88 research outputs found
Specialization vs diversification in research activities: the extent, intensity and relatedness of field diversification by individual scientists
We investigate whether and in what measure scientists tend to diversify their
research activity, and if this tendency varies according to their belonging to
different disciplinary areas. We analyze the nature of research diversification
along three dimensions: extent of diversification, intensity of
diversification, and degree of relatedness of topics in which researchers
diversifies. For this purpose we propose three bibliometric indicators, based
on the disciplinary placement of scientific output of individual scientists.
The empirical investigation shows that the extent of diversification is lowest
for scientists in Mathematics and highest in Chemistry; intensity of
diversification is lowest in Earth sciences and highest in Industrial and
information engineering; and degree of relatedness is lowest in Earth sciences
and highest in Chemistry.Comment: arXiv admin note: text overlap with arXiv:1810.1263
Do interdisciplinary research teams deliver higher gains to science?
The present paper takes its place in the stream of studies that analyze the
effect of interdisciplinarity on the impact of research output. Unlike previous
studies, in this study the interdisciplinarity of the publications is not
inferred through their citing or cited references, but rather by identifying
the authors' designated fields of research. For this we draw on the scientific
classification of Italian academics, and their publications as indexed in the
WoS over a five-year period (2004-2008). We divide the publications in three
subsets on the basis the nature of co-authorship: those papers coauthored with
academics from different fields, which show high intensity of inter-field
collaboration ("specific" collaboration, occurring in 110 pairings of fields);
those papers coauthored with academics who are simply from different
"non-specific" fields; and finally co-authorships within a single field. We
then compare the citations of the papers and the impact factor of the
publishing journals between the three subsets. The results show significant
differences, generally in favor of the interdisciplinary authorships, in only
one third (or slightly more) of the cases. The analysis provides the value of
the median differences for each pair of publication subsets
An Omnidirectional Aerial Platform for Multi-Robot Manipulation
The objectives of this work were the modeling, control and prototyping of a new fully-actuated
aerial platform. Commonly, the multirotor aerial platforms are under-actuated vehicles, since the
total propellers thrust can not be directed in every direction without inferring a vehicle body rotation.
The most common fully-actuated aerial platforms have tilted or tilting rotors that amplify
the aerodynamic perturbations between the propellers, reducing the efficiency and the provided
thrust. In order to overcome this limitation a novel platform, the ODQuad (OmniDirectional
Quadrotor), has been proposed, which is composed by three main parts, the platform, the mobile
and rotor frames, that are linked by means of two rotational joints, namely the roll and pitch
joints. The ODQuad is able to orient the total thrust by moving only the propellers frame by
means of the roll and pitch joints.
Kinematic and dynamic models of the proposed multirotor have been derived using the Euler-
Lagrange approach and a model-based controller has been designed. The latter is based on two
control loops: an outer loop for vehicle position control and an inner one for vehicle orientation
and roll-pitch joint control. The effectiveness of the controller has been tested by means of numerical
simulations in the MATLAB
c SimMechanics environment. In particular, tests in free motion
and in object transportation tasks have been carried out. In the transportation task simulation, a
momentum based observer is used to estimate the wrenches exchanged between the vehicle and
the transported object.
The ODQuad concept has been tested also in cooperative manipulation tasks. To this aim, a
simulation model was considered, in which multiple ODQuads perform the manipulation of a
bulky object with unknown inertial parameters which are identified in the first phase of the simulation.
In order to reduce the mechanical stresses due to the manipulation and enhance the system
robustness to the environment interactions, two admittance filters have been implemented: an external
filter on the object motion and an internal one local for each multirotor.
Finally, the prototyping process has been illustrated step by step. In particular, three CAD
models have been designed. The ODQuad.01 has been used in the simulations and in a preliminary
static analysis that investigated the torque values for a rough sizing of the roll-pitch joint
actuators. Since in the ODQuad.01 the components specifications and the related manufacturing
techniques have not been taken into account, a successive model, the ODQuad.02, has been designed.
The ODQuad.02 design can be developed with aluminum or carbon fiber profiles and 3D
printed parts, but each component must be custom manufactured. Finally, in order to shorten the
prototype development time, the ODQuad.03 has been created, which includes some components
of the off-the-shelf quadrotor Holybro X500 into a novel custom-built mechanical frame
Composite control Lyapunov functions for robust stabilization of constrained uncertain dynamical systems
This work presents innovative scientific results on the robust stabilization of constrained uncertain dynamical systems via Lyapunov-based state feedback control.
Given two control Lyapunov functions, a novel class of smooth composite control Lyapunov functions is presented. This class, which is based on the R-functions theory, is universal for the stabilizability of linear differential inclusions and has the following property. Once a desired controlled invariant set is fixed, the shape of the inner level sets can be made arbitrary close to any given ones, in a smooth and non-homothetic way. This procedure is an example of ``merging'' two control Lyapunov functions.
In general, a merging function consists in a control Lyapunov function whose gradient is a continuous combination of the gradients of the two parents control Lyapunov functions.
The problem of merging two control Lyapunov functions, for instance a global control Lyapunov function with a large controlled domain of attraction and a local one with a guaranteed local performance, is considered important for several control applications. The main reason is that when simultaneously concerning constraints, robustness and optimality, a single Lyapunov function is usually suitable for just one of these goals, but ineffective for the others.
For nonlinear control-affine systems, both equations and inclusions, some equivalence properties are shown between the control-sharing property, namely the existence of a single control law which makes simultaneously negative the Lyapunov derivatives of the two given control Lyapunov functions, and the existence of merging control Lyapunov functions.
Even for linear systems, the control-sharing property does not always hold, with the remarkable exception of planar systems.
For the class of linear differential inclusions, linear programs and linear matrix inequalities conditions are given for the the control-sharing property to hold.
The proposed Lyapunov-based control laws are illustrated and simulated on benchmark case studies, with positive numerical results
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