Erratum to “Mars low-latitude neutron distribution: Possible remnant near-surface water ice and a mechanism for its recent emplacement” [Icarus 175 (2005) 58-67]     

Bruce M. Jakosky  Michael T. Mellon  William C. Feldman  Robert M. Haberle 《Icarus》2005,178(1):291-293

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Detection of satellite remnants in the Galactic Halo with Gaia– I. The effect of the Galactic background, observational errors and sampling     

Anthony G. A. Brown  Hector M. Velázquez  Luis A. Aguilar 《Monthly notices of the Royal Astronomical Society》2005,359(4):1287-1305

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A 2dF survey of the Small Magellanic Cloud     

Christopher J. Evans  Ian D. Howarth  Michael J. Irwin  Adam W. Burnley  Timothy J. Harries 《Monthly notices of the Royal Astronomical Society》2004,353(2):601-623

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Spatial patterns of suspended sediment yields in a humid tropical watershed in Costa Rica     

Jagdish Krishnaswamy  Daniel D. Richter  Patrick N. Halpin  Michael S. Hofmockel 《水文研究》2001,15(12):2237-2257

An Erratum has been published for this article in Hydrological Processes 16(5) 2002, 1130–1131. Humid tropical regions are often characterized by extreme variability of fluvial processes. The Rio Terraba drains the largest river basin, covering 4767 km², in Costa Rica. Mean annual rainfall is 3139±419_sd mm and mean annual discharge is 2168±492_sd mm (1971–88). Loss of forest cover, high rainfall erosivity and geomorphologic instability all have led to considerable degradation of soil and water resources at local to basin scales. Parametric and non‐parametric statistical methods were used to estimate sediment yields. In the Terraba basin, sediment yields per unit area increase from the headwaters to the basin mouth, and the trend is generally robust towards choice of methods (parametric and LOESS) used. This is in contrast to a general view that deposition typically exceeds sediment delivery with increase in basin size. The specific sediment yield increases from 112±11·4_sd t km^?2 year^?1 (at 317·9 km² on a major headwater tributary) to 404±141·7_sd t km^?2 year^?1 (at 4766·7 km²) at the basin mouth (1971–92). The analyses of relationships between sediment yields and basin parameters for the Terraba sub‐basins and for a total of 29 basins all over Costa Rica indicate a strong land use effect related to intensive agriculture besides hydro‐climatology. The best explanation for the observed pattern in the Terraba basin is a combined spatial pattern of land use and rainfall erosivity. These were integrated in a soil erosion index that is related to the observed patterns of sediment yield. Estimated sediment delivery ratios increase with basin area. Intensive agriculture in lower‐lying alluvial fans exposed to highly erosive rainfall contributes a large part of the sediment load. The higher elevation regions, although steep in slope, largely remain under forest, pasture, or tree‐crops. High rainfall erosivity (>7400 MJ mm ha^?1 h^?1 year ^?1) is associated with land uses that provide inadequate soil protection. It is also associated with steep, unstable slopes near the basin mouth. Improvements in land use and soil management in the lower‐lying regions exposed to highly erosive rainfall are recommended, and are especially important to basins in which sediment delivery ratio increases downstream with increasing basin area. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Tumbling asteroids   总被引：1，自引：0，他引：1  

P. Pravec  A.W. Harris  P. Kušnirák  C.W. Hergenrother  M.D. Hicks  Yu.N. Krugly  M.C. Nolan  M. Kaasalainen  P. Brown  J.V. Lambert  S. Foglia 《Icarus》2005,173(1):108-131

We present both a review of earlier data and new results on non-principal axis rotators (tumblers) among asteroids. Among new tumblers found, the best data we have are for 2002 TD₆₀, 2000 WL₁₀₇, and (54789) 2001 MZ₇—each of them shows a lightcurve with two frequencies (full terms with linear combinations of the two frequencies are present in the lightcurve). For 2002 TD₆₀, we have constructed a physical model of the NPA rotation. Other recent objects which have been found to be likely tumblers based on their lightcurves that do not fit with a single periodicity are 2002 NY₄₀, (16067) 1999 RH₂₇, and (5645) 1990 SP. We have done a statistical analysis of the present sample of the population of NPA rotators. It appears that most asteroids larger than ∼0.4 km with estimated damping timescales (Harris, 1994, Icarus 107, 209) of 4.5 byr and longer are NPA rotators. The statistic of two short-period tumblers (D=0.04 and 0.4 km) with non-zero tensile strength suggests that for them the quantity μQ/T, where μ is the mechanical rigidity, Q is the elastic dissipation factor, and T is a spin excitation age (i.e., a time elapsed since the last significant spin excitation event), is greater by two to four orders of magnitude than the larger, likely rubble-pile tumblers. Among observational conditions and selection effects affecting detections of NPA rotations, there is a bias against detection of low-amplitude (small elongation) tumblers.  相似文献   

The Coma-Leo I distance ratio and the Hubble constant     

Michael D. Gregg 《New Astronomy》1997,1(4):363-371

The diameter-velocity dispersion relation in B, V, and K for three early-type galaxies in the Leo I (M96) group is derived from published photometry and kinematic data. The relations in all three colors have slopes which agree well with those for the Coma cluster. The RMS scatter of the Leo I galaxies in each color is extremely small, consistent with the group's compactness. These relations yield estimates of the Coma-Leo I distance ratio of 9.01 ± 0.51, 8.77 ± 0.43, and 8.82 ± 0.31, respectively, with a weighted mean of 8.84 ± 0.23. The general agreement among the three colors indicates that the early-type galaxies in Leo I and Coma have similar stellar populations.

The Coma-Leo I distance ratio coupled with estimates of the absolute distance to the Leo I group allows the Hubble constant to be determined, free of the uncertainties which arise when working with the Virgo cluster. Several high quality distance estimates are available from a variety of techniques: Cepheids in M96 (Tanvir, N.R., et al., 1995, Natur, 377, 27) and M95 (Graham, J.A., et al., 1997, ApJ, 477, 535), surface brightness fluctuations (Tonry, J.L., et al., 1997, ApJ, 475, 399), planetary nebulae luminosity functions (Ciardullo, R., et al., 1993, ApJ, 419, 479), and the luminosity of the red giant branch tip (Sakai, S., Freedman, W.L., & Madore, B.F., 1996, in: Formation of the Galactic Halo, Inside and Out, eds. H. Morrison & A. Sarajedini, PASP Conf. Series Vol. 92). Adopting a cosmic recession velocity of the Coma cluster in the microwave background frame of 7200 ± 300 km s⁻¹, these distance estimates lead to values of the Hubble constant ranging from 70 to 81 km s⁻¹ Mpc⁻¹, with an unweighted mean of 75 ± 6 km s⁻¹ Mpc⁻¹.  相似文献   

The impact of overfishing and El Niño on the condition factor and reproductive success of Peruvian hake, Merluccius gayi peruanus   总被引：1，自引：1，他引：0  

Michael Balln  Claudia Wosnitza-Mendo  Renato Guevara-Carrasco  Arnaud Bertrand 《Progress in Oceanography》2008,79(2-4):300

In this study we examine physiological responses of Peruvian hake (Merluccius gayi peruanus) to changes in their population structure and physical environment during the period 1971–2004. In particular, we assess the relative investment of energy in growth and/or reproduction of small (20–35 cm) and large (35–50 cm) hake. We calculated the (i) condition (Fulton’s K), (ii) gonad and (iii) gut fullness indices for 42,761 female hakes sampled from commercial landings; these indices indicate fish somatic, reproductive and feeding condition, respectively. Using Generalized Additive Models we then examined potential relationships between these indices and sea surface temperature anomalies and date. Drastic energy exhaustion and a decrease in female hake fecundity were observed during El Niño events. The long-term trend showed a general increase in condition factor and a decrease in gonad index for large hake between 1971 and 2004. Small hake exhibited a different trend with an increase in reproductive activity, which was accompanied by an earlier maturation. We hypothesise that the observed low investment of energy in reproduction by large female hake might be related to the lack of large males, due to a sex-selective fishery and the impact of El Niño. We suggest that fishing diminished hake reproductive capacity, modified the sex ratio in favour of females and increased population vulnerability to environmental stress, in particular to the El Niño. The impact of multidecadal variability and predators like the squid, Dosidicus gigas, remain unresolved until longer time series become available.  相似文献   

Intercluster Filaments of Galaxies Programme: pilot study survey and results     

Kevin A. Pimbblet  Michael J. Drinkwater 《Monthly notices of the Royal Astronomical Society》2004,347(1):137-143

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Substructure analysis of selected low-richness 2dFGRS clusters of galaxies     

William S. Burgett  Michael M. Vick  David S. Davis  Matthew Colless  Roberto De Propris  Ivan Baldry  Carlton Baugh  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Shaun Cole  Chris Collins  Warrick Couch  Nicholas Cross  Gavin Dalton  Simon Driver  George Efstathiou  Richard Ellis  Carlos S. Frenk  Karl Glazebrook  Edward Hawkins  Carole Jackson  Ofer Lahav  Ian Lewis  Stuart Lumsden  Steve Maddox  Darren Madgwick  Peder Norberg  John A. Peacock  Will Percival  Bruce Peterson  Will Sutherland  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,352(2):605-654

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Three-body encounters in the Galactic Centre: the origin of the hypervelocity star SDSS J090745.0+024507     

Alessia Gualandris  Simon Portegies Zwart  Michael S. Sipior 《Monthly notices of the Royal Astronomical Society》2005,363(1):223-228

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