation and contributed to VM in TN breast cancer. The related molecular pathways may be used as novel therapeutic targets for the inhibition of angiogenesis and metastasis in TN breast carcinoma.
As PT and CP symmetries are fundamental in physics, we establish a unified topological theory of PT and CP invariant metals and nodal superconductors, based on the mathematically rigorous KO theory. ...Representative models are constructed for all nontrivial topological cases in dimensions d=1, 2, and 3, with their exotic physical meanings being elucidated in detail. Intriguingly, it is found that the topological charges of Fermi surfaces in the bulk determine an exotic direction-dependent distribution of topological subgap modes on the boundaries. Furthermore, by constructing an exact bulk-boundary correspondence, we show that the topological Fermi points of the PT and CP invariant classes can appear as gapless modes on the boundary of topological insulators with a certain type of anisotropic crystalline symmetry.
Manipulating physical properties using the spin degree of freedom constitutes a major part of modern condensed matter physics and is a key aspect for spintronics devices. Using the newly discovered ...two-dimensional van der Waals ferromagnetic CrI3 as a prototype material, we theoretically demonstrated a giant magneto band-structure (GMB) effect whereby a change of magnetization direction significantly modifies the electronic band structure. Our density functional theory calculations and model analysis reveal that rotating the magnetic moment of CrI3 from out-of-plane to in-plane causes a direct-to-indirect bandgap transition, inducing a magnetic field controlled photoluminescence. Moreover, our results show a significant change of Fermi surface with different magnetization directions, giving rise to giant anisotropic magnetoresistance. Additionally, the spin reorientation is found to modify the topological states. Given that a variety of properties are determined by band structures, our predicted GMB effect in CrI3 opens a new paradigm for spintronics applications.
The sublattice symmetry on a bipartite lattice is commonly regarded as the chiral symmetry in the AIII class of the tenfold Altland-Zirnbauer classification. Here, we reveal the spatial nature of ...sublattice symmetry and show that this assertion holds only if the periodicity of primitive unit cells agrees with that of the sublattice labeling. In cases where the periodicity does not agree, sublattice symmetry is represented as a glide reflection in energy-momentum space, which inverts energy and simultaneously translates some k by π, leading to substantially different physics. Particularly, it introduces novel constraints on zero modes in semimetals and completely alters the classification table of topological insulators compared to class AIII. Notably, the dimensions corresponding to trivial and nontrivial classifications are switched, and the nontrivial classification becomes
instead of
. We have applied these results to several models, including the Hofstadter model both with and without dimerization.
Weyl semimetals are a class of materials that can be regarded as three-dimensional analogs of graphene upon breaking time-reversal or inversion symmetry. Electrons in a Weyl semimetal behave as Weyl ...fermions, which have many exotic properties, such as chiral anomaly and magnetic monopoles in the crystal momentum space. The surface state of a Weyl semimetal displays pairs of entangled Fermi arcs at two opposite surfaces. However, the existence of Weyl semimetals has not yet been proved experimentally. Here, we report the experimental realization of a Weyl semimetal in TaAs by observing Fermi arcs formed by its surface states using angle-resolved photoemission spectroscopy. Our first-principles calculations, which match remarkably well with the experimental results, further confirm that TaAs is a Weyl semimetal.
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