A review of the localities and flora of the lower Permian Karoo strata at Vereeniging, South Africa

Main articleThe Vereeniging fossil floras are particularly well known and often referred to, as it is among them that attached glossopteridophyte fructifications were first recorded. No recent review of the localities, flora and age of the deposits is available. The history of collecting and description of fossil plants from Vereeniging dates from 1879. Ten localities have been recorded to date, the most important of which are the three Leeukuil quarries from which a diverse flora has been collected and described over the past thirty years. Two of the localities are considered to fall within the Lower Ecca and the remaining eight within a restricted section of the Middle Ecca coal measures. The older flora is poorly known and is represented only by the genera Gangamopteris and Noeggerathiopsis. The younger flora is fairly comprehensively known and includes some 23 genera and 33 species of plants.Non

Optoelectronic developments for remote-handled maintenance tasks in ITER

Remotely handled maintenance tools operated in the future International Thermonuclear Experimental Reactor (ITER) will face a harsh radiation environment, with total dose level requirements of several MGy. Optical fiber data communication has been considered as an alternative to conventional electronic transmission between the control room and remote handled maintenance equipment, mainly owing to its insentivity to electro-magnetic interference and to its wavelength encoded multiplexing capabilities. In this paper we summarise main results obtained at SCK•CEN over the past years towards the development of radiation tolerant fibre-optic communication links and report on the radiation tolerance of various individual optical components such as optical fibres, laser diodes and photodetectors, as well as their associated electronic driver circuits

Magnetism: the Driving Force of Order in CoPt. A First-Principles Study

CoPt or FePt equiatomic alloys order according to the tetragonal L10 structure which favors their strong magnetic anisotropy. Conversely magnetism can influence chemical ordering. We present here {\it ab initio} calculations of the stability of the L10 and L12 structures of Co-Pt alloys in their paramagnetic and ferromagnetic states. They show that magnetism strongly reinforces the ordering tendencies in this system. A simple tight-binding analysis allows us to account for this behavior in terms of some pertinent parameters

RADAR performance experiments

Theoretical studies and experimental results obtained at Coulommiers airport showed the capability of Proust radar to detect wind shears, in clear air condition as well as in presence of clouds or rain. Several examples are presented: in a blocking highs situation an atmospheric wave system at the Brunt-Vaisala frequency can be clearly distinguished; in a situation of clouds without rain the limit between clear air and clouds can be easily seen; and a windshear associated with a gust front in rainy conditions is shown. A comparison of 30 cm clear air radar Proust and 5 cm weather Doppler radar Ronsard will allow to select the best candidate for wind shear detection, taking into account the low sensibility to ground clutter of Ronsard radar

Fabrication and Optical Properties of a Fully Hybrid Epitaxial ZnO-Based Microcavity in the Strong Coupling Regime

In order to achieve polariton lasing at room temperature, a new fabrication methodology for planar microcavities is proposed: a ZnO-based microcavity in which the active region is epitaxially grown on an AlGaN/AlN/Si substrate and in which two dielectric mirrors are used. This approach allows as to simultaneously obtain a high-quality active layer together with a high photonic confinement as demonstrated through macro-, and micro-photoluminescence ({\mu}-PL) and reflectivity experiments. A quality factor of 675 and a maximum PL emission at k=0 are evidenced thanks to {\mu}-PL, revealing an efficient polaritonic relaxation even at low excitation power.Comment: 12 pages, 3 figure

A high flux source of cold strontium atoms

We describe an experimental apparatus capable of achieving a high loading rate of strontium atoms in a magneto-optical trap operating in a high vacuum environment. A key innovation of this setup is a two dimensional magneto-optical trap deflector located after a Zeeman slower. We find a loading rate of 6x10^9/s whereas the lifetime of the magnetically trapped atoms in the 3P2 state is 54s.Comment: 12 pages, 16 figure