Observed parity-odd CMB temperature bispectrum

Parity-odd non-Gaussianities create a variety of temperature bispectra in the cosmic microwave background (CMB), defined in the domain: $\ell_1 + \ell_2 + \ell_3 = {\rm odd}$. These models are yet unconstrained in the literature, that so far focused exclusively on the more common parity-even scenarios. In this work, we provide the first experimental constraints on parity-odd bispectrum signals in WMAP 9-year temperature data, using a separable modal parity-odd estimator. Comparing theoretical bispectrum templates to the observed bispectrum, we place constraints on the so-called nonlineality parameters of parity-odd tensor non-Gaussianities predicted by several Early Universe models. Our technique also generates a model-independent, smoothed reconstruction of the bispectrum of the data for parity-odd configurations.Comment: 17 pages, 4 figures, 1 table. Accepted for publication in JCA

The optical detection of retinal ganglion cell damage

We provide an overview of developments in the use OCT imaging for the detection of retinal ganglion cell damage in vivo that avoid use of any exogenous ligands to label cells. The method employs high resolution OCT using broad spectral light sources to deliver axial resolution of under 5 microns. The resolution approximates that of cellular organelles, which undergo degenerative changes that progress to apoptosis as a result of axon damage. These degenerative changes are manifest as the loss of retinal ganglion cell dendrites and fragmentation of the subcellular network of organelles, in particular, the mitochondria that support dendritic structure. These changes can alter the light scattering behaviour of degenerating neurons. Using OCT imaging techniques to identify these signals in cultured neurons, we have demonstrated changes in cultured cells and in retinal explants. Pilot studies in human glaucoma suggest that similar changes are detectable in the clinical setting. High resolution OCT can be used to detect optical scatter signals that derive from the retinal ganglion cell layer and are associated with neuronal damage. These findings suggest that OCT instruments can be used to derive quantitative measurements of retinal ganglion cell damage. Critically, these signals can be detected at an early stage of retinal ganglion cell degeneration when cells could be protected or remodeled to support visual recovery

The interaction of economic and political inequality in Latin America

We investigate how economic inequality can persist in Latin America in the context of radical falls in political inequality in the last decades. Using data from Colombia, we focus on a critical facet of democratization - the entry of new politicians. We show that initial levels of inequality play a significant role in determining the impact of political entry on local institutions, policy, and development outcomes, which can impact future inequality. A vicious circle emerges whereby policies that reduce inequality are less likely to be adopted and implemented in places with relatively high inequality. We present evidence that this is caused both by the capture of new politicians and barriers to institution and state capacity building, and also by the fact that politicians committed to redistribution are less likely to win in relatively unequal places. Our results, therefore, help to reconcile the persistence of economic inequality with the new political context

Full Field Swept Source Optical Coherence Tomography

Optical Coherence Tomography (OCT) is a non-invasive volumetric imaging technique that offers micron scale resolution over several millimetres of depth penetration in tissue. The aim of the project was to develop Full Field Swept Source OCT (FFSSOCT), charting the specifications of the system throughout and drawing comparisons with available Fourier domain OCT (FDOCT) systems. A super luminescent diode (SLD) light source was tuned to different optical frequencies using an acousto-optical tunable filter. The successive optical frequencies were distributed across the sample in parallel and the sequential interference spectra were recorded with a high speed digital camera. Using a 5mW optical source at 850nm, 70dB sensitivity was ultimately achieved in a single five second acquisition, improving the original performance by 5dB and increasing acquisition and processing time significantly. Ex vivo retinal images of rat and tree shrew were recorded with multiple layers visible. All software was custom written in Labview, improving the user interface and processing time over the existing Matlab code. To enhance the performance of the system, the camera was subsequently upgraded from 15 to 45% quantum efficiency and from 250k to 1.3M pixels. The light source was also upgraded to 20mW. The software was improved with spectral processing and dispersion compensation. 85dB sensitivity was ultimately achieved. Further ex vivo retinal images were taken, showing comparative image quality to those of the same retinal samples recorded with FDOCT. Further attempts to increase the system performance were limited by internal reflections and interfering surfaces within the FFSSOCT design leading to saturation of the digital camera. In vivo imaging was attempted using software based phase jitter compensation. Improvement could be seen with simple reflecting structures

He Who Counts Elects: Determinants of Fraud in the 1922 Colombian Presidential Election

This paper constructs measures of the extent of ballot stuffing (fraudulent votes) and electoral coercion at the municipal level using data from Colombia's 1922 Presidential elections. Our main findings are that the presence of the state reduced the extent of ballot stuffing, but that of the clergy, which was closely imbricated in partisan politics, increased coercion. We also show that landed elites to some extent substituted for the absence of the state and managed to reduce the extent of fraud where they were strong. At the same time, in places which were completely out of the sphere of the state, and thus partisan politics, both ballot stuffing and coercion were relatively low. Thus the relationship between state presence and fraud is not monotonic.

Optophysiological characterisation of inner retina responses with high-resolution optical coherence tomography

Low coherence laser interferometry has revolutionised quantitative biomedical imaging of optically transparent structures at cellular resolutions. We report the first optical recording of neuronal excitation at cellular resolution in the inner retina by quantifying optically recorded stimulus-evoked responses from the retinal ganglion cell layer and comparing them with an electrophysiological standard. We imaged anaesthetised paralysed tree shrews, gated image acquisition, and used numerical filters to eliminate noise arising from retinal movements during respiratory and cardiac cycles. We observed increases in contrast variability in the retinal ganglion cell layer and nerve fibre layer with flash stimuli and gratings. Regions of interest were subdivided into three-dimensional patches (up to 5-15μm in diameter) based on response similarity. We hypothesise that these patches correspond to individual cells, or segments of blood vessels within the inner retina. We observed a close correlation between the patch optical responses and mean electrical activity of afferent visual neurons. While our data suggest that optical imaging of retinal activity is possible with high resolution OCT, the technical challenges are not trivial