[en] The LPNHE is a joint research unit (UMR 7585) of the National Institute of Nuclear Physics and Particle Physics (IN2P3), Institute of the National Centre for Scientific Research (CNRS), UPMC and Paris Diderot Paris 7. It hosts several research teams and technical services (computers, electronics, mechanical), and two support services (administration, logistics). The laboratory is engaged in several major experimental programs pursued in the framework of international collaborations with very large research facilities around the world, centers of particle accelerators and observatories. The research programs cover current issues in particle physics, astro-particle and cosmology. This report presents the activities of the laboratory during the years 1996-1997: 1 - Forewords; 2 - Physics experiments: LHC Physics with ATLAS, search for new physics at LEP (DELPHI), Neutrinos oscillation DIRAC experiment, Neutrinos oscillation (NOMAD, TONIC), HERA-H1 experiment, CP Violation (BaBar), DΦ experiment at Tevatron, study of gamma radiation sources (CAT), Supernovae, Auger Laboratory project; 3 - Technical activities and means (electronics, computers, mechanics departments); 4 - Laboratory life (Teaching, Administration and general services, Internal and external activities); 5 - Dissemination of scientific information; 6 - List of publications; 7 - staff

[en] The LPNHE is a joint research unit (UMR 7585) of the National Institute of Nuclear Physics and Particle Physics (IN2P3), Institute of the National Centre for Scientific Research (CNRS), UPMC and Paris Diderot Paris 7. It hosts several research teams and technical services (computers, electronics, mechanical), and two support services (administration, logistics). The laboratory is engaged in several major experimental programs pursued in the framework of international collaborations with very large research facilities around the world, centers of particle accelerators and observatories. The research programs cover current issues in particle physics, astro-particle and cosmology. This report presents the activities of the laboratory during the years 1998-1999: 1 - Forewords; 2 - Physics experiments: LHC Physics with ATLAS, search for new physics at LEP, DIRAC experiment, Neutrinos oscillation with NOMAD, TONIC and HERA-H1 experiments, CP Violation (BaBar), DΦ experiment at Tevatron, high-energy gamma astronomy, Supernovae, Pierre Auger Laboratory); 3 - Technical activities and means (electronics, computers, mechanics departments); 4 - Laboratory life (Teaching, Administration and general services, Internal and external activities); 5 - Dissemination of scientific information; 6 - List of publications; 7 - staff

[en] Highlights: • The goal is to model the DSC thermograms of melting of binaries solid solutions. • The melting is modeled taking into account the heat conduction inside the DSC cell. • An enthalpic method is used considering the enthalpies of ideal solutions. • A parametric study, taking into account the sample heating rates and also the masses of the samples has been done. • Methods to determine the phase diagram (liquidus and solidus) and the energy of melting are explained. - Abstract: In this paper, a model is developed in order to determine the melting thermogram of a binary mixture, presenting a solid solution. Considering the case of an ideal solution, whose enthalpy function is analytically derived, we highlight the large differences existing between the thermogram and the derivative of the enthalpy function. The influence of the heating rates and the mass of the sample are analyzed for different concentrations. Finally, in the case of a thermodynamical equilibrium, we describe how to construct the phase diagram of the solution (liquidus and solidus temperatures, total latent heat)

[en] Magnetic torque and magnetoresistance measurements have been performed in high magnetic field on the quasi-two-dimensional charge density wave (CDW) oxide bronze KMo₆O₁₇ . Several anomalies have been found below 28 T either on the torque or on the magnetoresistance data. They can be attributed predominantly to orbital effects. Magnetoresistance data obtained up to 55 T show that a transition takes place above 30 T. This transition may be due to the Pauli coupling. The new field-induced density wave state exhibits Shubnikov-de Haas (SdH) oscillations

[en] The physical properties, mostly transport, of the low dimensional molybdenum bronzes and oxides are reviewed. After a brief theoretical background the quasi 1D properties, including charge-density wave transport of the blue bronzes A_0.30MoO₃, and the quasi 2D systems, purple bronzes A_0.9Mo₆O₁₇ and Mo_nO_3n-1 oxides, are discussed. (H.W.). 172 refs.; 69 figs.; 4 tabs

[en] A fuel performance code for SFR oxide fuel pins, GERMINAL, is developed by CEA within the PLEIADES simulation framework. The present main goal of GERMINAL is to meet the needs of the design studies of ASTRID, the future Advanced Sodium Technological Reactor for Industrial Demonstration in France. Recent works have been conducted to improve the modelling of different physical mechanisms having a strong influence on the design criteria evaluation. Thus, the formulation of the fuel pellet fragments relocation model has been revisited, by introducing a dependency to the thermal gradient inside the pellet. The description of this mechanism represents a key point to evaluate the pellet-to-cladding gap closure and the margin to melting at beginning of life. Another evolution concerns the pellet-clad mechanical interaction. The ability to simulate a stronger interaction for fuel pins with a higher filling fraction has been acquired with a focused work on fuel mechanical behavior. A stronger mechanical interaction may also happen with lower power operating conditions and a cladding material remaining stable under irradiation. Moreover, the description of the thermochemistry of oxide fuel is currently being improved by coupling GERMINAL with the OpenCalphad thermodynamic calculation software. In doing this, the goal is to obtain a better prediction of the amount of volatile fission products being transported outside the fuel pellet, and then contributing to the “Joint Oxyde-Gaine” formation. With refined estimations of JOG volume and composition, we expect further to improve the evaluation of heat transfer through pellet-to-cladding gap at high burn-up, and also a more mechanistic description of cladding corrosion due to released fission products. These works are based on a systematic comparison of calculation results to post-irradiation measures, by integrating progressively additional objects to our validation base. This process leads to a wider validity range targeting ASTRID design, and brings out new working perspectives. (author)

[en] Stochastic resonance (SR) in nonlinear systems is a counterintuitive concept in which a weak periodic signal and noise cooperate and give rise to a maximum in the signal-to-noise ratio at the output of the system when the noise is tuned to a certain value. In the coherence resonance phenomenon (CR), there is no deterministic signal to be enhanced. Intrinsic oscillations are present as transients. Adding an optimum noise turns transients into coherent ones. We discuss the possible application of SR and CR concepts to CDW dynamics in quasi-one dimensional conductors. We show in a preliminary experiment that addition of white noise can modify the behavior of the CDW in the quasi-one dimensional conductor K_0.30MoO₃.

[en] We present an analytical model for a Roberts Linkage used as an ultra low frequency vibration isolator. The Roberts Linkage is a structure that simulates a very long radius conical pendulum, at a relatively small height. We show through an analytical solution that it is possible to independently tune the centre of percussion and the resonant frequency for arbitrary geometrical configurations. The result is shown to provide a practical tuning solution, which achieves near ideal vibration isolation.

[en] The huge increase in parallel computer capacity makes it possible to merge real time training simulators with sophisticated codes devoted to safety studies: The SCAR project will integrate the latest version of the CATHARE code in a simulator. A large benefit is expected in the computer code maintenance effort and in the level of confidence in the simulator validation. In the SCAR project objectives, all plant situations must be accurately represented: normal operation and accident situations like large transients (turbine trip, etc.), ATWS (loss of FW, etc.), SGTR, and LOCAs up to 12 inches; this means that the original CATHARE 6-equation model and fully implicit numerical scheme must be kept. In correspondence with the physical domain, the plant systems modeled extend to the Reactor Heat Removal System and require improvements in numerical robustness and reductions of the elementary computation time. (authors)

[en] In the blue bronzes A_0.30MoO₃ (A=K,Rb), two regimes for the CDW nonlinear conductivity have been identified: strongly damped CDW motion above ∼50K and CDW motion with almost no damping below ∼50K. In a search for an elastic signature of this CDW behavior, we performed ultrasonic measurements on Rb_0.30MoO₃ single crystals in the temperature range 4-300 K. Upon cooling, we have observed at ∼50K a large increase of the sound velocity for the longitudinal mode measured along the [-201], [1 0 2] and b directions as well as for the shear mode along the [-201] direction. In addition, a maximum in the ultrasonic attenuation is observed around 50 K. The results are discussed in relation with the changes in the CDW rigidity and in the dielectric response