Factorisation, Parton Entanglement and the Drell-Yan Process

We discuss the angular distribution of the lepton pair in the Drell-Yan process, hadron+hadron -> \gamma^* X -> l^+ l^- X. This process gives information on the spin-density matrix \rho^{(q,\bar{q})} of the annihilating quark-antiquark pair in q+\bar{q} -> l^+ l^-. There is strong experimental evidence that even for unpolarised initial hadrons \rho^{(q,\bar{q})} is nontrivial, and therefore the quark-antiquark system is polarised. We discuss the possibilities of a general \rho^{(q,\bar{q})} -which could be entangled- and a factorising \rho^{(q,\bar{q})}. We argue that instantons may lead to a nontrivial \rho^{(q,\bar{q})} of the type indicated by experiments.Comment: 14 pages, 2 figures, comments and references added; to appear in EPJ

Piezoceramics-based Devices for Active Balancing of Flexible Shafts

This paper focuses on vibration control of flexible shafts by means of rotorfixed piezoelectric materials. The target is to realize compact solutions for the suppression of problematic resonant vibration at so-called flexural critical speeds. For analysis, parametric finite element models of flexible rotors with piezoceramic sheets and strain or displacement sensors are developed, where the number of degrees of freedom is kept low. Several mechanisms which can destabilize flexible rotors are quantisized, such as rotor material damping, dissipation of currents induced in rotor-fixed piezoceramics and active feedback control proportional to rotor strain rates. The effectiveness of low frequency feedback and feedforward control for the suppression of the unbalance response is demonstrated using analytic and experimental results. Emphasis is on the interaction between the dynamics of the rotor and that of the connected electronic circuits. The experimental setup which is used for validation is a flexible shaft equipped with piezoceramic sheets and strain sensors. A slipring assembly is used to simplify measurements with, and control of, the sensors and actuators on the shaft and to facilitate the development of compact drive electronics

A new approach to model tyre/road contact

In the Structural Dynamics and Acoustics group at the University of Twente, we aim to develop a quantitative tyre/road noise model. An essential part of this model is an accurate contact algorithm which is fast enough to simulate tyre vibrations up to the acoustic frequencies. In this paper we present a contact algorithm, describing the contact between a tyre and a road surface, which has the potential to be made very fast using the multigrid techniques developed in the field of elasto-hydrodynamic lubrication. For the development of the algorithm a flexible ring model is used to describe the tyre. The friction model is based on Coulomb’s friction. We present (quasi-)static results obtained from the algorithm for various friction coefficients, as well as frictionless results for a rotating tyre. The vibrations of the tyre obtained by this model have been used to calculate the radiated sound field by means of a boundary element program (BEMSYS)

Hybrid isolation of structure-borne sound

Interior noise problems become more important due to the tendency to construct lighter vehicles. An important source for interior noise in a vehicle is the engine. The structural vibrations induced by the engine will transmit through the vehicle and will finally result in interior noise elsewhere in the vehicle, so-called structure-borne sound. To reduce the interior noise a solution is sought in a combination of passive and active isolation (hybrid isolation) of the engine. A project has been started to investigate this type of isolation and to develop experimentally validated numerical simulations for the design of hybrid isolation system. \ud This paper focuses on the numerical modelling approach for this type of problems. The model consists of a structural and a bounded acoustic part that are representative for a vehicle. The responses of both parts are determined efficiently with modal superposition. The controller design, necessary for the active part of the isolation, is performed with the optimal control theory that is based on minimization of a cost function. Different cost functions will be compared with each other with emphasis on the performance of the structural related cost functions (e.g. minimization of structural velocities) in comparison with the acoustical cost functions (e.g. minimization of sound pressures)

Effect of farming system changes on life cycle assessment indicators for dairy farms in the Italian Alps.

In some Alpine areas dairy farming is going through a process of intensification with significant changes in farming systems. The aim of this study was to investigate environmental performance of a sample of 31 dairy farms in an Alpine area of Lombardy with different levels of intensification. A cradle to farm gate life cycle assessment was performed including the following impact categories: land use, non-renewable energy use, climate change, acidification and eutrophication. From a cluster analysis it resulted that the group of farms with lowest environmental impacts were characterized by low stocking density and production intensity; farms that combined good environmental performances with medium gross margins were characterized also by high feed self-sufficiency and lowland availability. Environmental impacts of dairy farms in the mountain areas could be mitigated by the improvement of forage production and quality and by the practice of summer highland grazing, that significantly reduced eutrophication per kg of milk of the less self-sufficient farms