Intervention strategies for children and adolescent with disorders: from intrapsychic to transactional perspective

A large amount of studies and clinical evidence document the importance of infancy and early childhood influences on long term developmental trajectories toward mental health or psychopathology (Sameroff, 2000, 2010). Without healthy, productive adults no culture could continue to be successful. This concern is the main motivation for society to support child development research. Although the academic interests of contemporary developmental researchers range widely in cognitive and socialemotional domains, the political justification for supporting such studies is that they will lead to the understanding and ultimate prevention of behavioural problems that are costly to society. With these motivations and support, there have been major advances in our understanding of the intellectual, emotional, and social behaviour of children, adolescents and adults. This progress has forced conceptual reorientations from a unidirectionalunderstanding of development (e.g., parents affect children and not vice versa) toward a bidirectional conceptualization of development. Childrenare now assumed to affect and even select their environments as much as their environments affect their behaviour. Indeed, key among many of the most influential developmental theories in the past several decades is the assumption that children have bidirectional, or reciprocal, relationships with their environments (Bandura, 1977; Bronfenbrenner, 1979). To date, it is widely accepted that children’s healthy development is shaped by complex transactional processes among a variety of risk and protective factors, with cumulative risk factors increasing the prediction of emotional and behavioural problems (Anda et al., 2007; Rutter & Sroufe, 2000; Sameroff, 2000). Risk and protective factors include individual child characteristics such as genetic and constitutional propensities and cognitive strengths and vulnerabilities; parent characteristics such as mental health, education level, sense of efficacy, and resourcefulness; family factors such as quality of the parent-child relationship, emotional climate, and marital quality; community connectedness factors such as parental social support, social resources, and children’s peer relationships; and neighbourhood factors such as availability of resources, adequacy of housing, and levels of crime and violence (Sameroff & Fiese, 2000). The predictive value of these factors across many studies led to the development of transactional-bioecological models that attempt to conceptualize the relative contributions of proximal and distal risk and protective factors to children’s developmental outcome (Bronfenbrenner & Morris, 2006). In 1975, Sameroff and Chandler proposed the transactional model. This theoretical framework has become central to understanding the interplay between nature and nurture in explaining the development of positive and negative outcomes for children. The transactional model is a model of qualitative change. Sameroff asserted that the transactional model concerned qualitative rather than incremental change and that the underlying process was dialectical rather mechanistic in nature. The aim of this chapter is to explore this theoretical framework and its intervention strategies. In the first part, the transactional model will be described after a brief summary that will illustrate the transition from intrapsychic to transactional perspective. In the second part, intervention strategies for children and adolescent will be described. The attention of research on environmental risk and protective factors has fostered a more comprehensive understanding of what is necessary to improve the cognitive and social-emotional welfare of children and adolescents

On the interface polaron formation in organic field-effect transistors

A model describing the low density carrier state in an organic single crystal FET with high-$\kappa$ gate dielectrics is studied. The interplay between charge carrier coupling with inter-molecular vibrations in the bulk of the organic material and the long-range interaction induced at the interface with a polar dielectric is investigated. This interplay is responsible for the stabilization of a polaronic state with an internal structure extending on few lattice sites, at much lower coupling strengths than expected from the polar interaction alone. This effect could give rise to polaron self-trapping in high-$\kappa$ organic FET's without invoking unphysically large values of the carrier interface interaction.Comment: 9 pages, 9 figure

Effect of weak disorder in the Fully Frustrated XY model

The critical behaviour of the Fully Frustrated XY model in presence of weak positional disorder is studied in a square lattice by Monte Carlo methods. The critical exponent associated to the divergence of the chiral correlation length is found to be equal to 1.7 already at very small values of disorder. Furthermore the helicity modulus jump is found larger than the universal value expected in the XY model.Comment: 8 pages, 4 figures (revtex

Effects of electron-phonon coupling range on the polaron formation

The polaron features due to electron-phonon interactions with different coupling ranges are investigated by adopting a variational approach. The ground-state energy, the spectral weight, the average kinetic energy, the mean number of phonons, and the electron-lattice correlation function are discussed for the system with coupling to local and nearest neighbor lattice displacements comparing the results with the long range case. For large values of the coupling with nearest neighbor sites, most physical quantities show a strong resemblance with those obtained for the long range electron-phonon interaction. Moreover, for intermediate values of interaction strength, the correlation function between electron and nearest neighbor lattice displacements is characterized by an upturn as function of the electron-phonon coupling constant.Comment: 5 pages and 4 figure

Non-local composite spin-lattice polarons in high temperature superconductors

The non-local nature of the polaron formation in t-t'-t"-J model is studied in large lattices up to 64 sites by developing a new numerical method. We show that the effect of longer-range hoppings t' and t" is a large anisotropy of the electron-phonon interaction (EPI) leading to a completely different influence of EPI on the nodal and antinodal points in agreement with the experiments. Furthermore, nonlocal EPI preserves polaron's quantum motion, which destroys the antiferromagnetic order effectively, even at strong coupling regime, although the quasi-particle weight in angle-resolved-photoemission spectroscopy is strongly suppressed.Comment: 5 pages, 4 figure

A variational approach to the optimized phonon technique for electron-phonon problems

An optimized phonon approach for the numerical diagonalization of interacting electron-phonon systems is proposed. The variational method is based on an expansion in coherent states that leads to a dramatic truncation in the phonon space. The reliability of the approach is demonstrated for the extended Holstein model showing that different types of lattice distortions are present at intermediate electron-phonon couplings as observed in strongly correlated systems. The connection with the density matrix renormalization group is discussed.Comment: 4 figures; submitted to Phys. Rev.

Optical signatures of exciton-polarons from diagrammatic Monte Carlo

We study the interplay of electron-electron and electron-phonon interactions in the course of electron-hole bound state formation for gapped solid state systems. Adapting the essentially approximation-free diagrammatic Monte Carlo method for the calculation of the optical response, we discuss the absorption of light in correlated electron-phonon systems for the whole interaction and phonon frequency regimes. The spectral function obtained by analytical continuation from the imaginary-time current-current correlation function demonstrates the dressing of excitons by a phonon cloud when the coupling the lattice degrees of freedom becomes increasingly important, where notable differences show up between the adiabatic and anti-adiabatic cases.Comment: 6 pages, 5 figure

Topological quantum transition driven by charge-phonon coupling in the Haldane Chern insulator

In condensed matter physics many features can be understood in terms of their topological properties. Here we report evidence of a topological quantum transition driven by the charge-phonon coupling in the spinless Haldane model on a honeycomb lattice, a well-known prototypical model of Chern insulator. Starting from parameters describing the topological phase in the bare Haldane model, we show that the increasing of the strength of the charge lattice coupling drives the system towards a trivial insulator. The average number of fermions in the Dirac point, characterized by the lowest gap, exhibits a finite discontinuity at the transition point and can be used as direct indicator of the topological quantum transition. Numerical simulations show, also, that the renormalized phonon propagator exhibits a two peak structure across the quantum transition, whereas, in absence of the mass term in the bare Hadane model, there is indication of a complete softening of the effective vibrational mode signaling a charge density wave instability.Comment: 5 pages, 4 figure

Temperature dependence of the angle resolved photoemission spectra in the undoped cuprates: self-consistent approach to the t-J-Holstein model

We develop a novel self-consistent approach for studying the angle resolved photoemission spectra (ARPES) of a hole in the t-J-Holstein model giving perfect agreement with numerically exact Diagrammatic Monte Carlo data at zero temperature for all regimes of electron-phonon coupling. Generalizing the approach to finite temperatures we find that the anomalous temperature dependence of the ARPES in undoped cuprates is explained by cooperative interplay of coupling of the hole to magnetic fluctuations and strong electron-phonon interaction.Comment: 5 pages, 4 figure