Electronics and Chemistry: Varying Single Molecule Junction Conductance Using Chemical Substituents

We measure the low bias conductance of a series of substituted benzene diamine molecules while breaking a gold point contact in a solution of the molecules. Transport through these substituted benzenes is by means of nonresonant tunneling or superexchange, with the molecular junction conductance depending on the alignment of the metal Fermi level to the closest molecular level. Electron-donating substituents, which drive the occupied molecular orbitals up, increase the junction conductance, while electron-withdrawing substituents have the opposite effect. Thus for the measured series, conductance varies inversely with the calculated ionization potential of the molecules. These results reveal that the occupied states are closest to the gold Fermi energy, indicating that the tunneling transport through these molecules is analogous to hole tunneling through an insulating film.Comment: 14 pages, 4 figure

Performing as Mapping: An examination of the role of site-specific performance practice as a methodology to map and/or re-imagine sites of urban regeneration

This thesis is a practice-led enquiry that examines the role of site-specific performance as a methodology or set of tools to ‘map’ sites of urban regeneration, and thus seeks to build further links between performance and the spatial practices of architecture and urbanism. Performativity has emerged as an important critical concept across a range of social and spatial fields - as a way understanding of how personal and place identities are continuously (re)created through everyday performance. Meanwhile, practitioners and researchers have become increasingly interested in creating, documenting, and theorising models of theatre and performance that engage with sites and communities outside of the gallery or auditorium. The thesis traces the emergence of ‘site-specific’ performances as ‘more-than-representational’ cartographies - from the early experiments of the Situationist International and the ‘Happenings’, through everyday practices of walking and navigating cities, to emerging technological and ‘locative’ performance models. The definition of what constitutes (a) ‘site’ is tested by locating these practices within the broader participatory and relational ‘turns’ in contemporary art. While this ‘expansion’ has opened up opportunities for site-specific performance-makers to operate within spheres such as community engagement, wider concerns are raised by the rhetoric of ‘community empowerment’ and the instrumentalisation of creative practice by political and commissioning institutions. Keeping these issues in mind, this research builds upon Jane Rendell's call for the field of architecture and urbanism to embrace methods from public art and performance in order to operate as ‘critical spatial practices’. The thesis constructs an argument for the role of site-specific performance in articulating contested histories, claims, and potentials of the site. This proposition is explored through three case studies, including empirical and practice-based research with performance makers in complex and contested sites in northern England. This is supported by a survey of contemporary performance practices that directly address themes and sites of urban regeneration. Using the twin lenses of mapping and participation, the thesis demonstrates how performance(s) can articulate the multiplicity of stories, experiences, and potentials in marginalised or ‘interstitial’ urban sites. By introducing other agencies and temporalities to the site (‘gathering and showing’), site-specific practices have been shown to challenge dominant narratives and unsettle the stable or singular representations of places perpetuated by professional frameworks of urban development and regeneration

Zero modes in a system of Aharonov-Bohm fluxes

We study zero modes of two-dimensional Pauli operators with Aharonov--Bohm fluxes in the case when the solenoids are arranged in periodic structures like chains or lattices. We also consider perturbations to such periodic systems which may be infinite and irregular but they are always supposed to be sufficiently scarce

PERMISSIVE INFLUENCE OF STRESS IN THE EXPRESSION OF A U-SHAPED RELATIONSHIP BETWEEN SERUM CORTICOSTERONE LEVELS AND SPATIAL MEMORY ERRORS IN RATS

The relationship between glucocorticoids (GCs) and memory is complex, in that memory impairments can occur in response to manipulations that either increase or decrease GC levels. We investigated this issue by assessing the relationship between serum corticosterone (the primary rodent GC) and memory in rats trained in the radial arm water maze, a hippocampus-dependent spatial memory task. Each day, rats learned a new location of the hidden escape platform and then 30 min later their memory of the location of the platform was tested. Under control conditions, well-trained rats had excellent spatial memory and moderately elevated corticosterone levels (~26 μg/dl versus a baseline of ~2 μg/dl). Their memory was impaired when corticosterone levels were either reduced by metyrapone (a corticosterone synthesis inhibitor) or increased by acute stress (predator exposure), forming an overall U-shaped relationship between corticosterone levels and memory. We then addressed whether there was a causal relationship between elevated corticosterone levels and impaired memory. If elevated corticosterone levels were a sufficient condition to impair memory, then exogenously administered corticosterone, alone, should have impaired performance. However, we found that spatial memory was not impaired in corticosterone-injected rats that were not exposed to the cat. This work demonstrates that an intermediate level of corticosterone correlated with optimal memory, and either a decrease or an increase in corticosterone levels, in conjunction with strong emotionality, impaired spatial memory. These findings indicate that fear-provoking conditions, which are known to engage the amygdala, interact with stress levels of corticosterone to influence hippocampal functioning

Critical change in the Fermi surface of iron arsenic superconductors at the onset of superconductivity

The phase diagram of a correlated material is the result of a complex interplay between several degrees of freedom, providing a map of the material's behavior. One can understand (and ultimately control) the material's ground state by associating features and regions of the phase diagram, with specific physical events or underlying quantum mechanical properties. The phase diagram of the newly discovered iron arsenic high temperature superconductors is particularly rich and interesting. In the AE(Fe1-xTx)2As2 class (AE being Ca, Sr, Ba, T being transition metals), the simultaneous structural/magnetic phase transition that occurs at elevated temperature in the undoped material, splits and is suppressed by carrier doping, the suppression being complete around optimal doping. A dome of superconductivity exists with apparent equal ease in the orthorhombic / antiferromagnetic (AFM) state as well as in the tetragonal state with no long range magnetic order. The question then is what determines the critical doping at which superconductivity emerges, if the AFM order is fully suppressed only at higher doping values. Here we report evidence from angle resolved photoemission spectroscopy (ARPES) that critical changes in the Fermi surface (FS) occur at the doping level that marks the onset of superconductivity. The presence of the AFM order leads to a reconstruction of the electronic structure, most significantly the appearance of the small hole pockets at the Fermi level. These hole pockets vanish, i. e. undergo a Lifshitz transition, at the onset of superconductivity. Superconductivity and magnetism are competing states in the iron arsenic superconductors. In the presence of the hole pockets superconductivity is fully suppressed, while in their absence the two states can coexist.Comment: Updated version accepted in Nature Physic

The role of mutation rate variation and genetic diversity in the architecture of human disease

Background We have investigated the role that the mutation rate and the structure of genetic variation at a locus play in determining whether a gene is involved in disease. We predict that the mutation rate and its genetic diversity should be higher in genes associated with disease, unless all genes that could cause disease have already been identified. Results Consistent with our predictions we find that genes associated with Mendelian and complex disease are substantially longer than non-disease genes. However, we find that both Mendelian and complex disease genes are found in regions of the genome with relatively low mutation rates, as inferred from intron divergence between humans and chimpanzees, and they are predicted to have similar rates of non-synonymous mutation as other genes. Finally, we find that disease genes are in regions of significantly elevated genetic diversity, even when variation in the rate of mutation is controlled for. The effect is small nevertheless. Conclusions Our results suggest that gene length contributes to whether a gene is associated with disease. However, the mutation rate and the genetic architecture of the locus appear to play only a minor role in determining whether a gene is associated with disease

Virtual-pion and two-photon production in pp scattering

Two-photon production in pp scattering is proposed as a means of studying virtual-pion emission. Such a process is complementary to real-pion emission in pp scattering. The virtual-pion signal is embedded in a background of double-photon bremsstrahlung. We have developed a model to describe this background process and show that in certain parts of phase space the virtual-pion signal gives significant contribution. In addition, through interference with the two-photon bremsstrahlung background, one can determine the relative phase of the virtual-pion process

Low temperature thermal conductivity in a d-wave superconductor with coexisting charge order: Effect of self-consistent disorder and vertex corrections

Given the experimental evidence of charge order in the underdoped cuprate superconductors, we consider the effect of coexisting charge order on low-temperature thermal transport in a d-wave superconductor. Using a phenomenological Hamiltonian that describes a two-dimensional system in the presence of a Q=(\pi,0) charge density wave and d-wave superconducting order, and including the effects of weak impurity scattering, we compute the self-energy of the quasiparticles within the self-consistent Born approximation, and calculate the zero-temperature thermal conductivity using linear response formalism. We find that vertex corrections within the ladder approximation do not significantly modify the bare-bubble result that was previously calculated. However, self-consistent treatment of the disorder does modify the charge-order-dependence of the thermal conductivity tensor, in that the magnitude of charge order required for the system to become effectively gapped is renormalized, generally to a smaller value.Comment: 19 pages, 15 figure

A phase II trial of bendamustine in combination with rituximab in older patients with previously untreated diffuse large B-cell lymphoma

Bendamustine in combination with rituximab (BR) has been associated with high response rates and acceptable toxicity in older patients with relapsed/refractory diffuse large B-cell lymphoma (DLBCL). Evaluation of BR is warranted in the front-line setting for DLBCL patients not eligible for anthracyclines or for the elderly. In this phase II study, we enrolled DLBCL patients aged ≥65 years who were poor candidates for R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisone) to determine the efficacy and safety of BR in previously untreated stage II–IV DLBCL. Twenty-three patients were enrolled with a median age of 80 years. 52% of patients presented with poor functional status (Eastern Cooperative Oncology Group performance score of ≥2). The overall response rate was 78% with 12 complete responses (52%). At a median follow up of 29 months, the median overall survival was 10.2 months and the median progression-free survival was 5.4 months. The most common grade 3/4 adverse events were haematological. Combination therapy with BR demonstrates high response rates as front-line therapy in frail older patients with DLBCL, but survival rates were low. BR should be used with caution in future clinical trials involving older DLBCL patients with poor functional status