Microscopic theory of quantum anomalous Hall effect in graphene

We present a microscopic theory to give a physical picture of the formation of quantum anomalous Hall (QAH) effect in graphene due to a joint effect of Rashba spin-orbit coupling $\lambda_R$ and exchange field $M$. Based on a continuum model at valley $K$ or $K'$, we show that there exist two distinct physical origins of QAH effect at two different limits. For $M/\lambda_R\gg1$, the quantization of Hall conductance in the absence of Landau-level quantization can be regarded as a summation of the topological charges carried by Skyrmions from real spin textures and Merons from \emph{AB} sublattice pseudo-spin textures; while for $\lambda_R/M\gg1$, the four-band low-energy model Hamiltonian is reduced to a two-band extended Haldane's model, giving rise to a nonzero Chern number $\mathcal{C}=1$ at either $K$ or $K'$. In the presence of staggered \emph{AB} sublattice potential $U$, a topological phase transition occurs at $U=M$ from a QAH phase to a quantum valley-Hall phase. We further find that the band gap responses at $K$ and $K'$ are different when $\lambda_R$, $M$, and $U$ are simultaneously considered. We also show that the QAH phase is robust against weak intrinsic spin-orbit coupling $\lambda_{SO}$, and it transitions a trivial phase when $\lambda_{SO}>(\sqrt{M^2+\lambda^2_R}+M)/2$. Moreover, we use a tight-binding model to reproduce the ab-initio method obtained band structures through doping magnetic atoms on $3\times3$ and $4\times4$ supercells of graphene, and explain the physical mechanisms of opening a nontrivial bulk gap to realize the QAH effect in different supercells of graphene.Comment: 10pages, ten figure

Topological phases in gated bilayer graphene: Effects of Rashba spin-orbit coupling and exchange field

We present a systematic study on the influence of Rashba spin-orbit coupling, interlayer potential difference and exchange field on the topological properties of bilayer graphene. In the presence of only Rashba spin-orbit coupling and interlayer potential difference, the band gap opening due to broken out-of-plane inversion symmetry offers new possibilities of realizing tunable topological phase transitions by varying an external gate voltage. We find a two-dimensional $Z_2$ topological insulator phase and a quantum valley Hall phase in $AB$-stacked bilayer graphene and obtain their effective low-energy Hamiltonians near the Dirac points. For $AA$ stacking, we do not find any topological insulator phase in the presence of large Rashba spin-orbit coupling. When the exchange field is also turned on, the bilayer system exhibits a rich variety of topological phases including a quantum anomalous Hall phase, and we obtain the phase diagram as a function of the Rashba spin-orbit coupling, interlayer potential difference, and exchange field.Comment: 15 pages, 17figures, and 1 tabl

Psychometric properties of the Chinese version of the pediatric quality of life inventory 4.0 Generic core scales among children with short stature

BACKGROUND: The quality of life in children with short stature was rarely studied in China, so we explore these children’s quality of life and psychometric properties of the Chinese version of the Pediatric Quality of Life Inventory 4.0(PedsQL4.0) Generic Core Scales among children with short stature. METHODS: A total of 201 children aged 8 ~ 18 years from the short stature clinic and other clinics of capital institute of pediatrics attended this study. The questionnaires include demographic information and PedsQL4.0 generic core scales. According to children’s height, we divided them into three groups: short stature, normal short and normal group, then compared the score of scales by the height category. Moreover, we analyzed the reliability and validity of PedsQL4.0 generic core scales in these 201 children. RESULTS: The child self-report total PedsQL mean score, for the short stature, normal short and normal groups were 77.77 ± 9.69, 83.50 ± 8.56 and 87.36 ± 7.23; the parent-proxy total PedsQL mean score were 77.62 ± 10.50, 82.69 ± 8.35 and 84.91 ± 9.96 respectively. Both for children self- and parent proxy-reports, the Cronbach’s α coefficients of total scale, psychosocial health and social functioning ranged between 0.74 and 0.80, it ranged between 0.51 and 0.66 in other dimensions. For child self-reports, the correlation coefficients of 17 items’ scores (total 23 items) with the scores of dimensions they belong to were above 0.5, with the highest 0.759; the other 6 items’ correlation coefficients were below 0.5, with the lowest 0.280. For parent proxy-reports, the correlation coefficients of 19 items’ scores with the scores of dimension they belong to were above 0.5, with the highest 0.793, the other 4 items’ below 0.5 with the lowest 0.243. CONCLUSIONS: The quality of life in children with short stature is worse than their normal peers by Peds QL4.0 generic core scales, the statues of their quality of life was positively related to their stature

Primary synovial sarcoma of the heart

Primary synovial sarcoma of the heart is very rare, accounting for 5% of cardiac malignancies. Of the few cases reported in the literature to date, nearly all have had a very poor outcome. We present a further case. This uncommon malignancy has no specific symptoms during its development, which results in delayed diagnosis. Echocardiography, chest computed tomography, and magnetic resonance imaging can provide effective information about this tumor. With the identification of the characteristic and diagnostic chromosomal abnormality t(X; 18), this malignancy will become increasingly recognized. Synovial sarcoma of the heart requires surgical intervention to improve the prognosis. Adjuvant and/or genetic therapy pre- or postoperation can help prolong life. Chemotherapy is usually recommended as it may benefit the patients. The key to treatment in the future is to find new therapeutic agents. Further elucidation of the effects of this chromosomal abnormality may lead to better-directed therapies in future. (Cardiol J 2011; 18, 2: 128-133