Electrical tunability due to coalescence of exceptional points in parity-time symmetric waveguides.

We demonstrate theoretically the electric tunability due to the coalescence of exceptional points in PT-symmetric waveguides bounded by imperfect conductive layers. Owing to the competition effect of multimode interaction, multiple exceptional points and PT phase transitions could be attained in such a simple system, and their occurrences are strongly dependent on the boundary conductive layers. When the conductive layers become very thin, it is found that the oblique transmittance and reflectance of the same system can be tuned between zero and one by a small change in the carrier density. The results may provide an effective method for fast tuning and modulation of optical signals through electrical gating.

Anomalous Light Scattering by Topological PT-symmetric Particle Arrays.

Robust topological edge modes may evolve into complex-frequency modes when a physical system becomes non-Hermitian. We show that, while having negligible forward optical extinction cross section, a conjugate pair of such complex topological edge modes in a non-Hermitian -symmetric system can give rise to an anomalous sideway scattering when they are simultaneously excited by a plane wave. We propose a realization of such scattering state in a linear array of subwavelength resonators coated with gain media. The prediction is based on an analytical two-band model and verified by rigorous numerical simulation using multiple-multipole scattering theory. The result suggests an extreme situation where leakage of classical information is unnoticeable to the transmitter and the receiver when such a -symmetric unit is inserted into the communication channel.

Retrospective comparison of management of gastro-enteritis in hospitalised children.

In Hong Kong, bacterial pathogens, the majority of them Salmonellae, cause approximately one-third of paediatric admissions for diarrhoea. This study retrospectively reviewed inpatient gastro-enteritis management, with particular focus on antibiotic use. Antibiotics are generally recommended for Salmonella gastro-enteritis in infants under 3 months of age but not for older infants and children unless they are so toxic that bacteraemia is suspected. Three groups of children admitted with acute gastro-enteritis were randomly identified from a computerised discharge database. Based on pathological reports held in the case records department, the final groups for analysis were Salmonella (n = 86), rotavirus (n = 55) and non-specified (n = 126). Epi Info version 6 (CDC, Atlanta) was used for data entry and analysis. Compared with a combined rotavirus/non-specified group, the Salmonella group were significantly more likely to have blood (OR 6.1, 95% CI 3.2-11.7, p < 0.0001) and mucus (OR 4.8, 95% CI 2.6-8.9, p < 0.0001) in the stool, fever during admission (OR 3.6, 95% CI 1.6-8.4, p = 0.001), more stools per day (median 6.2 vs 4.2, p < 0.0001), a longer stay in hospital (median 3.4 vs 2 days, p < 0.0001) and to be younger (median 7.1 vs 14.6 mths, p < 0.0001). The Salmonella group were more likely to have been given antibiotics (38% vs 15%, OR 3.6, 95% CI 1.9-6.9, p < 0.0001) but age did not influence the likelihood that antibiotics would be given.