On the population, physical decay and orbital distribution of Jupiter family comets: Numerical simulations

We study the Jupiter family comet (JFC) population assumed to come from the Scattered Disk and transferred to the Jupiter’s zone through gravitational interactions with the Jovian planets. We shall define as JFCs those with orbital periods and Tisserand parameters in the range 2<T?3.1, while those comets coming from the same source, but that do not fulfill the previous criteria (mainly because they have periods ) will be called ‘non-JFCs’. We performed a series of numerical simulations of fictitious comets with a purely dynamical model and also with a more complete dynamical-physical model that includes besides nongravitational forces, sublimation and splitting mechanisms. With the dynamical model, we obtain a poor match between the computed distributions of orbital elements and the observed ones. However with the inclusion of physical effects in the complete model we are able to obtain good fits to observations. The best fits are attained with four splitting models with a relative weak dependence on q, and a mass loss in every splitting event that is less when the frequency is high and vice versa. The mean lifetime of JFCs with radii and is found to be of about 150-200 revolutions (∼. The total population of JFCs with radii within Jupiter’s zone is found to be of 450±50. Yet, the population of non-JFCs with radii in Jupiter-crossing orbits may be ∼4 times greater, thus leading to a whole population of JFCs + non-JFCs of ∼2250±250. Most of these comets have perihelia close to Jupiter’s orbit. On the other hand, very few non-JFCs reach the Earth’s vicinity (perihelion distances ) which gives additional support to the idea that JFCs and Halley-type comets have different dynamical origins. Our model allows us to define the zones of the orbital element space in which we would expect to find a large number of JFCs. This is the first time, to our knowledge, that a physico-dynamical model is presented that includes sublimation and different splitting laws. Our work helps to understand the role played by these erosion effects in the distribution of the orbital elements and lifetimes of JFCs.     

Dark Matter and Chemical Evolution of dSph Galaxies

We calculate chemical evolution models for 4 dwarf spheroidal satellites of the Milky Way (Carina, Ursa Minor, Leo I and Leo II) for which reliable non-parametric star formation histories have been derived. We find that galaxies showing one single burst of star formation (Ursa Minor and Leo II) require a dark halo slightly larger that the current estimates for their tidal radii for the gas heated by supernovae to be retained until the observed stellar population has formed. Systems showing extended star formation histories however (Carina and Leo I), are consistent with the idea that their tidally limited dark haloes provide the necessary gravitational potential wells to retain their gas. This revised version was published online in September 2006 with corrections to the Cover Date.     

Physical parameters of the O6.5V+B1V eclipsing binary system LS 1135

The 'All Sky Automated Survey' (ASAS) photometric observations of LS 1135, an O-type single-lined binary (SB1) system with an orbital period of 2.7 d, show that the system is also eclipsing performing a numerical model of this binary based on the Wilson–Devinney method. We obtained an orbital inclination     . With this value of the inclination, we deduced masses   M ₁∼ 30 ± 1 M_⊙  and   M ₂∼ 9 ± 1 M_⊙  , and radii   R ₁∼ 12 ± 1 R_⊙  and   R ₂∼ 5 ± 1 R_⊙  for primary and secondary components, respectively. Both the components are well inside their respective Roche lobes. Fixing the T _eff of the primary to the value corresponding to its spectral type (O6.5V), the T _eff obtained for the secondary component corresponds approximately to a spectral type of B1V. The mass ratio   M ₂/ M ₁∼ 0.3  is among the lowest known values for spectroscopic binaries with O-type components.     

On the instability region around the 5 : 3 Jovian resonance

Variations in the dynamic parameters of Phobos have been determined after reaching critical value of the semi-major axis = 7247 km at which zero-gravity on the surface of Phobos near the equator will take place. The rate of the variations will increase significantly, e.g., in the tidal energy dissipation by one order in magnitude. The total dissipated mechanical energy during the whole tidal history of the system has been estimated as -5.5 × 10²¹ kg m² s^-2, the total decrease in the second zonal Stokes parameter of Phobos as -6.6 × 10^-2.     

Stabilized finite elements for harmonic soil dynamics problems near the undrained-incompressible limit

Simple Finite Element models for soil dynamics and earthquake engineering problems in the frequency domain are a fast and valuable tool providing a first approximation before a full non-linear analysis in the time domain is performed.Quite often the problem concerns saturated soils with very small permeability and pore fluid of neglectable compressibility. In the limit, the permeability is assumed to be zero and the pore fluid incompressible. Here, engineers use standard finite element codes formulated in terms of displacements but incompressibility may result in volumetric locking of the mesh with a severe loss of accuracy.The purpose of this paper is to present a simple mixed finite element formulation in the frequency domain based on displacements and pore pressures as main variables. A suitable stabilization technique allowing for equal order interpolation of displacements and pressures has been introduced for incompressible and zero permeability limits.Of course, the range of application is limited to those problems in which the behaviour of the material can be approximated by linear models, and therefore modelling of phenomena such as liquefaction, cyclic mobility or cavitation occur is excluded.The paper shows as well an extremely simple way of coupling solid and water domains as it occurs for instance in quay walls under dynamic loading.     

江苏——南黄海地区地震活动趋势研究

根据１４９５￣１９９５年地震资料，对江苏－南黄海地区地震活动分期进行了划分，并对本世纪以来两个地震活跃幕以及地震活动趋势进行了详细讨论。基于统计分析方法，给出未来中强地震概率估计，并采用多种方法对未来地震进行了预测探讨。     

新疆地区7级强震的有序性及其预测意义的再认识

280年来，新疆及其邻近地区M≥7级强震在时间间隔上具有良好的有序性，各有序值之间关系密切，其序结构整齐规则，具有预测功能。据此跟踪讨论了1996年阿图什6．9级和喀喇昆仑山7．1级强震后该地区M≥7地震趋势。综合分析结果表明，下次M≥7强震可能发生在2004、2009和2015年前后。     

Traffic-related platinum group elements (PGE) in soils from Mexico City

The first evaluation of the distribution of platinum group elements (PGE) derived from automobile catalytic converters in urban soil samples in Mexico City was carried out. There are more than four millions cars in Mexico City and, at the present time, one third of them have catalytic converters. PGE concentrations in soils exposed to high traffic densities exceed the natural background values by upto two orders of magnitude and are directly influenced by traffic conditions. The highest concentrations of Pt, Pd and Rh in the analyzed samples are about 300, 70 and 40 μg/l, respectively. Although the PGE concentrations found in soil samples are relatively low, they represent an accumulation of only 10 yr. It is likely that the use of catalytic converters will dramatically change the distribution of these metals in the urban environment in the next decades.     

Triple-junction migration during Paleozoic plate convergence: the Aracena metamorphic belt, Hercynian massif, Spain

New data on the petrology and structure of the Aracena metamorphic belt shows that this is a subduction-related, low-pressure/high-temperature complex developed by plate convergence at the north margin of Gondwana during the Paleozoic. The low-pressure, inverted metamorphic gradient in MORB-derived amphibolites resulted from heating from the continental hanging wall during subduction. This implies that the previous heating of the continental rocks was related to subduction of an oceanic ridge and the creation of a slab window beneath the continental margin. This slab window brought the asthenosphere in contact with the continental margin inducing a shallow thermal anomaly and partial melting of the lithospheric mantle resulting in boninite magmatism.     

Morpho-tectonic evolution of the Marmara Sea inferred from multi-beam bathymetric and seismic data

In an initial stage, the Sea of Marmara developed as a graben and, in due course, considerable volumes of sediments were deposited in this basin. Before 200 ka, a new fault (New Marmara Fault) cutting through the whole basin developed, which postdated large sub-marine land sliding in the western part of the basin. This mass movement created the Western Ridge. The initiation of this strike-slip fault indicates that the extensional stress regime was replaced by a new, shearing stress field. In the eastern part of the Marmara Basin, the New Marmara Fault consists of two branches. The northern one replaces the normal faulting at the bottom of the northeastern slope of the basin. As a result, this slope has been rejuvenated. The southern branch is located along the central axis of the basin, forming the major extension of the North Anatolian Fault Zone within the region. Two restraining bends were formed because of the counterclockwise rotation of that part of the Anatolian Block. This resulted the uplifting of the Eastern Ridge and the formation of the positive flower structure within the Tekirdag Basin. The establishment of the compressional regime around the Sea of Marmara also resulted in the northwest–southeast shortening of the initial Marmara Basin.