High intensity X/ γ photon beams for nuclear physics and photonics

In this manuscript we review the challenges of Compton back-scattering sources in advancing photon beam performances in the1−20MeVenergy range, underlining the design criteria bringing tomaximum spectral luminosity and briefly describing the main achieve-ments in conceiving and developing new devices (multi-bunch RF cav-ities and Laser recirculators) for the case of ELI-NP Gamma BeamSystem (ELI-NP-GBS)

Finite element and finite volume-element simulation of pseudo-ECGs and cardiac alternans

In this paper, we are interested in the spatio-temporal dynamics of the transmembrane potential in paced isotropic and anisotropic cardiac tissues. In particular, we observe a specific precursor of cardiac arrhythmias that is the presence of alternans in the action potential duration. The underlying mathematical model consists of a reaction–diffusion system describing the propagation of the electric potential and the nonlinear interaction with ionic gating variables. Either conforming piecewise continuous finite elements or a finite volume-element scheme are employed for the spatial discretization of all fields, whereas operator splitting strategies of first and second order are used for the time integration. We also describe an efficient mechanism to compute pseudo-ECG signals, and we analyze restitution curves and alternans patterns for physiological and pathological cardiac rhythms

Impact des protections individuelles à effet de serre sur des plants d'arganier en conditions hydriques non limitantes.

La régénération de la forêt d'arganiers au Maroc est un échec complet, principalement à cause de l'abroutissement par les animaux domestiques. La protection individuelle de chaque jeune arganier par un abri-serre pourrait contribuer à permettre l'installation de nouveaux peuplements, en évitant les conflits entre les éleveurs et les forestiers. La croissance en longueur et en diamètre de jeunes plants d'arganiers, dans des conditions de bonne alimentation hydrique à l'intérieur de ces abris a fait l'objet de ce travail. On compare 4 modalités différentes d'abris à effet de serre, l'abri blanc aéré et l'abri blanc étanche, l'abri sombre aéré et l'abri sombre étanche. Les abris blancs et aérés donnent les meilleurs résultats

A Ga-doped SnO2 mesoporous contact for UV stable highly efficient perovskite solar cells

Increasing the stability of perovskite solar cells is a major challenge for commercialization. The highest efficiencies so far have been achieved in perovskite solar cells employing mesoporous TiO2 (m-TiO2). One of the major causes of performance loss in these m-TiO2-based perovskite solar cells is induced by UV- radiation. This UV instability can be solved by replacing TiO2 with SnO2; thus developing a mesoporous SnO2 (m-SnO2) perovskite solar cell is a promising approach to maximise efficiency and stability. However, the performance of mesoporous SnO2 (m-SnO2) perovskite solar cells has so far not been able to rival the performance of TiO2 based perovskite solar cells. In this study, for the first time, high-efficiency m-SnO2 perovskite solar cells are fabricated, by doping SnO2 with gallium, yielding devices that can compete with TiO2 based devices in terms of performance. We found that gallium doping severely decreases the trap state density in SnO2, leading to a lower recombination rate. This, in turn, leads to an increased open circuit potential and fill factor, yielding a stabilised power conversion efficiency of 16.4%. The importance of high-efficiency m-SnO2 based perovskite solar cells is underlined by stability data, showing a marked increase in stability under full solar spectrum illumination

Quadruple-peaked spectral line profiles as a tool to constrain gravitational potential of shell galaxies

Stellar shells observed in many giant elliptical and lenticular as well as a few spiral and dwarf galaxies, presumably result from galaxy mergers. Line-of-sight velocity distributions of the shells could, in principle, if measured with a sufficiently high S/N, constitute one of methods to constrain the gravitational potential of the host galaxy. Merrifield & Kuijken (1998) predicted a double-peaked line profile for stationary shells resulting from a nearly radial minor merger. In this paper, we aim at extending their analysis to a more realistic case of expanding shells, inherent to the merging process, whereas we assume the same type of merger and the same orbital geometry. We use analytical approach as well as test particle simulations to predict the line-of-sight velocity profile across the shell structure. Simulated line profiles are convolved with spectral PSFs to estimate the peak detectability. The resulting line-of-sight velocity distributions are more complex than previously predicted due to non-zero phase velocity of the shells. In principle, each of the Merrifield & Kuijken (1998) peaks splits into two, giving a quadruple-peaked line profile, which allows more precise determination of the potential of the host galaxy and, moreover, contains additional information. We find simple analytical expressions that connect the positions of the four peaks of the line profile and the mass distribution of the galaxy, namely the circular velocity at the given shell radius and the propagation velocity of the shell. The analytical expressions were applied to a test-particle simulation of a radial minor merger and the potential of the simulated host galaxy was successfully recovered. The shell kinematics can thus become an independent tool to determine the content and distribution of the dark matter in shell galaxies, up to ~100 kpc from the center of the host galaxy.Comment: 15 pages, 16 figures | v2: accepted for publication in A&A, minor language correction

Characteristics and turnover of exopolymeric substances in a hypersaline microbial mat

The properties and microbial turnover of exopolymeric substances (EPS) were measured in a hypersaline nonlithifying microbial mat (Eleuthera, Bahamas) to investigate their potential role in calcium carbonate (CaCO3) precipitation. Depth profiles of EPS abundance and enzyme activities indicated that c. 80% of the EPS were turned over in the upper 15-20 mm. Oxic and anoxic mat homogenates amended with low-molecular-weight (LMW) organic carbon, sugar monomers, and different types of EPS revealed rapid consumption of all substrates. When comparing the consumption of EPS with that of other substrates, only marginally longer lag times and lower rates were observed. EPS (5-8%) were readily consumed during the conversion of labile to refractory EPS. This coincided with a decrease in glucosidase activity and a decrease in the number of acidic functional groups on the EPS. Approximately half of the calcium bound to the EPS remained after 10 dialyses steps. This tightly bound calcium was readily available to precipitate as CaCO3. We present a conceptual model in which LMW organic carbon complexed with the tightly bound calcium is released upon enzyme activity. This increases alkalinity and creates binding sites for carbonate and allows CaCO3 to precipitate. Therefore, this model explains interactions between EPS and CaCO3 precipitation, and underscores the critical role of aerobic and anaerobic microorganisms in early diagenesis and lithification processe

Relativistic and Newtonian core-shell models: analytical and numerical results

We make a detailed analysis of Newtonian as well as relativistic core-shell models recently proposed to describe a black hole or neutron star surrounded by shells of matter, and in a seminal sense also galaxies, supernovae and star remnants since there are massive shell-like structures surrounding many of them and also evidences for many galactic nuclei hiding black holes. We discuss the unicity of the models in relation to their analyticity at the black hole horizon and also to the full elimination of conical singularities. Secondly, we study the role played by the presence/lack of discrete reflection symmetries about equatorial planes in the chaotic behavior of the orbits, which is to be contrasted with the almost universal acceptance of reflection symmetries as default assumptions in galactic modeling. We also compare the related effects if we change a true central black hole by a Newtonian central mass. The numerical findings are: 1- The breakdown of the reflection symmetry about the equatorial plane in both Newtonian and relativistic core-shell models does i) enhance in a significant way the chaoticity of orbits in reflection symmetric oblate shell models and ii) inhibit significantly also the occurrence of chaos in reflection symmetric prolate shell models. In particular, in the prolate case the lack of the reflection symmetry provides the phase space with a robust family of regular orbits that is otherwise not found at higher energies. 2- The relative extents of the chaotic regions in the relativistic cases (i. e. with a true central black hole) are significantly larger than in the corresponding Newtonian ones (which have just a $-1/r$ central potential).Comment: AASTEX, 22 pages plus 28 postscript figures, to appear in Ap.