Impact of data model and point density on aboveground forest biomass estimation from airborne LiDAR     

Mariano Garcia  Sassan Saatchi  Antonio Ferraz  Carlos Alberto Silva  Susan Ustin  Alexander Koltunov  Heiko Balzter 《Carbon balance and management》2017,12(1):4

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Tracer test to constrain CO<Subscript>2</Subscript> residual trapping and plume evolution     

Mehdi Zeidouni  Susan D. Hovorka  Kewei Shi 《Environmental Earth Sciences》2016,75(22):1451

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From regolith to rock by shock     

Susan Werner Kieffer 《Earth, Moon, and Planets》1975,13(1-3):301-320

A model for shock-lithification of terrestrial and lunar regolith is proposed that accounts for: (1) observed petrographic properties and densities of shock-lithified material from missile impact craters at White Sands, New Mexico and from Meteor Crater, Arizona; (2) observed petrographic textures of lunar soil and lunar soil analogues experimentally shocked to known pressures in laboratory experiments; (3) theoretical calculations of the behavior of air and water under shock compression; and (4) measured Hugoniot and release adiabat data on dry and wet terrestrial soils and lunar regolith. In this model it is proposed that air or an air-water mixture initially in the pores of terrestrial soil affects the behavior of the soil-air-water system under shock-loading. Shock-lithified rocks found at Meteor Crater are classified as ‘strongly lithified’ and ‘weakly lithified’ on the basis of their strength in hand specimen; only weakly lithified rocks are found at the missile impact craters. These qualitative strength properties are related to the mechanisms of bonding in the rocks. The densities of weakly lithified samples are directly related to the pressures to which they were shock-loaded. A comparison of the petrographic textures and densities of weakly lithified samples with textures and densities of ‘regolith’ shock-loaded to known pressures suggests that weakly lithified terrestrial samples formed at pressures well under 100 kb, probably under 50 kb. If terrestrial soils are shock-loaded to pressures between 100 and 200 kb by impact events of short duration, the pore pressure due to hot air or air-water mixtures exceeds the strength of the weak lithification mechanisms and fragmentation, rather than lithification, occurs. At pressures above 200 kb, lithification can occur because the formation of glass provides a lithification mechanism which has sufficient strength to withstand the pore pressure. During shock-lithification of lunar regolith at pressures below 50 kb, the material is compressed to intrinsic crystal density and remains at approximately that density upon release from the shocked state. It is proposed, however, that at pressures in excess of 50 kb, the release of trapped volatiles from lunar soil grains into fractures causes an expansion of the regolith during unloading from the shocked state.  相似文献   

Gaseous Jets in Comet Hale-Bopp (1995 O1)     

Lederer  Susan M.  Campins  Humberto  Osip  David J.  Schleicher  David G. 《Earth, Moon, and Planets》1997,78(1-3):131-136

We report the identification of gas jets in comet Hale-Bopp in OH, NH, CN, C₂ and C₃. This is the first time OH and NH jets without an obvious optical dust jet counterpart have been identified in narrowband comet images. We also confirm the existence of CN jets as reported by Larson et al. (1997) and Mueller et al. (1998). Jet features can be seen in the March and April 1997 datasets, approximately a month before and after perihelion. Our results contribute to the understanding of both the chemical properties of the comet as well as the physical mechanisms necessary to produce these features. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Anatomy of individual agglutinates from a lunar highland soil     

Abhijit BASU  David S. McKAY  Richard V. MORRIS  Susan J. WENTWORTH 《Meteoritics & planetary science》1996,31(6):777-782

Abstract— We report results of our investigation of the relationship between values of I_s/FeO (relative concentration of nanophase Fe⁰ divided by total FeO content), glass abundance, total Fe content, and degree of digestion of <20 μm clasts for 22 individual agglutinates (250–1000 μm) from the mature Apollo 16 soil 61181 (I_s/FeO = 82 units in the <250 μm fraction). Agglutinates are important products of space weathering on the Moon, and they influence spectral observations at visible and near-IR wavelengths. Values of I_s/FeO for individual agglutinates (250–1000 μm) within this single soil span a range from 3 to 262 units which is larger than the range observed for all Apollo 16 bulk soils (～0 to 110 units). No correlation was observed between I_s/FeO and glass abundance and FeO concentrations for either agglutinitic glass or whole agglutinate particles under investigation. Our results suggest that the variation in I_s/FeO for agglutinates from a single soil may be in part a consequence of natural mixing processes on the Moon that produce highly-variable environments (with respect to surface exposure) for agglutinate formation and in part to variable kinetics of reactions in an agglutinate melt, which are influenced by a variety of factors including melt composition, temperature, impactor velocity, and quench rate. We cannot exclude but do not see evidence for other processes including addition of exotic agglutinates, micrometeoritic bombardment into compositionally-diverse microtargets, recycling of agglutinates, preferential melting of very fine soil particles, and production of nanophase Fe⁰ in amorphous rims of very fine irradiated lunar grains contributing to the observed variation of I_s/FeO.  相似文献   

A numerical response of the middle atmosphere to the 11-year solar cycle     

Rolando R. Garcia  Susan Solomon  Raymond G. Roble  David W. Rusch 《Planetary and Space Science》1984,32(4):411-423

A two-dimensional numerical model with coupled photochemistry and dynamics has been used to investigate the response of the middle atmosphere (16–116 km) to changes in solar activity over the 11-year solar cycle. Model inputs that vary with solar cycle include solar radiation, cosmic ray and auroral ionization rates and the flux of NO_x at the model's upper boundary.In this study, the results of model runs for solar cycle minimum and maximum conditions are compared. In the stratosphere, using currently accepted estimates of changes in solar radiation at wavelengths longer than 180 nm, only small responses in ozone, temperature and zonal winds are obtained. On the other hand, changes at shorter wavelengths, and the effects of particle precipitation, lead to large variations in the abundances of trace species in the thermosphere and upper mesosphere. In particular, very large abundances of NO_x are produced above 90 km by auroral particle precipitation. Considerable amounts of NO_x are transported subsequently to the stratosphere by the global mean meridional circulation. It is shown that this excess NO_x can lead to significant decreases in ozone concentrations at high latitudes and that it may explain observations of nitrate deposition in Antarctic snow.  相似文献   

Ecological studies ofGracilaria asiatica andGracilaria lemaneiformis in Zhanshan Bay,Qingdao     

Susan H. Brawley  Fei Xiugeng 《中国海洋湖沼学报》1988,6(1):22-34

Natural populations ofG. asiatica Zhang & Xia andG. lemaneiformis (Bory) Weber van Bosse were studied during 1984 and 1986 in Zhanshan Bay, Qingdao (36°4'N, 120° 21'E). Rapid growth (length, weight) of these plants occurred between mid-May and late June (water temperatures, 15–20°C). The major epiphyte ofG. asiatica wasEnteromorpha linza, whilePunctaria latifolia was the major epiphyte ofG. lemaneiformis. Epiphytism declined throughout early summer, and epiphytes were rare after mid-July (1984); they did not reappear in late summer, although macrophyte growth declined abruptly after early July. Populations ofG. asiatica varied during late spring-early summer between adjacent sandy and rocky portions of the intertidal zone; plants at the sandy site were larger and epiphyte-free. Amphipod densities were low on both species ofGracilaria, but the most abundant species wereAmpithoe lacertosa, Caprella equilibra, C. krøyeri, C. scauraandPontogeneia rostrata. Additional information on general community structure is provided for theG. asiatica zone.  相似文献   

On the experimental silicification of microorganisms. III. Implications of the preservation of the green prokaryotic alga prochloron and other coccoids for interpretation of the microbial fossil record     

Susan Francis  Elso S. Barghoorn  Lynn Margulis 《Precambrian Research》1978,7(4):377-383

Evidence for Precambrian fossil eukaryotic microorganisms has been based on: (1) the presence of internal ‘spots’ which have been variously interpreted to be remains of nuclei or pyrenoids of photosynthetic plastids or other organelles; (2) tetrahedral tetrad arrangement of cells; (3) trilete scars interpreted to be indicative of meiotic division: (4) large cell diameters; and (5) putative mitotic cell divisions. These features have been reported in fossils preserved in Precambrian cherts. We have studied modern microbial mats, thought to be analogues of Precambrian fossil communities, and found they may be silicified by laboratory procedures. In microbial mats from Baja California we have found many ‘spot cells’ that we could identify as remains of cyanophytes. We have silicified the newly discovered large prokaryotic coccoid green alga Prochloron and have found that it, like many cyanophytes previously silicified, preserves its structure and maintains its initial dimensions. In laboratory-silicified prokaryotic organisms we have found that all of the above criteria, supposedly characteristic of eukaryotes, can be observed. We conclude that there is no compelling morphological evidence for fossil eukaryotic microbes from Precambrian cherts.  相似文献   

SPATIAL PATTERNS OF SUPPORT FOR A NUCLEAR WEAPONS FREEZE*     

Susan L. Cutter  H. Briavel Holcomb  Dianne Shatin 《The Professional geographer》1986,38(1):42-52

Support for a Freeze on nuclear weapons is greatest in the East with pockets of support in the Middle West and Pacific Coast States. Factors influencing the spatial pattern are Walker's innovativeness rankings, the number of peace/Freeze activist groups and the pattern of defense employment.  相似文献   

COUNTERURBANIZATION IN THE FEDERAL REPUBLIC OF GERMANY*     

Thomas Kontuly  Susan Wiard  Roland Vogelsang 《The Professional geographer》1986,38(2):170-181

Since Berry argued in 1976 that counterurbanization had replaced urbanization in the U.S., a debate has ensued as to whether the phenomenon also exists in Western Europe. Proponents of a developmental theory of counterurbanization contend that the phenomenon should be evident in countries which have achieved a very high level of socioeconomic development, including the Federal Republic of Germany (FRG). Most of the German and English language literature on the topic suggests the contrary for the FRG. Here urbanization and counterurbanization are restricted to specific geographic meanings, i.e., spatial agglomeration and deglomeration. Results from four interrelated tests show a trend toward counterurbanization evident as early as the 1960s in the post-war regional demographic data of the FRG.  相似文献