Kinetostatic Analysis and Solution Classification of a Planar Tensegrity Mechanism

Tensegrity mechanisms have several interesting properties that make them suitable for a number of applications. Their analysis is generally challenging because the static equilibrium conditions often result in complex equations. A class of planar one-degree-of-freedom (dof) tensegrity mechanisms with three linear springs is analyzed in detail in this paper. The kinetostatic equations are derived and solved under several loading and geometric conditions. It is shown that these mechanisms exhibit up to six equilibrium configurations, of which one or two are stable. Discriminant varieties and cylindrical algebraic decomposition combined with Groebner base elimination are used to classify solutions as function of the input parameters.Comment: 7th IFToMM International Workshop on Computational Kinematics, May 2017, Poitiers, France. 201

The Third International Symposium on Tilapia in Aquaculture

Tilapias, because of the low cost and relative ease of their production, are a potential food fish staple for many people ini tropical countries and a globally traded commodity. This volume of symposium proceedings shows a strong interest in production systems research and a dawning interest in socioeconomic research. Both of these fields of research are expected to receive much greater attention in the future as the economic and market importance of tilapia increases and as we seek to understand better the distribution of benefits of the different production technologies.Tilapia culture Tilapia, Oreochromis, Sarotherodon

Towards Mixed Gr{\"o}bner Basis Algorithms: the Multihomogeneous and Sparse Case

One of the biggest open problems in computational algebra is the design of efficient algorithms for Gr{\"o}bner basis computations that take into account the sparsity of the input polynomials. We can perform such computations in the case of unmixed polynomial systems, that is systems with polynomials having the same support, using the approach of Faug{\`e}re, Spaenlehauer, and Svartz [ISSAC'14]. We present two algorithms for sparse Gr{\"o}bner bases computations for mixed systems. The first one computes with mixed sparse systems and exploits the supports of the polynomials. Under regularity assumptions, it performs no reductions to zero. For mixed, square, and 0-dimensional multihomogeneous polynomial systems, we present a dedicated, and potentially more efficient, algorithm that exploits different algebraic properties that performs no reduction to zero. We give an explicit bound for the maximal degree appearing in the computations

Locked and Unlocked Polygonal Chains in 3D

In this paper, we study movements of simple polygonal chains in 3D. We say that an open, simple polygonal chain can be straightened if it can be continuously reconfigured to a straight sequence of segments in such a manner that both the length of each link and the simplicity of the chain are maintained throughout the movement. The analogous concept for closed chains is convexification: reconfiguration to a planar convex polygon. Chains that cannot be straightened or convexified are called locked. While there are open chains in 3D that are locked, we show that if an open chain has a simple orthogonal projection onto some plane, it can be straightened. For closed chains, we show that there are unknotted but locked closed chains, and we provide an algorithm for convexifying a planar simple polygon in 3D with a polynomial number of moves.Comment: To appear in Proc. 10th ACM-SIAM Sympos. Discrete Algorithms, Jan. 199

Frobenius groups of automorphisms and their fixed points

Suppose that a finite group $G$ admits a Frobenius group of automorphisms $FH$ with kernel $F$ and complement $H$ such that the fixed-point subgroup of $F$ is trivial: $C_G(F)=1$. In this situation various properties of $G$ are shown to be close to the corresponding properties of $C_G(H)$. By using Clifford's theorem it is proved that the order $|G|$ is bounded in terms of $|H|$ and $|C_G(H)|$, the rank of $G$ is bounded in terms of $|H|$ and the rank of $C_G(H)$, and that $G$ is nilpotent if $C_G(H)$ is nilpotent. Lie ring methods are used for bounding the exponent and the nilpotency class of $G$ in the case of metacyclic $FH$. The exponent of $G$ is bounded in terms of $|FH|$ and the exponent of $C_G(H)$ by using Lazard's Lie algebra associated with the Jennings--Zassenhaus filtration and its connection with powerful subgroups. The nilpotency class of $G$ is bounded in terms of $|H|$ and the nilpotency class of $C_G(H)$ by considering Lie rings with a finite cyclic grading satisfying a certain `selective nilpotency' condition. The latter technique also yields similar results bounding the nilpotency class of Lie rings and algebras with a metacyclic Frobenius group of automorphisms, with corollaries for connected Lie groups and torsion-free locally nilpotent groups with such groups of automorphisms. Examples show that such nilpotency results are no longer true for non-metacyclic Frobenius groups of automorphisms.Comment: 31 page

Fast Reduction of Bivariate Polynomials with Respect to Sufficiently Regular Gröbner Bases

International audienc

Workspace and Singularity analysis of a Delta like family robot

Workspace and joint space analysis are essential steps in describing the task and designing the control loop of the robot, respectively. This paper presents the descriptive analysis of a family of delta-like parallel robots by using algebraic tools to induce an estimation about the complexity in representing the singularities in the workspace and the joint space. A Gr{\"o}bner based elimination is used to compute the singularities of the manipulator and a Cylindrical Algebraic Decomposition algorithm is used to study the workspace and the joint space. From these algebraic objects, we propose some certified three dimensional plotting describing the the shape of workspace and of the joint space which will help the engineers or researchers to decide the most suited configuration of the manipulator they should use for a given task. Also, the different parameters associated with the complexity of the serial and parallel singularities are tabulated, which further enhance the selection of the different configuration of the manipulator by comparing the complexity of the singularity equations.Comment: 4th IFTOMM International Symposium on Robotics and Mechatronics, Jun 2015, Poitiers, France. 201

Reactions to graphic and text health warnings for cigarettes, sugar-sweetened beverages, and alcohol:An online randomized experiment of US adults.

We aimed to examine reactions to graphic versus text-only warnings for cigarettes, SSBs, and alcohol. A convenience sample of US adults completed an online survey in 2018 (n=1,352 in the analytic sample). We randomly assigned participants to view a: 1) text-only warning without efficacy information (i.e., message intended to increase consumers’ confidence in their ability to stop using the product), 2) text-only warning with efficacy information, 3) graphic warning without efficacy information, or 4) graphic warning with efficacy information. Participants viewed their assigned warning on cigarettes, SSBs, and alcohol, in a random order. Across product types, graphic warnings were perceived as more effective than text-only warnings (p<.001) and led to lower believability, greater reactance (i.e., resistance), more thinking about harms, and lower product appeal (all p<.05); policy support did not differ. Compared to SSB and alcohol warnings, cigarette warnings led to higher perceived message effectiveness, believability, fear, thinking about harms, policy support, and greater reductions in product appeal (all p<.05). The efficacy information did not influence any outcomes. Graphic warnings out-performed text-only warnings on key predictors of behavior despite causing more reactance

Impact of The Real Cost Campaign on Adolescents’ Recall, Attitudes, and Risk Perceptions about Tobacco Use: A National Study

The Food and Drug Administration’s (FDA) The Real Cost campaign advertisements (ads) have targeted U.S. youth with messages designed to prevent and reduce tobacco use. This study examined exposure to The Real Cost campaign, including ad and slogan recall, and associations with attitudes and risk perceptions among U.S. adolescents. We analyzed data from a nationally representative sample of adolescents aged 13 to 17 years (n = 1125) surveyed by phone from October 2014 to June 2015. We assessed aided recall of and attitudes toward four campaign ads and the one slogan. Logistic regression models assessed whether aided recall of The Real Cost ads or slogan was associated with perceived likelihood of serious health consequences of cigarette smoking. Most (88%) adolescents reported seeing or hearing at least one of four ads for The Real Cost, and 54% recalled The Real Cost slogan. The majority of adolescents reported more negative attitudes toward tobacco products after seeing or hearing the ads. Recall of any The Real Cost ad was significantly associated with greater perceptions of serious health consequences of cigarette smoking (Adjusted Odd Ratios (AOR) = 5.58, 95% Confidence Interval (CI) = 1.20–25.90). The FDA’s The Real Cost campaign has achieved very high reach and is associated with more negative attitudes toward tobacco products and greater risk perceptions of cigarette smoking among U.S. adolescents

Why pinning by surface irregularities can explain the peak effect in transport properties and neutron diffraction results in NbSe2 and Bi-2212 crystals?

The existence of a peak effect in transport properties (a maximum of the critical current as function of magnetic field) is a well-known but still intriguing feature of type II superconductors such as NbSe2 and Bi-2212. Using a model of pinning by surface irregularities in anisotropic superconductors, we have developed a calculation of the critical current which allows estimating quantitatively the critical current in both the high critical current phase and in the low critical current phase. The only adjustable parameter of this model is the angle of the vortices at the surface. The agreement between the measurements and the model is really very impressive. In this framework, the anomalous dynamical properties close to the peak effect is due to co-existence of two different vortex states with different critical currents. Recent neutron diffraction data in NbSe2 crystals in presence of transport current support this point of view