Spin splitting in open quantum dots

We present results from a theoretical and experimental study of spin-splitting in small open lateral quantum dots (i.e. in the regime when the dot is connected to the reservoirs via leads that support one or more propagating modes). We demonstrate that the magnetoconductance shows a pronounced splitting of the conductance peaks (or dips) which persists over a wide range of magnetic fields (from zero field to the edge-state regime) and is virtually independent of magnetic field. A numerical analysis of the conductance and the dot eigenspectrum indicates that this feature is related to a lifting of the spin degeneracy in the corresponding closed dot associated with the interaction between electrons of opposite spin.Comment: 4 pages, 4 figures 1 misdirected figure reference corrected mismatch between spin-up/spin-down notation in figure 3-4 and discussion corrected, clarifications in text adde

You Say Bully, I Say Bullied: School Culture and Definitions of Bullying in Two Elementary Schools

Purpose This chapter examines the definitions of bullying used by students and adults in elementary schools and the effects that these definitions had within the broader school culture. Design/methodology/approach I combine interviews with 53 students and 10 adults and over 430 hours of participant observation with fifth grade students at two rural elementary schools. Findings Definitions of bullying held by those in these schools typically differed from those used by researchers. Even when individuals held definitions that were in line with those used by researchers, however, a focus on identifying bullies rather than on behaviors that fit definitions of bullying contributed to a school culture in which negative interactions were normalized and student reports of these behaviors were discouraged. Research limitations/implications This study is limited to two elementary schools in the rural Midwest and cannot be seen as representative of all schools. Support for my findings from other research combined with similar definitions and school cultures in both schools, however, suggest that these definitions and practices are part of a broader cultural context of bullying in the United States. Practical implications These findings suggest that schools might be better served by focusing less on labels like bully and more on particular behaviors that are to be taken seriously by students, teachers, staff members, and principals. Originality/value Although other researchers have studied definitions of bullying, none have combined these definitions with observational data on the broader school contexts in which those definitions are created and used

Chemically-induced Mobility Gaps in Graphene Nanoribbons: A Route for Upscaling Device Performances

We report a first-principles based study of mesoscopic quantum transport in chemically doped graphene nanoribbons with a width up to 10 nm. The occurrence of quasibound states related to boron impurities results in mobility gaps as large as 1 eV, driven by strong electron-hole asymmetrical backscattering phenomena. This phenomenon opens new ways to overcome current limitations of graphene-based devices through the fabrication of chemically-doped graphene nanoribbons with sizes within the reach of conventional lithography.Comment: Nano Letters (in press

Right ventricular function parameters in pulmonary hypertension: echocardiography vs. cardiac magnetic resonance

BackgroundRight ventricular (RV) function is a major determinant of outcome in patients with pulmonary hypertension. Cardiac magnetic resonance (CMR) is gold standard to assess RV ejection fraction (RVEFCMR), however this is a crude measure. New CMR measures of RV function beyond RVEFCMR have emerged, such as RV lateral atrio-ventricular plane displacement (AVPDlat), maximum emptying velocity (S’CMR), RV fractional area change (FACCMR) and feature tracking of the RV free wall (FWSCMR). However, it is not fully elucidated if these CMR measures are in parity with the equivalent echocardiography-derived measurements: tricuspid annular plane systolic excursion (TAPSE), S’-wave velocity (S’echo), RV fractional area change (FACecho) and RV free wall strain (FWSecho). The aim of this study was to compare regional RV function parameters derived from CMR to their echocardiographic equivalents in patients with pulmonary hypertension and to RVEFCMR.MethodsFifty-five patients (37 women, 62 ± 15 years) evaluated for pulmonary hypertension underwent CMR and echocardiography. AVPDlat, S’CMR, FACCMR and FWSCMR from cine 4-chamber views were compared to corresponding echocardiographic measures and to RVEFCMR delineated in cine short-axis stack.ResultsA strong correlation was demonstrated for FAC whereas the remaining measurements showed moderate correlation. The absolute bias for S’ was 2.4 ± 3.0 cm/s (relative bias 24.1 ± 28.3%), TAPSE/AVPDlat 5.5 ± 4.6 mm (33.2 ± 25.2%), FWS 4.4 ± 5.8% (20.2 ± 37.5%) and for FAC 5.1 ± 8.4% (18.5 ± 32.5%). In correlation to RVEFCMR, FACCMR and FWSecho correlated strongly, FACecho, AVPDlat, FWSCMR and TAPSE moderately, whereas S’ had only a weak correlation.ConclusionThis study has demonstrated a moderate to strong correlation of regional CMR measurements to corresponding echocardiographic measures. However, biases and to some extent wide limits of agreement, exist between the modalities. Consequently, the equivalent measures are not interchangeable at least in patients with pulmonary hypertension. The echocardiographic parameter that showed best correlation with RVEFCMR was FWSecho. At present, FACecho and FWSecho as well as RVEFCMR are the preferred methods to assess and follow up RV function in patients with pulmonary hypertension. Future investigations of the CMR right ventricular measures, beyond RVEF, are warranted