864 research outputs found

    Continuous Steel Production and Apparatus

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    A process for continuous refining of steel via multiple distinct reaction vessels for melting, oxidation, reduction, and refining for delivery of steel continuously to, for example, a tundish of a continuous caster system, and associated apparatus

    Analysis of Primary/Containment Coupling Phenomena Characterizing the MASLWR Design During a SBLOCA Scenario

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    Today considering the world energy demand increase, the use of advanced nuclear power plants, have an important role in the environment and economic sustainability of country energy strategy mix considering the capacity of nuclear reactors of producing energy in safe and stable way contributing in cutting the CO2 emission (Bertel & Morrison, 2001; World Energy Outlook-Executive Summary, 2009; Wolde-Rufael & Menyah, 2010; Mascari et al., 2011d). According to the information’s provided by the “Power Reactor Information System” of the International Atomic Energy Agency (IAEA), today 433 nuclear power reactors are in operation in the world providing a total power installed capacity of 366.610 GWe, 5 nuclear reactors are in long term shutdown and 65 units are under construction (IAEA PRIS, 2011). In the last 20 years, the international community, taking into account the operational experience of the nuclear reactors, starts the development of new advanced reactor designs, to satisfy the demands of the people to improve the safety of nuclear power plants and the demands of the utilities to improve the economic efficiency and reduce the capital costs (D'Auria et al., 1993; Mascari et al., 2011c). Design simplifications and increased design margins are included in the advanced Light Water Reactors (LWR) (Aksan, 2005). In this framework, the project of some advanced reactors considers the use of emergency systems based entirely on natural circulation for the removal of the decay power in transient condition and in some reactors for the removal of core power during normal operating conditions (IAEA-TECDOC-1624, 2009; Mascari et al., 2010a; Mascari et al., 2011d). For example, if the normal heat sink is not available, the decay heat can be removed by using a passive connection between the primary system and heat exchangers (Aksan, 2005; Mascari et al., 2010a, Mascari, 2010b). The AP600/1000 (Advanced Plant 600/1000 MWe) design, for example, includes a Passive Residual Heat Removal (PRHR) system consisting of a C-Tube type heat exchanger immersed in the In-containment Refueling Water Storage Tank (IRWST) and connected to one of the Hot Legs (HL) (IAEA-TECDOC-1391, 2004; Reyes, 2005c; Gou et al., 2009; Mascari et al., 2010a). A PRHR from the core via Steam Generators (SG) to the atmosphere, considered in the WWER-1000/V-392 (Water Moderated, Water Cooled Energy Reactor) design, consists of heat exchangers cooled by atmospheric air, while the PRHR via SGs, considered in the WWER-640/V-407 design, consists of heat exchangers immersed in emergency heat removal tanks installed outside the containment (Kurakov et al., 2002; IAEA-TECDOC-1391, 2004; Gou et al., 2009; Mascari et al., 2010a). In the AC-600 (Advanced Chinese PWR) the PRHR heat exchangers are cooled by atmospheric air (IAEATECDOC 1281, 2002; Zejun et al., 2003; IAEA-TECDOC-1391, 2004; Gou et al., 2009; Mascari et al., 2010a) and in the System Integrated Modular Advanced Reactor (SMART) the PRHR heat exchangers are submerged in an in-containment refuelling water tank (IAEA-TECDOC- 1391, 2004; Lee & Kim, 2008; Gou et al., 2009; Mascari et al., 2010a). The International Reactor Innovative and Secure (IRIS) design includes a passive Emergency Heat Removal System (EHRS) consisting of an heat exchanger immersed in the Refueling Water Storage Tank (RWST). The EHRS is connected to a separate SG feed and steam line and the RWST is installed outside the containment structure (Carelli et al., 2004; Carelli et al., 2009; Mascari, 2010b; Chiovaro et al., 2011). In the advanced BWR designs the core water evaporates, removing the core decay heat, and condenses in a heat exchanger placed in a pool. Then the condensate comes back to the core (Hicken & Jaegers, 2002; Mascari et al., 2010a). For example, the SWR-1000 (Siede Wasser Reaktor, 1000 MWe) design has emergency condensers immersed in a core flooding pool and connected to the core, while the ESBWR (Economic Simplified Boiling Water Reactor) design uses isolation condensers connected to the Reactor Pressure Vessel (RPV) and immersed in external pools (IAEA-TECDOC-1391, 2004; Aksan, 2005; Mascari et al., 2010a). The designs of some advanced reactors rely on natural circulation for the removing of the core power during normal operation. Examples of these reactors are the MASLWR (Multi- Application Small Light Water Reactor), the ESBWR, the SMART and the Natural Circulation based PWR being developed in Argentina (CAREM)(IAEA-TECDOC-1391, 2004; IAEA -TECDOC-1474, 2005; Mascari et al., 2010a). In particular the MASLWR (Modro et al., 2003), figure 1, is a small modular integral Pressurized Water Reactor (PWR) relying on natural circulation during both steady-state and transient operation. In the development process of these advanced nuclear reactors, the analysis of single and two-phase fluid natural circulation in complex systems (Zuber, 1991; Levy, 1999; Reyes & King, 2003; IAEA-TECDOC-1474, 2005; Mascari et al., 2011e), under steady state and transient conditions, is crucial for the understanding of the physical and operational phenomena typical of these advanced designs. The use of experimental facilities is fundamental in order to characterize the thermal hydraulics of these phenomena and to develop an experimental database useful for the validation of the computational tools necessary for the operation, design and safety analysis of nuclear reactors. In general it is expensive to design a test facility to develop experimental data useful for the analyses of complex system, therefore reduced scaled test facilities are, in general, used to characterize them. Since the experimental data produced have to be applicable to the full-scale prototype, the geometrical characteristics of the facility and the initial and boundary conditions of the selected tests have to be correctly scaled. Since possible scaling distortions are present in the experimental facility design, the similitude of the main thermal hydraulic phenomena of interest has to be assured permitting their accurate experimental simulation (Zuber, 1991; Reyes, 2005b; Reyes et al., 2007; Mascari et al., 2011e). Fig. 1. MASLWR conceptual design layout (Modro et al, 2003; Reyes et al., 2007; Mascari et al., 2011a). Different computer codes have been developed to characterize two-phase flow systems, from a system and a local point of view. Accurate simulation of transient system behavior of a nuclear power plant or of an experimental test facility is the goal of the best estimate thermal hydraulic system code. The evaluation of a thermal hydraulic system code’s calculation accuracy is accomplished by assessment and validation against appropriate system thermal hydraulic data, developed either from a running system prototype or from a scaled model test facility, and characterizing the thermal hydraulic phenomena during both steady state and transient conditions. The identification and characterization of the relevant thermal hydraulic phenomena, and the assessment and validation of thermal hydraulic systems codes, has been the objective of multiple international research programs (Mascari et al., 2011a; Mascari et al., 2011c). In this international framework, Oregon State University (OSU) has constructed, under a U.S. Department of Energy grant, a system level test facility to examine natural circulation phenomena of importance to the MASLWR design. The scaling analysis of the OSUMASLWR experimental facility was performed in order to have an adequately simulation of the single and two-phase natural circulation, reactor system depressurization during a blowdown and the containment pressure response typical of the MASLWR prototype (Zuber, 1991; Reyes & King, 2003; Reyes, 2005b). A previous testing program has been conducted in order to assess the operation of the prototypical MASLWR under normal full pressure and full temperature conditions and to assess the passive safety systems under transient conditions (Modro et al. 2003; Reyes & King, 2003; Reyes, 2005b; Reyes et al., 2007; Mascari et al., 2011e). The experimental data developed are useful also for the assessment and validation of the computational tools necessary for the operation, design and safety analysis of nuclear reactors. For many years, in order to analyze the LWR reactors, the USNRC has maintained four thermal-hydraulic codes of similar, but not identical, capabilities, the RAMONA, RELAP5, TRAC-B and TRAC-P. In the last years, the USNRC is developing an advanced best estimate thermal hydraulic system code called TRAC/RELAP Advanced Computational Engine or TRACE, by merging the capabilities of these previous codes, into a single code (Boyac & Ward, 2000; TRACE V5.0, 2010; Reyes, 2005a; Mascari et al., 2011a). The validation and assessment of the TRACE code against the MASLWR natural circulation database, developed in the OSU-MASLWR test facility, is a novel effort. This chapter illustrates an analysis of the primary/containment coupling phenomena characterizing the MASLWR design mitigation strategy during a SBLOCA scenario and, in the framework of the performance assessment and validation of thermal hydraulic system codes, a qualitative analysis of the TRACE V5 code capability in reproducing it

    MINNESOTA CURRENT FARM SITUATION

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    These papers describe the current economic conditions and outline some of the opportunities facing Minnesota farmers as they complete 1998 and develop plans for 1999. The first paper, Prospects For Farm Income in 1998, describes the variation in net farm income farmers in the Southeastern and Southwestern Farm Management Associations have experienced over the past twenty years. The possible effects of 1998's low commodity prices and government program payments on net farm income are discussed in the context of this historical variation. This paper points out that some farmers are experiencing a very good year in 1998, while others may have very low net farm income this year. Those with high incomes in 1998 may be primarily interested in opportunities to enhance their cash flow for 1999, while those experiencing financial stress during 1998 may need to consider a wider range of adjustments as they plan for the coming year. The remaining papers provide information farmers may want to consider as they plan their marketing and financial strategies for the coming year. Financial Management Alternatives outlines a wide range of financial management alternatives that can be used to deal with cash flow problems. Some of these alternatives will be of interest to farmers who have difficulty in projecting a positive net cash flow with the relatively low commodity prices being projected for 1999. Others are of primary interest to farmers who have relatively high debt levels and must find ways to improve both their net cash flow and their debt/asset position. Some observers have suggested that the low commodity prices projected for 1999 may lead to reductions in cash rental rates. The paper, Cropland Rental Market Impacts of Low Crop Prices, discusses a procedure to estimate "fair rental rates", and provides an historical perspective of the impact low commodity prices have had on land rental rates. The remaining two papers, Situation and Outlook For the Livestock Sector, and Considerations in Developing a Corn/Soybean Marketing Plan for 1998/1999, discuss the major factors to evaluate and options to consider in developing a marketing plan for corn, soybeans, hogs and cattle for the coming year.Farm Management,

    Chronic Heart Failure and Exercise Intolerance: The Hemodynamic Paradox

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    Heart failure represents a major source of morbidity and mortality in industrialized nations. As the leading hospital discharge diagnosis in the United States in patients over the age of 65, it is also associated with substantial economic costs. While the acute symptoms of volume overload frequently precipitate inpatient admission, it is the symptoms of chronic heart failure, including fatigue, exercise intolerance and exertional dyspnea, that impact quality of life. Over the last two decades, research into the enzymatic, histologic and neurohumoral alterations seen with heart failure have revealed that hemodynamic derangements do not necessarily correlate with symptoms. This “hemodynamic paradox” is explained by alterations in the skeletal musculature that occur in response to hemodynamic derangements. Importantly, gender specific effects appear to modify both disease pathophysiology and response to therapy. The following review will discuss our current understanding of the systemic effects of heart failure before examining how exercise training and cardiac resynchronization therapy may impact disease course

    The Fourier Imaging X-ray Spectrometer (FIXS) for the Argentinian, Scout-launched satelite de Aplicaciones Cienficas-1 (SAC-1)

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    The Fourier Imaging X-ray Spectrometer (FIXS) is one of four instruments on SAC-1, the Argentinian satellite being proposed for launch by NASA on a Scout rocket in 1992/3. The FIXS is designed to provide solar flare images at X-ray energies between 5 and 35 keV. Observations will be made on arcsecond size scales and subsecond time scales of the processes that modify the electron spectrum and the thermal distribution in flaring magnetic structures

    Optically Active Selenium Vacancies in BaGa\u3csub\u3e4\u3c/sub\u3eSe\u3csub\u3e7\u3c/sub\u3e Crystals

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    Barium gallium selenide (BaGa4Se7) is a recently developed nonlinear optical material with a transmission window extending from 470 nm to 17 μm. A primary application of these crystals is the production of tunable mid-infrared laser beams via optical parametric oscillation. Unintentional point defects, such as selenium vacancies, cation vacancies (barium and/or gallium), and trace amounts of transition-metal ions, are present in BaGa4Se7 crystals and may adversely affect device performance. Electron paramagnetic resonance (EPR) and optical absorption are used to identify and characterize these defects. Five distinct EPR spectra, each representing an electron trapped at a selenium vacancy, are observed at low temperature (there are seven crystallographically inequivalent selenium sites in the crystal). One spectrum is stable at room temperature and is present before illumination. The other four are produced at lower temperatures with 532 nm laser light and are thermally unstable at room temperature. Each S = 1/2 singly ionized selenium vacancy has a large, nearly isotropic, hyperfine interaction with 69Ga and 71Ga nuclei at one neighboring Ga site. A significant portion of the unpaired spin resides in a 4s orbital on this adjacent Ga ion and gives principal values of the hyperfine matrices in the 3350–6400 MHz range. Broad photoinduced optical absorption bands in the visible and near-infrared are assigned to the selenium vacancies

    Alterations in Platelet Function and Cell-Derived Microvesicles in Recently Menopausal Women: Relationship to Metabolic Syndrome and Atherogenic Risk

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    A woman’s risk for metabolic syndrome (MS) increases at menopause, with an associated increase in risk for cardiovascular disease. We hypothesized that early menopause-related changes in platelet activity and concentrations of microvesicles derived from activated blood and vascular cells provide a mechanistic link to the early atherothrombotic process. Thus, platelet functions and cellular origin of blood-borne microvesicles in recently menopausal women (n = 118) enrolled in the Kronos Early Estrogen Prevention Study were correlated with components of MS and noninvasive measures of cardiovascular disease [carotid artery intima medial thickness (CIMT), coronary artery calcium (CAC) score, and endothelial reactive hyperemic index (RHI)]. Specific to individual components of the MS pentad, platelet number increased with increasing waist circumference, and platelet secretion of ATP and expression of P-selectin decreased with increasing blood glucose (p = 0.005) and blood pressure (p < 0.05), respectively. Waist circumference and systolic blood pressure were independently associated with monocyte- and endothelium-derived microvesicles (p < 0.05). Platelet-derived and total procoagulant phosphatidylserine-positive microvesicles, and systolic blood pressure correlated with CIMT (p < 0.05), but not with CAC or RHI. In summary, among recently menopausal women, specific platelet functions and concentrations of circulating activated cell membrane-derived procoagulant microvesicles change with individual components of MS. These cellular changes may explain in part how menopause contributes to MS and, eventually, to cardiovascular disease
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