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11.
We have produced high-resolution images of the nuclear region of M82 with SpectroCam-10, a mid-infrared instrument at the Palomar 5 m telescope. These images were taken at 11.7 m and 9.8 m with a 1m filter bandpass at the diffraction limit of 0.6 arcsec, making them the highest resolution maps yet available of M82. In addition, we have obtained high-resolution (/=2000) maps of the velocity field of the nuclear disk of M82 in the 12.81 m line emission of [NeII]. In these proceedings we present the 11.7 m image, which will appear together with the 9.8 m map and the [Ne II] spectra in a subsequent paper, now in preparation. This image shows very clearly a bridge structure joining the eastern and western clusters. 相似文献
12.
J. E. Van Cleve T. L. Hayward J. W. Miles G. E. Gull J. Schoenwald J. R. Houck 《Astrophysics and Space Science》1994,212(1-2):231-238
T Tauri stars are young stars usually surrounded by dusty disks similar to the one from which we believe our own Solar System formed. Most T Tauri stars exhibit a broad emission or absorption band between 7.5 and 13.5µm which is attributed to silicate grains in the circumstellar environment. We imaged three spatially resolved T Tauri binaries through a set of broadband filters which include the spectral region occupied by the silicate band. Two of these objects (T Tauri and Haro 6–10) are infrared companion systems in which one component is optically much fainter but contributes strongly in the infrared. Both infrared companions exhibit a deep silicate absorption which is not present in their primaries, indicating that they suffer very strong local extinction which may be due to an edge-on circumstellar disk or to a dense shell. We also took low resolution spectra of the silicate feature of two unresolved T Tauris to look for narrow features in the silicate band which would indicate the presence of specific minerals such as olivine. We observed GK Tau, for which Cohen and Witteborn (1985) reported a narrow emission feature at 9.7µm, but do not find evidence for this feature, and conclude that it is either time-dependent or an artifact of absorption by telluric ozone.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A. 相似文献
13.
Shubha N. Pandit April Hayward Jan de Leeuw Jurek Kolasa 《Journal of Geographical Systems》2010,12(4):389-407
Species distribution models are used extensively in predicting the distribution of vegetation across a landscape. Accuracy
of the species distribution maps produced by these models deserves attention, since low accuracy maps may lead to erroneous
conservation decisions. While plot size is known to influence measures of species richness, its effect on our ability to predict
species distribution ranges has not been tested. Our aim is to test whether the accuracy of the distribution maps produced
depend on the size of the plot (quadrat) used to collect biological data in the field. In this study, the presences of four
plant species were recorded in five sizes of circular plots, with radii ranging from 8 to 100 m. Logistic regression-based
models were used to predict the distributions of the four plant species based on empirical evidence of their relationship
with eight environmental predictors: distance to river, slope, aspect, altitude, and four principle component axes derived
using reflectance values from Aster images. We found that plot size affected the probability of recording the four species,
with reductions in plot size generally increasing the frequency of recorded absences. Plot size also significantly affected
the likelihood of correctly predicting the distribution of species whenever plot size was below the minimum size required
to consistently record species’ presence. Furthermore, the optimal plot size for fitting species distribution models varied
among species. Finally, plot size had little impact on overall accuracy, but a strong, positive impact on Kappa accuracy (which
provides a stronger measure of model accuracy by accounting for the effects of chance agreements between predictions and observations).
Our results suggest that optimal plot size must be considered explicitly in the creation of species distribution models if
they are to be successfully adopted into conservation efforts. 相似文献
14.
15.
Britt R. Scharringhausen Philip D. Nicholson Thomas L. Hayward Mitchell Troy 《Icarus》2003,162(2):385-390
We report near-infrared observations of Prometheus and Janus taken on 9 and 13 November 2000 (UT) with the Palomar Adaptive Optics System on the 5-m Hale telescope at Palomar Observatory. Dione, Rhea, and Tethys were used as guide “stars” for the adaptive optics system, and, though they were outside the isoplanatic patch of the region of interest, they allowed significant correction of the atmospheric turbulence.Prometheus, which is usually impossible to observe from the ground due to scattered light from the A ring, was imaged at superior conjunction with Saturn. At the time of the observations, the rings of Saturn were blocked by the southern limb of the planet while the moon passed just 0.35″ below the planet’s south pole. A K filter, in a methane absorption band, was used to suppress light from the disk of the planet, and template subtraction removed much of the scattered light from the A ring. Prometheus was found to be 21.9 ± 0.1° of mean longitude behind the position predicted by Voyager-era ephemerides, consistent with the orbital lag discovered during the 1995 ring-plane crossing. 相似文献
16.
The dynamics of an electron beam, under the effects of Coulomb collisions and classical Ohmic dissipation of the return current, is analysed for a background plasma with a temperature which is time dependent due to the heating effect of beam dissipation offset by thermal conductive cooling. It is shown that the plasma is heated toward a steady state, in time scales short compared to typical flare beam switch on times, and that in this steady state only two regimes of beam dynamics arise.For moderate values of the ratio of beam flux to plasma density (F
0/n), beam dynamics is dominated by direct Coulomb collisions as in the usual thick target treatment. With increase of F
0/n, before return current (classical) Ohmic losses can exceed collisions, the return current becomes unstable. In this latter regime beam dynamics is presumably dominated by wave generation and anomalous Ohmic dissipation of the return current, but no detailed treatment is attempted here. 相似文献
17.
Discontinuous tephra layers were discovered at Burney Spring Mountain, northern California. Stratigraphic relationships suggest that they are two distinct tephras. Binary plots and standard similarity coefficients of electron probe microanalysis data have been supplemented with principal component analysis to correlate the two tephra layers to known regional tephras. Using principal component analysis, we are furthermore able to bound our uncertainty in the correlation of the two tephra layers. After removal of outliers, within the 95% prediction interval, we can say that one tephra layer is likely the Rockland tephra, aged 565–610 ka, and the second layer is likely from Mt. Mazama, the Trego Hot Springs tephra, aged ~ 29 ka. In the case of the Rockland tephra, the new findings suggest that dispersal to the north was highly restricted. For Trego Hot Springs ash, the new findings extend the distribution to the southwest, with a rapid thinning in that direction. Coupled with considerations of regular tephra dispersal patterns, the results suggest that the primary dispersal direction for both tephras was to the south, and that occurrences in other directions are unlikely or otherwise anomalous. 相似文献
18.
19.
M. A. Hayward P. R. Blake P. R. Messenger A. Taube 《Australian Journal of Earth Sciences》2013,60(4):487-492
The presence of granitoid clasts in Devonian sequences of the Mt Morgan area has been considered indicative of a Late Devonian age, with the clasts derived from the Middle Devonian (377 Ma) Mt Morgan Trondhjemite. However, a sequence of limestone and volcanolithic arenites and breccias containing Middle Devonian corals and conodonts, overlies a granitoid‐bearing conglomerate in Station Creek. This sequence, previously mapped as Dee Volcanics, is now assigned to the Raspberry Creek Formation of the Capella Creek Group. Petrographic and geochemical similarities between the granitoid clasts and phases of the Mt Morgan Trondhjemite indicate formation in similar tectonic environments by similar magmatic processes. These clasts were derived from either an earlier phase of Mt Morgan Trondhjemite magmatism, or from a discrete earlier magmatic episode of similar type and inferred tectonic setting to the Mt Morgan intrusion. 相似文献
20.
Angus I. Best William Powrie Toby Hayward Max Barton 《Marine Georesources & Geotechnology》2013,31(4):315-331
Abstract Recent marine forensic investigations have largely unravelled the sequence of events concerning the sinking of the R.M.S. Titanic and its descent through nearly 3800 m of water to the seafloor on the morning of 15 April 1912. In particular, the velocity and attitude of the Titanic's bow section (at present lying upright, reasonably intact, and embedded by ~12 m at the prow) as it hit the bottom are of general interest to marine accident investigators. During the 1998 Titanic Science Expedition, a single sediment sample was retrieved from the seafloor (depth 20–30 cm) near the wreck by the deep water submersible, Nautile. Published geological studies suggest the seafloor in this area has remained largely undisturbed since 1912. Geotechnical analysis of the sediment sample reveals that the impact was probably a substantially undrained event and that the characteristic undrained shear strength of the sediment is ~25kPa within 10–16 m below the seafloor. A simple analytical model was used to calculate the embedment of a cuboid with dimensions and mass of the water-filled bow as a function of impact velocity, impact angle, and the undrained shear strength of the sediment. The results indicate the impossibility of a steep angle of impact and fast velocity. The most likely scenario is an impact velocity of 5–10 m/s at a fairly shallow angle (<40°), which corroborates the results of hydrodynamic investigations. 相似文献