Turing machines can be efficiently simulated by the General Purpose Analog Computer

The Church-Turing thesis states that any sufficiently powerful computational model which captures the notion of algorithm is computationally equivalent to the Turing machine. This equivalence usually holds both at a computability level and at a computational complexity level modulo polynomial reductions. However, the situation is less clear in what concerns models of computation using real numbers, and no analog of the Church-Turing thesis exists for this case. Recently it was shown that some models of computation with real numbers were equivalent from a computability perspective. In particular it was shown that Shannon's General Purpose Analog Computer (GPAC) is equivalent to Computable Analysis. However, little is known about what happens at a computational complexity level. In this paper we shed some light on the connections between this two models, from a computational complexity level, by showing that, modulo polynomial reductions, computations of Turing machines can be simulated by GPACs, without the need of using more (space) resources than those used in the original Turing computation, as long as we are talking about bounded computations. In other words, computations done by the GPAC are as space-efficient as computations done in the context of Computable Analysis

Análise preliminar da exploração florestal no Centro-sul do Brasil.

bitstream/item/215522/1/circ-tec13.pd

Análise do aproveitamento econômico do resíduo florestal.

Através de dados de pesquisas existentes sobre o conteúdo de nutrientes em resíduos florestais de Eucalyptus e Pinus, investigou-se a vantagem econômica da utilização dos resíduos, como energia ou como reciclagem de nutrientes no solo. Os resultados mostraram que o emprego dos resíduos florestais como energia se apresenta mais econômico, compensando, inclusive, a reposição de nutrientes através da adubação química. O baixo valor da equivalência da fitomassa em nutrientes, em relação ao de sua transformação em energia, e a proporção desfavorável dos preços de fertilizantes para o preço de energia, foram os principais fatores que afetaram essa economicidade

Chemical composition of bee pollen

Bee pollen, usually used as an important source of nutrients and micronutrients for the young bees in the hive, is also an important food for humans. This product is very rich in proteins, lipids, free sugars, carbohydrates, and it contains trace amounts of minerals, phenolic acids, flavonoids and a good range of vitamins. A brief look at bee pollen composition, it is easily recognised that it is a balanced food that can be used as a stand-alone food or as a nutritional supplement or even as a medicinal product. Several bioactivities, due to some of these compounds, were studied in bee pollen samples from different floral sources and the results conduce to important properties. The amount and diversity of micronutrients could induce vast benefits if used for health purposes following a complete risk assessment. Nevertheless, the results pointing towards the encouraged use of bee pollen, the risk assessment of some floral species containing toxic compounds has not been fully studied to insure the safety of consumption for all the gathered flowers, so this will also be discussed in this chapter. Admiration for its goodness and medicinal properties, bee pollen has been consumed for centuries, however, currently the efficacy and safety for all consumed products, foods, supplements or medicines is an important tool to guarantee correct quality control and essential to add value to the product. To summarise, in this chapter we will put the situation of gaps in bee pollen research into some kind of perspective, outlining some important points and discussing in more depth the implications of collecting samples, chemical composition and risk assessment.info:eu-repo/semantics/publishedVersio

a new approach for life cycle impact assessment

Publisher Copyright: © 2023 The AuthorsAll plastic contains additives. Once in the environment, these will start to leach out and will expose and harm aquatic biota, causing potentially lethal and sub-lethal toxic effects. Even though life cycle assessment covers the toxic impacts of several thousands of chemicals, models to assess the toxic impacts of plastic additives are only emerging. We gathered 461 data points from the literature (266 for freshwater and 195 for marine ecosystems) for 75 species belonging to 9 different phyla. The endpoints effective concentration and lethal concentration, no observed effects concentrations and lowest observed effect concentration tested in acute and chronic exposure, were harmonized into chronic values by applying extrapolation factors. The collected data points covered 75 main plastic additives. This allowed us to calculate 25 Effect factors, 19 for single chemicals and four for overarching categories (alkylphenols, benzophenones, brominated flame retardants and phosphates. In addition, we calculated an aggregated effect factor for chemicals that did not fit in any of the previous groups, as well as a Generic effect factor including 404 gathered data points. The estimated potentially affected fraction (PAF) for the single additives varied between 20.69 PAF·m3·kg−1 for diethyl phthalate and 11081.85 PAF·m3·kg−1 for 4-Nonylphenol. The factors can in future be combined with fate and exposure factors to derive a characterization factor for toxicity caused by additives in aquatic species. This is an important advancement for the assessment of the impacts of plastic debris on aquatic species, thus providing information for decision-makers, as well as guiding policies for the use of additives, ultimately aiming to make the plastic value chain more sustainable.publishersversionpublishe

Computability of ordinary differential equations

In this paper we provide a brief review of several results about the computability of initial-value problems (IVPs) defined with ordinary differential equations (ODEs). We will consider a variety of settings and analyze how the computability of the IVP will be affected. Computational complexity results will also be presented, as well as computable versions of some classical theorems about the asymptotic behavior of ODEs.info:eu-repo/semantics/publishedVersio

Application of Constructivist Grounded Theory in Nursing Research

Grounded Theory is a qualitative research method for collecting and analysing data and results into a substantive theory that is a theoretical interpretation of a delimited problem in a specific area of knowledge. In nursing, it allows to understand the process of social interaction and how the nursing team works in everyday situations. In this study we propose, based on the theoretical framework of Kathy Charmaz, to present the procedures for the application of the constructivist Grounded Theory in nursing research. Among these are the collection and analysis of concurrent data, constant comparison at all levels of analysis, initial, focused and axial coding, conducting memos, among other resources, construction of categories, evaluation and development of the theory

Generalized Totalizer Encoding for Pseudo-Boolean Constraints

Pseudo-Boolean constraints, also known as 0-1 Integer Linear Constraints, are used to model many real-world problems. A common approach to solve these constraints is to encode them into a SAT formula. The runtime of the SAT solver on such formula is sensitive to the manner in which the given pseudo-Boolean constraints are encoded. In this paper, we propose generalized Totalizer encoding (GTE), which is an arc-consistency preserving extension of the Totalizer encoding to pseudo-Boolean constraints. Unlike some other encodings, the number of auxiliary variables required for GTE does not depend on the magnitudes of the coefficients. Instead, it depends on the number of distinct combinations of these coefficients. We show the superiority of GTE with respect to other encodings when large pseudo-Boolean constraints have low number of distinct coefficients. Our experimental results also show that GTE remains competitive even when the pseudo-Boolean constraints do not have this characteristic.Comment: 10 pages, 2 figures, 2 tables. To be published in 21st International Conference on Principles and Practice of Constraint Programming 201

Solid Waste Mixtures as Constructed Wetlands Filling: Effect of Hydraulic Loading Rate on Nutrient Removal from Wastewater

This study aims to contribute to constructed wetlands’ (CWs) eco-efficiency by applying the concepts of circular economy and waste to treat waste. Five sets of lab-scale CWs with different combinations of filling materials were evaluated and the effect of the hydraulic loading rate (HLR) on the nutrient removal efficiencies was studied. Each CW set consisted of two, duplicate, plastic pots with solid waste filling supporting Phragmites australis macrophyte plants. The filling materials were layer combinations of limestone rock fragments, a waste from construction activities, and one of four other solid wastes: cork granulates from the cork industry (LCG); snail shells from the food and catering industry (LSS); coal slag from coal power plants (LCS); and clay brick fragments from construction activities (LBF). A reference set (LO) was filled only with limestone fragments. The CWs were operated using a low-strength wastewater in successive fill-and-drain cycles with a retention time of one to eight days and a one-day rest. Their removal efficiency was evaluated for COD, total phosphorus (TP) and total nitrogen (TN). All four CWs with mixed filling showed COD removal efficiencies higher than the reference CW and above 79%. The highest removal efficiency was achieved by the LCS CW (91 to 97%). The reference LO CW showed the highest TP removal efficiency. With exception of the LSS CW, the mixed filling CWs showed removal efficiencies close to the reference CW (above 55%). All but the LSS CW showed higher TN removal efficiencies than the reference CW (above 51%). The observed effect of HLR depends on the type of CW. The effect on COD, TP and TN removal efficiencies averaged 9%, 15% and 20%, respectively, for a range of HLR from 0.005 to 0.087 m/day. From this study it can be concluded that all tested layer-packed mixed solid waste fillings are adequate substrate combinations for nutrient removal from wastewater. Moreover, high nutrient removal efficiencies were maintained over a wide range of hydraulic loading rates. This innovative combination of waste materials can improve the CW adaptability to specific types of wastewater and contribute to reducing solid waste disposal in landfills.This work was supported by Program FEDER, ref. POCI-01-0145-FEDER-023314, project VALORBIO. The authors acknowledge the collaboration of the Lab.IPT staff and the assistance of the Instituto Politécnico de Tomar maintenance staff.info:eu-repo/semantics/publishedVersio

Tracer experiments with lithium chloride to evaluate the hydrodynamics of constructed wetlands. Comparison of alternative analytical methods

The characterization of water flow dynamics (hydrodynamics) through constructed wetlands is relevant for optimizing wastewater treatment. Although constructed wetlands consist of simple systems, the water flow is complex and irregular, therefore, the study of hydrodynamics requires the use of experimental technics such as tracer experiments. To evaluate the effects of the use of three different analytical methods to compute the concentration of lithium chloride on the main hydrodynamics parameters, tracer experiments were conducted in ten independent lab-scale constructed wetlands. The concentration of lithium chloride in the output flow of the wetlands was calculated by flame photometry, electrical conductivity using a calibration curve and electrical conductivity using the salt molar conductivity. The paired samples T-test or the non-parametric Wilcoxon’s Signed-Ranks test were used to demonstrate that the computed hydraulic retention time and the number of tanks accordingly with the tanks-in-series model were not significantly affected by the selected analytical method.This work has been financially supported by FEDER grant COMPETE-01-0145-023342 to project VALORBIO. Authors acknowledge the support of BIOTEC.ipt and Lab.IPT and the work of Carlos Ferreira, Isabel Silva and Alcino Serras.info:eu-repo/semantics/publishedVersio