Nullity conditions in paracontact geometry

The paper is a complete study of paracontact metric manifolds for which the Reeb vector field of the underlying contact structure satisfies a nullity condition (the condition \eqref{paranullity} below, for some real numbers $\tilde\kappa$ and $\tilde\mu$). This class of pseudo-Riemannian manifolds, which includes para-Sasakian manifolds, was recently defined in \cite{MOTE}. In this paper we show in fact that there is a kind of duality between those manifolds and contact metric $(\kappa,\mu)$-spaces. In particular, we prove that, under some natural assumption, any such paracontact metric manifold admits a compatible contact metric $(\kappa,\mu)$-structure (eventually Sasakian). Moreover, we prove that the nullity condition is invariant under $\mathcal{D}$-homothetic deformations and determines the whole curvature tensor field completely. Finally non-trivial examples in any dimension are presented and the many differences with the contact metric case, due to the non-positive definiteness of the metric, are discussed.Comment: Different. Geom. Appl. (to appear

Immunological analysis of SV40 early region products

Imperial Users onl

Flight Control Research Laboratory Unmanned Aerial System flying in turbulent air: an algorithm for parameter identification from flight data

This work addresses the identification of the dynamics of the research aircraft FCRL (Flight Control Research Laboratory) used for the Italian National Research Project PRIN2008 accounting for atmospheric turbulence. The subject vehicle is an unpressurized 2 seats, 427 kg maximum take of weight aircraft. It features a non retractable, tailwheel, landing gear and a powerplant made up of reciprocating engine capable of developing 60 HP, with a 60 inches diameter, two bladed, fixed pitch., tractor propeller. The aircraft stall speed is 41.6 kts, therefore it is capable of speeds up to about 115 kts (Sea level) and it will be cleared for altitudes up to 10.000 ft. The studied aircraft is equipped with a research avionic system composed by sensors and computers and their relative power supply subsystem. In particular the Sensors subsystem consists of : \uf02d Inertial Measurement Unit (three axis accelerometers and gyros) \uf02d Magnetometer (three axis) \uf02d Air Data Boom (static and total pressure port, vane sense for angle of attack and sideslip) \uf02d GPS Receiver and Antenna \uf02d Linear Potentiometers (Aileron, Elevator, Rudder and Throttle Command) \uf02d RPM (Hall Effect Gear Tooth Sensor) \uf02d Outside air temperature Sensor A nonlinear mathematical model of the subject aircraft longitudinal dynamics, has been tuned up through semi empirical methods, numerical simulations and ground tests. To taking into account the atmospheric turbulence the identification problem addressed in this work is solved by using the Filter error method approach .In this case, the mathematical model is given by the stochastic equations: \uf028 \uf029 \uf028 \uf028 \uf029 \uf028 \uf029 \uf028 \uf029 \uf029 \uf028 \uf029 \uf028 \uf028 \uf029 \uf028 \uf029 \uf029 \uf028 \uf029 \uf028 \uf029 \uf028 \uf029 \uf028 \uf029 0 0 , , , , , x t f x t u t w t y t h x t u t z k y k v k x t x \uf071 \uf071 \uf03d \uf03d \uf03d \uf02b \uf03d (1) where x is the state vector, u is the control input vector, f and h are dimensional general nonlinear vector functions, \uf071\uf020\uf020contains the unknown system parameters, z is the measurement vector ,w is the process noise and v(k) is the measurement noise. The presence of nonmeasurable process noise requires a suitable state estimator to propagate the states. To take into account model nonlinearities in the present paper an Extended Kalman Filter has been implemented as the estimation algorithm

Automatic Landing System for Civil Unmanned Aerial System

In spite of a number of potentially valuable civil UAS applications The International Regulations prohibit UAS from operating in the National Air Space. Maybe the primary reasons are safety concerns. In fact their ability to respond to emergent situations involving the loss of contact between the aircraft and the ground station poses a serious problem. Therefore, to an efficient safe insertion of UAS in the Civil Air Transport System one important element is their ability to perform automatic landing afterwards the failure. Moreover, the mathematical model of ground effect is usually neither included in the model of the aircraft during takeoff and landing nor in the design requirements of the control system Usually two different mathematical models of the aircraft are used during landing: the first Out the Ground Effect (OGE) and the second In Ground Effect (IGE). The objective of this paper is to design a longitudinal automatic landing system taking ground effect into account. The designed control system will be tested and implemented on board by using the Preceptor N3 Ultrapup aircraft. In fact, such aircraft is used as technological demonstrator of new control navigation and guidance algorithms in the context of \u201cResearch Project of National Interest\u201d (PRIN 2008) by Universities of Bologna, Palermo, Ferrara and the Second University of Naples. First of all, a general mathematical model of the studied aircraft is built to obtain non \u2013 linear analytical equations for aerodynamic coefficients both Out of Ground Effect and In Ground Effect conditions. According to previous researches, aerodynamic characteristics of the aircraft , have been modelled by means of hyperbolic equations in the whole flight envelope. So it is possible to use a single model during the whole landing phase taking into account the actual ground effect. To overcome the difficulties due to the use of nonlinear models of the aircraft in ground effect for designing the controller, the control system has been designed using the following approach: \uf02d The Landing flight path has been divided into two segments: the descending path for aircraft altitudes h > b (OGE) and the flare for h <= b ( IGE); \uf02d The flare manoeuvre starts for h = b; \uf02d An acceptable number of linear models has been obtained by means of linearization of the original nonlinear model in various flight conditions; \uf02d A modified gain scheduling approach has been employed for the synthesis of the controller. It is made by six PID and by a supervisor. This one, by using the actual flight altitude, schedules the set of gains to be inserted online, depending on the real flight condition. Several tests have been carried out by means of simulation, in Matlab Simulink environment. The obtained results show a good accuracy of the control system for trajectory tracking in ground proximity. Further developments of the present research will be the extension of the designed control system to the take-off phase. Afterwards the aircraft model will be improved by evaluating both lateral stability derivatives variations In Ground Effect and the bank angle derivatives (\uf066\uf020derivatives). The present methodology will be employed to design a Lateral Automatic Landing System. The obtained results could be used later on, with the purpose to realize a fully autonomous UAS

Proteopathogen, a protein database to study host-pathogen interaction

Comunicaciones a congreso

MACS: Multi-agent COTR system for Defense Contracting

The field of intelligent multi-agent systems has expanded rapidly in the recent past. Multi-agent architectures and systems are being investigated and continue to develop. To date, little has been accomplished in applying multi-agent systems to the defense acquisition domain. This paper describes the design, development, and related considerations of a multi-agent system in the area of procurement and contracting for the defense acquisition community