Stability of negative and positive trions in quantum wires

Binding energies of negative ($X^-$) and positive trions ($X^+$) in quantum wires are studied for strong quantum confinement of carriers which results in a numerical exactly solvable model. The relative electron and hole localization has a strong effect on the stability of trions. For equal hole and electron confinement, $X^+$ is more stable but a small imbalance of the particle localization towards a stronger hole localization e.g. due to its larger effective mass, leads to the interchange of $X^-$ and $X^+$ recombination lines in the photoluminescent spectrum as was recently observed experimentally. In case of larger $X^-$ stability, a magnetic field oriented parallel to the wire axis leads to a stronger increase of the $X^+$ binding energy resulting in a crossing of the $X^+$ and $X^-$ lines

Exciton and negative trion dissociation by an external electric field in vertically coupled quantum dots

We study the Stark effect for an exciton confined in a pair of vertically coupled quantum dots. A single-band approximation for the hole and a parabolic lateral confinement potential are adopted which allows for the separation of the lateral center-of-mass motion and consequently for an exact numerical solution of the Schr\"odinger equation. We show that for intermediate tunnel coupling the external electric field leads to the dissociation of the exciton via an avoided crossing of bright and dark exciton energy levels which results in an atypical form of the Stark shift. The electric-field-induced dissociation of the negative trion is studied using the approximation of frozen lateral degrees of freedom. It is shown that in a symmetric system of coupled dots the trion is more stable against dissociation than the exciton. For an asymmetric system of coupled dots the trion dissociation is accompanied by a positive curvature of the recombination energy line as a function of the electric field.Comment: PRB - in prin

Coerced Hospital Admission and Symptom Change-A Prospective Observational Multi-Centre Study

PMCID: PMC3227658 Freely available online via CCplosone.org

Loss to follow-up in longitudinal psychiatric research

Publisher version: http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8264315&fulltextType=RA&fileId=S1121189X0000283

Optical Absorption Spectra of Bipolarons

The absorption of large bipolarons is investigated using the path-integral method. The response of a bipolaron to an external electromagnetic field is derived in the framework of the memory-function approach. The bipolaron optical absorption spectrum consists of a series of relatively narrow peaks. The peculiarities of the bipolaron optical absorption as a function of the frequency of the electromagnetic field may be attributed to the transitions involving relaxed excited states and scattering states of a bipolaron.Comment: 14 pages, 3 figures, E-mail addresses: [email protected], [email protected]; to be published in Phys. Rev.

Bipolaron Binding in Quantum Wires

A theory of bipolaron states in quantum wires with a parabolic potential well is developed applying the Feynman variational principle. The basic parameters of the bipolaron ground state (the binding energy, the number of phonons in the bipolaron cloud, the effective mass, and the bipolaron radius) are studied as a function of sizes of the potential well. Two cases are considered in detail: a cylindrical quantum wire and a planar quantum wire. Analytical expressions for the bipolaron parameters are obtained at large and small sizes of the quantum well. It is shown that at $R\gg 1$ [where $R$ means the radius (halfwidth) of a cylindrical (planar) quantum wire, expressed in Feynman units], the influence of confinement on the bipolaron binding energy is described by the function $\sim 1/R^{2}$ for both cases, while at small sizes this influence is different in each case. In quantum wires, the bipolaron binding energy $W(R)$ increases logarithmically with decreasing radius. The shapes and the sizes of a nanostructure, which are favorable for observation of stable bipolaron states, are determined.Comment: 17 pages, 6 figures, E-mail addresses: [email protected]; [email protected]

Novas narrativas sociais: as práticas de mídia livre através do audiovisual

Dissertação de mestrado apresentada à Escola Superior de Comunicação Social como parte dos requisitos para obtenção de grau de mestre em Audiovisual e Multimédia.Com a proliferação e popularização dos aparatos móveis de comunicação digital e o avanço dos dispositivos conectados à Internet, a mídia ganhou novos contornos, tanto quantitativos quanto qualitativos. O intenso fluxo de mudanças, em constante curso e evolução, trouxe para as mãos do grande público o material e espaço necessários para ser ativo na transmissão de mensagens na sociedade; em contrapartida, gerou uma perda do controle do conteúdo, excesso de informação disponível e inúmeros novos formatos de transmissão. Este trabalho pretende revisitar a bibliografia da área ao longo das últimas décadas, ressaltando os debates e teorias levantadas de acordo com as principais mudanças na Comunicação Social. As principais características da cada época trarão um contexto macro de manifestações sociais que hoje também apresentam-se no contexto micro. O uso social dos meios de comunicação é o foco e ponto chave para discutir o papel social, efetivo ou potencial, da mídia. Para que o benefício de controlar os meios de produção da informação, bem como aproveitar a liberdade presente no ciberespaço, seja utilizado em prol da sociedade e em favor da democracia. A importância histórica e social do discurso e da narrativa será explicado para comprovar a importância do debate sobre a mídia livre, assim como as suas principais características e práticas, ilustradas através do objeto de estudo, o coletivo Mídia NINJA.ABSTRACT: With the proliferation and popularization of mobile digital communication devices and the advancement of devices connected to the Internet, the media has gained new contours, both quantitative and qualitative. The intense flow of change, in constant progress and evolution, has brought into the hands of the general public the material and space necessary to be active in the transmission of messages in society; on the other hand, generated a loss of control of the content, excessive information available and numerous new transmission formats. This work intends to revisit the bibliography of the area over the last decades, highlighting the debates and theories raised according to the main changes in social communication. The main characteristics of each period will bring a macro context of social manifestations that today also present themselves in the micro context. The social use of the media is the focus and key point to discuss the social role, effective or potential, of the media. So that the benefit of controlling the means of information production, as well as taking advantage of the freedom present in cyberspace, be used for the benefit of society and for democracy. The historical and social importance of discourse and narrative will be explained to prove the importance of the debate about free media, as well as its main characteristics and practices, illustrated through the object of study, the collective Mídia NINJA.N/

The development of the Quality Indicator for Rehabilitative Care (QuIRC): a measure of best practice for facilities for people with longer term mental health problems.

BACKGROUND: Despite the progress over recent decades in developing community mental health services internationally, many people still receive treatment and care in institutional settings. Those most likely to reside longest in these facilities have the most complex mental health problems and are at most risk of potential abuses of care and exploitation. This study aimed to develop an international, standardised toolkit to assess the quality of care in longer term hospital and community based mental health units, including the degree to which human rights, social inclusion and autonomy are promoted. METHOD: The domains of care included in the toolkit were identified from a systematic literature review, international expert Delphi exercise, and review of care standards in ten European countries. The draft toolkit comprised 154 questions for unit managers. Inter-rater reliability was tested in 202 units across ten countries at different stages of deinstitutionalisation and development of community mental health services. Exploratory factor analysis was used to corroborate the allocation of items to domains. Feedback from those using the toolkit was collected about its usefulness and ease of completion. RESULTS: The toolkit had excellent inter-rater reliability and few items with narrow spread of response. Unit managers found the content highly relevant and were able to complete it in around 90 minutes. Minimal refinement was required and the final version comprised 145 questions assessing seven domains of care. CONCLUSIONS: Triangulation of qualitative and quantitative evidence directed the development of a robust and comprehensive international quality assessment toolkit for units in highly variable socioeconomic and political contexts