On the velocity of jets powering hot spots similar to those in Cygnus A     

Guy Pelletier  Jacques Roland 《Astrophysics and Space Science》1984,100(1-2):351-357

Hot spots similar to those in the radio galaxy Cygnus A can be explained by the strong shock produced by a supersonic but classical jet \(\left( {u_{jet}< c/\sqrt 3 } \right)\) . The high integrated radio luminosity (L?2×10⁴⁴ erg s^?1) and the strength of mean magnetic field (B?2×10^?4 G) suggest the hot spots are the downstream flow of a very strong shock which generates the ultrarelativistic electrons of energy ?≥20 MeV. The fully-developed subsonic turbulence amplifies the magnetic field of the jet up to 1.6×10^?4 G by the dynamo effect. If we assume that the post-shock pressure is dominated by relativistic particles, the ratio between the magnetic energy density to the energy density in relativistic particles is found to be ?2×10^?2, showing that the generally accepted hypothesis of equipartition is not valid for hot spots. The current analysis allows the determination of physical parameters inside hot spots. It is found that:

1. The velocity of the upstream flow in the frame of reference of the shock isu ₁?0.2c. Radio observations indicate that the velocity of separation of hot spots isu _sep?0.05c, so that the velocity of the jet isu _jet=u ₁+u _sep?0.25c.
2. The density of the thermal electrons inside the hot spot isn ₂?5×10^?3 e ^? cm^?3 and the mass ejected per year to power the hot spot is ?4M ₀yr^?1.
3. The relativistic electron density is less than 20% of the thermal electron density inside the hot spot and the spectrum is a power law which continues to energies as low as 30 MeV.
4. The energy density of relativistic protons is lower than the energy density of relativistic electrons unlike the situation for cosmic rays in the Galaxy.

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Détection de carrières souterraines par sismique haute résolution à Annet-sur-Marne (France)Underground cavities detection by using high resolution seismics at Annet-sur-Marne (France)     

Gilles Grandjean  Guy Sénéchal  Adnand Bitri  Jean-Baptiste Daban 《Comptes Rendus Geoscience》2002,334(7):441-447

Seismic methods were tested to detect underground cavities in the surroundings of Annet-sur-Marne (Seine-et-Marne, France). Cavities are located in three Ludian gypsum layers, between 30 and 80 m in depth. A high resolution seismic profile 450 m long was carried out so that the first third and the other part are respectively above non-exploited and exploited areas. Data processing highlights a series of reflections related to the marl–gypsum interfaces in the non-exploited area, while these reflections disappear in the exploited area. With the help of numerical simulations, this feature is interpreted as a disorganisation of wave fronts reflected on interfaces because of the presence of cavities. To cite this article: G. Grandjean et al., C. R. Geoscience 334 (2002) 441–447.  相似文献   

Influence of the interplanetary magnetic field on cometary and primordial dust orbits: Applications of Lorentz scattering     

Guy J. Consolmagno 《Icarus》1980,43(2):203-214

The equations describing the change in orbital elements of interplanetary dust due to Lorentz-force accelerations are presented in a simplified form. Such accelerations depend on the charge state of the dust; results of theoretical calculations for five possible dust materials are presented. Under present-day conditions, it is possible that semiconducting material such as graphite might carry a net voltage near zero, compared with a roughly 10-V charge expected for other grains. The scattering of dust by a randomly changing magnetic field can be viewed analogously to the dust diffusing in space; the equations presented thus can be used to interpret observations of the present distribution of dust in terms of its possible sources and sinks. The stronger magnetic fields of the early solar system would have led to more vigorous scattering of the dust; particles as large as 1 mm could have been significantly transported by Lorentz scattering during this time.  相似文献   

Lorentz scattering of interplanetary dust     

Guy Consolmagno 《Icarus》1979,38(3):398-410

Charged dust grains in a turbulent magnetic field will see a Lorentz force due to the convection of the solar magnetic field past them at the solar wind velocity. Since the sign of this magnetic field is randomly varying, the direction of the force will be random, and the net effect will be to randomly scatter the orbital elements of these particles. The square roots of the mean square change in semimajor axis, inclination, and eccentricity are determined as a function of the particles' original orbital elements. Particles 3 μm in radius and smaller will have their motions strongly perturbed or dominated by Lorentz scattering. This scattering will have an effect comparable to, or greater than, the Poynting-Robertson effect on these particles for time scales comparable to their Poynting-Robertson lifetimes.  相似文献   

REE patterns versus the origin of the basaltic achondrites     

Guy J. Consolmagno 《Icarus》1979,40(3):522-530

The spectral uniqueness of asteroid 4 Vesta has led to suggestions that it is the eucrite parent body. However, there exist other basaltic achondrite types besides eucrites; either they also came from Vesta or else there exist other achondrite parent bodies. Howardites appear to be mixtures of eucrites and diogenites, and mesosiderites mixtures of eucrites or howardites and iron; thus one may infer that all four classes come from the same parent body. The REE patterns of eucrites and diogenites are modeled in order to test this hypothesis; eucrites can be made easily, but the patterns of diogenites are more difficult to match. The other basaltic achondrites are so rare that one cannot argue from statistics of abundances against a disrupted parent body for their origin. Pallasites and most irons likely had an origin separate from eucrites, again in parent bodies since disrupted.  相似文献   

Benthic primary production, respiration and remineralisation: in situ measurements in the soft-bottom Abra alba community of the western English Channel (North Brittany)     

Aline Mign  Dominique Davoult  Jean-Jacques Bourrand  Guy Boucher 《Journal of Sea Research》2005,53(4):223

In situ measurements of ammonium and carbon dioxide fluxes were performed using benthic chambers at the end of spring and the end of summer in two soft-bottom Abra alba communities of the western English Channel (North Brittany): the muddy sand community (5 m, about 10% of surface irradiance) and the fine-sand community (19 m, about 1% of surface irradiance). High rates of ammonium regeneration were measured in the two communities at the end of summer (296.03±40.07 and 201.7±62.74 μmolN m⁻² h⁻¹, respectively) as well as high respiration rates (2.60±0.94 and 2.23±0.59 mmolC m⁻² h⁻¹, respectively). Significant benthic gross primary production (up to 6.11 mmolC m⁻² h⁻¹) was measured in the muddy sand community but no benthic primary production was measured in the fine-sand community. It suggests that microphytobenthic production values used in simulations previously published for these two communities were overestimated while values of community respiration were underestimated. The study confirms that this benthic system is heterotrophic and strengthens the idea that an important pelagic-benthic coupling is required for the functioning in such coastal ecosystems.  相似文献   

The morphology and migration of transverse bars off the west-central Florida coast     

G. Gelfenbaum  Gregg R. Brooks   《Marine Geology》2003,200(1-4):273-289

A series of migrating shore-normal sandbars with wavelengths of 75–120 m and heights up to 2 m have been identified off the northern tip of Anna Maria Island, a barrier island on the west-central Florida coast. Similar features have been described elsewhere since the 1930s and termed ‘transverse bars’. The transverse bars identified off Anna Maria Island are found for about 3 km along the coast and extend 4 km offshore, well outside the normal surf-zone width. No cusps or any other associated beach expression is evident despite the fact that the bars come to within about 75 m of the beach. Sediments on the crests of the bars are a well-sorted fine quartz sand, whereas sediments in the troughs are a poorly sorted coarse carbonate shell hash. Historical aerial photographs and repeated high-resolution bathymetric surveys provide a means of quantifying the migration of the transverse bars. Analyses of orthorectified aerial photographs from the early 1940s through the mid 1990s clearly show movement or migration taking place in the bar field. In the 40-yr period from 1951 to 1991, the southern edge of the bar field moved 200–350 m to the south, with an average long-term migration rate of 8 m/yr. Repeated bathymetric surveys over an 8-month period give an average short-term migration rate of 21 m/yr to the south. Wave and current measurements suggest that southerly winds associated with the passage of cold fronts drive near-bed currents to the south that are strong enough to initiate sediment transport and cause the southerly migration of the transverse bars.  相似文献   

Structural geochemistry of gold mineralization in the Linglong-Jiaojia district, Shandong Province, China     

Huan-zhang LU Guy Archambault LI Yuansheng WEI Jiaxue 《中国地球化学学报》2007,26(3):215-234

The Linglong-Jiaojia district is one of the most important regions containing gold deposits in China. These gold deposits can be divided into: a) the pyrite-gold-quartz vein type (Linglong type), which is controlled by brittle-ductile to ductile deformation structures, and b) the alteration-zone type (Jiaojia type), characterized by small veinlets, or the disseminated type recognized in brittle shear zones. Lode gold deposits in the Jiaojia area occur in NE brittle fracture zones, formed in a dominantly simple shear deformation regime, mainly in thrust attitude with a minor sinistral strike slip component. In the Linglong area, the lode gold deposits are located at the intersection of three types of structures: NNE and NE brittle-ductile fault zones and the ENE ductile reverse shear zone in the south of the area. The structural characteristics of these brittle shear zones are consistent with a tectonic NNW-SSE principal stress field orientation. Similar stresses explain the ENE Qixia fold axes, the Potouqing and several other ENE reverse ductile shear zones elsewhere in the region, the Tancheng-Lujiang fault zone and its subsidiaries in the vicinity of the Linglong-Jiaojia district, as well as the southern ENE suture zone north of Qingdao. Therefore these structural systems occurred as part of different major tectonic events under NNW-SSE compression principal stress fields in the area. Gold deposits are hosted in smaller-scale structures within the brittle fault zones and brittle-ductile shear zones. Although ore bodies and, on a smaller scale, quartz ore veins often seem to be randomly oriented, it is possible to explain their distribution and orientation in terms of the simple shear deformation process under which they were developed. The progressive simple shear failure is characterized by various fracture modes (tension and shear) that intervene in sequence. The tension and shear fractures are influenced by the stress level (depth of burial beneath the paleosurface) in their structural behavior, show variable dilatancy (void openings) and extend on all scales. By making use of these characteristics, a progressive failure analysis can be applied to predicting the shape and extent of ore bodies as well as the styles of mineralization at any given location.  相似文献   

Sea-breeze scaling from numerical model simulations,Part I: Pure sea breezes     

Aurore Porson  Douw G. Steyn  Guy Schayes 《Boundary-Layer Meteorology》2007,122(1):17-29

Numerical model simulations of sea-breeze circulations under idealized conditions are subjected to dimensional analyses in order to resolve sea-breeze dynamical relations and unify previous results based on observations. The analysis is motivated by the fact that sea-breeze depth scaling and volume flux scaling are only partially understood. The analysis is based on nonlinear numerical modelling simulations in combination with recent observational scaling analyses. The analysis confirms scaling laws for sea-breeze strength dependence on governing variables and shows how the sea-breeze speed scale is controlled by surface heat flux. It also shows that the sea-breeze depth scale is controlled by stability. By combining sea-breeze speed and depth scales, the sea-breeze volume flux scale is determined by an equilibrium between the accumulated convergence of heat over land since sunrise and stable air advection from the sea surface.  相似文献   

A simple model for calculating tsunami flow speed from tsunami deposits   总被引：2，自引：0，他引：2  

Bruce E. Jaffe  Guy Gelfenbuam 《Sedimentary Geology》2007,200(3-4):347-361

This paper presents a simple model for tsunami sedimentation that can be applied to calculate tsunami flow speed from the thickness and grain size of a tsunami deposit (the inverse problem). For sandy tsunami deposits where grain size and thickness vary gradually in the direction of transport, tsunami sediment transport is modeled as a steady, spatially uniform process. The amount of sediment in suspension is assumed to be in equilibrium with the steady portion of the long period, slowing varying uprush portion of the tsunami. Spatial flow deceleration is assumed to be small and not to contribute significantly to the tsunami deposit. Tsunami deposits are formed from sediment settling from the water column when flow speeds on land go to zero everywhere at the time of maximum tsunami inundation. There is little erosion of the deposit by return flow because it is a slow flow and is concentrated in topographic lows. Variations in grain size of the deposit are found to have more effect on calculated tsunami flow speed than deposit thickness. The model is tested using field data collected at Arop, Papua New Guinea soon after the 1998 tsunami. Speed estimates of 14 m/s at 200 m inland from the shoreline compare favorably with those from a 1-D inundation model and from application of Bernoulli's principle to water levels on buildings left standing after the tsunami. As evidence that the model is applicable to some sandy tsunami deposits, the model reproduces the observed normal grading and vertical variation in sorting and skewness of a deposit formed by the 1998 tsunami.  相似文献