The calculation of optical absorption spectra using linear-scaling density-functional theory

The goal of the work presented in this thesis was to develop and implement a method for calculating optical absorption spectra for large electronic systems within a linear-scaling density-functional theory (LS-DFT) formalism. The key feature of this method was the development of a scheme for optimizing a set of localized orbitals to accurately represent unoccupied Kohn-Sham states, which are not well represented by the localized orbital basis sets used for ground state LS-DFT calculations. Three different schemes were compared for the calculation of unoccupied states using a one-dimensional “toy model” and the most promising of these, based on the use of a projection operator, was implemented in a fully-functional LS-DFT code. Using the toy model, two methods for the calculation of band structures within a localized basis set were investigated and some of the features required by localized basis sets in order to produce accurate band structures were identified. The method was tested by the application to both molecular and extended systems, with calculations of densities of states, band structures and optical absorption spectra. The results for the smaller systems were validated by comparison with a cubic-scaling plane-wave density-functional theory code, with which excellent agreement was achieved. Additionally, the method was shown to be linear-scaling for a conjugated polymer for system sizes up to 1000 atoms. The use of the projection method was shown to be crucial for calculating the above results, as was the implementation of a momentum operator based formalism for the calculation of spectra. Finally, it was shown that the method can be used to identify the transitions responsible for particular peaks in the spectra and is sensitive enough to distinguish between spectra for systems with very similar structures, demonstrating the capabilities of the method to aid the interpretation of experimental results

Don’t throw rocks from the side-lines: A sociomaterial exploration of organizational blogs as boundary objects

Purpose Social media such as blogs are being widely used in organizations in order to undertake internal communication and share knowledge, rendering them important boundary objects. A root metaphor of the boundary object domain is the notion of relatively static and inert objects spanning similarly static boundaries. A strong sociomaterial perspective allows the immisciblity of object and boundary to be challenged, since a key tenet of this perspective is the ongoing and mutually-constituted performance of the material and social. Design/methodology/approach The aim of our research is to draw upon sociomateriality to explore the operation of social media platforms as intra-organizational boundary objects. Given the novel perspective of this study and its social constructivist ontology, we adopt an exploratory, interpretivist research design. This is operationalized as a case study of the use of an organizational blog by a major UK government department over an extended period. A novel aspect of the study is our use of data released under a Freedom of Information request. Findings We present three exemplar instances of how the blog and organizational boundaries were performed in the situated practice of the case study organization. We draw on literature on boundary objects, blogs and sociomateriality in order to provide a theoretical explication of the mutually-constituted performance of the blog and organizational boundaries. We also invoke the notion of ‘extended chains of intra-action’ to theorise changes in the wider organization. Originality/value Adoption of a sociomaterial lens provides a highly novel perspective of boundary objects and organizational boundaries. The study highlights the indeterminate and dynamic nature of boundary objects and boundaries, with both being in an intra-active state of becoming, challenging conventional conceptions. The study demonstrates that specific material-discursive practices arising from the situated practice of the blog at the respective boundaries were performative, reconfiguring the blog and boundaries and being generative of further changes in the organization

Closing the Teacher Quality Gap in Philadelphia: New Hope and Old Hurdles

This study of teacher staffing issues in the School District of Philadelphia, the third in a series, outlines the degree to which the district has succeeded in upgrading teachers' professional credentials, recruiting and retaining them, and equitably distributing experienced and credentialed teachers across all types of schools. Since the passage of NCLB and the state's takeover of the district in 2001, the district has succeeded in improving the certification rates of its teachers, especially new teachers, and in drastically cutting the number of emergency-certified teachers and classroom vacancies. It has also improved new teacher retention and has modernized and decentralized its hiring process. At the same time, it has not been able to change the pattern of having the least qualified teachers in schools serving the highest percentages of poor and minority students nor its poor long-term rate of teacher retention. The district is also challenged to speed up and simplify its hiring and school placement process and to hire more minority teachers

Shared understandings of dementia? : An application of the Common Sense Self Regulation Model to a case study

Peer reviewedPostprin

Place and space in early Burma: a new look at ‘Pyu Culture'

Ancient Burma (Myanmar) is commonly split into Upper Burma ‘Pyu’ and Lower Burma Mon cultures, an ethnic classification of walled site cultures in the Irrawaddy (Ayeyarwaddy) basin that began with fourth to ninth century C.E. scripts. The early Buddhist archaeology, however, points to multiple groups and spreads far beyond the Irrawaddy drainage system. The Mon typology has profitably been unravelled in Aung-Thwin’s controversial study (2005), but, while his advocacy of the Pyu primacy has been questioned, rudimentary definitions of the first millennium C.E. ‘Pyu culture’ have remained largely unchallenged. The blinkered results of text primacy in defining ethnicity and cultural identity are addressed here, with data from recent discoveries used to identify a relational engagement between the brick walls and terracotta urns typical of early Buddhist cultures in Upper Burma. This localised integration of spatial and spiritual factors is further strengthened by a range of artefacts and indigenous texts

Recent Results in Chiral Perturbation Theory for Mesons Containing a Single Heavy Quark

Chiral symmetry and heavy quark symmetry constrain the interactions of mesons containing a single heavy quark with low-momentum pions. Chiral corrections to the Isgur-Wise function for $\bar B_s \rightarrow D_s^{(*)}$ versus $\bar B \rightarrow D^{(*)}$ semileptonic decay, the ratio of heavy meson decay constants $f_{D_s}/ f_D$ or $f_{B_s}/ f_B$, the amplitudes for $B_s - \bar B_s$ versus $B^0 - \bar B{\,}^0$ mixing, and the heavy meson mass splittings are calculated in chiral perturbation theory. (Invited talk Rencontres de Moriond 1993)Comment: UCSD/PTH 93-10, 6 pages, 2 figure

On the existence of conformally coupled scalar field hair for black holes in (anti-)de Sitter space

The Einstein-conformally coupled scalar field system is studied in the presence of a cosmological constant. We consider a massless or massive scalar field with no additional self-interaction, and spherically symmetric black hole geometries. When the cosmological constant is positive, no scalar hair can exist and the only solution is the Schwarzschild-de Sitter black hole. When the cosmological constant is negative, stable scalar field hair exists provided the mass of the scalar field is not too large.Comment: Minor changes, 32 pages, 11 figures, uses kluwer.cls, klucite.st