Landslide-induced wave in a small volcanic lake: Kasu Tephra Cone,Papua New Guinea     

T.?P.?WagnerEmail author  C.?O.?McKee  J.?Kuduon  R.?Kombua 《International Journal of Earth Sciences》2003,92(3):405-406

The south crater wall of a Quaternary tephra cone in the Highlands of Papua New Guinea collapsed on 20 April 1999 and sent a 150,000-m ³ landslide into its lake. Displacing 5–10% of the lake's volume, the landslide induced a 15-m-high wave which flattened vegetation throughout the crater interior, and broke over a low saddle in the crater's east rim where it destroyed two houses and injured 11 people, killing one.  相似文献   

Physical Properties of Dust in the Martian Atmosphere: Analysis of Contradictions and Possible Ways of Their Resolution     

Dlugach  Zh. M.  Korablev  O. I.  Morozhenko  A. V.  Moroz  V. I.  Petrova  E. V.  Rodin  A. V. 《Solar System Research》2003,37(1):1-19

Atmospheric aerosols play an important role in forming the Martian climate. However, the basic physical properties of the Martian aerosols are still poorly known; there are many contradictions in their estimates. We present an analytical overview of the published results and potentialities of various methods. We consider mineral dust. Zonally averaged data obtained from mapping IR instruments (TES and IRTM) give the optical thickness of mineral aerosols ₉ = 0.05–0.1 in the 9-m band for quite atmospheric conditions. There is a problem of comparing these estimates with those obtained in the visible spectral range. We suggest that the commonly used ratio _vis/₉ >2 depends on the interpretation and it may actually be smaller. The ratio _vis/₉ 1 is in better agreement with the IRIS data (materials like montmorillonite). If we assume that _vis/₉ = 1 and take into account the nonspherical particle shape, then the interpretation of ground-based integrated polarimetric observations ( < 0.04) can be reconciled with IR measurements from the orbit. However, for thin layers, the sensitivity of both methods to the optical thickness is poorly understood: on the one hand, polarimetry depends on the cloud cover and, on the other hand, the interpretation of IR measurements requires that the atmospheric temperature profile and the surface temperature and emissivity be precisely known. For quite atmospheric conditions, the local optical-thickness estimates obtained by the Bouguer–Lambert–Beer method and from the sky brightness measured from Viking 1 and 2 and Mars Pathfinder landers are much larger: = 0.3–0.6. Estimates of the contrasts in images from theVikingorbiters yield the same values. Thus, there is still a factor of 3 to 10 difference between different groups of optical-thickness estimates for the quiet atmosphere. This difference is probably explained by the contribution of condensation clouds and/or by local/time variations.  相似文献   

Eliminating Virtual Impactors with the Very Large Telescope: An ESO Program with the FORS2 Camera     

A.?BoattiniEmail author  G.?D’Abramo  H.?Scholl  O.?R.?Hainaut  R.?West  G.?Hahn  R.?Michelsen  G.?Forti  P.?Pravec  G.?B.?Valsecchi 《Earth, Moon, and Planets》2003,93(4):239-248

We have used the ESO Very Large Telescope (VLT) to perform as trometric observations of Near Earth Asteroids (NEAs) having remote collision possibilities with the Earth. The observations were made for those objects which became too faint to be observed elsewhere. Using the 4 hours allocated in the semester April–September 2003, 5 faint NEAs were observed. As a result, no NEA that could impact the Earth was lost.  相似文献   

Subcellular distribution of heavy metals in livers and kidneys of Stenella coeruleoalba and Tursiops truncatus from the Mediterranean Sea     

Storelli MM  Marcotrigiano GO 《Marine pollution bulletin》2002,44(1):74-79

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Transition from Gaseous Compounds to Aerosols in Titan's Atmosphere     

Sébastien LebonnoisE.L.O. Bakes  Christopher P. McKay 《Icarus》2002,159(2):505-517

We investigate the chemical transition of simple molecules like C₂H₂ and HCN into aerosol particles in the context of Titan's atmosphere. Experiments that synthesize analogs (tholins) for these aerosols can help illuminate and constrain these polymerization mechanisms. Using information available from these experiments, we suggest chemical pathways that can link simple molecules to macromolecules, which will be the precursors to aerosol particles: polymers of acetylene and cyanoacetylene, polycyclic aromatics, polymers of HCN and other nitriles, and polyynes. Although our goal here is not to build a detailed kinetic model for this transition, we propose parameterizations to estimate the production rates of these macromolecules, their C/N and C/H ratios, and the loss of parent molecules (C₂H₂, HCN, HC₃N and other nitriles, and C₆H₆) from the gas phase to the haze. We use a one-dimensional photochemical model of Titan's atmosphere to estimate the formation rate of precursor macromolecules. We find a production zone slightly lower than 200 km altitude with a total production rate of 4×10⁻¹⁴ g cm⁻² s⁻¹ and a C/N?4. These results are compared with experimental data, and to microphysical model requirements. The Cassini/Huygens mission will bring a detailed picture of the haze distribution and properties, which will be a great challenge for our understanding of these chemical processes.  相似文献   

A catalog of cosmic gamma-ray bursts detected by the PHEBUS instrument on the Granat observatory: October 1994–December 1996     

A. Yu. Tkachenko  O. V. Terekhov  R. A. Sunyaev  A. V. Kuznetsov  C. Barat  J. -P. Dezalay  G. Vedrenne 《Astronomy Letters》2002,28(6):353-365

We present the final part of the catalog of cosmic gamma-ray bursts (GRBs) observed in the PHEBUS experiment on the Granat orbiting astrophysical observatory. The first three parts of the catalog were published by Terekhov et al. (1994, 1995a) and Tkachenko et al. (1998). The fourth part contains information on 32 events recorded from October 1994 until December 1996. We give burst light curves in the energy range 100 keV to 1.6 MeV, integrated energy spectra, and information on the fluence and energy flux at the luminosity peak for energies above 100 keV. Over the entire period of its operation, the PHEBUS instrument detected 206 cosmic GRBs. The mean ?V/V_max? was 0.336±0.007. The mean hardness corresponding to the ratio of count numbers in the energy ranges 400–1000 and 100–400 keV is 0.428±0.018 for events with a duration shorter than 2 s and 0.231±0.004 for events with a duration longer than 2 s.  相似文献   

Total and methylmercury in a Brazilian estuary,Rio de Janeiro     

Kehrig HA  Costa M  Moreira I  Malm O 《Marine pollution bulletin》2002,44(10):1018-1023

Guanabara Bay, in Rio de Janeiro state, is impacted by organic matter, oil and heavy metals. The present study evaluated the total mercury (THg) and methylmercury (MeHg) concentrations and the MeHg to THg ratio (%MeHg) in water samples from different points of the bay and in 245 organisms of three different trophic levels sampled between 1990 and 2000. Dissolved mercury concentration in estuarine water samples ranged from 0.72 to 5.23 ngl(-1). THg and MeHg in mussel, ranging from 11.6 to 53.5 microg THg kg(-1) wet wt. and 4.5-21.0 microg MeHg kg(-1) wet wt., varied according to sampling point and water quality. Planktivorous fish and mussel presented similar MeHg concentrations, meanwhile THg in planktivorous fish were lower than in mussel. Carnivorous fish showed higher THg and MeHg concentrations (199.5 +/- 119.3, 194.7 +/- 112.7 microg kg(-1) wet wt. respectively) than organisms from other feeding habits and lower trophic levels. There was a significant difference in the %MeHg among trophic levels: mussel presented lower MeHg percentage (33%) than planktivorous fish (54%) and carnivorous fish (98%).  相似文献   

The sensitivity of the Ca II lines to the possible stratification of calcium abundance     

Grigoryeva  S.A.  Ozhogina  O.A.  Teplitskaya  R.B. 《Solar physics》2000,195(2):269-279

Chemical composition anomalies of the corona and solar wind (FIP effect) have their origins in the chromosphere. We study the influence of the possible stratification of abundances in the chromosphere on the shape of corresponding strong Fraunhofer line profiles. A rough estimate is made of this influence for some variants of the variation in elemental abundance a _el(m) (m being the column mass). Calculations are made for the K and 8542Å Caii lines in two semi-empirical models of the chromosphere above sunspot umbra. In practice it is difficult to realize a direct search of the FIP effect in the chromosphere for lack of self-consistent theoretical models of the chromosphere required to match observations to them. An attempt is therefore proposed to find indirect signatures of the effect using a statistically significant sample of spectra for different objects, say, sunspots with a different magnetic structure and a different age.  相似文献   

Temporal properties of He  I 1083 nm dark points     

MacQueen  R.M.  Hendrickson  M.A.  Woods  J.C.  Lecinski  A.R.  Elmore  D.F.  White  O.R. 《Solar physics》2000,191(1):85-96

The intensity of a sample of large, high-contrast and isolated dark points has been observed with full-disk images in the light of Hei 1083 nm from the Chromospheric Helium line Intensity Photometer (CHIP) on Mauna Loa, Hawaii. Temporal variations in the intensity encompassing a broad range of time scales have been recorded. Long-term changes in the intensity, although highly variable, are characterized by e-folding times on the order of 5 h. Superposed on these variations are frequent intensity variations, which occur over time scales ranging from the typical observing cadence of 3 min, to tens of minutes. Microflares-involving intensity changes of at least 50% over periods of minutes are observed frequently. Rapid cadence ( min) observations reveal differences between rise and decay times and shorter-term variations in the intensity profiles of these microflares.  相似文献   

A photometric and spectroscopic study of the Herbig Ae/Be star XY Per     

S. Yu. Melnikov  O. V. Ezhkova 《Astronomy Letters》2000,26(4):233-243

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