A qualitative model for the simulation of traffic behaviours in a multi-lane environment

Qualitative modelling of spatial relationships has often been considered as a contextindependent task that aims at a reasoning model in generic form. Despite the primary interest in these models, there is still a sufficiently large scope for context-dependent reasoning in space and time. This paper proposes a qualitative spatial reasoning model, oriented to the modelling and simulation of several cars acting in a multi-lane circuit, which can be considered as an illustrative example of a constrained frame of reference. The modelling objects of interest are individual cars whose cardinal relationships to external cars and actions are modelled. This dynamic system is analysed, and a set of interrelationships is identified at different levels of abstraction, together with inference rules that model the displacement of several cars in a circuit. The potential of this model is illustrated and calibrated using an agent-based prototype.     

The retrieval of cloud microphysical properties using satellite measurements and an in situ database

By combining AVHRR data from the NOAA satellites with information from a database of in situ measurements, large-scale maps can be generated of the microphysical parameters most immediately significant for the modelling of global circulation and climate. From the satellite data, the clouds can be classified into cumuliform, stratiform and cirrus classes and then into further sub-classes by cloud top temperature. At the same time a database of in situ measurements made by research aircraft is classified into the same sub-classes and a statistical analysis is used to derive relationships between the sub-classes and the cloud microphysical properties. These two analyses are then linked to give estimates of the microphysical properties of the satellite observed clouds. Examples are given of the application of this technique to derive maps of the probability of occurrence of precipitating clouds and of precipitating water content derived from a case study within the International Cirrus Experiment (ICE) held in 1989 over the North Sea.     

Magnetic fields around highly magnetized objects

The structure of the magnetic fields of a collapsed star is studied by tracing the flux lines in the quasi-vacuum approximation. The existence of a magnetic neutral line in a system of reference corotating with the star is studied, where magnetic energy dissipations into particle kinetic energy via plasma instabilities could occur.     

The relativistic quasilinear theory of particle acceleration by hydromagnetic turbulence

The quasilinear theory of acceleration of relativistic particles by hydromagnetic turbulence is treated in the adiabatic limit of small gyration radius. The theory is based on the relativistic Vlasov equation; however, a given pitch-angle scattering rate by microturbulence is postulated and is added to this equation. The resulting acceleration is found to be given by a diffusion coefficient in total momentum, which is proportional to the spectrum of turbulence with a rate coefficient . is a frequency that represents the efficiency of each wave component of the turbulence in producing acceleration. It is given as an integral over the solution of a differential equation in pitch angle. is evaluated in various limiting cases and is shown to lead to familiar forms of acceleration, such as Fermi acceleration and magnetic pumping. Thus, a comprehensive theory of these forms of heating is achieved.     

Early Pleistocene climate changes in the central Mediterranean region as inferred from integrated pollen and planktonic foraminiferal stable isotope analyses

Vegetation inherited from a Pliocene subtropical climate evolved through obliquity oscillations and global cooling leading to modern conditions. An integrated, highly time-resolved record of pollen and stable isotopes (δ¹⁸O and δ¹³C of Globigerina bulloides) was obtained to understand vegetation responses to Early Pleistocene climate changes. Continental and marine responses are compared in the Central Mediterranean region with a particular consideration of environmental changes during anoxic events.Pollen data illustrate vegetation dynamics as follows: [1] development of mesothermic elements (warm and humid conditions); [2] expansion of mid- and high-altitude elements (cooler but still humid conditions); and [3] strengthening of steppe and herb elements (cooler and dry conditions). These successions correlate with precession. δ¹⁸O variations recorded by Globigerina bulloides define two cycles (MIS 43-40) related to obliquity. At northern low- to mid-latitudes, the pollen signal records temperature and wetness changes related to precession even during global climate changes induced by obliquity. This may result in unexpected increasing wetness during glacial periods, which has to be considered specific to the Central and Eastern Mediterranean region. Lastly, an analysis of anoxic events reveals that enhanced runoff is indicated by increasing frequency of the riparian trees Liquidambar and Zelkova.     

Bulk-rock geochemistry and plagioclase zoning in lavas exposed along the northern flank of the Western Blanco Depression (Northeast Pacific): Insight into open-system magma chamber processes

The present study is based on a set of lavas and crosscutting dikes collected by dives along detailed vertical transects on the northern flank of the western part of the Blanco Transform Fault, Northeast Pacific. The studied area consists of a small basin, the Western Blanco Depression (WBD), extending from the southern end of the Juan de Fuca ridge to a pseudofault trace 60 km eastward. The Northern Scarp of the WBD comprises a volcanic unit overlying a sheeted-dike complex. Major and trace element data, coupled with Sr–Nd isotope ratios, reveal a two-component mantle source, composed by an isotopically depleted matrix variably veined by more enriched material. One chemical group (NS2), indistinguishable from the other Northern Scarp samples on the basis of trace element data, has an unusually depleted isotopic composition typical of a nearly pure mantle end-member. Some cogenetic samples of the Northern Scarp have been used to constrain the differentiation modalities. Anorthite and MgO content profiles in plagioclase xenocrysts and phenocrysts reveal (i) the existence of H₂O-bearing evolved melts in the mushy zones and (ii) the occurrence of mixing process between these melts and anhydrous mafic liquids. The hydration is supported by other petrographic features such as high magmatic fO₂ values, calculated from Fe–Ti oxide pairs, and the presence of pyroxene inclusions in plagioclase phenocrysts. Mixing, consistent with the existence of Ni-rich ferrobasalts, is interpreted to be the consequence of the reservoir refilling by mafic liquids (Mg# = 70). These petrological and geochemical evidences are combined with the evolution of Mg# with depth to suggest a periodic open-system magma chamber evolution beneath the southern end of the Juan de Fuca ridge.     

ESR dating of fluvial quartz: Estimate of the minimal distance transport required for getting a maximum optical bleaching

An ESR experimental study of artificial optical bleaching of sedimentary quartz has shown that the aluminum center was maximally bleached after a 6-month illumination equivalent to natural light. This duration seems too long to apply in natural conditions. Nevertheless, the measurement of the ESR intensity of aluminum centers in quartz extracted from modern sediments and deposited in sandy bars shows that the maximum bleaching has effectively been reached.

In order to determine the relationship between the bleaching and the distance covered by a quartz grain in a river, samples were collected along the Creuse River (France) from its spring to about 170 km downstream, where maximum bleaching levels were observed in previous studies. The ESR intensities of the aluminum and titanium centers in quartz were measured, using X-band spectroscopy, before and after artificial bleaching. The difference measured between these sub-samples shows that the maximum bleaching level is obtained in the course of the first kilometer. Hence, the assumption that ESR dating of fluvial sediment is based on the optical bleaching was validated.     

A dense array experiment for the observation of waveform perturbations

We analyze observed three-component seismograms recorded by a dense array of 21 short-period receivers (f>2 Hz) installed on a homogeneous Quaternary plain with 1.5×3.5 km² horizontal dimensions. The experiment was conducted in the district of Caille, in SE France for 3 months. The observed waveform data are related to diffraction and refraction of the direct wavefield by different geological structures and topographic morphologies surrounding the array. The origin of the coda energy following the energetic Pg or Sg arrivals is either influenced by heterogeneities close to and inside of the valley, for instance thrust of Jurassic limestones over Cretaceous marls in the northern and southern limits of the valley, or by heterogeneities located outside of the valley such as the interface unconformity between crystalline basement and sedimentary cover in the northern border of the Maures–Tanneron ranges. The main energetic arrivals of the seismograms arrive at the array with a definite range of azimuths that is not correlated with the event back-azimuth. Moreover, these arrivals do not appear with azimuths related to the characteristic NS and EW valley orientations, and thus may be related to heterogeneities located outside of the valley.     

Rainfall on the Sea: Surface Renewals and Wave Damping

Rainfall on the sea surface causes a variety of effects on the molecular boundary layers. Two such effects are the reduction of the surface renewal time period and the damping of short gravity waves being responsible for wave breaking at higher wave frequencies. The effects described recently by Schlüssel et al. are revaluated in order to fully include the varying raindrop velocity. New parameterizations are derived, which differ from the previous ones, and a substantially higher kinetic energy flux due to rain is found. The general conclusions about the impact on the thermal molecular boundary do not change, although we point to several minor errors in the calculations of Schlüssel et al. (1997).