含纳米流体热管性能计算模型的分析

将纳米流体应用在热管中进行热阻降低实验,可以得到理想的实验结果。然而,为了表征纳米流体在热管中的行为,目前所建立的热管和纳米流体的研究模型尚缺少深入讨论,特别是对于基础流体和纳米颗粒如碳纳米管或乙二醇的研究。因此,本研究先建立热管中纳米流体的流动方程,根据文献中热管的数据进行模拟。结果表明,实验测得的平均温度与预测结果有定性的一致性,误差在1.5%和23.9%之间。此外,实验得到的热管温度分布不能仅通过适当的热性能数值计算得到,这也表明沸腾现象比现有的应用模型更复杂。通过结合不同的性能模型,可以观察到纳米流体在此应用中存在最优的颗粒体积分数。

Important Issues and Results When Considering the Stochastic Representation of Wind Power Plants in a Generation Optimization Model: An Application to the Large Brazilian Interconnected Power System

Wind power has an increasing share of the Brazilian energy market and may represent 11.6% of total capacity by 2024. For large hydro-thermal systems having high-storage capacity, a complementarity between hydro and wind production could have important effects. The current optimization models are applied to dispatch power plants to meet the market demand and optimize the generation dispatches considering only hydroelectric and thermal power plants. The remaining sources, including wind power, small-hydroelectric plants and biomass plants, are excluded from the optimization model and are included deterministically. This work introduces a general methodology to represent the stochastic behavior of wind production aimed at the planning and operation of large interconnected power systems. In fact, considering the generation of the wind power source stochastically could show the complementarity between the hydro and wind power production, reducing the energy price in the spot market with the reduction of thermal power dispatches. In addition to that, with a reduction in wind power and a simultaneous dry-season occurrence, this model, is able to show the need of thermal power plants dispatches as well as the reduction of the risk of energy shortages.

异种金属搅拌摩擦焊AA5083和AA6082合金的搅拌区和热力影响区的变化（英文）

研究AA5083-O和AA6082-T6合金异种金属搅拌摩擦焊接头的成分、显微硬度(热力影响区)和织构的变化。采用电感耦合等离子体-原子发射光谱法测定焊缝区主要合金元素的含量。结果表明,搅拌摩擦焊过程中两种合金的主要合金元素的含量均略有下降,其中镁元素含量的变化最大。通过将两种合金母材与搅拌区的主要合金元素的质量分数相联系,估算搅拌区两种合金的相对比例,结果显示,焊缝后退侧的材料占比大于60%。另外,后退侧热力影响区硬度分布的变化主要受该区域晶粒尺寸变化的影响。最后,研究进一步表明,轴肩区与搅拌针区的织构成分不同。

Ruthenium Catalyst Supported on Multi-Walled Carbon Nanotubes for CO Oxidation

This work proposes the synthesis of the 5%wt Ru on MWCNT catalyst and the influence of feed rate and testing variables for low-temperature oxidation affecting the CO2 yield. Morphology and incorporation of the nanoparticles in carbon nanotubes were investigated by specific surface area (BET method);thermogravimetric analyses (TGA);X-ray diffraction;Raman spectroscopy, transmission electron microscopy (TEM) and XPS. The conversions of CO and O2 were mostly 100% in groups C1 and C2 (temperature between 200 and 500°C with low WHSV). In order to assess the effect of mass on catalytic activity, condition C3 was tested at even lower temperatures. In the tested catalyst, high activity (100% CO and O2 conversion) was observed, keeping it active under reaction conditions, suggesting oxi-reduction of the RuO2 at surface without affecting the MWCNT but Lewis acid influencing the CO2 yield.

Experiences of the Electricity System Operator Incentive Scheme in Great Britain

National Grid is the electricity system operator in Great Britain and has an unique feature in so far as it is one of the world’s few for-profit system operators. In addition, the commercially orientation of the British market rules means that nearly every action taken by National Grid to operate the system has a cost associated to it. Based on those factors and in order to encourage National Grid to seek continuous improvements and drive for efficient and economic system operation, the regulator (Ofgem) offers an incentive scheme, whereby a target is agreed annually and any savings in relation to this target are shared between consumers and National Grid in the form of a profit. It is in National Grid’s best interest to have mechanisms to mitigate the impacts of volatility in the costs it faces as system operator so that it can implement cost saving actions without the risk of windfall losses (or gains) arising from sudden changes in uncontrollable drivers. The purpose of this paper is to share the experiences of National Grid in the operation of Great Britain's electricity system, with a special interest on the mechanisms created to manage the associated costs in response to the incentive scheme. It does so by describing the market operation in Great Britain and the costs drivers impacting National Grid’s system operation and illustrating the steps recently taken by National Grid to propose volatility mitigation mechanisms. It concludes with the rationale and expected results from the latest proposals as consulted with the industry for introduction in the incentive scheme starting on 1st April 2011. It is worth noting that with this work, the authors wish to both share the experience with other system operators and regulators in the world, as well as give British market participants an insight on the inner workings of National Grid.

Optimization of Micromechanical Cleavage Technique of Natural Graphite by Chemical Treatment

In this work,we report a method to improve the efficiency of the micromechanical cleavage technique to obtain few-layers graphene samples, from natural graphite flakes, which were previously submitted to two chemical treatment times with H2SO4(17 and 25 hours). After the chemical treatment times, Raman spectroscopy reveals a hydrogenation of the few-layer graphene samples, which were obtained from the treated graphite flakes. To analyze the hydrogenation of the samples, the G and 2D bands of the Raman spectra of the treated and un-treated samples were analyzed and compared, as well as the I(2D)/I(G) ratio, revealing a p-doping on the treated samples when compared with the untreated samples. Our studies could be of great importance to obtain larger and greater amount of few-layer graphene samples.

Ductile Fracture Characterization for Medium Carbon Steel Using Continuum Damage Mechanics

This paper presents the ductility characterization for a medium carbon steel, for two microstructural conditions, that has been evaluated using the continuum damage mechanics theory, as proposed by Kachanov and developed by Lemaitre. Tensile tests were carried out using loading-unloading cycles in order to capture the gradual deterioration of the elastic modulus, which may be linked to the ductile damage increase with increasing plastic strain. The mechanical parameters for the isotropic damage evolution equation were obtained and then used as inputs for a plasticity-damage coupled nu- merical algorithm, validated through numerical simulations of the experimental tensile tests. A comparison between the SAE 1050 steels studied and two carbon steel alloys (obtained from the literature), provided some basic understanding of the influence of the carbon level on the evolution of the damage parameters. An empiric relationship for this set of parameters, which can provide useful data for preliminary studies envisaging prediction of ductile failure in carbon steels, is also presented.

Thermal Modeling of a Novel Heated Tip Injector for Otto Cycle Engines Powered by Ethanol

This work presents a thermal modeling of a new cold-start system technology designed for Otto cycle combustion based on the electromagnetic heating principle. Firstly, the paper presents a state-of-the-art review and presents the context of automobile industry where heated injectors are necessary. The novel method of electromagnetic heating principle to solve the cold-start problem is still in the development phase and it enables engine starting at low temperatures in vehicles powered by ethanol or flex-fuel vehicles (FFV). This new system technology should be available as an alternative to replace the existing system. Currently, the cold-start system uses an auxiliary gasoline tank, which brings some inconvenience for the user. Secondly, the aim was also to create a physical model that takes into consideration all the parameters involved on the heating process such as power heating and average heat transfer coefficient. The study is based on the lumped system theory to model the ethanol heating process. From the analysis, two ordinary differential equations arise, which allowed an analytical solution. Particularly, an ethanol heating curve inside the injector was obtained, an important parameter in the process. Comparison with experimental data from other authors is also provided. Finally, a sensitivity analysis of controlling parameters such as heating power and heat transfer coefficient variation. The paper is concluded with suggestions for further studies.

Studies on Production Planning of Dispersion Type U3Si2-Al Fuel in Plate-Type Fuel Elements for Nuclear Research Reactors

Several fuel plants that supply nuclear research reactors need to increase their production capacity in order to meet the growing demand for this kind of nuclear fuel. After the enlargement of the production capacity of such plants, there will be the need of managing the new production level. That level is usually the industrial one, which poses challenges to the managerial staff. Such challenges come from the fact that several of those plants operate today on a laboratorial basis and do not carry inventory. The change to the industrial production pace asks for new actions regarding planning and control. The production process based on the hydrolysis of UF6 is not a frequent production route for nuclear fuel. Production planning and control of the industrial level of fuel production on that production route is a new field of studies. The approach of the paper consists in the creation of a mathematical linear model for minimization of costs. We also carried out a sensitivity analysis of the model. The results help in minimizing costs in different production schemes and show the need of inventory. The mathematical model is dynamic, so that it issues better results if performed monthly. The management team will therefore have a clearer view of the costs and of the new, necessary production and inventory levels.

Applying a Context-based Method to Build a Knowledge Graph for the Blue Amazon

Knowledge graphs are employed in several tasks,such as question answering and recommendation systems,due to their ability to represent relationships between concepts.Automatically constructing such a graphs,however,remains an unresolved challenge within knowledge representation.To tackle this challenge,we propose CtxKG,a method specifically aimed at extracting knowledge graphs in a context of limited resources in which the only input is a set of unstructured text documents.CtxKG is based on OpenIE(a relationship triple extraction method)and BERT(a language model)and contains four stages:the extraction of relationship triples directly from text;the identification of synonyms across triples;the merging of similar entities;and the building of bridges between knowledge graphs of different documents.Our method distinguishes itself from those in the current literature(i)through its use of the parse tree to avoid the overlapping entities produced by base implementations of OpenIE;and(ii)through its bridges,which create a connected network of graphs,overcoming a limitation similar methods have of one isolated graph per document.We compare our method to two others by generating graphs for movie articles from Wikipedia and contrasting them with benchmark graphs built from the OMDb movie database.Our results suggest that our method is able to improve multiple aspects of knowledge graph construction.They also highlight the critical role that triple identification and named-entity recognition have in improving the quality of automatically generated graphs,suggesting future paths for investigation.Finally,we apply CtxKG to build BlabKG,a knowledge graph for the Blue Amazon,and discuss possible improvements.

Benchmarks for Pirá2.0,a Reading Comprehension Dataset about the Ocean,the Brazilian Coast,and Climate Change

Piráis a reading comprehension dataset focused on the ocean,the Brazilian coast,and climate change,built from a collection of scientific abstracts and reports on these topics.This dataset represents a versatile language resource,particularly useful for testing the ability of current machine learning models to acquire expert scientific knowledge.Despite its potential,a detailed set of baselines has not yet been developed for Pirá.By creating these baselines,researchers can more easily utilize Piráas a resource for testing machine learning models across a wide range of question answering tasks.In this paper,we define six benchmarks over the Pirádataset,covering closed generative question answering,machine reading comprehension,information retrieval,open question answering,answer triggering,and multiple choice question answering.As part of this effort,we have also produced a curated version of the original dataset,where we fixed a number of grammar issues,repetitions,and other shortcomings.Furthermore,the dataset has been extended in several new directions,so as to face the aforementioned benchmarks:translation of supporting texts from English into Portuguese,classification labels for answerability,automatic paraphrases of questions and answers,and multiple choice candidates.The results described in this paper provide several points of reference for researchers interested in exploring the challenges provided by the Pirádataset.

The challenges on operating a zero net energy building facing global warming conditions

This study proposes a methodology to evaluate the energy performance of existing Zero Energy Buildings and to prospect retrofit strategies in a Savannah climate,concerning the A2 scenario of emissions from the Fourth Report of the Intergovernmental Panel on Climate Change.The selected building to study is recognized for its high energy performance,named Centro SEBRAE de Sustentabilidade(CSS).Two efficient measures were considered:(i)improvement in the air conditioning system coefficient of performance(COP)and(ii)in the energy efficiency of the photovoltaic plates of generation on-site.The methodology is grounded in the potential bioclimatic concept and the employed steps applied were:preparation of climate archives in the 2020,2050 and 2080 time-slices;calibration of the computational model;evaluation of the retrofit strategies on its energy consumption efficiency through computer simulation.Considering the CSS has already attended mostly the bioclimatic strategies for the local climate and has high efficiency measures in its systems,the retrofit focused the air conditioning and PV system.The isolated retrofit of the air conditioning system was unable to guarantees the NZEB condition despite providing an adequate level of energy efficiency until 2080.The retrofit of the PV system was the only one that provides the NZEB condition for climate change scenarios.The contribution of this paper is to provide a guide to be used in NZEBs,with measures of optimization that provide high potential bioclimatic face to the local where it is built,making it possible to maintain this condition in scenarios of global warming.

The ecological performance of metallophyte plants thriving in geochemical islands is explained by the Inclusive Niche Hypothesis

Aims The Inclusive Niche Hypothesis has not been validated for plants using ecophysiological performance.The few experiments have measured growth and competition but not the physiological response of plants.A metallophyte plant that hyperaccumulates aluminium(Al),Plantago almogravensis,showed a defined spa-tial distribution by occurring mostly on vegetation gaps associ-ated with metalliferous areas(geochemical islands).This case was used to determine,in situ,whether the Inclusive Niche Hypothesis was suitable to explain the extent of the species real-ized niche.Methods The vegetation associated with P.almogravensis geochemical islands in the SW coast of Portugal was mapped.The biotic(neighbouring plants)and abiotic(edaphic)components of the niche were cor-related with parameters of the plant’s ecological and physiological performances(plant density and cover;leaf C and N concentration and isotopic composition;growth).The results were obtained using image analysis,abundance and morphological measures,isotopic signatures and chemical composition.Important Findings The species showed better physiological performance where its ecological performance was lower due to trade-offs with environ-mental constraints.The species’realized niche was mostly limited by shrub competition and soil Al-toxicity.These limits contribute to explain the rarity status of the species:the species has a poor capacity to compete but,due to an enhanced Al-tolerance and Al-hyperaccumulator trait,has the ability to find refuge in geochem-ical islands that are too harsh for most other species.This work,based on ecophysiological field studies,provides support for the Inclusive Niche Hypothesis relating to plant species.

Drought effects on the plasticity in vessel traits of two endemic Magnolia species in the tropical montane cloud forests of eastern Mexico

本文旨在探讨气候变化如何影响两种特有墨西哥木兰的导管性状可塑性和其每年的年轮宽度。尽管如此,很少有研究评估干旱对墨西哥东部热带山地云林导管性状的影响。通过生长年轮的数字图像,我们对所研究的墨西哥木兰树种的径向生长率、树龄和导管性状可塑性进行了评估,比较了两种墨西哥木兰树种在干旱年和非干旱年的导管密度、水力直径和传导面积百分比。本研究首次对墨西哥两个热带山地云林中的两个濒危木兰树种(Magnolia vovidesii和M.schiedeana)的多孔木质部导管性状对长期气候变化的可塑性进行了分析。结果发现,当比较干旱和非干旱年份时,温度和降水量与年轮宽度的差异密切相关。扩散型多孔木质导管解剖结构具有很高的可塑性,这与所研究的两种木兰树种的温度和/或水的有效性有关。我们的结论是,与非干旱年份相比,对干旱年份的解剖学适应导致了导管性状的大量减少;这些可塑的适应性在植物长期环境胁迫下的水分运输以及生存的安全性方面起着重要的作用。

Performance of aerogel as a thermal insulation material towards a sustainable design of residential buildings for tropical climates in Nigeria

The building sector accounts for nearly 40%of global energy consumption.In Nigeria,more than two-thirds of the consumption comes from residential buildings.Energy efficiency measures through the adoption of insulation materials are tools that could crash the peak demand of energy in buildings while improving its thermal comfort and aerogel is considered as the most effective material for insulation,owing to its unique thermal properties.In this paper,we present the performance of aerogel as a thermal insulation material towards a sustainable design of residential buildings for tropical climates in Nigeria.First,a typical residential building in the tropical region was modeled with conventional materials utilized in the region and was later modified through the application of aerogel material on various surfaces of the model.A whole building energy simulation was then carried out in each variation and the outcome was compared to effectively conclude on the significance of aerogel in terms of thermal comfort improvement and energy consumption reduction.Results show that aerogel had the highest influence when inserted in the attic and floor slabs of the designed model.A reduction of more than 6%was attained in the recorded indoor mean air and operative temperatures while still maintaining an acceptable humidity range.Concerning energy consumption,a reduction of more than 15%was achieved.However,the high price of aerogel may hinder its application on the studied building but could be a good investment where climate change and sustainability are of high importance and less concern is given to expenditure.Aerogel demonstrated significant potential with respect to both thermal comfort improvement and energy consumption reduction on the designed model.The outcome of the study is hoped to serve as a base reference for the insulation of residential buildings with similar climate and characteristics to the adopted case building.