Bulk meltwater flow and liquid water content of snowpacks mapped using the electrical self-potential (SP) method

Our ability to measure, quantify and assimilate hydrological properties and processes of snow in operational models is disproportionally poor compared to the significance of seasonal snowmelt as a global water resource and major risk factor in flood and avalanche forecasting. We show here that strong electrical self-potential fields are generated in melting in situ snowpacks at Rhone Glacier and Jungfraujoch Glacier, Switzerland. In agreement with theory, the diurnal evolution of self-potential magnitudes ( ∼ 60–250mV) relates to those of bulk meltwater fluxes (0–1.2 × 10−6m3s−1) principally through the permeability and the content, electrical conductivity and pH of liquid water. Previous work revealed that when fresh snow melts, ions are eluted in sequence and electrical conductivity, pH and self-potential data change diagnostically. Our snowpacks had experienced earlier stages of melt, and complementary snow pit measurements revealed that electrical conductivity ( ∼ 1–5 × 10−6Sm−1) and pH ( ∼ 6.5–6.7) as well as permeabilities (respectively  ∼ 9.7 × 10−5 and  ∼ 4.3 × 10−5m2 at Rhone Glacier and Jungfraujoch Glacier) were invariant. This implies, first, that preferential elution of ions was complete and, second, that our self-potential measurements reflect daily changes in liquid water contents. These were calculated to increase within the pendular regime from  ∼ 1 to 5 and  ∼ 3 to 5.5% respectively at Rhone Glacier and Jungfraujoch Glacier, as confirmed by ground truth measurements. We conclude that the electrical self-potential method is a promising snow and firn hydrology sensor owing to its suitability for (1) sensing lateral and vertical liquid water flows directly and minimally invasively, (2) complementing established observational programs through multidimensional spatial mapping of meltwater fluxes or liquid water content and (3) monitoring autonomously at a low cost. Future work should focus on the development of self-potential sensor arrays compatible with existing weather and snow monitoring technology and observational programs, and the integration of self-potential data into analytical frameworks.ISSN:1994-0416ISSN:1994-042

The Carnegie Astrometric Planet Search Program

We are undertaking an astrometric search for gas giant planets and brown dwarfs orbiting nearby low mass dwarf stars with the 2.5-m du Pont telescope at the Las Campanas Observatory in Chile. We have built two specialized astrometric cameras, the Carnegie Astrometric Planet Search Cameras (CAPSCam-S and CAPSCam-N), using two Teledyne Hawaii-2RG HyViSI arrays, with the cameras' design having been optimized for high accuracy astrometry of M dwarf stars. We describe two independent CAPSCam data reduction approaches and present a detailed analysis of the observations to date of one of our target stars, NLTT 48256. Observations of NLTT 48256 taken since July 2007 with CAPSCam-S imply that astrometric accuracies of around 0.3 milliarcsec per hour are achievable, sufficient to detect a Jupiter-mass companion orbiting 1 AU from a late M dwarf 10 pc away with a signal-to-noise ratio of about 4. We plan to follow about 100 nearby (primarily within about 10 pc) low mass stars, principally late M, L, and T dwarfs, for 10 years or more, in order to detect very low mass companions with orbital periods long enough to permit the existence of habitable, Earth-like planets on shorter-period orbits. These stars are generally too faint and red to be included in ground-based Doppler planet surveys, which are often optimized for FGK dwarfs. The smaller masses of late M dwarfs also yield correspondingly larger astrometric signals for a given mass planet. Our search will help to determine whether gas giant planets form primarily by core accretion or by disk instability around late M dwarf stars.Comment: 48 pages, 9 figures. in press, Publ. Astron. Soc. Pacifi

Lung injury caused by aspiration of organophosphorus insecticide and gastric contents in pigs

INTRODUCTION: Patients who require mechanical ventilation after self-poisoning with ingested organophosphorus (OP) insecticides often die. Aspiration of stomach contents may contribute to lung injury and lethality. This study was designed to assess the severity of direct and indirect pulmonary injury created by pulmonary instillation of mixtures of OP insecticide, solvent (Solv) and porcine gastric juice (GJ) compared to controls. METHODS: Terminally anaesthetised minipigs (groups n = 5) were exposed to sham bronchoscopy or given mixtures (0.5 mL/kg) of: saline, GJ, OP insecticide and GJ (OP + GJ), or Solv and GJ (Solv + GJ), placed into the right lung, and monitored for 48 h. Lung injury was assessed through analysis of bronchoalveolar lavage fluid (BALF), computed tomography and histopathology. RESULTS: OP + GJ created a direct lung injury consisting of neutrophil infiltration, oedema and haemorrhage, as well as indirect injury to the other lung. OP + GJ directly-injured lung parenchyma had increased concentrations of BALF protein, albumin, IL-6, IL-8 and C-reactive protein (CRP) at 24 h (p < 0.05), and BALF protein, albumin and CRP at 48 h (p < 0.05), when compared with controls. Aspiration of GJ produced similar direct effects to OP + GJ but less indirect lung injury. Lung injury was less severe after Solv + GJ, for combined lung histopathology scores (vs. OP + GJ, p < 0.05) and for the proportion of directly-injured lung that was poorly/non-aerated at 48 h. CONCLUSION: Pulmonary instillation of OP + GJ created more lung damage than controls or Solv + GJ. In patients with severe OP insecticide poisoning and reduced consciousness, early airway protection is likely to reduce pulmonary damage

The Orbit of the Eclipsing X-ray Pulsar EXO 1722-363

With recent and archival Rossi X-Ray Timing Explorer (RXTE) X-ray measurements of the heavily obscured X-ray pulsar EXO 1722-363 (IGR J17252-3616), we carried out a pulse timing analysis to determine the orbital solution for the first time. The binary system is characterized by a_x sin(i) = 101 +/- 3 lt-s and P_orb = 9.7403 +/- 0.0004 days (90% confidence), with the precision of the orbital period being obtained by connecting datasets separated by more than 7 years (272 orbital cycles). The orbit is consistent with circular, and e < 0.19 at the 90% confidence level. The mass function is 11.7 +/- 1.2 M_sun and confirms that this source is a High Mass X-ray Binary (HMXB) system. The orbital period, along with the previously known ~414 s pulse period, places this system in the part of the Corbet diagram populated by supergiant wind accretors. Using previous eclipse time measurements by Corbet et al. and our orbital solution, combined with the assumption that the primary underfills its Roche lobe, we find i > 61 degrees at the 99% confidence level, the radius of the primary is between 21 R_sun and 37 R_sun, and its mass is less than about 22 M_sun. The acceptable range of radius and mass shows that the primary is probably a supergiant of spectral type B0I-B5I. Photometric measurements of its likely counterpart are consistent with the spectral type and luminosity if the distance to the system is between 5.3 kpc and 8.7 kpc. Spectral analysis of the pulsar as a function of orbital phase reveals an evolution of the hydrogen column density suggestive of dense filaments of gas in the downstream wake of the pulsar, with higher levels of absorption seen at orbital phases 0.5-1.0, as well as a variable Fe K_alpha line.Comment: Submitted to ApJ, 11 pages, 11 figure

The observation of nitric acid-containing particles in the tropical lower stratosphere

Airborne in situ measurements over the eastern Pacific Ocean in January 2004 have revealed a new category of nitric acid (HNO₃)-containing particles in the tropical lower stratosphere. These particles are most likely composed of nitric acid trihydrate (NAT). They were intermittently observed in a narrow layer above the tropopause (18&plusmn;0.1 km) and over a broad geographic extent (>1100 km). In contrast to the background liquid sulfate aerosol, these particles are solid, much larger (1.7-4.7 &micro;m vs.&nbsp;0.1&micro;m in diameter), and significantly less abundant (<10^-4 cm^-3 vs.&nbsp;10 cm^-3). Microphysical trajectory models suggest that the NAT particles grow over a 6-14 day period in supersaturated air that remains close to the tropical tropopause and might be a common feature in the tropics. The small number density of these particles implies a highly selective or slow nucleation process. Understanding the formation of solid NAT particles in the tropics could improve our understanding of stratospheric nucleation processes and, therefore, dehydration and denitrification

Chandra and RXTE Spectra of the Burster GS 1826-238

Using simultaneous observations from Chandra and RXTE, we investigated the LMXB GS 1826-238 with the goal of studying its spectral and timing properties. The uninterrupted Chandra observation captured 6 bursts (RXTE saw 3 of the 6), yielding a recurrence time of 3.54 +/- 0.03 hr. Using the proportional counter array on board RXTE, we made a probable detection of 611 Hz burst oscillations in the decaying phases of the bursts with an average rms signal amplitude of 4.8%. The integrated persistent emission spectrum can be described as the dual Comptonization of ~ 0.3 keV soft photons by a plasma with kT_e ~ 20 keV and an optical depth of about 2.6 (interpreted as emission from the accretion disk corona), plus the Comptonization of hotter ~ 0.8 keV seed photons by a ~ 6.8 keV plasma (interpreted as emission from or near the boundary layer). We discovered evidence for a neutral Fe K\alpha emission line, and we found interstellar Fe L_II and Fe L_III absorption features. The burst spectrum can be fit by fixing the disk Comptonization parameters to the persistent emission best-fit values, and adding a blackbody. The blackbody/seed photon temperature at the peak of the burst is ~ 1.8 keV and returns to ~ 0.8 keV over 200 s. The blackbody radius is consistent with R_bb = 10.3-11.7 km assuming a distance of 6 kpc; however, by accounting for the fraction of the surface that is obscured by the disk as a function of binary inclination, we determined the source distance must actually be near 5 kpc in order for the stellar radius to lie within the commonly assumed range of 10-12 km.Comment: Accepted for publication in ApJ; 13 pages, 6 figure

High moon brightness and low ambient temperatures affect sloth predation by harpy eagles

Background: Climate plays a key role in the life histories of tropical vertebrates. However, tropical forests are only weakly seasonal compared with temperate and boreal regions. For species with limited ability to control core body temperature, even mild climatic variation can determine major behavioural outcomes, such as foraging and predator avoidance. In tropical forests, sloths are the arboreal vertebrate attaining the greatest biomass density, but their capacity to regulate body temperature is limited, relying on behavioural adaptations to thermoregulate. Sloths are largely or strictly nocturnal, and depend on crypsis to avoid predation. The harpy eagle (Harpia harpyja) is a sloth-specialist and exerts strong top-down control over its prey species. Yet the role of environmental variables on the regulation of predator-prey interactions between sloths and harpy eagles are unknown. The harpy eagle is considered Near Threatened. This motivated a comprehensive effort to reintroduce this species into parts of Mesoamerica. This effort incidentally enabled us to understand the prey profile of harpy eagles over multiple seasons. Methods: Our study was conducted between 2003 and 2009 at Soberanía National Park, Panamá. Telemetered harpy eagles were seen hunting and feeding on individual prey species. For each predation event, field assistants systematically recorded the species killed. We analysed the effects of climatic conditions and vegetation phenology on the prey species profile of harpy eagles using generalised linear mixed models. Results: Here we show that sloth predation by harpy eagles was negatively affected by nocturnal ambient light (i.e. bright moonshine) and positively affected by seasonally cool temperatures. We suggest that the first ensured low detectability conditions for sloths foraging at night and the second posed a thermally unsuitable climate that forced sloths to forage under riskier daylight. We showed that even moderate seasonal variation in temperature can influence the relationship between a keystone tropical forest predator and a dominant prey item. Therefore, predator-prey ecology in the tropics can be modulated by subtle changes in environmental conditions. The seasonal effects shown here suggest important demographic consequences for sloths, which are under top-down regulation from harpy eagle predation, perhaps limiting their geographic distribution at higher latitudes

Vegetable diversity in relation with subclinical atherosclerosis and 15-year atherosclerotic vascular disease deaths in older adult women

Increasing vegetable intake and diversity are recommended to maintain better health. Evidence for the health benefits of vegetable diversity, separate from total intake, is scarce. We aimed to investigate the associations of vegetable diversity with subclinical measures of atherosclerosis and atherosclerotic vascular disease (ASVD) mortality

The mediating effect of task presentation on collaboration and children's acquisition of scientific reasoning

There has been considerable research concerning peer interaction and the acquisition of children's scientific reasoning. This study investigated differences in collaborative activity between pairs of children working around a computer with pairs of children working with physical apparatus and related any differences to the development of children's scientific reasoning. Children aged between 9 and 10 years old (48 boys and 48 girls) were placed into either same ability or mixed ability pairs according to their individual, pre-test performance on a scientific reasoning task. These pairs then worked on either a computer version or a physical version of Inhelder and Piaget's (1958) chemical combination task. Type of presentation was found to mediate the nature and type of collaborative activity. The mixed-ability pairs working around the computer talked proportionally more about the task and management of the task; had proportionally more transactive discussions and used the record more productively than children working with the physical apparatus. Type of presentation was also found to mediated children's learning. Children in same ability pairs who worked with the physical apparatus improved significantly more than same ability pairs who worked around the computer. These findings were partially predicted from a socio-cultural theory and show the importance of tools for mediating collaborative activity and collaborative learning