Distribution of the organic matter in the channel-levees systems of the Congo mud-rich deep-sea fan (West Africa). Implication for deep offshore petroleum source rocks and global carbon cycle     

François Baudin  Jean-Robert Disnar  Philippe Martinez  Bernard Dennielou 《Marine and Petroleum Geology》2010

The quantity and the source of organic matter preserved in the Recent turbiditic channel-levees systems around 4000 m-depth off the Congo River were determined using bulk geochemical approaches (Rock-Eval, elemental and isotopic analyses) as well as molecular and optical analyses on selected samples. These mud-rich sediments contain high amount of organic matter (3% Corg on average), the origin of which is a mixture of terrestrial higher-plant debris and deeply oxidized phytoplanktonic material. Although the relative contribution of continental source versus marine source of the organic matter cannot be precisely quantified, the continental fraction appears significant (at least 70–80%) especially for such depths and distances from the coast. The organic matter distribution appears very homogeneous at different scales, from the single turbiditic event to the entire levee, and changes in accumulation rates have a little impact on the quantity and quality of preserved organic matter.  相似文献   

MedFlux: Investigations of particle flux in the Twilight Zone     

Cindy Lee  Robert A. Armstrong  J. Kirk Cochran  Anja Engel  Scott W. Fowler  Madeleine Goutx  Pere Masqu  Juan Carlos Miquel  Michael Peterson  Christian Tamburini  Stuart Wakeham 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(18):1363-1368

The MedFlux project was devised to determine and model relationships between organic matter and mineral ballasts of sinking particulate matter in the ocean. Specifically we investigated the ballast ratio hypothesis, tested various commonly used sampling and modeling techniques, and developed new technologies that would allow better characterization of particle biogeochemistry. Here we describe the rationale for the project, the biogeochemical provenance of the DYFAMED site, the international support structure, and highlights from the papers published here. Additional MedFlux papers can be accessed at the MedFlux web site (http://msrc.sunysb.edu/MedFlux/).  相似文献   

Observations of pulsating Ap stars in South Africa     

Peter Martinez  D. W. Kurtz 《Astrophysics and Space Science》1995,230(1-2):29-39

The rapidly oscillating Ap (roAp) stars currently represent the only main sequence stars other than the Sun which exhibit non-radial acoustic pulsations of high overtone. This makes them excellent subjects for asteroseismology, an approach which promises to yield accurate knowledge of the interior structures of stars. Of the 27 known roAp stars, 24 were discovered in Sutherland despite extensive searches conducted elsewhere. This paper reviews the discovery of the roAp phenomenon and describes the factors that contribute to the high discovery rate for these stars at Sutherland. Two long-term observational projects in progress at Sutherland are discussed,viz. the Cape roAp Star Survey and long-term monitoring of frequency variations in roAp stars.  相似文献   

Gravity waves in Jupiter's stratosphere, as measured by the Galileo ASI experiment     

Leslie A. Young  Roger V. Yelle  Alvin Seiff  Donn B. Kirk 《Icarus》2005,173(1):185-199

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Apollo 12 ropy glasses revisited   总被引：1，自引：0，他引：1  

S. J. Wentworth  D. S. McKay  D. J. Lindstrom  A. Basu  R. R. Martinez  D. D. Bogard  D. H. Garrison 《Meteoritics & planetary science》1994,29(3):323-333

Abstract— We analyzed ropy glasses from Apollo 12 soils 12032 and 12033 by a variety of techniques including SEM/EDX, electron microprobe analysis, INAA, and ³⁹Ar-⁴⁰Ar age dating. The ropy glasses have KREEP-like compositions different from those of local Apollo 12 mare soils; it is likely that the ropy glasses are of exotic origin. Mixing calculations indicate that the ropy glasses formed from a liquid enriched in KREEP and that the ropy glass liquid also contained a significant amount of mare material. The presence of solar Ar and a trace of regolith-derived glass within the ropy glasses are evidence that the ropy glasses contain a small regolith component Anorthosite and crystalline breccia (KREEP) clasts occur in some ropy glasses. We also found within these glasses clasts of felsite (fine-grained granitic fragments) very similar in texture and composition to the larger Apollo 12 felsites, which have a ³⁹Ar-⁴⁰Ar degassing age of 800 ± 15 Ma (Bogard et al, 1992). Measurements of ³⁹Ar-⁴⁰Ar in 12032 ropy glass indicate that it was degassed at the same time as the large felsite although the ropy glass was not completely degassed. The ropy glasses and felsites, therefore, probably came from the same source. Most early investigators suggested that the Apollo 12 ropy glasses were part of the ejecta deposited at the Apollo 12 site from the Copernicus impact Our new data reinforce this model. If these ropy glasses are from Copernicus, they provide new clues to the nature of the target material at the Copernicus she, a part of the Moon that has not been sampled directly.  相似文献   

Separation of gamma and hadron initiated air showers with energies between 20 and 500 TeV     

F. Arqueros  A. Karle  E. Lorenz  S. Martinez  R. Plaga  M. Rozanska 《Astroparticle Physics》1996,4(4):309-332

The discrimination between air showers initiated by γ rays and by hadrons is one of the fundamental problems in experimental cosmic-ray physics. The physics of this ‘γ/hadron separation’ is discussed in this paper. We restrict ourselves to the energy range from about 20 to 500 TeV, and take only the information contained in the lateral Čerenkov light distribution and the number of electrons at the detector level into consideration. An understanding of the differences between air showers generated by γ rays and those due to hadrons leads us to formulate suitable observables for the separation process. Angle integrating Čerenkov arrays (AICA) offer a promising new approach to ground-based γ-ray astronomy in the energy region from about 20 to 500 TeV. In order to establish this technique, an efficient suppression of the overwhelming hadronic background radiation is required. As an example for our general discussion, we present one method for γ/hadron separation in AICAs called ‘LES’. It is based on the simultaneous determination of the shower size and some characteristic parameters of the lateral distribution of the Čerenkov light. The potential inherent within this technique is demonstrated in quantitative detail for the existing ‘AIROBICC’ AICA. We also propose an objective measure of the intrinsic sensitivity of a detection scheme in ground-based γ-ray astronomy, the ‘reduced quality factor’. It is shown that AICAs may reach a sensitivity to γ-ray point sources in the high VHE range similar to that of the Čerenkov-telescope imaging technique in the low VHE region.  相似文献   

Areas of Polar Coronal Holes from 1996 Through 2010     

S. A. Hess Webber  N. Karna  W. D. Pesnell  M. S. Kirk 《Solar physics》2014,289(11):4047-4067

Polar coronal holes (PCHs) trace the magnetic variability of the Sun throughout the solar cycle. Their size and evolution have been studied as proxies for the global magnetic field. We present measurements of the PCH areas from 1996 through 2010, derived from an updated perimeter-tracing method and two synoptic-map methods. The perimeter-tracing method detects PCH boundaries along the solar limb, using full-disk images from the SOlar and Heliospheric Observatory/Extreme ultraviolet Imaging Telescope (SOHO/EIT). One synoptic-map method uses the line-of-sight magnetic field from the SOHO/Michelson Doppler Imager (MDI) to determine the unipolarity boundaries near the poles. The other method applies thresholding techniques to synoptic maps created from EUV image data from EIT. The results from all three methods suggest that the solar maxima and minima of the two hemispheres are out of phase. The maximum PCH area, averaged over the methods in each hemisphere, is approximately 6 % during both solar minima spanned by the data (between Solar Cycles 22/23 and 23/24). The northern PCH area began a declining trend in 2010, suggesting a downturn toward the maximum of Solar Cycle 24 in that hemisphere, while the southern hole remained large throughout 2010.  相似文献   

Cratering and modification of wet‐target craters: Projectile impact experiments and field observations of the Lockne marine‐target crater (Sweden)     

Jens Orm  Maurits Lindstrm  Alain Lepinette  Jesús Martinez‐Frias  Enrique Diaz‐Martinez 《Meteoritics & planetary science》2006,41(10):1605-1612

Abstract— Marine impacts are one category of crater formation in volatile targets. At target water depths exceeding the diameter of the impactor, the zones of vaporization, melting, and excavation of the standard land‐target cratering model develop partially or entirely in the water column. The part of the crater that has a potential of being preserved (seafloor crater) may to a great extent be formed by material emplacement and excavation processes that are very different from land‐target craters. These processes include a high‐energy, water‐jet‐driven excavation flow. At greater water depths, the difference in strength of the target layers causes a concentric crater to evolve. The crater consists of a wide water cavity with a shallow excavation flow along the seabed surrounding a nested, deeper crater in the basement. The modification of the crater is likewise influenced by the water through its forceful resurge to fill the cavity in the water mass and the seafloor. The resurge flow is strongly erosive and incorporates both ejecta and rip‐up material from the seabed surrounding the excavated crater. A combination of field observations and impact experiments has helped us analyze the processes affecting the zone between the basement crater and the maximum extent of the water cavity. The resurge erosion is facilitated by fragmentation of the upper parts of the solid target caused by a) spallation and b) vibrations from the shallow excavation flow and, subsequently, c) the vertical collapse of the water cavity rim wall. In addition, poorly consolidated and saturated sediments may collapse extensively, possibly aided by a violent expansion of the pore water volume when it turns into a spray during passage of the rarefaction wave. This process may also occur at impacts into water‐saturated targets without an upper layer of seawater present. Our results have implications for impacts on both Earth and Mars, and possibly anywhere in the solar system where volatiles exist/have existed in the upper part of the target.  相似文献   

Imaging Borrelly     

L.A Soderblom  D.C Boice  R.H Brown  R.L Kirk  R.M Nelson  B.R Sandel  N Thomas 《Icarus》2004,167(1):4-15

The nucleus, coma, and dust jets of short-period Comet 19P/Borrelly were imaged from the Deep Space 1 spacecraft during its close flyby in September 2001. A prominent jet dominated the near-nucleus coma and emanated roughly normal to the long axis of nucleus from a broad central cavity. We show it to have remained fixed in position for more than 34 hr, much longer than the 26-hr rotation period. This confirms earlier suggestions that it is co-aligned with the rotation axis. From a combination of fitting the nucleus light curve from approach images and the nucleus' orientation from stereo images at encounter, we conclude that the sense of rotation is right-handed around the main jet vector. The inferred rotation pole is approximately perpendicular to the long axis of the nucleus, consistent with a simple rotational state. Lacking an existing IAU comet-specific convention but applying a convention provisionally adopted for asteroids, we label this the north pole. This places the sub-solar latitude at ∼60° N at the time of the perihelion with the north pole in constant sunlight and thus receiving maximum average insolation.  相似文献   

Instruments, Detectors and the Future of Astronomy with Large Ground Based Telescopes     

Douglas A. Simons  Paola Amico  Dietrich Baade  Sam Barden  Randall Campbell  Gert Finger  Kirk Gilmore  Roland Gredel  Paul Hickson  Steve Howell  Norbert Hubin  Andreas Kaufer  Ralf Kohley  Philip MacQueen  Sergej Markelov  Mike Merrill  Satoshi Miyazaki  Hidehiko Nakaya  Darragh O'Donoghue  Tino Oliva  Andrea Richichi  Derrick Salmon  Ricardo Schmidt  Hongjun Su  Simon Tulloch  Maria Luisa García Vargas  R. Mark Wagner  Olivier Wiecha  Binxun Ye 《Experimental Astronomy》2005,19(1-3):15-44

Results of a survey of instrumentation and detector systems, either currently deployed or planned for use at telescopes larger than 3.5 m, in ground based observatories world-wide, are presented. This survey revealed a number of instrumentation design trends at optical, near, and mid-infrared wavelengths. Some of the most prominent trends include the development of vastly larger optical detector systems (> 10⁹ pixels) than anything built to date, and the frequent use of mosaics of near-infrared detectors – something that was quite rare only a decade ago in astronomy. Some future science applications for detectors are then explored, in an attempt to build a bridge between current detectors and what will be needed to support the research ambitions of astronomers in the future.  相似文献