Arguments hydrogéochimiques en faveur de Trias évaporitique non affleurant dans le massif du Djurdjura (dorsale kabyle, élément des Maghrébides)

L'analyse des eaux pose à nouveau la question de l'importance des faciès gypso-salifères dans le Trias de la dorsale kabyle du Djurdjura. Cette dernière est un élément de l'orogène alpin périméditerranéen où le Trias est décrit comme étant formé essentiellement de grès et de pélites avec des niveaux marneux et dolomitiques. Dans les régions telliennes, plus méridionales, il est représenté par des formations marno-gypsifères de grande épaisseur (Trias tellien), en position tectonique constamment anormale. On ne rencontre généralement pas de formations évaporitiques en surface dans le massif du Djurdjura. Les analyses chimiques de la majorité des sources le confirment. Toutefois la source de Tinzert, dont l'impluvium est constitué essentiellement de calcaires montre un cortège d'éléments d'origine évaporitique (fortes teneurs en chlorures, sodium et sulfates et la présence du strontium) et plaide pour la présence de niveaux évaporitiques du Trias, à la base de l'aquifère drainé par cette source. Le rapport Sr2+/Ca2+ (en ‰) de la source de Tinzert (3 1000 mg·l-1), sodium (> 500 mg·l-1), sulfates (> 200 mg·l-1) and potassium (> 25 mg·l-1).During flood periods, because of dilution and quick conduit flows in the upper calcareous zones, the water type becomes calcium bicarbonate. During this period, waters flowing out of the spring are traced by the limestone shallow waters (transit of epikarstic waters). On top and upstream from Tinzert, less than 20 metres to the South, Tala Agouni Lansar displays a very different chemical type, calcium bicarbonate. This fact demonstrates that Tinzert sodium chloride content is acquired by water which stays in the deep saturated zone (Figs. 3 et 4), and that longitudinal faults divide the lithological units into segments.Analyses of strontium in waters demonstrate that most of the springs (ABDESSELAM, 1995) have low Sr2+ contents (0.06-0.23 mg·l-1). Tinzert spring has a much higher content (0.35-1.83 mg·l-1 ; Table 1). The use of the Sr2+ /Ca2+ ratio (‰) enabled us to distinguish among aquifers completely developed in limestones, others related to Triassic sandstones and one related to salty layers. The map of Sr2+ /Ca2+ ratios indicates that the springs related to Triassic outcrops have the higher values (Fig. 3).According to the Sr2+ /Ca2+ ratio (‰), three groups can be distinguished:- springs related to limestones, with no relationship with Triassic formations, have a low Sr2+/Ca2+ ratio ( 5‰) classifies this water into the category of waters originating from the alpine Triassic evaporites (MEYBECK, 1984). This high ratio is coupled with the high sulfate, and especially the chloride and sodium content of these waters. This spring is situated on the trace of a north-east thrust sheet sole that probably includes Triassic in its lower part, which concerns the whole Haïzer massif of about 8 km. The water transit is probably either in the upper thrust sheet, or in the lower one, following the East-West axis lowering of the structure.The springs of the Djurdjura display well-differentiated hydrochemical responses. Several springs that only drain limestone have a standard calcium bicarbonate chemical type (Sr2+/Ca2+ < 1 ‰). Other springs (Sr2+/Ca2+ =1 - 1.5 ‰) are characteristic of waters that have flowed in the sandstone and dolomitic Triassic layers, which are observed on the outcrops. Tinzert spring at least, which drains the middle part of the limestone range (Fig. 4, Sr2+/Ca2+=3 - 8.77 ‰), is characterised by waters which have transited through the evaporitic Triassic. The waters of Tinzert spring have also high chloride, sodium and sulfate contents.In the Djurdjura, where evaporitic Triassic formations do not generally outcrop, except in very small lenses, an argument can be made for the existence of deep evaporitic Triassic deposits on the basis of the hydrochemical response of perennial springs

Magnon energies and phase transitions of ferrous iodide in a theoretical eight sublattice model

We show that a theoretical model in which the spins are divided into eight different sublattices describes reasonably well the FeI2 magnetic behaviour : in zero magnetic field three AFMR uniform-modes are observed, in high magnetic fields parallel to the spin direction, FeI2 presents a four step metamagnetic behaviour. A spin-wave calculation gives the uniform mode energies as a function of hA (the anisotropy field) and Jpq (the exchange coupling between p and q sublattices). Because of symmetry, the set of couplings Jpq may be expressed in terms of just four couplings and the values hA = 29.6 K, J12 = J 13 = - 1.6 K, J14 = — 8.4 K and J 15 = — 9.7 K give quantitative agreement between theory and experiment. By studying the elementary exchange interaction between ions, we show that the predominant interactions are with nearest and next nearest neighbours along the c axis.Nous montrons qu'un modèle théorique où l'on suppose l'existence de 8 sous-réseaux donne une bonne description du comportement magnétique de FeI2 : en champ nul on observe trois modes uniformes de résonance antiferromagnétique; en présence d'un fort champ magnétique, l'étude de l'aimantation a démontré l'existence d'un comportement métamagnétique en escalier. Un calcul d'onde de spin donne les énergies des modes uniformes en fonction de hA (champ d'anisotropie) et Jpq (couplage d'échange entre les sous-réseaux p et q). A cause des symétries, l'ensemble des Jpq peut s'exprimer à partir de 4 d'entre eux seulement, les valeurs h A = 29,6 K, J12 = J13 = - 1,6 K, J14 = — 8,4 K et J15 = - 9,7 K donnent alors un bon accord entre prévisions du modèle et résultats expérimentaux. L'analyse des couplages d'échange élémentaires entre ions, résultant des valeurs de Jpq obtenues, montre que les couplages les plus forts se font le long de l'axe c avec les ions des plans premier et deuxième voisins

Phonon dispersion curves in Cr2AlC single-crystals

Neutron inelastic scattering is used for the first time to measure phonon dispersion branches in Cr2AlC MAX phase single crystals with appreciable size. Phonon spectra are also calculated within the Density Functional Perturbation Theory (DFPT) framework and exhibit a very good match with experimental data, including high energy carbon-related optical branches. Both experiments and ab initio simulations confirm the existence of a substantial phonon gap and discard the presence of any softening mode or possible magnetic effect. IMPACT STATEMENT We synthesized Cr2AlC single-crystalline platelets with areas over 10 cm2. This breakthrough in materials synthesis was a prerequisite for measuring inelastic neutron scattering and phonon anisotropies

SDN/NFV-enabled Satellite Communications: Ground Segment Network Architecture for 5G Integration

This paper describes a novel architecture for SDN/NFV-enabled satellite ground segment systems that is conceived to facilitate the integration of the satellite component within 5G systems so that ubiquitous, highly available and reliable connectivity can be better supported

SDN/NFV-enabled Satellite Communications Networks: Opportunities, Scenarios and Challenges

In the context of next generation 5G networks, the satellite industry is clearly committed to revisit and revamp the role of satellite communications. As major drivers in the evolution of (terrestrial) fixed and mobile networks, Software Defined Networking (SDN) and Network Function Virtualisation (NFV) technologies are also being positioned as central technology enablers towards improved and more flexible integration of satellite and terrestrial segments, providing satellite network further service innovation and business agility by advanced network resources management techniques. Through the analysis of scenarios and use cases, this paper provides a description of the benefits that SDN/NFV technologies can bring into satellite communications towards 5G. Three scenarios are presented and analysed to delineate different potential improvement areas pursued through the introduction of SDN/NFV technologies in the satellite ground segment domain. Within each scenario, a number of use cases are developed to gain further insight into specific capabilities and to identify the technical challenges stemming from them