Applying cumulative exergy demand (CExD) indicators to the ecoinvent database

Goal, Scope and Background Exergy has been put forward as an indicator for the energetic quality of resources. The exergy of a resource accounts for the minimal work necessary to form the resource or for the maximally obtainable amount of work when bringing the resource’s components to their most common state in the natural environment. Exergy measures are traditionally applied to assess energy efficiency, regarding the exergy losses in a process system. However, the measure can be utilised as an indicator of resource quality demand when considering the specific resources that contain the exergy. Such an exergy measure indicates the required resources and assesses the total exergy removal from nature in order to provide a product, process or service. In the current work, the exergy concept is combined with a large number of life cycle inventory datasets available with ecoinvent data v1.2. The goal was, first, to provide an additional impact category indicator to Life-Cycle Assessment practitioners. Second, this work aims at making a large source of exergy scores available to scientific communities that apply exergy as a primary indicator for energy efficiency and resource quality demand. Methods The indicator Cumulative Exergy Demand (CExD) is introduced to depict total exergy removal from nature to provide a product, summing up the exergy of all resources required. CExD assesses the quality of energy demand and includes the exergy of energy carriers as well as of non-energetic materials. In the current paper, the exergy concept was applied to the resources contained in the ecoinvent database, considering chemical, kinetic, hydro-potential, nuclear, solar-radiative and thermal exergies. The impact category indicator is grouped into the eight resource categories fossil, nuclear, hydropower, biomass, other renewables, water, minerals, and metals. Exergy characterization factors for 112 different resources were included in the calculations. Results CExD was calculated for 2630 ecoinvent product and process systems. The results are presented as average values and for 26 specific groups containing 1197 products, processes and infrastructure units. Depending on the process/product group considered, energetic resources make up between 9% and 100% of the total CExD, with an average contribution of 88%. The exergy of water contributes on the average to 8% the total exergy demand, but to more than 90% in specific process groups. The average contribution of minerals and metal ores is 4%, but shows an average value as high as 38% and 13%, in metallic products and in building materials, respectively. Looking at individual processes, the contribution of the resource categories varies substantially from these average product group values. In comparison to Cumulative Energy Demand (CED) and the abiotic-resource-depletion category of CML 2001 (CML’01), non-energetic resources tend to be weighted more strongly by the CExD method. Discussion Energy and matter used in a society are not destroyed but only transformed. What is consumed and eventually depleted is usable energy and usable matter. Exergy is a measure of such useful energy. Therefore, CExD is a suitable energy based indicator for the quality of resources that are removed from nature. Similar to CED, CExD assesses energy use, but regards the quality of the energy and incorporates non-energetic materials like minerals and metals. However, it can be observed for non-renewable energy-intensive products that CExD is very similar to CED. Since CExD considers energetic and non-energetic resources on the basis of exhaustible exergy, the measure is comparable to resource indicators like the resource use category of Eco-indicator 99 and the resource depletion category of CML 2001. An advantage of CExD in comparison to these methods is that exergy is an inherent property of the resource. Therefore less assumptions and subjective choices need to be made in setting up characterization factors. However, CExD does not coversocietal demand (distinguishing between basic demand and luxury), availability or scarcity of the resource. As a consequence of the different weighting approach, CExD may differ considerably from the resource category indicators in Eco-indicator 99 and CML 2001. Conclusions The current work shows that the exergy concept can be operationalised in product life cycle assessments. CExD is a suitable indicator to assess energy and resource demand. Due to the consideration of the quality of energy and the integration of non-energetic resources, CExD is a more comprehensive indicator than the widely used CED. All of the eight CExD categories proposed are significant contributors to Cumulative Exergy Demand in at least one of the product groups analysed. In product or service assessments and comparative assertions, a careful and concious selection of the appropriate CExD-categories is required based on the energy and resource quality demand concept to be expressed by CExD. Recommendations and Perspectives A differentiation between the exergy of fossil, nuclear, hydro-potential, biomass, other renewables, water and mineral/metal resources is recommended in order to obtain a more detailed picture of resource quality demand and to recognise trade-offs between resource use, for instance energetic and non-energetic raw materials, or nonrenewable and renewable energies. ESS-Submission Editor: Dr. Gerald Rebitzer (Gerald.Rebitzer@alcan.com)     

Cumulative energy demand for selected renewable energy technologies

Calculation of Cumulative Energy Demand (CED) of various energy systems and the computation of their Energy Yield Ratio (EYR) suggests that one single renewable energy technology cannot be said to be the best. Due to the difference in availability of renewable energy sources, their suitability varies from place to place. Wind energy converters, solar water heating systems and photovoltaic systems have been analysed for different types of locations. Comparing the general bandwidth of performance of these technologies, however, the wind energy converters tend to be better, followed by solar water heating systems and photovoltaic systems. Since a major part of the methodology of findingCED is very close to that of life cycle assessment and also because of the dominance of environmental impacts caused by the energy demand in the entire life cycle of any product or system, it is suggested that theCED can be used as an indicator of environmental impacts, especially in the case of power producing systems. Keywords: Cumulative energy demand; life cycle assessment; energy yield ratio; photovoltaics; solar water heating; wind energy Abbreviations: CED — Cumulative Energy Demand; EYR — Energy Yield Ratio; LCA — Life Cycle Assessment; Photovoltaics — PV; WEC — Wind Energy Converters     

能源预测预警理论与方法研究进展

能源作为一种稀缺性的战略资源是国民经济增长和社会进步的物质基础,但是随着化石能源耗竭及能源使用造成的环境问题日趋严重,能源安全问题逐渐成为关注的焦点,而能源预测预警也成为能源系统科学领域的新兴学科,其内容包含能源安全理论、基于模型的能源供需预测和基于安全评价指标体系的能源预警等方面内容。通过系统回顾能源安全的理论及其演变的历程,重点综述了自上而下、自下而上和混合建模3种建模思路的能源预测模型,探讨了三类模型的优点和局限性,并根据能源安全预警评价指标浓缩信息的程度,将现有预警评价体系划分单个型指标评价体系和聚合型指标评价体系两大类。通过对以上研究内容的总结分析,明确了当前能源预测预警研究各领域的研究进展,及其在理论和应用方面的优势与不足。在未来研究中,建议从供应链的角度出发,考虑能源系统内部各因素及与外部因素的相互作用,构建基于链式的预警体系,以有效弥补现有研究中的不足。     

Life cycle assessment of electrical and thermal energy systems for commercial buildings

Background, Aim and Scope The objective of this life cycle assessment (LCA) study is to develop LCA models for energy systems in order to assess the potential environmental impacts that might result from meeting energy demands in buildings. The scope of the study includes LCA models of the average electricity generation mix in the USA, a natural gas combined cycle (NGCC) power plant, a solid oxide fuel cell (SOFC) cogeneration system; a microturbine (MT) cogeneration system; an internal combustion engine (ICE) cogeneration system; and a gas boiler. Methods LCA is used to model energy systems and obtain the life cycle environmental indicators that might result when these systems are used to generate a unit energy output. The intended use of the LCA analysis is to investigate the operational characteristics of these systems while considering their potential environmental impacts to improve building design using a mixed integer linear programming (MILP) optimization model. Results The environmental impact categories chosen to assess the performance of the energy systems are global warming potential (GWP), acidification potential (AP), tropospheric ozone precursor potential (TOPP), and primary energy consumption (PE). These factors are obtained for the average electricity generation mix, the NGCC, the gas boiler, as well as for the cogeneration systems at different part load operation. The contribution of the major emissions to the emission factors is discussed. Discussion The analysis of the life cycle impact categories indicates that the electrical to thermal energy production ratio has a direct influence on the value of the life cycle PE consumption factors. Energy systems with high electrical to thermal ratios (such as the SOFC cogeneration systems and the NGCC power plant) have low PE consumption factors, whereas those with low electrical to thermal ratios (such as the MT cogeneration system) have high PE consumption factors. In the case of GWP, the values of the life cycle GWP obtained from the energy systems do not only depend on the efficiencies of the systems but also on the origins of emissions contributing to GWP. When evaluating the life cycle AP and TOPP, the types of fuel as well as the combustion characteristics of the energy systems are the main factors that influence the values of AP and TOPP. Conclusions An LCA study is performed to eraluate the life cycle emission factors of energy systems that can be used to meet the energy demand of buildings. Cogeneration systems produce utilizable thermal energy when used to meet a certain electrical demand which can make them an attractive alternative to conventional systems. The life cycle GWP, AP, TOPP and PE consumption factors are obtained for utility systems as well as cogeneration systems at different part load operation levels for the production of one kWh of energy output. Recommendations and Perspectives Although the emission factors vary for the different energy systems, they are not the only factors that influence the selection of the optimal system for building operations. The total efficiencies of the system play a significant part in the selection of the desirable technology. Other factors, such as the demand characteristics of a particular building, influence the selection of energy systems. The emission factors obtained from this LCA study are used as coefficients of decision variables in the formulation of an MILP to optimize the selection of energy systems based on environmental criteria by taking into consideration the system efficiencies, emission characteristics, part load operation, and building energy demands. Therefore, the emission factors should not be regarded as the only criteria for choosing the technology that could result in lower environmental impacts, but rather one of several factors that determine the selection of the optimum energy system. ESS-Submission Editor: Arpad Horvath (horvath@ce.berkeley.edu)     

An overview of energy efficiency techniques in cluster computing systems

Two major constraints demand more consideration for energy efficiency in cluster computing: (a) operational costs, and (b) system reliability. Increasing energy efficiency in cluster systems will reduce energy consumption, excess heat, lower operational costs, and improve system reliability. Based on the energy-power relationship, and the fact that energy consumption can be reduced with strategic power management, we focus in this survey on the characteristic of two main power management technologies: (a) static power management (SPM) systems that utilize low-power components to save the energy, and (b) dynamic power management (DPM) systems that utilize software and power-scalable components to optimize the energy consumption. We present the current state of the art in both of the SPM and DPM techniques, citing representative examples. The survey is concluded with a brief discussion and some assumptions about the possible future directions that could be explored to improve the energy efficiency in cluster computing.     

Improvement in protein functional site prediction by distinguishing structural and functional constraints on protein family evolution using computational design

The prediction of functional sites in newly solved protein structures is a challenge for computational structural biology. Most methods for approaching this problem use evolutionary conservation as the primary indicator of the location of functional sites. However, sequence conservation reflects not only evolutionary selection at functional sites to maintain protein function, but also selection throughout the protein to maintain the stability of the folded state. To disentangle sequence conservation due to protein functional constraints from sequence conservation due to protein structural constraints, we use all atom computational protein design methodology to predict sequence profiles expected under solely structural constraints, and to compute the free energy difference between the naturally occurring amino acid and the lowest free energy amino acid at each position. We show that functional sites are more likely than non-functional sites to have computed sequence profiles which differ significantly from the naturally occurring sequence profiles and to have residues with sub-optimal free energies, and that incorporation of these two measures improves sequence based prediction of protein functional sites. The combined sequence and structure based functional site prediction method has been implemented in a publicly available web server.     

Offshore renewable energy and nature conservation: the case of marine tidal turbines in Northern Ireland

The global demand for renewable energy continues to increase rapidly and with it the necessity to develop and test new technologies to deliver the power. Offshore renewable energy sources that harness wind, wave or tidal power are of major interest. Technological advances in these directions have not been matched by a clear understanding of the environmental impacts of the new devices, with most existing research concentrated on the impacts of offshore wind farms. Decisions often continue to be made without the support of a clear evidence base. Here we use an underwater tidal turbine, SeaGen, constructed and operated within the Strangford Lough marine protected area in Northern Ireland, as a case study to explore the potential impacts of the turbine as points of concern and argumentation in the decision-making processes. We use information obtained from official documents and one-to-one interviews with the main stakeholders. Our results demonstrate that during the construction and operation of the turbine the perceptions and views of different stakeholders sometimes disagreed but were often surprisingly similar in relation to both likelihood and intensity of the potential impacts of the turbine on marine biodiversity, ecosystem services and human well-being in general. The overall consensus of views was refined and evolved under an adaptive management approach over the 10 years of the discussions and decision-making processes. The results are discussed in relation to cumulative gains in knowledge, future arrays of many underwater turbines and multiple use of oceans within social ecological systems to maintain the conservation of marine biodiversity.     

A system of systems approach to energy sustainability assessment: Are all renewables really green?

Renewable energies are emerging across the globe in an attempt to slow down global warming and to improve national energy security in face of the depleting fossil fuel reserves. However, the general policy of mandating the replacement of fossil fuels with the so-called “green” energies may not be as effective and environmental-friendly as previously thought, due to the secondary impacts of renewable energies on different natural resources. Thus, an integrated systems analysis framework is essential to selecting optimal energy sources that address global warming and energy security issues with minimal unintended consequences and undesired secondary impacts on valuable natural resources. This paper proposes a system of systems (SoS) framework to determine the relative aggregate footprint (RAF) of energy supply alternatives with respect to different sustainability criteria and uncertain performance values. Based on the proposed method, the RAF scores of a range of renewable and nonrenewable energy alternatives are determined using their previously reported performance values under four sustainability criteria, namely carbon footprint, water footprint, land footprint, and cost of energy production. These criteria represent environmental efficiency, water use efficiency, land use efficiency, and economic efficiency, respectively. The study results suggest that geothermal energy and biomass energy from miscanthus are the most and least resource-use efficient energy alternatives based on the performance data available in the literature. In addition, despite their lower carbon footprints, some renewable energy sources are less promising than non-renewable energy sources from a SoS perspective that considers the trade-offs between the greenhouse gas emissions of energies and their effects on water, ecosystem, and economic resources. Robustness analysis suggests that with respect to the existing performance values and uncertainties in the literature, solar thermal and hydropower have the most and least level of RAF robustness, respectively. Sensitivity analysis indicates that geothermal energy and ethanol from sugarcane, have the lowest and highest RAF sensitivity to resource availability, respectively.     

Evaluation of the energetic position of the lowest excited singlet state of beta-carotene by NEXAFS and photoemission spectroscopy.

In carotenoids the lowest energetic optical transition belonging to the pi-electron system is forbidden by symmetry, therefore the energetic position of the S(1) (2(1)A(g)) level can hardly be assessed by optical spectroscopy. We introduce a novel experimental approach: For molecules with pi-electron systems the transition C1s-->2p(pi*) from inner-atomic to the lowest unoccupied molecular orbital (LUMO) appears in X-ray absorption near edge spectra (NEXAFS) as an intense, sharp peak a few eV below the carbon K-edge. Whereas the peak position reflects the energy of the first excited singlet state in relation to the ionization potential of the molecule, intensity and width of the transition depend on hybridization and bonding partners of the selected atom. Complementary information can be obtained from ultraviolet photoelectron spectroscopy (UPS): At the low binding energy site of the spectrum a peak related to the highest occupied molecular orbital (HOMO) appears. We have measured NEXAFS and UPS of beta-carotene. Based on these measurements and quantum chemical calculations the HOMO and LUMO energies can be derived.     

Determination and interpretation of mechanical power in human movement: application to ergometer cycling

Based on a model consisting of three rigid links, an instantaneous power equation has been deduced for ergometer cycling which shows a causal relationship between power liberated in joint rotation on the one hand and the rate of change of segmental energy plus the power transferred to the pedal on the other. The shape and magnitude of these two types of power have been calculated by measurements of pedal force and cinematographic analysis and the results show fair agreement between them. When cycling at a mean exercise intensity of 340 W at 90 rpm, less than 28 W appears to be lost in the (necessary) changes of segmental energies. It is suggested that power liberated in the joints should be judged as the source of power in the power equation. It is, therefore, proposed that this power should be defined as external power in this and other human movement.     

Design of New and Potent Diethyl Thiobarbiturates as Urease Inhibitors: A Computational Approach

Urease is an important enzyme both in agriculture and medicine research. Strategies based on urease inhibition is critically considered as the first line treatment of infections caused by urease producing bacteria. Since, urease possess agro-chemical and medicinal importance, thus, it is necessary to search for the novel compounds capable of inhibiting this enzyme. Several computational methods were employed to design novel and potent urease inhibitors in this work. First docking simulations of known compounds consists of a set of arylidine barbiturates (termed as reference) were performed on the Bacillus pasteurii (BP) urease. Subsequently, two fold strategies were used to design new compounds against urease. Stage 1 comprised of the energy minimization of enzyme-ligand complexes of reference compounds and the accurate prediction of the molecular mechanics generalized born (MMGB) interaction energies. In the second stage, new urease inhibitors were then designed by the substitution of different groups consecutively in the aryl ring of the thiobarbiturates and N, N-diethyl thiobarbiturates of the reference ligands.. The enzyme-ligand complexes with lowest interaction energies or energies close to the calculated interaction energies of the reference molecules, were selected for the consequent chemical manipulation. This was followed by the substitution of different groups on the 2 and 5 positions of the aryl ring. As a result, several new and potent diethyl thiobarbiturates were predicted as urease inhibitors. This approach reflects a logical progression for early stage drug discovery that can be exploited to successfully identify potential drug candidates.     

国家公园旅游可持续性管理评估指标体系——以西藏色林错-普若岗日冰川国家公园潜在建设区为例

当前,国内外对于国家公园旅游可持续性的定义及其评估指标尚未形成共识,已有的部分指标存在可操作性较弱、管理成本较高等问题,无法直接应用于中国国家公园旅游可持续性的管理与评估。从三条路径构建国家公园旅游可持续性管理评估指标体系：以实际需求为导向,分析国家公园所在区域对旅游可持续性管理评估指标的需求;以国际共识为导向,检验《全球可持续旅游目的地标准》在国家公园的适用性;以实践为导向,梳理世界主要国家及地区国家公园旅游可持续性的管理重点。以色林错-普若岗日冰川国家公园（简称"色-普国家公园"）潜在建设区为例,建立国家公园旅游可持续性管理评估指标体系。从经济、社会、文化、生态环境等方面明确了色-普国家公园潜在建设区对管理评估指标体系的需求。经过适用性判定,识别在色-普国家公园潜在建设区具有较强适用性的可持续旅游目的地评估指标。通过频次统计,从经济、社会、文化、生态环境、制度建设等方面遴选世界主要国家及地区国家公园旅游可持续性的重点管理指标。所建立的色-普国家公园潜在建设区旅游可持续性管理评估指标体系包括5个一级指标,15个二级指标,36个三级指标。在此基础上,建议逐步建立健全监测与统计体系,为管理评估指标体系的应用提供支撑。     

Affinity and specificity of protein U1A-RNA complex formation based on an additive component free energy model

An MM-GBSA computational protocol was used to investigate wild-type U1A-RNA and F56 U1A mutant experimental binding free energies. The trend in mutant binding free energies compared to wild-type is well-reproduced. Following application of a linear-response-like equation to scale the various energy components, the binding free energies agree quantitatively with observed experimental values. Conformational adaptation contributes to the binding free energy for both the protein and the RNA in these systems. Small differences in DeltaGs are the result of different and sometimes quite large relative contributions from various energetic components. Residual free energy decomposition indicates differences not only at the site of mutation, but throughout the entire protein. MM-GBSA and ab initio calculations performed on model systems suggest that stacking interactions may nearly, but not completely, account for observed differences in mutant binding affinities. This study indicates that there may be different underlying causes of ostensibly similar experimentally observed binding affinities of different mutants, and thus recommends caution in the interpretation of binding affinities and specificities purely by inspection.     

An integrative and prospective approach to regional material flow analysis: Modeling the decarbonization of the North Rhine-Westphalian steel industry

North-Rhine Westphalia is the center of the German and European steel production. Its steel industry is heavily based on the primary production route and emits up to 30 Mt CO₂ annually. One possible and increasingly prominent alternative to reduce these emissions is the hydrogen-based direct reduction. While this technology allows for a near climate-neutral production of primary steel, it poses substantial impacts on regional energy and material flows. Hence, the aim of this paper is to quantify the alterations in energy and material flows over time via integrating top-down energy and material flow models with bottom-up process models. The resulting values of emissions, energy, and material flows are then used to develop prospective scenarios that depict the requirements and consequences of potential pathways toward a climate-neutral steel production by 2045. The outcomes show that decarbonizing the North Rhine-Westphalian steel industry leads to an additional demand for renewable energies of up to 52.5 TWh per year, which represents 10% of the current electricity production in Germany. As securing the green electricity demand is a large challenge, the study also analyzes the impact of a partial recourse to natural gas as a reducing agent in combination with other measures like carbon capture and utilization/storage. The results show that such a recourse would reduce the electricity demand to 36.8 TWh. Hence, the paper illustrates relevant implications of the different scenarios, which can be used by policymakers to develop more realistic and resilient strategies for reaching carbon neutrality.     

Assessing future energy and transport systems: the case of fuel cells

Goal, Scope and Background  Assessing future energy and transport systems is of major importance for providing timely information for decision makers. In the discussion of technology options, fuel cells are often portrayed as attractive options for power plants and automotive applications. However, when analysing these systems, the LCA analyst is confronted with methodological problems, particularly with data gaps and the requirement of forecasting and anticipation of future developments. This series of two papers aims at providing a methodological framework for assessing future energy and transport systems (Part 1) and applies this to the two major application areas of fuel cells (Part 2). Methods  To allow the LCA of future energy and transport systems, forecasting tools like, amongst others, cost estimation methods and process simulation of systems are investigated with respect to the applicability in LCAs of future systems (Part 1). The manufacturing process of an SOFC stack is used as an illustration for the forecasting procedure. In Part 2, detailed LCAs of fuel cell power plants and power trains are carried out including fuel (hydrogen, methanol, gasoline, diesel and natural gas) and energy converter production. To compare it with competing technologies, internal combustion engines (automotive applications) and reciprocating engines, gas turbines and combined cycle plants (stationary applications) are also analysed. Results and Discussion  Principally, the investigated forecasting methods are suitable for future energy system assessment. The selection of the best method depends on different factors such as required ressources, quality of the results and flexibility. In particular, the time horizon of the investigation determines which forecasting tool may be applied. Environmentally relevant process steps exhibiting a significant time dependency shall always be investigated using different independent forecasting tools to ensure stability of the results. The results of the LCA underline that, in general, fuel cells offer advantages in the impact categories usually dominated by pol-lutant emissions, such as acidification and eutrophication, whereas for global warming and primary energy demand, the situation depends on a set of parameters such as driving cycle and fuel economy ratio in mobile applications and thermal/total efficiencies in stationary applications. For the latter impact categories, the choice of the primary energy carrier for fuel production (renewable or fossil) dominates the impact reduction. With increasing efficiency and improving emission performance of the conventional systems, the competition in both mobile and stationary applications is getting even stronger. The production of the fuel cell system is of low overall significance in stationary applications, whereas in vehicles, the lower life-time of the vehicle leads to a much higher significance of the power train production. Recommendations and Perspectives  In future, rapid technological and energy economic development will bring further advances for both fuel cells and conventional energy converters. Therefore, LCAs at such an early stage of the market development can only be considered preliminary. It is an essential requirement to accompany the ongoing research and development with iterative LCAs, constantly pointing at environmental hot spots and bottlenecks.     

Effect of different glucose supply conditions on neuronal energy metabolism

The glucose-excited neurons in brain can sense blood glucose levels and reflect different firing states, which are mainly associated with regulation of blood glucose and energy demand in the brain. In this paper, a new model of glucose-excited neuron in hypothalamus is proposed. The firing properties and energy consumption of this type of neuron under conditions of different glucose levels are simulated and analyzed. The results show that the firing rate and firing duration of the neuron both increase with increasing extracellular glucose levels, but the maximum energy power for an AP is reduced. Further study suggests that the neuron firstly absorbs energy substrates (e.g. glucose) from the blood to prepare for the high energy demand of high-frequency spikes.     

Energetics of growth in House martins (Delichon urbica)

Energy requirements for growth and maintenance of nestling House martins was studied in relation to brood size and age. Parallel studies of feeding rates and faecal output were made. The effect of mutual insulation between members of the brood on metabolism was of significance for reducing maintenance energy requirements. Of great value for predicting the peak energy demand of the brood was the number of young and their individual requirements for growth and maintenance at different ages. Power equations are given for predicting brood assimilation, faecal output and feeding frequency in relation to brood size. The impact of food scarcity on growth patterns was assessed. The large lipid stores of nestlings served as an energy reserve during adverse conditions both before and after fledging. Asynchronous hatching in large broods is interpreted as a mechanism which serves to minimize the peak in energy demand which occurs about 12 days after the brood hatches.     

Cell ATP level of Saccharomyces cerevisiae sensitively responds to culture growth and drug-inflicted variations in membrane integrity and PDR pump activity

Cellular ATP level in Saccharomyces cerevisiae was measured during culture growth of strain US50-18C overproducing all major PDR pumps and its isogenic mutants variously deleted in these pumps. It was found to be inversely proportional to the intensity of cell metabolism during different growth phases and to the activity of PDR pumps, which are thus among major ATP consumers in the cells. The ATP level was increased when membrane integrity was affected by 0.5% butanol, and further increased by compound 23.1, a semisynthetic phenol lipid derivative that acts as inhibitor of Pdr5p and Snq2p pumps. The magnitude of increase in cell ATP caused by inhibition of Pdr5p pump by compound 23.1 and the Pdr5p pump inhibitor FK506 used for comparison reflects the activity and hence the energy demand of the pump. The rise in cell ATP caused by different PDR pump inhibitors can be thus used as an indicator of pump activity and the potency of the inhibitor.     

Power capacity: A key element in sustainability assessment

In the field of complex energetics, human societies to survive follow the same ‘maximum power principle’ as other living systems. In this view, human societies developed because they have been able to increase “their capacity to convert energy at a given time rate” rather than simply increase “their level of energy consumption”. This was translated into an increase of the level of ‘power capacity’ in human societies so far. Yet, one can expect that the level of power capacity will be altered in light of the unavoidable progressive depletion of fossil energy resources. The systemic study of power capacity in sustainability assessment is therefore essential for facing the external constraints ahead.Starting from the characterization commonly used in energy systems engineering, this paper seeks to clarify the concept of power capacity when used in sustainability assessment. It provides explicit methods of assessment for the different types of power capacity used by human societies. Power capacity refers to the converters transforming energy flows at a given time rate. Dealing with societal transitions therefore requires being able to characterize properly those converters in addition to the study of energy flows. However, this requires extending the timescale typically considered in conventional energy analysis which entails several epistemological problems over sustainability assessment.     

Effects of non-aqueous solvents on CO2 absorption in monoethanolamine: Ab initio calculations

Monoethanolamine (MEA) is the most typical alkanolamine and its aqueous solutions are widely used for CO₂ absorption with mature technology, but the regeneration process is energy consuming. To reduce the energy demand, non-aqueous solvents, such as methanol and ethanol are proposed to substitute water in amine solutions. To understand the influence of the aqueous and non-aqueous solvents on CO₂ capture process, the chemical reactions of MEA absorbing CO₂ were conducted via ab initio calculations. The non-aqueous solvents discussed in this paper are methanol, ethanol, 1-propanol and 2-propanol. The reaction patterns were investigated and energy barriers were observed. The results show that zwitterion formation and the followed intermolecular hydrogen transfer are proven to be the most possible reaction pattern in both aqueous and non-aqueous solvents. The energy analysis shows that the forward reaction energy barriers increase while the backward barriers decrease as the solvent changes from water to methanol, ethanol, 1-propanol and 2-propanol in turn. The decreases of the energy barriers for backward processes are much higher than the corresponding increases for forward processes. These results indicate that lower energies are required in non-aqueous solvents than in water during the desorption reactions and the non-aqueous solvents are very promising to reduce the regeneration energy consumption in MEA capturing CO₂ process. Moreover, the reaction energy gaps between different solvation effects were found to have linear relationship with the logarithm of the dielectric constant difference, which could provide an easy way to theoretically predict the reaction energies of monoethanolamine absorbing CO₂ in other solvation effect and can be used to screen appropriate CO₂ capture solvent.