STUDY ON THE DYNAMIC PROCESS OF RILL EROSION OF LOESS SLOPE SURFACE   总被引：3，自引：0，他引：3  

Zhanbin LI . Kexin LU  Wenfeng DING The State key Laboratory of Loess Plateau  Dry Land Farming    Yangling  Shaanxi  P.R.China. Xi''''an University of Technology    Xi''''an  Shaanxi  P.R.China. 《国际泥沙研究》2001,16(2)

1 mTRODUCTIONAs a woridwide concem, excessive water erosion induces land degradation, causes losses of plantnutrients, and Ieads to off site enVironmental problems such as sedimentahon streams and reservoirs. mllerosion, which results from concentraed flow in a lindted and confined space, plays imPortant roles inthe erosion systCm on uPland areas. Data listed in Table l show its contribution and imPoftance to thetOtal slope soil losses. In the last decades, stodies on the physical mecha…  相似文献   

Managing side effects of cultural tourism development: The case of Zhouzhuang   总被引：3，自引：0，他引：3  

XU Hong-gang  TAG Wei 《中国地理科学(英文版)》2001,11(4):356-365

IPROBLEMS DEFINITIONthis will have increased to．6 billion（WEI,1999）．In比r＊Sdr＊＊＊＊＊＊S,山u＊。dd＊＊引ly厅＊＊J砒e如卜小1．IIncreasing Demand for Tourism lions of dollars yearly．Acco巾lug to WEI et al．（199）,Chinese tourismhunsm Is a relatively new social activity that has Industry has been developingveryfast．hurlsm Incomerecently eme侣ed as a global phenomenon．The World will keepon growingforthe…  相似文献   

Offshore oil platforms and fouling communities in the southern Arabian Gulf (Abu Dhabi)   总被引：1，自引：0，他引：1  

Stachowitsch M  Kikinger R  Herler J  Zolda P  Geutebrück E 《Marine pollution bulletin》2002,44(9):853-860

This study examined the fouling organisms on the legs of offshore oil platforms at two sites in the southern Arabian Gulf (offshore Abu Dhabi, United Arab Emirates). 100% of the metal structures was colonized by encrusting organisms. Both the number of individuals and the total biomass tended to decrease with depth. The total weight of dead shells always exceeded that of living organisms. Sessile filter feeders dominated the biomass, whereas small mobile forms had the largest number of individuals. The biomass at the deeper platform (22 m) was dominated by bivalves, barnacles and bryozoans, while polychaetes and amphipods had the greatest number of individuals. Biomass values here ranged from 1 g/0.1 m2 at 20 m to 147 g/0.1 m2 at 5 m; the corresponding individual numbers were 266 (20 m) and 11,814 indiv./0.1 m2 (5 m). The results at the shallower platform (11 m) differed in several respects: barnacles clearly dominated over bivalves, and sponges exceeded byrozoans, while total individual numbers fell due to a decline in polychaete dominance. Biomass values here ranged from 84 g/0.1 m2 at 10 m to 153 g/0.1 m2 at 0 m; the corresponding individual numbers were 695 (10 m) and 3,125 indiv./0.1 m2 (0 m). The potential role of such fouling communities on artificial structures in the Gulf is discussed.  相似文献   

Improvements in the epifauna of the Crouch Estuary (United Kingdom) following a decline in TBT concentrations     

Rees HL  Waldock R  Matthiessen P  Pendle MA 《Marine pollution bulletin》2001,42(2):137-144

In the United Kingdom, the use of TBT-based anti-fouling paints on small vessels was banned in 1987, and a biological study of the Crouch Estuary, a yachting centre on the south-eastern English coastline, was initiated in order to monitor any associated changes. The macrobenthic infauna and epifauna were sampled between 1987 and 1992, and again in 1997. Epifaunal sampling in 1997 showed that an earlier increase in sedentary taxa had been sustained, and also that a large population of the native oyster Ostrea edulis had become established upstream. Multivariate analysis revealed continuance of a trend towards directional change in community composition at inner estuary stations, where TBT concentrations were historically much higher. These observations, along with evidence of established populations of a range of ascidian species in the inner estuary after an initial marked increase in densities, provide circumstantial evidence of an underlying improvement in environmental conditions following the TBT ban in 1987.  相似文献   

Mercury in fish from Patos and Mirim Lagoons, Southern Brazil     

Niencheski LF  Windom HL  Baraj B  Wells D  Smith R 《Marine pollution bulletin》2001,42(12):1403-1406

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X-Raying the Star Formation History of the Universe     

Cavaliere A  Giacconi R  Menci N 《The Astrophysical journal》2000,536(2):L77-L80

We discuss a new method for inferring the stellar mass of a distant galaxy of known redshift based on the combination of a near-IR luminosity and multiband optical photometry. The typical uncertainty for field galaxies with I<22 in the redshift range 0相似文献   

Measurement of a Peak in the Cosmic Microwave Background Power Spectrum from the North American Test Flight of Boomerang     

Mauskopf PD  Ade PA  de Bernardis P  Bock JJ  Borrill J  Boscaleri A  Crill BP  DeGasperis G  De Troia G  Farese P  Ferreira PG  Ganga K  Giacometti M  Hanany S  Hristov VV  Iacoangeli A  Jaffe AH  Lange AE  Lee AT  Masi S  Melchiorri A  Melchiorri F  Miglio L  Montroy T  Netterfield CB  Pascale E  Piacentini F  Richards PL  Romeo G  Ruhl JE  Scannapieco E  Scaramuzzi F  Stompor R  Vittorio N 《The Astrophysical journal》2000,536(2):L59-L62

We describe a measurement of the angular power spectrum of anisotropies in the cosmic microwave background (CMB) at scales of 0&fdg;3 to 5 degrees from the North American test flight of the Boomerang experiment. Boomerang is a balloon-borne telescope with a bolometric receiver designed to map CMB anisotropies on a long-duration balloon flight. During a 6 hr test flight of a prototype system in 1997, we mapped more than 200 deg(2) at high Galactic latitudes in two bands centered at 90 and 150 GHz with a resolution of 26&arcmin; and 16&farcm;5 FWHM, respectively. Analysis of the maps gives a power spectrum with a peak at angular scales of 1 degrees with an amplitude 70 μK(CMB).  相似文献   

Reconciling Spectroscopic Electron Temperature Measurements in the Solar Corona with In Situ Charge State Observations     

Esser R  Edgar RJ 《The Astrophysical journal》2000,534(1):L71-L74

We present new results on the recently discovered 69 ms X-ray pulsar AXS J161730-505505, the sixth youngest example of a rotation-powered pulsar. We have undertaken a comprehensive X-ray-observing campaign of AXS J161730-505505 with the ASCA, BeppoSAX, and RXTE observatories and follow its long-term spin-down history between 1989 and 1999 using these observations and archival Ginga and ASCA data sets. The spin-down is not simply described by a linear function as originally thought, but instead we find evidence of a giant glitch (DeltaP&solm0;P greater, similar10-6) between 1993 August and 1997 September, perhaps the largest yet observed from a young pulsar. The glitch is well described by steps in P and P&d2; accompanied by a persistent P&d3; similar to those seen in the Vela pulsar. The pulse profile of AXS J161730-505505 presents a single asymmetric peak that is maintained over all observation epochs. The energy spectrum is also steady over time, characterized by a highly absorbed power law with a photon index Gamma=1.4+/-0.2, consistent with that found for other young rotation powered pulsars.  相似文献   

The Discovery of a Second Field Methane Brown Dwarf from Sloan Digital Sky Survey Commissioning Data     

Tsvetanov ZI  Golimowski DA  Zheng W  Geballe TR  Leggett SK  Ford HC  Davidsen AF  Uomoto A  Fan X  Knapp GR  Strauss MA  Brinkmann J  Lamb DQ  Newberg HJ  Rechenmacher R  Schneider DP  York DG  Lupton RH  Pier JR  Annis J  Csabai I  Hindsley RB  Ivesic Z  Munn JA  Thakar AR  Waddell P 《The Astrophysical journal》2000,531(1):L61-L65

We report the discovery of a second field methane brown dwarf from the commissioning data of the Sloan Digital Sky Survey (SDSS). The object, SDSS J134646.45-003150.4 (hereafter SDSS 1346-00), was selected because of its very red color and stellar appearance. Its spectrum between 0.8 and 2.5 μm is dominated by strong absorption bands of H2O and CH4 and closely mimics those of Gliese 229B and SDSS 162414.37+002915.6 (hereafter SDSS 1624+00), two other known methane brown dwarfs. SDSS 1346-00 is approximately 1.5 mag fainter than Gliese 229B, suggesting that it lies about 11 pc from the Sun. The ratio of flux at 2.1 μm to that at 1.27 μm is larger for SDSS 1346-00 than for Gliese 229B and SDSS 1624+00, which suggests that SDSS 1346-00 has a slightly higher effective temperature than the others. Based on a search area of 130 deg2 and a detection limit of z*=19.8, we estimate a space density of 0.05 pc-3 for methane brown dwarfs with Teff approximately 1000 K in the 40 pc3 volume of our search. This estimate is based on small-sample statistics and should be treated with appropriate caution.  相似文献   

6Li from Solar Flares     

Ramaty R  Tatischeff V  Thibaud JP  Kozlovsky B  Mandzhavidze N 《The Astrophysical journal》2000,534(2):L207-L210

By introducing a hitherto ignored 6Li producing process, due to accelerated 3He reactions with 4He, we show that accelerated particle interactions in solar flares produce much more 6Li than 7Li. By normalizing our calculations to gamma-ray data, we demonstrate that the 6Li produced in solar flares, combined with photospheric 7Li, can account for the recently determined solar wind lithium isotopic ratio, obtained from measurements in lunar soil, provided that the bulk of the flare-produced lithium is evacuated by the solar wind. Further research in this area could provide unique information on a variety of problems, including solar atmospheric transport and mixing, solar convection and the lithium depletion issue, and solar wind and solar particle acceleration.  相似文献