The experimentally observed correlated insulating states and quantum anomalous Hall (QAH) effect in twisted bilayer graphene (TBG) have drawn significant attention. However, up to date, the specific ...mechanisms of these intriguing phenomena are still open questions. Using an all-band Hartree-Fock variational method, we have explained the correlated insulating states and QAH effects at some integer fillings of the flat bands in TBG. Our results indicate that states breaking flavor (valley and spin) symmetries are energetically favored at all integer fillings. In particular, the correlated insulating states at ±1/2 filling and at the charge neutrality point are all valley polarized states which break C2z and time-reversal (T ) symmetries but preserve C2zT symmetry. Such valley polarized states exhibit "moiré orbital antiferromagnetic ordering" on an emergent honeycomb lattice with compensating circulating current pattern in the moiré supercell. Within the same theoretical framework, our calculations indicate that the C = ∓ 1 QAH states at ± 3/4 fillings of the magic-angle TBG are spin and orbital ferromagnetic states, which emerge when a staggered sublattice potential is present. We find that the nonlocalness of the exchange interactions tends to enhance the bandwidth of the low-energy bands due to the exchange-hole effect, which reduces the gaps of the correlated insulator phases. The nonlocal exchange interactions also dramatically enhance the spin polarization of the system, which significantly stabilizes the orbital and spin ferromagnetic QAH state at 3/4 filling of TBG aligned with hexagonal boron nitride (hBN). We also predict that, by virtue of the orbital ferromagnetic nature, the QAH effects at electron and hole fillings of hBN-aligned TBG would exhibit hysteresis loops with opposite chiralities.
We study the electronic structures and topological properties of (M+N)-layer twisted graphene systems. We consider the generic situation thatN-layer graphene is placed on top of the otherM-layer ...graphene and is twisted with respect to each other by an angleθ. In such twisted multilayer graphene systems, we find that there exist two low-energy flat bands for each valley emerging from the interface between theMlayers and theNlayers. These two low-energy bands in the twisted multilayer graphene system possess valley Chern numbers that are dependent on both the number of layers and the stacking chiralities. In particular, when the stacking chiralities of theMlayers andNlayers are opposite, the total Chern number of the two low-energy bands for each valley equals±(M+N−2)(per spin). If the stacking chiralities of theMlayers and theNlayers are the same, then the total Chern number of the two low-energy bands for each valley is±(M−N)(per spin). The valley Chern numbers of the low-energy bands are associated with large, valley-contrasting orbital magnetizations, suggesting the possible existence of orbital ferromagnetism and anomalous Hall effect once the valley degeneracy is lifted either externally by a weak magnetic field or internally by Coulomb interaction through spontaneous symmetry breaking. Such an orbital ferromagnetic state is characterized by chiral current loops circulating around theAAregion of the moiré pattern, which can be experimentally detected.
Dysbiosis, departure of the gut microbiome from a healthy state, has been suggested to be a powerful biomarker of disease incidence and progression
. Diagnostic applications have been proposed for ...inflammatory bowel disease diagnosis and prognosis
, colorectal cancer prescreening
and therapeutic choices in melanoma
. Noninvasive sampling could facilitate large-scale public health applications, including early diagnosis and risk assessment in metabolic
and cardiovascular diseases
. To understand the generalizability of microbiota-based diagnostic models of metabolic disease, we characterized the gut microbiota of 7,009 individuals from 14 districts within 1 province in China. Among phenotypes, host location showed the strongest associations with microbiota variations. Microbiota-based metabolic disease models developed in one location failed when used elsewhere, suggesting that such models cannot be extrapolated. Interpolated models performed much better, especially in diseases with obvious microbiota-related characteristics. Interpolation efficiency decreased as geographic scale increased, indicating a need to build localized baseline and disease models to predict metabolic risks.
Objective
Seizure occurs when the balance between excitatory and inhibitory (E/I) inputs to neurons is perturbed, resulting in abnormal electrical activity. This study investigated whether an ...existing E/I imbalance in neural networks is a useful diagnostic biomarker for Rolandic epilepsy by a resting‐state dynamic causal modeling‐based support vector machine (rs‐DCM‐SVM) algorithm.
Methods
This multicenter study enrolled a discovery cohort (76 children with Rolandic epilepsy and 76 normal controls NCs) and a replication cohort (59 children with Rolandic epilepsy and 60 NCs). Spatial independent component analysis was used to seven canonical neural networks, and a total of 25 regions of interest were selected from these networks. The rs‐DCM‐SVM classifier was used for individual classification, consensus feature selection, and feature ranking.
Results
The rs‐DCM‐SVM classifier showed that the E/I imbalance in brain networks is a useful neuroimaging biomarker for Rolandic epilepsy, with an accuracy of 88.2% and 81.5% and an area under curve of .92 and .83 in the discovery and the replication cohorts, respectively. Consensus brain regions with the highest contributions to the classification were located within the epilepsy‐related networks, indicating that this classifier was suitable. Consensus functional connection pairs with the highest contributions to the classification were associated with an excitation network loop and an inhibition network loop. The excitation loop mediated the integration of advanced cognitive networks (subcortex, dorsal attention, default mode, executive control, and salience networks), whereas the inhibition loop was involved in the segregation of sensorimotor and language networks. The two loops showed functional segregation.
Significance
Brain E/I imbalance has potential to serve as a biomarker for individual classification in children with Rolandic epilepsy, and might be an important mechanism for causing seizures and cognitive impairment in children with Rolandic epilepsy.
Rechargeable aqueous zinc-ion batteries are promising energy storage devices due to their high safety and low cost. However, they remain in their infancy because of the limited choice of positive ...electrodes with high capacity and satisfactory cycling performance. Furthermore, their energy storage mechanisms are not well established yet. Here we report a highly reversible zinc/sodium vanadate system, where sodium vanadate hydrate nanobelts serve as positive electrode and zinc sulfate aqueous solution with sodium sulfate additive is used as electrolyte. Different from conventional energy release/storage in zinc-ion batteries with only zinc-ion insertion/extraction, zinc/sodium vanadate hydrate batteries possess a simultaneous proton, and zinc-ion insertion/extraction process that is mainly responsible for their excellent performance, such as a high reversible capacity of 380 mAh g
and capacity retention of 82% over 1000 cycles. Moreover, the quasi-solid-state zinc/sodium vanadate hydrate battery is also a good candidate for flexible energy storage device.
Dirac and Weyl semimetals both exhibit arc-like surface states. However, whereas the surface Fermi arcs in Weyl semimetals are topological consequences of the Weyl points themselves, the surface ...Fermi arcs in Dirac semimetals are not directly related to the bulk Dirac points, raising the question of whether there exists a topological bulk-boundary correspondence for Dirac semimetals. In this work, we discover that strong and fragile topological Dirac semimetals exhibit one-dimensional (1D) higher-order hinge Fermi arcs (HOFAs) as universal, direct consequences of their bulk 3D Dirac points. To predict HOFAs coexisting with topological surface states in solid-state Dirac semimetals, we introduce and layer a spinful model of an s-d-hybridized quadrupole insulator (QI). We develop a rigorous nested Jackiw-Rebbi formulation of QIs and HOFA states. Employing ab initio calculations, we demonstrate HOFAs in both the room- (α) and intermediate-temperature (α″) phases of Cd
As
, KMgBi, and rutile-structure (Formula: see text-) PtO
.
Herein, we report a practical two‐step synthetic route to α‐arylpyrrolidines through Suzuki–Miyaura cross‐coupling and enantioselective copper‐catalyzed intramolecular hydroamination reactions. The ...excellent stereoselectivity and broad scope for the transformation of substrates with pharmaceutically relevant heteroarenes render this method a practical and versatile approach for pyrrolidine synthesis. Additionally, this intramolecular hydroamination strategy facilitates the asymmetric synthesis of tetrahydroisoquinolines and medium‐ring dibenzo‐fused nitrogen heterocycles.
An enantioselective copper‐catalyzed intramolecular hydroamination reaction can be used jointly with the Suzuki–Miyaura cross‐coupling to yield a diverse array of α‐arylpyrrolidine scaffolds that contain pharmaceutically relevant heteroarenes with excellent enantiomeric purity under mild conditions. Furthermore, this intramolecular hydroamination strategy is applicable to the asymmetric syntheses of six‐ to nine‐membered benzo‐fused nitrogen heterocycles.
Conjugate addition of carbon nucleophiles to electron‐deficient olefins is one of the most powerful methods for forming carbon–carbon bonds. Despite great achievements in controlling the selectivity, ...variation of the carbon nucleophiles remains largely underexplored, with this approach relying mostly on organometallic reagents. Herein, we report that naturally abundant carbonyls can act as latent carbon nucleophiles for conjugate additions through a ruthenium‐catalyzed process, with water and nitrogen as innocuous byproducts. The key to our success is homogeneous ruthenium(II) catalysis, combined with phosphines as spectator ligands and hydrazine as the reducing agent. This chemistry allows the incorporation of highly functionalized alkyl fragments into a vast array of electron‐deficient olefins under mild reaction conditions in a reaction complementary to the classical organometallic‐reagent‐based conjugate additions mediated or catalyzed by “soft” transition metals.
Hidden talents: Carbonyls can act as latent carbon nucleophiles for conjugate additions through a ruthenium‐catalyzed process. The reaction relies on homogeneous ruthenium(II) catalysis combined with phosphines as spectator ligands and hydrazine as the reducing agent. This method enables the incorporation of highly functionalized alkyl fragments into a vast array of electron‐deficient olefins under mild reaction conditions. EWG=electron‐withdrawing grop
We study the anomalous Hall effect, magneto-optical properties, and nonlinear optical properties of twisted bilayer graphene aligned with hexagonal boron nitride substrate, as well as twisted double ...bilayer graphene systems. We show that non-vanishing valley polarizations in twisted graphene systems would give rise to the anomalous Hall effect, which can be tuned by in-plane magnetic fields. The valley polarized states are also associated with giant Faraday and Kerr rotations in the terahertz frequency regime. Moreover, we propose that the twisted graphene systems exhibit colossal nonlinear optical responses by virtue of the inversion-symmetry breaking, the small bandwidth, and the small excitation gaps of the systems. In twisted double bilayer graphene, we find that certain components of the nonlinear photo-conductivity tensor are directly proportional to the orbital magnetization of the system, which would exhibit remarkable hysteresis behavior in response to perpendicular magnetic fields.
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