Littérature scientifique sur le sujet « Micro-scale ORC »
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Articles de revues sur le sujet "Micro-scale ORC"
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Ancona, M. A., M. Bianchi, L. Branchini, A. De Pascale, F. Melino, S. Ottaviano, A. Peretto et C. Poletto. « Experimental and numerical investigation of a micro-ORC system for heat recovery from data centers ». Journal of Physics : Conference Series 2385, no 1 (1 décembre 2022) : 012122. http://dx.doi.org/10.1088/1742-6596/2385/1/012122.
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Abstract In the effort to enhance the recovery of waste energy, data centers are drawing attention because of the huge amount of heat discharged from the computer racks. Organic Rankine cycle (ORC) power systems are a viable solution to exploit servers’ waste heat, as it is available at very low temperatures. The purpose of this study is to assess the feasibility of integrating a micro-ORC system into data centers cooling systems and its potential energy saving. An experimental analysis is carried out on a kW-scale ORC test bench, with R134a as working fluid. Heat is supplied at temperatures and flow rates in the range respectively 40-55 °C and 1.8-5 m3/h, consistently with typical values observed in data centers application, showing the second law efficiency varying between 5% and 13%. Furthermore, a steady-state model of the micro-ORC has been recalibrated and validated against experimental data; the built-in volume ratio of the reciprocating piston expander has been optimized to improve the filling performance of the machine. A parametric analysis, varying the boundary conditions within their range of interest for this application, and the working fluid (R1234yf and R1234ze(E)), shows that a maximum second law efficiency of 30% is achievable with R1234ze(E).
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Peris, Bernardo, Joaquín Navarro-Esbrí, Francisco Molés, Jose Pascual Martí et Adrián Mota-Babiloni. « Experimental characterization of an Organic Rankine Cycle (ORC) for micro-scale CHP applications ». Applied Thermal Engineering 79 (mars 2015) : 1–8. http://dx.doi.org/10.1016/j.applthermaleng.2015.01.020.
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Casari, Nicola, Ettore Fadiga, Michele Pinelli, Saverio Randi et Alessio Suman. « Pressure Pulsation and Cavitation Phenomena in a Micro-ORC System ». Energies 12, no 11 (8 juin 2019) : 2186. http://dx.doi.org/10.3390/en12112186.
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Micro-ORC systems are usually equipped with positive displacement machines such as expanders and pumps. The pumping system has to guarantee the mass flow rate and allows a pressure rise from the condensation to the evaporation pressure values. In addition, the pumping system supplies the organic fluid, characterized by pressure and temperature very close to the saturation. In this work, a CFD approach is developed to analyze from a novel point of view the behavior of the pumping system of a regenerative lab-scale micro-ORC system. In fact, starting from the liquid receiver, the entire flow path, up to the inlet section of the evaporator, has been numerically simulated (including the Coriolis flow meter installed between the receiver and the gear pump). A fluid dynamic analysis has been carried out by means of a transient simulation with a mesh morphing strategy in order to analyze the transient phenomena and the effects of pump operation. The analysis has shown how the accuracy of the mass flow rate measurement could be affected by the pump operation being installed in the same circuit branch. In addition, the results have shown how the cavitation phenomenon affects the pump and the ORC system operation compared to control system actions.
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Falbo, Luigi, et Sergio Bova. « Performance analysis of a bio-diesel fired engine bottoming with micro-ORC ». Journal of Physics : Conference Series 2385, no 1 (1 décembre 2022) : 012116. http://dx.doi.org/10.1088/1742-6596/2385/1/012116.
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Abstract The purpose of this work is to investigate the performance in terms of electric power and electric efficiency of a 11kW bio-diesel internal combustion engine (ICE) coupled with a micro Organic Rankine Cycle (ORC) both in design and off-design conditions. A zero dimensional (0D) thermodynamical engine model has been developed to predict the electric and thermal power with 100% biodiesel fuel (B100). B100 has been selected for the performance analysis of the integrated system due its lower environmental impact. For the ORC system, a subcritical thermodynamic model has been used with various working fluid (R245fa, R1233zd(E), R134a, R1234ze(E) and R1234ze(Z)). A plate heat exchanger (PHEX) has been adopted as evaporator of the organic cycle to directly recover the thermal power of the exhaust gas. Both models have been validated using experimental data from literature. Two different expander configurations, dynamic and volumetric, has been investigated. Model validations show good agreement with the experimental and literature data, respectively. Moreover, the results highlight that the micro-ORC could achieve a maximum electric efficiency of about 7% at full load with R1234ze(Z). Although at part load the dynamic expander show better performance, the volumetric expander has been selected for the system analysis due to its real suitability for small and micro scale ORC. Combined system results show a maximum enhancement of engine efficiency of about 5%, and better results, in terms of good compromise between electric efficiency and operating range width, has been shown for R1233zd(E). Furthermore, the direct coupling of the PHEX with the exhaust gases allows to have heat exchange evaporator areas below 2 m2 for all analysed fluids.
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Moradi, Ramin, Emanuele Habib, Enrico Bocci et Luca Cioccolanti. « Component-Oriented Modeling of a Micro-Scale Organic Rankine Cycle System for Waste Heat Recovery Applications ». Applied Sciences 11, no 5 (24 février 2021) : 1984. http://dx.doi.org/10.3390/app11051984.
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Organic Rankine cycle (ORC) systems are some of the most suitable technologies to produce electricity from low-temperature waste heat. In this study, a non-regenerative, micro-scale ORC system was tested in off-design conditions using R134a as the working fluid. The experimental data were then used to tune the semi-empirical models of the main components of the system. Eventually, the models were used in a component-oriented system solver to map the system electric performance at varying operating conditions. The analysis highlighted the non-negligible impact of the plunger pump on the system performance Indeed, the experimental results showed that the low pump efficiency in the investigated operating range can lead to negative net electric power in some working conditions. For most data points, the expander and the pump isentropic efficiencies are found in the approximate ranges of 35% to 55% and 17% to 34%, respectively. Furthermore, the maximum net electric power was about 200 W with a net electric efficiency of about 1.2%, thus also stressing the importance of a proper selection of the pump for waste heat recovery applications.
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Jradi, Muhyiddine, et Saffa Riffat. « Performance Analysis of an Innovative ORC-based Micro-scale CCHP System under Lebanese Conditions ». International Journal of Thermodynamics 22, no 2 (23 mai 2019) : 98–105. http://dx.doi.org/10.5541/ijot.494481.
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Jradi, Muhyiddine, Jinxing Li, Hao Liu et Saffa Riffat. « Micro-scale ORC-based combined heat and power system using a novel scroll expander ». International Journal of Low-Carbon Technologies 9, no 2 (20 février 2014) : 91–99. http://dx.doi.org/10.1093/ijlct/ctu012.
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Liu, Hao, Yingjuan Shao et Jinxing Li. « A biomass-fired micro-scale CHP system with organic Rankine cycle (ORC) – Thermodynamic modelling studies ». Biomass and Bioenergy 35, no 9 (octobre 2011) : 3985–94. http://dx.doi.org/10.1016/j.biombioe.2011.06.025.
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Kicinski, J., et G. Zywica. « Prototype of the domestic CHP ORC energy system ». Bulletin of the Polish Academy of Sciences Technical Sciences 64, no 2 (1 juin 2016) : 417–24. http://dx.doi.org/10.1515/bpasts-2016-0047.
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Abstract The Institute of Fluid-Flow Machinery (IMP PAN) in Gdansk pursues its own research in fields such as technologies that use renewable energy sources efficiently, including in particular the small-scale combined heat and power (CHP) systems. This article discusses the design concepts for the prototype of small CHP ORC (organic Rankine cycle) energy system, developed under the research project. The source of heat is a boiler designed for biomass combustion. Electricity was generated using specially designed oil-free vapour micro-turbine. The turbo-generator has compact structure and hermetical casing thanks to the use of gas bearings lubricated by working medium. All energy system components are controlled and continuously monitored by a coherent automation and control system. The article also discusses selected experimental results conducted under laboratory conditions. Thermal-flow tests were presented that allow for an assessment of the operation of energy system components. Additionally, energy performance results of the turbo-generator were given including power obtained at various cycle parameters. The achieved results have shown that the developed energy system operated in accordance with design solutions. Electricity derived from the energy system prototype was around 2 kW, with boiler’s thermal power of 25 kW. The research has also confirmed that this system can be used in a domestic environment.
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Spale, Jan, Guk Chol Jun, Vaclav Novotny, Philipp Streit, Andreas P. Weiß et Michal Kolovratnik. « Development of a 10 kW class axial impulse single stage turboexpander for a micro-CHP ORC unit ». EPJ Web of Conferences 264 (2022) : 01044. http://dx.doi.org/10.1051/epjconf/202226401044.
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Development of micro ORC systems with 1-15 kW power output for micro-cogeneration and waste heat recovery at the Czech Technical University in Prague, University Centre for Energy Efficient Buildings (CTU UCEEB) has over ten years of history with many successes. These include 6 different ORC units, all with in-house designed rotary vane expanders (RVE) of many versions throughout this development. Among main advantages of the RVE belong relatively simple and robust design at low cost even at very small series of single-unit production and all that with acceptable efficiency. The ORC units operate with hexamethyldisiloxane (MM) working fluid at high pressure ratios and expansion ratios and the isentropic efficiency of RVE has a limit at these conditions around 60%, often however only at values around 50%. While this might be enough on a cost side for commercialization of this technology, in pursuit of higher efficiency solutions, different expander technology needs to be selected. A turbo-expander is a logical choice with prospect of higher efficiency. At the same time, a literature review has found a lack of reported detailed experimental data for micro (5-50 kW) turbo-expanders, possibly hindering global development towards economically feasible solutions. A project named Dexpand, “Optimised expanders for small-scale distributed energy systems” aims at these issues by objectives in designing, optimizing, manufacturing and testing several ORC expanders with MM and isobutane and their subsequent performance mapping and comparison. One major task is a design of a turboexpander for a 120 kWth biomass fired microcogeneration ORC unit currently operated at the CTU UCEEB. An axial impulse single stage turboexpander was selected as a suitable choice, providing a prospect of a decent efficiency at technically manageable rotational speed and size. This paper provides a detail of currently performed design activities, starting from boundary conditions specification, over development and optimization of a 1D model, preliminary 2D CFD calculations and finishing in a state of a robust and detailed 3D CFD model with a real gas model. Note that the working fluid, high molar mass organic vapour, is highly non-ideal in its behaviour and the flow conditions with pressure design ratio around 13 is highly supersonic (nozzle outlet isentropic Mach number exceeds 2). The current results based on 3D CFD indicate a prospect of an isentropic efficiency 71% at mechanical power output of 11 kW. Lastly, ongoing and future work is outlined, which includes aerodynamic optimization based on the developed 3D CFD model and construction design of the entire turbine assembly.
Thèses sur le sujet "Micro-scale ORC"
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Lindqvist, Jakob, et Niklas Faber. « Performance evaluation in post integrated organic Rankine cycle systems : A study on operational systems utilizing low grade heat ». Thesis, Linköpings universitet, Mekanisk värmeteori och strömningslära, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-150371.
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Organic Rankine cycles can be integrated with district heating systems and in applications of biogas digestion. Evaluating the performance of the installations by Againity AB in Ronneby and Norrköping, Sweden, is a unique opportunity which can support the establishment of ORC technology in the waste heat recovery market, unveiling its feasibilities and limitations. Operational data gathered from October 2017 until April 2018, provides this thesis with information about the ORC-systems. A method using Coolprop and Matlab has been used to detect steady-state series in the Ronneby installation using moving standard deviation and inclination criteria. By screening the data and selecting these series, analytical equations can be used to determine the performance of the installations and map the linear relationship between variables like pressure and generator power. The largest impact on the system in Ronneby is developed in the condenser. Large coolant volume flow creates large heat sink capacity and higher generator efficiency and power. However, with increasing generator power the condenser pressure decrease. Lower condenser pressure results in a decreased evaporation pressure, which could be maintained if the pump was able to run at higher frequencies. The Plant in Norrköping needs further studies and a review of its sensors. The code in Matlab is a resource to Againity and Linköpings university for future work in performance evaluation. It can be used to detect errors in energy balance, local readings, and picture the machines' performance graphically.
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Barbosa, Leo. « EXAMINATION OF MICRO-SCALE SULFIDE DISTRIBUTION FOR THE GOLD MINERALIZATION IN THE LAPPBERGET DEPOSIT, GARPENBERG MINE, SWEDEN : TOWARDS A GEOMETALLURGICAL APPROACH ». Thesis, Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-87022.
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Ore characterization studies are of great importance to the mining industry, especially when dealing with precious metals by-products. It is a way towards increasing mining efficiency. The Swedish Boliden’s Zn–Pb–Ag–(Cu–Au) Lappberget Deposit is the main ore body at the Garpenberg Mine producing concentrates of zinc, lead, copper, and a gravity concentrate of silver and gold, which accounts for a significant revenue for the mine. Garpenberg Mine is an ancient and traditional mining site in Sweden, nonetheless the Lappberget deposit is a relatively recent discovery and there are still on-going studies on this ore body. More recently detailed ore investigations have been carried out on the sulfides and silver mineralization in different geological domains within the Lappberget deposit. In this context, the present work is focused on investigating the gold mineralization of the deposit, aiming to study the occurrence and distribution of gold minerals, characterize the gold in the ore and how its characteristics affect gold recoveries during its processing. To achieve these goals, different investigative methods were applied on drill core samples of the footwall disseminated to semi-massive mineralization (FWD), and on samples from the gravity concentrator at Boliden’s processing plant. The techniques applied were optical microscopy, scanning electron microscopy, energy dispersive x-ray spectrometry, electron probe microanalysis, laser ablation inductively couple plasma mass spectrometry, and bulk chemical analysis. The main findings pointed electrum as the main gold mineral, occurring with a strong sulfide association, in a variety of textures and grain sizes. The study also identified the occurrence of Au-Bi alloy, not previously described in literature of the Garpenberg region. The potential of invisible gold in the sulfide carriers was also a subject of investigation, as well as the evaluation of the characteristics of the samples from the gravity concentrator.
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talluri, lorenzo. « Micro turbo expander design for small scale ORC : Tesla turbine ». Doctoral thesis, 2019. http://hdl.handle.net/2158/1153897.
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Over the last years, the increase in energy consumption coupled with ever more stringent regulations on pollutants emissions and the massive advent of renewables in the energy market, have promoted the development of distributed energy systems and thus of an increasing interest towards small and micro power generation systems. In this context, the ORC progressively became the leading technology in the field of low size energy conversion systems (<100 kW) and low temperature applications (<150°C). Nonetheless, this technology still deserves further developments, especially regarding the design of specific components, which should grant features of reliability, acceptable performance level and, often even more important, affordable price in order to ensure the attractiveness of the whole energy system. It is the case of the small and micro expanders (tens to few kW scale). A possible solution for micro–size expanders is the Tesla expander, which is a viscous bladeless turbine that holds the desired characteristics of low cost and reliability. This expander was first developed by N. Tesla at the beginning of the 20th century, but it did not stir up much attention due to the strong drive towards large centralized power plants, where this technology becomes no longer competitive against those belonging to bladed expanders. In the recent years, due to the increasing appeal towards micro power generation and energy recovery from wasted flows, this cost effective expander technology rose a renovated interest.
In the present study, a 2D numerical model is realized and a design procedure of a Tesla turbine for ORC applications is proposed. A throughout optimization method is developed by evaluating the losses of each component and by introducing an innovative rotor model. The main optimizing parameters of the turbine, such as the rotor inlet/outlet diameter ratio, channel width–rotor diameter ratio and tangential velocity–rotational speed ratio at rotor inlet are highlighted and assessed.
The 2D model results are further exploited through the development of 3D computational investigation, which allows an accurate comprehension of the flow characteristics, which are difficult to depict with a 2D code.
Finally, two prototypes are designed, realized and tested. The former one is designed to work with air as working fluid, with the stator made in ABS with additive manufacturing technique, in order to show a possible cost effective way of realization. The obtained experimental results of this prototype well match the numerical predictions. A 94 W net power output with 11.2% efficiency are measured.
The second prototype is designed to work with organic fluids (specifically with R404A), and it is ultimately tested with R1233zd(E). A standard metal manufacturing is followed for this prototype. The achieved experimental results confirmed the validity and the large potential applicative chances of this emerging technology, especially in the field of micro
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sizes, low inlet temperature and low expansion ratios. 371 W net power output at 10% shaft efficiency are obtained.
The experimental results allowed the validation of numerical models, which was among the main objectives of this work. In this way, the numerical procedure may be reliably employed as the tool for the accurate and optimised design of Tesla turbines for organic Rankine cycles but also for applications with gas like air.
As a final remark, it can be affirmed that the operability of the Tesla expander was demonstrated in this work. Thus, it may be considered as a suitable and realizable solution to tackle one of the present issues related to micro expanders, namely high costs and low reliability, which, moreover, suffers off design conditions only to a limited extent.
The realization of a reliable design tool is another fundamental outcome of the present work.
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FAGIOLI, FEDERICO. « Sviluppo di micro-ORC total power a energia solare : progettazione e test sperimentali ». Doctoral thesis, 2017. http://hdl.handle.net/2158/1084548.
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Progettazione e test di un impianto ORC alimentato ad energia solare su scala domestica. Caratterizzazione sperimentale dei componenti ed elaborazione di strategie di ottimizzazione energetica del sistema. Domestic scale, solar driven ORC power plant design, development and experimental tests. Components experimental characterization and elaboration of energy optimization strategies
Livres sur le sujet "Micro-scale ORC"
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Gray, Barbara, et Jill Purdy. Cross-Level Dynamics. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198782841.003.0010.
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To adequately characterize partnerships, we need to view them as cross-level phenomena (i.e. involving partners from different geographical or jurisdictional levels) because agreements that make sense at one level do not necessarily translate to levels above or below the original one. Scale of organizing refers to the spatial or temporal dimensions of a partnership and plays an important role in shaping how issue fields are defined. When partners frame issues at different scale, this can pose difficulties for partnership formation, representation, and design and also for evaluating outcomes. Several examples illustrate how scale differences add complexity and may create tradeoffs among desired partnership outcomes. The chapter distinguishes between the physical setting (space) and place (which has meanings, symbols, memories, narratives, norms, and power relations attached). Level of analysis (micro, meso, macro) is also important for studying partnerships and understanding how they change institutional fields.
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Cave, Terence. Towards a Passing Theory of Literary Understanding. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198794776.003.0010.
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Relevance theory offers a model of communication where utterances are constantly updated by the speaker, inviting the listener to engage in a corresponding activity of inferential adjustment. In the case of literature, the potential time-scale of this activity is expanded, whether by the length of the text, the passage of historical time, or the demands of close reading. How then do incremental effects operate within the virtual time of literary utterance? How does one effect become a platform or trigger for others? This chapter touches on issues such as the situated logic of collocation and the ‘echoic’ as a way of approaching literary allusiveness, and brings together the micro-analysis of a line of poetry with a broader-scope reflection on the principles that operate over extended fictions. Adapting to literary understanding Davidson’s notion of a ‘passing theory’, it tracks the time-bound, ephemeral passage of verbal events through the reader’s cognitive focus.
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Richter-Devroe, Sophie. Women's Political Activism in Palestine. University of Illinois Press, 2018. http://dx.doi.org/10.5622/illinois/9780252041860.001.0001.
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What does doing politics mean in a context of occupation, settler-colonialism, and prolonged state violence such as Palestine? This book traces Palestinian women’s forms of political activism, ranging from peacebuilding and popular resistance to their everyday survival and coping strategies. Over the last decades, the Israeli occupation has tightened its grip on Palestinian life; settler-colonial violence against Palestinians has risen, and Palestine is more fragmented—politically, socially and spatially—than ever. For most Palestinians, neither the official liberal peace agenda nor the liberationist resistance paradigm offers promising solutions to unlock the status quo of political paralysis in Palestine today. Instead, they simply try to get by and struggle through quotidian, small-scale, informal efforts to establish a livable environment for themselves and their loved ones. Women play a major role in these micro politics. The ethnographically grounded analysis in this book focuses on the intricate dynamics of daily life in Palestine, tracing the emergent politics that women practice and articulate there. Rather than being guided by larger categories, such as party politics, social movements, or binaries between the public and the private, it zeroes in on women’s own, often complex and ambiguous, everyday politics. Shedding light on contemporary gendered political culture and alternative “politics from below” in the region, the books invites a rethinking of the functionings, shapes, and boundaries of the political.
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Cukierman, Alex. Central Banks. Oxford University Press, 2018. http://dx.doi.org/10.1093/acrefore/9780190228637.013.64.
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The first CBs were private institutions that were given a monopoly over the issuance of currency by government in return for help in financing the budget and adherence to the rules of the gold standard. Under this standard the price of gold in terms of currency was fixed and the CB could issue or retire domestic currency only in line with gold inflows or outflows. Due to the scarcity of gold this system assured price stability as long as it functioned. Wars and depressions led to the replacement of the gold standard by the more flexible gold exchange standard. Along with restrictions on international capital flows this standard became a major pillar of the post–WWII Bretton Woods system. Under this system the U.S. dollar (USD) was pegged to gold, and other countries’ exchange rates were pegged to the USD. In many developing economies CBs functioned as governmental development banks.Following the world inflation of the 1970s and the collapse of the Bretton Woods system in 1971, eradication of inflation gradually became the explicit number one priority of CBs. The hyperinflationary experiences of the first half of the 20th century, which were mainly caused by over-utilization of the printing press to finance budgetary expenditures, convinced policymakers in developed economies, following Germany’s lead, that the conduct of monetary policy should be delegated to instrument independent CBs, that governments should be prohibited from borrowing from them, and that the main goal of the CB should be price stability. During the late 1980s and the 1990s numerous CBs obtained instrument independence and started to operate on inflation targeting systems. Under this system the CB is expected to use interest rate policy to deliver a low inflation rate in the long run and to stabilize fluctuations in economic activity in the short and medium terms. In parallel the fixed exchange rates of the Bretton Woods system were replaced by flexible rates or dirty floats. The conjunction of more flexible rates and IT effectively moved the control over exchange rates from governments to CBs.The global financial crisis reminded policymakers that, of all public institutions, the CB has a comparative advantage in swiftly preventing the crisis from becoming a generalized panic that would seriously cripple the financial system. The crisis precipitated the financial stability motive into the forefront of CBs’ policy concerns and revived the explicit recognition of the lender of last resort function of the CB in the face of shocks to the financial system. Although the financial stability objective appeared in CBs’ charters, along with the price stability objective, also prior to the crisis, the crisis highlighted the critical importance of the supervisory and regulatory functions of CBs and other regulators. An important lesson from the crisis was that micro-prudential supervision and regulation should be supplemented with macro-prudential regulation and that the CB is the choice institution to perform this function. The crisis led CBs of major developed economies to reduce their policy rates to zero (and even to negative values in some cases) and to engage in large-scale asset purchases that bloat their balance sheets to this day. It also induced CBs of small open economies to supplement their interest rate policies with occasional foreign exchange interventions.
Chapitres de livres sur le sujet "Micro-scale ORC"
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Cristoferi, Davide. « “I nostri contadini solevano istare molto meglio per lo addrieto che ora” : mezzadria, proprietà cittadina e disuguaglianza economica in Toscana, sec. XV-XVI ». Dans Disuguaglianza economica nelle società preindustriali : cause ed effetti / Economic inequality in pre-industrial societies : causes and effect, 275–99. Florence : Firenze University Press, 2020. http://dx.doi.org/10.36253/978-88-5518-053-5.19.
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This paper studies through a quantitative analysis at micro-scale (the pieve of San Giovanni in Petroio in Mugello) in 1427-1512 the relation between the growing economic inequality of the Florentine rural society found by recent research and a peculiar share-cropping system, the mezzadria. By focusing on the mechanisms of wealth redistribution of this system, the paper suggests the role of mezzadria whether in increasing in the long-run the concentration of land property and in providing for the poorest social layers of rural population at subsistence level. In this regard, the paper contributes to explore the role of institutions in increasing wealth concentration from Middle Ages to the Early Modern times.
Actes de conférences sur le sujet "Micro-scale ORC"
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Kim, Donghoi, Rubén M. Montañés, Luca Riboldi, Lars O. Nord, Jan Spale et Vaclav Novotny. « Design optimization of small-scale ORC cycles for fluctuating heat source ». Dans 63rd International Conference of Scandinavian Simulation Society, SIMS 2022, Trondheim, Norway, September 20-21, 2022. Linköping University Electronic Press, 2022. http://dx.doi.org/10.3384/ecp192029.
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Organic Rankine cycles (ORC) are efficient technologies for waste heat recovery (WHR) at low to mid temperatures. For the design of ORC power cycles, several thermodynamic parameters should be considered. A challenge related to small scale (<50 kW) ORC cycles is to define the optimal process given frequent variability in a heat source. Many relevant applications require robust ORC systems to perform under varying heat source loads. This is an area where the body of knowledge must be further developed.In this work, the design of small-scale ORC cycles with varying heat source conditions is addressed by means of system modelling, simulation, and optimization. A framework is presented that consists of multi-scale optimization for the design of small-scale ORC systems considering seasonal and hourly heat source variations. The framework is developed as a flexible tool allowing to include fit-for-purpose models of key elements of the cycle, such as expander and heat exchanger, to suitably simulate off-design performance.The optimization framework has been tested on a case study representing a woodchips-fired micro-cogeneration unit via ORC. The case study is representative of an existing unit operating at the Czech Technical University (CTU) in Prague. The results indicate that the tool delivers an ORC design that has a 5 % larger accumulated power production with the hourly variation of the heat source during one year than the original ORC solely optimized at the design heat source condition. The optimal ORC system also shows a 33 % smaller nominal capacity and size of heat exchangers than the ORC at the reference design, indicating a potential reduction in the capital cost.
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Gusev, Sergei, et Martijn van den Broek. « Analysis and Comparison Between Fixed and Variable Volume Ratio Expander for Micro-Scale ORC ». Dans ASME 2015 Power Conference collocated with the ASME 2015 9th International Conference on Energy Sustainability, the ASME 2015 13th International Conference on Fuel Cell Science, Engineering and Technology, and the ASME 2015 Nuclear Forum. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/power2015-49271.
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Waste heat recovery has become very important in the last decennia. The Organic Rankine Cycle is the most popular technology to transform waste heat into mechanical work or electricity. While large and medium scale installations are widely available on the market for various temperature and power levels, small scale ORCs are still in a pre-commercial phase because of a relatively high specific price. To make small scale ORCs more attractive for potential customers, the price has to be drastically reduced which means reducing the manufacturing and assembling operations, the number of parts in assemblies and unification of these assemblies. In addition, the performance has to be increased by using advanced cycle architectures and the right fluids. Not only the right choice of the working fluid is important but also the expander built-in volume ratio (BVR) has to be optimal or improved. Neither a fixed volume ratio expander, nor a turbine can provide an optimal expansion of a working fluid in a wide range of operating conditions [1]. In automotive applications, for instance, a strongly fluctuating heat input will be introduced to an ORC unit. To estimate losses caused by non-optimal operation, a model of a volumetric expander has been developed and verified using the result of extensive test campaigns with a screw expander. The volume ratio of the expander mentioned cannot be physically changed, so under widely changing pressure ratio, caused by varying inlet waste heat and ambient temperatures, it operates mostly far from its design point. The model gives a possibility to vary the BVR in order to compare a fixed-volume ratio expander with a variable one. Benefits from replacement of this expander by an adaptive one are studied. Only steady states are taken into account since there is no dynamic model of this expander developed yet. As a consequence of the results obtained, a concept of a variable volume ratio expander is proposed.
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Song, Jian, et Chun-wei Gu. « 1-D Model Analysis of Tesla Turbine for Small Scale Organic Rankine Cycle (ORC) System ». Dans ASME Turbo Expo 2017 : Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-63797.
Texte intégralRésumé :
Energy shortage and environmental deterioration are two crucial issues that the developing world has to face. In order to solve these problems, conversion of low grade energy is attracting broad attention. Among all of the existing technologies, Organic Rankine Cycle (ORC) has been proven to be one of the most effective methods for the utilization of low grade heat sources. Turbine is a key component in ORC system and it plays an important role in system performance. Traditional turbine expanders, the axial flow turbine and the radial inflow turbine are typically selected in large scale ORC systems. However, in small and micro scale systems, traditional turbine expanders are not suitable due to large flow loss and high rotation speed. In this case, Tesla turbine allows a low-cost and reliable design for the organic expander that could be an attractive option for small scale ORC systems. A 1-D model of Tesla turbine is presented in this paper, which mainly focuses on the flow characteristics and the momentum transfer. This study improves the 1-D model, taking the nozzle limit expansion ratio into consideration, which is related to the installation angle of the nozzle and the specific heat ratio of the working fluid. The improved model is used to analyze Tesla turbine performance and predict turbine efficiency. Thermodynamic analysis is conducted for a small scale ORC system. The simulation results reveal that the ORC system can generate a considerable net power output. Therefore, Tesla turbine can be regarded as a potential choice to be applied in small scale ORC systems.
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Malavolta, Massimo, Asfaw Beyene et Mauro Venturini. « Experimental Implementation of a Micro-Scale ORC-Based CHP Energy System for Domestic Applications ». Dans ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-37208.
Texte intégralRésumé :
Because of the renewed interest in renewable energy as well as increased emphasis on alternative technologies, micropower-generating systems have attracted considerable research interest over the last decade. However, micro-scale power generation for low grade heat recovery applications, i.e. as low as 1–3 kW - for domestic use, are characterized by very low efficiencies and relatively high specific cost. For economic viability, these factors make it imperative that the heat source remains “free”, such as solar or geothermal energy. In this paper, a small-scale Organic Rankine Cycle (ORC) is presented. The small-scale ORC module was built and tested at San Diego State University lab, aimed at producing electricity and hot water from ultra-low grade heat source that can be tapped from solar collectors and low temperature exhaust heat. The system was built for economic viability and flexibility, tailored for a domestic use. The tests demonstrated that the system offered CHP capability, with electric and thermal power output suitable for a domestic application. It also offered high operational flexibility, since the scroll expander could work with a high temperature range, accommodating an even-significant drop of the heat source temperature. Therefore, it can be conveniently used to capture solar and low-temperature energy sources. The system could be produced at an overall cost of less than $3,000 (USD 2010).
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Patel, Bhavesh, Vaibhav Jain, Surendra Singh kachhwaha et Nanji J. Hadia. « THERMODYNAMIC STUDY OF MICRO SCALE ORGANIC RANKINE CYCLE (ORC) USING MODIFIED GOUY-STODOLA EQUATION ». Dans First Thermal and Fluids Engineering Summer Conference. Connecticut : Begellhouse, 2016. http://dx.doi.org/10.1615/tfesc1.ecv.012774.
Texte intégral
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Camporeale, Sergio Mario, Patrizia Domenica Ciliberti, Bernardo Fortunato, Marco Torresi et Antonio Marco Pantaleo. « Externally Fired Micro Gas Turbine and ORC Bottoming Cycle : Optimal Biomass/Natural Gas CHP Configuration for Residential Energy Demand ». Dans ASME Turbo Expo 2015 : Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-43571.
Texte intégralRésumé :
Small scale Combined Heat and Power (CHP) plants present lower electric efficiency in comparison to large scale ones, and this is particularly true when biomass fuels are used. In most cases, the use of both heat and electricity to serve on site energy demand is a key issue to achieve acceptable global energy efficiency and investment profitability. However, the heat demand follows a typical daily and seasonal pattern and is influenced by climatic conditions, in particular in the case of residential and tertiary end users. During low heat demand periods, a lot of heat produced by the CHP plant is discharged. In order to increase the electric conversion efficiency of small scale micro turbine for heat and power cogeneration, a bottoming ORC system can be coupled to the cycle, however this option reduces the temperature and quantity of cogenerated heat available to the load. In this perspective, the paper presents the results of a thermo-economic analysis of small scale CHP plants composed by a micro gas turbine (MGT) and a bottoming Organic Rankine Cycle (ORC), serving a typical residential energy demand. For the topping cycle three different configurations are examined: 1) a simple recuperative micro gas turbine fuelled by natural gas (NG), 2) a dual fuel EFGT cycle, fuelled by biomass and natural gas (50% energy input) (DF) and 3) an externally fired gas turbine (EFGT) with direct combustion of biomass (B). The bottoming cycle is a simple saturated Rankine cycle with regeneration and no superheating. The ORC cycle and the fluid selection are optimized on the basis of the available exhaust gas temperature at the turbine exit. The research assesses the influence of the thermal energy demand typology (residential demand with cold, mild and hot climate conditions) and CHP plant operational strategies (baseload vs heat driven vs electricity driven operation mode) on the global energy efficiency and profitability of the following three configurations: A) MGT with cogeneration; B) MGT+ ORC without cogeneration; C) MGT+ORC with cogeneration. In all cases, a back-up boiler is assumed to match the heat demand of the load (fed by natural gas or biomass). The research explores the profitability of bottoming ORC in view of the following tradeoffs: (i) lower energy conversion efficiency and higher investment cost of high biomass input rate with respect to natural gas; (ii) higher efficiency but higher costs and reduced heat available for cogeneration in the bottoming ORC; (ii) higher primary energy savings and revenues from feed-in tariff available for biomass electricity fed into the grid.
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Mitterhofer, Matthias, et Matthew Orosz. « Dynamic Simulation and Optimization of an Experimental Micro-CSP Power Plant ». Dans ASME 2015 9th International Conference on Energy Sustainability collocated with the ASME 2015 Power Conference, the ASME 2015 13th International Conference on Fuel Cell Science, Engineering and Technology, and the ASME 2015 Nuclear Forum. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/es2015-49333.
Texte intégralRésumé :
Small scale solar thermal systems are increasingly investigated in the context of decentralized energy supply, due to favorable costs of thermal energy storage (TES) in comparison with battery storage for otherwise economical PV generation. The present study provides the computational framework and results of a one year simulation of a low-cost pilot 3kWel micro-Concentrated Solar Power (micro-CSP) plant with TES. The modeling approach is based on a dynamic representation of the solar thermal loop and a steady state model of the Organic Rankine Cycle (ORC), and is validated to experimental data from a test site (Eckerd College, St. Petersburg, Florida). The simulation results predict an annual net electricity generation of 4.08 MWh/a. Based on the simulation, optimization studies focusing on the Organic Rankine Cycle (ORC) converter of the system are presented, including a control strategy allowing for a variable pinch point in the condenser that offers an annual improvement of 14.0% in comparison to a constant condensation pinch point. Absolute electricity output is increased to 4.65 MWh/a. Improvements are due to better matching to expander performance and lower condenser fan power because of higher pinch points. A method, incorporating this control strategy, is developed to economically optimize the ORC components. The process allows for optimization of the ORC subsystem in an arbitrary environment, e.g. as part of a micro-grid to minimize Levelized electricity costs (LEC). The air-cooled condenser is identified as the driving component for the ORC optimization as its influence on overall costs and performance is of major significance. Application of the optimization process to various locations in Africa illustrates economic benefits of the system in comparison to diesel generation.
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Bianchi, M., A. De Pascale, F. Melino, A. Peretto et L. Branchini. « Investigations on a Test Bench for Integrated ORC-FC Micro-CHP Energy Systems ». Dans ASME Turbo Expo 2014 : Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/gt2014-26914.
Texte intégralRésumé :
Micro-CHP (Combined Heat and Power) energy systems are potentially suitable for residential and tertiary utilities, typically characterized by low-grade heat demand and limited electric-to-thermal energy demand ratio values. Different innovative and under development CHP technologies are currently investigated in small scale units, but a standard has not been identified till now. Moreover, depending on the load request, the produced electricity can be used, stored in electric accumulator or in the external net, or integrated with other external sources. Contextually, the available heat can be used, accumulated inside the system or dissipated. The actual convenience of small size CHP systems depends on the demand profiles and the operation management logic. A test facility is being developed, at the University of Bologna, for the experimental characterization of the cogenerative performance of small scale hybrid power systems, composed of micro-CHP systems of different technologies: a Micro Rankine Cycles (MRC), a Proton Exchange Membrane (PEM) Fuel Cells (FC), a battery and a heat recovery subsystem. The test set-up is also integrated with an external load simulator, in order to generate variable load profiles. This report describes the main characteristics of the implemented test bench, the selection procedure of the adopted micro-CHP unit and expected performance. Further the development of a calculation code able to simulate the performance of the considered systems will be described. This calculation code has been applied to design the components of the test bench. More in details, in this paper the sizing of the electrical energy storage system, and of the thermal and H2 storage tanks will be presented and discussed.
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Reale, Fabrizio, Raniero Sannino, Raffaela Calabria et Patrizio Massoli. « Numerical Study of a Small-Scale Micro Gas Turbine-ORC Power Plant Integrated With a Biomass Gasifier ». Dans ASME Turbo Expo 2020 : Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/gt2020-15401.
Texte intégralRésumé :
Abstract The paper is focused on coupling a small-scale power plant, based on a micro gas turbine (mGT) and a bottoming Organic Rankine Cycle (ORC), with a biomass gasifier. The aim of this study is to define the optimal strategies to maximize the benefits related to distributed generation and to promote the organic solid waste gasification, in terms of energy efficiency and renewable sources exploitation. In particular, they were investigated the energetic performances of the system when the micro gas turbine was fed with several fuel blends, made by specific volume concentration of syngas and biogas. The low heating value of both considered fuels implies the necessity of operating the mGT in peculiar conditions as determined by the performance maps of compressor and turbine. Then, the thermodynamic analyses of the whole energy system have been carried out to evaluate the performance for each fuel. The high hydrogen content of syngas and the different thermodynamic properties of the studied fuel blends required a deeper investigation of the combustion process. In order to analyze the combustion stability and the fluid dynamic aspects, an accurate investigation of combustion chamber has been performed through a CFD solver. Finally, a comparison of the plant performances for each fuel blend have been reported, along with opportunities and critical aspects related to power plant integration.
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Reale, Fabrizio, Vincenzo Iannotta et Raffaele Tuccillo. « Numerical Study of a Micro Gas Turbine Integrated With a Supercritical CO2 Brayton Cycle Turbine ». Dans ASME Turbo Expo 2018 : Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-76656.
Texte intégralRésumé :
The primary need of reducing pollutant and greenhouse gas emissions has led to new energy scenarios. The interest of research community is mainly focused on the development of energy systems based on renewable resources and energy storage systems and smart energy grids. In the latter case small scale energy systems can become of interest as nodes of distributed energy systems. In this context micro gas turbines (MGT) can play a key role thanks to their flexibility and a strategy to increase their overall efficiency is to integrate gas turbines with a bottoming cycle. In this paper the authors analyze the possibility to integrate a MGT with a super critical CO2 Brayton cycle turbine (sCO2 GT) as a bottoming cycle (BC). A 0D thermodynamic analysis is used to highlight opportunities and critical aspects also by a comparison with another integrated energy system in which the waste heat recovery (WHR) is obtained by the adoption of an organic Rankine cycle (ORC). While ORC is widely used in case of middle and low temperature of the heat source, s-CO2 BC is a new method in this field of application. One of the aim of the analysis is to verify if this choice can be comparable with ORC for this operative range, with a medium-low value of exhaust gases and very small power values. The studied MGT is a Turbec T100P.
Rapports d'organisations sur le sujet "Micro-scale ORC"
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Blundell, S. Micro-terrain and canopy feature extraction by breakline and differencing analysis of gridded elevation models : identifying terrain model discontinuities with application to off-road mobility modeling. Engineer Research and Development Center (U.S.), avril 2021. http://dx.doi.org/10.21079/11681/40185.
Texte intégralRésumé :
Elevation models derived from high-resolution airborne lidar scanners provide an added dimension for identification and extraction of micro-terrain features characterized by topographic discontinuities or breaklines. Gridded digital surface models created from first-return lidar pulses are often combined with lidar-derived bare-earth models to extract vegetation features by model differencing. However, vegetative canopy can also be extracted from the digital surface model alone through breakline analysis by taking advantage of the fine-scale changes in slope that are detectable in high-resolution elevation models of canopy. The identification and mapping of canopy cover and micro-terrain features in areas of sparse vegetation is demonstrated with an elevation model for a region of western Montana, using algorithms for breaklines, elevation differencing, slope, terrain ruggedness, and breakline gradient direction. These algorithms were created at the U.S. Army Engineer Research Center – Geospatial Research Laboratory (ERDC-GRL) and can be accessed through an in-house tool constructed in the ENVI/IDL environment. After breakline processing, products from these algorithms are brought into a Geographic Information System as analytical layers and applied to a mobility routing model, demonstrating the effect of breaklines as obstacles in the calculation of optimal, off-road routes. Elevation model breakline analysis can serve as significant added value to micro-terrain feature and canopy mapping, obstacle identification, and route planning.
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Lever, James, Emily Asenath-Smith, Susan Taylor et Austin Lines. Assessing the mechanisms thought to govern ice and snow friction and their interplay with substrate brittle behavior. Engineer Research and Development Center (U.S.), décembre 2021. http://dx.doi.org/10.21079/1168142742.
Texte intégralRésumé :
Sliding friction on ice and snow is characteristically low at temperatures common on Earth’s surface. This slipperiness underlies efficient sleds, winter sports, and the need for specialized tires. Friction can also play micro-mechanical role affecting ice compressive and crushing strengths. Researchers have proposed several mechanisms thought to govern ice and snow friction, but directly validating the underlying mechanics has been difficult. This may be changing, as instruments capable of micro-scale measurements and imaging are now being brought to bear on friction studies. Nevertheless, given the broad regimes of practical interest (interaction length, temperature, speed, pressure, slider properties, etc.), it may be unrealistic to expect that a single mechanism accounts for why ice and snow are slippery. Because bulk ice, and the ice grains that constitute snow, are solids near their melting point at terrestrial temperatures, most research has focused on whether a lubricating water film forms at the interface with a slider. However, ice is extremely brittle, and dry-contact abrasion and wear at the front of sliders could prevent or delay a transition to lubricated contact. Also, water is a poor lubricant, and lubricating films thick enough to separate surface asperities may not form for many systems of interest. This article aims to assess our knowledge of the mechanics underlying ice and snow friction.
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Gust, Sarah. Global Universal Basic Skills : Current Deficits and Implications for World Development. Research on Improving Systems of Education (RISE), octobre 2022. http://dx.doi.org/10.35489/bsg-risewp_2022/114.
Texte intégralRésumé :
How far is the world away from ensuring that every child obtains the basic skills needed to be internationally competitive? And what would accomplishing this mean for world development? Based on the micro data of international and regional achievement tests, we map achievement onto a common (PISA) scale. We then estimate the share of children not achieving basic skills for 159 countries that cover 98.1 percent of world population and 99.4 percent of world GDP. We find that at least two-thirds of the world’s youth do not reach basic skill levels, ranging from 24 percent in North America to 89 percent in South Asia and 94 percent in Sub-Saharan Africa. Our economic analysis suggests that the present value of lost world economic output due to missing the goal of global universal basic skills amounts to over $700 trillion over the remaining century, or 11 percent of discounted GDP.
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Pinet, N., O. H. Ardakani, J. Cesar, D. C. Petts, C. Debuhr et P J Sack. Exploring the link between organic matter and Carlin-type gold mineralization : new insights from Yukon deposits. Natural Resources Canada/CMSS/Information Management, 2022. http://dx.doi.org/10.4095/330086.
Texte intégralRésumé :
The link between organic matter and gold in sediment-hosted Carlin-type deposits is controversial. This study aims to tackle this potential link by documenting the occurrence of organic matter in a single borehole from a Carlin-type gold deposit in Yukon and by considering, in a preliminary way, the spatial and/or temporal relationship between organic matter and gold mineralization. The sedimentary succession hosting the Conrad deposit was relatively rich in organic matter, possibly related to Archea. Despite the high maturation of samples, the total organic carbon (TOC) content of the limestone unit averages 1.31 wt. % (maximum = 3.18 wt. %). Petrographic observations indicate that pore and fracture filling pyrobitumen is the dominant organic matter maceral in the studied samples. This type of pyrobitumen was matured after its emplacement, indicating that hydrocarbon fluids cannot have served as an agent for gold transport. Pyrobitumen disseminated in the rock or associated with stylolites are also documented. The correlation between TOC and Tl (the best proxy for Au) for selected samples and the high As content of pyrobitumen filling pores may suggest a link between organic matter content and gold deposition, but this was not demonstrated by LA-ICP-MS micro-scale mapping. This study also highlights the challenges of establishing a direct spatial relationship between 'invisible' gold and very small (&lt; 10 µm) pyrobitumen particles.
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Haider, Huma. Scalability of Transitional Justice and Reconciliation Interventions : Moving Toward Wider Socio-political Change. Institute of Development Studies (IDS), mars 2021. http://dx.doi.org/10.19088/k4d.2021.080.
Texte intégralRésumé :
Literature focusing on the aftermath of conflict in the Western Balkans, notes that many people remain focused on stereotypes and prejudices between different ethnic groups stoking fear of a return to conflict. This rapid review examines evidence focussing on various interventions that seek to promote inter-group relations that are greatly elusive in the political realm in the Western Balkan. Socio-political change requires a growing critical mass that sees the merit in progressive and conciliatory ethnic politics and is capable of side-lining divisive ethno-nationalist forces. This review provides an evidence synthesis of pathways through which micro-level, civil-society-based interventions can produce ‘ripple effects’ in society and scale up to affect larger geographic areas and macro-level socio-political outcomes. These interventions help in the provision of alternative platforms for dealing with divisive nationalism in post-conflict societies. There is need to ensure that the different players participating in reconciliation activities are able to scale up and attain broader reach to ensure efficacy and hence enabling them to become ‘multiplier of peace.’ One such way is by providing tools for activism. The involvement of key people and institutions, who are respected and play an important role in the everyday life of communities and participants is an important factor in the design and success of reconciliation initiatives. These include the youth, objective media, and journalists. The transformation of conflict identities through reconciliation-related activities is theorised as leading to the creation of peace constituencies that support non-violent approaches to conflict resolution and sustainable peace The success of reconciliation interventions largely depends on whether it contributes to redefining otherwise antagonistic identities and hostile relationships within a community or society.
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Shpigel, Muki, Allen Place, William Koven, Oded (Odi) Zmora, Sheenan Harpaz et Mordechai Harel. Development of Sodium Alginate Encapsulation of Diatom Concentrates as a Nutrient Delivery System to Enhance Growth and Survival of Post-Larvae Abalone. United States Department of Agriculture, septembre 2001. http://dx.doi.org/10.32747/2001.7586480.bard.
Texte intégralRésumé :
The major bottlenecks in rearing the highly priced gastropod abalone (Haliotis spp.) are the slow growth rate and the high mortality during the first 8 to 12 weeks following metamorphosis and settling. The most likely reason flor these problems is related to nutritional deficiencies in the diatom diet on which the post larvae (PL) feed almost exclusively in captivity. Higher survival and improved growth rate will reduce the considerable expense of hatchery-nursery resisdence time and thereflore the production costs. BARD supported our research for one year only and the support was given to us in order to prove that "(1) Abalone PL feed on encapsulated diatoms, and (2) heterotrophic diatoms can be mass produced." In the course of this year we have developed a novel nutrient delivery system specifically designed to enhance growth and survival of post-larval abalone. This approach is based on the sodium-alginate encapsulation of heterotrophically grown diatoms or diatom extracts, including appetite-stimulating factors. Diatom species that attract the PL and promote the highest growth and survival have been identified. These were also tested by incorporating them (either intact cells or as cell extracts) into a sodium-alginate matrix while comparing the growth to that achieved when using diatoms (singel sp. or as a mixture). A number of potential chemoattractants to act as appetite-stimulating factors for abalone PL have been tested. Preliminary results show that the incorporation of the amino acid methionine at a level of 10-3M to the sodim alginate matrix leads to a marked enhancement of growth. The results ol these studies provided basic knowledge on the growth of abalone and showed that it is possible to obtain, on a regular basis, survival rates exceeding 10% for this stage. Prior to this study the survival rates ranged between 2-4%, less than half of the values achieved today. Several diatom species originated from the National Center for Mariculture (Nitzchia laevis, Navicula lenzi, Amphora T3, and Navicula tennerima) and Cylindrotheca fusiformis (2083, 2084, 2085, 2086 and 2087 UTEX strains, Austin TX) were tested for heterotrophic growth. Axenic colonies were initially obtained and following intensive selection cycles and mutagenesis treatments, Amphora T3, Navicula tennerima and Cylindrotheca fusiformis (2083 UTEX strain) were capable of growing under heterotrophic conditions and to sustain highly enriched mediums. A highly efficient selection procedure as well as cost effective matrix of media components were developed and optimized. Glucose was identified as the best carbon source for all diatom strains. Doubling times ranging from 20-40 h were observed, and stable heterotroph cultures at a densities range of 103-104 were achieved. Although current growth rates are not yet sufficient for full economical fermentation, we estimate that further selections and mutagenesis treatments cycles should result in much faster growing colonies suitable for a fermentor scale-up. As rightfully pointed out by one of the reviewers, "There would be no point in assessing the optimum levels of dietary inclusions into micro-capsules, if the post-larvae cannot be induced to consume those capsules in the first place." We believe that the results of the first year of research provide a foundationfor the continuation of this research following the objectives put forth in the original proposal. Future work should concentrate on the optimization of incorporation of intact cells and cell extracts of the developed heterotrophic strains in the alginate matrix, as well as improving this delivery system by including liposomes and chemoattractants to ensure food consumption and enhanced growth.
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Kimhi, Ayal, Barry Goodwin, Ashok Mishra, Avner Ahituv et Yoav Kislev. The dynamics of off-farm employment, farm size, and farm structure. United States Department of Agriculture, septembre 2006. http://dx.doi.org/10.32747/2006.7695877.bard.
Texte intégralRésumé :
Objectives: (1) Preparing panel data sets for both the United States and Israel that contain a rich set of farm attributes, such as size, specialization, and output composition, and farmers’ characteristics such as off-farm employment status, education, and family composition. (2) Developing an empirical framework for the joint analysis of all the endogenous variables of interest in a dynamic setting. (3) Estimating simultaneous equations of the endogenous variables using the panel data sets from both countries. (4) Analyzing, using the empirical results, the possible effects of economic policies and institutional changes on the dynamics of the farm sector. An added objective is analyzing structural changes in farm sectors in additional countries. Background: Farm sectors in developed countries, including the U.S. and Israel, have experienced a sharp decline in their size and importance during the second half of the 20th century. The overall trend is towards fewer and larger farms that rely less on family labor. These structural changes have been a reaction to changes in technology, in government policies, and in market conditions: decreasing terms of trade, increasing alternative opportunities, and urbanization pressures. As these factors continue to change, so does the structure of the agricultural sector. Conclusions: We have shown that all major dimensions of structural changes in agriculture are closely interlinked. These include farm efficiency, farm scale, farm scope (diversification), and off-farm labor. We have also shown that these conclusions hold and perhaps even become stronger whenever dynamic aspects of structural adjustments are explicitly modeled using longitudinal data. While the results vary somewhat in the different applications, several common features are observed for both the U.S. and Israel. First, the trend towards the concentration of farm production in a smaller number of larger farm enterprises is likely to continue. Second, at the micro level, increased farm size is negatively associated with increased off-farm labor, with the causality going both ways. Third, the increase in farm size is mostly achieved by diversifying farm production into additional activities (crops or livestock). All these imply that the farm sector converges towards a bi-modal farm distribution, with some farms becoming commercial while the remaining farm households either exit farming altogether or continue producing but rely heavily on off-farm income. Implications: The primary scientific implication of this project is that one should not analyze a specific farm attribute in isolation. We have shown that controlling for the joint determination of the various farm and household attributes is crucial for obtaining meaningful empirical results. The policy implications are to some extent general but could be different in the two countries. The general implication is that farm policy is an important determinant of structural changes in the farm sector. For the U.S., we have shown the different effects of coupled and decoupled (direct) farm payments on the various farm attributes, and also shown that it is important to take into account the joint farm-household decisions in order to conduct a meaningful policy analysis. Only this kind of analysis explains the indirect effect of direct farm payments on farm production decisions. For Israel, we concluded that farm policy (or lack of farm policy) has contributed to the fast structural changes we observed over the last 25 years. The sharp change of direction in farm policy that started in the early 1980s has accelerated structural changes that could have been smoother otherwise. These accelerated structural changes most likely lead to welfare losses in rural areas.