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101.
Late Pleistocene–Holocene environments in Valle Carbajal, Tierra del Fuego, Argentina 总被引:1,自引:0,他引:1
Ana María Borromei Andrea Coronato Mirta Quattrocchio Jorge Rabassa Silvia Grill Claudio Roig 《Journal of South American Earth Sciences》2007,23(4):321-335
The authors discuss Late Pleistocene–Holocene depositional environments in one of the Fuegian Andes valleys on the basis of palynological, geomorphological, and sedimentological analyses from two sites located near the Beagle Channel. The results obtained at these localities reinforce and refine the Late Pleistocene–Holocene climatic pattern previously recorded there. A colder period, associated with the Younger Dryas stadial event, is suggested by low Nothofagus pollen frequency, and communities of grass, low scrub, and shrub heath expanded into the low/middle slopes (10,310 14C yr BP). By ca. 9500 14C yr BP, warmer and drier conditions occurred, as evidenced by the development of open-grown vegetation in the valley floors (pollen zone O-3), followed by the expansion of open Nothofagus woodland (pollen zone O-2) in the middle Holocene. The milder climate subsequently changed, as indicated by the spreading of the closed forest and mire (pollen zone O-1), to more humid and cooler conditions during the last ca. 5000 yr BP. 相似文献
102.
103.
Carlo Bernasconi 《Pure and Applied Geophysics》1956,33(1):1-8
Riassunto L’A., partendo dall’idea di minimizzare l’energia di deformazione della rete geografica ellissoidica, supposta elastica, per
adattarla a una sfera, determina una corrispondenza fra l’ellissoide di rotazione e la sfera locale in un intorno del punto
di osculazione fino a 250 km di raggio. Ne risultano semplici formule per le correzioni angolari ai limiti dell’intorno e
per la trasformazione delle coordinate.
Successivamente l’A. sottopone a un esame critico varie funzioni che, estremate, dànno luogo a buone rappresentazioni dell’intero
ellissoide sulla sfera ed introduce una nuova latitudine, utile per la costruzione di carte geografiche globulari, che risulta
media fra la latitudine geocentrica e quella ridotta.
Dr.Carlo Bernasconi, Istituto Geofisico e Geodetico dell’Università diGenova. 相似文献
Summary The Author, starting from the idea of minimizing the deformation energy of the ellipsoidic geographical network, which he supposes to be perfectly elastic in order to adapt it to a sphere, determines a correspondence between the rotation ellipsoid and the local sphere in the neighbourhood of the osculation point, to the distance of 250 km. He hereby deduces simple formulas for the angular corrections in the border of the neighbourhood and for appropriate transformation of coordinates. In the second part the A. takes into critical examination some functions, which, minimized, afford good representation of the whole ellipsoid on the sphere; he also introduces a new latitude that is revealed useful for the construction of globular geographical maps and numerically can be considered as a mean between the geocentric latitude and the reduced one.
Dr.Carlo Bernasconi, Istituto Geofisico e Geodetico dell’Università diGenova. 相似文献
104.
Dr. Carlo Bernasconi 《Pure and Applied Geophysics》1956,35(1):1-7
Riassunto L'A., partendo dal principio che un sistema di osservazioni di diversa precisione è riducibile a un sistema di osservazioni di uguale precisione, propone una nuova formula per la valutazione dell'errore medio dell'unità di peso. Tale formula non si annulla nel caso di misure che, pur essendo di peso diverso, sono uguali fra loro. — Nella seconda parte l'A. avanza l'ipotesi che un aspetto geometrico della compensazione di misure miste sia quello di trasformare una figura in un'altra, soddisfacente prefissate condizioni, con un minimo di deformazione; ritiene che tale minimo possa anche non essere dato da una combinazione lineare dei quadrati degli errori lineari e angolari.
Summary Basing himself on the principle that a system of observations of different precision may be reduced to a system of observations of the same precision, the Author proposes a new formula for a valuation of the standard error of the weight unit. Such formula is not nullified in case of measurements which, though of different weights, are equal. — In the second part the Author puts forward the hypothesis that a geometric aspect of the compensation of different kinds of measures, is of transforming a figure, wich satisfies given conditions, into another by the least deformation. He believes that such least deformation may be obtained without making a linear combination of linear and angular squared errors.相似文献
105.
We propose a new formal definition of discovery for a Solar System object. It is based on an objective and mathematically
rigorous algorithm to assess when a set of observations is enough to constitute a discovery. When this definition is satisfied,
in almost all cases the orbit is defined well enough to establish the nature of the object discovered (Main Belt vs. Near
Earth Asteroid, Trans-Neptunian vs. long period comet). The frequency of occurrence of exceptions is estimated by a set of
numerical experiments.
The availability of a non-subjective definition of discovery allows some rules to be adopted for the assignment of discovery
credit with a minimum risk of dispute. Such rules should be fair, encourage good practice by the observers and acknowledge
the contribution of the orbit computers providing the identifications and the orbits, as well as the one of all the contributing
observers. 相似文献
106.
107.
Armando Manzali Andrea De Luca Patrizia A. Caraveo 《Astrophysics and Space Science》2007,308(1-4):601-605
We report on our analysis of two XMM-Newton observations of the Vela pulsar performed in December 2000 (total exposure time:
96.5 ks). We succeeded in resolving the pulsar spectrum from the surrounding bright nebular emission taking advantage both
of the accurate calibration of the EPIC point spread function and of the Chandra/HRC surface brightness map of the nebula.
This made it possible to assess to pulsar spectral shape disentangling its thermal and non-thermal components. Exploiting
the photon harvest, we have also been able to perform a phase-resolved study of the pulsar emission.
相似文献
108.
David J. Ampleford Andrea Ciardi Sergey V. Lebedev Simon N. Bland Simon C. Bott Jeremy P. Chittenden Gareth N. Hall Adam Frank Eric Blackman 《Astrophysics and Space Science》2007,307(1-3):29-34
We present experimental data on the steady state deflection of a highly supersonic jet by a side-wind in the laboratory. The
use of a long interaction region enables internal shocks to fully cross the jet, leading to the development of significantly
more structure in the jet than in previous work with a similar setup (Lebedev et al., 2004). The ability to control the length
of the interaction region in the laboratory allows the switch between a regime representing a clumpy jet or wind and a regime
similar to a slowly varying mass loss rate. The results indicate that multiple internal oblique shocks develop in the jet
and the possible formation of a second working surface as the jet attempts to tunnel through the ambient medium. 相似文献
109.
All the confirmed Soft Gamma-ray Repeaters have been observed with the EPIC instrument on the XMM–Newton satellite. We review
the results obtained in these observations, providing the most accurate spectra on the persistent X-ray emission in the 1–10
keV range for these objects, and discuss them in the context of the magnetar interpretation.
相似文献
110.
Deep‐water coral habitats are scattered throughout slope depths (360–800 m) off the Southeastern United States (SEUS, Cape Lookout, North Carolina, to Cape Canaveral, Florida), contributing substantial structure and diversity to bottom habitats. In some areas (e.g. off North Carolina) deep corals form nearly monotypic (Lophelia pertusa) high profile mounds, and in other areas (e.g. off Florida) many species may colonize hard substrata. Deep coral and hard substrata ecosystems off the SEUS support a unique fish assemblage. Using the Johnson‐Sea‐Link submersible (in 2000–2005, 65 dives), and a remotely operated vehicle (in 2003, five dives), fishes were surveyed in nine deep reef study areas along the SEUS slope. Forty‐two benthic reef fish species occurred in deep reef habitats in these study areas. Species richness was greatest on the two coral banks off Cape Lookout, North Carolina (n = 23 and 27 species) and lowest on the two sites off Cape Canaveral, Florida (n = 7 and 8 species). Fish assemblages exhibited significantly (ANOSIM, Global R = 0.69, P = 0.001) different patterns among sites. Stations sampled off North Carolina (three study areas) formed a distinct group that differed from all dives conducted to the south. Although several species defined the fish assemblages at the North Carolina sites, Laemonema barbatulum, Laemonema melanurum, and Helicolenus dactylopterus generally had the most influence on the definition of the North Carolina group. Fish assemblages at three sites within the central survey area on the Blake Plateau were also similar to each other, and were dominated by Nezumia sclerorhynchus and L. melanurum. Synaphobranchus spp. and Neaumia sclerorhynchus differentiated the two southern sites off Cape Canaveral, Florida, from the other station groups. Combinations of depth and habitat type had the most influence on these station groups; however, explicit mechanisms contributing to the organization of these assemblages remain unclear. 相似文献