Learning 2-opt Heuristics for the Traveling Salesman Problem via Deep Reinforcement Learning

Recent works using deep learning to solve the Traveling Salesman Problem (TSP) have focused on learning construction heuristics. Such approaches find TSP solutions of good quality but require additional procedures such as beam search and sampling to improve solutions and achieve state-of-the-art performance. However, few studies have focused on improvement heuristics, where a given solution is improved until reaching a near-optimal one. In this work, we propose to learn a local search heuristic based on 2-opt operators via deep reinforcement learning. We propose a policy gradient algorithm to learn a stochastic policy that selects 2-opt operations given a current solution. Moreover, we introduce a policy neural network that leverages a pointing attention mechanism, which unlike previous works, can be easily extended to more general k-opt moves. Our results show that the learned policies can improve even over random initial solutions and approach near-optimal solutions at a faster rate than previous state-of-the-art deep learning methods.Comment: To appear in Proceedings Machine Learning Research - ACML 202

A novel vasoactive proline-rich oligopeptide from the skin secretion of the frog Brachycephalus ephippium.

Proline-rich oligopeptides (PROs) are a large family which comprises the bradykinin-potentiating peptides (BPPs). They inhibit the activity of the angiotensin I-converting enzyme (ACE) and have a typical pyroglutamyl (Pyr)/proline-rich structure at the N- and C-terminus, respectively. Furthermore, PROs decrease blood pressure in animals. In the present study, the isolation and biological characterization of a novel vasoactive BPP isolated from the skin secretion of the frog Brachycephalus ephippium is described. This new PRO, termed BPP-Brachy, has the primary structure WPPPKVSP and the amidated form termed BPPBrachyNH2 inhibits efficiently ACE in rat serum. In silico molecular modeling and docking studies suggest that BPP-BrachyNH2 is capable of forming a hydrogen bond network as well as multiple van der Waals interactions with the rat ACE, which blocks the access of the substrate to the C-domain active site. Moreover, in rat thoracic aorta BPP-BrachyNH2 induces potent endothelium-dependent vasodilatation with similar magnitude as captopril. In DAF-FM DA-loaded aortic cross sections examined by confocal microscopy, BPP-BrachyNH2 was found to increase the release of nitric oxide (NO). Moreover, BPP-BrachyNH2 was devoid of toxicity in endothelial and smooth muscle cell cultures. In conclusion, the peptide BPP-BrachyNH2 has a novel sequence being the first BPP isolated from the skin secretion of the Brachycephalidae family. This opens for exploring amphibians as a source of new biomolecules. The BPP-BrachyNH2 is devoid of cytotoxicity and elicits endothelium-dependent vasodilatation mediated by NO. These findings open for the possibility of potential application of these peptides in the treatment of endothelial dysfunction and cardiovascular diseases

Climate seasonality limits leaf carbon assimilation and wood productivity in tropical forests

The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associated canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is < 2000ĝ€-mmĝ€-yrĝ'1 (water-limited forests) and to radiation otherwise (light-limited forests). On the other hand, independent of climate limitations, wood productivity and litterfall are driven by seasonal variation in precipitation and evapotranspiration, respectively. Consequently, light-limited forests present an asynchronism between canopy photosynthetic capacity and wood productivity. First-order control by precipitation likely indicates a decrease in tropical forest productivity in a drier climate in water-limited forest, and in current light-limited forest with future rainfall < 2000ĝ€-mmĝ€-yrĝ'1. Author(s) 2016.Fil: Wagner, Fabien H.. Instituto Nacional de Pesquisas Espaciais; BrasilFil: Hérault, Bruno. Ecologie Des Forets de Guyane; BrasilFil: Bonal, Damien. Institut National de la Recherche Agronomique; FranciaFil: Stahl, Clment. Universiteit Antwerp; BélgicaFil: Anderson, Liana O.. National Center For Monitoring And Early Warning Of Natural Disasters; BrasilFil: Baker, Timothy R.. University Of Leeds; Reino UnidoFil: Sebastian Becker, Gabriel. Universidad de Hohenheim; AlemaniaFil: Beeckman, Hans. Royal Museum For Central Africa; BélgicaFil: Boanerges Souza, Danilo. Ministério da Ciência, Tecnologia, Inovações. Instituto Nacional de Pesquisas da Amazônia; BrasilFil: Cesar Botosso, Paulo. Ministerio da Agricultura Pecuaria e Abastecimento de Brasil. Empresa Brasileira de Pesquisa Agropecuaria; BrasilFil: Bowman, David M. J. S.. University of Tasmania; AustraliaFil: Bräuning, Achim. Universitat Erlangen-Nuremberg; AlemaniaFil: Brede, Benjamin. Wageningen University And Research Centre; Países BajosFil: Irving Brown, Foster. Universidade Federal Do Acre; BrasilFil: Julio Camarero, Jesus. Instituto Boliviano de Investigacion Forestal Bolivia; BoliviaFil: Camargo, Plnio Barbosa. Universidade de Sao Paulo; BrasilFil: Cardoso, Fernanda C.G.. Universidade Federal do Paraná; BrasilFil: Carvalho, Fabrcio Alvim. Universidade Federal de Juiz de Fora; BrasilFil: Castro, Wendeson. Universidade Federal Do Acre; BrasilFil: Koloski Chagas, Rubens. Universidade de Sao Paulo; BrasilFil: Chave, Jrome. Centre National de la Recherche Scientifique; FranciaFil: Chidumayo, Emmanuel N.. University Of Zambia; ZambiaFil: Clark, Deborah A.. University Of Missouri-st. Louis; Estados UnidosFil: Regina Capellotto Costa, Flavia. Ministério da Ciência, Tecnologia, Inovações. Instituto Nacional de Pesquisas da Amazônia; BrasilFil: Couralet, Camille. Royal Museum For Central Africa; BélgicaFil: Henrique Da Silva Mauricio, Paulo. Universidade Federal Do Acre; BrasilFil: Dalitz, Helmut. Universidad de Hohenheim; AlemaniaFil: Resende De Castro, Vinicius. Universidade Federal de Vicosa; BrasilFil: Milani, Jaanan Eloisa De Freitas. Universidade Federal do Paraná; BrasilFil: Roig Junent, Fidel Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla | Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Museo de Historia Natural de San Rafael - Ianigla; Argentin

Evaluation of PCR and multiplex PCR in relation to nested PCR for diagnosing Theileria equi

Conventional PCR (PCRTeq) for diagnosing Theileria equi and multiplex PCR (M/PCRTeq-Bc) for diagnosing T. equi and Babesia caballi were comparatively evaluated with nested PCR (N/PCR-Teq) for diagnosing equine piroplasmosis. In DNA sensitivity determinations, in multiple dilutions of equine blood that had tested positive for T. equi, PCR-Teq and N/PCR-Teq detected hemoparasite DNA in the larger dilutions (1:128), but did not differ significantly from the M/PCRTeq-Bc (1:64). In analyses on equine serum tested by ELISA, there was high agreement between this serological test and PCR-Teq (k = 0.780) and moderate agreement with N/PCR-Teq (k = 0.562) and M/PCRTeq-Bc (k = 0.488). PCR-Teq found a higher frequency of T. equi both in extensively and intensively reared horses, but this was not significant in relation to N/PCR-Teq (P>0.05), and both PCRs indicated that there was an endemic situation regarding T. equi in the population of horses of this sample. PCR-Teq was only significantly different from M/PCR-Teq-Bc (P<0.05). PCR-Teq presented high sensitivity and specificity, comparable to N/PCR-Teq, but with the advantage of higher speed in obtaining results and lower costs and risks of laboratory contamination. This accredits PCR-Teq for epidemiological studies and for determinations on affected horses