8,143 research outputs found
Kinematic Analysis and Trajectory Planning of the Orthoglide 5-axis
The subject of this paper is about the kinematic analysis and the trajectory
planning of the Orthoglide 5-axis. The Orthoglide 5-axis a five degrees of
freedom parallel kinematic machine developed at IRCCyN and is made up of a
hybrid architecture, namely, a three degrees of freedom translational parallel
manip-ulator mounted in series with a two degrees of freedom parallel spherical
wrist. The simpler the kinematic modeling of the Or-thoglide 5-axis, the higher
the maximum frequency of its control loop. Indeed, the control loop of a
parallel kinematic machine should be computed with a high frequency, i.e.,
higher than 1.5 MHz, in order the manipulator to be able to reach high speed
motions with a good accuracy. Accordingly, the direct and inverse kinematic
models of the Orthoglide 5-axis, its inverse kine-matic Jacobian matrix and the
first derivative of the latter with respect to time are expressed in this
paper. It appears that the kinematic model of the manipulator under study can
be written in a quadratic form due to the hybrid architecture of the Orthoglide
5-axis. As illustrative examples, the profiles of the actuated joint angles
(lengths), velocities and accelerations that are used in the control loop of
the robot are traced for two test trajectories.Comment: Appears in International Design Engineering Technical Conferences \&
Computers and Information in Engineering Conference, Aug 2015, Boston, United
States. 201
Origin of non-linear piezoelectricity in III-V semiconductors: Internal strain and bond ionicity from hybrid-functional density functional theory
We derive first- and second-order piezoelectric coefficients for the
zinc-blende III-V semiconductors, {Al,Ga,In}-{N,P,As,Sb}. The results are
obtained within the Heyd-Scuseria-Ernzerhof hybrid-functional approach in the
framework of density functional theory and the Berry-phase theory of electric
polarization. To achieve a meaningful interpretation of the results, we build
an intuitive phenomenological model based on the description of internal strain
and the dynamics of the electronic charge centers. We discuss in detail first-
and second-order internal strain effects, together with strain-induced changes
in ionicity. This analysis reveals that the relatively large importance in the
III-Vs of non-linear piezoelectric effects compared to the linear ones arises
because of a delicate balance between the ionic polarization contribution due
to internal strain relaxation effects, and the contribution due to the
electronic charge redistribution induced by macroscopic and internal strain
Unmanned localization of sperm whales in realistic scenarios
In this paper an unmanned sperm whale localization
technique is presented. It focuses on the localization of sperm
whales using a two-hydrophone array passive localization system.
It is based on the beamforming technique and on the time delay
between the direct and surface reflected wavefronts. The
proposed method is based on that presented by E. K. Skarsoulis
[1] and it aims to develop a low computational complexity signal
processing system, which can operate autonomously in remote
buoys with power and computational limitations. This study
consists on the analysis of the improvements provided by using
beamforming theory on the method proposed in [1]. The
eqnipment used mainly composed of two hydrophone arrays
deployed near the surface. It was found that the accuracy of this
methodology depends on the array's location and can be
improved by increasing the depth and the separation between
the arrays and/or decreasing the angle formed by the line which
crosses through the arrays with respect to the horizontal plane.
The performance of the proposed method is evaluated
through simulations using a real sperm whale signal in deep
water, in presence of low and high SNR. The enhancements are
proven in the extraction of the direct and surface-reflection
arrival times as well as the arrival angle for each path under
realistic conditions.The authors would like to thanks the Instituto Superior the
Engenharia of the University of Algarve, for receiving the
first author under an European Union ERASMUS grant when
this work was carried. This work is funded by the FCT project
PHITOM [PTDCIEEA-TEU71263/2006]
Typing Quantum Superpositions and Measurement
We propose a way to unify two approaches of non-cloning in quantum lambda-calculi. The first approach is to forbid duplicating variables, while the second is to consider all lambda-terms as algebraic-linear functions. We illustrate this idea by defining a quantum extension of first-order simply-typed lambda-calculus, where the type is linear on superposition, while allows cloning base vectors. In addition, we provide an interpretation of the calculus where superposed types are interpreted as vector spaces and non-superposed types as their basis.Fil: DĂaz Caro, Alejandro. Universidad Nacional de Quilmes. Departamento de Ciencia y TecnologĂa; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Dowek, Gilles. Institut National de Recherche en Informatique et en Automatique; Franci
Determination of convection terms and quasi-linearities appearing in diffusion equations
We consider the highly nonlinear and ill posed inverse problem of determining some general expression appearing in the a diffusion equation from measurements of solutions on the lateral boundary. We consider both linear and nonlinear expression. In the linear case, the equation is a convection-diffusion equation and our inverse problem corresponds to the unique recovery, in some suitable sense, of a time evolving velocity field associated with the moving quantity as well as the density of the medium in some rough setting described by non-smooth coefficients on a Lipschitz domain. In the nonlinear case, we prove the recovery of more general quasilinear expression appearing in a non-linear parabolic equation. Our result give a positive answer to the unique recovery of a general vector valued first order coefficient, depending on both time and space variable, and to the unique recovery inside the domain of quasilinear terms, from measurements restricted to the lateral boundary, for diffusion equations
The observational limit of wave packets with noisy measurements
The authors consider the problem of recovering an observable from certain measurements containing random errors. The observable is given by a pseudodifferential operator while the random errors are generated by a Gaussian white noise. The authors show how wave packets can be used to partially recover the observable from the measurements almost surely. Furthermore, they point out the limitation of wave packets to recover the remaining part of the observable, and show how the errors hide the signal coming from the observable. The recovery results are based on an ergodicity property of the errors produced by wave packets
Scattering with critically-singular and δ-shell potentials
The authors consider a scattering problem for electric potentials that have a component which is critically singular in the sense of Lebesgue spaces, and a component given by a measure supported on a compact Lipschitz hypersurface. They study direct and inverse point-source scattering under the assumptions that the potentials are real-valued and compactly supported. To solve the direct scattering problem, the authors introduce two functional spaces ---sort of Bourgain type spaces--- that allow to refine the classical resolvent estimates of Agmon and Hörmander, and Kenig, Ruiz and Sogge. These spaces seem to be very useful to deal with the critically-singular and δ-shell components of the potentials at the same time. Furthermore, these spaces and their corresponding resolvent estimates turn out to have a strong connection with the estimates for the conjugated Laplacian used in the context of the inverse Calderón problem. In fact, the authors derive the classical estimates by Sylvester and Uhlmann, and the more recent ones by Haberman and Tataru after some embedding properties of these new spaces. Regarding the inverse scattering problem,the authors prove uniqueness for the potentials from point-source scattering data at fix energy. To address the question of uniqueness the authors combine some of the most advanced techniques in the construction of complex geometrical optics solutions
The CalderĂłn problem with corrupted data
We consider the inverse CalderĂłn problem consisting of determining the conductivity inside a medium by electrical measurements on its surface. Ideally, these measurements determine the Dirichlet-to-Neumann map and, therefore, one usually assumes the data to be given by such map. This situation corresponds to having access to infinite-precision measurements, which is totally unrealistic. In this
paper, we study the CalderĂłn problem assuming the data to contain measurement errors and provide
formulas to reconstruct the conductivity and its normal derivative on the surface. Additionally, we state the rate convergence of the method. Our approach is theoretical and has a stochastic flavour
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