Solution intervals for variables in spatial RCRCR linkages

© 2019. ElsevierAn analytic method to compute the solution intervals for the input variables of spatial RCRCR linkages and their inversions is presented. The input-output equation is formulated as the intersection of a single ellipse with a parameterized family of ellipses, both related with the possible values that certain dual angles determined by the configuration of the mechanism can take. Bounds for the angles of the input pairs of the RCRCR and RRCRC inversions are found by imposing the tangency of two ellipses, what reduces to analyzing the discriminant of a fourth degree polynomial. The bounds for the input pair of the RCRRC inversion is found as the intersection of a single ellipse with the envelope of the parameterized family of ellipses. The method provides the bounds of each of the assembly modes of the mechanism as well as the local extrema that may exist for the input variablePeer ReviewedPostprint (author's final draft

Competitive function approximation for reinforcement learning

The application of reinforcement learning to problems with continuous domains requires representing the value function by means of function approximation. We identify two aspects of reinforcement learning that make the function approximation process hard: non-stationarity of the target function and biased sampling. Non-stationarity is the result of the bootstrapping nature of dynamic programming where the value function is estimated using its current approximation. Biased sampling occurs when some regions of the state space are visited too often, causing a reiterated updating with similar values which fade out the occasional updates of infrequently sampled regions. We propose a competitive approach for function approximation where many different local approximators are available at a given input and the one with expectedly best approximation is selected by means of a relevance function. The local nature of the approximators allows their fast adaptation to non-stationary changes and mitigates the biased sampling problem. The coexistence of multiple approximators updated and tried in parallel permits obtaining a good estimation much faster than would be possible with a single approximator. Experiments in different benchmark problems show that the competitive strategy provides a faster and more stable learning than non-competitive approaches.Preprin

Online EM with weight-based forgetting

In the online version of the EM algorithm introduced by Sato and Ishii (2000), a time-dependent discount factor is introduced for forgetting the effect of the old estimated values obtained with an earlier, inaccurate estimator. In their approach, forgetting is uniformly applied to the estimators of each mixture component depending exclusively on time, irrespective of theweight attributed to each unit for the observed sample. This causes an excessive forgetting in the less frequently sampled regions. To address this problem, we propose a modification of the algorithm that involves a weight-dependent forgetting, different for each mixture component, in which old observations are forgotten according to the actual weight of the new samples used to replace older values. A comparison of the timedependent versus the weight-dependent approach shows that the latter improves the accuracy of the approximation and exhibits much greater stability.Peer Reviewe

Probabilistic Extensions of the Erd\H os-Ko-Rado Property

The classical Erd\H os-Ko-Rado (EKR) Theorem states that if we choose a family of subsets, each of size (k), from a fixed set of size (n (n > 2k)), then the largest possible pairwise intersecting family has size (t ={n-1\choose k-1}). We consider the probability that a randomly selected family of size (t=t_n) has the EKR property (pairwise nonempty intersection) as $n$ and $k=k_n$ tend to infinity, the latter at a specific rate. As $t$ gets large, the EKR property is less likely to occur, while as $t$ gets smaller, the EKR property is satisfied with high probability. We derive the threshold value for $t$ using Janson's inequality. Using the Stein-Chen method we show that the distribution of $X_0$, defined as the number of disjoint pairs of subsets in our family, can be approximated by a Poisson distribution. We extend our results to yield similar conclusions for $X_i$, the number of pairs of subsets that overlap in exactly $i$ elements. Finally, we show that the joint distribution $(X_0, X_1, ..., X_b)$ can be approximated by a multidimensional Poisson vector with independent components.Comment: 18 page

Acantholippia salsoloides : Phytochemical Composition and Biological Potential of a Thujonic Population

Acantholippia salsoloides (Verbenaceae) is an aromatic plant widespread in the Andean region. The infusion (leaves and flowers) is widely used as a digestive stimulant as well as for the treatment of various diseases in traditional medicine. A. salsoloides attributes its common name “rica-rica” to the fresh and sweet fragrance of the plant. In this work, 2 different polar extracts and the essential oil of a selected rica-rica population were studied. The phenolic composition was analyzed by high-performance liquid chromatography diode array detector; the essential oil profile was determined by gas-chromatography ion-trap mass spectrometry/flame ionization detection. For all extracts, the antibacterial potential was performed by in vitro assays; the antioxidant and α-glucosidase inhibition were determined in decoction and hydroethanolic extracts. The volatile profile allowed the identification of 26 volatile compounds, β-thujone (84%) being the major one in this rica-rica population. Eighteen phenolic compounds were identified; isoferulic acid (16%-18%) and cynaroside (45%-47%) were the larger ones. In a general way, the hydroethanolic extract was more active against Staphylococcus aureus and Micrococcus luteus (minimum inhibitory concentrations= 0.3- 1.3 mg/mL). Both polar extracts have strong antiradical activities although decoction extract proved to be more active against DPPH· (half-maximal inhibitory concentration [IC50] =36 µg/mL) and O2•− (IC50 =28 µg/mL) while hydroethanolic extract shows higher action over α-glucosidase (IC50 =217 µg/mL). The results suggest that A. salsoloides leaves and flowers may be an interesting source of natural antioxidants, antidiabetics, or antimicrobials, and could be used in dietary supplements, medicinal products and pharmaceutical formulations.Fil: Celaya, Liliana Soledad. Universidad Nacional de Jujuy. Centro Interdisciplinario de Investigaciones En Tecnologias y Desarrollo Social Para El Noa. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Saltajujuy. Centro Interdisciplinario de Investigaciones En Tecnologias y Desarrollo Social Para El Noa.; Argentina. Universidad Nacional de Misiones; ArgentinaFil: Viturro, Carmen Ines. Universidad Nacional de Jujuy. Centro Interdisciplinario de Investigaciones En Tecnologias y Desarrollo Social Para El Noa. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Saltajujuy. Centro Interdisciplinario de Investigaciones En Tecnologias y Desarrollo Social Para El Noa.; Argentina. Universidad Nacional de Jujuy; ArgentinaFil: Silva, Luís R.. Universidade da Beira Interior; Portuga