Littérature scientifique sur le sujet « Endogenous exit »
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Articles de revues sur le sujet "Endogenous exit"
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Mantovani, Andrea, et Giordano Mion. « Advertising and endogenous exit in a differentiated duopoly ». Recherches économiques de Louvain 72, no 1 (2006) : 19–47. http://dx.doi.org/10.1017/s0770451800007168.
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SummaryIn this paper we consider a two-stage duopoly game where firms first decide whether to invest in advertising and then compete in prices. Advertising has two effects: a market enlargement for both firms and a predatory gain for the investing firm only.Both symmetric and asymmetric equilibria may arise. The two most interesting cases are a coordination game where both firms investing and non-investing are equilibria, and a chicken game where only one firm invests while the other is possibly driven (endogenously) out of the market. Our results suggest that product differentiation has an ambiguous impact on investment in advertising and that strong product substitutabihty may induce a coordination problem.
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Mantovani, Andrea, et Giordano Mion. « Advertising and endogenous exit in a differentiated duopoly ». Recherches économiques de Louvain 72, no 1 (2006) : 19. http://dx.doi.org/10.3917/rel.721.0019.
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Lavrutich, Maria N. « Capacity choice under uncertainty in a duopoly with endogenous exit ». European Journal of Operational Research 258, no 3 (mai 2017) : 1033–53. http://dx.doi.org/10.1016/j.ejor.2016.09.048.
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Chang, Myong-Hun. « Entry, Exit, and the Endogenous Market Structure in Technologically Turbulent Industries ». Eastern Economic Journal 37, no 1 (28 décembre 2010) : 51–84. http://dx.doi.org/10.1057/eej.2010.55.
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Bayer, Christian. « Investment timing and predatory behavior in a duopoly with endogenous exit ». Journal of Economic Dynamics and Control 31, no 9 (septembre 2007) : 3069–109. http://dx.doi.org/10.1016/j.jedc.2006.10.006.
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Wang, Z. M., H. Yang et D. M. Livingston. « Endogenous E2F-1 promotes timely G0 exit of resting mouse embryo fibroblasts ». Proceedings of the National Academy of Sciences 95, no 26 (22 décembre 1998) : 15583–86. http://dx.doi.org/10.1073/pnas.95.26.15583.
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Cont, Rama, et Lakshithe Wagalath. « RUNNING FOR THE EXIT : DISTRESSED SELLING AND ENDOGENOUS CORRELATION IN FINANCIAL MARKETS ». Mathematical Finance 23, no 4 (13 février 2012) : 718–41. http://dx.doi.org/10.1111/j.1467-9965.2011.00510.x.
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Lys, Thomas Z., et Jayanthi Sunder. « Endogenous entry/exit as an alternative explanation for the disciplining role of independent analysts ». Journal of Accounting and Economics 45, no 2-3 (août 2008) : 317–23. http://dx.doi.org/10.1016/j.jacceco.2008.02.001.
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Thiel, Jurre H. « Adviser Compensation, Endogenous Entry, and the Advice Gap ». American Economic Journal : Microeconomics 14, no 3 (1 août 2022) : 76–130. http://dx.doi.org/10.1257/mic.20200074.
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To prevent biased advice, regulators increasingly ban commission payments to financial advisers. Such bans are associated with “advice gaps,” meaning that advice becomes less accessible. To understand the trade-off between the quality and accessibility of advice, this paper develops a model of price competition in advice markets with endogenous entry of advisers. While commission bans increase consumer surplus in the short run, they hurt the profitability of advisers. In the long run, advisers exit the market, advice becomes inaccessible, and consumer surplus decreases. These results imply that accounting for the endogeneity of market structure is important when regulating advice. (JEL D82, J33, L51, L84, L88, M52)
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Saito, Yuta. « A Note on Time Inconsistency and Endogenous Exits from a Currency Union ». Games 13, no 2 (23 février 2022) : 21. http://dx.doi.org/10.3390/g13020021.
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This paper investigates the effects of members’ exits from a currency union on the credibility of the common currency. In our currency union model, the inflation rate of the common currency is determined by majority voting among N member countries that are heterogeneous with respect to their output shocks. Once an inflation rate of the common currency has been selected, each member decides whether to remain in the currency union or not. If a member decides to exit, it has to pay a fixed social cost and individually chooses the inflation rate of its currency. Unlike previous research on this topic, we focus on the possibility of achieving an optimal outcome, which generates no inflation bias, when more than one member is expected to leave the currency union. We show that the optimal outcome can only be achieved if no members leave the currency union.
Thèses sur le sujet "Endogenous exit"
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Mattiuzzo, G. « Cell entry and exit of porcine endogenous retrovirus A : receptors and release inhibitor ». Thesis, University College London (University of London), 2010. http://discovery.ucl.ac.uk/19218/.
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Following the discovery that porcine endogenous retrovirus (PERV) can infect human cells, the potential risk of a zoonotic infection by PERV has been a major obstacle in the xenotransplantation field. The aim of this thesis is to gain a better understanding of PERV biology, so as to help assess and reduce the risk of PERV zoonosis. PERV subgroup A can enter human cells through two human PERV-A receptors (huPAR-1 and -2). To determine critical regions in the receptor for PERV-A infection, chimeric receptors between huPAR-2 and the non functional murine PAR (muPAR) have been analysed. A single amino acid difference (amino acid 109) was found responsible for the inability of muPAR to mediate PERV-A binding and infection. These results were then applied to the evaluation of PERV infection of non-human primates (NHP). NHP could represent an ideal animal model for assessing the risk of zoonosis following long-term exposure to porcine material. However, PERV does not infect NHP cells with the same efficiency as it does human cells. The data presented in this thesis suggests that in some NHP species the poor infectivity is due to mutation of the same critical amino acid (a.a.109) described for muPAR. However, African green monkey cells express two functional receptors and other mechanisms are likely to be responsible for the low susceptibility to PERV-A infection. Secondly, I evaluated the effect of a release inhibitor as a possible strategy to reduce PERV dissemination from pig cells. Human tetherin can inhibit retrovirus production from cells. I showed that overexpression of human and newly cloned porcine tetherin in pig cells can reduce the release of PERV. My data suggests that tetherin-expressing transgenic pigs could represent a safer donor in xenotransplantation.
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BARBARO, BIANCA. « Sectoral shocks and banking crises in a schumpeterian model of endogenous firm dynamics ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2019. http://hdl.handle.net/10281/241309.
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In the first chapter, e build a two-sector (capital and final goods) model with endogenous firm
dynamics to study the effects of permanent productivity shocks in the final
goods sector. Firms are characterised by idiosyncratic productivity levels
and decreasing returns to scale. Shocks are modelled as a sudden
improvement of the technology frontier accessed by new entrants, which then
gradually spreads to incumbent firms. The shock drives less efficient firms
out of the market and unambiguously raises productivity and output in the
long run. By contrast, creative destruction is strongly limited by the
initial fall in the relative price of capital goods. This latter result is
driven by the wealth effect of the shock on consumption dynamics and by the
ensuing reduction in savings and in demand for capital goods. The smaller
scale of production of this sector is associated with increased efficiency and
to a reduced relative price of capital goods. As a result, production costs
in the final goods sector, fall and fewer incumbents exit the market.
Relative to what would happen in a standard one sector model, we obtain
a contraction in the initial employment fall associated with the shock.
In the second chapter, We build a business cycle model characterized by endogenous firms dynamic, idiosyncratic productivity levels and by a financial sector.
Starting from a set-up \`{a} la Gerlter and Karadi (2011 \cite{gertler2011model}), we extend the financial sector including firms' default and the possibility to roll-over borrowing condition to unproductive firms. We find that a technology improvement discourages debt roll-over, reducing the share of Non-performing loans (NPL) and unproductive incumbent through the entry of new and more productive firms. New entrants, raise market competition and increase interest rates, financial intermediaries incentive to renegotiated debt condition decrease and the same happens to the share of NPLs. Furthermore, an adverse shock to financial intermediaries capital triggers an ever-greening mechanism that increases the share of NPLs in bankers balance sheets and persistently reduces aggregate productivity.I In the first chapter, e build a two-sector (capital and final goods) model with endogenous firm dynamics to study the effects of permanent productivity shocks in the final goods sector. Firms are characterised by idiosyncratic productivity levels and decreasing returns to scale. Shocks are modelled as a sudden improvement of the technology frontier accessed by new entrants, which then gradually spreads to incumbent firms. The shock drives less efficient firms out of the market and unambiguously raises productivity and output in the long run. By contrast, creative destruction is strongly limited by the initial fall in the relative price of capital goods. This latter result is driven by the wealth effect of the shock on consumption dynamics and by the ensuing reduction in savings and in demand for capital goods. The smaller scale of production of this sector is associated with increased efficiency and to a reduced relative price of capital goods. As a result, production costs in the final goods sector, fall and fewer incumbents exit the market. Relative to what would happen in a standard one sector model, we obtain a contraction in the initial employment fall associated with the shock. In the second chapter, We build a business cycle model characterized by endogenous firms dynamic, idiosyncratic productivity levels and by a financial sector. Starting from a set-up \`{a} la Gerlter and Karadi (2011 \cite{gertler2011model}), we extend the financial sector including firms' default and the possibility to roll-over borrowing condition to unproductive firms. We find that a technology improvement discourages debt roll-over, reducing the share of Non-performing loans (NPL) and unproductive incumbent through the entry of new and more productive firms. New entrants, raise market competition and increase interest rates, financial intermediaries incentive to renegotiated debt condition decrease and the same happens to the share of NPLs. Furthermore, an adverse shock to financial intermediaries capital triggers an ever-greening mechanism that increases the share of NPLs in bankers balance sheets and persistently reduces aggregate productivity.
Livres sur le sujet "Endogenous exit"
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Hausenloy, Derek, et Derek Yellon, dir. An Introduction to Cardioprotection. Oxford University Press, 2011. http://dx.doi.org/10.1093/med/9780199544769.003.0001.
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• In its broadest sense, the term ‘cardioprotection’ encompasses ‘all mechanisms and means that contribute to the preservation of the heart by reducing or even preventing myocardial damage’• However, for the purposes of this book, the term ‘cardioprotection’ will refer to the endogenous mechanisms and therapeutic strategies that reduce or prevent myocardial damage induced by acute ischaemia-reperfusion injury• In this context, cardioprotection begins with the primary prevention of coronary heart disease and includes the reduction of myocardial injury sustained during coronary artery bypass graft surgery, and an acute myocardial infarction, conditions with considerable morbidity and mortality• An understanding of the pathophysiology of acute myocardial ischaemia-reperfusion injury is essential when designing new cardioprotective strategies• Several methods exist for both quantifying myocardial damage induced by acute ischaemia-reperfusion injury and for assessing myocardial salvage following the application of cardioprotective strategies• Importantly, novel cardioprotective strategies must be capable of preventing and reducing myocardial damage over and above that provided by current optimal therapy.
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Spence, Charles. Orienting Attention. Sous la direction de Anna C. (Kia) Nobre et Sabine Kastner. Oxford University Press, 2014. http://dx.doi.org/10.1093/oxfordhb/9780199675111.013.015.
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The last 30 years or so have seen a rapid rise in research on attentional orienting from a crossmodal perspective. The majority of this research has tended to focus on the consequences of the covert orienting of attention (either to a sensory modality or spatial location) for both perception and neural information processing. The results of numerous studies have now highlighted the robust crossmodal links that exist in the case of both overt and covert, and both exogenous and endogenous spatial orienting. Neuroimaging studies have started to highlight the neural circuits underlying such crossmodal effects. Researchers are increasingly using transcranial magnetic stimulation in order to lesion temporarily putative areas within these networks; the aim of such research often being to determine whether attentional orienting is controlled by supramodal versus modality-specific neural systems that are somehow linked (this is known as the ‘separable-but-linked’ hypothesis). The available research demonstrates that crossmodal attentional orienting (and multisensory integration—from which it is sometimes hard to distinguish) can affect the very earliest stages of information processing in the human brain.
Chapitres de livres sur le sujet "Endogenous exit"
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Gangopadhyay, Partha, et Robert F. Owen. « A Model of International Entry and Exit with Endogenous Sunk Costs in Vertical Markets ». Dans Theorizing International Trade, 69–100. Singapore : Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-1759-9_4.
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Kabbara, Sami, Neil Kelkar, Mandi D. Conway et Gholam A. Peyman. « Endogenous Endophthalmitis : Etiology and Treatment ». Dans Eye Infections - Recent Advances in Diagnosis and Treatment [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.96766.
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This chapter comprehensively covers all aspects of endogenous endophthalmitis from systemic infectious agents, with an emphasis on reported and newer etiologies to broaden the diagnostic and investigative acumen of treating ophthalmic providers. The discussion includes the etiology of metastatic endophthalmitis and diagnostic investigations, including polymerase chain reaction (PCR), for identification of bacterial and viral infections involving the eye in both immunosuppressed in non-immunosuppressed patients. Additionally, we present clinical and diagnostic findings of fungal infections, protozoal infections, and helminthic infections. Pediatric cases are also reported and etiologies described. We discuss both etiology and diagnostic challenges. Current therapeutic modalities and outcomes are reviewed. While no two cases of metastatic endophthalmitis are the same, some similarities may exist that allow us to generalize how to approach and treat this potentially sight- and life-threatening spectrum of diseases and find the underlying systemic cause.
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Moreira, António. « Entrepreneurial Tourism ». Dans Advances in Electronic Government, Digital Divide, and Regional Development, 376–404. IGI Global, 2016. http://dx.doi.org/10.4018/978-1-4666-9567-2.ch017.
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The chapter presents an entrepreneurial perspective to rural tourism. It is based on the utilization of endogenous resources that exist within a rural region, and leads to a group of business opportunities related to tourism, craftwork, and agriculture, which are taken into account to define the strategic objectives for the ADRIMAG region. The chapter follows a qualitative approach to business opportunities. Through our analysis, it was possible to create, in a simple manner, a group of business opportunities based on the endogenous resources of the region. With this study, we expect to bring forth an entrepreneurial perspective that will sustainably foster tourism development within rural regions, but with high potential for tourism attraction.
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Choudhary, Pratik, et Stephanie A. Amiel. « Hypoglycaemia in the treatment of diabetes mellitus ». Dans Oxford Textbook of Endocrinology and Diabetes, 1849–61. Oxford University Press, 2011. http://dx.doi.org/10.1093/med/9780199235292.003.1435.
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Hypoglycaemia (low blood glucose concentration) is the most important acute complication of the pharmacological treatment of diabetes mellitus. Low blood glucose impairs brain (and, potentially, cardiac) function. The brain has minimal endogenous stores of energy, with small amounts of glycogen in astroglial cells. The brain is therefore largely dependent on circulating glucose as the substrate to fuel cerebral metabolism and support cognitive performance. If blood glucose levels fall sufficiently, cognitive dysfunction is inevitable. In health, efficient glucose sensing and counterregulatory mechanisms exist to prevent clinically significant hypoglycaemia. These are impaired by diabetes and by its therapies. Patients with diabetes rank fear of hypoglycaemia as highly as fear of chronic complications such as nephropathy or retinopathy (1). Fear of hypoglycaemia, hypoglycaemia itself and attempts to avoid hypoglycaemia limit the degree to which glycaemic control can be intensified to reduce the risk of chronic complications of diabetes both for type 1 and type 2 diabetes.
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Dennenmoser, Stefan, John H. Christy et Martin Thiel. « Rhythms and Reproduction ». Dans Reproductive Biology, 472–502. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780190688554.003.0017.
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Reproductive rhythms can be found in numerous crustacean species. This chapter reviews the temporal scales of rhythms and how these rhythms are entrained and maintained by external cues and endogenous clocks. The occurrence and synchrony of rhythms vary along latitudinal and depth gradients, which may depend on the availability of zeitgebers (e.g., temperature and photoperiod), changing selective pressures such as predation risk, and variability in larval development rates that affect the timing and synchrony of reproductive rhythms. Commonly observed rhythms are reproductive migrations and synchronized larval release, which are often timed to reduce predation risk for newly hatched larvae. In crustaceans, reproductive rhythms rarely evolve under pure density-dependent selection for synchrony. Pure density dependence is common in marine broadcast-spawning invertebrates like corals, which rely on accumulation of gametes in time and space to ensure fertilization. Instead, (density-independent) selection for synchrony with environmental cycles that track changes in factors affecting fitness such as energy expenditure, predation risk, or food availability seems to be the rule, although some exceptions may exist. In contrast to natural selection, the possible contribution of sexual selection on reproductive rhythms has rarely been considered. Selection for enhanced mating possibilities should favor reproductive synchrony, but deviations from synchrony will affect the operational sex ratio and influence sexual selection. Finally, the chapter discusses the possibility of sexual conflict over reproductive timing between males and females and explores circumstances under which synchronous reproductive rhythms might be abandoned.
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Berthold, Peter. « Geographic Variation and the Microevolution of Avian Migratory Behavior ». Dans Geographic Variation in Behavior. Oxford University Press, 1999. http://dx.doi.org/10.1093/oso/9780195082951.003.0012.
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The study of migratory behavior is, at a fundamental level, the study of geographic variation in behavior. This is necessarily the case when residency grounds at either end of the migratory route differ in spatial extent, because different directional movement patterns will be required of individuals from different parts of the two ranges. As many migratory animals are widespread, substantial differences in migratory routes exist among populations of single species (examples in Dadswell et al. 1987, Baker 1991, Dingle 1991, Groot and Margolis 1991, Berthold 1993). Because the individuals that migrate often have not done so before and often do not have older migration-experienced individuals to follow (e.g., Baker 1991, Berthold 1996), the study of navigational mechanisms and their genetic underpinnings is essential to understanding migratory behavior. Naturalists have long been captivated by the problem of control mechanisms in migratory behavior. As early as 1702, von Pernau suggested that birds were “driven at the proper time by a hidden drive.” In modern terms, this amounted to suggesting that migratory behavior was triggered by innate or genetically programmed stimuli, rather than by environmental factors alone. This speculation was supported by the discovery of endogenous annual cycles more than 260 years later (see Gwinner 1986 for a review). Our understanding of the control mechanisms of migratory behavior has expanded rapidly during the last 90 years. Research in the field has elucidated, for example, genetic and endocrine control mechanisms and their interface with environmental cues such as photoperiod, relationships between environmental conditions, such as weather and food availability and the timing of migration, and unique physiological and morphological correlates of migratory behavior (for reviews, see Berthold and Terrill 1991, Berthold 1996). Birds, fishes, and insects have proven especially valuable subjects for the study of migratory behavior, and all show substantial population differentiation in migratory patterns within species (Dadswell et al. 1987, Dingle 1991, Groot and Margolis 1991, Berthold 1993). In this chapter I focus on migratory behavior in birds, especially that in the blackcap, Sylvia atricapilla, an Old World warbler that has been the subject of extensive research in my laboratory since the early 1970s.
Actes de conférences sur le sujet "Endogenous exit"
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Béguin, S., et H. C. Hemker. « THE MODE OF ACTION OF PENTOSAN POLYSULPHATE IN PLASMA ». Dans XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1643249.
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We developed a method which enables as to compute the course of prothrombinase activity in clotting plasma (H.C. Hemker, G.M. Willems, S. Béguin: Thromb. Haemostas. 56, 9-17, 1986) and used this for a study of the effect of pentosan polysulphate (PPS) on thrombin generation.When added to normal plasma in the concentration range of 0-8 μg/ml PPS induces a linear increase of the pseudo first order decay constant of endogenous thrombin like heparin does, 1 ug of PPS being equivalent to 0.045 Aig of heparin. Contrary to heparin this action is partly (∼ 65%) dependent upon AT III and partly (∼ 35%) upon heparin cofactor II.In normal plasma PPS causes an inhibition of both extrinsic and intrinsic prothrombinase formation. Only in the intrinsic system an increase of the lag time of prothrombinase appearance is observed. Unlike heparin, PPS does not inhibit factor IXa induced thrombin formation neither does it inhibit prothrombinase formation in the presence of preactivated factor VIII. The prolongation of the lag times must therefore be ascribed to inhibition by PPS of the activation of factor VIII.The inhibition of extrinsic prothrombinase formation by PPS increases with progressive dilution of thromboplastin and is not seen in haemophilia A or B plasma. This demonstrates the existance of a factor VIII and IX dependent process in extrinsic coagulation that gains in importance when the potency of factgr VII-tissue factor complex decreases, i.e. the Josso pathway.PPS, but also heparin causes an unexplained increase of prothrombinase action in haemophIIic plasma. The same phenomenon may be expected to exist in normal plasma, be it obscured by a concomitant inhibition. This, together with the incomplete inhibition of factor VIII activation by PPS makes that we cannot use this inhibitor as a means to quantitate the Josso pathway. The best estimate that we can obtain is that, in the presence of 2% thromboplastin, the factor IX dependent activation of factor X contributes more then 20% to prothrombinase generation.
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Pesteil, A., D. Cellier, O. Domercq, V. Perrot et J. C. Boniface. « CREATE : Advanced CFD for HPC Performance Improvement ». Dans ASME Turbo Expo 2012 : Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/gt2012-68844.
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The present paper provides an overview of technological evolutions aimed at improving the aerodynamic performance of Snecma’s High Pressure Compressors. Several concepts were investigated under its CREATE compressor research program, involving an extensive simulation effort. An overview of the computational approaches involved in the evaluation and selection of innovative and most promising concepts will be given in the paper. The main topics dealt with are: 1) Aeromechanical optimization of airfoils and flow path: In recent years, great efforts have been made to improve the aerodynamic design of airfoils. Among them, optimization methods have been progressively implemented in the design process with an increased complexity logic. The latest methods used at Snecma involve multi-objective, multi-parameters aeromechanical optimization including mean camber line, stacking axis, flow path contouring and more. This work is illustrated by two practical examples. 2) Vortex generators: In order to control the flow, vortex generators can be forecasted as a promising step forward. The goal is to create exogenous vorticity that will counter-balance the endogenous vorticity. Thus they appear as a tool to reduce losses and improve stability in highly loaded turbomachinery devices such as modern high pressure compressors. This section of the paper will give an overview of the dedicated numerical simulations completed. 3) Clocking: Numerous studies are related to the benefit drawn from turbine clocking on turbomachinery performance. However, fewer examples of successful compressor clocking exist. The recent capability of computational fluid dynamics tools to reduce the computational effort necessary to investigate such an issue (by the use of harmonic balance methodology) gives the opportunity for a renewed evaluation. 4) Optimization of shroud leakage flow with main flow: A strong interaction exists with the secondary flows originated in the inner flow path cavities. Coupled main flow path and cavities aerodynamic simulations were conducted to improve the relevance of the computations and understand the mechanisms involved. 5) Tandem bladings and splitters in axial rotors: The last aspect of the study was focused on dual blading concepts. After a brief review of the literature, some simulations were carried out to explore the relevance of such concepts from the viewpoint of modern high pressure compressors performance improvement.
Rapports d'organisations sur le sujet "Endogenous exit"
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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.
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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.
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Funkenstein, Bruria, et Cunming Duan. GH-IGF Axis in Sparus aurata : Possible Applications to Genetic Selection. United States Department of Agriculture, novembre 2000. http://dx.doi.org/10.32747/2000.7580665.bard.
Texte intégralRésumé :
Many factors affect growth rate in fish: environmental, nutritional, genetics and endogenous (physiological) factors. Endogenous control of growth is very complex and many hormone systems are involved. Nevertheless, it is well accepted that growth hormone (GH) plays a major role in stimulating somatic growth. Although it is now clear that most, if not all, components of the GH-IGF axis exist in fish, we are still far from understanding how fish grow. In our project we used as the experimental system a marine fish, the gilthead sea bream (Sparus aurata), which inhabits lagoons along the Mediterranean and Atlantic coasts of Europe, and represents one of the most important fish species used in the mariculture industry in the Mediterranean region, including Israel. Production of Sparus is rapidly growing, however, in order for this production to stay competitive, the farming of this fish species has to intensify and become more efficient. One drawback, still, in Sparus extensive culture is that it grows relatively slow. In addition, it is now clear that growth and reproduction are physiological interrelated processes that affect each other. In particular sexual maturation (puberty) is known to be closely related to growth rate in fish as it is in mammals, indicating interactions between the somatotropic and gonadotropic axes. The goal of our project was to try to identify the rate-limiting components(s) in Sparus aurata GH-IGF system which might explain its slow growth by studying the ontogeny of growth-related genes: GH, GH receptor, IGF-I, IGF-II, IGF receptor, IGF-binding proteins (IGFBPs) and Pit-1 during early stages of development of Sparus aurata larvae from slow and fast growing lines. Our project was a continuation of a previous BARD project and could be divided into five major parts: i) obtaining additional tools to those obtained in the previous project that are necessary to carry out the developmental study; ii) the developmental expression of growth-related genes and their cellular localization; iii) tissue-specific expression and effect of GH on expression of growth-related genes; iv) possible relationship between GH gene structure, growth rate and genetic selection; v) the possible role of the IGF system in gonadal development. The major findings of our research can be summarized as follows: 1) The cDNAs (complete or partial) coding for Sparus IGFBP-2, GH receptor and Pit-1 were cloned. Sequence comparison reveals that the primary structure of IGFBP-2 protein is 43-49% identical to that of zebrafish and other vertebrates. Intensive efforts resulted in cloning a fragment of 138 nucleotides, coding for 46 amino acids in the proximal end of the intracellular domain of GH receptor. This is the first fish GH receptor cDNA that had been cloned to date. The cloned fragment will enable us to complete the GH - receptor cloning. 2) IGF-I, IGF-II, IGFBP-2, and IGF receptor transcripts were detected by RT-PCR method throughout development in unfertilized eggs, embryos, and larvae suggesting that these mRNAs are products of both the maternal and the embryonic genomes. Preliminary RT-PCR analysis suggest that GH receptor transcript is present in post-hatching larvae already on day 1. 3) IGF-1R transcripts were detected in all tissues tested by RT-PCR with highest levels in gill cartilage, skin, kidney, heart, pyloric caeca, and brain. Northern blot analysis detected IGF receptor only in gonads, brain and gill cartilage but not in muscle; GH increased slightly brain and gill cartilage IGF-1R mRNA levels. 4) IGFBP-2 transcript were detected only in liver and gonads, when analyzed by Northern blots; RT-PCR analysis revealed expression in all tissues studied, with the highest levels found in liver, skin, gonad and pyloric caeca. 5) Expression of IGF-I, IGF-II, IGF-1R and IGFBP-2 was analyzed during gonadal development. High levels of IGF-I and IGFBP-2 expression were found in bisexual young gonads, which decreased during gonadal development. Regardless of maturational stage, IGF-II levels were higher than those of IGF-L 6) The GH gene was cloned and its structure was characterized. It contains minisatellites of tandem repeats in the first and third introns that result in high level of genetic polymorphism. 7) Analysis of the presence of IGF-I and two types of IGF receptor by immunohistochemistry revealed tissue- and stage-specific expression during larval development. Immunohistochemistry also showed that IGF-I and its receptors are present in both testicular and ovarian cells. Although at this stage we are not able to pinpoint which is the rate-limiting step causing the slow growth of Sparus aurata, our project (together with the previous BARD) yielded a great number of experimental tools both DNA probes and antibodies that will enable further studies on the factors regulating growth in Sparus aurata. Our expression studies and cellular localization shed new light on the tissue and developmental expression of growth-related genes in fish.