Causal structure of the entanglement renormalization ansatz

We show that the multiscale entanglement renormalization ansatz (MERA) can be reformulated in terms of a causality constraint on discrete quantum dynamics. This causal structure is that of de Sitter space with a flat spacelike boundary, where the volume of a spacetime region corresponds to the number of variational parameters it contains. This result clarifies the nature of the ansatz, and suggests a generalization to quantum field theory. It also constitutes an independent justification of the connection between MERA and hyperbolic geometry which was proposed as a concrete implementation of the AdS-CFT correspondence

A Technique for the Nondestructive Detection of Voids and Composition Anomalies in Metal Matrix Composite Wires Using X or γ Rays

An initial study of a technique proposed for the nondestructive testing of metal matrix composites is the subject of this paper. These composites are manufactured in the form of approximately 1/2-mm-diameter “precursor” wires. Larger structures are fabricated by diffusion bonding of lay-ups. Reliable nondestructive quality control indicators of wire integrity have not yet been developed although a number of possibilities are being examined.1 Testing of the precursor wires is difficult because current manufacturing processes produce wires that may be entirely satisfactory but that vary in cross-sectional geometry, in surface properties, and sometimes in the amount of matrix material that is present. Techniques based on observations of wire resistance, surface emissivity, and sound emission signatures are difficult to interpret because of these characteristics. Wire imaging using x-ray or neutron techniques is also difficult because large lengths of wire must be examined with a resolution in the plane of the wire exceeding 50 line pairs per millimeter

Conicoid Mirrors

The first order equation relating object and image location for a mirror of arbitrary conic-sectional shape is derived. It is also shown that the parabolic reflecting surface is the only one free of aberration and only in the limiting case of distant sources.Comment: 9 page

‘The show must go on!’ Fieldwork, mental health and wellbeing in Geography, Earth and Environmental Sciences

Fieldwork is central to the identity, culture and history of academic Geography, Earth and Environmental Sciences (GEES). However, in this paper we recognise that, for many academic staff, fieldtrips can be a profoundly challenging “ordeal,” ill‐conducive to wellness or effective pedagogic practice. Drawing on research with 39 UK university‐based GEES academics who self‐identify as having a mental health condition, we explore how mental health intersects with spaces and expectations of fieldwork in Higher Education. We particularly focus on their accounts of undertaking undergraduate residential fieldtrips and give voice to these largely undisclosed experiences. Their narratives run counter to normative, romanticised celebrations of fieldwork within GEES disciplines. We particularly highlight recurrent experiences of avoiding fieldwork, fieldwork‐as‐ ordeal, and “coping” with fieldwork, and suggest that commonplace anxieties within the neoliberal academy – about performance, productivity, fitness‐to‐work, self‐presentation, scrutiny and fear‐of‐falling‐behind – are felt particularly intensely during fieldwork. In spite of considerable work to make fieldwork more accessible to students, we find that field‐based teaching is experienced as a focal site of distress, anxiety and ordeal for many GEES academics with common mental health conditions. We conclude with prompts for reflection about how fieldwork could be otherwise

Apollo experience report: Assessment of metabolic expenditures

A significant effort was made to assess the metabolic expenditure for extravehicular activity on the lunar surface. After evaluation of the real-time data available to the flight controller during extravehicular activity, three independent methods of metabolic assessment were chosen based on the relationship between heart rate and metabolic production, between oxygen consumption and metabolic production, and between the thermodynamics of the liquid-cooled garment and metabolic production. The metabolic assessment procedure is analyzed and discussed. Real-time use of this information by the Apollo flight surgeon is discussed. Results and analyses of the Apollo missions and comments concerning future applications are included

Measuring patient-perceived quality of care in US hospitals using Twitter

BACKGROUND: Patients routinely use Twitter to share feedback about their experience receiving healthcare. Identifying and analysing the content of posts sent to hospitals may provide a novel real-time measure of quality, supplementing traditional, survey-based approaches. OBJECTIVE: To assess the use of Twitter as a supplemental data stream for measuring patient-perceived quality of care in US hospitals and compare patient sentiments about hospitals with established quality measures. DESIGN: 404 065 tweets directed to 2349 US hospitals over a 1-year period were classified as having to do with patient experience using a machine learning approach. Sentiment was calculated for these tweets using natural language processing. 11 602 tweets were manually categorised into patient experience topics. Finally, hospitals with ≥50 patient experience tweets were surveyed to understand how they use Twitter to interact with patients. KEY RESULTS: Roughly half of the hospitals in the US have a presence on Twitter. Of the tweets directed toward these hospitals, 34 725 (9.4%) were related to patient experience and covered diverse topics. Analyses limited to hospitals with ≥50 patient experience tweets revealed that they were more active on Twitter, more likely to be below the national median of Medicare patients (p<0.001) and above the national median for nurse/patient ratio (p=0.006), and to be a non-profit hospital (p<0.001). After adjusting for hospital characteristics, we found that Twitter sentiment was not associated with Hospital Consumer Assessment of Healthcare Providers and Systems (HCAHPS) ratings (but having a Twitter account was), although there was a weak association with 30-day hospital readmission rates (p=0.003). CONCLUSIONS: Tweets describing patient experiences in hospitals cover a wide range of patient care aspects and can be identified using automated approaches. These tweets represent a potentially untapped indicator of quality and may be valuable to patients, researchers, policy makers and hospital administrators