Solar system history as recorded in the saturnian ring structure     

Hannes Alfvén 《Astrophysics and Space Science》1983,97(1):79-94

The paper is based on Holberg's analysis of the Voyager photographs in both reflected and transparent light, combined with occultation data of stars seen through the rings. Besides rapidly varying phenomena (spokes, braided ring, etc.), which according to Mendis are due to gravito-electromagnetic effects, the ring consists of abulk structure, a fine structure, and also ahyperfine structure, showing more than 10000 ringlets. The large number of ringlets can be explained by the Baxter-Thompson ‘negative diffusion’. This gives the ringlets a stability which makes it possible to interprete them as ‘fossils’, which originated at cosmogonic times. It is shown that thebulk structure can be explained by the combined ‘cosmogonic shadows’ of Mimas, the co-orbiting satellites, and the Shepherd satellites. This structure originated at the transition from the plasma phase to the planetesimal phase (which probably took place 4–5×10⁹ y ago). Further, Holberg has discovered that the shadows are not simple void region but exhibit a certain characteristic ‘signature’. This is not yet understood theoretically. Parts of thefine structure are explained by Holberg as resonances with the satellites. Parts are here interpreted as cosmogonic shadow effects. However, there are a number of ringlets which can neither be explained by cosmogonic nor by resonance effects. The most important conclusion is that an analysis of the ring data is likely to lead to areconstruction of the plasma-planetesimal transition with an accuracy of a few percent.  相似文献   

Interstellar clouds and the formation of stars     

Hannes Alfvén  Per Carlqvist 《Astrophysics and Space Science》1978,55(2):487-509

Part I gives a survey of the drastic revision of cosmic plasma physics which is precipitated by the exploration of the magnetosphere throughin situ measurements. The pseudo-plasma formalism, which until now has almost completely dominated theoretical astrophysics, must be replaced by an experimentally based approach involving the introduction of a number of neglected plasma phenomena, such as electric double layers, critical velocity, and pinch effect. The general belief that star light is the main ionizer is shown to be doubtful; hydromagnetic conversion of gravitational and kinetic energy may often be much more important.In Part II the revised plasma physics is applied to dark clouds and star formation. Magnetic fields do not necessarily counteract the contraction of a cloud; they may just as well pinch the cloud. Magnetic compression may be the main mechanism for forming interstellar clouds and keeping them together.Part III treats the formation of stars in a dusty cosmic plasma cloud. Star formation is due to an instability, but it is very unlikely that it has anything to do with the Jeans instability. A reasonable mechanism is that the sedimentation of dust (including solid bodies of different size) is triggering off a gravitationally assisted accretion. A stellesimal accretion analogous to the planetesimal accretion leads to the formation of a star surrounded by a very low density hollow in the cloud. Matter falling in from the cloud towards the star is the raw material for the formation of planets and satellites.The study of the evolution of a dark cloud leads to a scenario of planet formation which is reconcilable with the results obtained from studies based on solar system data. This means that the new approach to cosmical plasma physics discussed in Part I logically leads to a consistent picture of the evolution of dark clouds and the formation of solar systems.  相似文献   

Geology of the Heimaey volcanic centre, south Iceland: early evolution of a central volcano in a propagating rift?     

Hannes Mattsson  rmann Hskuldsson 《Journal of Volcanology and Geothermal Research》2003,127(1-2):55-71

Heimaey is the southernmost and also the youngest of nine volcanic centres in the southward-propagating Eastern Volcanic Zone, Iceland. The island of Heimaey belongs to the Vestmannaeyjar volcanic system (850 km²) and is situated 10 km off the south coast of Iceland. Although Heimaey probably started to form during the Upper Pleistocene all the exposed subaerial volcanics (10 monogenetic vents covering an area of 13.4 km²) are of Holocene age. Heimaey is composed of roughly equal amounts of tuff/tuff-breccias and lavas as most eruptions involve both a phreatomagmatic and an effusive phase. The compositions of the extrusives are predominantly alkali basalts belonging to the sodic series. Repeated eruptions on Heimaey, and the occurrence of slightly more evolved rocks (i.e. hawaiite approaching mugearite), might indicate that the island is in an early stage of forming a central volcano in the Vestmannaeyjar system. This is further substantiated by the development of a magma chamber at 10–20 km depth during the most recent eruption in 1973 and by the fact that the average volume of material produced in a single eruption on Heimaey is 0.32 km³ (dense rock equivalent), which is twice the value reported for the Vestmannaeyjar system as a whole. We find no support for the previously postulated episodic behaviour of the volcanism in the Vestmannaeyjar system. However, the oldest units exposed above sea level, i.e. the Norðurklettar ridge, probably formed over a 500-year interval during the deglaciation of southern Iceland. The absence of equilibrium phenocryst assemblages in the Heimaey lavas suggests that magma rose quickly from depth, without long-time ponding in shallow-seated crustal magma chambers. Eruptions on Heimaey have occurred along two main lineaments (N45°E and N65°E), which indicate that it is seismic events associated with the southward propagation of the Eastern Volcanic Zone that open pathways for the magma to reach the surface. Continuing southward propagation of the Eastern Volcanic Zone suggests that the frequency of volcanic eruptions in the Vestmannaeyjar system might increase with time, and that Heimaey may develop into a central volcano like the mature volcanic centres situated on the Icelandic mainland.  相似文献   

Fractional crystallization of Si-undersaturated alkaline magmas leading to unmixing of carbonatites on Brava Island (Cape Verde) and a general model of carbonatite genesis in alkaline magma suites     

Daniel Weidendorfer  Max W. Schmidt  Hannes B. Mattsson 《Contributions to Mineralogy and Petrology》2016,171(5):43

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Zum Abbau von Formaldehyd durch adaptierte Bakterien     

U. Behrens  J. Hannes 《洁净——土壤、空气、水》1984,12(1):39-45

Municipal activated sludge was cultivated in a medium composed of formaldehyde, glucose and mineral salt. By passages with increasing formaldehyde content a bacterial culture was selected which remained active also at initial concentrations of 1 g/1 formaldehyde. With this culture, formaldehyde and glucose were oxidized simultaneously to formate and gluconate, which subsequently served simultaneously as substrate for the growth of bacteria. Glucose alone was also oxidized to gluconate, which then was used as substrate for growth. Formaldehyde alone was only oxidized. If the actual formaldehyde concentration was kept low, however, by fed-batch cultivation, it was assimilated also through formate formation. The biochemical background and the importance of the findings for the purification of formaldehyde-containing wastewaters are discussed.  相似文献   

Reporting negative results to stimulate experimental hydrology: discussion of “The role of experimental work in hydrological sciences – insights from a community survey”*     

Tim van Emmerik  Andrea Popp  Anna Solcerova  Hannes Müller  Rolf Hut 《水文科学杂志》2020,65(Z2):1269-1272

ABSTRACT

Experimental work in hydrology is in decline. Based on a community survey, Blume et al. showed that the hydrological community associates experimental work with greater risks. One of the main issues with experimental work is the higher chance of negative results (defined here as when the expected or wanted result was not observed despite careful experimental design, planning and execution), resulting in a longer and more difficult publishing process. Reporting on negative results would avoid putting time and resources into repeating experiments that lead to negative results, and give experimental hydrologists the scientific recognition they deserve. With this commentary, we propose four potential solutions to encourage reporting on negative results, which might contribute to a stimulation of experimental hydrology.  相似文献   

Caledonian eclogite-facies metamorphism of Early Proterozoic protoliths from the North-East Greenland Eclogite Province     

Hannes K. Brueckner  Jane A. Gilotti  Allen P. Nutman 《Contributions to Mineralogy and Petrology》1998,130(2):103-120

High-pressure metamorphic assemblages occur in mafic, ultramafic and a few intermediate rocks in a gneiss complex that covers an area of approximately 400 × 100 km in the North-East Greenland Caledonides. Detailed petrologic and geochronologic studies were carried out on three samples in order to clarify the P-T-t evolution of this eclogite province. Geothermobarometry yields temperature estimates of 700–800 °C and pressure estimates of at least 1.5 GPa from an eclogite sensu stricto and as high as 2.35 GPa for a garnet websterite. The eclogite defines a garnet-clinopyroxene-amphibole-whole rock Sm-Nd isochron age of 405 ± 24 Ma (MSWD 0.9). Isofacial garnet websterites define garnet-clinopyroxene-orthopyroxene-amphibole-whole rock-(biotite) ages of 439 ± 8 Ma (MSWD =2.1) for a coarse-grained sample and 370 ± 12 Ma (MSWD=0.6) for a finer-grained variety. Overgrowths on zircons from the fine-grained pyroxenite and the eclogite give a pooled ²⁰⁶Pb/²³⁸U SHRIMP age of 377 ± 7 Ma (n=4). Significantly younger Rb-Sr biotite ages of 357 ± 8, 330 ± 6 and 326 ± 6 agree with young Rb-Sr, K-Ar and ⁴⁰Ar/³⁹Ar mineral ages from the gneiss complex and indicate slow cooling of the eclogitic rocks. High-pressure metamorphism may have been at least 439 Ma old (Siluro-Ordovician) with cooling through amphibolite-facies conditions in the Devonian and continued crustal thinning and exhumation well into the Carboniferous. Sm-Nd whole rock model ages indicate the eclogite protoliths are Early Proterozoic in age, while ²⁰⁷Pb/²⁰⁶Pb SHRIMP ages of 1889 ± 18 and 1981 ± 8 from anhedral zircon cores probably reflect Proterozoic metasomatism. The samples have negative ɛ_Nd values (−5 to −16) and elevated ⁸⁷Sr/⁸⁶Sr ratios (0.708–0.715), consistent with field evidence that the eclogite protoliths were an integral part of the continental crust long before Caledonian metamorphism. The presence of a large Caledonian eclogite terrane in Greenland requires modification of current tectonic models that postulate subduction of Baltica beneath Laurentia during the Caledonian orogeny. Received: 9 October 1996 / Accepted: 7 July 1997  相似文献   

Airborne near-real-time monitoring of assembly and parking areas in case of large-scale public events and natural disasters     

Hannes Römer  Jens Kersten  Ralph Kiefl  Stefan Plattner  Alexander Mager  Stefan Voigt 《International journal of geographical information science》2014,28(4):682-699

A critical requirement for an effective and coordinated response by public entities tasked with management, security, and relief during large-scale public events or natural disasters is the availability of current situational information. However, today there is a lack of comprehensive operational systems allowing a near-real-time (NRT) collection, visualization, and provision of situational information for larger areas. In this study a methodological framework is proposed, which allows an NRT extraction and visualization of situational information based on aerial image acquisition. The framework combines digital image analysis using a generic supervised information extraction approach based on statistical modeling with a downstream web-based visualization component realized through an automatic update of web services. Even though being applicable for different scenarios, the workflow will be demonstrated for the specific use-case of a NRT monitoring of open spaces including assembly and parking areas. Compared to other approaches, image analysis results indicate a high robustness and a low demand for computational power sources (7 seconds per image). Due to a high degree of automation, the proposed workflow contributes to a NRT ‘end-to-end’ monitoring system, which was developed within the VABENE (German acronym for ‘traffic management under large-scale public events and disaster conditions’) project covering all parts from the acquisition of raw aerial imagery to the dissemination of information products to end-users.  相似文献   

Sedimentology,three‐dimensional geobody reconstruction and carbon dioxide origin of Pleistocene travertine deposits in the Ballık area (south‐west Turkey)          下载免费PDF全文

Hannes Claes  Jeroen Soete  Koen Van Noten  Hamdy El Desouky  Marcelle Marques Erthal  Frank Vanhaecke  Mehmet Özkul  Rudy Swennen 《Sedimentology》2015,62(5):1408-1445

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Magnetization of celestial bodies with special application to the primeval Earth and Moon     

Hannes Alfvén  Lennart Lindberg 《Earth, Moon, and Planets》1974,10(3-4):323-335

The magnetic fields of celestial bodies are usually supposed to be due to a ‘hydromagnetic dynamo’. This term refers to a number of rather speculative processes which are supposed to take place in the liquid core of a celestial body. In this paper we shall follow another approach which is more closely connected with hydromagnetic processes well-known from the laboratory, and hence basically less speculative. The paper should be regarded as part of a general program to connect cosmical phenomena with phenomena studied in the laboratory. As has been demonstrated by laboratory experiments, a poloidal magnetic field may be increased by the transfer of energy from a toroidal magnetic field through kink instability of the current system. This mechanism can be applied to the fluid core of a celestial body. Any differential rotation will produce a toroidal field from an existing poloidal field, and the kink instability will feed toroidal energy back to the poloidal field, and hence amplify it. In the Earth-Moon system the tidal braking of the Earth's mantle acts to produce a differential angular velocity between core and mantle. The braking will be transferred to the core by hydromagnetic forces which at the same time give rise to a strong magnetic field. The strength of the field will be determined by the rate of tidal braking. It is suggested that the magnetization of lunar rocks from the period ?4 to ?3 Gyears derives from the Earth's magnetic field. As the interior of the Moon immediately after accretion probably was too cool to be melted, the Moon could not produce a magnetic field by hydromagnetic effects in its core. The observed lunar magnetization could be produced by such an amplified Earth field even if the Moon never came closer than 10 or 20 Earth's radii. This hypothesis might be checked by magnetic measurements on the Earth during the same period.  相似文献