Nonreciprocal Transmission and Reflection of a Chirally Coupled Quantum Dot.

We report strongly nonreciprocal behavior for quantum dot exciton spins coupled to nanophotonic waveguides under resonant laser excitation. A clear dependence of the transmission spectrum on the propagation direction is found for a chirally coupled quantum dot, with spin up and spin down exciton spins coupling to the left and right propagation directions, respectively. The reflection signal shows an opposite trend to the transmission, which a numerical model indicates is due to direction-selective saturation of the quantum dot. The chiral spin-photon interface we demonstrate breaks reciprocity of the system and opens the way to spin-based quantum optical components such as optical diodes and circulators in a chip-based solid-state environment.

Electro-mechanical control of an on-chip optical beam splitter containing an embedded quantum emitter.

We demonstrate electro-mechanical control of an on-chip GaAs optical beam splitter containing a quantum dot single-photon source. The beam splitter consists of two nanobeam waveguides, which form a directional coupler (DC). The splitting ratio of the DC is controlled by varying the out-of-plane separation of the two waveguides using electromechanical actuation. We reversibly tune the beam splitter between an initial state, with emission into both output arms, and a final state with photons emitted into a single output arm. The device represents a compact and scalable tuning approach for use in III-V semiconductor integrated quantum optical circuits.

Monte Carlo study of the ordering in a strongly frustrated liquid crystal.

We have performed Monte Carlo simulations to investigate the temperature dependence of the ordering of the side chains of the X-shaped liquid crystal molecules which are arranged in a hexagonal array. Each hexagon contains six side chains, one from each side of the hexagon. Each liquid crystal molecule has two, dissimilar, side chains, one that contains silicon and one that contains fluorine. Like chains attract each other more strongly than unlike chains and this drives an order-disorder transition. The system is frustrated because it is not possible to find a configuration in which all the hexagons are occupied by either all silicon or all fluorine chains. There are two phase transitions. If only pairwise interactions are included it is found that there is an interesting fluctuating phase between the disordered phase and the fully ordered ground state. This did not agree with the experiments where an intermediate phase was seen that had long range order on one of the three sublattices. Agreement was found when the calculations were modified to include attractive three-body interactions between the silicon chains.

The effects of accessibility on general practitioner consultations, out-patient attendances and in-patient admissions in Norfolk, England.

A social survey was conducted to investigate the effects of accessibility on contacts with general practitioners and hospitals under the National Health Service in the predominantly rural county of Norfolk. Random samples of adults were taken close to hospital and general practitioner services in the city of Norwich, in villages close to Norwich with and without a general practitioner surgery and in villages relatively remote from the city with and without a surgery. General practitioner consultation rates, out-patient attendance rates and in-patient admissions were all found to decline with decreasing accessibility. For people with a long-standing illness, the main difference in rates was between urban and rural areas. The groups most affected in the rural areas were those with the highest relative need of health care. Their counterparts in the city used the health services much more. For the larger section of the sample, those with no long-standing illness, the most significant differences were between the various rural locations. Here, both distance to a surgery and distance to the city hospitals were associated with decreasing consultation, out-patient and in-patient rates. The main trend was of young mobile people with high expectations in places with readily accessible health services using those services more than would be expected from their usage rates elsewhere. There was also evidence among the people with no long-standing illness of less prosperous sub-groups being affected by remoteness at the out-patient stage.

Analysing geographic variations in mortality using Poisson regression: the example of ischaemic heart disease in England and Wales 1969-1973.

This paper describes how Poisson regression techniques can be used to examine the relationship between mortality and possible explanatory variables over a series of areas in cases where the number of deaths involved is relatively low. As an example an analysis is carried out on deaths from ischaemic heart disease among young adults in the county boroughs of England and Wales during 1969-1973. The results of the study indicate that the number of deaths was higher for males than females and was positively related to age, the size of the 'at risk' population and crowding, but negatively associated with water hardness and the size of the New Commonwealth population. A comparison of the Poisson and log-normal regression models clearly shows that the latter provides an inferior goodness of fit and unreliable results. It is therefore concluded that when the number of deaths is small there are both theoretical and practical advantages in using Poisson regression to analyse mortality data.

Role of branch surgeries in a rural area.

Surveys of general practitioners and rural residents were conducted in Norfolk to establish the characteristics of branch surgeries in the district and the patients who use them. The branch surgeries tend to serve an unrepresentative section of patients, predominantly those disadvantaged both in health and personal mobility-those from manual social classes, the elderly and those without cars. While doctors and patients were agreed that lower standards of care are provided in most branch surgeries compared with main surgeries, the evidence suggests that branch surgeries nevertheless meet a social need.