45 research outputs found
Meta-Reinforcement Learning by Tracking Task Non-stationarity
No full textMany real-world domains are subject to a structured non-stationarity which affects the agent's goals and the environmental dynamics. Meta-reinforcement learning (RL) has been shown successful for training agents that quickly adapt to related tasks. However, most of the existing meta-RL algorithms for non-stationary domains either make strong assumptions on the task generation process or require sampling from it at training time. In this paper, we propose a novel algorithm (TRIO) that optimizes for the future by explicitly tracking the task evolution through time. At training time, TRIO learns a variational module to quickly identify latent parameters from experience samples. This module is learned jointly with an optimal exploration policy that takes task uncertainty into account. At test time, TRIO tracks the evolution of the latent parameters online, hence reducing the uncertainty over future tasks and obtaining fast adaptation through the meta-learned policy. Unlike most existing methods, TRIO does not assume Markovian task-evolution processes, it does not require information about the non-stationarity at training time, and it captures complex changes undergoing in the environment. We evaluate our algorithm on different simulated problems and show it outperforms competitive baselines
Corrigendum to “Venetoclax in combination with hypomethylating agents in previously untreated patients with acute myeloid leukemia ineligible for intensive treatment: a real-life multicenter experience” [Leukemia Res. 114 (March 2022) 106803](S0145212622000297)(10.1016/j.leukres.2022.106803)
No full textThe authors regret “Rosaria Sancettai is entered as co-author instead of Renato Bassan”. The authors would like to apologise for any inconvenience caused
The effect of hydroperiod on seed banks in semi-permanent prairie wetlands
No full textIn 1985, 24 bottom samples were collected in each of two slightly brackish,semi-permanent prairie wetlands (P1 and P4) with different hydroperiods. The main objective was to determine if hydroperiod affected seed pool characteristics. Additionally, 48 samples were collected in 1986 from wetland P1 to determine if seed bank composition changed annually without a change in mature vegetation.
Seed bank composition was determined by placing soil samples in a greenhouse, then counting and identifying emerged seedlings. As a check against the seedling emergence method, seeds were separated and identified microscopically in one-third of the 1985 samples. Results indicated that the emergence method was an accurate technique for assessing seed pool composition.
The wetlands did not differ in floristic composition (i.e., presence/absence) but did in species densities. The mean relative density of mudflat annuals in all seed pool samples was significantly greater in wetland P4 (82%) than in P1 (52%). A shorter hydroperiod in this wetland produces more frequent drawdowns and a greater input of mudflat annual seeds. Conversely, seeds of emergent species were more abundant in the seed bank of wetland Pl (48%) compared to P4 (17%). The former wetland has a longer hydroperiod and less frequent drawdowns, and thus, the primary seed input is from emergent plants.Master of Scienc
Response of semi-permanent prairie wetland to climate change: a spatial simulation model
No full textThe objective of this research was to assess the potential effects of global warming on the hydrology and vegetation in semi-permanent wetlands located in the glaciated prairie region of North Dakota. As a means to that objective, a spatially-defined simulation model of the vegetation dynamics in these wetlands was constructed.
A hydrologic component of the model estimated water levels based on precipitation, runoff, potential evaporation and transpiration. Amount and distribution of emergent cover and open water were modeled using a geographical information system. Vegetation response to changes in water level was based on seed bank composition, seedling recruitment, establishment and plant survivorship. Simulation results were compared to actual distributions from aerial photographs (1979-89).
Results showed that the model was relatively good at calculating changes in water level for average years. Late-summer water levels were overestimated during dry years due to limitations in the Thornthwaite method of calculating potential evapotranspiration.
In general, changes in the ratio of emergent cover to open water were accurately simulated. Tests of the model elucidated two areas that needed improvement. First, seedlings germinated too quickly on exposed mudflats in the model when drawdown occurred late in the season. The actual wetland had a thick mat of dried, submergent vegetation on top of the mudflats which impeded germination, which the model did not consider. Second, model conversions between open water and deep marsh vegetation were not always timed correctly. If water depth crossed a threshold value for a given period of time a cell would change its type. In reality, tolerance of emergents to deep water is more complex. A probability function with respect to time and water depth rather than a threshold value would better represent this relationship.
The model was used to assess the potential effects of global warming on the cover cycle in one wetland. An 11-year simulation was run using a normal versus greenhouse climate. Although water level fluctuations still occurred, peak values were significantly lower in the warming scenario and the wetland dried in most years. Simulations also revealed a significant change in the vegetation, from a nearly balanced cover ratio to a completely closed basin with no open water areas.Ph. D
On Properties of Pair Operations
No full textFor any closure operation \cl and interior operation \ri on a class of -modules, we develop the theory of \cl-prereductions and \ri-postexpansions. A pair operation is a generalization of closure and interior operations. Using Epstein, R.G. and Vassilev\u27s duality \cite{ERGV-nonres}, we show that these notions are in fact dual to each other. We discuss the relationship between the core and hull and prereductions and postexpansions. We further the thematic notion of duality and seek to understand how it arises in the context of properties pair operations can be endowed with and focus on inner product spaces and properties demonstrated by the orthogonal complement. Finally, constructions of pair operations through ring extensions and collections will be explored with relation to how the new operation can preserve certain properties
Aproveitamento industrial dos descartes de pós-colheita.
No full textA seleção e a classificação de banana nas propriedades geram um volume de descartes que não é utilizado ou que é usado na alimentação animal, na adubação do bananal e no preparo de composto orgânico. Uma parcela desses descartes pode ser aproveitada na agroindústria, desde que apresente qualidade adequada. Para o aproveitamento dos descartes de pós-colheita, existem inúmeras formas, tanto da banana verde, quanto da madura. É possível obter produtos à base da massa da polpa de banana madura (néctar de banana, doces de massas, suco de banana concentrado e clarificado), produtos derivados da fruta madura (banana-passa, bebidas e alcóolicas e etanol, vinagre de banana, banana em calda), produtos à base de banana verde (farinha de banana, chips de banana) e do processamento mínimo
Defesa e território de forrageamento das colônias do cupim Neotropical Ruptitermes reconditus (Isoptera, Termitidae, Apicotermitinae)
No full textOs cupins camicases são assim chamados pois realizam comportamento de defesa caracterizado pela ruptura da parede lateral abdominal e consequente liberação de secreção pegajosa que imobiliza e mata o inseto inimigo. Ruptitermes reconditus é uma das espécies que apresentam este comportamento explosivo dos operários cujos órgãos deiscentes são responsáveis pela liberação de secreção pegajosa. Entretanto, pouco se sabe a respeito da eficiência deste comportamento desempenhado pelos operários e se todos os indivíduos possuem a capacidade ou estão aptos a executar esta tarefa. Além disso, por ser uma espécie subterrânea, não há informações na literatura sobre a extensão de seus ninhos. Desse modo, o presente trabalho teve por objetivos: otimizar a coleta por meio de diferentes iscas celulósicas; verificar a efetividade do comportamento de defesa de operários de R. reconditus por meio de bioensaios; correlacionar o indivíduo envolvido no ato de explosão com a idade relativa por meio de morfometria do formato da mandíbula e dimensionar a área de forrageio para se ter uma noção da extensão de seus ninhos. Os bioensaios foram realizados utilizando-se operários de R. reconditus tendo como adversários os cupins das espécies Coptotermes gestroi e Heterotermes tenuis e formigas do gênero Camponotus. Posteriormente, realizou-se a morfometria das mandíbulas de todos os operários de R. reconditus utilizados nos bioensaios para correlação entre o comportamento de defesa e a idade relativa do indivíduo (medida pelo desgaste mandibular). No período entre Setembro de 2013 a Março de 2014 armadilhas com diferentes iscas celulósicas foram instaladas para coleta dos indivíduos. Os mapeamentos de colônias de R. reconditus foram realizados medindo-se a distância entre os orifícios de saída dos forrageiros e colocando estes indivíduos em confronto por meio de bioensaios de agressividade. Os resultados indicam que...Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq
