Roberto Zanasi

Electric and magnetic properties of the aromatic sixty-carbon cage

Abstract We report the use of large supercomputer resources to perform the first ab initio calculations on the polarisability and magnetisability of C 60 and its smaller analogue C 20 2+ . It is found that both molecules have the high polarisability characteristic of π systems and the diamagnetic magnetisability typical of aromatic molecules. Insofar as it is possible to extrapolate to the basis-set limit, the calculations predict net diamagnetism for the clusters, and a diamagnetic effect on the NMR chemical shift of an encapsulated atom.

MOLECULAR MAGNETIC PROPERTIES WITHIN CONTINUOUS TRANSFORMATIONS OF ORIGIN OF THE CURRENT DENSITY

A new method for the calculation of molecular magnetic susceptibility and nuclear magnetic shielding is presented. It is based on continuous transformations of origin of the current density which make the transverse part of the paramagnetic current vanish. For any molecule all the components of the nuclear magnetic shielding tensor provided by the new method are independent on the origin of the gauge, whereas the components of the magnetizability tensor are translationally invariant only for center‐symmetric molecules (they, in general, show a linear dependence on the shift of origin). This method, termed CTOCD‐PZ, has been implemented for the theoretical determination of molecular magnetic properties via numerical integration techniques and, from preliminar results obtained for methane and carbon dioxide molecules, reveals reliable.

Brief Nonlinear filters for the generation of smooth trajectories

A nonlinear variable structure (VS) system is presented, suitable for smooth trajectory generation in motion control system. Joined to a rough reference trajectory generator (step, ramp, etc.) it provides smooth output signals according to user-selectable bounds on trajectory derivatives. The bounds on output derivatives can be changed during system operation without impairing system stability. Moreover, minimum time response with guaranteed no overshoot is ensured both in the continuous and discrete-time implementations. The main contribution of the paper lies in the discrete-time version of the trajectory generator. The performance of the proposed nonlinear filters is tested through simulation experiments. Simulation results concerning the use of the discrete filter in a position tracking control system are also presented.

Sliding mode using discontinuous control algorithms of integral type

This paper deals with the robust stabilization of continuous-time dynamical systems in the presence of parametric and external time-varying disturbances. Modified Variable Structure control algorithms with additional integral terms are considered here and analysed. A comparison with a typical ‘static’ VS algorithm is made. Static VS algorithms can reject completely the disturbance only if the amplitude of the switching term, in the control input, is larger than the amplitude of the disturbance itself. This paper shows how it is possible, by adding an integral term in the VS control algorithm, to reach and remain in the sliding mode if the amplitude of the switching term is smaller than the amplitude of the disturbance. Some simulations supporting the theoretical results are reported and discussed.

The Power-Oriented Graphs technique: System modeling and basic properties

In this paper the Power-Oriented Graphs (POG) technique is introduced and its basic graphical properties are compared with those of the Bond Graph (BG) technique. The two techniques are based on the same concepts, are equivalent from a mathematical point of view and use two different graphical representations for modeling physical systems. The BG schemes are quite compact and more flexible in the exact description of all the power connections within the system. The POG schemes are easier to use for beginners and use vectorial compact forms when the system complexity increases. The paper ends describing some “dissipative” properties of the POG state space models.

Smooth profile generation for a tile printing machine

In this paper a digital filter is proposed for the generation of smooth set points for motion control systems. The proposed nonlinear filter produces profiles with bounded velocity and acceleration starting from rough reference signals (steps and ramps). An actual implementation of the filter for a tile printing machine is presented and experimental results are reported.

Modeling of Automotive Control Systems Using Power Oriented Graphs

The basic idea of the power-oriented graphs (POG) modeling technique is to use the power interaction between subsystems as basic concept for modeling. This approach is theoretically supported by the definition and the properties of the port-controlled Hamiltonian systems and allows the modeling of a wide variety of systems involving different energetic domains. Differently from the bond graphs technique, based on the same concept, the POG modeling technique solves explicitly the causality problem. By this way, the POG schemes are easily readable, close to the computer implementation and allow reliable simulations using every computer simulator. This paper introduces the properties of the POG technique and presents some examples related to automotive control systems

Dynamics of a N -links manipulator by using power-oriented graphs

Abstract In this paper, a modeling technique named “Power-Oriented Graphs” (POG) is used for deriving the dynamic equations of a n -links manipulator. Firstly, the dynamic model of the “elastic” manipulator is determined. Then the corresponding “rigid” model, when the elasticities of the joints tend to zero, is obtained by means of a “congruent transformation” performed in the state space. The transformation is rectangular, so the system is transformed and reduced at the same time. The “rigid” dynamic model of the manipulator obtained with the POG technique shows an internal structure very similar to the one recently obtained with the “spatial operators” approach.

Dynamic modeling and control of electro-hydraulic wet clutches

This paper proposes an energy-based detailed dynamic model of an hydraulic multi-plate clutch actuator controlled by an electro valve with internal pressure feedback. The proposed system model has been validated by comparison with experimental measurements. Based on the main features of the electro-hydraulic clutch actuator system, two clutch pressure control strategies are proposed and the tracking performances are tested through simulation experiments.

Calculation of Molecular Magnetic-properties Within the Landau Gauge In Hydrogen-fluoride, Ammonia, and Methane Molecules

The magnetic susceptibility and the nuclear magnetic shielding tensors of HF, NH3, and CH4 molecules in the presence of a spatially uniform time‐independent magnetic field have been calculated within the Landau gauge for the vector potential. The random‐phase approximation has been used, adopting flexible Gaussian basis sets of large size. Magnetic susceptibilities are quite harder to evaluate accurately in the Landau gauge than in Coulomb gauge. Calculated nuclear magnetic shieldings are close to the Hartree–Fock limit. Sum rules for charge conservation and origin independence of magnetic susceptibility and nuclear magnetic shieldings are fairly well satisfied by basis sets of extended size.