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It is widely known that fossil fuels are limited; consequently, the generation of new sources of energy in a clean and environmentally friendly manner is a research priority. Bioethanol appears to be one potential solution, especially second-generation production from renewable biomass.In order to use lignocellulosic feedstock to produce bioethanol, its polysaccharide components, cellulose and hemicellulose, must be hydrolysed into soluble sugars, which can then be converted into ethanol by fermentative microorganisms such as Geobacillus thermoglucosidasius TM242 used by the company ReBio Technologies Ltd.To date, the cost of commercial enzymes used during the hydrolysis process remains a major economic consideration in the production of second-generation bioethanol as an alternative fuel. The research project presented in this thesis aims to improve this rate-limiting step of microbial bioethanol production through an investigation of the different enzymes associated with hemicellulose hydrolysis. Firstly, the TM242 genome sequence revealed a number of genes encoding glycoside-hydrolases. Six of these genes were cloned and expressed in E. coli and the recombinant enzymes characterised; three of them, two β-xylosidases and an α arabinofuranosidase, are relevant to xylan hydrolysis, and were found to be highly active and thermostable. Crystallisation of one of the β-xylosidases permitted the determination of a high-resolution (1.7 Å) structure of the apo-enzyme along with a lower resolution (2.6 Å) structure of the enzyme-substrate complex, resulting in the first reported structure of a GH52 family member (Espina et al., 2014).Secondly, as the TM242 microorganism lacks xylanase enzymes, four genes encoding xylanases from closely-related Geobacillus strains were cloned and expressed in E. coli, with one of them being also successfully cloned and expressed in G. thermoglucosidasius TM242. This heterologous xylanase was secreted in active form representing an enhanced biomass utilisation by TM242.In conclusion, it is felt that the findings presented here have the potential to make a valuable contribution towards second-generation bioethanol production.

Artículos en revistas This paper presents the principles of a centralized underfrequency load-shedding (UFLS) scheme based on a frequency stability boundary curve suitable for small isolated power systems. The centralized UFLS scheme is illustrated in case of two small isolated Spanish power systems. info:eu-repo/semantics/publishedVersion

This report has been commissioned by Friends of the Earth England Wales and Northern Ireland (FoE) to independently review evidence on key issues relating to the potential new fleet of nuclear power stations that may be built in the UK over the period 2017 to 2030. The report draws primarily on peer-reviewed academic literature although this is supplemented with “grey” literature from credible government, consultancy and policy sources. It is not an exhaustive review of all the issues and writing concerning civil nuclear power but has a specific scope outlined below (see Annex 1 for full Terms of Reference). Nuclear power is quite unlike both fossil fuels and renewable sources of electricity generation with a particular set of characteristics that may be beneficial or problematic. The main purpose of this report is to provide a succinct appraisal of key issues relevant to the plans for a new generation of reactors in the UK, namely:• safety• radioactive waste disposal• proliferation of nuclear weapons• economics of nuclear power• siting and planning of low carbon generation• employment • issues in managing a low carbon grid• interactions between nuclear power and other low carbon technologiesThese issues are presented in separate sections as reviews of existing primary research and not as new research findings. The penultimate section, Chapter 11, presents new work by Tyndall Manchester on the carbon dioxide emissions implications of using gas rather than building a new series of nuclear power stations. We calculate the emissions output if the shortfall in electricity generation were to be met by the use of combined cycle gas turbines (CCGT). Alternative renewable energy sources are not considered as their direct emissions are negligible and similar to those from nuclear stations. A range of scenarios is presented for different combinations of rates and extent of nuclear construction and the availability and performance of carbon capture and storage technology. This report is intended for detailed consideration by the staff and members of Friends of the Earth and does not include an executive summary. Direct recommendations as to the appropriateness of a new fleet of nuclear stations in the UK have not been made by the authors. It is also important to note that some key aspects are highly contextual and contingent upon future circumstance.

Common hornbeam (Carpinus betulus) is one of the most important spring pollen allergens widespread in the Czech Republic. This study evaluates the changes in Carpinus betulus flowering and the length of the blooming period in the Czech Republic during 1991-2020. Temporal and spatial evaluations in the timing of the flowering and the length of the blooming period were investigated at different altitudinal levels. Moreover, the changes in mean air temperature and precipitation total in spring months (March-April-May) were assessed, including the correlation with phenological data. Geographic Information System methods, the Mann-Kendall test and Pearson's correlation coefficient were used for processing. The flowering of Carpinus betulus changed significantly over time during the 1991-2020 period. The linear models predicted early flowering in Carpinus betulus at different altitudes (27 days at > 701 m 18 days at 501-700 m and 13 days at 301-500 m) significantly (p<0.001) over the last three decades. Furthermore, the length of the blooming period of Carpinus betulus has been shortened (4 days) at the 301-500 m a.s.l. altitudinal level significantly (p<0.05). The strongest correlation was predominantly observed between flowering and the mean air temperature (March-April-May).

Nordhaus (1973) has in his seminal contribution addressed two emerging questions in the field of energy economics. First, how do current market prices of natural resources reflect true scarcity fro...

Although hydrothermal carbonization of biomass components is known to be mainly governed by reaction temperature, consistent reports on the effect and statistical significance of process conditions on hydrochar properties are still lacking. The objective of this research was to determine the importance and significance of reaction temperature, retention time and solid load on the properties of hydrochar produced from an industrial lignocellulosic sludge residue. According to the results, reaction temperature and retention time had a statistically significant effect on hydrochar ash content, solid yield, carbon content, O/C-ratio, energy densification and energy yield as reactor solid load was statistically insignificant for all acquired models within the design range. Although statistically significant, the effect of retention time was 3-7 times lower than that of reaction temperature. Predicted dry ash-free solid yields of attained hydrochar decreased to approximately 40% due to the dissolution of biomass components at higher reaction temperatures, as respective oxygen contents were comparable to subbituminous coal. Significant increases in the carbon contents of hydrochar led to predicted energy densification ratios of 1-1.5 with respective energy yields of 60-100%. Estimated theoretical energy requirements of carbonization were dependent on the literature method used and mainly controlled by reaction temperature and reactor solid load. The attained results enable future prediction of hydrochar properties from this feedstock and help to understand the effect of process conditions on hydrothermal treatment of lignocellulosic biomass.

Artículos en revistas This work develops a stochastic optimization model for the creation of a bidding strategy for a generator in an energy call option auction similar to Brazil's, i.e., where the bidder can offer both the premium and the strike price. The objective of the model is to maximize the bidder's competitiveness while ensuring that the project's target rate of return is achieved with a given probability, for example 95%. The problem's complexity is compounded by uncertainties in fuel supply and the need to switch between fuels. The generators face the conundrum of bidding a single strike price to cover the expenses generated by using multiple types of fuels. We address the problem of finding bidding strategies which, taking into account uncertainty in fuel supply and risk constraints, set the combination of strike price and option premium that ensure a desired risk-adjusted return for greenfield dual-fuel thermal plants. info:eu-repo/semantics/publishedVersion

Abstract Water transport control is the major issue of direct methanol fuel cell. High water flow rates through the fuel cell imply extra water feeding at the anode and flooding at the cathode. In the present work, water transport and flooding in the direct methanol fuel cell are investigated through both experimental and modeling analyses and an interpretation of such phenomena is proposed. The model is validated on the experimental data of two different fuel cells in an extensive range of operating conditions. The analysis elucidates that water transport through the cathode diffusion layer is determined by vapor diffusion, slightly affected by current density, and by liquid water permeation proportional to current density, that occurs when liquid pressure in the electrode exceeds a threshold value. To simulate the effects of cathode diffusion layer flooding two mechanisms must be considered simultaneously: superficial pore obstruction, proportional to liquid water concentration in cathode channel, and bulk pore obstruction, proportional to liquid water permeation. The modeling analysis proposes the correlations to reproduce the effects of cathode flooding and permits to discuss the onset and magnitude of such phenomenon and the influence of micro-porous layer.