1,863 research outputs found
Probing Strongly Coupled Chameleons with Slow Neutrons
We consider different methods to probe chameleons with slow neutrons.
Chameleon modify the potential of bouncing neutrons over a flat mirror in the
terrestrial gravitational field. This induces a shift in the energy levels of
the neutrons which could be detected in current experiments like GRANIT.
Chameleons between parallel plates have a field profile which is bubble-like
and which would modify the phase of neutrons in interferometric experiments. We
show that this new method of detection is competitive with the bouncing neutron
one, hopefully providing an efficient probe of chameleons when strongly coupled
to matter
Uniqueness domains and non singular assembly mode changing trajectories
Parallel robots admit generally several solutions to the direct kinematics
problem. The aspects are associated with the maximal singularity free domains
without any singular configurations. Inside these regions, some trajectories
are possible between two solutions of the direct kinematic problem without
meeting any type of singularity: non-singular assembly mode trajectories. An
established condition for such trajectories is to have cusp points inside the
joint space that must be encircled. This paper presents an approach based on
the notion of uniqueness domains to explain this behaviour
An algebraic method to check the singularity-free paths for parallel robots
Trajectory planning is a critical step while programming the parallel
manipulators in a robotic cell. The main problem arises when there exists a
singular configuration between the two poses of the end-effectors while
discretizing the path with a classical approach. This paper presents an
algebraic method to check the feasibility of any given trajectories in the
workspace. The solutions of the polynomial equations associated with the
tra-jectories are projected in the joint space using Gr{\"o}bner based
elimination methods and the remaining equations are expressed in a parametric
form where the articular variables are functions of time t unlike any numerical
or discretization method. These formal computations allow to write the Jacobian
of the manip-ulator as a function of time and to check if its determinant can
vanish between two poses. Another benefit of this approach is to use a largest
workspace with a more complex shape than a cube, cylinder or sphere. For the
Orthoglide, a three degrees of freedom parallel robot, three different
trajectories are used to illustrate this method.Comment: Appears in International Design Engineering Technical Conferences &
Computers and Information in Engineering Conference , Aug 2015, Boston,
United States. 201
Non-singular assembly mode changing trajectories in the workspace for the 3-RPS parallel robot
Having non-singular assembly modes changing trajectories for the 3-RPS
parallel robot is a well-known feature. The only known solution for defining
such trajectory is to encircle a cusp point in the joint space. In this paper,
the aspects and the characteristic surfaces are computed for each operation
mode to define the uniqueness of the domains. Thus, we can easily see in the
workspace that at least three assembly modes can be reached for each operation
mode. To validate this property, the mathematical analysis of the determinant
of the Jacobian is done. The image of these trajectories in the joint space is
depicted with the curves associated with the cusp points
Accuracy (Trueness and Precision) of Cone Calorimeter Tests with and Without a Vitiated Air Enclosure
AbstractOver the last few years, new many laboratory fire tests have been developed. One such test is the controlled atmosphere cone calorimeter (CACC). Until now this bench-scale test has not been standardized and the device design differs from one laboratory to another. These differences can affect measurement accuracyaaAccuracy: The closeness of agreement between a test result and the accepted reference value. (truenessbbTrueness: The closeness of agreement between the average value obtained from a large series of test results and an accepted reference value. and precisionccPrecision: The closeness of agreement between independent test results obtained under stipulated conditions.) and direct comparison of literature results is difficult. No studies have been conducted to understand the effect of the design on the fire behaviour of materials and measurement accuracy in the CACC. The present publication focuses on these effects under ambient and non-ambient oxygen conditions. Several designs were investigated using Poly(methyl)methacrylate (PMMA) as the test material. Statistical analyses were performed in some cases to assess the data. The results are presented and discussed
On the determination of cusp points of 3-R\underline{P}R parallel manipulators
This paper investigates the cuspidal configurations of 3-RPR parallel
manipulators that may appear on their singular surfaces in the joint space.
Cusp points play an important role in the kinematic behavior of parallel
manipulators since they make possible a non-singular change of assembly mode.
In previous works, the cusp points were calculated in sections of the joint
space by solving a 24th-degree polynomial without any proof that this
polynomial was the only one that gives all solutions. The purpose of this study
is to propose a rigorous methodology to determine the cusp points of
3-R\underline{P}R manipulators and to certify that all cusp points are found.
This methodology uses the notion of discriminant varieties and resorts to
Gr\"obner bases for the solutions of systems of equations
Downlink Radio Resource Management for QoS Provisioning in OFDMA Systems:with emphasis on Admission Control and Packet Scheduling
Formal verification in Coq of program properties involving the global state effect
The syntax of an imperative language does not mention explicitly the state,
while its denotational semantics has to mention it. In this paper we present a
framework for the verification in Coq of properties of programs manipulating
the global state effect. These properties are expressed in a proof system which
is close to the syntax, as in effect systems, in the sense that the state does
not appear explicitly in the type of expressions which manipulate it. Rather,
the state appears via decorations added to terms and to equations. In this
system, proofs of programs thus present two aspects: properties can be verified
{\em up to effects} or the effects can be taken into account. The design of our
Coq library consequently reflects these two aspects: our framework is centered
around the construction of two inductive and dependent types, one for terms up
to effects and one for the manipulation of decorations
Cusp Points in the Parameter Space of Degenerate 3-RPR Planar Parallel Manipulators
This paper investigates the conditions in the design parameter space for the
existence and distribution of the cusp locus for planar parallel manipulators.
Cusp points make possible non-singular assembly-mode changing motion, which
increases the maximum singularity-free workspace. An accurate algorithm for the
determination is proposed amending some imprecisions done by previous existing
algorithms. This is combined with methods of Cylindric Algebraic Decomposition,
Gr\"obner bases and Discriminant Varieties in order to partition the parameter
space into cells with constant number of cusp points. These algorithms will
allow us to classify a family of degenerate 3-RPR manipulators.Comment: ASME Journal of Mechanisms and Robotics (2012) 1-1
- …