Direct optical injection locking of 20 GHz superlattice oscillators

For the first time, a direct optically injection-locked oscillator based on the Esaki-Tsu effect in superlattices is reported. The microwave output power is -7 dBm at 20 GHz with an optical input power of -10 dBm at a wavelength of 1.3 μm     

An efficient spectral method based on an orthogonal decomposition of the velocity for transition analysis in wall bounded flow

As a consequence of the Helmholtz–Hodge theorem, any divergence-free vector field can be decomposed in two L²-orthogonal, solenoidal vector fields expressed in terms of projections of the velocity and vorticity fields, on an arbitrary direction in space. Based on this type of decomposition and the choice of the wall-normal direction, an efficient spectral code is developed for incompressible flows developing between two parallel walls. The method relies on a weak formulation of the Navier–Stokes equations in the two corresponding divergence-free subspaces. The approximation is based on Fourier expansions in two directions and on the Chebyshev basis proposed by Moser et al. in the third direction in order to satisfy the wall boundary conditions. The method accuracy is validated for the plane Poiseuille linear stability problem and compared with the case of a spectral collocation method. Simulations of by-pass transition in boundary layers developing between two parallel walls are then presented. Since, by construction, the two orthogonal vector fields of the decomposition are associated respectively to the Orr–Sommerfeld and the Squire modes of the linear stability theory, the method makes it possible to evaluate kinetic energy transfers due to the coupling between these two scalar modes and their interactions with the base flow. The decomposition is also used to describe the structure of finite-length streaks in the earlier stages of transition.     

Gas-cooled fast reactors—Status of CEA preliminary design studies

The gas-cooled fast reactor (GFR) is one of the six reactor concepts selected in the frame of the Generation IV initiative. The most significant GFR option is the use of a helium high temperature primary coolant. The helium option is very attractive (chemical inertness, neutron transparency, etc.) but it leads to very specific thermal-hydraulic issues.As far as the reactor core design is concerned, a ceramic fuel concept with a good thermal conductivity has been chosen. The main requirement is to obtain an average exit core temperature of 850 °C (energy conversion efficiency) with a maximum fuel temperature of about 1200 °C and with a low core pressure drop (in order to ease the decay heat removal). The main core characteristics have been determined for two reactor powers: a medium one (600 MWth) and a large one (2400 MWth). For various reasons, this latter became the CEA reference choice. A consistent set of core parameters has been determined taking into account the different constraints including the thermal-hydraulics. The reference arrangement proposed is based on plate fuel elements.A significant issue for the GFR is the decay heat removal. An innovative approach has been chosen in case of loss of coolant accidents (LOCAs). A “guard containment” enclosing the primary system is used to maintain a medium gas pressure (10 bar) in order to remove the decay heat by low power forced convection systems in the short term and natural convection systems in the long term. This guard containment is not pressurized during normal operations and can be a metallic structure.As far as the energy conversion system is concerned, an indirect-combined cycle has been chosen. The significant advantages of this choice are: a moderate core inlet temperature (400 °C instead of 480 °C for the direct cycle) and an attractive compactness of the primary system (facilitating the guard containment design).Due to the novelty of these options, a significant effort of components pre-sizing and design calculations has been achieved. Following this effort, a CATHARE model of the reactor system has been made and the calculation of the reactor steady-state confirms the consistency of the overall system pre-sizing. This model has been used for a first transient calculation. Other types of transients have to be analyzed, however, it is thought that the proposed GFR design can reach the safety requirements of Generation IV systems.     

The MEGAPIE 1 MW target in support to ADS development: status of R&D and design

The MEGAPIE project is aimed at designing, building and operating a liquid metal spallation neutron target as a key experiment on the road to an experimental accelerator driven system and to improve the neutron flux at the PSI spallation source. The design of the target system has been completed. The target configuration and the operating conditions have been defined and the expected performance assessed. A preliminary safety analysis has been performed considering normal, off-normal and accident conditions and a corresponding report has been submitted to the authorities for licensing. The experience gained up to now shows that MEGAPIE may well be the first liquid metal target to be irradiated under high power beam conditions.     

Switched chattering control vs. backlash/friction phenomena in electrical servo-motors

A switched control algorithm is developed to globally stabilize an electrical servo-motor operating under uncertainty conditions in the presence of complex non-linear phenomena such as backlash, stick-slip motion, etc. The controller constructed is referred to as a chattering controller and it does not rely on the generation of sliding motions while providing robustness features similar to those possessed by their sliding mode counterparts. Particularly, the chattering controller ensures robustness against external disturbances with the a priori known norm bounds, thus rejecting the influence of undesired backlash/friction effects on the motor. Stability analysis, given within the Lyapunov functions framework extended to discontinuous dynamic systems, additionally reveals a finite time convergence of the system trajectories to the equilibrium point. Performance issues of the controller are illustrated in a simulation study.     

In Vitro Studies Regarding the Safety of Chitosan and Hyaluronic Acid-Based Nanohydrogels Containing Contrast Agents for Magnetic Resonance Imaging

The aim of this study was to investigate the biocompatibility of contrast agents, such as gadolinium 1, 4, 7, 10 tetraazacyclo-dodecane tetraacetic acid (GdDOTA) and gadolinium dioctyl terephthalate (GdDOTP), encapsulated in a polymeric matrix containing chitosan and hyaluronic acid using RAW264.7 murine macrophages and human blood samples. The cell viability and cytotoxicity were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays, while cell cycle analysis was determined in RAW264.7 cells using flow cytometry. The mitochondrial membrane potential (MMP), hemolytic index, complement activation, and thrombogenic potential of gadolinium (Gd) containing nanohydrogels were measured by fluorometric and spectrophotometric methods. Taken together, our results demonstrate the good bio- and hemocompatibility of chitosan-based nanohydrogels with the RAW264.7 cell line and human blood cells, suggesting that these could be used as injectable formulations for the magnetic resonance imaging diagnostic of lymph nodes.     

Adult biphenotypic acute leukaemia: an entity with poor prognosis which is related to unfavourable cytogenetics and P-glycoprotein over-expression

Ewes actively immunized against alpha N, the N-terminal peptide of inhibin alpha 43 precursor, have lowered fertility associated with ovulation failure, restricted tissue remodelling and reduced matrix metalloproteinase-2 activity in the follicular fluid at the time of expected ovulation. This could be due to altered ratios of matrix metalloproteinase-2 and tissue inhibitor of matrix metalloproteinase (TIMP-1), or to the onset of atresia in antral follicles destined to ovulate. The objectives of the present study were to investigate the effects of immunization against alpha N on the localization of TIMP-1 in ovine follicles, and on follicular growth and atresia in the follicular phase. Ewes were either immunized against alpha N or remained as controls and the ovaries were removed before (0, n = 4) and at 12 h (n = 4) and 24 h (n = 4) after hCG administration in a synchronized follicular phase, 48 h after removal of intravaginal pessaries. Observations were made on a single section taken through the largest follicle present in the ovaries of each ewe. There were no healthy antral follicles > 1 mm in immunized ovaries (0/29) compared with controls (16/31) (P < 0.001), whereas the proportion of healthy antral follicles < 1 mm was the same in each group (9/19 versus 5/12). TIMP-1 immunoactivity was localized in large luteal cells, smooth muscle and endothelial cells, and in all antral follicles, including oocytes. At the time of hCG administration, no TIMP-1 immunoreactivity was detected in the apical region of the follicular wall of large follicles (> 6 mm) compared with the rest of the follicle wall, but staining appeared in the apical granulosa layer 24 h later. In newly formed corpora lutea, TIMP-1 expression was found along the invaginating vascular layer. There was no effect of immunization on the patterns of TIMP-1 immunoreactivity, suggesting that changes in TIMP-1 are not involved in the effects of alpha N. These data are consistent with a paracrine role for alpha N in the selection and atresia of antral follicles, and for TIMP-1 in tissue reorganization and steroidogenesis at the time of ovulation.     

French comparison exercise with the rotating neutron spectrometer, 'ROSPEC'

The French laboratories in charge of 'neutron' dosimetry using the spectrometer 'ROSPEC', formed a working group in 2001. The participants began to study the behaviour of the instrument with a comparison exercise in broad energy neutron fields recommended by the International Organisation for Standardisation (ISO) and available at the LMDN in Cadarache. The complete version of the ROSPEC is made up of six spherical proportional counters fixed to a rotating platform. These counters cover different energy ranges which overlap each other to provide a link between the detectors, within the energy range from thermal neutrons to 4.5 MeV. The irradiation configurations chosen were ISO standard sources (252Cf, (252Cf+D2O)(/Cd), 241Am-Be) and the SIGMA facility. The results show that the 'thermal and epithermal' neutron fluence was widely overestimated by the spectrometer in all configurations.     

Influences of bioavailability, trophic position, and growth on methylmercury in hakes (Merluccius merluccius) from Northwestern Mediterranean and Northeastern Atlantic

Methylmercury (MeHg) determinations in hake, its food-chain, and the surrounding waters and sediments allowed us to show that the higher length or age normalized mercury concentrations of Northwestern Mediterranean (Gulf of Lions: GoL) muscle hakes compared to its Northeastern Atlantic (Bay of Biscay: BoB) counterpart are due to both biotic and abiotic differences between their ecosystems. Bioenergetic modeling reveals that the slower growth rate of Mediterranean hake favors the MeHg bioaccumulation in the fish muscle and explains most of the difference between GOL and BoB hake populations. In addition, the waters of the Mediterranean hake habitat favor a higher MeHg exposition, due to the upper position of the thermohalocline, where MeHg is formed. Furthermore, we show that, within the Mediterranean hake population, a major increase in the biomagnification power (the slope of the relationships between logMeHg and δ(15)N), from 0.36 up to 1.12, occurs when individuals enter adulthood, resulting from the combined effects of lowering growth rate and change in feeding habits. Finally, δ(15)N normalized Hg concentrations indicate that the highest Hg concentrations are for hake from the shelf edge and the lowest are for hake from the Rh?ne prodelta area, suggesting a lower Hg bioavailability in inshore environments, consistent with MeHg distributions in water, sediment, and preys.