Electron-electron and spin-orbit interactions in armchair graphene ribbons

The effects of intrinsic spin-orbit and Coulomb interactions on low-energy properties of finite width graphene armchair ribbons are studied by means of a Dirac Hamiltonian. It is shown that metallic states subsist in the presence of intrinsic spin-orbit interactions as spin-filtered edge states, in contrast with the insulating behavior predicted for graphene planes. A charge-gap opens due to Coulomb interactions in neutral ribbons, that vanishes as $\Delta\sim 1/W$, with a gapless spin sector. Weak intrinsic spin-orbit interactions do not change the insulating behavior. Explicit expressions for the width-dependent gap and various correlation functions are presented.Comment: Will appear in PR

Graphene zigzag ribbons, square lattice models and quantum spin chains

We present an extended study of finite-width zigzag graphene ribbons (ZGRs) based on a tight-binding model with hard-wall boundary conditions. We provide an exact analytic solution that clarifies the origin of the predicted width dependence on the conductance through junctions of ribbons with different widths. An analysis of the obtained solutions suggests a new description of ZGRs in terms of coupled chains. We pursue these ideas further by introducing a mapping between the ZGR model and the Hamiltonian for N-coupled quantum chains as described in terms of 2N Majorana fermions. The proposed mapping preserves the dependence of ribbon properties on its width thus rendering metallic ribbons for N odd and zero-gap semiconductor ribbons for N even. Furthermore, it reveals a close connection between the low-energy properties of the ZGR model and a continuous family of square lattice model Hamiltonians with similar width-dependent properties that includes the $\pi-$flux and the trivial square lattice models. As a further extension, we show that this new description makes it possible to identify various aspects of the physics of graphene ribbons with those predicted by models of quantum spin chains (QSCs)

Quantum spin Hall phase in neutral zigzag graphene ribbons

We present a detailed description of the nature of the wavefunction and spin distribution of the zero energy modes of zigzag graphene ribbons (ZGRs) in the presence of the intrinsic spin_orbit (I-SO) interaction. These states characterize the quantum spin Hall (QSH) phase in graphene ribbons. We provide analytic expressions for wavefunctions and show how these evolve as the strength of the interaction and the ribbon width are changed. For odd-width ribbons, we show that its insulating nature precludes the existence of a QSH phase. For these systems the I-SO interaction is predicted to have a stronger effect as shown by the enhancement of the gap as the interaction strength is turned on

Enhancement of the Kondo effect through Rashba spin-orbit interactions

We analyze the physics of a one-orbital Anderson impurity model in a two-dimensional electron gas in the presence of Rashba spin-orbit (RSO) interactions in the Kondo regime. The spin SU(2) symmetry breaking results in an effective two-band electron gas coupled to the impurity. The Kondo regime is obtained by a Schrieffer-Wolff transformation revealing the existence of a parity breaking term with the form of the Dzyaloshinsky-Moriya (DM) interaction. The DM term vanishes at the particle-hole symmetric point of the system, but it has important effects otherwise. Performing a renormalization group (RG) analysis we find that the model describes a two-channel Kondo system with ferro- and anti-ferromagnetic couplings. Furthermore, the DM term renormalizes the antiferromagnetic Kondo coupling producing an exponential enhancement of the Kondo temperature. We suggest that these effects can be observed in semiconducting systems, as well as in graphene and topological insulators.Comment: 4 pages, 1 figure. Final published versio

Medical Dominance in Nursing Education: Qualitative content analysis

Background: Training specialist manpower requires social justice in higher education and inequality leads to the emergence of hierarchies of power and types of dominant or dominated groups. Aim: The aim of the present study was to explain the perceptions and experiences of the heads of nursing departments of Iranian nursing schools regarding medical dominance in nursing education. Methods: The present study was a conventional content analysis. Data collection was carried out using purposeful sampling and in-depth semi-structured interviews with 24 participants. The data analysis process was performed according to Graneheim and Lundman’s qualitative content analysis (2004).  Findings: Data analysis led to the emergence of the theme of "Medical dominance in nursing education" and the three main categories of “physician-centered university education", "weakened educational status", and "belittling nursing education in medical system”. Conclusion: The findings of the present study indicated that physicians enjoy special and superior position in the structure of the Ministry of Health and Medical Education of Iran. Physicians manage the entire system including medical education due to their greater power in managing the system at all micro and macro levels. Thus, other disciplines including nursing education, which are closely related to medicine, are highly ignored

Quantum Interferences and Electron Transfer in Photosystem I

We have studied the electron transfer occurring in the photosystem I (PSI) reaction center from the special pair to the first iron–sulfur cluster. Electronic structure calculations performed at the DFT level were employed to determine the on-site energies of the fragments comprising PSI, as well as the charge transfer integrals between neighboring pairs. This electronic Hamiltonian was then used to compute the charge transfer dynamics, using the stochastic surrogate Hamiltonian approach to account for the coherent propagation of the electronic density but also for its energy relaxation and decoherence. These simulations give reasonable transfer time ranging from subpicoseconds to nanoseconds and predict coherent oscillations for several picoseconds. Due to these long-lasting coherences, the propagation of the electronic density can be enhanced or inhibited by quantum interferences. The impact of random fluctuations and asymmetries on these interferences is then discussed. Random fluctuations lead to a classical transport where both constructive and destructive quantum interferences are suppressed. Finally it is shown that an energy difference of 0.15 eV between the on-site energies of the phylloquinones leads to a highly efficient electron transfer even in presence of strong random fluctuations

Adolescent transport and unintentional injuries: a systematic analysis using the Global Burden of Disease Study 2019

Background Globally, transport and unintentional injuries persist as leading preventable causes of mortality and morbidity for adolescents. We sought to report comprehensive trends in injury-related mortality and morbidity for adolescents aged 10-24 years during the past three decades. Methods Using the Global Burden of Disease, Injuries, and Risk Factors 2019 Study, we analysed mortality and disability-adjusted life-years (DALYs) attributed to transport and unintentional injuries for adolescents in 204 countries. Burden is reported in absolute numbers and age-standardised rates per 100 000 population by sex, age group (10-14, 15-19, and 20-24 years), and sociodemographic index (SDI) with 95% uncertainty intervals (UIs). We report percentage changes in deaths and DALYs between 1990 and 2019. Findings In 2019, 369 061 deaths (of which 214337 [58%] were transport related) and 31.1 million DALYs (of which 16.2 million [52%] were transport related) among adolescents aged 10-24 years were caused by transport and unintentional injuries combined. If compared with other causes, transport and unintentional injuries combined accounted for 25% of deaths and 14% of DALYs in 2019, and showed little improvement from 1990 when such injuries accounted for 26% of adolescent deaths and 17% of adolescent DALYs. Throughout adolescence, transport and unintentional injury fatality rates increased by age group. The unintentional injury burden was higher among males than females for all injury types, except for injuries related to fire, heat, and hot substances, or to adverse effects of medical treatment. From 1990 to 2019, global mortality rates declined by 34.4% (from 17.5 to 11.5 per 100 000) for transport injuries, and by 47.7% (from 15.9 to 8.3 per 100000) for unintentional injuries. However, in low-SDI nations the absolute number of deaths increased (by 80.5% to 42 774 for transport injuries and by 39.4% to 31 961 for unintentional injuries). In the high-SDI quintile in 2010-19, the rate per 100 000 of transport injury DALYs was reduced by 16.7%, from 838 in 2010 to 699 in 2019. This was a substantially slower pace of reduction compared with the 48.5% reduction between 1990 and 2010, from 1626 per 100 000 in 1990 to 838 per 100 000 in 2010. Between 2010 and 2019, the rate of unintentional injury DALYs per 100 000 also remained largely unchanged in high-SDI countries (555 in 2010 vs 554 in 2019; 0.2% reduction). The number and rate of adolescent deaths and DALYs owing to environmental heat and cold exposure increased for the high-SDI quintile during 2010-19. Interpretation As other causes of mortality are addressed, inadequate progress in reducing transport and unintentional injury mortality as a proportion of adolescent deaths becomes apparent. The relative shift in the burden of injury from high-SDI countries to low and low-middle-SDI countries necessitates focused action, including global donor, government, and industry investment in injury prevention. The persisting burden of DALYs related to transport and unintentional injuries indicates a need to prioritise innovative measures for the primary prevention of adolescent injury