Electrically reconfigurable non-volatile metasurface using low-loss optical phase-change material.

Active metasurfaces promise reconfigurable optics with drastically improved compactness, ruggedness, manufacturability and functionality compared to their traditional bulk counterparts. Optical phase-change materials (PCMs) offer an appealing material solution for active metasurface devices with their large index contrast and non-volatile switching characteristics. Here we report a large-scale, electrically reconfigurable non-volatile metasurface platform based on optical PCMs. The optical PCM alloy used in the devices, Ge2Sb2Se4Te (GSST), uniquely combines giant non-volatile index modulation capability, broadband low optical loss and a large reversible switching volume, enabling notably enhanced light-matter interactions within the active optical PCM medium. Capitalizing on these favourable attributes, we demonstrated quasi-continuously tuneable active metasurfaces with record half-octave spectral tuning range and large optical contrast of over 400%. We further prototyped a polarization-insensitive phase-gradient metasurface to realize dynamic optical beam steering.

Reconfigurable all-dielectric metalens with diffraction-limited performance.

Active metasurfaces, whose optical properties can be modulated post-fabrication, have emerged as an intensively explored field in recent years. The efforts to date, however, still face major performance limitations in tuning range, optical quality, and efficiency, especially for non-mechanical actuation mechanisms. In this paper, we introduce an active metasurface platform combining phase tuning in the full 2π range and diffraction-limited performance using an all-dielectric, low-loss architecture based on optical phase change materials (O-PCMs). We present a generic design principle enabling binary switching of metasurfaces between arbitrary phase profiles and propose a new figure-of-merit (FOM) tailored for reconfigurable meta-optics. We implement the approach to realize a high-performance varifocal metalens operating at 5.2 µm wavelength. The reconfigurable metalens features a record large switching contrast ratio of 29.5 dB. We further validate aberration-free and multi-depth imaging using the metalens, which represents a key experimental demonstration of a non-mechanical tunable metalens with diffraction-limited performance.

Diffractive Interface Theory: nonlocal polarizability approach to the optics of metasurfaces: erratum.

A typo in the software implementation of Diffractive Interface Theory [Opt. Express23, 2764 (2015)10.1364/OE.23.002764] was found during subsequent research. The typo was corrected, yielding better-than-originally-reported agreement between Diffractive Interface Theory and full-wave numerical solutions of Maxwell equations.

Diffractive interface theory: nonlocal susceptibility approach to the optics of metasurfaces.

We present a formalism for understanding the electromagnetism of metasurfaces, optically thin composite films with engineered diffraction. The technique, diffractive interface theory (DIT), takes explicit advantage of the small optical thickness of a metasurface, eliminating the need for solving for light propagation inside the film and providing a direct link between the spatial profile of a metasurface and its diffractive properties. Predictions of DIT are compared with full-wave numerical solutions of Maxwell's equations, demonstrating DIT's validity and computational advantages for optically thin structures. Applications of the DIT range from understanding of fundamentals of light-matter interaction in metasurfaces to efficient analysis of generalized refraction to metasurface optimization.

Shared cultural norms for justice in water institutions: results from Fiji, Ecuador, Paraguay, New Zealand, and the U.S.

It is widely agreed that current institutions are insufficient to meet global water challenges, and extensive institutional reforms are needed. To achieve effective local water management, institutional rules should be congruent with local cultural norms. Conversely, a major potential challenge is posed by tensions between institutional rules and local cultural norms for justice. We propose and demonstrate a new approach to cross-cultural analysis designed to investigate this tension, which can assess when local cultural norms are likely to facilitate or impede the acceptance of specific institutional rules. Using data from 238 respondents in five global sites (in Fiji, Ecuador, Paraguay, New Zealand, and the U.S.) analyzed using cultural consensus analysis, we find evidence of culturally-shared norms of justice in water institutions in at least six domains: a human right to water, water governance, water access, environmental stewardship, aspects of water markets, and aspects of water quality and health. Additionally, local cultural models across sites differed on only two topics: (1) ownership and allocation and (2) restrictions and enforcement. Indigenous heritage is the best single predictor of views on controversial institutional rules dealing with water restrictions/enforcement and ownership/allocation. This approach can help build effective water management solutions by identifying cases in which specific institutional reforms are congruent with local cultural norms (or not), and when those will matter most.

A randomized trial of peer review: the UK National Chronic Obstructive Pulmonary Disease Resources and Outcomes Project: three-year evaluation.

RATIONALE: Peer review has been widely used within the National Health Service to facilitate health quality improvement but evaluation has been limited particularly over the longer-term. Change within the National Health Service (NHS) can take a prolonged period--1-2 years--to occur. We report here a 3-year evaluation of the largest randomized trial of peer review ever conducted in the UK. AIM: To evaluate whether targeted mutual peer review of respiratory units brings about improvements in services for chronic obstructive pulmonary disease (COPD) over 3 years. METHODS: The peer review intervention was a reciprocal supportive exercise that included clinicians, hospital management, commissioners and patients, which focused on the quality of the provision of four specific evidence-based aspects of COPD care. RESULTS: Follow-up at 36 months demonstrated limited significant quantitative differences in the quality of services offered in the two groups but a strong trend in favour of intervention sites. Qualitative data suggested many benefits of peer review in most but not all intervention units and some control teams. The data identify factors that promote and obstruct change. CONCLUSION: The findings demonstrate significant change in service provision over 3 years in both control and intervention sites with great variability in both groups. The combined quantitative and qualitative findings indicate that targeted mutual peer review is associated with improved quality of care, improvements in service delivery and with changes within departments that promote and are precursors to quality improvement. The generic findings of this study have potential implications for the application of peer review throughout the NHS.

Co-morbidities and 90-day outcomes in hospitalized COPD exacerbations.

COPD exacerbations resulting in hospitalization are accompanied by high mortality and morbidity. The contribution of specific co-morbidities to acute outcomes is not known in detail: existing studies have used either administrative data or small clinical cohorts and have provided conflicting results. Identification of co-existent diseases that affect outcomes provides opportunities to address these conditions proactively and improve overall COPD care. Cases were identified prospectively on admission then underwent retrospective case note audit to collect data including co-morbidities on up to 60 unselected consecutive acute COPD admissions between March and May in each hospital participating in the 2008 UK National COPD audit. Outcomes recorded were death in hospital, length of stay, and death and readmission at 90 days after index admission. 232 hospitals collected data on 9716 patients, mean age 73, 50% male, mean FEV1 42% predicted. Prevalence of co-morbidities were associated with increased age but better FEV1 and ex-smoker status and with worse outcomes for all four measures. Hospital mortality risk was increased with cor pulmonale, left ventricular failure, neurological conditions and non-respiratory malignancies whilst 90 day death was also increased by lung cancer and arrhythmias. Ischaemic and other heart diseases were important factors in readmission. This study demonstrates that co-morbidities adversely affect a range of short-term patient outcomes related to acute admission to hospital with exacerbations of COPD. Recognition of relevant accompanying diseases at admission provides an opportunity for specific interventions that may improve short-term prognosis.

The UK National Chronic Obstructive Pulmonary Disease Resources and Outcomes Project--a feasibility study of large-scale clinical service peer review.

RATIONALE, AIMS AND OBJECTIVES: Service provision and clinical outcomes for patients admitted with chronic obstructive pulmonary disease remain unacceptably variable despite guidelines and performance feedback of national audit, data. This study aims to assess the impact of mutual peer review on service improvement. The initial phase of this study was to assess the feasibility and determine the practicalities of delivering such a peer review programme on a large scale. METHODS: All UK acute hospitals were invited to participate in a reciprocal peer review programme administered by a central team from three UK health organizations. Hospitals with the most resources were paired with those with the least (as defined in a baseline survey) and pairs randomized on a 3:2 basis into intervention or control groups. A number of key quality indicators were derived to measure service levels at the beginning and end of the study. Peer review teams included clinicians and managers from acute and primary care organizations and when possible a patient representative. Visits were focussed on four key areas of chronic obstructive pulmonary disease service. Teams were to agree service improvements and submit plans signed off by participants. Monthly change diaries were to be used to record progress towards agreed goals. RESULTS: A total of 100 hospitals participated in the programme. Overall, 52 of 54 peer review visits took place within a 4-week time frame and all units submitted service improvement plans within an agreed time frame. Secondary care representatives participated in all visits, primary care in 30 but patients in only 17. The mean number of diaries returned was 2, but 94% of units returned initial and final versions. CONCLUSIONS: It is possible to deliver successful large-scale mutual peer review using a limited but focussed programme. Participation of patients and use of change diaries requires further evaluation.

Current and planned palliative care service provision for chronic obstructive pulmonary disease patients in 239 UK hospital units: comparison with the gold standards framework.

Patients with chronic obstructive pulmonary disease report a symptom burden similar in magnitude to terminal cancer patients yet service provision and access has been reported as poor. In the absence of a specific national chronic obstructive pulmonary disease service framework the gold standards framework might support service developments. We surveyed 239 UK acute hospital units admitting chronic obstructive pulmonary disease patients, comprising 98% of all acute trusts, about their current and planned provision for palliative care services. Only 49% of units had a formal referral pathway for palliative care and only 13% had a policy of initiating end-of-life discussions with appropriate patients. Whilst 66% of units had plans to develop palliative care services, when mapped against the gold standards framework few were directly relevant and only three of the seven key standards were covered to any significant degree. We conclude that service provision remains poor and access is hindered by a lack of proactive initiation of discussion. Planned developments in chronic obstructive pulmonary disease palliative care services also lack a strategic framework that risks holistic design.