Formation of the regular satellites of giant planets in an extended gaseous nebula I: subnebula model and accretion of satellites     

Ignacio Mosqueira  Paul R. Estrada 《Icarus》2003,163(1):198-231

We model the subnebulae of Jupiter and Saturn wherein satellite accretion took place. We expect each giant planet subnebula to be composed of an optically thick (given gaseous opacity) inner region inside of the planet’s centrifugal radius (where the specific angular momentum of the collapsing giant planet gaseous envelope achieves centrifugal balance, located at rCJ ∼ 15R_J for Jupiter and rCS ∼ 22R_S for Saturn) and an optically thin, extended outer disk out to a fraction of the planet’s Roche-lobe (R_H), which we choose to be ∼R_H/5 (located at ∼150 R_J near the inner irregular satellites for Jupiter, and ∼200R_S near Phoebe for Saturn). This places Titan and Ganymede in the inner disk, Callisto and Iapetus in the outer disk, and Hyperion in the transition region. The inner disk is the leftover of the gas accreted by the protoplanet. The outer disk may result from the nebula gas flowing into the protoplanet during the time of giant planet gap-opening (or cessation of gas accretion). For the sake of specificity, we use a solar composition “minimum mass” model to constrain the gas densities of the inner and outer disks of Jupiter and Saturn (and also Uranus). Our model has Ganymede at a subnebula temperature of ∼250 K and Titan at ∼100 K. The outer disks of Jupiter and Saturn have constant temperatures of 130 and 90 K, respectively.Our model has Callisto forming in a time scale ∼10⁶ years, Iapetus in 10⁶-10⁷ years, Ganymede in 10³-10⁴ years, and Titan in 10⁴-10⁵ years. Callisto takes much longer to form than Ganymede because it draws materials from the extended, low density portion of the disk; its accretion time scale is set by the inward drift times of satellitesimals with sizes 300-500 km from distances ∼100R_J. This accretion history may be consistent with a partially differentiated Callisto with a ∼300-km clean ice outer shell overlying a mixed ice and rock-metal interior as suggested by Anderson et al. (2001), which may explain the Ganymede-Callisto dichotomy without resorting to fine-tuning poorly known model parameters. It is also possible that particulate matter coupled to the high specific angular momentum gas flowing through the gap after giant planet gap-opening, capture of heliocentric planetesimals by the extended gas disk, or ablation of planetesimals passing through the disk contributes to the solid content of the disk and lengthens the time scale for Callisto’s formation. Furthermore, this model has Hyperion forming just outside Saturn’s centrifugal radius, captured into resonance by proto-Titan in the presence of a strong gas density gradient as proposed by Lee and Peale (2000). While Titan may have taken significantly longer to form than Ganymede, it still formed fast enough that we would expect it to be fully differentiated. In this sense, it is more like Ganymede than like Callisto (Saturn’s analog of Callisto, we expect, is Iapetus). An alternative starved disk model whose satellite accretion time scale for all the regular satellites is set by the feeding of planetesimals or gas from the planet’s Roche-lobe after gap-opening is likely to imply a long accretion time scale for Titan with small quantities of NH₃ present, leading to a partially differentiated (Callisto-like) Titan. The Cassini mission may resolve this issue conclusively. We briefly discuss the retention of elements more volatile than H₂O as well as other issues that may help to test our model.  相似文献   

Neoliberalism and natural resource management: Agri-environmental standards and the governing of farming practices   总被引：1，自引：0，他引：1  

Vaughan Higgins  Jacqui Dibden  Chris Cocklin 《Geoforum》2008,39(5):1776-1785

Private standards and certification schemes are widely acknowledged as playing an increasingly important role in agri-environmental governance. While much of the existing research concludes that these mechanisms consolidate the global extension of neoliberalism – enhancing the power of corporate actors to the detriment of smaller producers – we argue that this overlooks the complex ways in which standards are used by governments and farmers in the governing of farming practices. Focusing specifically on a process standard – Environmental Management Systems (EMS) – promoted by the Australian government as a way of verifying the ‘clean and green’ status of agricultural exports, we examine how one regional group of producers has sought to use EMS standards in practice. Our analysis of a case study in the state of Victoria appears to confirm that EMS was a successful instrument for the extension of neoliberal governance, reinforcing the production of neoliberal subjectivities and practices amongst farmer participants and enabling the government to compensate for gaps in environmental provision. However, it would be a mistake to interpret the development of this EMS scheme as an example of naïve farmers manipulated by the state. In practice, farmers used the opportunities provided by government funding to undertake actions which expressed their own agri-environmental values and practices. Establishment of an EMS and associated eco-label enabled producers to demonstrate and extend their capacity to act as good environmental stewards. Our research highlights how the local application of environmental standards negotiates and shapes, rather than simply contributes to, neoliberal rule.  相似文献   

海洋水色卫星遥感器特性参数探讨     

于连生 《海洋技术学报》2001,20(2):76-80

为了评价海洋水色卫星遥感器特性参数的优劣，确定仪器的计量特性及其使用价值，准确的理解和科学的定义仪器的特性参数是非常重要的。作者曾有幸参加了海洋水色卫星的立项论证工作，本文就作者的一些工作体会，对海洋水色卫星遥感器的特性参数作初步探讨。  相似文献   

Preparation of a geotechnical microzonation model using Geographical Information Systems based on Multicriteria Decision Analysis   总被引：3，自引：0，他引：3  

a&#x;l Kolat  Vedat Doyuran  Can Ayday  M. Lütfi Süzen 《Engineering Geology》2006,87(3-4):241-255

The purpose of this study is to develop a geotechnical microzonation model using Geographical Information Systems (GIS) based on Multicriteria Decision Analysis (MCDA). As study area, the Eskişehir downtown area has been chosen. Eskişehir is one of the most rapidly growing cities in central Turkey. The model inputs include slope, flood susceptibility, soil, depth to groundwater table, swelling potential, and liquefaction potential. The weight and rank values are assigned to the layers and to the classes of each layer respectively. The assignment of the weight/rank values and the analysis are realized by the application of two different decision models, namely Simple Additive Weighting (SAW) and Analytic Hierarchy Process (AHP) methods. The geotechnical microzonation maps prepared as outputs of these methods are found to be consistent with each other and confirmed by the experts within the study area. The geotechnical microzonation map prepared using the AHP method is recommended as the final map of the study.  相似文献   

Hazard Zoning for Landslides Connected to Torrential Floods in the Jerte Valley (Spain) by using GIS Techniques   总被引：2，自引：0，他引：2  

Carrasco  R.M.  Pedraza  J.  Martin-Duque  J.F.  Mattera  M.  Sanz  M.A.  Bodoque  J.M. 《Natural Hazards》2003,30(3):361-381

The Jerte Valley is anortheast-southwest tending graben located in the mountainous region of west central Spain (Spanish Central System). Mass movements have been a predominant shaping process on the Valley slopes during the Quaternary. Present day activity is characterized as either `first-time failure' (shallow debris slides and debris flows) or `reactivations' of pre-existing landslides deposits.A delineation of landslide hazard zoningwithin the Valley has been carried out by using the detailed documentation of a particular event (a debris slide and a sequel torrential flood, which occurred on the Jubaguerra stream gorge), and GIS techniques. The procedure has had four stages, which are: (1) the elaboration of a susceptibility map (spatial prediction) of landslides; (2) the elaboration of a map of `restricted susceptibility' in the particular case of slopes that are connected to streams and torrents (gorges); (3) the elaboration of a digital model which relates the altitude to the occurrence probability of those particular precipitation conditions which characterized the Jubaguerra event and (4) the combination of the probability model with the `restricted susceptibility map', to establish `critical zones' or areas which are more prone to the occurrence of phenomena that have same typology as this one.  相似文献   

A time-space based approach for mapping rainfall-induced shallow landslide hazard   总被引：2，自引：0，他引：2  

Mowen Xie  Tetsuro Esaki  Meifeng Cai 《Environmental Geology》2004,46(6-7):840-850

A rainfall-induced shallow landslide is a major hazard in mountainous terrain, but a time-space based approach is still an unsettled issue for mapping rainfall-induced shallow landslide hazards. Rain induces a rise of the groundwater level and an increase in pore water pressure that results in slope failures. In this study, an integrated infinite slope analysis model has been developed to evaluate the influence of infiltration on surficial stability of slopes by the limit equilibrium method. Based on this new integrated infinite slope analysis model, a time-space based approach has been implemented to map the distributed landslide hazard in a GIS (Geographic Information Systems) and to evaluate the shallow slope failure induced by a particular rainfall event that accounts for the rainfall intensity and duration. The case study results in a comprehensive time-space landslide hazard map that illustrates the change of the safety factor and the depth of the wetting front over time.  相似文献   

Aquifer’s vulnerability to pollution: a space, time and event dependent measure     

E. Cameron 《Environmental Geology》2005,47(5):653-659

  相似文献   

SoFISHticated policy – social perspectives on the fish conflict in the Northeast Atlantic     

《Marine Policy》2016

Ecosystem changes currently question the traditional allocation of fishing rights and quotas in the fishery of Northeast Atlantic mackerel and Norwegian spring-spawning herring in the Northeast Atlantic. Variability in the distribution of these highly migratory species escalated in a political conflict between member states of the European Union, Iceland, the Faroe Islands and Norway, which is a driving force for unsustainable fishery. The aim of this paper is to investigate this conflict by outlining the social understandings of diverse stakeholders by using the Q methodology. The method reduced the complexity of numerous opinions, detected four distinct perspectives and simultaneously categorised the participating stakeholders. Although the perspectives differ in various elements, the protection of economic interests seems to dominate over the quest for sustainability. The call of all stakeholders in this study to clarify the fishing rights in the Northeast Atlantic reveals a clear deficiency of the current international fishery management in handling abrupt ecological changes and the necessity to acknowledge this as a complex adaptive system.  相似文献   

A MASCOTTE-based characterization of MCSs over Spain, 2000–2002     

R. García-Herrera  E. Hernndez  D. Paredes  D. Barriopedro  J.F. Correoso  L. Prieto 《Atmospheric Research》2005,73(3-4):261-282

A 3-year Mesoscale Convective Systems (MCSs) database, which extends from 2000 to 2002, has been built for the Iberian Peninsula and the Balearic Islands using the objective method MASCOTTE (MAximum Spatial COrrelation Technique). It was originally developed to track the evolution of convective systems over the Amazon region; after modifications, it is able to track MCS evolution even with an hour and a half of missed images and provides essential information of both dynamical and morphological characteristics of MCSs. MASCOTTE is tested against a visual and subjective method, and is found to offer advantages such as automation and a simple and efficient operation that make it very useful for building large MCS databases.Thirty-five MCSs were found between June and October, most of them originated along the Mediterranean coast and near the Pyrenees, showing an increasing occurrence from June to September, when the maximum is found. The regions most influenced by MCS occurrences are Balearic Islands, Valencia, Catalonia, Murcia and the Basque Country. The MCSs tend to be small, short-lived and linear, usually moving eastward or northeastward with low velocities.The MCSs-associated precipitation presents high variability, ranging from 80 to 0 mm h⁻¹ as maximum hourly records. Two different convective regions are identified based on MCS behavior in extreme precipitation events: Northern Spain (the Basque Country) with abundant and continuous precipitation regime but little MCS influence, and the Mediterranean coast, where precipitation is sporadic but much more intense.  相似文献   

建立工程勘察资料信息系统的设计思想   总被引：1，自引：0，他引：1  

陈荣斌  陈道清 《上海国土资源》2002,(4):58-61

随着计算机技术的发展和应用的普及，人们对信息的处理和信息的利用提出了更高的要求。信息系统能及时地输出和传递所需的信息。本文简要地探讨了工程勘察资料信息系统的开发思路。  相似文献