Orbital order, stacking defects and spin-fluctuations in the pp-electron molecular solid RbO2_2

We examine magnon and orbiton behavior in localized O$_2$ anti-bonding molecular $\pi^*$ orbitals using an effective Kugel-Khomskii Hamiltonian derived from a two band Hubbard model with hopping parameters taken from {\em ab initio} density functional calculations. The considerable difference between intraband and interband hoppings leads to a strong coupling between the spin wave dispersion and the orbital ground state, providing a straightforward way of experimentally determining the orbital ground state from the measured magnon dispersion. The near degeneracy of different orbital ordered states leads to stacking defects which further modulate spin-fluctuation spectra. Proliferation of orbital domains disrupts long-range magnetic order, thus causing a significant reduction in the observed N\'eel temperature.Comment: 5 pages, 2 figure

First-Principles Study of Electronic and Vibrational Properties of BaHfN2_2

The transition metal nitride BaHfN$_2$, which consists of weakly bonded neutral slabs of closed shell ions, has structural and chemical similarities to other layered nitrides which have impressive superconducting T$_c$ when electron doped: A$_x$HfNCl, A$_x$ZrNCl, A$_x$TiNCl, with $T_c= 25.5$, $15.2$ and $16.5$ K, respectively for appropriate donor (A) concentrations $x$. These similarities suggest the possibility of BaHfN$_2$ being another relatively high T$_c$ nitride upon doping, with effects of structure and the role of specific transition metal ions yet to be understood. We report first-principles electronic structure calculations for stoichiometric BaHfN$_2$ using density functional theory with plane-wave basis sets and separable dual-space Gaussian pseudopotentials. An indirect band gap of 0.8 eV was obtained and the lowest conduction band is primarily of Hf 5$d_{xy}$ character, similar to $\beta$-ZrNCl and $\alpha$-TiNCl. The two N sites, one in the Hf layer and another one in the Ba layer, were found to have very anisotropic Born effective charges (BEC):deviations from the formal charge (-3) are opposite for the two sites, and opposite for the two orientations (in-plane, out of plane). LO-TO splittings and comparison of BECs and dielectric constant tensors to those of related compounds are discussed, and the effect of electron doping on the zone-center phonons is reported.Comment: 11 pages, 5 figure

The crucial importance of the t2gt_{2g}--ege_g hybridization in transition metal oxides

We studied the influence of the trigonal distortion of the regular octahedron along the (111) direction, found in the $\rm CoO_2$ layers. Under such a distortion the $t_{2g}$ orbitals split into one $a_{1g}$ and two degenerated $e_g^\prime$ orbitals. We focused on the relative order of these orbitals. Using quantum chemical calculations of embedded clusters at different levels of theory, we analyzed the influence of the different effects not taken into account in the crystalline field theory; that is metal-ligand hybridization, long-range crystalline field, screening effects and orbital relaxation. We found that none of them are responsible for the relative order of the $t_{2g}$ orbitals. In fact, the trigonal distortion allows a mixing of the $t_{2g}$ and $e_g$ orbitals of the metallic atom. This hybridization is at the origin of the $a_{1g}$--$e_g^\prime$ relative order and of the incorrect prediction of the crystalline field theory

First Principles Study of the Electronic and Vibrational Properties of LiNbO2

In the layered transition metal oxide LiNbO$_2$ the Nb$^{3+}$ ($4d^2$) ion is trigonal-prismatically coordinated with O ions, with the resulting crystal field leading to a single band system for low energy properties. A tight-binding representation shows that intraplanar second neighbor hopping $t_2 = 100$ meV dominates the first neighbor interaction ($t_1 = 64$ meV). The first and third neighbor couplings are strongly modified by oxygen displacements of the symmetric Raman-active vibrational mode, and electron-phonon coupling to this motion may provide the coupling mechanism for superconductivity in Li-deficient samples (where $T_c = 5$ K). We calculate all zone-center phonon modes, identify infrared (IR) and Raman active modes, and report LO-TO splitting of the IR modes. The Born effective charges for the metal ions are found to have considerable anisotropy reflecting the degree to which the ions participate in interlayer coupling and covalent bonding. Insight into the microscopic origin of the valence band density, composed of Nb $d_{z^2}$ states with some mixing of O $2p$ states, is obtained from examining Wannier functions for these bands.Comment: 12 pages, 7 figures; Updated with reviewer comments; Updated reference

Reporting on novel complex intervention development for adults with social communication impairments after acquired brain injury

Purpose: Interventions are often poorly described in published controlled trials, with relatively little information regarding intervention development, content and fidelity. This makes it difficult to conduct replication studies, interpret and compare findings across studies and for therapists to deliver the intervention in clinical practice. Complete reporting of interventions (including fidelity) is now recommended for treatment studies, and this standardised approach is achieved using the Template for Intervention Description and Replication (TIDieR). The aim of this paper is to describe the multi-phase process of developing a novel intervention for adults with acquired brain injury (ABI), and report on the findings from involving practicing therapists in this process. Methods: Phase 1 involved a review of relevant literature and specifying the intervention as a prototype intervention manual. Phase 2 comprised a focus group with eight practicing therapists exploring their experiences and perceptions of the intervention, potential active components, and essential elements; it also included review of the prototype manual. Data from the focus group discussion was transcribed and analysed thematically. Phase 3 investigated actual fidelity of the intervention undertaken, achieved by observers viewing videoed sessions and appraising against the fidelity checklist, which was then analysed using Cohen’s kappa. Results: Project-based intervention was defined as having six essential elements: a project or tangible end product focus; group-based intervention; individualised communication-based goals; communication partner involvement; acknowledgement and support of participants’ cognitive ability; and consideration and plan to address impaired awareness. Analysis of focus group data revealed four themes of essential elements; group context; therapeutic skills; and manual core components and informed the development of a fidelity checklist with 13 essential and 6 desirable criteria. Fidelity assessed using percent agreement was acceptable for almost all rater pairs; where significant, Kappa coefficients had values ranging from poor to excellent (k=0.34 – 1.0) depending on rater pair and session. Discussion: The TIDieR framework provided a clear systematic approach for the complete description and reporting of a complex communication intervention for people with ABI. This paper comprehensively described the development and manualisation of an intervention in collaboration with practicing therapists which can be used for future testing. In addition, the process undertaken has the potential to inform rehabilitation researchers in other fields on the development of complex interventions

Material-Specific Investigations of Correlated Electron Systems

We present the results of numerical studies for selected materials with strongly correlated electrons using a combination of the local-density approximation and dynamical mean-field theory (DMFT). For the solution of the DMFT equations a continuous-time quantum Monte-Carlo algorithm was employed. All simulations were performed on the supercomputer HLRB II at the Leibniz Rechenzentrum in Munich. Specifically we have analyzed the pressure induced metal-insulator transitions in Fe2O3 and NiS2, the charge susceptibility of the fluctuating-valence elemental metal Yb, and the spectral properties of a covalent band-insulator model which includes local electronic correlations.Comment: 14 pages, 7 figures, to appear in "High Performance Computing in Science and Engineering, Garching 2009" (Springer

Electronic Structure Calculation by First Principles for Strongly Correlated Electron Systems

Recent trends of ab initio studies and progress in methodologies for electronic structure calculations of strongly correlated electron systems are discussed. The interest for developing efficient methods is motivated by recent discoveries and characterizations of strongly correlated electron materials and by requirements for understanding mechanisms of intriguing phenomena beyond a single-particle picture. A three-stage scheme is developed as renormalized multi-scale solvers (RMS) utilizing the hierarchical electronic structure in the energy space. It provides us with an ab initio downfolding of the global band structure into low-energy effective models followed by low-energy solvers for the models. The RMS method is illustrated with examples of several materials. In particular, we overview cases such as dynamics of semiconductors, transition metals and its compounds including iron-based superconductors and perovskite oxides, as well as organic conductors of kappa-ET type.Comment: 44 pages including 38 figures, to appear in J. Phys. Soc. Jpn. as an invited review pape

Criar uma idiocultura para promover o desenvolvimento de crianças com paralisia cerebral

This study presents the preliminary results of the adaptation of an educational system called the Fifth Dimension (5D), in which social interaction is a means for generalizing information and a basis for the development of skills beyond the constituent tasks. Originally created by Michael Cole - Laboratory for Comparative Human Cognition at the University of California at San Diego (UCSD) - this system was, for the first time, applied to a rehabilitation setting with children with brain injury, at the SARAH Network of Neurorehabilitation Hospitals, in Brazil. Undergraduate college students majoring in psychology and education participate in the program and interact with children who have cerebral palsy, engaging in playful/educational activities of collaborative learning. While interacting with the child, the student is encouraged to put formal theoretical concepts and personal experience into practice. In this article, we describe the changes made to the original program to adapt it to the rehabilitation setting as well as the artefacts that mediate the activity, necessary for the interaction and expression of the child with cerebral palsy. Also discussed and presented are the effects of the activity on the child's development - based on the parents' reports - and the impact on the learning process of the undergraduate students. The program opens alternative pathways for a reflection on, and education of, the child with brain injury, based on the development of individual potential, context and interests.Este estudo apresenta os resultados preliminares da adaptação de um sistema educacional, chamado Quinta Dimensão, no qual a interação social é um meio para a generalização da informação e base para o desenvolvimento de habilidades. Foi criado originalmente por Michael Cole no Laboratório de Cognição Humana Comparada, Universidade da Califórnia, San Diego, e pela primeira vez é aplicado em um contexto de reabilitação com crianças com lesão cerebral na Rede SARAH de Neurorreabilitação, Brasília. Alunos de graduação em psicologia e pedagogia participam do programa e interagem de maneira lúdica e educativa com crianças com paralisia cerebral. Ambos são envolvidos em atividades de aprendizagem colaborativa. Na interação com a criança, os alunos são encorajados a colocar em prática conceitos teóricos formais e, também, vivências individuais. Resultados indicam efeitos positivos sobre o desenvolvimento da criança e aprendizagem do aluno de graduação e mostram caminhos alternativos na educação da criança deficiente. Neste artigo, descrevemos as alterações feitas no programa original para adaptá-lo à reabilitação configurada, assim como os artefatos que medeiam a atividade, necessário para a interação e expressão da criança com paralisia cerebral. Também são discutidos e apresentados os efeitos da atividade sobre o desenvolvimento da criança - com base em relatórios dos pais - e do impacto sobre o processo de aprendizagem dos alunos de graduação. O programa abre caminhos alternativos para uma reflexão sobre e educação da criança com lesão cerebral, com base no desenvolvimento do potencial individual, o contexto e os interesses

"They brought you back to the fact you're not the same": Sense of self after traumatic brain injury

This paper considers contexts following traumatic brain injury, exploring what may be at stake when dominant expectations predict a ‘lost’ or ‘broken’ self. I explore stories co-constructed with one young man and his mother to illustrate their personal and intersubjective understandings of identity, at times conflicting, within family interactions and when encountering normative practices of neurorehabilitation clinicians. The ower relations portrayed confront this man’s narrative attempts to align his present and pre-injury self, including standard assessments delineating change, administered by healthcare professionals. I consider a need for greater attention to interaction-generated disruption to sense of self, wthin contemporary conceptualisations of ‘person-centred care’

Mapping Philanthropic Foundations’ Characteristics: towards an international integrative framework of foundation types

As philanthropic foundations take on increasingly prominent sociopolitical roles, the need for stronger conceptualizations of foundations as an organizational form is articulated widely across academic, policy, and practice contexts. Building on institutional research’s tradition of categorizing, classifying and typologizing organizational forms, our article critically explores the different ways in which foundations have been cast and differentiated in international academic and practice literatures. Examining and integrating these, we propose an integrative framework of foundation types. Incorporating 13 categories—three contextual, five organizational, and five strategic ones—the framework allows for clarifying distinctions and identifying commonalities between different foundation forms, offering a basis for developing more reflective and differentiated research and practice knowledge