Protostellar Collapse Induced by Compression     

Hennebelle Patrick  Belloche Arnaud  Whitworth Anthony  André Philippe 《Astrophysics and Space Science》2004,292(1-4):355-360

We present numerical simulations of the evolution of low-mass, isothermal, molecular cores which are subjected to an increase in external pressure. If the external pressure increases very slowly, the core approaches instability quite quasi-statically. However, for faster compressions, a compression wave is driven into the core (Hennebelle, P., Whitworth, A., Gladwin, P. and André, P.: 2003a MNRAS 340, 870). Quantitative comparisons with observational velocity and density profiles are presented. The consequences of this compression for the fragmentation of the cloud is investigated and discussed.  相似文献   

Topological and geometric characterization of fault networks using 3-dimensional Generalized maps     

Yvon Halbwachs  Gabriel Courrioux  Xavier Renaud  Philippe Repusseau 《Mathematical Geology》1996,28(5):625-656

The consistent geometric and topological representation of a fault network is possible through a method based on the implementation of 3-dimensional Generalized maps (3-G-map) enabling all subdivisions of space to be represented. The fault network is modeled as an assemblage of polygonal faces from a set of geometric data on the faults and a knowledge of the relationships between the faults. The resultant model is expressed in terms of a 3-G-map in which volume, surface, and topological information is constructed taking into account computed intersections between faults and known interception relations. The fault network can be edited through an interactive 3-D viewer which provides several tools for navigating within the 3-G-map. Information relevant to a fault network, such as block geometry, connectivity, adjacencies, and connectivity relationships, can be obtained by exploring the data structure of the 3-G-map. The fault network architecture is made comprehensive through interactive modeling and visualization.  相似文献   

A constitutive model for the dynamic and high‐pressure behaviour of a propellant‐like material: Part II: Model development and applications     

Harv Trumel  Andr Dragon  Alain Fanget  Philippe Lambert 《国际地质力学数值与分析法杂志》2001,25(6):581-603

This paper presents the second part of a work that aims at developing a mechanical model for the behaviour of propellant‐like materials under high confining pressure and strain rate. The model is to be employed to determine the temperature rise due to mechanical dissipation during a dynamic penetration event. Using the kinematical and thermodynamic background derived in the first part, a viscoelastic–viscoplastic–compaction model is put forward and identified. Viscoelasticity and compaction refer to the elastomeric nature of the material, while viscoplasticity, including implicit damage through dilatancy, reflects its granular nature. Some numerical exercises are performed, in view of determining the major model forces and weaknesses, and of assessing the numerical algorithm robustness. A penetration event is preliminarily simulated, and a temperature rise field predicted. Necessary model improvements are finally discussed, together with several ways of research for a longer term approach. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Revealing the Nature of the Obscured High Mass X-ray Binary IGR J16318-4848     

Sylvain Chaty  Philippe Filliatre 《Astrophysics and Space Science》2005,297(1-4):235-244

The X-ray source IGR J16318-4848 was the first source discovered by INTEGRAL on January 29, 2003. The high energy spectrum exhibits such a high column density that the source is undetectable in X-rays below 2 keV. On February 23–25, 2003 we triggered a Target of Opportunity (ToO) Program using the EMMI and SOFI instruments on the New Technology Telescope of the European Southern Observatory (La Silla) to get optical and near-infrared (NIR) observations. We discovered the optical counterpart, and confirmed the already proposed candidate in the NIR. NIR spectroscopy revealed a large amount of emission lines, including forbidden iron lines and P-Cygni profiles, showing a strong similarity with CI Cam, another strongly absorbed source. Together with the spectral energy distribution (SED), these data point to a high luminosity, high temperature source, with an intrinsic absorption greater than the interstellar absorption, but two orders of magnitude below the X-ray absorption. All these observations show that IGR J16318-4848 is a high mass X-ray binary (HMXB) at a distance between 0.9 and 6.2 kpc, the mass donor being an early-type star, probably a sgB[e] star, surrounded by a dense and absorbing circumstellar material. This would make the second HMXB with a sgB[e] star as the mass donor after CI Cam. Other sources, discovered by INTEGRAL near IGR J16318-4848 in the direction of the Norma arm, present the same characteristics, at least in X-rays. Such sources may represent a different evolutionary state of X-ray binaries previously undetected with the lower energy space telescopes; if it is so, a new class of strongly absorbed X-ray binaries is being unveiled by INTEGRAL. Out of the 15 sources present in this region, only one might be associated with an unidentified EGRET source: IGR J16393-4643. Therefore these obscured INTEGRAL sources do not seem to be powerful high energy (E > 100 MeV) emitters. Based on observations collected at the European Southern Observatory, Chile (proposal ESO N^∘ 70.D-0340).  相似文献   

Modelling a geo-composite cell using discrete analysis     

David Bertrand  Franois Nicot  Philippe Gotteland  Stphane Lambert 《Computers and Geotechnics》2005,32(8):564-577

Reinforced soil structures can be used to protect infrastructures against rockfalls. An innovative way to implement such protection is to construct the front face using a cellular assembly. This paper focuses on the cellular scale, with the cell a complex heterogeneous material, composed of a wire netting box filled with rocky particles. The behaviour of a single cell was modelled using the discrete element method, thus accounting for the interaction between the rocky particles and the interaction between the box and the rocky particles. A constitutive model was developed and calibrated along confined compression loading paths, then preliminary elements of validation were obtained from the simulation of unconfined compression tests.  相似文献   

Dating of Little Ice Age glacier fluctuations in the tropical Andes: Charquini glaciers,Bolivia, 16°S     

Antoine Rabatel  Vincent Jomelli  Philippe Naveau  Bernard Francou  Delphine Grancher 《Comptes Rendus Geoscience》2005,337(15):1311-1322

Fluctuations of the Charquini glaciers (Cordillera Real, Bolivia) have been reconstructed for the Little Ice Age (LIA) from a set of 10 moraines extending below the present glacier termini. A lichenometric method using the Rhizocarpon geographicum was used to date the moraines and reconstruct the main glacier fluctuations over the period. The maximum glacier extent occurred in the second half of the 17th century, followed by nearly continuous retreat with three interruptions during the 18th and the 19th centuries, marked by stabilisation or minor advances. Results obtained in the Charquini area are first compared with other dating performed in the Peruvian Cordillera Blanca and then with the fluctuations of documented glaciers in the Northern Hemisphere. Glacier fluctuations along the tropical Andes (Bolivia and Peru) were in phase during the LIA and the solar forcing appears to be important during the period of glacier advance. Compared with the Northern Hemisphere mid-latitudes, the major advance observed on these glaciers during the first half of the 19th century is not present in the tropical Andes. This discrepancy may be due to regional scale climate variations. To cite this article: A. Rabatel et al., C. R. Geoscience 337 (2005).  相似文献   

Paleo-deviatoric stress magnitudes from calcite twins and related structural permeability evolution in minor faults: Example from the toarcian shale of the French Causses Basin, Aveyron, France     

Joël Constantin  Philippe Laurent  Pierre Vergly  Justo Cabrera 《Tectonophysics》2007,429(1-2):79-97

The relationship between deformation and so-called fluid paleotransfers in minor faults has been analysed in an argillaceous formation located in the Causses Basin in France. The fluid paleotransfers are related to the fault activity to a large extent. We attempt to estimate the intensity of paleo-deviatoric stress magnitudes under which the fault activity may have occurred and consequently, the change in the structural fault permeability. The paleo-deviatoric stress magnitudes were calculated with the inverse method of Etchecopar applied to calcite twinning. The measured crystals are contained within the core zone of minor faults and this study is based on a previous complete microtectonic and microstructural analysis of the faults. In this paper, analysis of calcite twinning has been applied for the first time to vein fillings associated small faults in a context of relatively weak deformation, a condition ensured by the tectonic and structural analysis. Calculation and discussion of the paleo-deviatoric stress tensors in relation to the evolution of the structural fault permeability and to the hydraulic behaviour of the faults are the aim of this paper. The analysed faults, created and active during the same tectonic event, were permeable under a (σ₁–σ₃) mean value of 40–50 MPa. On the other hand, the reactivation of faults during a second tectonic event implies mean (σ₁–σ₃) value higher than 40–50 MPa, especially for the faults that are poorly oriented with respect to the principal tectonic stress directions. The core zone of these faults remained sealed and impermeable or became permeable by development of microcracks inside the pre-existing fillings.  相似文献   

Erratum to “The identification of an active fault by a multidisciplinary study at the archaeological site of Sagalassos (SW Turkey)” [Tectonophysics Volume 420 (2006) 371–387]     

Dominique Similox-Tohon  Manuel Sintubin  Philippe Muchez  Griet Verhaert  Kris Vanneste  Max Fernandez  Sara Vandycke  Hannelore Vanhaverbeke  Marc Waelkens   《Tectonophysics》2007,435(1-4):55-62

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The identification of an active fault by a multidisciplinary study at the archaeological site of Sagalassos (SW Turkey)     

Dominique Similox-Tohon  Manuel Sintubin  Philippe Muchez  Griet Verhaert  Kris Vanneste  Max Fernandez  Sara Vandycke  Hannelore Vanhaverbeke  Marc Waelkens   《Tectonophysics》2006,420(3-4):371-387

The archaeological site of Sagalassos (SW Turkey) is located in a region characterized by the absence of any significant recent seismic activity, contrary to adjacent regions. However, the assessment of earthquake-related damage at the site suggests that the earthquakes that have been demonstrated to have struck this Pisidian city in ca. AD 500 and in the middle or second half of the 7th century AD are characterized by an MSK intensity of at least VIII and occurred on a fault very close to the city. Different investigation techniques (archaeoseismology, remote sensing and geomorphology, surface geology and structural data, 2D resistivity imaging and palaeoseismological trenching) have been applied at the archaeological site and its direct surroundings in search for the causative fault of these earthquakes. This multidisciplinary approach shows that each of the different approaches independently provides only partial, non-conclusive information with respect to the fault identification. Integration is imperative to give a conclusive answer in the search for the causative fault. This study has, indeed, revealed the existence of a to date unknown active normal fault system passing underneath ancient Sagalassos, i.e. the Sagalassos fault. A historical coseismic surface rupture event on this fault could be identified. This event possibly corresponds to the devastating Sagalassos earthquakes of ca. AD 500 and the middle or second half of the 7th century AD. Finally, this study demonstrates that in the particular geodynamic setting of SW Turkey archaeological sites with extensive earthquake-related damage form an important tool in any attempt to asses the seismic hazard.  相似文献   

Acid-base activity of live bacteria: Implications for quantifying cell wall charge     

Jacqueline Claessens  Yvonne van Lith  Philippe Van Cappellen 《Geochimica et cosmochimica acta》2006,70(2):267-276

To distinguish the buffering capacity associated with functional groups in the cell wall from that resulting from metabolic processes, base or acid consumption by live and dead cells of the Gram-negative bacterium Shewanella putrefaciens was measured in a pH stat system. Live cells exhibited fast consumption of acid (pH 4) or base (pH 7, 8, 9, and 10) during the first few minutes of the experiments. At pH 5.5, no acid or base was required to maintain the initial pH constant. The initial amounts of acid or base consumed by the live cells at pH 4, 8, and 10 were of comparable magnitudes as those neutralized at the same pHs by intact cells killed by exposure to gamma radiation or ethanol. Cells disrupted in a French press required higher amounts of acid or base, due to additional buffering by intracellular constituents. At pH 4, acid neutralization by suspensions of live cells stopped after 50 min, because of loss of viability. In contrast, under neutral and alkaline conditions, base consumption continued for the entire duration of the experiments (5 h). This long-term base neutralization was, at least partly, due to active respiration by the cells, as indicated by the build-up of succinate in solution. Qualitatively, the acid-base activity of live cells of the Gram-positive bacterium Bacillus subtilis resembled that of S. putrefaciens. The pH-dependent charging of ionizable functional groups in the cell walls of the live bacteria was estimated from the initial amounts of acid or base consumed in the pH stat experiments. From pH 4 to 10, the cell wall charge increased from near-zero values to about −4 × 10⁻¹⁶ mol cell⁻¹ and −6.5 × 10⁻¹⁶ mol cell⁻¹ for S. putrefaciens and B. subtilis, respectively. The similar cell wall charging of the two bacterial strains is consistent with the inferred low contribution of lipopolysaccharides to the buffering capacity of the Gram-negative cell wall (of the order of 10%).  相似文献