196746 research outputs found
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Likelihood-based inference in temporal hierarchies
No full textWe consider the importance of correctly specifying the variance–covariance matrix to allow information to be shared between aggregation levels when reconciling forecasts in a temporal hierarchy. We propose a novel framework for parametric modelling of the variance–covariance matrix, along with an iterative algorithm for maximum likelihood estimation. The covariance between aggregation levels can be modelled by aggregating the lower-level errors and disaggregating information from the higher levels. Using the likelihood approach, statistical inference can be applied to identify a parsimonious parametric structure for the variance–covariance matrix. We test and discuss different structures for how forecast errors are connected across aggregation levels and present a framework for simplifying these structures using Wald and likelihood-ratio tests. We evaluate the proposed method in a simulation study and through an application to day-ahead electricity load forecasting and find that it performs well compared to optimal shrinkage estimation.<br/
Recovery and Characterization of Cellulosic Ethanol from Fermentation of Sugarcane Bagasse
No full textIndustrial production of ethanol by fermentation using renewable feedstock such as sugarcane stalks has been demonstrated as a sustainable fuel chain in Brazil. This work focused on the production of cellulosic ethanol from sugarcane bagasse in a pilot scale unit by applying the current bioprocessing strategies with the aim of recovering and characterizing the end products. The feedstock was pretreated at 190 °C and a residence time of 10 min. Enzymatic hydrolysis was performed with commercial cellulolytic enzymes. Fermentation’s substrates were formulated with hydrolysate and supplemented with 8%wt sugarcane molasses. The fermentations were set up to mimic the conventional industrial fermentation in Brazil’s ethanol distilleries at high cell density with cell recycling. The fermentation resulted in a reproducible performance by the yield of 0.49 g/g, productivity of 6.96 g/(L∙h), and cell viability of 95.3%. Ethanol was recovered in a lab-scale distillation batch system. Distilled fractions showed higher content of higher alcohols and sulfur content than the standard specification of ANP (National Agency of Petroleum - Brazilian Agency) for ethanol fuel. The distillation bottom product (vinasse) presented most characteristics suitable for fertilizer or biogas applications, except for sodium and sulfate content. Therefore, for a successful technology, transference processing adjustments should be made to make the product commercially suitable and the side stream compatible for disposal as fertilizer or digestion for biogas production
An umbrella review of product-service systems: Analysis of review papers characteristics, research trends and underexplored topics
No full textProduct-Service systems (PSS) is a somewhat established field, and many literature reviews looking at the state-of-the-art in PSS research have been conducted. Nevertheless, a broad picture of all research developed over the years and the progress of the field is still missing. Aiming to provide a clear picture of how the literature has evolved over the years and the status of the body of knowledge on the topic, this paper analyzes PSS-related literature review papers, identifies what aspects of this body of research are well developed, the progress achieved so far and remaining underexplored topics. An umbrella review (i.e., a review of reviews) was conducted, selecting 45 PSS-related review papers. The characteristics of the reviews are classified according to seven review types. A PSS-related literature review timeline is developed, divided into four research periods according to the publications’ focus (themes, macro-topics and topics), similarities, timeframe, and review types. The results show that descriptive reviews are the most common in PSS-related literature. The paper provides a general picture of PSS-related literature review papers, focusing on the review types, thematic evolution, topics covered by the analyzed reviews, and underexplored research topics that could contribute to bring new insights to PSS-related research. There is a lack of quantitative studies in PSS literature; therefore, meta-analyses have not been developed in the area until now. Research on PSS business model and innovation topics are scare, and could be connected with marketing and strategy. The research opportunities highlighted in this study offer a broader perspective to readers as those cover the point of view of different authors from different research fields. More studies synthesizing the results of PSS-related research and contrasting the opinions of the different research communities should be conducted to advance PSS knowledge
Evaluation of spectral line mixing models and the effects on high pressure radiative heat transfer calculations
No full textAt higher pressures, the spectral lines in a gas spectrum can become more broadened and shifted due to collisional effects, leading to increased spectral line mixing. In the present study, we have reviewed different line mixing models for modeling the absorption spectra for three gases of CO, CO, and HO and applied these models to simulate radiative spectra for pressures within approximately 5–100 bar. The simulated data were compared with the yet-published high-pressure spectral experimental data as well as experimental data published in the literature. It has been found that the empirical “pseudo-Lorentz” line shape model considering the line mixing effects shows the best performance for modeling high-pressure gas spectra for the tested conditions, which is easy to be implemented and relatively accurate, thus is recommended for high-pressure radiative heat transfer calculations in engineering applications. Based on the selected “pseudo-Lorentz” line mixing model, we have constructed a high-pressure absorption coefficients database for CO, CO, and HO for pressure ranging from 1 bar to 80 bar. The newly generated database considering the spectral line mixing effects was tested for radiative heat transfer calculations, and the results were compared with the ones without considering the line mixing effects. The significance of ignoring the line mixing effects on radiative heat transfer calculations under different pressures was evaluated with one-dimensional radiative heat transfer benchmark cases. The high-pressure absorption coefficients database is available from the corresponding author upon request
From anaerobic digestion to single cell protein synthesis:A promising route beyond biogas utilization
No full textThe accumulation of a large amount of organic solid waste and the lack of sufficient protein supply worldwide are two major challenges caused by rapid population growth. Anaerobic digestion is the main force of organic waste treatment, and the high-value utilization of its products (biogas and digestate) has been widely concerned. These products can be used as nutrients and energy sources for microorganisms such as microalgae, yeast, methane-oxidizing bacteria(MOB), and hydrogen-oxidizing bacteria(HOB) to produce single cell protein(SCP), which contributes to the achievement of sustainable development goals. This new model of energy conversion can construct a bioeconomic cycle from waste to nutritional products, which treats waste without additional carbon emissions and can harvest high-value biomass. Techno-economic analysis shows that the SCP from biogas and digestate has higher profit than biogas electricity generation, and its production cost is lower than the SCP using special raw materials as the substrate. In this review, the case of SCP-rich microorganisms using anaerobic digestion products for growth was investigated. Some of the challenges faced by the process and the latest developments were analyzed, and their potential economic and environmental value was verified
Life-cycle assessment as a prospection stage for the biochemical methane potential of pretreated lignocellulosic biomass
No full textThe goal of neutrality in greenhouse gas emissions has intensified the search for renewable fuels. However, it is crucial to ensure sustainability of new technologies before proposing their implementation. This study proposes the use of life-cycle assessment (LCA) as an intermediary tool to identify critical hotspots in the exploration of hydrothermal pretreatment of lignocellulosic biomass, followed by biochemical methane potential assessment. Brewer s spent grain (BSG) was investigated, and laboratory-scale results were applied in an attributional assessment model with business-as-usual serving as the baseline. The LCA revealed that assumptions made in the lab could pose limitations. In Brazil, the two-stage co-digestion of pretreated hydrothermal BSG showed promising prospects, with a reduction to a new value of -54 kg CO2-eq Ton-1 BSG compared to 90 kg CO2-eq Ton-1 BSG in the business-as-usual scenario. Within the top ten global beer producing countries, only Brazil and Spain demonstrated potential for exploring this proposal
The fine-grained temporal dynamics of social timing: a window into sociality of embodied social agents Comment on “The evolution of social timing” by L. Verga, S. A. Kotz, & A. Ravignani
No full textSynthetic Fluorine Metabolism:Expanding the Boundaries of Microbial Biochemistry for Organofluorine Biosynthesis
No full textFluorine (F) is the 13th most abundant element on the Earth’s crust, just ahead of Carbon. Despite its pervasiveness, the presence of F in the biosphere is negligible, and only few tens of organofluorines are known today. Organofluorines are compounds of extreme value, widely used in many fields such as pharmaceuticals, agriculture and materials. Our society benefits from several fluorinated products, and none of them has a biological origin. Thus, F holds a high importance for materials development and biotechnological solutions. The scarcity of natural organofluorines results in a narrow biochemical spectrum and the consequent scarceness of specialized biocatalysts. Much of the biochemistry of halogens (X) involve the oxidation of halide ions (X–) to halonium ions (X+) or halide radicals (X·). Due to the extreme electronegativity of the F atom, such an oxidation approach is unfeasible. To date, only one family of enzymes have recognized to catalyse the formation of a C–F bond: fluorinases. The first enzyme of this kind was discovered in the soil bacterium Streptomyces cattleya, encoded in the biosynthetic gene cluster of the fluorination pathway responsible for the synthesis of virtually all know natural organofluorines. Because of its uniqueness, such pathway is the cornerstone for the construction of cell factories for de novo biosynthesis of organofluorines. Since its discovery, the fluorination pathway has been identified in other members of the Actinomycetes phylum and new enzyme variants are becoming accessible. Furthermore, due to the small steric hindrance of the F atom, which has a slightly smaller atomic radius than Hydrogen, is not uncommon for enzymes to promiscuously accept fluorinated substrates. This property can lead to the development of new–to–nature biochemistries in microbial factories and new manufacturing technologies for organofluorines.In this work, I have investigated how foreign fluorinated metabolites can alter the metabolism of the Gram–negative bacterium Escherichia coli and how they are naturally assimilated into the metabolic network. Synthetic routes for assimilation and de novo synthesis of different organofluorines were then introduced in two well–known bacterial workhorses: E. coli and the non–pathogenic soil bacterium Pseudomonas putida. Finally, I investigated how enzymes promiscuity can be exploited to catalyse novel reactions for the biosynthesis of the non–canonical amino acid 4–fluoro–L–threonine. From a broad perspective, this study characterizes different aspects of natural and synthetic F–metabolism, combining observations of bacterial biochemistry and exploring the biotechnological potential of expanding a ‘fluorinated’ metabolism with synthetic biology tools. The findings open the path for further development of robust cell factories for biobased production of difficult–to–produce organofluorines, as well as the biosynthesis of new–to–nature compounds of commercial interest
Impact of Variable Water Chemistry on PFOS-Goethite Interactions:Experimental Evidence and Surface Complexation Modeling
No full textPerfluorooctanesulfonate (PFOS) has become a major concern due to its widespread occurrence in the environment and severe toxic effects. In this study, we investigate PFOS sorption on goethite surfaces under different water chemistry conditions to understand the impact of variable groundwater chemistry. Our investigation is based on multiple lines of evidence, including (i) a series of sorption experiments with varying pH, ionic strength, and PFOS initial concentration, (ii) IR spectroscopy analysis, and (iii) surface complexation modeling. PFOS was found to bind to goethite through a strong hydrogen-bonded (HB) complex and a weaker outer-sphere complex involving Na+ coadsorption (OS-Na+). The pH and ionic strength of the solution had a nontrivial impact on the speciation and coexistence of these surface complexes. Acidic conditions and low ionic strength promoted hydrogen bonding between the sulfonate headgroup and protonated hydroxo surface sites. Higher electrolyte concentrations and pH values hindered the formation of strong hydrogen bonds upon the formation of a ternary PFOS-Na+-goethite outer-sphere complex. The findings of this study illuminate the key control of variable solution chemistry on PFOS adsorption to mineral surfaces and the importance to develop surface complexation models integrating mechanistic insights for the accurate prediction of PFOS mobility and environmental fate