Restricting Voting Rights in Modern America

The Supreme Court’s Shelby County v. Holder ruling invalidating Section 4(b) of the Voting Rights Act of 1965 is in part a product of efforts to resist further transformations to the traditional American institutional arrangements that have conferred advantages on whites, especially disproportionate political power. Those efforts in resistance are not likely to succeed in the long run. But they may embroil American elections and American governance in paralyzing conflicts for years to come.La décision de la Cour suprême dans l’arrêt Comté de Shelby c. Holder, invalidant la Section 4 (b) de la Loi sur les droits de vote de 1965, est en partie le produit d’une volonté de maintenir les avantages particulièrement disproportionnée des Blancs en matière de pouvoir politique et de résister à toutes les nouvelles tentatives transformation des arrangements institutionnels américains traditionnels. Ces efforts de résistance ne sont pas susceptibles de réussir sur le long terme. Mais ils peuvent entrainer les élections américaines et la gouvernance américaine dans des conflits paralysants pour les années à venir

Accurate polarization within a unified Wannier function formalism

We present an alternative formalism for calculating the maximally localized Wannier functions in crystalline solids, obtaining an expression which is extremely simple and general. In particular, our scheme is exactly invariant under Brillouin zone folding, and therefore it extends trivially to the Gamma-point case. We study the convergence properties of the Wannier functions, their quadratic spread and centers as obtained by our simplified technique. We show how this convergence can be drastically improved by a simple and inexpensive ``refinement'' step, which allows for very efficient and accurate calculations of the polarization in zero external field.Comment: 9 pages, 4 figure

Predicting polarization enhancement in multicomponent ferroelectric superlattices

Ab initio calculations are utilized as an input to develop a simple model of polarization in epitaxial short-period CaTiO3/SrTiO3/BaTiO3 superlattices grown on a SrTiO3 substrate. The model is then combined with a genetic algorithm technique to optimize the arrangement of individual CaTiO3, SrTiO3 and BaTiO3 layers in a superlattice, predicting structures with the highest possible polarization and a low in-plane lattice constant mismatch with the substrate. This modelling procedure can be applied to a wide range of layered perovskite-oxide nanostructures providing guidance for experimental development of nanoelectromechanical devices with substantially improved polar properties.Comment: 4 pages, submitted to PR

Motivations and experiences of UK students studying abroad

This report summarises the findings of research aimed at improving understanding of the motivations behind the international diploma mobility of UK student

Geometric phases and Wannier functions of Bloch electrons in 1-dimension

We present a formal expression for Wannier functions of composite bands of 1-D Bloch electrons in terms of parallel-transported Bloch functions and their non-Abelian geometric phases. Spatial decay properties of these Wannier functions are studied in the case of simple bands of 1-D model insulator and metal. Within first-principles density functional theory, we illustrate the formalism through the construction of Wannier functions of polyethylene and polyacetylene.Comment: 4 pages, 4 figure

The ferroelectric transition in YMnO3_3 from first principles

We have studied the structural phase transition of multiferroic YMnO$_3$ from first principles. Using group-theoretical analysis and first-principles density functional calculations of the total energy and phonons, we perform a systematic study of the energy surface around the prototypic phase. We find a single instability at the zone-boundary which couples strongly to the polarization. This coupling is the mechanism that allows multiferroicity in this class of materials. Our results imply that YMnO$_3$ is an improper ferroelectric. We suggest further experiments to clarify this point.Comment: published version, PRB (rapid comm), slight change in presentatio

The mediating role of visuospatial planning skills on adaptive function among young adult survivors of childhood brain tumors

The Boston Qualitative Scoring System (BQSS) was used as a method to examine executive skills on the Rey-Osterrieth complex figure (ROCF). Young adult survivors of childhood brain tumor (N = 31) and a demographically-matched comparison group (N = 33) completed the ROCF copy version and Grooved Pegboard, and informants were administered the Scales of Independent Behavior-Revised (SIB-R) and Behavior Rating Inventory of Executive Function (BRIEF). Survivors had significantly lower BQSS planning and SIB-R community living skills and greater perseveration. Mediation analyses found that BQSS planning skills mediate the relationship between group and community living skills. Convergent findings of the BRIEF Planning, and discriminant findings with the BQSS Fragmentation, BRIEF Emotional Control, and Grooved Pegboard support the planning construct as the specific mediator in this model. Together, these findings highlight the role of planning skills in adaptive functions of young adult survivors of childhood brain tumor