Determination of the Electrochemical Properties of a Soluble Aqueous FeS Species Present in Sulfidic Solutions     

Stephen M. Theberge  George W. Luther III 《Aquatic Geochemistry》1997,3(3):191-211

Field and laboratory data are presented that show a soluble FeS species(FeS_aq) exists in sulfidic seawater solutions, and is observedwhen the IAP exceeds the K_sp of amorphous FeS. TheFeS_aq yields a discrete signal (double peak) using square-wavevoltammetry and two one-electron waves in sampled DC polarographyexperiments at the Hg electrode. The aqueous FeS species reacts irreversiblyat the electrode as a single FeS subunit and not as a polymeric entity. Thepeak potential of FeS_aq occurs at -1.1 V whereas the peakpotential of Fe occurs at-1.45 V; the positive shift for Fe²⁺ reduction inFeS_aq indicates a change in geometry for Fe²⁺from octahedral to tetrahedral. The kinetics of electron transfer at theelectrode are determined to be similar for both Fe²⁺ andFeS_aq. Molecular orbital energy diagrams, further indicatethat Fe(II) does change from octahedral to tetrahedral geometry in solution.First, Fe(II) exists as octahedralFe in solution whichundergoes a substitution reaction of bisulfide for water. The resultingcomplex, Fe(H₂O)₅(HS)⁺, thentransforms to a tetrahedral complex on further addition of sulfide. Thisgeometry change is consistent with the formation of amorphous FeS thatconverts to mackinawite which has tetrahedral Fe(II). The process is entropydriven because of the water loss that occurs. The overall sequence can berepresented as: Soluble FeS species are important asreactants in the formation of iron-sulfide minerals including pyrite.  相似文献   

Can the Red Rectangle Molecular Emission Bands Be Assigned to C?     

Robert J. Glinski  Joseph A. Nuth  III 《Astrophysics and Space Science》1997,249(1):143-149

We review the current information on the unique group of visibleemission bands known as the Red Rectangle bands (RRBs). A laboratoryspectrum exactly matching these bands is not yet available; however, thereis sufficient reason to hypothesize phosphorescence from C₃ asthe source. The points in favor of the C₃/RRB hypothesis canbe summarized as follows: (1) The RRBs are found in the spatial locationwhere carbonaceous grains are being impinged upon by a bipolar outflow. (2)C₃ is known to accompany circumstellar carbon grains and mayconstitute a magic fragment in the UV photofragmentation ofC_n clusters. (3) Our recent observation of the spin-forbiddenCO Cameron emission bands in this object suggests that charged particleimpact excites triplet states. (4) The energy of the lowest triplet state ofC₃ is known to be very close to that of the RRBs. (5) The RRBsdisplay a vibrational spacing that is quantitatively consistent withC₃, including a rare negative anharmonicity.  相似文献   

The work of the diode array: He 10 830 observations of spicules and subflares     

David M. Rust  Charles A. Bridges III 《Solar physics》1975,43(1):129-145

At a spatial resolution of 1″ and with spectral passbands of 0.25–0.47 Å, the chromospheric fine structure was studied with an array of 512 silicon photodiodes. The high quantum efficiency of the diodes in the near infrared allowed low noise spectroheliograms to be constructed from observations in the lines of H i, Ca ii, and He i. Magnetograms of the underlying photosphere were obtained simultaneously. Tachograms in the He 10830 Å line revealed 1″ points and elongated features that are interpreted as spicules seen against the disk. Active regions and filaments at 10830 are compared with Hα and Ca ii (8542 Å) features. Filament contrast increases with the proximity of bright plage. Twelve subflares were studied and in eight cases, 3–5″ kernels of He I emission appeared over small, growing pores or over 5″ patches of magnetic field emerging through the photosphere. All the subflares showed 10830 emission, contrary to established belief that the 10830 line goes into emission only in the largest flares. All the subflares included at least one emission kernel over regions where the photospheric magnetic field, as seen with a resolution of 1–2″, broke down into a mosaic of both polarities with 3–5″ diam. elements.  相似文献   

Numerical model of the Moon's rotation     

R. J. Cappallo  R. W. King  C. C. Counselman III  I. I. Shapiro 《Earth, Moon, and Planets》1981,24(3):281-289

We have integrated numercially the differential equtions for the Moon's rotation with respect to an inertial coordinate system, and the variational equations for (i) the six initial conditions of the rotation; (ii) the moment-of-inertia ratios and ; and (iii) the coefficients of the third-degree gravitational harmonics. When these integrations are used in conjunction with our current lunar-orbit and Earth-rotation models, and all of the relevant initial conditions and parameters are adjusted to fit five years of McDonald Observatory lunar laser ranging observations, the root-mean-square (rms) of the postfit range residuals is 28 cm. When we adjust the lunar-rotation initial conditions separately to fit the physical libration angles given by the numerical model of Williams (1975), we find an rms orientation difference over a six-year interval of 0.03 arcsecond, after removal of a constant bias. A similar comparison of our model with the semi-analytical model of Eckhardt (1981) yields an rms orientation difference of 0.2 arcsecond.  相似文献   

Metamorphic assemblages and the direction of flow metamorphic fluids in four instances of serpentinization     

Dr. I. Barnes  John B. Rapp  James R. O'Neil  Richard A. Sheppard  Arthur J. Gude III 《Contributions to Mineralogy and Petrology》1973,38(1):80-80

  相似文献   

European advanced marine electronic instrumentation : A US perspective     

Porter Hoagland  III  Hauke L. Kite-Powell 《Marine Policy》1991,15(6)

This article presents a US perspective on the influence of government policies on the nature and development of advanced marine electronic instrumentation (MEI) technologies in Europe. US firms traditionally have enjoyed a strong international competitive advantage in the MEI field, but European institutions are undergoing rapid changes that may affect the competitive position of firms in advanced technology industries. These include the consolidation of firms in specific markets and the increased emphasis on centralized, collaborative ‘technology transfer’ research efforts across sectors and across national borders. We expect broadly defined marine markets to grow in Europe. The best policy for US firms may well be one of cautious optimism and close attention to the potential for business relationships with established and emerging European firms.  相似文献   

Geochemical constraints on the distribution of gas hydrates in the Gulf of Mexico     

C. K. Paull  W. Ussler III  T. Lorenson  W. Winters  J. Dougherty 《Geo-Marine Letters》2005,25(5):273-280

Gas hydrates are common within near-seafloor sediments immediately surrounding fluid and gas venting sites on the continental slope of the northern Gulf of Mexico. However, the distribution of gas hydrates within sediments away from the vents is poorly documented, yet critical for gas hydrate assessments. Porewater chloride and sulfate concentrations, hydrocarbon gas compositions, and geothermal gradients obtained during a porewater geochemical survey of the northern Gulf of Mexico suggest that the lack of bottom simulating reflectors in gas-rich areas of the gulf may be the consequence of elevated porewater salinity, geothermal gradients, and microbial gas compositions in sediments away from fault conduits.  相似文献   

Gemini GMOS/IFU spectroscopy of NGC 1569 – I. Mapping the properties of a young star cluster and its environment     

M. S. Westmoquette  K. M. Exter †  L. J. Smith  J. S. Gallagher III 《Monthly notices of the Royal Astronomical Society》2007,381(3):894-912

  相似文献   

Climate-induced boreal forest change: Predictions versus current observations   总被引：4，自引：0，他引：4  

Amber J. Soja  Nadezda M. Tchebakova  Nancy H.F. French  Michael D. Flannigan  Herman H. Shugart  Brian J. Stocks  Anatoly I. Sukhinin  E.I. Parfenova  F. Stuart Chapin III  Paul W. Stackhouse  Jr. 《Global and Planetary Change》2007,56(3-4):274

For about three decades, there have been many predictions of the potential ecological response in boreal regions to the currently warmer conditions. In essence, a widespread, naturally occurring experiment has been conducted over time. In this paper, we describe previously modeled predictions of ecological change in boreal Alaska, Canada and Russia, and then we investigate potential evidence of current climate-induced change. For instance, ecological models have suggested that warming will induce the northern and upslope migration of the treeline and an alteration in the current mosaic structure of boreal forests. We present evidence of the migration of keystone ecosystems in the upland and lowland treeline of mountainous regions across southern Siberia. Ecological models have also predicted a moisture-stress-related dieback in white spruce trees in Alaska, and current investigations show that as temperatures increase, white spruce tree growth is declining. Additionally, it was suggested that increases in infestation and wildfire disturbance would be catalysts that precipitate the alteration of the current mosaic forest composition. In Siberia, 7 of the last 9 yr have resulted in extreme fire seasons, and extreme fire years have also been more frequent in both Alaska and Canada. In addition, Alaska has experienced extreme and geographically expansive multi-year outbreaks of the spruce beetle, which had been previously limited by the cold, moist environment. We suggest that there is substantial evidence throughout the circumboreal region to conclude that the biosphere within the boreal terrestrial environment has already responded to the transient effects of climate change. Additionally, temperature increases and warming-induced change are progressing faster than had been predicted in some regions, suggesting a potential non-linear rapid response to changes in climate, as opposed to the predicted slow linear response to climate change.  相似文献   

High-resolution atmospheric observations by the Mars Odyssey Thermal Emission Imaging System     

Ai Inada  Mark I. Richardson  Timothy H. McConnochie  Melissa J. Strausberg  Huiqun Wang  James F. Bell III 《Icarus》2007,192(2):378-395

High-resolution observations of atmospheric phenomena by the Mars Odyssey Thermal Emission Imaging System (THEMIS) during its first mapping year are presented. An atmospheric campaign was implemented on the basis of previous spacecraft imaging. This campaign, however, proved of limited success. This appears to be due to the late local time of the Odyssey orbit (the locations of activity at 4–6 p.m. appear to be different from those at 2 p.m.). Ironically, images targeting the surface were more useful for study of the atmosphere than those images specifically targeting atmospheric features. While many previously recognized features were found, novel THEMIS observations included persistent clouds in the southern polar layered deposits, dust or condensate plumes on the northern polar layered deposits, dust plumes as constituent parts of local dust storms, and mesospheric clouds. The former two features tend to be aligned parallel and normal to polar troughs, respectively, suggesting a wind system directed normal to troughs and radially outward from the center of the polar deposits. This is consistent with katabatic drainage of air off the polar deposits, analogous to flow off Antarctica. The observation of dust lifting plumes at unprecedented resolution associated with local dust storms not only demonstrates the importance of mean wind stresses (as opposed to dust devils) in initiation of dust storms, but is also seen to be morphologically identical to dust lifting in terrestrial dust storms. As Odyssey moves to earlier local times, we suggest that the atmospheric campaign from the first mapping year be repeated.  相似文献