A sophisticated lander for scientific exploration of Mars: scientific objectives and implementation of the Mars-96 Small Station     

Linkin V  Harri AM  Lipatov A  Belostotskaja K  Derbunovich B  Ekonomov A  Khloustova L  Kremnev R  Makarov V  Martinov B  Nenarokov D  Prostov M  Pustovalov A  Shustko G  Jarvinen I  Kivilinna H  Korpela S  Kumpulainen K  Lehto A  Pellinen R  Pirjola R  Riihela P  Salminen A  Schmidt W  McKay CP 《Planetary and Space Science》1998,46(6-7):717-737

A mission to Mars including two Small Stations, two Penetrators and an Orbiter was launched at Baikonur, Kazakhstan, on 16 November 1996. This was called the Mars-96 mission. The Small Stations were expected to land in September 1997 (Ls approximately 178 degrees), nominally to Amazonis-Arcadia region on locations (33 N, 169.4 W) and (37.6 N, 161.9 W). The fourth stage of the Mars-96 launcher malfunctioned and hence the mission was lost. However, the state of the art concept of the Small Station can be applied to future Martian lander missions. Also, from the manufacturing and performance point of view, the Mars-96 Small Station could be built as such at low cost, and be fairly easily accommodated on almost any forthcoming Martian mission. This is primarily due to the very simple interface between the Small Station and the spacecraft. The Small Station is a sophisticated piece of equipment. With the total available power of approximately 400 mW the Station successfully supports an ambitious scientific program. The Station accommodates a panoramic camera, an alpha-proton-x-ray spectrometer, a seismometer, a magnetometer, an oxidant instrument, equipment for meteorological observations, and sensors for atmospheric measurement during the descent phase, including images taken by a descent phase camera. The total mass of the Small Station with payload on the Martian surface, including the airbags, is only 32 kg. Lander observations on the surface of Mars combined with data from Orbiter instruments will shed light on the contemporary Mars and its evolution. As in the Mars-96 mission, specific science goals could be exploration of the interior and surface of Mars, investigation of the structure and dynamics of the atmosphere, the role of water and other materials containing volatiles and in situ studies of the atmospheric boundary layer processes. To achieve the scientific goals of the mission the lander should carry a versatile set of instruments. The Small Station accommodates devices for atmospheric measurements, geophysical and geochemical studies of the Martian surface and interior, and cameras for descent phase and panoramic views. These instruments would be able to contribute remarkably to the process of solving some of the scientific puzzles of Mars.  相似文献   

On radiating stellar collapse with shear     

Kesh S. Govinder  Megan Govender  & Roy Maartens 《Monthly notices of the Royal Astronomical Society》1998,299(3):809-810

Relativistic models of radiating stellar collapse with shear require careful checking of all the equations and quantities involved. We illustrate this by showing that, in a recently proposed model, the metric ansatz is in fact too restrictive to allow any radial evolution to occur, and only tangential evolution is possible. Furthermore, the assumption of pressure isotropy is shown to reduce the model to the static case without radiation or shear.  相似文献   

Barrier island stratigraphy and Holocene history of west-central Florida   总被引：4，自引：0，他引：4  

Richard A. Davis  Jr.  Kristin E. Yale  John M. Pekala  Megan V. Hamilton 《Marine Geology》2003,200(1-4):103-123

Although the morphology of the barrier-inlet system along the west-central Florida coast is quite complicated, the stratigraphy of these barriers is rather simple. The basal Holocene unit in most cores is an organic-rich, muddy sand that represents a vegetated, paralic marine, coastal environment similar to that which is north and south of the present barrier system. Above that unit is a muddy, bioturbated sand that displays a marine fauna at most locations but also contains Crassostrea virginica in a few places. These sediments accumulated in a low-energy marine setting that may or may not have been protected by a barrier island. Much of this facies also represents sediment that was delivered as washover deposits in an intertidal or subtidal setting and was subsequently bioturbated. The facies that can be attributed to a barrier island with some certainty are no more than 3000 years old, and on most islands, are much younger. These are the shelly sand and sorted sand facies. The shelly strata represent deposition in nearshore, beach, supratidal washover or intertidal spillover environments, and tidal inlet and tidal delta channels, whereas the sorted sand is typical of eolian deposition in dunes or the backbeach and some tidal delta elements. The presence of Holocene oyster beds offshore of a present barrier suggests that some of these islands formed significantly offshore and moved to their present position through washover. It is likely that most of these barriers initially formed through upward shoaling by waves. Although there is significant morphologic difference between the wave-dominated and mixed-energy, drumstick barrier islands, their stratigraphy is quite similar. The only significant difference is the presence of extensive progradation on at least part of the drumstick islands and a relatively high amount of former washover deposits on the wave-dominated type.  相似文献   

Climate change,ecosystems and smallholder agriculture in Central America: an introduction to the special issue     

Pablo Imbach  Megan Beardsley  Claudia Bouroncle  Claudia Medellin  Peter Läderach  Hugo Hidalgo  Eric Alfaro  Jacob Van Etten  Robert Allan  Debbie Hemming  Roger Stone  Lee Hannah  Camila I. Donatti 《Climatic change》2017,140(1):1-4

  相似文献   

Hyperfiltration of sodium chloride through kaolinite membranes under relatively low-heads – Implications for groundwater assessment     

Megan Hart  T.M. WhitworthEliot Atekwana 《Applied Geochemistry》2008

Three relatively low-head hyperfiltration experiments were conducted to investigate clay membrane behavior at lower hydraulic heads. Dilute Cl⁻ solutions (187 and 336 mg/L) were forced through thin layers of kaolinite (0.67–1.62 mm) under heads ranging between 1.45 and 1.89 m. At the end of each experiment, there was a Cl⁻ concentration increase (15–29%) within the cell. The concentration increase is attributable to solute-sieving by the kaolinite. Calculated final concentration increases at the membrane face ranged between 1.51 and 1.65 times the initial concentration and the calculated values of the reflection coefficient ranged between 0.35 and 0.40. These experiments show that clays are capable of significant hyperfiltration effects at lower pressure heads more typical of natural aquifers. Consequently, hyperfiltration effects may need to be considered in a broad spectrum of shallow subsurface processes in which these effects have been regarded as inconsequential; particularly in perched aquifers.  相似文献   

Ubiquitous interactive visualization of 3D mantle convection using a web-portal with Java and Ajax framework     

James B. S. G. Greensky  Wojciech Walter Czech  David A. Yuen  Michael Richard Knox  Megan Rose Damon  Shi Steve Chen  M. Charley Kameyama 《Visual Geosciences》2008,13(1):105-115

We have developed a new strategy and espouse a novel paradigm for large-scale computing and real-time interactive visualization. This philosophy calls for intense interactive sessions for a couple of hours at a time at the expense of storing data on many disk drives during regular or heroic runs on massively parallel systems. We have already carried out successfully real-time volume-rendering visualization by employing hundreds of processors for a grid with over 25 million unknowns. Both Cartesian and spherical 3D mantle convection are visualized. The volume-rendered images are viewed on a large display device, with many panels holding around 13 million pixels. We will employ a software strategy involving an hierarchical rendering service, which will have as software an Ajax interface for interactive visualization of large data sets on many different platforms from desktop PC’s to hand-held devices, such as the OQO and the Nokia N-800. An option for stereo viewing is also implemented. We have installed a user interface as web application, using Java and Ajax framework in order to achieve over the Internet reasonable accessibility to our ongoing runs. Our goal is to expand the array of interactive devices, which will make it feasible to carry out ubiquitous visualization and monitoring of large-scale simulations or onsite events and to allow for collaborations across oceans.  相似文献   

Assessing SWAT's performance in the Kaskaskia River watershed as influenced by the number of calibration stations used          下载免费PDF全文

Li‐Chi Chiang  Yongping Yuan  Megan Mehaffey  Michael Jackson  Indrajeet Chaubey 《水文研究》2014,28(3):676-687

The Future Midwestern Landscapes (FML) project is part of the U.S. Environmental Protection Agency's Ecosystem Services Research Program. The goal of the FML project is to quantify changes in ecosystem services across the Midwestern region as a result of the growing demand for biofuels. Watershed models are an efficient way to quantify ecosystem services of water quality and quantity. By calibrating models, we can better capture watershed characteristics before they are applied to make predictions. The Kaskaskia River watershed in Illinois was selected to investigate the effectiveness of different calibration strategies (single‐site and multi‐site calibrations) for streamflow, total suspended sediment (TSS) and total nitrogen (TN) loadings using the Soil and Water Assessment Tool. Four USGS gauges were evaluated in this study. Single‐site calibration was performed from a downstream site to an upstream site, and multi‐site calibration was performed and fine‐tuned based on the single‐site calibration results. Generally, simulated streamflow and TSS were not much affected by different calibration strategies. However, when single‐site calibration was performed at the most downstream site, the Nash–Sutcliffe efficiency (NSE) values for TN ranged between ?0.09 and 0.53 at the other sites; and when single‐site calibration was performed at the most upstream site, the NSE values ranged between ?8.38 and ?0.07 for the other sites. The NSE values for TN were improved to 0.5 – 0.59 for all four sites when multi‐site calibration was performed. The results of the multi‐site calibration and validation showed an improvement on model performance on TN and highlighted that multi‐site calibrations are needed to assess the hydrological and water quality processes at various spatial scales. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

A method to map riparian exotic vegetation (Salix spp.) area to inform water resource management          下载免费PDF全文

Tanya M. Doody  Megan Lewis  Richard G. Benyon  Guy Byrne 《水文研究》2014,28(11):3809-3823

Hydrological processes within riparian environments worldwide are impacted when introduced species invade. Monitoring and management at substantial expense, are subsequently required to combat deleterious effects on the environment and stream hydrology. Willow species (Salicaceae: Salix spp.) introduced into Australia have spread throughout many riparian systems causing adverse environmental impacts, with high rates of water extraction when located within stream beds (in‐stream willows) thus altering hydrology. Strategies exist to manage willows; however, simpler, more cost‐effective methods are required to map and monitor spatial and temporal distributions. A method is presented to discriminate willow stands from surrounding native riparian vegetation using a single, very high 2 m resolution multispectral WorldView‐2 satellite image. A combination of spectral bands ‘coastal blue’ (400–450 nm), ‘red’ (630–690 nm), ‘red edge’ (705–745 nm) and ‘near infrared2’ (860–1040 nm), minimum noise fraction transformation, median filtering and maximum likelihood supervised classification provided the highest discriminatory power within a 25 km² study area. Of the spectral bands, coastal blue, red edge and near infrared2 are new bands that are not available in other multispectral sensors. These bands proved critical to the success of discriminating willows from other land cover categories (overall accuracy of 97%). Stream channels were defined by incorporating a LiDAR‐derived digital elevation model to discriminate between willows on stream banks and within stream beds. Canopy area estimates of in‐stream willows, coupled with water savings estimates from willow removal, suggest removal of 10.4 ha of Salix fragilis canopy from within river channels in the study area will potentially return 41 ML year^?1 to the environment. The method presented improves our understanding of willow impacts on hydrology and aids decisions regarding willow removal for water resource management. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Effects of Shoreline Armoring on Beach Wrack Subsidies to the Nearshore Ecotone in an Estuarine Fjord     

Sarah M. Heerhartz  Megan N. Dethier  Jason D. Toft  Jeffery R. Cordell  Andrea S. Ogston 《Estuaries and Coasts》2014,37(5):1256-1268

The ecological significance of algal and seagrass wrack subsidies has been well-documented for exposed-coast sandy beaches but is relatively unstudied in lower-energy and mixed-sediment beaches. In marine nearshore environments where beaches are fringed with riparian vegetation, the potential for reciprocal subsidies between marine and terrestrial ecosystems exists. Within the marine-terrestrial ecotone, upper intertidal “wrack zones” accumulate organic debris from algae, seagrass, and terrestrial plant sources and provide food and shelter for many organisms. Human modification also occurs within this ecotone, particularly in the form of armoring structures for bank stabilization that physically disrupt the connectivity between ecosystems. We conducted detailed wrack and log surveys in spring and fall over 3 years at 29 armored–unarmored beach pairs in Puget Sound, WA, USA. Armoring lowered the elevation of the interface between marine and terrestrial ecosystems and narrowed the width of the intertidal transition zone. Armored beaches had substantially less wrack overall and a lower proportion of terrestrial plant material, while marine riparian zones (especially trees overhanging the beach) were an important source of wrack to unarmored beaches. Armored beaches also had far fewer logs in this transition zone. Thus, they lacked biogenic habitat provided by logs and riparian wrack as well as the organic input used by wrack consumers. Results such as these that demonstrate armoring-associated loss of connectivity across the marine-terrestrial ecotone may be useful in informing conservation, restoration, and management actions.  相似文献   

Multivariate Analysis of Water Quality and Plankton Assemblages in an Urban Estuary     

Megan B. Rothenberger  Thomas Swaffield  Alyssa J. Calomeni  Carolyn D. Cabrey 《Estuaries and Coasts》2014,37(3):695-711

Raritan Bay, located between the states of New York and New Jersey, has a long history of cultural eutrophication and associated harmful algal blooms (HABs). Despite striking chemical and biological alterations occurring in Raritan Bay, publications in the early 1960s were the last to report consecutive measurements of both water quality parameters and plankton species composition in this system. The objectives of this study were to characterize water quality trends and plankton composition in a eutrophic estuary, compare current environmental conditions to those documented in Raritan Bay 50 years ago (i.e., at the same six sampling sites), and to further clarify the relationship among nutrients, secondary consumers, and algal bloom generation in this system using ordination techniques. This study (monthly data collected from April 2010–October 2012) indicates that Raritan Bay continues to exhibit numerous symptoms of eutrophication, including high algal biomass, high turbidity, violations of the dissolved oxygen standard to protect fish health, and blooms of potentially harmful phytoplankton species. Altered spatial and temporal patterns for nitrate and soluble reactive phosphorus (SRP) over the past 50 years may suggest new, changing, or expanding sources of nutrients. A total of 14 HAB species have been identified, including Heterosigma akashiwo, which formed a bloom in the upper Raritan Bay during summer 2012 in association with hypoxic conditions. Multivariate analyses indicate that abundance of this species is positively associated with high temperature, salinity, nitrate, and SRP and negatively associated with spring river discharge rates and total zooplankton abundance in Raritan Bay.  相似文献