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101.
We have carried out radio studies of the surroundings of the superluminal microquasar GRS 1915+105. Our main goal was to understand the possible relation of GRS 1915+105 with two infrared/radio sources that appear symmetrically located with respect to GRS 1915+105 and aligned with the position angle of the relativistic ejecta. We have also studied a nearby supernova remnant to test if the event that created the remnant could have been the progenitor of this hard X-ray binary. 相似文献
102.
B. John Makario Londoño A. John Jairo Sanchez E. Luis Eduardo Toro Fernando Gil Cruz Olga Patricia Bohorquez 《Bulletin of Volcanology》1998,59(8):556-561
Coda Q–1 was calculated at Nevado del Ruiz Volcano (NRV) before and after two phreatomagmatic eruptions (November 1985, September
1989) and for a period of stability (May 1987) using a functional form for coda derived from a single scattering model (Sato
1977). Substantial changes were found before and after the eruptions. The highest value of Q–1 was found during the November 1985 eruption, an intermediate value for the September 1989 eruption, and the lowest value
for May 1987. It seems that the changes in coda Q–1 at NRV have a still-unknown relationship with the volume or magnitude of the eruption. A relatively strong frequency dependence
was found for all periods. Also Q–1 clearly changed with time, suggesting that the scattering was strong for the eruption of November 1985 and decreased for
the eruption of September 1989, and that the intrinsic absorption probably increased. This suggests the possibility that crystallization
is taking place in the NRV magma. The clear change of coda Q–1 before and after the eruptions at NRV also suggests the possibility that coda Q–1 is a premonitory tool of activity at this volcano.
Received: 25 October 1996 / Accepted: 21 January 1998 相似文献
103.
A subset of 2660 shallow earthquakes (0–50 km) that occurred from 1988 to 1996 in south central Alaska between 155°W and 145°W and 59°N and 63°N was relocated using the joint hypocenter determination (JHD) method. Both P- and S-wave observations recorded by the regional seismic network were used. Events were relocated in twenty different groups based on their geographic location and depth using two velocity models. As a result of the relocation, the majority of the hypocenters shifted downward, while the epicenter locations did not change significantly. The distribution of the shallow subduction zone earthquakes indicates the existence of two seismically independent blocks, with one block occupying the northeastern part and the other occupying the central and western parts of the study area. The boundary between the blocks is marked by a 15 to 20 km wide seismicity gap to the southeast of 149.5°W and 62°N. The analysis of the fault plane solutions for shallow subduction zone earthquakes shows that an overwhelming majority of the solutions represent normal, oblique-normal or strike-slip faulting with predominant WNW-ESE orientation of T-axes. This indicates a down-dip extensional regime for the subducting slab at shallow depths. Very few earthquakes yielded fault plane solutions consistent with thrusting on a contact zone between the overriding and subducting plates. This result may be an indication that currently either the strain energy is not released at the contact zone or it is associated with aseismic motion. 相似文献
104.
Dabrio Cristino J. Zazo Cari Lario Javier Goy José Luis Sierro Francisco J. Borja Francisco González José Ángel Flores José Abel 《Geologie en Mijnbouw》1998,77(3-4):263-281
This first sedimentary interpretation of two incised-valley fills in the Gulf of Cádiz (southern Spain), which accumulated during the last fourth-order eustatic cycle in response to fluvial incision, changes of sea level, and correlative deposition, relates the filling of the estuarine basins and their barriers with four regional progradation phases, H1 to H4. The cases studied are the wave-dominated Guadalete, and the mixed, tide and wave-dominated Odiel-Tinto estuaries. The sequence boundary is a type-1 surface produced during the lowstand of the Last Glacial period ca. 18 000 14C yr BP. No fluvial lowstand deposits were found in the area. Due to rapid transgression the valley fills consist of transgressive and highstand sediments. The maximum landward advance of the estuarine barriers occurred ca. 6500–6000 14C yr BP during the maximum of the Flandrian transgression, but there is no evidence of sea level rising appreciably above the present. A large part of the estuaries was filled during H1 (ca. 6500–4400 14C yr BP) but ravinement by shifting tidal inlets destroyed most of the coeval barriers. During the H2 phase (ca. 4200–2550 14C yr BP) sedimentation was favoured by arid conditions and concentrated in the axial estuarine zones and the barriers. Between H2 and H3 prevailing winds changed from W to WSW, increasing spit growth to the east and south-east. Progradation of bay-head deltas and flood-plains during H3 (ca. 2300–800 14C yr BP) and H4 (500 yr ago to the present) further reduced the accommodation space in the largely-filled valleys, and sediment by-passed the estuaries and accumulated in the estuarine barriers as fast-growing spits. Arid conditions and increasing human activity have caused rapid coastal modifications. 相似文献
105.
A. Blanco A. Borghesi E. Epifani S. Fonti V. Orofino F. Strafella 《Astrophysics and Space Science》1998,262(1):107-113
The main constituents of the dust, produced around late-type carbon stars, are thought to be carbon and silicon carbide (SiC), although their exact nature is not yet well established. This subject has been addressed by several authors and good fits of a large number of IRAS sources (chosen among the carbon stars exhibiting the SiC feature at about 11.3 m) were obtained. In this work we use the same procedure on a limited number of objects, of the same type, taking into account the variability of such sources and the changes induced in their IR spectra. For this purpose, the chosen stars have been observed with a spectral resolution higher than that available for the IRAS data (/ 50), using the CGS3 instrument of the UKIRT telescope, both in the low ( / 160) and in the high ( / 500) resolution configuration. The results are discussed and some preliminary conclusions are drawn. 相似文献
106.
Orbit classification in arbitrary 2D and 3D potentials 总被引:1,自引:0,他引:1
Daniel D. Carpintero & Luis A. Aguilar 《Monthly notices of the Royal Astronomical Society》1998,298(1):1-21
A method of classifying generic orbits in arbitrary 2D and 3D potentials is presented. It is based on the concept of spectral dynamics introduced by Binney &38; Spergel that uses the Fourier transform of the time series of each coordinate. The method is tested using a number of potentials previously studied in the literature and is shown to distinguish correctly between regular and irregular orbits, to identify the various families of regular orbits (boxes, loops, tubes, boxlets, etc.), and to recognize the second-rank resonances that bifurcate from them. The method returns the position of the potential centre and, for 2D potentials, the orientation of the principal axes as well, should this be unknown. A further advantage of the method is that it has been encoded in a FORTRAN program that does not require user intervention, except for 'fine tuning' of search parameters that define the numerical limits of the code. The automatic character makes the program suitable for classifying large numbers of orbits. 相似文献
107.
Dr. Luis Dalla Salda 《International Journal of Earth Sciences》1981,70(3):1030-1042
Metamorphic and granitoid rocks of the El Cristo area, southern part of Tandilia Range, are considered in terms of structural, lithological and geochronological data.The abovementioned area was affected before 2000 m. y. by a first tectono-thermal event that was followed by a second episode of intense SW-NE folding. The latter accompanied or followed by a metamorphism of almandine grade and strong synkinematic to latekinematic granitization during the span 1800-1520 m. y.Succeeding episodes of metamorphism and deformation were less intense and culminated in the local development of a 900 m. y. granite, chloritization and some brittle deformation.
Zusammenfassung Tektonische, lithologische und geochronologische Daten der metamorphen und granitischen Gesteine der El Cristo Gegend im südlichen Teil des Tandilia Gebirges werden diskutiert.Vor mehr als 2000 Ma wurde dieses Gebiet erstmals von einem tektonothermalen Ereignis erfa\t, gefolgt von einer zweiten Episode starker SW-NE gerichteter Faltung. Letztere wurde begleitet oder gefolgt von einer Almandingrad Metamorphose und starker synbis spÄtkinematischer Granitisierung wÄhrend der Zeitspanne 1800 bis 1520 Ma.Darauffolgende Metamorphosen und Deformationsereignisse waren weniger intensiv und endeten um 900 Ma in Lokaler Granitintrusion, Chloritisierung und spröder Deformation.
Résumé Des roches métamorphiques et granitoÏdes de la région de Cristo font ici l'objet d'une discussion sur la base de données structurales, lithologiques et géochronologiques.La région mentionnée a été marquée d'abord, il y a plus de 2000 millions d'années, par une phénomène thermo-tectonique, suivi, dans une seconde phase, d'un plissement important dirigé SO-NE. Celui-ci a été accompagné ou suivi par un métamorphisme à almandin et par une intense granitisation syncinématique à tardicinématique au cours de la période 1800-1500 m. a.Des épisodes de métamorphisme et de déformation moins intenses s'ensuivirent, qui aboutirent au développement local, vers 900 m. a., d'une intrusion granitique, avec chloritisation et déformations cassantes.
, - , 2000 - , SW-NE. 1800 1520 . , 900 .相似文献
108.
109.
William A. Bonner Neal E. Blair Richard M. Lemmon Jose J. Flores Glenn E. Pollock 《Geochimica et cosmochimica acta》1979,43(11):1841-1846
The optically pure d- and l-enantiomers of isovaline (I), which cannot be racemized by ordinary chemical mechanisms involving α-hydrogen removal, and which has been isolated in apparently racemic form from the Murchison meteorite, have been subjected to partial radiolysis by the ionizing radiation from a 3000 Ci 60Co γ-ray source. Both in the anhydrous and hydrated solid states and as solid sodium or hydrochloride salts each enantiomer suffered significant radioracemization of the undestroyed residue during its partial radiolysis. The sodium salt of isovaline in 0.1 M aqueous solution suffered extensive radiolysis with relatively small radiation doses, but showed no detectable radioracemization. The significance of these observations with respect to the primordial enantiomeric composition of the isovaline (and other amino acids) indigenous to meteroties is discussed. 相似文献
110.
Luciano Sbriz Margarita R. Aquino Natividad M. Alberto de rodriguez Scott W. Fowler Jose L. Sericano 《Marine pollution bulletin》1998,36(12):971-979
Bivalves (Crassostrea rizhophorae, Isognomon alatus, Codakia orbicularis Linné, and Tellina fausta) and sediment samples collected from 12 locations along the Dominican Republic coastline were used to assess the degree of nearshore contamination by selected chlorinated hydrocarbons and heavy metals. Concentrations of total chlordanes, DDTs and PCBs ranged from 0.51 to 7.47 ng/g, < MDL to 30.9 ng/g and 11.3 to 82.3 ng/g, and from < MDL to 1.73 ng/g, 0.21 to 12.5 ng/g and 0.46 to 41.9 ng/g in bivalves and surface sediments, respectively. The concentration ranges of predominantly anthropogenic Cu, Pb and Zn were 3.08–866 μg/g, 0.08–1.46 μg/g and 22.9–4380 μg/g in bivalve soft parts and 1.01–111 mg/g, 0.420–134 μg/g and 1.96–277 μg/g in surface sediments, respectively. Mercury concentrations ranged from 0.290 to 7.02 μg/g and from 0.096 to 0.565 μg/g in both matrices. The relatively high Hg concentrations found in bivalves from two stations in Bahia Samana, near to a known source of past Hg contamination in the sediments, require a more in-depth survey of the area. In general the concentrations of selected chlorinated hydrocarbons and trace metals, compared with those reported for the same matrices in the Caribbean and west Atlantic coastal areas, show at present the existence of only very localized contamination problems in the Dominican Republic. 相似文献