Stress tensor for a scalar field in a spatially varying background potential: Divergences, "renormalization," anomalies, and Casimir forces

Motivated by a desire to understand quantum fluctuation energy densities and stress within a spatially varying dielectric medium, we examine the vacuum expectation value for the stress tensor of a scalar field with arbitrary conformal parameter, in the background of a given potential that depends on only one spatial coordinate. We regulate the expressions by incorporating a temporal-spatial cutoff in the (imaginary) time and transverse-spatial directions. The divergences are captured by the zeroth- and second-order WKB approximations. Then the stress tensor is "renormalized" by omitting the terms that depend on the cutoff. The ambiguities that inevitably arise in this procedure are both duly noted and restricted by imposing certain physical conditions; one result is that the renormalized stress tensor exhibits the expected trace anomaly. The renormalized stress tensor exhibits no pressure anomaly, in that the principle of virtual work is satisfied for motions in a transverse direction. We then consider a potential that defines a wall, a one-dimensional potential that vanishes for $z<0$ and rises like $z^\alpha$, $\alpha>0$, for $z>0$. The full finite stress tensor is computed numerically for the two cases where explicit solutions to the differential equation are available, $\alpha=1$ and 2. The energy density exhibits an inverse linear divergence as the boundary is approached from the inside for a linear potential, and a logarithmic divergence for a quadratic potential. Finally, the interaction between two such walls is computed, and it is shown that the attractive Casimir pressure between the two walls also satisfies the principle of virtual work (i.e., the pressure equals the negative derivative of the energy with respect to the distance between the walls).Comment: 20 pages, 6 figure

Effects of tidal range on mooring systems of wave energy converters

Wave energy converters are currently proposed to be deployed near coastal area for the closeness to the infrastructure and for ease of maintenance in order to reduce operational costs. The motivation behind this work is the fact that the deployment depths during the highest and lowest tides will have a significant effect on the mooring system of WECs. In this paper, the issue will be investigated by numerical modelling (using ANSYS AQWA) for both catenary and taut moorings to examine the performance of the mooring system in varying tides. The case study being considered is the ¼- scale wave energy test site in Galway Bay off the west coast of Ireland where some marine renewable energy devices can be tested. In this test site, the tidal range is macro-tidal with a range of approximately 6 m which is a large value relative to the water depth. In the numerical analysis, ANSYS AQWA suite has been used to simulate moored devices under wave excitation at varying tidal ranges. Results show that the highest tide will give rise to larger forces. While at lower depths, slackening of the mooring occurs. Therefore, the mooring lines must be designed to accommodate both situations

Cultural Connections and Shared Origins between Cham and Dvāravatī: A comparison of common artistic and architectural motifs, ca. 7th – 10th centuries CE

This chapter contributes to our understanding of the regional connectedness of the Southeast Asian mainland by identifying networks that linked Campā with the Dvāravatī culture of central and northeast Thailand. Commonalities of decorative detail in architecture, sculpture and, in particular, sema stones are taken as evidence of direct contact between these two regions of the Southeast Asian mainland. Care is made to distinguish between shared motifs resulting from the common iconographic vocabulary originating from India, and patterns stemming from intra-regional links. In this respect, the rare quality of the artwork produced at sites in Campā and Dvāravatī indicates that the work was done by a single school of artists that travelled between them in search of patronage and employment. Routes of travel are identified on this basis, particularly those that cross the Lao Bảo pass and go through Muang Fa Daed (Kalasin province, northeast Thailand). Indeed, it is argued that Muang Fa Daed was the centre of an important intermediate territory located between Campā and Dvāravatī that had multiple and complex interactions with both, as well as the key regional centre of Champassak

On acceptance conditions for membrane systems: characterisations of L and NL

In this paper we investigate the affect of various acceptance conditions on recogniser membrane systems without dissolution. We demonstrate that two particular acceptance conditions (one easier to program, the other easier to prove correctness) both characterise the same complexity class, NL. We also find that by restricting the acceptance conditions we obtain a characterisation of L. We obtain these results by investigating the connectivity properties of dependency graphs that model membrane system computations

Predicting end-of-life in patients with an exacerbation of COPD by routine clinical assessment

SummaryThe purpose of this study was to determine if routine clinical assessment could reliably predict in-hospital death in patients admitted with acute exacerbation of COPD (AECOPD).MethodsIn a case-crossover study the case records of AECOPD related deaths were reviewed. Clinical and laboratory variables including performance status (WHO-PS) and a composite physiological score (early warning score, EWS) at initial clinical assessment on final admission (FA) and penultimate admission (PA) for AECOPD were compared.ResultsSixty patients included in study, female 60%, mean age (SD) 75 (8.7) years. 98% had ≥2 admissions for AECOPD. On univariate analysis variables associated with death were: Charlson score, WHO-PS, EWS, pH<7.35, Urea and CRP. On multivariate analysis predictors of mortality were: WHO-PS (OR 95% CI: 4.9 (1.06–22.61); p=0.04) and EWS (OR 95% CI: 3.39 (1.56–7.41); p=0.002). ROC analysis of relationship between combined WHO-PS/EWS score and death gave AUC 0.86; a total score≥6 had sensitivity 78% and specificity 86.2% and on multivariate analysis OR (95% CI) for death was 19.3 (4.3–86.2); p<0.0005.ConclusionIn-hospital deaths from AECOPD may be predicted by assessment of WHO-PS and EWS on admission to hospital

The only known egg of the Night Parrot? A molecular and morphometric assessment of an alleged egg from the Tanami Desert

The Night Parrot Pezoporus occidentalis is a much sought-after, recently ‘rediscovered’, endangered nocturnal parrot, endemic to arid Central Australia. Very little is known of its ecology, and its eggs have never been formally described. The literature on the eggs of the Night Parrot is collated here, and the provenance of an alleged Night Parrot egg found in the Tanami Desert, Northern Territory, in 1983 was assessed using DNA analysis and physical characteristics. Anecdotal reports from the late 19th–early 20th Century indicate that the Night Parrot lays a clutch of two to six roundish, white eggs. We suggest that its eggs are probably similar to and slightly larger than those of its congener, the Ground Parrot P. wallicus. The alleged Night Parrot egg was definitively identified by mitochondrial DNA analysis to be from the Brown Quail Synoicus ypsilophorus. This represents the first evidence of breeding by this species in the Tanami Desert, and lays to rest a long-standing misconception regarding the parrot

Complementary network-based approaches for exploring genetic structure and functional connectivity in two vulnerable, endemic ground squirrels

The persistence of small populations is influenced by genetic structure and functional connectivity. We used two network-based approaches to understand the persistence of the northern Idaho ground squirrel (Urocitellus brunneus) and the southern Idaho ground squirrel (U. endemicus), two congeners of conservation concern. These graph theoretic approaches are conventionally applied to social or transportation networks, but here are used to study population persistence and connectivity. Population graph analyses revealed that local extinction rapidly reduced connectivity for the southern species, while connectivity for the northern species could be maintained following local extinction. Results from gravity models complemented those of population graph analyses, and indicated that potential vegetation productivity and topography drove connectivity in the northern species. For the southern species, development (roads) and small-scale topography reduced connectivity, while greater potential vegetation productivity increased connectivity. Taken together, the results of the two network-based methods (population graph analyses and gravity models) suggest the need for increased conservation action for the southern species, and that management efforts have been effective at maintaining habitat quality throughout the current range of the northern species. To prevent further declines, we encourage the continuation of management efforts for the northern species, whereas conservation of the southern species requires active management and additional measures to curtail habitat fragmentation. Our combination of population graph analyses and gravity models can inform conservation strategies of other species exhibiting patchy distributions

Fifty Years of Archaeological Research at Dong Mae Nang Muang, an Ancient Gateway to the Upper Chao Phraya Basin

Dong Mae Nang Muang, in Banpotpisai district, Nakorn Sawan province is the present-day name for the site of Thanya Pura, one of the northernmost settlements of Dvaravati culture (6th–11th centuries CE) in central Thailand. Research conducted to date extends from the first surveys and excavations by the Fine Arts Department in 1956 and 1967 to recent projects of master’s degree students of the Faculty of Archaeology, Silpakorn University and the Fine Arts Department, Lopburi, 2008–2009. The material culture and archaeological record of the site, its period of occupation, state of preservation of extant monuments and new evidence of inhumation practices are discussed. The evidence shows that Dong Mae Nang Muang was an important political, economic, religious and artistic centre in the Upper Chao Phraya Basin