Weyl problem and Casimir effects in spherical shell geometry

We compute the generic mode sum that quantifies the effect on the spectrum of a harmonic field when a spherical shell is inserted into vacuum. This encompasses a variety of problems including the Weyl spectral problem and the Casimir effect of quantum electrodynamics. This allows us to resolve several long-standing controversies regarding the question of universality of the Casimir self-energy; the resolution comes naturally through the connection to the Weyl problem. Specifically we demonstrate that in the case of a scalar field obeying Dirichlet or Neumann boundary conditions on the shell surface the Casimir self-energy is cutoff-dependent while in the case of the electromagnetic field perturbed by a conductive shell the Casimir self-energy is universal. We additionally show that an analog non-relativistic Casimir effect due to zero-point magnons takes place when a non-magnetic spherical shell is inserted inside a bulk ferromagnet.Comment: 9 pages, minor changes, additional references added, version to be published in Phys. Rev.

Un/making difference through performance and mediation in contemporary Africa

This special issue of the Journal of African Cultural Studies grew out of a panel we organized at the European Conference on African Studies in Lisbon in June 2013. Our starting point was the observation of a massive revival of cultural and religious identities across the African continent, stretching from post-apartheid South Africa to Islamist groups in parts of West Africa. In the early twenty-first century, Africa appears to be witnessing a historical moment characterized by a resurgence of a politics of difference that, regardless of the heterogeneous forms in which it materializes, shares an uncanny ability to produce and sustain identities based on a politics of difference

Un/making difference through performance and mediation in contemporary Africa

This special issue of the Journal of African Cultural Studies grew out of a panel we organized at the European Conference on African Studies in Lisbon in June 2013. Our starting point was the observation of a massive revival of cultural and religious identities across the African continent, stretching from post-apartheid South Africa to Islamist groups in parts of West Africa. In the early twenty-first century, Africa appears to be witnessing a historical moment characterized by a resurgence of a politics of difference that, regardless of the heterogeneous forms in which it materializes, shares an uncanny ability to produce and sustain identities based on a politics of difference

Quantitative assessment of airborne exposures generated during common cleaning tasks: a pilot study

Background: A growing body of epidemiologic evidence suggests an association between exposure to cleaning products with asthma and other respiratory disorders. Thus far, these studies have conducted only limited quantitative exposure assessments. Exposures from cleaning products are difficult to measure because they are complex mixtures of chemicals with a range of physicochemical properties, thus requiring multiple measurement techniques. We conducted a pilot exposure assessment study to identify methods for assessing short term, task-based airborne exposures and to quantitatively evaluate airborne exposures associated with cleaning tasks simulated under controlled work environment conditions. Methods: Sink, mirror, and toilet bowl cleaning tasks were simulated in a large ventilated bathroom and a small unventilated bathroom using a general purpose, a glass, and a bathroom cleaner. All tasks were performed for 10 minutes. Airborne total volatile organic compounds (TVOC) generated during the tasks were measured using a direct reading instrument (DRI) with a photo ionization detector. Volatile organic ingredients of the cleaning mixtures were assessed utilizing an integrated sampling and analytic method, EPA TO-17. Ammonia air concentrations were also measured with an electrochemical sensor embedded in the DRI. Results: Average TVOC concentrations calculated for 10 minute tasks ranged 0.02 - 6.49 ppm and the highest peak concentrations observed ranged 0.14-11 ppm. TVOC time concentration profiles indicated that exposures above background level remained present for about 20 minutes after cessation of the tasks. Among several targeted VOC compounds from cleaning mixtures, only 2-BE was detectable with the EPA method. The ten minute average 2- BE concentrations ranged 0.30 -21 ppm between tasks. The DRI underestimated 2-BE exposures compared to the results from the integrated method. The highest concentration of ammonia of 2.8 ppm occurred during mirror cleaning. Conclusions: Our results indicate that airborne exposures from short-term cleaning tasks can remain in the air even after tasks' cessation, suggesting potential exposures to anyone entering the room shortly after cleaning. Additionally, 2-BE concentrations from cleaning could approach occupational exposure limits and warrant further investigation. Measurement methods applied in this study can be useful for workplace assessment of airborne exposures during cleaning, if the limitations identified here are addressed

Characterization of occupational exposures to cleaning products used for common cleaning tasks-a pilot study of hospital cleaners

Background: In recent years, cleaning has been identified as an occupational risk because of an increased incidence of reported respiratory effects, such as asthma and asthma-like symptoms among cleaning workers. Due to the lack of systematic occupational hygiene analyses and workplace exposure data, it is not clear which cleaning-related exposures induce or aggravate asthma and other respiratory effects. Currently, there is a need for systematic evaluation of cleaning products ingredients and their exposures in the workplace. The objectives of this work were to: a) identify cleaning products' ingredients of concern with respect to respiratory and skin irritation and sensitization; and b) assess the potential for inhalation and dermal exposures to these ingredients during common cleaning tasks. Methods: We prioritized ingredients of concern in cleaning products commonly used in several hospitals in Massachusetts. Methods included workplace interviews, reviews of product Materials Safety Data Sheets and the scientific literature on adverse health effects to humans, reviews of physico-chemical properties of cleaning ingredients, and occupational hygiene observational analyses. Furthermore, the potential for exposure in the workplace was assessed by conducting qualitative assessment of airborne exposures and semi-quantitative assessment of dermal exposures. Results: Cleaning products used for common cleaning tasks were mixtures of many chemicals, including respiratory and dermal irritants and sensitizers. Examples of ingredients of concern include quaternary ammonium compounds, 2-butoxyethanol, and ethanolamines. Cleaning workers are at risk of acute and chronic inhalation exposures to volatile organic compounds (VOC) vapors and aerosols generated from product spraying, and dermal exposures mostly through hands. Conclusion: Cleaning products are mixtures of many chemical ingredients that may impact workers' health through air and dermal exposures. Because cleaning exposures are a function of product formulations and product application procedures, a combination of product evaluation with workplace exposure assessment is critical in developing strategies for protecting workers from cleaning hazards. Our task based assessment methods allowed classification of tasks in different exposure categories, a strategy that can be employed by epidemiological investigations related to cleaning. The methods presented here can be used by occupational and environmental health practitioners to identify intervention strategies

Enabling real-time multi-messenger astrophysics discoveries with deep learning

Multi-messenger astrophysics is a fast-growing, interdisciplinary field that combines data, which vary in volume and speed of data processing, from many different instruments that probe the Universe using different cosmic messengers: electromagnetic waves, cosmic rays, gravitational waves and neutrinos. In this Expert Recommendation, we review the key challenges of real-time observations of gravitational wave sources and their electromagnetic and astroparticle counterparts, and make a number of recommendations to maximize their potential for scientific discovery. These recommendations refer to the design of scalable and computationally efficient machine learning algorithms; the cyber-infrastructure to numerically simulate astrophysical sources, and to process and interpret multi-messenger astrophysics data; the management of gravitational wave detections to trigger real-time alerts for electromagnetic and astroparticle follow-ups; a vision to harness future developments of machine learning and cyber-infrastructure resources to cope with the big-data requirements; and the need to build a community of experts to realize the goals of multi-messenger astrophysics

Zooarchaeological reconstruction of newly excavated Middle Pleistocene deposits from Elandsfontein, South Africa

The current study provides the first zooarchaeological account of systematically excavated faunal material from Elandsfontein, South Africa (ca. 1.0 – 0.6 Ma). Archaeological assemblages of this age typically lack well-preserved faunal remains recovered in primary association with artifacts, and thus studies have primarily focused on lithic technology. The sizeable faunal sample from Elandsfontein, South Africa is a rare exception and has dramatically influenced the way that we interpret early hominin foraging behavior during this time. Surface collections, starting in the 1950s, recovered ~13,000 mammalian fossils and more than 160 Acheulean artifacts. The Elandsfontein faunal assemblage was interpreted as having accumulated through natural mortality and subsequent scavenging by carnivores and hominins, with hominins playing a very minimal role in carcass modification. Low frequencies of stone tool cutmarks were taken as evidence that Acheulean hominins had limited ability to obtain large carcasses. However, this interpretation contrasts with a growing body of evidence suggesting that many Acheulean hominins across sub-Saharan Africa not only had access to large mammal carcasses but were often the primary agents of accumulation and modification. The majority of the original Elandsfontein faunal material was collected from deflation surfaces and lacks sufficient contextual information. We conducted a detailed zooarchaeological analysis of faunal remains from four recent excavations within the Elandsfontein dune field. Our results differ from those based on surface collections and suggest multiple agents of bone accumulation with varying degrees of hominin and carnivore activity across the paleolandscape. Frequencies of hominininduced butchery are higher (up to 3.6% NISP) than reported for previously collected samples (<1% of limb surfaces) and demonstrate butchery of megafauna on at least two occasions. Our findings indicate that earlier zooarchaeological studies at Elandsfontein underestimate the degree of hominin contribution to the fossil assemblage and do not take into account the complicated taphonomic history across the paleolandscape. The results of this analysis are congruent with recent studies suggesting that Acheulean hominins and their Oldowan producing predecessors had regular access to large carcasses and that megafauna were an essential component of the diet for early Homo