抽油机悬点投影测量仪     

文志雄  戚克军  李明  曾南志 《大地测量与地球动力学》2002,22(1):110-113

油田抽油机的抽油杆幌动幅度过大，是引起抽油杆断裂的一个重要因素，检测这种幌动幅度是防止抽油杆断裂的一种有效手段。设计了一种基于面阵CCD和普通半导体激光器（LD）测量这种幌动的悬点投影测量方法，通过数字卷积滤波，达到了范围为0－40mm，误差＜0.2mm的技术检测指标。  相似文献   

MANGALA VALLES, MARS: ASSESSMENT OF EARLY STAGES OF FLOODING AND DOWNSTREAM FLOOD EVOLUTION     

Gil J. Ghatan  James W. Head  Lionel Wilson 《Earth, Moon, and Planets》2005,96(1-2):1-57

The Mangala Valles system is an ∼ ∼900 km fluvially carved channel system located southwest of the Tharsis rise and is unique among the martian outflow channels in that it heads at a linear fracture within the crust as opposed to a collapsed region of chaos as is the case with the circum-Chryse channels. Mangala Valles is confined within a broad, north–south trending depression, and begins as a single valley measuring up to 350 km wide that extends northward from a Memnonia Fossae graben, across the southern highlands toward the northern lowlands. Approximately 600 km downstream, this single valley branches into multiple channels, which ultimately lose their expression at the dichotomy boundary. Previous investigations of Mangala Vallis suggested that many of the units mapped interior to the valley were depositional, related to flooding, and that a minimum of two distinct periods of flooding separated by tens to hundreds of millions of years were required to explain the observed geology. We use infrared and visible images from the THermal EMission Imaging System (THEMIS), and topographic data from the Mars Orbiting Laser Altimeter (MOLA), to investigate the nature of the units mapped within Mangala Vallis. We find that the geomorphology of the units, as well as their topographic and geographic distribution, are consistent with most of them originating from a single assemblage of volcanic flow deposits, once continuous with volcanic flows to the south of the Memnonia Fossae source graben. These flows resurfaced the broad, north–south trending depression into which Mangala Vallis formed prior to any fluvial activity. Later flooding scoured and eroded this volcanic assemblage north of the Mangala source graben, resulting in the present distribution of the units within Mangala Vallis. Additionally, our observations suggest that a single period of catastrophic flooding, rather than multiple periods separated by tens to hundreds of millions of years, is consistent with and can plausibly explain the interior geology of Mangala Vallis. Further, we present a new scenario for the source and delivery of water to the Mangala source graben that models flow of groundwater through a sub-cryosphere aquifer and up a fracture that cracks the cryosphere and taps this aquifer. The results of our model indicate that the source graben, locally enlarged to a trough near the head region of Mangala, would have required less than several days to fill up prior to any spill-over of water to the north. Through estimates of the volume of material missing from Mangala (13,000–20,000 km³), and calculation of mean discharge rates through the channel system (∼ ∼5 × 10⁶ m³ s⁻¹), we estimate that the total duration of fluvial activity through the Mangala Valles was 1–3 months.  相似文献   

Geology and tectonics of the Themis Regio-Lavinia Planitia-Alpha Regio-Lada Terra area,Venus: Results from Arecibo image data     

D. A. Senske  D. B. Campbell  J. W. Head  P. C. Fisher  A. A. Hine  A. deCharon  S. L. Frank  S. T. Keddie  K. M. Roberts  E. R. Stofan  J. C. Aubele  L. S. Crumpler  N. Stacy 《Earth, Moon, and Planets》1991,55(2):97-161

New radar images obtained from the Arecibo Observatory (resolution 1.5–4.0 km) for portions of the southern hemisphere of Venus show that: the upland of Phoebe Regio contains the southern extension of Devana Chasma, a rift zone extending 4200 km south from Theia Mons and interpreted as a zone of extension; Alpha Regio, the only large region of tessera within the imaged area, is similar to tessera mapped elsewhere on the planet and covers a smaller percentage of the surface than that observed in the northern high latitudes; the upland made of Ushas, Innini and Hathor Montes consists of three distinct volcanic constructs; Themis Regio is mapped as an ovoid chain of radar-bright arcuate single and double ring structures, edifices and bright lineaments. This area is interpreted as a region of mantle upwelling and on the basis of apparent split and separated features, a zone of localized faulting and extension. Linear zones of deformation in Lavinia Planitia are characterized by lineament belts that are often locally elevated, are similar to ridge belts mapped in the northern high latitudes and are interpreted to be characterized mainly by compression; radar-bright lava complexes within Lavinia Planitia are unique to this part of the planet and are interpreted to represent areas of eruption of high volumes of extremely fluid lava; the upland of Lada Terra is bound to the north by a linear deformation zone interpreted as extensional, is characterized by large ovoids and coronae, is interpreted to be associated with an area of mantle upwelling, and is in contrast to the northern high latitude highland of Ishtar Terra. Regions of plains in the southern hemisphere cover about 78%; of the mapped area and are interpreted to be volcanic in origin. Located within the area imaged (10–78 S) are 52 craters interpreted to be of impact origin ranging from 8 to 157 km in diameter. On the basis of an overall crater density of 0.94 craters/10⁶ km², it is determined that the age of this part of the Venus surface is similar to the 0.3 to 1.0 billion year age calculated for the equatorial region and northern high latitudes. The geologic characteristics of the portion of the Venus southern hemisphere imaged by Arecibo are generally similar to those mapped elsewhere on the planet. This part of the planet is characterized by widespread volcanic plains, large volcanic edifices, and zones of linear belt deformation. The southern hemisphere of Venus differs from northern high latitudes in that tessera makes up only a small percentage of the surface area and the ovoid chain in Themis Regio is unique to this part of the planet. On the basis of the analysis presented here, the southern hemisphere of Venus is interpreted to be characterized by regions of mantle upwelling on a variety of scales (ovoids, region made up of Ushas, Innini and Hathor Montes), upwelling and extension (Themis Regio) and localized compression (lineament belts in Lavinia Planitia).  相似文献   

Results of TV imaging of Phobos (Experiment VSK-Fregat)     

Avanesov G  Zhukov B  Ziman YA  Kostenko V  Kuzmin A  Murav'ev V  Fedotov V  Bonev B  Mishev D  Petkov D  Krumov A  Simeonov S  Boycheva V  Uzunov YU  Weide GG  Halmann D  Pössel W  Head J  Murchie S  Schkuratov YuG  Berghänel R  Danz M  Mangoldt T  Pihan U  Smith B 《Planetary and Space Science》1991,39(1-2):281-295

From February to March 1989 the Phobos 2 spacecraft took 37 TV images of Phobos at a distance of 190-1100 km. These images complement Mariner-9 and Viking data by providing higher-resolution coverage of a large region West of the crater Stickney (40-160 degrees W) and by providing disk-resolved measurements of surface brightness at a greater range of wavelengths and additional phase angles. These images have supported updated mapping and characterization of large craters and grooves, and have provided additional observations of craters' and grooves' bright rims. Variations in surface visible/near-infrared color ratio of almost a factor of 2 have been recognized; these variations appear to be associated with the ejecta of specific large impact craters. Updated determinations of satellite mass and volume allow calculation of a more accurate value of bulk density, 1.90 +/- 0.1 g cm-3. This is significantly lower than the density of meteoritic analogs to Phobos' surface, suggesting a porous interior perhaps containing interstitial ice.  相似文献   

Deep submarine pyroclastic eruptions: theory and predicted landforms and deposits   总被引：1，自引：0，他引：1  

James W. Head  III  Lionel Wilson   《Journal of Volcanology and Geothermal Research》2003,121(3-4):155-193

Submarine pyroclastic eruptions at depths greater than a few hundred meters are generally considered to be rare or absent because the pressure of the overlying water column is sufficient to suppress juvenile gas exsolution so that magmatic disruption and pyroclastic activity do not occur. Consideration of detailed models of the ascent and eruption of magma in a range of sea floor environments shows, however, that significant pyroclastic activity can occur even at depths in excess of 3000 m. In order to document and illustrate the full range of submarine eruption styles, we model several possible scenarios for the ascent and eruption of magma feeding submarine eruptions: (1) no gas exsolution; (2) gas exsolution but no magma disruption; (3) gas exsolution, magma disruption, and hawaiian-style fountaining; (4) volatile content builds up in the magma reservoir leading to hawaiian eruptions resulting from foam collapse; (5) magma volatile content insufficient to cause fragmentation normally but low rise speed results in strombolian activity; and (6) volatile content builds up in the top of a dike leading to vulcanian eruptions. We also examine the role of bulk-interaction steam explosivity and contact-surface steam explosivity as processes contributing to volcaniclastic formation in these environments. We concur with most earlier workers that for magma compositions typical of spreading centers and their vicinities, the most likely circumstance is the quiet effusion of magma with minor gas exsolution, and the production of somewhat vesicular pillow lavas or sheet flows, depending on effusion rate. The amounts by which magma would overshoot the vent in these types of eruptions would be insufficient to cause any magma disruption. The most likely mechanism of production of pyroclastic deposits in this environment is strombolian activity, due to the localized concentration of volatiles in magma that has a low rise rate; magmatic gas collects by bubble coalescence, and ascends in large isolated bubbles which disrupt the magma surface in the vent, producing localized blocks, bombs, and pyroclastic deposits. Another possible mode of occurrence of pyroclastic deposits results from vulcanian eruptions; these deposits, being characterized by the dominance of angular blocks of country rocks deposited in the vicinity of a crater, should be easily distinguishable from strombolian and hawaiian eruptions. However, we stress that a special case of the hawaiian eruption style is likely to occur in the submarine environment if magmatic gas buildup occurs in a magma reservoir by the upward drift of gas bubbles. In this case, a layer of foam will build up at the top of the reservoir in a sufficient concentration to exceed the volatile content necessary for disruption and hawaiian-style activity; the deposits and landforms are predicted to be somewhat different from those of a typical primary magmatic volatile-induced hawaiian eruption. Specifically, typical pyroclast sizes might be smaller; fountain heights may exceed those expected for the purely magmatic hawaiian case; cooling of descending pyroclasts would be more efficient, leading to different types of proximal deposits; and runout distances for density flows would be greater, potentially leading to submarine pyroclastic deposits surrounding vents out to distances of tens of meters to a kilometer. In addition, flows emerging after the evacuation of the foam layer would tend to be very depleted in volatiles, and thus extremely poor in vesicles relative to typical flows associated with hawaiian-style eruptions in the primary magmatic gas case. We examine several cases of reported submarine volcaniclastic deposits found at depths as great as 3000 m and conclude that submarine hawaiian and strombolian eruptions are much more common than previously suspected at mid-ocean ridges. Furthermore, the latter stages of development of volcanic edifices (seamounts) formed in submarine environments are excellent candidates for a wide range of submarine pyroclastic activity due not just to the effects of decreasing water depth, but also to: (1) the presence of a summit magma reservoir, which favors the buildup of magmatic foams (enhancing hawaiian-style activity) and episodic dike emplacement (which favors strombolian-style eruptions); and (2) the common occurrence of alkalic basalts, the CO₂ contents of which favor submarine explosive eruptions at depths greater than tholeiitic basalts. These models and predictions can be tested with future sampling and analysis programs and we provide a checklist of key observations to help distinguish among the eruption styles.  相似文献   

A well‐established Early–Middle Pleistocene marine sequence on south‐east Zakynthos island,western Greece: Magneto‐biostratigraphic constraints and palaeoclimatic implications     

Maria D. Papanikolaou  Maria V. Triantaphyllou  Ellen S. Platzman  Philip L. Gibbard  Conall Mac Niocaill  Martin J. Head 《第四纪科学杂志》2011,26(5):523-540

The chronostratigraphy of a long, onshore Early–Middle Pleistocene marine sedimentary sequence on the south‐east part of Zakynthos island, Greece, is presented. Correlation of the succession with the isotope record of Ocean Drilling Program Site 963 reveals the combined influence of tectonics and eustacy in this area. The sequence is divided into three formations by two main unconformities that apparently relate to sea‐level lowstands associated with two major northern hemisphere glaciations, those of marine isotope stages (MIS) 22 and 12. The Zakynthos sequence in many ways is comparable with the Italian Valle di Manche section. Magnetostratigraphic and rock magnetic analyses, supported by biostratigraphy, document the position of the Matuyama/Brunhes Chron boundary (0.77 Ma), the top and base of the Jaramillo Subchron (0.99–1.07 Ma), the Cobb Mountain Subchron (1.173–1.185 Ma) and the top of the Olduvai Subchron (1.78 Ma). The underlying strata are constrained exclusively by detailed nannofossil biostratigraphy extending at least to the lowermost Pleistocene at around 2.54 Ma and therefore certainly incorporating the base of the Olduvai Subchron (1.95 Ma) and possibly the Gauss/Matuyama Chron boundary (2.58 Ma). In addition, a remarkable increase in sedimentation rate (from 3.2 and 28 cm ka^?1 to 167 cm ka^?1) and hence resolution above the Matuyama/Brunhes boundary (Middle Pleistocene) reveals one short‐lived magnetic excursion, possibly 17a (0.66 Ma), within the normal polarity Brunhes Chron. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Microbial–silica interactions in Icelandic hot spring sinter: possible analogues for some Precambrian siliceous stromatolites     

Kurt O. Konhauser  Vernon R. Phoenix  Simon H. Bottrell  David G. Adams  & Ian M. Head 《Sedimentology》2001,48(2):415-433

Silicified deposits, such as sinters, occur in several modern geothermal environments, but the mechanisms of silicification (and crucially the role of microorganisms in their construction) are still largely unresolved. Detailed examination of siliceous sinter, in particular sections of microstromatolites growing at the Krisuvik hot spring, Iceland, reveals that biomineralization contributes a major component to the overall structure, with approximately half the sinter thickness attributed to silicified microorganisms. Almost all microorganisms observed under the scanning electron microscope (SEM) are mineralized, with epicellular silica ranging in thickness from < 5 μm coatings on individual cells, to regions where entire colonies are cemented together in an amorphous silica matrix tens of micrometres thick. Within the overall profile, there appears to be two very distinct types of laminae that alternate repeatedly throughout the microstromatolite: ‘microbial’ layers are predominantly consisting of filamentous, intact, vertically aligned, biomineralized cyanobacteria, identified as Calothrix and Fischerella sp.; and weakly laminated silica layers which appear to be devoid of any microbial component. The microbial layers commonly have a sharply defined base, overlying the weakly laminated silica, and a gradational upper surface merging into the weakly laminated silica. These cyclic laminations are probably explained by variations in microbial activity. Active growth during spring/summer allows the microorganisms to keep pace with silicification, with the cell surfaces facilitating silicification, while during their natural slow growth phase in the dark autumn/winter months silicification exceeds the bacteria’s ability to compensate (i.e. grow upwards). At this stage, the microbial colony is probably not essential to microstromatolite formation, with silicification presumably occurring abiogenically. When conditions once again become favourable for growth, recolonization of the solid silica surface by free‐living bacteria occurs: cell motility is not responsible for the laminations. We have also observed that microbial populations within the microstromatolite, some several mm in depth, appear viable, i.e. they still have their pigmentation, the trichomes are not collapsed, cell walls are unbroken, cytoplasm is still present and they proved culturable. This suggests that the bulk of silicification occurred rapidly, probably while the cells were still alive. Surprisingly, however, measurements of light transmittance through sections of the microstromatolite revealed that photosynthetically active light (PAL) only transmitted through the uppermost 2 mm. Therefore the ‘deeper’ microbial populations must have either: (i) altered their metabolic pathways; (ii) become metabolically inactive; or (iii) the deeper populations may be dominated by different microbial assemblages from that of the surface. From these collective observations, it now seems unequivocal that microstromatolite formation is intimately linked to microbial activity and that the sinter fabric results from a combination of biomineralization, cell growth and recolonization. Furthermore, the similarities in morphology and microbial component to some Precambrian stromatolites, preserved in primary chert, suggests that we may be witnessing contemporaneous biomineralization processes and growth patterns analogous to those of the early Earth.  相似文献   

Diffuse scattering of radar on the surface of Venus: Origin and implications for the distribution of soils     

D. L. Bindschadler  J. W. Head 《Earth, Moon, and Planets》1988,42(2):133-149

Previous analysis of PV altimeter data has shown that ~25% of the surface of Venus is characterized by low values of reflectivity, interpreted as being due to the presence of porous materials such as soils. However, examination of a corrected reflectivity data set in combination with PV altimeter data suggests that no more than 5% of the surface of Venus is covered by soils more than several to tens of cm in depth. Most regions of apparent low reflectivity are instead interpreted to be due to the presence of small (5–50 cm) roughness elements on the surface that cause diffuse scattering at the 17 cm PV wavelength. Regions of low apparent reflectivity are of interest because of a correlation with tessera, a complex tectonic unit mapped from Venera 15/16 SAR data. Regions of tessera are characterized by a complex system of intersecting ridges and valleys thought to be of tectonic origin. Examination of possible models for the form of diffuse scatterers in the tessera suggests that they are rock fragments and originate from a mass-wasting process that is linked to the rugged nature of the terrain. Further, these diffuse scatterers are associated with other tectonic landforms, suggesting that they originate as part of tectonic deformation of the surface. Viewed from a geologic standpoint, the PV data sets are important tools for understanding tectonic, volcanic, and degradational processes on Venus, as well as for future interpretation of data from the Magellan mission.  相似文献   

Antarctic dry valleys: Microclimate zonation, variable geomorphic processes, and implications for assessing climate change on Mars     

David R. Marchant  James W. Head III 《Icarus》2007,192(1):187-222

The Antarctic Dry Valleys (ADV) are generally classified as a hyper-arid, cold-polar desert. The region has long been considered an important terrestrial analog for Mars because of its generally cold and dry climate and because it contains a suite of landforms at macro-, meso-, and microscales that closely resemble those occurring on the martian surface. The extreme hyperaridity of both Mars and the ADV has focused attention on the importance of salts and brines on soil development, phase transitions from liquid water to water ice, and ultimately, on process geomorphology and landscape evolution at a range of scales on both planets. The ADV can be subdivided into three microclimate zones: a coastal thaw zone, an inland mixed zone, and a stable upland zone; zones are defined on the basis of summertime measurements of atmospheric temperature, soil moisture, and relative humidity. Subtle variations in these climate parameters result in considerable differences in the distribution and morphology of: (1) macroscale features (e.g., slopes and gullies); (2) mesoscale features (e.g., polygons, including ice-wedge, sand-wedge, and sublimation-type polygons, as well as viscous-flow features, including solifluction lobes, gelifluction lobes, and debris-covered glaciers); and (3) microscale features (e.g., rock-weathering processes/features, including salt weathering, wind erosion, and surface pitting). Equilibrium landforms are those features that formed in balance with environmental conditions within fixed microclimate zones. Some equilibrium landforms, such as sublimation polygons, indicate the presence of extensive near-surface ice; identification of similar landforms on Mars may also provide a basis for detecting the location of shallow ice. Landforms that today appear in disequilibrium with local microclimate conditions in the ADV signify past and/or ongoing shifts in climate zonation; understanding these shifts is assisting in the documentation of the climate record for the ADV. A similar type of landform analysis can be applied to the surface of Mars where analogous microclimates and equilibrium landforms occur (1) in a variety of local environments, (2) in different latitudinal bands, and (3) in units of different ages. Documenting the nature and evolution of the ADV microclimate zones and their associated geomorphic processes is helping to provide a quantitative framework for assessing the evolution of climate on Mars.  相似文献   

Seasonal and depth-dependent variations in the size and lipid contents of stage 5 copepodites of Calanus finmarchicus in the waters of the Newfoundland Shelf and the Labrador Sea     

Pierre Pepin  Erica J.H. Head 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(6):989-1002

We report on the variation in energy reserves of individual C5 copepodites of Calanus finmarchicus from the Newfoundland continental shelf and the Labrador Sea collected from surface and overwintering (or bottom) depths prior to, during and after the expected timing of the onset of diapause. Overall, the trend was for a decreasing average prosome length as the year progressed for all locations although the decline was smallest in the Labrador Sea and greatest in the deep waters of the continental shelf. The size of the oil sac was closely linked to the weight of the copepodite but the form of this relationship showed substantial variations with depth and season. We show a clear increase in the relative oil sac volume for C. finmarchicus between late spring and late summer, by which time some animals had descended to diapause depths. The progressive decrease in oil sac volume of animals sampled at depth in the Labrador Sea between September and December suggests a significant loss of energy reserves during diapause. From the distribution of volumes and body sizes in December we estimate that 23–53% of individuals would not be able to meet the energetic cost of moulting and early gonad development. Overall, some of our observations appear to invalidate earlier hypotheses concerning the governing role of lipids in the life history of C. finmarchicus. However, assessment of the factors that influence entry into dormancy should be based on the relative probabilities of alternative strategies for successful reproduction (e.g. entering dormancy vs. continuing into a second generation).  相似文献