Spin-to-Orbital Angular Momentum Conversion in Semiconductor Microcavities

We experimentally demonstrate a technique for the generation of optical beams carrying orbital angular momentum using a planar semiconductor microcavity. Despite being isotropic systems, the transverse electric - transverse magnetic (TE-TM) polarization splitting featured by semiconductor microcavities allows for the conversion of the circular polarization of an incoming laser beam into the orbital angular momentum of the transmitted light field. The process implies the formation of topological entities, a pair of optical half-vortices, in the intracavity field

Quality performance of teachers: work environment, work attitude, and principal supervision: qualitative investigation

One of the most important factors in the face of the educational system is the quality of teachers’ performance. The goal of this study is to ascertain whether the teachers’ high-quality performance is actually impacted by the work environment, work attitude, and principal supervision. In this qualitative investigation, the Heideggerian Phenomenology design was employed. This study seeks to comprehend the phenomenon from the participant’s point of view and through their experiences. In this study, the purposive method was employed, and participants were chosen to expound on their experiences as general education teachers at PAU Excellencia Global Academy Foundation, Inc., teaching in an inclusion classroom. It has been discovered that the key to creating a positive learning environment in the classroom is workgroup encouragement, especially having good relationships with the principal. How frequently teachers must deal with unruly and aggressive students have largely defined teaching obstacles. A teacher’s perception of the supportive environment at school improved as he or she gained experience

Referral of sexual violence against children: How do children and caregivers use a formal child protection mechanism in Harare, Zimbabwe?

Despite widespread expansion of policies to prevent and respond to violence over the past three decades, sexual violence against children remains common globally. Zimbabwe has expansive legal and policy frameworks to prevent, and formal services to respond to, sexual violence. Yet evidence is lacking about how children and caregivers use formal referral mechanisms. This study conducted secondary qualitative analysis of sexual violence cases [N=74] processed in Harare Magistrates Court and referred to Childline Zimbabwe, in October-November 2020, to examine which experiences children and/or their caregivers formally refer as sexual violence; how they perceive and manage these experiences; and how this relates to national policy contexts. Caregivers, particularly female, were central to reporting sexual violence. Data suggested that some forms of sexual violence were formally referred, including community sexual assault and abuse within families, however some adolescent girls faced blame and shame. There were gaps in reporting of sexual violence against boys, and sexual violence from dating partners or authority figures, with data suggesting that gendered stigma, shame, and fears of institutional authority, were barriers for reporting. Caregivers also reported consensual adolescent sexual relationships to police. These findings contribute to the limited evidence on forms of sexual violence that are and are not formally referred globally, and in sub-Saharan African settings. Existing policy frameworks in Zimbabwe can be strengthened around age of maturity, adolescent sexuality, sidelining of boy survivors, and the role of schools in child protection. Interventions should support caregivers’ efforts to report violence, while also addressing gendered blame and stigma, and stigmatisation of adolescent sexuality

Optical manipulation of the wave function of quasiparticles in a solid

Polaritons in semiconductor microcavities are hybrid quasiparticles consisting of a superposition of photons and excitons. Due to the photon component, polaritons are characterized by a quantum coherence length in the several micron range. Owing to their exciton content, they display sizeable interactions, both mutual and with other electronic degrees of freedom. These unique features have produced striking matter wave phenomena, such as Bose-Einstein condensation, or parametric processes able to generate quantum entangled polariton states. Recently, several paradigms for spatial confinement of polaritons in semiconductor devices have been established. This opens the way to quantum devices in which polaritons can be used as a vector of quantum information. An essential element of each quantum device is the quantum state control. Here we demonstrate control of the wave function of confined polaritons, by means of tailored resonant optical excitation. By tuning the energy and momentum of the laser, we achieve precise control of the momentum pattern of the polariton wave function. A theoretical model supports unambiguously our observations

Spatial dynamics of confined semiconductor microcavity polaritons

We report on the dynamics of confined zero-dimensional polaritons. We excite resonantly discrete polariton states optically with a tailored picosecond laser pulse and observe their emission time resolved in the two-dimensional k space or real space. We are able to distinguish between three regimes. When the laser excites only one state no dynamics are observed. When a small number of well separated states are excited, the dynamics are described in terms of interference. When a quasicontinuum of states is excited, the dynamics are described in terms of ballistically propagating two-dimensional (2D) polaritons which scatter elastically at the potential barriers. The measured propagation velocities are reproduced with the theory of 2D polaritons, which sustains our interpretation

Symmetry-breaking Effects for Polariton Condensates in Double-Well Potentials

We study the existence, stability, and dynamics of symmetric and anti-symmetric states of quasi-one-dimensional polariton condensates in double-well potentials, in the presence of nonresonant pumping and nonlinear damping. Some prototypical features of the system, such as the bifurcation of asymmetric solutions, are similar to the Hamiltonian analog of the double-well system considered in the realm of atomic condensates. Nevertheless, there are also some nontrivial differences including, e.g., the unstable nature of both the parent and the daughter branch emerging in the relevant pitchfork bifurcation for slightly larger values of atom numbers. Another interesting feature that does not appear in the atomic condensate case is that the bifurcation for attractive interactions is slightly sub-critical instead of supercritical. These conclusions of the bifurcation analysis are corroborated by direct numerical simulations examining the dynamics of the system in the unstable regime.MICINN (Spain) project FIS2008- 0484

Collisional damping of dipole oscillations in a trapped polariton gas

We study the relaxation dynamics of a trapped polariton gas in the nonlinear regime. We excite the three lowest energy states of the system and observe the time evolution of the polariton density in the momentum space. At a low excitation power, the dynamics is characterized by dipole oscillations of constant amplitude. A damping of these oscillations is observed at a high excitation power. It is attributed to collisional relaxation within the coherent polariton gas. We investigate the dependence of this effect on the excitation power, polarization, and polariton excitonic content to highlight the role of polariton-polariton scattering. The experiments are described in the frame of a Gross-Pitaevskii mean-field theory. We find a good agreement between the theoretical simulations and the experimental observations. Analysis of the theoretical model reveals that multiple parametric scattering and final-state stimulation are responsible for the damping of the oscillations

Transformations in network governance: the case of migration intermediaries

types: Article"This is an Accepted Manuscript of an article published by Taylor & Francis in Journal of Ethnic and Migration Studies on 3 February 2015 available online: http://wwww.tandfonline.com/10.1080/1369183X.2014.1003803Market liberalisation has fundamentally changed state interventions in the supply of services and supportive infrastructure across a range of public services. While this trend has been relatively well documented, there has been a dearth of research into the changing nature of state interventions in migration and mobility. Indeed the increasing presence of migration intermediaries to service the many and varied needs of migrant workers, particularly skilled migrants, remains significantly under-researched both theoretically and empirically. In providing an analysis of the location, role and changing nature of migration intermediaries, we highlight the implications of commercially-driven governance structures. In particular we suggest that the shift from government to network governance has important implications for skilled migration including: inequities in access to information regarding the process of migration and labour market integration; and, greater dependence on (largely unregulated) private intermediaries. Accordingly, we present empirical examples of migration intermediaries to illustrate their role and the relationship with and implications of their exchange with migrants

Sialic acid receptor detection in the human respiratory tract: evidence for widespread distribution of potential binding sites for human and avian influenza viruses

<p>Abstract</p> <p>Background</p> <p>Influenza virus binds to cell receptors via sialic acid (SA) linked glycoproteins. They recognize SA on host cells through their haemagglutinins (H). The distribution of SA on cell surfaces is one determinant of host tropism and understanding its expression on human cells and tissues is important for understanding influenza pathogenesis. The objective of this study therefore was to optimize the detection of α2,3-linked and α2,6-linked SA by lectin histochemistry by investigating the binding of Sambucus nigra agglutinin (SNA) for SAα2,6Gal and Maackia amurensis agglutinin (MAA) for SAα2,3Gal in the respiratory tract of normal adults and children.</p> <p>Methods</p> <p>We used fluorescent and biotinylated SNA and MAA from different suppliers on archived and prospectively collected biopsy and autopsy specimens from the nasopharynx, trachea, bronchus and lungs of fetuses, infants and adults. We compared different methods of unmasking for tissue sections to determine if these would affect lectin binding. Using serial sections we then compared the lectin binding of MAA from different suppliers.</p> <p>Results</p> <p>We found that unmasking using microwave treatment in citrate buffer produced increased lectin binding to the ciliated and glandular epithelium of the respiratory tract. In addition we found that there were differences in tissue distribution of the α2,3 linked SA when 2 different isoforms of MAA (MAA1 and MAA2) lectin were used. MAA1 had widespread binding throughout the upper and lower respiratory tract and showed more binding to the respiratory epithelium of children than in adults. By comparison, MAA2 binding was mainly restricted to the alveolar epithelial cells of the lung with weak binding to goblet cells. SNA binding was detected in bronchial and alveolar epithelial cells and binding of this lectin was stronger to the paediatric epithelium compared to adult epithelium. Furthermore, the MAA lectins from 2 suppliers (Roche and EY Labs) tended to only bind in a pattern similar to MAA1 (Vector Labs) and produced a different binding pattern to MAA2 from Vector Labs.</p> <p>Conclusion</p> <p>The lectin binding pattern of MAA may vary depending on the supplier and the different isoforms of MAA show a different tissue distribution in the respiratory tract. This finding is important if conclusions about the potential binding sites of SAα2,3 binding viruses, such as influenza or human parainfluenza are to be made.</p