A nonperturbative study of three dimensional quantum electrodynamics with N flavours of fermion

This work is concerned with the breaking of chiral symmetry in gauge theories and the associated generation of a dynamical mass scale. We investigate this phenomenon in the context of a simple model, three dimensional QED, where the complicating factor of infinite renormalisations is absent. This model possesses an intrinsic scale, set by the coupling [e(^2)] = M, and it is the relationship between this and the dynamically generated mass scale that is of interest. The chiral symmetry breaking mechanism is investigated using the Schwinger Dyson equations which are then truncated in a nonperturbative manner using the Ball-Chiu vertex ansatz. The complexity of the resulting coupled fermion-photon system means that the photon is initially replaced by its perturbative form. Numerical investigations of this simplified system then reveal the existence of an exponential relationship, in terms of the dimensionless parameter N, between the intrinsic and dynamical mass scales, m ~ e(^2) exp(-cN). Contrary to the assertions of Appelquist et al the wavefunction renormalisation was found to be nonperturbative and crucial in determining this behaviour. The sensitivity of this mechanism to the nonperturbative behaviour of the photon is investigated. A simple analysis shows it to be far stronger than previously expected. This is confirmed by a numerical analysis of the coupled photon-fermion system which suggest the relationship between the two scales in the theory is of the form m ~ e(^2) exp(-cN(^2)). This model therefore illustrates how a large hierarchy of scales may naturally occur in a gauge theory, for instance N=3 m/a ~ 10(^-5). Finally an investigation of the gauge dependence of this approach is initiated. The softening of the photon in the low momentum region is shown to amplify automatically any inadequacy of the vertex ansatz by factors of O(a/m) in all but the Landau gauge. It is therefore expected that any incomplete vertex form will result in the generation of a "critical gauge", ɛ(_e), below which chiral symmetry breaking solutions will not exist. A path of further investigation is suggested

Alzheimer's disease: synaptic dysfunction and Aβ

Synapse loss is an early and invariant feature of Alzheimer's disease (AD) and there is a strong correlation between the extent of synapse loss and the severity of dementia. Accordingly, it has been proposed that synapse loss underlies the memory impairment evident in the early phase of AD and that since plasticity is important for neuronal viability, persistent disruption of plasticity may account for the frank cell loss typical of later phases of the disease. Extensive multi-disciplinary research has implicated the amyloid β-protein (Aβ) in the aetiology of AD and here we review the evidence that non-fibrillar soluble forms of Aβ are mediators of synaptic compromise. We also discuss the possible mechanisms of Aβ synaptotoxicity and potential targets for therapeutic intervention

Morphological and architectural control of hydroxyapatite growth

SIGLEAvailable from British Library Document Supply Centre- DSC:DX185465 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Simultaneous Formation of FeOx Electrocatalyst Coating within Hematite Photoanodes for Solar Water Splitting

Depositing an oxygen evolution electrocatalyst on the intricate pores of semiconductor light-absorbing layers of photoanodes for photoelectrochemical solar water splitting is an efficient way to improve their performance, but it adds extra costs and difficulties. In this work, we present a synthesis of hematite (-Fe2O3) photoanodes with a self-derived conductive amorphous FeOx electrocatalyst coating. Hematite-FeOx photoanodes were prepared via FeOOH precursors modified with low levels of lactic acid additive. In absence of lactic acid, FeOOH consisted of lepidocrocite nanorods that resulted in -Fe2O3 particulate photoanodes with sharp crystal edges upon doctor blading and calcination. Lactic acid addition however resulted in goethite and amorphous FeOOH that formed -Fe2O3 particulate photoanodes coated by a thin conductive amorphous FeOx layer. Electron microscopies revealed the thickness of this layer was controlled with the addition of lactic acid in the preparation. Photoelectrochemical characterization including Tafel plots, impedance spectroscopy, hole scavenger measurements and intensity modulated photocurrent spectrocopy confirmed the FeOx layer behaved as an FeOOH electrocatalyst, enhancing charge transfer efficiency and minimizing electron-hole surface recombination. Such coating increased the electrochemically-active surface area and amount of surface states. Photocurrent increased from 0.32 to 1.39 mA cm-2 at 1.23 VRHE under simulated sunlight, remarkable results for an auto-co-catalyzed and simple solution-process deposition

Simultaneous Formation of FeOx Electrocatalyst Coating within Hematite Photoanodes for Solar Water Splitting

Depositing an oxygen evolution electrocatalyst on the intricate pores of semiconductor light-absorbing layers of photoanodes for photoelectrochemical solar water splitting is an efficient way to improve their performance, but it adds extra costs and difficulties. In this work, we present a synthesis of hematite (-Fe2O3) photoanodes with a self-derived conductive amorphous FeOx electrocatalyst coating. Hematite-FeOx photoanodes were prepared via FeOOH precursors modified with low levels of lactic acid additive. In absence of lactic acid, FeOOH consisted of lepidocrocite nanorods that resulted in -Fe2O3 particulate photoanodes with sharp crystal edges upon doctor blading and calcination. Lactic acid addition however resulted in goethite and amorphous FeOOH that formed -Fe2O3 particulate photoanodes coated by a thin conductive amorphous FeOx layer. Electron microscopies revealed the thickness of this layer was controlled with the addition of lactic acid in the preparation. Photoelectrochemical characterization including Tafel plots, impedance spectroscopy, hole scavenger measurements and intensity modulated photocurrent spectrocopy confirmed the FeOx layer behaved as an FeOOH electrocatalyst, enhancing charge transfer efficiency and minimizing electron-hole surface recombination. Such coating increased the electrochemically-active surface area and amount of surface states. Photocurrent increased from 0.32 to 1.39 mA cm-2 at 1.23 VRHE under simulated sunlight, remarkable results for an auto-co-catalyzed and simple solution-process deposition