The evolution of an impact-generated atmosphere

Shock wave and thermodynamic data for rock-forming and volatile-bearing minerals are used to determine minimum impact velocities (v_cr) and minimum impact pressures (p_cr) required to form a primary H₂O atmosphere during planetary accretion from chondritelike planetesimals. The escape of initially released water from an accreting planet is controlled by the dehydration efficiency. Since different planetary surface porosities will result from formation of a regolith, v_cr and p_cr can vary from 1.5 to 5.8 km/sec and from 90 to 600 kbar, respectively, for target porosities between 0 and ～45%. On the basis of experimental data, hydration rates for forsterite and enstatite are derived. For a global regolith layer on the Earth's surface, the maximum hydration rate equals 6 × 10¹⁰ g H₂O sec^?1 during accretion of the Earth. Attenuation of impact-induced shock pressure is modeled to the extent that the amount of released water as a function of projectile radius, impact velocity, weight fraction of water in the target, target porosity, and dehydration efficiency can be estimated. The two primary processes considered are the impact release of water bound in hydrous minerals (e.g., serpentine) and the subsequent reincorporation of free water by hydration of forsterite and enstatite. These processes are described in terms of model calculations for the accretion of the Earth. Parameters which lead to a primary atmosphere/hydrosphere are: an accretion time of ? 1.6 × 10⁸years, the use of an accretion model defined by Weidenschilling (1974, 1976), a mean planetesimal radius of 0.5 km, a hydration rate of 6 × 10¹⁰ g H₂O sec^?1 inferred from a mean porosity of ～ 10% for the upper 1 km of the accreting Earth, and values for the dehydration efficiency, DE, of 0.55 and 0.07 for the maximum and minimum pressure decay model, respectively. Conditions which prohibit the formation of a primary atmosphere include an accretion time much longer than 1.6 × 10⁸ years, a hydration rate for forsterite and enstatite well in excess of 6 × 10¹⁰ g H₂O sec^?1, and a dehydration efficiency DE < 0.07. We conclude that the concept of dehydration efficiency is of dominant importance in determining the degree to which an accreting planet acquires an atmosphere during its formation.     

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Ohne Zusammenfassung     

Beobachtungen der Geminiden und Quadrantiden

Geminids and Quadrantids are probably observed for only about 100 years. Due to perturbations of their orbits rapid variations occur. A change in the Geminid rate profile can not be found from observations. Observations of Geminids and Quadrantids from Arbeitskreis Meteore are compared with Perseid results. Around their activity peaks we find an increasing number of bright meteors. At the same time the population index r decreases for Perseids and Quadrantids, while it increases for Geminids. From this behaviour we estimate the increase of the number density to fainter magnitude classes for the three showers.     

A scanning microphotometer with an on-line data reduction for large field Schmidt plates

The mechanical and electronic device of the microphotometer is described. The on-line data compression is performed in the domain of the HAAR transform of the measurement points. This method provides a fast treatment of the measurement data in the computer and changes the large data material sampled in equidistant steps whose width can be chosen by the seeing condition into a non-equidistant grid whose widths depend only on the characteristic length of the signal. The grain noise is eliminated. An automatical discrimination between stars and galaxies is possible. The accuracy of the photometry was tested by comparing with the photoelectrically determined B-brightness distribution of M 81.     

Berriasian (Early Cretaceous) radiometric ages from the Grindstone Creek Section, Sacramento Valley, California

The Grindstone Creek Section, Glenn County, Northern California is a sequence of hemipelagic mudstone, siltstone and sandstone interbedded with concretionary limestone and a few thin tuffs and bentonites. Two tuffs have been collected from a narrow interval of this sequence and subjected to mineralogical and isotopic analyses. U&z.sbnd;Pb isotopic analyses of zircon fractions from these volcanic horizons indicate an age of 137.1 + 1.6/−0.6 Ma. A detailed investigation has been conducted on the calcareous nannofossil stratigraphy of this section based on numerous samples with moderately preserved assemblages. The nannoflora is largely of Tethyan affinity, and allows direct correlation with the Berriasian stratotype section, with sections with published magnetostratigraphies and with a DSDP site drilled between known magnetic anomalies. The dated tuffs lie in the lower part of the upper BerriasianCretarhabdus angustiforatus Zone (Assipetra infracretacea Subzone) and within the narrow range ofRhagodiscus nebulosus. At three different sections, this subzone can be correlated with M-sequence Polarity Zones M16 and M16n. An independent magnetostratigraphic correlation is provided at DSDP Site 387, drilled between anomalies M15 and M16, where basal sediments containR. nebulosus. Buchia collected within a meter of the lower tuff lie within theB. uncitoides Zone which is Berriasian in age. The upper tuff level, which occurs 65 m above the lower tuff, is situated within the overlyingB. pacifica Zone. This zone had previously been correlated with the early Valanginian, but is clearly also partly of Berriasian age based on nannofossil stratigraphy. Our results allow an estimate of the age of the Berriasian-Valanginian and Jurassic-Cretaceous boundaries of 135.1 Ma and 141.1 Ma, respectively, and these fall within the range of, but differ significantiy from, several published time-scales.     

Synthetic scenario generation of monthly streamflows conditioned to the El Niño–Southern Oscillation: application to operation planning of hydrothermal systems

Stochastic Environmental Research and Risk Assessment - The Brazilian Interconnected Power System is hydro dominated and characterized by large reservoirs presenting multi-year regulation...     

2009年9月印度尼西亚巴东地震

2009年9月30日,印度尼西亚巴东市发生7.6级地震。之后,印度尼西亚又接连遭受了几次强震袭击,如2009年12月23日6.1级、2010年3月6日7.1级、2010年4月7日7.8级和2010年5月9日7.4级地震。2010年6月16日一天之内,印度尼西亚又接连发生了3次地震,震级分别为6.3级、7.0级和6.3级。2010年2月,由John McCloskey领军的一个科学家团队就2009年9月巴东地震致函英国《自然—地球科学》杂志(Nature Geoscience),题为:The September 2009 Padang Earthquake。信中提出警告:印度尼西亚苏门答腊沿海地区或将发生引发巨大海啸的强烈地震,其灾害程度足以造成与2004年南亚大海啸相匹敌的惨重伤亡,提醒居民要为更加强烈的地震来袭做好准备。为此,"Nature Geoscience"特发表了一篇社论,题为:Earthquakes off Sumatra(见本期译文"苏门答腊近海地震")。下边是John McCloskey等致"Nature Geoscience"的信函译文。     

Using the SDIlight Approach in Teaching a Geoinformatics Master

ITC, the Faculty of Geo–Information Science and Earth Observation of the University of Twente, is an institute that aims at capacity building and institutional development, specifically in developing countries. In our Geoinformatics curriculum, we emphasise two principles. The first addresses the systematics of purposeful spatial data production and uptake into computerised systems; the second addresses the methodical construction of these computerised systems, applying principles of model – driven architecture, formal specification and transformational design of SDI nodes. The term Spatial Data Infrastructure (SDI) usually denotes large, complex systems, but its principles can also be applied in simple and cost–effective ways. This approach we have called SDI^light and it is of particular interest to our students that come from developing countries. We work with and build a software stack consisting of free and open source components. To achieve interoperability, we emphasise the use of open standards from the Open Geospatial Consortium and others. In this paper, we explain how our students apply the SDI^light approach in the GeoinformaticsMaster degree course. An important part of that course is a Case Study Application Building & Programming, in which students apply their knowledge in a ‘real–world’ project, with a focus on geo–information engineering skills. We conclude with a section that evaluates the effectiveness of using the SDI^light concept in teaching our Geoinformatics Master, and on the more general applicability of the methodology.     

Matching INSPIRE Quality of Service Requirements with Hybrid Clouds

A lot of effort has been invested in Spatial Data Infrastructures (SDIs) during the last decade regarding interoperable standards for services and data. But still the scalability and performance of SDI services is reported to be crucial especially if they are accessed concurrently by a high number of users. Furthermore, laws and provisions such as the INSPIRE directive specify challenging requirements regarding the performance, availability and scalability of SDI services. This article presents a Hybrid Cloud architecture for matching INSPIRE‐related Quality of Service (QoS) requirements, without investing in rarely used hardware in advance, by occupying external third‐party resources on a pay‐as‐you‐go basis. The presented Hybrid Cloud is a composition of a local IT‐infrastructure (Private Cloud) and the computational resources of third‐party vendors (Public Cloud). The local infrastructure is laid out to handle the average main load of a service and in lasting peak times additional resources of external providers are allocated and integrated on demand into the local infrastructure to provide sufficient service quality automatically. A proof‐of‐concept implementation of the proposed Hybrid Cloud approach is evaluated and benchmarked with respect to INSPIRE‐related QoS requirements.