2005年中国天坑考察报告

2005年朱学稳教授组织实施了"中国天坑考察项目",并取得了圆满成功.本文是此次考察的总结报告,内容包括重庆和广西喀斯特区天坑(大型塌陷漏斗)的实地考察,以及在桂林中国地质科学院岩溶地质研究所为正式通过对天坑定义举行的研讨会.     

Sapphires from Sri Lanka

A rural industry of small‐scale mining, for sapphires and a host of other gemstones, is alive and thriving at Ratnapura in Sri Lanka. The minerals are extracted from alluvial gravels and colluvium, and most are then cut and polished locally for use in jewellery.     

The rotational and physical properties of the Centaur (32532) 2001 PT13

We present observations of the Centaur (32532) 2001 PT₁₃ taken between September 2000 and December 2000. A multi-wavelength lightcurve was assembled from V-, R- and J-band photometry measurements. Analysis of the lightcurve indicates that there are two peaks of slightly different brightness, a rotation period of 0.34741±0.00005 day, and a maximum photometric range of 0.18 mag. We obtained VRJHK colors (V-R=0.50±0.01, V-J=1.69±0.02, V-H=2.19±0.04, and V-K=2.30±0.04) that are consistent with the grey KBO/Centaur population. The V-R color shows no variation as a function of rotational phase; however, we cannot exclude the possibility that rotational variations are present in the R-J color. Assuming a 4% albedo, we estimate that 2001 PT₁₃ has an effective diameter of 90 km and a minimum axial ratio a/b of 1.18. We find no evidence of a coma and place an upper limit of 15 g s⁻¹ on the dust production rate.     

Klondike Gold

In 1896, the world's greatest gold rush descended on the Klondike, in northern Canada. The hardships endured on the journey there and then in hand-mining the frozen ground are the stuff of legends. But the 'mother lode' was never found, and only recently have the origins of the gold been recognized. After the madness and the extravagance of the initial rush, mining methods evolved, and there are miners still working the Klondike today.     

THE PROBLEM OF LONG-TERM STORAGE IN RESERVOIRS

Abstract

The geometry of a meandering stream depends strongly on the relative stream size (Q ^2/5 / g ^1/5)/D, on the valley slope, Sv, and on the charge, Q _s/Q, where Q and Q _s are the fluid and sediment discharges respectively, g is acceleration due to gravity and D is the mean sediment size. The geometry depends less strongly on the relative settling size of sediment, D/(v ^2/3 / g ^1/3), where v is the kinematic viscosity. For constant values of Q, S _v and D, the effect of increase of charge reduces the meander length, M _L, and the mean channel surface width, B, whereas meander width, M _B, bend radius, R _M, and mean channel depth, H, increase, For a constant value of (Q ^2/5 / g^1/5)/D the values of M _L, M _B, R _M and B increase with the increase of valley slope but the value of H tends to decrease.     

Photo‐feature: World of Geology

World of Geology is a book that was born from the back pages of Geology Today: a celebration of the richness of the diversity of geological sites worldwide, and a fitting tribute to the impact of a magazine that is marking its thirty‐fifth year in 2019. This photo‐feature revisits some of the spectacular images that have faetured on its back pages over the years     

St Francis: the world's worst dam site

Lying just north of Los Angeles, the total collapse of the St Francis Dam in 1928 has been described as America's worst civil engineering disaster of the twentieth century. Although poorly remembered among today's residents of Los Angeles, the event is better known to engineering geologists. The dam's failure was largely due to the geology of its site, which was inappropriate to the point of disastrous, in more ways than one.     

Photometric analysis of the nucleus of Comet 81P/Wild 2 from Stardust images

The disk-resolved flyby images of the nucleus of Comet 81P/Wild 2 collected by Stardust are used to perform a detailed study of the photometric properties of this cometary nucleus. A disk-integrated phase function from phase angle 11° to about 100° is measured and modeled. A phase slope of 0.0513 ± 0.0002 mag/deg is found, with a V-band absolute magnitude of 16.29 ± 0.02. Hapke’s photometric model yields a single-scattering albedo of 0.034, an asymmetry factor of phase function −0.53, a geometric albedo 0.059, and a V-band absolute magnitude of 16.03 ± 0.07. Disk-resolved photometric modeling from both the Hapke model and the Minnaert model results in 11% model RMS, indicating small photometric variations. The roughness parameter is modeled to be 27 ± 5° from limb-darkening profile. The modeled single-scattering albedo and asymmetry factor of the phase function are 0.038 ± 0.004 and −0.52 ± 0.04, respectively, consistent with those from disk-integrated phase function. The bulk photometric properties of the nucleus of Wild 2 are comparable with those of other cometary nuclei. The photometric variations on the surface of the nucleus of Wild 2 are at a level of or smaller than 15%, much smaller than those on the nucleus of Comet 19P/Borrelly and comparable or smaller than those on the nucleus of Comet 9P/Tempel 1. The similar photometric parameters of the nuclei of Wild 2, Tempel 1, and the non-source areas of fan jets on Borrelly may reflect the typical photometric properties of the weakly active surfaces on cometary nuclei.