Directed flow of charged particles at midrapidity relative to the spectator plane in Pb-Pb collisions at √sNN=2.76 TeV

The directed flow of charged particles at midrapidity is measured in Pb-Pb collisions at √sNN=2.76 TeV relative to the collision symmetry plane defined by the spectator nucleons. A negative slope of the rapidity-odd directed flow component with approximately 3 times smaller magnitude than found at the highest RHIC energy is observed. This suggests a smaller longitudinal tilt of the initial system and disfavors the strong fireball rotation predicted for the LHC energies. The rapidity-even directed flow component is measured for the first time with spectators and found to be independent of pseudorapidity with a sign change at transverse momenta pT between 1.2 and 1.7 GeV/c. Combined with the observation of a vanishing rapidity-even pT shift along the spectator deflection this is strong evidence for dipolelike initial density fluctuations in the overlap zone of the nuclei. Similar trends in the rapidity-even directed flow and the estimate from two-particle correlations at midrapidity, which is larger by about a factor of 40, indicate a weak correlation between fluctuating participant and spectator symmetry planes. These observations open new possibilities for investigation of the initial conditions in heavy-ion collisions with spectator nucleons. © 2013 CERN

Analysis of chip formation mechanisms and modelling of slabber process

During the primary transformation in wood industry, logs are faced with conical rough milling cutters commonly named slabber or canter heads. Chips produced consist of raw materials for pulp paper and particleboard industries. The process efficiency of these industries partly comes from particle size distribution. However, chips formation is greatly dependent on milling conditions and material variability. Thus, this study aims at better understanding and predicting chips production in wood milling. The different mechanisms of their formation are studied through orthogonal cutting experiments at high cutting speed for beech and Douglas fir. Within these conditions, ejection of free water inside wood can be observed during fragmentation, particularly on beech. As previously seen in quasi-static experiments, chip thickness is proportional to the nominal cut thickness. Moreover, the grain orientation has a great influence on the cutting mechanisms, so as the nominal cut and the grows rings widths. This chip fragmentation study finally allows the improvement of the cutting conditions in rough milling. In order to optimize machine design as well as cutting geometry, a geometrical model of a generic slabber head is developed. This model allows the study of the effective cutting kinematics, the log-cutting edges interactions and the effective wood grain direction during cutting. This paper describes the great influence of the carriage position on cutting conditions. The results obtained here can be directly used by milling machine manufacturers.Allocation Spécifique Normalie