Quasiperiodic Heisenberg antiferromagnets in two dimensions

This is a review of the properties of 2d quantum quasiperiodic antiferromagnets as reported in studies that have been carried out in the last decade. Many results have been obtained for perfectly ordered as well as for disordered two dimensional bipartite quasiperiodic tilings. The theoretical methods used include spin wave theory, and renormalization group along with Quantum Monte Carlo simulations. These methods all show that the ground state of these unfrustrated antiferromagnets have N\'eel type order but with a highly complex spatial distribution of local staggered magnetization. The ground state properties, excitation energies and spatial dependence, structure factor, and local susceptibilities are presented. The effects of introducing geometrical disorder on the magnetic properties are discussed.Comment: 21 pages, 29 figure

Open theoretical problems in the physics of aperiodic systems

Quasicrystals have intrigued and stimulated research in a large number of disciplines. Mathematicians, physicists, chemists, metallurgists and materials scientists have found in them a fertile ground for new insights and discoveries. In the quarter century that has ensued since the publication of the experimental observation of a quasiperiodic Al-Mn alloy \cite{shecht}, many different kinds of quasiperiodic alloys have been manufactured and studied. The physical properties of quasicrystals are no less interesting than the unusual structural properties that led to their discovery in 1984. In this review, I present some of the properties that characterize quasicrystals, briefly discuss several types of theories that have been put forward, and describe some new behaviors that might be investigated by experiment.Comment: 6 pages, 5 figures, plenary lecture for CMAC (Complex metallic alloys) workshop (Zagreb, 2009

Density of states and magnetic susceptibilities on the octagonal tiling

We study electronic properties as a function of the six types of local environments found in the octagonal tiling. The density of states has six characteristic forms, although the detailed structure differs from site to site since no two sites are equivalent in a quasiperiodic tiling. We present the site-dependent magnetic susceptibility of electrons on this tiling, which also has six characteristic dependences. We show the existence of a non-local spin susceptibility, which decays with the square of the distance between sites and is the quasiperiodic version of Ruderman-Kittel oscillations. These results are obtained for a tight-binding Hamiltonian with pure hopping.Finally, we investigate the formation of local magnetic moments when electron-electron interactions are included.Comment: 8 pages, LaTeX, figures on reques

The role of nongovernmental organizations in primary education - a study of six NGOs in India

Nongovernmental organizations (NGOs) extend education to underprivileged children in India, and develop innovations that improve the quality of primary education. In this study of six NGOs working with school-age children in India, the author shows the potential benefits of a government-NGO alliance to achieve universal primary education. The author emphasizes several areas in which collaboration can be particularly fruitful. 1) Targeting under-served children: The Government could support the efforts of NGOs to bring out-of-school children into schools, through timely supply of teachers, classroom space, and other resources. Targeted action is needed to reach different types of out-of-school children - those who work, those who live in slums, those on the street, those who are members of tribes, or of migrant families, and those who live in places without schools. To encourage young, first-generation learners to stay in school, requires a supportive, and nurturing environment. To help make learning interesting, and worthwhile for such children, teachers in government schools could receive special training in new methods developed by NGOs. 2) Enhancing quality: Improving the quality of education requires working closely with key agents of change, such as teachers, school heads, school management committees, and village education committees. To develop a cadre of trainers for primary school teachers, teacher training institutes would do well to evaluate, and learn from NGO models for teacher training. Teachers need a range of knowledge, and skills to teach underprivileged children effectively. Here again, NGO models would be a useful tool for teacher training institutes. NGOs, and the government could collaborate in developing appropriate, and flexible learning assessment tools, in line with innovative teaching, and learning methods. But without safeguards, large-scale replication by the government of such NGO innovations as the"alternative school"and the"voluntary teacher"could lower the quality of education. 3) Government-NGO links: The Government and NGOs will need to share a common vision on how to achieve universal primary education if India is to reach this goal. NGOs can be credible partners with the government in shaping policies for primary education. This entails collaboration, rather than parallel initiatives by NGOs. To stay at the cutting edge in education, NGOs should continually evaluate, and refine their models. If NGOs are to play a policy role in education, two areas that have been neglected will need to be addressed - NGO capacity building, and organizational development.Primary Education,Teaching and Learning,Health Monitoring&Evaluation,Gender and Education,Curriculum&Instruction