Detection of 3-Minute Oscillations in Full-Disk Lyα\alpha Emission During A Solar Flare

In this Letter we report the detection of chromospheric 3-minute oscillations in disk-integrated EUV irradiance observations during a solar flare. A wavelet analysis of detrended Lyman-alpha (from GOES/EUVS) and Lyman continuum (from SDO/EVE) emission from the 2011 February 15 X-class flare (SOL2011-02-15T01:56) revealed a $\sim$3-minute period present during the flare's main phase. The formation temperature of this emission locates this radiation to the flare's chromospheric footpoints, and similar behaviour is found in the SDO/AIA 1600\AA\ and 1700\AA\ channels, which are dominated by chromospheric continuum. The implication is that the chromosphere responds dynamically at its acoustic cutoff frequency to an impulsive injection of energy. Since the 3-minute period was not found at hard X-ray energies (50-100 keV) in RHESSI data we can state that this 3-minute oscillation does not depend on the rate of energization of non-thermal electrons. However, a second period of 120 s found in both hard X-ray and chromospheric emission is consistent with episodic electron energization on 2-minute timescales. Our finding on the 3-minute oscillation suggests that chromospheric mechanical energy should be included in the flare energy budget, and the fluctuations in the Lyman-alpha line may influence the composition and dynamics of planetary atmospheres during periods of high activity.Comment: 6 pages, 5 figures. Accepted for publication in Astrophysics Journal Letter

Methyl mercury dynamics in a tidal wetland quantified using in situ optical measurements

Author Posting. © American Society of Limnology and Oceanography, 2011. This article is posted here by permission of American Society of Limnology and Oceanography for personal use, not for redistribution. The definitive version was published in Limnology and Oceanography 56 (2011): 1355-1371, doi:10.4319/lo.2011.56.4.1355.We assessed monomethylmercury (MeHg) dynamics in a tidal wetland over three seasons using a novel method that employs a combination of in situ optical measurements as concentration proxies. MeHg concentrations measured over a single spring tide were extended to a concentration time series using in situ optical measurements. Tidal fluxes were calculated using modeled concentrations and bi-directional velocities obtained acoustically. The magnitude of the flux was the result of complex interactions of tides, geomorphic features, particle sorption, and random episodic events such as wind storms and precipitation. Correlation of dissolved organic matter quality measurements with timing of MeHg release suggests that MeHg is produced in areas of fluctuating redox and not limited by buildup of sulfide. The wetland was a net source of MeHg to the estuary in all seasons, with particulate flux being much higher than dissolved flux, even though dissolved concentrations were commonly higher. Estimated total MeHg yields out of the wetland were approximately 2.5 µg m−2 yr−1—4–40 times previously published yields—representing a potential loading to the estuary of 80 g yr−1, equivalent to 3% of the river loading. Thus, export from tidal wetlands should be included in mass balance estimates for MeHg loading to estuaries. Also, adequate estimation of loads and the interactions between physical and biogeochemical processes in tidal wetlands might not be possible without long-term, high-frequency in situ measurements.This work was supported by funding from the California Bay Delta Authority Ecosystem Restoration and Drinking Water Programs (grant ERP-00-G01) and matching funds from the U.S. Geological Survey Cooperative Research Program

Mercury Dynamics in a San Francisco Estuary Tidal Wetland: Assessing Dynamics Using In Situ Measurements

We used high-resolution in situ measurements of turbidity and fluorescent dissolved organic matter (FDOM) to quantitatively estimate the tidally driven exchange of mercury (Hg) between the waters of the San Francisco estuary and Browns Island, a tidal wetland. Turbidity and FDOM-representative of particle-associated and filter-passing Hg, respectively-together predicted 94 % of the observed variability in measured total mercury concentration in unfiltered water samples (UTHg) collected during a single tidal cycle in spring, fall, and winter, 2005-2006. Continuous in situ turbidity and FDOM data spanning at least a full spring-neap period were used to generate UTHg concentration time series using this relationship, and then combined with water discharge measurements to calculate Hg fluxes in each season. Wetlands are generally considered to be sinks for sediment and associated mercury. However, during the three periods of monitoring, Browns Island wetland did not appreciably accumulate Hg. Instead, gradual tidally driven export of UTHg from the wetland offset the large episodic on-island fluxes associated with high wind events. Exports were highest during large spring tides, when ebbing waters relatively enriched in FDOM, dissolved organic carbon (DOC), and filter-passing mercury drained from the marsh into the open waters of the estuary. On-island flux of UTHg, which was largely particle-associated, was highest during strong winds coincident with flood tides. Our results demonstrate that processes driving UTHg fluxes in tidal wetlands encompass both the dissolved and particulate phases and multiple timescales, necessitating longer term monitoring to adequately quantify fluxes

Mass Flux Measurement of Two Phase Dense Spray Using a Coupled Impulse Probe and PDPA Technique

Mass flux and void fraction measurement in a multiphase dense spray is a challenging task. The Phase Doppler Particle Anemometer (PDPA) cannot provide accurate mass flux measurements in a highly turbulent multiphase spray due to the presence of non-spherical and multiple droplets in the probe volume. A combined measurement of momentum data from the impulse probe and velocity data from the PDPA provides a fairly reasonable estimate of mass flux data in the two phase spray envelope. Experimental results show that mass flux at 60Dn (Dn= nozzle diameter of 3.10 mm) downstream of a horizontal nozzle tip is 0.033 kg/s, 0.034 kg/s and 0.0005 kg/s obtained from the theoretical value, impulse probe method and PDPA technique, respectively. This study will help answer some of the fundamental questions about the mass flux distribution in the two phase dense spray, which will aid in the improvement of the multiphase atomization design process in industrial applications

A case control study examining the feasibility of using eye tracking perimetry to differentiate patients with glaucoma from healthy controls

Abstract To explore the feasibility of using Saccadic Vector Optokinetic Perimetry (SVOP) to differentiate glaucomatous and healthy eyes. A prospective case–control study was performed using a convenience sample recruited from a single university glaucoma clinic and a group of healthy controls. SVOP and standard automated perimetry (SAP) was performed with testing order randomised. The reference standard was a diagnosis of glaucoma based a comprehensive ophthalmic examination and abnormality on standard automated perimetry (SAP). The index test was SVOP. 31 patients with glaucoma and 24 healthy subjects were included. Mean SAP mean deviation (MD) in those with glaucoma was − 8.7 ± 7.4 dB, with mean SAP and SVOP sensitivities of 23.3 ± 0.9 dB and 22.1 ± 4.3 dB respectively. Participants with glaucoma were significantly older. On average, SAP sensitivity was 1.2 ± 1.4 dB higher than SVOP (95% limits of agreement = − 1.6 to 4.0 dB). SVOP sensitivity had good ability to differentiate healthy and glaucomatous eyes with a 95% CI for area under the curve (AUC) of 0.84 to 0.96, similar to the performance of SAP sensitivity (95% CI 0.86 to 0.97, P = 0.60). For 80% specificity, SVOP had a 95% CI sensitivity of 75.7% to 94.8% compared to 77.8% to 96.0% for SAP. SVOP took considerably longer to perform (514 ± 54 s compared to 267 ± 76 s for SAP). Eye tracking perimetry may be useful for detection of glaucoma but further studies are needed to evaluate SVOP within its intended sphere of use, using an appropriate design and independent reference standard