Bright source of spectrally uncorrelated polarization-entangled photons with nearly single-mode emission

We present results of a bright polarization-entangled photon source operating at 1552 nm via type-II collinear degenerate spontaneous parametric down-conversion in a periodically poled potassium titanyl phosphate crystal. We report a conservative inferred pair generation rate of 123,000 pairs/s/mW into collection modes. Minimization of spectral and spatial entanglement was achieved by group velocity matching the pump, signal and idler modes and through properly focusing the pump beam. By utilizing a pair of calcite beam displacers, we are able to overlap photons from adjacent down-conversion processes to obtain polarization-entanglement visibility of 94.7 +/- 1.1% with accidentals subtracted.Comment: 4 pages, 7 color figures. Revised manuscript includes the following changes: corrected pair generation rate from 44,000/s/mW pump to 123,000/s/mW pump; replaced Fig. 1b to enhance clarity; minor alterations to the title, abstract and introduction; grammatical correction

Novel Cascaded Ultra Bright Pulsed Source of Polarization Entangled Photons

A new ultra bright pulsed source of polarization entangled photons has been realized using type-II phase matching in spontaneous parametric down conversion process in two cascaded crystals. The optical axes of the crystals are aligned in such a way that the extraordinarily (ordinarily) polarized cone from one crystal overlaps with the ordinarily (extraordinarily) polarized cone from the second crystal. This spatial overlapping removes the association between the polarization and the output angle of the photons that exist in a single type-II down conversion process. Hence, entanglement of photons originating from any point on the output cones is possible if a suitable optical delay line is used. This delay line is particularly simple and easy to implement.Comment: 8 pages 8 figure

The electrophysiology of face perceptions in Williams Syndrome

Williams Syndrome is a rare genetic disorder in which the processing of faces and visual 'perception' has been argued to be intact despite other 'deficits' of visuospatial processing. In contrast, the theoretical approach taken in this thesis argues that the brains of those with developmental disorders cannot be legitimately viewed in terms of sparing and impairment, but must be considered as having atypical properties emergent as a result of atypical development. The event-related potential technique is used to provide evidence of abnormalities of perception of visual stimuli, including faces, even within the first 250ms of processing. A new approach to the brain imaging of people with developmental disorders is discussed. The thesis concludes by proposing an 'abnormal binding' hypothesis which aims to explain the nature and neural basis of the visuo-cognitive processing abnormalities in Williams Syndrome

Numerical study of the thermodynamics of clinoatacamite

We study the thermodynamic properties of the clinoatacamite compound, Cu_2(OH)_3Cl, by considering several approximate models. They include the Heisenberg model on (i) the uniform pyrochlore lattice, (ii) a very anisotropic pyrochlore lattice, and (iii) a kagome lattice weakly coupled to spins that sit on a triangular lattice. We utilize the exact diagonalization of small clusters with periodic boundary conditions and implement a numerical linked-cluster expansion approach for quantum lattice models with reduced symmetries, which allows us to solve model (iii) in the thermodynamic limit. We find a very good agreement between the experimental uniform susceptibility and the numerical results for models (ii) and (iii), which suggests a weak ferromagnetic coupling between the kagome and triangular layers in clinoatacamite. We also study thermodynamic properties in a geometrical transition between a planar pyrochlore lattice and the kagome lattice.Comment: 7 pages, 7 figure

Development and characterization for the automated surface mount assembly

Development of the ability to automatically assemble surface mount devices on circuits is described, including the characterization of the assembly process and improvements made to the system to increase the accuracy and repeatability of this process. The accuracy and repeatability of the system were characterized by measurements of the individual system components as well as the actual placement of components on a specially designed gauge. The forces and stresses experienced by the components when handled by the system were analyzed. The ability to deliver surface mount components to the system was developed by the design and development of stick magazines, vibratory feeders, a feeder control system, and an automatic stick magazine loader

Violation of Bell's Inequality with Photons from Independent Sources

We report a violation of Bell's inequality using one photon from a parametric down-conversion source and a second photon from an attenuated laser beam. The two photons were entangled at a beam splitter using the post-selection technique of Shih and Alley [Phys. Rev. Lett. 61, 2921 (1988)]. A quantum interference pattern with a visibility of 91% was obtained using the photons from these independent sources, as compared with a visibility of 99.4% using two photons from a central parametric down-conversion source.Comment: 4 pages, 5 figures; minor change

Synthesis of Nucleoside 5′-O-α,β-methylene-β-triphosphates and Evaluation of Their Potency Towards Inhibition of HIV-1 Reverse Transcriptase

A polymer-bound α,β-methylene-β-triphosphitylating reagent was synthesized and subjected to reactions with unprotected nucleosides, followed by oxidation, deprotection of cyanoethoxy groups, and acidic cleavage to afford nucleoside 5′-O-α,β-methylene-β-triphosphates. Among all the compounds, cytidine 5′-O-α,β-methylene-β-triphosphate inhibited RNase H activity of HIV-1 reverse transcriptase with a Ki value of 225 μM

Investigating the timecourse of accessing conversational implicatures during incremental sentence interpretation

Many contextual inferences in utterance interpretation are explained as following from the nature of conversation and the assumption that participants are rational. Recent psycholinguistic research has focussed on certain of these ‘Gricean’ inferences and have revealed that comprehenders can access them in online interpretation. However there have been mixed results as to the time-course of access. Some results show that Gricean inferences can be accessed very rapidly, as rapidly as any other contextually specified information (Sedivy, 2003; Grodner, Klein, Carbery, & Tanenhaus, 2010); while other studies looking at the same kind of inference suggest that access to Gricean inferences are delayed relative to other aspects of semantic interpretation (Huang & Snedeker, 2009; in press). While previous timecourse research has focussed on Gricean inferences that support the online assignment of reference to definite expressions, the study reported here examines the timecourse of access to scalar implicatures, which enrich the meaning of an utterance beyond the semantic interpretation. Even if access to Gricean inference in support of reference assignment may be rapid, it is still unknown whether genuinely enriching scalar implicatures are delayed. Our results indicate that scalar implicatures are accessed as rapidly as other contextual inferences. The implications of our results are discussed in reference to the architecture of language comprehension

A brave new world: the new normal for general practice after the COVID-19 pandemic

General practice in the UK transformed almost overnight in March 2020 in response to the COVID-19 pandemic. Practices largely shut their doors, face-to-face consultations almost exclusively became remote consultations, research evidence was implemented within days of being published, and much routine work postponed and labelled ‘non-essential’. As we settle into this (temporary) new way of working, we have a unique opportunity to reflect on our old and new working practices and decide what we should continue, change, and stop doing. Specifically, we consider what this ‘new normal’ could be in terms of remote consulting, practice re-organisation, use and implementation of evidence, advanced care planning, patient behaviour and chronic disease management, and implications for future practice, research, and policy