Use of voltammetric solid-state (micro)electrodes for studying biogeochemical processes: Laboratory measurements to real time measurements with an in situ electrochemical analyzer (ISEA)     

George W. Luther III  Brian T. Glazer  Shufen Ma  Robert E. Trouwborst  Tommy S. Moore  Edouard Metzger  Chareonkwan Kraiya  Tim J. Waite  Gregory Druschel  Bjrn Sundby  Martial Taillefert  Donald B. Nuzzio  Timothy M. Shank  Brent L. Lewis  Paul J. Brendel 《Marine Chemistry》2008,108(3-4):221-235

Solid-state voltammetric (micro)electrodes have been used in a variety of environments to study biogeochemical processes. Here we show the wealth of information that has been obtained in the study of sediments, microbial mats, cultures and the water column including hydrothermal vents. Voltammetric analyzers have been developed to function with operator guidance and in unattended mode for temporal studies with an in situ electrochemical analyzer (ISEA). The electrodes can detect the presence (or absence) of a host of redox species and trace metals simultaneously. The multi-species capacity of the voltammetric electrode can be used to examine complex heterogeneous environments such as the root zone of salt marsh sediments. The data obtained with these systems clearly show that O₂ and Mn²⁺ profiles in marine sedimentary porewaters and in microbial biofilms on metal surfaces rarely overlap indicating that O₂ is not a direct oxidant for Mn²⁺. This lack of overlap was suggested originally by Joris Gieskes' group. In waters emanating from hydrothermal vents, Fe²⁺, H₂S and soluble molecular FeS clusters (FeS_aq) are detected indicating that the reactants for the pyrite formation reaction are H₂S and soluble molecular FeS clusters. Using the ISEA with electrodes at fixed positions, data collected continuously over three days near a Riftia pachyptila tubeworm field generally show that O₂ and H₂S anti-correlate and that H₂S and temperature generally correlate. Unlike sedimentary environments, the data clearly show that Riftia live in areas where both O₂ and H₂S co-exist so that its endosymbiont bacteria can perform chemosynthesis. However, physical mixing of diffuse flow vent waters with oceanic bottom waters above or to the side of the tubeworm field can dampen these correlations or even reverse them. Voltammetry is a powerful technique because it provides chemical speciation data (e.g.; oxidation state and different elemental compounds/ions) as well as quantitative data. Because (micro)organisms occupy environmental niches due to the system's chemistry, it is necessary to know chemical speciation. Voltammetric methods allow us to study how chemistry drives biology and how biology can affect chemistry for its own benefit.  相似文献   

Storm runoff and sediment losses from forest clearcutting and stand re‐establishment with best management practices in East Texas,USA     

Matthew W. McBroom  R. Scott Beasley  Mingteh Chang  George G. Ice 《水文研究》2008,22(10):1509-1522

Nine small (2·5 ha) and four large (70–135 ha) watersheds were instrumented in 1999 to evaluate the effects of intensive silvicultural practices with best management practices (BMPs) on runoff and stream water quality in the Western Gulf Coastal Plain of East Texas, USA. Two treatments were implemented in 2002: a conventional treatment with clearcutting and herbicide site preparation, and an intensive treatment that added subsoiling, fertilization and a release herbicide application. Watershed effects were compared with results from a previously conducted study on the same watersheds in 1981, in which two combinations of harvesting and mechanical site preparation without BMPs were evaluated. Due to the reduction in evapotranspirational demand, total storm runoff increased on all six treated small watersheds following harvest by 0·94 to 13·73 cm in 2003. Runoff increases were not statistically significant on the treated large watersheds. Total first‐year sediment loss was significantly greater on two of the conventional and one of the intensive small watersheds. The greatest first‐year increase was 540·1 kg ha^?1, only one‐fifth of that observed on these watersheds from shearing and windrowing without BMPs in 1981. First‐year sediment loss was significantly greater on the intensive large watershed following harvest, but not on the conventional large watershed. These data suggest that BMPs are very effective in reducing potential water quality impacts from intensive silvicultural practices. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

The Spectral Irradiance Monitor: Measurement Equations and Calibration   总被引：2，自引：0，他引：2  

Jerald W. Harder  Juan Fontenla  George Lawrence  Thomas Woods  Gary Rottman 《Solar physics》2005,230(1-2):169-204

The Spectral Irradiance Monitor (SIM) is a satellite-borne spectrometer aboard the Solar Radiation and Climate Experiment (SORCE) that measures solar irradiance between 200 and 2700 nm. This instrument employs a Fèry prism as a dispersing element, an electrical substitution radiometer (ESR) as the primary detector, and four additional photodiode detectors for spectral scanning. Assembling unit level calibrations of critical components and expressing the sensitivity in terms of interrelated measurement equations supplies the instrument's radiant response. The calibration and analysis of the spectrometer's dispersive and transmissive properties, light aperture metrology, and detector characteristics provide the basis for these measurement equations. The values of critical calibration parameters, such as prism and detector response degradation, are re-measured throughout the mission to correct the ground-based calibration.  相似文献   

The 2dF Galaxy Redshift Survey: correlation with the ROSAT-ESO flux-limited X-ray galaxy cluster survey     

Matt Hilton  Chris Collins  Roberto De Propris  Ivan K. Baldry  Carlton M. Baugh  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Shaun Cole  Matthew Colless  Warrick J. Couch  Gavin B. Dalton  Simon P. Driver  George Efstathiou  Richard S. Ellis  Carlos S. Frenk  Karl Glazebrook  Carole A. Jackson  Ofer Lahav  Ian Lewis  Stuart Lumsden  Steve J. Maddox  Darren Madgwick  Peder Norberg  John A. Peacock  Bruce A. Peterson  Will Sutherland  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2005,363(2):661-674

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Boltzmann Equilibrium of Endothermic Heavy Nuclear Synthesis in the Universe and a Quark Relation to the Magic Numbers     

Heinrich Hora  George H. Miley  Frederick Osman 《Astrophysics and Space Science》2005,298(1-2):247-253

As laser–plasma interactions access ever-increasing ranges of plasma temperatures and densities, it is interesting to consider whether they will some day shed light on questions concerning nuclear synthesis. One such open question is the process of endothermic nuclear synthesis for elements with A > 60, thought to have taken place at a point in time during the big bang, or currently in supernovae. We present an explanation based on a Boltzmann equilibrium condition, in combination with the change of the Fermi-statistics from the relativistic branch for hadrons from higher than nuclear densities to the lower density subrelativistic branch. The Debye length confinement of nuclei breaks down at the relativistic change, thus leading to the impossibility of nucleation of the quark-gluon state at higher than nuclear densities. Taking the increment for the proton number Z as Z′ = 10 of the measured standard abundance distribution (SAD) of the elements for a Boltzmann probability for heavy element synthesis, a sequence 3 ⁿ was found with the exponent n for the sequence of the magic numbers. The jump between the magic numbers 20 and 28 does not need then the usual spin-orbit explanation.  相似文献   

Characteristics and OSL minimum ages of relict fluvial deposits near Sossus Vlei,Tsauchab River,Namibia, and a regional climate record for the last 30 ka     

George A. Brook  Pradeep Srivastava  Eugene Marais 《第四纪科学杂志》2006,21(4):347-362

The present end‐point of the Tsauchab River is at Sossus Vlei, 30 km into the Namib Sand Sea. Interdune deposits in three depressions west and southwest of the vlei include channel and interdune lithofacies associations but no deposits typical of river end‐points or of groundwater seepage into interdune areas. The two lithofacies associations show that the Tsauchab River extended further into the sand sea in the past. It had a well‐developed channel and a higher flow than today that caused flooding of adjacent interdune areas. OSL 4‐mm aliquot minimum ages indicate that the Tsauchab River reached 2–3 km beyond its present end‐point at ca. 25 ka and ca. 9–7 ka, and that the river was more active from 0.9–0.3 ka. The eastward migration of the river end‐point since ca. 7 ka suggests a reduction in flood magnitude accompanied by the gradual invasion of the Sossus Vlei area by dunes. The regional data indicate an additional wet interval at ca. 15 ka that is so far not recorded in the Sossus area. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Foreword     

George W. Housner 《地震工程与工程振动(英文版)》2003,2(1):i-i

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Foreword     

George W. Housner 《地震工程与工程振动(英文版)》2005,4(1):i-i

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Results from the AIM-IT Meteor Tracking System     

Peter S. Gural  Peter M. Jenniskens  George Varros 《Earth, Moon, and Planets》2004,95(1-4):541-552

The recent development and data collection results of the Astrobiology Instrumentation for Meteor Imaging and Tracking (AIM-IT) system, has demonstrated an ability to point narrow field-of-view instruments at transient events such as meteors. AIM-IT uses the principle of tracking moving objects via a paired set of relay mirrors along with an integrated hardware/software solution, to acquire and track meteors in real-time. Development of the instrument has progressed from a prototype rocker-box system through more recent use of a fast response mirror system during several meteor shower campaigns. Several narrow field of view instruments have been deployed using AIM-IT including high spatial resolution video, high frame rate video, and meteor spectrographic equipment. Analysis of the imagery shows evidence for meteor fragmentation in as many as 20% of the meteors tracked thus far. The success of the AIM-IT technology in tracking meteors during their luminous flight provides a new tool in enhancing the capabilities and data volume that can be obtained with existing narrow field of view instruments.  相似文献   

The self-regulated winds of long-period variable stars     

Curtis Struck  Daniel C. Smith  Lee Anne Willson  Gary Turner  George H. Bowen 《Monthly notices of the Royal Astronomical Society》2004,353(2):559-570

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