Canonical Reduction of Tensors and the Physical Properties of Condensed Matter: Application to Optics

International audienceA general framework for the description of the physical properties of matter by a canonical reduction procedure of tensors is presented; besides geometrical symmetries, this paper emphasizes the role of intrinsic symmetries which are due either to the indiscernability of some of the physical quantities involved or to thermodynamical arguments. The intrinsic symmetries are expressed through the behaviour of the tensors describing the investigated property under the effect of some index permutation. The scheme of reduction of any tensor into parts that are irreducible not only with respect to rotations and inversion but also with respect to index permutations is shown and examples are given in the area of light-matter interaction

γδ T Cell Selection: Is Anyone Useless?

In this issue of Immunity, a study by Jensen et al. (2008) suggests that T cell-receptor engagement during development affects γδ T cell polarization toward either interferon-γ or interleukin-17 production. This might underlie their unique innate ability to regulate inflammation

Demystifying Distributed Leadership: How Understanding Principles of Practice and Perceptions Regarding Ambiguity Can Enhance the Leadership Capacity of Department Chairs

Due to increased accountability, demands, and responsibilities, principals struggle to effectively lead schools. Therefore, they look to strengthen the structure and operations of schools by utilizing distributed leadership and the role of department chairs to build leadership capacity and improve school culture (Elmore, 2000; Harris, 2005; Spillane, 2008). A critical aspect of distributed leadership is a school’s organizational culture or “the way we do things around here” (Bryk & Schneider, 2003), which can positively or negatively influence any school initiative. Since organizational culture can foster collaboration and a shared commitment to school goals, which in turn can build leadership capacity, the school culture’s capacity to influence the success or demise of any shared leadership model is explored. Unfortunately, ambiguity within distributed leadership and the role of department chair complicate effective implementation of distributed leadership by impeding task completion and successful navigation of relationships (Mehta, Gardia, & Rathmore, 2010). Due to ever changing administration and complex and at times paradoxical mandates, a certain level of ambiguity will always exist in schools. Therefore, school leaders should accept ambiguity not as a stigma but as an asset and necessary adaptive skill that gives people the confidence and motivation to navigate the unknown. The conceptual framework for this study incorporates my experiences as a principal and former department chair, as well as the theoretical anchors of distributed leadership, role theory, organizational leadership theories, self-efficacy, and organizational commitment. This study utilized an ethnographic qualitative approach, relying on a descriptive single case study strategy of inquiry to examine the unique relationships that exist between a principal and her department chairs to identify specific examples of and participants’ perceptions towards distributed leadership, school culture, and incidents of role ambiguity. Research methods included individual and small group interviews, direct non-participatory observations, and analysis of site documents. Key principles of distributed leadership, as well as descriptions of how ambiguity and school culture can influence distributed leadership are explored in the findings, which are intended to help school systems conceptualize a framework for successful and efficacious implementation of distributed leadership

Human Rights in Russia and the Former Soviet Republics: Civil Society and Human Rights

A dynamic civil society is essential to a functioning democracy. After the fall of the Soviet Union there was hope that Russia could create a robust civil society to compliment its burgeoning democracy, but 15 years after the fall neither occurrence appears to be the case. Instead of an open society, Russian civil society faces challenges of oppression, threats of violence, an overbearing bureaucracy, and a constitution open to interpretation. The following research outlines some of the obstacles facing Russia’s civil society and addresses how the government is restricting civil society functions