[en] The diamond difference (DD) spatial discretization has long been a work horse of the neutron transport community. For nearly as long as DD has been used in neutron transport, it has been observed that DD produces undamped, non-physical angular fluxes in spatially under resolved problems and can fail in the thick diffusion limit. A long list of alternative spatial discretizations, all with better physics properties: accuracy, robustness, and/or preservation of the thick diffusion limit, have been proposed as alternatives to DD. Unfortunately, these alternative spatial discretizations also require significantly more floating point operations (FLOPs) per unknown compared to DD. Historically, neutron transport problems of interest have been able to be resolved sufficiently that DD is accurate enough and FLOPs have been the computational performance bottleneck controlling time to solution. Thus, in practice DD has been and remains a preferred spatial discretization for neutron transport simulations. Trends in computing architecture are leading to a new paradigm where data movement, not FLOPs will control time to solution. This presents an opportunity to improve neutron transport physics by reconsidering more FLOP intensive spatial discretization than DD without incurring a time to solution penalty. In this work, we consider the improved simple corner balance (ISCB) spatial discretization, a unique alternative to DD that has the same memory footprint as DD, and detail efforts to improve its computational performance. The ISCB spatial discretization is a more FLOP intensive spatial discretization than DD with the same memory footprint as DD. Though designed to maximize FLOP intensity, third party libraries such as LAPACK are not tuned for the unique, frequent, small linear algebra needs of neutron transport problems. While hand coding a sparse Gauss elimination is likely to be faster than a dense matrix solve (CM vs. HGE), were LAPACK suitable for small linear algebra problems, we would not have seen a performance increase with decreased numbers of LAPACK calls for the Schur complement solve (SC4 vs. SC1). Significant effort has reduced the relative compute time of ISCB to DD, but on current computer architectures DD is still faster than ISCB. Future work comparing the overall efficiency of ISCB to DD may reveal that while ISCB is slower than DD on current computers, ISCB is more accurate than DD by a factor greater than the compute time slowdown. As new computer architectures become available, we will test our hypothesis that neutron transport simulations will be bandwidth limited, ideally rendering the additional FLOPs required by ISCB to be 'free' [in terms of time to solution]. (authors)

[en] We demonstrate the trapping and manipulation of single neutral atoms in reconfigurable arrays of optical tweezers. Our approach offers unparalleled speed by using a Texas instruments digital micro-mirror device as a holographic amplitude modulator with a frame rate of 20 000 per second. We show the trapping of static arrays of up to 20 atoms, as well as transport of individually selected atoms over a distance of 25 μm with laser cooling and 4 μm without. We discuss the limitations of the technique and the scope for technical improvements. (paper)

[en] Well-maintained pavements reduce occurring severe accidents on horizontal curves. For this reason, the monitoring and evaluation of pavement conditions are important. This study evaluates pavement conditions considering volumetric degradation or displacement on 11 horizontal curves in forest roads, depending on meteorological conditions, traffic effects, and curve parameters. Within this context, pavement displacement (degradation) was investigated and measured with terrestrial laser scanning (TLS) for a year on a monthly basis. In this study, two multiple regression models were developed to estimate the degradation values of a forest road. According to model 1, which was developed to estimate the loss volume values, the adjusted R² was 0.658. For model 2, which was developed to estimate the gain volume values, the adjusted R² was 0.490. Validations of models were evaluated with different statistical tests. In conclusion, volumetric degradation can be calculated with TLS-based data. Forest road designers should determine horizontal curve characteristics, taking into consideration the pavement degradation and traffic safety.

[en] Poloidal asymmetries of impurities are commonly observed experimentally. Density asymmetry is already known to impact significantly the neoclassical prediction of impurity fluxes. In this article, the effect of impurity pressure asymmetry and anisotropy on the neoclassical flux of impurity is derived analytically. This prediction is compared with simulations performed with the gyrokinetic code GYSELA, featuring both turbulent and neoclassical transports. A fair agreement is found between the analytical prediction and the result of the simulation. On the special cases which are considered, the effects of impurity pressure asymmetry and anisotropy are shown to play a prominent role in the modification of the neoclassical impurity transport. (paper)

[en] The author reviews the more or less irreversible consequences of climate warming: higher sea levels, loss of particular ecosystems, more forest fires, more heat waves, the propagation of invading species,... A low-carbon future is an absolute necessity and nuclear power can be a solution as a global solution but also as a partial solution for compensating the intermittency of renewable energies or by providing high temperatures for hydrogen production. Many energy combinations involving nuclear energy are being studied in the world, particularly in China. The release of CO₂ by road transport is important (29% of CO₂ releases in France) and can be dramatically cut down by adopting electric cars. (A.C.)

[en] The ability to accurately model neutronics is key to the design of safe nuclear systems. The proper assessment of the impact that nuclear data covariance has on the uncertainty of integral parameters is essential for establishing safety margins. In the methods used for the propagation of uncertainty today, two major approximations are made for ease of computation: cross sections are energy-condensed (multigroup) and their covariance data is treated as temperature invariant. The accurate handling of the temperature dependence of covariance data represents a largely unstudied area. The impact of this effect on integral parameter uncertainty is unknown in magnitude and direction. To attempt to gauge this effect, the lowest lying s-wave resonance of ²³⁸U is analyzed and its uncertainty as a function of temperature determined through random sampling of its parameters. One path forward for addressing this issue is by use of a windowed multipole parameter (WMP) library and sensitivity methods in Monte Carlo simulation. WMP is a resonance based representation of cross sections that allow for convenient on-the-fly Doppler broadening. A full WMP library has been developed for cross section reconstruction, but work on the development of a functional corresponding covariance library is underway. Some proposals in this effort are discussed. (authors)