“Bumerang” Must Return to Earth

Solar System Research - The “Bumerang” space mission to the satellites of Mars is discussed. The purpose of the mission is to study the satellites and return of soil samples from Phobos...     

Asteroid hazard,real problems and practical actions

The paper refers to the current status of asteroid hazard in Russia and abroad. The authors emphasize the relevance of a sober assessment of its real state and specific circumstances working from the principle of reasonable sufficiency. The paper presents a practical approach to the asteroid hazard problem. It consists of a proposal for a mission to the Apophis asteroid and to define the main parameters of this hazardous celestial body. The article also considers how the spacecraft would look, as well as its mission profile for the period of 2012–2014.     

Effective linear damping and stiffness coefficients of nonlinear systems for design spectrum based analysis

A stochastic approach for obtaining reliable estimates of the peak response of nonlinear systems to excitations specified via a design seismic spectrum is proposed. This is achieved in an efficient manner without resorting to numerical integration of the governing nonlinear equations of motion. First, a numerical scheme is utilized to derive a power spectrum which is compatible in a stochastic sense with a given design spectrum. This power spectrum is then treated as the excitation spectrum to determine effective damping and stiffness coefficients corresponding to an equivalent linear system (ELS) via a statistical linearization scheme. Further, the obtained coefficients are used in conjunction with the (linear) design spectrum to estimate the peak response of the original nonlinear systems. The cases of systems with piecewise linear stiffness nonlinearity, along with bilinear hysteretic systems are considered. The seismic severity is specified by the elastic design spectrum prescribed by the European aseismic code provisions (EC8). Monte Carlo simulations pertaining to an ensemble of nonstationary EC8 design spectrum compatible accelerograms are conducted to confirm that the average peak response of the nonlinear systems compare reasonably well with that of the ELS, within the known level of accuracy furnished by the statistical linearization method. In this manner, the proposed approach yields ELS which can replace the original nonlinear systems in carrying out computationally efficient analyses in the initial stages of the aseismic design of structures under severe seismic excitations specified in terms of a design spectrum.     

Anisotropy of magnetic susceptibility investigations of the St Malo dyke swarm (Brittany, France): emplacement mechanism of doleritic intrusions

A high-quality aeromagnetic survey of northern Brittany (line spacing 250  m; flight elevation 150  m) has been used to delineate the Lower Carboniferous St Malo dyke swarm in detail. The dyke swarm fans at its northern and southern ends, and is affected by N60° sinistral transcurrent faults. After restoration of these offsets, the full structure trends in a N–S direction. Small dykes are not imaged, and only one-third of the swarm is evidenced by magnetism. Gravity and magnetic modelling shows that the swarm overlies a single N–S elongated magma chamber.
  The distribution of K _max inclinations of anisotropy of magnetic susceptibility (AMS) suggests that the dykes display a fanning magma flow in section. Computed K _max inclinations are usually shallower than the measured geological dips, probably because the flow becomes more disturbed as the dyke becomes shallower. We observe that the mean susceptibility values increase when the magma flow is steeper than about 70°.
  A detailed cross-section of St Briac dyke, which is part of the St Malo dyke swarm, reveals that the main carrier of magnetization is magnetite in the centre of the dyke and magnetite + maghaemite on its rims. The emplacement of the St Malo dyke swarm could have been contemporaneous with the N60° shearing which displaced the dyke swarm by about 20  km. The dyke swarm is cut at its southern end by an E–W-orientated fault which probably acted during Late Carboniferous times.     

Bathymay : la structure sous-marine de Mayotte révélée par l'imagerie multifaisceaux

The BATHYMAY marine survey was carried out in January 2004 around the French volcanic island of Mayotte, onboard the research vessel Marion Dufresne 2. Multibeam bathymetry revealed for the first time the morphology of the whole outer slope. Preliminary interpretations show broad canyons that deeply incise the slope, numerous volcanoes and huge landslides. Large submarine plateaus are also highlighted, bounded by steep cliffs and active normal faults. A model for Mayotte is suggested, in which eruptive activity, sometimes influenced by normal faulting, was concentrated along a N140° regional line (the Comoros archipelago axis), with landslide activity concentrated on the northeastern and southwestern flanks of this line. To cite this article: J.-C. Audru et al., C. R. Geoscience 338 (2006).     

Deterministic and stochastic analyses of a nonlinear system with a Biot visco‐elastic element

In the paper the Biot hysteretic model involving an infinite collection of elements whose dynamic characteristics are specified through a probability density‐like function is re‐examined; in the limit case, the Biot model yields a dynamic system with ideal hysteretic damping which is known to be problematic for random vibration analysis. It is shown that bona fide Monte Carlo simulations can be conducted for the Biot model by treating, cautiously, the integrodifferential equation which is involved; this is based on recursive calculations of double integrals encountered in the representation of the system dynamics. The numerical results which pertain to the Monte Carlo studies are further used to assess the accuracy of a statistical linearization procedure adopted in determining the response of the hysteretically damped system to white noise. Published in 2001 by John Wiley & Sons, Ltd.     

Optimality in the estimation of a MA system from a long AR model for simulation studies

The determination of moving average (MA) models from a prior autoregressive (AR) approximation of a specified (target) spectral matrix is addressed; this is done in context with the need to simulate ground shaking and other natural phenomena as multivariate random processes. First, an existing technique based on a direct modeling of the target expression is revisited. In this regard, the influence of the order of the prior AR approximation, and the number of its harmonics used in the determination of the MA model, is described. Further, a simple selection technique of these parameters is presented that leads to an optimum MA approximation. Next, the relationship between a method based on the Cholesky factorization of the coveriance matrix and the present technique is investigated to derive additional insight into its convergence properties. Finally, an alternative modeling technique based on an AR representation of the inverse of the target spectral matrix is presented.     

Long-term changes in the benthic communities of the Sea of Azov related to the sedimentation and hydrological regime

The following periods reflected in the composition and distribution of benthic communities are distinguished in the development of the Sea of Azov during the last 80 years: (1) prior to the regulation of the Don River discharge, (2) after its regulation, (3) stabilization of the Don River hydrological regime, and (4) desalination of the sea. The distribution of benthic communities in the Sea of Azov is characterized by concentric patterns, which are distorted due to the changes in the hydrological and oxygen regimes after oxygen depletion. The basic factors that influence the distribution of macrozoobenthic communities are the aeration regime of the sea and the character of the sediment accumulation. The steady distribution of benthic communities composed largely of euryhaline species adapted to the conditions of an unstable salinity in the Sea of Azov shows no correlation with the salinity fluctuations from 9 to 14‰ during the 80-year-long period.     

Taking into account the kinematic effect in methods used for computation of the floodplain riverbeds discharge capacity

Analysis of several methods used for computation of the discharge capacity of floodplain riverbeds showed necessity of taking into account the kinematic effect. This can be done by using the most promising yet not enough developed methodology that is based on the simultaneous equations that describe motion of a stream, mass of which varies along its length. Performed experiments allowed obtaining the correlation between the inertial terms of this equation system, the stream depth and the angle between the divergent dynamic axes of interacting flows. Their maximum values are 80.1 and 24.2%; thus, they are quite significant.