21The design, realization and operation of a prototype or "demonstrator" version of an active target and time projection chamber (ACTAR TPC) for experiments in nuclear physics is presented in detail. The heart of the detection system features a micromegas gas amplifier coupled to a high-density pixelated pad plane with square pad sizes of 2×2 mm 2 . The detector has been thoroughly tested with several different gas mixtures over a wide range of pressures and using a variety of sources of ionizing radiation including laser light, an α-particle source and heavy-ion beams of 24 Mg and 58 Ni accelerated to energies of 4.0 MeV/u. Results from these tests and characterization of the detector response over a wide range of operating conditions will be described. These developments have served as the basis for the design of a larger detection system that is presently under construction.1

While the 12 C(α, γ) 16 O reaction plays a central role in nuclear astrophysics, the cross section at energies relevant to hydrostatic helium burning is too small to be directly measured in the laboratory. The β-delayed α spectrum of 16 N can be used to constrain the extrapolation of the E1 component of the S-factor; however, with this approach the resulting S-factor becomes strongly correlated with the assumed βα branching ratio. We have remeasured the βα branching ratio by implanting 16 N ions in a segmented Si detector and counting the number of βα decays relative to the number of implantations. Our result, 1.49(5) × 10 −5 , represents a 24 % increase compared to the accepted value and implies an increase of ≈ 13 % in the extrapolated S-factor.

International audienceThe fission of a variety of actinides was induced by fusion and transfer reactions between a 238U beam and 12C nuclei, in the active target MAYA. The performance of MAYA was studied, as well as its capability to reconstruct the fission-fragment trajectories. Furthermore, a full characterization of the different transfer reactions was achieved, and the populated excitation-energy distributions were investigated as a function of the kinetic energy in the entrance channel. The ratio between transfer-and fusion-induced fission cross-sections was also determined, in order to investigate the competition between both reaction types and its evolution with the incident energy. The experimental results will be discussed with a view to forthcoming radioactive-ion beam facilities, and next-generation active-target setups

Abstract-This paper describes a study of background estimation in Modular x and gamma-ray Sensor (MXGS) on-board ESA's Atmosphere-Space Interactions Monitor (ASIM) mission, using Geant4 simulations and SPENVIS packages for particle flux generations.Index Terms-Environmental radiation effects, Monte Carlo background estimation, semiconductor device radiation effects, space station based experiment.

The unbound nucleus 7 He has been investigated via the reaction of a 16.8 MeV 6 He radioactive ion beam on a 9 Be target. The measurement of the outgoing 8 Be through its well characterized two-α decay permitted the energy of the 6 He +n system to be reconstructed. Through comparison with a complete Monte Carlo simulation incorporating R-matrix lineshapes, the 7 He ground state was determined to lie 0.380(28) MeV above the neutron decay with a width of = 0.179(21) MeV. A neutron spectroscopic factor SF = 0.608(18) was extracted in agreement with the most recent calculations. Significant evidence was found for a broad resonance lying at 2.6(2) MeV above threshold with a FWHM = 2.3(3) MeV. These parameters are fully consistent with the properties of 1/2 − state reported by Wuosmaa et al. [Phys. Rev. C 72, 061301(R) (2005)]. Limits were also put on the presence of narrow resonances seen in earlier experiments.

The sand tiger shark (Carcharias taurus) is a coastal species distributed in temperate and sub‐tropical waters, classified as ‘Vulnerable’ at global level and ‘Critically endangered’ in eastern Australia, south‐western Atlantic Ocean, and Mediterranean Sea. Six populations (north‐western Atlantic, Brazil, South Africa, Japan, eastern Australia, and western Australia) with low genetic diversity and limited gene flow were identified worldwide, but genetic information for many other geographic areas are still missing. Specifically, this species is listed in several reports as part of the Mediterranean fauna, even if there has been a lack of catches and sightings in recent years in this basin. To clarify the origin of C. taurus individuals caught in the past in the Mediterranean Sea, historical samples were genetically analysed. Nine samples with certain Mediterranean origin were collected from different European museums. DNA was extracted and ~600 bp of the mitochondrial DNA control region were amplified using eight overlapping species‐specific primer pairs. Sequences obtained were aligned with all the haplotypes globally known so far. Genetic analysis revealed the misidentification of one museum specimen. Among the remaining Mediterranean historical samples, three different haplotypes were recovered. Two of them previously observed only in South Africa and one described in both South African and Brazilian populations. Results suggest a genetic relationship between Mediterranean sand tiger sharks and those from the western Indian Ocean. According to previous studies, we hypothesized that, during the Pleistocene, the cold Benguela upwelling barrier was temporarily reduced allowing the passage of C. taurus individuals from the Indian to Atlantic Ocean. After the restoration of this phylogeographic barrier some individuals were trapped in the Atlantic Ocean and probably migrated northward colonizing the western African coasts and the Mediterranean Sea.

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In an optical LAN based on linear topology there are important issues, as the connection of new nodes and the amount of cumulative losses encountered by optical signals, which make it difficult to meet the general requirements of LAN, such as expansibility, reliability and modularity. On the contrary the star topology shows a positive feature in terms of reliability and expansibility. This paper deals with a protocol conceived for fiber optics LANs based on coherent transmission. It is particularly suitable for implementation in a star topology, which allows both integration of services over the same network and high speed operation of the physical layer. Moreover, such protocol allows to avoid collision problems, which in general arise into a star topology network. In particular, this last problem is solved by the protocol on the ground of the knowledge of nodes Queue Status, which is achieved considering that in a star topology the star center is the only shared resource.By measuring the distance from nodes to the star center and communicating in each header the packets priority and the status of the node, it is possible to guarantee the continuity of the information flow in the star center. In such a way the influence of network propagation delay on protocol performance is reduced. The performance evaluation of the protocol in terms of delay a packet and the average throughput of the single node is presented and discussed.