Impact-generated atmospheres over Titan, Ganymede, and Callisto     

Zahnle K  Pollack JB  Grinspoon D  Dones L 《Icarus》1992,95(1):1-23

The competition between impact erosion and impact supply of volatiles to planetary atmospheres can determine whether a planet or satellite accumulates an atmosphere. In the absence of other processes (e.g., outgassing), we find either that a planetary atmosphere should be thick, or that there should be no atmosphere at all. The boundary between the two extreme cases is set by the mass and velocity distributions and intrinsic volatile content of the impactors. We apply our model specifically to Titan, Callisto, and Ganymede. The impacting population is identified with comets, either in the form of stray Uranus-Neptune planetesimals or as dislodged Kuiper belt comets. Systematically lower impact velocities on Titan allow it to retain a thick atmosphere, while Callisto and Ganymede get nothing. Titan's atmosphere may therefore be an expression of a late-accreting, volatile-rich veneer. An impact origin for Titan's atmosphere naturally accounts for the high D/H ratio it shares with Earth, the carbonaceous meteorites, and Halley. It also accounts for the general similarity of Titan's atmosphere to those of Triton and Pluto, which is otherwise puzzling in view of the radically different histories and bulk compositions of these objects.  相似文献   

下地壳基性麻粒岩流变强度实验研究   总被引：3，自引：0，他引：3  

王永锋  章军锋  金振民  H.W.Green 《矿物岩石地球化学通报》2008,27(Z1)

镁铁质基性麻粒岩被认为可能是大陆下地壳的主要组成岩石[1,2],涉及当前地球动力学研究中地壳变形和高原隆升,壳幔边界的力学耦合与拆离,底侵和拆沉作用等一系列地球动力学问题阳[3,4],具有重要的地球动力学意义.大陆下地壳的流变学性质是我们深入认识这些地球深部过程的关键点之一.  相似文献   

磷处理粉煤灰可作农业土壤磷源   总被引：2，自引：0，他引：2  

申俊峰  M.A.Powell  D.B.Hayden 《地学前缘》2008,15(6):112

粉煤灰(简称CCP或ash)具有改良土壤,增加植物产量的功能。此外,由于它特殊的多孔结构,也可用作吸纳并承载植物养分的载体。用NaH2PO4配制成含磷0.10mol/L浓度的溶液,对采自加拿大西安大略省Sarnia地区Lambton电厂的底灰(bottomash)进行振荡浸渍处理。结果表明,振荡浸渍66h后的粉煤灰中磷含量可达784×10-6。以磷处理粉煤灰、未进行磷处理的粉煤灰和石英砂按比例混合,作为基本生长介质进行玉米种植实验,其中实验配方设计为生长介质中含磷量分别为标准含磷浓度(50×10-6)的10%、25%、50%、75%和100%。生长26、34和46d后分别与不含磷的空白配方、施加含氮-磷-钾为0-20-0标准磷肥并控制磷含量为标准浓度(50×10-6)配方进行生物产量对比。生长实验结果表明,以磷处理粉煤灰供磷的生长介质,当含磷量为标准浓度的25%至100%时,其植物生长量就比添加标准浓度磷肥的配方好。种植46d后的生物生长量统计结果显示,含磷分别为标准浓度50%、75%和100%的实验介质中,玉米杆的鲜重较施标准磷肥介质中玉米分别增长39.46%、42.73%和46.13%;玉米杆干重依次增加29.71%、13.39%和28.87%;根鲜重平均增加16.62%;根干重平均增加14.03%。上述实验结果启示,粉煤灰可以很好地吸纳承载磷养分,并持续供给植物吸收生长,如果采用吸纳磷(或其他养分)的粉煤灰改良砂质土壤将有重要意义。  相似文献   

Detection of a new interstellar molecular ion, H2COH+ (protonated formaldehyde)     

Ohishi M  Ishikawa SI  Amano T  Oka H  Irvine WM  Dickens JE  Ziurys LM  Apponi AJ 《The Astrophysical journal》1996,471(1):L61-L64

A new interstellar molecular ion, H2COH+ (protonated formaldehyde), has been detected toward Sgr B2, Orion KL, W51, and possibly in NGC 7538 and DR21(OH). Six transitions were detected in Sgr B2(M). The 1(1,0)-1(0,1) transition was detected in all sources listed above. Searches were also made toward the cold, dark clouds TMC-1 and L134N, Orion (3N, 1E), and a red giant, IRC + 10216, without success. The excitation temperatures of H2COH+ are calculated to be 60-110 K, and the column densities are on the order of 10(12)-10(14) cm-2 in Sgr B2, Orion KL, and W51. The fractional abundance of H2COH+ is on the order of 10(-11) to 10-(9), and the ratio of H2COH+ to H2CO is in the range 0.001-0.5 in these objects. The values in Orion KL seem to be consistent with the "early time" values of recent model calculations by Lee, Bettens, & Herbst, but they appear to be higher than the model values in Sgr B2 and W51 even if we take the large uncertainties of column densities of H2CO into account. We suggest production routes starting from CH3OH may play an important role in the formation of H2COH+.  相似文献   

The spatial mobility of two generations of young adults in Norway     

Baccaini B  Courgeau D 《International journal of population geography : IJPG》1996,2(4):333-359

"This article presents results from a longitudinal study using data from the Norwegian population register, combined with data from the 1970 and 1980 censuses. For two generations, those born in 1948 and 1958, successive migrations are considered and the effects of various sociodemographic characteristics on migratory behaviour are explored....Event-history analysis is used to examine the duration of stay at the place reached at age 22, and the effects of individual characteristics on this duration. Since a distinction is made between intra- and inter-regional migration, it has been possible to show that these effects vary significantly depending on whether we are dealing with short- or long-distance migration."  相似文献   

A photochemical model of the martian atmosphere     

Nair H  Allen M  Anbar AD  Yung YL  Clancy RT 《Icarus》1994,111(1):124-150

The factors governing the amounts of CO, O2, and O3 in the martian atmosphere are investigated using a minimally constrained, one-dimensional photochemical model. We find that the incorporation of temperature-dependent CO2 absorption cross sections leads to an enhancement in the water photolysis rate, increasing the abundance of OH radicals to the point where the model CO abundance is smaller than observed. Good agreement between models and observations of CO, O2, O3, and the escape flux of atomic hydrogen can be achieved, using only gas-phase chemistry, by varying the recommended rate constants for the reactions CO + OH and OH + HO2 within their specified uncertainties. Similar revisions have been suggested to resolve discrepancies between models and observations of the terrestrial mesosphere. The oxygen escape flux plays a key role in the oxygen budget on Mars; as inferred from the observed atomic hydrogen escape, it is much larger than recent calculations of the exospheric escape rate for oxygen. Weathering of the surface may account for the imbalance. Quantification of the escape rates of oxygen and hydrogen from Mars is a worthwhile objective for an upcoming martian upper atmospheric mission. We also consider the possibility that HOx radicals may be catalytically destroyed on dust grains suspended in the atmosphere. Good agreement with the observed CO mixing ratio can be achieved via this mechanism, but the resulting ozone column is much higher than the observed quantity. We feel that there is no need at this time to invoke heterogeneous processes to reconcile models and observations.  相似文献   

Nitrogen sulfide in quiescent dark clouds     

McGonagle D  Irvine WM  Ohishi M 《The Astrophysical journal》1994,422(2):621-625

We report the first detection of interstellar nitrogen sulfide (NS) in cold dark clouds. Several components of the 2 pi 1/2, J = 3/2 --> 1/2 and J = 5/2 --> 3/2 transitions were observed in TMC-1 and L134N. The inferred column density for TMC-1 is NNS approximately 8 x 10(12)cm-2 toward the NH3 peak in that cloud, and in L134N is NNS approximately 3 x 10(12)cm-2 toward the position of peak NH3 emission. These values correspond to fractional abundances relative to molecular hydrogen of fNS approximately 8 x 10(-10) for TMC-1, and fNS approximately 6 x 10(-10) for L134N. The NS emission is extended along the TMC-1 ridge and is also extended in L134N. The measured abundances are significantly higher than those predicted by some recent gas phase ion-molecule models.  相似文献   

Theoretical infrared spectra of some model polycyclic aromatic hydrocarbons: effect of ionization     

De Frees DJ  Miller MD  Talbi D  Pauzat F  Ellinger Y 《The Astrophysical journal》1993,408(2):530-538

In order to test the hypothesis of ionized polycyclic aromatic hydrocarbons (PAHs) as possible carriers of the UIR bands, we realized a computational exploration on selected PAHs of small dimension in order to identify which changes ionization would induce on their IR spectra. In this study we performed ab initio calculations of the spectra of neutral and positively ionized naphthalene, anthracene, and pyrene. The results are significantly important. The frequencies in the cations are slightly shifted with respect to the neutral species, but no general conclusion can be reached from the three molecules considered. By contrast, the relative intensities of most vibrations are strongly affected by ionization, leading to a much better agreement between the calculated CH/CC vibration intensity ratios and those deduced from observations.  相似文献   

Evidence of ancient life at 207 m depth in a granitic aquifer     

Pedersen K  Ekendahl S  Tullborg EL  Furnes H  Thorseth I  Tumyr O 《Geology》1997,25(9):827-830

The results of electron-microscopy investigations of calcite precipitated in a water-conducting fracture in a ca. 1800 Ma granitic rock from 207 m below sea level at the island of Aspo on the southeastern (Baltic) coast of Sweden are compared with measurements of carbon, oxygen, and sulfur isotope composition of the calcite and embedded pyrite. Parts of the calcite had extremely low delta 13C values, indicative of biological activity, and contained bacteria-like microfossils occurring in colonies and as typical biofllms. X-ray microanalysis demonstrated these fossils to be enriched in carbon. Our results provide evidence for ancient life in deep granitic rock aquifers and suggest that the modern microbial life found there is intrinsic. Modeling historical and present geochemical processes in deep granitic aquifers should, therefore, preferably include biologically catalyzed reactions. The results also suggest that the search for life on other planets, e.g., Mars, should include subsurface material.  相似文献   

在应用计算机解释印度拉贾斯坦邦西部贾伊萨梅尔地区比尔马尼亚盆地地质特征中地质数据的分析          下载免费PDF全文

S.C.马瑟  D.S.乔汉 《沉积与特提斯地质》1995,(2):28-39

最近十年来研究的地质数据包括比尔马尼亚盆地岩相的地层、岩性、岩石、粒度和地球化学资料。这些数据已进入专用的“Ｆｏｘｓｅｄｂａ”数据表以建立比尔马尼亚盆地的数据总库。采用Ｈａｒｗａｒｄ制图法在ｘ－ｙ轴（粒度参数和地球化学数据）上作图。该盆地各种岩相的环境解释模式都配备有“图象”软件。最后,上述资料被用来解释所推断的比尔马尼亚盆地各种岩相的沉积环境。该盆地的沉积充填物含硅质碎屑、碳酸盐和磷块岩相的混合组合,指示变幻不定的沉积环境,即有若干具间歇海进事件的沉积海退事件。结果,磷块岩主要形成一种浅水正化学沉积和异化学沉积的复杂组合。  相似文献