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Sample records for attrition resistant iron-based

  1. ATTRITION RESISTANT IRON-BASED FISCHER-TROPSCH CATALYSTS

    Energy Technology Data Exchange (ETDEWEB)

    K. Jothimurugesan; James G. Goodwin, Jr.; Santosh K. Gangwal

    1999-10-01

    Fischer-Tropsch (FT) synthesis to convert syngas (CO + H{sub 2}) derived from natural gas or coal to liquid fuels and wax is a well-established technology. For low H{sub 2} to CO ratio syngas produced from CO{sub 2} reforming of natural gas or from gasification of coal, the use of Fe catalysts is attractive because of their high water gas shift activity in addition to their high FT activity. Fe catalysts are also attractive due to their low cost and low methane selectivity. Because of the highly exothermic nature of the FT reaction, there has been a recent move away from fixed-bed reactors toward the development of slurry bubble column reactors (SBCRs) that employ 30 to 90 {micro}m catalyst particles suspended in a waxy liquid for efficient heat removal. However, the use of FeFT catalysts in an SBCR has been problematic due to severe catalyst attrition resulting in fines that plug the filter employed to separate the catalyst from the waxy product. Fe catalysts can undergo attrition in SBCRs not only due to vigorous movement and collisions but also due to phase changes that occur during activation and reaction.

  2. Attrition Resistant Iron-Based Catalysts For F-T SBCRs

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    Adeyinka A. Adeyiga

    2006-01-31

    The Fischer-Tropsch (F-T) reaction provides a way of converting coal-derived synthesis gas (CO+ H{sub 2}) to liquid fuels. Since the reaction is highly exothermic, one of the major problems in control of the reaction is heat removal. Recent work has shown that the use of slurry bubble column reactors (SBCRs) can largely solve this problem. The use of iron-(FE) based catalysts is attractive not only due to their low cost and ready availability, but also due to their high water-gas shift activity which makes it possible to use these catalysts with low H{sub 2}/CO ratios. However, a serious problem with the use of Fe catalysts in a SBCR is their tendency to undergo attrition. This can cause fouling/plugging of downstream filters and equipment; makes the separation of catalyst from the oil/wax product very difficult, if not impossible; and results in a steady loss of catalyst from the reactor. Under a previous Department of Energy (DOE)/University Research Grant (UCR) grant, Hampton University reported, for the first time, the development of demonstrably attrition-resistant Fe F-T synthesis catalysts having good activity, selectivity, and attrition resistance. These catalysts were prepared by spray drying Fe catalysts with potassium (K), copper (Cu), and silica (SiO{sub 2}) as promoters. SiO{sub 2} was also used as a binder for spray drying. These catalysts were tested for activity and selectivity in a laboratory-scale fixed-bed reactor. Fundamental understanding of attrition is being addressed by incorporating suitable binders into the catalyst recipe. This has resulted in the preparation of a spray dried HPR-43 catalyst having average particle size (aps) of 70 {micro}m with high attrition resistance. This HPR-43 attrition resistant, active and selective catalyst gave 95% CO conversion through 125 hours of testing in a fixed-bed at 270 C, 1.48 MPa, H{sub 2}/CO=0.67 and 2.0 NL/g-cat/h with C{sub 5+} selectivity of >78% and methane selectivity of less than 5% at an

  3. Novel Attrition-Resistant Fischer Tropsch Catalyst

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    Weast, Logan, E.; Staats, William, R.

    2009-05-01

    There is a strong national interest in the Fischer-Tropsch synthesis process because it offers the possibility of making liquid hydrocarbon fuels from reformed natural gas or coal and biomass gasification products. This project explored a new approach that had been developed to produce active, attrition-resistant Fischer-Tropsch catalysts that are based on glass-ceramic materials and technology. This novel approach represented a promising solution to the problem of reducing or eliminating catalyst attrition and maximizing catalytic activity, thus reducing costs. The technical objective of the Phase I work was to demonstrate that glass-ceramic based catalytic materials for Fischer-Tropsch synthesis have resistance to catalytic deactivation and reduction of particle size superior to traditional supported Fischer-Tropsch catalyst materials. Additionally, these novel glass-ceramic-based materials were expected to exhibit catalytic activity similar to the traditional materials. If successfully developed, the attrition-resistant Fischer-Tropsch catalyst materials would be expected to result in significant technical, economic, and social benefits for both producers and public consumers of Fischer-Tropsch products such as liquid fuels from coal or biomass gasification. This program demonstrated the anticipated high attrition resistance of the glass-ceramic materials. However, the observed catalytic activity of the materials was not sufficient to justify further development at this time. Additional testing documented that a lack of pore volume in the glass-ceramic materials limited the amount of surface area available for catalysis and consequently limited catalytic activity. However, previous work on glass-ceramic catalysts to promote other reactions demonstrated that commercial levels of activity can be achieved, at least for those reactions. Therefore, we recommend that glass-ceramic materials be considered again as potential Fischer-Tropsch catalysts if it can be

  4. Attrition Resistant Fischer-Tropsch Catalysts Based on FCC Supports

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    Adeyiga, Adeyinka

    2010-02-05

    Commercial spent fluid catalytic cracking (FCC) catalysts provided by Engelhard and Albemarle were used as supports for Fe-based catalysts with the goal of improving the attrition resistance of typical F-T catalysts. Catalysts with the Ruhrchemie composition (100 Fe/5 Cu/4.2 K/25 spent FCC on mass basis) were prepared by wet impregnation. XRD and XANES analysis showed the presence of Fe{sub 2}O{sub 3} in calcined catalysts. FeC{sub x} and Fe{sub 3}O{sub 4} were present in the activated catalysts. The metal composition of the catalysts was analyzed by ICP-MS. F-T activity of the catalysts activated in situ in CO at the same conditions as used prior to the attrition tests was measured using a fixed bed reactor at T = 573 K, P = 1.38 MPa and H{sub 2}:CO ratio of 0.67. Cu and K promoted Fe supported over Engelhard provided spent FCC catalyst shows relatively good attrition resistance (8.2 wt% fines lost), high CO conversion (81%) and C{sub 5}+ hydrocarbons selectivity (18.3%).

  5. Corrosion resistance and electrochemical potentiokinetic reactivation testing of some iron-base hardfacing alloys

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    Cockeram, B.V.

    1999-11-01

    Hardfacing alloys are weld deposited on a base material to provide a wear resistant surface. Commercially available iron-base hardfacing alloys are being evaluated for replacement of cobalt-base alloys to reduce nuclear plant activation levels. Corrosion testing was used to evaluate the corrosion resistance of several iron-base hardfacing alloys in highly oxygenated environments. The corrosion test results indicate that iron-base hardfacing alloys in the as-deposited condition have acceptable corrosion resistance when the chromium to carbon ratio is greater than 4. Tristelle 5183, with a high niobium (stabilizer) content, did not follow this trend due to precipitation of niobium-rich carbides instead of chromium-rich carbides. This result indicates that iron-base hardfacing alloys containing high stabilizer contents may possess good corrosion resistance with Cr:C < 4. NOREM 02, NOREM 01, and NoCo-M2 hardfacing alloys had acceptable corrosion resistance in the as-deposited and 885 C/4 hour heat treated condition, but rusting from sensitization was observed in the 621 C/6 hour heat treated condition. The feasibility of using an Electrochemical Potentiokinetic Reactivation (EPR) test method, such as used for stainless steel, to detect sensitization in iron-base hardfacing alloys was evaluated. A single loop-EPR method was found to provide a more consistent measurement of sensitization than a double loop-EPR method. The high carbon content that is needed for a wear resistant hardfacing alloy produces a high volume fraction of chromium-rich carbides that are attacked during EPR testing. This results in inherently lower sensitivity for detection of a sensitized iron-base hardfacing alloy than stainless steel using conventional EPR test methods.

  6. New Wear Resistant Iron-Base Matrix Materials For The Fabrication Of Sintered Diamond Tools

    Directory of Open Access Journals (Sweden)

    Konstanty J.

    2015-06-01

    Full Text Available The possibility of the use of inexpensive iron-base powders in the production of sintered diamond tools is again explored. Ball-milled Fe-Ni-Cu-Sn-C and Fe-Mn-Cu-Sn-C powders were consolidated to a virtually pore-free condition by hot pressing at 900°C. The resultant materials are characterised by a combination of high Knoop hardness, 260-440 and yield strength, 780-1350 MPa, and resistance to abrasion. These properties can be significantly modified by changing the milling time.

  7. Highly attrition resistant sorbents for desulfurization of hot coal gases

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    Slimane, R.B.; Abbasian, J.; Zarnegar, M.K.; Wangerow, J.R.; Carty, R.H.

    1998-07-01

    One of the main obstacles in the commercialization of high-temperature desulfurization systems for Integrated Gasification Combined Cycle (IGCC) power generation processes is the development of regenerable sulfur sorbents with suitable physical and chemical characteristics. The focus of much of the current research on sorbent development has been on the use of zinc-based sorbents. These sorbents have been the subject of extensive pilot-scale and process development work; however, they have been shown to suffer from sulfate formation and zinc volatilization, leading to sorbent degradation over multi-cycle use. Therefore, investigation of non-zinc based sorbents is a logical approach to develop an effective alternative. An effective alternative to zinc-based sorbents could be manganese-based sorbents which have recently been shown to withstand high temperature ({gt} 750 C) operation and also maintain structural and reactive integrity over many cycles. However, because of process equipment limitations and other process variables such as fuel gas alkali content, a number of investigators have recently argued that the benefit to be gained by lower temperature application may outweigh the slight loss of efficiency, resulting in lower overall cost of electricity. Desulfurization temperatures {lt} 538 C have been recommended to provide the best compromise between process equipment limitations and higher temperature operation. This paper reports on an on-going research program to develop novel, highly reactive, attrition-resistant, and regenerable manganese-based sorbents for the removal of hydrogen sulfide (H{sub 2}S) from coal-derived fuel gases at temperatures of 316 to 538 C and pressures up to 300 psig. The primary focus of this study is placed on the preparation (method and composition), characterization, and evaluation of a number of sorbent formulations to identify the most suitable manganese-based sorbent. The manganese-based sorbent formulations prepared to

  8. Iron-Based Amorphous Metals:The High Performance Corrosion Resistant Materials(HPCRM) Program

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    Farmer, J

    2007-07-09

    An overview of the High-Performance Corrosion-Resistant Materials (HPCRM) Program, which was co-sponsored by the Defense Advanced Research Projects Agency (DARPA) Defense Sciences Office (DSO) and the United States Department of Energy (DOE) Office of Civilian and Radioactive Waste Management (OCRWM), is discussed. Programmatic investigations have included a broad range of topics: alloy design and composition; materials synthesis; thermal stability; corrosion resistance; environmental cracking; mechanical properties; damage tolerance; radiation effects; and important potential applications. Amorphous alloys identified as SAM2X5 (Fe{sub 49.7}Cr{sub 17.7}Mn{sub 1.9}Mo{sub 7.4}W{sub 1.6}B{sub 15.2}C{sub 3.8}Si{sub 2.4}) and SAM1651 (Fe{sub 48}Mo{sub 14}Cr{sub 15}Y{sub 2}C{sub 15}B{sub 6}) have been produced as melt-spun ribbons, drop-cast ingots and thermal-spray coatings. Chromium (Cr), molybdenum (Mo) and tungsten (W) additions provided corrosion resistance, while boron (B) enabled glass formation. Earlier electrochemical studies of melt-spun ribbons and ingots of these amorphous alloys demonstrated outstanding passive film stability. More recently thermal-spray coatings of these amorphous alloys have been made and subjected to long-term salt-fog and immersion tests. Good corrosion resistance has been observed during salt-fog testing. Corrosion rates were measured in situ with linear polarization, while simultaneously monitoring the open-circuit corrosion potentials. Reasonably good performance was observed. The sensitivity of these measurements to electrolyte composition and temperature was determined. The high boron content of this particular amorphous metal makes this amorphous alloy an effective neutron absorber, and suitable for criticality control applications. In general, the corrosion resistance of such iron-based amorphous metals is maintained at operating temperatures up to the glass transition temperature. These materials are much harder than conventional

  9. Iron-Based Amorphous-Metals: High-Performance Corrosion-Resistant Material (HPCRM) Development

    Energy Technology Data Exchange (ETDEWEB)

    Farmer, J C; Choi, J S; Saw, C; Haslam, J; Day, D; Hailey, P; Lian, T; Rebak, R; Perepezko, J; Payer, J; Branagan, D; Beardsley, B; D' Amato, A; Aprigliano, L

    2008-01-09

    An overview of the High-Performance Corrosion-Resistant Materials (HPCRM) Program, which was co-sponsored by the Defense Advanced Research Projects Agency (DARPA) Defense Sciences Office (DSO) and the United States Department of Energy (DOE) Office of Civilian and Radioactive Waste Management (OCRWM), is discussed. Programmatic investigations have included a broad range of topics: alloy design and composition; materials synthesis; thermal stability; corrosion resistance; environmental cracking; mechanical properties; damage tolerance; radiation effects; and important potential applications. Amorphous alloys identified as SAM2X5 (Fe{sub 49.7}Cr{sub 17.7}Mn{sub 1.9}Mo{sub 7.4}W{sub 1.6}B{sub 15.2}C{sub 3.8}Si{sub 2.4}) and SAM1651 (Fe{sub 48}Mo{sub 14}Cr{sub 15}Y{sub 2}C{sub 15}B{sub 6}) have been produced as melt-spun ribbons, drop-cast ingots and thermal-spray coatings. Chromium (Cr), molybdenum (Mo) and tungsten (W) additions provided corrosion resistance, while boron (B) enabled glass formation. Earlier electrochemical studies of melt-spun ribbons and ingots of these amorphous alloys demonstrated outstanding passive film stability. More recently thermal-spray coatings of these amorphous alloys have been made and subjected to long-term salt-fog and immersion tests. Good corrosion resistance has been observed during salt-fog testing. Corrosion rates were measured in situ with linear polarization, while simultaneously monitoring the open-circuit corrosion potentials. Reasonably good performance was observed. The sensitivity of these measurements to electrolyte composition and temperature was determined. The high boron content of this particular amorphous metal makes this amorphous alloy an effective neutron absorber, and suitable for criticality control applications. In general, the corrosion resistance of such iron-based amorphous metals is maintained at operating temperatures up to the glass transition temperature. These materials are much harder than conventional

  10. Attrition resistant catalyst for dimethyl ether synthesis in fluidized-bed reactor

    Institute of Scientific and Technical Information of China (English)

    Li-hua TENG

    2008-01-01

    Fluidized-bed reactor is a candidate for dimethyi ether(DME)synthesis from syngas because of its excellent heat removal capability.In Order to improve the attrition resistance of catalyst,an amount of silica sol as binder was added to the catalyst composed of methanol synthesis component CuO/ZnO/Al2O3 and methanol dehydration component HZSM-5,which was prepared by coprecipitation and shaped by spray drying to get spherical particles.The effect of silica sol on the catalytic activity was investigated in a fixed-bed flow microreactor.Based on the experiment results,silica sol in the range of 0~20wt% had small effect on the catalytie activity.Generally,the CO conversion and DME yield decreased with the increase in concen.tration of silica sol,while the attrition resistance of catalysts increased with increasing silica sol,indicating that it was feasible to improve the attrition resistance without greatly sacrificing the activity of catalyst.In addition,the characterizations of catalysts were carried out using Brunauer-Emmett-Teller(BET),X-ray powder diffraction(XRD)and temperature programmed reduction (TPR).

  11. Highly Attrition Resistant Zinc Oxide-Based Sorbents for H2S Removal by Spray Drying Technique

    Energy Technology Data Exchange (ETDEWEB)

    Ryu, C.K.; Lee, J.B.; Ahn, D.H.; Kim, J.J.; Yi, C.K.

    2002-09-19

    Primary issues for the fluidized-bed/transport reactor process are high attrition resistant sorbent, its high sorption capacity and regenerability, durability, and cost. The overall objective of this project is the development of a superior attrition resistant zinc oxide-based sorbent for hot gas cleanup in integrated coal gasification combined cycle (IGCC). Sorbents applicable to a fluidized-bed hot gas desulfurization process must have a high attrition resistance to withstand the fast solid circulation between a desulfurizer and a regenerator, fast kinetic reactions, and high sulfur sorption capacity. The oxidative regeneration of zinc-based sorbent usually initiated at greater than 600 C with highly exothermic nature causing deactivation of sorbent as well as complication of sulfidation process by side reaction. Focusing on solving the sorbent attrition and regenerability of zinc oxide-based sorbent, we have adapted multi-binder matrices and direct incorporation of regeneration promoter. The sorbent forming was done with a spray drying technique that is easily scalable to commercial quantity.

  12. Iron-Based Amorphous-Metals: High-Performance Corrosion-Resistant Materials (HPCRM) Development Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Farmer, J C; Choi, J; Saw, C; Haslem, J; Day, D; Hailey, P; Lian, T; Rebak, R; Perepezko, J; Payer, J; Branagan, D; Beardsley, B; D' Amato, A; Aprigliano, L

    2009-03-16

    An overview of the High-Performance Corrosion-Resistant Materials (HPCRM) Program, which was co-sponsored by the Defense Advanced Research Projects Agency (DARPA) Defense Sciences Office (DSO) and the United States Department of Energy (DOE) Office of Civilian and Radioactive Waste Management (OCRWM), is discussed. Programmatic investigations have included a broad range of topics: alloy design and composition; materials synthesis; thermal stability; corrosion resistance; environmental cracking; mechanical properties; damage tolerance; radiation effects; and important potential applications. Amorphous alloys identified as SAM2X5 (Fe{sub 49.7}Cr{sub 17.7}Mn{sub 1.9}Mo{sub 7.4}W{sub 1.6}B{sub 15.2}C{sub 3.8}Si{sub 2.4}) and SAM1651 (Fe{sub 48}Mo{sub 14}Cr{sub 15}Y{sub 2}C{sub 15}B{sub 6}) have been produced as melt-spun ribbons, drop-cast ingots and thermal-spray coatings. Chromium (Cr), molybdenum (Mo) and tungsten (W) additions provided corrosion resistance, while boron (B) enabled glass formation. Earlier electrochemical studies of melt-spun ribbons and ingots of these amorphous alloys demonstrated outstanding passive film stability. More recently thermal-spray coatings of these amorphous alloys have been made and subjected to long-term salt-fog and immersion tests. Good corrosion resistance has been observed during salt-fog testing. Corrosion rates were measured in situ with linear polarization, while simultaneously monitoring the open-circuit corrosion potentials. Reasonably good performance was observed. The sensitivity of these measurements to electrolyte composition and temperature was determined. The high boron content of this particular amorphous metal make this amorphous alloy an effective neutron absorber, and suitable for criticality control applications. In general, the corrosion resistance of these iron-based amorphous metals is maintained at operating temperatures up to the glass transition temperature. These materials are much harder than conventional

  13. FY05 HPCRM Annual Report: High-Performance Corrosion-Resistant Iron-Based Amorphous Metal Coatings

    Energy Technology Data Exchange (ETDEWEB)

    Farmer, J; Choi, J; Haslam, J; Day, S; Yang, N; Headley, T; Lucadamo, G; Yio, J; Chames, J; Gardea, A; Clift, M; Blue, G; Peters, W; Rivard, J; Harper, D; Swank, D; Bayles, R; Lemieux, E; Brown, R; Wolejsza, T; Aprigliano, L; Branagan, D; Marshall, M; Meacham, B; Aprigliano, L; Branagan, D; Marshall, M; Meacham, B; Lavernia, E; Schoenung, J; Ajdelsztajn, L; Dannenberg, J; Graeve, O; Lewandowski, J; Perepezko, J; Hildal, K; Kaufman, L; Boudreau, J

    2007-09-20

    New corrosion-resistant, iron-based amorphous metals have been identified from published data or developed through combinatorial synthesis, and tested to determine their relative corrosion resistance. Many of these materials can be applied as coatings with advanced thermal spray technology. Two compositions have corrosion resistance superior to wrought nickel-based Alloy C-22 (UNS No. N06022) in some very aggressive environments, including concentrated calcium-chloride brines at elevated temperature. Two Fe-based amorphous metal formulations have been found that appear to have corrosion resistance comparable to, or better than that of Ni-based Alloy C-22, based on breakdown potential and corrosion rate. Both Cr and Mo provide corrosion resistance, B enables glass formation, and Y lowers critical cooling rate (CCR). SAM1651 has yttrium added, and has a nominal critical cooling rate of only 80 Kelvin per second, while SAM2X7 (similar to SAM2X5) has no yttrium, and a relatively high critical cooling rate of 610 Kelvin per second. Both amorphous metal formulations have strengths and weaknesses. SAM1651 (yttrium added) has a low critical cooling rate (CCR), which enables it to be rendered as a completely amorphous thermal spray coating. Unfortunately, it is relatively difficult to atomize, with powders being irregular in shape. This causes the powder to be difficult to pneumatically convey during thermal spray deposition. Gas atomized SAM1651 powder has required cryogenic milling to eliminate irregularities that make flow difficult. SAM2X5 (no yttrium) has a high critical cooling rate, which has caused problems associated with devitrification. SAM2X5 can be gas atomized to produce spherical powders of SAM2X5, which enable more facile thermal spray deposition. The reference material, nickel-based Alloy C-22, is an outstanding corrosion-resistant engineering material. Even so, crevice corrosion has been observed with C-22 in hot sodium chloride environments without buffer

  14. A Comparison of the Corrosion Resistance of Iron-Based Amorphous Metals and Austenitic Alloys in Synthetic Brines at Elevated Temperature

    Energy Technology Data Exchange (ETDEWEB)

    Farmer, J C

    2008-11-25

    Several hard, corrosion-resistant and neutron-absorbing iron-based amorphous alloys have now been developed that can be applied as thermal spray coatings. These new alloys include relatively high concentrations of Cr, Mo, and W for enhanced corrosion resistance, and substantial B to enable both glass formation and neutron absorption. The corrosion resistances of these novel alloys have been compared to that of several austenitic alloys in a broad range of synthetic brines, with and without nitrate inhibitor, at elevated temperature. Linear polarization and electrochemical impedance spectroscopy have been used for in situ measurement of corrosion rates for prolonged periods of time, while scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDAX) have been used for ex situ characterization of samples at the end of tests. The application of these new coatings for the protection of spent nuclear fuel storage systems, equipment in nuclear service, steel-reinforced concrete will be discussed.

  15. Iron-based amorphous alloys and methods of synthesizing iron-based amorphous alloys

    Science.gov (United States)

    Saw, Cheng Kiong; Bauer, William A.; Choi, Jor-Shan; Day, Dan; Farmer, Joseph C.

    2016-05-03

    A method according to one embodiment includes combining an amorphous iron-based alloy and at least one metal selected from a group consisting of molybdenum, chromium, tungsten, boron, gadolinium, nickel phosphorous, yttrium, and alloys thereof to form a mixture, wherein the at least one metal is present in the mixture from about 5 atomic percent (at %) to about 55 at %; and ball milling the mixture at least until an amorphous alloy of the iron-based alloy and the at least one metal is formed. Several amorphous iron-based metal alloys are also presented, including corrosion-resistant amorphous iron-based metal alloys and radiation-shielding amorphous iron-based metal alloys.

  16. Telomere attrition due to infection.

    Directory of Open Access Journals (Sweden)

    Petteri Ilmonen

    Full Text Available BACKGROUND: Telomeres--the terminal caps of chromosomes--become shorter as individuals age, and there is much interest in determining what causes telomere attrition since this process may play a role in biological aging. The leading hypothesis is that telomere attrition is due to inflammation, exposure to infectious agents, and other types of oxidative stress, which damage telomeres and impair their repair mechanisms. Several lines of evidence support this hypothesis, including observational findings that people exposed to infectious diseases have shorter telomeres. Experimental tests are still needed, however, to distinguish whether infectious diseases actually cause telomere attrition or whether telomere attrition increases susceptibility to infection. Experiments are also needed to determine whether telomere erosion reduces longevity. METHODOLOGY/PRINCIPAL FINDINGS: We experimentally tested whether repeated exposure to an infectious agent, Salmonella enterica, causes telomere attrition in wild-derived house mice (Mus musculus musculus. We repeatedly infected mice with a genetically diverse cocktail of five different S. enterica strains over seven months, and compared changes in telomere length with sham-infected sibling controls. We measured changes in telomere length of white blood cells (WBC after five infections using a real-time PCR method. Our results show that repeated Salmonella infections cause telomere attrition in WBCs, and particularly for males, which appeared less disease resistant than females. Interestingly, we also found that individuals having long WBC telomeres at early age were relatively disease resistant during later life. Finally, we found evidence that more rapid telomere attrition increases mortality risk, although this trend was not significant. CONCLUSIONS/SIGNIFICANCE: Our results indicate that infectious diseases can cause telomere attrition, and support the idea that telomere length could provide a molecular

  17. Theoretical Analyses and Experimental Investigations of Selective Carbothermal Reactions of Vanadium-Bearing Titanomagnetite Concentrates for Preparation of Iron-Based Wear-Resistant Material

    Science.gov (United States)

    Zhang, Guangming; Feng, Keqin; Yue, Huifang

    2016-09-01

    Based on FACTSage® software, this paper focuses on the thermodynamic calculations of selective carbothermal reactions of vanadium-bearing titanomagnetite concentrates for preparing iron-based wear-resistant material directly from vanadium-bearing titanomagnetite concentrates. The calculations show that it was most likely to generate metallic iron, titanium carbide and vanadium carbide among all possible carbothermal reactions of vanadium-bearing titanomagnetite concentrates in a vacuum of 10 Pa. The equilibrium composition calculations indicate that Fe3O4 can be reduced to metallic iron by carbon above 400°C, FeTiO3 can be converted into TiC by carbon above 800°C and V2O5 can be converted into VC by carbon above 600°C in a vacuum of 10 Pa. The investigations demonstrated that the percentage of ferrous oxides reduced to metallic iron was about 96%, the conversion percentage of FeTiO3 into TiC was about 75% and the conversion percentage of V2O5 into VC was about 94% after the selective carbothermal reactions of vanadium-bearing titanomagnetite concentrates at 1300°C for 3 h in a vacuum of 10 Pa.

  18. Co-Production of Electricity and Hydrogen Using a Novel Iron-based Catalyst

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    Hilaly, Ahmad; Georgas, Adam; Leboreiro, Jose; Arora, Salil; Head, Megann; Trembly, Jason; Turk, Brian; Gupta, Raghubir

    2011-09-30

    The primary objective of this project was to develop a hydrogen production technology for gasification applications based on a circulating fluid-bed reactor and an attrition resistant iron catalyst. The work towards achieving this objective consisted of three key activities: • Development of an iron-based catalyst suitable for a circulating fluid-bed reactor • Design, construction, and operation of a bench-scale circulating fluid-bed reactor system for hydrogen production • Techno-economic analysis of the steam-iron and the pressure swing adsorption hydrogen production processes. This report describes the work completed in each of these activities during this project. The catalyst development and testing program prepared and iron-based catalysts using different support and promoters to identify catalysts that had sufficient activity for cyclic reduction with syngas and steam oxidation and attrition resistance to enable use in a circulating fluid-bed reactor system. The best performing catalyst from this catalyst development program was produced by a commercial catalyst toll manufacturer to support the bench-scale testing activities. The reactor testing systems used during material development evaluated catalysts in a single fluid-bed reactor by cycling between reduction with syngas and oxidation with steam. The prototype SIP reactor system (PSRS) consisted of two circulating fluid-bed reactors with the iron catalyst being transferred between the two reactors. This design enabled demonstration of the technical feasibility of the combination of the circulating fluid-bed reactor system and the iron-based catalyst for commercial hydrogen production. The specific activities associated with this bench-scale circulating fluid-bed reactor systems that were completed in this project included design, construction, commissioning, and operation. The experimental portion of this project focused on technical demonstration of the performance of an iron-based catalyst and a

  19. First language attrition

    NARCIS (Netherlands)

    Schmid, Monika S.

    2013-01-01

    Speakers who live in an L2 environment for an extended period of time often experience change in the way in which they use their L1, a process referred to as L1 attrition. This article provides an overview of language attrition phenomena at various linguistic levels. However, attrition cannot be tri

  20. Telomere attrition and diabetes mellitus.

    Science.gov (United States)

    Tamura, Yoshiaki; Takubo, Kaiyo; Aida, Junko; Araki, Atsushi; Ito, Hideki

    2016-03-01

    Type 2 diabetes mellitus (DM) is a disease characterized by dysfunction of various organs. Recent studies have shown a close relationship between DM and telomere attrition in leukocytes. In patients with DM or impaired glucose tolerance, excessive oxidative stress induces damage to telomeres and shortens their length. Furthermore, it is suggested that telomere length is a good surrogate marker for mortality and diabetic complications in DM patients. We recently found that telomere length in pancreatic β-cells is also shortened in DM patients, potentially leading to an impaired capacity for proliferation and insulin secretion, and accelerated cell death. In contrast, leukocyte telomere length has also been reported in patients with obesity or insulin resistance, both of which are frequently associated with type 2 DM. In an animal model, it has been shown that telomere attrition in adipose tissue induces insulin resistance. Taken together, the available data suggest that hyperglycemia, oxidative stress, and telomere attrition in pancreatic β-cells and adipocytes create a vicious cycle that underlies the pathophysiology of type 2 DM. Inhibition of telomere attrition in various organs, including pancreatic β-cells, could be a new approach for preventing the progression of DM and its complications.

  1. High-Performance Corrosion-Resistant Materials: Iron-Based Amorphous-Metal Thermal-Spray Coatings: SAM HPCRM Program ? FY04 Annual Report ? Rev. 0 - DARPA DSO & DOE OCRWM Co-Sponsored Advanced Materials Program

    Energy Technology Data Exchange (ETDEWEB)

    Farmer, J; Haslam, J; Wong, F; Ji, S; Day, S; Branagan, D; Marshall, M; Meacham, B; Buffa, E; Blue, C; Rivard, J; Beardsley, M; Buffa, E; Blue, C; Rivard, J; Beardsley, M; Weaver, D; Aprigliano, L; Kohler, L; Bayles, R; Lemieux, E; Wolejsza, T; Martin, F; Yang, N; Lucadamo, G; Perepezko, J; Hildal, K; Kaufman, L; Heuer, A; Ernst, F; Michal, G; Kahn, H; Lavernia, E

    2007-09-19

    The multi-institutional High Performance Corrosion Resistant Materials (HPCRM) Team is cosponsored by the Defense Advanced Projects Agency (DARPA) Defense Science Office (DSO) and the Department of Energy (DOE) Office of Civilian Radioactive Waste Management (OCRWM), and has developed new corrosion-resistant, iron-based amorphous metals that can be applied as coatings with advanced thermal spray technology. Two compositions have corrosion resistance superior to wrought nickel-based Alloy C-22 (UNS No. N06022) in very aggressive environments, including concentrated calcium-chloride brines at elevated temperature. Corrosion costs the Department of Defense billions of dollars every year, with an immense quantity of material in various structures undergoing corrosion. For example, in addition to fluid and seawater piping, ballast tanks, and propulsions systems, approximately 345 million square feet of structure aboard naval ships and crafts require costly corrosion control measures. The use of advanced corrosion-resistant materials to prevent the continuous degradation of this massive surface area would be extremely beneficial. The Fe-based corrosion-resistant, amorphous-metal coatings under development may prove of importance for applications on ships. Such coatings could be used as an 'integral drip shield' on spent fuel containers, as well as protective coatings that could be applied over welds, thereby preventing exposure to environments that might cause stress corrosion cracking. In the future, such new high-performance iron-based materials could be substituted for more-expensive nickel-based alloys, thereby enabling a reduction in the $58-billion life cycle cost for the long-term storage of the Nation's spent nuclear fuel by tens of percent.

  2. Language Attrition Research: An Introduction.

    Science.gov (United States)

    Weltens, Bert; Cohen, Andrew D.

    1989-01-01

    Reviews key issues generally addressed in studies of language attrition, including the effects of instructional methods on long-term retention, the effects of proficiency level on attrition, attrition's different effects on various language skills, typical forgetting curves, and typical attrition orders. 26 references.(CB)

  3. Attrition Cost Model Instruction Manual

    Science.gov (United States)

    Yanagiura, Takeshi

    2012-01-01

    This instruction manual explains in detail how to use the Attrition Cost Model program, which estimates the cost of student attrition for a state's higher education system. Programmed with SAS, this model allows users to instantly calculate the cost of attrition and the cumulative attrition rate that is based on the most recent retention and…

  4. Second language acquisition and attrition

    OpenAIRE

    Schmid, Monika; Köpke, Barbara

    2011-01-01

    International audience; This issue consists of a collection of papers that focus on structural/grammatical aspects of the process of first language attrition. It presents an overview of current research, methodological issues and important questions regarding first language attrition. In particular, it addresses the two most prominent issues in current L1 attrition research: Can attrition effects impact on features of core syntax, or are they limited to interface phenomena?, and: What is the ...

  5. First Language Attrition

    Science.gov (United States)

    Schmid, Monika S.

    2016-01-01

    Language attrition research has developed in several clearly delimited phases spanning, roughly, each of the three decades between 1982 and 2012 (see Kopke & Schmid 2004 for a more detailed overview and analysis). The first phase was an era of stocktaking, with a number of symposia, collected volumes and special issues of journals. All of…

  6. Iron-based Arc Spraying Cored Wire with Chlorine Corrosion and Oxidation Resistance%抗氧化耐氯腐蚀电弧喷涂铁基粉芯线材

    Institute of Scientific and Technical Information of China (English)

    魏琪; 刘旭; 李辉; 印志勇

    2012-01-01

    采用304L不锈钢带包覆铬、镰、钼、铝、稀土等金属粉末制备粉芯丝材,使用电弧喷涂方法制备涂层,研究了合金元素成分对涂层抗高温氧化性能和抗氯腐蚀性能的影响,并与传统的Ni - Cr- Ti涂层(PS45)的性能进行了对比.结果表明,Cr元素的抗氧化性能要好于Ni元素,在氯腐蚀环境下,Ni元素的耐腐蚀性能比Cr元素更为优异,添加适当数量的Al元素、Mo元素对耐氯腐蚀性能有一定的促进作用.所研制的LJ-1铁基涂层在650℃温度下具有良好的抗高温氧化性能和耐氯腐蚀的性能,其抗氧化性能和耐氯腐蚀性能分别是Ni-Cr-Ti涂层(PS45)的0.74倍和0.67倍,但涂层成本大幅度降低,性价比提高.%A flux cored wire is developed by 304L stainless steel-strip wrapping metal powder composed of Ni, Cr, Al, Mo and rare earth elements, and the self-developed wire was sprayed by arc spraying to prepare the iron-based coating. The effects of the alloying elements on the high temperature chlorine corrosion and high temperature oxidation resistance was studied < and the performance was compared with the traditional Ni -Cr-Ti coating (PS45). It is shown that the oxidation resistance of Cr is better than Ni. In chlorine corrosion environments, Ni has better corrosion resistance than Cr. The corrosion resistance is improved by adding appropriate amount of Al and Mo element. The LJ -1 coating has excellent high temperature chlorine corrosion that is 0. 74 times the PS45 coating and high temperature oxidation resistance that is 0. 67 times the PS45 coating under 650 ℃. However, the cost of the coating is reduced significantly, and the value is good.

  7. Phase stability and large in-plane resistivity anisotropy in the 112-type iron-based superconductor Ca1 -xLaxFeAs2

    Science.gov (United States)

    Kang, Chang-Jong; Birol, Turan; Kotliar, Gabriel

    2017-01-01

    The recently discovered high-Tc superconductor Ca1 -xLaxFeAs2 is a unique compound not only because of its low-symmetry crystal structure but also because of its electronic structure, which hosts Dirac-like metallic bands resulting from (spacer) zigzag As chains. We present a comprehensive first-principles theoretical study of the electronic and crystal structures of Ca1 -xLaxFeAs2 . After discussing the connection between the crystal structure of the 112 family, which Ca1 -xLaxFeAs2 is a member of, with the other known structures of Fe pnictide superconductors, we check the thermodynamic phase stability of CaFeAs2, and similar hyphothetical compounds SrFeAs2 and BaFeAs2 which, we find, are slightly higher in energy. We calculate the optical conductivity of Ca1 -xLaxFeAs2 using the DFT+DMFT method and predict a large in-plane resistivity anisotropy in the normal phase, which does not originate from electronic nematicity, but is enhanced by the electronic correlations. In particular, we predict a 0.34 eV peak in the y y component of the optical conductivity of the 30% La-doped compound, which corresponds to coherent interband transitions within a fast-dispersing band arising from the zigzag As chains, which are unique to this compound. We also study the Landau free energy for Ca1 -xLaxFeAs2 including the order parameter relevant for the nematic transition and find that the free energy does not have any extra terms that could induce ferro-orbital order. This explains why the presence of As chains does not broaden the nematic transition in Ca1 -xLaxFeAs2 .

  8. Current status of iron-based superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Kamihara, Yoichi, E-mail: kamihara_yoichi@appi.keio.ac.jp [Keio University, Department of Applied Physics and Physico-Informatics, Faculty of Science and Technology (Japan)

    2012-03-15

    Current status of iron-based superconductors is summarized. Although short range magnetic ordering and magnetic phase separation of Fe are controversial, (long range) magnetic and electronic phase diagrams of iron based superconductors can be classified into two-type. Antiferromagnetic ordering of itinerant Fe does not coexist with superconducting phase of SmFeAsO{sub 1 - x}F{sub x}. The very large H{sub c2} of iron-based superconductors attract us to attempts at applications.

  9. Current status of iron-based superconductors

    Science.gov (United States)

    Kamihara, Yoichi

    2012-03-01

    Current status of iron-based superconductors is summarized. Although short range magnetic ordering and magnetic phase separation of Fe are controversial, (long range) magnetic and electronic phase diagrams of iron based superconductors can be classified into two-type. Antiferromagnetic ordering of itinerant Fe does not coexist with superconducting phase of SmFeAsO1 - xFx. The very large H c2 of iron-based superconductors attract us to attempts at applications.

  10. Language Attrition: The Fate of the Start.

    Science.gov (United States)

    Hansen, Lynne

    2001-01-01

    Reviews the literature on psycholinguistic aspects of language attrition over the past half decade. Discusses evidence from studies on hesitation phenomena in attriter speech, variables affecting language attrition, and relearning. (Author/VWL)

  11. FY05 HPCRM Annual Report: High-Performance Corrosion-Resistant Iron-Based Amorphous Metal Coatings Evaluation of Corrosion Reistance FY05 HPCRM Annual Report # Rev. 1DOE-DARPA Co-Sponsored Advanced Materials Program

    Energy Technology Data Exchange (ETDEWEB)

    Farmer, J C; Haslam, J J; Day, S D

    2007-09-19

    New corrosion-resistant, iron-based amorphous metals have been identified from published data or developed through combinatorial synthesis, and tested to determine their relative corrosion resistance. Many of these materials can be applied as coatings with advanced thermal spray technology. Two compositions have corrosion resistance superior to wrought nickel-based Alloy C-22 (UNS No. N06022) in some very aggressive environments, including concentrated calcium-chloride brines at elevated temperature. Two Fe-based amorphous metal formulations have been found that appear to have corrosion resistance comparable to, or better than that of Ni-based Alloy C-22, based on breakdown potential and corrosion rate. Both Cr and Mo provide corrosion resistance, B enables glass formation, and Y lowers critical cooling rate (CCR). SAM1651 has yttrium added, and has a nominal critical cooling rate of only 80 Kelvin per second, while SAM2X7 (similar to SAM2X5) has no yttrium, and a relatively high critical cooling rate of 610 Kelvin per second. Both amorphous metal formulations have strengths and weaknesses. SAM1651 (yttrium added) has a low critical cooling rate (CCR), which enables it to be rendered as a completely amorphous thermal spray coating. Unfortunately, it is relatively difficult to atomize, with powders being irregular in shape. This causes the powder to be difficult to pneumatically convey during thermal spray deposition. Gas atomized SAM1651 powder has required cryogenic milling to eliminate irregularities that make flow difficult. SAM2X5 (no yttrium) has a high critical cooling rate, which has caused problems associated with devitrification. SAM2X5 can be gas atomized to produce spherical powders of SAM2X5, which enable more facile thermal spray deposition. The reference material, nickel-based Alloy C-22, is an outstanding corrosion-resistant engineering material. Even so, crevice corrosion has been observed with C-22 in hot sodium chloride environments without buffer

  12. Teachers' Language: L1 Attrition in Russian-English Bilinguals

    Science.gov (United States)

    Isurin, Ludmila

    2007-01-01

    The present study reports on the evidence of first language (L1) attrition in a population that may appear to be the most resistant to L1 changes. Russian monolinguals (n=3) and Russian-English bilinguals (n=10) participated in the study. The bilinguals were graduate students teaching Russian as a foreign language at a U.S. university. The data…

  13. The influence of Chinese context on attrition of English tense

    Directory of Open Access Journals (Sweden)

    Deng Huan

    2016-01-01

    Full Text Available From psycholinguistic aspect, language learning not only requires acquisition and progression, but it also exists in attrition and regression. Within Chinese as a native language, the learning and living environment would directly affect the language input and contact for English as a foreign language (EFL learner. English tense is totally different from that of Chinese in terms of concept. Based on Inverse Hypothesis, the present thesis aims to take English tense as a breakthrough point in this diachronic research, as well as to reveal and analyze the variability of mastering tenses for EFL learners. Meanwhile, it also strives to validate the feasibility of slowing down the speed of language attrition by increasing the English input and contact. In Chinese context, how to resist attrition effectively and retain their acquired language abilities will yield a lot of benefits to language teaching and learning both for teachers and EFL learners.

  14. Cast iron-base alloy for cylinder/regenerator housing

    Science.gov (United States)

    Witter, Stewart L.; Simmons, Harold E.; Woulds, Michael J.

    1985-01-01

    NASACC-1 is a castable iron-base alloy designed to replace the costly and strategic cobalt-base X-40 alloy used in the automotive Stirling engine cylinder/generator housing. Over 40 alloy compositions were evaluated using investment cast test bars for stress-rupture testing. Also, hydrogen compatibility and oxygen corrosion resistance tests were used to determine the optimal alloy. NASACC-1 alloy was characterized using elevated and room temperature tensile, creep-rupture, low cycle fatigue, heat capacity, specific heat, and thermal expansion testing. Furthermore, phase analysis was performed on samples with several heat treated conditions. The properties are very encouraging. NASACC-1 alloy shows stress-rupture and low cycle fatigue properties equivalent to X-40. The oxidation resistance surpassed the program goal while maintaining acceptable resistance to hydrogen exposure. The welding, brazing, and casting characteristics are excellent. Finally, the cost of NASACC-1 is significantly lower than that of X-40.

  15. Iron-Based Superconductors as topological matter

    Science.gov (United States)

    Hu, Jiangping

    We show the existence of non-trivial topological properties in Iron-based superconductors. Several examples are provided, including (1) the single layer FeSe grown on SrTiO3 substrate, in which an topological insulator phase exists due to the band inversion at M point; (2) CaFeAs2, a staggered intercalation compound that integrates both quantum spin hall and superconductivity in which the nontrivial topology stems from the chain-like As layers away from FeAs layers; (3) the Fe(Te,Se) thin films in which the nontrivial Z2 topological invariance originates from the parity exchange at Γ point that is controlled by the Te(Se) height; (4 nontrivial topology that is driven by the nematic order in FeSe. These results lay ground for integrating high Tc superconductivity with topological properties to realize new emergent phenomena, such as majorana particles, in iron-based high temperature superconductors

  16. Topological properties in Iron-Based Superconductors

    Science.gov (United States)

    Hu, Jiangping; Hao, Ningning; Wu, X. X.

    2015-03-01

    We show the existence of non-trivial topological properties in Iron-based superconductors. Several examples are provided, including (1) the single layer FeSe grown on SrTiO3 substrate, in which an topological insulator phase exists due to the band inversion at M point; (2) CaFeAs2, a staggered intercalation compound that integrates both quantum spin hall and superconductivity in which the nontrivial topology stems from the chain-like As layers away from FeAs layers; (3) the Fe(Te,Se) thin films in which the nontrivial Z2 topological invariance originates from the parity exchange at ? point that is controlled by the Te(Se) height. These results lay ground for integrating high Tc superconductivity with topological properties to realize new emergent phenomena, such as majorana particles, in iron-based high temperature superconductors. The work is supported by NSFC and the Ministry of Science and Technology of China.

  17. Studies of anisotropy of iron based superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Murphy, Jason [Iowa State Univ., Ames, IA (United States)

    2013-01-01

    To study the electronic anisotropy in iron based superconductors, the temperature dependent London penetration depth, Δλ (T), have been measured in several compounds, along with the angular dependent upper critical field, Hc2(T). Study was undertaken on single crystals of Ba(Fe1-xCox)2As2 with x=0.108 and x=0.127, in the overdoped range of the doping phase diagram, characterized by notable modulation of the superconducting gap. Heavy ion irradiation with matching field doses of 6 T and 6.5 T respectively, were used to create columnar defects and to study their effect on the temperature Δλ (T). The variation of the low-temperature penetration depth in both pristine and irradiated samples was fitted with a power-law function Δλ (T) = ATn. Irradiation increases the magnitude of the pre-factor A and decreases the exponent n, similar to the effect on the optimally doped samples. This finding supports the universal s± scenario for the whole doping range. Knowing that the s± gap symmetry exists across the superconducting dome for the electron doped systems, we next looked at λ (T), in optimally - doped, SrFe2(As1-xPx)2, x =0.35. Both, as-grown (Tc ~ 25 K) and annealed (Tc ~ 35 K) single crystals of SrFe2(As1-xPx)2 were measured. Annealing decreases the absolute value of the London penetration depth from λ(0) = 300 ± 10 nm in as-grown samples to λ (0) = 275±10 nm. At low temperatures, λ (T) ~ T indicates a superconducting gap with line nodes. Analysis of the full-temperature range superfluid density is consistent with the line nodes, but differs from the simple single-gap d-wave. The observed behavior is very similar to that of BaFe2(As1-xPx)2, showing that isovalently substituted pnictides are inherently different from

  18. Microstructure and performance of reactive plasma clad high chromium iron based ceramic reinforcing wear-resistance coating%反应等离子熔覆高铬铁基金属陶瓷增强耐磨涂层组织与性能

    Institute of Scientific and Technical Information of China (English)

    王立梅

    2011-01-01

    利用反应等离子熔覆技术、以Fe-Cr-C-W-Ni合金粉末为原料,在Q235钢表面制得了Cr7C3高铬铁基金属陶瓷增强耐磨复合涂层.利用SEM、EDS和X射线衍射分析了涂层的显微组织,在室温干滑动磨损试验条件下测试了涂层的耐磨性.结果表明:反应等离子熔覆CE7C3高铬铁基金属陶瓷增强耐磨复合涂层硬度高、组织均匀、与基材之间为完全冶金结合;涂层在室温干滑动磨损试验条件下表现出优异的耐磨性,涂层磨损的质量损失随载荷增加十分缓慢,涂层具有优异的载荷特性.%A wear resistant high chromium iron based ceramic reinforcing wear-resistance coating was fabricated on substrate of a Q235 steel by plasma cladding using the Fe-Cr-C-W-Ni alloy powders. Microstructure of the coating was characterized by OM, SEM, EDS and XRD. Wear resistance of the coating was tested under dry sliding wear condition at room temperature. Results indicate that the plasma clad high chromium iron based ceramic reinforced wear-resistance composite coating has a rapidly solidified homogeneous microstructure consisting of Cr7C3 ceramal primary particles uniformly distributed in the Cr7C3/γ-Fe eutectic matrix and is metallurgically bonded to the Q235 steel substrate. The plasma clad composite coating has high hardness and excellent wear resistance under dry sliding wear test conditions. Wear mass loss of the coating is increased slowly with the load increased and it has excellent load characteristic.

  19. Photoemission study of iron-based superconductor

    Institute of Scientific and Technical Information of China (English)

    Liu Zhong-Hao; Cai Yi-Peng; Zhao Yan-Ge; Jia Lei-Lei; Wang Shan-Cai

    2013-01-01

    The iron-based superconductivity (IBSC) is a great challenge in correlated system.Angle-resolved photoemission spectroscopy (ARPES) provides electronic structure of the IBSCs,the pairing strength,and the order parameter symmetry.Here,we briefly review the recent progress in IBSCs and focus on the results from ARPES.The ARPES study shows the electronic structure of “122”,“111”,“11”,and “122*” families of IBSCs.It has been agreed that the IBSCs are unconventional superconductors in strong coupling region.The order parameter symmetry basically follows s± form with considerable out-of-plane contribution.

  20. High temperature oxidation behavior of ODS iron-base alloys for nuclear energy application

    Energy Technology Data Exchange (ETDEWEB)

    Li, M.; Zhou, Z.; Liao, L.; Chen, W.; Ge, C. [Univ. of Science and Technology Beijing, School of Materials Science and Engineering, Beijing (China)

    2010-07-01

    Oxide dispersion strengthened (ODS) iron based alloys are considered as promising high temperature structural material for advanced nuclear energy systems due to its higher creep strength and radiation damage resistance than conventional commercial steels. In this study, the oxidation behavior of ODS iron based alloys with different Cr content (12-18%) was investigated by exposing samples at high temperature of 700℃ and 1000℃ in atmosphere environment, the exposure time is up to 500 h. Results showed that 14Cr and 18Cr ODS alloys exhibited better oxidation resistance than 12Cr ODS alloys. For the same chromium content, the oxidation resistance of ODS alloys are better than that of non-ODS alloys. (author)

  1. Quantification of corrosion resistance of a new-class of criticality control materials: thermal-spray coatings of high-boron iron-based amorphous metals - Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4

    Energy Technology Data Exchange (ETDEWEB)

    Farmer, J C; Choi, J S; Shaw, C K; Rebak, R; Day, S D; Lian, T; Hailey, P; Payer, J H; Branagan, D J; Aprigliano, L F

    2007-03-28

    An iron-based amorphous metal, Fe{sub 49.7}Cr{sub 17.7}Mn{sub 1.9}Mo{sub 7.4}W{sub 1.6}B{sub 15.2}C{sub 3.8}Si{sub 2.4} (SAM2X5), with very good corrosion resistance was developed. This material was produced as a melt-spun ribbon, as well as gas atomized powder and a thermal-spray coating. Chromium (Cr), molybdenum (Mo) and tungsten (W) provided corrosion resistance, and boron (B) enabled glass formation. The high boron content of this particular amorphous metal made it an effective neutron absorber, and suitable for criticality control applications. Earlier studies have shown that ingots and melt-spun ribbons of these materials have good passive film stability in these environments. Thermal spray coatings of these materials have now been produced, and have undergone a variety of corrosion testing, including both atmospheric and long-term immersion testing. The modes and rates of corrosion have been determined in the various environments, and are reported here.

  2. Disfluency Markers in L1 Attrition

    Science.gov (United States)

    Schmid, Monika S.; Fagersten, Kristy Beers

    2010-01-01

    Based on an analysis of the speech of long-term emigres of German and Dutch origin, the present investigation discusses to what extent hesitation patterns in language attrition may be the result of the creation of an interlanguage system, on the one hand, or of language-internal attrition patterns on the other. We compare speech samples elicited…

  3. Maturational Constraints and First Language Attrition

    Science.gov (United States)

    Bylund, Emanuel

    2009-01-01

    The aim of the article is to examine how first language attrition research on maturational constraints interprets and links its findings to current views on maturation in the field of second language acquisition. It is argued that attrition research exhibits certain inconsistencies in the interpretation of the structural characteristics of the…

  4. Disfluency Markers in L1 Attrition

    NARCIS (Netherlands)

    Schmid, Monika S.; Faegersten, Kristy Beers; Fägersten, K.B.

    2010-01-01

    Based on an analysis of the speech of long-term emigres of German and Dutch origin, the present investigation discusses to what extent hesitation patterns in language attrition may be the result of the creation of an interlanguage system, on the one hand, or of language-internal attrition patterns o

  5. Minimizing Attrition in Online Degree Courses

    Science.gov (United States)

    Boton, Eliani Colferai; Gregory, Sue

    2015-01-01

    The number of online programs in the higher education sector has increased dramatically in the last decade, and with it, an increase in attrition has become a recurring problem worldwide. Literature suggests that elements of culture, motivation, learning management systems and online pedagogy play a major role in attrition rates in the higher…

  6. Modeling Attrition in Organizations from Email Communication

    Science.gov (United States)

    2013-09-08

    diversity in SocialCom/PASSAT/ BigData /EconCom/BioMedCom 2013 978-0-7695-5137-1/13 $26.00 © 2013 IEEE DOI 10.1109/SocialCom.2013.52 331 possible reasons...that company size, industry and pay scales play a key role in determining attrition rate [1]: • Larger companies tend to have lower rates of attrition... Industries that employ a large number of unskilled labor have a higher rate of attrition as compared to the ones that largely require skilled labor

  7. Studies of anisotropy of iron based superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Murphy, Jason A. [Iowa State Univ., Ames, IA (United States)

    2013-01-01

    To study the electronic anisotropy in iron based superconductors, the temperature dependent London penetration depth, Δλ(T), have been measured in several compounds, along with the angular dependent upper critical field, Hc2(T). Study was undertaken on single crystals of Ba(Fe1-xCox)2As2 with x=0.108 and x=0.127, in the overdoped range of the doping phase diagram, characterized by notable modulation of the superconducting gap. Heavy ion irradiation with matching field doses of 6 T and 6.5 T respectively, were used to create columnar defects and to study their effect on the temperature Δλ(T). The variation of the low-temperature penetration depth in both pristine and irradiated samples was fitted with a power-law function Δλ(T) = ATn. Irradiation increases the magnitude of the pre-factor A and decreases the exponent n, similar to the effect on the optimally doped samples. This finding supports the universal s ± scenario for the whole doping range.

  8. Meissner holes in iron-based superconductors

    Science.gov (United States)

    Tamegai, Tsuyoshi; Mohan, Shyam; Tsuchiya, Yuji; Nakajima, Yasuyuki

    2012-02-01

    Magnetic flux penetrates into a superconductor in the form of quantized vortices. This process is usually described by the Bean model, and the flux front forms a regular pattern reflecting the shape of the sample. However, a novel form of flux penetration accompanying wiggling fronts between vortices and antivortices has been observed in YBa2Cu3O7-δ upon remagnetization [1]. Such a phenomenon is ascribed to the presence of special arrangements of vortices at the front accompanying flux free regions and excess current around it. The flux free region is called as `Mesissner hole'. We have performed extensive magneto-optical imagings of iron-based superconductor single crystals and found similar anomalous features for the first time in superconductors other than 123-type cuprates [2]. Implications of this finding will be discussed with possible origins of the anomalous vortex arrangements. [1] V. K. Vlasko-Vlasov et al., Phys. Rev. B 56, 5622 (1997). [2] S. Mohan, Y. Tsuchiya, Y. Nakajima, and T. Tamegai, Phys. Rev. B 84, 18050X (2011).

  9. High-Performance Corrosion-Resistant Iron-Based Amorphous Metals - The Effects of Composition, Structure and Environment: Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4

    Energy Technology Data Exchange (ETDEWEB)

    Farmer, J; Haslam, J; Day, S; Lian, T; Saw, C; Hailey, P; Choi, J; Yang, N; Bayles, R; Aprigliano, L; Payer, J; Perepezko, J; Hildal, K; Lavernia, E; Ajdelsztajn, L; Branagan, D J; Beardsely, M B

    2006-10-20

    Several Fe-based amorphous metal formulations have been identified that appear to have corrosion resistance comparable to (or better than) that of Ni-based Alloy C-22 (UNS No. N06022), based on measurements of breakdown potential and corrosion rate in seawater. Both chromium (Cr) and molybdenum (Mo) provide corrosion resistance, boron (B) enables glass formation, and rare earths such as yttrium (Y) lower critical cooling rate (CCR). SAM2X5 (Fe{sub 49.7}Cr{sub 17.7}Mn{sub 1.9}Mo{sub 7.4}W{sub 1.6}B{sub 15.2}C{sub 3.8}Si{sub 2.4}) has no yttrium, and is characterized by relatively high critical cooling rates of approximately 600 Kelvin per second. Data for the SAM2X5 formulation is reported here. In contrast to yttrium-containing iron-based amorphous metals, SAM2X5 can be readily gas atomized to produce spherical powders which enable more facile thermal spray deposition. The reference material, nickel-based Alloy C-22, is an outstanding corrosion-resistant engineering material. Even so, crevice corrosion has been observed with C-22 in hot sodium chloride environments without buffer or inhibitor. SAM2X5 also experiences crevice corrosion under sufficiently harsh conditions. Both Alloy C-22 and Type 316L stainless lose their resistance to corrosion during thermal spraying, due to the formation of deleterious intermetallic phases which depletes the matrix of key alloy elements, whereas SAM2X5 can be applied as coatings with the same corrosion resistance as a fully-dense completely amorphous melt-spun ribbon, provided that its amorphous nature is preserved during thermal spraying. The hardness of Type 316L Stainless Steel is approximately 150 VHN, that of Alloy C-22 is approximately 250 VHN, and that of HVOF SAM2X5 ranges from 1100-1300 VHN [MRS12-13]. Such hardness makes these materials particularly attractive for applications where corrosion-erosion and wear are also issues. Since SAM2X5 has high boron content, it can absorb neutrons efficiently, and may therefore find

  10. Social Factors in Second Language Attrition.

    Science.gov (United States)

    Gardner, R. C.; And Others

    1985-01-01

    Describes a study of the effects on second language attrition of attitudes, motivations, and reported language use by learners during a six-month period after the completion of an intensive French course. (SED)

  11. Method of coating an iron-based article

    Science.gov (United States)

    Magdefrau, Neal; Beals, James T.; Sun, Ellen Y.; Yamanis, Jean

    2016-11-29

    A method of coating an iron-based article includes a first heating step of heating a substrate that includes an iron-based material in the presence of an aluminum source material and halide diffusion activator. The heating is conducted in a substantially non-oxidizing environment, to cause the formation of an aluminum-rich layer in the iron-based material. In a second heating step, the substrate that has the aluminum-rich layer is heated in an oxidizing environment to oxidize the aluminum in the aluminum-rich layer.

  12. Highly mobile carriers in iron-based superconductors

    Science.gov (United States)

    Ovchenkov, Y. A.; Chareev, D. A.; Kulbachinskii, V. A.; Kytin, V. G.; Presnov, D. E.; Volkova, O. S.; Vasiliev, A. N.

    2017-03-01

    The field and temperature dependencies of the resistivity and Hall effect are measured for FeSe{}1-xS{}x (x = 0.04, 0.09, and 0.19) single crystals. Sample FeSe{}0.81S{}0.19 does not show a transition to an orthorhombic phase and at low temperatures exhibits transport properties, which are very different from those of orthorhombic samples. The behavior of FeSe{}0.81S{}0.19 is well described by the simple two-band model with comparable values of the hole and electron mobilities. The characteristics of the low-temperature transport properties of the orthorhombic Fe(SeS) samples are largely determined by the presence of a small number of highly mobile carriers, which may originate from the local regions of the Fermi surface, presumably, nearby the Van Hove singularity points. Our results, for the first time, demonstrate a strong evolution of a tiny band of highly mobile electrons at a tetragonal to orthorhombic quantum phase transition. The behavior of this band can be the reason for the diverging nematic susceptibility, determined from elastoresistivity, which is considered one of the most intriguing phenomena in the physics of iron-based superconductors.

  13. Crystal chemistry and structural design of iron-based superconductors

    Institute of Scientific and Technical Information of China (English)

    Jiang Hao; Sun Yun-Lei; Xu Zhu-An; Cao Guang-Han

    2013-01-01

    The second class of high-temperature superconductors (HTSCs),iron-based pnictides and chalcogenides,necessarily contain Fe2X2 (“X” refers to a pnictogen or a chalcogen element) layers,just like the first class of HTSCs which possess the essential CuO2 sheets.So far,dozens of iron-based HTSCs,classified into nine groups,have been discovered.In this article,the crystal-chemistry aspects of the known iron-based superconductors are reviewed and summarized by employing “hard and soft acids and bases (HSAB)” concept.Based on these understandings,we propose an alternative route to exploring new iron-based superconductors via rational structural design.

  14. Towards a Model of Language Attrition: Neurobiological and Psychological Contributions

    OpenAIRE

    Yoshitomi, Asako

    1992-01-01

    Research in L2 attrition is a relatively new enterprise which is in need of a comprehensive theory/model. This paper presents a tentative cognitive-psychological model of language attrition, which draws on information from studies in L2 attrition, neurobiology, and psychology. This is to demonstrate that a model based on consideration of the brain has the potential of providing a plausible account of the process of language attrition, as well as the process of language acquisition.

  15. Predicting Student Attrition with Data Mining Methods

    Science.gov (United States)

    Delen, Dursun

    2012-01-01

    Affecting university rankings, school reputation, and financial well-being, student retention has become one of the most important measures of success for higher education institutions. From the institutional perspective, improving student retention starts with a thorough understanding of the causes behind the attrition. Such an understanding is…

  16. Foreign Language Anxiety and Student Attrition.

    Science.gov (United States)

    Bailey, Phillip; Onwuegbuzie, Anthony J.; Daley, Christine E.

    2003-01-01

    Examines the role of anxiety in predicting student attrition in college-level foreign language courses. Reports that students who dropped out of their foreign language classes were significantly more likely to report higher levels of input, processing, and output anxiety. Provides recommendations for instructors. (Contains 28 references.) (CAK)

  17. Child Language Attrition: A Longitudinal Case Study.

    Science.gov (United States)

    Tomiyama, Machiko

    2000-01-01

    Examines the second stage of natural second language attrition in the first language environment observed in a Japanese male returnee child. The subject spent 7 years in the United States, was 8-years-old when he returned, and was highly proficient in English. The second stage is characterized by a period of change in syntax and morphology,…

  18. Attrition in Psychotherapy: A Survival Analysis

    Science.gov (United States)

    Roseborough, David John; McLeod, Jeffrey T.; Wright, Florence I.

    2016-01-01

    Purpose: Attrition is a common problem in psychotherapy and can be defined as clients ending treatment before achieving an optimal response. Method: This longitudinal, archival study utilized data for 3,728 clients, using the Outcome Questionnaire 45.2. A Cox regression proportional hazards (hazard ratios) model was used in order to better…

  19. EDITORIAL: Focus on Iron-Based Superconductors FOCUS ON IRON-BASED SUPERCONDUCTORS

    Science.gov (United States)

    Hosono, Hideo; Ren, Zhi-An

    2009-02-01

    pace of research within the last year, iron-based superconductors have revealed several unique properties such as a high upper critical field and a robustness to impurities. Participation of five 3d-orbitals in the Fermi levels also means that the electronic structure is complex compared with the cuprates. So, we now have a new family of superconductors and it is worth stressing that we have only just begun looking at the many varieties of candidate materials containing an iron square lattice. At this time we do not know whether a material with a critical temperature greater than 100 K exists, or if completely new properties are to be found. However, as a research community we should go ahead with hope and 'strike while the iron is hot'—this saying is always true! This focus issue of New Journal of Physics was put together to provide a broad-based, free-to-read snapshot of the current state of research in this rapidly emerging field. The papers included cover many aspects related to material exploration, physical analysis, and the theory of these materials, and, as editors, we thank the authors for their fine contributions, and the many referees for their considerable efforts that have ensured fast publication. As an aside, the first special issue on this SUBject was published in November 2008 in the Journal of the Physical Society of Japan (vol 77, supplement c) as the proceedings of the International Symposium on Iron-Pnictide Superconductors held in Tokyo on 29-30 June 2008. We would like to encourage the community to read both issues. On a final note we would like to acknowledge the staff of New Journal of Physics for all of their efficient work in bringing this collection to fruition. Focus on Iron-Based Superconductors Contents Microwave response of superconducting pnictides: extended s+/- scenario O V Dolgov, A A Golubov and D Parker Orbital and spin effects for the upper critical field in As-deficient disordered Fe pnictide superconductors G Fuchs, S

  20. Student and Instructor Perceptions of Attrition in Community College Online Beginning Spanish Classes

    Science.gov (United States)

    McDonnell, Thomas

    2012-01-01

    This qualitative multiple comparative case study investigated attrition in online Spanish language courses, from both instructor and student perspectives. Attrition rates in online courses have been found to be up to 50% higher than attrition rates in face to face courses, when studying the phenomenon of attrition in higher education. Attrition is…

  1. Korean Language Studies: Motivation and Attrition

    Directory of Open Access Journals (Sweden)

    Julie Damron

    2012-08-01

    Full Text Available The purposes of this study were to determine attrition rates of students learning Korean in university courses, their motivations to study the target language, why many drop out, and what educators can do to address and decrease high rates of attrition. A survey was administered to 129 students enrolled in lower-level (101–202 Korean language classes during the years 2005–2010 at a large, private university in the Rocky Mountain region of the United States. Self-identifying heritage students comprised 45.7% of those who completed the survey. Surveys were administered to students via email and returned in the same manner; as such, they represent a response and convenience sample. Five of the 12 survey questions utilized a 5-point Likert scale. The overall attrition rate from class to class during this time period was 85%. Students identified that the most motivating factors in their decision to take Korean were “It’s an important language,” “Future career benefits,” and “I have Korean heritage.” More students desired to learn only basic words and phrases than any one other proficiency category. The most common reason for quitting Korean was that it didn’t fit students’ schedules. Likewise, students indicated that had a following course been offered at a different time or if a language lab offering tutoring were made available, they might have been influenced to continue taking Korean. Surveys also addressed language-learning anxiety. Based on the results gathered, this study makes suggestions for improving Korean language instruction in order to reduce student attrition.

  2. Expectations and voluntary attrition in nursing students.

    Science.gov (United States)

    O'Donnell, Hugh

    2011-01-01

    This paper presents a series of findings generated during a larger study which aimed to develop a theoretical understanding of the reasons why nursing students voluntarily leave pre-registration nursing programmes. In this study, significant incongruence was found to exist between student expectations of pre-registration nursing programmes and the reality of these programmes following entry. The resulting dissonance was identified as an important factor in student decisions to voluntarily withdraw. A single case study design was selected to explore the causes of voluntary attrition in nursing students within a School of Nursing and Midwifery. The study population was obtained through purposeful sampling and consisted of 15 students who had previously voluntarily withdrawn from pre-registration nursing programmes. A semi-structured interview method was used to collect data from study participants. The interview schedule developed for use in the study reflected the key components of the conceptual model of higher education (HE) student attrition (Tinto, 1975, 1987, 1993). All interviews were tape recorded to facilitate later transcription. The Cyclical or Interactive Model of Qualitative Research (Miles and Huberman, 1994) was used to analyse data collected from study participants. This paper describes the unrealistic range of expectations which nursing students have of nursing, the information sources and experiences which inform student expectations and how ambiguous expectations contributed to voluntarily attrition.

  3. Iron-based 1D nanostructures by electrospinning process.

    Science.gov (United States)

    Eid, Cynthia; Brioude, Arnaud; Salles, Vincent; Plenet, Jean-Claude; Asmar, Roy; Monteil, Yves; Khoury, Randa; Khoury, Antonio; Miele, Philippe

    2010-03-26

    Iron-based 1D nanostructures have been successfully prepared using an electrospinning technique and varying the pyrolysis atmospheres. Hematite (Fe(2)O(3)) nanotubes and polycrystalline Fe(3)C nanofibers were obtained by simple air or mixed gas (H(2), Ar) annealing treatments. Using the air annealing treatment, a high control of the morphology as well as of the wall thickness of the nanotubes was demonstrated with a direct influence of the starting polymer concentration. When mixed gases (H(2) and Ar) were used for the annealing treatments, for the first time polycrystalline Fe(3)C nanofibers composed of carbon graphitic planes were obtained, ensuring Fe(3)C nanoparticle stability and nanofiber cohesion. The morphology and structural properties of all these iron-based 1D nanostructures were fully characterized by SEM, TEM, XRD and Raman spectroscopy.

  4. Flight Screening Program Effects on Attrition in Undergraduate Pilot Training

    Science.gov (United States)

    1987-08-01

    AFHRL-TP-86-59rttC p - -FLIGHT SCRELNING PROGRAM EFFECTS ONAIR FORCE ATTRITION IN UNDERGRADUATE PILOT TRAINING H U Peter Stoker David R. Hunter So...SCREENING PROGRAM EFFECTS ON ATTRITION IN UNOERGRADUATE PILOT TRAININS Peter Stoker David R. Hunter Jeffrey E. Kantor John C. Quebe, MaJor, USAF...Attrition (Cals With sc700€1h r Test crsNall) . . .. .*,., *. 1 1. 26 A-36 Predictien of T-3? Phase Pass Oyreall Attrition Results by FW brades far

  5. Multiple phase transitions in Pauli limited iron-based superconductors

    OpenAIRE

    Ptok, Andrzej

    2015-01-01

    Specific heat measurements have been successfully used to probe unconventional superconducting phases in one-band heavy-fermion and organic superconductors. We extend the method to study successive phase transitions in multi-band materials such as iron based superconductors. The signatures are multiple peaks in the specific heat, at low temperatures and high magnetic field, which can lead the experimental verification of unconventional superconducting states with non-zero total momentum.

  6. Spin excitations in hole-overdoped iron-based superconductors

    Science.gov (United States)

    Horigane, K.; Kihou, K.; Fujita, K.; Kajimoto, R.; Ikeuchi, K.; Ji, S.; Akimitsu, J.; Lee, C. H.

    2016-01-01

    Understanding the overall features of magnetic excitation is essential for clarifying the mechanism of Cooper pair formation in iron-based superconductors. In particular, clarifying the relationship between magnetism and superconductivity is a central challenge because magnetism may play a key role in their exotic superconductivity. BaFe2As2 is one of ideal systems for such investigation because its superconductivity can be induced in several ways, allowing a comparative examination. Here we report a study on the spin fluctuations of the hole-overdoped iron-based superconductors Ba1-xKxFe2As2 (x = 0.5 and 1.0; Tc = 36 K and 3.4 K, respectively) over the entire Brillouin zone using inelastic neutron scattering. We find that their spin spectra consist of spin wave and chimney-like dispersions. The chimney-like dispersion can be attributed to the itinerant character of magnetism. The band width of the spin wave-like dispersion is almost constant from the non-doped to optimum-doped region, which is followed by a large reduction in the overdoped region. This suggests that the superconductivity is suppressed by the reduction of magnetic exchange couplings, indicating a strong relationship between magnetism and superconductivity in iron-based superconductors. PMID:27615691

  7. Spin excitations in hole-overdoped iron-based superconductors.

    Science.gov (United States)

    Horigane, K; Kihou, K; Fujita, K; Kajimoto, R; Ikeuchi, K; Ji, S; Akimitsu, J; Lee, C H

    2016-09-12

    Understanding the overall features of magnetic excitation is essential for clarifying the mechanism of Cooper pair formation in iron-based superconductors. In particular, clarifying the relationship between magnetism and superconductivity is a central challenge because magnetism may play a key role in their exotic superconductivity. BaFe2As2 is one of ideal systems for such investigation because its superconductivity can be induced in several ways, allowing a comparative examination. Here we report a study on the spin fluctuations of the hole-overdoped iron-based superconductors Ba1-xKxFe2As2 (x = 0.5 and 1.0; Tc = 36 K and 3.4 K, respectively) over the entire Brillouin zone using inelastic neutron scattering. We find that their spin spectra consist of spin wave and chimney-like dispersions. The chimney-like dispersion can be attributed to the itinerant character of magnetism. The band width of the spin wave-like dispersion is almost constant from the non-doped to optimum-doped region, which is followed by a large reduction in the overdoped region. This suggests that the superconductivity is suppressed by the reduction of magnetic exchange couplings, indicating a strong relationship between magnetism and superconductivity in iron-based superconductors.

  8. Principals' Perceptions of Teacher Attrition in Indiana Catholic Schools, Checking for Agreement with Ingersoll's Theoretical Framework on Teacher Attrition in Private Schools

    Science.gov (United States)

    Brettnacher, Joseph A.

    2012-01-01

    Problem. Some Catholic schools report high teacher attrition rates. Understanding reasons for teacher attrition and responding to those issues is one of the many responsibilities of principals. However, it is unclear what Catholic principals understand about teacher attrition. Ingersoll's extensive research on teacher attrition has provided a…

  9. Warm compacted NbC particulate reinforced iron-base composite(Ⅱ)--Microstructure and properties

    Institute of Scientific and Technical Information of China (English)

    李元元; 肖志瑜; 倪东惠; 夏伟; 陈维平

    2002-01-01

    Effects of different sintering temperature and sintering time on the relative density of the sintered compacts were studied to obtain the optimal sintering parameters for the fabrication of NbC particulate reinforced iron-b ase composite. With optimal sintering temperature of 1 280 ℃ and sintering time of 80 min, wear-resisting, high density NbC particulate reinforced iron-base composites can be obtained using warm compaction powder metallurgy. The microstructure , relative density, mechanical properties and tribological behaviors of the sintered composites were studied. The results indicate that the mechanical properties of the sintered compacts were closely related to the sintered density. The iron -base composite materials with different combinations of mechanical properties and tribological behaviors were developed for different applications. One of the developed composite, which contains 10%NbC, possesses a high strength of 815 Mpa with a remarkable friction and wear behaviors. The other developed composite, which contains 15%NbC, possesses a lesser strength of 515 Mpa but with excellent friction and wear behaviors.

  10. The Role of Language Aptitude in First Language Attrition: The Case of Pre-Pubescent Attriters

    Science.gov (United States)

    Bylund, Emanuel; Abrahamsson, Niclas; Hyltenstam, Kenneth

    2010-01-01

    While language aptitude has been investigated actively within second language research, there is a current dearth of research on the effects of aptitude in cases of attrition. The aim of the present investigation was to explore the role of language aptitude for L1 proficiency in speakers who experienced a break with their L1 setting prior to…

  11. Analysis of Early Military Attrition Behavior.

    Science.gov (United States)

    1984-06-01

    Quitting,’ Review of Economics and Statistics, Vol. 62., August 1980, pp. 388-398. Vroom , Victor , Work and Motivation, Wiley, New York, 1974. Warner, John...and older recruits are more attrition-prone than younger recruits. 4M gg~~mi~yCLAIPICTIOWOF H S AGK(’ 0 g~tr.E R-3069-MIL Analysis of Early Military...marginal revenue product (MRP). Thus, lit - h (MRPit - wit) (2) where lit is the probability of a worker with t years of tenure being laid off a job i

  12. Exploring the Effects of Student Aid on Attrition.

    Science.gov (United States)

    Stampen, Jacob O.; Cabrera, Alberto F.

    1986-01-01

    A study is discussed that examined the role of student aid, gender, ethnic status, academic performance in high school, and age on attrition rates, showing how each of these variables affects attrition rates during each of the 3 successive years of undergraduate education. (MLW)

  13. The Regression Hypothesis as a Framework for First Language Attrition

    Science.gov (United States)

    Keijzer, Merel

    2010-01-01

    In an attempt to explain first language attrition in emigrant populations, this paper investigates the explanatory power of a framework that has--until now--received little attention: the regression hypothesis (Jakobson, 1941). This hypothesis predicts that the order of attrition is the reverse of the order of acquisition. The regression…

  14. Perceptions of Selected Navajo Elders Regarding Navajo Language Attrition.

    Science.gov (United States)

    Yazzie, Evangeline Parsons

    1996-01-01

    Interview excerpts in Navajo and English convey the perceptions of Navajo elders regarding Navajo language attrition, including monolingual Navajo-speaking elders' isolation and loneliness, the loss of social control in mixed families of speakers and nonspeakers of Navajo, and the loss of culture that accompanies Native language attrition.…

  15. Research on First Language Attrition of Morphosyntax in Adult Bilinguals

    Science.gov (United States)

    Gurel, Ayse

    2008-01-01

    This article presents a selective review of previous research findings on first language (L1) attrition. The review is intentionally limited in scope as it only discusses studies on morphosyntactic attrition in the L1 grammar of adult bilinguals. To this end--and in order to present the most current line of research in this field--I first report…

  16. Towards a Model of Language Attrition: Neurobiological and Psychological Contributions.

    Science.gov (United States)

    Yoshitomi, Asako

    1992-01-01

    Presents a tentative cognitive-psychological model of language attrition, which draws on information from studies in second language attrition, neurobiology and psychology. Notes that this model is presented to demonstrate that a model based on consideration of the brain has the potential of providing a plausible account of the process of language…

  17. The Impact of Attrition on Vocabulary Knowledge among Saudi Teachers

    Science.gov (United States)

    Alharthi, Thamer

    2014-01-01

    This two-year longitudinal study tracks the extent of vocabulary attrition among Arabic-speaking English graduate teachers. Data were collected through pre-post tests of receptive and productive vocabulary knowledge. The results showed drastic attrition in vocabulary knowledge soon after the end of formal instruction followed by slight gain,…

  18. Incorporating direct marketing activity into latent attrition models

    NARCIS (Netherlands)

    Schweidel, David A.; Knox, George

    2013-01-01

    When defection is unobserved, latent attrition models provide useful insights about customer behavior and accurate forecasts of customer value. Yet extant models ignore direct marketing efforts. Response models incorporate the effects of direct marketing, but because they ignore latent attrition, th

  19. Penetrating a Wall of Introspection: A Critical Attrition Analysis

    Science.gov (United States)

    Johannsen, Bjorn Friis; Rump, Camilla Osterberg; Linder, Cedric

    2013-01-01

    This paper presents a critical analysis of student discourse on attrition as it unfolds in interviews on early departure from higher education. A synthesis of relevant studies and modelling done in the field shows that essential aspects affecting attrition and retention can be effectively conceptualized and acted upon in terms of the interplay…

  20. Predictors of attrition among rural breast cancer survivors.

    Science.gov (United States)

    Meneses, Karen; Azuero, Andres; Su, Xiaogang; Benz, Rachel; McNees, Patrick

    2014-02-01

    Attrition can jeopardize both internal and external validity. The goal of this secondary analysis was to examine predictors of attrition using baseline data of 432 participants in the Rural Breast Cancer Survivors study. Attrition predictors were conceptualized based on demographic, social, cancer treatment, physical health, and mental health characteristics. Baseline measures were selected using this conceptualization. Bivariate tests of association, discrete-time Cox regression models and recursive partitioning techniques were used in analysis. Results showed that 100 participants (23%) dropped out by Month 12. Non-linear tree analyses showed that poor mental health and lack of health insurance were significant predictors of attrition. Findings contribute to future research efforts to reduce research attrition among rural underserved populations.

  1. Limestone fragmentation and attrition during fluidized bed oxyfiring

    Energy Technology Data Exchange (ETDEWEB)

    Fabrizio Scala; Piero Salatino [Istituto di Ricerche sulla Combustione - CNR, Napoli (Italy)

    2010-04-15

    Attrition/fragmentation of limestone under simulated fluidized bed oxyfiring conditions was investigated by means of an experimental protocol that had been previously developed for characterization of attrition/fragmentation of sorbents in air-blown atmospheric fluidized bed combustors. The protocol was based on the use of different and mutually complementary techniques. The extent and pattern of attrition by surface wear in the dense phase of a fluidized bed were assessed in experiments carried out with a bench scale fluidized bed combustor under simulated oxyfiring conditions. Sorbent samples generated during simulated oxyfiring tests were further characterized from the standpoint of fragmentation upon high velocity impact by means of a purposely designed particle impactor. Results showed that under calcination-hindered conditions attrition and fragmentation patterns are much different from those occurring under air-blown atmospheric combustion conditions. Noteworthy, attrition/fragmentation enhanced particle sulfation by continuously regenerating the exposed particle surface. 13 refs., 8 figs.

  2. High pressure superconductivity in iron-based layered compounds studied using designer diamonds

    Energy Technology Data Exchange (ETDEWEB)

    Tsoi, Georgiy; Stemshorn, Andrew K; Vohra, Yogesh K [Department of Physics, University of Alabama at Birmingham (UAB), Birmingham, AL 35294 (United States); Wu, Phillip M [Department of Physics, Duke University, Durham, NC 27708 (United States); Hsu, F C; Huang, Y L; Wu, M K; Yeh, K W [Institute of Physics, Academia Sinica-Nankang, Taipei, Taiwan (China); Weir, Samuel T [Lawrence Livermore National Laboratory, Mail Stop L-041, Livermore, CA 94550 (United States)

    2009-06-10

    High pressure superconductivity in iron-based superconductor FeSe{sub 0.5}Te{sub 0.5} has been studied up to 15 GPa and 10 K using an eight probe designer diamond anvil in a diamond anvil cell device. Four probe electrical resistance measurements show the onset of superconductivity (T{sub c}) at 14 K at ambient pressure with T{sub c} increasing with increasing pressure to 19 K at a pressure of 3.6 GPa. At higher pressures beyond 3.6 GPa, T{sub c} decreases and extrapolation suggests non-superconducting behavior above 10 GPa. The loss of superconductivity coincides with the pressure induced disordering of the Fe(SeTe){sub 4} tetrahedra reported at 11 GPa in x-ray diffraction studies at ambient temperature. (fast track communication)

  3. Effect of mechanical attrition on microstructure and properties of electro-deposition coatings on NdFeB

    Institute of Scientific and Technical Information of China (English)

    董雪亮; 王德仁; 曾阳庆

    2014-01-01

    Surface mechanical attrition treatment (SMAT) was developed to synthesize nanostructure coatings on alloy surface. The SMAT action was applied in the process of Ni and Cu electroplating coatings on NdFeB substrates in this paper. The role of me-chanical attrition during barrel plating on the microstructure, mechanical and corrosion resistant properties of the coatings was exam-ined. The scanning electron microscopy (SEM) observation showed that the mechanical attrition could refine grain size, markedly smooth the coating surface and obviously decrease the number of pore in the coatings. The continuous collisions of glass balls onto the NdFeB samples could induce more beneficial nucleation defects on the coating, which was helpful for increasing nucleation sites and the nucleation rate. The mechanical attrition could also restrain the heterogeneous growth of the coating grain tips due to the abra-sive action of stainless steel balls. The Tafel polarization curve experimental results indicated that SMAT process could enhance the corrosion resistance of coatings on NdFeB. The scratching test revealed that the binding force between coating and NdFeB substrate could be improved dramatically with SMAT process.

  4. Thermoelectric properties of iron-based superconductors and parent compounds

    Science.gov (United States)

    Pallecchi, Ilaria; Caglieris, Federico; Putti, Marina

    2016-07-01

    Herewith, we review the available experimental data of thermoelectric transport properties of iron-based superconductors and parent compounds. We discuss possible physical mechanisms into play in determining the Seebeck effect, from whence one can extract information about Fermi surface reconstruction and Lifshitz transitions, multiband character, coupling of charge carriers with spin excitations and its relevance in the unconventional superconducting pairing mechanism, nematicity, quantum critical fluctuations close to the optimal doping for superconductivity, correlation. Additional information is obtained from the analysis of the Nernst effect, whose enhancement in parent compounds must be related partially to multiband transport and low Fermi level, but mainly to the presence of Dirac cone bands at the Fermi level. In the superconducting compounds, large Nernst effect in the normal state is explained in terms of fluctuating precursors of the spin density wave state, while in the superconducting state it mirrors the usual vortex liquid dissipative regime. A comparison between the phenomenology of thermoelectric behavior of different families of iron-based superconductors and parent compounds allows to evidence the key differences and analogies, thus providing clues on the rich and complex physics of these fascinating unconventional superconductors.

  5. First Language Attrition: An Investigation of Taiwanese Tones and Tone Sandhi

    Science.gov (United States)

    Chang, Yufen

    2012-01-01

    First language (L1) attrition research focuses on syntactic and morphological deterioration in environments where L1 "attriters" rarely have contact with their L1, such as immigrants. There is no study that investigates L1 attrition in tones and in contexts where L1 can still be often heard. This study examines this attrition type in…

  6. Performance test of single step continuous dry attrition mill

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Young Woo; Joung, C. Y.; Lee, Y. W.; Na, S. H.; Kim, H. S.; Kim, S

    2001-02-01

    This report describes the improvement of the two-step attrition mill to solve problems associated with its complexity and those of batch type attrition mill as well as the results of the performance test in view of the comparison. In the performance test of the improved single step continuous attrition mill, powder milling and discharge time per pass was systematically measured, and UO{sup 2}-5wt%CeO{sub 2} powder mixture, UO{sup 2}-5wt%CeO{sub 2} powder mixture with poreformer, M{sub 3}O{sub 8} powder and/or MO2 scrap were milled to compare the performance of the milling operations between the 2-step attrition mill and improved single-step attrition mill. The results of the performance test shows, in addition to its improved milling operation, an improved function in less contamination with impurities, simpler handling with easier operation and maintenance and hence, less contamination of operational location, especially when used for the operation in a confinement system, for the improved single step attrition mill compared with a batch type or continuous 2-step attrition mill.

  7. Waiting Time Increases Risk of Attrition in Gambling Disorder Treatment

    DEFF Research Database (Denmark)

    Linnet, Jakob; Pedersen, Anders Sune

    2014-01-01

    completion in gambling disorder. We compared 48 gambling disorder sufferers with a 56% completion rate (21 non-completers and 27 completers). Binomial logistic regression analysis showed that waiting time from initial contact to the first session with a therapist was a significant predictor of risk...... of attrition: longer waiting times were associated with increased risk of attrition. Age, gender, or comorbidity was not associated with an increased risk of attrition. These data suggest that gambling disorder sufferers benefit from fast access to treatment, and that longer waiting time increases the risk...

  8. The Role of Personality Type on Minority Attrition at the US Naval Academy

    Science.gov (United States)

    2002-06-01

    MBTI ISTP ISTJ ISFP ISFJ INTP INTJ INFP INFJ ESTP ESTJ ESFP ESFJ ENTP ENTJ ENFP ENFJ C ou nt 400 300 200 100 0 33 Table 12: Minority Attrition...16 personality types, were predictive of attrition/persistence (see Table 13). Two personality types ENFP and INFP , were significantly more likely to...attrite. Specifically, ENFP had an attrition rate of 31.7%, in comparison with all those of other types (18.1%). Similarly, INFP had an attrition

  9. Thermal fluctuation conductivity and dimensionality in iron-based superconductors

    Science.gov (United States)

    Wang, Rui; Li, Ding-Ping

    2016-09-01

    The time-dependent Ginzburg-Landau Lawrence-Doniach model is used to investigate the superconducting fluctuation electrical conductivities. The theoretical result based on the self-consistent Gaussian approximation is used to fit the transport measurement data of iron-based superconductors F-doped LaOFeAs and BaFe2-xNixAs2. We demonstrate that LaOFeAs shows layered behavior, while BaFe2-xNixAs2 is more of a 3D feature. The conductivity in the region near Tc is well described by the theoretical formula. Project supported by the National Natural Science Foundation of China (Grant No. 11274018).

  10. One-Sign Order Parameter in Iron Based Superconductor

    Directory of Open Access Journals (Sweden)

    Bernd Büchner

    2012-03-01

    Full Text Available The onset of superconductivity at the transition temperature is marked by the onset of order, which is characterized by an energy gap. Most models of the iron-based superconductors find a sign-changing (s± order parameter [1–6], with the physical implication that pairing is driven by spin fluctuations. Recent work, however, has indicated that LiFeAs has a simple isotropic order parameter [7–9] and spin fluctuations are not necessary [7,10], contrary to the models [1–6]. The strength of the spin fluctuations has been controversial [11,12], meaning that the mechanism of superconductivity cannot as yet be determined. We report the momentum dependence of the superconducting energy gap, where we find an anisotropy that rules out coupling through spin fluctuations and the sign change. The results instead suggest that orbital fluctuations assisted by phonons [13,14] are the best explanation for superconductivity.

  11. MDR-TB in Puducherry, India: reduction in attrition and turnaround time in the diagnosis and treatment pathway.

    Science.gov (United States)

    Shewade, H D; Govindarajan, S; Thekkur, P; Palanivel, C; Muthaiah, M; Kumar, A M V; Gupta, V; Sharath, B N; Tripathy, J P; Vivekananda, K; Roy, G

    2016-12-21

    Setting: A mixed-methods operational research (OR) study was conducted to examine the diagnosis and treatment pathway of patients with presumptive multidrug-resistant tuberculosis (MDR-TB) during 2012-2013 under the national TB programme in Puducherry, India. High pre-diagnosis and pre-treatment attrition and the reasons for these were identified. The recommendations from this OR were implemented and we planned to assess systematically whether there were any improvements. Objectives: Among patients with presumptive MDR-TB (July-December 2014), 1) to determine pre-diagnosis and pre-treatment attrition, 2) to determine factors associated with pre-diagnosis attrition, 3) to determine the turnaround time (TAT) from eligibility to testing and from diagnosis to treatment initiation, and 4) to compare these findings with those of the previous study (2012-2013). Design: This was a retrospective cohort study based on record review. Results: Compared to the previous study, there was a decrease in pre-diagnosis attrition from 45% to 24% (P TB co-infection or those with extra-pulmonary TB not undergoing drug susceptibility testing. Conclusion: The implementation of findings from OR resulted in improved programme outcomes.

  12. The Career Officer Attrition Dilemma: An Underlying Cause

    Science.gov (United States)

    2007-11-02

    BOOMER, XER, & MILLENIAL TRAITS COMPARISON ..................................... 23 vii viii THE CAREER OFFICER ATTRITION DILEMMA: AN UNDERLYING... MILLENIAL TRAITS COMPARISON cause serious frustration both for the senior leadership and their subordinates. Even as the Xers begin to take over from

  13. Effect of electromagnetic stirring on the microstructure and wear behavior of iron-based composite coatings

    Institute of Scientific and Technical Information of China (English)

    Jiangbo Cheng; Binshi Xu; Xiubing Liang; Yixiong Wu; Zhengun Liu

    2008-01-01

    The effect of electromagnetic stirring on the microstructure and wear behavior of coatings has been investigated. A series of iron-based coatings were fabricated by the plasma-transferred arc cladding process by applying different magnetic field currents. The microstructure and wear resistance of the composite coatings were characterized by scanning electron microscope (SEM), energy dispersive X-ray analysis (EDAX), X-ray diffraction (XRD), and wet sand rubber wheel abrasion tester. The experimental results showed that the microstructure of the coatings was mainly theγ-Fe matrix and (Cr, Fe)7C3 carbide reinforced phase. The coatings were metallurgically bonded to the substrate. With increasing magnetic field current, the amount of the block-like (Cr, Fe)7C>3 carbide reinforced phase increased at first, reached a local maximum, and then decreased sharply. When the magnetic field current reached 3 A, the block-like (Cr, Fe)7C3 carbides with high volume fraction were uniformly distributed in the matrix and the coating displayed a high microhardness and an excellent wear resistance under the wear test condition.

  14. Superconductivity at 55 K in Iron-Based F-Doped Layered Quaternary Compound Sm[O1-xFx]FeAs

    Institute of Scientific and Technical Information of China (English)

    REN Zhi-An; ZHOU Fang; ZHAO Zhong-Xian; LU Wei; YANG Jie; YI Wei; SHEN Xiao-Li; LI Zheng-Cai; CHE Guang-Can; DONG Xiao-Li; SUN Li-Ling

    2008-01-01

    We report the superconductivity in iron-based oxyarsenide Sm[O1-xFx]FeAs, with the onset resistivity transition temperature at 55.0K and Meissner transition at 54.6K. This compound has the same crystal structure as LaOFeAs with shrunk crystal lattices, and becomes the superconductor with the highest critical temperature among all materials besides copper oxides up to now.

  15. The management of over closured anterior teeth due to attrition

    Directory of Open Access Journals (Sweden)

    Eha Djulaeha

    2009-12-01

    Full Text Available Background: Tooth is the hardest tissue in human body, that can be injured because of attrition process. For old people, denture attrition process is caused by psysiological process relating with the mastication function which also supported by some bad habits such an bruxism, premature contact, and consuming habit of abrasive food. Attrition or abrasion can also be happened with patien’t dentition who does not have teeth subtutition for long time due the lost of their maxillary as well as mandibulary. The pasient will loose their vertical dimension of occlusion, injure, and the lower jaw becomes over closed which is called over closure. Purpose: This article reported the management of over closured anterior teeth due to attrition. Case: a seventy six year old woman patient came to Prosthodontic Clinic in Faculty of Dentistry, Airlangga University, to rehabilitate her upper and lower severe attrited anterior teeth and her posterior teeth. The patient has experienced of wearing acrylic removable mandibular partial denture ten years ago. Unfortunaly, the denture was uncomfortable, and she did not wear it anymore since five years ago. Case management: The severe attrition of anterior teeth with the lost of occlusal vertical dimension can be treated by improving the occlusal vertical dimension gradually. The treatment is then followed by the increasing of the height of the anterior teeth by lengthening the crown teeth of upper jaw with 12 units of span bridge and the acrylic removable partial denture of lower jaw. Conclusion: The severe attrition of anterior teeth with the lost of occlusal vertical dimension can be treated by improving the occlusal vertical dimension gradually, using long span bridge and acrylic removable partial denture.

  16. Characterization of a Rapidly Solidified Iron-Based Superalloy

    Science.gov (United States)

    Smugeresky, J. E.

    1982-09-01

    Rapidly-solidified powders of an iron-based superalloy were characterized before and after consolidation by hot isostatic pressing. Powders made by inert gas atomization were compared to powders made by centrifugal atomization. Although many of the powder characteristics were similar, the microstructures were not. The inert gas atomized powder structure is cellular while the centrifugally atomized powder structure is dendritic. In general the finer powder particles have the finer micro-structure with the effect more noticeable in centrifugally atomized powders. After consolidation, the differences in microstructure are more dependent on the consolidation temperature and post-consolidation heat treatment than in the powder type or size. Higher consolidation temperatures and/or post-consolidation heat treatment will result in transformation of the as-solidified microstructures. The transformed microstructure and the mechanical properties can in some cases be related to the as-solidified structure. Heat treatment is needed to obtain mechanical properties equivalent to those of ingot metallurgy processed material.

  17. Highly attrition resistant sorbents for desulfurization of hot coal gases

    Energy Technology Data Exchange (ETDEWEB)

    Slimane, R.B.; Abbasian, J.; Zarnegar, M.K. [Institute of Gas Technology, Des Plaines, IL (United States)] [and others

    1998-04-01

    One of the main obstacles in the commercialization of high-temperature desulfurization systems for Integrated Gasification Combined Cycle (IGCC) power generation processes is the development of regenerable sulfur sorbents with suitable physical and chemical characteristics. The focus of much of the current research on sorbent development has been on the use of zinc-based sorbents. These sorbents have been the subject of extensive pilot-scale and process development work; however, they have been shown to suffer from sulfate formation and zinc volatilization, leading to sorbent degradation over multi-cycle use. Therefore, investigation of non-zinc based sorbents is a logical approach to develop an effective alternative. An effective alternative to zinc-based sorbents could be manganese-based sorbents which have recently been shown to withstand high temperature ({ge} 750{degrees}C) operation and also maintain structural and reactive integrity over many cycles. However, because of process equipment limitations and other process variables such as fuel gas alkali content, a number of investigators have recently argued that the benefit to be gained by lower temperature application may outweigh the slight loss of efficiency, resulting in lower overall cost of electricity. Desulfurization temperatures {le} 538{degrees}C have been recommended to provide the best compromise between process equipment limitations and higher temperature operation.

  18. Proximal attrition facets: morphometric, demographic, and aging characteristics.

    Science.gov (United States)

    Sarig, Rachel; Hershkovitz, Israel; Shvalb, Nir; Sella-Tunis, Tatiana; May, Hila; Vardimon, Alexander D

    2014-08-01

    Although interproximal attrition is considered to be limited in modern populations, it has important clinical implications. However, in contrast to occlusal attrition, proximal attrition receives limited scientific attention. The main purpose of the current study was to fill this void. Seven-hundred and sixty-five teeth were collected from 255 skulls of subjects 18-75 yr of age. For each individual, three mandibular teeth (the first and second premolars and the first molar) were examined for proximal attrition facets (PAFs). The results provide detailed information on the size, shape, and location of the facets according to age cohort, gender, and ethnicity. The validity of the method used to measure the facets was also examined. The major findings were as follows: PAFs are usually located on the upper half of the crown proximal aspect; in each tooth, the mesial facet is more lingually positioned and the distal facet is more buccally positioned; the majority of the facets are subrectangular in shape; the size of the facets tends to increase in an anteroposterior direction (from premolars to molars); and facet size and location are age- and sex-dependent and ethnicity-independent. It is our recommendation that dentists bear in mind that interproximal attrition is a dynamic, long-term process and needs to be considered in many clinical scenarios.

  19. Attrition of undergraduate nursing students at selected South African universities

    Directory of Open Access Journals (Sweden)

    Erna Roos

    2016-02-01

    Full Text Available Background: The nursing profession forms the backbone of many healthcare systems. It therefore needs a consistent supply of registered nurses to deliver continuous and safe quality healthcare, and to replace the nurses leaving or retiring from the profession. Attrition actively occurs among nursing students in South Africa and threatens the future supply of registered nurses. Aim: The aim of the study was to describe the attrition rate at selected South African universities and the factors influencing undergraduate nursing students to discontinue their nursing studies at these universities. Method: A quantitative descriptive design was followed. Heads of the nursing departments at the selected universities captured data with a specifically designed questionnaire. Thereafter their former nursing students provided information via a structured telephonic interview on the reasons why they discontinued the nursing programme. Results: The study revealed that attrition of undergraduate nursing students for three intake years (2007, 2008 and 2009 at the participating universities was between 39.3% and 58.7%. Academic and financial reasons as well as poor wellness and health were the main causes for attrition. Another factor was failure to cope with the demands of the clinical environment. Conclusion: Attrition might not occur immediately when a nursing student is challenged, as the student might exploit the various types of support offered. Although some nursing students do benefit from the offered support, a large number of nursing students still discontinue the undergraduate nursing programme.

  20. Blood Telomere Length Attrition and Cancer Development in the Normative Aging Study Cohort

    Directory of Open Access Journals (Sweden)

    Lifang Hou

    2015-06-01

    Interpretation: Age-related BTL attrition was faster in cancer cases but their age-adjusted BTL attrition began decelerating as diagnosis approached. This may explain prior inconsistencies and help develop BTL as a cancer detection biomarker.

  1. Confirming the Lanchestrian linear-logarithmic model of attrition

    Energy Technology Data Exchange (ETDEWEB)

    Hartley, D.S. III.

    1990-12-01

    This paper is the fourth in a series of reports on the breakthrough research in historical validation of attrition in conflict. Significant defense policy decisions, including weapons acquisition and arms reduction, are based in part on models of conflict. Most of these models are driven by their attrition algorithms, usually forms of the Lanchester square and linear laws. None of these algorithms have been validated. The results of this paper confirm the results of earlier papers, using a large database of historical results. The homogeneous linear-logarithmic Lanchestrian attrition model is validated to the extent possible with current initial and final force size data and is consistent with the Iwo Jima data. A particular differential linear-logarithmic model is described that fits the data very well. A version of Helmbold's victory predicting parameter is also confirmed, with an associated probability function. 37 refs., 73 figs., 68 tabs.

  2. Strategies to Engage Online Students and Reduce Attrition Rates

    Directory of Open Access Journals (Sweden)

    Frankie Keels Williams

    2007-07-01

    Full Text Available Attrition continues to be a major issue in higher education. Attrition rates for classes taught through distance education are 10 – 20% higher than classes taught in a face-to-face setting. Educators should engage students early and often, using different learning strategies customized to the class content and the students’ pre-existing knowledge. The goal for the professor is to develop relationships with the students such that they feel comfortable in the environment. The professor should facilitate learner-learner integration and collaboration so that they will learn from one another and expand their knowledge base together. Through an integrative literature review, this article presents key concepts in online learning and a review of different methods of engaging students with the goals of enhancing the learning process and reducing attrition rates.

  3. The Influence of Second Language Attrition on Foreign Language Teaching

    Institute of Scientific and Technical Information of China (English)

    李臻

    2012-01-01

    Besides the sessions of teaching and learning in language learning activities,language attrition,as the concomitant product of language acquisition,exerts significant impact on language teaching,especially on foreign language teaching.By exploring this phenomenon,some effective ways against language attrition can be found in order to maximize foreign language teaching.This paper is about to illustrate the relevant theories from scholars at home and abroad,and providing some ways to help foreign language learners maintain the language proficiency.

  4. Examining the relationship between mental, physical, and organizational factors associated with attrition during maritime forces training

    NARCIS (Netherlands)

    Binsch, O.; Banko, K.M.; Veenstra, B.J.; Valk, P.J.L.

    2015-01-01

    For infantry units of the Dutch Ministry of Defence, high attrition rates (varying from 42 to 68%) during initial training are a persisting problem. The reasons for this attrition are diverse. Having better insight into the causes of attrition is a prerequisite for implementing preventive measures.

  5. Microbial synthesis of iron-based nanomaterials—A review

    Indian Academy of Sciences (India)

    Abhilash; K Revati; B D Pandey

    2011-04-01

    Nanoparticles are the materials having dimensions of the order of 100 nm or less. They exhibit a high surface/volume ratio leading to different properties far different from those of the bulk materials. The development of uniform nanoparticles has been intensively pursued because of their technological and fundamental scientific importance. A number of chemical methods are available and are extensively used, but these are often energy intensive and employ toxic chemicals. An alternative approach for the synthesis of uniform nanoparticles is the biological route that occurs at ambient temperature, pressure and at neutral pH. The main aim of this review is to enlist and compare various methods of synthesis of iron-based nanoparticles with emphasis on the biological method. Biologically induced and controlled mineralization mechanisms are the two modes through which the micro-organisms synthesize iron oxide nanoparticles. In biologically induced mineralization (BIM) mode, the environmental factors like pH, pO2, pCO2, redox potential, temperature etc govern the synthesis of iron oxide nanoparticles. In contrast, biologically controlled mineralization (BCM) process initiates the micro-organism itself to control the synthesis. BIM can be observed in the Fe(III) reducing bacterial species of Shewanella, Geobacter, Thermoanaerobacter, and sulphate reducing bacterial species of Archaeoglobus fulgidus, Desulfuromonas acetoxidans, whereas BCM mode can be observed in the magnetotactic bacteria (MTB) like Magnetospirillum magnetotacticum, M. gryphiswaldense and sulphate-reducing magnetic bacteria (Desulfovibrio magneticus). Magnetite crystals formed by Fe(III)-reducing bacteria are epicellular, poorly crystalline, irregular in shapes, having a size range of 10–50 nm super-paramagnetic particles, with a saturation magnetization value ranging from 75–77 emu/g and are not aligned in chains. Magnetite crystals produced by MTB have uniform species-specific morphologies and sizes

  6. Interplay between superconductivity and magnetism in iron-based superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Chubukov, Andrey V [University of Wisconsin

    2015-06-10

    This proposal is for theoretical work on strongly correlated electron systems, which are at the center of experimental and theoretical activities in condensed-matter physics. The interest to this field is driven fascinating variety of observed effects, universality of underlying theoretical ideas, and practical applications. I propose to do research on Iron-based superconductors (FeSCs), which currently attract high attention in the physics community. My goal is to understand superconductivity and magnetism in these materials at various dopings, the interplay between the two, and the physics in the phase in which magnetism and superconductivity co-exist. A related goal is to understand the origin of the observed pseudogap-like behavior in the normal state. My research explores the idea that superconductivity is of electronic origin and is caused by the exchange of spin-fluctuations, enhanced due to close proximity to antiferromagnetism. The multi-orbital/multi-band nature of FeSCs opens routes for qualitatively new superconducting states, particularly the ones which break time-reversal symmetry. By all accounts, the coupling in pnictdes is below the threshold for Mott physics and I intend to analyze these systems within the itinerant approach. My plan is to do research in two stages. I first plan to address several problems within weak-coupling approach. Among them: (i) what sets stripe magnetic order at small doping, (ii) is there a preemptive instability into a spin-nematic state, and how stripe order affects fermions; (iii) is there a co-existence between magnetism and superconductivity and what are the system properties in the co-existence state; (iv) how superconductivity emerges despite strong Coulomb repulsion and can the gap be s-wave but with nodes along electron FSs, (v) are there complex superconducting states, like s+id, which break time reversal symmetry. My second goal is to go beyond weak coupling and derive spin-mediated, dynamic interaction between

  7. Crystal growth iron based pnictide compounds; Kristallzuechtung eisenbasierter Pniktidverbindungen

    Energy Technology Data Exchange (ETDEWEB)

    Nacke, Claudia

    2012-11-15

    The present work is concerned with selected crystal growth method for producing iron-based superconductors. The first part of this work introduces significant results of the crystal growth of BaFe{sub 2}As{sub 2} and the cobalt-substituted compound Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} with x{sub Nom} = 0.025, 0.05, 0.07, 0.10 and 0.20. For this purpose a test procedure for the vertical Bridgman method was developed. The second part of this work contains substantial results for growing a crystal of LiFeAs and the nickel-substituted compound Li{sub 1-δ}Fe{sub 1-x}Ni{sub x}As with x{sub Nom} = 0.015, 0.025, 0.05, 0.06, 0.075 and 0.10. For this purpose a test procedure for the melt flow process has been developed successfully. [German] Die vorliegende Arbeit befasst sich mit ausgewaehlten Kristallzuechtungsverfahren zur Herstellung eisenbasierter Supraleiter. Der erste Teil dieser Arbeit fuehrt wesentliche Ergebnisse der Kristallzuechtung von BaFe{sub 2}As{sub 2} sowie der Cobalt-substituierten Verbindung Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} mit x{sub Nom} =0.025, 0.05, 0.07, 0.10 und 0.20 auf. Hierzu wurde eine Versuchsdurchfuehrung fuer das vertikale Bridgman-Verfahren konzipiert, mit welcher erfolgreich Kristalle dieser Zusammensetzungen gezuechtet wurden. Der zweite Teil dieser Arbeit enthaelt wesentliche Ergebnisse zur Kristallzuechtung von LiFeAs sowie der Nickel-substituierten Verbindung Li{sub 1-δ}Fe{sub 1-x}Ni{sub x}As mit x{sub Nom} = 0.015, 0.025, 0.05, 0.06, 0.075 und 0.10. Hierfuer wurde erfolgreich eine Versuchsdurchfuehrung fuer das Schmelzfluss-Verfahren entwickelt.

  8. "Who Leaves?" Teacher Attrition and Student Achievement. Working Paper 23

    Science.gov (United States)

    Boyd, Donald; Grossman, Pamela; Lankford, Hamilton; Loeb, Susanna; Wyckoff, James

    2009-01-01

    This paper analyzes attrition patterns among teachers in New York City public elementary and middle schools and explores whether teachers who transfer among schools, or leave teaching entirely, are more or less effective than those who remain. We find that the first-year teachers who are less effective in improving student math scores have higher…

  9. Should all attrition households in rural panel datasets be tracked?

    DEFF Research Database (Denmark)

    Walelign, Solomon Zena

    2016-01-01

    Panel surveys are always subject to attrition: the original number of respondents is reduced over time and this process potentially affects the internal and external validity of a study. This is a common challenge in rural panel surveys in developing countries, where ‘attritors’ are typically not...

  10. Evolutionary dynamics of a smoothed war of attrition game.

    Science.gov (United States)

    Iyer, Swami; Killingback, Timothy

    2016-05-07

    In evolutionary game theory the War of Attrition game is intended to model animal contests which are decided by non-aggressive behavior, such as the length of time that a participant will persist in the contest. The classical War of Attrition game assumes that no errors are made in the implementation of an animal׳s strategy. However, it is inevitable in reality that such errors must sometimes occur. Here we introduce an extension of the classical War of Attrition game which includes the effect of errors in the implementation of an individual׳s strategy. This extension of the classical game has the important feature that the payoff is continuous, and as a consequence admits evolutionary behavior that is fundamentally different from that possible in the original game. We study the evolutionary dynamics of this new game in well-mixed populations both analytically using adaptive dynamics and through individual-based simulations, and show that there are a variety of possible outcomes, including simple monomorphic or dimorphic configurations which are evolutionarily stable and cannot occur in the classical War of Attrition game. In addition, we study the evolutionary dynamics of this extended game in a variety of spatially and socially structured populations, as represented by different complex network topologies, and show that similar outcomes can also occur in these situations.

  11. Language Attrition, Language Shift, and Ethnolinguistic Vitality in Australia.

    Science.gov (United States)

    Yagmur, Kutlay; de Bot, Kees; Korzilius, Hubert

    1999-01-01

    Presents findings of research investigating first-language attrition of Turkish speakers in Australia and the role of subjunctive ethnolinguistic vitality perceptions in that process. Examines the relationship between societal factors and individuals' perceptions of the language contact situation as reflected in their speech behavior. (Author/VWL)

  12. Compensatory Strategies of First-Language-Attrited Children

    Science.gov (United States)

    Syahdan

    2012-01-01

    This article explores the compensatory strategies used by two Indonesian children who experienced first language attrition when acquiring English in the English-speaking environment. They use compensatory strategies to compensate for their lack of competence in first language. They employ both interlingual strategies and discourse strategies when…

  13. On the L1 Attrition of the Spanish Present Tense

    Science.gov (United States)

    Cuza, Alejandro

    2010-01-01

    This study examines the potential native language (L1) attrition of the ongoing value of the Spanish present tense among long-term Spanish immigrants. Based on the assumption of second-language (L2) transfer and proposals on the permeability of interface-conditioned structures, it is hypothesized that long-term Spanish immigrants will show…

  14. Lexical Attrition in Younger and Older Bilingual Adults

    Science.gov (United States)

    Goral, Mira; Libben, Gary; Obler, Loraine K.; Jarema, Gonia; Ohayon, Keren

    2008-01-01

    Healthy monolingual older adults experience changes in their lexical abilities. Bilingual individuals immersed in an environment in which their second language is dominant experience lexical changes, or attrition, in their first language. Changes in lexical skills in the first language of older individuals who are bilinguals, therefore, can be…

  15. Selected Factors of Language Learning and Language Attrition.

    Science.gov (United States)

    Papalia, Anthony

    This study began with a survey of twenty-eight school districts of Erie County, New York, and its aims were to determine and compare attrition in foreign languages in those districts. The data, obtained through discussion with teachers, interviews with students, questionnaires, and Flander's Interaction Analysis, assisted in the formulation of the…

  16. Who Stays, Who Leaves? Attrition among First-Term Enlistees

    Science.gov (United States)

    1989-05-01

    helped them select the occupation of their choice and a convenient entry data. Because so many enlistees enter through DEP- virtually all seniors-it is...perhaps not surprising that DEP participation alone has no significant correlation with attrition. Still, Baldwin and I) aula found that DEP participation

  17. Toward a Grounded Theory of Nursing Student Attrition

    Science.gov (United States)

    Cook, Lenora

    2010-01-01

    Attrition of students from a nursing program is a significant concern. It is even more critical now because there are not enough nurses to fill all open positions in the healthcare industry. It is predicted the shortage will worsen in the next decade as an aging society increases the number of people requiring nursing care. While increasing the…

  18. The Erosion of the Enlisted Force: A Study of Attrition

    Science.gov (United States)

    1999-04-01

    with a high school diploma (32.5 percent). Homeschooling data indicates an attrition rate of 38.5 percent, or 7 percent less than those with a GED...enjoying robust economy; the number of veterans has declined and they are upset over benefit erosion; and Generation X does not trust large institutions

  19. 铁基超导体材料和物理研究%Iron-Based Superconducting Materials and Pairing Mechanism

    Institute of Scientific and Technical Information of China (English)

    闻海虎

    2015-01-01

    自2008年初在铁砷/铁卤(FeAs/FeSe)基材料中发现高温超导电性以来,已经有至少7种结构类型的材料被合成出来了。其中在“1111”体系中,电阻和磁化测量得到的超导转变温度可达56 K,而且有迹象表明超导转变温度有可能会继续升高。在铁基超导体的正常态,有很多非常规电子特性,如反铁磁性和四方-正交结构相变等也被观察到。铁基超导体是典型的多带超导体,具有较长的相干长度、近三维的电子特性、很高的上临界磁场及不可逆磁场和很强的磁通钉扎能力等物理性质,因此它们在强磁场方面有很好的应用前景。简单综述了铁基超导材料的结构类型,针对几种主要结构类型的性质进行了描述,对电子配对的机理问题作了比较详尽的阐述,结合临界电流和临界磁场行为,展望了铁基超导体的应用前景。%Since the discovery of high temperature superconductivity in the iron pnictide /chalcogenide materials,at least seven related structural types have been fabricated.In the 1 1 1 1 system,the highest superconducting transition tem-perature (Tc )measured by resistivity and magnetization can reach 56 K.There are some hints that the Tc can be in-creased to higher values.The iron-based superconductors have multiband feature.Many unconventional electronic proper-ties in the normal state of iron-based superconductors have been discovered.The iron based superconductors have relative-ly longer coherence length,more three dimensional electronic property,higher upper critical field and irreversibility field, very strong flux pinning,therefore they have the great potential for applications for producing high magnetic field.In this short overview,we will give a brief survey about the development of materials and physics of iron-based superconductors. We give detailed descriptions on the properties for several kinds of materials with the major structures

  20. Quels changements linguistiques dans l'attrition de la L1 chez le bilingue tardif (What Linguistic Changes in the Attrition of the L1 in Late Bilinguals)?

    Science.gov (United States)

    Kopke, Barbara

    2001-01-01

    This article reports on a psycholinguistic study of first language attrition in German first generation immigrants. On the basis of the individual variation in performance evidenced by the data, the study claims that first language (L1) attrition in late bilinguals is not only the consequence of a lack of use. A comparison of the performance of…

  1. Grammatical Gender in American Norwegian Heritage Language: Stability or Attrition?

    Science.gov (United States)

    Lohndal, Terje; Westergaard, Marit

    2016-01-01

    This paper investigates possible attrition/change in the gender system of Norwegian heritage language spoken in America. Based on data from 50 speakers in the Corpus of American Norwegian Speech (CANS), we show that the three-gender system is to some extent retained, although considerable overgeneralization of the masculine (the most frequent gender) is attested. This affects both feminine and neuter gender forms, while declension class markers such as the definite suffix remain unaffected. We argue that the gender category is vulnerable due to the lack of transparency of gender assignment in Norwegian. Furthermore, unlike incomplete acquisition, which may result in a somewhat different or reduced gender system, attrition is more likely to lead to general erosion, eventually leading to complete loss of gender.

  2. Grammatical Gender in American Norwegian Heritage Language: Stability or attrition?

    Directory of Open Access Journals (Sweden)

    Terje eLohndal

    2016-03-01

    Full Text Available This paper investigates possible attrition/change in the gender system of Norwegian heritage language spoken in America. Based on data from 50 speakers in the Corpus of American Norwegian Speech (CANS, we show that the three-gender system is to some extent retained, although considerable overgeneralization of the masculine (the most frequent gender is attested. This affects both feminine and neuter gender forms, while declension class markers such as the definite suffix remain unaffected. We argue that the gender category is vulnerable due to the lack of transparency of gender assignment in Norwegian. Furthermore, unlike incomplete acquisition, which may result in a somewhat different or reduced gender system, attrition is more likely to lead to general erosion, eventually leading to complete loss of gender.

  3. Relationship between Academic Performance, Spatial Competence, Learning Styles and Attrition

    Directory of Open Access Journals (Sweden)

    Marianela Noriega Biggio

    2013-04-01

    Full Text Available This paper discusses the results of research on factors affecting academic performance and attrition in a sample of 1,500 freshman students majoring in architecture, design and urbanism at the Universidad de Buenos Aires, Argentina [University of Buenos Aires, Argentina] who were enrolled in a drafting course. The hypotheses we tested concern the mediating role of learning styles on the relationship between spatial competence and academic performance, learning-style differences by gender and cohort, and the relationship between attrition, spatial competence level and learning style. Statistical analysis of the data was performed and spatial competence enhanced by motivational profile was found to predict final achievement. Educational implications are identified, highlighting the need to promote in students those academic behaviors that characterize a self-regulated learning style and encourage the use of specific intellectual abilities.

  4. Waivered Recruits: An Evaluation of Their Performance and Attrition Risk

    Science.gov (United States)

    2011-03-01

    school degree graduate (HSDG) Nontraditional HSDGa Tier II Tier III a. Nontraditional HSDGs have a homeschool or adult education diploma, or have...characteristics that affect their attrition risk. We also 11. While a reduction in force may not be considered a "good" thing, it is certainly legitimate...race/ethnicity, marital status, number of children , AFQT score, months spent in DEP, education, gender, and FY of accession. We also control for

  5. COMPENSATORY STRATEGIES OF FIRST-LANGUAGE-ATTRITED CHILDREN

    Directory of Open Access Journals (Sweden)

    Syahdan Syahdan

    2012-01-01

    Full Text Available This article explores the compensatory strategies used by two Indonesian children who experienced first language attrition when acquiring English in the English-speaking environment. They use compensatory strategies to compensate for their lack of competence in first language. They employ both interlingual strategies and discourse strategies when they have difficulties in communication. Interlingual strategies used are codeswitching and lexical borrowings and the discourse strategies are overt comments, appeal for assistance, and avoidance.

  6. Predictors of Attrition in the Finnish Conscript Service

    Science.gov (United States)

    2006-11-01

    Dawson et al., 1994; Kassel, Jackson, & Unrod, 2000; Lazarus & Folkman , 1984; Pierce & Lydon, 1998; Thompson & Gignac, 2001). These expectations toward...of Navy attrition. II. A demonstration of potential usefulness for screening. (Report No. 01-06). Military Medicine, 167, 770-776. Lazarus , R. S... Folkman , S. (1984). Stress, appraisal, and coping. New York: Springer. Manigart, P., & Prensky, D. (1982). Recruitment and retention of volunteers

  7. Non-parallel processing: Gendered attrition in academic computer science

    Science.gov (United States)

    Cohoon, Joanne Louise Mcgrath

    2000-10-01

    This dissertation addresses the issue of disproportionate female attrition from computer science as an instance of gender segregation in higher education. By adopting a theoretical framework from organizational sociology, it demonstrates that the characteristics and processes of computer science departments strongly influence female retention. The empirical data identifies conditions under which women are retained in the computer science major at comparable rates to men. The research for this dissertation began with interviews of students, faculty, and chairpersons from five computer science departments. These exploratory interviews led to a survey of faculty and chairpersons at computer science and biology departments in Virginia. The data from these surveys are used in comparisons of the computer science and biology disciplines, and for statistical analyses that identify which departmental characteristics promote equal attrition for male and female undergraduates in computer science. This three-pronged methodological approach of interviews, discipline comparisons, and statistical analyses shows that departmental variation in gendered attrition rates can be explained largely by access to opportunity, relative numbers, and other characteristics of the learning environment. Using these concepts, this research identifies nine factors that affect the differential attrition of women from CS departments. These factors are: (1) The gender composition of enrolled students and faculty; (2) Faculty turnover; (3) Institutional support for the department; (4) Preferential attitudes toward female students; (5) Mentoring and supervising by faculty; (6) The local job market, starting salaries, and competitiveness of graduates; (7) Emphasis on teaching; and (8) Joint efforts for student success. This work contributes to our understanding of the gender segregation process in higher education. In addition, it contributes information that can lead to effective solutions for an

  8. Pressure dependence of the thermoelectric power of the iron-based high-T{sub c} superconductor SmFeAsO{sub 0.85}

    Energy Technology Data Exchange (ETDEWEB)

    Kang, N; Auban-Senzier, P; Pasquier, C R [Laboratoire de Physique des Solides, Universite Paris-Sud, 91405 Orsay (France); Ren, Z A; Yang, J; Che, G C; Zhao, Z X [National Laboratory for Superconductivity, Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190 (China)], E-mail: kang@lps.u-psud.fr

    2009-02-15

    We have measured the thermoelectric power S of the iron-based superconductor SmFeAsO{sub 0.85} as a function of temperature at various pressures up to 1.1 GPa. The magnitude of thermoelectric power increases with decreasing temperature and exhibits a maximum at a characteristic temperature T* ({approx}110 K at ambient pressure), whereas the temperature dependence of the resistance shows metallic behavior. The superconducting transition temperature T{sub c} and T* decrease monotonically with pressure. We discuss our results in terms of the effects of Fermi-surface nesting and orbit degeneracy in the new iron-oxypnictides.

  9. High efficiency iron electrode and additives for use in rechargeable iron-based batteries

    Energy Technology Data Exchange (ETDEWEB)

    Narayan, Sri R.; Prakash, G. K. Surya; Aniszfeld, Robert; Manohar, Aswin; Malkhandi, Souradip; Yang, Bo

    2017-02-21

    An iron electrode and a method of manufacturing an iron electrode for use in an iron-based rechargeable battery are disclosed. In one embodiment, the iron electrode includes carbonyl iron powder and one of a metal sulfide additive or metal oxide additive selected from the group of metals consisting of bismuth, lead, mercury, indium, gallium, and tin for suppressing hydrogen evolution at the iron electrode during charging of the iron-based rechargeable battery. An iron-air rechargeable battery including an iron electrode comprising carbonyl iron is also disclosed, as is an iron-air battery wherein at least one of the iron electrode and the electrolyte includes an organosulfur additive.

  10. Iron-based superconductors: A new family to find the origin of high Tc superconductivity

    Institute of Scientific and Technical Information of China (English)

    Dao-xin Yao

    2011-01-01

    Since the discovery of iron-based superconductors in 2008 [1],a new tide of study on high Tc superconductors spreads worldwide quickly.After a few years' intensive study,many new compounds of iron-based superconductors have been found and their properties have been disclosed.The great achievement is attributed to the modern experimental techniques,fast developing numerical methods and improved theories during the study of cuprate superconductors or more generally strongly correlated electron systems.For instance,the Fermi surface,band structure and superconducting gap for a new compound could be measured quickly by modern ARPES technique [2].

  11. Iron-based materials as tar cracking catalyst in waste gasification

    Energy Technology Data Exchange (ETDEWEB)

    Nordgreen, Thomas

    2011-07-01

    The treatment of municipal solid waste (MSW) in Sweden has changed during the past decades due to national legislation and European Union directives. The former landfills have more or less been abandoned in favour of material recycling and waste incineration. On a yearly basis approximately 2.2 million tonnes waste are incinerated in Sweden with heat recovery and to some extent also with electricity generation, though at a low efficiency. It is desirable to alter this utilisation and instead employ MSW as fuel in a fluid bed gasification process. Then electrical energy may be produced at a much higher efficiency. However, MSW contain about 1 % chlorine in the form of ordinary table salt (NaCl) from food scraps. This implies that the tar cracking catalyst, dolomite, which is normally employed in gasification, will suffer from poisoning if applied under such conditions. Then the tar cracking capacity will be reduced or vanish completely with time. Consequently, an alternative catalyst, more resistant to chlorine, is needed. Preliminary research at KTH has indicated that iron in its metallic state may possess tar cracking ability. With this information at hand and participating in the project 'Energy from Waste' an experimental campaign was launched. Numerous experiments were conducted using iron as tar cracking catalyst. First iron sinter pellets from LKAB were employed. They were reduced in situ with a stream of hydrogen before they were applied. Later iron-based granules from Hoeganaes AB were tested. These materials were delivered in the metallic state. In all tests the KTH atmospheric fluidised bed gasifier with a secondary catalytic reactor housing the catalytic material was deployed. Mostly, the applied fuel was birch. The results show that metallic iron possesses an intrinsic ability, almost in the range of dolomite, to crack tars. Calculations indicate that iron may be more resistant to chlorine than dolomite. The exploration of metallic iron

  12. Properties and Application of Iron-based Shape Memory Alloy

    Institute of Scientific and Technical Information of China (English)

    Li Jian-chen; Jiang Qing; Dai Jun

    2005-01-01

    The properties of FeMnSiCrNi shape memory alloy were investigated. The results show that the best shape memory effect of Fel4Mn6Si9Cr5Ni alloy is 85%. The transformation amount of the ε→γ transformation is not complete after heating the alloy to 1000 K, As and Af points drop with increased transformation enthalpy ( △Hγ→ε) by thermal cycling and increased prestrain. The alloy shows also good creep and stress relaxation resistance. In addition, the alloy having a tensile force of 20 kN and a sealing pressure of 6 MPa can satisfy requirements for possible industrial application on pipe joints.

  13. Tunable 0–π transition by interband coupling in iron-based superconductor Josephson junctions

    Science.gov (United States)

    Tao, Y. C.; Liu, S. Y.; Bu, N.; Wang, J.; Di, Y. S.

    2016-01-01

    An extended four-component Bogoliubov–de Gennes equation is applied to study the Josephson effect in ballistic limit between either two iron-based superconductors (SCs) or an iron-based SC and a conventional s-wave SC, separated by a normal metal. A 0–π transition as a function of interband coupling strength α is always exhibited, arising from the tuning of mixing between the two trajectories with opposite phases. The novel property can be experimentally used to discriminate the {s}+/- -wave pairing symmetry in the iron-based SCs from the {s}++-wave one in MgB2. The effect of interface transparency on the 0–π transition is also presented. The 0–π transition as a function of α is wholly distinct from that as a function of barrier strength or temperature in recent theories (Linder et al 2009 Phys. Rev. B 80 020503(R)). The possible experimental probe of the phase-shift effect in iron-based SC Josephson junctions is commented on as well.

  14. Effects of Cerium on Reduction of Non-Chromium Iron Based CO Shift Catalyst

    Institute of Scientific and Technical Information of China (English)

    苏运来; 胡捷; 马卓娜; 杜宝石; 郭益群

    2001-01-01

    The effects of Ce on reduction of non-chromium iron based CO shift catalyst were studied by XRD, TPR, SEM and XPS. The results show that Ce refines Fe2O3 grains and riches on the surface of catalyst in the process of reduction, which leads to decrease of the initial reductive temperature and increase of the final reductive temperature.

  15. Investigation of Amorphous/Nanocrystalline Iron-Based Thermal Barrier Coatings

    Science.gov (United States)

    Bobzin, K.; Öte, M.; Königstein, T.

    2017-02-01

    Because of their favorable thermophysical properties, good machinability and low material costs, iron-based coatings which exhibit a highly amorphous/nanocrystalline microstructure are currently in the focus of research. Considering the crystallization temperature of the material, iron-based coatings might be the next generation of thermal barrier coatings (TBCs) for low-temperature systems, reducing thermal losses. The objective of this research project is the development of highly amorphous, iron-based coatings. For this purpose, amorphous feedstock materials with different chromium contents have been developed and characterized regarding their microstructures, phase compositions, crystallization temperatures and amorphous content. The results show that the amorphous content is reduced with increasing particle size and chromium content. The coatings were deposited by air plasma spraying (APS) and high-velocity oxygen fuel spraying (HVOF). It is shown that all coatings exhibit amorphous structures. HVOF coatings show a smaller amount of amorphous content compared to the feedstock materials, indicating crystallization occurring in not fully melted particles or insufficient rapid cooling. The APS process can increase the amount of amorphous content compared to the feedstock material, as shown for x Cr = 15%. All coatings proof good thermal shock behavior. Lowest thermal diffusivity values were determined for APS coatings, which confirms the potential of iron-based TBCs.

  16. Investigation of Amorphous/Nanocrystalline Iron-Based Thermal Barrier Coatings

    Science.gov (United States)

    Bobzin, K.; Öte, M.; Königstein, T.

    2017-01-01

    Because of their favorable thermophysical properties, good machinability and low material costs, iron-based coatings which exhibit a highly amorphous/nanocrystalline microstructure are currently in the focus of research. Considering the crystallization temperature of the material, iron-based coatings might be the next generation of thermal barrier coatings (TBCs) for low-temperature systems, reducing thermal losses. The objective of this research project is the development of highly amorphous, iron-based coatings. For this purpose, amorphous feedstock materials with different chromium contents have been developed and characterized regarding their microstructures, phase compositions, crystallization temperatures and amorphous content. The results show that the amorphous content is reduced with increasing particle size and chromium content. The coatings were deposited by air plasma spraying (APS) and high-velocity oxygen fuel spraying (HVOF). It is shown that all coatings exhibit amorphous structures. HVOF coatings show a smaller amount of amorphous content compared to the feedstock materials, indicating crystallization occurring in not fully melted particles or insufficient rapid cooling. The APS process can increase the amount of amorphous content compared to the feedstock material, as shown for x Cr = 15%. All coatings proof good thermal shock behavior. Lowest thermal diffusivity values were determined for APS coatings, which confirms the potential of iron-based TBCs.

  17. High resistivity iron-based, thermally stable magnetic material for on-chip integrated inductors

    Energy Technology Data Exchange (ETDEWEB)

    Deligianni, Hariklia; Gallagher, William J.; Mason, Maurice; O' Sullivan, Eugene J.; Romankiw, Lubomyr T.; Wang, Naigang

    2017-03-07

    An on-chip magnetic structure includes a palladium activated seed layer and a substantially amorphous magnetic material disposed onto the palladium activated seed layer. The substantially amorphous magnetic material includes nickel in a range from about 50 to about 80 atomic % (at. %) based on the total number of atoms of the magnetic material, iron in a range from about 10 to about 50 at. % based on the total number of atoms of the magnetic material, and phosphorous in a range from about 0.1 to about 30 at. % based on the total number of atoms of the magnetic material. The magnetic material can include boron in a range from about 0.1 to about 5 at. % based on the total number of atoms of the magnetic material.

  18. Combatting Pilot Attrition in the USAF in the 1990s

    Science.gov (United States)

    1990-05-01

    PROCESSUS DE BONIFICATION INITIAL INDICATION- INDICATION INITIA.LE 1 The first indication of a problern in a trade 1 . La premiere indication qu’iI...problrme. II ne ments dramatically if the attrition rate is still servirait rien d’accdldrer le recrutement d’une unusually high due to a basic...overstated? In the case of sont-elles exagdrdes? En cas de difficultds de the hard to recruit or train, is the overall require recrutement ou de formation

  19. Who Leaves? Teacher Attrition and Student Achievement. NBER Working Paper No. 14022

    Science.gov (United States)

    Boyd, Donald; Grossman, Pam; Lankford, Hamilton; Loeb, Susanna; Wyckoff, James

    2008-01-01

    Almost a quarter of entering public-school teachers leave teaching within their first three years. High attrition would be particularly problematic if those leaving were the more able teachers. The goal of this paper is estimate the extent to which there is differential attrition based on teachers' value-added to student achievement. Using data…

  20. Attrition in Developmental Psychology: A Review of Modern Missing Data Reporting and Practices

    Science.gov (United States)

    Nicholson, Jody S.; Deboeck, Pascal R.; Howard, Waylon

    2017-01-01

    Inherent in applied developmental sciences is the threat to validity and generalizability due to missing data as a result of participant drop-out. The current paper provides an overview of how attrition should be reported, which tests can examine the potential of bias due to attrition (e.g., t-tests, logistic regression, Little's MCAR test,…

  1. Spiritual Practices as a Means of Coping with and Ameliorating Stress to Reduce Teacher Attrition

    Science.gov (United States)

    Hartwick, James M. M.; Kang, Shin Ji

    2013-01-01

    Teacher attrition has been a serious problem in maintaining quality education in the United States. Although the research produced extensive documentation on teachers' stress and attrition, little attention has been paid to their spiritual stress coping strategies. This article documents various spiritual practices as a means of coping with…

  2. Characterization of Nanocrystalline Aluminum Alloy 5083 Powders Produced by Cryogenic Attrition

    Science.gov (United States)

    2014-11-01

    Characterization of Nanocrystalline Aluminum Alloy 5083 Powders Produced by Cryogenic Attrition by Tiffany Ngo ARL-TN-0643...November 2014 Characterization of Nanocrystalline Aluminum Alloy 5083 Powders Produced by Cryogenic Attrition Tiffany Ngo Weapons and... Materials Research Directorate, ARL Approved for public release; distribution is unlimited

  3. Understanding attrition from international Internet health interventions: a step towards global eHealth.

    Science.gov (United States)

    Geraghty, Adam W A; Torres, Leandro D; Leykin, Yan; Pérez-Stable, Eliseo J; Muñoz, Ricardo F

    2013-09-01

    Worldwide automated Internet health interventions have the potential to greatly reduce health disparities. High attrition from automated Internet interventions is ubiquitous, and presents a challenge in the evaluation of their effectiveness. Our objective was to evaluate variables hypothesized to be related to attrition, by modeling predictors of attrition in a secondary data analysis of two cohorts of an international, dual language (English and Spanish) Internet smoking cessation intervention. The two cohorts were identical except for the approach to follow-up (FU): one cohort employed only fully automated FU (n = 16 430), while the other cohort also used 'live' contact conditional upon initial non-response (n = 1000). Attrition rates were 48.1 and 10.8% for the automated FU and live FU cohorts, respectively. Significant attrition predictors in the automated FU cohort included higher levels of nicotine dependency, lower education, lower quitting confidence and receiving more contact emails. Participants' younger age was the sole predictor of attrition in the live FU cohort. While research on large-scale deployment of Internet interventions is at an early stage, this study demonstrates that differences in attrition from trials on this scale are (i) systematic and predictable and (ii) can largely be eliminated by live FU efforts. In fully automated trials, targeting the predictors we identify may reduce attrition, a necessary precursor to effective behavioral Internet interventions that can be accessed globally.

  4. Second/Foreign Language Teacher Efficacy and Its Relationship to Professional Attrition

    Science.gov (United States)

    Swanson, Peter

    2012-01-01

    There is a shortage of second/foreign language (S/FL) teachers in many parts of the world and the attrition rates are startling. The present study, grounded in social cognitive theory, investigates Canadian and US teachers' (N = 1065) sense of efficacy in teaching languages as it relates to teacher attrition. Findings indicate that S/FL teachers…

  5. Differential Effects of Language Attrition in the Domains of Verb Placement and Object Expression

    Science.gov (United States)

    Flores, Cristina

    2012-01-01

    This study investigates the differential effects of language attrition in two diverse linguistic domains: verb placement and object expression. Linguistic phenomena at the syntax--discourse interface, such as object expression, have been shown to be more vulnerable to attrition than narrow syntax properties, such as verb placement. This study aims…

  6. Who Will Stay and Who Will Leave? Predicting Secondary English Teacher Attrition Risk

    Science.gov (United States)

    Hancock, Carl B.; Scherff, Lisa

    2010-01-01

    Although there are considerable large-scale data on teacher attrition, few researchers have culled information specifically related to English teachers' risk for attrition. This study examines the effects of teacher characteristics, teaching conditions, student variables, self-efficacy, external support, and salary on secondary English language…

  7. Brain Bases for First Language Lexical Attrition in Bengali-English Speakers

    Science.gov (United States)

    Datta, Hia

    2010-01-01

    Change of first language (L1) status from the most stable language to a less accessible language over the life-span of a bilingual individual is termed "language attrition". Such a shift in ease of L1 access has been reported to affect the lexicon (Pelc, 2001) more than other aspects of language. However, whether L1 attrition is affected by…

  8. Variables in Second Language Attrition: Advancing the State of the Art

    Science.gov (United States)

    Bardovi-Harlig, Kathleen; Stringer, David

    2010-01-01

    This article provides a comprehensive synthesis of research on language attrition to date, with a view to establishing a theoretically sound basis for future research in the domain of second language (L2) attrition. We identify the variables that must be tracked in populations who experience language loss, and we develop a general model for the…

  9. Language Aptitude in First Language Attrition: A Study on Late Spanish-Swedish Bilinguals

    Science.gov (United States)

    Bylund, Emanuel; Ramírez-Galan, Pedro

    2016-01-01

    Language aptitude remains one of the most understudied predictor variables in L1 attrition research. The current study seeks to address this gap by investigating the effects of language aptitude on L1 retention in late attriters. Forty L1 Spanish-L2 Swedish bilinguals living in Sweden participated in the study, along with 20 functionally…

  10. Study of Attrition Documentation at the U.S. Navy Recruit Training Command

    Science.gov (United States)

    2006-03-01

    personality disorder ; 7.6 million (3.6 percent) had antisocial personality disorder ; 6.5 million (3.1 percent) had schizoid ... Disorders Mental Retardation Paranoid Personality Disorder Narcissistic Personality Disorder Schizoid Personality Disorder Avoidant Personality ...documenting attrition. The specific reasons for psychiatric attrition include the following: Personality Disorder , Adjustment

  11. The Cost of College Attrition at Four-Year Colleges & Universities. Policy Perspectives

    Science.gov (United States)

    Raisman, Neal

    2013-01-01

    This report, an analysis of 1669 U.S. institutions, is a first-time study of the relationship of attrition to revenues lost in four-year public, private, and for-profit colleges and universities on an annual basis. The report is the result of a study investigating the financial impact of attrition on four-year colleges and universities. Other…

  12. Impact of a Spiral Organic Curriculum on Student Attrition and Learning

    Science.gov (United States)

    Grove, Nathaniel P.; Hershberger, James W.; Bretz, Stacey Lowery

    2008-01-01

    At Miami University, the attrition rate in the year-long organic chemistry sequence for pre-medical majors typically ranges from 30-50%. To decrease attrition, the Department of Chemistry and Biochemistry developed an innovative, spiral curriculum. Unlike a traditional organic chemistry course that moves sequentially through the material, the…

  13. Plenary address: Aging attriters : How methodological challenges can help construct bilingual theories

    NARCIS (Netherlands)

    Keijzer, Merel

    2016-01-01

    (First) language attrition has long established itself as a subfield of the broader realm of bilingualism studies. As such, it can feed off well-researched bilingualism constructs such as transfer, and (bi)directional language interference. But attrition can itself also feed back into bilingual theo

  14. Can I use a Panel? Panel Conditioning and Attrition Bias in Panel Surveys

    NARCIS (Netherlands)

    Das, J.W.M.; Toepoel, V.; van Soest, A.H.O.

    2007-01-01

    Over the past decades there has been an increasing use of panel surveys at the household or individual level, instead of using independent cross-sections. Panel data have important advantages, but there are also two potential drawbacks: attrition bias and panel conditioning effects. Attrition bias c

  15. From emigrant to expat : Changed perspectives on first language attrition in a digital era

    NARCIS (Netherlands)

    Keijzer, Merel

    2015-01-01

    L1 attrition is the (partial) language loss that is found in healthy individuals who stop routinely using their L1 after moving to an L2 environment. Over the years, the phenomenon has attracted much interest, from the general public who have (directly and indirectly) experienced attrition, but also

  16. Cumulative stress in research animals: Telomere attrition as a biomarker in a welfare context?

    Science.gov (United States)

    Bateson, Melissa

    2016-02-01

    Progress in improving animal welfare is currently limited by the lack of objective methods for assessing lifetime experience. I propose that telomere attrition, a cellular biomarker of biological age, provides a molecular measure of cumulative experience that could be used to assess the welfare impact of husbandry regimes and/or experimental procedures on non-human animals. I review evidence from humans that telomere attrition is accelerated by negative experiences in a cumulative and dose-dependent manner, but that this attrition can be mitigated or even reversed by positive life-style interventions. Evidence from non-human animals suggests that despite some specific differences in telomere biology, stress-induced telomere attrition is a robust phenomenon, occurring in a range of species including mice and chickens. I conclude that telomere attrition apparently integrates positive and negative experience in an accessible common currency that translates readily to novel species--the Holy Grail of a cumulative welfare indicator.

  17. Carbon attrition during the circulating fluidized bed combustion of a waste-derived fuel

    Energy Technology Data Exchange (ETDEWEB)

    Arena, U. [Consiglio Nazionale delle Ricerche, Naples (Italy). Inst. for Combustion Research; Naples Univ. (Italy). Dept. of Environmental Sciences; Mastellone, M.L. [Naples Univ. Federico II (Italy). Dept. of Chemical Engineering

    1999-07-01

    A biomass obtained as residue from food manufacturing of pine nuts was batchwise fed in a laboratory scale circulating fluidized bed combustor. The apparatus was operated under both inert and oxidizing conditions in order to establish the relative importance of purely mechanical attrition and combustion-assisted attrition in generating carbon fines. For each run, carbon load and carbon particle size distribution in the riser and rates of attrited carbon fines escaping from the combustor were determined as a function of time. A parallel investigation was carried out with a bubbling fluidized bed combustor in order to point out peculiarities of attrition in the two apparatus. Results were compared with those obtained by burning in the same combustor a bituminous coal and a packaging-derived fuel, obtained from monomaterial collections of polyethylene terephtalate bottles. A different attrition phenomenology was found for each fuel and its peculiar features were taken into account. (orig.)

  18. "Die Muttersprache Vergisst Man Nicht"--or Do You? A Case Study in L1 Attrition and Its (Partial) Reversal

    Science.gov (United States)

    Stolberg, Doris; Munch, Alexandra

    2010-01-01

    Is it possible to undo or reverse language attrition? In other words, has there been, in the case of attrition, a permanent change with respect to the speaker's L1 knowledge, or do we only see temporary effects on the control of that knowledge? It is proposed here that the concept of attrition should include the temporary loss of language skills…

  19. Attrition of Canadian Internet pharmacy websites: what are the implications?

    Science.gov (United States)

    Veronin, Michael A; Clancy, Kristen M

    2013-01-01

    Background The unavailability of Internet pharmacy websites may impact a consumer’s drug purchases and health care. Objective To address the issue of attrition, a defined set of Canadian Internet pharmacy websites was examined at three separate time intervals. Methods In February to March 2006, 117 distinct, fully functional “Canadian Internet pharmacy” websites were located using the advanced search options of Google and the uniform resource locator (URL) for each website was recorded. To determine website attrition, each of the 117 websites obtained and recorded from the previous study was revisited at two later periods of time within a 4-year period. Results After approximately 4 years and 5 months, only 59 (50.4%) sites were found in the original state. Thirty-four sites (29.1%) had moved to a new URL address and were not functioning as the original Internet pharmacy. For 24 sites (20.5%) the viewer was redirected to another Canadian Internet pharmacy site. Conclusion Of concern for patients if Internet pharmacy sites were suddenly inaccessible would be the disruption of continuity of care. PMID:23983491

  20. Penetrating a wall of introspection: a critical attrition analysis

    Science.gov (United States)

    Johannsen, Bjørn Friis; Rump, Camilla Østerberg; Linder, Cedric

    2013-03-01

    This paper presents a critical analysis of student discourse on attrition as it unfolds in interviews on early departure from higher education. A synthesis of relevant studies and modelling done in the field shows that essential aspects affecting attrition and retention can be effectively conceptualized and acted upon in terms of the interplay between student and institution. These aspects were used in combination with James Gee's notion of Discourse models to design a unique framing for interpretation of interviews aimed at bringing out new causal dynamics that lie in this interplay. To illustrate this interpretation, Aristotle's notion of four causes is used. The analysis presented is a study of interviews with seven former physics students about their early departure. This framing of the analysis was necessary because the students' description of how they understood their actions did not explicitly reveal interplay between student and institution. These details lay behind a `wall of introspection' that otherwise posed a serious challenge to the use of student testimony as direct means to identify and address issues of early departure. The results are used to discuss research implications.

  1. The network of corporate clients: customer attrition at commercial banks

    Science.gov (United States)

    Lublóy, Á.; Szenes, M.

    2008-12-01

    Commercial banks might profit from the adoption of methods widely used in network theory. A decision making process might become biased if one disregards network effects within the corporate client portfolio. This paper models the phenomenon of customer attrition by generating a weighted and directed network of corporate clients linked by financial transactions. During the numerical study of the agent-based toy model we demonstrate that multiple steady states may exist. The statistical properties of the distinct steady states show similarities. We show that most companies of the same community choose the same bank in the steady state. In contrast to the case for the steady state of the Barabási-Albert network, market shares in this model equalize by network size. When modeling customer attrition in the network of 3 × 105 corporate clients, none of the companies followed the behavior of the initial switcher in three quarters of the simulations. The number of switchers exceeded 20 in 1% of the cases. In the worst-case scenario a total of 688 companies chose a competitor bank. Significant network effects have been discovered; high correlation prevailed between the degree of the initial switcher and the severity of the avalanche effect. This suggests that the position of the corporate client in the network might be much more important than the underlying properties (industry, size, profitability, etc) of the company.

  2. Mining Rare Events Data for Assessing Customer Attrition Risk

    Science.gov (United States)

    Au, Tom; Chin, Meei-Ling Ivy; Ma, Guangqin

    Customer attrition refers to the phenomenon whereby a customer leaves a service provider. As competition intensifies, preventing customers from leaving is a major challenge to many businesses such as telecom service providers. Research has shown that retaining existing customers is more profitable than acquiring new customers due primarily to savings on acquisition costs, the higher volume of service consumption, and customer referrals. For a large enterprise, its customer base consists of tens of millions service subscribers, more often the events, such as switching to competitors or canceling services are large in absolute number, but rare in percentage, far less than 5%. Based on a simple random sample, popular statistical procedures, such as logistic regression, tree-based method and neural network, can sharply underestimate the probability of rare events, and often result a null model (no significant predictors). To improve efficiency and accuracy for event probability estimation, a case-based data collection technique is then considered. A case-based sample is formed by taking all available events and a small, but representative fraction of nonevents from a dataset of interest. In this article we showed a consistent prior correction method for events probability estimation and demonstrated the performance of the above data collection techniques in predicting customer attrition with actual telecommunications data.

  3. Magnetic Lifshitz transition and its consequences in multi-band iron-based superconductors

    Science.gov (United States)

    Ptok, Andrzej; Kapcia, Konrad J.; Cichy, Agnieszka; Oleś, Andrzej M.; Piekarz, Przemysław

    2017-01-01

    In this paper we address Lifshitz transition induced by applied external magnetic field in a case of iron-based superconductors, in which a difference between the Fermi level and the edges of the bands is relatively small. We introduce and investigate a two-band model with intra-band pairing in the relevant parameters regime to address a generic behaviour of a system with hole-like and electron-like bands in external magnetic field. Our results show that two Lifshitz transitions can develop in analysed systems and the first one occurs in the superconducting phase and takes place at approximately constant magnetic field. The chosen sets of the model parameters can describe characteristic band structure of iron-based superconductors and thus the obtained results can explain the experimental observations in FeSe and Co-doped BaFe2As2 compounds. PMID:28165043

  4. Ab-initio electronic structure method for substitutional disorder applied to iron-based superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Herbig, Alexander

    2016-02-12

    An ab-initio electronic structure method for substitutionally disordered real materials is developed within a pseudopotential density functional theory approach. The method is validated against exact diagonalization and for simple disordered CuZn alloys. The developed method is applied to iron-based superconductors. In particular, band renormalization effects due to various chemical substitutions in BaFe{sub 2}As{sub 2} are investigated and their Cooper pair breaking effects are compared.

  5. Synthesis and characterization of homogeneous interstitial solutions of nitrogen and carbon in iron-based lattices

    DEFF Research Database (Denmark)

    Brink, Bastian Klüge

    work in synthesis and characterization of interstitial solutions ofnitrogen and carbon in iron-based lattices. In order to avoid the influences of gradients incomposition and residual stresses, which are typically found in treated surface layers,homogenous samples are needed. These were prepared from...... pure iron or austeniticstainless steel using gaseous mixtures of ammonia, hydrogen, acetylene and propene atelevated temperatures.Structural and magnetic properties have been characterized with neutron diffraction,vibrating sample magnetometry and Mössbauer spectroscopy. Thermal expansion...

  6. Effect of external magnetic field on the coexistence of SC and AFM in iron based superconductors

    Science.gov (United States)

    Goi, S. K.; Pradhan, B.; Behera, Srikanta; Parida, P. K.; Mishra, R. N.

    2017-03-01

    We have studied the interplay of antiferromagnetism and superconductivity in presence of an applied external magnetic field for the iron based superconductors. For the purpose we have proposed a model Hamiltonian and solved it self-consistently by using the Zubarev's technique of double time Green's function technique. The self-consistent gap equations are solved numerically and interpreted the gap values from the of density of states plots.

  7. Stabilizing the spin vortex crystal phase in two-dimensional iron-based superconductors

    Science.gov (United States)

    O'Halloran, Joseph; Agterberg, D. F.; Chen, M. X.; Weinert, M.

    2017-02-01

    We present an investigation of the magnetic structure for iron-based superconductors (FeSCs) when inversion symmetry is broken, such as in substrate-supported monolayers or in the presence of a c -axis electric field. We perform group-, mean-field-, and density-functional-theoretic analyses on a model system of monolayer iron selenide (FeSe) on a strontium titanate [SrTiO3 (001)] substrate. Our group- and mean-field-theoretic calculations are more generally applicable to thin films of the rest of the 11 (e.g., FeSe) family of iron-based superconductors, as well as to thin films of the 111 (e.g., LiFeAs) and 1111 (e.g., LaOFeAs) families, as these all belong to the same space group. We find that in systems with a collinear antiferromagnetic phase in bulk, when inversion symmetry is broken, the transition is instead into a "spin vortex crystal" phase and that a further phase transition can occur at a lower temperature in some circumstances. The spin vortex crystal is a C4-symmetric magnetic phase which is related to this parent C2-symmetric collinear antiferromagnetic (stripe) phase which is ubiquitous among the iron-based superconductors.

  8. Health workforce attrition in the public sector in Kenya: a look at the reasons

    Directory of Open Access Journals (Sweden)

    Muchiri Stephen

    2009-07-01

    Full Text Available Abstract Background Kenya, like many other countries in sub-Saharan Africa, has been affected by shortages of health workers in the public sector. Data on the rates and leading reasons for health workers attrition in the public sector are key in developing effective, evidence-based planning and policy on human resources for health. Methods This study analysed data from a human resources health facility survey conducted in 2005 in 52 health centres and 22 public hospitals (including all provincial hospitals across all eight provinces in Kenya. The study looked into the status of attrition rates and the proportion of attrition due to retirement, resignation or death among doctors, clinical officers, nurses and laboratory and pharmacy specialists in surveyed facilities. Results Overall health workers attrition rates from 2004 to 2005 were similar across type of health facility: provincial hospitals lost on average 4% of their health workers, compared to 3% for district hospitals and 5% for health centres. However, there are differences in the patterns of attrition rates by cadre. Attrition among doctors and registered nurses was much higher at the provincial hospitals than at district hospitals or health centres, whereas the opposite pattern was observed for laboratory and pharmacy staff (lost at a higher rate in lower-level facilities. In provincial hospitals, doctors had higher attrition rates than clinical officers, and registered nurses had higher attrition rates than enrolled nurses. In contrast, attrition of enrolled and registered nurses in district hospitals and health centres was similar. The main reason for health worker attrition (all cadres combined at each level of facility was retirement, followed by resignation and death. However, resignation drives attrition among doctors and clinical officers; retirement accounts for the main share of attrition among nurses and pharmacy staff; and death is the primary reason for attrition among

  9. Laboratory comparison of four iron-based filter materials for drainage water phosphate treatment.

    Science.gov (United States)

    Allred, Barry J; Racharaks, Ratanachat

    2014-09-01

    A laboratory investigation evaluated phosphate (PO4(3-)) drainage water treatment capabilities of four iron-based filter materials. The iron-based filter materials tested were zero-valent iron (ZVI), porous iron composite (PIC), sulfur modified iron (SMI), and iron oxide/ hydroxide (IOH). Only filter material retained on a 60-mesh sieve (> 0.25 mm) was used for evaluation. The laboratory investigation included saturated falling-head hydraulic conductivity tests, contaminant removal or desorption/dissolution batch tests, and low-to-high flow rate saturated solute transport column tests. Each of the four iron-based filter materials have sufficient water flow capacity as indicated by saturated hydraulic conductivity values that in most cases were greater than 1 x 10(-2) cm/s. For the 1, 10, and 100 ppm PO4(3-)-P contaminant removal batch tests, each of the four iron-based filter materials removed at least 95% of the PO4(3-)-P originally present. However, for the 1000 ppm PO4(3-)-P contaminant removal batch tests, IOH by far exhibited the greatest removal effectiveness (99% PO4(3-)-P removal), followed by SMI (72% PO4(3-)-P removal), then ZVI (62% PO4(3-)-P removal), and finally PIC (15% PO4(3-)-P removal). The desorption/dissolution batch test results, especially with respect to SMI and IOH, indicate that once PO4(3-) is adsorbed/precipitated onto surfaces of iron-based filter material particles, this PO4(3-) becomes fixed and is then not readily desorbed/dissolved back into solution. The results from the column tests showed that regardless of low or high flow rate (contact time ranged from a few hours to a few minutes) and PO4(3-) concentration (1 ppm or 10 ppm PO4(3-)-P), PIC, SMI, and IOH reduced PO4(3-)-P concentrations to below detection limits, while ZVI removed at least 90% of the influent PO4(3-)-P. Consequently, these laboratory results indicate that the ZVI, PIC, SMI, and IOH filter materials all exhibit promise for phosphate drainage water treatment.

  10. 热处理对铁基复合材料性能的影响%Effects of Heat Treatment on Properties of Iron-based Composite Materials

    Institute of Scientific and Technical Information of China (English)

    孙凯; 安宁; 付拴拴; 贺一为

    2012-01-01

    为了提高铁基表面复合材料的使用寿命,使其具有较高的表面硬度和耐磨性的同时,使其心部具有较好的塑性和韧性.本实验对铁基复合材料的热处理工艺进行了研究.结果表明:在980℃油淬保温2h加上200℃回火4h的热处理工艺下可以使基体组织得到了进一步强化,基体硬度可提高9%,韧性提高11%;而热处理对复合硬化层的硬度基本没有影响.%In order to improve the life of composite material on iron-based surface, with a high surface hardness and wear resistance, good plasticity and toughness, effects of heat treatment process on iron-based composite materials were studied. The results show that: after oil quenched at 980 ℃ , 180 ℃, tempered 4 h at 200 ℃, the matrix structure is strengthened, the hardness increases by 9%, and toughness increases by 11%. Heat treatment has no effects on the hardness of composite layer.

  11. Thermodynamic study and modelling of iron-based melts for adequate prediction of modern ladle metallurgy processes

    Science.gov (United States)

    Zaitsev, A. I.; Rodionova, I. G.; Shaposhnikov, N. G.; Zemlyanko, O. A.; Karamisheva, N. A.

    2008-02-01

    The representation of iron-based melts as associated liquids have been developed basing on the detail experimental investigation and analysis of available data on their thermodynamic properties and phase equilibria. It has allowed, for the first time, to interpret adequately the reactivity of the earth metals in the iron-based melts and to predict with high precision the reactions of metal refinement and non-metallic inclusions modifying in modern ladle metallurgy.

  12. Realization and Application of Customer Attrition Early Warning Model in Security Company

    Directory of Open Access Journals (Sweden)

    Shen Yizhen

    2012-09-01

    Full Text Available In this paper, we propose the customer attrition early warning model based on data warehouse and data mining technologies, which is achieved and applied in our security company. The modeling variables can be selected by means of the combination with decision tree and the gradual regression in Logistic regression. Then customer attrition early warning model can be constructed based on Logistic regression. The results show that the model can strongly promote the customer attrition capturing rate, push on the building of the company customer marketing management and customer service management organization, and economize the marketing cost. The company profits promotion and trade competitive power can be promised.

  13. Telomere attrition in beta and alpha cells with age.

    Science.gov (United States)

    Tamura, Yoshiaki; Izumiyama-Shimomura, Naotaka; Kimbara, Yoshiyuki; Nakamura, Ken-Ichi; Ishikawa, Naoshi; Aida, Junko; Chiba, Yuko; Matsuda, Yoko; Mori, Seijiro; Arai, Tomio; Fujiwara, Mutsunori; Poon, Steven S S; Ishizaki, Tatsuro; Araki, Atsushi; Takubo, Kaiyo; Ito, Hideki

    2016-06-01

    We have reported telomere attrition in β and α cells of the pancreas in elderly patients with type 2 diabetes, but it has not been explored how the telomere lengths of these islet cells change according to age in normal subjects. To examine the telomere lengths of β and α cells in individuals without diabetes across a wide range of ages, we conducted measurement of the telomere lengths of human pancreatic β and α cells obtained from 104 autopsied subjects without diabetes ranging in age from 0 to 100 years. As an index of telomere lengths, the normalized telomere-centromere ratio (NTCR) was determined for β (NTCRβ) and α (NTCRα) cells by quantitative fluorescence in situ hybridization (Q-FISH). We found NTCRβ and NTCRα showed almost the same levels and both decreased according to age (p telomeres of β and α cells become shortened with normal aging process.

  14. Disorder-promoted C4-symmetric magnetic order in iron-based superconductors

    Science.gov (United States)

    Hoyer, Mareike; Fernandes, Rafael M.; Levchenko, Alex; Schmalian, Jörg

    2016-04-01

    In most iron-based superconductors, the transition to the magnetically ordered state is closely linked to a lowering of structural symmetry from tetragonal (C4) to orthorhombic (C2). However, recently, a regime of C4-symmetric magnetic order has been reported in certain hole-doped iron-based superconductors. This novel magnetic ground state can be understood as a double-Q spin density wave characterized by two order parameters M1 and M2 related to each of the two Q vectors. Depending on the relative orientations of the order parameters, either a noncollinear spin-vortex crystal or a nonuniform charge-spin density wave could form. Experimentally, Mössbauer spectroscopy, neutron scattering, and muon spin rotation established the latter as the magnetic configuration of some of these optimally hole-doped iron-based superconductors. Theoretically, low-energy itinerant models do support a transition from single-Q to double-Q magnetic order, but with nearly degenerate spin-vortex crystal and charge-spin density wave states. In fact, extensions of these low-energy models including additional electronic interactions tip the balance in favor of the spin-vortex crystal, in apparent contradiction with the recent experimental findings. In this paper we revisit the phase diagram of magnetic ground states of low-energy multiband models in the presence of weak disorder. We show that impurity scattering not only promotes the transition from C2 to C4-magnetic order, but it also favors the charge-spin density wave over the spin-vortex crystal phase. Additionally, in the single-Q phase, our analysis of the nematic coupling constant in the presence of disorder supports the experimental finding that the splitting between the structural and stripe-magnetic transition is enhanced by disorder.

  15. Achievement and Attrition Rate Differences between Traditional and Internet-Based Beginning Spanish Courses.

    Science.gov (United States)

    Despain, J. Scott

    2003-01-01

    Describes a 2.5 year study on the achievement and attrition ate differences between a beginning university-level Spanish course delivered in the classroom and the same course taught over the Internet. Results are discussed. (Author/VWL)

  16. Mechanistic Based DEM Simulation of Particle Attrition in a Jet Cup

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Wei; DeCroix, David; Sun, Xin

    2014-02-01

    The attrition of particles is a major industrial concern in many fluidization systems as it can have undesired effects on the product quality and on the reliable operation of process equipment. Therefore, to accomodate the screening and selection of catalysts for a specific process in fluidized beds, risers, or cyclone applications, their attrition propensity is usually estimated through jet cup attrition testing, where the test material is subjected to high gas velocities in a jet cup. However, this method is far from perfect despite its popularity, largely due to its inconsistency in different testing set-ups. In order to better understand the jet cup testing results as well as their sensitivity to different operating conditions, a coupled computational fluid dynamic (CFD) - discrete element method (DEM) model has been developed in the current study to investigate the particle attrition in a jet cup and its dependence on various factors, e.g. jet velocity, initial particle size, particle density, and apparatus geometry.

  17. Aligned carbon nanotubes catalytically grown on iron-based nanoparticles obtained by laser-induced CVD

    OpenAIRE

    Le Normand, Francois; Cojocaru, Costel Sorin; Ersen, Ovidiu; Legagneux, Pierre; Gangloff, Laurent; Fleaca, C.; Alexandrescu, Rodica; Dumitrache, Florin; Morjan, Ion

    2007-01-01

    International audience; Iron-based nanoparticles are prepared by a laser-induced chemical vapor deposition (CVD) process. They are characterized as body-centered Fe and Fe2O3 (maghemite/magnetite) particles with sizes ::;5 and 10 nm, respectively. The Fe particles are embedded in a protective carbon matrix. Both kind of particles are dispersed by spin-coating on SiO2/Si(1 0 0) flat substrates. They are used as catalyst to grow carbon nanotubes by a plasma- and filaments-assisted catalytic CVD...

  18. Use of iron-based technologies in contaminated land and groundwater remediation: A review

    Energy Technology Data Exchange (ETDEWEB)

    Cundy, Andrew B. [School of Environment and Technology, University of Brighton, Lewes Road, Brighton BN2 4GJ (United Kingdom)], E-mail: A.Cundy@brighton.ac.uk; Hopkinson, Laurence [School of Environment and Technology, University of Brighton, Lewes Road, Brighton BN2 4GJ (United Kingdom); Whitby, Raymond L.D. [School of Pharmacy and Biomolecular Sciences, University of Brighton, Lewes Road, Brighton BN2 4GJ (United Kingdom)

    2008-08-01

    Reactions involving iron play a major role in the environmental cycling of a wide range of important organic, inorganic and radioactive contaminants. Consequently, a range of environmental clean-up technologies have been proposed or developed which utilise iron chemistry to remediate contaminated land and surface and subsurface waters, e.g. the use of injected zero zero-valent iron nanoparticles to remediate organic contaminant plumes; the generation of iron oxyhydroxide-based substrates for arsenic removal from contaminated waters; etc. This paper reviews some of the latest iron-based technologies in contaminated land and groundwater remediation, their current state of development, and their potential applications and limitations.

  19. Fatigue Life Prediction of Ductile Iron Based on DE-SVM Algorithm

    Science.gov (United States)

    Yiqun, Ma; Xiaoping, Wang; lun, An

    the model, predicting fatigue life of ductile iron, based on SVM (Support Vector Machine, SVM) has been established. For it is easy to fall into local optimum during parameter optimization of SVM, DE (Differential Evolution algorithm, DE) algorithm was adopted to optimize to improve prediction precision. Fatigue life of ductile iron is predicted combining with concrete examples, and simulation experiment to optimize SVM is conducted adopting GA (Genetic Algorithm), ACO (Ant Colony Optimization) and POS (Partial Swarm Optimization). Results reveal that DE-SVM algorithm is of a better prediction performance.

  20. Contribution to the Study of the Relation between Microstructure and Electrochemical Behavior of Iron-Based FeCoC Ternary Alloys

    Directory of Open Access Journals (Sweden)

    Farida Benhalla-Haddad

    2012-01-01

    Full Text Available This work deals with the relation between microstructure and electrochemical behavior of four iron-based FeCoC ternary alloys. First, the arc-melted studied alloys were characterized using differential thermal analyses and scanning electron microscopy. The established solidification sequences of these alloys show the presence of two primary crystallization phases (δ(Fe and graphite as well as two univariante lines : peritectic L+(Fe↔(Fe and eutectic L↔(Fe+Cgraphite. The ternary alloys were thereafter studied in nondeaerated solution of 10−3 M NaHCO3 + 10−3 M Na2SO4, at 25°C, by means of the potentiodynamic technique. The results indicate that the corrosion resistance of the FeCoC alloys depends on the carbon amount and the morphology of the phases present in the studied alloys.

  1. Analysis of thermoelectric properties of high-temperature complex alloys of nickel-base, iron-base and cobalt-base groups

    Science.gov (United States)

    Holanda, R.

    1984-01-01

    The thermoelectric properties alloys of the nickel-base, iron-base, and cobalt-base groups containing from 1% to 25% 106 chromium were compared and correlated with the following material characteristics: atomic percent of the principle alloy constituent; ratio of concentration of two constituents; alloy physical property (electrical resistivity); alloy phase structure (percent precipitate or percent hardener content); alloy electronic structure (electron concentration). For solid-solution-type alloys the most consistent correlation was obtained with electron concentration, for precipitation-hardenable alloys of the nickel-base superalloy group, the thermoelectric potential correlated with hardener content in the alloy structure. For solid-solution-type alloys, no problems were found with thermoelectric stability to 1000; for precipitation-hardenable alloys, thermoelectric stability was dependent on phase stability. The effects of the compositional range of alloy constituents on temperature measurement uncertainty are discussed.

  2. Characteristics and Trends of Attrition from the United States Naval Academy

    Science.gov (United States)

    2006-06-01

    costs account for about 150% of an employee’s annual salary (Gale, 2002). Previous research has examined attrition associated with “ plebe ” summer; the...indoctrination period for incoming freshmen or plebes (Hollenbach, 2003). Plebe summer is arguably the most difficult time for Plebes during their...Academy career and attrition is expected. Plebe summer is a particularly demanding time for the new Midshipmen and, although they are thoroughly

  3. Predictors of Attrition and Academic Success of Medical Students: A 30-Year Retrospective Study

    OpenAIRE

    Silvija Maslov Kruzicevic; Katarina Josipa Barisic; Adriana Banozic; Carlos David Esteban; Damir Sapunar; Livia Puljak

    2012-01-01

    AIM: To determine attrition and predictors of academic success among medical students at University of Split, Croatia. METHODS: We analysed academic records of 2054 students enrolled during 1979-2008 period. RESULTS: We found that 26% (533/2054) of enrolled students did not graduate. The most common reasons for attrition were 'personal' (36.4%), transfer to another medical school (35.6%), and dismissal due to unsatisfactory academic record (21.2%). Grade point average (GPA) and study duration...

  4. Attrition and success rates of accelerated students in nursing courses: a systematic review

    OpenAIRE

    Doggrell, Sheila Anne; Schaffer, Sally

    2016-01-01

    Background There is a comprehensive literature on the academic outcomes (attrition and success) of students in traditional/baccalaureate nursing programs, but much less is known about the academic outcomes of students in accelerated nursing programs. The aim of this systematic review is to report on the attrition and success rates (either internal examination or NCLEX-RN) of accelerated students, compared to traditional students. Methods For the systematic review, the databases (Pubmed, Cinah...

  5. The impact of attrition on the representativeness of cohort studies of older people

    Directory of Open Access Journals (Sweden)

    Brilleman Samuel L

    2010-08-01

    Full Text Available Abstract Background There are well-established risk factors, such as lower education, for attrition of study participants. Consequently, the representativeness of the cohort in a longitudinal study may deteriorate over time. Death is a common form of attrition in cohort studies of older people. The aim of this paper is to examine the effects of death and other forms of attrition on risk factor prevalence in the study cohort and the target population over time. Methods Differential associations between a risk factor and death and non-death attrition are considered under various hypothetical conditions. Empirical data from the Australian Longitudinal Study on Women's Health (ALSWH for participants born in 1921-26 are used to identify associations which occur in practice, and national cross-sectional data from Australian Censuses and National Health Surveys are used to illustrate the evolution of bias over approximately ten years. Results The hypothetical situations illustrate how death and other attrition can theoretically affect changes in bias over time. Between 1996 and 2008, 28.4% of ALSWH participants died, 16.5% withdrew and 10.4% were lost to follow up. There were differential associations with various risk factors, for example, non-English speaking country of birth was associated with non-death attrition but not death whereas being underweight (body mass index Conclusions Deaths occur in both the target population and study cohort, while other forms of attrition occur only in the study cohort. Therefore non-death attrition may cause greater bias than death in longitudinal studies. However although more than a quarter of the oldest participants in the ALSWH died in the 12 years following recruitment, differences from the national population changed only slightly.

  6. The implications of selective attrition for estimates of intergenerational elasticity of family income

    OpenAIRE

    Schoeni, Robert F.; Wiemers, Emily E.

    2015-01-01

    Numerous studies have estimated a high intergenerational correlation in economic status. Such studies do not typically attend to potential biases that may arise due to survey attrition. Using the Panel Study of Income Dynamics – the data source most commonly used in prior studies – we demonstrate that attrition is particularly high for low-income adult children with low-income parents and particularly low for high-income adult children with high-income parents. Because of this pattern of attr...

  7. Relations between Select21 Predictor Measures and First-Term Attrition

    Science.gov (United States)

    2008-02-01

    Control X X X Interpersonal Skills- Diplomacy X X X Lie Scale X X X Narcissism X X X Peer Leadership X X X 1.76 Respect for Authority X Self - Esteem X X X...attrition, namely Fitness Motivation, Self - Esteem , Army Identification, and Stress Tolerance (see Table 12). For the most part, these scales...top predictors of training attrition in Project First Term (e.g., pre-service fitness, generalized self -efficacy, pre-service positive affect towards

  8. Weight Loss Expectations and Attrition in Treatment-Seeking Obese Women

    Directory of Open Access Journals (Sweden)

    Riccardo Dalle Grave

    2015-10-01

    Full Text Available Objective: The analysis of the relation between weight loss goals and attrition in the treatment of obesity has produced conflicting results. The aim of the present study was to investigate the role of weight loss goals on attrition in a cohort of obese women seeking treatment at 8 Italian medical centres. Methods: 634 women with obesity, consecutively enrolled in weight loss programmes, were included in the study. Weight loss goals were evaluated with the Goals and Relative Weights Questionnaire (GRWQ, reporting a sequence of unrealistic (‘dream' and ‘happy' and more realistic (‘acceptable' and ‘disappointing' weight loss goals. Attrition was assessed at 12 months on the basis of patients' medical records. Results: At 12 months, 205/634 patients (32.3% had interrupted their programme and were lost to follow-up. After adjustment for age, baseline weight, education and employment status, attrition was significantly associated with higher percent acceptable and disappointing weight loss targets, not with dream and happy weight loss. Conclusion: In ‘real world' clinical settings, only realistic expectations might favour attrition whenever too challenging, whereas unrealistic weight loss goals have no effect. Future studies should assess the effect of interventions aimed at coping with too challenging weight goals on attrition.

  9. Nanosized iron based permeable reactive barriers for nitrate removal - Systematic review

    Science.gov (United States)

    Araújo, Rui; Castro, Ana C. Meira; Santos Baptista, João; Fiúza, António

    2016-08-01

    It is unquestionable that an effective decision concerning the usage of a certain environmental clean-up technology should be conveniently supported. Significant amount of scientific work focussing on the reduction of nitrate concentration in drinking water by both metallic iron and nanomaterials and their usage in permeable reactive barriers has been worldwide published over the last two decades. This work aims to present in a systematic review of the most relevant research done on the removal of nitrate from groundwater using nanosized iron based permeable reactive barriers. The research was based on scientific papers published between 2004 and June 2014. It was performed using 16 combinations of keywords in 34 databases, according to PRISMA statement guidelines. Independent reviewers validated the selection criteria. From the 4161 records filtered, 45 met the selection criteria and were selected to be included in this review. This study's outcomes show that the permeable reactive barriers are, indeed, a suitable technology for denitrification and with good performance record but the long-term impact of the use of nanosized zero valent iron in this remediation process, in both on the environment and on the human health, is far to be conveniently known. As a consequence, further work is required on this matter, so that nanosized iron based permeable reactive barriers for the removal of nitrate from drinking water can be genuinely considered an eco-efficient technology.

  10. Study on mechanical properties of warm compacted iron-base materials

    Institute of Scientific and Technical Information of China (English)

    李元元; 倪东惠; 肖志瑜; 张大童; 陈维平

    2002-01-01

    Mechanical properties of the warm compacted iron-base powder metallurgy materials were compared with those of conventional cold compacted materials. Factors such as compaction temperature, lubricant concentration and lubricant′s property were studied. A lubricant for warm compaction powder metallurgy was developed. An iron-based powder metallurgy material with a green density of 7.31 g/cm3 (a relative density of 92.5%) can be obtained by pressing the powder at 700 MPa and 175 ℃. The sintered materials have a density of 7.2 g/cm3, an elongation of 2.1% and a tensile strength of 751 MPa compared to 546 MPa using conventional cold compaction with the same lubricant and 655 MPa using warm compaction with other lubricant. Compact density and mechanical properties were influenced strongly by the compacting temperature. Although the best quality compacts can be obtained at 175 ℃, warm compaction within 165 to 185 ℃ can give high density compacts. Evidence shows that compact density depends on the friction coefficient of the lubricant.

  11. Local destruction of superconductivity by non-magnetic impurities in mesoscopic iron-based superconductors.

    Science.gov (United States)

    Li, Jun; Ji, Min; Schwarz, Tobias; Ke, Xiaoxing; Van Tendeloo, Gustaaf; Yuan, Jie; Pereira, Paulo J; Huang, Ya; Zhang, Gufei; Feng, Hai-Luke; Yuan, Ya-Hua; Hatano, Takeshi; Kleiner, Reinhold; Koelle, Dieter; Chibotaru, Liviu F; Yamaura, Kazunari; Wang, Hua-Bing; Wu, Pei-Heng; Takayama-Muromachi, Eiji; Vanacken, Johan; Moshchalkov, Victor V

    2015-07-03

    The determination of the pairing symmetry is one of the most crucial issues for the iron-based superconductors, for which various scenarios are discussed controversially. Non-magnetic impurity substitution is one of the most promising approaches to address the issue, because the pair-breaking mechanism from the non-magnetic impurities should be different for various models. Previous substitution experiments demonstrated that the non-magnetic zinc can suppress the superconductivity of various iron-based superconductors. Here we demonstrate the local destruction of superconductivity by non-magnetic zinc impurities in Ba0.5K0.5Fe2As2 by exploring phase-slip phenomena in a mesoscopic structure with 119 × 102 nm(2) cross-section. The impurities suppress superconductivity in a three-dimensional 'Swiss cheese'-like pattern with in-plane and out-of-plane characteristic lengths slightly below ∼1.34 nm. This causes the superconducting order parameter to vary along abundant narrow channels with effective cross-section of a few square nanometres. The local destruction of superconductivity can be related to Cooper pair breaking by non-magnetic impurities.

  12. Studies of the gap structure of iron-based superconductors using magnetic penetration depth

    Science.gov (United States)

    Carrington, Antony

    2011-06-01

    This article reviews experiments to determine the structure of the superconducting gap in the iron-based superconductors. It focuses on insights provided by measurements of the temperature dependence of magnetic penetration depth but also discusses the information provided by other measurements especially thermal conductivity. The article includes background theory on the types of gap structure suggested for the iron-based superconductors as well as the general theory of penetration depth in conventional and unconventional superconductors. The effect of impurity scattering on each candidate gap structure is important for the interpretation of data and so will also be discussed. Penetration depth data for single crystals of the following compounds is reviewed: SmFeAsO 0.8F 0.2, FeTe 0.5Se 0.5, LaFePO, KFe 2As 2 and BaFe 2(As 0.67P 0.33) 2 along with discussion on related materials such as K- and Co-doped BaFe 2As 2.

  13. Rapid solidification processing of iron-base alloys for structural applications

    Energy Technology Data Exchange (ETDEWEB)

    Flinn, J.E.

    1991-09-01

    The response of iron-base alloys to rapid solidification is reviewed with an emphasis on the effects of processing on the microstructure and mechanical property behavior. The processing topics addressed are powder atomization, powder consolidation, joining, and thermal-mechanical exposure. The value of rapid solidification processing (RSP) lies in the ability to promote compositional homogeneity and retention of fine and stable (to high temperatures) microstructures. Achieving the maximum benefit from RSP requires proper application of the basic principles of composition control and rapid crystallization. This investigation has disclosed two very important facets of the RSP approach that can be applied using current technologies. Dissociated oxygen appears to play a significant role in stabilizing microstructural features. In conjunction with oxygen, vacancies trapped during crystallization provide a very stable matrix dispersion for enhanced strengthening. With a fundamental understanding of the response of iron-base alloys to RSP, alloys can be designed that will have substantially better properties and performance than their conventionally processed counterparts. 77 refs., 94 figs., 14 tabs.

  14. Softening of the elastic shear mode C{sub 66} in iron-based superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Boehmer, Anna; Burger, Philipp [Karlsruher Institut fuer Technologie, Institut fuer Festkoerperphysik, D-76021 Karlsruhe (Germany); Karlsruher Institut fuer Technologie, Fakultaet fuer Physik, D-76128 Karlsruhe (Germany); Hardy, Frederic; Schweiss, Peter; Fromknecht, Rainer; Wolf, Thomas; Meingast, Christoph [Karlsruher Institut fuer Technologie, Institut fuer Festkoerperphysik, D-76021 Karlsruhe (Germany); Reinecker, Marius; Schranz, Wilfried [Universitaet Wien, Fakultaet fuer Physik, A-1090 Wien, Vienna (Austria)

    2013-07-01

    The structural phase transition of underdoped iron-based superconductors is accompanied by a large softening of the elastic shear mode C{sub 66}, which has attracted considerable attention. This softening has been discussed both in terms of orbital and spin-nematic fluctuations which would be responsible for the structural phase transition and, possibly, superconductivity. However, sample requirements have so far restricted experimental investigations of C{sub 66} (via measurements of the ultrasound velocity) to the Ba(Fe,Co){sub 2}As{sub 2} system. Here, we report on a new technique, based on a three-point bending setup, to probe the Young's modulus of a sample with a capacitance dilatometer. For certain orientations, the Young's modulus is related to the elastic constant C{sub 66} whose effective temperature dependence can be obtained. Platelet-like samples, as frequently encountered for iron-based systems, are easily studied with our setup. Data on several systems are presented and discussed.

  15. Second Language Attrition : Selected Bibliography(English Teaching)

    OpenAIRE

    富山, 真知子; 山本, 貴美枝; トミヤマ, マチコ; ヤマモト, キミエ; Machiko, TOMIYAMA; Kimie, YAMAMOTO

    2002-01-01

    持っていた言語を失う事,すなわち「言語喪失」(language attrition)の現象はさまざまである.病理学的理由による失語症のような場合もあれば,歴史的,政治的,社会的理由による言語の消滅もある.また,自然な状況下でも言語は失われる.授業で習った外国語を使わないでいると忘れてしまうのも,言語喪失の現象の一環である.言語の喪失を,主として心理言語学的な立場から研究するという分野は,1980年にペンシルベニア大学で開催された会議に端を発するが,この20余年来,研究分野も細分化され,研究者も地域的に広がって急速に発展を見せている.本稿は言語喪失の心理言語学的研究の中で,「第二言語喪失」(second language attrition)に焦点を当て,主要な文献をリストしている.心理言語学的な立場から構成されているので,社会学的な文献,例えば「言語の取り替え」(language shift)や「言語の死」(language death)に関するもの,さらに,病理学的なもの,加齢によるものなどは含まれていない.また,心理言語学的なものでも「第一言語の喪失」(first langu...

  16. Pressure-induced superconductivity in the iron-based ladder material BaFe2S3.

    Science.gov (United States)

    Takahashi, Hiroki; Sugimoto, Akira; Nambu, Yusuke; Yamauchi, Touru; Hirata, Yasuyuki; Kawakami, Takateru; Avdeev, Maxim; Matsubayashi, Kazuyuki; Du, Fei; Kawashima, Chizuru; Soeda, Hideto; Nakano, Satoshi; Uwatoko, Yoshiya; Ueda, Yutaka; Sato, Taku J; Ohgushi, Kenya

    2015-10-01

    All the iron-based superconductors identified so far share a square lattice composed of Fe atoms as a common feature, despite having different crystal structures. In copper-based materials, the superconducting phase emerges not only in square-lattice structures but also in ladder structures. Yet iron-based superconductors without a square-lattice motif have not been found, despite being actively sought out. Here, we report the discovery of pressure-induced superconductivity in the iron-based spin-ladder material BaFe2S3, a Mott insulator with striped-type magnetic ordering below ∼120 K. On the application of pressure this compound exhibits a metal-insulator transition at about 11 GPa, followed by the appearance of superconductivity below Tc = 14 K, right after the onset of the metallic phase. Our findings indicate that iron-based ladder compounds represent promising material platforms, in particular for studying the fundamentals of iron-based superconductivity.

  17. A Study of Foreign Language Attrition, English Development and its strategies%外语磨蚀与大学生英语学习发展与策略研究

    Institute of Scientific and Technical Information of China (English)

    谢艳娟; 余小兵; 刘源甫

    2013-01-01

      外语学习的过程带来外语听、说、读、写、译等各项语言技能的渐进式发展,而外语教育结束后的短期或长期近似语言接触空白又会构成语言磨蚀,从而让前期的语言劳动和付出打了折扣。当前,语蚀现象关注总体上处于缺位状态。研究在梳理语蚀研究成果的基础上,对英语磨蚀进行了实证调查和分析,进而为大学英语教和学提出耐磨蚀、抗磨蚀的“教学”策略。%  Foreign language learning boosts progressive development of foreign language skills such as listening,speaking,reading, writing and translation,etc. However,a short or long period of time after the foreign language education ends constitutes a language attrition because there’s no or less language contact for the students. Accordingly the former labor and effort paid for language learning suffer a huge loss. At present,the concern about language attrition is on the whole in the absence of state. Based on the review of previous researches on foreign language attrition,an empirical investigation and analysis of English attrition is carried out,which in turn proposes some attrition-resistant measures for the College English Teaching and Learning.

  18. Against professional advice: treatment attrition among pregnant methamphetamine users

    Directory of Open Access Journals (Sweden)

    Terplan M

    2011-10-01

    Full Text Available Brianna Lindsay1, Jennifer Albrecht1, Mishka Terplan1,21Department of Epidemiology and Public Health, University of Maryland, 2Department of Obstetrics, Gynecology, and Reproductive Science, University of Maryland School of Medicine, Baltimore, MD, USAAbstract: Pregnant methamphetamine users who leave substance use treatment against professional advice may be at risk of poorer health outcomes. To examine the hypothesis that methamphetamine use during pregnancy may be associated with leaving substance use treatment against professional advice, the 2006 Treatment Episode Data Set was analyzed. A logistic regression adjusting for age, race, service setting, prior substance abuse treatment, criminal justice referral, and education was conducted. Inclusion criteria were met by 18,688 pregnant admissions; 26.4% identified methamphetamines as their primary substance of use. Frequency of use was identified as an effect modifier, therefore results were stratified by less than weekly use and weekly or more use. Methamphetamine use was significantly associated with leaving treatment against professional advice regardless of usage level. However, the odds of leaving treatment were greater among women using methamphetamine less than weekly. Further investigation into this association may be warranted due to the complications that may result from methamphetamine use during pregnancy.Keywords: pregnancy, methamphetamines, treatment, attrition

  19. Rethinking race and attrition in nursing programs: a hermeneutic inquiry.

    Science.gov (United States)

    Jordan, J D

    1996-01-01

    This hermeneutic study examined the lived experience of four self-identified African-American students enrolled in predominantly white baccalaureate nursing programs. An understanding of the following concerns was sought: (1) Does being black matter in an educational program that is predominantly white? (2) Does being black in a predominantly white nursing program hinder a student's ability or desire to continue toward his or her educational goal? These concerns were guided by the major research question: What is the meaning of being black in a predominantly white nursing program? Critical hermeneutic inquiry, as explicated by Jurgen Habermas, was used as the philosophical framework. Audiotaped interviews were transcribed and subsequently analyzed by a team of researchers. Three constitutive patterns emerged from the analysis of the texts: Being Different/Being the Same, Student As Teacher: Toward a Surrogate Pedagogy, and Resoluteness: I'll See You at Graduation. Findings suggest that empirical research concerning the attrition of blacks from predominantly white nursing programs must include a description of what it means to be black or different in these settings.

  20. Computational toxicology: Its essential role in reducing drug attrition.

    Science.gov (United States)

    Naven, R T; Louise-May, S

    2015-12-01

    Predictive toxicology plays a critical role in reducing the failure rate of new drugs in pharmaceutical research and development. Despite recent gains in our understanding of drug-induced toxicity, however, it is urgent that the utility and limitations of our current predictive tools be determined in order to identify gaps in our understanding of mechanistic and chemical toxicology. Using recently published computational regression analyses of in vitro and in vivo toxicology data, it will be demonstrated that significant gaps remain in early safety screening paradigms. More strategic analyses of these data sets will allow for a better understanding of their domain of applicability and help identify those compounds that cause significant in vivo toxicity but which are currently mis-predicted by in silico and in vitro models. These 'outliers' and falsely predicted compounds are metaphorical lighthouses that shine light on existing toxicological knowledge gaps, and it is essential that these compounds are investigated if attrition is to be reduced significantly in the future. As such, the modern computational toxicologist is more productively engaged in understanding these gaps and driving investigative toxicology towards addressing them.

  1. Forms of Attrition in a Longitudinal Study of Religion and Health in Older Adults and Implications for Sample Bias.

    Science.gov (United States)

    Hayward, R David; Krause, Neal

    2016-02-01

    The use of longitudinal designs in the field of religion and health makes it important to understand how attrition bias may affect findings in this area. This study examines attrition in a 4-wave, 8-year study of older adults. Attrition resulted in a sample biased toward more educated and more religiously involved individuals. Conditional linear growth curve models found that trajectories of change for some variables differed among attrition categories. Ineligibles had worsening depression, declining control, and declining attendance. Mortality was associated with worsening religious coping styles. Refusers experienced worsening depression. Nevertheless, there was no evidence of bias in the key religion and health results.

  2. Where Have All the Rodents Gone? The Effects of Attrition in Experimental Research on Cancer and Stroke.

    Directory of Open Access Journals (Sweden)

    Constance Holman

    2016-01-01

    Full Text Available Given small sample sizes, loss of animals in preclinical experiments can dramatically alter results. However, effects of attrition on distortion of results are unknown. We used a simulation study to analyze the effects of random and biased attrition. As expected, random loss of samples decreased statistical power, but biased removal, including that of outliers, dramatically increased probability of false positive results. Next, we performed a meta-analysis of animal reporting and attrition in stroke and cancer. Most papers did not adequately report attrition, and extrapolating from the results of the simulation data, we suggest that their effect sizes were likely overestimated.

  3. Nanoscale structure and atomic disorder in the iron-based chalcogenides.

    Science.gov (United States)

    Saini, Naurang Lal

    2013-02-01

    The multiband iron-based superconductors have layered structure with a phase diagram characterized by a complex interplay of charge, spin and lattice excitations, with nanoscale atomic structure playing a key role in their fundamental electronic properties. In this paper, we briefly review nanoscale structure and atomic disorder in iron-based chalcogenide superconductors. We focus on the Fe(Se,S)1-x Te x (11-type) and K0.8Fe1.6Se2 (122-type) systems, discussing their local structure obtained by extended x-ray absorption fine structure. Local structure studies on the Fe(Se,S)1-x Te x system reveal clear nanoscale phase separation characterized by coexisting components of different atomic configurations, similar to the case of random alloys. In fact, the Fe-Se/S and Fe-Te distances in the ternary Fe(Se,S)1-x Te x are found to be closer to the respective distances in the binary FeSe/FeS and FeTe systems, showing significant divergence of the local structure from the average one. The observed features are characteristic of ternary random alloys, indicating breaking of the local symmetry in these materials. On the other hand, K0.8Fe1.6Se2 is known for phase separation in an iron-vacancy ordered phase and an in-plane compressed lattice phase. The local structure of these 122-type chalcogenides shows that this system is characterized by a large local disorder. Indeed, the experiments suggest a nanoscale glassy phase in K0.8Fe1.6Se2, with the superconductivity being similar to the granular materials. While the 11-type structure has no spacer layer, the 122-type structure contains intercalated atoms unlike the 1111-type REFeAsO (RE = rare earth) oxypnictides, having well-defined REO spacer layers. It is clear that the interlayer atomic correlations in these iron-based superconducting structures play an important role in structural stability as well as superconductivity and magnetism.

  4. Magnetic order close to superconductivity in the iron-based layered LaO1-xFxFeAs systems.

    Science.gov (United States)

    de la Cruz, Clarina; Huang, Q; Lynn, J W; Li, Jiying; Ratcliff, W; Zarestky, J L; Mook, H A; Chen, G F; Luo, J L; Wang, N L; Dai, Pengcheng

    2008-06-12

    Following the discovery of long-range antiferromagnetic order in the parent compounds of high-transition-temperature (high-T(c)) copper oxides, there have been efforts to understand the role of magnetism in the superconductivity that occurs when mobile 'electrons' or 'holes' are doped into the antiferromagnetic parent compounds. Superconductivity in the newly discovered rare-earth iron-based oxide systems ROFeAs (R, rare-earth metal) also arises from either electron or hole doping of their non-superconducting parent compounds. The parent material LaOFeAs is metallic but shows anomalies near 150 K in both resistivity and d.c. magnetic susceptibility. Although optical conductivity and theoretical calculations suggest that LaOFeAs exhibits a spin-density-wave (SDW) instability that is suppressed by doping with electrons to induce superconductivity, there has been no direct evidence of SDW order. Here we report neutron-scattering experiments that demonstrate that LaOFeAs undergoes an abrupt structural distortion below 155 K, changing the symmetry from tetragonal (space group P4/nmm) to monoclinic (space group P112/n) at low temperatures, and then, at approximately 137 K, develops long-range SDW-type antiferromagnetic order with a small moment but simple magnetic structure. Doping the system with fluorine suppresses both the magnetic order and the structural distortion in favour of superconductivity. Therefore, like high-T(c) copper oxides, the superconducting regime in these iron-based materials occurs in close proximity to a long-range-ordered antiferromagnetic ground state.

  5. Pair correlations in iron-based superconductors: Quantum Monte Carlo study

    Energy Technology Data Exchange (ETDEWEB)

    Kashurnikov, V.A.; Krasavin, A.V., E-mail: avkrasavin@gmail.com

    2014-08-01

    The new generalized quantum continuous time world line Monte Carlo algorithm was developed to calculate pair correlation functions for two-dimensional FeAs-clusters modeling of iron-based superconductors using a two-orbital model. The data obtained for clusters with sizes up to 10×10 FeAs-cells favor the possibility of an effective charge carrier's attraction that is corresponding the A{sub 1g}-symmetry, at some parameters of interaction. The analysis of pair correlations depending on the cluster size, temperature, interaction, and the type of symmetry of the order parameter is carried out. - Highlights: • New generalized quantum continuous time world line Monte Carlo algorithm is developed. • Pair correlation functions for two-dimensional FeAs-clusters are calculated. • Parameters of two-orbital model corresponding to attraction of carriers are defined.

  6. Aligned carbon nanotubes catalytically grown on iron-based nanoparticles obtained by laser-induced CVD

    Energy Technology Data Exchange (ETDEWEB)

    Le Normand, F. [Groupe Surfaces and Interfaces, IPCMS, UMR 7504 CNRS, Bat 70, 23 rue du Loess, 67034 Strasbourg Cedex (France)], E-mail: Francois.Le-Normand@ipcms.u-strasbg.fr; Cojocaru, C.S.; Ersen, O. [Groupe Surfaces and Interfaces, IPCMS, UMR 7504 CNRS, Bat 70, 23 rue du Loess, 67034 Strasbourg Cedex (France); Legagneux, P.; Gangloff, L. [THALES R and T, Departementale 128, 91747 Palaiseau Cedex (France); Fleaca, C. [Groupe Surfaces and Interfaces, IPCMS, UMR 7504 CNRS, Bat 70, 23 rue du Loess, 67034 Strasbourg Cedex (France); National Institute for Lasers, Plasma and Radiation Physics, Laser Department, P.O. Box MG-36, R-76900 Bucharest (Romania); Alexandrescu, R.; Dumitrache, F.; Morjan, I. [National Institute for Lasers, Plasma and Radiation Physics, Laser Department, P.O. Box MG-36, R-76900 Bucharest (Romania)

    2007-12-15

    Iron-based nanoparticles are prepared by a laser-induced chemical vapor deposition (CVD) process. They are characterized as body-centered Fe and Fe{sub 2}O{sub 3} (maghemite/magnetite) particles with sizes {<=}5 and 10 nm, respectively. The Fe particles are embedded in a protective carbon matrix. Both kind of particles are dispersed by spin-coating on SiO{sub 2}/Si(1 0 0) flat substrates. They are used as catalyst to grow carbon nanotubes by a plasma- and filaments-assisted catalytic CVD process (PE-HF-CCVD). Vertically oriented and thin carbon nanotubes (CNTs) were grown with few differences between the two samples, except the diameter in relation to the initial size of the iron particles, and the density. The electron field emission of these samples exhibit quite interesting behavior with a low turn-on voltage at around 1 V/{mu}m.

  7. Aligned carbon nanotubes catalytically grown on iron-based nanoparticles obtained by laser-induced CVD

    Science.gov (United States)

    Le Normand, F.; Cojocaru, C. S.; Ersen, O.; Legagneux, P.; Gangloff, L.; Fleaca, C.; Alexandrescu, R.; Dumitrache, F.; Morjan, I.

    2007-12-01

    Iron-based nanoparticles are prepared by a laser-induced chemical vapor deposition (CVD) process. They are characterized as body-centered Fe and Fe 2O 3 (maghemite/magnetite) particles with sizes ≤5 and 10 nm, respectively. The Fe particles are embedded in a protective carbon matrix. Both kind of particles are dispersed by spin-coating on SiO 2/Si(1 0 0) flat substrates. They are used as catalyst to grow carbon nanotubes by a plasma- and filaments-assisted catalytic CVD process (PE-HF-CCVD). Vertically oriented and thin carbon nanotubes (CNTs) were grown with few differences between the two samples, except the diameter in relation to the initial size of the iron particles, and the density. The electron field emission of these samples exhibit quite interesting behavior with a low turn-on voltage at around 1 V/μm.

  8. Development of iron-based nanoparticles for Cr(VI removal from drinking water

    Directory of Open Access Journals (Sweden)

    Vourlias G.

    2013-01-01

    Full Text Available A great deal of research over recent decades has been motivated by the requirement to lower the concentration of chromium in drinking water. This study has been conducted to determine the feasibility of iron-based nanoparticles for chromium removal from contaminated water. Single Fe, Fe3O4 and binary Fe/Fe3O4 nanoparticles were grown at the 45-80 nm size range using the solar physical vapor deposition technique and tested as potential hexavalent chromium removing agents from aqueous solutions. Due to their higher electron donation ability compared to the Fe3O4 ones, single Fe nanoparticles exhibited the highest Cr(VI removal capacity of more than 3 µg/mg while maintaining a residual concentration 50 µg/L, equal to the regulation limit for drinking water. In combination to their facile and fast magnetic separation, the applicability of the studied particles in water treatment facilities should be considered.

  9. Processing of New Materials by Additive Manufacturing: Iron-Based Alloys Containing Silver for Biomedical Applications

    Science.gov (United States)

    Niendorf, Thomas; Brenne, Florian; Hoyer, Peter; Schwarze, Dieter; Schaper, Mirko; Grothe, Richard; Wiesener, Markus; Grundmeier, Guido; Maier, Hans Jürgen

    2015-07-01

    In the biomedical sector, production of bioresorbable implants remains challenging due to improper dissolution rates or deficient strength of many candidate alloys. Promising materials for overcoming the prevalent drawbacks are iron-based alloys containing silver. However, due to immiscibility of iron and silver these alloys cannot be manufactured based on conventional processing routes. In this study, iron-manganese-silver alloys were for the first time synthesized by means of additive manufacturing. Based on combined mechanical, microscopic, and electrochemical studies, it is shown that silver particles well distributed in the matrix can be obtained, leading to cathodic sites in the composite material. Eventually, this results in an increased dissolution rate of the alloy. Stress-strain curves showed that the incorporation of silver barely affects the mechanical properties.

  10. Warm compaction of Al2O3 particulate reinforced powder metallurgy iron-base composite

    Institute of Scientific and Technical Information of China (English)

    倪东惠; 陈维平; 肖志瑜; 邵明; 张双益

    2002-01-01

    Mechanical properties of the warm compacted alumina particulate reinforced powder metallurgy composite materials was compared with those of the materials obtained by conventional cold compaction. Factors affecting the properties of the warm compacted material such as compaction temperature, lubricant content and alumina content were studied. A 3%(mass fraction) alumina particulate reinforced iron-base composite with a green density of 7.0g/cm3 can be obtained by pressing the powder with a pressure of 700MPa at 175℃. The sintered materials have a density of 6.88g/cm3, a tensile strength of 512MPa and an elongation of 1.3%. Results show that as alumina content increases, density and mechanical properties of the composite decrease.

  11. Collective magnetic excitations of C4-symmetric magnetic states in iron-based superconductors

    Science.gov (United States)

    Scherer, Daniel D.; Eremin, Ilya; Andersen, Brian M.

    2016-11-01

    We study the collective magnetic excitations of the recently discovered C4-symmetric spin-density-wave states of iron-based superconductors with particular emphasis on their orbital character based on an itinerant multiorbital approach. This is important since the C4-symmetric spin-density-wave states exist only at moderate interaction strengths where damping effects from a coupling to the continuum of particle-hole excitations strongly modify the shape of the excitation spectra compared to predictions based on a local moment picture. We uncover a distinct orbital polarization inherent to magnetic excitations in C4-symmetric states, which provide a route to identify the different commensurate magnetic states appearing in the continuously updated phase diagram of the iron-pnictide family.

  12. Development of Iron-based Closed-Cell Foams by Powder Forging and Rolling

    Science.gov (United States)

    Paswan, Dayanand; Mistry, Dhananjay; Sahoo, K. L.; Srivastava, V. C.

    2013-08-01

    In the present investigation, an attempt has been made to develop in situ sandwich Fe-based foams using powder forging and rolling. Several metal carbonates are first studied by thermo gravimetric analysis to find out their suitability to be used as foaming agent for iron-based foams. Barium carbonate is found to be the most promising foaming agent among other suitable options studied such as SrCO3, CaCO3, MgCO3, etc. The effects of process parameters such as precursor composition, sintering temperature, foaming temperature and time, and content of foaming agent have been studied. The microstructural characteristics of the sintered precursor have been studied by means of optical and scanning electron microscopy. It was found that a good pore structure can be obtained using 2-3% C in Fe and 3% BaCO3 as foaming agent and by foaming at around 1350 °C for 3-6 min.

  13. Nontrivial Role of Interlayer Cation States in Iron-Based Superconductors.

    Science.gov (United States)

    Guterding, Daniel; Jeschke, Harald O; Mazin, I I; Glasbrenner, J K; Bascones, E; Valentí, Roser

    2017-01-06

    Unconventional superconductivity in iron pnictides and chalcogenides has been suggested to be controlled by the interplay of low-energy antiferromagnetic spin fluctuations and the particular topology of the Fermi surface in these materials. Based on this premise, one would also expect the large class of isostructural and isoelectronic iron germanide compounds to be good superconductors. As a matter of fact, they, however, superconduct at very low temperatures or not at all. In this work we establish that superconductivity in iron germanides is suppressed by strong ferromagnetic tendencies, which surprisingly do not originate from changes in bond angles or bond distances with respect to iron pnictides and chalcogenides, but are due to changes in the electronic structure in a wide range of energies happening upon substitution of atom species (As by Ge and the corresponding spacer cations). Our results indicate that superconductivity in iron-based materials may not always be fully understood based on d or d-p model Hamiltonians only.

  14. Nematic fluctuations, fermiology and the pairing potential in iron-based superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Kretzschmar, Florian

    2015-08-18

    The thesis comprises a systematic study on the doping, temperature and momentum dependent electron dynamics in iron-based superconductors using inelastic light scattering. The observation of Bardasis-Schrieffer modes in the excitation spectrum of superconducting Ba{sub 0.6}K{sub 0.4}Fe{sub 2}As{sub 2} is reported and the energy and symmetry dependence of the modes are analyzed. The analysis yields the identification of a strong subdominant component of the interaction potential V(k,k{sup '}). Strong nematic fluctuations are investigated in Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2}. The nature of the fluctuations and the origin of nematicity in Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} are identified.

  15. Effect of sintering parameters on warm compacted iron-based material

    Institute of Scientific and Technical Information of China (English)

    李元元; 肖志瑜; 倪东惠; 夏伟; 陈维平

    2003-01-01

    Iron-based powder metallurgy material was prepared by warm compaction at 125℃ using a compacting pressure of 700 Mpa.Sintering temperature ranging from 1100℃ to 1300℃ and sintering time ranging from 40min to 80 min were used to study the effects of sintering parameters on the compacts.Die wall lubrication polytetrafluoroethylene(PTFE)emulsion was also applied in combination with warm compaction in hope to increase the compact density and the mechanical properties of the sintered material.Green and sintered density,spring back effect and sinter shrinkage were measured.Mechanical properties of both as-sinter and heat treated samples were also measured.Results show that mechanical properties of the sintered compacts increase with the increase of sintering temperature and sintering time.Sample prepared by die wall lubricated warm compaction always shows higher density and mechanical properties.

  16. Development of iron-based nanoparticles for Cr(VI) removal from drinking water

    Science.gov (United States)

    Simeonidis, K.; Tziomaki, M.; Angelakeris, M.; Martinez-Boubeta, C.; Balcells, Ll.; Monty, C.; Mitrakas, M.; Vourlias, G.; Andritsos, N.

    2013-01-01

    A great deal of research over recent decades has been motivated by the requirement to lower the concentration of chromium in drinking water. This study has been conducted to determine the feasibility of iron-based nanoparticles for chromium removal from contaminated water. Single Fe, Fe3O4 and binary Fe/Fe3O4 nanoparticles were grown at the 45-80 nm size range using the solar physical vapor deposition technique and tested as potential hexavalent chromium removing agents from aqueous solutions. Due to their higher electron donation ability compared to the Fe3O4 ones, single Fe nanoparticles exhibited the highest Cr(VI) removal capacity of more than 3 µg/mg while maintaining a residual concentration 50 µg/L, equal to the regulation limit for drinking water. In combination to their facile and fast magnetic separation, the applicability of the studied particles in water treatment facilities should be considered.

  17. THE BEHAVIOR OF HOMOGENEOUS IRON-BASED CATALYSTS BEARING PYRIDINE DIIMINE LIGANDS FOR ETHYLENE POLYMERIZATION

    Institute of Scientific and Technical Information of China (English)

    Jiao-ming Qiu; Ling-gang Sun; You-liang Hu; Yu-fei Li

    2000-01-01

    The polymerization of ethylene by two iron-based catalysts,{[2,6-ArN=C(Me)2C5H3N]FeCl2} (Ar = 2,6-C6H3-Me2Ⅰ; 2,6-C6H3 (I-Pr)2 Ⅱ) has been investigated. Catalyst Ⅱ produces higher molecular weight polyethylene (PE) and broadened polydispersities relative to catalyst Ⅰ under analogous conditions and all polymers are linear. The kinetic profiles with iron catalysts showed a smooth pattern during both rate build-up and rate lowering, which are different from the metallocene catalysts. The polymerization activity increases with Al/Fe value and an optimum temperature range at 40~45 ℃ was observed. The molecular weight of PE decreases with the increase of Al/Fe ratio and rise of polymerization temperature.

  18. High pressure structures of "111" type iron-based superconductors predicted from first-principles.

    Science.gov (United States)

    Zhang, Xinxin; Wang, Yanchao; Ma, Yanming

    2012-11-21

    The high-pressure crystal structures of the "111" type iron-based superconductors: NaFeAs, LiFeP and LiFeAs have been systematically explored by using particle-swarm structural searches. It was found that though these iron-based superconductors are chemically similar, they adopted distinct structural phase transitions: P4/nmm→Cmcm→P3m1 for NaFeAs, P4/nmm→Cmcm→I4mm for LiFeP, and P4/nmm→P3m1 →I4mm→P6(3)/mmc for LiFeAs under high pressure. The high pressure orthorhombic Cmcm phase preserved the structural features of FeX(4)(X = As, P) tetrahedral layers present in the ambient-pressure P4/nmm structure. However, the FeX(4) tetrahedrons in the Cmcm phase were clearly distorted, leading to changes in the electronic behavior around the Fermi level. Under higher pressures, the FeX(4) layered structural features were no longer persistent and three-dimensional crystal structures were stabilized in other P3m1, I4mm, and P6(3)/mmc phases, which featured FeAs(5)/FeAs(6) hexahedron and octahedrons, FeX(5) tetragonal pyramids, and FeAs(6) octahedrons, respectively. Analysis of the electronic density of states suggests that most of the high pressure phases are metallic except for the tetragonal I4mm phase, which possesses a narrow band gap. This semiconducting state might relate to the tetragonal pyramid structure formed by FeX(5) unit, which might be favorable for charge localization.

  19. Nanoscale probe of magnetism, orbital occupation, and structural distortions in iron-based superconductors

    Science.gov (United States)

    Cantoni, Claudia

    2014-03-01

    Local probes of atomic and electronic structures with sub-nanometer spatial resolution can provide additional insights into the physics of iron-based superconductors (FBS) by resolving the influence of inhomogeneities that are typically averaged over by bulk-sensitive techniques. Here we apply aberration-corrected scanning transmission electron microscopy coupled with electron energy loss spectroscopy to a wide class of iron-based superconductors and parent compounds to decipher the interplay between crystal distortions, local magnetic moment, orbital occupancy, and charge doping in these complex materials. In addition to revealing universal trends for hole concentration and local magnetic moment across families of FBS, we directly observe the effects of magneto-elastic coupling in 122 arsenides at room temperature, well above the structural and antiferromagnetic transition. The presence of atomic displacements indicates that the C4 tetragonal symmetry is already broken at room temperature in unstrained crystals, lowering the symmetry to orthorhombic (I2mm), and that all of the crystals are twinned with domains the size of a few nanometers. By tracking these local atomic displacements as a function of doping level x, in Ba(Fe1-xCox)2 As2, we find that the domain size correlates with the magnitude of the dynamic Fe moment, and both are enhanced near optimal doping where the ordered moment is suppressed. The non-monotonic behavior of the local Fe magnetic moment is linked to the strong coupling between lattice, spin, and orbital degrees of freedom. Research supported by the Materials Sciences and Engineering Division Office of Basic Energy Sciences, U.S. Department of Energy.

  20. Mechanochemical method for producing iron-based nitrogen-containing nanocrystalline alloys

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Iron-based products account the main volume of powder metallurgy production. Nevertheless its strength and reliability are not enough in comparison with classical cast materials. So that is why making nanostructural powder materials allows to increase strength and extend the range of products. A principally new way of nanostructure production is possible by means of iron mechanical alloying with nitride-forming and nitrogen both at the same time.Unlike classical technology of internal nitrogenation, nitrogen saturation, in our case, occurs by whole volume at plastic deformation conditions. A review of experimental results of phase forming alloys in the Fe-Ni, Fe-Ni-Cr, Fe-Ni-N, Fe-Ni-Cr-N, Fe-Cr-Ni systems prepared by mechanical alloying are given. The influence of the technological parameters of mechanical alloying, atmosphere of mechanical activation on nitrogen content and phase composition of examined alloys has been studied. Experimental results of the influence of mechanical alloying technological parameters on degree of ammonia dissociation and nitrogen content in examined alloys are presented. Heat treatment influence of mechanically alloyed, nitrogen-containing alloys on theirphase composition and structure are investigated.It was shown that using mechanical alloying, it's possible to prepare high-alloyed iron-based alloys containing more than 1% of nitrogen. It was established that technology of mechanical alloying in ammonia atmosphere allows to prepare austenitic steels with nanocrystalline structure, which affords high value of yield stress. Physico-chemical patterns of interaction between the nitrogen-containing atmosphere and nitride-forming elements under their mutual mechanical activation conditions were established in consequence of theoretical and experimental researches. Some scientific principles of nanocrystalline materials were gained by quantitative description of correlation between the mechanical dose, nitrogen potertial, nitrogen content

  1. Low-energy microscopic models for iron-based superconductors: a review

    Science.gov (United States)

    Fernandes, Rafael M.; Chubukov, Andrey V.

    2017-01-01

    The development of sensible microscopic models is essential to elucidate the normal-state and superconducting properties of the iron-based superconductors. Because these materials are mostly metallic, a good starting point is an effective low-energy model that captures the electronic states near the Fermi level and their interactions. However, in contrast to cuprates, iron-based high-T c compounds are multi-orbital systems with Hubbard and Hund interactions, resulting in a rather involved 10-orbital lattice model. Here we review different minimal models that have been proposed to unveil the universal features of these systems. We first review minimal models defined solely in the orbital basis, which focus on a particular subspace of orbitals, or solely in the band basis, which rely only on the geometry of the Fermi surface. The former, while providing important qualitative insight into the role of the orbital degrees of freedom, do not distinguish between high-energy and low-energy sectors and, for this reason, generally do not go beyond mean-field. The latter allow one to go beyond mean-field and investigate the interplay between superconducting and magnetic orders as well as Ising-nematic order. However, they cannot capture orbital-dependent features like spontaneous orbital order. We then review recent proposals for a minimal model that operates in the band basis but fully incorporates the orbital composition and symmetries of the low-energy excitations. We discuss the results of the renormalization group study of such a model, particularly of the interplay between superconductivity, magnetism, and spontaneous orbital order, and compare theoretical predictions with experiments on iron pnictides and chalcogenides. We also discuss the impact of the glide-plane symmetry on the low-energy models, highlighting the key role played by the spin-orbit coupling.

  2. Magnetism, Superconductivity, and Spontaneous Orbital Order in Iron-Based Superconductors: Which Comes First and Why?

    Science.gov (United States)

    Chubukov, Andrey V.; Khodas, M.; Fernandes, Rafael M.

    2016-10-01

    Magnetism and nematic order are the two nonsuperconducting orders observed in iron-based superconductors. To elucidate the interplay between them and ultimately unveil the pairing mechanism, several models have been investigated. In models with quenched orbital degrees of freedom, magnetic fluctuations promote stripe magnetism, which induces orbital order. In models with quenched spin degrees of freedom, charge fluctuations promote spontaneous orbital order, which induces stripe magnetism. Here, we develop an unbiased approach, in which we treat magnetic and orbital fluctuations on equal footing. Key to our approach is the inclusion of the orbital character of the low-energy electronic states into renormalization group (RG) analysis. We analyze the RG flow of the couplings and argue that the same magnetic fluctuations, which are known to promote s+- superconductivity, also promote an attraction in the orbital channel, even if the bare orbital interaction is repulsive. We next analyze the RG flow of the susceptibilities and show that, if all Fermi pockets are small, the system first develops a spontaneous orbital order, then s+- superconductivity, and magnetic order does not develop down to T =0 . We argue that this scenario applies to FeSe. In systems with larger pockets, such as BaFe2 As2 and LaFeAsO, we find that the leading instability is either towards a spin-density wave or superconductivity. We argue that in this situation nematic order is caused by composite spin fluctuations and is vestigial to stripe magnetism. Our results provide a unifying description of different iron-based materials.

  3. Concealed d-wave pairs in the s± condensate of iron-based superconductors.

    Science.gov (United States)

    Ong, Tzen; Coleman, Piers; Schmalian, Jörg

    2016-05-17

    A central question in iron-based superconductivity is the mechanism by which the paired electrons minimize their strong mutual Coulomb repulsion. In most unconventional superconductors, Coulomb repulsion is minimized through the formation of higher angular momentum Cooper pairs, with Fermi surface nodes in the pair wavefunction. The apparent absence of such nodes in the iron-based superconductors has led to a belief they form an s-wave ([Formula: see text]) singlet state, which changes sign between the electron and hole pockets. However, the multiorbital nature of these systems opens an alternative possibility. Here, we propose a new class of [Formula: see text] state containing a condensate of d-wave Cooper pairs, concealed by their entanglement with the iron orbitals. By combining the d-wave ([Formula: see text]) motion of the pairs with the internal angular momenta [Formula: see text] of the iron orbitals to make a singlet ([Formula: see text]), an [Formula: see text] superconductor with a nontrivial topology is formed. This scenario allows us to understand the development of octet nodes in potassium-doped Ba1-x KXFe2As2 as a reconfiguration of the orbital and internal angular momentum into a high spin ([Formula: see text]) state; the reverse transition under pressure into a fully gapped state can then be interpreted as a return to the low-spin singlet. The formation of orbitally entangled pairs is predicted to give rise to a shift in the orbital content at the Fermi surface, which can be tested via laser-based angle-resolved photoemission spectroscopy.

  4. Manufacture of iron-based, amorphous coatings with high fracture toughness

    Science.gov (United States)

    Bobzin, K.; Öte, M.; Königstein, T.

    2017-03-01

    Amorphous iron-based material have excellent corrosion behaviour, show good tribological performances and exhibit interesting thermophysical properties. The deposition as a coating system by thermal spraying technology is an innovative approach to manufacture these materials. In this study, the mechanical properties of three iron-based amorphous coatings with different chromium content xCr = 0, 5 and 15 at.% are presented deposited by means of High Velocity Oxygen Fuel Spraying. For the determination of the amorphous content the linear relationship between crystallization energy and amount of amorphous structures is used. Comparing the crystallization energies of amorphous ribbons manufactured by melt spinning to those of feedstock materials and free standing coatings, assumptions regarding the amorphous contents are drawn. The results show that the amorphous content in the feedstock material is influenced by the amount of chromium content. Furthermore, the amorphous content of all coatings do not exceed those of the feedstock materials. Powder xCr = 15 at.% and the corresponding coating exhibit smallest amount of amorphous structure, presumably due to a not fully melted state of the impacting particles. The values of fracture toughness of the coatings are determined by means of indentation and subsequent measurement of the crack lengths. Furthermore, values of indentation modulus and hardness are measured and compared to each other. While length of indentation cracks decreases with increasing chromium content, an increase in indention modulus and hardness is observed. In comparison to ceramic reference YSZ and the steel reference 1.4404, all amorphous coatings show promising properties such as low indentation crack lengths and high hardness.

  5. Early Adverse Events and Attrition in SSRI Treatment: A Suicide Assessment Methodology Study (SAMS) Report

    Science.gov (United States)

    Warden, Diane; Trivedi, Madhukar H.; Wisniewski, Stephen R.; Kurian, Benji; Zisook, Sidney; Kornstein, Susan G.; Friedman, Edward S.; Miyahara, Sachiko; Leuchter, Andrew F.; Fava, Maurizio; Rush, John

    2011-01-01

    Adverse events during selective serotonin reuptake inhibitor (SSRI) treatment are frequent and may lead to premature treatment discontinuation. If attrition is associated with early worsening of side effects or the frequency, intensity, or burden of side effects, interventions to maximize retention could be focused on patients with these events. Outpatient participants (n=265) with nonpsychotic major depressive disorder entered an 8-week trial with an SSRI. At baseline and week 2, specific side effects were evaluated with the Systematic Assessment for Treatment Emergent Events – Systematic Inquiry, and at week 2 the Frequency, Intensity, and Burden of Side Effects Rating globally assessed side effects. Attrition was defined by those participants who left treatment after week 2 but before week 8. No specific week 2 side effect, either treatment emergent or with worsening intensity, was independently associated with attrition. Global ratings of side effect frequency, intensity, or burden at week 2 were also not associated with subsequent attrition. Neither global ratings nor specific side effects at week 2 were related to patient attrition during SSRI treatment. Other factors appear to contribute to patient decisions about continuing with treatment. PMID:20473060

  6. Hydrolysis behavior of zirconium diboride during attrition milling

    Energy Technology Data Exchange (ETDEWEB)

    Yin Jie; Zhang Hui; Yan Yongjie [State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100039 (China); Huang Zhengren, E-mail: zrhuang@mail.sic.ac.cn [State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100039 (China); Liu Xuejian [State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100039 (China); Yang Yong, E-mail: yangyong@mail.sic.ac.cn [State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100039 (China); Jiang Dongliang [State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100039 (China)

    2012-03-15

    Highlights: Black-Right-Pointing-Pointer The surface was mainly covered of Zr-O, B-O and B-OH bonds after hydrolysis. Black-Right-Pointing-Pointer ZrB{sub 2} powder tended to behave like a B{sub 2}O{sub 3}-modified surface by milling treatment. Black-Right-Pointing-Pointer The surface B/Zr atomic ratio decreased from water to ethanol medium. Black-Right-Pointing-Pointer The nano-sized oxide layer ({approx}5 nm) was observed and helped to improve the dispersion of ZrB{sub 2} particles in dilute aqueous media. - Abstract: The hydrolysis behavior of ZrB{sub 2} powder during attrition milling was studied in de-ionized water and ethanol. Surface characterization, thermal analysis, chemical analysis and electron microscopy were utilized to analyze the surface properties of as-milled powders. The results proved that the surface of ZrB{sub 2} powder was mainly composed of Zr-O, B-O and B-OH bonds as hydrolysis proceeded, and the amount of surface B-O bond was found to increase rapidly in water, suggesting a more B{sub 2}O{sub 3}-like surface behavior were developed. Results also showed when milled at 300 rpm for 4 h in water, 64.45 at% of B was in the form of B{sub 2}O{sub 3} at a thickness of {approx}3 nm from the surface. The nano-sized surface Zr-B-O oxide layer ({approx}5 nm in thickness) could help to improve the dispersion of powder in aqueous media.

  7. Enhanced boronizing kinetics of alloy steel assisted by surface mechanical attrition treatment

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Haopeng, E-mail: hpyang1993@163.com; Wu, Xiaochun, E-mail: xcwu@staff.shu.edu.cn; Yang, Zhe; Pu, Shengjun; Wang, Hongbin

    2014-03-25

    Highlights: • Nanostructured surface layer is fabricated on H13 steel assisted by SMAT. • The boronizing kinetics of SMAT sample can be enhanced remarkably. • Borided layer can delay fatigue cracks initiation and impede their propagation. -- Abstract: A nanostructured surface layer was fabricated on AISI H13 steel by means of surface mechanical attrition treatment (SMAT). Boronizing behaviors of the SMAT samples were systematically investigated in comparison with their coarse-grained counterparts. The boron diffusion depth of the SMAT sample with pack boriding treatment at 600 °C for 2 h was about 8 μm, which was much deeper than that of the coarse-grained sample. A much thicker borided layer on the SMAT sample can be synthesized by a duplex boronizing treatment at 600 °C followed by at a higher temperature. The borided layer was composed with monophase of Fe{sub 2}B and the growth of it exhibited a (0 0 2) preferred orientation. Moreover, the activation energy of boron diffusion for the SMAT sample is 140.3 kJ/mol, which is much lower than 209.4 kJ/mol for the coarse-grained counterpart. The results indicate that the boronizing kinetics can be significantly enhanced in the SMAT sample with a duplex boronizing treatment. Furthermore, the thermal fatigue tests show that the borided layer with excellent oxidation resistance and mechanical strength at elevated temperatures could effectively delay the thermal fatigue cracks initiation and impede their propagation. Therefore, the thermal fatigue property of H13 steel with a duplex boronizing treatment can be improved remarkably.

  8. PREFACE: Celebrating 100 years of superconductivity: special issue on the iron-based superconductors Celebrating 100 years of superconductivity: special issue on the iron-based superconductors

    Science.gov (United States)

    Crabtree, George; Greene, Laura; Johnson, Peter

    2011-12-01

    In honor of this year's 100th anniversary of the discovery of superconductivity, this special issue of Reports on Progress in Physics is a dedicated issue to the 'iron-based superconductors'—a new class of high-temperature superconductors that were discovered in 2008. This is the first time the journal has generated a 'theme issue', and we provide this to the community to provide a 'snapshot' of the present status, both for researchers working in this fast-paced field, and for the general physics community. Reports on Progress in Physics publishes three classes of articles—comprehensive full Review Articles, Key Issues Reviews and, most recently, Reports on Progress articles that recount the current status of a rapidly evolving field, befitting of the articles in this special issue. It has been an exciting year for superconductivity—there have been numerous celebrations for this centenary recounting the fascinating history of this field, from seven Nobel prizes to life-saving discoveries that brought us medically useful magnetic resonance imaging. The discovery of a completely new class of high-temperature superconductors, whose mechanism remains as elusive as the cuprates discovered in 1986, has injected a new vitality into this field, and this year those new to the field were provided with the opportunity of interacting with those who have enjoyed a long history in superconductivity. Furthermore, as high-density current carriers with little or no power loss, high-temperature superconductors offer unique solutions to fundamental grid challenges of the 21st century and hold great promise in addressing our global energy challenges. The complexity and promise of these materials has caused our community to more freely share our ideas and results than ever before, and it is gratifying to see how we have grown into an enthusiastic global network to advance the field. This invited collection is true to this agenda and we are delighted to have received contributions

  9. Removal of As, Cd, Cr, Cu, Ni and Zn from polluted water using an iron based sorbent

    DEFF Research Database (Denmark)

    Genc-Fuhrman, Hülya; Wu, P.; Zhou, Y.;

    2008-01-01

    In this study fixed-bed sorption filters are filled with an iron based sorbent (ferrosorp plus, FP) and used to remove a range of heavy metals (i.e. As, Cd, Cr, Cu, Ni, and Zn) from polluted water. It is found that FP is very effective at simultaneous removal of the heavy metals, and the magnitud...

  10. The Effect of State Unemployment Rate on Attrition for First-Term U.S. Navy Enlisted Personnel

    Science.gov (United States)

    2011-03-01

    through homeschooling attrited at a rate of 8.0 percent. Recruits who reported to have not graduated from high school attrited at a rate of 11.6 percent...is not that diverse. Females account for 18 percent of the population. Enlisted personnel, who are unmarried and have no children , accounted for 95

  11. Biases in Estimating Treatment Effects Due to Attrition in Randomized Controlled Trials and Cluster Randomized Controlled Trials: A Simulation Study

    Science.gov (United States)

    Dong, Nianbo; Lipsey, Mark W.

    2011-01-01

    Attrition occurs when study participants who were assigned to the treatment and control conditions do not provide outcome data and thus do not contribute to the estimation of the treatment effects. It is very common in experimental studies in education as illustrated, for instance, in a meta-analysis studying "the effects of attrition on baseline…

  12. Derivation and Evaluation of a Risk-Scoring Tool to Predict Participant Attrition in a Lifestyle Intervention Project.

    Science.gov (United States)

    Jiang, Luohua; Yang, Jing; Huang, Haixiao; Johnson, Ann; Dill, Edward J; Beals, Janette; Manson, Spero M; Roubideaux, Yvette

    2016-05-01

    Participant attrition in clinical trials and community-based interventions is a serious, common, and costly problem. In order to develop a simple predictive scoring system that can quantify the risk of participant attrition in a lifestyle intervention project, we analyzed data from the Special Diabetes Program for Indians Diabetes Prevention Program (SDPI-DP), an evidence-based lifestyle intervention to prevent diabetes in 36 American Indian and Alaska Native communities. SDPI-DP participants were randomly divided into a derivation cohort (n = 1600) and a validation cohort (n = 801). Logistic regressions were used to develop a scoring system from the derivation cohort. The discriminatory power and calibration properties of the system were assessed using the validation cohort. Seven independent factors predicted program attrition: gender, age, household income, comorbidity, chronic pain, site's user population size, and average age of site staff. Six factors predicted long-term attrition: gender, age, marital status, chronic pain, site's user population size, and average age of site staff. Each model exhibited moderate to fair discriminatory power (C statistic in the validation set: 0.70 for program attrition, and 0.66 for long-term attrition) and excellent calibration. The resulting scoring system offers a low-technology approach to identify participants at elevated risk for attrition in future similar behavioral modification intervention projects, which may inform appropriate allocation of retention resources. This approach also serves as a model for other efforts to prevent participant attrition.

  13. Examining the Relationship Between Mental, Physical, and Organizational Factors Associated With Attrition During Maritime Forces Training.

    Science.gov (United States)

    Binsch, Olaf; Banko, Katherine M; Veenstra, Bertil J; Valk, Pierre J L

    2015-11-01

    For infantry units of the Dutch Ministry of Defence, high attrition rates (varying from 42 to 68%) during initial training are a persisting problem. The reasons for this attrition are diverse. Having better insight into the causes of attrition is a prerequisite for implementing preventive measures. To achieve this, a monitoring assessment system was developed that integrated the effects of physical, mental, and organizational determinants on operational readiness. The aim of this study was to implement the monitoring tools and to establish the set of determinants that best predicted attrition during infantry training of new recruits. Eighty-five recruits were monitored over a 24-week infantry training course. Before the training, recruits were screened for medical, psychological, and physical wellness. During the monitoring phase, mental, physiological, and organizational indicants were obtained using an array of tools such as questionnaires, chest belt monitors (for heart rate, acceleration, and skin temperature measurements), and computerized tests (e.g., vigilance, long-term memory). Survival analyses were used to tease out the determinants of individual and grouped predictors of attrition. Nearly half the recruits (47%) failed the training. Attrition was predicted by both physiological and mental determinants. However, the organizational determinant "trainers' judgment" on the "recruits' military quality" dominated the physiological and mental determinants. It was concluded that the monitoring system was successfully implemented during infantry training, and that the survival analysis method emphasized on single effects and interactions between the different determinants. Based on the current findings, we recommend several steps to successfully implement a monitoring method in settings with high demands.

  14. Factors contributing to attrition behavior in diabetes self-management programs: A mixed method approach

    Directory of Open Access Journals (Sweden)

    Offenheim Ana

    2008-02-01

    Full Text Available Abstract Background Diabetes self-management education is a critical component in diabetes care. Despite worldwide efforts to develop efficacious DSME programs, high attrition rates are often reported in clinical practice. The objective of this study was to examine factors that may contribute to attrition behavior in diabetes self-management programs. Methods We conducted telephone interviews with individuals who had Type 2 diabetes (n = 267 and attended a diabetes education centre. Multivariable logistic regression was performed to identify factors associated with attrition behavior. Forty-four percent of participants (n = 118 withdrew prematurely from the program and were asked an open-ended question regarding their discontinuation of services. We used content analysis to code and generate themes, which were then organized under the Behavioral Model of Health Service Utilization. Results Working full and part-time, being over 65 years of age, having a regular primary care physician or fewer diabetes symptoms were contributing factors to attrition behaviour in our multivariable logistic regression. The most common reasons given by participants for attrition from the program were conflict between their work schedules and the centre's hours of operation, patients' confidence in their own knowledge and ability when managing their diabetes, apathy towards diabetes education, distance to the centre, forgetfulness, regular physician consultation, low perceived seriousness of diabetes, and lack of familiarity with the centre and its services. There was considerable overlap between our quantitative and qualitative results. Conclusion Reducing attrition behaviour requires a range of strategies targeted towards delivering convenient and accessible services, familiarizing individuals with these services, increasing communication between centres and their patients, and creating better partnerships between centres and primary care physicians.

  15. Patient attrition from the HIV antiretroviral therapy program at two hospitals in Haiti

    Science.gov (United States)

    Puttkammer, Nancy H.; Zeliadt, Steven B.; Baseman, Janet G.; Destiné, Rodney; Domerçant, Jean Wysler; Coq, Nancy Rachel Labbé; Raphael, Nernst Atwood; Sherr, Kenneth; Tegger, Mary; Yuhas, Krista; Barnhart, Scott

    2016-01-01

    Objective To identify factors associated with antiretroviral therapy (ART) attrition among patients initiating therapy in 2005–2011 at two large, public-sector department-level hospitals, and to inform interventions to improve ART retention. Methods This retrospective cohort study used data from the iSanté electronic medical record (EMR) system. The study characterized ART attrition levels and explored the patient demographic, clinical, temporal, and service utilization factors associated with ART attrition, using time-to-event analysis methods. Results Among the 2 023 patients in the study, ART attrition on average was 17.0 per 100 person-years (95% confidence interval (CI): 15.8–18.3). In adjusted analyses, risk of ART attrition was up to 89% higher for patients living in distant communes compared to patients living in the same commune as the hospital (hazard ratio: 1.89, 95%CI: 1.54–2.33; P < 0.001). Hospital site, earlier year of ART start, spending less time enrolled in HIV care prior to ART initiation, receiving a non-standard ART regimen, lacking counseling prior to ART initiation, and having a higher body mass index were also associated with attrition risk. Conclusions The findings suggest quality improvement interventions at the two hospitals, including: enhanced retention support and transportation subsidies for patients accessing care from remote areas; counseling for all patients prior to ART initiation; timely outreach to patients who miss ART pick-ups; “bridging services” for patients transferring care to alternative facilities; routine screening for anticipated interruptions in future ART pick-ups; and medical case review for patients placed on non-standard ART regimens. The findings are also relevant for policymaking on decentralization of ART services in Haiti. PMID:25563149

  16. Lead optimization attrition analysis (LOAA): a novel and general methodology for medicinal chemistry.

    Science.gov (United States)

    Munson, Mark; Lieberman, Harvey; Tserlin, Elina; Rocnik, Jennifer; Ge, Jie; Fitzgerald, Maria; Patel, Vinod; Garcia-Echeverria, Carlos

    2015-08-01

    Herein, we report a novel and general method, lead optimization attrition analysis (LOAA), to benchmark two distinct small-molecule lead series using a relatively unbiased, simple technique and commercially available software. We illustrate this approach with data collected during lead optimization of two independent oncology programs as a case study. Easily generated graphics and attrition curves enabled us to calibrate progress and support go/no go decisions on each program. We believe that this data-driven technique could be used broadly by medicinal chemists and management to guide strategic decisions during drug discovery.

  17. Risk Attitudes, Sample Selection and Attrition in a Longitudinal Field Experiment

    DEFF Research Database (Denmark)

    Harrison, Glenn W.; Lau, Morten Igel

    Longitudinal experiments allow one to compare inferences about behavior over time for the same individuals, and evaluate the temporal stability of latent preferences. But longitudinal experiments entail the possibility of sample selection and sample attrition over time, confounding inferences about...... to findings of temporal stability in overall risk aversion. However, that stability is around different levels of risk aversion than one might naively infer without the controls for sample selection and attrition we are able to implement. This evidence of “randomization bias” from sample selection...... is important given the popularity of field experiments that rely on randomization, and the effects that risk attitudes have for economic behavior in general....

  18. Language attrition: an experimental qualitative study on english – spanish adult bilinguals

    OpenAIRE

    2013-01-01

    XVIII Jornades de Foment de la Investigació de la Facultat de Ciències Humanes i Socials (Any 2013) nterest in bilingualism and the effects it has on cognitive development has been subject to immense study and investigation. A relatively new concept associated with bilingualism is attrition. Only in the past 30 years has the study of language attrition become a sub-field of linguistics. It began with a conference in 1980 at the University of Pennsylvania, titled Loss of Language Skills (L...

  19. Adherence and Attrition in a Web-Based Lifestyle Intervention for People with Metabolic Syndrome.

    Directory of Open Access Journals (Sweden)

    Leila Jahangiry

    2014-09-01

    Full Text Available The aim of this study was to determine adherence and attrition rates in a lifestyle intervention for people with metabolic syndrome.Adherence and attrition data from a randomized controlled trial were collected. Participants were classified as adherence group if they completed assessments at 3 and 6 months follow-up and as attrition group if they did not. Physical activity and quality of life was measured using the International Physical Activity Questionnaire (IPAQ and the Short Form Health Survey (SF-36. Generalized Estimating Equations (GEE was used to explore predictors of attrition.The mean age of participants (n=160 was 44.1 years. Attrition rate in the intervention and control groups at first follow-up were the same (20%. However, the control group had significantly higher attrition rate (%33.7 compared to the intervention group (%20 at 6 months follow up. Results showed that low educated participants were more likely to not stay in the study than better educated participants (OR=2.95,CI:1.39-6.33,P=0.05. According with length of the study, attrition was decreased at six month (OR=0.66,CI:0.52-0.83,P<0.001. Also, some aspects of health-related quality of life contributed to the attrition rate. Those who had higher scores on general health (OR=0.66,CI:0.54-0.97,P=0.023, social functioning (OR=0.44,CI:0.40-0.76,P=0.032, role emotional (OR=0.74,CI:0.54-0.98,P=0.18, vitality (OR=0.55,CI:0.38-0.90,P=0.015 and mental health (OR=0.63,CI:0.45-0.85,P=0.033 were more likely to stay in the study.It remains a concern that Web-based lifestyle programs may fail to reach those who need it most. Participant in the study generally had better quality of life than those who were lost to follow up.

  20. Magnetic and orbital ordering in the iron-based superconductors. Role of spin-orbit coupling

    Energy Technology Data Exchange (ETDEWEB)

    Ahn, Felix; Eremin, Ilya [Institut fuer Theoretische Physik III, Ruhr-Universitaet Bochum (Germany); Knolle, Johannes [Max Planck Institute for the Physics of Complex Systems, Dresden (Germany); Fernandes, Rafael [School of Physics and Astronomy, University of Minnesota, Minneapolis, MN (United States)

    2015-07-01

    We analyze the magnetic ordering in the iron-based superconductors in presence of spin-orbit coupling. Based on several tight-binding parametrizations of the 3d electron states we show how the spin-orbit coupling introduces the anisotropy of the magnetization of the striped antiferromagnetic state by lifting the degeneracy of all three components of the magnetization m{sub x}, m{sub y} and m{sub z}. The orientation of the magnetic moment is determined by the contribution of the xy, xz, and yz orbitals to the electronic states near the Fermi level of the electron and hole bands and is determined by the electron filling. We find that within an itinerant approach the magnetic ordering is most favorable along the wavevector of the striped AF state. This appears to be a natural consequence of the spin-orbit coupling in the striped AF state where the ferro-orbital order of the xz and yz orbitals is only a consequence of the striped AF order. We further analyze the role of spin-orbit coupling for the C{sub 4} magnetic structure where SDW order parameters with both wavevectors, Q{sub x} = (π,0) and Q{sub y} = (0,π), coexist.

  1. Fermi surface deformation in a simple iron-based superconductor, FeSe

    Science.gov (United States)

    Coldea, Amalia; Watson, Matthew; Kim, Timur; Haghighirad, Amir; McCollam, Alix; Hoesch, Moritz; Schofield, Andrew

    2015-03-01

    One of the outstanding problems in the field superconductivity is the identification of the normal state out of which superconductivity emerges. FeSe is one of the simplest and most intriguing iron-based superconductors, since in its bulk form it undergoes a structural transition before it becomes superconducting, whereas its single-layer form is believed to be a high-temperature superconductor. The nature of the structural transition, occurring in the absence of static magnetism, is rather unusual and how the electronic structure is stabilized by breaking of the rotational symmetry is the key to understand the superconductivity in bulk FeSe. Here we report angle-resolved photoemission spectroscopy measurements on FeSe that gives direct access to the band structure and orbital-dependent effects. We complement our studies on bulk FeSe with low-temperature angular-dependent quantum oscillation measurements using applied magnetic fields that are sufficiently strong to suppress superconductivity and reach the normal state. These studies reveal a strong deformation of Fermi surface through the structural transition driven by electronic correlations and orbital-dependent effects. . This work was supported by EPSRC, UK (EP/I004475/1), Diamond Light Source, UK and HFML, Nijmegen.

  2. A route for a strong increase of critical current in nanostrained iron-based superconductors.

    Science.gov (United States)

    Ozaki, Toshinori; Wu, Lijun; Zhang, Cheng; Jaroszynski, Jan; Si, Weidong; Zhou, Juan; Zhu, Yimei; Li, Qiang

    2016-10-06

    The critical temperature Tc and the critical current density Jc determine the limits to large-scale superconductor applications. Superconductivity emerges at Tc. The practical current-carrying capability, measured by Jc, is the ability of defects in superconductors to pin the magnetic vortices, and that may reduce Tc. Simultaneous increase of Tc and Jc in superconductors is desirable but very difficult to realize. Here we demonstrate a route to raise both Tc and Jc together in iron-based superconductors. By using low-energy proton irradiation, we create cascade defects in FeSe0.5Te0.5 films. Tc is enhanced due to the nanoscale compressive strain and proximity effect, whereas Jc is doubled under zero field at 4.2 K through strong vortex pinning by the cascade defects and surrounding nanoscale strain. At 12 K and above 15 T, one order of magnitude of Jc enhancement is achieved in both parallel and perpendicular magnetic fields to the film surface.

  3. Die wall lubricated warm compaction of iron-based powder metallurgy material

    Institute of Scientific and Technical Information of China (English)

    倪东惠; 陈维平; 肖志瑜; 温利平; 吴苑标

    2002-01-01

    Lubricant is harmful to the mechanical properties of the sintered materials. Die wall lubrication was applied on warm compaction powder metallurgy in the hope of reducing the concentration level of the admixed lubricant. Iron-based samples were prepared by die wall lubricated warm compaction at 175℃, using a compacting pressure of 550MPa. Emulsified polytetrafluoroethylene(PTFE) was used as die wall lubricant. Admixed lubricant concentration ranging from 0 to 0.5% was tested. Extremely low admixed lubricant contents were used. Results show that in addition to the decrease in ejection forces, the green density of the compacts increases with the decrease of admixed lubricant content until it reaches the maximum at 0.06% of lubricant content, then decreases with the decrease of admixed lubricant content. The mechanical properties of the sintered compacts that contain more than 0.06% admixed lubricant are better than those of the samples that contain lesser lubricant. No scoring was observed in all die wall lubricated experiments.

  4. Orbital-selective Mott phase of Cu-substituted iron-based superconductors

    Science.gov (United States)

    Liu, Yang; Zhao, Yang-Yang; Song, Yun

    2016-07-01

    We study the phase transition in Cu-substituted iron-based superconductors with a new developed real-space Green’s function method. We find that Cu substitution has strong effect on the orbital-selective Mott transition introduced by the Hund’s rule coupling. The redistribution of the orbital occupancy which is caused by the increase of the Hund’s rule coupling, gives rise to the Mott-Hubbard metal-insulator transition in the half-filled d xy orbital. We also find that more and more electronic states appear inside that Mott gap of the d xy orbital with the increase of Cu substitution, and the in-gap states around the Fermi level are strongly localized at some specific lattice sites. Further, a distinctive phase diagram, obtained for the Cu-substituted Fe-based superconductors, displays an orbital-selective insulating phase, as a result of the cooperative effect of the Hund’s rule coupling and the impurity-induced disorder.

  5. Effect of Manganese Incorporation Manner on an Iron-Based Catalyst for Fischer-Tropsch Synthesis

    Institute of Scientific and Technical Information of China (English)

    Tingzhen Li; Yong Yang; Chenghua Zhang; Zhichao Tao; Haijun Wan; Xia An; Hongwei Xiang; Yongwang Li

    2007-01-01

    A systematic study was undertaken to investigate the effects of the manganese incorporation manner on the textural properties,bulk and surface phase compositions,reduction/carburization behaviors,and surface basicity of an iron-based Fischer-Tropsch synthesis (FTS) catalyst.The catalyst samples were characterized by N2 Physisorption,X-ray photoelectron spectroscopy(XPS),H2(or CO) temperature-programmed reduction(TPR),CO2 temperature-programmed desorption(TPD),and Mossbauer spectroscopy.The FTS performance of the catalysts was studied in a slurry-phase continuously stirred tank reactor(CSTR).The characterization results indicated that the manganese promoter incor-porated by using the coprecipitation method could improve the dispersion of iron oxide,and decrease the size of the iron oxide crystallite.The manganese incorporated with the impregnation method is enriched on the catalyst's surface.The manganese promoter added with the impregnation method suppresses the reduction and carburization of the catalyst in H2,CO,and syngas because of the excessive enrichment of manganese on the catalyst surface.The catalyst added manganese using the coprecipitation method has the highest CO conversion (51.9%) and the lowest selectivity for heavy hydrocarbons(C12+).

  6. Factors Contributing to Attrition as Reported by Leavers of Secondary Agriculture Programs

    Science.gov (United States)

    Lemons, Laura L.; Brashears, M. Todd; Burris, Scott; Meyers, Courtney; Price, Margaret A.

    2015-01-01

    There exists in our profession a persistent shortage of quality teachers in our high school agricultural education classrooms. A multitude of studies have identified challenges faced by agriculture teachers, however, few, if any, have investigated reasons for attrition by directly asking leavers why they left. This study sought to identify reasons…

  7. Factors of Attrition in Cohort Doctoral Education: A Self-Determination Theory Perspective

    Science.gov (United States)

    Garcia, Linda Ann

    2013-01-01

    Attrition rates, completion rates, and time to degree are the key areas researchers have sought to examine influencing factors and patterns of behavior that describe the departure process of students in doctoral study. Through the lens of self-determination theory (Deci & Ryan, 1985), the purpose of this phenomenological qualitative study was…

  8. Toothbrush abrasion, simulated tongue friction and attrition of eroded bovine enamel in vitro

    NARCIS (Netherlands)

    Vieira, A.; Overweg, E.; Ruben, J. L.; Huysmans, M. C. D. N. J. M.

    2006-01-01

    Objectives: Enamel erosion results in the formation of a softened layer that is susceptible to disruption by mechanical factors such as brushing abrasion, tongue friction and attrition. The aim of this study was to investigate the individual contribution of those mechanical insults to the enamel los

  9. Predictors of attrition and academic success of medical students: a 30-year retrospective study.

    Directory of Open Access Journals (Sweden)

    Silvija Maslov Kruzicevic

    Full Text Available AIM: To determine attrition and predictors of academic success among medical students at University of Split, Croatia. METHODS: We analysed academic records of 2054 students enrolled during 1979-2008 period. RESULTS: We found that 26% (533/2054 of enrolled students did not graduate. The most common reasons for attrition were 'personal' (36.4%, transfer to another medical school (35.6%, and dismissal due to unsatisfactory academic record (21.2%. Grade point average (GPA and study duration of attrition students were significantly associated with parental education. There were 1126 graduates, 395 men and 731 women. Their average graduation GPA was 3.67±0.53 and study duration 7.6±2.44 years. During 5-year curriculum only 6.4% (42/654 of students graduated in time, and 55% (240/472 of students graduated in time after curriculum was extended to 6 years. Variables predicting whether a student will graduate or not were high school grades, entrance exam score and year of enrollment. Significant predictors of graduation grades were high school grades and entrance exam score. Entrance exam score predicted length of studying. CONCLUSION: Preadmission academic qualifications and year of enrollment predict academic success in medical school. More attention should be devoted to high attrition.

  10. Personality, attrition and weight loss in treatment seeking women with obesity.

    Science.gov (United States)

    Dalle Grave, R; Calugi, S; Compare, A; El Ghoch, M; Petroni, M L; Colombari, S; Minniti, A; Marchesini, G

    2015-10-01

    Studies on small samples or in single units applying specific treatment programmes found an association between some personality traits and attrition and weight loss in individuals treated for obesity. We aimed to investigate whether pre-treatment personality traits were associated with weight loss outcomes in the general population of women with obesity. Attrition and weight loss outcomes after 12 months were measured in 634 women with obesity (mean age, 48; body mass index (BMI), 37.8 kg m(-2)) seeking treatment at eight Italian medical centres, applying different medical/cognitive behavioural programmes. Personality traits were assessed with the Temperament and Character Inventory (TCI), eating disorder features with the Binge Eating Scale (BES) and Night Eating Questionnaire (NEQ). Within the 12-month observation period, 32.3% of cases were lost to follow-up. After adjustment for demographic confounders and the severity of eating disorders, no TCI personality traits were significantly associated with attrition, while low scores of the novelty seeking temperament scale remained significantly associated with weight loss ≥ 10% (odds ratio, 0.983; 95% confidence interval, 0.975-0.992). Additional adjustment for education and job did not change the results. We conclude that personality does not systematically influence attrition in women with obesity enrolled into weight loss programmes in the community, whereas an association is maintained between novelty seeking and weight loss outcome. Studies adapting obesity interventions on the basis of individual novelty seeking scores might be warranted to maximize the results on body weight.

  11. Attrition in Chronic Disease Self-Management Programs and Self-Efficacy at Enrollment

    Science.gov (United States)

    Verevkina, Nina; Shi, Yunfeng; Fuentes-Caceres, Veronica Alejandra; Scanlon, Dennis Patrick

    2014-01-01

    Among other goals, the Chronic Disease Self-Management Program (CDSMP) is designed to improve self-efficacy of the chronically ill. However, a substantial proportion of the enrollees often leave CDSMPs before completing the program curriculum. This study examines factors associated with program attrition in a CDSMP implemented in a community…

  12. Parent-Child Interaction Therapy in a Community Setting: Examining Outcomes, Attrition, and Treatment Setting

    Science.gov (United States)

    Lanier, Paul; Kohl, Patrica L.; Benz, Joan; Swinger, Dawn; Moussette, Pam; Drake, Brett

    2011-01-01

    Objectives: The purpose of this study was to evaluate Parent-Child Interaction Therapy (PCIT) deployed in a community setting comparing in-home with the standard office-based intervention. Child behavior, parent stress, parent functioning, and attrition were examined. Methods: Using a quasi-experimental design, standardized measures at three time…

  13. Who Stays and for How Long: Examining Attrition in Canadian Graduate Programs

    Science.gov (United States)

    DeClou, Lindsay

    2016-01-01

    Attrition from Canadian graduate programs is a point of concern on a societal, institutional, and individual level. To improve retention in graduate school, a better understanding of what leads to withdrawal needs to be reached. This paper uses logistic regression and discrete-time survival analysis with time-varying covariates to analyze data…

  14. Vocabulary Attrition among Adult English as a Foreign Language Persian Learners

    Science.gov (United States)

    Asgari, Azadeh; Bin Mustapha, Ghazali

    2010-01-01

    This study aims to investigate the attrition rate of EFL concrete and abstract vocabulary among continuing and non-continuing Iranian female and male English language learners across different proficiency levels. They are students of a University and majored in different fields (between 20 and 25 years old). There was no treatment in this study…

  15. Teacher Efficacy and Attrition: Helping Students at Introductory Levels of Language Instruction Appears Critical

    Science.gov (United States)

    Swanson, Peter B.

    2010-01-01

    Nationally, there is a shortage of foreign language educators, and the rate of attrition in certain areas of the southeastern part of the United States is startling. The researcher investigated foreign language teachers' (N = 463) perceived efficacy teaching languages in Georgia, and findings suggest there is a link between perceived efficacy and…

  16. Selectivity in L1 Attrition: Differential Object Marking in Spanish Near-Native Speakers of English

    Science.gov (United States)

    Chamorro, Gloria; Sturt, Patrick; Sorace, Antonella

    2016-01-01

    Previous research has shown L1 attrition to be restricted to structures at the interfaces between syntax and pragmatics, but not to occur with syntactic properties that do not involve such interfaces ("Interface Hypothesis", Sorace and Filiaci in "Anaphora resolution in near-native speakers of Italian." "Second Lang…

  17. Age and Proficiency in L2 Attrition: Data from Two Siblings

    Science.gov (United States)

    Tomiyama, Machiko

    2009-01-01

    This paper investigates whether any difference exists in the degree of second language attrition between two siblings in terms of grammatical complexity, grammatical accuracy, lexical complexity, and lexical productivity based on their storytelling data collected over the period of 31 months. The subjects' L1 and L2 are Japanese and English,…

  18. Does Reading in Shallow L1 Orthography Slow Attrition of Language-Specific Morphological Structures?

    Science.gov (United States)

    Zaretsky, Elena; Bar-Shalom, Eva G.

    2010-01-01

    This study looks at the relationship between L1 (Russian) attrition and L1 reading ability in Russian-English-speaking bilingual children. Ten Russian-English bilingual children and 10 adults participated in this study. Nine out of 10 children participants were born in the US and used L1 as their primary language of interaction within the family,…

  19. Attrition from Student Affairs: Perspectives from Those Who Exited the Profession

    Science.gov (United States)

    Marshall, Sarah M.; Gardner, Megan Moore; Hughes, Carole; Lowery, Ute

    2016-01-01

    Attrition of student affairs professionals is an issue of concern for the profession. This mixed methods study highlights reasons why participants left their student affairs careers. Seven general themes emerged from the study, including burnout, salary issues, career alternatives, work/family conflict, limited advancement, supervisor issues and…

  20. Student Nurse Attrition: Use of an Exit-Interview Procedure To Determine Students' Leaving Reasons.

    Science.gov (United States)

    Glossop, Christine

    2002-01-01

    Attrition from a nursing program in Wales was studied through exit interviews with 105 students who left from 1996-1999. Academic difficulties, wrong career choice, and family, health, and financial problems were key reasons. Almost half had at least two reasons for leaving, suggesting a complex interplay of factors. (Contains 39 references.) (SK)

  1. The Structure of Secondary School Teacher Job Satisfaction and Its Relationship with Attrition and Work Enthusiasm

    Science.gov (United States)

    Weiqi, Chen

    2007-01-01

    This study used the results of a questionnaire survey of 230 secondary school teachers to analyze the factors constituting job satisfaction and its effects on teacher attrition and work enthusiasm. The results show that (a) the structure of secondary school teacher job satisfaction is made up of ten components and is consistent with the model put…

  2. Factors related to attrition from trauma-focused cognitive behavioral therapy.

    Science.gov (United States)

    Wamser-Nanney, Rachel; Steinzor, Cazzie E

    2016-12-23

    Attrition from child trauma-focused treatments such as Trauma-Focused Cognitive Behavioral Therapy (TF-CBT) is common; yet, the factors of children who prematurely terminate are unknown. The aim of the current study was to identify risk factors for attrition from TF-CBT. One hundred and twenty-two children (ages 3-18; M=9.97, SD=3.56; 67.2% females; 50.8% Caucasian) who received TF-CBT were included in the study. Demographic and family variables, characteristics of the trauma, and caregiver- and child-reported pretreatment symptoms levels were assessed in relation to two operational definitions of attrition: 1) clinician-rated dropout, and 2) whether the child received an adequate dose of treatment (i.e., 12 or more sessions). Several demographic factors, number of traumatic events, and children's caregiver-rated pretreatment symptoms were related to clinician-rated dropout. Fewer factors were associated with the adequate dose definition. Child Protective Services involvement, complex trauma exposure, and child-reported pretreatment trauma symptoms were unrelated to either attrition definition. Demographics, trauma characteristics, and level of caregiver-reported symptoms may help to identify clients at risk for premature termination from TF-CBT. Clinical and research implications for different operational definitions and suggestions for future work will be presented.

  3. A Comparison of the FY03 and FY99 First Term Attrition Study Cohorts

    Science.gov (United States)

    2005-09-01

    Model Testing We used Mplus analysis software to fit all of the structural models we examined (Muthen & Muthen, 2001). One distinct benefit of this...2001). Mplus user’s guide. 2 nd Edition. Los Angeles: Muthen & Muthen. Putka, D.J. (2004a). Composition and prediction of attrition through 48 months of

  4. The measurement of change in functional ability: dealing with attrition and the floor/ceiling effect

    DEFF Research Database (Denmark)

    Holstein, Bjørn E; Avlund, Kirsten; Due, Pernille;

    2006-01-01

    , functional ability at baseline, relative wealth, social network, self-rated health, and life-satisfaction. Inclusion of the dead in statistical models for the study of change in functional ability reduced the attrition problem. A logistic model for paired observations of functional ability at two points...

  5. Treatment of Human-Caused Trauma: Attrition in the Adult Outcomes Research

    Science.gov (United States)

    Matthieu, Monica; Ivanoff, Andre

    2006-01-01

    Attrition or dropout is the failure of a participant to complete, comply, or the prematurely discontinuation or discharge from treatment, resulting in lost data and affecting outcomes. This review of 10 years of adult posttraumatic stress disorder (PTSD) treatment outcome literature specific to Criterion A events of human origin examines how…

  6. The influence of temperature on limestone sulfation and attrition under fluidized bed combustion conditions

    Energy Technology Data Exchange (ETDEWEB)

    Montagnaro, Fabio [Dipartimento di Chimica - Universita degli Studi di Napoli Federico II, Complesso Universitario del Monte di Sant' Angelo, 80126 Napoli (Italy); Salatino, Piero [Istituto di Ricerche sulla Combustione - CNR, Piazzale Vincenzo Tecchio 80, 80125 Napoli (Italy); Dipartimento di Ingegneria Chimica - Universita degli Studi di Napoli Federico II, Piazzale Vincenzo Tecchio 80, 80125 Napoli (Italy); Scala, Fabrizio [Istituto di Ricerche sulla Combustione - CNR, Piazzale Vincenzo Tecchio 80, 80125 Napoli (Italy)

    2010-04-15

    The influence of temperature on attrition of two limestones during desulfurization in a fluidized bed reactor was investigated. Differences in the microstructure of the two limestones were reflected by a different thickness of the sulfate shell formed upon sulfation and by a different value of the ultimate calcium conversion degree. Particle attrition and fragmentation were fairly small under moderately bubbling fluidization conditions for both limestones. An increase of temperature from 850 C to 900 C led to an increase of the attrition rate, most likely because of a particle weakening effect caused by a faster CO{sub 2} evolution during calcination. This weakening effect, however, was not sufficiently strong to enhance particle fragmentation in the bed. The progress of sulfation, associated to the build-up of a hard sulfate shell around the particles, led in any case to a decrease of the extent of attrition. Sulfation at 900 C was less effective than at 850 C, and this was shown to be related to the porosimetric features of the different samples. (author)

  7. In Their Own Words: A Text Analytics Investigation of College Course Attrition

    Science.gov (United States)

    Michalski, Greg V.

    2014-01-01

    Excessive course attrition is costly to both the student and the institution. While most institutions have systems to quantify and report the numbers, far less attention is typically paid to each student's reason(s) for withdrawal. In this case study, text analytics was used to analyze a large set of open-ended written comments in which…

  8. In Their Own Words: A Text Analytics Investigation of College Course Attrition

    Science.gov (United States)

    Michalski, Greg V.

    2014-01-01

    Excessive course attrition is costly to both the student and the institution. While most institutions have systems to quantify and report the numbers, far less attention is typically paid to each student's reason(s) for withdrawal. In this case study, text analytics was used to analyze a large set of open-ended written comments in which students…

  9. Retention, Attrition, and Mobility among Teachers and Administrators in West Virginia. REL 2016-161

    Science.gov (United States)

    Lochmiller, Chad R.; Adachi, Eishi; Chesnut, Colleen E.; Johnson, Jerry

    2016-01-01

    Members of the West Virginia School Leadership Research Alliance partnered with Regional Educational Laboratory Appalachia to study the average retention, attrition, and mobility rates among teachers and administrators in the West Virginia public school system. There is increasing evidence nationwide that low teacher and administrator retention…

  10. Disappearing Act: Persistence and Attrition of Uniform Resource Locators (URLs) in an Open Access Medical Journal

    Science.gov (United States)

    Nagaraja, Aragudige; Joseph, Shine A.; Polen, Hyla H.; Clauson, Kevin A.

    2011-01-01

    Purpose: The aim of this paper is to assess and catalogue the magnitude of URL attrition in a high-impact, open access (OA) general medical journal. Design/methodology/approach: All "Public Library of Science Medicine (PLoS Medicine)" articles for 2005-2007 were evaluated and the following items were assessed: number of entries per issue; type of…

  11. Telomeric attrition with age and temperature in Eastern mosquitofish ( Gambusia holbrooki)

    Science.gov (United States)

    Rollings, Nicky; Miller, Emily; Olsson, Mats

    2014-03-01

    Telomeric attrition has repeatedly been found to correlate with the ageing of organisms; however, recent research is increasingly showing that the determinants of attrition dynamics are not well understood. This study examined the relative telomere lengths in Eastern mosquitofish, Gambusia holbrooki, kept at different temperatures and at different ages. Newly born fry were randomly selected for one of four treatment groups: 20, 30, 20-30, and 30-20 °C, where the third and fourth treatment groups were gradually changed from their starting temperature to their final temperature between days 10 and 14. Telomere length was measured, and it was found that length decreased with age and that fish exposed to the 20 °C treatment had significantly shorter telomeres than those that received the 30-20 °C treatment. Telomeric attrition with age agrees with results previously found in studies of telomeres; however, the variation in attrition with temperature was not simply predictable and may be the synergistic effects of temperature and some other factor.

  12. The pattern of attrition from an antiretroviral treatment program in Nigeria.

    Directory of Open Access Journals (Sweden)

    Solomon Odafe

    Full Text Available OBJECTIVE: To evaluate the rate and factors associated with attrition of patients receiving ART in tertiary and secondary hospitals in Nigeria. METHODS AND FINDINGS: We reviewed patient level data collected between 2007 and 2010 from 11 hospitals across Nigeria. Kaplan-Meier product-limit and Cox regression were used to determine probability of retention in care and risk factors for attrition respectively. Of 6,408 patients in the cohort, 3,839 (59.9% were females, median age of study population was 33years (IQR: 27-40 and 4,415 (69% were from secondary health facilities. The NRTI backbone was Stavudine (D4T in 3708 (57.9% and Zidovudine (ZDV in 2613 (40.8% of patients. Patients lost to follow up accounted for 62.7% of all attrition followed by treatment stops (25.3% and deaths (12.0%. Attrition was 14.1 (N = 624 and 15.1% (N = 300 in secondary and tertiary hospitals respectively (p = 0.169 in the first 12 months on follow up. During the 13 to 24 months follow up period, attrition was 10.7% (N = 407 and 19.6% (N = 332 in secondary and tertiary facilities respectively (p<0.001. Median time to lost to follow up was 11.1 (IQR: 6.1 to 18.5 months in secondary compared with 13.6 (IQR: 9.9 to 17.0 months in tertiary sites (p = 0.002. At 24 months follow up, male gender [AHR 1.18, 95% CI: 1.01-1.37, P = 0.038]; WHO clinical stage III [AHR 1.30, 95%CI: 1.03-1.66, P = 0.03] and clinical stage IV [AHR 1.90, 95%CI: 1.20-3.02, p = 0.007] and care in a tertiary hospital [AHR 2.21, 95% CI: 1.83-2.67, p<0.001], were associated with attrition. CONCLUSION: Attrition could potentially be reduced by decentralizing patients on ART after the first 12 months on therapy to lower level facilities, earlier initiation on treatment and strengthening adherence counseling amongst males.

  13. Attrition among Women and Minorities in Earth and Space Science (ESS) Graduate Programs

    Science.gov (United States)

    Alexander, C. J.; Hawthorne, C.; Allen, W. R.; Alvarez, R.; Geisler, J.

    2001-05-01

    Recent data collected by the American Geological Institute (AGI) indicates that the rate of enrollment of ethnic minorities in the geosciences has steadily declined since the 1980's, and in that time the number of geoscience degrees awarded to ethnic minorities has been fairly steady at less than 1%. Data from the National Science Foundation suggests that only 43 of 186 Universities offering an ESS program have ever graduated an ethnic minority in the history of their program. Factors contributing to these abysmal figures differ for different ethnic-minority groups. We will address institutional obstacles to graduate learning which result in above-normal attrition of ethnic-minorities in ESS graduate programs. The recent studies show an attrition rate of 70% among African American males in ESS graduate programs, while among Hispanic females the attrition rate is only 3%. Studies by sociologists have recently shown that some law schools and medical schools have traits in common with these geoscience departments in the rates at which degrees are awarded to ethnic minorities. Institutional barriers encountered by ethnic minorities in graduate schools may take many forms, but can also be as simple as a lack of community support. In the 1990's the California Institute of Technology (Caltech) made a commitment to the retention of women in their graduate and undergraduate schools. Their program included mentoring, focussed tutoring, self-esteem support groups, and other retention efforts. Under this program, the attrition rate of women has dramatically slowed. In this paper, we will discuss the AGI data, the program instituted by Caltech, possible causes of attrition among populations of Hispanic, and African American males and females, as well as potential programs to address these problems. We will also present, from the nationwide study, data on geoscience departments which have been relatively successful at retaining and graduating ethnic minorities in Earth and Space

  14. Confusing similar words: ERP correlates of lexical-semantic processing in first language attrition and late second language acquisition.

    Science.gov (United States)

    Kasparian, Kristina; Steinhauer, Karsten

    2016-12-01

    First language (L1) attrition is a socio-linguistic circumstance where second language (L2) learning coincides with changes in exposure and use of the native-L1. Attriters often report experiencing a decline in automaticity or proficiency in their L1 after a prolonged period in the L2 environment, while their L2 proficiency continues to strengthen. Investigating the neurocognitive correlates of attrition alongside those of late L2 acquisition addresses the question of whether the brain mechanisms underlying both L1 and L2 processing are strongly determined by proficiency, irrespective of whether the language was acquired from birth or in adulthood. Using event-related-potentials (ERPs), we examined lexical-semantic processing in Italian L1 attriters, compared to adult Italian L2 learners and to Italian monolingual native speakers. We contrasted the processing of classical lexical-semantic violations (Mismatch condition) with sentences that were equally semantically implausible but arguably trickier, as the target-noun was "swapped" with an orthographic neighbor that differed only in its final vowel and gender-marking morpheme (e.g., cappello (hat) vs. cappella (chapel)). Our aim was to determine whether sentences with such "confusable nouns" (Swap condition) would be processed as semantically correct by late L2 learners and L1 attriters, especially for those individuals with lower Italian proficiency scores. We found that lower-proficiency Italian speakers did not show significant N400 effects for Swap violations relative to correct sentences, regardless of whether Italian was the L1 or the L2. Crucially, N400 response profiles followed a continuum of "nativelikeness" predicted by Italian proficiency scores - high-proficiency attriters and high-proficiency Italian learners were indistinguishable from native controls, whereas attriters and L2 learners in the lower-proficiency range showed significantly reduced N400 effects for "Swap" errors. Importantly, attriters

  15. EFFECTIVENESS OF USING DILUTE OXALIC ACID TO DISSOLVEHIGH LEVEL WASTE IRON BASED SLUDGE SIMULANT

    Energy Technology Data Exchange (ETDEWEB)

    Ketusky, E

    2008-07-11

    At the Savannah River Site (SRS), near Aiken South Carolina, there is a crucial need to remove residual quantities of highly radioactive iron-based sludge from large select underground storage tanks (e.g., 19,000 liters of sludge per tank), in order to support tank closure. The use of oxalic acid is planned to dissolve the residual sludge, hence, helping in the removal. Based on rigorous testing, primarily using 4 and 8 wt% oxalic acid solutions, it was concluded that the more concentrated the acid, the greater the amount of residual sludge that would be dissolved; hence, a baseline technology on using 8 wt% oxalic acid was developed. In stark contrast to the baseline technology, reports from other industries suggest that the dissolution will most effectively occur at 1 wt% oxalic acid (i.e., maintaining the pH near 2). The driver for using less oxalic acid is that less (i.e., moles) would decrease the severity of the downstream impacts (i.e., required oxalate solids removal efforts). To determine the initial feasibility of using 1 wt% acid to dissolve > 90% of the sludge solids, about 19,000 liters of representative sludge was modeled using about 530,000 liters of 0 to 8 wt% oxalic acid solutions. With the chemical thermodynamic equilibrium based software results showing that 1 wt% oxalic acid could theoretically work, simulant dissolution testing was initiated. For the dissolution testing, existing simulant was obtained, and an approximate 20 liter test rig was built. Multiple batch dissolutions of both wet and air-dried simulant were performed. Overall, the testing showed that dilute oxalic acid dissolved a greater fraction of the stimulant and resulted in a significantly larger acid effectiveness (i.e., grams of sludge dissolved/mole of acid) than the baseline technology. With the potential effectiveness confirmed via simulant testing, additional testing, including radioactive sludge testing, is planned.

  16. Shock Wave Response of Iron-based In Situ Metallic Glass Matrix Composites

    Science.gov (United States)

    Khanolkar, Gauri R.; Rauls, Michael B.; Kelly, James P.; Graeve, Olivia A.; Hodge, Andrea M.; Eliasson, Veronica

    2016-03-01

    The response of amorphous steels to shock wave compression has been explored for the first time. Further, the effect of partial devitrification on the shock response of bulk metallic glasses is examined by conducting experiments on two iron-based in situ metallic glass matrix composites, containing varying amounts of crystalline precipitates, both with initial composition Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4. The samples, designated SAM2X5-600 and SAM2X5-630, are X-ray amorphous and partially crystalline, respectively, due to differences in sintering parameters during sample preparation. Shock response is determined by making velocity measurements using interferometry techniques at the rear free surface of the samples, which have been subjected to impact from a high-velocity projectile launched from a powder gun. Experiments have yielded results indicating a Hugoniot Elastic Limit (HEL) to be 8.58 ± 0.53 GPa for SAM2X5-600 and 11.76 ± 1.26 GPa for SAM2X5-630. The latter HEL result is higher than elastic limits for any BMG reported in the literature thus far. SAM2X5-600 catastrophically loses post-yield strength whereas SAM2X5-630, while showing some strain-softening, retains strength beyond the HEL. The presence of crystallinity within the amorphous matrix is thus seen to significantly aid in strengthening the material as well as preserving material strength beyond yielding.

  17. Microstructural development and mechanical properties of iron based cermets processed by pressureless and spark plasma sintering

    Energy Technology Data Exchange (ETDEWEB)

    Alvaredo, P. [Department of Materials Science and Engineering, IQMAAB, University Carlos III Madrid, Avda. de la Universidad, 30, 28911 Leganes (Spain); Gordo, E., E-mail: elena.gordo@uc3m.es [Department of Materials Science and Engineering, IQMAAB, University Carlos III Madrid, Avda. de la Universidad, 30, 28911 Leganes (Spain); Van der Biest, O.; Vanmeensel, K. [Katholieke Universiteit Leuven, Kasteelpark Arenberg, 44 3001 Heverlee (Belgium)

    2012-03-15

    Highlights: Black-Right-Pointing-Pointer Processing of Fe-based cermets by pressureless sintering and spark plasma sintering. Black-Right-Pointing-Pointer Influence of carbon content on the sintering mechanism and hardness. Black-Right-Pointing-Pointer The cermet phase diagram was calculated and permits to explain the microstructure. Black-Right-Pointing-Pointer SPS provides ferritic matrix and different carbide distribution than CPS samples. Black-Right-Pointing-Pointer Pressureless sintered samples contain retained austenite at room temperature. - Abstract: Iron-based cermets are an interesting class of metal-ceramic composites in which properties and the factors influencing them are to be explored. In this work the metal matrix contains Cr, W, Mo and V as alloying elements, and the hard phase is constituted by 50 vol% of titanium carbonitride (TiCN) particles. The work studies the influence of the C content and the processing method on the sinterability, microstructure and hardness of the developed cermet materials. For that purpose, cermet samples with different C content in the matrix (0 wt%, 0.25 wt%, 0.5 wt%, 1.0 wt%) were prepared by conventional pressureless sintering (CPS) and, in order to achieve finer microstructures and to reduce the sintering time, by spark plasma sintering (SPS). The density and hardness (HV30) of the processed materials was evaluated, while their phase composition and microstructure was characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The equilibrium phase diagram of the composite material was calculated by ThermoCalc software in order to elucidate the influence of the carbon content on the obtained phases and developed microstructures.

  18. Magnetic property of iron-based superconductors%铁基超导体的磁性研究

    Institute of Scientific and Technical Information of China (English)

    王少雷; 张莉

    2012-01-01

    The brief history and applications of superconductivity was introduced. The structure of iron-based superconductors and magnetic materials were classified. Taking BaFe2As2 for example, the research on the coexistence of superconductivity and magnetism were summarized. In the meantime the abundant magnetic properties of iron-based superconductors such as SmOCoAs was discussed to show the importance of magnetic property of iron-based superconductors. Finally, viewpoints on the research of the mechanism of high Tc superconductivity and the discovery of new superconductors are presented.%介绍了超导电性的发展简史及其广阔用途,介绍了铁基超导体的结构分类和物质的磁性分类;以BaFe2As2为例综述了铁基超导体中铁磁和超导共存的研究现状,同时以SmOCoAs为例研究了1111相中丰富的磁结构,从而阐明磁性在铁基超导电性研究中的重要地位;最后针对高温超导微观机理研究和超导新材料探索提出了见解.

  19. A defect detection method for MgB2 superconducting and iron-based Ba(Fe,Co)2As2 wires

    Science.gov (United States)

    Gajda, D.; Morawski, A.; Zaleski, A.; Yamamoto, A.; Cetner, T.

    2016-04-01

    In this article, a method allowing for the detection of damage in iron-based superconducting bulks and MgB2 wires is presented. MgB2 wires were made of in situ material with ex situ MgB2 barrier. The iron superconductor studied was Ba(Fe,Co)2As2. This material was surrounded by Nb barrier and placed inside an iron tube. All samples were annealed in the isostatic pressure of 1 GPa. Transport measurements were made using a four-contact probe. The transition of Nb and ex situ MgB2 barrier from superconducting into resistive state (first transition) was observed at a temperature range from 5 K to 10 K and can be attributed to damage in either the Nb or ex situ MgB2 barrier in these samples. For samples with a damaged barrier, it was not possible to determine the critical current density of the wires. The analysis indicates that annealing at 1 GPa leads to the Ba(Fe,Co)2As2 material with critical temperatures of 27 K and 21.5 K at upper critical flux density (Bc2) of 14 T.

  20. Research on the Bonding and Strengthening Mechanism of Iron-based Alloy Plated Layers%合金镀铁层的结合和强化机理研究

    Institute of Scientific and Technical Information of China (English)

    董文仲; 阎军; 贾珊中; 刘勇; 董文胜; 董玉华

    2011-01-01

    铁元素资源丰富、价格便宜,推广镀铁技术符合国家可持续发展战略要求.合金镀铁技术是在无刻蚀镀铁工艺的基础上,在镀铁液中加入一定量的Ni和Co,沉积成含有Ni和Co的合金镀铁层.施镀工艺采用电压控制方式,镀前对基体金属表面进行对称交流活化,使基体金属表面形成"微融活化态",合金镀铁层与基体金属完全融为一体的金属键结合,其力学性能显著提高,结合强度可达460 MPa.能够满足在高速运转和高密度承载的条件下使用要求,并在大量工业应用中得到证实.在机电产品再制造中,合金镀铁具有广阔的应用前景.文中通过对合金镀铁层和单金属镀铁层用扫描电镜观察检验、法向拉力试验和耐磨性能试验,分析并讨论了合金镀铁层的结合和强化机理.%Ferrum is a kind of cheap and abundant resources, and popularizing iron plating technology to remanufacture mechanical and electrical products is up to the national strategy of sustainable development. Iron-based alloy plating remanufacture technology is a kind of technology which developed from iron plating without etching technology. In order to get iron-based alloy plating layers, nickle and cobalt were Added into the plating solution. Volt-control mode was adopted and the symmetrical AC activating procedure on the surface of metrix metal was finished before plating to get "Micro Melt Activation" which make the bond of the iron-based alloy plated layer and metallic matrix to a whole. Iron-based alloy plating layers with excellent mechanical properties is a good remanufacture technology. And the interface bonding strength could reach to 460 MPa. Plenty of applied cases in the remanufactured mechanical and electrical products proved that the iron-based alloy plating layers could completely satisfied the requirement under high running and high density loading conditions. The bonding and strengthening mechanism of the iron-based alloy

  1. The impact of motor axon misdirection and attrition on behavioral deficit following experimental nerve injuries.

    Directory of Open Access Journals (Sweden)

    Jacob Daniel de Villiers Alant

    Full Text Available Peripheral nerve transection and neuroma-in-continuity injuries are associated with permanent functional deficits, often despite successful end-organ reinnervation. Axonal misdirection with non-specific reinnervation, frustrated regeneration and axonal attrition are believed to be among the anatomical substrates that underlie the poor functional recovery associated with these devastating injuries. Yet, functional deficits associated with axonal misdirection in experimental neuroma-in-continuity injuries have not yet been studied. We hypothesized that experimental neuroma-in-continuity injuries would result in motor axon misdirection and attrition with proportional persistent functional deficits. The femoral nerve misdirection model was exploited to assess major motor pathway misdirection and axonal attrition over a spectrum of experimental nerve injuries, with neuroma-in-continuity injuries simulated by the combination of compression and traction forces in 42 male rats. Sciatic nerve injuries were employed in an additional 42 rats, to evaluate the contribution of axonal misdirection to locomotor deficits by a ladder rung task up to 12 weeks. Retrograde motor neuron labeling techniques were utilized to determine the degree of axonal misdirection and attrition. Characteristic histological neuroma-in-continuity features were demonstrated in the neuroma-in-continuity groups and poor functional recovery was seen despite successful nerve regeneration and muscle reinnervation. Good positive and negative correlations were observed respectively between axonal misdirection (p<.0001, r(2=.67, motor neuron counts (attrition (p<.0001, r(2=.69 and final functional deficits. We demonstrate prominent motor axon misdirection and attrition in neuroma-in-continuity and transection injuries of mixed motor nerves that contribute to the long-term functional deficits. Although widely accepted in theory, to our knowledge, this is the first experimental evidence to

  2. Alarming attrition rates among HIV-infected individuals in pre-antiretroviral therapy care in Myanmar, 2011–2014

    Directory of Open Access Journals (Sweden)

    Myo Minn Oo

    2016-08-01

    Full Text Available Background: High retention rates have been documented among patients receiving antiretroviral therapy (ART in Myanmar. However, there is no information on human immunodeficiency virus (HIV-infected individuals in care before initiation of ART (pre-ART care. We assessed attrition (loss-to-follow-up [LTFU] and death rates among HIV-infected individuals in pre-ART care and their associated factors over a 4-year period. Design: In this retrospective cohort study, we extracted routinely collected data of HIV-infected adults (>15 years old entering pre-ART care (June 2011–June 2014 as part of an Integrated HIV Care (IHC programme, Myanmar. Attrition rates per 100 person-years and cumulative incidence of attrition were calculated. Factors associated with attrition were examined by calculating hazard ratios (HRs. Results: Of 18,037 HIV-infected adults enrolled in the IHC programme, 11,464 (63% entered pre-ART care (60% men, mean age 37 years, median cluster of differentiation 4 (CD4 cell count 160 cells/µL. Of the 11,464 eligible participants, 3,712 (32% underwent attrition of which 43% were due to deaths and 57% were due to LTFU. The attrition rate was 78 per 100 person-years (95% CI, 75–80. The cumulative incidence of attrition was 70% at the end of a 4-year follow-up, of which nearly 90% occurred in the first 6 months. Male sex (HR 1.5, 95% CI 1.4–1.6, WHO clinical Stage 3 and 4, CD4 count <200 cells/µL, abnormal BMI, and anaemia were statistically significant predictors of attrition. Conclusions: Pre-ART care attrition among persons living with HIV in Myanmar was alarmingly high – with most attrition occurring within the first 6 months. Strategies aimed at improving early HIV diagnosis and initiation of ART are needed. Suggestions include comprehensive nutrition support and intensified monitoring to prevent pre-ART care attrition by tracking patients who do not return for pre-ART care appointments. It is high time that Myanmar moves

  3. 语言磨蚀研究中的问题探析%On the Problems in Language Attrition Research

    Institute of Scientific and Technical Information of China (English)

    董延彪

    2012-01-01

    There are still many problems in language attrition research at present, which will certainly interfere the study of language attrition in Chinese context. Based on the literatures of language attrition, the author mainly ana- lyzes three questions: how to define language attrition, how to distinguish language attrition from forgetting, and how to comprehend the relationship between language attrition and language acquisition. This paper further points out that analyses of those problems will make us better understand language attrition. On the other hand, the out- comes of other fields such as psychology, social linguistics, neurolinguistics, and language testing should be ab- sorbed into developing language attrition research.%目前,语言磨蚀研究中仍然存在许多问题,如对语言磨蚀定义的界定、对语言磨蚀和遗忘这两个概念的区分、对语言磨蚀和语言习得的关系的认识等,这些问题势必影响我们开展汉语语境下的语言磨蚀研究。对语言磨蚀研究中存在的这些问题的探讨是为了对语言磨蚀本身有一个更深刻的认识.进而更好地开展语言磨蚀研究,不至于偏离这一领域。另一方面还需要不断吸收借鉴诸如心理学、社会语言学、神经语言学、测试学等领域的成果来发展语言磨蚀研究。

  4. HIGHWAY INFRASTRUCTURE FOCUS AREA NEXT-GENERATION INFRASTRUCTURE MATERIALS VOLUME I - TECHNICAL PROPOSAL & MANAGEMENTENHANCEMENT OF TRANSPORTATION INFRASTRUCTURE WITH IRON-BASED AMORPHOUS-METAL AND CERAMIC COATINGS

    Energy Technology Data Exchange (ETDEWEB)

    Farmer, J C

    2007-12-04

    The infrastructure for transportation in the United States allows for a high level of mobility and freight activity for the current population of 300 million residents, and several million business establishments. According to a Department of Transportation study, more than 230 million motor vehicles, ships, airplanes, and railroads cars were used on 6.4 million kilometers (4 million miles) of highways, railroads, airports, and waterways in 1998. Pipelines and storage tanks were considered to be part of this deteriorating infrastructure. The annual direct cost of corrosion in the infrastructure category was estimated to be approximately $22.6 billion in 1998. There were 583,000 bridges in the United States in 1998. Of this total, 200,000 bridges were steel, 235,000 were conventional reinforced concrete, 108,000 bridges were constructed using pre-stressed concrete, and the balance was made using other materials of construction. Approximately 15 percent of the bridges accounted for at this point in time were structurally deficient, primarily due to corrosion of steel and steel reinforcement. Iron-based amorphous metals, including SAM2X5 (Fe{sub 49.7}Cr{sub 17.7}Mn{sub 1.9}Mo{sub 7.4}W{sub 1.6}B{sub 15.2}C{sub 3.8}Si{sub 2.4}) and SAM1651 (Fe{sub 48}Mo{sub 14}Cr{sub 15}Y{sub 2}C{sub 15}B{sub 6}) have been developed, and have very good corrosion resistance. These materials have been prepared as a melt-spun ribbons, as well as gas atomized powders and thermal-spray coatings. During electrochemical testing in several environments, including seawater at 90 C, the passive film stabilities of these materials were found to be comparable to that of more expensive high-performance alloys, based on electrochemical measurements of the passive film breakdown potential and general corrosion rates. These materials also performed very well in standard salt fog tests. Chromium (Cr), molybdenum (Mo) and tungsten (W) provided corrosion resistance, and boron (B) enabled glass formation

  5. Parent–Child Interaction Therapy in a Community Setting: Examining Outcomes, Attrition, and Treatment Setting

    Science.gov (United States)

    Lanier, Paul; Kohl, Patrica L.; Benz, Joan; Swinger, Dawn; Moussette, Pam; Drake, Brett

    2014-01-01

    Objectives The purpose of this study was to evaluate Parent-Child Interaction Therapy (PCIT) deployed in a community setting comparing in-home with the standard office-based intervention. Child behavior, parent stress, parent functioning, and attrition were examined. Methods Using a quasi-experimental design, standardized measures at three time points were collected from parent-child dyads (n=120) with thirty-seven families completing treatment. Results Growth modeling analyses indicate significant improvements in child and parent outcomes in both treatment settings with more rapid improvements in parent outcomes within office-based treatment. Attrition was predicted by income and parent functioning. Conclusion PCIT delivered in the community can produce measureable improvements. In-home PCIT is a feasible option but future research should consider benefits and costs. Treatment completion remains a challenge. PMID:24839378

  6. A Selective Mutism Arising from First Language Attrition, Successfully Treated with Paroxetine-CBT Combination Treatment.

    Science.gov (United States)

    Serra, Agostino; Di Mauro, Paola; Andaloro, Claudio; Maiolino, Luigi; Pavone, Piero; Cocuzza, Salvatore

    2015-10-01

    After immersion in a foreign language, speakers often have difficulty retrieving native-language words and may experience a decrease in its proficiency, this phenomenon, in the non-pathological form, is known as first language attrition. Self-perception of this low native-language proficiency and apprehension occurring when speaking is expected and, may sometimes lead these people to a state of social anxiety and, in extreme forms, can involve the withholding of speech as a primitive tool for self-protection, linking them to selective mutism. We report an unusual case of selective mutism arising from first language attrition in an Italian girl after attending a two-year "German language school", who successfully responded to a paroxetine-cognitive behavioral treatment (CBT) combination treatment.

  7. A Study of the Causes of Attrition Among Adult on a Fully Online Training Course

    Directory of Open Access Journals (Sweden)

    Michael McMahon

    2013-05-01

    Full Text Available An online course was piloted in an Institute of Technology in Ireland for the purpose of providing training in best practice in presenting to people with dyslexia. The course was delivered fully online with no required attendances and with no interaction between participants. None of the participants in the pilot of the course completed the course. This study applies a model developed by Chyung to focus on the possible causes of the attrition and examine means by which attrition can be ameliorated. The findings show that the sense of isolation attached to learning alone is a very significant factor which often has a negative effect on the persistence of the learner to complete the course of study. Strategies to reduce this isolation are suggested.

  8. Characterization of superconducting properties of BSCCO powder prepared by attrition milling

    Energy Technology Data Exchange (ETDEWEB)

    Patel, R H [Brockhouse Institute for Materials Research, McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4M1 (Canada); Nabialek, A [Brockhouse Institute for Materials Research, McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4M1 (Canada); Niewczas, M [Brockhouse Institute for Materials Research, McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4M1 (Canada)

    2005-03-01

    The nonconventional technique of attrition milling has been used to produce superconducting BSCCO powder from the starting powders of oxides and carbonates of Bi, Sr, Ca and Cu. This process shows a drastic reduction in processing time by 80% from the conventional solid-state reaction. The completion of the reaction was determined by x-ray diffraction of the milled powder. The superconducting property characterization was done for the critical transition temperature and the critical current density of the processed powder by magnetic methods. The attrition milled powder shows a T{sub c} of about 87 K after two high temperature treatments for 60 h and J{sub c} of the order of 10{sup 6} A cm{sup -2} at 4 K. The superconducting properties of the processed powder are discussed in the framework of the Bean model.

  9. Losing a Language in Childhood: A Longitudinal Case Study on Language Attrition

    Science.gov (United States)

    Flores, Cristina

    2015-01-01

    This paper is based upon a longitudinal study of L2 attrition in a bilingual child who grew up in an L2 migration background (Germany) and moved to the country of origin (Portugal) at the age of nine, experiencing a "dominance shift from the L2 to the L1." The study aims to analyze the effects of language loss in L2 German. Data…

  10. A Longitudinal Examination of First Term Attrition and Reenlistment among FY1999 Enlisted Accessions

    Science.gov (United States)

    2005-11-01

    formed, we proceeded to fit the preliminary model to the data. We used Mplus analysis software to fit all of the structural models (Muthen & Muthen...coefficients indexing the direct effect of variables on attrition are probit regression coefficients. Mplus uses the probit rather than logit link function...analyses were conducted within Mplus (Muthen & Muthen, 2001) using the same general modeling strategy described in Chapter 4. That is, we began by

  11. Non-Rated Air Force Line Officer Attrition Rates Using Survival Analysis

    Science.gov (United States)

    2015-03-26

    required and expected . Additionally, the experience they gather throughout their careers is invaluable to the success of the Air Force and cannot be...The service commitments and career paths tend to be relatively equal within this group, so the attrition behavior was expected to be approximately the... females , given that they are in the same yeargroup, career field, etc. Although the actual reason cannot be determined based on this data, one can attribute

  12. ART attrition and risk factors among Option B+ patients in Haiti: A retrospective cohort study

    Science.gov (United States)

    Domerçant, Jean Wysler; Adler, Michelle; Yuhas, Krista; Myrtil, Martine; Young, Paul; François, Kesner; Grand’Pierre, Reynold; Lowrance, David

    2017-01-01

    Objectives In October 2012, the Haitian Ministry of Health endorsed the “Option B+” strategy to eliminate mother-to-child transmission of HIV and achieve HIV epidemic control. The objective of this paper is to assess and identify risk factors for attrition from the national ART program among Option B+ patients in the 12 months after ART initiation. Design This retrospective cohort study included patients newly initiating ART from October 2012-August 2013 at 68 ART sites covering 45% of all newly enrolled ART patients in all regions of Haiti. Methods With data from electronic medical records, we carried out descriptive analysis of sociodemographic, clinical, and pregnancy-related correlates of ART attrition, and used a modified Poisson regression approach to estimate relative risks in a multivariable model. Results There were 2,166 Option B+ patients who initiated ART, of whom 1,023 were not retained by 12 months (47.2%). One quarter (25.3%) dropped out within 3 months of ART initiation. Protective factors included older age, more advanced HIV disease progression, and any adherence counseling prior to ART initiation, while risk factors included starting ART late in gestation, starting ART within 7 days of HIV testing, and using an atypical ART regimen. Discussion Our study demonstrates early ART attrition among Option B+ patients and contributes evidence on the characteristics of women who are most at risk of attrition in Haiti. Our findings highlight the importance of targeted strategies to support retention among Option B+ patients. PMID:28264045

  13. The Effect of Different Enlistment Ages on First-Term Attrition Rate

    Science.gov (United States)

    2014-03-01

    attrition data for enlistees by educational background, AFQT score, and age at the time of enlistment, gender, and race/ ethnic group. To determine...Inter-service separation Code (ISC), AFQT score and category, military service, and ethnicity . Records having separation dates earlier than the...30 51 Lesotho 18 24 52 Liberia 18 53 Lithuania 18 54 Luxembourg 18 24 55 Macedonia 18 56 Madagascar 18 25 57 Malawi 18 58 Malaysia

  14. Annotated Bibliography: Research on Enlisted Attrition in the U.S. Army

    Science.gov (United States)

    2007-07-01

    Behavioral and Social Sciences. (AD A320 954) This paper was the final report of an extensive research project, which focused on the development...should be clarified in recruiting manuals ; there should be a reconsideration of the use of moral waivers in light of these findings and an...DC: Gebicke, M. E. (AD A320 285) United States General Accounting Office. (1997). Military attrition: Better screening of enlisted personnel

  15. Inter-disciplinary management of a patient with severely attrited teeth

    Directory of Open Access Journals (Sweden)

    Padmanabhan Shyam

    2010-01-01

    Full Text Available With increased awareness about dental esthetics, multidisciplinary periodontal therapy has begun to gain momentum. Management of severely attrited teeth is a challenging situation and is dealt with a multidisciplinary approach. In cases of severe tooth wear, the crown height is drastically reduced, in some cases up to the gingival level. This might require a contribution from the disciplines of endodontics, periodontics, orthodontics and prosthodontics for predictable results. Herein we describe the management of one such case.

  16. Effect of acidity upon attrition-corrosion of human dental enamel.

    Science.gov (United States)

    Wu, Yun-Qi; Arsecularatne, Joseph A; Hoffman, Mark

    2015-04-01

    Attrition-corrosion is a synthesized human enamel wear process combined mechanical effects (attrition) with corrosion. With the rising consumption of acidic food and beverages, attrition-corrosion is becoming increasingly common. Yet, research is limited and the underlying mechanism remains unclear. In this study, in vitro wear loss of human enamel was investigated and the attrition-corrosion process and wear mechanism were elucidated by the analysis of the wear scar and its subsurface using focused ion beam (FIB) sectioning and scanning electron microscopy (SEM). Human enamel flat-surface samples were prepared with enamel cusps as the wear antagonists. Reciprocating wear testing was undertaken under load of 5N at the speed of 66 cycle/min for 2250 cycles with lubricants including citric acid (at pH 3.2 and 5.5), acetic acid (at pH 3.2 and 5.5) and distilled water. All lubricants were used at 37°C. Similar human enamel flat-surface samples were also exposed to the same solutions as a control group. The substance loss of enamel during wear can be linked to the corrosion potential of a lubricant used. Using a lubricant with very low corrosion potential (such as distilled water), the wear mechanism was dominated by delamination with high wear loss. Conversely, the wear mechanism changed to shaving of the softened layer with less material loss in an environment with medium corrosion potential such as citric acid at pH 3.2 and 5.5 and acetic acid at pH 5.5. However, a highly corrosive environment (e.g., acetic acid at pH 3.2) caused the greatest loss of substance during wear.

  17. Language, Teaching and Attrition: A Study on Selected Teachers Who Left the Profession

    Directory of Open Access Journals (Sweden)

    Aminu Aliyu Wushishi

    2016-02-01

    Full Text Available Nigeria is a country with over 520 different languages, the multitude nature of languages is making instructions so difficult in Schools, particularly in North-Central Nigeria where they have students with different language background attending the same school. The difficulty of smooth teaching in this kind of situation is leading to attrition among teachers. This study examines the situation of selected teachers in Niger State, Nigeria, who left the teaching profession as a result of difficulty in teaching their students, whom they said cannot efficiently understand the official language of instruction (English. The teachers highlighted their main reason of leaving the profession which is mainly associated with language problem among students, they added that, the massive failure of students in the final examination has a link with the student’s inability to understand what the teachers are teaching because of their poor background in English language. The paper recommends the use of one major local language (Hausa in teaching the students, this will make learning easy and students will efficiently comprehend instructions from their teachers, which may go a long way in reducing attrition. Keywords: Language, Teaching, Attrition

  18. Schistosoma mansoni: migration and attrition of irradiated and challenge schistosomula in the mouse

    Energy Technology Data Exchange (ETDEWEB)

    Mastin, A.J.; Wilson, R.A. (York Univ. (UK)); Bickle, Q.D. (Winches Farm Field Station, St. Albans (UK))

    1983-08-01

    The fate of irradiated, immunizing cercariae and challenge schistosomula was investigated in mice using a quantitative, histological technique which would appear to be more efficient in estimating parasite numbers in skin and lungs than does the tissue mincing and incubation recovery technique used previously by other workers. There was evidence for slight retardation of irradiated parasite migration in skin, but death of schistosomula in the skin appeared negligible. The majority of irradiated parasites remained in the lungs until at least day 21 after infection, and that most schistosomula observed at this time were dead. In mice immunized with irradiated cercariae there was no evidence of attrition of the challenge infection in the skin. The migration profile of challenge parasites in the lungs of immunized animals was not significantly different from that of normal parasites in the lungs of naive animals. Dead challenge parasites were observed in the lungs but their numbers were not considered great enough to account for the final attrition measured by perfusion. It is suggested that the remainder of the attrition of challenge schistosomula may occur in the systemic and/or hepatic portal circulation.

  19. Factors influencing nursing students' academic and clinical performance and attrition: an integrative literature review.

    Science.gov (United States)

    Pitt, Victoria; Powis, David; Levett-Jones, Tracy; Hunter, Sharyn

    2012-11-01

    Predicted workforce shortages have resulted in government initiatives to increase student numbers in preregistration nursing education. In tandem schools of nursing need to ensure students' progress and complete. The aim of this review was to identify factors that influence preregistration nursing students' academic performance, clinical performance and attrition. An integrative review of both quantitative and qualitative literature was conducted using validated appraisal checklists. The review included studies published from 1999 to 2011 in the databases: MEDLINE, CINAHL, Proquest nursing, Proquest Education (via Proquest 5000), ERIC, Journals@Ovid, PsychINFO and ScienceDirect. Studies were categorised according to their impact on academic progression, clinical progression and attrition. Forty four studies were found; most used quantitative methodologies. The review identified that few studies explored factors that impact on students' clinical performance. The four categories that potentially impact on nursing students' academic performance and attrition were: demographic, academic, cognitive and personality/behavioural factors. The challenge for universities committed to students' success is to develop strategies aimed at addressing these factors that are appropriate to specific contexts and student cohorts.

  20. Reliability of Dental Attrition as a Sole Parameter for Age Estimation among North Western Adult Indians

    Directory of Open Access Journals (Sweden)

    J. Arora

    2014-09-01

    Full Text Available Dental ageing is important in medico legal cases when teeth are the only material available to the investigating agencies for identification of the deceased. Attrition, which is the wear of occlusal surface of tooth (a physiological change; can be used as a determinant parameter for this purpose. The present study has been undertaken to examine the reliability of attrition as a sole parameter for age estimation among North Western adult Indians. 109 (43males, 66 females single rooted freshly extracted teeth ranging in age from 18-75years were studied. Teeth were fixed, cleaned and sectioned labiolingually upto thickness of 1mm. Sections were then mounted and attrition was graded from 0-3 according to Gustafson’s method. Scores were subjected to regression equation to estimate age of an individual. Results of the present study revealed that this parameter is reliable in individuals of ≤ 60 years with an error of ±10years. However, periodontal disease severely affected the accuracy of age estimation from this parameter as is evident from the results. Statistically no significant difference was noted in absolute mean error of age in different age groups. No significant difference was observed in absolute mean error of age in both the sexes.

  1. Growing up Overseas: Perceptions of Second Language Attrition and Retrieval Amongst Expatriate Children in India

    Directory of Open Access Journals (Sweden)

    Steve R. Sider

    2004-12-01

    Full Text Available Abstract This study involves expatriate children whose first language (L1 is English and who learned Hindi as their second language (L2 while their parents worked in India. The purpose of the study was to investigate the linguistic experiences of the children after they had left India, particularly experiences with L2 attrition. Through semi-structured interviews, subjects shared their stories of L2 acquisition and attrition. Common experiences which contributed to the attrition of the L2 included periods of non-use of the L2, social responses to the use of the L2, the lack of development of Hindi literacy and subjects’ attitude toward using the L2. Some of the subjects were able to retrieve the L2 on return trips to India and an examination is made of their perceptions of what supported this retrieval process. These include exposure to the “environment” of India and personal motivation. The conclusion provides questions and suggestions for further research to contribute to a better understanding of the linguistic experiences of expatriate children.

  2. Effect of Al2O3 Binder on the Precipitated Iron-Based Catalysts for Fischer-Tropsch Synthesis

    Institute of Scientific and Technical Information of China (English)

    Hai-Jun Wan; Bao-Shan Wu; Xia An; Ting-Zhen Li; Zhi-Chao Tao; Hong-Wei Xiang; Yong-Wang Li

    2007-01-01

    A series of iron-based Fischer-Tropsch synthesis (FTS) catalysts incorporated with Al2O3 binder were prepared by the combination of co-precipitation and spray drying technology. The catalyst samples were characterized by using N2 physical adsorption, temperature-programmed reduction/desorption (TPR/TPD) and M(o)ssbauer effect spectroscopy (MES) methods. The characterization results indicated that the BET surface area increases with increasing Al2O3 content and passes through a maximum at the Al2O3/Fe ratio of 10/100 (weight basis). After the point, it decreases with further increase in Al2O3 content. The incorporation of Al2O3 binder was found to weaken the surface basicity and suppress the reduction and carburization of iron-based catalysts probably due to the strong K-Al2O3 and Fe-Al2O3 interactions. Furthermore, the H2 adsorption ability of the catalysts is enhanced with increasing Al2O3 content. The FTS performances of the catalysts were tested in a slurry-phase continuously stirred tank reactor (CSTR) under the reaction conditions of 260 ℃, 1.5 MPa, 1000 h-1 and molar ratio of H2/CO 0.67 for 200 h. The results showed that the addition of small amounts of Al2O3 affects the activity of iron-based catalysts to a little extent. However, with further increase of Al2O3 content, the FTS activity and water gas shift reaction (WGS) activity are decreased severely. The addition of appropriate Al2O3 do not affect the product selectivity, but the catalysts incorporated with large amounts of Al2O3 have higher selectivity for light hydrocarbons and lower selectivity for heavy hydrocarbons.

  3. Toxicity of iron-based nanoparticles to green algae: Effects of particle size, crystal phase, oxidation state and environmental aging.

    Science.gov (United States)

    Lei, Cheng; Zhang, Luqing; Yang, Kun; Zhu, Lizhong; Lin, Daohui

    2016-11-01

    With the increasing environmental application and discharge of iron-based nanoparticles (NPs), a comprehensive understanding of their fate and ecotoxicological effect in the aquatic environment is very urgent. In this study, toxicities of 4 zero-valent iron NPs (nZVI) of different sizes, 2 Fe2O3 NPs of different crystal phases, and 1 type of Fe3O4 NPs to a green alga (Chlorella pyrenoidosa) were investigated, with a focus on the effects of particle size, crystal phase, oxidation state, and environmental aging. Results show that the algal growth inhibition of nZVI increased significantly with decreasing particle size; with similar particle sizes (20-30 nm), the algal growth inhibition decreased with oxidation of the NPs with an order of nZVI > Fe3O4 NPs > Fe2O3 NPs, and α-Fe2O3 NPs presented significantly higher toxicity than γ-Fe2O3 NPs. The NP-induced oxidative stress was the main toxic mechanism, which could explain the difference in algal toxicity of the NPs. The NP-cell heteroagglomeration and physical interactions also contributed to the nanotoxicity, whereas the effect of NP dissolution was negligible. The aging in distilled water and 3 surface water samples for 3 months increased surface oxidation of the iron-based NPs especially nZVI, which decreased the toxicity to algae. These findings will be helpful for the understanding of the fate and toxicity of iron-based NPs in the aquatic environment.

  4. Iron aluminide useful as electrical resistance heating elements

    Energy Technology Data Exchange (ETDEWEB)

    Sikka, V.K.; Deevi, S.C.; Fleischhauer, G.S.; Hajaligol, M.R.; Lilly, A.C. Jr.

    1999-11-02

    The invention relates generally to aluminum containing iron-base alloys useful as electrical resistance heating elements. The aluminum containing iron-base alloys have improved room temperature ductility, electrical resistivity, cyclic fatigue resistance, high temperature oxidation resistance, low and high temperature strength, and/or resistance to high temperature sagging. The alloy has an entirely ferritic microstructure which is free of austenite and includes, in weight %, over 4% Al, {le}1% Cr and either {ge}0.05% Zr or ZrO{sub 2} stringers extending perpendicular to an exposed surface of the heating element or {ge}0.1% oxide dispersoid particles. The alloy can contain 14--32% Al, {le}2% Ti, {le}2% Mo, {le}1% Zr, {le}1% C, {le}0.1% B, {le}30% oxide dispersoid and/or electrically insulating or electrically conductive covalent ceramic particles, {le}1% rare earth metal, {le}1% oxygen, {le}3% Cu, balance Fe.

  5. Oxidation, carburization and/or sulfidation resistant iron aluminide alloy

    Energy Technology Data Exchange (ETDEWEB)

    Sikka, Vinod K.; Deevi, Seetharama C.; Fleischhauer, Grier S.; Hajaligol, Mohammad R.; Lilly, Jr., A. Clifton

    2003-08-19

    The invention relates generally to aluminum containing iron-base alloys useful as electrical resistance heating elements. The aluminum containing iron-base alloys have improved room temperature ductility, electrical resistivity, cyclic fatigue resistance, high temperature oxidation resistance, low and high temperature strength, and/or resistance to high temperature sagging. The alloy has an entirely ferritic microstructure which is free of austenite and includes, in weight %, over 4% Al, .ltoreq.1% Cr and either .gtoreq.0.05% Zr or Zro.sub.2 stringers extending perpendicular to an exposed surface of the heating element or .gtoreq.0.1% oxide dispersoid particles. The alloy can contain 14-32% Al, .ltoreq.2% Ti, .ltoreq.2% Mo, .ltoreq.1% Zr, .ltoreq.1% C, .ltoreq.0.1% B. .ltoreq.30% oxide dispersoid and/or electrically insulating or electrically conductive covalent ceramic particles, .ltoreq.1% rare earth metal, .ltoreq.1% oxygen, .ltoreq.3% Cu, balance Fe.

  6. Iron aluminide useful as electrical resistance heating elements

    Energy Technology Data Exchange (ETDEWEB)

    Sikka, Vinod K. (Oak Ridge, TN); Deevi, Seetharama C. (Oak Ridge, TN); Fleischhauer, Grier S. (Midlothian, VA); Hajaligol, Mohammad R. (Richmond, VA); Lilly, Jr., A. Clifton (Chesterfield, VA)

    2001-01-01

    The invention relates generally to aluminum containing iron-base alloys useful as electrical resistance heating elements. The aluminum containing iron-base alloys have improved room temperature ductility, electrical resistivity, cyclic fatigue resistance, high temperature oxidation resistance, low and high temperature strength, and/or resistance to high temperature sagging. The alloy has an entirely ferritic microstructure which is free of austenite and includes, in weight %, over 4% Al, .ltoreq.1% Cr and either .gtoreq.0.05% Zr or ZrO.sub.2 stringers extending perpendicular to an exposed surface of the heating element or .gtoreq.0.1% oxide dispersoid particles. The alloy can contain 14-32% Al, .ltoreq.2% Ti, .ltoreq.2% Mo, .ltoreq.1% Zr, .ltoreq.1% C, .ltoreq.0.1% B, .ltoreq.30% oxide dispersoid and/or electrically insulating or electrically conductive covalent ceramic particles, .ltoreq.1% rare earth metal, .ltoreq.1% oxygen, .ltoreq.3% Cu, balance Fe.

  7. Iron aluminide useful as electrical resistance heating elements

    Energy Technology Data Exchange (ETDEWEB)

    Sikka, Vinod K. (Oak Ridge, TN); Deevi, Seetharama C. (Oak Ridge, TN); Fleischhauer, Grier S. (Midlothian, VA); Hajaligol, Mohammad R. (Richmond, VA); Lilly, Jr., A. Clifton (Chesterfield, VA)

    1999-01-01

    The invention relates generally to aluminum containing iron-base alloys useful as electrical resistance heating elements. The aluminum containing iron-base alloys have improved room temperature ductility, electrical resistivity, cyclic fatigue resistance, high temperature oxidation resistance, low and high temperature strength, and/or resistance to high temperature sagging. The alloy has an entirely ferritic microstructure which is free of austenite and includes, in weight %, over 4% Al, .ltoreq.1% Cr and either .gtoreq.0.05% Zr or ZrO.sub.2 stringers extending perpendicular to an exposed surface of the heating element or .gtoreq.0.1% oxide dispersoid particles. The alloy can contain 14-32% Al, .ltoreq.2% Ti, .ltoreq.2% Mo, .ltoreq.1% Zr, .ltoreq.1% C, .ltoreq.0.1% B, .ltoreq.30% oxide dispersoid and/or electrically insulating or electrically conductive covalent ceramic particles, .ltoreq.1% rare earth metal, .ltoreq.1% oxygen, .ltoreq.3% Cu, balance Fe.

  8. Orbital fluctuation theory in iron-based superconductors: s-wave superconductivity, structure transition, and impurity-induced nematic order

    OpenAIRE

    Kontani, H.; Inoue, Y.; Saito, T.; Yamakawa, Y.; Onari, S.

    2012-01-01

    The main features in iron-based superconductors would be (i) the orthorhombic transition accompanied by remarkable softening of shear modulus, (ii) high-Tc superconductivity close to the orthorhombic phase, and (iii) nematic transition in the tetragonal phase. In this paper, we present a unified explanation for them, based on the orbital fluctuation theory, considering both the e-ph and the Coulomb interaction. It is found that a small e-ph coupling constant ($\\lambda ~ 0.2$) is enough to pro...

  9. Creep-rupture behavior of a developmental cast-iron-base alloy for use up to 800 deg C

    Science.gov (United States)

    Titran, Robert H.; Scheuermann, Coulson M.

    1987-01-01

    A promising iron-base cast alloy is being developed as part of the DOE/NASA Stirling Engine Systems Project under contract DEN 3-282 with the United Technologies Research Center. This report presents the results of a study at the Lewis Research Center of the alloy's creep-rupture properties. The alloy was tested under a variety of conditions and was found to exhibit the normal 3-stage creep response. The alloy compared favorably with others being used or under consideration for the automotive Stirling engine cylinder/regenerator housing.

  10. Attrition of Knowledge Workforce in Healthcare in Northern parts of India – Health Information Technology as a Plausible Retention Strategy

    Directory of Open Access Journals (Sweden)

    Indrajit Bhattacharya

    2012-06-01

    Full Text Available Faced with a global shortage of skilled health workers due to attrition, countries are struggling to build and maintain optimum knowledge workforce in healthcare for delivering quality healthcare services. Forces that affect healthcare professionals’ turnover needs to be addressed before a competent uniformly adoptable strategy could be proposed for mitigating the problem. In this study we investigate the effects of the socio–demographic characteristics on attrition of healthcare knowledge workforce in northern parts of India that have a wide gradient of rural and urban belt, taking into account both public and private healthcare organizations. For this purpose healthcare professional attrition tracking survey (HATS was designed. The data has been collected from a random sample of 807 respondents consisting of doctors, nurses, paramedics and administrators to explore the relationships between various factors acting as antecedents in affecting the job satisfaction, commitment and intention of a healthcare professional to stay in the job. Structured questionnaires were utilized as the data collection tools. Descriptive statistics, factor analysis and path analysis were carried out using multiple regression and correlation to propose a model that best explains the theoretical assumption of factors leading to attrition. Six factors of attrition namely compensation and perks, work life balance, sense of accomplishment, work load, need for automation and technology improvement, substandard nature of work have been identified as the main factors with a data reliability of 0.809%. It has also been identified that the intention to shift is a major decision maker that affects attrition and in turn affected by job satisfaction dimensions. Based on the survey response and analysis, a highly possible strategy of utilizing information technology implementation for increasing worker motivation, job satisfaction and commitment to reduce attrition has been

  11. Determinants of Attrition to Follow-Up in a Multicentre Cohort Study in Children-Results from the IDEFICS Study

    Directory of Open Access Journals (Sweden)

    Sabrina Hense

    2013-01-01

    Full Text Available Cohort participant retention is a crucial element and may depend on several factors. Based on data from a multicentre cohort of European children, the effect of baseline participation on attrition and the association with and the impact of single determinants in relation to the extent of attrition were investigated. Data was available for 16,225 children from the IDEFICS baseline survey (2007/2008. Attrition was defined as nonparticipation in the first follow-up examination (2009/2010. Determinants of attrition were analysed by logistic regression. The statistical significance level was set at α=0.01 to account for the large sample size. The strongest associations were seen for baseline item non-response, especially when information on migration background (odds ratio (OR = 1.55; 99% confidence interval (CI: 1.04, 2.31, single parenthood (OR = 1.37; 99% CI: 1.12, 1.67, or well-being (OR = 1.46; 99% CI: 1.19, 1.79 was lacking. Drop-out proportion rose with the number of missing items. Overweight, low education, single parenthood and low well-being scores were independent determinants of attrition. Baseline participation, and the individual determinant effects seemed unrelated to the variation of the extent of attrition between study centres. A high level of item nonresponse as well as overweight and disadvantageous sociodemographic conditions were identified as main attrition determinants, suggesting the consideration of these aspects in conduct and analysis of cohort studies in childhood obesity research.

  12. Impact of Dynamic Orbital Correlations on Magnetic Excitations in the Normal State of Iron-Based Superconductors

    Science.gov (United States)

    Lee, Wei-Cheng; Lv, Weicheng; Tranquada, John; Phillips, Philip

    2013-03-01

    We show here that orbital degrees of freedom produce a distinct signature in the magnetic excitation spectrum of iron-based superconductors above the magnetic ordering temperature. Because dxz and dyz orbitals are strongly connected with Fermi surface topology, the nature of magnetic excitations can be modified significantly due to the presence of either static or fluctuating orbital correlations. Within a five-orbital itinerant model, we show that static orbital order generally leads to an enhancement of commensurate magnetic excitations even when the original Fermi surface lacks nesting at commensurate wavevectors. When long-range orbital order is absent, Gaussian fluctuations beyond the standard random-phase approximation capture the effects of fluctuating orbital correlations on the magnetic excitations. We find that commensurate magnetic excitations can also be enhanced if the orbital correlations are strong. We propose that this unusual incommensurate-to-commensurate transformation is an important signature to distinguish orbital from spin physics in the normal state of iron-based superconductors. This work is supported by the Center for Emergent Superconductivity, a DOE Energy Frontier Research Center, Grant No. DE-AC0298CH1088.

  13. Mössbauer studies of the peculiar magnetism in parent compounds of the iron-based superconductors

    Science.gov (United States)

    Jasek, A. K.; Komędera, K.; Błachowski, A.; Ruebenbauer, K.; Żukrowski, J.; Bukowski, Z.; Karpinski, J.

    2015-02-01

    A review of the magnetism in the parent compounds of the iron-based superconductors is given based on the transmission Mössbauer spectroscopy of 57Fe and 151Eu. It was found that the 3d magnetism is of the itinerant character with varying admixture of the spin-polarized covalent bonds. For the '122' compounds, a longitudinal spin density wave (SDW) develops. In the case of the EuFe2As2, a divalent europium arranges in an anti-ferromagnetical order at a much lower temperature as compared with the onset of SDW. These two magnetic systems remain almost uncoupled one to another. For the non-stoichiometric Fe1+xTe parent of the '11' family, one has a transversal SDW and magnetic order of the interstitial iron with relatively high and localized magnetic moments. These two systems are strongly coupled one to another. For the 'grand parent' of the iron-based superconductors FeAs, one observes two mutually orthogonal phase-related transversal SDW on the iron sites. There are two sets of such spin arrangements due to two crystallographic iron sites. The FeAs exhibits the highest covalency among the compounds studied, but it has still a metallic character. A contribution to XVI National Conference on Superconductivity, Zakopane, Poland, 7-12 October 2013.

  14. Iron-based superconductivity,then and now%铁基超导的前世今生

    Institute of Scientific and Technical Information of China (English)

    罗会仟

    2014-01-01

    High temperature superconductivity is one of the unresolved problems at the cutting edge of condensed matter physics, stimulated greatly by the recent discovery and studies of iron-based superconductors. Here we briefly review the history and basic concepts of superconduc-tivity, and the status of current research on copper-oxide high temperature superconductors. We will explain why iron-based superconductivity is so important as a key bridge between convention-al and high temperature superconductivity, and remark, in particular, on the significant contribu-tions from China.%高温超导机理被誉为凝聚态物理学前沿研究皇冠上的明珠,铁基超导的发现和研究极大地促进了人们对高温超导电性的理解。文章将简要回顾超导研究的历史和基本概念,介绍铜基高温超导研究的现状及困难,详述铁基超导的发现及其在高温超导研究中的关键桥梁作用,着重介绍中国科学家在铁基超导洪流中做出的重要贡献。

  15. Elevated temperature corrosion behavior of iron-base ternary alloys that develop Cr/sub 2/O/sub 3/ and/or Al/sub 2/O/sub 3/ barrier scales

    Energy Technology Data Exchange (ETDEWEB)

    Nagarajan, V.; Levy, A.V.

    1978-05-01

    The elevated temperature corrosion behavior of iron-base ternary alloys that develop Cr/sub 2/O/sub 3/ and/or Al/sub 2/O/sub 3/ barrier scales was investigated by exposing them to a mixed gas environment at 982/sup 0/C whose PO/sub 2/ was approximately 10/sup -18/ atm and whose PS/sub 2/ was approximately 10/sup -6/ atm. The alloys containing 18% Cr and 2.5 to 5% Al had the best corrosion resistance of the alloys tested. They developed a duplex Cr/sub 2/O/sub 3//Al/sub 2/O/sub 3/ scale through which sulfur did not readily diffuse. The 18% Cr alloy containing only 1% Al formed a Cr/sub 2/O/sub 3/ scale and had poor corrosion resistance because of rapid sulfur diffusion through the scale. Alloys that contained 10% Al and 0 to 15% Cr did not have good corrosion resistance because of sulfur diffusion through the single Al/sub 2/O/sub 3/ scale which formed. Alloys with 18% Cr that contained Si as a ternary addition did not develop continuous SiO/sub 2/ layers beneath the Cr/sub 2/O/sub 3/ outer scale and exhibited poor corrosion resistance.

  16. Structural transformations of amorphous iron-based alloys upon abrasive and thermal treatments

    Science.gov (United States)

    Korshunov, L. G.; Shabashov, V. A.; Litvinov, A. V.; Chernenko, N. L.

    2010-05-01

    Wear resistance and structural changes have been investigated in amorphous alloys Fe64Co30Si3B3 and Fe73.5Nb3Cu1Si13.5B9 upon wear using a fixed abrasive. The structural studies have been performed by the methods of metallography, electron microscopy, and Mössbauer spectroscopy. It has been shown that the abrasive resistance of amorphous alloys is 1.6-3.1 times lower than that of high-carbon tool steels, which have a close level of hardness. The low abrasive wear resistance of amorphous alloys is caused by the deformation softening of the alloy surface in the process of wear. The major volume of the deformed surface layer of the alloys preserves the amorphous state. Its structural changes upon wear are characterized by the formation of inhomogeneities (fragments with a size of 10-50 nm) and by a decrease in the width of the strongest “halo” in the selected-area electron-diffractions patterns. In the amorphous matrix of the Fe64Co30Si3B3 alloy, a strong magnetic texture is formed and a redistribution of atoms occurs, which leads to an increase in the local shortrange order corresponding to FeB, Fe2B, Fe3B and α-Fe phases. In microvolumes of a thin (several μm) surface layer, the formation of a nanocrystalline structure (on the order of several volume %) was revealed. A tempering of the Fe73.5Cu1Nb3S13.5B9 alloy at temperatures below 500°C does not affect the hardness and wear resistance of the alloy. At 500°C, there occurs an increase in microhardness and wear resistance of the Fe73.5Cu1Nb3S13.5B9 alloy as a result of the formation in it of a nanocrystalline structure with the retention of a certain amount of the amorphous phase. The complete crystallization of the alloy at 540°C increases the brittleness of the alloy, which leads to a sharp reduction in its wear resistance.

  17. Attrition of full-time faculty from schools of nursing with baccalaureate and graduate programs, 2010 to 2011.

    Science.gov (United States)

    Fang, Di; Bednash, Geraldine D

    2014-01-01

    The shortage of qualified faculty has been consistently reported as a major barrier impeding acceptance of all qualified applicants into nursing programs. In addition to faculty recruitment, the attrition of faculty is also a concern for schools of nursing. In this study, we found that nationally 11.8% of full-time faculty who worked in 2010 left their full-time jobs by 2011. Nearly half of total attrition, or 5.7% of full-time faculty members, were related to leaving for nonacademic nursing positions, whereas another 20% of attrition, or 2.4% of full-time faculty, resulted from retirement. Nearly 20% of faculty egressions, or 2.2% of full-time faculty, was due to leaving for nursing administrative positions or full-time faculty positions in an academic setting. Leaving for part-time faculty positions made up slightly more than 10% of faculty attrition or 1.3% of full-time faculty. Our bivariate analysis identifies distinctive academic and demographic profiles of faculty who left full-time positions for different reasons, and our multivariate analysis further shows that different individual and institutional attributes are significantly associated with different types of attrition.

  18. First Language Attrition Induces Changes in Online Morphosyntactic Processing and Re-Analysis: An ERP Study of Number Agreement in Complex Italian Sentences.

    Science.gov (United States)

    Kasparian, Kristina; Vespignani, Francesco; Steinhauer, Karsten

    2016-11-07

    First language (L1) attrition in adulthood offers new insight on neuroplasticity and the role of language experience in shaping neurocognitive responses to language. Attriters are multilinguals for whom advancing L2 proficiency comes at the cost of the L1, as they experience a shift in exposure and dominance (e.g., due to immigration). To date, the neurocognitive mechanisms underlying L1 attrition are largely unexplored. Using event-related potentials (ERPs), we examined L1-Italian grammatical processing in 24 attriters and 30 Italian native-controls. We assessed whether (a) attriters differed from non-attriting native speakers in their online detection and re-analysis/repair of number agreement violations, and whether (b) differences in processing were modulated by L1-proficiency. To test both local and non-local agreement violations, we manipulated agreement between three inflected constituents and examined ERP responses on two of these (subject, verb, modifier). Our findings revealed group differences in amplitude, scalp distribution, and duration of LAN/N400 + P600 effects. We discuss these differences as reflecting influence of attriters' L2-English, as well as shallower online sentence repair processes than in non-attriting native speakers. ERP responses were also predicted by L1-Italian proficiency scores, with smaller N400/P600 amplitudes in lower proficiency individuals. Proficiency only modulated P600 amplitude between 650 and 900 ms, whereas the late P600 (beyond 900 ms) depended on group membership and amount of L1 exposure within attriters. Our study is the first to show qualitative and quantitative differences in ERP responses in attriters compared to non-attriting native speakers. Our results also emphasize that proficiency predicts language processing profiles, even in native-speakers, and that the P600 should not be considered a monolithic component.

  19. Iron-based alloy and nitridation treatment for PEM fuel cell bipolar plates

    Science.gov (United States)

    Brady, Michael P [Oak Ridge, TN; Yang, Bing [Oak Ridge, TN; Maziasz, Philip J [Oak Ridge, TN

    2010-11-09

    A corrosion resistant electrically conductive component that can be used as a bipolar plate in a PEM fuel cell application is composed of an alloy substrate which has 10-30 wt. % Cr, 0.5 to 7 wt. % V, and base metal being Fe, and a continuous surface layer of chromium nitride and vanadium nitride essentially free of base metal. A oxide layer of chromium vanadium oxide can be disposed between the alloy substrate and the continuous surface nitride layer. A method to prepare the corrosion resistant electrically conductive component involves a two-step nitridization sequence by exposing the alloy to a oxygen containing gas at an elevated temperature, and subsequently exposing the alloy to an oxygen free nitrogen containing gas at an elevated temperature to yield a component where a continuous chromium nitride layer free of iron has formed at the surface.

  20. General English Attrition and Its Significance for Business English Teaching/Learning of Prospective Economists

    Directory of Open Access Journals (Sweden)

    Slavica Čepon

    2007-06-01

    Full Text Available This article summarizes some of the findings of a large-scale study of the foreign language needs of economics students (Čepon 2007. It focuses on the rationale behind the lengthy period of disuse of general English (GE during economics students’ first year of undergraduate study. The article presents evidence for processes of GE attrition that slowly set in and are deemed to be particularly detrimental to economics. It is also important to determine exactly which language needs are essential for the future professional development of the economics graduates. It is hoped that this will spur foreign language policy renewal.

  1. Attitudes of non-practicing chiropractors: a pilot survey concerning factors related to attrition

    Directory of Open Access Journals (Sweden)

    Wyatt Lawrence H

    2010-11-01

    Full Text Available Abstract Background Research into attitudes about chiropractors who are no longer engaged in active clinical practice is non-existent. Yet non-practicing chiropractors (NPCs represent a valid sub-group worthy of study. Aim The purpose of this research was to assess attrition attitudes of NPCs about the chiropractic profession and develop a scale to assess such attitudes. Methods A 48 item survey was developed using the PsychData software. This survey included 35 Likert-style items assessing various aspects of the profession namely financial, educational, psychosocial and political. An internet discussion site where NPCs may be members was accessed for recruitment purposes. Results A total of 70 valid responses were received for analysis. A majority of respondents were male with 66% being in non-practice status for 3 to 5 years and less with 43% indicating that they had graduated since the year 2000. Most respondents were employed either in other healthcare professions and non-chiropractic education. A majority of NPCs believed that business ethics in chiropractic were questionable and that overhead expense and student loans were factors in practice success. A majority of NPCs were in associate practice at one time with many believing that associates were encouraged to prolong the care of patients and that associate salaries were not fair. Most NPCs surveyed believed that chiropractic was not a good career choice and would not recommend someone to become a chiropractor. From this survey, a 12 item scale was developed called the "chiropractor attrition attitude scale" for future research. Reliability analysis of this novel scale demonstrated a coefficient alpha of 0.90. Conclusion The low response rate indicates that findings cannot be generalized to the NPC population. This study nonetheless demonstrates that NPCs attrition attitudes can be assessed. The lack of a central database of NPCs is a challenge to future research. Appropriate

  2. Ni-P-SiC composite coatings electroplated on carbon steel assisted by mechanical attrition

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Ni-P-SiC composite coatings were electroplated on carbon steel substrate assisted by mechanical attrition(MA).The MA action was conducted by dispersing glass balls on the cathodic surface,vibrating in the horizontal direction.The experimental results show that,under the assistant of MA action,the adhesion of Ni-P-SiC coating on the steel substrate can be improved effectively,and the Ni-P-SiC coatings exhibit a crystallized structure and Ni-P matrix can combine tightly with SiC particles,and the hardness and...

  3. Attrition in longitudinal randomized controlled trials: home visits make a difference

    Directory of Open Access Journals (Sweden)

    Peterson Janey C

    2012-11-01

    Full Text Available Abstract Background Participant attrition in longitudinal studies can introduce systematic bias, favoring participants who return for follow-up, and increase the likelihood that those with complications will be underestimated. Our aim was to examine the effectiveness of home follow-up (Home F/U to complete the final study evaluation on potentially “lost” participants by: 1 evaluating the impact of including and excluding potentially “lost” participants (e.g., those who required Home F/U to complete the final evaluation on the rates of study complications; 2 examining the relationship between timing and number of complications on the requirement for subsequent Home F/U; and 3 determining predictors of those who required Home F/U. Methods We used data from a randomized controlled trial (RCT conducted from 1991–1994 among coronary artery bypass graft surgery patients that investigated the effect of High mean arterial pressure (MAP (intervention vs. Low MAP (control during cardiopulmonary bypass on 5 complications: cardiac morbidity/mortality, neurologic morbidity/mortality, all-cause mortality, neurocognitive dysfunction and functional decline. We enhanced completion of the final 6-month evaluation using Home F/U. Results Among 248 participants, 61 (25% required Home F/U and the remaining 187 (75% received Routine F/U. By employing Home F/U, we detected 11 additional complications at 6 months: 1 major neurologic complication, 6 cases of neurocognitive dysfunction and 4 cases of functional decline. Follow-up of 61 additional Home F/U participants enabled us to reach statistical significance on our main trial outcome. Specifically, the High MAP group had a significantly lower rate of the Combined Trial Outcome compared to the Low MAP group, 16.1% vs. 27.4% (p=0.032. In multivariate analysis, participants who were ≥ 75 years (OR=3.23, 95% CI 1.52-6.88, p=0.002 or on baseline diuretic therapy (OR=2.44, 95% CI 1.14-5.21, p=0.02 were more

  4. Attrition tendinitis of long head of biceps brachii in relation to humeral head osteonecrosis: case report.

    Science.gov (United States)

    Wiesler, Ethan R; Sarlikiotis, Thomas; Mavrogenis, Andreas F; Kokkalis, Zinon T

    2013-01-01

    This case report identifies a 41-year-old male patient who developed anterior shoulder pain in the setting of humeral head osteonecrosis. As a consequence of the cartilage degeneration, multiple loose bodies formed and migrated into the bicipital tendon sheath, causing attrition tendinitis, which was a feature of the clinical presentation. The patient was treated by a combination of arthroscopic glenohumeral joint debridement and open tenodesis of the biceps using a suture anchor. Follow-up revealed asymptomatic shoulder function by 18 months. This is the first report in the literature of bicipital tendinitis in the context of avascular necrosis of the shoulder.

  5. Determinants of Attrition to Follow-Up in a Multicentre Cohort Study in Children-Results from the IDEFICS Study

    DEFF Research Database (Denmark)

    Hense, Sabrina; Pohlabeln, Hermann; Michels, Nathalie;

    2013-01-01

    at 훼 = 0 . 0 1 to account for the large sample size. The strongest associations were seen for baseline item non-response, especially when information on migration background (odds ratio (OR) = 1.55; 99% confidence interval (CI): 1.04, 2.31), single parenthood (OR = 1.37; 99% CI: 1.12, 1.67), or well......-being (OR = 1.46; 99% CI: 1.19, 1.79) was lacking. Drop-out proportion rose with the number of missing items. Overweight, low education, single parenthood and low well-being scores were independent determinants of attrition. Baseline participation, and the individual determinant effects seemed unrelated......Cohort participant retention is a crucial element and may depend on several factors. Based on data from a multicentre cohort of European children, the effect of baseline participation on attrition and the association with and the impact of single determinants in relation to the extent of attrition...

  6. Progress and prospect on the research of new iron-based high-Tc superconductors

    Institute of Scientific and Technical Information of China (English)

    Xian-hui CHEN

    2010-01-01

    @@ Since the discovery of high-Tc copper oxides, researches on high-Tc superconductors and their physical mechanism have become one of the hottest topics in condensed matter physics. In conventional superconductors, superconductivity occurs at very low temperatures. When superconductive, a material presents zero resistance and diamagnetism which is called Meissner Effect. The highTc superconductors are the materials whose superconducting transition temperatures are beyond the McMillan limit of 39 K. However, up to now, the mechanism of the copper oxide superconductors is still under debate.

  7. Superconductivity in iron-based compounds (Scientific session of the Physical Sciences Division of the Russian Academy of Sciences, 29 January 2014)

    Science.gov (United States)

    2014-08-01

    A scientific session of the Physical Sciences Division of the Russian Academy of Sciences (RAS), entitled 'Superconductivity in iron-based compounds', was held on 29 January 2014 at the conference hall of the Lebedev Physical Institute, RAS. The agenda of the session, announced on the website http://www.gpad.ac.ru of the RAS Physical Sciences Division listed the following reports: (1) Eremin I M (Institut für Theoretische Physik III, Ruhr-Universität Bochum, Bochum, Deutschland; Kazan (Volga region) Federal University, Kazan, Russian Federation) "Antiferromagnetism in iron-based superconductors: interaction of the magnetic, orbital, and lattice degrees of freedom"; (2) Korshunov M M (Kirenskii Institute of Physics, Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk) "Superconducting state in iron-based materials and spin-fluctuation pairing theory"; (3) Kuzmicheva T E (Lebedev Physical Institute, Russian Academy of Sciences, Moscow; Lomonosov Moscow State University) "Andreev spectroscopy of iron-based superconductors: temperature dependence of the order parameters and scaling of Δ_L, S with T_C"; (4) Eltsev Yu F (Lebedev Physical Institute, Russian Academy of Sciences, Moscow) "Synthesis and study of the magnetic and transport properties of iron-based superconductors of the 122 family". Papers written on the basis of oral presentations 1-4 are published below. • Antiferromagnetism in iron-based superconductors: magnetic order in the model of delocalized electrons, I M Eremin Physics-Uspekhi, 2014, Volume 57, Number 8, Pages 807-813 • Superconducting state in iron-based materials and spin-fluctuation pairing theory, M M Korshunov Physics-Uspekhi, 2014, Volume 57, Number 8, Pages 813-819 • Andreev spectroscopy of iron-based superconductors: temperature dependence of the order parameters and scaling of Δ_L, S with T_C, T E Kuzmicheva, S A Kuzmichev, M G Mikheev, Ya G Ponomarev, S N Tchesnokov, V M Pudalov, E P Khlybov, N D Zhigadlo Physics

  8. ADVANCED NICKEL-BASED AND NICKEL-IRON-BASED SUPERALLOYS FOR CIVIL ENGINEERING APPLICATIONS

    Institute of Scientific and Technical Information of China (English)

    U. Brill

    2005-01-01

    The use of high-temperature materials is especially important in power station construction,heating systems engineering, furnace industry, chemical and petrochemical industry, waste incineration plants, coal gasification plants and for flying gas turbines in civil and military aircrafts and helicopters. Particularly in recent years, the development of new processes and the drive to improve the economics of existing processes have increased the requirements significantly so that it is necessary to change from well-proven materials to new alloys. Hitherto, heat resistant ferritic steels sufficed in conventional power station constructions for temperatures up to 550℃ newly developed ferritic/martensitic steels provide sufficient strength up to about 600-620℃. In new processes, e.g. fiuidized-bed combustion of coal, process temperatures up to 900℃ occur. However, this is not the upper limit, since in combustion engines, e.g. gas turbines. Material temperatures up to 1100℃ are reached locally. Similar development trends can also be identified in the petrochemical industry and in the heat treatment and furnace engineering. The advance to ever higher material temperatures now not only has the consequence of having to use materials with enhanced high-strength properties, considerable attention now also has to be given to their chemical stability in corrosive media. Therefore not only examples of the use of high-temperature alloys for practical applications will be given but also be contributed to some general rules for material selection with regard to their high-temperature strength and corrosion resistance.

  9. Glass-Forming Ability of an Iron-Based Alloy Enhanced by Co Addition and Evaluated by a New Criterion

    Institute of Scientific and Technical Information of China (English)

    CHEN Qing-Jun; SHEN Jun; FAN Hong-Bo; SUN Jian-Fei; HUANG Yong-Jiang; MCCARTNEY D. G.

    2005-01-01

    @@ A new Fe-based alloy that can be cast into a fully amorphous rod with a diameter of at least 16mm by the conventional copper-mould casting technique is obtained by partially replacing Fe with Co in a previously reported Fe-based bulk metallic glass. The preliminary thermodynamic analysis indicates that the Co-containing alloy has a significantly lower Gibbs free energy difference between the undercooled melt and the corresponding crystalline solid, compared to the Co-free alloy, reflecting the dramatic role of the Co addition in stabilizing the supercooled melt and facilitating glass formation in iron-based alloys. Here, a new criterion, derived from the classical nucleation and growth theory, is introduced to evaluate the glass-forming ability of Fe-based bulk metallic glasses.

  10. Effect of Addition Sequence during Neutralization and Precipitation on Iron-based Catalysts for High Temperature Shift Reaction

    Institute of Scientific and Technical Information of China (English)

    Li Wei; Zhu Jianhua; Mou Zhanjun

    2007-01-01

    The preparation of the iron-based catalysts promoted by cobalt with a small amount of copper and aluminum for the high temperature shift reaction (HTS) with different sequences of adding catalyst raw materials during neutralization and precipitation was investigated. XRD,BET and particle size distribution (PSD) were used to characterize the prepared catalysts. It was found that the catalyst crystals were all γ-Fe2O3,and the intermediate of the catalyst after aging was Fe3O4. The crystallographic form of the catalyst and its intermediate was not affected by the addition sequence in the neutralization and precipitation process. The results showed that the specific surface area and the particle size of the catalysts depended on the addition sequence to the mother liquor. Cobalt with a small amount of copper and aluminum could increase the specific surface area and decrease the particle size of catalysts.

  11. Continuous production of iron-based nanocrystals by laser pyrolysis. Effect of operating variables on size, composition and magnetic response

    Science.gov (United States)

    Malumbres, A.; Martínez, G.; Mallada, R.; Hueso, J. L.; Bomatí-Miguel, O.; Santamaría, J.

    2013-08-01

    Well dispersed iron-based magnetic nanoparticles have been prepared by gas phase laser-driven decomposition of iron pentacarbonyl. Agglomeration of the newly synthesized nanoparticles could be avoided by using a liquid collection system in which the exit stream from the laser reactor was bubbled through triethylene glycol (TREG). The effect of different experimental parameters (precursor concentration, laser power, working pressure, residence time) was studied and, by selecting the appropriate conditions, the size of the resulting magnetic nanocrystals could be tuned from ultrasmall (ca. 2.5 nm) to around 12 nm. For nanoparticle sizes around 10 nm and larger a metallic iron core could be preserved. These iron/iron oxide core-shell compositions exhibit very high values of magnetization, 127 emu g-1.

  12. Spin and quadrupolar orders in the spin-1 bilinear-biquadratic model for iron-based superconductors

    Science.gov (United States)

    Luo, Cheng; Datta, Trinanjan; Yao, Dao-Xin

    2016-06-01

    Motivated by the recent experimental and theoretical progress of the magnetic properties in iron-based superconductors, we provide a comprehensive analysis of the extended spin-1 bilinear-biquadratic (BBQ) model on the square lattice. Using a variational approach at the mean-field level, we identify the existence of various magnetic phases, including conventional spin dipolar orders (ferro- and antiferromagnet), novel quadrupolar orders (spin nematic), and mixed dipolar-quadrupolar orders. In contrast to the regular Heisenberg model, the elementary excitations of the spin-1 BBQ model are described by the SU(3) flavor-wave theory. By fitting the experimental spin-wave dispersion, we determine the refined exchange couplings corresponding to the collinear antiferromagnetic iron pnictides. We also present the dynamic structure factors of both spin dipolar and quadrupolar components with connections to the future experiments.

  13. Effects of sample attrition in a longitudinal study of the association between alcohol intake and all-cause mortality

    DEFF Research Database (Denmark)

    Thygesen, Lau C; Johansen, Christoffer; Keiding, Niels;

    2008-01-01

    to evaluate how attrition affected the association between alcohol intake and mortality. The statistical methods used for dealing with missing values were complete case analysis, carry last observation forward, simple imputations, multiple imputation and weighting. FINDINGS: Abstinence and high alcohol intake......, current smoking, physical inactivity and high body mass index increased the odds of dropping out, whereas being married, more years of education, skilled occupation, high income and large residential area decreased the odds. Attrition was associated with increased mortality and incidence rates of heart...

  14. Effect of mass transfer limitations on catalyst performance during reduction and carburization of iron based Fischer-Tropsch synthesis catalysts

    Institute of Scientific and Technical Information of China (English)

    Akbar; Zamaniyan; Yadollah; Mortazavi; Abbas; Ali; Khodadadi; Ali; Nakhaei; Pour

    2013-01-01

    Existence of intraparticle mass transfer limitations under typical Fischer-Tropsch synthesis has been reported previously,but there is no suitable study on the existence of intraparticle diffusion limitations under pretreatment steps (reduction and activation) and their effect on catalytic performance for iron based catalysts.In this study,Fe-Cu-La-SiO2 catalysts were prepared by co-precipitation method.To investigate the intraparticle mass transfer limitation under reduction,activation and reaction steps,and its effect on catalytic performance,catalyst pellets with different sizes of 6,3,1 and 0.5 mm have been prepared.All catalysts were calcined,pretreated and tested under similar conditions.The catalysts were activated in hydrogen (5%H2in N2) at 450℃ for 3 h and exposed to syngas (H2/CO=1) at 270℃ and atmospheric pressure for 40 h.Afterwards,FTS reaction tests were performed for approximately 120 h to reach steady state conditions at 290℃,17 bar and a feed flow (syngas H2/CO=1) rate of 3 L/h (STP).Using small pellets resulted in higher CO conversion,FT reaction rate and C5+ productivity as compared with larger pellets.The small pellets reached steady state conditions just 20 h after starting the reaction.Whereas for larger pellets,CO conversion,FT reaction rate and C5+ productivity increased gradually,and reached steady state and maximum values after 120 h of operation.The results illustrate that mass transfer limitations exist not only for FTS reaction but also for the reduction and carburization steps which lead to various phase formation through catalyst activation.Also the results indicate that some effects of mass transfer limitations in activation step,can be compensated in the reaction step.The results can be used for better design of iron based catalyst to improve the process economy.

  15. Polyvinylpyrrolidone and arsenic-induced changes in biological responses of model aquatic organisms exposed to iron-based nanoparticles

    Science.gov (United States)

    Llaneza, Verónica; Rodea-Palomares, Ismael; Zhou, Zuo; Rosal, Roberto; Fernández-Pina, Francisca; Bonzongo, Jean-Claude J.

    2016-08-01

    The efficiency of zero-valent iron particles used in the remediation of contaminated groundwater has, with the emergence of nanotechnology, stimulated interest on the use of nano-size particles to take advantage of high-specific surface area and reactivity characteristics of nanoparticles (NPs). Accordingly, engineered iron-NPs are among the most widely used nanomaterials for in situ remediation. However, while several ecotoxicity studies have been conducted to investigate the adverse impacts of these NPs on aquatic organisms, research on the implications of spent iron-based NPs is lacking. In this study, a comparative approach is used, in which the biological effects of three iron-based NPs (Fe3O4 and γ-Fe2O3 NPs with particle sizes ranging from 20 to 50 nm, and Fe0-NPs with an average particle size of 40 nm) on Raphidocelis subcapitata (formely known as Pseudokirchneriella subcapitata) and Daphnia magna were investigated using both as-prepared and pollutant-doped Fe-based NPs. For the latter, arsenic (As) was used as example sorbed pollutant. The results show that improved degree of NP dispersion by use of polyvinylpyrrolidone overlapped with both increased arsenic adsorption capacity and toxicity to the tested organisms. For R. subcapitata, Fe-oxide NPs were more toxic than Fe0-NPs, due primarily to differences in the degree of NPs aggregation and ability to produce reactive oxygen species. For the invertebrate D. magna, a similar trend of biological responses was observed, except that sorption of As to Fe0-NPs significantly increased the toxic response when compared to R. subcapitata. Overall, these findings point to the need for research on downstream implications of NP-pollutant complexes generated during water treatment by injection of NPs into aquatic systems.

  16. A computational investigation of attrition-enhanced chiral symmetry breaking in conglomerate crystals

    Science.gov (United States)

    Ricci, Francesco; Stillinger, Frank H.; Debenedetti, Pablo G.

    2013-11-01

    Attrition-enhanced chiral symmetry breaking in crystals, also known as Viedma ripening, is a remarkable phenomenon from a variety of perspectives. By providing a direct route to solid-phase homochirality in a controllable manner, it is of inherent interest to those who study chiral symmetry-breaking/amplification mechanisms. When applied to intrinsically chiral molecules, Viedma ripening may have implications for the origin of biological homochirality, as well as applications in chiral drug resolution. Despite an abundance of research, the mechanistic details underlying this phenomenon have not been unambiguously elucidated. We employ a Monte Carlo algorithm to study this driven system, in order to gain further insights into the mechanisms capable of reproducing key experimental signatures. We provide a comprehensive numerical investigation of how the model parameters (attrition rate, liquid-phase racemization kinetics, and the relative rates of growth and dissolution kinetics) impact the system's overall behavior. It is shown that size-dependent crystal solubility alone is insufficient to reproduce most of the experimental signatures of Viedma ripening, and that some form of a solid-phase chiral feedback mechanism must be invoked in order to reproduce experimentally observed behavior. In this work, such feedback mechanisms can take the form of agglomeration, or of artificial modification of the size dependent growth kinetics.

  17. Environmentally friendly pretreatment of plant biomass by planetary and attrition milling.

    Science.gov (United States)

    Kim, Hyeon Jeong; Lee, Siseon; Kim, Jungbae; Mitchell, Robert J; Lee, Jin Hyung

    2013-09-01

    This study evaluated the use of planetary and attrition milling as pretreatment processes for lignocellulosic biomass using rice straw. Planetary milling reduced the rice straw crystallinity from 0.48 to 0.11. Since the samples could be milled and enzymatically treated using the same media, loss of the biomass due to washing was effectively eliminated. In contrast, conventional sodium hydroxide and soaking in aqueous ammonia (SAA) processes showed a loss of 34.2% and 14.8%, respectively. Furthermore, milling produced significantly lower concentrations of soluble phenolics than the alkali treatments. Using a bioluminescent bioreporter strain that is sensitive to these phenolics, neither of the milled samples elicited a response while the sodium hydroxide and SAA samples led to a 25.8 and 4.7 -fold induction, respectively. Although planetary milling produced more reducing sugars than attrition milling before saccharification, both had similar monosaccharide yields, i.e., 0.38 and 0.34 g/g-biomass, respectively, when 40 g/l rice straw was treated.

  18. Determinants of telomere attrition over 1 year in healthy older women: stress and health behaviors matter.

    Science.gov (United States)

    Puterman, E; Lin, J; Krauss, J; Blackburn, E H; Epel, E S

    2015-04-01

    Telomere length, a reliable predictor of disease pathogenesis, can be affected by genetics, chronic stress and health behaviors. Cross-sectionally, highly stressed postmenopausal women have shorter telomeres, but only if they are inactive. However, no studies have prospectively examined telomere length change over a short period, and if rate of attrition is affected by naturalistic factors such as stress and engagement in healthy behaviors, including diet, exercise, and sleep. Here we followed healthy women over 1 year to test if major stressors that occurred over the year predicted telomere shortening, and whether engaging in healthy behaviors during this period mitigates this effect. In 239 postmenopausal, non-smoking, disease-free women, accumulation of major life stressors across a 1-year period predicted telomere attrition over the same period-for every major life stressor that occurred during the year, there was a significantly greater decline in telomere length over the year of 35 bp (P<0.05). Yet, these effects were moderated by health behaviors (interaction B=0.19, P=0.04). Women who maintained relatively higher levels of health behaviors (1 s.d. above the mean) appeared to be protected when exposed to stress. This finding has implications for understanding malleability of telomere length, as well as expectations for possible intervention effects. This is the first study to identify predictors of telomere length change over the short period of a year.

  19. Determinants of telomere attrition over one year in healthy older women: Stress and health behaviors matter

    Science.gov (United States)

    Puterman, Eli; Lin, Jue; Krauss, Jeffrey; Blackburn, Elizabeth H.; Epel, Elissa S.

    2014-01-01

    Telomere length, a reliable predictor of disease pathogenesis, can be affected by genetics, chronic stress, and health behaviors. Cross-sectionally, highly stressed post-menopausal women have shorter telomeres, but only if they are inactive. However, no studies have prospectively examined telomere length change over a short period, and if rate of attrition is affected by naturalistic factors such as stress and engagement in healthy behaviors. Here we followed healthy women over one year to test if major stressors that occurred over the year predicted telomere shortening, and whether engaging in healthy behaviors during this period mitigates this effect. In 239 post-menopausal, non-smoking, disease-free women, accumulation of major life stressors across a one-year period predicted telomere attrition over the same period - for every major life stressor that occurred during the year, there was a significantly greater decline in telomere length over the year of 35 base pairs (p < .05). Yet, these effects were moderated by health behaviors (interaction B = 0.19, p = .04). Women who maintained relatively higher levels of health behaviors (one standard deviation above the mean) appeared to be protected when exposed to stress. This finding has implications for understanding malleability of telomere length, as well as expectations for possible intervention effects. This is the first study to identify predictors of telomere length change over the short period of a year. PMID:25070535

  20. Attrition in Chronic Disease Self-Management Programs and self-efficacy at enrollment.

    Science.gov (United States)

    Verevkina, Nina; Shi, Yunfeng; Fuentes-Caceres, Veronica Alejandra; Scanlon, Dennis Patrick

    2014-12-01

    Among other goals, the Chronic Disease Self-Management Program (CDSMP) is designed to improve self-efficacy of the chronically ill. However, a substantial proportion of the enrollees often leave CDSMPs before completing the program curriculum. This study examines factors associated with program attrition in a CDSMP implemented in a community setting. We used data from the Our Pathways to Health program, implemented in Humboldt County, California, from 2008 to 2011. Our conceptual framework is based on Bandura's self-efficacy theory, and we used logistic regression to investigate whether baseline self-efficacy and other members' efficacy are associated with participants dropping out of the CDSMP. Twenty-three percent of the participants did not complete the program similar to previous studies. Lower baseline self-efficacy increased the odds of dropout, but other members' efficacy was not associated with differential odds of dropout. Age, educational difference between the individual and the group, weekday sessions, and social/role activity limitations are also found to be associated with program attrition. Our results suggest that participants with low starting self-efficacy may need extra help to complete the program. Further research is needed to understand how to effectively provide additional support to this group.

  1. When Is Ignorance Bliss? The Effects of Inaccurate Self-Assessments of Knowledge on Learning and Attrition

    Science.gov (United States)

    Sitzmann, Traci; Johnson, Stefanie K.

    2012-01-01

    Two studies were conducted to examine the implications of inaccurate self-appraisals in online training. Self-assessment of knowledge moderated the effects of trainees' performance on subsequent performance and attrition. Performance was highest after uniformly positive ratings (i.e., high self-assessment and high performance), followed by…

  2. A Study of Attrition and the Use of Student Learning Communities in the Computer Science Introductory Programming Sequence

    Science.gov (United States)

    Howles, Trudy

    2009-01-01

    Student attrition and low graduation rates are critical problems in computer science education. Disappointing graduation rates and declining student interest have caught the attention of business leaders, researchers and universities. With weak graduation rates and little interest in scientific computing, many are concerned about the USA's ability…

  3. After the Two-Year Commitment: A Quantitative and Qualitative Inquiry of Teach For America Teacher Retention and Attrition

    Science.gov (United States)

    Heineke, Amy J.; Mazza, Bonnie Streff; Tichnor-Wagner, Ariel

    2014-01-01

    Teach For America (TFA), an organization that places college graduates as teachers in low-income areas for 2 years, contributes to teacher attrition. With this mixed methods study in one urban region, we investigated teachers' professional decisions at the end of 2 years. Respondents fell into categories in relation to the organization's…

  4. Perceived Foreign Accent in First Language Attrition and Second Language Acquisition: The Impact of Age of Acquisition and Bilingualism

    Science.gov (United States)

    Hopp, Holger; Schmid, Monika S.

    2013-01-01

    This study investigates constraints on ultimate attainment in second language (L2) pronunciation in a direct comparison of perceived foreign accent of 40 late L2 learners and 40 late first language (L1) attriters of German. Both groups were compared with 20 predominantly monolingual controls. Contrasting participants who acquired the target…

  5. Research Findings on Early First Language Attrition: Implications for the Discussion on Critical Periods in Language Acquisition

    Science.gov (United States)

    Francis, Norbert

    2005-01-01

    Childhood bilingualism may develop toward a steady state of balanced competence in 2 languages or toward an imbalanced competence in which one of the child's languages begins to undergo attrition or early stabilization. In child second language learning an analogous distinction is often drawn between additive and subtractive bilingualism. This…

  6. First Language Attrition in the Speech of Dutch-English Bilinguals: The Case of Monozygotic Twin Sisters

    Science.gov (United States)

    Mayr, Robert; Price, Sacha; Mennen, Ineke

    2012-01-01

    Recent years have seen a proliferation of research on attrition in L1 speech (de Leeuw, Mennen & Scobbie, in press; de Leeuw, Schmid & Mennen, 2010; Dmitrieva, Jongman & Sereno, 2010; Mennen, 2004). Adding to this line of inquiry, the present study investigates the speech of a 62-year-old bilingual monozygotic twin who emigrated to an L2-speaking…

  7. Strong bioresorbable Ca phosphate-PLA nanocomposites with uniform phase distribution by attrition milling and high pressure consolidation.

    Science.gov (United States)

    Rakovsky, Artoum; Gotman, Irena; Rabkin, Eugen; Gutmanas, Elazar Y

    2013-02-01

    Highly dense bioresorbable Ca-deficient HA-PLA (CDHA-PLA) and β-TCP-PLA nanocomposite materials with high (up to 80 vol%) contents of the calcium phosphate (CaP) phase and homogeneous phase distribution were prepared via attrition milling followed by high pressure consolidation at ambient temperature. The microstructure and mechanical properties of the materials obtained were studied as a function of milling time and PLA amount. Attrition milling resulted in disintegration of β-TCP powder agglomerates down to 50-150 nm, disintegration of CDHA agglomerates and refinement of 15 × 150 nm(2) CDHA nanoparticles to a size of 8 × 20 nm(2), and in a uniform distribution of the polymer component. Very high compressive strengths up to 400 MPa and high bending strengths up to 70 MPa were obtained. For both β-TCP and CDHA-based nanocomposites, the strength characteristics increased with milling time and decreased with increasing PLA content. For CDHA-based nanocomposites, attrition milling resulted in decrease of ductility while for β-TCP-40 vol% PLA the ductility increased. The observed behavior may be a result of formation of homogeneous, relatively thick (tens of nanometers), ductile PLA layers in β-TCP-PLA nanocomposites, but very thin (several nanometers) PLA layers in attrition milled CDHA-PLA nanocomposites. Degradation of compressive and bending strength in aqueous solutions was observed for all the studied CaP-PLA nanocomposites.

  8. Lexical Attrition of General and Special English Words after Years of Non-Exposure: The Case of Iranian Teachers

    Science.gov (United States)

    Abbasian, Reza; Khajavi, Yaser

    2010-01-01

    This study sought to investigate the rate of attrition in general and special vocabulary in and out of context. Participants of the study were 210 male Persian literature teachers with different years of non-exposure to English (2, 4, 5, 6, 7, 8 &10) after graduating from university. They were selected through purposive sampling from among…

  9. Psychological attributes and changes in disability among low-functioning older persons : Does attrition affect the outcomes?

    NARCIS (Netherlands)

    Kempen, GIJM; van Sonderen, E

    2002-01-01

    The impact of attrition was studied in a two-wave panel study on the associations between psychological attributes (mastery, self-efficacy expectancies) and disability increase among low-functioning older persons (n=753, 76.4% participated at the follow-up 2 years later). The results showed that: (1

  10. Perceived foreign accent in first language attrition and second language acquisition : The impact of age of acquisition and bilingualism

    NARCIS (Netherlands)

    Hopp, Holger; Schmid, Monika S.

    2013-01-01

    This study investigates constraints on ultimate attainment in second language (L2) pronunciation in a direct comparison of perceived foreign accent of 40 late L2 learners and 40 late first language (L1) attriters of German. Both groups were compared with 20 predominantly monolingual controls. Contra

  11. From Attrition to Retention: A Narrative Inquiry of Why Beginning Teachers Leave and Then Rejoin the Profession

    Science.gov (United States)

    Harfitt, Gary James

    2015-01-01

    The issue of beginning teachers leaving the profession in the first few years of their career represents a global problem, and while discrepancies exist over precise numbers, there is consensus that the attrition rate of new teachers is high. This paper reports on a narrative inquiry into two beginning teachers who left the profession after just…

  12. The influence of autonomy support on self-regulatory processes and attrition in the Royal Dutch Navy

    NARCIS (Netherlands)

    Delahaij, R.; Theunissen, N.C.M.; Six, C.

    2014-01-01

    The purpose of this study was to investigate the underlying mechanisms that explain the influence of instructor support on attrition levels within Navy basic military training. Based on self-determination theory, we hypothesized that higher autonomy support leads to lower intent to quit, mediated by

  13. Job Satisfaction, Self-Efficacy, Burnout, and Path of Teacher Certification: Predictors of Attrition in Special Education Teachers

    Science.gov (United States)

    Johnson, Bradley W.

    2010-01-01

    This study investigated the constructs of job satisfaction, self-efficacy, burnout and path of certification in relation to attrition of special education teachers. A correlational, predictive design assessed the five facets of the abridged Job Descriptive Index and the abridged Job in General survey, the factors of the Teacher Self-Efficacy…

  14. Teacher Attrition and Mobility during the Teach for America Clustering Strategy in Miami-Dade County Public Schools

    Science.gov (United States)

    Hansen, Michael; Backes, Ben; Brady, Victoria

    2016-01-01

    Retaining effective teachers is a key policy priority nationwide, particularly in districts that serve large numbers of disadvantaged students. We investigate whether a change in the Miami region's Teach for America (TFA) placement strategy was accompanied by changes in teacher attrition and mobility decisions. Our results suggest that the…

  15. The Relationship between Organizational Climate and Selected Variables of Productivity-Reading Achievement, Teacher Experience and Teacher Attrition.

    Science.gov (United States)

    Smith, Stanley Jeffery

    This study investigated the relationship between organizational climate and selected organizational variables--reading achievement, teacher experience, and teacher attrition. The study sample consisted of the total teaching staffs and 642 randomly selected students from five elementary schools in a metropolitan school district. Data were collected…

  16. Inside the Black Box of Doctoral Education: What Program Characteristics Influence Doctoral Students' Attrition and Graduation Probabilities?

    Science.gov (United States)

    Ehrenberg, Ronald G.; Jakubson, George H.; Groen, Jeffrey A.; So, Eric; Price, Joseph

    2007-01-01

    The Andrew W. Mellon Foundation's Graduate Education Initiative (GEI) provided funding to 54 departments in the humanities and related social sciences during the 1990s to improve their PhD programs. This article estimates the aspects of PhD programs the GEI influenced and how these aspects influenced attrition and graduation probabilities. It uses…

  17. Factors associated with long-term antiretroviral therapy attrition among adolescents in rural Uganda: a retrospective study

    Directory of Open Access Journals (Sweden)

    Stephen Okoboi

    2016-07-01

    Full Text Available Introduction: As access to antiretroviral therapy (ART increases, the success of treatment programmes depends on ensuring high patient retention in HIV care. We examined retention and attrition among adolescents in ART programmes across clinics operated by The AIDS Support Organization (TASO in Uganda, which has operated both facility- and community-based distribution models of ART delivery since 2004. Methods: Using a retrospective cohort analysis of patient-level clinical data, we examined attrition and retention in HIV care and factors associated with attrition among HIV-positive adolescents aged 10–19 years who initiated ART at 10 TASO clinics between January 2006 and December 2011. Retention in care was defined as the proportion of adolescents who had had at least one facility visit within the six months prior to 1 June 2013, and attrition was defined as the proportion of adolescents who died, were lost to follow-up, or stopped treatment. Descriptive statistics and Cox proportional hazards regression models were used to determine the levels of retention in HIV care and the factors associated with attrition following ART initiation. Results: A total of 1228 adolescents began ART between 2006 and 2011, of whom 57% were female. The median duration in HIV care was four years (IQR=3–6 years. A total of 792 (65% adolescents were retained in care over the five-year period; 36 (3% had died or transferred out and 400 (32% were classified as loss to follow-up. Factors associated with attrition included being older (adjusted hazard ratio (AHR=1.38, 95% confidence interval (CI 1.02–1.86, having a higher CD4 count (250+ cells/mm3 at treatment initiation (AHR=0.49, 95% CI 0.34–0.69 and HIV care site with a higher risk of attrition among adolescents in Gulu (AHR=2.26; 95% CI 1.27–4.02 and Masindi (AHR=3.30, 95% CI 1.87–5.84 and a lower risk of attrition in Jinja (AHR=0.24, 95% CI 0.08–0.70. Having an advanced WHO clinical stage at initiation

  18. Stalagmite Survival: 500kyr of Cyclical Growth and Natural Attrition of Stalagmites in Sulawesi

    Science.gov (United States)

    Scroxton, N.; Gagan, M. K.; Dunbar, G. B.; Ayliffe, L. K.; Hantoro, W. S.; Shen, C. C.; Hellstrom, J. C.; Zhao, J. X.; Cheng, H.; Edwards, R. L.; Sun, H.; Rifai, H.

    2014-12-01

    Numerous speleothem studies have analysed the age distribution of stalagmites harvested from multiple caves and inferred important changes in paleoclimates to explain stalagmite growth phases. However, stalagmites take tens to hundreds of thousands of years to grow, and thus the twin desires to preserve the cave condition for future generations and advance palaeoclimate science are often in conflict. In this study we use U/Th ages from low impact mini-cores extracted in situ from the bases of stalagmites, thus keeping the intrinsic value of the cave intact. Our case study is based on 77 individual stalagmites drilled in situ in thirteen caves located in and around Bantimurung-Bulusaraung National Park, South Sulawesi, Indonesia. The stalagmites grew during discrete time intervals within the last ~530,000 years, and analysis of their age distribution shows an exponential decrease in the number of older stalagmites surviving to the present day. The age distribution indicates that the rate of natural attrition of stalagmites is approximately constant through time, probably in response to a number of natural processes, including downward erosion of the karst terrain, cave collapse, in-cave erosional processes and in-cave sedimentation covering stalagmites. Natural attrition of stalagmites is likely to be a general cave phenomenon, and has important implications for cave conservation because it highlights that random removal of stalagmites without prior knowledge of their ages will result in unnecessary replication and a failure to sample the full length of the available paleoclimate record. Departure from this "normal" exponential profile can be used to infer palaeoclimate information: significant deviations are produced by periods of more frequent stalagmite growth, inferred here to reflect increases in monsoon rainfall over Sulawesi (345-340, 75-70 and 10-5 kyr BP). By adjusting the record to account for stalagmite attrition, more statistically robust paleoclimate

  19. Efficient and stable iron based perovskite La0.9Ca0.1Fe0.9Nb0.1O3-δ anode material for solid oxide fuel cells

    Science.gov (United States)

    Kong, Xiaowei; Zhou, Xiaoliang; Tian, Yu; Wu, Xiaoyan; Zhang, Jun; Zuo, Wei; Gong, Xiaobo; Guo, Zhanhu

    2016-06-01

    A novel La0.9Ca0.1Fe0.9Nb0.1O3-δ (LCFNb) perovskite for solid oxide fuel cells (SOFCs) anode is prepared by means of the citrate-nitrate route and composited with Ce0.8Sm0.2O1.9 (SDC) by impregnation method to form nano-scaled LCFNb/SDC anode catalytic layers. The single cells with LCFNb and LCFNb/SDC impregnated anodes both achieve relatively high power output with maximum power densities (MPDs) reaching up to 610, 823 mW·cm-2 in H2 at 800 °C, respectively, presenting a high potential of LCFNb for use as SOFCs anode. The power outputs of the single cells with LCFNb/SDC composite anode in CO and syngas (COsbnd H2 mixture) are almost identical to that in H2 at each testing temperature. This composite anode also presents excellent durability in both H2 and CO for as long as 50 h, showing desirable anti-reduction and carbon deposition resistance abilities. Besides, the cell output is stable in 100 ppm H2Ssbnd H2 atmospheres for 20 h at a current density of 600 mA·cm-2 with negligible sulfur accumulation on the anode surface. Hence, a novel iron based perovskite LCFNb anode with remarkable cell performance, carbon deposition resistance and sulfur poisoning tolerance for SOFCs is successfully obtained.

  20. Five-year survey of medical student attrition in a medical school in Nigeria: a pilot study

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    Ogugua A Egwu

    2010-10-01

    Full Text Available Ogugua A Egwu1, Godson E Anyanwu21Department of Anatomy, Faculty of Basic Medical Sciences, Ebonyi State University, Ebonyi State; 2Department of Anatomy, College of Medicine, Faculty of Medical Sciences, University of Nigeria, Enugu State, NigeriaBackground: Student attrition represents a waste of career opportunity and, at times, results in a holistic loss of sense of self-worth for the students involved. The aim of this study was to evaluate the nature, causes, and impact of medical student attrition in Nigeria.Method: A pilot analysis was undertaken using the records of students who failed at medical school as a result of inability to pass the second MBBS examination at Ebonyi State University, Abakaliki, Nigeria, between 2002 and 2007. Some of these students were interviewed using a structured questionnaire.Results: Data analysis showed that 58 (7.8% of the students admitted into preclinical class withdrew from their study. Thirty-six (62.1% were males and the rest were females. Thirteen of those withdrawn were interviewed, and 53.8% of them believed they had poor academic ability, while 15.4% attributed their withdrawal to family pressure. No record of guidance or counseling session programs was noted for these students either at the point of withdrawal from the faculty and on the choice of a new career path.Conclusion: As a result of the high attrition rate due to low academic ability, efforts should be made to check students for evidence of this at the point of admission to medicine training. Also, more accommodating teaching programs should be encouraged in faculties to accommodate students with such challenges. Good guidance and counseling programs should be encouraged to handle these inevitable cases of attrition when they occur, to avoid the demoralizing low self-esteem that plagues these individuals for the rest of their lives.Keywords: medical students, attrition, medical education, Nigeria

  1. Attrition of Knowledge Workforce in Healthcare in Northern parts of India – Health Information Technology as a Plausible Retention Strategy

    Directory of Open Access Journals (Sweden)

    R. K. Suri

    2012-01-01

    Full Text Available Faced with a global shortage of skilled health workers due to attrition, countries are struggling to build and maintain an optimum knowledge workforce in healthcare for delivering quality healthcare services. Forces that affect healthcare professional turnover needs to be addressed before a competent uniformly adoptable strategy could be proposed for mitigating the problem. In this study we investigate the effect of the socio –demographic characteristics on attrition of healthcare knowledge workforce in northern parts of India that have a wide gradient of rural and urban belt, taking into account both public and private healthcare organizations. For this purpose healthcare professional attrition tracking survey (HATS was designed. The data has been collected from a random sample of 807 respondents consisting of doctors, nurses, paramedics and administrators to explore the relationships between various factors acting as antecedents in affecting the job satisfaction, commitment and intention of a healthcare professional to stay in the job. Structured questionnaires were utilized as the data collection tools. Both public and private healthcare organizations in urban and rural areas were covered for the survey. Descriptive statistics and factor analyses using analysis on Rotated Factor Matrix using Principal Components Analysis (PCA in SPSS 16.0 package were carried out. Six factors of attrition namely Compensation and perks, Work Life Balance, Sense of Accomplishment, Work load leading to exhaustion, Need for automation and technology improvement, Break Monotony of Work have been identified as the main factors with a data reliability of 0.809%. Based on the survey response and analysis, a highly possible strategy of utilizing information technology implementation for increasing worker motivation, job satisfaction and commitment to reduce attrition has been proposed.

  2. Retention and risk factors for attrition in a large public health ART program in Myanmar: a retrospective cohort analysis.

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    Aye Thida

    Full Text Available BACKGROUND: The outcomes from an antiretroviral treatment (ART program within the public sector in Myanmar have not been reported. This study documents retention and the risk factors for attrition in a large ART public health program in Myanmar. METHODS: A retrospective analysis of a cohort of adult patients enrolled in the Integrated HIV Care (IHC Program between June 2005 and October 2011 and followed up until April 2012 is presented. The primary outcome was attrition (death or loss-follow up; a total of 10,223 patients were included in the 5-year cumulative survival analysis. Overall 5,718 patients were analyzed for the risk factors for attrition using both logistic regression and flexible parametric survival models. RESULT: The mean age was 36 years, 61% of patients were male, and the median follow up was 13.7 months. Overall 8,564 (84% patients were retained in ART program: 750 (7% were lost to follow-up and 909 (9% died. During the 3 years follow-up, 1,542 attritions occurred over 17,524 person years at risk, giving an incidence density of 8.8% per year. The retention rates of participants at 12, 24, 36, 48 and 60 months were 86, 82, 80, 77 and 74% respectively. In multivariate analysis, being male, having high WHO staging, a low CD4 count, being anaemic or having low BMI at baseline were independent risk factors for attrition; tuberculosis (TB treatment at ART initiation, a prior ART course before program enrollment and literacy were predictors for retention in the program. CONCLUSION: High retention rate of IHC program was documented within the public sector in Myanmar. Early diagnosis of HIV, nutritional support, proper investigation and treatment for patients with low CD4 counts and for those presenting with anaemia are crucial issues towards improvement of HIV program outcomes in resource-limited settings.

  3. Predictors of Study Attrition in a Randomized Controlled Trial Evaluating a Perinatal Home-Visiting Program with Mothers with Psychosocial Vulnerabilities.

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    Stéphanie Foulon

    Full Text Available Randomised controlled trials evaluating perinatal home-visiting programs are frequently confronted with the problem of high attrition rates. The aim of the present study is to identify predictors of study attrition in a trial evaluating a perinatal home-visiting program in France.CAPEDP is a French randomized trial comparing a perinatal home-visiting program using psychologists versus usual care (N = 440. The first assessment was at inclusion into the trial at the 27th week of pregnancy and the final assessment when the child reached the age of two. Attrition rates were calculated at 3 and 24 months postpartum. Stepwise logistic regression was used to identify predictors of early (between inclusion and 3 months postpartum and later (between 3 and 24 months postpartum attrition among social, psychological and parenting factors.Attrition rates were 17% and 63% at 3 and 24 months respectively. At 24 months, there was significantly more attrition in the control arm (70.6% compared to the intervention arm (55.2%. Five independent predictors of early attrition were identified: having already had an abortion; having greater attachment insecurity as measured with the Vulnerable Attachment Style Questionnaire (VASQ; having lower global severity of psychiatric symptoms as assessed with the Symptom Check-List (SCL-90 at inclusion, being neither currently employed nor studying; and declaring no tobacco consumption during pregnancy. Being randomized into the control arm, having undergone early parental loss before age 11 and having lower global severity of psychiatric symptoms (SCL-90 at 3 months postpartum were the only variables associated with later attrition.This study provides key information for identifying mothers who may require specific support to avoid study attrition in trials evaluating a home-visiting program.

  4. Facile fabrication of iron-based superhydrophobic surfaces via electric corrosion without bath

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Qinghe [College of Materials Science and Engineering, China University of Mining and Technology, Xuzhou, Jiangsu 221116 (China); Liu, Hongtao, E-mail: liuht100@126.com [College of Materials Science and Engineering, China University of Mining and Technology, Xuzhou, Jiangsu 221116 (China); Chen, Tianchi [College of Mechanical & Electrical Engineering, China University of Mining and Technology, Xuzhou, Jiangsu 221116 (China); Wei, Yan; Wei, Zhu [College of Materials Science and Engineering, China University of Mining and Technology, Xuzhou, Jiangsu 221116 (China)

    2016-04-30

    Graphical abstract: - Highlights: • This paper investigates the fabrication techniques towards superhydrophobic surface on carbon steel substrate via electric corrosion without a bath. • It has a vital significance to the industrialization of the fabrication of superhydrophobic surface on hard metal due to the advantages such as low cost, high efficiency, can be prepared in a large area, easy to construct in the field. • The preparation approach is so facile and time-saving that it delivers an opportunity to construct a superhydrophobic surface on carbon steel substrate and provides the feasibility for industrial application of superhydrophobic surface. • The as-prepared surface has many excellent properties, like low adhesive property, anti-corrosion ability, mechanical durability and anti-icing performance. - Abstract: Superhydrophobic surface is of wide application in the field of catalysis, lubrication, waterproof, biomedical materials, etc. The superhydrophobic surface based on hard metal is worth further study due to its advantages of high strength and wear resistance. This paper investigates the fabrication techniques towards superhydrophobic surface on carbon steel substrate via electric corrosion and studies the properties of as-prepared superhydrophobic surface. The hydrophobic properties were characterized by a water sliding angle (SA) and a water contact angle (CA) measured by the Surface tension instrument. A Scanning electron microscope was used to analyze the structure of the corrosion surface. The surface compositions were characterized by an Energy Dispersive Spectrum. The Electrochemical workstation was used to measure its anti-corrosion property. The anti-icing performance was characterized by a steam-freezing test in Environmental testing chamber. The SiC sandpaper and 500 g weight were used to test the friction property. The research result shows that the superhydrophobic surface can be successfully fabricated by electrocorrosion on

  5. Factors associated with attrition, mortality, and loss to follow up after antiretroviral therapy initiation: data from an HIV cohort study in India

    Directory of Open Access Journals (Sweden)

    Gerardo Alvarez-Uria

    2013-09-01

    Full Text Available Background: Studies from sub-Saharan Africa have shown high incidence of attrition due to mortality or loss to follow-up (LTFU after initiating antiretroviral therapy (ART. India is the third largest country in the world in terms of HIV infected people, but predictors of attrition after ART initiation are not well known. Design: We describe factors associated with attrition, mortality, and LTFU in 3,159 HIV infected patients who initiated ART between 1 January 2007 and 4 November 2011 in an HIV cohort study in India. The study included 6,852 person-years with a mean follow-up of 2.17 years. Results: After 5 years of follow-up, the estimated cumulative incidence of attrition was 37.7%. There was no significant difference between attrition due to mortality and attrition due to LTFU. Having CD4 counts <100 cells/µl and being homeless [adjusted hazard ratio (aHR 3.1, 95% confidence interval (CI 2.6–3.8] were associated with a higher risk of attrition, and female gender (aHR 0.64, 95% CI 0.6–0.8 was associated with a reduced risk of attrition. Living near a town (aHR 0.82, 95% CI 0.7–0.999 was associated with a reduced risk of mortality. Being single (aHR 1.6, 95% CI 1.2–2.3, illiteracy (aHR 1.3, 95% CI 1.1–1.6, and age <25 years (aHR 1.3, 95% CI 1–1.8 were associated with an increased risk of LTFU. Although the cumulative incidence of attrition in patients diagnosed with tuberculosis after ART initiation was 47.4%, patients who started anti-tuberculous treatment before ART had similar attrition to patients without tuberculosis (36 vs. 35.2%, P=0.19 after four years of follow-up. Conclusions: In this cohort study, the attrition was similar to the one found in sub-Saharan Africa. Earlier initiation of ART, improving the diagnosis of tuberculosis before initiating ART, and giving more support to those patients at higher risk of attrition could potentially reduce the mortality and LTFU after ART initiation.

  6. Metacognitive Strategies and Lexical Attrition%元认知策略与词汇磨蚀

    Institute of Scientific and Technical Information of China (English)

    袁军兰

    2013-01-01

    As the New Curriculum Standard in 2012 comes out, the importance of vocabulary teaching draws more attention by educators. This paper starts from the definition of metacognitive strategies and its importance, studying how to apply metacogni⁃tive strategies into highschool vocabulary teaching to alleviate lexical attrition.%  随着2012高中英语课程标准的出台,词汇教学的重要性越来越引起国内英语教育工作者的关注。该文从元认知策略的概念界定及其重要性入手,浅析如何将元认知策略应用于高中英语词汇教学中,减轻高中英语词汇磨蚀。

  7. Application of a Duration Model in Programs for Prevention of University Attrition

    Directory of Open Access Journals (Sweden)

    Verónica Herrero

    2013-12-01

    Full Text Available Institutional practices related to the prevention of desertion of university students increasingly require validated instruments in order to anticipate such behavior. In this regard, different statistical models generated from information related to the students themselves, their homes, their academic performance, among other determinants have demonstrated to be of crucial value. This study aims to demonstrate the importance of a series of determinants explored in other studies. The main objective is to apply a dropout rate predictive model with at risk university students in order to generate early and progressively more effective results. The research demonstrates the usefulness of the duration models in a sample of classroom students and the capacity to anticipate behavior of permanence/attrition across time. This was done with risk estimates using the Cox model.

  8. A Study on Reasons of Attrition and Strategies for Employee Retention

    Directory of Open Access Journals (Sweden)

    N.Silpa

    2015-12-01

    Full Text Available The success of any manufacturing organization depends largely on the workers are considered as the backbone of any company. The study was mainly undertaken to identify the level of employee’s attitude, the dissatisfaction factors they face in the organization and for what reason they prefer to change their job. Once the levels of employee’s attitude are identified, it would be possible for the management to take necessary action to reduce attrition level. Since they are considered as backbone of the company, their progression will lead to the success of the company for the long run. This study can be helpful in knowing, why the employees prefer to change their job and which factors make employee dissatisfy. Since the study is critical issue, it is needed by the originations in order to assess the overall interest and the feelings of the employees towards their Retention.

  9. Strategies for lowering attrition rates and raising NCLEX-RN pass rates.

    Science.gov (United States)

    Higgins, Bonnie

    2005-12-01

    This study was designed to determine strategies to raise the NCLEX-RN pass rate and lower the attrition rate in a community college nursing program. Ex-post facto data were collected from 213 former nursing student records. Qualitative data were collected from 10 full-time faculty, 30 new graduates, and 45 directors of associate degree nursing programs in Texas. The findings linked the academic variables of two biology courses and three components of the preadmission test to completion of the nursing program. A relationship was found between one biology course, the science component of the preadmission test, the HESI Exit Examination score, and the nursing skills course to passing the NCLEX-RN. Qualitative data indicated preadmission requirements, campus counselors, remediation, faculty, test-item writing, and teaching method were instrumental in completion of the program and passing the NCLEX-RN.

  10. Average widths of grain boundaries in nanophase alloys synthesized by mechanical attrition

    Science.gov (United States)

    Fultz, B.; Kuwano, H.; Ouyang, H.

    1995-04-01

    Many binary ferrous alloys were synthesized by mechanical attrition in a high-energy ball mill. X-ray diffractometry and transmission electron microscopy were used to measure grain sizes, which were as small as a few nanometers in several alloys. The nanocrystalline alloys showed new features in their Mössbauer spectra, which we associated with 57Fe atoms at and near grain boundaries. The experimental data on the fraction of 57Fe atoms at and near grain boundaries were correlated to the measured grain sizes to obtain an average width of the grain boundaries. The average grain-boundary widths of the fcc alloys Fe-Mn and Ni-Fe were approximately 0.5 nm, but the average widths of grain boundaries in the bcc alloys Cr-Fe, Mo-Fe, and Fe-Ti were somewhat larger than 1 nm.

  11. Thermal conductivity of the iron-based superconductor FeSe: Nodeless gap with strong two-band character

    Science.gov (United States)

    Bourgeois-Hope, Patrick; Badoux, Sven; Doiron-Leyraud, Nicolas; Taillefer, Louis; Chi, Shun; Liang, Ruixing; Hardy, Walter; Bonn, Doug

    The thermal conductivity κ of the iron-based superconductor FeSe was measured at temperatures down to 50 mK in magnetic fields up to 17 T. In zero magnetic field, the residual linear term in the T = 0 limit, κ0 / T , is vanishingly small. Application of a magnetic field H causes no increase in κ0 / T initially. Those two facts show that there are no zero-energy quasiparticles that carry heat and therefore no nodes in the superconducting gap of FeSe. The full field dependence of κ0 / T has the classic shape of a two-band superconductor, such as MgB2. It rises initially with a characteristic field H* ~=Hc 2 / 25 , and then more slowly up to Hc 2 = 14 T. We interpret this in terms of a small gap ΔA ~=Δ0 / 5 on some part of the Fermi surface, with a large gap ΔB =Δ0 in the region that controls Hc 2.

  12. Photovoltaic effect in iron-based SmO0.7F0.3FeAs superconductors

    Science.gov (United States)

    Yang, F.; Y Liu, Z.; Y Han, M.; Chang, F. G.

    2015-06-01

    A remarkable photovoltaic effect in an iron-based SmO0.7F0.3FeAs-Ag system has been observed in the temperature range from 50 to 300 K. An interface potential exists directly from the superconductor to the metal electrode, which provides the separation force for the photo-induced electron-hole pairs. The mechanism of this interface potential is completely different below and above the superconducting transition temperature and has been discussed in terms of the proximity effect and Schottky barrier, respectively. In contrast to that found in the YBCO-Ag system, a photovoltaic effect of opposite polarity is obtained in a SmO0.7F0.3FeAs-Ag system at a normal state, consistent with the different type of charge carriers in these two superconductors. A very fast laser response (7.5 ms) may open a door to new device applications such as optical sensors.

  13. Thermal Conductivity of the Iron-Based Superconductor FeSe: Nodeless Gap with a Strong Two-Band Character.

    Science.gov (United States)

    Bourgeois-Hope, P; Chi, S; Bonn, D A; Liang, R; Hardy, W N; Wolf, T; Meingast, C; Doiron-Leyraud, N; Taillefer, Louis

    2016-08-26

    The thermal conductivity κ of the iron-based superconductor FeSe was measured at temperatures down to 75 mK in magnetic fields up to 17 T. In a zero magnetic field, the electronic residual linear term in the T=0  K limit, κ_{0}/T, is vanishingly small. The application of a magnetic field B causes an exponential increase in κ_{0}/T initially. Those two observations show that there are no zero-energy quasiparticles that carry heat and therefore no nodes in the superconducting gap of FeSe. The full field dependence of κ_{0}/T has the classic two-step shape of a two-band superconductor: a first rise at very low field, with a characteristic field B^{⋆}≪B_{c2}, and then a second rise up to the upper critical field B_{c2}. This shows that the superconducting gap is very small (but finite) on one of the pockets in the Fermi surface of FeSe. We estimate that the minimum value of the gap, Δ_{min}, is an order of magnitude smaller than the maximum value, Δ_{max}.

  14. Progress in development of coated indexable cemented carbide inserts for machining of iron based work piece materials

    Science.gov (United States)

    Czettl, C.; Pohler, M.

    2016-03-01

    Increasing demands on material properties of iron based work piece materials, e.g. for the turbine industry, complicate the machining process and reduce the lifetime of the cutting tools. Therefore, improved tool solutions, adapted to the requirements of the desired application have to be developed. Especially, the interplay of macro- and micro geometry, substrate material, coating and post treatment processes is crucial for the durability of modern high performance tool solutions. Improved and novel analytical methods allow a detailed understanding of material properties responsible for the wear behaviour of the tools. Those support the knowledge based development of tailored cutting materials for selected applications. One important factor for such a solution is the proper choice of coating material, which can be synthesized by physical or chemical vapor deposition techniques. Within this work an overview of state-of-the-art coated carbide grades is presented and application examples are shown to demonstrate their high efficiency. Machining processes for a material range from cast iron, low carbon steels to high alloyed steels are covered.

  15. Nonaqueous System of Iron-Based Ionic Liquid and DMF for the Oxidation of Hydrogen Sulfide and Regeneration by Electrolysis.

    Science.gov (United States)

    Guo, Zhihui; Zhang, Tingting; Liu, Tiantian; Du, Jun; Jia, Bing; Gao, Shujing; Yu, Jiang

    2015-05-05

    To improve the hydrogen sulfide removal efficiency with the application of an iron-based imidazolium chloride ionic liquid (Fe(III)-IL) as desulfurizer, Fe(II) and N,N-dimethylformamide (DMF) are introduced to Fe(III)-IL to construct a new nonaqueous desulfurization system (Fe(III/II)-IL/DMF). Following desulfurization, the system can be regenerated using the controlled-potential electrolysis method. The addition of Fe(II) in Fe(III)-IL is beneficial for the hydrogen sulfide removal and the electrochemical regeneration of the desulfurizer. The addition of DMF in Fe(III/II)-IL does not change the structure of Fe(III/II)-IL but clearly decreases the acidity, increases the electrolytic current, and decreases the stability of the Fe-Cl bond in Fe(III/II)-IL. Fe(III/II)-IL/DMF can remove hydrogen sulfide and can be regenerated through an electrochemical method more efficiently than can Fe(III/II)-IL. After six cycles, the desulfurization efficiency remains higher than 98%, and the average conversion rate of Fe(II) is essentially unchanged. No sulfur peroxidation occurs, and the system remains stable. Therefore, this new nonaqueous system has considerable potential for removing H2S in pollution control applications.

  16. Static and dynamic cyclic oxidation of 12 nickel-, cobalt-, and iron-base high-temperature alloys

    Science.gov (United States)

    Barrett, C. A.; Johnston, J. R.; Sanders, W. A.

    1978-01-01

    Twelve typical high-temperature nickel-, cobalt-, and iron-base alloys were tested by 1 hr cyclic exposures at 1038, 1093, and 1149 C and 0.05 hr exposures at 1093 C. The alloys were tested in both a dynamic burner rig at Mach 0.3 gas flow and in static air furnace for times up to 100 hr. The alloys were evaluated in terms of specific weight loss as a function of time, and X-ray diffraction analysis and metallographic examination of the posttest specimens. A method previously developed was used to estimate specific metal weight loss from the specific weight change of the sample. The alloys were then ranked on this basis. The burner-rig test was more severe than a comparable furnace test and resulted in an increased tendency for oxide spalling due to volatility of Cr in the protective scale and the more drastic cooling due to the air-blast quench of the samples. Increased cycle frequency also increased the tendency to spall for a given test exposure. The behavior of the alloys in both types of tests was related to their composition and their tendency to form scales. The alloys with the best overall behavior formed alpha-Al2O3 aluminate spinels.

  17. Phase transitions in a frustrated biquadratic Heisenberg model with coupled orbital degrees of freedom for iron-based superconductors

    Science.gov (United States)

    Zhuo, W. Z.; Qin, M. H.; Dong, S.; Li, X. G.; Liu, J.-M.

    2016-03-01

    In this paper, we study a biquadratic Heisenberg model with coupled orbital degrees of freedom by using a Monte Carlo simulation to investigate the phase transitions in iron-based superconductors. The antiferroquadrupolar state, which may be related to the magnetism of FeSe [R. Yu and Q. Si, Phys. Rev. Lett. 115, 116401 (2015), 10.1103/PhysRevLett.115.116401], is stabilized by the anisotropic biquadratic interaction induced by a ferro-orbital-ordered state. It is revealed that the orbital and nematic transitions occur at the same temperature for all the cases, supporting the mechanism of the orbital-driven nematicity as revealed in most recent experiments [S. H. Baek, D. V. Efremov, J. M. Ok, J. S. Kim, J. van den Brink, and B. Büchner, Nat. Mater. 14, 210 (2015), 10.1038/nmat4138]. In addition, it is suggested that the orbital interaction may lead to the separation of the structural and magnetic phase transitions, as observed in many families of iron pnictides.

  18. Hierarchically-Porous Carbon Derived from a Large-Scale Iron-based Organometallic Complex for Versatile Energy Storage.

    Science.gov (United States)

    Fan, Chao-Ying; Li, Huan-Huan; Wang, Hai-Feng; Sun, Hai-Zhu; Wu, Xing-Long; Zhang, Jing-Ping

    2016-06-22

    Inspired by the preparation of the hierarchically-porous carbon (HPC) derived from metal organic frameworks (MOFs) for energy storage, in this work, a simple iron-based metal- organic complex (MOC), which was simpler and cheaper compared with the MOF, was selected to achieve versatile energy storage. The intertwined 1 D nanospindles and enriched-oxygen doping of the HPC was obtained after one-step carbonization of the MOC. When employed in lithium-ion batteries, the HPC exhibited reversible capacity of 778 mA h g(-1) after 60 cycles at 50 mA g(-1) . Moreover, the HPC maintained a capacity of 188 mA h g(-1) after 400 cycles at 100 mA g(-1) as the anode material in a sodium-ion battery. In addition, the HPC served as the cathode matrix for evaluation of a lithium-sulfur battery. The general preparation process of the HPC is commercial, which is responsible for the large-scale production for its practical application.

  19. An iron-based beverage, HydroFerrate fluid (MRN-100, alleviates oxidative stress in murine lymphocytes in vitro

    Directory of Open Access Journals (Sweden)

    Gollapudi Sastry

    2009-05-01

    Full Text Available Abstract Background Several studies have examined the correlation between iron oxidation and H2O2 degradation. The present study was carried out to examine the protective effects of MRN-100 against stress-induced apoptosis in murine splenic cells in vitro. MRN-100, or HydroFerrate fluid, is an iron-based beverage composed of bivalent and trivalent ferrates. Methods Splenic lymphocytes from mice were cultured in the presence or absence of MRN-100 for 2 hrs and were subsequently exposed to hydrogen peroxide (H2O2 at a concentration of 25 μM for 14 hrs. Percent cell death was examined by flow cytometry and trypan blue exclusion. The effect of MRN-100 on Bcl-2 and Bax protein levels was determined by Western blot. Results Results show, as expected, that culture of splenic cells with H2O2 alone results in a significant increase in cell death (apoptosis as compared to control (CM cells. In contrast, pre-treatment of cells with MRN-100 followed by H2O2 treatment results in significantly reduced levels of apoptosis. In addition, MRN-100 partially prevents H2O2-induced down-regulation of the anti-apoptotic molecule Bcl-2 and upregulation of the pro-apoptotic molecule Bax. Conclusion Our findings suggest that MRN-100 may offer a protective effect against oxidative stress-induced apoptosis in lymphocytes.

  20. Direct decomposition of nitric oxide in low temperature over iron-based perovskite-type catalyst modified by Ru

    Institute of Scientific and Technical Information of China (English)

    LI Li; ZHANG Mi-lin; YUAN Fu-long; SHI Ke-ying; ZHANG Guo; ZHANG Dan

    2006-01-01

    Iron-based perovskite-type compounds modified by Ru were prepared through sol-gel process to study its catalytic activity of NOx direct decomposition at low temperature and evaluate the conversion of NO under the experimental conditions. The catalytic activity of La0.9Ce0.1Fe0.8-nCo0.2RunO3 ( n = 0.01,0.03,0.05,0.07,0.09)series for the NO, NO-CO two components, CO-HC-NO three components were also analyzed. The catalytic investigation evidenced that the presence of Ru is necessary for making highly activity in decomposition of nitric oxide even at low temperature (400 ℃ ) and La0.9Ce0.9Fe0.75Co0.2Ru0.05O3( n = 0. 05 ) has better activity in all the samples, the conversion of it is 58.5%. With the reducing gas (CO, C3 H6 )added into the gas, the catalyst displayed very high activity in decomposition of NO and the conversion of it is 80% and 92. 5% separately.

  1. Surface nanocrystallization by surface mechanical attrition treatment and its effect on structure and properties of plasma nitrided AISI 321 stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Lin Yimin [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, 18 Middle Tianshui Road, Lanzhou 730000 (China) and Graduate School of the Chinese Academy of Sciences, Beijing 100039 (China)]. E-mail: linyimin_2001@yahoo.com.cn; Lu Jian [LASMIS, University of Technology of Troyes, 10000 Troyes (France); Wang Liping [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, 18 Middle Tianshui Road, Lanzhou 730000 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100039 (China); Xu Tao [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, 18 Middle Tianshui Road, Lanzhou 730000 (China); Xue Qunji [State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, 18 Middle Tianshui Road, Lanzhou 730000 (China)]. E-mail: qjxue@ns.lzb.ac.cn

    2006-12-15

    A plastic deformation surface layer with nanocrystalline grains was produced on AISI 321 austenitic stainless steel by means of surface mechanical attrition treatment (SMAT). Low-temperature nitriding of SMAT and un-SMAT AISI 321 stainless steel was carried out in pulsed-DC glow discharge. The effect of SMAT pretreatment on the microstructure and properties of the stainless steel were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Vickers hardness tester and UMT-2MT tribometer. The results show that the plasma nitriding of AISI 321 steel can be enhanced considerably by means of SMAT process before nitriding, and a much thicker nitrogen diffusion layer with higher hardness was obtained for the SMAT samples when compared with un-SMAT samples. In addition, the wear resistance and load capacity of the nitrided layers on the SMAT samples was much higher than that of the un-SMAT samples due to the thicker S phase case and the gradient nitrogen diffusion layer.

  2. Steam reforming of tar derived from lignin over pompom-like potassium-promoted iron-based catalysts formed on calcined scallop shell.

    Science.gov (United States)

    Guan, Guoqing; Kaewpanha, Malinee; Hao, Xiaogang; Zhu, Ai-Min; Kasai, Yutaka; Kakuta, Seiji; Kusakabe, Katsuki; Abudula, Abuliti

    2013-07-01

    In order to understand the improvement effect of potassium (K) on the catalytic activity of iron-loaded calcined scallop shell (CS) for the steam reforming tar derived from biomass, various K precursors were applied for the catalyst preparation. It is found that pompom-like iron-based particles with a mesoporous structure were easily formed on the surface of calcined scallop shell (CS) when K2CO3 was used as K precursor while no such kind of microsphere was formed when other kinds of K precursors such as KOH and KNO3 were applied. The optimum K-loading amount for the preparation of this catalyst was investigated. Based on the experimental results obtained, a mechanism for the formation of these microspheres was proposed. This pompom-like potassium-promoted iron-based catalyst showed a better catalytic activity and reusability for the steam reforming of tar derived from lignin.

  3. The Dissertation Story: What Is the Relationship between the Officer Candidate School Attrition Rate and Officer Training Command, Naval Service Training Command and Navy Recruiting Command Leadership Intervention?

    Science.gov (United States)

    2013-03-01

    only Navy enlisted sailor accession training source. Over 35,000 civilian volunteers are annually transformed into sailors following their eight...assumed, implied or arbitrarily set based on the optics of one digit or two digit integers. The threshold of acceptable rates of attrition should be...A-School Attrition: Reasons and Results ( CRM No. 88-149). Retrieved from Defense Technical Information Center database. (AD-A205858) Carretta, T

  4. The Next Best Alternative to an Ideal Recruit: Attrition Characteristics of Recruits with Waivers and Low Educational Credentials in the U.S. Army

    Science.gov (United States)

    2009-03-01

    order to recruit more high quality recruits, services typically need to spend more money on enlistment bonuses, educational benefits , advertisements...policies can affect attrition rates: homeschooled students from states with minimal regulation have higher attrition rates than homeschooled students from...morale or motivation of other recruits. These factors should also be taken into account in making cost benefit analysis of increasing the number of

  5. Recent progress in the synthesis of magnetic titania/iron-based, composite nanoparticles manufactured by laser pyrolysis

    Science.gov (United States)

    Fleaca, C. T.; Scarisoreanu, M.; Morjan, I.; Alexandrescu, R.; Dumitrache, F.; Luculescu, C.; Morjan, I. P.; Birjega, R.; Niculescu, A.-M.; Filoti, G.; Kuncser, V.; Vasile, E.; Danciu, V.; Popa, M.

    2014-05-01

    We report the continuous, single step synthesis of titania/iron-based magnetic nanocomposites in a single step using gas-phase laser pyrolysis technique by separately and simultaneously introducing the precursors (together with C2H4 sensitizer) in the reaction zone: Fe(CO)5 on the central flow and, using air as carrier, TiCl4 on the annular coflow. The laser power and, for the last experiment, the injection geometry were modified in order to change the Fe/Ti ratio in the resulted nanopowders. Due to the specific geometry, the reaction zone (visible as a flame) have a reductive inner central zone surrounded by and oxidative environment, allowing the formation of the metallic-carbidic iron and/or iron-doped titania and iron oxide nanophases. The raw Fe-containing nanopowders have a ferromagnetic behavior, those synthesized at higher laser power and gas velocities show significant saturation magnetization Ms values (10-12 emu/g), whereas those obtained (with higher yield and carbon content) at lower laser power and gas velocities (using wider central nozzle cross-section) have a very weak magnetization (Ms ∼ 0.05 emu/g) in spite of the higher ethylene carried Fe(CO)5 flow. The powders were annealed in air at 400 °C show lower carbon content and, for those highly Fe-doped, the hematite phase formation. Preliminary tests using UV light confirm the photocatalytic action of the annealed nanopowders in salicylic acid degradation process in solution.

  6. Pairing symmetries of several iron-based superconductor families and some similarities with cuprates and heavy-fermions

    Directory of Open Access Journals (Sweden)

    Das Tanmoy

    2012-03-01

    Full Text Available We show that, by using the unit-cell transformation between 1 Fe per unit cell to 2 Fe per unit cell, one can qualitatively understand the pairing symmetry of several families of iron-based superconductors. In iron-pnictides and iron-chalcogenides, the nodeless s±-pairing and the resulting magnetic resonance mode transform nicely between the two unit cells, while retaining all physical properties unchanged. However, when the electron-pocket disappears from the Fermi surface with complete doping in KFe2As2, we find that the unit-cell invariant requirement prohibits the occurrence of s±-pairing symmetry (caused by inter-hole-pocket nesting. However, the intra-pocket nesting is compatible here, which leads to a nodal d-wave pairing. The corresponding Fermi surface topology and the pairing symmetry are similar to Ce-based heavy-fermion superconductors. Furthermore, when the Fermi surface hosts only electron-pockets in KyFe2-xSe2, the inter-electron-pocket nesting induces a nodeless and isotropic d-wave pairing. This situation is analogous to the electron-doped cuprates, where the strong antiferromagnetic order creates similar disconnected electron-pocket Fermi surface, and hence nodeless d-wave pairing appears. The unit-cell transformation in KyFe2-xSe2 exhibits that the d-wave pairing breaks the translational symmetry of the 2 Fe unit cell, and thus cannot be realized unless a vacancy ordering forms to compensate for it. These results are consistent with the coexistence picture of a competing order and nodeless d-wave superconductivity in both cuprates and KyFe1.6Se2.

  7. Magnetorheological properties of sodium sulphonate capped electrolytic iron based MR fluid: a comparison with CI based MR fluid

    Science.gov (United States)

    Vinod, Sithara; John, Reji; Philip, John

    2017-02-01

    Magnetorheological fluids have numerous engineering applications due to their interesting field assisted rheological behavior. Most commonly used dispersed phase in MR fluids is carbonyl iron (CI). The relatively high cost of CI warrants the need to develop cheaper alternatives to CI, without compromising rheological properties. With the above goal in mind, we have synthesized sodium sulphonate capped electrolytic iron based MR fluid and studied their magnetorheological properties. The results are compared with that of CI based MR fluid. EI and CI particles of average particle size of ∼10 μm with fumed silica particles additives are used in the present study. The dynamic yield stress for EI and CI based MR fluid were found to vary with field strength with an exponent of roughly 1.2 and 1.24, respectively. The slightly lower static and dynamic yield stress values of EI based MR fluid is attributed to the lower magnetization and polydispersity values. The dynamic yield stress showed a decrease of 18.73% and 61.8% for field strengths of 177 mT and 531 mT, respectively as the temperature was increased from 293 to 323 K. The optorheological studies showed a peak in the loss moduli, close to the crossover point of the storage and loss moduli, due to freely moving large sized aggregates along the shear direction that are dislodged from the rheometer plates at higher strains. Our results suggests that EI based MR fluids have magnetorheological behavior comparable to that of CI based MR fluids. As EI is much cheaper than CI, our findings will have important commercial implications in producing cost effective EI based MR fluids.

  8. High attrition among HIV-infected patients with advanced disease treated in an intermediary referral center in Maputo, Mozambique

    Directory of Open Access Journals (Sweden)

    Lucas Molfino

    2014-04-01

    Full Text Available Background: In Mozambique, antiretroviral therapy (ART scale-up has been successfully implemented. However, attrition in care remains a major programmatic challenge. In 2009, an intermediary-level HIV referral center was created in Maputo to ensure access to specialized care for HIV-infected patients with complications (advanced clinical-immunological stage, Kaposi sarcoma, or suspected ART failure. Objective: To determine the attrition from care and to identify risk factors that lead to high attrition among patients referred to an intermediary-level HIV referral center. Design: This was a retrospective cohort study from 2009 to 2011. Results: A total of 1,657 patients were enrolled, 847 (51% were men, the mean age was 36 years (standard deviation: 11, the mean CD4 count was 27 cells/µl (interquartile range: 11–44, and one-third were severely malnourished. The main reasons for referral were advanced clinical stages (WHO stages 3 and 4, and CD4 count <50 cells/µl in 70% of the cases, and 19% had Kaposi sarcoma. The overall attrition rate was 28.7 per 100 person-years (PYs – the mortality rate was 5.0 (95% confidence interval [CI]: 4.2–5.9 per 100 PYs, and the loss-to-follow-up rate was 23.7 (95% CI: 21.9–25.6 per 100 PYs. There were 793 attritions – 137 deaths and 656 lost to follow-up (LTFU; 77% of all attrition happened within the first year. The factors independently associated with attrition were male sex (adjusted hazard ratio [aHR]: 1.15, 95% CI: 1.0–1.3, low body mass index (aHR: 1.51, 95% CI: 1.2–1.8, WHO clinical stage 3 or 4 (aHR: 1.30, 95% CI: 1.0–1.6; and aHR: 1.91, 95% CI: 1.4–2.5, later year of enrollment (aHR 1.61, 95% CI 1.3–1.9, and ‘being already on ART’ at enrollment (aHR 13.71, 95% CI 11.4–16.4. Conclusions: Attrition rates among HIV-infected patients enrolled in an intermediary referral center were high, mainly related to advanced stage of clinical disease. Measures are required to address this

  9. Attritional rupture of extensor pollicis longus: a rare complication following elastic stable intramedullary nailing of a paediatric radial fracture.

    LENUS (Irish Health Repository)

    Sproule, James A

    2011-01-01

    Elastic stable intramedullary nail fixation has become established as an acceptable method of treatment for diaphyseal fractures of both forearm bones in the paediatric population. It is considered safe, minimally invasive and does not compromise physeal growth. We report a case of delayed rupture of extensor pollicis longus due to attrition over the sharp edges of a protruding nail end after elastic stable intramedullary nailing of a paediatric radial diaphyseal fracture.

  10. 粉末冶金铁基零件蒸汽处理易出现问题及解决方法%Problems Occurred During the Steam Treatment of Iron Base Powder Metallurgy Parts and the Solving Methods

    Institute of Scientific and Technical Information of China (English)

    王兴法; 杨俊茹

    2011-01-01

    蒸汽处理是一种提高粉末冶金零件耐腐蚀性、密封性等性能的常用方法.本文基于蒸汽处理基本原理,对粉末冶金铁基零件蒸汽处理后易出现的质量问题进行了分析,并通过实验研究,提出了利用调节工艺参数(温度、蒸汽处理时间、单位气体流量)和改变蒸汽炉料筐内零件摆放方式等措施,解决了质量问题,取得了较好的效果.%Steam treatment is a commonly used method to improve corrosion resistance, sealing and other properties of powder metallurgy parts. Based on the basic principle of the steam treatment, the common quality problems of iron base powder metallurgy parts after steam treatment are analyzed. With the experiment research, the measurements of adjusting the process parameters (temperature, steam treatment time and unit gas flow) and changing the places of steam parts within the basket in the steam oven are put forward to solve the problems. The research results achieved better effect.

  11. 75 FR 55769 - Certain Corrosion-Resistant Carbon Steel Flat Products From the Republic of Korea: Notice of...

    Science.gov (United States)

    2010-09-14

    ... coated with corrosion-resistant metals such as zinc, aluminum, or zinc-, aluminum-, nickel- or iron-based... substances in addition to the metallic coating, in coils (whether or not in successively superimposed layers... coating. Also excluded from this order are clad products in straight lengths of 0.1875 inch or more...

  12. 76 FR 55004 - Certain Corrosion-Resistant Carbon Steel Flat Products From the Republic of Korea: Preliminary...

    Science.gov (United States)

    2011-09-06

    ... rectangular shape, either clad, plated, or coated with corrosion-resistant metals such as zinc, aluminum, or zinc-, aluminum-, nickel- or iron-based alloys, whether or not corrugated or painted, varnished or coated with plastics or other nonmetallic substances in addition to the metallic coating, in...

  13. 76 FR 15291 - Certain Corrosion-Resistant Carbon Steel Flat Products From the Republic of Korea: Notice of...

    Science.gov (United States)

    2011-03-21

    ... rectangular shape, either clad, plated, or coated with corrosion-resistant metals such as zinc, aluminum, or zinc-, aluminum-, nickel- or iron-based alloys, whether or not corrugated or painted, varnished or coated with plastics or other nonmetallic substances in addition to the metallic coating, in...

  14. 75 FR 13490 - Certain Corrosion-Resistant Carbon Steel Flat Products from the Republic of Korea: Notice of...

    Science.gov (United States)

    2010-03-22

    ... with corrosion-resistant metals such as zinc, aluminum, or zinc-, aluminum-, nickel- or iron-based... substances in addition to the metallic coating, in coils (whether or not in successively superimposed layers..., varnished or coated with plastics or other nonmetallic substances in addition to the metallic coating....

  15. 77 FR 14501 - Certain Corrosion-Resistant Carbon Steel Flat Products From the Republic of Korea: Notice of...

    Science.gov (United States)

    2012-03-12

    ... coated with corrosion-resistant metals such as zinc, aluminum, or zinc-, aluminum-, nickel- or iron-based... substances in addition to the metallic coating, in coils (whether or not in successively superimposed layers..., varnished or coated with plastics or other nonmetallic substances in addition to the metallic coating....

  16. When did they leave, and why? A retrospective case study of attrition on the Nottingham undergraduate medical course

    Directory of Open Access Journals (Sweden)

    Yates Janet

    2012-06-01

    Full Text Available Abstract Background As part of a wider study into students who experience difficulties, we examined the course files of those who had failed to graduate. This was an exploratory, descriptive study investigating how many students left after academic failure or non-academic problems, or simply changed their minds about reading medicine, and at what stage. The aim of the study was to increase our knowledge about the timings of, and reasons for, attrition. This understanding might help to reduce student loss in the future, by informing selection procedures and improving pastoral support at critical times. It might also assist in long-term workforce planning in the NHS. Methods Relevant data on admission and course progress were extracted manually from the archived files of students who had failed to graduate from five recent consecutive cohorts (entry in 2000–2004 inclusive, using a customised Access database. Discrete categories of information were supplemented with free text entries. Results 1188 students registered over the five-year entry period and 73 (6% failed to graduate. The highest rates of attrition (46/1188, 4% occurred during the first two years (largely preclinical studies, with 34 students leaving voluntarily, including 11 within the first semester, and 12 having their courses terminated for academic failure. Seventeen left at the end of the third year (Honours course plus early clinical practice and the remaining ten during the final two clinical years. The reasons for attrition were not always clear-cut and often involved a mixture of academic, personal, social and health factors, especially mental health problems. Conclusions The causes of attrition are complex. A small number of students with clear academic failure might require individual educational interventions for remediation. However, this could have substantial resource implications for the Faculty. Mental health problems predominate in late course attrition and may have

  17. Attrition biases in a study of Euro-American and African-American marriages.

    Science.gov (United States)

    Oggins, Jean

    2004-06-01

    Based on survey data from 174 Euro-American and 199 African-American newlywed couples, this study analyzed attrition biases by comparing first-year responses of couples who stayed in the study into its third year (133 Euro-American and 115 African-American couples) with responses from the initial sample. Stayers--who were more likely than leavers to be better educated, wealthier, and Euro-American--tended to report happier, more affirming, more communicative marriages. For stayers, compared to a random subsample of the original sample, first-year marital happiness also correlated significantly less strongly with first-year reports of receiving affirmation from a spouse, having an unsupportive spouse, and engaging in marital conflict. Further, race differences in predictors of happiness for the initial sample were not evident among stayers, perhaps due to smaller variances in reported marital happiness and frequency of conflict for African-American stayers compared to African Americans in the original sample. Methodological implications for cross-cultural longitudinal studies are discussed.

  18. Exit from dormancy provokes DNA-damage-induced attrition in haematopoietic stem cells.

    Science.gov (United States)

    Walter, Dagmar; Lier, Amelie; Geiselhart, Anja; Thalheimer, Frederic B; Huntscha, Sina; Sobotta, Mirko C; Moehrle, Bettina; Brocks, David; Bayindir, Irem; Kaschutnig, Paul; Muedder, Katja; Klein, Corinna; Jauch, Anna; Schroeder, Timm; Geiger, Hartmut; Dick, Tobias P; Holland-Letz, Tim; Schmezer, Peter; Lane, Steven W; Rieger, Michael A; Essers, Marieke A G; Williams, David A; Trumpp, Andreas; Milsom, Michael D

    2015-04-23

    Haematopoietic stem cells (HSCs) are responsible for the lifelong production of blood cells. The accumulation of DNA damage in HSCs is a hallmark of ageing and is probably a major contributing factor in age-related tissue degeneration and malignant transformation. A number of accelerated ageing syndromes are associated with defective DNA repair and genomic instability, including the most common inherited bone marrow failure syndrome, Fanconi anaemia. However, the physiological source of DNA damage in HSCs from both normal and diseased individuals remains unclear. Here we show in mice that DNA damage is a direct consequence of inducing HSCs to exit their homeostatic quiescent state in response to conditions that model physiological stress, such as infection or chronic blood loss. Repeated activation of HSCs out of their dormant state provoked the attrition of normal HSCs and, in the case of mice with a non-functional Fanconi anaemia DNA repair pathway, led to a complete collapse of the haematopoietic system, which phenocopied the highly penetrant bone marrow failure seen in Fanconi anaemia patients. Our findings establish a novel link between physiological stress and DNA damage in normal HSCs and provide a mechanistic explanation for the universal accumulation of DNA damage in HSCs during ageing and the accelerated failure of the haematopoietic system in Fanconi anaemia patients.

  19. In Situ Synthesis of Nanocrystalline Intermetallic Compound Layer during Surface Mechanical Attrition Treatment of Zirconium

    Institute of Scientific and Technical Information of China (English)

    SUNCai-yun; XIEJi-jia; WUXiao-lei; HONGYou-shi; LIUGang; LUJian; LUKe

    2004-01-01

    The surface mechanical attrition treatment (SMAT) technique was developed to synthesize a nanocrystalline (NC) layer on the surface of metallic materials for upgrading their overall properties and performance. In this paper, by means of SMAT to a pure zirconium plate at the room temperature, repetitive multidirectional peening of steel shots (composition (wt%): 1C, 1.5Cr, base Fe) severely deformed the surface layer. A NC surface layer consisting of the intermetallic compound FeCr was fabricated on the surface of the zirconium. The microstructure characterization of the surface layer was performed by using X-ray diffraction analysis, optical microscopy, scanning and transmission electron microscopy observations. The NC surface layer was about 25μm thick and consisted of the intermetallic compound FeCr with an average grain size of 25+10 nm. The deformation-induced fast diffusion of Fe and Cr from the steel shots into Zr occurred during SMAT, leading to the formation of intermetallic compound. In addition, the NC surface layer exhibited an ultrahigh nanohardness of 10.2 GPa.

  20. POSSIBILITY OF BENEFICIATION OF SILICA SAND FROM THE CROATIAN DEPOSITS USING ATTRITION SCRUBBING

    Directory of Open Access Journals (Sweden)

    Ivan Sobota

    2011-12-01

    Full Text Available To meet high quality requirements defined for specific industrial applications, the raw sand often has to be subjected to extensive physical and chemical processing. The possibility of achieving silica sand concentrate of required quality depends mostly on raw sand properties, primarily mineral impurity types and contents, and features of applied beneficiation methods. When the impurities occur in the form of oxide coatings on the surfaces of the single sand grains, attriton scrubbing is applied. By reducing the proportion of oxide coatings on the grains, the quality of sand can be improved. With the aim to determine the possibilities of the beneficiation of silica sand from significant Croatian deposits (“Vrtlinska”, “Štefanac” and “Španovica” and achieve concentrate grade complying with the requirements of domestic industry, laboratory tests were conducted on three raw sand samples with different SiO2 and impurity contents. Grain size distribution, chemical and mineral composition of raw sand samples, and the possibility of their quality improvement by applying the washing, classification and attrition scrubbing were defined by analysis of test results (the paper is published in Croatian.

  1. Attrition of limestones by impact loading in fluidized beds: The influence of reaction conditions

    Energy Technology Data Exchange (ETDEWEB)

    Scala, Fabrizio [Istituto di Ricerche sulla Combustione, Consiglio Nazionale delle Ricerche, Napoli (Italy); Salatino, Piero [Istituto di Ricerche sulla Combustione, Consiglio Nazionale delle Ricerche, Napoli (Italy); Dipartimento di Ingegneria Chimica, Universita degli Studi di Napoli Federico II, Napoli (Italy)

    2010-09-15

    The extent of attrition associated with impact loading was studied for five different limestones pre-processed in fluidized bed under different reaction conditions. The experimental procedure was based on the measurement of the amount and the particle size distribution of the debris generated upon impact of sorbent samples against a target at velocities between 10 and 45 m/s. The effect of calcination, sulfation and calcination/re-carbonation on impact damage was assessed. Fragmentation by impact loading of the limestones was significant and increased with the impact velocity. Lime samples displayed the largest propensity to undergo impact damage, followed by sulfated, re-carbonated and raw limestones. Fragmentation of the sulfated samples followed a pattern typical of the failure of brittle materials. On the other hand, the behaviour of lime samples better conformed to a disintegration failure mode, with extensive generation of very fine fragments. Raw limestone and re-carbonated lime samples followed either of the two patterns depending on the sorbent nature. The extent of particle fragmentation increased after multiple impacts, but the incremental amount of fragments generated upon one impact decreased with the number of successive impacts. (author)

  2. An attrition-resistant zinc titanate sorbent for sulfur. Final technical report, September 1, 1992--August 31, 1993

    Energy Technology Data Exchange (ETDEWEB)

    Swisher, J.H. [Southern Illinois Univ., Carbondale, IL (United States). Dept. of Mechanical Engineering and Energy Processes

    1993-12-31

    In the continuing search for good sorbent materials to remove sulfur for hot, coal-derived gases, zinc titanate sorbents have shown great promise. The objective of this project was to extend the work of prior investigators by developing improvements in the compressive strength and, therefore, the cycle life of these sorbents while maintaining good chemical reactivity. Fifteen formulations were prepared and evaluated. The best properties were obtained by blending relatively course (two micron) ZnO and TiO{sub 2} powders to obtain a composition of 50%Zn{sub 2}TiO{sub 4}-50%TiO{sub 2}. When sintered at 1000{degrees}C, it had a compressive strength of 28 MPa or 147 N/mm, which is four times higher than values obtained by prior investigators. It also performed well in thermogravimetric analysis measurements of reactivity, both in screening tests and in simulated coal gas.

  3. Magnetic properties and pairing tendencies of the iron-based superconducting ladder BaFe2S3 : Combined ab initio and density matrix renormalization group study

    Science.gov (United States)

    Patel, Niravkumar D.; Nocera, Alberto; Alvarez, Gonzalo; Arita, Ryotaro; Moreo, Adriana; Dagotto, Elbio

    2016-08-01

    The recent discovery of superconductivity under high pressure in the two-leg ladder compound BaFe2S3 [H. Takahashi et al., Nat. Mater. 14, 1008 (2015), 10.1038/nmat4351] opens a broad avenue of research, because it represents the first report of pairing tendencies in a quasi-one-dimensional iron-based high-critical-temperature superconductor. Similarly, as in the case of the cuprates, ladders and chains can be far more accurately studied using many-body techniques and model Hamiltonians than their layered counterparts, particularly if several orbitals are active. In this publication, we derive a two-orbital Hubbard model from first principles that describes individual ladders of BaFe2S3 . The model is studied with the density matrix renormalization group. These first reported results are exciting for two reasons: (i) at half-filling, ferromagnetic order emerges as the dominant magnetic pattern along the rungs of the ladder, and antiferromagnetic order along the legs, in excellent agreement with neutron experiments; and (ii) with hole doping, pairs form in the strong coupling regime, as found by studying the binding energy of two holes doped on the half-filled system. In addition, orbital selective Mott phase characteristics develop with doping, with only one Wannier orbital receiving the hole carriers while the other remains half-filled. These results suggest that the analysis of models for iron-based two-leg ladders could clarify the origin of pairing tendencies and other exotic properties of iron-based high-critical-temperature superconductors in general.

  4. 外语磨蚀的影响因素及对策思考%On the factors affecting foreign language attrition and countermeasures

    Institute of Scientific and Technical Information of China (English)

    夏章洪

    2012-01-01

    分析了磨蚀前外语水平、受蚀时间、与受蚀语的接触、年龄、外语习得方式、社会情感因素、读写能力和性别等八大因素对外语磨蚀的影响,并结合我国实际,尝试性地提出相应的解决对策,期望政府部门、学校、教师及学习者本人共同努力,来应对外语磨蚀,提高学习效率。%This paper analyzes the eight factors affecting foreign language attrition,that is,language proficiency level prior to attrition,time since the onset of attrition,exposure to the target language,age at the onset of language attrition,foreign language instruction,social affective factors,literacy and sex.Moreover,some corresponding solving strategies are advanced tentatively in light of the practical situations in our country.Governments,schools,instructors and learners are required to work together to fight against foreign language attrition and improve the learning efficiency.

  5. Plastic deformation to enhance plasma-assisted nitriding: On surface contamination induced by Surface Mechanical Attrition Treatment

    Science.gov (United States)

    Samih, Youssef; Novelli, Marc; Thiriet, Tony; Bolle, Bernard; Allain, Nathalie; Fundenberger, Jean-Jacques; Marcos, Grégory; Czerwiec, Thierry; Grosdidier, Thierry

    2014-08-01

    The Surface Mechanical Attrition Treatment is a recent technique leading to the formation of nanostructured layers by the repeated action of impacting balls. While several communications have revealed possible contamination of the SMATed surfaces, the nature of this surface contamination was analyzed in the present contribution for the treatment of an AISI 316L stainless steel. It is shown, by a combination of Transmission Electron Microscopy and Glow Discharge - Optical Emission Spectrometry, that the surface was alloyed with Ti, Al and V coming from the sonotrode that is used to move the balls as well as Zr coming from the zirshot® balls themselves.

  6. Evolution of texture and microstructure in pulsed electro-deposited Cu treated by Surface Mechanical Attrition Treatment (SMAT)

    Energy Technology Data Exchange (ETDEWEB)

    Blonde, Romain [LETAM, CNRS 3143, Universite Paul Verlaine-Metz, Ile du Saulcy, 57045 Metz (France); Chan, Hoi-Lam [The Hong Kong Polytechnic University, Hung Hom, Kowloon (Hong Kong); Allain-Bonasso, Nathalie [LETAM, CNRS 3143, Universite Paul Verlaine-Metz, Ile du Saulcy, 57045 Metz (France); Bolle, Bernard [LETAM, Ecole Nationale d' Ingenieurs de Metz, Ile du Saulcy, 57045 Metz (France); Grosdidier, Thierry [LETAM, CNRS 3143, Universite Paul Verlaine-Metz, Ile du Saulcy, 57045 Metz (France); Lu, Jian, E-mail: mmmelu@inet.polyu.edu.h [The Hong Kong Polytechnic University, Hung Hom, Kowloon (Hong Kong)

    2010-08-15

    This paper presents the microstructure and texture evolution in pulsed electro-deposited copper samples and the additional effect of the Surface Mechanical Attrition Treatment (SMAT), which were analyzed by means of electron backscattering and X-ray diffractions. A transition in the microstructure was observed as the thickness of the deposit increased: from randomly oriented equiaxed (3D) nanograins at the beginning of the deposition process towards elongated (2D) nanograins having a strong <1 1 0> fibre texture. Meanwhile, the SMAT treatment is shown to randomize the strong texture of the electrodeposits.

  7. Mechanical Behavior of Ultrafine Gradient Grain Structures Produced via Ambient and Cryogenic Surface Mechanical Attrition Treatment in Iron

    Directory of Open Access Journals (Sweden)

    Heather A. Murdoch

    2015-06-01

    Full Text Available Ambient and cryogenic surface mechanical attrition treatments (SMAT are applied to bcc iron plate. Both processes result in significant surface grain refinement down to the ultrafine-grained regime; the cryogenic treatment results in a 45% greater grain size reduction. However, the refined region is shallower in the cryogenic SMAT process. The tensile ductility of the grain size gradient remains low (<10%, in line with the expected behavior of the refined surface grains. Good tensile ductility in a grain size gradient requires the continuation of the gradient into an undeformed region.

  8. Iron-based adsorbent prepared from Litchi peel biomass via pyrolysis process for the removal of pharmaceutical pollutant from synthetic aqueous solution.

    Science.gov (United States)

    Foletto, Vitória Segabinazzi; Ferreira, Ananda Bulegon; da Cruz Severo, Eric; Collazzo, Gabriela Carvalho; Foletto, Edson Luiz; Dotto, Guilherme Luiz

    2017-03-10

    A porous iron-based adsorbent obtained from litchi peel via pyrolysis process was prepared in this work, in order to evaluate its adsorptive potential for the removal of a pharmaceutical dye (amaranth) from aqueous solution. The material was characterized by X-ray diffraction, nitrogen adsorption-desorption isotherms, and scanning electron microscopy. Several isotherm and kinetic models were tested aiming to represent the amaranth dye adsorption. The prepared sample presented magnetic property, and a mesoporous texture constituted of graphite and three iron-based phases. The adsorption kinetics of amaranth on the adsorbent followed the pseudo-second-order model, whereas the equilibrium data were in good agreement with the BET isotherm, being represented by a sigmoid-shaped adsorption isotherm. The maximum adsorption capacity for the amaranth dye was found to be 44.87 mg g(-1), demonstrating that the material prepared in this work showed to be a promising adsorbent for the removal of amaranth from aqueous solution.

  9. Copper-tuned magnetic order and excitations in iron-based superconductors Fe1+yTe1-xSex

    Science.gov (United States)

    Wen, Jinsheng; Xu, Zhijun; Xu, Guangyong; Lumsden, Mark; Matsuda, Masaaki; Valdivia, Patrick; Bourret, Edith; Lee, Dunghai; Gu, Genda; Tranquada, John; Birgeneau, Robert

    2012-02-01

    We report neutron scattering results on the Cu-substitution effects in the iron-based superconductors, Fe1+yTe1-xSex. In the parent compound, it is found that Cu drives the low-temperature magnetic ground state from long-range commensurate antiferromagnetic order in Fe1.06TeCu0.04 to short-range incommensurate order in FeTeCu0.1. In the former sample, the structural and magnetic ordering temperature is 40 K; in FeTeCu0.1, the structural phase transition is not obvious and a transition to the spin-glass state is found at 22 K. Cu suppresses superconductivity in FeTe0.5Se0.5---Tc is reduced to 7 K with a 2% Cu doping, and no superconductivity is found in the 10% Cu-doped sample. In the meantime, the intensity and energy of the resonance mode are suppressed in the 2% Cu-doped sample, while there is no resonance in the non-superconducting sample. Besides, the low-temperature magnetic excitation spectra are distinct for these two samples, with the superconducting one having an ``hour-glass" shape and the other one having a ``waterfall" shape. Our results provide further insights on the interplay between magnetism and superconductivity in the iron-based superconductors.

  10. Robustness of s-wave pairing symmetry in iron-based superconductors and its implications for fundamentals of magnetically driven high-temperature superconductivity

    Science.gov (United States)

    Hu, Jiangping; Yuan, Jing

    2016-10-01

    Based on the assumption that the superconducting state belongs to a single irreducible representation of lattice symmetry, we propose that the pairing symmetry in all measured iron-based superconductors is generally consistent with the A 1 g s-wave. Robust s-wave pairing throughout the different families of iron-based superconductors at different doping regions signals two fundamental principles behind high- T c superconducting mechanisms: (i) the correspondence principle: the short-range magnetic-exchange interactions and the Fermi surfaces act collaboratively to achieve high- T c superconductivity and determine pairing symmetries; (ii) the magnetic-selection pairing rule: superconductivity is only induced by the magnetic-exchange couplings from the super-exchange mechanism through cation-anion-cation chemical bonding. These principles explain why unconventional high- T c superconductivity appears to be such a rare but robust phenomena, with its strict requirements regarding the electronic environment. The results will help us to identify new electronic structures that can support high- T c superconductivity.

  11. The Property of Phonon Gap in Iron-Based Superconductors FeSe, LiFeAs and SrFeAsF

    Science.gov (United States)

    Wang, Wei; Li, Bin; He, Junqi; Sun, Jiafa

    2017-03-01

    First-principles calculations are performed for iron-based superconductors FeSe, LiFeAs and SrFeAsF, and the reasons of generation and loss of the phonon gaps in them are analyzed by analogy with electronic energy band theory. In iron-based superconductors FeSe and LiFeAs, lattice vibrations are affected by so strong changes in the periodic potential that the phonon spectra open a full gap. After considering electron-spin interactions, the enhancement of the periodic potential results in a broadening of the gap. From binary FeSe to ternary LiFeAs to quaternary SrFeAsF, the full phonon gap undergoes the process from decrease to disappearance, which is closely related to the frequencies overlapping of different atoms by vibrations. The fewer the material components and the larger the atomic number ratio, the more possible the production of the full phonon gap or the appearance of wider gap. In addition, the phonon gaps of FeSe and LiFeAs locate around the frequency of 10^{12} Hz, whose filtering properties for elastic waves are hopefully to be applied in quantum acoustics.

  12. Reconciling viability and cost-effective shape memory alloy options – A review of copper and iron based shape memory metallic systems

    Directory of Open Access Journals (Sweden)

    Kenneth Kanayo Alaneme

    2016-09-01

    Full Text Available Shape memory alloys (SMAs are group of alloys that display anthropomorphic characteristics. These alloys recover their pre-deformed morphology when heated above their transition temperatures after being deformed in their lower temperature phase (martensitic phase. This unique material behavior is explored in industrial and technological applications where capacity for strain recovery is a key design parameter. Copper and iron based SMAs are largely viewed as potential cost effective substitute to Ni–Ti SMAs judging from their promising shape memory properties, damping capacity and other functional properties. Despite their outstanding potentials, the susceptibility of copper based SMAS to phase stabilization, transition hysteresis, aging and brittleness creates doubt on the possibility of transiting from the realm of potential to functional long term use in engineering applications. On the other hand the low percentage shape recovery in the Fe based SMAs also creates a gap between the theory and potential use of these alloys. This paper takes a critical look at the science of shape memory phenomena as applicable to copper and iron based SMA systems. It also covers the limitations of these systems, the effect of processing parameters on these alloys, proposed solutions to limitations associated with this group of shape memory alloys and thoughts for future consideration.

  13. The Property of Phonon Gap in Iron-Based Superconductors FeSe, LiFeAs and SrFeAsF

    Science.gov (United States)

    Wang, Wei; Li, Bin; He, Junqi; Sun, Jiafa

    2016-12-01

    First-principles calculations are performed for iron-based superconductors FeSe, LiFeAs and SrFeAsF, and the reasons of generation and loss of the phonon gaps in them are analyzed by analogy with electronic energy band theory. In iron-based superconductors FeSe and LiFeAs, lattice vibrations are affected by so strong changes in the periodic potential that the phonon spectra open a full gap. After considering electron-spin interactions, the enhancement of the periodic potential results in a broadening of the gap. From binary FeSe to ternary LiFeAs to quaternary SrFeAsF, the full phonon gap undergoes the process from decrease to disappearance, which is closely related to the frequencies overlapping of different atoms by vibrations. The fewer the material components and the larger the atomic number ratio, the more possible the production of the full phonon gap or the appearance of wider gap. In addition, the phonon gaps of FeSe and LiFeAs locate around the frequency of 10^{12} Hz, whose filtering properties for elastic waves are hopefully to be applied in quantum acoustics.

  14. Design, Synthesis, and Mechanistic Evaluation of Iron-Based Catalysis for Synthesis Gas Conversion to Fuels and Chemicals

    Energy Technology Data Exchange (ETDEWEB)

    Enrique Iglesia; Akio Ishikawa; Manual Ojeda; Nan Yao

    2007-09-30

    ) structural evolution of Fe-Zn oxide promoted with K and Cu, and (ii) evaluation of hydrocarbon and CH{sub 4} formation rates during activation procedures at various temperature and H{sub 2}/CO ratios. On the basis of the obtained results, we suggest that lower reactor temperature can be sufficient to activate catalysts and lead to the high FTS performance. In this project, we have also carried out a detailed kinetic and mechanistic study of the Fischer-Tropsch Synthesis with Fe-based catalysts. We have proposed a reaction mechanism with two CO activation pathways: unassisted and H-assisted. Both routes lead to the formation of the same surface monomers (CH{sub 2}). However, the oxygen removal mechanism is different. In the H-assisted route, oxygen is removed exclusively as water, while oxygen is rejected as carbon dioxide in the unassisted CO dissociation. The validity of the mechanism here proposed has been found to be in agreement with the experimental observation and with theoretical calculations over a Fe(110) surface. Also, we have studied the validity of the mechanism that we propose by analyzing the H{sub 2}/D{sub 2} kinetic isotope effect (r{sub H}/r{sub D}) over a conventional iron-based Fischer-Tropsch catalyst Fe-Zn-K-Cu. We have observed experimentally that the use of D{sub 2} instead of H{sub 2} leads to higher hydrocarbons formation rates (inverse kinetic isotopic effect). On the contrary, primary carbon dioxide formation is not influenced. These experimental observations can be explained by two CO activation pathways. We have also explored the catalytic performance of Co-based catalysts prepared by using inverse micelles techniques. We have studied several methods in order to terminate the silanol groups on SiO{sub 2} support including impregnation, urea homogeneous deposition-precipitation, or zirconium (IV) ethoxide titration. Although hydroxyl groups on the SiO{sub 2} surface are difficult to be stoichiometrically titrated by ZrO{sub 2}, a requirement to

  15. Arc-Sprayed Iron-Based Coatings for Erosion-Corrosion Protection of Boiler Tubes at Elevated Temperatures

    Science.gov (United States)

    Pokhmurskii, Vasyl; Student, Mykhailo; Gvozdeckii, Volodymyr; Stypnutskyy, Taras; Student, Oleksandra; Wielage, Bernhard; Pokhmurska, Hanna

    2013-06-01

    Wire arc spraying is an economically attractive thermal spray process that is especially interesting for the protection of large-scale parts or constructions. This study presents the results of the development and investigation of a number of cored wires based on the Fe-Cr-Al system with minor addition of alloying elements (B, Mn, Ni, Si, Ti, Mg, etc.). The microstructure of the coatings, their electrochemical behavior, and isothermal oxidation performance over a temperature range of 20-700 °C were investigated. Erosion resistance at elevated temperatures was determined with a laboratory test unit under test conditions that have simulated the work conditions in fossil-fuel-fired boilers. It was established that the oxidation resistance and the gas-abrasive wear resistance of arc-sprayed coatings depend mostly on the coating microstructure and homogeneity of element distribution rather than on the general alloying level and microhardness of the coating. A new parameter for coating characterization, namely, the coefficient of chemical microheterogeneity, K CMH, is introduced to quantify this influence. Formation of the coating microstructure at elevated temperatures and its influence on the protection ability of the coating are discussed.

  16. Electron correlations and orbital selectivities in multiorbital mo dels for iron-based sup erconductors%铁基超导体多轨道模型中的电子关联与轨道选择∗

    Institute of Scientific and Technical Information of China (English)

    俞榕

    2015-01-01

    We review the recent theoretical progress of the multiorbital effects on the electron correlations in iron-based superconductors. Studying the metal-to-insulator transitions of the multiorbital Hubbard models for parent compounds of iron-based superconductors, a Mott transition is generally realized. The natures of both the Mott insulating and the metallic phases are affected by the Hund’s rule coupling. In alkaline iron selenides, Hund’s rule coupling stabilizes a novel orbital-selective Mott phase, in which the iron 3d xy orbital is Mott localized, while other 3d orbitals are still itinerant. We discuss the effects of the orbital selectivity on normal state properties and the superconductivity of the iron-based systems.

  17. Microstructure and wear resistance of spray-formed supermartensitic stainless steel

    Directory of Open Access Journals (Sweden)

    Guilherme Zepon

    2013-06-01

    Full Text Available Since the early 90's the oil industry has been encouraging the development of corrosion and wear resistant alloys for onshore and offshore pipeline applications. In this context supermartensitic stainless steel was introduced to replace the more expensive duplex stainless steel for tubing applications. Despite the outstanding corrosion resistance of stainless steels, their wear resistance is of concern. Some authors reported obtaining material processed by spray forming, such as ferritic stainless steel, superduplex stainless steel modified with boron, and iron-based amorphous alloys, which presented high wear resistance while maintaining the corrosion performance1,2. The addition of boron to iron-based alloys promotes the formation of hard boride particles (M2B type which improve their wear resistances3-9. This work aimed to study the microstructure and wear resistance of supermartensitic stainless steel modified with 0.3 wt. (% and 0.7 wt. (% processed by spray forming (SF-SMSS 0.3%B and SF-SMSS 0.7%B, respectively. These boron contents were selected in order to improve the wear resistance of supermartensitic stainless steel through the formation of uniformly distributed borides maintaining the characteristics of the corrosion resistant matrix. SF-SMSS 0.7%B presents an abrasive wear resistance considerably higher than spray-formed supermartensitic stainless steel without boron addition (SF-SMSS.

  18. Comparative analysis of heat transfer,ash deposition and attrition performances on different extended surfaces%不同扩展换热面传热、积灰、磨损特性对比

    Institute of Scientific and Technical Information of China (English)

    赵虹; 周霭琳; 施浩勋; 陈理帅; 邓芙蓉; 杨建国; 胡劲逸

    2015-01-01

    To optimize and select the low temperature heat exchanger,comparative analysis on heat transfer, ash deposition and attrition performances of H-finned tubes and spiral finned tubes was conducted,by ther-modynamic calculation and numerical simulation methods.The results show that,with conventional struc-tural parameters,the spiral finned tube with unit length has higher heat transfer efficiency,and its steel consumption (flow resistance)is only 42.87% (61.45%)of that of the H-finned tube when heat transfer rate is the same.Due to the special groove structure,the swirling generated in the H-finned tube has the opposite direction to the malnstream.It shocks to the tube lee side vertically,so the H-finned tube can a-chieve ash self-removing.The abrasion of the H-finned tubes is lighter overall,and the fin has no sideway scouring.Therefore,the spiral finned tube has better heat transfer property while the H-finned tube has ad-vantages in ash deposition and attrition resistance.%为了对低温换热器优化选型,利用热力计算和数值模拟的方法,对比分析了螺旋肋片管和 H型鳍片管的传热、积灰、磨损特性.结果表明:常规结构参数下,单位长度的螺旋肋片管具有更大的换热效率,在达到相同换热量时,其钢材消耗是 H 型鳍片管的42.87%,烟气阻力是 H型鳍片管的61.45%;H 型鳍片管由于其特殊的沟槽结构,形成的涡流方向与主流速度相反,垂直冲刷基管背风面,达到自清灰的目的,其鳍片无侧向气流冲刷,整体磨损较轻.因此,螺旋肋片管的换热性能更好,但 H 型鳍片管的防积灰和耐磨性均优于螺旋肋片管.

  19. Impact of educational level on study attrition and evaluation of web-based computer-tailored interventions: results from seven randomized controlled trials

    NARCIS (Netherlands)

    Reinwand, D.A.; Crutzen, R.; Elfeddali, I.; Schneider, F.; Schulz, D.N.; Smit, E.S.; Stanczyk, N.E.; Tange, H.; Voncken-Brewster, V.; Walthouwer, M.J.L.; Hoving, C.; de Vries, H.

    2015-01-01

    Background: Web-based computer-tailored interventions have shown to be effective in improving health behavior; however, high dropout attrition is a major issue in these interventions. Objective: The aim of this study is to assess whether people with a lower educational level drop out from studies mo

  20. Are good learners also good forgetters? : A retrieval induced forgetting perspective of L1 attrition in an L2 immersed context

    NARCIS (Netherlands)

    Keijzer, Merel

    2014-01-01

    One finding that is notoriously reported by any study examining first language (L1) attrition in a second language (L2) immersed environment is the substantial individual variation: some individuals showcase dramatically reduced linguistic performance, while the linguistic behavior of others remains

  1. Relationship between Measures of Academic Quality and Undergraduate Student Attrition: The Case of Higher Education Institutions in the Colombian Caribbean Region

    Science.gov (United States)

    Martínez, Anabella; Borjas, Mónica; Herrera, Mariela; Valencia, Jorge

    2015-01-01

    Undergraduate student attrition is a major concern in higher education. It is usually explained by the impact of student attributes; however, recent developments in student success literature point to the need of exploring institutional practices that may impact a student's decision to abandon their studies. The current weight of academic quality…

  2. Why They Leave: The Impact of Stereotype Threat on the Attrition of Women and Minorities from Science, Math and Engineering Majors

    Science.gov (United States)

    Beasley, Maya A.; Fischer, Mary J.

    2012-01-01

    This paper examines the effects of group performance anxiety on the attrition of women and minorities from science, math, and engineering majors. While past research has relied primarily on the academic deficits and lower socioeconomic status of women and minorities to explain their absence from these fields, we focus on the impact of stereotype…

  3. I Ain't Gonna Make It. Comparing Job Demands-Resources and Attrition Intention Between Senior Teachers and Senior Employees of Six Other Occupational Categories in Flanders.

    Science.gov (United States)

    Van Droogenbroeck, Filip; Spruyt, Bram

    2016-07-01

    Teachers are often thought to retire early and have more stress and burnout than other human service professionals. In this article, we investigate attrition intention amongst senior teachers and senior employees of six other blue- and white-collar occupational categories using the Job Demands-Resources (JD-R) model. We followed a two-step approach. First, analysis of variance and logistic regression analysis was used to assess differences in the level of job demands, resources, and attrition intention between occupations for male and female employees separately. Subsequently, multiple group path analysis was used to assess the invariance of the JD-R model across occupational groups and genders. We used representative data gathered in Flanders among 6,810 senior employees (45 years or older). Results indicate that there are differences in the determinants of attrition intention between men and women. The differences in attrition intention are minimal between occupations once controlled for job demands and resources. In addition, the JD-R model is largely invariant across white-collar occupations and gender. We provide support for both the energetic and motivational process of the JD-R model.

  4. Methods to Limit Attrition in Longitudinal Comparative Effectiveness Trials: Lessons from the Lithium Use for Bipolar Disorder (LiTMUS) Study

    Science.gov (United States)

    Sylvia, Louisa G.; Reilly-Harrington, Noreen A.; Leon, Andrew C.; Kansky, Christine I.; Ketter, Terence A.; Calabrese, Joseph R.; Thase, Michael E.; Bowden, Charles L.; Friedman, Edward S.; Ostacher, Michael J.; Iosifescu, Dan V.; Severe, Joanne; Nierenberg, Andrew A.

    2013-01-01

    Background High attrition rates which occur frequently in longitudinal clinical trials of interventions for bipolar disorder limit the interpretation of results. Purpose The aim of this article is to present design approaches that limited attrition in the Lithium Use for Bipolar Disorder (LiTMUS) Study. Methods LiTMUS was a 6-month randomized, longitudinal multi-site comparative effectiveness trial that examined bipolar participants who were at least mildly ill. Participants were randomized to either low to moderate doses of lithium or no lithium, in addition to other treatments needed for mood stabilization administered in a guideline-informed, empirically supported, and personalized fashion (N=283). Results Components of the study design that may have contributed to the low attrition rate of the study included use of: (1) an intent-to-treat design; (2) a randomized adjunctive single-blind design; (3) participant reimbursement; (4) intent-to-attend the next study visit (includes a discussion of attendance obstacles when intention is low); (5) quality care with limited participant burden; and (6) target windows for study visits. Limitations Site differences and the effectiveness and tolerability data have not been analyzed yet. Conclusions These components of the LiTMUS study design may have reduced the probability of attrition which would inform the design of future randomized clinical effectiveness trials. PMID:22076437

  5. Development of an Iron-Based Hardfacing Material Reinforced with Fe-(TiW)C Composite Powder

    Science.gov (United States)

    Correa, E. O.; Alcantara, N. G.; Tecco, D. G.; Kumar, R. V.

    2007-05-01

    The objective of this work is to investigate the correlation of microstructure with wear resistance in a hardfacing material reinforced with Fe-(TiW)C composite powder particles. This material was designed for cladding components subjected to highly abrasive conditions and was deposited on a low-carbon steel substrate by open arc welding. The theoretical and experimental work undertaken includes solidification study, microstructural characterization, and abrasive wear testing. Microstructural analysis of the hardfaced top layer of the alloy showed the presence of TiWC carbide particles and TiNbC carbides randomly distributed in a eutectic mixture matrix γ/M7C3 containing primary austenite dendrites. Microstructural examinations also showed that hard and fine spherulitic carbides, in which a Ti-rich MC carbide core was encircled by MC carbide enriched with Nb and W, were homogeneously distributed in the matrix. The energy-dispersive spectroscopy (EDS) mapping of spherulitic carbides showed that the any added Nb replaced a significant part of W in the Fe-(TiW)C powder, and W preferentially partitioned into other carbides and matrix during solidification. Abrasion test results showed that the preceding carbides improve the wear resistance of the hardfacing material in comparison with conventional Fe-Cr-C and Fe-Cr-C-Nb alloys, especially under high stress conditions.

  6. The effect of boron on the wear behavior of iron-based hardfacing alloys for nuclear power plants valves

    Science.gov (United States)

    Yoo, Jeong Wan; Lee, Seong Hun; Yoon, Chong S.; Kim, Seon Jin

    2006-06-01

    The effect of boron of Fe-Cr-C-Si alloys, replacing Stellite 6 traditionally used in nuclear power industry, on the high temperature wear resistance was characterized. Sliding wear tests of Fe-Cr-C-Si-xB (x = 0.3, 0.6, 1.0 and 2.0 wt%) alloys were performed in air at temperatures ranging from 300 to 725 K under a contact stress of 103 MPa. Low-boron alloys containing less than 0.6 wt% boron showed the excellent wear resistance than any other tested alloys in an elevated temperature. The improvement was associated with the matrix hardening by promotion of the γ → α‧ strain-induced martensitic transformation occurred during wear. In addition, protective oxide layers formed on the contacting surface reduced the wear loss by minimizing the direct metal-to-metal contact. However, high-boron alloys containing more than 1 wt% boron showed somewhat larger amount of wear loss than low-boron alloys due to the absence of the strain-induced martensitic transformation and the presence of the brittle FeB particles connected with easy crack initiation.

  7. Structural symmetries of the 112-type iron-based superconductor (Ca1-xLax)FeAs2 studied using nonlinear and ultrafast optics

    Science.gov (United States)

    Harter, John; Chu, Hao; Jiang, Shan; Ni, Ni; Hsieh, David

    The crystal structure of the newly discovered 112-type iron-based superconductors contains symmetry-breaking arsenic chains, avoiding the need for local probes or uniaxial strain in order to study the ubiquitous electronic nematic state that exists in the vicinity of magnetic order in the iron pnictides. In addition, the 112-type materials are the first known high-temperature superconductors without a center of inversion, with interesting ramifications for Cooper pairing in the superconducting state. We present details of the structure of 112-type (Ca1-xLax)FeAs2 using rotational anisotropy second harmonic generation and pump-probe transient reflectivity experiments. These all-optical techniques are complimentary to conventional diffraction measurements and enable a precise determination of crystallographic symmetries. Our measurements highlight the novel structural properties of the 112-type materials.

  8. Characterization of Mo additions in iron-based Fischer-Tropsch catalysts using X-ray absorption spectroscopy and X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Campos, A. [Cain Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA 70803 (United States)], E-mail: acampo2@lsu.edu; Spivey, J.J. [Cain Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA 70803 (United States); Roy, A. [J. Bennett Johnson, Sr., Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, LA 70806 (United States); Lohitharn, N.; Goodwin, J.; Lotero, E. [Department of Chemical and Biomolecular Engineering, Clemson University, 127 Earle Hall, Clemson, SC 29634 0909 (United States); Lamb, H. [Department of Chemical and Biomolecular Engineering, Engineering Building I, Box 7905, 911 Partners Way, Raleigh, NC 27695 (United States)

    2007-11-11

    An iron-based Fischer-Tropsch catalyst with a low concentration of molybdenum (90Fe/10Mo/5Cu/17Si) used as a promoter was characterized by X-ray absorption spectroscopy (XAS) and X-ray diffractometry (XRD). The catalyst was prepared using coprecipitation, pretreated in CO, then one sample passivated and one calcined. The XRD data show that after CO pretreatment the calcined and passivated catalysts are almost amorphous with respect to Fe{sub 2}O{sub 3} with nanoparticle size of 10 and 100 A for Fe{sub 3}C (only present in the passivated sample). Least squares fitting of the XANES region show that the calcined and passivated samples were similar in the bulk and surface structures, with the calcined samples completely oxidized. As expected, K and L{sub III} edges Mo-XANES shows only small molybdenum carbide formation compared to iron carbide.

  9. Raman spectroscopic studies on single crystals of the iron-based superconductor SmFeAsO{sub 1-x}F{sub x}

    Energy Technology Data Exchange (ETDEWEB)

    Jursic, Ivan; Schoenes, Joachim [Technische Universitaet Braunschweig, Institut fuer Physik der Kondensierten Materie, 38106 Braunschweig (Germany); Bukowski, Zbigniew; Karpinski, Janusz [ETH Zuerich, Laboratorium fuer Festkoerperphysik, 8093 Zuerich (Switzerland)

    2009-07-01

    The recent discovery of superconductivity in iron-based oxypnctides has led to a great interest in this new class of non-cuprate high-T{sub c} superconductors. Though theoretical work predicts a small electron-phonon coupling, which means that this should not be the driving mechanism for the observed T{sub c}'s in this class of material, the exact coupling mechanism is still under debate. We present Raman studies on superconducting SmFeAsO{sub 1-x}F{sub x} single crystals where the T{sub c} was determined by SQUID magnetometric measurements to be 34 K. At room temperature polarized measurements were performed to assign the phonon modes. Furthermore studies at different temperatures reaching from 5K to 300K were done to investigate the phonon behavior. The phonon frequencies shift with temperature and we investigate this shift in terms of electron-phonon coupling.

  10. First-Principles Study of Antimony Doping Effects on the Iron-Based Superconductor CaFe(SbxAs1-x)2

    Science.gov (United States)

    Nagai, Yuki; Nakamura, Hiroki; Machida, Masahiko; Kuroki, Kazuhiko

    2015-09-01

    We study antimony doping effects on the iron-based superconductor CaFe(SbxAs1-x)2 by using the first-principles calculation. The calculations reveal that the substitution of a doped antimony atom into As of the chainlike As layers is more stable than that into FeAs layers. This prediction can be checked by experiments. Our results suggest that doping homologous elements into the chainlike As layers, which only exist in the novel 112 system, is responsible for rising up the critical temperature. We discuss antimony doping effects on the electronic structure. It is found that the calculated band structures with and without the antimony doping are similar to each other within our framework.

  11. The effect of preparation factors on the structural and catalytic properties of mesoporous nanocrystalline iron-based catalysts for high temperature water gas shift reaction

    Energy Technology Data Exchange (ETDEWEB)

    Meshkani, Fereshteh; Rezaei, Mehran [University of Kashan, Kashan (Iran, Islamic Republic of)

    2015-07-15

    A systematic study was done on the effect of preparation factors on the structural and catalytic properties of mesoporous nanocrystalline iron-based catalysts in high temperature water gas shift reaction. The catalysts were prepared by coprecipitation method, and the effect of the main preparation factors (pH, refluxing temperature, refluxing time, concentration of the precursors solution) was studied. The catalysts were characterized by powder X-ray diffraction (XRD), N{sub 2} adsorption (BET), Temperature programmed reduction (TPR), transmission and scanning electron microscopies (TEM, SEM) techniques. The results revealed that the preparation factors affected the textural and catalytic properties of the Fe-Cr-Cu catalyst. The results showed that the prepared catalyst with the highest activity showed higher specific surface area compared to commercial catalyst and consequently exhibited higher activity in high temperature water gas shift reaction. The TEM analysis showed a nanostructure for this sample with crystallite size less than 20 nm.

  12. Magnetic resonance imaging reveals detailed spatial and temporal distribution of iron-based nanoparticles transported through water-saturated porous media

    Science.gov (United States)

    Cuny, Laure; Herrling, Maria Pia; Guthausen, Gisela; Horn, Harald; Delay, Markus

    2015-11-01

    The application of engineered nanoparticles (ENP) such as iron-based ENP in environmental systems or in the human body inevitably raises the question of their mobility. This also includes aspects of product optimization and assessment of their environmental fate. Therefore, the key aim was to investigate the mobility of iron-based ENP in water-saturated porous media. Laboratory-scale transport experiments were conducted using columns packed with quartz sand as model solid phase. Different superparamagnetic iron oxide nanoparticles (SPION) were selected to study the influence of primary particle size (dP = 20 nm and 80 nm) and surface functionalization (plain, -COOH and -NH2 groups) on particle mobility. In particular, the influence of natural organic matter (NOM) on the transport and retention behaviour of SPION was investigated. In our approach, a combination of conventional breakthrough curve (BTC) analysis and magnetic resonance imaging (MRI) to non-invasively and non-destructively visualize the SPION inside the column was applied. Particle surface properties (surface functionalization and resulting zeta potential) had a major influence while their primary particle size turned out to be less relevant. In particular, the mobility of SPION was significantly increased in the presence of NOM due to the sorption of NOM onto the particle surface resulting in a more negative zeta potential. MRI provided detailed spatially resolved information complementary to the quantitative BTC results. The approach can be transferred to other porous systems and contributes to a better understanding of particle transport in environmental porous media and porous media in technical applications.

  13. Physician distribution and attrition in the public health sector of Ethiopia

    Directory of Open Access Journals (Sweden)

    Assefa T

    2016-12-01

    other regions from elsewhere in the country. The Poisson regression model revealed a decreased incidence of turnover among physicians born between the years 1975 and 1985 (incident rate ratio [IRR]: 0.63; 95% confidence interval [CI]: 0.51, 0.79 and among those who were born prior to 1975 (IRR: 0.24; 95% CI: 0.17, 0.34 compared to those who were born after 1985. Female physicians were 1.4 times (IRR: 1.44; 95% CI: 1.14, 1.81 more likely to move out from their duty stations compared to males. In addition, physicians working in district hospitals were 2 times (IRR: 2.14; 95% CI: 1.59, 2.89 more likely to move out and those working in general hospitals had 1.39 times (IRR: 1.39; 95% CI: 1.08, 1.78 increased rate of turnover in comparison with those who were working in referral hospitals. Physicians working in the Amhara region had 2 times (IRR: 2.01; 95% CI: 1.49, 2.73 increased risk of turnover in comparison with those who were working in the capital, Addis Ababa. The probability of migration did not show a statistically significant difference in all other regions (P>0.05. Conclusion: The public health sector physician workforce largely constituted of male physicians, young and less experienced. High turnover rate among females, the young and less experienced physicians, and those working in distant places (district hospitals indicate the need for special attention in devising human resources management and retention strategies. Keywords: health workforce, physician retention, physician turnover/migration/attrition

  14. The Role of Attrition and Solids Recovery in a Chemical Looping Combustion Process; Effet de l'attrition et de la recuperation des particules dans le procede de combustion en boucle chimique

    Energy Technology Data Exchange (ETDEWEB)

    Kramp, M.; Thon, A.; Hartge, E.U.; Heinrich, S.; Werther, J. [Institute of Solids Process Engineering and Particle Technology, Hamburg University of Technology, 21071 Hamburg (Germany)

    2011-03-15

    In the present work, the steady-state behavior of a Chemical Looping Combustion process of interconnected fluidized bed reactors is simulated. The simulations have been carried out in two different scales, 50 kWth and 100 MWth. Attrition model derived from small scale laboratory experiments has been employed for the prediction of the process behavior in terms of attrition and Oxygen Carrier loss. Information on Oxygen Carrier characteristics and reaction kinetics were taken from literature. Realistic circulation mass flows of Oxygen Carrier particles are obtained and Oxygen Carrier losses are quantified. The large scale process looses significantly more Oxygen Carrier than the small scale process based on the same amount of thermal energy produced. Incomplete conversion in the air reactor could be identified as a critical point. Another issue is the fuel gas bypassing the Oxygen Carrier particles through bubbles in the large scale process which leads to lowered fuel conversions. The simulations indicate that a similar performance of a pilot scale and a large scale process is not guaranteed due to the scale-up effect on fluid dynamics. Furthermore, the simulations allow an assessment of the influence of the quality of the solids recovery system on the Oxygen Carrier loss. The distribution of the losses between possible origins is investigated and different changes in the solids recovery system are discussed regarding their potential to decrease the Oxygen Carrier loss. For example, the addition of a second-stage cyclone after the air reactor of the large scale process reduces the Oxygen Carrier loss significantly. (authors)

  15. Personality Disorder in Adult Attention-Deficit/Hyperactivity Disorder: Attrition and Change During Long-term Treatment.

    Science.gov (United States)

    Gift, Thomas E; Reimherr, Frederick W; Marchant, Barrie K; Steans, Tammy A; Wender, Paul H

    2016-05-01

    Personality disorders (PDs) are commonly found in adults with attention-deficit/hyperactivity disorder (ADHD) and are associated with increased ADHD symptoms and psychosocial impairment. To assess the impact of PDs or personality traits on retention rates in ADHD trials and whether treating ADHD affects the expression of PD, data were analyzed from 2 methylphenidate trials. Assessment of PDs and personality traits included using the Wisconsin Personality Disorders Inventory IV and the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition Personality Disorders. Attention-deficit/hyperactivity disorder symptoms were evaluated using the Wender-Reimherr Adult Attention Deficit Disorder Scale. Major findings were that subjects with cluster A, cluster B, passive-aggressive, or more than 1 PD showed more attrition. Subjects dropping out also had more schizoid and narcissistic traits. Attention-deficit/hyperactivity disorder symptoms (p Disorders Inventory IV items that improved most, 8 resembled ADHD or oppositional defiant disorder symptoms.

  16. Thermal stability of nanocrystalline layer prepared by surface mechanical attrition in 0Cr18Ni9Ti stainless steel

    Institute of Scientific and Technical Information of China (English)

    WANG Hong-bin; WU Xiao-chun; XU Ling-yun

    2004-01-01

    By means of surface mechanical attrition (SMA), a nanostructured surface layer was formed on a 0Cr18Ni9Ti austenite stainless steel plate. A strain-induced martensite transformation was observed during SMA treatment, and a single magnetic martensite phase layer with thickness of about 30 μm was gotten. The grain growth and phase transformations in the nanocrystalline layer are investigated during heating. The grain growth exponent for nanocrystalline polycrystalline steel is estimated. The kinetics mechanism governing the grain growth in the nanocrystalline layer is discussed. The martensite in the surface layer is quite stable and the temperature at which the reverse transformation of martensite to austenite starts during heating is about 500 ℃.

  17. Effect of treatment time on characterization and properties of nanocrystalline surface layer in copper induced by surface mechanical attrition treatment

    Indian Academy of Sciences (India)

    Farzad Kargar; M Laleh; T Shahrabi; A Sabour Rouhaghdam

    2014-08-01

    Nanocrystalline surface layers were synthesized on pure copper by means of surface mechanical attrition treatment (SMAT) at various treatment times. The microstructural features of the surface layers produced by SMAT were systematically characterized by optical microscopy (OM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. Hardness and surface roughness measurements were also carried out. It is found that the thickness of the deformed layer increased from 50 to 500 m with increasing treatment time from 10 to 300 min, while the average grain size of the top surface layer decreased from 20 to 7 nm. Hardness of the all SMATed samples decreased with depth. Furthermore, the hardness of the top surface layer of the SMATed samples was at least two times higher than that of the un-treated counterpart. Surface roughness results showed different trend with treatment time. Amounts of PV and a values first sharply increased and then decreased.

  18. Characterization and Properties of Nanostructured Surface Layer in a Low Carbon Steel Subjected to Surface Mechanical Attrition

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    A nanostructured surface layer was synthesized on a Iow carbon steel by using surface mechanical attrition (SMA)technique. The refined microstructure of the surface layer was characterized by means of different techniques,and the hardness variation along the depth was examined. Experimental results show that the microstructure isinhomogeneous along the depth. In the region from top surface to about 40μm deep, the grain size increases fromabout 10 nm to 100 nm. In the adjacent region of about 40~80μm depth, the grain size increases from about 100nm to 1000 nm. The grain refinement can be associated with the activity of dislocations. After the SMA treatment,the hardness of the surface layer is enhanced significantly compared with that of the original sample, which canprimarily be attributed to the grain refinement.

  19. Measurement of microstructural parameters of nanocrystalline Fe-30 wt.%Ni alloy produced by surface mechanical attrition treatment

    Energy Technology Data Exchange (ETDEWEB)

    Li Wei; Xu Weizong; Wang Xiaodong [Schools of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Rong Yonghua [Schools of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China)], E-mail: yhrong@sjtu.edu.cn

    2009-04-17

    Fe-30 wt.%Ni alloy was severely plastic deformed through surface mechanical attrition treatment (SMAT) for different times and the nanocrystalline surface layers were produced on surface. The microstructural parameters such as the average crystallite size, root mean square microstrain, dislocation density and stored elastic energy were measured by using X-ray diffraction line profile analysis (XLPA) and transmission electron microscopy (TEM). The high values of dislocation density and stored elastic energy were obtained in the SMAT samples. The average crystallite size measured by XLPA is compared with that observed on TEM. The high-resolution TEM (HRTEM) micrograph confirms the presence of high density of dislocations obtained by XLPA, accompanying the presence of heavy distortion of lattice, which is different from that in the tensile-deformed sample.

  20. A validation of the fibre orientation and fibre length attrition prediction for long fibre-reinforced thermoplastics

    Science.gov (United States)

    Hopmann, Ch.; Weber, M.; van Haag, J.; Schöngart, M.

    2015-05-01

    To improve the mechanical performance of polymeric parts, fibre reinforcement has established in industrial applications during the last decades. Next to the widely used Short Fibre-reinforced Thermoplastics (SFT) the use of Long Fibre-reinforced Thermoplastics (LFT) is increasingly growing. Especially for non-polar polymeric matrices like polypropylene (PP), longer fibres can significantly improve the mechanical performance. As with every kind of discontinuous fibre reinforcement the fibre orientations (FO) show a high impact on the mechanical properties. On the contrary to SFT where the local fibre length distribution (FLD) can be often neglected, for LFT the FLD show a high impact on the material's properties and has to be taken into account in equal measure to the FOD. Recently numerical models are available in commercial filling simulation software and allow predicting both the local FOD and FLD in LFT parts. The aim of this paper is to compare i.) the FOD results and ii) the FLD results from available orientation- and fibre length attrition-models to those obtained from experimental data. The investigations are conducted by the use of different injection moulded specimens made from long glass fibre reinforced PP. In order to determine the FOD, selected part sections are examined by means of Computed Tomographic (CT) analyses. The fully three dimensional measurement of the FOD is then performed by digital image processing using grey scale correlation. The FLD results are also obtained by using digital image processing after a thermal pyrolytic separation of the polymeric matrix from the fibres. Further the FOD and the FLD are predicted by using a reduced strain closure (RSC) as well as an anisotropic rotary diffusion - reduced strain closure model (ARD-RSC) and Phelps-Tucker fibre length attrition model implemented in the commercial filling software Moldflow, Autodesk Inc., San Rafael, CA, USA.

  1. A validation of the fibre orientation and fibre length attrition prediction for long fibre-reinforced thermoplastics

    Energy Technology Data Exchange (ETDEWEB)

    Hopmann, Ch.; Weber, M.; Haag, J. van; Schöngart, M. [Institute of Plastics Processing (IKV) at RWTH Aachen University, Pontstr. 49, 52062 Aachen (Germany)

    2015-05-22

    To improve the mechanical performance of polymeric parts, fibre reinforcement has established in industrial applications during the last decades. Next to the widely used Short Fibre-reinforced Thermoplastics (SFT) the use of Long Fibre-reinforced Thermoplastics (LFT) is increasingly growing. Especially for non-polar polymeric matrices like polypropylene (PP), longer fibres can significantly improve the mechanical performance. As with every kind of discontinuous fibre reinforcement the fibre orientations (FO) show a high impact on the mechanical properties. On the contrary to SFT where the local fibre length distribution (FLD) can be often neglected, for LFT the FLD show a high impact on the material’s properties and has to be taken into account in equal measure to the FOD. Recently numerical models are available in commercial filling simulation software and allow predicting both the local FOD and FLD in LFT parts. The aim of this paper is to compare i.) the FOD results and ii) the FLD results from available orientation- and fibre length attrition-models to those obtained from experimental data. The investigations are conducted by the use of different injection moulded specimens made from long glass fibre reinforced PP. In order to determine the FOD, selected part sections are examined by means of Computed Tomographic (CT) analyses. The fully three dimensional measurement of the FOD is then performed by digital image processing using grey scale correlation. The FLD results are also obtained by using digital image processing after a thermal pyrolytic separation of the polymeric matrix from the fibres. Further the FOD and the FLD are predicted by using a reduced strain closure (RSC) as well as an anisotropic rotary diffusion - reduced strain closure model (ARD-RSC) and Phelps-Tucker fibre length attrition model implemented in the commercial filling software Moldflow, Autodesk Inc., San Rafael, CA, USA.

  2. Resistance-resistant antibiotics.

    Science.gov (United States)

    Oldfield, Eric; Feng, Xinxin

    2014-12-01

    New antibiotics are needed because drug resistance is increasing while the introduction of new antibiotics is decreasing. We discuss here six possible approaches to develop 'resistance-resistant' antibiotics. First, multitarget inhibitors in which a single compound inhibits more than one target may be easier to develop than conventional combination therapies with two new drugs. Second, inhibiting multiple targets in the same metabolic pathway is expected to be an effective strategy owing to synergy. Third, discovering multiple-target inhibitors should be possible by using sequential virtual screening. Fourth, repurposing existing drugs can lead to combinations of multitarget therapeutics. Fifth, targets need not be proteins. Sixth, inhibiting virulence factor formation and boosting innate immunity may also lead to decreased susceptibility to resistance. Although it is not possible to eliminate resistance, the approaches reviewed here offer several possibilities for reducing the effects of mutations and, in some cases, suggest that sensitivity to existing antibiotics may be restored in otherwise drug-resistant organisms.

  3. A short leucocyte telomere length is associated with development of insulin resistance

    DEFF Research Database (Denmark)

    Verhulst, Simon; Dalgård, Christine; Labat, Carlos

    2016-01-01

    AIMS/HYPOTHESIS: A number of studies have shown that leucocyte telomere length (LTL) is inversely associated with insulin resistance and type 2 diabetes mellitus. The aim of the present longitudinal cohort study, utilising a twin design, was to assess whether shorter LTL predicts insulin resistance...... and insulin resistance over an average of 12 years were performed in a subset of the Registry consisting of 338 (184 monozygotic and 154 dizygotic) same-sex twin pairs. RESULTS: Age at baseline examination was 37.4 ± 9.6 (mean ± SD) years. Baseline insulin resistance was not associated with age......-dependent changes in LTL (attrition) over the follow-up period, whereas baseline LTL was associated with changes in insulin resistance during this period. The shorter the LTL at baseline, the more pronounced was the increase in insulin resistance over the follow-up period (p 

  4. 机械研磨化学复合镀Ni-P-Al2O3工艺%Technology of mechanical attrition and chemical composite plating with Ni-P-Al2O3

    Institute of Scientific and Technical Information of China (English)

    李亚敏; 王丽波; 刘洪军

    2012-01-01

    采用机械研磨化学复合镀工艺在模具锌合金表面获得Ni-P-Al2O3复合镀层,研究镀液成分、纳米Al2O3加入量和工艺条件对镀速的影响.结果表明:硫酸镍、次亚磷酸钠和纳米Al2O3在镀液中的含量均存在极限值,超过极限值后镀速开始下降;在镀液不发生分解时,pH值和温度的提高使镀速迅速上升;机械研磨使镀速显著减小,但玻璃球直径大小对镀速影响不大.优化工艺条件下镀速可达12~13 μm/h,在此工艺下获得的镀层硬度高、耐蚀性好.%Depositional Ni-P-Al2O3 coatings was obtained on mould surface of zinc alloy by means of mechanical attrition and chemical composite plating technique, and the effect of bath ingredients, nano Al2O3 addition content, and process conditions on the deposition rate was investigated. The result showed that the nickel sulfate, sodium hypophosphite and nano-Al2O3 content in the bath were limited and over the limiting value the plating rate began to decline. And the deposition rate increased rapidly with the bath temperature and pH value as there was no bath decomposition, but it reduced markedly due to mechanical attrition. The size of the glass ball had less influence on it The peak value of the deposition rate was 12~13 μm/h in the optimized process condition, the new coating showed high hardness and good corrosion resistance.

  5. Recent Advances in Iron-Based Superconducting Wires and Tapes%新型铁基超导线带材的研究进展

    Institute of Scientific and Technical Information of China (English)

    林鹤; 马衍伟

    2013-01-01

    新型铁基超导材料具有较高的临界转变温度、超高的上临界场和非常小的各向异性等优点,在高场磁体领域应用前景广阔。目前粉末装管法已广泛应用于铁基超导线带材的制备,临界电流密度在4.2 K和10 T下高达1.7×104 A/cm2,接近实用化水平。首先介绍了铁基超导材料的典型结构与基本超导特性,详细评述了铁基超导粉末的合成和粉末装管法的工艺流程,主要包括元素配比、热处理工艺以及粉末装管原位法和先位法的对比分析,重点探讨了影响线带材临界电流密度的因素及其关键制备技术。通过包套材料的选择、掺杂改性、热等静压和轧制织构等方法来解决线带材中包套与超导芯易反应、杂相多、致密度低以及晶界弱连接等难题。此外还简要介绍了多芯线带材的最新研究进展。最后,对铁基超导线带材的发展趋势做了展望。%The newly discovered iron-based superconductors have caused great interest for high-field applications due to their good properties such as high transition temperature , ultrahigh upper critical field and low anisotropy .The iron-based superconducting wires and tapes are commonly prepared by the powder-in-tube ( PIT) process.In this paper, we focus on the fabrication techniques to realize high Jc values such as chemical composition , optimal heating conditions , sheath mate-rial, doped elements, hot isostatic press and rolling texture, particularly for the 122-type pnictide wires and tapes.Excit-ingly, so far high transport Jc value of 1.7 ×104 A/cm2 at 4.2 K and 10 T has been obtained in iron-based tapes, closed to the practical level.Finally, a perspective and future development of PIT pnictide wires and tapes are given .

  6. Psychological and sociodemographic predictors of premature discontinuation of a 1-year multimodal outpatient weight-reduction program: an attrition analysis

    Directory of Open Access Journals (Sweden)

    Liebl ME

    2012-03-01

    Full Text Available Anne Ahnis1, Andrea Riedl1, Andrea Figura1, Elisabeth Steinhagen-Thiessen2, Max E Liebl3, Burghard F Klapp11Internal Medicine and Dermatology, Medical Department, Division of Psychosomatic Medicine, Charité – Universitätsmedizin Berlin, Campus Mitte, 2Internal Medicine with Gastroenterology and Nephrology, Specialty network of Gastroenterology, Endocrinology and Metabolic Diseases, Division of Lipid Metabolism, Charité – Universitätsmedizin Berlin, Campus Virchow-Klinikum, 3Medical Department, Division of Rheumatology and Clinical Immunology, Department for Physical Medicine, Charité – Universitätsmedizin Berlin, Campus Mitte, Berlin, GermanyObjective: Attrition rates of up to 77% have been reported in conservative weight-reduction programs for the treatment of obesity. In view of the cost of such programs to the health system, there is a need to identify the variables that predict premature discontinuation of treatment. Previous studies have focused mainly on somatic and sociodemographic parameters. The prospective influence of psychological factors has not been systematically investigated to date.Methods: A total of 164 patients (138 of whom were women with a mean age of 45 years and a mean body mass index of 39.57 participated in a 1-year outpatient weight-reduction program at the Charité – Universitätsmedizin Berlin University Hospital. The program included movement therapy, dietary advice, psychoeducational and behavioral interventions, relaxation procedures, and consultations with a specialist in internal medicine and a psychologist. Patients also underwent regular laboratory and psychological testing. The results were evaluated using a t-test, χ2-test, and logistic regression analysis.Results: Seventy-one of the 164 patients (61 women, mean age = 43 years, mean body mass index = 39.53 withdrew before the end of the program (attrition rate = 43.3%. While there were no differences between the somatic and metabolic

  7. Signature of the Leggett mode in the A1 g Raman response: From MgB2 to iron-based superconductors

    Science.gov (United States)

    Cea, T.; Benfatto, L.

    2016-08-01

    The Raman response in a superconductor is a powerful probe to investigate the symmetry of the superconducting gap. Here we show that in a multiband superconductor it also offers the unique opportunity to establish whether the driving pairing interaction has an intraband or interband character. In the model with one hole and one electron band the full gauge-invariant Raman response, obtained by accounting for the fluctuations of both the density and superconducting phase degrees of freedom, is always dominated by the Leggett mode, regardless its nature. However, while in the case of intraband-dominated pairing the Josephson-like phase fluctuations of the two condensates identify a well-defined peak, as observed in MgB2, for dominant interband pairing the Leggett resonance is pushed at twice the largest gap, resembling apparently a pair-breaking peak. The latter case is in very good agreement with experimental data in iron-based superconductors, suggesting that an interband pairing mechanism should be at play in these systems. These results have also interesting implications for the nonlinear optical response probed by means of intense THz fields.

  8. Struture stability and compressibility of iron-based superconductor Nd(O0.88F0.12)FeAs under high pressure.

    Science.gov (United States)

    Zhao, Jinggeng; Wang, Luhong; Dong, Dawei; Liu, Zhiguo; Liu, Haozhe; Chen, Genfu; Wu, Dan; Luo, Jianlin; Wang, Nanlin; Yu, Yong; Jin, Changqing; Guo, Quanzhong

    2008-10-22

    The high-pressure angle-dispersive X-ray diffraction experiments on the iron-based superconductor Nd(O0.88F0.12)FeAs were performed up to 32.7 GPa at room temperature. An isostructural phase transition starts at approximately 10 GPa. When pressure is higher than 13.5 GPa, Nd(O0.88F0.12)FeAs completely transforms to a high-pressure phase, which remains the same tetragonal structure with a larger a-axis and smaller c-axis than those of the low-pressure phase. The ambient conditions isothermal bulk moduli B0 are derived as 102(2) and 245(9) GPa for the low-pressure phase and high-pressure phase, respectively. The structure analysis based on the Rietveld refinement methods shows the difference of pressure dependence of the Fe-As and Nd-(O, F) bonding distances, as well as As-Fe-As and Nd-(O, F)-Nd angles between the low-pressure phase and high-pressure phase.

  9. Enhanced Coagulation-Flocculation Performance of Iron-Based Coagulants: Effects of PO4(3- and SiO3(2- Modifiers.

    Directory of Open Access Journals (Sweden)

    Wei Chen

    Full Text Available PO4(3- and SiO3(2- are often used as modifier to improve stability and aggregating ability of the iron-base coagulants, however, there are few reports about their detailed comparison between the coagulation performance and mechanisms. In this study, three coagulants--polyferric phosphoric sulfate (PFPS, polysilicon ferric sulfate (PFSS, and polyferric sulfate (PFS were synthesized; their structure and morphology were characterized by Fourier transformed infrared (FT-IR spectroscopy, X-ray diffraction (XRD and Scanning electron microscope (SEM. Alkali titration and Ferron species analysis were employed to investigate the hydrolysis performance and species distribution. Jar test was conducted to measure their coagulation behaviors at different dosage, pH, and temperatures in which the flocs properties were measured. The results showed that a number of new compounds were formed due to the presence of PO4(3- and SiO3(2-. Moreover, PFPS and PFSS had similar level in Fea as well as Feb. Among them, PFPS produced more multi-core iron atoms polymer and content of Feb, and the formed flocs were larger and denser. It exhibited superior coagulation performance in terms of turbidity reduction, UV254 removal and residual ferric concentration. Jar test and floc breakage/regrowth experiments indicated other than charge neutrality, the dominated mechanism involved in PFSS was the adsorption between polysilicic acid and solution particle, while PFPS was sweeping, entrapment/adsorption resulting from larger polymer colloid of Fe-P chemistry bond.

  10. Emergent loop-nodal s(±)-wave superconductivity in CeCu(2)Si(2): similarities to the iron-based superconductors.

    Science.gov (United States)

    Ikeda, Hiroaki; Suzuki, Michi-To; Arita, Ryotaro

    2015-04-10

    Heavy-fermion superconductors are prime candidates for novel electron-pairing states due to the spin-orbital coupled degrees of freedom and electron correlations. Superconductivity in CeCu_{2}Si_{2} discovered in 1979, which is a prototype of unconventional (non-BCS) superconductors in strongly correlated electron systems, still remains unsolved. Here we provide the first report of superconductivity based on the advanced first-principles theoretical approach. We find that the promising candidate is an s_{±}-wave state with loop-shaped nodes on the Fermi surface, different from the widely expected line-nodal d-wave state. The dominant pairing glue is magnetic but high-rank octupole fluctuations. This system shares the importance of multiorbital degrees of freedom with the iron-based superconductors. Our findings reveal not only the long-standing puzzle in this material, but also urge us to reconsider the pairing states and mechanisms in all heavy-fermion superconductors.

  11. Comparing the detection of iron-based pottery pigment on a carbon-coated sherd by SEM-EDS and by Micro-XRF-SEM.

    Science.gov (United States)

    Pendleton, Michael W; Washburn, Dorothy K; Ellis, E Ann; Pendleton, Bonnie B

    2014-03-01

    The same sherd was analyzed using a scanning electron microscope with energy dispersive spectroscopy (SEM-EDS) and a micro X-ray fluorescence tube attached to a scanning electron microscope (Micro-XRF-SEM) to compare the effectiveness of elemental detection of iron-based pigment. To enhance SEM-EDS mapping, the sherd was carbon coated. The carbon coating was not required to produce Micro-XRF-SEM maps but was applied to maintain an unbiased comparison between the systems. The Micro-XRF-SEM analysis was capable of lower limits of detection than that of the SEM-EDS system, and therefore the Micro-XRF-SEM system could produce elemental maps of elements not easily detected by SEM-EDS mapping systems. Because SEM-EDS and Micro-XRF-SEM have been used for imaging and chemical analysis of biological samples, this comparison of the detection systems should be useful to biologists, especially those involved in bone or tooth (hard tissue) analysis.

  12. Effects of an iron-based fuel-borne catalyst and a diesel particle filter on exhaust toxicity in lung cells in vitro.

    Science.gov (United States)

    Steiner, Sandro; Czerwinski, Jan; Comte, Pierre; Heeb, Norbert V; Mayer, Andreas; Petri-Fink, Alke; Rothen-Rutishauser, Barbara

    2015-08-01

    Metal-containing fuel additives catalyzing soot combustion in diesel particle filters are used in a widespread manner, and with the growing popularity of diesel vehicles, their application is expected to increase in the near future. Detailed investigation into how such additives affect exhaust toxicity is therefore necessary and has to be performed before epidemiological evidence points towards adverse effects of their application. The present study investigates how the addition of an iron-based fuel additive (Satacen®3, 40 ppm Fe) to low-sulfur diesel affects the in vitro cytotoxic, oxidative, (pro-)inflammatory, and mutagenic activity of the exhaust of a passenger car operated under constant, low-load conditions by exposing a three-dimensional model of the human airway epithelium to complete exhaust at the air-liquid interface. We could show that the use of the iron catalyst without and with filter technology has positive as well as negative effects on exhaust toxicity compared to exhaust with no additives: it decreases the oxidative and, compared to a non-catalyzed diesel particle filter, the mutagenic potential of diesel exhaust, but increases (pro-)inflammatory effects. The presence of a diesel particle filter also influences the impact of Satacen®3 on exhaust toxicity, and the proper choice of the filter type to be used is of importance with regards to exhaust toxicity. Figure ᅟ.

  13. Language Attrition Studies in Context of Bilingual Mental Lexicon%二语心理词库视域下的语言磨蚀研究

    Institute of Scientific and Technical Information of China (English)

    苏恩

    2016-01-01

    Most of the researchers believe that increasing contact between second language learners and target language can slow down language attrition.However,the author holds the view that this way is too mechanized and lack of theoretical bases.We should start from the procedure of language attrition to understand its essence and retard its speed from where it begins.According to previous stud-ies,the language attrition begins with vocabulary while syntax and phonics rise superior to it.Therefore,this study aims to explore the organization of bilingual mental lexicon by a word association test,finding out which kind of organization pattern can effectively weaken language attrition.%许多学者认为可以通过增加二语学习者与目标语的接触机会来减缓语言磨蚀,但是这种方法过于机械化且缺乏理论依据。应该从源头入手,以语言磨蚀的过程作为出发点,从本质上了解语蚀,才能减缓语言磨蚀的速度。语蚀一般始于词汇磨蚀,句法和语音基本不受语言磨蚀的影响。因此,可以通过心理语言学中的词汇联想测试法,来探究二语心理词库的组织模式,并筛选寻找能够有效减缓语蚀发生速度的组织模式。

  14. Predictors of attrition and immunological failure in HIV-1 patients on highly active antiretroviral therapy from different healthcare settings in Mozambique.

    Directory of Open Access Journals (Sweden)

    Claudia Palladino

    Full Text Available In Mozambique, the evaluation of retention in HIV care and ART programmes is limited. To assess rate and predictors of attrition (no retention in care and HAART effectiveness in HIV-1 infected patients who pay for medication and laboratory testing in Mozambique, we conducted a multicenter survey of HIV-1-infected patients who started HAART during 2002-2006. Cox proportional hazard models were used to assess risk of attrition and of therapy failure. Overall, 142 patients from 16 healthcare centers located in the capital city Maputo were followed-up for 22.2 months (12.1-46.7. The retention rate was 75%, 48% and 37% after one, two and three years, respectively. Risk of attrition was lower in patients with higher baseline CD4 count (P = 0.022 and attending healthcare center 1 (HCC1 (P = 0.013. The proportion of individuals with CD4 count ≤ 200 cells/µL was 55% (78/142 at baseline and decreased to 6% (3/52 at 36 months. Among the patients with available VL, 86% (64/74 achieved undetectable VL levels. The rate of immunologic failure was 17.2% (95% CI: 12.6-22.9 per 100 person-years. Risk of failure was associated to higher baseline CD4 count (P = 0.002, likely reflecting low adherence levels, and decreased with baseline VL ≥ 10,000 copies/mL (P = 0.033. These results suggest that HAART can be effective in HIV-1 infected patients from Mozambique that pay for their medication and laboratory testing. Further studies are required to identify the causes for low retention rates in patients with low CD4 counts and to better understand the association between healthcare setting and attrition rate.

  15. Predictors of attrition and immunological failure in HIV-1 patients on highly active antiretroviral therapy from different healthcare settings in Mozambique.

    Science.gov (United States)

    Palladino, Claudia; Briz, Verónica; Bellón, José María; Bártolo, Inês; Carvalho, Patrícia; Camacho, Ricardo; Muñoz-Fernández, M Ángeles; Bastos, Rui; Manuel, Rolanda; Casanovas, José; Taveira, Nuno

    2013-01-01

    In Mozambique, the evaluation of retention in HIV care and ART programmes is limited. To assess rate and predictors of attrition (no retention in care) and HAART effectiveness in HIV-1 infected patients who pay for medication and laboratory testing in Mozambique, we conducted a multicenter survey of HIV-1-infected patients who started HAART during 2002-2006. Cox proportional hazard models were used to assess risk of attrition and of therapy failure. Overall, 142 patients from 16 healthcare centers located in the capital city Maputo were followed-up for 22.2 months (12.1-46.7). The retention rate was 75%, 48% and 37% after one, two and three years, respectively. Risk of attrition was lower in patients with higher baseline CD4 count (P = 0.022) and attending healthcare center 1 (HCC1) (P = 0.013). The proportion of individuals with CD4 count ≤ 200 cells/µL was 55% (78/142) at baseline and decreased to 6% (3/52) at 36 months. Among the patients with available VL, 86% (64/74) achieved undetectable VL levels. The rate of immunologic failure was 17.2% (95% CI: 12.6-22.9) per 100 person-years. Risk of failure was associated to higher baseline CD4 count (P = 0.002), likely reflecting low adherence levels, and decreased with baseline VL ≥ 10,000 copies/mL (P = 0.033). These results suggest that HAART can be effective in HIV-1 infected patients from Mozambique that pay for their medication and laboratory testing. Further studies are required to identify the causes for low retention rates in patients with low CD4 counts and to better understand the association between healthcare setting and attrition rate.

  16. Treatment refusal/attrition among adults randomly assigned to programs at a drug treatment campus: The New Jersey Substance Abuse Treatment Campus, Seacaucus, NJ.

    Science.gov (United States)

    Condelli, W S; Koch, M A; Fletcher, B

    2000-06-01

    The New Jersey Substance Abuse Treatment Campus was funded to assess the feasibility of establishing a new model for delivering substance abuse treatment services and to serve as a research laboratory for conducting comparative evaluations of those services. The 350-bed campus was designed to improve treatment effectiveness by providing special services needed by underserved populations, and reduce treatment costs by serving large numbers of clients, centralizing services, and sharing facilities. First-time clients who met preliminary eligibility requirements during phone screening were randomly assigned to therapeutic community and chemical dependency programs. We used data collected on 1,573 adults who were ultimately accepted for admission to analyze treatment refusals and attrition during the 25 days after admission. Only 6.4% of the clients refused admission when informed of their treatment assignment. Planned duration of the residential phase of treatment, gender, and language spoken (English/Spanish) interacted with one another and differentially predicted treatment refusal/attrition. These findings may be useful for understanding treatment refusal and attrition in substance abuse treatment programs.

  17. Retention of HIV-Infected Children in the First 12 Months of Anti-Retroviral Therapy and Predictors of Attrition in Resource Limited Settings: A Systematic Review.

    Science.gov (United States)

    Abuogi, Lisa L; Smith, Christiana; McFarland, Elizabeth J

    2016-01-01

    Current UNAIDS goals aimed to end the AIDS epidemic set out to ensure that 90% of all people living with HIV know their status, 90% initiate and continue life-long anti-retroviral therapy (ART), and 90% achieve viral load suppression. In 2014 there were an estimated 2.6 million children under 15 years of age living with HIV, of which only one-third were receiving ART. Little literature exists describing retention of HIV-infected children in the first year on ART. We conducted a systematic search for English language publications reporting on retention of children with median age at ART initiation less than ten years in resource limited settings. The proportion of children retained in care on ART and predictors of attrition were identified. Twelve studies documented retention at one year ranging from 71-95% amongst 31877 African children. Among the 5558 children not retained, 4082 (73%) were reported as lost to follow up (LFU) and 1476 (27%) were confirmed to have died. No studies confirmed the outcomes of children LFU. Predictors of attrition included younger age, shorter duration of time on ART, and severe immunosuppression. In conclusion, significant attrition occurs in children in the first 12 months after ART initiation, the majority attributed to LFU, although true outcomes of children labeled as LFU are unknown. Focused efforts to ensure retention and minimize early mortality are needed as universal ART for children is scaled up.

  18. Predictors of two forms of attrition in a longitudinal health study involving ageing participants: An analysis based on the Whitehall II study

    Directory of Open Access Journals (Sweden)

    Mein Gill

    2012-10-01

    Full Text Available Abstract Background Longitudinal studies are crucial providers of information about the needs of an ageing population, but their external validity is affected if partipants drop out. Previous research has identified older age, impaired cognitive function, lower educational level, living alone, fewer social activities, and lower socio-economic status as predictors of attrition. Methods This project examined attrition in participants of the Whitehall II study aged between 51–71 years, using data from questionnaires participants have completed biennially since 1985 when the study began. We examine the possibility of two distinct forms of attrition – non-response and formally requesting to withdraw – and whether they have different predictors. Potential predictors were age, gender, marital status, occupational grade, retirement, home ownership, presence of longstanding illness, SF-36 quality of life scores, social participation and educational level comparing participants and those who had withdrawn from the study. Results The two forms of attrition share many predictors and are associated but remain distinct. Being older, male, having a lower job grade, not being a home owner, not having a long standing illness, having higher levels of education, and not having retired, were all associated with a greater probability of non-response; being married was associated with higher probability in women and lower in men. Being older, male, having a lower job grade, not being a home owner, having lower SF-36 scores, taking part in fewer social activities, and not having a long standing illness, were all associated with greater probability of withdrawal. Conclusions The results suggest a strong gender effect on both routes not previously considered in analyses of attrition. Investigators of longitudinal studies should take measures to retain older participants and lower level socio-economic participants, who are more likely to cease participating

  19. Why (and how) they decide to leave: A grounded theory analysis of STEM attrition at a large public research university

    Science.gov (United States)

    Minutello, Michael F.

    A grounded theory investigation of STEM attrition was conducted that describes and explains why undergraduates at a large Mid-Atlantic research university decided to leave their initial STEM majors to pursue non-STEM courses of study. Participants ultimately decided to leave their initial STEM majors because they were able to locate preferable non-STEM courses of study that did not present the same kinds of obstacles they had encountered in their original STEM majors. Grounded theory data analysis revealed participants initially enrolled in STEM majors with tenuous motivation that did not withstand the various obstacles that were present in introductory STEM coursework. Obstacles that acted as demotivating influences and prompted participants to locate alternative academic pathways include the following: (1.) disengaging curricula; (2.) competitive culture; (3.) disappointing grades; (4.) demanding time commitments; and (5.) unappealing career options. Once discouraged from continuing along their initial STEM pathways, participants then employed various strategies to discover suitable non-STEM majors that would allow them to realize their intrinsic interests and extrinsic goals. Participants were largely satisfied with their decisions to leave STEM and have achieved measures of personal satisfaction and professional success.

  20. Retention and Attrition of Umbundu in São Tomé and Príncipe

    Directory of Open Access Journals (Sweden)

    Gerardo Augusto Lorenzino

    2015-12-01

    Full Text Available A major event in the modern history of São Tomé and Príncipe, located in the Gulf of Guinea, was the recruitment of contracted labor from Angola, Mozambique, and Cape Verde between 1870 and 1960. This article will address one linguistic effect of this large-scale migration, namely, the retention and attrition of the Umbundu language spoken by the Tongas, who are descendants of the indentured laborers who never repatriated back to their homes in Africa. As opposed to noncontact Umbundu, the Tonga Umbundu (TUm of São Tomé has a simplified nominal class system and significant borrowings from the Portuguese lexicon, which became part of the TUm class system through incorporation. The sociolinguistic factors that will be considered in evaluating the nature of the Tongas’ linguistic heritage are (a the language situation that best explains the retention of Umbundu and (b the typological distance between TUm, Afro-Portuguese Creoles, and Portuguese language.

  1. Accelerated telomere attrition is associated with relative household income, diet and inflammation in the pSoBid cohort.

    Directory of Open Access Journals (Sweden)

    Paul G Shiels

    Full Text Available BACKGROUND: It has previously been hypothesized that lower socio-economic status can accelerate biological ageing, and predispose to early onset of disease. This study investigated the association of socio-economic and lifestyle factors, as well as traditional and novel risk factors, with biological-ageing, as measured by telomere length, in a Glasgow based cohort that included individuals with extreme socio-economic differences. METHODS: A total of 382 blood samples from the pSoBid study were available for telomere analysis. For each participant, data was available for socio-economic status factors, biochemical parameters and dietary intake. Statistical analyses were undertaken to investigate the association between telomere lengths and these aforementioned parameters. RESULTS: The rate of age-related telomere attrition was significantly associated with low relative income, housing tenure and poor diet. Notably, telomere length was positively associated with LDL and total cholesterol levels, but inversely correlated to circulating IL-6. CONCLUSIONS: These data suggest lower socio-economic status and poor diet are relevant to accelerated biological ageing. They also suggest potential associations between elevated circulating IL-6, a measure known to predict cardiovascular disease and diabetes with biological ageing. These observations require further study to tease out potential mechanistic links.

  2. The effects of three different food acids on the attrition-corrosion wear of human dental enamel

    Science.gov (United States)

    Zhang, Yichi; Arsecularatne, Joseph A.; Hoffman, Mark

    2015-07-01

    With increased consumption of acidic drinks and foods, the wear of human teeth due to attrition in acidic environments is an increasingly important issue. Accordingly, the present paper investigates in vitro the wear of human enamel in three different acidic environments. Reciprocating wear tests in which an enamel cusp slides on an enamel flat surface were carried out using acetic, citric and lactic acid lubricants (at pH 3-3.5). Distilled water was also included as a lubricant for comparison. Focused ion beam milling and scanning electron microscopy imaging were then used to investigate the enamel subsurfaces following wear tests. Nanoindentation was used to ascertain the changes in enamel mechanical properties. The study reveals crack generation along the rod boundaries due to the exposure of enamel to the acidic environments. The wear mechanism changes from brittle fracture in distilled water to ploughing or shaving of the softened layer in acidic environments, generating a smooth surface with the progression of wear. Moreover, nanoindentation results of enamel samples which were exposed to the above acids up to a duration of the wear tests show decreasing hardness and Young’s modulus with exposure time.

  3. The application of inelastic neutron scattering to explore the significance of a magnetic transition in an iron based Fischer-Tropsch catalyst that is active for the hydrogenation of CO

    Energy Technology Data Exchange (ETDEWEB)

    Warringham, Robbie; McFarlane, Andrew R.; Lennon, David, E-mail: David.Lennon@Glasgow.ac.uk [School of Chemistry, University of Glasgow, Joseph Black Building, Glasgow, Scotland G12 8QQ (United Kingdom); MacLaren, Donald A. [School of Physics and Astronomy, University of Glasgow, The Kelvin Building, Glasgow, Scotland G12 8QQ (United Kingdom); Webb, Paul B.; Tooze, Robert P. [Sasol Technology UK Ltd., Purdie Building, North Haugh, St Andrews, Fife KY16 9ST (United Kingdom); Taylor, Jon; Ewings, Russell A.; Parker, Stewart F. [ISIS Facility, STFC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX (United Kingdom)

    2015-11-07

    An iron based Fischer-Tropsch synthesis catalyst is evaluated using CO hydrogenation at ambient pressure as a test reaction and is characterised by a combination of inelastic neutron scattering (INS), powder X-ray diffraction, temperature-programmed oxidation, Raman scattering, and transmission electron microscopy. The INS spectrum of the as-prepared bulk iron oxide pre-catalyst (hematite, α-Fe{sub 2}O{sub 3}) is distinguished by a relatively intense band at 810 cm{sup −1}, which has previously been tentatively assigned as a magnon (spinon) feature. An analysis of the neutron scattering intensity of this band as a function of momentum transfer unambiguously confirms this assignment. Post-reaction, the spinon feature disappears and the INS spectrum is characterised by the presence of a hydrocarbonaceous overlayer. A role for the application of INS in magnetic characterisation of iron based FTS catalysts is briefly considered.

  4. Drug Resistance

    Science.gov (United States)

    HIV Treatment Drug Resistance (Last updated 3/2/2017; last reviewed 3/2/2017) Key Points As HIV multiplies in the ... the risk of drug resistance. What is HIV drug resistance? Once a person becomes infected with HIV, ...

  5. Antibiotic Resistance

    Science.gov (United States)

    ... lives. But there is a growing problem of antibiotic resistance. It happens when bacteria change and become able ... resistant to several common antibiotics. To help prevent antibiotic resistance Don't use antibiotics for viruses like colds ...

  6. The Study of Diamond Graphitization under the Action of Iron-based Catalyst%铁基作用下的金刚石石墨化研究

    Institute of Scientific and Technical Information of China (English)

    郭晓光; 翟昌恒; 金洙吉; 郭东明

    2015-01-01

    通过构建含催化剂铁的金刚石仿真模型,进行了金刚石石墨化的三维分子动力学仿真,获得了金刚石在铁基催化剂作用下的石墨化机理.并对化学气相沉积金刚石进行了摩擦化学抛光试验,验证了铁基金属对金刚石石墨化的催化作用.分子动力学仿真结果表明铁原子的存在会降低金刚石石墨化的转变温度,进一步的微观结构分析可以得出,在催化剂作用下的石墨化机理是:铁原子价电子层中的未配对电子与金刚石原子的电子相互作用,形成了化学键,对金刚石原子产生吸引作用,使其逐渐变为石墨结构.所以铁基催化剂具有催化作用的原因就是铁原子价电子层结构中含有未配对的电子,而且与金刚石原子结构符合对准原则.试验结果验证了仿真结论的正确性.研究结果表明,金属铁的存在会加速金刚石石墨化的过程,利于对金刚石刀具的超精密加工.%In order to get the graphitization mechanism of diamond under the action of iron-based catalyst, a three-dimensional molecular dynamics (MD) simulation is performed on a particular model containing iron and diamond atoms. And the friction chemical polishing experiments for the chemical vapor deposition (CVD) diamond is conducted to validate the catalytic action of the iron-based metal on diamond graphitization. The results of molecular dynamics simulation show that the presence of iron atoms will reduce the transformation temperature of diamond graphitization. By analyzing the microstructure, the graphitization mechanism with catalyst can be concluded that the chemical bonds are formed by the interaction between the unpaired electrons in the valence shell of iron atoms and the electrons of diamond atoms, which will attract the diamond atoms and make them become graphite structure gradually. For the mechanism of the catalysis of iron for diamond graphitization, there are two critical reasons. On one hand, there are

  7. Fenton-like oxidation of 2,4-DCP in aqueous solution using iron-based nanoparticles as the heterogeneous catalyst.

    Science.gov (United States)

    Li, Renchao; Gao, Ying; Jin, Xiaoying; Chen, Zuliang; Megharaj, Mallavarapu; Naidu, Ravendra

    2015-01-15

    In this report, various iron-based nanoparticles (nZVI, n-Ni/Fe, n-Pd/Fe) were used for both heterogeneous Fenton oxidation of 2,4-dichlorophenol (2,4-DCP) and reductive dechlorination of 2,4-DCP in order to understand their roles in the Fenton oxidation and the reductive degradation of 2,4-DCP. The dechlorination efficiency of 2,4-DCP using nZVI, n-Ni/Fe, n-Fe/Pd and Fe(2)(+) was 6.48%, 6.80%, 15.95%, 5.02%, while Fenton oxidation efficiency of 2,4-DCP was 57.87%, 34.23%, 27.94%, 19.61% after 180 min, respectively. The new findings included a higher dechlorination using n-Fe/Pd due to Pd effective catalysis and the effective heterogeneous Fenton oxidation using nZVI depending on reductive dechlorination and heterogeneous Fenton oxidation occurs simultaneously. However, nZVI as the potential catalyst for heterogeneous Fenton was observed, and SEM, EDS and XRD demonstrate that change on the nZVI surface occurred due to the Fe(2+) leaching, and Total Organic Carbon (TOC) (30.71%) shows that 2,4-DCP was degraded. Furthermore, the experiment indicates that the pH values and concentration of 2,4-DCP significantly impacted on the heterogeneous Fenton oxidation of 2,4-DCP and the data fits well with the pseudo first-order kinetic model, which was a diffusion-controlled reaction. Finally, a possible mechanism for degradation of 2,4-DCP was proposed.

  8. Enhanced graphitization of c-CVD grown multi-wall carbon nanotube arrays assisted by removal of encapsulated iron-based phases under thermal treatment in argon

    Energy Technology Data Exchange (ETDEWEB)

    Boncel, Slawomir, E-mail: slawomir.boncel@polsl.pl [Department of Organic Chemistry, Biochemistry and Biotechnology, Silesian University of Technology, Krzywoustego 4, 44-100 Gliwice (Poland); Koziol, Krzysztof K.K., E-mail: kk292@cam.ac.uk [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, CB3 0FS Cambridge (United Kingdom)

    2014-05-01

    Graphical abstract: - Highlights: • Annealing of the c-CVD MWCNT arrays toward complete removal of iron nanoparticles. • The ICP-AES protocol established for quantitative analysis of Fe-content in MWCNTs. • The vertical alignment from the as-grown MWCNT arrays found intact after annealing. • A route to decrease number of defects/imperfections in the MWCNT graphene walls. • A foundation for commercial purification of c-CVD derived MWCNTs. - Abstract: The effect of annealing on multi-walled carbon nanotube (MWCNT) arrays grown via catalytic Chemical Vapour Deposition (c-CVD) was studied. The treatment enabled to decrease number of defects/imperfections in the graphene walls of MWCNTs’, which was reflected in Raman spectroscopy by reduction of the I{sub D}/I{sub G} ratio by 27%. Moreover, the vertical alignment from the as-synthesized nanotube arrays was found intact after annealing. Not only graphitization of the nanotube walls occurred under annealing, but the amount of metal iron-based catalyst residues (interfering with numerous physicochemical properties, and hence applications of MWCNTs) was reduced from 9.00 wt.% (for pristine MWCNTs) to 0.02 wt.% as detected by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). This value, established by a new analytical protocol, is the lowest recorded by now for purified c-CVD MWCNTs and, due to operating under atmospheric pressure, medium temperature regime (as for annealing processes), reasonable time-scale and metal residue non-specificity, it could lay the foundation for commercial purification of c-CVD derived MWCNTs.

  9. Significant contribution of As 4 p orbitals to the low-lying electronic structure of the 112-type iron-based superconductor Ca 0.9La 0.1FeAs 2

    Science.gov (United States)

    Li, M. Y.; Liu, Z. T.; Zhou, W.; Yang, H. F.; Shen, D. W.; Li, W.; Jiang, J.; Niu, X. H.; Xie, B. P.; Sun, Y.; Fan, C. C.; Yao, Q.; Liu, J. S.; Shi, Z. X.; Xie, X. M.

    2015-01-01

    We report a systematic polarization-dependent angle-resolved photoemission spectroscopy study of the three-dimensional electronic structure of the recently discovered 112-type iron-based superconductor Ca1 -xLaxFeAs2 (x =0.1 ). Besides the commonly reported three holelike and two electronlike bands in iron-based superconductors, we resolve one additional holelike band around the zone center and one more fast-dispersing band near the X point in the vicinity of the Fermi level. By tuning the polarization and the energy of incident photons, we are able to identify the specific orbital character and the kz dependence of all bands. Combining these results with band calculations, we find that As 4 pz and 4 px(4 py) orbitals contribute significantly to the additional three-dimensional holelike band and the narrow band, respectively. Also, there is considerable hybridization between the As 4 pz and Fe 3 d orbitals in the additional holelike band, which suggests strong coupling between the unique arsenic zigzag bond layers and the FeAs layers therein. Our findings provide a comprehensive picture of the orbital character of the low-lying band structure of 112-type iron-based superconductors, which can be a starting point for the further understanding of their unconventional superconductivity.

  10. Observation of the anisotropic Dirac cone in the band dispersion of 112-structured iron-based superconductor Ca0.9La0.1FeAs2

    Science.gov (United States)

    Liu, Z. T.; Xing, X. Z.; Li, M. Y.; Zhou, W.; Sun, Y.; Fan, C. C.; Yang, H. F.; Liu, J. S.; Yao, Q.; Li, W.; Shi, Z. X.; Shen, D. W.; Wang, Z.

    2016-07-01

    CaFeAs2 is a parent compound of recently discovered 112-type iron-based superconductors. It is predicted to be a staggered intercalation compound that naturally integrates both quantum spin Hall insulating and superconducting layers and an ideal system for the realization of Majorana modes. We performed a systematical angle-resolved photoemission spectroscopy and first-principles calculation study of the slightly electron-doped CaFeAs2. We found that the zigzag As chain of 112-type iron-based superconductors play a considerable role in the low-energy electronic structure, resulting in the characteristic Dirac-cone like band dispersion as the prediction. Our experimental results further confirm that these Dirac cones only exist around the X but not Y points in the Brillouin zone, breaking the S4 symmetry at iron sites. Our findings present the compelling support to the theoretical prediction that the 112-type iron-based superconductors might host the topological nontrivial edge states. The slightly electron doped CaFeAs2 would provide us a unique opportunity to realize and explore Majorana fermion physics.

  11. Research on Language Attrition in China--Based on Literature Review%语言磨蚀研究在中国--基于相关文献分析

    Institute of Scientific and Technical Information of China (English)

    汤朝菊; 马玉玲; 汤甜; 张丽

    2015-01-01

    Language attrition is a phenomenon of language competence decay or loss which happened in the process of language learning. Researching language attrition is instructive for both foreign and native language teaching and learning. This paper summarized the main issues of language attrition discussed in China based on the literature review (CNKI database). The findings show that language attrition research is independently becoming a sub-field of applied linguistics in China. The process of research experienced the journey of introducing the theoretical and tentative results from other countries and then applying into our situation. With more and more research scholars’ concerns, most topics related to attrition were supported by academic funds. Basically, most researches focused on foreign language attrition contrast to native language attrition. The main research aspects are concerning the empirical tests, influence factors, reason analysis. The problems reflected as follows: The various tentative researches on language attrition are seldom related to the language acquisition; the interactive effects among attrition factors were not detected. It is necessary to do cross-disciplinary analysis with other subjects such as psychology, cognitive linguistics, neuro-linguistics and social linguistics. Meanwhile, further work should be done on native language and dialects attrition. Future research will be focused on the language community attrition and follow-up research on the time-ranged attrition. Most work will be done on establishing attrition theories applicable into Chinese linguistic environment.%语言磨蚀(语蚀)是语言学习过程中语言能力减弱或损失现象,研究语言磨蚀对外语及母语教学都有指导意义。基于CNKI相关文献发现我国语蚀研究从国外引介走向本土研究,已经作为应用语言学的研究领域,相关课题大多得到基金资助;研究角度走向多元,主要从实证研究、影响

  12. Cross Cultural Adaptation, Validity, and Reliability of the Farsi Breastfeeding Attrition Prediction Tools in Iranian Pregnant Women

    Science.gov (United States)

    Mortazavi, Forough; Mousavi, Seyed Abbas; Chaman, Reza; Khosravi, Ahmad; Janke, Jill R.

    2015-01-01

    Background: The rate of exclusive breastfeeding in Iran is decreasing. The breastfeeding attrition prediction tools (BAPT) have been validated and used in predicting premature weaning. Objectives: We aimed to translate the BAPT into Farsi, assess its content validity, and examine its reliability and validity to identify exclusive breastfeeding discontinuation in Iran. Materials and Methods: The BAPT was translated into Farsi and the content validity of the Farsi version of the BAPT was assessed. It was administered to 356 pregnant women in the third trimester of pregnancy, who were residents of a city in northeast of Iran. The structural integrity of the four-factor model was assessed in confirmatory factor analysis (CFA) and exploratory factor analysis (EFA). Reliability was assessed using Cronbach’s alpha coefficient and item-subscale correlations. Validity was assessed using the known-group comparison (128 with vs. 228 without breastfeeding experience) and predictive validity (80 successes vs. 265 failures in exclusive breastfeeding). Results: The internal consistency of the whole instrument (49 items) was 0.775. CFA provided an acceptable fit to the a priori four-factor model (Chi-square/df = 1.8, Root Mean Square Error of Approximation (RMSEA) = 0.049, Standardized Root Mean Square Residual (SRMR) = 0.064, Comparative Fit Index (CFI) = 0.911). The difference in means of breastfeeding control (BFC) between the participants with and without breastfeeding experience was significant (P BFC) subscale were higher in women who were on exclusive breastfeeding than women who were not, at four months postpartum (P < 0.05). Conclusions: This study validated the Farsi version of BAPT. It is useful for researchers who want to use it in Iran to identify women at higher risks of Exclusive Breast Feeding (EBF) discontinuation. PMID:26019910

  13. Design of a rotary reactor for chemical-looping combustion. Part 2: Comparison of copper-, nickel-, and iron-based oxygen carriers

    KAUST Repository

    Zhao, Zhenlong

    2014-04-01

    Chemical-looping combustion (CLC) is a novel and promising option for several applications including carbon capture (CC), fuel reforming, H 2 generation, etc. Previous studies demonstrated the feasibility of performing CLC in a novel rotary design with micro-channel structures. Part 1 of this series studied the fundamentals of the reactor design and proposed a comprehensive design procedure, enabling a systematic methodology of designing and evaluating the rotary CLC reactor with different OCs and operating conditions. This paper presents the application of the methodology to the designs with three commonly used OCs, i.e., copper, nickel, and iron. The physical properties and the reactivities of the three OCs are compared at operating conditions suitable for the rotary CLC. Nickel has the highest reduction rate, but relatively slow oxidation reactivity while the iron reduction rate is most sensitive to the fuel concentration. The design parameters and the operating conditions for the three OCs are selected, following the strategies proposed in Part 1, and the performances are evaluated using a one-dimensional plug-flow model developed previously. The simulations show that for all OCs, complete fuel conversion and high carbon separation efficiency can be achieved at periodic stationary state with reasonable operational stabilities. The nickel-based design includes the smallest dimensions because of its fast reduction rate. The operation of nickel case is mainly limited to the slow oxidation rate, and hence a relatively large share of air sector is used. The iron-based design has the largest size, due to its slow reduction reactivity near the exit or in the fuel purge sector where the fuel concentration is low. The gas flow temperature increases monotonically for all the cases, and is mainly determined by the solid temperature. In the periodic state, the local temperature variation is within 40 K and the thermal distortion is limited. The design of the rotary CLC is

  14. Data on the recurrence of breast tumors fit a model in which dormant cells are subject to slow attrition but can randomly awaken to become malignant

    DEFF Research Database (Denmark)

    Stein, Wilfred D; Litman, Thomas

    2006-01-01

    We successfully modeled the recurrence of tumors in breast cancer patients, assuming that: (i) A breast cancer patient is likely to have some circulating metastatic cells, even after initial surgery. (ii) These metastatic cells are dormant. (iii) The dormant cells are subject to attrition...... by the body's immune system, or by random apoptosis or senescence. (iv) Recurrence suppressor mechanisms exist. (v) When such genes are disabled by random mutations, the dormant metastatic cell is activated, and will develop to a cancer recurrence. The model was also fitted to data on the survival...

  15. Antimicrobial Resistance

    Science.gov (United States)

    ... emergence and spread of antibacterial resistance, including optimal use of antibiotics in both humans and animals. A global action plan on antimicrobial resistance was adopted by Member States at the ...

  16. Pathways in STEM: Factors affecting the retention and attrition of talented men and women from the STEM pipeline

    Science.gov (United States)

    Heilbronner, Nancy N.

    attrition was interest in another (non-STEM) field. Participants placed little importance on other reasons for leaving STEM that were identified in previous research, such as competition, social isolation, or financial considerations.

  17. Opposite Effects of Early-Life Competition and Developmental Telomere Attrition on Cognitive Biases in Juvenile European Starlings.

    Directory of Open Access Journals (Sweden)

    Melissa Bateson

    Full Text Available Moods are enduring affective states that we hypothesise should be affected by an individual's developmental experience and its current somatic state. We tested whether early-life adversity, induced by manipulating brood size, subsequently altered juvenile European starlings' (Sturnus vulgaris decisions in a judgment bias task designed to provide a cognitive measure of mood. We predicted that starlings from larger broods, specifically those that had experienced more nest competitors larger than themselves would exhibit reduced expectation of reward, indicative of a 'pessimistic', depression-like mood. We used a go/no-go task, in which 30 starlings were trained to probe a grey card disc associated with a palatable mealworm hidden underneath and avoid a different shade of grey card disc associated with a noxious quinine-injected mealworm hidden underneath. Birds' response latencies to the trained stimuli and also to novel, ambiguous stimuli intermediate between these were subsequently tested. Birds that had experienced greater competition in the nest were faster to probe trained stimuli, and it was therefore necessary to control statistically for this difference in subsequent analyses of the birds' responses to the ambiguous stimuli. As predicted, birds with more, larger nest competitors showed relatively longer latencies to probe ambiguous stimuli, suggesting reduced expectation of reward and a 'pessimistic', depression-like mood. However, birds with greater developmental telomere attrition--a measure of cellular aging associated with increased morbidity and reduced life-expectancy that we argue could be used as a measure of somatic state--showed shorter latencies to probe ambiguous stimuli. This would usually be interpreted as evidence for a more positive or 'optimistic' affective state. Thus, increased competition in the nest and poor current somatic state appear to have opposite effects on cognitive biases. Our results lead us to question

  18. Development on iron-based moving bed chemical looping process%铁基移动床化学链技术进展

    Institute of Scientific and Technical Information of China (English)

    许迪恺; Tong Andrew; 曾亮; 罗四维; 范良士

    2014-01-01

    在日益增长的能源需求与日益严峻的全球气候变化带来的双重压力下,清洁、高效且经济的能源利用方法显得尤为重要。将化学链概念用于传统化石能源的转化是一种前景广阔的新技术。化学链燃烧利用载氧体间接转化含碳燃料,同时实现二氧化碳的捕集。俄亥俄州立大学研发了采用铁基载氧体和移动床反应器的化学链技术,可实现天然气、煤、生物质等多种燃料向电力、氢、液体燃料等产品的零排放转化。目前,合成气化学链(syngas chemical looping, SCL)和煤直接化学链(coal direct chemical looping, CDCL)技术两套25 kWth级小试装置已成功运行总计超过850 h,一套250 kWth级的高压SCL装置即将投入示范运行。%Driven by increasing demands for energy and concerns for climate change, more attention are paid to the development of clean, efficient, and economical technologies for energy conversion, among which chemical looping is considered as a promising alternative for fossil fuel conversion. Chemical looping processes enable highly efficient in situ CO2 capture in oxidation of carbonaceous fuels by making use of solid oxygen carriers. The Ohio State University (OSU) has developed a unique chemical looping technology utilizing iron-based oxygen carrier and moving bed reactors. Thermodynamic analysis shows that counter-current moving bed reactor can maximize oxygen carrier conversion while fully converting fuels, enabling high purity H2 production by iron-steam reaction. OSU chemical looping is highly flexible for converting a variety of gaseous and solid fuels to electricity, H2, and chemicals with CO2 captured. To date, the syngas chemical looping (SCL) technology and the coal direct chemical looping technology has been successfully operated for more than 850 h in total on two 25 kWth sub-pilot units. A 250 kWth high pressure SCL pilot unit is constructed at National Carbon Capture Center

  19. Foreign Language Attrition.

    Science.gov (United States)

    de Bot, Kees; Weltens, Bert

    1995-01-01

    Reviews recent research on language maintenance and language loss, focusing on the loss of a second language in a first language environment, the linguistic aspects of loss, and relearning a "lost" language. An annotated bibliography discusses nine important works in the field. (43 references) (MDM)

  20. Dental Hygiene Student Attrition.

    Science.gov (United States)

    Young, Lynda J.; Fellows, Avis L.

    1981-01-01

    A study to determine differences between graduating and withdrawing students in the University of Minnesota Dental Hygiene program is discussed. The identification of differences may prove useful in the selection process for future classes through identification of students likely to complete their education. (MLW)

  1. Marine Officer Attrition Model.

    Science.gov (United States)

    1984-06-01

    California 93943 6. LTC M. Hagee . HCMC, Code MPP Washington, D.C. 22314 7. MAJ W. J. Esmann 1 4509 Banf Street Annandale, VA 22314 7.. o, .’ 73 , , !,. -.% ~~"% .," ~M E D 𔃾’ 4AN DTI

  2. Pressure-induced phase transitions and correlation between structure and superconductivity in iron-based superconductor Ce(O(0.84)F(0.16))FeAs.

    Science.gov (United States)

    Zhao, Jinggeng; Liu, Haozhe; Ehm, Lars; Dong, Dawei; Chen, Zhiqiang; Liu, Qingqing; Hu, Wanzheng; Wang, Nanlin; Jin, Changqing

    2013-07-15

    High-pressure angle-dispersive X-ray diffraction experiments on iron-based superconductor Ce(O(0.84)F(0.16))FeAs were performed up to 54.9 GPa at room temperature. A tetragonal to tetragonal isostructural phase transition starts at about 13.9 GPa, and a new high-pressure phase has been found above 33.8 GPa. At pressures above 19.9 GPa, Ce(O(0.84)F(0.16))FeAs completely transforms to a high-pressure tetragonal phase, which remains in the same tetragonal structure with a larger a-axis and smaller c-axis than those of the low-pressure tetragonal phase. The structure analysis shows a discontinuity in the pressure dependences of the Fe-As and Ce-(O, F) bond distances, as well as the As-Fe-As and Ce-(O, F)-Ce bond angles in the transition region, which correlates with the change in T(c) of this compound upon compression. The isostructural phase transition in Ce(O(0.84)F(0.16))FeAs leads to a drastic drop in the superconducting transition temperature T(c) and restricts the superconductivity at low temperature. For the 1111-type iron-based superconductors, the structure evolution and following superconductivity changes under compression are related to the radius of lanthanide cations in the charge reservoir layer.

  3. 大学英语第二课堂--规避语言磨蚀的有效手段%The Second Classroom of College English:An Effective Means to Avoid Language Attrition

    Institute of Scientific and Technical Information of China (English)

    吴敏

    2014-01-01

    语言磨蚀是语言习得过程中的产物,并已成为英语学习中的制约因素。如何减少和防止语言磨蚀是很多高校英语教师面临的共同问题。本文是基于语言磨蚀理论来探讨大学英语第二课堂建设的重要性,提出了如何通过第二课堂来弥补第一课堂的缺陷以及如何有效规避语言磨蚀。%Language attrition is a product in the process of lan-guage acquisition, and has become a factor restraining English learning. How to reduce and avoid language attrition is a common issue faced by many college English teachers. Based on language attrition theory, this paper explores the importance of the second classroom construction for college English, and proposes how to make up for the deficiencies of the first classroom with the second classroom and how to effectively avoid language attrition.

  4. Why Miss Dove Left and Where She Went: A Case Study of Teacher Attrition in a Metropolitan School System in the Southeast. Occasional Papers in Educational Policy Analysis. Paper No. 414.

    Science.gov (United States)

    Berry, Barnett

    A case study of teacher attrition in one southeastern metropolitan school system that employs approximately 4,000 teachers was undertaken to determine which teachers left, why, and where they went. Of the 210 teachers in the system who resigned during the 1983-84 academic year, 16 percent were K-6, 13 percent were special education/speech, 13…

  5. Camptothecin resistance

    DEFF Research Database (Denmark)

    Brangi, M; Litman, Thomas; Ciotti, M;

    1999-01-01

    The mitoxantrone resistance (MXR) gene encodes a recently characterized ATP-binding cassette half-transporter that confers multidrug resistance. We studied resistance to the camptothecins in two sublines expressing high levels of MXR: S1-M1-80 cells derived from parental S1 colon cancer cells...... and MCF-7 AdVp3,000 isolated from parental MCF-7 breast cancer cells. Both cell lines were 400- to 1,000-fold more resistant to topotecan, 9-amino-20(S)-camptothecin, and the active metabolite of irinotecan, 7-ethyl-10-hydroxycamptothecin (SN-38), than their parental cell lines. The cell lines...... demonstrated much less resistance to camptothecin and to several camptothecin analogues. Reduced accumulation and energy-dependent efflux of topotecan was demonstrated by confocal microscopy. A significant reduction in cleavable complexes in the resistant cells could be observed after SN-38 treatment...

  6. Attrition in Long-Term Nutrition Research Studies: A Commentary by the European Society for Pediatric Gastroenterology, Hepatology, and Nutrition Early Nutrition Research Working Group.

    Science.gov (United States)

    Fewtrell, Mary S; Domellöf, Magnus; Hojsak, Iva; Hulst, Jessie M; Kennedy, Kathy; Koletzko, Berthold; Mihatsh, Walter; Stijnen, Theo

    2016-01-01

    Long-term follow-up of randomised trials and observational studies provide the best evidence presently available to assess long-term effects of nutrition, and such studies are an important component in determining optimal infant feeding practices. Attrition is, however, an almost inevitable occurrence with increasing age at follow-up. There is a common assumption that studies with <80% follow-up rates are invalid or flawed, and this criticism seems to be more frequently applied to follow-up studies involving randomised trials than observational studies. In this article, we explore the basis and evidence for this "80% rule" and discuss the need for greater consensus and clear guidelines for analysing and reporting results in this specific situation.

  7. Local thermal property analysis by scanning thermal microscopy of an ultrafine-grained copper surface layer produced by surface mechanical attrition treatment

    Energy Technology Data Exchange (ETDEWEB)

    Guo, F.A. [Suzhou Institute for Nonferrous Metals Processing Technology, No. 200 Shenxu Road, Suzhou Industrial Park, Suzhou 215021 (China) and Unite de Thermique et d' Analyse Physique, Laboratoire d' Energetique et d' Optique, Universite de Reims, BP 1039, 51687 Reims Cedex 2 (France)]. E-mail: guofuan@yahoo.com; JI, Y.L. [Suzhou Institute for Nonferrous Metals Processing Technology, No. 200 Shenxu Road, Suzhou Industrial Park, Suzhou 215021 (China); Trannoy, N. [Unite de Thermique et d' Analyse Physique, Laboratoire d' Energetique et d' Optique, Universite de Reims, BP 1039, 51687 Reims Cedex 2 (France); Lu, J. [LASMIS, Universite de Technologie de Troyes, 12 Rue Marie Curie, Troyes 10010 (France)

    2006-06-15

    Scanning thermal microscopy (SThM) was used to map thermal conductivity images in an ultrafine-grained copper surface layer produced by surface mechanical attrition treatment (SMAT). It is found that the deformed surface layer shows different thermal conductivities that strongly depend on the grain size of the microstructure: the thermal conductivity of the nanostructured surface layer decreases obviously when compared with that of the coarse-grained matrix of the sample. The role of the grain boundaries in thermal conduction is analyzed in correlation with the heat conduction mechanism in pure metal. A theoretical approach, based on this investigation, was used to calculate the heat flow from the probe tip to the sample and then estimate the thermal conductivities at different scanning positions. Experimental results and theoretical calculation demonstrate that SThM can be used as a tool for the thermal property and microstructural analysis of ultrafine-grained microstructures.

  8. Telomere attrition and restoration in the normal teleost Oryzias latipes are linked to growth rate and telomerase activity at each life stage.

    Science.gov (United States)

    Hatakeyama, Hitoshi; Yamazaki, Hiromi; Nakamura, Ken-Ichi; Izumiyama-Shimomura, Naotaka; Aida, Junko; Suzuki, Hiroetsu; Tsuchida, Shuichi; Matsuura, Masaaki; Takubo, Kaiyo; Ishikawa, Naoshi

    2016-01-01

    Telomere shortening occurs when cells divide, both in vitro and in vivo. On the other hand, telomerase is able to maintain telomere length in cells by adding TTAGGG repeats to the ends of telomeres. However, the interrelationships existing among telomere length, telomerase activity and growth in vertebrates remain to be clarified. In the present study we measured telomere length (terminal restriction fragment length), telomerase activity and body growth of Oryzias latipes from the embryo stage until senescence. During the rapid growth stage (age 0-7 months), telomeres shortened in parallel with decreasing telomerase activity. Then, during adolescence (age 7 months - 1 year), telomeres lengthened quickly as growth slowed and telomerase activity increased. In the adult stage (age 1-4 years) characterized by little growth, telomerase activity decreased gradually and telomeres shortened. Our data indicate that telomere attrition and restoration are linked to growth and telomerase activity, and suggest that critical loss of telomere homeostasis is associated with mortality in this animal.

  9. Antibiotic Resistance

    DEFF Research Database (Denmark)

    Munck, Christian

    morbidity and mortality as well as an increase in the cost of treatment. Understanding how bacteria respond to antibiotic exposure gives the foundations for a rational approach to counteract antimicrobial resistance. In the work presented in this thesis, I explore the two fundamental sources...... of antimicrobial resistance: (1) adaptive mutations and (2) horizontal acquisition of resistance genes from antibiotic gene reservoirs. By studying the geno- and phenotypic changes of E. coli in response to single and drug-pair exposures, I uncover the evolutionary trajectories leading to adaptive resistance. I...... to rationally design drug combinations that limit the evolution of antibiotic resistance due to counteracting evolutionary trajectories. My results highlight that an in-depth knowledge about the genetic responses to the individual antimicrobial compounds enables the prediction of responses to drug combinations...

  10. Energy saving using solar filters with iron base in windows; Ahorro de energia usando filtros solares con base en hierro en ventanas

    Energy Technology Data Exchange (ETDEWEB)

    Chavez Galan, Jesus

    2003-07-01

    For the high temperature seasons, the radiation emitted by the sun later introduced through the windows, provokes a great thermal gain in the buildings causing within them an excessive warming. For the cold seasons, the exterior is at low temperature and the window is the main element through which the building losses the heat generated in the interior. The former turns out into an elevated energy consumption (mainly electricity) to obtain the conditions of human thermal comfort; this altogether with the growing energy demand that the residential, commercial and public sector experiences in Mexico, constitutes a serious problem. As a proposal for the solution to the problem of thermal discomfort generated in the interior of the buildings because of the inadequate properties of the construction materials, in this work were developed solar filers with iron base by means of which it is obtained a selective control of the solar radiation that is transmitted through the windows. These solar filters consist in thin films of FeO deposited over subtracts of lime-soda glass (the most used in our country for buildings) of 600 x 300 x 3 mm, by means of the sputtering technique added with a radio frequency and flat magnetrons, starting from a pure iron target of 127 x 254 mm and using an argon plasma. To obtain the desired oxidation degree in the iron, small samples (45 x 22 mm) were subjected to a heating process in a reducing atmosphere constituted by 50% H{sub 2} + 50% N{sub 2} for a period of time of 10 minutes at a temperature of 400 centigrade. The solar filters with the FeO base present a transmissibility of 30.2 % for the visible interval of the electromagnetic spectrum (radiation with a wave length of 380-780 nm) and of 39.9 % for the near infrared (radiation with a wave length of 780-2500 nm); while the reflectivity is of 17.5 and 19% for the visible intervals and near infrared of electromagnetic spectrum respectively. A simulation was performed by means of the

  11. Tool wear mechanism in turning of novel wear-resisting aluminum bronze

    Institute of Scientific and Technical Information of China (English)

    倪东惠; 夏伟; 张大童; 郭国文; 邵明

    2003-01-01

    Tool wear and wear mechanism during the turning of a wear-resisting aluminum bronze have been stud-ied. Tool wear samples were prepared by using M2 high-speed steel and YW1 cemented carbide tools to turn a novelhigh strength, wear resisting aluminum bronze without coolant and lubricant. Adhesion of workpiece materials wasfound on tool's surface. Under the turning condition used in this study major wear mechanisms for turning aluminumbronze using M2 high-speed steel tool are diffusion wear, adhesive wear and plastic deformation and shear on thecrater. Partial melting of high-speed steel on the rake plays a role in the tool wear also. Major wear mechanisms forturning aluminum bronze using YW1 cemented carbide tool are diffusion wear, attrition wear and sliding wear. Tocontrol the machining temperature is essential to reduce tool wear.

  12. Non-conventional superconducting fluctuations in Ba(Fe1-xRhx)2As2 iron-based superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Bossoni, L. [Univ. of Pavia (Italy); Romano, L. [Univ. of Parma (Italy); Canfield, Paul C. [Ames Lab., Ames, IA (United States); Lascialfari, A. [Univ. degli Studi di Milano (Italy)

    2014-09-17

    We measured the static uniform spin susceptibility of Ba(Fe1-xRhx)2As2 iron-based superconductors, over a broad range of doping (0.041x0.094) and magnetic fields. At small fields (H ≤ 1 kOe) we observed, above the transition temperature Tc, the occurrence of precursor diamagnetism, which is not ascribable to the Ginzburg–Landau theory. On the contrary, our data agree with a phase fluctuation model, which has been used to interpret a similar phenomenology occurring in the high-Tc cuprate superconductors. Additionally, in the presence of strong fields, the unconventional fluctuating diamagnetism is suppressed, whereas Ginzburg–Landau fluctuations are found, in agreement with literature.

  13. Lantibiotic resistance.

    Science.gov (United States)

    Draper, Lorraine A; Cotter, Paul D; Hill, Colin; Ross, R Paul

    2015-06-01

    The dramatic rise in the incidence of antibiotic resistance demands that new therapeutic options will have to be developed. One potentially interesting class of antimicrobials are the modified bacteriocins termed lantibiotics, which are bacterially produced, posttranslationally modified, lanthionine/methyllanthionine-containing peptides. It is interesting that low levels of resistance have been reported for lantibiotics compared with commercial antibiotics. Given that there are very few examples of naturally occurring lantibiotic resistance, attempts have been made to deliberately induce resistance phenotypes in order to investigate this phenomenon. Mechanisms that hinder the action of lantibiotics are often innate systems that react to the presence of any cationic peptides/proteins or ones which result from cell well damage, rather than being lantibiotic specific. Such resistance mechanisms often arise due to altered gene regulation following detection of antimicrobials/cell wall damage by sensory proteins at the membrane. This facilitates alterations to the cell wall or changes in the composition of the membrane. Other general forms of resistance include the formation of spores or biofilms, which are a common mechanistic response to many classes of antimicrobials. In rare cases, bacteria have been shown to possess specific antilantibiotic mechanisms. These are often species specific and include the nisin lytic protein nisinase and the phenomenon of immune mimicry.

  14. 大学英语第二课堂建设——基于语言磨蚀角度的思考%On the second classroom in college English teaching——based on language attrition

    Institute of Scientific and Technical Information of China (English)

    覃薇

    2012-01-01

      Language attrition is the co-product of language acquisition, whose prevention is a common problem confronted by all college English teachers. This paper analyses the significance of college English second classroom and proposes how to construct it effectively from the prospect of language attrition.%  语言磨蚀是语言习得的伴生产物,减少和防止语言磨蚀是广大高校英语教师所面临的共同课题。文章从语言磨蚀的角度探讨了建构大学英语第二课堂的必要性,提出了如何在语言磨蚀理论指导下有效地进行大学英语第二课堂建设

  15. Full-mouth composite rehabilitation of a mixed erosion and attrition patient: a case report with v-shaped veneers and ultra-thin CAD/CAM composite overlays.

    Science.gov (United States)

    Bahillo, Jose; Jané, Luis; Bortolotto, Tissiana; Krejci, Ivo; Roig, Miguel

    2014-10-01

    Loss of tooth substance has become a common pathology in modern society. It is of multifactorial origin, may be induced by a chemical process or by excessive attrition, and frequently has a combined etiology. Particular care should be taken when diagnosing the cause of dental tissue loss, in order to minimize its impact. Several publications have proposed the use of minimally invasive procedures to treat such patients in preference to traditional full-crown rehabilitation. The use of composite resins, in combination with improvements in dental adhesion, allows a more conservative approach. In this paper, we describe the step-by-step procedure of full-mouth composite rehabilitation with v-shaped veneers and ultra-thin computer-aided design/computer-assisted manufacture (CAD/CAM)- generated composite overlays in a young patient with a combination of erosion and attrition disorder.

  16. Direct Production of a Novel Iron-Based Nanocomposite from the Laser Pyrolysis of Fe(CO5/MMA Mixtures: Structural and Sensing Properties

    Directory of Open Access Journals (Sweden)

    R. Alexandrescu

    2010-01-01

    Full Text Available Iron/iron oxide-based nanocomposites were prepared by IR laser sensitized pyrolysis of Fe(CO5 and methyl methacrylate (MMA mixtures. The morphology of nanopowder analyzed by TEM indicated that mainly core-shell structures were obtained. X-ray diffraction techniques evidence the cores as formed mainly by iron/iron oxide crystalline phases. A partially degraded (carbonized polymeric matrix is suggested for the coverage of the metallic particles. The nanocomposite structure at the variation of the laser density and of the MMA flow was studied. The new materials prepared as thick films were tested for their potential for acting as gas sensors. The temporal variation of the electrical resistance in presence of NO2, CO, and CO2, in dry and humid air was recorded. Preliminary results show that the samples obtained at higher laser power density exhibit rather high sensitivity towards NO2 detection and NO2 selectivity relatively to CO and CO2. An optimum working temperature of 200°C was found.

  17. Microstructure and Wear Properties of FeCrC, FeW and Feti Modified Iron Based Alloy Coating Deposited by PTA Process on AISI 430 Steel

    Directory of Open Access Journals (Sweden)

    Teker T.

    2014-10-01

    Full Text Available The plasma transferred arc (PTA process was used for developing wear resistance of AISI 430 steel substrate. Appropriate quantities of FeCrC, FeW and FeTi powders were combined to create conditions that synthesized M7C3 particles into reinforced Fe-based composite surface coating. The phase transformations on new created coated surfaces were comprehensively examined by using a combination of scanning electron microscopy (SEM, microanalysis by energy dispersive spectrometry (EDS, X-Ray diffraction (XRD, microhardness and abrasive wear tests. The microstructure studies of the superficial layers of the coating revealed presence of a mixture of the dendritic phase structure of austenite (γ and fine eutectic M7C3 carbides. The results show that; the concentrations of the elements (Cr, W, Ti added as ferroalloys, the size of dendrites formed in the coated surface, the change of hardness of the coated surfaces, the carbide volume rate and thickness of the coating changed by the variation of the processing parameters (ratio of reinforcement particulates and heat input.

  18. 铁基超导体的量子临界行为∗%Quantum criticalities in carrier-dop ed iron-based sup erconductors

    Institute of Scientific and Technical Information of China (English)

    李政; 周睿; 郑国庆

    2015-01-01

    state compared with the optimal doping sample suggests that the coexisting region is an unusual state and deserves further investigation. Secondly, we conducted transport measurements in electron-doped BaFe2−xNixAs2 system, and found a T-linear resistivity at two critical points. One is at the optimal doping xc1 =0.10, while the other is in the overdoped region xc2 =0.14. We found that 1/T1 is nearly T-independent above Tc at xc1 where TN =0, which indicates that xc1 is a magnetic QCP and the observed T-linear resistivity is due to the quantum fluctuation. We find that 1/T1 close to the optimal doping in both Ba1−xKxFe2As2 and LaFeAsO1−xFx also shows a similar behavior as in BaFe2−xNixAs2. The results suggest that superconductivity in these compounds is strongly tied to the quantum antiferromagnetic spin fluctuation. We further studied the structural transition in BaFe2−xNixAs2 by NMR. Since the a-axis and b-axis are not identical below the nematic structural transition temperature Ts, the electric field-gradient becomes asymmetric. Therefore the NMR satellite peaks associated with nuclear spin I = 3/2 of 75As split for a twinned single crystal, when the external magnetic field is applied along a- or b-axis. We were able to track the nematic structural transition up to x=0.12. The Ts extrapolates to zero at x=0.14 which suggests that xc2 is a QCP associated with a nematic structural phase transition and the T-linear resistivity at xc2 is therefore due to the QCP. No existing theories can explain such behavior of the resistivity and we call for theoretical investigations in this regard.

  19. Androgen resistance.

    Science.gov (United States)

    Hughes, Ieuan A; Deeb, Asma

    2006-12-01

    Androgen resistance causes the androgen insensitivity syndrome in its variant forms and is a paradigm of clinical syndromes associated with hormone resistance. In its complete form, the syndrome causes XY sex reversal and a female phenotype. Partial resistance to androgens is a common cause of ambiguous genitalia of the newborn, but a similar phenotype may result from several other conditions, including defects in testis determination and androgen biosynthesis. The biological actions of androgens are mediated by a single intracellular androgen receptor encoded by a gene on the long arm of the X chromosome. Mutations in this gene result in varying degrees of androgen receptor dysfunction and phenotypes that often show poor concordance with the genotype. Functional characterization and three-dimensional modelling of novel mutant receptors has been informative in understanding the mechanism of androgen action. Management issues in syndromes of androgen insensitivity include decisions on sex assignment, timing of gonadectomy in relation to tumour risk, and genetic and psychological counselling.

  20. Anticoagulant Resistance

    DEFF Research Database (Denmark)

    Heiberg, Ann-Charlotte

    Although sewer rat control is carried out in more than 80 % of all Danish municipalities, with usage of large amounts of anticoagulant rodenticides, knowledge on anticoagulant resistance among rats living in the sewers is limited. As rat problems in urban areas are believed to be related to sewer...... problems (70-90 % in UK and DK) unawareness of resistance amongst these populations of Brown rats may constitute a future control problem and knowledge on this issue has become crucial. Rats were captured in sewers from seven different locations in the suburban area of Copenhagen. Locations was chosen...... to represent different sewer rat management strategies i) no anticoagulants for approx. 20 years ii) no anticoagulants for the last 5 years and iii) continuous control for many years. Animals were tested for resistance to bromadiolone by Blood-Clotting Response test, as bromadiolone is the most frequently used...