1,233 research outputs found
High Chern number quantum anomalous Hall phases in graphene ribbons with Haldane orbital coupling
We investigate possible phase transitions among the different quantum
anomalous Hall (QAH) phases in a zigzag graphene ribbon under the influence of
the exchange field. The effective tight-binding Hamiltonian for graphene is
made up of the hopping term, the Kane-Mele and Rashba spin-orbit couplings as
well as the Haldane orbital term. We find that the variation of the exchange
field results in bulk gap-closing phenomena and phase transitions occur in the
graphene system. If the Haldane orbital coupling is absent, the phase
transition between the chiral (anti-chiral) edge state () and
the pseudo-quantum spin Hall state () takes place. Surprisingly, when
the Haldane orbital coupling is taken into account, an intermediate QSH phase
with two additional edge modes appears in between phases and .
This intermediate phase is therefore either the hyper-chiral edge state of high
Chern number or anti-hyper-chiral edge state of when the
direction of exchange field is reversed. We present the band structures, edge
state wave functions and current distributions of the different QAH phases in
the system. We also report the critical exchange field values for the QAH phase
transitions.Comment: 4 figure
A modified T. Chan’s preconditioner for Toeplitz systems
AbstractWe present a modified T. Chan’s preconditioner for solving Toeplitz linear systems by the preconditioned conjugate gradient (PCG) method in this paper. Especially, we give some results when the matrices are Hermitian positive definite Toeplitz matrices. The operation and convergence of the PCG method are discussed. Numerical examples presented illustrate the effectiveness of the preconditioner obtained
Some remarks on compositeness of
Recently LHCb experimental group find an exotic state from the
process . A key question is if it is just a
molecule or may have confined tetraquark ingredient. To investigate this,
different methods are taken, including two channel ( and
) K-matrix unitarization and single channel Flatt\'e-like
parametrization method analysed by pole counting rule and spectral density
function sum rule. It demonstrates that is a molecular state, though
the possibility that there may exist elementary ingredient can not be excluded,
by rough analysis on its production rate
Clinical effect of high-flow revascularization in microsurgery combined with endoscopic endonasal surgery for skull base tumors with intracranial and extracranial involvement
BackgroundThe objective of the study is to investigate the surgical methods and clinical effects of high-flow revascularization in microsurgery combined with endoscopic endonasal surgery for skull base tumors with intracranial and extracranial involvement.MethodsThe relationships between skull base tumors and internal carotid artery (ICA), tumor location and size, and the extent of tumor invasion were assessed. Preoperative CT perfusion (CTP), magnetic resonance (MR) perfusion-weighted imaging (PWI) (MR-PWI), and digital subtraction angiography (DSA) were performed to evaluate collateral circulation and brain tissue perfusion. Then craniotomy through the fronto-orbitozygomatic approach was performed, based on which four cases received extended middle skull base approach+Dolenc approach + Fukushima bypass type I, and six cases received extended middle skull base approach+Fukushima bypass type III. After surgery, DSA, CT angiogram (CTA), and CTP/PWI were performed to evaluate the patency of the reconstructed vessels and cerebral perfusion, and contrast-enhanced MRI to evaluate the degree of tumor resection. All patients were followed up for 6–12 months.ResultsAmong the 10 cases investigated, gross total resection was achieved in 8 cases, subtotal resection in 1 case, and partial resection in 1 case, as confirmed by CT and enhanced MRI. The patency of revascularization vessels was observed using fluorescein angiography during the operation in all patients and via DSA and CTA postoperatively in nine patients. One patient underwent ventilator-assisted ventilation because of respiratory failure and failed to undergo DSA and CTA. Regarding postoperative complications, one patient developed watershed cerebral infarction on the operated side but no sequelae after drug treatment, three patients developed facial numbness, which improved after 3 months, and two patients experienced worsened diplopia. After 6 to 12 months of follow-up on the nine evaluable patients, the Glasgow Outcome Scale (GOS) was 4–5 after surgery. In addition, 6-month follow-up results showed that one patient with clival chondrosarcoma developed recurrence on contrast-enhanced MRI, while no relapse was observed in the other patients.ConclusionFor skull base tumors with intracranial and extracranial invasion and involving the ICA, revascularization might improve the total resection rate and reduce the recurrence rate and risk of intraoperative bleeding and postoperative ischemia
{μ2-6,6′-Dimethoxy-2,2′-[butane-1,4-diylbis(nitrilomethylidyne)]diphenolato}trinitratocopper(II)neodymium(III)
In the title complex, [CuNd(C20H22N2O4)(NO3)3], the CuII ion is coordinated in a distorted square-planar environment by two O atoms and two N atoms of a tetradentate Schiff base ligand. The NdIII ion is ten-coordinated by three bis-chelating nitrate groups and four O atoms of the Schiff base ligand. The atoms of one of the nitrato ligands are disordered over two sets of sites, with refined occupancies of 0.567 (13) and 0.433 (17)
Factorization and Unitarity in Superstring Theory
The overall coefficient of the two-loop 4-particle amplitude in superstring
theory is determined by making use of the factorization and unitarity. To
accomplish this we computed in detail all the relevant tree and one-loop
amplitudes involved and determined their overall coefficients in a consistent
way.Comment: LaTex file, 19 pages, 4 figures; v2, minor corrections and figures
corrected; v3, minor corrections with the English, to be published in JHE
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