Electrodynamics of Amorphous Media at Low Temperatures

Amorphous solids exhibit intrinsic, local structural transitions, that give rise to the well known quantum-mechanical two-level systems at low temperatures. We explain the microscopic origin of the electric dipole moment of these two-level systems: The dipole emerges as a result of polarization fluctuations between near degenerate local configurations, which have nearly frozen in at the glass transition. An estimate of the dipole's magnitude, based on the random first order transition theory, is obtained and is found to be consistent with experiment. The interaction between the dipoles is estimated and is shown to contribute significantly to the Gr\"{u}neisen parameter anomaly in low $T$ glasses. In completely amorphous media, the dipole moments are expected to be modest in size despite their collective origin. In partially crystalline materials, however, very large dipoles may arise, possibly explaining the findings of Bauer and Kador, J. Chem. Phys. {\bf 118}, 9069 (2003).Comment: Submitted for publication; April 27, 2005 versio

Mobilising the global significance of multidisciplinary discourses of performativity: lessons from an Australian major league baseballer in the United States and Australian circus performers

The discursive construction and expression of multiple forms of identities (self and other; individual, group and community; local, national and international) continue to exercise scholars across a wide range of disciplines, who in turn sometimes seek to exorcise less constructive and enabling representations of certain kinds of marginalised identities. This multi-valenced character of identity discourses is illustrated starkly in the very different status and forms of capital of two occupationally mobile communities with whom this paper is concerned. One group is the highly successful internationally mobile major league baseball players – specifically in this case an Australian player who spent many years travelling the baseball circuits in the United States. The other group is the circuses who travel from place to place in Australia providing public entertainment based on equally specialised skill sets. The paper presents a critically engaged and theoretically informed discourse analysis of empirical data collected with the two groups. The analysis is framed by selected aspects of Judith Butler’s notion of performativity, augmented with more recent theorisation in the field and taking note of the critiques of the concept. The analysis interrogates the discourses of mobility and performativity across the three disciplines of sports biography, life course studies and the sociology of education, in the process distilling areas of potential convergence while acknowledging the appropriate aspects of disciplinary specificity. The analysis is clustered around the emergent organising themes of constructions of home, selfhood and otherness, and multiple identities created and communicated through repeated performances of evolving skills. The paper concludes by examining possible implications of this analysis for contemporary debates about global discourses related to in/equality, discrimination and marginalisation, with particular reference to current and possible future developments in the European polity and society

Recurrent laryngeal nerve palsy due to impacted dental plate in the thoracic oesophagus: case report

<p>Abstract</p> <p>Background</p> <p>Retained oesophageal foreign bodies must be urgently removed to prevent potentially serious complications. Recurrent laryngeal nerve palsy is rare and has not been reported in association with a foreign body in the thoracic oesophagus.</p> <p>Case presentation</p> <p>We present a case of a dental plate in the thoracic oesophagus that caused high dysphagia. Delayed diagnosis led to a recurrent laryngeal nerve palsy, which persisted despite successful surgical removal of the foreign body.</p> <p>Conclusion</p> <p>Oesophagoscopy is essential to fully assess patients with persistent symptoms after foreign body ingestion, irrespective of the level of dysphagia. Recurrent laryngeal nerve palsy may indicate impending perforation and should prompt urgent evaluation and treatment.</p

A Unifying Framework for the Circle Criterion and Other Quadratic Stability Criteria

We present a result on the existence of a common quadratic Lyapunov function for a pair of linear timeinvariant systems. We show that this result characterises, generalises, and provides new perspectives on several well-known stability results. In particular, new time-domain formulations of the Circle Criterion and Meyer’s extension of the KYP lemma are presented

Distribution of total mercury and methylated mercury species in Central Arctic Ocean water and ice

The central Arctic Ocean remains largely unexplored when it comes to the presence and cycling of mercury and its methylated forms including mono- and dimethylmercury (MMeHg and DMeHg, respectively). In this study, we quantified total Hg (HgT) and methylated Hg species in seawater, ice cores, snow, brine, and water from melt ponds collected during the SWEDARCTIC 2016 expedition to the Amerasian and Eurasian side of the Lomonosov Ridge. In the water column, concentrations of HgT, MMeHg and DMeHg ranged from 0.089 to 1.5 pM, &lt;25 to 520 fM and from &lt;1.6 to 160 fM, respectively. HgT was enriched in surface waters while MMeHg and DMeHg were low at the surface (i.e. in the polar mixed layer) and enriched at a water depth of around 200–400 m. A 1:2 ratio of DMeHg to MMeHg was observed in the water column suggesting a lower ratio in the central parts of the Arctic Ocean than what has previously been reported from other parts of the Arctic Ocean. At the ice stations, average HgT ranged from 0.97 \ub1 1.2 pM in the ice cores to 27 \ub1 17 pM in melt pond waters and average MeHgT (total MeHg) from 28 \ub1 15 fM in brine to 130 \ub1 18 fM in melt pond water. The HgT observed in melt ponds and brine was an order of magnitude greater than HgT observed in surface waters and HgT in the upper part of the ice-cores was ~4–8 times higher HgT in comparison to lower layers. Our study suggests that ice may act as a source of HgT to surface waters but not to be a likely source of the methylated Hg forms. Unlike elemental Hg, DMeHg did not enrich in surface waters covered by ice. Concentrations of DMeHg observed in the ice cores and other samples collected from the ice stations were low, suggesting ice to not act as a source of DMeHg to the atmosphere nor to surface waters

Sources and Deposition of Reactive Gaseous Mercury in the Marine Atmosphere

Observations of reactive gaseous mercury (RGM) in marine air show a consistent diurnal cycle with minimum at night, rapid increase at sunrise, maximum at midday, and rapid decline in afternoon. We use a box model for the marine boundary layer (MBL) to interpret these observations in terms of RGM sources and sinks. The morning rise and midday maximum are consistent with oxidation of elemental mercury (Hg0) by Br atoms, requiring <2 ppt BrO in most conditions. Oxidation of Hg0 by Br accounts for 35–60% of the RGM source in our model MBL, with most of the remainder contributed by oxidation of Hg0 by ozone (5–20%) and entrainment of RGM-rich air from the free troposphere (25–40%). Oxidation of Hg0 by Cl is minor (3–7%), and oxidation by OH cannot reproduce the observed RGM diurnal cycle, suggesting that it is unimportant. Fitting the RGM observations could be achieved in the model without oxidation of Hg0 by ozone (leaving Br as the only significant oxidant) by increasing the entrainment flux from the free troposphere. The large relative diurnal amplitude of RGM concentrations implies rapid loss with a lifetime of only a few hours. We show that this can be quantitatively explained by rapid, mass-transfer-limited uptake of RGM into sea-salt aerosols as HgCl3− and HgCl42−. Our results suggest that 80–95% of HgII in the MBL should be present in sea-salt aerosol rather than gas-phase, and that deposition of sea-salt aerosols is the major pathway delivering HgII to the ocean.Earth and Planetary SciencesEngineering and Applied Science

An intercomparison of procedures for the determination of total mercury in seawater and recommendations regarding mercury speciation during GEOTRACES cruises

Author Posting. © Association for the Sciences of Limnology and Oceanography, 2012. This article is posted here by permission of Association for the Sciences of Limnology and Oceanography for personal use, not for redistribution. The definitive version was published in Limnology and Oceanography: Methods 10 (2012): 90-100, doi:10.4319/lom.2012.10.90.We conducted a laboratory intercomparison of total mercury (Hg) determination in seawater collected during U.S. GEOTRACES Intercalibration cruises in 2008 and 2009 to the NW Atlantic and NE Pacific Oceans. Results indicated substantial disagreement between the participating laboratories, which appeared to be affected most strongly by bottle cleanliness and preservation procedures. In addition, we examined the effectiveness of various collection and sample preparation procedures that may be used on future GEOTRACES cruises. The type of sampling system and filtration medium appeared to make little difference to results. Finally, and in light of results from experiments that considered sample bottle material effect and the development of new methods for CH3Hg+ extraction from seawater, we propose a recommended procedure for determining all four of the major Hg species in seawater (elemental, dimethyl-, monomethyl-, and total Hg).This work was supported by the National Science Foundation program in Chemical Oceanography under grants OCE–0825157, –0825108, –0825583 and –0825068

On Orbit ISS Oxygen Generation System Operation Status

The International Space Station (ISS) United States Orbital Segment (USOS) Oxygen Generation System (OGS) has accumulated almost a year of operation at varied oxygen production rates within the US Laboratory Module (LAB) since it was first activated in July 2007. It was operated intermittently through 2009 and 2010, due to filter clogging and acid accumulation in the recirculation loop. Since the installation of a deionizing bed in the recirculation loop in May of 2011 the OGA has been operated continuously. Filters in the recirculation loop have clogged and have been replaced. Hydrogen sensors have drifted apart, and a power failure may have condensed water on a hydrogen sensor. A pump delta pressure sensor failed, and a replacement new spare pump failed to start. Finally, the voltage across the cell stack increased out of tolerance due to cation contamination, and the cell stack was replaced. This paper will discuss the operating experience and characteristics of the OGS, as well as operational issues and their resolution