Photoelectric photometry of asteroids 9 Metis, 18 Melpomene, 60 Echo, 116 Sirona, 230 Athamantis, 694 Ekard,and 1984 KD     

Kenneth W. Zeigler  William B. Florence 《Icarus》1985,62(3):512-517

Photoelectric observations of seven asteroids were made from Gila Observatory between October 14, 1983, and June 21, 1984. The following synodic rotational periods and amplitudes are reported: 9 Metis, P = 5.04 hr, ΔM = 0.05; 18 Melpomene, P = 11.570 hr, ΔM = 0.22; 60 Echo, P = 25.208 hr, ΔM = 0.22; 116 Sirona, P = 12.028 hr, ΔM = 0.42; 230 Athamantis, P = 23.99 hr, ΔM > 0.20; 694 Ekard, P = 5.925 hr, ΔM = 0.50; 1984 KD, P = 1.97 hr, ΔM = 0.26. The rotational periods reported for asteroid 60 Echo, 116 Sirona, 694 Ekard, and 1984 KD represent completely new results. The synodic rotational period reported for asteroid 1984 KD is tentative and is based largely upon the observations of a single night. The reported synodic periods of the remaining six asteroids are based upon a minimum of 3 nights of photometric observations.  相似文献   

Some aspects of coronal streamer dynamics     

Wim J. Weber 《Solar physics》1977,53(1):59-77

Observations of coronal streamers suggest that these configurations are stationary in terms of the convective time scale, but not with respect to the diffusive processes. In this paper, the diffusive time scale is estimated and the thickness of a stationary streamer where convective and diffusive processes are balanced turns out to be very small.Instead of balancing the terms in the magnetic equation to obtain a zero time derivative, we suggest that the diffusive part is negligible and therefore, the convective term must be zero in the largest part of the streamer. This can be obtained by introducing flux transport through the streamer.We show that the arising convective model is to be understood from evolutionary arguments; the upward flux transport leads to a time scale for the life of a streamer, related to the evolution of the underlying magnetic field. Slight differences occur between stationary models and the present model; these differences are shown not to be in conflict with radio observations.  相似文献   

Aliphatic and aromatic hydrocarbons in sediments of Santos and Cananéia, SP, Brazil.   总被引：2，自引：0，他引：2  

F N Nishigima  R R Weber  M C Bícego 《Marine pollution bulletin》2001,42(11):1064-1072

Sediment samples from Santos and Cananéia, S?o Paulo Brazil were analysed by GC-FID and GC-MS for aliphatic and aromatic hydrocarbons in order to gather information on the degree of contamination by oil and other biogenic contributions. Concentrations of total n-alkanes in Santos varied from 1.05 to 4.29 microg g(-1) and aromatic hydrocarbons from 0.08 to 42.39 microg g(-1). In Cananéia total n-alkanes varied from 4.37 to 157.90 microg g(-1). However, aromatic hydrocarbons were not detected. In Cananéia n-alkanes of terrestrial plants with high molecular weight predominate (n-C25, n-C27, n-C29, n-C31 and n-C33). In Santos, a more uniform distribution of the n-alkanes and aromatic hydrocarbons was found at all the sediment stations. The hydrocarbon data from stations close to the Saboó Wharf, at Alemoa and in the COSIPA Channel revealed alarming levels of acenaphthylene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene and chrysene.  相似文献   

Les « Porphyroı̈des » de Bretagne méridionale : une unité de HP–BT dans la chaı̂ne hercynienneEvidence for HP–LT Hercynian metamorphism within the ‘Porphyroı̈des’ of South Brittany (France)     

Florence Le Hébel  Olivier Vidal  Jean-Robert Kienast  Denis Gapais 《Comptes Rendus Geoscience》2002,334(3):205-211

The so-called ‘Porphyro??des’ Unit of South Brittany is located below units marked by an early HP–LT event (blueschists from the Île de Groix) and above units marked by Upper Carboniferous HT metamorphism. P–T estimates in the Porphyro??des (at Belle-Île-en-Mer), using the phengite–chlorite thermobarometer, indicate pressures around 8 kbar and temperatures of 350–400 °C. These new estimates suggest that the early tectonic history of the ‘Porphyro??des’ should be linked to that of the overlying Blueschists, and imply a much larger areal extension of the HP–LT domain in this part of the Hercynian Belt. To cite this article: F. Le Hébel et al., C. R. Geoscience 334 (2002) 205–211.  相似文献   

Evidence of a major environmental change recorded in a macrotidal bay (Marennes-Oléron Bay, France) by correlation between VHR seismic profiles and cores     

Isabelle Billeaud  Eric Chaumillon  Olivier Weber 《Geo-Marine Letters》2005,25(1):1-10

New, very high-resolution (25 cm) seismic profiles have revealed the internal architecture of the infilling of a macrotidal bay, the Marennes-Oléron Bay, France. Within this geometry, a major seismic unconformity has been correlated with core data. This correlation provides evidence that the seismic unconformity corresponds to a sharp grain-size decrease. Both seismic and core data indicate that this change of grain size can be interpreted as a record of a recent (around 1,000 years b.p.) decrease in hydrodynamical energy with time and/or a larger supply of fine-grained material. This recent environmental change can be related to natural infilling of the Marennes Oléron Bay, and to tidal prism decrease, increasing human activities (e.g. land reclamation, deforestation, agricultural land use) and climate fluctuations during the late Holocene, such as the transition between the cold period of the Dark Ages (1,550–1,050 years b.p.) and the Medieval warm period (1,050–550 years b.p.).  相似文献   

A few months-old storm-generated turbidite deposited in the Capbreton Canyon (Bay of Biscay, SW France)   总被引：1，自引：1，他引：1  

T. Mulder  O. Weber  P. Anschutz  F. Jorissen  J.-M. Jouanneau 《Geo-Marine Letters》2001,21(3):149-156

A gravity core taken in the canyon of Capbreton shows a succession of sedimentary facies which can be interpreted as three superimposed Bouma sequences. The turbiditic sequences are covered by an oxidised layer which contains live benthic foraminiferal faunas indicating a reprisal of hemipelagic deposition. Activities of ²³⁴Th and ²¹⁰Pb suggest that the most recent turbidite was deposited between early December 1999 and mid-January 2000. During this period, the most probable natural event able to trigger a turbidity current was the violent storm which affected the French Atlantic coast on 27 December 1999. The turbidity current could have been caused by a sediment failure due to an excess in pore pressure generated by the storm waves, an increase of the littoral drift, or the dissipation of the along-coast water bulge through the canyon. This sub-recent turbidite shows that the canyon experiences modern gravity processes, despite the lack of a direct connection with a major sediment source.  相似文献   

Combining consecutive short arcs into long arcs for precise and efficient GPS Orbit Determination   总被引：1，自引：1，他引：0  

G. Beutler  E. Brockmann  U. Hugentobler  L. Mervart  M. Rothacher  R. Weber 《Journal of Geodesy》1996,70(5):287-299

The final products of theCODE Analysis Center (Center for Orbit Determination in Europe) of theInternational GPS Service for Geodynamics (IGS) stem fromoverlapping 3-day-arcs. Until 31 December, 1994 these long arcs were computedfrom scratch, i.e. by processing three days of observations of about 40 stations (by mid 1995 about 60 stations were used) of the IGS Global Network in our parameter estimation program GPSEST. Becauseone-day-arcs have to be produced first (for the purpose of error detection etc.) the actual procedure was rather time-consuming. In the present article we develop the mathematical tools necessary to form long arcs based on the normal equation systems of consecutive short arcs (one-day-solutions in the case of CODE). The procedure in its simplest version is as follows:

• Each short arc is described bysix initial conditions and a number of dynamical orbit parameters (e.g. radiation pressure parameters). The resulting long arc in turn shall be based onn consecutive short arcs and described bysix initial conditions and again the same number of dynamical parameters as in the short arcs..
• By asking position and velocity to be continuous at the boundaries of the short arcs we obtain a long arc which is actually defined by one set of initial conditions andn sets of dynamical parameters (ifn short arcs are combined)..
• By asking the dynamical parameters to be identical in consecutive short arcs, the resulting long arc is characterized by exactly the same number of orbit parameters as each of the short arcs.
• This procedure isnot yet optimized becauseformally all n sets of orbit parameters have to be set up and solved for in the long arc solution (although they are not independent). In order to allow for an optimized solution we derive all necessary relations to eliminate the unnecessary parameters in the combination. Each long arc is characterized by the actual number of independent orbit parameters. The resulting procedure isvery efficient.

From the point of view of the result the new procedure iscompletely equivalent to an actual re-evaluation of all observations pertaining to the long arc. It is much more efficient and flexible, however because it allows us to construct 2-day-arcs, 3-day-arcs, etc. based on the previously stored daily normal equation systems without requiring much additional CPU time. The theory is developed in the first four sections. Technical aspects are dealt with in appendices A and B. The actual implementation into the Bernese GPS Software system and test results are given in section 5.  相似文献   

Calcmylonites and solution transfer in a Devonian reef at Warstein,Germany   总被引：1，自引：1，他引：0  

Jacob de Roo  Johannes Duyster  Klaus Weber 《International Journal of Earth Sciences》1992,81(2):333-346

Massive limestone complexes of Late Palaeozoic age are scattered across the allochthonous foreland of the Hercynides in Germany. One of these complexes is situated at Warstein. Stratigraphic facies studies have represented the Warstein complex as a reef in a coastal shelf. Our study emphasizes that at least part of the reef consists of a pile of calcmylonites.The calcmylonites have a strong foliation (S_m) and lineation (L_m) and a structural asymmetry indicating non-coaxial deformation. X-ray textures and calcite microstructures show that the mylonitization involved intracrystalline deformation and dynamic recrystallization. These processes competed with solution transfer, as the mylonites are corroded at S_m-parallel stylolites and contain carbonate veins. Cathodoluminescopy shows that some veins are parallel to S_m and have been recrystallized, whereas others are normal to S_m and retain a fibrous crackseal microstructure. The latter type created limestones showing a pair of preferred grain boundary orientations; one normal to S_m, one in S_m. This orthogonal boundary fabric is distinct from crystalplastic fabrics: the latter show only one preferred grain boundary orientation (in S_m).

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Zusammenfassung Massenkalkkomplexe spätpaläozoischen Alters liegen verstreut über das allochthone Vorland des Variszischen Gebirges in Deutschland. Einer dieser Komplexe liegt bei Warstein. Stratigraphische Faziesstudien haben den Warsteiner Komplex als ein Riff in einem küstennahen Schelf dargestellt. Die vorliegende Arbeit betont, daß wenigstens ein Teil des Riffes aus einer Stapelung von Kalkmyloniten besteht.Die Kalkmylonite haben eine starke Foliation (S_m) und Lineation (L_m), und eine strukturelle Asymmetrie die auf nicht-koaxiale Verformung hinweist. Röntgentexturen und Calcitmikrostrukturen zeigen, daß die Mylonitisierung intrakristalline Verformung und dynamische Rekristallisation beinhaltet. Diese Prozesse müssen mit Lösungstransport konkurriert haben, da die Mylonite an S_m-parallelen Styloliten korrodiert sind und Karbonatgänge erhalten. Kathodolumineskopie zeigt, daß einige Gänge (parallel zu S_m) rekristallisiert sind, während andere (senkrecht zu S_m) eine faserige crack-seal Mikro-Struktur enthalten. Der letzte Typ ist verbunden mit Konformgefügen. Diese unterscheiden sich von kristallplastischen Kornformgefügen, da sie eine zweite bevorzugte Korngrenzorientierung aufweisen, die senkrecht zur ersten (in S_m) einfällt.

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Résumé Les complexes de calcaires massifs de l'Âge paléozoîque supérieure sont repandus sur l'avantpays allochthone des Hercynides en Allemagne. Un de ces complexes est situé à Warstein. Les Études de faciès stratigraphiques ont répresenté le complexe à Warstein comme un Récif littoral. Notre étude montre que au moins partie de ce «Récif» consiste en un empilement des calcmylonites.Les calcmylonites ont une foliation (S_m) et linéation (L_m) fort, et une asymmetrie structurale indiquant de la déformation non-coaxiale. Les textures röntgenographiques et les microstructures calcitiques montrent que la mylonitization était incluse de déformation intracristalline et récristallisation dynamique. Ces processus auront été en compétition avec dissolution-cristallization («solution transfer»), car les mylonites sont corrodées aux stylolites parallel à S_m et contient des veines carbonatiques. La cathodoluminescopie montre que quelques veines (parallel à S_m) sont récristallisées, pendant que les autres (perpendiculaire à S_m) ont retenu une microstructure fibreuse («crack-seal»). Le dernier type est lié avec des fabriques de forme des grains. Ils se sont distingués des fabriques de plasticité cristalline par la présence d'une deuxième orientation préférentielle des bordures des grains, perpendiculaire à la première (dans S_m).

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. Warstein'a. , . , , , »« . (S_m) (L_m), , . , - , . , .. , S_m, . , , S_m, , , S_m, = »crack-seal«. : , S_m.

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New insights into the history and origin of the southern Maya block,SE México: U–Pb–SHRIMP zircon geochronology from metamorphic rocks of the Chiapas massif     

Bodo Weber  Alexander Iriondo  Wayne R. Premo  Lutz Hecht  Peter Schaaf 《International Journal of Earth Sciences》2007,96(2):253-269

The histories of the pre-Mesozoic landmasses in southern México and their connections with Laurentia, Gondwana, and among themselves are crucial for the understanding of the Late Paleozoic assembly of Pangea. The Permian igneous and metamorphic rocks from the Chiapas massif as part of the southern Maya block, México, were dated by U–Pb zircon geochronology employing the SHRIMP (sensitive high resolution ion microprobe) facility at Stanford University. The Chiapas massif is composed of deformed granitoids and orthogneisses with inliers of metasedimentary rocks. SHRIMP data from an anatectic orthogneiss demonstrate that the Chiapas massif was part of a Permian (∼ 272 Ma) active continental margin established on the Pacific margin of Gondwana after the Ouachita orogeny. Latest Permian (252–254 Ma) medium- to high-grade metamorphism and deformation affected the entire Chiapas massif, resulting in anatexis and intrusion of syntectonic granitoids. This unique orogenic event is interpreted as the result of compression due to flat subduction and accretionary tectonics. SHRIMP data of zircon cores from a metapelite from the NE Chiapas massif yielded a single Grenvillian source for sediments. The majority of the zircon cores from a para-amphibolite from the SE part of the massif yielded either 1.0–1.2 or 1.4–1.5 Ga sources, indicating provenance from South American Sunsás and Rondonian-San Ignacio provinces.  相似文献   

The origin of rutile-ilmenite aggregates (“nigrine”) in alluvial-fluvial placers of the Hagendorf pegmatite province, NE Bavaria, Germany     

H. G. Dill  F. Melcher  M. Füßl  B. Weber 《Mineralogy and Petrology》2007,89(3-4):133-158

Summary Titanium placer deposits occur in alluvial-fluvial drainage systems which dissect Moldanubian gneisses intruded by Late Variscan pegmatites (Hagendorf province) in southern Germany. Based upon their texture (zonation, exsolution lamellae, intergrowth), microchemical data (Nb, Cr, Ta, V, Fe, W, Sn) and mineral inclusions, two major grain types of intergrown rutile and ilmenite have been established. Grains of type A are always zoned and consist of rutile cores enveloped by ilmenite containing small inclusions of wolframite. A core-rim transition zone is characterized by complex relations of rutile and ilmenite, with rutile lamellae being rich in Nb, V and Fe. Types B1 and B2 aggregates consist of ilmenite with lamellae of niobian rutile and/or ilmenorutile, and additionally have inclusions of ferrocolumbite, pyrochlore, betafite, sphalerite, pyrrhotite and Fe oxides. Such grain types featuring an intimate intergrowth of rutile and ilmenite were called nigrine. Type-C grains are quite similar in their morphological appearance but consist of W-enriched rutile devoid of mineral inclusions and reaction products. Pseudorutile and leucoxene replacing minerals of the nigrine aggregates are presumably caused by supergene alteration under fluctuating redox conditions. Phosphate and aluminum remobilized by supergene processes led to the formation of hydrous Ti-rich phases containing Al, P and Fe. High Nb and W concentrations in nigrine aggregates and in rutile type C may be taken as a marker for highly differentiated granites or pegmatites. This has implications for both, heavy-mineral-based provenance analysis and stream sediment exploration.  相似文献